Safety assessment of L-Arg oral intake in healthy subjects: a systematic review of randomized control trials

L-Arg is a nonessential amino acid but has many physiological roles. Accordingly, L-Arg has been used in various fields, but there is only limited information available about its safety upon overdose. Generally, the no-observed adverse effect level (NOAEL) is used when setting the upper amount for chemical substances. Recently, systematic reviews have been used to assess the safety as well as the effectiveness and usefulness of them. Therefore, we conducted an assessment of the safety of the oral intake of L-Arg in healthy subjects using gastrointestinal symptoms as an index. We limited the study design to only double-blind randomized controlled trials and searched PubMed, Cochrane Library, EBSCOhost, and Ichushi-Web from inception until May 2021. Assessment of the quality of studies was conducted using the Cochrane Collaboration tool and Jadad score, and the random effects model was used for data analysis. Ultimately, 34 studies were selected for inclusion in this work. The dosage of L-Arg used in the studies ranged from 2000 to 30,000 mg/day (or/one-time dose), and the treatment duration was 1-84 days. The increased risk of gastrointestinal symptoms associated with L-Arg intake from 23 studies (647 participants in total) in which such symptoms were reported was 0.01 (95% confidence interval: - 0.02-0.04), which was not significant difference. NOAEL was estimated as 7531 mg/ one-time dose using a weighted change-point regression model (UMIN000046133).Registration and protocol: Umin.ac.jp as UMIN000046133.

Lactoferrin Suppresses Decreased Locomotor Activities by Improving Dopamine and Serotonin Release in the Amygdala of Ovariectomized Rats

BACKGROUND

Decreases in female hormones not only affect bone metabolism and decrease bone mass, but also affect the central nervous system, causing brain disorders such as depression and dementia. Administration of estradiol by hormone replacement therapy can improve dementia, while reduced estradiol in ovariectomized (OVX) model rats can reduce both bone density and locomotor activity. The antidepressant fluvoxamine, which is widely used in clinical practice, can improve this effect on locomotor reduction. Similarly, lactoferrin (LF) can reportedly improve inhibitory locomotion due to stress.

OBJECTIVE

In this study, we examined the effect of LF on neurite outgrowth in vitro and in vivo using PC12 cells and rats, respectively.

METHODS

We performed an in vivo study in which 8-week-old female OVX rats were administered LF five days a week for 6 weeks from the day after surgery. After administration was completed, spontaneous locomotor activity in the dark period, immobility time in a forced swim test, and release amount of dopamine and serotonin in the brain were measured.

RESULTS

LF was found to have a neurite outgrowth function in PC12 cells. Moreover, LF was found to improve OVX-induced decreases in locomotor activity and increases in immobility time in the forced swim test. Furthermore, the administration of LF elicited significant recovery of decreased dopamine and serotonin release in the brains of OVX group rats.

CONCLUSION

These results strongly suggest that LF improved OVX-induced decreases in momentum during the dark period and, moreover, that release of dopamine and serotonin in the brain was involved in this effect.

Endogenous Apelin Is Protective Against Age-Associated Loss of Retinal Ganglion Cells in Mice

Age-associated loss of retinal ganglion cells (RGCs) causes visual deficits, but there is not yet any therapeutic agent to prevent the loss of these cells. Herein, we report that apelin, an endogenous peptide ligand of APJ receptor, is protective against the age-related loss of RGCs in mice. The mRNA expression of apelin was reduced in the retina of old mice compared with that in young mice, whereas retinal APJ expression increased with age. Immunofluorescence staining showed that APJ was present in RGCs and their surrounding cells expressed apelin. In addition, both functional and histological analyses demonstrated that apelin deficiency accelerated the loss of RGCs associated with age in mice. These results suggest that endogenous apelin plays a protective role against the degeneration of RGCs and that the apelinergic axis may be a new target for preventing age-related visual impairment.

High-speed AFM reveals accelerated binding of agitoxin-2 to a K+ channel by induced fit

Agitoxin-2 (AgTx2) from scorpion venom is a potent blocker of K⁺ channels. The docking model has been elucidated, but it remains unclear whether binding dynamics are described by a two-state model (AgTx2-bound and AgTx2-unbound) or a more complicated mechanism, such as induced fit or conformational selection. Here, we observed the binding dynamics of AgTx2 to the KcsA channel using high-speed atomic force microscopy. From images of repeated binding and dissociation of AgTx2 to the channel, single-molecule kinetic analyses revealed that the affinity of the channel for AgTx2 increased during persistent binding and decreased during persistent dissociation. We propose a four-state model, including high- and low-affinity states of the channel, with relevant rate constants. An induced-fit pathway was dominant and accelerated binding by 400 times. This is the first analytical imaging of scorpion toxin binding in real time, which is applicable to various biological dynamics including channel ligands, DNA-modifier proteins, and antigen-antibody complexes.