ABSTRACT
The widespread application of stevia-based sweeteners in food products has resulted in the need for reliable analytical methods for measuring the purity and identity of high-purity steviol glycoside ingredients. The objective of this research was to develop and validate a new reversed-phase separation method capable of separating and quantifying nine steviol glycosides present in typical high-purity stevia extract ingredients. Results of the study established the linearity of the method at a correlation factor of 1.000 for the two major components and other minor components of this food ingredient. Method accuracy values were in the range of 99.1-100.9%. The percent relative standard deviation for six independent assay determinations was 1.0%. The method was determined to be robust for minor changes in column temperature, initial acetonitrile content, flow rate, and wavelength. The validated high-performance liquid chromatography method was found to be suitable to be included by USP as a Food Chemicals Codex compendial standard for steviol glycosides.
Subject(s)
Chromatography, High Pressure Liquid/methods , Diterpenes, Kaurane/analysis , Glycosides/analysis , Sweetening Agents , Drug Stability , Food QualityABSTRACT
Fatty acid synthase (FAS), the enzyme responsible for the de novo synthesis of fatty acids, is highly expressed in ovarian cancers and most common human carcinomas. Inhibition of FAS and activation of AMP-activated protein kinase (AMPK) have been shown to be cytotoxic to human cancer cells in vitro and in vivo. In this report, we explore the cytotoxic mechanism of action of FAS inhibition and show that C93, a synthetic FAS inhibitor, increases the AMP/ATP ratio, activating AMPK in SKOV3 human ovarian cancer cells, which leads to cytotoxicity. As a physiologic consequence of AMPK activation, acetyl-CoA carboxylase (ACC), the rate-limiting enzyme of fatty acid synthesis, was phosphorylated and inhibited whereas glucose oxidation was increased. Despite these attempts to conserve energy, the AMP/ATP ratio increased with worsening cellular redox status. Pretreatment of SKOV3 cells with compound C, an AMPK inhibitor, substantially rescued the cells from C93 cytotoxicity, indicating its dependence on AMPK activation. 5-(Tetradecyloxy)-2-furoic acid, an ACC inhibitor, did not activate AMPK despite inhibiting fatty acid synthesis pathway activity and was not significantly cytotoxic to SKOV3 cells. This indicates that substrate accumulation from FAS inhibition triggering AMPK activation, not end-product depletion of fatty acids, is likely responsible for AMPK activation. C93 also exhibited significant antitumor activity and apoptosis against SKOV3 xenografts in athymic mice without significant weight loss or cytotoxicity to proliferating cellular compartments such as bone marrow, gastrointestinal tract, or skin. Thus, pharmacologic FAS inhibition selectively activates AMPK in ovarian cancer cells, inducing cytotoxicity while sparing most normal human tissues from the pleiotropic effects of AMPK activation.
Subject(s)
Enzyme Inhibitors/pharmacology , Fatty Acid Synthases/antagonists & inhibitors , Multienzyme Complexes/metabolism , Ovarian Neoplasms/drug therapy , Ovarian Neoplasms/enzymology , Protein Serine-Threonine Kinases/metabolism , AMP-Activated Protein Kinases , Amino Acid Sequence , Animals , Cell Line, Tumor , Enzyme Activation , Fatty Acids/metabolism , Female , Furans/pharmacology , Glucose/metabolism , Humans , Mice , Mice, Inbred BALB C , Molecular Sequence Data , NAD/metabolism , Ovarian Neoplasms/metabolism , Oxidation-Reduction , Xenograft Model Antitumor AssaysABSTRACT
Two recent papers in Science reported the X-ray structures of the large, organizationally distinct animal and fungal fatty acid synthases at 5 A. These new structural insights have unexpected implications for enzyme function for the other "iterative" and "assembly line" megasynthases.
Subject(s)
Fatty Acid Synthases/chemistry , Animals , Catalytic Domain , Crystallography, X-Ray , Fungi/enzymology , Models, Molecular , Molecular Structure , Protein Structure, Quaternary , Protein Structure, TertiaryABSTRACT
The focus of this review is to highlight the structure, bioactivity and biosynthesis of naturally occurring aryl-C-glycosides. General synthetic methods and their relevance to proposed biochemical mechanisms for the aryl-C-glycoside bond formation are also presented.
Subject(s)
Biological Products , Glycosides , Biological Products/biosynthesis , Biological Products/chemical synthesis , Biological Products/chemistry , Biological Products/pharmacology , Glycosides/biosynthesis , Glycosides/chemical synthesis , Glycosides/chemistry , Glycosides/pharmacology , Molecular StructureABSTRACT
The biosynthetic gene cluster for the pluramycin-type antitumor antibiotic hedamycin has been cloned from Streptomyces griseoruber. Sequence analysis of the 45.6 kb region revealed a variety of unique features such as a fabH homolog (KSIII), an acyltransferase (AT) gene, a set of type I polyketide synthase (PKS) genes, and two putative C-glycosyltransferase genes. As the first report of the cloning of the biosynthetic gene cluster for the pluramycin antibiotics, this work suggests that the biosynthesis of pluramycins utilize an iterative type I PKS system for the generation of a novel starter unit that subsequently primes the type II PKS system. It also implicates the involvement of a second catalytic ketosynthase (KSIII) to regulate this unusual priming step. Gene disruption is used to confirm the importance of both type I and II PKS genes for the biosynthesis of hedamycin.
