8-Aminopurines in the Cardiovascular and Renal Systems and Beyond

Screening of compounds comprising 8-substituted guanine revealed that 8-aminoguanosine and 8-aminoguanine cause diuresis/natriuresis/glucosuria, yet decrease potassium excretion. Subsequent investigations demonstrated that 8-aminoguanosine's effects are mediated by its metabolite 8-aminoguanine. The mechanism by which 8-aminoguanine causes diuresis/natriuresis/glucosuria involves inhibition of PNPase (purine nucleoside phosphorylase), which increases renal interstitial inosine levels. Additional evidence suggests that inosine, via indirect or direct adenosine A_2B receptor activation, increases renal medullary blood flow which enhances renal excretory function. Likely, 8-aminoguanine has pleiotropic actions that also alter renal excretory function. Indeed, the antikaliuretic effects of 8-aminoguanine are independent of PNPase inhibition. 8-Aminoguanine is an endogenous molecule; nitrosative stress leads to production of biomolecules containing 8-nitroguanine moieties. Degradation of these biomolecules releases 8-nitroguanosine and 8-nitro-2'-deoxyguanosine which are converted to 8-aminoguanine. Also, guanosine and guanine per se may contribute to 8-aminoguanine formation. 8-Aminoinosine, 8-aminohypoxanthine, and 8-aminoxanthine likewise induce diuresis/natriuresis/glucosuria, yet do not reduce potassium excretion. Thus, there are several pharmacologically active 8-aminopurines with nuanced effects on renal excretory function. Chronic treatment with 8-aminoguanine attenuates hypertension in deoxycorticosterone/salt rats, prevents strokes, and increases lifespan in Dahl salt-sensitive rats on a high salt diet and attenuates the metabolic syndrome in rats; 8-aminoguanosine retards progression of pulmonary hypertension in rats and anemia and organ damage in sickle cell mice. 8-Aminoguanine reverses age-associated lower urinary tract dysfunction and retinal degeneration. 8-Aminopurines represent a new class of agents (and potentially endogenous factors) that have beneficial effects on the cardiovascular system and kidneys and may turn back the clock in age-associated diseases.