(5-(3-thienyl)tetrazol-1-yl)acetic-acid and Diabetic-Neuropathies

To investigate the characteristic features of diabetic neuropathy in type 2 diabetes mellitus, Otsuka Long-Evans Tokushima fatty (OLETF) rats, an animal model of human type 2 diabetes mellitus, and non-diabetic Long-Evans Tokushima Otsuka (LETO) rats were fed with or without sucrose and/or an aldose reductase inhibitor, [5-(3-thienyl) tetrazol-1-yl] acetic acid (TAT), for 24 weeks, and physiological, biochemical and morphological assessments were performed. Sucrose administration caused remarkable hyperglycemia in OLETF rats but not in LETO rats. Sucrose-fed OLETF rats demonstrated delayed nerve conduction velocity, decreased coefficient of variation of R-R interval, reduced sciatic nerve blood flow, increased platelet aggregation activity, a lower concentration of erythrocyte 2,3-diphosphoglycerate, and decreased Na+/K+-ATPase activity in sciatic nerves, compared with the non-sucrose-fed OLETF and LETO rats. TAT prevented all these deficits except hyperglycemia. Sorbitol and fructose accumulation and myo-inositol depletion in tail nerves of sucrose-fed OLETF rats were ameliorated by TAT. Myelinated fiber size and density in sural nerves of sucrose-fed OLETF rats were decreased and increased, respectively, compared with non-sucrose-fed OLETF and LETO rats. These morphological abnormalities were normalized by TAT. These observations suggest that the sucrose-fed OLETF rat developed diabetic neuropathy not only electrophysiologically but also histologically, and that an aldose reductase inhibitor, TAT, possesses therapeutic value for the treatment of diabetic neuropathy.

Topics: 2,3-Diphosphoglycerate; Aldehyde Reductase; Animals; Diabetes Mellitus, Type 2; Diabetic Neuropathies; Dietary Sucrose; Enzyme Inhibitors; Erythrocytes; Humans; Hyperglycemia; Male; Neural Conduction; Platelet Aggregation; Rats; Rats, Inbred OLETF; Rats, Long-Evans; Regional Blood Flow; Sciatic Nerve; Sodium-Potassium-Exchanging ATPase; Tetrazoles; Thiophenes

To investigate the relationship between polyol pathway hyperactivity and altered carnitine metabolism in the pathogenesis of diabetic neuropathy, the effects of an aldose reductase inhibitor, [5-(3-thienyl) tetrazol-1-yl]acetic acid (TAT), and a carnitine analog, acetyl-L-carnitine (ALC), on neural functions and biochemistry and hemodynamic factors were compared in streptozotocin-diabetic rats. Significantly delayed motor nerve conduction velocity, decreased R-R interval variation, reduced sciatic nerve blood flow and decreased erythrocyte 2, 3-diphosphoglycerate concentrations in diabetic rats were all ameliorated by treatment with TAT (administered with rat chow containing 0.05% TAT, approximately 50 mg/kg/day) or ALC (by gavage, 300 mg/kg/day) for 4 weeks. Platelet hyperaggregation activity in diabetic rats was diminished by TAT but not by ALC. TAT decreased sorbitol accumulation and prevented not only myo-inositol depletion but also free-carnitine deficiency in diabetic nerves. On the other hand, ALC also increased the myo-inositol as well as the free-carnitine content without affecting the sorbitol content. These observations suggest that there is a close relationship between increased polyol pathway activity and carnitine deficiency in the development of diabetic neuropathy and that an aldose reductase inhibitor, TAT, and a carnitine analog, ALC, have therapeutic potential for the treatment of diabetic neuropathy.

Topics: Acetylcarnitine; Aldehyde Reductase; Animals; Body Weight; Carnitine; Diabetes Mellitus, Experimental; Diabetic Neuropathies; Enzyme Inhibitors; Hemodynamics; Male; Neural Conduction; Polymers; Rats; Rats, Sprague-Dawley; Sciatic Nerve; Tetrazoles; Thiophenes

In an animal model of human non-insulin dependent diabetes mellitus (NIDDM), Otsuka Long-Evans Tokushima Fatty (OLETF) rats were fed with sucrose for 8 weeks to obtain severe hyperglycemia. The effects of sucrose administration on peripheral nerve functions, motor nerve conduction velocity (MNCV) and coefficient of variance of R-R interval (CVR-R), were investigated with concomitant measuring of sciatic nerve blood flow (SNBF), ADP-induced platelet aggregation and polyol content in the sciatic nerves. The effects of an aldose reductase inhibitor, TAT, on these parameters were also studied. Administration of sucrose to OLETF rats caused significant body weight reduction and remarkable hyperglycemia. Sucrose-fed OLETF rats demonstrated significantly delayed MNCV, decreased CVR-R, reduced SNBF and increased platelet aggregation activity to ADP. Sorbitol and fructose accumulation, and myo-inositol depletion in sciatic nerves were observed only in sucrose-fed OLETF rats. These abnormalities were all ameliorated by the treatment with TAT. These observations suggest that the sucrose-fed OLETF rat is a useful animal model for studying the pathogenesis of diabetic neuropathy in human NIDDM, and that an aldose reductase inhibitor is a useful therapeutic agent for the treatment of diabetic neuropathy.

Topics: Aldehyde Reductase; Animals; Blood Glucose; Body Weight; Diabetes Mellitus, Type 2; Diabetic Neuropathies; Disease Models, Animal; Enzyme Inhibitors; Insulin; Lipids; Male; Platelet Aggregation; Platelet Aggregation Inhibitors; Polymers; Rats; Regional Blood Flow; Sciatic Nerve; Sucrose; Tetrazoles; Thiophenes

The effects of propionyl-L-carnitine (PCAL) on caudal motor nerve conduction velocity, the coefficient of variation of the R-R interval on the electrocardiogram, and sciatic nerve blood flow were compared with those of [5-(3-thienyl)tetrazol-1-yl] acetic acid monohydrate, an aldose reductase inhibitor, in rats with streptozotocin-induced diabetes. Diabetic control rats showed significantly delayed nerve conduction (P < .05), decreased R-R variability (P < .05) and reduced sciatic nerve blood flow (P < .05). Oral administration of PCAL (0.5 g/kg/day) and [5-(3-thienyl)tetrazol-1-yl] acetic acid monohydrate (0.05% in the diet: 60 mg/kg/day) for 8 weeks significantly improved both nerve conduction (P < .05) and R-R variability (P < .05) in diabetic rats, along with the normalization of sciatic nerve blood flow. PCAL treatment increased the nerve tissue levels of carnitine and myo-inositol and reduced the serum triglyceride level in diabetic rats. Our results suggests that PCAL could have therapeutic potential for the treatment of diabetic neuropathy.

Topics: Aldehyde Reductase; Animals; Blood Glucose; Body Weight; Carbohydrate Metabolism; Cardiotonic Agents; Carnitine; Cauda Equina; Diabetes Mellitus, Experimental; Diabetic Neuropathies; Electrocardiography; Enzyme Inhibitors; Heart Conduction System; Lipids; Male; Motor Neurons; Neural Conduction; Rats; Rats, Wistar; Sciatic Nerve; Tetrazoles; Thiophenes

To investigate the relationship between metabolic and vascular factors, especially polyol pathway and platelet aggregation, in the pathogenesis of diabetic neuropathy, the effects of a novel potent aldose reductase inhibitor, TAT ((5-(3-thienyl) tetrazol-1-yl) acetic acid monohydrate) on adenosine diphosphate-induced platelet aggregation, polyol contents in platelets, motor nerve conduction velocity (MNCV), and sciatic nerve blood flow (SNBF) were examined in streptozotocin-induced diabetic rats. Diabetic rats demonstrated hyperaggregation in response to adenosine diphosphate, accompanied by sorbitol and fructose accumulation and myoinositol depletion in platelets. Treatment with TAT improved these abnormalities in diabetic rats. A delayed MNCV and a reduced SNBF in diabetic rats were normalized by the administration of TAT. These observations suggest that increased polyol pathway activity plays an important role in platelet aggregation in the development of diabetic neuropathy and that aldose reductase inhibitor is useful for the treatment of diabetic neuropathy from the viewpoint not only of metabolic factors but also of vascular factors.

Topics: Adenosine Diphosphate; Aldehyde Reductase; Ampholyte Mixtures; Animals; Blood Glucose; Blood Platelets; Diabetes Mellitus, Experimental; Diabetic Neuropathies; Enzyme Inhibitors; Male; Neural Conduction; Platelet Aggregation; Polymers; Rats; Rats, Wistar; Sciatic Nerve; Streptozocin; Tetrazoles; Thiophenes

(5-(3-Thienyl)tetrazol-1-yl)acetic acid (TAT), a novel potent aldose reductase inhibitor, was administered for 4 weeks to rats with streptozotocin-induced diabetes. Physiological and biochemical studies were subsequently conducted on rat nerve tissue and erythrocyte sorbitol content was estimated. Sciatic nerve blood flow (SNBF) was markedly lower (about 43.4%) in untreated diabetic (DC) rats than in non-diabetic controls (NC). A significant delay in caudal motor nerve conduction velocity (MNCV) and significantly higher glucose, sorbitol and fructose values were observed in the sciatic nerve, accompanied by a markedly higher sorbitol concentration in erythrocytes. In contrast, TAT-treated diabetic groups (DT-10, DT-40 and DT-200) had significantly higher SNBF, MNCV and sciatic nerve myo-inositol values and lower sciatic nerve sorbitol and fructose levels and erythrocyte sorbitol concentration than the DC group. There were good correlations between SNBF and MNCV (r = 0.672, P < 0.001) and between SNBF and erythrocyte sorbitol (r = 0.455, P < 0.003). These findings suggest that both vascular and metabolic factors play an important role in diabetic neuropathy and the effect of aldose reductase inhibitors on diabetic neuropathy may be mediated by at least these two factors.

Topics: Aldehyde Reductase; Animals; Blood Glucose; Body Weight; Diabetes Mellitus, Experimental; Diabetic Neuropathies; Erythrocytes; Fructose; Glucose; Inositol; Male; Motor Neurons; Neural Conduction; Peripheral Nerves; Rats; Rats, Sprague-Dawley; Reference Values; Regional Blood Flow; Regression Analysis; Sciatic Nerve; Sorbitol; Tail; Tetrazoles; Thiophenes; Time Factors

TAT ([5-(3-thienyl)tetrazol-1-yl]acetic acid) is a novel aldose reductase (AR) inhibitor. It exhibited highly potent inhibition of partially purified AR from rat lens (IC50 = 2.1 x 10(-8) M), rabbit lens (IC50 = 2.3 x 10(-8) M) and human placenta (IC50 = 2.8 x 10(-8) M). On the other hand, TAT had a weak inhibitory activity against mouse liver aldehyde reductase (ALR) (IC50 = 2.4 x 10(-6) M) and poor inhibitory activity against several adenine nucleotide-requiring enzymes. Against rat lens AR, TAT exhibited an uncompetitive inhibition at a concentration of 1.0 x 10(-8) M and a mixed type inhibition at higher concentrations. TAT inhibited sorbitol accumulation in the isolated rat sciatic nerve (IC50 = 1.0 x 10(-6) M), rat lens (IC50 = 5.7 x 10(-6) M), human erythrocytes (IC50 = 2.5 x 10(-7) M), and rabbit erythrocytes (IC50 = 2.1 x 10(-7) M) incubated with high glucose concentrations. The oral administration of TAT (5-100 mg/kg/day) to streptozotocin (STZ)-induced diabetic rats during a 5-day treatment period decreased the sorbitol content in the sciatic nerve, dose-dependently (ED50: 8.8 mg/kg/day for the prevention and 9.0 mg/kg/day for the reversal). Moreover, TAT (2.5-40 mg/kg/day) improved the decreased motor nerve conduction velocity (MNCV) after a 14-day treatment period. There was a significant correlation between MNCV and sciatic nerve sorbitol content. From these results, TAT is expected to be useful for the clinical treatment of diabetic complications.

Topics: Aldehyde Reductase; Animals; Diabetic Neuropathies; Humans; In Vitro Techniques; Male; Mice; Mice, Inbred C57BL; Neural Conduction; Rabbits; Rats; Rats, Sprague-Dawley; Sciatic Nerve; Sorbitol; Sugar Alcohols; Tetrazoles; Thiophenes