Atherosclerosis Supplements 17 C (2015) 17–22 www.elsevier.com/locate/atherosclerosis
Effect of ezetimibe on cholesterol absorption and lipoprotein composition in diabetes and metabolic syndrome Massimo Federici * University of Rome “Tor Vergata”, Department of Systems Medicine and Center for Atherosclerosis “Policlinico Tor Vergata”, Rome, Italy
Abstract Ezetimibe exerts multiple favorable effects on the lipoprotein profile and reduces some inflammatory markers. Decreasing cholesterol synthesis with statin treatment can cause a compensatory increase in cholesterol absorption that reduces the efficacy of statin therapy, whereas addition of a cholesterol absorption inhibitor can improve outcomes. Recent evidence suggests a beneficial effect on atherosclerosis. In patients with diabetes, the effect of insulin resistance on low-density lipoprotein metabolism combined with the effect of hyperglycemia on cholesterol absorption may further diminish the favorable effects of statins. Further analysis is needed also to determine whether the stronger effects of ezetimibe seen in patients with diabetes are a consequence of an interaction of the drug with specific mechanisms. © 2015 Elsevier Ireland Ltd. All rights reserved. Keywords: Ezetimibe; Insulin resistance; Lipoprotein metabolism; Diabetes; Metabolic syndrome
Recent studies have confirmed an effect of ezetimibe on atherosclerosis [1,2]. Whether this result is mediated only by its effect of cholesterol absorption is an area of active investigation. Inhibition of cholesterol synthesis by statins has been associated with a compensatory increase in intestinal cholesterol absorption. A crossover study, conducted on hyperlipidemic men receiving atorvastatin 40 mg/day vs placebo, shows that atorvastatin significantly increased intestinal mRNA levels of Niemann-Pick C1-like 1 protein (NPC1L1), as well as 3-hydroxy-3-methyl-glutaryl-CoA (HMG-CoA) reductase, low-density lipoprotein receptor (LDLR), proprotein convertase subtilisin/kexin type 9 (PCSK9), sterol regulatory element-binding protein-2 (SREBP2), and hepatocyte nuclear factor 4alpha (HNF-4α) [3]. There was a positive correlation between the lipogenesis markers SREBP-2 and HNF-4α, and the expression of NPC1L1 at the intestinal level in hyperlipidemic men. Thus, when statin administration decreases cholesterol synthesis, the body adapts by increasing cholesterol absorption. * University of Rome “Tor Vergata”, Department of Systems Medicine and Center for Atherosclerosis “Policlinico Tor Vergata”, Via Montpellier 1, 00133 Rome, Italy. Tel.: +39 0672 596 889. E-mail address: [email protected]. 1567-5688/© 2015 Elsevier Ireland Ltd. All rights reserved.
Abnormalities in cholesterol metabolism in type 2 diabetes include enhanced cholesterol synthesis and reduced cholesterol absorption. Also insulin resistance and obesity have been found to be associated with elevated cholesterol synthesis and low cholesterol absorption in cross-sectional studies [4–8]. Despite these observations, which are based mostly on indirect markers of cholesterol metabolism, diabetic dyslipidemia is typically characterized by increased very low density lipoprotein (VLDL) and reduced highdensity lipoprotein (HDL), but surprisingly no change in low-density lipoprotein (LDL) cholesterol levels [9]. To explain this conundrum, it has been proposed that the increased hepatic VLDL lipids and apolipoprotein B (apoB) secretion characteristic of type 2 diabetes and metabolic syndrome are balanced by increased LDL fractional catabolism, at least in early type 2 diabetes, when subjects are hyperinsulinemic [10]. This effect is mediated in part by the insulin receptor, which influences LDL fractional catabolism by regulating LDLR protein levels. Insulin receptor knockdown suppresses hepatic LDLR expression via a pathway that involves mammalian target of rapamycin complex 1, hepatocyte nuclear factor 1-alpha and PCSK9. Although direct proof in humans is still lacking, it is intriguing to speculate that in the early phases
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of diabetes, which are characterized by mild insulin resistance, hyperinsulinemia is able to maintain normal LDLR expression and LDL catabolism, keeping total cholesterol in the physiological range [10]. This may explain the normal total cholesterol levels observed in early diabetes. On the contrary, in advanced disease, when chronic insulin resistance leads to beta cell failure and relative hypoinsulinemia, the insulin receptor/LDL receptor positive loop is lost, resulting in reduced LDLR expression and a lower LDL fractional catabolic rate (FCR) that may explain the hypercholesterolemia observed in patients with long-standing diabetes. Experimental studies in control and streptozotocin diabetic rats that reveal another important aspect to consider: increased expression of NPC1L1 and reduced expression of ATP-binding cassette sub-family G members 5 and 8 (ABCG5 and ABCG8) are correlated with abnormally high chylomicron and VLDL levels [11]. The guidelines for cardiovascular prevention in subjects with diabetes recommend early statin treatment; however, decreasing cholesterol synthesis may provoke a compensatory increase in cholesterol absorption. The effects of insulin resistance on LDL metabolism combined with the effects of hyperglycemia on molecules mediating cholesterol absorption may diminish the favorable effects of statins in diabetic subjects. These observations support the addition of ezetimibe to statin therapy in subjects with diabetes. Clinical data show that combination therapy with a statin plus ezetimibe has a positive effect on lipid profiles, and especially on apoB. Ruggenenti et al. found that adding ezetimibe to ongoing simvastatin therapy improved the pro-atherogenic lipoprotein profile in patients with type 2 diabetic who had failed to reach recommended lipid targets with statin therapy alone. LDL cholesterol (LDL-C) and total cholesterol and apoB significantly decreased by 30.9, 21.6, and 19.6%,
respectively, in patients randomized to ezetimibe compared to placebo [12]. Another study compared the effect of ezetimibe on different lipoprotein classes and on apoB-100 kinetics in obese subjects. The effect of ezetimibe on apoB is independent of simvastatin, and is stronger with combination therapy. Both weight loss alone and weight loss plus ezetimibe resulted in significant reductions in VLDL apoB-100 concentrations (−13 and −19%, respectively) and secretion rates (−29 and −13%, respectively), without significant changes in the FCR of VLDL apoB-100 (+3 and +8%, respectively) [13]. In the LDL fraction, ezetimibe plus weight loss significantly decreased the plasma concentration of LDL apoB-100 with a significant increase in its FCR, compared to weight loss alone (Table 1). Another important finding from this study was that addition of ezetimibe to the weight loss diet further decreased intrahepatic triglycerides (IHTG), in spite of similar changes in body weight (Fig. 1) and Homeostasis Model Assessment (HOMA) scores between groups. The HOMA score is a marker of hepatic insulin resistance, so the effect of ezetimibe on this marker is intriguing because it shows that treatment can influences insulin resistance. The same study also concluded that addition of ezetimibe to weight loss may reduce hepatic steatosis and inflammation. Clearly, we cannot exclude that the effect of Ezetimibe on HOMA is a consequence of the reduced hepatic steatosis. A study in miniature pigs investigated the effects of ezetimibe and ezetimibe plus simvastatin treatment compared with control on apoB metabolism, showing that ezetimibe was efficacious at inhibiting absorption and decreasing plasma concentrations of phytosterols (Fig. 2) [14]. The combination of ezetimibe plus simvastatin decreased apoB100 concentrations in both VLDL and LDL fractions by reducing VLDL production and enhancing LDL clearance via the LDLR. Ezetimibe inhibited cholesterol absorption
Table 1 Kinetic indices for apoB-100 before and after intervention in the weight loss and ezetimibe plus weight loss groups Weight loss (n = 10)
VLDL–apoB-100 Concentration (mg/L) Fractional catabolic rate (pools/day) Production rate (mg/kg FFM/day) IDL–apoB-100 Concentration (mg/L) Fractional catabolic rate (pools/day) Production rate (mg/kg FFM/day) LDL–apoB-100 Concentration (mg/L) Fractional catabolic rate (pools/day) Production rate (mg/kg FFM/day)
Ezetimibe plus weight loss (n = 15)
0
22 weeks
0
22 weeks
142 ± 123 4.8 ± 1.1 41 ± 5
123 ± 19† 3.8 ± 0.4 29 ± 7†
134 ± 12 3.9 ± 0.4 38 ± 3
109 ± 11† 4.2 ± 0.3 32 ± 4†
76 ± 10 3.9 ± 0.7 20 ± 3
74 ± 12 3.6 ± 0.3 18 ± 2
82 ± 9 3.5 ± 0.4 20 ± 2
65 ± 9§ 4.5 ± 0.5§ 18 ± 2
957 ± 61 0.35 ± 0.03 26 ± 3
885 ± 36 0.34 ± 0.03 22 ± 2
952 ± 76 0.31 ± 0.02 22 ± 1
774 ± 62*‡ 0.39 ± 0.03*‡ 21 ± 2
Data are means ± SEM. *P < 0.01, value significantly different from baseline value. † P < 0.05. ‡ P < 0.05, value significantly different using general linear modeling after adjustment for relative changes in the weight loss group. § P = 0.06, value different from baseline value. VLDL, very low density lipoprotein; apoB, apolipoprotein B; FFM, free fat mass (vis a vis body composition); IDL, intermediate density lipoprotein; LDL, low density lipoprotein. (Reproduced with permission from Diabetes Care 2010 May;33(5):1134–9 [13].)
A. Moschetta / Atherosclerosis Supplements 17 C (2015) 9–11
Fig. 1. Effects of weight loss alone and ezetimibe plus weight loss on hepatic triglyceride content in obese subjects. *P < 0.05, value significantly different from baseline value. **Value significantly different using general linear modeling after adjustment for weight loss group. (Reproduced with permission from Diabetes Care 2010 May;33(5):1134–9 [13].)
and resulted in an increase in cholesterol synthesis that was blocked by addition of simvastatin. This significantly reduced hepatic cholesterol and increased hepatic LDLR expression. NPC1L1 expression increased in both intestine and liver with ezetimibe alone and with combination treatment, consistent with its regulation by intra-cellular cholesterol. Thus in the pig model, simultaneous blocking of NPC1L1 with ezetimibe and inhibition of cholesterol synthesis with simvastatin produces significant reductions in LDL apoB-100, compared to either therapy alone. This provides further lowering of LDL-C through a complementary mechanism of action. Ezetimibe effects also levels of oxidized LDL, which is considered a better predictor of adverse cardiovascular events than standard lipid parameters. A randomized study of 100 patients with coronary artery disease assigned patients to atorvastatin+ezetimibe (40/10 mg/day) or to
19
atorvastatin 40 mg/day plus placebo. The ezetimibe group had a greater reduction in total LDL-C, compared to placebo, and importantly, the levels of oxidized LDL decreased in the ezetimibe group, from 51 ± 13 to 46 ± 10 U/L (P = 0.01 vs baseline and P = 0.02 vs final level with placebo), while it did not change in the placebo group [15]. Type 2 diabetes is associated with atherogenic changes in postprandial triglyceride-rich lipoproteins. Bozzetto et al. evaluated whether inhibiting intestinal cholesterol absorption with ezetimibe influences chylomicrons and VLDL particles with fasting and after a standard meal in patients with type 2 diabetes receiving statin therapy [16]. Results obtained after 6 weeks of treatment strongly suggest that inhibiting intestinal cholesterol absorption has effects on the composition of lipoproteins. Ezetimibe affected all the parameters examined in the study (Fig. 3), resulting in the production of less atherogenic, cholesterol-poor chylomicrons and VLDL. Thus, ezetimibe is able to improve the postprandial lipoprotein profile in people with type 2 diabetes. In this kind of trial, other nutritional aspects are generally not analyzed, which may lead to confounding of results obtained with drug therapies, for example by particular nutritional attitudes of patients with type 2 diabetes. Morrone et al. evaluated the lipid-altering efficacy and factors associated with treatment response of ezetimibe combined with statin and statin monotherapy in a pooled analysis of 27 randomized double blind, placebo- or active comparator-controlled clinical trials (n = 21,794) [17]. The results reveal a body of robust data confirming that combination therapy provides superior results in terms of reduction of lipids and lipoprotein particles. Ezetimibe plus statin produces significantly greater reductions in LDL-C, total-cholesterol, non-HDL-C, ApoB, triglycerides, lipid ratios, high-sensitivity C-reactive protein, as well as significantly greater increases in HDL-C and ApoA1. Combination therapy was associated with significantly higher achievement of therapeutic targets for LDL-C (13–50%),
Fig. 2. Comparison of the percent change from control (no treatment) in pigs treated with ezetimibe alone, simvastatin alone, or ezetimibe plus simvastatin for the following parameters: circled numbers represent apoB pool sizes; numbers next to arrows represent mean transport rates (production rates), and numbers in italics next to arrows represent fractional catabolic rates. Conversion values of apoB to LDL represent apoB from VLDL plus intermediate density lipoprotein. (Reproduced with permission from J Lipid Res 2007 Mar;48(3):699–708 [14].)
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Fig. 3. Postprandial composition of lipoprotein fractions with ezetimibe and placebo after 6 weeks of treatment in patients with type 2 diabetes receiving statin therapy. (Adapted from Atherosclerosis 2011 Jul;217(1):142–8 [16].)
non-HDL-C (12–45%), and ApoB (10–26%), compared to statin monotherapy. The effect of ezetimibe was larger in patients with diabetes. Interestingly, combination therapy was associated with a reduction in the production of inflammatory factors by monocytes, suggesting a link with activation of the inflammatory process. In hypercholesterolemic patients, combination of simvastatin with ezetimibe may also reduce membrane expression of toll-like receptors, key players in the innate immune system, [18]. In the multicenter, double-blind, crossover PostprAndial eNdothelial function After Combination of Ezetimibe and
simvAstatin (PANACEA) Study, 100 abdominally obese patients with metabolic syndrome were randomly assigned to receive simvastatin 80 mg/day or simvastatin/ezetimibe 10/10 mg/day, and assessed for plasma lipids and endothelial function (flow mediated dilatation and peripheral arterial tonometry) after 6 weeks [19]. No differences were observed in endothelial function; similar reductions in LDL-C levels were observed with simvastatin 80 mg/day or simvastatin/ezetimibe 10/10 mg/day; however, there was no control arm in this study. A meta-analysis of six randomized trials (n = 213) conducted before September 2011 indicated no differences in effects on endothelial function between
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Fig. 3 (continued).
high dosage statin and the combination of low dosage statin plus ezetimibe [20]. Subsequently, a smaller study found that both of these therapies improved endothelia function to a similar extent with similar reductions in LDL-C, compared to an untreated control arm [21]. Nochioka et al. found that ezetimibe significantly improved endothelial function compared to pravastatin in 19 healthy subjects [22]. Finally, Matsue et al. conducted a randomized trial in 243 patients with coronary artery disease and hypercholesterolemia not controlled with atorvastatin 10 mg/day [23]. Patients were randomized to atorvastatin 20 mg/day or atorvastatin/ezetimibe 10/10 mg/day and the primary endpoint was change in endothelial function (peripheral arterial tone). Endothelial function was significantly improved with high dosage atorvastatin, but not affected by the addition of ezetimibe 10 mg/day to existing therapy with atorvastatin 10 mg/day.
Conclusions Ezetimibe exerts multiple favorable effects on the lipoprotein profile and reduces some inflammatory markers. Regarding whether ezetimibe treatment influences endotheTable 2 Summary of the effects of ezetimibe Effect
Evidence
↓ ↓ ↓ ↑ ↓ ↓ ↓ ↓ ↓ ↓ ↑ ?
yes ? yes/? yes yes yes yes Yes Yes Yes ? ?
ApoB Intrahepatic TG Low grade Inflammation LDL fractional catabolic rate VLDL production rate Oxidized LDL Postprandial TG Postprandial ApoB48/ApoB100 Postprandial Large LDL Postprandial IDL Glucose tolerance Endothelial function
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lial function, more studies that include a control untreated arm are needed to answer this. Further analysis is needed also to determine whether the stronger effects of ezetimibe seen in patients with diabetes are a consequence of an interaction of the drug with specific mechanisms. The effects of ezetimibe are summarized in Table 2. Disclosure This work was funded by an unrestricted grant by MSD Italia Srl. The sponsor had no role in reviewing the literature, drafting or reviewing the paper, or in the decision to submit the manuscript for publication. All views expressed are solely those of the author. The author would like to thank Editamed Srl for editorial assistance in the preparation of the manuscript.
[12]
[13]
[14]
[15]
References [16] [1] Bogiatzi C, Spence JD. Ezetimibe and regression of carotid atherosclerosis: importance of measuring plaque burden. Stroke 2012 Apr;43(4):1153–5. [2] Luo P, Li L, Wang LX, Zhu HH, Du S, Wu SL, Han YG, Wang GG. Effects of atorvastatin in combination with ezetimibe on carotid atherosclerosis in elderly patients with hypercholesterolemia. Genet Mol Res 2014 Apr 3;13(2):2377–84. [3] Tremblay AJ, Lamarche B, Lemelin V, Hoos L, Benjannet S, Seidah NG, Davis HR Jr, Couture P. Atorvastatin increases intestinal expression of NPC1L1 in hyperlipidemic men. J Lipid Res 2011 Mar;52(3):558–65. [4] Simonen PP, Gylling HK, Miettinen TA. Diabetes contributes to cholesterol metabolism regardless of obesity. Diabetes Care 2002 Sep;25(9):1511–5. [5] Simonen P, Gylling H, Miettinen TA. The validity of serum squalene and non-cholesterol sterols as surrogate markers of cholesterol synthesis and absorption in type 2 diabetes. Atherosclerosis 2008 Apr;197(2):883–8. [6] Gylling H, Hallikainen M, Pihlajamäki J, Simonen P, Kuusisto J, Laakso M, Miettinen TA. Insulin sensitivity regulates cholesterol metabolism to a greater extent than obesity: lessons from the METSIM Study. J Lipid Res 2010 Aug;51(8):2422–7. [7] Pihlajamäki J, Gylling H, Miettinen TA, Laakso M. Insulin resistance is associated with increased cholesterol synthesis and decreased cholesterol absorption in normoglycemic men. J Lipid Res 2004 Mar;45(3):507–12. [8] Miettinen TA, Gylling H. Cholesterol absorption efficiency and sterol metabolism in obesity. Atherosclerosis 2000 Nov;153(1): 241–8. [9] Krauss RM. Lipids and lipoproteins in patients with type 2 diabetes. Diabetes Care 2004 Jun;27(6):1496–504. [10] Ai D, Chen C, Han S, Ganda A, Murphy AJ, Haeusler R, Thorp E, Accili D, Horton JD, Tall AR. Regulation of hepatic LDL receptors by mTORC1 and PCSK9 in mice. J Clin Invest 2012 Apr 2;122(4):1262–70. [11] Lally S, Owens D, Tomkin GH. Genes that affect cholesterol synthesis, cholesterol absorption, and chylomicron assembly: the
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relationship between the liver and intestine in control and streptozotosin diabetic rats. Metabolism 2007 Mar;56(3):430–8. Ruggenenti P, Cattaneo D, Rota S, Iliev I, Parvanova A, Diadei O, Ene-Iordache B, Ferrari S, Bossi AC, Trevisan R, Belviso A, Remuzzi G; Ezetimibe and Simvastatin in Dyslipidemia of Diabetes (ESD) Study Group. Effects of combined ezetimibe and simvastatin therapy as compared with simvastatin alone in patients with type 2 diabetes: a prospective randomized double-blind clinical trial. Diabetes Care 2010 Sep;33(9):1954–6. Chan DC, Watts GF, Gan SK, Ooi EM, Barrett PH. Effect of ezetimibe on hepatic fat, inflammatory markers, and apolipoprotein B-100 kinetics in insulin-resistant obese subjects on a weight loss diet. Diabetes Care 2010 May;33(5):1134–9. Telford DE, Sutherland BG, Edwards JY, Andrews JD, Barrett PH, Huff MW. The molecular mechanisms underlying the reduction of LDL apoB-100 by ezetimibe plus simvastatin. J Lipid Res 2007 Mar;48(3):699–708. Azar RR, Badaoui G, Sarkis A, Azar M, Aydanian H, Harb S, Achkouty G, Kassab R. Effect of ezetimibe/atorvastatin combination on oxidized low density lipoprotein cholesterol in patients with coronary artery disease or coronary artery disease equivalent. Am J Cardiol 2010 Jul 15;106(2):193–7. Bozzetto L, Annuzzi G, Corte GD, Patti L, Cipriano P, Mangione A, Riccardi G, Rivellese AA. Ezetimibe beneficially influences fasting and postprandial triglyceride-rich lipoproteins in type 2 diabetes. Atherosclerosis 2011 Jul;217(1):142–8. Morrone D, Weintraub WS, Toth PP, Hanson ME, Lowe RS, Lin J, Shah AK, Tershakovec AM. Lipid-altering efficacy of ezetimibe plus statin and statin monotherapy and identification of factors associated with treatment response: a pooled analysis of over 21,000 subjects from 27 clinical trials. Atherosclerosis 2012 Aug; 223(2):251–61. Moutzouri E, Tellis CC, Rousouli K, Liberopoulos EN, Milionis HJ, Elisaf MS, Tselepis AD. Effect of simvastatin or its combination with ezetimibe on Toll-like receptor expression and lipopolysaccharide-induced cytokine production in monocytes of hypercholesterolemic patients. Atherosclerosis 2012 Dec;225(2): 381–7. Westerink J, Deanfield JE, Imholz BP, Spiering W, Basart DC, Coll B, Kastelein JJ, Visseren FL. High-dose statin monotherapy versus low-dose statin/ezetimibe combination on fasting and postprandial lipids and endothelial function in obese patients with the metabolic syndrome: The PANACEA study. Atherosclerosis 2013 Mar;227(1):118–24. Ye Y, Zhao X, Zhai G, Guo L, Tian Z, Zhang S. Effect of high-dose statin versus low-dose statin plus ezetimibe on endothelial function: a meta-analysis of randomized trials. J Cardiovasc Pharmacol Ther 2012 Dec;17(4):357–65. Grigore L, Raselli S, Garlaschelli K, Redaelli L, Norata GD, Pirillo A, Catapano AL. Effect of treatment with pravastatin or ezetimibe on endothelial function in patients with moderate hypercholesterolemia. Eur J Clin Pharmacol 2013 Mar;69(3):341–6. Nochioka K, Tanaka S, Miura M, Zhulanqiqige do E, Fukumoto Y, Shiba N, Shimokawa H. Ezetimibe improves endothelial function and inhibits Rho-kinase activity associated with inhibition of cholesterol absorption in humans. Circ J 2012;76(8):2023–30. Matsue Y, Matsumura A, Suzuki M, Hashimoto Y, Yoshida M. Differences in action of atorvastatin and ezetimibe in lowering lowdensity lipoprotein cholesterol and effect on endothelial function: randomized controlled trial. Circ J 2013;77(7):1791–8.
Effect of ezetimibe on cholesterol absorption and lipoprotein composition in diabetes and metabolic syndrome Massimo Federici * University of Rome “Tor Vergata”, Department of Systems Medicine and Center for Atherosclerosis “Policlinico Tor Vergata”, Rome, Italy
Abstract Ezetimibe exerts multiple favorable effects on the lipoprotein profile and reduces some inflammatory markers. Decreasing cholesterol synthesis with statin treatment can cause a compensatory increase in cholesterol absorption that reduces the efficacy of statin therapy, whereas addition of a cholesterol absorption inhibitor can improve outcomes. Recent evidence suggests a beneficial effect on atherosclerosis. In patients with diabetes, the effect of insulin resistance on low-density lipoprotein metabolism combined with the effect of hyperglycemia on cholesterol absorption may further diminish the favorable effects of statins. Further analysis is needed also to determine whether the stronger effects of ezetimibe seen in patients with diabetes are a consequence of an interaction of the drug with specific mechanisms. © 2015 Elsevier Ireland Ltd. All rights reserved. Keywords: Ezetimibe; Insulin resistance; Lipoprotein metabolism; Diabetes; Metabolic syndrome
Recent studies have confirmed an effect of ezetimibe on atherosclerosis [1,2]. Whether this result is mediated only by its effect of cholesterol absorption is an area of active investigation. Inhibition of cholesterol synthesis by statins has been associated with a compensatory increase in intestinal cholesterol absorption. A crossover study, conducted on hyperlipidemic men receiving atorvastatin 40 mg/day vs placebo, shows that atorvastatin significantly increased intestinal mRNA levels of Niemann-Pick C1-like 1 protein (NPC1L1), as well as 3-hydroxy-3-methyl-glutaryl-CoA (HMG-CoA) reductase, low-density lipoprotein receptor (LDLR), proprotein convertase subtilisin/kexin type 9 (PCSK9), sterol regulatory element-binding protein-2 (SREBP2), and hepatocyte nuclear factor 4alpha (HNF-4α) [3]. There was a positive correlation between the lipogenesis markers SREBP-2 and HNF-4α, and the expression of NPC1L1 at the intestinal level in hyperlipidemic men. Thus, when statin administration decreases cholesterol synthesis, the body adapts by increasing cholesterol absorption. * University of Rome “Tor Vergata”, Department of Systems Medicine and Center for Atherosclerosis “Policlinico Tor Vergata”, Via Montpellier 1, 00133 Rome, Italy. Tel.: +39 0672 596 889. E-mail address: [email protected]. 1567-5688/© 2015 Elsevier Ireland Ltd. All rights reserved.
Abnormalities in cholesterol metabolism in type 2 diabetes include enhanced cholesterol synthesis and reduced cholesterol absorption. Also insulin resistance and obesity have been found to be associated with elevated cholesterol synthesis and low cholesterol absorption in cross-sectional studies [4–8]. Despite these observations, which are based mostly on indirect markers of cholesterol metabolism, diabetic dyslipidemia is typically characterized by increased very low density lipoprotein (VLDL) and reduced highdensity lipoprotein (HDL), but surprisingly no change in low-density lipoprotein (LDL) cholesterol levels [9]. To explain this conundrum, it has been proposed that the increased hepatic VLDL lipids and apolipoprotein B (apoB) secretion characteristic of type 2 diabetes and metabolic syndrome are balanced by increased LDL fractional catabolism, at least in early type 2 diabetes, when subjects are hyperinsulinemic [10]. This effect is mediated in part by the insulin receptor, which influences LDL fractional catabolism by regulating LDLR protein levels. Insulin receptor knockdown suppresses hepatic LDLR expression via a pathway that involves mammalian target of rapamycin complex 1, hepatocyte nuclear factor 1-alpha and PCSK9. Although direct proof in humans is still lacking, it is intriguing to speculate that in the early phases
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of diabetes, which are characterized by mild insulin resistance, hyperinsulinemia is able to maintain normal LDLR expression and LDL catabolism, keeping total cholesterol in the physiological range [10]. This may explain the normal total cholesterol levels observed in early diabetes. On the contrary, in advanced disease, when chronic insulin resistance leads to beta cell failure and relative hypoinsulinemia, the insulin receptor/LDL receptor positive loop is lost, resulting in reduced LDLR expression and a lower LDL fractional catabolic rate (FCR) that may explain the hypercholesterolemia observed in patients with long-standing diabetes. Experimental studies in control and streptozotocin diabetic rats that reveal another important aspect to consider: increased expression of NPC1L1 and reduced expression of ATP-binding cassette sub-family G members 5 and 8 (ABCG5 and ABCG8) are correlated with abnormally high chylomicron and VLDL levels [11]. The guidelines for cardiovascular prevention in subjects with diabetes recommend early statin treatment; however, decreasing cholesterol synthesis may provoke a compensatory increase in cholesterol absorption. The effects of insulin resistance on LDL metabolism combined with the effects of hyperglycemia on molecules mediating cholesterol absorption may diminish the favorable effects of statins in diabetic subjects. These observations support the addition of ezetimibe to statin therapy in subjects with diabetes. Clinical data show that combination therapy with a statin plus ezetimibe has a positive effect on lipid profiles, and especially on apoB. Ruggenenti et al. found that adding ezetimibe to ongoing simvastatin therapy improved the pro-atherogenic lipoprotein profile in patients with type 2 diabetic who had failed to reach recommended lipid targets with statin therapy alone. LDL cholesterol (LDL-C) and total cholesterol and apoB significantly decreased by 30.9, 21.6, and 19.6%,
respectively, in patients randomized to ezetimibe compared to placebo [12]. Another study compared the effect of ezetimibe on different lipoprotein classes and on apoB-100 kinetics in obese subjects. The effect of ezetimibe on apoB is independent of simvastatin, and is stronger with combination therapy. Both weight loss alone and weight loss plus ezetimibe resulted in significant reductions in VLDL apoB-100 concentrations (−13 and −19%, respectively) and secretion rates (−29 and −13%, respectively), without significant changes in the FCR of VLDL apoB-100 (+3 and +8%, respectively) [13]. In the LDL fraction, ezetimibe plus weight loss significantly decreased the plasma concentration of LDL apoB-100 with a significant increase in its FCR, compared to weight loss alone (Table 1). Another important finding from this study was that addition of ezetimibe to the weight loss diet further decreased intrahepatic triglycerides (IHTG), in spite of similar changes in body weight (Fig. 1) and Homeostasis Model Assessment (HOMA) scores between groups. The HOMA score is a marker of hepatic insulin resistance, so the effect of ezetimibe on this marker is intriguing because it shows that treatment can influences insulin resistance. The same study also concluded that addition of ezetimibe to weight loss may reduce hepatic steatosis and inflammation. Clearly, we cannot exclude that the effect of Ezetimibe on HOMA is a consequence of the reduced hepatic steatosis. A study in miniature pigs investigated the effects of ezetimibe and ezetimibe plus simvastatin treatment compared with control on apoB metabolism, showing that ezetimibe was efficacious at inhibiting absorption and decreasing plasma concentrations of phytosterols (Fig. 2) [14]. The combination of ezetimibe plus simvastatin decreased apoB100 concentrations in both VLDL and LDL fractions by reducing VLDL production and enhancing LDL clearance via the LDLR. Ezetimibe inhibited cholesterol absorption
Table 1 Kinetic indices for apoB-100 before and after intervention in the weight loss and ezetimibe plus weight loss groups Weight loss (n = 10)
VLDL–apoB-100 Concentration (mg/L) Fractional catabolic rate (pools/day) Production rate (mg/kg FFM/day) IDL–apoB-100 Concentration (mg/L) Fractional catabolic rate (pools/day) Production rate (mg/kg FFM/day) LDL–apoB-100 Concentration (mg/L) Fractional catabolic rate (pools/day) Production rate (mg/kg FFM/day)
Ezetimibe plus weight loss (n = 15)
0
22 weeks
0
22 weeks
142 ± 123 4.8 ± 1.1 41 ± 5
123 ± 19† 3.8 ± 0.4 29 ± 7†
134 ± 12 3.9 ± 0.4 38 ± 3
109 ± 11† 4.2 ± 0.3 32 ± 4†
76 ± 10 3.9 ± 0.7 20 ± 3
74 ± 12 3.6 ± 0.3 18 ± 2
82 ± 9 3.5 ± 0.4 20 ± 2
65 ± 9§ 4.5 ± 0.5§ 18 ± 2
957 ± 61 0.35 ± 0.03 26 ± 3
885 ± 36 0.34 ± 0.03 22 ± 2
952 ± 76 0.31 ± 0.02 22 ± 1
774 ± 62*‡ 0.39 ± 0.03*‡ 21 ± 2
Data are means ± SEM. *P < 0.01, value significantly different from baseline value. † P < 0.05. ‡ P < 0.05, value significantly different using general linear modeling after adjustment for relative changes in the weight loss group. § P = 0.06, value different from baseline value. VLDL, very low density lipoprotein; apoB, apolipoprotein B; FFM, free fat mass (vis a vis body composition); IDL, intermediate density lipoprotein; LDL, low density lipoprotein. (Reproduced with permission from Diabetes Care 2010 May;33(5):1134–9 [13].)
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Fig. 1. Effects of weight loss alone and ezetimibe plus weight loss on hepatic triglyceride content in obese subjects. *P < 0.05, value significantly different from baseline value. **Value significantly different using general linear modeling after adjustment for weight loss group. (Reproduced with permission from Diabetes Care 2010 May;33(5):1134–9 [13].)
and resulted in an increase in cholesterol synthesis that was blocked by addition of simvastatin. This significantly reduced hepatic cholesterol and increased hepatic LDLR expression. NPC1L1 expression increased in both intestine and liver with ezetimibe alone and with combination treatment, consistent with its regulation by intra-cellular cholesterol. Thus in the pig model, simultaneous blocking of NPC1L1 with ezetimibe and inhibition of cholesterol synthesis with simvastatin produces significant reductions in LDL apoB-100, compared to either therapy alone. This provides further lowering of LDL-C through a complementary mechanism of action. Ezetimibe effects also levels of oxidized LDL, which is considered a better predictor of adverse cardiovascular events than standard lipid parameters. A randomized study of 100 patients with coronary artery disease assigned patients to atorvastatin+ezetimibe (40/10 mg/day) or to
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atorvastatin 40 mg/day plus placebo. The ezetimibe group had a greater reduction in total LDL-C, compared to placebo, and importantly, the levels of oxidized LDL decreased in the ezetimibe group, from 51 ± 13 to 46 ± 10 U/L (P = 0.01 vs baseline and P = 0.02 vs final level with placebo), while it did not change in the placebo group [15]. Type 2 diabetes is associated with atherogenic changes in postprandial triglyceride-rich lipoproteins. Bozzetto et al. evaluated whether inhibiting intestinal cholesterol absorption with ezetimibe influences chylomicrons and VLDL particles with fasting and after a standard meal in patients with type 2 diabetes receiving statin therapy [16]. Results obtained after 6 weeks of treatment strongly suggest that inhibiting intestinal cholesterol absorption has effects on the composition of lipoproteins. Ezetimibe affected all the parameters examined in the study (Fig. 3), resulting in the production of less atherogenic, cholesterol-poor chylomicrons and VLDL. Thus, ezetimibe is able to improve the postprandial lipoprotein profile in people with type 2 diabetes. In this kind of trial, other nutritional aspects are generally not analyzed, which may lead to confounding of results obtained with drug therapies, for example by particular nutritional attitudes of patients with type 2 diabetes. Morrone et al. evaluated the lipid-altering efficacy and factors associated with treatment response of ezetimibe combined with statin and statin monotherapy in a pooled analysis of 27 randomized double blind, placebo- or active comparator-controlled clinical trials (n = 21,794) [17]. The results reveal a body of robust data confirming that combination therapy provides superior results in terms of reduction of lipids and lipoprotein particles. Ezetimibe plus statin produces significantly greater reductions in LDL-C, total-cholesterol, non-HDL-C, ApoB, triglycerides, lipid ratios, high-sensitivity C-reactive protein, as well as significantly greater increases in HDL-C and ApoA1. Combination therapy was associated with significantly higher achievement of therapeutic targets for LDL-C (13–50%),
Fig. 2. Comparison of the percent change from control (no treatment) in pigs treated with ezetimibe alone, simvastatin alone, or ezetimibe plus simvastatin for the following parameters: circled numbers represent apoB pool sizes; numbers next to arrows represent mean transport rates (production rates), and numbers in italics next to arrows represent fractional catabolic rates. Conversion values of apoB to LDL represent apoB from VLDL plus intermediate density lipoprotein. (Reproduced with permission from J Lipid Res 2007 Mar;48(3):699–708 [14].)
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Fig. 3. Postprandial composition of lipoprotein fractions with ezetimibe and placebo after 6 weeks of treatment in patients with type 2 diabetes receiving statin therapy. (Adapted from Atherosclerosis 2011 Jul;217(1):142–8 [16].)
non-HDL-C (12–45%), and ApoB (10–26%), compared to statin monotherapy. The effect of ezetimibe was larger in patients with diabetes. Interestingly, combination therapy was associated with a reduction in the production of inflammatory factors by monocytes, suggesting a link with activation of the inflammatory process. In hypercholesterolemic patients, combination of simvastatin with ezetimibe may also reduce membrane expression of toll-like receptors, key players in the innate immune system, [18]. In the multicenter, double-blind, crossover PostprAndial eNdothelial function After Combination of Ezetimibe and
simvAstatin (PANACEA) Study, 100 abdominally obese patients with metabolic syndrome were randomly assigned to receive simvastatin 80 mg/day or simvastatin/ezetimibe 10/10 mg/day, and assessed for plasma lipids and endothelial function (flow mediated dilatation and peripheral arterial tonometry) after 6 weeks [19]. No differences were observed in endothelial function; similar reductions in LDL-C levels were observed with simvastatin 80 mg/day or simvastatin/ezetimibe 10/10 mg/day; however, there was no control arm in this study. A meta-analysis of six randomized trials (n = 213) conducted before September 2011 indicated no differences in effects on endothelial function between
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Fig. 3 (continued).
high dosage statin and the combination of low dosage statin plus ezetimibe [20]. Subsequently, a smaller study found that both of these therapies improved endothelia function to a similar extent with similar reductions in LDL-C, compared to an untreated control arm [21]. Nochioka et al. found that ezetimibe significantly improved endothelial function compared to pravastatin in 19 healthy subjects [22]. Finally, Matsue et al. conducted a randomized trial in 243 patients with coronary artery disease and hypercholesterolemia not controlled with atorvastatin 10 mg/day [23]. Patients were randomized to atorvastatin 20 mg/day or atorvastatin/ezetimibe 10/10 mg/day and the primary endpoint was change in endothelial function (peripheral arterial tone). Endothelial function was significantly improved with high dosage atorvastatin, but not affected by the addition of ezetimibe 10 mg/day to existing therapy with atorvastatin 10 mg/day.
Conclusions Ezetimibe exerts multiple favorable effects on the lipoprotein profile and reduces some inflammatory markers. Regarding whether ezetimibe treatment influences endotheTable 2 Summary of the effects of ezetimibe Effect
Evidence
↓ ↓ ↓ ↑ ↓ ↓ ↓ ↓ ↓ ↓ ↑ ?
yes ? yes/? yes yes yes yes Yes Yes Yes ? ?
ApoB Intrahepatic TG Low grade Inflammation LDL fractional catabolic rate VLDL production rate Oxidized LDL Postprandial TG Postprandial ApoB48/ApoB100 Postprandial Large LDL Postprandial IDL Glucose tolerance Endothelial function
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lial function, more studies that include a control untreated arm are needed to answer this. Further analysis is needed also to determine whether the stronger effects of ezetimibe seen in patients with diabetes are a consequence of an interaction of the drug with specific mechanisms. The effects of ezetimibe are summarized in Table 2. Disclosure This work was funded by an unrestricted grant by MSD Italia Srl. The sponsor had no role in reviewing the literature, drafting or reviewing the paper, or in the decision to submit the manuscript for publication. All views expressed are solely those of the author. The author would like to thank Editamed Srl for editorial assistance in the preparation of the manuscript.
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