Hypoglycemic mechanism of intestinal bypass surgery in type 2 diabetic rats.

To investigate the effect of duodenal-jejunal bypass (DJB) surgery on postoperative blood glucose in type 2 diabetic rats, and further explore possible mechanisms for the effect of surgical treatment of type 2 diabetes. Forty rats with type 2 diabetes were randomly assigned to 4 groups (n = 10 rats per group), which subsequently underwent DJB, new biliopancreatic diversion (NBPD) or duodenal-jejunal exclusion (DJE) surgery or a sham operation (SHAM). Fasting glucose, 2-h postprandial glucose and blood lipids were measured, and the mRNA in liver and intestinal tissue for bile acid receptor (FXR), as well as the FXR protein expression in the liver tissues were determined. Postprandial blood glucose and fasting TG and FFA in the DJB and NBPD groups were significantly lower than those in the SHAM group and preoperative (p < 0.05) at 8 weeks postoperation. Liver FXR protein was expressed at significantly higher in the DJB and NBPD groups than in the other two (p < 0.05), and the intestinal FXR mRNA in the DJE group were highest. DJB up-regulates the expression of bile acid receptors in the liver and down-regulates those receptors in the intestinal tract via biliopancreatic diversion. This process reduces TG levels, and subsequently any lipotoxicity to islet cells to produce a hypoglycemic effect.

Colesevelam Reduces Ethanol-Induced Liver Steatosis in Humanized Gnotobiotic Mice.

Alcohol-related liver disease is associated with intestinal dysbiosis. Functional changes in the microbiota affect bile acid metabolism and result in elevated serum bile acids in patients with alcohol-related liver disease. The aim of this study was to identify the potential role of the bile acid sequestrant colesevelam in a humanized mouse model of ethanol-induced liver disease. We colonized germ-free (GF) C57BL/6 mice with feces from patients with alcoholic hepatitis and subjected humanized mice to the chronic-binge ethanol feeding model. Ethanol-fed gnotobiotic mice treated with colesevelam showed reduced hepatic levels of triglycerides and cholesterol, but liver injury and inflammation were not decreased as compared with non-treated mice. Colesevelam reduced hepatic cytochrome P450, family 7, subfamily a, polypeptide 1 (Cyp7a1) protein expression, although serum bile acids were not lowered. In conclusion, our findings indicate that colesevelam treatment mitigates ethanol-induced liver steatosis in mice.

The effects, underlying mechanism and interactions of dexamethasone exposure during pregnancy on maternal bile acid metabolism.

As important members in steroids related signal pathways, bile acids are very important in regulating substance metabolism and immune homeostasis. However, bile acids are highly cytotoxic, and the excessive accumulation can induce several abnormalities such as cholestatic liver injury. It is known that the bile acid metabolism alters during pregnancy and mostly will not result in pathologies. However, the effect of dexamethasone exposure during pregnancy on bile acid metabolism is still unknown. In this study, pregnant Wistar rats were subcutaneously administered dexamethasone (0.2 mg/kg.d) or saline from gestation day 9-21, while virgin rats were given the same treatment for 13 days. We found that, physiological pregnancy or dexamethasone exposure during non-pregnancy did not affect maternal serum TBA level and liver function. Nevertheless, dexamethasone exposure during pregnancy increased serum TBA level and accompanied with liver injury. Furthermore, we discovered that the conservation of bile acid homeostasis under pregnancy or dexamethasone exposure was maintained through compensatory pathways. However, dexamethasone exposure during pregnancy tipped the balance of liver bile acid homeostasis by increasing classical synthesis and decreasing efflux and uptake. In addition, dexamethasone exposure during pregnancy also increased serum estrogen level and nuclear receptors mRNA expression levels. Finally, two-way ANOVA analysis showed that dexamethasone exposure during pregnancy could induce or facilitate maternal cholestasis and liver injury by up-regulating ERα and CYP7A1 expression. This study confirmed that dexamethasone exposure during pregnancy was related to maternal intrahepatic cholestasis of pregnancy and should be carefully monitored in clinical settings.

Interactions Between Regulatory Variants in CYP7A1 (Cholesterol 7α-Hydroxylase) Promoter and Enhancer Regions Regulate CYP7A1 Expression.

BACKGROUND: CYP7A1 (cholesterol 7α-hydroxylase) catalyzes the rate-limiting step in bile acid biosynthesis from cholesterol-a main pathway for cholesterol removal from the body. CYP7A1 single-nucleotide polymorphisms (SNPs) are associated with total cholesterol and LDL (low-density lipoprotein) levels, risk of cardiovascular diseases, and other phenotypes; however, results are inconsistent, and causative variants remain uncertain, except for a frequent promoter SNP (rs3808607). METHODS: We used chromatin conformation capture (4C assay), chromatin immunoprecipitation qPCR assay in hepatocytes, and CRISPR (clustered regularly interspaced short palindromic repeats)-mediated genome editing in hepatocellular carcinoma cell line cells to identify regulatory regions for CYP7A1. We then screened for SNPs located in regulatory regions, testing effects on reporter gene assays and on hepatic CYP7A1 expression by measuring allelic mRNA expression imbalance. RESULTS: 4C assays showed several regions interacting with CYP7A1 promoter. CRISPR-mediated genome editing in hepatocellular carcinoma cell line cells revealed a novel CYP7A1 enhancer and a repressor region, located >10 kb downstream of the CYP7A1 promoter. SNP screening with an allelic mRNA expression imbalance in human livers and reporter gene assays identified a frequent functional SNP (rs9297994) located in the downstream CYP7A1 enhancer region. SNP rs9297994 is in high linkage disequilibrium with promoter SNP rs3808607 but has opposite effects on CYP7A1 mRNA expression. Their combined effects using a 2-SNP model robustly associate with hepatic CYP7A1 mRNA expression, ranging >2 orders of magnitude. Moreover, only the 2-SNP model, but not each SNP alone, is significantly associated with LDL levels, risk of coronary artery disease, statin response, and diabetes mellitus in several clinical cohorts, including CATHGEN (Catheterization Genetics) and Framingham. CONCLUSIONS: Two interacting regulatory SNPs modulate CYP7A1 expression and are associated with risk of coronary artery disease and diabetes mellitus.

On the Role of Illness Duration and Nutrient Restriction in Cholestatic Alterations that Occur During Critical Illness.

BACKGROUND AND AIMS: Elevated markers of cholestasis are common in response to critical illness, and associated with adverse outcome. The role of illness duration and of nutrient restriction on underlying molecular pathways of such cholestatic responses have not been thoroughly investigated. METHODS: In a mouse model of surgery- and sepsis-induced critical illness, molecular pathways of cholestasis were investigated up to 7 days. To assess which changes are explained by illness-induced lack of feeding, nutrient-restricted healthy mice were studied and compared with ad libitum fed healthy mice. Furthermore, serum bile acid (BA) concentrations were quantified in 1,114 human patients with either short or long intensive care unit (ICU) stay, matched for type and severity of illness, up to ICU-day-7. RESULTS: In critically ill mice, either evoked by surgery or sepsis, circulating and hepatic BA-levels progressively increased with time from day-3 onward, preceded by unsuppressed or upregulated CYP7A1 and CYP27A1 protein expression. From 30 h onward, nuclear farnesoid-X-receptor-retinoid-X-receptor staining was significantly suppressed in both critically ill groups, followed from day-3 onward by decreased gene expression of the apical exporter BA-specific export pump and increased expression of basolateral exporters multidrug resistance-associated protein 3 (MRP3) and MRP4. Nutrient restriction in healthy mice only partly mirrored illness-induced alterations in circulating BA and BA-transporters, without changing nuclear receptors or synthesis markers expression. Also in human critically ill patients, serum BA increased with time in long-stay patients only, similarly for patients with or without sepsis. CONCLUSIONS: Circulating BA concentrations rose days after onset of sepsis- and surgery-induced, critical illness, only partially explained by lack of feeding, preceded by suppressed nuclear feedback-sensors and ongoing BA synthesis. Expression of transporters suggested ongoing reversed BA-flow toward the blood.

Iron depletion induces hepatic secretion of biliary lipids and glutathione in rats.

Iron depletion (ID) has been shown to induce the liver expression of Cyp7a1, the rate-limiting enzyme initiating conversion of cholesterol to bile acids (BA), although the effect on bile acids metabolism and bile production is unknown. Therefore, we investigated changes in bile secretion and BA synthesis during diet-induced iron depletion (ID) in rats. ID increased bile flow along with augmented biliary excretion of bile acids, glutathione, cholesterol and phospholipids. Accordingly, we found transcriptional upregulation of the Cyp7a1, Cyp8b1, and Cyp27a1 BA synthetic enzymes, as well as induction of the Abcg5/8 cholesterol transporters in ID rat livers. In contrast, intravenous infusion of 3H-taurocholate failed to elicit any difference in biliary secretion of this compound in the ID rats. This corresponded with unchanged expression of canalicular rate-limiting transporters for BA as well as glutathione. We also observed that ID substantially changed the spectrum of BA in bile and decreased plasma concentrations of BA and cholesterol. Experiments with differentiated human hepatic HepaRG cells confirmed human CYP7A1 orthologue upregulation resulting from reduced iron concentrations. Results employing a luciferase reporter gene assay suggest that the transcriptional activation of the CYP7A1 promoter under ID conditions works independent of farnesoid X (FXR), pregnane X (PXR) and liver X (LXRα) receptors activation. It can be concluded that this study characterizes the molecular mechanisms of modified bile production as well as cholesterol as along with BA homeostasis during ID. We propose complex upregulation of BA synthesis, and biliary cholesterol secretion as the key factors affected by ID.

Bile Salt Homeostasis in Normal and Bsep Gene Knockout Rats with Single and Repeated Doses of Troglitazone.

The interference of bile acid secretion through bile salt export pump (BSEP) inhibition is one of the mechanisms for troglitazone (TGZ)-induced hepatotoxicity. Here, we investigated the impact of single or repeated oral doses of TGZ (200 mg/kg/day, 7 days) on bile acid homoeostasis in wild-type (WT) and Bsep knockout (KO) rats. Following oral doses, plasma exposures of TGZ were not different between WT and KO rats, and were similar on day 1 and day 7. However, plasma exposures of the major metabolite, troglitazone sulfate (TS), in KO rats were 7.6- and 9.3-fold lower than in WT on day 1 and day 7, respectively, due to increased TS biliary excretion. With Bsep KO, the mRNA levels of multidrug resistance-associated protein 2 (Mrp2), Mrp3, Mrp4, Mdr1, breast cancer resistance protein (Bcrp), sodium taurocholate cotransporting polypeptide, small heterodimer partner, and Sult2A1 were significantly altered in KO rats. Following seven daily TGZ treatments, Cyp7A1 was significantly increased in both WT and KO rats. In the vehicle groups, plasma exposures of individual bile acids demonstrated variable changes in KO rats as compared with WT. WT rats dosed with TGZ showed an increase of many bile acid species in plasma on day 1, suggesting the inhibition of Bsep. Conversely, these changes returned to base levels on day 7. In KO rats, alterations of most bile acids were observed after seven doses of TGZ. Collectively, bile acid homeostasis in rats was regulated through bile acid synthesis and transport in response to Bsep deficiency and TGZ inhibition. Additionally, our study is the first to demonstrate that repeated TGZ doses can upregulate Cyp7A1 in rats.

Osteopontin Deficiency Alters Biliary Homeostasis and Protects against Gallstone Formation.

The precipitation of excess biliary cholesterol as solid crystals is a prerequisite for cholesterol gallstone formation, which occurs due to disturbed biliary homeostasis. Biliary homeostasis is regulated by an elaborate network of genes in hepatocytes. If unmanaged, the cholesterol crystals will aggregate, fuse and form gallstones. We have previously observed that the levels of osteopontin (OPN) in bile and gallbladder were reduced in gallstone patients. However, the role and mechanism for hepatic OPN in cholesterol gallstone formation is undetermined. In this study, we found that the expression of hepatic OPN was increased in gallstone patients compared with gallstone-free counterparts. Then, we observed that OPN-deficient mice were less vulnerable to cholesterol gallstone formation than wild type mice. Further mechanistic studies revealed that this protective effect was associated with alterations of bile composition and was caused by the increased hepatic CYP7A1 expression and the reduced expression of hepatic SHP, ATP8B1, SR-B1 and SREBP-2. Finally, the correlations between the expression of hepatic OPN and the expression of these hepatic genes were validated in gallstone patients. Taken together, our findings reveal that hepatic OPN contributes to cholesterol gallstone formation by regulating biliary metabolism and might be developed as a therapeutic target for gallstone treatments.

Hsp90 and hepatobiliary transformation during sea lamprey metamorphosis.

BACKGROUND: Biliary atresia (BA) is a human infant disease with inflammatory fibrous obstructions in the bile ducts and is the most common cause for pediatric liver transplantation. In contrast, the sea lamprey undergoes developmental BA with transient cholestasis and fibrosis during metamorphosis, but emerges as a fecund adult. Therefore, sea lamprey liver metamorphosis may serve as an etiological model for human BA and provide pivotal information for hepatobiliary transformation and possible therapeutics. RESULTS: We hypothesized that liver metamorphosis in sea lamprey is due to transcriptional reprogramming that dictates cellular remodeling during metamorphosis. We determined global gene expressions in liver at several metamorphic landmark stages by integrating mRNA-Seq and gene ontology analyses, and validated the results with real-time quantitative PCR, histological and immunohistochemical staining. These analyses revealed that gene expressions of protein folding chaperones, membrane transporters and extracellular matrices were altered and shifted during liver metamorphosis. HSP90, important in protein folding and invertebrate metamorphosis, was identified as a candidate key factor during liver metamorphosis in sea lamprey. Blocking HSP90 with geldanamycin facilitated liver metamorphosis and decreased the gene expressions of the rate limiting enzyme for cholesterol biosynthesis, HMGCoA reductase (hmgcr), and bile acid biosynthesis, cyp7a1. Injection of hsp90 siRNA for 4 days altered gene expressions of met, hmgcr, cyp27a1, and slc10a1. Bile acid concentrations were increased while bile duct and gall bladder degeneration was facilitated and synchronized after hsp90 siRNA injection. CONCLUSIONS: HSP90 appears to play crucial roles in hepatobiliary transformation during sea lamprey metamorphosis. Sea lamprey is a useful animal model to study postembryonic development and mechanisms for hsp90-induced hepatobiliary transformation.

Orphan nuclear receptor oestrogen-related receptor γ (ERRγ) plays a key role in hepatic cannabinoid receptor type 1-mediated induction of CYP7A1 gene expression.

Bile acids are primarily synthesized from cholesterol in the liver and have important roles in dietary lipid absorption and cholesterol homoeostasis. Detailed roles of the orphan nuclear receptors regulating cholesterol 7α-hydroxylase (CYP7A1), the rate-limiting enzyme in bile acid synthesis, have not yet been fully elucidated. In the present study, we report that oestrogen-related receptor γ (ERRγ) is a novel transcriptional regulator of CYP7A1 expression. Activation of cannabinoid receptor type 1 (CB1 receptor) signalling induced ERRγ-mediated transcription of the CYP7A1 gene. Overexpression of ERRγ increased CYP7A1 expression in vitro and in vivo, whereas knockdown of ERRγ attenuated CYP7A1 expression. Deletion analysis of the CYP7A1 gene promoter and a ChIP assay revealed an ERRγ-binding site on the CYP7A1 gene promoter. Small heterodimer partner (SHP) inhibited the transcriptional activity of ERRγ and thus regulated CYP7A1 expression. Overexpression of ERRγ led to increased bile acid levels, whereas an inverse agonist of ERRγ, GSK5182, reduced CYP7A1 expression and bile acid synthesis. Finally, GSK5182 significantly reduced hepatic CB1 receptor-mediated induction of CYP7A1 expression and bile acid synthesis in alcohol-treated mice. These results provide the molecular mechanism linking ERRγ and bile acid metabolism.

On the formation of 7-ketocholesterol from 7-dehydrocholesterol in patients with CTX and SLO.

A new mechanism for formation of 7-ketocholesterol was recently described involving cytochrome P-450 (CYP)7A1-catalyzed conversion of 7-dehydrocholesterol into 7-ketocholesterol with cholesterol-7,8-epoxide as a side product. Some patients with cerebrotendinous xanthomatosis (CTX) and all patients with Smith-Lemli-Opitz syndrome (SLO) have markedly increased levels of 7-dehydrocholesterol in plasma and tissues. In addition, the former patients have markedly upregulated CYP7A1. We hypothesized that these patients may produce 7-ketocholesterol from 7-dehydrocholesterol with formation of cholesterol-7,8-epoxide as a side product. In accord with this hypothesis, two patients with CTX were found to have increased levels of 7-ketocholesterol and 7-dehydrocholesterol, as well as a significant level of cholesterol-7,8-epoxide. The latter steroid was not detectable in plasma from healthy volunteers. Downregulation of CYP7A1 activity by treatment with chenodeoxycholic acid reduced the levels of 7-ketocholesterol in parallel with decreased levels of 7-dehydrocholesterol and cholesterol-7,8-epoxide. Three patients with SLO were found to have markedly elevated levels of 7-ketocholesterol as well as high levels of cholesterol-7,8-epoxide. The results support the hypothesis that 7-dehydrocholesterol is a precursor to 7-ketocholesterol in SLO and some patients with CTX.

Involvement of hepatic IL-1 in the strain-dependent sex differences in serum total cholesterol levels in rats.

The strain and sex differences in serum total cholesterol (TC) levels were examined in F344 and Sprague-Dawley (SD) rats. A sex difference (male

Effect of licorice flavonoid oil on cholesterol metabolism in high fat diet rats.

Dietary licorice fravonoid oil (LFO) significantly decreased hepatic cholesterol and plasma lipoprotein cholesterol levels in high-fat diet rats. It significantly suppressed hydroxymethylglutaryl-CoA synthase activity and increased cholesterol 7α-hydroxylase activity. The low density lipoprotein receptor mRNA level was significantly increased by LFO. These results suggest that dietary LFO improves cholesterol metabolism in obese animals.

Identification of endocrine disrupting chemicals activating SXR-mediated transactivation of CYP3A and CYP7A1.

Endocrine disrupting chemicals (EDCs) have emerged as a major public health issue because of their potentially disruptive effects on physiological hormonal actions. SXR (steroid xenobiotic receptor), also known as NR1I2, regulates CYP3A expression in response to exogenous chemicals, such as EDCs, after binding to SXRE (SXR response element). In our study, luciferase assay showed that 14 out of 55 EDCs could enhance SXR-mediated rat or human CYP3A gene transcription nearly evenly, and could also activate rat CYP7A1 gene transcription by cross-interaction of SXR and LXRE (LXRα response element). SXR diffused in the nucleus without ligand, whereas intranuclear foci of liganded SXR were produced. Furthermore, endogenous mRNA expression of CYP3A4 gene was enhanced by the 14 positive EDCs. Our results suggested a probable mechanism of EDCs disrupting the steroid or xenobiotic metabolism homeostasis via SXR.

Nuclear receptors HNF4α and LRH-1 cooperate in regulating Cyp7a1 in vivo.

Fibroblast growth factor 19 (FGF19) is a postprandial enterokine induced by the nuclear bile acid receptor, FXR, in ileum. FGF19 inhibits bile acid synthesis in liver through transcriptional repression of cholesterol 7α-hydroxylase (CYP7A1) via a mechanism involving the nuclear receptor SHP. Here, in a series of loss-of-function studies, we show that the nuclear receptors HNF4α and LRH-1 have dual roles in regulating Cyp7a1 in vivo. First, they cooperate in maintaining basal Cyp7a1 expression. Second, they enable SHP binding to the Cyp7a1 promoter and facilitate FGF19-mediated repression of bile acid synthesis. HNF4α and LRH-1 promote active transcription histone marks on the Cyp7a1 promoter that are reversed by FGF19 in a SHP-dependent manner. These findings demonstrate that both HNF4α and LRH-1 are important regulators of Cyp7a1 transcription in vivo.

Interleukin-1 controls the constitutive expression of the Cyp7a1 gene by regulating the expression of Cyp7a1 transcriptional regulators in the mouse liver.

Our previous study using interleukin-1α/ß-knockout (IL-1-KO) and wild-type (WT) mice demonstrated that IL-1 acts as a positive factor for constitutive gene expression of hepatic cytochrome P4507a1 (Cyp7a1). In this study, to clarify the role of IL-1 in the expression of the hepatic Cyp7a1 gene, we focused on Cyp7a1 transcriptional regulators such as α-fetoprotein transcription factor (FTF), liver X receptor α (LXRα), hepatocyte nuclear factor 4α (HNF4α) and small heterodimer partner (SHP) and examined the effects of IL-1 on their gene expression by real-time reverse-transcription polymerase chain reaction using IL-1-KO and WT mice. We observed no significant differences between sex-matched IL-1-KO and WT mice with regard to gene expression levels of FTF, LXRα, and HNF4α, all of which are positive transcriptional regulators for the Cyp7a1 gene. However, interindividual differences in hepatic FTF and LXRα expression were closely dependent on the gene expression level(s) of hepatic IL-1 and tumor necrosis factor-α (TNF-α), while interindividual differences in hepatic HNF4α were clearly correlated with the expression of IL-1, but not TNF-α. In contrast, the gene expression level of SHP, which is a negative transcriptional regulator of the Cyp7a1 gene through inhibition of FTF function, was higher in IL-1-KO mice than in sex-matched WT mice. These findings demonstrate that, like TNF-α, IL-1 positively controls the gene expression of Cyp7a1 transcriptional upregulators but, in contrast to the previously reported action of TNF-α, IL-1 also acts to downregulate SHP gene expression.

Beneficial effects of colchicine on 17alpha-ethynylestradiol-induced cholestasis in rats.

Colchicine (CAS 64-86-8) is considered to have a hepatoprotective effect and play a role in biliary excretion. 17alpha-Ethynylestradiol (EE) (5 mg/kg, subcutaneously, daily, for 5 days) causes intrahepatic cholestasis by reducing both the influx and efflux of bile acid in hepatocytes, resulting in a decrease in bile flow. The objective of this study was to evaluate whether colchicine has any effect on EE-induced cholestasis. The effects of colchicine treatment on EE-induced cholestasis in rats for 5 consecutive days were evaluated. The serum components and enzymatic activity were assayed. In addition, the bile flow and biliary excretion were determined. Furthermore, western blot analysis was used to measure the expression of farnesoid X receptor (FXR), bile salt export pump (BSEP), multidrug resistance-associated protein 2 (MRP2), and cholesterol 7alpha-hydroxylase (CYP7A1). Colchicine not only significantly inhibited the elevation of cholestasis-related serum components and enzyme activity but also significantly attenuated the decrease of the bile flow and biliary excretion. Colchicine also remarkably increased the hepatic expression of FXR, BSEP and MRP2, but decreased that of CYP7A1. Our data indicates that colchicine treatment attenuated EE-induced cholestasis in rats, most likely by promoting bile flow and biliary excretion, and reduced the synthesis of bile acids.

Overexpression of cholesterol 7α-hydroxylase promotes hepatic bile acid synthesis and secretion and maintains cholesterol homeostasis.

UNLABELLED: We reported previously that mice overexpressing cytochrome P450 7a1 (Cyp7a1; Cyp7a1-tg mice) are protected against high fat diet-induced hypercholesterolemia, obesity, and insulin resistance. Here, we investigated the underlying mechanism of bile acid signaling in maintaining cholesterol homeostasis in Cyp7a1-tg mice. Cyp7a1-tg mice had two-fold higher Cyp7a1 activity and bile acid pool than did wild-type mice. Gallbladder bile acid composition changed from predominantly cholic acid (57%) in wild-type to chenodeoxycholic acid (54%) in Cyp7a1-tg mice. Cyp7a1-tg mice had higher biliary and fecal cholesterol and bile acid secretion rates than did wild-type mice. Surprisingly, hepatic de novo cholesterol synthesis was markedly induced in Cyp7a1-tg mice but intestine fractional cholesterol absorption in Cyp7a1-tg mice remained the same as wild-type mice despite the presence of increased intestine bile acids. Interestingly, hepatic but not intestinal expression of several cholesterol (adenosine triphosphate-binding cassette G5/G8 [ABCG5/G8], scavenger receptor class B, member 1) and bile acid (ABCB11) transporters were significantly induced in Cyp7a1-tg mice. Treatment of mouse or human hepatocytes with a farnesoid X receptor (FXR) agonist GW4064 or bile acids induced hepatic Abcg5/g8 expression. A functional FXR binding site was identified in the Abcg5 gene promoter. Study of tissue-specific Fxr knockout mice demonstrated that loss of the Fxr gene in the liver attenuated bile acid induction of hepatic Abcg5/g8 and gallbladder cholesterol content, suggesting a role of FXR in the regulation of cholesterol transport. CONCLUSION: This study revealed a new mechanism by which increased Cyp7a1 activity expands the hydrophobic bile acid pool, stimulating hepatic cholesterol synthesis and biliary cholesterol secretion without increasing intestinal cholesterol absorption. This study demonstrated that Cyp7a1 plays a critical role in maintaining cholesterol homeostasis and underscores the importance of bile acid signaling in regulating overall cholesterol homeostasis.

A chronic high-cholesterol diet paradoxically suppresses hepatic CYP7A1 expression in FVB/NJ mice.

Cholesterol 7α-hydroxylase (CYP7A1) encodes for the rate-limiting step in the conversion of cholesterol to bile acids in the liver. In response to acute cholesterol feeding, mice upregulate CYP7A1 via stimulation of the liver X receptor (LXR) α. However, the effect of a chronic high-cholesterol diet on hepatic CYP7A1 expression in mice is unknown. We demonstrate that chronic cholesterol feeding (0.2% or 1.25% w/w cholesterol for 12 weeks) in FVB/NJ mice results in a >60% suppression of hepatic CYP7A1 expression associated with a >2-fold increase in hepatic cholesterol content. In contrast, acute cholesterol feeding induces a >3-fold upregulation of hepatic CYP7A1 expression. We show that chronic, but not acute, cholesterol feeding increases the expression of hepatic inflammatory cytokines, tumor necrosis factor (TNF)α, and interleukin (IL)-1ß, which are known to suppress hepatic CYP7A1 expression. Chronic cholesterol feeding also results in activation of the mitogen activated protein (MAP) kinases, c-Jun N-terminal kinase (JNK) and extracellular signal-regulated kinase (ERK). Furthermore, we demonstrate in vitro that suppression of CYP7A1 by TNFα and IL-1ß is dependent on JNK and ERK signaling. We conclude that chronic high-cholesterol feeding suppresses CYP7A1 expression in mice. We propose that chronic cholesterol feeding induces inflammatory cytokine activation and liver damage, which leads to suppression of CYP7A1 via activation of JNK and ERK signaling pathways.

Sustained upregulation of sodium taurocholate cotransporting polypeptide and bile salt export pump and downregulation of cholesterol 7α-hydroxylase in the liver of patients with end-stage primary biliary cirrhosis.

To examine the mRNA expression of hepatobiliary transporters in primary biliary cirrhosis (PBC) patients and to compare bile acid absorption, synthesis, and efflux in patients with non-end-stage and end-stage PBC, we obtained liver samples from PBC patients by percutaneous needle biopsy. End-stage PBC was defined as follows: histological stage IV; cirrhosis; serum total bilirubin, ≥4.0 mg/dl; and Child-Pugh Class C. The mRNA expression levels of sodium taurocholate cotransporting polypeptide (NTCP), bile salt export pump (BSEP), and hepatic cholesterol 7α-hydroxylase (CYP7A1) were significantly higher in the PBC patients than in the controls (P < 0.01). The mRNA levels of NTCP and BSEP were significantly higher in the end-stage PBC patients than in the controls (P < 0.01). However, hepatic CYP7A1 mRNA expression decreased significantly (by 70%) in the patients with end-stage PBC as compared to the controls and the patients with non-end-stage PBC (P < 0.01). The hepatic expression of transporters mediating bile acid influx and efflux showed sustained elevation, whereas that of the rate-limiting enzyme for bile acid biosynthesis was attenuated in the end-stage PBC patients. Thus, mechanisms may be present preventing the accumulation of toxic bile acids in the hepatocytes of end-stage PBC patients.