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M. D. Cooke, P. Kothary, M. A. Del Monte; The Effect of Acute Insulin Exposure on P38 Kinase Production in Human Retinal Epithelial Cells. Invest. Ophthalmol. Vis. Sci. 2010;51(13):62.
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© ARVO (1962-2015); The Authors (2016-present)
Metaplastic human retinal pigment epithelial (hRPE) cells have been implicated in the pathogenesis of proliferative eye diseases and proliferative diabetic retinopathy (PDR). Acute insulin therapy given to diabetic patients has been linked to a transient increase in PDR by a mechanism involving up-regulation of Vascular Endothelial Growth Factor (VEGF). Since VEGF causes abnormal proliferation of vascular endothelial and hRPE cells via a mechanism that may involve regulation by the P38 mitogen-activated protein kinase (P38), we investigated the effect of insulin and of SB203580 (SB), an inhibitor of P38 activity, on P38 production in in vitro cultured hRPE cells.
Primary hRPE cell cultures were prepared from donor human eyes obtained from the Michigan Eye Bank. 3H-thymidine incorporation and direct cell counting by the trypan blue exclusion method (T) were performed to quantitate cell proliferation. Synthesis of P38 was measured quantitatively by immunoprecipitation of 14C-methionine labeled P38 and qualitatively by immunocytochemistry. Cell numbers are expressed as cells/µL. A Student "t" test was used to compare groups of data.
Insulin (0-5 µg/mL) increased hRPE cell proliferation in a dose-dependent manner. In addition, insulin (0-5 µg/mL) stimulated 14C-methionine-P38 synthesis in hRPE cells also in a dose-dependent manner. SB inhibited the insulin-stimulated 14C-methionine-P38 synthesis (774±110 vs. 1039±156, CPM±SEM, n=6, p≤0.05) in hRPE cells. SB also decreased proliferation as determined by T (42±6 vs. 75±14, n=3, p≤0.05). Immunocytochemical studies confirmed increased immuno-reactivity of P38 in hRPE cells exposed to insulin alone compared to the immuno-reactivity in cells exposed to insulin and SB.
Insulin is a mitogen for hRPE cells. It stimulates P38 production in hRPE cells. SB, an inhibitor of P38, inhibited insulin-stimulated P38 production. Thus, a P38 inhibitor given concurrently with acute insulin treatment may be effective in reducing the exacerbation in retinopathy seen in some diabetic patients.
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