Peroxisome proliferator activating compounds in edible plants and mushrooms with potential health beneficial effects

Obesity is a condition with serious effects on human health and the economy. Obesity is a risk factor linked to metabolic syndrome, including insulin resistance, impaired glucose tolerance, type 2 diabetes, hyperlipidemia, steatohepatitis, cardiovascular disease, and some types of cancer that burden the medical system and have negative effects on the quality of life. At the individual level, retaining healthy lifestyles with increasing physical activities, controlled nutrition input, and elevated fruit and vegetable consumption are applied to control body weight. Drugs and supplements are also used to combat obesity and related disorders. Unfortunately, there are at present a limited number of drugs that can be used for treatment of obesity, and many of them have serious side effects. Thus, there is a growing demand for finding safe alternatives for the current drugs from natural resources such as secondary plant- or fungal metabolites. Plants or fungi may be important natural resources for the discovery of anti-obesity activities. In this thesis, we have investigated and searched to find novel candidate bioactive compounds from nature that are beneficial for treatment of obesity and associated metabolic syndrome using a targeted approach. Because of their known relevance in regulating fat metabolism, we focused on the nuclear hormone receptor class, peroxisome proliferator activator receptors (PPARs). A bioassay-based approach was applied using CALUX-type PPARα, δ, γ-based reporter gene assays to discover and evaluate potential PPAR-based bioactivities from plants and fungi towards treatment of obesity. In chapter 2, a workup method was developed to extract potential PPAR ligands from a variety of plants and fungi collected from forests in Vietnam and from edible mushrooms. The extracts were screened for PPAR activities by using a full panel of PPARα, δ, γ, CALUX bioassays. The results showed that PPAR agonistic activity was found in most samples; in particular, PPARδ agonistic activity was observed in fungi. Interestingly, high PPARs agonistic activity was found in edible mushrooms such as oysters and white button mushrooms. This may suggest that edible mushrooms may exert anti-obesogenic effects on humans through diet. Chapter 3 is a follow-up of the work described in chapter 2. White button mushroom (WBM) was selected for further research aimed at finding PPARs natural agonists. Effect-directed analysis was employed to purify WBM-derived PPAR agonists by using a stepwise fractionation of three LC columns (biphenyl semi-prep column, F5 column, and C18 column) and bioactivity-guided fractionation using PPARα, δ, γ -based CALUX assays to pinpoint the bioactive fractions. Finally, a highly purified PPAR active fraction was analysed by time-of-flight LC-MS/MS and nuclear magnetic resonance (NMR) spectroscopy. The main PPAR active ligand of WBM was identified as linoleic acid. The results suggested that low levels of linoleic acid in WBM might be beneficial for consumers in terms of anti-obesity effects. In chapter 4, the potential physiological effects of white button mushroom-derived linoleic acid fraction (WBM-LA) and the effects of the WBM β-glucan fraction were evaluated on 3T3-L1 cells. Β-glucan and WBM-LA active fractions clearly inhibited fat accumulation without cytotoxic effects in the 3T3-L1 cells. The suppression effects of WBM-LA and WBM-β-glucan were clearly different, whereby WBM-β-glucan showed a strong inhibiting effect in both white- and brown fat cell differentiation pathways, while the effect of WBM-LA on differentiation pathways was not clear. In the last chapter 5, This chapter summarizes the main findings in this thesis and discusses the findings in the context of international literature. The potential use as anti-obesogens of the observed bioactivities in terms of application in human health is discussed. An outlook of future work and applications is provided as well.