In this study, human intestinal cells (Caco-2 cells) were incubated without or with 100µl /ml Echinacea extracts for 5 hours, after which total RNA was extracted and assayed using reverse transcription-PCR. The results from reverse transcript-PCR suggest that Echinacea extracts are capable of up-regulating the level of ApoA-I gene expression. Caco-2 cells incubated with Echinacea extracts exhibited approximately a 17-fold increase in the level of gene expression as compared to Caco-2 cells without Echinacea extracts (Figure 1). The relative amount of apoA-I protein secreted by the cells into the culture media was also analysed using protein immuno-precipitation followed by SDS-PAGE. Based on the results obtained from densitometric scanning, apoA-I protein synthesis was increased by approximately 3-folds after incubating with Echinacea extracts for 5 hours as compared to the cells without Echinacea extracts (Figure 2). The two sets of results show that Echinacea extracts are capable of up-regulating both gene expression and protein expression of apoA-I, thus supporting the hypothesis that human intestinal cells (Caco-2 cells) incubated with Echinacea extracts will exhibit higher levels of apoA-l gene expression and apoA-l protein expression as compared those without Echinacea extracts.
Since apoA-I is the major protein component of HDL, an increased level of apoA-I expression may imply that a higher level of HDL. In this experiment, Echinacea extracts significantly upregulated apoA-I synthesis, which may in turn result in a higher level of HDL in the body. Experiment using transgenetic and knockout mice have shown that the level of apoA-I expression can directly affect HDL levels which can influence atherosclerosis susceptibility (Rubin et al, 1991) as apoA-I protein is also involved in the synthesis and assembly of HDL. This is supported by Tsujita et al (2005) who found that the main mechanism for HDL assembly by endogenous apoA-I in HepG2 cells is aided by apoA-I, which interacts with cellular ABCA1 to generate HDL. Hence, Echinacea extracts, which are capable of increase apoA-I expression, would also play a part in regulating HDL concentration in the human body.
Although it is clearly shown that Echinacea are capable of regulation apoA-I gene expression, the underlying mechanism has yet been fully elucidated. However, by comparing results with other studies, possible reaction pathways of Echinacea extracts in regulation of apoA-I gene expression can still be suggested. Lamon-Fava and Micherone (2004) conducted an experiment showing that estrogen and genistein increase apoA-I gene transcription in Hep G2, a human liver carcinoma cell line.