Blood levels and nephrotoxicity of cyclosporin A and G in rats

Fluconazole plus cyclosporine: a fungicidal combination effective against experimental endocarditis due to Candida albicans

Recent observations demonstrated that fluconazole plus cyclosporine (Cy) synergistically killed Candida albicans in vitro. This combination was tested in rats with C. albicans experimental endocarditis. The MICs of fluconazole and Cy for the test organism were 0.25 and >10 mg/liter, respectively. Rats were treated for 5 days with either Cy, amphotericin B, fluconazole, or fluconazole-Cy. Although used at high doses, the peak concentrations of fluconazole in the serum of rats (up to 4.5 mg/liter) were compatible with high-dose fluconazole therapy in humans. On the other hand, Cy concentrations in serum (up to 4.5 mg/liter) were greater than recommended therapeutic levels. Untreated rats demonstrated massive pseudohyphal growth in both the vegetations and the kidneys. However, only the kidneys displayed concomitant polymorphonuclear infiltration. The therapeutic results reflected this dissociation. In the vegetations, only the fungicidal fluconazole-Cy combination significantly decreased fungal densities compared to all groups, including amphotericin B (P < 0.0001). In the kidneys, all regimens except the Cy regimen were effective, but fluconazole-Cy remained superior to amphotericin B and fluconazole alone in sterilizing the organs (P < 0.0001). While the mechanism responsible for the fluconazole-Cy interaction is hypothetical, this observation opens new perspectives for fungicidal combinations between azoles and other drugs.

Synergism between long-acting bromocryptine microcapsules and cyclosporine A in the prevention of various autoimmune diseases in rats

Pre-treatment of male Sprague-Dawley rats with long-acting bromocryptine microcapsules (CBLA) significantly inhibited the arthritic response to Freund's complete adjuvant and reduced weight loss, thymolysis, splenomegaly and leukocytosis. In the prevention of adjuvant arthritis (AA), the combination of CBLA plus sub-optimal doses of cyclosporine A (CsA) was more efficient than either of the drugs alone. Sub-optimal doses of CsA were 0.1 and 1.0 mg/kg/day s.c. for 5 days. Furthermore, CBLA alone did not decrease the incidence of experimental allergic uveitis (EAU) in the male Lewis rats. Low-dose CsA reduced the incidence of uveitis by 50%, and with the addition of CBLA, 100% of rats were protected. Low-dose CsA was 2 mg/kg/day i.m. for 14 days. Long-term treatment of male Sprague-Dawley rats with CBLA alone reduced the incidence and severity of spontaneous autoimmune periarteritis nodosa (PN) in a dose-dependent manner; CsA was less potent than CBLA, and only additive effects were obtained. Finally, for the prevention of spontaneous autoimmune insulin-dependent diabetes (DM), the administration of CBLA did not improve the effect of a low-dose CsA in male BB rats. Nevertheless, a delay in onset of DM could be achieved. A sequential therapy using CsA plus CBLA clearly showed beneficial effects. The dose of CsA was 10 mg/kg p.o. 6 days/week for 21 weeks. Compared with Sprague-Dawley or Lewis male rats, BB male rats showed only weak prolactin suppression after the same doses of CBLA. It is suggested that the use of CBLA may be particularly beneficial in autoimmune disorders. The effectiveness of the combination therapy CBLA plus CsA, however, was dependent on the model considered. Various factors could play a role: (1) the different ways of administering CsA (s.c. in AA, i.m. in EAU and PN, oral in DM); (2) strain-dependency in the capacity of CBLA to suppress Prl secretion; and (3) at least in the BB rats, the transient increase of CsA bioavailibility which was possibly induced by CBLA.

Experimental nephrotoxicity, hepatotoxicity and pharmacokinetics of cyclosporin G versus cyclosporin A

Cyclosporin G (CsG) is an analogue of cyclosporin A (CsA) with strong immunosuppressive activity. We compared these two drugs in a rat model in which salt depletion promotes irreversible renal interstitial fibrosis with renal dysfunction in animals given CsA for three weeks. When both drugs were given in the same dosage on a weight basis (15 mg/kg/day, subcutaneously), CsA blood levels were higher than CsG (3305 vs. 1824 ng/ml, P < 0.001). This could be explained by a higher CsG clearance (6.4 vs. 4.3 ml/min/kg in CsA, P < 0.0001) resulting in smaller CsG area under the curve. There was also lower renal and hepatic CsG tissue concentrations. CsA induced a dramatic decrease in GFR, 0.14 in CsA versus 0.67 ml/min/100 g in control, P < 0.001, and increased urinary excretion of N-acetyl beta-D-glucosaminidase (NAG), 21 in CsA versus 13 IU/gCr in control rats, P < 0.001. CsG-treated and control rats had similar GFR and urinary NAG. When CsA dosage was decreased to 7.5 mg/kg blood levels were similar to those found with CsG 15 mg/kg. CsA at this dose caused a reduced GFR (0.29 ml/min/100 g) and an increased urinary NAG (20 IU/gCr) (P < 0.01 vs. control for both). Both dosages of CsA induced considerable cortical and medullary injury (interstitial fibrosis and tubular atrophy), more severe than the histological damage found in CsG-treated rats. Neither drug promoted significant changes in liver function or histology.(ABSTRACT TRUNCATED AT 250 WORDS)

A randomized pilot study of cyclosporin G in renal transplantation

Animal studies have suggested that the analogue cyclosporin G (CyG) may be less nephrotoxic than cyclosporin A (CyA). A pilot study was therefore performed in 10 primary cadaveric renal allograft recipients who were randomized to receive posttransplant immunosuppression with either CyA or CyG. The follow-up time was a minimum of 1 year. One graft was lost in each group. All patients in both groups experienced at least one acute rejection episode. Episodes of acute nephrotoxicity were observed in both groups. Renal function, as assessed by determinations of the serum creatinine level and chromium-ethylene diamine tetra-acetic acid (Cr-EDTA) clearance, did not differ between the two groups. Renal allograft biopsies showed a significantly higher degree of fibrosis in the CyG group than in the CyA group. All CyG-treated patients evidenced laboratory signs of acute liver toxicity, which was dose-dependent and reversible. Today, all CyG-treated patients have been switched to CyA. This study shows that immunosuppression after renal transplantation in man is possible with CyG; however, it does not seem to have any advantages over CyA.

Cyclosporine analogues

Numerous analogues of cyclosporine A (CsA) have been produced and studied. Although these analogues have given considerable insight into structure-activity relationships, none have been shown to have the safety and efficacy of CsA. The most promising of these analogues is cyclosporine G (CsG) in which norvaline is substituted for alpha-aminobutyric acid at the 2 position. Comparative studies of CsG and CsA in animals have produced conflicting results both in terms of nephrotoxicity and the effectiveness of CsG as an immunosuppressive agent. It is evident from these studies that there exist species and strain differences in the metabolism of CsG, sensitivity to its toxic effects and, probably, to its immunological effectiveness. Studies will have to be performed in humans to determine whether, for a given immunosuppressive effect, CsG is less or more toxic than CsA.

Cyclosporine A versus cyclosporine G: a comparative study of survival, hepatotoxicity, nephrotoxicity, and splenic atrophy in BALB/c mice

Our group has previously shown that cyclosporine A (CSA) but not cyclosporine G (CSG) causes splenic atrophy in a BALB/c mouse model. We have now extended our studies to observations of the effect of the two drugs on other parenchymal organs and on the nervous system. Groups of mice (N = 30) were given 150 mg/kg per day of either CSA or CSG and were compared to two control groups. Absorption of the drugs was similar in the two groups, although CSG blood levels were slightly higher. Animals treated with CSA, but not CSG, lost up to 50% of body weight over a 3-week period. Overall mortality was much higher in the CSA group. Blood urea levels were significantly higher in both treatment groups than in controls and were significantly higher in the CSA than in the CSG group. CSA-treated animals showed marked histological changes in their kidneys, the most prominent of which was proximal tubular vacuolation. Both drugs showed some hepatotoxicity, both histologically and biochemically; the histological changes were more marked in the CSA group. There was no pancreatic toxicity at this dose, either histologically or in terms of blood-sugar concentrations. Mice treated with CSA, but not with CSG, showed marked behavioral changes, including hyperactivity and irritability. The most intriguing observation was the effect of CSA, but not CSG, on the spleen. There was atrophy of lymphoid tissue in both the B and the T cell areas, although the most prominent change was in the periarterial lymphatic sheaths. These changes may be of significance in the long-term maintenance of immunosuppression and graft acceptance.(ABSTRACT TRUNCATED AT 250 WORDS)