The effect of black seed (Nigella sativa) extract on lipid metabolism in HepG2 cells.

Black seed extract stimulates apolipoprotein A-I (apo A-I) gene expression in hepatocytes and intestinal cells in part by elevating peroxisome proliferator-activated receptor α (PPARα) and retinoid X receptor α (RXRα) levels. To explore potential ramifications of these observations, we examined the effects of black seed extract on hepatocyte lipid content and expression of key transcriptional regulators of fatty acid ß-oxidation and lipogenesis in HepG2 cells. PPARα, peroxisome proliferator-activated receptor γ (PPARγ), RXRα, thyroid hormone receptor ß (TRß), sterol-responsive element binding protein 1 (SREBP1), and sterol-responsive element binding protein 2 (SREBP2) levels were measured in black seed extract treated liver-derived HepG2 cells. Black seed extract treatment increased PPARα and RXRα expression and decreased intracellular neutral lipid content. Black seed extract treatment increased TRß expression and activity, and PPARα activity. In contrast, PPARγ, SREBP1 and SREBP2 levels were decreased in black seed extract treated cells. Black seed extract treatment also increased acyl-CoA synthetase long chain family member 5 (ACSL5), peroxisomal acyl-CoA oxidase 1 (ACOX1), and carnitine palmitoyl transferase 1A (CPT-1A) expression, three PPARα-dependent rate-limiting genes that facilitate fatty acid oxidation, similar to fenofibrate. PPARα knockdown reversed the effects of fenofibrate and blackseed on ACSL5, ACOX1, and CPT-1A expression. In conclusion, black seed extract-mediated lipid lowering in HepG2 cells is associated with increased expression of fatty acid oxidation enzymes and PPARα and reduced lipogenic signaling. Thus black seed extract may be potentially beneficial in metabolic diseases such as diabetes, cardiovascular disease, and metabolic syndrome.

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 black seed (Nigella sativa) extract on FOXO3 expression in HepG2 cells.

Black seed extracts are known to alter cellular metabolism through multiple signaling pathways. Since Forkhead box transcription factor 3 (FOXO3) has a significant role in regulating cellular metabolism, the effect of lipid extracts of black seed (Sativa nigella) on FOXO3 levels and AKT and 5-AMP activated protein kinase α (AMPKα) signaling was measured in HepG2 hepatoma cells. FOXO3 levels, phosphorylation, and nuclear exclusion were measured by Western blot, as were AKT and AMPK expression and activity using phosphorylation-specific antibodies. Apolipoprotein A-I expression, a black seed-responsive gene, was measured by Western blot. Treatment with black seed extract increased FOXO3 phosphorylation and decreased its expression. In contrast to control cells where FOXO3 was located primarily in the nucleus, in black seed-treated HepG2 cells, FOXO3 was localized primarily to the cytoplasm. These changes in FOXO3 phosphorylation, expression, and localization were accompanied by increased AKT activity. Black seed also decreased AMPKα activity but increased AMPKα expression. Lipid extracts from black seeds inhibit FOXO3 activity and thereby modulate the expression of FOXO3-dependent genes.