Lactate: The Fallacy of Oversimplification

Lactate, an Essential Metabolic Marker in the Diagnosis and Management of Pediatric Conditions

Measurement of circulating lactate is an essential diagnostic tool in pediatric medicine, playing a crucial role in assessing metabolic status and tissue oxygenation. Initially regarded as a byproduct of anaerobic metabolism, recent research has expanded our understanding of lactate's roles across various physiological systems, from energy metabolism to immune modulation and neurological health. Elevated lactate levels are widely utilized to monitor critical conditions such as sepsis, trauma, and hypoxic-ischemic injury, offering valuable prognostic information in intensive care settings. Notably, lactate dynamics-particularly trends in serial measurements-are more effective than single readings for predicting clinical outcomes, especially in sepsis and trauma. Measurement of circulating lactate in different body fluids (blood, cerebrospinal fluid, and umbilical blood) provides critical insights into neonatal health and central nervous system involvement. However, challenges remain, including the need for non-invasive and rapid point-of-care testing, particularly in neonatal populations. Our aim was to review and synthesize the current literature on the role and particularities of measurement of circulating lactate in pediatric pathology. Emerging technologies, such as machine learning models and small molecule inhibitors, show promise in advancing lactate regulation and predicting hemodynamic instability. As the role of lactate in pediatric pathology continues to evolve, optimizing measurement protocols and exploring new therapeutic strategies will enhance early detection, intervention, and clinical outcomes for critically ill children.

Renal mitochondria response to sepsis: a sequential biopsy evaluation of experimental porcine model

BACKGROUND

The pathophysiology of sepsis-induced acute kidney injury remains elusive. Although mitochondrial dysfunction is often perceived as the main culprit, data from preclinical models yielded conflicting results so far. The aim of this study was to assess the immune-metabolic background of sepsis-associated renal dysfunction using sequential biopsy approach with mitochondria function evaluation in a large clinically relevant porcine models mimicking two different paces and severity of sepsis and couple this approach with traditional parameters of renal physiology.

METHODS

In this randomized, open-label study, 15 anaesthetized, mechanically ventilated and instrumented (renal artery flow probe and renal vein catheter) pigs were randomized in two disease severity groups-low severity (LS) sepsis (0.5 g/kg of autologous faeces intraperitoneally) and high severity (HS) sepsis (1 g/kg of autologous faeces intraperitoneally). Sequential cortical biopsies of the left kidney were performed and a pyramid-shaped kidney specimen with cortex, medulla and renal papilla was resected and processed at the end of the experiment. Oxygraphic data and western blot analysis of proteins involved in mitochondrial biogenesis and degradation were obtained.

RESULTS

In contrast to increased mitochondrial activity observed in LS sepsis, a significant decrease in the oxidative phosphorylation capacity together with an increase in the respiratory system uncoupling was observed during the first 24 h after sepsis induction in the HS group. Those changes preceded alterations of renal haemodynamics. Furthermore, serum creatinine rose significantly during the first 24 h, indicating that renal dysfunction is not primarily driven by haemodynamic changes. Compared to cortex, renal medulla had significantly lower oxidative phosphorylation capacity and electron-transport system activity. PGC-1-alfa, a marker of mitochondrial biogenesis, was significantly decreased in HS group.

CONCLUSIONS

In this experimental model, unique sequential tissue data show that the nature and dynamics of renal mitochondrial responses to sepsis are profoundly determined by the severity of infectious challenge and resulting magnitude of inflammatory insult. High disease severity is associated with early and stepwise progression of mitochondria dysfunction and acute kidney injury, both occurring independently from later renal macro-haemodynamic alterations. Our data may help explain the conflicting results of preclinical studies and suggest that sepsis encompasses a very broad spectrum of sepsis-induced acute kidney injury endotypes.

The Role of Lactate Metabolism in Heart Failure and Cardiogenic Shock: Clinical Insights and Therapeutic Implications

Heart failure (HF) is associated with poor prognosis, especially when it progresses to cardiogenic shock (CS), where survival rates substantially decline. A key area of interest is the role of blood lactate as a biomarker in these conditions. Lactate is produced under normal physiological conditions but increases with impaired tissue perfusion, a hallmark of HF and CS. Elevated lactate levels result from increased production, reduced clearance or both and are often associated with worse outcomes. Traditionally considered a byproduct of anaerobic metabolism, lactate is now recognized as an important energy substrate, particularly in myocardial tissue during periods of metabolic stress. Recent studies suggest that dynamic lactate monitoring, including lactate clearance (LC), may provide critical insights into patients' prognoses and responses to therapy. Serial measurements of lactate have been shown to predict survival in critically ill patients, including those with HF and CS. In CS, elevated lactate levels correlate with increased mortality risk, and LC is emerging as an important parameter in treatment protocols. Despite growing evidence of lactate's clinical relevance, research is needed to establish standardized thresholds and optimal monitoring timelines. Understanding the complexities of lactate metabolism and its role in HF and CS could lead to improved risk stratification and more personalized treatment approaches.

The roles of lactate and the interplay with m6A modification in diseases

Lactate exhibits various biological functions, including the mediation of histone and non-histone lactylation to regulate gene transcription, influencing the activity of T lymphocytes, NK cells, and macrophages in immune suppression, activating G protein-coupled receptor 81 for signal transduction, and serving as an energy substrate. The m6A modification represents the most prevalent post-transcriptional epigenetic alteration. It is regulated by m6A-related regulatory enzymes (including methyltransferases, demethylases, and recognition proteins) that control the transcription, splicing, stability, and translation of downstream target RNAs. Lactate-mediated lactylation at histone H3K18 can modulate downstream target m6A modifications by enhancing the transcriptional expression levels of m6A-related regulatory enzymes. These enzymes play a crucial role in the progression of diseases such as cancer, fibrosis (in both liver and lung), myocardial ischemia, cerebral hemorrhage, and sepsis. Furthermore, m6A-related regulatory enzymes are also subject to lactylation by lactate. In turn, these regulatory enzymes can influence key glycolytic pathway enzymes or modify lactate transporter MCT4 via m6A alterations to impact lactate levels and subsequently affect lactylation processes.

The possible role of hypoxia-induced exosomes on the fibroblast metabolism in idiopathic pulmonary fibrosis

Idiopathic pulmonary fibrosis (IPF) has a high incidence and prevalence among patients over 65 years old. While its exact etiology remains unknown, several risk factors have recently been identified. Hypoxia is associated with IPF due to the abnormal architecture of lung parenchyma and the accumulation of extracellular matrix produced by activated fibroblasts. Exosomes play a crucial role in intercellular communication during both physiological and pathological processes, including hypoxic diseases like IPF. Recent findings suggest that a hypoxic microenvironment influences the content of exosomes in various diseases, thereby altering cellular metabolism. Although the role of exosomes in IPF is an emerging area of research, the significance of hypoxic exosomes as inducers of metabolic reprogramming in fibroblasts is still underexplored. In this study, we analyze and discuss the relationship between hypoxia, exosomal cargo, and the metabolic reprogramming of fibroblasts in the progression of IPF.

Sepsis-induced changes in pyruvate metabolism: insights and potential therapeutic approaches

Sepsis is a heterogeneous syndrome resulting from a dysregulated host response to infection. It is considered as a global major health priority. Sepsis is characterized by significant metabolic perturbations, leading to increased circulating metabolites such as lactate. In mammals, pyruvate is the primary substrate for lactate production. It plays a critical role in metabolism by linking glycolysis, where it is produced, with the mitochondrial oxidative phosphorylation pathway, where it is oxidized. Here, we provide an overview of all cytosolic and mitochondrial enzymes involved in pyruvate metabolism and how their activities are disrupted in sepsis. Based on the available data, we also discuss potential therapeutic strategies targeting these pyruvate-related enzymes leading to enhanced survival.

Biomarkers in cardiogenic shock: old pals, new friends

In cardiogenic shock, biomarkers should ideally help make the diagnosis, choose the right therapeutic options and monitor the patient in addition to clinical and echocardiographic indices. Among "old" biomarkers that have been used for decades, lactate detects, quantifies, and follows anaerobic metabolism, despite its lack of specificity. Renal and liver biomarkers are indispensable for detecting the effect of shock on organ function and are highly predictive of poor outcomes. Direct biomarkers of cardiac damage such as cardiac troponins, B-type natriuretic and N-terminal pro-B-type natriuretic peptides have a good prognostic value, but they lack specificity to detect a cardiogenic cause of shock, as many factors influence their plasma concentrations in critically ill patients. Among the biomarkers that have been more recently described, dipeptidyl peptidase-3 is one of the most interesting. In addition to its prognostic value, it could represent a therapeutic target in cardiogenic shock in the future as a specific antibody inhibits its activity. Adrenomedullin is a small peptide hormone secreted by various tissues, including vascular smooth muscle cells and endothelium, particularly under pathological conditions. It has a vasodilator effect and has prognostic value during cardiogenic shock. An antibody inhibits its activity and so adrenomedullin could represent a therapeutic target in cardiogenic shock. An increasing number of inflammatory biomarkers are also of proven prognostic value in cardiogenic shock, reflecting the inflammatory reaction associated with the syndrome. Some of them are combined to form prognostic proteomic scores. Alongside clinical variables, biomarkers can be used to establish biological "signatures" characteristic of the pathophysiological pathways involved in cardiogenic shock. This helps describe patient subphenotypes, which could in the future be used in clinical trials to define patient populations responding specifically to a treatment.

Effects of sodium lactate injection on meat quality and lactate content in broiler chickens: emphasis on injection method and dosage

This study aims to develop an experimental model of high lactate levels in broilers to mimic the condition of birds under stress or diseases and evaluate its consequent effects on meat quality. The injection sites and dosage effects were compared separately in 2 experiments. Experiment 1 includes 3 injection sites: intraperitoneal injection, intramuscular injection, and subcutaneous injection. Experiment 2 was a dosage experiment based on the results of Experiment 1: sodium lactate intraperitoneal injection group with 1.5, 3, 6 mM concentration. The results showed that injecting sodium lactate intraperitoneally, intramuscularly, or subcutaneously all significantly decreased body weight and breast muscle weight while elevating lactic acid levels in both the blood and breast muscle of broilers. Moreover, all 3 injection methods caused a significant reduction in pH24h and an increase in the shear force value of breast muscle. In addition, dose-response experiments of intraperitoneal injection showed that a concentration of 3 mM and 6 mM were significantly decreased body weight and breast muscle weight in broiler chickens, accompanied by a notable increase in breast muscle lactate content. Compared to the control group, intraperitoneal injections of 1.5 mM, 3 mM, and 6 mM sodium lactate treatments significantly reduced the yellowness values of the breast muscle. As the dose of sodium lactate increased, the shear force value of the breast meat exhibited linear and quadratic increments, while the drip loss decreased linearly. Intraperitoneal injection of 3 mM sodium lactate also significantly reduced the pH24h of broiler breast muscle. In addition, an increased dose of lactate injections up-regulated the glycolytic pathway responsible for endogenous lactate production in the breast muscle by upregulating the expression of phosphofructokinase, pyruvate kinase and lactate dehydrogenase A. In conclusion, intraperitoneal injection of sodium lactate at 3 mM directly increased breast muscle lactate levels, providing a valuable method for establishing a high-level lactate model in poultry.

Lactate Monitoring in Intensive Care: A Comprehensive Review of Its Utility and Interpretation

Lactate monitoring is critical in managing critically ill patients in intensive care settings. Elevated lactate levels often signify underlying metabolic disturbances such as tissue hypoxia, anaerobic metabolism, or impaired lactate clearance, which are prevalent in conditions like sepsis, shock, and trauma. Understanding the physiological basis of lactate production and its significance in clinical practice is essential for interpreting its diagnostic and prognostic value. This comprehensive review aims to explore the utility of lactate monitoring across various critical care scenarios. It provides an overview of lactate's metabolic pathways, methods of measurement, and the clinical implications of interpreting lactate levels in different contexts. Additionally, the review discusses current evidence on lactate-guided therapeutic interventions and highlights challenges and limitations to their application. By synthesizing the existing literature and clinical insights, this review aims to enhance the understanding of the role of lactate monitoring in assessing disease severity, guiding treatment strategies, and predicting outcomes in critically ill patients. Ultimately, this review underscores the importance of integrating lactate monitoring into routine clinical practice to optimize patient care and improve clinical outcomes in intensive care settings.

Uncommon Millettia pachycarpa Benth poisoning: A case report

BACKGROUND

Millettia pachycarpa Benth, rich in rotenone, can disrupt the mitochondrial electron transport chain. Ingestion may cause respiratory and central nervous system depression, and in severe cases, lead to death. This is the first detailed clinical case report of M. pachycarpa Benth poisoning, aiming to help systematization of diagnosis and treatment.

PATIENT CONCERNS

An elderly male who lost consciousness for 3 hours after consuming the fruit of M. pachycarpa Benth. Arterial blood gas analysis indicated a significant decrease in pH, a sharp increase in lactate levels, and elevated CO2 partial pressure with normal O2 partial pressure.

DIAGNOSIS

The patient was diagnosed with food intoxication by M. pachycarpa Benth, concomitant with aspiration pneumonia and distributive shock.

INTERVENTIONS

The patient was given continuous renal replacement therapy (CRRT) and invasive mechanical ventilation.

OUTCOMES

The patient was successfully discharged after 5 days of hospitalization. Follow-up after 2 weeks showed no significant discomfort.

CONCLUSION

Isolated CO2 retention without hypoxemia, significantly reduced pH, and markedly elevated lactate levels strongly suggest poisoning by M. pachycarpa Benth. CRRT and invasive mechanical ventilation are beneficial for patients. Early implementation of CRRT to remove toxins and early initiation of assisted ventilation to improve respiratory failure are recommended upon suspicion of the disease.

High Glucose Increases Lactate and Induces the Transforming Growth Factor Beta-Smad 1/5 Atherogenic Pathway in Primary Human Macrophages

Hundreds of millions of people worldwide are expected to suffer from diabetes mellitus. Diabetes is characterized as a dynamic and heterogeneous disease that requires deeper understanding of the pathophysiology, genetics, and metabolic shaping of this disease and its macro/microvascular complications. Macrophages play an essential role in regulating local immune responses, tissue homeostasis, and disease pathogenesis. Here, we have analyzed transforming growth factor beta 1 (TGFβ1)/Smad signaling in primary human macrophages grown in normal (NG) and high-glucose (HG; +25 mM glucose) conditions. Cell culture lactate concentration and cellular phosphofructokinase (PFK) activity were increased in HG concentrations. High glucose levels in the growth media led to increased macrophage mRNA expression of TGFβ1, and TGFβ-regulated HAMP and PLAUR mRNA levels, while the expression of TGFβ receptor II remained unchanged. Stimulation of cells with TGFβ1 protein lead to Smad2 phosphorylation in both NG and HG conditions, while the phosphorylation of Smad1/5 was detected only in response to TGFβ1 stimulation in HG conditions. The use of the specific Alk1/2 inhibitor dorsomorphin and the Alk5 inhibitor SB431542, respectively, revealed that HG conditions led TGFβ1 to activation of Smad1/5 signaling and its downstream target genes. Thus, high-glucose activates TGFβ1 signaling to the Smad1/5 pathway in primary human macrophages, which may contribute to cellular homeostasis in a harmful manner, priming the tissues for diabetic complications.

Lactic Acid Chemical Peeling in Skin Disorders

Lactic acid is the most widely occurring natural organic acid in nature. It not only exhibits mild and safe properties but also possesses multiple physiological activities, such as antibacterial effects, immune regulation, and promotion of wound healing, making it one of the most popular chemical peeling agents. Chemical peels are commonly used in the field of aesthetic dermatology as a non-invasive therapeutic approach. This research aims to provide valuable references for clinical dermatologists by summarizing the characteristics of lactic acid, elucidating its mechanism of action in peeling, and investigating the clinical applications of this compound. Furthermore, it anticipates the potential for lactic acid to be the most suitable chemical peeling agent for Chinese skin.