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The toxicity of cinnabar, a naturally occurring mercury sulphide (HgS), has long been referred to soluble mercury chloride (HgCl2). To investigate whether the speciation of mercury plays a role in its disposition and toxicity, we hereby investigated and compared cinnabar with soluble HgCl2 and pure insoluble HgS in mice on mercury absorption, tissue distribution and in relation to the biological effects. The male C57BL/6J mice were treated by oral administration of various doses of cinnabar, with 0.01 g/kg of HgCl2 for comparison, or the same dose of cinnabar or pure HgS (0.1 g/kg), once a day for 10 consecutive days. The total mercury contents in serum and tissue (brain, kidney, liver) were measured by atomic fluorescence spectrometer (AFS). The biological effects investigated involved monoamine neurotransmitters (serotonin, 5-HT) in brain as an indicator of therapeutic function, and serum alanine transaminase (ALT) as a marker of hepatic damage, blood urea nitrogen (BUN) and serum creatinine as markers for renal function. The mercury absorption of cinnabar or HgS was much less than that of HgCl2. The mercury levels in brains of the cinnabar group were only slightly changed and kept in a steady-state with the dose elevated. Cinnabar or HgS suppressed brain 5-HT levels. HgCl2 could not cause any changes in brain 5-HT although the mercury level increased considerably. The results revealed that cinnabar or HgS is markedly different from HgCl2 in mercury absorption, tissue distribution and influence on brain 5-HT levels, which suggests that the pharmacological and/or toxicological effects of cinnabar undertake other pathways from mercuric ions. [ABSTRACT FROM AUTHOR]

Abstract: The aim of this study was to explore the neuropharmacological mechanism of cinnabar. The anxiolytic effect of cinnabar on anxiety-like behaviors in mice was investigated using the elevated plus maze test. The changes in the levels of monoamine neurotransmitters and their metabolites and the activity of monoamine oxidase (MAO) in the brain of mice were determined. The results indicate that cinnabar possessed anxiolytic effects after chronic administration (p.o.) at effective doses in association with the declined brain serotonin (5-HT) level. The cinnabar showed no effects on 5-HT metabolism pathway. The results suggested the potential importance of the brain serotonergic system. The 5-HT metabolism pathway may be not involved in the anxiolytic effects of cinnabar. [Copyright &y& Elsevier]

Abstract: Ethnopharmacological relevance: Cinnabar (Cin), a naturally occurring mercuric sulfide (HgS), is a mineral widely used in traditional Chinese medicine throughout history. As for the toxicity of cinnabar, one important assumption is that cinnabar may be transformed into highly toxic methylmercury by gastrointestinal flora. There is no evidence in humans to support this assumption. Aim of the study: To investigate the biotransformation of cinnabar (HgS) in the human intestinal bacteria with modern analytical techniques. Materials and methods: A gas chromatograph, equipped with electron capture detection (GC-ECD) and mass spectrometry (GC–MS), were used to detect the formation of methylmercury after incubation of cinnabar with human intestinal bacteria. The content of soluble mercury in the bacteria media was determined by cold vapor-atomic absorption spectrometry (CV-AAS). In addition, X-ray absorption near-edge structure spectroscopy (XANES) was used to confirm the possible transformation of cinnabar in the bacteria media, and under mimetic intestinal condition by measuring the species of sulfur and mercury in the reaction extraction of cinnabar and Na2S mixture. Results: No methylmercury was detected by both GC-ECD and GC–MS, which suggest that cinnabar (HgS) is not methylated in the human intestine. A small amount of soluble mercury was found to be released in the flora medium of HgS or cinnabar by CV-AAS. The XANES analyses revealed that polysulfides exist in the flora medium, and the simulated results showed that the products by incubating cinnabar with Na2S were mercuric polysulfides. Conclusion: These results showed that under gut flora conditions cinnabar would be transformed into mercuric polysulfides rather than methylmercury. Our work provides evidences of nontoxic transformation of cinnabar in the human intestinal bacteria. [Copyright &y& Elsevier]

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. [Copyright &y& Elsevier]