Large-Scale Screening of Natural Products Transactivating Peroxisome Proliferator-Activated Receptor alpha Identifies 9S-Hydroxy-10E,12Z,15Z-Octadecatrienoic Acid and Cymarin as Potential Compounds Capable of Increasing Apolipoprotein A-I Transcription in Human Liver Cells

Increasing apolipoprotein A-I (apoA-I), the predominant protein of high-density lipoprotein (HDL) particles, has favorable effects on atherogenic risk factors. Here, we investigated the effects of peroxisome proliferator-activated receptor alpha (PPAR alpha) transactivating compounds on apoA-I transcription in HepG2 cells. A transient PPAR alpha agonist transactivation assay was used to screen 2500 natural compounds. To analyze the effects on apoA-I transcription, human hepatocellular liver carcinoma (HepG2) were exposed to 0.1, 1, and 10 mu g/mL of the natural PPAR alpha transactivators. ApoA-I mRNA expression was determined by quantitative polymerase chain reaction. Extensive dose-response experiments were performed using compounds that increased apoA-I transcription by minimally 20%. Kelch-like ECH-associated protein 1 (KEAP) and carnitine palmitoyltransferase 1 alpha (CPT1 alpha) expression were used respectively to confirm Bromodomain-containing protein 4 inhibition or PPAR alpha activation. Twenty-eight natural compounds increased PPAR alpha transactivation by at least twofold. Despite the increased CPT1 alpha expression seen after the addition of most PPAR alpha activating compounds, CPT1 alpha expression and PPAR alpha transactivation did not correlate. Addition of 0.05 mu g/mL 9S-hydroxy-10E,12Z,15Z-octadecatrienoic acid (9(S)-HOTrE) increased apoA-I mRNA expression by 35%, whereas 10-25 mu g/mL of cymarin increased apoA-I transcription by 37%. However, combining cymarin and 9(S)-HOTrE did not result in a synergistic effect, in contrast this combination even decreased apoA-I transcription. ApoA-I transcription involves multiple regulatory players, and PPAR alpha transactivation alone is not sufficient. A search for natural compounds resembling the molecular structure of 9(S)-HOTrE or cymarin could aid to find additional components that increase apoA-I transcription.