Immunopharmacodynamic studies of cyclosporine in patients awaiting renal transplantation

Effect of low dose cyclosporine and sirolimus on hepatic drug metabolism in the rat1

BACKGROUND

We examined the effect cyclosporine (CsA) and sirolimus (SRL) alone and in combination on hepatic cytochrome P450-mediated metabolism in rats.

METHODS

Rats were given 1 mg/kg of CsA or 0.4 mg/kg of SRL alone or in combination via constant intravenous infusion. Renal function was evaluated at the end of treatment. Blood samples were obtained to estimate CsA and SRL concentrations. Hepatic microsomes were prepared for immunoblotting and catalytic assays.

RESULTS

CsA alone did not alter serum creatinine levels. SRL given alone or in combination with CsA produced a significant increase in urine output without changes in fluid balance. Although CsA and SRL administered alone caused damage to renal proximal tubules, the two-drug combination dramatically increased the renal structural damage. CsA alone suppressed cytochrome P450 (CYP) 3A2 protein levels by 39% (P=0.012) and catalytic activity by 30% (P=0.042). SRL alone reduced catalytic activity by 38% (P=0.012). Combination therapy reduced both CYP3A2 levels by 55% (P<0.001) and catalytic activity by 55% (P=0.001). CYP2C11 protein expression or catalytic activity were not changed in any group. CYP2A1 protein expression and catalytic activity were both significantly reduced in rats given CsA or/and SRL. Steady-state CsA levels were increased during concurrent SRL dosing, however, SRL concentrations were not changed by CsA coadministration.

CONCLUSIONS

Concurrent SRL dosing increases CsA concentrations due to inhibition of hepatic CYP3A2 protein expression. Nephrotoxicity caused by combination therapy is due to CsA elevating levels of SRL or by SRL itself. Concurrent administration of CsA and SRL in transplant patients should be performed with caution.

Inhibition of Stimulated Interleukin-2 Production in Whole Blood: A Practical Measure of Cyclosporine Effect

Background: Prediction of cyclosporine (CSA) efficacy and toxicity in individual patients is difficult. There is no practical, biologically relevant, pharmacodynamic measure of CSA effect. A major effect of CSA is to decrease interleukin-2 (IL-2) production; however, measurement of this effect in isolated lymphocytes as a marker of response to CSA has been problematic.

Methods: CSA inhibition of phytohemagglutinin-P (PHA)-stimulated IL-2 production, measured by ELISA, was studied ex vivo in whole blood drawn before, and after subjects received 4 mg/kg oral CSA.

Results: Four hours after CSA was administered, the mean (± SD) CSA concentration was 702 ± 196 μg/L and PHA-stimulated IL-2 production decreased by 68.7% ± 17.2% (P &lt;0.0001; n = 17). Twenty-four hours after CSA was administered, concentrations were low (64 ± 24 μg/L), with no inhibition of IL-2 production. A rapid, concentration-dependent response occurred. Maximum CSA concentrations (944 ± 187 μg/L) and maximum inhibition of IL-2 production (86.9% ± 13.7%) occurred 90 min after subjects received CSA. In vitro, 32.5–1200 μg/L CSA also inhibited PHA-stimulated IL-2 production in whole blood in a dose-dependent fashion with a similar IC50 (∼300–400 μg/L) ex vivo and in vitro.

Conclusion: In the search for a pharmacodynamic marker to better guide immunosuppressive therapy, the relationship between this simple, biologically relevant measure of CSA effect and clinical outcome should be determined.

Unbound cyclosporine and allograft rejection after heart transplantation

BACKGROUND

To determine the impact of cyclosporine plasma protein binding on organ rejection after cardiac transplantation, the incidence of cardiac rejection episodes was compared among patients who had differing levels of cyclosporine plasma fraction unbound (fU).

METHODS

Forty-six consecutive cardiac transplant recipients were sampled at 1, 3, 6, and 12 months after transplantation, and cyclosporine plasma fU was determined, using a specially developed equilibrium dialysis method. At the completion of the study, incidences of cardiac rejection episodes were compared among patients having mean cyclosporine fU (Csfu) that were low (LCsfu; mean+/-SD, 1.33+/-0.10%, n=15), intermediate (ICsfu; 1.60+/-0.07%, n= 16), and high (HCsfu; 1.99+/-0.30%, n=15).

RESULTS

Percentage of endomyocardial biopsies (grade 3a, 3b, and 4) with respect to the total number of biopsies performed in the first 3 months after transplant was significantly higher in the LCsfu group than the other groups (40.9% in LCsfu vs. 28.5% for ICsfu and 32.1% for HCsfu groups, P=0.02). The linearized rate of rejection (episodes of rejection/100 patient-days) in the first month after transplant was 6.5+/-1.7 for LCsfu, 3.5+/-0.8 for ICsfu and 4.3+/-0.9 for the HCsfu group (P<0.05, low vs. intermediate-high). The mean (95% confidence interval) of time interval between the first and second episodes of rejections was 10.7 (5.6-16.0) days for LCsfu, 18.0 (8.6-29.0) days for the ICsfu, and 26.0 (15.1-36.9) days for the HCsfu group (P<0.01). The total number of rejections requiring treatment per patient in the first 3 months after transplant was higher in the LCsfu group compared with the others (4.0+/-1.7 episodes for LCsfu vs. 2.9+/-1.1 for ICsfu and 3.2+/-1.2 episodes for HCsfu; P<0.05). Four patients in the low group, one patient in the intermediate group, and no patients in the high group required treatment with total lymphoid irradiation (P<0.02).

CONCLUSIONS

This finding suggests that patients with lower levels of cyclosporine fU are more prone to cardiac rejection and that the level of cyclosporine fraction unbound may be clinically important for determination of response to cyclosporine therapy.