Mode of action of sulfoxides in preventing loss of activity of 11β-hydroxylase in cultured bovine adrenocortical cells

Previously, loss of 11β-hydroxylase activity when adrenocortical cells are incubated with the pseudosubstrate cortisol was found to be reduced when the concentration of oxygen was lowered, or when butylated hydroxyanisole (BHA) or dimethyl sulfoxide (Me₂SO) were included in the medium. In the present experiments, we tested the hypothesis that Me₂SO protects 11β-hydroxylase by scavenging OH^• radicals. Substances known to react with OH^• at high rates and non-toxic enough to be used at concentrations of 10-100 mM, including several alcohols, benzoate and radioprotectant thiols, did not prevent loss of activity of 11β-hydroxylase in the presence of 50 μM cortisol. Two of the alcohols, ethanol and glycerol, as well as Me₂SO, were radioprotective in cultured bovine adrenocortical cells. Therefore free OH^• radicals do not appear to be involved in loss of 11β-hydroxylase activity. When sulfoxides other than dimethyl sulfoxide were tested for their ability to protect 11β-hydroxylase in the presence of cortisol, several aryl sulfoxides, particularly dibenzyl sulfoxide, as well as dipropyl sulfoxide, were active at concentrations to 1 200 of that required for Me₂SO. Previously, we have demonstrated that 11β-hydroxylase inhibitors, particularly metyrapone, effectively protect against loss of 11β-hydroxylase activity in the presence of pseudosubstrates and therefore we examined whether sulfoxides may act by directly inhibiting 11β-hydroxylase. Me₂SO showed an ED₅₀ for inhibition of 11β-hydroxylase activity of > 1 M, in contrast to its ED₅₀ for protection of 34 mM. For metyrapone, however, the ED₅₀ for inhibition of the enzyme (250 nM) was close to that for protection of activity (270 nM). The other sulfoxides showed ED₅₀-values for inhibition of 11β-hydroxylase that were substantially higher than the ED₅₀-values for protection. Sulfoxides may have a mixed mode of action in protection of 11β-hydroxylase activity, as previously shown for phenols; they may protect by radical scavenging, but may also need to bind close to the active site of the enzyme where destructive radicals may be formed.