Protective effect of d-alanine against acute kidney injury

Abstract

Background. Recent studies revealed the connection between amino acid chirality and diseases. We previously reported that the gut microbiota produced various D-amino acids in a murine acute kidney injury (AKI) model. Here, we further explore the pathophysiological role of D-Alanine (Ala) in AKI. Methods. We analyzed the transcripts of the N-methyl-D-aspartate (NMDA) receptor, a receptor for D-Ala, in tubular epithelial cells (TECs). Then, the therapeutic effect of D-Ala was assessed in vivo and in vitro. Lastly, the plasma level of D-Ala was evaluated in AKI patients. Results. The Grin genes encoding NMDA receptor subtypes were expressed in TECs. Hypoxia condition changes the gene expressions of Grin1, Grin2A and Grin2B. D-Ala protected TECs from hypoxia-related cell injury and induced proliferation after hypoxia. These protective effects are associated with the chirality of D-Ala. D-Ala inhibits ROS production and improves mitochondrial membrane potential, through NMDA receptor signaling. The ratio of D-Ala/L-Ala was increased in feces, plasma, and urine after the induction of I/R. Moreover, enterobacteriaceae, such as Escherichia coli, Klebsiella oxytoca produced D-Ala. The oral administration of D-Ala ameliorated kidney injury after I/R induction in mice. The deficiency of NMDA subunit NR1 on tubular cell worsened kidney damage in AKI. In addition, the plasma level of D-Ala was increased and reflected the level of renal function in AKI patients. Conclusions. D-Ala has protective effects on I/R-induced kidney injury. Moreover, the plasma level of D-Ala reflects the eGFR in AKI patients. D-Ala could be a promising therapeutic target and potential biomarker for AKI.

Increased levels of oral Streptococcus-derived d-alanine in patients with chronic kidney disease and diabetes mellitus

“…Saliva and stool were collected from patients with CKD as samples of the oral and gut microbiota, respectively, and both microbiotas were found to produce D-Ala. Salivary levels of D-Ala were higher in patients with CKD than in healthy controls. We have previously confirmed in an AKI mouse model that D-Ala was transferred into the blood by drinking water administration and was renoprotective 11 . Therefore, plasma D-Ala levels may have increased in patients with CKD owing to an increase in salivary D-Ala levels.…”

“…The main sources of D-Ala are believed to be the microbiota, diet, and endogenous biosynthesis. We have previously found that many D-AAs, including D-Ser and D-Ala, are not detectable in stools of germ-free mice but are observed in those of normal mice 10 , 11 . In addition, many bacterial species encode alanine racemase, which is a D-Ala synthase 24 , 25 ; D-Ala is required for the peptidoglycan component in the bacterial cell wall.…”

“…However, the localization and function of d -isomers have been clarified with the advent of novel technologies 10 – 13 . Furthermore, it has become clear that bacteria are the main source of D-AAs 10 , 11 , 14 , and the levels of D-AAs reflect changes in the microbiota in various pathological conditions. We have previously reported that acute kidney injury (AKI) alters the gut microbiota and the levels of its metabolites d -serine (D-Ser) 10 and d -alanine (D-Ala) 11 .…”

“…Furthermore, it has become clear that bacteria are the main source of D-AAs 10 , 11 , 14 , and the levels of D-AAs reflect changes in the microbiota in various pathological conditions. We have previously reported that acute kidney injury (AKI) alters the gut microbiota and the levels of its metabolites d -serine (D-Ser) 10 and d -alanine (D-Ala) 11 . In addition to patients with AKI, those with CKD 15 , 16 and DM 17 also exhibit changes in the gut microbiota.…”

Human pluripotent stem cell-derived kidney organoids reveal tubular epithelial pathobiology of heterozygousHNF1B-associated dysplastic kidney malformations

“…Of note, components of the glutamate signalling system have been identified in mature mammalian kidneys in vivo and in kidney cell epithelial cell lines (Hediger, 1999; Valdivielso et al, 2020) e.g. GRIN2B in hypoxic murine kidney tubules (Iwata et al, 2022) and GRIN2A in murine kidney tubules (Iwata et al, 2022) with SLC7A11 , and SLC1A in PT cells (Wang et al, 2020; Shayakul et al, 1997; Welbourne et al, 1999). Importantly, increased monosodium glutamate dietary intake in rats leads to increased glomerular filtration rate, which the NMDA receptor antagonist MK-801 reduced (Mahieu et al, 2016).…”