Pharmacokinetic Differences between Pantoprazole Enantiomers in Rats

Metabolites are overlooked in environmental risk assessments and monitoring of pharmaceuticals: The case study of pantoprazole

The proton-pump inhibitor pantoprazole (PPZ) is one of the most consumed pharmaceuticals worldwide. Despite its high usage, reported PPZ concentrations in environmental water samples are comparatively low, which can be explained by the extensive metabolism of PPZ in the human body. Since most previous studies did not consider human PPZ metabolites it can be assumed that the current environmental exposure associated with the application of PPZ is substantially underestimated. In our study, 4'-O-demethyl-PPZ sulfide (M1) was identified as the predominant PPZ metabolite by analyzing urine of a PPZ consumer as well as the influent and effluent of a wastewater treatment plant (WWTP) using liquid chromatography coupled to high resolution mass spectrometry (LC-HRMS). M1 was found to be ubiquitously present in WWTP effluents (max. concentration: 3 000 ng/L) and surface waters in Germany. On average, the surface water concentrations of M1 were approximately 30 times higher than those of the parent compound PPZ. Laboratory scale experiments demonstrated that activated carbon can considerably adsorb M1 und thus improve its removal during wastewater and drinking water treatment. Laboratory ozonation experiments showed a fast oxidation of M1, accompanied by the formation of several ozonation products. Certain ozonation products (identities confirmed via synthesized reference standards) were also detected in water samples collected after ozonation in a full-scale WWTP. Overall lower signal intensities were observed in the effluents of a sand filter and biologically active granular activated carbon filter, suggesting that the compounds were significantly removed during these post-ozonation treatment stages.

Enantioselective metabolism of fenpropathrin enantiomers by carboxyl/choline esterase 6 in Tetranychus cinnabarinus

BACKGROUND

Tetranychus cinnabarinus is a polyphagous pest mite commonly found in agriculture. As an excellent acaricide, fenpropathrin (FEN) is frequently used to control T. cinnabarinus in agriculture. However, commercial FEN is a racemate with two enantiomers, R-FEN and S-FEN. Considering that investigations on the metabolism of FEN by T. cinnabarinus are based on racemate FEN, it is important to investigate the enantioselective metabolism of FEN in T. cinnabarinus.

RESULTS

S-FEN was more toxic to T. cinnabarinus than R-FEN by more than 68.8-fold. Moreover, the synergist bioassay revealed that carboxylesterase and cytochrome P450 were the primary enzymes engaged in the detoxification of FEN in T. cinnabarinus, with carboxylesterase playing a leading role. Seven genes were substantially different after the induction of S-FEN and R-FEN. TcCCE06 was screened and selected as a key gene that related to FEN metabolism in T. cinnabarinus. The metabolic results showed that the recombinant TcCCE06 effectively metabolized 32.1% of the R-FEN and 13.8% of the S-FEN within 4 h of incubation. Moreover, R-FEN was demonstrated to have a higher affinity for the TcCCE06 protein than S-FEN based on molecular docking.

CONCLUSION

Our results indicated that TcCCE06 mediates the enantioselective metabolism of FEN in T. cinnabarinus. Our findings will contribute to a more comprehensive understanding of the mechanisms underlying the differential toxicity of the FEN enantiomers against T. cinnabarinus. Furthermore, they also provide a new perspective for the development of enantiomer-enriched acaricides with higher activity and lower pesticide dosage and pollution risks. © 2023 Society of Chemical Industry.

Herbicidal activity and differential metabolism of lactofen in rat and loach on an enantiomeric level

Enantioselectivity of chiral compounds is receiving growing concern. Lactofen, a chiral herbicide widely used in field crops and vegetables to control broadleaf weeds, is still sold as racemate. In this work, the herbicidal activity and metabolism behavior of lactofen were investigated on an enantiomeric level. Two common broadleaf weeds (Eclipta prostrata L. and Portulaca oleracea L.) were used to evaluate the herbicidal activity of rac-/R- and S-lactofen, and their metabolism behavior in loach and rat liver microsomes was explored. Higher herbicidal activity of S-lactofen was observed, with the 20d-EC₅₀ values being 1.9-3.4 times lower than R-lactofen. Both loach and rat liver microsomes had ability to metabolize rac-lactofen, with half-lives of 1.93 and 1.28 h, respectively. Enantioselective metabolism behaviors were observed in loach and rat liver microsomes and the direction of enantioselectivity were different. R-lactofen was preferentially metabolized in loach liver microsome, while S-lactofen was preferentially metabolized in rat liver microsome. No interconversion of R- and S-lactofen was found. Besides, the main metabolic pathways of R- and S-lactofen were found to be significantly different. R-lactofen was metabolized to R-desethyl lactofen in both loach and rat liver microsomes without further metabolism. However, S-lactofen was metabolized to both S-desethyl lactofen and acifluorfene in rat liver microsome, which was mainly metabolized to acifluorfene in loach liver microsome. This study indicated enantioselectivity and metabolites should be taken into consideration when overall evaluating the environmental behavior of lactofen.

Efficacy of S-pantoprazole 10 mg in the Symptom Control of Non-erosive Reflux Disease: A Phase III Placebo-controlled Trial

Background/Aims

S-isomer (S) pantoprazole is more bioavailable and less dependent on cytochrome 2C19 than is racemic pantoprazole. We aim to evaluate the efficacy and safety of 10 mg S-pantoprazole for treatment of non-erosive reflux disease (NERD).

Methods

In this phase 3, double-blind, randomized placebo controlled, multicenter study, 174 NERD patients were randomized to one of both treatment groups 10 mg S-pantoprazole, or placebo once daily for 4 weeks. Symptoms and safety were assessed. The efficacy endpoints were complete relief of symptoms, > 50% improvement of all reflux symptoms and recurrence.

Results

Eighty-eight patients were assigned to the S-pantoprazole group (25 males, mean 43.7 years old) and 86 to the placebo group (32 males, mean 43.0 years old), and 163 patients were subjected to full Analysis Set. A higher proportion of patients in the S-pantoprazole group had complete symptom relief (42.0 % [34/81] vs 17.1% [14/82], P < 0.001) and > 50% symptom responses (66.0% vs 50.0%, P = 0.010 for heartburn; 64.2% vs 28.0%, P = 0.010 for acid regurgitation; and 51.9% vs 30.5%, P = 0.03 for epigastric discomfort) compared to the placebo group. The factors associated with poor responsiveness to PPI were older age, female, greater body mass index, and severe baseline symptoms.

Conclusions

Low dose of S-pantoprazole (10 mg) for 4 weeks was more efficacious than placebo in providing reflux symptom relief in patients with NERD, especially acid regurgitation. More doses or longer periods of treatment with S-pantoprazole would be needed to completely eliminate symptoms.

Intragastric pH effect of 20mg of levo-pantoprazole versus 40mg of racemic pantoprazole the first seven days of treatment in patients with gastroesophageal reflux disease

INTRODUCTION/AIM

Levo-pantoprazole, the S-enantiomer of pantoprazole, is a proton pump inhibitor that has been shown in animal studies to be faster and stronger than its racemic formulation. There are no studies on humans and therefore our aim was to evaluate the effects of levo-pantoprazole versus racemic pantoprazole on intragastric pH.

MATERIALS AND METHODS

A randomized controlled study was conducted on patients with erosive gastroesophageal reflux disease that were given 20mg of levo-pantoprazole (n = 15) versus 40mg of racemic pantoprazole (n = 15) for 7 days. Baseline and end-of-treatment symptom evaluation and intragastric pH measurement were carried out.

RESULTS

There were no differences between the groups in the baseline evaluations. From 40 to 115min after the first dose of levo-pantoprazole, the mean intragastric pH was higher, compared with that of racemic pantoprazole (p < 0.05). After one week, levo-pantoprazole and racemic pantoprazole significantly reduced intragastric acid production and its esophageal exposure (p < 0.05). Even though there was no statistically significant difference, a larger number of patients that received levo-pantoprazole stated that their heartburn improved within the first 3 days.

CONCLUSIONS

The S-enantiomer of pantoprazole (levo-pantoprazole) had a faster and stronger effect with respect to acid suppression, compared with its racemic formulation. Although the effect on symptoms was faster with levo-pantoprazole, occurring within the first days of treatment, it was equivalent to that of the racemate at one week of treatment.

Isomer-selective distribution of 3-n-butylphthalide (NBP) hydroxylated metabolites, 3-hydroxy-NBP and 10-hydroxy-NBP, across the rat blood-brain barrier

AIM

To investigate the mechanisms underlying the isomer-selective distribution of 3-n-butylphthalide (NBP) hydroxylated metabolites, 3-hydroxy-NBP (3-OH-NBP) and 10-hydroxy-NBP (10-OH-NBP), across the blood brain barrier (BBB).

METHODS

After oral administration of NBP (20 mg/kg) to rats, the pharmacokinetics of two major hydroxylated metabolites, 3-OH-NBP and 10-OH-NBP, in plasma and brains were investigated. Plasma and brain protein binding of 3-OH-NBP and 10-OH-NBP was also assessed. To evaluate the influences of major efflux transporters, rats were pretreated with the P-gp inhibitor tariquidar (10 mg/kg, iv) and BCRP inhibitor pantoprazole (40 mg/kg, iv), then received 3-OH-NBP (12 mg/kg, iv) or 10-OH-NBP (3 mg/kg, iv). The metabolic profile of NBP was investigated in rat brain homogenate.

RESULTS

After NBP administration, the plasma exposure of 3-OH-NBP was 4.64 times that of 10-OH-NBP, whereas the brain exposure of 3-OH-NBP was only 11.8% of 10-OH-NBP. In the rat plasma, 60%±5.2% of 10-OH-NBP was unbound to proteins versus only 22%±2.3% of 3-OH-NBP being unbound, whereas in the rat brain, free fractions of 3-OH-NBP and 10-OH-NBP were 100%±9.7% and 49.9%±14.1%, respectively. In the rats pretreated with tariquidar and pantoprazole, the unbound partition coefficient Kp,uu of 3-OH-NBP was significantly increased, while that of 10-OH-NBP showed a slight but not statistically significant increase. Incubation of rat brain homogenate with NBP yielded 3-OH-NBP but not 10-OH-NBP.

CONCLUSION

The isomer-selective distribution of 10-OH-NBP and 3-OH-NBP across the BBB of rats is mainly attributed to the differences in plasma and brain protein binding and the efflux transport of 3-OH-NBP. The abundant 10-OH-NBP is not generated in rat brains.

Is (+)-[13C]-pantoprazole better than (±)-[13C]-pantoprazole for the breath test to evaluate CYP2C19 enzyme activity?

Recently, we have shown that the (+)-[(13)C]-pantoprazole is more dependent on CYP2C19 metabolic status than (-)-[(13)C]-pantoprazole. In this study, we tested the hypothesis that (+)-[(13)C]-pantoprazole is a more sensitive and selective probe for evaluating CYP2C19 enzyme activity than the racemic mixture. (+)-[(13)C]-pantoprazole (95 mg) was administered orally in a sodium bicarbonate solution to healthy volunteers. Breath and plasma samples were collected before and up to 720 min after dosing. The (13)CO2 in exhaled breath samples was measured by infrared spectrometry. Ratios of (13)CO2/(12)CO2 after (+)-[(13)C]-pantoprazole relative to (13)CO2/(12)CO2 at baseline were expressed as delta over baseline (DOB). (+)-[(13)C]-pantoprazole concentrations were measured by HPLC. Genomic DNA extracted from whole blood was genotyped for CYP2C19*2, *3 and *17 using Taqman assays. Statistically significant differences in the area under the plasma concentration time curve (AUCplasma(0-∞) (p < 0.001) and oral clearance (<0.01) of (+)-[(13)C]-pantoprazole as well as in the breath test indices (delta over baseline, DOB30; and area under the DOB versus time curve, AUCDOB(0-120)) (p < 0.01) were observed among poor, intermediate and extensive metabolizer of CYP2C19. DOB30 and AUCDOB(0-120) adequately distinguished poor metabolizer from intermediate and extensive metabolizer of CYP2C19. Breath test indices significantly correlated with plasma elimination parameters of (+)-[(13)C]-pantoprazole (Pearson correlations: -0.68 to -0.73). Although relatively higher breath test indices were observed after administration of (+)-[(13)C]-pantoprazole (this study) than after (±)-[(13)C]-pantoprazole (previous study), the performance of the racemic and the enantiomer as marker of CYP2C19 activity remained similar. Our data confirm that the metabolism of (+)-[(13)C]-pantoprazole is highly dependent on CYP2C19 metabolic status, but the breath test derived from it is not superior to the racemic [(13)C]-pantoprazole in evaluating CYP2C19 activity in vivo. Thus, racemic [(13)C]-pantoprazole which is relatively easy to synthesize and more stable than (+)-[(13)C]-pantoprazole is adequate as a probe of this enzyme.

Efficacy of S-pantoprazole 20 mg compared with pantoprazole 40 mg in the treatment of reflux esophagitis: a randomized, double-blind comparative trial

BACKGROUND

S-isomer (S) pantoprazole is known to be more effective and less dependent on cytochrome 2C19 than R-isomer (R)-pantoprazole.

AIM

The purpose of this study was to compare the efficacy and safety of S-pantoprazole 20 mg versus pantoprazole 40 mg for treatment of reflux esophagitis.

METHODS

This multi-center, double-blind, randomized trial enrolled patients with endoscopically documented reflux esophagitis. Patients were assigned to receive either 20 mg S-pantoprazole or 40 mg pantoprazole once daily for 4 weeks. Endoscopy and symptoms were assessed after 4 weeks of treatment. In patients whose reflux esophagitis was not resolved at 4 weeks, treatment was extended to 8 weeks and symptoms were reassessed. Heartburn, chest pain, acid regurgitation, globus, and overall symptoms were rated. The primary efficacy endpoint was healing of esophagitis, and secondary endpoints were symptomatic and endoscopic improvement.

RESULTS

Sixty-seven patients in the S-pantoprazole group (52 male, mean age 51 years) and 62 in the pantoprazole group (61 male, mean age 50 years) were analyzed per protocol. The healing rate of reflux esophagitis was 85 % at 4 weeks and 94 % at 8 weeks in the S-pantoprazole group, which did not differ from those in the pantoprazole group (84 and 97 %, respectively). After treatment, individual and overall gastroesophageal reflux disease (GERD) symptoms and esophagitis improved compared with baseline inflammation in both groups. Intergroup differences in symptoms and endoscopic healing were not significant.

CONCLUSION

The efficacy and safety of 20 mg S-pantoprazole were comparable to those of 40 mg pantoprazole for treatment of reflux esophagitis and symptomatic improvement of GERD.

Stereoselective interaction of pantoprazole with ABCG2. II. In vitro flux analysis

(-)Pantoprazole [(-)PAN] accumulated in rat milk stereoselectively, and this accumulation was attributed to rat Abcg2 (rAbcg2). In contrast, flux experiments at 25 μM showed that (+)pantoprazole [(+)PAN] was preferentially transported by rAbcg2. The purpose of the current study was to comprehensively evaluate the transport of PAN isomers in empty-Madin-Darby canine kidney II (MDCKII) and MDCKII cells expressing the human/rat (ABCG2/rAbcg2) isoforms at concentrations ranging from 3 to 200 μM. The apical-to-basolateral and basolateral-to-apical directional flux and the asymmetry efflux ratios were virtually identical for both isomers in empty (mock transfected)-MDCKII monolayers but were concentration dependent for both isomers in ABCG2 (human/rat)-MDCKII. Kinetic analysis using predicted cellular concentrations showed that (-)PAN had an 8-fold lower K(M) compared with (+)PAN for both rAbcg2 (0.25 versus 1.85 μM) and ABCG2 (0.6 versus 5.32 μM). (+)PAN had a 3-fold higher T(Max) compared with the (-)PAN for both rAbcg2 (7.86 versus 2.49 nmol/h · cm(2)) and ABCG2 (10.2 versus 3.29 nmol/h · cm(2)). Effective ABCG2 surface-area permeability of (-)PAN was 9920 and 5480 (μl/h)/cm(2) for rAbcg2 and ABCG2, respectively, compared with the (+)PAN isomer (4250 and 1920 μl/h · cm(2), respectively). These results indicate a stereoselective interaction of PAN with similar kinetic parameters for both human and rat ABCG2. (-)PAN is a better substrate than (+)PAN for ABCG2/rAbcg2 and provide a rationale for the preferential accumulation of (-)PAN into rat milk.

Pharmacologically active compounds in the environment and their chirality

Pharmacologically active compounds including both legally used pharmaceuticals and illicit drugs are potent environmental contaminants. Extensive research has been undertaken over the recent years to understand their environmental fate and toxicity. The one very important phenomenon that has been overlooked by environmental researchers studying the fate of pharmacologically active compounds in the environment is their chirality. Chiral drugs can exist in the form of enantiomers, which have similar physicochemical properties but differ in their biological properties such as distribution, metabolism and excretion, as these processes (due to stereospecific interactions of enantiomers with biological systems) usually favour one enantiomer over the other. Additionally, due to different pharmacological activity, enantiomers of chiral drugs can differ in toxicity. Furthermore, degradation of chiral drugs during wastewater treatment and in the environment can be stereoselective and can lead to chiral products of varied toxicity. The distribution of different enantiomers of the same chiral drug in the aquatic environment and biota can also be stereoselective. Biological processes can lead to stereoselective enrichment or depletion of the enantiomeric composition of chiral drugs. As a result the very same drug might reveal different activity and toxicity and this will depend on its origin and exposure to several factors governing its fate in the environment. In this critical review a discussion of the importance of chirality of pharmacologically active compounds in the environmental context is undertaken and suggestions for directions in further research are made. Several groups of chiral drugs of major environmental relevance are discussed and their pharmacological action and disposition in the body is also outlined as it is a key factor in developing a full understanding of their environmental occurrence, fate and toxicity. This review will be of interest to environmental scientists, especially those interested in issues associated with environmental contamination with pharmacologically active compounds and chiral pollutants. As the review will outline current state of knowledge on chiral drugs, it will be of value to anyone interested in the phenomenon of chirality, chiral drugs, their stereoselective disposition in the body and environmental fate (212 references).

Determination of tenatoprazole enantiomers and their enantioselective pharmacokinetics in rats

The enantioselective pharmacokinetics of tenatoprazole were studied in Wistar rats after the administration of a single oral dose of rac-tenatoprazole. Serial plasma samples were collected; and the pharmacokinetic behavior of each enantiomer was characterized using a sequential achiral and chiral liquid chromatographic method. Tenatoprazole was extracted from a small aliquot of plasma (100 microl) by one-step extraction using hexane-dichloromethane-isopropanol (20:10:1, v/v/v) as extract solvent. Plasma drug concentration-time data were analyzed for each enantiomer by using a noncompartmental method. The AUC(0-infinity) and C(max) values of (+)-tenatoprazole were significantly greater than those of (-)-tenatoprazole (P < 0.001). The mean AUC(0-infinity) value of (+)-tenatoprazole was 7.5 times greater than that of (-)-tenatoprazole after oral administration of rac-tenatoprazole to rats at a dose of 5 mg/kg. There are also significant differences in t(1/2) and CL/F (P < 0.01 and P < 0.001, respectively) values between enantiomers. This study suggests that the pharmacokinetics of tenatoprazole are enantioselective in rats.

The role of molecular interaction fields on enantioselective and nonselective separation of chiral sulfoxides

The separation of a series of 23 asymmetric sulfoxides, including the three proton pump inhibitors (PPI) omeprazole, lansoprazole and pantoprazole was investigated by HPLC, under reversed-phase elution with amylose tris(3,5-dimethylphenylcarbamate), amylose tris[(S)-1-phenylethylcarbamate] and amylose tris(3,5-dimethoxyphenylcarbamate) chiral stationary phases, CSP1-3, respectively. The whole set of sulfoxides showed better enantioselectivity and enantioresolution on CSP1. However, the three PPI were enantioseparated only when using CSP1 and CSP3. It was observed an improved enantioselectivity and enantioresolution on CSP3. The mechanisms of retention were evaluated by molecular interaction fields (MIF) generated via GRID force field, which yielded the geometric reasons leading to the scenario outlined. The enantioselective and nonselective interactions are discussed in terms of the reported selectivity. The steric structural outline of the CSP nonselective interaction sites is of major importance to deliver the sulfoxides to the chiral selective sites where the enantioselective interactions take place.