Targeted proteomics identifies potential biomarkers of dysglycaemia, beta cell function and insulin sensitivity in Black African men and women.

AIMS/HYPOTHESIS: Using a targeted proteomics approach, we aimed to identify and validate circulating proteins associated with impaired glucose metabolism (IGM) and type 2 diabetes in a Black South African cohort. In addition, we assessed sex-specific associations between the validated proteins and pathophysiological pathways of type 2 diabetes. METHODS: This cross-sectional study included Black South African men (n=380) and women (n=375) who were part of the Middle-Aged Soweto Cohort (MASC). Dual-energy x-ray absorptiometry was used to determine fat mass and visceral adipose tissue, and fasting venous blood samples were collected for analysis of glucose, insulin and C-peptide and for targeted proteomics, measuring a total of 184 pre-selected protein biomarkers. An OGTT was performed on participants without diabetes, and peripheral insulin sensitivity (Matsuda index), HOMA-IR, basal insulin clearance, insulin secretion (C-peptide index) and beta cell function (disposition index) were estimated. Participants were classified as having normal glucose tolerance (NGT; n=546), IGM (n=116) or type 2 diabetes (n=93). Proteins associated with dysglycaemia (IGM or type 2 diabetes) in the MASC were validated in the Swedish EpiHealth cohort (NGT, n=1706; impaired fasting glucose, n=550; type 2 diabetes, n=210). RESULTS: We identified 73 proteins associated with dysglycaemia in the MASC, of which 34 were validated in the EpiHealth cohort. Among these validated proteins, 11 were associated with various measures of insulin dynamics, with the largest number of proteins being associated with HOMA-IR. In sex-specific analyses, IGF-binding protein 2 (IGFBP2) was associated with lower HOMA-IR in women (coefficient -0.35; 95% CI -0.44, -0.25) and men (coefficient -0.09; 95% CI -0.15, -0.03). Metalloproteinase inhibitor 4 (TIMP4) was associated with higher insulin secretion (coefficient 0.05; 95% CI 0.001, 0.11; p for interaction=0.025) and beta cell function (coefficient 0.06; 95% CI 0.02, 0.09; p for interaction=0.013) in women only. In contrast, a stronger positive association between IGFBP2 and insulin sensitivity determined using an OGTT (coefficient 0.38; 95% CI 0.27, 0.49) was observed in men (p for interaction=0.004). A posteriori analysis showed that the associations between TIMP4 and insulin dynamics were not mediated by adiposity. In contrast, most of the associations between IGFBP2 and insulin dynamics, except for insulin secretion, were mediated by either fat mass index or visceral adipose tissue in men and women. Fat mass index was the strongest mediator between IGFBP2 and insulin sensitivity (total effect mediated 40.7%; 95% CI 37.0, 43.6) and IGFBP2 and HOMA-IR (total effect mediated 39.1%; 95% CI 31.1, 43.5) in men. CONCLUSIONS/INTERPRETATION: We validated 34 proteins that were associated with type 2 diabetes, of which 11 were associated with measures of type 2 diabetes pathophysiology such as peripheral insulin sensitivity and beta cell function. This study highlights biomarkers that are similar between cohorts of different ancestry, with different lifestyles and sociodemographic profiles. The African-specific biomarkers identified require validation in African cohorts to identify risk markers and increase our understanding of the pathophysiology of type 2 diabetes in African populations.

Waist circumference thresholds predicting incident dysglycaemia and type 2 diabetes in Black African men and women.

AIMS: To determine the waist circumference (WC) thresholds for the prediction of incident dysglycaemia and type 2 diabetes (T2D) in Black South African (SA) men and women and to compare these to the advocated International Diabetes Federation (IDF) Europid thresholds. MATERIALS AND METHODS: In this prospective study, Black SA men (n = 502) and women (n = 527) from the Middle-aged Sowetan Cohort study who had normal or impaired fasting glucose at baseline (2011-2015) were followed up until 2017 to 2018. Baseline measurements included anthropometry, blood pressure and fasting glucose, HDL cholesterol and triglyceride concentrations. At follow-up, glucose tolerance was assessed using an oral glucose tolerance test. The Youden index was used to determine the optimal threshold of WC to predict incident dysglycaemia and T2D. RESULTS: In men, the optimal WC threshold was 96.8 cm for both dysglycaemia and T2D (sensitivity: 56% and 70%; specificity: 74% and 70%, respectively), and had higher specificity (P < 0.001) than the IDF threshold of 94 cm. In women, the optimal WC threshold for incident dysglycaemia was 91.8 cm (sensitivity 86%, specificity 37%) and for T2D it was 95.8 cm (sensitivity 85%, specificity 45%), which had lower sensitivity, but higher specificity to predict incident dysglycaemia and T2D than the IDF threshold of 80 cm (sensitivity: 97% and 100%; specificity: 12% and 11%, respectively)). CONCLUSIONS: We show for the first time using prospective cohort data from Africa that the IDF Europid WC thresholds are not appropriate for an African population, and show that African-specific WC thresholds perform better than the IDF Europid thresholds to predict incident dysglycaemia and T2D.

Risk factors of impaired fasting glucose and type 2 diabetes in Yaoundé, Cameroon: a cross sectional study.

BACKGROUND: The prevalence of diabetes is increasing worldwide, particularly in low and middle income countries, where treatment and control are often unavailable and inaccessible. Information on risk factors at local and regional levels is of utmost importance for tailored prevention programmes to curb the rise in diabetes. The current study was undertaken to investigate the prevalence of Impaired Fasting Glucose (IFG)/Type 2 Diabetes (T2D) and its risk factors in the adult population in Biyem-Assi-Yaoundé, Cameroon. METHODS: Information on cardiovascular risk factors using the WHO STEPwise approach was obtained for 1623 men and women aged 25 years and older of the CAMBoD Project in Biyem-Assi, Yaoundé, Cameroon. T2D was defined as fasting capillary glucose (FCG) ≥ 7.0 mmol/l and/or being on diabetes medication, IFG/T2D as FCG ≥ 6.1 mmol/l and/or being on diabetes medication. Descriptive statistics and multivariate logistic regression analyses were used to describe prevalence of IFG/T2D, prevalence of risk factors for IFG/T2D and to investigate the association of risk factors with prevalence of IFG/T2D. RESULTS: Prevalence of T2D and of IFG/T2D was 3.3% and 5.7%. Prevalence of hypertension, obesity and abdominal obesity (elevated waist circumference) was 26.6%, 28.4% and 34.9%, respectively. Age and abdominal obesity were significantly associated with IFG/T2D in multivariate logistic regression. CONCLUSION: For successful primary prevention of T2D in the general population in Cameroon tailored efforts to address obesity, particularly abdominal obesity, and associated life-style factors are warranted.

SHBG, Free Testosterone, and Type 2 Diabetes Risk in Middle-aged African Men: A Longitudinal Study.

Objectives: To investigate longitudinal changes in SHBG and free testosterone (free T) levels among Black middle-aged African men, with and without coexistent HIV, and explore associations with incident dysglycaemia and measures of glucose metabolism. Design: This longitudinal study enrolled 407 Black South African middle-aged men, comprising primarily 322 men living without HIV (MLWOH) and 85 men living with HIV (MLWH), with normal fasting glucose at enrollment. Follow-up assessments were conducted after 3.1 ± 1.5 years. Methods: At baseline and follow-up, SHBG, albumin, and total testosterone were measured and free T was calculated. An oral glucose tolerance test at follow-up determined dysglycaemia (impaired fasting glucose, impaired glucose tolerance, type 2 diabetes) and glucose metabolism parameters including insulin sensitivity (Matsuda index), insulin resistance (homeostasis model assessment of insulin resistance), and beta(ß)-cell function (disposition index). The primary analysis focussed on MLWOH, with a subanalysis on MLWH to explore whether associations in MLWOH differed from MLWH. Results: The prevalence of dysglycaemia at follow-up was 17% (n = 55) in MLWOH. Higher baseline SHBG was associated with a lower risk of incident dysglycaemia (odds ratio 0.966; 95% confidence interval 0.945-0.987) and positively associated with insulin sensitivity (ß = 0.124, P < .001) and ß-cell function (ß = 0.194, P = .001) at follow-up. Free T did not predict dysglycaemia. In MLWH, dysglycaemia prevalence at follow-up was 12% (n = 10). Neither baseline SHBG nor free T were associated with incident dysglycaemia and glucose metabolism parameters in MLWH. Conclusion: SHBG levels predict the development of dysglycaemia in middle-aged African men but do not exhibit the same predictive value in MLWH.

Regional adiposity and insulin sensitivity - interactions with menopause and HIV in middle-aged Black African women.

OBJECTIVE: To explore depot-specific functional aspects of adipose tissue, examining the putative role for menopause and HIV status on insulin sensitivity (SI) and beta-cell function in Black South African women. METHODS: Women (n = 92) from the Middle-Aged Soweto Cohort, including premenopausal HIV-negative (n = 21); premenopausal women living with HIV (WLWH; n = 11); postmenopausal HIV-negative (n = 42); postmenopausal WLWH (n = 18) underwent the following tests: body composition (dual energy x-ray absorptiometry); fasting bloods for sex hormones, inflammation and adipokines; frequently sampled intravenous glucose tolerance test for SI and beta-cell function (disposition index, DI); abdominal (aSAT) and gluteal subcutaneous adipose tissue (gSAT) biopsies for cell size and mRNA expression of adipokines, inflammation, and estrogen receptors [ER]. RESULTS: Depot-specific associations between gene expression and insulin parameters did not differ by HIV or menopause status. Pooled analysis showed significant models for SI (P = 0.002) and DI (P = 0.003). Higher SI was associated with lower leptin and CD11c expression in aSAT and higher adiponectin in gSAT. Higher DI was associated with higher aSAT and gSAT expression of adiponectin, LPL, ERα, and PPARγ, and lower leptin in aSAT. WLWH had higher expression of adiponectin and lower expression of leptin in both aSAT (P = 0.002 and P = 0.005) and gSAT (P = 0.004 and P = 0.002), respectively, and a larger proportion of smaller cells in aSAT (P < 0.001). CONCLUSION: Insulin sensitivity and beta cell function were distinctively associated with aSAT and gSAT. While menopause did not influence these relationships, HIV had a significant effect on adipose tissue, characterised by variations in cell size distribution and transcript levels within the depots.

Physical behaviors and their association with type 2 diabetes mellitus risk markers in urban South African middle-aged adults: an isotemporal substitutionapproach.

INTRODUCTION: To examine the associations between physical behaviors and type 2 diabetes mellitus (T2DM) risk markers in middle-aged South African men and women. RESEARCH DESIGN AND METHODS: This cross-sectional study included middle-aged men (n=403; age: median (IQR), 53.0 (47.8-58.8) years) and women (n=324; 53.4 (49.1-58.1) years) from Soweto, South Africa. Total movement volume (average movement in milli-g) and time (minutes/day) spent in different physical behaviors, including awake sitting/lying, standing, light intensity physical activity (LPA) and moderate-to-vigorous intensity physical activity (MVPA), were determined by combining the signals from two triaxial accelerometers worn simultaneously on the hip and thigh. All participants completed an oral glucose tolerance test, from which indicators of diabetes risk were derived. Associations between physical behaviors and T2DM risk were adjusted for sociodemographic factors and body composition. RESULTS: Total movement volume was inversely associated with measures of fasting and 2-hour glucose and directly associated with insulin sensitivity, basal insulin clearance, and beta-cell function, but these associations were not independent of fat mass, except for basal insulin clearance in women. In men, replacing 30 min of sitting/lying, standing or LPA with the same amount of MVPA time was associated with 1.2-1.4 mmol/L lower fasting glucose and 12.3-13.4 mgl2/mUmin higher insulin sensitivity. In women, substituting sitting/lying with the same amount of standing time or LPA was associated with 0.5-0.8 mmol/L lower fasting glucose. Substituting 30 min sitting/lying with the same amount of standing time was also associated with 3.2 mgl2/mUmin higher insulin sensitivity, and substituting 30 min of sitting/lying, standing or LPA with the same amount of MVPA time was associated with 0.25-0.29 ng/mIU higher basal insulin clearance in women. CONCLUSION: MVPA is important in reducing T2DM risk in men and women, but LPA appears to be important in women only. Longitudinal and intervention studies warranted to provide more specific PA recommendations.

Physical Activity Behaviors of a Middle-Age South African Cohort as Determined by Integrated Hip and Thigh Accelerometry.

PURPOSE: Descriptive studies of objectively measured physical activity behaviors in African populations are rare. We developed a method of combining hip and thigh accelerometery signals to quantify and describe physical behaviors in middle-age South African men and women. METHODS: We integrated signals from two triaxial accelerometers worn simultaneously during free-living, in a subsample of the Middle-age Soweto Cohort ( n = 794; mean (SD) age, 53.7 (6.3) yr). Acceleration time series from the accelerometers were combined and movement-related acceleration was derived using Euclidean Norm Minus One (in milligrams), to determine total movement volume (mean Euclidean Norm Minus One) and nonmovement time (<28 m g ), light-intensity physical activity (LPA; 28-85 m g ), and moderate- to vigorous-intensity physical activity (MVPA; >85 m g ); thigh pitch angle and a sleep diary were used to divide nonmovement time (in minutes per day) into sleep, awake sitting/lying, and standing. Sociodemographic factors were self-reported, and weight and height were measured. RESULTS: Mean (SD) wear time was 128 (48) h. Movement volume was 15.0 (6.5) m g for men and 12.2 (3.4) m g for women. Men spent more time in MVPA and sitting/lying, whereas women spent more time standing. Age was inversely associated with movement volume, MVPA, and LPA. When compared with their normal-weight counterparts, men who were overweight or obese spent less time in MVPA, whereas women who were overweight or obese spent less time in LPA and more time sitting/lying. Socioeconomic status was inversely associated with total movement volume, MVPA, and time spent sleeping, and positively associated with time spent sitting/lying, in both men and women. CONCLUSIONS: Integrating signals from hip and thigh accelerometers enables characterization of physical behaviors that can be applied in an African population.

Increased risk for type 2 diabetes in relation to adiposity in middle-aged Black South African men compared to women.

Aims: Despite a higher prevalence of overweight/obesity in Black South African women compared to men, the prevalence of type 2 diabetes (T2D) does not differ. We explored if this could be due to sex differences in insulin sensitivity, clearance and/or beta-cell function and also sex-specific associations with total and regional adiposity. Methods: This cross-sectional study included 804 Black South African men (n = 388) and women (n = 416). Dual-energy X-ray absorptiometry was used to measure total and regional adiposity. Insulin sensitivity (Matsuda index), secretion (C-peptide index) and clearance (C-peptide/insulin ratio) were estimated from an oral glucose tolerance test. Results: After adjusting for sex differences in the fat mass index, men were less insulin sensitive and had lower beta-cell function than women (P < 0.001), with the strength of the associations with measures of total and central adiposity being greater in men than women (P < 0.001 for interactions). Further, the association between total adiposity and T2D risk was also greater in men than women (relative risk ratio (95% CI): 2.05 (1.42-2.96), P < 0.001 vs 1.38 (1.03-1.85), P = 0.031). Conclusion: With increasing adiposity, particularly increased centralisation of body fat linked to decreased insulin sensitivity and beta-cell function, Black African men are at greater risk for T2D than their female counterparts.

Sex Differences in the Associations of Nutrient Patterns with Total and Regional Adiposity: A Study of Middle-Aged Black South African Men and Women.

The study evaluated the association between nutrient patterns with body fat and regional adiposity in middle-aged black South African (SA) men and women and determined if this differed by sex. Body fat and regional adiposity (dual-energy x-ray absorptiometry), and dietary intake (7-day quantified food frequency questionnaire) were measured in black SA men (n = 414) and women (n = 346). Using principal component analysis, nutrient patterns were computed from 25 nutrients in the combined sample. Four nutrient patterns were extracted, explaining 67% of the variance in nutrient intake. Animal and fat, as well as the vitamin C, sugar, and potassium driven patterns, were positively associated with total adiposity. In contrast, the retinol and vitamin B12 pattern was associated with the centralisation of fat. Notably, the strength of the association between the animal-driven nutrient pattern and BMI was greater in men (1.14 kg/m2, 95% CI (0.63-1.66)) than in women (0.81 kg/m2, 95% CI (0.25-1.36)) (Pint = 0.017). In contrast, the plant-driven pattern was associated with higher abdominal subcutaneous adipose tissue (SAT) in women (44 cm2, 95% CI (22-67)) but not men (Pint = 1.54 × 10-4). These differences suggest that although men and women have similar nutrient patterns, their associations with the whole body and regional body fat are different.

Effects of Single and Multiple Blood Pressure Measurement Strategies on the Prediction of Prevalent Screen-Detected Diabetes Mellitus: A Population-Based Survey.

The authors investigated the effects of single and multiple blood pressure (BP) measurements during the same encounter on screen-detected diabetes risk. Data for 9018 Cameroonian adults from a community-based survey were used. Resting BP was measured three times 5 minutes apart. Logistic regressions were used to compute the odd ratio (OR) per standard deviation (SD) higher BP variables. Systolic BP, diastolic BP, and mean arterial pressure (MAP), but not pulse pressure, were related to prevalent diabetes. The highest OR (95% confidence interval [CI]) per SD higher pressure were recorded for MAP (OR, 1.16; 95% CI, 1.05-1.28) and systolic BP (OR, 1.15; 95% CI, 1.04-1.27). Estimates of the association were highest for the first, then third, and lastly the second BP measurements. Estimates from average BP measurements were not better than those from single measurement. Single BP measurement is more effective for diabetes risk screening than multiple measurements. Community-based diabetes strategies utilizing a single measurement are simple without compromising the yield.