In vivo noninvasive measurement of skin autofluorescence biomarkers relate to cardiovascular disease in mice

Background and objective: The formation of reactive oxygen species (ROS) is associated with cardiovascular disease (CVD). High dietary cholesterol can significantly alter the delicate balance between pro-oxidation and antioxidant defences leading to reactive oxygen species formation in the vasculature, without significant structural changes in tissue composition. We aimed to establish a methodology for the noninvasive assessment of skin fluorescent biomarkers in mice. Materials and methods: C57/black/6 wild-type (WT; n = 25) male mice were subdivided to receive normal rodent chow (n = 11) or a high cholesterol diet (2% cholesterol; n = 14) for 20 weeks. Skin autofluorescence measurements were made on the backs of anaesthetized (1.5-2% isoflurane in oxygen) mice. A laser probe was used to make simultaneous measurements of: collagen, elastin, nicotinamide pyridoxine, flavins, lipofuscin and β-carotene. Results are expressed as group mean in arbitrary units (AU) ± standard error (SE). Hearts were excised and weighed (mg); cardiac hypertrophy was measured by ratio [heart weight (mg)/bodyweight (g) ± SE]. Student's t-test was used for statistical significance analysis (p ≤ 0.05). Results: There were no significant differences between cholesterol- and chow-fed animals for collagen (34 ± 5AU vs. chow 34 ± 4 AU, p = 0.51) and elastin (66 ± 6 AU vs. chow 82 ± 7 AU, p = 0.11). Significant differences were evident for nicotinamide adenine dinucleotide (92 ± 7 AU vs. chow 118 ± 7 AU, p = 0.01), pyridoxine (56 ± 4 AU vs. chow 73 ± 4 AU, p = 0.01), flavins (44 ± 3 AU vs. chow 57 ± 4 AU, p = 0.01), lipofuscin (35 ± 3 AU vs. chow 46 ± 3 AU, p = 0.01) and β-carotene (19 ± 2 AU vs. chow 25 ± 2 AU, p = 0.01). Cholesterol-fed animals had significantly heavier hearts (7 ± 0.3 ratio vs. chow 5 ± 0.1 ratio, p = 0.001). Conclusion: Cholesterol feeding induced cardiovascular disease as noted by cardiac hypertrophy in wild-type mice. A reduction was observed in pyridoxine, nicotinamide adenine dinucleotide, flavins, lipofuscin and β-carotene, which are established risk factors for cardiovascular disease. We report no significant changes in structural proteins collagen and elastin, suggesting no generalized tissue restructuring, which might otherwise explain the observed pathological differences.