Effects of KR-33028, a novel Na+ /H+ exchanger-1 inhibitor, on glutamate-induced neuronal cell death and ischemia-induced cerebral infarct

Abstract We investigated the effects of a novel Na+ /H+ exchanger-1 (NHE-1) inhibitor KR-33028 on glutamate excitotoxicity in cultured neuron cells in vitro and cerebral infarct in vivo by comparing its potency with that of zoniporide, a well-known, highly potent NHE-1 inhibitor. KR-33028 inhibited NHE-1 activation in a concentration-dependent manner (IC50 = 2.2 nM), with 18-fold greater potency than that of zoniporide (IC50 = 40.7 nM). KR-33028 significantly attenuated glutamate-induced LDH release with approximately 100 times lower EC25 than that of zoniporide in cortical neurons in vitro (EC25 of 0.007 and 0.81 μM, respectively), suggesting its 100-fold greater potency than zoniporide in producing anti-necrotic effect. In addition, the EC50 of KR-33028 for anti-apoptotic effect was 100 times lower than that of zoniporide shown by TUNEL positivity (0.005 and 0.62 μM, respectively) and caspase-3 activity (0.01 and 2.64 μM, respectively). Furthermore, the EC50 value of KR-33028 against glutamate-induced intracellular Ca2+ overload was also 100 times lower than that of zoniporide (EC50 of 0.004 and 0.65 μM, respectively). In the in vivo cerebral infarct model (60 min middle cerebral artery occlusion followed by 24 h reperfusion), KR-33028 reduced infarct size in a dose-dependent manner. Its ED25 value, however, was quite similar to that of zoniporide (ED25 of 0.072 and 0.097 mg/kg, respectively). Hence these results suggest that the novel NHE-1 inhibitor, KR-33028, could be an efficient therapeutic tool to protect neuronal cells against ischemic injury.