| Herbs and soil bacteria have been arguably the most important sources of therapeutic agents throughout human history. Numerous bioactive compounds have been isolated and characterized from these classical sources of natural products. Because of the long history of research on herbs and soil bacteria, they are sometimes perceived as "exhausted" sources of secondary metabolites. These classical sources of natural products, however, can still include compounds with previously overlooked chemical and biological properties. The unifying theme of this thesis study is to uncover such hidden potential of natural products. To this end, these classical sources of secondary metabolites have been examined from new angles.;The first two chapters of this thesis describe the examination of oriental herbal formulations with biomarker-guided screening, which has been established recently in our group. In this method, natural products are screened based on their ability to modulate the expression of mRNA biomarkers, which are the genes associated with therapeutic effects of herbal medicine. Importantly, herbal formulations have never been screened in this manner. Thus, biomarker-guided screening can serve as a powerful approach to uncover hidden therapeutic potential of natural products.;Chapter 1 describes the biomarker-guided screening of a "blood cleansing" herbal formulation called Toki-shakuyaku-san (TSS). This formulation has long been used to alleviate various disorders associated with poor blood circulation. Our screening revealed that a simple polyacetylene compound, (6E,12E)-tetradecadiene-8,10-diyne-1,3-diol diacetate (TDEYA), which has been considered as an "inactive" precursor of other metabolites, regulates the expression of genes associated with blood coagulation, such as COX-2, SerpinB2, and perlecan. Identification of this polyacetylene compound is important because it may open a new paradigm of treating circulation disorders through manipulation of gene expression by small molecules.;Chapter 2 describes the biomarker-guided screening of another herbal formulation, Juzen-taiho-to (JTT), which is widely known as "immune booster" formulation. In fact, JTT is clinically used in Japan to reinvigorate the immune system of cancer patients undergoing chemotherapy and radiation therapy. It is believed that many beneficial effects of JTT are mediated by monocytes and macrophages. Key monocyte-stimulants in JTT have been difficult to identify despite many years of intensive studies by us and others. However, JTT biomarker-guided screening identified beta-glucosylceramides (cerebrosides) as the first group of monocyte-stimulants in JTT. This discovery is an important first step to gain mechanistic insights into the clinically tested immunostimulatory effects of JTT.;Finally, chapter 3 describes the screening of secondary metabolites from culturable bacteria from soil samples collected throughout the State of New York. While traditional screenings of secondary metabolites in soil bacteria focus on the search for new antibiotics, our screening looked for a compound with structural complexity which provides us with an access to the pharmacological spaces that are difficult to reach through organic synthesis. This is an important new goal of the screening of bacterial metabolites, because complex molecules of bacterial origin can now be produced from simple carbon sources through metabolic engineering. This study isolated and structurally characterized cyclooctatin B (COB), a new diterpene with a fused 5-8-5 ring system and unique U-shaped conformation. Our preliminary analyses suggest that COB can undergo remarkably elegant cascade reactions when its environment turns mildly acidic. Thus, COB may constitute a new class of pH-sensing bacterial metabolites with a variety of chemical, pharmaceutical, and engineering applications. |
