Ethnic differences in beta cell function occur independently of insulin sensitivity and pancreatic fat in black and white men

Myths and methodologies: Assessing glycaemic control and associated regulatory mechanisms in human physiology research

Accurate measurements of glycaemic control and the underpinning regulatory mechanisms are vital in human physiology research. Glycaemic control is the maintenance of blood glucose concentrations within optimal levels and is governed by physiological variables including insulin sensitivity, glucose tolerance and β-cell function. These can be measured with a plethora of methods, all with their own benefits and limitations. Deciding on the best method to use is challenging and depends on the specific research question(s). This review therefore discusses the theory and procedure, validity and reliability and any special considerations of a range common methods used to measure glycaemic control, insulin sensitivity, glucose tolerance and β-cell function. Methods reviewed include glycosylated haemoglobin, continuous glucose monitors, the oral glucose tolerance test, mixed meal tolerance test, hyperinsulinaemic euglycaemic clamp, hyperglycaemic clamp, intravenous glucose tolerance test and indices derived from both fasting concentrations and the oral glucose tolerance test. This review aims to help direct understanding, assessment and decisions regarding which method to use based on specific physiology-related research questions.

Insulin sensitivity and skeletal muscle mitochondrial respiration in Black and White women with obesity

OBJECTIVES

Non-Hispanic black women (BW) have a greater risk of type 2 diabetes (T2D) and insulin resistance (IR) compared to non-Hispanic white women (WW). The mechanisms leading to these differences are not understood, and it is unclear whether synergistic effects of race and obesity impact disease risk. To understand the interaction of race and weight, hepatic and peripheral IR were compared in WW and BW with and without obesity.

METHODS

Hepatic and peripheral IR was measured by a labeled, hyperinsulinemic-euglycemic clamp in BW (n=32) and WW (n=32) with and without obesity. Measurements of body composition, cardiorespiratory fitness, and skeletal muscle (SM) respiration were completed. Data were analyzed by mixed model ANOVA.

RESULTS

Subjects with obesity had greater hepatic and peripheral IR and lower SM respiration (P<0.001). Despite 14% greater insulin (P=0.066), BW tended to have lower peripheral glucose disposal (Rd; P=0.062), which was driven by women without obesity (P=0.002). BW had significantly lower glucose production (P=0.005), hepatic IR (P=0.024), and maximal coupled and uncoupled respiration (P<0.001) than WW. Maximal coupled and uncoupled SM mitochondrial respiration was strongly correlated with peripheral and hepatic IR (P<0.01).

CONCLUSION

While BW without obesity had lower Rd than WW, race and obesity did not synergistically impact peripheral IR. Paradoxically, WW with obesity had greater hepatic IR compared to BW. Relationships between SM respiration and IR persisted across a range of body weight. These data provide support for therapies in BW, like exercise, that improve SM mitochondrial respiration to reduce IR and T2D risk.

Determining the 1-hour post-load glucose which identifies diabetes in Africans: Insight from the Africans in America study

Diagnosing diabetes by shortening the OGTT to 1-h and substituting 1-h post-load glucose (PG) ≥ 209 mg/dL for 2-h PG≥200 mg/dL has been proposed. One-hour PG≥209 mg/dL is from a meta-analysis without any African-descent populations. Our data suggest 1-h PG≥183 mg/dL maybe more optimal for Africans. As with waist circumference guidelines, population-specific thresholds may be appropriate.

Beta cell lipotoxicity in the development of type 2 diabetes: the need for species-specific understanding

The propensity to develop type 2 diabetes (T2D) is known to have both environmental and hereditary components. In those with a genetic predisposition to T2D, it is widely believed that elevated concentrations of circulatory long-chain fatty acids (LC-FFA) significantly contribute towards the demise of insulin-producing pancreatic β-cells - the fundamental feature of the development of T2D. Over 25 years of research support that LC-FFA are deleterious to β-cells, through a process termed lipotoxicity. However, the work underpinning the theory of β-cell lipotoxicity is mostly based on rodent studies. Doubts have been raised as to whether lipotoxicity also occurs in humans. In this review, we examine the evidence, both in vivo and in vitro, for the pathogenic effects of LC-FFA on β-cell viability and function in humans, highlighting key species differences. In this way, we aim to uncover the role of lipotoxicity in the human pathogenesis of T2D and motivate the need for species-specific understanding.

Ethnicity/race, parent educational attainment, and obesity associated with prediabetes in children

BACKGROUND/OBJECTIVES

Obesity and other predictors of type 2 diabetes disproportionally affect Hispanic and Black children in the US compared to non-Hispanic White (NHW) children. Yet, the prevalence of prediabetes in children remains unestablished, and guidelines for screening young children are lacking. This study examined the relationships between demographic factors and prediabetes in vulnerable youth in central Texas.

SUBJECTS/METHODS

This is a cross-sectional analysis of baseline data from 976 3rd-5th graders (7-12 years) who participated in TX Sprouts, a school-based gardening, nutrition, and cooking trial in 16 elementary schools serving mainly children from minority backgrounds and lower-income households. Measures collected included age, sex, ethnicity, free/reduced-priced school lunch (FRL) status, parent educational attainment (questionnaires), BMI from height (stadiometer) and weight (TANITA scale), and prediabetes status from fasting plasma glucose (FPG) and HbA1c. Regressions examined cross-sectional associations between demographics and FPG, HbA1c, and prediabetes.

RESULTS

Children were 47% male, 67% Hispanic, and 10% Black, with a mean age of 9.3 years; 71% received FRL, 50% had overweight/obesity, and 26% had prediabetes. Prediabetes rates were 2.8 and 4.8 times higher in Hispanic and Black children compared to NHW children, respectively (p ≤ 0.001), and 1.5 times higher in children with obesity versus normal BMI (p = 0.02). Children of parents with only an 8th-grade education, some high school education, or a high school degree had 3.1, 2.7, and 2.2 times higher odds of having prediabetes compared to children of college graduates, respectively (p ≤ 0.004). Analyses with FPG and HbA1c yielded similar results.

CONCLUSION

These findings suggest a potential need for earlier screening, more comprehensive testing guidelines, and prevention programs tailored toward minority children, children with obesity, and children of parents with low educational attainment. Future research should explore this finding in a larger, nationally representative sample.

A Scoping Review of Trials Designed to Achieve Remission of Type 2 Diabetes with Lifestyle Intervention Alone: Implications for Sub-Saharan Africa

According to the International Diabetes Federation, sub-Saharan Africa is experiencing the highest anticipate increase in the prevalence of type 2 diabetes (T2D) in the world and has the highest percent of people living with T2D who are undiagnosed. Therefore, diagnosis and treatment need prioritization. However, pharmacological hypoglycemics are often unavailable and bariatric surgery is not an option. Therefore, the ability to induce T2D remission through lifestyle intervention alone (LSI-alone) needs assessment. This scoping review evaluated trials designed to induce T2D remission by LSI-alone. PubMed, Embase, Cochrane, and CINAHL databases were searched for trials designed to induce T2D remission through LSI-alone. Of the 928 identified, 63 duplicates were removed. With abstract review, 727 irrelevant articles were excluded. After full-text review, 112 inappropriate articles were removed. The remaining 26 articles described 16 trials. These trials were published between 1984 and 2021 and were conducted in 10 countries, none of which were in Africa. Remission rates varied across trials. Predictors of remission were 10% weight loss and higher BMI, lower A1C and shorter T2D duration at enrollment. However, LSI-alone regimens for newly diagnosed and established T2D were very different. In newly diagnosed T2D, LSI-alone were relatively low-cost and focused on exercise and dietary counseling with or without calorie restriction (~1500 kcal/d). Presumably due to differences in cost, LSI-alone trials in newly diagnosed T2D had higher enrollments and longer duration. For established T2D trials, the focus was on arduous phased dietary interventions; phase 1: low-calorie meal replacement (<1000 kcal/day); phase 2: food re-introduction; phase 3: weight maintenance. In short, LSI-alone can induce remission in both newly diagnosed and established T2D. To demonstrate efficacy in Africa, initial trials could focus on newly diagnosed T2D. Insight gained could provide proof of concept and a foundation in Africa on which successful studies of LSI-alone in established T2D could be built.

Black New Yorkers with Type 2 Diabetes: Afro-Caribbean Immigrants Have Lower BMI and Lower Waist Circumference than African Americans

OBJECTIVE

Using the 2013/2014 New York City (NYC) Health and Nutrition Examination Survey (NYCHANES) data, this exploratory study examined whether (a) type 2 diabetes (diabetes) prevalence differed between NYC Afro-Caribbeans and African Americans; (b) anthropometric, biochemical, and sociodemographic diabetes profiles differed between and within groups; and (c) diabetes odds differed between and within groups.

METHODS

Diabetes was defined as prior diagnosis, HbA1c ≥ 6.5% (7.8 mmol/L), or fasting glucose ≥ 126 mg/dL. Weighted logistic regression estimated diabetes odds by nativity and either waist circumference (WC) (cm) or BMI (kg/m²). All regression models controlled for age, hypertension, gender, education, income, marital status, physical activity, and smoking.

RESULTS

Among Afro-Caribbeans (n = 81, 65% female, age (mean ± SE) 49 ± 2 years, BMI 29.2 ± 0.7 kg/m²) and African Americans (n = 118, 50% female, age 47 ± 2 years, BMI 30.3 ± 0.9 kg/m²), Afro-Caribbeans with diabetes had lower BMI (29.9 ± 0.8 kg/m² vs. 34.6 ± 1.7 kg/m², P = 0.01) and lower WC (102 ± 2 cm vs. 114 ± 3 cm, P = 0.002) than African Americans with diabetes. Afro-Caribbeans with diabetes had lower prevalence of obesity (33.2% vs. 74.7%) and higher prevalence of overweight (57.2% vs. 13.5%) (P = 0.02) than African Americans with diabetes. Odds of diabetes did not differ between Afro-Caribbeans and African Americans. In models predicting the effect of WC, diabetes odds increased with WC (OR = 1.07 (95% CI 1.02, 1.11), P = 0.003) and age (OR = 1.09 (95% CI 1.03-1.15), P = 0.003) for African Americans only. In models predicting the effect of BMI, diabetes odds increased for Afro-Caribbeans with age (OR = 1.06 (1.01, 1.11)*, P = 0.04) and hypertension (OR = 5.62 (95% CI 1.04, 30.42), P = 0.045), whereas for African Americans, only age predicted higher diabetes odds (OR = 1.08 (95% CI 1.03, 1.14), P = 0.003).

CONCLUSIONS

In NYC, Afro-Caribbeans with diabetes have lower BMI and lower WC than African Americans with diabetes, but odds of diabetes do not differ. Combining African-descent populations into one group obscures clinical differences and generalizes diabetes risk.

When Sugar Reaches the Liver: Phenotypes of Patients with Diabetes and NAFLD

Type 2 diabetes mellitus (T2DM) and non-alcoholic fatty liver disease (NAFLD) have been traditionally linked to one another. Recent studies suggest that NAFLD may be increasingly common in other types of diabetes such as type 1 diabetes (T1DM) and less frequently ketone-prone and Maturity-onset Diabetes of the Young (MODY) diabetes. In this review, we address the relationship between hyperglycemia and insulin resistance and the onset and progression of NAFLD. In addition, despite the high rate of patients with T2DM and other diabetes phenotypes that can alter liver metabolism and consequently develop steatosis, fibrosis, and cirrhosis, NALFD screening is not still implemented in the daily care routine. Incorporating a clinical algorithm created around a simple, non-invasive, cost-effective model would identify high-risk patients. The principle behind managing these patients is to improve insulin resistance and hyperglycemia states with lifestyle changes, weight loss, and new drug therapies.

Exploring the determinants of ethnic differences in insulin clearance between men of Black African and White European ethnicity

AIM

People of Black African ancestry, who are known to be at disproportionately high risk of type 2 diabetes (T2D), typically exhibit lower hepatic insulin clearance compared with White Europeans. However, the mechanisms underlying this metabolic characteristic are poorly understood. We explored whether low insulin clearance in Black African (BA) men could be explained by insulin resistance, subclinical inflammation or adiponectin concentrations.

METHODS

BA and White European (WE) men, categorised as either normal glucose tolerant (NGT) or with T2D, were recruited to undergo the following: a mixed meal tolerance test with C-peptide modelling to determine endogenous insulin clearance; fasting serum adiponectin and cytokine profiles; a hyperinsulinaemic-euglycaemic clamp to measure whole-body insulin sensitivity; and magnetic resonance imaging to quantify visceral adipose tissue.

RESULTS

Forty BA (20 NGT and 20 T2D) and 41 WE (23 NGT and 18 T2D) men were studied. BA men had significantly lower insulin clearance (P = 0.011) and lower plasma adiponectin (P = 0.031) compared with WE men. In multiple regression analysis, ethnicity, insulin sensitivity and plasma adiponectin were independent predictors of insulin clearance, while age, visceral adiposity and tumour necrosis factor alpha (TNF-α) did not significantly contribute to the variation.

CONCLUSION

These data suggest that adiponectin may play a direct role in the upregulation of insulin clearance beyond its insulin-sensitising properties.

Insulin sensitivity and kinetics in African American and White people with obesity: Insights from different study protocols

OBJECTIVE

Studies that used an intravenous glucose tolerance test (IVGTT) have suggested that race is an important modulator of insulin sensitivity, β-cell function, and insulin clearance. However, the validity of the IVGTT has been challenged.

METHODS

This study assessed insulin sensitivity and insulin kinetics in non-Hispanic White (NHW, n = 29) and African American (AA, n = 14) people with obesity by using a hyperinsulinemic-euglycemic pancreatic clamp with glucose tracer infusion, an oral glucose tolerance test (OGTT), and an IVGTT.

RESULTS

Hepatic insulin sensitivity was better in AA participants than in NHW participants. Muscle insulin sensitivity, insulin secretion in relation to plasma glucose during the OGTT, and insulin clearance during basal conditions during the hyperinsulinemic-euglycemic pancreatic clamp and during the OGTT were not different between AA participants and NHW participants. The acute insulin response to the large glucose bolus administered during the IVGTT was double in AA participants compared with NHW participants because of increased insulin secretion and reduced insulin clearance.

CONCLUSIONS

AA individuals are not more insulin resistant than NHW individuals, and the β-cell response to glucose ingestion and postprandial insulin clearance are not different between AA individuals and NHW individuals. However, AA individuals have greater insulin secretory capacity and reduced insulin clearance capacity than NHW individuals and might be susceptible to hyperinsulinemia after consuming very large amounts of glucose.

Association of low fasting C-peptide levels with cardiovascular risk, visit-to-visit glucose variation and severe hypoglycemia in the Veterans Affairs Diabetes Trial (VADT)

Aims

Low C-peptide levels, indicating beta-cell dysfunction, are associated with increased within-day glucose variation and hypoglycemia. In advanced type 2 diabetes, severe hypoglycemia and increased glucose variation predict cardiovascular (CVD) risk. The present study examined the association between C-peptide levels and CVD risk and whether it can be explained by visit-to-visit glucose variation and severe hypoglycemia.

Materials and methods

Fasting C-peptide levels at baseline, composite CVD outcome, severe hypoglycemia, and visit-to-visit fasting glucose coefficient of variation (CV) and average real variability (ARV) were assessed in 1565 Veterans Affairs Diabetes Trial participants.

Results

There was a U-shaped relationship between C-peptide and CVD risk with increased risk with declining levels in the low range (< 0.50 nmol/l, HR 1.30 [95%CI 1.05–1.60], p = 0.02) and with rising levels in the high range (> 1.23 nmol/l, 1.27 [1.00–1.63], p = 0.05). C-peptide levels were inversely associated with the risk of severe hypoglycemia (OR 0.68 [0.60–0.77]) and visit-to-visit glucose variation (CV, standardized beta-estimate − 0.12 [SE 0.01]; ARV, − 0.10 [0.01]) (p < 0.0001 all). The association of low C-peptide levels with CVD risk was independent of cardiometabolic risk factors (1.48 [1.17–1.87, p = 0.001) and remained associated with CVD when tested in the same model with severe hypoglycemia and glucose CV.

Conclusions

Low C-peptide levels were associated with increased CVD risk in advanced type 2 diabetes. The association was independent of increases in glucose variation or severe hypoglycemia. C-peptide levels may predict future glucose control patterns and CVD risk, and identify phenotypes influencing clinical decision making in advanced type 2 diabetes.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12933-021-01418-z.

Short-Term SGLT2 Inhibitor Administration Does Not Alter Systemic Insulin Clearance in Type 2 Diabetes

Background: Decreased insulin clearance could be a relatively upstream abnormality in obesity, metabolic syndrome, and nonalcoholic fatty liver disease. Previous studies have shown that sodium-glucose cotransporter 2 inhibitor (SGLT2i) increases insulin–C-peptide ratio, a marker of insulin clearance, and improves metabolic parameters. We evaluated the effects of the SGLT2i tofogliflozin on metabolic clearance rate of insulin (MCRI) with a hyperinsulinemic euglycemic clamp study, the gold standard for measuring systemic insulin clearance. Methods: Study participants were 12 Japanese men with type 2 diabetes. We evaluated MCRI and tissue-specific insulin sensitivity with a hyperinsulinemic euglycemic clamp (insulin infusion rate, 40 mU/m²·min) before and immediately after a single dose (n = 12) and 8 weeks (n = 9) of tofogliflozin. We also measured ectopic fat in muscle and liver and the abdominal fat area using ¹H-magnetic resonance spectroscopy and magnetic resonance imaging, respectively, before and after 8 weeks of tofogliflozin. Results: MCRI did not change after a single dose of tofogliflozin (594.7 ± 67.7 mL/min·m² and 608.3 ± 90.9 mL/min·m², p = 0.61) or after 8 weeks (582.5 ± 67.3 mL/min·m² and 602.3 ± 67.0 mL/min·m², p = 0.41). The 8-week treatment significantly improved glycated hemoglobin and decreased body weight (1.7%) and the subcutaneous fat area (6.4%), whereas insulin sensitivity and ectopic fat in muscle and liver did not change significantly. Conclusions: MCRI did not change after a single dose or 8 weeks of tofogliflozin. Increased MCRI does not precede a decrease in body fat or improved glycemic control.

Cardiovascular outcomes of antidiabetes medications by race/ethnicity: A systematic review and meta-analysis

BACKGROUND

The consistency of cardiovascular risk reduction by antidiabetes medications across racial and ethnic groups remains unclear. The aim of this study was to analyze racial/ethnic patterns in the results of cardiovascular outcomes trials of antidiabetes medications in people with type 2 diabetes.

METHOD

PubMed and Cochrane library databases were searched from the inception dates to December 2020. Cardiovascular outcome trials in type 2 diabetes that randomized participants to antidiabetes medication or control treatment and reported results by race/ethnic groups or region were included.

RESULTS

A total of 19 studies were included in this meta-analysis. Among White participants, treatment with antidiabetes medications significantly decreased the risk of composite cardiovascular outcomes when compared with placebo treatment (OR = 0.88, 95% CI 0.83-0.94, p < 0.05). Among Asian participants, antidiabetes medications also significantly decreased the risk of composite cardiovascular outcomes when compared with control treatment (OR = 0.80, 95% CI 0.74-0.86, p < 0.05). A similar pattern was found when analyzing the effects of antidiabetes medications vs. control treatment in other racial/ethnic groups comprising mostly Hispanics and Pacific Islanders (OR = 0.87, 95% CI 0.78-0.98, p < 0.05). However, among Black participants, treatment with antidiabetes medications resulted in nominal but non-significant decreases in the composite cardiovascular outcomes when compared with control treatment (OR = 0.84, 95% CI 0.62-1.14, p = 0.26).

CONCLUSIONS

The present meta-analysis showed cardiovascular safety of antidiabetes medications in people with type 2 diabetes from all racial/ethnic groups studied; however, significant composite cardiovascular risk reductions were demonstrated only in White and Asian participants. To determine whether antidiabetes drugs confer consistent cardiovascular benefits in Black and other racial/ethnic participants requires more investigations in the future.

Anthropometric cut-offs to identify hyperglycemia in an Afro-Caribbean population: a cross-sectional population-based study from Barbados

INTRODUCTION

Body mass index (BMI) and waist circumference (WC) cut-offs associated with hyperglycemia may differ by ethnicity. We investigated the optimal BMI and WC cut-offs for identifying hyperglycemia in the predominantly Afro-Caribbean population of Barbados.

RESEARCH DESIGN AND METHODS

A cross-sectional study of 865 individuals aged ≥25 years without known diabetes or cardiovascular disease was conducted. Hyperglycemia was defined as fasting plasma glucose ≥5.6 mmol/L or hemoglobin A_1c ≥5.7% (39 mmol/mol). The Youden index was used to identify the optimal cut-offs from the receiver operating characteristic (ROC) curves. Further ROC analysis and multivariable log binomial regression were used to compare standard and data-derived cut-offs.

RESULTS

The prevalence of hyperglycemia was 58.9% (95% CI 54.7% to 63.0%). In women, optimal BMI and WC cut-offs (27 kg/m² and 87 cm, respectively) performed similarly to standard cut-offs. In men, sensitivities of the optimal cut-offs of BMI ≥24 kg/m² (72.0%) and WC ≥86 cm (74.0%) were higher than those for standard BMI and WC obesity cut-offs (30.0% and 25%-46%, respectively), although with lower specificity. Hyperglycemia was 70% higher in men above the data-derived WC cut-off (prevalence ratio 95% CI 1.2 to 2.3).

CONCLUSIONS

While BMI and WC cut-offs in Afro-Caribbean women approximate international standards, our findings, consistent with other studies, suggest lowering cut-offs in men may be warranted to improve detection of hyperglycemia. Our findings do, however, require replication in a new data set.