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

Previously, loss of 11 beta-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 11 beta-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 11 beta-hydroxylase in the presence of 50 microM 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 11 beta-hydroxylase activity. When sulfoxides other than dimethyl sulfoxide were tested for their ability to protect 11 beta-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 11 beta-hydroxylase inhibitors, particularly metyrapone, effectively protect against loss of 11 beta-hydroxylase activity in the presence of pseudosubstrates and therefore we examined whether sulfoxides may act by directly inhibiting 11 beta-hydroxylase. Me2SO showed an ED50 for inhibition of 11 beta-hydroxylase activity of greater than 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 11 beta-hydroxylase that were substantially higher than the ED50-values for protection. Sulfoxides may have a mixed mode of action in protection of 11 beta-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.