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The Influence of Zinc on Caspase-3 and DNA Breakdown in Cultured Human Retinal Pigment Epithelial Cells
John P. M. Wood, DPhil;
Neville N. Osborne, PhD, DSc
Arch Ophthalmol. 2001;119:81-88.
Objectives To investigate the role of extracellular zinc on the death process of
cultured human retinal pigment epithelial (RPE) cells.
Methods Confluent cells on borosilicate glass coverslips were treated with substances
in serum-free growth medium for various times and were analyzed for death
by means of changes in morphologic features, numbers of attached cells, and
terminal deoxynucleotidyl transferase–mediated deoxyuridine triphosphate
nick-end labeling (TUNEL) procedure. Some cultures were also exposed to experimental
ischemia (defined as a lack of oxygen, glucose, and serum). Electrophoresis
and Western blotting and enzyme assays were used to investigate changes in
expression of the protease enzyme, caspase-3.
Results Experimental ischemia caused death of RPE cells. Zinc sulfate had no
effect on these cells at low concentrations (100 pmol/L to 10 nmol/L), but
protected them at higher concentrations ( 10 µmol/L) and appeared
to exacerbate cell death at still greater concentrations. Moreover, zinc compounds
(>10 µmol/L) also induced death of cells in control cultures that could
be blocked by zinc chelators and partially by the caspase-3 inhibitor, DEVD-FMK.
Zinc also increased the amount of the active form of caspase-3 in RPE cells.
Conclusions Zinc salts protect RPE cells from experimental ischemia–induced
death at low concentrations (100 pmol/L-10 nmol/L). However, at higher concentrations,
zinc causes cell death and alters the cellular level of caspase-3. These observations
are consistent with the death process being apoptosis.
Clinical Relevance Zinc supplements are taken by many individuals. Low doses of zinc can
protect RPE cells against ischemic-type insults as may occur in certain ocular
complaints. Furthermore, high concentrations of zinc can damage RPE cells.
Because zinc ions are known to be taken up by RPE cells from the choroidal
circulation, the actual therapeutic dose taken by patients is critical.
From the Nuffield Laboratory of Ophthalmology, University of Oxford,
Oxford, England.
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