Identification of Skp1 as a target of mercury sulfide for neuroprotection

The safety assessment of cinnabar: Effects of co-administration with selenium on renal toxicity in mice

BACKGROUND

Cinnabar is a mercury-containing mineral traditionally used in Chinese medicine and can induce kidney injury via mercury toxicity. Given that cinnabar contains elements such as selenium, it is reasonable to hypothesize that its multi-element composition may regulate nephrotoxicity through intermetallic interactions. To validate this hypothesis and clarify the distinct renal toxicity between cinnabar and single mercury compounds, we compared the nephrotoxic effects of cinnabar, Zhu-Sha-An-Shen-Wan (ZSASW), mercuric sulfide (HgS), and mercuric nitrate (Hg(NO₃)₂). By co-administration with sodium selenite (Na₂SeO₃), this study related to the nephrotoxicity of cinnabar was improved from the perspective of metal-element interactions, which provided a new perspective for the safety assessment of mercury-containing medicines.

METHODS

Mice were gavaged with 0.5 % CMC-Na solution, cinnabar (50.0 and 200 mg/kg), HgS (50.0 mg/kg), Na2SeO3 (1.00 mg/kg), cinnabar (50.0 mg/kg)+Na2SeO3 (1.00 mg/kg), HgS (50.0 mg/kg)+Na2SeO3 (1.00 mg/kg), ZSASW (600 mg/kg), ZSASW (600 mg/kg)+Na2SeO3 (1.00 mg/kg) or Hg(NO3)2 (0.900 mg/kg in Hg2+) daily for 30 days. Renal histopathology was assessed by H&E staining. Related protein expression was measured by Western blotting. Renal total Hg (THg) concentration in kidney was determined by cold vapor atomic fluorescence spectroscopy.

RESULT

Western blotting revealed significantly decreased OAT1 and GPX4 levels in all experimental groups compared to the Control group (P < 0.05). NF-κB activation occurred in the Hg(NO₃)₂, Cinnabar-H, HgS, and HgS-Na₂SeO₃ groups. Hg(NO₃)₂ administration caused a significant decline in body weight growth rate (P < 0.001), severe renal tubular degeneration with epithelial cell swelling, and the highest renal THg concentration (773.77 % exceeding the Control group). Na₂SeO₃ alone induced inflammatory infiltration and tubular epithelial degeneration. The Cinnabar-H and HgS groups exhibited distinct renal damage (localized tubular degeneration and vascular hyaline degeneration, respectively) with elevated renal THg concentration (330.74 % and 347.95 % exceeding the Control group). The Cinnabar-L, Cinnabar-Na₂SeO₃, ZSASW, and ZSASW-Na₂SeO₃ groups maintained normal histology despite increased renal mercury content (227.46 %, 40.57 %, 67.2 %, and 556.56 % exceeding the Control group). Co-administration of Na₂SeO₃ with HgS restored OAT1 and GPX4 expression (P < 0.001), suppressed NF-κB activation, and minimally altered renal mercury accumulation (RSD=0.45 %). Na₂SeO₃ reduced mercury levels in the cinnabar-treated mice (57.07 % reduction) but increased accumulation in ZSASW-treated mice (292.65 % increase).

CONCLUSION

This study confirms that cinnabar and ZSASW exhibit lower toxicity than mercuric sulfide or mercuric nitrate. Multi-component synergistic or antagonistic effects need to be considered when studying the mechanism of action of cinnabar-related drugs.

Mercuric sulfide nanoparticles suppress the neurobehavioral functions of Caenorhabditis elegans through a Skp1-dependent mechanism

Cinnabar is the naturally occurring mercuric sulfide (HgS) and concerns about its safety have been grown. However, the molecular mechanism of HgS-related neurotoxicity remains unclear. S-phase kinase-associated protein 1 (Skp1), identified as the target protein of HgS, plays a crucial role in the development of neurological diseases. This study aims to investigate the neurotoxic effects and molecular mechanism of HgS based on Skp1 using the Caenorhabditis elegans (C. elegans) model. We prepared the HgS nanoparticles and conducted a comparative analysis of neurobehavioral differences in both wild-type C. elegans (N2) and a transgenic strain of C. elegans (VC1241) with a knockout of the SKP1 homologous gene after exposure to HgS nanoparticles. Our results showed that HgS nanoparticles could suppress locomotion, defecation, egg-laying, and associative learning behaviors in N2 C. elegans, while no significant alterations were observed in the VC1241 C. elegans. Furthermore, we conducted a 4D label-free proteomics analysis and screened 504 key proteins significantly affected by HgS nanoparticles through Skp1. These proteins play pivotal roles in various pathways, including SNARE interactions in vesicular transport, TGF-beta signaling pathway, calcium signaling pathway, FoxO signaling pathway, etc. In summary, HgS nanoparticles at high doses suppress the neurobehavioral functions of C. elegans through a Skp1-dependent mechanism.