NAD+ precursor concentrations are elevated in the follicular fluid of mares following oral supplementation of nicotinic acid

Abstract

Niacin deficiency has recently been associated with congenital malformations in humans and embryonic death and resorption in mice (Shi et al. New England Journal of Medicine. 2017; 377(6):544-552). Mares suffer from high rates of early embryonic loss (Newcombe. Equine Veterinary Education. 12(2):88-101), the aetiology of which remains unknown. Increasing the levels of nicotinamide adenine dinucleotide (NAD+) through supplementing NAD+ precursors has resulted in an improvement in oocyte quality in mice (Bertoldo et al. Cell Rep. 2020; 30: 1670-1681). However, little is known regarding the requirement of niacin and NAD+ in reproductive processes in the mare. The aim of this study was to determine the effect of oral nicotinic acid (NA) supplements, a form of niacin, on the composition of nicotinamide adenine dinucleotide (NAD+) metabolites in the blood and follicular fluid of mares. Vehicle alone or NA (3 g per os) was administered to 7 mares over a minimum of 3 consecutive days during the oestrous cycle. Blood samples were collected immediately prior tosupplemental feeding and at follicular fluid aspiration. Follicular fluid was collected from the dominant follicle through transvaginal ultrasound guided aspiration. Blood and follicular fluid samples were processed and analysed by mass spectrometry. The concentration of nicotinamide mononucleotide (NMN) in the follicular fluid of NA-fed mares was greater than that in the corresponding plasma (15.0 ± 6.5 vs. 3.3 ± 0.9 ng/µL; p < 0.05) and in the follicular fluid of vehicle-fed mares (1.5 ± 0.5 ng/µL; p < 0.001). Meanwhile, the concentration of NA, nicotinamide (NAM) and nicotinuric acid (NUR) tended to be greater in the follicular fluid of NA supplemented mares (1043.9 ± 953.5, 1641.7 ± 256.1 and 5.5 ± 5.1 ng/µL) than in the corresponding plasma (70.8 ± 15.4, 875.6 ± 361.1 and 0.6 ± 0.2, respectively; p < 0.1). The results show that NA supplementation increased the bioavailability of NAD+ precursors in the follicular fluid of the dominant follicle, which is proposed to better promote the maturation of good quality oocytes, especially in older mares.