Comparison of the effects of ascorbyl gamma-linolenic acid and gamma-linolenic acid in the correction of neurovascular deficits in diabetic rats

Associations of serum gamma-linolenic acid levels with erythema severity and anxiety/depression status in patients with rosacea

BACKGROUND

The development of rosacea is suggested to be closely associated with lipid metabolism, inflammation, and anxiety/depression. Gamma linolenic acid (GLA) is a key factor participating in lipid metabolism, which is also confirmed to regulate the inflammatory response. However, the associations of serum GLA levels with rosacea severity and psychological status still remain unclear.

OBJECTIVE AND LIMITATIONS OF THE STUDY

The present study aimed to investigate the associations of gamma linolenic acid (GLA), a key factor participating in lipid metabolism and the inflammatory response, with rosacea severity and psychological status. The present study still had some limitations. First, this study is a cross-sectional study and does not provide longitudinal evidence about the relationship between GLA and rosacea; Second, the cohort in this study is also relatively small, and a larger cohort is needed in further investigation to reveal the potential role of lipid metabolism in the pathogenesis of rosacea.

METHODS

A total of 62 rosacea patients were consecutively recruited. Patient's Self-Assessment (PSA) scale and Clinician Erythema Assessment (CEA) as well as 7-item Generalized Anxiety Disorder (GAD-7) and 9-item Patient Health Questionnaire (PHQ-9) were conducted to evaluate the degree of erythema severity and anxiety/depression, respectively. Serum GLA levels were determined by gas chromatography mass.

RESULTS

Lower levels of serum GLA in rosacea patients were observed (p<0.001), and subgroup analysis revealed that patients with higher-level GLA had lower scores of PSA, CEA, GAD-7 and PHQ-9. Moreover, Spearman correlation analysis uncovered that serum GLA levels were negatively associated with PSA, CEA, GAD-7 as well and PHQ-9 scores, respectively. Linear regression model found that serum GLA levels at baseline were a predictive factor for prognosis of clinical outcomes after 1-month conventional treatment.

CONCLUSION

The present study indicates that lower levels of serum GLA in rosacea patients are negatively associated with the degree of erythema and anxiety/depression status.

New Horizons in Diabetic Neuropathies: An Updated Review on their Pathology, Diagnosis, Mechanism, Screening Techniques, Pharmacological, and Future Approaches

BACKGROUND

One of the largest problems for global public health is diabetes mellitus (DM) and its micro and macrovascular consequences. Although prevention, diagnosis, and treatment have generally improved, its incidence is predicted to keep rising over the coming years. Due to the intricacy of the molecular mechanisms, which include inflammation, oxidative stress, and angiogenesis, among others, discovering treatments to stop or slow the course of diabetic complications is still a current unmet need.

METHODS

The pathogenesis and development of diabetic neuropathies may be explained by a wide variety of molecular pathways, hexosamine pathways, such as MAPK pathway, PARP pathway, oxidative stress pathway polyol (sorbitol) pathway, cyclooxygenase pathway, and lipoxygenase pathway. Although diabetic neuropathies can be treated symptomatically, there are limited options for treating the underlying cause.

RESULT

Various pathways and screening models involved in diabetic neuropathies are discussed, along with their possible outcomes. Moreover, both medicinal and non-medical approaches to therapy are also explored.

CONCLUSION

This study highlights the probable involvement of several processes and pathways in the establishment of diabetic neuropathies and presents in-depth knowledge of new therapeutic approaches intended to stop, delay, or reverse different types of diabetic complications.

Bone marrow-derived mesenchymal stem cells: A promising therapeutic option for the treatment of diabetic foot ulcers

Chronic wounds fail to heal through the three normal stages of healing (inflammatory, proliferative, and remodelling), resulting in a chronic tissue injury that is not repaired within the average time limit. Patients suffering from type 1 and type 2 diabetes are prone to develop diabetic foot ulcers (DFUs), which commonly develop into chronic wounds that are non treatable with conventional therapies. DFU develops due to various risk factors, such as peripheral neuropathy, peripheral vascular disease, arterial insufficiency, foot deformities, trauma and impaired resistance to infection. DFUs have gradually become a major problem in the health care system worldwide. In this review, we not only focus on the pathogenesis of DFU but also comprehensively summarize the outcomes of preclinical and clinical studies thus far and the potential therapeutic mechanism of bone marrow-derived mesenchymal stem cells (BMSCs) for the treatment of DFU. Based on the published results, BMSC transplantation can contribute to wound healing through growth factor secretion, anti-inflammation, differentiation into tissue-specific cells, neovascularization, re-epithelialization and angiogenesis in DFUs. Moreover, clinical trials showed that BMSC treatment in patients with diabetic ulcers improved ulcer healing and the ankle-brachial index, ameliorated pain scores, and enhanced claudication walking distances with no reported complications. In conclusion, although BMSC transplantation exhibits promising therapeutic potential in DFU treatment, additional studies should be performed to confirm their efficacy and long-term safety in DFU patients.

γ-Linolenic Acid Prevents Lipid Metabolism Disorder in Palmitic Acid-Treated Alpha Mouse Liver-12 Cells by Balancing Autophagy and Apoptosis via the LKB1-AMPK-mTOR Pathway

Excessive fat deposition is the main character in nonalcoholic fatty liver disease (NAFLD), while γ-linolenic acid (GLA) is a polyunsaturated fatty acid that can reduce lipid deposition. This study investigated the effect and regulatory mechanism of GLA (100 μM) on lipid metabolism in alpha mouse liver 12 (AML-12) cells treated by 400 μM palmitic acid (PA). GLA reduced lipid content and increased fatty acid β oxidation, as indicated by decreasing triglyceride and cholesterol contents and increasing mRNA and protein expressions of CPT1α and PPARα. GLA relieved oxidative stress caused by PA, upregulated mRNA levels of superoxide dismutase and glutathione peroxidase, and decreased reactive oxygen species content. GLA reduced apoptosis, as indicated by decreases in the BAX/BCL2 expression level and apoptosis percentage. GLA activated autophagy, autophagosome-lysosome fusion, and LKB1-AMPK-mTOR signaling and upregulated mRNA and protein expressions of Beclin-1, autophagy-related 5, and liver kinase B1 (LKB1). These effects of GLA on lipid metabolism disorders of PA-treated hepatocytes were reversed by autophagy inhibitor 3MA and AMPK inhibitor compound C, confirming our conclusions. Overall, GLA can protect AML-12 cells from lipid metabolism disorder caused by PA via balancing autophagy and apoptosis mediated by the LKB1-AMPK-mTOR pathway. Consequently, GLA, as a dietary supplement, can help to prevent and treat NAFLD by regulating lipid metabolism and autophagy.

Morin exerts neuroprotection via attenuation of ROS induced oxidative damage and neuroinflammation in experimental diabetic neuropathy

Morin, a bioflavonoid with diverse pharmacological effects against various diseases; in most cases morin protective effects were attributed to its detoxifying effect against reactive oxygen species (ROS). Diabetic neuropathy (DN) is a chronic, debilitating neuronal pain associated with intense generation of free radicals and proinflammatory cytokine accumulation in peripheral neurons. We investigated the pharmacological effect of morin against metabolic excess mediated mitochondrial ROS generation and corresponding effect on Nrf2, NF-κB pathways in Streptozotocin (STZ)-induced diabetic rats and in high glucose insulted Mouse neuroblastoma cell line, Neuro 2A (N2A). Animals were evaluated for nerve function parameters, motor and sensory nerve conduction velocities (MNCV and SNCV) and nerve blood flow (NBF) followed by TUNEL and immunoblot analysis. Mitochondrial function was evaluated by performing JC-1 and MitoSOX assays in high glucose (30 mM) incubated N2A cells. Diabetic animals showed significant impairment in MNCV, SNCV, and NBF as well as increased pain hypersensitivity. However, oral administration of morin at 50 and 100 mg/kg improved SNCV, MNCV, and NBF and reduced sensorimotor alterations (hyperalgesia and allodynia) in diabetic animals. Studies in N2A cells have revealed that morin ameliorated the high glucose-induced mitochondrial superoxide production, membrane depolarization, and total ROS generation. Morin effectively counteracted NF-κB-mediated neuroinflammation by reducing ROS mediated IKK activation and increased Nrf2-mediated antioxidant defenses in high glucose-induced N2A cells. The results of our study suggest that morin has exquisite role in offering neuroprotection in experimental DN and further clinical investigation may reward in finding better alternative for the management of DN. © 2017 BioFactors, 44(2):109-122, 2018.

Vascular Impairment of Epineurial Arterioles of the Sciatic Nerve: Implications for Diabetic Peripheral Neuropathy

This article reviews the impact of diabetes and its treatment on vascular function with a focus on the reactivity of epineurial arterioles, blood vessels that provide circulation to the sciatic nerve. Another focus is the relationship between the dysregulation of neurovascular function and diabetic peripheral neuropathy. Diabetic peripheral neuropathy is a debilitating disorder that occurs in more than 50 percent of patients with diabetes. The etiology involves metabolic, vascular, and immunologic pathways besides neurohormonal growth factor deficiency and extracellular matrix remodeling. In the light of this complex etiology, an effective treatment for diabetic peripheral neuropathy has not yet been identified. Current opinion postulates that any effective treatment for diabetic peripheral neuropathy will require a combination of life style and therapeutic interventions. However, a more comprehensive understanding of the factors contributing to neurovascular and neural dysfunction in diabetes is needed before such a treatment strategy can be developed. After reading this review, the reader should have gained insight into the complex regulation of vascular function and blood flow to the sciatic nerve, and the impact of diabetes on numerous elements of vascular reactivity of epineurial arterioles of the sciatic nerve.

Diabetic foot ulcer--A review on pathophysiology, classification and microbial etiology

As the prevalence of diabetes is increasing globally, secondary complications associated to this endocrinal disorder are also ascending. Diabetic foot ulcers are potentially modifying complications. Disruption of harmony in glucose homeostasis causes hyperglycemic status, results in activation of certain metabolic pathways which in their abnormal state subsequently leads to development of vascular insufficiency, nerve damages headed by ulceration in lower extremity due to plantar pressures and foot deformity. Insult to foot caused by trauma at the affected site goes unnoticeable to patient due to loss of sensation. Among the above mention causes, resistance to infection is also considered as chief modulator of pathophysiological image of diabetic foot lesions. Healing as well as non-healing nature of ulcer relies upon the wound microbial communities and the extent of their pathogenicity. A validated classification system of foot ulcer is primarily necessary for clinicians in management of diabetic foot problems. Another aspect which needs management is proper identification of causative pathogen causing infection. The way of approaches presently employed in the diagnosis for treatment of foot ulcer colonized by different microbes is conventional techniques. Conventional diagnostic methods are widely acceptable since decades. But in recent years newly invented molecular techniques are exploring the use of 16S ribosomal regions specific to prokaryotes in bacterial identification and quantification. Molecular techniques would be a better choice if engaged, in finding the specific species harboring the wound.

Advanced Diabetic Neuropathy: A Point of no Return?

Diabetic peripheral neuropathy is the most common complication of long-standing diabetes mellitus which frequently results in clinically significant morbidities e.g. pain, foot ulcers and amputations. During its natural course it progresses from initial functional changes to late, poorly reversible, structural changes. Various interconnected pathogenetic concepts of diabetic neuropathy have been proposed based on metabolic and vascular factors, mostly derived from long-term hyperglycemia. These pathogenetic mechanisms have been targeted in several experimental and clinical trials. This review summarizes available, mainly morphological data from interventions designed to halt the progression or achieve the reversal of established diabetic neuropathy, which include the recovery of normoglycemia by pancreas or islet transplantation, polyol pathway blockade by aldose reductase inhibitors, mitigation of oxidative stress by the use of antioxidants or correction of abnormalities in essential fatty acid metabolism. Unfortunately, to date, no treatment based on pathogenic considerations has shown clear positive effects and thus early institution of optimal glycemic control remains the only available measure with proven efficacy in preventing or halting progression of diabetic neuropathy. Further experimental and clinical research employing objective reproducible parameters is clearly needed. Novel non-invasive or minimally invasive methods e.g. corneal confocal microscopy or epidermal nerve fiber counts may represent potentially useful instruments for the objective assessment of nerve damage and monitoring of treatment effects.

Local gene transduction of cyclooxygenase-1 increases blood flow in injured atherosclerotic rabbit arteries

BACKGROUND

Cyclooxygenase-1 (COX-1) is the rate-limiting component in the synthesis of prostacyclin (PGI2), an important vasodilator and antithrombotic molecule. In balloon-injured, atherosclerosis-free porcine arteries, COX-1 gene transduction increases PGI2 production, induces durable vasodilation, and reduces thrombus formation. We tested the effectiveness of COX-1 local gene transduction for the prevention of postangioplasty restenosis in atherosclerotic arteries in a hypercholesterolemic rabbit model.

METHODS AND RESULTS

We injured 1 carotid artery in 43 Watanabe heritable hyperlipidemic rabbits and performed local gene transduction using a viral vector containing the COX-1 gene (AdCOX-1, n=22) or no genes (Adnull, n=21). Three days later, AdCOX-1-treated arteries stimulated with arachidonic acid produced 100% more PGI2 (P<0.01), 400% more prostaglandin E2 (PGE2) (P<0.01), 400% more prostaglandin E1 (PGE1) (P<0.01), and 250% more cAMP (P<0.05) than Adnull-treated arteries. Twenty-eight days after treatment, Doppler sonography showed that blood flow velocity was preserved in AdCOX-1-treated arteries (ratio 0.92, injured compared with contralateral uninjured carotid artery) but reduced in Adnull-treated arteries (ratio 0.39), suggesting that AdCOX-1 prevented restenosis after injury. COX-1-transduced arteries also showed 80% greater lumen area 28 days after injury (P<0.01).

CONCLUSIONS

The effectiveness of COX-1 in preventing restenosis and preserving normal blood flow 28 days after injury results from increased lumen area caused by durable vasodilation. COX-1 efficacy correlates with an early increase in the production of PGI2, PGE2, PGE1 (known to cause vasodilation), and cAMP. These results demonstrate for the first time that COX-1 gene transduction is an effective treatment for the prevention of postangioplasty restenosis of atherosclerotic arteries under clinically relevant conditions.

Peripheral nerve dysfunction in experimental diabetes is mediated by cyclooxygenase-2 and oxidative stress

Glucose-mediated oxidative stress and alterations in cyclooxygenase (COX) pathway activity with secondary deficits of endoneurial perfusion have been implicated in the pathogenesis of experimental diabetic neuropathy (EDN). We have previously reported that activation of the COX-2 pathway is an important mediator of neurochemical and neurovascular defects in EDN in a rat model. Considering that chemical COX inhibition may exert other pharmacological effects in addition to inhibition of COX activity, the aim of this study was to explore the role of COX-2 in experimental diabetic neuropathy, using a COX-2 knockout mouse model. Here we provide evidence that COX-2 inactivation had a protective effect against diabetes-induced motor and sensory nerve conduction slowing and impaired nerve antioxidative defense that were clearly manifest in the wild-type (COX-2(+/+)) diabetic mice. These preliminary data support the role of the activation of the COX-2 pathway in mediating sensory and motor nerve conduction velocity deficits in EDN. These findings also suggest that the COX-2 pathway seems to be an important modulator of oxidative stress in EDN.

Angiotensin-Converting Enzyme Inhibitors and Angiotensin II Receptor Blockers Effectively and Directly Potentiate Superoxide Scavenging by Polymorphonuclear Leukocytes from Patients with Type 2 Diabetes Mellitus

BACKGROUND

Angiotensin-converting enzyme inhibitors (ACEIs) and angiotensin II type 1 receptor blockers (ARBs) have potent antioxidant effects in addition to antihypertensive effects.

METHODS

We investigated the ability of ACEIs and ARBs to enhance the superoxide scavenging ability of polymorphonuclear leukocytes (PMNLs) from type 2 diabetic patients (n = 32) and healthy subjects (n = 32). The scavenging ability (U/10(3) cells) of superoxide was measured by electron spin resonance. We used ascorbic acid as a positive control antioxidant and tested captopril, temocapril (an inactive form of ACEI), and temocaprilate (an active form of ACEI) as ACEIs, as well as RNH-6270 as an ARB.

RESULTS

Captopril, temocaprilate, and RNH-6270 showed dose-dependent enhancement in scavenging ability. The scavenging ability with captopril and temocaprilate was greater than with RNH-6270. The changes in scavenging ability induced by all of the drugs in diabetic patients were similar to the changes in healthy subjects. A high-glucose medium (400-800 mg/dL) greatly attenuated the drug-induced enhancement of scavenging ability.

CONCLUSIONS

We demonstrated that both ACEIs and ARBs enhance superoxide scavenging by PMNLs from type 2 diabetic patients and that a high-glucose environment markedly attenuates the ability of these drugs to augment superoxide scavenging.

Prevention and partial reversal of diabetes-induced changes in enteric nerves of the rat ileum by combined treatment with alpha-lipoic acid and evening primrose oil

Treatment with alpha-lipoic acid (LA) or evening primrose oil (EPO), individually, fails to prevent diabetes-induced changes in enteric nerves. Since synergy between these treatments has been reported, the aim was to investigate the effectiveness of combined LA/EPO treatment. LA and EPO were administered in the diet (approximately 80 and 200 mg/kg/day, respectively) to control and diabetic (induced by streptozotocin, 65 mg/kg, i.p.) rats. For prevention, treatment started after 1 week and lasted 7 weeks. For reversal, treatment lasted 4 weeks and was initiated after 8 weeks. Nerves supplying the ileum containing vasoactive intestinal polypeptide (VIP), calcitonin gene-related peptide (CGRP) and noradrenaline (NA) were examined immunohistochemically or biochemically. Diabetes caused a significant increase in VIP-containing cell bodies (p<0.001), decrease in NA content (p<0.01) and loss of CGRP-immunoreactivity. LA/EPO treatment totally prevented diabetes-induced changes in VIP (p<0.001) and CGRP and partially reversed (p<0.05) these changes once they had been allowed to develop. In contrast, treatment had no effect on diabetes-induced changes in NA-containing nerves. Therefore, LA and EPO are only effective at treating diabetes-induced changes in some enteric nerves when administered in combination. However, diabetes-induced changes in NA-containing nerves are resistant to treatment.

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.

Differential metabolism of dihomo-gamma-linolenic acid and arachidonic acid by cyclo-oxygenase-1 and cyclo-oxygenase-2: implications for cellular synthesis of prostaglandin E1 and prostaglandin E2

Prostaglandin (PG) E(1) has been shown to possess anti-inflammatory properties and to modulate vascular reactivity. These activities are sometimes distinct from those of PGE(2), suggesting that endogenously produced PGE(1) may have some beneficial therapeutic effects compared with PGE(2). Increasing the endogenous formation of PGE(1) requires optimization of two separate processes, namely, enrichment of cellular lipids with dihomo-gamma-linolenic acid (20:3 n-6; DGLA) and effective cyclo-oxygenase-dependent oxygenation of substrate DGLA relative to arachidonic acid (AA; 20:4 n-6). DGLA and AA had similar affinities (K(m) values) and maximal reaction rates (V(max)) for cyclo-oxygenase-2 (COX-2), whereas AA was metabolized preferentially by cyclo-oxygenase-1 (COX-1). To overcome the kinetic preference of COX-1 for AA, CP-24879, a mixed Delta(5)/Delta(6) desaturase inhibitor, was used to enhance preferential accumulation of DGLA over AA in cells cultured in the presence of precursor gamma-linolenic acid (18:3 n-6). This protocol was tested in two cell lines and both yielded a DGLA/AA ratio of approx. 2.8 in the total cellular lipids. From the enzyme kinetic data, it was calculated that this ratio should offset the preference of COX-1 for AA over DGLA. PGE(1) synthesis in the DGLA-enriched cells was increased concurrent with a decline in PGE(2) formation. Nevertheless, PGE(1) synthesis was still substantially lower than that of PGE(2). It appears that employing a dietary or a combined dietary/pharmacological paradigm to augment the cellular ratio of DGLA/AA is not an effective route to enhance endogenous synthesis of PGE(1) over PGE(2), at least in cells/tissues where COX-1 predominates over COX-2.

Effects of protein kinase Cbeta inhibition on neurovascular dysfunction in diabetic rats: interaction with oxidative stress and essential fatty acid dysmetabolism

BACKGROUND

Elevated protein kinase C (PKC) activity is thought to play a substantial role in the aetiology of diabetic microvascular complications, the PKCbeta isoform being identified as particularly important. Neuropathy has a vascular component; therefore, one aim was to assess whether the PKCbeta inhibitor, LY333531, could correct nerve conduction velocity (NCV) and perfusion deficits in diabetic rats. Neurovascular dysfunction also depends on oxidant stress and impaired omega-6 essential fatty acid metabolism; correctable by antioxidant and gamma-linolenic acid (GLA) treatments, respectively. A second aim was to assess whether there were interactions between these mechanisms and PKCbeta-mediated effects.

METHODS

Diabetes was induced by streptozotocin; duration was 8 weeks. NCV was monitored and blood flow was assessed by hydrogen clearance microelectrode polarography.

RESULTS

Diabetes caused 19.7% and 13.9% reductions in sciatic motor and saphenous sensory NCV, respectively. Two weeks of LY333531 treatment dose-dependently corrected these deficits. A dose of 10 mg kg(-1) day(-1) gave non-diabetic NCV values and also completely corrected a 50% diabetic reduction in sciatic endoneurial blood flow. Low-dose (0.25 mg kg(-1) day(-1)) LY333531 had modest effects ( approximately 20% correction) on NCV and sciatic perfusion. However, when combined with equi-effective doses of the antioxidants vitamin E or alpha-lipoic acid, or GLA, motor and sensory NCV and sciatic nerve perfusion were in the non-diabetic range. The joint effect was equivalent to that of the 10 mg kg(-1) day(-1) LY333531 dose, demonstrating synergism between PKCbeta, oxidative stress and essential fatty acid mechanisms.

CONCLUSIONS

LY333531, alone or combined with antioxidants or GLA, could form the basis for therapeutic intervention in neuropathy, which requires assessment in clinical trials.

High glucose concentrations abolish the superoxide dismutase response of leukocytes to ascorbic acid or troglitazone in type 2 diabetes mellitus

The hypoglycemic drug, troglitazone (TGZ) has antioxidant activity. Superoxide dismutase (SOD) removes superoxide produced by cells. We measured the response of SOD-like activity (deltaSOD) to ascorbic acid (AA) or TGZ using electron spin resonance at various glucose concentrations in polymorphonuclear leukocytes from 18 type 2 diabetic patients and 18 healthy controls. In control and diabetic subjects, ASOD in response to AA was dose-dependent (maximal effect at 100 ng/ml). Maximal response occurred 2 min after AA addition (50 ng/ml). In cells from diabetic patients, ASOD with 25 ng/ml AA was significantly less than for healthy controls. The deltaSOD with AA changed little at glucose concentration from 0 to 200 mg/dl. In patient and control cells, higher glucose concentrations (400 to 800 mg/dl) reduced ASOD with AA. Response patterns with TGZ resembled those with AA. deltaSOD with AA correlated positively with glycosylated hemoglobin A1c.

CONCLUSIONS

The present data suggest that an amerioration of blood glucose on high levels in diabetic patients plays an important role in an antioxidant efficacy of TGZ and AA on leukocytes in patients.

Cataract development in diabetic sand rats treated with alpha-lipoic acid and its gamma-linolenic acid conjugate

BACKGROUND

Diabetes commonly leads to long-term complications such as cataract. This study investigated the effects of alpha-lipoic acid (LPA) and its gamma-linolenic acid (GLA) conjugate on cataract development in diabetic sand rats.

METHODS

Two separate experiments were conducted. In Experiment 1, sand rats were fed a "high-energy" diet (70% starch), an acute model of Type 2 diabetes, and injected with LPA. In Experiment 2, the animals received a "medium-energy" diet (59% starch), a chronic diabetic model, and were intubated with LPA or its GLA conjugate. Throughout the experiments, blood glucose levels and cataract development were measured. At the termination of the experiments, lens aldose reductase (AR) activity and lenticular reduced glutathione (GSH) levels were analyzed.

RESULTS

LPA injection significantly inhibited cataract development and reduced blood glucose levels in rats fed the "high-energy" diet. Lens AR activity tended to be lower, while lenticular GSH levels increased. In sand rats fed a "medium-energy" diet (59% starch), LPA intubation had no effect on blood glucose levels and cataract development but GSH levels were increased. In contrast, sand rats intubated with GLA conjugate showed the highest blood glucose levels and accelerated cataract development. The conjugate treatment also decreased lenticular GSH content.

CONCLUSIONS

The hypoglycemic effects of LPA are beneficial in the prevention of acute symptoms of Type 2 diabetes. It remains to be shown that the antioxidant activity of LPA is responsible for prevention or inhibition of cataract progression in sand rats.

Effects of antioxidants on nerve and vascular dysfunction in experimental diabetes

Reactive oxygen species (ROS) are elevated by metabolic changes in diabetes, including autoxidation and increased advanced glycation. Endogenous protection by the glutathione redox cycle is also compromised by the competing NADPH requirement of elevated polyol pathway flux. Antioxidant treatment strategies prevent or reverse nerve conduction velocity (NCV) deficits in diabetic rats. These include lipophilic scavengers such as butylated hydroxytoluene, probucol and vitamin E, more hydrophilic agents like alpha-lipoic acid and acetyl cysteine, and transition metal chelators that inhibit autoxidation. In the long-term, elevated ROS cause cumulative damage to neurons and Schwann cells, however, they also have a deleterious effect on nerve blood flow in the short term. This causes endoneurial hypoxia, which is responsible for early NCV deficits. Antioxidant treatment corrects the blood flow deficit and promotes normal endoneurial oxygenation. ROS cause antioxidant-preventable vascular endothelium abnormalities, neutralizing nitric oxide mediated vasodilation and increasing reactivity to vasoconstrictors. Unsaturated fatty acids are a major target for ROS and essential fatty acid metabolism is impaired by diabetes. Gamma-linolenic acid stimulates vasodilator prostanoid production, and there are marked synergistic interactions between gamma-linolenic acid and antioxidants. This has encouraged the development of novel drugs such as ascorbyl-gamma-linolenic acid and gamma-linolenic acid-lipoic acid with enhanced therapeutic potential.

Glucose-induced oxidative stress and programmed cell death in diabetic neuropathy

The Diabetes Control and Complications Trial (DCCT) established the importance of hyperglyemia and other consequences of insulin deficiency in the pathogenesis of diabetic neuropathy, but the precise mechanisms by which metabolic alterations produce peripheral nerve fiber damage and loss remain unclear. Emerging data from human and animal studies suggest that glucose-derived oxidative stress may play a central role, linking together many of the other currently invoked pathogenetic mechanisms such as the aldose reductase and glycation pathways, vascular dysfunction, and impaired neurotrophic support. These relationships suggest combinations of pharmacological interventions that may synergistically protect the peripheral nervous system (PNS) against the metabolic derangements of diabetes mellitus.

Metabolic effects of gamma-linolenic acid-alpha-lipoic acid conjugate in streptozotocin diabetic rats

Data suggesting the involvement of increased oxidative stress in the pathophysiology of diabetes has raised interest in the potential therapeutic benefit of antioxidants. Although beneficial metabolic effects of antioxidant supplementation have been suggested, an antioxidant mode of action, particularly in skeletal muscle, has not been documented. In the present study, we evaluate the metabolic effects of a gamma-linolenic acid-alpha-lipoic acid conjugate (GLA-LA) in streptozotocin-induced diabetic rats, and assess its potential mode of action by comparing its effects with equimolar administration of LA and GLA alone. Ten days of oral supplementation of 20 mg/kg body weight GLA-LA, but not LA or GLA alone, caused a mild reduction in fasting blood glucose concentration as compared with vehicle-treated diabetic rats (375 +/- 11 vs. 416 +/- 16 mg/dl, p = 0.03), with no change in fasting plasma insulin levels. A peripheral insulin-sensitizing effect could be observed with GLA-LA, LA, and GLA treatments, as demonstrated by a significant (p < 0.04) 23%, 13%, and 10% reduction, respectively, in the area under the glucose curve following an intravenous insulin tolerance test. This effect was associated with a 67% and 50% increase in GLUT4 protein content in the membranes of gastrocnemius muscle of GLA-LA and LA-treated animals, respectively; however, no change was observed with GLA treatment alone. Interestingly, both GLA-LA and LA treatments corrected a diabetes-related decrease in the gastrocnemius muscle low-molecular-weight reduced thiols content. These data demonstrate insulin-sensitizing properties of the GLA-LA conjugate by distinct mechanisms attributable to each of its components, which are associated with antioxidant effects.

Importance of dietary gamma-linolenic acid in human health and nutrition

Considerable debate remains regarding the distinct biological activities of individual polyunsaturated fatty acids (PUFA). One of the most interesting yet controversial dietary approaches has been the possible prophylactic role of dietary gamma-linolenic acid (GLA) in treating various chronic disease states. This strategy is based on the ability of diet to modify cellular lipid composition and eicosanoid (cyclooxygenase and lipoxygenase) biosynthesis. Recent studies demonstrate that dietary GLA increases the content of its elongase product, dihomo-gamma-linolenic acid (DGLA), within cell membranes without concomitant changes in arachidonic acid (AA). Subsequently, upon stimulation, DGLA can be converted by inflammatory cells to 15-(S)-hydroxy-8,11,13-eicosatrienoic acid and prostaglandin E1. This is noteworthy because these compounds possess both anti-inflammatory and antiproliferative properties. Although an optimal feeding regimen to maximize the potential benefits of dietary GLA has not yet been determined, it is the purpose of this review to summarize the most recent research that has focused on objectively and reproducibly determining the mechanism(s) by which GLA may ameliorate health problems.

Effect of gammalinolenic acid, dihomogammalinolenic acid, ascorbyl-6-gammalinolenic acid, and ascorbyl-6-dihomo gammalinolenic acid on histamine- and methacholine-induced contraction of the isolated guinea pig tracheal chain

The relaxant effects of gammalinolenic acid (GLA) and dihomo gammalinolenic acid (DGLA) were compared to the relaxant effect of arachidonic acid (AA). The effect of the combination of ascorbate to form the novel drugs ascorbyl-6-gammalinolenic acid (ascorbyl-6-GLA) and ascorbyl-6-dihomo gammalinolenic acid (ascorbyl-6-DGLA) were investigated and the role of the epithelial cells was determined. Salbutamol was used as control. The isolated tracheas of six to eight guinea pigs were used in each experiment and suspended in organ baths filled with Krebs-Henseleit solution and aerated with 95% O2 and 5% CO2. The relaxant effects produced for histamine-contracted preparations were as follows: AA=71.2+/-0.2%, GLA=55.2+/-4.2%, DGLA=69.8+/-3.9%, ascorbyl-6-GLA =26.2+/-5.1% and ascorbyl-6-DGLA=54.5+/-2.4%. For methacholine-contracted preparations: AA=46.6+/-3.2%, GLA=55.0+/-9.5%, DGLA=61.8+/-2.7%, ascorbyl-6-GLA=40.0+/-8.0% and ascorbyl-6-DGLA=88.0+/-15.3%. Ascorbyl-6-GLA and ascorbyl-6-DGLA had mainly a decreased relaxant effect compared to GLA and DGLA, except ascorbyl-6-DGLA after methacholine-induced contraction, which showed a significant increased relaxant effect. The removal of the epithelium showed decreased relaxant effects for the drugs except AA, which showed increased values after methacholine contraction. Histamine-contracted preparations showed varied results. Ascorbyl-6-GLA showed an increased relaxant effect, DGLA was unaffected with no additional effect, and AA, GLA and ascorbyl-6-DGLA showed decreased relaxant effects. In conclusion, it is clear that the contractant and the availability of epithelial cells could ultimately determine the results, though the mechanism remains very complex. The benefit of added ascorbate is still unclear and warrants more investigation.

Cilazapril and dietary gamma-linolenic acid prevent the deficit in sciatic nerve conduction velocity in the streptozotocin diabetic rat

Young adult male Hooded Wistar rats were rendered diabetic by administration of streptozotocin and maintained for 5 weeks on a diet containing either 6% olive oil as the total source of fat (OO diet), or purified gamma-linolenic acid (GLA) at a concentration of 0.5% with the remaining 5.5% provided by olive oil (GLA diet). Rats were treated with the angiotensin converting inhibitor, cilazapril, administered in the drinking water at a dose of 20 mg kg-1 body weight day-1. For the OO diet groups, sciatic nerve conduction velocity (NCV) in diabetic rats was reduced by 32% (p < 0.01) in comparison with nondiabetic (vehicle-treated) rats and 27.5% (p < 0.05) in comparison with diabetic rats treated with cilazapril. Diabetic, cilazapril-treated rats showed no reduction in NCV. For the nondiabetic, diabetic, and diabetic plus cilazapril groups fed GLA, the NCV was not significantly different, indicating that dietary GLA also prevented the deficit in the NCV induced by the diabetic state. Analysis of the sciatic nerve endoneurial phospholipid fatty acids revealed a significant reduction in the proportion of GLA and an elevation in the proportion of linoleic acid in the diabetic groups compared with the nondiabetic groups and this was independent of the cilazapril treatment or the dietary lipid supplement. Sciatic nerve myo-inositol content was unaltered while mannose, fructose, glucose, and sorbitol levels were elevated in the diabetic groups and these changes were independent of the cilazapril treatment or the dietary lipid supplement. These results indicate that in the rat, cilazapril treatment or dietary GLA, at the doses tested, are effective in preventing the deficit in the NCV induced by diabetes.

Effects of dietary supplementation with arachidonic acid rich oils on nerve conduction and blood flow in streptozotocin-diabetic rats

Diabetes mellitus is associated with defective essential fatty acid desaturation. In experimental models this contributes to characteristic reductions in peripheral nerve conduction velocity (NCV) and blood flow, which may be corrected by dietary supplementation with gamma-linolenic acid (GLA) rich oils to bypass the delta-6 desaturation deficit. There is debate about the mechanism of this improvement, including whether it depends on synthesis of series 1 prostanoids derived from di-homo GLA or series 2 prostanoids from arachidonic acid (ARA). The aim was to assess the efficacy of two ARA-rich (approximately 39% content) oils in correcting neurovascular dysfunction in streptozotocin-induced diabetic rats. After 6 weeks of untreated diabetes, rats were treated for a further 2 weeks with 1% dietary oil supplements before assessment of sciatic motor NCV and endoneurial blood flow. NCV was 19% reduced in diabetic rats and this was largely (approximately 86%) corrected by both oil treatments. A 48% deficit in endoneurial nutritive blood flow with diabetes was approximately 70% reversed by the two oils, vascular conductance being in the non-diabetic range. Thus, nerve conduction and perfusion deficits in diabetic rats are corrected by ARA-rich oil treatment. The magnitudes of these changes were similar to expectations based on previous studies of GLA-rich oils, therefore it is likely that the neurovascular effect of increased synthesis of series 2 prostanoids makes a major contribution to the beneficial action of n-6 essential fatty acids in experimental diabetic neuropathy.

Neurovascular effects of L-carnitine treatment in diabetic rats

The aims were to ascertain whether L-carnitine could prevent nerve blood flow and conduction deficits in 1-month diabetic rats and to examine potential neurovascular mechanisms using co-treatment with the nitric oxide synthase inhibitor, NG-nitro-L-arginine. A 19.8% diabetic deficit in sciatic motor conduction velocity was 57.4% attenuated by L-carnitine treatment. Similarly, a 47.7% reduction in sciatic nutritive (capillary) endoneurial blood flow was 48.6% blocked by L-carnitine. Joint treatment with NG-nitro-L-arginine completely abolished the effects on nerve conduction and nutritive flow. However, L-carnitine treatment did not alter a 50.8% diabetic deficit in total sciatic endoneurial flow, which was further depressed (61%) by NG-nitro-L-arginine co-treatment. Thus, the effect of L-carnitine on nerve conduction in diabetic rats depends on changes in the endoneurial perfusion pattern by an action that may involve the nitric oxide system of vasa nervorum.