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Two enantiomers of lactic acid exist. While L-lactic acid is a common compound of human metabolism, D-lactic acid is produced by some strains of microorganism or by some less relevant metabolic pathways. While L-lactic acid is an endogenous compound, D-lactic acid is a harmful enantiomer. Exposure to D-lactic acid can happen by various ways including contaminated food and beverages and by microbiota during some pathological states like short bowel syndrome. The exposure to D-lactic acid cannot be diagnosed because the common analytical methods are not suitable for distinguishing between the two enantiomers. In this review, pathways for D-lactic acid, pathological processes, and diagnostical and analytical methods are introduced followed by figures and tables. The current literature is summarized and discussed.

Lactic acid (LA) is an important platform chemical due to its significant applications in various fields and its use as a monomer for the production of biodegradable poly(lactic acid) (PLA). Free LA production is required to get rid of CaSO4, a waste material produced during fermentation at neutral pH which will lead to easy purification of LA required for the production of biodegradable PLA. Additionally, there is no need to use corrosive acids to release free LA from the calcium lactate produced during neutral fermentation. To date, several attempts have been made to improve the acid tolerance of lactic acid bacteria (LAB) by using both genome-shuffling approaches and rational design based on known mechanisms of LA tolerance and gene deletion in yeast strains. However, the lack of knowledge and the complexity of acid-tolerance mechanisms have made it challenging to generate LA-tolerant strains by simply modifying few target genes. Currently, adaptive evolution has proven an efficient strategy to improve the LA tolerance of individual/engineered strains. The main objectives of this article are to summarize the conventional biotechnological LA fermentation processes to date, assess their overall economic and environmental cost, and to introduce modern LA fermentation strategies for free LA production. In this review, we provide a broad overview of free LA fermentation processes using robust LAB that can ferment in acidic environments, the obstacles to these processes and their possible solutions, and the impact on future development of free LA fermentation processes commercially.

Metabolic flux analysis in mice reveals that lactate often acts as the primary carbon source for the tricarboxylic acid cycle both in normal tissues and in tumour microenvironments. Lactate fuels the citric acid cycle Glucose is thought to be the primary source of fuel for the tricarboxylic acid (TCA) cycle, also known as the citric acid cycle, which produces important metabolites and energy. Sheng Hui et al . now perform whole-body metabolite analysis in mice. They find that circulating lactate rather than glucose can be a major source of carbon and hence fuel for TCA metabolism in both fed and fasting mice. They furthermore show this to be the case in tumour tissue. Mammalian tissues are fuelled by circulating nutrients, including glucose, amino acids, and various intermediary metabolites. Under aerobic conditions, glucose is generally assumed to be burned fully by tissues via the tricarboxylic acid cycle (TCA cycle) to carbon dioxide. Alternatively, glucose can be catabolized anaerobically via glycolysis to lactate, which is itself also a potential nutrient for tissues 1 and tumours 2 , 3 , 4 , 5 . The quantitative relevance of circulating lactate or other metabolic intermediates as fuels remains unclear. Here we systematically examine the fluxes of circulating metabolites in mice, and find that lactate can be a primary source of carbon for the TCA cycle and thus of energy. Intravenous infusions of 13 C-labelled nutrients reveal that, on a molar basis, the circulatory turnover flux of lactate is the highest of all metabolites and exceeds that of glucose by 1.1-fold in fed mice and 2.5-fold in fasting mice; lactate is made primarily from glucose but also from other sources. In both fed and fasted mice, 13 C-lactate extensively labels TCA cycle intermediates in all tissues. Quantitative analysis reveals that during the fasted state, the contribution of glucose to tissue TCA metabolism is primarily indirect (via circulating lactate) in all tissues except the brain. In genetically engineered lung and pancreatic cancer tumours in fasted mice, the contribution of circulating lactate to TCA cycle intermediates exceeds that of glucose, with glutamine making a larger contribution than lactate in pancreatic cancer. Thus, glycolysis and the TCA cycle are uncoupled at the level of lactate, which is a primary circulating TCA substrate in most tissues and tumours.

l -lactate modifies proteins through lactylation 1 , but how this process occurs is unclear. Here we identify the alanyl-tRNA synthetases AARS1 and AARS2 (AARS1/2) as intracellular l -lactate sensors required for l -lactate to stimulate the lysine lactylome in cells. AARS1/2 and the evolutionarily conserved Escherichia coli orthologue AlaRS bind to l -lactate with micromolar affinity and they directly catalyse l -lactate for ATP-dependent lactylation on the lysine acceptor end. In response to l -lactate, AARS2 associates with cyclic GMP–AMP synthase (cGAS) and mediates its lactylation and inactivation in cells and in mice. By establishing a genetic code expansion orthogonal system for lactyl-lysine incorporation, we demonstrate that the presence of a lactyl moiety at a specific cGAS amino-terminal site abolishes cGAS liquid-like phase separation and DNA sensing in vitro and in vivo. A lactyl mimetic knock-in inhibits cGAS, whereas a lactyl-resistant knock-in protects mice against innate immune evasion induced through high levels of l -lactate. MCT1 blockade inhibits cGAS lactylation in stressed mice and restores innate immune surveillance, which in turn antagonizes viral replication. Thus, AARS1/2 are conserved intracellular l -lactate sensors and have an essential role as lactyltransferases. Moreover, a chemical reaction process of lactylation targets and inactivates cGAS. The tRNA synthases AARS1 and AARS2 are identified as evolutionarily conserved sensors of intracellular l -lactate to mediate the global lysine lactylome.

Hyperpolarized [1-13C]pyruvate magnetic resonance spectroscopic imaging (MRSI) is a noninvasive metabolic-imaging modality that probes carbon flux in tissues and infers the state of metabolic reprograming in tumors. Prevailing models attribute elevated hyperpolarized [1-13C]pyruvate-to-[1-13C]lactate conversion rates in aggressive tumors to enhanced glycolytic flux and lactate dehydrogenase A (LDHA) activity (Warburg effect). By contrast, we find by cross-sectional analysis using genetic and pharmacological tools in mechanistic studies applied to well-defined genetically engineered cell lines and tumors that initial hyperpolarized [1-13C]pyruvate-to-[1-13C]lactate conversion rates as well as global conversion were highly dependent on and critically rate-limited by the transmembrane influx of [1-13C]pyruvate mediated predominately by monocarboxylate transporter-1 (MCT1). Specifically, in a cell-encapsulated alginate bead model, induced short hairpin (shRNA) knockdown or overexpression of MCT1 quantitatively inhibited or enhanced, respectively, unidirectional pyruvate influxes and [1-13C]pyruvate-to-[1-13C]lactate conversion rates, independent of glycolysis or LDHA activity. Similarly, in tumor models in vivo, hyperpolarized [1-13C]pyruvate-to-[1-13C]lactate conversion was highly dependent on and critically rate-limited by the induced transmembrane influx of [1-13C]pyruvate mediated by MCT1. Thus, hyperpolarized [1-13C]pyruvate MRSI measures primarily MCT1-mediated [1-13C]pyruvate transmembrane influx in vivo, not glycolytic flux or LDHA activity, driving a reinterpretation of this maturing new technology during clinical translation. Indeed, Kaplan–Meier survival analysis for patients with pancreatic, renal, lung, and cervical cancers showed that high-level expression of MCT1 correlated with poor overall survival, and only in selected tumors, coincident with LDHA expression. Thus, hyperpolarized [1-13C]pyruvate MRSI provides a noninvasive functional assessment primarily of MCT1 as a clinical biomarker in relevant patient populations.

Background The concept of “skin boosters” has evolved, marking a shift from traditional uses of hyaluronic acid (HA) fillers primarily for augmenting skin volume to a more diverse application aimed at improving dermal conditions. Restylane Vital and other HA fillers have been repurposed to combat skin aging and wrinkles by delivering HA directly to the dermis. Objectives This review aims to define the term “skin booster” and to discuss the various components that constitute skin boosters. It seeks to provide a comprehensive overview of the different ingredients used in skin boosters, their roles, and their impact on enhancing dermal conditions. Methods A comprehensive review was conducted, focusing on representative skin booster ingredients. The approach involved analyzing the different elements used in skin boosters and their specific roles in enhancing dermal improvement. Results The findings indicate that skin boosters, encompassing a range of ingredients, are effective in improving the condition of the skin's dermis. The review identifies key ingredients in skin boosters and their specific benefits, including hydration, elasticity improvement, and wrinkle reduction. Conclusions Skin boosters represent a significant development in dermatological treatments, offering diverse benefits beyond traditional HA fillers. This review provides valuable insights into the constituents of skin boosters and their effectiveness, aiding readers in making informed decisions about these treatments. The potential of skin boosters in dermatological practice is considerable, warranting further research and application.

Background The time course of blood lactate levels could be helpful to assess a patient’s response to therapy. Although the focus of published studies has been largely on septic patients, many other studies have reported serial blood lactate levels in different groups of acutely ill patients. Methods We performed a systematic search of PubMed, Science Direct, and Embase until the end of February 2016 plus reference lists of relevant publications. We selected all observational and interventional studies that evaluated the capacity of serial blood lactate concentrations to predict outcome. There was no restriction based on language. We excluded studies in pediatric populations, experimental studies, and studies that did not report changes in lactate values or all-cause mortality rates. We separated studies according to the type of patients included. We collected data on the number of patients, timing of lactate measurements, minimum lactate level needed for inclusion if present, and suggested time interval for predictive use. Results A total of 96 studies met our criteria: 14 in general ICU populations, five in general surgical ICU populations, five in patients post cardiac surgery, 14 in trauma patients, 39 in patients with sepsis, four in patients with cardiogenic shock, eight in patients after cardiac arrest, three in patients with respiratory failure, and four in other conditions. A decrease in lactate levels over time was consistently associated with lower mortality rates in all subgroups of patients. Most studies reported changes over 6, 12 or 24 hrs, fewer used shorter time intervals. Lactate kinetics did not appear very different in patients with sepsis and other types of patients. A few studies suggested that therapy could be guided by these measurements. Conclusions The observation of a better outcome associated with decreasing blood lactate concentrations was consistent throughout the clinical studies, and was not limited to septic patients. In all groups, the changes are relatively slow, so that lactate measurements every 1–2 hrs are probably sufficient in most acute conditions. The value of lactate kinetics appears to be valid regardless of the initial value.

Fermentation of various food stuffs by lactic acid bacteria is one of the oldest forms of food biopreservation. Bacterial antagonism has been recognized for over a century, but in recent years, this phenomenon has received more scientific attention, particularly in the use of various strains of lactic acid bacteria (LAB). Certain strains of LAB demonstrated antimicrobial activity against foodborne pathogens, including bacteria, yeast and filamentous fungi. Furthermore, in recent years, many authors proved that lactic acid bacteria have the ability to neutralize mycotoxin produced by the last group. Antimicrobial activity of lactic acid bacteria is mainly based on the production of metabolites such as lactic acid, organic acids, hydroperoxide and bacteriocins. In addition, some research suggests other mechanisms of antimicrobial activity of LAB against pathogens as well as their toxic metabolites. These properties are very important because of the future possibility to exchange chemical and physical methods of preservation with a biological method based on the lactic acid bacteria and their metabolites. Biopreservation is defined as the extension of shelf life and the increase in food safety by use of controlled microorganisms or their metabolites. This biological method may determine the alternative for the usage of chemical preservatives. In this study, the possibilities of the use of lactic acid bacteria against foodborne pathogens is provided. Our aim is to yield knowledge about lactic acid fermentation and the activity of lactic acid bacteria against pathogenic microorganisms. In addition, we would like to introduce actual information about health aspects associated with the consumption of fermented products, including probiotics.

Hypoxia and glycolysis have long been appreciated to promote immune cell activation. In 2019, several studies highlighted a counterbalancing homeostatic function for the glycolytic metabolite lactate. Lactate directly suppresses signalling pathways and modifies histones to play an important role in regulating macrophage polarization, tumour immunity and antiviral responses.Studies in the field of inflammation in 2019 have highlighted a counterbalancing homeostatic function for the glycolytic metabolite lactate, which is produced in hypoxic conditions, such as in tumours and chronic inflammation. Lionel Ivashkiv describes how lactate suppresses inflammatory signalling pathways and regulates macrophage polarization.

Lactic acid can synthesize high value-added chemicals such as poly lactic acid. In order to further minimize the cost of lactic acid production, some effective strategies (e.g., effective mutagenesis and metabolic engineering) have been applied to increase productive capacity of lactic acid bacteria. In addition, low-cost cheap raw materials (e.g., cheap carbon source and cheap nitrogen source) are also used to reduce the cost of lactic acid production. In this review, we summarized the recent developments in lactic acid production, including efficient strain modification technology (high-efficiency mutagenesis means, adaptive laboratory evolution, and metabolic engineering), the use of low-cost cheap raw materials, and also discussed the future prospects of this field, which could promote the development of lactic acid industry.