Hydroxypheophytin a Stereoisomers as Principal Bioactive Compounds from Spirulina for the Reduction of Lipids and Appetite

The rising prevalence of obesity calls for the development of novel treatments. Spirulina is known for its beneficial effects on metabolic health; however, the specific bioactive compounds have not yet been identified. This work aims to address this gap through the bioassay-guided isolation of lipid-reducing compounds from Limnospira platensis using zebrafish larvae. The primary bioactive compounds identified were the stereoisomers of 132-hydroxypheophytin a (132-hpa), with 132-(R)-hpa (2) (EC50 = 1.7 μM) that showed seven times higher lipid-reducing potential than 132-(S)-hpa (1) (EC50 = 11.7 μM). Both isomers prevented lipid accumulation in an in vitro steatosis model using oleic acid-overloaded HepG2 cells, and both remediated steatosis following prior lipid accumulation. Both compounds reduced Paramecia intake with similar EC50 values, but only 132-(S)-hpa (1) suppressed liposome intake (EC50 = 22.5 μM), which indicates different mechanisms of appetite regulation. No effects were observed on tissue glucose uptake or β-cell regeneration after ablation. Together, these findings identify the isomers of 132-hpa (1 and 2) as the principal bioactive compounds of spirulina, with differing lipid reduction potencies and appetite suppression, underscoring the importance of C-132 configuration for biological activity.