Lactate and risk of incident diabetes in a case-cohort of the atherosclerosis risk in communities (ARIC) study

Circulating Metabolite Biomarkers of Glycemic Control in Youth-Onset Type 2 Diabetes

OBJECTIVE

We aimed to identify metabolites associated with loss of glycemic control in youth-onset type 2 diabetes.

RESEARCH DESIGN AND METHODS

We measured 480 metabolites in fasting plasma samples from the TODAY (Treatment Options for Type 2 Diabetes in Adolescents and Youth) study. Participants (N = 393; age 10-17 years) were randomly assigned to metformin, metformin plus rosiglitazone, or metformin plus lifestyle intervention. Additional metabolomic measurements after 36 months were obtained in 304 participants. Cox models were used to assess baseline metabolites, interaction of metabolites and treatment group, and change in metabolites (0-36 months), with loss of glycemic control adjusted for age, sex, race, treatment group, and BMI. Metabolite prediction models of glycemic failure were generated using elastic net regression and compared with clinical risk factors.

RESULTS

Loss of glycemic control (HbA1c ≥8% or insulin therapy) occurred in 179 of 393 participants (mean 12.4 months). Baseline levels of 33 metabolites were associated with loss of glycemic control (q < 0.05). Associations of hexose and xanthurenic acid with treatment failure differed by treatment randomization; youths with higher baseline levels of these two compounds had a lower risk of treatment failure with metformin alone. For three metabolites, changes from 0 to 36 months were associated with loss of glycemic control (q < 0.05). Changes in d-gluconic acid and 1,5-AG/1-deoxyglucose, but not baseline levels of measured metabolites, predicted treatment failure better than changes in HbA1c or measures of β-cell function.

CONCLUSIONS

Metabolomics provides insight into circulating small molecules associated with loss of glycemic control and may highlight metabolic pathways contributing to treatment failure in youth-onset diabetes.

Polymyalgia rheumatica shows metabolomic alterations that are further altered by glucocorticoid treatment: Identification of metabolic correlates of fatigue

OBJECTIVE

In polymyalgia rheumatica (PMR), glucocorticoids (GCs) relieve pain and stiffness, but fatigue may persist. We aimed to explore the effect of disease, GCs and PMR symptoms in the metabolite signatures of peripheral blood from patients with PMR or the related disease, giant cell arteritis (GCA).

METHODS

Nuclear magnetic resonance spectroscopy was performed on serum from 40 patients with untreated PMR, 84 with new-onset confirmed GCA, and 53 with suspected GCA who later were clinically confirmed non-GCA, and 39 age-matched controls. Further samples from PMR patients were taken one and six months into glucocorticoid therapy to explore relationship of metabolites to persistent fatigue. 100 metabolites were identified using Chenomx and statistical analysis performed in SIMCA-P to examine the relationship between metabolic profiles and, disease, GC treatment or symptoms.

RESULTS

The metabolite signature of patients with PMR and GCA differed from that of age-matched non-inflammatory controls (R2 > 0.7). There was a smaller separation between patients with clinically confirmed GCA and those with suspected GCA who later were clinically confirmed non-GCA (R2 = 0.135). In PMR, metabolite signatures were further altered with glucocorticoid treatment (R2 = 0.42) but did not return to that seen in controls. Metabolites correlated with CRP, pain, stiffness, and fatigue (R2 ≥ 0.39). CRP, pain, and stiffness declined with treatment and were associated with 3-hydroxybutyrate and acetoacetate, but fatigue did not. Metabolites differentiated patients with high and low fatigue both before and after treatment (R2 > 0.9). Low serum glutamine was predictive of high fatigue at both time points (0.79-fold change).

CONCLUSION

PMR and GCA alter the metabolite signature. In PMR, this is further altered by glucocorticoid therapy. Treatment-induced metabolite changes were linked to measures of inflammation (CRP, pain and stiffness), but not to fatigue. Furthermore, metabolite signatures distinguished patients with high or low fatigue.

Exploring Salivary Metabolic Alterations in Type 2 Diabetes: Implications for Dental Caries and Potential Influences of HbA1c and Vitamin D Levels

Diabetes mellitus is considered to be the most common health issue affecting almost 1 in 11 adults globally. Oral health complications including xerostomia, periodontal disease, dental caries, and soft tissue lesions are prevalent among individuals with diabetes, and therefore an understanding of the potential association between salivary metabolites and dental caries progression would enable the early detection and prevention of this non-communicable disease. Therefore, the aim of this study was to compare salivary biomarkers between individuals with type 2 diabetes (T2DM) with those without this disorder (ND) using 1H NMR-based metabolomics strategies. The objectives were to identify T2DM-associated biomarker signatures and their potential impact on dental caries. In addition, HbA1c and vitamin D levels were also analysed for this purpose.

METHODS

Stimulated whole-mouth saliva (SWS) samples were collected from T2DM and ND (n = 30 in each case) participants randomly selected from a group of 128 participants recruited for this case-control study. All participants were advised to refrain from eating, drinking, and smoking for at least 1-2 h prior to sample collection. Following preparation, SWS supernatants underwent 1H NMR analysis at an operating frequency of 800 MHz, and the dataset acquired was analysed using a range of multivariate metabolomics techniques.

RESULTS

Metabolomics analysis of data acquired demonstrated that, together with up- and downregulated blood HbA1c and vitamin D levels, key salivary discriminators between these two classifications included lactate, taurine, creatinine, α-glucose, and formate to a lesser extent. The bacterial catabolites lactate and formate were both significantly upregulated in the T2DM group, and these have previously been implicated in the pathogenesis of dental caries. Significance analysis of metabolites (SAM)-facilitated AUROC analysis yielded an 83% accuracy for this distinction.

CONCLUSION

In conclusion, this study highlights the significant differences in salivary metabolites between individuals with T2DM and healthy controls. Such differences appear to be related to the development and progression of dental caries in T2DM patients.

Unique features of β-cell metabolism are lost in type 2 diabetes

Pancreatic β cells play an essential role in the control of systemic glucose homeostasis as they sense blood glucose levels and respond by secreting insulin. Upon stimulating glucose uptake in insulin-sensitive tissues post-prandially, this anabolic hormone restores blood glucose levels to pre-prandial levels. Maintaining physiological glucose levels thus relies on proper β-cell function. To fulfill this highly specialized nutrient sensor role, β cells have evolved a unique genetic program that shapes its distinct cellular metabolism. In this review, the unique genetic and metabolic features of β cells will be outlined, including their alterations in type 2 diabetes (T2D). β cells selectively express a set of genes in a cell type-specific manner; for instance, the glucose activating hexokinase IV enzyme or Glucokinase (GCK), whereas other genes are selectively "disallowed", including lactate dehydrogenase A (LDHA) and monocarboxylate transporter 1 (MCT1). This selective gene program equips β cells with a unique metabolic apparatus to ensure that nutrient metabolism is coupled to appropriate insulin secretion, thereby avoiding hyperglycemia, as well as life-threatening hypoglycemia. Unlike most cell types, β cells exhibit specialized bioenergetic features, including supply-driven rather than demand-driven metabolism and a high basal mitochondrial proton leak respiration. The understanding of these unique genetically programmed metabolic features and their alterations that lead to β-cell dysfunction is crucial for a comprehensive understanding of T2D pathophysiology and the development of innovative therapeutic approaches for T2D patients.

Prehospital lactate-glucose interaction in acute life-threatening illnesses: metabolic response and short-term mortality

BACKGROUND AND IMPORTANCE

Lactate is an already recognized biomarker for short-term mortality. However, how glycemia and diabetes affect the predictive ability of lactate needs to be revealed.

OBJECTIVE

To determine how hypoglycemia, normoglycemia, and hyperglycemia modify the predictive ability of lactate for short-term mortality (3 days). The secondary objective was to evaluate the predictive ability of lactate in diabetic patients.

DESIGN, SETTINGS AND PARTICIPANTS

Prospective, observational study performed between 26 October 2018 and 31 December 2022. Multicenter, EMS-delivery, ambulance-based study, considering 38 basic life support units and 5 advanced life support units referring to four tertiary care hospitals (Spain). Eligible patients were adults recruited from among all phone requests for emergency assistance who were later evacuated to emergency departments.

OUTCOMES MEASURE AND ANALYSIS

The primary outcome was in-hospital mortality from any cause within the third day following EMS attendance. The main predictors considered were lactate, blood glucose levels and previous diabetes.

MAIN RESULTS

A total of 6341 participants fulfilled the inclusion criteria. 68 years (IQR: 51-80); 41.4% were female. The 3-day in-hospital mortality rate was 3.5%. The predictive capacity of lactate for 3-day mortality was only significantly different between normo-glycemia and hyperglycemia. The best predictive result was for normo-glycemia - AUC = 0.897 (95% CI: 0.881-0.913) - then hyperglycemia - AUC = 0.819 (95% CI: 0.770-0.868) and finally, hypoglycemia - AUC = 0.703 (95% CI: 0.422-0.983). The stratification according to diabetes presented no statistically significant difference, and the predictive results were AUC = 0.924 (95% CI: 0.892-0.956), AUC = 0.906 (95% CI: 0.884-0.928), and AUC = 0.872 (95% CI: 0.817-0.927) for nondiabetes, uncomplicated cases, and end-organ damage diabetes, respectively.

CONCLUSION

Our results demonstrated that glycemia, but not diabetes, alters the predictive ability of lactate. Therefore, hyperglycemia should be considered when interpreting lactate, since this could improve screening to detect cryptic shock conditions.

Lactate transporter MCT1 in hepatic stellate cells promotes fibrotic collagen expression in nonalcoholic steatohepatitis

Circulating lactate is a fuel source for liver metabolism but may exacerbate metabolic diseases such as nonalcoholic steatohepatitis (NASH). Indeed, haploinsufficiency of lactate transporter monocarboxylate transporter 1 (MCT1) in mice reportedly promotes resistance to hepatic steatosis and inflammation. Here, we used adeno-associated virus (AAV) vectors to deliver thyroxin binding globulin (TBG)-Cre or lecithin-retinol acyltransferase (Lrat)-Cre to MCT1fl/fl mice on a choline-deficient, high-fat NASH diet to deplete hepatocyte or stellate cell MCT1, respectively. Stellate cell MCT1KO (AAV-Lrat-Cre) attenuated liver type 1 collagen protein expression and caused a downward trend in trichrome staining. MCT1 depletion in cultured human LX2 stellate cells also diminished collagen 1 protein expression. Tetra-ethylenglycol-cholesterol (Chol)-conjugated siRNAs, which enter all hepatic cell types, and hepatocyte-selective tri-N-acetyl galactosamine (GN)-conjugated siRNAs were then used to evaluate MCT1 function in a genetically obese NASH mouse model. MCT1 silencing by Chol-siRNA decreased liver collagen 1 levels, while hepatocyte-selective MCT1 depletion by AAV-TBG-Cre or by GN-siRNA unexpectedly increased collagen 1 and total fibrosis without effect on triglyceride accumulation. These findings demonstrate that stellate cell lactate transporter MCT1 significantly contributes to liver fibrosis through increased collagen 1 protein expression in vitro and in vivo, while hepatocyte MCT1 appears not to be an attractive therapeutic target for NASH.

Development of Serum Lactate Level-Based Nomograms for Predicting Diabetic Kidney Disease in Type 2 Diabetes Mellitus Patients

Purpose

To establish nomograms integrating serum lactate levels and traditional risk factors for predicting diabetic kidney disease (DKD) in type 2 diabetes mellitus (T2DM) patients.

Patients and methods

A total of 570 T2DM patients and 100 healthy subjects were enrolled. T2DM patients were categorized into normal and high lactate groups. Univariate and multivariate logistic regression analyses were employed to identify independent predictors for DKD. Then, nomograms for predicting DKD were established, and the model performance was evaluated using the area under the receiver operating characteristic curve (AUC), calibration, and decision curve analysis (DCA).

Results

T2DM patients exhibited higher lactate levels compared to those in healthy subjects. Glucose, platelet, uric acid, creatinine, and hypertension were independent factors for DKD in T2DM patients with normal lactate levels, while diabetes duration, creatinine, total cholesterol, and hypertension were indicators in high lactate levels group (P<0.05). The AUC values were 0.834 (95% CI, 0.776 to 0.891) and 0.741 (95% CI, 0.688 to 0.795) for nomograms in both normal lactate and high lactate groups, respectively. The calibration curve demonstrated excellent agreement of fit. Furthermore, the DCA revealed that the threshold probability and highest Net Yield were 17-99% and 0.36, and 24-99% and 0.24 for the models in normal lactate and high lactate groups, respectively.

Conclusion

The serum lactate level-based nomogram models, combined with traditional risk factors, offer an effective tool for predicting DKD probability in T2DM patients. This approach holds promise for early risk assessment and tailored intervention strategies.

Lactate transporter MCT1 in hepatic stellate cells promotes fibrotic collagen expression in nonalcoholic steatohepatitis

Circulating lactate is a fuel source for liver metabolism but may exacerbate metabolic diseases such as nonalcoholic steatohepatitis (NASH). Indeed, haploinsufficiency of lactate transporter monocarboxylate transporter 1 (MCT1) in mice reportedly promotes resistance to hepatic steatosis and inflammation. Here, we used adeno-associated virus (AAV) vectors to deliver thyroxin binding globulin (TBG)-Cre or lecithin-retinol acyltransferase (Lrat)-Cre to MCT1fl/fl mice on a choline deficient, high fat NASH diet to deplete hepatocyte or stellate cell MCT1, respectively. Stellate cell MCT1KO (AAV-Lrat-Cre) attenuated liver type 1 collagen protein expression and caused a downward trend in trichrome staining. MCT1 depletion in cultured human LX2 stellate cells also diminished collagen 1 protein expression. Tetra-ethylenglycol-cholesterol (Chol)-conjugated siRNAs, which enter all hepatic cell types, and hepatocyte-selective tri-N-acetyl galactosamine (GN)-conjugated siRNAs were then used to evaluate MCT1 function in a genetically obese NASH mouse model. MCT1 silencing by Chol-siRNA decreased liver collagen 1 levels, while hepatocyte-selective MCT1 depletion by AAV-TBG-Cre or by GN-siRNA unexpectedly increased collagen 1 and total fibrosis without effect on triglyceride accumulation. These findings demonstrate that stellate cell lactate transporter MCT1 significantly contributes to liver fibrosis through increased collagen 1 protein expression in vitro and in vivo, while hepatocyte MCT1 appears not to be an attractive therapeutic target for NASH.

Metabolic Differences in Diabetic Kidney Disease Patients with Normoalbuminuria versus Moderately Increased Albuminuria

Key Points

The pathophysiological mechanisms of diabetic kidney disease (DKD) with normal (nonalbuminuric DKD) versus moderately increased albuminuria (A-DKD) are not well-understood. Fatty acid biosynthesis and oxydation, gluconeogenesis, TCA cycle, and glucose-alanine cycle were more disturbed in patients with A-DKD compared with those with nonalbuminuric DKD with identical eGFR. DKD patients with and without microalbuminuria could represent different clinical phenotypes.

Background

The pathophysiological mechanisms of diabetic kidney disease (DKD) with normal versus moderately increased albuminuria (nonalbuminuric DKD [NA-DKD] and A-DKD) are currently not well-understood and could have implications for diagnosis and treatment.

Methods

Fourteen patients with NA-DKD with urine albumin–creatinine ratio <3 mg/mmol, 26 patients with A-DKD with albumin–creatinine ratio 3–29 mg/mmol, and 60 age- and sex-matched healthy controls were randomly chosen from a population-based cohort study (Nord-Trøndelag Health Study-3, Norway). Seventy-four organic acids, 21 amino acids, 21 biogenic acids, 40 acylcarnitines, 14 sphingomyelins, and 88 phosphatidylcholines were quantified in urine. One hundred forty-six patients with diabetes from the US-based Chronic Renal Insufficiency Cohort study were used to verify main findings.

Results

Patients with NA-DKD and A-DKD had similar age, kidney function, diabetes treatment, and other traditional risk factors. Still, partial least-squares discriminant analysis showed strong metabolite-based separation (R2, 0.82; Q2, 0.52), with patients with NA-DKD having a metabolic profile positioned between the profiles of healthy controls and patients with A-DKD. Seventy-five metabolites contributed significantly to separation between NA-DKD and A-DKD (variable importance in projection scores ≥1.0) with propionylcarnitine (C3), phosphatidylcholine C38:4, medium-chained (C8) fatty acid octenedioic acid, and lactic acid as the top metabolites (variable importance in projection scores, 2.7–2.2). Compared with patients with NA-DKD, those with A-DKD had higher levels of short-chained acylcarnitines, higher long-chained fatty acid levels with more double bounds, higher branched-chain amino acid levels, and lower TCA cycle intermediates. The main findings were similar by random forest analysis and in the Chronic Renal Insufficiency Cohort study. Formal enrichment analysis indicated that fatty acid biosynthesis and oxydation, gluconeogenesis, TCA cycle, and glucose-alanine cycle were more disturbed in patients with A-DKD compared with those with NA-DKD with identical eGFR. We also found indications of a Warburg-like effect in patients with A-DKD (i.e. , metabolism of glucose to lactate despite adequate oxygen).

Conclusion

DKD patients with normoalbuminuria differ substantially in their metabolic disturbances compared with patients with moderately increase albuminuria and could represent different clinical phenotypes.

Greater reliance on glycolysis is associated with lower mitochondrial substrate oxidation and insulin sensitivity in infant myogenic MSCs

Individuals with insulin resistance and obesity display higher skeletal muscle production of nonoxidized glycolytic products (i.e., lactate), and lower complete mitochondrial substrate oxidation to CO2. These findings have also been observed in individuals without obesity and are associated with an increased risk for metabolic disease. The purpose of this study was to determine if substrate preference is evident at the earliest stage of life (birth) and to provide a clinical blood marker (lactate) that could be indicative of a predisposition for metabolic disease later. We used radiolabeled tracers to assess substrate oxidation and insulin sensitivity of myogenically differentiated mesenchymal stem cells (MSCs), a proxy of infant skeletal muscle tissue, derived from umbilical cords of full-term infants. We found that greater production of nonoxidized glycolytic products (lactate, pyruvate, alanine) is directly proportional to lower substrate oxidation and insulin sensitivity in MSCs. In addition, we found an inverse relationship between the ratio of complete glucose oxidation to CO2 and infant blood lactate at 1 mo of age. Collectively, considering that higher lactate was associated with lower MSC glucose oxidation and has been shown to be implicated with metabolic disease, it may be an early indicator of infant skeletal muscle phenotype.NEW & NOTEWORTHY In infant myogenically differentiated mesenchymal stem cells, greater production of nonoxidized glycolytic products was directly proportional to lower substrate oxidation and insulin resistance. Glucose oxidation was inversely correlated with infant blood lactate. This suggests that innate differences in infant substrate oxidation exist at birth and could be associated with the development of metabolic disease later in life. Clinical assessment of infant blood lactate could be used as an early indicator of skeletal muscle phenotype.

The pyruvate dehydrogenase complex: Life's essential, vulnerable and druggable energy homeostat

Found in all organisms, pyruvate dehydrogenase complexes (PDC) are the keystones of prokaryotic and eukaryotic energy metabolism. In eukaryotic organisms these multi-component megacomplexes provide a crucial mechanistic link between cytoplasmic glycolysis and the mitochondrial tricarboxylic acid (TCA) cycle. As a consequence, PDCs also influence the metabolism of branched chain amino acids, lipids and, ultimately, oxidative phosphorylation (OXPHOS). PDC activity is an essential determinant of the metabolic and bioenergetic flexibility of metazoan organisms in adapting to changes in development, nutrient availability and various stresses that challenge maintenance of homeostasis. This canonical role of the PDC has been extensively probed over the past decades by multidisciplinary investigations into its causal association with diverse physiological and pathological conditions, the latter making the PDC an increasingly viable therapeutic target. Here we review the biology of the remarkable PDC and its emerging importance in the pathobiology and treatment of diverse congenital and acquired disorders of metabolic integration.

Warburg Effect as a Novel Mechanism for Homocysteine-Induced Features of Age-Related Macular Degeneration

Age-related macular degeneration (AMD) is a major cause of blindness. Recent studies have reported impaired glycolysis in AMD patients with a high lactate/pyruvate ratio. Elevated homocysteine (Hcy) (Hyperhomocysteinemia, HHcy) was observed in several clinical studies, reporting an association between HHcy and AMD. We established the effect of HHcy on barrier function, retinal pigment epithelium (RPE) structure, and induced choroidal neovascularization (CNV) in mice. We hypothesize that HHcy contributes to AMD by inducing a metabolic switch in the mitochondria, in which cells predominantly produce energy by the high rate of glycolysis, or "Warburg", effect. Increased glycolysis results in an increased production of lactate, cellular acidity, activation of angiogenesis, RPE barrier dysfunction, and CNV. Evaluation of cellular energy production under HHcy was assessed by seahorse analysis, immunofluorescence, and western blot experiments. The seahorse analysis evaluated the extracellular acidification rate (ECAR) as indicative of glycolysis. HHcy showed a significant increase in ECAR both in vivo using (Cystathionine β-synthase) cbs^+/- and cbs^-/- mice retinas and in vitro (Hcy-treated ARPE-19) compared to wild-type mice and RPE cells. Moreover, HHcy up-regulated glycolytic enzyme (Glucose transporter-1 (GlUT-1), lactate dehydrogenase (LDH), and hexokinase 1 (HK1)) in Hcy-treated ARPE-19 and primary RPE cells isolated from cbs^+/+, cbs^+/-, and cbs^-/- mice retinas. Inhibition of GLUT-1 or blocking of N-methyl-D-aspartate receptors (NMDAR) reduced glycolysis in Hcy-treated RPE and improved albumin leakage and CNV induction in Hcy-injected mice eyes. The current study suggests that HHcy causes a metabolic switch in the RPE cells from mitochondrial respiration to glycolysis during AMD and confirms the involvement of NMDAR in this process. Therefore, targeting Glycolysis or NMDAR could be a novel therapeutic target for AMD.

Ultrasensitive sensors reveal the spatiotemporal landscape of lactate metabolism in physiology and disease

Despite its central importance in cellular metabolism, many details remain to be determined regarding subcellular lactate metabolism and its regulation in physiology and disease, as there is sensitive spatiotemporal resolution of lactate distribution, and dynamics remains a technical challenge. Here, we develop and characterize an ultrasensitive, highly responsive, ratiometric lactate sensor, named FiLa, enabling the monitoring of subtle lactate fluctuations in living cells and animals. Utilizing FiLa, we demonstrate that lactate is highly enriched in mammalian mitochondria and compile an atlas of subcellular lactate metabolism that reveals lactate as a key hub sensing various metabolic activities. In addition, FiLa sensors also enable direct imaging of elevated lactate levels in diabetic mice and facilitate the establishment of a simple, rapid, and sensitive lactate assay for point-of-care clinical screening. Thus, FiLa sensors provide powerful, broadly applicable tools for defining the spatiotemporal landscape of lactate metabolism in health and disease.

Characterization of diet-dependent temporal changes in circulating short-chain fatty acid concentrations: A randomized crossover dietary trial

BACKGROUND

Production of SCFAs from food is a complex and dynamic saccharolytic fermentation process mediated by both human and gut microbial factors. Knowledge of SCFA production and of the relation between SCFA profiles and dietary patterns is lacking.

OBJECTIVES

Temporal changes in SCFA concentrations in response to 2 contrasting diets were investigated using a novel GC-MS method.

METHODS

Samples were obtained from a randomized, controlled, crossover trial designed to characterize the metabolic response to 4 diets. Participants (n = 19) undertook these diets during an inpatient stay (of 72 h). Serum samples were collected 2 h after breakfast (AB), after lunch (AL), and after dinner (AD) on day 3, and a fasting sample (FA) was obtained on day 4. The 24-h urine samples were collected on day 3. In this substudy, samples from the 2 extreme diets representing a diet with high adherence to WHO healthy eating recommendations and a typical Western diet were analyzed using a bespoke GC-MS method developed to detect and quantify 10 SCFAs and precursors in serum and urine samples.

RESULTS

Considerable interindividual variation in serum SCFA concentrations was observed across all time points, and temporal fluctuations were observed for both diets. Although the sample collection timing exerted a greater magnitude of effect on circulating SCFA concentrations, the unhealthy diet was associated with a lower concentration of acetic acid (FA: coefficient: -17.0; SE: 5.8; P-trend = 0.00615), 2-methylbutyric acid (AL: coefficient: -0.1; SE: 0.028; P-trend = 4.13 × 10-4 and AD: coefficient: -0.1; SE: 0.028; P-trend = 2.28 × 10-3), and 2-hydroxybutyric acid (FA: coefficient: -15.8; SE: 5.11; P-trend: 4.09 × 10-3). In contrast, lactic acid was significantly higher in the unhealthy diet (AL: coefficient: 750.2; SE: 315.2; P-trend = 0.024 and AD: coefficient: 1219.3; SE: 322.6; P-trend: 8.28 × 10-4).

CONCLUSIONS

The GC-MS method allowed robust mapping of diurnal patterns in SCFA concentrations, which were affected by diet, and highlighted the importance of standardizing the timing of SCFA measurements in dietary studies. This trial was registered on the NIHR UK clinical trial gateway and with ISRCTN as ISRCTN43087333.

Lactate-induced lactylation in skeletal muscle is associated with insulin resistance in humans

Elevated circulating lactate has been associated with obesity and insulin resistance. The aim of the current study was to determine if lactate-induced lysine lactylation (kla), a post-translational modification, was present in human skeletal muscle and related to insulin resistance. Fifteen lean (Body Mass Index: 22.1 ± 0.5 kg/m2) and fourteen obese (40.6 ± 1.4 kg/m2) adults underwent a muscle biopsy and 2-h oral glucose tolerance test. Skeletal muscle lactylation was increased in obese compared to lean females (19%, p < 0.05) and associated with insulin resistance (r = 0.37, p < 0.05) in the whole group. Skeletal muscle lactylation levels were significantly associated with markers of anaerobic metabolism (plasma lactate and skeletal muscle lactate dehydrogenase [LDH], p < 0.05) and negatively associated with markers of oxidative metabolism (skeletal muscle cytochrome c oxidase subunit 4 and Complex I [pyruvate] OXPHOS capacity, p < 0.05). Treatment of primary human skeletal muscle cells (HSkMC) with sodium lactate for 24 h increased protein lactylation and IRS-1 serine 636 phosphorylation in a similar dose-dependent manner (p < 0.05). Inhibition of glycolysis (with 2-deoxy-d-glucose) or LDH-A (with sodium oxamate or LDH-A siRNA) for 24 h reduced HSkMC lactylation which paralleled reductions in culture media lactate accumulation. This study identified the existence of a lactate-derived post-translational modification in human skeletal muscle and suggests skeletal muscle lactylation could provide additional insight into the regulation of skeletal muscle metabolism, including insulin resistance.

Clarifying the link between the blood lactate concentration and cardiovascular risk

The blood lactate value at rest (Lac_rest) is linked to cardiovascular outcomes. It is unclear whether this association holds true in younger, healthy subjects, especially as the pathophysiological connection between Lac_rest and cardiometabolic disease is not well understood. The aim of this study is clarifying the link between Lac_rest and cardiovascular risk, and to study explanatory factors for the variance of Lac_rest concerning metabolism and physical activity in a population of healthy patient-athletes. The distribution and intra-individual variability of Lac_rest was assessed based on 9051 samples. The 10-year cardiovascular risk was then approximated using the Framingham risk score in a group of 1315 samples from patient-athletes. Cross-validated linear regression was used to analyze explanatory variables for Lac_rest and 10-year cardiovascular risk. Lac_rest is weakly associated with the Framingham score. This association disappears when adjusting for blood lipids. Lac_rest is also linked to the predominant type of exercise with endurance athletes featuring a higher Lac_rest. Lac_rest does not independently predict the estimated cardiovascular risk but is associated with lipid parameters. Moreover, the intra-individual variability of Lac_rest is high in a relevant number of subjects, which does not point towards the feasibility to use Lac_rest as an individual risk factor.

Emerging Roles of Myeloid-Derived Suppressor Cells in Diabetes

Diabetes is a syndrome characterized by hyperglycemia with or without insulin resistance. Its etiology is attributed to the combined action of genes, environment and immune cells. Myeloid-derived suppressor cell (MDSC) is a heterogeneous population of immature cells with immunosuppressive ability. In recent years, different studies have debated the quantity, activity changes and roles of MDSC in the diabetic microenvironment. However, the emerging roles of MDSC have not been fully documented with regard to their interactions with diabetes. Here, the manifestations of MDSC and their subsets are reviewed with regard to the incidence of diabetes and diabetic complications. The possible drugs targeting MDSC are discussed with regard to their potential of treating diabetes. We believe that understanding MDSC will offer opportunities to explain pathological characteristics of different diabetes. MDSC also will be used for personalized immunotherapy of diabetes.

Basigin deficiency prevents anaplerosis and ameliorates insulin resistance and hepatosteatosis

Monocarboxylates, such as lactate and pyruvate, are precursors for biosynthetic pathways, including those for glucose, lipids, and amino acids via the tricarboxylic acid (TCA) cycle and adjacent metabolic networks. The transportation of monocarboxylates across the cellular membrane is performed primarily by monocarboxylate transporters (MCTs), the membrane localization and stabilization of which are facilitated by the transmembrane protein basigin (BSG). Here, we demonstrate that the MCT/BSG axis sits at a crucial intersection of cellular metabolism. Abolishment of MCT1 in the plasma membrane was achieved by Bsg depletion, which led to gluconeogenesis impairment via preventing the influx of lactate and pyruvate into the cell, consequently suppressing the TCA cycle. This net anaplerosis suppression was compensated in part by the increased utilization of glycogenic amino acids (e.g., alanine and glutamine) into the TCA cycle and by activated ketogenesis through fatty acid β-oxidation. Complementary to these observations, hyperglycemia and hepatic steatosis induced by a high-fat diet were ameliorated in Bsg-deficient mice. Furthermore, Bsg deficiency significantly improved insulin resistance induced by a high-fat diet. Taken together, the plasma membrane–selective modulation of lactate and pyruvate transport through BSG inhibition could potentiate metabolic flexibility to treat metabolic diseases.

Maternal Metabolites Associated With Gestational Diabetes Mellitus and a Postpartum Disorder of Glucose Metabolism

CONTEXT

Gestational diabetes is associated with a long-term risk of developing a disorder of glucose metabolism. However, neither the metabolic changes characteristic of gestational diabetes in a large, multi-ancestry cohort nor the ability of metabolic changes during pregnancy, beyond glucose levels, to identify women at high risk for progression to a disorder of glucose metabolism has been examined.

OBJECTIVE

This work aims to identify circulating metabolites present at approximately 28 weeks' gestation associated with gestational diabetes mellitus (GDM) and development of a disorder of glucose metabolism 10 to 14 years later.

METHODS

Conventional clinical and targeted metabolomics analyses were performed on fasting and 1-hour serum samples following a 75-g glucose load at approximately 28 weeks' gestation from 2290 women who participated in the Hyperglycemia and Adverse Pregnancy Outcome (HAPO) Study. Postpartum metabolic traits included fasting and 2-hour plasma glucose following a 75-g glucose load, insulin resistance estimated by the homeostasis model assessment of insulin resistance, and disorders of glucose metabolism (prediabetes and type 2 diabetes) during the HAPO Follow-Up Study.

RESULTS

Per-metabolite analyses identified numerous metabolites, ranging from amino acids and carbohydrates to fatty acids and lipids, before and 1-hour after a glucose load that were associated with GDM as well as development of a disorder of glucose metabolism and metabolic traits 10 to 14 years post partum. A core group of fasting and 1-hour metabolites mediated, in part, the relationship between GDM and postpartum disorders of glucose metabolism, with the fasting and 1-hour metabolites accounting for 15.7% (7.1%-30.8%) and 35.4% (14.3%-101.0%) of the total effect size, respectively. For prediction of a postpartum disorder of glucose metabolism, the addition of circulating fasting or 1-hour metabolites at approximately 28 weeks' gestation showed little improvement in prediction performance compared to clinical factors alone.

CONCLUSION

The results demonstrate an association of multiple metabolites with GDM and postpartum metabolic traits and begin to define the underlying pathophysiology of the transition from GDM to a postpartum disorder of glucose metabolism.

Environmental pollution and diabetes mellitus

Diabetes mellitus (DM) is a chromic metabolic disease that affects a large segment of the population worldwide. Physical inactivity, poor nutrition, and genetic predisposition are main risk factors for disease development. In the last decade, it was clear to the scientific community that DM development is linked to a novel disease inducer that was later defined as diabetogenic factors of pollution and endocrine disrupting agents. Environmental pollution is exponentially increasing in uncontrolled manner in several countries. Environmental pollutants are of diverse nature and toxicities, including polyaromatic hydrocarbons (PAHs), pesticides, and heavy metals. In the current review, we shed light on the impact of each class of these pollutants and the underlined molecular mechanism of diabetes induction and biological toxicities. Finally, a brief overview about the connection between coronavirus disease 2019 and diabetes pandemics is presented.

Influence of endocrine disease on l-lactate concentrations in blood of ponies

Background

Blood l‐lactate concentrations are higher in people with developing or established diabetes mellitus and insulin resistance.

Objectives

To investigate whether blood l‐lactate concentrations are positively correlated with measures of insulin dysregulation (ID) or increased autumnal ACTH concentrations in ponies.

Animals

Systemically healthy client‐owned ponies (n = 101).

Methods

Prospective case‐control study. Blood samples were obtained from 101 clinically healthy ponies. Breed, weight, height, and subjective and objective measures of body condition were recorded. Blood l‐lactate, glucose, triglyceride, total adiponectin, and ACTH concentrations were measured and an oral sugar test (OST) was carried out. Correlations between blood l‐lactate and variables of endocrine health were determined.

Results

Using a seasonal cutoff point of ACTH concentrations ≥47 pg/mL, 55 ponies had increased autumnal ACTH concentrations and 45 did not. Using a basal insulin concentration of >50 μiU/mL, 42 ponies were diagnosed with ID and 58 were not. Using a 60 minutes after OST cutoff point of >45 μiU/mL, 57 ponies had ID and 37 did not. Blood l‐lactate concentrations were significantly lower in obese (average body condition score ≥ 7/9) compared to nonobese ponies (0.6 mmol/L; range, 0.0‐1.9 mmol/L vs 0.8 mmol/L; range, 0.3‐2.7 mmol/L; P = .01). No other significant correlations were detected. No differences were detected between ponies with and without increased autumnal ACTH concentrations (0.7 mmol/L; range, 0.0‐2.7 mmol/L vs 0.7 mmol/L; range, 0.3‐1.8 mmol/L; P = .84) and with and without ID (0.7 mmol/L; range, 0.3‐2.7 mmol/L vs 0.8 mmol/L; range, 0.0‐1.6 mmol/L; P = .63).

Conclusions and Clinical Importance

Results do not support an effect of endocrine status on l‐lactate concentrations in blood of ponies.

Ockham's razor and the metabolic syndrome

The broad effects of bariatric/metabolic surgery on virtually every tissue and organ system remain unexplained. Weight loss, although a major factor, does not fully account for the rapid, full, and durable remission of type 2 diabetes, return of islet function, reduction of the prevalence of cancers, increase in gray matter of the brain, and decrease in all-cause mortality. This review supports the thesis that the metabolic syndrome is not a group of separate diseases but rather multiple expressions of a shared defect in the utilization of carbohydrates and lipids. That error is probably caused by a dysmetabolic signal from the foregut, stimulated by food, that limits entry of 2-carbon fragments into the tricarboxylic acid cycle, the accumulation of lactate and, in turn, increases in glucose and insulin. Surgery limits that signal by reducing contact between food and foregut mucosa. Speciation of that signal(s) may offer a new pathway for drug development.

Effect of Chronic Exercise Training on Blood Lactate Metabolism Among Patients With Type 2 Diabetes Mellitus: A Systematic Review and Meta-Analysis

Purpose: To assess the effect of chronic exercise training on blood lactate metabolism at rest (i.e., basal lactate concentrations) and during exercise (i.e., blood lactate concentration at a fixed load, load at a fixed blood lactate concentration, and load at the individual blood lactate threshold) among patients with type 2 diabetes mellitus (T2DM). Methods: PubMed (MedLine), Embase, Web of Science, and Scopus were searched. Randomized controlled trials, non-randomized controlled trials, and case-control studies using chronic exercise training (i.e., 4 weeks) and that assessed blood lactate concentrations at rest and during exercise in T2DM patients were included. Results: Thirteen studies were eligible for the systematic review, while 12 studies with 312 participants were included into the meta-analysis. In the pre-to-post intervention meta-analysis, chronic exercise training had no significant effect on changes in basal blood lactate concentrations (standardized mean difference (SMD) = -0.20; 95% CI, -0.55 to 0.16; p = 0.28), and the results were similar when comparing the effect of intervention and control groups. Furthermore, blood lactate concentration at a fixed load significantly decreased (SMD = -0.73; 95% CI, -1.17 to -0.29; p = 0.001), while load at a fixed blood lactate concentration increased (SMD = 0.40; 95% CI, 0.07 to 0.72; p = 0.02) after chronic exercise training. No change was observed in load at the individual blood lactate threshold (SMD = 0.28; 95% CI, -0.14 to 0.71; p = 0.20). Conclusion: Chronic exercise training does not statistically affect basal blood lactate concentrations; however, it may decrease the blood lactate concentrations during exercise, indicating improvements of physical performance capacity which is beneficial for T2DM patients' health in general. Why chronic exercise training did not affect basal blood lactate concentrations needs further investigation.

Untargeted metabolomics reveals plasma metabolites predictive of ectopic fat in pancreas and liver as assessed by magnetic resonance imaging: the TOFI_Asia study

BACKGROUND

Excess visceral obesity and ectopic organ fat is associated with increased risk of cardiometabolic disease. However, circulating markers for early detection of ectopic fat, particularly pancreas and liver, are lacking.

METHODS

Lipid storage in pancreas, liver, abdominal subcutaneous adipose tissue (SAT) and visceral adipose tissue (VAT) from 68 healthy or pre-diabetic Caucasian and Chinese women enroled in the TOFI_Asia study was assessed by magnetic resonance imaging/spectroscopy (MRI/S). Plasma metabolites were measured with untargeted liquid chromatography-mass spectroscopy (LC-MS). Multivariate partial least squares (PLS) regression identified metabolites predictive of VAT/SAT and ectopic fat; univariate linear regression adjusting for potential covariates identified individual metabolites associated with VAT/SAT and ectopic fat; linear regression adjusted for ethnicity identified clinical and anthropometric correlates for each fat depot.

RESULTS

PLS identified 56, 64 and 31 metabolites which jointly predicted pancreatic fat (R2Y = 0.81, Q2 = 0.69), liver fat (RY2 = 0.8, Q2 = 0.66) and VAT/SAT ((R2Y = 0.7, Q2 = 0.62)) respectively. Among the PLS-identified metabolites, none of them remained significantly associated with pancreatic fat after adjusting for all covariates. Dihydrosphingomyelin (dhSM(d36:0)), 3 phosphatidylethanolamines, 5 diacylglycerols (DG) and 40 triacylglycerols (TG) were associated with liver fat independent of covariates. Three DGs and 12 TGs were associated with VAT/SAT independent of covariates. Notably, comparison with clinical correlates showed better predictivity of ectopic fat by these PLS-identified plasma metabolite markers.

CONCLUSIONS

Untargeted metabolomics identified candidate markers of visceral and ectopic fat that improved fat level prediction over clinical markers. Several plasma metabolites were associated with level of liver fat and VAT/SAT ratio independent of age, total and visceral adiposity, whereas pancreatic fat deposition was only associated with increased sulfolithocholic acid independent of adiposity-related parameters, but not age.

Suppression of uric acid and lactate production by sodium acetate ameliorates hepatic triglyceride accumulation in fructose-insulin resistant pregnant rats

High fructose intake has been associated with perturbed lipid, uric acid and lactate homeostasis. However, consumption of fructose-sweetened beverages is not usually regulated during pregnancy. The effect of short-chain fatty acid (acetate) on the metabolic effects of high fructose intake during pregnancy is not known. We hypothesized that acetate prevents gestational fructose-induced hepatic triglyceride (TG) accumulation by suppressing uric acid and lactate production. Pregnant Wistar rats were randomly separated into three groups (n = 6/group) receiving drinking water (CON), 10 % (w/v) fructose drink (FRU) and 10 % (w/v) fructose with 200 mg/kg (w/w; p.o.) sodium acetate (FRU + ACE) daily for nineteen days. Fructose intake resulted in increased body weight gain, liver weight, fluid intake, visceral fat, insulin resistance, fasting blood glucose, insulin, plasma and hepatic TG, total cholesterol, free fatty acid, lipid peroxidation, adenosine deaminase, xanthine oxidase, uric acid, lactate, lactate dehydrogenase, and liver injury marker enzymes. However, gestational high fructose intake led to depressed plasma and hepatic glucose-6-phosphate dehydrogenase (G6PD)-dependent antioxidant barrier, adenosine and food intake. All these effects except water intake and food intake were abated by sodium acetate. These results demonstrate that maternal fructose-enriched drink would cause hepatic TG accumulation that is associated with perturbed glucose, uric acid, lactate homeostasis, and G6PD-dependent antioxidant barrier. These results also demonstrate that acetate protects the liver against gestational fructose-induced TG accumulation by inhibiting uric acid and lactate production. Thus, acetate may be useful in the treatment of hyperuricemia- and hyperlactatemia-related disorders.

Plasma Lactate as a Marker for Metabolic Health

Blood lactate concentrations traditionally have been used as an index of exercise intensity or clinical hyperlactatemia. However, more recent data suggest that fasting plasma lactate can also be indicative of the risk for subsequent metabolic disease. The hypothesis presented is that fasting blood lactate accumulation reflects impaired mitochondrial substrate use, which in turn influences metabolic disease risk.

Interactions among endotoxin, uric acid, and lactate in relation to the risk of type 2 diabetes: A population-based study

BACKGROUND

Blood levels of endotoxin, uric acid (UA), or lactate (LAC) are associated with type 2 diabetes mellitus (T2DM). Thus, we explored the interactions among blood endotoxin, UA, and LAC levels and the risk of T2DM.

METHODS

This population-based cross-sectional study included 2520 Chinese adults. Fasting blood endotoxin, UA, and LAC levels were determined and the cut-off values were obtained from the receiver operating characteristic curve analysis. The study population was classified into two or four subgroups based on low or high, or both low and high levels of endotoxin, UA, and LAC, respectively.

RESULTS

The odds ratios (ORs) for T2DM (all P < .05) were higher in the high groups than the low groups of endotoxin, UA, or LAC, respectively. Participants in the groups with high levels of both endotoxin and UA, endotoxin and LAC, or UA and LAC, had 4.71 (95% CI 3.01-7.37), 5.13 (95% CI 3.29-7.99), or 3.73 (95% CI 2.34-5.94) times higher risk for T2DM compared to those in groups with low levels of both endotoxin and UA, endotoxin and LAC, or UA and LAC (all P < 0.05), respectively. In the interaction analysis, an interactive effect between endotoxin and UA (P < .05), or endotoxin and LAC (P < .05), but not UA and LAC, was observed that contributed to an increased risk of T2DM.

CONCLUSIONS

The interaction between levels of endotoxin and UA or levels of endotoxin and LAC was related to an increased risk of T2DM in the Chinese population.

Mitochondrial DNA copy number and diabetes: the Atherosclerosis Risk in Communities (ARIC) study

INTRODUCTION

Mitochondrial DNA copy number (mtDNA-CN) is a measure of mitochondrial dysfunction and is associated with diabetes in experimental models. To explore the temporality of mitochondrial dysfunction and diabetes, we estimated the prevalent and incident association of mtDNA-CN and diabetes.

RESEARCH DESIGN AND METHODS

We assessed the associations of mtDNA-CN measured from buffy coat with prevalent and incident diabetes, stratified by race, in 8954 white and 2444 black participants in the Atherosclerosis Risk in Communities (ARIC) study, an observational cohort study. Follow-up for incident analyses was complete through visit 6, 2016.

RESULTS

Mean age at mtDNA-CN measurement was 57 years and 59% were female. Prevalence of diabetes at time of mtDNA-CN measurement was higher in blacks (563/2444, 23%) than whites (855/8954, 10%). The fully adjusted odds of prevalent diabetes for the 10th vs 90th percentile of mtDNA-CN was 1.05 (95% CI 0.74 to 1.49) among black and 1.49 (95% CI 1.20 to 1.85) among white participants. Over a median follow-up time of 19 years (Q1, Q3: 11, 24 years), we observed 617 incident diabetes cases among 1744 black and 2121 cases among 7713 white participants free of diabetes at baseline. The fully adjusted hazard of incident diabetes for the 10th vs 90th percentile of mtDNA-CN was 1.07 (95% CI 0.84 to 1.38) among black and 0.97 (95% CI 0.86 to 1.10) among white participants.

CONCLUSIONS

Lower mtDNA-CN in buffy coat was associated with prevalent diabetes in white but not black ARIC participants. Lower mtDNA-CN was not associated with incident diabetes over 20 years of follow-up in whites or blacks.

Effects of carbohydrate quality and amount on plasma lactate: results from the OmniCarb trial

INTRODUCTION

Plasma lactate is a marker of non-oxidative glucose metabolism associated with progression to diabetes. We examined the effect of carbohydrate quality (glycemic index (GI)) and amount (%kcal) on plasma lactate. We hypothesized that low GI (≤45 (g)) versus high (≥65 (G)) and low %kcal from carbohydrate (40% kcal (c)) versus high (58% kcal (C)) each would reduce lactate levels.

RESEARCH DESIGN AND METHODS

We measured lactate in OmniCarb, a randomized, cross-over trial of four diets in overweight/obese adults without diabetes or cardiovascular disease (N=163). The four diets were high carbohydrate+high GI (CG, reference), high carbohydrate+low GI (Cg), low carbohydrate+high GI (cG), and low carbohydrate+low GI (cg). Participants (N=163) consumed each of the four diets over a 5-week period, separated by 2-week washout periods. Plasma lactate levels were measured at baseline, during which the participants consumed their own diets, and after each 5-week period.

RESULTS

Baseline plasma lactate was 1.2 mmol/L. In the setting of high carbohydrate amount, reducing GI lowered plasma lactate non-significantly by 0.08 mmol/L (Cg vs CG: 95% CI -0.16 to 0.00; p=0.06). In the setting of high GI, reducing carbohydrate amount lowered plasma lactate by 0.10 mmol/L (cG vs CG: 95% CI -0.19 to -0.02; p=0.02). The combined effect of reducing GI and carbohydrate proportion in the diet (cg vs CG) was similar (cg vs CG: -0.08; 95% CI -0.16 to 0.00; p=0.04). All four diets reduced plasma lactate compared with baseline.

CONCLUSIONS

Compared with a diet with high GI and high carbohydrate amount, diets with low GI and/or low carbohydrate amount reduced plasma lactate. Whether this change in lactate leads to long-term change in glucose metabolism needs to be examined.

TRIAL REGISTRATION NUMBER

NCT00608049.

Glycolysis/gluconeogenesis- and tricarboxylic acid cycle-related metabolites, Mediterranean diet, and type 2 diabetes

BACKGROUND

Glycolysis/gluconeogenesis and tricarboxylic acid (TCA) cycle metabolites have been associated with type 2 diabetes (T2D). However, the associations of these metabolites with T2D incidence and the potential effect of dietary interventions remain unclear.

OBJECTIVES

We aimed to evaluate the association of baseline and 1-y changes in glycolysis/gluconeogenesis and TCA cycle metabolites with insulin resistance and T2D incidence, and the potential modifying effect of Mediterranean diet (MedDiet) interventions.

METHODS

We included 251 incident T2D cases and 638 noncases in a nested case-cohort study within the PREDIMED Study during median follow-up of 3.8 y. Participants were allocated to MedDiet + extra-virgin olive oil, MedDiet + nuts, or control diet. Plasma metabolites were measured using a targeted approach by LC-tandem MS. We tested the associations of baseline and 1-y changes in glycolysis/gluconeogenesis and TCA cycle metabolites with subsequent T2D risk using weighted Cox regression models and adjusting for potential confounders. We designed a weighted score combining all these metabolites and applying the leave-one-out cross-validation approach.

RESULTS

Baseline circulating concentrations of hexose monophosphate, pyruvate, lactate, alanine, glycerol-3 phosphate, and isocitrate were significantly associated with higher T2D risk (17-44% higher risk for each 1-SD increment). The weighted score including all metabolites was associated with a 30% (95% CI: 1.12, 1.51) higher relative risk of T2D for each 1-SD increment. Baseline lactate and alanine were associated with baseline and 1-y changes of homeostasis model assessment of insulin resistance. One-year increases in most metabolites and in the weighted score were associated with higher relative risk of T2D after 1 y of follow-up. Lower risks were observed in the MedDiet groups than in the control group although no significant interactions were found after adjusting for multiple comparisons.

CONCLUSIONS

We identified a panel of glycolysis/gluconeogenesis-related metabolites that was significantly associated with T2D risk in a Mediterranean population at high cardiovascular disease risk. A MedDiet could counteract the detrimental effects of these metabolites.This trial was registered at controlled-trials.com as ISRCTN35739639.

Sodium acetate protects against nicotine-induced excess hepatic lipid in male rats by suppressing xanthine oxidase activity

Fatty liver is the hepatic consequence of chronic insulin resistance (IR) and related syndromes. It is mostly accompanied by inflammatory and oxidative molecules. Increased activity of xanthine oxidase (XO) exerts both inflammatory and oxidative effects and has been implicated in metabolic derangements including non-alcoholic fatty liver disease. Short chain fatty acids (SCFAs) elicit beneficial metabolic alterations in IR and related syndromes. In the present study, we evaluated the preventive effects of a SCFA, acetate, on nicotine-induced dysmetabolism and fatty liver. Twenty-four male Wistar rats (n = 6/group): vehicle-treatment (p.o.), nicotine-treated (1.0 mg/kg; p.o.), sodium acetate-treated (200 mg/kg; p.o.) and nicotine + sodium acetate-treated groups. The treatments lasted for 8 weeks. IR was estimated by oral glucose tolerance test and homeostatic model assessment of IR. Plasma and hepatic free fatty acid, triglyceride (TG), glutathione peroxidase, adenosine deaminase (ADA), XO and uric acid (UA) were measured. Nicotine exposure resulted in reduced body weight, liver weight, visceral adiposity, glycogen content and glycogen synthase activity. Conversely, exposure to nicotine increased fasting plasma glucose, lactate, IR, plasma and hepatic TG, free fatty acid, TG/HDL-cholesterol ratio, lipid peroxidation, liver function enzymes, plasma and hepatic UA, XO and ADA activities. However, plasma and hepatic glucose-6-phosphate dehydrogenase-dependent antioxidant defense was not affected by nicotine. Concomitant treatment with acetate ameliorated nicotine-induced effects. Taken together, these results indicate that nicotine exposure leads to excess deposition of lipid in the liver by enhancing XO activity. The results also imply that acetate confers hepatoprotection and is accompanied by decreased XO activity.

Potential therapeutic effect of Moroccan propolis in hyperglycemia, dyslipidemia, and hepatorenal dysfunction in diabetic rats

OBJECTIVES

The effect of propolis collected in Morocco on blood glucose, lipid profile, liver enzymes, and kidney function was investigated in control and diabetic rats.

MATERIALS AND METHODS

Antioxidant activity of propolis was evaluated with the use of DPPH, 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid) (ABTS•+), ferric reducing power and total antioxidant activity assay. To study its effect in streptozotocin (STZ)-induced diabetes, the rats were divided into eight groups; four control and four diabetics. The animals received distilled water, glibenclamide, or propolis extract, 50 mg/kg/BW) or 100 mg/kg/b.wt, daily for 15 days. Blood glucose, triglyceride, lactic acid dehydrogenase, liver enzymes, creatinine, blood urea, lipid profile, and body weight were measured on day 15 after commencement of the treatment.

RESULTS

Propolis has a strong antioxidant activity and high total flavonoids and polyphenols content. Glibenclamide and propolis have no significant effect on lipid parameters, and renal and hepatic function in non-diabetic rats. However, propolis or glibenclamide caused a significant lowering of blood glucose after a single administration and at day 15 after daily administration in diabetic rats (P<0.05). Both interventions significantly lowered lactic acid dehydrogenase, increased body weight, and ameliorated dyslipidemia and abnormal liver and kidney function caused by diabetes. The effect of propolis was dose-dependent and in a high dose it was more potent than glibenclamide.

CONCLUSION

Propolis exhibited strong antihyperglycemic, antihyperlipidemic, and hepato-renal protective effects in diabetes, and significantly lowered the elevated lactic acid dehydrogenase. The study demonstrated for the first-time the effect of Moroccan propolis in diabetes and it will pave the way for clinical investigations.

Correlation between l-lactate and glucose concentrations and body condition score in healthy horses and ponies

Background

Blood l‐lactate and glucose concentrations were higher in ponies with gastrointestinal disease than in horses, possibly because of differences in body condition (BC).

Objectives

To investigate whether l‐lactate and glucose concentrations correlate with BC and differ between healthy horses and ponies.

Animals

Systemically healthy client‐owned ponies (n = 101) and horses (n = 51).

Methods

Prospective observational study. Breed, weight, height, and subjective and objective measures of BC were recorded and l‐lactate and glucose concentrations were measured. Correlations between l‐lactate and glucose concentrations and BC were established. The association between l‐lactate concentrations, equid type (pony or horse), BC, age, and glucose concentrations was investigated using a multivariable model.

Results

Weak but significant (P = .001) negative correlations were detected between l‐lactate concentration and average BC score (r = −0.29), heart girth:height ratio (r = −0.27), and age (r = −0.27). Glucose concentrations were significantly (P < .001) positively correlated with neck length:heart girth ratio (r = 0.37) and heart girth:height ratio (r = 0.31). l‐lactate and glucose concentrations were weakly correlated (r = 0.15; P = .04). In the final multivariable model, age (−0.02 ± 0.006; P = .001) and heart girth:height ratio (−1.74 ± 0.53; P = .001) were significantly associated with the natural logarithm of l‐lactate concentration (Lnl‐Lactate). This represents a 2% decrease in l‐lactate concentration per year increase in age and 10% decrease in l‐lactate concentration per 0.06 unit increase in heart girth:height ratio.

Conclusions and Clinical Importance

In healthy horses and ponies, age and BC significantly influence l‐lactate concentrations.

Plasma lactate as a marker of metabolic health: Implications of elevated lactate for impairment of aerobic metabolism in the metabolic syndrome

BACKGROUND

Fasting lactate is elevated in metabolic diseases and could possibly be predictive of the risk of developing the metabolic syndrome.

METHODS

Plasma samples were analyzed for fasting lactate to compare lean subjects, nondiabetic subjects with severe obesity, and metabolically impaired subjects. Subjects with severe obesity were studied 1 week before and 1 week to 9 months after gastric bypass surgery. Subjects with components of the metabolic syndrome were studied before and after 6 months of an exercise intervention.

RESULTS

Metabolically impaired subjects had higher fasting lactate concentrations (P < .0001) and respond to a glucose or insulin challenge with higher lactates than non-obese subjects (P < .004). Lactate was significantly reduced a week after gastric bypass surgery (P < .05) and further reduced 1 to 9 months after surgery (0.95 ± 0.04 mM in non-obese, 1.26 ± 0.12 mM in subjects with severe obesity, and 0.68 ± 0.03 mM 1-3 months after gastric bypass). Six months of chronic exercise resulted in a 16% reduction (P = .028) in fasting lactate.

CONCLUSION

Fasting plasma lactate was elevated in obese subjects with the metabolic syndrome compared with healthy lean individuals. Lactate was reduced by exercise and bariatric surgery, interventions that improve metabolic health and risk for subsequent disease. The results of this study and those previously published by our research group suggest that elevated lactate may be caused by an impairment in aerobic metabolism and may offer a metric assessing the severity of the metabolic syndrome.

Retrospective evaluation of the association between admission blood glucose and l-lactate concentrations in ponies and horses with gastrointestinal disease (2008-2016): 545 cases

OBJECTIVES

A recent study described increased l-lactate concentrations in ponies with gastrointestinal disease compared to horses, but blood glucose (BG) concentrations were not considered. The study tested the hypothesis that BG and l-lactate concentrations are correlated in horses and ponies with gastrointestinal disease and that BG concentrations, not equid type (pony vs horse), are an independent predictor of L-lactate concentrations. It was further hypothesized that equid type was an independent predictor of BG concentrations.

DESIGN

Retrospective study 2008-2016.

SETTING

University teaching hospital.

ANIMALS

Admission data from 545 animals (384 horses and 161 ponies) with gastrointestinal disease.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Data collected included signalment, clinicopathological findings on admission, and nature and location of the gastrointestinal lesion (strangulating vs non-strangulating and large vs small intestinal lesion). The association between admission blood l-lactate concentrations, equid type (pony or horse) and BG concentrations was investigated in a multivariable model. Admission l-lactate and BG concentrations were strongly correlated (n = 522; r = 0.63; P < 0.001). Ponies had significantly higher l-lactate (2.7 mmol/L (0.5-18.0 mmol/L) vs 1.4 mmol/L (0.3-19 mmol/L); P < 0.001) and BG concentrations than horses (8.4 mmol/L (4.2-24.4 mmol/L); 151 mg/dL (76-439 mg/dL) vs 6.9 mmol/L (3.4-26.8 mmol/L); 124 mg/dL (61-482 mg/dL); P < 0.001). In the multivariable analysis, l-lactate concentrations were significantly and positively associated with admission BG concentrations in all animals and also with equid type. For each millimole per liter (18 mg/dL) increase in BG, l-lactate concentrations increased by 7.9% (5.9, 9.9); P < 0.001. In comparison to ponies, l-lactate concentrations were decreased by 27.7% (37.4, 16.5); P < 0.001 in horses. Admission BG concentrations were significantly and positively associated with l-lactate concentrations in all animals. For each millimole per liter increase in l-lactate concentration, BG concentration increased by 6.2% (4.7, 7.6; P < 0.001). Admission BG concentrations were not associated with equid type.

CONCLUSION

Admission BG concentrations and equid type are independent predictors of blood l-lactate concentrations in equids with gastrointestinal disease, but their relationship requires further investigation.

Seafood intake and the development of obesity, insulin resistance and type 2 diabetes

We provide an overview of studies on seafood intake in relation to obesity, insulin resistance and type 2 diabetes. Overweight and obesity development is for most individuals the result of years of positive energy balance. Evidence from intervention trials and animal studies suggests that frequent intake of lean seafood, as compared with intake of terrestrial meats, reduces energy intake by 4–9 %, sufficient to prevent a positive energy balance and obesity. At equal energy intake, lean seafood reduces fasting and postprandial risk markers of insulin resistance, and improves insulin sensitivity in insulin-resistant adults. Energy restriction combined with intake of lean and fatty seafood seems to increase weight loss. Marine n-3 PUFA are probably of importance through n-3 PUFA-derived lipid mediators such as endocannabinoids and oxylipins, but other constituents of seafood such as the fish protein per se, trace elements or vitamins also seem to play a largely neglected role. A high intake of fatty seafood increases circulating levels of the insulin-sensitising hormone adiponectin. As compared with a high meat intake, high intake of seafood has been reported to reduce plasma levels of the hepatic acute-phase protein C-reactive protein level in some, but not all studies. More studies are needed to confirm the dietary effects on energy intake, obesity and insulin resistance. Future studies should be designed to elucidate the potential contribution of trace elements, vitamins and undesirables present in seafood, and we argue that stratification into responders and non-responders in randomised controlled trials may improve the understanding of health effects from intake of seafood.

Proton Transport Chains in Glucose Metabolism: Mind the Proton

The Embden-Meyerhof-Parnas (EMP) pathway comprises eleven cytosolic enzymes interacting to metabolize glucose to lactic acid [CH3CH(OH)COOH]. Glycolysis is largely considered as the conversion of glucose to pyruvate (CH3COCOO-). We consider glycolysis to be a cellular process and as such, transporters mediating glucose uptake and lactic acid release and enable the flow of metabolites through the cell, must be considered as part of the EMP pathway. In this review, we consider the flow of metabolites to be coupled to a flow of energy that is irreversible and sufficient to form ordered structures. This latter principle is highlighted by discussing that lactate dehydrogenase (LDH) complexes irreversibly reduce pyruvate/H+ to lactate [CH3CH(OH)COO-], or irreversibly catalyze the opposite reaction, oxidation of lactate to pyruvate/H+. However, both LDH complexes are considered to be driven by postulated proton transport chains. Metabolism of glucose to two lactic acids is introduced as a unidirectional, continuously flowing pathway. In an organism, cell membrane-located proton-linked monocarboxylate transporters catalyze the final step of glycolysis, the release of lactic acid. Consequently, both pyruvate and lactate are discussed as intermediate products of glycolysis and substrates of regulated crosscuts of the glycolytic flow.

Association of Low-Moderate Arsenic Exposure and Arsenic Metabolism with Incident Diabetes and Insulin Resistance in the Strong Heart Family Study

BACKGROUND

High arsenic exposure has been related to diabetes, but at low-moderate levels the evidence is mixed. Arsenic metabolism, which is partly genetically controlled and may rely on certain B vitamins, plays a role in arsenic toxicity.

OBJECTIVE

We evaluated the prospective association of arsenic exposure and metabolism with type 2 diabetes and insulin resistance.

METHODS

We included 1,838 American Indian men and women free of diabetes (median age, 36 y). Arsenic exposure was assessed as the sum of inorganic arsenic (iAs), monomethylarsonate (MMA), and dimethylarsinate (DMA) urine concentrations (ΣAs). Arsenic metabolism was evaluated by the proportions of iAs, MMA, and DMA over their sum (iAs%, MMA%, and DMA%). Homeostasis model assessment for insulin resistance (HOMA2-IR) was measured at baseline and follow-up visits. Incident diabetes was evaluated at follow-up.

RESULTS

Median ΣAs, iAs%, MMA%, and DMA% was 4.4 μg/g creatinine, 9.5%, 14.4%, and 75.6%, respectively. Over 10,327 person-years of follow-up, 252 participants developed diabetes. Median HOMA2-IR at baseline was 1.5. The fully adjusted hazard ratio [95% confidence interval (CI)] for incident diabetes per an interquartile range increase in ΣAs was 1.57 (95% CI: 1.18, 2.08) in participants without prediabetes at baseline. Arsenic metabolism was not associated with incident diabetes. ΣAs was positively associated with HOMA2-IR at baseline but negatively with HOMA2-IR at follow-up. Increased MMA% was associated with lower HOMA2-IR when either iAs% or DMA% decreased. The association of arsenic metabolism with HOMA2-IR differed by B-vitamin intake and AS3MT genetics variants.

CONCLUSIONS

Among participants without baseline prediabetes, arsenic exposure was associated with incident diabetes. Low MMA% was cross-sectional and prospectively associated with higher HOMA2-IR. Research is needed to confirm possible interactions of arsenic metabolism with B vitamins and AS3MT variants on diabetes risk. https://doi.org/10.1289/EHP2566.

Urinary pH is a predictor of diabetes in men; a population based large scale cohort study

AIMS

Previous cross-sectional studies revealed that patients with type 2 diabetes were associated with low urine pH. However, the association between urinary pH and incident type 2 diabetes is still unclear. Thus, we investigated the association between urinary pH and incident type 2 diabetes.

METHODS

This is a 5-year observational study of 3119men. We divided participants into four groups according to quartile of urinary pH. Multivariate logistic regression analysis was performed to calculate adjusted odds ratios (ORs) and 95% CIs for incident type 2 diabetes. We adjusted for age, body mass index, smoking, exercise, alcohol consumption, hypertension, hypertriglyceridemia, low high-density lipoprotein cholesterol levels and impaired fasting glycaemia.

RESULTS

In the follow-up examination, 113men diagnosed as diabetes. The proportion of incident diabetes was 6.9% (case/N=22/318) in the lowest urinary pH group (urinary pH = 5.0), 3.4% (46/1366) in the second lowest group (urinary pH = 5.5), 3.5% (30/856) in the third lowest group (urinary pH = 6.0) and 2.6% (15/579) in the highest group (urinary pH≥6.5). The lowest urinary pH group was associated with the increased risk of incident diabetes compared to the other urinary pH groups (multivariate OR=1.91, 95% CI 1.05-3.36, p=0.033 for the second lowest, multivariate OR=1.99, 95% CI 1.05-3.71, p=0.036 for the third lowest and multivariate OR 2.69, 95% CI 1.30-5.72, p=0.008 for the highest urinary pH groups).

CONCLUSIONS

Low urine pH is an independent predictor of diabetes. We suggest that the urine pH can be an easy practical marker for diabetes.

Oxamate Enhances the Anti-Inflammatory and Insulin-Sensitizing Effects of Metformin in Diabetic Mice

Metformin (MET) is the first-line drug for treating type 2 diabetes mellitus (T2DM). However, MET increases blood lactate levels in patients with T2DM. Lactate possesses proinflammatory properties and causes insulin resistance (IR). Oxamate (OXA), a lactate dehydrogenase inhibitor, can decrease tissue lactate production and blood lactate levels. This study was conducted to examine the effects of the combination of OXA and MET on inflammation, and IR in diabetic db/db mice. Supplementation of OXA to MET led to lowered tissue lactate production and serum lactate levels compared to MET alone, accompanied with further decreased tissue and blood levels of pro-inflammatory cytokines, along with better insulin sensitivity, beta-cell mass, and glycemic control in diabetic db/db mice. These results show that OXA enhances the anti-inflammatory and insulin-sensitizing effects of MET through the inhibition of tissue lactate production in db/db mice.

GCKR and PPP1R3B identified as genome-wide significant loci for plasma lactate: the Atherosclerosis Risk in Communities (ARIC) study

AIM

To investigate the genetic influence of circulating lactate level, a marker of oxidative capacity associated with diabetes.

METHODS

We conducted a genome-wide association study of log-transformed plasma lactate levels in 6901 European-American participants in the Atherosclerosis Risk in Communities study. For regions that achieved genome-wide significance in European-American participants, we conducted candidate region analysis in African-American subjects and tested for interaction between metformin use and the index single nucleotide polymorphisms for plasma lactate in European-American subjects.

RESULTS

The genome-wide association study in European-American subjects identified two genome-wide significant loci, GCKR (rs1260326, T allele β=0.08; P=1.8×10(-47) ) and PPP1R3B/LOC157273 (rs9987289, A allele β=0.06; P=1.6×10(-9) ). The index single nucleotide polymorphisms in these two loci explain 3.3% of the variance in log-transformed plasma lactate levels among the European-American subjects. In the African-American subjects, based on a region-significant threshold, the index single nucleotide polymorphism at GCKR was associated with plasma lactate but that at PPP1R3B/LOC157273 was not. Metformin use appeared to strengthen the association between the index single nucleotide polymorphism at PPP1R3B/LOC157273 and plasma lactate in European-American subjects (P for interaction=0.01).

CONCLUSIONS

We identified GCKR and PPP1R3B/LOC157273 as two genome-wide significant loci of plasma lactate. Both loci are associated with other diabetes-related phenotypes. These findings increase our understanding of the genetic control of lactate metabolism.

Age-related impairments in skeletal muscle PDH phosphorylation and plasma lactate are indicative of metabolic inflexibility and the effects of exercise training

The purpose of this study was to determine whether plasma lactate and skeletal muscle glucose regulatory pathways, specifically PDH dephosphorylation, are impaired during hyperinsulinemic conditions in middle- to older-aged individuals and determine whether exercise training could improve key variables responsible for skeletal muscle PDH regulation. Eighteen young (19-29 yr; n = 9 males and 9 females) and 20 middle- to older-aged (57-82 yr; n = 10 males and 10 females) individuals underwent a 2-h euglycemic hyperinsulinemic clamp. Plasma samples were obtained at baseline and at 30, 50, 90, and 120 min for analysis of lactate, and skeletal muscle biopsies were performed at 60 min for analysis of protein associated with glucose metabolism. In response to insulin, plasma lactate was elevated in aged individuals when normalized to insulin action. Insulin-stimulated phosphorylation of skeletal muscle PDH on serine sites 232, 293, and 300 decreased in young individuals only. Changes in insulin-stimulated PDH phosphorylation were positively related to changes in plasma lactate. No age-related differences were observed in skeletal muscle phosphorylation of LDH, GSK-3α, or GSK-3β in response to insulin or PDP1, PDP2, PDK2, PDK4, or MPC1 total protein. Twelve weeks of endurance- or strength-oriented exercise training improved insulin-stimulated PDH dephosphorylation, which was related to a reduced lactate response. These findings suggest that impairments in insulin-induced PDH regulation in a sedentary aging population contribute to impaired glucose metabolism and that exercise training is an effective intervention for treating metabolic inflexibility.

Lean Seafood Intake Reduces Postprandial C-peptide and Lactate Concentrations in Healthy Adults in a Randomized Controlled Trial with a Crossover Design

BACKGROUND

Recently we showed that lean seafood consumption reduced circulating triacylglycerol (TG) and VLDL concentrations and prevented an elevated total-to-HDL-cholesterol ratio relative to intake of a nonseafood diet.

OBJECTIVE

We aimed to elucidate whether diet-induced altered carbohydrate metabolism could be a contributing factor to the previously observed different lipoprotein patterns.

METHODS

This was a secondary outcome and explorative randomized controlled trial with a crossover design in 20 healthy adults (7 men and 13 women) that were 50.6 ± 3.4 (mean ± SEM) y old, weighed 75.7 ± 2.5 kg, and had a body mass index (BMI, in kg/m(2)) of 25.6 ± 0.7. After a 3-wk run-in period and separated by a 5-wk wash-out period, the participants consumed 2 balanced diets [in percentage of energy (energy%); 29% fat, 52% carbohydrates, 19% protein] for 4 wk. The diets varied in the main protein sources; 60 energy% of total protein was from either lean seafood or nonseafood sources. On the first and last day of each diet period, fasting and postprandial blood samples were collected before and after consumption of test meals (in energy%; 28% fat, 52% carbohydrates, 20% protein) with cod or lean beef.

RESULTS

The diets did not alter serum insulin and glucose concentrations. However, relative to the nonseafood diet period, the lean seafood diet period reduced postprandial C-peptide (P = 0.04) and lactate (P = 0.012) concentrations and fasting and postprandial TG/HDL-cholesterol ratios (P = 0.002). Hence, different postprandial lactate levels occurred at equal glucose concentrations.

CONCLUSIONS

Even though the diets did not alter serum insulin and glucose concentrations, intake of the lean seafood compared with the nonseafood diet reduced postprandial concentrations of C-peptide and lactate and the TG/HDL-cholesterol ratio in healthy adults in a manner that may affect the long-term development of insulin resistance, type 2 diabetes, and cardiovascular disease. This trial was registered at www.clinicaltrials.gov as NCT01708681.

Metabolite Signatures of Metabolic Risk Factors and their Longitudinal Changes

CONTEXT

Metabolic dysregulation underlies key metabolic risk factors—obesity, dyslipidemia, and dysglycemia.

OBJECTIVE

To uncover mechanistic links between metabolomic dysregulation and metabolic risk by testing metabolite associations with risk factors cross-sectionally and with risk factor changes over time.

DESIGN

Cross-sectional—discovery samples (n = 650; age, 36–69 years) from the Framingham Heart Study (FHS) and replication samples (n = 670; age, 61–76 years) from the BioImage Study, both following a factorial design sampled from high vs low strata of body mass index, lipids, and glucose. Longitudinal—FHS participants (n = 554) with 5–7 years of follow-up for risk factor changes.

SETTING

Observational studies.

PARTICIPANTS

Cross-sectional samples with or without obesity, dysglycemia, and dyslipidemia, excluding prevalent cardiovascular disease and diabetes or dyslipidemia treatment. Age- and sex-matched by group.

INTERVENTIONS

None.

MAIN OUTCOME MEASURE(S)

Gas chromatography-mass spectrometry detected 119 plasma metabolites. Cross-sectional associations with obesity, dyslipidemia, and dysglycemia were tested in discovery, with external replication of 37 metabolites. Single- and multi-metabolite markers were tested for association with longitudinal changes in risk factors.

RESULTS

Cross-sectional metabolite associations were identified with obesity (n = 26), dyslipidemia (n = 21), and dysglycemia (n = 11) in discovery. Glutamic acid, lactic acid, and sitosterol associated with all three risk factors in meta-analysis (P < 4.5 × 10−4). Metabolites associated with longitudinal risk factor changes were enriched for bioactive lipids. Multi-metabolite panels explained 2.5–15.3% of longitudinal changes in metabolic traits.

CONCLUSIONS

Cross-sectional results implicated dysregulated glutamate cycling and amino acid metabolism in metabolic risk. Certain bioactive lipids were associated with risk factors cross-sectionally and over time, suggesting their upstream role in risk factor progression. Functional studies are needed to validate findings and facilitate translation into treatments or preventive measures.