Liver size and indices of drug metabolism in alcoholics

Summary The role of liver size in drug metabolism was investigated in 34 chronic alcoholics and 28 controls by comparing antipyrine half-life with biopsy content and total amount of hepatic cytochrome P-450 (P-450) and liver weight. Liver size was significantly greater in alcoholics than in controls. Total P-450 was increased and antipyrine metabolism was enhanced in alcoholics with normal histology of the liver. In subjects with alcoholic hepatitis or cirrhosis, the antipyrine half-life was prolonged and P-450 was decreased. Alcoholics with fatty liver had a reduced P-450 content, but the total amount of P-450 and the antipyrine half-life were normal. The results demonstrate in alcoholics that an enlarged liver of normal histological appearance is associated with enhanced drug metabolism. In subjects with fatty liver the drug metabolizing capacity per unit weight of liver is often impaired, but the increase in liver size leads to undisturbed total oxidizing capacity and normal in vivo metabolism. In alcoholic hepatitis drug metabolism is impaired in spite of hepatomegaly. In cirrhosis the enlargement of the liver appears to compensate for the decreased P-450 content resulting in only slightly decreased total P-450, and the severely impaired in vivo drug metabolism may be due to derangement of blood flow.     

Hepatic blood flow and drug metabolism in patients on enzyme-inducing anticonvulsants

Summary Liver blood flow and indices of hepatic drug metabolism (antipyrine elimination rate and cytochrome P-450 concentration in liver biopsy specimens) were studied in 19 epileptics on long-term anticonvulsant treatment, and in 18 controls. The size of the liver and the total estimated liver blood flow were greater in the epileptics than in the controls, whereas the relative liver blood flow (per unit weight of the liver) was not significantly different. The epileptics had higher cytochrome P-450 levels and they eliminated antipyrine faster than the controls. It was concluded that long-term ingestion of enzyme-inducing anticonvulsants is associated with an increase in the total hepatic blood flow in parallel with the increase in liver size, and not as an independent phenomenon. Since the relative perfusion rate of the hepatocytes was unchanged, the enhanced activity of drug metabolizing enzymes is presumed to be mainly responsible for the increased drug clearance observed in epileptic subjects.     

Measurement of hepatic drug-metabolizing enzyme activity in man

Summary Three parameters of hepatic drug metabolism, cytochrome P-450 (P-450) content, antipyrine metabolism and urinary excretion of glucaric acid (GA) were investigated in 161 patients who underwent diagnostic liver needle biopsy. P-450 and antipyrine metabolism, but not GA were related to histological changes in liver. All the parameters were significantly increased in subjects treated with enzyme-inducing drugs, the extent of induction being related to alterations in liver histology. The largest responses were seen in subjects with an intact liver and the smallest in those with hepatitis or cirrhosis. Therapy with inducers partly compensated for the impairement in drug metabolism caused by the disease process; thus, some patients with altered liver had normal values in the tests if they had been treated with inducers. There were significant correlations between in vivo and in vitro parameters of drug metabolism, but in the interpretation of data selection of the material and the parameters influenced the results. Thus, the antipyrine plasma clearance rate was directly related to P-450 and GA values, whereas the correlation between the latter and the drug half-life was non-linear. Also, comparison of selected groups of patients resulted in better correlations between the indices of drug metabolism than in the entire series. The results demonstrate that the overall picture of hepatic drug metabolism in man is largely determined by histological changes in the liver and by exposure to drugs, which are reflected differently in various assays of hepatic drug metabolism. Quantitative evaluation of these factors, and selection of the appropriate assay method, seem to be of importance in investigating hepatic drug metabolism in man.     

Histological changes in the liver and indices of drug metabolism in alcoholics

Summary The drug metabolizing capacity of the liver was investigated in 27 consecutive alcoholics by comparison of in vivo (antipyrine kinetics) and in vitro (cytochrome P-450) indices of drug metabolism with quantitative histological determinations of fat, trabeculae and non-fatty parenchyma in liver biopsies, and with biochemical liver function tests. The reduced amount of hepatic parenchyma in the biopsies was related to diminished drug metabolizing capacity, both in vivo and in vitro. The accumulation of fat alone did not significantly alter the kinetics of antipyrine, although it was associated with reduced cytochrome P-450 content. The replacement of parenchyma by fibrous tissue resulted in a decrease both in antipyrine clearance rate and cytochrome P-450 content. There was a logarithmic correlation between the kinetic parameters of antipyrine and cytochrome P-450 in the entire series, whereas a linear relationship was found in the alcoholic subjects in the various diagnostic groups. A non-linear relationship was also found between biochemical liver function tests and the in vivo and in vitro indices of drug metabolism. The results demonstrate that drug metabolizing capacity in alcoholics is related to ethanol-induced changes in the liver. quantitative evaluation of hepatic parenchymal changes, together with tests of the functional capacity of the liver, might be of significance value in predicting the ability of alcoholics to metabolize drugs.     

Liver size and indices of drug metabolism in epileptics.

1 The relationship between liver size and in vivo (antipyrine kinetics) and in vitro (cytochrome P-450) drug metabolism was investigated in twenty-one epileptics on long-term anticonvulsant therapy and in controls. 2 The epileptics exhibited significant enlargement of the liver and enhancement of drug metabolism compared to the controls. 3 Liver size correlated to antipyrine kinetics only in controls. Concentration of cytochrome P-450 in liver biopsy specimens correlated with liver size neither in controls nor in epileptics. 4 The total hepatic cytochrome P-450, estimated on the basis of liver weight and cytochrome P-450 concentration of biopsy samples, correlated linearly with antipyrine kinetics, except in patients with the most severely disturbed liver architecture. 5 Measurement of liver size is essential when comparing in vivo and in vitro drug metabolism, but the changes in liver histology are also of great importance.     

Plasma high-density lipoproteins and hepatic microsomal enzyme induction

Summary The relationship between high-density lipoproteins (HDL) in plasma and hepatic structure and microsomal function has been investigated in 54 patients undergoing diagnostic liver biopsy. Plasma HDL cholesterol and major apoproteins were correlated with hepatic histology and microsomal enzyme activity assessed directly as liver cytochrome P-450 concentration and indirectly by plasma antipyrine clearance rate. HDL cholesterol, the concentrations of apoproteins A-I and A-II, the HDL cholesterol/total cholesterol ratio and cytochrome P-450 were low in subjects with moderate or severe hepatic fatty infiltration or cirrhosis when compared with the values for subjects with a normal liver. HDL cholesterol and apoprotein A-I and the HDL cholesterol/total cholesterol ratio were directly proportional to the amount of non-fatty parenchyma in the livers. Subjects with a normal liver undergoing treatment with enzyme-inducing drugs, such as phenytoin, phenobarbital and primidone, had higher HDL cholesterol, apoproteins A-I and A-II, HDL cholesterol/total cholesterol ratio, cytochrome P-450 and antipyrine clearance rate than subjects not receiving such therapy. Treatment with inducers appeared to have compensated for the effect of liver disease in lowering plasma HDL. In the entire population, and also in subjects not taking inducing drugs, when considered separately, plasma HDL cholesterol, apoproteins A-I and A-II and the HDL cholesterol/total cholesterol ratio were significantly correlated with cytochrome P-450 concentration. In subjects on enzyme inducers, HDL cholesterol and apoprotein A-I levels and the HDL cholesterol/total cholesterol ratio were proportional to the magnitude of the induction. Serum triglycerides were inversely proportional to the measures of liver microsomal enzyme activity. The lipoprotein pattern, high HDL cholesterol and apoproteins A-I and A-II, and high HDL cholesterol/total cholesterol ratio that accompany microsomal induction are characterized by a reduced risk of atherosclerotic vascular disease and a prolonged expectation of life. The plasma changes presumably reflect the effect of enzyme inducers, such as phenytoin and phenobarbital on hepatic lipids and proteins.The results have been presented at the annual meetings of the American Society for Clinical Pharmacology and Therapeutics, Kansas City, Missouri, 21–23 March 1979 [24] and the Scandinavian Society for Atherosclerosis Research, Turku, Finland, 31 August-1 September 1979 [23]     

Liver size in evaluating drug metabolizing capacity in man.

Liver size, cytochrome P-450 (P-450) concentration in liver biopsy specimens and antipyrine kinetics were studied in 112 consecutive patients undergoing diagnostic liver biopsy. Compared to subjects with normal parenchyma, those with slight or severe parenchymal alterations had enlarged livers with low P-450 concentration and slow antipyrine elimination. In the normal group, the mean P-450 concentration (+/- 1 SD) was 11.10 +/- 2.14 nmol/g liver tissue and the total amount (estimated liver weight g X P-450 concentration nmol/g) 16.06 +/- 3.29 mumol. Previous therapy with enzyme inducing drugs was associated with enlarged liver in subjects with normal histological findings and with fast antipyrine elimination and high P-450 in all groups. Antipyrine elimination rate correlated with liver weight only in subjects with normal parenchyma. The total amount of P-450 was generally more closely related to its concentration than to the estimated liver weight, although in many individual cases a large liver was able to compensate a low P-450 concentration so that the total P-450 was at the normal level. Despite normal or high total P-450, in vivo drug metabolism was impaired in subjects with altered parenchyma, suggesting that other factors were limiting antipyrine elimination in liver disease.     

Roles of hepatic blood flow and enzyme activity in the kinetics of propranolol and sotalol.

1 The roles of the hepatic blood flow and the drug oxidizing enzyme system in eliminating oral propranolol and sotalol were studied in twelve subjects with biopsy proven liver parenchymal disease. 2 The apparent plasma clearance of propranolol was closely related both to the in vivo (antipyrine test) and in vitro (cytochrome P-450) indices of the activity of the hepatic mixed function oxidase system. 3 Propranolol clearance had also a clear relationship to the estimated liver blood flow. Altered flow was, however, suggested to be a minor factor when compared with changes in the enzyme system. 4 The elimination rate of sotalol had no correlation to the indices of hepatic drug metabolism or to the estimated liver blood flow. 5 It is concluded that both the deteriorated sinusoidal perfusion and the decreased mass of drug metabolizing enzymes may be responsible for the impaired elimination of oral propranolol in subjects with parenchymal liver disease.     

Influence of short-term water deprivation on antipyrine disposition

The effects of acute (96 h) water deprivation on the disposition kinetics of antipyrine and hepatic cytochrome P-450 content were investigated in male rats. The disposition kinetics of antipyrine in rats deprived of water for 96 h was altered significantly: the total body clearance and steady-state volume of distribution decreased by 27.1 and 22.4%, respectively, as compared to control rats. There was no significant change in the disposition rate constant as a result of simultaneous changes in the volume of distribution and clearance. There was a 51.4% decrease in the hepatic cytochrome P-450 content in water-deprived rats. These results suggest that the pharmacokinetic changes observed in acute water deprivation with a model drug, antipyrine, are related to a decrease in total body water and to a reduced amount and/or activity of the hepatic microsomal oxidative enzymes.     

Effects of erythromycin on hepatic drug-metabolizing enzymes in humans

In rats, erythromycin has been shown to induce microsomal enzymes and to promote its own transformation into a metabolite which forms an inactive complex with reduced cytochrome P-450. To determine whether similar effects also occur in humans, we studied hepatic microsomal enzymes from six untreated patients and six patients treated with erythromycin propionate, 2 g per os daily for 7 days In the treated patients, NADPH-cytochrome c reductase activity was increased; the total cytochrome P-450 concn was also increased but part of the total cytochrome P-450 was complexed by an erythromycin metabolite. The concn of uncomplexed (active) cytochrome P-450 was not significantly modified and the activity of hexobarbital hydroxylase remained unchanged. We also measured the clearance of antipyrine in six other patients; this clearance was not significantly decreased when measured again on the seventh day of the erythromycin propionate treatment. We conclude that the administration of erythromycin propionate induces microsomal enzymes and results in the formation of an inactive cytochrome P-450-metabolite complex in humans. However, the concn of uncomplexed (active) cytochrome P-450 and tests for in vitro and in vivo drug metabolism were not significantly modified.     

Formation of an inactive cytochrome P-450 Fe(II)-metabolite complex after administration of troleandomycin in humans

In rats, it has been shown that troleandomycin induces its own transformation into a metabolite forming an inactive complex with reduced cytochrome P-450. To determine whether similar effects occur in humans, we studied hepatic microsomes from 6 untreated patients and 6 patients treated with troleandomycin, 2 g per os daily for 7 days. In the treated patients, NADPH-cytochrome c reductase activity was increased by 48%; total cytochrome P-450 concentration was also increased, but 33% of total cytochrome P-450 was complexed by a troleandomycin metabolite. The cytochrome P-450 Fe(II)-metabolite complex exhibited properties identical to those of the inactive complex formed in rats: it exhibited a Soret peak at 456 nm, was unable to bind CO, and was destroyed by addition of 50 μM potassium ferrciyanide.We also measured the clearance of antipyrine in 6 other subjects. This clearance was decreased by 45% when measured again on the seventh day of the troleandomycin treatment. We conclude that repeated administration of troleandomycin induces microsomal enzymes, produces an inactive cytochrome P-450 Fe(II)-metabolite complex, and decreases the clearance of antipyrine in humans.     

Drug metabolism in man: in vivo and in vitro correlations.

In man the liver drug metabolizing ability may be determined by assaying drug kinetics after its administration or by measuring activity of drug metabolizing enzymes from liver biopsies. Little is known about the relationship between these parameters. We investigated the problem by determining in vivo (antipyrine kinetics) and in vitro (cytochrome P-450) indices of drug metabolism in 150 consecutive patients with diagnostic liver biopsy. In patients with normal liver histology cytochrome P-450 content ranged 10.3 umole/g and the half-life 9.5 hrs. In general, alterations in liver histology were related to the changes in drug metabolism; the patients with severe changes had prolonged half-life and low cytochrome P-450, whereas the changes in those with slight parenchymal alterations were less pronounced. The relationship between in vivo and in vitro drug metabolism was non-linear in the whole material, and linear when comparing severe ill patients with controls or in subjects with closely equal liver histology. The results emphasize the importance of evaluating the liver histology when investigating in vivo and in vitro drug metabolism in man.     

Correlations between cytochrome P-450 and oxidative metabolism of benzo[a]pyrene and 7-ethoxycoumarin in human liver in vitro and antipyrine elimination in vivo

Cytochrome P-450 content was correlated to aryl hydrocarbon hydroxylase and 7-ethoxycoumarin O-de-ethylase activities in human liver biopsy samples in vitro. Antipyrine half-life and clearance were measured in the same patients in vivo. The results were compared with data obtained in rat liver in vitro. The correlation of cytochrome P-450 content with aryl hydrocarbon hydroxylase activity in human liver biopsy samples was relatively good (r = 0.75, p < 0.001), but that with 7-ethoxycoumarin O-de-ethylase activity was much poorer (r = 0.42, p < 0.001). The good correlation between cytochrome P-450 content and aryl hydrocarbon hydroxylase activity in biopsy samples from patients with widely varying hepatic disease processes, exposure to inducers, history of cigarette smoking, etc., is in contrast with the data obtained in the rat, where the corresponding correlation in a population treated with different inducers and inhibitors was rather poor (r = 0.37, p < 0.01). This poor correlation was caused mainly by the nonequal effects of polycyclic aromatic hydrocarbons on cytochrome P-450 and aryl hydrocarbon hydroxylase. Cigarette smoking was not found to induce human liver drug or carcinogen metabolism. Aryl hydrocarbon hydroxylase activity in vitro and antipyrine half-life or clearance in vivo were correlated (r = 0.36, p < 0.01 and r = 0.35, p < 0.01, respectively), indicating a weak, but statistically significant association between these parameters. This study suggests that correlations between in vitro and in vivo measurements of drug metabolism are not strong enough for the tests to be used as predictive tests in experimental or clinical research.     

The effect of some benzimidazoles on the disposition of antipyrine and tolbutamide from the rat isolated perfused liver

The anthelmintic benzimidazoles, mebendazole, albendazole and flubendazole have been screened for any propensity to alter the disposition of antipyrine and tolbutamide in the rat isolated perfused liver preparation. The benzimidazoles were added as a 2.5 mg bolus dose into the perfusate reservoir 5 min before the administration of either antipyrine or tolbutamide. Neither mebendazole or albendazole produced any significant effect on the pharmacokinetics of either of the substrate drugs. In contrast, flubendazole significantly decreased the clearance of antipyrine (by 40%) indicating inhibition of mixed function oxidase activity. However, flubendazole did not alter the disposition of tolbutamide. The results suggest that not all benzimidazoles inhibit hepatic drug metabolizing enzymes and that different forms of cytochrome P-450 are involved in the metabolism of antipyrine and tolbutamide.     

A model of cytochrome P-450-centered hepatic dysfunction in drug metabolism induced by cobalt-protoporphyrin administration

Cobalt-protoporphyrin treatment disrupts cytochrome P-450-centered drug metabolism and is known to decrease significantly the cytochrome P-450 content of the liver. This study assesses further the correlations between biochemical and functional changes induced by Co-protoporphyrin. Specifically, it confirmed the fall in cytochrome P-450 levels in liver and demonstrated that both NADPH-cytochrome P-450 reductase and NADH-cytochrome b5 reductase activities decreased in a dose-dependent manner, albeit to a lesser degree, upon Co-protoporphyrin administration. Furthermore, plasma clearance of the marker drug aminopyrine fell off abruptly with a minimal decrease in cytochrome P-450 content, and then monotonically with its further depletion. Both aminopyrine and caffeine demethylation, as measured by the amount of radiolabeled CO2 exhaled, also decreased with diminishing cytochrome P-450 content. With aminopyrine the decrease was abrupt but with caffeine biphasic, consistent with preferential isozyme depletion. The drop in oxidative drug metabolism measured by these two in vivo techniques occurred in the absence of organellar damage to hepatocytes, as observed by electron microscopy. In vitro studies of aminopyrine metabolism in microsomes prepared from rats with and without Co-protoporphyrin injection proved to be consistent with the in vivo studies. Moreover aminopyrine Vmax decreased and Km increased with decreasing cytochrome P-450 content, suggesting preferential isozyme depletion. Furthermore, the changes in aminopyrine intrinsic clearance predicted by the in vitro Vmax and Km values agreed with those measured by in vivo plasma clearance. Taken together, these data suggest that Co-protoporphyrin treatment can be used to produce a model of altered cytochrome P-450-centered drug metabolism, as measured consistently by several techniques. However, this model appears to be more complex than one involving nonspecific depletion of cytochrome P-450 alone, and may be influenced also by concomitant changes in the electron transport chain or other aspects of hepatic metabolism.     

Effects of chronic parenteral carbohydrate administration on hepatic drug metabolism in the rat.

Effects of chronic parenteral carbohydrate administration on hepatic microsomal enzyme activity were studied in the rat. Intraperitoneal injections of either glucose or fructose (2.88 g daily for 7 days) significantly decreased hepatic cytochrome P-450 content and ethylmorphine N-demethylase and aniline hydroxylase activities. By the 5th day, cytochrome P-450 content decreased to 70-76% and ethylmorphine N-demethylase activity to 66-69% of control values. Aniline hydroxylase activity was not significantly altered until the 7th day, by which time it was 77-79% of control values. In vivo assessment of hepatic drug-metabolizing capacity using antipyrine as a test drug confirmed these decreases observed in vitro. Two major conclusions of these experiments are that such variables as time and dose of carbohydrate administration can affect the magnitude of the changes produced and that each parameter measured exhibited a distinctive pattern of change with time. Chronic carbohydrate administration produced hepatic fatty infiltration and glycogen depletion. Since all groups received identical amounts of specific nutrients, fatty infiltration was probably due to increased lipogenesis with decreased hepatic oxidative metabolism of fat. During these experiments neither hypoinsulinemia nor increased levels of cyclic AMP were observed. The molecular mechanisms responsible for hepatic glycogen depletion and decreased MFO activities remain to be established.     

Diabetes and elimination of antipyrine in man: an analysis of 298 patients classified by type of diabetes,age, sex,duration of disease and liver involvement

Effects of diabetes on hepatic drug metabolism in man has not yet been adequately clarified. Two hundred ninety-eight diabetic patients, classified by type of the disease, age, gender, duration of therapy and liver involvement, were investigated. The antipyrine plasma clearance rate and cytochrome P450 content determinations in liver biopsies of subjects with diagnostic liver biopsy were used as indices of hepatic drug metabolising capacity. Drug metabolism was reduced as a function of age. Antipyrine elimination rate was dependent on the type of diabetes (type 1 versus type 2) and gender. Untreated type 1 patients eliminated antipyrine rapidly and insulin treatment normalised antipyrine elimination (clearance rates 89.5 +/- 20.3 versus 58.8 +/- 17.2 ml/min.; P<0.001). Males aged 16-59 years, but not over 60, who responded insufficiently to insulin therapy, had a rapid antipyrine elimination, which could be normalised by readjustment of insulin administration. Women with insufficient glucose control on insulin therapy had antipyrine elimination rate comparable to controls. Among type 2 diabetic patients, women metabolised antipyrine normally, but men over 40 years of age showed a reduced antipyrine metabolism. In conclusion: Drug metabolism in diabetes is affected by the type of disease, therapy and its effectiveness, and age and gender of the patients. These factors should be taken into account when evaluating overall drug metabolism in diabetic patients. This is especially important when investigating pharmacokinetics of new drugs for diabetic patients at different phases of the disease.     

Theophylline-rifampicin interaction: non-selective induction of theophylline metabolic pathways.

The effect of rifampicin pre-treatment (600 mg daily for 6 days) on theophylline disposition at steady state was investigated in six healthy males. Following rifampicin treatment total plasma clearance of theophylline increased by 82%. Theophylline clearance through each metabolic pathway was increased, 1-demethylation by (116 +/- 34%) (mean +/- s.e. mean), 3-demethylation by (91 +/- 16%) and 8-oxidation by (81 +/- 17%). Renal clearance of unchanged drug was not altered. Previous studies have suggested that two forms of cytochrome P-450 are involved in theophylline metabolism, one mediating the N-demethylations and the other 8-oxidation. Thus, unlike the selective inductive effect of rifampicin on antipyrine metabolic pathways, rifampicin does not differentially affect those forms of cytochrome P-450 involved in theophylline metabolism. The extent to which theophylline metabolism is induced by rifampicin is likely to have important clinical consequences.     

Diabetes and Elimination of Antipyrine in Man: An Analysis of 298 Patients Classified by Type of Diabetes,Age, Sex,Duration of Disease and Liver Involvement*

Abstract: Effects of diabetes on hepatic drug metabolism in man has not yet been adequately clarified. Two hundred ninety‐eight diabetic patients, classified by type of the disease, age, gender, duration of therapy and liver involvement, were investigated. The antipyrine plasma clearance rate and cytochrome P450 content determinations in liver biopsies of subjects with diagnostic liver biopsy were used as indices of hepatic drug metabolising capacity. Drug metabolism was reduced as a function of age. Antipyrine elimination rate was dependent on the type of diabetes (type 1 versus type 2) and gender. Untreated type 1 patients eliminated antipyrine rapidly and insulin treatment normalised antipyrine elimination (clearance rates 89.5±20.3 versus 58.8±17.2 ml/min.; P<0.001). Males aged 16–59 years, but not over 60, who responded insufficiently to insulin therapy, had a rapid antipyrine elimination, which could be normalised by readjustment of insulin administration. Women with insufficient glucose control on insulin therapy had antipyrine elimination rate comparable to controls. Among type 2 diabetic patients, women metabolised antipyrine normally, but men over 40 years of age showed a reduced antipyrine metabolism. In conclusion: Drug metabolism in diabetes is affected by the type of disease, therapy and its effectiveness, and age and gender of the patients. These factors should be taken into account when evaluating overall drug metabolism in diabetic patients. This is especially important when investigating pharmacokinetics of new drugs for diabetic patients at different phases of the disease.     

Drug metabolism in epileptics: in vivo and in vitro correlations.

1. The effect of inducing drug therapy on the relationship between in vitro (cytochrome P-450 content) and in vivo (antipyrine kinetics) was investigated by comparing eleven consecutively treated epileptics with two groups of controls, eleven subjects with normal liver histology and eleven disease matched non-epileptics, all underwent diagnostice liver biopsy. 2. The epileptics had significantly higher cytochrom P-450 level in biopsies and they also metabolized antipyrine faster than the controls. 3. Decrease in antipyrine half-life in epileptics was related with alterations in liver histology, whereas the level of cytochrome P-450 was not. 4. There was a linear relationship between these two indices of enzyme induction when regressed on logarithmic data.