In vitro studies on dissolved substance of cinnabar: Chemical species and biological properties

Cinnabar is one of traditional Chinese medicines widely used in many Asian countries. It is also a medicine with potential toxicity especially when taking overdose. Up to date, studies on the mechanism of the biological activity of cinnabar were still insufficient.

Aim of the study

To investigate the possible bioactive species from cinnabar after oral administration, which is the fundamental of biological effects of cinnabar.

Materials and methods

Under mimetic intestinal and gastric conditions, the chemical components dissolved from cinnabar were analyzed by infrared spectroscopy (IR) and Raman spectroscopy. Furthermore, binding of mercuric species of cinnabar extractions to human serum protein (HSA) was characterized and their intestinal permeability was determined using the Caco-2 cell monolayer. The cytotoxicity of cinnabar extractions was assessed on human kidney-2 (HK-2) cell.

Results

Major dissolved species included mercuric polysulfide (i.e. HgS₂(OH)⁻ and Hg₃S₂Cl₂). The apparent permeability coefficient (P_app) of mercuric polysulfides was (1.6 ± 0.3) × 10⁻⁶ cm/s, which is slightly lower than that of mercuric chloride (HgCl₂). Unlike HgCl₂, mercuric polysulfides exhibited two tightly binding sites to HSA and had little effect on viability of HK-2 cells.

Conclusion

Mercuric polysulfides, as the major dissolved components, may serve as the active species of cinnabar exhibiting pharmacological and/or toxicological effects.