Role of cholesterol crystals in atherosclerosis is unmasked by altering tissue preparation methods

Standard tissue preparation for light and scanning electron microscopy (SEM) uses ethanol as a dehydrating agent but that can also dissolve cholesterol crystals (CC) leaving behind empty tissue imprints or "clefts". Cholesterol crystals may contribute to plaque rupture by their sharp tips that can tear membranes and trigger inflammation. Therefore, use of ethanol in tissue processing can mask the pathological role of CC. Here we evaluated the amount of cholesterol dissolved from CC with single and complete series of standard graded ethanol concentrations (25-100%) used in tissue preparation. Also, solubility of CC in ethanol at physiological levels was measured. Furthermore, we compared the effect of ethanol on CC in fresh human atherosclerotic plaques to matched segments dehydrated using vacuum (-1 atm, 12h). Tissue crystal density ranging from 0 to +3 was measured semi-quantitatively by SEM. For CC exposed to 25% and 100% ethanol for 10 min each, 0.38% and 95% of CC were dissolved respectively. Also, increase in CC solubility was significant at physiological levels of ethanol (0.16%) compared to water (43.4 ± 18.0 ng/mL vs. 30.9 ± 13.9 ng/mL; p < 0.05). We speculate that this could represent a potential mechanism of cardio-protective effects of alcohol consumption. In atherosclerotic plaques, CC density was lower in ethanol vs. saline treatment (+1.2 vs. +2.8; P < 0.01) with visible dissolving noted by SEM. Ethanol has been used for centuries in tissue preparation for microscopy. Here we demonstrate how current tissue preparation methods greatly alter histological findings with SEM by masking the potential mechanism of plaque rupture.