<b>Neuroprotective effects of curcumin in mercury–silver compound–exposed <i>Nauphoeta cinerea</i> nymphs</b>

Abstract

Mercury and silver from dental amalgams accumulate in tissues, triggering oxidative stress and cellular dysfunction that foster neurodegeneration, while curcumin, a polyphenol with potent antioxidant and neuroprotective activity, emerges as a promising dietary agent to counteract metal-induced neural injury. This study investigated the neuroprotective effects of curcumin against neurotoxicity induced by combined exposure to mercury and silver, two primary constituents of dental amalgams, in Nauphoeta cinerea. Three groups of Nauphoeta cinerea (cockroaches, n = 20) nymphs were subjected to a combination of 544 mg of mercury chloride and 170 mg of silver nitrate, with or without dietary supplementation of curcumin (80 mg). Following a 7-day treatment, motor functions, biochemical markers, and gene expression were evaluated. Curcumin-treated nymphs exhibited significant (p < 0.05) increases in motor activity, enhanced mobility, and less immobility. Biochemical tests indicated increased antioxidant levels, alongside reduced reactive oxygen species and lipid peroxidation. Moreover, levels of monoamine oxidase were significantly reduced in the curcumin-treated groups. Surprisingly, acetylcholinesterase levels did not significantly reduce in the metal-combination-treated groups. Gene expression analyses revealed the increase of antioxidant enzymes, such as thioredoxin, in nymphs treated with curcumin, relative to the metal‑combination exposed group and the control group. The findings indicate that curcumin alleviated neurotoxicity caused by mixed metals via regulating oxidative stress and neurochemical imbalances while also increasing the expression of genes related to antioxidant defences. This work underscores curcumin's potential as a functional dietary element for the prevention of neurodegenerative disorders linked to environmental exposure to toxic metals, offering significant insights into its therapeutic implications.