Abstract
Metal ions are notorious environmental contaminants, some causing toxicity at exquisitely low (ppm-level) concentrations. Yet, the redox properties of metal ions make them attractive candidates for bio-therapeutics. Titanates are insoluble particulate compounds of titanium and oxygen with crystalline surfaces that bind metal ions; these compounds offer a means to scavenge metal ions in environmental contexts or deliver them in therapeutic contexts while limiting systemic exposure and toxicity. In either application, the toxicological properties of titanates are crucial. To date, the accurate measurement of the in vitro toxicity of titanates has been complicated by their particulate nature, which interferes with many assays that are optical density (OD)-dependent, and at present, little to no in vivo titanate toxicity data exist. Compatibility data garnered thus far for native titanates in vitro are inconsistent and lacking in mechanistic understanding. These data suggest that native titanates have little toxicity toward several oral and skin bacteria species, but do suppress mammalian cell metabolism in a cells-pecific manner. Titanate compounds bind several types of metal ions, including some common environmental toxins, and enhance delivery to bacteria or cells. Substantial work remains to address the practical applicability of titanates. Nevertheless, titanates have promise to serve as novel vehicles for metal-based therapeutics or as a new class of metal scavengers for environmental applications.
Highlights
Alkali metal titanates are a class of inorganic compounds that generally feature a layered structure in which the anionic titania layers are separated by exchangeable cations
Using OSC2 and diploid fibroblast (WI-38) cell types, this study reported that suppression of cellular mitochondrial function by native titanates was not restricted to rapidly growing cells; WI-38, which have a far slower growth rate than OSC2, were suppressed 30-40% by monosodium titanate (MST)
In-vitro evidence to-date suggests that titanates are not toxic to several strains of bacteria, but that they suppress mammalian cell metabolism of several cell types by 30-50% vs. unexposed controls
Summary
Alkali metal titanates are a class of inorganic compounds that generally feature a layered structure in which the anionic titania layers are separated by exchangeable cations. Titanate compounds bind several types of metal ions, including some common environmental toxins, and enhance delivery to bacteria or cells. Initial studies of the biological effects of native particles (without metals), [2] exposed mammalian (human) monocytic cells (THP1) in vitro to MST (monosodium titanate) particles for 24-72 h, using mitochondrial (MTT) or monocytic secretory (TNFα) activities as indicators of cell response.
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