Herbs, spices and cardiovascular disease 133
anions as measured by nitro blue tetrazolium reduction in a xanthine-xanthine oxidase
system (Krishnakantha, 1993).
In another model system involving garlic, the approach has been to use an in vitro
system to show whether garlic supplement can prevent or reduce the oxidation of
LDL. In the in vitro cell free system CuSO 4 was used to oxidise LDL and the product,
thiobarbituric acid (TBARS), measured after 24 hours incubation in the presence and
absence of the garlic supplement, AGE (Lau, 2001). The supplement exerted a
concentration-dependent inhibition of Cu++ induced oxidation of LDL. All four water-
soluble compounds derived from garlic, N-acetyl-S allyl cysteine, S allyl cysteine,
alliin and allyl mercaptocysteine showed significant inhibition of LDL oxidation.
8.4.2 Animal studies
Animals have been used to establish the anti-oxidant potential of selected herbs and
spices. These studies indicated the presence of compounds in ginger, which directly
affected cholesterol metabolism. Activity of hepatic cholesterol–7-alpha-hydroxylase,
the rate-limiting enzyme in bile acid biosynthesis was significantly elevated in ginger-
fed rats. The conversion of cholesterol to bile acids is an important method of eliminating
cholesterol from the body (Sambaiah and Srinivasin, 1991). In addition Tanabe et al.
(1993) have recently isolated a new compound from ginger rhizomes, (E)-8b, 17-
epoxylabd-12-ene-15,1 16-dial (ZT) that lowered plasma cholesterol levels in
experimentally induced hypercholesterolemia in mice.
Oxidative modification of LDL is thought to play a key role in the pathogenesis of
atherosclerosis. The lipid peroxidation lowering associated with ginger consumption
was demonstrated in apoliprotein E deficient mice, i.e., mice that were prone to
develop atherosclerosis (Fuhram et al., 2000). Mice that consumed ginger (250 mcg
of extract/day in their drinking water showed significant reduction in their basal
concentration of LDL associated lipid peroxidases. The experimental data suggests a
strong positive effect of ginger on plasma lipid composition that may be important
for the prevention of atherosclerotic events. In a further study the oxidative stress
induced by malathion (a pesticide) into rats was overcome by introducing ginger into
the rats’ diet. Ginger was able to lower lipid peroxidation in rats by influencing the
enzymic blood level of the phase 2 enzymes, superoxide dismutase, catalase and
glutathione peroxidase, known to be involved in antioxidant activity (Ahmed et al.,
2000).
The effect of dietary supplements of oregano essential oil was investigated on the
performance of rabbits and the susceptibility of the produced raw and thermally
treated muscle tissue to lipid oxidation during refrigerated storage (Spais et al.,
2004). A total of 96 weaned rabbits were separated into four equal groups with three
sub groups. One group was given the basal diet and served as control, two groups
were administered diets supplemented with oregano essential oil at levels of 100 and
200 mg/kg diet whereas the remaining group was given a diet supplemented with a-
tocopherol acetate at 200 mg/kg. During the 42-day experimental period body weight
and feed intake were recorded weekly and the food conversion ratio was calculated.
Dietary oregano exerted no growth-promoting effects on rabbits. With increased
supplementation of oregano essential oil, malondialddehyde values decreased in both
raw and thermally treated muscles during refrigerated storage. This finding suggests
that dietary oregano essential oil exerted a significant antioxidant effect. Dietary
supplementation of oregano essential oil at the level of 200 mg/kg was more effective