Biotransformation in monkey brain: coupling of sulfation to glutathione conjugation

Phenol sulfotransferase (PST, EC 2.8.2.1) and glutathione-S-transferase (GST, EC 2.5.1.18), the phase II biotransformation enzymes inactivate many exo- and endogenous compounds. The effect of PST substrates (catecholamines, simple phenols, selected phenolic drugs) and PST products (phenolic sulfates) on GST activity was investigated to identify possible interactions between sulfation and glutathione conjugation in the brain. Two soluble forms of PST and two forms of GST were isolated from monkey (Rhesus macacus) brain cortex. Catecholamines, hypertensive and hypotensive drugs which are sulfated by monkey brain PSTs slightly inhibit the activity of brain GSTs. The greatest inhibitory effect was observed with neurotoxic compounds such as 6-OHDA and manganese. The commonly used analgesic drugs inhibit both GST forms. These enzymes are also inhibited by phenacetin, the precursor of paracetamol, and prototype salicylates such as sodium salicylate and acetylsalicylic acid. The effect of simple phenols and their sulfated metabolites on GST activity varies. The obtained results point to a possible interaction between sulfation and glutathione conjugation in vivo since many physiologically, therapeutically and toxicologically active compounds which are sulfated by brain phenol sulfotransferases may be bound by brain glutathione-S-transferases. These compounds may lose their activity (on being bound to GST) and expose the brain to the toxic electrophiles (by decreasing GST activity).