Angiotensin-converting enzyme (ACE)-inhibition in cirrhosis. Pharmacokinetics and dynamics of the ACE-inhibitor cilazapril (Ro 31-2848)

Simultaneously Predicting the Pharmacokinetics of CES1-Metabolized Drugs and Their Metabolites Using Physiologically Based Pharmacokinetic Model in Cirrhosis Subjects

Hepatic carboxylesterase 1 (CES1) metabolizes numerous prodrugs into active ingredients or direct-acting drugs into inactive metabolites. We aimed to develop a semi-physiologically based pharmacokinetic (semi-PBPK) model to simultaneously predict the pharmacokinetics of CES1 substrates and their active metabolites in liver cirrhosis (LC) patients. Six prodrugs (enalapril, benazepril, cilazapril, temocapril, perindopril and oseltamivir) and three direct-acting drugs (flumazenil, pethidine and remimazolam) were selected. Parameters such as organ blood flows, plasma-binding protein concentrations, functional liver volume, hepatic enzymatic activity, glomerular filtration rate (GFR) and gastrointestinal transit rate were integrated into the simulation. The pharmacokinetic profiles of these drugs and their active metabolites were simulated for 1000 virtual individuals. The developed semi-PBPK model, after validation in healthy individuals, was extrapolated to LC patients. Most of the observations fell within the 5th and 95th percentiles of simulations from 1000 virtual patients. The estimated AUC and Cmax were within 0.5-2-fold of the observed values. The sensitivity analysis showed that the decreased plasma exposure of active metabolites due to the decreased CES1 was partly attenuated by the decreased GFR. Conclusion: The developed PBPK model successfully predicted the pharmacokinetics of CES1 substrates and their metabolites in healthy individuals and LC patients, facilitating tailored dosing of CES1 substrates in LC patients.

Isoflavones enhance pharmacokinetic exposure of active lovastatin acid via the upregulation of carboxylesterase in high-fat diet mice after oral administration of Xuezhikang capsules

Xuezhikang capsule (XZK) is a traditional Chinese medicine that contains lovastatin (Lv) for hyperlipidemia treatment, although it has fewer side effects than Lv. However, the pharmacokinetic mechanisms contributing to its distinct efficacy and low side effects are unclear. Mice were fed a high-fat diet (HFD) for 6 weeks to induce hyperlipidemia. We first conducted the pharmacokinetic studies in HFD mice following oral administration of Lv (10 mg/kg, i.g.) and found that HFD remarkably decreased the active form of Lv (the lovastatin acid, LvA) exposure in the circulation system, especially in the targeting organ liver, with a declined conversion from Lv to LvA, whereas the Lv (responsible for myotoxicity) exposure in muscle markedly increased. Then we compared the pharmacokinetic profiles of Lv in HFD mice after the oral administration of XZK (1200 mg/kg, i.g.) or an equivalent dose of Lv (10 mg/kg, i.g.). A higher exposure of LvA and lower exposure of Lv were observed after XZK administration, suggesting a pharmacokinetic interaction of some ingredients in XZK. Further studies revealed that HFD promoted the inflammation and inhibited carboxylesterase (CES) activities in the intestine and the liver, thus contributing to the lower transformation of Lv into LvA. In contrast, XZK inhibited the inflammation and upregulated CES in the intestine and the liver. Finally, we evaluated the effects of monacolins and phytosterols, the fractional extracts of isoflavones, on inflammatory LS174T or HepG2 cells, which showed that isoflavones inhibited inflammation, upregulated CES, and markedly enhanced the conversion of Lv into LvA. For the first time, we provide evidence that isoflavones and Lv in XZK act in concert to enhance the efficacy and reduce the side effects of Lv.

Decreased potency of fimasartan in liver cirrhosis was quantified using mixed-effects analysis

Fimasartan is a nonpeptide angiotensin II receptor blocker. In a previous study that compared the pharmacokinetics (PK) of fimasartan between patients with hepatic impairment (cirrhosis) and healthy subjects, the exposure to fimasartan was found to be higher in patients, but the decrease of blood pressure (BP) was not clinically significant in those with moderate hepatic impairment. The aims of this study were to develop a population PK-pharmacodynamic (PD) model of fimasartan and to evaluate the effect of hepatic function on BP reduction by fimasartan using previously published data. A 2-compartment linear model with mixed zero-order absorption followed by first-order absorption with a lag time adequately described fimasartan PK, and the effect of fimasartan on BP changes was well explained by the inhibitory sigmoid function in the turnover PK-PD model overlaid with a model of circadian rhythm (NONMEM version 7.2). According to our PD model, the lower BP responses in hepatic impairment were the result of the increased fimasartan EC₅₀ in patients, rather than from a saturation of effect. This is congruent with the reported pathophysiological change of increased plasma ACE and renin activity in hepatic cirrhosis.

The role of human carboxylesterases in drug metabolism: have we overlooked their importance?

Carboxylesterases are a multigene family of mammalian enzymes widely distributed throughout the body that catalyze the hydrolysis of esters, amides, thioesters, and carbamates. In humans, two carboxylesterases, hCE1 and hCE2, are important mediators of drug metabolism. Both are expressed in the liver, but hCE1 greatly exceeds hCE2. In the intestine, only hCE2 is present and highly expressed. The most common drug substrates of these enzymes are ester prodrugs specifically designed to enhance oral bioavailability by hydrolysis to the active carboxylic acid after absorption from the gastrointestinal tract. Carboxylesterases also play an important role in the hydrolysis of some drugs to inactive metabolites. It has been widely believed that drugs undergoing hydrolysis by hCE1 and hCE2 are not subject to clinically significant alterations in their disposition, but evidence exists that genetic polymorphisms, drug-drug interactions, drug-disease interactions and other factors are important determinants of the variability in the therapeutic response to carboxylesterase-substrate drugs. The implications for drug therapy are far-reaching, as substrate drugs include numerous examples from widely prescribed therapeutic classes. Representative drugs include angiotensin-converting enzyme inhibitors, angiotensin receptor blockers, antiplatelet drugs, statins, antivirals, and central nervous system agents. As research interest increases in the carboxylesterases, evidence is accumulating of their important role in drug metabolism and, therefore, the outcomes of pharmacotherapy.

Impact of Disease States on the Pharmacokinetics and Pharmacodynamics of Angiotensin-Converting Enzyme Inhibitors

The pharmacokinetics and pharmacodynamics of angiotensin-converting enzyme inhibitors (ACE) in elderly patients and patients with renal and hepatic impairment were examined, and a role for an AUC/EC50 ratio to guide dosing was evaluated. A Medline and International Pharmaceutical Abstracts search was used to identify human studies and abstracts. Relevant data were evaluated and summarized. Dosing regimens were compared using an AUC/EC50 ratio. Most studies evaluating ACE inhibitors in renal impairment report a strong linear correlation between creatine clearance and drug elimination. AUC and EC50 values for these drugs in elderly subjects appear similar to younger and hypertensive patients. There is increased AUC in some patients with hepatic impairment. Pharmacodynamic data are conflicting. Prolonged ACE inhibition is evident in renal impairment but not necessarily other disease states. ACE inhibitor dosing for hypertension is reasonable based on pharmacokinetics and EC50 values. Further individualization of therapy may improve outcomes, and using the threshold AUC/EC50 ratio may help guide appropriate dosing.

Lipopolysaccharide down-regulates carbolesterases 1 and 2 and reduces hydrolysis activity in vitro and in vivo via p38MAPK-NF-κB pathway

Carboxylesterases constitute a class of enzymes that hydrolyze drugs containing such functional groups as carboxylic acid ester, amide, and thioester. Hydrolysis of many drugs is reduced in liver diseases such as hepatitis and cirrhosis. In this study, we have demonstrated, in vitro and in vivo, treatment with LPS decreased the expression of HCE1 and HCE2 and the capacity of hydrolytic activity. In HepG2 cells, the decreased expression by LPS occurred at both mRNA and protein levels. Both HCE1 and HCE2 promoters were significantly repressed by LPS, and the repression was comparable with the decrease in HCE1 and HCE2 mRNA, suggesting the transrepression is responsible for suppressed expression. Further study showed that both PDTC, a NF-κB inhibitor, and SB203580, a p38MAPK inhibitor, could abolish the repression of HCE1 and HCE2 mediated by LPS, but U0126, a selective ERK1/2 inhibitor, could not do so, suggesting the repression of HCE1 and HCE2 by LPS through the p38MAPK-NF-κB pathway. In addition, being pretreated with LPS, HepG2 cells altered the cellular responsiveness to ester therapeutic agents, including clopidogrel (hydrolyzed by HCE1) and irinotecan (hydrolyzed by HCE2). The altered cellular responsiveness occurred at low micromolar concentrations, suggesting that suppressed expression of carboxylesterases by LPS has profound pharmacological and toxicological consequences, particularly with those that are hydrolyzed in an isoform-specific manner. This study provides new insight into the understanding of the pharmacological and toxicological effects and the mechanisms for repressing drug metabolism enzymes in inflammation.

Interleukin-6 alters the cellular responsiveness to clopidogrel, irinotecan, and oseltamivir by suppressing the expression of carboxylesterases HCE1 and HCE2

Carboxylesterases constitute a class of enzymes that play important roles in the hydrolytic metabolism of drugs and other xenobiotics. Patients with liver conditions such as cirrhosis show increased secretion of proinflammatory cytokines [e.g., interleukin-6 (IL-6)] and decreased capacity of hydrolysis. In this study, we provide a molecular explanation linking cytokine secretion directly to the decreased capacity of hydrolytic biotransformation. In both primary hepatocytes and HepG2 cells, treatment with IL-6 decreased the expression of human carboxyl-esterases HCE1 and HCE2 by as much as 60%. The decreased expression occurred at both mRNA and protein levels, and it was confirmed by enzymatic assay. In cotransfection experiments, both HCE1 and HCE2 promoters were significantly repressed, and the repression was comparable with the decrease in HCE1 and HCE2 mRNA, suggesting that transrepression is responsible for the suppressed expression. In addition, pretreatment with IL-6 altered the cellular responsiveness in an opposite manner of overexpression of HCE1 and HCE2 toward various ester therapeutic agents (e.g., clopidogrel). Transfection of HCE1, for example, decreased the cytotoxicity induced by antithrombogenic agent clopidogrel, whereas pretreatment with IL-6 increased the cytotoxicity. Such a reversal was observed with other ester drugs, including anticancer agent irinotecan and anti-influenza agent oseltamivir. The altered cellular responsiveness was observed when drugs were assayed at sub- and low-micromolar concentrations, suggesting that suppressed expression of carboxylesterases by IL-6 has profound pharmacological consequences, particularly with those that are hydrolyzed in an isoform-specific manner.

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.