Species differences in small intestinal exposure-related epithelial vacuolation in rats and dogs treated with a heteroaryldihydropyrimidine molecule

Small intestinal epithelial vacuolation induced by a heteroaryldihydropyrimidine compound (HAP-1) was observed in rats but not in dogs at termination in screening toxicity studies, despite the plasma exposure being higher in dogs. To understand the species differences, investigational studies with multiple time points following single dose (SD) and 7-day repeated dose (RD) were conducted in both species at doses resulting in comparable plasma exposures. In rats, epithelial vacuolation in the duodenum and jejunum were observed at all time points. In dogs, transient vacuolation was noted at 8 h post-SD (SD_8h) and 4 h post-RD (RD_4 h), but not at termination (RD_24 h). Special stains demonstrated lipid accumulation within enterocytes in both species and intracytoplasmic inclusion bodies in rats. Transmission electron microscopy identified these inclusion bodies as endoplasmic reticulum (ER) membranous structures. Transcriptomic analysis on jejunal mucosa at SD_8 h and RD_24 h revealed perturbations of lipid metabolism-related genes at SD_8 h in both species, but not at RD_24 h in dogs. ER stress-related gene changes at both time points were observed in rats only. Despite comparable HAP-1 plasma exposures, the duodenum and jejunum tissue concentrations of HAP-1 and acyl glucuronide metabolite were >5- and >30-fold higher in rats than in dogs, respectively. In vitro, similar cytotoxicity was observed in rat and dog duodenal organoids treated with HAP-1. In conclusion, HAP-1-induced intestinal epithelial vacuolation was related to lipid metabolism dysregulation in both species and ER-related injuries in rats only. The species differences were likely related to the difference in intestinal exposure to HAP-1 and its reactive metabolite.

The Prevalence of Several Treatments in Preventing the Back Conversion of Acyl Glucuronide Metabolites in Abbreviated New Drug Applications

The bioanalysis of drugs that undergo acyl glucuronidation presents an analytical challenge due to poor stability of acyl glucuronide metabolites in biological matrices. The objective of this study was to investigate the impact of back conversion of acyl glucuronide metabolites on drug concentration measurement in bioequivalence (BE) studies submitted to Abbreviated New Drug Applications (ANDAs). The prevalence of several treatments for preventing the back conversion of acyl glucuronide metabolites and the results of incurred sample reanalysis (ISR) were analyzed. In total, 322 ANDAs for 26 drugs known to generate acyl glucuronide metabolites were surveyed. Many studies have applied multiple preventive treatments during the clinical and bioanalytical phases. More than two-thirds (67.2%) of the studies utilized procedures of lowering the temperature for sample collection during clinical phase. Fewer studies have utilized procedures for lowering the pH of plasma samples (12.3%) or adding enzyme inhibitors (4.4%) in the clinical phase. A small fraction (16.9%) validated the pre-study method in the presence of the acyl glucuronide metabolites. The majority (62.2%) of the studies employed the procedure of lowering the pH during the sample extraction process in the bioanalytical phase. Among the studies that had significantly higher (p-value < 0.01 by sign test) ISR results than the corresponding original concentration values, 41 BE studies did not carry out any preventive treatments during the bioanalysis phase, suggesting that back conversion of acyl glucuronide metabolites to parent drugs may be present in these studies. The awareness of appropriate treatments of study samples for possible back-conversions of acyl glucuronide metabolites is expected to assist generic drug applicants in improving the quality of their future applications.

Species differences in liver microsomal hydrolysis of acyl glucuronide in humans and rats

Acyl glucuronides (AGs) are known as one of the causes of idiosyncratic drug toxicity (IDT). Although AGs can be enzymatically hydrolysed by β-glucuronidase and esterase, much information on their characteristics and species differences is lacking. This study was aimed to clarify species differences in AG hydrolysis between human and rat liver microsomes (HLM and RLM).To evaluate the AG hydrolysis profile, and the contribution of β-glucuronidase and esterase towards AG hydrolysis in HLM and RLM, nonsteroidal anti-inflammatory drugs (NSAIDs) were used. AGs were incubated with 0.1 M Tris-HCl buffer (pH 7.4) and 0.3 mg/mL HLM or RLM in the absence or presence of β-glucuronidase inhibitor, D-saccharic acid 1,4-lactone (D-SL) and esterase inhibitor, phenylmethylsulfonyl fluoride (PMSF).AGs of mefenamic acid (MEF-AG) and etodolac (ETO-AG) showed significantly higher AG hydrolysis rates in RLM than in HLM. Esterases were found to serve as AG hydrolases dominantly in HLM, whereas both esterases and β-glucuronidase equally contribute to AG hydrolysis in RLM. However, MEF-AG and ETO-AG were hydrolysed only by β-glucuronidase.We demonstrated for the first time that the activity of AG hydrolases towards NSAID-AGs differs between humans and rats.

Investigation of Human in vivo Metabolism of SEP-227900 Using the Samples from a Randomized First-in-Human Study by LC-UV/HRMS and NMR

OBJECTIVE

To explore the human in vivo metabolism of SEP-227900 (4H-furo[3, 2-b]pyrrole-carboxylic acid, m.w 151.03), a D-amino-acid oxidase (DAAO) inhibitor by using plasma and urine samples from first-in-human study.

METHODS

The human plasma and urine samples were from a single dose cohort that consisted of 9 healthy male volunteers each received 80-mg dose of SEP-227900 orally. The pooled pre-dose urine and the pooled 0-24 h urine sample were created across 9 subjects by equal volume. Plasma samples were pooled by equal volume across 9 subjects to obtain 0-12 h plasma for metabolite searching, and also pooled by timepoints across 9 subjects to obtain 0.5-, 5-, and 12-h plasma for semi-quantitation. The plasma was de-proteinized by acetonitrile (1:3 v/v plasma-acetonitrile) then the supernatant was dried down, reconstituted and injected for LC-HRMS/UV analysis. The urine sample was just simply centrifuged before analysis. LC-HRMS/UV was utilized to search predictable and unknown metabolites and estimate their relative abundances. Accurate mass measurement by Orbitrap-MS and MS/MS were used for metabolite identification. Chromatographic separation was achieved on a MACMOD AQ C8 column (250 × 4.6 mm, 5-µm) with a gradient mobile phase (A: 10 mM NH4Ac; B: acetonitrile; flowrate: 0.700 ml/min) for a total run-time of 65 min. The definite position in the molecule for the glucuronidation metabolism was characterized by detected migration phenomenon, methylation with diazomethane (CH2N2), and NMR.

RESULTS

Unchanged parent drug and four metabolite peaks were detected in humans: M1 was a mono-oxidative metabolite of SEP-227900; M2 was a glucuronide conjugate of SEP-227900; M3 was a glycine conjugate of SEP-227900; and M4 was a glycine conjugate of M1. The specific position of the oxidation in M1 solely based on the mass spectral (MS and MS/MS) data was not identified. However, for the major metabolite M2, the acyl glucuronidation was unambiguously determined through multiple pieces of experimental evidence such as the observation of a migration pattern, mono-methylation by diazomethane, and NMR measurement. This determination is of significance related to the safety evaluation of an investigational new drug development. The glycine conjugate of SEP-227900, i.e. M3 was found to be the most abundant metabolite in human urine (approximately 3-fold higher level as the glucuronide level). All together (mainly glycine-conjugate and glucuronide), it resulted in greater than 80% of the dosed amount in urine excretion (a separate measurement showed 23% of the dosed amount in urine excretion as the glucuronide).

CONCLUSION

Four metabolites were found in humans: SEP-227900-glycine conjugate, SEP227900-glucuronide, mono-oxidative metabolite and its consequent glycine conjugate. The glucuronide metabolite was identified as the acyl glucuronide. Greater than 80% of the dosed amount of SEP-227900 was excreted in urine mainly in the forms of glycine- and glucuronide- conjugates.

The Role of Uptake and Efflux Transporters in the Disposition of Glucuronide and Sulfate Conjugates

Glucuronidation and sulfation are the most typical phase II metabolic reactions of drugs. The resulting glucuronide and sulfate conjugates are generally considered inactive and safe. They may, however, be the most prominent drug-related material in the circulation and excreta of humans. The glucuronide and sulfate metabolites of drugs typically have limited cell membrane permeability and subsequently, their distribution and excretion from the human body requires transport proteins. Uptake transporters, such as organic anion transporters (OATs and OATPs), mediate the uptake of conjugates into the liver and kidney, while efflux transporters, such as multidrug resistance proteins (MRPs) and breast cancer resistance protein (BCRP), mediate expulsion of conjugates into bile, urine and the intestinal lumen. Understanding the active transport of conjugated drug metabolites is important for predicting the fate of a drug in the body and its safety and efficacy. The aim of this review is to compile the understanding of transporter-mediated disposition of phase II conjugates. We review the literature on hepatic, intestinal and renal uptake transporters participating in the transport of glucuronide and sulfate metabolites of drugs, other xenobiotics and endobiotics. In addition, we provide an update on the involvement of efflux transporters in the disposition of glucuronide and sulfate metabolites. Finally, we discuss the interplay between uptake and efflux transport in the intestine, liver and kidneys as well as the role of transporters in glucuronide and sulfate conjugate toxicity, drug interactions, pharmacogenetics and species differences.

Toxicological role of an acyl glucuronide metabolite in diclofenac-induced acute liver injury in mice

The acyl glucuronide (AG) metabolites of carboxylic acid-containing drugs are potentially chemically reactive and are suggested to be implicated in toxicity, including hepatotoxicity, nephrotoxicity and drug hypersensitivity reactions. However, it remains unknown whether AG formation is related to toxicity in vivo. In this study, we sought to determine whether AG is involved in the pathogenesis of liver injury using a mouse model of diclofenac (DIC)-induced liver injury. Mice that were administered DIC alone exhibited significantly increased plasma alanine aminotransferase levels, whereas mice that were pretreated with the UDP-glucuronosyltransferase inhibitor (-)-borneol (BOR) exhibited suppressed alanine aminotransferase levels at 3 and 6 h after DIC administration although not significant at 12 h. The plasma DIC-AG concentrations were significantly lower in BOR- and DIC-treated mice than in mice treated with DIC alone. The mRNA expression levels of chemokine (C-X-C motif) ligand 1 (CXCL1), CXCL2 and the neutrophil marker CD11b were reduced in the livers of mice that had been pretreated with BOR compared to those that had been administered DIC alone, whereas mRNA expression of the macrophage marker F4/80 was not altered. An immunohistochemical analysis at 12 h samples revealed that the numbers of myeloperoxidase- and lymphocyte antigen 6 complex-positive cells that infiltrated the liver were significantly reduced in BOR- and DIC-treated mice compared to mice that were treated with DIC alone. These results indicate that DIC-AG is partly involved in the pathogenesis of DIC-induced acute liver injury in mice by activating innate immunity and neutrophils. Copyright © 2016 John Wiley & Sons, Ltd.

Metabolic Activation of Rhein: Insights into the Potential Toxicity Induced by Rhein-Containing Herbs

Rhein is a major component of the many medicinal herbs such as rhubarb. Despite wide use, intoxication cases associated with rhein-containing herbs are often reported. The present work aimed to investigate if rhein was subject to metabolic activation leading to toxicity. Upon incubations with different species of liver microsomes, three monoglucuronides were identified, corresponding to two hydroxyl glucuronides and one acyl glucuronide via the carboxyl group, respectively. Further study revealed that rhein acyl glucuronide was chemically reactive, and showed cytotoxicity toward hepatocarcinoma cells. In addition, significant species differences in glucuronidation of rhein were observed between laboratory animals and humans. Reaction phenotyping experiments demonstrated that rhein acyl glucuronide was catalyzed predominantly by uridine 5'-diphospho-glucuronosyltransferase 1A1, 1A9, and 2B7. Taken together, the present study confirmed that rhein could be metabolically activated via the formation of acyl glucuronide, especially in human.

Absorption, distribution, metabolism and excretion of novel phosphodiesterase type 4 inhibitor ASP3258 in rats

The potent and selective phosphodiesterase 4 inhibitor ASP3258 is a novel therapeutic agent for asthma and chronic obstructive pulmonary disease (COPD). After a single oral administration to rats, ASP3258 is rapidly absorbed with a bioavailability of 106%. In situ absorption data indicated that ASP3258 is mainly absorbed in the small intestine. Tissue distribution data after oral administration of (14)C-ASP3258 showed rapid and extensive distribution to various tissues. Excluding the gastrointestinal tract, the tissues with the highest concentrations were liver, heart and plasma. Liquid chromatography-nuclear magnetic resonance spectroscopy data revealed that O-glucuronidation of the carboxylic acid moiety of ASP3258 (formation of an acyl glucuronide) plays a key role in metabolism. No indication was found that the acyl glucuronide reacted with proteins in plasma or tissues. When (14)C-ASP3258 was orally administered to intact rats, urinary and fecal excretion accounted for 1.3% and 100.6% of the administered radioactivity, respectively. After a single oral administration of (14)C-ASP3258 to bile-cannulated rats, urinary and biliary excretion accounted for 0.7% and 93.8% of the administered radioactivity, respectively. These findings suggest that fecal excretion via bile plays an important role in the elimination of ASP3258-derived radioactivity. In vitro metabolic profiles were relatively similar among the species examined, suggesting that our findings in rats may help us to understand pharmacokinetics, efficacy and safety profiles in humans and other species.

Discovery of PF-04620110, a Potent, Selective, and Orally Bioavailable Inhibitor of DGAT-1

Acyl-CoA:diacylglycerol acyltransferase-1 (DGAT-1) catalyzes the final committed step in the biosynthesis of triglycerides. DGAT-1 knockout mice have been shown to be resistant to diet-induced obesity and have increased insulin sensitivity. Thus, inhibition of DGAT-1 may represent an attractive target for the treatment of obesity or type II diabetes. Herein, we report the discovery and characterization of a potent and selective DGAT-1 inhibitor PF-04620110 (3). Compound 3 inhibits DGAT-1 with an IC50 of 19 nM and shows high selectivity versus a broad panel of off-target pharmacologic end points. In vivo DGAT-1 inhibition has been demonstrated through reduction of plasma triglyceride levels in rodents at doses of ≥0.1 mg/kg following a lipid challenge. On the basis of this pharmacologic and pharmacokinetic profile, compound 3 has been advanced to human clinical studies.

Mechanistic modelling of tesaglitazar pharmacokinetic data in subjects with various degrees of renal function--evidence of interconversion

WHAT IS ALREADY KNOWN ABOUT THIS SUBJECT

Tesaglitazar, is predominantly metabolized (to an acyl glucuronide of the parent compound) and 20% of given dose is found unchanged in the urine. Acyl glucuronides are know to be unstable and can become hydrolysed back to parent compound, a phenomena called interconversion.

WHAT THIS STUDY ADDS

A likely mechanism (interconversion) for the cause of the increased exposure of tesaglitazar in subjects with impaired renal function. A possible modelling framework to evaluate interconversion without dosing of the metabolite based on the simultaneous analysis of plasma and urine data from a group of subjects with varying renal function. A mechanistic understanding of the pharmacokinetic properties of tesaglitazar and its metabolite. AIMS To develop a mechanistic pharmacokinetic (PK) model for tesaglitazar and its metabolite (an acyl glucuronide) following oral administration of tesaglitazar to subjects with varying renal function, and derive an explanation for the increased plasma exposure of tesaglitazar in subjects with impaired renal function.

METHODS

Data were from a 6-week study in subjects with renal insufficiency and matched controls undergoing repeated oral dosing with tesaglitazar (n = 41). Compartmental population PK modelling was employed to describe the PK of tesaglitazar and its metabolite, in plasma and urine, simultaneously. Two hypotheses were tested to investigate the increased exposure of tesaglitazar in subjects with renal functional impairment: tesaglitazar metabolism is correlated with renal function, or metabolite elimination is reduced in renal insufficiency, leading to increased hydrolysis (interconversion) to the parent compound via biliary circulation.

RESULTS

The hypothesis for interconversion was best supported by the data. The population PK model included first-order absorption, two-compartment disposition and separate renal (0.027 l h(-1)) and metabolic (1.9 l h(-1)) clearances for tesaglitazar. The model for the metabolite; one-compartment disposition with renal (saturable, V(max) = 0.19 micromol l(-1) and K(m) = 0.04 micromol l(-1)) and nonrenal clearances (1.2 l h(-1)), biliary secretion (12 h(-1)) to the gut, where interconversion and reabsorption (0.8 h(-1)) of tesaglitazar occurred.

CONCLUSION

A mechanistic population PK model for tesaglitazar and its metabolite was developed in subjects with varying degrees of renal insufficiency. The model and data give insight into the likely mechanism (interconversion) of the increased tesaglitazar exposure in renally impaired subjects, and separate elimination and interconversion processes without dosing of the metabolite.

Glucuronide and glucoside conjugation of mycophenolic acid by human liver, kidney and intestinal microsomes

Mycophenolic acid (MPA) is primarily metabolized to a phenolic glucuronide (MPAG) as well as to two further minor metabolites: an acyl glucuronide (AcMPAG) and a phenolic glucoside (MPAG1s). This study presents investigations of the formation of these metabolites by human liver (HLM), kidney (HKM), and intestinal (HIM) microsomes, as well as by recombinant UDP-glucuronosyltransferases. HLM (n=5), HKM (n=6), HIM (n=5) and recombinant UGTs were incubated in the presence of either UDP-glucuronic acid or UDP-glucose and various concentrations of MPA. Metabolite formation was followed by h.p.l.c. All microsomes investigated formed both MPAG and AcMPAG. Whereas the efficiency of MPAG formation was greater with HKM compared to HLM, AcMPAG formation was greater with HLM than HKM. HIM showed the lowest glucuronidation efficiency and the greatest interindividual variation. The capacity for MPAGls formation was highest in HKM, while no glucoside was detected with HIM. HKM produced a second metabolite when incubated with MPA and UDP-glucose, which was labile to alkaline treatment. Mass spectrometry of this metabolite in the negative ion mode revealed a molecular ion of m/z 481 compatible with an acyl glucoside conjugate of MPA. All recombinant UGTs investigated were able to glucuronidate MPA with K:(M:) values ranging from 115.3 to 275.7 microM l(-1) and V(max) values between 29 and 106 pM min(-1) mg protein(-1). Even though the liver is the most important site of MPA glucuronidation, extrahepatic tissues particularly the kidney may play a significant role in the overall biotransformation of MPA in man. Only kidney microsomes formed a putative acyl glucoside of MPA.

Stereoselective pharmacokinetics of ketoprofen and ketoprofen glucuronide in end-stage renal disease: evidence for a 'futile cycle' of elimination

AIMS

To assess if futile cycling of ketoprofen occurs in patients with decreased renal function.

METHODS

Ketoprofen was administered to six haemodialysis-dependent patients with end-stage renal disease as single (50 mg) or multiple doses (50 mg three times daily, for 7 days). Plasma and dialysate concentrations of the unconjugated and glucuronidated R- and S-enantiomers of ketoprofen were determined using h.p.l.c. following the single and multiple dosing.

RESULTS

The oral clearance was decreased and terminal elimination half-lives of R- and S-ketoprofen and the corresponding acyl glucuronides were increased in functionally anephric patients compared with healthy subjects. In contrast with the R-isomers, S-ketoprofen and S-ketoprofen glucuronide exhibited an unexpected accumulation (2.7-3. 8 fold) after repeated dosing achieving S:R ratios of 3.3+/-1.7 and 11.2+/-5.3, respectively. The plasma dialysis clearances for R- and S-ketoprofen glucuronides were 49.4+/-19.8 and 39.0+/-15.9 ml min-1, respectively, and 10.8+/-17.6 and 13.3+/-23.5 ml min-1 for unconjugated R- and S-ketoprofen.

CONCLUSIONS

The selective accumulation of S-ketoprofen and its acyl glucuronide are consistent with amplification of chiral inversion subsequent to futile cycling between R-ketoprofen and R-ketoprofen glucuronide. Severe renal insufficiency, and possibly more modest decrements, results in a disproportionate increase in systemic exposure to the S-enantiomer which inhibits both pathologic and homeostatic prostaglandin synthesis.

Identification of glucoside and carboxyl-linked glucuronide conjugates of mycophenolic acid in plasma of transplant recipients treated with mycophenolate mofetil

1. Mycophenolic acid (MPA), is primarily metabolized in the liver to 7-O-MPA-beta-glucuronide (MPAG). Using RP-h.p.l.c. we observed three further MPA metabolites, M-1, M-2, M-3, in plasma of transplant recipients on MMF therapy. To obtain information on the structure and source of these metabolites: (A) h.p.l.c. fractions containing either metabolite or MPA were collected and analysed by tandem mass spectrometry; (B) the metabolism of MPA was studied in human liver microsomes in the presence of UDP-glucuronic acid, UDP-glucose or NADPH; (C) hydrolysis of metabolites was investigated using beta-glucosidase, beta-glucuronidase or NaOH; (D) cross-reactivity of each metabolite was tested in an immunoassay for MPA (EMIT). 2. Mass spectrometry of M-1, M-2, MPA and MPAG in the negative ion mode revealed molecular ions of m/z 481, m/z 495, m/z 319 and m/z 495 respectively. 3. Incubation of microsomes with MPA and UDP-glucose produced M-1, with MPA and UDP-glucuronic acid MPAG and M-2 were formed, while with MPA and NADPH, M-3 was observed. 4. Beta-Glucosidase hydrolysed M-1 completely. Beta-Glucuronidase treatment led to a complete disappearance of MPAG whereas the amount of M-2 was reduced by approximately 30%. Only M-2 was labile to alkaline treatment. 5. M-2 and MPA but not M-1 and MPAG cross-reacted in the EMIT assay. 6. These results suggest that: (i) M-1 is the 7-OH glucose conjugate of MPA; (ii) M-2 is the acyl glucuronide conjugate of MPA; (iii) M-3 is derived from the hepatic CYP450 system.