Original Full Length Article Gender- and dose-related effects of cyclosporin A on hepatic and bone metabolism Walter Jäger a , Huiqing Xu b , Katrin Wlcek a , Christiane Schüler c , Franz Rubel d , Reinhold G. Erben b, c, ⁎ a Department. of Clinical Pharmacy and Diagnostics, University of Vienna, 1090 Vienna, Austria b Institute of Physiology, Physiological Chemistry and Animal Nutrition, Ludwig Maximilians University, 80539 Munich, Germany c Department of Biomedical Sciences, University of Veterinary Medicine, 1210 Vienna, Austria d Department of Farm Animals and Veterinary Public Health, University of Veterinary Medicine, 1210 Vienna, Austria abstract article info Article history: Received 27 July 2011 Revised 1 October 2011 Accepted 4 October 2011 Available online 14 October 2011 Edited by: Rene Rizzoli Keywords: Cyclosporin A Bone metabolism Estrogen Androgens Drug metabolism Previous data have shown gender-related differences in the skeletal effects of the immunosuppressive drug cyclosporin A (CsA) in rats. To test the hypothesis that the gender-related skeletal effects of CsA are caused by gender-specific metabolism of this drug, we treated aged male and female sham-operated, gonadectomized (GX) as well as sex hormone-supplemented GX rats with 5 mg/kg CsA three times per week for 2 months, and analyzed the bone phenotype as well as the concentrations of CsA and its major metabolites AM1, AM1c, AM9, and AM4N in blood, urine, and liver tissue. CsA treatment induced high turnover osteopenia in males, but not females. Male rats showed several-fold higher CsA and CsA metabolite blood levels com- pared with females. Renal clearance data revealed that CsA undergoes selective tubular reabsorption in male, but not female rats. However, a mathematical modeling approach demonstrated that the higher CsA blood levels in males were almost exclusively caused by a 6-fold lower hepatic clearance rate compared with females. In addition, we subcutaneously treated female rats with up to 6-fold higher doses of CsA. Sim- ilar to males, high dose CsA induced high turnover osteopenia in female rats. Our data show that the gender- related differences in the skeletal effects of CsA are caused by a higher hepatic clearance rate for CsA in female compared to male rats, and not by a differential skeletal response to CsA. Moreover, our study indicates that CsA blood levels of ≤200 ng/ml measured by HPLC do not induce high turnover osteopenia in aged rats. © 2011 Elsevier Inc. All rights reserved. Introduction The immunosuppressive drug cyclosporin A (CsA) is still one of the most important pillars of immunosuppressive therapy after organ transplantations and in autoimmune diseases. CsA is a fungal cyclical undecapeptide isolated from Tolypocladium inflatum [1] which inhibits T cell activation via transcriptional suppression of the interleukin-2 gene [2]. One of the potential untoward side effects of immunosuppres- sive therapy with CsA is a negative effect on the skeleton. The majority of experimental studies in rats have shown that CsA induces a high turnover osteopenia at higher doses [3–5]. However, the molecular mechanism of this effect is still obscure. Clinical studies examining the skeletal effects of CsA in transplant patients have yielded conflicting results. Studies in heart transplant patients [6,7], liver transplant pa- tients [8,9], kidney transplant patients [10–12], or patients receiving bone marrow transplantation [13] indicated a deleterious effect of CsA on bone mass, while some trials in kidney transplant patients on monotherapy with CsA did not suggest CsA-induced bone loss [14–17]. Therefore, the clinical relevance of the potentially deleterious bony effect of CsA is unclear at present. In a previous study, we made the interesting observation that CsA is antiresorptive and bone- sparing in aged female rats but increases bone resorption and reduces bone mass in aged male rats [18]. The gender-specific skeletal effects of CsA were not modulated by sex hormones or gonadectomy [18]. This intriguing observation led us to hypothesize that there may either be gender-related differences in the response of bone cells or T lympho- cytes to CsA, or gender-related differences in the metabolism of this drug leading to different skeletal responses. There is good evidence suggesting that CsA metabolism may in- deed be profoundly different in male and female rats [18–20]. After 4 months of chronic subcutaneous CsA administration we found that blood levels of CsA were several-fold higher in male compared with female rats, and that exogenous administration of supraphysio- logical doses of estradiol from estradiol-containing slow release pel- lets in ovariectomized (OVX) rats strongly reduced CsA blood levels [18]. Moreover, it has been shown that female rats clear CsA faster than male rats after a single intravenous injection [21] mainly due Bone 50 (2012) 140–148 Abbreviations: ANOVA, analysis of variance; BMD, bone mineral density; BW, body weight; CsA, cyclosporin A; E 2 , 17β-estradiol; GX, gonadectomized; HRT, hormone re- placement therapy; MCT, medium chain triglycerides; OATP, organic anion transporter; OVX, ovariectomized; ORX, orchiectomized; pQCT, peripheral quantitative computed to- mography; RE, renal excretion; RIA, radioimmunoassay; SHAM, sham-operated; T, testos- terone undecanoate. ⁎ Corresponding author at: Institute of Physiology, Pathophysiology, and Biophysics, Dept. of Biomedical Sciences, University of Veterinary Medicine, Veterinaerplatz 1, 1210 Vienna, Austria. Fax: + 43 1 250 77 4559. E-mail address: Reinhold.Erben@vetmeduni.ac.at (R.G. Erben). 8756-3282/$ – see front matter © 2011 Elsevier Inc. All rights reserved. doi:10.1016/j.bone.2011.10.005 Contents lists available at SciVerse ScienceDirect Bone journal homepage: www.elsevier.com/locate/bone