The Importance of Calretinin in the Detection of Early Alterations of the Sensory Retina in Hypercholesterolemia Experimental Model

Abstract

Purpose: : The objective of this study is to demonstrate, by immunohistochemical examinations, the early abnormalities of the sensory retina induced by hypercholesterolemia in rabbit eyes.

Methods: : New Zealand rabbits were divided into two groups: CG with 6 rabbits was fed by normal diet for 6 weeks: G1 with 12 rabbits was initially fed by 1% cholesterol diet for two weeks and from the 14^th day on a 0.5% cholesterol diet. The rabbits underwent the following examinations: seric dosages of total cholesterol, triglycerides, cholesterol HDL, and fasting glycemia at the beginning of the experiment, on the 14^th and 42^nd days, when they were euthanized. The eyes underwent an immunohistochemical analysis with the monoclonal antibodies anti-calretinin and anti-glial fibrillary acidic protein (GFAP). The Mann-Whitney nonparametric test was selected to compare the groups in relation to the variables of this study. To compare the analyzed areas within each group the Wilcoxon nonparametric test was also used. Values of p<0.05 indicated statistical significance.

Results: : On Day 14, a significant increase in the glucose and total cholesterol levels of G1 was observed, representing a significant difference in relation to CG. On the euthanasia day, an significant increase in G1 weight, glucose and total cholesterol levels was observed. Ganglion cells in G1 presented more immunoreactivity to anti-calretinin, although the difference did not show statistical significance in relation to CG (p=0.091). Conversely, G1 cells elements presented significant immunoreactivity to this antibody (p<0.001). No immunoreactivity to GFAP was observed in both groups.

Conclusions: : This study has shown that a hypercholesterolemic diet may induce early abnormalities in the sensory retina in rabbits. The anti-calretinin monoclonal antibody revealed calcium accumulation inside the nerve cells, evidencing the early degeneration of the retinal cells induced by the increase in the levels of seric cholesterol. The ischemia in the present model has caused Ca (2+) influx into the neuronal retinal cells, evidencing cellular damage. However, this has not caused cell death. Such findings can explain GFAP negativity in both groups.

Keywords: retinal degenerations: cell biology • degenerations/dystrophies • apoptosis/cell death