Purpose: Over the past few decades, docosahexaenoic acid (DHA) has gained special attention for management of cholesterol-associated metabolic disorders and neurodegenerative diseases such as Alzheimer's disease (AD) owing to its neuroprotective, anti-inflammatory and hypolipidemic properties. Several epidemiological studies have reported the effect of DHA in reducing the risk of developing AD by lowering cholesterol. Hypercholesterolemia is a pro-amyloidogenic factor influencing the enzymatic processing of amyloid-β precursor protein (AβPP) to toxic β-amyloid. However, the mechanism by which DHA modulates the cholesterol pathway has not been established. Thus, the objective of this study was to investigate the mechanism of regulation of cholesterol metabolism by DHA in an AβPP695 overexpressing AD cell model.
Methods: A gas chromatography/mass spectrometry method was developed and validated for the targeted profiling of 11 cholesterol metabolites in DHA-treated Chinese hamster ovary wild-type (CHO-wt) and AβPP695 overexpressing (CHO-AβPP695) cells. The differential metabolite profiles between DHA- and vehicle-treated groups were further analyzed using fold change values of the ratio of concentration of metabolites in CHO-AβPP695 to CHO-wt cells. Effect of DHA on key rate-limiting enzymatic activities within the cholesterol pathway was established using biochemical assays.
Results: Our results showed that DHA reduced the levels of key cholesterol anabolites and catabolites in CHO-AβPP695 cells as compared to CHO-wt cells. Further enzymatic studies revealed that the cholesterol-lowering effect of DHA was mediated by regulating HMG-CoA reductase and squalene epoxidase enzyme activities.
Conclusion: We demonstrate for the first time the dual effects of DHA in inhibiting HMG-CoA reductase and squalene epoxidase and modulating the sterol biosynthesis axis of the cholesterol pathway in AβPP695 overexpressing AD. Our novel findings underscore the potential of DHA as a multi-target hypocholesterolemic agent for the prophylaxis of AD and other cholesterol-associated diseases.
Keywords: Amyloid β-precursor protein (AβPP); Cholesterol; Docosahexaenoic acid (DHA); Gas chromatography; HMG-CoA reductase; Metabonomics; Squalene epoxidase.