Histological classification and collagen distribution in atherosclerotic plaques in aorta of hypercholesterolemic rabbits

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Objective: To analyze the histopathological aspect of atheroma plaques in the aorta of rabbits submitted to diet modification and different evolution times. Methods: Aortic fragments of rabbits submitted to the following protocols were analyzed: all animals received a diet plus 0.5% cholesterol for 3months and/or followed by: group A (n=8) - sacrificed at 3months; group B (n=10) - followed by 3months of standard diet; group C (n=20) followed by 3months of 0.1% cholesterol diet; group D (n=12) - followed by 9months of 0.1% cholesterol diet. Histological sections of aortic arch fragment were analyzed in hematoxylin-eosin and picro-sirius red staining. The atherosclerotic plaques were analyzed, classifying them according to the predominance of cellularity (type 2) or presence of extracellular matrix and fibromuscular cap (type 3) and associated with a large amount of extracellular cholesterol crystals (type 4). Results: We did not observe a statistically significant difference in the intima/mediarelationship, although there was a tendency to larger plaques in groups with lipid diet for prolonged time (p<0.06). We found after 3months of hypercholesterolemic diet (group A), high serum cholesterol levels (1972±127 mg/dL) and plaques with higher cellularity (type 2), destructuring of the media layer, especially along the internal elastic lamina. The modification of the diet for 3months (groups B and C) reduced serum cholesterol levels, modifying the characteristics of the plaque, verifying more developed plaques (types 3 and 4) in animals with lipid diet. After 12months (group D) plaques with matrix predominance in relation to cellularity were observed, with a large amount of crystal of cholesterol and collagen fibers. Conclusion: The normalization of the diet or reduction of the lipid content modifies the histology of the plaque, evolving with higher extracellular matrix content.