Elsevier

Biomedicine & Pharmacotherapy

Volume 87, March 2017, Pages 451-460
Biomedicine & Pharmacotherapy

Citrus leaf extract reduces blood pressure and vascular damage in repeatedly heated palm oil diet-Induced hypertensive rats

https://doi.org/10.1016/j.biopha.2016.12.075Get rights and content

Abstract

Prolonged consumption of repeatedly heated vegetable oil increases blood pressure. This study aimed to determine the effects of Citrus leaf extract, (CLE) on blood pressure, blood pressure-regulating enzymes and mediators, as well as aortic histomorphometry in heated palm oil induced-hypertension. Male Sprague Dawley rats (n = 56) were divided into seven groups; control group was given normal diet and the other groups were fed with palm oil-enriched diet (15% w/w) either fresh (FPO), five-time-heated (5HPO) or ten-time-heated (10HPO) with or without CLE (0.15%, w/w) supplementation. CLE supplementation reduced the heated oil-raising effect of blood pressure, plasma TBARS, thromboxane and angiotensin-1 converting enzyme in 5HPO but not in 10HPO group. CLE increased serum heme oxygenase-1 in both 5HPO and 10HPO groups. CLE supplementation reduced the increase in aortic intima-media thickness, intima-media area and circumferential wall tension in 5HPO group but not in 10HPO group. These findings suggested that CLE supplementation reduces the blood pressure-raising effects of 5HPO and vascular damage, possibly through its antioxidant effect by modulating vasoactive mediators and blood pressure-regulating enzymes.

Introduction

Fresh vegetable oils, which are rich in unsaturated fatty acids and antioxidants, are beneficial in reducing risk of cardiovascular disease [1]. The oils are commonly used for frying in food preparation and repeatedly used to save cost [2]. This habit is practiced not only in developing countries but also in developed countries [3], [4]. However, the quality of the oils deteriorates after repeated heating, which includes increased viscosity and darkening in color, due to altered fatty acid composition of the oil [5].

Heated vegetable oil undergoes thermal oxidation and a series of chemical reactions which generate polar compounds and reactive oxygen species (ROS), namely hydroxyl, alkoxy and peroxyl radicals, leading to increased oxidative stress [6]. Oxidative stress promotes vascular inflammation, endothelial dysfunction, and imbalance between vasodilation and vasoconstriction agents which eventually lead to the development of hypertension [7], [8], [9], [10], [11], [12], [13]. Previous studies in rats showed that prolonged intake of repeatedly heated palm and soy oil increased lipid peroxidation [12], [13] and blood pressure [8], [9], [10], [11], [12] as well as causing the imbalance between vasodilator and vasoconstrictor mediators in favor of vasoconstriction [11], [15]. Furthermore, studies by Ng et al. [9] reported the involvement of adverse vascular remodeling in the heated vegetable oil-induced hypertension in rat model.

The extract (CLE) is derived from Citrus spp. leaves (Rutaceae family) consisting of combinations of C. hystrix, C. aurantifolia, C. microcarpa and C. sinensis [16–18], developed and patented (patent number: US8425969B2) by Universiti Putra Malaysia researchers. It is used to reduce vegetable oil thermal oxidation. [19]. The established extraction methods for acquiring CLE was designed to effectively isolate and extract polyphenols in particular the flavonoids, such as diosmin, lutein, obacunone, isoquercitrin, hesperidin, didymin, eriocitrin, neocriocitrin, narirutin, naringin, neohesperidin and 7-OH flavonone [19]. Flavonoids are the most abundant polyphenols subgroup detected in citrus plants in Malaysia [16], [17], [18]. Previously, Sukalingam et al. [20] shown that CLE which was also named as ADD-X (patent no: US 8425969B2), reduced blood pressure and improved oxidative stress status in atherosclerotic rat model. Citrus species generally have antihypertensive effect attributed to their flavonoid-rich composition except for citrus aurantium [21], [22], [23], [24], [25]. We postulated that CLE may prevent blood pressure-raising effect of heated oil by regulating the vasoactive mediators and vascular remodeling apart from antioxidant effect. Therefore, this study was undertaken to evaluate the effects of CLE extract on blood pressure, blood pressure-regulating enzymes and mediators including angiotensin converting enzyme (ACE), heme oxygenase-1 (HO-1), thromboxane (TXA2) and prostacyclin (PGI2), lipid peroxidation (TBARS) as well as vascular histomorphometry in rats fed with heated oil.

Section snippets

Materials

CLE was obtained from Institute of Bioscience, Universiti Putra Malaysia, Selangor. Palm oil was purchased from Lam Soon Edible Oils, Selangor, Malaysia. TBARS, thromboxane B2 and 6-keto-PGF kits were purchased from Cayman Chemical, Ann Arbor, MI, USA. Heme oxygenase-1 and ACE kits were purchased from Cloud-Clone Corp, Houston, TX, USA. Other chemicals were obtained from Sigma-Aldrich Chemical Co. (St. Louis, MO, USA). The chemical characteristics of CLE determined by HPLC, LC–MS and FTIR are

Blood pressure

Fig. 2 shows systolic blood pressure at week 0 (pre-treatment) and week 16 (post-treatment) of all experimental groups. There was no difference in blood pressure at 0 week among all groups. At week 16, the blood pressure was significantly increased in 5HPO and 10HPO group compared to control and FPO groups, as well as their respective values at week 0 (p < 0.05). The blood pressure in 5HPO + CLE group was significantly lower compared to 5HPO group at week 16 (p < 0.05). However, blood pressure in

Discussion

Five and ten times heated palm oil increase blood pressure after 16 weeks. This finding was consistent with previous studies which reported that consumption of repeatedly heated vegetable oil increase blood pressure [8], [9], [10], [11], [12], [28]. Thermally oxidized vegetable oil contains polar compounds and reactive oxygen species (ROS) that cause increased oxidative stress upon prolonged consumption [6]. Oxidative stress promotes vascular inflammation and endothelial dysfunction which

Conclusions

CLE supplementation was able to attenuate the blood pressure raising effect of 5HPO but not in 10HPO. The reductions of blood pressure in heated vegetable oil-induced hypertension were paralleled with improvement in aortic histomorphometry. CLE supplementation also reduced TBARS, thromboxane and ACE activity while increased HO-1 activity. It is therefore suggested that CLE reduces blood pressure and vascular damage in heated palm oil diet-induced hypertension.

Conflict of interest

The authors declare that there is no conflict of interest.

Acknowledgments

This study was funded by grant GUP-2013-059. The authors would like to express the appreciation to Mr. Fadhlullah Zuhair Japar Sidek and Mrs. Juliana Abd Hamid for their excellent technical assistance.

References (62)

  • K.O. O’Leary et al.

    Effect of flavonoids and Vitamin E on cyclooxygenase-2 (COX-2) transcription

    Mutat. Res.

    (2004)
  • K. Hayashi et al.

    Adaptation and remodelling of vascular wall; biomechanical response to hypertension

    J. Mech. Behav. Biomed. Mater.

    (2009)
  • R. Romano et al.

    Frying performance of high oleic oil enriched in biophenols during discontinuous and prolonged thermal treatment

    Food Nutr. Sci.

    (2013)
  • A. Azman et al.

    Level of knowledge, attitude and practice of night market outlet operator in Kuala Lumpur regarding the usage of repeatedly heated cooking oil

    Med. J. Malaysia

    (2012)
  • G. Phiri et al.

    The quality of cooking oil used in informal food processing in Malawi: a preliminary study

    Int. J. Consumer Stud.

    (2006)
  • N. Totani et al.

    Is the frying oil in deep-fried foods safe?

    J. Oleo. Sci.

    (2006)
  • A.K.S. Rani et al.

    Quality changes in trans and trans free fats/oils and products during frying

    Eur. Food Res. Technol.

    (2010)
  • C.Y. Ng et al.

    The role of repeatedly heated soybean oil in the development of hypertension in rats: association with vascular inflammation

    Int. J. Exp. Pathol.

    (2012)
  • C.Y. Ng et al.

    Involvement of inflammation and adverse vascular remodelling in the blood pressure raising effect of repeatedly heated palm oil in rats

    Int. J. Vasc. Med.

    (2012)
  • X.F. Leong et al.

    Association of elevated blood pressure and impaired vasorelaxation in experimental Sprague-Dawley rats fed with heated vegetable oil

    Lipid Health Dis.

    (2010)
  • X.F. Leong et al.

    Intake of repeatedly heated palm oil causes elevation in blood pressure with impaired vasorelaxation in rats, Tohoku

    J. Exp. Med.

    (2009)
  • X.F. Leong et al.

    Effect of repeatedly heated palm olein on blood pressure-regulating enzymes activity and lipid peroxidation in rats

    Malays. J. Med. Sci.

    (2012)
  • S.K. Adam et al.

    Effects of repeatedly heated palm oil on serum lipid profile, lipid peroxidation and homocystein levels in a post-menopausal rat model

    Mcgill J. Med.

    (2008)
  • S.K. Adam et al.

    Heating reduces vitamin E content in palm and soy oils

    Malays. J. Biochem. Mol. Biol.

    (2007)
  • B.S. Nurul-Iman et al.

    Virgin coconut oil prevents blood pressure elevation and improves endothelial functions in rats fed with repeatedly heated palm oil

    Evid. Based Complement. Alternat. Med.

    (2013)
  • M.F.A. Ghafar et al.

    Flavonoid hesperidine, total phenolic contents and antioxidant activities from Citrus species

    Afr. J. Biotechnol.

    (2010)
  • K. Ghasemi et al.

    Antioxidant activity, phenol and flavonoid contents of 13 citrus species peels and tissues

    Pak. J. Pharm. Sci.

    (2009)
  • N.A. Idris et al.

    Antioxidative activity of Malaysian herb extracts in refined, bleached and deodorized palm olein

    J. Oil Palm Res.

    (2008)
  • S. Mohamed, F. Mohd Nor, Cooking oil composition with additive to reduce oil absorption. Patent No.: US8425969B2,...
  • K. Sukalingam et al.

    Consumption of ADD-X and repeatedly heated palm oil on the blood pressure and oxidative stress markers in ovarectomized rats

    Int. J. Pharmacol.

    (2016)
  • S.J. Stohs et al.

    Effects of p-synephrine alone and in combination with selected bioflavonoids on resting metabolism, blood pressure, heart rate and self-reported mood changes

    Int. J. Med. Sci.

    (2011)
  • Cited by (24)

    • Enrichment of Beverages With Health Beneficial Ingredients

      2019, Value-Added Ingredients and Enrichments of Beverages: Volume 14: The Science of Beverages
    View all citing articles on Scopus
    View full text