CATARACT / IOL |
An ounce of prevention ... by Matt Young EyeWorld Contributing Editor |
|||
 Could antioxidants someday cause this kind of tool—and the rest of your
phaco kit—to go out of fashion? Source: Takayuki Akahoshi, M.D.
Phacoemulsification—the technique Charles Kelman, M.D.,
introduced in 1967 to emulsify the lens nucleus with ultrasonic waves,
whereby eliminating cataracts without a large incision—remains
unchallenged today as the gold standard. But could there be another,
better standard out there? Scientific research is beginning to point to cataract prevention as a serious
alternative to a cataract cure. Specifically, researchers are looking at
sodium pyruvate as a topical agent to prevent cataracts from ever forming
by protecting against oxidative stress. “The compound penetrates the cornea in measurable amounts, the levels
observed being adequate to offer protection against oxidative stress,” wrote
Shambhu D. Varma, Ph.D., Department of Ophthalmology and Visual Sciences,
University of Maryland School of Medicine, Baltimore, in the December 2008
issue of Ophthalmologica. Other antioxidants exist, as does systemic intake of sodium pyruvate, but
Dr. Varma noted the potential toxicity of such agents and usage. Although
much research remains, cataract prevention is no longer a matter that is
being taken lightly.
An agent of change?
Dr. Varma and colleagues looked at 37 patients slated for cataract surgery,
instilling one drop of 5% sodium pyruvate in the scheduled eye two hours
pre-op. The agent was applied in an artificial tear, and drops were applied
four times at 10-minute intervals. At the beginning of surgery, an aqueous
sample was withdrawn. “The level of pyruvate in the aqueous samples of patients that did
not receive pyruvate eye drops accounted for only 0.145 +/– 0.06 mM,” Dr.
Varma reported. “In the group given pyruvate, the levels rose to 0.525
+/– 0.22, 0.525 +/– 0.14 and 0.35 +/– 0.16 mM for patients
aged 14–18, 30–45 and 50–72 years, respectively. This increase
obviously represents true pyruvate that actually penetrated from that contained
in the eye drop preparation.” The concentration is also likely to be non-toxic. “Being highly water
soluble, it can also be easily compounded with most other common additives
in the eye drop such as the components of the commonly used buffers and the
preservatives,” Dr. Varma reported. The same cannot be said of other agents. “Previous studies have demonstrated
that many antioxidants are anti-cataractogenic, such as flavonoids, ascorbate,
vitamin E and pyruvate,” Dr. Varma noted. “However, these compounds,
except pyruvate, can also become pro-oxidant, and consequently, can become
toxic, especially in the presence of trace metals.”
Further, pyruvate has the potential to be especially effective as an antioxidant
preventing cataracts. “Pyruvate, apart from being endogenously derived with no known toxicity,
has the advantage of its dual mode of action—as a reactive oxygen species
scavenger as well as a metabolic agonist,” Dr. Varma reported. “Hence,
in addition to scavenging reactive oxygen species, it is capable of overcoming
the metabolic inhibition known to be associated with aging as well as diabetes.
In addition, it also inhibits protein glycation, another important contributing
factor in cataract formation.”
Already, other research has shown pyruvate as efficacious in reducing cataract
risk. In the April 1999 issue of Free Radical Research, Dr. Varma demonstrated
the efficacy of systemic pyruvate in attenuating cataract formation in rats.
Rats were fed a diet of 30% galactose and developed nuclear lens opacity
within 30 days. “This was delayed if the diet and water contained, in addition, 2%
sodium pyruvate,” Dr. Varma noted. “The incidence of cataract
in [the pyruvate] group was 0% at day 30 and only 25% at day 55.”
Meanwhile, in the October 2007 issue of the Journal of Ocular Pharmacology
and Therapeutics, Dr. Varma found that ultraviolet cataracts in rat lens
organ culture studies were prevented by pyruvate. “A protective effect of this keto acid against UV-induced tissue damage
has been shown for the first time, suggesting its clinical usefulness against
UV irradiation–induced pathologies,” Dr. Varma reported. Dr. Varma suggests the time is right to pursue clinical trials with pyruvate. “It should be feasible to carry out clinical trials with this compound
aimed at preventing and treating intraocular diseases such as cataracts and
diabetic retinopathy induced by intraocular generation of reactive oxygen
species and consequent oxidative stress,” Dr. Varma wrote in Ophthalmologica.
Despite the advances in cataract prevention, Mohan Rajan, M.D., medical director,
Rajan Eye Care Hospital, Chennai, India, says antioxidants will only be able
to delay the onset of cataract, not prevent it completely. “We did a study on this at the University of Madras [Chennai],” Dr.
Rajan said. That research found that systemic antioxidants halted lens opacities
from progressing but didn’t decrease the existing cataract, he said. “Oxidative stress is one of the factors in cataract development, but
cataract is multifactorial,” Dr. Rajan said. Instead, Dr. Rajan is confident that either phacoemulsification or extracapsular
cataract extraction will be able to reduce the backlog of cataract surgery
patients. Editors’ note:
Dr. Varma has no financial interests related to this study. Dr. Rajan
has no financial interests related to his comments. Contact information |
||||
