In a recent study, 18 male APP/PS1 mice were intraperitoneally injected with 30 mg/kg NAD⁺ at 20 weeks of age and once every other day for 4 weeks.
These transgenic mice were used as they develop the behavioral and pathological features of AD similar to humans and are commonly used in studies of AD.
AD is a degenerative disease of the nervous system. Studies have demonstrated that energy metabolism abnormalities are closely related to the development of early AD.
The energy metabolism of failing neurons often precedes, or occurs simultaneously, with cognitive impairment.
NAD⁺ supplementation reversed symptoms of cognitive decline in these mice and restored levels of NAD⁺, SIRT1, ATP and other metabolites.
- NAD⁺ treatment increased NAD⁺ level and NAD⁺/NADH ratio.
- NAD⁺ treatment improved the expression of NAMPT and SIRT1 in the brain.
- NAD⁺ treatment improves ATP content present in the cortex and hippocampus.
- NAD⁺ treatment reduces amyloid plaques present in the cortex and hippocampus.
- NAD⁺ alleviated the spatial learning and memory deficits associated with increased senile plaques.
The administration of NAD⁺ alleviated the spatial learning and memory of APP/PS1 mice and reduced senile plaques. Administration of NAD⁺ may also increase the expression of the key protein NAMPT and its related protein sirtuin1 as well as the synthesis of NAD⁺. Therefore, increasing NAMPT expression levels may promote NAD⁺ production. Their regulation could form the basis for a new therapeutic strategy. NAD⁺ acts as a neuroprotective agent via several mechanisms, including the prevention of ATP depletion.
Results present in the study corroborated the idea that cortex and hippocampal NAD⁺ levels and NAMPT expression declined in early stage AD model mice.
The decrease of NAMPT leads to NAD⁺ decrease, while NADH levels were not affected, leading to a decrease in the NAD⁺/NADH ratio.
Maintenance of NAD⁺/NADH ratio is critical for mitochondrial function, including ATP synthesis, and it was identified that ATP also decreased in the cortex and hippocampus.
In various animal models, age‑related metabolic decline is positively correlated with the decline of NAD⁺, and the change of NAD⁺/NADH ratio can regulate sirtuin enzymes, including SIRT1.
This study found that intraperitoneal injection of NAD⁺ also increased levels of SIRT1.
*Note – A previous study by Dr. Sinclair published in June 2019 found that supplying old mice with NMN for 2 weeks renewed growth of endothelial cells, resulting in increased cerebral blood flow and reversed cognitive decline to that of the 3-month-old control mice. That study used 500 mg/kg of NMN, while this current study used 30 mg/kg of NAD⁺.
NAD⁺ treatment increases NAD⁺ level and NAD⁺/NADH ratio
in APP/PS1 transgenic mice.
Cortex: Compared with the control group, the NAD⁺ content in the hippocampus in the APP/PS1 group was significantly decreased, while the NADH level was not significantly changed with the NAD⁺/NADH ratio decreasing.
Hippocampus: The NAD⁺ content in the hippocampus in the NAD⁺ group was significantly increased and the NAD⁺/NADH ratio was significantly increased, while no noticeable change in the NADH level was recorded.
NAD⁺ treatment improves ATP content of the cortex and
hippocampus in APP/PS1 transgenic mice.
ATP content in the cortex and hippocampus was measured in each group of mice.
Cortex: The results demonstrated that the ATP content in the cortex in the APP/PS1 group was significantly decreased while the ATP content in the cortex in the NAD⁺ group was significantly increased.
Hippocampus: In the APP/PS1 group, the ATP content in the hippocampus was significantly decreased. The ATP content in the hippocampus in the NAD⁺ group was significantly increased.
NAD⁺ treatment improves the expression of NAMPT and SIRT1 in the brain of APP/PS1 mice.
It was observed that the expression of NAMPT protein and SIRT1 enzyme in the cortex and hippocampus in APP/PS1 group was decreased compared with the control group.
Intraperitoneally injecting NAD⁺ increased the expression of NAMPT and SIRT1 in the cortex and hippocampus in the NAD⁺ treated mice.
NAD⁺ treatment reduces amyloid plaques present in the cortex and hippocampus of APP/PS1 transgenic mice.
To measure senile plaques, staining with Thioflavin S in the cortex and hippocampus was conducted.
As expected, the AD mice presented numerous plaques at 6 months of age as compared with the control mice in the cortex and hippocampus; however, following NAD⁺ treatment, very few green fluorescent plaques were observed in the cortex and hippocampus of NAD⁺ treated mice.
NAD⁺ alleviated the spatial learning and memory deficits and reduced senile plaques in mice.
APP/PS1 mice exhibit impaired performance.
With greater frequency of training days, the time to complete a maze test decreased with control mice, while the APP/PS1 mice showed very little increase in escape speed. These results suggest that the learning and memory abilities of AD mice were significantly impaired.
For the mice given NAD⁺ (shown in grey), the time to complete maze testing was significantly shorter than that of APP/PS1 mice.
In the spacial learning experiment on the sixth day, after
removing a dividing platform it was found that APP/PS1 mice exhibited greatly decreased time spent in the target area compared with control group mice, indicating that the spatial memory ability of AD mice was impaired.
Following NAD⁺ treatment, the NAD⁺ mice spent more time in the target quadrant compared with the APP/PS1 mice, and nearly as much as the control group.
Sublingual delivery may be more bioavailable than IP Injection
IP injection is a more efficient delivery method for NAD⁺ or NAD⁺ precursors directly to the liver when compared to the same molecules delivered in capsules, food, or water.
With intraperitoneal injection, the primary route of absorption is via the mesenteric vessels, which drain into the portal vein and pass through the liver before reaching the bloodstream.
IP avoids the GI tract, but is still sent directly to the liver wherein NAD⁺ and associated precursors are converted to NAM before reaching the bloodstream.
Sublingual delivery is not filtered by the liver and can reach systemic circulation intact, and therefore results in greater bioavailability than direct injection.