Metabolism of pantoprazole involving conjugation with glutathione in rats

Investigation of Bemethyl Biotransformation Pathways by Combination of LC-MS/HRMS and In Silico Methods

Bemethyl is an actoprotector, an antihypoxant, and a moderate psychostimulant. Even though the therapeutic effectiveness of bemethyl is well documented, there is a gap in knowledge regarding its metabolic products and their quantitative and qualitative characteristics. Since 2018, bemethyl is included to the Monitoring Program of the World Anti-Doping Agency, which highlights the challenge of identifying its urinary metabolites. The objective of the study was to investigate the biotransformation pathways of bemethyl using a combination of liquid chromatography-high-resolution mass spectrometry and in silico studies. Metabolites were analyzed in a 24 h rat urine collected after oral administration of bemethyl at a single dose of 330 mg/kg. The urine samples were prepared for analysis by a procedure developed in the present work and analyzed by high performance liquid chromatography–tandem mass spectrometry. For the first time, nine metabolites of bemethyl with six molecular formulas were identified in rat urine. The most abundant metabolite was a benzimidazole–acetylcysteine conjugate; this biotransformation pathway is associated with the detoxification of xenobiotics. The BioTransformer and GLORY computational tools were used to predict bemethyl metabolites in silico. The molecular docking of bemethyl and its derivatives to the binding site of glutathione S-transferase has revealed the mechanism of bemethyl conjugation with glutathione. The findings will help to understand the pharmacokinetics and pharmacodynamics of actoprotectors and to improve antihypoxant and adaptogenic therapy.

Identification of the New In Vivo Metabolites of Ilaprazole in Rat Plasma after Oral Administration by LC-MS: In Silico Prediction of the H+/K+-ATPase Inhibitor

Ilaprazole is a proton pump inhibitor used to treat digestive diseases. In this study, blood samples were collected after oral administration of ilaprazole and prepared by liquid–liquid extraction. The metabolites of ilaprazole were detected by liquid chromatography–high-resolution mass spectrometry (LC-HRMS) and LC-MSⁿ. A total of twelve in vivo metabolites were detected in rat plasma and six new metabolites of ilaprazole, including one reductive metabolite with sulfide (M3), two hydroxylated metabolites with sulfoxide (M7 and M8), and three oxidative metabolites with sulfone (M9, M11, and M12), were identified. The possible metabolic pathways of ilaprazole and the fragmentation behaviors of its metabolites were elucidated. The result of the in silico prediction indicates that all the new metabolites showed the potential ability to inhibit H⁺/K⁺-ATPase activity.

Pharmacokinetics and Tissue Levels of Pantoprazole in Neonatal Calves After Intravenous Administration

Background: Neonatal calves are at risk of developing abomasal ulceration, but there is a lack of pharmacokinetic data for potential anti-ulcerative therapies, such as pantoprazole, in ruminant species. Objective: The study objectives were to estimate plasma pharmacokinetic parameters for pantoprazole in neonatal dairy calves after intravenous (IV) administration. A secondary objective was to quantify the concentrations of pantoprazole in edible tissues after IV dosing. Methods: Pantoprazole was administered to 9 neonatal Holstein calves at a dose of 1 mg/kg IV. Plasma samples were collected over 24 h and analyzed via HPLC-MS for determining pantoprazole concentrations. Pharmacokinetic parameters were derived via non-compartmental analysis. Tissue samples were collected at 1, 3, and 5 days after administration and analyzed via HPLC-MS. Results: Following IV administration, plasma clearance, elimination half-life, and volume of distribution of pantoprazole were estimated at 4.46 mL/kg/min, 2.81 h, and 0.301 L/kg, respectively. The global extraction ratio was estimated at 0.053 ± 0.015. No pantoprazole was detected in the edible tissues 1, 3, or 5 days after administration. A metabolite, pantoprazole sulfone was detected in all the edible tissues 1 and 3 days after administration. Conclusion: The reported plasma clearance for pantoprazole is less than that reported for alpacas but higher than reported in foals. The elimination half-life in calves appears to be longer than observed in foals and alpacas. While pantoprazole sulfone was detected in the tissues after IV administration, further research is needed as to the metabolism and potential tissue accumulation of other pantoprazole metabolites in calves. Future pharmacodynamic studies are necessary to determine the efficacy of pantoprazole on abomasal acid suppression in calves.

Role of Genetic Polymorphisms of Cytochrome P450 2C19 in Pantoprazole Metabolism and Pantoprazole-based Helicobacter pylori Eradication Regimens

BACKGROUND

Cytochrome P450 (CYP450) enzymes play an important role in the metabolism of 70-80% of the currently used medications, including proton pump inhibitors. There are some data analyzing the impact of gene polymorphisms of CYP450 enzymes on most widely used PPIs, such as omeprazole, however, the data on pantoprazole are highly lacking.

OBJECTIVE

To summarize the most recent publications and studies on the role of polymorphisms of the genes encoding CYP450 enzyme 2C19 in the metabolism of pantoprazole and pantoprazole based Helicobacter pylori eradication regimens.

METHODS

We performed a non-systematic search of the available literature on the selected topic.

RESULTS AND CONCLUSION

The data on cytochrome P450 gene polymorphisms and their role in pantoprazole metabolism and pantoprazole based Helicobacter pylori eradication remain conflicting. Individual differences in pantoprazole metabolism might be partly related to genetic polymorphisms of CYP450 enzymes. Most of the studies support the observation that cytochrome 2C19 polymorphisms have an impact on the pharmacokinetics of pantoprazole and its therapeutic effects: poor metabolizers of PPIs are more likely to have a better response to pantoprazole therapy and achieve better H. pylori eradication rates compared to rapid metabolizers. The determination of alleles that are associated with decreased (e.g., *2, *3 alleles) or increased (e.g., *17 allele) cytochrome 2C19 enzyme activity might be used as predictive factors for the potential of acid suppression and the success of Helicobacter pylori eradication. Overall, currently available data do not provide robust evidence, therefore, the application of genetic polymorphisms of cytochrome enzymes in clinical practice still cannot be recommended as routine practice for personalized pantoprazole prescription strategies.

Metabolic and Pharmaceutical Aspects of Fluorinated Compounds

The applications of fluorine in drug design continue to expand, facilitated by an improved understanding of its effects on physicochemical properties and the development of synthetic methodologies that are providing access to new fluorinated motifs. In turn, studies of fluorinated molecules are providing deeper insights into the effects of fluorine on metabolic pathways, distribution, and disposition. Despite the high strength of the C-F bond, the departure of fluoride from metabolic intermediates can be facile. This reactivity has been leveraged in the design of mechanism-based enzyme inhibitors and has influenced the metabolic fate of fluorinated compounds. In this Perspective, we summarize the literature associated with the metabolism of fluorinated molecules, focusing on examples where the presence of fluorine influences the metabolic profile. These studies have revealed potentially problematic outcomes with some fluorinated motifs and are enhancing our understanding of how fluorine should be deployed.

Antioxidant protection enzyme activity in the blood serum and large intestinal mucosa of rats with prolonged gastric hypochlorhydria and given multiprobiotics

The activity of antioxidant protection enzymes in the blood serum and colon mucosa in rats was studied under the conditions of 28-days administration of omeprazole on its own and omeprazole together with multiprobiotics "Symbiter" and "Apibact". Physiological and biochemical study methods were applied. It was found that after omeprazole administration, the activity of superoxide dismutase in the blood serum decreased, and the activity of catalase increased compared to the control. With the co-administration of omeprazole and multiprobiotics, the activity of superoxide dismutase increased compared to the group of rats that received omeprazole only during the same time, but remained less compared to the control group. The content of reduced glutathione in the blood serum of rats after administration of omeprazole decreased, the activity of glutathione peroxidase and glutathione transferase increased, and the activity of glutathione reductase decreased compared to the control. With co-administration of omeprazole and multiprobiotics, the serum RG content was at the control level, the activity of glutathione reductase exceeded the control values. The activity of glutathione reductase decreased compared to the group receiving omeprazole only. The activity of glutathione reductase increased and did not differ from the control values. In the colon mucosa, superoxide dismutase and catalase activity decreased compared to control. With the combined administration of omeprazole and multiprobiotics, superoxide dismutase and catalase activity increased and even exceeded the control values. With the administration of omeprazole, the reduced glutathione content in the colon mucosa was lower than that in the control. The activity of glutathione peroxidase increased and glutathione transferase and activity of glutathione reductase decreased compared to the control. With co-administration of omeprazole and multiprobiotics to rats, the reduced glutathione content increased compared to the group of rats administered omeprazole only, and even exceeded that in the control.

Structural alert/reactive metabolite concept as applied in medicinal chemistry to mitigate the risk of idiosyncratic drug toxicity: a perspective based on the critical examination of trends in the top 200 drugs marketed in the United States

Because of a preconceived notion that eliminating reactive metabolite (RM) formation with new drug candidates could mitigate the risk of idiosyncratic drug toxicity, the potential for RM formation is routinely examined as part of lead optimization efforts in drug discovery. Likewise, avoidance of "structural alerts" is almost a norm in drug design. However, there is a growing concern that the perceived safety hazards associated with structural alerts and/or RM screening tools as standalone predictors of toxicity risks may be over exaggerated. In addition, the multifactorial nature of idiosyncratic toxicity is now well recognized based upon observations that mechanisms other than RM formation (e.g., mitochondrial toxicity and inhibition of bile salt export pump (BSEP)) also can account for certain target organ toxicities. Hence, fundamental questions arise such as: When is a molecule that contains a structural alert (RM positive or negative) a cause for concern? Could the molecule in its parent form exert toxicity? Can a low dose drug candidate truly mitigate metabolism-dependent and -independent idiosyncratic toxicity risks? In an effort to address these questions, we have retrospectively examined 68 drugs (recalled or associated with a black box warning due to idiosyncratic toxicity) and the top 200 drugs (prescription and sales) in the United States in 2009 for trends in physiochemical characteristics, daily doses, presence of structural alerts, evidence for RM formation as well as toxicity mechanism(s) potentially mediated by parent drugs. Collectively, our analysis revealed that a significant proportion (∼78-86%) of drugs associated with toxicity contained structural alerts and evidence indicating that RM formation as a causative factor for toxicity has been presented in 62-69% of these molecules. In several cases, mitochondrial toxicity and BSEP inhibition mediated by parent drugs were also noted as potential causative factors. Most drugs were administered at daily doses exceeding several hundred milligrams. There was no obvious link between idiosyncratic toxicity and physicochemical properties such as molecular weight, lipophilicity, etc. Approximately half of the top 200 drugs for 2009 (prescription and sales) also contained one or more alerts in their chemical architecture, and many were found to be RM-positive. Several instances of BSEP and mitochondrial liabilities were also noted with agents in the top 200 category. However, with relatively few exceptions, the vast majority of these drugs are rarely associated with idiosyncratic toxicity, despite years of patient use. The major differentiating factor appeared to be the daily dose; most of the drugs in the top 200 list are administered at low daily doses. In addition, competing detoxication pathways and/or alternate nonmetabolic clearance routes provided suitable justifications for the safety records of RM-positive drugs in the top 200 category. Thus, while RM elimination may be a useful and pragmatic starting point in mitigating idiosyncratic toxicity risks, our analysis suggests a need for a more integrated screening paradigm for chemical hazard identification in drug discovery. Thus, in addition to a detailed assessment of RM formation potential (in relationship to the overall elimination mechanisms of the compound(s)) for lead compounds, effects on cellular health (e.g., cytotoxicity assays), BSEP inhibition, and mitochondrial toxicity are the recommended suite of assays to characterize compound liabilities. However, the prospective use of such data in compound selection will require further validation of the cellular assays using marketed agents. Until we gain a better understanding of the pathophysiological mechanisms associated with idiosyncratic toxicities, improving pharmacokinetics and intrinsic potency as means of decreasing the dose size and the associated "body burden" of the parent drug and its metabolites will remain an overarching goal in drug discovery.

Pharmacokinetic Differences between Pantoprazole Enantiomers in Rats

PURPOSE

The purpose of this study was to quantitatively clarify the contribution of the absorption, protein binding, and metabolism of cytochrome P450 enzymes to the enantioselective pharmacokinetics of pantoprazole enantiomers in rats.

METHODS

The enantioselective pharmacokinetics of pantoprazole enantiomers was estimated by an oral administration of racemic pantoprazole to rats. The pharmacokinetic differences between pantoprazole enantiomers were evaluated by the experiments of the in situ perfusion into rat small intestine, the protein binding, and the in vitro metabolism in rat liver microsomes of pantoprazole enantiomers.

RESULTS

The mean area under the curve value of S-pantoprazole was 1.5 times greater than that of R-pantoprazole after administration of racemic pantoprazole to rats (20 mg/kg, p.o.). There were significant differences in k(e) (p < 0.05), t1/2 (p < 0.01), and mean residence time (p < 0.01) values between the two enantiomers. In the in situ absorption study, the absorption rate constants were of no significant differences between the two enantiomers. The mean unbound fraction of R-pantoprazole was slightly greater than that of S-pantoprazole. The intrinsic clearance (CLint) of the formation of the 5'-O-demethyl metabolite from S-pantoprazole was 4-fold lower than that from R-pantoprazole. However, the CLint value for the sulfone and 6-hydroxy metabolites from S-pantoprazole was higher than that from R-pantoprazole. The sum of the CLint of the formation of all three metabolites was 3.06 and 4.82 mL/min/mg protein for S- and R-pantoprazole, respectively.

CONCLUSIONS

This study suggests that the enantioselective pharmacokinetics of pantoprazole enantiomers in rats is probably ascribable to their enantioselective metabolism, which is contributed by all the three metabolic pathways, including sulfoxide oxidation, 4'-O-demethylation, and 6-hydroxylation.