Streptozotocin-induced Diabetic Neuropathy Research Articles

Combination Therapy with Flupirtine and Opioid: Studies in Rat Pain Models

Flupirtine is an established clinical analgesic for mild to moderate musculoskeletal pain states. It has recently been shown to be a KCNQ2-3 potassium channel opener. These experiments were performed to see if this property could be useful in treating pain states characterized by central sensitization with the drug either given alone or in combination with morphine. Experiments were performed in rats in an observer-blinded fashion with vehicle controls. Nonsedating doses of flupirtine, morphine, and combinations containing both drugs were defined using the rotarod test and open-field activity monitoring. Dose-response relationships were determined for nonsedating doses of both drugs given alone and together in combination in causing antinociception in two nociception paradigms: carrageenan paw inflammation and streptozotocin-induced diabetic neuropathy. Flupirtine and morphine, when given alone at the highest nonsedating doses, caused slight to moderate antinociception in both paradigms. Flupirtine also caused significant increases in morphine antinociception in both models. In carrageenan paw inflammation, complete reversal of carrageenan-induced hyperalgesia was caused by 10 mg/kg flupirtine in combination with 0.4 mg/kg morphine. These doses of the two drugs were ineffective when given alone, but the combination caused complete antinociception in this model of inflammatory pain. In the diabetic neuropathy model, morphine 3.2 mg/kg given alone caused no significant antinociception. However, a lower dose of morphine (1.6 mg/kg shown to be ineffective when it was given alone) given in combination with flupirtine 10 mg/kg caused highly significant antinociceptive effects causing complete reversal of hyperalgesia caused by diabetic neuropathy (P < 0.001, one-way analysis of variance). This combination of drugs was not sedating. Flupirtine increases morphine antinociception without causing an increase in sedation. Flupirtine should be investigated as an adjunct analgesic with opioids for the management of patients with pain states involving central sensitization.

Zonisamide Suppresses Pain Symptoms of Formalin-Induced Inflammatory and Streptozotocin-Induced Diabetic Neuropathy

We evaluated the effects of zonisamide on inflammatory and neuropathic pain using the mouse formalin test and streptozotocin (STZ)-induced diabetic mice with a reduced withdrawal threshold to mechanical stimuli, respectively. When administered systemically (subcutaneously, s.c.), intracerebroventricularly (i.c.v.) or intrathecally (i.t.) before formalin injection, zonisamide (3 and 10 mg/kg, s.c., 10 and 30 μg, i.c.v., or i.t.) significantly reduced licking/biting behavior during the second phase of the formalin test in a dose-dependent manner. However, zonisamide (30 μg, i.t.) did not affect the second phase of the formalin test when given after the first phase, suggesting that it can prevent the development of injury-induced hyperexcitability of the spinal dorsal horn triggered by the repetitive nociceptive input during the first phase. Moreover, zonisamide administered into the dorsal hindpaw ipsilateral but not contralateral to the formalin injection partly reduced the second phase. Thus it is likely that zonisamide generates analgesic effects in the formalin test via both central and peripheral mechanisms. In mice with STZ-induced diabetes, zonisamide (10 and 30 mg/kg, s.c. or 10 and 30 μg, i.t.) reversed the mechanical hyperexcitability. Our results suggest that zonisamide can be a useful therapeutic agent, presumably for both prevention and reversal of pathophysiologic pain.

Early Changes in Insulin Receptor Signaling and Pain Sensation in Streptozotocin-Induced Diabetic Neuropathy in Rats

The objective of the present study was to evaluate the time course of changes in peripheral nerve insulin receptor (IR) signaling and compare observed findings with behavioral responses to noxious mechanical and thermal stimuli in streptozotocin (STZ)-diabetic rats over 12 weeks of diabetes. Diabetic rats developed mechanical hyperalgesia, as indicated by decreased paw withdrawal thresholds to mechanical stimuli that were detectable after 2 weeks of diabetes; they also developed thermal hypoalgesia, as indicated by increased tail flick latencies to thermal stimuli that were detectable at 1 week of diabetes. Western blot analysis revealed decreased phosphorylated: total IR protein ratio that was detectable as early as 2 weeks of diabetes, whereas phosphorylated:total Akt protein ratio was decreased at 2 weeks and increased at 12 weeks of diabetes with unchanged PI-3K protein levels. To our knowledge, the present study is the first to demonstrate that impaired peripheral nerve IR signaling, as indicated by decreased phosphorylated:total IR protein ratio, coincides with early mechanical hyperalgesia and thermal hypoalgesia in STZ-diabetic rats. This finding may improve understanding of how altered pain sensation develops rapidly in this model. This study examined peripheral nerve IR signaling during the early course of altered nociception in STZ-diabetic rats. In diabetic rats, impaired peripheral nerve IR signaling is observed shortly after STZ injection, as is altered nociception. This finding suggests a possible role of impaired IR signaling in diabetic sensory neuropathy.

Synergistic Interactions Between a KCNQ Channel Opener and an Opioid: Flupirtine and Morphine in Rat Pain Models Including Neuropathic Pain

Purpose of the study: Flupirtine is an established clinical analgesic for mild to moderate musculoskeletal pain states. It has recently been shown to be a KCNQ 2–3 potassium channel opener. These experiments were performed to see if this property could be useful in treating more severe pain states characterised by central sensitisation with the drug either given alone or in combination with morphine. Methods: Experiments were performed in rats in an observer blinded fashion with vehicle controls. Non sedating doses of flupirtine, morphine and combinations containing both drugs were defined using the rotarod technique. Dose response relationships were determined for non sedating doses of both drugs given alone and together in combination in causing antinociception in three nociception paradigms: electrical pain; carrageenan paw inflammation; streptozotocin-induced diabetic neuropathy. Results: Flupirtine and morphine when given alone caused slight to moderate antinociception in all three paradigms. Flupirtine also caused significant increases in morphine antinociception in all three models. In carrageenan paw inflammation complete reversal of carrageenan-induced hyperalgesia was caused by 10 mg/kg flupirtine in combination with 0.4 mg/kg morphine. These doses of the two drugs were ineffective when given alone but the combination caused complete antinociception in this model of inflammatory pain. In the diabetic neuropathy model (see figure) morphine 3.2 mg/kg given alone caused significant antinociception but the size of that response was significantly less than that caused by a lower dose of morphine (1.6 mg/kg shown to be ineffective when it was given alone) given in combination with flupirtine 10 mg/kg (p < 0.001; one way ANOVA). ![Figure][1] Conclusions: Flupirtine should be investigated as an adjunct analgesic with opioids for the management of patients with severe pain states involving central sensitization. [1]: pending:yes

EFFECTS OF TROLOX ON NERVE DYSFUNCTION, THERMAL HYPERALGESIA AND OXIDATIVE STRESS IN EXPERIMENTAL DIABETIC NEUROPATHY

1. Diabetic neuropathy is one of the most common complications of diabetes and oxidative stress has been implicated to play a major role in its pathophysiology. 2. In the present study, we targeted oxidative stress using trolox, an anti-oxidant, in streptozotocin-induced diabetic neuropathy in rats. 3. Compared with control rats, diabetic rats showed significant deficits in motor nerve conduction velocity (MNCV; 49.91 +/- 1.94 vs 42.77 +/- 1.39 m/s, respectively) and nerve blood flow (NBF; 107.98 +/- 8.22 vs 38.9 +/- 2.7 arbitarary perfusion units, respectively) after 8 weeks of diabetes. Tail flick latencies for cold and hot immersion tests were also significantly reduced in diabetic rats, indicating thermal hyperalgesia. These observations indicate development of diabetic neuropathy. 4. A significant decrease in the activity of anti-oxidant enzymes (superoxide dismutase and catalase) and an increase in lipid peroxidation were observed in sciatic nerves from diabetic rats compared with age-matched control rats. Alterations in the activity of anti-oxidant enzymes and lipid peroxidation in diabetic rats indicate oxidative stress in diabetic neuropathy. 5. Two weeks treatment with trolox (10 and 30 mg/kg, i.p.) started on completion of the 6th week of diabetes significantly improved MNCV, NBF and inhibited thermal hyperalgesia. Trolox treatment also improved the activity of anti-oxidant enzymes and inhibited lipid peroxidation in sciatic nerves of diabetic rats. 6. The results of the present study suggest the beneficial effects of trolox in experimental diabetic neuropathy.

(667): Bicifadine is an efficacious analgesic in animal models of neuropathic pain

Bicifadine (DOV 220,075), a balanced inhibitor of norepinephrine and serotonin uptake, was evaluated in two models of neuropathic pain: streptozotocin-induced diabetic neuropathy, and the spinal nerve ligation (SNL) model (Kim and Chung, 1992). In the diabetic neuropathy model, the effect of bicifadine on the paw pressure withdrawal threshold was determined using the Randall-Selitto test. Bicifadine’s efficacy in reducing mechanical allodynia in the SNL model was measured using Semmes-Weinstein filaments and its effects on mechanical and thermal hyperalgesia were evaluated with the Randall-Selitto test and a focused beam of infrared radiation, respectively. Bicifadine dose-dependently reduced the nociceptive threshold for paw withdrawal in diabetic rats (ED50= 5 mg/kg PO). Similarly, bicifadine reduced mechanical allodynia in the SNL model, with a maximum anti-allodynic action observed at 40mg/kg PO, an effect comparable in magnitude to 300 mg/kg PO of gabapentin. In addition, bicifadine induced anti-mechanical (ED50= 12 mg/kg PO) and thermal (MED 12.5 mg/kg PO) hyperalgesic effects. The effect of bicifadine in blocking mechanical hyperalgesia in the SNL model reached a maximum at 60 minutes and remained significant up to 120 minutes after administration. Its effects in blocking thermal hyperalgesia reached a maximum at 30 minutes and lasted up to 240 minutes after administration. Chronic administration (50mg/kg/day, 5 days, PO) of bicifadine did not result in the development of analgesic tolerance, with efficacy in reducing mechanical hyperalgesia in SNL rats similar to acute bicifadine (50mg/kg). In contrast, repeated administration of morphine (128 mg/kg/D, 5 days, PO) resulted in a significant reduction in efficacy. In conclusion, bicifadine is a potent and efficacious analgesic in two well-described models of neuropathic pain, and exhibits no abuse potential.

Intraepidermal nerve fiber density in rat foot pad: neuropathologic–neurophysiologic correlation

Quantification of cutaneous innervation in rat footpad is a useful tool to investigate sensory small-diameter nerve fibers, which are affected early in peripheral neuropathies. The aim of this work was to provide normative reference data on the density of intraepidermal nerve fibers (IENFs) and Langerhans cells in the hindpaw footpad of Sprague-Dawley and Wistar rats. We also evaluated the sensibility of IENF density by comparing neuropathologic findings with neurophysiologic examination and the presence of peripheral neuropathy in two well-characterized animal models of neuropathy. IENF density was quantified in 22 Sprague-Dawley rats and 13 Wistar rats and compared with 19 age-matched Sprague-Dawley rats with streptozotocin-induced diabetic neuropathy and 30 age-matched Wistar rats with cisplatin- or paclitaxel-induced neuropathy. Antidromic tail sensory nerve conduction velocity (SNCV) was assessed in all animals. IENF and Langerhans cell densities were constant in healthy Sprague-Dawley rats at any age, and they were similar to those observed in healthy Wistar rats. In neuropathic rats, both SNCV and IENF density were significantly reduced with respect to controls. Quantification of IENF density was significantly correlated with changes in conduction velocity. Diabetic neuropathy rats alone showed a significantly higher density of Langerhans cells compared with controls. Our study demonstrated that IENF density quantification correlates with SNCV changes and suggests that this might represent a useful outcome measurement in experimental neuropathies.

Role of Calcium Signalling in the Development of Pain Syndromes

A comparative analysis of two models of nociceptive and neuropathic pain in rodents, carrageenan peripheral inflammation of soft tissues and streptozotocin-induced diabetic neuropathy, is presented in the review. Modern concepts on the pathways of transmission of pain information are analyzed. A few aspects of possible involvement at calcium signalling in neurons in the development of pain syndromes are discussed.

Fluoxetine attenuates thermal hyperalgesia through 5-HT 1/2 receptors in streptozotocin-induced diabetic mice

Diabetic neuropathic pain, an important microvascular complication in diabetes mellitus, is recognised as one of the most difficult types of pain to treat. A lack of understanding of its aetiology, inadequate relief, development of tolerance and potential toxicity of classical antinociceptives warrant the investigation of newer agents to relieve this pain. The aim of the present study was to explore the antinociceptive effect and possible mechanism of action of a serotonin reuptake inhibitor, fluoxetine, in streptozotocin-induced diabetic mice. Four weeks after a single intraperitoneal injection of streptozotocin (200 mg/kg), mice were tested in the tail-immersion and hot-plate assays. Diabetic mice exhibited significant hyperalgesia compared with control mice. Fluoxetine (10 and 20, but not 5 mg/kg, i.p.) injected into diabetic mice produced an antinociceptive effect in both the tail-immersion and hot-plate assays. The percentage maximum possible effect (% MPE) produced by fluoxetine (20 mg/kg, i.p.) was significantly lower in diabetic mice than in control mice. The antinociceptive effect of fluoxetine (20 mg/kg) in diabetic mice was dose-dependently potentiated by pindolol (5 and 10 mg/kg, i.p., a selective 5-HT 1A/1B receptor antagonist), attenuated by ritanserin (1 and 2 mg/kg, i.p., a selective 5-HT 2A/2C receptor antagonist) and remained unaffected by ondansetron (1 and 2 mg/kg, i.p., a selective 5-HT 3 receptor antagonist) in both test systems. These results suggest that fluoxetine-induced antinociception primarily involves serotonin pathway modulation through 5-HT 1 and 5-HT 2 receptors, but not through 5-HT 3 receptors, in the chronic pain associated with streptozotocin-induced diabetic neuropathy. Further, the potentiation of the antinociceptive effect of fluoxetine by pindolol indicates the usefulness of a combination of an antidepressant and a 5-HT 1A/1B receptor antagonist in the treatment of diabetic neuropathic pain in humans.

Neuroprotective effect of docosahexaenoic acid-enriched phospholipids in experimental diabetic neuropathy.

A deficiency in essential fatty acid metabolism has been widely reported in both human and animal diabetes. Fish oil supplementations (n-3 fatty acids), containing docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA), were less effective on diabetic neuropathy than (n-6) fatty acids. This partial effect of (n-3) fatty acids might be attributed to the presence of EPA, a competitor of arachidonic acid, which enhanced the diabetes-induced decrease of this fatty acid in serum and tissues. For determining whether a supplementation with DHA alone could prevent neuropathy in streptozotocin-induced diabetes, diabetic rats were given daily, by gavage, liposomes containing DHA phospholipids, at a dose of 60 mg/kg. Eight weeks of diabetes induced significant decreases in nerve conduction velocity (NCV), nerve blood flow (NBF), and sciatic nerve and erythrocyte (red blood cells [RBCs]) Na,K-ATPase activities. DHA phospholipids totally prevented the decrease in NCV and NBF observed during diabetes when compared with the nonsupplemented diabetic group. DHA phospholipids also prevented the Na,K-ATPase activity decrease in RBC but not in sciatic nerve. Moreover, DHA level in sciatic nerve membranes was correlated with NCV. These results demonstrate a protective effect of daily doses of DHA on experimental diabetic neuropathy. Thus, treatment with DHA phospholipids could be suitable for evaluation in clinical trials.

Preferential expression of IGF-I in small DRG neurons and down-regulation following injury.

In this study, we examined the expression of insulin-like growth factor I (IGF-I) and its receptor (IGF-IR) in dorsal root ganglia (DRG) neurons in two rodent models of nerve injury: sciatic nerve axotomy and streptozotocin-induced (STZ) painful diabetic neuropathy. We demonstrate that IGF-I and its receptor are preferentially expressed in small (< 25 microm diameter) DRG neurons. There is a significant down-regulation in the expression of IGF-I and IGF-IR in the small DRG neurons of STZ rats by 59% and 71%, respectively. A parallel reduction in expression is shown in axotomized < 25 microm diameter DRG neurons for IGF-I (47%) but not for IGF-IR. The loss of IGF-I support to a population of predominantly nociceptive neurons may contribute to neuropathic pain observed in these models.

Herpes Simplex-Mediated Gene Transfer of Nerve Growth Factor Protects Against Peripheral Neuropathy in Streptozotocin-Induced Diabetes in the Mouse

Peripheral neuropathy is a common and debilitating complication of diabetes. In animal models, neurotrophic factors can prevent progression of the neuropathy, but adverse effects prevent systemic administration in adequate doses to treat human disease. We examined whether gene transfer with replication-defective genomic herpes simplex virus (HSV) vectors modified to express nerve growth factor (NGF) could be used to prevent progression of neuropathy in mice. Diabetes induced by streptozotocin (STZ) resulted in a sensory neuropathy manifest by a decrease in the foot sensory nerve amplitude (FSA; control = 20 +/- 0.1 microV, treated = 14 +/- 0.1 microV). Transduction of dorsal root ganglia in vivo with an HSV-based vector expressing NGF under the control of the human cytomegalovirus immediate early promoter (vector SHN) or the HSV latency active promoter 2 (vector SLN) by footpad inoculation 2 weeks after STZ administration protected against the decrease in FSA (22 +/- 1.4 microV and 21 +/- 1.7 microV, respectively) measured 4 weeks later. Injection of SHN into inguinal adipose tissue 2 weeks after onset of diabetes also prevented the decrease in FSA (20 +/- 3.3 microV). These results suggest that gene transfer with an NGF-producing herpes-based vector may prove useful in the treatment of diabetic neuropathy.

Autonomic neuropathy in streptozotocin diabetic rats: effect of acetyl- l-carnitine

The present study was designed to characterize cardiac autonomic neuropathy in streptozotocin-induced (45 mg/kg i.v.) diabetic rat by analysis of heart rate variability (HRV), and to assess, in this model, the effects of treatment with acetyl- l-carnitine (ALC). Heart rate was reduced in diabetic rats (332±22 vs. 411±35 beat per min; P<0.0001). This bradycardia was partly reversed with ALC (369±52 beat per min; P<0.05 vs. untreated). Both time- and frequency-domain parameters of HRV were significantly reduced in diabetic rats. The reduction of spectral power was around 50% at high frequencies and about 70% at low frequencies, suggesting a decrease of parasympathetic activity. Low/high frequency ratio was significantly decreased in diabetic rats suggesting decreased sympathetic tone, while nonlinear analysis indicated a reduction of the chaotic complexity of heart rate dynamics in diabetic rats. Standard deviation of heart rate in ALC-treated rats was significantly higher than in untreated diabetic rats ( P<0.0001). ALC counteracts the reduction of the power spectrum observed in diabetic animals ( P<0.0005) normalizing the spectra profile. ALC restored chaotic complexity of heart rate dynamics. These results on the whole indicate that both sympathetic and parasympathetic cardiac tone were reduced significantly in diabetic rats and that ALC treatment prevents the development of autonomic neuropathy in streptozotocin-induced diabetes in rats.

Gene expression of antioxidant enzymes in experimental diabetic neuropathy.

Chronic hyperglycemia results in a large deficit in nerve blood flow. Both autoxidative- and ischemia-induced lipid peroxidation occurs, with resultant peripheral sensory neuropathy in streptozotocin-induced diabetes in the rat. Free radical defenses, especially involving antioxidant enzymes, have been suggested to be reduced, but scant information is available on chronic hyperglycemia. We evaluated the gene expression of glutathione peroxidase, catalase, and superoxide dismutase (cuprozinc and manganese separately) in L4,5 dorsal root ganglion (DRG) and superior cervical ganglion, as well as enzyme activity of glutathione peroxidase in DRG and sciatic nerve in experimental diabetic neuropathy of 3 months and 12 months durations. We also evaluated nerve electrophysiology of caudal, sciatic-tibial, and digital nerves. A nerve conduction deficit was seen in all nerves in experimental diabetic neuropathy at both 3 and 12 months. Gene expression of glutathione peroxidase, catalase, cuprozinc superoxide dismutase, and manganese superoxide dismutase were not reduced in experimental diabetic neuropathy at either 3 or 12 months. Catalase mRNA was significantly increased in experimental diabetic neuropathy at 12 months. Glutathione peroxidase enzyme activity was normal in sciatic nerve. We conclude that gene expression is not reduced in peripheral nerve tissues in very chronic experimental diabetic neuropathy. Changes in enzyme activity may be related to duration of diabetes or due to post-translational modifications.

P-498 - Pathophysiological role of NGF and GDNF in streptozotocin-induced diabetic neuropathy

P-498 - Pathophysiological role of NGF and GDNF in streptozotocin-induced diabetic neuropathy

Pathophysiological role of nitric oxide in streptozotocin-induced diabetic neuropathy

Pathophysiological role of nitric oxide in streptozotocin-induced diabetic neuropathy

Neuronal Nitric Oxide Synthase mRNA Upregulation in Rat Sensory Neurons after Spinal Nerve Ligation: Lack of a Role in Allodynia Development

Pharmacological evidence suggests a functional role for spinal nitric oxide (NO) in the modulation of thermal and/or inflammatory hyperalgesia. To assess the role of NO in nerve injury-induced tactile allodynia, we examined neuronal NO synthase (nNOS) expression in the spinal cord and dorsal root ganglia (DRG) of rats with tactile allodynia because of either tight ligation of the left fifth and sixth lumbar spinal nerves or streptozotocin-induced diabetic neuropathy. RNase protection assays indicated that nNOS mRNA (1) was upregulated in DRG, but not spinal cord, neurons on the injury side beginning 1 d after nerve ligation, (2) peaked (approximately 10-fold increase) at 2 d, and (3) remained elevated for at least 13 weeks. A corresponding increase in DRG nNOS protein was also observed and localized principally to small and occasionally medium-size sensory neurons. In rats with diabetic neuropathy, there was no significant change in DRG nNOS mRNA. However, similar increases in DRG nNOS mRNA were observed in rats that did not develop allodynia after nerve ligation and in rats fully recovered from allodynia 3 months after the nerve ligation. Systemic treatment with a specific pharmacological inhibitor of nNOS failed to prevent or reverse allodynia in nerve-injured rats. Thus, regulation of nNOS may contribute to the development of neuronal plasticity after specific types of peripheral nerve injury. However, upregulation of nNOS is not responsible for the development and/or maintenance of allodynia after nerve injury.

Lipoic Acid Improves Nerve Blood Flow, Reduces Oxidative Stress, and Improves Distal Nerve Conduction in Experimental Diabetic Neuropathy

To determine whether lipoic acid (LA) will reduce oxidative stress in diabetic peripheral nerves and improve neuropathy. We used the model of streptozotocin-induced diabetic neuropathy (SDN) and evaluated the efficacy of LA supplementation in improving nerve blood flow (NBF), electrophysiology, and indexes of oxidative stress in peripheral nerves affected by SDN, at 1 month after onset of diabetes and in age-matched control rats. LA, in doses of 20, 50, and 100 mg/kg, was administered intraperitoneally five times per week after onset of diabetes. NBF in SDN was reduced by 50%; LA did not affect the NBF of normal nerves but improved that of SDN in a dose-dependent manner. After 1 month of treatment, LA-supplemented rats (100 mg/kg) exhibited normal NBF. The most sensitive and reliable indicator of oxidative stress was reduction in reduced glutathione, which was significantly reduced in streptozotocin-induced diabetic and alpha-tocopherol-deficient nerves; it was improved in a dose-dependent manner in LA-supplemented rats. The conduction velocity of the digital nerve was reduced in SDN and was significantly improved by LA. These studies suggest that LA improves SDN, in significant part by reducing the effects of oxidative stress. The drug may have potential in the treatment of human diabetic neuropathy.

The influence of sulindac on experimental streptozotocin-induced diabetic neuropathy.

We studied the influence of sulindac, a nonsteroidal anti-inflammatory agent on experimental streptozotocin-induced diabetic neuropathy. Untreated diabetic rats were compared with nondiabetic rats, diabetic rats treated with low dose insulin and diabetic rats given sulindac (6.0 mg/kg by gavage 5 of 7 days weekly). Neuropathy was assessed by following serial in vivo motor and sensory caudal conduction, resistance to ischemic conduction failure, and in vitro conduction in sural myelinated and unmyelinated sensory fibers. The impact of low dose insulin and sulindac treatment on the microenvironment of the L4 dorsal root ganglion and sciatic endoneurium was assessed by measuring local perfusion and oxygen tension after 16 weeks of diabetes. Sulindac normalized conduction velocity in caudal sensory fibers, sural myelinated fibers and sural unmyelinated fibers, and reduced the number of diabetic cataracts. Sulindac also normalized a deficit in dorsal root ganglion blood flow and a reduction in sciatic endoneurial oxygen tension in diabetic rats. Low dose insulin improved neuropathy as well but the pattern of benefits was less robust than that of sulindac. Sulindac may be a candidate for a clinical trial in human diabetic polyneuropathy.

Characterization of a Novel Aldose Reductase Inhibitor, TAT, and Its Effects on Streptozotocin-Induced Diabetic Neuropathy in Rats

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.