Natural killer (NK) cells play an important role in suppressing the progression of cancer by activating themselves through the production of cytokines or by killing cancer cells. Previously we found that the addition of IL-2 to NK-92 cells induced the production of IFN-γ, IL-10, IL-6, and LT-α, and that arsenite (As(III)) suppressed the production of these cytokines. Here we examined the effects of As(III) on the production of IFN-γ, IL-10, IL-6, and LT-α following stimulation with IL-12, which activates NK cells similarly to IL-2, or with the combined addition of IL-2 and IL-12 in NK-92 cells. The results showed that IFN-γ and IL-10 were produced in response to IL-12 alone, whereas IL-6 and LT-α were detected only when IL-12 was co-treated with IL-2. The production of all four cytokines induced by IL-2, IL-12, or IL-2 + IL-12 was suppressed by concurrent exposure to As(III) in NK-92 cells. Exposure of primary NK cells isolated from mouse spleens to As(III) also inhibited the IL-2 + IL-12‒induced increase in IFN-γ production. Furthermore, when IL-2 + IL-12 was added to primary NK cells collected from the spleens of mice that had consumed drinking water containing 50 ppm or 100 ppm As(III) for 7 months, IFN-γ production was significantly reduced. This report is the first to demonstrate that As(III) inhibits cytokine production induced by IL-2 and/or IL-12 not only in cultured NK cells but also in primary NK cells derived from mouse spleen.

The safety profile of newly-manufactured β-nicotinamide mononucleotide (NMN) was assessed using an in vitro mutagenicity test and oral toxicity studies. In the mutagenicity test, a reverse mutation assay (Ames test) was performed using five Salmonella typhimurium strains (TA98, TA1535, TA100, and TA1537) and Escherichia coli strain, WP2 uvrA. These tester strains were exposed to NMN in the absence and presence of a metabolic activation system (rat liver S9). The results of the range-finding test and main test showed no bacterial growth inhibition or increase in the number of revertant colonies in the tester strains at any concentration, regardless of metabolic activation. In oral toxicity studies, Sprague–Dawley rats [Crl:CD(SD)] were gavaged with NMN in water once daily at a dose of 2000 mg/kg (acute toxicity study) or once daily for 91 d at a dose of 300 and 1000 mg/kg (subchronic toxicity study). Each group contained five males and five females in the acute toxicity study and ten males and ten females in the subchronic toxicity study. The results of the acute toxicity study showed that NMN caused no deaths, treatment-related adverse events, or changes in body weight during and after treatment. The minimum lethal dose was higher than 2000 mg/kg in both sexes. The results of the subchronic toxicity study showed that there were no marked changes in body weight, feed intake, ophthalmology results, clinical results (urinalysis, hematology, coagulation, and blood chemistry), and pathological results (organ weight, necropsy, and histopathology), and the no-observed-adverse-effect level was 1000 mg/kg/day in both sexes.