REGULATION OF ADENOSINE CONCENTRATION AND CYTOPROTECTIVE EFFECTS OF NOVEL REVERSIBLE ADENOSINE-DEAMINASE INHIBITORS

The physiological role of adenosine (Ado) is well known. Although a nu mber of pharmacological attempts have been made to manipulate Ado conc entrations in ischemic conditions in different tissues, none have been clinically accepted up to now, mostly due to insufficient elevation o f Ado concentrations or unacceptable toxicity. In this study, we evalu ated the biochemical and pharmacological actions of several novel eryt hro-9-(2-hydroxy-3-nonyl)adenine (EHNA) analogs to identify new revers ible adenosine deaminase (ADA) inhibitors with potential clinical util ity. In cell culture experiments, these compounds elevate cellular Ado concentrations under conditions of simulated ischemic stress but very little, if any, under normoxic conditions. Two compounds were selecte d for study: 9'-chloro-EHNA (CPC-405) and 9'-phthalimldo-EHNA (CPC-406 ), which specifically inhibit ADA in cell-free preparations as well as in intact cells. CPC-405 and CPC-406 do not affect adenosine kinase a ctivity, and they do not affect adenosine transport (influx). CPC-405 and CPC-406 are also more potent than EHNA in elevating adenosine rele ase from human astrocytoma cells and bovine heart microvascular endoth elial cells in 2-deoxyglucose-simulated ischemia or under anaerobic co nditions. Inhibition of adenosine deaminase by CPC-405 or CPC-406, as well as the 2'-deoxyadenosine toxicity expressed in the presence of th ese ADA inhibitors, is reversed when the inhibitors are removed by was hing the cells. In the isolated rat heart model of ischemia, these nov el ADA inhibitors showed enhanced recovery of left ventricular end-dia stolic pressure, left ventricular developed pressure, +dP/dt(max) and -dP/dt(max). In the rat hippocampal slice model of hypoxia, these comp ounds also showed neuroprotective effects on CA1 hypoxic injury. In co nclusion, these novel ADA inhibitors may represent clinically useful A do elevating compounds that show cardioprotective, as well as neuropro tective, effects. Also, their potential for immunotoxicity, if any, ap pears to be transient in nature, representing an important clinical ad vantage compared with tight-binding ADA inhibitors such as deoxycoform ycin.