REVIEW URRENT C OPINION
Exploiting the therapeutic potential of leptin signaling in cachexia Robert H. Mak a, Wai W. Cheung a, and Arieh Gertler b
Purpose of review The anorexia-cachexia syndrome is a complication of many chronic conditions including cancer, chronic obstructive pulmonary disease, congestive heart failure, and chronic kidney disease (CKD). Leptin levels are significantly elevated in CKD patients and are associated with markers of poor nutritional status as well as mortality and morbidity. This review will focus on the mechanism and exploit the therapeutic potential of leptin signaling in CKD-associated cachexia. Recent findings Studies in db/db mice show that the lack of leptin receptor is protective against CKD-induced cachexia. Blockade of leptin’s downstream mediators, such as melanocortin-4 receptor, attenuated CKD-associated cachexia. Pegylation of leptin antagonists resulted in a potent and effective long-acting reagents suitable for in-vivo studies or therapies. Pegylated leptin antagonist treatment ameliorates CKD-associated cachexia in mice. Summary Leptin antagonism may represent a viable therapeutic strategy for cachexia in CKD. Keywords cachexia, chronic kidney disease, inflammation, leptin
INTRODUCTION Cachexia is prevalent among patients with chronic diseases such as cancer, chronic kidney disease (CKD), congestive heart failure, HIV infection, and chronic obstructive pulmonary disease (COPD) [1]. It is to be distinguished from malnutrition, which is defined as the consequence of insufficient food intake or an improper diet. Malnutrition is characterized by hunger, which is an adaptive response, whereas anorexia is prevalent in patients with wasting or cachexia [1,2,3]. Energy expenditure decreases as a protective mechanism in malnutrition, whereas it remains inappropriately high in cachexia or wasting [4]. In malnutrition, fat mass is preferentially lost and lean body mass and muscle mass is preserved. In cachexia or wasting, muscle is wasted and fat is relatively underutilized [5–7]. Restoring adequate food intake or altering the composition of the diet reverses malnutrition. Nutrition supplementation does not totally reverse cachexia or wasting [8,9]. Longevity has consistently been observed in patients with CKD who have more muscle and/or fat, who report better appetite, and who eat more [1]. Although inadequate nutritional intake may contribute to the cachexia syndrome, www.supportiveandpalliativecare.com
recent evidence indicates that other factors, including systemic inflammation, perturbations of appetite-controlling hormones from reduced renal clearance, aberrant neuropeptide signaling, insulin and insulin-like growth factor resistance, and metabolic acidosis, may be important in the pathogenesis of the cachexia syndrome [1,5,7,8,10].
LEPTIN PHYSIOLOGY AND ITS POTENTIAL ROLE IN CACHEXIA Leptin is an anorexigenic hormone as well as a cytokine produced in adipose tissues. It is a 146 amino acid mature protein produced by adipocytes,
a
Division of Pediatric Nephrology, Rady Children’s Hospital San Diego, University of California San Diego, La Jolla, California, USA and bInstitute of Biochemistry, Food Science and Nutrition, Hebrew University of Jerusalem, Rehovot, Israel Correspondence to Robert H. Mak, MD, PhD, Division of Pediatric Nephrology, Rady Children’s Hospital San Diego, University of California San Diego, 9500 Gilman Drive, La Jolla, CA 92093-0634, USA. Tel: +1 858 822 6717; e-mail: [email protected] Curr Opin Support Palliat Care 2014, 8:352–357 DOI:10.1097/SPC.0000000000000092 Volume 8 Number 4 December 2014
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The therapeutic potential of leptin signaling in cachexia Mak et al.
hormone binds to melanocortin receptor and inhibits food intake, primarily via type-4 melanocortin receptor (MC4R). AgRP is an endogenous antagonist of MC4R [11 ] (Fig. 1). Low leptin levels are responsible for the compensatory increase in appetite and body weight and decreased energy expenditure following caloric deprivation. Cachexia is a complication of many chronic conditions including cancer, COPD, congestive heart failure, CKD, and aging, whereby the decrease in body weight and food intake is not followed by a compensatory increase in appetite or decreased energy expenditure [1,8,10,12]. Leptin is also a proinflammatory cytokine; it increases in response to acute infection and plays a role on CD4þ T lymphocyte proliferation, macrophage phagocytosis, and the secretion of inflammatory cytokines such as interleukin (IL)-1 and tumor necrosis factor alpha (TNF-a) [15]. Cross-talk between leptin and inflammatory signaling, known to be activated in the above-mentioned cachectic conditions, may be responsible for this paradox [11 ]. For the purpose of this review, we will focus on the anorexia-cachexia syndrome in CKD.
KEY POINTS Cachexia is prevalent among patients with chronic diseases such as cancer, CKD, congestive heart failure, HIV infection, and COPD.
&
Leptin levels are significantly elevated in CKD and ESRD patients and are associated with markers of poor nutritional status as well as decline in renal function. Blockade of leptin receptor and leptin’s downstream signaling mediators, such as MC4R, attenuated CKDassociated cachexia. Pegylated leptin antagonist treatment ameliorated CKDassociated cachexia in mice, suggesting that leptin antagonism may represent a viable therapeutic strategy for cachexia in CKD.
&
and it is a member of the adipocytokine family [11 ]. Leptin is a product of the obese gene secreted by adipocytes in proportion to fat mass. It decreases food intake and increases energy expenditure by affecting the balance between orexigenic and anorexigenic hypothalamic pathways (Table 1) [11 ,12]. Leptin regulates energy homeostasis through signal transduction in the arcuate nucleus of the hypothalamus in which it interacts with neuropeptide Y (NPY) and agouti-related peptide (AgRP), acting as an antagonist to ghrelin. The major metabolic action of leptin is mediated through signaling from the hypothalamus to peripheral tissues via the autonomic nervous system. Leptin also influences the hypothalamopituitary-adrenal and hypothalamopituitary-thyroid axes [13,14]. Fasting decreases plasma leptin concentration, whereas refeeding reverses this decline, with leptin playing a role in long-term energy balance. Leptin suppresses food intake by counteracting the activity of neurons containing NPY and AgRP and by increasing the activity of neurons expressing a-melanocytestimulating hormone. a-Melanocyte-stimulation
&
&
LEPTIN IN CHRONIC KIDNEY DISEASE CKD-associated anorexia appears to be multifactorial and predicts clinical outcomes [1,11 ]. High plasma levels of insulin, leptin, and uremic toxins induce MC4R stimulation to increase energy expenditure and decrease food intake. Importantly, CKDassociated cachexia is linked to higher morbidity and mortality. The hyperleptinemia seen in patients with CKD may be due to poor renal clearance, overproduction, or both. Leptin levels are significantly elevated in CKD and end-stage renal disease (ESRD) patients and are associated with markers of poor nutritional status, such as low serum albumin and hypercatabolism as well as decline in renal function [16]. In children with CKD, an inverse linear correlation between leptin levels and energy &
Table 1. Summary of markers of appetite regulation in various cachectic states Circulating leptin levels
POMC/a-MSH hypothalamic levels
NPY/AgRP hypothalamic levels
Circulating inflammatory markers
Hypothalamic inflammatory markers
"
#
"#
"
Condition
Appetite
Body weight
Cancer cachexia
##
##
##
#
#
"
# #
CHF-induced cachexia
#
#
#
#
Unknown
Unknown
#
Unknown
#
"
Pulmonary cachexia
#
#
#
Unknown
Unknown
"
Unknown
CKD cachexia
##
##
"#
Unknown
Unknown
"#
Unknown
Aging cachexia
##
##
##
"
#
"#
Unknown
#–supported by human model data; –supported by animal model data. AgRP, agouti-related peptide; CHF, chronic heart failure; CKD, chronic kidney disease; a-MSH a-melanocyte-stimulating hormone; NPY, neuropeptide Y; POMC, pro-opiomelanocortin. & Adapted with permission from [11 ].
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Cachexia, nutrition and hydration
Cancer, CHF, COPD, CKD, aging
Cytokines Neuron MC-4R α-MSH NPY/AgRP
Food intake
POMC/CART
Energy expenditure
Arcuate nucleus
Leptin
Adipose tissue
FIGURE 1. Summary of the effects of peripheral hormones on hypothalamic regulation of food intake and energy expenditure. AgRP, Agouti-related peptide; CART, cocaine-amphetamine-related peptide; CKD, chronic kidney disease; COPD, chronic obstructive pulmonary disease; MC4R, type-4 melanocortin receptor; a-MSH, alpha-melanocyte-stimulating hormone; NPY, neuropeptide Y; POMC, pro-opiomelanocortin. Adapted with permission from [11 ]. &
intake expressed as the percentage of recommended dietary allowance has been reported [17]. Elevated serum leptin levels were thought to contribute to the development of anorexia and poor nutrition in patients with CKD. In a cross-sectional study in children with ESRD on hemodialysis, Besbas et al. [18] showed that higher leptin levels were present in severely malnourished patients than in those without malnutrition (Fig. 2). In a longitudinal study of patients with ESRD on peritoneal dialysis,
Stenvinkel et al. [19] demonstrated that serum leptin level and body fat content increase markedly during peritoneal dialysis. Patients who lost lean body mass during peritoneal dialysis had higher initial C-reactive protein levels (CRP) and increased their serum leptin levels significantly during peritoneal dialysis compared with those patients who gained lean body mass [19] (Fig. 3). A stepwise multiple regression
60 Gained LBM Lost LBM
Serum leptin (ng/ml)
Serum leptin (pg/ml)
50
60
40
20
40
30
20
10
0
0
Malnutrition n=7
Without malnutrition n = 10
Control n=9
FIGURE 2. Serum leptin levels in hemodialyzed children and controls according to malnutrition. Adapted with permission from [18]. 354
** *
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Initial examination
Follow-up
FIGURE 3. Serum leptin levels before and during PD in patients who lost (n ¼25 ) or gained (n ¼ 11) lean body mass during treatment with PD. LBM, lean body mass; LEPR, leptin receptor; PD, peritoneal dialysis. Adapted with permission from [19]. Volume 8 Number 4 December 2014
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The therapeutic potential of leptin signaling in cachexia Mak et al.
analysis demonstrated independent associations between changes in serum leptin and changes in both body fat mass and log CRP, respectively. Serum leptin concentrations have been shown to inversely associate with survival in some studies [11 ]. In others, leptin was shown to correlate with fat mass rather than independently affecting food intake or mortality [20]. Patients with CKD may have an acquired leptin receptor disorder resulting in central insensitivity or resistance, similar to obese individuals. Leptin reduces hypothalamic NPY levels and increases sympathetic activity with hyperinsulinemia, resulting in appetite suppression [11 ]. Supporting this hypothesis is the observation of increased sympathetic activity, via elevated dopamine, norepinephrine, and serotonin levels, found in patients with CKD. Elevated serum acute phase reactants, including CRP and several cytokines, most prominently IL-6 and TNF-a, are found in CKD patients and may be associated with reduced appetite in dialysis patients [1,8,10,12]. Increased inflammation in renal failure is multifactorial, and possible factors include decreased renal clearance and increased production of proinflammatory cytokines [1,21–23]. The mediators of inflammation act on the central nervous system to alter both appetite and metabolic rate. Studies in db/db mice show that the lack of leptin receptor is protective against CKD-induced cachexia [1,24]. Furthermore, manipulation of leptin’s downstream mediators in the hypothalamus, MC4R, by either gene deletion or by using antagonists of its receptor, confirms the relevance of this pathway in mediating anorexia and weight loss in the setting of CKD. We showed that genetic or pharmacological blockade of the MC4R attenuated CKD-associated cachexia [24]. However, the potential clinical utility of this approach has been limited by the need to deliver AgRP into the ventricles of the brain. NBI-12i is a small molecule MC4R antagonist that penetrates the central nervous system after peripheral administration. We showed that NBI-12i attenuates CKD-associated cachexia. NBI-12i exhibited additional desirable metabolic effects beyond the nutritional effects of stimulating appetite. NBI-12i-treated uremic mice gained lean body mass and fat mass and had a lower basal metabolic rate, whereas vehicle-treated and diet-supplemented CKD mice with the same caloric intake lost both lean body mass and fat mass and had an increased basal metabolic rate [25]. The protective effects of NBI-12i may be because of the normalization of the upregulation in uncoupling protein expression seen in CKD mice. These data underscore the importance of melanocortin signaling in the pathogenesis of CKD-associated &
&
cachexia and demonstrate the potential of peripheral administration of MC4R antagonists as a novel therapeutic approach. Recently, a cross-sectional study of 217 hemodialysis patients showed that those in the lowest tertile of ghrelin levels had the lowest BMI, highest CRP, and highest leptin levels [26]. These patients had increased mortality risk, despite adjustment for age, sex, and dialysis history. Moreover, those in this group with cachexia or protein-energy wasting had the highest all-cause and cardiovascular mortality risk (hazards ratios 3.34 and 3.54, respectively). In the setting of CKD, there is the opportunity to manipulate leptin levels not only by administering recombinant leptin but also by removing leptin from circulation using super-flux polysulfone dialyzers. Van Tellingen et al. [27] tried such an approach and although leptin levels were significantly reduced, no other parameters, such as appetite or body composition, were examined [27,28]. Thus, the effectiveness of this intervention remains unknown. Taken together, the evidence shows that cachexia in patients with CKD and ESRD is associated with poor prognosis. Elevated levels of leptin are likely results of decreased renal clearance and disease-related inflammation. Activation of the melanocortin system by leptin is key in the pathophysiology of CKD-associated cachexia. Further studies to explore the efficacy of therapeutic options, including polysulfone dialyzers to lower leptin levels, are needed to determine the role of leptin in this setting.
POTENTIAL ROLE OF LEPTIN RECEPTOR ANTAGONISTS Elevated serum leptin levels correlate with inflammation and predict changes in lean body mass in patients with CKD, and activation of the melanocortin system by leptin signaling mediates the pathophysiology of CKD-associated cachexia. Thus, a potential therapeutic strategy would be the use of a leptin receptor antagonist. Cheung et al. [29 ] tested whether treatment with a pegylated leptin receptor antagonist (PLA) may attenuate cachexia in mice with CKD. CKD and sham mice received vehicle or PLA (2 or 7 mg/kg per day). At these doses, PLA did not influence serum leptin levels in mice. Treatment with 7 mg/kg per day PLA stimulated appetite and weight gain, improved lean mass and muscle function, reduced energy expenditure, and normalized the levels of hepatic TNF-a and IL-6 mRNA in mice with CKD. Furthermore, treatment with 7 mg/kg per day PLA attenuated the CKDassociated increase in the transcriptional and protein abundance of uncoupling proteins that
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&&
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Cachexia, nutrition and hydration
mediates thermogenesis, and it normalized the molecular signatures of processes associated with muscle wasting in CKD, including proteolysis, myogenesis and muscle regeneration, and expression of proinflammatory muscle cytokines, such as IL-1a, IL-1b, and IL-6 and TNF-a [29 ]. These results suggest that leptin antagonism may represent a viable therapeutic strategy for cachexia in CKD. Whether this will be a successful strategy in the clinical setting remains to be tested in patients with CKD-associated cachexia, in which preservation of muscle mass is associated with a survival advantage. This strategy may also be useful in other clinical conditions presenting with the cachexia syndrome, such as cancer, heart failure, HIV infection, and COPD. &&
PHARMACOLOGY OF NOVEL PEGYLATED LEPTIN RECEPTOR ANTAGONISTS As there is no structural information of leptin:leptin receptor structure, we examined the known structures of IL-6-receptor complexes (IL-6/gp130) [30] and IL-6/IL-6Ra/gp130 complex [31] in which site III of the cytokine was first identified, we examined the interface between the tips of the vIL-6 bundle, comprising an A-B loop of IL-6 and the edge of one of the IL-6-receptor’s immunoglobulin-like domain (IGD)b-sheets. We further analyzed the corresponding A-B loop in leptin and though its sequence differed greatly in length and in composition compared with IL-6, we were able to identify, thanks to the use of the sensitive bidimensional Hydrophobic Cluster Analysis [32], a common short b-strand which interacts in the vIL6/gp130 complex, a strand in the receptor IGD. This strand was located before the first strand of the IGD core and was predicted to also be present in LEPR IGD. To verify this hypothesis and to test its generality, we prepared and purified to homogeneity several ovine and human recombinant leptin Ala mutants in the A-B loop (L39A/D40A, L39A/D40A/F41A, and L39A/D40A/ F41A/I41A) and documented their activity as potent competitive LEPR antagonists [33]. To verify the preservation and importance of this sequence for activation of LEPRs, we also prepared the corresponding muteins of mouse and rat leptin and documented their antagonistic activity [34]. Random mutagenesis of mouse leptin antagonist (L39A/ D40A/F41) followed by selection of high-affinity mutants by yeast-surface display indicated that replacing residue D23 with a nonnegatively charged amino acid (most specifically with Leu) leads to dramatically enhanced affinity of leptin toward LEPR resulting in development of superactive mouse, human, ovine, and rat leptin antagonists 356
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(D23L/L39A/D40A/F41A) expressed in Escherichia coli, refolded and purified to homogeneity as monomeric proteins [35–37]. Pegylation of leptin antagonists resulted in a potent and effective long-acting reagents suitable for in-vivo studies or therapies [38].
CONCLUSION Leptin levels are significantly elevated in CKD patients and are associated with markers of poor nutritional status as well as mortality and morbidity. Blockade of leptin’s downstream mediators such as, melanocortin receptor 4, attenuated the CKDassociated cachexia. Leptin antagonist treatment ameliorates CKD-associated cachexia in mice. Leptin antagonism may represent a viable therapeutic strategy for cachexia in CKD. Acknowledgements This work was supported, in part, by funding from National Institutes of Health Grant NIDDK R01 DK50780, BioLine Innovations, Jerusalem, Israel, and Neurocrine Biosciences, San Diego, California. Conflicts of interest There are no conflicts of interest.
REFERENCES AND RECOMMENDED READING Papers of particular interest, published within the annual period of review, have been highlighted as: & of special interest && of outstanding interest 1. Mak RH, Ikizler TA, Kovesdy CP, et al. Wasting in chronic kidney disease. J Cachexia Sarcopenia Muscle 2011; 2:9–25. 2. Kalantar-Zadeh K, Ikizler TA, Block G, et al. Malnutrition–inflammation complex syndrome in dialysis patients: causes and consequence. Am J Kidney Dis 2003; 42:864–881. 3. Kalantar-Zadeh K, Block G, McAllister CJ, et al. Appetite and inflammation, nutrition, anemia, and clinical outcome in hemodialysis patients. Am J Clin Nutr 2004; 80:299–307. 4. Wang AY, Sea MM, Tang N, et al. Resting energy expenditure and subsequent mortality risk in peritoneal dialysis patients. J Am Soc Nephrol 2004; 15:3134–3143. 5. Mak RH, Cheung W. Energy homeostasis and cachexia in chronic kidney disease. Pediatr Nephrol 2006; 21:1807–1814. 6. Mitch WE. Insights into the abnormalities of chronic renal disease attributed to malnutrition. J Am Soc Nephrol 2002; 13 (Suppl 1):S22–S27. 7. Mitch WE. Proteolytic mechanisms, not malnutrition, cause loss of muscle mass in kidney failure. J Ren Nutr 2006; 16:208–211. 8. Mak RH, Cheung W. Therapeutic strategy for cachexia in chronic kidney disease. Curr Opin Nephrol Hypertens 2007; 16:542–546. 9. Cano NJ, Fouque D, Roth H, et al. Intradialytic parenteral nutrition does not improve survival in malnourished hemodialysis patients: a 2-year multicenter, prospective, randomized study. J Am Soc Nephrol 2007; 18:2583– 2591. 10. Mak RH, Cheung WW, Zhan JY, et al. Cachexia and protein-energy wasting in children with chronic kidney disease. Pediatr Nephrol 2012; 27:173–181. 11. Engineer DR, Garcia JM. Leptin in anorexia and cachexia syndrome. Int J Pept & 2012; 2012:287457. This review presents the evidence and potential mechanisms mediating changes in the leptin pathway in the setting of anorexia and cachexia associated with chronic diseases. 12. Gunta SS, Mak RH. Ghrelin and leptin pathophysiology in chronic kidney disease. Pediatr Nephrol 2013; 28:611–616.
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The therapeutic potential of leptin signaling in cachexia Mak et al. 13. Blouet C, Schwartz GJ. Hypothalamic nutrient sensing in the control of energy homeostasis. Behav Brain Res 2010; 209:1–12. 14. Sahu A. Minireview: a hypothalamic role in energy balance with special emphasis on leptin. Endocrinology 2004; 14:2613–2620. 15. Lord GM. Leptin as a proinflammatory cytokine. Contrib Nephrol 2006; 151:151–164. 16. Liao MT, Sung CC, Hung KC, et al. Insulin resistance in patients with chronic kidney disease. J Biomed Biotechnol 2012; 2012:691369. 17. Rees L, Shaw V. Nutrition in children with CRF and on dialysis. Pediatr Nephrol 2007; 22:1689–1702. 18. Besbas N, Ozaltin F, Cos¸kun T, et al. Relationship of leptin and insulin-like growth factor I to nutritional status in hemodialyzed children. Pediatr Nephrol 2003; 18:1255–1259. 19. Stenvinkel P, Lindholm B, Lonnqvist F, et al. Increases in serum leptin levels during peritoneal dialysis are associated with inflammation and a decrease in lean body mass. J Am Soc Nephrol 2000; 11:1303–1309. 20. Beberashvili I, Sinuani I, Azar A, et al. Longitudinal study of leptin levels in chronic hemodialysis patients. Nutr J 2011; 10:68. 21. De Vriese AS. Prevention and treatment of acute renal failure in sepsis. J Am Soc Nephrol 2003; 14:792–805. 22. Carrero JJ, Stenvinkel P, Cuppari L, et al. Etiology of the protein-energy wasting syndrome in chronic kidney disease: a consensus statement from the International Society of Renal Nutrition and Metabolism (ISRNM). J Ren Nutr 2013; 23:77–90. 23. Miyamoto T, Carrero JJ, Stenvinkel P. Inflammation as a risk factor and target for therapy in chronic kidney disease. Curr Opin Nephrol Hypertens 2011; 20:662–668. 24. Cheung W, Yu PX, Little BM, et al. Role of leptin and melanocortin signaling in uremia-associated cachexia. J Clin Invest 2005; 115:1659–1665. 25. Cheung W, Kuo HJ, Markison S, et al. Peripheral administration of the melanocortin-4 receptor antagonist NBI-12i ameliorates uremia-associated cachexia in mice. J Am Soc Nephrol 2007; 18:2517–2524. 26. Carrero JJ, Nakashima A, Qureshi AR, et al. Protein-energy wasting modifies the association of ghrelin with inflammation, leptin, and mortality in hemodialysis patients. Kidney Int 2011; 79:749–756. 27. Van Tellingen A, Grooteman MPC, Schoorl M, et al. Enhanced long-term reduction of plasma leptin concentrations by super-flux polysulfone dialysers. Nephrol Dial Transplant 2004; 19:1198–1203.
28. Javor ED, Cochran EK, Musso C, et al. Long-term efficacy of leptin replacement in patients with generalized lipodystrophy. Diabetes 2005; 54:1994– 2002. 29. Cheung WW, Ding W, Gunta SS, et al. Pegulated leptin antagonist treatment && ameliorates CKD-associated cachexia in mice. J Am Soc Nephrol 2014; 25:119–128. This study investigated the effects of PLA in a mouse model of CKD. Pegylated leptin receptor antagonists may represent a novel therapeutic modality for CKDassociated cachexia. 30. Chow D, He X, Snow AL, et al. Structure of an extracellular gp130 cytokine receptor signaling complex. Science 2001; 291:2150–2155. 31. Boulanger MJ, Chow DC, Brevnova EE, et al. Hexameric structure and assembly of the interleukin-6/IL-6alpha-receptor/gp130 complex. Science 2003; 300:2101–2104. 32. Callebaut I, Labesse G, Durand P, et al. Deciphering protein sequence information through hydrophobic cluster analysis (HCA): current status and perspectives. Cell Mol Life Sci 1997; 53:621–645. 33. Niv-Spector L, Gonen-Berger D, Gourdou I, et al. Identification of the hydrophobic strand in the A-B loop of leptin as major binding site III: implications for large-scale preparation of potent recombinant human and ovine leptin antagonists. Biochem J 2005; 391:221–230. 34. Salomon G, Niv-Spector L, Gussakovsky EE, et al. Large-scale preparation of biologically active mouse and rat leptins and their L39A/D40A/F41A muteins which act as potent antagonists. Protein Expr Purif 2006; 47:128– 136. 35. Shpilman M, Niv-Spector L, Katz M, et al. Development and characterization of high affinity leptins and leptin antagonists. J Biol Chem 2011; 286:4429– 4442. 36. Niv-Spector L, Shpilman M, Boisclair Y, et al. Large-scale preparation and characterization of nonpegylated and pegylated superactive ovine leptin antagonist. Protein Expr Purif 2012; 81:186–192. 37. Jamroz-Wis´niewska A, Gertler A, Solomon G, et al. Leptin-induced endothelium-dependent vasorelaxation of peripheral arteries in lean and obese rats: role of nitric oxide and hydrogen sulfide. PLoS One 2014; 9:e86744. 38. Elinav E, Niv-Spector L, Katz M, et al. Pegylated leptin antagonist is a potent orexigenic agent: preparation and mechanism of activity. Endocrinology 2009; 150:3083–3091.
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Exploiting the therapeutic potential of leptin signaling in cachexia Robert H. Mak a, Wai W. Cheung a, and Arieh Gertler b
Purpose of review The anorexia-cachexia syndrome is a complication of many chronic conditions including cancer, chronic obstructive pulmonary disease, congestive heart failure, and chronic kidney disease (CKD). Leptin levels are significantly elevated in CKD patients and are associated with markers of poor nutritional status as well as mortality and morbidity. This review will focus on the mechanism and exploit the therapeutic potential of leptin signaling in CKD-associated cachexia. Recent findings Studies in db/db mice show that the lack of leptin receptor is protective against CKD-induced cachexia. Blockade of leptin’s downstream mediators, such as melanocortin-4 receptor, attenuated CKD-associated cachexia. Pegylation of leptin antagonists resulted in a potent and effective long-acting reagents suitable for in-vivo studies or therapies. Pegylated leptin antagonist treatment ameliorates CKD-associated cachexia in mice. Summary Leptin antagonism may represent a viable therapeutic strategy for cachexia in CKD. Keywords cachexia, chronic kidney disease, inflammation, leptin
INTRODUCTION Cachexia is prevalent among patients with chronic diseases such as cancer, chronic kidney disease (CKD), congestive heart failure, HIV infection, and chronic obstructive pulmonary disease (COPD) [1]. It is to be distinguished from malnutrition, which is defined as the consequence of insufficient food intake or an improper diet. Malnutrition is characterized by hunger, which is an adaptive response, whereas anorexia is prevalent in patients with wasting or cachexia [1,2,3]. Energy expenditure decreases as a protective mechanism in malnutrition, whereas it remains inappropriately high in cachexia or wasting [4]. In malnutrition, fat mass is preferentially lost and lean body mass and muscle mass is preserved. In cachexia or wasting, muscle is wasted and fat is relatively underutilized [5–7]. Restoring adequate food intake or altering the composition of the diet reverses malnutrition. Nutrition supplementation does not totally reverse cachexia or wasting [8,9]. Longevity has consistently been observed in patients with CKD who have more muscle and/or fat, who report better appetite, and who eat more [1]. Although inadequate nutritional intake may contribute to the cachexia syndrome, www.supportiveandpalliativecare.com
recent evidence indicates that other factors, including systemic inflammation, perturbations of appetite-controlling hormones from reduced renal clearance, aberrant neuropeptide signaling, insulin and insulin-like growth factor resistance, and metabolic acidosis, may be important in the pathogenesis of the cachexia syndrome [1,5,7,8,10].
LEPTIN PHYSIOLOGY AND ITS POTENTIAL ROLE IN CACHEXIA Leptin is an anorexigenic hormone as well as a cytokine produced in adipose tissues. It is a 146 amino acid mature protein produced by adipocytes,
a
Division of Pediatric Nephrology, Rady Children’s Hospital San Diego, University of California San Diego, La Jolla, California, USA and bInstitute of Biochemistry, Food Science and Nutrition, Hebrew University of Jerusalem, Rehovot, Israel Correspondence to Robert H. Mak, MD, PhD, Division of Pediatric Nephrology, Rady Children’s Hospital San Diego, University of California San Diego, 9500 Gilman Drive, La Jolla, CA 92093-0634, USA. Tel: +1 858 822 6717; e-mail: [email protected] Curr Opin Support Palliat Care 2014, 8:352–357 DOI:10.1097/SPC.0000000000000092 Volume 8 Number 4 December 2014
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The therapeutic potential of leptin signaling in cachexia Mak et al.
hormone binds to melanocortin receptor and inhibits food intake, primarily via type-4 melanocortin receptor (MC4R). AgRP is an endogenous antagonist of MC4R [11 ] (Fig. 1). Low leptin levels are responsible for the compensatory increase in appetite and body weight and decreased energy expenditure following caloric deprivation. Cachexia is a complication of many chronic conditions including cancer, COPD, congestive heart failure, CKD, and aging, whereby the decrease in body weight and food intake is not followed by a compensatory increase in appetite or decreased energy expenditure [1,8,10,12]. Leptin is also a proinflammatory cytokine; it increases in response to acute infection and plays a role on CD4þ T lymphocyte proliferation, macrophage phagocytosis, and the secretion of inflammatory cytokines such as interleukin (IL)-1 and tumor necrosis factor alpha (TNF-a) [15]. Cross-talk between leptin and inflammatory signaling, known to be activated in the above-mentioned cachectic conditions, may be responsible for this paradox [11 ]. For the purpose of this review, we will focus on the anorexia-cachexia syndrome in CKD.
KEY POINTS Cachexia is prevalent among patients with chronic diseases such as cancer, CKD, congestive heart failure, HIV infection, and COPD.
&
Leptin levels are significantly elevated in CKD and ESRD patients and are associated with markers of poor nutritional status as well as decline in renal function. Blockade of leptin receptor and leptin’s downstream signaling mediators, such as MC4R, attenuated CKDassociated cachexia. Pegylated leptin antagonist treatment ameliorated CKDassociated cachexia in mice, suggesting that leptin antagonism may represent a viable therapeutic strategy for cachexia in CKD.
&
and it is a member of the adipocytokine family [11 ]. Leptin is a product of the obese gene secreted by adipocytes in proportion to fat mass. It decreases food intake and increases energy expenditure by affecting the balance between orexigenic and anorexigenic hypothalamic pathways (Table 1) [11 ,12]. Leptin regulates energy homeostasis through signal transduction in the arcuate nucleus of the hypothalamus in which it interacts with neuropeptide Y (NPY) and agouti-related peptide (AgRP), acting as an antagonist to ghrelin. The major metabolic action of leptin is mediated through signaling from the hypothalamus to peripheral tissues via the autonomic nervous system. Leptin also influences the hypothalamopituitary-adrenal and hypothalamopituitary-thyroid axes [13,14]. Fasting decreases plasma leptin concentration, whereas refeeding reverses this decline, with leptin playing a role in long-term energy balance. Leptin suppresses food intake by counteracting the activity of neurons containing NPY and AgRP and by increasing the activity of neurons expressing a-melanocytestimulating hormone. a-Melanocyte-stimulation
&
&
LEPTIN IN CHRONIC KIDNEY DISEASE CKD-associated anorexia appears to be multifactorial and predicts clinical outcomes [1,11 ]. High plasma levels of insulin, leptin, and uremic toxins induce MC4R stimulation to increase energy expenditure and decrease food intake. Importantly, CKDassociated cachexia is linked to higher morbidity and mortality. The hyperleptinemia seen in patients with CKD may be due to poor renal clearance, overproduction, or both. Leptin levels are significantly elevated in CKD and end-stage renal disease (ESRD) patients and are associated with markers of poor nutritional status, such as low serum albumin and hypercatabolism as well as decline in renal function [16]. In children with CKD, an inverse linear correlation between leptin levels and energy &
Table 1. Summary of markers of appetite regulation in various cachectic states Circulating leptin levels
POMC/a-MSH hypothalamic levels
NPY/AgRP hypothalamic levels
Circulating inflammatory markers
Hypothalamic inflammatory markers
"
#
"#
"
Condition
Appetite
Body weight
Cancer cachexia
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##
##
#
#
"
# #
CHF-induced cachexia
#
#
#
#
Unknown
Unknown
#
Unknown
#
"
Pulmonary cachexia
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#
#
Unknown
Unknown
"
Unknown
CKD cachexia
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##
"#
Unknown
Unknown
"#
Unknown
Aging cachexia
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##
##
"
#
"#
Unknown
#–supported by human model data; –supported by animal model data. AgRP, agouti-related peptide; CHF, chronic heart failure; CKD, chronic kidney disease; a-MSH a-melanocyte-stimulating hormone; NPY, neuropeptide Y; POMC, pro-opiomelanocortin. & Adapted with permission from [11 ].
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Cachexia, nutrition and hydration
Cancer, CHF, COPD, CKD, aging
Cytokines Neuron MC-4R α-MSH NPY/AgRP
Food intake
POMC/CART
Energy expenditure
Arcuate nucleus
Leptin
Adipose tissue
FIGURE 1. Summary of the effects of peripheral hormones on hypothalamic regulation of food intake and energy expenditure. AgRP, Agouti-related peptide; CART, cocaine-amphetamine-related peptide; CKD, chronic kidney disease; COPD, chronic obstructive pulmonary disease; MC4R, type-4 melanocortin receptor; a-MSH, alpha-melanocyte-stimulating hormone; NPY, neuropeptide Y; POMC, pro-opiomelanocortin. Adapted with permission from [11 ]. &
intake expressed as the percentage of recommended dietary allowance has been reported [17]. Elevated serum leptin levels were thought to contribute to the development of anorexia and poor nutrition in patients with CKD. In a cross-sectional study in children with ESRD on hemodialysis, Besbas et al. [18] showed that higher leptin levels were present in severely malnourished patients than in those without malnutrition (Fig. 2). In a longitudinal study of patients with ESRD on peritoneal dialysis,
Stenvinkel et al. [19] demonstrated that serum leptin level and body fat content increase markedly during peritoneal dialysis. Patients who lost lean body mass during peritoneal dialysis had higher initial C-reactive protein levels (CRP) and increased their serum leptin levels significantly during peritoneal dialysis compared with those patients who gained lean body mass [19] (Fig. 3). A stepwise multiple regression
60 Gained LBM Lost LBM
Serum leptin (ng/ml)
Serum leptin (pg/ml)
50
60
40
20
40
30
20
10
0
0
Malnutrition n=7
Without malnutrition n = 10
Control n=9
FIGURE 2. Serum leptin levels in hemodialyzed children and controls according to malnutrition. Adapted with permission from [18]. 354
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Initial examination
Follow-up
FIGURE 3. Serum leptin levels before and during PD in patients who lost (n ¼25 ) or gained (n ¼ 11) lean body mass during treatment with PD. LBM, lean body mass; LEPR, leptin receptor; PD, peritoneal dialysis. Adapted with permission from [19]. Volume 8 Number 4 December 2014
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The therapeutic potential of leptin signaling in cachexia Mak et al.
analysis demonstrated independent associations between changes in serum leptin and changes in both body fat mass and log CRP, respectively. Serum leptin concentrations have been shown to inversely associate with survival in some studies [11 ]. In others, leptin was shown to correlate with fat mass rather than independently affecting food intake or mortality [20]. Patients with CKD may have an acquired leptin receptor disorder resulting in central insensitivity or resistance, similar to obese individuals. Leptin reduces hypothalamic NPY levels and increases sympathetic activity with hyperinsulinemia, resulting in appetite suppression [11 ]. Supporting this hypothesis is the observation of increased sympathetic activity, via elevated dopamine, norepinephrine, and serotonin levels, found in patients with CKD. Elevated serum acute phase reactants, including CRP and several cytokines, most prominently IL-6 and TNF-a, are found in CKD patients and may be associated with reduced appetite in dialysis patients [1,8,10,12]. Increased inflammation in renal failure is multifactorial, and possible factors include decreased renal clearance and increased production of proinflammatory cytokines [1,21–23]. The mediators of inflammation act on the central nervous system to alter both appetite and metabolic rate. Studies in db/db mice show that the lack of leptin receptor is protective against CKD-induced cachexia [1,24]. Furthermore, manipulation of leptin’s downstream mediators in the hypothalamus, MC4R, by either gene deletion or by using antagonists of its receptor, confirms the relevance of this pathway in mediating anorexia and weight loss in the setting of CKD. We showed that genetic or pharmacological blockade of the MC4R attenuated CKD-associated cachexia [24]. However, the potential clinical utility of this approach has been limited by the need to deliver AgRP into the ventricles of the brain. NBI-12i is a small molecule MC4R antagonist that penetrates the central nervous system after peripheral administration. We showed that NBI-12i attenuates CKD-associated cachexia. NBI-12i exhibited additional desirable metabolic effects beyond the nutritional effects of stimulating appetite. NBI-12i-treated uremic mice gained lean body mass and fat mass and had a lower basal metabolic rate, whereas vehicle-treated and diet-supplemented CKD mice with the same caloric intake lost both lean body mass and fat mass and had an increased basal metabolic rate [25]. The protective effects of NBI-12i may be because of the normalization of the upregulation in uncoupling protein expression seen in CKD mice. These data underscore the importance of melanocortin signaling in the pathogenesis of CKD-associated &
&
cachexia and demonstrate the potential of peripheral administration of MC4R antagonists as a novel therapeutic approach. Recently, a cross-sectional study of 217 hemodialysis patients showed that those in the lowest tertile of ghrelin levels had the lowest BMI, highest CRP, and highest leptin levels [26]. These patients had increased mortality risk, despite adjustment for age, sex, and dialysis history. Moreover, those in this group with cachexia or protein-energy wasting had the highest all-cause and cardiovascular mortality risk (hazards ratios 3.34 and 3.54, respectively). In the setting of CKD, there is the opportunity to manipulate leptin levels not only by administering recombinant leptin but also by removing leptin from circulation using super-flux polysulfone dialyzers. Van Tellingen et al. [27] tried such an approach and although leptin levels were significantly reduced, no other parameters, such as appetite or body composition, were examined [27,28]. Thus, the effectiveness of this intervention remains unknown. Taken together, the evidence shows that cachexia in patients with CKD and ESRD is associated with poor prognosis. Elevated levels of leptin are likely results of decreased renal clearance and disease-related inflammation. Activation of the melanocortin system by leptin is key in the pathophysiology of CKD-associated cachexia. Further studies to explore the efficacy of therapeutic options, including polysulfone dialyzers to lower leptin levels, are needed to determine the role of leptin in this setting.
POTENTIAL ROLE OF LEPTIN RECEPTOR ANTAGONISTS Elevated serum leptin levels correlate with inflammation and predict changes in lean body mass in patients with CKD, and activation of the melanocortin system by leptin signaling mediates the pathophysiology of CKD-associated cachexia. Thus, a potential therapeutic strategy would be the use of a leptin receptor antagonist. Cheung et al. [29 ] tested whether treatment with a pegylated leptin receptor antagonist (PLA) may attenuate cachexia in mice with CKD. CKD and sham mice received vehicle or PLA (2 or 7 mg/kg per day). At these doses, PLA did not influence serum leptin levels in mice. Treatment with 7 mg/kg per day PLA stimulated appetite and weight gain, improved lean mass and muscle function, reduced energy expenditure, and normalized the levels of hepatic TNF-a and IL-6 mRNA in mice with CKD. Furthermore, treatment with 7 mg/kg per day PLA attenuated the CKDassociated increase in the transcriptional and protein abundance of uncoupling proteins that
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Cachexia, nutrition and hydration
mediates thermogenesis, and it normalized the molecular signatures of processes associated with muscle wasting in CKD, including proteolysis, myogenesis and muscle regeneration, and expression of proinflammatory muscle cytokines, such as IL-1a, IL-1b, and IL-6 and TNF-a [29 ]. These results suggest that leptin antagonism may represent a viable therapeutic strategy for cachexia in CKD. Whether this will be a successful strategy in the clinical setting remains to be tested in patients with CKD-associated cachexia, in which preservation of muscle mass is associated with a survival advantage. This strategy may also be useful in other clinical conditions presenting with the cachexia syndrome, such as cancer, heart failure, HIV infection, and COPD. &&
PHARMACOLOGY OF NOVEL PEGYLATED LEPTIN RECEPTOR ANTAGONISTS As there is no structural information of leptin:leptin receptor structure, we examined the known structures of IL-6-receptor complexes (IL-6/gp130) [30] and IL-6/IL-6Ra/gp130 complex [31] in which site III of the cytokine was first identified, we examined the interface between the tips of the vIL-6 bundle, comprising an A-B loop of IL-6 and the edge of one of the IL-6-receptor’s immunoglobulin-like domain (IGD)b-sheets. We further analyzed the corresponding A-B loop in leptin and though its sequence differed greatly in length and in composition compared with IL-6, we were able to identify, thanks to the use of the sensitive bidimensional Hydrophobic Cluster Analysis [32], a common short b-strand which interacts in the vIL6/gp130 complex, a strand in the receptor IGD. This strand was located before the first strand of the IGD core and was predicted to also be present in LEPR IGD. To verify this hypothesis and to test its generality, we prepared and purified to homogeneity several ovine and human recombinant leptin Ala mutants in the A-B loop (L39A/D40A, L39A/D40A/F41A, and L39A/D40A/ F41A/I41A) and documented their activity as potent competitive LEPR antagonists [33]. To verify the preservation and importance of this sequence for activation of LEPRs, we also prepared the corresponding muteins of mouse and rat leptin and documented their antagonistic activity [34]. Random mutagenesis of mouse leptin antagonist (L39A/ D40A/F41) followed by selection of high-affinity mutants by yeast-surface display indicated that replacing residue D23 with a nonnegatively charged amino acid (most specifically with Leu) leads to dramatically enhanced affinity of leptin toward LEPR resulting in development of superactive mouse, human, ovine, and rat leptin antagonists 356
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(D23L/L39A/D40A/F41A) expressed in Escherichia coli, refolded and purified to homogeneity as monomeric proteins [35–37]. Pegylation of leptin antagonists resulted in a potent and effective long-acting reagents suitable for in-vivo studies or therapies [38].
CONCLUSION Leptin levels are significantly elevated in CKD patients and are associated with markers of poor nutritional status as well as mortality and morbidity. Blockade of leptin’s downstream mediators such as, melanocortin receptor 4, attenuated the CKDassociated cachexia. Leptin antagonist treatment ameliorates CKD-associated cachexia in mice. Leptin antagonism may represent a viable therapeutic strategy for cachexia in CKD. Acknowledgements This work was supported, in part, by funding from National Institutes of Health Grant NIDDK R01 DK50780, BioLine Innovations, Jerusalem, Israel, and Neurocrine Biosciences, San Diego, California. Conflicts of interest There are no conflicts of interest.
REFERENCES AND RECOMMENDED READING Papers of particular interest, published within the annual period of review, have been highlighted as: & of special interest && of outstanding interest 1. Mak RH, Ikizler TA, Kovesdy CP, et al. Wasting in chronic kidney disease. J Cachexia Sarcopenia Muscle 2011; 2:9–25. 2. Kalantar-Zadeh K, Ikizler TA, Block G, et al. Malnutrition–inflammation complex syndrome in dialysis patients: causes and consequence. Am J Kidney Dis 2003; 42:864–881. 3. Kalantar-Zadeh K, Block G, McAllister CJ, et al. Appetite and inflammation, nutrition, anemia, and clinical outcome in hemodialysis patients. Am J Clin Nutr 2004; 80:299–307. 4. Wang AY, Sea MM, Tang N, et al. Resting energy expenditure and subsequent mortality risk in peritoneal dialysis patients. J Am Soc Nephrol 2004; 15:3134–3143. 5. Mak RH, Cheung W. Energy homeostasis and cachexia in chronic kidney disease. Pediatr Nephrol 2006; 21:1807–1814. 6. Mitch WE. Insights into the abnormalities of chronic renal disease attributed to malnutrition. J Am Soc Nephrol 2002; 13 (Suppl 1):S22–S27. 7. Mitch WE. Proteolytic mechanisms, not malnutrition, cause loss of muscle mass in kidney failure. J Ren Nutr 2006; 16:208–211. 8. Mak RH, Cheung W. Therapeutic strategy for cachexia in chronic kidney disease. Curr Opin Nephrol Hypertens 2007; 16:542–546. 9. Cano NJ, Fouque D, Roth H, et al. Intradialytic parenteral nutrition does not improve survival in malnourished hemodialysis patients: a 2-year multicenter, prospective, randomized study. J Am Soc Nephrol 2007; 18:2583– 2591. 10. Mak RH, Cheung WW, Zhan JY, et al. Cachexia and protein-energy wasting in children with chronic kidney disease. Pediatr Nephrol 2012; 27:173–181. 11. Engineer DR, Garcia JM. Leptin in anorexia and cachexia syndrome. Int J Pept & 2012; 2012:287457. This review presents the evidence and potential mechanisms mediating changes in the leptin pathway in the setting of anorexia and cachexia associated with chronic diseases. 12. Gunta SS, Mak RH. Ghrelin and leptin pathophysiology in chronic kidney disease. Pediatr Nephrol 2013; 28:611–616.
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The therapeutic potential of leptin signaling in cachexia Mak et al. 13. Blouet C, Schwartz GJ. Hypothalamic nutrient sensing in the control of energy homeostasis. Behav Brain Res 2010; 209:1–12. 14. Sahu A. Minireview: a hypothalamic role in energy balance with special emphasis on leptin. Endocrinology 2004; 14:2613–2620. 15. Lord GM. Leptin as a proinflammatory cytokine. Contrib Nephrol 2006; 151:151–164. 16. Liao MT, Sung CC, Hung KC, et al. Insulin resistance in patients with chronic kidney disease. J Biomed Biotechnol 2012; 2012:691369. 17. Rees L, Shaw V. Nutrition in children with CRF and on dialysis. Pediatr Nephrol 2007; 22:1689–1702. 18. Besbas N, Ozaltin F, Cos¸kun T, et al. Relationship of leptin and insulin-like growth factor I to nutritional status in hemodialyzed children. Pediatr Nephrol 2003; 18:1255–1259. 19. Stenvinkel P, Lindholm B, Lonnqvist F, et al. Increases in serum leptin levels during peritoneal dialysis are associated with inflammation and a decrease in lean body mass. J Am Soc Nephrol 2000; 11:1303–1309. 20. Beberashvili I, Sinuani I, Azar A, et al. Longitudinal study of leptin levels in chronic hemodialysis patients. Nutr J 2011; 10:68. 21. De Vriese AS. Prevention and treatment of acute renal failure in sepsis. J Am Soc Nephrol 2003; 14:792–805. 22. Carrero JJ, Stenvinkel P, Cuppari L, et al. Etiology of the protein-energy wasting syndrome in chronic kidney disease: a consensus statement from the International Society of Renal Nutrition and Metabolism (ISRNM). J Ren Nutr 2013; 23:77–90. 23. Miyamoto T, Carrero JJ, Stenvinkel P. Inflammation as a risk factor and target for therapy in chronic kidney disease. Curr Opin Nephrol Hypertens 2011; 20:662–668. 24. Cheung W, Yu PX, Little BM, et al. Role of leptin and melanocortin signaling in uremia-associated cachexia. J Clin Invest 2005; 115:1659–1665. 25. Cheung W, Kuo HJ, Markison S, et al. Peripheral administration of the melanocortin-4 receptor antagonist NBI-12i ameliorates uremia-associated cachexia in mice. J Am Soc Nephrol 2007; 18:2517–2524. 26. Carrero JJ, Nakashima A, Qureshi AR, et al. Protein-energy wasting modifies the association of ghrelin with inflammation, leptin, and mortality in hemodialysis patients. Kidney Int 2011; 79:749–756. 27. Van Tellingen A, Grooteman MPC, Schoorl M, et al. Enhanced long-term reduction of plasma leptin concentrations by super-flux polysulfone dialysers. Nephrol Dial Transplant 2004; 19:1198–1203.
28. Javor ED, Cochran EK, Musso C, et al. Long-term efficacy of leptin replacement in patients with generalized lipodystrophy. Diabetes 2005; 54:1994– 2002. 29. Cheung WW, Ding W, Gunta SS, et al. Pegulated leptin antagonist treatment && ameliorates CKD-associated cachexia in mice. J Am Soc Nephrol 2014; 25:119–128. This study investigated the effects of PLA in a mouse model of CKD. Pegylated leptin receptor antagonists may represent a novel therapeutic modality for CKDassociated cachexia. 30. Chow D, He X, Snow AL, et al. Structure of an extracellular gp130 cytokine receptor signaling complex. Science 2001; 291:2150–2155. 31. Boulanger MJ, Chow DC, Brevnova EE, et al. Hexameric structure and assembly of the interleukin-6/IL-6alpha-receptor/gp130 complex. Science 2003; 300:2101–2104. 32. Callebaut I, Labesse G, Durand P, et al. Deciphering protein sequence information through hydrophobic cluster analysis (HCA): current status and perspectives. Cell Mol Life Sci 1997; 53:621–645. 33. Niv-Spector L, Gonen-Berger D, Gourdou I, et al. Identification of the hydrophobic strand in the A-B loop of leptin as major binding site III: implications for large-scale preparation of potent recombinant human and ovine leptin antagonists. Biochem J 2005; 391:221–230. 34. Salomon G, Niv-Spector L, Gussakovsky EE, et al. Large-scale preparation of biologically active mouse and rat leptins and their L39A/D40A/F41A muteins which act as potent antagonists. Protein Expr Purif 2006; 47:128– 136. 35. Shpilman M, Niv-Spector L, Katz M, et al. Development and characterization of high affinity leptins and leptin antagonists. J Biol Chem 2011; 286:4429– 4442. 36. Niv-Spector L, Shpilman M, Boisclair Y, et al. Large-scale preparation and characterization of nonpegylated and pegylated superactive ovine leptin antagonist. Protein Expr Purif 2012; 81:186–192. 37. Jamroz-Wis´niewska A, Gertler A, Solomon G, et al. Leptin-induced endothelium-dependent vasorelaxation of peripheral arteries in lean and obese rats: role of nitric oxide and hydrogen sulfide. PLoS One 2014; 9:e86744. 38. Elinav E, Niv-Spector L, Katz M, et al. Pegylated leptin antagonist is a potent orexigenic agent: preparation and mechanism of activity. Endocrinology 2009; 150:3083–3091.
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