Original Research ArticleEffect of CLA supplementation on factors related to vascular dysfunction in arteries of orchidectomized rats
Introduction
The vascular endothelium is a monolayer of flat epithelial cells located between the circulating blood and the underlying connective tissue. Normal functioning of the endothelium is crucial to maintain vascular homeostasis, in such a way that the properties of endothelial cells are modified in response to various stimuli, such as hemodynamic changes and chemical signals, through the production and release of endothelial factors [1]. The vascular endothelium acts as a permeable barrier, maintains the extracellular matrix, modulates the vascular tone and an anti-thrombogenic environment, regulates growth and immune response, and modifies lipoproteins in the arterial wall [2].
When the endothelium fails to fuSlfill these roles, endothelial dysfunction occurs, with the concomitant pathogenesis of vascular diseases. In the lack of suitable compensatory mechanisms, changes in the vascular structure occurs. A key vasculopathy is atherosclerosis, characterized by histopathological damage in the structure of the artery, by accumulation of cholesterol, macrophages and smooth muscle cells and increased reactive oxygen species (ROS), ultimately restricting blood flow through the artery [3]. Cholesterol oxidation products (COPs) are generated through the enzymatically and non-enzymatically oxidation of cholesterol [4]; COPs contribute significantly to vascular remodeling that occurs in atherosclerosis and are crucial in endothelial dysfunction given their ability to induce inflammation, oxidative stress and apoptosis [5].
The cardioprotective effect of sex hormones is widely recognized [6,7]; and a murine orchidectomized model has been chosen to study the effects caused by their deficiency. We have investigated different effects caused by orchidectomy on vascular function, which are summarized in a complete alteration in the production of endothelial factors and the endothelial phenotype [[8], [9], [10], [11], [12], [13], [14]]. In the search for approaches to maintain vascular health, dietary fatty acids have been studied. Several reports have suggested that fatty acids exert variable effects on the vascular function of endothelial cells [15]. Polyunsaturated fatty acids (PUFAs), play an important role in the regulation of many physiological processes, such as inflammation, glycemic control, lipid metabolism and oxidative stress; which are closely related to the development of cardiovascular diseases [16]. CLA has attracted scientific interest since it could have beneficial effects associated with cardiovascular disease. Some of these properties are anti-atherosclerotic, anti-diabetic, anti-inflammatory, and immune-modulating. CLA is defined as a group of isomers of linoleic acid (C18:2 c9c12, ω-6), characterized by the presence of conjugated double bonds [17].
There are at least 28 known isomers of CLA, of which, the most important for their biological activity are c9,t11-CLA and t10,c12-CLA; both isomers are the most naturally abundant, and represent ca. 85–90 % and 10 % respectively [18]. CLA is naturally produced by rumen bacteria that isomerize linoleic acid [19], but ruminants can also synthesize it from vaccenic acid through Δ9-desaturase [20]. Another endogenous production pathway for CLA is through the metabolism of PUFAs such as linoleic acid and α-linolenic acid, through intestinal bacteria isolated from humans. This mechanism of CLA production has also been described in rodents [21,22].
Therefore, natural sources of CLA are beef, lamb, and dairy products. CLA can also be prepared synthetically from oils rich in linoleic acid, such as safflower, sunflower, corn and soybean oils, through alkaline isomerization that converts linoleic acid to CLA. This process produces a proportion of 40–45 % c9t,11-CLA and 40–45 % t10,c12-CLA, and the rest consists of small amounts of other CLA isomers [23].
Our hypothesis is that CLA supplementation could have a preventive effect on vascular dysfunction induced by the loss of sex hormones. Provided the significant role of endothelial dysfunction in the development of vascular diseases and its correlation with sexual hormone deficiency, it is important to investigate the effect of CLA on factors involved in vascular function regulation under this context in an orchidectomized murine model. We examined the effects of CLA supplemented diet on the orchidectomy-induced alterations on variables related to endothelial dysfunction.
The aim of this study was to identify and quantify the content of COPs and cholesterol in the arteries of orchidectomized rats fed a diet enriched with CLA, as well as to investigate the production of other factors related to endothelial dysfunction such as TXA2, PGI2, NO, and antioxidant activity in the arteries.
Section snippets
Materials
Dietary components were purchased from Harlan Teklad Inc. (Madison, WI). Concentrated CLA was a gift from Stepan Specialty Products LLC (Maywood, NJ). All analytical grade solvents were supplied by Tecsiquim (Mexico City) and reagents from Sigma-Aldrich (Mexico City). Commercial immunoassay kits were used for the determination of TXB2, 6-keto-PGF1 and colorimetric kits for the nitrate/nitrite determination of Cayman Chemicals®. 2,2-Diphenyl-1-picrilhydrazil (DPPH) for antioxidant activity was
Release of prostanoids
The basal release of the prostanoids TXA2 and PGI2, from the aorta and mesenteric arteries, is shown in Fig. 1, Fig. 2. In both arteries, the orchidectomized rats fed the control diet released a higher content of the two prostanoids compared to the healthy rats fed with the control diet. On the other hand, the group of orchidectomized rats fed with CLA had a lower content of prostanoids compared to the orchidectomized group fed with the control diet and without significant difference with
Discussion
It is known that the endothelial function is regulated by various factors that together maintain the homeostasis of the blood vessels [31]. In previous studies we have reported that the loss of gonadal function through orchidectomy enhances the rise of COPs in the aorta and mesenteric arteries [32], favors an atherogenic lipid profile [33,34], increases prostanoids synthesis and decreases NO production [[10], [11], [12], [13], [14]]. This happened in such a way that we examined the impact of a
Acknowledgments
The authors wish to thank Cesia J. Rojas for her support on biochemical analyses and Laura N. Bober, for performing the surgeries. This study was supported by graduate fellowships to authors Rojas and Villalpando from CONACyT (Mexico).
References (69)
- et al.
Vascular endothelium - Gatekeeper of vessel health
Atherosclerosis
(2016) - et al.
Systematic review and meta-analysis suggest that dietary cholesterol intake increases risk of breast cancer
Nutr. Res.
(2016) - et al.
Androgen deprivation increases neuronal nitric oxide metabolism and its vasodilator effect in rat mesenteric arteries
Nitric Oxide-Biology Chem.
(2005) - et al.
Isomer specific effects of Conjugated Linoleic Acid on macrophage ABCG1 transcription by a SREBP-1c dependent mechanism
Biochem. Biophys. Res. Commun.
(2007) - et al.
A simple method for the isolation and purification of total lipides from animal tissues
J. Biol. Chem.
(1957) - et al.
Pressurized liquid extraction of lipids for the determination of oxysterols in egg-containing food
J. Chromatogr. A
(2001) - et al.
Conjugated linoleic acid improves blood pressure by increasing adiponectin and endothelial nitric oxide synthase activity
J. Nutr. Biochem.
(2012) - et al.
Conjugated linoleic acid isomers strongly improve the redox status of bovine mammary epithelial cells (BME-UV1)
J. Dairy Sci.
(2015) - et al.
The effect of conjugated linoleic acid supplements on oxidative and antioxidative status of dairy cows
J. Dairy Sci.
(2016) - et al.
Conjugated linoleic acid induces lipid peroxidation in humans
FEBS Lett.
(2000)