Apoptotic mechanisms within the retina in Staphylococcus epidermidis experimental endophthalmitis

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Abstract
Aim To investigate the potential involvement of apoptosis and its regulators Bcl-2, Bax, and Fas within the retina in Staphylococcus epidermidis experimental endophthalmitis. Methods Endophthalmitis was induced in 48 male Lewis rats by unilateral 25-μl intravitreal injection of 7,000 viable organisms of slime-producing S. epidermidis strain ATCC 35983 (experimental group). Forty-eight other Lewis rats received a similar sterile normal saline injection (control group). The injected eyes were graded for clinical inflammation and were removed in groups at 6, 12, 24, 48, 72, and 168 hours post-injection. After surgical separation, retinal tissue specimens were fixed, and paraffin sections underwent hematoxylin-eosin staining, immunohistochemistry against Bcl-2, Bax, and Fas, and TUNEL assay for detection of apoptotic cells. Following morphometric analysis, the apoptotic body index (ABI) was calculated. Results While Bcl-2 expression was absent, Bax and Fas expression and apoptosis in ganglion cells, bipolar cells, and photoreceptors, were significantly higher in the experimental group compared to the control group (P < 0.05). In the experimental group, inflammation peaked at 24 hours, Bax and Fas expression at 48 hours and the ABI at 72 hours post-injection. Conclusion Apoptosis is increased within the retina in S. epidermidis experimental endophthalmitis through upregulation of Bax and Fas, peaking soon after peak inflammation.