The Effect of End-to-Side Portacaval Shunt on Cyclosporine Pharmacokinetics in Rats

Pharmaceutical Research -     

Production of synergistic but nonidentical mechanisms of immunosuppression by rapamycin and cyclosporine.

We report that the mechanism of rapamycin (RAP) inhibition is synergistic, but nonidentical, to the mechanism of CsA inhibition. Like CsA, RAP inhibits T cell proliferation following mitogen (PHA) and/or alloantigen (MLR) stimulation. RAP levels of 100, 33, 11, 3.6, 1.2, and less than 1 ng/ml reduced PHA stimulation by 81%, 84%, 81%, 83%, 62%, and 33%, respectively, without cytotoxicity. The RAP concentration required to achieve 50% proliferative inhibition of either mitogen (PHA) or MLR assays revealed an interindividual variability of 5 pg/ml RAP (2 individuals), 1 ng/ml (3 individuals), and 100 ng/ml (2 individuals). Unlike CsA, RAP proliferative inhibition was not restricted to the G0 phase of the cell cycle. Addition of 100, 10, or 1 ng/ml RAP at the onset (G0), or 24 hr following cultivation (G1) similarly inhibited DNA synthesis by 42%, 42%, and 41% compared with 44%, 48%, and 47%, respectively. PWM-stimulated B cell proliferation was primarily RAP-sensitive during the G0 phase of the cell cycle. RAP at 100, 10, and 1 ng/ml inhibited B cell proliferation 46%, 51%, and 50% when added during G0 but only 15%, 20%, and 20% when added during G1. Generation of a cyclosporine-sensitive cytoplasmic activation signal, activator of DNA replication (ADR), was reduced by RAP. RAP reduction did not correlate directly with T cell proliferative inhibition (as does CsA). RAP-induced proliferative inhibition of 40% and 80% resulted in ADR inhibition of 16% and 33%. Proliferative inhibition was synergistically increased when CsA and RAP were used in combination, whereas ADR inhibition was only additively enhanced. Mechanistic disparity between RAP and CsA may potentiate clinical immunosuppression when RAP and CsA are used together.     

Use of anti-CD25 monoclonal antibody in combination with rapamycin to eliminate cyclosporine treatment during the induction phase of immunosuppression.

BACKGROUND: Cyclosporine and tacrolimus are associated with drug-induced renal dysfunction that may exacerbate recovery from ischemic injuries during the first month posttransplant. We sought to use anti-CD25 (anti-interleukin-2 receptor) monoclonal antibodies in combination with sirolimus (rapamycin) to avoid cyclosporine therapy during the early postoperative period in six renal transplant recipients deemed to be at high risk for delayed graft function. METHODS: Six consecutive patients deemed to be at high risk for delayed graft function were treated with rapamycin (2-12 mg/day), anti-CD25 monoclonal antibodies, and steroids, withholding inception of cyclosporine therapy until the serum creatinine fell below 3.0 mg/dl. RESULTS: During the first 2 months posttransplant, none of the patients displayed clinical or histopathological evidence of acute allograft rejection episodes, cytokine release syndrome, or hypersensitivity reactions. None of the patients received even empiric bolus or high-dose steroid therapy for a presumed rejection episode. All patients recovered renal graft function within 8 weeks posttransplant. To date all patients have stable renal graft function. Five patients have serum creatinine levels between 0.8 to 1.3 mg/dl at 6 months and the other patient has a serum creatinine level of 1.7 mg/dl at present follow-up of 2 months posttransplant. CONCLUSION: During the early posttransplant period anti-CD25 monoclonal antibodies combined with rapamycin and steroids offer a promising baseline therapy to avoid cyclosporine exposure and facilitate recovery from ischemic/reperfusion injuries.     

Donor-specific antigen and cyclosporine in rat islet allografts

Combination therapy with one dose of 3 M KCl extracted donor-soluble antigen (Ag) and a short course of cyclosporine (CsA) has proven to prolong the survival of kidney allografts by enhancing specific T-suppressor populations. This regimen is tested in rat islet allografts in this study (Lewis to ACI). A 3-day perioperative course of 10 mg/kg/day CsA on Days -1, 0, and 1 did not prolong graft survival (MST = 10.7 +/- 2.5 days vs 9.4 +/- 1.2 days in controls). When this course of CsA therapy was combined with a single dose of donor antigen on Day -1, the survival time was prolonged slightly but significantly (MST = 14.0 +/- 5.8 days). Three cycles of a 3-day course of CsA therapy at 7-day intervals, a total of nine doses of 10 mg/kg/day CsA, were effective in delaying rejection of islet allografts (MST = 26.4 +/- 30.3). Moreover, combined therapy with donor antigen and three cycles of a 3-day course of CsA prolonged the survival of islet allografts (MST = 57.7 +/- 51.4 days) with 50% of recipients still normoglycemic at 60 days after transplantation. These findings indicate that the combination therapy of donor antigen with a short course of CsA has a powerful effect to prevent the rejection of islet allografts, as shown in kidney allografts, in rats.     

Comparison of steady-state trough sirolimus samples by HPLC and a radioreceptor assay

OBJECTIVES: We have previously identified a minor immunophilin of 52 kDa molecular weight capable of binding tacrolimus and sirolimus. Because immunophilins are capable of binding both parent drug and metabolites and HPLC assays are typically used to assess parent drug in clinical situations, we used this immunophilin in a radioreceptor assay (RRA) to determine if any metabolites not included in the HPLC measurement would bind to the immunophilin and be associated with thrombocytopenia in patients receiving sirolimus. DESIGN AND METHODS: We tested 51 steady-state trough whole blood samples from non-thrombocytopenic patients and 51 steady-state trough samples from thrombocytopenic patients and compared them to HPLC measurements of parent drug in the same samples. We also tested whole blood samples spiked with authentic sirolimus metabolites using RRA to ascertain the effect these metabolites have on the technique. RESULTS: We found minimal cross-reactivity in this assay for sirolimus metabolites (binding ranged from <10% to 26%), and good correlation of the radioreceptor assay with HPLC (linear regression slope 0.92, y-intercept 0.79). There was no statistically significant difference between the RRA and HPLC results in two patient groups-thrombocytopenic and non-thrombocytopenic-using the paired t-test (p<0.005) and Bland-Altman analysis. CONCLUSIONS: These findings indicate that although the RRA could be substituted for HPLC in therapeutic drug monitoring, the 52 kDa immunophilin does not offer an advantage in terms of detecting metabolites associated with thrombocytopenia. However, the RRA offers the advantages of shorter turnaround time, smaller sample volume and potential for automation.     

Current immunosuppressant regimens: considerations for critical care

While current immunosuppressive drug regimens have significantly increased the rate of successful transplantation outcomes, they convey potentially serious and overlapping adverse effects. Cyclosporine and tacrolimus are the cornerstones of current immunosuppression, achieving excellent one-year renal graft survival rates. Other promising new drugs include sirolimus, which has been demonstrated to reduce efficacy failure rates among renal transplant recipients, and everolimus, which is currently undergoing clinical trials. Agents targeting novel sites in the immune response or disrupting the ischemia-reperfusion cascades are currently under development. Among them, only FTY720 is undergoing large-scale human clinical trials. With its unique mechanism of action and synergistic interactions with cyclosporine and sirolimus, it may provide the foundation for a new era in immunosuppression.