Superficial vs Deep Subcutaneous Adipose Tissue: Sex-Specific Associations With Hepatic Steatosis and Metabolic Traits

Analysis of Physiological Oxygen Concentrations in Different Abdominal Fat Layers by Body Mass Index

BACKGROUND

Physiological oxygen concentration in adipose tissue is closely linked to metabolic disorders such as chronic inflammation and insulin resistance. However, the nature of the variation in the oxygen levels of adipose tissue with body mass index (BMI) and depths of abdominal fat remain unclear. Therefore, this study aimed to elucidate the patterns of oxygen concentration in adipose tissue layers according to BMI.

METHODS

In this study, patients undergoing abdominal fat removal surgery were divided into the normal-weight (NW) or overweight-obese (OW) groups based on their BMI. Oxygen concentrations in abdominal superficial (sSAT) and deep subcutaneous adipose tissue (dSAT) were measured. The oxygen consumption rate, mean cell area, and capillary density in both tissue layers were compared between the two groups. Furthermore, the interaction between these three variables, BMI, and adipose tissue oxygen concentration, was analyzed using linear regression.

RESULTS

A total of 42 patients were recruited in this study and we observed that oxygen concentration in the sSAT was significantly lower than in the dSAT, irrespective of BMI. In terms of the oxygen concentration in the dSAT, OW's was significantly lower than that of NW's. Linear regression analysis revealed a significant correlation between dSAT oxygen concentration and BMI, mean adipocyte area, and vascular density.

CONCLUSION

Individuals who are obese have significantly lower oxygen levels in the deep abdominal adipose tissue, and this is influenced by BMI, adipocyte area, and capillary density.

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Novel Proteome Targets Marking Insulin Resistance in Metabolic Syndrome

CONTEXT/OBJECTIVE

In order to better understand which metabolic differences are related to insulin resistance in metabolic syndrome (MetSyn), we used hyperinsulinemic-euglycemic (HE) clamps in individuals with MetSyn and related peripheral insulin resistance to circulating biomarkers.

DESIGN/METHODS

In this cross-sectional study, HE-clamps were performed in treatment-naive men (n = 97) with MetSyn. Subjects were defined as insulin-resistant based on the rate of disappearance (Rd). Machine learning models and conventional statistics were used to identify biomarkers of insulin resistance. Findings were replicated in a cohort with n = 282 obese men and women with (n = 156) and without (n = 126) MetSyn. In addition to this, the relation between biomarkers and adipose tissue was assessed by nuclear magnetic resonance imaging.

RESULTS

Peripheral insulin resistance is marked by changes in proteins related to inflammatory processes such as IL-1 and TNF-receptor and superfamily members. These proteins can distinguish between insulin-resistant and insulin-sensitive individuals (AUC = 0.72 ± 0.10) with MetSyn. These proteins were also associated with IFG, liver fat (rho 0.36, p = 1.79 × 10-9) and visceral adipose tissue (rho = 0.35, p = 6.80 × 10-9). Interestingly, these proteins had the strongest association in the MetSyn subgroup compared to individuals without MetSyn.

CONCLUSIONS

MetSyn associated with insulin resistance is characterized by protein changes related to body fat content, insulin signaling and pro-inflammatory processes. These findings provide novel targets for intervention studies and should be the focus of future in vitro and in vivo studies.

This Is What Metabolic Dysfunction-Associated Steatotic Liver Disease Looks Like: Potential of a Multiparametric MRI Protocol

Metabolic dysfunction-associated steatotic liver disease (MASLD) is a prevalent condition with a broad spectrum defined by liver biopsy. This gold standard method evaluates three features: steatosis, activity (ballooning and lobular inflammation), and fibrosis, attributing them to certain grades or stages using a semiquantitative scoring system. However, liver biopsy is subject to numerous restrictions, creating an unmet need for a reliable and reproducible method for MASLD assessment, grading, and staging. Noninvasive imaging modalities, such as magnetic resonance imaging (MRI), offer the potential to assess quantitative liver parameters. This review aims to provide an overview of the available MRI techniques for the three criteria evaluated individually by liver histology. Here, we discuss the possibility of combining multiple MRI parameters to replace liver biopsy with a holistic, multiparametric MRI protocol. In conclusion, the development and implementation of such an approach could significantly improve the diagnosis and management of MASLD, reducing the need for invasive procedures and paving the way for more personalized treatment strategies.

Sex-specific association of visceral and subcutaneous adipose tissue volumes with systemic inflammation and innate immune cells in people living with obesity

BACKGROUND AND AIMS

Obesity predisposes to metabolic and cardiovascular diseases. Adipose tissue inflammation and systemic inflammation contribute to these complications. There are strong sex differences in adipose tissue distribution and in systemic inflammation. Women have more subcutaneous adipose tissue (SAT) and less visceral adipose tissue (VAT) than men. We explored the sex differences in the association between the different adipose compartments and inflammatory markers that are important in cardiometabolic disease pathophysiology.

METHODS

Single-center observational cohort study with 302 individuals with a BMI ≥ 27 kg/m2. We were unable to acquire MRI data from seven individuals and from another 18 the MRI data were not usable, resulting in 277 people (155 men, 122 women), aged 55-81 years.

INTERVENTION

We performed the following measurements: abdominal magnetic resonance imaging to measure VAT, and SAT (deep and superficial) volumes; circulating leukocyte counts and cytokine production capacity of peripheral blood mononuclear cells (PBMCs), circulating cytokines, adipokines, and targeted proteomics; abdominal sSAT biopsies for histology and gene expression.

RESULTS

Only in women, (s)SAT volume was associated with circulating leukocytes, monocytes, and neutrophils. Circulating IL-6 and IL-18BP were associated with SAT volume in women and VAT in men. Several circulating proteins, including monocyte-colony-stimulating factor 1 and hepatocyte growth factor, are associated with sSAT in women and VAT in men. Only in women, SAT volume is associated with SAT expression of inflammatory proteins, including leptin, CD68, TNFα and IL-1α.

CONCLUSION

In women living with obesity, abdominal SAT volume, especially sSAT, is associated with circulating leukocytes and inflammatory proteins. In men, these parameters mainly show associations with VAT volume. This could be because only in women, sSAT volume is associated with sSAT expression of inflammatory proteins. These findings underscore that future research on adipose tissue in relation to cardiometabolic and cardiovascular disease should take sex differences into account.

Sex-specific Association Between Adipose Tissue Inflammation and Vascular and Metabolic Complications of Obesity

CONTEXT

Adipose tissue (AT) inflammation predisposes to insulin resistance and metabolic syndrome in obesity.

OBJECTIVE

To investigate the association between adipocyte size, AT inflammation, systemic inflammation, and metabolic and atherosclerotic complications of obesity in a sex-specific manner.

DESIGN

Cross-sectional cohort study.

SETTING

University hospital in the Netherlands.

PARTICIPANTS

A total of 302 adult subjects with a body mass index (BMI) ≥ 27 kg/m2.

MAIN OUTCOME MEASURES

We obtained subcutaneous abdominal fat biopsies and systematically assessed, in a sex-specific manner, associations of several parameters of AT inflammation (including adipocyte size, macrophage content, crown-like structures, and gene expression) to biomarkers of systemic inflammation, leukocyte number and function, and to the presence of metabolic syndrome, insulin resistance, and carotid atherosclerotic plaques, assessed with ultrasound.

RESULTS

Adipocyte size was associated with metabolic syndrome and AT macrophage content with insulin resistance. In contrast, none of the AT parameters was associated with carotid atherosclerosis, although mRNA expression of the anti-inflammatory IL-37 was associated with a lower intima-media thickness. We revealed profound sex-specific differences, with an association between BMI and adipocyte size, and between adipocyte size and metabolic syndrome in men only. Also, only men showed an association between adipocyte size, AT expression of leptin and MCP-1, and AT macrophage numbers, and between AT inflammation (crown-like structure number) and several circulating inflammatory proteins, including high specificity C-reactive protein, and IL-6.

CONCLUSIONS

Inflammation in abdominal subcutaneous adipose tissue is more related to the metabolic than the atherosclerotic complications of obesity, and there are profound sex-specific differences in the association between BMI, adipocyte size, AT inflammation, and systemic inflammation, which are much stronger in men than women.

Analysis of Superficial Subcutaneous Fat Camper's and Scarpa's Fascia in a United States Cohort

Together, the Camper's and Scarpa's fasciae form the superficial fat layer of the abdominal wall. Though they have clinical and surgical relevance, little is known about their role in body composition across diverse patient populations. This study aimed to determine the relationship between patient characteristics, including sex and body mass index, and the distribution of Camper's and Scarpa's fascial layers in the abdominal wall. A total of 458 patients' abdominal CT examinations were segmented via CoreSlicer 1.0 to determine the surface area of each patient's Camper's, Scarpa's, and visceral fascia layers. The reproducibility of segmentation was corroborated by an inter-rater analysis of segmented data for 20 randomly chosen patients divided between three study investigators. Pearson correlation and Student's t-test analyses were performed to characterize the relationship between fascia distribution and demographic factors. The ratios of Camper's fascia, both as a proportion of superficial fat (r = -0.44 and p < 0.0001) and as a proportion of total body fat (r = -0.34 and p < 0.0001), showed statistically significant negative correlations with BMI. In contrast, the ratios of Scarpa's fascia, both as a proportion of superficial fat (r = 0.44 and p < 0.0001) and as a proportion of total body fat (r = 0.41 and p < 0.0001), exhibited statistically significant positive correlations with BMI. Between sexes, the females had a higher ratio of Scarpa's facia to total body fat compared to the males (36.9% vs. 31% and p < 0.0001). The ICC values for the visceral fat, Scarpa fascia, and Camper fascia were 0.995, 0.991, and 0.995, respectively, which were all within the 'almost perfect' range (ICC = 0.81-1.00). These findings contribute novel insights by revealing that as BMI increases the proportion of Camper's fascia decreases, while the ratio of Scarpa's fascia increases. Such insights expand the scope of body composition studies, which typically focus solely on superficial and visceral fat ratios.

Metabolic dysfunction and nonalcoholic fatty liver disease risk in individuals with a normal body mass index

PURPOSE OF REVIEW

Nonalcoholic fatty liver disease (NAFLD) is strongly associated with obesity, but is also common in individuals with a normal body mass index (BMI), who also experience the hepatic inflammation, fibrosis, and decompensated cirrhosis associated with NAFLD progression. The clinical evaluation and treatment of NAFLD in this patient population are challenging for the gastroenterologist. A better understanding of the epidemiology, natural history, and outcomes of NAFLD in individuals with normal BMI is emerging. This review examines the relationship between metabolic dysfunction and clinical characteristics associated with NAFLD in normal-weight individuals.

RECENT FINDINGS

Despite a more favorable metabolic profile, normal-weight NAFLD patients exhibit metabolic dysfunction. Visceral adiposity may be a critical risk factor for NAFLD in normal-weight individuals, and waist circumference may be better than BMI for assessing metabolic risk in these patients. Although screening for NAFLD is not presently recommended, recent guidelines may assist clinicians in the diagnosis, staging, and management of NAFLD in individuals with a normal BMI.

SUMMARY

Individuals with a normal BMI likely develop NAFLD as a result of different etiologies. Subclinical metabolic dysfunction may be a key component of NAFLD in these patients, and efforts to better understand this relationship in this patient population are needed.

Sex differences in body composition in people with prediabetes and type 2 diabetes as compared with people with normal glucose metabolism: the Maastricht Study

AIMS/HYPOTHESIS

Obesity is a major risk factor for type 2 diabetes. However, body composition differs between women and men. In this study we investigate the association between diabetes status and body composition and whether this association is moderated by sex.

METHODS

In a population-based cohort study (n=7639; age 40-75 years, 50% women, 25% type 2 diabetes), we estimated the sex-specific associations, and differences therein, of prediabetes (i.e. impaired fasting glucose and/or impaired glucose tolerance) and type 2 diabetes (reference: normal glucose metabolism [NGM]) with dual-energy x-ray absorptiometry (DEXA)- and MRI-derived measures of body composition and with hip circumference. Sex differences were analysed using adjusted regression models with interaction terms of sex-by-diabetes status.

RESULTS

Compared with their NGM counterparts, both women and men with prediabetes and type 2 diabetes had more fat and lean mass and a greater hip circumference. The differences in subcutaneous adipose tissue, hip circumference and total and peripheral lean mass between type 2 diabetes and NGM were greater in women than men (women minus men [W-M] mean difference [95% CI]: 15.0 cm2 [1.5, 28.5], 3.2 cm [2.2, 4.1], 690 g [8, 1372] and 443 g [142, 744], respectively). The difference in visceral adipose tissue between type 2 diabetes and NGM was greater in men than women (W-M mean difference [95% CI]: -14.8 cm2 [-26.4, -3.1]). There was no sex difference in the percentage of liver fat between type 2 diabetes and NGM. The differences in measures of body composition between prediabetes and NGM were generally in the same direction, but were not significantly different between women and men.

CONCLUSIONS/INTERPRETATION

This study indicates that there are sex differences in body composition associated with type 2 diabetes. The pathophysiological significance of these sex-associated differences requires further study.

Adipose tissue dysfunction and visceral fat are associated with hepatic insulin resistance and severity of NASH even in lean individuals

BACKGROUND & AIMS

Non-alcoholic fatty liver disease (NAFLD) is a heterogeneous disorder, but the factors that determine this heterogeneity remain poorly understood. Adipose tissue dysfunction is causally linked to NAFLD since it causes intrahepatic triglyceride (IHTG) accumulation through increased hepatic lipid flow, due to insulin resistance and pro-inflammatory adipokines release. While many studies in NAFLD have looked at total adiposity (i.e. mainly subcutaneous fat, SC-AT), it is still unclear the possible impact of visceral fat (VF). Thus, we investigated how VF versus SC-AT was related to NAFLD severity in lean, overweight and obese individuals versus lean controls.

METHODS

Thirty-two non-diabetic NAFLD with liver biopsy (BMI 21.4-34.7 kg/m² ) and eight lean individuals (BMI 19.6-22.8 kg/m² ) were characterized for fat distribution (VF, SC-AT and IHTG by magnetic resonance imaging), lipolysis and insulin resistance by tracer infusion, free fatty acids (FFAs) and triglyceride (TAG) concentration and composition (by mass spectrometry).

RESULTS

Intrahepatic triglyceride was positively associated with lipolysis, adipose tissue insulin resistance (Adipo-IR), TAG concentrations, and increased saturated/unsaturated FFA ratio. Compared to controls VF was higher in NAFLD (including lean individuals), increased with fibrosis stage and associated with insulin resistance in liver, muscle and adipose tissue, increased lipolysis and decreased adiponectin levels. Collectively, our results suggest that VF accumulation, given its location close to the liver, is one of the major risk factors for NAFLD.

CONCLUSIONS

These findings propose VF as an early indicator of NAFLD progression independently of BMI, which may allow for evidence-based prevention and intervention strategies.