Department of Pharmaceutical Sciences, St, John's University, College of Pharmacy and Allied Health Professions, 8000 Utopia Parkway, Jamaica, New York 11439, USA.
J Biomed Sci. 2010 Aug 24;17 Suppl 1(Suppl 1):S16. doi: 10.1186/1423-0127-17-S1-S16.
Poly(ADP-ribose) is a NAD+-requiring, DNA-repairing, enzyme playing a central role in pancreatic beta-cell death and in the development of endothelial dysfunction in humans and experimental animals. PARP activation is also relevant to the development of complications of diabetes. Hence, agents capable of inhibiting PARP may be useful in preventing the development of diabetes and in slowing down complications of diabetes.
PARP inhibition was assessed with a colorimetric assay kit. Molecular docking studies on the active site of PARP were conducted using the crystalline structure of the enzyme available as Protein Data Bank Identification No. 1UK1. Type 2 diabetes was induced in male Sprague-Dawley rats with streptozotocin (STZ, 60 mg/kg, i.p.). The test compounds (3-aminobenzamide = 3-AB, nicotinamide = NIC, taurine = TAU) were given by the i.p. route 45 min before STZ at 2.4 mM/kg (all three compounds) or 1.2 and 3.6 mM/kg (only NIC and TAU). Blood samples were collected at 24 hr after STZ and processed for their plasma. The plasma samples were used to measure glucose, insulin, cholesterol, triglycerides, malondialdehyde, nitric oxide, and glutathione levels using reported methods.
3-AB, NIC and TAU were able to inhibit PARP, with the inhibitory potency order being 3-AB>NIC> or =TAU. Molecular docking studies at the active site of PARP showed 3-AB and NIC to interact with the binding site for the nicotinamide moiety of NAD+ and TAU to interact with the binding site for the adenine moiety of NAD+. While STZ-induced diabetes elevated all the experimental parameters examined and lowered the insulin output, a pretreatment with 3-AB, NIC or TAU reversed these trends to a significant extent. At a dose of 2.4 mm/kg, the protective effect decreased in the approximate order 3-AB>NIC> or =TAU. The attenuating actions of both NIC and TAU were dose-related except for the plasma lipids since NIC was without a significant effect at all doses tested.
At equal molar doses, 3-AB was generally more potent than either TAU or NIC as an antidiabetogenic agent, but the differences were not as dramatic as would have been predicted from their differences in PARP inhibitory potencies. NIC and TAU demonstrated dose-related effects, which in the case of TAU were only evident at doses > or =2.4 mM/kg. The present results also suggest that in the case of NIC and TAU an increase in dose will enhance the magnitude of their attenuating actions on diabetes-related biochemical alterations to that achieved with a stronger PARP inhibitor such as 3-AB. Hence, dosing will play a critical role in clinical studies assessing the merits of NIC and TAU as diabetes-preventing agents.
聚（ADP-核糖）是一种需要 NAD+的、修复 DNA 的酶，在胰岛β细胞死亡和人类及实验动物内皮功能障碍的发展中起核心作用。PARP 的激活也与糖尿病并发症的发展有关。因此，能够抑制 PARP 的药物可能有助于预防糖尿病的发生，并减缓糖尿病并发症的发展。
使用比色法测定试剂盒评估 PARP 抑制作用。利用可从蛋白质数据库识别号 1UK1 获得的酶的晶体结构进行 PARP 活性部位的分子对接研究。雄性 Sprague-Dawley 大鼠用链脲佐菌素（STZ，60mg/kg，腹腔内注射）诱导 2 型糖尿病。测试化合物（3-氨基苯甲酰胺=3-AB、烟酰胺=尼克酰胺、牛磺酸=TAU）在 STZ 前 45 分钟以 2.4mM/kg（所有三种化合物）或 1.2 和 3.6mM/kg（仅尼克酰胺和 TAU）的剂量通过腹腔内给药。在 STZ 后 24 小时采集血液样本并进行血浆处理。使用报道的方法测量血浆样品中的葡萄糖、胰岛素、胆固醇、甘油三酯、丙二醛、一氧化氮和谷胱甘肽水平。
3-AB、尼克酰胺和 TAU 能够抑制 PARP，抑制效力顺序为 3-AB＞尼克酰胺＞或=TAU。PARP 活性部位的分子对接研究表明，3-AB 和尼克酰胺与 NAD+的烟酰胺部分的结合位点相互作用，而 TAU 与 NAD+的腺嘌呤部分的结合位点相互作用。虽然 STZ 诱导的糖尿病升高了所有检查的实验参数，并降低了胰岛素的分泌，但 3-AB、尼克酰胺或 TAU 的预处理在很大程度上逆转了这些趋势。在 2.4mm/kg 的剂量下，保护作用的降低顺序约为 3-AB＞尼克酰胺＞或=TAU。尼克酰胺和 TAU 的衰减作用均呈剂量依赖性，除了血浆脂质外，因为尼克酰胺在所有测试剂量下均无显著作用。
在等摩尔剂量下，3-AB 作为抗糖尿病药物通常比 TAU 或尼克酰胺更有效，但差异并不像它们在 PARP 抑制活性方面的差异那样显著。尼克酰胺和 TAU 表现出剂量相关的作用，而在 TAU 的情况下，仅在剂量≥2.4mM/kg 时才明显。目前的结果还表明，在尼克酰胺和 TAU 的情况下，增加剂量将增强其对糖尿病相关生化改变的衰减作用的幅度，使其达到更强的 PARP 抑制剂（如 3-AB）的效果。因此，剂量将在评估尼克酰胺和 TAU 作为预防糖尿病药物的临床研究中发挥关键作用。
