Adherent human mesangial cells (HMC) were unable to phagocytose serum-treated zymosan (STZ), nevertheless this stimulus (1 mg/ml) induced a marked immediate increase of H2O2 and O2- release at a rate of 3.15 ± 0.35 and 3.40 ± 0.12 nmol/106 HMC/hr. respectively. Zymosan alone resulted in no release of either H2O2 or O2-. Phorbol myristate acetate (PMA, 2 × 10-6 M) had only marginal effects on HMC leading to the generation of 0.273 ± 0.014 nmol O2-/106 HMC/hr. After a lag period, human recombinant tumor necrosis factor-α (TNF-α) and human recombinant interleukin 1-α (IL-1α) both induced significant O2- production measured as SOD inhibitable reduction of cytochrome c, 5 × 10-5 M, by adherent HMC for up to five hours, the maximum rates being 3.04 ± 0.08 and 3.2 ± 0.08 nmol/106 HMC/hr for IL-1α and TNF-α, respectively. Significant O2- release was detectable at 0.625 ng/ml (37 PM) IL-1α or 1 ng/ml (59 pM) TNF-α (P < 0.05). Catalase inhibitable H2O2 production was also induced by IL-1α and TNF-α in a dose dependent manner. Using scopoletin (40 nM) and 1 μM peroxidase we fluorimetrically measured 1.73 ± 0.14 and 1.49 ± 0.19 nmol H2O2/106 HMC/hr induced by IL-1α (25 ng/ml) and TNF-α (20 ng/ml). Finally, we ascertained the type of radical species produced by HMC stimulated by cytokines employing ESR-spin-trapping with DMPO. These results demonstrated that O2- was the primary radical species formed. We have thus established for the first time that HMC are able to generate significant oxygen radicals in response to IL-1α and TNF-α, in amounts comparable to that produced by monocytes. These findings may be relevant to the pathogenesis of human glomerulonephritis.
