The 8-Aminopurine Hypothesis

我们已经发现，8-氨基鸟嘌呤（8A-鸟嘌呤），一种天然存在的8-氨基嘌呤，具有独特的 药理学特征，即，它发挥利尿、利钠、促葡萄糖排泄、抗利尿钾和抗高血压活性。 此外，8A-鸟嘌呤可保护Dahl SS大鼠免受靶器官损伤，并延长其寿命。 高盐饮食，由于预防盐引起的中风的效果。因为8-氨基鸟苷（8A- 鸟苷）在体循环中转化为8A-鸟嘌呤，这种8-氨基嘌呤具有与 8A-鸟嘌呤。8A-鸟嘌呤（和8A-鸟苷通过其代谢为8A-鸟嘌呤）的作用机制是 主要是通过抑制嘌呤核苷磷酸化酶（PNTR）。重要的是，在初步实验中，我们 观察到在Dahl SS大鼠中，高盐饮食（4%）降低了内源性肾间质中8A- 鸟苷和8A-鸟嘌呤分别提高85%和100%。这些初步研究表明， 盐摄入诱导8-氨基嘌呤缺乏症，至少在Dahl SS大鼠中是如此;但这一发现必须在 Dahl SS大鼠并在其他高血压模型中进行测试。我们发现8-氨基肌苷（8A-Ino）和 8-氨基次黄嘌呤（8A-HX）具有与8A-鸟苷和8A-鸟嘌呤非常相似的化学结构， 分别是天然存在的肌苷和次黄嘌呤的类似物;因此，我们 推测这些化合物也可能是具有有益生物活性的内源性8-氨基嘌呤。 因为没有人研究过8A-Ino或8A-HX的生物学效应，我们进行了初步的研究。 这些化合物的肾脏研究。这些初步研究表明，8A-Ino和8A-HX都可能具有 对肾功能的影响与8A-鸟苷和8A-鸟嘌呤相似，但可能更有效 在这方面然而，这些发现必须得到证实。此外，尚不清楚：1）8A-Ino的作用是否 8A-Ino和8A-HX是否具有抗高血压和器官- 保护作用; 3）8A-Ino和8A-HX，如8A-鸟苷和8A-鸟嘌呤，是否是天然存在的; 以及4）它们的生物合成是否也被高盐饮食抑制。我们的出版物和 初步发现激发了我们的“8-氨基嘌呤假说”，该假说假定：1）8 A-鸟苷， 8A-鸟嘌呤、8A-Ino和8A-HX包含天然存在的8-氨基嘌呤系统， 利钠，抗高血压和器官保护; 2）8-氨基嘌呤缺乏有助于盐- 敏感性高血压、靶器官损害和死亡率; 3）8-氨基嘌呤缺乏可 经口服8-氨基嘌呤治疗纠正。在这里，我们建议进一步测试这一假设：1） 阐明8A-Ino和8A-HX的肾效应; 2）确定高盐饮食是否诱导缺乏症 在所有4种8-氨基嘌呤中;和3）确定8A-Ino和8A-HX，像8A-鸟苷和8A-鸟嘌呤， 具有抗高血压活性和防止靶器官损伤。最后，我们将探讨 8A-Ino和8A-HX的作用机制不仅涉及抑制PNTR，而且涉及抑制黄嘌呤氧化酶。

We have discovered that 8-aminoguanine (8A-Guanine), a naturally-occurring 8-aminopurine, has a unique pharmacological profile, i.e., it exerts diuretic, natriuretic, glucosuric, antikaluretic and antihypertensive activity. In addition, 8A-Guanine protects against target-organ damage and increases the lifespan of Dahl SS rats on a high salt diet, an effect due to prevention of salt-induced strokes. Because 8-aminoguanosine (8A- Guanosine) is converted to 8A-Guanine in the systemic circulation, this 8-aminopurine has similar effects to 8A-Guanine. The mechanism of action of 8A-Guanine (and 8A-Guanosine via its metabolism to 8A-Guanine) is mostly via inhibition of purine nucleoside phosphorylase (PNPase). Importantly, in preliminary experiments we observed that in Dahl SS rats a high salt diet (4%) reduced endogenous renal interstitial levels of 8A- Guanosine and 8A-Guanine by 85% and 100%, respectively. These preliminary studies suggest that a high salt intake induces 8-aminopurine deficiency, at least in Dahl SS rats; but this finding must be confirmed in Dahl SS rats and tested in other models of hypertension. It occurred to us that 8-aminoinosine (8A-Ino) and 8-aminohypoxanthine (8A-HX) have chemical structures very similar to 8A-Guanosine and 8A-Guanine, respectively, and are analogues of naturally-occurring inosine and hypoxanthine, respectively; therefore we reasoned that these compounds too may be endogenous 8-aminopurines with beneficial biological activities. Because no one has ever examined the biological effects of either 8A-Ino or 8A-HX, we conducted preliminary renal studies with these compounds. These preliminary studies suggest that both 8A-Ino and 8A-HX may have effects on renal function similar to those of 8A-Guanosine and 8A-Guanine, but may be even more efficacious in this regard. However, these findings must be confirmed. Also, it is unknown: 1) whether the effects of 8A-Ino are mediated via its metabolism to 8A-HX; 2) whether 8A-Ino and 8A-HX have antihypertensive and organ- protective effects; 3) whether 8A-Ino and 8A-HX, like 8A-Guanosine and 8A-Guanine, are naturally-occurring; and 4) whether their biosynthesis is also suppressed by a high salt diet. Together, our published and preliminary findings motivate our “8-AMINOPURINE HYPOTHESIS”, which postulates that: 1) 8A-Guanosine, 8A-Guanine, 8A-Ino and 8A-HX comprise a naturally-occurring 8-aminopurine system that is natriuretic, antihypertensive and organ-protective; 2) 8-aminopurine deficiency contributes to salt- sensitive hypertension, target-organ damage and mortality; and 3) 8-aminopurine deficiency can be corrected by oral treatment with 8-aminopurines. Here we propose to further test this hypothesis by: 1) elucidating the renal effects of 8A-Ino and 8A-HX; 2) determining whether a high salt diet induces a deficiency in all 4 8-aminopurines; and 3) determining whether 8A-Ino and 8A-HX, like 8A-Guanosine and 8A-Guanine, have antihypertensive activity and prevent target organ damage. Finally, we will explore whether the mechanism of action of 8A-Ino and 8A-HX involves not only inhibition of PNPase, but also of xanthine oxidase.