Increasing levels of a so-called anti-aging molecule may boost treatments for diseases that affect the liver and kidneys.
Nicotinamide adenine dinucleotide (NAD+) is called the "anti-aging molecule" because research has shown that its levels fall with age and that restoring them can extend years of good health and even longevity itself.
This molecule plays a key role in several biological processes that help cells get energy and stay healthy, such as metabolism, DNA repair, gene expression, and cell signaling.
Scientists class NAD+ as a coenzyme, meaning that it does not act alone but helps the enzymes that drive these vital cell processes.
One family of enzymes that NAD+ has an ancient "intimate connection" with is the sirtuins.
Studies have shown that as NAD+ declines with age, it reduces sirtuin activity in ways that affect the communication between the cell nucleus and its mitochondria, which are the tiny compartments that produce energy for the cell.
Control of NAD+ is 'evolutionarily conserved'
The recent study, which the École Polytechnique Fédérale de Lausanne (EPFL) in Switzerland led, features in the journal Nature. It demonstrates two compounds that could restore fallen levels of NAD+ in the liver and kidneys.
Cells synthesize NAD+ from scratch using the amino acid tryptophan as the main building block.
This "de novo synthesis" requires the presence of certain enzymes, including one called aminocarboxymuconate-semialdehyde decarboxylase (ACMSD), which has the effect of limiting the production of NAD+.
The team describe the way in which ACMSD controls NAD+ levels in cells as being "evolutionarily conserved."
Their investigation demonstrated that the mechanism was the same in both Caenorhabditis elegans, a type of worm, and mice, and that blocking ACMSD increased both NAD+ and mitochondrial activity.
Selective ACMSD inhibitors
The researchers discovered that blocking ACMSD also raised the activity of one of the sirtuins that NAD+ works with. The combination of elevated sirtuin activity and increased NAD+ synthesis boosted mitochondrial activity.
Working with TES Pharma, the team then tested the effect of two selective ACMSD blockers in animal models of nonalcoholic fatty liver disease and kidney damage. Both compounds seemed to "preserve" liver and kidney function.
"Since the enzyme is mostly found in the kidneys and liver," says first study author Elena Katsyuba, of the Interfaculty Institute of Bioengineering at EPFL, "we wanted to test the capacity of the ACMSD inhibitors to protect these organs from injury."
As ACMSD does not occur elsewhere in the body, the finding could pave the way for a protective treatment that boosts NAD+ without affecting other organs.
"Put simply, the enzyme will not be missed by an organ that does not have it anyway."