Kagami Crystal (Japan)

ABSTRACT In this study, we examined clinical and cohort data to explore the potential renoprotective effects of natto (fermented soybeans) consumption and its relationship with D‐amino acids. In a clinical study, ten healthy adults consumed one 40‐g pack of natto three times in a single day, and plasma and urine samples were collected 1 h and 24 h after intake. In a 5‐year cohort of 295 adults, natto intake was categorized as none (0 g/day), low (1–10 g/day), middle (11–25 g/day), or high (> 25 g/day). The plasma and urinary D‐alanine levels increased significantly after natto consumption. In the cohort, the adjusted mean annual changes in estimated glomerular filtration rate (eGFR, mL/min/1.73 m 2 ) were −1.41, −0.78, −1.01, and −1.01 for the none, low, middle, and high groups, respectively. Low natto intake was significantly associated with a slower decline in eGFR, although no dose‐dependent trend was observed. No significant differences in gut microbiota diversity or composition were found across intake groups. Natto consumption was associated with increased plasma D‐alanine levels and a slower decline in renal function. Further studies are warranted to clarify the mechanisms underlying these associations.

The sensitivity of currently available screening tools for urothelial carcinoma (UC) remains unsatisfactory particularly at early stages. Hence, we aimed to establish a novel blood-based screening tool for urothelial carcinoma. We measured serum d-amino acid levels in 108 and 192 patients with and without UC individuals in the derivation cohort, and 15 and 25 patients with and without UC in the validation cohort. Serum d-asparagine levels were significantly higher in patients with UC than in those without UC (p < 0.0001). We developed a novel screening equation for the diagnosis of urothelial carcinoma using d-asparagine in serum and estimated the glomerular filtration rate (eGFR). Serum d-asparagine levels adjusted for eGFR exhibited high performance in the diagnosis of UC (AUC-ROC, 0.869; sensitivity, 80.6 %; specificity, 82.7 %), even in early-stage UC (AUC-ROC: 0.859, sensitivity: 83.3 %, specificity: 82.3 %), which were previously misdiagnosed via urinary occult blood or urine cytology. This established strategy combined with urinary occult blood, improves diagnostic ability (sensitivity: 93.7 %, specificity: 70.1 %).

Transporter research primarily relies on the canonical substrates of well-established transporters. This approach has limitations when studying transporters for the low-abundant micromolecules, such as micronutrients, and may not reveal physiological functions of the transporters. While D-serine, a trace enantiomer of serine in the circulation, was discovered as an emerging biomarker of kidney function, its transport mechanisms in the periphery remain unknown. Here, using a multi-hierarchical approach from body fluids to molecules, combining multi-omics, cell-free synthetic biochemistry, and ex vivo transport analyses, we have identified two types of renal D-serine transport systems. We revealed that the small amino acid transporter ASCT2 serves as a D-serine transporter previously uncharacterized in the kidney and discovered D-serine as a noncanonical substrate of the sodium-coupled monocarboxylate transporters (SMCTs). These two systems are physiologically complementary, but ASCT2 dominates the role in the pathological condition. Our findings not only shed light on renal D-serine transport, but also clarify the importance of non-canonical substrate transport. This study provides a framework for investigating multiple transport systems of various trace micromolecules under physiological conditions and in multifactorial diseases.

For the discovery of sensitive biomarkers of kidney function focusing on chiral amino acids, a multiple heart-cutting two-dimensional (2D) liquid chromatography-mass spectrometry (LC-MS)/MS system has been designed/developed. As the target analytes, alanine (Ala), aspartic acid, glutamic acid (Glu), leucine (Leu), lysine, methionine, phenylalanine (Phe), proline (Pro), serine (Ser), and valine were selected considering the presence of their d-forms in mammals. The 2D LC-MS/MS system consisted of the nonenantioselective reversed-phase separation of the target amino acids, the separations of the d- and l-enantiomers, and detection using MS/MS. Using the method, the plasma chiral amino acids, precolumn derivatized with 4-fluoro-7-nitro-2,1,3-benzoxadiazole, were isolated from other intrinsic substances, then determined without losing sensitivity by the fully automated whole-peak volume transfer operation from first to second dimension. In all of the tested plasma samples obtained from five healthy individuals and 15 patients with chronic kidney disease (CKD), the target chiral amino acids were determined without interference. In healthy individuals, the levels of all the tested d-amino acids were regulated in the low ranges. In contrast, the % d values of Glu, Leu, and Phe significantly increased with the progress of kidney dysfunction, besides the previously reported values of d-Ala, Pro, and Ser. Concerning Phe, the significant increase of the % d values (p < 0.05) was reported for the first time even in the mild CKD group compared to those of the healthy group; d-Phe might be a more sensitive marker than the previously reported d-forms. These results demonstrated the potential of these d-forms as the sensitive biomarkers of kidney function for the early diagnosis of CKD.

d-Serine modulates excitatory neurotransmission by binding to N-methyl-d-aspartate glutamate receptors. d-Amino acid oxidase (DAO) degrades d-amino acids, such as d-serine, in the central nervous system, and is associated with neurological and psychiatric disorders. However, cell types that express brain DAO remain controversial, and whether brain DAO influences systemic d-amino acids in addition to brain d-serine remains unclear. Here, we created astrocyte-specific DAO-conditional knockout mice. Knockout in glial fibrillary acidic protein-positive cells eliminated DAO expression in the hindbrain and increased d-serine levels significantly in the cerebellum. Brain DAO did not influence levels of d-amino acids in the forebrain or periphery. These results show that astrocytic DAO regulates d-serine specifically in the hindbrain.

d-serine, a long-term undetected enantiomer of serine, is a biomarker that reflects kidney function and disease activity. The physiologic functions of d-serine are unclear. The dynamics of d-serine were assessed by measuring d-serine in human samples of living kidney donors using two-dimensional high-performance liquid chromatography, and by autoradiographic studies in mice. The effects of d-serine on the kidney were examined by gene expression profiling and metabolic studies using unilateral nephrectomy mice, and genetically modified cells. Unilateral nephrectomy in human living kidney donors decreases urinary excretion and thus increases the blood level of d-serine. d-serine is quickly and dominantly distributed to the kidney on injection in mice, suggesting the kidney is a main target organ. Treatment of d-serine at a low dose promotes the enlargement of remnant kidney in mouse model. Mechanistically, d-serine activates the cell cycle for tissue remodeling through an mTOR-related pathway. d-serine is a physiologic molecule that promotes kidney remodeling. Besides its function as a biomarker, d-serine has a physiologic activity that influences kidney function.

Histological examination was made to identify JG cells on the kidneys of eleven species of Chondrichthyes and two species of Cyclostomi. However, the JG cells could not be detected in them.