Effect of lipid extracts from edible blue‐green algae, Nostoc commune var. Sphaeroides Kützing and Spirulina Platensis, on the regulation of genes for cholesterol and lipid metabolism in HepG2 cells

Abstract

We previously demonstrated that lipid extract (LE) from an edible blue‐green alga, Nostoc commune var. Sphaeroides Kützing (NO), inhibited the expression of genes involved in lipogenesis, cholesterol synthesis and LDL uptake by repressing maturation of sterol regulatory element binding protein 1 (SREBP‐1) and SREBP‐2 in HepG2 cells. To compare the effect of NO with Spirulina Platensis (SP), the most common BGA for human consumption, LE was prepared with dichloromethane/methanol (2:1) from two blue‐green algae species and HepG2 cells were incubated with the algal LE for 24 hr. Both algal LE decreased mRNA levels of LDL receptor (LDLR), HMG‐CoA reductase (HMGR) and SREBP‐2 in a dose‐dependent manner (0–100 g/ml). Protein levels of the genes were also diminished by algal LE except mature SREBP‐2 protein in NO LE‐treated cells. Fatty acid synthase (FAS) and stearoyl CoA desaturase mRNA as well as FAS protein levels were significantly lowered by NO and SP LE with concomitant decreases in SREBP‐1c mRNA and its mature protein. The results suggest NO and SP LE contain bioactive components that inhibit SREBP‐1c expression and maturation to repress lipogenic gene expression; and different mechanism may mediate the repressive effect of NO and SP LE on the expression of LDLR and HMGR because mature SREBP‐2 protein was not diminished by NO LE whereas SP LE markedly reduced the protein levelsGrant Funding Source: NIH R21AT005152