Homocysteine Excess and Vascular Endothelium Dysfunction: Delineating the Pathobiological Mechanisms

A GLP-1 analog lowers ER stress and enhances protein folding to ameliorate homocysteine-induced endothelial dysfunction

Hyperhomocysteinemia (HHcy) is an independent risk factor for cardiovascular diseases and increases mortality in type 2 diabetic patients. HHcy induces endoplasmic reticulum (ER) stress and oxidative stress to impair endothelial function. The glucagon-like peptide 1 (GLP-1) analog exendin-4 attenuates endothelial ER stress, but the detailed vasoprotective mechanism remains elusive. The present study investigated the beneficial effects of exendin-4 against HHcy-induced endothelial dysfunction. Exendin-4 pretreatment reversed homocysteine-induced impairment of endothelium-dependent relaxations in C57BL/6 mouse aortae ex vivo. Four weeks subcutaneous injection of exendin-4 restored the impaired endothelial function in both aortae and mesenteric arteries isolated from mice with diet-induced HHcy. Exendin-4 treatment lowered superoxide anion accumulation in the mouse aortae both ex vivo and in vivo. Exendin-4 decreased the expression of ER stress markers (e.g., ATF4, spliced XBP1, and phosphorylated eIF2α) in human umbilical vein endothelial cells (HUVECs), and this change was reversed by cotreatment with compound C (CC) (AMPK inhibitor). Exendin-4 induced phosphorylation of AMPK and endothelial nitric oxide synthase in HUVECs and arteries. Exendin-4 increased the expression of endoplasmic reticulum oxidoreductase (ERO1α), an important ER chaperone in endothelial cells, and this effect was mediated by AMPK activation. Experiments using siRNA-mediated knockdown or adenoviral overexpression revealed that ERO1α mediated the inhibitory effects of exendin-4 on ER stress and superoxide anion production, thus ameliorating HHcy-induced endothelial dysfunction. The present results demonstrate that exendin-4 reduces HHcy-induced ER stress and improves endothelial function through AMPK-dependent ERO1α upregulation in endothelial cells and arteries. AMPK activation promotes the protein folding machinery in endothelial cells to suppress ER stress.

Ameliorative effect of ozagrel, a thromboxane A2 synthase inhibitor, in hyperhomocysteinemia-induced experimental vascular cognitive impairment and dementia

The present study investigates the effect of ozagrel, a selective thromboxane A2 (TXA2) inhibitor, in rat model of hyperhomocysteinemia (HHcy)-induced vascular cognitive impairment and dementia (VCID). Wistar rats were administered L-methionine (1.7 g/kg/day; p.o. × 8 weeks) to induce VCID. Morris water maze (MWM) test was employed to assess learning and memory. Endothelial dysfunction was assessed in the isolated aorta by observing endothelial-dependent vasorelaxation and levels of serum nitrite. Various biochemical and histopathological estimations were also performed. L-methionine produced significant impairment in endothelium-dependent vasorelaxation and decreases serum nitrite levels indicating endothelial dysfunction. Further, these animals performed poorly on MWM, depicting impairment of learning and memory. Further, a significant rise in brain oxidative stress level (indicated by increase in brain thiobarbituric acid-reactive species and decrease in reduced glutathione levels), brain acetylcholinesterase activity, brain myeloperoxidase activity, brain TNF-α and IL-6 levels, and brain leukocyte (neutrophil) infiltration was also observed. Treatment of ozagrel (10 and 20 mg/kg, p. o.)/donepezil (0.5 mg/kg, i.p., serving as standard) ameliorated L-methionine-induced endothelial dysfunction, memory deficits, and biochemical and histopathological changes. It may be concluded that ozagrel markedly improved endothelial dysfunction, learning and memory, and biochemical and histopathological alteration associated with L-methionine-induced VCID and that TXA2 can be considered as an important therapeutic target for the management of VCID.

Tadalafil ameliorates memory deficits, oxidative stress, endothelial dysfunction and neuropathological changes in rat model of hyperhomocysteinemia induced vascular dementia

AIM

The present study investigates the potential of Tadalafil, a phosphodiesterase-5 inhibitor, in a rat model of hyperhomocysteinemia induced vascular dementia.

METHODS

Hyperhomocysteinemia induced vascular dementia in Wistar rats was produced by administering l-Methionine (1.7 g/kg/day; p.o.×8 weeks). Learning and memory was assessed by employing Morris water maze (MWM) test. Endothelial dysfunction was assessed through acetylcholine-induced endothelial-dependent vasorelaxation and serum nitrite levels. Various other biochemical and histopathological estimations were also performed.

RESULTS

l-Methionine produced significant impairment in acetylcholine-induced endothelium-dependent vasorelaxation and a decrease in serum nitrite levels indicating endothelial dysfunction. Further, these animals performed poorly on Morris water maze, depicting impairment of learning and memory. There was a significant rise in brain oxidative stress level (indicated by an increase in brain thiobarbituric acid reactive species and a decrease in reduced glutathione levels). Increase in brain acetylcholinesterase activity; brain myeloperoxidase activity and brain neutrophil infiltration (a marker of inflammation) were also observed. Tadalafil (5 and 10 mg/kg, p.o.)/Donepezil (0.5 mg/kg, i.p., serving as standard) treatment ameliorated l-Methionine induced endothelial dysfunction; memory deficits; biochemical and histopathological changes in a significant manner.

CONCLUSIONS

It may be concluded that tadalafil has shown efficacy in the rat model of l-Methionine induced vascular dementia and that phosphodiesterase-5 can be considered as an important therapeutic target for the treatment of vascular dementia.

Melatonin attenuates homocysteine-induced injury in human umbilical vein endothelial cells

Homocysteine (Hcy) is a major risk factor for vascular disease and is closely associated with endothelial dysfunction. Melatonin is a neurohormone that is mostly produced by the pineal gland. Studies have reported that melatonin exhibits neuroprotective effects in several neurodegenerative disorders. The aim of the current study was to investigate the possible protective effect of melatonin against Hcy-induced endothelial cell apoptosis in human umbilical vein endothelial cells (HUVECs) and to explore the underlying mechanisms. HUVECs were exposed to Hcy in the presence or absence of melatonin. The effect of melatonin on viability was examined by MTT assay. Intracellular reactive oxygen species (ROS) levels were determined by 2',7'-dichlorofluorescein diacetate (DCF-DA). Further, expression of Bax, Bcl-2, and caspase-3 was analyzed by Western blot analysis. Lipid peroxidation (LPO) levels, total antioxidant power (TAP), and total thiol molecules were also evaluated. The results of this study revealed that melatonin significantly prevented Hcy-induced loss in cell viability in HUVECs. It was found that ROS significantly increased in the presence of Hcy, whereas melatonin reduced ROS production. Melatonin also downregulated Bax, upregulated Bcl-2, and decreased the expression and activity of caspase-3. Hcy increased the levels of LPO, and this effect was significantly attenuated by melatonin. Melatonin also increased the levels of TAP and total thiol molecules. It was concluded that melatonin played a protective role against Hcy-induced endothelium cell apoptosis through inhibition of ROS accumulation and the mitochondrial-dependent apoptotic pathway.