Identification of metabolism-related key genes as potential biomarkers for pathogenesis of immune thrombocytopenia

Immune thrombocytopenia (ITP), an acquired autoimmune disease, is characterized by immune-mediated platelet destruction. A biomarker is a biological entity that contributes to disease pathogenesis and reflects disease activity. Metabolic alterations are reported to be associated with the occurrence of various diseases. As metabolic biomarkers for ITP have not been identified. This study aimed to identify metabolism-related differentially expressed genes as potential biomarkers for pathogenesis of ITP using bioinformatic analyses.The microarray expression data of the peripheral blood mononuclear cells were downloaded from the Gene Expression Omnibus database (GSE112278 download link: https://www.ncbi.nlm.nih.gov/geo/query/acc.cgi?acc=GSE112278 ). Key module genes were intersected with metabolism-related genes to obtain the metabolism-related key candidate genes. The hub genes were screened based on the degree function in the coytoscape sofware. The key ITP-related genes were subjected to functional enrichment analysis. Immune infiltration analysis was performed using a single-sample gene set enrichment analysis algorithm to evaluate the differential infiltration levels of immune cell types between ITP patient and control. Molecular subtypes were identified based on the expression of hub genes. The expression of hub genes in the ITP patients was validated using quantitative real-time polymerase chain reaction analysis. This study identified five hub genes (ADH4, CYP7A1, CYP1A2, CYP8B1, and NR1H4), which were be associated with the pathogenesis of ITP, and two molecular subtypes of ITP. Among these hub genes, CYP7A1 and CYP8B1 involved in cholesterol metabolism,were further verified in clinical samples.

Therapeutic Potential of Danyankang Capsule in High-Fat Diet-Induced Cholelithiasis and Its Impact on Liver FXR Signaling and Gut Microbiota

Cholelithiasis, commonly known as gallstones, represents a prevalent hepatobiliary disorder. This study aimed to elucidate the therapeutic role and mechanism of Danyankang capsulein treating cholelithiasis induced by a high-fat diet in C57BL/6 mice. The therapeutical potential of Danyankang was assessed through biochemical analyses, histopathological examinations, protein detection, and 16S rDNA sequencing. A high-fat diet resulted in cholelithiasis manifestation in mice, with discernable abnormal serum biochemical indices and disrupted biliary cholesterol homeostasis. Danyankang treatment notably ameliorated liver inflammation symptoms and rectified serum and liver biochemical abnormalities. Concurrently, it addressed biliary imbalances. Elevated expressions of toll-like receptor 4 (TLR4), nuclear factor-kappaB (NF-κB)/pNF-κB, HMGCR, CYP7A1, and CYP8B1 observed at the inception of cholelithiasis, were notably reduced upon Danyankang administration. Furthermore, 16S rDNA analysis revealed a decline in species number and diversity of the intestinal flora in cholelithiasis-treated mice, while the decline was reversed with Danyankang treatment. Danyankang capsules reduced the abundance of Verrucomicrobiota and increased the abundance of Actinobacteriota and Proteobacteria. In conclusion, the present study demonstrates that Danyankang exerts potent therapeutic efficacy against high-fat diet-induced cholelithiasis. This beneficial outcome is potentially linked to the inhibition of the TLR4/pNF-κB and SHP/CYP7A1/CYP8B1 signaling pathways, as well as the enhancement of intestinal flora species abundance.

Fucogalactan Sulfate (FS) from Laminaria japonica Regulates Lipid Metabolism in Diet-Induced Humanized Dyslipidemia Mice via an Intestinal FXR-FGF19-CYP7A1/CYP8B1 Pathway

Our previous study found that fucogalactan sulfate (FS) from Laminaria japonica exhibited significant hypolipidemic effects. To further elucidate the mechanism, we first constructed a dyslipidemia mouse model with humanized gut microbiota and proved the main differential metabolic pathway involved bile acid metabolism. Then, we evaluated the beneficial effects of FS on dyslipidemia in this model mice, which revealed that oral FS administration reduced serum cholesterol levels and mitigated liver fat accumulation. Gut microbiota and microbiome analysis showed FS increased the abundance of Ruminococcaceae_NK4A214_group, GCA-900066755, and Eubacterium, which were positively associated with the fecal DCA, β-MCA, and HDCA. Further investigation demonstrated that FS inhibited the hepatic farnesoid X receptor (FXR), while activating the intestinal FXR-FGF19 pathway, leading to suppression of CYP7A1 and CYP8B1, as well as potentially reduced bile acid synthesis and lipid absorption. Overall, FS regulated lipid metabolism in diet-induced humanized dyslipidemia mice via the bile acid-mediated intestinal FXR-FGF19-CYP7A1/CYP8B1 pathway.

Discovery biomarker to optimize obeticholic acid treatment for non-alcoholic fatty liver disease

The response rate to obeticholic acid (OCA), a potential therapeutic agent for non-alcoholic fatty liver disease, is limited. This study demonstrated that upregulation of the alternative bile acid synthesis pathway increases the OCA treatment response rate. The hepatic transcriptome and bile acid metabolite profile analyses revealed that the alternative bile acid synthesis pathway (Cyp7b1 and muricholic acid) in the OCA-responder group were upregulated compared with those in the OCA-non-responder group. Intestinal microbiome analysis also revealed that the abundances of Bacteroidaceae, Parabacteroides, and Bacteroides, which were positively correlated with the alternative bile acid synthesis pathway, were higher in the OCA-responder group than in the non-responder group. Pre-study hepatic mRNA levels of Cyp8b1 (classic pathway) were downregulated in the OCA-responder group. The OCA response rate increased up to 80% in cases with a hepatic Cyp7b1/Cyp8b1 ratio ≥ 5.0. Therefore, the OCA therapeutic response can be evaluated based on the Cyp7b1/Cyp8b1 ratio or the alternative/classic bile acid synthesis pathway activity.

Long-term oral administration of Epimedii Folium induced cholestasis in mice by interfering with bile acid transport

ETHNOPHARMACOLOGICAL RELEVANCE

Epimedii Folium (EF) is a common traditional Chinese medicine that functions as a tonifying kidney yang to strengthen bones and muscles and dispel wind dampness (limb pain, lethargy, nausea, anorexia, and loose stools). Several studies have reported the potential risk of cholestatic liver damage from EF use; however, there have been few investigations of EF-induced cholestasis, particularly the underlying mechanisms.

AIMS OF THE STUDY

The purpose of this study was to evaluate the risk of EF-induced cholestasis in vivo and to explore the mechanisms of action.

MATERIALS AND METHODS

ICR mice were orally administered a water extract of EF (WEF) in doses of 6.5 and 19.5 g/kg/day for 14 weeks. Liver-to-body weight ratios, body weight, histopathological examination, and biochemical analyses were performed to assess WEF-induced cholestasis in the mice. Genes associated with bile acid (BA) metabolism and transport, including sodium taurocholate cotransporting polypeptide (NTCP), cytochrome P450 8B1 (CYP8B1), bile-salt export pump (BSEP), multidrug resistance P-glycoproteins 1 (MDR1), and farnesoid X receptor (FXR), were measured at the transcript and protein levels to investigate the potential mechanisms through which cholestasis is aroused by EF.

RESULTS

After administration of WEF for 14 weeks, mice in the high-dose WEF group showed poor health with an increased liver-to-body weight ratio as well as higher serum aminotransferase, alkaline phosphatase, direct bilirubin, and total BA levels. Compared with the control group, mRNA expression of NTCP and cholesterol 7a-hydroxylase (CYP7A1) increased, and levels of BSEP, MDR1, multidrug resistance-associated protein 2, and multidrug resistance-associated protein 3 decreased in the WEF-treated group. NTCP, BSEP, MDR1, and CYP8B1 showed similar mRNA and protein expression trends.

CONCLUSION

We demonstrated that the long-term oral administration of WEF causes cholestatic liver injury in mice, which is consistent with reported clinical cases. Furthermore, we found that the destruction of BA metabolism and transport is involved in WEF-induced cholestasis. The fine-scale molecular mechanisms of WEF-induced cholestasis and the active compounds of EF need further study.

Cluster Analysis of SF-36 Scales as a Predictor of Spinal Pain Patients Response to a Multidisciplinary Pain Management Approach Beginning with Epidural Steroid Injection

OBJECTIVE

To investigate whether grouping of patients with back pain into similar behavioral patient profiles using SF-36 scores is predictive of outcome following 1-year treatment in a multidisciplinary spine center beginning with referral for epidural steroid injection.

DESIGN

A prospective observational study was conducted on 81 consecutive patients selected for epidural steroid injections by independent physicians following common institutional criteria. Each patient completed a baseline SF-36 questionnaire as well as a numerical response pain scale. The initial SF-36 data were used to place each patient into one of three subgroups (Highly Functional, Emotional Adapters, and Dysfunctional). Follow-up SF-36 and numerical response pain scale questionnaires were completed by the patients at 1 month and 12 months following the initial epidural steroid injection.

RESULTS

Results revealed significant improvement among all three patient subgroups following multidisciplinary treatment at both 1 month and 12 months. Few differences in outcome occurred among the subgroups.

CONCLUSION

The SF-36-determined subgroups did not predict response to a multidisciplinary pain clinic. All three subgroups showed similar improvement following treatment.

On the mechanism of bile acid inhibition of rat sterol 12alpha-hydroxylase gene (CYP8B1) transcription: roles of alpha-fetoprotein transcription factor and hepatocyte nuclear factor 4alpha

The sterol 12alpha-hydroxylase (CYP8B1) is a key enzyme of the bile acid biosynthetic pathway. It regulates the composition of bile acids in bile, i.e. ratio between cholic acid (CA) and chenodeoxycholic acid (CDCA). In similarity with cholesterol 7alpha-hydroxylase (CYP7A1), this enzyme is subjected to a negative feedback regulation by bile acids. It has been recently reported that bile acid-activated farnesoid X receptor (FXR) induces the small heterodimer partner (SHP) that interacts with alpha-fetoprotein transcription factor (FTF) and down-regulates CYP7A1 transcription. We studied whether the same mechanism also regulated rat CYP8B1 gene transcription. Feeding rats with CDCA caused a 40-50% decrease of CYP8B1 and hepatocyte nuclear factor 4alpha (HNF4alpha) mRNA expression levels. This was associated with an increase in FTF mRNA expression, but SHP mRNA expression was not altered. Electrophoretic mobility shift assay (EMSA) and transient transfection assay of promoter/reporter genes coupled to mutagenesis analysis identified a putative bile acid response element (BARE) that has an HNF4alpha binding site embedded in two overlapping FTF binding sites. Mutation of the HNF4alpha binding site markedly reduced basal promoter activity and its repression by bile acids. Cotransfection with FTF strongly repressed CYP8B1 transcription. Interestingly, HNF4alpha could overcome the inhibitory effects of FTF and bile acids. We conclude that FTF and HNF4alpha not only play critical roles on CYP8B1 gene transcription, but also mediate bile acid feedback inhibition. This study reveals a novel mechanism by which bile acids inhibit rat CYP8B1 gene transcription by inducing FTF and inhibiting HNF4alpha expression.

Differential effects of sterol regulatory binding proteins 1 and 2 on sterol 12 alpha-hydroxylase. SREBP-2 suppresses the sterol 12 alpha-hydroxylase promoter

The most important pathway for the catabolism and excretion of cholesterol in mammals is the formation of bile acids. Improper regulation of this pathway has implications for atherosclerosis, cholesterol gallstone formation, and some lipid storage diseases. Sterol 12 alpha-hydroxylase (12 alpha-hydroxylase) is required for cholic acid biosynthesis. The alpha(1)-fetoprotein transcription factor FTF is crucial for the expression and the bile acid-mediated down-regulation of 12 alpha-hydroxylase. Cholesterol, on the other hand, down-regulates expression of the 12 alpha-hydroxylase gene. In this study, we show that the two sterol regulatory binding proteins (SREBPs) have opposite effects on the 12 alpha-hydroxylase promoter. SREBP-1 activated the 12 alpha-hydroxylase promoter, as it does with many other cholesterol-regulated genes. In contrast, SREBP-2 suppressed 12 alpha-hydroxylase promoter activity. SREBP-1 mediates the cholesterol-down-regulation of 12 alpha-hydroxylase promoter by binding to two inverted sterol regulatory elements found approximately 300 nucleotides from the transcriptional initiation site. SREBP-2 mediated suppression of 12 alpha-hydroxylase without binding to its promoter. Data are presented suggesting that SREBP-2 suppresses the 12 alpha-hydroxylase promoter by interacting with FTF. This is the first report of a promoter responding oppositely to two members of the SREBP family of transcription factors. These studies provide a novel function and mode of action of a SREBP protein.

Removal of the bile acid pool upregulates cholesterol 7alpha-hydroxylase by deactivating FXR in rabbits

We investigated the role of the orphan nuclear receptor farnesoid X receptor (FXR) in the regulation of cholesterol 7alpha-hydroxylase (CYP7A1), using an in vivo rabbit model, in which the bile acid pool, which includes high affinity ligands for FXR, was eliminated. After 7 days of bile drainage, the enterohepatic bile acid pool, in both New Zealand White and Watanabe heritable hyperlipidemic rabbits, was depleted. CYP7A1 activity and mRNA levels increased while FXR was deactivated as indicated by reduced FXR protein and changes in the expression of target genes that served as surrogate markers of FXR activation in the liver and ileum, respectively. Hepatic bile salt export pump mRNA levels and ileal bile acid-binding protein decreased while sterol 12alpha-hydroxylase and sodium/taurocholate cotransporting polypeptide mRNA levels increased in the liver. In addition, hepatic FXR mRNA levels decreased significantly. The data, taken together, indicate that FXR was deactivated when the bile acid pool was depleted such that CYP7A1 was upregulated. Further, lack of the high affinity ligand supply was associated with downregulation of hepatic FXR mRNA levels.

Transcriptional regulation of the human sterol 12alpha-hydroxylase gene (CYP8B1): roles of heaptocyte nuclear factor 4alpha in mediating bile acid repression

Sterol 12alpha-hydroxylase catalyzes the synthesis of cholic acid and controls the ratio of cholic acid over chenodeoxycholic acid in the bile. Transcription of CYP8B1 is inhibited by bile acids, cholesterol, and insulin. To study the mechanism of CYP8B1 transcription by bile acids, we have cloned and determined 3389 base pairs of the 5'-upstream nucleotide sequences of the human CYP8B1. Deletion analysis of CYP8B1/luciferase reporter activity in HepG2 cells revealed that the sequences from -57 to +300 were important for basal and liver-specific promoter activities. Hepatocyte nuclear factor 4alpha (HNF4alpha) strongly activated human CYP8B1 promoter activities, whereas cholesterol 7alpha-hydroxylase promoter factor (CPF), an NR5A2 family of nuclear receptors, had much less effect. Electrophoretic mobility shift assay identified an overlapping HNF4alpha- and CPF-binding site in the +198/+227 region. The human CYP8B1 promoter activities were strongly repressed by bile acids, and the bile acid response element was localized between +137 and +220. Site-directed mutagenesis of the HNF4alpha-binding site markedly reduced promoter activity and its response to bile acid repression. On the other hand, mutation of the CPF-binding site had little effect on promoter activity and bile acid inhibition. A negative nuclear receptor, small heterodimer partner markedly inhibited transactivation of CYP8B1 by HNF4alpha. Mammalian two-hybrid assay confirmed that HNF4alpha interacted with small heterodimer partner. Furthermore, bile acids and farnesoid X receptor reduced the expression of nuclear HNF4alpha in HepG2 cells and rat livers and its binding to DNA. Bile acids and farnesoid X receptor also inhibited mouse HNF4alpha gene transcription. In summary, our data revealed the critical roles HNF4alpha play on CYP8B1 transcription and its repression by bile acids. Bile acids repress human CYP8B1 transcription by reducing the transactivation activity of HNF4alpha through interaction of HNF4alpha with SHP and reduction of HNF4alpha expression in the liver.

Suppression of sterol 12alpha-hydroxylase transcription by the short heterodimer partner: insights into the repression mechanism

Cholesterol conversion to bile acids is subject to a feedback regulatory mechanism by which bile acids down-regulate their own synthesis. This regulation occurs at the level of transcription of several genes encoding enzymes in the bile acid biosynthetic pathway. One of these enzymes is sterol 12alpha-hydroxylase/CYP8B1 (12alpha-hydroxylase), the specific enzyme required for cholic acid synthesis. The levels of this enzyme determine the ratio of cholic acid to chenodeoxycholic acid and thus the hydrophobicity of the circulating bile acid pool. Previous studies from this laboratory showed that fetoprotein transcription factor (FTF) is required for 12alpha-hydroxylase promoter activity and bile acid-mediated regulation. Here, we report that the short heterodimer partner (SHP) suppresses 12alpha-hydroxylase promoter activity via an interaction with FTF. Hepatic nuclear factor-4 (HNF-4) binds and activates the 12alpha-hydroxylase promoter and is required for 12alpha-hydroxylase promoter activity. Although HNF-4 interacts with SHP, it is not involved in SHP-mediated suppression of 12alpha-hydroxylase promoter activity. FTF and not HNF-4 is the factor involved in regulation of 12alpha-hydroxylase promoter activity by bile acids through its interaction with SHP. Finally, interaction of SHP with FTF displaces FTF binding to its sites within the 12alpha-hydroxylase promoter. These results provide insights into the mechanism of action of bile acid-mediated regulation of sterol 12alpha-hydroxylase transcription.

Expression of sterol 12alpha-hydroxylase alters bile acid pool composition in primary rat hepatocytes and in vivo

BACKGROUND & AIMS

The rate of 12alpha-hydroxylation of bile acid intermediates is believed to determine the ratio of cholic acid (CA) to chenodeoxycholic acid (CDCA) biosynthesis and the overall hydrophobicity of the bile acid pool. The aim of this study was to determine the effects of the level of expression of sterol 12alpha-hydroxylase (CYP8b1) and cholesterol 7alpha-hydroxylase (CYP7a1) on rates of CA biosynthesis and bile acid pool composition.

METHODS

Expression of CYP8b1 and CYP7a1 was accomplished through infection of primary rat hepatocytes (PRH) or intact male SD rats with replication-defective recombinant adenoviruses encoding either CYP8b1 or CYP7a1.

RESULTS

Increased expression of CYP7a1 over basal levels in PRH dramatically increased bile acid biosynthesis (586% +/- 82%, P < 0.001) but did not alter the ratio of CA to CDCA. Conversely, increased expression of CYP8b1 in vitro had no significant effect on the rates of total bile acid synthesis but significantly increased (4.1-fold) the rates of CA biosynthesis, resulting in an increase in the CA-CDCA ratio from 1:6.6 to 2.8:1. In whole rats, increased CYP8b1 expression over basal levels markedly increased the CA in the bile acid pool from 36% +/- 3.4% to 50% +/- 2.9% in 5 days. CDCA and its muricholic acid derivatives decreased from 64% +/- 3.4% to 50% +/- 2.9%.

CONCLUSIONS

Increased expression of CYP8b1 led to a marked increase in CA biosynthesis both in PRH and in whole animals. CYP8b1 is capable of 12alpha-hydroxylating bile acid intermediates from both the classic and acidic pathways.

Circadian rhythms of sterol 12alpha-hydroxylase, cholesterol 7alpha-hydroxylase and DBP involved in rat cholesterol catabolism

Circadian rhythms of important enzymes involved in the conversion of cholesterol to bile acids [sterol 12alpha-hydroxylase (12alpha-hydroxylase) and cholesterol 7alpha-hydroxylase (7alpha-hydroxylase)] and an albumin site D-binding protein (DBP) were examined in rats. When the animals were fed freely, they usually ate in the dark and the circadian rhythms of activities of 12alpha-hydroxylase and 7alpha-hydroxylase showed the same peaks (at 10 p.m.) and lows (at 2 p.m.). Their mRNA levels were determined at four timepoints: 3 a.m., 10 a.m., 3 p.m. and 10 p.m. A maximum of the rhythm of 12alpha-hydroxylase was observed at 3 p.m. and the minimum at 3 a.m. These results are distinct from those of 7alpha-hydroxylase, whose maximum point was at 10 p.m. and minimum at 3 p.m. When the rats were fed only in the day-time (from 9 a.m. to 5 p.m.), a marked shift of the activity and mRNA rhythms was observed with both enzymes. The circadian rhythms of the activities of both enzymes showed the same peaks (at 3 p.m.), but the mRNA levels of 12alpha-hydroxylase were distinct from those of 7alpha-hydroxylase, whose maximum point was at 3 a.m. and minimum at 10 p.m. Differences between the maximum and the minimum points of each enzyme mRNA level were statistically significant (P < 0.01 for 12alpha-hydroxylase and 0.05 for 7alpha-hydroxylase). Moreover, circadian rhythms of DBP were also markedly shifted with the change of feeding period. The maximum mRNA level was observed at 10 p.m. instead of 10 a.m. and the minimum was at 10 a.m. instead of 10 p.m.

The peroxisome proliferator-activated receptor alpha (PPARalpha) regulates bile acid biosynthesis

Fibrates are a group of hypolipidemic agents that efficiently lower serum triglyceride levels by affecting the expression of many genes involved in lipid metabolism. These effects are exerted via the peroxisome proliferator-activated receptor alpha (PPARalpha). In addition, fibrates also lower serum cholesterol levels, suggesting a possible link between the PPARalpha and cholesterol metabolism. Bile acid formation represents an important pathway for elimination of cholesterol, and the sterol 12alpha-hydroxylase is a branch-point enzyme in the bile acid biosynthetic pathway, which determines the ratio of cholic acid to chenodeoxycholic acid. Treatment of mice for 1 week with the peroxisome proliferator WY-14,643 or fasting for 24 h both induced the sterol 12alpha-hydroxylase mRNA in liver. Using the PPARalpha knockout mouse model, we show that the induction by both treatments was dependent on the PPARalpha. A reporter plasmid containing a putative peroxisome proliferator-response element (PPRE) identified in the rat sterol 12alpha-hydroxylase promoter region was activated by treatment with WY-14,643 in HepG2 cells, being dependent on co-transfection with a PPARalpha expression plasmid. The rat 12alpha-hydroxylase PPRE bound in vitro translated PPARalpha and retinoid X receptor alpha, albeit weakly, in electrophoretic mobility shift assay. Treatment of wild-type mice with WY-14,643 for 1 week resulted in an increased relative amount of cholic acid, an effect that was abolished in the PPARalpha null mice, verifying the functionality of the PPRE in vivo.

Alpha 1-fetoprotein transcription factor is required for the expression of sterol 12alpha -hydroxylase, the specific enzyme for cholic acid synthesis. Potential role in the bile acid-mediated regulation of gene transcription

Cholesterol conversion to bile acids occurs via the "classic" (neutral) or the "alternative" (acidic) bile acid biosynthesis pathways. Sterol 12alpha-hydroxylase/CYP8b1 is the specific enzyme required for cholic acid synthesis. The levels of this enzyme determine the ratio of cholic acid to chenodeoxycholic acid and thus the hydrophobicity of the circulating bile acid pool. Expression of the 12alpha-hydroxylase gene is tightly down-regulated by hydrophobic bile acids. In this study, we report the characterization of two DNA elements that are required for both the 12alpha-hydroxylase promoter activity and bile acid-mediated regulation. Mutation of these elements suppresses 12alpha-hydroxylase promoter activity. Mutations of any other part of the promoter do not alter substantially the promoter activity or alter regulation by bile acids relative to the wild type promoter. These two DNA elements bind alpha(1)-fetoprotein transcription factor (FTF), a member of the nuclear receptor family. We also show that overexpression of FTF in a non-liver cell line activates the sterol 12alpha-hydroxylase promoter. These studies demonstrate the crucial role of FTF for the expression and regulation of a critical gene in the bile acid biosynthetic pathways.

Regulation of sterol 12alpha-hydroxylase and cholic acid biosynthesis in the rat

BACKGROUND & AIMS

Sterol 12alpha-hydroxylase (CYP8b1) is required for the biosynthesis of cholic acid (CA) and hence helps determine the ratio of CA to chenodeoxycholic acid (CDCA) in bile. This study examined the in vivo regulation of CYP8b1 in the rat by bile acids, cholesterol, and thyroxine.

METHODS

The specific activities (SAs), messenger RNA (mRNA) levels, and transcriptional activities of CYP8b1 were determined in intact rats and rats with biliary diversion.

RESULTS

CA, CDCA, and deoxycholic acid (DCA), fed as a supplement to the diet, down-regulated CYP8b1 SAs by 99% +/- 0%, 72% +/- 10%, and 98% +/- 1%, respectively. Under these same conditions, mRNA levels decreased by 93% +/- 7%, 60% +/- 11%, and 93% +/- 4%, respectively. Intraduodenal infusion of taurocholate (36 micromol/h. 100 g rat(-1)) decreased SAs and mRNA levels by 63% +/- 8% and 74% +/- 8%, respectively. Ursodeoxycholic acid (UDC) and hyocholic acid (HC) feeding increased CYP8b1 SAs by 119% +/- 21% and 65% +/- 18%, respectively. CA feeding decreased CYP8b1 transcriptional activity by 72%. Complete biliary diversion increased CYP8b1 SAs and mRNA levels by 150% +/- 30% and 287% +/- 51%, respectively. Cholesterol feeding decreased CYP8b1 mRNA by 39% +/- 8%. In intact rats, a single injection of thyroid hormone eliminated CYP8b1 activity.

CONCLUSIONS

CYP8b1 is transcriptionally down-regulated by hydrophobic but not hydrophilic bile acids. Cholesterol feeding and a single thyroid hormone injection repressed CYP8b1 in the face of induction of cholesterol 7alpha-hydroxylase (CYP7a1 by the new nomenclature) SAs. These results suggest that cholesterol, thyroid hormone, and hydrophobic bile acids are important regulators of CYP8b1 and consequently of the bile acid pool composition.

Insulin is a dominant suppressor of sterol 12 alpha-hydroxylase P450 (CYP8B) expression in rat liver: possible role of insulin in circadian rhythm of CYP8B

Sterol 12 alpha-hydroxylase (CYP8B) is a key enzyme for regulating the cholic acid/chenodeoxycholic acid ratio in bile acid biosynthesis. The hepatic CYP8B level was elevated in streptozotocin-induced diabetic rats, and the elevated CYP8B was suppressed by insulin administration [Ishida, H. et al. (1999) J. Biochem. 126, 19-25]. The streptozotocin-induced elevation of hepatic CYP8B mRNA concomitantly responded to the decrement of the serum insulin level. The CYP8B mRNA level in the cultivated rat hepatoma H4TG cells was strongly suppressed by insulin, although it was affected by dibutyryl cAMP or thyroxine to lesser extents. These observations demonstrate that CYP8B expression is dominantly regulated by the direct action of insulin on hepatocytes. A marked circadian rhythm (maximum at 13:00-16:00 and minimum at 1:00) was observed both on the mRNA level and the activity of CYP8B. This rhythm was shifted from that of cholesterol 7 alpha-hydroxylase, a rate-limiting enzyme of bile acid biosynthesis, showing a maximum at 22:00 and a minimum at 10:00, and this shift might oscillate the cholic acid/chenodeoxycholic acid ratio, which is increased in the late afternoon and decreased at midnight. The rhythm of CYP8B was the inverse of the circadian variation of serum insulin level and was similar to the circadian rhythm of glucose 6-phosphatase. These facts and the potent suppressive effect of insulin on CYP8B indicate that the oscillation of the serum insulin may be a factor in producing the circadian rhythm of CYP8B.

Thyroid hormone suppresses hepatic sterol 12alpha-hydroxylase (CYP8B1) activity and messenger ribonucleic acid in rat liver: failure to define known thyroid hormone response elements in the gene

Sterol 12alpha-hydroxylase (CYP 8B1) is a microsomal cytochrome P450 enzyme involved in bile acid synthesis that is of critical importance for the composition of bile acids formed in the liver. Thyroidectomy of rats caused a more than twofold increase of CYP8B1 and an almost fourfold increase of the corresponding mRNA levels compared to sham-operated rats. Treatment of intact rats with thyroxine caused a 60% reduction of enzyme activity and a 50% reduction of mRNA levels compared to rats injected with saline only. To investigate whether the promoter of the gene contains thyroid hormone response elements, the complete structure of the rat gene was defined. In similarity with the corresponding gene in mouse, rabbit and man, the rat gene was found to lack introns. It had an open reading frame containing 1500 bp corresponding to a protein of 499 amino acid residues. Although thyroid hormone decreased CYP8B1 activity and mRNA in vivo, no hitherto described thyroid hormone response elements were identified 1883 bases upstream of the transcription start site. It is concluded that rat CYP8B1 is regulated by thyroid hormone at the mRNA level. The results are discussed in relation to the structure of the gene coding for the enzyme.

Structure and chromosomal assignment of the sterol 12alpha-hydroxylase gene (CYP8B1) in human and mouse: eukaryotic cytochrome P-450 gene devoid of introns

Sterol 12alpha-hydroxylase (CYP8B1) is a hepatic cytochrome P-450 that controls the ratio of cholic acid over chenodeoxycholic acid in bile and thus controls the solubility of cholesterol. Both the human and the mouse CYP8B1 complementary DNA and gene were cloned and structurally characterized. Surprisingly, the genomic DNA from both species was found to lack introns. The major transcript of the human gene was estimated to be 3950 bp, and the putative promoter region was estimated to be at least 1360 bp. The murine structural gene was found to span approximately 3 kb. By using FISH and radiation hybrid mapping techniques, the human CYP8B1 gene was located to chromosome 3p21.3-p22, whereas FISH mapped the murine counterpart to chromosome 9qF4, a region that is homologous to the third human chromosome. The results from the chromosome mapping and Southern blotting indicated that the gene is present in a single copy. Transcription of the mouse and human CYP8B1 genes was initiated from a position situated 51 and 35 bases, respectively, downstream of a consensus TATA box. A homology of 21% for the promoter regions of mouse and human may indicate differences in transcriptional regulation. Although a potent induction of CYP8B1 mRNA was observed upon starvation of mice, the mechanism behind this effect was not revealed by analysis of the promoter for potential cis-acting elements. In the human promoter, several possible cis-acting regions were identified but none of them could be directly related to bile acid metabolism. After transfection of COS cells with the human coding region, mRNA and enzymatic activity for the 12alpha-hydroxylase were identified. This is the first mammalian cytochrome P-450 gene reported to lack introns. The importance of this structural feature for evolution and gene regulation is discussed.