Ayurvedic processing of α-HgS gives novel physicochemistry and distinct toxicokinetics in zebrafish

Pharmacology, Toxicology, and Rational Application of Cinnabar, Realgar, and Their Formulations

Ethnopharmacological Relevance. Mineral medicines are widely used traditional Chinese medicines with curative effects. These medicines are used for many refractory diseases. Aim of the Review. In this review, cinnabar (HgS) and realgar (As₂S₂) serve as examples of mineral medicines, and their pharmacology, therapeutic toxicity, use in traditional medicine mixtures, and research perspectives are discussed. Materials and Methods. A search was performed for the literature on cinnabar and realgar in PubMed, the Chinese Pharmacopeia, Google, and other sources. The search included studies using single herbs, traditional formulations, or novel dosage forms. Results. Cinnabar and cinnabar formulas exhibit good efficacy for sedation, sleep improvement, anxiety alleviation, and brain protection. However, previous studies on neurotransmitters have reached different conclusions, and detailed pharmacological mechanisms are lacking. Realgar and its formulas exert promising antitumor activity through regulation of cell cycle arrest, intrinsic and extrinsic apoptosis, induction of differentiation, autophagy, metabolic reprogramming, matrix metalloproteinase-9 (MMP-9) signaling, and reactive oxygen species (ROS) generation. In addition, realgar can be used to treat a variety of refractory diseases by regulating immunity and exerting antibacterial, antiviral, and other effects. However, the existing pharmacological research on the use of realgar for epidemic prevention is insufficient, and animal experiments and research at the cellular level are lacking. Inappropriate applications of cinnabar and realgar can cause toxicity, including neurotoxicity, liver toxicity, kidney toxicity, and genotoxicity. The toxicological mechanism is complex, and molecular-level research is limited. For clinical applications, theory and clinical experience must be combined to guide scientific and rational drug use and to achieve reduced toxicity and increased efficacy through the use of modern preparation methods or combined drugs. Notably, when cinnabar and realgar are used to treat targeted diseases, these agents have a bidirectional effect of “treatment” and “toxicity” on the central nervous system in pathological and normal states. The pharmacological and toxicological mechanisms need to be elucidated in greater detail in the future. Overall, systematic research is needed to provide a basis for better promotion of the rational use of cinnabar and realgar in the clinic. Conclusion. Mineral medicines are multicomponent, multiactivity, and multitargeted substances. The pharmacology and mechanisms of the toxicity and action of realgar and cinnabar are extremely complex. A number of Chinese medicinal preparations of realgar and cinnabar have demonstrated unique efficacy in the treatment of refractory diseases.

Explaining Ayurvedic preparation of Rasasindura, its toxicological effects on NIH3T3 cell line and zebrafish larvae

Rasasindura is a mercury-based medicinal formulation that contains HgS (>99%). Although cinnabar ore was a well-known mineral in the past, the Ayurvedic practitioner adopted a critical and tedious procedure for the preparation of Rasasindura. Therefore, it is essential to understand the Ayurvedic process in the perspective of material science. Further, a toxicity study is also required as mercury is the main component in Rasasindura. Here, in the present study, we characterized Rasasindura and one of its intermediates (Kajjali) to understand the physicochemical changes that occur in the Ayurvedic process. Furthermore, we have assessed the toxicity of Kajjali and Rasasindura in NIH3T3 cell lines and zebrafish larvae. XRD analysis of Rasasindura confirms it as a highly pure α-HgS with size ranges from nano to micron sizes (starting from ∼80 nm). Whereas, Kajjali is a β-HgS having lower size ranges (starting from ∼30 nm). Rasasindura did not show significant cytotoxicity on NIH3T3 cell line up to 75 ppm, whereas for Kajjali, cytotoxicity was observed above 20 ppm. The higher toxicity of Kajjali is due to higher penetration of particles into the cells. However, in zebrafish larvae, even at too high concentrations (1000 ppm), both Rasasindura and Kajjali did not show any toxicity or morphological changes. This study concludes that Rasasindura is not toxic up to a reasonable concentration. Further, these two drugs did not contain toxic organic mercuric compound; otherwise, it could have been lethal to the zebrafish larvae.

Adaptive mechanisms induced by sparingly soluble mercury sulfide (HgS) in zebrafish: Behavioural and proteomics analysis

Mercury (Hg) causes great health concerns due to its extreme neurotoxicity. However, here we show that pretreatment of sparingly soluble mercury compound (HgS) could induce adaptive mechanisms in zebrafish, which can resist the neurotoxic effects of mercury chloride (HgCl₂). In this study, zebrafish were treated with HgS (in the form of 99% HgS arising from traditional Ayurvedic medicine Rasasindura (RS), chosen for its particle and crystallite sizes). This work was prompted by the traditional use of this form of HgS to treat nervous and immune-related diseases. Our investigation on zebrafish behaviour showed that RS pretreated fish group (RS-HG) was less severely affected by HgCl₂ exposure, as compared to the RS non-treated (VC-HG) group. Further, biochemical tests showed that RS pretreatment prevents alteration of reactive oxygen species (ROS), acetylcholinesterase (AChE), and cortisol as compared to the VC-HG group. Proteomics and bioinformatics studies of zebrafish brain tissues suggested that Rasasindura (RS-HG group) protects alteration of various protein expression related to KEGG pathways, including citrate cycle (TCA cycle) and glutathione metabolism that are directly or indirectly linked to the oxidative stress, against HgCl₂ induced neurotoxicity. We found that adaptive mechanisms were initiated by the initiation of response to stress (enrichment of GO:0006950 pathway), due to the accumulation of a small amount of ionic Hg (60 ± 10 ng/g) after 15 days of RS treatment. These adaptive mechanisms avoid further adverse neurotoxicity of HgCl₂. Thus, HgS (RS) pretreatment can induce protective effects in zebrafish.