Interactions between anthocyanins, cholesterol metabolism and PON-1 in relation to HDL quality and CVD risk

Background: Data from epidemiological studies demonstrate an inverse association between high intakes of anthocyanins and risk of cardiovascular disease. The human and animal dietary intervention studies also showed that consumption of anthocyaninrich extracts and foods causes beneficial changes in lipid profiles. However, the potential mechanisms of action are yet to be fully elucidated; in particular, is it the anthocyanins per se or their metabolites that cause the changes, and what are the gene/protein targets in the lipoprotein metabolic pathways? Therefore, the aim of this research was to develop a mechanistic understanding of how anthocyanins and/or their metabolites alter lipid/lipoprotein metabolism and improve HDL function. Approaches: Using cultured macrophages, the effects of the two main dietary anthocyanins and a large number of their metabolites on the expression of key genes involved in reverse cholesterol transport (RCT), and on the expression and enzyme activities of paraoxonase-1 (PON1) (marker of HDL function) were tested at physiologically relevant concentrations. The effects of anthocyanin consumption on cholesterol efflux transporters was investigated by quantifying the expression of ABCA1 and ABCG1 in aortic and liver tissues from ApoE-/- mice that had consumed diets supplemented with anthocyanin-expressing tomatoes compared to mice that had consumed diets supplemented with anthocyanin-free (control) red tomatoes. The broader effects of three major anthocyanin metabolites was assessed using RNA seq to study genome-wide changes in gene expression in cultured human macrophages. A randomized placebo-controlled crossover human intervention study was conducted using purified anthocyanin extracts to investigate the effects of consuming anthocyanins on lipid/lipoprotein profiles and biomarkers of HDL function and interactions with PON1 genotype. Results: None of the tested anthocyanins or their metabolites significantly altered the expression of cholesterol transporter (ABCA1, ABCG1) or scavenger receptor (MSR1, SCARB1 and CD36) genes (the key genes involved in RCT), nor did they affect the expression of the PON1 gene or the activities of the enzyme. In addition, RNA seq analysis revealed that treatment with the three major anthocyanin metabolites did not cause any significant changes in the expression of macrophage genes or affect pathways related with atherosclerosis. In the human dietary intervention with high doses of isolated anthocyanins, no significant changes in lipid profiles, ApoA1, ApoB1, HDL subfractions and biomarkers of glycemic control were observed compared to the placebo after 4 weeks of intervention. The human intervention also showed no significant interaction between the consumption of anthocyanin, biomarkers of HDL function, PON1 activities and PON1 genotype. Conclusion: In conclusion, the data in this thesis do not support the notion that anthocyanins or their metabolites improve lipid/lipoprotein profiles and biomarkers of HDL function