Expression of constitutive cyclo-oxygenase (COX-1) in rats with streptozotocin-induced diabetes; effects of treatment with evening primrose oil or an aldose reductase inhibitor on COX-1 mRNA levels

Neuroprotective Effects of a Hydrogen Sulfide Donor in Streptozotocin-Induced Diabetic Rats

Diabetic neuropathy is an important long-term complication of diabetes. This study explored the hypothesis that hydrogen sulfide (H2S) ameliorates neuropathic pain by controlling antiapoptotic and pro-apoptotic processes. The effects of a slow-releasing H2S donor, GYY4137, on the expression of antiapoptotic and pro-apoptotic genes and proteins, such as B-cell lymphoma 2 (Bcl2) and Bcl-2-like protein 4 (Bax), as well as caspases, cyclooxygenase (COX)-1 and COX-2, monocytes/macrophages, and endothelial cells, in the spinal cord of male Sprague-Dawley rats with streptozotocin-induced peripheral diabetic neuropathy, were investigated using reverse transcription-PCR, western blot and immunohistochemistry. The antihypoalgesic activities of GYY4137 on diabetic rats were evaluated using the tail flick test. Treatment of diabetic rats with GYY4137 attenuated thermal hypoalgesia and prevented both the diabetes-induced increase in Bax mRNA expression (p = 0.0032) and the diabetes-induced decrease in Bcl2 mRNA expression (p = 0.028). The GYY4137-treated diabetic group had increased COX-1 (p = 0.015), decreased COX-2 (p = 0.002), reduced caspase-7 and caspase-9 protein expression (p < 0.05), and lower numbers of endothelial and monocyte/macrophage cells (p < 0.05) compared to the non-treated diabetic group. In summary, the current study demonstrated the protective properties of H2S, which prevented the development of neuropathy related behavior, and suppressed apoptosis activation pathways and inflammation in the spinal cord. H2S-releasing drugs could be considered as possible treatment options of diabetic peripheral neuropathy.

Non-enzymatic modifications of prostaglandin H synthase 1 affect bifunctional enzyme activity - Implications for the sensitivity of blood platelets to acetylsalicylic acid

Due to its ability to inhibit the blood platelet PGHS-1, acetylsalicylic acid (ASA, Aspirin(®)) is widely used as a preventive agent in atherothrombotic diseases. However, its beneficial effects seem to be lower in diabetic patients, suggesting that protein glycation may impair effective ASA-mediated acetylation process. On the other hand, it is proposed that ASA can prevent some of the late complications of diabetes by lowering the extent of glycation at protein free amino groups. The aim of this work was to evaluate the extents of non-enzymatic N-glycosylation (glycation) and acetylation of blood platelet PGHS-1 (COX-1) and the competition between glycation and acetylation was investigated in order to demonstrate how these two reactions may compete against platelet PGHS-1. When PGHS-1 was incubated with glycating/acetylating agents (glucose, Glu; 1,6-bisphosphofructose, 1,6-BPF; methylglyoxal, MGO, acetylsalicylic acid, ASA), the enzyme was modified in 13.4 ± 1.6, 5.3 ± 0.5, 10.7 ± 1.2 and 6.4 ± 1.1 mol/mol protein, respectively, and its activity was significantly reduced. The prior glycation/carbonylation of PGHS-1 with Glu, 1,6-BPF or MGO decreased the extent of acetylation from 6.4 ± 1.1 down to 2.5 ± 0.2, 3.6 ± 0.3 and 5.2 ± 0.2 mol/mol protein, respectively, but the enzyme still remained susceptible to the subsequent inhibition of its activity with ASA. When PGHS-1 was first acetylated with ASA and then incubated with glycating/carbonylating agents, we observed the following reductions in the enzyme modifications: from 13.4 ± 1.6 to 8.7 ± 0.6 mol/mol protein for Glu, from 5.3 ± 0.5 to 3.9 ± 0.3 mol/mol protein for 1,6-BPF and from 10.7 ± 1.2 to 7.5 ± 0.5 mol/mol protein for MGO, however subsequent glycation/carbonylation did not significantly affect PGHS-1 function. Overall, our outcomes allow to better understand the structural aspects of the chemical competition between glycation and acetylation of PGHS-1.

Arachidonic acid and its COX1/2 metabolites inhibit interferon-γ mediated induction of indoleamine-2,3 dioxygenase in THP-1 cells and human monocytes

Using human acute monocytic leukaemic THP-1 cells and human primary monocytes, this study examined the ability of arachidonic acid (AA) to modulate the activity of the IFNγ signalling cascade and its downstream effector indoleamine 2,3-dioxygenase (IDO). We established that AA inhibited IDO enzyme activity with an IC(50) of 20 μM in THP-1 cells and 12 μM in monocytes, and this was due to reduced expression of INDO1 mRNA and reduced level of IDO protein. Further mechanistic analysis revealed that AA interfered with the transcriptional function of the IFNγ signalling pathway by reducing phosphorylation of signal transducer and activator of transcription (STAT1) on tyrosine 701. The importance of AA metabolism via the COX and LOX pathways was investigated using inhibitors. Indomethacin, but not nordihydroguaiaretic acid, prevented the AA-mediated inhibition of STAT1 phosphorylation and thereby IDO enzymatic activity in THP-1 cells and monocytes. This is the first study to demonstrate that AA inhibits the IFNγ/STAT/IDO pathway, and this function is mediated by COX1/2 produced metabolites of AA. We now have evidence demonstrating that the AA metabolites, prostaglandins A(2) and D(2,) were highly inhibitory towards the IFNγ pathway, while prostaglandin E(2) had no effect. Together, these results indicate that the fatty acid AA has the potential to modulate the immunosuppressive activity of IDO and may form the basis of novel inhibitory compounds.

Differentially expressed angiogenic genes in diabetic erectile tissue - results from a microarray screening

Diabetes-induced metabolic derangements promote endothelial malfunction, contributing to erectile dysfunction (ED). However, it remains unclear which angiogenic molecular mechanisms are deregulated in diabetic corpus cavernosum (CC). We investigated early and late alterations in cavernosal angiogenic gene expression associated to diabetes. Angiogenic changes were assessed in penile tissue of streptozotocin-induced Wistar rats, in an early (2-week) and established stage (8-week) of diabetes. Differentially expressed genes were identified by microarrays and expression data validated by quantitative real-time PCR (qrt-PCR). At protein level, quantitative immunohistochemistry confirmed the arrays data and dual immunofluorescence for selected alterations and α-smooth muscle actin (α-SMA) identified the cellular location of target proteins. The selected differentially expressed genes were also evaluated in human non-diabetic and diabetic CC by quantitative immunolabeling. At 2-week diabetes there was no differential gene expression between non-diabetic and diabetic CC. At 8-week, 10 genes were found down-regulated in diabetics. The results were validated by qrt-PCR for the insulin-like growth factor-1 (Igf1) and the natriuretic peptide receptor-1 (Npr1) genes. Dual immunofluorescence for IGF-1/ α-SMA showed predominant localization of IGF-1 in SM. NPR-1 expression was diffuse and mostly present in trabecular fibroblasts and SM. Quantitative immunostaining confirmed the decreased expression of both proteins in diabetic tissues. Concordantly, we detected a significant reduction in IGF-1 and NPR-1 protein expressions in human diabetic samples. Microarray analysis identified 10 angiogenic-related molecules deregulated in CC of established diabetes. Among them, IGF-1 and NPR-1 were significantly down-regulated and might result in preventive/therapeutic targets for ED management.

A review of phytotherapy of Acne vulgaris

Acne vulgaris (acne) is a cutaneous pleomorphic disorder of the pilosebaceous unit involving abnormalities in sebum production and is characterized by both inflammatory (papules, pustules and nodules) and non-inflammatory (comedones, open and closed) lesions. Propionibacterium acnes and Staphylococcus epidermidis are common pus-forming microbes responsible for the development of various forms of acne. This disease remains a common condition in industrialized societies, with many mainstream treatment options available. There are many acne products on the market, and making an appropriate selection can be daunting. Common therapies that are used for the treatment of acne include topical, systemic, hormonal, herbal and combination therapy. Topically used agents are benzoyl peroxide, antibiotics and retinoid. Systemically used agents are antibiotics and isotretinoin. However, all such treatments carry risks and none is completely satisfactory. Natural alternatives are gaining greater research support, and have much to offer clinically in this disorder. This review focuses primarily on herbal treatments for acne that show scientific evidence of clinical efficacy, as well as the more common herbs shown to be useful in the treatment of this dermatologic disorder.

The effects of resveratrol on cyclooxygenase-1 and cyclooxygenase-2 mRNA and protein levels in diabetic rat kidneys

Cyclooxygenase (COX), which have the isoforms of COX-1 and COX-2, is the key enzyme of prostaglandins biosynthesis. Especially, COX-2 is induced in inflammatory disease such as Diabetes Mellitus (DM). Resveratrol (RSV), a natural antioxidant, has a beneficial role in prevention of inflammatory disease. We investigated the changes of COX-1 and COX-2 mRNA expression and protein level in diabetic rat kidney after RSV treatment. Three months-old, 44 Wistar albino male rats, which were divided into six groups such as control group, sodium citrate buffer (sham control) group, diabetic group (DM), Dimethyl Sulfoxide induced control group, RSV treated sham control group (RSV) and RSV treated diabetic group (DM + RSV) were used for the study. Experimental diabetes was induced by intraperitoneal injection of 55 mg/kg Streptozotocin. After the induction of chronic diabetes 10 mg/kg per day RSV was administered intraperitoneally for 4 weeks. In this study. RSV has no significant effect on COX-1 mRNA expression in diabetic rat kidney (P > 0.05). Immunohistochemical study showed that COX-1 expression was slightly inhibited in RSV group and was not significantly supressed in DM + RSV group. When comparing control and treated groups, there were no significant differences in COX-2 mRNA or protein levels (P > 0.05). In conclusion, our results indicate that resveratrol do not significantly affect COX gene and protein expression. Therefore, different therapy strategies such as combination with other antidiabetic drugs may tried in STZ induced animal model for reducing diabetic symptoms and altering COX-1 and COX-2 mRNA or protein levels.

Eicosanoids and renal vascular function in diseases

Arachidonic acid metabolites are vital for the proper control of renal haemodynamics and, when not properly controlled, can contribute to renal vascular injury and end-stage renal disease. Three major enzymatic pathways, COX (cyclo-oxygenase), CYP450 (cytochrome P450) and LOX (lipoxygenase), are responsible for the metabolism of arachidonic acid metabolites to bioactive eicosanoids. These eicosanoids can dilate or constrict the renal vasculature and maintain vascular resistance in the face of changing vasoactive hormones. Renal vascular generation of eicosanoids is altered in pathophysiological conditions such as hypertension, diabetes, metabolic syndrome and acute renal failure. Experimental evidence supports the concept that altered eicosanoid metabolism contributes to renal haemodynamic alterations and the development and progression of nephropathy. The possible beneficial renal vascular actions of enzymatic inhibitors, eicosanoid analogues and receptor antagonists have been examined in hypertension, diabetes and metabolic syndrome. This review highlights the roles of renal vascular eicosanoids in the pathogenesis of nephropathy and therapeutic targets for renal disease related to hypertension, diabetes, metabolic syndrome and acute renal failure.

Role of insulin on PGE2 generation during LPS-induced lung inflammation in rats

Alterations in arachidonic acid (AA) metabolism have been reported to occur in diabetes mellitus. The present study was carried out to verify if these alterations are due to the relative lack of insulin or to high levels of blood glucose. Male Wistar rats were rendered diabetic by alloxan injection (42 mg/kg, i.v.), 10 or 30 days before the experiments. Some diabetic rats received a single dose (4 IU, s.c.) of NPH insulin 2 h before an intratracheal instillation of lipopolysaccharide (LPS, 750 microg) or saline. Six hours after LPS challenge, the following parameters were analysed: blood glucose levels, total and differential leukocyte counts in bronchoalveolar lavage (BAL) fluid; linoleic acid and AA content in blood neutrophils (HPLC), and levels of prostaglandin (PG)E(2) in BAL (ELISA). Relative to controls, a reduced number of neutrophils (18%) and decreased amounts of PGE(2) (40%) were observed in the BAL fluid of diabetic rats in response to LPS. A single dose of insulin was not able to reduce blood sugar levels to normal values, but instead resulted in the normalization of both leukocyte migration to the lungs and levels of PGE(2). Accordingly, these abnormalities might be primarily linked to a continuing insulin deficiency rather than to secondary hyperglycaemia occurring in the diabetic rat. In conclusion, data presented suggest that insulin might regulate neutrophil migration and generation of PGE(2) during the course of acute lung injury induced by LPS.

Inhibition of cyclooxygenase-2, but not cyclooxygenase-1, reduces prostaglandin E2 secretion from diabetic rat retinas

Up-regulation of cyclooxygenase-2 occurs in retinal cells during the early onset of diabetic retinopathy. Under these conditions, prostaglandin production is elevated, which in turn leads to an increased expression of vascular endothelial growth factor (VEGF)--a growth factor implicated in vascular leakage and neovascularization. In this ex vivo study, we tested whether cyclooxygenase-1 or cyclooxygenase-2 is responsible for diabetes-induced secretion of prostaglandin E2 from isolated rat retinas. Celecoxib, a selective cyclooxygenase-2 inhibitor, significantly inhibited prostaglandin E2 secretion, whereas SC560 [5-(4-chlorophenyl)-1-(4-methoxyphenyl)-3-trifluoromethylpyrazole], a selective cyclooxygenase-1 inhibitor, had no inhibitory effect. These results suggests that the enzymatic activity of cyclooxygenase-2, but not cyclooxygenase-1, results in prostaglandin E2 secretion under diabetic conditions.

Interaction between NO and COX pathways in retinal cells exposed to elevated glucose and retina of diabetic rats

A nonselective inhibitor of cyclooxygenase (COX; high-dose aspirin) and a relatively selective inhibitor of inducible nitric oxide synthase (iNOS; aminoguanidine) have been found to inhibit development of diabetic retinopathy in animals, raising a possibility that NOS and COX play important roles in the development of retinopathy. In this study, the effects of hyperglycemia on retinal nitric oxide (NO) production and the COX-2 pathway, and the interrelationship of the NOS and COX-2 pathways in retina and retinal cells, were investigated using a general inhibitor of NOS [N(G)-nitro-l-arginine methyl ester (l-NAME)], specific inhibitors of iNOS [l-N(6)-(1-iminoethyl)lysine (l-NIL)] and COX-2 (NS-398), and aspirin and aminoguanidine. In vitro studies used a transformed retinal Müller (glial) cell line (rMC-1) and primary bovine retinal endothelial cells (BREC) incubated in 5 and 25 mM glucose with and without these inhibitors, and in vivo studies utilized retinas from experimentally diabetic rats (2 mo) treated or without aminoguanidine or aspirin. Retinal rMC-1 cells cultured in high glucose increased production of NO and prostaglandin E(2) (PGE(2)) and expression of iNOS and COX-2. Inhibition of NO production with l-NAME or l-NIL inhibited all of these abnormalities, as did aminoguanidine and aspirin. In contrast, inhibition of COX-2 with NS-398 blocked PGE(2) production but had no effect on NO or iNOS. In BREC, elevated glucose increased NO and PGE(2) significantly, whereas expression of iNOS and COX-2 was unchanged. Viability of rMC-1 cells or BREC in 25 mM glucose was significantly less than at 5 mM glucose, and this cell death was inhibited by l-NAME or NS-398 in both cell types and also by l-NIL in rMC-1 cells. Retinal homogenates from diabetic animals produced significantly greater than normal amounts of NO and PGE(2) and of iNOS and COX-2. Oral aminoguanidine and aspirin significantly inhibited all of these increases. The in vitro results suggest that the hyperglycemia-induced increase in NO in retinal Müller cells and endothelial cells increases production of cytotoxic prostaglandins via COX-2. iNOS seems to account for the increased production of NO in Müller cells but not in endothelial cells. We postulate that NOS and COX-2 act together to contribute to retinal cell death in diabetes and to the development of diabetic retinopathy and that inhibition of retinopathy by aminoguanidine or aspirin is due at least in part to inhibition of this NO/COX-2 axis.

Vascular endothelial growth factor and diabetic retinopathy: pathophysiological mechanisms and treatment perspectives

Retinal neovascularization and macular edema are central features of diabetic retinopathy, the major cause of blindness in the developed world. Current treatments are limited in their efficacy and are associated with significant adverse effects. Characterization of the molecular and cellular processes involved in vascular growth and permeability has led to the recognition that the angiogenic growth factor and vascular permeability factor vascular endothelial growth factor (VEGF) plays a pivotal role in the retinal microvascular complications of diabetes. Therefore, VEGF represents an exciting target for therapeutic intervention in diabetic retinopathy. This review highlights the current understanding of the mechanisms that regulate VEGF gene expression and mediate its biological effects and how these processes may become altered during diabetes. The cellular and molecular alterations that characterize experimental models of diabetes are considered in relation to the influence of high glucose-mediated oxidative stress on VEGF expression and on the mechanisms of VEGF's actions under hyperglycemic induction. Finally, potential therapeutic strategies for preventing VEGF overexpression or blocking its pathological effects in the diabetic retina are considered.

Celecoxib, a selective cyclooxygenase-2 inhibitor, inhibits retinal vascular endothelial growth factor expression and vascular leakage in a streptozotocin-induced diabetic rat model

Overexpression of vascular endothelial growth factor (VEGF) is implicated in the development of vascular leakage and retinal neovascularization in diabetic subjects. The objective of this study was to determine whether celecoxib, a selective cyclooxygenase-2 enzyme inhibitor, reaches ocular tissues following oral administration and inhibits the retinal VEGF expression and vascular leakage in a streptozotocin-induced diabetic rat model. After administering a single intraperitoneal injection of streptozotocin (60 mg/kg) to Sprague-Dawley rats and ensuring the induction of diabetes at the end of 24 h, celecoxib was administered b.i.d. by oral gavage (50 mg/kg). On day 8, the animals were sacrificed and the retinal VEGF and cyclooxygenase-2 mRNA levels, ocular tissue celecoxib concentrations, and the vitreous/plasma protein ratio were determined. In diabetic rats, the retinal VEGF mRNA expression was 2.3-fold compared to controls, with a corresponding increase in cyclooxygenase-2 mRNA expression. Celecoxib treatment inhibited VEGF mRNA expression without any significant reduction in cyclooxygenase-2 mRNA. Furthermore, the retinal vascular leakage estimated as vitreous to plasma protein ratio increased in diabetic animals from 0.35+/-0.1 to 1.1+/-0.1 and celecoxib treatment significantly decreased this ratio to 0.4+/-0.1. Celecoxib levels were 24.8+/-6.6, 1.9+/-1, 1.7+/-0.8, and 6.9+/-0.9 ng/mg in the retina, vitreous, lens, and cornea, respectively. The plasma celecoxib levels were 85+/-24 ng/ml. Thus, celecoxib reaches the retina after oral administration and reduces diabetes-induced retinal VEGF mRNA expression and vascular leakage by inhibiting the activity of cyclooxygenase-2 enzyme.

Elevated spinal cyclooxygenase and prostaglandin release during hyperalgesia in diabetic rats

Diabetic rats display exaggerated hyperalgesic behavior in response to noxious stimuli that may model aspects of painful diabetic neuropathy. This study examined the contribution of spinal prostaglandin production to this exaggerated hyperalgesic behavior. Rats were implanted with spinal dialysis probes and received noxious stimulation to the hind paw by subcutaneous injection of 0.5% formalin solution. Prostaglandin E(2) (PGE(2)) was measured in dialysates of lumbar spinal cerebrospinal fluid concurrent with behavioral responses to formalin injection. In separate experiments, formalin-evoked behavioral responses were measured after intrathecal delivery of either a cyclooxygenase inhibitor or an EP(1) receptor antagonist, and cyclooxygenase protein was measured in spinal cord homogenates. Diabetic rats exhibited exaggerated behavioral responses to paw formalin injection and a concurrent prolongation of formalin-evoked PGE(2) release. Formalin-evoked behavioral responses were dose-dependently reduced in diabetic rats by spinal delivery of a cyclooxygenase inhibitor or an EP(1) receptor antagonist. Protein levels of cyclooxygenase-2 were elevated in the spinal cord of diabetic rats, whereas cyclooxygenase-1 protein was reduced. Hyperalgesic behavior in diabetic rats is associated with both increased cyclooxygenase-2 protein and cyclooxygenase-mediated PGE(2) release. Spinal delivery of selective inhibitors of cyclooxygenase-2 or antagonists of prostaglandin receptors may have therapeutic potential for treating painful diabetic neuropathy.

Immunohistochemical and functional correlations of renal cyclooxygenase-2 in experimental diabetes

Prostaglandins (PGs) generated by the enzyme cyclooxygenase (COX) have been implicated in the pathological renal hemodynamics and structural alterations in diabetes mellitus, but the role of individual COX isoenzymes in diabetic nephropathy remains unknown. We explored COX-1 and COX-2 expression and hemodynamic responses to the COX-1 inhibitor valeryl salicylate (VS) or the COX-2 inhibitor NS398 in moderately hyperglycemic, streptozotocin-diabetic (D) and control (C) rats. Immunoreactive COX-2 was increased in D rats compared with C rats and normalized by improved glycemic control. Acute systemic administration of NS398 induced no significant changes in mean arterial pressure and renal plasma flow in either C or D rats but reduced glomerular filtration rate in D rats, resulting in a decrease in filtration fraction. VS had no effect on renal hemodynamics in D rats. Both inhibitors decreased urinary excretion of PGE(2). However, only NS398 reduced excretion of thromboxane A(2). In conclusion, we documented an increase in renal cortical COX-2 protein expression associated with a different renal hemodynamic response to selective systemic COX-2 inhibition in D as compared with C animals, indicating a role of COX-2-derived PG in pathological renal hemodynamic changes in diabetes.

Early changes in lipid peroxidation and antioxidative defense in diabetic rat retina: effect of DL-alpha-lipoic acid

This study was designed to (1) evaluate retinal lipid peroxidation in early diabetes by the method specific for free malondialdehyde and 4-hydroxyalkenals, (2) identify impaired antioxidative defense mechanisms and (3) assess if enhanced retinal oxidative stress in diabetes is prevented by the potent antioxidant, DL-alpha-lipoic acid. The groups included control and streptozotocin-diabetic rats treated with or without DL-alpha-lipoic acid (100 mg kg(-1) day(-1), i.p., for 6 weeks). All parameters were measured in individual retinae. 4-Hydroxyalkenal concentration was increased in diabetic rats (2.63+/-0.60 vs. 1.44+/-0.30 nmol/mg soluble protein in controls, P<0.01), and this increase was prevented by DL-alpha-lipoic acid (1.20+/-0.88, P<0.01 vs. untreated diabetic group). Malondialdehyde, reduced glutathione (GSH) and oxidized glutathione (GSSG) concentrations were similar among the groups. Superoxide dismutase, glutathione peroxidase (GSHPx), glutathione reductase (GSSGRed) and glutathione transferase (GSHTrans) activities were decreased in diabetic rats vs. controls. Quinone reductase was upregulated in diabetic rats, whereas catalase and cytoplasmic NADH oxidase activities were unchanged. DL-alpha-Lipoic acid prevented changes in superoxide dismutase and quinone reductase activities induced by diabetes without affecting the enzymes of glutathione metabolism. In conclusion, accumulation of 4-hydroxyalkenals is an early marker of oxidative stress in the diabetic retina. Increased lipid peroxidation occurs in the absence of GSH depletion, and is prevented by DL-alpha-lipoic acid.

A review of current research on the effect of diabetes mellitus on the eye

It is estimated that almost one million Australians will have diabetes by the year 2000. Of those with diabetes a significant proportion will have eye-related conditions, the most debilitating being diabetic retinopathy. Appropriate identification and treatment can result in prevention of visual loss and blindness. The importance of diabetes as a cause of blindness in our community is realised by the commencement of a national program by the National Health and Medical Research Council to develop clinical practice guidelines for the management of diabetic retinopathy. The development of these guidelines was based on available evidence following an extensive review of the literature up to May 1996. This review is a summary of our advances in research on the effect of diabetes on various aspects of the eye and vision over the past two years. This review is a compilation of articles of research on the effect of diabetes on various aspects of the eye and vision. As a result of the enormous amount of effort and work by scientists and clinicians around the world, as well as space restrictions, the review covers the past two years only. Although every effort has been made to include as many research articles as possible, not all articles of research are covered. It is intended that this review provide an overview of the latest trends in research, particularly relating to new techniques and methods in the study of diabetes in ocular tissue as well as the new theories in the development of ocular damage to each of the tissue.

Evening primrose oil treatment corrects reduced conduction velocity but not depletion of arachidonic acid in nerve from streptozotocin-induced diabetic rats

The effects of evening primrose oil (EPO) treatment, a source of gamma-linolenic acid, on the proportions of arachidonoyl-containing molecular species (ACMS) in sciatic nerve phosphatidylcholine and phosphatidylethanolamine were determined in conjunction with alterations in nerve conduction velocity. Normal and diabetic rats were either untreated or fed a dietary supplement containing isocalorically equivalent amounts of either EPO or corn oil for the duration of the experiment. After 8 weeks of streptozotocin-induced diabetes, nerve conduction velocity was reduced 16% and this deficit was prevented by either EPO or corn oil treatment. Neither EPO nor corn oil supplementation significantly increased the depressed proportions of ACMS. The level of the linoleoyl-containing molecular species, 16:0/18:2, was elevated in the phospholipids from untreated diabetic rats and was further increased by EPO treatment. These results are consistent with decreased activity of the delta6 desaturase that is required for arachidonic acid synthesis in vivo, but suggests that an accompanying deficit in the subsequent delta5 desaturase-catalyzed reaction may be rate-limiting. These findings indicate that maintenance of normal ACMS levels is not required for prevention of diminished nerve conduction velocity and suggest that other factors influenced by an altered polyunsaturated fatty acid pattern, such as metabolites of linoleic acid or gamma-linolenic acid other than arachidonic acid, the energy state of the nerve or the degree of membrane fluidity may contribute to impaired nerve conduction velocity in diabetic neuropathy.

Effect of sciatic nerve crush on local and target tissue production of neurotrophin-3 transcripts in rats

The effect of sciatic nerve crush in adult rats on neurotrophin-3 (NT-3) mRNA expression at the site of crush and in ipsilateral foot skin was studied using competitive reverse transcription-polymerase chain reaction (cRT-PCR). Mid-sciatic nerve crush resulted in a significant reduction in the expression of NT-3 mRNA in nerve segments distal to the injury site at 3 and 7 days (approximate 60% decrease; P < 0.01). The reduced NT-3 rnRNA expression started to increase at days 14 post-crush and returned towards control levels at 21 days following the crush. The nerve segment proximal to the crush site showed a similar changed pattern of NT-3 mRNA expression. The effects of denervation on NT-3 mRNA expression in foot skin were also studied. Reduced expression of NT-3 was observed by 7 days post-crush, with a 25% decrease observed by 14 days (P < 0.002). Levels of NT-3 mRNA had returned to normal by 21 days post-crush. The results show that changes in axon-Schwann cell contact do not account for the nerve crush induced loss, or subsequent recovery, of NT-3 mRNA expression in nerve.