BackgroundPoly(ADP-ribose) is a NAD+-requiring, DNA-repairing, enzyme playing a central role in pancreatic β-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.MethodsPARP 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.Results3-AB, NIC and TAU were able to inhibit PARP, with the inhibitory potency order being 3-AB>NIC>>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≥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.ConclusionsAt 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 ≥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.

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Taking into account the proven effectiveness of antioxidants in preventing experimentally induced diabetes in laboratory animals, this study was carried out with the specific purpose of comparing the effectiveness of two known antioxidants, the β-aminosulfonate taurine (TAU) and β-aminothiosulfonate thiotaurine (TTAU), in preventing biochemical, functional and histological alterations indicative of -diabetic nephropathy. In the study, streptozotocin (60 mg/kg, orally) was used to induce type 2 diabetes mellitus in Sprague-Dawley rats. Starting on day 15 and continuing up to day 56, the rats received a daily single 2.4 mmol/kg oral dose of a sulfur-containing compound (TAU or TTAU) or 4 U/kg subcutaneous dose of isophane insulin (INS). Rats not receiving any treatment served as controls. After obtaining a 24 h urine sample, the animals were sacrificed by decapitation on day 57, and their blood and kidneys immediately collected. Diabetic rats exhibited marked hyperglycemia, hypoinsulinemia, hypoproteinemia, hyponatremia, hyperkalemia, azotemia, hypercreatinemia, increased plasma TGF β(1), lipid peroxidation, plasma and kidney nitrite, and urine output; decreased glutathione redox status in plasma and kidney, decreased urine Na(+) and K(+), proteinuria and hypocreatinuria. Without exceptions, all the treatment compounds were found to markedly and variously attenuate these changes. Confirmation of protection by INS, TAU and TTAU was provided by the results of histological examination of kidney sections and which showed a more normal appearance than sections from diabetic animals. In most instances protection by TTAU was about equal to that by INS but greater than that by TAU.

In this study, the actions of taurine (TAU), a sulfonate, and thiotaurine (TTAU), a thiosulfonate, on diabetes-mediated biochemical alterations in red blood cells (RBCs) and plasma and on the RBC membrane, morphology and spectrin distribution were examined in rats. Diabetes was induced in male Sprague-Dawley rats with streptozotocin (60 mg/kg i.p.) and allowed to progress for 14 days. From days to 56, the rats received a daily, 2.4 mmol/kg, oral dose of TAU or TTAU, 2 mL oral dose of physiological saline or 4 U/kg subcutaneous dose of isophane insulin (INS). Naive rats served as the control group. The rats were sacrificed on day 57 and their blood was collected to measure HbA(1c), to isolate intact RBCs, and to obtain plasma. A 6-weeks treatment with INS effectively lowered the elevations in plasma glucose, cholesterol, triglycerides, and plasma and RBC malondialdehyde and glutathione disulfide while effectively counteracting the decreases in plasma INS, plasma and RBC glutathione redox status, and plasma and RBC activities of antioxidant enzymes caused by diabetes. Also, INS returned the echynocytic appearance and peripheral location of spectrin seen in RBCs from diabetic rats to the normal discocytic shape and uniform distribution. TAU and TTAU were as effective as INS in inhibiting malondialdehyde formation, changes in redox status and oxidative stress in both the plasma and RBC, but were much less effective in controlling hyperglycemia and hypoinsulinemia. Furthermore TTAU was more effective than INS or TAU in lowering the increase in cholesterol to phospholipids ratio in the RBC membrane and, unlike TAU, it was able to normalize the RBC morphology and spectrin distribution.

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