The A, B, C, D and E of viral hepatitis: new agents for old diseases.
Explore the source record for details and available documents.
Australia↗
Biomedical subjects
G C Farrell
Publications and source records attributed to G C Farrell.
Chronic non-A, non-B hepatitis: lack of correlation between biochemical and morphological activity, and effects of immunosuppressive therapy on disease progression.
A study was made of 52 patients considered to probably have chronic non-A, non-B hepatitis who were seen during an eight-year period at Westmead Hospital, Sydney. The patients were followed for a median of 28 months to assess the natural history of the disease and, in a small number of patients, the effect of immunosuppressive therapy on disease progression was examined. In 94% of cases, infection appeared to have been acquired by a parenteral route; the remainder were sporadic infections. Fifty-six per cent of the patients had mild constitutional symptoms and the remainder were asymptomatic. Similarly, 54% of patients had no signs of chronic liver disease and none exhibited signs of hepatic decompensation. Liver biopsies were performed in 42 patients; chronic active hepatitis with or without cirrhosis was present in 90%. However, neither the presence of symptoms nor the degree of biochemical abnormality were predictive of disease severity as determined histologically. Among eight patients treated with corticosteroids (with or without azathioprine), six underwent follow-up liver biopsy. Quantitative analysis of inflammatory and fibrotic changes indicated significant (p less than 0.01) progression of histological severity during a median 33 months (range 7-98 months) between biopsies with cirrhosis developing in four instances. In contrast, among the seven untreated patients rebiopsied after a median of 16.0 months (range 11-37 months) there was no overall change in histological severity and only one patient developed cirrhosis. it is concluded that histological assessment is required in all patients suspected of having chronic non-A, non-B hepatitis as other means of assessment are unreliable.(ABSTRACT TRUNCATED AT 250 WORDS)
Adult↗
Release of Ca2+ from the endoplasmic reticulum is not the mechanism for bile acid-induced cholestasis and hepatotoxicity in the intact rat liver.
The hypothesis that monohydroxy bile acids exert their cholestatic and hepatotoxic effects via a sustained elevation of cytosolic [Ca2+] was tested in the isolated perfused rat liver. Infusion of the specific inhibitor of microsomal Ca2+ sequestration, 2,5-di(tert-butyl)-1,4-benzohydroquinone (tBuBHQ) (25 microM for 10 min) produced efflux of Ca2+ from the liver and a sustained (20 min) increase in cytosolic [Ca2+] as indicated by the threefold increase in hepatic glucose output. Release of the endoplasmic reticular Ca2+ pool was demonstrated by the complete abolition of vasopressin- and phenylephrine-induced Ca2+ exchange between the liver and perfusate. Despite the profound perturbation of intracellular Ca2+ homeostasis produced by tBuBHQ, there was no decrease in bile flow and no evidence of hepatocellular injury (for 60 min), as indicated by lactate dehydrogenase release. In contrast, lithocholic acid (25 microM for 10 or 30 min) or taurolithocholic acid (5 microM for 10 or 30 min) produced an 80-90% inhibition of bile flow and a progressive increase in perfusate lactate dehydrogenase activity. During and after bile acid infusion, there was no change in Ca2+ fluxes between liver and perfusate, no stimulation of glucose output from the liver, and hormone-stimulated Ca2+ responses were preserved. It is concluded that the mechanisms for bile acid-induced cholestasis and hepatotoxicity in the intact liver are not attributable to changes in intracellular Ca2+ homeostasis, and especially not to prolonged release or depletion of Ca2+ sequestered in the endoplasmic reticulum.
Bile↗
2,5-Di(tert-butyl)-1,4-benzohydroquinone--a novel mobilizer of the inositol 1,4,5-trisphosphate-sensitive Ca2+ pool.
Isolated hepatocytes and the isolated perfused rat liver have been used to study the alterations of cytosolic free Ca2+ concentration ([Ca2+]i) produced by 2,5-di(tert-butyl)-1,4-benzohydroquinone (tBuBHQ), a potent inhibitor of hepatic microsomal Ca2+ sequestration (Moore, G.A., McConkey, D.J., Kass, G.E.N., O'Brien, P.J. and Orrenius, S. FEBS Lett., 224, 331-336), (1987). Addition of tBuBHQ to isolated hepatocytes caused a rapid increase in [Ca2+]i which was similar in magnitude to the [Ca2+]i elevation induced by the Ca2+ mobilizing hormone, vasopressin. In contrast with vasopressin which caused a Ca2+ transient, tBuBHQ elevated [Ca2+]i to a new steady state that was maintained for up to 15-20 min. When vasopressin was administered during the tBuBHQ-induced period of elevated [Ca2+]i, [Ca2+]i rapidly returned to basal levels. Similarly, if vasopressin was administered just prior to tBuBHQ, the resultant tBuBHQ-dependent change in [Ca2+]i was transient, and not sustained. The hydroquinone mobilized the same intracellular Ca2+ pool as inositol 1,4,5-trisphosphate, but tBuBHQ did not produce any detectable inositol polyphosphate accumulation. tBuBHQ stimulated glucose release from perifused hepatocytes, mimicking the effect of vasopressin. In the perfused liver, tBuBHQ infusion produced a single, slow and prolonged release of Ca2+ into the perfusate and inhibition of subsequent vasopressin-induced Ca2+ effluxes. Inhibition of the response to vasopressin was reversed over time, and closely correlated with the extent of inhibition of both Ca2+ sequestration and (Ca2+-Mg2+)-ATPase activity in microsomes isolated from the isolated perfused liver.(ABSTRACT TRUNCATED AT 250 WORDS)
Animals↗
Interferon down regulates the male-specific cytochrome P450IIIA2 in rat liver.
The aim of this study was to clarify the mechanism by which cytochrome P450 (P450)-mediated catalytic activity is decreased following interferon (IFN) administration. Microsomal steroid hydroxylation was assessed to test the hypothesis that IFN selectively decreases the activities of individual P450 isozymes in male rats. Thus, recombinant rat IFN gamma (r-rat IFN gamma) treatment produced 40% and 17% reductions in androst-4-ene-3,17-dione (androstenedione) 6 beta- and 16 beta-hydroxylation, respectively. Androstenedione 16 alpha- and 7 alpha-hydroxylation were unaltered following r-rat IFN gamma treatment. Similar changes in the androstenedione hydroxylation pathways were observed following administration of naturally derived rat IFN alpha/beta. Microsomal levels of P450IIIA2, the male-specific constitutive steroid 6 beta-hydroxylase, were lower after administration of r-rat IFN gamma (42% of control fractions). Furthermore, hepatic P450IIIA2 mRNA was found to be decreased to a similar extent by r-rat IFN gamma. These findings suggest that IFN selectively decreases the content of this isozyme by a mechanism involving altered mRNA regulation. Sex steroids were unlikely to have mediated the decrease in P450IIIA2 levels since serum estradiol and testosterone levels were unchanged by r-rat IFN gamma. In order to determine whether IFN alters the expression of P450IIIA1, a steroid-inducible member of the P450IIIA gene subfamily which is not expressed in untreated rat liver, adult female rats (which lack P450IIIA2) were coadministered pregnenolone 16 alpha-carbonitrile and r-rat IFN gamma. However, IFN failed to impair the induction of androstenedione 6 beta-hydroxylation produced by pregnenolone 16 alpha-carbonitrile. These findings suggest that although IFN decreases the expression of P450IIIA2, it may not down regulate the expression of other steroid-inducible P450IIIA proteins. In view of the existence of human P450IIIA orthologs which catalyze the metabolism of several important therapeutic agents, the findings of this study may help predict possible drug interactions in patients receiving IFN.
Animals↗
Human cytochrome P450 isoforms. Their genetic heterogeneity and induction by omeprazole.
Explore the source record for details and available documents.
Animals↗
Serial antipyrine clearance studies detect altered hepatic metabolic function during spontaneous and interferon-induced changes in chronic hepatitis B disease activity.
The present study was performed to establish whether sequential determinations of antipyrine clearance, using a simplified two-point test, are sensitive and specific indicators of changes in chronic hepatitis B disease activity. Sixteen patients were studied on four or more occasions during 18 to 30 months. Eleven patients were treated with recombinant human alpha-interferon (2.5, 5.0 or 10 X 10(6) per m2, intramuscularly, three times per week, for 24 weeks), and five patients were untreated controls. Among seven patients, (six interferon-treated and one control) who lost hepatitis B e antigen from serum, antipyrine clearance improved by 46% (range: 20 to 160%) from 0.37 +/- 0.14 ml per kg per min (mean +/- S.D.) to 0.54 +/- 0.13 ml per kg per min, p less than 0.005. This change paralleled the loss of symptoms and reduction of serum ALT levels (from 206 +/- 189 IU per liter (mean +/- S.D.) to 38 +/- 12 IU per liter, p less than 0.005). Conversely, antipyrine clearance declined to previous levels when reactivation of chronic hepatitis B with reappearance of HBeAg in serum occurred. Regardless of changes in hepatitis B serology, when serum ALT values fluctuated by more than 20% (presumed to reflect fluctuations in necroinflammatory activity of the liver disease), antipyrine clearance also changed whereas serum albumin and bilirubin concentrations and prothrombin time did not. It is concluded that antipyrine clearance is a more sensitive and specific parameter than conventional indices for assessing hepatic metabolic function during changes in chronic hepatitis B disease activity. Remission in disease with loss of HBeAg from serum is associated with improved hepatic metabolic function as determined by the antipyrine clearance test.
Adult↗
Rat but not human interferons suppress hepatic oxidative drug metabolism in rats.
An animal model suitable for in vivo studies of interferon-mediated suppression of hepatic oxidative drug metabolism has been developed. Rats were injected with either recombinant human interferon alpha A, recombinant human interferon gamma, recombinant rat interferon gamma, or vehicle and experiments were performed 24 h later. In some animals theophylline elimination was determined twice (10 days apart), once after interferon and once after vehicle. Theophylline clearance was also determined in the isolated perfused rat liver after pretreatment of animals with interferon or vehicle. Pretreatment of animals with rat interferon gamma significantly reduced theophylline clearance in the intact rat but neither human interferon alpha A nor human interferon gamma altered theophylline elimination in vivo. Similar results were observed in the isolated perfused rat liver. We then examined whether the effects of interferon on hepatic drug metabolism were generalized or confined to individual cytochrome P450 isozymes; androstenedione hydroxylation pathways were used as catalytic probes for individual cytochrome P450 isozymes. Rat interferon gamma (but not human interferon alpha A) decreased levels of total hepatic microsomal P450 and reduced androstenedione 16 beta-hydroxylation. The formation of three other hydroxylated androstenedione metabolites appeared reduced to a similar extent, although these changes were not significant. It is concluded that autologous but not heterologous interferons impair oxidative drug metabolism in the rat. The reduction of hepatic P450 produced by interferon may result from the suppression of multiple isozymes.
Androstenedione↗
Downregulation of the male-specific hepatic microsomal steroid 16 alpha-hydroxylase, cytochrome P-450UT-A, in rats with portal bypass. Relevance to estradiol accumulation and impaired drug metabolism in hepatic cirrhosis.
Elevated serum estradiol concentrations and specific changes in the biliary excretion of some androstenedione metabolites have been reported in male rats with portal bypass produced by portal vein ligation (PVL). In this study, the hypothesis that male-specific forms of cytochrome P-450 are altered after PVL was tested by measuring microsomal steroid hydroxylase activities. Consistent with earlier findings in the intact animal, androstenedione 16 alpha-hydroxylase activity was reduced after PVL to 44% of control (P less than 0.05). Other pathways of androstenedione hydroxylation, and total estrogen formation (after androstenedione aromatization) were unchanged. Although total estrogen formation was not different, a sevenfold greater proportion of estradiol was produced in PVL rat microsomes. Additional experiments revealed that PVL selectively reduced the rate of microsomal estradiol 16 alpha-hydroxylation (to 56% of control, P less than 0.02). Levels of cytochrome P-450UT-A, the microsomal steroid 16 alpha-hydroxylase, were lower after PVL (56% of control, P less than 0.05), so that the present observations are consistent with the earlier suggestion that portal bypass is associated with the selective downregulation of this enzyme. Since downregulation of cytochrome P-450UT-A also occurs in experimental hepatic cirrhosis, portal hypertension may well contribute significantly to altered drug metabolism in liver disease. Impaired hepatic elimination of androstenedione by hydroxylation may indirectly enhance extrahepatic aromatization of the androgen. The decreased activity of hepatic estradiol 16 alpha-hydroxylation after PVL would enhance the accumulation of estradiol, the biologically more potent estrogen.
Androstenedione↗
Effect of liver regeneration on hepatic cytochrome P450 isozymes and serum sex steroids in the male rat.
Partial hepatectomy in male adult rats results in raised serum estrogen levels and demasculinization of certain aspects of hepatic metabolism. Some constitutive forms of hepatic cytochrome P450 are sex-dependent and we have previously demonstrated demasculinization of cytochrome P450 isozyme distribution in a rat model of cirrhosis. As liver regeneration is an integral component of cirrhosis, the present study was performed to ascertain the effects of regeneration on hepatic cytochrome P450 isozyme composition and serum sex steroid concentrations. Adult male rats were subjected to 65% partial hepatectomy or sham-operation. The position-specific hydroxylation of androstenedione was used as a probe for isozyme activity. Serum sex steroids, hepatic enzymes, and hepatic deoxyribonucleic acid synthesis were measured in groups of animals at 0, 6, 24, 48, and 72 h. By 72 h total microsomal cytochrome P450 in partially hepatectomized animals had fallen to 66% of that in nonoperated animals. In both partially hepatectomized and sham-operated animals, androstenedione 7 alpha- and 16 beta-hydroxylase activity returned to preoperative levels by 48 h. However, the male-specific androstenedione 16 alpha- and 6 beta-hydroxylase activities and aromatase activity remained suppressed in partially hepatectomized liver. Serum estradiol increased eightfold in partially hepatectomized rats and peaked at 6 h followed by a gradual fall to control values. No change in serum estradiol was observed in sham-operated animals. We conclude that demasculinization of hepatic oxidative metabolism occurs in regenerating rat liver. The early rise in serum estradiol is consistent with a role for this hormone in the changes in cytochrome P450 observed, and possibly the process of liver regeneration.
Androstenedione↗
Effects of long-term choline deficiency on hepatic microsomal cytochrome P-450-mediated steroid and xenobiotic hydroxylases in the female rat.
Total cytochrome P-450 levels decreased to about 80% of control in hepatic microsomes from female rats maintained for 30 weeks on a choline-deficient diet. Livers from these rats were fibrotic and had extensive fatty infiltration but, unlike livers of male rats on the same regimen, were not cirrhotic. Steroid hydroxylase activities were assessed in microsomes of female rats that received the choline-deficient diet and it was noted that the activity of the cytochrome P-450 UT-F-mediated steroid 7 alpha-hydroxylase was decreased to about 50% of the activity present in choline-supplemented control rat microsomes. Similar decreases were observed for microsomal androstenedione 6 beta-hydroxylase and aniline 4-hydroxylase activities. In female rat hepatic microsomes these two activities are probably mediated by the isozyme cytochrome P-450 ISF-G. In contrast to these findings, the activities of four other xenobiotic metabolising enzymes, as well as rates of microsomal steroid 16 alpha- and 16 beta-hydroxylation, were unchanged from control. Thus, in hepatic microsomes from choline-deficient female rats, it appears likely that levels of the non-sexually differentiated cytochromes P-450 UT-F and ISF-G are decreased. Unlike the situation in male rats, long term choline deficiency does not appear to influence levels of sexually-differentiated P-450 enzymes in the female rat.
Androstenedione↗
Hepatic microsomal metabolism of androst-4-ene-3,17-dione: relative importance of ring hydroxylation and aromatization in control and induced rat liver.
The purpose of these studies was to determine whether oestrogen production is a quantitatively important pathway in the hepatic microsomal metabolism of androst-4-ene-3,17-dione. The effects of the enzyme inducing agents phenobarbitone and beta-naphthoflavone on microsomal cytochrome P-450-mediated androst-4-ene-3,17-dione hydroxylation and aromatization was investigated in the rat in vitro. In microsomal fractions from untreated rats the ratio of hydroxylated products to aromatized (oestrogenic) metabolites was 33:1. Phenobarbitone pretreatment of rats increased total hydroxylation by about 20% but did not change the ratio of hydroxylated to aromatized products (27:1). In contrast, beta-naphthoflavone induction decreased total hydroxylation to about 35% of control but did not affect total aromatization. Thus the ratio of hydroxylation to aromatization was significantly lower than in control microsomes (17:1). The principal aromatized products were oestriol and 2-hydroxyoestradiol-17 beta, with oestradiol-17 beta and its 4-hydroxy metabolite as minor products; no oestrone was observed. In further studies of the microsomal metabolism of oestrone, the major product was oestradiol-17 beta whereas hydroxylated metabolites were only minor products. Oestradiol-17 beta, in contrast, was hydroxylated to a considerable extent. These findings suggest that oestrone is a better substrate for the microsomal 17 beta-oxidoreductase than it is for cytochrome P-450. It therefore appears likely that any oestrone formed from the aromatization of androst-4-ene-3,17-dione would be readily converted to oestradiol-17 beta which, in turn, is subject to cytochrome P-450-mediated hydroxylation. Although the liver is a site of C19-steroid aromatization, it appears unlikely that this organ could contribute significantly to serum oestrogen levels since microsomal hydroxylases are readily able to convert aromatized products to biologically inactive metabolites.
Androstenedione↗
Towards the eradication of hepatitis B in Australia.
Explore the source record for details and available documents.
Australia↗
Source of raised serum estrogens in male rats with portal bypass.
We sought to establish the mechanism for the raised serum estrogen levels that occur in male rats with portal hypertension and resultant portal bypass. Using the portal vein ligated (PVL) rat model, we evaluated plasma steroid hormone concentrations, metabolic clearance rate (MCR) of estradiol, and hepatic metabolism of androstenedione to estrogens and other products. In contrast to serum testosterone levels that were reduced, serum androstenedione levels were normal in the PVL rat. Estradiol MCR was measured by a constant intravenous infusion technique and was found to be similar in PVL and control animals. Androstenedione MCR was determined during constant intravenous infusion of [3H]androstenedione, and the resultant radiolabeled steroids present in plasma were separated by thin layer chromatography. The MCR of androstenedione was not diminished in PVL rats compared with controls. However, there was a sevenfold increase in the plasma estradiol derived from [3H]androstenedione in rats with portal bypass. Examination of radiolabel excreted in bile during infusion of [3H]androstenedione showed that 25-46% of this steroid was converted to estradiol in PVL rats compared with less than 3% in control male rats (P less than 0.001). Moreover, there was a selective reduction in the excretion of 16 alpha-hydroxyandrostenedione, a finding which suggested that the metabolism of androstenedione via this pathway was decreased. Androstenedione 16 alpha-hydroxylation is known to be catalyzed by a male-specific cytochrome P-450 isoform, P-450UT-A. We conclude that raised plasma estradiol levels after portal bypass in male rats are due to increased production rates, resulting in turn from enhanced aromatization of androstenedione to estradiol. On the basis of the observed specific changes in androstenedione hydroxylation pathways, it is proposed that alterations in levels of sex-specific forms of cytochrome P-450 occur in male rats with portal bypass and could account for the enhanced formation of estradiol.
Androstenedione↗
Altered hepatic calcium homeostasis in guinea pigs with halothane-induced hepatotoxicity.
Exposure of guinea pigs to 1% halothane in air for 4 hr resulted in extensive centrizonal hepatic necrosis in 70% of animals examined 2 to 3 days later. In contrast, confluent hepatic necrotic lesions were not present in animals studied 24 hr after halothane exposure; only microvascular fatty change of hepatocytes with occasional necrotic cells was observed at that time (in 84% of animals). This delayed onset of lesion development afforded the opportunity to study microsomal membrane composition and indices of Ca++ homeostasis before and after the onset of halothane-induced hepatic necrosis. Hepatic microsomal cytochrome P-450 levels were unaltered 24 hr after halothane exposure, but fell to approximately 50% of control values at 72 hr. This indicates that such changes were most likely the result of hepatocellular necrosis. Microsomal lipid composition, including the relative proportions of individual phospholipids, was unaltered during halothane-induced hepatotoxicity. In contrast, microsomal Ca++ sequestration, as assessed by 45Ca uptake, was reduced 24 hr after halothane exposure compared with controls (2.76 +/- 1.32 nmol/mg of protein per min, vs. 6.63 +/- 2.88 nmol/mg of protein per min, P less than .001). This early change in microsomal Ca++ uptake was associated with a 10-fold increase in total hepatic Ca++ content at 24 hr. Subsequent changes in hepatic Ca++ content were proportionate to the severity of liver necrosis. The observation that abnormalities of hepatic Ca++ homeostasis antedate the presence of liver cell necrosis is consistent with a role for altered Ca++ fluxes in the mechanism of halothane-induced liver injury.
Alanine Transaminase↗
Inhibition of theophylline metabolism by interferon.
1 day after a single intramuscular injection of recombinant human interferon alpha A in 5 patients with stable chronic active hepatitis B and 4 healthy controls theophylline clearance was significantly reduced and theophylline elimination half-life was significantly increased. There was a clear relation between pre-treatment and post-treatment theophylline clearance rates, indicating that the greatest effect of interferon was in subjects who were fast metabolisers of theophylline. These observations support the contention that the actions of endogenous interferon may account for the effects of immunisations and viral infections on hepatic drug metabolism. Moreover, treatment with interferon may cause clinically important drug interactions.
Adult↗
Impaired androgen 16 alpha-hydroxylation in hepatic microsomes from carbon tetrachloride-cirrhotic male rats.
Hepatic cirrhosis produced by repeated inhalation of carbon tetrachloride is associated with reduced levels of microsomal cytochrome P450. In this study the C19-steroids androstenedione and testosterone were used as specific probes of the functional activity of several forms of cytochrome P450 in microsomal fractions from control and cirrhotic rat liver. The principal finding, that androstenedione 16 alpha-hydroxylation and testosterone 2 alpha-, 16 alpha-, and 17 alpha-hydroxylation were reduced to 14%-38% of control activity, strongly suggests that levels of the male sexually differentiated cytochrome P450 (P(450)16 alpha) are decreased in hepatic cirrhosis. The activity of other cytochrome P450-mediated C19-steroid hydroxylases, with the exception of androstenedione 6 beta-hydroxylase, appeared essentially unaltered in microsomes from cirrhotic rats. Cirrhosis induced by carbon tetrachloride was also associated with greatly decreased activity of the microsomal cytochrome P450-independent 17 beta-oxidoreductase, an enzyme that catalyzes the conversion of androstenedione to testosterone. Consequently, and in view of the impaired activity of cytochrome P450-mediated testosterone 17 alpha-hydroxylation, the capacity of cirrhotic microsomes to catalyze the interconversion of androstenedione and testosterone was much lower than that of control microsomes. The present data confirm and extend earlier observations that selective impairment of drug oxidation pathways occurs in hepatic cirrhosis. These changes are unrelated to the acute toxicity produced by carbon tetrachloride exposure. The available evidence supports the assertion that specific forms of cytochrome P450 are subject to altered regulation in cirrhosis.
Androgens↗
Brain gamma-aminobutyric acid receptor binding is normal in rats with thioacetamide-induced hepatic encephalopathy despite elevated plasma gamma-aminobutyric acid-like activity.
Brain gamma-aminobutyric acid (GABA) receptor density, affinity, and function, and plasma GABA-like activity were determined in rats with acute hepatic encephalopathy induced by an intraperitoneal injection of thioacetamide. In addition, the effect of various stress factors on brain GABA binding was assessed. Plasma GABA-like activity was significantly increased in rats with thioacetamide-induced hepatic encephalopathy compared with rats injected with vehicle alone (1506 +/- 993 nM, n = 7 vs. 367 +/- 97 nM, n = 9, mean +/- SD; p less than 0.001). In contrast, there were no alterations in either brain GABA receptor binding or in GABA-enhanced benzodiazepine binding in rats with hepatic encephalopathy when compared with relevant controls. However, rats that had received intraperitoneal injections of thioacetamide or vehicle (0.15 M NaCl) had significantly more low-affinity GABA receptors than rats that had neither been injected nor handled before killing (8769 +/- 1101 vs. 2710 +/- 757 fmol/mg protein, mean +/- SEM, p less than 0.001). We concluded that stress factors appear to be important causes of altered brain GABA binding. Brain GABA receptor binding and function, however, are unaltered in rats with thioacetamide-induced hepatic encephalopathy despite elevated plasma GABA-like activity.
Animals↗