Suppression of Hepatic CYP3A1/2 and CYP2C11 by Cyclosporine Is Not Mediated by Altering Growth Hormone Levels

Abstract

Cyclosporine (CsA) suppresses drug metabolism by decreasing cytochrome P450 (P450) enzyme levels in rat liver. Growth hormone (GH) is known to pretranslationally regulate P450 expression. Thus, the suppression of P450 by CsA may involve GH as an intermediate. To address this question, we examined the effects of administering exogenous GH via twice daily subcutaneous injections and in conjunction with chronic subcutaneous CsA administration for 14 days on hepatic P450 expression. CsA alone decreased CYP3A1/2 and CYP2C11 significantly, in a manner similar to that previously found. When administered in the absence of CsA, GH also suppressed CYP3A1/2 and CYP2C11 protein levels as compared with GH vehicle. In the presence of CsA, GH did not cause further suppression of either CYP3A1/2 or CYP2C11 expression when compared with CsA treatment with GH vehicle. Testosterone in vitro catalytic assays confirmed that CsA and GH separately cause significant decreases in activity levels. Also, the concomitant administration of GH and CsA caused lowered production of 16␣-, 2␣-, 6␤-, and 2␤-hydroxytestosterone as compared with the administration of GH with CsA vehicle and as compared with the administration of GH vehicle with CsA. This study shows that GH is a dominating factor over CsA in determining hepatic P450 expression and activity. In addition, CsA does not seem to alter GH levels as a mediating event in suppressing P450 expression and activity. Since CsA given in combination with GH further suppressed P450 activity as compared with CsA given in combination with vehicle, this suggests that changes in hormonal status are likely to be one of the many factors that is responsible for the lack of a clear association between cyclosporine dosing and markers of toxicity.Immune suppression has been an effective avenue of treatment for several conditions including preventing organ transplantation rejection and autoimmune disease. One potent immunosuppressive drug, cyclosporine (CsA), a cyclic undecapeptide of fungal origin, is often used as the drug of choice following organ transplantation. CsA is mainly used for the prevention of allograft rejection and for the prevention of graft-versus-host disease following a bone marrow transplant, as well as for the treatment of arthritis (Tugwell et al., 1987). Although CsA is known to affect interleukins 3 and 4 (IL-3, IL-4), tumor necrosis factor-␣, and B cells, it primarily imparts its immunosuppressive action by preventing IL-2 synthesis from activated T cells (Bunjes et al., 1981).Despite the effectiveness of CsA in suppressing the immune response, there exist several potentially harmful side effects, including nephrotoxicity, hepatotoxicity, and hypertension (Borel, 1990). Since CsA is not only a substrate, but also an inhibitor of CYP3A2, it can modify hepatic drug metabolism in rats following chronic therapy (Brunner et al., 1996). CsA suppresses cytochrome P450 (P450) protein expression, which could then hinder further metabolism of CsA (Cunningham et al., 1985;Brunner et al...

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“…CYP3A2 and 2C11 metabolic activity was determined by in vitro analysis of testosterone hydroxylation as previously described (Lu et al, 2003). Reaction mixtures consisted of 1-ml volumes containing 0.1 M potassium phosphate, 250 M testosterone in methanol, 200 g of hepatic microsomal protein, and a NADPH regenerating system consisting of 5 mM NADP ϩ , 100 mM glucose 6-phosphate, and 100 mM magnesium chloride.…”

“…Dried extracts were then dissolved in 200 l of methanol and stored at 4°C until further analysis. Testosterone metabolites were separated and quantified by high-pressure liquid chromatography according to a previously described method (Lu et al, 2003).…”

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“…The organic phase was transferred to a clean tube, evaporated under a constant stream of air, dissolved in 200 μl of methanol and stored in a sealed tube at 4°C until further analysis. Testosterone metabolites were separated and quantified by HPLC according to a previously described method (Lu, 2003). Peak areas of corresponding hydroxylation metabolites were measured and compared to peak areas of the internal standard within the same run.…”