Mechanism of increased gluconeogenesis in noninsulin-dependent diabetes mellitus. Role of alterations in systemic, hepatic, and muscle lactate and alanine metabolism

Origin and Roles of Alanine and Glutamine in Gluconeogenesis in the Liver, Kidneys, and Small Intestine under Physiological and Pathological Conditions

Alanine and glutamine are the principal glucogenic amino acids. Most originate from muscles, where branched-chain amino acids (valine, leucine, and isoleucine) are nitrogen donors and, under exceptional circumstances, a source of carbons for glutamate synthesis. Glutamate is a nitrogen source for alanine synthesis from pyruvate and a substrate for glutamine synthesis by glutamine synthetase. The following differences between alanine and glutamine, which can play a role in their use in gluconeogenesis, are shown: (i) glutamine appearance in circulation is higher than that of alanine; (ii) the conversion to oxaloacetate, the starting substance for glucose synthesis, is an ATP-consuming reaction for alanine, which is energetically beneficial for glutamine; (iii) most alanine carbons, but not glutamine carbons, originate from glucose; and (iv) glutamine acts a substrate for gluconeogenesis in the liver, kidneys, and intestine, whereas alanine does so only in the liver. Alanine plays a significant role during early starvation, exposure to high-fat and high-protein diets, and diabetes. Glutamine plays a dominant role in gluconeogenesis in prolonged starvation, acidosis, liver cirrhosis, and severe illnesses like sepsis and acts as a substrate for alanine synthesis in the small intestine. Interactions among muscles and the liver, kidneys, and intestine ensuring optimal alanine and glutamine supply for gluconeogenesis are suggested.

Exogenous d ‐β‐hydroxybutyrate lowers blood glucose in part by decreasing the availability of L‐alanine for gluconeogenesis

Background

Interventions that induce ketosis simultaneously lower blood glucose and the explanation for this phenomenon is unknown. Additionally, the glucose‐lowering effect of acute ketosis is greater in people with type 2 diabetes (T2D). On the contrary, L‐alanine is a gluconeogenic substrate secreted by skeletal muscle at higher levels in people with T2D and infusing of ketones lower circulating L‐alanine blood levels. In this study, we sought to determine whether supplementation with L‐alanine would attenuate the glucose‐lowering effect of exogenous ketosis using a ketone ester (KE).

Methods

This crossover study involved 10 healthy human volunteers who fasted for 24 h prior to the ingestion of 25 g of d‐β‐hydroxybutyrate (βHB) in the form of a KE drink (ΔG^®) on two separate visits. During one of the visits, participants additionally ingested 2 g of L‐alanine to see whether L‐alanine supplementation would attenuate the glucose‐lowering effect of the KE drink. Blood L‐alanine, L‐glutamine, glucose, βHB, free fatty acids (FFA), lactate and C‐peptide were measured for 120 min after ingestion of the KE, with or without L‐alanine.

Findings

The KE drinks elevated blood βHB concentrations from negligible levels to 4.52 ± 1.23 mmol/L, lowered glucose from 4.97 ± SD 0.39 to 3.77 ± SD 0.40 mmol/L, and lowered and L‐alanine from 0.56 ± SD 0.88 to 0.41 ± SD 0.91 mmol/L. L‐alanine in the KE drink elevated blood L‐Alanine by 0.68 ± SD 0.15 mmol/L, but had no significant effect on blood βHB, L‐glutamine, FFA, lactate, nor C‐peptide concentrations. By contrast, L‐alanine supplementation significantly attenuated the ketosis‐induced drop in glucose from 28% ± SD 8% to 16% ± SD 7% (p < .01).

Conclusions

The glucose‐lowering effect of acutely elevated βHB is partially due to βHB decreasing L‐alanine availability as a substrate for gluconeogenesis.

Alpha-to-beta cell trans-differentiation for treatment of diabetes

Diabetes mellitus is a significant cause of morbidity and mortality in the United States and worldwide. According to the CDC, in 2017, ∼34.2 million of the American population had diabetes. Also, in 2017, diabetes was the seventh leading cause of death and has become the number one biomedical financial burden in the United States. Insulin replacement therapy and medications that increase insulin secretion and improve insulin sensitivity are the main therapies used to treat diabetes. Unfortunately, there is currently no radical cure for the different types of diabetes. Loss of β cell mass is the end result that leads to both type 1 and type 2 diabetes. In the past decade, there has been an increased effort to develop therapeutic strategies to replace the lost β cell mass and restore insulin secretion. α cells have recently become an attractive target for replacing the lost β cell mass, which could eventually be a potential strategy to cure diabetes. This review highlights the advantages of using α cells as a source for generating new β cells, the various investigative approaches to convert α cells into insulin-producing cells, and the future prospects and problems of this promising diabetes therapeutic strategy.

Sodium hydrosulfide has no additive effects on nitrite-inhibited renal gluconeogenesis in type 2 diabetic rats

OBJECTIVE

Increased renal and hepatic gluconeogenesis are important sources of fasting hyperglycemia in type 2 diabetes (T2D). The inhibitory effect of co-administration of sodium nitrite and sodium hydrosulfide (NaSH) on hepatic but not renal gluconeogenesis has been reported in rats with T2D. The present study aimed to determine the effects of co-administration of sodium nitrite and NaSH on the expression of genes involved in renal gluconeogenesis in rats with T2D.

METHODS

T2D was induced by a combination of a high-fat diet and low-dose streptozotocin (30 mg/kg). Male Wistar rats were divided into 5 groups (n = 6/group): Control, T2D, T2D + nitrite, T2D + NaSH, and T2D + nitrite+NaSH. Nitrite and NaSH were administered for nine weeks at a dose of 50 mg/L (in drinking water) and 0.28 mg/kg (daily intraperitoneal injection), respectively. Serum levels of urea and creatinine, and mRNA expressions of PEPCK, G6Pase, FBPase, PC, PI3K, AKT, PGC-1α, and FoxO1 in the renal tissue, were measured at the end of the study.

RESULTS

Nitrite decreased mRNA expression of PEPCK by 39%, G6Pase by 43%, FBPase by 41%, PC by 63%, PGC-1α by 45%, and FoxO1 by 27% in the renal tissue of rats with T2D; co-administration of nitrite and NaSH further decreases FoxO1, while had no additive effects on the tissue expression of the other genes. In addition, nitrite+NaSH decreased elevated serum urea levels by 58% and creatinine by 37% in rats with T2D.

CONCLUSION

The inhibitory effect of nitrite on gluconeogenesis in T2D rats is at least in part due to decreased mRNA expressions of renal gluconeogenic genes. Unlike effects on hepatic gluconeogenesis, co-administration of nitrite and NaSH has no additive effects on genes involved in renal gluconeogenesis in rats with T2D.

Ins and Outs of the TCA Cycle: The Central Role of Anaplerosis

The reactions of the tricarboxylic acid (TCA) cycle allow the controlled combustion of fat and carbohydrate. In principle, TCA cycle intermediates are regenerated on every turn and can facilitate the oxidation of an infinite number of nutrient molecules. However, TCA cycle intermediates can be lost to cataplerotic pathways that provide precursors for biosynthesis, and they must be replaced by anaplerotic pathways that regenerate these intermediates. Together, anaplerosis and cataplerosis help regulate rates of biosynthesis by dictating precursor supply, and they play underappreciated roles in catabolism and cellular energy status. They facilitate recycling pathways and nitrogen trafficking necessary for catabolism, and they influence redox state and oxidative capacity by altering TCA cycle intermediate concentrations. These functions vary widely by tissue and play emerging roles in disease. This article reviews the roles of anaplerosis and cataplerosis in various tissues and discusses how they alter carbon transitions, and highlights their contribution to mechanisms of disease. Expected final online publication date for the Annual Review of Nutrition, Volume 41 is September 2021. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Metabolic profile distinguishes laminitis-susceptible and -resistant ponies before and after feeding a high sugar diet

Background

Insulin dysregulation (ID) is a key risk factor for equine endocrinopathic laminitis, but in many cases ID can only be assessed accurately using dynamic tests. The identification of other biomarkers could provide an alternative or adjunct diagnostic method, to allow early intervention before laminitis develops. The present study characterised the metabolome of ponies with varying degrees of ID using basal and postprandial plasma samples obtained during a previous study, which examined the predictive power of blood insulin levels for the development of laminitis, in ponies fed a high-sugar diet. Samples from 10 pre-laminitic (PL – subsequently developed laminitis) and 10 non-laminitic (NL – did not develop laminitis) ponies were used in a targeted metabolomic assay. Differential concentration and pathway analysis were performed using linear models and global tests.

Results

Significant changes in the concentration of six glycerophospholipids (adj. P ≤ 0.024) and a global enrichment of the glucose-alanine cycle (adj. P = 0.048) were found to characterise the response of PL ponies to the high-sugar diet. In contrast, the metabolites showed no significant association with the presence or absence of pituitary pars intermedia dysfunction in all ponies.

Conclusions

The present results suggest that ID and laminitis risk are associated with alterations in the glycerophospholipid and glucose metabolism, which may help understand and explain some molecular processes causing or resulting from these conditions. The prognostic value of the identified biomarkers for laminitis remains to be investigated in further metabolomic trials in horses and ponies.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12917-021-02763-7.

S1P Signaling Pathways in Pathogenesis of Type 2 Diabetes

The pathogenesis of type 2 diabetes mellitus (T2DM) is very complicated. The currently well-accepted etiology is the "Ominous Octet" theory proposed by Professor Defronzo. Since presently used drugs for T2DM have limitations and harmful side effects, studies regarding alternative treatments are being conducted. Analyzing the pharmacological mechanism of biomolecules in view of pathogenesis is an effective way to assess new drugs. Sphingosine 1 phosphate (S1P), an endogenous lipid substance in the human body, has attracted increasing attention in the T2DM research field. This article reviews recent study updates of S1P, summarizing its effects on T2DM with respect to pathogenesis, promoting β cell proliferation and inhibiting apoptosis, reducing insulin resistance, protecting the liver and pancreas from lipotoxic damage, improving intestinal incretin effects, lowering basal glucagon levels, etc. With increasing research, S1P may help treat and prevent T2DM in the future.

Long-term co-administration of sodium nitrite and sodium hydrosulfide inhibits hepatic gluconeogenesis in male type 2 diabetic rats: Role of PI3K-Akt-eNOS pathway

OBJECTIVE

A deficiency in hydrogen sulfide (H₂S) and nitric oxide (NO) contributes to the development of type 2 diabetes (T2D). An inhibitory effect on liver gluconeogenesis has been reported in rats with T2D with co-administration of sodium nitrite and sodium hydrosulfide (NaSH); the underlying mechanisms have however not yet been elucidated. The aim of this study is to determine the long-term effects of co-administering sodium nitrite and NaSH on expression of genes involved in liver gluconeogenesis in rats with T2D.

METHODS

T2D was induced using a high fat diet combined with low-dose of streptozotocin (30 mg/kg). Rats were divided into 5 groups (n = 7/group): Control, T2D, T2D + nitrite, T2D + NaSH, and T2D + nitrite+NaSH. Nitrite (50 mg/L) and NaSH (0.28 mg/kg) were administered for 9 weeks. Intraperitoneal pyruvate tolerance test (PTT) was performed at the end of the ninth week and mRNA expressions of PI3K, Akt, eNOS, PEPCK, G6Pase, and FBPase were measured in the liver.

RESULTS

Co-administration of nitrite and NaSH decreased elevated serum glucose concentrations during PTT. Compared to T2D + nitrite, co-administration of nitrite and NaSH resulted in significant increases in mRNA expression of PI3K, Akt, and eNOS and significant decreases in mRNA expression of G6Pase and FBPase but had no effect on PEPCK expression.

CONCLUSION

Long-term NaSH administration at low-dose, potentiated the inhibitory effects of nitrite on mRNA expression of key liver gluconeogenic enzymes in rats with T2D. This inhibitory effect of nitrite and NaSH co-administration on gluconeogenesis were associated with increased gene expression of PI3K, Akt, and eNOS in the liver.

Tracking the carbons supplying gluconeogenesis

As the burden of type 2 diabetes mellitus (T2DM) grows in the 21st century, the need to understand glucose metabolism heightens. Increased gluconeogenesis is a major contributor to the hyperglycemia seen in T2DM. Isotope tracer experiments in humans and animals over several decades have offered insights into gluconeogenesis under euglycemic and diabetic conditions. This review focuses on the current understanding of carbon flux in gluconeogenesis, including substrate contribution of various gluconeogenic precursors to glucose production. Alterations of gluconeogenic metabolites and fluxes in T2DM are discussed. We also highlight ongoing knowledge gaps in the literature that require further investigation. A comprehensive analysis of gluconeogenesis may enable a better understanding of T2DM pathophysiology and identification of novel targets for treating hyperglycemia.

Metabolomics and correlation network analyses of core biomarkers in type 2 diabetes

The identification of metabolic pathways and the core metabolites provide novel molecular targets for the prevention and treatment of diseases. Diabetes is often accompanied with multiple metabolic disorders including hyperglycemia and dyslipidemia. Analysis of the variances of plasma metabolites is critical for identifying potential therapeutic targets for diabetes. In the current study, non-diabetic subjects with normal glucose tolerance and diabetics (age 40-60 years; n = 42 per group) were selected and plasma samples were analyzed by GC-MS for various metabolites profiling followed by network analysis. Our study identified 24 differential metabolites that were mainly enriched in protein synthesis, lipid and amino acid metabolism. Furthermore, we applied the correlation network analysis on these differential metabolites in fatty acid and amino acid metabolism and identified glycerol, alanine and serine as the hub metabolites in diabetic group. In addition, we measured the activities of enzymes in gluconeogenesis and amino acid metabolism and found significant higher activities of fructose 1,6-bisphosphatase, pyruvate carboxylase, lactate dehydrogenase, aspartate aminotransferase and alanine aminotransferase in diabetic patients. In contrast, the enzyme activities of glycolysis pathway (e.g., hexokinase, phosphofructokinase and pyruvate kinase) and TCA cycle (e.g., isocitrate dehydrogenase, succinate dehydrogenase, fumarate hydratase and malate dehydrogenase) were reduced in diabetes. Together, our studies showed that the linoleic acid and amino acid metabolism were the most affected metabolic pathways and glycerol, alanine and serine could play critical role in diabetes. The integration of network analysis and metabolic data could provide novel molecular targets or biomarkers for diabetes.

The effect of hyperlactatemia timing on the outcomes after cardiac surgery

Background

Several studies linked postoperative hyperlactatemia to worse outcomes in adult patients undergoing cardiac surgery. However, data on the effect of timing of hyperlactatemia on outcomes are scarce. We sought to determine the prevalence of early hyperlactatemia (EHL) and its impact on clinical outcomes compared to late hyperlactatemia (LHL) in patients undergoing ACS procedures.

Results

We included 305 consecutive adult patients who underwent cardiac surgery procedures between July 2017 and Nov 2019 at a single institution. Lactate level was measured in the first 10 h after surgery and EHL was defined as lactate level > 3 mmol/L in the first hour after surgery. Logistic regression analysis was performed to determine predictors of EHL. Seventeen percent (n = 52) had EH while 83% (n = 253) did not. Patients with EHL had significantly longer cardiopulmonary bypass (P = 0.001) and cross-clamp (P = 0.001) times due to increased surgical complexity in this group. Early hyperlactatemia was associated with increased post-operative extracorporeal membrane oxygenation (ECMO) support (0% vs 5.7%, P < 0.001), longer intensive care unit stay (P = 0.004), and increased hospital mortality (0% vs. 3.8%, P = 0.009). Cardiopulmonary bypass time (OR 1.001; 95% CI 1.011–1.012, P = 0.02) and glucose level (OR 1.2; 95% CI 1.1–1.3, P = 0.003) were independently associated with increased rate of EHL. In contrast, diabetes mellitus (OR 0.26; 95% CI 0.12–0.55, P < 0.001) significantly attenuated the rate of EHL.

Conclusions

Early hyperlactatemia after cardiac surgery was associated with increased morbidity and mortality. Late hyperlactatemia was very common and had a self-limiting and benign course.

Fundamentals about onset and progressive disease character of type 2 diabetes mellitus

ResearchGate is a world wide web for scientists and researchers to share papers, ask and answer questions, and find collaborators. As one of the more than 15 million members, the author uploads research output and reads and responds to some of the questions raised, which are related to type 2 diabetes. In that way, he noticed a serious gap of knowledge of this disease among medical professionals over recent decades. The main aim of the current study is to remedy this situation through providing a comprehensive review on recent developments in biochemistry and molecular biology, which can be helpful for the scientific understanding of the molecular nature of type 2 diabetes. To fill up the shortcomings in the curricula of medical education, and to familiarize the medical community with a new concept of the onset of type 2 diabetes, items are discussed like: Insulin resistance, glucose effectiveness, insulin sensitivity, cell membranes, membrane flexibility, unsaturation index (UI; number of carbon-carbon double bonds per 100 acyl chains of membrane phospholipids), slow-down principle, effects of temperature acclimation on phospholipid membrane composition, free fatty acids, energy transport, onset of type 2 diabetes, metformin, and exercise. Based on the reviewed data, a new model is presented with proposed steps in the development of type 2 diabetes, a disease arising as a result of a hypothetical hereditary anomaly, which causes hyperthermia in and around the mitochondria. Hyperthermia is counterbalanced by the slow-down principle, which lowers the amount of carbon-carbon double bonds of membrane phospholipid acyl chains. The accompanying reduction in the UI lowers membrane flexibility, promotes a redistribution of the lateral pressure in cell membranes, and thereby reduces the glucose transporter protein pore diameter of the transmembrane glucose transport channel of all Class I GLUT proteins. These events will set up a reduction in transmembrane glucose transport. So, a new blood glucose regulation system, effective in type 2 diabetes and its prediabetic phase, is based on variations in the acyl composition of phospholipids and operates independent of changes in insulin and glucose concentration. UI assessment is currently arising as a promising analytical technology for a membrane flexibility analysis. An increase in mitochondrial heat production plays a pivotal role in the existence of this regulation system.

The Metformin Paradox

INTRODUCTION

The Diabetes Prevention Program study results indicated that metformin therapy was not as beneficial as a lifestyle modification for delaying the development of type 2 diabetes in individuals at high risk of the disease. A key feature in the etiology of type 2 diabetes mellitus, which appears in the prediabetic phase, is a significant deficiency, compared to healthy controls, in highly flexible poly-cis-unsaturated fatty acyl chains in membrane phospholipids. This deficiency lowers membrane flexibility, which in turn, reduces the amount of all functional Class I glucose transporters, and thereby reduces glucose-mediated ATP production. This leads to an increase in essentially saturated free fatty acid (FFA) levels for fatty-acid-mediated ATP production, which will set up a vicious cycle of raising the levels of essentially saturated FFAs and lowering the level of transmembrane glucose transport. Metformin suppresses hepatic gluconeogenesis, which reduces the plasma glucose concentration.

CONCLUSION

We hypothesize that chronic metformin treatment leads to an additional increase in essentially saturated FFAs, which causes an additional rise in membrane stiffness and hypoxia. So we propose that all these metformin-mediated activities accelerated the onset of type 2 diabetes in the participants of the metformin group in the Diabetes Prevention Program study, compared to the participants of the lifestyle-intervention group in this study. We propose that the biochemical reactions, involved in the fatty-acid-mediated ATP production, play an important part in the increase of the observed essentially saturated FFA concentrations. These statements should also extend to the metformin therapy of individuals with type 2 diabetes.

Roux-en-Y gastric bypass surgery restores insulin-mediated glucose partitioning and mitochondrial dynamics in primary myotubes from severely obese humans

Background/Objectives:

Impaired insulin-mediated glucose partitioning is an intrinsic metabolic defect in skeletal muscle from severely obese humans (BMI ≥ 40 kg/m²). Roux-en-Y gastric bypass (RYGB) surgery has been shown to improve glucose metabolism in severely obese humans. The purpose of the study was to determine the effects of RYGB surgery on glucose partitioning, mitochondrial network morphology, and markers of mitochondrial dynamics skeletal muscle from severely obese humans.

Subject/Methods:

Human skeletal muscle cells were isolated from muscle biopsies obtained from RYGB patients (BMI = 48.0 ± 2.1, n=7) prior to, 1-month and 7-months following surgery and lean control subjects (BMI = 22.4 ± 1.1, n=7). Complete glucose oxidation, non-oxidized glycolysis rates, mitochondrial respiratory capacity, mitochondrial network morphology and regulatory proteins of mitochondrial dynamics were determined in differentiated human myotubes.

Results:

Myotubes derived from severely obese humans exhibited enhanced glucose oxidation (13.5%; 95%CI [7.6, 19.4], P = 0.043) and reduced non-oxidized glycolysis (−1.3%; 95%CI [−11.1, 8.6]) in response to insulin stimulation at 7-months after RYGB when compared to the pre-surgery state (−0.6%; 95%CI [−5.2, 4.0] and 19.5%; 95%CI [4.0, 35.0], P =0.006), and were not different from the lean controls (16.7%; 95%CI [11.8, 21.5] and 1.9%; 95%CI [−1.6, 5.4], respectively). Further, number of fragmented mitochondria and Drp1(Ser⁶¹⁶) phosphorylation and were trended to reduced/reduced (0.0104, 95%CI [0.0085, 0.0126], P = 0.091 and 0.0085, 95%CI [0.0068, 0.0102], P = 0.05) in myotubes derived from severely obese humans at 7-months after RYGB surgery in comparison to the pre-surgery state. Finally, Drp1(Ser⁶¹⁶) phosphorylation was negatively correlated with insulin-stimulated glucose oxidation (r = −0.49, P = 0.037).

Conclusion/Interpretation:

These data indicate that an intrinsic metabolic defect of glucose partitioning in skeletal muscle from severely obese humans is restored by RYGB surgery. The restoration of glucose partitioning may be regulated through reduced mitochondrial fission protein Drp1 phosphorylation.

Pyruvate-Carboxylase-Mediated Anaplerosis Promotes Antioxidant Capacity by Sustaining TCA Cycle and Redox Metabolism in Liver

The hepatic TCA cycle supports oxidative and biosynthetic metabolism. This dual responsibility requires anaplerotic pathways, such as pyruvate carboxylase (PC), to generate TCA cycle intermediates necessary for biosynthesis without disrupting oxidative metabolism. Liver-specific PC knockout (LPCKO) mice were created to test the role of anaplerotic flux in liver metabolism. LPCKO mice have impaired hepatic anaplerosis, diminution of TCA cycle intermediates, suppressed gluconeogenesis, reduced TCA cycle flux, and a compensatory increase in ketogenesis and renal gluconeogenesis. Loss of PC depleted aspartate and compromised urea cycle function, causing elevated urea cycle intermediates and hyperammonemia. Loss of PC prevented diet-induced hyperglycemia and insulin resistance but depleted NADPH and glutathione, which exacerbated oxidative stress and correlated with elevated liver inflammation. Thus, despite catalyzing the synthesis of intermediates also produced by other anaplerotic pathways, PC is specifically necessary for maintaining oxidation, biosynthesis, and pathways distal to the TCA cycle, such as antioxidant defenses.

Brain insulin action in schizophrenia: Something borrowed and something new

Insulin signaling in the central nervous system is at the intersection of brain and body interactions, and represents a fundamental link between metabolic and cognitive disorders. Abnormalities in brain insulin action could underlie the development of comorbid schizophrenia and type 2 diabetes. Among its functions, central nervous system insulin is involved in regulation of striatal dopamine levels, peripheral glucose homeostasis, and feeding regulation. In this review, we discuss the role and importance of central nervous system insulin in schizophrenia and diabetes pathogenesis from a historical and mechanistic perspective. We describe central nervous system insulin sites and pathways of action, with special emphasis on glucose metabolism, cognitive functioning, inflammation, and food preferences. Finally, we suggest possible mechanisms that may explain the actions of central nervous system insulin in relation to schizophrenia and diabetes, focusing on glutamate and dopamine signaling, intracellular signal transduction pathways, and brain energetics. Understanding the interplay between central nervous system insulin and schizophrenia is essential to disentangling this comorbid relationship and may provide novel treatment approaches for both neuropsychiatric and metabolic dysfunction. This article is part of the issue entitled 'Special Issue on Antipsychotics'.

Changes in hepatic metabolic profile during the evolution of STZ-induced diabetic rats via an 1H NMR-based metabonomic investigation

Background: The present study aimed to explore the changes in the hepatic metabolic profile during the evolution of diabetes mellitus (DM) and verify the key metabolic pathways. Methods: Liver samples were collected from diabetic rats induced by streptozotocin (STZ) and rats in the control group at 1, 5, and 9 weeks after STZ administration. Proton nuclear magnetic resonance spectroscopy (¹H NMR)-based metabolomics was used to examine the metabolic changes during the evolution of DM, and partial least squares-discriminate analysis (PLS-DA) was performed to identify the key metabolites. Results: We identified 40 metabolites in the ¹H NMR spectra, and 11 metabolites were further selected by PLS-DA model. The levels of α-glucose and β-glucose, which are two energy-related metabolites, gradually increased over time in the DM rats, and were significantly greater than those of the control rats at the three-time points. The levels of choline, betaine, and methionine decreased in the DM livers, indicating that the protective function in response to liver injury may be undermined by hyperglycemia. The levels of the other amino acids (leucine, alanine, glycine, tyrosine, and phenylalanine) were significantly less than those of the control group during DM development. Conclusions: Our results suggested that the hepatic metabolic pathways of glucose, choline-betaine-methionine, and amino acids were disturbed during the evolution of diabetes, and that choline-betaine-methionine metabolism may play a key role.

Altered tricarboxylic acid cycle flux in primary myotubes from severely obese humans

BACKGROUND/OBJECTIVE

The partitioning of glucose toward glycolytic end products rather than glucose oxidation and glycogen storage is evident in skeletal muscle with severe obesity and type 2 diabetes. The purpose of the present study was to determine the possible mechanism by which severe obesity alters insulin-mediated glucose partitioning in human skeletal muscle.

SUBJECTS/METHODS

Primary human skeletal muscle cells (HSkMC) were isolated from lean (BMI = 23.6 ± 2.6 kg/m2, n = 9) and severely obese (BMI = 48.8 ± 1.9 kg/m2, n = 8) female subjects. Glucose oxidation, glycogen synthesis, non-oxidized glycolysis, pyruvate oxidation, and targeted TCA cycle metabolomics were examined in differentiated myotubes under basal and insulin-stimulated conditions.

RESULTS

Myotubes derived from severely obese subjects exhibited attenuated response of glycogen synthesis (20.3%; 95% CI [4.7, 28.8]; P = 0.017) and glucose oxidation (5.6%; 95% CI [0.3, 8.6]; P = 0.046) with a concomitant greater increase (23.8%; 95% CI [5.7, 47.8]; P = 0.004) in non-oxidized glycolytic end products with insulin stimulation in comparison to the lean group (34.2% [24.9, 45.1]; 13.1% [8.6, 16.4], and 2.9% [-4.1, 12.2], respectively). These obesity-related alterations in glucose partitioning appeared to be linked with reduced TCA cycle flux, as 2-[14C]-pyruvate oxidation (358.4 pmol/mg protein/min [303.7, 432.9] vs. lean 439.2 pmol/mg protein/min [393.6, 463.1]; P = 0.013) along with several TCA cycle intermediates, were suppressed in the skeletal muscle of severely obese individuals.

CONCLUSIONS

These data suggest that with severe obesity the partitioning of glucose toward anaerobic glycolysis in response to insulin is a resilient characteristic of human skeletal muscle. This altered glucose partitioning appeared to be due, at least in part, to a reduction in TCA cycle flux.

Treatment approach to type 2 diabetes: Past, present and future

Type 2 diabetes mellitus (DM) is a lifelong metabolic disease, characterized by hyperglycaemia which gradually leads to the development and progression of vascular complications. It is recognized as a global burden disease, with substantial consequences on human health (fatality) as well as on health-care system costs. This review focuses on the topic of historical discovery and understanding the complexity of the disease in the field of pathophysiology, as well as development of the pharmacotherapy beyond insulin. The complex interplay of insulin secretion and insulin resistance developed from previously known "ominous triumvirate" to "ominous octet" indicate the implication of multiple organs in glucose metabolism. The pharmacological approach has progressed from biguanides to a wide spectrum of medications that seem to provide a beneficial effect on the cardiovascular system. Despite this, we are still not achieving the target treatment goals. Thus, the future should bring novel antidiabetic drug classes capable of acting on several levels simultaneously. In conclusion, given the raising burden of type 2 DM, the best present strategy that could contribute the most to the reduction of morbidity and mortality should be focused on primary prevention.

Involvement of AMPK activation in the inhibition of hepatic gluconeogenesis by Ficus carica leaf extract in diabetic mice and HepG2 cells

The aim of this study was to explore the possible mechanisms of Ficus carica leaf (FCL) extract in suppressing hepatic gluconeogenesis in diabetic mice. Diabetic mice (streptozotocin-induced) received 1 g/kg of FCL extract twice a day for 6 weeks. Fasting blood glucose levels were measured and a 2-h oral glucose tolerance test was conducted. AMP-activated protein kinase (AMPK), phosphoenolpyruvate carboxykinase (PEPCK), glucose-6-phosphatase (G6Pase), and peroxisome proliferator activated receptor-γ coactivator-1α (PGC-1α) expression was examined. HepG2 hepatocytes were treated with FCL extract and an AMPK inhibitor (compound C) or agonist (AICAR), and PEPCK, G6pase, PGC-1α, AMPK, forkhead transcription factor O1 (FOXO1), and hepatic nuclear factor 4α (HNF4α) expression was determined. The results showed that FCL extract inhibited the expression of PEPCK and G6Pase in the liver of diabetic mice and HepG2 hepatocytes. FCL extract activated AMPK and decreased PGC-1α, HNF4α, and FOXO1 expression. The AMPK inhibitor attenuated those effects through inhibiting gluconeogenesis, while the AMPK agonist partially enhanced gluconeogenesis. In conclusion, FCL extract inhibits hepatic gluconeogenesis via activation of AMPK and down-regulation of gluconeogenic enzymes.

Energy metabolism of white adipose tissue and insulin resistance in humans

BACKGROUND

Insulin resistance not only occurs in obesity, but also in lipodystrophy. Although adipose tissue mass affects metabolic fluxes and participates in interorgan crosstalk, the role of energy metabolism within white adipose tissue for insulin resistance is less clear.

MATERIALS AND METHODS

A Medline search identified in vivo studies in humans on energy and lipid metabolism in subcutaneous (SAT) and visceral adipose tissue (VAT). Studies in adipocyte cultures and transgenic animal models were included for the better understanding of the link between abnormal energy metabolism in adipose tissue and insulin resistance.

RESULTS

The current literature indicates that higher lipolysis and lower lipogenesis in VAT compared to SAT enhance portal delivery of lipid metabolites (glycerol and fatty acids) to the liver. Thus, the lower lipolysis and higher lipogenesis in SAT favour storage of excess lipids and allow for protection of insulin-sensitive tissues from lipotoxic effects. In insulin-resistant humans, enhanced lipolysis and impaired lipogenesis in adipose tissue lead to release of cytokines and lipid metabolites, ultimately promoting insulin resistance. Adipose tissue of insulin-resistant humans also displays lower expression of proteins involved in mitochondrial function. In turn, this leads to lower availability of mitochondria-derived energy sources for lipogenesis in adipose tissue.

CONCLUSIONS

Abnormal mitochondrial function in human white adipose tissue likely contributes to the secretion of lipid metabolites and lactate, which are linked to insulin resistance in peripheral tissues. However, the relevance of adipose tissue energy metabolism for the regulation of human insulin sensitivity remains to be further elucidated.

Effect of Progressive Weight Loss on Lactate Metabolism: A Randomized Controlled Trial

OBJECTIVE

Lactate is an intermediate of glucose metabolism that has been implicated in the pathogenesis of insulin resistance. This study evaluated the relationship between glucose kinetics and plasma lactate concentration ([LAC]) before and after manipulating insulin sensitivity by progressive weight loss.

METHODS

Forty people with obesity (BMI = 37.9 ± 4.3 kg/m2 ) were randomized to weight maintenance (n = 14) or weight loss (n = 19). Subjects were studied before and after 6 months of weight maintenance and before and after 5%, 11%, and 16% weight loss. A hyperinsulinemic-euglycemic clamp procedure in conjunction with [6,6-2 H2 ]glucose tracer infusion was used to assess glucose kinetics.

RESULTS

At baseline, fasting [LAC] correlated positively with endogenous glucose production rate (r = 0.532; P = 0.001) and negatively with insulin sensitivity, assessed as the insulin-stimulated glucose disposal (r = -0.361; P = 0.04). Progressive (5% through 16%) weight loss caused a progressive decrease in fasting [LAC], and the decrease in fasting [LAC] after 5% weight loss was correlated with the decrease in endogenous glucose production (r = 0.654; P = 0.002) and the increase in insulin sensitivity (r = -0.595; P = 0.007).

CONCLUSIONS

This study demonstrates the interrelationships among weight loss, hepatic and muscle glucose kinetics, insulin sensitivity, and [LAC], and it suggests that [LAC] can serve as an additional biomarker of glucose-related insulin resistance.

GLP-1 receptor agonist ameliorates obesity-induced chronic kidney injury via restoring renal metabolism homeostasis

Increasing evidence indicates that obesity is highly associated with chronic kidney disease (CKD). GLP-1 receptor (GLP-1R) agonist has shown benefits on kidney diseases, but its direct role on kidney metabolism in obesity is still not clear. This study aims to investigate the protection and metabolic modulation role of liraglutide (Lira) on kidney of obesity. Rats were induced obese by high-fat diet (HFD), and renal function and metabolism changes were evaluated by metabolomic, biological and histological methods. HFD rats exhibited systemic metabolic disorders such as obesity, hyperlipidemia and impaired glucose tolerance, as well as renal histological and function damages, while Lira significantly ameliorated these adverse effects in HFD rats. Metabolomic data showed that Lira directly reduced renal lipids including fatty acid residues, cholesterol, phospholipids and triglycerides, and improved mitochondria metabolites such as succinate, citrate, taurine, fumarate and nicotinamide adenine dinucleotide (NAD+) in the kidney of HFD rats. Furthermore, we revealed that Lira inhibited renal lipid accumulation by coordinating lipogenic and lipolytic signals, and partly rescued renal mitochondria function via Sirt1/AMPK/PGC1α pathways in HFD rats. This study suggested that Lira alleviated HFD-induced kidney injury at least partly via directly restoring renal metabolism, thus GLP-1R agonist is a promising therapy for obesity-associated CKD.

Diabetes Is Associated With Reduced Stress Hyperlactatemia in Cardiac Surgery

OBJECTIVE

Hyperglycemia and hyperlactatemia are associated with increased morbidity and mortality in critical illness. We evaluated the relationship among hyperlactatemia, glycemic control, and diabetes mellitus (DM) after cardiac surgery.

RESEARCH DESIGN AND METHODS

This was a retrospective cohort study of 4,098 cardiac surgery patients treated between 2011 and 2015. Patients were stratified by DM and glucose-lowering medication history. Hyperglycemia (glucose >180 mg/dL), hypoglycemia (<70 mg/dL), and the hyperglycemic index were assessed postoperatively (48 h). The relationship between lactate and glucose levels was modeled using generalized linear regression. Mortality was analyzed using an extended Cox regression model.

RESULTS

Hyperglycemia occurred in 26.0% of patients without DM (NODM), 46.5% with DM without prior drug treatment (DMNT), 62.8% on oral medication (DMOM), and 73.8% on insulin therapy (DMIT) (P < 0.0001). Hypoglycemia occurred in 6.3%, 9.1%, 8.8%, and 10.8% of NODM, DMNT, DMOM, and DMIT, respectively (P = 0.0012). The lactate levels of all patients were temporarily increased with surgery. This increase was greater in patients who also had hyperglycemia or hypoglycemia and was markedly attenuated in patients with DM. Peak lactate was 5.8 mmol/L (95% CI 5.6, 6.0) in NODM with hyperglycemia vs. 3.3 (95% CI 3.2, 3.4) without hyperglycemia; in DMNT: 4.8 (95% CI 4.4, 5.2) vs. 3.4 (95% CI 3.1, 3.6); in DMOM: 3.8 (95% CI 3.5, 4.1) vs. 2.9 (95% CI 2.7, 3.1); and in DMIT: 3.3 (95% CI 3.0, 3.5) vs. 2.7 (95% CI 2.3, 3.0). Increasing lactate levels were associated with increasing mortality; increasing glucose reduced this effect in DM but not in NODM (P = 0.0069 for three-way interaction).

CONCLUSIONS

Stress hyperlactatemia is markedly attenuated in patients with DM. There is a three-way interaction among DM, stress hyperlactatemia, and stress hyperglycemia associated with mortality after cardiac surgery.

Nutrition from the Inside Out

Nearly 50 years ago, I set out to investigate the clinical problem of hypoglycemia in children with illnesses that limited their food intake. My goal was to gather accurate and precise measurable data. At the time, I wasn't interested in nutrition as a discipline defined in its more general or popular sense. To address the specific problem that interested me required development of entirely new methods based on stable, nonradioactive tracers that satisfied the conditions of accuracy and precision. At the time, I had no inclination of the various theoretical and practical problems that would have to be solved to achieve this goal. Some are briefly described here. Nor did I have the slightest idea that developing the field would result in a fundamental change in how human clinical investigation was conducted, with the eventual replacement of radiotracers with stable isotopically labeled ones, even for adult clinical investigation. Additionally, I had no inclination that the original questions would open avenues to much broader questions of practical nutritional relevance. Moreover, only much later as the editor of The American Journal of Clinical Nutrition did I appreciate the policy implications of how nutritional data are presented in the scientific literature. At least in part, less accurate and precise measurements and less than full transparency in reporting nutritional data have resulted in widespread debate about the public policy recommendations and guidelines that are the intended result of collecting the data in the first place. This article provides a personal recollection (with all the known faults of self-reporting and retrospective memory) of the journey that starts with measurement certainty and ends with policy uncertainty.

Exercise timing and blood lactate concentrations in individuals with type 2 diabetes

The purpose of this study was to characterize how resistance exercise prior to or after a meal alters fasting and postprandial blood lactate concentrations in individuals with type 2 diabetes. Obese individuals with type 2 diabetes (N = 12) completed three 2-day trials, including (i) no exercise (NoEx), (ii) resistance exercise prior to dinner (Ex-M), and (iii) resistance exercise beginning at 45 min postdinner (M-Ex). During day 1 of each trial, fasting and postprandial blood lactate concentrations, perceived exertion, and substrate oxidation were measured, and subsequently on day 2 the following morning fasting blood lactate was measured. The premeal lactate incremental area under the curve (iAUC) during Ex-M (109 ± 66 mmol·L−1·1.6 h−1) was over 100-fold greater (P < 0.01) compared with NoEx (−15 ± 24 mmol·L−1·1.6 h−1) and M-Ex (−2 ± 18 mmol·L−1·1.6 h−1). The postprandial lactate iAUC during M-Ex (304 ± 116 mmol·L−1·4 h−1) was over 2-fold greater (P < 0.01) compared with NoEx (149 ± 74 mmol·L−1·4 h−1) and Ex-M (−140 ± 196 mmol·L−1·4 h−1). Average lactate during exercise was ∼45% greater (P = 0.03) during M-Ex (3.2 ± 0.9 mmol/L) compared with Ex-M (2.2 ± 0.9 mmol/L), but the change in lactate during Ex-M (2.4 ± 1.6 mmol/L) or M-Ex (2.3 ± 1.3 mmol/L) was not different (P > 0.05). Perceived exertion, substrate oxidation, or fasting blood lactate concentrations the day after testing were not different between trials. Blood lactate concentrations during acute resistance exercise are greater when exercise is performed in the postprandial period. Acute resistance exercise performed the night prior does not alter fasting blood lactate concentrations the following morning.

Optimal nutrition and the ever-changing dietary landscape: a conference report

The field of nutrition has evolved rapidly over the past century. Nutrition scientists and policy makers in the developed world have shifted the focus of their efforts from dealing with diseases of overt nutrient deficiency to a new paradigm aimed at coping with conditions of excess-calories, sedentary lifestyles and stress. Advances in nutrition science, technology and manufacturing have largely eradicated nutrient deficiency diseases, while simultaneously facing the growing challenges of obesity, non-communicable diseases and aging. Nutrition research has gone through a necessary evolution, starting with a reductionist approach, driven by an ambition to understand the mechanisms responsible for the effects of individual nutrients at the cellular and molecular levels. This approach has appropriately expanded in recent years to become more holistic with the aim of understanding the role of nutrition in the broader context of dietary patterns. Ultimately, this approach will culminate in a full understanding of the dietary landscape-a web of interactions between nutritional, dietary, social, behavioral and environmental factors-and how it impacts health maintenance and promotion.

Simultaneous in vivo assessment of cardiac and hepatic metabolism in the diabetic rat using hyperpolarized MRS

Understanding and assessing diabetic metabolism is vital for monitoring disease progression and improving treatment of patients. In vivo assessments, using MRI and MRS, provide non-invasive and accurate measurements, and the development of hyperpolarized ¹³ C spectroscopy in particular has been demonstrated to provide valuable metabolic data in real time. Until now, studies have focussed on individual organs. However, diabetes is a systemic disease affecting multiple tissues in the body. Therefore, we have developed a technique to simultaneously measure metabolism in both the heart and liver during a single acquisition. A hyperpolarized ¹³ C MRS protocol was developed to allow acquisition of metabolic data from the heart and liver during a single scan. This protocol was subsequently used to assess metabolism in the heart and liver of seven control male Wistar rats and seven diabetic rats (diabetes was induced by three weeks of high-fat feeding and a 30 mg/kg injection of streptozotocin). Using our new acquisition, we observed decreased cardiac and hepatic pyruvate dehydrogenase flux in our diabetic rat model. These diabetic rats also had increased blood glucose levels, decreased insulin, and increased hepatic triglycerides. Decreased production of hepatic [1-¹³ C]alanine was observed in the diabetic group, but this change was not present in the hearts of the same diabetic animals. We have demonstrated the ability to measure cardiac and hepatic metabolism simultaneously, with sufficient sensitivity to detect metabolic alterations in both organs. Further, we have non-invasively observed the different reactions of the heart and liver to the metabolic challenge of diabetes.

Metabolic Profiling of Total Physical Activity and Sedentary Behavior in Community-Dwelling Men

Objective

Physical activity is known to be preventive against various non-communicable diseases. We investigated the relationship between daily physical activity level and plasma metabolites using a targeted metabolomics approach in a population-based study.

Methods

A total of 1,193 participants (male, aged 35 to 74 years) with fasting blood samples were selected from the baseline survey of a cohort study. Information on daily total physical activity, classified into four levels by quartile of metabolic equivalent scores, and sedentary behavior, defined as hours of sitting per day, was collected through a self-administered questionnaire. Plasma metabolite concentrations were quantified by capillary electrophoresis mass spectrometry method. We performed linear regression analysis models with multivariable adjustment and corrected p-values for multiple testing in the original population (n = 808). The robustness of the results was confirmed by replication analysis in a separate population (n = 385) created by random allocation.

Results

Higher levels of total physical activity were associated with various metabolite concentrations, including lower concentrations of amino acids and their derivatives, and higher concentrations of pipecolate (FDR p <0.05 in original population). The findings persisted after adjustment for age, body mass index, smoking, alcohol intake, and energy intake. Isoleucine, leucine, valine, 4-methyl-2-oxoisopentanoate, 2-oxoisopentanoate, alanine, and proline concentrations were lower with a shorter sitting time.

Conclusions

Physical activity is related to various plasma metabolites, including known biomarkers for future insulin resistance or type 2 diabetes. These metabolites might potentially play a key role in the protective effects of higher physical activity and/or less sedentary behavior on non-communicable diseases.

Oxamate Improves Glycemic Control and Insulin Sensitivity via Inhibition of Tissue Lactate Production in db/db Mice

Oxamate (OXA) is a pyruvate analogue that directly inhibits the lactate dehydrogenase (LDH)-catalyzed conversion process of pyruvate into lactate. Earlier and recent studies have shown elevated blood lactate levels among insulin-resistant and type 2 diabetes subjects and that blood lactate levels independently predicted the development of incident diabetes. To explore the potential of OXA in the treatment of diabetes, db/db mice were treated with OXA in vivo. Treatment of OXA (350–750 mg/kg of body weight) for 12 weeks was shown to decrease body weight gain and blood glucose and HbA1c levels and improve insulin secretion, the morphology of pancreatic islets, and insulin sensitivity in db/db mice. Meanwhile, OXA reduced the lactate production of adipose tissue and skeletal muscle and serum lactate levels and decreased serum levels of TG, FFA, CRP, IL-6, and TNF-α in db/db mice. The PCR array showed that OXA downregulated the expression of Tnf, Il6, leptin, Cxcr3, Map2k1, and Ikbkb, and upregulated the expression of Irs2, Nfkbia, and Pde3b in the skeletal muscle of db/db mice. Interestingly, LDH-A expression increased in the islet cells of db/db mice, and both treatment of OXA and pioglitazone decreased LDH-A expression, which might be related to the improvement of insulin secretion. Taken together, increased lactate production of adipose tissue and skeletal muscle may be at least partially responsible for insulin resistance and diabetes in db/db mice. OXA improved glycemic control and insulin sensitivity in db/db mice primarily via inhibition of tissue lactate production. Oxamic acid derivatives may be a potential drug for the treatment of type 2 diabetes.

Measurements of Gluconeogenesis and Glycogenolysis: A Methodological Review

Gluconeogenesis is a complex metabolic process that involves multiple enzymatic steps regulated by myriad factors, including substrate concentrations, the redox state, activation and inhibition of specific enzyme steps, and hormonal modulation. At present, the most widely accepted technique to determine gluconeogenesis is by measuring the incorporation of deuterium from the body water pool into newly formed glucose. However, several techniques using radioactive and stable-labeled isotopes have been used to quantitate the contribution and regulation of gluconeogenesis in humans. Each method has its advantages, methodological assumptions, and set of propagated errors. In this review, we examine the strengths and weaknesses of the most commonly used stable isotopes methods to measure gluconeogenesis in vivo. We discuss the advantages and limitations of each method and summarize the applicability of these measurements in understanding normal and pathophysiological conditions.

Hyperlactatemia in type 2 diabetes: Can physical training help?

Type 2 diabetic patients often exhibit hyperlactatemia in association with a reduced aerobic-oxidative capacity and a restricted lactate transport. Studies suggest a link between increased lactate levels and the manifestation and progression of insulin resistance. However, the specificities of molecular mechanisms remain unclear, and it is not entirely clear whether elevated lactate levels are a cause or consequence of type 2 diabetes. This review focuses on lactate as a key molecule in diabetes and provides an overview of how regular physical activity can be helpful in normalizing elevated lactate levels in type 2 diabetic patients. Physical training may reduce lactate production and reinforce lactate transport and clearance among this particular patient group. We emphasize the crucial role physical training plays in the therapy of type 2 diabetes due to evidence that pharmacological treatment with metformin, which is commonly used in the first-line therapy of type 2 diabetes, does not help reducing lactate levels.

Increased gluconeogenesis in youth with newly diagnosed type 2 diabetes

AIMS/HYPOTHESIS

The role of increased gluconeogenesis as an important contributor to fasting hyperglycaemia at diabetes onset is not known. We evaluated the contribution of gluconeogenesis and glycogenolysis to fasting hyperglycaemia in newly diagnosed youths with type 2 diabetes following an overnight fast.

METHODS

Basal rates (μmol kg(FFM) (-1) min(-1)) of gluconeogenesis ((2)H2O), glycogenolysis and glycerol production ([(2)H5] glycerol) were measured in 18 adolescents (nine treatment naive diabetic and nine normal-glucose-tolerant obese adolescents).

RESULTS

Type 2 diabetes was associated with higher gluconeogenesis (9.2 ± 0.6 vs 7.0 ± 0.3 μmol kg(FFM) (-1) min(-1), p < 0.01), plasma fasting glucose (7.0 ± 0.6 vs 5.0 ± 0.2 mmol/l, p = 0.004) and insulin (300 ± 30 vs 126 ± 31 pmol/l, p = 0.001). Glucose production and glycogenolysis were similar between the groups (15.4 ± 0.3 vs 12.4 ± 1.4 μmol kg(FFM) (-1) min(-1), p = 0.06; and 6.2 ± 0.8 vs 5.3 ± 0.7 μmol kg(FFM) (-1) min(-1), p = 0.5, respectively). After controlling for differences in adiposity, gluconeogenesis, glycogenolysis and glucose production were higher in diabetic youth (p ≤ 0.02). Glycerol concentration (84 ± 6 vs 57 ± 6 μmol/l, p = 0.01) and glycerol production (5.0 ± 0.3 vs 3.6 ± 0.5 μmol kg(FFM) (-1) min(-1), p = 0.03) were 40% higher in youth with diabetes. The increased glycerol production could account for only ~1/3 of substrate needed for the increased gluconeogenesis in diabetic youth.

CONCLUSION/INTERPRETATIONS

Increased gluconeogenesis was a major contributor to fasting hyperglycaemia and hepatic insulin resistance in newly diagnosed untreated adolescents and was an early pathological feature of type 2 diabetes. Increased glycerol availability may represent a significant source of new carbon substrates for increased gluconeogenesis but would not account for all the carbons required to sustain the increased rates.

The effect of high-fat diet and streptozotocin-induced diabetes and endurance training on plasma levels of calcitonin gene-related peptide and lactate in rats

OBJECTIVE

The aim of this study was to investigate the effect of type 2 diabetes induced by high-fat diet and streptozotocin, and the effect of endurance training on basal circulating levels of calcitonin gene-related peptide (CGRP) and lactate.

METHODS

Male Wistar rats were randomly divided into 4 groups: 1) control (n=8); 2) trained (n=8); 3) diabetic (n=8) and 4) trained diabetic (n=8). At the age of 7 weeks, diabetes was induced by feeding the animals a high-fat diet and injecting them with a low dose of streptozotocin (35 mg/kg). The animals at 10 weeks of age underwent an endurance training protocol on a treadmill for 7 weeks. Plasma lactate concentrations were measured by a lactate assay kit, and an enzyme immunoassay kit was used to measure CGRP.

RESULTS

The diabetic rats showed significant increases in plasma CGRP (3.0±1 ng/mL vs. 0.5±0.3 ng/mL, p<0.001) and plasma lactate levels (3.6±0.5 mmol/L vs. 1.3±0.5 mmol/L, p<0.001). Further, significant decrease in basal plasma lactate (2.6±0.5 mmol/L vs. 3.6±0.5 mmol/L, p<0.025) but not plasma CGRP levels (2.5±1.2 ng/mL vs. 3.0±1.3 ng/mL) were found in the diabetic subjects after the endurance training.

CONCLUSIONS

The results showed that endurance training could modify the basal circulating levels of lactate but not CGRP, which were elevated in this model of type 2 diabetic rats, indicating the lack of correspondence between the endurance training-induced changes of lactate and CGRP in this model of diabetes.

Simulated games activity vs continuous running exercise: a novel comparison of the glycemic and metabolic responses in T1DM patients

To compare the glycemic and metabolic responses to simulated intermittent games activity and continuous running exercise in type 1 diabetes. Nine patients (seven male, two female; 35 ± 4 years; HbA1c 8.1 ± 0.2%/65 ± 2 mmol/mol) treated on a basal-bolus regimen completed two main trials, a continuous treadmill run (CON) or an intermittent running protocol (INT). Patients arrived to the laboratory fasted at ∼ 08:00 h, replicating their usual pre-exercise meal and administering a 50% reduced dose of rapid-acting insulin before exercising. Blood glucose (BG), K(+) , Na(++) , pH, triglycerides, serum cortisol and NEFA were measured at baseline and for 60 min post-exercise. Interstitial glucose was measured for a further 23 h under free-living conditions. Following exercise, BG declined under both conditions but was less under INT (INT -1.1 ± 1.4 vs CON -5.3 ± 0.4 mmol/L, P = 0.037), meaning more patients experienced hypoglycemia (BG ≤ 3.5 mmol/L; CON n = 3 vs INT n = 2) but less hyperglycemia (BG ≥ 10.9 mmol/L; CON n = 0 vs INT n = 6) under CON. Blood lactate was significantly greater, and pH lower, with a temporal delay in K(+) under INT (P < 0.05). No conditional differences were observed in other measures during this time, or in interstitial glucose concentrations during the remaining 23 h after exercise. Simulated games activity carries a lower risk of early, but not late-onset hypoglycemia than continuous running exercise in type 1 diabetes.

Cancer cachexia and diabetes: similarities in metabolic alterations and possible treatment

Cancer cachexia is a metabolic syndrome featuring many alterations typical of type 2 diabetes (T2D). While muscle wasting is a hallmark of cachexia, epidemiological evidence also supports an accelerated age-related muscle loss in T2D. Insulin resistance manifests in both conditions and impairs glucose disposal and protein anabolism by tissues. A greater contribution of gluconeogenesis to glucose production may limit amino acid availability for muscle protein synthesis, further aggravating muscle loss. In the context of inter-dependence between glucose and protein metabolism, the present review summarizes the current state of knowledge on alterations that may lead to muscle wasting in human cancer. By highlighting the similarities with T2D, a disease that has been more extensively studied, the objective of this review is to provide a better understanding of the pathophysiology of cancer cachexia and to consider potential treatments usually targeted for T2D. Nutritional approaches aimed at stimulating protein anabolism might include specially formulated food with optimal protein and amino acid composition. Because the gradual muscle loss in T2D may be attenuated by diabetes treatment, anti-diabetic drugs might be considered in cachexia treatment. Metformin emerges as a choice candidate as it acts both on reducing gluconeogenesis and improving insulin sensitivity, and has demonstrated tumour suppressor properties in multiple cancer types. Such a multimodal approach to slow or reverse muscle wasting in cachexia warrants further investigation.

Lactate metabolism during exercise in patients with mitochondrial myopathy

Patients with mitochondrial DNA mutations often have elevated plasma lactate at rest and during exercise, but it is unknown whether the high lactate levels are caused by a high production, an impaired oxidation or a combination. We studied lactate kinetics in 10 patients with mtDNA mutations and 10 matched healthy control subjects at rest and during cycle exercise with a combination of femoral arterio-venous differences of lactate, and lactate tracer dilution methodology. During exercise, lactate concentration and production rates were several-fold higher in patients, but despite mitochondrial dysfunction, lactate was oxidized in muscle to the same extent as in healthy control subjects. This surprisingly high ability to burn lactate in working muscle with defective mitochondria, probably relates to the variability of oxidative capacity among muscle fibers. The data suggests that lactate is not solely an indicator of impaired oxidative capacity, but an important fuel for oxidative metabolism, even in muscle with severely impaired mitochondrial function.

Estrogen treatment after ovariectomy protects against fatty liver and may improve pathway-selective insulin resistance

Pathway-selective insulin resistance where insulin fails to suppress hepatic glucose production but promotes liver fat storage may underlie glucose and lipid abnormalities after menopause. We tested the mechanisms by which estrogen treatment may alter the impact of a high-fat diet (HFD) when given at the time of ovariectomy (OVX) in mice. Female C57BL/6J mice underwent sham operation, OVX, or OVX with estradiol (E2) treatment and were fed an HFD. Hyperinsulinemic-euglycemic clamps were used to assess insulin sensitivity, tracer incorporation into hepatic lipids, and liver triglyceride export. OVX mice had increased adiposity that was prevented with E2 at the time of OVX. E2 treatment increased insulin sensitivity with OVX and HFD. In sham and OVX mice, HFD feeding induced fatty liver, and insulin reduced hepatic apoB100 and liver triglyceride export. E2 treatment reduced liver lipid deposition and prevented the decrease in liver triglyceride export during hyperinsulinemia. In mice lacking the liver estrogen receptor α, E2 after OVX limited adiposity but failed to improve insulin sensitivity, to limit liver lipid deposition, and to prevent insulin suppression of liver triglyceride export. In conclusion, estrogen treatment may reverse aspects of pathway-selective insulin resistance by promoting insulin action on glucose metabolism but limiting hepatic lipid deposition.

Arsenic and diabetes: current perspectives

Arsenic is a naturally occurring toxic metalloid of global concern. Many studies have indicated a dose-response relationship between accumulative arsenic exposure and the prevalence of diabetes mellitus (DM) in arseniasis-endemic areas in Taiwan and Bangladesh, where arsenic exposure occurs through drinking water. Epidemiological researches have suggested that the characteristics of arsenic-induced DM observed in arseniasis-endemic areas in Taiwan and Mexico are similar to those of non-insulin-dependent DM (Type 2 DM). These studies analyzed the association between high and chronic exposure to inorganic arsenic in drinking water and the development of DM, but the effect of exposure to low to moderate levels of inorganic arsenic on the risk of DM is unclear. Navas-Acien et al. recently proposed that a positive association existed between total urine arsenic and the prevalence of Type 2 DM in people exposed to low to moderate levels of arsenic. However, the diabetogenic role played by arsenic is still debated upon. An increase in the prevalence of DM has been observed among residents of highly arsenic-contaminated areas, whereas the findings from community-based and occupational studies in low-arsenic-exposure areas have been inconsistent. Recently, a population-based cross-sectional study showed that the current findings did not support an association between arsenic exposure from drinking water at levels less than 300 μg/L and a significantly increased risk of DM. Moreover, although the precise mechanisms for the arsenic-induced diabetogenic effect are still largely undefined, recent in vitro experimental studies indicated that inorganic arsenic or its metabolites impair insulin-dependent glucose uptake or glucose-stimulated insulin secretion. Nevertheless, the dose, the form of arsenic used, and the experimental duration in the in vivo studies varied greatly, leading to conflicting results and ambiguous interpretation of these data with respect to human exposure to arsenic in the environment. Moreover, the experimental studies were limited to the use of arsenic concentrations much higher than those relevant to human exposure. Further prospective epidemiological studies might help to clarify this controversy. The issues about environmental exposure assessment and appropriate biomarkers should also be considered. Here, we focus on the review of mechanism studies and discuss the currently available evidence and conditions for the association between environmental arsenic exposure and the development of DM.

The existence of an insulin-stimulated glucose and non-essential but not essential amino acid substrate interaction in diabetic pigs

BACKGROUND

The generation of energy from glucose is impaired in diabetes and can be compensated by other substrates like fatty acids (Randle cycle). Little information is available on amino acids (AA) as alternative energy-source in diabetes. To study the interaction between insulin-stimulated glucose and AA utilization in normal and diabetic subjects, intraportal hyperinsulinaemic euglycaemic euaminoacidaemic clamp studies were performed in normal (n=8) and streptozotocin (120 mg/kg) induced diabetic (n=7) pigs of ~40-45 kg.

RESULTS

Diabetic vs normal pigs showed basal hyperglycaemia (19.0±2.0 vs 4.7±0.1 mmol/L, P<.001) and at the level of individual AA, basal concentrations of valine and histidine were increased (P<.05) whereas tyrosine, alanine, asparagine, glutamine, glutamate, glycine and serine were decreased (P<.05). During the clamp, diabetic vs normal pigs showed reduced insulin-stimulated glucose clearance (4.4±1.6 vs 16.0±3.0 mL/kg·min, P<.001) but increased AA clearance (166±22 vs 110±13 mL/kg· min, P<.05) at matched arterial euglycaemia (5-7 mmol/L) and euaminoacidaemia (2.8-3.5 mmol/L). The increase in AA clearance was mainly caused by an increase in non-essential AA clearance (93.6±13.8 vs 46.6±5.4 mL/kg·min, P<.01), in particular alanine (14.2±2.4 vs 3.2±0.4 mL/kg·min, P<.001). Essential AA clearance was largely unchanged (72.9±8.5 vs 63.3±8.5 mL/kg· min), however clearances of threonine (P<.05) and tyrosine (P<.01) were increased in diabetic vs normal pigs (8.1±1.3 vs 5.2±0.5, and 14.3±2.5 vs 6.4±0.7 mL/kg· min, respectively).

CONCLUSIONS

The ratio of insulin-stimulated glucose versus AA clearance was decreased 5.4-fold in diabetic pigs, which was caused by a 3.6-fold decrease in glucose clearance and a 2.0-fold increase in non-essential AA clearance. In parallel with the Randle concept (glucose-fatty acid cycle), the present data suggest the existence of a glucose and non-essential AA substrate interaction in diabetic pigs whereby reduced insulin-stimulated glucose clearance seems to be partly compensated by an increase in non-essential AA clearance whereas essential AA are preferentially spared from an increase in clearance.