Inhibitory Effect Of Cyclosporin A Research Articles

Role of Cyclosporin A in Macromolecular Synthesis of β-Cells

Wistar rats developed hypoinsulinemia and hyperglycemia within 7 days when treated daily with 40 mg/kg body wt of cyclosporin A (CsA) and recovered from the metabolic alteration within 1 wk when CsA treatment was terminated. By light microscopy, there was no lymphocytic infiltration, but cytoplasmic vacuolization in the islets of Langerhans from the CsA-treated rats was seen. By electron microscopy, severe degranulation, cytoplasmic vacuolization, and dilation of endoplasmic reticulum were clearly seen in the pancreatic beta-cells. Islet cells isolated from the CsA-treated rats showed greater than 50% reduction in mRNA synthesis. A similar inhibitory pattern of mRNA synthesis was observed in in vitro CsA-treated (10 micrograms/ml) human pancreatic islet cells from one biopsy sample and in similarly treated rat insulinoma cells (RINm5F). The inhibitory effect of CsA on mRNA synthesis in RINm5F cells was dose dependent, with a 50%-inhibiting dose of 5 micrograms/ml. In addition to the inhibition of mRNA synthesis, CsA also inhibited protein and DNA syntheses, although the inhibitory effect on these macromolecular syntheses was significantly less than that on mRNA synthesis. However, there was only a minor effect of CsA on in vitro transcription and translation compared with that on RINm5F and islet cells. It is concluded that CsA-induced degranulation of the beta-cells in Wistar rats, accompanied by hypoinsulinemia and hyperglycemia, may be due to indirect, reversible interference of the cellular function primarily involved in mRNA synthesis.

Interleukin-2 effect on the inhibition of mixed lymphocyte reaction induced by cyclosporin A.

Cyclosporin A (CsA) was found to have remarkable immune suppressive properties without the usual significant myelotoxicity and to be a clinically very useful agent to prevent rejection of organ transplantation or bone marrow transplantation graft-versus-host disease in recently. The inhibitory effect of CsA on the production of interleukin-2 (IL-2) has been implicated as a major reason accounting for CsA mediated immunosuppression. But the exact mode of its immunosuppressive effect remains unclear. We studied the influence of CsA and exogenous IL-2 on the proliferative response in allogeneic mixed lymphocyte culture.The results were as follows: There is apparent inhibition of proliferative response in mixed lymphocyte reaction (MLR) by CsA in a dose-dependent manner, where optimal concentration is approximately 0.5 ug∼1.0 ug/ml.The time-course sequential studies indicated that the lymphocyte response was markedly dependent on the time of addition of CsA to the culture ongoing MLR, the inhibitory effect of proliferative response by CsA was markedly abolished after 20 hours of the culture (Mean cpm 12,578±1,445/28,324±319).At the beginning of the MLR, an addition of both CsA and exogenous IL-2 (human, 2.0 U/ml) was found to have no appreciable immunosuppressive effect.Exogenous human IL-2 abolished the CsA effect on the MLR but mouse IL-2 could not.

Selective suppression of an early step in human B cell activation by cyclosporin A.

The effect of cyclosporin A (CsA), a fungal metabolite with immunosuppressive properties, on the induction of human B cell proliferation and differentiation, has been described. CsA had a selective inhibitory effect on the activation phase of the cell cycle vs. the proliferation phase following preactivation of the cells. Cell enlargement and RNA synthesis of small resting B cells triggered by anti-mu were inhibited by addition of CsA (5-500 ng/ml). The inhibitory effect of CsA was found only when the drug was added within 24 h of initiation of culture. In marked contrast, once small B cells were activated by anti-mu, the resulting large, activated B cells could be induced to initiate DNA synthesis by incubation with B cell growth factor (BCGF), and addition of CsA (1-1,000 ng/ml) to the culture did not suppress this BCGF-induced B cell proliferation. Addition of CsA to cultures of B cells which had been preactivated with Staphylococcus aureus Cowan strain I (SAC) and were already proliferating did not suppress B cell differentiation factor (BCDF)-induced differentiation of these cells. Thus, these data indicate that CsA can be used as a pharmacologic tool to dissect out human B cell responses into two distinct steps: (a) the initial activation step induced by anti-Ig, which is characterized by cell enlargement, RNA synthesis, and expression of receptors for BCGF; and (b) the proliferative step induced by BCGF in these preactivated B cells that undergo DNA synthesis and can then go on to differentiate in the presence of BCDF. In this regard, CsA selectively suppresses an early step of human B cell activation and has little inhibitory effect on the subsequent factor-dependent proliferation and differentiation.

In Vitro Effects of Cyclosporin A on Human B‐Cell Responses

The in vitro effects of cyclosporin A (CsA) on T-cell-dependent and T-cell-independent mitogen responses of human B cells were studied. T-cell-dependent, pokeweed mitogen (PWM)-induced B-cell proliferation and B-cell differentiation to Ig-secreting cells were significantly inhibited by CsA, when purified B cells were cultured with T-cell helper factor containing supernatants instead of T cells. This indicates that the inhibitory effect of CsA on T-cell-dependent, PWM-induced B-cell proliferation and differentiation is not exclusively due to direct effects on helper T cells. B-cell proliferations induced by anti-IgM antibodies and by Staphylococcus aureus bacteria were also found to be sensitive to CsA. Since both types of reactions are T-cell-independent, the concept that responses of human B cells can also be affected by CsA in ways that seem to be independent of the well-documented direct effects of CsA on T cells is further supported. This seems not to be a general phenomenon, however. Epstein-Barr-virus-induced activation of human B cells, as reported previously and also observed by us, is completely insensitive to CsA. It seems, therefore, that certain B-cell activation mechanisms are sensitive to CsA while others remain unaltered. The difference between these two reaction patterns cannot be exclusively explained by a T-cell dependence or T-cell independence of these responses. CsA effects on certain functional B-cell subsets or interference with accessory cell mechanisms might be responsible.