Mechanisms underlying suppression of noradrenaline-induced contraction by prolonged treatment with advanced glycation end-products in organ-cultured rat carotid artery

Methylglyoxal impairs ATP- and UTP-induced relaxation in the rat carotid arteries

Although methylglyoxal (MGO), a highly reactive dicarbonyl compound, influences the functioning of the vasculature, modulating its effects on vascular reactivity to various substances remains unclear, especially purinoceptor ligands. Therefore, we sought to investigate the direct effects of MGO on relaxation induced by adenosine 5'-triphosphate (ATP) and uridine 5'-triphosphate (UTP) in isolated rat carotid arteries. When carotid arteries were exposed to MGO (420 μM for 1 h), relaxation induced by acetylcholine or sodium nitroprusside was not affected by MGO. However, ATP- and UTP-induced relaxation was impaired by MGO compared with the control. In both ATP- and UTP-induced relaxation, endothelial denudation, incubation with the nitric oxide (NO) synthase inhibitor N^G-nitro-L-arginine or the selective P2Y purinoceptor 2 (P2Y₂) receptor antagonist AR-C118925XX reduced relaxation in both the control and MGO groups, while the differences between the control and MGO groups were eliminated. The cyclooxygenase (COX) inhibitor indomethacin inhibited the differences in ATP/UTP-mediated relaxations between the control and MGO groups. Moreover, N-acetyl-L-cysteine (NAC), an antioxidant, could augment carotid arterial relaxation induced by ATP/UTP in the presence of MGO. MGO increased arachidonic acid-induced contraction, which was suppressed by NAC. Following both ATP/UTP stimulation, MGO increased the release of prostanoids. These results suggest that MGO impaired ATP- and UTP-induced relaxation in carotid arteries, which was caused by suppressed P2Y₂ receptor-mediated signaling and reductions in endothelial NO. Moreover, MGO partially contributed to COX-derived vasoconstrictor prostanoids through increased oxidative stress.

Relationships between advanced glycation end products (AGEs), vasoactive substances, and vascular function

Vascular smooth muscle cells (VSMCs) and endothelial cells (ECs) are major cell types that control vascular function, and hence dysfunction of these cells plays a key role in the development and progression of vasculopathies. Abnormal vascular responsiveness to vasoactive substances including vasoconstrictors and vasodilators has been observed in various arteries in diseases including diabetes, hypertension, chronic kidney diseases, and atherosclerosis. Several substances derived from ECs tightly control vascular function, such as endothelium-derived relaxing and contracting factors, and it is known that abnormal vascular signaling of these endothelium-derived substances is often observed in various diseases. Derangement of signaling in VSMCs and altered function influence vascular reactivity to vasoactive substances and tone, which are important determinants of vascular resistance and blood pressure. However, understanding the molecular mechanisms underlying abnormalities of vascular functions in pathological states is difficult because multiple substances interact in the development of these processes. Advanced glycation end products (AGEs), a heterogeneous group of bioactive compounds, are thought to contribute to vascular dysfunction, which in turn cause the development of several diseases including diabetes, hypertension, stroke, and atherosclerosis. A growing body of evidence suggests that AGEs could affect these cells and modulate vascular function. This study is focused on the link between AGEs and functions of ECs and VSMCs, particularly the modulative effects of AGEs on vascular reactivities to vasoactive substances.

Methylglyoxal augments uridine diphosphate-induced contraction via activation of p38 mitogen-activated protein kinase in rat carotid artery

The methylglyoxal elicits diverse adverse effects on the body. Uridine diphosphate, an extracellular nucleotide, plays an important role as a signaling molecule controlling vascular tone. This study aimed to evaluate the relationship between methylglyoxal and uridine diphosphate-induced carotid arterial contraction in rats. Additionally, we examined whether p38 mitogen-activated protein kinase (MAPK) would involve such responses. Organ baths were conducted to determine vascular reactivity in isolated carotid arterial rings, and western blotting was used for protein analysis. Treatment with methylglyoxal to carotid arterial rings showed concentration-dependent augmentation to uridine diphosphate-induced contraction in the absence and presence of NG-nitro-L-arginine, which is a nitric oxide synthase inhibitor, whereas, methylglyoxal did not affect serotonin- or isotonic high K+-induced contraction in the presence of a nitric oxide synthase inhibitor. Under nitric oxide synthase inhibition, SB203580, which is a selective p38 MAPK inhibitor, suppressed uridine diphosphate-induced contraction in both the control and methylglyoxal-treated groups, and the difference in uridine diphosphate-induced contraction was abolished by SB203580 treatment. The levels of phosphorylated p38 MAPK were increased by methylglyoxal in carotid arteries, not only under the basal condition but also under uridine diphosphate stimulation. The suppression of uridine diphosphate-induced contraction by a highly selective cell-permeable protein kinase C inhibitor bisindolylmaleimide I was observed in the methylglyoxal-treated group but not in the controls. Moreover, methylglyoxal-induced augmentation of uridine diphosphate-induced contraction was prevented by N-acetyl-L-cysteine. These results suggest that methylglyoxal could enhance uridine diphosphate-induced contraction in rat carotid arteries and may be caused by activation of p38 MAPK and protein kinase C and increased oxidative stress.