Modulation of protein kinase C by heavy metals

Area of Science:

• Neurochemistry
• Enzymology
• Toxicology

Background:

• Protein kinase C (PKC) is crucial for neuronal signaling, requiring calcium and phosphatidylserine (PS) for activation.
• Metal ions can interfere with vital cellular processes, including enzyme function.

Purpose of the Study:

• To investigate the in vitro inhibitory effects of mercury (Hg), lead (Pb), and methyl mercury (CH3Hg) on rat brain PKC activity.
• To determine the protective role of dithiols and monothiols against metal-induced inhibition of PKC.

Main Methods:

• Enzyme inhibition assays were performed using varying concentrations of Hg, Pb, and CH3Hg.
• IC50 values were calculated to determine the potency of each metal.
• Phorbol ester binding assays assessed the impact of metals on ligand interaction.
• Protective effects of dithiothreitol (DTT) and glutathione (GSH) were evaluated.

Main Results:

• Hg, Pb, and CH3Hg inhibited PKC activity in a concentration-dependent manner, with CH3Hg being the most potent inhibitor (IC50 = 0.22 microM).
• Both basal and PS-stimulated PKC activities were inhibited, with the latter showing higher sensitivity to Pb and Hg.
• Metal ions also inhibited phorbol ester binding to PKC, with Hg and CH3Hg being more potent.
• Dithiothreitol (DTT) protected PKC activity from metal inhibition, whereas glutathione (GSH) did not.

Conclusions:

• Mercury, lead, and methyl mercury are potent inhibitors of rat brain PKC activity in vitro.
• Dithiols effectively protect PKC from metal-induced inhibition, suggesting a role for specific chemical structures in mitigating neurotoxicity.
• These findings highlight the potential for heavy metal disruption of critical neuronal signaling pathways.