Deep subcutaneous adipose tissue lipid unsaturation associates with intramyocellular lipid content

Abdominal adipose tissue and liver fat imaging in very low birth weight adults born preterm: birth cohort with sibling-controls

Preterm birth at very low birth weight (VLBW, < 1500 g) is associated with an accumulation of cardiovascular and metabolic risk factors from childhood at least to middle age. Small-scale studies suggest that this could partly be explained by increased visceral or ectopic fat. We performed magnetic resonance imaging on 78 adults born preterm at VLBW in Finland between 1978 and 1990 and 72 term same-sex siblings as controls, with a mean age of 29 years. We collected T1-weighted images from the abdomen, and magnetic resonance spectra from the liver, subcutaneous abdominal adipose tissue, and tibia. The adipose tissue volumes of VLBW adults did not differ from their term siblings when adjusting for age, sex, and maternal and perinatal factors. The mean differences were as follows: subcutaneous − 0.48% (95% CI − 14.8%, 16.3%), visceral 7.96% (95% CI − 10.4%, 30.1%), and total abdominal fat quantity 1.05% (95% CI − 13.7%, 18.4%). Hepatic triglyceride content was also similar. VLBW individuals displayed less unsaturation in subcutaneous adipose tissue (− 4.74%, 95% CI − 9.2%, − 0.1%) but not in tibial bone marrow (1.68%, 95% CI − 1.86%, 5.35%). VLBW adults displayed similar adipose tissue volumes and hepatic triglyceride content as their term siblings. Previously reported differences could thus partly be due to genetic or environmental characteristics shared between siblings. The VLBW group displayed less unsaturation in subcutaneous abdominal adipose tissue, suggesting differences in its metabolic activity and energy storage.

Fat unsaturation measures in tibial, subcutaneous and breast adipose tissue using short and long TE MRS at 3 T

Fat unsaturation and poly-unsaturation measures can be obtained in vivo with magnetic resonance spectroscopy (MRS) through the olefinic (≈5.4 ppm) and diallylic (≈2.8 ppm) resonances, respectively. Long echo time (TE) MRS sequences have been previously optimized for olefinic/methylene (≈1.3 ppm) or olefinic/methyl (≈0.9 ppm) measures. The objectives of this work, using a Point RESolved Spectroscopy (PRESS) sequence, are to: 1) Investigate olefinic, methyl and methylene resonance decay in subcutaneous, tibial, and breast adipose tissue to determine if a direct comparison of unsaturation measures can be made without correction for T₂ losses. 2) Assess intra-individual fat unsaturation and poly-unsaturation measures in the three adipose tissues. 3) Estimate correction factors for olefinic to methylene ratios to compensate for J-coupling and T₂ relaxation losses that take place when increasing PRESS TE from 40 ms to 200 ms (previously optimized long-TE). 4) Investigate the utility of an inversion recovery for resolving the olefinic resonance from water in adipose tissue. PRESS spectra were acquired from the three adipose regions (breast in female only) in healthy volunteers at 3 T. It was found that olefinic and methyl signal decays faster in breast tissue compared to in tibial bone marrow. Poly-unsaturation measures (diallylic/methylene) differ for tibial bone marrow compared to subcutaneous and breast adipose tissue, with average values of 1.7 ± 0.4, 2.2 ± 0.4, and 2.3 ± 0.8%, respectively. PRESS (TE = 40 ms) with an inversion recovery resolves the olefinic and water resonances in breast tissue with a signal to noise ratio approximately six times greater than that using PRESS with a TE of 200 ms. Stimulated Echo Acquisition Mode (STEAM) with a TE of 20 ms (mixing time of 20 ms) was also combined with IR to resolve the olefinic resonance from that of water is spinal bone marrow.

Metabolic Profile and Body Composition in Twins Concordant and Discordant for Physical Exercise

The aim of this study was to evaluate the differences in the metabolic profile and body composition of monozygotic (MZ) twins concordant and discordant for the practice of physical exercise. The sample consisted of 92 MZ twins (72.5% female and 27.5% male, mean age 25.4 ± 5.69 years), registered with the Brazilian Registry of Twins, residing in Natal, Brazil. Data collection was carried out between the years 2016 and 2018. On day 1, subjects underwent a whole-body fitness evaluation, including measures of weight, height, body composition by Dual-Energy X-ray Absorptiometry and the Cardiorespiratory Exercise Test. On day 2, 10 ml blood samples were collected (overnight fasting) to determine the lipid profile and fasting glucose. The sample was separated into three groups: Active Concordant twins (Concordant A, n = 44 subjects), Inactive Concordant twins (Concordant I, n = 22 subjects) and Discordant pairs for Physical Exercise (Discordant PE, n = 26 subjects). The results demonstrated a difference between the discordant twins for exercise and also between the active versus sedentary groups, indicating a causal effect of exercise on the fat percentage, maximum oxygen consumption (VO2max) and second ventilatory threshold variables. Between groups, a difference was also observed between the groups in ventilatory threshold, very low-density lipoprotein and triglycerides. We concluded that, regardless of genetics, the practice of physical exercise was sufficient to generate alterations in body composition and VO2max in MZ twins, but not in the lipid profile or fasting glucose.

Analysis of muscle, hip, and subcutaneous fat in osteoporosis patients with varying degrees of fracture risk using 3T Chemical Shift Encoded MRI

Osteoporosis (OP) is a major disease that affects 200 million people worldwide. Fatty acid metabolism plays an important role in bone health and plays an important role in bone quality and remodeling. Increased bone marrow fat quantity has been shown to be associated with a decrease in bone mineral density (BMD), which is used to predict fracture risk. Chemical-Shift Encoded magnetic resonance imaging (CSE-MRI) allows noninvasive and quantitative assessment of adipose tissues (AT). The aim of our study was to assess hip or proximal femoral bone marrow adipose tissue (BMAT), thigh muscle (MUS), and subcutaneous adipose tissue (SAT) in 128 OP subjects matched for age, BMD, weight and height with different degrees of fracture risk assessed through the FRAX score (low, moderate and high). Our results showed an increase in BMAT and in MUS in high compared to low fracture risk patients. We also assessed the relationship between fracture risk as assessed by FRAX and AT quantities. Overall, the results of this study suggest that assessment of adipose tissue via 3T CSE-MRI provides insight into the pathophysiology fracture risk by showing differences in the bone marrow and muscle fat content in subjects with similarly osteoporotic BMD as assessed by DXA, but with varying degrees of fracture risk as assessed by FRAX.

Greater Reduction in Abdominal Than in Upper Arms Subcutaneous Fat in 10- to 12-Year-Old Tennis Players: A Volumetric MRI Study

Background: Little is known about the impact of long term participation in sports and subcutaneous fat volume in children. This study aimed at determining whether tennis participation is associated with lower subcutaneous adipose tissue volume (SATv) in the abdominal and upper extremities in children. Methods: Magnetic resonance imaging (MRI) was used to determine the SATv stored in the abdominal region and upper arms in seven tennis players and seven inactive children matched by height and age (147 cm and 10.9 years). All participants were in Tanner stage 1 or 2. Results: Playing tennis was associated with 48% (P = 0.001) lower abdominal SATv and 17-18% (P > 0.05) lower upper arms SATv compared to controls. The ratio between abdominal/upper arms SATv was larger in the controls vs. tennis players (69% P = 0.001). The SATv was similar in the dominant and non-dominant arm within each group. Conclusion: Playing tennis during childhood is associated with reduced SATv in the abdominal region and a more favorable regional distribution of fat. Despite the large amount of contractile activity of the playing (dominant) arm, there was no indication of between-arms differences in SATv.

Increased body fat mass and androgen metabolism - A twin study in healthy young women

OBJECTIVE

Obesity may alter serum steroid concentrations and metabolism. We investigated this in healthy young women with increased body fat and their leaner co-twin sisters.

DESIGN

Age and genetic background both strongly influence serum steroid levels and body composition. This is a cross-sectional study of 13 female monozygotic twin pairs (age, 23-36 years), ten of which were discordant for body mass index (median difference in body weight between the co-twins, 19 kg).

METHODS

We determined body composition by dual energy X-ray absorptiometry and magnetic resonance imaging, serum androgens by liquid chromatography-tandem mass spectrometry, and mRNA expression of genes in subcutaneous adipose tissue and adipocytes.

RESULTS

The heavier women had lower serum dehydroepiandrosterone (DHEA), dihydrotestosterone (DHT), and sex hormone-binding globulin (SHBG) (P < 0.05 for all) compared to their leaner co-twins with no differences in serum testosterone or androstenedione levels. Serum DHEA correlated inversely with %body fat (r = -0.905, P = 0.002), and DHT positively with SHBG (r = 0.842, P = 0.002). In adipose tissue or adipocytes, expressions of STS (steroid sulfatase) and androgen-related genes were significantly higher in the heavier compared to the leaner co-twin, and within pairs, correlated positively with adiposity but were not related to serum androgen levels. None of the serum androgen or SHBG levels correlated with indices of insulin resistance.

CONCLUSIONS

Serum DHEA levels were best predicted by %body fat, and serum DHT by SHBG. These or other serum androgen concentrations did not reflect differences in androgen-related genes in adipose tissue. General or intra-abdominal adiposity were not associated with increased androgenicity in young women.

Bone marrow fat contributes to insulin sensitivity and adiponectin secretion in premenopausal women

PURPOSE

Bone marrow fat is a functionally distinct adipose tissue that may contribute to systemic metabolism. This study aimed at evaluating a possible association between bone marrow fat and insulin sensitivity indices.

METHODS

Fifty obese (n = 23) and non-obese (n = 27) premenopausal women underwent proton magnetic resonance spectroscopy to measure vertebral bone marrow fat content and unsaturation index at L4 level. Abdominal visceral, subcutaneous fat, and epicardial fat were also measured using magnetic resonance imaging. Bone mineral density was measured by dual-energy X-ray absorptiometry. Body composition was assessed by bioelectrical impedance analysis. Fasting serum glucose, insulin, lipids, adiponectin were measured; the insulin resistance index HOMA (HOMA-IR) was calculated.

RESULTS

Bone marrow fat content and unsaturation index were similar in obese and non-obese women (38.5 ± 0.1 vs. 38.6 ± 0.1%, p = 0.994; 0.162 ± 0.065 vs. 0.175 ± 0.048, p = 0.473, respectively). Bone marrow fat content negatively correlated with insulin and HOMA-IR (r = -0.342, r = -0.352, respectively, p = 0.01) and positively with high density lipoprotein cholesterol (r = 0.270, p = 0.043). From a multivariate regression model including lnHOMA-IR as a dependent variable and visceral, subcutaneous, epicardial fat, and bone marrow fat as independent variables, lnHOMA-IR was significantly associated with bone marrow fat (β = -0.008 ± 0.004, p = 0.04) and subcutaneous fat (β = 0.003 ± 0.001, p = 0.04). Bone marrow fat, among the other adipose depots, was a significant predictor of circulating adiponectin (β = 0.147 ± 0.060, p = 0.021). Bone marrow fat unsaturation index negatively correlated with visceral fat (r = -0.316, p = 0.026).

CONCLUSIONS

There is a relationship between bone marrow fat content and insulin sensitivity in obese and non-obese premenopausal women, possibly mediated by adiponectin secretion. Visceral fat does not seem to regulate bone marrow fat content while it may affect bone marrow fat composition.

Adipose tissue and liver

Adipose tissue and liver are central tissues in whole body energy metabolism. Their composition, structure, and function can be noninvasively imaged using a variety of measurement techniques that provide a safe alternative to an invasive biopsy. Imaging of adipose tissue is focused on quantitating the distribution of adipose tissue in subcutaneous and intra-abdominal (visceral) adipose tissue depots. Also, detailed subdivisions of adipose tissue can be distinguished with modern imaging techniques. Adipose tissue (or adipocyte) accumulation or infiltration of other organs can also be imaged, with intramuscular adipose tissue a common example. Although liver fat content is now accurately imaged using standard magnetic resonance imaging (MRI) techniques, inflammation and fibrosis are more difficult to determine noninvasively. Liver imaging efforts are therefore concerted on developing accurate imaging markers of liver fibrosis and inflammatory status. Magnetic resonance elastography (MRE) is presently the most reliable imaging technique for measuring liver fibrosis but requires an external device for introduction of shear waves to the liver. Methods using multiparametric diffusion, perfusion, relaxometry, and hepatocyte-specific MRI contrast agents may prove to be more easily implemented by clinicians, provided they reach similar accuracy as MRE. Adipose tissue imaging is experiencing a revolution with renewed interest in characterizing and identifying distinct adipose depots, among them brown adipose tissue. Magnetic resonance spectroscopy provides an interesting yet underutilized way of imaging adipose tissue metabolism through its fatty acid composition. Further studies may shed light on the role of fatty acid composition in different depots and why saturated fat in subcutaneous adipose tissue is a marker of high insulin sensitivity.