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Age associated changes in human tissue NAD(H) and oxidative stress markers.

Background

Oxidative damage occurs with advancing age due to an imbalance between free radical and reactive species (ROS) production and cellular antioxidant defence mechanisms. Increased levels of ROS can result in disordered cellular metabolism due to lipid peroxidation, protein-cross linking, DNA damage and the depletion of nicotinamide adenine dinucleotide (NAD+). NAD+ is a ubiquitous pyridine nucleotide that plays an essential role in important biological reactions, from ATP production and secondary messenger signalling, to transcriptional regulation and DNA repair. Chronic oxidative stress may be associated with NAD+ depletion and a subsequent decrease in metabolic regulation and cell viability.

In genomic DNA repair NAD+ is the sole substrate for the DNA nick sensor poly (ADP-ribose) polymerase (PARP). The PARP family of enzymes, in particular PARP-1, are DNA binding enzymes activated by ROS initiated breaks to the DNA and are critical to the base excision repair process1. PARP-1 and its essential substrate, NAD+, are therefore critical to the DNA repair process following oxidative damage and hence continuing cell survival.

In addition to its role in, PARP activity, NAD+ also serves as a substrate for a new class of enzymes known as the sirtuin family. Gene silencing by this family of enzymes has been correlated directly with longer lifespan3.

Although a number of studies have demonstrated elevated levels of oxidative stress mediated damage in aged tissue, to our knowledge, no study has yet reported on changes in human tissue NAD+ levels during the aging process. Our lab has recently submitted two papers based on studies we have carried out in aged female Wister rats. These studies have demonstrated a significant reduction in NAD+ levels and consequent reduction in SIRT1 activity and increased p53 acetylation with age, closely correlating with increased levels of lipid peroxidation, protein carbonyl formation and DNA damage. The current study will build on the aforementioned studies using human tissue obtained during scheduled orthopaedic surgery from a range of patients (20-70 years).

Study Aims

  • To characterise and quantify changes in NAD+ metabolism in biopsied human tissue.
  • To quantify the levels of oxidative stress, total antioxidant, NAD+ levels, PARP, Sirt1 and mitochondrial activities.

References

  1. Bouchard et al. (2003). PARP-1, a determinant of cell survival in response to DNA damage.Exp. Hematology 31, 446-454.
  2. Pacher P and C Szabó (2007) Role of poly(ADP-ribose) polymerase 1 (PARP-1) in cardiovascular diseases: the therapeutic potential of PARP inhibitors. Cardiovasc. Drug Rev. 25 (3), 235-260.

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