Orally administrated D-arginine exhibits higher enrichment in the brain and milk than L-arginine in ICR mice

Abstract

D-Amino acids exert various physiological functions and are widely present in animals. However, they are absorbed to a lesser extent than L-amino acids. Little is known about D-arginine (D-Arg); however, its isomer L-Arg serves as a substrate for several metabolites and exhibits various functions including promotion of growth hormone secretion. Milk is the only nutrient source for infants; it plays an important role during their initial growth and brain development. No studies have evaluated the availability of D-Arg in the brain and milk in mammals. Here, we have studied the differential availability of orally administered D-and L-Arg in the brain and milk using ICR mice. Our results revealed that without D-Arg administration, D-Arg was undetectable in both plasma and brain samples. However, the plasma D-Arg was about twice the concentration of L-Arg post administration of the same. In the cerebral cortex and hypothalamus, L-Arg concentration remained almost constant for over period of 90 min after L-Arg treatment. Nevertheless, the L-Arg concentration decreased after D-Arg administration with time compared to the case post L-Arg administration. Contrastingly, D-Arg level sharply increased at both the brain regions with time after D-Arg treatment. Furthermore, L-Arg concentration in the milk hardly increased after L-Arg administration. Interestingly, oral administration of D-Arg showed efficient enrichment of D-Arg in milk, compared with L-Arg. Thus, our results imply that D-Arg may be available for brain development and infant nourishment through milk as an oral drug and/or nutrient supplement.

Supplementation of L-Ornithine Could Increase Sleep-like Behavior in the Mouse Pups

“…Nagaoka et al [15] reported that free amino acids in mouse milk were metabolized in the mammary glands, since the activity of L-amino acid oxidase was high. L-Arginine transfer to milk is certainly low [16], but L-ornithine, a metabolite of L-arginine investigated here, seemed to transfer to milk more easily than L-arginine. This is close to the results observed with L-serine [17].…”

“…Consequently, the content of free amino acids targeted by L-amino acid oxidase was very low in conventional milk [15]. For instance, the L-arginine concentration in the milk showed a meager increase of 5 nmol/mL in the L-arginine administration group, while it was significantly increased by about 150 nmol/mL in the plasma as compared to the control group [16]. On the other hand, although L-serine levels did not change significantly in the plasma of the L-serinetreated group, their levels in maternal milk were high (more than 100 nmol/mL) compared with the control group.…”

Enhancement of l-amino acid oxidase production by Bacillus subtilis HLZ-68 with oxygen-vector and asymmetric degradation of dl-arginine to d-arginine

“…Adding D-arginine to food can effectively improve its water solubility and extend its shelf life [6]. A study in mice has also suggested that D-arginine may be added to milk to enhance infant brain development [7]. With the widespread use of D-arginine in the food and pharmaceutical industries, the market demands for D-arginine have also increased.…”