Ascorbic acid and alpha-tocopherol down-regulate apolipoprotein A-I gene expression in HepG2 and Caco-2 cell lines

A systematic review and meta-analysis on the impact of oral vitamin E supplementation on apolipoproteins A1 and B100

BACKGROUND AND AIM

Cardiovascular diseases (CVDs) are the number one cause of mortality worldwide. Apolipoprotein B (ApoB), apolipoprotein A1 (ApoA1), and ApoB/ApoA1 ratio are considered as predictors of CVD alongside with lipid profile. Evidence suggest that nutrients with antioxidant properties, especially vitamin E, are essential for a healthy cardiovascular system. The aim of present meta-analysis was to determine the effect alpha-tocopherol on ApoA1 and ApoB levels.

METHODS

PubMed-Medline and SCOPUS databases and Google Scholar were searched up to July 2021. Random-effects model was employed to perform meta-analysis. In order to find heterogeneity sources, subgroup analysis was performed. Trim and fill analysis was performed in case of presence of publication bias. Quality assessment was performed using Cochrane Collaboration's tool.

RESULTS

Seven eligible studies, involving 1284 individuals were included. Mean age of participants ranged between 25.4 and 59 years. There was no significant effect of vitamin E supplementation on Apo A1 (SMD = 0.22 IU/d; 95% CI: -0.38, 0.28; P = 0.481) and Apo B levels (SMD = -0.62 IU/d; 95% CI: -1.94, 0.70; P = 0.360).

CONCLUSION

No remarkable effect of vitamin E supplementation was observed on ApoA1 and ApoB levels in adults. Additional studies investigating the influence of vitamin E on apolipoproteins as primary outcome with larger sample size are suggested.

Comparison of the effect of Dietary Approaches to Stop Hypertension diet and American Diabetes Association nutrition guidelines on lipid profiles in patients with type 2 diabetes: A comparative clinical trial

AIM

The present study aimed to compare the effects of the Dietary Approaches to Stop Hypertension (DASH) diet and American Diabetes Association (ADA) guidelines on the lipid profiles of patients with type 2 diabetes.

METHODS

In a 12-week clinical trial, 80 patients with type 2 diabetes aged 18-65 years were randomly allocated into the case (n = 40) and control (n = 40) groups. The case group received the DASH diet and the control group consumed a dietary pattern in accordance with the ADA guidelines. Fasting blood samples were measured for triglyceride (TG), low-density lipoprotein (LDL), total cholesterol (TC), high-density lipoprotein (HDL), very low-density lipoprotein (VLDL) and free fatty acid (FFA). Moreover, physical activity and 24-hour dietary recall (24 hours) were assessed at baseline and end of the study.

RESULTS

The DASH diet and diabetic diet (in accordance with the ADA guidelines) for 12 weeks significantly decreased TG, TC and VLDL (P < 0.05). FFA showed a significant decrease in both the groups, which was greater in the cases compared with the control group (P = 0.049).

CONCLUSIONS

Compliance with any DASH or diabetic diet for 12 weeks in patients with type 2 diabetes had beneficial effects on cardiometabolic risks.

Induction of apolipoprotein A-I gene expression by black seed (Nigella sativa) extracts

CONTEXT

Black seed [Nigella sativa L. (Ranunculaceae)] has been shown in animal models to lower serum cholesterol levels.

OBJECTIVES

In order to determine if extracts from black seed have any effects on high-density lipoprotein (HDL), we characterized the effects of black seed extract on apolipoprotein A-I (apo A-I) gene expression, the primary protein component of HDL.

MATERIALS AND METHODS

Hepatocytes (HepG2) and intestinal cells (Caco-2) were treated with black seed extracts, and Apo A-I, peroxisome proliferator-activated receptor α (PPARα), and retinoid-x-receptor α (RXRα) were measured by Western blot analysis. Apo A-I mRNA levels were measured by quantitative real-time polymerase chain reaction and apo A-I gene transcription was measured by transient transfection of apo A-I reporter plasmids.

RESULTS

Extracts from black seeds significantly increased hepatic and intestinal apo A-I secretion, as well as apo A-I mRNA and gene promoter activity. This effect required a PPARα binding site in the apo A-I gene promoter. Treatment of the extract with either heat or trypsin had no effect on its ability to induce apo A-I secretion. Treatment with black seed extract induced PPARα expression 9-fold and RXRα expression 2.5-fold. Furthermore, the addition of PPARα siRNA but not a control siRNA prevented some but not all the positive effects of black seed on apo A-I secretion.

DISCUSSION

Black seed extract is a potent inducer of apo A-I gene expression, presumably by enhancing PPARα/RXRα expression.

CONCLUSIONS

We conclude that black seed may have beneficial effects in treating dyslipidemia and coronary heart disease.

The effect of nutritional supplements on serum high-density lipoprotein cholesterol and apolipoprotein A-I

One of the factors contributing to the increased risk of developing premature atherosclerosis is low plasma concentrations of high-density lipoprotein (HDL) cholesterol. Multiple potential mechanisms account for the cardioprotective effects of HDL and its main protein apolipoprotein A-I (apo A-I). Diet has an important role in modulating HDL cholesterol level. The widespread use of nutritional supplements may also alter the biology of HDL. In this review, we discuss the effect of select nutritional supplements on serum HDL cholesterol and apo A-I levels. Some nutritional supplements, such as phytosterols, soy proteins, and black seed extracts, may increase HDL cholesterol levels, while others such as cholic acid and high doses of commonly used antioxidant vitamins may downregulate HDL cholesterol levels and reduce its cardioprotection. Multiple mechanisms are involved in the regulation of HDL levels, so changes in production and clearance of HDL may have different clinical implications. The clinical relevance of the changes in HDL and apo A-I caused by nutrient supplementation needs to be tested in controlled clinical trials.

Serum vitamins A and E as modifiers of lipid trait genetics in the National Health and Nutrition Examination Surveys as part of the Population Architecture using Genomics and Epidemiology (PAGE) study

Both environmental and genetic factors impact lipid traits. Environmental modifiers of known genotype-phenotype associations may account for some of the "missing heritability" of these traits. To identify such modifiers, we genotyped 23 lipid-associated variants identified previously through genome-wide association studies (GWAS) in 2,435 non-Hispanic white, 1,407 non-Hispanic black, and 1,734 Mexican-American samples collected for the National Health and Nutrition Examination Surveys (NHANES). Along with lipid levels, NHANES collected environmental variables, including fat-soluble macronutrient serum levels of vitamin A and E levels. As part of the Population Architecture using Genomics and Epidemiology (PAGE) study, we modeled gene-environment interactions between vitamin A or vitamin E and 23 variants previously associated with high-density lipoprotein cholesterol (HDL-C), low-density lipoprotein cholesterol (LDL-C), and triglyceride (TG) levels. We identified three SNP × vitamin A and six SNP × vitamin E interactions at a significance threshold of p < 2.2 × 10(-3). The most significant interaction was APOB rs693 × vitamin E (p = 8.9 × 10(-7)) for LDL-C levels among Mexican-Americans. The nine significant interaction models individually explained 0.35-1.61% of the variation in any one of the lipid traits. Our results suggest that vitamins A and E may modify known genotype-phenotype associations; however, these interactions account for only a fraction of the overall variability observed for HDL-C, LDL-C, and TG levels in the general population.

Dyslipidemia in type 2 diabetes mellitus

Dyslipidemia is one of the major risk factors for cardiovascular disease in diabetes mellitus. The characteristic features of diabetic dyslipidemia are a high plasma triglyceride concentration, low HDL cholesterol concentration and increased concentration of small dense LDL-cholesterol particles. The lipid changes associated with diabetes mellitus are attributed to increased free fatty acid flux secondary to insulin resistance. The availability of multiple lipid-lowering drugs and supplements provides new opportunities for patients to achieve target lipid levels. However, the variety of therapeutic options poses a challenge in the prioritization of drug therapy. The prevalence of hypercholesterolemia is not increased in patients with diabetes mellitus, but mortality from coronary heart disease increases exponentially as a function of serum cholesterol levels, and lowering of cholesterol with statins reduces diabetic patients' relative cardiovascular risk. Although drug therapy for dyslipidemia must be individualized, most people with diabetes mellitus are candidates for statin therapy, and often need treatment with multiple agents to achieve therapeutic goals.

Obesity-related changes in high-density lipoprotein metabolism

Obesity is associated with a 3-or-more-fold increase in the risk of fatal and nonfatal myocardial infarction (1,2,3,4,5,6). The American Heart Association has reclassified obesity as a major, modifiable risk factor for coronary heart disease (7). The increased prevalence of premature coronary heart disease in obesity is attributed to multiple factors (8,9,10). A principal contributor to this serious morbidity is the alterations in plasma lipid and lipoprotein levels. The dyslipidemia of obesity is commonly manifested as high plasma triglyceride levels, low high-density lipoprotein cholesterol (HDLc), and normal low-density lipoprotein cholesterol (LDLc) with preponderance of small dense LDL particles (7,8,9,10). However, there is a considerable heterogeneity of plasma lipid profile in overweight and obese people. The precise cause of this heterogeneity is not entirely clear but has been partly attributed to the degree of visceral adiposity and insulin resistance. The emergence of glucose intolerance or a genetic predisposition to familial combined hyperlipidemia will further modify the plasma lipid phenotype in obese people (11,12,13,14,15).

Structure, function and amyloidogenic propensity of apolipoprotein A-I

Apolipoprotein A-I, the major structural apolipoprotein of high-density lipoproteins, efficiently protects humans from cholesterol accumulation in tissues; however, it can cause systemic amyloidosis in the presence of peculiar amino acid replacements. The wild-type molecule also has an intrinsic tendency to generate amyloid fibrils that localise within the atherosclerotic plaques. The structure, folding and metabolism of normal apolipoprotein A-I are extremely complex and as yet not completely clarified, but their understanding appears essential for the elucidation of the amyloid transition. We reviewed present knowledge on the structure, function and amyloidogenic propensity of apolipoprotein A-I with the aim of highlighting the possible molecular mechanisms that might contribute to the pathogenesis of this disease. Important clues on apolipoprotein A-I amyloidogenesis may be obtained from classical comparative studies of the properties of the wild-type versus the amyloidogenic counterpart. Additionally, in the case of apoA-I, further insights on the molecular mechanisms underlying its amyloidogenic propensity may derive from comparative studies between amyloidogenic variants and other mutations associated with hypoalphalipoproteinemia without amyloidosis.