Demonstration of a critical role for free fatty acids in mediating counterregulatory stimulation of gluconeogenesis and suppression of glucose utilization in humans

Potential Benefits of Antioxidant Phytochemicals in Type 2 Diabetes

The clinical relationship between diabetes and inflammation is well established. Evidence clearly indicates that disrupting oxidant-antioxidant equilibrium and elevated lipid peroxidation could be a potential mechanism for chronic kidney disease associated with type 2 diabetes mellitus (T2DM). Under diabetic conditions, hyperglycemia, especially inflammation, and increased reactive oxygen species generation are bidirectionally associated. Inflammation, oxidative stress, and tissue damage are believed to play a role in the development of diabetes. Although the exact mechanism underlying oxidative stress and its impact on diabetes progression remains uncertain, the hyperglycemia-inflammation-oxidative stress interaction clearly plays a significant role in the onset and progression of vascular disease, kidney disease, hepatic injury, and pancreas damage and, therefore, holds promise as a therapeutic target. Evidence strongly indicates that the use of multiple antidiabetic medications fails to achieve the normal range for glycated hemoglobin targets, signifying treatment-resistant diabetes. Antioxidants with polyphenols are considered useful as adjuvant therapy for their potential anti-inflammatory effect and antioxidant activity. We aimed to analyze the current major points reported in preclinical, in vivo, and clinical studies of antioxidants in the prevention or treatment of inflammation in T2DM. Then, we will share our speculative vision for future diabetes clinical trials.

Decreased branched-chain amino acids and elevated fatty acids during antecedent hypoglycemia in type 1 diabetes

INTRODUCTION

Hypoglycemia is a major limiting factor in achieving recommended glycemic targets for people with type 1 diabetes. Exposure to recurrent hypoglycemia results in blunted hormonal counter-regulatory and symptomatic responses to hypoglycemia. Limited data on metabolic adaptation to recurrent hypoglycemia are available. This study examined the acute metabolic responses to hypoglycemia and the effect of antecedent hypoglycemia on these responses in type 1 diabetes.

RESEARCH DESIGN AND METHODS

Twenty-one outpatients with type 1 diabetes with normal or impaired awareness of hypoglycemia participated in a study assessing the response to hypoglycemia on 2 consecutive days by a hyperinsulinemic glucose clamp. Participants underwent a period of normoglycemia and a period of hypoglycemia during the hyperinsulinemic glucose clamp. Plasma samples were taken during normoglycemia and at the beginning and the end of the hypoglycemic period. Metabolomic analysis of the plasma samples was conducted using comprehensive two-dimensional gas chromatography with time-of-flight mass spectrometry.

RESULTS

In total, 68 metabolites were studied. On day 1, concentrations of the branched-chain amino acids, leucine (p=3.8×10-3) and isoleucine (p=2.2×10-3), decreased during hypoglycemia. On day 2, during hypoglycemia, five amino acids (including leucine and isoleucine) significantly decreased, and two fatty acids (tetradecanoic and oleic acids) significantly increased (p<0.05). Although more metabolites responded to hypoglycemia on day 2, the responses of the single metabolites were not statistically significant between the 2 days.

CONCLUSIONS

In individuals with type 1 diabetes, one episode of hypoglycemia decreases leucine and isoleucine concentrations. Antecedent hypoglycemia results in the decrement of five amino acids and increases the concentrations of two fatty acids, suggesting an alteration between the two hypoglycemic episodes, which could indicate a possible adaptation. However, more studies are needed to gain a comprehensive understanding of the consequences of these alterations.

TRIAL REGISTRATION NUMBER

NCT01337362.

Sociodemographic, anthropometric, and lifestyle correlates of prediabetes and type 2 diabetes in europe: The Feel4Diabetes study

BACKGROUND AND AIMS

The current work aimed to identify the predominant correlates of prediabetes and T2DM among a variety of socio-demographic, anthropometric and lifestyle indices, in a large sample of adults from families at high risk for T2DM.

METHODS AND RESULTS

In this cross-sectional study, 2816 adults were recruited from low-socioeconomic areas in high-income countries (HICs) (Belgium-Finland), HICs under austerity measures (Greece-Spain), and low/middle-income countries (LMICs) (Bulgaria-Hungary). A positive association between the male sex (OR, 95% C.I.2.77 (1.69-4.54)) and prediabetes was revealed compared to females, while there was a negative association between younger age (<45 years) (OR, 95% C.I. 0.58 (0.37-0.92)), and low/medium levels of waist circumference (OR, 95% C.I. 0.44 (0.22-0.89)) with prediabetes compared to older age and high levels of waist circumference, respectively. Concerning T2DM, 0-0.5 cups/day of fruits and berries (OR, 95% C.I.2. 13 (1.16-3.91)) and 150-300 g fish/week (OR, 95% C.I. 2.55 (1.01-6.41)) have a positive association compared to higher consumptions, respectively. Conversely, <1 cup/week legumes (OR, 95% C.I. 0.55 (0.31-0.99) as well as 0-0.5 servings (OR, 95% C.I. 0.34 (0.12-0.95) and 0.5-1 servings (OR, 95% C.I. 0.37 (0.19-0.71) of full-fat dairy/day have a negative association compared to higher consumptions, respectively.

CONCLUSION

These findings indicate the need for diabetes prevention measures targeting young adults and especially men, above 45 years of age, with central obesity and poor dietary habits and prioritize vulnerable groups and populations living in LMICs.

NATIONAL CLINICAL TRIAL NUMBER

NCT02393872.

How Perturbated Metabolites in Diabetes Mellitus Affect the Pathogenesis of Hypertension?

The presence of hypertension (HTN) in type 2 diabetes mellitus (DM) is a common phenomenon in more than half of the diabetic patients. Since HTN constitutes a predictor of vascular complications and cardiovascular disease in type 2 DM patients, it is of significance to understand the molecular and cellular mechanisms of type 2 DM binding to HTN. This review attempts to understand the mechanism via the perspective of the metabolites. It reviewed the metabolic perturbations, the biological function of perturbated metabolites in two diseases, and the mechanism underlying metabolic perturbation that contributed to the connection of type 2 DM and HTN. DM-associated metabolic perturbations may be involved in the pathogenesis of HTN potentially in insulin, angiotensin II, sympathetic nervous system, and the energy reprogramming to address how perturbated metabolites in type 2 DM affect the pathogenesis of HTN. The recent integration of the metabolism field with microbiology and immunology may provide a wider perspective. Metabolism affects immune function and supports immune cell differentiation by the switch of energy. The diverse metabolites produced by bacteria modified the biological process in the inflammatory response of chronic metabolic diseases either. The rapidly evolving metabolomics has enabled to have a better understanding of the process of diseases, which is an important tool for providing some insight into the investigation of diseases mechanism. Metabolites served as direct modulators of biological processes were believed to assess the pathological mechanisms involved in diseases.

Liver glycogen-induced enhancements in hypoglycemic counterregulation require neuroglucopenia

Iatrogenic hypoglycemia is a prominent barrier to achieving optimal glycemic control in patients with diabetes, in part due to dampened counterregulatory hormone responses. It has been demonstrated that elevated liver glycogen content can enhance these hormonal responses through signaling to the brain via afferent nerves, but the role that hypoglycemia in the brain plays in this liver glycogen effect remains unclear. During the first 4 h of each study, the liver glycogen content of dogs was increased by using an intraportal infusion of fructose to stimulate hepatic glucose uptake (HG; n = 13), or glycogen was maintained near fasting levels with a saline infusion (NG; n = 6). After a 2-h control period, during which the fructose/saline infusion was discontinued, insulin was infused intravenously for an additional 2 h to bring about systemic hypoglycemia in all animals, whereas brain euglycemia was maintained in a subset of the HG group by infusing glucose bilaterally into the carotid and vertebral arteries (HG-HeadEu; n = 7). Liver glycogen content was markedly elevated in the two HG groups (43 ± 4, 73 ± 3, and 75 ± 7 mg/g in NG, HG, and HG-HeadEu, respectively). During the hypoglycemic period, arterial plasma glucose levels were indistinguishable between groups (53 ± 2, 52 ± 1, and 51 ± 1 mg/dL, respectively), but jugular vein glucose levels were kept euglycemic (88 ± 5 mg/dL) only in the HG-HeadEu group. Glucagon and epinephrine responses to hypoglycemia were higher in HG compared with NG, whereas despite the increase in liver glycogen, neither increased above basal in HG-HeadEu. These data demonstrate that the enhanced counterregulatory hormone secretion that accompanies increased liver glycogen content requires hypoglycemia in the brain.NEW & NOTEWORTHY It is well known that iatrogenic hypoglycemia is a barrier to optimal glycemic regulation in patients with diabetes. Our data confirm that increasing liver glycogen content 75% above fasting levels enhances hormonal responses to insulin-induced hypoglycemia and demonstrate that this enhanced hormonal response does not occur in the absence of hypoglycemia in the brain. These data demonstrate that information from the liver regarding glycogen availability is integrated in the brain to optimize the counterregulatory response.

Myocardium Metabolism in Physiological and Pathophysiological States: Implications of Epicardial Adipose Tissue and Potential Therapeutic Targets

The main energy substrate of adult cardiomyocytes for their contractility are the fatty acids. Its metabolism generates high ATP levels at the expense of high oxygen consumption in the mitochondria. Under low oxygen supply, they can get energy from other substrates, mainly glucose, lactate, ketone bodies, etc., but the mitochondrial dysfunction, in pathological conditions, reduces the oxidative metabolism. In consequence, fatty acids are stored into epicardial fat and its accumulation provokes inflammation, insulin resistance, and oxidative stress, which enhance the myocardium dysfunction. Some therapies focused on improvement the fatty acids entry into mitochondria have failed to demonstrate benefits on cardiovascular disorders. Oppositely, those therapies with effects on epicardial fat volume and inflammation might improve the oxidative metabolism of myocardium and might reduce the cardiovascular disease progression. This review aims at explain (a) the energy substrate adaptation of myocardium in physiological conditions, (b) the reduction of oxidative metabolism in pathological conditions and consequences on epicardial fat accumulation and insulin resistance, and (c) the reduction of cardiovascular outcomes after regulation by some therapies.

A ketone monoester drink reduces the glycemic response to an oral glucose challenge in individuals with obesity: a randomized trial

BACKGROUND

Exogenous ketones make it possible to reach a state of ketosis that may improve metabolic control in humans.

OBJECTIVES

The main objective of this study was to determine whether the ingestion of a ketone monoester (KE) drink before a 2-h oral-glucose-tolerance test (OGTT) would lower blood glucose concentrations. Secondary objectives were to determine the impact of KE on nonesterified fatty acid (NEFA) concentration and glucoregulatory hormones.

METHODS

We conducted a randomized controlled crossover experiment in 15 individuals with obesity (mean ± SD age: 47 ± 10 y; BMI: 34 ± 5 kg/m2). After an overnight fast, participants consumed a KE drink [(R)-3-hydroxybutyl (R)-3-hydroxybutyrate; 0.45 mL/kg body weight] or taste-matched control drink 30 min before completing a 75-g OGTT. Participants and study personnel performing laboratory analyses were blinded to each condition.

RESULTS

The KE increased d-β-hydroxybutyrate to a maximum of ∼3.4 mM (P < 0.001) during the OGTT. Compared with the control drink, KE reduced glucose (-11%, P = 0.002), NEFA (-21%, P = 0.009), and glucagon-like peptide 1 (-31%, P = 0.001) areas under the curve (AUCs), whereas glucagon AUC increased (+11%, P = 0.030). No differences in triglyceride, C-peptide, and insulin AUCs were observed after the KE drink. Mean arterial blood pressure decreased and heart rate increased after the KE drink (both P < 0.01).

CONCLUSIONS

A KE drink consumed before an OGTT lowered glucose and NEFA AUCs with no increase in circulating insulin. Our results suggest that a single drink of KE may acutely improve metabolic control in individuals with obesity. Future research is warranted to examine whether KE could be used safely to have longer-term effects on metabolic control. This trial was registered at clinicaltrials.gov as NCT03461068.

Impact of Hypoglycemia on Brain Metabolism During Diabetes

Diabetes is a metabolic disease afflicting millions of people worldwide. A substantial fraction of world's total healthcare expenditure is spent on treating diabetes. Hypoglycemia is a serious consequence of anti-diabetic drug therapy, because it induces metabolic alterations in the brain. Metabolic alterations are one of the central mechanisms mediating hypoglycemia-related functional changes in the brain. Acute, chronic, and/or recurrent hypoglycemia modulate multiple metabolic pathways, and exposure to hypoglycemia increases consumption of alternate respiratory substrates such as ketone bodies, glycogen, and monocarboxylates in the brain. The aim of this review is to discuss hypoglycemia-induced metabolic alterations in the brain in glucose counterregulation, uptake, utilization and metabolism, cellular respiration, amino acid and lipid metabolism, and the significance of other sources of energy. The present review summarizes information on hypoglycemia-induced metabolic changes in the brain of diabetic and non-diabetic subjects and the manner in which they may affect brain function.

Effects of insulin-induced hypoglycaemia on lipolysis rate, lipid oxidation and adipose tissue signalling in human volunteers: a randomised clinical study

AIMS/HYPOTHESIS

The aims of this study were to determine the role of lipolysis in hypoglycaemia and define the underlying intracellular mechanisms.

METHODS

Nine healthy volunteers were randomised to treatment order of three different treatments (crossover design). Treatments were: (1) saline control; (2) hyperinsulinaemic hypoglycaemia (HH; i.v. bolus of 0.1 U/kg insulin); and (3) hyperinsulinaemic euglycaemia (HE; i.v. bolus of 0.1 U/kg insulin and 20% glucose). Inclusion criteria were that volunteers were healthy, aged >18 years, had a BMI between 19 and 26 kg/m², and provided both written and oral informed consent. Exclusion criteria were the presence of a known chronic disease (including diabetes mellitus, epilepsy, ischaemic heart disease and cardiac arrhythmias) and regular use of prescription medication. The data was collected at the medical research facilities at Aarhus University Hospital, Denmark. The primary outcome was palmitic acid flux. Participants were blinded to intervention order, but caregivers were not.

RESULTS

Adrenaline (epinephrine) and glucagon concentrations were higher during HH than during both HE and control treatments. NEFA levels and lipid oxidation rates (determined by indirect calorimetry) returned to control levels after 105 min. Palmitate flux was increased to control levels during HH (p = NS) and was more than twofold higher than during HE (overall mean difference between HH vs HE, 114 [95% CI 64, 165 μmol/min]; p < 0.001). In subcutaneous adipose tissue biopsies, we found elevated levels of hormone-sensitive lipase (HSL) and perilipin-1 phosphorylation 30 min after insulin injection during HH compared with both control and HE. There were no changes in the levels of adipose triglyceride lipase (ATGL), comparative gene identification-58 (CGI-58) or G₀/G₁ switch gene 2 (G0S2) proteins. Insulin-stimulated phosphorylation of Akt and mTOR were unaffected by hypoglycaemia. Expression of the G0S2 gene increased during HE and HH compared with control, without changes in ATGL (also known as PNPLA2) or CGI-58 (also known as ABHD5) mRNA levels.

CONCLUSIONS/INTERPRETATION

These findings suggest that NEFAs become a major fuel source during insulin-induced hypoglycaemia and that lipolysis may be an important component of the counter-regulatory response. These effects appear to be mediated by rapid stimulation of protein kinase A (PKA) and HSL, compatible with activation of the β-adrenergic catecholamine signalling pathway.

TRIAL REGISTRATION

ClinicalTrials.gov NCT01919788 FUNDING: : The study was funded by Aarhus University, the Novo Nordisk Foundation and the KETO Study Group/Danish Agency for Science Technology and Innovation (grant no. 0603-00479, to NM).

Liver glucose metabolism in humans

Information about normal hepatic glucose metabolism may help to understand pathogenic mechanisms underlying obesity and diabetes mellitus. In addition, liver glucose metabolism is involved in glycosylation reactions and connected with fatty acid metabolism. The liver receives dietary carbohydrates directly from the intestine via the portal vein. Glucokinase phosphorylates glucose to glucose 6-phosphate inside the hepatocyte, ensuring that an adequate flow of glucose enters the cell to be metabolized. Glucose 6-phosphate may proceed to several metabolic pathways. During the post-prandial period, most glucose 6-phosphate is used to synthesize glycogen via the formation of glucose 1-phosphate and UDP–glucose. Minor amounts of UDP–glucose are used to form UDP–glucuronate and UDP–galactose, which are donors of monosaccharide units used in glycosylation. A second pathway of glucose 6-phosphate metabolism is the formation of fructose 6-phosphate, which may either start the hexosamine pathway to produce UDP-N-acetylglucosamine or follow the glycolytic pathway to generate pyruvate and then acetyl-CoA. Acetyl-CoA may enter the tricarboxylic acid (TCA) cycle to be oxidized or may be exported to the cytosol to synthesize fatty acids, when excess glucose is present within the hepatocyte. Finally, glucose 6-phosphate may produce NADPH and ribose 5-phosphate through the pentose phosphate pathway. Glucose metabolism supplies intermediates for glycosylation, a post-translational modification of proteins and lipids that modulates their activity. Congenital deficiency of phosphoglucomutase (PGM)-1 and PGM-3 is associated with impaired glycosylation. In addition to metabolize carbohydrates, the liver produces glucose to be used by other tissues, from glycogen breakdown or from de novo synthesis using primarily lactate and alanine (gluconeogenesis).

Acute Treatment With XMetA Activates Hepatic Insulin Receptors and Lowers Blood Glucose in Normal Mice

It has been proposed that monoclonal antibodies may become therapeutics for metabolic diseases such as diabetes mellitus. We have previously characterized an allosteric monoclonal antibody to the human insulin receptor (IR), XMetA, that activated metabolic signaling leading to enhanced glucose transport in cultured cells, and chronically reduced fasting blood glucose levels in mouse models of diabetes mellitus. Under acute dosing conditions, the large size of an IR-binding antibody like XMetA (∼ 150 kDa) could lead to a more rapid access into liver, an insulin sensitive tissue with well-fenestrated capillaries, when compared to other insulin sensitive tissues with non-fenestrated capillaries, such as muscle and adipose. Thus, in the present study we administered XMetA (10 mg/kg) and insulin (0.5 U/kg) via IV injection, and for 90 min compared their effects on blood glucose lowering and IR activation in three of the major insulin-sensitive tissues of the normal fasted mouse: liver, adipose, and muscle. Like insulin, XMetA lowered blood glucose levels, although the effect was less rapid. Insulin activated IR autophosphorylation and Akt phosphorylation in liver, fat, and muscle. In contrast, IR activation by XMetA was primarily observed in the liver. Both insulin and XMetA lowered β-hydroxybutyrate levels in plasma; however, only insulin reduced both non-esterified fatty acids (NEFA) and glycerol concentrations. These data indicate that, in normal mice, acute glucose regulation by XMetA is largely mediated by its action on the liver.

Biomarkers of Insulin for the Diagnosis of Hyperinsulinemic Hypoglycemia in Infants and Children

OBJECTIVE

To evaluate thresholds of various biomarkers for defining excess insulin activity to recognize congenital hyperinsulinism.

STUDY DESIGN

This was a retrospective chart review of diagnostic fasting tests in children with ketotic hypoglycemia (n = 30) and genetically/pathology confirmed congenital hyperinsulinism (n = 28). Sensitivity and specificity for congenital hyperinsulinism were determined for plasma insulin, β-hydroxybutyrate, free fatty acids (FFA), C-peptide, insulin-like growth factor binding protein-1 (IGFBP-1), and the glycemic response to glucagon (through the glucagon stimulation test [GST]) at the time of hypoglycemia.

RESULTS

Only 23 of the 28 subjects with congenital hyperinsulinism had detectable insulin (median, 6.7 μIU/mL), and insulin was undetectable in all subjects with ketotic hypoglycemia. Compared with ketotic hypoglycemia, subjects with congenital hyperinsulinism had higher GST values (57 vs 13 mg/dL; ΔGST ≥30 mg/dL in 24 of 27 subjects with congenital hyperinsulinism vs 0 of 30 subjects with ketotic hypoglycemia) and C-peptide levels (1.55 vs 0.11 ng/mL), with lower levels of FFA (0.82 vs 2.51 mM) and IGFBP-1 (59.5 vs 634 ng/mL). At the time of hypoglycemia, the upper limits of β-hydroxybutyrate and FFA in subjects with congenital hyperinsulinism were higher than reported previously (β-hydroxybutyrate <1.8 mM and FFA <1.7 mM), providing the best sensitivity for congenital hyperinsulinism vs ketotic hypoglycemia. A C-peptide level ≥0.5 ng/mL was 89% sensitive and 100% specific, and an IGFBP-1 level ≤110 ng/mL was 85% sensitive and 96.6% specific.

CONCLUSION

Because low or undetectable insulin level during hypoglycemia does not exclude the diagnosis of hyperinsulinism, C-peptide and IGFBP-1 may inform the diagnosis of congenital hyperinsulinism. In this group of children with well-defined congenital hyperinsulinism, thresholds for "suppressed" β-hydroxybutyrate and FFA are higher than previously reported levels.

Targeting fatty acid metabolism to improve glucose metabolism

Disturbances in fatty acid metabolism in adipose tissue, liver, skeletal muscle, gut and pancreas play an important role in the development of insulin resistance, impaired glucose metabolism and type 2 diabetes mellitus. Alterations in diet composition may contribute to prevent and/or reverse these disturbances through modulation of fatty acid metabolism. Besides an increased fat mass, adipose tissue dysfunction, characterized by an altered capacity to store lipids and an altered secretion of adipokines, may result in lipid overflow, systemic inflammation and excessive lipid accumulation in non-adipose tissues like liver, skeletal muscle and the pancreas. These impairments together promote the development of impaired glucose metabolism, insulin resistance and type 2 diabetes mellitus. Furthermore, intrinsic functional impairments in either of these organs may contribute to lipotoxicity and insulin resistance. The present review provides an overview of fatty acid metabolism-related pathways in adipose tissue, liver, skeletal muscle, pancreas and gut, which can be targeted by diet or food components, thereby improving glucose metabolism.

Adipose triglyceride lipase deletion from adipocytes, but not skeletal myocytes, impairs acute exercise performance in mice

Adipose triglyceride lipase (ATGL) is the rate-limiting enzyme mediating triacylglycerol hydrolysis in virtually all cells, including adipocytes and skeletal myocytes, and hence, plays a critical role in mobilizing fatty acids. Global ATGL deficiency promotes skeletal myopathy and exercise intolerance in mice and humans, and yet the tissue-specific contributions to these phenotypes remain unknown. The goal of this study was to determine the relative contribution of ATGL-mediated triacylglycerol hydrolysis in adipocytes vs. skeletal myocytes to acute exercise performance. To achieve this goal, we generated murine models with adipocyte- and skeletal myocyte-specific targeted deletion of ATGL. We then subjected untrained mice to acute peak and submaximal exercise interventions and assessed exercise performance and energy substrate metabolism. Impaired ATGL-mediated lipolysis within adipocytes reduced peak and submaximal exercise performance, reduced peripheral energy substrate availability, shifted energy substrate preference toward carbohydrate oxidation, and decreased HSL Ser(660) phosphorylation and mitochondrial respiration within skeletal muscle. In contrast, impaired ATGL-mediated lipolysis within skeletal myocytes was not sufficient to reduce peak and submaximal exercise performance or peripheral energy substrate availability and instead tended to enhance metabolic flexibility during peak exercise. Furthermore, the expanded intramyocellular triacylglycerol pool in these mice was reduced following exercise in association with preserved HSL phosphorylation, suggesting that HSL may compensate for impaired ATGL action in skeletal muscle during exercise. These data suggest that adipocyte rather than skeletal myocyte ATGL-mediated lipolysis plays a greater role during acute exercise in part because of compensatory mechanisms that maintain lipolysis in muscle, but not adipose tissue, when ATGL is absent.

Changes in glucose and fat metabolism in response to the administration of a hepato-preferential insulin analog

Endogenous insulin secretion exposes the liver to three times higher insulin concentrations than the rest of the body. Because subcutaneous insulin delivery eliminates this gradient and is associated with metabolic abnormalities, functionally restoring the physiologic gradient may provide therapeutic benefits. The effects of recombinant human insulin (HI) delivered intraportally or peripherally were compared with an acylated insulin model compound (insulin-327) in dogs. During somatostatin and basal portal vein glucagon infusion, insulin was infused portally (PoHI; 1.8 pmol/kg/min; n = 7) or peripherally (PeHI; 1.8 pmol/kg/min; n = 8) and insulin-327 (Pe327; 7.2 pmol/kg/min; n = 5) was infused peripherally. Euglycemia was maintained by glucose infusion. While the effects on liver glucose metabolism were greatest in the PoHI and Pe327 groups, nonhepatic glucose uptake increased most in the PeHI group. Suppression of lipolysis was greater during PeHI than PoHI and was delayed in Pe327 infusion. Thus small increments in portal vein insulin have major consequences on the liver, with little effect on nonhepatic glucose metabolism, whereas insulin delivered peripherally cannot act on the liver without also affecting nonhepatic tissues. Pe327 functionally restored the physiologic portal-arterial gradient and thereby produced hepato-preferential effects.

Novel PEGylated basal insulin LY2605541 has a preferential hepatic effect on glucose metabolism

The impact of the novel basal insulin LY2605541 (LY) on hepatic and nonhepatic glucose uptake (non-HGU) was evaluated. Conscious dogs underwent euglycemic clamps with tracer and hepatic balance measurements. Clamp period infusions were peripheral venous regular insulin (0.1 nmol ⋅ kg(-1) ⋅ h(-1) [control], n = 6) or LY (bolus [nmol/kg], continuous [nmol ⋅ kg(-1) ⋅ h(-1)]: 0.5, 0.5 [n = 6]; 0.375, 0.375 [n = 5]; 0.25, 0.25 [n = 4]), somatostatin, and glucose, as well as intraportal glucagon (basal). During the clamp, the dogs switched from net hepatic glucose output to uptake (rates reached 2.1 ± 1.2, 0.9 ± 2.1, 8.6 ± 2.3, and 6.0 ± 1.1 µmol ⋅ kg(-1) ⋅ min(-1) within 5 h in control, LY0.25, LY0.375, and LY0.5, respectively). Non-HGU in LY increased less than in control; the ratio of change from basal in non-HGU to change in net hepatic glucose balance, calculated when glucose infusion rates (GIRs) were ~20 µmol ⋅ kg(-1) ⋅ min(-1) in all groups, was higher in control (1.17 ± 0.38) versus LY0.25 (0.39 ± 0.33), LY0.375 (-0.01 ± 0.13), and LY0.5 (-0.09 ± 0.07). Likewise, the change from baseline in glucose Rd-to-Ra ratio was greatest in control (1.4 ± 0.3 vs. 0.6 ± 0.4, 0.5 ± 0.2, and 0.6 ± 0.2 in LY0.25, LY0.375, and LY0.5, respectively). In contrast to exogenously administered human insulin, LY demonstrated preferential hepatic effects, similar to endogenously secreted insulin. Therefore, the analog might reduce complications associated with current insulin therapy.

Impaired amino acid metabolism contributes to fasting-induced hypoglycemia in fatty acid oxidation defects

The importance of mitochondrial fatty acid β-oxidation (FAO) as a glucose-sparing process is illustrated by patients with inherited defects in FAO, who may present with life-threatening fasting-induced hypoketotic hypoglycemia. It is unknown why peripheral glucose demand outpaces hepatic gluconeogenesis in these patients. In this study, we have systematically addressed the fasting response in long-chain acyl-CoA dehydrogenase-deficient (LCAD KO) mice. We demonstrate that the fasting-induced hypoglycemia in LCAD KO mice was initiated by an increased glucose requirement in peripheral tissues, leading to rapid hepatic glycogen depletion. Gluconeogenesis did not compensate for the increased glucose demand, which was not due to insufficient hepatic glucogenic capacity but rather caused by a shortage in the supply of glucogenic precursors. This shortage in supply was explained by a suppressed glucose-alanine cycle, decreased branched-chain amino acid metabolism and ultimately impaired protein mobilization. We conclude that during fasting, FAO not only serves to spare glucose but is also indispensable for amino acid metabolism, which is essential for the maintenance of adequate glucose production.

Glucose homeostasis, obesity and diabetes

Plasma glucose levels are maintained within a narrow range in normal individuals. Both insulin-dependent and insulin-independent processes contribute to fasting and postprandial plasma glucose regulation. The brain and nervous system are insulin independent. Muscle and adipose tissue are responsive to insulin and can use either glucose or ketones and free fatty acids as their primary metabolic fuel. The essential components of metabolic syndrome are obesity, glucose intolerance, insulin resistance, lipid disturbances, and hypertension. The risk of type 2 diabetes increases exponentially as body mass index increases above about 25 kg/m2. The links between obesity and type 2 diabetes include proinflammatory cytokines, insulin resistance, deranged fatty acid metabolism, and cellular processes. Modest weight reduction can improve glycaemic control and reduce diabetes risk. Obesity also leads to hyperinsulinaemia and insulin resistance, with a progressive decrease in insulin secretory function. Ageing is another important risk factor for metabolic disorders, including obesity, impaired glucose tolerance, and type 2 diabetes.

Fatty acids-stress attenuates gluconeogenesis induction and glucose production in primary hepatocytes

BACKGROUND

Hepatic gluconeogenesis tightly controls blood glucose levels in healthy individuals, yet disorders of fatty acids (FAs) oxidation are characterized by hypoglycemia. We studied the ability of free-FAs to directly inhibit gluconeogenesis, as a novel mechanism that elucidates the hypoglycemic effect of FAs oxidation defects.

METHODS

Primary rat hepatocytes were pre-treated with FAs prior to gluconeogenic stimuli with glucagon or dexamethasone and cAMP.

RESULTS

Pre-treatment with 1 mM FAs (mixture of 2:1 oleate:palmitate) for 1 hour prior to gluconeogenic induction, significantly decreases the induced expression of the gluconeogenic genes phosphoenolpyruvate carboxykinase (PEPCK) and glucose-6-phosphatase (G6pase) as well as the induced glucose production by the cells. The inhibitory effect of FAs upon gluconeogenesis is abolished when pre-treatment is elongated to 18 hours, allowing clearance of FAs into triglycerides by the cells. Replacement of palmitate with the non-metabolic fatty acid 2-bromopalmitate inhibits esterification of FAs into triglycerides. Accordingly, the increased exposure to unesterified-FAs allows their inhibitory effect to be extended even when pre-treatment is elongated to 18 hours. Similar changes were caused by FAs to the induction of peroxisome-proliferator-activated receptor-γ coactivator 1α (PGC1α) expression, indicating this transcriptional coactivator as the mediating link of the effect. This inhibitory effect of FAs upon gluconeogenic induction is shown to involve reduced activation of cAMP response element-binding (CREB) transcription factor.

CONCLUSIONS

The present results demonstrate that free-FAs directly inhibit the induced gluconeogenic response in hepatocytes. Hence, high levels of free-FAs may attenuate hepatic gluconeogenesis, and liver glucose output.

High levels of dietary fat impair glucose homeostasis in rainbow trout

This study was designed to assess the effects of dietary fat levels on glucose homeostasis in rainbow trout under prolonged hyperglycaemia induced by high carbohydrate intake. Trout were fed identical amounts of one of two iso-energetic diets containing either a low (LFD, 3%) or a high fat level (HFD, 20%) and similar amounts of digestible carbohydrates (26-30%) for 14 days. While a single high fat meal reduced glycaemia compared with a low fat meal, the consumption of a high fat diet for 14 days resulted in prolonged hypergylcaemia and reduced plasma glucose clearance in response to an exogenous glucose or insulin challenge. The hyperglycaemic phenotype in trout was characterised by a reduction of the activities of lipogenic and glucose phosphorylating enzymes with a concomitant stimulation of enzymes involved in glucose production in the liver and reduced glycogen levels in the white muscle. Impaired glucose tolerance (IGT) was further associated with a significant reduction of insulin receptor substrate 1 (IRS1) protein content in muscle, and with a poor response of HFD fed fish to an exogenous insulin load, suggestive of impaired insulin signalling in trout fed with a HFD. To our knowledge, this is the first study showing that a teleost can also develop a high fat-induced IGT, characterised by persistent hyperglycaemia and reduced insulin sensitivity, established symptoms of IGT and the prediabetic insulin-resistant state in mammals. Our results also provide evidence that persistent hyperglycaemia after a high carbohydrate meal stems from a metabolic interaction between dietary macronutrients rather than from high carbohydrate intake alone.

How type of parturition and health status influence hormonal and metabolic profiles in newborn foals

Thyroid hormones, insulin growth factor I (IGF-I) and non-esterified fatty acids (NEFA) represent important hormonal and metabolic factors associated with perinatal growth and maturation. Their action could be influenced by the type of parturition and the health status of the foal and therefore the aim of this work is to evaluate their plasma concentrations in newborn foals during the first 2 wks of life. Three groups of subjects were enrolled: 15 healthy foals born by spontaneous parturition, 24 healthy foals born by induced parturition and 26 pathologic foals. From each of the healthy foals, blood was collected at 10, 20 and 30 minutes, 3 and 12 hours from birth, daily from Day 1 to Day 7, and at Day 10 and 14 of life. In pathologic foals samples were collected twice a day from the day of admission at the hospital until the day of discharge or death. Thyroid hormones (T3 and T4) and IGF-I were analyzed by radioimmunoassay and NEFA by enzymatic-colorimetric methods. In all the three groups a declining trend of T3 and T4 plasma concentrations was detectable, with lower levels in the pathologic group compared to healthy foals. Spontaneous foals showed higher levels of T3 at 7 d compared to induced foals, while T4 levels were higher in spontaneous vs. induced foals before 6 h of life, at three and seven days. IGF-I showed increasing plasma concentrations in all three considered groups. No differences were found between healthy and pathologic foals. NEFA in spontaneous and induced healthy foals showed a declining trend with higher levels during the first hours of life. Pathologic foals presented higher levels compared to spontaneous foals only at 24 h and 10 d. These data suggest that the type of foaling could influence the reference ranges for thyroid hormones. Moreover, pathologic foals showed some hormonal and metabolic differences related to their health status. Above all changes of thyroid hormones levels, early in postnatal life, could be a cause, and not only a consequence, of the diseased condition of these foals.

Atopic dermatitis causes lipid accumulation in the liver of NC/Nga mouse

Various factors have been reported to influence lipid metabolism and cause metabolic syndrome. However, the influence of allergy on the liver that plays important role of lipid metabolism has not been clarified. The aim of this study was to examine the influence of allergy on lipid metabolism of liver. A model of atopic dermatitis was developed in the NC/Nga mouse using picryl chloride to induce allergy. Lipid metabolism parameters were measured and the mechanism of changes in these parameters was examined using DNA microarray analysis and quantitative reverse transcriptase PCR. Triacylglycerol accumulation was promoted in the liver in the mouse atopic dermatitis model despite reductions in food intake, body weight gain, and serum glucose. As this mechanism, it was thought that atopic dermatitis caused the suppression of fatty acid β-oxidation. These results suggest that atopic dermatitis causes lipid accumulation in the liver.

Kidney: its impact on glucose homeostasis and hormonal regulation

According to current textbook wisdom the liver is the exclusive site of glucose production in humans in the postabsorptive state. Although animal and in vitro studies have documented that the kidney is capable of gluconeogenesis, glucose production by the human kidney has been regarded as negligible. This knowledge is based on net balance measurements across the kidney. Recent studies combining isotopic and balance techniques have demonstrated that the human kidney is involved in the regulation of glucose homeostasis by making glucose via gluconeogenesis, taking up glucose from the circulation, and by reabsorbing glucose from the glomerular filtrate. The human liver and kidneys release approximately equal amounts of glucose via gluconeogenesis in the postabsorptive state. In the postprandial state, although overall endogenous glucose release decreases substantially, renal gluconeogenesis actually increases by approximately 2-fold. Following meal ingestion, glucose utilization by the kidney increases. Increased glucose uptake into the kidney may be implicated in diabetic nephropathy. Normally each day, ∼ 180 g of glucose is filtered by the kidneys; almost all of this is reabsorbed by means of sodium glucose cotransporter 2 (SGLT2), expressed in the proximal tubules. However, the capacity of SGLT2 to reabsorb glucose from the renal tubules is finite and when plasma glucose concentrations exceed a threshold, glucose begins to appear in the urine. Renal glucose release is stimulated by epinephrine and is inhibited by insulin. Handling of glucose by the kidney is altered in type 2 diabetes mellitus (T2DM): renal gluconeogenesis and renal glucose uptake are increased in both the postabsorptive and postprandial states, and renal glucose reabsorption is also increased Since renal glucose release is almost exclusively due to gluconeogenesis, it seems that the kidney is as important gluconeogenic organ as the liver. The most important renal gluconeogenic precursors appear to be lactae glutamine and glycerol.

Effects of Mixed Isoenergetic Meals on Fat and Carbohydrate Metabolism during Exercise in Older Men

The present study was designed to investigate the effects of four different meals on fat and CHO metabolism during subsequent exercise in elderly males. Eight healthy males (age: 63.3 ± 5.2 years) reported to the physiology laboratory on four separate occasions, each of which was allocated for the performance of a 30-minute exercise on a cycle ergometer at 60% after having normal (N), high fat (HF), high carbohydrate high glycaemic index (HGI) and high carbohydrate low glycaemic index (LGI) meals. Fat oxidation during exercise after the meals ( g/min;  g/min;  g/min;  g/min) was not significant (), and neither were the rates of carbohydrate oxidation (, , , and  g/m). NEFA concentration increased after HF () but decreased after HGI and LGI (). Glucose concentration decreased as a result of exercise after HF, and LGI () whereas insulin concentration decreased significantly during exercise after N, HF, and HGI (). It can be concluded that, in elderly males, feeding isoenergetic meals containing different proportions of carbohydrate and fat do not significantly alter oxidation of fat and CHO during exercise in spite of changes in some circulating metabolites.

A general introduction to the biochemistry of mitochondrial fatty acid β-oxidation

Over the years, the mitochondrial fatty acid β-oxidation (FAO) pathway has been characterised at the biochemical level as well as the molecular biological level. FAO plays a pivotal role in energy homoeostasis, but it competes with glucose as the primary oxidative substrate. The mechanisms behind this so-called glucose-fatty acid cycle operate at the hormonal, transcriptional and biochemical levels. Inherited defects for most of the FAO enzymes have been identified and characterised and are currently included in neonatal screening programmes. Symptoms range from hypoketotic hypoglycaemia to skeletal and cardiac myopathies. The pathophysiology of these diseases is still not completely understood, hampering optimal treatment. Studies of patients and mouse models will contribute to our understanding of the pathogenesis and will ultimately lead to better treatment.

Mechanisms of insulin resistance after insulin-induced hypoglycemia in humans: the role of lipolysis

OBJECTIVE

Changes in glucose metabolism occurring during counterregulation are, in part, mediated by increased plasma free fatty acids (FFAs), as a result of hypoglycemia-activated lipolysis. However, it is not known whether FFA plays a role in the development of posthypoglycemic insulin resistance as well.

RESEARCH DESIGN AND METHODS

We conducted a series of studies in eight healthy volunteers using acipimox, an inhibitor of lipolysis. Insulin action was measured during a 2-h hyperinsulinemic-euglycemic clamp (plasma glucose [PG] 5.1 mmo/l) from 5:00 p.m. to 7:00 p.m. or after a 3-h morning hyperinsulinemic-glucose clamp (from 10 a.m. to 1:00 p.m.), either euglycemic (study 1) or hypoglycemic (PG 3.2 mmol/l, studies 2-4), during which FFA levels were allowed to increase (study 2), were suppressed by acipimox (study 3), or were replaced by infusing lipids (study 4). [6,6-(2)H(2)]-Glucose was infused to measure glucose fluxes.

RESULTS

Plasma adrenaline, norepinephrine, growth hormone, and cortisol levels were unchanged (P > 0.2). Glucose infusion rates (GIRs) during the euglycemic clamp were reduced by morning hypoglycemia in study 2 versus study 1 (16.8 +/- 2.3 vs. 34.1 +/- 2.2 micromol/kg/min, respectively, P < 0.001). The effect was largely removed by blockade of lipolysis during hypoglycemia in study 3 (28.9 +/- 2.6 micromol/kg/min, P > 0.2 vs. study 1) and largely reproduced by replacement of FFA in study 4 (22.3 +/- 2.8 micromol/kg/min, P < 0.03 vs. study 1). Compared with study 2, blockade of lipolysis in study 3 decreased endogenous glucose production (2 +/- 0.3 vs. 0.85 +/- 0.1 micromol/kg/min, P < 0.05) and increased glucose utilization (16.9 +/- 1.85 vs. 28.5 +/- 2.7 micromol/kg/min, P < 0.05). In study 4, GIR fell by approximately 23% (22.3 +/- 2.8 micromol/kg/min, vs. study 3, P = 0.058), indicating a role of acipimox per se on insulin action.

CONCLUSION

Lipolysis induced by hypoglycemia counterregulation largely mediates posthypoglycemic insulin resistance in healthy subjects, with an estimated overall contribution of approximately 39%.

Free fatty acids are associated with pulse pressure in women, but not men, with type 1 diabetes mellitus

Cardiovascular disease (CVD) is the leading cause of death in type 1 diabetes mellitus (T1D). Pulse pressure, a measure of arterial stiffness, is elevated in T1D and associated with CVD. Free fatty acids (FFAs), elevated in women and abdominal adiposity, are also elevated in T1D and CVD. We thus examined the association of fasting FFAs with pulse pressure and coronary artery calcification (CAC, a marker of coronary atherosclerotic burden) in an adult population (n = 150) of childhood-onset T1D and whether any such associations varied by abdominal adiposity and sex. Mean age and diabetes duration were 42 and 33 years, respectively, when CAC, visceral abdominal adiposity (VAT), and subcutaneous abdominal adiposity (SAT) were determined by electron beam tomography. Free fatty acids were determined by in vitro colorimetry. Pulse pressure was calculated as systolic blood pressure minus diastolic blood pressure. Free fatty acids were log transformed before analyses, and all analyses were controlled for serum albumin. Free fatty acids were associated with pulse pressure in women (r = 0.24, P = .04), but not in men (r = 0.07, P = .55). An interaction for the prediction of pulse pressure was noted between FFAs and both VAT (P = .03) and SAT (P = .008) in women, but only a marginal interaction with SAT (P = .09) and no interaction for VAT (P = .40) with FFAs were observed in men. In multivariable linear regression analysis allowing for serum albumin, age, height, heart rate, albumin excretion rate, hemoglobin A(1c), high-density lipoprotein cholesterol, hypertension medication use, FFAs, SAT, and the interaction between FFAs and SAT, the interaction between FFAs and SAT remained associated with pulse pressure in women (FFAs, P = .04; interaction term, P = .03), but not men (FFAs, P = .32; interaction term, P = .32). FFAs showed no association with log-transformed CAC. Although FFAs were not associated with CAC in either sex, they were associated with pulse pressure in women and their effect appeared to vary by abdominal adiposity, particularly SAT. This finding might help explain the loss of the sex difference in CVD in T1D.

Central but not systemic lipid infusion augments the counterregulatory response to hypoglycemia

This study tests the hypothesis that lipids could act as an alternative fuel source in the brain during insulin-induced hypoglycemia. Male Sprague-Dawley rats were subjected to hyperinsulinemic (5 mU.kg(-1).min(-1)) hypoglycemic (approximately 50 mg/dl) clamps. In protocol 1, intralipid (IL), a fat emulsion, was infused intravenously to prevent the fall in free fatty acid levels that occurs in response to hyperinsulinemic hypoglycemia. Intravenous lipid infusion did not alter the counterregulatory responses to hypoglycemia. To test whether IL could have central effects in mediating the counterregulatory response to hypoglycemia, in protocol 2 the brains of precannulated rats were intracerebroventricularly (icv) infused with IL or artificial cerebrospinal fluid (aCSF) as control. Unexpectedly, the epinephrine and glucagon response to hypoglycemia was significantly augmented with icv IL infusion. To determine whether central IL infusion could restore defective counterregulation, in protocol 3 rats were made recurrently hypoglycemic (RH) for 3 days and on the 4th day underwent hyperinsulinemic hypoglycemic clamps with icv IL or aCSF infusion. RH rats had the expected impaired epinephrine response to hypoglycemia, and icv IL infusion again significantly augmented the epinephrine response in RH rats to normal. With regard to our experimental model of hypoglycemic counterregulation, we conclude that 1) systemic lipid infusion did not alter the counterregulatory response to hypoglycemia, 2) the icv infusion of lipids markedly increased CSF FFA levels and paradoxically augmented the epinephrine and glucagon responses, and 3) the blunted sympathoadrenal response in recurrently hypoglycemic rats was completely normalized with the icv lipid infusion. It is concluded that, in the setting of insulin-induced hypoglycemia, increased brain lipids can enhance the sympathoadrenal response.

Impact of visceral adipose tissue on liver metabolism and insulin resistance. Part II: Visceral adipose tissue production and liver metabolism

Excess visceral adipose tissue is associated with anomalies of blood glucose homoeostasis, elevation of plasma triglycerides and low levels of high-density lipoprotein cholesterol that contribute to the development of type-2 diabetes and cardiovascular syndromes. Visceral adipose tissue releases a large amount of free fatty acids and hormones/cytokines in the portal vein that are delivered to the liver. The secreted products interact with hepatocytes and various immune cells in the liver. Altered liver metabolism and determinants of insulin resistance associated with visceral adipose tissue distribution are discussed, as well as, determinants of an insulin-resistant state promoted by the increased free fatty acids and cytokines delivered by visceral adipose tissue to the liver.

The role of adipose tissue dysfunction in the pathogenesis of obesity-related insulin resistance

Research of the past decade has increased our understanding of the role adipose tissue plays in health and disease. Adipose tissue is now recognized as a highly active metabolic and endocrine organ. Adipocytes are of importance in buffering the daily influx of dietary fat and exert autocrine, paracrine and/or endocrine effects by secreting a variety of adipokines. The normal function of adipose tissue is disturbed in obesity, and there is accumulating evidence to suggest that adipose tissue dysfunction plays a prominent role in the development and/or progression of insulin resistance. Obese individuals often have enlarged adipocytes with a reduced buffering capacity for lipid storage, thereby exposing other tissues to an excessive influx of lipids, leading to ectopic fat deposition and insulin resistance in situations where energy intake exceeds energy expenditure. In addition, adipose tissue blood flow is decreased in obesity. This impairment may affect lipid handling in adipose tissue and, thereby, further contribute to excessive fat storage in non-adipose tissues. On the other hand, adipose tissue hypoperfusion may induce hypoxia in this tissue. Adipose tissue hypoxia may result in disturbances in adipokine secretion and increased macrophage infiltration in adipose tissue, events that are frequently observed in obesity. In this review, it is discussed how enlarged adipocytes, an impaired blood flow through adipose tissue, adipose tissue hypoxia, adipose tissue inflammation and macrophage infiltration are interrelated and may induce insulin resistance.

Change in pancreatic B-cell function (HOMA-B) varies in different populations with similar genetic backgrounds but different environments

OBJECTIVE

To determine whether pancreatic B-cell function varies in different populations with similar genetic backgrounds but different environments.

RESEARCH DESIGN/METHODS

We compared a specific migrant Gujarati community in the UK (n = 205) with people still resident in the same villages of origin in Gujarat, India (n = 246). Pancreatic B-cell function (HOMA-B) was determined and the influence of age, migration and other factors was explored.

RESULTS

As anticipated, there was an age-related decline in log(HOMA-B) in both groups. However, the age-related fall in log(HOMA-B) was more pronounced in the UK than in Gujarat (normalized beta-0.29 vs. -0.14, P for difference = 0.03). The decline of HOMA-B with age persisted after adjustment for body mass index (UK beta = -0.31; Gujarat beta = -0.16, P = 0.015, P < 0.001). There was no significant change in insulin sensitivity (HOMA-S) with age at either site, although insulin sensitivity was lower in the UK. Fasting non-estrified fatty acid (NEFA) levels rose with age in the UK but not in Gujarat (P = 0.003 for difference in gradients). In multiple linear regression analysis, lower log(HOMA-B) was independently associated with higher fasting log(NEFA) levels; normalized beta = -0.24, P < 0.001, age; beta = -0.16, P = 0.005, higher log(insulin-like growth factor binding protein-1); beta = -0.19, P = 0.007 and lower body mass index; beta = 0.26, P = 0.001. This model accounted for 25% of the variability in HOMA-B.

CONCLUSIONS

HOMA-B as a measure of B-cell function declines more rapidly with age in the migrant UK group than in Gujarat. This may be a direct consequence of chronically higher NEFA exposure in the UK group.

Fatty acid-induced inflammation and insulin resistance in skeletal muscle and liver

Plasma free fatty acid (FFA) levels are elevated in obesity. FFA, by causing insulin resistance in muscle, liver, and endothelial cells, contributes to the development of type 2 diabetes mellitus (T2DM), hypertension, dyslipidemia, and nonalcoholic fatty liver disease (NAFLD). The mechanism through which FFA induces insulin resistance involves intramyocellular and intrahepatocellular accumulation of triglycerides and diacylglycerol, activation of several serine/threonine kinases, reduction in tyrosine phosphorylation of the insulin receptor substrate (IRS)-1/2, and impairment of the IRS/phosphatidylinositol 3-kinase pathway of insulin signaling. FFA also produces low-grade inflammation in skeletal muscle and liver through activation of nuclear factor-kappaB, resulting in release of several proinflammatory and proatherogenic cytokines. Thus, elevated FFA levels (due to obesity or to high-fat feeding) cause insulin resistance in skeletal muscle and liver, which contributes to the development of T2DM, and produce low-grade inflammation, which contributes to the development of atherosclerotic vascular diseases and NAFLD.

Acute, same-day effects of antecedent exercise on counterregulatory responses to subsequent hypoglycemia in type 1 diabetes mellitus

Exercise-induced hypoglycemia can occur within hours after exercise in type 1 diabetes mellitus (T1DM) patients. This study tested the hypothesis that an acute exercise bout causes (within hours) blunted autonomic and metabolic responses to subsequent hypoglycemia in patients with T1DM. Twelve T1DM patients (3 W/9 M) were studied during a single-step, 2-h hyperinsulinemic (572 +/- 4 pmol/l) hypoglycemic (2.8 +/- 0.1 mmol/l) clamp 2 h after either a hyperinsulinemic euglycemic (AM EUG) or hypoglycemic clamp (AM HYPO) or after sitting in a chair with basal insulin infusion (AM CON) or 90 min of moderate-intensity exercise (50% Vo(2 max), AM EX). Both AM HYPO and AM EX significantly blunted epinephrine responses and muscle sympathetic nerve activity responses to subsequent hypoglycemia compared with both control groups. Endogenous glucose production was significantly lower and the exogenous glucose infusion rate needed to maintain the hypoglycemic level was significantly greater during subsequent hypoglycemia in AM EX vs. CON. Rate of glucose disposal (Rd) was significantly reduced following AM HYPO. In summary, within 2.5 h, both moderate-intensity AM EX and AM HYPO blunted key autonomic counterregulatory responses. Despite this, glucose Rd was reduced during afternoon hypoglycemia following morning hypoglycemia, indicating posthypoglycemic insulin resistance. After morning exercise, endogenous glucose production was blunted, but glucose Rd was maintained during afternoon hypoglycemia, thereby indicating reduced metabolic defenses against hypoglycemia. These data suggest that exercise-induced counterregulatory failure can occur very rapidly, increasing the risk for hypoglycemia in T1DM within hours.

Multiple defects in counterregulation of hypoglycemia in modestly advanced type 2 diabetes mellitus

In type 2 diabetes mellitus (T2DM), little is known about hormonal responses to hypoglycemia. In particular, beta-cell responses to hypoglycemia have not been carefully investigated and potentially because of confounding factors or insufficient power, conflicting data have been obtained regarding growth hormone responses. We therefore compared hormonal responses including rates of insulin secretion during a 2-hour hyperinsulinemic hypoglycemic clamp in a relatively large number of nondiabetic (n=21) and moderately insulin-deficient subjects with T2DM (homeostasis model assessment of beta-cell function [HOMA-%B], 751+/-160 vs 1144+/-83 [pmol/L]/[mmol/L], P<.04) (n=14) matched for age, sex, and body mass index. Subjects with T2DM were excluded for antecedent hypoglycemia, and baseline glycemia was controlled by a variable infusion of insulin overnight. Although both groups of subjects had indistinguishable plasma glucose levels at baseline and virtually identical levels of plasma insulin and glucose throughout the hypoglycemic clamp, insulin secretion decreased more slowly in the subjects with T2DM. The time required for insulin secretion to decline to half its baseline level was markedly increased (38.9+/-4.9 vs 22.3+/-1.3 minutes [SD], P<.01), and insulin secretion decreased to a lesser extent (-0.79+/-0.17 vs -1.51+/-0.09 [pmol/L]/kg per minute, P<.002). Moreover, responses of glucagon (28.3+/-7.3 vs 52.8+/-7.0 ng/L, P<.05) and growth hormone (2.9+/-0.8 vs 6.3+/-0.9 ng/mL, P<.04) were reduced in the subjects with T2DM, whereas responses of epinephrine, norepinephrine, and cortisol were similar to those in nondiabetic subjects (all P>0.6). We conclude that multiple defects exist in hormonal responses to hypoglycemia in T2DM with moderate beta-cell failure. These include delayed and reduced decreases in insulin secretion, and impaired increases of plasma glucagon and growth hormone.

Dual age-dependent effect of ghrelin administration on serum level of insulin-like growth factor-1 and gastric growth in young rats

Ghrelin is a circulating growth hormone-releasing peptide primarily isolated from human and rat stomach. The aim of present study was to investigate the effect of ghrelin administration on gastric growth in suckling, and young peripubertal 7-week-old rats. Rats were treated for 7 days with saline or ghrelin (4, 8 or 16 nmol/kg/dose) intraperitoneally twice a day. Suckling rats were treated from the fist postnatal day.

RESULTS

Treatment with ghrelin did not affect animal weight in suckling rats; whereas in 7-week-old animals, administration of ghrelin caused a significant increase in body weight. In suckling rats, ghrelin decreased the gastric weight, DNA synthesis and DNA content. In young 7-week-old peripubertal rats, treatment with ghrelin increased food intake and animal body weight. This effect was accompanied with a significant increase in gastric mucosa weight, DNA synthesis and DNA content. Treatment with ghrelin increased serum level of growth hormone in all rats tested, but this result was much higher in 7-week-old peripubertal rats than in suckling rats. Serum level of insulin-like growth factor-1 was not affected by ghrelin administration in suckling rats. In contrast, ghrelin caused a significant increase in serum level of insulin-like growth factor-1 in 7-week-old peripubertal rats. We conclude that administration of ghrelin exhibits biphasic effect on gastric growth in young rats: in suckling rats, ghrelin reduces gastric growth, whereas in young 7-week-old animals, treatment with ghrelin stimulates gastric growth. The growth-promoting effect of ghrelin in the stomach seems to depend on the stimulation of food intake and the release of insulin-like growth factor-1.

Role of the decrement in intraislet insulin for the glucagon response to hypoglycemia in humans

OBJECTIVE

Animal and in vitro studies indicate that a decrease in beta-cell insulin secretion, and thus a decrease in tonic alpha-cell inhibition by intraislet insulin, may be an important factor for the increase in glucagon secretion during hypoglycemia. However, in humans this role of decreased intraislet insulin is still unclear.

RESEARCH DESIGN AND METHODS

We studied glucagon responses to hypoglycemia in 14 nondiabetic subjects on two separate occasions. On both occasions, insulin was infused from 0 to 120 min to induce hypoglycemia. On one occasion, somatostatin was infused from -60 to 60 min to suppress insulin secretion, so that the decrement in intraislet insulin during the final 60 min of hypoglycemia would be reduced. On the other occasion, subjects received an infusion of normal saline instead of the somatostatin.

RESULTS

During the 2nd h of the insulin infusion, when somatostatin or saline was no longer being infused, plasma glucose ( approximately 2.6 mmol/l) and insulin levels ( approximately 570 pmol/l) were comparable in both sets of experiments (both P > 0.4). In the saline experiments, insulin secretion remained unchanged from baseline (-90 to -60 min) before insulin infusion and decreased from 1.20 +/- 0.12 to 0.16 +/- 0.04 pmol . kg(-1) . min(-1) during insulin infusion (P < 0.001). However, in the somatostatin experiments, insulin secretion decreased from 1.18 +/- 0.12 pmol . kg(-1) . min(-1) at baseline to 0.25 +/- 0.09 pmol . kg(-1) . min(-1) before insulin infusion so that it did not decrease further during insulin infusion (-0.12 +/- 0.10 pmol . kg(-1) . min(-1), P = 0.26) indicating the complete lack of a decrement in intraislet insulin during hypoglycemia. This was associated with approximately 30% lower plasma glucagon concentrations (109 +/- 7 vs. 136 +/- 9 pg/ml, P < 0.006) and increments in plasma glucagon above baseline (41 +/- 8 vs. 67 +/- 11 pg/ml, P < 0.008) during the last 15 min of the hypoglycemic clamp. In contrast, increases in plasma growth hormone were approximately 70% greater during hypoglycemia after somatostatin infusion (P < 0.007), suggesting that to some extent the increases in plasma glucagon might have reflected a rebound in glucagon secretion.

CONCLUSIONS

These results provide direct support for the intraislet insulin hypothesis in humans. However, the exact extent to which a decrement in intraislet insulin accounts for the glucagon responses to hypoglycemia remains to be established.

Effects of oral fat load on insulin output and glucose tolerance in healthy control subjects and obese patients without diabetes

OBJECTIVE

Elevated plasma nonesterified fatty acid (NEFA) concentrations cause peripheral and hepatic insulin resistance and may play an important role in regulating glucose-induced insulin secretion. The aim of our study was to investigate the influence of physiologically elevated NEFA levels on glucose-stimulated insulin secretion in order to find evidence that NEFAs are a potential factor predisposing for type 2 diabetes and related metabolic disorders, which are known risk factors for cardiovascular disease.

RESEARCH DESIGN AND METHODS

We combined an orally administered fat emulsion with an intravenous glucose tolerance test and measured the time course of NEFA, insulin, and glucose. In order to find pathological conditions we applied the experiment to healthy and obese subjects.

RESULTS

The main findings are a significant increase in glucose-stimulated insulin secretion after oral fat load in both groups compared with the condition without preceding fat ingestion and a prolonged insulin secretion after fat load in obese patients compared with control subjects.

CONCLUSIONS

The results provide evidence that fat ingestion modulates beta-cell function and that NEFA is a plausible mediator that acts as a link between fat and glucose metabolism by modulating glucose-stimulated insulin secretion. Under the condition of elevated plasma levels of NEFA, this mechanism may be responsible for hyperinsulinemia in obese patients and a potential target of type 2 diabetes prevention strategies.

Pancreatic islet adaptation to fasting is dependent on peroxisome proliferator-activated receptor alpha transcriptional up-regulation of fatty acid oxidation

The cellular response to fasting and starvation in tissues such as heart, skeletal muscle, and liver requires peroxisome proliferator-activated receptor-alpha (PPARalpha)-dependent up-regulation of energy metabolism toward fatty acid oxidation (FAO). PPARalpha null (PPARalphaKO) mice develop hyperinsulinemic hypoglycemia in the fasting state, and we previously showed that PPARalpha expression is increased in islets at low glucose. On this basis, we hypothesized that enhanced PPARalpha expression and FAO, via depletion of lipid-signaling molecule(s) for insulin exocytosis, are also involved in the normal adaptive response of the islet to fasting. Fasted PPARalphaKO mice compared with wild-type mice had supranormal ip glucose tolerance due to increased plasma insulin levels. Isolated islets from the PPARalpha null mice had a 44% reduction in FAO, normal glucose use and oxidation, and enhanced glucose-induced insulin secretion. In normal rats, fasting for 24 h increased islet PPARalpha, carnitine palmitoyltransferase 1, and uncoupling protein-2 mRNA expression by 60%, 62%, and 82%, respectively. The data are consistent with the view that PPARalpha, via transcriptionally up-regulating islet FAO, can reduce insulin secretion, and that this mechanism is involved in the normal physiological response of the pancreatic islet to fasting such that hypoglycemia is avoided.

Insulin therapy and hypoglycaemia: the size of the problem

BACKGROUND AND METHODS

Hypoglycaemia is a fact of life for people with diabetes mellitus. Mild, asymptomatic episodes occur once or twice a week in insulin-treated diabetic subjects. Asymptomatic hypoglycaemia, including nocturnal hypoglycaemia, occurs in about 25% of diabetic subjects treated with insulin therapy. Mild hypoglycaemia, if recurrent, induces unawareness of hypoglycaemia and impairs glucose counterregulation, which in turn predisposes to severe hypoglycaemia. Even brief hypoglycaemia can cause profound dysfunction of the brain. Prolonged, severe hypoglycaemia can cause permanent neurological sequels. In addition, it is possible that hypoglycaemia may accelerate the vascular complications of diabetes by increasing platelet aggregation and/or fibrinogen formation. Finally, hypoglycaemia may be fatal. Hypoglycaemia induced by insulin as treatment of type 1 diabetes mellitus (T1 DM) is not the consequence of diabetes, but invariably of the non-physiological replacement of insulin.

RESULTS

A number of studies have demonstrated that by moving from non-physiological to more physiological models of insulin therapy, most of the hypoglycaemia problems may be overcome, the percentage of glycated hemoglobin (A1c) decreased, and the quality of life improved. Interestingly, in T1 DM with hypoglycaemia unawareness, prevention of hypoglycaemia reverses not only unawareness but also improves glucose counterregulation, primarily the responses of adrenaline.

CONCLUSIONS

In order to best prevent hypoglycaemia, insulin should preferably be given as continuous subcutaneous infusion via a minipump (the 'golden standard') or multiple daily insulin administrations with insulin analogues (basal insulin glargine, meal insulin rapid-acting insulin analogues) in T1 DM.

FFAs are not involved in regulation of gluconeogenesis and glycogenolysis in adults with uncomplicated P. falciparum malaria

In normal subjects, elevation of plasma free fatty acid (FFA) levels stimulates gluconeogenesis (GNG) and inhibits glycogenolysis (GLY). In adults with uncomplicated Plasmodium falciparum malaria, GNG is increased and GLY decreased. To test the hypothesis that FFAs are regulators of GNG and GLY in uncomplicated falciparum malaria, we investigated the effect of inhibition of lipolysis by acipimox in 12 patients with uncomplicated falciparum malaria. Six of them were given acipimox, and six served as controls. Also as controls, six matched healthy subjects were studied on two occasions with and without acipimox. After 16 h of fasting, glucose production and GNG were significantly higher in the malaria patients compared with the healthy controls (P = 0.003 and < 0.0001, respectively), whereas GLY was significantly lower (P < 0.001), together with elevated plasma concentrations of cortisol and glucagon. During the study, glucose production in patients declined over time (P < 0.0001), without a statistically significant difference between the acipimox-treated and untreated patients. In controls, however, with acipimox the decline was less outspoken compared with nontreated controls (P = 0.005). GNG was unchanged over time in patients as well as in healthy controls, and no influence of acipimox was found. In patients, GLY declined over time (P < 0.001), without a difference between acipimox-treated and untreated patients. In contrast, in controls treated with acipimox, no change over time was found, which was statistically different from the decline in untreated controls (P = 0.002). In conclusion, in falciparum malaria, FFAs are not involved in regulation of glucose production, nor of GNG or GLY.

Gluconeogenesis and Glycogenolysis in Health and Diabetes

Reviewed are data on gluconeogenesis (GNG) and glycogenolysis (GL) obtained in healthy volunteers and diabetic patients with newer, quantitative methods. Specifically addressed are effects of overnight and prolonged fasting, of acute changes in serum insulin and plasma free fatty acid (FFA) levels, as well as acute changes of combined FFA and insulin levels on GNG and GL in nondiabetic subjects and of abnormalities in GNG and GL in patients with type 1 and type 2 diabetes.

Effects of low and moderate antecedent exercise on counterregulatory responses to subsequent hypoglycemia in type 1 diabetes

Antecedent moderate-intensity exercise has been shown to blunt autonomic, neuroendocrine, and metabolic counterregulatory responses to subsequent hypoglycemia in nondiabetic individuals. The aims of the current study were to determine 1) whether this occurs in type 1 diabetic patients and 2) whether the degree of blunting is dependent on exercise intensity. Twenty-seven type 1 diabetic patients (13 women and 14 men) were studied during a single-step, 2-h hyperinsulinemic (9 pmol x kg(-1) x min(-1))-hypoglycemic (approximately 2.8 mmol/l) clamp 1 day after two 90-min exercise bouts at 30% (n = 11) or at 50% (n = 11) Vo(2max) or after no prior stress (control subjects, n = 25). After prior exercise at both 30 and 50% Vo(2max), epinephrine (1,959 +/- 553 and 1,528 +/- 424 vs. 3,420 +/- 424 pmol/l, respectively; P < 0.05) and pancreatic polypeptide (97 +/- 32 and 98 +/- 8 vs. 223 +/- 32 pmol/l, respectively; P < 0.05) responses to subsequent hypoglycemia were significantly lower compared with those of control subjects. Endogenous glucose production was significantly lower, while glucose utilization and, consequently, the exogenous glucose infusion rate needed to maintain hypoglycemia were significantly greater after both exercise intensities compared with that of control subjects. Muscle sympathetic nerve activity was significantly reduced by prior exercise of both intensities at baseline (16 +/- 4 and 22 +/- 4 vs. 31 +/- 3 bursts/min) and during hypoglycemia (22 +/- 4 and 27 +/- 5 vs. 41 +/- 3 bursts/min) compared with that of control subjects (P < 0.05). Total hypoglycemic symptoms were also significantly lower (P < 0.05) in both exercise groups compared with the control group. In summary, repeated episodes of prolonged exercise of both low and moderate intensities blunted key autonomic (epinephrine and pancreatic polypeptide) and metabolic (endogenous glucose production and peripheral glucose uptake) counterregulatory responses to next-day hypoglycemia in type 1 diabetes.

Counterregulatory hormone and symptom responses to insulin-induced hypoglycemia in the postprandial state in humans

Plasma counterregulatory hormones and symptoms were measured during hypoglycemia in the postprandial and in the fasting state in humans to establish differences in physiological responses. We studied 8 nondiabetic subjects and 10 subjects with type 1 diabetes on two different occasions during clamped insulin-induced hypoglycemia (2.4 mmol/l) in the sitting position. On one occasion, subjects ate a standard mixed meal, and on the other they remained fasting. In response to postprandial as compared with fasting hypoglycemia, nondiabetic subjects exhibited lower total symptom scores (6.6 +/- 0.4 vs. 11.5 +/- 0.8, P = 0.001), which was due to less hunger (1.1 +/- 0.1 vs. 4.2 +/- 0.2), lower suppression of plasma C-peptide (0.23 +/- 0.1 vs. 0.08 +/- 0.07 nmol/l, P = 0.032), and greater responses of plasma glucagon (248 +/- 29 vs. 163 +/- 25 ng x l(-1) x min(-1), P = 0.018), plasma adrenaline (4.5 +/- 0.6 vs. 3.1 +/- 0.4 nmol x l(-1) x min(-1), P = 0.037), norepinephrine (3.8 +/- 0.3 vs. 3.2 +/- 0.2 nmol x l(-1) x min(-1), P = 0.037), and pancreatic polypeptide (217 +/- 12 vs. 159 +/- 22 pmol x l(-1) x min(-1), P = 0.08). Except for plasma C-peptide, responses in diabetic subjects were similarly affected. Notably, in diabetic subjects responses of glucagon, which were absent in the fasting state, nearly normalized after a meal. In conclusion, in the postprandial compared with the fasting hypoglycemic state, total symptoms are less, but counterregulatory hormones are greater and responses of glucagon nearly normalize in type 1 diabetic subjects.

Nutritional effects of fat on carbohydrate metabolism

Obesity is commonly associated with elevated plasma levels of free fatty acids (FFAs). High levels of FFA have emerged as a major link between obesity and insulin resistance/type 2 diabetes (T2DM). Thus, acute and chronic elevations of plasma FFAs produce insulin resistance in skeletal muscle and liver. In skeletal muscle, FFA-induced insulin resistance is associated with accumulation of intramyocellular triglyceride and diacylglycerol, and with activation of protein kinase C (the beta and delta isoforms). It is suggested that FFAs interfere with insulin signalling via PKC-induced serine phosphorylation of the insulin receptor substrate-1. In the liver, FFAs cause insulin resistance by interfering with insulin suppression of glycogenolysis. In beta-cells, FFAs potentiate glucose-stimulated insulin secretion acutely and chronically. It is postulated that this prevents the development of T2DM in most (>80%) obese insulin-resistant people who have FFA-mediated insulin resistance. Elevated levels of FFA also seem to activate a pro-inflammatory and pro-atherogenic pathway (the IkappaB/NFkappaB pathway) and may be responsible, at least in part, for the increase in atherosclerotic vascular disease seen in patients with T2DM. As increased plasma levels account for up to 50% of insulin resistance in obese patients with T2DM, lowering of plasma FFAs could be a new and promising approach to the treatment of T2DM.

Fish oil prevents the adrenal activation elicited by mental stress in healthy men

OBJECTIVES

A diet rich in n-3 fatty acids (fish oils) is associated with reduced risks of cardiovascular and metabolic diseases, but the mechanisms remain incompletely understood. Sympathoadrenal activation is postulated to be involved in the pathogenesis of these diseases, and may be inhibited by n-3 fatty acids. We therefore evaluated the effects of a diet supplemented with n-3 fatty acids on the stimulation of the sympathetic nervous system and of stress hormones elicited by a mental stress.

METHODS

Seven human volunteers were studied on two occasions, before and after 3 weeks of supplementation with 7.2 g/day fish oil. On each occasion, the concentrations of plasma cortisol, and catecholamines, energy expenditure (indirect calorimetry), and adipose tissue lipolysis (plasma non esterified fatty acid concentrations) were monitored in basal conditions followed by a 30 min mental stress (mental arithmetics and Stroop's test) and a 30 min recovery period.

RESULTS

In control conditions, mental stress significantly increased heart rate, mean blood pressure, and energy expenditure. It increased plasma epinephrine from 60.9 +/- 6.2 to 89.3 +/- 16.1 pg/ml (p<0.05), plasma cortisol from 291 +/- 32 to 372 +/- 37 micromol/l (p<0.05) and plasma non esterified fatty acids from 409 +/- 113 to 544 +/- 89 micromol/l (p<0.05). After 3 weeks of a diet supplemented with n-3 fatty acids, the stimulation by mental stress of plasma epinephrine, cortisol, energy expenditure, and plasma non esterified fatty acids concentrations, were all significantly blunted.

CONCLUSION

Supplementation with n-3 fatty acids inhibits the adrenal activation elicited by a mental stress, presumably through effects exerted at the level of the central nervous system.