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

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 3 months and/or followed by: group A (n=8) - sacrificed at 3 months; group B (n=10) - followed by 3 months of standard diet; group C (n=20) followed by 3 months of 0.1% cholesterol diet; group D (n=12) - followed by 9 months 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/media relationship, although there was a tendency to larger plaques in groups with lipid diet for prolonged time (p<0.06). We found after 3 months 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 3 months (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 12 months (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.