J Korean Med Sci.  2019 Nov;34(42):e266. 10.3346/jkms.2019.34.e266.

Telmisartan Inhibits Nitric Oxide Production and Vessel Relaxation via Protein Phosphatase 2A-mediated Endothelial NO Synthase-Ser¹¹⁷⁹ Dephosphorylation

Affiliations
  • 1Department of Pharmacology, Yeungnam University College of Medicine, Daegu, Korea. biohyong@hanmail.net

Abstract

BACKGROUND
Apart from its blood pressure-lowering effect by blocking the renin-angiotensin-aldosterone system, telmisartan, an angiotensin II type 1 receptor blocker (ARB), exhibits various ancillary effects including cardiovascular protective effects in vitro. Nonetheless, the protective effects of telmisartan in cerebrocardiovascular diseases are somewhat variable in large-scale clinical trials. Dysregulation of endothelial nitric oxide (NO) synthase (eNOS)-derived NO contributes to the developments of various vascular diseases. Nevertheless, the direct effects of telmisartan on endothelial functions including NO production and vessel relaxation, and its action mechanism have not been fully elucidated. Here, we investigated the mechanism by which telmisartan regulates NO production and vessel relaxation in vitro and in vivo.
METHODS
We measured nitrite levels in culture medium and mouse serum, and performed inhibitor studies and western blot analyses using bovine aortic endothelial cells (BAECs) and a hyperglycemic mouse model. To assess vessel reactivity, we performed acetylcholine (ACh)-induced vessel relaxation assay on isolated rat aortas.
RESULTS
Telmisartan decreased NO production in normoglycemic and hyperglycemic BAECs, which was accompanied by reduced phosphorylation of eNOS at Ser¹¹â·â¹ (p-eNOS-Ser¹¹â·â¹). Telmisartan increased the expression of protein phosphatase 2A catalytic subunit (PP2Ac) and co-treatment with okadaic acid completely restored telmisartan-inhibited NO production and p-eNOS-Ser¹¹â·â¹ levels. Of the ARBs tested (including losartan and fimasartan), only telmisartan decreased NO production and p-eNOS-Ser¹¹â·â¹ levels, and enhanced PP2Ac expression. Co-treatment with GW9662 had no effect on telmisartan-induced changes. In line with in vitro observations, telmisartan reduced serum nitrite and p-eNOS-Ser¹¹â·â¹ levels, and increased PP2Ac expression in high fat diet-fed mice. Furthermore, telmisartan attenuated ACh-induced rat aorta relaxation.
CONCLUSION
We demonstrated that telmisartan inhibited NO production and vessel relaxation at least in part by PP2A-mediated eNOS-Ser¹¹â·â¹ dephosphorylation in a peroxisome proliferator-activated receptor γ-independent manner. These results may provide a mechanism that explains the inconsistent cerebrocardiovascular protective effects of telmisartan.

Keyword

Telmisartan; Nitric Oxide; Endothelial Nitric Oxide Synthase; Protein Phosphatase 2A; Vessel Relaxation; Phosphorylation

MeSH Terms

Acetylcholine
Animals
Aorta
Blotting, Western
Catalytic Domain
Endothelial Cells
In Vitro Techniques
Losartan
Mice
Mice, Obese
Nitric Oxide Synthase Type III
Nitric Oxide*
Okadaic Acid
Peroxisomes
Phosphorylation
Protein Phosphatase 2
Rats
Receptor, Angiotensin, Type 1
Relaxation*
Renin-Angiotensin System
Vascular Diseases
Acetylcholine
Losartan
Nitric Oxide
Nitric Oxide Synthase Type III
Okadaic Acid
Protein Phosphatase 2
Receptor, Angiotensin, Type 1
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