Zemelen
van rijst tegen hoge bloeddruk en hoog cholesterol.*
Het
enzym ACE activeert bepaalde peptides die op hun beurt de samentrekking van
bloedvaten bevorderen waardoor hoge bloeddruk ontstaat. Veel gebruikte
medicijnen tegen hoge bloeddruk zijn ACE remmers, die de bloeddruk kunnen
verlagen doch ook duidelijke bijwerkingen kennen. Onderzoekers hebben nu
ontdekt dat de zemelen van rijst ook ACE remmende werking hebben en daardoor
de bloeddruk doen verlagen. Zemelen van rijst zijn de donkere buitenste laag
van de rijst met de kiem. Deze wordt doorgaans tijdens het productieproces
van rijst verwijderd omdat het de houdbaarheid van rijst nadelig beïnvloedt.
Uit een andere studie blijkt dat de olie in de zemelen van rijst veel vitamine E in de vorm van tocotrienol bevat. Bij dieren deed dit tocotrienol de totale cholesterolwaarden met ruim 40% dalen het het slechte cholesterol (LDL) wel met 60%. De dagelijkse hoeveelheid tocotrienol, omgerekend voor mensen, die als optimaal gevonden werd is 375 mg. Dat is een hoeveelheid die iedereen zonder problemen langdurig kan nemen. Uit nog niet gepubliceerd onderzoek door dezelfde wetenschapper bleek uit een kleine proef bij mensen dat met deze dosis binnen 4 weken het totaal cholesterol 10% en het LDL met 26% daalden.Uit eerdere studies was al gebleken dat de tocotrienol ook heel effectief is in het voorkomen en bestrijden van kanker.
-Hypertension
(high blood pressure) is a major risk factor for stroke, coronary heart
disease, and renal vascular disease. A number of drugs on the market combat
hypertension by inhibiting the antiotensin-1-converting enzyme (ACE). ACE
activates peptides called angiotensins, and these in turn cause constriction
of blood vessels and thus increase blood pressure. Although ACE inhibitors
can be effective in lowering blood pressure, they can can also cause severe
side effects.
Researchers
have recently expended much effort to find bioactive components in food that
can reduce the risk of cardiovascular disease. They have found that fruits
and vegetables are protective, possibly due to the presence of antioxidants
that scavenge reactive oxygen species, which occur in many organs and may
play a role in several cardiovascular disease pathways.
One
potential source of antioxidants is rice bran, which is the outer layer
containing the germ of the grain and is removed during milling and polishing.
The bran is 12-13% oil and has high levels of dietary fibers (beta-glucan,
pectin, and gum). It is removed because its oils can quickly become rancid
and reduce rice's shelf life. However, the health benefits of its fiber and
antioxidants have led to the inclusion of bran in a number of health food
products.
Recently,
researchers showed that black rice bran inhibited atherosclerotic plaque
formation in rabbits. In the March 8 issue of the Journal of
Agricultural and Food Chemistry, researchers at Tohoku University (Sendai,
Japan) and the National Research Institute of Brewing (Hiroshima, Japan)
reported that rice bran extracts also reduce hypertension in rats (J.
Agric. Food Chem. 2005, 54(5) 1914 - 1920).
The
team investigated two rice bran fractions: an ethanol fraction (EF), and a
driselase fraction (DF). Driselase is a mixture of enzymes capable of
hydolyzing the components of plant cell walls. The researchers performed an
extraction of the fiber using 70% ethanol, then filtered off the remaining
solid, concentrating the ethanol to produce the EF. They suspended the
remaining solids in buffer and subjected them to driselase overnight, then
concentrated the liquid fraction to produce the DF. The researchers found
that the EF contained much of the lipid component of rice bran, while the DF
captured most of the nonlipid components.
When
rats that had developed spontaneous hypertension received the fractions as a
dietary supplement, both caused the rats to exhibit reduced blood pressure,
inhibited ACE activity, and reduced glucose levels, among other effects,
compared with rats fed a control diet. The fractions also reduced the
rats’ urinary levels of hydroxy-2´-deoxyguanosine (8-OHdG), which is a
byproduct of DNA oxidation and a marker of oxidative DNA damage and
oxidative stress.
The
researchers also conducted in vitro studies to confirm the extracts'
inhibitory effects on ACE, and they conclude that ACE inhibition in plasma
is the primary mechanism by which bran fractions reduce hypertension.
Further experiments revealed that phenols and ferulic acid in the bran
fractions contributed to their biological effects. Ferulic acid occurs
abundantly in plant leaves and seeds, where it links to lignin and other
biopolymers and acts as a strong antioxidant.
Rice
bran joins a list of other foods with ACE inhibition properties, including
tofuyu (a version of tofu), Indonesian dried-salted fish, and mushrooms.
-Can Rice Bran Oil Melt Away Cholesterol?
A
natural component of rice bran oil lowers cholesterol
in rats, and ongoing research also shows it may have potential as an anti-cancer
and anti-infection agent in humans, according to a University of Rochester
scientist who has studied the antioxidant since
1996.
The latest findings from
Mohammad Minhajuddin, Ph.D., and colleagues, are reported in the Food and
Chemical Toxicology journal. They show that total cholesterol
levels in animals dropped by 42 percent, and LDL or "bad
cholesterol" levels dropped up to 62 percent, after their diets
were supplemented with a concentrated form of Vitamin E called tocotrienol
rich fraction or TRF isolated from rice bran oil.
Vitamin E, which has been
widely studied for its health benefits, consists of both tocopherols and
tocotrienols. Much research has focused on the tocopherols derived from corn,
wheat and soybean. But the tocotrienols (TRF) seem to have greater
antioxidant properties and are becoming more noteworthy in scientific
research, Minhajuddin says. TRF is derived from barley, oats, palm and rice
bran.
The best form of TRF
comes from rice bran oil, which is contained in the outer grain hull of rice.
Its properties inhibit the activity of HMG-CoA reductase, an enzyme involved
in cholesterol biosynthesis. However, since taking any form of Vitamin
E for a long time can be harmful, the purpose of Minhajuddin's latest
reported research was to find the minimum dose of TRF that provided the
maximum antioxidants and effectively lowered cholesterol.
The results: The most
effective dose in rats was 8 IU kg/day. Extrapolated to humans, a person
with an average body weight of 154 pounds would get around 560 IU, which is
close to the 400 IU of Vitamin E normally taken. (The upper tolerable intake
of Vitamin E is 1500 IU).
Researchers have been
investigating natural ways (besides diet and exercise) to achieve lower
cholesterol levels, despite the popularity and effectiveness of statin
drugs. Although millions of Americans take statins and do well, they are
expensive and they come with side effects. So far, scientists have not found
any adverse effects of tocotrienols, says Minhajuddin, a research associate
in the Department of Pediatrics.
Minhajuddin, who is from
India, also has preliminary, unpublished data from a study he conducted in
that country, showing that TRF reduces cholesterol in humans as well as in
animals. Five healthy volunteers with total cholesterol levels in the "normal"
range of 170-230 mg/dL, who ingested TRF in capsule form at a dose of 8 IU
kg/day for four weeks, saw their cholesterol levels drop by 10 percent with
a 26-percent decline in LDL-cholesterol levels. A case study of a 5-year-old
boy in India, who had a genetic defect (familial hypercholesterolemia) that
caused his total cholesterol to climb to 440 mg/dL, resulted in a 20-percent
decline after about two months of tocotrienol supplements. The boy's
cholesterol did rise again, however, after 100 weeks of TRF supplements.
In addition, Minhajuddin
and colleagues previously showed in animals that TRF reacts with liver
enzymes in such a way that it clears toxic substances from the organ, and
reduces or stabilizes liver tumors. The group concluded that long-term use
of tocotrienol might reduce overall cancer risk, according to published
research last year in the European Journal of Cancer Prevention. Currently,
Minhajuddin's research group is using a scientific model to study infection
and the immune system, and how to regulate the expression of a gene called
ICAM-1 on the surface of endothelial cells.
###
Much of Minhajuddin's research on TRF was carried out in India until he joined the UR faculty in 2003. A Research Fellowship from the Indian Council of Agricultural Research, New Delhi, funded his work.
( Maart 2006)
