On the mechanisms of neuroprotection by creatine and phosphocreatine

Creatine and phosphocreatine were evaluated for their ability to prevent de ath of cultured striatal and hippocampal neurons exposed to either glutamat e or 3-nitropropionic acid (3NP) and to inhibit the mitochondrial permeabil ity transition in CNS mitochondria. Phosphocreatine (PCr), and to a lesser extent creatine (Cr), but not (5R,10S)-(+)-5-methyl-10,11-dihydro-5H-[-dibe nzo[a,d]cyclohepten-5,10-imine hydrogen maleate (MK801), dose-dependently a meliorated 3NP toxicity when applied simultaneously with the 3NP in Mg2+-fr ee media. Pretreatment of PCr for 2 or 5 days and Cr for 5 days protected a gainst glutamate excitotoxicity equivalent to that achieved by MK801 post-t reatment. The combination of PCr or Cr pretreatment and MK801 post-treatmen t did not provide additional protection, indicating that both prevented the toxicity attributable to secondary glutamate release. To determine if Cr o r PCr directly inhibited the permeability transition, mitochondrial swellin g and depolarization were assayed in isolated, purified brain mitochondria. PCr reduced the amount of swelling induced by calcium by 20%. Cr decreased mitochondrial swelling when inhibitors of creatine kinase octamer-dimer tr ansition were present. However, in brain mitochondria prepared from rats fe d a diet supplemented with 2% creatine for 2 weeks, the extent of calcium-i nduced mitochondrial swelling was not altered. Thus, the neuroprotective pr operties of PCr and Cr may reflect enhancement of cytoplasmic high-energy p hosphates but not permeability transition inhibition.