Reduced hepatic content of dehydroepiandrosterone sulphotransferase in chronic liver diseases

Sources of Interindividual Variability

The efficacy, safety, and tolerability of drugs are dependent on numerous factors that influence their disposition. A dose that is efficacious and safe for one individual may result in sub-therapeutic or toxic blood concentrations in others. A significant source of this variability in drug response is drug metabolism, where differences in presystemic and systemic biotransformation efficiency result in variable degrees of systemic exposure (e.g., AUC, C_max, and/or C_min) following administration of a fixed dose.Interindividual differences in drug biotransformation have been studied extensively. It is recognized that both intrinsic factors (e.g., genetics, age, sex, and disease states) and extrinsic factors (e.g., diet , chemical exposures from the environment, and the microbiome) play a significant role. For drug-metabolizing enzymes, genetic variation can result in the complete absence or enhanced expression of a functional enzyme. In addition, upregulation and downregulation of gene expression, in response to an altered cellular environment, can achieve the same range of metabolic function (phenotype), but often in a less predictable and time-dependent manner. Understanding the mechanistic basis for variability in drug disposition and response is essential if we are to move beyond the era of empirical, trial-and-error dose selection and into an age of personalized medicine that will improve outcomes in maintaining health and treating disease.

Thyroid Dysfunction and Cholesterol Gallstone Disease

Cholesterol gallstone disease (CGD) affects 10-15% of the adult population worldwide and the prevalence increases as a result of longer life expectancy as well as rising obesity in the general population. Beside well established CGD risk factors including environmental and genetic determinants (LITH genes), a correlation between thyroid dysfunction and CGD has been suggested in several human and murine studies. Although the precise underlying mechanisms are poorly understood, thyroid hormones may impact bile flow, bile composition and the maintenance of the enterohepatic circulation. Further there is evidence that thyroid hormones possibly impact LITH genes which are regulated by nuclear receptors (NRs). A better understanding of the CGD pathomechanisms might contribute to personalized prevention and therapy of highly prevalent and economically significant digestive disease. This review presents the current knowledge about the association between CGD and thyroid hormone dysfunction.

Liver Expression of Sulphotransferase 2A1 Enzyme Is Impaired in Patients with Primary Sclerosing Cholangitis: Lack of the Response to Enhanced Expression of PXR

BACKGROUND/AIM

Sulphotransferase 2A1 (SULT2A1) exerts hepatoprotective effects. Transcription of SULT2A1 gene is induced by pregnane-X-receptor (PXR) and can be repressed by miR-378a-5p. We studied the PXR/SULT2A1 axis in chronic cholestatic conditions: primary sclerosing cholangitis (PSC) and primary biliary cirrhosis (PBC).

MATERIALS/METHODS

Western-blot/PCRs for SULT2A1/PXR were performed in PSC (n = 11), PBC (n = 19), and control liver tissues (n = 19). PXR and SULT2A1 mRNA was analyzed in intestinal tissues from 22 PSC patients. Genomic DNA was isolated from blood of PSC patients (n = 120) and an equal number of healthy volunteers. Liver miRNA expression was evaluated using Affymetrix-Gene-Chip miRNA4.0.

RESULTS

Increased PXR protein was observed in both PSC and PBC compared to controls and was accompanied by a significant increase of SULT2A1 in PBC but not in PSC. Decreased expression of SULT2A1 mRNA was also seen in ileum of patients with PSC. Unlike PBC, miRNA analysis in PSC has shown a substantial increase in liver miR-378a-5p.

CONCLUSIONS

PSC is characterized by disease-specific impairment of SULT2A1 expression following PXR activation, a phenomenon which is not noted in PBC, and may account for the impaired hepatoprotection in PSC. miRNA analysis suggests that SULT2A1 expression in PSC may be regulated by miR-378a-5p, connoting its pathogenic role.

The Role of Liver in Determining Serum Colon-Derived Uremic Solutes

Evidence has shown that indoxyl sulfate (IS) and p-cresyl sulfate (PCS) may be alternative predictors of clinical outcomes in chronic kidney disease (CKD). Both toxins are derived from the gastrointestinal tract and metabolised in the liver. However, it is unclear whether the liver affects the production of IS and PCS. Here, we explore the association between IS and PCS levels in liver cirrhosis and a CKD-based cohort (N = 115). Liver and kidney function was assessed and classified by a Child-Pugh score (child A–C) and a modified version of the Modification of Diet in Renal Disease (MDRD) equation (Stages 1–4), respectively. An animal model was also used to confirm the two toxin levels in a case of liver fibrosis. In patients with early liver cirrhosis (child A), IS and PCS were significantly associated with CKD stages. In contrast, serum IS and PCS did not significantly change in advanced liver cirrhosis (child C). A stepwise multiple linear regression analysis also showed that T-PCS was significantly associated with stages of liver cirrhosis after adjusting for other confounding factors (B = -2.29, p = 0.012). Moreover, the serum and urine levels of T-PCS and T-IS were significantly lower in rats with liver failure than in those without (p<0.01, p<0.05 and p<0.01, p<0.05, respectively). These results indicated that in addition to the kidneys, the liver was an essential and independent organ in determining serum IS and PCS levels. The production rate of IS and PCS was lower in patients with advanced liver cirrhosis.

Sources of interindividual variability

The efficacy, safety, and tolerability of drugs are dependent on numerous factors that influence their disposition. A dose that is efficacious and safe for one individual may result in sub-therapeutic or toxic blood concentrations in other individuals. A major source of this variability in drug response is drug metabolism, where differences in pre-systemic and systemic biotransformation efficiency result in variable degrees of systemic exposure (e.g., AUC, C max, and/or C min) following administration of a fixed dose.Interindividual differences in drug biotransformation have been studied extensively. It is well recognized that both intrinsic (such as genetics, age, sex, and disease states) and extrinsic (such as diet, chemical exposures from the environment, and even sunlight) factors play a significant role. For the family of cytochrome P450 enzymes, the most critical of the drug metabolizing enzymes, genetic variation can result in the complete absence or enhanced expression of a functional enzyme. In addition, up- and down-regulation of gene expression, in response to an altered cellular environment, can achieve the same range of metabolic function (phenotype), but often in a less reliably predictable and time-dependent manner. Understanding the mechanistic basis for drug disposition and response variability is essential if we are to move beyond the era of empirical, trial-and-error dose selection and into an age of personalized medicine that brings with it true improvements in health outcomes in the therapeutic treatment of disease.

Downregulation of sulfotransferase expression and activity in diseased human livers

Sulfotransferase (SULT) function has been well studied in healthy human subjects by quantifying mRNA and protein expression and determining enzyme activity with probe substrates. However, it is not well known if sulfotransferase activity changes in metabolic and liver disease, such as diabetes, steatosis, or cirrhosis. Sulfotransferases have significant roles in the regulation of hormones and excretion of xenobiotics. In the present study of normal subjects with nonfatty livers and patients with steatosis, diabetic cirrhosis, and alcoholic cirrhosis, we sought to determine SULT1A1, SULT2A1, SULT1E1, and SULT1A3 activity and mRNA and protein expression in human liver tissue. In general, sulfotransferase activity decreased significantly with severity of liver disease from steatosis to cirrhosis. Specifically, SULT1A1 and SULT1A3 activities were lower in disease states relative to nonfatty tissues. Alcoholic cirrhotic tissues further contained lower SULT1A1 and 1A3 activities than those affected by either of the two other disease states. SULT2A1, on the other hand, was only reduced in alcoholic cirrhotic tissues. SULT1E1 was reduced both in diabetic cirrhosis and in alcoholic cirrhosis tissues, relative to nonfatty liver tissues. In conclusion, the reduced levels of sulfotransferase expression and activity in diseased versus nondiseased liver tissue may alter the metabolism and disposition of xenobiotics and affect homeostasis of endobiotic sulfotransferase substrates.

Substrate inhibition in human hydroxysteroid sulfotransferase SULT2A1: studies on the formation of catalytically non-productive enzyme complexes

The cytosolic sulfotransferase hSULT2A1 is the major hydroxysteroid (alcohol) sulfotransferase in human liver, and it catalyzes the 3'-phosphoadenosine-5'-phosphosulfate (PAPS)-dependent sulfation of various endogenous hydroxysteroids as well as many xenobiotics that contain alcohol and phenol functional groups. The hSULT2A1 often displays substrate inhibition, and we have hypothesized that a key element in this response to increasing substrate concentration is the formation of non-productive ternary dead-end enzyme complexes involving the nucleotide product, adenosine 3',5'-diphosphate (PAP). One of these substrates for hSULT2A1 is dehydroepiandrosterone (DHEA), a major circulating steroid hormone in humans that serves as precursor to both androgens and estrogens. We have utilized DHEA in both initial velocity studies and equilibrium binding experiments in order to evaluate the potential role of ternary complexes in substrate inhibition of the enzyme. Our results indicate that hSULT2A1 forms non-productive ternary complexes that involve either DHEA or dehydroepiandrosterone sulfate, and the formation of these ternary complexes displays negative cooperativity in the binding of DHEA.

Serum dehydroepiandrosterone sulphate levels in patients with non-alcoholic fatty liver disease

BACKGROUND

Dehydroepiandrosterone (DHEA) is an adrenal hormone reported to prevent body weight gain, diabetes mellitus and atherosclerosis. We hypothesized that DHEA is involved in the pathophysiology of non-alcoholic fatty liver disease (NAFLD) often associated with obesity and insulin resistance. In this study, we aimed to examine the clinical significance of serum DHEA sulfate (DHEAS) in patients with NAFLD.

METHODS

We determined serum DHEAS, serum alanine aminotransferase (ALT), serum lipids, plasma fasting glucose and insulin levels in 158 Japanese men who had neither viral hepatic diseases nor alcohol intake exceeding 20 g/day. NAFLD was diagnosed by the presence of fatty change of the liver by echotomographic examination.

RESULTS

Among the study subjects, 69 were diagnosed as having NAFLD. Their serum DHEAS levels were significantly higher than in 89 subjects without NAFLD. Serum DHEAS levels in 19 NAFLD patients with elevated ALT levels (>40 U/L) were significantly higher than in the other 50 NAFLD patients with normal ALT levels (≤40 U/L). Multivariate regression analysis demonstrated that serum ALT was positively correlated with serum DHEAS, serum triglyceride and body mass index.

CONCLUSION

Serum DHEAS levels are increased in patients with NAFLD with elevated ALT levels. Increased serum DHEAS may be a component of the pathophysiology of NAFLD.

Lower circulating levels of dehydroepiandrosterone, independent of insulin resistance, is an important determinant of severity of non-alcoholic steatohepatitis in Japanese patients

AIM

  The biological basis of variability in histological progression of non-alcoholic fatty liver disease (NAFLD) remains unknown. Dehydroepiandrosterone (DHEA), the most abundant steroid hormone, has been shown to influence sensitivity to reactive oxygen species, insulin sensitivity and expression of peroxisome proliferator-activated receptor-α. Our aim was to determine whether more histologically advanced NAFLD is associated with low circulating levels of DHEA in Japanese patients.

METHODS

  Serum samples were obtained in 133 Japanese patients with biopsy-proven NAFLD and in 399 sex- and age-matched healthy people undergoing health checkups. Serum levels of sulfated DHEA (DHEA-S) were measured by chemiluminescent enzyme immunoassay.

RESULTS

  Serum DHEA-S levels in NAFLD patients were similar to those in the control group. Of 133 patients, 90 patients were diagnosed as non-alcoholic steatohepatitis (NASH): 73 patients had stage 0-2, and 17 had stage 3 or 4. Patients with advanced NAFLD (NASH with fibrosis stage 3 or 4) had lower plasma levels of DHEA-S than patients with mild NAFLD (simple steatosis or NASH with fibrosis stage 0-2). The area under the receiver operating characteristic curve for DHEA in separating patients with and without advanced fibrosis was 0.788. A "dose effect" of lower DHEA-S and incremental fibrosis stage was observed with a mean DHEA-S of 170.4 ± 129.2, 137.6 ± 110.5, 96.2 ± 79.3, 61.2 ± 46.3 and 30.0 ± 32.0 µg/dL for fibrosis stages 0, 1, 2, 3, and 4, respectively. The association between DHEA-S and severity of NAFLD persisted after adjusting for age, sex and insulin resistance.

CONCLUSION

  Low circulating DHEA-S might have a role in the development of advanced NASH.

Bile Acid sulfation: a pathway of bile acid elimination and detoxification

Sulfotransferase-2A1 catalyzes the formation of bile acid-sulfates (BA-sulfates). Sulfation of BAs increases their solubility, decreases their intestinal absorption, and enhances their fecal and urinary excretion. BA-sulfates are also less toxic than their unsulfated counterparts. Therefore, sulfation is an important detoxification pathway of BAs. Major species differences in BA sulfation exist. In humans, only a small proportion of BAs in bile and serum are sulfated, whereas more than 70% of BAs in urine are sulfated, indicating their efficient elimination in urine. The formation of BA-sulfates increases during cholestatic diseases. Therefore, sulfation may play an important role in maintaining BA homeostasis under pathologic conditions. Farnesoid X receptor, pregnane X receptor, constitutive androstane receptor, and vitamin D receptor are potential nuclear receptors that may be involved in the regulation of BA sulfation. This review highlights current knowledge about the enzymes and transporters involved in the formation and elimination of BA-sulfates, the effect of sulfation on the pharmacologic and toxicologic properties of BAs, the role of BA sulfation in cholestatic diseases, and the regulation of BA sulfation.

Testosterone suppresses protective responses of the liver to blood-stage malaria

Testosterone induces a lethal outcome in otherwise self-healing blood-stage malaria caused by Plasmodium chabaudi. Here, we examine possible testosterone effects on the antimalaria effectors spleen and liver in female C57BL/6 mice. Self-healing malaria activates gating mechanisms in the spleen and liver that lead to a dramatic reduction in trapping activity, as measured by quantifying the uptake of 3-mum-diameter fluorescent polystyrol particles. However, testosterone delays malaria-induced closing of the liver, but not the spleen. Coincidently, testosterone causes an approximately 3- to 28-fold depression of the mRNA levels of nine malaria-responsive genes, out of 299 genes tested, only in the liver and not in the spleen, as shown by cDNA arrays and Northern blotting. Among these are the genes encoding plasminogen activator inhibitor (PAI1) and hydroxysteroid sulfotransferase (STA2). STA2, which detoxifies bile acids, is suppressed 10-fold by malaria and an additional 28-fold by testosterone, suggesting a severe perturbation of bile acid metabolism. PAI1 is protective against malaria, since disruption of the PAI1 gene results in partial loss of the ability to control the course of P. chabaudi infections. Collectively, our data indicate that the liver rather than the spleen is a major target organ for testosterone-mediated suppression of resistance against blood-stage malaria.

Low plasma levels of dehydroepiandrosterone sulphate in HIV-positive patients coinfected with hepatitis C virus

OBJECTIVES

To evaluate plasma levels of dehydroepiandrosterone sulphate (DHEAS) in a cohort of HIV-infected patients and to analyse factors associated with DHEAS levels.

METHODS

We conducted a cross-sectional survey in the Nîmes University Hospital cohort of HIV-infected patients in south-eastern France. All HIV-infected patients with at least one outpatient visit between 1 January and 1 September 2002 were included in the study. Sociodemographic, clinical, therapeutic, immuno-virological and plasma DHEAS level data were collected during this period. Hepatitis C virus (HCV) coinfection was defined as the presence of HCV antibody with positive RNA. To identify factors associated with plasma DHEAS levels, Spearman's rank correlation and univariate and multivariate linear regression analyses were used.

RESULTS

The DHEAS plasma level was measured in 137 patients (104 men and 33 women), 37 (27.0%) of whom were HCV coinfected. The median age of the patients was 39.1 years [interquartile range (IQR): 34.9-48.7] for women and 41.8 years (36.5-47.7) for men. The median DHEAS level was 5.5 micromol/L (IQR: 2.3-8.8) for the whole sample of 137 patients, and was lower in women (2.4 micromol/L; 1.5-6.6) than in men (6.1 micromol/L; 2.5-9.0) (P<0.01), and lower in patients coinfected with HCV (2.1 micromol/L; 0.6-6.7) than in those not coinfected (6.6 micromol/L; 3.0-9.1) (P<0.01). Of all prognostic factors studied in the variance covariance analysis, three factors were associated with DHEAS: age, gender and HCV coinfection. Subgroup analysis revealed that the age-adjusted mean of the DHEAS level was lower in HCV coinfected patients for both women (1.3+/-1.1 micromol/L) and men (4.0+/-0.7 micromol/L), compared with patients not HCV coinfected (women, 5.3+/-0.7 micromol/L; men, 7.2+/-0.4 micromol/L) (P<0.01).

CONCLUSIONS

This is the first report of the determination of DHEAS plasma levels in HIV/HCV coinfected patients. When age and sex were taken into account, the DHEAS plasma level was found to be significantly lower in HCV coinfected patients. To date, the pathophysiology of such findings is unknown.

Regulation of a xenobiotic sulfonation cascade by nuclear pregnane X receptor (PXR)

The nuclear receptor PXR (pregnane X receptor) protects the body from hepatotoxicity of secondary bile acids such as lithocholic acid (LCA) by inducing expression of the hydroxylating cytochrome P450 enzyme CYP3A and promoting detoxification. We found that activation of PXR also increases the activity and gene expression of the phase II conjugating enzyme dehydroepiandrosterone sulfotransferase (STD) known to sulfate LCA to facilitate its elimination. This activation is direct and appears to extend to other xenobiotic sulfotransferases as well as to 3'-phosphoadenosine 5'-phosphosulfate synthetase 2 (PAPSS2), an enzyme that generates the donor cofactor for the reaction. Because sulfation plays an important role in the metabolism of many xenobiotics, prescription drugs, and toxins, we propose that PXR serves as a master regulator of the phase I and II responses to facilitate rapid and efficient detoxification and elimination of foreign chemicals.

Crystal structure of human dehydroepiandrosterone sulphotransferase in complex with substrate

Dehydroepiandrosterone sulphotransferase (DHEA-ST) is an enzyme that converts dehydroepiandrosterone (DHEA), and some other steroids, into their sulphonated forms. The enzyme catalyses the sulphonation of DHEA on the 3alpha-oxygen, with 3'-phosphoadenosine-5'-phosphosulphate contributing the sulphate. The structure of human DHEA-ST in complex with its preferred substrate DHEA has been solved here to 1.99 A using molecular replacement with oestradiol sulphotransferase (37% sequence identity) as a model. Two alternative substrate-binding orientations have been identified. The primary, catalytic, orientation has the DHEA 3alpha-oxygen and the highly conserved catalytic histidine in nearly identical positions as are seen for the related oestradiol sulphotransferase. The substrate, however, shows rotations of up to 30 degrees, and there is a corresponding rearrangement of the protein loops contributing to the active site. This may also reflect the low identity between the two enzymes. The second orientation penetrates further into the active site and can form a potential hydrogen bond with the desulphonated cofactor 3',5'-phosphoadenosine (PAP). This second site contains more van der Waal interactions with hydrophobic residues than the catalytic site and may also reflect the substrate-inhibition site. The PAP position was obtained from the previously solved structure of DHEA-ST co-crystallized with PAP. This latter structure, due to the arrangement of loops within the active site and monomer interactions, cannot bind substrate. The results presented here describe details of substrate binding to DHEA-ST and the potential relationship to substrate inhibition.

Effect of tauroursodeoxycholate and S-adenosyl-L-methionine on 17beta-estradiol glucuronide-induced cholestasis

BACKGROUND/AIMS

S-adenosyl-L-methionine (SAMe) and tauroursodeoxycholate (TUDC) exert an additive ameliorating effect on taurolithocholate (TLC)-induced cholestasis. The aims were to investigate the protective effect of SAMe on 17beta-estradiol-glucuronide (17betaEG) cholestasis and to find out whether SAMe and TUDC may exert an additive, ameliorating effect.

METHODS

Hepatocyte couplet function was assessed by canalicular vacuolar accumulation (cVA) of cholyllysylfluorescein (CLF). Cells were co-treated with 17betaEG and SAMe, TUDC, or both (protection study), or treated with 17betaEG and then with SAMe, TUDC or both (reversion study) before CLF uptake. Couplets were also co-treated with SAMe and dehydroepiandrosterone (DHEA), a competitive substrate for the sulfotransferase involved in 17betaEG detoxification. The effects of 17betaEG, SAMe and TUDC were also examined on intracellular distribution of F-actin.

RESULTS

Both SAMe and TUDC significantly protected against, and reversed, 17betaEG-induced cholestasis, but their effects were not additive. DHEA abolished the protective effect of SAMe. 17BetaEG did not affect the uptake of CLF into hepatocytes at the concentrations used, and also, it did not affect the intracellular distribution of F-actin.

CONCLUSIONS

17BetaEG does not affect the uptake of CLF into hepatocytes. SAMe and TUDC protect and reverse 17betaEG-induced cholestasis, but without an additive effect. Protection by SAMe may involve facilitating the sulfation of 17betaEG.