Polyol pathway, 2,3-diphosphoglycerate in erythrocytes and diabetic neuropathy in rats

2,3-Diphosphoglyceric Acid Alleviating Hypoxic-Ischemic Brain Damage through p38 MAPK Modulation

Neonatal hypoxic-ischemic encephalopathy (HIE) is a critical condition characterized by significant brain damage due to insufficient blood flow and oxygen delivery at birth, leading to high rates of neonatal mortality and long-term neurological deficits worldwide. 2,3-Diphosphoglyceric acid (2,3-DPG), a small molecule metabolite prevalent in erythrocytes, plays an important role in regulating oxygen delivery, but its potential neuroprotective role in hypoxic-ischemic brain damage (HIBD) has yet to be fully elucidated. Our research reveals that the administration of 2,3-DPG effectively reduces neuron damage caused by hypoxia-ischemia (HI) both in vitro and in vivo. We observed a notable decrease in HI-induced neuronal cell apoptosis, attributed to the downregulation of Bax and cleaved-caspase 3, alongside an upregulation of Bcl-2 expression. Furthermore, 2,3-DPG significantly alleviates oxidative stress and mitochondrial damage induced by oxygen-glucose deprivation/reperfusion (OGD/R). The administration of 2,3-DPG in rats subjected to HIBD resulted in a marked reduction in brain edema and infarct volume, achieved through the suppression of neuronal apoptosis and neuroinflammation. Using RNA-seq analysis, we validated that 2,3-DPG offers protection against neuronal apoptosis under HI conditions by modulating the p38 MAPK pathway. These insights indicated that 2,3-DPG might act as a promising novel therapeutic candidate for HIE.

NMDA Receptors and Indices of Energy Metabolism in Erythrocytes: Missing Link to the Assessment of Efficiency of Oxygen Transport in Hepatic Encephalopathy

Hepatic encephalopathy (HE) is a neuropsychiatric syndrome that develops in patients with severe liver dysfunction and/or portocaval shunting. Despite more than a century of research into the relationship between liver damage and development of encephalopathy, pathogenetic mechanisms of hepatic encephalopathy have not yet been fully elucidated. It is generally recognized, however, that the main trigger of neurologic complications in hepatic encephalopathy is the neurotoxin ammonia/ammonium, concentration of which in the blood increases to toxic levels (hyperammonemia), when detoxification function of the liver is impaired. Freely penetrating into brain cells and affecting NMDA-receptor-mediated signaling, ammonia triggers a pathological cascade leading to the sharp inhibition of aerobic glucose metabolism, oxidative stress, brain hypoperfusion, nerve cell damage, and formation of neurological deficits. Brain hypoperfusion, in turn, could be due to the impaired oxygen transport function of erythrocytes, because of the disturbed energy metabolism that occurs in the membranes and inside erythrocytes and controls affinity of hemoglobin for oxygen, which determines the degree of oxygenation of blood and tissues. In our recent study, this causal relationship was confirmed and novel ammonium-induced pro-oxidant effect mediated by excessive activation of NMDA receptors leading to impaired oxygen transport function of erythrocytes was revealed. For a more complete evaluation of "erythrocytic" factors that diminish brain oxygenation and lead to encephalopathy, in this study, activity of the enzymes and concentration of metabolites of glycolysis and Rapoport-Lubering shunt, as well as morphological characteristics of erythrocytes from the rats with acute hyperammoniemia were determined. To elucidate the role of NMDA receptors in the above processes, MK-801, a non-competitive receptor antagonist, was used. Based on the obtained results it can be concluded that it is necessary to consider ammonium-induced morphofunctional disorders of erythrocytes and hemoglobinemia which can occur as a result of alterations in highly integrated networks of metabolic pathways may act as an additional systemic "erythrocytic" pathogenetic factor to prevent the onset and progression of cerebral hypoperfusion in hepatic encephalopathy accompanied by hyperammonemia.

Erythrocytes Functionality in SARS-CoV-2 Infection: Potential Link with Alzheimer's Disease

Coronavirus disease 2019 (COVID-19) is a rapidly spreading acute respiratory infection caused by SARS-CoV-2. The pathogenesis of the disease remains unclear. Recently, several hypotheses have emerged to explain the mechanism of interaction between SARS-CoV-2 and erythrocytes, and its negative effect on the oxygen-transport function that depends on erythrocyte metabolism, which is responsible for hemoglobin-oxygen affinity (Hb-O2 affinity). In clinical settings, the modulators of the Hb-O2 affinity are not currently measured to assess tissue oxygenation, thereby providing inadequate evaluation of erythrocyte dysfunction in the integrated oxygen-transport system. To discover more about hypoxemia/hypoxia in COVID-19 patients, this review highlights the need for further investigation of the relationship between biochemical aberrations in erythrocytes and oxygen-transport efficiency. Furthermore, patients with severe COVID-19 experience symptoms similar to Alzheimer's, suggesting that their brains have been altered in ways that increase the likelihood of Alzheimer's. Mindful of the partly assessed role of structural, metabolic abnormalities that underlie erythrocyte dysfunction in the pathophysiology of Alzheimer's disease (AD), we further summarize the available data showing that COVID-19 neurocognitive impairments most probably share similar patterns with known mechanisms of brain dysfunctions in AD. Identification of parameters responsible for erythrocyte function that vary under SARS-CoV-2 may contribute to the search for additional components of progressive and irreversible failure in the integrated oxygen-transport system leading to tissue hypoperfusion. This is particularly relevant for the older generation who experience age-related disorders of erythrocyte metabolism and are prone to AD, and provide an opportunity for new personalized therapies to control this deadly infection.

The effects of short term hyperglycemia on human red blood cells studied using Raman spectroscopy and optical trap

Management of postprandial hyperglycemia is important for preventing severe complications like cardiovascular disease in diabetes patients. The associated glycemic instability in postprandial hyperglycemia may also cause disorders in circulating red blood cells (RBCs). Therefore, effects of short-term hyperglycemic stress on RBCs such as occur in the postprandial condition, have been studied here ex vivo using single-cell Raman spectroscopy and optical trapping. RBCs incubated in high glucose containing media relevant to postprandial hyperglycemia were studied for changes with respect to controls by analyzing the single-cell Raman spectra acquired with Raman optical tweezers with 532 nm excitation light. Use of 532 nm light for exciting Raman spectra also results in simultaneous photoreduction of intracellular hemoglobin (Hb). The level of photoreduction was noticed to be limited in hyperglycemia-exposed cells in comparison to the control. Since this suggests formation of permanently oxidized Hb in hyperglycemia-exposed RBCs, a fluorescence study was performed which showed elevated levels of oxidative stress in these cells. The changes in the RBC membrane, which may result due to higher levels of oxidative stress, were investigated using optical stretching experiments under the laser trap. The results indicated a loss of elasticity for the RBC membrane due to hyperglycemic exposure.

The Erythrocytic Hypothesis of Brain Energy Crisis in Sporadic Alzheimer Disease: Possible Consequences and Supporting Evidence

Alzheimer’s disease (AD) is a fatal form of dementia of unknown etiology. Although amyloid plaque accumulation in the brain has been the subject of intensive research in disease pathogenesis and anti-amyloid drug development; the continued failures of the clinical trials suggest that amyloids are not a key cause of AD and new approaches to AD investigation and treatment are needed. We propose a new hypothesis of AD development based on metabolic abnormalities in circulating red blood cells (RBCs) that slow down oxygen release from RBCs into brain tissue which in turn leads to hypoxia-induced brain energy crisis; loss of neurons; and progressive atrophy preceding cognitive dysfunction. This review summarizes current evidence for the erythrocytic hypothesis of AD development and provides new insights into the causes of neurodegeneration offering an innovative way to diagnose and treat this systemic disease.

Metabolic Abnormalities of Erythrocytes as a Risk Factor for Alzheimer's Disease

Alzheimer's disease (AD) is a slowly progressive, neurodegenerative disorder of uncertain etiology. According to the amyloid cascade hypothesis, accumulation of non-soluble amyloid β peptides (Aβ) in the Central Nervous System (CNS) is the primary cause initiating a pathogenic cascade leading to the complex multilayered pathology and clinical manifestation of the disease. It is, therefore, not surprising that the search for mechanisms underlying cognitive changes observed in AD has focused exclusively on the brain and Aβ-inducing synaptic and dendritic loss, oxidative stress, and neuronal death. However, since Aβ depositions were found in normal non-demented elderly people and in many other pathological conditions, the amyloid cascade hypothesis was modified to claim that intraneuronal accumulation of soluble Aβ oligomers, rather than monomer or insoluble amyloid fibrils, is the first step of a fatal cascade in AD. Since a characteristic reduction of cerebral perfusion and energy metabolism occurs in patients with AD it is suggested that capillary distortions commonly found in AD brain elicit hemodynamic changes that alter the delivery and transport of essential nutrients, particularly glucose and oxygen to neuronal and glial cells. Another important factor in tissue oxygenation is the ability of erythrocytes (red blood cells, RBC) to transport and deliver oxygen to tissues, which are first of all dependent on the RBC antioxidant and energy metabolism, which finally regulates the oxygen affinity of hemoglobin. In the present review, we consider the possibility that metabolic and antioxidant defense alterations in the circulating erythrocyte population can influence oxygen delivery to the brain, and that these changes might be a primary mechanism triggering the glucose metabolism disturbance resulting in neurobiological changes observed in the AD brain, possibly related to impaired cognitive function. We also discuss the possibility of using erythrocyte biochemical aberrations as potential tools that will help identify a risk factor for AD.

Protective effect of magnesium-25 carrying porphyrin-fullerene nanoparticles on degeneration of dorsal root ganglion neurons and motor function in experimental diabetic neuropathy

Diabetic neuropathy (DN) is the most common peripheral neuropathy and long-term complication of diabetes. In view of the pathological basis for the treatment of DN, it is important to prevent nerve degeneration. Most of the current treatment strategies are symptomatic therapies. In this study, we evaluated the effectiveness of magnesium-25, carrying porphyrin-fullerene nanoparticles, on diabetes-induced neuropathy. Previous studies have suggested that dorsal root ganglion (DRG) neurons comprise a specific target and may be responsible for the known complications of DN. Experimental DN was induced by intraperitoneal injection of streptozotocin (STZ) (45 mg/kg). Different forms of magnesium including (25)Mg-PMC16, (24)Mg-PMC16 and MgCl(2) were administered intravenously in equal dose (0.5 LD(50)) at 48-hr intervals before STZ injection. Peripheral nerves were studied after 2 months of diabetes in groups using qualitative approaches, morphometric analysis of DRG neurons and motor function tests. We showed that STZ-induced DN caused morphological abnormalities in DRG neurons comprising changes in area, diameter and number of A and B cells as well as motor dysfunction in DN. Moreover, our findings indicated that administration of (25)Mg-PMC16 as a magnetic form of Mg improved morphological abnormalities and motor dysfunctions significantly, whereas other forms of Mg were ineffective.

Benefit of magnesium-25 carrying porphyrin-fullerene nanoparticles in experimental diabetic neuropathy

Diabetic neuropathy (DN) is a debilitating disorder occurring in most diabetic patients without a viable treatment yet. The present work examined the protective effect of (25)Mg-PMC(16) nanoparticle (porphyrin adducts of cyclohexil fullerene-C60) in a rat model of streptozotocin (STZ)-induced DN. (25)Mg-PMC(16) (0.5 lethal dose(50) [LD(50)]) was administered intravenously in two consecutive days before intraperitoneal injection of STZ (45 mg/kg). (24)Mg-PMC(16) and MgCl(2) were used as controls. Blood 2,3-diphosphoglycerate (2,3-DPG), oxidative stress biomarkers, adenosine triphosphate (ATP) level in dorsal root ganglion (DRG) neurons were determined as biomarkers of DN. Results indicated that 2,3-DPG and ATP decreased whereas oxidative stress increased by induction of DN which all were improved in (25)Mg-PMC(16)-treated animals. No significant changes were observed by administration of (24)Mg-PMC(16) or MgCl(2) in DN rats. It is concluded that in DN, oxidative stress initiates injuries to DRG neurons that finally results in death of neurons whereas administration of (25)Mg-PMC(16) by release of Mg and increasing ATP acts protectively.

The role of polyol pathway in glucose-induced apoptosis of cultured retinal pericytes

The pathogenesis of pericyte loss, an initial deficit in the early stage of diabetic retinopathy, remains unclear. Recent studies have suggested that polyol pathway hyperactivity and apoptosis may be involved in pericyte loss. The mechanisms of the glucose-induced apoptosis in retinal pericytes were investigated to evaluate the pathogenesis of diabetic retinopathy. Under the 20 mM glucose condition, intracellular calcium concentrations and caspase-3 activities were significantly increased, and reduced glutathione (GSH) contents were significantly decreased compared with those under the 5.5 mM glucose condition. These abnormalities were all significantly prevented by an aldose reductase inhibitor, SNK-860. Glucose-induced apoptosis was partially but significantly prevented by SNK-860, an inhibitor of calcium-dependent cysteine protease, calpain, or GSH supplementation, and completely normalized by a caspase-3 inhibitor. These observations suggest that glucose-induced apoptosis in retinal pericytes, as one of the pathogenic factors of diabetic retinopathy, would be mediated through an aldose reductase-sensitive pathway including calcium-calpain cascade and increased oxidative stress, and that caspase-3 would be located furthest downstream of these apoptotic signals.

Nerve and ganglion blood flow in diabetes: an appraisal

Vasa nervorum, the vascular supply to peripheral nerve trunks, and their associated cell bodies in ganglia have unique anatomical and physiological characteristics. Several different experimental approaches toward understanding the changes in vase nervorum following injury and disease have been used. Quantative techniques most widely employed have been microelectrode hydrogen clearance palarography and [14C]iodoantipyrine autoradiographic distribution, whereas estimates of red blood cell flux using a fiber-optic laser Doppler probe offer real time data at different sites along the nerve trunk. There are important caveats about the use of these techniques, their advantages, and their limitations. Reports of nerve blood flow require careful documentation of physiological variables, including mean arterial pressure and nerve temperature during the recordings. Several ischemic models of the peripheral nerve trunk have addressed the ischemic threshold below which axonal degeneration ensues (< 5ml/100 g/min). Following injury, rises in local blood flow reflect acitons of vasoactive peptides, nitric oxide, and the development of angiogenesis. In experimental diabetes, a large number of studies have documented reductions in nerve blood flow and tandem corrections of nerve blood flow and conduction slowing. A significant proportions, however, of the work can be criticized on the basis of methodology and interpretation. Similarly, not all work has confirmed that reductions of nerve blood flow are an invariable feature of experimental or human diabetic polyneuropathy. Therefore, while there is disagreement as to whether early declines in nerve blood flow "account" for diabetic polyneuropathy, there is unquestioned eveidence of early microangiopathy. Abnormalities of vase nervorum and micorvessels supplying ganglia at the very least develop parallel to and together with changes in neurons, Schwann cells, and axons.

Transition metals and polyol pathway in the development of diabetic neuropathy in rats

BACKGROUND

The transition metal-catalyzed reaction is a major source of oxygen free radicals, which play an important role in vascular dysfunction leading to ischemia in diabetic tissues. The inhibition of polyol pathway hyperactivity has been reported to ameliorate neurovascular abnormalities in diabetic rats and has been proposed to improve the oxygen free radical scavenging capacity. The present study was conducted to compare the effect of a transition metal chelating agent, trientine (TRI), on diabetic neuropathy with that of an aldose reductase inhibitor, NZ-314 (NZ).

METHODS

Diabetic rats were divided into three groups: (1). untreated, (2). TRI-treated, and (3). NZ-treated. TRI (20 mg/kg) or NZ (100 mg/kg) was administered by gavage or chow containing NZ, respectively, for 8 weeks. Motor nerve conduction velocity (MNCV), coefficient of variation of the R - R interval on electrocardiogram (CVr-r), sciatic nerve blood flow (SNBF), platelet aggregation activities, and serum concentrations of malondialdehyde were measured.

RESULTS

Untreated diabetic rats showed delayed MNCV, decreased CV(R-R), and reduced SNBF compared to normal rats. TRI or NZ completely prevented these deficits. Platelet hyperaggregation activities in diabetic rats were prevented by NZ, but not by TRI. Increased concentrations of malondialdehyde in diabetic rats were partially but significantly ameliorated by either TRI or NZ.

CONCLUSIONS

These observations suggest that increased free radical formation through the transition metal-catalyzed reaction plays an important role in the development of diabetic neuropathy and that the preventive effect of an aldose reductase inhibitor on diabetic neuropathy may also be mediated by decreasing oxygen free radicals.

Fidarestat (SNK-860), a potent aldose reductase inhibitor, normalizes the elevated sorbitol accumulation in erythrocytes of diabetic patients

Sorbitol accumulation in nerves has been regarded as one of the major causes of diabetic neuropathy. In this study, fidarestat (SNK-860; 1 mg daily), a potent new aldose reductase inhibitor (ARI), or the commercially available ARI epalrestat (150 mg daily), was administered for 4 weeks to 58 Type 2 diabetic patients. Treatment with these drugs had no effect on glycemic control, judging from plasma glucose and HbA(1c) levels. However, fidarestat treatment normalized the elevated sorbitol content of erythrocytes under fasting as well as postprandial conditions. In contrast, the effect of epalrestat was minimal. There were no major side effects with fidarestat. Thus, fidarestat is considered to be a potent and promising ARI, possibly useful for both preventing and treating diabetic neuropathy. Further studies are needed to clarify how much the occurrence and progression of diabetic neuropathy are inhibited by normalizing sorbitol elevation with fidarestat treatment.

Physiological and morphometric analyses of neuropathy in sucrose-fed OLETF rats

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.

Aldose reductase inhibition prevents glucose-induced apoptosis in cultured bovine retinal microvascular pericytes

The pathogenesis of pericyte loss, an initial deficit in the early stage of diabetic retinopathy, remains unclear. Polyol pathway hyperactivity has been implicated in the pathogenesis of diabetic retinopathy, and recent studies have suggested that apoptosis may be involved in pericyte loss. The present study was conducted to investigate whether high glucose induces apoptosis in cultured bovine retinal pericytes. The effect of an aldose reductase inhibitor, SNK-860, was also examined. After a 5 day incubation with various concentrations of glucose (5.5-40 m M) in the presence or absence of SNK-860, the cell viability and the percentages of dead cells were measured, and staining with the TUNEL method and Hoechst 33342, and DNA electrophoresis were performed. High glucose reduced the viability and increased the percentages of dead cells. TUNEL-positive cells were observed in pericytes under high glucose, but not in those under 5.5 m M glucose. In the staining of nuclei with Hoechst 33342, the percentage of apoptotic cells in total cells counted under high glucose was higher than that under 5.5 m M glucose. DNA electrophoresis of pericytes cultured with high glucose demonstrated a 'ladder pattern'. Hyperosmolarity also induced apoptosis in pericytes, but less than that by high glucose. SNK-860 inhibited the glucose-induced apoptosis in pericytes. These observations suggest that the pericyte loss in diabetic retinopathy involves an apoptotic process, and that the polyol pathway hyperactivity plays an important role in inducing apoptosis in pericytes by high glucose.

Diabetic Neuropathies

There are currently no treatments available (beyond optimal control of hyperglycemia) that arrest or reverse progressive diabetic polyneuropathy. Consultation with a diabetologist is indicated for patients with poorly controlled disease and polyneuropathy. Immunotherapy for diabetic lumbosacral plexopathy has been advocated but is not supported to date by class 1 clinical trial evidence. Pharmacologic treatment for painful neuropathy may include topical anesthetics, capsaicin cream, anticonvulsants, tricyclic antidepressants, mexiletine, and opioids. Gabapentin, a newer anticonvulsant, has an attractive side-effect profile (a consideration in older patients) and has fewer interactions with other drugs. Amitriptyline may cause excessive sedation, postural hypotension, constipation, and urinary retention, but low evening doses (10 to 25 mg), slowly titrated upward, may offer relief from nocturnal pain. Opioids should not be withheld from patients with severe pain or with intolerance of or contraindications to other agents. A single physician should supervise their use.

Increased peripheral nerve microvessels in early experimental diabetic neuropathy: quantitative studies of nerve and dorsal root ganglia

Microangiopathy is an important complication of diabetes mellitus and neovascularity is a feature of human diabetic retinopathy. The objective of this work was to evaluate numbers, areas and size distributions of whole nerve, endoneurial and dorsal root ganglia perfused microvessels in a detailed fashion using unfixed tissues from rats with experimental diabetes. Experimental neuropathy was studied in male Sprague-Dawley rats 12 weeks after streptozotocin or citrate buffer injection. Electrophysiological recordings of sciatic-tibial motor and caudal sensory fibers identified conduction slowing in diabetes indicating neuropathy. Diabetics had a rise in the numbers of whole nerve microvessels and endoneurial microvessels with associated rises in vessel densities and total vessel luminal areas. Increased vessel numbers in 15-30 microm diameter size ranges were particularly prominent. There was a rise in summed vascular areas in diabetics but the mean luminal area of vessels was not increased. Similar, but not significant trends were observed in a selective analysis of endoneurial vessels alone. In contrast, dorsal root ganglia microvessels were not increased in number. Early experimental diabetic neuropathy is associated with increased numbers of microvessels supplying the peripheral nerve trunk, likely representing neovascularity.

Diabetic neuropathies: features and mechanisms

Diabetic neuropathies include both focal neuropathies and diffuse polyneuropathy. Polyneuropathy, the most common of the diabetic neuropathies excluding focal entrapment, has not yet been explained by a single disease mechanism despite intensive investigation. A number of abnormalities appear to cascade into a 'vicious cycle' of progressive microvascular disease associated with motor, sensory and autonomic fiber loss. These abnormalities include excessive polyol (sugar alcohol) flux through the aldose reductase pathway, functional and structural alterations of nerve microvessels, nerve and ganglia hypoxia, oxidative stress, nonspecific glycosylation of axon and microvessel proteins, and impairment in the elaboration of trophic factors critical for peripheral nerves and their ganglia. While an initiating role for nerve ischemia in the development of polyneuropathy has been proposed, the evidence for it can be questioned. The role of sensory and autonomic ganglia in the development of polyneuropathy has had relatively less attention despite the possibility that they may be vulnerable to a variety of insults, particularly neurotrophin deficiency. Superimposed on the deficits of polyneuropathy is the failure of diabetic nerves to regenerate as effectively as nondiabetics. Polyneuropathy has not yet yielded to specific forms of treatment but a variety of new trials addressing plausible hypotheses have been initiated. This review will summarize some of the clinical, pathological and experimental work applied toward understanding human diabetic neuropathy and will emphasize ideas on pathogenesis.

Amelioration of neurovascular deficits in diabetic rats by a novel aldose reductase inhibitor, GP-1447: minor contribution of nitric oxide

The effects of a novel potent aldose reductase inhibitor, GP-1447 [3-[(4,5,7-trifluorobenzothiazol-2-yl)methyl]-5-methylphenylace tic acid] on the sciatic nerve blood flow in streptozotocin-induced diabetic rats were examined. Blood flow was analyzed in terms of mass, i.e. the volume of blood in tissue, and of velocity, i.e. the velocity of the blood flow. In diabetic rats, a 63% decrease in blood flow due to a decrease in velocity was observed. The blood mass in the same animals fluctuated, thereby increasing its range of values. Treatment with GP-1447 at a dose of 30 mg/kg per day for 4 consecutive weeks following a 3-week period without treatment ameliorated the reduced blood flow by 51%, and was accompanied by a recovery of velocity. The increase in the range of blood mass values was reversed by treatment with GP-1447. The restoration of the range of blood mass values, but not that of the blood flow, by GP-1447 was blocked by treatment with the nitric oxide (NO) synthase inhibitor, NG-nitro-L-arginine. Motor nerve conduction velocity (MCV) changes in parallel with blood flow values, while it is inversely proportionate to alterations in the range of blood mass values. It is suggested that the observed beneficial effect of GP-1447 on blood flow is involved in the restoration of decreased MCV in diabetes. It would appear that GP-1447-induced amelioration of neurovascular defects is not mediated solely by the improvement of the NO system.