Associations between Lifestyle-Related Diseases and Transporters Involved in Intestinal Absorption and Biliary Excretion of Cholesterol

Is there a role of lipid-lowering therapies in the management of fatty liver disease?

Atherogenic dyslipidemia is characterized by increased triglyceride-rich lipoproteins and low high-density lipoprotein cholesterol concentrations. It is highly prevalent in non-alcoholic fatty liver disease (NAFLD) and contributes to the increased cardiovascular risk associated with this condition. Alongside insulin resistance it plays an important pathogenetic role in NAFLD/non-alcoholic steatohepatitis (NASH) development and progression. It has been shown that cholesterol-lowering reduces cardiovascular risk more in NAFLD vs non-NAFLD high-risk individuals. This evidence highlights the importance of effective lipid modulation in NAFLD. In this narrative review the effects of the most commonly used lipid-lowering therapies on liver outcomes alongside their therapeutic implications in NAFLD/NASH are critically discussed. Preclinical and clinical evidence suggests that statins reduce hepatic steatosis, inflammation and fibrosis in patients with NAFLD/NASH. Most data are derived from observational and small prospective clinical studies using changes in liver enzyme activities, steatosis/fibrosis scores, and imaging evidence of steatosis as surrogates. Also, relevant histologic benefits were noted in small biopsy studies. Atorvastatin and rosuvastatin showed greater benefits, whereas data for other statins are scarce and sometimes conflicting. Similar studies to those of statins showed efficacy of ezetimibe against hepatic steatosis. However, no significant anti-inflammatory and anti-fibrotic actions of ezetimibe have been shown. Preclinical studies showed that fibrates through peroxisome proliferator-activated receptor (PPAR)α activation may have a role in NAFLD prevention and management. Nevertheless, no relevant benefits have been noted in human studies. Species-related differences in PPARα expression and its activation responsiveness may help explain this discrepancy. Omega-3 fatty acids reduced hepatic steatosis in numerous heterogeneous studies, but their benefits on hepatic inflammation and fibrosis have not been established. Promising preliminary data for the highly purified eicosapentaenoic acid require further confirmation. Observational studies suggest that proprotein convertase subtilisin/kexin9 inhibitors may also have a role in the management of NAFLD, though this needs to be established by future prospective studies.

Usefulness of human jejunal spheroid-derived differentiated intestinal epithelial cells for the prediction of intestinal drug absorption in humans

This study aimed to demonstrate the usefulness of human jejunal spheroid-derived differentiated intestinal epithelial cells as a novel in vitro model for clarifying the impact of intestinal drug-metabolizing enzymes and transporters on the intestinal absorption of substrate drugs in humans. Three-dimensional human intestinal spheroids were successfully established from surgical human jejunal specimens and expanded for a long period using L-WRN-conditioned medium, which contains Wnt3a, R-spondin 3, and noggin. The mRNA expression levels of intestinal pharmacokinetics-related genes in the human jejunal spheroid-derived differentiated intestinal epithelial cells were drastically increased over a 5-day period after seeding compared with those in human jejunal spheroids and were approximately the same as those in human jejunal tissue over a culture period of at least 13 days. Activities of typical drug-metabolizing enzymes (cytochrome P450 [CYP] 3A, CYP2C9, uridine 5'-diphospho-glucuronosyltransferase 1A, and carboxylesterase 2) and uptake/efflux transporters (peptide transporter 1/SLC15A1, P-glycoprotein, and breast cancer resistance protein) in the differentiated cells were confirmed. Furthermore, intestinal availability (Fg) values estimated from the apical-to-basolateral permeation clearance across cell monolayer showed a good correlation with the in vivo Fg values in humans for five CYP3A substrate drugs (Fg range, 0.35-0.98). In conclusion, the functions of major intestinal drug-metabolizing enzymes and transporters could be maintained in human jejunal spheroid-derived differentiated intestinal epithelial cells. This model would be useful for the quantitative evaluation of the impact of intestinal drug-metabolizing enzymes and transporters on the intestinal absorption of substrate drugs in humans. Significance Statement Limited information is available regarding the quantitative prediction of the impact of drug-metabolizing enzymes and transporters on the human intestinal absorption of substrates using in vitro assays with differentiated cells derived from human intestinal spheroids/organoids. We confirmed the functions of typical drug-metabolizing enzymes and transporters in human jejunal spheroid-derived differentiated intestinal epithelial cells and demonstrated that Fg values estimated from apical-to-basolateral permeation clearance across cell monolayers showed a good correlation with in vivo human Fg values for CYP3A substrate drugs.

Ganoderma lucidum spore ethanol extract attenuates atherosclerosis by regulating lipid metabolism via upregulation of liver X receptor alpha

CONTEXT

Ganoderma lucidum (Leyss.ex Fr.) Karst (Ganodermataceae) is a fungus that has been used in traditional Chinese medicine.

OBJECTIVE

This is the first investigation of the lipid-lowering and anti-atherosclerotic effects of Ganoderma lucidum spore ethanol extract (EEG) in hyperlipidemic rabbits.

MATERIALS AND METHODS

Fifty-four Japanese rabbits were randomly divided into six groups (n = 9): control, model, atorvastatin and three EEG groups (6, 24 and 96 mg/kg/day, p.o.). Control group was administered a normal diet and other groups were administered a high-fat diet to induce hyperlipidaemia and atherosclerosis for 14 weeks. During this time, lipid profiles were recorded; lipid testing and histopathological examination of aorta and liver were conducted. LXRα and its downstream genes expression in the liver and small intestine were examined. The effect of EEG on macrophage cholesterol efflux and ABCA1/G1 expression was observed under silenced LXRα expression.

RESULTS

EEG reduced serum cholesterol (20.33 ± 3.62 mmol/L vs 34.56 ± 8.27 mmol/L for the model group) and LDL-C, reduced the area of arterial plaques (24.8 ± 10% vs 53.9 ± 15.2% for the model group) and Intima/Medium thickness ratio, increased faecal bile acid content, upregulated LXRα, CYP7A1, ABCA1/G1, ABCG5/G8 expression in the liver, small intestine and macrophages. After silencing LXRα in macrophages, the ability of EEG to promote cholesterol efflux was inhibited.

DISCUSSION AND CONCLUSION

EEG exert lipid-lowering and anti-atherosclerotic effects via upregulating expression of LXRα and downstream genes associated with reverse cholesterol transport and metabolism. However, whether PPARα/γ are involved in the up-regulation of LXR expression by EEG remains to be elucidated.

[Translational Research Based on Understanding the Regulatory Mechanisms of in Vivo Behaviors of Fat-soluble Compounds]

Several fat-soluble compounds such as cholesterol and fat-soluble vitamins have important physiological activities in the body, and their excess and/or deficiency have been reported to be closely associated with the onset and progression of several conditions such as lifestyle-related diseases. It is important to clarify not only the physiological activities but also in vivo kinetics of fat-soluble compounds to understand their in vivo activity (toxicity). This review introduces our recent (reverse) translational research in a combination of basic and clinical studies to reveal the regulatory mechanisms of in vivo behaviors of fat-soluble compounds and effects of their disruption in humans.

Hepatic Expression of Niemann-Pick C1-Like 1, a Cholesterol Reabsorber from Bile, Exacerbates Western Diet-Induced Atherosclerosis in LDL Receptor Mutant Mice

Westernization of dietary habits increases lipid intake and is responsible for increased numbers of patients with atherosclerotic diseases. Niemann-Pick C1-Like 1 (NPC1L1)-a cholesterol importer-plays a crucial role in dietary cholesterol absorption in the intestine and is closely associated with several lipid-related diseases, including atherosclerosis. NPC1L1 is highly expressed in the liver and intestine in humans, whereas NPC1L1 expression is low in the rodent liver. Due to species differences in the tissue distribution of NPC1L1, there are limited studies on the pathophysiological role of hepatic NPC1L1, a cholesterol reabsorber from bile. In the present study, to explore whether hepatic NPC1L1 is involved in the development/progression of atherosclerosis, we compared four kinds of atherosclerosis mouse models with different expression levels of NPC1L1 in the intestinal and liver tissues in a genetic background of dysfunctional low-density lipoprotein receptor mutation. Western diet (WD)-induced hyperlipidemia and atherosclerotic plaque formation were more severe in mice expressing NPC1L1 in both the liver and intestine (plasma cholesterol, 839.5 mg/dl; plaque area, 29.5% of total aorta), compared with mice expressing NPC1L1 only in the intestine (plasma cholesterol, 573.1 mg/dl; plaque area, 13.3% of total aorta). Such hepatic NPC1L1-mediated promotion of hyperlipidemia and atherosclerosis was not observed in mice not expressing intestinal NPC1L1 and mice treated with ezetimibe, an NPC1L1 inhibitor used clinically for dyslipidemia. These results suggested that hepatic NPC1L1 promotes WD-induced dyslipidemia and atherosclerosis in concert with intestinal NPC1L1. Our findings provide novel insights into the pathophysiological importance of hepatic NPC1L1 in development/progression of atherosclerosis. SIGNIFICANCE STATEMENT: Niemann-Pick C1-Like 1 (NPC1L1) protein, a cholesterol importer and a molecular target of ezetimibe clinically used for dyslipidemia, is highly expressed not only in the intestine, but also in the liver in humans, although the pathophysiological importance of hepatic NPC1L1 in atherosclerotic diseases remained unclear. By using novel mouse models to separately analyze the effects of hepatic and intestinal NPC1L1 on the development/progression of atherosclerosis, we first demonstrated that hepatic NPC1L1 accelerates Western diet-induced atherosclerotic plaque formation in an intestinal NPC1L1-dependent and an ezetimibe-sensitive manner.