Hugan Qingzhi tablets attenuates endoplasmic reticulum stress in nonalcoholic fatty liver disease rats by regulating PERK and ATF6 pathways.

BACKGROUND: Endoplasmic reticulum (ER) stress, promoting lipid metabolism disorders and steatohepatitis, contributes significantly to the pathogenesis of nonalcoholic fatty liver disease (NAFLD). Hugan Qingzhi tablets (HQT) has a definite effect in the clinical treatment of NAFLD patients, but its mechanism is still unclear. This study aims to investigate the effects of HQT on ER stress in the liver tissues of NAFLD rats and explore the underlying mechanism. METHODS: The NAFLD rat model was managed with high-fat diet (HFD) for 12weeks. HQT was administrated in a daily basis to the HFD groups. Biochemical markers, pro-inflammatory cytokines, liver histology were assayed to evaluate HQT effects in HFD-induced NAFLD rats. Furthermore, the expression of ER stress-related signal molecules including glucose regulating protein 78 (GRP78), protein kinase RNA-like endoplasmic reticulum kinase (PERK), p-PERK, eukaryotic translation initiation factor 2α (EIF2α), p-EIF2α, activating transcription factor 4 (ATF4), acetyl-coenzyme A-carboxylase (ACC), activating transcription factor (ATF6), and nuclear factor-kappa B-p65 (NF-κB-p65) were detected by western blot and/or qRT-PCR. RESULTS: The histopathological characteristics and biochemical data indicated that HQT exhibited protective effects on HFD-induced NAFLD rats. Furthermore, it caused significant reduction in the expression of ERS markers, such as GRP78, PERK, p-PERK, and ATF6, and subsequently downregulated the expression of EIF2α, p-EIF2α ATF4, ACC, and NF-κB-p65. CONCLUSIONS: The results suggested that HQT has protective effect against hepatic steatosis and inflammation in NAFLD rats by attenuating ER stress, and the potential mechanism is through inhibition of PERK and ATF6 pathways.

Hugan Qingzhi medication ameliorates free fatty acid-induced L02 hepatocyte endoplasmic reticulum stress by regulating the activation of PKC-δ.

BACKGROUND: Previous studies have found that Hugan Qingzhi tablet (HQT) has significant lipid-lowering and antioxidant effects on non-alcoholic fatty liver disease (NAFLD). Moreover, the results of proteomic analysis confirmed that various proteins in endoplasmic reticulum stress (ERS) pathway were activated and recovered by HQT. However, its mechanism remains confused. The purpose of this study was to explore the effects of HQT-medicated serum on hepatic ERS and its relevant mechanisms. METHODS: L02 cells were induced by Free Fatty Acid (FFA) for 24 h to establish a model of hepatic ERS and pretreated with the drug-medicated rat serum for 24 h. Accumulation of intracellular lipid was evaluated using Oil Red O staining and Triglyceride detection kit. The morphological changes of ER were observed by TEM. PKC-δ was silenced by specific siRNA. Western blot and RT-qPCR were applied to detect the expression of markers related to ERS, calcium disorder, steatosis and insulin resistance. The fluorescence of Ca2+ influx was recorded using fluorescence spectrophotometer. RESULTS: HQT-medicated serum significantly decreased the intracellular TG content. Furthermore, it caused significant reduction in the expression of ERS markers and an improvement in ER structure of L02 cells. PKC-δ was activated into phosphorylated PKC-δ in FFA-induced L02 hepatocytes while these changes can be reversed by HQT-medicated serum. Silencing PKC-δ in L02 cells can restore the expression and activity of SERCA2 in ER and down-regulate the expression of IP3R protein to maintain intracellular calcium homeostasis, so as to relieve FFA-induced ERS and its lipid accumulation and insulin resistance. CONCLUSIONS: The results concluded that HQT-medicated serum exerts protective effects against hepatic ERS, steatosis and insulin resistance in FFA-induced L02 hepatocyte. And its potential mechanism might be down-regulating the activation of PKC-δ and stabilization of intracellular calcium.

Modulation of the Gut Microbiota in Rats by Hugan Qingzhi Tablets during the Treatment of High-Fat-Diet-Induced Nonalcoholic Fatty Liver Disease.

BACKGROUND: Accumulative evidence showed that gut microbiota was important in regulating the development of nonalcoholic fatty liver disease (NAFLD). Hugan Qingzhi tablet (HQT), a lipid-lowering and anti-inflammatory medicinal formula, has been used to prevent and treat NAFLD. However, its mechanism of action is unknown. The aim of this study was to confirm whether HQT reversed the gut microbiota dysbiosis in NAFLD rats. METHODS: We established an NAFLD model of rats fed with a high-fat diet (HFD), which was given different interventions, and measured the level of liver biochemical indices and inflammatory factors. Liver tissues were stained with hematoxylin-eosin and oil red O. Changes in the gut microbiota composition were analyzed using 16S rRNA sequencing. RESULTS: The hepatic histology and biochemical data displayed that HQT exhibited protective effects on HFD-induced rats. Moreover, HQT also reduced the abundance of the Firmicutes/Bacteroidetes ratio in HFD-fed rats and modified the gut microbial species at the genus level, increasing the abundances of gut microbiota which were reported to have an effect on relieving NAFLD, such as Ruminococcaceae, Bacteroidales_S24-7_group, Bifidobacteria, Alistipes, and Anaeroplasma, and significantly inhibiting the relative abundance of Enterobacteriaceae, Streptococcus, Holdemanella, Allobaculum, and Blautia, which were reported to be potentially related to NAFLD. Spearman's correlation analysis found that [Ruminococcus]_gauvreauii_group, Lachnoclostridium, Blautia, Allobaculum, and Holdemanella exhibited significant (p < 0.001) positive correlations with triglyceride, cholesterol, low-density lipoprotein cholesterol, interleukin-6, interleukin-1ß, tumor necrosis factor-α, and body weight and negative correlations with high-density lipoprotein cholesterol (p < 0.001). The norank_f__Bacteroidales_S24-7_group and Alistipes showed an opposite trend. Moreover, the HQT could promote flavonoid biosynthesis compared with the HFD group. CONCLUSION: In summary, the HQT has potential applications in the prevention and treatment of NAFLD, which may be closely related to its modulatory effect on the gut microbiota.

Isobaric tags for relative and absolute quantitation (iTRAQ)-based proteomics for the investigation of the effect of Hugan Qingzhi on non-alcoholic fatty liver disease in rats.

ETHNOPHARMACOLOGICAL RELEVANCE: Hugan Qingzhi tablet (HQT), a traditional Chinese medicine formula has been adopted for preventing and treating nonalcoholic fatty liver disease (NAFLD). AIM: In order to explore the anti-NAFLD mechanisms of HQT, iTRAQ-based proteomic was employed to investigate the expression profiles of proteins in NAFLD rats induced by high-fat diet after HQT treatment. MATERIALS AND METHODS: The NAFLD rat model was administrated with high-fat diet (HFD) for 12weeks. HQT was administrated in a daily basis to the HFD groups. Biochemical markers, liver histology, pro-inflammatory cytokines, and oxidative stress/antioxidant biomarkers were assayed to evaluate HQT effects in HFD-induced NAFLD rats. Furthermore, the combined strategy of iTRAQ labeling with strong cation exchange-non-liquid chromatography-tandem mass spectrometry (SCX-non-LC-MS/MS) analysis were employed to explore the mechanisms of HQT's protective effect against NAFLD in rats. Western blotting was performed to verify the proteomic results. RESULTS: The histopathologic characteristics and biochemical data showed that HQT exhibited protective effects on HFD-induced NAFLD rats. After being analyzed by the combined strategy of iTRAQ with LC-MS/MS and subsequent investigation, we identified 275 differentially expressed proteins in the HFD group, compared to the control; 207 altered proteins in the HQT high dose + HFD group, compared to the HFD group; and 316 altered proteins in the HQT high dose + HFD group, compared to the control. Based on the Kyoto Encyclopedia of Gene and Genomes (KEGG) pathway mapping, the conclusion has reached that several pathways including microbial metabolism in diverse environments, fatty acid metabolism, inflammatory response, oxidative stress, bile secretion, and peroxisome proliferator activated receptor (PPAR) signaling pathway were closely related to the effects of HQT in HFD-induced NAFLD in rats. Furthermore, several differentially expressed proteins, including phytanoyl-CoA 2-hydroxylase (PHYH), acyl-CoA synthetase 1 long chain (ACSL1), hemopexin, Alpha-1-acid glycoprotein (ORM1), fatty acid binding protein 4 (FABP4), soluble sulphotransferase 2a1 (Sult2a1), and argininosuccinate synthase 1 (ASS1) were verified by the western blotting analysis and these results were consistent with the data obtained from the proteomics analysis. CONCLUSIONS: Our results not only confirm that Hugan Qingzhi exhibits a significant protective effect in HFD-induced NAFLD rats but also provide a better understanding for the treatments of NAFLD.

Data for iTRAQ-based quantification of the effect of HuganQingzhi on non-alcoholic fatty liver disease in rats.

The data presented in this article are related to the research article entitled "Isobarictags for relative and absolute quantitation (iTRAQ) -based proteomics for the investigation of the effect of HuganQingzhi on non-alcoholic fatty liver disease in rats" (Yao et al., 2017) [1]. This article describes the effect of HuganQingzhi on non-alcoholic fatty liver disease in rats at the level of the proteome (HFD: control, HH: control, HH: HFD, respectively). The field dataset is available to criticize or extended analyzes in public.

Isobaric Tags for Relative and Absolute Quantitation (iTRAQ)-Based Proteomic Analysis of Hugan Qingzhi and Its Protective Properties against Free Fatty Acid-Induced L02 Hepatocyte Injury.

In previous research, Hugan Qingzhi, a traditional Chinese medicine, was shown to have protective effects against hepatic steatosis. However, its activity against non-alcoholic fatty liver disease (NAFLD) and the mechanisms by which it exerts its effects remain unknown. In the present study, the effects of Hugan Qingzhi on free fatty acid (FFA)-induced L02 cells were examined. The techniques of iTRAQ labeling, together with strong cation exchange-non-liquid chromatography-tandem mass spectrometry (SCX-non-LC-MS/MS) analysis and serum pharmacology, were used to evaluate the effects of Hugan Qingzhi-medicated serum on FFA-induced L02 hepatocyte injury. Results identified 355 differentially expressed proteins following FFA treatment, compared with a control group; 359 altered proteins in the Hugan Qingzhi high dose + FFA treatment group, compared with the FFA treatment group; and 365 altered proteins in the Hugan Qingzhi high dose + FFA treatment group, compared with the control group. Based on the Kyoto Encyclopedia of Gene and Genomes pathway enrichment analysis, it is concluded that several pathways including those of microbial metabolism in diverse environments, fatty acid metabolism, peroxisome proliferator activated receptor signaling, and mitogen-activated protein kinase signaling are closely associated with the effects of Hugan Qingzhi-medicated serum in FFA-induced L02 hepatocyte injury. Furthermore, several differentially expressed proteins, including heat shock protein 27 (HSP27), acetyl-CoA acetyltransferase 1, calnexin, and integrin-linked kinase, were validated by western blotting. A target-specific HSP27 siRNA was used to investigate further the function of HSP27, and it was found that HSP27 might have a key role in the observable effects of Hugan Qingzhi-medicated serum in FFA-induced L02 hepatocyte injury. The results not only confirmed that Hugan Qingzhi exhibits a significant protective effect in FFA-induced L02 hepatocyte injury, but also suggest insights into the mechanism of such protective effects.

[Effect of Hugan Qingzhi tablets on AMPK pathway activation and NF-κB-p65 protein expression in the liver of rats with nonalcoholic fatty liver disease].

OBJECTIVE: To investigate the effect of Hugan Qingzhi tablets on lipid metabolism and inflammation in rats fed on high-fat diet and explore the underlying mechanisms. METHODS: Sixty male Sprague-Dawley rats were randomly divided into 6 groups, namely HFD group (with high-fat diet and distilled water), control group (with normal diet and distilled water), fenofibrate group (with high-fat diet and treatment with 0.1 g

Alisol A 24-Acetate Prevents Hepatic Steatosis and Metabolic Disorders in HepG2 Cells.

BACKGROUND: Non-alcoholic fatty liver disease (NAFLD) is closely associated with metabolic disorders including hepatic lipid accumulation and inflammation. Alisol A 24-acetate, a triterpene from Alismatis rhizome, has multiple biologic activities such as hypolipidemic, anti-inflammatory and anti-diabetic. Thus we hypothesized that Alisol A 24 -acetate would have effect on NAFLD. The present study was conducted to investigate the therapeutic effects and potential mechanisms of Alisol A 24-acetate against hepatic steatosis in a free fatty acids (FFAs) induced NAFLD cell model. METHODS: This study was divided into four groups including Control group, Model group (FFA group), Alisol A 24-acetate (FFA+A) group, Fenofibrate (FFA+F) group. Preventive role of Alisol A 24-acetate was evaluated using 10µM Alisol A 24-acetate plus 1 mM FFA (oleate:palmitate=2:1) incubated with HepG2 cells for 24 h, which was determined by Oil Red O Staining, Oil Red O based colorimetric assay and intracellular triglyceride (TG) content. Besides, the inflammatory cytokines tumor necrosis factor (TNF)- α, interleukin (IL)-6 levels as well as the protein and mRNA expressions that were involved in fatty acid synthesis and oxidation including Adiponectin, AMP-activated protein kinase (AMPK) α, peroxisome proliferator-activated receptor (PPAR) α, sterol regulatory element binding protein 1c (SREBP-1c), acetyl-CoA carboxylase (ACC), fatty acid synthase (FAS), carnitine palmitoyltransferase 1 (CPT1) and acyl coenzyme A oxidase 1 (ACOX1) were detected. RESULTS: Alisol A 24-acetate significantly decreased the numbers of lipid droplets, Oil Red O lipid content, and intracellular TG content. Besides, inflammatory cytokines TNF-α, IL-6 levels were markedly inhibited by Alisol A 24-acetate. Furthermore, Alisol A 24-acetate effectively increased the protein and mRNA expressions of Adiponectin, the phosphorylation of AMPKα, CPT1 and ACOX1, whereas decreased SREBP-1c, the phosphorylation of ACC and FAS at both protein and mRNA levels. However, there was no significant effect on the protein and mRNA expressions of PPARα by Alisol A 24-acetate. CONCLUSIONS: These results demonstrated that Alisol A 24-acetate effectively ameliorated hepatic steatosis likely through Adiponectin, which activated AMPKα signaling pathways via down-regulating SREBP-1c, ACC, FAS and up-regulating CPT1 and ACOX1, and inhibited inflammation. Thereby, Alisol A 24-acetate could be a promising candidate for the treatment of NAFLD.

Distribution and factors affecting adsorption of sterols in the surface sediments of Bosten Lake and Manas Lake, Xinjiang.

This study investigated the concentrations and distribution of eight sterol compounds in the surface sediments of Bosten Lake and Manas Lake, Xinjiang, China. The ratios of sterols as diagnostic indices were used to identify pollution sources. The sediment of the two lakes was selected as an adsorbent to investigate the adsorption behaviour of sterols. Results showed that the sterols were widely distributed in the sediments of the lakes in the study areas. The total concentrations of the detected sterols in Bosten Lake and in Manas Lake were 1.584-27.897 and 2.048-18.373 µg g(-1)∙dw, respectively. In all of the sampling sites, the amount of faecal sterols was less than that of plant sterols. ß-sitosterol was the dominant plant sterol with a mean concentration of 2.378 ± 2.234 µg g(-1)∙dw; cholesterol was the most abundant faecal sterol with a mean concentration of 1.060 ± 1.402 µg g(-1)∙dw. The pollution level was higher in Bosten Lake than in Manas Lake. Majority of the ratios clearly demonstrated that the contamination by human faecal sources was occurring at stations which are adjacent to residential areas and water inlets. The adsorption behaviour of sterols to sediment suggested that the sterol adsorption coefficients were reduced as temperature increased. As salinity increased, the adsorption quantity also increased. As pH increased, the sediment adsorption of sterol slightly increased because the strong alkaline solution is not conducive to the adsorption of sterols. The ratios between sterols did not change largely with the change in external factors.

Hugan Qingzhi Exerts Anti-Inflammatory Effects in a Rat Model of Nonalcoholic Fatty Liver Disease.

Ethnopharmacological Relevance. The Hugan Qingzhi tablet (HQT) is a traditional Chinese medicine used for treating NAFLD (nonalcoholic fatty liver disease). The present study evaluated the anti-inflammatory effects of HQT in rats with NAFLD. Materials and Methods. HQT was administered daily to the NAFLD experimental groups. Biochemical markers, histopathological data, and oxidative stress/antioxidant biomarkers were determined. Proinflammatory cytokines interleukin-1ß (IL-1ß), tumor necrosis factor α (TNF-α), and interleukin-6 (IL-6) were detected by enzyme-linked immunoassay. Expressions of silent information regulator 1 (SIRT1) and acetylated-nuclear-factor kappaB-p65 (Ac-NF-κB-p65) were performed by western blotting. Results. At high and moderate doses, HQT was highly effective in decreasing serum alanine aminotransferase (P < 0.01), aspartate aminotransferase (P < 0.01), hepatic total cholesterol (P < 0.01), triglycerides (P < 0.01), and free fatty acid levels (P < 0.01). Moreover, high and moderate doses of HQT reduced hepatic levels of the proinflammatory cytokines TNF-α (P < 0.01), IL-1ß (P < 0.01), and IL-6 (P < 0.01), enhanced SIRT1 expression, and depressed Ac-NF-κB-p65 expression at protein level. Conclusions. In our NAFLD rat model, HQT exerted substantial anti-inflammatory and antioxidant activities, possibly involving the regulation of SIRT1 and Ac-NF-κB-p65 expression.

Characterization of the exocrine pancreas in the male Zucker diabetic fatty rat model of type 2 diabetes mellitus following 3 months of treatment with sitagliptin.

Sitagliptin, a dipeptidyl peptidase-4 (DPP-4) inhibitor-based incretin therapy intended for the treatment of type 2 diabetes mellitus (T2DM), has not been linked to adverse effects on the pancreas in prospective clinical trials or in nonclinical toxicology studies. To further assess potential pancreatic effects, sitagliptin was studied in the male Zucker diabetic fatty (ZDF) rat model of T2DM. Following 3 months of oral dosing with vehicle, or sitagliptin at doses 3- to 19-fold above the clinically therapeutic plasma concentration, which increased active plasma glucagon-like peptide-1 levels up to approximately 3-fold, or following 3 months of oral dosing with metformin, a non-incretin-based reference T2DM treatment, the pancreas of male ZDF rats was evaluated using qualitative and quantitative histopathology techniques. In the quantitative evaluation, proliferative index was calculated in exocrine pancreatic ducts and ductules using computer-based image analysis on sections stained by immunohistochemistry for cytokeratin (a cytoplasmic epithelial cell marker) and Ki-67 (a nuclear marker of recent cell division). Relative to controls, sitagliptin treatment did not alter disease progression based on detailed clinical signs and clinical pathology assessments. Sitagliptin treatment did not result in pancreatitis or any adverse effect on the pancreas based on a qualitative histopathology evaluation. Proliferative index did not increase with sitagliptin treatment based on quantitative assessment of more than 5000 sections of pancreas, where control group means ranged from 0.698-0.845% and sitagliptin-treated group means ranged from 0.679-0.701% (P = .874). Metformin treatment was similarly evaluated and found not to have adverse effects on pancreas.

Distribution of sterols and the sources of pollution in surface sediments of Ulungur lake, Xinjiang.

Domestic sewage discharged into lakes brings great pressure to the ecological environment. This study selected sediment from an inland lake as a research object to evaluate pollution of the environment. Eight sterols were used to evaluate the content of pollutants, while the ratios of sterols were used as the index to analyze the sources of pollution. The correlations were analyzed between sterols and total organic carbon (TOC), salinity and particle size. The distribution and composition of sterol compounds were determined in 12 surface sediment samples collected from Ulungur lake. The total concentrations of detected sterols in the sediments ranged from 1.3 to 36.3 µg/g.dw. The most abundant sterol detected was ß-sitosterol (STI) with average concentrations of 2.6 µg/g.dw, followed by cholesterol (CHOE), stigmasterol (STIG) and stigmastanol (STAN). The concentration of coprostanol (COP) was between 0.03 and 1.66 µg/g.dw. Through correlation analysis, it was found that there was a significant correlation between fecal sterols and plant sterols. So the plant sterols shall not be neglected in evaluating the sources of pollution for their impact to identify the fecal sources. The study suggests that the composition and distribution of sterols in surface sediment provide useful information for environmental contamination monitoring and assessment in the inland lake.

Diacylglycerol acyltransferase-1 (DGAT1) inhibition perturbs postprandial gut hormone release.

Diacylglycerol acyltransferase-1 (DGAT1) is a potential therapeutic target for treatment of obesity and related metabolic diseases. However, the degree of DGAT1 inhibition required for metabolic benefits is unclear. Here we show that partial DGAT1 deficiency in mice suppressed postprandial triglyceridemia, led to elevations in glucagon-like peptide-1 (GLP-1) and peptide YY (PYY) only following meals with very high lipid content, and did not protect from diet-induced obesity. Maximal DGAT1 inhibition led to enhanced GLP-1 and PYY secretion following meals with physiologically relevant lipid content. Finally, combination of DGAT1 inhibition with dipeptidyl-peptidase-4 (DPP-4) inhibition led to further enhancements in active GLP-1 in mice and dogs. The current study suggests that targeting DGAT1 to enhance postprandial gut hormone secretion requires maximal inhibition, and suggests combination with DPP-4i as a potential strategy to develop DGAT1 inhibitors for treatment of metabolic diseases.

Butyrate and propionate protect against diet-induced obesity and regulate gut hormones via free fatty acid receptor 3-independent mechanisms.

Short-chain fatty acids (SCFAs), primarily acetate, propionate, and butyrate, are metabolites formed by gut microbiota from complex dietary carbohydrates. Butyrate and acetate were reported to protect against diet-induced obesity without causing hypophagia, while propionate was shown to reduce food intake. However, the underlying mechanisms for these effects are unclear. It was suggested that SCFAs may regulate gut hormones via their endogenous receptors Free fatty acid receptors 2 (FFAR2) and 3 (FFAR3), but direct evidence is lacking. We examined the effects of SCFA administration in mice, and show that butyrate, propionate, and acetate all protected against diet-induced obesity and insulin resistance. Butyrate and propionate, but not acetate, induce gut hormones and reduce food intake. As FFAR3 is the common receptor activated by butyrate and propionate, we examined these effects in FFAR3-deficient mice. The effects of butyrate and propionate on body weight and food intake are independent of FFAR3. In addition, FFAR3 plays a minor role in butyrate stimulation of Glucagon-like peptide-1, and is not required for butyrate- and propionate-dependent induction of Glucose-dependent insulinotropic peptide. Finally, FFAR3-deficient mice show normal body weight and glucose homeostasis. Stimulation of gut hormones and food intake inhibition by butyrate and propionate may represent a novel mechanism by which gut microbiota regulates host metabolism. These effects are largely intact in FFAR3-deficient mice, indicating additional mediators are required for these beneficial effects.

In vivo responsiveness to ezetimibe correlates with niemann-pick C1 like-1 (NPC1L1) binding affinity: Comparison of multiple species NPC1L1 orthologs.

Ezetimibe is the first in class 2-azetidinone that decreases plasma cholesterol by blocking intestinal cholesterol absorption. Ezetimibe effectively reduces plasma cholesterol in several species including human, monkey, dog, hamster, rat, and mouse, but the potency ranges widely. One potential factor responsible for this variation in responsiveness is diversity in ezetimibe metabolism. After oral administration, ezetimibe is glucuronidated. Both ezetimibe and the glucuronide lower plasma cholesterol; however, the glucuronide exhibits greater potency. Recent identification of Niemann-Pick C1 Like-1 (NPC1L1) as the molecular target of ezetimibe enables direct binding studies to be performed. Here, we report the cloning of NPC1L1 derived from multiple species and assess amino acid sequence homology among human, monkey, dog, hamster, rat, and mouse. The rank order of affinity of glucuronidated ezetimibe for NPC1L1 in each species correlates with the rank order of in vivo activity with monkey > dog > hamster and rat >> mouse. Ezetimibe analogs that bind to NPC1L1 exhibit in vivo cholesterol-lowering activity, whereas compounds that do not bind NPC1L1 are inactive. Specific structural components of ezetimibe are identified as critical for binding to NPC1L1. The results demonstrate that small variations in ezetimibe structure or in NPC1L1 amino acid sequence can profoundly influence ezetimibe/NPC1L1 interaction and consequently in vivo activity. The results demonstrate that the ability of compounds to bind to NPC1L1 is the major determinant of in vivo responsiveness.

Characterization of the putative native and recombinant rat sterol transporter Niemann-Pick C1 Like 1 (NPC1L1) protein.

The exact mechanistic pathway of cholesterol absorption in the jejunum of the small intestines is a poorly understood process. Recently, a relatively novel gene, Niemann-Pick C1 Like 1 (NPC1L1), was identified as being critical for intestinal sterol absorption in a pathway which is sensitive to sterol absorption inhibitors such as ezetimibe. NPC1L1 is a multi-transmembrane protein, with a putative sterol sensing domain. Very little else is known about the NPC1L1 protein. In this report, we characterize the native and recombinant rat NPC1L1 protein. We show that NPC1L1 is a 145 kDa membrane protein, enriched in the brush border membrane of the intestinal enterocyte and is highly glycosylated. In addition, sequential detergent extraction of enterocytes result in highly enriched preparations of NPC1L1. An engineered Flag epitope tagged rat NPC1L1 cDNA was expressed as recombinant protein in CHO cells and demonstrated cell surface expression, similar to the native rat protein. These biochemical data indicate that NPC1L1 exists as a predominantly cell surface membrane expressed protein, consistent with its proposed role as the putative intestinal sterol transporter.

Niemann-Pick C1 Like 1 (NPC1L1) is the intestinal phytosterol and cholesterol transporter and a key modulator of whole-body cholesterol homeostasis.

Niemann-Pick C1 Like 1 (NPC1L1) is a protein localized in jejunal enterocytes that is critical for intestinal cholesterol absorption. The uptake of intestinal phytosterols and cholesterol into absorptive enterocytes in the intestine is not fully defined on a molecular level, and the role of NPC1L1 in maintaining whole body cholesterol homeostasis is not known. NPC1L1 null mice had substantially reduced intestinal uptake of cholesterol and sitosterol, with dramatically reduced plasma phytosterol levels. The NPC1L1 null mice were completely resistant to diet-induced hypercholesterolemia, with plasma lipoprotein and hepatic cholesterol profiles similar to those of wild type mice treated with the cholesterol absorption inhibitor ezetimibe. Cholesterol/cholate feeding resulted in down-regulation of intestinal NPC1L1 mRNA expression in wild type mice. NPC1L1 deficiency resulted in up-regulation of intestinal hydroxymethylglutaryl-CoA synthase mRNA and an increase in intestinal cholesterol synthesis, down-regulation of ABCA1 mRNA, and no change in ABCG5 and ABCG8 mRNA expression. NPC1L1 is required for intestinal uptake of both cholesterol and phytosterols and plays a major role in cholesterol homeostasis. Thus, NPC1L1 may be a useful drug target for the treatment of hypercholesterolemia and sitosterolemia.

Niemann-Pick C1 Like 1 protein is critical for intestinal cholesterol absorption.

Dietary cholesterol consumption and intestinal cholesterol absorption contribute to plasma cholesterol levels, a risk factor for coronary heart disease. The molecular mechanism of sterol uptake from the lumen of the small intestine is poorly defined. We show that Niemann-Pick C1 Like 1(NPC1L1) protein plays a critical role in the absorption of intestinal cholesterol. NPC1L1 expression is enriched in the small intestine and is in the brush border membrane of enterocytes. Although otherwise phenotypically normal, NPC1L1-deficient mice exhibit a substantial reduction in absorbed cholesterol, which is unaffected by dietary supplementation of bile acids. Ezetimibe, a drug that inhibits cholesterol absorption, had no effect in NPC1L1 knockout mice, suggesting that NPC1L1 resides in an ezetimibe-sensitive pathway responsible for intestinal cholesterol absorption.

The identification of intestinal scavenger receptor class B, type I (SR-BI) by expression cloning and its role in cholesterol absorption.

The molecular mechanisms of cholesterol absorption in the intestine are poorly understood. With the goal of defining candidate genes involved in these processes a fluorescence-activated cell sorter-based, retroviral-mediated expression cloning strategy has been devised. SCH354909, a fluorescent derivative of ezetimibe, a compound which blocks intestinal cholesterol absorption but whose mechanism of action is unknown, was synthesized and shown to block intestinal cholesterol absorption in rats. Pools of cDNAs prepared from rat intestinal cells enriched in enterocytes were introduced into BW5147 cells and screened for SCH354909 binding. Several independent clones were isolated and all found to encode the scavenger receptor class B, type I (SR-BI), a protein suggested by others to play a role in cholesterol absorption. SCH354909 bound to Chinese hamster ovary (CHO) cells expressing SR-BI in specific and saturable fashion and with high affinity (K(d) approximately 18 nM). Overexpression of SR-BI in CHO cells resulted in increased cholesterol uptake that was blocked by micromolar concentrations of ezetimibe. Analysis of rat intestinal sections by in situ hybridization demonstrated that SR-BI expression was restricted to enterocytes. Cholesterol absorption was determined in SR-B1 knockout mice using both an acute, 2-h, assay and a more chronic fecal dual isotope ratio method. The level of intestinal cholesterol uptake and absorption was similar to that seen in wild-type mice. When assayed in the SR-B1 knockout mice, the dose of ezetimibe required to inhibit hepatic cholesterol accumulation induced by a cholesterol-containing 'western' diet was similar to wild-type mice. Thus, the binding of ezetimibe to cells expressing SR-B1 and the functional blockade of SR-B1-mediated cholesterol absorption in vitro suggest that SR-B1 plays a role in intestinal cholesterol metabolism and the inhibitory activity of ezetimibe. In contrast studies with SR-B1 knockout mice suggest that SR-B1 is not essential for intestinal cholesterol absorption or the activity of ezetimibe.