OPHTHALMOLOGY NEWS |
Gingko biloba ... for the eye? by Matt Young EyeWorld Contributing Editor |
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This most recent study found that the ginkgo biloba extract GBE protects
against apoptosis induced by high glucose in lens epithelial cells.
“Therefore, GBE has a potential protective effect against diabetic
cataract formation,” wrote study co-author Xiao-xing Yin, Ph.D., Department
of Clinical Pharmacology, Xuzhou Medical College, Xuzhou, China.
Promising ginkgo biloba results
“It is generally accepted that the apoptosis of HLEC [human lens epithelial
cells] is associated with the development of cataracts,” Dr. Yin reported. “High
glucose is presumed to be an initiating agent and is regarded as a major
cause of lens opacity.”
Indeed, in Dr. Yin’s study, in high glucose circumstances, the apoptosis
rate increased, with HLEC having the typical apoptotic nuclei. “When the cells were co-cultured with GBE, all of the earlier indexes
were significantly ameliorated correspondingly in a dose-dependent manner,” Dr.
Yin wrote. “These results demonstrate that GBE can strikingly inhibit
cell apoptosis induced by high glucose and has potent cytoprotective action.”
How GBE inhibits cell apoptosis, however, remains unclear. However, there
does appear to be a specific effect on aldose reductase (AR). High glucose
is presumed to be an apoptosis initiating agent, which in turn induces oxidative
stress and activates AR. “AR may be an essential mediator of cell death induced by high glucose,” Dr.
Yin reported. “In our study, AR activities of the cells incubated in
high glucose increased significantly, and decreased dramatically when incubated
with GBE. This result strongly suggests that GBE has a potent inhibitory
effect on the activation of AR.”
Additionally, cysteine aspartases (caspases) are needed for apoptosis induced
by various stimuli, Dr. Yin noted. “In our study, we found that caspase-3 activity increased in high glucose,
while in cells with GBE treatment, it decreased significantly, suggesting
that high glucose-induced apoptosis was required for the caspase dependent
pathway in HLEC,” Dr. Yin reported. “The inhibitory effects of
GBE on cell apoptosis involved inhibition of caspase-3 activation.”
Dr. Yin found other evidence to suggest GBE cuts down on apoptosis, but the
bottom line is this: Ginkgo biloba “may vitally postpone DC [diabetic
cataract].”
Other research
The September-October 2004 issue of the Japanese Journal of Ophthalmology
also carried a study that found rat lenses were protected by ginkgo biloba
from radiation-induced cataracts. Experimental Eye Research carried a study in July 2003 that performed a molecular
assessment of ginkgo biloba for use as a potential ophthalmic drug. “Ginkgo biloba was found to be an excellent antioxidant,” the
researchers reported. “It readily scavenges reactive oxygen and nitrogen
radicals and inhibits oxidative modifications that occur to proteins in vitro.
It enters intact cells and protects them from alloxan-mediated and light-mediated
stress, and the nuclear DNA from single strand breaks. It also effectively
inhibits chemically induced apoptosis.”
However, ingesting GBE may carry some ocular risk itself, as one case study
reported in the September 2003 issue of the Postgraduate Medical Journal
found that a woman developed a retrobulbar hemorrhage after peribulbar local
anesthetic injection. Ginkgo biloba tablets may have predisposed her to the
hemorrhage, the authors reported. Clearly, though, it was a single case study and therefore inconclusive at
best. What can be concluded today is that ginkgo biloba may protect against
early cataract formation in some cases.
John D. Sheppard, M.D., professor of ophthalmology, microbiology, and immunology,
Eastern Virginia Medical School, Norfolk, Va., also uses ginkgo “for
a lot of hopeless glaucoma patients.”
It’s difficult to prove that ginkgo works for glaucoma, but there is
some compelling evidence. This is helpful for people who have lost significant
visual field in one eye and are motivated to take better care of their eye
sight with whatever they can. Dr. Sheppard is a bit more skeptical of the ability of gingko to prevent
cataract formation, though. Cataract takes longer to develop than glaucoma, it has a very difficult grading
system, and it is very difficult to measure in a slitlamp research situation.
These factors make it hard to understand cataract formation itself, let alone
prevention, Dr. Sheppard said. Editors’ note:
Dr. Yin has no financial interests related to the Acta Pharmacologica
Sinica study. Dr. Sheppard has no financial interests related to
his comments. Contact information |
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Of
late, there are several published studies about ginkgo biloba’s
effect on ocular conditions, the latest of which was printed in the
September 2008 issue of Acta Pharmacologica Sinica.
