Elsevier

Journal of Ethnopharmacology

Volume 133, Issue 2, 27 January 2011, Pages 315-323
Journal of Ethnopharmacology

Ethanol extract of seeds of Oenothera odorata induces vasorelaxation via endothelium-dependent NO-cGMP signaling through activation of Akt-eNOS-sGC pathway

https://doi.org/10.1016/j.jep.2010.09.024Get rights and content

Abstract

Aim of study

The vasorelaxant effect of ethanol extract of seeds of Oenothera odorata (Onagraceae) (one species of evening primroses) (ESOO) and its mechanisms involved were defined.

Materials and methods

Changes in vascular tension, guanosine 3′,5′-cyclic monophosphate (cGMP) levels, and Akt expression were measured in carotid arterial rings from rats. Seeds of Oenothera odorata were extracted with ethanol (94%) and the extract was filtered, concentrated and stored at −70 °C.

Results

ESOO relaxed endothelium-intact, but not endothelium-denuded, carotid arterial rings in a concentration-dependent manner. Similarly, ESOO increased cGMP levels of the carotid arterial rings. Pretreatment of endothelium-intact arterial rings with L-NAME, an inhibitor of nitric oxide synthase (NOS), or ODQ, an inhibitor of soluble guanylyl cyclase (sGC), blocked the ESOO-induced vasorelaxation and increase in cGMP levels. Nominally Ca2+-free but not L-typed Ca2+ channel inhibition attenuated the ESOO-induced vasorelaxation. Thapsigargin, Gd3+, and 2-aminoethyl diphenylborinate, modulators of store-operated Ca2+ entry (SOCE), significantly attenuated the ESOO-induced vasorelaxation and increase in cGMP levels. Further, wortmannin, an inhibitor of Akt, attenuated the ESOO-induced vasorelaxation and increases in cGMP levels and phosphorylated Akt2 expression. K+ channel blockade with TEA, 4-aminopyridine, and glibenclamide attenuated the ESOO-induced vascular relaxation.

Conclusion

Taken together, the present study demonstrates that ESOO relaxes vascular smooth muscle via endothelium-dependent NO-cGMP signaling through activation of the Akt-eNOS-sGC pathway.

Graphical abstract

A schematic proposal for the mechanisms responsible for the ESOO-induced vascular relaxation.

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Introduction

Systemic arterial hypertension is known to be closely related to the dysfunction of the vascular endothelial cells (Vanhoutte et al., 2005). Vascular endothelial cells regulate the function of the underlying vascular smooth muscle cells and the diameter of the vessels. The changes in arterial resistance are under the precise balance between the vascular contraction and relaxation.

In the course of in vitro screening for the vascular relaxant activity from the medicinal plants, it was found that ethanol extract of seeds of Oenothera odorata Jacq (Onagraceae) (one species of evening primroses) (ESOO) elicited a distinctive vasorelaxant activity. In East Asia, evening primrose seeds were used to invigorate the circulation of blood and then reduce cardiovascular diseases such as hypertension and hyperlipidemia (Xiao, 1994). Evening primrose seed oil (obtained from seeds of Oenothera biennis L.) has been used to protect body from variety of diseases, skin diseases, diabetic complications, reproductive disorders, inflammatory disorders, and cardiovascular disorders (Horrobin, 1992, Jack et al., 2002, Blumenthal, 2003). It was shown that primrose seeds contain about 14% fixed oil, which is composed of 65–75% linoleic acid; 7–10% γ-linolenic acid (GLA); oleic, palmitic, and stearic acids; and the steroids campesterol and β-sitosterol (Blumenthal, 2003). The fatty acid GLA has been known to be useful in the treatment of breast cancer, hardening of the arteries, heart disease, high blood pressure, eczema, cirrhosis, rheumatoid arthritis, menopause, paramenstrual syndrome, and multiple sclerosis (Blumenthal, 2003). Also, long-term treatment with evening primrose oil has been reported to prevent a deficit of endothelium-dependent vascular relaxation of a resistance vessel from diabetic rats (Jack et al., 2002).

The vascular endothelial cells perform homeostatic functions for the normal blood vessels and regulate vascular tone through the production of vasoactive factors (Furchgott and Zawadzki, 1980, Furchgott and Vanhoutte, 1989, Shepherd and Katusic, 1991). Endothelium produces potent vasodilators such as endothelium-derived relaxing factor (EDRF, Furchgott and Zawadzki, 1980), prostacyclin (Moncada and Vane, 1978, Jaffe, 1985) and endothelium-derived hyperpolarizing factor (EDHF, Beny and Brunet, 1988, Feletou and Vanhoutte, 2007). The former EDRF is NO (Ignarro et al., 1987, Palmer et al., 1987, Furchgott and Vanhoutte, 1989).

Endothelium-derived NO has been recognized as a pleiotropic biological mediator regulating vascular smooth muscle relaxation (Ignarro et al., 1987). The vascular production of NO depends on the function of endothelial NO synthase (eNOS). In vascular smooth muscle cells, NO-mediated activation of the enzyme soluble guanylyl cyclase (sGC) catalyzes the formation of the second messenger guanosine 3′,5′-cyclic monophosphate (cGMP), leading to vascular relaxation (Rapoport and Murad, 1983). To the best of our knowledge, effects of ESOO on the vascular tension have not been studied yet. In the present study, therefore, we examined the vascular relaxant activity of extract of ESOO and investigated its mechanisms of vasorelaxation.

Section snippets

Extraction of ESOO

The seeds of Oenothera odorata Jacq (SOO) were purchased from the Hanyakjae-mart (Yeong Cheon, Korea). A voucher specimen SOO (No. DH 128) was authenticated by professor Tae Oh Kwon, College of Life Science and Natural Resources, Wonkwang University, and deposited at the Herbarium of the Professional Graduate School of Oriental Medicine, Wonkwang University, Iksan, Jeonbuk, Republic of Korea. A sample (1.2 kg) was extracted with 12 L of 94% ethanol (OCI Company, Seoul, Korea) at room temperature

HPLC profile and 1H NMR analysis

The HPLC pattern of ESOO indicated that most peaks eluted with the strong elution solvent, suggesting the presence of non-polar metabolites as a major components (Fig. 1A and B). To suggest the type(s) of major components present in ESOO, the peaks eluted between 70 and 80 min were collected and the 1H NMR of the collected fraction was recorded (Fig. 2). The analysis of 1H NMR suggests that the fraction contained fatty acid with non-conjugated double bond(s) as indicated by the presence of

Discussion

The present study demonstrates that ESOO relaxes vascular smooth muscle via endothelium-dependent NO-cGMP signaling through the activation of the Akt- and SOCE-eNOS pathways. It was also shown that activation of K+ channels, especially, K+ATP channels, is involved in the ESOO-induced vascular relaxation.

Endothelial cells respond to various neurohumoral and physical stimuli by releasing endothelium-dependent vasodilators such as EDRF (Furchgott and Zawadzki, 1980), prostacyclin (Moncada and

Acknowledgments

This research was supported by Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education, Science and Technology (No. R13-2008-028-01000-0).

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