Effects of poly(ADP-ribose) polymerase inhibition on dysfunction of non-adrenergic non-cholinergic neurotransmission in gastric fundus in diabetic rats

Berberine ameliorates the neurological dysfunction of the gastric fundus by promoting calcium channels dependent release of ACh in STZ-induced diabetic rats

Background

It has been reported diabetic gastroparesis is related to diabetic autonomic neuropathy of the gastrointestinal tract, and berberine (BBR) could ameliorate diabetic central and peripheral neuropathy. However, the influence of BBR on the function and motility of the gastric fundus nerve is unclear.

Methods

A diabetic rat model was constructed, and HE staining was used to observe the morphological changes in the gastric fundus. The changes in cholinergic and nitrogen-related neurochemical indexes and the effects of BBR on them were measured using Elisa. The effects of BBR on the neural function and motility of gastric fundus were investigated by electric field stimulation (EFS) induced neurogenic response in vitro.

Results

In the early stage of STZ-induced diabetic rats, the contractile response of gastric fundus induced by EFS was disorder, disturbance of contraction amplitude, and the cell bodies of neurons in the myenteric plexus of gastric fundus presented vacuolar lesions. Administration with BBR could improve the above symptoms. BBR further enhanced the contraction response in the presence of a NOS inhibitor or the case of inhibitory neurotransmitters removal. Interestingly, the activity of ACh could affect NO release directly and the enhancement of BBR on contractile response was canceled by calcium channel blockers completely.

Conclusions

In the early stage of STZ-induced diabetic rats, the neurogenic contractile response disorder of the gastric fundus is mainly related to cholinergic and nitrergic nerve dysfunction. BBR promotes the release of ACh mainly by affecting the calcium channel to improve the neurological dysfunction of the gastric fundus.

Cerebral Vasodilator Property of Poly(ADP-Ribose) Polymerase Inhibitor (PJ34) in the Neonatal and Adult Mouse Is Mediated by the Nitric Oxide Pathway

The poly(ADP-ribose) polymerase (PARP) inhibitor PJ34 has been reported to improve endothelial dysfunction in the peripheral system. We addressed the role of PJ34 on the vascular tone and vasoreactivity during development in the mouse brain. Blood flows were measured in the basilar trunk using ultrasonography. Cerebral vasoreactivity or vasodilation reserve was estimated as a percentage increase in mean blood flow velocities (mBFV) recorded under normoxia-hypercapnia in control and after PJ34 administration. Non-selective and selective eNOS and nNOS inhibitors were used to evaluate the role of NO-pathway into the hemodynamic effects of PJ34. PJ34 increased mBFVs from 15.8 ± 1.6 to 19.1 ± 1.9 cm/s (p = 0.0043) in neonatal, from 14.6 ± 1.4 to 16.1 ± 0.9 cm/s (p = 0.0049) in adult, and from 15.7 ± 1.7 to 17.5 ± 2.0 cm/s (p = 0.0024) in aged mice 48 h after administration. These PJ34 values were similar to those measured in age-matched control mice under normoxia-hypercapnia. This recruitment was mediated through the activation of constitutive NO synthases in both the neonatal (38.2 ± 6.7 nmol/min/mg protein) and adult (31.5 ± 4.4 nmol/min/mg protein) brain, as compared to age-matched control brain (6.9 ± 0.4 and 6.3 ± 0.7 nmol/min/mg protein), respectively. In addition, quite selective eNOS inhibitor was able to inhibit the recruitment. PJ34 by itself is able to increase cerebral blood flow through the NO-pathway activation at least over 48 h after a single administration.

Oxaliplatin-induced enteric neuronal loss and intestinal dysfunction is prevented by co-treatment with BGP-15

BACKGROUND AND PURPOSE

Gastrointestinal side effects of chemotherapy are an under-recognized clinical problem, leading to dose reduction, delays and cessation of treatment, presenting a constant challenge for efficient and tolerated anti-cancer treatment. We have found that oxaliplatin treatment results in intestinal dysfunction, oxidative stress and loss of enteric neurons. BGP-15 is a novel cytoprotective compound with potential HSP72 co-inducing and PARP inhibiting properties. In this study, we investigated the potential of BGP-15 to alleviate oxaliplatin-induced enteric neuropathy and intestinal dysfunction.

EXPERIMENTAL APPROACH

Balb/c mice received oxaliplatin (3 mg·kg^-1 ·day^-1 ) with and without BGP-15 (15 mg·kg^-1 ·day^-1 : i.p.) tri-weekly for 14 days. Gastrointestinal transit was analysed via in vivo X-ray imaging, before and after treatment. Colons were collected to assess ex vivo motility, neuronal mitochondrial superoxide and cytochrome c levels and for immunohistochemical analysis of myenteric neurons.

KEY RESULTS

Oxaliplatin-induced neuronal loss increased the proportion of neuronal NO synthase-immunoreactive neurons and increased levels of mitochondrial superoxide and cytochrome c in the myenteric plexus. These changes were correlated with an increase in PARP-2 immunoreactivity in the colonic mucosa and were attenuated by BGP-15 co-treatment. Significant delays in gastrointestinal transit, intestinal emptying and pellet formation, impaired colonic motor activity, reduced faecal water content and lack of weight gain associated with oxaliplatin treatment were restored to sham levels in mice co-treated with BGP-15.

CONCLUSION AND IMPLICATIONS

Our results showed that BGP-15 ameliorated oxidative stress, increased enteric neuronal survival and alleviated oxaliplatin-induced intestinal dysfunction, suggesting that BGP-15 may relieve the gastrointestinal side effects of chemotherapy.

Biology of diabetic neuropathy

More than half of all patients with diabetes develop neuropathic disorders affecting the distal sensory and/or motor nerves, or autonomic or cranial nerve functions. Glycemic control can decrease the incidence of neuropathy but is not adequate alone to prevent or treat the disease. This chapter introduces diabetic neuropathy with a morphological description of the disease then describes our current understanding of metabolic and molecular mechanisms that contribute to neurovascular dysfunctions. Key mechanisms include glucose and lipid imbalances and insulin resistance that are interconnected via oxidative stress, inflammation, and altered gene expression. These complex interactions should be considered for the development of new treatment strategies against the onset or progression of neuropathy. Advances in understanding the combined metabolic stressors and the novel study of epigenetics suggest new therapeutic targets to combat this morbid and intractable disease affecting millions of patients with type 1 or type 2 diabetes.

Autonomic neuropathy in experimental models of diabetes mellitus

Autonomic neuropathy complicates diabetes by increasing patient morbidity and mortality. Surprisingly, considering its importance, development and exploitation of animal models has lagged behind the wealth of information collected for somatic symmetrical sensory neuropathy. Nonetheless, animal studies have resulted in a variety of insights into the pathogenesis, neuropathology, and pathophysiology of diabetic autonomic neuropathy (DAN) with significant and, in some cases, remarkable correspondence between rodent models and human disease. Particularly in the study of alimentary dysfunction, findings in intrinsic intramural ganglia, interstitial cells of Cajal and the extrinsic parasympathetic and sympathetic ganglia serving the bowel vie for recognition as the chief mechanism. A body of work focused on neuropathologic findings in experimental animals and human subjects has demonstrated that axonal and dendritic pathology in sympathetic ganglia with relative neuron preservation represents one of the neuropathologic hallmarks of DAN but it is unlikely to represent the entire story. There is a surprising selectivity of the diabetic process for subpopulations of neurons and nerve terminals within intramural, parasympathetic, and sympathetic ganglia and innervation of end organs, afflicting some while sparing others, and differing between vascular and other targets within individual end organs. Rather than resulting from a simple deficit in one limb of an effector pathway, autonomic dysfunction may proceed from the inability to integrate portions of several complex pathways. The selectivity of the diabetic process appears to confound a simple global explanation (e.g., ischemia) of DAN. Although the search for a single unifying pathogenetic hypothesis continues, it is possible that autonomic neuropathy will have multiple pathogenetic mechanisms whose interplay may require therapies consisting of a cocktail of drugs. The role of multiple neurotrophic substances, antioxidants (general or pathway specific), inhibitors of formation of advanced glycosylation end products and drugs affecting the polyol pathway may be complex and therapeutic elements may have both salutary and untoward effects. This review has attempted to present the background and current findings and hypotheses, focusing on autonomic elements including and beyond the typical parasympathetic and sympathetic nervous systems to include visceral sensory and enteric nervous systems.

Pathogenesis of diabetic neuropathy: focus on neurovascular mechanisms

Neuropathies of the peripheral and autonomic nervous systems affect up to half of all people with diabetes, and are major risk factors for foot ulceration and amputation. The aetiology is multifactorial: metabolic changes in diabetes may directly affect neural tissue, but importantly, neurodegenerative changes are precipitated by compromised nerve vascular supply. Experiments in animal models of diabetic neuropathy suggest that similar metabolic sequelae affect neurons and vasa nervorum endothelium. These include elevated polyol pathway activity, oxidative stress, the formation of advanced glycation and lipoxidation end products, and various pro-inflammatory changes such as elevated protein kinase C, nuclear factor κB and p38 mitogen activated protein kinase signalling. These mechanisms do not work in isolation but strongly interact in a mutually facilitatory fashion. Nitrosative stress and the induction of the enzyme poly (ADP-ribose) polymerase form one important link between physiological stressors such as reactive oxygen species and the pro-inflammatory mechanisms. Recently, evidence points to endoplasmic stress and the unfolded protein response as forming another crucial link. This review focuses on the aetiopathogenesis of neurovascular changes in diabetic neuropathy, elucidated in animal studies, and on putative therapeutic targets the majority of which have yet to be tested for efficacy in clinical trials.

Poly(ADP-ribose)polymerase inhibition counteracts renal hypertrophy and multiple manifestations of peripheral neuropathy in diabetic Akita mice

Poly(ADP-ribose) polymerase (PARP) activation has been implicated in the pathogenesis of diabetic complications, including nephropathy and peripheral neuropathy. This study aimed at evaluating the manifestations of both complications in diabetic Akita mice, a model of Type 1 (insulin-dependent) diabetes, and their amenability to treatment with the potent PARP inhibitor, 10-(4-methyl-piperazin-1-ylmethyl)-2H-7-oxa-1,2-diaza-benzo[de] anthracen-3-one (GPI-15427). Male non-diabetic C57Bl6/J and diabetic C57Bl/6-Ins2Akita/J (Akita) mice were maintained with or without treatment with GPI-15427, 30 mg/kg/day, for 4 weeks starting from 16 weeks of age. Sixteen week-old Akita mice displayed sensory nerve conduction velocity (SNCV) deficit, whereas the motor nerve conduction velocity (MNCV) tended to decrease, but the difference with controls did not achieve statistical significance. They also developed thermal and mechanical hypoalgesia and tactile allodynia. SNCV deficit, mechanical hypoalgesia, and tactile allodynia progressed with age whereas the severity of thermal hypoalgesia was similar in 16- and 20-week-old Akita mice. PARP inhibition alleviated, although it did not completely reverse, SNCV deficit, thermal and mechanical hypoalgesia and tactile allodynia. Sixteen-week-old Akita mice displayed MNCV deficit (41.3±2.5 vs. 51.0±1.2 m/sec in non-diabetic controls, P<0.01), axonal atrophy of myelinated fibers, kidney hypertrophy, and albuminuria. MNCV slowing, axonal atrophy, and kidney hypertrophy, but not albuminuria, were less severe in GPI-15427-treated age-matched Akita mice. Neuroprotective and nephroprotective effects of PARP inhibition were not due to alleviation of diabetic hyperglycemia, or peripheral nerve p38 mitogen-activated protein kinase activation. GPI-15427 did not affect any variables in control mice. In conclusion, the findings support an important role for PARP activation in diabetic peripheral neuropathy and kidney hypertrophy associated with Type 1 diabetes, and provide rationale for development and further studies of PARP inhibitors, for the prevention and treatment of these complications.

Different roles of 12/15-lipoxygenase in diabetic large and small fiber peripheral and autonomic neuropathies

Up-regulation of 12/15-lipoxygenase, which converts arachidonic acid to 12(S)- and 15(S)-hydroxyeicosatetraenoic acids, causes impaired cell signaling, oxidative-nitrosative stress, and inflammation. This study evaluated the role for 12/15-lipoxygenase in diabetic large and small fiber peripheral and autonomic neuropathies. Control and streptozotocin-diabetic wild-type and 12/15-lipoxygenase-deficient mice were maintained for 14 to 16 weeks. 12/15-lipoxygenase gene deficiency did not affect weight gain or blood glucose concentrations. Diabetic wild-type mice displayed increased sciatic nerve 12/15-lipoxygenase and 12(S)-hydroxyeicosatetraenoic acid levels. 12/15-lipoxygenase deficiency prevented or alleviated diabetes-induced thermal hypoalgesia, tactile allodynia, motor and sensory nerve conduction velocity deficits, and reduction in tibial nerve myelinated fiber diameter, but not intraepidermal nerve fiber loss. The frequencies of superior mesenteric-celiac ganglion neuritic dystrophy, the hallmark of diabetic autonomic neuropathy in mouse prevertebral sympathetic ganglia, were increased 14.8-fold and 17.2-fold in diabetic wild-type and 12/15-lipoxygenase-deficient mice, respectively. In addition, both diabetic groups displayed small (<1%) numbers of degenerating sympathetic neurons. In conclusion, whereas 12/15-lipoxygenase up-regulation provides an important contribution to functional changes characteristic for both large and small fiber peripheral diabetic neuropathies and axonal atrophy of large myelinated fibers, its role in small sensory nerve fiber degeneration and neuritic dystrophy and neuronal degeneration characteristic for diabetic autonomic neuropathy is minor. This should be considered in the selection of endpoints for future clinical trials of 12/15-lipoxygenase inhibitors.

New therapeutic and biomarker discovery for peripheral diabetic neuropathy: PARP inhibitor, nitrotyrosine, and tumor necrosis factor-{alpha}

This study evaluated poly(ADP-ribose) polymerase (PARP) inhibition as a new therapeutic approach for peripheral diabetic neuropathy using clinically relevant animal model and endpoints, and nitrotyrosine (NT), TNF-alpha, and nitrite/nitrate as potential biomarkers of the disease. Control and streptozotocin-diabetic rats were maintained with or without treatment with orally active PARP inhibitor 10-(4-methyl-piperazin-1-ylmethyl)-2H-7-oxa-1,2-diaza-benzo[de]anthracen-3-one (GPI-15,427), 30 mg kg(-1) d(-1), for 10 wk after first 2 wk without treatment. Therapeutic efficacy was evaluated by poly(ADP-ribosyl)ated protein expression (Western blot analysis), motor and sensory nerve conduction velocities, and tibial nerve morphometry. Sciatic nerve and spinal cord NT, TNF-alpha, and nitrite/nitrate concentrations were measured by ELISA. NT localization in peripheral nervous system was evaluated by double-label fluorescent immunohistochemistry. A PARP inhibitor treatment counteracted diabetes-induced motor and sensory nerve conduction slowing, axonal atrophy of large myelinated fibers, and increase in sciatic nerve and spinal cord NT and TNF-alpha concentrations. Sciatic nerve NT and TNF-alpha concentrations inversely correlated with motor and sensory nerve conduction velocities and myelin thickness, whereas nitrite/nitrate concentrations were indistinguishable between control and diabetic groups. NT accumulation was identified in endothelial and Schwann cells of the peripheral nerve, neurons, astrocytes, and oligodendrocytes of the spinal cord, and neurons and glial cells of the dorsal root ganglia. The findings identify PARP as a compelling drug target for prevention and treatment of both functional and structural manifestations of peripheral diabetic neuropathy and provide rationale for detailed evaluation of NT and TNF-alpha as potential biomarkers of its presence, severity, and progression.

Peripheral neuropathy in mice with neuronal nitric oxide synthase gene deficiency

Evidence for the important role of the potent oxidant peroxynitrite in peripheral diabetic neuropathy and neuropathic pain is emerging. This study evaluated the contribution of neuronal nitric oxide synthase (nNOS) to diabetes-induced nitrosative stress in peripheral nerve and dorsal root ganglia, and peripheral nerve dysfunction and degeneration. Control and nNOS-/- mice were made diabetic with streptozotocin, and maintained for 6 weeks. Peroxynitrite injury was assessed by nitrotyrosine and poly(ADP-ribose) immunoreactivities. Peripheral diabetic neuropathy was evaluated by measurements of sciatic motor and hind-limb digital sensory nerve conduction velocities, thermal algesia, tactile allodynia, and intraepidermal nerve fiber density. Control nNOS-/- mice displayed normal motor nerve conduction velocity and thermal response latency, whereas sensory nerve conduction velocity was slightly lower compared with non-diabetic wild-type mice, and tactile response threshold and intraepidermal nerve fiber density were reduced by 47 and 38%, respectively. Both diabetic wild-type and nNOS-/- mice displayed enhanced nitrosative stress in peripheral nerve. In contrast to diabetic wild-type mice, diabetic nNOS-/- mice had near normal nitrotyrosine and poly(ADP-ribose) immunofluorescence in dorsal root ganglia. Both diabetic wild-type and nNOS-/- mice developed motor and sensory nerve conduction velocity deficits and thermal hypoalgesia although nNOS gene deficiency slightly reduced severity of the three disorders. Tactile response thresholds were similarly decreased in control and diabetic nNOS-/- mice compared with non-diabetic wild-type mice. Intraepidermal nerve fiber density was lower by 27% in diabetic nNOS-/- mice compared with the corresponding non-diabetic group, and by 20% in diabetic nNOS-/- mice compared with diabetic wild-type mice. In conclusion, nNOS is required for maintaining the normal peripheral nerve function and small sensory nerve fibre innervation. nNOS gene deficiency does not protect from development of nerve conduction deficit, sensory neuropathy and intraepidermal nerve fiber loss.

Role of nitrosative stress in the pathogenesis of diabetic vascular dysfunction

Here we overview the role of reactive nitrogen species (nitrosative stress) and associated pathways in the pathogenesis of diabetic vascular complications. Increased extracellular glucose concentration, a principal feature of diabetes mellitus, induces a dysregulation of reactive oxygen and nitrogen generating pathways. These processes lead to a loss of the vascular endothelium to produce biologically active nitric oxide (NO), which impairs vascular relaxations. Mitochondria play a crucial role in this process: endothelial cells placed in increase extracellular glucose respond with a marked increase in mitochondrial superoxide formation. Superoxide, when combining with NO generated by the endothelial cells (produced by the endothelial isoform of NO synthase), leads to the formation of peroxynitrite, a cytotoxic oxidant. Reactive oxygen and nitrogen species trigger endothelial cell dysfunction through a multitude of mechanisms including substrate depletion and uncoupling of endothelial isoform of NO synthase. Another pathomechanism involves DNA strand breakage and activation of the nuclear enzyme poly(ADP-ribose) polymerase (PARP). PARP-mediated poly(ADP-ribosyl)ation and inhibition of glyceraldehyde-3-phosphate dehydrogenase importantly contributes to the development of diabetic vascular complications: it induces activation of multiple pathways of injury including activation of nuclear factor kappa B, activation of protein kinase C and generation of intracellular advanced glycation end products. Reactive species generation and PARP play key roles in the pathogenesis of 'glucose memory' and in the development of injury in endothelial cells exposed to alternating high/low glucose concentrations.

Role of nitrosative stress in the pathogenesis of diabetic vascular dysfunction

Here we overview the role of reactive nitrogen species (nitrosative stress) and associated pathways in the pathogenesis of diabetic vascular complications. Increased extracellular glucose concentration, a principal feature of diabetes mellitus, induces a dysregulation of reactive oxygen and nitrogen generating pathways. These processes lead to a loss of the vascular endothelium to produce biologically active nitric oxide (NO), which impairs vascular relaxations. Mitochondria play a crucial role in this process: endothelial cells placed in increase extracellular glucose respond with a marked increase in mitochondrial superoxide formation. Superoxide, when combining with NO generated by the endothelial cells (produced by the endothelial isoform of NO synthase), leads to the formation of peroxynitrite, a cytotoxic oxidant. Reactive oxygen and nitrogen species trigger endothelial cell dysfunction through a multitude of mechanisms including substrate depletion and uncoupling of endothelial isoform of NO synthase. Another pathomechanism involves DNA strand breakage and activation of the nuclear enzyme poly(ADP-ribose) polymerase (PARP). PARP-mediated poly(ADP-ribosyl)ation and inhibition of glyceraldehyde-3-phosphate dehydrogenase importantly contributes to the development of diabetic vascular complications: it induces activation of multiple pathways of injury including activation of nuclear factor kappa B, activation of protein kinase C and generation of intracellular advanced glycation end products. Reactive species generation and PARP play key roles in the pathogenesis of 'glucose memory' and in the development of injury in endothelial cells exposed to alternating high/low glucose concentrations.

Aldose reductase inhibitor fidarestat counteracts diabetes-associated cataract formation, retinal oxidative-nitrosative stress, glial activation, and apoptosis

This study was aimed at evaluating the potent and specific aldose reductase inhibitor fidarestat, on diabetes-associated cataract formation, and retinal oxidative-nitrosative stress, glial activation, and apoptosis. Control and streptozotocin-diabetic rats were treated with or without fidarestat (16 mg kg(-1)d(-1)) for 10 weeks after an initial 2-week period without treatment. Lens changes were evaluated by indirect ophthalmoscopy and portable slit lamp. Nitrotyrosine, poly(ADP-ribose), and glial fibrillary acidic protein expression were assessed by immunohistochemistry. The rate of apoptosis was quantified in flat-mounted retinas by TUNEL assay with immunoperoxidase staining. To dissect the effects of high glucose exposure in retinal microvascular cells, primary bovine retinal pericytes and endothelial cells were cultured in 5 or 30 mM glucose, with or without fidarestat (10 microM) for 3-14 days. Apoptosis was assessed by TUNEL assay, nitrotyrosine and poly(ADP-ribose) by immunocytochemistry, and Bax and Bcl-2 expression by Western blot analyses. Fidarestat treatment prevented diabetic cataract formation and counteracted retinal nitrosative stress, and poly(ADP-ribose) polymerase activation, as well as glial activation. The number of TUNEL-positive nuclei (mean +/- SEM) was increased approximately 4-fold in diabetic rats vs. controls (207+/-33 vs. 49+/-4, p<0.01), and this increase was partially prevented by fidarestat (106+/-34, p<0.05 vs. untreated diabetic group). The apoptotic cell number increased with the prolongation of exposure of both pericytes and endothelial cells to high glucose levels. Fidarestat counteracted nitrotyrosine and poly(ADP-ribose) accumulation and apoptosis in both cell types. Antiapoptotic effect of fidarestat in high glucose-exposed retinal pericytes was not associated with the inhibition of Bax or increase in Bcl-2 expression. In conclusion, the findings, i) support an important role for aldose reductase in diabetes-associated cataract formation, and retinal oxidative-nitrosative stress, glial activation, and apoptosis, and ii) provide a rationale for the development of aldose reductase inhibitors, and, in particular, fidarestat, for the prevention and treatment of diabetic ocular complications.

PARP inhibition or gene deficiency counteracts intraepidermal nerve fiber loss and neuropathic pain in advanced diabetic neuropathy

Evidence that poly(ADP-ribose) polymerase (PARP) activation plays an important role in diabetic complications is emerging. This study evaluated the role of PARP in rat and mouse models of advanced diabetic neuropathy. The orally active PARP inhibitor 10-(4-methylpiperazin-1-ylmethyl)-2H-7-oxa-1,2-diaza-benzo[de]anthracen-3-one (GPI-15427; formulated as a mesilate salt, 30 mg kg(-1) day(-1) in the drinking water for 10 weeks after the first 2 weeks without treatment) at least partially prevented PARP activation in peripheral nerve and DRG neurons, as well as thermal hypoalgesia, mechanical hyperalgesia, tactile allodynia, exaggerated response to formalin, and, most importantly, intraepidermal nerve fiber degeneration in streptozotocin-diabetic rats. These findings are consistent with the lack of small sensory nerve fiber dysfunction in diabetic PARP -/- mice. Furthermore, whereas diabetic PARP +/+ mice displayed approximately 46% intraepidermal nerve fiber loss, diabetic PARP -/- mice retained completely normal intraepidermal nerve fiber density. In conclusion, PARP activation is an important contributor to intraepidermal nerve fiber degeneration and functional changes associated with advanced Type 1 diabetic neuropathy. The results support a rationale for the development of potent and low-toxicity PARP inhibitors and PARP inhibitor-containing combination therapies.

Nitrosative stress and peripheral diabetic neuropathy in leptin-deficient (ob/ob) mice

Nitrosative stress contributes to nerve conduction slowing, thermal hypoalgesia, and impaired nitrergic innervation in animal models of Type 1 diabetes. The role for reactive nitrogen species in Type 2 diabetes-associated neuropathy remains unexplored. This study evaluated the role for nitrosative stress in functional and structural neuropathic changes in ob/ob mice, a model of Type 2 diabetes with mild hyperglycemia and obesity. Two structurally diverse peroxynitrite decomposition catalysts, Fe(III) tetrakis-2-(N-triethylene glycol monomethyl ether)-pyridyl porphyrin (FP15) and Fe(III) tetra-mesitylporphyrin octasulfonate (FeTMPS), were administered to control and 8-week-old ob/ob mice for 3 weeks at the doses of 5 mg kg(-1) day(-1) (FP15) and 5 and 10 mg kg(-1) day(-1) (FeTMPS). The 11-week-old ob/ob mice developed motor nerve conduction velocity (MNCV) and hind-limb digital sensory nerve conduction velocity (SNCV) deficits, thermal hypoalgesia, tactile allodynia, and a remarkable ( approximately 78%) loss of intraepidermal nerve fibers. They also had increased nitrotyrosine and poly(ADP-ribose) immunofluorescence in the sciatic nerve, spinal cord, and dorsal root ganglion neurons. Treatment with two structurally diverse peroxynitrite decomposition catalysts was associated with restoration of normal MNCV and SNCV, and alleviation of thermal hypoalgesia. Tactile response thresholds increased in response to peroxynitrite decomposition catalyst treatment, but still remained approximately 2.7- to 3.2-fold lower compared with non-diabetic controls. Intraepidermal nerve fiber loss was not alleviated by either FP15 or FeTMPS. Nitrotyrosine and poly(ADP-ribose) immunofluorescence in sciatic nerve, spinal cord, and dorsal root ganglia of peroxynitrite decomposition catalyst-treated ob/ob mice were essentially normal. In conclusion, nitrosative stress plays an important role in functional abnormalities associated with large motor, large sensory, and small sensory fiber neuropathy, but not in small sensory nerve fiber degeneration, in this animal model. Peroxynitrite decomposition catalysts alleviate Type 2 diabetes-associated sensory nerve dysfunction, likely by mechanism(s) not involving arrest of degenerative changes or enhanced regeneration of small sensory nerve fibers.