Cyclosporine's dual mechanism of action in inhibiting generation of the cytoplasmic activation signal and the nuclear response thereto.
The mechanism of cyclosporine's action was dissected using protocols admixing cytoplasmic extracts to trigger isolated nuclei prepared after phytohemagglutinin, OKT3, or mixed lymphocyte culture stimulation of normal volunteer and renal transplant recipient lymphocytes. CsA at 100-1000 ng/ml doses prevented cytoplasmic extracts of cells activated in vitro by OKT3 or MLC from triggering incorporation of radiolabeled nucleotides by resting isolated nuclei. In addition, nuclei isolated from cells previously treated with 200-1000 ng/ml of CsA were refractory to the potent cytoplasmic signal extracted from OKT3- or MLC-stimulated cells. CsA less effectively inhibited phytohemagglutinin-stimulated responses. CsA, but not its inactive analog cyclosporin H, inhibited 3H-thymidine incorporation into in situ nuclei. The inhibited cytoplasmic signal generation and nuclear responsiveness observed with normal lymphocytes exposed to CsA in vitro also was demonstrated with cells from renal transplant recipients who had been treated with CsA for less than 6 months. The impaired response of isolated patient lymphocyte nuclei to in vitro triggering with activated cytoplasmic extracts correlated with intranuclear CsA concentrations, but not with serum levels assessed with monoclonal antibodies selective for CsA or nonselective for CsA plus metabolites. Furthermore, patients displaying drug-induced nephrotoxicity had elevated intranuclear CsA, but not CsA plus metabolite, concentrations compared with stable transplant recipients. Thus, CsA addition in vitro or administration in vivo causes stereospecific inhibition, particularly for CD3 stimuli, of the cytoplasmic activation signal, and, to a lesser extent, of the subsequent nuclear response.
Citterio
F
F
Department of Surgery, University of Texas Medical School, Houston 77030.
Kahan
B D
BD
D000911:Antibodies, Monoclonal / Q000494:pharmacology; D002467:Cell Nucleus / Q000502:physiology; D003524:Cyclosporins / Q000378:metabolism / Q000494:pharmacology*; D003593:Cytoplasm / Q000502:physiology; D004247:DNA / Q000096:biosynthesis; D004305:Dose-Response Relationship, Drug; D006801:Humans; D007376:Interleukin-2 / Q000494:pharmacology; D016030:Kidney Transplantation / Q000276:immunology*; D008213:Lymphocyte Activation / Q000187:drug effects*; D016853:Muromonab-CD3; D010835:Phytohemagglutinins / Q000494:pharmacology
D000911:Antibodies, Monoclonal; D003524:Cyclosporins; D007376:Interleukin-2; D016853:Muromonab-CD3; D010835:Phytohemagglutinins; D004247:DNA