Hepatol Int (2015) 9:183–191 DOI 10.1007/s12072-015-9613-5
REVIEW ARTICLE
New cellular and molecular targets for the treatment of portal hypertension Jordi Gracia-Sancho • Raquel Maeso-Dı´az • Anabel Ferna´ndez-Iglesias • Marı´a Navarro-Zornoza Jaime Bosch
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Received: 31 October 2014 / Accepted: 10 February 2015 / Published online: 5 March 2015 Ó Asian Pacific Association for the Study of the Liver 2015
Abstract Portal hypertension (PH) is a common complication of chronic liver disease, and it determines most complications leading to death or liver transplantation in patients with liver cirrhosis. PH results from increased resistance to portal blood flow through the cirrhotic liver. This is caused by two mechanisms: (a) distortion of the liver vascular architecture and (b) hepatic microvascular dysfunction. Increment in hepatic resistance is latterly accompanied by splanchnic vasodilation, which further aggravates PH. Hepatic microvascular dysfunction occurs early in the course of chronic liver disease as a consequence of inflammation and oxidative stress and determines loss of the normal phenotype of liver sinusoidal endothelial cells (LSEC). The cross-talk between LSEC and hepatic stellate cells induces activation of the latter, which in turn proliferate, migrate and increase collagen deposition around the sinusoids, contributing to fibrogenesis, architectural disruption and angiogenesis. Therapy for PH aims at correcting these pathophysiological abnormalities: liver injury, fibrogenesis, increased hepatic vascular tone and splanchnic vasodilatation. Continuing liver injury may be counteracted specifically by etiological treatments, while architectural disruption and fibrosis can be ameliorated by a variety of anti-fibrogenic drugs and
J. Gracia-Sancho (&) R. Maeso-Dı´az A. Ferna´ndez-Iglesias M. Navarro-Zornoza J. Bosch (&) Barcelona Hepatic Hemodynamic Laboratory, Liver Unit, Hospital Clı´nic-Institut d’Investigacions Biome`diques August Pi i Sunyer (IDIBAPS) and Centro de Investigacio´n Biome´dica en Red de Enfermedades Hepa´ticas y Digestivas (CIBERehd), University of Barcelona, Rossello´ 149, 4th Floor, 08036 Barcelona, Spain e-mail: [email protected] J. Bosch e-mail: [email protected]
anti-angiogenic strategies. Sinusoidal endothelial dysfunction is ameliorated by statins and other drugs increasing NO availability. Splanchnic hyperemia can be counteracted by non-selective beta-blockers (NSBBs), vasopressin analogs and somatostatin analogs. Future treatment of portal hypertension will evolve to use etiological treatments together with anti-fibrotic agents and/or drugs improving microvascular function in initial stages of cirrhosis (preprimary prophylaxis), while NSBBs will be added in advanced stages of the disease. Keywords Cirrhosis Liver LSEC Endothelium Simvastatin Liver sinusoidal endothelial cells Hepatic stellate cells
Cirrhotic portal hypertension Portal hypertension is a very frequent and severe complication of chronic liver disease. Its consequences, which include bleeding from gastro-esophageal varices, ascites, hepatorenal syndrome, spontaneous bacterial peritonitis, hepatopulmonary syndrome, hyperkinetic syndrome, and hepatic encephalopathy, represent the first non-neoplastic cause of death and liver transplantation in patients with chronic liver disease [1–4]. Moreover, it is associated with primary liver cancer development, together with an increase in the mortality rate [5]. In recent decades, great efforts have been devoted to better understand the pathophysiology of portal hypertension, clearly demonstrating that an increase in the hepatic vascular resistance (HVR), due both to marked anatomic changes in the liver vasculature and to the de-regulation of hepatic cells phenotype, represents the primary factor in the development of portal hypertension. Secondarily to the
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increased HVR, a progressive splanchnic vasodilatation that increases portal blood inflow further aggravates portal hypertension and its complications. Additionally, intrahepatic shunts development markedly interfere with metabolic and O2 exchange between the sinusoidal blood and the hepatocytes, further deteriorating liver function.
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pointing out that paracrine interactions between sinusoidal cells may be extremely important in their phenotypic deregulations. It has been demonstrated that dysfunctional LSEC or KC paracrinally impair HSC phenotype [15, 16], which becomes proliferative and pro-contractile. Future studies will define if these paracrine interactions occurring during cirrhosis progression are fed back in the opposite direction.
Increased hepatic vascular resistance in cirrhosis Sinusoidal cells de-regulation in cirrhosis As mentioned, a significant increment in HVR results in portal hypertension development. A majority of the increased HVR is a consequence of the architectural distortions originated by the chronic liver tissue damage due to viral infection, toxic-induced, autoimmune and metabolic causes, together with the reiterative activation of the wound healing reaction [6]. However, recent studies have unravelled that a significant de-regulation of the hepatic cells phenotype further contributes to raise the hepatic resistance. This dynamic and reversible component of HVR was first described by Bhathal and Grossmann [7] and may represent up to 30–40 % of the total increased HVR in cirrhosis. Hepatic cells influencing the hepatic vascular tone involve sinusoidal and extra-sinusoidal elements, and mainly include liver sinusoidal endothelial cells (LSEC), Kupffer cells (KC), and contractile cells [hepatic stellate cells (HSC), myofibroblasts, and vascular smooth muscle cells] [8–10]. Microvascular dysfunction of the cirrhotic liver Vascular cells de-regulation within the cirrhotic liver leads to the development and establishment of the misnamed term ‘‘endothelial dysfunction’’, physiologically defined as a vasodilator deficient response of the liver microcirculation to HVR-elevating stimuli, such as increments in the portal blood inflow or in the concentration of vasoconstrictors. Considering the advances in the field, liver endothelial dysfunction should probably be re-termed to ‘‘liver microvascular dysfunction’’. Indeed, we now know that all sinusoidal cells participate in the pathological vasoactive response of the cirrhotic liver (Fig. 1). Due to the disease, LSEC and KC acquire a predominantly vasoconstrictor phenotype which is further exacerbated in response to biomechanical, pathogenic and inflammatory stimuli [8, 11, 12]. In addition, hepatic contractile elements become hyper-responsive to vasocontrictors and markedly increase the vascular tone [13, 14]. It is important to denote that the underlying mechanisms responsible for sinusoidal cells phenotype modifications are not completely understood. Nevertheless, results interesting to highlight recent discoveries
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LSEC form the wall of the hepatic sinusoids and represent approximately 15 % of liver cells. These types of endothelial cells possess a unique phenotype, they lack an organized basal membrane and their cytoplasm is penetrated by open fenestrae that form clusters termed sieve plates, making the hepatic sinusoidal endothelium discontinuous [17, 18]. LSEC have important roles in the parenchymal distribution of nutrients and O2, modulation of the hepatic vascular tone, blood pathogens clearance, and intrahepatic cells communication [4, 8, 19]. Facing an injury, LSEC are the primary cells affected by the blood-transported noxa, before evidence of hepatocyte damage are observed [20]. In particular, LSEC lose their vasoprotective phenotype (event denominated pseudocapillarization and morphologically defined by development of basal membrane and reduction in porosity), becoming vasoconstrictor, pro-inflammatory and prothrombotic. LSEC pseudo-capillarization is associated with increased expression of CD31, VCAM-1, COX-1 and ET1, together with lower expression of Stabilin-1/2, CD32b and Reca-1 [21–23]. In addition, capillarized LSEC produce lower amounts of nitric oxide (NO) and significantly elevated amounts of vasoconstrictor prostanoids, such as thromboxane A2 (TXA2) [11, 24]. HSC, initially termed ‘‘fat-storing cells’’, are localized in the space of Disse, account for 5–8 % of total liver cells, and have important roles in retinoid metabolism and modulation of the hepatic vascular tone [13, 25]. Indeed, due to their particular intrahepatic distribution, wrapping up to four LSEC per HSC and adhering each other through tight junctions, HSC response to vasoactive substances leads to accurately control vascular tone, and therefore portal pressure. In response to injury or certain stimuli, HSC become ‘‘activated’’ and start to proliferate and release large amounts of extracellular matrix (ECM) components, including collagen and proteglycans, which lead to the modification of the hepatic structure/architecture. HSC morphology changes to a myofibroblast-like phenotype, they lose their retinoid droplets and express de novo smooth muscle proteins, including alpha-smooth muscle actin [9]. In addition, activated HSC exhibit hyper-
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Fig. 1 Main features of liver microvascular dysfunction due to chronic liver disease
contractile response to vasoconstrictor molecules, and diminished response to vasodilators, thus contributing to increase the HVR [4, 26]. KC are the liver resident macrophages and show an irregular distribution within the hepatic tissue. KC are more numerous and exhibit higher lysosomal and endocytic activities in the portal areas than cells localized in midzonal and pericentral segments of the sinusoids [27]. The main roles of KC encompass phagocytosis and uptake of particulates and macromolecules, antigen presentation, and release of soluble mediators. In cirrhosis, KC undergo inflammatory activation contributing to increase the HVR. They promote direct increase of vascular tone through the release of vasoconstrictor substances, such as TXA2 and Cys-LT, and contribute to fibrogenesis due to paracrine activation of HSC [12, 16, 28]. Vasoactive factors modulating the hepatic microcirculation in cirrhosis Increased activity of different endogenous vasoconstrictors has been demonstrated in the cirrhotic liver, including endothelin, norepinephrine, angiotensin II, vasopressin, leukotrienes, and thromboxane A2 [4, 29–33]. Although it is now clear that the above described contractile agents play a role in the cirrhotic liver microcirculatory dysfunction, the phospholipase A2—cycloxygenase1—thromboxane A2 (PLA2—COX1—TXA2S) molecular axis represents the most extensively characterized [11, 22, 32, 34, 35]. Studies from our team and others demonstrated that LSEC and KC from cirrhotic livers exhibit an up-regulation in this pathway, and more
importantly, that its blockade significantly improves hepatic microcirculation in cirrhosis. Indeed, in livers from experimental models of cirrhosis, over-expression of PLA2 (which would increase the biodisponibility of the prostanoids precursor arachidonic acid) and endothelial upregulations of COX-1 and TXA2 synthase (enzymes responsible for vasoconstrictors production) have been observed [11]. Inhibition of COX or COX-1, or blockade of the TXA2 receptor results in amelioration of hepatic endothelial dysfunction and reduction in portal pressure [22, 32, 35]. On the other hand, a markedly decreased bioavailability of the vasodilator NO has been described in the cirrhotic liver. Low NO levels result from both decreased endothelial NO synthase (eNOS) translation efficiency [36] and enzymatic activity [37, 38], and from increased NO scavenging by elevated oxidative stress [33]. Reduced eNOS activity is attributed to several post-translational alterations, including reduced eNOS phosphorylation at its activation sites, low levels of its co-factor tetrahydrobiopterin (BH4), and increased interaction with caveolin and asymmetric-dimethyl-arginine (ADMA) [38–42]. Elevated oxidative stress, which leads to NO scavenging to form peroxynitrite, is due to elevated radical oxygen species (ROS) formation by cycloxygenase and xanthine oxidase, and to reduced superoxide dismutase-mediated elimination of ROS [33]. Interestingly, NADPH oxidasederived oxidative stress is not responsible for NO scavenging in the cirrhotic liver [43]. In addition to the herein mentioned regulatory mechanisms for the COX1-TXA2 and the NO systems, a recent study demonstrated that these two vasoactive mediators reciprocally influence each other in the cirrhotic
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liver endothelium [44]. In fact, inhibition of TXA2 production results in increments in NO levels, and NO supplementation results in reduction of TXA2 production. These findings suggest that NO supplementation in cirrhosis would have a dual beneficial effect, restoring the decreased vasodilator content and attenuating the exaggerated vasoconstrictor production. Increased portal blood inflow in cirrhosis As stated before, and secondarily to the increase in the HRV, cirrhotic portal hypertension is further aggravated and perpetuated due to an increment in the portal system blood flow derived from a marked splanchnic vasodilatation. This is an adaptive response to defective liver parenchyma perfusion, and it is mainly mediated by vasoactive substances produced by the splanchnic vascular system [3]. Similarly to what happens within the liver circulation, different mesenteric vascular cells contribute to the splanchnic vasodilatation, and consequently to portal blood inflow increase. Endothelial cells generate exaggerated amounts of vasodilator messengers including NO, glucagon, and PGI2, which will paracrinally affect smooth muscle cells leading to their relaxation [3, 45–47]. In addition, a marked down-regulation in the RhoA/Rho-kinase pathway in the systemic circulation has been described, which probably will further contribute to splanchnic vascular hypocontractility and vasodilatation [48]. Please note that, although the vasoactive pathways and mediators are practically the same in the hepatic and in the systemic circulations, they work in an opposite manner. Increased vascular tone within the cirrhotic liver is mediated by a limited amount of vasodilators, and an exaggerated amount and response to vasoconstrictors; whereas in the extrahepatic vascular bed an overproduction of vasodilators together with a hyporesponse to vasocontrictors exists. Beyond to splanchnic hyperemia, and most probably due to it, portal hypertension is further aggravated by the development of an extensive network of portal-systemic collateral vessels that very much determine the progression of patients due to their role in portal hypertension complications including gastro-oesophageal varices bleeding and portosystemic encephalopathy [3]. Recent data demonstrate that VEGF-dependent angiogenesis plays a major role in the development and maintenance of the portocollateral vasculature in cirrhosis [49–51].
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analogs and somatostatin analogs have demonstrated efficient reduction in portal pressure due to the correction in the splanchnic hyperemia. Contrarily, safe and reliable strategies to reduce the HVR in cirrhotic patients still represent a pending issue. Discovery of the molecular pathways responsible for the increment in HVR, namely, fibrosis, microvascular dysfunction and angiogenesis, has led to the design and experimental assessment of novel therapies, which in fact have reported very promising results. In animal models of cirrhosis, hepatic fibrosis regression can be achieved using different strategies. Three with higher potential are herein described: 1.
2.
3.
Statins: These commonly prescribed drugs possess several beneficial effects unrelated to their lipid-lower properties. Indeed, statins administration to cirrhotic animals induces a marked regression in liver fibrosis [52, 53]. This remarkable effect is mainly derived from its capability to de-activate and promote the apoptosis of HSC through a mechanism mostly dependent on the transcription factor Kruppel-like factor 2 (KLF2) [53]. Indeed, activation of KLF2 leads to a profound amelioration in HSC phenotype derived from the activation of antioxidant and anti-inflammatory pathways dependent on the nuclear factor (erythroidderived 2)-like 2 (Nfr2). In addition, and as explained below, statins also ameliorate the LSEC phenotype that, in turn, paracrinally improves HSC status [54] (Fig. 2). Antioxidants: Resveratrol, a polyphenolic compound naturally found in plants and fruits, showed marked anti-fibrotic effects when administered to cirrhotic animals [55]. Administration of a new recombinant formulation of the human MnSOD to cirrhotic rats promoted a 52 % regression of liver fibrosis [56]. More recently, green tea extract has also shown beneficial effects on liver fibrosis [57]. Obeticholic acid: A recent study demonstrated that its administration to cirrhotic animals produces a significant amelioration in the HSC phenotype [58]; ongoing phase II–III clinical trials will clarify whether obeticholic acid has an effect on liver fibrosis.
Microvascular dysfunction of cirrhotic livers can be improved through strategies targeting its main pathophysiological events (described in ‘‘Vasoactive factors modulating the hepatic microcirculation in cirrhosis’’ section) (Fig. 3; Table 1).
Targets for therapy 1. Reduction in portal pressure can be achieved by either diminishing HVR, splanchnic hyperemia, or both. Up to now, non-selective beta-blockers (NSBB), vasopressin
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Arachidonic acid-derived vasoconstriction can be blunted administering in vivo the TXA2 receptor blocker Terutroban [35], which reported an 18 % reduction in portal pressure in cirrhotic animals
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Fig. 2 Amelioration of sinusoidal cells phenotype in cirrhosis through the administration of statins: role of the transcription factor KLF2. Direct and paracrine effects [53, 54]
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3.
Fig. 3 Underlying mechanisms of recently described therapeutic strategies to improve the microvascular dysfunction of cirrhotic livers. AA arachidonic acid pathway, BH4 tetrahydrobiopterin, DDAH dimethylarginine-dimethylaminohydrolase, eNOS endothelial nitric oxide synthase, HSC hepatic stellate cells, KLF2 kruppel-like factor 2, LSEC liver sinusoidal endothelial cells, NF-kB nuclear factor kappalight-chain-enhancer of activated B cells, NO nitric oxide, Nrf2 nuclear factor (erythroid-derived 2)-like 2, OA obeticholic acid, ROS radical oxygen species, TGFb transforming growth factor beta, VEGF vascular endothelial growth factor
together with an improvement in LSEC and HSC phenotype. Similarly, the Cysteinil-Leukotrienes antagonist Montelukast results in marked reduction in
4.
portal pressure, both in basal conditions and upon KC stimulation with LPS [28]. HSC hyper-contractility can be normalized using a HSC-targeted Rho-kinase inhibitor [59], or the peptide hormone Relaxin [60]. In this last study, HSC phenotype improvement due to relaxin was accompanied by a significant reduction in portal pressure both in animals with early- and advanced-cirrhosis, however amelioration in fibrosis was only observed in animals with mild liver injury. Endothelial NO production can be improved by shortand long-term exogenous administration of the eNOS cofactor BH4, which improves eNOS activity and microsvascular dysfunction, and therefore reduces portal pressure [42, 61]. In addition, a very recent paper described that the administration of obeticholic acid promotes the synthesis of the ADMA-metabolizer dimethylargininedimethylaminohydrolase-1 (DDAH-1), markedly improving eNOS activity in cirrhotic rats [62]. Sinusoidal NO bioavailability can be increased administering antioxidants, which reduce the elevated levels of oxidative stress of the cirrhotic liver and concomitantly reduce NO scavenging by the superoxide radical [63–65]. Finally, cirrhotic LSEC phenotype can be efficiently improved administering statins, especially simvastatin, which up-regulate the expression and activity of the transcription factor KLF2 conferring a vasoprotective phenotype to the hepatic endothelium [36, 54, 66, 67]. Remarkably, in a randomized controlled trial, simvastatin has been demonstrated
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Table 1 Pharmacological treatments targeting the elevated hepatic vascular resistance in experimental models of liver cirrhosis Treatment
Target molecule
Target cell
Antioxidants (vitamins, resveratrol, rMnSOD, NAC) [55, 56, 63, 75]
O2-—mediated NO scavenging
LSEC (???)
Rho kinase
HSC (???)
BH4 [42, 61]
eNOS activity
LSEC (??)
Leptin blocker [76]
O2-—mediated NO scavenging
LSEC (??)
Metformin [77]
O2-—mediated NO scavenging
LSEC (???)
Montelukast [28]
Cys-LTs
HSC (?)
Nitroflurbiprofen [78]
COX
LSEC (?) KC (?)
Obeticholic acid [58, 62]
DDAH-1
LSEC (??)
Relaxin [60]
DDAH-2
LSEC (??)
Rho kinase
HSC (??) LSEC (?)
RXFP1
HSC (?)
eNOS activity
LSEC (??)
Spinorolactone [79]
eNOS activity
LSEC (??)
Statins [36, 52–54, 66, 67, 80]
Rho kinase eNOS activity
HSC (???) LSEC (???)
Terutroban [35]
KLF2 transcriptional programs
LSEC (???) HSC (???) KC (???)
Rho kinase
HSC (???)
eNOS activity
LSEC (??)
TXA2 receptor
HSC (??) LSEC (??)
Treatments administered in vivo to cirrhotic animals are herein summarized rMnSOD human recombinant superoxide dismutase, NAC, n-acetylcisteine, O2 superoxide radical, NO nitric oxide, LSEC liver sinusoidal endothelial cells, BH4 tetrahydrobiopterin, HSC hepatic stellate cells, Cys-LTs cysteinil leukotrienes, KC kupffer cells, DDAH dimethylargininedimethylaminohydrolase, RXFP relaxin receptor family protein, eNOS endothelial nitric oxide synthase, KLF2 kruppel-like factor 2, TXA2 thromboxane A2 ??? Demonstrated, ?? Most probably, ? Likely
effective in improving portal hypertension [68], and more recently, the protective effects of long-term simvastatin administration against portal hypertensionderived complications have also been proved [69]. Angiogenesis inhibition targeting the vascular endothelial growth factor (VEGF), platelet-derived growth factor (PDGF) and/or pigment epithelium-derived growth factor (PEDF) pathways showed marked positive effects on portal hypertension [70, 71]. Nevertheless, very recent data introduced two interesting novel concepts regarding targeting angiogenesis in cirrhosis: (1) VEGF has a dual role in cirrhosis, namely, it promotes fibrogenesis during disease progression, but it is completely necessary for fibrosis resolution [72], and (2) inhibition of pathological angiogenesis through the up-regulation of the endogenous angioinhibitor vasohibin-1 reveals remarkable beneficial effects, totally comparable to exogenously administered anti-angiogenesis drugs [73]. Altogether, these facts strongly support the notion of inhibiting angiogenesis just in the right
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amount, trying to not disturb physiological vessel formation. This could be accomplished by administering very low doses of anti-angiogenesis drugs, like Sorafenib [51], or modulating endogenous anti-angiogenic pathways.
Conclusion and perspective Scientific progress in the field achieved during recent decades has very much changed our understanding of the pathophysiology of portal hypertension. Indeed, the discovery and characterization of the dynamic (and therefore pharmacologically reversible) component of the elevated HVR in cirrhosis, together with the description of sinusoidal cells de-regulation during liver injury, and the potential reversibility of liver fibrosis, opened several research avenues to develop new strategies aimed to definitely improve portal hypertension, and therefore patients survival.
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Although considerable efforts have focused on testing and validating these new strategies, significant amelioration of liver cirrhosis and portal hypertension will be more efficiently translated to the bedside by means of strategies able to multi-target different pathophysiological mechanisms (i.e. microvascular dysfunction ? angiogenesis, or fibrosis ? microvascular dysfunction). Fortunately, some of the previously described agents, like statins, effectively do it. In addition, possible cumulative or synergistic effects of combining NSBB ? strategies reducing HVR are encouraging. Indeed, a single report combining sorafenib ? propranolol showed synergistic effects of both strategies, with an overall 30 % reduction in portal pressure [74]. Evidently, further studies combining other strategies, which may also specifically focus on genetic targets, are still necessary.
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Acknowledgements Research from Dr. Gracia-Sancho & Prof. Bosch teams is funded by grants from the Ministerio de Economı´a y Competitividad (Ramo´n y Cajal program & ACI colabora), the Instituto de Salud Carlos III (FIS & CIBEREHD), and the European Union (fondos FEDER).
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Compliance with ethical requirements and Conflict of interest This article does not contain any studies with human or animal subjects. Jordi Gracia-Sancho, Raquel Maeso-Dı´az, Anabel Ferna´ndez-Iglesias, Marı´a Navarro-Zornoza and Jaime Bosch declare that they have no conflict of interest.
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49. Fernandez M, Mejias M, Angermayr B, Garcia-Pagan JC, Rodes J, Bosch J. Inhibition of VEGF receptor-2 decreases the development of hyperdynamic splanchnic circulation and portal-systemic collateral vessels in portal hypertensive rats. J Hepatol 2005;43:98–103 50. Fernandez M, Mejias M, Garcia-Pras E, Mendez R, Garcia-Pagan JC, Bosch J. Reversal of portal hypertension and hyperdynamic splanchnic circulation by combined vascular endothelial growth factor and platelet-derived growth factor blockade in rats. Hepatology 2007;46:1208–1217 51. Mejias M, Garcia-Pras E, Tiani C, Miquel R, Bosch J, Fernandez M. Beneficial effects of sorafenib on splanchnic, intrahepatic, and portocollateral circulations in portal hypertensive and cirrhotic rats. Hepatology 2009;49:1245–1256 52. Trebicka J, Hennenberg M, Odenthal M, Shir K, Klein S, Granzow M, et al. Atorvastatin attenuates hepatic fibrosis in rats after bile duct ligation via decreased turnover of hepatic stellate cells. J Hepatol 2010;53:702–712 53. Marrone G, Maeso-Dı´az R, Garcia-Cardena G, Garcia-Pagan JC, Bosch J, Gracia-Sancho J. KLF2 exerts anti-fibrotic and vasoprotective effects in cirrhotic rat livers: behind the molecular mechanisms of statins. Gut 2014; doi:10.1136/gutjnl-2014-308338 54. Marrone G, Russo L, Rosado E, Hide D, Garcia-Cardena G, Garcia-Pagan JC, et al. The transcription factor KLF2 mediates hepatic endothelial protection and paracrine endothelial-stellate cell deactivation induced by statins. J Hepatol 2013;58:98–103 55. Di Pascoli M, Divi M, Rodriguez-Vilarrupla A, Rosado E, Gracia-Sancho J, Vilaseca M, et al. Resveratrol improves intrahepatic endothelial dysfunction and reduces hepatic fibrosis and portal pressure in cirrhotic rats. J Hepatol 2013;58:904–910 56. Guillaume M, Rodriguez-Vilarrupla A, Gracia-Sancho J, Rosado E, Mancini A, Bosch J, et al. Recombinant human manganese superoxide dismutase reduces liver fibrosis and portal pressure in CCl4-cirrhotic rats. J Hepatol 2013;58:240–246 57. Hsu SJ, Wang SS, Hsin IF, Lee FY, Huang HC, Huo TI, et al. Green tea polyphenol decreases the severity of portosystemic collaterals and mesenteric angiogenesis in rats with liver cirrhosis. Clin Sci (Lond) 2014;126:633–644 58. Verbeke L, Farre R, Trebicka J, Komuta M, Roskams T, Klein S, et al. Obeticholic acid, a farnesoid X receptor agonist, improves portal hypertension by two distinct pathways in cirrhotic rats. Hepatology 2014;59:2286–2298 59. Klein S, Van Beuge MM, Granzow M, Beljaars L, Schierwagen R, Kilic S, et al. HSC-specific inhibition of Rho-kinase reduces portal pressure in cirrhotic rats without major systemic effects. J Hepatol 2012;57:1220–1227 60. Fallowfield JA, Hayden AL, Snowdon VK, Aucott RL, Stutchfield BM, Mole DJ, et al. Relaxin modulates human and rat hepatic myofibroblast function and ameliorates portal hypertension in vivo. Hepatology 2014;59:1492–1504 61. Matei V, Rodriguez-Vilarrupla A, Deulofeu R, Garcia-Caldero H, Fernandez M, Bosch J, et al. Three-day tetrahydrobiopterin therapy increases in vivo hepatic NOS activity and reduces portal pressure in CCl4 cirrhotic rats. J Hepatol 2008;49:192–197 62. Mookerjee RP, Mehta G, Balasubramaniyan V, Mohamed F, Davies N, Sharma V, et al. Hepatic dimethylarginine-dimethylaminohydrolase1 is reduced in cirrhosis and is a target for therapy in portal hypertension. J Hepatol 2014;10 63. Hernandez-Guerra M, Garcia-Pagan JC, Turnes J, Bellot P, Deulofeu R, Abraldes JG, et al. Ascorbic acid improves the intrahepatic endothelial dysfunction of patients with cirrhosis and portal hypertension. Hepatology 2006;43:485–491 64. Yang YY, Lee TY, Huang YT, Chan CC, Yeh YC, Lee FY, et al. Asymmetric dimethylarginine (ADMA) determines the improvement of hepatic endothelial dysfunction by vitamin E in cirrhotic rats. Liver Int 2012;32:48–57
Hepatol Int (2015) 9:183–191 65. De Gottardi A, Berzigotti A, Seijo S, D’Amico M, Thormann W, Abraldes JG, et al. Postprandial effects of dark chocolate on portal hypertension in patients with cirrhosis: results of a phase 2, double-blind, randomized controlled trial. Am J Clin Nutr 2012;96:584–590 66. Abraldes JG, Rodriguez-Vilarrupla A, Graupera M, Zafra C, Garcia-Caldero H, Garcia-Pagan JC, et al. Simvastatin treatment improves liver sinusoidal endothelial dysfunction in CCl(4) cirrhotic rats. J Hepatol 2007;46:1040–1046 67. Trebicka J, Hennenberg M, Laleman W, Shelest N, Biecker E, Schepke M, et al. Atorvastatin lowers portal pressure in cirrhotic rats by inhibition of RhoA/Rho-kinase and activation of endothelial nitric oxide synthase. Hepatology 2007;46:242–253 68. Abraldes JG, Albillos A, Banares R, Turnes J, Gonzalez R, Garcia-Pagan JC, et al. Simvastatin lowers portal pressure in patients with cirrhosis and portal hypertension: a randomized controlled trial. Gastroenterology 2009;136:1651–1658 69. Abraldes JG, Villanueva C, Aracil C, Turnes J, HernandezGuerra M, Genesca J, et al. Addition of simvastatin to standard treatment improves survival after variceal bleeding in patients with cirrhosis. A double-blind randomized trial (NCT01095185). J Hepatol 2014;60:S525 70. Bosch J, Abraldes JG, Fernandez M, Garcia-Pagan JC. Hepatic endothelial dysfunction and abnormal angiogenesis: new targets in the treatment of portal hypertension. J Hepatol 2010;53:558–567 71. Mejias M, Coch L, Berzigotti A, Garcia-Pras E, Gallego J, Bosch J, et al. Antiangiogenic and antifibrogenic activity of pigment epithelium-derived factor (PEDF) in bile duct-ligated portal hypertensive rats. Gut 2014. doi:10.1136/gutjnl-2014-307138 72. Yang L, Kwon J, Popov Y, Gajdos GB, Ordog T, Brekken RA, et al. Vascular endothelial growth factor promotes fibrosis resolution and repair in mice. Gastroenterology 2014;146:1339–1350 73. Coch L, Mejias M, Berzigotti A, Garcia-Pras E, Gallego J, Bosch J, et al. Disruption of negative feedback loop between vasohibin-
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77.
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1 and vascular endothelial growth factor decreases portal pressure, angiogenesis, and fibrosis in cirrhotic rats. Hepatology 2014;60:633–647 D’Amico M, Mejias M, Garcia-Pras E, Abraldes JG, Garcia-Pagan JC, Fernandez M, et al. Effects of the combined administration of propranolol plus sorafenib on portal hypertension in cirrhotic rats. Am J Physiol Gastrointest Liver Physiol 2012;302:G1191–1198 Yang YY, Lee KC, Huang YT, Wang YW, Hou MC, Lee FY, et al. Effects of N-acetylcysteine administration in hepatic microcirculation of rats with biliary cirrhosis. J Hepatol 2008;49:25–33 Delgado MG, Gracia-Sancho J, Marrone G, Rodriguez-Vilarupla A, Deulofeu R, Abraldes JG, et al. Leptin receptor blockade reduces intrahepatic vascular resistance and portal pressure in an experimental model of rat liver cirrhosis. Am J Physiol Gastrointest Liver Physiol 2013;305:G496–G502 Tripathi D, Erice E, Gracia-Sancho J, Garcia-Caldero H, Sarin SK, Bosch J, et al. Metformin reduces hepatic resistance and portal pressure in CCl4 and BDL cirrhotic rats. Hepatology 2013;58:294A–297A Laleman W, Van Landeghem L, Van der Elst I, Zeegers M, Fevery J, Nevens F. Nitroflurbiprofen, a nitric oxide-releasing cyclooxygenase inhibitor, improves cirrhotic portal hypertension in rats. Gastroenterology 2007;132:709–719 Luo W, Meng Y, Ji HL, Pan CQ, Huang S, Yu CH, et al. Spironolactone lowers portal hypertension by inhibiting liver fibrosis, ROCK-2 activity and activating NO/PKG pathway in the bile-duct-ligated rat. PLoS ONE 2012;7:e34230 Klein S, Klosel J, Schierwagen R, Korner C, Granzow M, Huss S, et al. Atorvastatin inhibits proliferation and apoptosis, but induces senescence in hepatic myofibroblasts and thereby attenuates hepatic fibrosis in rats. Lab Invest 2012;92:1440–1450
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REVIEW ARTICLE
New cellular and molecular targets for the treatment of portal hypertension Jordi Gracia-Sancho • Raquel Maeso-Dı´az • Anabel Ferna´ndez-Iglesias • Marı´a Navarro-Zornoza Jaime Bosch
•
Received: 31 October 2014 / Accepted: 10 February 2015 / Published online: 5 March 2015 Ó Asian Pacific Association for the Study of the Liver 2015
Abstract Portal hypertension (PH) is a common complication of chronic liver disease, and it determines most complications leading to death or liver transplantation in patients with liver cirrhosis. PH results from increased resistance to portal blood flow through the cirrhotic liver. This is caused by two mechanisms: (a) distortion of the liver vascular architecture and (b) hepatic microvascular dysfunction. Increment in hepatic resistance is latterly accompanied by splanchnic vasodilation, which further aggravates PH. Hepatic microvascular dysfunction occurs early in the course of chronic liver disease as a consequence of inflammation and oxidative stress and determines loss of the normal phenotype of liver sinusoidal endothelial cells (LSEC). The cross-talk between LSEC and hepatic stellate cells induces activation of the latter, which in turn proliferate, migrate and increase collagen deposition around the sinusoids, contributing to fibrogenesis, architectural disruption and angiogenesis. Therapy for PH aims at correcting these pathophysiological abnormalities: liver injury, fibrogenesis, increased hepatic vascular tone and splanchnic vasodilatation. Continuing liver injury may be counteracted specifically by etiological treatments, while architectural disruption and fibrosis can be ameliorated by a variety of anti-fibrogenic drugs and
J. Gracia-Sancho (&) R. Maeso-Dı´az A. Ferna´ndez-Iglesias M. Navarro-Zornoza J. Bosch (&) Barcelona Hepatic Hemodynamic Laboratory, Liver Unit, Hospital Clı´nic-Institut d’Investigacions Biome`diques August Pi i Sunyer (IDIBAPS) and Centro de Investigacio´n Biome´dica en Red de Enfermedades Hepa´ticas y Digestivas (CIBERehd), University of Barcelona, Rossello´ 149, 4th Floor, 08036 Barcelona, Spain e-mail: [email protected] J. Bosch e-mail: [email protected]
anti-angiogenic strategies. Sinusoidal endothelial dysfunction is ameliorated by statins and other drugs increasing NO availability. Splanchnic hyperemia can be counteracted by non-selective beta-blockers (NSBBs), vasopressin analogs and somatostatin analogs. Future treatment of portal hypertension will evolve to use etiological treatments together with anti-fibrotic agents and/or drugs improving microvascular function in initial stages of cirrhosis (preprimary prophylaxis), while NSBBs will be added in advanced stages of the disease. Keywords Cirrhosis Liver LSEC Endothelium Simvastatin Liver sinusoidal endothelial cells Hepatic stellate cells
Cirrhotic portal hypertension Portal hypertension is a very frequent and severe complication of chronic liver disease. Its consequences, which include bleeding from gastro-esophageal varices, ascites, hepatorenal syndrome, spontaneous bacterial peritonitis, hepatopulmonary syndrome, hyperkinetic syndrome, and hepatic encephalopathy, represent the first non-neoplastic cause of death and liver transplantation in patients with chronic liver disease [1–4]. Moreover, it is associated with primary liver cancer development, together with an increase in the mortality rate [5]. In recent decades, great efforts have been devoted to better understand the pathophysiology of portal hypertension, clearly demonstrating that an increase in the hepatic vascular resistance (HVR), due both to marked anatomic changes in the liver vasculature and to the de-regulation of hepatic cells phenotype, represents the primary factor in the development of portal hypertension. Secondarily to the
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increased HVR, a progressive splanchnic vasodilatation that increases portal blood inflow further aggravates portal hypertension and its complications. Additionally, intrahepatic shunts development markedly interfere with metabolic and O2 exchange between the sinusoidal blood and the hepatocytes, further deteriorating liver function.
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pointing out that paracrine interactions between sinusoidal cells may be extremely important in their phenotypic deregulations. It has been demonstrated that dysfunctional LSEC or KC paracrinally impair HSC phenotype [15, 16], which becomes proliferative and pro-contractile. Future studies will define if these paracrine interactions occurring during cirrhosis progression are fed back in the opposite direction.
Increased hepatic vascular resistance in cirrhosis Sinusoidal cells de-regulation in cirrhosis As mentioned, a significant increment in HVR results in portal hypertension development. A majority of the increased HVR is a consequence of the architectural distortions originated by the chronic liver tissue damage due to viral infection, toxic-induced, autoimmune and metabolic causes, together with the reiterative activation of the wound healing reaction [6]. However, recent studies have unravelled that a significant de-regulation of the hepatic cells phenotype further contributes to raise the hepatic resistance. This dynamic and reversible component of HVR was first described by Bhathal and Grossmann [7] and may represent up to 30–40 % of the total increased HVR in cirrhosis. Hepatic cells influencing the hepatic vascular tone involve sinusoidal and extra-sinusoidal elements, and mainly include liver sinusoidal endothelial cells (LSEC), Kupffer cells (KC), and contractile cells [hepatic stellate cells (HSC), myofibroblasts, and vascular smooth muscle cells] [8–10]. Microvascular dysfunction of the cirrhotic liver Vascular cells de-regulation within the cirrhotic liver leads to the development and establishment of the misnamed term ‘‘endothelial dysfunction’’, physiologically defined as a vasodilator deficient response of the liver microcirculation to HVR-elevating stimuli, such as increments in the portal blood inflow or in the concentration of vasoconstrictors. Considering the advances in the field, liver endothelial dysfunction should probably be re-termed to ‘‘liver microvascular dysfunction’’. Indeed, we now know that all sinusoidal cells participate in the pathological vasoactive response of the cirrhotic liver (Fig. 1). Due to the disease, LSEC and KC acquire a predominantly vasoconstrictor phenotype which is further exacerbated in response to biomechanical, pathogenic and inflammatory stimuli [8, 11, 12]. In addition, hepatic contractile elements become hyper-responsive to vasocontrictors and markedly increase the vascular tone [13, 14]. It is important to denote that the underlying mechanisms responsible for sinusoidal cells phenotype modifications are not completely understood. Nevertheless, results interesting to highlight recent discoveries
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LSEC form the wall of the hepatic sinusoids and represent approximately 15 % of liver cells. These types of endothelial cells possess a unique phenotype, they lack an organized basal membrane and their cytoplasm is penetrated by open fenestrae that form clusters termed sieve plates, making the hepatic sinusoidal endothelium discontinuous [17, 18]. LSEC have important roles in the parenchymal distribution of nutrients and O2, modulation of the hepatic vascular tone, blood pathogens clearance, and intrahepatic cells communication [4, 8, 19]. Facing an injury, LSEC are the primary cells affected by the blood-transported noxa, before evidence of hepatocyte damage are observed [20]. In particular, LSEC lose their vasoprotective phenotype (event denominated pseudocapillarization and morphologically defined by development of basal membrane and reduction in porosity), becoming vasoconstrictor, pro-inflammatory and prothrombotic. LSEC pseudo-capillarization is associated with increased expression of CD31, VCAM-1, COX-1 and ET1, together with lower expression of Stabilin-1/2, CD32b and Reca-1 [21–23]. In addition, capillarized LSEC produce lower amounts of nitric oxide (NO) and significantly elevated amounts of vasoconstrictor prostanoids, such as thromboxane A2 (TXA2) [11, 24]. HSC, initially termed ‘‘fat-storing cells’’, are localized in the space of Disse, account for 5–8 % of total liver cells, and have important roles in retinoid metabolism and modulation of the hepatic vascular tone [13, 25]. Indeed, due to their particular intrahepatic distribution, wrapping up to four LSEC per HSC and adhering each other through tight junctions, HSC response to vasoactive substances leads to accurately control vascular tone, and therefore portal pressure. In response to injury or certain stimuli, HSC become ‘‘activated’’ and start to proliferate and release large amounts of extracellular matrix (ECM) components, including collagen and proteglycans, which lead to the modification of the hepatic structure/architecture. HSC morphology changes to a myofibroblast-like phenotype, they lose their retinoid droplets and express de novo smooth muscle proteins, including alpha-smooth muscle actin [9]. In addition, activated HSC exhibit hyper-
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Fig. 1 Main features of liver microvascular dysfunction due to chronic liver disease
contractile response to vasoconstrictor molecules, and diminished response to vasodilators, thus contributing to increase the HVR [4, 26]. KC are the liver resident macrophages and show an irregular distribution within the hepatic tissue. KC are more numerous and exhibit higher lysosomal and endocytic activities in the portal areas than cells localized in midzonal and pericentral segments of the sinusoids [27]. The main roles of KC encompass phagocytosis and uptake of particulates and macromolecules, antigen presentation, and release of soluble mediators. In cirrhosis, KC undergo inflammatory activation contributing to increase the HVR. They promote direct increase of vascular tone through the release of vasoconstrictor substances, such as TXA2 and Cys-LT, and contribute to fibrogenesis due to paracrine activation of HSC [12, 16, 28]. Vasoactive factors modulating the hepatic microcirculation in cirrhosis Increased activity of different endogenous vasoconstrictors has been demonstrated in the cirrhotic liver, including endothelin, norepinephrine, angiotensin II, vasopressin, leukotrienes, and thromboxane A2 [4, 29–33]. Although it is now clear that the above described contractile agents play a role in the cirrhotic liver microcirculatory dysfunction, the phospholipase A2—cycloxygenase1—thromboxane A2 (PLA2—COX1—TXA2S) molecular axis represents the most extensively characterized [11, 22, 32, 34, 35]. Studies from our team and others demonstrated that LSEC and KC from cirrhotic livers exhibit an up-regulation in this pathway, and more
importantly, that its blockade significantly improves hepatic microcirculation in cirrhosis. Indeed, in livers from experimental models of cirrhosis, over-expression of PLA2 (which would increase the biodisponibility of the prostanoids precursor arachidonic acid) and endothelial upregulations of COX-1 and TXA2 synthase (enzymes responsible for vasoconstrictors production) have been observed [11]. Inhibition of COX or COX-1, or blockade of the TXA2 receptor results in amelioration of hepatic endothelial dysfunction and reduction in portal pressure [22, 32, 35]. On the other hand, a markedly decreased bioavailability of the vasodilator NO has been described in the cirrhotic liver. Low NO levels result from both decreased endothelial NO synthase (eNOS) translation efficiency [36] and enzymatic activity [37, 38], and from increased NO scavenging by elevated oxidative stress [33]. Reduced eNOS activity is attributed to several post-translational alterations, including reduced eNOS phosphorylation at its activation sites, low levels of its co-factor tetrahydrobiopterin (BH4), and increased interaction with caveolin and asymmetric-dimethyl-arginine (ADMA) [38–42]. Elevated oxidative stress, which leads to NO scavenging to form peroxynitrite, is due to elevated radical oxygen species (ROS) formation by cycloxygenase and xanthine oxidase, and to reduced superoxide dismutase-mediated elimination of ROS [33]. Interestingly, NADPH oxidasederived oxidative stress is not responsible for NO scavenging in the cirrhotic liver [43]. In addition to the herein mentioned regulatory mechanisms for the COX1-TXA2 and the NO systems, a recent study demonstrated that these two vasoactive mediators reciprocally influence each other in the cirrhotic
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liver endothelium [44]. In fact, inhibition of TXA2 production results in increments in NO levels, and NO supplementation results in reduction of TXA2 production. These findings suggest that NO supplementation in cirrhosis would have a dual beneficial effect, restoring the decreased vasodilator content and attenuating the exaggerated vasoconstrictor production. Increased portal blood inflow in cirrhosis As stated before, and secondarily to the increase in the HRV, cirrhotic portal hypertension is further aggravated and perpetuated due to an increment in the portal system blood flow derived from a marked splanchnic vasodilatation. This is an adaptive response to defective liver parenchyma perfusion, and it is mainly mediated by vasoactive substances produced by the splanchnic vascular system [3]. Similarly to what happens within the liver circulation, different mesenteric vascular cells contribute to the splanchnic vasodilatation, and consequently to portal blood inflow increase. Endothelial cells generate exaggerated amounts of vasodilator messengers including NO, glucagon, and PGI2, which will paracrinally affect smooth muscle cells leading to their relaxation [3, 45–47]. In addition, a marked down-regulation in the RhoA/Rho-kinase pathway in the systemic circulation has been described, which probably will further contribute to splanchnic vascular hypocontractility and vasodilatation [48]. Please note that, although the vasoactive pathways and mediators are practically the same in the hepatic and in the systemic circulations, they work in an opposite manner. Increased vascular tone within the cirrhotic liver is mediated by a limited amount of vasodilators, and an exaggerated amount and response to vasoconstrictors; whereas in the extrahepatic vascular bed an overproduction of vasodilators together with a hyporesponse to vasocontrictors exists. Beyond to splanchnic hyperemia, and most probably due to it, portal hypertension is further aggravated by the development of an extensive network of portal-systemic collateral vessels that very much determine the progression of patients due to their role in portal hypertension complications including gastro-oesophageal varices bleeding and portosystemic encephalopathy [3]. Recent data demonstrate that VEGF-dependent angiogenesis plays a major role in the development and maintenance of the portocollateral vasculature in cirrhosis [49–51].
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analogs and somatostatin analogs have demonstrated efficient reduction in portal pressure due to the correction in the splanchnic hyperemia. Contrarily, safe and reliable strategies to reduce the HVR in cirrhotic patients still represent a pending issue. Discovery of the molecular pathways responsible for the increment in HVR, namely, fibrosis, microvascular dysfunction and angiogenesis, has led to the design and experimental assessment of novel therapies, which in fact have reported very promising results. In animal models of cirrhosis, hepatic fibrosis regression can be achieved using different strategies. Three with higher potential are herein described: 1.
2.
3.
Statins: These commonly prescribed drugs possess several beneficial effects unrelated to their lipid-lower properties. Indeed, statins administration to cirrhotic animals induces a marked regression in liver fibrosis [52, 53]. This remarkable effect is mainly derived from its capability to de-activate and promote the apoptosis of HSC through a mechanism mostly dependent on the transcription factor Kruppel-like factor 2 (KLF2) [53]. Indeed, activation of KLF2 leads to a profound amelioration in HSC phenotype derived from the activation of antioxidant and anti-inflammatory pathways dependent on the nuclear factor (erythroidderived 2)-like 2 (Nfr2). In addition, and as explained below, statins also ameliorate the LSEC phenotype that, in turn, paracrinally improves HSC status [54] (Fig. 2). Antioxidants: Resveratrol, a polyphenolic compound naturally found in plants and fruits, showed marked anti-fibrotic effects when administered to cirrhotic animals [55]. Administration of a new recombinant formulation of the human MnSOD to cirrhotic rats promoted a 52 % regression of liver fibrosis [56]. More recently, green tea extract has also shown beneficial effects on liver fibrosis [57]. Obeticholic acid: A recent study demonstrated that its administration to cirrhotic animals produces a significant amelioration in the HSC phenotype [58]; ongoing phase II–III clinical trials will clarify whether obeticholic acid has an effect on liver fibrosis.
Microvascular dysfunction of cirrhotic livers can be improved through strategies targeting its main pathophysiological events (described in ‘‘Vasoactive factors modulating the hepatic microcirculation in cirrhosis’’ section) (Fig. 3; Table 1).
Targets for therapy 1. Reduction in portal pressure can be achieved by either diminishing HVR, splanchnic hyperemia, or both. Up to now, non-selective beta-blockers (NSBB), vasopressin
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Arachidonic acid-derived vasoconstriction can be blunted administering in vivo the TXA2 receptor blocker Terutroban [35], which reported an 18 % reduction in portal pressure in cirrhotic animals
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Fig. 2 Amelioration of sinusoidal cells phenotype in cirrhosis through the administration of statins: role of the transcription factor KLF2. Direct and paracrine effects [53, 54]
2.
3.
Fig. 3 Underlying mechanisms of recently described therapeutic strategies to improve the microvascular dysfunction of cirrhotic livers. AA arachidonic acid pathway, BH4 tetrahydrobiopterin, DDAH dimethylarginine-dimethylaminohydrolase, eNOS endothelial nitric oxide synthase, HSC hepatic stellate cells, KLF2 kruppel-like factor 2, LSEC liver sinusoidal endothelial cells, NF-kB nuclear factor kappalight-chain-enhancer of activated B cells, NO nitric oxide, Nrf2 nuclear factor (erythroid-derived 2)-like 2, OA obeticholic acid, ROS radical oxygen species, TGFb transforming growth factor beta, VEGF vascular endothelial growth factor
together with an improvement in LSEC and HSC phenotype. Similarly, the Cysteinil-Leukotrienes antagonist Montelukast results in marked reduction in
4.
portal pressure, both in basal conditions and upon KC stimulation with LPS [28]. HSC hyper-contractility can be normalized using a HSC-targeted Rho-kinase inhibitor [59], or the peptide hormone Relaxin [60]. In this last study, HSC phenotype improvement due to relaxin was accompanied by a significant reduction in portal pressure both in animals with early- and advanced-cirrhosis, however amelioration in fibrosis was only observed in animals with mild liver injury. Endothelial NO production can be improved by shortand long-term exogenous administration of the eNOS cofactor BH4, which improves eNOS activity and microsvascular dysfunction, and therefore reduces portal pressure [42, 61]. In addition, a very recent paper described that the administration of obeticholic acid promotes the synthesis of the ADMA-metabolizer dimethylargininedimethylaminohydrolase-1 (DDAH-1), markedly improving eNOS activity in cirrhotic rats [62]. Sinusoidal NO bioavailability can be increased administering antioxidants, which reduce the elevated levels of oxidative stress of the cirrhotic liver and concomitantly reduce NO scavenging by the superoxide radical [63–65]. Finally, cirrhotic LSEC phenotype can be efficiently improved administering statins, especially simvastatin, which up-regulate the expression and activity of the transcription factor KLF2 conferring a vasoprotective phenotype to the hepatic endothelium [36, 54, 66, 67]. Remarkably, in a randomized controlled trial, simvastatin has been demonstrated
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Table 1 Pharmacological treatments targeting the elevated hepatic vascular resistance in experimental models of liver cirrhosis Treatment
Target molecule
Target cell
Antioxidants (vitamins, resveratrol, rMnSOD, NAC) [55, 56, 63, 75]
O2-—mediated NO scavenging
LSEC (???)
Rho kinase
HSC (???)
BH4 [42, 61]
eNOS activity
LSEC (??)
Leptin blocker [76]
O2-—mediated NO scavenging
LSEC (??)
Metformin [77]
O2-—mediated NO scavenging
LSEC (???)
Montelukast [28]
Cys-LTs
HSC (?)
Nitroflurbiprofen [78]
COX
LSEC (?) KC (?)
Obeticholic acid [58, 62]
DDAH-1
LSEC (??)
Relaxin [60]
DDAH-2
LSEC (??)
Rho kinase
HSC (??) LSEC (?)
RXFP1
HSC (?)
eNOS activity
LSEC (??)
Spinorolactone [79]
eNOS activity
LSEC (??)
Statins [36, 52–54, 66, 67, 80]
Rho kinase eNOS activity
HSC (???) LSEC (???)
Terutroban [35]
KLF2 transcriptional programs
LSEC (???) HSC (???) KC (???)
Rho kinase
HSC (???)
eNOS activity
LSEC (??)
TXA2 receptor
HSC (??) LSEC (??)
Treatments administered in vivo to cirrhotic animals are herein summarized rMnSOD human recombinant superoxide dismutase, NAC, n-acetylcisteine, O2 superoxide radical, NO nitric oxide, LSEC liver sinusoidal endothelial cells, BH4 tetrahydrobiopterin, HSC hepatic stellate cells, Cys-LTs cysteinil leukotrienes, KC kupffer cells, DDAH dimethylargininedimethylaminohydrolase, RXFP relaxin receptor family protein, eNOS endothelial nitric oxide synthase, KLF2 kruppel-like factor 2, TXA2 thromboxane A2 ??? Demonstrated, ?? Most probably, ? Likely
effective in improving portal hypertension [68], and more recently, the protective effects of long-term simvastatin administration against portal hypertensionderived complications have also been proved [69]. Angiogenesis inhibition targeting the vascular endothelial growth factor (VEGF), platelet-derived growth factor (PDGF) and/or pigment epithelium-derived growth factor (PEDF) pathways showed marked positive effects on portal hypertension [70, 71]. Nevertheless, very recent data introduced two interesting novel concepts regarding targeting angiogenesis in cirrhosis: (1) VEGF has a dual role in cirrhosis, namely, it promotes fibrogenesis during disease progression, but it is completely necessary for fibrosis resolution [72], and (2) inhibition of pathological angiogenesis through the up-regulation of the endogenous angioinhibitor vasohibin-1 reveals remarkable beneficial effects, totally comparable to exogenously administered anti-angiogenesis drugs [73]. Altogether, these facts strongly support the notion of inhibiting angiogenesis just in the right
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amount, trying to not disturb physiological vessel formation. This could be accomplished by administering very low doses of anti-angiogenesis drugs, like Sorafenib [51], or modulating endogenous anti-angiogenic pathways.
Conclusion and perspective Scientific progress in the field achieved during recent decades has very much changed our understanding of the pathophysiology of portal hypertension. Indeed, the discovery and characterization of the dynamic (and therefore pharmacologically reversible) component of the elevated HVR in cirrhosis, together with the description of sinusoidal cells de-regulation during liver injury, and the potential reversibility of liver fibrosis, opened several research avenues to develop new strategies aimed to definitely improve portal hypertension, and therefore patients survival.
Hepatol Int (2015) 9:183–191
Although considerable efforts have focused on testing and validating these new strategies, significant amelioration of liver cirrhosis and portal hypertension will be more efficiently translated to the bedside by means of strategies able to multi-target different pathophysiological mechanisms (i.e. microvascular dysfunction ? angiogenesis, or fibrosis ? microvascular dysfunction). Fortunately, some of the previously described agents, like statins, effectively do it. In addition, possible cumulative or synergistic effects of combining NSBB ? strategies reducing HVR are encouraging. Indeed, a single report combining sorafenib ? propranolol showed synergistic effects of both strategies, with an overall 30 % reduction in portal pressure [74]. Evidently, further studies combining other strategies, which may also specifically focus on genetic targets, are still necessary.
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Acknowledgements Research from Dr. Gracia-Sancho & Prof. Bosch teams is funded by grants from the Ministerio de Economı´a y Competitividad (Ramo´n y Cajal program & ACI colabora), the Instituto de Salud Carlos III (FIS & CIBEREHD), and the European Union (fondos FEDER).
19.
Compliance with ethical requirements and Conflict of interest This article does not contain any studies with human or animal subjects. Jordi Gracia-Sancho, Raquel Maeso-Dı´az, Anabel Ferna´ndez-Iglesias, Marı´a Navarro-Zornoza and Jaime Bosch declare that they have no conflict of interest.
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