It is unclear whether the decline of NAD+ levels is due to a decreased synthesis or increased consumption
Mice should be at least 10 months old for inclusion in a middle agegroup and the upper age limit is about 14 - 15 months. This phase correlates to humans from 38 - 47 years old. Mice ranging from 18 - 24 months of age correlate with humans ranging from 56 - 69 years of age.
Why then only in aging mice? Mice are considered middle-aged by 1 year and by 18 months are equivalent to 62 human years, having past the reproductive phase and on the cusp of senescence (Dutta and Sengupta, 2016).
https://www.fabriceleu.com/wp-content/uploads/2018/05/animaldosetohumandoseconversion.pdf Mouse dose in mg/kg * 3 and divide by 37 E.g. mouse dose was 1 g/kg of body weight = 0.08 g/kg and for a 0 kg person it is 4.9 gram
References and Literature
NAD+ Repletion Rescues Female Fertility during Reproductive Aging.through NMN supplementation, in mice https://www.ncbi.nlm.nih.gov/pubmed/32049001 https://www.cell.com/cell-reports/fulltext/S2211-1247(20)30083-8
Having demonstrated that in vivo NMN treatment in aged animals improved oocyte quality and increased ovulation rate and birth rates, we next showed that supplementing embryo culture media with NMN improved embryo development in embryos derived from oocytes from aged animals, but not young animals, supporting the idea that this intervention addresses an age-related deficit in oocyte NAD+ levels. This finding is highly relevant to the clinical practice of IVF. In addition to age-related issues of decreased oocyte numbers and oocyte quality, mitotic aneuploidy ( Munné et al., 2002 ) and poor preimplantation embryo development ( Janny and Menezo, 1996 ) limit the number of euploid blastocysts available for transfer with increasing maternal age. The increasing preference for blastocyst-stage transfers in clinical IVF underscores the importance of reaching more advanced developmental milestones ( National Perinatal Epidemiology and Statistics Unit, 2016 ) and clinical demand for interventions that can improve embryo development. Although this study used NMN as an NAD+ precursor, alternative precursors from other pathways also raise NAD+, most notably NR ( Trammell et al., 2016 ). We anticipate that this and similar compounds will also exhibit efficacy in oocyte quality and fertility, and it is unlikely that these effects are unique to NMN.
Twelve-month-old animals were treated with NMN for 4 weeks (2 g/L, drinking water), and MII oocytes were collected from oviducts following PMSG and hCG stimulation. Oocytes from NMN-treated, aged (12-month-old) animals had a larger diameter (Figure 2F), which may be relevant given that oocytes with smaller diameters are associated with poorer outcomes following IVF ( Atzmon et al., 2017 , Marquard et al., 2011 ). A separate cohort of oocytes was subjected to IVF, and at day 6, the proportion of embryos that reached blastocyst formation was assessed (Figure 2G), with a trend toward improved blastocyst formation rates. We next sought to determine whether in vivo NMN treatment would alter subsequent inner cell mass development of blastocysts, which is highly predictive of pregnancy success ( Lane and Gardner, 1997 ). Twelve-month-old mice were treated with NMN in drinking water for 2, 7, 14, or 28 days, and oocytes subjected to IVF. At day 6, embryos were subjected to differential staining of the inner cell mass. The length of NMN treatment in animals correlated with improvements in inner cell mass size (Figure 2H), and to confirm that this translated to improved fertility outcomes, we treated a cohort of 13-month-old animals with two different doses of NMN (drinking water, 0.5 and 2 g/L) for 4 weeks before the introduction of a male of proven fertility. Breeding performance as determined by pregnancy, live births, and litter size was then assessed for the following 9 weeks, from 14–16 months of age (Figures 2I–2M). NMN treatment improved the time to first live birth (Figure 2J) and the overall proportion of animals achieving live birth during the breeding trial (Figure 2K), though this surprisingly occurred at the lower dose of NMN (0.5 g/L), suggesting that previous experiments were performed at a dose that benefited oocyte quality but may have adversely affected other aspects of fertility. This could be related to an upper limit to NMN tolerability or the increased formation of the NMN degradation product nicotinamide, which is a sirtuin inhibitor ( Bitterman et al., 2002 ). These data from orthogonal pharmacological and genetic approaches show that increasing NAD+ enhances ovulation rate, oocyte quality, and overall live birth rates in aged female mice, though they point to an optimum range of dosing.