Effects of alpha-lipoic acid on endothelial function in aged diabetic and high-fat fed rats

High L-carnitine concentrations do not prevent late diabetic complications in type 1 and 2 diabetic patients

Increased intake of L-carnitine, a cofactor in cellular energy metabolism, is recommended for diabetic patients with late complications. However, its clinical benefits remain controversial. We hypothesized that patients with low L-carnitine levels would have an increased rate of diabetic complications. To test this hypothesis, we evaluated the relationship of L-carnitine concentrations in blood with the prevalence and severity of late diabetic complications in type 1 and 2 diabetic patients. Human blood samples were collected from 93 and 87 patients diagnosed as having type 1 or type 2 diabetes, respectively, and 122 nondiabetic individuals. The determination of free L-carnitine concentrations in whole blood lysates was performed using ultra-performance liquid chromatography with tandem mass spectrometry. In diabetic patients, diabetic complications such as neuropathy, retinopathy, nephropathy, or hypertension were recorded. The average L-carnitine concentration in the blood of control subjects was 33 ± 8 nmol/mL, which was not significantly different from subgroups of patients with type 1 (32 ± 10 nmol/mL) or type 2 diabetes (36 ± 11 nmol/mL). Patients with low (<20 nmol/mL) l-carnitine levels did not have increased occurrences of late diabetic complications. In addition, patient subgroups with higher L-carnitine concentrations did not have decreased prevalence of late diabetic complications. Our results provide evidence that higher L-carnitine concentrations do not prevent late diabetic complications in type 1 and 2 diabetic patients.

Methylglyoxal promotes oxidative stress and endothelial dysfunction

Modern diets can cause modern diseases. Research has linked a metabolite of sugar, methylglyoxal (MG), to the development of diabetic complications, but the exact mechanism has not been fully elucidated. The present study was designed to investigate whether MG could directly influence endothelial function, oxidative stress and inflammation in Wistar and Goto-Kakizaki (GK) rats, an animal model of type 2 diabetes. Wistar and GK rats treated with MG in the drinking water for 3 months were compared with the respective control rats. The effects of MG were investigated on NO-dependent vasorelaxation in isolated rat aortic arteries from the different groups. Insulin resistance, NO bioavailability, glycation, a pro-inflammatory biomarker monocyte chemoattractant protein-1 (MCP-1) and vascular oxidative stress were also evaluated. Methylglyoxal treated Wistar rats significantly reduced the efficacy of NO-dependent vasorelaxation (p<0.001). This impairment was accompanied by a three fold increase in the oxidative stress marker nitrotyrosine. Advanced glycation endproducts (AGEs) formation was significantly increased as well as MCP-1 and the expression of the receptor for AGEs (RAGE). NO bioavailability was significantly attenuated and accompanied by an increase in superoxide anion immunofluorescence. Methylglyoxal treated GK rats significantly aggravated endothelial dysfunction, oxidative stress, AGEs accumulation and diminished NO bioavailability when compared with control GK rats. These results indicate that methylglyoxal induced endothelial dysfunction in normal Wistar rats and aggravated the endothelial dysfunction present in GK rats. The mechanism is at least in part by increasing oxidative stress and/or AGEs formation with a concomitant increment of inflammation and a decrement in NO bioavailability. The present study provides further evidence for methylglyoxal as one of the causative factors in the pathogenesis of atherosclerosis and development of macrovascular diabetic complication.

Diabetes and alpha lipoic Acid

Diabetes mellitus is a multi-faceted metabolic disorder where there is increased oxidative stress that contributes to the pathogenesis of this debilitating disease. This has prompted several investigations into the use of antioxidants as a complementary therapeutic approach. Alpha lipoic acid, a naturally occurring dithiol compound which plays an essential role in mitochondrial bioenergetic reactions, has gained considerable attention as an antioxidant for use in managing diabetic complications. Lipoic acid quenches reactive oxygen species, chelates metal ions, and reduces the oxidized forms of other antioxidants such as vitamin C, vitamin E, and glutathione. It also boosts antioxidant defense system through Nrf-2-mediated antioxidant gene expression and by modulation of peroxisome proliferator activated receptors-regulated genes. ALA inhibits nuclear factor kappa B and activates AMPK in skeletal muscles, which in turn have a plethora of metabolic consequences. These diverse actions suggest that lipoic acid acts by multiple mechanisms, many of which have only been uncovered recently. In this review we briefly summarize the known biochemical properties of lipoic acid and then discussed the oxidative mechanisms implicated in diabetic complications and the mechanisms by which lipoic acid may ameliorate these reactions. The findings of some of the clinical trials in which lipoic acid administration has been tested in diabetic patients during the last 10 years are summarized. It appears that the clearest benefit of lipoic acid supplementation is in patients with diabetic neuropathy.

Lycopene attenuates endothelial dysfunction in streptozotocin-induced diabetic rats by reducing oxidative stress

CONTEXT

Diabetes mellitus is characterized by oxidative stress, which in turn induces endothelial dysfunction. As a potent antioxidant compound, lycopene might rescue diabetic endothelial dysfunction by reducing oxidative stress.

OBJECTIVE

The present study investigated whether lycopene could lower oxidative stress and attenuate endothelial dysfunction in diabetic rats.

METHODS

Different doses of lycopene (10, 30, and 60 mg/kg/day, p.o.) were administered for 30 days to streptozotocin (STZ) (60 mg/kg)-induced diabetic rats. Biochemical parameters and aortic malondialdehyde (MDA) content, superoxidase dismutase (SOD) activity, nitric oxide (NO) levels, constitutive NOS (cNOS) activity, and inducible NOS (iNOS) activity were determined. Endothelium-dependent and endothelium-independent vasorelaxation were measured in aortas for estimating endothelial function.

RESULTS

Compared with normal controls, endothelial function was significantly reduced in diabetic rats and the blunted endothelial function was dependently ameliorated with lycopene treatment. Compared with normal controls, the serum oxidized low-density lipoprotein (ox-LDL) levels, the aortic MDA levels, and iNOS activity in diabetic rats were increased by 113, 197, and 100%, respectively, whereas aortic SOD activity, NO levels, and cNOS activity were decreased by 73, 53, and 65%, respectively. Exogenous administration of lycopene to diabetic rats caused a dose-dependent decrease of serum glucose and ox-LDL levels, an increase of aortic SOD activity, NO levels, and cNOS activity, and a decrease of aortic MDA levels and iNOS activity.

CONCLUSION

Chronic lycopene treatment could attenuate endothelial dysfunction by reducing oxidative stress in STZ-induced diabetic rats. These results indicate that chronic lycopene treatment might be useful in preventing diabetic vascular complications associated with endothelial dysfunction.

Metformin restores endothelial function in aorta of diabetic rats

BACKGROUND AND PURPOSE

The effects of metformin, an antidiabetic agent that improves insulin sensitivity, on endothelial function have not been fully elucidated. This study was designed to assess the effect of metformin on impaired endothelial function, oxidative stress, inflammation and advanced glycation end products formation in type 2 diabetes mellitus.

EXPERIMENTAL APPROACH

Goto-Kakizaki (GK) rats, an animal model of nonobese type 2 diabetes, fed with normal and high-fat diet during 4 months were treated with metformin for 4 weeks before evaluation. Systemic oxidative stress, endothelial function, insulin resistance, nitric oxide (NO) bioavailability, glycation and vascular oxidative stress were determined in the aortic rings of the different groups. A pro-inflammatory biomarker the chemokine CCL2 (monocyte chemoattractant protein-1) was also evaluated.

KEY RESULTS

High-fat fed GK rats with hyperlipidaemia showed increased vascular and systemic oxidative stress and impaired endothelial-dependent vasodilatation. Metformin treatment significantly improved glycation, oxidative stress, CCL2 levels, NO bioavailability and insulin resistance and normalized endothelial function in aorta.

CONCLUSION AND IMPLICATIONS

Metformin restores endothelial function and significantly improves NO bioavailability, glycation and oxidative stress in normal and high-fat fed GK rats. This supports the concept of the central role of metformin as a first-line therapeutic to treat diabetic patients in order to protect against endothelial dysfunction associated with type 2 diabetes mellitus.

Impact of α-lipoic acid on liver peroxisome proliferator-activated receptor-α, vascular remodeling, and oxidative stress in insulin-resistant rats

This study sought to determine the impact of α-lipoic acid (LA) on superoxide anion (O(2)(•-)) production and peroxisome proliferator-activated receptor-α (PPARα) expression in liver tissue, plasma free fatty acids (FFA), and aortic remodeling in a rat model of insulin resistance. Sprague-Dawley rats (50-75 g) were given either tap water or a drinking solution containing 10% D-glucose for 14 weeks, combined with a diet with or without LA supplement. O(2)(•-) production was measured by lucigenin chemiluminescence, and PPAR-α expression by Western blotting. Cross-sectional area (CSA) of the aortic media and lumen and number of smooth muscle cells (SMC) were determined histologically. Glucose increased systolic blood pressure (SBP), plasma levels of glucose and insulin, and insulin resistance (HOMA index). All of these effects were attenuated by LA. Whereas glucose had no effect on liver PPAR-α protein level, it decreased plasma FFA. LA decreased the aortic and liver O(2)(•-) production, body weight, and plasma FFA levels in control and glucose-treated rats. Liver PPAR-α protein levels were increased by LA, and negatively correlated with plasma FFA. Medial CSA was reduced in all glucose-treated rats, and positively correlated with plasma FFA but not with SBP or aortic O(2)(•-) production. Glucose also reduced aortic lumen area, so that the media-to-lumen ratio remained unchanged. The ability of LA to lower plasma FFA appears to be mediated, in part, by increased hepatic PPAR-α expression, which may positively affect insulin resistance. Glucose-fed rats may serve as a unique model of aortic atrophic remodeling in hypertension and early metabolic syndrome.

Atorvastatin exerts its anti-atherosclerotic effects by targeting the receptor for advanced glycation end products

Recent studies demonstrated the beneficial role of atorvastatin in reducing the risk of cardiovascular morbidity and mortality in patients with diabetes mellitus and/or metabolic syndrome. To investigate the mechanisms underlying the anti-atheroscleroic action of atorvastatin, we examined the expression of the receptor for advanced glycation end products (RAGE) and its downstream target gene, monocyte chemoattractant protein-1 (MCP-1) using real-time PCR. In in vitro studies, exposure to high glucose or AGE induced oxidative stress and activation of the AGE/RAGE system in human umbilical vein endothelial cells. Treatment of the cells with atorvastatin significantly released the oxidative stress by restoring the levels of glutathione and inhibited the RAGE upregulation. In diabetic Goto Kakisaki (GK) rats fed with a high-fat diet for 12weeks, RAGE and MCP-1 were upregulated in the aortas, and there was a significant correlation between RAGE and MCP-1 mRNA abundance (r=0.482, P=0.031). Treatment with atorvastatin (20mg/kg qd) significantly downregulated the expression of RAGE and MCP-1. These data thus demonstrate a novel "pleiotropic" activity of atorvastatin in reducing the risk of cardiovascular diseases by targeting RAGE expression.

A Regenerative Antioxidant Protocol of Vitamin E and α-Lipoic Acid Ameliorates Cardiovascular and Metabolic Changes in Fructose-Fed Rats

Type 2 diabetes is a major cause of cardiovascular disease. We have determined whether the metabolic and cardiovascular changes induced by a diet high in fructose in young adult male Wistar rats could be prevented or reversed by chronic intervention with natural antioxidants. We administered a regenerative antioxidant protocol using two natural compounds: α-lipoic acid together with vitamin E (α-tocopherol alone or a tocotrienol-rich fraction), given as either a prevention or reversal protocol in the food. These rats developed glucose intolerance, hypertension, and increased collagen deposition in the heart together with an increased ventricular stiffness. Treatment with a fixed combination of vitamin E (either α-tocopherol or tocotrienol-rich fraction, 0.84 g/kg food) and α-lipoic acid (1.6 g/kg food) normalized glucose tolerance, blood pressure, cardiac collagen deposition, and ventricular stiffness in both prevention and reversal protocols in these fructose-fed rats. These results suggest that adequate antioxidant therapy can both prevent and reverse the metabolic and cardiovascular damage in type 2 diabetes.

α-Lipoic acid ameliorates foam cell formation via liver X receptor α-dependent upregulation of ATP-binding cassette transporters A1 and G1

α-Lipoic acid (α-LA), a key cofactor in cellular energy metabolism, has protective activities in atherosclerosis, yet the detailed mechanisms are not fully understood. In this study, we examined whether α-LA affects foam cell formation and its underlying molecular mechanisms in murine macrophages. Treatment with α-LA markedly attenuated oxidized low-density lipoprotein (oxLDL)-mediated cholesterol accumulation in macrophages, which was due to increased cholesterol efflux. Additionally, α-LA treatment dose-dependently increased protein levels of ATP-binding cassette transporter A1 (ABCA1) and ABCG1 but had no effect on the protein expression of SR-A, CD36, or SR-BI involved in cholesterol homeostasis. Furthermore, α-LA increased the mRNA expression of ABCA1 and ABCG1. The upregulation of ABCA1 and ABCG1 by α-LA depended on liver X receptor α (LXRα), as evidenced by an increase in the nuclear levels of LXRα and LXRE-mediated luciferase activity and its prevention of the expression of ABCA1 and ABCG1 after inhibition of LXRα activity by the pharmacological inhibitor geranylgeranyl pyrophosphate (GGPP) or knockdown of LXRα expression with small interfering RNA (siRNA). Consistently, α-LA-mediated suppression of oxLDL-induced lipid accumulation was abolished by GGPP or LXRα siRNA treatment. In conclusion, LXRα-dependent upregulation of ABCA1 and ABCG1 may mediate the beneficial effect of α-LA on foam cell formation.

The role of oxidative stress and effect of alpha-lipoic acid in reexpansion pulmonary edema - an experimental study

INTRODUCTION

We investigated the role of oxidative stress in the pathogenesis of reexpansion pulmonary edema (RPE) and effect of alpha-lipoic acid (ALA) in the prevention of RPE.

MATERIAL AND METHODS

There were 4 groups consisting of 10 rats in each group; control group (CG), α-lipoic acid group (ALAG), reexpansion pulmonary edema group (RPEG), reexpansion pulmonary edema plus α-lipoic acid group (RPE + ALAG). In all the groups, all rats were sacrificed 2 hours after the reexpansion of lungs. To indicate oxidative stress malondialdehyde (MDA), and to indicate antioxidant status superoxide dismutase (SOD), catalase (CAT) and glutathione peroxides (GPx) were measured in the lungs of rats.

RESULTS

Mean MDA value was lower in CG (7.02 ±0.14) and in ALAG (6.95 ±0.11) than the other groups (p = 0.001). It was highest in RPEG (8.89 ±0.21) (p = 0.001). It was lower in RPE + ALA G (7.21 ±0.32) than RPEG (p = 0.001). Antioxidant levels: GPx (37.21 ±3.01), CAT (2.87 ±0.14) and SOD (100.12 ±12.39) were lowest in RPEG among all groups (p = 0.001). These values were GPx (45.21 ±3.54), CAT (3.24 ±0.21) and SOD (172.36 ±15.48) in RPE + ALA G and were greater than those of RPEG (p = 0.001). While normal pulmonary parenchyma was seen in 2 rats in RPE + ALAG, it was not seen in RPEG. Pulmonary edema was seen in 1 rat in RPE + ALAG; however, it was seen in 3 in RPEG.

CONCLUSIONS

Oxidative stress might have an important role in the pathogenesis of RPE. In addition, ALA treatment might contribute in preventing RPE.

Enhancement of mesenteric artery contraction to 5-HT depends on Rho kinase and Src kinase pathways in the ob/ob mouse model of type 2 diabetes

BACKGROUND AND PURPOSE

Arteries from hypertensive subjects are reportedly hyperresponsive to 5-hydroxytryptamine (5-HT), but it remains unclear whether this is true in chronic type 2 diabetes. We have assessed responses to 5-HT shown by mesenteric arteries from type 2 diabetic ob/ob mice (27-32 weeks old) and have identified the molecular mechanisms involved.

EXPERIMENTAL APPROACH

Contractions of mesenteric rings to 5-HT were examined in vitro. Activation of mesenteric RhoA, Rho kinase and Src was measured by Western blotting or by modified enzyme-linked immunosorbent assay.

KEY RESULTS

Concentration-dependent contractions to 5-HT were greater in mesenteric rings from the ob/ob than in those from the age-matched control ('Lean') group. In each group, there was no significant change in the 5-HT-induced contractions after inhibition of nitric oxide synthase (with N(G)-nitro-L-arginine), of cyclooxygenase (with indomethacin) or of protein kinase C (with chelerythrine). However inhibition of the MEK/ERK pathway (with PD98059) decreased the response to 5-HT. Although the diabetes-related enhancement of the 5-HT response was preserved with each of these inhibitors, enhancement was abolished by a Rho kinase inhibitor (Y27632) and by Src kinase inhibitors (PP1 analogue or Src kinase inhibitor I). 5-HT-induced activation of RhoA, Rho kinase and Src kinase in mesenteric arteries was greater in the ob/ob than in the Lean group, but the expression of RhoA, Rho kinase isoforms and Src did not differ between these groups.

CONCLUSIONS AND IMPLICATIONS

These results suggest that the enhancement of 5-HT-induced contraction in mesenteric arteries from ob/ob mice may be attributable to increased activation of RhoA/Rho kinase and Src kinase.

The use of alpha-lipoic acid (ALA), gamma linolenic acid (GLA) and rehabilitation in the treatment of back pain: effect on health-related quality of life

The aim of this trial was to evaluate the effects of alpha-lipoic acid (ALA) and gamma-linolenic acid (GLA) and the beneficial effect of physical exercise on positive sensory symptoms and neuropathic pain in patients with compressive radiculopathy syndrome from disc-nerve root conflict. Often these painful syndromes after the acute event, tend to recurr becoming subacute or chronic syndromes that become for the period of interest disabiling is an event very important in these cases proper prevention, based on a maintenance drug therapy and the strengthening exercises of paravertebral muscles, flexibility exercises on the spine and when needed on the reduction of body weight. In this Observational Cohort, two-arm trial, 203 patients were enrolled and divided into two groups, the first, ALA and GLA group, (n = 101) received oral dose of 600 mg of alpha-lipoic acid (ALA) and 360 mg of gamma-linolenic acid (GLA) and a rehabilitation program for six weeks, the second (n = 102) treated with only rehabilitation program. Patients were recruited at the centre of Physical Medicine and Rehabilitation, they underwent a physiatric examination at the primary outcome (t0) and secondary outcomes were recorded at monitoring visits scheduled at two weeks = t1, four weeks = t2, six weeks = t3, and at the same has been administered the following scale: VAS scale, SF-36, Oswestry Low Back Pain Disability Questionnaire, Aberdeen Back Pain Scale (ABPS), Revised Leeds Disability Questionnaire (LDQ), Roland and Morris Disability Questionnaire. Significant improvements was noted in the ALA and GLA group for paresthesia, stabbing and burning pain, as showed by VAS (Visual Analogue Scale), Oswestry Low Back Pain Disability Questionnaire, Aberdeen Low Back Pain Scale; also, improvements of quality of life has been noted, in the same group, as showed by SF-36, LDQ (Revised Leeds Disability Questionnaire), Roland and Morris disability questionnaire. All these outcome measure showed statistically significant decreases. Oral treatment with alpha-lipoic acid (ALA) and gamma-linolenic acid (GLA) for six weeks in synergy with rehabilitation therapy improved neuropathic symptoms and deficits in patients with radicular neuropathy.

Endothelium in pharmacology: 30 years on

In this issue, BJP is proud to publish an Endothelium Themed Section to celebrate the life of Robert F. Furchgott, who died on May 19th 2009. It is 30 years since he discovered endothelium-derived relaxant factor and a decade since he was awarded the Nobel Prize for this work. His discovery has led to an array of new therapeutic targets. The themed section includes three reviews on the pathophysiology of the endothelium and the drug targets that this presents, four research papers and three commentaries on research. This themed section also forms the nucleus of an online Virtual Issue that collects in one place further reviews and research papers on the topic of the 'Endothelium' that BJP and our sister journal BJCP have published in the past year, and that should help researchers and students to find the latest work in this field.

Alpha-lipoic acid as a dietary supplement: molecular mechanisms and therapeutic potential

Alpha-lipoic acid (LA) has become a common ingredient in multivitamin formulas, anti-aging supplements, and even pet food. It is well-defined as a therapy for preventing diabetic polyneuropathies, and scavenges free radicals, chelates metals, and restores intracellular glutathione levels which otherwise decline with age. How do the biochemical properties of LA relate to its biological effects? Herein, we review the molecular mechanisms of LA discovered using cell and animal models, and the effects of LA on human subjects. Though LA has long been touted as an antioxidant, it has also been shown to improve glucose and ascorbate handling, increase eNOS activity, activate Phase II detoxification via the transcription factor Nrf2, and lower expression of MMP-9 and VCAM-1 through repression of NF-kappa B. LA and its reduced form, dihydrolipoic acid, may use their chemical properties as a redox couple to alter protein conformations by forming mixed disulfides. Beneficial effects are achieved with low micromolar levels of LA, suggesting that some of its therapeutic potential extends beyond the strict definition of an antioxidant. Current trials are investigating whether these beneficial properties of LA make it an appropriate treatment not just for diabetes, but also for the prevention of vascular disease, hypertension, and inflammation.

Lipoic acid prevents body weight gain induced by a high fat diet in rats: effects on intestinal sugar transport

Several studies have suggested that oxidative stress might cause and aggravate the inflammatory state associated with obesity and could be the link between excessive weight gain and its related disorders such as insulin resistance and cardiovascular diseases. Thus, antioxidant treatment has been proposed as a therapy to prevent and manage obesity and associated complications. Therefore, the aim of the present study was to investigate the effects of supplementation of a standard or high fat diet with the antioxidant lipoic acid (LA) during 56 days, on body weight gain, adiposity, feed efficiency and intestinal sugar absorption, in male Wistar rats. LA supplementation induced a lower body weight gain and adipose tissue size in both control or high fat fed rats accompanied by a reduction in food intake. The group fed on a high fat diet and treated with LA (OLIP group) showed a lower body weight gain than its corresponding Pair-Fed (PF) group (P < 0.05), which received the same amount of food than LA-treated animals but with no LA. In fact, LA induced a reduction on feed efficiency and also significantly decreased intestinal alpha-methylglucoside (alpha-MG) absorption both in lean and obese rats. These results suggest that the beneficial effects of dietary supplementation with LA on body weight gain are mediated, at least in part, by the reduction observed in food intake and feed efficiency. Furthemore, the inhibitory action of LA on intestinal sugar transport could explain in part the lower feed efficiency observed in LA-treated animals and therefore, highlighting the beneficial effects of LA on obesity.

Protective effects of mildronate in an experimental model of type 2 diabetes in Goto-Kakizaki rats

BACKGROUND AND PURPOSE

Mildronate [3-(2,2,2-trimethylhydrazinium) propionate] is an anti-ischaemic drug whose mechanism of action is based on its inhibition of L-carnitine biosynthesis and uptake. As L-carnitine plays a pivotal role in the balanced metabolism of fatty acids and carbohydrates, this study was carried out to investigate whether long-term mildronate treatment could influence glucose levels and prevent diabetic complications in an experimental model of type 2 diabetes in Goto-Kakizaki (GK) rats.

EXPERIMENTAL APPROACH

GK rats were treated orally with mildronate at doses of 100 and 200 mg.kg(-1) daily for 8 weeks. Plasma metabolites reflecting glucose and lipids, as well as fructosamine and beta-hydroxybutyrate, were assessed. L-carnitine concentrations were measured by ultra performance liquid chromatography with tandem mass spectrometry. An isolated rat heart ischaemia-reperfusion model was used to investigate possible cardioprotective effects. Pain sensitivity was measured with a tail-flick latency test.

KEY RESULTS

Mildronate treatment significantly decreased L-carnitine concentrations in rat plasma and gradually decreased both the fed- and fasted-state blood glucose. Mildronate strongly inhibited fructosamine accumulation and loss of pain sensitivity and also ameliorated the enhanced contractile responsiveness of GK rat aortic rings to phenylephrine. In addition, in mildronate-treated hearts, the necrosis zone following coronary occlusion was significantly decreased by 30%.

CONCLUSIONS AND IMPLICATIONS

These results demonstrate for the first time that in GK rats, an experimental model of type 2 diabetes, mildronate decreased L-carnitine contents and exhibited cardioprotective effects, decreased blood glucose concentrations and prevented the loss of pain sensitivity. These findings indicate that mildronate treatment could be beneficial in diabetes patients with cardiovascular problems.

Endothelial dysfunction and vascular disease

The endothelium can evoke relaxations (dilatations) of the underlying vascular smooth muscle, by releasing vasodilator substances. The best characterized endothelium-derived relaxing factor (EDRF) is nitric oxide (NO). The endothelial cells also evoke hyperpolarization of the cell membrane of vascular smooth muscle (endothelium-dependent hyperpolarizations, EDHF-mediated responses). Endothelium-dependent relaxations involve both pertussis toxin-sensitive G(i) (e.g. responses to serotonin and thrombin) and pertussis toxin-insensitive G(q) (e.g. adenosine diphosphate and bradykinin) coupling proteins. The release of NO by the endothelial cell can be up-regulated (e.g. by oestrogens, exercise and dietary factors) and down-regulated (e.g. oxidative stress, smoking and oxidized low-density lipoproteins). It is reduced in the course of vascular disease (e.g. diabetes and hypertension). Arteries covered with regenerated endothelium (e.g. following angioplasty) selectively loose the pertussis toxin-sensitive pathway for NO release which favours vasospasm, thrombosis, penetration of macrophages, cellular growth and the inflammatory reaction leading to atherosclerosis. In addition to the release of NO (and causing endothelium-dependent hyperpolarizations), endothelial cells also can evoke contraction (constriction) of the underlying vascular smooth muscle cells by releasing endothelium-derived contracting factor (EDCF). Most endothelium-dependent acute increases in contractile force are due to the formation of vasoconstrictor prostanoids (endoperoxides and prostacyclin) which activate TP receptors of the vascular smooth muscle cells. EDCF-mediated responses are exacerbated when the production of NO is impaired (e.g. by oxidative stress, ageing, spontaneous hypertension and diabetes). They contribute to the blunting of endothelium-dependent vasodilatations in aged subjects and essential hypertensive patients.

Lipoic acid significantly restores, in rats, the age-related decline in vasomotion

BACKGROUND AND PURPOSE

The age-related decline in vasorelaxation is largely due to ceramide-induced induction of phosphatase 2A (PP2A), which limits nitric oxide synthase (eNOS) phosphorylation at stimulatory sites. We hypothesized that ceramide accumulation was from an age-related loss of endothelial glutathione (GSH) and subsequent activation of neutral sphingomyelinase (nSMase), an enzyme whose activity increases when GSH is limited.

EXPERIMENTAL APPROACH

Old (30-32 mo) F344xBN rats were given (R)-alpha-lipoic acid (LA), an agent known to induce GSH synthesis. Vasorelaxation was measured in aortic rings; GSH and ceramide levels, activity of nSMase and eNOS phosphorylation (by Western blot) was measured in aortic endothelial cells, isolated from the same aortas.

KEY RESULTS

In old animals, endothelium-dependent relaxation in aortic rings was decreased, GSH levels and its redox state in aortic endothelia were over 30% lower and nSMase activity and endothelial ceramide levels were three-fold increased, relative to young (2-4 mo) rats. LA treatment of old animals improved relaxation in aortic rings, reversed the changes in endothelial GSH, in nSMase activities and in ceramide levels. Similar effects on GSH levels and nSMase activity in old rats were also induced by treatment with GSH monoethylester. Activation (by phosphorylation) of eNOS was decreased by about 50% in old rats and this age-related decrease was partially reversed by LA treatment.

CONCLUSIONS AND IMPLICATIONS

Decreased endothelial GSH was partly responsible for the age-related loss of vascular endothelial function and LA might be therapeutically evaluated to treat endothelial dysfunction.