d-Alanine as a biomarker and a therapeutic option for severe influenza virus infection and COVID-19

d-Alanine, a Circadian Metabolite that Regulates Glucose Metabolism and Viral Infection

d-Alanine, a rare d-amino acid, exhibits a clear circadian rhythm and is present in organs associated with glucose metabolism. Recent findings have revealed that d-alanine acts on the circadian rhythm, thereby regulating physiological processes related to circadian cycles that are essential for maintaining body homeostasis. The regulation of circadian rhythm by d-alanine is vital for correcting blood glucose levels in diabetic conditions. In viral infections, d-alanine serves as a sensitive biomarker that reflects the severity of the infection, as its level drastically decreases due to consumption. Supplementation with d-alanine is effective to alleviate the progression of viral infections, potentially through the maintenance of the circadian rhythm and its associated immune responses. In addition to its role as a circadian biomarker, d-alanine also functions as a circadian regulator and exerts a wide range of physiological effects. This review summarizes the physiological roles of d-alanine as a circadian metabolite.

Bioactive Molecules from Tropical American Plants: Potential Anti-Inflammatory Agents for Cytokine Storm Management

The cytokine storm, a hyperinflammatory response characterized by the excessive release of pro-inflammatory mediators such as TNFα, INFγ, IL-1β, IL-6, and GM-CSF, has been identified as a critical factor in the progression and severity of acute inflammatory conditions. Regulating these pathways is essential for mitigating systemic damage and improving outcomes. Natural products from tropical American plants have shown significant potential in modulating these hyperinflammatory responses. Key polyphenols, like quercetin and luteolin, found in plants such as Achyrocline satureioides and Mangifera indica demonstrate the downregulation of NF-κB and inhibition of pro-inflammatory cytokines. Alkaloids, such as berberine and mitraphylline, isolated from Berberis species and Uncaria tomentosa, respectively, have shown potent effects in suppressing nitric oxide production and regulating inflammasomes. Terpenoids, including parthenolide from Tanacetum parthenium and curcumol from Curcuma longa, exhibit multitarget activity, reducing cytokine levels and inhibiting key inflammatory enzymes like COX-2 and iNOS. These findings highlight the immense potential of bioactive compounds from tropical American plants as modulators of immune-inflammatory pathways, providing a foundation for developing effective therapeutic agents to counteract the severe effects of cytokine storms.

Detection of Fast Decliner of Diabetic Kidney Disease Using Chiral Amino Acid Profiling: A Pilot Study

Biomarkers for the prediction of diabetic kidney disease are still unsatisfactory. Although D-amino acids have been shown to reflect kidney conditions, their efficacy in treating diabetic kidney disease (DKD) has not been demonstrated. This study explored the potential role of D-amino acids as progression markers for DKD, an aspect not addressed previously. We performed comprehensive D-amino acid measurements and collected the longitudinal estimated glomerular filtration rate (eGFR) data of 135 patients. We defined fast decliners (FDs) as patients exhibiting >10% decline from baseline eGFR per year and compared the D-amino acid levels of FDs and non-FDs. Then, we verified that D-amino acids could predict FDs independent of creatinine levels. In patients with diabetic kidney disease, D-serine, D-alanine, and D-proline were only detected in the blood, while 15 D-amino acids were detected in the urine. Using supervised orthogonal partial least squares analysis, blood D-serine and urine D-amino acid levels were identified as features characterizing diabetic kidney disease. Baseline blood D-serine levels and ratios did not differ between the FD and non-FD groups; however, short-term changes in blood D-serine levels differed. This study emphasized the significance of D-serine as a prognostic marker for DKD, an aspect not identified in previous research.

Kinetic analysis of D-Alanine upon oral intake in humans

D-Alanine, a rare enantiomer of alanine, can potentially alleviate the worsening of viral infections and maintain circadian rhythm. This study aimed to analyze the kinetics of D-Alanine upon oral intake. Five healthy volunteers were administered D-Alanine as a single oral dose at 11,236 or 33,708 µmoL (1-3 g). Upon intake of the lower dose, the plasma level of D-Alanine reached its peak concentration of 588.4 ± 40.9 µM with a peak time of 0.60 ± 0.06 h. The compartment model estimated the clearance of D-Alanine at 12.5 ± 0.3 L/h, or 208 ± 5 mL/min, distribution volume of 8.3 ± 0.7 L and half-life of 0.46 ± 0.04 h, suggesting a rapid clearance of D-Alanine. The peak concentration and area under the curve increased proportionally upon intake of the higher dose, while the clearance, distribution volume and half-life did not. The urinary ratio of D-Alanine per sum of D- and L-Alanine reached its peak of nearly 100%, followed by a slow decline. The peak time of the urinary ratio was 1.15 ± 0.15 h, showing a time lag of blood to urine excretion. Fractional excretion, a ratio of the clearance of a substance per a standard molecule in kidney, of D-Alanine increased from 14.0 ± 5.8% to 64.5 ± 10.3%; the latter corresponded to the urinary clearance of D-Alanine as about 77 mL/min for an adult, with a peak time of 1.90 ± 0.56 h. D-Alanine was quickly absorbed and appeared in blood, followed by urinary excretion. This kinetic analysis increases our fundamental knowledge of the oral intake of D-Alanine for the chronic dosing. Trial number: #UMIN000050865. Date of registration: 2023/6/30.

Viral entry and translation in brain endothelia provoke influenza-associated encephalopathy

Influenza-associated encephalopathy (IAE) is extremely acute in onset, with high lethality and morbidity within a few days, while the direct pathogenesis by influenza virus in this acute phase in the brain is largely unknown. Here we show that influenza virus enters into the cerebral endothelium and thereby induces IAE. Three-weeks-old young mice were inoculated with influenza A virus (IAV). Physical and neurological scores were recorded and temporal-spatial analyses of histopathology and viral studies were performed up to 72 h post inoculation. Histopathological examinations were also performed using IAE human autopsy brains. Viral infection, proliferation and pathogenesis were analyzed in cell lines of endothelium and astrocyte. The effects of anti-influenza viral drugs were tested in the cell lines and animal models. Upon intravenous inoculation of IAV in mice, the mice developed encephalopathy with brain edema and pathological lesions represented by micro bleeding and injured astrocytic process (clasmatodendrosis) within 72 h. Histologically, massive deposits of viral nucleoprotein were observed as early as 24 h post infection in the brain endothelial cells of mouse models and the IAE patients. IAV inoculated endothelial cell lines showed deposition of viral proteins and provoked cell death, while IAV scarcely amplified. Inhibition of viral transcription and translation suppressed the endothelial cell death and the lethality of mouse models. These data suggest that the onset of encephalopathy should be induced by cerebral endothelial infection with IAV. Thus, IAV entry into the endothelium, and transcription and/or translation of viral RNA, but not viral proliferation, should be the key pathogenesis of IAE.

Enantiomer-Specific Colorimetric Tandem Assays for Salivary d-Alanine Associated with Gastric Cancer

Salivary d-alanine (d-Ala) and d-proline (d-Pro) are of concern for their potential in the noninvasive diagnosis of gastric cancer (GC). Most reports have succeeded in determining the total concentration of d-Ala and d-Pro. However, for personalized diagnosis and better elucidation of the underlying specific correlation of d-Ala (or d-Pro) with GC, it is desirable to determine the specific concentration of d-Ala or d-Pro. Herein, we propose an enantiomer-specific tandem assay of d-Ala based on the colorimetric reaction between 2,4-dinitrophenylhydrazine and pyruvic acid generated from the deamination of d-Ala catalyzed by d-amino acid oxidase, which is easily distinguished from l-form amino acids, d-Pro, and many other species. A linear concentration range is established from 20 to 400 μmol/L with a limit of detection of 1.01 μmol/L. Real saliva sample tests reveal that the levels of d-Ala in GC cases are remarkably higher than those in healthy individuals, which offers a simple and low-cost strategy for GC diagnosis. Simultaneously, the total concentrations of d-Ala and d-Pro in saliva are determined. Hence, the concentration of d-Pro and the proportion of d-Ala could be calculated, which further provides more molecule- and individual-specific information. This research may offer a convenient method for noninvasive diagnosis of GC and pave a new route to explore the potentials of rare d-form amino acids in disease diagnosis and treatment.

d -Alanine Affects the Circadian Clock to Regulate Glucose Metabolism in the Kidney

Key Points

d -Alanine affects the circadian clock to regulate gluconeogenesis in the kidney. d -Alanine itself has a clear intrinsic circadian rhythm, which is regulated by urinary excretion, and acts on the circadian rhythm. d -Alanine is a signal activator for circadian rhythm and gluconeogenesis through circadian transcriptional network.

Background

The aberrant glucose circadian rhythm is associated with the pathogenesis of diabetes. Similar to glucose metabolism in the kidney and liver, d -alanine, a rare enantiomer of alanine, shows circadian alteration, although the effect of d- alanine on glucose metabolism has not been explored. Here, we show that d- alanine acts on the circadian clock and affects glucose metabolism in the kidney.

Methods

The blood and urinary levels of d -alanine in mice were measured using two-dimensional high-performance liquid chromatography system. Metabolic effects of d -alanine were analyzed in mice and in primary culture of kidney proximal tubular cells from mice. Behavioral and gene expression analyses of circadian rhythm were performed using mice bred under constant darkness.

Results

d- Alanine levels in blood exhibited a clear intrinsic circadian rhythm. Since this rhythm was regulated by the kidney through urinary excretion, we examined the effect of d -alanine on the kidney. In the kidney, d -alanine induced the expressions of genes involved in gluconeogenesis and circadian rhythm. Treatment of d- alanine mediated glucose production in mice. Ex vivo glucose production assay demonstrated that the treatment of d -alanine induced glucose production in primary culture of kidney proximal tubular cells, where d -amino acids are known to be reabsorbed, but not in that of liver cells. Gluconeogenetic effect of d -alanine has an intraday variation, and this effect was in part mediated through circadian transcriptional network. Under constant darkness, treatment of d- alanine normalized the circadian cycle of behavior and kidney gene expressions.

Conclusions

d- Alanine induces gluconeogenesis in the kidney and adjusts the period of the circadian clock. Normalization of circadian cycle by d -alanine may provide the therapeutic options for life style–related diseases and shift workers.

The gut-joint axis mediates the TNF-induced RA process and PBMT therapeutic effects through the metabolites of gut microbiota

The gut-joint axis, one of the mechanisms that mediates the onset and progression of joint and related diseases through gut microbiota, and shows the potential as therapeutic target. A variety of drugs exert therapeutic effects on rheumatoid arthritis (RA) through the gut-joint axis. However, the anti-inflammatory and immunomodulatory effect of novel photobiomodulatory therapy (PBMT) on RA need further validation and the involvement of gut-joint axis in this process remains unknown. The present study demonstrated the beneficial effects of PBMT on RA, where we found the restoration of gut microbiota homeostasis, and the related key pathways and metabolites after PBMT. We also discovered that the therapeutic effects of PBMT on RA mainly through the gut-joint axis, in which the amino acid metabolites (Alanine and N-acetyl aspartate) play the key role and rely on the activity of metabolic enzymes in the target organs. Together, the results prove that the metabolites of amino acid from gut microbiota mediate the regulation effect on the gut-joint axis and the therapeutic effect on rheumatoid arthritis of PBMT.

D-Serine as a sensor and effector of the kidney

D-Serine, a rare enantiomer of serine, is a biomarker of kidney disease and function. The level of D-serine in the human body is precisely regulated through the urinary clearance of the kidney, and its clearance serves as a new measure of glomerular filtration rate with a lower bias than creatinine clearance. D-Serine also has a direct effect on the kidneys and mediates the cellular proliferation of tubular cells via mTOR signaling and induces kidney remodeling as a compensatory reaction to the loss of kidney mass. In living kidney donors, the removal of the kidney results in an increase in blood D-serine level, which in turn accelerates kidney remodeling and augments kidney clearance, thus reducing blood levels of D-serine. This feedback system strictly controls D-serine levels in the body. The function of D-serine as a biomarker and modulator of kidney function will be the basis of precision medicine for kidney diseases.

Blood levels of d-amino acids reflect the clinical course of COVID-19

d-Amino acids, rare enantiomers of amino acids, have been identified as biomarkers and therapeutic options for COVID-19. Methods for monitoring recovery are necessary for managing COVID-19. On the other hand, the presence of SARS-CoV2 virus in the blood is associated with worse outcomes. We investigated the potential of d-amino acids for assessing recovery from severe COVID-19. In patients with severe COVID-19 requiring artificial ventilation, the blood levels of d-amino acids, including d-alanine, d-proline, d-serine, and d-asparagine, which were lower than the normal range before treatment, quickly and transiently increased and surpassed the upper limit of the normal range. This increase preceded the recovery of respiratory function, as indicated by ventilation weaning. The increase in blood d-amino acid levels was associated with the disappearance of the virus in the blood, but not with inflammatory manifestations or blood cytokine levels. d-Amino acids are sensitive biomarkers that reflect the recovery of the clinical course and blood viral load. Dynamic changes in blood d-amino acid levels are key indicators of clinical course.

Salivary Metabolomic Analysis Reveals Amino Acid Metabolism Shift in SARS-CoV-2 Virus Activity and Post-Infection Condition

The SARS-CoV-2 virus primarily infects salivary glands suggesting a change in the saliva metabolite profile; this shift may be used as a monitoring instrument during SARS-CoV-2 infection. The present study aims to determine the salivary metabolomic profile of patients with and post-SARS-CoV-19 infection. Patients were without (PCR-), with SARS-CoV-2 (PCR+), or post-SARS-CoV-2 infection. Unstimulated whole saliva was collected, and the ¹H spectra were acquired in a 500 MHz Bruker nuclear magnetic resonance spectrometer at 25 °C. They were subjected to multivariate analysis using principal component analysis (PCA) and partial least squares discriminant analysis (PLS-DA), as well as univariate analysis through t-tests (SPSS 20.0, IL, USA), with a significance level of p < 0.05. A distinction was found when comparing PCR- subjects to those with SARS-CoV-2 infection. When comparing the three groups, the PLS-DA cross-validation presented satisfactory accuracy (ACC = 0.69, R2 = 0.39, Q2 = 0.08). Seventeen metabolites were found in different proportions among the groups. The results suggested the downregulation of major amino acid levels, such as alanine, glutamine, histidine, leucine, lysine, phenylalanine, and proline in the PCR+ group compared to the PCR- ones. In addition, acetate, valerate, and capronic acid were higher in PCR- patients than in PCR+. Sucrose and butyrate were higher in post-SARS-CoV-2 infection compared to PCR-. In general, a reduction in amino acids was observed in subjects with and post-SARS-CoV-2 disease. The salivary metabolomic strategy NMR-based was able to differentiate between non-infected individuals and those with acute and post-SARS-CoV-19 infection.