Regulation of renal cytochrome P-450. Effects of two-thirds hepatectomy, cholestasis, biliary cirrhosis and post-necrotic cirrhosis on hepatic and renal microsomal enzymes

Molecular changes in hepatic metabolism and transport in cirrhosis and their functional importance

Liver cirrhosis is the common endpoint of many hepatic diseases and represents a relevant risk for liver failure and hepatocellular carcinoma. The progress of liver fibrosis and cirrhosis is accompanied by deteriorating liver function. This review summarizes the regulatory and functional changes in phase I and phase II metabolic enzymes as well as transport proteins and provides an overview regarding lipid and glucose metabolism in cirrhotic patients. Interestingly, phase I enzymes are generally downregulated transcriptionally, while phase II enzymes are mostly preserved transcriptionally but are reduced in their function. Transport proteins are regulated in a specific way that resembles the molecular changes observed in obstructive cholestasis. Lipid and glucose metabolism are characterized by insulin resistance and catabolism, leading to the disturbance of energy expenditure and wasting. Possible non-invasive tests, especially breath tests, for components of liver metabolism are discussed. The heterogeneity and complexity of changes in hepatic metabolism complicate the assessment of liver function in individual patients. Additionally, studies in humans are rare, and species differences preclude the transferability of data from rodents to humans. In clinical practice, some established global scores or criteria form the basis for the functional evaluation of patients with liver cirrhosis, but difficult treatment decisions such as selection for transplantation or resection require further research regarding the application of existing non-invasive tests and the development of more specific tests.

Portal hyperperfusion: mechanism of injury and stimulus for regeneration in porcine small-for-size transplantation

Understanding the pathogenesis of small-for-size (SFS) syndrome is critical to expanding the applicability of partial liver transplantation. We aimed to characterize its acute presentation and association with alterations in hepatic hemodynamics, microstructure, and regeneration in a porcine model. Eighteen SFS liver transplants were performed. Donors underwent 70% hepatectomy. Partial grafts were implanted into larger recipients. Whole liver transplants were also performed (n = 6). Recipients were followed until death or for 5 days. Hemodynamics were measured, and tissue was sampled intraoperatively and at the study end. Serum was sampled regularly during follow-up. Seventeen SFS transplants and 6 whole liver transplants were included. SFS grafts represented 23.2% (19.3%-25.3%) of the recipients' standard liver volume. The survival rate was 29% and 100% in the SFS and whole liver groups, respectively. The portal venous flow, pressure gradient, and resistance were significantly higher in recipients of SFS grafts versus whole livers after portal and arterial reperfusion. Arterial flow as a percentage of the total liver blood flow was significantly lower after reperfusion in SFS grafts and remained so when measured again after 5 days. Markers of endothelial cell injury increased soon after reperfusion, and those of hepatocellular injury increased later; both predicted the appearance of either graft failure or histological recovery. Proliferative activity peaked earlier and higher among nonsurvivors in the SFS group. Surviving grafts demonstrated a slower but maintained rise in regenerative activity, although metabolic activity failed to improve. In SFS transplantation in the acute setting, portal hyperperfusion is a stimulus for regeneration but may simultaneously cause irreparable endothelial injury. This porcine model not only helps to elucidate the inciting factors in SFS pathogenesis but also offers a clinically relevant means to study its prevention.

Living donor liver transplant recipients achieve relatively higher immunosuppressant blood levels than cadaveric recipients

Two recent brief reports suggest that recipients of living donor liver transplants achieve higher levels of immunosuppressive agents than cadaveric (CAD) liver transplant recipients administered the same dose. These results could have important implications regarding the dosing of immunosuppressives in living donor liver transplant recipients. We report our findings relative to immunosuppressive doses and levels in a cohort of 46 living donor liver transplant recipients. Immunosuppressive blood levels and doses were recorded weeks 1, 2, 3, and 4 and months 2, 3, 4, 5, and 6 for 46 living donor liver transplant recipients and 66 matched CAD liver transplant recipients who underwent transplantation between August 1997 and May 2001. The ratio of level to dose also was recorded at each interval. The mean overall cyclosporine A dose was similar in living donor liver transplant recipients (323 mg/d) compared with CAD recipients (344 mg/d; P = not significant [NS]). The mean overall tacrolimus dose was 15% lower in patients who underwent living donor liver transplantation (LDLT; 5.7 mg/d) than CAD transplantation (6.7 mg/d), although statistical significance was not achieved (P =.08). The mean overall cyclosporine A level was 18% higher in those undergoing LDLT (275 ng/mL) than CAD transplantation (234 ng/mL; P =.015). The mean overall tacrolimus level was the same in living donor liver transplant recipients (10.8 ng/mL) and CAD recipients (10.2 ng/mL; P = NS). The overall cyclosporine A level-dose ratio was 26% higher for those undergoing LDLT (0.83) than CAD transplantation (0.66; P =.01). The overall tacrolimus level-dose ratio was 26% higher for those undergoing LDLT (1.82) than CAD transplantation (1.44; P =.01). In conclusion, (1) living donor liver transplant recipients achieve higher blood levels of tacrolimus and cyclosporine A for a given dose compared with CAD recipients, and (2) this difference is observed up to 6 months after transplantation, when hepatic regeneration is completed.

Bile duct ligation and oxidative stress in the rat: effects in liver and kidney

In the liver, seven days of bile duct ligation (BDL) decreases the cytochrome P-450 content and the UDP-glucuronyl transferase activity. Also, a decrease in the water soluble antioxidant mechanism reflected in the activities of the enzymes superoxide dismutase (SOD), catalase and the glutathione peroxidase (GTPx) was found in the liver but not in the kidney. Despite an increase in the amount of the GSH in the liver, increased lipid peroxidation is produced in the BDL rats, as indicated by the levels of malondialdehyde (MDA). The kidney responded in a different way to cholestasis, decreasing only the UDP-glucuronyl transferase activity and increasing the levels of GSH and MDA. In the red blood cells the activity of the antioxidant enzymes SOD, GTPx and catalase and the content of GSH were not modulated by cholestasis. In conclusion, disturbance of the oxidant-antioxidant balance might be responsible for cholestatic liver injury and impaired renal function in BDL rats.

Putrescine decreases cytochrome P450 3A4 levels during liver regeneration in the rat

BACKGROUND/AIMS

The mechanism by which many cytochrome P450 (CYP) isozymes decrease during liver regeneration is unclear. Peptides and growth factors are thought to be involved. Putrescine, the first polyamine synthesised by ornithine decarboxylase, peaks early following partial hepatectomy and is known to play an essential role in hepatic regeneration. Gamma amino butyric acid was reported as a physiologic inhibitor of ornithine decarboxylase. In this work we studied the possible involvement of putrescine in the CYP reduction during liver regeneration.

METHODS

Hepatectomised, putrescine-treated sham, and GABA-treated hepatectomised rats were used throughout. Total hepatic cytochrome P450, o-dealkylase activities (CYP1A1 and CYP2B1/2), nifedipine oxidase activity (CYP3A4), and Western blot assays of their respective apoproteins were analysed in liver microsomes. Putrescine levels in hepatic tissue were also measured.

RESULTS

Partial hepatectomy and putrescine treatment induced a significant diminution in total CYP (50% and 30% of sham-operated rats, respectively). Gamma amino butyric acid treatment prevented this decrease in partially hepatectomised rats. Nifedipine oxidase activity of partially hepatectomised and putrescine-treated rats significantly decreased to 43% and 60% of that in sham-operated rats, respectively. Again, gamma amino butyric acid prevented the diminution in partially hepatectomised rats. No significant changes were observed in o-dealkylase activities.

CONCLUSIONS

These results show that inducible CYP1A1 and CYP2B1/2, which are important in carcinogen metabolisation, are preserved after partial hepatectomy. However, constitutive CYP3A4, which represents 50% of total CYP and metabolises drugs like nifedipine, warfarin, acetaminophen, cyclosporin and FK-506, is reduced during liver regeneration. Our experiments suggest that endogenous putrescine is, at least, partly responsible for this decrease.

Liver damage induced by bile duct ligation affects CYP isoenzymes differently in rats

We examined the influence of liver damage induced by bile duct ligation on the activity and the expression of hepatic cytochrome P450 (CYP) 1A, 2B, 2C6, 2C11, 2E1 and 3A2 in male Sprague-Dawley rats. In the ligation group, testosterone 2 alpha-, 16 alpha-, and 6 beta-hydroxylase activities were severely decreased, whereas ethoxyresorufin O-deethylase and progesterone 21-hydroxylase activities relatively remained. Pentoxyresorufin O-deethylase and chlorzoxazone 6-hydroxylase activities were reduced to approximately one thirds those of control. The protein contents of these isoenzymes expressed in hepatic microsomes of the ligation group were decreased to 45%, 32%, 79%, 13%, 58%, and 23% of control for CYP1A, 2B, 2C6, 2C11, 2E1 and 3A2, respectively. The rank order of magnitude of the influence of bile duct ligation on CYP isoenzymes, assessed by the reduction in the enzyme activity and the protein content, corresponded with each other except CYP1A. The reduction of the enzyme activities significantly correlated with the reduction in the protein contents of different isoenzymes. These results suggested that bile duct ligation affected CYP isoenzyme activities and contents with different extent.

Microsomal and peroxisomal fatty acid oxidation in bile duct ligated rats: a comparative study between liver and kidney

1. Microsomal cytochrome P-450 and peroxisomal fatty acid oxidation was studied in the kidney of rats 7 days after bile duct ligation (BDL) and a comparative study between kidney and liver was done. 2. Only in the liver did cholestasis decrease the cytocrome P-450 content and the peroxisomal fatty acid beta-oxidation, the catalase activity, and the microsomal metabolism of lauric acid and aminopyrine. 3. In contrast, cholestasis did not influence these activities in the kidney. The microsomal and peroxisomal activities studied responded in a coordinate way to cholestasis. 4. These results could suggest the possibility of a cause-and-effect relationship between microsomal cytochrome P-450 and peroxisomal activity.

Influence of partial hepatectomy in rats on the activity of hepatic microsomal enzymatic systems

The influence of partial hepatectomy on the activity of the hepatic microsomal enzymatic systems was determined in rats. Cytochrome P-450, cytochrome b5, four mixed functional oxidase (MFO) activities (microsomal aniline hydroxylase, p-nitroanisole O-demethylase, aminopyrine N-demethylase and NADPH cytochrome c reductase) and glutathione levels were measured in unhepatectomized rats (control group) and in hepatectomized rats 12 h, 24 h, 3 days and 6 days after 70% hepatectomy. Following surgery the remaining lobes of the liver grow rapidly in order to restore the original liver mass. Partial hepatectomy significantly reduces cytochrome P-450 and b5 content in the remaining liver as well as the four MFO activities studied. But when the enzymatic systems are expressed as nmoles/mg microsomal protein, only cytochrome P-450 shows statistical differences. The hepatic biotransformation capacity of drugs and xenobiotics decreases during the regeneration period due to the reduction of hepatic mass rather than because of a reduction of their metabolic capacity. Glutathione levels are increased after partial hepatectomy but increased glutathione-dependent protector mechanisms are not expected.

Microsomal and peroxisomal fatty acid oxidation in liver of rats with bile duct ligation and two-thirds hepatectomy

Microsomal cytochrome P450 and peroxisomal activity were studied in liver of rats 7 days after two-thirds hepatectomy or bile duct ligation (BDL). Both surgical models decreased the hepatic microsomal cytochrome P450 content, but only cholestasis, produced by BDL, decrease the microsomal metabolism of lauric acid and aminopyrine, peroxisomal fatty acid beta-oxidation and catalase activity. The microsomal and peroxisomal activities responded in a coordinate way to cholestasis and two-thirds hepatectomy. These results suggest a cause-effect relationship between the microsomal cytochrome P450 and peroxisomal activity.

Microsomal function in biliary obstructed rats: effects of S-adenosylmethionine

BACKGROUND/AIMS

S-adenosylmethionine has been reported to have beneficial effects in the treatment of different chronic liver diseases and to protect against different hepatotoxic agents. The aim of this study was to investigate whether S-adenosylmethionine treatment might contribute to improved microsomal function in chronically biliary obstructed rats.

METHODS

Secondary biliary cirrhosis was induced by 28 days of bile duct obstruction. Groups of control and cirrhotic animals received S-adenosylmethionine (10 mg/kg per day) through the experimental period.

RESULTS

Bile duct obstruction resulted in a marked increase in lipid peroxidation levels and decreases in glutathione concentration, microsomal membrane fluidity, microsomal cytochrome P-450 content, NADPH-cytochrome P-450 reductase activity and the activities of the aniline hydroxylase, aminopyrine demethylase and ethoxycoumarin deethylase. Reductions in glutathione and cytochrome P-450 concentration were not corrected by S-adenosylmethionine, but lipid peroxidation, the decrease in the activities of the various microsomal monooxygenases and the reduction in microsomal membrane fluidity were partially prevented. A significant relationship was found between membrane fluidity and aniline hydroxylase, aminopyrine demethylase or ethoxycoumarin deethylase activities.

CONCLUSIONS

S-adenosylmethionine administration partially preserves microsomal function. This effect could be associated to the protection of membrane function by restoring transmethylation reactions.

Comparison of hepatic and extrahepatic drug-metabolizing enzyme activities in rats given single or multiple challenge infections with Fasciola hepatica

The activity of drug-metabolizing enzymes was compared in liver, kidneys and lungs of rats given single or repetitive fluke infections. Fascioliasis was induced by oral administration of 20 metacercariae of F. hepatica to rats, either 6, or 12 and 6, or 12, 9 and 6 weeks before sacrifice. In the liver of mono-infected rats, significant reductions (24-67%) were observed in microsomal content of cytochrome P450 and all P450-dependent monooxygenases investigated. Conjugations to glutathione or acetate were lowered by 34-50% in these animals. In multiply infected animals, a majority of specific enzymatic activities were unchanged, while some monooxygenase activities such as aminopyrine demethylation or benzo(a)pyrene hydroxylation were increased by 26-76% in the liver of tri-infected rats. A renal compensatory process occurred in all infected groups, since cytochrome P450, benzphetamine demethylation and glutathione conjugation were significantly increased. By contrast, dealkylation of benzphetamine and pentoxyresorufin were decreased in the lungs of monoinfected rats. The development of parasite resistance would account for the recovery of liver drug metabolizing capabilities in multi-infected animals.

Is intestinal cytosolic glutathione S-transferase an alternative detoxification pathway in two-thirds hepatectomized rats?

The present study was designed to investigate the effect of partial (two-thirds) hepatectomy (PH) on hepatic and intestinal glutathione S-transferases (GSTs) activities. A significant decrease of cytosolic hepatic GSTs activity was observed after the PH. The lowest value of hepatic GSTs was obtained 48 h after the surgery. On the other hand, intestinal GSTs activities increased after PH, reaching the highest values 48 h after the hepatic lobes resection. The hepatic GSTs activities diminution was attributed, in part, to the high accumulation of bile acids in the liver tissue of hepatectomized rats, also demonstrated by a higher retention of [14C] taurocholate. The kinetic analysis performed with 1-chloro-2,4-dinitrobenzene (CDNB) as substrate showed two sets of parameters, indicating the presence of isozymes of high and low affinities. Vmax1 and Vmax2 were lower in PH rats suggesting a non competitive inhibition mechanism. The inhibitory effect of bile acids decreased during liver regeneration process of hepatectomized rats disappearing at 7 days after PH. Conversely, in non regenerating rats (GABA treated) the inhibitory mechanism was still observed at 7 days after the surgery. The increase of intestinal GSTs activities (isozymes of high and low affinities) was attributed to the presence of polyamines, mainly putrescine, produced during the hepatic regeneration process. In this regard, it was showed that GABA treatment, which inhibits polyamine synthesis, completely abolished the increase on intestinal GSTs activities. Finally, the treatment with exogenous putrescine showed that in hepatectomized and sham-operated rats, the polyamine induced GSTs activities in both tissues. In PH rats, the putrescine dependent increase of hepatic GSTs was masked by the inhibitory effect of bile acids. In addition, a summation effect of endogenous and exogenous putrescine was probably the reason of the induction of intestinal GSTs after PH. The GSH/GSSG ratio did not change during the treatments, as well as the microsomal GST activity of both tissues. The work points out the hypothetical detoxification power of the intestine during the hepatocellular insufficiency which follows a two-thirds hepatectomy.

Caffeine demethylation measured by breath analysis in experimental liver injury in the rat

To assess the effects of experimental liver injury on caffeine metabolism, 1 muCi/kg b.w. of [3-methyl 14C]-caffeine (together with 5 mg/kg b.w. of the cold compound) was injected i.p. to four different experimental groups and respective controls of unanesthetized male Sprague-Dawley rats. Exhaled 14CO2 was completely collected during 4 h and peak exhalation rate and fraction of dose recovered were calculated. 1/3 hepatectomy affected 14CO2 exhalation to a limited extent, decreasing solely peak exhalation rate (p < 0.05 compared to sham-operated controls). 2/3 hepatectomy, on the other hand, resulted in significant reduction (p < 0.01) in both peak exhalation rate (by 59%) and fraction of dose recovered (by 47%), that were proportionate to the loss of liver mass (59%). End-to-side portocaval shunt led to the well-documented hepatic "atrophy", liver weight being diminished on average to 50% within 2 weeks of surgery; however, reductions in peak exhalation rate (by 75%) and fraction of dose recovered (by 64%) were even more pronounced. Finally, 48 h bile duct ligation was equivalent to "functional 2/3 hepatectomy", peak exhalation rate (by 65%) and fraction of dose recovered (by 56%) being markedly diminished despite increased liver weight. These results indicate that 14CO2 exhalation curves following administration of specifically labelled caffeine are quantitative indicators of acute or chronic loss of functioning liver mass. In addition, the 3-demethylation pathway appears to be particularly sensitive to the inhibitory effects of cholestasis on microsomal function.

Differential effect of micronodular and biliary cirrhosis on epidermal growth factor receptor expression in the rat

Cirrhosis is characterized by fibrogenesis, hepatocyte necrosis and the formation of regenerative nodules. Modulation of the epidermal growth factor receptor is an early event during regeneration. We have recently demonstrated alterations in the epidermal growth factor receptor during the development of biliary cirrhosis. The aim of the present study was to compare epidermal growth factor receptor distribution, expression and binding in biliary cirrhosis to that occurring in micronodular cirrhosis induced by phenobarbital/CCl4 exposition. Biliary cirrhosis and micronodular cirrhosis had similar functional impairment as assessed by the aminopyrine breath test. Epidermal growth factor receptor binding capacity was reduced in both models (control vs micronodular cirrhosis vs biliary cirrhosis: (mean +/- 1 SD) 60 +/- 22 vs 16 +/- 12 vs 27 +/- 9 fmol/mg protein, p < 0.05), while the binding constant was increased in biliary cirrhosis only. The receptor mass in plasma membrane, determined by Western blotting, was not changed. Distribution of epidermal growth factor receptor was assessed immunohistochemically on tissue sections. In both models, cytoplasmic staining was decreased and basolateral plasma membrane labeling was maintained. Nuclear localization was found in biliary cirrhosis only. In conclusion, in both models, cirrhosis induces an alteration in the binding properties, but not in the number of epidermal growth factor receptors in the plasma membrane. The loss of cytoplasmic epidermal growth factor receptor could reflect alterations in expression and/or in intracellular trafficking. This is supported by the reduced mRNA steady state levels for epidermal growth factor receptor which were found in both models, presumably representing down-regulation.(ABSTRACT TRUNCATED AT 250 WORDS)

Structure-function relationship in secondary biliary cirrhosis in the rat. Stereologic and hemodynamic characterization of a model

Secondary biliary cirrhosis in the rat is an attractive model since unlike other models it does not rely on exogenous toxic compounds to induce cirrhosis. However, because little is known about the microcirculatory abnormalities of this model, this study investigated hemodynamics in rats with predefined functional impairment and related them to different aspects of stereologically quantified structure. All animals with at least 50% reduction in microsomal function, assessed by the aminopyrine breath test, had portal hypertension. The sinusoidal space, as assessed by multiple indicator dilution in the perfused liver, was reduced whereas large vessel space was increased. This reduction in sinusoidal space could contribute to increased portal resistance. The degree of intrahepatic shunting varied as assessed by a microsphere technique (13.9 vs. 0.5% in controls). These alterations were confirmed by stereological analysis. Numerically, there was excellent agreement between functional indicator dilution data and anatomic quantitation. Microvascular exchange was impaired as in other models of cirrhosis as shown by a reduced extravascular albumin space (4.5 vs. 2.2%, p < 0.01). In contrast to alterations in vascular space, this functional impairment was not reflected in the stereologically assessed space of Disse which averaged 5% of liver volume in both groups. Finally, in spite of reduced microsomal function in vivo (aminopyrine breath test) and in vitro (aminopyrine N-demethylase activity), the smooth endoplasmic reticulum was maintained (4.3 vs. 3.5 m2/ml cytosol, n.s.), which demonstrates that microsomal function in this model is reduced per unit hepatocyte. This suggests that the sick-cell hypothesis applies to secondary biliary cirrhosis in the rat.

The effect of partial hepatectomy on the metabolism, distribution, and nephrotoxicity of para-methylthiobenzamide in the rat

Para-Methylthiobenzamide (PMTB) produces injury to the liver and kidney. Toxicity is mediated via its biotransformation to a reactive S,S-dioxide metabolite. The objective of this study was to examine the role of hepatic metabolism in the production of PMTB-induced renal toxicity. Renal injury was assessed in partially hepatectomized and sham-operated rats and the effect of this procedure on the distribution and metabolism of PMTB was examined. The in vitro oxidation of PMTB and [14C]thiobenzamide by rat kidney microsomes was also examined. Plasma urea levels and renal cortical slice uptake of organic ions were used to monitor renal function. Partial hepatectomy alone did not alter renal function nor raise blood urea nitrogen levels. Nephrotoxicity resulted when a nonnephrotoxic dose of PMTB (1.2 mmol/kg) was given to partially hepatectomized rats. An HPLC method was used for measurement of PMTB and its metabolites para-methylthiobenzamide S-oxide (PMTBSO) and para-methylbenzamide (PMBA) in plasma and kidney. Hepatectomy delayed the removal of this dose of PMTB from plasma and allowed greater concentrations of PMTB and PMTBSO to accumulate in plasma and kidney at 6 and 15 hr. The level of PMBA was similar in both groups at 6 hr, but was increased in plasma and kidney of the hepatectomized group at 15 hr. Kidney microsomes rapidly converted PMTB to PMTBSO and small amounts of PMBA. [14C]TB was oxidized by microsomes to thiobenzamide S-oxide, benzamide, and covalently bound metabolites. The results indicate that partial hepatectomy lowered the threshold for the expression of nephrotoxicity by PMTB. This procedure is associated with an increased renal accumulation of PMTB and PMTBSO, which are both sequentially transformed to the toxic metabolite.

The microsomal monooxygenase system of regenerating liver. An examination of the role of estradiol in the demasculinization of drug metabolism produced by 2/3 partial hepatectomy

Declines in total cytochrome P450 content and in monooxygenase activities associated with some male specific isozymes of cytochrome P450 have been reported in the rat following 2/3 partial hepatectomy (2/3 PH). In the present study, we examined the effects of 2/3 PH on hepatic microsomal monooxygenase activities towards testosterone, the alkoxyresorufins, p-nitrophenol and carbon tetrachloride in male rats. Levels of P450 apoproteins were determined by Western blot analysis. The effects of hepatectomy and sham operations on plasma growth hormone (GH) pulse profiles and the effects of a single acute dose of estradiol (E2) were studied to determine the role of these factors in 2/3 PH mediated changes in oxidative metabolism. 2/3 PH produced substantial decreases in testosterone hydroxylation at positions 16 alpha, 2 alpha and 7 alpha, but only a small decrease in hydroxylation at position 6 beta. Reductions in CYP 2C11 (P450h) and CYP 2A1 (P450a) expression were observed with Western blot analysis down to 19 and 41% of control values, respectively, but insignificant effects were observed on expression of CYP 3A (P450p family) proteins recognized by a polyclonal antibody raised against rat CYP 3A2 (P450pcn2). In contrast, acute E2 treatment caused a 2-fold increase in expression of CYP 2A1 apoprotein and significantly decreased expression of CYP 2E1 (P450j) apoprotein and dependent monooxygenase activities, but had no significant effect on expression of CYP 2C11. Both sham operations and 2/3 PH caused a temporary decrease in plasma GH concentrations, but secretion returned towards normal 24-48 hr after both operations. These data suggest that some factor other than GH or E2 must be involved in the selective suppression of some P450 isozymes observed after 2/3 PH.

Generation of free radicals during the reductive metabolism of nilutamide by lung microsomes: possible role in the development of lung lesions in patients treated with this anti-androgen

The pulmonary metabolism of nilutamide, a nitroaromatic anti-androgen drug leading to pulmonary lesions in a few recipients, has been investigated in rats. Incubation of nilutamide (1 mM) with rat lung microsomes and NADPH under anaerobic conditions led to the formation of the nitro anion free radical, as indicated by ESR spectroscopy. The steady state concentration of this radical was not decreased by CO or SKF 525-A (two inhibitors of cytochrome P450), but was decreased by NADP+ (10 mM) or p-chloromercuribenzoate (0.47 mM) (two inhibitors of NADPH-cytochrome P450 reductase activity). Anaerobic incubations of [3H]nilutamide (0.1 mM) with rat lung microsomes and a NADPH-generating system resulted in the in vivo covalent binding of [3H]nilutamide metabolites to microsomal proteins; covalent binding required NADPH; it was decreased in the presence of NADP+ (10 mM), or in the presence of the nucleophile glutathione (10 mM), but was unchanged in the presence of carbon monoxide. Under aerobic conditions, in contrast, the nitro anion free radical was reoxidized by oxygen, and its ESR signal was not detected. Covalent binding was essentially suppressed. Instead, there was consumption of NADPH and oxygen, and production of superoxide anion and hydogen peroxide. We conclude that nilutamide is reduced by rat lung microsomes NADPH-cytochrome P450 reductase into a nitro anion free radical. In anaerobiosis, the radical is reduced further to covalent binding species. In the presence of oxygen, in contrast, this nitro anion free radical undergoes redox cycling, with the generation of reactive oxygen species.

Differential effect of biliary and micronodular cirrhosis on oxidative drug metabolism. In vivo-in vitro correlations of dextromethorphan metabolism in rat models

Oxidative drug metabolism is impaired in liver cirrhosis; it is unclear, however, whether this depends on the etiology of cirrhosis. Therefore, we studied the metabolism of dextromethorphan in two rat models: biliary cirrhosis induced by bile duct ligation and micronodular cirrhosis induced by chronic exposure to CCl4/phenobarbital. Results were compared with aminopyrine N-demethylation assessed by a breath test in vivo; the latter was reduced to a similar extent in biliary (-41%) and micronodular (-37%) cirrhosis compared to controls. In contrast, clearance of dextromethorphan was significantly (P less than 0.001) reduced in biliary (25.4 +/- 5.3 mL/min/kg) but not in micronodular cirrhosis (48.6 +/- 15.6) as compared to controls (62.2 +/- 16.2). Intrinsic clearance of dextromethorphan in vitro was reduced by 95% and 63% in biliary and micronodular cirrhosis, respectively (P less than 0.001 vs controls). It correlated with dextromethorphan clearance in vivo (r = 0.68, P less than 0.001) whereas correlation with aminopyrine N-demethylation was weak (r = 0.42, P less than 0.05). Our results demonstrate a differential effect of biliary and micronodular cirrhosis on isoenzymes responsible for aminopyrine and dextromethorphan demethylation.

Renal cytochrome P-450-dependent metabolism of arachidonic acid in cirrhotic rats

Cirrhosis was induced in Wistar-Kyoto rats by intragastric administration of carbon tetrachloride. Microsomes were obtained from the renal cortex and outer medulla and incubated with [14C]arachidonic acid (AA) (0.2-0.4 microCi) in the presence or absence of indomethacin, NADPH, and SKF-525A. Cytochrome P-450-dependent AA metabolites (those whose formation required NADPH, were inhibited by SKF-525A, but not by indomethacin) were separated by thin-layer chromatography and high-pressure liquid chromatography (HPLC). Compared to controls, total synthesis of cytochrome P-450-dependent AA metabolites was reduced in cirrhotic rats (renal cortex: cirrhotics 380 +/- 52 vs. controls 493 +/- 68 pg/mg protein per 30 min; p less than 0.05; renal outer medulla: cirrhotics 304 +/- 57 vs. controls 387 +/- 53 pg/mg protein per 30 min; p less than 0.05). The cytochrome P-450-dependent AA metabolites were composed of three peaks separated by HPLC. Peak I, which had a retention time of 16.3 +/- 0.3 min and comigrated with 11,12-dihydroxyeicosatrienoic acid, and peak II, which had a retention time of 18.7 +/- 0.4 min and comigrated with 19- and 20-hydroxyeicosatetraenoic acid, were not different in cirrhotics and controls. Peak III, which had a retention time of 26.8 +/- 0.3 min, and comigrated with 11,12-epoxyeicosatrienoic acid, was significantly decreased in the renal cortex of cirrhotic rats compared to controls (cirrhotics 316 +/- 40 vs. controls 473 +/- 89 pg/mg protein per 30 min; p less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

In micronodular cirrhosis, hepatocytes retain a normal C-25 hydroxylation capacity toward vitamin D3: a study using the rat carbon tetrachloride-induced cirrhotic model

To test further the competence of the cirrhotic liver to metabolize vitamin D3 at C-25, hepatocytes were isolated from controls and from CCl4-induced cirrhotic rat livers, as well as from partially hepatectomized rats. The transformation of D3 into 25-hydroxyvitamin D3 was studied in the presence of 10(7) hepatocytes at D3 concentrations of 20 nmol/L to 15.4 mumol/L. Histologically, micronodular cirrhosis was present in all CCl4-treated rats, whereas controls had normal livers; portal venous pressure (p less than 0.008) and intrahepatic collagen content (p less than 0.0001) were significantly increased in CCl4-treated rats, whereas no difference was found between the two groups in the total and ionized serum calcium, D3 metabolites, ALT, AST and alkaline phosphatase. Cytochrome P-450 was 0.27 +/- 0.02 and 0.25 +/- 0.02 nmol/10(6) hepatocytes in controls and cirrhotic rats (N.S.), and it significantly increased in both groups after phenobarbital or 3-methylcholanthrene administration (p less than 0.0001). 25-Hydroxyvitamin D3 formation was best described by power law equations and varied between 0.02 +/- 0.0004 and 29.57 +/- 2.8 in controls, and 0.024 +/- 0.0004 and 32.0 +/- 7.0 pmol.hr-1.10(6) hepatocytes-1 in cirrhotic rats. No statistically significant difference was found in the slopes of the 25-hydroxyvitamin D3 formation, but the y-axis intercept was found to be lower in cirrhotic rats under basal resting conditions (p less than 0.005). Inducers of the mixed function oxidases significantly increased 25-hydroxyvitamin D3 formation in controls as well as in cirrhotic rats (p less than 0.005). Moreover, both groups were found to respond similarly to the addition of modulators of the enzyme such as the calcium ionophore A23187 and parathyroid hormone. Partial hepatectomy was also without effect on the activation of D3. Furthermore, the cell sequestration of D3 was also found to be unperturbed in hepatocytes obtained from either cirrhotic or partially hepatectomized livers. The data indicate that in well-compensated micronodular cirrhosis, the C-25 hydroxylation of D3 is generally intrinsically normal at the cellular level and that it also remains fully responsive to in vivo and in vitro modulators of its activity.

Variation in drug-metabolizing enzyme activities during the growth of human Hep G2 hepatoma cells

1. The activities of several drug-metabolizing enzymes change during the growth cycle (exponential growth to confluence) of Hep G2 cells in culture. As the rate of cell growth slowed down (days 7 to 10 after passage) the activities of ethoxy- and methoxy-resorufin O-dealkylase and of NADPH cytochrome c- and NADH cytochrome b5-reductase increased. In contrast, the O-dealkylations of pentoxy- and benzyloxy-resorufin did not change significantly during culture. 2. UDP-glucuronyltransferase activities also showed substrate-dependent alterations with time in culture. In contrast, glutathione-S-transferase activity remained constant despite a decline in the intracellular reduced glutathione content. 3. Epoxide hydrolase activity altered throughout time in culture, with an initial decrease in activity followed by a marked increase between days 7 and 10 after passage. 4. These results indicate the importance of standardizing the protocol with regard to the timing of experiments within the growth period of the cells when using hepatoma cell lines for assessing the metabolism and cytotoxicity of chemicals.

Studies on the hyperplasia ('regeneration') of the rat liver following partial hepatectomy. Changes in lipid peroxidation and general biochemical aspects

Using the experimental model of partial hepatectomy in the rat, we have examined the relationship between cell division and lipid peroxidation activity. In rats entrained to a regime of 12 h light/12 h dark and with a fixed 8 h feeding period in the dark phase, partial hepatectomy is followed by a rapid regeneration of liver mass with cycles of synchronized cell division at 24 h intervals. The latter phenomenon is indicated in this study by pulses of thymidine kinase activity having maxima at 24 h, 48 h and 72 h after partial hepatectomy. Microsomes prepared from regenerating livers show changes in lipid peroxidation activity (induced by NADPH/ADP/iron or by ascorbate/iron), which is significantly decreased relative to that in microsomes from sham-operated controls, again at 24 h, 48 h and 72 h after the operation. This phenomenon has been investigated with regard to possible underlying changes in the content of microsomal fatty acids, the microsomal enzymes NADPH:cytochrome c reductase and cytochrome P-450, and the physiological microsomal antioxidant alpha-tocopherol. The cycles of decreased lipid peroxidation activity are apparently due, at least in part, to changes in microsomal alpha-tocopherol content that are closely associated in time with thymidine kinase activity.

Differential effects of partial hepatectomy on hepatic and renal heme and cytochrome P450 metabolism

Partial hepatectomy has been suggested to affect hepatic and renal cytochrome P450 content and the related drug metabolizing enzyme system. In addition, cytochrome P450 and its dependent activities have been shown to be regulated by the availability of cellular heme. We, therefore, studied cytochrome P450 in addition to the level of heme oxygenase, the rate-limiting enzyme of heme catabolism, and delta-aminolevulinic acid (ALA) synthase, the rate-limiting enzyme of heme synthesis, in the remnant liver and intact kidneys of rats after two-thirds hepatectomy. The level of hepatic heme oxygenase was elevated threefold in partially hepatectomized rats as compared to sham-operated rats, while ALA synthase was decreased by 40%. This was reflected in decreased hepatic cytochrome P450 content, ie, from 0.689 +/- 0.175 nmole/mg to 0.505 +/- 0.089 nmole/mg protein and associated decreased drug metabolizing enzymes: aryl hydrocarbon hydroxylase, 7-ethoxycoumarin-O-deethylase, and benzphetamine N-demethylase, by 40%, 40%, and 47%, respectively. In contrast, renal heme oxygenase was not changed after hepatectomy, whereas renal ALA synthase was increased by fourfold. Renal cytochrome P450, aryl hydrocarbon hydroxylase, 7-ethoxycoumarin-O-deethylase, and benzphetamine N-demethylase were increased after partial hepatectomy by 84%, 360%, 165% and 406%, respectively. These data indicate that partial hepatectomy decreases liver cytochrome P450 levels by inducing heme oxygenase and inhibiting ALA synthase activities. In this situation the kidney plays a substitutive role in metabolizing endogenous substrates oxygenated by cytochrome P450 isozymes.

Inhibition of cytochrome P-450p (P450IIIA1) gene expression during liver regeneration from two-thirds hepatectomy in the rat

Regenerating liver from partial hepatectomy (HPX) is known to exhibit a strong and transient deficiency in both spectrally detectable microsomal cytochrome P-450 (P-450) and related monooxygenase activities. Male Wistar rats (250-300 g) were HPX or sham operated and liver was excised at different times after operation. The time course of accumulation of five different forms of P-450 (including P-450b/e, P-450c, P-450d, P-450p and P-450UT-A) was determined in the regenerating liver, by Western blots developed with specific antibodies. With the exception of P-450c, whose level was not affected, the accumulation of other forms strongly decreased during the first 24 hr after HPX. For P-450b/e and P-450d, 80% of initial level was restored at 96 hr, whereas for P-450p and P-450UT-A, two major forms in control rat liver, the accumulation was only 20-25% of the initial, 1 week after HPX. No significant decrease was observed in sham operated animals. Plasmid pDex 12 containing a cDNA insert coding for P-450p was used to further investigate the effects of HPX on P-450p mRNA level and gene transcription. Northern blot analysis of RNA from regenerating liver (cDNA insert of pDex 12 being used as a probe) demonstrated that P-450p mRNA level decreased strongly to a minimum 12 hr after operation. This was correlated with a strong and transient decrease in P-450p gene transcription determined from nuclear run on experiments, the time course of which, however, did not account for the early decrease in mRNA level. We conclude that P-450p deficiency in the regenerating liver results from a combination of transient inhibition of gene transcription and early increase of mRNA degradation. Time course and amplitude of the decrease in P-450 UT-A accumulation suggest an inhibition of gene transcription as observed with P-450p.

Aminopyrine N-demethylation by rats with liver cirrhosis. Evidence for the intact cell hypothesis. A morphometric-functional study

The intact cell hypothesis states that a reduced number of intrinsically normal hepatocytes, together with hemodynamic alterations, explains decreased drug metabolism in cirrhosis. We explored this hypothesis by comparing results of the aminopyrine breath test with in vitro measurements of aminopyrine N-demethylation and morphometrically determined liver cell volume in a rat model of cirrhosis. Aminopyrine N-demethylation in vivo (ABT-k) was 0.98 +/- 0.10/h (mean +/- SD) in controls. The cirrhotic rats were separated into those with normal (NCR) and those with abnormal ABT-k (PCR). Microsomal aminopyrine N-demethylase averaged 2.08 +/- 0.77 and 2.09 +/- 0.54 mumol/min in controls and NCRs, respectively; it was reduced to 1.00 +/- 0.81 mumol/min (p less than 0.02) in PCRs. Morphometrically determined hepatocellular volume was 18.8 +/- 2.8, 17.1 +/- 1.9, and 11.6 +/- 6.1 ml in controls, NCRs, and PCRs, respectively, PCRs being lower than controls (p less than 0.01) and NCRs (p less than 0.05). When N-demethylase and cytochrome P450 were related to hepatocellular volume (in milliliters), no significant difference between the three groups was apparent. We conclude that reduced aminopyrine N-demethylation in progressed cirrhosis is mainly due to a loss of liver cell volume. The function per liver cell volume remains constant, however, thus favoring the intact cell hypothesis for the handling of slowly metabolized compounds such as aminopyrine.

Effects of chronic treatment with amiodarone on hepatic demethylation and cytochrome P450

The effect of chronic treatment with amiodarone on hepatic oxidative metabolism using an in-vivo [14C]aminopyrine breath test and on hepatic cytochrome P450 was examined in Wistar rats. Aminopyrine demethylation was significantly impaired but returned to pretreatment values following amiodarone for 4 weeks. In contrast the levels of cytochrome P450 were significantly depressed during treatment and at 4 weeks following treatment. While an inhibitory effect on oxidative metabolism may explain the reported drug interactions with amiodarone, the discrepancy between its in-vivo effects and cytochrome P450 levels may suggest the development of 'compensatory' extra-hepatic site of drug metabolism.

Metabolic activation of the tricyclic antidepressant amineptine--II. Protective role of glutathione against in vitro and in vivo covalent binding

Incubation of [11-14C]amineptine (1 mM) with an NADPH-generating system and hamster liver microsomes resulted in the in vitro covalent binding of an amineptine metabolite to microsomal proteins; this binding was decreased by 41-71% in the presence of cysteine, lysine, glycine or glutathione (0.5 mM). An inverse relationship was found between the concentration of glutathione in the incubation mixture (0.25-4 mM) and the extent of covalent binding in vitro, which became undetectable at concentrations of glutathione of 2 mM and higher. Administration of [11-14C]amineptine (300 mg/kg-1 i.p.) to hamsters pretreated with phorone (500 mg/kg i.p.) resulted in the in vivo covalent binding of an amineptine metabolite to hepatic proteins. This binding was increased by phenobarbital-pretreatment and decreased by piperonyl butoxide-pretreatment. After various doses of phorone (150-500 mg/kg), an inverse relationship was found between hepatic glutathione content and in vivo covalent binding. Administration of amineptine alone (300 mg/kg i.p.) depleted hepatic glutathione by 16% only; in these animals, in vivo covalent binding was undetectable from background. Amineptine (300 mg/kg i.p.) did not produce hepatic necrosis, even in hamsters pretreated with phorone and/or phenobarbital. We conclude that physiologic concentrations of glutathione essentially prevent the in vivo covalent binding of an amineptine metabolite to hepatic proteins, and that this binding does not produce liver cell necrosis in hamsters.

Metabolic activation of the tricyclic antidepressant amineptine--I. Cytochrome P-450-mediated in vitro covalent binding

Incubation of [14C]amineptine (1 mM) with hamster liver microsomes resulted in the irreversible binding of an amineptine metabolite to microsomal proteins. Covalent binding measured in the presence of various concentrations of amineptine (0.0625-1 mM) followed Michaelis-Menten kinetics. Pretreatment with phenobarbital increased not only the Vmax, but also the Km, for this binding. Covalent binding required NADPH and molecular oxygen and was decreased when the incubation was made in the presence of inhibitors of cytochrome P-450 such as piperonyl butoxide (4 mM), SKF 525-A (4 mM) or carbon monoxide (80:20 CO-O2 atmosphere). In contrast, binding was increased when microsomes from untreated hamsters were incubated in the presence of 0.5 mM 1,1,1-trichloropropene 2,3-oxide, an inhibitor of epoxide hydrolase. Metabolic activation also occurred in kidney microsomes. In vitro covalent binding to kidney microsomal proteins required NADPH and was decreased by piperonyl butoxide (4 mM) but was not increased by pretreatment with phenobarbital. We conclude that amineptine is activated by hamster liver and kidney microsomes into a chemically reactive metabolite that covalently binds to microsomal proteins.

Relation between renal and hepatic excretion of drugs: III. Comparison of various methods reducing the renal or hepatic excretory capacity of rats

In previous investigations bilateral nephrectomy (NX) and bile duct ligation (DL) were used to interrupt the renal or biliary excretion route, respectively. But competent doubt arose concerning the comparability of both interferences. In the case of DL the liver could influence the possible compensatory increase of renal excretion capacity; after removal of both kidneys such feedback on the liver is impossible. Therefore the corresponding operations were tested: bilateral ureter obstruction (UO) and so-called functional hepatectomy (fHX) caused by ligation of the porta hepatis. The time courses of a compensatory intensification of the excretory function of liver or kidney have been demonstrated. The following general conclusions can be drawn: fHX is characterized by some drawbacks because of its severe negative systemic effects. Thus DL should be preferred because the compensatory renal excretion capacity can be investigated without a significant reduction of the animal's vital forces. In contrast, NX seems to be the method of choice interrupting renal excretion. It is possible to remove both kidneys without a disturbance of other organ functions and the unpredictable effects of the hydronephrotic kidneys after UO on the whole organism are excluded. At least it is optimal to perform clearance studies approximately 24 h after both NX/UO or DL, because already at this time the phenomena of compensation have become maximal.