title: Sirolimus, but not the structurally related RAD (everolimus), enhances the negative effects of cyclosporine on mitochondrial metabolism in the rat brain.
abstract: Clinical studies have shown enhancement of cyclosporine toxicity when co-administered with the immunosuppressant sirolimus. We evaluated the biochemical mechanisms underlying the sirolimus/cyclosporine interaction on rat brain metabolism using magnetic resonance spectroscopy (MRS) and compared the effects of sirolimus with those of the structurally related RAD. Two-week-old rats (25 g) were allocated to the following treatment groups (all n=6): I. control, II. cyclosporine (10 mg kg(-1) d(-1)), III. sirolimus (3 mg kg(-1) d(-1)), IV. RAD (3 mg kg(-1) d(-1)), V. cyclosporine+sirolimus and VI. cyclosporine+RAD. Drugs were administered by oral gavage for 6 days. Twelve hours after the last dose, metabolic changes were assessed in brain tissue extracts using multinuclear MRS. Cyclosporine significantly inhibited mitochondrial glucose metabolism (glutamate: 78+/-6% of control; GABA: 67+/-12%; NAD(+): 76+/-3%; P<0.05), but increased lactate production. Sirolimus and RAD inhibited cytosolic glucose metabolism via lactate production (sirolimus: 81+/-3% of control, RAD: 69+/-2%; P<0.02). Sirolimus enhanced cyclosporine-induced inhibition of mitochondrial glucose metabolism (glutamate: 60+/-4%; GABA: 59+/-8%; NAD(+): 45+/-5%; P<0.02 versus cyclosporine alone). Lactate production was significantly reduced. In contrast, RAD antagonized the effects of cyclosporine (glutamate, GABA, and NAD(+), not significantly different from controls). The results can partially be explained by pharmacokinetic interactions: co-administration increased the distribution of cyclosporine and sirolimus into brain tissue, while co-administration with RAD decreased cyclosporine brain tissue concentrations. In addition RAD, but not sirolimus, distributed into brain mitochondria. The combination of cyclosporine/RAD compares favourably to cyclosporine/sirolimus in regards to their effects on brain high-energy metabolism and tissue distribution in the rat.
authors.affiliation: Department of Biopharmaceutical Sciences, University of California, San Francisco, California, CA 94143, USA.
authors.forename: N
authors.initials: N
authors.lastname: Serkova
authors.forename: W
authors.initials: W
authors.lastname: Jacobsen
authors.forename: C U
authors.initials: CU
authors.lastname: Niemann
authors.forename: L
authors.initials: L
authors.lastname: Litt
authors.forename: L Z
authors.initials: LZ
authors.lastname: Benet
authors.forename: D
authors.initials: D
authors.lastname: Leibfritz
authors.forename: U
authors.initials: U
authors.lastname: Christians
mesh_terms: D000818:Animals; D001224:Aspartic Acid / Q000031:analogs & derivatives / Q000187:drug effects / Q000378:metabolism; D001835:Body Weight / Q000187:drug effects; D001921:Brain / Q000187:drug effects* / Q000378:metabolism; D016572:Cyclosporine / Q000097:blood / Q000494:pharmacology; D004357:Drug Synergism; D000068338:Everolimus; D018698:Glutamic Acid / Q000187:drug effects / Q000378:metabolism; D005973:Glutamine / Q000187:drug effects / Q000378:metabolism; D007166:Immunosuppressive Agents / Q000097:blood / Q000494:pharmacology*; D009682:Magnetic Resonance Spectroscopy; D008928:Mitochondria / Q000187:drug effects* / Q000378:metabolism; D062907:Oxaloacetic Acid / Q000378:metabolism; D010710:Phosphates / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D020123:Sirolimus / Q000031:analogs & derivatives / Q000097:blood / Q000494:pharmacology; D015430:Weight Gain / Q000187:drug effects; D005680:gamma-Aminobutyric Acid / Q000187:drug effects / Q000378:metabolism
chemical_list: D007166:Immunosuppressive Agents; D010710:Phosphates; D005973:Glutamine; D062907:Oxaloacetic Acid; D001224:Aspartic Acid; D018698:Glutamic Acid; D005680:gamma-Aminobutyric Acid; D016572:Cyclosporine; C000179:N-acetylaspartate; D000068338:Everolimus; D020123:Sirolimus