Agriculture Reference
In-Depth Information
3.
Raw extracts of
A. fistulosum
lowered systolic blood pressure and prolonged
bleed times in rats, possibly by suppression of platelet aggregation in blood
clotting.
4.
Mice inoculated with bladder cancer cells and then provided with 500 mg
garlic/100 ml of drinking water showed significant reductions in tumour
volume and mortality over controls.
Cellular and biochemical studies
1.
The most widely reported pharmacological effect of alliums and extracts from
them is their inhibition of the aggregation of blood platelets. Platelet aggregation
occurs in blood clot formation and can cause thrombosis. Substances in alliums
are therefore powerful anti-thrombotics. Very low concentrations of the
compounds ajoene from garlic and cepaenes from onions (see Fig. 8.4) can
inhibit platelet aggregation.
2.
Studies using rat and human liver cells have shown precisely which points in
the biosynthetic pathway of cholesterol are inhibited by which substances from
garlic (Gebhardt and Beck, 1996; Keusgen, 2002). Allicin inhibits three
enzymes in the pathway, ajoene two of the same enzymes and diallyl disulfide
one of the enzymes. Diallyl disulfide also induces a higher level of cyclic
adenosine monophosphate (cAMP), which leads to more of the inactive
phosphorylated form of two enzymes early in the biosynthetic pathways of
cholesterol and fatty acid synthesis. Concentrations of 0.5 mM allicin or ajoene
caused a 30% decrease in cholesterol biosynthesis; this is medically more
desirable than a total inhibition. Clearly, the action of garlic in this process is
complex, and different forms of garlic (fresh or extracted) that contain different
active compounds all have cholesterol-lowering potential.
In contrast to these positive results, there are other studies showing no benefits
from alliums or substances derived from them on aspects of disease. For
example, a randomized study on adults with moderately elevated cholesterol
found no benefit in terms of reduced cholesterol of consuming an average-sized
(4 g) garlic clove, or its equivalent as garlic powder or extract, daily for 6
months (Gardner
et al.
, 2007). The reasons for conflicting reports are not clear,
although the amounts of allium ingested may be a factor. The latter study
involved eating only moderate amounts of garlic that could be part of a normal
diet for many people.
Antioxidants and the prevention of free radical damage
The oxidative breakdown of food that provides metabolic energy for all aerobic
organisms, including humans, produces as an undesirable by-product certain
highly reactive groups with an unpaired outer electron, variously known as
