Molecular characterization of functional UDP-glucuronosyltransferases 1A and 2B in common marmosets

Evaluation and comparison of pharmacokinetic profiles and safety of two extended-release buprenorphine formulations in common marmosets (Callithrix jacchus)

While sustained-release buprenorphine (BSR) is used as a long-lasting opioid analgesic in common marmosets (Callithrix jacchus), there are no published studies on pharmaceutical-grade extended-release buprenorphine options such as Ethiqa XR (EXR) for this species. However, BSR is a compounded product and has been reported to cause injection site reactions in multiple species, including marmosets. Additionally, now with the availability of EXR, a pharmaceutical-grade veterinary product, the use of BSR in laboratory animals is not compliant with the Guide for the Care and Use of Laboratory Animals (Guide) unless scientifically justified and approved by the IACUC. We compared pharmacokinetic and safety profiles of BSR (0.15 mg/kg) and EXR (0.1-0.2 mg/kg) administered subcutaneously to adult marmosets. Blood was collected by venipuncture of the saphenous vein at multiple time points (0.25-72 h) and analyzed by liquid chromatography-tandem mass spectrometry (LC-MS/MS). EXR between 0.1 and 0.2 mg/kg resulted in a dose-dependent increase in Cmax (1.43-2.51 ng/mL) and were not statistically different from BSR (1.82 ng/mL). Tmax, lambdaz, and t1/2 were not statistically different between formulations. Mean plasma buprenorphine concentrations for BSR and EXR exceeded the therapeutic threshold (0.1 ng/mL) within 0.25 h and lasted for > 72 h. Mild sedation, but neither respiratory depression nor ataxia, was observed for both formulations. BSR injection sites had significantly higher histopathological scores compared to EXR. Video recordings for monitoring drug-induced behavioral changes showed increased animal activity levels after BSR and EXR versus saline controls. Norbuprenorphine, a buprenorphine metabolite associated with respiratory depression, was detected in the plasma after BSR and EXR administration as well as by in vitro liver microsome assays. In conclusion, we recommend using EXR over BSR as a long-lasting buprenorphine analgesic in marmosets because EXR is a pharmaceutical-grade formulation that is compliant with FDA guidelines and the Guide as well as exhibits comparable PK and safety profiles as BSR.

Drug-oxidizing and conjugating non-cytochrome P450 (non-P450) enzymes in cynomolgus monkeys and common marmosets as preclinical models for humans

Many drug oxidations and conjugations are mediated by a variety of cytochromes P450 (P450) and non-P450 enzymes in humans and non-human primates. These non-P450 enzymes include aldehyde oxidases (AOX), carboxylesterases (CES), flavin-containing monooxygenases (FMO), glutathione S-transferases (GST), arylamine N-acetyltransferases (NAT),sulfotransferases (SULT), and uridine 5'-diphospho-glucuronosyltransferases (UGT) and their substrates include both endobiotics and xenobiotics. Cynomolgus macaques (Macaca fascicularis, an Old-World monkey) are widely used in preclinical studies because of their genetic and physiological similarities to humans. However, many reports have indicated the usefulness of common marmosets (Callithrix jacchus, a New World monkey) as an alternative non-human primate model. Although knowledge of the drug-metabolizing properties of non-P450 enzymes in non-human primates is relatively limited, new research has started to provide an insight into the molecular characteristics of these enzymes in cynomolgus macaques and common marmosets. This mini-review provides collective information on the isoforms of non-P450 enzymes AOX, CES, FMO, GST, NAT, SULT, and UGT and their enzymatic profiles in cynomolgus macaques and common marmosets. In general, these non-P450 cynomolgus macaque and marmoset enzymes have high sequence identities and similar substrate recognitions to their human counterparts. However, these enzymes also exhibit some limited differences in function between species, just as P450 enzymes do, possibly due to small structural differences in amino acid residues. The findings summarized here provide a foundation for understanding the molecular mechanisms of polymorphic non-P450 enzymes and should contribute to the successful application of non-human primates as model animals for humans.

Pharmacokinetics of Single-Dose Intramuscular and Subcutaneous Injections of Buprenorphine in Common Marmosets (Callithrix jacchus)

Although buprenorphine is the most frequently used opioid analgesic in common marmosets (Callithrix jacchus), there is limited information in the literature supporting current dosing regimens used for this species. The purpose of this study was to determine the pharmacokinetic profiles of single-dose buprenorphine HCl administered intramuscularly (IM) at 0.01 mg/kg in 6 adult marmosets (1.8 to 12.8 y old; 2 males, 4 females) and subcutaneously (SQ) at 0.01 mg/kg in 6 adult marmo- sets (2.3-4.4 y old; 3 males, 3 females) by mass spectrometry. Blood was collected at multiple time points from 0.25 to 24 h from unsedated animals following a hybrid sparse-serial sampling design. The maximal observed plasma concentration of buprenorphine (Cmax ) administered IM (2.57 ± 0.95 ng/mL) was significantly higher than administered SQ (1.47 ± 0.61 ng/mL). However, the time to Cmax (Tmax) was not statistically different between routes (17.4 ± 6 min for IM and 19.8 ± 7.8 min for SQ). The time of the last quantifiable concentration of buprenorphine was 5 ± 1.67 h for IM compared with 6.33 ± 1.51 h for SQ, which was not statistically different. The mean buprenorphine plasma concentration-time curves were used to propose a dosing frequency of 4 to 6 h for buprenorphine at 0.01 mg/kg IM or SQ based on a theoretical therapeutic plasma concentration threshold of 0.1 ng/mL. Based on the mean pharmacokinetic parameters and plasma-concentration time curves, both IM and SQ routes of buprenorphine at this dose provide a rapid increase in the plasma concentration of buprenorphine above the therapeutic threshold, and may be more effective for acute rather than long-lasting analgesia. Further studies are needed to examine repeated dosing regimens and the efficacy of buprenorphine in common marmosets.

Human total clearance values and volumes of distribution of typical human cytochrome P450 2C9/19 substrates predicted by single-species allometric scaling using pharmacokinetic data sets from common marmosets genotyped for P450 2C19

Common marmosets (Callithrix jacchus) are small non-human primates that genetically lack cytochrome P450 2C9 (CYP2C9). Polymorphic marmoset CYP2C19 compensates by mediating oxidations of typical human CYP2C9/19 substrates.Twenty-four probe substrates were intravenously administered in combinations to marmosets assigned to extensive or poor metaboliser (PM) groups by CYP2C19 genotyping. Eliminations from plasma of cilomilast, phenytoin, repaglinide, tolbutamide, and S-warfarin in the CYP2C19 PM group were significantly slow; these drugs are known substrates of human CYP2C8/9/19.Human total clearance values and volumes of distribution of the 24 test compounds were extrapolated using single-species allometric scaling with experimental data from marmosets and found to be mostly comparable with the reported values.Human total clearance values and volumes of distribution of 15 of the 24 test compounds similarly extrapolated using reported data sets from cynomolgus or rhesus monkeys were comparable to the present predicted results, especially to those based on data from PM marmosets.These results suggest that single-species allometric scaling using marmosets, being small, has advantages over multiple-species-based allometry and could be applicable for pharmacokinetic predictions at the discovery stage of drug development.

Genetic variants of UDP-glucuronosyltransferases 1A1, 1A6, and 1A9 in cynomolgus and rhesus macaques

1. In the cynomolgus macaque, UDP-glucuronosyltransferases (UGTs) 1As have similar molecular and enzymatic characteristics to those of their human orthologs. However, genetic polymorphisms in major cynomolgus UGT1A1/6/9 have not been investigated. 2. We re-sequenced UGT1A1, UGT1A6, and UGT1A9 in 186 cynomolgus macaques (bred in Cambodia, China, or Indonesia) and 54 rhesus macaques and found 15, 13, and 26 non-synonymous variants, respectively. 3. Of these UGT1A1, UGT1A6, and UGT1A9 variants, respectively, 10, 9, and 12 were unique to cynomolgus macaques; 4, 1, and 2 were unique to rhesus macaques; and 1, 2, and 5 were found in both cynomolgus and rhesus macaques. The frequency of the UGT1A1 mutation G69R was 23%, 28%, and 63% in cynomolgus macaques bred in Cambodia, China, and Indonesia, respectively, and 97% in rhesus macaques. 4. The O-glucuronidation activities of liver microsomes from cynomolgus and rhesus macaques with respect to estradiol, serotonin, and propofol were measured. Among these activities, liver microsomes from cynomolgus macaques heterozygous for UGT1A1 G69R (n = 11) showed significantly reduced estradiol 3-O-glucuronidation activities compared with those from wild-type animals (n = 38). 5. These results suggest genetic variants such as UGT1A1 G69R could influence the UGT1A1-mediated glucuronidation of drugs in cynomolgus and rhesus macaques.

Expression of functional sulfotransferases (SULT) 1A1, 1A3, 1B1, 1C2, 1E1, and 2A1 in common marmosets

Cytosolic sulfotransferases (SULTs), which mediate the conjugation of drugs with 3'-phosphoadenosine-5'-phosphosulfate, have been characterized in humans and cynomolgus monkeys. However, SULTs remain to be evaluated in common marmosets, a species of non-human primate often employed in drug metabolism and pharmacokinetic studies of endogenous and exogenous compounds. In this study, marmoset SULT1A1, 1A3, 1B1, 1C2, 1E1, and 2A1 cDNAs were isolated and characterized, based on genome data. The deduced amino acid sequences of these marmoset SULT cDNAs had high identities (90-95%) with their human orthologs, except for marmoset SULT2A1, which was only 81% identical to human SULT2A1. The amino acid sequences of the orthologs of these six SULTs in marmosets, monkeys, and humans were closely clustered in a phylogenetic tree. The structures and genomic organizations of marmoset SULT genes were similar to those of their human orthologs. Among the five marmoset tissues analyzed, SULT mRNAs showed typical expression patterns. The most abundant SULT mRNAs were SULT1B1 in liver, small intestine, and kidney; SULT1E1 in lung; and SULT1A3 in brain. Recombinant marmoset SULT1A1, 1A3, 1B1, 1C2, 1E1, and 2A1 proteins expressed in bacterial cytosolic fractions mediated sulfate conjugations with 3'-phosphoadenosine-5'-phosphosulfate of the following typical human SULT substrates: dopamine, 1-naphthol, p-nitrophenol, estradiol, and dehydroepiandrosterone. Taken together, these wide-ranging results suggest functional and molecular similarities of SULTs among marmosets, monkeys, and humans.

Utility of Common Marmoset (Callithrix jacchus) Embryonic Stem Cells in Liver Disease Modeling, Tissue Engineering and Drug Metabolism

The incidence of liver disease is increasing significantly worldwide and, as a result, there is a pressing need to develop new technologies and applications for end-stage liver diseases. For many of them, orthotopic liver transplantation is the only viable therapeutic option. Stem cells that are capable of differentiating into all liver cell types and could closely mimic human liver disease are extremely valuable for disease modeling, tissue regeneration and repair, and for drug metabolism studies to develop novel therapeutic treatments. Despite the extensive research efforts, positive results from rodent models have not translated meaningfully into realistic preclinical models and therapies. The common marmoset Callithrix jacchus has emerged as a viable non-human primate model to study various human diseases because of its distinct features and close physiologic, genetic and metabolic similarities to humans. C. jacchus embryonic stem cells (cjESC) and recently generated cjESC-derived hepatocyte-like cells (cjESC-HLCs) could fill the gaps in disease modeling, liver regeneration and metabolic studies. They are extremely useful for cell therapy to regenerate and repair damaged liver tissues in vivo as they could efficiently engraft into the liver parenchyma. For in vitro studies, they would be advantageous for drug design and metabolism in developing novel drugs and cell-based therapies. Specifically, they express both phase I and II metabolic enzymes that share similar substrate specificities, inhibition and induction characteristics, and drug metabolism as their human counterparts. In addition, cjESCs and cjESC-HLCs are advantageous for investigations on emerging research areas, including blastocyst complementation to generate entire livers, and bioengineering of discarded livers to regenerate whole livers for transplantation.

Molecular characterization of UDP-glucuronosyltransferases 3A and 8A in cynomolgus macaques

UDP-glucuronosyltransferases (UGTs) are drug-metabolizing enzymes essential for the metabolism of endogenous substrates and xenobiotics. The cynomolgus macaque is a nonhuman primate species widely used in drug metabolism studies. The molecular characteristics of UGTs have been extensively investigated in humans, but they remain to be elucidated in cynomolgus macaques. In this study, cynomolgus macaque UGT3A1, UGT3A2, and UGT8A1 cDNAs were isolated and characterized. Amino acid sequences deduced from cynomolgus UGT3A1, UGT3A2, and UGT8A1 cDNAs were highly identical with their human orthologs (93, 96, and 99%, respectively) and were closely clustered in a phylogenetic tree. In the genome, cynomolgus UGT3A and UGT8A genes were located in the regions corresponding to those of their human orthologs. Among the 10 tissue types analyzed, expression of cynomolgus UGT3A1 and UGT3A2 mRNAs was detected in liver, kidney, and testis; the UGT3A1 and UGT3A2 mRNAs were most abundant in liver and testis, respectively. Cynomolgus UGT8A1 was most abundantly expressed in kidney, followed by brain, jejunum, and testis. These results suggest that cynomolgus UGT3As and UGT8A1 have molecular similarities to their human orthologs.