PSUN137 Suppression of endogenous insulin secretion during euglycemic hyperinsulinemia – effects of obesity

Hyperinsulinemia is strongly linked with excessive body fat. However, with the exception of plasma glucose concentrations, the other factors regulating insulin secretion are under-studied. We examined the effects of hyperinsulinemia itself on beta cell insulin secretion during exogenous insulin and glucose infusions in adults with insulin-resistant upper body (UBO), insulin-sensitive lower body obesity (LBO) and non-obese controls.

Data from the euglycemic, hyperinsulinemic clamp studies of 33 volunteers (9 controls, 5 LBO, 19 UBO) was analyzed; basal and insulin-suppressed (residual) insulin secretion rates were determined using deconvolution of C-peptide concentrations. Obesity phenotype was determined using waist: hip ratio and body composition was assessed with dual-energy X-ray absorptiometry and abdominal computed tomography. Plasma insulin concentrations were log transformed to achieve a normal distribution before statistical analysis.

The plasma glucose concentration change during the clamp was 0.3 (SD: 3) mg/dl, and similar among groups (p=0.7). Median, achieved serum insulin concentrations was 66 (IQR: 45-105) mIU/mL, and greater in participants with obesity. Fasting insulin secretion rates were 0.093 (SD: 0.029), 0.158 (SD: 0.036), and 0.216 (0.078) nmol/min in controls, LBO and UBO, respectively (UBO p<0.001 vs. other groups). Insulin secretion was suppressed by 28% during hyperinsulinemia with no between group differences (p= 0.69). The ratios of insulin secretion rate (from C-peptide deconvolution) to serum insulin concentration (nmol/min per mIU/mL) was 0.058 (SD: 0.015) in controls, 0.090 (SD: 0.016) in LBO and 0.111 (SD: 0.039) in UBO (UBO vs. other groups P = 0.001). The ratio of insulin secretion rates to plasma insulin concentrations was correlated with BMI (r=0.69, P <0.001).

We conclude that adults with obesity have greater residual insulin secretion during an exogenous insulin infusion and that this is related to upper body fat distribution. However, because the proportional suppression of endogenous insulin secretion is similar in these groups, this could indicate the primary abnormality is fasting insulin secretion.

Presentation: Sunday, June 12, 2022 12:30 p.m. - 2:30 p.m.

American Association of Clinical Endocrinology Clinical Practice Guideline: Developing a Diabetes Mellitus Comprehensive Care Plan-2022 Update

OBJECTIVE

The objective of this clinical practice guideline is to provide updated and new evidence-based recommendations for the comprehensive care of persons with diabetes mellitus to clinicians, diabetes-care teams, other health care professionals and stakeholders, and individuals with diabetes and their caregivers.

METHODS

The American Association of Clinical Endocrinology selected a task force of medical experts and staff who updated and assessed clinical questions and recommendations from the prior 2015 version of this guideline and conducted literature searches for relevant scientific papers published from January 1, 2015, through May 15, 2022. Selected studies from results of literature searches composed the evidence base to update 2015 recommendations as well as to develop new recommendations based on review of clinical evidence, current practice, expertise, and consensus, according to established American Association of Clinical Endocrinology protocol for guideline development.

RESULTS

This guideline includes 170 updated and new evidence-based clinical practice recommendations for the comprehensive care of persons with diabetes. Recommendations are divided into four sections: (1) screening, diagnosis, glycemic targets, and glycemic monitoring; (2) comorbidities and complications, including obesity and management with lifestyle, nutrition, and bariatric surgery, hypertension, dyslipidemia, retinopathy, neuropathy, diabetic kidney disease, and cardiovascular disease; (3) management of prediabetes, type 2 diabetes with antihyperglycemic pharmacotherapy and glycemic targets, type 1 diabetes with insulin therapy, hypoglycemia, hospitalized persons, and women with diabetes in pregnancy; (4) education and new topics regarding diabetes and infertility, nutritional supplements, secondary diabetes, social determinants of health, and virtual care, as well as updated recommendations on cancer risk, nonpharmacologic components of pediatric care plans, depression, education and team approach, occupational risk, role of sleep medicine, and vaccinations in persons with diabetes.

CONCLUSIONS

This updated clinical practice guideline provides evidence-based recommendations to assist with person-centered, team-based clinical decision-making to improve the care of persons with diabetes mellitus.

Assessment of Disparities in Diabetes Mortality in Adults in US Rural vs Nonrural Counties, 1999-2018

IMPORTANCE

US rural vs nonrural populations have striking disparities in diabetes care. Whether rurality contributes to disparities in diabetes mortality is unknown.

OBJECTIVE

To examine rates and trends in diabetes mortality based on county urbanization.

DESIGN, SETTING, AND PARTICIPANTS

In this observational, cross-sectional study, the US Centers for Disease Control and Prevention Wide-Ranging Online Data for Epidemiologic Research database was searched from January 1, 1999, to December 31, 2018, for diabetes as a multiple cause and the underlying cause of death among residents aged 25 years or older in US counties. County urbanization was categorized as metro, medium-small, and rural. Weighted multiple linear regression models and jackknife resampling, with a 3-segment time component, were used. The models included exposures with up to 3-way interactions and were age standardized to the 2009-2010 population. The analyses were conducted from July 1, 2020, to February 1, 2022.

EXPOSURES

County urbanization (metro, medium-small, or rural), gender (men or women), age group (25-54, 55-74, or ≥75 years), and region (Midwest, Northeast, South, or West).

MAIN OUTCOMES AND MEASURES

Annual diabetes mortality rate per 100 000 people.

RESULTS

From 1999-2018, based on 4 022 238 309 person-years, diabetes was a multiple cause of death for 4 735 849 adults aged 25 years or older. As a multiple cause, diabetes mortality rates in 2017-2018 vs 1999-2000 were highest and unchanged in rural counties (157.2 [95% CI, 150.7-163.7] vs 154.1 [95% CI, 148.2-160.1]; P = .49) but lower in medium-small counties (123.6 [95% CI, 119.6-127.6] vs 133.6 [95% CI, 128.4-138.8]; P = .003) and urban counties (92.9 [95% CI, 90.5-95.3] vs 109.7 [95% CI, 105.2-114.1]; P < .001). In 2017-2018 vs 1999-2000, mortality rates were higher in rural men (+18.2; 95% CI, 14.3-22.1) but lower in rural women (-14.0; 95% CI, -17.7 to -10.3) (P < .001 for both). In the 25- to 54-year age group, mortality rates in 2017-2018 vs 1999-2000 showed a greater increase in rural counties (+9.4; 95% CI, 8.6-10.2) compared with medium-small counties (+4.5; 95% CI, 4.0-5.0) and metro counties (+0.9; 95% CI, 0.4-1.4) (P < .001 for all). Of all regions and urbanization levels, the mortality rate in 2017-2018 vs 1999-2000 was higher only in the rural South (+13.8; 95% CI, 7.6-20.0; P < .001).

CONCLUSIONS AND RELEVANCE

In this cross-sectional study, US rural counties had the highest overall diabetes mortality rate. The determinants of persistent rural disparities, in particular for rural men and for adults in the rural South, require investigation.

Lawson Criterion for Ignition Exceeded in an Inertial Fusion Experiment

For more than half a century, researchers around the world have been engaged in attempts to achieve fusion ignition as a proof of principle of various fusion concepts. Following the Lawson criterion, an ignited plasma is one where the fusion heating power is high enough to overcome all the physical processes that cool the fusion plasma, creating a positive thermodynamic feedback loop with rapidly increasing temperature. In inertially confined fusion, ignition is a state where the fusion plasma can begin "burn propagation" into surrounding cold fuel, enabling the possibility of high energy gain. While "scientific breakeven" (i.e., unity target gain) has not yet been achieved (here target gain is 0.72, 1.37 MJ of fusion for 1.92 MJ of laser energy), this Letter reports the first controlled fusion experiment, using laser indirect drive, on the National Ignition Facility to produce capsule gain (here 5.8) and reach ignition by nine different formulations of the Lawson criterion.

Effects of liraglutide on gastrointestinal functions and weight in obesity: A randomized clinical and pharmacogenomic trial

OBJECTIVE

This study aimed to determine the effects of a long-acting glucagon-like peptide-1 (GLP-1) receptor agonist, liraglutide, and placebo subcutaneously over 16 weeks on weight and gastric functions and to evaluate associations of single-nucleotide polymorphisms in GLP1R (rs6923761) and TCF7L2 (rs7903146) with effects of liraglutide.

METHODS

The study conducted a randomized, parallel-group, placebo-controlled, 16-week trial of liraglutide, escalated to 3 mg subcutaneously daily in 136 otherwise healthy adults with obesity. Weight, gastric emptying of solids (GES), gastric volumes, satiation, and body composition measured at baseline and after treatment were compared in two treatment groups using analysis of covariance.

RESULTS

Liraglutide (n = 59) and placebo (n = 65) groups completed treatment. Relative to placebo, liraglutide increased weight loss at 5 and 16 weeks (both p < 0.05), slowed time to half GES (T_1/2 ) at 5 and 16 weeks (both p < 0.001), and increased fasting gastric volume (p = 0.01) and satiation (p < 0.01) at 16 weeks. GES T_1/2 was positively correlated with weight loss on liraglutide (both p < 0.001). After 16 weeks of liraglutide, GLP1R rs6923761 (AG/AA vs. GG) was associated with reduced percent body fat (p = 0.062), and TCF7L2 rs7903146 (CC vs. CT/TT) was associated with lower body weight (p = 0.015).

CONCLUSIONS

Liraglutide, 3 mg, induces weight loss with delay in GES T_1/2 and reduces calorie intake. Slowing GES and variations in GLP1R and TCF7L2 are associated with liraglutide effects in obesity.

The Effect of Glucagon on Protein Catabolism During Insulin Deficiency: Exchange of Amino Acids Across Skeletal Muscle and the Splanchnic Bed

Transient insulin deprivation with concurrent hyperglucagonemia is a catabolic state that can occur in type 1 diabetes. To evaluate glucagon's catabolic effect in the setting of its glucogenic effect, we measured the regional exchanges of amino acid metabolites (amino-metabolites) across muscle and splanchnic beds in 16 healthy humans during either somatostatin followed by glucagon or saline infusion alone. Despite a twofold or greater increase in the regional exchange of amino-metabolites by glucagon, whole-body kinetics and concentrations of amino acids (AA) remained stable. Glucagon increased the splanchnic uptake of not only gluconeogenic but also essential (EAA) AA while increasing their release from the muscle bed. Regional tracer-based kinetics and 3-methylhistidine release indicate that EAA release from muscle is likely caused by reduced protein synthesis rather than increased protein degradation. Furthermore, many metabolites known to affect insulin action and metabolism were altered by hyperglucagonemia including increase in branched-chain AA and keto acids of leucine and isoleucine in arterial plasma. Further, an increase in arterial concentrations of α-aminoadipic acid arising from increased conversion from lysine in the splanchnic bed was noted. These results demonstrate that hyperglucagonemia during hypoinsulinemia increases net muscle protein catabolism and substantially increases the exchange of amino metabolites across splanchnic and muscle beds.

The relationship between insulin and glucagon concentrations in non-diabetic humans

Abnormal postprandial suppression of glucagon in Type 2 diabetes (T2DM) has been attributed to impaired insulin secretion. Prior work suggests that insulin and glucagon show an inverse coordinated relationship. However, dysregulation of α-cell function in prediabetes occurs early and independently of changes in β-cells, which suggests insulin having a less significant role on glucagon control. We therefore, sought to examine whether hepatic vein hormone concentrations provide evidence to further support the modulation of glucagon secretion by insulin. As part of a series of experiments to measure the effect of diabetes-associated genetic variation in TCF7L2 on islet cell function, hepatic vein insulin and glucagon concentrations were measured at 2-minute intervals during fasting and a hyperglycemic clamp. The experiment was performed on 29 nondiabetic subjects (age = 46 ± 2 years, BMI 28 ± 1 Kg/m2 ) and enabled post-hoc analysis, using Cross-Correlation and Cross-Approximate Entropy (Cross-ApEn) to evaluate the interaction of insulin and glucose. Mean insulin concentrations rose from fasting (33 ± 4 vs. 146 ± 12 pmol/L, p < 0.01) while glucagon was suppressed (96 ± 8 vs. 62 ± 5 ng/L, p < 0.01) during the clamp. Cross-ApEn was used to measure pattern reproducibility in the two hormones using glucagon as control mechanism (0.78 ± 0.03 vs. 0.76 ± 0.03, fasting vs. hyperglycemia) and using insulin as a control mechanism (0.78 ± 0.02 vs. 0.76 ± 0.03, fasting vs. hyperglycemia). Values did not differ between the two scenarios. Cross-correlation analysis demonstrated a small in-phase coordination between insulin and glucagon concentrations during fasting, which inverted during hyperglycemia. This data suggests that the interaction between the two hormones is not driven by either. On a minute-to-minute basis, direct control and secretion of glucagon is not mediated (or restrained) by insulin.

The Effect of Diabetes-Associated Variation in TCF7L2 on Postprandial Glucose Metabolism When Glucagon and Insulin Concentrations Are Matched

Background: The rs7903146 variant in the TCF7L2 gene is associated with defects in postprandial insulin and glucagon secretion and increased risk of type 2 diabetes. However, it is unclear if this variant has effects on glucose metabolism that are independent of islet function. Methods: We studied 54 nondiabetic subjects on two occasions where endogenous hormone secretion was inhibited by somatostatin. Twenty-nine subjects were homozygous for the diabetes-associated allele (TT) and 25 for the diabetes-protective allele (CC) at rs7903146, but otherwise matched for anthropometric characteristics. On 1 day, glucagon infused at a rate of 0.65 ng/kg/min, and at 0 min prevented a fall in glucagon (nonsuppressed day). On the contrary, infusion commenced at 120 min to create a transient fall in glucagon (suppressed day). Subjects received glucose (labeled with [3-³H]-glucose) infused to mimic the systemic appearance of oral glucose. Insulin was infused to mimic a prandial insulin response. Endogenous glucose production (EGP) was measured using the tracer dilution technique. Results: Lack of glucagon suppression increased postchallenge glucose concentrations and impaired EGP suppression. However, in the presence of matched insulin and glucagon concentrations, genetic variation in TCF7L2 did not alter glucose metabolism. Conclusion: These data suggest that genetic variation in TCF7L2 alters glucose metabolism through changes in islet hormone secretion.

Biology of Activating Transcription Factor 4 (ATF4) and Its Role in Skeletal Muscle Atrophy

Activating transcription factor 4 (ATF4) is a multifunctional transcription regulatory protein in the basic leucine zipper superfamily. ATF4 can be expressed in most if not all mammalian cell types, and it can participate in a variety of cellular responses to specific environmental stresses, intracellular derangements, or growth factors. Because ATF4 is involved in a wide range of biological processes, its roles in human health and disease are not yet fully understood. Much of our current knowledge about ATF4 comes from investigations in cultured cell models, where ATF4 was originally characterized and where further investigations continue to provide new insights. ATF4 is also an increasingly prominent topic of in vivo investigations in fully differentiated mammalian cell types, where our current understanding of ATF4 is less complete. Here, we review some important high-level concepts and questions concerning the basic biology of ATF4. We then discuss current knowledge and emerging questions about the in vivo role of ATF4 in one fully differentiated cell type, mammalian skeletal muscle fibers.

Hepatic Artery Embolization for Palliation of Symptomatic Hypoglycemia in Patients With Hepatic Insulinoma Metastases

Context

Insulinoma is a pancreatic neuroendocrine tumor that causes hyperinsulinemic hypoglycemia. Symptomatic hypoglycemia related to hepatic insulinoma metastases may be addressed with liver-directed therapies such as hepatic artery embolization.

Objective

This work aimed to determine the safety and effectiveness of bland hepatic artery embolization (HAE) for palliation of symptomatic hypoglycemia in patients with hepatic insulinoma metastases refractory to medical management.

Methods

An institutional review board–approved retrospective review was undertaken of all patients with a tissue (n = 18) or imaging (n = 2) diagnosis of hepatic insulinoma metastases and symptomatic hyperinsulinemic hypoglycemia refractory to medical management who underwent bland HAE at a single center between January 1, 1998 and November 1, 2020. Twenty patients (10 women, 10 men; mean age, 56 years; range, 18-84 years) were identified who individually underwent 1 (n = 7), 2 (n = 5), 3 (n = 5), 4 (n = 2), or 5 (n = 1) HAEs, for an overall total of 45 HAEs. Post-HAE hypoglycemia recurrence was defined as onset of adrenergic symptoms (eg, sweating, weakness, tremor), neuroglycopenic symptoms (eg, confusion, loss of consciousness), and/or documented serum glucose of less than 50 mg/dL, in the absence of an alternative explanation. Median time to first hypoglycemia recurrence, hypoglycemia-free survival (HFS), and overall survival (OS) were calculated using Kaplan-Meier method.

Results

Before HAE, all patients experienced adrenergic or neuroglycopenic symptoms alleviated by glucose intake, and 60% (n = 12) of patients had documented serum glucose of less than 50 mg/dL within 1 week of the first treatment. Median post-HAE follow-up was 9.4 months (mean, 26 months; range, 0.1-190 months). Postprocedural hypoglycemic symptom relief after the first HAE was reported in 100% (n = 20) of patients before discharge or at follow-up. Post-HAE hypoglycemia recurrence occurred in 60% (n = 12) of patients with a median time to first hypoglycemia recurrence of 2 months (mean, 14 months; range, 0.2-60 months). After the first HAE, median HFS was 14.5 months, and median OS was 16 months. One patient experienced labile postprocedure blood glucose levels requiring intensive care unit admission for intravenous dextrose. Otherwise, no major procedure-related complications occurred.

Conclusion

Bland HAE is a safe, effective, and repeatable procedure for palliation of symptomatic hypoglycemia in patients with hepatic insulinoma metastases refractory to medical management.

Insulin secretion and action and the response of endogenous glucose production to a lack of glucagon suppression in nondiabetic subjects

Type 2 diabetes is a disease characterized by impaired insulin secretion and defective glucagon suppression in the postprandial period. We examined the effect of impaired glucagon suppression on glucose concentrations and endogenous glucose production (EGP) at different degrees of insulin secretory impairment. The contribution of anthropometric characteristics, peripheral, and hepatic insulin action to this variability was also examined. To do so, we studied 54 nondiabetic subjects on two occasions in which endogenous hormone secretion was inhibited by somatostatin, with glucagon infused at a rate of 0.65 ng/kg/min, at 0 min to prevent a fall in glucagon (nonsuppressed day) or at 120 min to create a transient fall in glucagon (suppressed day). Subjects received glucose (labeled with [3-³H]-glucose) infused to mimic the systemic appearance of 50-g oral glucose. Insulin was infused to mimic a prandial insulin response in 18 subjects, another 18 received 80% of the dose, and the remaining 18 received 60%. EGP was measured using the tracer-dilution technique. Decreased prandial insulin resulted in greater % increase in peak glucose but not in integrated glucose concentrations attributable to nonsuppressed glucagon. The % change in integrated EGP was unaffected by insulin dose. Multivariate regression analysis, adjusted for age, sex, weight, and insulin dose, did not show a relationship between the EGP response to impaired suppression of glucagon and insulin action as measured at the time of screening by oral glucose tolerance. A similar analysis for hepatic insulin action also did not show a relationship with the EGP response. These data indicate that the effect of impaired glucagon suppression on EGP is independent of anthropometric characteristics and insulin action.NEW & NOTEWORTHY In prediabetes, anthropometric characteristics as well as insulin action do not alter the hepatic response to glucagon. The postprandial suppression or lack of suppression of glucagon secretion is an important factor governing postprandial glucose tolerance independent of insulin secretion.

Association of plasma ceramides with prevalent and incident type 2 diabetes mellitus in middle and older aged adults

AIMS

The role of ceramides in the pathogenesis of type 2 diabetes mellitus (T2DM) is incompletely characterized. Given that ceramides represent therapeutic targets to disrupt the euglycemia-T2DM transition, we aimed to characterize their association with prevalent and incident T2DM in a novel cohort.

METHODS

We examined the cross-sectional and longitudinal association of baseline ceramides with prevalent and incident T2DM among 1423 adults (47% women; median (range) baseline age 72 (51-95) years) in the Mayo Clinic Study of Aging cohort. We examined the associations of ceramides with prevalent T2DM (adjusted odds ratio [95% confidence interval]) at baseline and incident T2DM (adjusted hazard ratio [95% confidence interval]) during median follow-up of 6.2 years, after adjusting for demographic and metabolic factors.

RESULTS

Among 1423 adults, there were 222 prevalent and 37 incident cases of T2DM. In cross-sectional analyses, higher levels of ceramide C16:0 were associated with lower odds of prevalent T2DM (aOR 0.84 [0.71-0.99];P = 0.03) whereas C18:0 (aOR 1.27 [1.06-1.42];P = 0.01), C18:0/16:0 (aOR 1.41 [1.22-1.62]; P < 0.001) and C18:0/24:0 (aOR 1.22 [1.05-1.41]; P = 0.01) were associated with higher odds. In Cox hazard regression models, C18:0/16:0 (aHR 1.63 [1.26-2.10];P < 0.001) and C18:0 (aHR 1.53 [1.12-2.08];P = 0.01) were associated with increased risk of incident T2DM.

CONCLUSIONS

In this prospective population-based cohort, ceramides were associated with prevalent T2DM (C16:0,C18:0, C18:0/C16:0 ratio, C18:0/C24:0 ratio) and incident T2DM (C18:0, C18:0/C16:0 ratio) and could suggest targets for the primary and secondary prevention of T2DM.

Pro-inflammatory β cell small extracellular vesicles induce β cell failure through activation of the CXCL10/CXCR3 axis in diabetes

Coordinated communication among pancreatic islet cells is necessary for maintenance of glucose homeostasis. In diabetes, chronic exposure to pro-inflammatory cytokines has been shown to perturb β cell communication and function. Compelling evidence has implicated extracellular vesicles (EVs) in modulating physiological and pathological responses to β cell stress. We report that pro-inflammatory β cell small EVs (cytokine-exposed EVs [cytoEVs]) induce β cell dysfunction, promote a pro-inflammatory islet transcriptome, and enhance recruitment of CD8+ T cells and macrophages. Proteomic analysis of cytoEVs shows enrichment of the chemokine CXCL10, with surface topological analysis depicting CXCL10 as membrane bound on cytoEVs to facilitate direct binding to CXCR3 receptors on the surface of β cells. CXCR3 receptor inhibition reduced CXCL10-cytoEV binding and attenuated β cell dysfunction, inflammatory gene expression, and leukocyte recruitment to islets. This work implies a significant role of pro-inflammatory β cell-derived small EVs in modulating β cell function, global gene expression, and antigen presentation through activation of the CXCL10/CXCR3 axis.

Burden and management of type 2 diabetes in rural United States

In the United States, rural areas have a higher burden of type 2 diabetes (T2DM) compared to urban areas. However, there is limited information on risk factors and interventions that improve the primary prevention and management of T2DM in rural areas. To synthesize current knowledge on T2DM in rural areas and to guide healthcare providers and policy makers, we reviewed five scientific databases and the grey literature over the last decade (2010-2020). We described classification systems for rurality and the T2DM burden based on rurality and region (West, South, Midwest, and Northeast). We highlighted risk factors for T2DM in rural compared to urban areas, and summarized interventions to screen and manage T2DM based on opportunistic screening, T2DM self-management, community-based initiatives, as well as interventions targeting comorbidities and T2DM. Several studies identified the co-existence of T2DM and depression/psychological symptoms, which could reduce adherence to non-pharmacologic and pharmacologic management of T2DM. We highlighted the role of technology in education and counselling of patients with geographic and financial barriers to accessing care, which is exacerbated by the SARS-CoV-2 coronavirus disease-19 pandemic. We identified knowledge gaps and next steps in improving T2DM care in rural areas. There is an urgent need for interventions tailored to rural areas given that rural Americans currently experience a disproportionate burden of T2DM and are encumbered by its associated morbidity, mortality, and loss in economic productivity.

Adipose tissue macrophage populations and inflammation are associated with systemic inflammation and insulin resistance in obesity

Obesity is accompanied by numerous systemic and tissue-specific derangements, including systemic inflammation, insulin resistance, and mitochondrial abnormalities in skeletal muscle. Despite growing recognition that adipose tissue dysfunction plays a role in obesity-related disorders, the relationship between adipose tissue inflammation and other pathological features of obesity is not well-understood. We assessed macrophage populations and measured the expression of inflammatory cytokines in abdominal adipose tissue biopsies in 39 nondiabetic adults across a range of body mass indexes (BMI 20.5-45.8 kg/m²). Skeletal muscle biopsies were used to evaluate mitochondrial respiratory capacity, ATP production capacity, coupling, and reactive oxygen species production. Insulin sensitivity (S_I) and β cell responsivity were determined from test meal postprandial glucose, insulin, c-peptide, and triglyceride kinetics. We examined the relationships between adipose tissue inflammatory markers, systemic inflammatory markers, S_I, and skeletal muscle mitochondrial physiology. BMI was associated with increased adipose tissue and systemic inflammation, reduced S_I, and reduced skeletal muscle mitochondrial oxidative capacity. Adipose-resident macrophage numbers were positively associated with circulating inflammatory markers, including tumor necrosis factor-α (TNFα) and C-reactive protein (CRP). Local adipose tissue inflammation and circulating concentrations of TNFα and CRP were negatively associated with S_I, and circulating concentrations of TNFα and CRP were also negatively associated with skeletal muscle oxidative capacity. These results demonstrate that obese humans exhibit increased adipose tissue inflammation concurrently with increased systemic inflammation, reduced insulin sensitivity, and reduced muscle oxidative capacity and suggest that adipose tissue and systemic inflammation may drive obesity-associated metabolic derangements.NEW AND NOTEWORTHY Adipose inflammation is proposed to be at the nexus of the systemic inflammation and metabolic derangements associated with obesity. The present study provides evidence to support adipose inflammation as a central feature of the pathophysiology of obesity. Adipose inflammation is associated with systemic and peripheral metabolic derangements, including increased systemic inflammation, reduced insulin sensitivity, and reduced skeletal muscle mitochondrial respiration.

Measurement of Pulsatile Insulin Secretion: Rationale and Methodology

Pancreatic β-cells are responsible for the synthesis and exocytosis of insulin in response to an increase in circulating glucose. Insulin secretion occurs in a pulsatile manner, with oscillatory pulses superimposed on a basal secretion rate. Insulin pulses are a marker of β-cell health, and secretory parameters, such as pulse amplitude, time interval and frequency distribution, are impaired in obesity, aging and type 2 diabetes. In this review, we detail the mechanisms of insulin production and β-cell synchronization that regulate pulsatile insulin secretion, and we discuss the challenges to consider when measuring fast oscillatory secretion in vivo. These include the anatomical difficulties of measuring portal vein insulin noninvasively in humans before the hormone is extracted by the liver and quickly removed from the circulation. Peripheral concentrations of insulin or C-peptide, a peptide cosecreted with insulin, can be used to estimate their secretion profile, but mathematical deconvolution is required. Parametric and nonparametric approaches to the deconvolution problem are evaluated, alongside the assumptions and trade-offs required for their application in the quantification of unknown insulin secretory rates from known peripheral concentrations. Finally, we discuss the therapeutical implication of targeting impaired pulsatile secretion and its diagnostic value as an early indicator of β-cell stress.

Limitations of the fasting proinsulin to insulin ratio as a measure of β-cell health in people with and without impaired glucose tolerance

BACKGROUND

The fasting proinsulin to insulin ratio is elevated in people with type 2 diabetes and has been suggested as a marker of β-cell health. However, its utility in discriminating between individuals with varying degrees of β-cell dysfunction is unclear. Proinsulin has a very different half-life to insulin and unlike insulin does not undergo hepatic extraction prior to reaching the systemic circulation. Given these limitations, we sought to examine the relationship between fasting and postprandial concentrations of β-cell polypeptides (proinsulin, insulin and C-peptide) in people with normal and impaired glucose tolerance in differing metabolic environments.

DESIGN

Subjects were studied on two occasions in random order while undergoing an oral challenge. During one study day, free fatty acids were elevated (to induce insulin resistance) by infusion of Intralipid with heparin. Proinsulin to insulin and proinsulin to C-peptide ratios were calculated for the 0-, 30-, 60- and 240-minute time points. Insulin action (Si) and β-cell responsivity (Φ) indices were calculated using the oral minimal model.

RESULTS

The fasting proinsulin to c-peptide or fasting proinsulin to insulin ratios did not differ between groups and did not predict subsequent β-cell responsivity to glucose during the glycerol or Intralipid study days in either group.

CONCLUSIONS

Among nondiabetic individuals, the fasting proinsulin to insulin ratio is not a useful marker of β-cell function.

Insulin Pulse Characteristics and Insulin Action in Non-diabetic Humans

OBJECTIVE

Pulsatile insulin secretion is impaired in diseases such as type 2 diabetes that are characterized by insulin resistance. This has led to the suggestion that changes in insulin pulsatility directly impair insulin signaling. We sought to examine the effects of pulse characteristics on insulin action in humans, hypothesizing that a decrease in pulse amplitude or frequency is associated with impaired hepatic insulin action.

METHODS

We studied 29 nondiabetic subjects on two occasions. On 1 occasion, hepatic and peripheral insulin action was measured using a euglycemic clamp. The deuterated water method was used to estimate the contribution of gluconeogenesis to endogenous glucose production. On a separate study day, we utilized nonparametric stochastic deconvolution of frequently sampled peripheral C-peptide concentrations during fasting to reconstruct portal insulin secretion. In addition to measuring basal and pulsatile insulin secretion, we used approximate entropy to measure orderliness and Fourier transform to measure the average, and the dispersion of, insulin pulse frequencies.

RESULTS

In univariate analysis, basal insulin secretion (R2 = 0.16) and insulin pulse amplitude (R2 = 0.09) correlated weakly with insulin-induced suppression of gluconeogenesis. However, after adjustment for age, sex, and weight, these associations were no longer significant. The other pulse characteristics also did not correlate with the ability of insulin to suppress endogenous glucose production (and gluconeogenesis) or to stimulate glucose disappearance.

CONCLUSIONS

Overall, our data demonstrate that insulin pulse characteristics, considered independently of other factors, do not correlate with measures of hepatic and peripheral insulin sensitivity in nondiabetic humans.