comparative study of glucose homeostasis, lipids and lipoproteins, HDL functionality, and cardiometabolic parameters in modestly severely obese African Americans and White Americans with prediabetes: implications for the metabolic paradoxes

Data-driven Cluster Analysis Reveals Increased Risk for Severe Insulin-deficient Diabetes in Black/African Americans

CONTEXT

Diabetes is a heterogenic disease and distinct clusters have emerged, but the implications for diverse populations have remained understudied.

OBJECTIVE

Apply cluster analysis to a diverse diabetes cohort in the US Deep South.

DESIGN

Retrospective hierarchical cluster analysis of electronic health records from 89 875 patients diagnosed with diabetes between January 1, 2010, and December 31, 2019, at the Kirklin Clinic of the University of Alabama at Birmingham, an ambulatory referral center.

PATIENTS

Adult patients with International Classification of Diseases diabetes codes were selected based on available data for 6 established clustering parameters (glutamic acid decarboxylase autoantibody; hemoglobin A1c; body mass index; diagnosis age; HOMA2-B; HOMA2-IR); ∼42% were Black/African American.

MAIN OUTCOME MEASURE(S)

Diabetes subtypes and their associated characteristics in a diverse adult population based on clustering analysis. We hypothesized that racial background would affect the distribution of subtypes. Outcome and hypothesis were formulated prior to data collection.

RESULTS

Diabetes cluster distribution was significantly different in Black/African Americans compared to Whites (P < .001). Black/African Americans were more likely to have severe insulin-deficient diabetes (OR, 1.83; 95% CI, 1.36-2.45; P < .001), associated with more serious metabolic perturbations and a higher risk for complications (OR, 1.42; 95% CI, 1.06-1.90; P = .020). Surprisingly, Black/African Americans specifically had more severe impairment of β-cell function (homoeostatic model assessment 2 estimates of β-cell function, C-peptide) (P < .001) but not being more obese or insulin resistant.

CONCLUSION

Racial background greatly influences diabetes cluster distribution and Black/African Americans are more frequently and more severely affected by severe insulin-deficient diabetes. This may further help explain the disparity in outcomes and have implications for treatment choice.

Ethnic Disparities in the Risk Factors, Morbidity, and Mortality of Cardiovascular Disease in People With Diabetes

Cardiovascular disease (CVD) is the leading cause of death in people with diabetes. Compared with European Americans, African Americans have more favorable lipid profiles, as indicated by higher high-density lipoprotein cholesterol, lower triglycerides, and less dense low-density lipoprotein particles. The less atherogenic lipid profile translates to lower incidence and prevalence of CVD in African Americans with diabetes, despite higher rates of hypertension and obesity. However, African Americans with CVD experience worse clinical outcomes, including higher mortality, compared with European Americans. This mini-review summarizes the epidemiology, pathophysiology, mechanisms, and management of CVD in people with diabetes, focusing on possible factors underlying the "African American CVD paradox" (lower CVD incidence/prevalence but worse outcomes). Although the reasons for the disparities in CVD outcomes remain to be fully elucidated, we present a critical appraisal of the roles of suboptimal control of risk factors, inequities in care delivery, several biological factors, and psychosocial stress. We identify gaps in current knowledge and propose areas for future investigation.

Aging Affects Insulin Resistance, Insulin Secretion, and Glucose Effectiveness in Subjects with Normal Blood Glucose and Body Weight

AIM

Several studies have demonstrated that factors including diabetes, including insulin resistance (IR), glucose effectiveness (GE), and the first and second phase of insulin secretion (FPIS, SPIS) could easily be calculated using basic characteristics and biochemistry profiles. Aging is accompanied by deteriorations of insulin resistance (IR) and insulin secretion. However, little is known about the roles of aging in the different phases of insulin secretion (ISEC), i.e., the first and second phase of insulin secretion (FPIS, SPIS), and glucose effectiveness (GE).

METHODS

In total, 169 individuals (43 men and 126 women) recruited from the data bank of the Meei-Jaw (MJ) Health Screening Center and Cardinal Tien Hospital Data Access Center between 1999 and 2008, with a similar fasting plasma glucose (FPG: 90 mg/dL) and BMI (men: 23 kg/m², women 22 kg/m²) were enrolled. The IR, FPIS, SPIS, and GE were estimated using our previously developed equations shown below. Pearson correlation analysis was conducted to assess the correlations between age and four diabetes factors (DFs: IR, FPIS, SPIS, and GE). The equations that are used to calculate the DF in the present study were built and published by our group.

RESULTS

The age of the participants ranged from 18 to 78 years. Men had higher FPIS but lower HDL-C levels than women (2.067 ± 0.159, 1.950 ± 0.186 μU/min and 1.130 ± 0.306, 1.348 ± 0.357 mmol/dl, accordingly). The results of the Pearson correlation revealed that age was negatively related to the IR and GE in both genders (IR: r = -0.39, p < 0.001 for men, r = -0.24, p < 0.003 for women; GE: r = 0.66, p < 0.001 for men, r = 0.78, p < 0.001 for women). At the same time, the FPIS was also only found to be negatively correlated with age in females (r = -0.238, p = 0.003), but there was no difference in the SPIS and age among both genders.

CONCLUSIONS

We have found that in Chinese subjects with a normal FPG level (90 mg/dL) and body mass index (men: 23 kg/m², women: 22: kg/m²), age is negatively related to the IR and GE among both genders. Only the FPIS was found to be negatively related to age in women. The tightness of their relationships, from the highest to the lowest, are GE, FPIS, and IR. These results should be interpreted with caution because of the small sample size.

Cardiometabolic risk factors and cardiovascular disease predictions in older African and European Americans

Cardiometabolic (CMO) risks factors do not provide similar cardiovascular disease (CVD) predictions in young African (AA) and European Americans (EA) adults. Whether CMO risk predictions contribute to this disparity in older adults is unclear. We hypothesize that older AA CMO clustering pattern will be different from EA clustering patterns when determine with non-fasting lipid and lipoproteins. The participants were 106 older adults (66 AA and 40 EA) from a working/middle class neighborhood (income $46,364 – $80,904) in an urban North Carolina community. The participants were evaluated for CMO risk factors (total cholesterol, high- (HDL) and low-density lipoproteins (LDL), triglyceride (TG), glycosylated hemoglobin (HbA1c), systolic –SBP- and diastolic blood pressures -DBP), body mass index (BMI), body fat % (BF%) and timed up and go test (assessed falls risk and physical function). The AA participants were heavier, had higher BMI, BF%, and timed up and go values (p < 0.01). The data were evaluated for differences (t-test) and Pearson correlations for relationships. If data differ by p < 0.05 the data were significantly different. The AA had a 17.6 % higher HDL (64.7 vs 55.1 mg/dL – p < 0.05) and 7.6 % higher HbA1c (5.8 vs 5.4 % – p < 0.01) than EA. Higher HDL values in EA indicate lower CVD risks. The HDL paradox for AA (AA had higher HDL values, but greater CVD risks) was observed and the HbA1c difference may be misleading, as similar glucose values in AA tend to have higher HbA1c values. Lipid, lipoprotein, and blood pressure was not different between the races. AA had higher body composition and HDL values. Although future research on this topic with larger samples, dietary data and detailed descriptions of participations medications is warranted to validate findings from this study. These data suggest older AA and EA adults with similar environmental conditions have similar CMO risks when measures with none fasting blood samples. Since AA have a greater prevalence of CVD, these finding suggests that population specific CMO risk factor clustering may be more effective predictors of CVD for AA.

Ethnic disparities attributed to the manifestation in and response to type 2 diabetes: insights from metabolomics

Type 2 diabetes (T2D) associated health disparities among different ethnicities have long been known. Ethnic variations also exist in T2D related comorbidities including insulin resistance, vascular complications and drug response. Genetic heterogeneity, dietary patterns, nutrient metabolism and gut microbiome composition attribute to ethnic disparities in both manifestation and progression of T2D. These factors differentially regulate the rate of metabolism and metabolic health. Metabolomics studies have indicated significant differences in carbohydrate, lipid and amino acid metabolism among ethnicities. Interestingly, genetic variations regulating lipid and amino acid metabolism might also contribute to inter-ethnic differences in T2D. Comprehensive and comparative metabolomics analysis between ethnicities might help to design personalized dietary regimen and newer therapeutic strategies. In the present review, we explore population based metabolomics data to identify inter-ethnic differences in metabolites and discuss how (a) genetic variations, (b) dietary patterns and (c) microbiome composition may attribute for such differences in T2D.

A Systematic Review of Beta Cell Function in Adults of Black African Ethnicity

BACKGROUND

Understanding ethnic differences in beta cell function has important implications for preventative and therapeutic strategies in populations at high risk of type 2 diabetes (T2D). The existing literature, largely drawn from work in children and adolescents, suggests that beta cell function in black African (BA) populations is upregulated when compared to white Europeans (WE).

METHODS

A systematic literature search was undertaken in June 2018 to identify comparative studies of beta cell function between adults (>age 18 years) of indigenous/diasporic BA and WE ethnicity. All categories of glucose tolerance and all methodologies of assessing beta cell function in vivo were included.

RESULTS

41 studies were identified for inclusion into a qualitative synthesis. The majority were studies in African American populations (n = 30) with normal glucose tolerance (NGT)/nondiabetes (n = 25), using intravenous glucose stimulation techniques (n = 27). There were fewer studies in populations defined as only impaired fasting glucose/impaired glucose tolerance (IFG/IGT) (n = 3) or only T2D (n = 3). Although BA broadly exhibited greater peripheral insulin responses than WE, the relatively small number of studies which measured C-peptide to differentiate between beta cell insulin secretion and hepatic insulin extraction (n = 14) had highly variable findings. In exclusively IGT or T2D cohorts, beta cell insulin secretion was found to be lower in BA compared to WE.

CONCLUSIONS

There is inconsistent evidence for upregulated beta cell function in BA adults, and they may in fact exhibit greater deficits in insulin secretory function as glucose intolerance develops.

Assessing the predictive accuracy of oral glucose effectiveness index using a calibration model

PURPOSE

Current reference methods for measuring glucose effectiveness (GE) are the somatostatin pancreatic glucose clamp and minimal model analysis of frequently sampled intravenous glucose tolerance test (FSIVGTT), both of which are laborious and not feasible in large epidemiological studies. Consequently, surrogate indices derived from an oral glucose tolerance test (OGTT) to measure GE (oGE) have been proposed and used in many studies. However, the predictive accuracy of these surrogates has not been formally validated. In this study, we used a calibration model analysis to evaluate the accuracy of surrogate indices to predict GE from the reference FSIVGTT (Sg_MM).

METHODS

Subjects (n = 123, mean age 48 ± 11 years; BMI 35.9 ± 7.3 kg/m²) with varying glucose tolerance (NGT, n = 37; IFG/IGT, n = 78; and T2DM, n = 8) underwent FSIVGTT and OGTT on two separate days. Predictive accuracy was assessed by both root mean squared error (RMSE) of prediction and leave-one-out cross-validation-type RMSE of prediction (CVPE).

RESULTS

As expected, insulin sensitivity, Sg_MM, and oGE were reduced in subjects with T2DM and IFG/IGT when compared with NGT. Simple linear regression analyses revealed a modest but significant relationship between oGE and Sg_MM (r = 0.25, p < 0.001). However, using calibration model, measured Sg_MM and predicted Sg_MM derived from oGE were modestly correlated (r = 0.21, p < 0.05) with the best fit line suggesting poor predictive accuracy. There were no significant differences in CVPE and RMSE among the surrogates, suggesting similar predictive ability.

CONCLUSIONS

Although OGTT-derived surrogate indices of GE are convenient and feasible, they have limited ability to robustly predict GE.

Pathogenic Mechanisms of Prediabetes in Obese vs. Very Obese African American Women: Implications for Diabetes Prevention

BACKGROUND

The influence of obesity on the development of prediabetes among African American women (AAW) remains uncertain. Thus, we investigated whether the pathogenic mechanisms of prediabetes differ in obese (OB, BMI<35 kg/m2) and very obese (VOB, BMI>35 kg/m2) AAW.

SUBJECTS/METHODS

We recruited 26-OB and 41-VOB, AAW with prediabetes, mean age (46.3 ± 10.3 years), A1C (5.9 ± 0.4%) and BMI (38.3 ± 8.2 kg/m2). OGTT and FSIVGT were performed in each subject. Body composition (% body fat) was measured using DEXA. Si, Sg acute insulin response to glucose (AIRg) and disposition index (DI) were calculated using minimal model method.

RESULTS

Mean BMI (32.6 ± 1.9 vs. 42.8 ± 5.5 kg/m2) and %body fat (44.7 ± 2.0 vs. 49.6 ± 2.2%) were significantly (p = 0.0001) lower in OB vs VOB. Mean fasting and post-glucose challenge, (glucose, insulin, c-peptide) levels were significantly (p = 0.03-0.0001) lower in OB vs VOB. Mean Si and Sg was not different. Mean AIRg tended to be higher (808 ± 776 vs. 535 ± 443 (x min [uU/L] -1), p = 0.106) whereas DI was greater (1999 ± 1408 vs. 1511 ± 1033, (×10-2 x min-1), p = 0.01) in OB vs VOB subjects.

CONCLUSION

We found that OB and VOB AAW had similar Si and Sg, but VOB showed attenuated AIRg and DI. These parameters should be considered when developing primary prevention programs in AAW with prediabetes.

Ethnic Disparities in Endothelial Function and Its Cardiometabolic Correlates: The Pathobiology of Prediabetes in A Biracial Cohort Study

BACKGROUND

Endothelial function (EF) reflects the balance between vasodilatory and vasoconstrictive factors produced by (or acting on) the innermost lining of blood vessels. Endothelial dysfunction, an imbalance between these factors that favors vasoconstriction, has been associated with increased risk for cardiovascular disease. However, the influence of race/ethnicity and glycemic status on association between EF and cardiovascular risk factors remain to be clarified.

SUBJECTS AND METHODS

We assessed EF in relation to glycemia and cardiometabolic profile in African-American (AA) and European-American (EA) offspring of parents with type 2 diabetes (T2D), who are participants in the prospective pathobiology and reversibility of prediabetes in a biracial cohort (PROP-ABC) study. Assessments at enrollment included a 75 g oral glucose tolerance test (OGTT), blood pressure, anthropometry, body composition (DEXA), and lipid profile. Other assessments were insulin sensitivity and resting energy expenditure. EF was measured using flow-mediated vasodilation (EndoPAT 2000) and expressed as reactive hyperemia index (RHI).

RESULTS

We studied 190 subjects (100 AA, 90 C), mean age (±SD) 53.1 ± 9.1 years, and body mass index 30.6 ± 6.8 kg/m2. Based on OGTT data, 96 subjects (52 AA, 44 EA) had prediabetes and 94 subjects were normoglycemic (48 AA and 46 EA). The RHI was lower in AA than EA (2.17 ± 0.55 vs. 2.36 ± 0.72, P = 0.05) and in prediabetic than normoglycemic subjects (2.14 ± 0.62 vs. 2.38 ± 0.65, P = 0.013). Using RHI ≤ 1.68 as diagnostic cut-off, 19% of participants with prediabetes and 10% of normoglycemic participants had endothelial dysfunction (P = 0.04). In univariate models, RHI was positively associated with age and HDL cholesterol levels, and inversely associated with adiposity, diastolic blood pressure, and 2hr plasma glucose. The association between RHI and adiposity was stronger in men than women. The association between RHI and age, glucose and HDL cholesterol displayed marked ethnic disparities.

CONCLUSION

In our biracial cohort comprising offspring of parents with T2D, prediabetes increased the risk of endothelial dysfunction. However, the association between EF and cardiometabolic risk factors was significantly modified by ethnicity and gender. Our findings support current understanding of endothelial dysfunction as an early sensitive indicator of cardiometabolic risk.

Effect of body mass index on diabetogenesis factors at a fixed fasting plasma glucose level

Aim

The present study evaluated the relative influence of body mass index (BMI) on insulin resistance (IR), first-phase insulin secretion (FPIS), second-phase insulin secretion (SPIS), and glucose effectiveness (GE) at a fixed fasting plasma glucose level in an older ethnic Chinese population.

Methods

In total, 265 individuals aged 60 years with a fasting plasma glucose level of 5.56 mmol/L were enrolled. Participants had BMIs of 20.0–34.2 kg/m². IR, FPIS, SPIS, and GE were estimated using our previously developed equations. Pearson correlation analysis was conducted to assess the correlations between the four diabetogenesis factors and BMI. A general linear model was used to determine the differences in the percentage of change among the four factor slopes against BMI.

Results

Significant correlations were observed between BMI and FPIS, SPIS, IR, and GE in both women and men, which were higher than those reported previously. In men, BMI had the most profound effect on SPIS, followed by IR, FPIS, and GE, whereas in women, the order was slightly different: IR, followed by FPIS, SPIS, and GE. Significant differences were observed among all these slopes, except for the slopes between FPIS and SPIS in women (p = 0.856) and IR and FPIS in men (p = 0.258).

Conclusions

The contribution of obesity to all diabetes factors, except GE, was higher than that reported previously. BMI had the most profound effect on insulin secretion in men and on IR in women in this 60-year-old cohort, suggesting that lifestyle modifications for obesity reduction in women remain the most important method for improving glucose metabolism and preventing future type 2 diabetes mellitus.

Clinical and Histologic Characterization of Nonalcoholic Steatohepatitis in African American Patients

OBJECTIVE

There has been a widespread misconception among physicians that African Americans are protected from developing nonalcoholic steatohepatitis (NASH). However, a formal histologic and metabolic comparison against well-matched Caucasians has never been performed.

RESEARCH DESIGN AND METHODS

Sixty-seven African American patients were matched 2:1 to Caucasians (n = 134) for age, sex, BMI, hemoglobin A_1c, and prevalence of type 2 diabetes mellitus (T2DM). Screening for NASH included measurement of intrahepatic triglyceride content by proton MRS (¹H-MRS), followed by a liver biopsy if patients had hepatic steatosis. Insulin resistance was estimated during an oral glucose tolerance test using the Matsuda Index.

RESULTS

Compared with Caucasians, African American patients had a lower intrahepatic triglyceride content (mean ± SD 6.1 ± 6.8% vs. 9.4 ± 7.5%, P = 0.007) and the presence of nonalcoholic fatty liver disease (NAFLD) was less common (25.0% vs. 51.9%, P = 0.003). However, prevalence of NASH was not different between ethnicities in patients with NAFLD (57.1% vs. 73.3%, P = 0.12). Moreover, they showed similar severity in each of the individual histologic parameters (inflammation, ballooning, and fibrosis). Among patients with NAFLD, insulin resistance was similar between both ethnic groups (Matsuda Index: 3.3 ± 1.8 vs. 3.1 ± 1.9, P = 0.61; adipose tissue insulin resistance [Adipo-IR] index: 5.7 ± 4.6 vs. 6.4 ± 4.7 mmol/L ⋅ µU/mL, P = 0.53) but appeared to be worse in African American versus Caucasian patients without NAFLD (Matsuda Index: 4.9 ± 3.6 vs. 7.0 ± 4.9, P = 0.11; Adipo-IR: 3.9 ± 2.8 vs. 2.7 ± 2.3 mmol/L ⋅ µU/mL, P = 0.06). African American patients also had lower plasma triglycerides and higher HDL cholesterol, independent of the severity of intrahepatic triglyceride.

CONCLUSIONS

Although African Americans have lower intrahepatic triglyceride accumulation, once NAFLD develops, NASH occurs as frequently, and as severe, as in Caucasian patients. Therefore, African Americans with NAFLD should be screened for NASH with the same degree of clinical resolve as in Caucasian patients.

Effect of Caloric Restriction on Metabolic Dysfunction of Young Rapacz Familial Hypercholesterolemic Swine (Sus scrofa)

The Rapacz familial hypercholesterolemic (FH) swine model is well-characterized and used for studies of both spontaneous and inducible atherosclerosis but has not been used for studies of metabolic dysfunction to date. We examined whether parameters of metabolic syndrome including weight and adiposity, serum cholesterol, and glucoregulatory function could be modulated by restriction of caloric intake in the FH swine. Three groups of FH swine (n = 6 per group) were fed without restriction (AL), 80% of AL caloric intake, or 60% of AL caloric intake for 8.8 ± 0.5 mo beginning 2 wk after weaning. Caloric intake influenced the rate and magnitude of body weight gain and change in adiposity, as determined by dual-emission X-ray absorptiometry. At the conclusion of the study, pigs in the AL group reached a total least-square mean body weight of 94.2 kg and fat mass of 31.1%, whereas those fed 80% AL were 71.6 kg and 24.3% fat, and swine fed 60% AL were 46.1 kg and 14.1% fat. Serum cholesterol was greater in AL than 60% AL pigs at the end of the study. At 10 mo of age, intravenous glucose tolerance testing, performed to assess glucoregulatory function, indicated significant differences in serum glucose clearance profiles and insulin sensitivity between the AL- and 60% AL-fed swine. The AL-fed animals showed almost 5-fold lower insulin sensitivity when compared with animals fed 60% AL caloric intake. These results highlight the value of the FH swine model to study metabolic dysfunction due to changes in caloric intake.

Association between ethnicity and obesity with high-density lipoprotein (HDL) function and subclass distribution

BACKGROUND

Obesity and low high-density lipoprotein-cholesterol (HDL-C) levels are associated with cardiovascular risk. Surprisingly, despite a greater prevalence of obesity and lower HDL concentrations than white women, black South African women are relatively protected against ischaemic heart disease.

METHODS

We investigated whether this apparent discrepancy may be related to different HDL function and subclass distribution in black and white, normal-weight and obese South African women (n = 40). HDL functionality was assessed by measuring paraoxonase (PON) activity, platelet activating factor acetylhydrolase (PAF-AH) activity, Oxygen Radical Absorbance Capacity (ORAC) and quantification of the expression of vascular cell adhesion molecule in endothelial cells. PON-1 and PAF-AH expression was determined in isolated HDL and serum using Western blotting. Levels of large, intermediate and small HDL subclasses were measured using the Lipoprint® system.

RESULTS

PON activity was lower in white compared to black women (0.49 ± 0.09 U/L vs 0.78 ± 0.10 U/L, p < 0.05), regardless of PON-1 protein levels. Obese black women had lower PAF-AH activity (9.34 ± 1.15 U/L vs 13.89 ± 1.21 U/L, p <0.05) and HDL-associated PAF-AH expression compared to obese white women. Compared to normal-weight women, obese women had lower large HDL, greater intermediate and small HDL; an effect that was more pronounced in white women than black women. There were no differences in antioxidant capacity or anti-inflammatory function across groups.

CONCLUSIONS

Our data show that both obesity and ethnicity are associated with differences in HDL functionality, while obesity was associated with decreases in large HDL subclass distribution. Measuring HDL functionality and subclass may, therefore, be important factors to consider when assessing cardiovascular risk.

Circulating cell-free mitochondrial DNA as the probable inducer of early endothelial dysfunction in the prediabetic patient

Recent evidence has shown that 346million people in the world have diabetes mellitus (DM); this number will increase to 439million by 2030. In addition, current data indicate an increase in DM cases in the population between 40 and 59years of age. Diabetes is associated with the development of micro- and macro-vascular complications, derived from chronic hyperglycemia on the endothelium. Some reports demonstrate that people in a prediabetic state have a major risk of developing early endothelial dysfunction (ED). Today, it is accepted that individuals considered as prediabetic patients are in a pro-inflammatory state associated with endothelial and mitochondrial dysfunction. It is important to mention that impaired mitochondrial functionality has been linked to endothelial apoptosis and release of mitochondrial DNA (mtDNA) in patients with sepsis, cardiac disease, or atherosclerosis. This free mtDNA could promote ED, as well as other side effects on the vascular system through the activation of the toll-like receptor 9 (TLR9). TLR9 is expressed in different cell types (e.g., T or B lymphocytes, mastocytes, and epithelial and endothelial cells). It is localized intracellularly and recognizes non-methylated dinucleotides of viral, bacterial, and mitochondrial DNA. Recently, it has been reported that TLR9 is associated with the pathogenesis of lupus erythematosus, rheumatoid arthritis, and autoimmune diabetes. In this work, it is hypothesized that the increase in the levels of circulating mtDNA is the trigger of early ED in the prediabetic patient, and later on in the older patient with diabetes, through activation of the TLR9 present in the endothelium.