Acute Exposure to Glycated Proteins Impaired in the Endothelium-Dependent Aortic Relaxation: A Matter of Oxidative Stress

Chronically increased levels of high molecular weight advanced glycation end products (HMW-AGEs) are known to induce cardiovascular dysfunction. Whether an acute increase in HMW-AGE levels affects vascular function remains unknown. In this study, we examined whether acute exposure to HMW-AGEs disturbs aortic vasomotor function. Aortae were obtained from healthy male rats and were acutely pre-treated with HMW-AGEs in organ baths. Aortic relaxation responses to cumulative doses of acetylcholine (ACh), in the presence or absence of superoxide dismutase (SOD), were measured after precontraction with phenylephrine (PE). Furthermore, levels of 3-nitrotyrosine were evaluated on aortic paraffine sections. In our study, we show that acute exposure to HMW-AGEs significantly decreases the aortic relaxation response to ACh. SOD pre-treatment prevents acute HMW-AGEs-induced impairment by limiting superoxide formation. In conclusion, our data demonstrate that acute exposure to HMW-AGEs causes adverse vascular remodelling, characterised by disturbed vasomotor function due to increased oxidative stress. These results create opportunities for future research regarding the acute role of HMW-AGEs in cardiovascular dysfunction.

PTPRG is an ischemia risk locus essential for HCO3--dependent regulation of endothelial function and tissue perfusion

Acid-base conditions modify artery tone and tissue perfusion but the involved vascular-sensing mechanisms and disease consequences remain unclear. We experimentally investigated transgenic mice and performed genetic studies in a UK-based human cohort. We show that endothelial cells express the putative HCO3--sensor receptor-type tyrosine-protein phosphatase RPTPγ, which enhances endothelial intracellular Ca2+-responses in resistance arteries and facilitates endothelium-dependent vasorelaxation only when CO2/HCO3- is present. Consistent with waning RPTPγ-dependent vasorelaxation at low [HCO3-], RPTPγ limits increases in cerebral perfusion during neuronal activity and augments decreases in cerebral perfusion during hyperventilation. RPTPγ does not influence resting blood pressure but amplifies hyperventilation-induced blood pressure elevations. Loss-of-function variants in PTPRG, encoding RPTPγ, are associated with increased risk of cerebral infarction, heart attack, and reduced cardiac ejection fraction. We conclude that PTPRG is an ischemia susceptibility locus; and RPTPγ-dependent sensing of HCO3- adjusts endothelium-mediated vasorelaxation, microvascular perfusion, and blood pressure during acid-base disturbances and altered tissue metabolism.

Fenugreek (Trigonella Foenum-Graecum) Seed Flour and Diosgenin Preserve Endothelium-Dependent Arterial Relaxation in a Rat Model of Early-Stage Metabolic Syndrome

Fenugreek is a common herb possessing several bioactive components including diosgenin. Here, dietary fenugreek seed flour and diosgenin were evaluated on a model of endothelium-dependent vasorelaxation by abdominal aortas isolated from rats receiving high-fat, high-sugar diet (HFHSD). 60 male Wistar rats were randomized into six groups: (i) negative control getting conventional rat feed regimen; (ii) positive control receiving HFHSD; (iii) a test group fed 2 g/kg bw/day fenugreek seed flour (containing 10 mg/kg bw/day diosgenin) + HFHSD; (iv) three test groups fed 1, 10 and 50 mg/kg bw/day diosgenin + HFHSD. Alimentary treatments were carried out for six weeks. The abdominal aortas were isolated, and 2 mm wide rings were sectioned off and mounted at a resting tension of 10 mN in organ baths containing Krebs solution (36 °C) exposed to 95% O₂ and 5% CO₂. After 60-min incubation, a norepinephrine concentration-response (E/c) curve was generated to determine their half-maximal effective concentration (EC₅₀) value. After 60-min wash-out, a pre-contraction with norepinephrine EC₅₀ was made, followed by an acetylcholine E/c curve. Plasma glutathione levels, glutathione-handling enzyme activities and blood antioxidant capacities were also determined. HFHSD significantly decreased the dilatory response to acetylcholine and increased plasma glutathione levels and these effects were significantly reversed by fenugreek seed flour, 10 and 50 mg/kg bw/day diosgenin. Both fenugreek and diosgenin treatments prevent HFHSD-induced endothelial dysfunction and redox changes. As fenugreek treatment was more effective at lower acetylcholine concentrations than diosgenin treatments, components of fenugreek other than diosgenin may contribute to the beneficial effects of dietary fenugreek seed flour.

The nitric oxide donor pentaerythritol tetranitrate can preserve endothelial function in established atherosclerosis

Recent results suggested that long-term treatment with a low dose of the organic nitrate pentaerythritol tetranitrate (PETN, 6 mg kg(-1) per day) for 16 weeks slightly decreases aortic superoxide production in normal rabbits. We sought to determine if PETN can preserve endothelium dependent relaxation (EDR) in atherosclerotic rabbits. Three groups of 9 - 10 New Zealand White rabbits received a cholesterol chow (0.75%) for 16 weeks. One group (CHOL16) served as control and two groups were fed for another 16 weeks a cholesterol-chow without (CHOL32) or with 6 mg PETN kg(-1) per day (PETN32). Isolated aortic rings of CHOL16 showed a typical impairment of EDR with a maximal relaxation at 1 microM acetylcholine of 28+/-16%. In CHOL32-rings EDR was completely impaired. In striking contrast, EDR in PETN32 (24+/-15%) was similar to that of CHOL16 indicating a protective effect of PETN on endothelial function. Vascular superoxide production measured with the lucigenin method was not different between the groups. Aortic lesion formation in PETN32 was smaller than in CHOL32 (P<0.008). The onset of copper-induced LDL-oxidation (lag-time) after 16 weeks of cholesterol feeding (214+/-9 min) was reduced in CHOL32 (168+/-24 min, P=0.035) but not in PETN32 (220+/-21 min). This indicates prevention of increased LDL oxidation by PETN. The halfmaximal effective vasodilator concentrations of PETN (in -logM) were identical in CHOL16 (7.9+/-0.1), CHOL32 (7.6+/-0.2) and PETN32 (7.7+/-0.2). Similar results were obtained with S-nitroso-N-acetyl-D,L-penicillamine. These data suggest that PETN can reduce the progression of lesion formation, endothelial dysfunction and of LDL-oxidation in established atherosclerosis.

Vascular endothelial growth factor attenuates trauma-induced injury in rats

Endothelial dysfunction and loss of nitric oxide (NO) is an integral part of the initiation and maintenance of the inflammatory process such as that occurring in traumatic shock, and is considered responsible for much of the trauma induced microvascular injury. We investigated the effects of a vascular endothelial growth factor (VEGF) in a rat model of traumatic shock. Pentobarbital-anaesthetized rats subjected to Noble-Collip drum trauma developed a shock state characterized by marked hypotension and a 93% mortality rate with a mean survival time of 108+/-10 min in 14 rats. Accompanying these effects was a significant degree of endothelial dysfunction and a markedly elevated intestinal myeloperoxidase (MPO) activity. Treatment with 125 microg kg(-1) VEGF administered intravenously 18 h pre-trauma, increased survival rate to 67% (P<0.01), and prolonged survival time to 252+/-24 min in 12 rats (P<0.01). VEGF also significantly preserved the endothelium-dependent relaxation to ACh indicating a preservation of endothelium-derived NO. Our results indicate that endothelial dysfunction with its accompanying loss of NO plays an important role in tissue injury associated with trauma, and that preservation of NO is beneficial in traumatic shock. The mechanisms of the protective effect of VEGF in trauma involves preservation of eNOS function and diminished neutrophil accumulation resulting in reduced neutrophil-mediated tissue injury. British Journal of Pharmacology (2000) 129, 71 - 76