Sirolimus, but not the structurally related RAD (everolimus), enhances the negative effects of cyclosporine on mitochondrial metabolism in the rat brain

Abstract

1 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 e ects of sirolimus with those of the structurally related RAD. 2 Two-week-old rats (25 g) were allocated to the following treatment groups (all n=6): I. control, II. cyclosporine (10 mg kg 71 d 71 ), III. sirolimus (3 mg kg 71 d 71 ), IV. RAD (3 mg kg 71 d 71 ), 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. 3 Cyclosporine signi®cantly inhibited mitochondrial glucose metabolism (glutamate: 78+6% of control; GABA: 67+12%; NAD + : 76+3%; P50.05), but increased lactate production. Sirolimus and RAD inhibited cytosolic glucose metabolism via lactate production (sirolimus: 81+3% of control, RAD: 69+2%; P50.02). Sirolimus enhanced cyclosporine-induced inhibition of mitochondrial glucose metabolism (glutamate: 60+4%; GABA: 59+8%; NAD + : 45+5%; P50.02 versus cyclosporine alone). Lactate production was signi®cantly reduced. In contrast, RAD antagonized the e ects of cyclosporine (glutamate, GABA, and NAD + , not signi®cantly di erent from controls). 4 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. 5 The combination of cyclosporine/RAD compares favourably to cyclosporine/sirolimus in regards to their e ects on brain high-energy metabolism and tissue distribution in the rat.

Inhibition of mTOR induces autophagy and reduces toxicity of polyglutamine expansions in fly and mouse models of Huntington disease

“…Thus, we concluded that the ability of rapamycin to inhibit mTOR activity might be impaired after prolonged huntingtin expression or increased aggregate formation 8 . Therefore, early treatment with rapamycin may attenuate Huntington disease in vivo, as rapamycin (and its analogs) are lipophilic, show good blood-brain barrier penetration [11][12][13][14] and are designed for long-term use in humans 11 .…”

Organ-specific response to inhibition of mitochondrial metabolism by cyclosporine in the rat

“…Rats were treated with 10 mg/kg per day CyA or a vehicle solution (n = 5 each) for a period of 6 days in order to establish constant drug tissue levels. This oral dose was chosen on the basis of our previous dose-funding studies for the brain [20] and heart [12]. During the study period, the animals were closely monitored, including daily evaluations of appearance, grooming, appetite, behavior, activity, and body weight.…”

“…For MRS, we extracted the collected frozen tissue samples using a dual perchloric acid (PCA)/lipid extraction procedure [20]. The powdered frozen tissue was added to 6 ml of ice-cold 12% PCA for protein precipitation and subsequently homogenized using electrical homogenizer.…”

Modulation of calcineurin activity in mouse brain by chronic oral administration of cyclosporine A

“…Brain tissue was highly resistant to inhibition by CsA because physiological barriers, such as the blood-brain barrier (BBB), and the abundance of CsA-binding proteins, such as immunophilins, determined the degree to which CsA accumulated in each tissue in vivo. CsA was primarily taken up from lipoprotein at the blood-brain interface, but because of the tight junctions at the blood-brain and blood-CSF barriers, CsA effectively became trapped in cerebral endothelial cells and the choroid plexus (22). In addition, Dohgu et al (23) investigated the mechanism by which CsA causes BBB dysfunction in rodent brain endothelial cells.…”