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Prevention of Detrimental Effect of Cyclosporin A on Vascular Ingrowth of Transplanted Pancreatic Islets With Verapamil

The revascularization of pancreatic islet clusters transplanted beneath the renal capsule was studied in a syngeneic mouse model. The degree of vascular ingrowth was visualized by in vivo fluorescence microscopy (fluorescein isothiocyanate-dextran) and judged by a semiquantitative method from coded video recordings. The recipients of isografts were divided into four groups, depending on their daily immunosuppressive treatment: 1) none (controls), 2) 15 mg/kg cyclosporin A (CsA), 3) 0.4 mg/kg verapamil + 15 mg/kg CsA, and 4) 20–30 mg/kg methylprednisolone. In control animals, capillary ingrowth was first demonstrated on day 6, followed by progressive vascularization up to day 34. After 6 mo, the vascular architecture was similar to that seen in normal islets in situ. CsA alone significantly decreased vascular ingrowth on day 14 compared with controls (P < .02). Verapamil prevented the detrimental effect of CsA (P < .01), probably by improving renal subcapsular blood flow. Methylprednisolone did not affect revascularization compared with control animals at day 14. We conclude that CsA inhibits vascular ingrowth into transplanted pancreatic islets, which is likely to have clinical implications. The prevention of CsA vascular ingrowth inhibition by a calcium antagonist indicates a possible approach to the correction of this problem, particularly when the renal capsule is used as the recipients transplant site.

Protection against cyclosporine-induced impairment of renal microcirculation by verapamil in mice.

Fluorescence microscopy was used to examine the effect of cyclosporine (CsA) infusion on renal subcapsular (cortical) blood flow in 53 living mice, using FITC-dextran (MW: 156,000) as a fluorescent marker. CsA (8–19 mg/kg body weight) given i.v. for 1 min induced complete inhibition of blood flow. A complete standstill of flow was also obtained during a continuous infusion with a rate of 0.8–2 mg/kg/min. With lower infusion rates (0.15–0.23 mg/kg/min), blood flow was partially impaired. In all experiments, the decrease in flow occurred after a 15–25 min delay, suggesting a CsA metabolite or exhaustion of a protective mechanism as the causative agent. Pretreatment with an α-blocking agent, phentolamine (1.0 mg/kg), did not prevent the CsA-induced inhibition of blood flow. In contrast, pretreatment with a calcium antagonist, verapamil (0.3–0.4 mg/kg), prevented the impairment of blood flow at low (0.15–0.23 mg/kg/min), and partially at higher (0.8–2.4 mg/kg/min) rates of CsA infusion. Clinical studies are warranted to explore the role of calcium antagonists in the prevention of posttransplant acute cyclosporine-induced nephrotoxicity.

IN VIVO FLUORESCENCE MICROSCOPY OF KIDNEY SUBCAPSULAR BLOOD FLOW IN MICE EFFECTS OF CYCLOSPORINE, (NVA)-CYCLOSPORINE, AND ISRADIPINE, A NEW CALCIUM ANTAGONIST

The subcapsular kidney microcirculation in mice was observed through a fluorescence microscope, recorded on videotape, and examined for response to infusions of cyclosporine A (CsA) and cyclosporine G (CsG). Coded video recordings were evaluated by a semiquantitative method. CsA infusion (1.6 +/- 0.4 mg/kg/min) induced a nearly complete inhibition of the subcapsular blood flow. At lower infusion rates (0.46 +/- 0.2 mg/kg/min), the blood flow inhibition was less pronounced. CsG infusions at corresponding rates induced significantly less inhibition. Pretreatment with a new calcium antagonist, isradipine (18-20 micrograms/kg bwt), completely prevented the CsA-induced impairment of subcapsular microcirculation. The calcium antagonist, however, did not improve blood flow when administered after induction of inhibition by CsA (16.8 +/- 2.5 mg/kg), emphasizing the importance of pretreatment. This study suggests hypoperfusion due to vasoconstriction as an important pathophysiologic mechanism for CsA-induced nephrotoxicity. CsG, when given at corresponding rates, induced less inhibition of the blood flow. Pretreatment with a calcium antagonist, isradipine, completely prevented a CsA-induced inhibition of blood flow, suggesting a potential value in the prevention of CsA-induced nephrotoxicity.

Verapamil (VP) improves the outcome after renal transplantation (CRT)

Calcium antagonists (CATs) have a role in the management of certain types of renal insufficiency. These include prophylaxis against post-transplant-associated acute renal failure and cyclosporine A (CsA)-induced renal dysfunction. For the transplanted kidney, CATs may be beneficial in several settings. First, a CAT during organ procurement protects the kidney during ischemic periods. Second, CATs given perioperatively protect the kidney during reperfusion and early after transplantation. Third, CATs also offer protection against CsA nephrotoxicity.

Improvement of cadaver renal transplantation outcomes with verapamil: a review☆

Although cyclosporin A (CsA) has allowed substantial advances in organ transplantation due to its immunosuppressive properties, its use is complicated by its direct nephrotoxic effects. Initial studies with mice confirmed that CsA caused a dose-related inhibition of the subcapsular microcirculation; subsequent clinical investigations have confirmed this inhibitory effect. Efforts to circumvent CsA-induced nephrotoxicity have focused on calcium antagonists. For example, when the calcium antagonist verapamil was administered before the initiation of CsA, renal blood flow was maintained. Verapamil therapy was also associated with significantly fewer rejection episodes (3 of 22; 14%) within 4 weeks of transplantation than CsA therapy alone (10 of 18; 56%). In a current study, verapamil 10 mg was injected into the renal artery during surgery, followed by 120 mg tid orally for 14 days. This regimen reduced delayed function incidents (the need for dialysis) during the first post-transplant week. Excluding nonfunctioning kidneys and technical failures, there were no graft losses secondary to rejection in patients treated with verapamil. The beneficial effects of verapamil therapy on transplant outcome may be related to its ability to protect cells from ischemia, the selective vasodilation of the efferent arteriole, elevated CsA blood levels, and inherent immunosuppressive properties.

The protective effect of verapamil on mouse islets transplanted under the kidney capsule.

Islets from normal NMRI mice were transplanted under the kidney capsule of syngeneic recipients. The graft-bearing mice were divided into 4 groups treated daily with cremophor alone (control), cyclosporine (25 mg/kg body wt), CsA in combination with the calcium antagonist verapamil (0.4 mg/kg), or verapamil alone. After 3 weeks the grafts were removed, analyzed for insulin secretory dynamics in a perifusion system, and extracted for their contents of insulin. The graft insulin content was significantly decreased by CsA, an effect counteracted by verapamil. As compared with controls, all treatments increased the basal insulin at 2.8 mmol/L glucose. CsA together with verapamil enhanced the biphasic secretory response to 16.7 mmol/L glucose, whether expressed per graft or per unit of insulin content. The glucose-stimulated insulin release per graft was greater after combining CsA with verapamil than after CsA alone. It is concluded that CsA has adverse effects on islets transplanted to the kidney, and that these effects can be ameliorated by combining the immunosuppressant with verapamil.