A model for the role of the proline-linked pentose-phosphate pathway in phenolic phytochemical bio-synthesis and mechanism of action for human health and environmental applications.
The combination of immunodeficiency, inflammatory process and nutritional status that is characteristic of infective and food-borne illness is more evident in chronic diet- and environment-influenced chronic diseases such as diabetes, obesity, cardiovascular disease, cancer, arthritis and neuro-degeneration diseases. These chronic diseases tend to be oxidation-linked and may manifest in communities around the world, irrespective of income. In addressing the challenges of the above diseases, a significant role for dietary phytochemicals is emerging. Phytochemicals are required from a spectrum of food for at least their antioxidant role, if not for other properties, to protect tissues from activities that manifest themselves into what we call chronic disease. Among the diverse groups of phytochemicals, phenolic antioxidants and antimicrobials from food plants are being targeted for designed dietary intervention to manage major oxidation-linked diseases such as diabetes, cardiovascular diseases, arthritis, cognition diseases and cancer. Foods containing phenolic phytochemicals are also being targeted to manage bacterial infections associated with chronic diseases such as peptic ulcer, urinary tract infections, dental caries and food-borne bacterial infections. Plants produce phenolic metabolites as a part of growth, developmental and stress adaptation response. These stress and developmental responses are being harnessed to design consistent phytochemical profiles for safety and clinical relevancy using novel tissue culture and bioprocessing technologies. The biochemical strategy for harnessing phenolic phytochemicals for human health and wellness is based on the hypothesis that phenolic metabolites in plants are efficiently produced through an alternative mode of metabolism linking proline synthesis with pentose-phosphate pathway. In this model, stress-induced proline biosynthesis is coupled to pentose-phosphate pathway, driving the synthesis of NADPH(2) and sugar phosphates for anabolic pathways, including phenolic and antioxidant response pathways, while simultaneously providing reducing equivalents needed for mitochondrial oxidative phosphorylation in the form of proline as an alternative to NADH from Krebs/TCA cycle. Based on this model, tissue culture techniques and elicitation concepts have been used to stimulate phenolic metabolites with an antioxidant response in germinating seeds, sprouts and clonal lines of dietary plants. From our initial investigations, a model has been proposed in which the proline-linked pentose-phosphate pathway is suggested to be critical for modulating protective antioxidant response pathways in diverse biological systems, including biochemical and cellular pathways important for human health. The proposed proline-linked pentose-phosphate pathway model provides a mechanism for understanding the mode of action of phenolic phytochemicals in modulating antioxidant pathways and provides avenues by which dietary approaches may manage oxidation-linked chronic and infectious diseases. The model also has implications for the development of antimicrobial phenolic phytochemicals against bacterial pathogens in an era of increasing antibiotic resistance. Further, this model also has relevance for improving fungal and yeast-based food bioprocessing for designing functional foods and for environmental bioremediation using plant and microbial systems, as well as for improving agricultural and food systems in harsh environments.