130 Handbook of herbs and spices
if not eliminated these highly reactive free radicals will react with, and potentially
alter, the structure and function of cell membranes, lipoproteins, cellular proteins,
carbohydrates RNA and DNA. The function of the antioxidant compounds is to
donate electrons to the free radicals thereby reducing their damaging effect. This is
particularly important in such chronic ailments as cardiovascular disease (Blomhoff,
2005).
Cardiovascular disease is a major source of mortality in industrial societies including
many below the age of 50. Atherosclerosis, which is the initial stage of the disease
and can lead to hypertension and heart attacks, is a disease of the arteries where the
inner layer becomes thickened by fatty deposits and fibrous tissue leading to a condition
known as hardening of the arteries. Fatty streaks, which are the earliest indication of
atherosclerosis, are areas of yellow discolouration on the inner surface of the artery
but do not protrude into the lumen or disturb the blood flow. The streaks are characterised
by the sub-endothelial accumulation of large foam cells filled with intracellular lipid.
The foam cells, which are derived from macrophages and smooth muscle cells are the
likely precursors of fibrous plaques, structures that form pale grey elevated lesions,
which may project into the arterial wall and reduce the blood flow through the vessel.
Calcification of the fibrous plaque leads to rigidity of the artery and hypertension
while rupture of the plaque releases material into the bloodstream causing a thrombus
to form. Occlusion of the vessel locally or following transport to distant sites can lead
to myocardial infarctions or strokes (Bhattacharyya and Libby 1998).
8.3.1 Herbs, spices and cholesterol
The level of cholesterol in the blood is an important factor in the development of
atherosclerosis. When fats are ingested as part of the diet, cholesterol and triglycerides
are absorbed in the intestine and finally transferred to the venous circulation. These
large molecules are hydrolysed by the enzyme lipoprotein lipase, which releases fatty
acids into peripheral tissues while the metabolic remnants composed largely of
cholesterol remain in the circulation. The liver in an endogenous cycle of cholesterol
production and metabolism releases very low density lipoprotein (VLDL) into the
circulation. Lipoprotein lipase acts on VLDL at muscle cells and adipose tissue to
release free fatty acids into the cells as before and the residue, intermediate density
lipoprotein (IDL), which contains esterified cholesterol remains in circulation. Further
processing results in cholesterol-rich low-density lipoprotein (LDL) which is largely
taken up by the liver. Cholesterol released back into circulation is transported by
high-density lipoprotein (HDL) which returns the cholesterol to the liver via IDL and
LDL for recycling into lipoproteins or excretion in the bile. The HDL appears to act
in a protective role while elevated levels of LDL correlates with a high incidence of
atherosclerosis. The level of cholesterol particularly LDL is critical (Bhattacharyya
and Libby, 1998). One route to lowering the level of cholesterol in the body is
through the increased intake of fibre (Brown et al., 1999). Herbs that are able to bind
to bile salts through their fibre component and remove them from the body will
stimulate cholesterol breakdown (Murcia et al., 2004; Zeng and Wang 2001).
The risk factor in atherosclerosis, such as high LDL or low HDL concentrations
can lead to excess cholesterol available being taken up by the intimal layer which is
the inner layer lining the lumen of the arteries. High LDL predisposes the arteries to
endothelial dysfunction by making them more permeable to the transport of LDL.
Once within the intima, LDL accumulates in the subendothelial space by binding to