The effects of high ambient glucose on the radiosensitivity of retinal microvascular endothelial cells and pericytes.
OBJECTIVE
The metabolic peturbations of diabetes cause functional and structural changes in the retinal microvasculature which are termed diabetic retinopathy. Exposure of the eye to ionising radiation results in retinal vascular damage with a clinical manifestation known as radiation retinopathy. Anecdotal studies have suggested that exposure to even low levels of ionising radiation may accelerate development of pathological changes in the retinal vessels of patients with diabetes. This in vitro study was designed to test the hypothesis that the combination of a high ambient glucose environment (mimicking hyperglycaemia and diabetes) along with exposure to ionising radiation would result in more accentuated damage to cultured retinal vascular cells.


METHODS
Retinal microvascular endothelial cells and pericytes were propagated for 5 days in either 5 mM (euglycaemia) or 15 mM (hyperglycaemia) glucose. Cells were irradiated with 250, 500 or 1000 cGy of ionising radiation using a 6 MV beam photon accelerator which was used for radiotherapy. Similarly treated but unirradiated cells were used as controls. DNA damage was assessed using the single-cell gel electrophoresis (comet) assay.


RESULTS
Unirradiated control cells pre-exposed to glucose at either 5 mM or 15 mM for 5 days showed no significant difference in mean percentage tail DNA representing damage. However, in both pericytes and endothelial cells exposed to ionising radiation, cells cultured in 15 mM glucose showed significantly higher levels of DNA damage compared with those cultured in 5 mM glucose, with maximal differences being seen at the higher radiation doses (500 and 1000 cGy).


CONCLUSIONS
This study has demonstrated that retinal microvascular cells cultured in high glucose express more DNA damage when exposed ionising radiation. These findings have important implications for the management of patients with diabetes if they require radiotherapy for neoplastic disease.
Department of Ophthalmology and Vision Science, Queen's University of Belfast, Belfast, Northern Ireland.
William
W
Patton
Heather
H
Gillespie
Leslie
L
Frew
Maureen
M
Burns
Sheena
S
Lewis
Usha
U
Chakravarthy
D000818:Animals; D001205:Ascorbic Acid / Q000494:pharmacology; D002417:Cattle; D002478:Cells, Cultured; D020552:Comet Assay; D004249:DNA Damage; D004730:Endothelium, Vascular / Q000187:drug effects* / Q000528:radiation effects*; D005947:Glucose / Q000494:pharmacology*; D006943:Hyperglycemia / Q000150:complications; D020286:Pericytes / Q000187:drug effects* / Q000528:radiation effects*; D011836:Radiation Tolerance; D011839:Radiation, Ionizing; D012171:Retinal Vessels / Q000187:drug effects / Q000528:radiation effects; D024505:Tocopherols / Q000494:pharmacology
D005947:Glucose; D001205:Ascorbic Acid; D024505:Tocopherols