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Coenzyme
Q10 and Parkinson's Disease
PD is a
chronic, progressive neurological disease that affects about 500,000
people in the United States. It results from the loss of brain cells
that produce the neurotransmitter dopamine and causes tremor, stiffness
of the limbs and trunk, impaired balance and coordination, and slowing
of movements. Patients also sometimes develop other symptoms, including
difficulty swallowing, disturbed sleep, and emotional problems. PD usually
affects people over the age of 50, but it can affect younger people
as well. While levodopa and other drugs can ease the symptoms of PD,
none of the current treatments has been shown to slow the course of
the disease. The investigators believe coenzyme Q10 works by improving the function of mitochondria, the "powerhouses" that produce energy in cells. Coenzyme Q10 is an important link in the chain of chemical reactions that produces this energy. It also is a potent antioxidant — a chemical that "mops up" potentially harmful chemicals generated during normal metabolism. Previous studies carried out by Dr. Shults, Richard Haas, M.D., of UCSD and Flint Beal, M.D., of Cornell University have shown that coenzyme Q10 levels in mitochondria from PD patients are reduced and that mitochondrial function in these patients is impaired. Animal studies have shown that coenzyme Q10 can protect the area of the brain that is damaged in PD. Dr. Shults and colleagues also conducted a pilot study with PD patients which showed that consumption of up to 800 mg/day of coenzyme Q10 was well-tolerated and significantly increased the level of coenzyme Q10 in the blood.
All of the
patients who took part in the new study had the three primary features
of PD — tremor, stiffness, and slowed movements — and had
been diagnosed with the disease within 5 years of the time they were
enrolled. After an initial screening and baseline blood tests, the patients
were randomly divided into four groups. Three of the groups received
coenzyme Q10 at three different doses (300 mg/day, 600 mg/day, and 1,200
mg/day), along with vitamin E, while a fourth group received a matching
placebo that contained vitamin E alone. Each participant received a
clinical evaluation 1 month later and every 4 months for a total of
16 months or until the investigator determined that the patient needed
treatment with levodopa. None of the participants or the study investigators
knew which treatment each patient had received until the study ended. The investigators
found that most side effects of coenzyme Q10 were mild, and none of
the patients required a reduction of their dose. The percentage of people
receiving coenzyme Q10 who reported side effects was not significantly
different from that of the placebo group. During the study period, the
group that received the largest dose of coenzyme Q10 (1,200 mg/day)
had 44 percent less decline in mental function, motor (movement) function,
and ability to carry out activities of daily living, such as feeding
or dressing themselves. The greatest effect was on activities of daily
living. The groups that received 300 mg/day and 600 mg/day developed
slightly less disability than the placebo group, but the effects were
less than those in the group that received the highest dosage of coenzyme
Q10. The groups that received coenzyme Q10 also had significant increases
in the level of coenzyme Q10 in their blood and a significant increase
in energy-producing reactions within their mitochondria. The results
of this study suggest that doses of coenzyme Q10 as high as 1,200 mg/day
are safe and may be more effective than lower doses, says Dr. Shults.
The findings are consistent with those of a recently published study
of patients with early Huntington's disease — another degenerative
neurological disorder — that showed slightly less functional decline
in groups that received 600 mg/day of coenzyme Q10 . The new
study also used an efficient phase II clinical trial design - developed
by biostatistician David Oakes, Ph.D., of the University of Rochester,
and other study investigators - which should be useful for testing other
drugs that might slow the progression of PD, says Dr. Shults. The design
allowed the researchers to study the effects of three doses plus a placebo
in less than 3 years, and to obtain useful data about the compound's
effectiveness. Dr. Shults
and his colleagues strongly caution patients against taking coenzyme
Q10 until a larger, definitive trial can be conducted. Because coenzyme
Q10 is classified as a dietary supplement, it is not regulated by the
U.S. Food and Drug Administration. The versions of the supplement sold
in stores may differ, they may not contain potentially beneficial amounts
of the compound, and taking coenzyme Q10 over a number of years may
be costly, says Dr. Shults. In addition, the current study included
only a small number of patients, and the findings may not extend to
people in later stages of PD or to those who are at risk but have not
been diagnosed with the disorder, he notes. Finally, if many people
begin taking coenzyme Q10 because of these early results, it might make
it impossible for investigators to find enough patients to carry out
definitive studies of the compound's effectiveness and the proper dosages,
since patients must not be taking any treatments in order to be considered
for enrollment in a definitive trial. The investigators are now planning
a larger clinical trial that will examine the effects of 1,200 mg/day
of coenzyme Q10 , and possibly a higher dose as well, in a larger number
of patients.
The NINDS
is a component of the National Institutes of Health in Bethesda, Maryland,
and is the nation's primary supporter of biomedical research on the
brain and nervous system.
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