Comparison of in vitro and in vivo biotransformation in patients with liver disease of differing severity

Liver Cirrhosis Affects the Pharmacokinetics of the Six Substrates of the Basel Phenotyping Cocktail Differently

Background

Activities of hepatic cytochrome P450 enzymes (CYPs) are relevant for hepatic clearance of drugs and known to be decreased in patients with liver cirrhosis. Several studies have reported the effect of liver cirrhosis on CYP activity, but the results are partially conflicting and for some CYPs lacking.

Objective

In this study, we aimed to investigate the CYP activity in patients with liver cirrhosis with different Child stages (A-C) using the Basel phenotyping cocktail approach.

Methods

We assessed the pharmacokinetics of the six compounds and their CYP-specific metabolites of the Basel phenotyping cocktail (CYP1A2: caffeine, CYP2B6: efavirenz, CYP2C9: flurbiprofen, CYP2C19: omeprazole, CYP2D6: metoprolol, CYP3A: midazolam) in patients with liver cirrhosis (n = 16 Child A cirrhosis, n = 15 Child B cirrhosis, n = 5 Child C cirrhosis) and matched control subjects (n = 12).

Results

While liver cirrhosis only marginally affected the pharmacokinetics of the low to moderate extraction drugs efavirenz and flurbiprofen, the elimination rate of caffeine was reduced by 51% in patients with Child C cirrhosis. For the moderate to high extraction drugs omeprazole, metoprolol, and midazolam, liver cirrhosis decreased the elimination rate by 75%, 37%, and 60%, respectively, increased exposure, and decreased the apparent systemic clearance (clearance/bioavailability). In patients with Child C cirrhosis, the metabolic ratio (ratio of the area under the plasma concentration–time curve from 0 to 24 h of the metabolite to the parent compound), a marker for CYP activity, decreased by 66%, 47%, 92%, 73%, and 43% for paraxanthine/caffeine (CYP1A2), 8-hydroxyefavirenz/efavirenz (CYP2B6), 5-hydroxyomeprazole/omeprazole (CYP2C19), α-hydroxymetoprolol/metoprolol (CYP2D6), and 1′-hydroxymidazolam/midazolam (CYP3A), respectively. In comparison, the metabolic ratio 4-hydroxyflurbiprofen/flurbiprofen (CYP2C9) remained unchanged.

Conclusions

Liver cirrhosis affects the activity of CYP isoforms differently. This variability must be considered for dose adjustment of drugs in patients with liver cirrhosis.

Clinical Trial Registration

NCT03337945.

Supplementary Information

The online version contains supplementary material available at 10.1007/s40262-022-01119-0.

CREBH determines the severity of sulpyrine-induced fatal shock

Although the pyrazolone derivative sulpyrine is widely used as an antipyretic analgesic drug, side effects, including fatal shock, have been reported. However, the molecular mechanism underlying such a severe side effect is largely unclear. Here, we report that the transcription factor CREBH that is highly expressed in the liver plays an important role in fatal shock induced by sulpyrine in mice. CREBH-deficient mice were resistant to experimental fatal sulpyrine shock. We found that sulpyrine-induced expression of cytochrome P450 2B (CYP2B) family genes, which are involved in sulpyrine metabolism, in the liver was severely impaired in CREBH-deficient mice. Moreover, introduction of CYP2B in CREBH-deficient liver restored susceptibility to sulpyrine. Furthermore, ectopic expression of CREBH up-regulated CYP2B10 promoter activity, and in vivo knockdown of CREBH in wild-type mice conferred a significant resistance to fatal sulpyrine shock. These data demonstrate that CREBH is a positive regulator of CYP2B in response to sulpyrine administration, which possibly results in fatal shock.

Dose adjustment in patients with liver disease

Unfortunately, there is no endogenous marker for hepatic clearance that can be used as a guide for drug dosing. In order to predict the kinetic behaviour of drugs in cirrhotic patients, agents can be grouped according to their extent of hepatic extraction. For drugs with a high hepatic extraction (low bioavailability in healthy subjects), bioavailability increases and hepatic clearance decreases in cirrhotic patients. If such drugs are administered orally to cirrhotic patients, their initial dose has to be reduced according to hepatic extraction. Furthermore, their maintenance dose has to be adapted irrespective of the route of administration, if possible, according to kinetic studies in cirrhotic patients. For drugs with a low hepatic extraction, bioavailability is not affected by liver disease, but hepatic clearance may be affected. For such drugs, only the maintenance dose has to be reduced, according to the estimated decrease in hepatic drug metabolism. For drugs with an intermediate hepatic extraction, initial oral doses should be chosen in the low range of normal in cirrhotic patients and maintenance doses should be reduced as for high extraction drugs. In cholestatic patients, the clearance of drugs with predominant biliary elimination may be impaired. Guidelines for dose reduction in cholestasis exist for many antineoplastic drugs, but are mostly lacking for other drugs with biliary elimination. Dose adaptation of such drugs in cholestatic patients is, therefore, difficult and has to be performed according to pharmacological effect and/or toxicity. Importantly, the dose of drugs with predominant renal elimination may also have to be adapted in patients with liver disease. Cirrhotic patients often have impaired renal function, despite a normal serum creatinine level. In cirrhotic patients, creatinine clearance should, therefore, be measured or estimated to gain a guideline for the dosing of drugs with predominant renal elimination. Since the creatinine clearance tends to overestimate glomerular filtration in cirrhotic patients, the dose of a given drug may still be too high after adaptation to creatinine clearance. Therefore, the clinical monitoring of pharmacological effects and toxicity of such drugs is important. Besides the mentioned kinetic changes, the dynamics of some drugs is also altered in cirrhotic patients. Examples include opiates, benzodiazepines, NSAIDs and diuretics. Such drugs may exhibit unusual adverse effects that clinicians should be aware of for their safe use. However, it is important to realise that the recommendations for dose adaptation remain general and cannot replace accurate clinical monitoring of patients with liver disease treated with critical drugs.

Potential impact of steatosis on cytochrome P450 enzymes of human hepatocytes isolated from fatty liver grafts

Liver grafts discarded for transplantation because of macrosteatosis can constitute a valuable source of human hepatocytes for in vitro metabolic and pharmacotoxicological studies or for therapeutic applications. A condition for using hepatocyte suspensions for these purposes is the preservation of their metabolic competence and, particularly, drug-metabolizing enzymes. A reduction in microsomal cytochrome P450 (P450) activities was observed in fatty livers (>40% steatosis) with respect to normal tissue. Similarly, decreased levels of 7-ethoxycoumarin O-deethylation and testosterone metabolism were observed in human hepatocyte cultures prepared from steatotic liver tissue. To clarify the potential impact of lipid accumulation on human hepatic P450 enzymes, we have used an in vitro model of "cellular steatosis" by incubation of cultured hepatocytes with increasing concentrations (0.25-3 mM) of long-chain free fatty acids (FFA). A dose-dependent accumulation of lipids in the cytosol is induced by FFA mixture. Hepatocytes exposed to 1 mM FFA for 14 h showed lower activity values of CYP1A2, CYP2A6, CYP2B6, CYP2C9, CYP2D6, CYP2E1, and CYP3A4 enzymes than nontreated hepatocytes (about 45-65% reduction). This treatment also produced significant decreases in CYP1A2, CYP2A6, CYP2C9, CYP2D6, CYP2E1, and CYP3A4 mRNA to about 55 to 75% of mRNA levels in control cells. Our results suggest that although human hepatocytes isolated from steatotic liver show reduced P450 activities, they are metabolically competent and can be used for drug metabolism studies.

Evidence for concurrent effects of exposure to environmental cadmium and lead on hepatic CYP2A6 phenotype and renal function biomarkers in nonsmokers

We examined the interrelationships between phenotype of hepatic cytochrome P450 2A6 (CYP2A6), nephropathy, and exposure to cadmium and lead in a group of 118 healthy Thai men and women who had never smoked. Their urinary Cd excretion ranged from 0.05 to 2.36 microg/g creatinine, whereas their urinary Pb excretion ranged from 0.1 to 12 microg/g creatinine. Average age and Cd burden of women and men did not differ. Women, however, on average showed a 46% higher urinary Pb excretion (p < 0.001) and lower zinc status, suggested by lower average serum Zn and urinary Zn excretion compared with those in men. Cd-linked nephropathy was detected in both men and women. However, Pb-linked nephropathy was seen only in women, possibly because of higher Pb burden coupled with lower protective factors, notably of Zn (p < 0.001), in women compared with men. In men, Pb burden showed a negative association with CYP2A6 activity (adjusted beta = -0.29, p = 0.003), whereas Cd burden showed a positive association with CYP2A6 activity (adjusted beta = 0.38, p = 0.001), suggesting opposing effects of Cd and Pb on hepatic CYP2A6 phenotype. The weaker correlation between Cd burden CYP2A6 activity in women despite similarity in Cd burden between men and women is consistent with opposing effects of Pb and Cd on hepatic CYP2A6 phenotypic expression. A positive correlation between Cd-linked nephropathy (urinary N-acetyl-beta-D-glucosaminidase excretion) and CYP2A6 activity in men (r = 0.39, p = 0.002) and women (r = 0.37, p = 0.001) suggests that Cd induction of hepatic CYP2A6 expression and Cd-linked nephropathy occurred simultaneously.

Strategies and molecular probes to investigate the role of cytochrome P450 in drug metabolism: focus on in vitro studies

Drug metabolism is the major determinant of drug clearance and, because of polymorphic or inducible expression of drug-metabolising cytochrome P450s (CYPs), is the factor most frequently responsible for interindividual differences in pharmacokinetics. A number of well characterised CYP substrates and inhibitors have been identified that allow precise measurements of individual CYP isoforms. Their use, alone or in combination, facilitates the phenotype characterisation of hepatocytes in vitro and in vivo. Two procedures are used for in vitro investigation of the metabolic profile of a drug: incubation with microsomes and incubation with metabolically competent cells. The major limitation of microsomes is that they express phase I activities, but only part of phase II activities, and can only be used for short incubation times. When intact cells are used, gene expression, metabolic pathways, cofactors/enzymes and plasma membrane are largely preserved, but fully differentiated cells such as primary cultured hepatocytes need to be used, since hepatoma cell lines have only very low and partial CYP expression. CYP-engineered cells or their microsomes ('supersomes') have made the identification of the CYPs involved in the metabolism of a drug candidate straightforward and easier. Inhibition of CYP is an undesirable feature for a drug candidate, and needs to be addressed by examining whether the drug candidate inhibits the metabolism of other compounds or whether other compounds inhibit the metabolism of the drug candidate. Such experiments can be conducted both with microsomes and in cells. The major limitation of microsomes is that inhibition parameters may not accurately reflect the situation in vivo, since the contribution of drug transport is not considered. The best picture of a potential drug-drug interaction can be obtained in metabolically competent hepatocytes. Screening of CYP inducers cannot be done in microsomes. It requires the use of a cellular system fully capable of transcribing and translating CYP genes, and can be monitored in vitro as an increase in enzyme mRNA or activity. Human hepatocytes in primary culture respond well to enzyme inducers during the first few days; this ability is lost thereafter. Rat hepatocytes are much less stable and soon become unresponsive to inducers. Hepatoma cell lines respond poorly to inducers, although the induction of a few isoenzymes has been reported. Primary cultured hepatocytes are still the unique in vitro model that allows global examination of the inductive potential of a drug.

The effect of sepsis during parenteral nutrition on hepatic microsomal function in rats

STUDY OBJECTIVE

To investigate the effect of sepsis during parenteral nutrition on hepatic cytochrome P450 (CYP) activity in rats.

DESIGN

Prospective, randomized, controlled study.

SETTING

University-based animal research laboratory.

ANIMALS

Twenty adult male Sprague-Dawley rats.

INTERVENTION

The animals were cannulated intravenously and randomized to receive parenteral nutrition (PN), intravenous live Escherichia coli 4 x 10(8) colony-forming units/100 g body weight for 2 consecutive days with PN (PNEC), or chow (CH).

MEASUREMENTS AND MAIN RESULTS

Both PN alone and PNEC resulted in a progressive decline in hepatic CYP concentration compared with CH (0.53 +/- 0.10, 0.41 +/- 0.17, and 0.35 +/- 0.14 nmol/mg microsomal protein, respectively, p < 0.05). Parenteral nutrition alone was associated with a 57% decrease in isoenzyme ethoxycoumarin-O-deethylase activity (ECOD) compared with CH, but sepsis did not further decrease ECOD activity any more than PN alone (0.103 +/- 0.049, 0.044 +/- 0.018, and 0.050 +/- 0.020 nmol/mg microsomal protein/min, respectively, p < 0.05).

CONCLUSION

Hepatic CYP concentration declines with PN and is further decreased when compounded by sepsis. The disproportional decrease in ECOD activity relative to CYP concentration with PN is unchanged by sepsis, indicating a selective alteration in hepatic isoenzymes by PN.

Variation in coumarin 7-hydroxylase activity associated with genetic polymorphism of cytochrome P450 2A6 and the body status of iron stores in adult Thai males and females

The relationships between catalytic activity of cytochrome P450 2A6 (CYP2A6), polymorphism of CYP2A6 gene, gender and levels of body iron stores were analysed in a sample group of 202 apparently healthy Thais, aged 19-47 years. Eleven individuals were found to have high activity of CYP2A6, judged by the relatively large amounts (11.2-14.6 mg) of 7-hydroyxcoumarin (7-OHC) excreted 3 h following administration of 15 mg of coumarin. Ten individuals, however, did not excrete any 7-OHC. Of these 10, four were found to have no CYP2A6 gene (whole gene deletion; CYP2A6*4 allele). The frequency of the CYP2A6 alleles; *1A, *1B and *4 in the whole sample group was 52, 40 and 8% while the frequency of the CYP2A6 gene types; *1A/*1A, *1A/*1B, *1B/*1B, *1A/*4, *1B/*4, *4/*4 was 29, 41, 16, 7, 5 and 2%. Subjects having CYP2A6*1A/*1B gene-type group were found to have higher rates of coumarin 7-hydroxylation compared with those of the CYP2A6*1B/*1B and CYP2A6*1A/*4 gene types. The inter-individual variability in CYP2A6 catalytic activity was therefore attributed in part to the CYP2A6 genetic polymorphism. Variation in CYP2A6 activity in this sample group was not associated with gender but, interestingly, it did show an inverse association with plasma ferritin; an indicator of body iron stores. Higher rates of coumarin 7-hydroxylation were found in individuals with low body iron stores (plasma ferritin < 20 microg/l) compared with subjects having normal body iron store status. Subjects (n = 16) with iron overload (plasma ferritin > 300 microg/l) also tended to have elevated rates of coumarin 7-hydroxylation. These results suggest an increased CYP2A6 expression in subjects who have excessive body iron stores. Further investigations into the underlying factors that may lead to increased expression of CYP2A6 in association with abnormal body iron stores are currently in progress in our laboratory.

Pharmacokinetics of diclofenac sodium in chronic active hepatitis and alcoholic cirrhosis

The objective of this study was to assess the pharmacokinetics of diclofenac sodium and its five metabolites following administration of a 150 mg oral dose to healthy subjects and patients with either chronic active hepatitis of varying morphology or alcoholic cirrhosis. Six healthy subjects, 6 chronic active hepatitis patients, and 6 alcoholic cirrhosis patients were enrolled in this prospective, open-label, parallel study. Blood samples were drawn at 0, 0.25, 0.5, 0.75, 1, 2, 4, 6, 8, 12, 24, 48, 72, 144, 312, and 480 hours, and urine samples were collected for 144 hours after administration of a single oral dose of diclofenac sodium. The mean area under the serum concentration-time curve extrapolated to infinity, oral clearance, half-life, maximal concentration, and time to peak concentration for diclofenac and its metabolites were determined and compared using analysis of variance. Cirrhotics had a mean +/- SD diclofenac AUC value (19,114 +/- 6806 ng.h/ml) significantly different (p < 0.02) from hepatitis patients (6071 +/- 1867 ng.h/ml) and healthy subjects (7008 +/- 2006 ng.h/ml), whereas healthy subjects and hepatitis patients had similar values. Comparable results were found for 4'-hydroxydiclofenac. The AUC values for 3'-hydroxydiclofenac and 3'-hydroxy-4'methoxydiclofeanc were significantly different when healthy subjects were compared to cirrhotics. However, hepatitis subjects were not significantly different from either group. The results indicate that hepatitis does not alter the pharmacokinetics of diclofenac. Alcoholic cirrhosis increased the mean diclofenac AUC approximately three times compared to normal subjects, indicating that one-third of the usual dose in cirrhotics would produce equivalent AUC values in normal subjects and subjects with alcoholic cirrhosis. However, since pharmacodynamic measurements were not made and no increase in untoward or side effects was noted in the alcoholic cirrhosis patients after a single dose, maintenance doses should be titrated to patients response.

Effects of liver disease on pharmacokinetics. An update

Liver disease can modify the kinetics of drugs biotransformed by the liver. This review updates recent developments in this field, with particular emphasis on cytochrome P450 (CYP). CYP is a rapidly expanding area in clinical pharmacology. The information currently available on specific isoforms involved in drug metabolism has increased tremendously over the latest years, but knowledge remains incomplete. Studies on the effects of liver disease on specific isoenzymes of CYP have shown that some isoforms are more susceptible than others to liver disease. A detailed knowledge of the particular isoenzyme involved in the metabolism of a drug and the impact of liver disease on that enzyme can provide a rational basis for dosage adjustment in patients with hepatic impairment. The capacity of the liver to metabolise drugs depends on hepatic blood flow and liver enzyme activity, both of which can be affected by liver disease. In addition, liver failure can influence the binding of a drug to plasma proteins. These changes can occur alone or in combination; when they coexist their effect on drug kinetics is synergistic, not simply additive. The kinetics of drugs with a low hepatic extraction are sensitive to hepatic failure rather than to liver blood flow changes, but drugs having a significant first-pass effect are sensitive to alterations in hepatic blood flow. The drugs examined in this review are: cardiovascular agents (angiotensin converting enzyme inhibitors, angiotensin II receptor antagonists, calcium antagonists, ketanserin, antiarrhythmics and hypolipidaemics), diuretics (torasemide), psychoactive and anticonvulsant agents (benzodiazepines, flumazenil, antidepressants and tiagabine), antiemetics (metoclopramide and serotonin antagonists), antiulcers (acid pump inhibitors), anti-infectives and antiretroviral agents (grepafloxacin, ornidazole, pefloxacin, stavudine and zidovudine), immunosuppressants (cyclosporin and tacrolimus), naltrexone, tolcapone and toremifene. According to the available data, the kinetics of many drugs are altered by liver disease to an extent that requires dosage adjustment; the problem is to quantify the required changes. Obviously, this requires the evaluation of the degree of hepatic impairment. At present there is no satisfactory test that gives a quantitative measure of liver function and its impairment. A critical evaluation of these methods is provided. Guidelines providing a rational basis for dosage adjustment are illustrated. Finally, it is important to consider that liver disease not only affects pharmacokinetics but also pharmacodynamics. This review also examines drugs with altered pharmacodynamics.

Clinical importance of non-genetic and genetic cytochrome P450 function tests in liver disease

Liver disease is associated with reduced metabolic capacity for drugs that are metabolized by oxidative biotransformation. Three cytochrome P450 (P450 or CYP) gene families in liver microsomes (CYP 1, CYP2 and CYP3) appear to be responsible for much of the drug metabolism that takes place. The genetic polymorphism of the CYPs responsible for debrisoquine/ sparteine (CYP2D6) metabolism and S-mephenytoin (CYP2C19) metabolism has been well documented, but information on the impairment of each isoform in liver disease is still limited. There are two types of hepatic P450 function tests. One type consists of non-genetic P450 function tests (CYP1A2, 2A6, 2C9/10, 2E1 and 3A3/4), and probe drugs include caffeine, catalysed by CYP1A2, coumarin by CYP2A6, phenytoin by CYP2C6, chlorzoxazone by CYP2E1, and nifedipine, erythromycin and lidocaine by CYP3A3/4. The second type of genetic P450 function tests (CYP2C19 and CYP2D6) involves probe drugs such as S-mephenytoin, catalysed by CYP2C19, and debrisoquine and sparteine, catalysed by CYP2D6. The metabolism of the probe drugs used in non-genetic P450 function tests in patients with liver disease falls into two categories: reduced (CYP1A2, CYP2C, 2E1 and 3A) and unchanged (CYP2C). In genetic P450 function tests there seems to be a lesser degree of inhibition in poor metabolizers (PMs) than extensive metabolizers (EMs) among patients with liver disease. There have been very few reports on changes in metabolism of the probe drugs used in genetic P450 function tests in liver disease. In this paper the subject is reviewed.