Cyclosporin B

To elucidate the function of protein disulfide isomerase (PDI), we screened for PDI-binding proteins in a bovine liver extract using affinity column chromatography. One of the binding proteins was identified by SDS-PAGE and N-terminal amino acid sequence analysis to be cyclophilin B (Cyp B). Use of the BIACORE system revealed that purified bovine Cyp B bound specifically to bovine PDI with a K(D) value of 1.19 x 10(-5) M. Interestingly, the binding affinity between PDI and Cyp B was strengthened by preincubation of the Cyp B with cyclosporin A (CsA), yielding a K(D) value of 3.67 x 10(-6) M. Although the interaction between PDI and Cyp B affected neither the isomerase activity of PDI nor the peptidyl-prolyl cis-trans isomerase activity of Cyp B, Cyp B increased the chaperone activity of PDI. However, the complex of Cyp B and CsA completely inhibited the chaperone activity of PDI. Thus, PDI and Cyp B appear to cooperate with each other to regulate the functional expression of proteins in vivo.

Cyclosporin A (CsA), a hydrophobic peptide, mainly known for its immunosuppressant properties, has shown a broad range of biological activities, including antimalarial action. Since CsA was found to be active on membrane level, it was subjected for investigations involving membrane models. Our former studies on interactions between CsA and different membrane lipids using Langmuir monolayer technique indicated its affinity for sphingomyelin (SM). Inspired by this finding we have extended our experiments on multicomponent systems and performed systematic investigations of CsA behavior towards artificial membranes containing different mutual proportion of sphingomyelin and cholesterol (Chol). Langmuir monolayer results have been complemented with in-situ films structure visualization applying Brewster angle microscopy (BAM) and, after films transfer onto solid support, atomic force microscopy (AFM). Our results show that cyclosporin A introduced to SM:Chol mixed monolayers distributes differently, depending on SM-to-Chol proportion. In raft-mimicking (2:1) stoichiometry, even distribution of the drug within SM:Chol matrix was observed. However, in SM:Chol model membranes of different proportion (3:1; 1:1; 1:2), containing either the excess of unbound sphingomyelin or cholesterol in addition to model lipid raft domains, introduction of CsA induced a phase separation.

Cyclosporin A (CyA) is a potent immunomodulatory agent with an increasing number of clinical applications. Although its precise mechanisms of action are yet to be elucidated, one of the most important known properties of CyA is its ability to inhibit the production of cytokines involved in the regulation of T cell activation. There is also evidence for direct effects on other cell types, such as B cells, macrophages, and bone and cartilage cells. The effects of CyA on T cells and on bone, cartilage and synovial cells, which can produce a range of cytokines, are of interest in the study of inflammatory diseases such as RA. It has been shown, for example, that in vitro CyA inhibits bone resorption induced by interleukin-1, 1,25-dihydroxy-vitamin D3, parathyroid hormone and prostaglandin E2. In vivo, it protects against adjuvant arthritis.

The immunosuppressant cyclosporin is a P-glycoprotein (P-gp) substrate whose impaired function has been associated with an increased risk of cyclosporin-induced nephrotoxicity following renal transplantation. This study investigated the relationship between blood and allograft cyclosporin concentration, and the effect of P-gp expression. Fifty biopsy samples were obtained from 39 renal transplant recipients who received cyclosporin as part of maintenance immunosuppression. Blood cyclosporin concentrations (2 hours postdose) were obtained from clinical records, matching allograft cyclosporin concentrations were measured in frozen biopsy tissue by liquid chromatography-tandem mass spectrometry, and allograft P-gp expression was assessed by immunohistochemistry. Blood and allograft cyclosporin concentrations in the 1st month post-transplantation ranged from 505-2005 μg/L and 0.01-16.7 ng/mg tissue, respectively. Dose was the only significant predictor of allograft cyclosporin concentrations (adjusted R2= .24, F-statistic = 11.52, P = .0019), with no effect of P-gp expression or blood cyclosporin concentrations. P-gp expression is not the major determinant of allograft cyclosporin concentrations.