The number of patients with colitis has been increasing year by year. Recently, intestinal inflammation, as one of the factors for its onset, has been demonstrated to be induced by P2X7 receptor-mediated activation of colonic immune cells such as mast cells. Activation of P2X7 receptor (P2X7R) is known to be inhibited by divalent metal cations such as magnesium, but whether or not magnesium administration prevents/relieves colitis is unknown so far. Here, we report that oral (per os (p.o.)) administration of MgCl 2 and ingestion of commercially available magnesium-rich mineral hard water relieves dextran sulfate sodium (DSS)-induced colitis in mice. Colitis was induced through ingestion of a 3% (w/v) DSS solution ad libitum for 10 d. Brilliant blue G (BBG, a P2X7R antagonist), MgCl 2 or magnesium-rich mineral hard water was administered p.o. to mice via gastric intubation once a day or ad libitum from a day before DSS administration for 11 times or 11 d, respectively. DSS-treated mice exhibited a low disease activity index, a short colon and a high histological score compared to in control mice. As BBG (250 mg/kg, p.o.), administration of a MgCl 2 solution (100 or 500 mg/kg, p.o.) and ad libitum ingestion of the magnesium-rich mineral hard water (212 ppm as magnesium) partially, but significantly, attenuated the severity of colitis by decreasing the accumulation of P2X7R-immunopositive mast cells in the colon. Therefore, prophylactic p.o. administration/ingestion of magnesium is considered to be partially effective to protect mice against DSS-induced colitis by inhibiting P2X7R-mediated activation/accumulation of colonic mast cells.

P2X7 receptor (P2X7R), a purinergic receptor, is involved in pathophysiological events such as inflammation and cell death, and thus is an attractive target for therapeutic approaches. It is reported that divalent metal cations (DMCs) inhibit P2X7R activation and that there are species differences in their inhibitory effects. To extrapolate the findings in experimental animals to humans, these species differences have to be clarified, but species differences in the sensitivity of P2X7R to DMCs between man and mouse have not been demonstrated. Here we performed direct comparison of the inhibitory effects of DMCs on human and mouse P2X7R activation. Cell lines constitutively expressing human and mouse P2X7R were used, and their P2X7R activation was evaluated as means of YO-PRO-1 dye uptake. MgCl 2 , NiCl 2 , ZnCl 2 , CuCl 2 and CaCl 2 dose-dependently decreased agonist-induced YO-PRO-1 uptake via both human and mouse P2X7Rs. Apparent differences in the inhibitory profiles for NiCl 2 and CaCl 2 between them were found, and the IC 50 values of DMCs were in the order of CaCl 2 >MgCl 2 >NiCl 2 ≈ZnCl 2 >CuCl 2 for both human and mouse P2X7Rs. In this study, we demonstrate that human P2X7R exhibits different sensitivity to nickel and calcium compared with the case of the mouse one, while there is no species difference in the sensitivity of their P2X7Rs to magnesium, zinc and copper, suggesting that the effects of magnesium, zinc and copper on P2X7R-associated pathophysiological events in humans might be predicted from those in mice.Key words P2X7 receptor; divalent metal cation; species difference; IC 50 value ATP is an energy currency, and the finding of purinergic receptors (P2Rs) revealed another role of it as a signaling molecule. For instance, ATP acts as a neuro-and glio-transmitter in the neuronal system, and as a regulator of inflammatory response in immune system. 1-3) P2Rs are classified into two groups, ionotropic P2XRs and metabotropic P2YRs.4,5) Of P2XRs, P2X7R has unique characteristics, and its affinity for ATP is extremely low and its prolonged activation leads to formation of channels/pores. 6,7) In neuronal cells, extensive activation of P2X7Rs causes the death of neurons, 8,9) and induces microglial activation 10) and astrocytic engulfing activity. 11,12) In immune cells, ATP-induced P2X7R activation triggers Nod-like receptor family, pyrin domain containing 3 (NLRP3) inflammasome activation, followed by generation/ release of inflammatory cytokines.13-15) Kurashima et al. demonstrated that activation of P2X7R expressed by resident mast cells in the colon induces initiation of inflammation through the release of chemokines and cytokines, and exacerbation of inflammation through the recruitment of neutrophils, and robust release of cytokines in inflammatory bowel disease model mice and Crohn's disease patients.16) These findings strongly indicate that P2X7Rs are an attractive target for the development of therapeutic approaches for various diseases such as neurodegenerative disorders, inflammatory dise...