Quantitative Evaluation of D-Lactate Pathophysiology: New Insights into the Mechanisms Involved and the Many Areas in Need of Further Investigation

Advances in Chiral Metabolomic Profiling and Biomarker Discovery

Chiral metabolomics entails the enantioselective measurement of the metabolome present in a biological system. Over recent years, it has garnered significant interest for its potential in discovering disease biomarkers and aiding clinical diagnostics. D-Amino acids and D-hydroxy acids, traditionally overlooked as unnatural, are now emerging as novel signaling molecules and potential biomarkers for a range of metabolic disorders, brain diseases, kidney disease, diabetes, and cancer. Despite their significance, simultaneous measurements of multiple classes of chiral metabolites in a biological system remain challenging. Hence, limited information is available regarding the metabolic pathways responsible for synthesizing D-amino/hydroxy acid and their associated pathophysiological mechanisms in various diseases. Capitalizing on recent advancements in sensitive analytical techniques, researchers have developed various targeted chiral metabolomic methods for the analysis of chiral biomarkers. Here, we highlight the pivotal role of chiral metabolic profiling studies in disease diagnosis, prognosis, and therapeutic interventions. Furthermore, we describe cutting-edge chromatographic and mass spectrometry methods that enable enantioselective analysis of chiral metabolites. These advanced techniques are instrumental in unraveling the complexities of disease biomarkers, contributing to the ongoing efforts in disease biomarker discovery.

Lysine L-lactylation is the dominant lactylation isomer induced by glycolysis

Lysine L-lactylation (Kl-la) is a novel protein posttranslational modification (PTM) driven by L-lactate. This PTM has three isomers: Kl-la, N-ε-(carboxyethyl)-lysine (Kce) and D-lactyl-lysine (Kd-la), which are often confused in the context of the Warburg effect and nuclear presence. Here we introduce two methods to differentiate these isomers: a chemical derivatization and high-performance liquid chromatography analysis for efficient separation, and isomer-specific antibodies for high-selectivity identification. We demonstrated that Kl-la is the primary lactylation isomer on histones and dynamically regulated by glycolysis, not Kd-la or Kce, which are observed when the glyoxalase system was incomplete. The study also reveals that lactyl-coenzyme A, a precursor in L-lactylation, correlates positively with Kl-la levels. This work not only provides a methodology for distinguishing other PTM isomers, but also highlights Kl-la as the primary responder to glycolysis and the Warburg effect.

Evaluation of a Burkholderia ambifaria strain from plants as a novel promising probiotic in dental caries management

Background

Probiotics serve as a novel preventive or therapeutic approach for dental caries owing to their ability to reverse dysbiosis and restore a healthy microbiota. Here, we identified Burkholderia ambifaria AFS098024 as a probiotic candidate isolated from plants.

Methods

The safety of B. ambifaria was evaluated by hemolytic activity, D-lactic acid production and antibiotic susceptibility. In vitro biofilm model derived from the saliva of caries-free and caries-active donors and in vivo rat caries model were used to assess the efficacy of B. ambifaria in caries prevention and treatment.

Results

B. ambifaria was safe as a probiotic candidate and it could integrate with in vitro biofilm model. It significantly reduced the biomass and lactate production of biofilms from caries-active donors and disrupted biofilm structures. B. ambifaria effectively reduced the severity of carious lesions in rat molars, regardless of the inoculation sequence. Molars pretreated or treated with B. ambifaria demonstrated notably higher enamel volumes. Additionally, colonization of rat molars by B. ambifaria persisted for 6 weeks.

Conclusion

The B. ambifaria strain used in this study holds promise as a probiotic for inhibiting dental caries, both in vitro and in vivo.

Synovial fluid D-lactate - a pathogen-specific biomarker for septic arthritis: a prospective multicenter study

OBJECTIVES

The performance of synovial fluid biomarker D-lactate to diagnose septic arthritis (SA) and differentiate it from crystal-induced arthritis (CA), other non-infectious rheumatic joint diseases (RD) and osteoarthrosis (OA) was evaluated.

METHODS

Consecutive adult patients undergoing synovial fluid aspiration due to joint pain were prospectively included in different German and Swiss centers. Synovial fluid was collected for culture, leukocyte count and differentiation, detection of crystals, and D-lactate concentration. Youden's J statistic was used to determine optimal D-lactate cut-off value on the receiver operating characteristic (ROC) curve by maximizing sensitivity and specificity.

RESULTS

In total 231 patients were included. Thirty-nine patients had SA and 192 aseptic arthritis (56 patients with OA, 68 with CA, and 68 with RD). The median concentration of synovial fluid D-lactate was significantly higher in patients with SA than in those with OA, CA, and RD (p<0.0001, p<0.0001 and p<0.0001, respectively). The optimal cut-off of synovial fluid D-lactate to diagnose SA was 0.033 mmol/L with a sensitivity of 92.3 % and specificity of 85.4 % independent of previous antimicrobial treatment. Sensitivity and specificity of synovial fluid leukocyte count at a cut-off of 20,000 cells/µL was 81.1 % and 80.8 %, respectively.

CONCLUSIONS

Synovial fluid D-lactate showed a high performance for diagnosing SA which was superior to synovial fluid leukocyte count. Given its high sensitivity and specificity, it serves as both an effective screening tool for SA and a differentiator between SA and RD, especially CA.

In vitro evaluation of microbial D- and L-lactate production as biomarkers of infection

Mammalian cells produce and metabolize almost exclusively L-lactate, bacterial species have the capacity to produce both D-lactate and L-lactate. The aim of this study was to evaluate the intrinsic production of D- and L-lactate in the most common pathogenic microorganisms causing septic arthritis (SA) and periprosthetic joint infection (PJI) as a potential biomarker for the diagnosis of infection. Following microorganisms were grown according to ATCC culture guides and tested for production of D- and L-lactate: Staphylococcus aureus (ATCC 43300), Staphylococcus epidermidis (ATCC 35984), Enterococcus faecalis (ATCC 19433), Streptococcus pyogenes (ATCC 19615), Escherichia coli (ATCC 25922), Pseudomonas aeruginosa (ATCC 27853), Cutibacterium acnes (ATCC 11827), and Candida albicans (ATCC 90028). Pathogens were inoculated in 8 ml of appropriate liquid media and incubated as planktonic or biofilm form in either aerobic, anaerobic or CO2 atmosphere up to 312 h. D- and L-lactate measurements were performed at different time points: 0, 6, 9, 12 and 24 h, then once per day for slow-growing pathogens. Samples were serially diluted and plated for colony counting. Liquid culture media without microorganisms served as a negative control. Production of D-lactate was observed in all tested microorganisms, whereas no L-lactate was detected in E. coli, P. aeruginosa, and C. albicans. Maximal concentration of D-lactate was produced by S. aureus (10.99 mmol/L), followed by E. coli (1.22 mmol/L), and S. epidermidis (0.48 mmol/L). Maximal L-lactate concentration was observed in S. pyogenes (10.12 mmol/L), followed by S. aureus (9.71 mmol/L), E. faecalis (2.64 mmol/L), and S. epidermidis (2.50 mmol/L). S. epidermidis bacterial biofilm produced significantly higher amount of D- and L-lactate compared to planktonic form (p = 0.015 and p = 0.002, respectively). Our study has demonstrated that the most common pathogenic microorganisms causing SA and PJI have the capability to generate measurable amounts of D-lactate in both planktonic and biofilm form, highlighting the practical value of this biomarker as an indicator for bacterial and fungal infections. In contrast to D-lactate, the absence of L-lactate production in certain tested bacteria, as well as in fungi, suggests that L-lactate is not eligible as a biomarker for diagnosing microbial infections.

Nanopore Identification of L-, D-Lactic Acids, D-Glucose and Gluconic Acid in the Serum of Human and Animals

DL-Lactic acid and D-glucose are important human health indicators. Their aberrant levels in body fluids may indicate a variety of human pathological conditions, suggesting an urgent need of daily monitoring. However, simultaneous and rapid analysis of DL-lactic acid and D-glucose using a sole but simple sensing system has never been reported. Here, an engineered Mycobacterium smegmatis porin A (MspA) nanopore is used to simultaneously identify DL-lactic acid and D-glucose. Highly distinguishable nanopore event features are reported. Assisted with a custom machine learning algorithm, direct identification of DL-lactic acid and D-glucose is performed with human serum, demonstrating its sensing reliability against complex and heterogeneous samples. This sensing strategy is further applied in the analysis of different animal serum samples, according to which gluconic acid is further identified. The serum samples from different animals report distinguishable levels of DL-lactic acid, D-glucose and gluconic acid, suggesting its potential applications in agricultural science and breeding industry. This sensing strategy is generally direct, rapid, economic and requires only ≈µL of input serum, suitable for point of care testing (POCT) applications.

Exploring D-Lactate as a Biomarker for Acute Intestinal Necrosis in 2958 Patients: A Prospective Cross-Sectional Study

BACKGROUND

Timely diagnosis of acute intestinal necrosis (AIN) is lifesaving, but challenging due to unclear clinical presentation. D-lactate has been proposed as an AIN biomarker.

OBJECTIVES

We aimed to test the diagnostic performance in a clinical setting.

METHODS

We performed a cross-sectional prospective study, including all adult patients with acute referral to a single tertiary gastrointestinal surgical department during 2015-2016 and supplemented by enrollment of high-risk in-hospital patients suspected of having AIN during 2016-2019. AIN was verified intraoperatively, and D-lactate was analyzed using an automatic spectrophotometric set-up. A D-lactate cut-off for AIN was estimated using the receiver operating characteristic curve. The performance according to patient subgroups was estimated using the area under the receiver operating characteristic curve (AUC). Given the exploratory nature of this study, a formal power calculation was not feasible.

RESULTS

Forty-four AIN patients and 2914 controls were enrolled. The D-lactate cut-off was found to be 0.0925 mM. Due to lipemic interference, D-lactate could not be quantified in half of the patients, leaving 23 AIN patients and 1456 controls for analysis. The AUC for the diagnosis of AIN by D-lactate was 0.588 (95% confidence interval 0.475-0.712), with a sensitivity of 0.261 and specificity of 0.892. Analysis of high-risk patients showed similar results (AUC 0.579; 95% confidence interval 0.422-0.736).

CONCLUSION

D-lactate showed low sensitivity for AIN in both average-risk and high-risk patients. Moreover, lipemic interference precluded valid spectrophotometric assessment of D-lactate in half of the patients, further disqualifying the clinical utility of D-lactate as a diagnostic marker for AIN.

Clostridium perfringens α toxin damages the immune function, antioxidant capacity and intestinal health and induces PLCγ1/AMPK/mTOR pathway-mediated autophagy in broiler chickens

Clostridium perfringens α toxin is generated by all types of C. perfringens and is closely related to necrotic enteritis in poultry. This study was conducted to investigate the effects of α toxin on immune function, antioxidant capacity, intestinal health and the underlying mechanisms in broiler chickens. A total of 144 twenty-day-old broiler chickens were randomly assigned to four treatments. On d 21, the birds were intraperitoneally injected with PBS (control group) or α toxin at 0.025, 0.1 or 0.4 U/kg of body weight. Samples were collected at 3 h and 24 h post injection (p.i.). Results showed that α toxin challenge linearly decreased the average daily gain during the 3 days after infection and decreased plasma IgA and IgM levels 3 h p.i. Plasma diamine oxidase and d-lactate levels were linearly elevated by α toxin challenge at 3 h p.i. and 24 h p.i. Alpha toxin challenge linearly decreased plasma and jejunal mucosal catalase, glutathione peroxidase and total superoxide dismutase activities at 3 h p.i. and linearly decreased glutathione peroxidase and total superoxide dismutase activities at 24 h p.i. The ileal villus height to crypt depth ratio decreased linearly with increasing α toxin levels at 3 h p.i. and 24 h p.i. Alpha toxin challenge linearly elevated jejunal IL-1β, IL-6, IL-8 and tumor necrosis factor α mRNA expression at 3 h p.i. Additionally, α toxin challenge linearly reduced the jejunal claudin-1, claudin-3 and zonula occludens 1 mRNA expression at 3 h p.i. and the claudin-3, occludin and zonula occludens 1 mRNA expression at 24 h p.i. What's more, α toxin linearly increased the jejunal PLCγ1, AMPKα1 and ATG5 mRNA expression and linearly decreased the mTOR mRNA expression. In conclusion, C. perfringens α toxin challenge decreased body weight gain, impaired immune function, antioxidant capacity and intestinal health, and induced PLCγ1/AMPK/mTOR pathway-mediated autophagy. The recommended intraperitoneal injection dose for moderate injury was 0.1 U/kg of body weight and the recommended sampling time was 3 h p.i. in broiler chickens.

High-Performance Genetically Encoded Green Fluorescent Biosensors for Intracellular l-Lactate

l-Lactate is a monocarboxylate produced during the process of cellular glycolysis and has long generally been considered a waste product. However, studies in recent decades have provided new perspectives on the physiological roles of l-lactate as a major energy substrate and a signaling molecule. To enable further investigations of the physiological roles of l-lactate, we have developed a series of high-performance (ΔF/F = 15 to 30 in vitro), intensiometric, genetically encoded green fluorescent protein (GFP)-based intracellular l-lactate biosensors with a range of affinities. We evaluated these biosensors in cultured cells and demonstrated their application in an ex vivo preparation of Drosophila brain tissue. Using these biosensors, we were able to detect glycolytic oscillations, which we analyzed and mathematically modeled.

The Metabolic Syndrome, a Human Disease

This review focuses on the question of metabolic syndrome (MS) being a complex, but essentially monophyletic, galaxy of associated diseases/disorders, or just a syndrome of related but rather independent pathologies. The human nature of MS (its exceptionality in Nature and its close interdependence with human action and evolution) is presented and discussed. The text also describes the close interdependence of its components, with special emphasis on the description of their interrelations (including their syndromic development and recruitment), as well as their consequences upon energy handling and partition. The main theories on MS's origin and development are presented in relation to hepatic steatosis, type 2 diabetes, and obesity, but encompass most of the MS components described so far. The differential effects of sex and its biological consequences are considered under the light of human social needs and evolution, which are also directly related to MS epidemiology, severity, and relations with senescence. The triggering and maintenance factors of MS are discussed, with especial emphasis on inflammation, a complex process affecting different levels of organization and which is a critical element for MS development. Inflammation is also related to the operation of connective tissue (including the adipose organ) and the widely studied and acknowledged influence of diet. The role of diet composition, including the transcendence of the anaplerotic maintenance of the Krebs cycle from dietary amino acid supply (and its timing), is developed in the context of testosterone and β-estradiol control of the insulin-glycaemia hepatic core system of carbohydrate-triacylglycerol energy handling. The high probability of MS acting as a unique complex biological control system (essentially monophyletic) is presented, together with additional perspectives/considerations on the treatment of this 'very' human disease.

Histone lactylation regulates cancer progression by reshaping the tumor microenvironment

As a major product of glycolysis and a vital signaling molecule, many studies have reported the key role of lactate in tumor progression and cell fate determination. Lactylation is a newly discovered post-translational modification induced by lactate. On the one hand, lactylation introduced a new era of lactate metabolism in the tumor microenvironment (TME), and on the other hand, it provided a key breakthrough point for elucidation of the interaction between tumor metabolic reprogramming and epigenetic modification. Studies have shown that the lactylation of tumor cells, tumor stem cells and tumor-infiltrating immune cells in TME can participate in the development of cancer through downstream transcriptional regulation, and is a potential and promising tumor treatment target. This review summarized the discovery and effects of lactylation, as well as recent research on histone lactylation regulating cancer progression through reshaping TME. We also focused on new strategies to enhance anti-tumor effects via targeting lactylation. Finally, we discussed the limitations of existing studies and proposed new perspectives for future research in order to further explore lactylation targets. It may provide a new way and direction to improve tumor prognosis.

Gut barrier dysfunction and endotoxemia in heart failure: A dangerous connubium?

Heart failure (HF) is a leading cause of death worldwide despite recent advances in pharmacological treatments. Gut microbiota dysbiosis and gut barrier dysfunction with consequent bacterial translocation and increased blood endotoxemia has gained much attention as one of the key pathogenetic mechanisms contributing to increased mortality of patients at risk or with cardiovascular disease. Indeed, increased blood levels of lipopolysaccharide (LPS), a glycolipid of outer membrane of gut gram-negative bacteria, have been detected in patients with diabetes, obesity and nonalcoholic fatty liver disease or in patients with established coronary disease such as myocardial infarction or atrial fibrillation, suggesting endotoxemia as aggravating factor via systemic inflammation and eventually vascular damage. Upon interaction with its receptor Toll-like receptor 4 (TLR4) LPS may, in fact, act at different cellular levels so eliciting formation of proinflammatory cytokines or exerting a procoagulant activity. Increasing body of evidence pointed to endotoxemia as factor potentially deteriorating the clinical course of patients with HF, that, in fact, is associated with gut dysbiosis-derived changes of gut barrier functionality and eventually bacteria or bacterial product translocation into systemic circulation. The aim of this review is to summarize current experimental and clinical evidence on the mechanisms linking gut dysbiosis-related endotoxemia with HF, its potential negative impact with HF progression, and the therapeutic strategies that can counteract endotoxemia.

A metagenomic study of gut viral markers in amyloid-positive Alzheimer's disease patients

BACKGROUND

Mounting evidence suggests the involvement of viruses in the development and treatment of Alzheimer's disease (AD). However, there remains a significant research gap in metagenomic studies investigating the gut virome of AD patients, leaving gut viral dysbiosis in AD unexplored. This study aimed to fill this gap by conducting a metagenomics analysis of the gut virome in both amyloid-positive AD patients (Aβ + ADs) and healthy controls (HCs), with the objective of identifying viral signatures linked with AD.

METHOD

Whole-genome sequence (WGS) data from 65 human participants, including 30 Aβ + ADs and 35 HCs, was obtained from the database NCBI SRA (Bio Project: PRJEB47976). The Metaphlan3 pipeline and linear discriminant analysis effect size (LEfSe) analysis were utilized for the bioinformatics process and the detection of viral signatures, respectively. In addition, the Benjamini-Hochberg method was applied with a significance cutoff of 0.05 to evaluate the false discovery rate for all biomarkers identified by LEfSe. The CombiROC model was employed to determine the discriminatory power of the viral signatures identified by LEfSe.

RESULTS

Compared to HCs, the gut virome profiles of Aβ + ADs showed lower alpha diversity, indicating a lower bacteriophage richness. The Siphoviridae family was decreased in Aβ + ADs. Significant decreases of Lactococcus phages were found in Aβ + ADs, including bIL285, Lactococcus phage bIL286, Lactococcus phage bIL309, and Lactococcus phage BK5 T, Lactococcus phage BM13, Lactococcus phage P335 sensu lato, Lactococcus phage phiLC3, Lactococcus phage r1t, Lactococcus phage Tuc2009, Lactococcus phage ul36, and Lactococcus virus bIL67. The predictive combined model of these viral signatures obtained an area under the curve of 0.958 when discriminating Aβ + ADs from HCs.

CONCLUSION

This is the first study to identify distinct viral signatures in the intestine that can be used to effectively distinguish individuals with AD from HCs.

Microbiota dysbiosis caused by dietetic patterns as a promoter of Alzheimer's disease through metabolic syndrome mechanisms

Microbiota dysbiosis and metabolic syndrome, consequences of a non-adequate diet, generate a feedback pathogenic state implicated in Alzheimer's disease development. The lower production of short chain fatty acids (SCFAs) under dysbiosis status leads to lipid homeostasis deregulation and decreases Angptl4 release and AMPK activation in the adipose tissue, promoting higher lipid storage (adipocyte hypertrophy) and cholesterol levels. Also, low SCFA generation reduces GPR41 and GPR43 receptor activation at the adipose tissue (increasing leptin release and leptin receptor resistance) and intestinal levels, reducing the release of GLP-1 and YPP. Therefore, lower satiety sensation and energy expenditure occur, promoting a weight gaining environment mediated by higher food intake and lipid storage, developing dyslipemia. In this context, higher glucose levels, together with higher free fatty acids in the bloodstream, promote glycolipotoxicity, provoking a reduction in insulin released, insulin receptor resistance, advanced glycation products (AGEs) and type 2 diabetes. Intestinal dysbiosis and low SCFAs reduce bacterial biodiversity, increasing lipopolysaccharide (LPS)-producing bacteria and intestinal barrier permeability. Higher amounts of LPS pass to the bloodstream (endotoxemia), causing a low-grade chronic inflammatory state characterized by higher levels of leptin, IL-1β, IL-6 and TNF-α, together with a reduced release of adiponectin and IL-10. At the brain and neuronal levels, the generated insulin resistance, low-grade chronic inflammation, leptin resistance, AGE production and LPS increase directly impact the secretase enzymes and tau hyperphosphorylation, creating an enabling environment for β-amyloid senile plaque and tau tangled formations and, as a consequence, Alzheimer's initiation, development and maintenance.

Lactate limits CNS autoimmunity by stabilizing HIF-1α in dendritic cells

Dendritic cells (DCs) have a role in the development and activation of self-reactive pathogenic T cells1,2. Genetic variants that are associated with the function of DCs have been linked to autoimmune disorders3,4, and DCs are therefore attractive therapeutic targets for such diseases. However, developing DC-targeted therapies for autoimmunity requires identification of the mechanisms that regulate DC function. Here, using single-cell and bulk transcriptional and metabolic analyses in combination with cell-specific gene perturbation studies, we identify a regulatory loop of negative feedback that operates in DCs to limit immunopathology. Specifically, we find that lactate, produced by activated DCs and other immune cells, boosts the expression of NDUFA4L2 through a mechanism mediated by hypoxia-inducible factor 1α (HIF-1α). NDUFA4L2 limits the production of mitochondrial reactive oxygen species that activate XBP1-driven transcriptional modules in DCs that are involved in the control of pathogenic autoimmune T cells. We also engineer a probiotic that produces lactate and suppresses T cell autoimmunity through the activation of HIF-1α-NDUFA4L2 signalling in DCs. In summary, we identify an immunometabolic pathway that regulates DC function, and develop a synthetic probiotic for its therapeutic activation.

Early detection of plasma d-lactate: Toward a new highly-specific biomarker of bacteraemia?

Background

Bloodstream infections are a leading cause of mortality. Their detection relies on blood cultures (BCs) but time to positivity is often between tens of hours and days. d-lactate is a metabolite widely produced by bacteria but very few in human. We aimed to evaluate d-lactate, d-lactate/l-lactate ratio and d-lactate/total lactate ratio in plasma as potential early biomarkers of bacteraemia on a strictly biological standpoint.

Methods

A total of 228 plasma specimens were collected from patients who had confirmed bacteraemia (n = 131) and healthy outpatients (n = 97). Specific l-lactate and d-lactate analyses were performed using enzymatic assays and analytical performances of d-lactate, d-lactate/total lactate and d-lactate/l-lactate ratios for the diagnosis of bacteraemia were assessed.

Results

A preliminary in vitro study confirmed that all strains of Escherichia coli, Klebsiella pneumoniae and Staphylococcus aureus were able to produce d-lactate at significant levels. In patients, plasma d-lactate level was the most specific biomarker predicting a bacteraemia profile with a specificity and predictive positive value of 100% using a cut-off of 131 μmol.L^-1. However, sensitivity and negative predictive value were rather low, estimated at 31% and 52%, respectively. d-lactate displayed an Area Under Receiver Operating Characteristic (AUROC) curve of 0.696 with a P value < 0.0001. There was no difference of d-lactate levels between BCs bottles positive for Gram-positive or Gram-negative bacteria (p = 0.55).

Conclusion

d-lactate shows promise as a specific early biomarker of bacterial metabolism. The development of rapid automated assays could raise clinical applications for infectious diseases diagnosis including early bacteraemia prediction.

Impairment of Mesenteric Perfusion as a Marker of Major Bleeding in Trauma Patients

The majority of potentially preventable mortality in trauma patients is related to bleeding; therefore, early recognition and effective treatment of hemorrhagic shock impose a cardinal challenge for trauma teams worldwide. The reduction in mesenteric perfusion (MP) is among the first compensatory responses to blood loss; however, there is no adequate tool for splanchnic hemodynamic monitoring in emergency patient care. In this narrative review, (i) methods based on flowmetry, CT imaging, video microscopy (VM), measurement of laboratory markers, spectroscopy, and tissue capnometry were critically analyzed with respect to their accessibility, and applicability, sensitivity, and specificity. (ii) Then, we demonstrated that derangement of MP is a promising diagnostic indicator of blood loss. (iii) Finally, we discussed a new diagnostic method for the evaluation of hemorrhage based on exhaled methane (CH₄) measurement. Conclusions: Monitoring the MP is a feasible option for the evaluation of blood loss. There are a wide range of experimentally used methodologies; however, due to their practical limitations, only a fraction of them could be integrated into routine emergency trauma care. According to our comprehensive review, breath analysis, including exhaled CH₄ measurement, would provide the possibility for continuous, non-invasive monitoring of blood loss.

Targeting cancer lactate metabolism with synergistic combinations of synthetic catalysts and monocarboxylate transporter inhibitors

Synthetic anticancer catalysts offer potential for low-dose therapy and the targeting of biochemical pathways in novel ways. Chiral organo-osmium complexes, for example, can catalyse the asymmetric transfer hydrogenation of pyruvate, a key substrate for energy generation, in cells. However, small-molecule synthetic catalysts are readily poisoned and there is a need to optimise their activity before this occurs, or to avoid this occurring. We show that the activity of the synthetic organometallic redox catalyst [Os(p-cymene)(TsDPEN)] (1), which can reduce pyruvate to un-natural D-lactate in MCF7 breast cancer cells using formate as a hydride source, is significantly increased in combination with the monocarboxylate transporter (MCT) inhibitor AZD3965. AZD3965, a drug currently in clinical trials, also significantly lowers the intracellular level of glutathione and increases mitochondrial metabolism. These synergistic mechanisms of reductive stress induced by 1, blockade of lactate efflux, and oxidative stress induced by AZD3965 provide a strategy for low-dose combination therapy with novel mechanisms of action.

Targeted lactate dehydrogenase genes silencing in probiotic lactic acid bacteria: A possible paradigm shift in colorectal cancer treatment?

Even though the pathophysiology of colorectal cancer (CRC) is complicated and poorly understood, interactions between risk factors appear to be key in the development and progression of the malignancy. The popularity of using lactic acid bacteria (LAB) prebiotics and probiotics to modulate the tumor microenvironment (TME) has grown widely over the past decade. The objective of this study was therefore to determine the detrimental effects of LAB-derived lactic acid in the colonic mucosa in colorectal cancer management. Six library databases and a web search engine were used to execute a structured systematic search of the existing literature, considering all publications published up until August 2022. A total of 7817 papers were screened, all of which were published between 1995 and August 2022. However, only 118 articles met the inclusion criterion. Lactic acid has been directly linked to the massive proliferation of cancerous cells since the glycolytic pathway provides cancerous cells with not only ATP, but also biosynthetic intermediates for rapid growth and proliferation. Our research suggests that targeting LAB metabolic pathways is capable of suppressing tumor growth and that the LDH gene is critical for tumorigenesis. Silencing of Lactate dehydrogenase, A (LDHA), B (LDHB), (LDHL), and hicD genes should be explored to inhibit fermentative glycolysis yielding lactic acid as the by-product. More studies are necessary for a solid understanding of this topic so that LAB and their corresponding lactic acid by-products do not have more adverse effects than their widely touted positive outcomes in CRC management.

Engineered probiotics limit CNS autoimmunity by stabilizing HIF-1α in dendritic cells

Dendritic cells (DCs) control the generation of self-reactive pathogenic T cells. Thus, DCs are considered attractive therapeutic targets for autoimmune diseases. Using single-cell and bulk transcriptional and metabolic analyses in combination with cell-specific gene perturbation studies we identified a negative feedback regulatory pathway that operates in DCs to limit immunopathology. Specifically, we found that lactate, produced by activated DCs and other immune cells, boosts NDUFA4L2 expression through a mechanism mediated by HIF-1α. NDUFA4L2 limits the production of mitochondrial reactive oxygen species that activate XBP1-driven transcriptional modules in DCs involved in the control of pathogenic autoimmune T cells. Moreover, we engineered a probiotic that produces lactate and suppresses T-cell autoimmunity in the central nervous system via the activation of HIF-1α/NDUFA4L2 signaling in DCs. In summary, we identified an immunometabolic pathway that regulates DC function, and developed a synthetic probiotic for its therapeutic activation.

Relevance of biomarkers indicating gut damage and microbial translocation in people living with HIV

The intestinal barrier has the daunting task of allowing nutrient absorption while limiting the entry of microbial products into the systemic circulation. HIV infection disrupts the intestinal barrier and increases intestinal permeability, leading to microbial product translocation. Convergent evidence has shown that gut damage and an enhanced level of microbial translocation contribute to the enhanced immune activation, the risk of non-AIDS comorbidity, and mortality in people living with HIV (PLWH). Gut biopsy procedures are invasive, and are not appropriate or feasible in large populations, even though they are the gold standard for intestinal barrier investigation. Thus, validated biomarkers that measure the degree of intestinal barrier damage and microbial translocation are needed in PLWH. Hematological biomarkers represent an objective indication of specific medical conditions and/or their severity, and should be able to be measured accurately and reproducibly via easily available and standardized blood tests. Several plasma biomarkers of intestinal damage, i.e., intestinal fatty acid-binding protein (I-FABP), zonulin, and regenerating islet-derived protein-3α (REG3α), and biomarkers of microbial translocation, such as lipopolysaccharide (LPS) and (1,3)-β-D-Glucan (BDG) have been used as markers of risk for developing non-AIDS comorbidities in cross sectional analyses and clinical trials, including those aiming at repair of gut damage. In this review, we critically discuss the value of different biomarkers for the estimation of gut permeability levels, paving the way towards developing validated diagnostic and therapeutic strategies to repair gut epithelial damage and to improve overall disease outcomes in PLWH.

An evaluation of the protective effects of chlorogenic acid on broiler chickens in a dextran sodium sulfate model: a preliminary investigation

This study was conducted to investigate the protective effects of chlorogenic acid (CGA) on broilers subjected to dextran sodium sulfate (DSS)-induced intestinal damage. One hundred and forty-four 1-day-old male Arbor Acres broiler chicks were allocated into one of 3 groups with 6 replicates of eight birds each for a 21-d trial. The treatments included: 1) Control group: normal birds fed a basal diet; 2) DSS group: DSS-treated birds fed a basal diet; and 3) CGA group: DSS-treated birds fed a CGA-supplemented control diet. An oral DSS administration via drinking water was performed from 15 to 21 d of age. Compared with the control group, DSS administration reduced 21-d body weight and weight gain from 15 to 21 d, but increased absolute weight of jejunum and absolute and relative weight of ileum (P < 0.05). DSS administration elevated circulating D-lactate concentration and diamine oxidase activity (P < 0.05), which were partially reversed when supplementing CGA (P < 0.05). The oral administration with DSS decreased villus height and villus height/crypt depth ratio, but increased crypt depth in jejunum and ileum (P < 0.05). Compared with the control group, DSS administration increased serum glutathione level and jejunal catalase activity and malonaldehyde accumulation, but decreased jejunal glutathione level (P < 0.05). In contrast, feeding a CGA-supplemented diet normalized serum glutathione and jejunal malonaldehyde levels, and increased jejunal glutathione concentration in DSS-administrated birds (P < 0.05). Additionally, CGA supplementation reduced ileal malonaldehyde accumulation in DSS-treated birds (P < 0.05). DSS challenge increased levels of serum interferon-γ and interleukin-6, jejunal interleukin-1β, tumor necrosis factor-α, and interleukin-6, and ileal interleukin-1β and interleukin-6 when compared with the control group (P < 0.05). The elevated serum interferon-γ and ileal interleukin-6 levels were normalized to control values when supplementing CGA (P < 0.05). The results suggested that CGA administration could partially prevent DSS-induced increased intestinal permeability, oxidative damage, and inflammation in broilers, although it did not improve their growth performance and intestinal morphology.

Integrated genome-based assessment of safety and probiotic characteristics of Lactiplantibacillus plantarum PMO 08 isolated from kimchi

Lactiplantibacillus plantarum PMO 08 has been used as a probiotic starter culture for plant-based fermented beverages, with various health-promoting effects such as cholesterol-lowering and anti-inflammatory activities. This study aimed to analyze the genome sequence of Lp. plantarum PMO 08 and identify its safety and probiotic characteristics at the genomic level. For this, complete genome sequencing was conducted to investigate the genes associated with risk and probiotic characteristics by using Pacbio combined with Illumina HiSeq. This bacterial strain has one circular chromosome of 3,247,789 bp with 44.5% G + C content and two plasmids of 50,296 bp with 39.0% G + C content and 19,592 bp with 40.5% G + C content. Orthologous average nucleotide identity analysis showed that PMO 08 belongs to the Lp. plantarum group with 99.14% similarity to Lp. plantarum WCFS1. No deleterious genes were determined in the virulence factor analysis, and no hemolysin activity or secondary bile salt synthesis were detected in vitro test. In the case of antibiotic resistance analysis, PMO 08 was resistant to ampicillin in vitro test, but these genes were not transferable. In addition, the strain showed same carbohydrate utilization with Lp. plantarum WCFS1, except for mannopyranoside, which only our strain can metabolize. The strain also harbors a gene for inositol monophosphatase family protein related with phytate hydrolysis and have several genes for metabolizing various carbohydrate which were rich in plant environment. Furthermore, in probiotic characteristics several genes involved in phenotypes such as acid/bile tolerance, adhesion ability, and oxidative stress response were detected in genome analysis. This study demonstrates that Lp. plantarum PMO 08 harbors several probiotic-related genes (with no deleterious genes) and is a suitable probiotic starter for plant-based fermentation.

Lactylation, an emerging hallmark of metabolic reprogramming: Current progress and open challenges

Lactate, the end product of glycolysis, efficiently functions as the carbon source, signaling molecules and immune regulators. Lactylation, being regulated by lactate, has recently been confirmed as a novel contributor to epigenetic landscape, not only opening a new era for in-depth exploration of lactate metabolism but also offering key breakpoints for further functional and mechanistic research. Several studies have identified the pivotal role of protein lactylation in cell fate determination, embryonic development, inflammation, cancer, and neuropsychiatric disorders. This review summarized recent advances with respect to the discovery, the derivation, the cross-species landscape, and the diverse functions of lactylation. Further, we thoroughly discussed the discrepancies and limitations in available studies, providing optimal perspectives for future research.

The role and mechanism of histone lactylation in health and diseases

Whether under anaerobic or aerobic conditions, glycolysis results in production of lactate. Increasing evidence suggests that lactate serves as a multifunctional signaling molecule that develops non-metabolic activities in addition to serving as a key metabolite to link glycolysis and oxidative phosphorylation. Histone posttranslational modification patterns (HPTMs) are essential epigenetic processes controlling a variety of biological activities. Proteomics based on mass spectrometry (MS) has been used to progressively reveal new HPTMs. Recent discoveries of histone lactylation modification mediated by lactate and subsequent research demonstrating its involvement in cancer, inflammation, lung fibrosis, and other conditions suggest that it plays a significant role in immune regulation and homeostasis maintenance. This review provides a brief overview of the complicated control of histone lactylation modification in both pathological and physiological conditions.

An evaluation of graded levels of beta-sitosterol supplementation on growth performance, antioxidant status, and intestinal permeability-related parameters and morphology in broiler chickens at an early age

This study was designed to examine the effects of different levels of beta-sitosterol (BS) supplementation on growth performance, serum biochemical indices, redox status, and intestinal permeability-related parameters and morphology of young broilers. Two hundred and forty male Arbor Acres broiler chicks were allocated into 5 groups of 6 replicates with 8 birds each, and fed a basal diet supplemented with 0, 25, 50, 75, and 100 mg/kg BS for 21-d, respectively. The BS quadratically decreased feed conversion ratio during 1 to 14 d and 1 to 21 d, with its effect being more prominent at 25 or 50 mg/kg (P < 0.05). The BS linearly and quadratically reduced 14-d plasma diamine oxidase activity and D-lactate level, and this effect was more pronounced when its supplemental level was 25 or 50 mg/kg (P < 0.05). The BS linearly increased duodenal villus height (VH) and quadratically increased jejunal VH and ratio of VH and crypt depth (CD) at 14 d, and these effects in 25 mg/kg group were more remarkable (P < 0.05). Similarly, BS linearly or quadratically increased VH and ratio of VH and CD, but decreased CD in the jejunum and ileum at 21 d, with these effects being more pronounced at 50 mg/kg (P < 0.05). The BS supplementation especially at 50 or 75 mg/kg linearly or quadratically reduced 14-d serum and 21-d hepatic malondialdehyde concentration, and increased serum glutathione peroxidase and catalase activities at 14 and 21 d (P < 0.05). Moreover, the BS administration linearly and/or quadratically increased glutathione peroxidase, catalase, and superoxide dismutase activities and glutathione level, and reduced malondialdehyde accumulation in the intestinal mucosa at 14 and/or 21 d, and these consequences were more significant in 50 to 100 mg/kg BS-supplemented groups (P < 0.05). The results demonstrated that BS administration could improve growth performance, intestinal barrier function, and antioxidant status of broilers at an early age, with these effects being more pronounced at a level of 50 mg/kg.

Intestinal Permeability Associated with the Loss of Skeletal Muscle Strength in Middle-Aged and Older Adults in Rural Area of Beijing, China

The association between intestinal permeability and sarcopenia remains unclear, and few studies have mentioned the relationship between intestinal permeability and skeletal muscle strength. The present cross-sectional community study was conducted in a rural area of Beijing to explore the association between intestinal permeability and handgrip strength (HGS) in middle-aged and older adults. Serum lipopolysaccharide (LPS), diamine oxidase (DAO) and D-lactate were detected to evaluate intestinal permeability. Gut microbiota (GM) and its potential interaction were also analyzed in the decision tree model. HGS was negatively correlated with DAO (r = −0.396, p < 0.01) in males. The negative association between HGS and DAO remained significant with the adjustment of covariates (β = −1.401, p < 0.05). Serum DAO and LPS were both negatively associated with HGS in middle-aged and older males, with the significant interactions of GM in the decision tree model, and D-lactate showed a negative association with HGS in females. Therefore, intestinal permeability was associated with the loss of skeletal muscle strength in middle-aged and older adults, and serum DAO may be a novel predictor for the loss of skeletal muscle strength in middle-aged and older males.

The regulatory effects of lactic acid on neuropsychiatric disorders

Lactic acid is produced mainly in astrocytes in the brain and serves as a substance that supplies energy to neurons. In recent years, numerous studies identified the potential effects of lactic acid on the central nervous system and demonstrated its role in regulating brain function as an energy metabolism substrate or cellular signaling molecule. Both deficiency and accumulation of lactic acid cause neurological dysfunction, which further lead to the development of neuropsychiatric disorders, such as Major depressive disorder, Schizophrenia, Alzheimer's disease, and Multiple sclerosis. Although an association between lactic acid and neuropsychiatric disorders was reported in previous research, the underlying pathogenic mechanisms remain unclear. Therefore, an in-depth understanding of the molecular mechanisms by which lactic acid regulates brain function is of significance for the early diagnosis and prevention of neuropsychiatric disorders. In this review, we summarize evidence that is focused on the potential mechanisms of lactic acid as a signaling molecule involved in the pathogenesis of neuropsychiatric disorders and propose a new mechanism by which lactic acid regulates brain function and disease through the microbiota-gut-brain axis to offer new insight into the prevention and treatment of neuropsychiatric diseases.

Role of Lactate in Inflammatory Processes: Friend or Foe

During an inflammatory process, shift in the cellular metabolism associated with an increase in extracellular acidification are well-known features. This pH drop in the inflamed tissue is largely attributed to the presence of lactate by an increase in glycolysis. In recent years, evidence has accumulated describing the role of lactate in inflammatory processes; however, there are differences as to whether lactate can currently be considered a pro- or anti-inflammatory mediator. Herein, we review these recent advances on the pleiotropic effects of lactate on the inflammatory process. Taken together, the evidence suggests that lactate could exert differential effects depending on the metabolic status, cell type in which the effects of lactate are studied, and the pathological process analyzed. Additionally, various targets, including post-translational modifications, G-protein coupled receptor and transcription factor activation such as NF-κB and HIF-1, allow lactate to modulate signaling pathways that control the expression of cytokines, chemokines, adhesion molecules, and several enzymes associated with immune response and metabolism. Altogether, this would explain its varied effects on inflammatory processes beyond its well-known role as a waste product of metabolism.

Dietary palygorskite-based antibacterial agent supplementation as an alternative to antibiotic improves growth performance, intestinal mucosal barrier function, and immunity in broiler chickens

The aim of this study was to evaluate effects of palygorskite-based antibacterial agent (PAA) as an alternative to antibiotic on growth performance, intestinal barrier function, and immunity in broilers. Three hundred and eighty-four mixed-sex 1-day-old Ross 308 broiler chicks were allocated into 6 groups of 8 replicates with 8 birds each. Birds were given a basal diet, an antibiotic diet (50 mg/kg chlortetracycline), and the basal diet supplemented with 250, 500, 1,000, and 2,000 mg/kg PAA for 42 d, respectively. Compared with control group, supplementing 1,000 mg/kg PAA reduced overall feed conversion ratio (P < 0.05), with its value being similar to that of antibiotic group (P > 0.05). However, a higher level of PAA (2,000 mg/kg) increased feed conversion ratio during the late period (P < 0.05). The 1,000 and 2,000 mg/kg PAA decreased plasma endotoxin and D-lactate levels at 42 d (P < 0.05) to comparable values (P > 0.05). The 1,000 mg/kg PAA decreased jejunal crypt depth, while 500 and 1,000 mg/kg PAA increased the ratio between jejunal villus height and crypt depth at 42 d (P < 0.05), with their values being similar to antibiotic group (P > 0.05). The highest level of PAA increased 42-d jejunal mucosal secretory immunoglobulin A and immunoglobulin M concentrations (P < 0.05). The 1,000 and 2,000 mg/kg PAA reduced 21-d interleukin-1β and tumor necrosis factor-α (TNF-α) levels in serum and ileal mucosa and 42-d interferon-γ level in serum and jejunal mucosa (P < 0.05), which did not differ from antibiotic group (P > 0.05). Moreover, PAA administration, regardless of its dosage, reduced 42-d serum TNF-α concentration, and 500 to 2,000 mg/kg PAA decreased 21-d and 42-d jejunal and 42-d ileal mucosal TNF-α levels (P < 0.05), with their values being comparable with antibiotic group (P > 0.05). The results suggested that PAA as an alternative to antibiotic could improve growth performance, intestinal barrier function, and immunity of broilers, and its optimal dosage was 1,000 mg/kg.

Gut-liver axis in cirrhosis: Are hemodynamic changes a missing link?

Recent evidence suggests that the condition of the gut and its microbiota greatly influence the course of liver disease, especially cirrhosis. This introduces the concept of the gut–liver axis, which can be imagined as a chain connected by several links. Gut dysbiosis, small intestinal bacterial overgrowth, and intestinal barrier alteration lead to bacterial translocation, resulting in systemic inflammation. Systemic inflammation further causes vasodilation, arterial hypotension, and hyperdynamic circulation, leading to the aggravation of portal hypertension, which contributes to the development of complications of cirrhosis, resulting in a poorer prognosis. The majority of the data underlying this model were obtained initially from animal experiments, and most of these correlations were further reproduced in studies including patients with cirrhosis. However, despite the published data on the relationship of the disorders of the gut microbiota with the complications of cirrhosis and the proposed pathogenetic role of hemodynamic disorders in their development, the direct relations between gut dysbiosis and hemodynamic changes in this disease are poorly studied. They remain a missing link in the gut–liver axis and a challenge for future research.

The Serum Citrulline and D-Lactate are Associated with Gastrointestinal Dysfunction and Failure in Critically Ill Patients

Objective

This study attempted to screen and combine effective biomarkers to analyse the association between these biomarkers and gastrointestinal failure (GIF) in critically ill patients.

Methods

A total of 110 critically ill patients with acute gastrointestinal injury (AGI) admitted to ICU were enrolled. The AGI grade was determined by the AGI classification proposed by ESICM. There were 67 patients in gastrointestinal dysfunction (GID) group (AGI grade II), 43 patients in GIF group (AGI grade III–IV), and 41 healthy adults in healthy control (HC) group. APACHE II and SOFA score were used to evaluate the disease severity. Peripheral blood samples of patients were collected within 24 hours of admission to the ICU (prior-treatment) and after the conventional medication therapy for 7 consecutive days (post-treatment). Citrulline serum level was detected by high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) method, and D-lactate and lipopolysaccharide (LPS) serum levels were measured by ELISA. Pearson correlation, logistic regression, and ROC curve analysis were used.

Results

Patients with GID or GIF had lower serum level of citrulline, while higher levels of D-lactate and LPS than HC. Compared with GID patients, serum level of citrulline was reduced, while D-lactate and LPS were elevated in GIF patients. Correlation analysis displayed that serum levels of citrulline, D-lactate, and LPS were associated with the APACHE II and SOFA score in patients with GID or GIF. Logistics regression analysis showed that citrulline and D-lactate were risk for both GID and GIF. ROC curve analysis exhibited that combination of citrulline and D-lactate had relatively high value to distinguish GID from HC, GIF from GID, and GIF from HC.

Conclusion

Serum citrulline and D-lactate were associated with severity of GIF, combination of citrulline and D-lactate improved the diagnostic efficacy to identify GIF in critically ill patients.

Preventive Effects of Bacillus licheniformis on Heat Stroke in Rats by Sustaining Intestinal Barrier Function and Modulating Gut Microbiota

Heat stroke (HS) models in rats are associated with severe intestinal injury, which is often considered as the key event at the onset of HS. Probiotics can regulate the gut microbiota by inhibiting the colonization of harmful bacteria and promoting the proliferation of beneficial bacteria. Here, we investigated the preventive effects of a probiotic Bacillus licheniformis strain (BL, CMCC 63516) on HS rats as well as its effects on intestinal barrier function and gut microbiota. All rats were randomly divided into four groups: control (Con) + PBS (pre-administration with 1 ml PBS twice a day for 7 days, without HS induction), Con + BL group (pre-administration with 1 ml 1 × 10⁸ CFU/ml BL twice a day for 7 days, without HS induction), HS + PBS (PBS, with HS induction), and HS + BL (BL, with HS induction). Before the study, the BL strain was identified by genomic DNA analysis. Experimental HS was induced by placing rats in a hot and humid chamber for 60 min until meeting the diagnostic criterion of HS onset. Body weight, core body temperature, survival rate, biochemical markers, inflammatory cytokines, and histopathology were investigated to evaluate the preventive effects of BL on HS. D-Lactate, I-FABP, endotoxin, and tight-junction proteins were investigated, and the fluorescein isothiocyanate-dextran (FD-4) test administered, to assess the degree of intestinal injury and integrity. Gut microbiota of rats in each group were analyzed by 16S rRNA sequencing. The results showed that pre-administration with BL significantly attenuated hyperthermia, reduced HS-induced death, alleviated multiple-organ injury, and decreased the levels of serum inflammatory cytokines. Furthermore, BL sustained the intestinal barrier integrity of HS rats by alleviating intestinal injury and improving tight junctions. We also found that BL significantly increased the ratios of two probiotic bacteria, Lactobacillus and Lactococcus. In addition, Romboutsia, a candidate biomarker for HS diagnosis, was unexpectedly detected. In summary, BL pre-administration for 7 days has preventative effects on HS that may be mediated by sustaining intestinal barrier function and modulating gut microbiota.

Quantitative Assessment of Blood Lactate in Shock: Measure of Hypoxia or Beneficial Energy Source

Blood lactate concentration predicts mortality in critically ill patients and is clinically used in the diagnosis, grading of severity, and monitoring response to therapy of septic shock. This paper summarizes available quantitative data to provide the first comprehensive description and critique of the accepted concepts of the physiology of lactate in health and shock, with particular emphasis on the controversy of whether lactate release is simply a manifestation of tissue hypoxia versus a purposeful transfer ("shuttle") of lactate between tissues. Basic issues discussed include (1) effect of nonproductive lactate-pyruvate exchange that artifactually enhances flux measurements obtained with labeled lactate, (2) heterogeneous tissue oxygen partial pressure (Krogh model) and potential for unrecognized hypoxia that exists in all tissues, and (3) pathophysiology that distinguishes septic from other forms of shock. Our analysis suggests that due to exchange artifacts, the turnover rate of lactate and the lactate clearance are only about 60% of the values of 1.05 mmol/min/70 kg and 1.5 L/min/70 kg, respectively, determined from the standard tracer kinetics. Lactate turnover reflects lactate release primarily from muscle, gut, adipose, and erythrocytes and uptake by the liver and kidney, primarily for the purpose of energy production (TCA cycle) while the remainder is used for gluconeogenesis (Cori cycle). The well-studied physiology of exercise-induced hyperlactatemia demonstrates massive release from the contracting muscle accompanied by an increased lactate clearance that may occur in recovering nonexercising muscle as well as the liver. The very limited data on lactate kinetics in shock patients suggests that hyperlactatemia reflects both decreased clearance and increased production, possibly primarily in the gut. Our analysis of available data in health and shock suggests that the conventional concept of tissue hypoxia can account for most blood lactate findings and there is no need to implicate a purposeful production of lactate for export to other organs.