The sequence identity of CYP A with
The sequence identity of CYP3A163 with CYP3A sequences from other species is maximum in reptiles ranging (75-91)%, gradually decreasing from trpv1 (63-71)% to mammals 62% to downwards based on evolutionary distances. The high level of homology with CYP3A77 in Alligator mississippiensis suggest that CYP3A163 shares similar structural, functional and regulatory profiles such as strong induction of CYP3A77 in Alligator mississippiensis by dexamethasone and toxaphene . The results suggest comparable catalytic profile of CYP3A163 with human CYP3A4 and require further validation by molecular docking analysis, catalytic and mutagenic studies. This study opens more avenues to investigate evolution of this incredible species in relation to CYP superfamily, to establish the structure-activity relationship and mechanism of action, to explore functional breadth, to find therapeutic, toxicological effects of xenobiotics and to improve the health and survival rate contributing in the conservation management practices.
Declaration of interest
Introduction The glucocorticoid receptor (GR) mediates the hepatic regulation and expression of cytochrome P450 genes which are engaged in the metabolism of drugs and endogenous compounds. Of the cytochrome CYP isoforms, CYP3A is one of the most important cytochrome P450 subfamilies responsible for the metabolism of clinically important drugs and endogenous steroids . Interestingly, conditional inactivation of the glucocorticoid receptor gene in cells expressing dopamine-β-hydroxylase, an enzyme necessary for the synthesis of noradrenaline and adrenaline in the central and the peripheral nervous systems, showed that glucocorticoid-dependent signaling was required for the survival of chromaffin cells . The abovedescribed action also seems to be important for the metabolic function of the liver, since chromaffin cells can be seen in the liver to form clusters in portal areas, or are spotted as single cells in the walls of liver sinusoids and in the region below the connective capsule . Regulation of the expression of mouse CYP3A genes is under multi-hormonal control, in which the growth hormone (GH) and sex hormones play a pivotal role . Furthermore, the noradrenergic system is engaged in the regulation of CYP3A activity. Previous studies have shown that intraperitoneal administration of DSP-4 markedly decreases the activity of CYP3A, but not its protein level, in the liver of male rats . But recent studies have indicated that intracerebroventricular administration of low doses of DSP-4 decreases both the activity and the protein of CYP3A, in the liver of male rats . However, the fact is that DSP-4 which is a toxin specific to noradrenergic neurons in the central and the peripheral nervous system can also very easy pass the brain-blood barrier (to the brain and out of the brain) independently of the routes of administration of DSP-4 [3, 4]. Therefore, the present preliminary study investigated the effect of glucocorticoid receptor selective ablation in the noradrenergic system on the activity of the CYP3A isoform in mouse liver.
Materials and Methods
Results and Discussion Mouse liver microsomes showed a significant capacity for testosterone 6β-hydroxylation (which was specifically catalyzed by CYP3A), which was generally greater in female compared to male mice [1, 9]. In the present study, a significant decrease in the rate of testosterone 6β-hydroxylation (a functional marker of CYP3A activity) was observed in female mutant mice compared to control female animals (Fig. 1A). In contrast, the rate of testosterone 6β-hydroxylation in male mutant mice remained unchanged compared to control males following selective ablation of the GR in the noradrenergic system (Fig. 1B). Interestingly, the level of CYP3A activity in female mutant mice was similar to that found in male mice (Figs. 1A and 1B). Regarding murine CYP3A, it was shown that CYP3A was one of female predominant cytochrome P450 isoforms in mouse liver . Interestingly, the expression of female predominant mouse CYP3A41 and CYP3A44 genes was at high levels in both sexes immediately after birth. Subsequently, the expression level of CYP3A41 and CYP3A44 genes was modified during the pubertal period and maximally reduced 5 weeks after birth in males . A developmental expression of male mouse CYP3A11 and CYP3A13 was also observed . The maximum expression level of CYP3A11 and CYP3A13 genes was reached between 4 and 8 weeks after birth . Moreover, the targeted disruption of the glucocorticoid receptor indicated that the receptor was not obligatory for the glucocorticoid or rifampin induction of CYP3A expression at both mRNA and protein levels in adult glucocrticoid receptor-null mice . However, the presence of pregnane X receptor (PXR), a confirmed mediator of CYP3A induction, accounts for similar effects of both GR agonists and antagonists on CYP3A gene expression . In our study, the general activity of CYP3A in mutant animals was reduced to 68% of the control in female mouse liver, while the enzyme activity remained unchanged in that organ in male mice. The above findings suggest that the full basal activity of mouse CYP3A can be indirectly modified by the GR in the noradrenergic system during the pubertal period. Of note, selective ablation of the GR in the noradrenergic system did not destroy the central and the peripheral noradrenergic system.