Kiumars Vadiei

Prevention of Cyclosporine-Induced Nephrotoxicity with Pentoxifylline

Although cyclosporine (CSA) is established in the prevention of allograft rejection, its use has been associated with dose-limiting toxicities, most notably to the kidney and liver. To date, the pathogenesis of the acute form of nephrotoxicity is unclear but may be related to inhibition of vasodilatory prostaglandins resulting in vasoconstriction and ischemia. The present study investigated the coadministration of CSA with a unique hemorheologic agent, pentoxifylline (PTX), in the murine model. A total of 48 rats were orally dosed with CSA 25 mg/kg for 10 days with either PTX 45 mg/kg i.p. or saline every 12 hr. Posttreatment renal function, assessed by creatinine (CCR) and inulin (CIN) clearances and renal electrolyte handling, was compared with baseline data and between groups. In an attempt to assess prostaglandin-mediated changes in enteral absorption, oral CSA pharmacokinetics with and without PTX were compared to the pharmacokinetics of similar groups (N = 8) administered i.v. CSA. Mean CIN of rats coadministered CSA and PTX (942 +/- 214 microliters/min/g KW) was similar to control rats 884 +/- 185 microliters/min/g KW); both were significantly greater than CSA alone (537 +/- 211 microliters/min/g KW; p less than .01). Likewise, percent of baseline CCR was significantly reduced in rats treated CSA (61 +/- 24%) compared to controls 113 +/- 41%) and rats coadministered PTX (117 +/- 75%; p less than .05). No differences in percent change from baseline electrolyte handling were observed among groups. Further, no differences in CSA pharmacokinetics with or without PTX were found.(ABSTRACT TRUNCATED AT 250 WORDS)

Pentoxifylline in amphotericin B toxicity rat model.

The mechanism of acute nephrotoxicity following the administration of amphotericin B (AmpB) remains unclear despite a number of studies describing hypermagnesuria, hyperkaluria, and hemodynamic changes. The present experiments attempted to elucidate the mechanism by using a novel hemorheologic probe, pentoxifylline (PTX). Acute studies were performed with rats given single intravenous doses of AmpB (1 mg/kg of body weight) with or without intraperitoneal PTX (45 mg/kg). Renal function, assessed by inulin clearance (CLIN) and electrolyte handling, and morphology were compared with those of controls given sterile water and PTX. A significant decrease in CLIN not observed in rats given AmpB and PTX or in the controls was found in rats given AmpB. Electrolyte handling was not different among groups. Whereas pronounced (3 and 4+ on a scale of mild to significant [1+ to 4+]) vascular congestion was found in rats given AmpB, rats coadministered PTX had mild (1 and 2+) medullary and glomerular vascular congestion. In chronic studies, intravenous AmpB (1 mg/kg per day) or sterile water was coadministered with intraperitoneal PTX (45 mg/kg every 12 h) or saline for 10 days. Mean CLIN of rats coadministered AmpB and PTX was not significantly different from that of PTX control rats (1.61 +/- 0.19 versus 1.31 +/- 0.29 ml/min per g of kidney weight). A 46% decline in CLIN was found in rats treated with AmpB and saline (P less than 0.05). Renal sodium and potassium excretions were increased in both AmpB-treated groups compared with controls. Coupled with histologic evidence of the acute studies, these data suggest that the benefit of PTX in the prevention of AmpB-induced nephrotoxicity is, in part, due to vascular decongestion. Images

In vitro evaluation of liposomal cyclosporine

The commercially available intravenous formulation of cyclosporine (CSA) is associated with acute hemodynamic changes, resulting in significant renal dysfunction. The present study investigated the properties of two liposomal CSA formulations: dimyristoylphosphatidylcholine (DMPC): stearylamine 7:1 (A) and DMPC: dimyristoylphosphatidylglycerol (DMPG) 4:1 molar ratio (B) developed as an alternative for the i.v. CSA. The optimal drug: lipid weight ratio was 1:20 for both formulations. The liposomal suspensions were obtained by rehydrating the lyophilized powder containing CSA and the lipids with saline. CSA entrapment was 90–95% for both formulations. The encapsulation efficiency of the lyophilized powder stored at 2–5°C was 95% at 24 h and not significantly different with either formulation. The encapsulation efficiency of liposomal formulations A and B in saline was 99 ± 1 and 50 ± 1%, respectively, after 5 days. In 50% serum, the encapsulation efficiency measured as percentage drug remaining entrapped at different time points was 90 ± 3 and 53 ± 4% for A and B, respectively, at 24 h. In vitro activity of both liposomal formulations demonstrated greater potency compared to the commercially available CSA i.v. formulation (A, 69.3 ± 14.8%; B, 50.8 ± 11.5%; i.v., 27.4 ± 20.6% inhibition of T-lymphocyte proliferation; p < 0.05 at 10−3 mM). The present study shows that liposomes can be used as a drug delivery system for CSA and result in an enhanced in vitro immunosuppressive potency compared with the i.v. formulation.

Pharmacokinetic and pharmacodynamic evaluation of liposomal cyclosporine

The pharmacokinetics and renal toxicity of two liposomal intravenous preparations of cyclosporine (CSA) (A, dimyristoylphosphatidylcholine (DMPC): stearylamine molar ratio 7:1; and B, DMPC: dimyristoylphosphatidylglycerol molar ratio 4:1) were assessed in the murine model and compared to the commercially available intravenous formulation of CSA (IV) and drug-free controls. No significant differences in steady-state area beneath the whole blood concentration-time curves were found between formulations and IV following 10 mg/kg per day CSA for 10 days. However, the apparent volume of distribution was significantly greater in A compared to B or IV formulations (13.82 ± 2.9 vs. 7.23 ± 3.98 and 7.67 ± 3.01 l/kg, p < 0.05), most likely due to the significantly prolonged biologic half-life of this formulation. Although the glomerular filtration rate was not significantly different between A and saline controls (1056 ± 536 and 1130 ± 550 μl/min per g KW, respectively), dosing with B or IV resulted in significant impairment (522 ± 429 and 572 ± 353 μl/min per g kidney weight (KW), respectively; p < 0.05). Triglyceride levels remained unchanged in all groups. However, cholesterol concentrations were significantly increased compared to baseline in rats administered formulation A (98 ± 31 vs. 70 ± 19 mg/dl; p < 0.05). In summary, dosing of liposomal formulation A resulted in equivalent concentrations of CSA as the IV formulation without the dose-limiting nephrotoxicity. These data offer a nontoxic delivery system for intravenous CSA.

Time-dependent pharmacokinetics and toxicity of cyclosporine

Although the circadian pattern of cyclosporine (CSA) pharmacokinetics and toxicity has been described previously in both animal and clinical studies, the mechanism of this action is unknown. The present study compared the pharmacokinetics and experimental nephrotoxicity of chronic CSA in both the genetically-hyperlipidemic rat model and the lean litter-mate. Once daily dosing (25 mg/kg via gavage) was either at the start of the active (1900) or inactive (0700) cycle (Nov 1987 to Jan 1988). Serial serum samples following the final dose were assayed by both polyclonal (nonspecific) and monoclonal (specific for parent CSA) RIA. Renal toxicity was assessed by 24-hr creatinine clearances, fractional clearances of sodium and potassium, and inulin clearances (CIN). Despite a greater than 2-fold increase in serum CSA concentrations, there were no changes in renal function in obese rats dosed at the start of the active period compared to the inactive period. Furthermore, mean CIN of the lean group administered drug at the start of the active period was not significantly different from time-matched placebo-treated lean rats. However, there was an 80% drop in CIN in rats treated with CSA at the start of the inactive period compared to control group. There were no differences in electrolyte handling. Insulin concentrations, independent of time of dosing, were markedly elevated in obese rats dosed CSA compared to placebo-treated obese or both lean groups. Serum triglyceride levels were significantly correlated with pharmacokinetic parameters of total but not parent CSA. In summary, significant differences in toxicity were observed due to time of dosing and lipid profiles. Although the mechanism of this action remains unclear, it appears that increased non-fasting serum triglyceride levels following the active period most likely reduced CSA distribution into kidney tissue preventing the dose-limiting nephrotoxicity.

Circadian Variation in Renal Function of the Obese Rat

The influence of food and water intake on renal function was assessed by comparisons between the hyperphagic Zucker obese rat and its lean littermate, which demonstrates nocturnal dominance in activity. Serum creatinine and cortisol levels, creatine kinase activities, creatinine and urine clearances, and sodium and potassium excretion rates were measured over a 24-hour period in both lean and obese rats (n = 24 each). Six rats in each group were studied every 8 h to permit characterization over a 12-hour light/dark cycle at 2-hour intervals. Urine and creatinine clearances were increased in lean rats during the dark phase coincident with onset of eating. Similarly, renal sodium and potassium excretion rates were markedly increased during the dark cycle, despite relatively constant serum potassium and sodium levels over the 24-hour period. In contrast, no circadian patterns in urine and creatinine clearances were found in the obese rat, which exhibits continuous feeding habits throughout the 24-hour period. Moreover, renal electrolyte excretion in the obese rat was modestly increased during the dark cycle, unlike the significant differences over time observed in lean rats. Serum creatinine levels were increased during the dark cycle in both rat groups. Creatine kinase activity, a measure of ambulatory activity, was constant in lean rats during the study period. Although creatine kinase activity was increased in obese rats during the dark cycle, no correlations with renal functional parameters were found. These results indicate that differences in food and water intake are significant determinants in diurnal cyclic changes in renal function.

Attenuation of amphotericin-B nephrotoxicity in the candidiasis rat model

Dose-limiting nephrotoxicity has hampered the clinical usefulness of amphotericin-B (AmpB). Recently, vascular decongestants, such as pentoxifylline, have shown benefit in reducing drug-associated renal damage of AmpB in rats. The present study investigated a dose-dependent protection of a structurally similar methylxanthine, HWA-448, in the candidiasis rat model given a single dose of AmpB. Forty-eight hours after inoculation with Candida albicans, each rat was treated with 0.8 mg/kg of AmpB or sterile water; animals were further randomized to receive 0.5, 1, 5, or 10 mg/kg i.v. of HWA-448 or saline given every 12 h for 3 doses. Kidney fungal counts, morphology, and renal function were compared between treatment groups upon completion of the study. Rats administered AmpB with HWA-448 had markedly improved renal function compared with those given AmpB alone; these effects were independent of the administered dose of HWA-448. The antifungal effect of AmpB was not impaired with concomitant HWA-448. Marked accumulation of granulomas and organisms was found in all rat groups. In summary, coadministration of low doses of HWA-448 attenuated the dose-limiting nephrotoxicity without impairing the antifungal effect of AmpB.

Antifungal activity of HWA-138 and amphotericin B in experimental systemic candidiasis.

HWA-138, a pentoxifylline analog, has been shown to increase yeast urinary clearance and to reduce yeast counts in the kidneys of rats infected with Candida albicans. Furthermore, HWA-138 has also been shown to prevent amphotericin B-induced acute renal failure in rats. We report here on the effects of HWA-138 alone and in combination with amphotericin B in the treatment of systemic candidiasis in mice. When single doses of HWA-138 were administered intravenously (10, 25, or 50 mg/kg of body weight) into infected mice, no significant improvement in survival was observed. In infected mice treated intravenously with multiple doses of HWA-138 (10, 25, or 50 mg/kg once daily for 5 consecutive days), a significant increase in survival time was seen only in animals also receiving 25 mg of HWA-138 per kg (14 +/- 3 days test versus 9 +/- 1 days control; P less than 0.05). The coadministration of subtherapeutic doses of amphotericin B and HWA-138 resulted in increased survival time. Combination therapy with amphotericin B (0.1-mg/kg single dose) and HWA-138 (10-, 25-, or 50-mg/kg multiple doses) resulted in a significant increase in survival time over controls (19 +/- 4, 19 +/- 5, and 21 +/- 9 days, respectively, versus 9 +/- 3 days; P less than 0.05). Combination therapy with amphotericin B (0.2-mg/kg single dose) and HWA-138 (10-, 25-, or 50-mg/kg multiple doses) also resulted in a significant increase in survival time over controls (24 +/- 6, 24 +/- 6, and 24 +/- 6, respectively, versus 9 +/- 3 days; P less than 0.05). Combination therapy with amphotericin B (0.2-mg/kg single dose) and HWA-138 (10-, 25-, or 50-mg/kg multiple doses) also resulted in a significant increase in survival time over controls (24 +/- 6, 24 +/- 6, and 24 +/- 6, respectively, versus 9 +/- 3 days; P < 0.05). Variance analysis of these findings indicate synergistic activity between amphotericin B and HWA-138 in the treatment of experimental candidiasis in mice.

Cyclosporine pharmacokinetics and effect in the Type I diabetic rat model

SummaryRecent clinical studies have demonstrated the potential benefit of the T-cell-specific immunosuppressant, cyclosporine, in the treatment of Type I insulin-dependent diabetes. In the present study, steady-state cyclosporine pharmacokinetics, fasting glucose and insulin levels and renal function were examined in stable insulin-dependent diabetic rats and compared to non-diabetic rats. Mean creatinine clearance 30 days following diabetes induction was not significantly different from saline controls. Cyclosporine treatment (5 mg/kg/day i.v. for 13 days) did not significantly alter creatinine clearance in either group; however, renal function of vehicle-treated diabetic rats was markedly reduced compared to other groups. Serum insulin concentrations were significantly greater in diabetic rats treated with cyclosporine compared to the control group (35.1±22.7 vs. 16.0±8.1 μU/ml;P<0.05). Glucose levels were proportionately reduced in diabetic rats treated with cyclosporine. Area under the concentration-time curve, half-life and volume of distribution of cyclosporine were significantly reduced in diabetic rats compared to non-diabetic controls. In summary, the pharmacokinetics and pharmacodynamics of cyclosporine were significantly different in the insulin-dependent diabetic rat model compared to normal controls. Furthermore, short-term cyclosporine therapy reduced the extent of experimental diabetic nephropathy observed in this model.