Sex differences and androgenic regulation of esterases in the house mouse

Evaluation of Clopidogrel Conjugation Metabolism: PK Studies in Man and Mice of Clopidogrel Acyl Glucuronide

The existence of a glucuronide conjugate of the major circulating clopidogrel metabolites, called clopidogrel acyl glucuronide (CAG), is already known. However, information regarding its pharmacokinetics (PK), metabolism, and clearance are modest. We investigated in vivo the potential CAG trans-esterification to clopidogrel (reaction occurring in vitro in particular conditions) by administering the metabolite to mice. Experiments were then carried out on men, clopidogrel administered alone or followed by activated charcoal intake (intestinal reabsorption blockade). Study objectives included: PK comparison of CAG, clopidogrel carboxylic acid (CCA), and clopidogrel in plasma, determination of their elimination patterns in urine and feces, and tracking of charcoal-induced changes in PK and/or urinary excretion that would indicate relevant enterohepatic recycling of CAG. In mice, CAG was rapidly hydrolyzed to CCA after oral administration, whereas by intravenous route metabolic conversion to CCA was delayed. No levels of clopidogrel were detected in mice plasma, excluding any potential trans-esterification or other form of back-conversion in vivo. PK experiments in man showed that CAG is hydrolyzed in the gastrointestinal tract (very low concentrations in feces), but there is no evidence of enterohepatic recirculation. Quantitation of the three moieties in stool samples accounted for only 1.2% of an administered dose, suggesting that other yet unknown metabolites/degradation products formed through metabolic processes and/or the activity of local microflora are mainly excreted by this route. In man CAG was confirmed as one of the major terminal metabolites of clopidogrel, with a PK behavior similar to CCA.

Regulation of mouse liver microsomal esterases by clofibrate and sexual hormones

Carboxylesterase activity was measured using six different substrates in microsomal preparations from female and ovariectomized female mice in order to evaluate the effects of female sex hormones on esterase expression. With three of the substrates (alpha-naphthyl acetate and esters 2 and 3), esterase activity was the same in both groups; however, with the others (rho-nitrophenyl acetate and esters 1 and 4), there was a small increase in activity in ovariectomized females, compared with intact females. Castration of males followed by treatment with testosterone caused only transient increases in activity for four of the substrates (alpha-naphthyl acetate and esters 1, 2, and 3) and no change in activity for the other two (rho-nitrophenyl acetate and ester 4). Treatment of male and female mice with the peroxisome proliferator clofibrate, with or without testosterone, resulted in increased hydrolysis of alpha-naphthyl acetate and rho-nitrophenyl acetate, but little change for the other substrates. Clofibrate also induced alpha-naphthyl acetate and rho-nitrophenyl acetate hydrolysis in castrated males, but clofibrate and testosterone administrated together resulted in significant increases of activity with all substrates, which were greater than the additive effects of the two compounds administered separately. These results indicate that clofibrate causes significant alterations in the regulation of esterase activity, whereas sex hormones only cause small changes. However, it would seem that testosterone can synergize the effect of clofibrate in castrated males, resulting in higher levels of activity than with clofibrate alone. Finally, an overall increase in esterase activity might be due to a large increase in the activity of a few esterases or to a small increase in many esterases. Enzyme staining of native polyacrylamide gels reveals that the latter is true, with the majority of esterases present in mouse liver microsomes being induced to a small degree by clofibrate.

Pregnancy-associated esterase in sera of baboons

Baboon serum samples were resolved by starch gel electrophoresis and polyacrylamide gradient gel electrophoresis and stained with naphthol substrates for esterase activity. An esterase that hydrolyzed alpha-naphthyl butyrate in preference to alpha-naphthyl acetate was found in very high activities in some individuals but not others. It migrated just cathodal of the albumin band in starch gels. In polyacrylamide gradient gels, it co-migrated with albumin and had an apparent molecular weight of approximately 65,000 daltons. Electrophoretic analysis by gel electrophoresis of random serum samples from male and female baboons indicated that this esterase was present only in the sera of pregnant baboons. Further investigation of serial samples collected from carefully monitored baboons confirmed that the amount of activity of this esterase was correlated with stage of pregnancy. Therefore, it was named pregnancy esterase (PE). PE was detectable by gel electrophoresis and chromogenic staining techniques as early as day 30 of pregnancy; its activity gradually increased with progressive pregnancy and reached maximum activity near full term (182 days). Soon after parturition, the activity of PE decreased rapidly and was not detected in maternal sera by day 14 postpartum. No evidence of PE was detected in sera of pregnant humans.

Identification and development of a genetically closely-linked carboxylesterase family of the mouse liver

Six carboxylesterase isozymes (viz. ES-1, ES-6, ES-9, ES-20, ES-22 and ES-24), governed by esterase gene cluster 1 on chromosome 8 of the house mouse, were identified electrophoretically in liver supernatants using their biochemical, genetic and developmental characteristics. ES-1 and ES-20 were expressed as liver-specific forms. The peri- and postnatal development of the six isozymes indicated that they were individually regulated at the genetic level, although the isozymes were regulated as a group when compared to genetically unrelated esterases. The concept of evolutionary divergence following repeated gene duplication of an ancestral esterase structural gene was extended to cover divergence of the temporal (regulatory) genes associated with the multigene family. Allelic variation of the temporal genes was more limited than that of the corresponding structural genes.

Sex differences in liver non-specific esterases of the green frog Rana esculenta

1. Liver esterases of the green frog Rana esculenta have been fractionated on disc electrophoresis, thin-layer electrofocusing and column electrofocusing. 2. The enzyme resolves in several molecular forms some of which result sex dependent, since they disappear in castrated animals and can be induced by sex hormone administration. 3. The enzyme molecular forms which depend on female hormones might be involved in cellular modifications of hepatocytes related to yolk protein synthesis. induced by sex hormone administration. 3. The enzyme molecular forms which depend on female hormones might be involved in cellular modifications of hepatocytes related to yolk protein synthesis.