Lipoproteins are macromolecular assemblies of lipids and proteins that are essential for the transportation of the water insoluble lipids in the circulation. The major lipoproteins, are low density lipoproteins (LDL) and high-density lipoproteins (HDL). LDL, also called the “bad cholesterol”, delivers cholesterol to peripheral tissues and is directly correlated with increased risk of cardiovascular disease, stroke and type II diabetes. HDL, on the other hand, is called the “good cholesterol” as it removes excess cholesterol from peripheral tissues for elimination by the liver in a process called reverse cholesterol transport (RCT). HDL is therefore, cardioprotective. The first and rate-limiting step in HDL biogenesis involves interaction of apolipoprotein A-I (apoA-I), the major protein of HDL, with the membrane transporter ABCA1 to promote cholesterol efflux to form nascent HDL.
Food additives and sugar substitutes have been widely consumed in recent years. While the FDA deems sweeteners such as stevia, sucralose, acesulfame and erythritol and food dyes such as Sunset Yellow and Allura Red safe for human consumption, their direct effects on HDL biogenesis are unknown.
In this study, we examined effects of the above-mentioned additives and sugar substitutes on HDL biogenesis using macrophage-derived cells, J774. We used a fluorescent analog, BODPIY-cholesterol, to label the cholesterol pool and to measured its efflux by
fluorescence. HDL biogenesis was determined by analyzing efflux media using native PAGE followed by immunoblotting using antibodies to apoA-I. Lipids were determined using cholera toxin subunit B to detect the ganglioside GM1.
We found that all sweeteners and food dyes exerted inhibitory effects on cholesterol efflux and HDL biogenesis to varying degrees under physiologically-relevant concentrations. Steviol, the metabolite of stevia, appeared to exert the largest inhibition. It reduced cholesterol efflux by > 50% and HDL biogenesis was reduced the most, as compared to the other sugar substitutes. Under control conditions nascent HDL particles varying from less than 7 to about 12 nm diameter produced. However, under most experimental conditions, additives appeared to have an impact on the larger particles (8-12 nm diameter) as they were either reduced substantially or absent). Interestingly, the sweetener Erythritol at low concentration (5mg/ml) was inhibitory but at higher concentration (15 mg/ml) appears to reverse this effect.
Since ABCA1 is essential for optimal cholesterol efflux and HDL biogenesis, we hypothesized that their inhibition by food additives and sugar substitutes was due to a decreased level of ABCA1. Surprisingly, we found that ABCA1 level under all conditions were either similar or higher than control levels. Therefore, we suggest that the additives used in this study presumably led to mislocalization of ABCA1 and/or caused a conformational change of the transporter. This could result in decreased binding of apoA-I thus leading to reduced cholesterol efflux resulting in decreased HDL biogenesis.
On the basis of this study we suggest that the FDA guidelines should be modified and sugar substitutes and foods containing artificial dyes should be consumed in moderation.
| Identifer | oai:union.ndltd.org:bu.edu/oai:open.bu.edu:2144/42207 |
| Date | 01 March 2021 |
| Creators | Talwar, Aarushi |
| Contributors | Herscovitz, Haya |
| Source Sets | Boston University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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