The Antihypertensive Effect of Black Garlic(Allium Sativum) in Spontaneously
Hypertensive Rats via Scavenging of Free
Radicals
Yelian Miao*1, Jieyu Chen2, Guangyong Zhou3, Xiaobian Xu4, Qimei Zhang5, Jining Wang6
*1,3,4,5College of Food Science and Light Industrial Engineering, Nanjing University of Technology, Jiangsu 211816,
China
2 Faculty of Bioresource Science, Akita Prefectural University, Akita 010-0195, Japan
6 School of Economics and Management, Nanjing University of Technology, Jiangsu 211816, China
*1ylmiao@njut.edu.cn
Received 17 Sep, 2013; Accepted 10 Nov, 2013; Published 10 Jan, 2014
© 2014 Science and Engineering Publishing Company

Abstract

Black garlic (Allium sativum) is a new garlic product with high free-radical-scavenging ability. In the present study, the antihypertensive effect of black garlic was investigated in vivo using spontaneously hypertensive rats (SHRs, 185±12 mm Hg) as the test animals. Total antioxidant capacity (TAOC) and malondialdehyde (MDA) content in both plasma and hypothalamic paraventricular nucleus (PVN) of the rats were measured to explore underlying biochemical mechanism of the antihypertensive effect. The administration of black garlic for 14 days significantly lowered the blood pressure of SHRs to 121±10 mm Hg (with a decline rate of 34.6% in average), while it did not affect the normal blood pressure of Wistar rats. The black garlic had more antihypertensive effect on SHRs than fresh garlic. In the plasma of SHRs receiving the black garlic, the T-AOC increased from 4.2±1.0 U/mL to 5.4±1.1 U/mL (with an increase rate of 28.6% in average), and the MDA content decreased correspondingly from 10.2±2.2 nmol/mL to 7.9±0.7 nmol/mL (with a decrease rate of 22.5% in average). In the PVN of SHRs receiving the black garlic, the T-AOC increased from 4.4±0.7 U/mg-protein to 7.2±1.6 U/mg-protein (with an increase rate of 63.6% in average), and the MDA content decreased correspondingly from 8.2±1.5 nmol/mgprotein to 3.9±1.2 nmol/mg-protein (with a decrease rate of 52.4% in average). The findings indicated that the black garlic exerts a potential antihypertensive effect through scavenging excessive oxygen free radicals (OFRs) in the plasma and PVN of SHRs. Keywords Black Garli, Antioxidant Activit, Antihypertensive Effect, Oxygen Free Radical, Hypertension

Abbreviations

CSAR, cardiac sympathetic afferent reflex
FRAP, ferric reducing ability of plasma
MDA, malondialdehyde
OFRs, oxygen free radicals
PVN, paraventricular nucleus
SHRs, spontaneously hypertensive rats
T-AOC, total antioxidant capacity
TBA, thiobarbituric acid

Introduction

Hypertension is a commonly occurring cardiovascular disease in the world. It is estimated that by 2025, the incidence of hypertension will increase to 24% in developed countries and to 80% in developing countries (Messerli et al., 2007; Quiñones et al., 2013). Hypertension may be caused by oxygen free radicals (OFRs) in the human body (Russo et al., 1998; Bogdan et al., 2000). Antioxidant therapy helps to scavenge excessive OFRs, and to prevent the pathogenesis of hypertension and its complications (Vaziri et al., 2000; Ortiz et al., 2001). Recent research also indicated that excessive OFRs in hypothalamic paraventricular nucleus (PVN) contribute to the potentiation of vasoconstrictor angiotensin II (Ang II) and cardiac sympathetic afferent reflex (CSAR), which may induce hypertension (Han et al., 2007; Grassi et al., 1999). In contrast, microinjection of tempol (i.e. a superoxide anion scavenger) into the PVN of hypertensive rats can abolish the potentiation of Ang II and CSAR, and lower the high blood pressure (Han et al., 2011; Koga et al., 2008). Black garlic (Allium sativum) is a new garlic product processed by the fermentation of fresh garlic in a temperature- and humidity–controlled room for a month. It is black in color with a fruit-like sweetness and non-irritating order. In particular, black garlic has outstanding antioxidative activity since it is rich in bioactive compounds such as ajoene, S-allyl-L-cysteine and polyphenols (Zhou et al., 2010; Wang et al., 2010; Kim et al., 2012). Experimentation on rats showed that black garlic has a higher ability to increase antioxidase activity, and to decrease malondialdehyde (MDA) content in the blood and the liver tissue, in comparison with fresh garlic (Apitz-Castro et al., 1992; Zhu et al., 2008). The heat-extracts of black garlic enforces anti-tumor activity with a 50% cure rate of BALB/c mouse fibrosarcoma since it enhances the cellular immunity by raising the activity of natural killer cells (Sasaki et al., 2007). Black garlic also has favourable hepatoprotective, nephroprotective, hypolipidemic, and antiobesity effects, but no hypoglycemic effects (Jung et al., 2011). A black garlic formulation containing 10% black garlic extract is effective in protecting skin from UVB photodamage (Kim et al., 2012). In the present study, black garlic with high freeradical-scavenging ability was prepared, and its antihypertensive effect was investigated in vivo using spontaneously hypertensive rats (SHRs) as the test animals. Total antioxidant capacity (T-AOC) and MDA content in both plasma and PVN of the rats were measured to explore underlying biochemical mechanism of the antihypertensive effect.

Materials and Methods

Garlics

Fresh garlic (Allium sativum) with purple skin, produced in Henan province, was obtained from a local market in Nanjing, China. Black garlic was prepared by maintaining the fresh garlic in an incubator with a temperature of 65℃ and a relative humidity of 70% for 30 days (Miao, 2006). The content of main compounds and the free-radicalscavenging ability of fresh and black garlics are shown in Table 1. Moisture was measured by drying a 5 g garlic sample at 105℃ for 24 h. Alliin and S-allyl-Lcrysteine were measured using a high performance liquid chromatograph (HPLC) system (Ichikawa et al., 2006; Kodera et al., 2002). Total polyphenols were measured with the Folin–Ciocalteu method (Li et al., 2009; Kim et al., 2012). Ajoene was measured using a LC-MS system and its amount was expressed by the peak area of LC chromatogram (Iberl et al., 1990; Fu, 2006). The free-radical-scavenging ability was determined with the ABTS method (Re et al., 1999; Zulueta et al., 2008). The content of main compounds and the free-radical-scavenging ability were expressed on the basis of dry garlic. The black garlic contained only little alliin and other volatile organic sulfides, so that it did not have unacceptable odor and sharp taste of fresh garlic. Moreover, the black garlic had a freeradical-scavenging ability of 63.4 g-Trolox/kg, which was about 9 times higher than that of fresh garlic. The black garlic’s high ability of free-radical-scavenging resulted from remarkable increases in the content of bioactive compounds, i.e. total polyphenols, ajoene and S-allyl-L-cysteine.

Preparation of Animal Model

Normotensive Wistar rats (male: n=18, female: n=18) and spontaneously hypertensive rats (SHRs, male: n=18, female: n=18), weighing approximately 150-260 g (20-week-old), were supplied by Shanghai Laboratory Animal Center of Chinese Academy of Sciences. The male Wistar rats, female Wistar rats, male SHRs and female SHRs were housed separately in polycarbonate boxes, and had free access to food and tap water. The animal room was maintained at approximately 22°C and 50% humidity with a 12-h light/dark cycle. All of animal experimental design was approved by the Institutional Animal Care and Ethical Committee of Nanjing Medical University

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THE ANTIHYPERTENSIVE EFFECT OF BLACK GARLIC(ALLIUM SATIVUM) IN SPONTANEOUSLY HYPERTENSIVE RATS VIA SCAVENGING OF FREE ( PART 2)
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