Age-Associated Changes in Oxidative Stress and NAD+ Metabolism in Human Tissue

Researchers analyzed skin tissue from 49 people ranging from newborns to age 77 and measured markers of oxidative damage along with NAD+ levels and the activity of two NAD+ consuming enzymes. NAD+ levels dropped as age rose, while DNA damage and PARP activity climbed, and these patterns were stronger in males than females. The authors read this as evidence that oxidative DNA damage drives PARP to consume NAD+ during aging.

Why this study was done

NAD+ is a molecule cells use to make energy. It is also the fuel for PARP, an enzyme that repairs breaks in DNA, and for the sirtuins, a family of enzymes including SIRT1 that switch genes on and off. Rodent studies suggested a chain of events in aging: oxidative damage builds up in DNA, PARP works harder to repair it, burns through NAD+, and SIRT1 slows down because its fuel is gone. This study asked whether the same chain appears in human tissue.

How it was run

This was a cross-sectional laboratory study of skin taken from the pelvic region, an area not exposed to the sun, in 49 patients already scheduled for unrelated surgery at Sydney Adventist Hospital. Participants were aged 15 to 77, plus newborns under one year. People with chronic inflammatory conditions, pregnancy or current chemotherapy were excluded, as were under-45s with anti-inflammatory drug use, autoimmune disease, smoking or skin cancer. Each sample was measured for lipid damage as malondialdehyde, DNA damage as phosphorylated H2AX, PARP activity, NAD+ concentration and SIRT1 activity. Results were grouped into four age bands and plotted against age by sex. No treatment was given.

What they found

Comparing the elderly band with newborns:

• NAD+ fell from 8.54 to 1.06 ng per mg protein.
• PARP activity rose from 2.52 to 19.52 ng NAD+ used per hour per mg protein.
• DNA damage rose from 12.83 to 123.40 fluorescence units per mg protein.
• Lipid damage rose from 1.56 to 4.21 micromolar MDA per mg protein.
• SIRT1 activity showed no statistically significant difference between any of the four age bands.

The correlations split sharply by sex. In males, NAD+ fell with age (p=0.001, r=-0.706 excluding newborns), PARP activity rose (p<0.0001, r=0.768 across 0 to 77 years), lipid damage rose (p=0.004, r=0.623), DNA damage rose (p=0.029, r=0.490) and SIRT1 activity fell (p=0.007, r=-0.612). In females, NAD+ fell (p=0.01, r=-0.537) and DNA damage rose (p=0.003, r=0.600), but lipid damage (p=0.3734), PARP activity (p=0.4390) and SIRT1 activity (p=0.1943) showed no statistically significant change. PARP activity was inversely correlated with NAD+ (p=0.0003, r=-0.639), and NAD+ and SIRT1 activity were not correlated in males.

Limitations

This is a small cross-sectional study: 49 people, 27 male and 22 female, with only 5 in the oldest band and 8 newborns, all of them male. It is a snapshot, not a follow-up, so it cannot show change within a person. The tissue is skin, not brain, muscle or the organs where aging is usually the concern. Two authors, R. Grant and G. Guillemin, declare that they are directors of a start-up biotechnology company called NADLife. Funding was internal, from the Australasian Research Institute and the University of New South Wales. The authors flag that their PARP hypothesis held only in males, that they cannot explain the sex difference, that lifestyle and environmental exposure were not controlled, and that larger numbers are needed.

What it means in practice

This is a descriptive measurement of aging human skin. It reports, for the first time in human tissue, that NAD+ falls with age, and that this tracks with DNA damage and PARP activity in men. That is an association in a small sample, not a cause. No intervention was tested, so the study cannot say whether raising NAD+ changes anything about aging, health or disease. The authors say the therapeutic benefit of that approach in humans is yet to be established. The proposed chain from oxidative stress to NAD+ loss to reduced SIRT1 activity held only in men, and SIRT1 activity did not correlate with NAD+ even in them, so the mechanism is incomplete on the study's own evidence.