Glucose Flux through the Hexose Monophosphate Shunt and NADP(H) Levels during in vitro Ageing of Human Skin Fibroblasts

Abstract

In cultured human skin fibroblasts the glucose flux through the hexose monophosphate shunt (HMS) amounts to 4% of the glucose flux through the glycolytic pathway. Upon in vitro ageing the rate of glucose utilization through the HMS is decreased more than 50%. This decrease in HMS was not caused by a limiting enzymatic capacity since glucose utilization through the HMS could be raised at least 30-fold in both ‘young’ and ‘aged’ fibroblasts upon stimulation with phenazine methosulphate. This effect of in vitro ageing upon glucose metabolism was also not due to differences in proliferation rate between ‘young’ and ‘aged’ human fibroblasts, since there was no difference in glucose utilization between proliferating and growth-inhibited (confluently cultured) fibroblasts. The NADPH/NADP ratio was found to be decreased by 12% in ‘aged’ cells.

Quantification and visualization of cellular NAD(P)H in young and aged female facial skin within vivotwo-photon tomography

“…They serve critical roles in both catabolic and anabolic processes. For example, NADPH is the reducing cofactor used by fatty acid synthetase in lipid biosynthesis and by desmolases and hydroxylases in steroid biosynthesis . NADH and NADPH [NAD(P)H, hereafter] are, therefore, considered as fundamental energy biomarkers within cells.…”

Differential Growth Inhibition of Human Diploid Fibroblasts by 2-Deoxyglucose and Antimycin A with Ageing in vitro

“…Any increase in anaerobic glycolysis could act to reduce glucose flux through the hexose monophosphate shunt and, in fact, a highly significant decline in glucose utiliza tion via the hexose monophosphate shunt recently has been reported [17], For cells in culture this must lead to a major restriction in the availability of ribose moieties for the synthesis of RNA, DNA and nucleotide coenzymes and NADPH for reductive bio synthesis. Thus a logical explanation can be advanced for the decline in HDF growth during the latter part of cellular life-span in vitro, culminating in senescence and the ces sation of mitosis.…”