A multi-hierarchical approach reveals d-serine as a hidden substrate of sodium-coupled monocarboxylate transporters.

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 non-canonical 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.

Mammals sustain amino acid homochirality against chiral conversion by symbiotic microbes.

Mammals exhibit systemic homochirality of amino acids in L-configurations. While ribosomal protein synthesis requires rigorous chiral selection for L-amino acids, both endogenous and microbial enzymes convert diverse L-amino acids to D-configurations in mammals. However, it is not clear how mammals manage such diverse D-enantiomers. Here, we show that mammals sustain systemic stereo dominance of L-amino acids through both enzymatic degradation and excretion of D-amino acids. Multidimensional high performance liquidchromatography analyses revealed that in blood, humans and mice maintain D-amino acids at less than several percent of the corresponding L-enantiomers, while D-amino acids comprise ten to fifty percent of the L-enantiomers in urine and feces. Germ-free experiments showed that vast majority of D-amino acids, except for D-serine, detected in mice are of microbial origin. Experiments involving mice that lack enzymatic activity to catabolize D-amino acids showed that catabolism is central to the elimination of diverse microbial D-amino acids, whereas excretion into urine is of minor importance under physiological conditions. Such active regulation of amino acid homochirality depends on maternal catabolism during the prenatal period, which switches developmentally to juvenile catabolism along with the growth of symbiotic microbes after birth. Thus, microbial symbiosis largely disturbs homochirality of amino acids in mice, whereas active host catabolism of microbial D-amino acids maintains systemic predominance of L-amino acids. Our findings provide fundamental insight into how the chiral balance of amino acids is governed in mammals and further expand the understanding of interdomain molecular homeostasis in host-microbial symbiosis.

An infant of 26 weeks gestation with congenital miliary tuberculosis complicated by chronic lung disease requiring CPAP was diagnosed on Day 104 of life: congenital tuberculosis was confirmed by detection of calcified ovaries in his mother.

INTRODUCTION: Early diagnosis of tuberculosis (TB) in infants is important but is commonly missed because the symptoms are often non-specific. CASE PRESENTATION: A Nepalese male infant born at 26 weeks gestation and weighing 1227 g (97th centile) was admitted to the neonatal intensive care unit (NICU) immediately after birth for the management of his prematurity. After extubation on Day 8, his oxygen saturation became unstable and he required nasal continuous positive airway pressure with oxygen for 3 months. On Day 104, further detailed evaluation was required because there was no improvement in his respiratory condition. A computed tomography (CT) scan demonstrated scattered miliary nodules in both lung fields. Acid-fast staining for the mycobacteria and TB polymerase chain reaction (PCR) of the sputum obtained directly by laryngeal aspiration confirmed Mycobacterium tuberculosis. On Day 105, he was therefore transferred to a tertiary care hospital for further intensive care. Pathology findings suggested placental involvement with TB owing to chronic endometrial infection. In addition, a maternal abdominal CT scan demonstrated bilateral calcified lesions in the ovaries. He completed antituberculous chemotherapy and was discharged 3 months later. At 18 months of age there are no sequelae and his development is almost normal. None of the infants or medical personnel who were exposed in the NICU developed secondary TB. CONCLUSION: In neonates with persistent respiratory distress, neonatologists should consider TB infection as a differential diagnosis. ABBREVIATIONS: CLD: chronic lung disease; CRP: C-reactive protein; CT: computed tomography; IGRA: interferon-γ release assay; IVF-ET: in vitro fertilisation-embryo transfer; N-CPAP: nasal continuous positive airway pressure; NICU: neonatal intensive care unit; PCR: polymerase chain reaction; PROM: premature rupture of membranes; TB: tuberculosis; WBC: white blood cells.

The influence on renal function of ibuprofen treatment for patent ductus arteriosus in extremely low birthweight infants.

BACKGROUND: Ibuprofen (IBU) has been used recently for the treatment of patent ductus arteriosus (PDA) in Japan. We aimed to investigate the efficacy and adverse events of IBU and compare them with those of indomethacin (IND) as PDA treatment for extremely low-birthweight infants (ELBWIs), focusing on short-term renal function. METHODS: A case-control study was conducted on 16 ELBWIs. The data from eligible patients were divided into two groups. Ten patients had undergone IND treatment (IND group) between January 2017 and June 2018, whereas six had undergone IBU treatment (IBU group) for PDA between July 2018 and December 2018. The IND group received 0.1 mg/kg/12h IND IV infusion for three doses, whereas the IBU group received 10 mg/kg IV IBU infusion followed by 5 mg/kg/day for 2 days. We compared the efficacy for PDA closure and renal impairment between the two groups. RESULTS: No significant differences in primary closure rates and the PDA ligation required were observed between the two groups. No significant differences were observed between the incidence of intraventricular hemorrhage and gastrointestinal complications in both groups. Changes in urine volume (%) in the IBU group were significantly higher than in the IND group at 24-36 h post-administration. The urinary L-type fatty acid binding protein concentration level at 7 days of life was significantly lower in the IBU group than in the IND group. CONCLUSION: Although IBU was comparable to IND in PDA closure rate, IBU was superior to short-term renal injury in ELBWIs.

Influence of oxidative stress on D-aspartyl endopeptidase activity.

It is strongly suggested that D-aspartic acid (D-Asp)-containing proteins are spontaneously generated by oxidative stress and would cause many aging-related misfolding diseases, such as cataracts, prion disease, and Alzheimer's disease. We have identified a D-Asp-containing protein-specific protease, D-aspartyl endopeptidase (DAEP), from mammalian mitochondria, serving as a scavenger against the noxious D-Asp-containing protein. Recently, it has been shown that the activity of Lon, an ATP-dependent protease degrading oxidatively damaged proteins in mitochondria, decreases with aging by oxidative stress. However, an obvious relation between DAEP activity and oxidative stress with aging remains to be demonstrated. In the present study, we showed that there was a remarkable decrease in DAEP activity in superoxide dismutase-deficient mice, which formed excess reactive oxygen species (ROS). Our result suggests that a decrease in DAEP activity by oxidative stress may cause the accumulation of D-Asp-containing protein, leading to mitochondria-associated diseases.

Antioxidant, EUK-8, prevents murine dilated cardiomyopathy.

BACKGROUND: Mice lacking manganese-superoxide dismutase (Mn-SOD) activity exhibit the typical pathology of dilated cardiomyopathy (DCM). In the present study, presymptomatic and symptomatic mutant mice were treated with the SOD/catalase mimetic, EUK-8. METHODS AND RESULTS: Presymptomatic heart/muscle-specific Mn-SOD-deficient mice (H/M-Sod2(-/-)) were treated with EUK-8 (30 mg x kg(-1) . day(-1)) for 4 weeks, and then cardiac function and the reactive oxygen species (ROS) production in their heart mitochondria were assessed. EUK-8 treatment suppressed the progression of cardiac dysfunction and diminished ROS production and oxidative damage. Furthermore, EUK-8 treatment effectively reversed the cardiac dilatation and dysfunction observed in symptomatic H/M-Sod2(-/-) mice. Interestingly, EUK-8 treatment repaired a molecular defect in connexin43. CONCLUSIONS: EUK-8 treatment can prevent and cure murine DCM, so SOD/catalase mimetic treatment is proposed as a potential therapy for DCM.

Asymptomatic emphysematous cholecystitis.

Emphysematous cholecystitis (EC) is a life-threatening complication of acute cholecystitis. Its clinical manifestations are usually vague, but asymptomatic cases are very rare. We present such a case with an emphasis on sonographic (US) findings. In this case, detection of gas echoes in the gallbladder wall and the surrounding hepatic tissue led us to an appropriate treatment. US is now the technique of first choice for diagnosing gallbladder diseases, and knowledge of US findings encountered in this case can help prevent a hazardous delay in emergent treatment.