Backgrounder
Mitochondria are long, oval-shaped specialized components within cells that are responsible for converting nutrients into energy. These tiny organelles consume more than 80 percent of the oxygen humans breathe and use it to make over 90 percent of the energy that cells need to function. Mitochondria contain their own DNA, separate from a cell's nuclear DNA.
Located in the cell's cytoplasm outside the nucleus, mitochondria consist of two sets of membranes, a smooth outer coat and an inner membrane arranged in tube-like folds called cristae. The inner membrane contains the components of the electron transport chain, a series of compounds that transfer electrons to oxygen in the process of energy production.
An important compound involved in the electron transport chain is ubiquinone, a small molecule also known as coenzyme Q10, that acts as an electron carrier.
First identified in 1957, coenzyme Q10 (ubiquinone) is a compound naturally made in the body. A coenzyme is a small molecule that, by itself, does not catalyze a reaction. Rather, a coenzyme enhances an enzyme, which is a protein that speeds up a chemical reaction. The "10" in coenzyme Q10, refers to a portion of the coenzyme's chemical structure.
In addition to its role in the metabolic process, coenzyme Q10 is known to act as an antioxidant that helps neutralize cell-damaging molecules known as free radicals.
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| Illustrating the internal structures of a synaptic mitochondria, the top image emphasizes the dominant lamellar (flat and layered) nature of cristae. The middle image shows a slice through the volume, emphasizing the cross-section through a tubular cristae segment. Synaptic mitochondria tend to have fewer tubular segments than those in other neuronal compartments. The bottom image shows the close association of the mitochondrion with the synaptic membrane and cluster of vesicles. |
Mitochondrial Function and Coenzyme Q 10 in Parkinson's Disease
Patients with Parkinson's disease have lost dopamine-producing nerve cells in the substantia nigra, a part of the mid-brain's grey matter.
Previous research has shown that interference with a certain step in mitochondrial energy production, called complex I, causes an increase in the number of oxygen free radicals, which are known to be toxic to cells, such as those in the substantia nigra.
To determine if there might be a connection between mitochondrial function and Parkinson's disease, Clifford Shults, M.D. and Richard Haas, M.D., in the UCSD Department of Neurosciences, began a series of experiments. Reasoning that the reduction in complex I activity might be part of the process that resulted in death of the dopamine-producing nerve cells, they compared the mitochondrial function in platelets of early-stage Parkinsonian patients not yet on medication, to control groups. They found that the activity of complex I was significantly lower in the Parkinsonian patients.
To evaluate the potential effect of medications such as levodopa, the researchers evaluated platelet mitochondrial function in 11 patients who had received carbidopa/levodopa or selegiline. Neither of the treatments affected the mitochondrial function.
Knowing that an important molecule involved in the electron transport process in mitochondria is coenzyme Q10, Shults and Haas worked with Flint Beal, M.D., formerly at Massachusetts General Hospital (and currently at Weill Medical College, Cornell University), to measure the levels of coenzyme Q10 in the platelet mitochondria and found that coenzyme Q10levels were significantly lower in Parkinsonian patients, as compared to the control group. In follow-up investigations first with mice and then a pilot study with 15 human patients, the researchers provided coenzyme Q10 supplements. In the animals, they found that the dopaminergic nerve fibers were significantly preserved. In the human patients, the coenzyme Q10 was well tolerated and evaluations of patients' plasma levels showed a trend toward an increase in complex I activity.
These findings led to the recent study by the Parkinson Study Group, a consortium of more than 50 Parkinson's disease centers in the United States and Canada.
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Return to newsrelease: http://health.ucsd.edu/news/2002/10_14_Shults.html
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