The intestine as a regulator of cholesterol homeostasis in diabetes. ATHEROSCLEROSIS SUPP. 2008;9:27-32. [PMID: 18693145 DOI: 10.1016/j.atherosclerosissup.2008.05.012]

Mechanism of the Regulation of Plasma Cholesterol Levels by PI(4,5)P2

Elevated low-density lipoprotein (LDL) cholesterol (LDLc) is one of the most well-established risk factors for cardiovascular disease, while high levels of high-density lipoprotein (HDL) cholesterol (HDLc) have been associated with protection from cardiovascular disease. Cardiovascular disease remains one of the leading causes of death worldwide; thus it is important to understand mechanisms that impact LDLc and HDLc metabolism. In this chapter, we will discuss molecular processes by which phosphatidylinositol-(4,5)-bisphosphate, PI(4,5)P₂, is thought to modulate LDLc or HDLc. Section 1 will provide an overview of cholesterol in the circulation, discussing processes that modulate the various forms of lipoproteins (LDL and HDL) carrying cholesterol. Section 2 will describe how a PI(4,5)P₂ phosphatase, transmembrane protein 55B (TMEM55B), impacts circulating LDLc levels through its ability to regulate lysosomal decay of the low-density lipoprotein receptor (LDLR), the primary receptor for hepatic LDL uptake. Section 3 will discuss how PI(4,5)P₂ interacts with apolipoprotein A-I (apoA1), the key apolipoprotein on HDL. In addition to direct mechanisms of PI(4,5)P₂ action on circulating cholesterol, Sect. 4 will review how PI(4,5)P₂ may indirectly impact LDLc and HDLc by affecting insulin action. Last, as cholesterol is controlled through intricate negative feedback loops, Sect. 5 will describe how PI(4,5)P₂ is regulated by cholesterol.

Comparison of Efficacy and Safety of Statin-Ezetimibe Combination Therapy with Statin Monotherapy in Patients with Diabetes: A Meta-Analysis of Randomized Controlled Studies

INTRODUCTION

Dyslipidemia in diabetes mellitus is characterized by hypertriglyceridemia, low high-density lipoprotein cholesterol (HDL-C), and elevated low-density lipoprotein cholesterol (LDL-C). Additionally, the potentially increased risk of morbidity and mortality following atherosclerotic cardiovascular diseases should be considered in the treatment of dyslipidemia in patients with diabetes.

METHODS

We performed a meta-analysis of the published data to compare the effects of HMG-CoA reductase inhibitor (statin)-ezetimibe combination therapy and statin monotherapy on lipid and glucose parameters in patients with diabetes. We also compared safety based on the adverse events reported for the two groups.

RESULTS

In total, 17 articles were included in this meta-analysis. In the efficacy assessment, the combination treatment afforded a significantly greater reduction in LDL-C than did statin monotherapy (standard difference in means 0.691; 95% confidence interval 0.534-0.847). A significantly greater improvement effect was observed in the levels of HDL-C, total cholesterol, triglyceride, and apolipoprotein B, but not apolipoprotein A1, with combination therapy than with statin monotherapy. Additionally, combination therapy reduced fasting blood glucose levels more significantly than did statin monotherapy. In terms of safety, there were no significant differences in treatment-related adverse events between the two treatments.

CONCLUSIONS

Statin-ezetimibe combination therapy enhances levels of LDL-C and other lipids without increasing the risk of adverse events compared with statin monotherapy. The present meta-analysis presents valid evidence for appropriate drug regimens to treat dyslipidemia in patients with diabetes.

REGISTRATION

PROSPERO Identifier Number CRD42021244578.

Apolipoprotein C1: Its Pleiotropic Effects in Lipid Metabolism and Beyond

Apolipoprotein C1 (apoC1), the smallest of all apolipoproteins, participates in lipid transport and metabolism. In humans, APOC1 gene is in linkage disequilibrium with APOE gene on chromosome 19, a proximity that spurred its investigation. Apolipoprotein C1 associates with triglyceride-rich lipoproteins and HDL and exchanges between lipoprotein classes. These interactions occur via amphipathic helix motifs, as demonstrated by biophysical studies on the wild-type polypeptide and representative mutants. Apolipoprotein C1 acts on lipoprotein receptors by inhibiting binding mediated by apolipoprotein E, and modulating the activities of several enzymes. Thus, apoC1 downregulates lipoprotein lipase, hepatic lipase, phospholipase A2, cholesterylester transfer protein, and activates lecithin-cholesterol acyl transferase. By controlling the plasma levels of lipids, apoC1 relates directly to cardiovascular physiology, but its activity extends beyond, to inflammation and immunity, sepsis, diabetes, cancer, viral infectivity, and-not last-to cognition. Such correlations were established based on studies using transgenic mice, associated in the recent years with GWAS, transcriptomic and proteomic analyses. The presence of a duplicate gene, pseudogene APOC1P, stimulated evolutionary studies and more recently, the regulatory properties of the corresponding non-coding RNA are steadily emerging. Nonetheless, this prototypical apolipoprotein is still underexplored and deserves further research for understanding its physiology and exploiting its therapeutic potential.

Ezetimibe increases hepatic iron levels in mice fed a high-fat diet

Accumulating evidence suggests that ezetimibe may be a promising agent for treatment of nonalcoholic fatty liver disease and steatohepatitis (NAFLD/NASH). Phlebotomy and dietary iron restriction reduce serum transaminase in NAFLD/NASH patients. Recent studies have shown that a mutual effect exists between lipid metabolism and iron metabolism. Accordingly, we examined the effect of ezetimibe on iron metabolism in mice fed a high-fat diet with or without iron. We fed C57BL/6 mice the following diets for 12 weeks. Experiment 1 comprised [1] a control diet (C), [2] C plus ezetimibe (0.3 mg/day; 4 weeks) (CE), [3] a high-fat diet (H), and [4] H plus ezetimibe (HE). Experiment 2 comprised [1] C containing carbonyl iron (average; 22.4 mg/day; 6 weeks) (CI), [2] CI plus ezetimibe (CIE), [3] H containing carbonyl iron (HI), and [4] HI plus ezetimibe (HIE). Blood, livers, and duodenum were removed after 12 weeks. In experiment 1, the hepatic iron levels were higher in HE than H, whereas there was no difference between C and CE. Hepatic mRNA expression of transferrin receptor 1 and 2, ferritins, and hepcidin were increased more in CE than C, and more in HE than H. In the duodenum, divalent metal transporter 1, ferritin H, and hephaestin mRNA levels were increased in CE compared with C. In experiment 2, hepatic iron concentrations were higher in HIE than HI. Hepatic mRNA expression of ferritin L and hepcidin were increased in HIE compared with HI. In duodenum, ferritin L mRNA was increased in HIE compared with CIE. Ezetimibe induced hepatic iron uptake transporter expression in mice fed a high-fat diet, causing increased hepatic iron concentrations.

D-Glucose modulates intestinal Niemann-Pick C1-like 1 (NPC1L1) gene expression via transcriptional regulation

The expression of intestinal Niemann-Pick C1-like 1 (NPC1L1) cholesterol transporter has been shown to be elevated in patients with diseases associated with hypercholesterolemia such as diabetes mellitus. High levels of glucose were shown to directly increase the expression of NPC1L1 in intestinal epithelial cells, but the underlying mechanisms are not fully defined. The present studies were, therefore, undertaken to examine the transcriptional regulation of NPC1L1 expression in human intestinal Caco2 cells in response to glucose. Removal of glucose from the culture medium of Caco2 cells for 24 h significantly decreased the NPC1L1 mRNA, protein expression, as well as the promoter activity. Glucose replenishment significantly increased the promoter activity of NPC1L1 in a dose-dependent manner compared with control cells. Exposure of Caco2 cells to nonmetabolizable form of glucose, 3-O-methyl-d-glucopyranose (OMG) had no effect on NPC1L1 promoter activity, indicating that the observed effects are dependent on glucose metabolism. Furthermore, glucose-mediated increase in promoter activity was abrogated in the presence of okadaic acid, suggesting the involvement of protein phosphatases. Glucose effects on several deletion constructs of NPC1L1 promoter demonstrated that cis elements mediating the effects of glucose are located in the region between -291 and +56 of NPC1L1 promoter. Consistent with the effects of glucose removal on NPC1L1 expression in Caco2 cells, 24-h fasting resulted in a significant decrease in the relative expression of NPC1L1 in mouse jejunum. In conclusion, glucose appears to directly modulate NPC1L1 expression via transcriptional mechanisms and the involvement of phosphatase-dependent pathways.

Recent advances in small bowel diseases: Part II

As is the case in all areas of gastroenterology and hepatology, in 2009 and 2010 there were many advances in our knowledge and understanding of small intestinal diseases. Over 1000 publications were reviewed, and the important advances in basic science as well as clinical applications were considered. In Part II we review six topics: absorption, short bowel syndrome, smooth muscle function and intestinal motility, tumors, diagnostic imaging, and cystic fibrosis.

A review of the role of apolipoprotein C-II in lipoprotein metabolism and cardiovascular disease

The focus of this review is on the role of apolipoprotein C-II (apoC-II) in lipoprotein metabolism and the potential effects on the risk of cardiovascular disease (CVD). We searched PubMed/Scopus for articles regarding apoC-II and its role in lipoprotein metabolism and the risk of CVD. Apolipoprotein C-II is a constituent of chylomicrons, very low-density lipoprotein, low-density lipoprotein, and high-density lipoprotein (HDL). Apolipoprotein C-II contains 3 amphipathic α-helices. The lipid-binding domain of apoC-II is located in the N-terminal, whereas the C-terminal helix of apoC-II is responsible for the interaction with lipoprotein lipase (LPL). At intermediate concentrations (approximately 4 mg/dL) and in normolipidemic subjects, apoC-II activates LPL. In contrast, both an excess and a deficiency of apoC-II are associated with reduced LPL activity and hypertriglyceridemia. Furthermore, excess apoC-II has been associated with increased triglyceride-rich particles and alterations in HDL particle distribution, factors that may increase the risk of CVD. However, there is not enough current evidence to clarify whether increased apoC-II causes hypertriglyceridemia or is an epiphenomenon reflecting hypertriglyceridemia. A number of pharmaceutical interventions, including statins, fibrates, ezetimibe, nicotinic acid, and orlistat, have been shown to reduce the increased apoC-II concentrations. An excess of apoC-II is associated with increased triglyceride-rich particles and alterations in HDL particle distribution. However, prospective trials are needed to assess if apoC-II is a CVD marker or a risk factor in high-risk patients.

Gut-liver interaction in triglyceride-rich lipoprotein metabolism

The liver and intestine have complementary and coordinated roles in lipoprotein metabolism. Despite their highly specialized functions, assembly and secretion of triglyceride-rich lipoproteins (TRL; apoB-100-containing VLDL in the liver and apoB-48-containing chylomicrons in the intestine) are regulated by many of the same hormonal, inflammatory, nutritional, and metabolic factors. Furthermore, lipoprotein metabolism in these two organs may be affected in a similar fashion by certain disorders. In insulin resistance, for example, overproduction of TRL by both liver and intestine is a prominent component of and underlies other features of a complex dyslipidemia and increased risk of atherosclerosis. The intestine is gaining increasing recognition for its importance in affecting whole body lipid homeostasis, in part through its interaction with the liver. This review aims to integrate recent advances in our understanding of these processes and attempts to provide insight into the factors that coordinate lipid homeostasis in these two organs in health and disease.

Lipid-altering efficacy and safety profile of combination therapy with ezetimibe/statin vs. statin monotherapy in patients with and without diabetes: an analysis of pooled data from 27 clinical trials

AIM

This post hoc analysis compared the lipid-altering efficacy and safety of ezetimibe 10 mg plus statin (EZE/statin) vs. statin monotherapy in hypercholesterolaemic patients with and without diabetes.

METHODS

A pooled analysis of 27 previously published, randomized, double-blind, active- or placebo-controlled clinical trials comprising 21 794 adult patients with (n = 6541) and without (n = 15253) diabetes receiving EZE/statin or statin alone for 4-24 weeks evaluated percentage change from baseline in lipids and other parameters. Consistency of the treatment effect across the subgroups was tested using treatment × subgroup interaction. No multiplicity adjustments were made.

RESULTS

Treatment effects within both subgroups were generally consistent with the overall population. EZE/statin was more effective than statin alone in improving low-density lipoprotein cholesterol (LDL-C), total cholesterol (TC), high-density lipoprotein cholesterol (HDL-C), triglycerides (TGs), non-HDL-C, apolipoprotein (apo) B and high-sensitivity C-reactive protein (hs-CRP) in the overall population and both subgroups. Patients with diabetes achieved significantly larger reductions in LDL-C, TC and non-HDL-C compared with non-diabetic patients. Incidences of adverse events or creatine kinase elevations were similar between groups. A small but significantly higher incidence of alanine aminotransferase or aspartate aminotransferase elevations was seen in patients receiving EZE/statin (0.6%) vs. statin monotherapy (0.3%) in the overall population.

CONCLUSIONS

Treatment with EZE/statin vs. statin monotherapy provided significantly larger reductions in LDL-C, TC, TG, non-HDL-C, apo B and hs-CRP and significantly greater increases in HDL-C, with a similar safety profile in patients with and without diabetes. Reductions in LDL-C, TC and non-HDL-C were larger in patients with diabetes than in patients without diabetes.