Abstract
We previously demonstrated the capacity of the hydroxylamine metabolite of sulfamethoxazole (SMX-HA) to inhibit mitogen-induced T-cell proliferation. We studied the interaction of SMX-HA with the immuno-suppressants cyclosporin A (CsA), FK506 and rapamycin. Human peripheral blood mononuclear leukocytes were treated with SMX-HA and combined in culture with CsA or FK506 or rapamycin. The cells were stimulated with phytohaemaglutinin, and phorbol myristate acetate and proliferation was determined by cellular uptake of3H-thymidine. Using median-effect analysis and concentration reduction index calculations to assess immunosuppressive drug interactions, we produced synergistic immunosuppression by SMX-HA/CsA and SMX-HA/FK506. Concentration reductions at the 50% inhibitory level of over 46-fold and 64-fold with CsA and FK506, respectively, were observed with 25 μM SMX-HA, and this effect was not associated with reduced cell viability. SMX-HA failed to augment the suppressive capacity of rapamycin in inhibiting mitogen-induced cellular proliferation. SMX-HA at immunosuppressive concentrations also failed to interfere with interleukin-2 mRNA transcription and interleukin-2 protein production, which suggests that signaling events proximal to cytokine production are not affected by the metabolite. Synergy between SMX-HA/FK506 and SMX-HA/CsA suggests that the mechanism(s) of action of reactive sulfonamide metabolites may occur in later stages of lymphocyte activation.
Footnotes
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Send reprint requests to: Dr. Michael J. Rieder, M.D., Ph.D., Molecular Virology and Gene Therapy Group, Robarts Research Institute, University of Western Ontario, 100 Perth Dr., London, Ontario, N6A 5K8.
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↵1 This work was supported by a grant from the Kidney Foundation of Canada. Dr. Rieder has a PMAC/MRC Career Award. Mr. Hess has an MRC/NHRDP Studentship.
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↵2 Present address: Department of Biochemistry, American University of Beirut, Beirut, Lebanon.
- Abbreviations:
- CsA
- cyclosporin A
- CRI50
- concentration reduction index at 50% suppression
- DMSO
- dimethylsulfoxide
- ELISA
- enzyme-linked immuno-absorbent assay
- FKBP
- FK506-binding protein
- IFN
- interferon
- IL-2
- interleukin-2
- PBML
- peripheral blood mononuclear leukocytes
- MTT
- 3-[4,5-Dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide
- PCR
- polymerase chain reaction
- PMA
- phorbol myristate acetate
- PHA
- phytohemaglutinin
- RPMI
- Rosewell Park Memorial Institute
- RT
- reverse transcriptase
- SMX-HA
- hydroxylamine of sulfamethoxazole
- TCR
- T-cell receptor
- TNF
- tumor necrosis factor
- Received May 10, 1996.
- Accepted December 16, 1996.
- The American Society for Pharmacology and Experimental Therapeutics
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