D-Aspartic Acid in Vertebrate Reproduction: Animal Models and Experimental Designs

Abstract

This article reviews the animal models and experimental designs that have been used during the past twenty years to demonstrate the prominent role played by D-aspartate (D-Asp) in the reproduction of vertebrates, from amphibians to humans. We have tabulated the findings of in vivo and in vitro experiments that demonstrate the effects of D-Asp uptake on hormone production and gametogenesis in vertebrate animal models. The contribution of each animal model to the existing knowledge on the role of D-Asp in reproductive processes has been discussed. A critical analysis of experimental designs has also been carried out. Experiments performed on wild animal species suggest a role of D-Asp in the mechanisms that regulate the reproductive cycle. Several in vivo and in vitro studies carried out on mouse and rat models have facilitated an understanding of the molecular pathways activated by D-Asp in both steroidogenesis and spermatogenesis, with particular emphasis on testosterone biosynthesis. Some attempts using D-Asp for the improvement of reproductive activity in animals of commercial interest have yielded mixed results. The increased transcriptome activity of enzymes and receptors involved in the reproductive activity in D-Asp-treated broiler roosters revealed further details on the mechanism of action of D-Asp on the reproductive processes. The close relationship between D-Asp and reproductive activity has emerged, particularly in relation to its effects exerted on semen quality, proposing therapeutic applications of this amino acid in andrology and in medically-assisted procreation techniques.

Relationships between Seminal Plasma Metabolites, Semen Characteristics and Sperm Kinetics in Donkey (Equus asinus)

“…Alanine is a non-essential amino acid that at high concentrations affects sperm motility and decreases post-thaw sperm motility [ 30 ]. Glutamate is an excitatory amino acid sharing receptors with D-aspartate (for review see [ 31 ]). Recent studies have demonstrated that these receptors are expressed in rat and mouse testes and located in spermatogonia and Leydig cells [ 32 ].…”

Preliminary Investigation on the Ameliorative Role Exerted by D-Aspartic Acid in Counteracting Ethane Dimethane Sulfonate (EDS) Toxicity in the Rat Testis

“…They received commercial food pellets ad libitum. Rats ( n = 15) were divided into three groups: the first group ( n = 5) was allowed to drink a solution consisting of 20 mM D-Asp for 15 days [ 39 ]; to the second group of rats ( n = 5), fresh water for 15 days was given. At the end of the above period, both groups were injected intraperitoneally with EDS (100 mg/kg body wt in DMSO–dH 2 O 1:3 v/v; 200 μL/animal).…”

A Proteomics Signature of Mild Hypospadias: A Pilot Study

“…In terms of downstream products, we found lower concentrations of aspartate in moderate and severe hypospadias but not in mild hypospadias ( 42 ). This finding is of interest as aspartate modulates steroidogenesis in Leydig cells ( 43 – 45 ). In addition, it has been shown that aspartate increases testosterone, dihydrotestosterone (DHT), luteinizing hormone (LH), and gonadotropin-releasing hormone (GnRH) levels, as well as stAR mRNA and protein expression levels and AR protein expression levels ( 46 – 50 ).…”