Ectopic fat deposition in populations of black African ancestry: A systematic review and meta-analysis

Association between Body Fat Distribution and Nonalcoholic Fatty Liver Disease/Fibrosis Based on Race/Ethnicity

BACKGROUND

Body fat distribution may impact nonalcoholic fatty liver disease (NAFLD) and significant fibrosis differently according to race/ethnicity. We determined the relationship between body fat distribution and NAFLD/significant fibrosis according to race/ethnicity.

METHODS

A cross-sectional study of 2,395 participants used the National Health and Nutrition Examination Survey 2017 to 2018. NAFLD and significant fibrosis (≥F2) were defined by controlled attenuation parameter scores and liver stiffness measurements on transient elastography, respectively. Visceral and subcutaneous fat volumes were defined by dual-energy X-ray absorptiometry.

RESULTS

The odds ratio (OR) for NAFLD per 1-standard deviation in visceral fat volume and subcutaneous fat volume was 2.05 (95% confidence interval [CI], 1.36 to 3.09) and 1.48 (95% CI, 1.04 to 2.09) in total population, respectively. Visceral fat in non-Hispanic Blacks had the highest odds for NAFLD (OR, 2.86; 95% CI, 1.45 to 5.62), and non-Hispanic Whites (OR, 2.29; 95% CI, 1.19 to 4.40) and non-Hispanic Asians (OR, 1.61; 95% CI, 1.13 to 2.29) were in order. Significant associations between subcutaneous fat volume (OR, 2.10; 95% CI, 1.34 to 3.29; P=0.003) or visceral fat volume (OR, 1.35; 95% CI, 1.05 to 1.73; P=0.023) and significant fibrosis were noted among individuals with NAFLD. Hispanics had the highest odds for NAFLD-associated significant fibrosis (OR, 2.74; 95% CI, 1.32 to 5.70 per 1-standard deviation in subcutaneous fat volume), and non-Hispanic Whites (OR, 2.35; 95% CI, 1.11 to 4.98) and non-Hispanic Asians (OR, 2.01; 95% CI, 1.01 to 4.01) were in order.

CONCLUSION

Visceral adiposity was associated with NAFLD and significant fibrosis despite the association of subcutaneous adiposity in NAFLD and significant fibrosis. Racial/ethnic differences in the association between body fat distribution on NAFLD and significant fibrosis were noted.

Intrapancreatic fat deposition and nutritional treatment: the role of various dietary approaches

Ectopic fat accumulation in various organs and tissues, such as the liver, muscle, kidney, heart, and pancreas, is related to impaired capacity of adipose tissue to accumulate triglycerides, as a consequence of overnutrition and an unhealthy lifestyle. Ectopic fat promotes organ dysfunction and is a key factor in the development and progression of cardiometabolic diseases. Interest in intrapancreatic fat deposition (IPFD) has developed in the last few years, particularly in relation to improvement in methodological techniques for detection of fat in the pancreas, and to growing evidence for the role that IPFD might have in glucose metabolism disorders and cardiometabolic disease. Body weight reduction represents the main option for reducing fat, and the evidence consistently shows that hypocaloric diets are effective in reducing IPFD. Changes in diet composition, independently of changes in energy intake, might offer a more feasible and safe alternative treatment to energy restriction. This current narrative review focused particularly on the possible beneficial role of the diet and its nutrient content, in hypocaloric and isocaloric conditions, in reducing IPFD in individuals with high cardiometabolic risk, highlighting the possible effects of differences in calorie quantity and calorie quality. This review also describes plausible mechanisms by which the various dietary approaches could modulate IPFD.

Ethnic differences in postprandial fatty acid trafficking and utilization between overweight and obese White European and Black African-Caribbean men

Black African-Caribbean (BAC) populations are at greater risk of cardiometabolic disease than White Europeans (WE), despite exhibiting lower fasting triacylglycerol (TAG) concentrations. However, limited data exist regarding postprandial fatty acid metabolism in BAC populations. This study determined the ethnic differences in postprandial fatty acid metabolism between overweight and obese WE and BAC men. WE [n = 10, age 33.3 ± 1.7 yr; body mass index (BMI) = 26.8 (25.8-31.0) kg/m2] and BAC [n = 9, age 27.9 ± 1.0 yr; BMI = 27.5 (26.0-28.6) kg/m2] men consumed two consecutive (at 0 and 300 min) moderate-to-high-fat meals-the first labeled with [U-13C]palmitate. The plasma concentration and appearance of meal-derived fatty acids in very-low-density lipoprotein (VLDL)-TAG, chylomicron-TAG, and nonesterified fatty acid (NEFA) were determined over an 8-h postprandial period. Indirect calorimetry with 13CO2 enrichment determined total and meal-derived fatty acid oxidation rates, and plasma β-hydroxybutyrate (3-OHB) concentration was measured to assess ketogenesis. BAC exhibited lower postprandial TAG [area under the curve (AUC0-480) = 671 (563-802) vs. 469 (354-623) mmol/L/min, P = 0.022] and VLDL-TAG [AUC0-480 = 288 ± 30 vs. 145 ± 27 mmol/L/min, P = 0.003] concentrations than WE. The appearance of meal-derived fatty acids in VLDL-TAG was lower in BAC than in WE (AUC0-480 = 133 ± 12 vs. 78 ± 13 mmol/L/min, P = 0.007). Following the second meal, BAC showed a trend for lower chylomicron-TAG concentration [AUC300-480 = 69 (51-93) vs. 43 (28-67) mmol/L/min, P = 0.057]. There were no ethnic differences in the appearance of chylomicron-TAG, cumulative fatty acid oxidation, and the NEFA:3-OHB ratio (P > 0.05). In conclusion, BAC exhibit lower postprandial TAG concentrations compared with WE men, driven by lower VLDL-TAG concentrations and possibly lower chylomicron-TAG in the late postprandial period. These findings suggest that postprandial fatty acid trafficking may be a less important determinant of cardiometabolic risk in BAC than in WE men.NEW & NOTEWORTHY Postprandial TAG is lower in Black African-Caribbean men than in White European men, and this is likely driven by lower meal-derived VLDL-TAG in Black African-Caribbean men. This observation could suggest that fatty acid trafficking may be a less important determinant of cardiometabolic risk in Black Africans than in White European men.

Myofiber-specific lipidomics unveil differential contributions to insulin sensitivity in individuals of African and European ancestry

Aims

Individuals of African ancestry (AA) present with lower insulin sensitivity compared to their European counterparts (EA). Studies show ethnic differences in skeletal muscle fiber type (lower type I fibers in AA), muscle fat oxidation capacity (lower in AA), whilst no differences in total skeletal muscle lipids. However, skeletal muscle lipid subtypes have not been examined in this context. We hypothesize that lower insulin sensitivity in AA is due to a greater proportion of type II (non-oxidative) muscle fibers, and that this would result in an ancestry-specific association between muscle lipid subtypes and peripheral insulin sensitivity. To test this hypothesis, we examined the association between insulin sensitivity and muscle lipids in AA and EA adults, and in an animal model of insulin resistance with muscle-specific fiber types.

Methods

In this cross-sectional study, muscle biopsies were obtained from individuals with a BMI ranging from normal to overweight with AA (N = 24) and EA (N = 19). Ancestry was assigned via genetic admixture analysis; peripheral insulin sensitivity via hyperinsulinaemic-euglycemic clamp; and myofiber content via myosin heavy chain immunohistochemistry. Further, muscle types with high (soleus) and low (vastus lateralis) type I fiber content were obtained from high-fat diet-induced insulin resistant F1 mice and littermate controls. Insulin sensitivity in mice was assessed via intraperitoneal glucose tolerance test. Mass spectrometry (MS)-based lipidomics was used to measure skeletal muscle lipid.

Results

Compared to EA, AA had lower peripheral insulin sensitivity and lower oxidative type 1 myofiber content, with no differences in total skeletal muscle lipid content. Muscles with lower type I fiber content (AA and vastus from mice) showed lower levels of lipids associated with fat oxidation capacity, i.e., cardiolipins, triacylglycerols with low saturation degree and phospholipids, compared to muscles with a higher type 1 fiber content (EA and soleus from mice). Further, we found that muscle diacylglycerol content was inversely associated with insulin sensitivity in EA, who have more type I fiber, whereas no association was found in AA. Similarly, we found that insulin sensitivity in mice was associated with diacylglycerol content in the soleus (high in type I fiber), not in vastus (low in type I fiber).Conclusions; Our data suggest that the lipid contribution to altered insulin sensitivity differs by ethnicity due to myofiber composition, and that this needs to be considered to increase our understanding of underlying mechanisms of altered insulin sensitivity in different ethnic populations.

Cardiometabolic disease in Black African and Caribbean populations: an ethnic divergence in pathophysiology?

In the UK, populations of Black African and Caribbean (BAC) ethnicity suffer higher rates of cardiometabolic disease than White Europeans (WE). Obesity, leading to increased visceral adipose tissue (VAT) and intrahepatic lipid (IHL), has long been associated with cardiometabolic risk, driving insulin resistance and defective fatty acid/lipoprotein metabolism. These defects are compounded by a state of chronic low-grade inflammation, driven by dysfunctional adipose tissue. Emerging evidence has highlighted associations between central complement system components and adipose tissue, fatty acid metabolism and inflammation; it may therefore sit at the intersection of various cardiometabolic disease risk factors. However, increasing evidence suggests an ethnic divergence in pathophysiology, whereby current theories fail to explain the high rates of cardiometabolic disease in BAC populations. Lower fasting and postprandial TAG has been reported in BAC, alongside lower VAT and IHL deposition, which are paradoxical to the high rates of cardiometabolic disease exhibited by this ethnic group. Furthermore, BAC have been shown to exhibit a more anti-inflammatory profile, with lower TNF-α and greater IL-10. In contrast, recent evidence has revealed greater complement activation in BAC compared to WE, suggesting its dysregulation may play a greater role in the high rates of cardiometabolic disease experienced by this population. This review outlines the current theories of how obesity is proposed to drive cardiometabolic disease, before discussing evidence for ethnic differences in disease pathophysiology between BAC and WE populations.

Differences in substrate metabolism between African American and Caucasian infants: evidence from mesenchymal stem cells

Type 2 diabetes is more prevalent in African American (AA) than Caucasian (C) adults. Furthermore, differential substrate utilization has been observed between AA and C adults, but data regarding metabolic differences between races at birth remains scarce. The purpose of the present study was to determine if there are racial differences in substrate metabolism evident at birth using a mesenchymal stem cells (MSCs) collected from offspring umbilical cords. Using radio-labeled tracers, MSCs from offspring of AA and C mothers were tested for glucose and fatty acid metabolism in the undifferentiated state and while undergoing myogenesis in vitro. Undifferentiated MSCs from AA exhibited greater partitioning of glucose toward nonoxidized glucose metabolites. In the myogenic state, AA displayed higher glucose oxidation, but similar fatty acid oxidation rates. In the presence of both glucose and palmitate, but not palmitate only, AA exhibit a higher rate of incomplete fatty acid oxidation evident by a greater production of acid-soluble metabolites. Myogenic differentiation of MSCs elicits an increase in glucose oxidation in AA, but not in C. Together, these data suggest that metabolic differences between AA and C races exist at birth.NEW & NOTEWORTHY African Americans, when compared with Caucasians, display greater insulin resistance in skeletal muscle. Differences in substrate utilization have been proposed as a factor for this health disparity; however, it remains unknown how early these differences manifest. Using infant umbilical cord-derived mesenchymal stem cells, we tested for in vitro glucose and fatty acid oxidation differences. Myogenically differentiated MSCs from African American offspring display higher rates of glucose oxidation and incomplete fatty acid oxidation.

Pathophysiology of type 2 diabetes in sub-Saharan Africans

Sub-Saharan Africa (SSA) is the region with the highest projected rates of increase in type 2 diabetes (129% by 2045), which will exacerbate the already high prevalence of type 2 diabetes complications and comorbidities in SSA. In addition, SSA is grappling with poverty-related health problems and infectious diseases and is also undergoing the most rapid rates of urbanisation globally. These socioenvironmental and lifestyle factors may interact with genetic factors to alter the pathophysiological sequence leading to type 2 diabetes in sub-Saharan African populations. Indeed, current evidence from SSA and the diaspora suggests that the pathophysiology of type 2 diabetes in Black Africans is different from that in their European counterparts. Studies from the diaspora suggest that insulin clearance is the primary defect underlying the development of type 2 diabetes. We propose that, among Black Africans from SSA, hyperinsulinaemia due to a combination of both increased insulin secretion and reduced hepatic insulin clearance is the primary defect, which promotes obesity and insulin resistance, exacerbating the hyperinsulinaemia and eventually leading to beta cell failure and type 2 diabetes. Nonetheless, the current understanding of the pathogenesis of type 2 diabetes and the clinical guidelines for preventing and managing the disease are largely based on studies including participants of predominately White European ancestry. In this review, we summarise the existing knowledge base and data from the only non-pharmacological intervention that explores the pathophysiology of type 2 diabetes in SSA. We also highlight factors that may influence the pathogenesis of type 2 diabetes in SSA, such as social determinants, infectious diseases and genetic and epigenetic influences.

Mitochondrial Phenotype as a Driver of the Racial Dichotomy in Obesity and Insulin Resistance

African Americans (AA) are disproportionately burdened by metabolic diseases. While largely unexplored between Caucasian (C) and AA, differences in mitochondrial bioenergetics may provide crucial insight to mechanisms for increased susceptibility to metabolic diseases. AA display lower total energy expenditure and resting metabolic rate compared to C, but paradoxically have a higher amount of skeletal muscle mass, suggestive of inherent energetic efficiency differences between these races. Such adaptations would increase the chances of overnutrition in AA; however, these disparities would not explain the racial difference in insulin resistance (IR) in healthy subjects. Hallmarks associated with insulin resistance (IR), such as reduced mitochondrial oxidative capacity and metabolic inflexibility are present even in healthy AA without a metabolic disease. These adaptations might be influential of mitochondrial “substrate preference” and could play a role in disproportionate IR rates among races. A higher glycolytic flux and provision of shuttles transferring electrons from cytosol to mitochondrial matrix could be a contributing factor in development of IR via heightened reactive oxygen species (ROS) production. This review highlights the above concepts and provides suggestions for future studies that could help delineate molecular premises behind potential impairments in insulin signaling and metabolic disease susceptibility in AA.