Stearic acid content of abdominal adipose tissues in obese women

Abstract

Objective: Subcutaneous (SC) adipose tissue stearic acid (18:0) content and stearoyl-CoA desaturase-1 (SCD1)-mediated production of oleic acid (18:1) have been suggested to be altered in obesity. The objective of our study was to examine abdominal adipose tissue fatty acid content and SCD1 mRNA/protein level in women.

Subjects and methods: Fatty acid content was determined by capillary gas chromatography in SC and omental (OM) fat tissues from two subgroups of 10 women with either small or large OM adipocytes. Samples from 10 additional women were used to measure SCD1 mRNA and protein expression, total extracellular signal-regulated kinase 1/2 (ERK1/2) and phosphorylated ERK1/2 protein as well as insulin receptor (IR) expression levels.

Results: OM fat 18:0 content was significantly lower in women with large OM adipocytes compared with women who had similar adiposity, but small OM adipocytes (2.37±0.45 vs 2.75±0.30 mg per 100 g adipose tissue, respectively, P0.05). OM fat 18:0 content was negatively related to the visceral adipose tissue area (r=-0.44, P=0.05) and serum triglyceride levels (r=-0.56, P<0.05), while SC fat 18:0 content was negatively correlated with total body fat mass (BFM) (r=-0.48, P<0.05) and fasting insulin concentration (r=-0.73, P<0.005). SC adipose tissue desaturation index (18:1/18:0), SCD1 expression and protein levels were positively correlated with BFM. Moreover, obese women were characterized by a reduced OM/SC ratio of SCD1 mRNA and protein levels. A similar pattern was observed for ERK1/2 and IR expression.

Conclusion: The presence of large adipocytes and increased adipose mass in a given fat compartment is related to reduced 18:0 content and increased desaturation index in women, independently of dietary fat intake. The depot-specific difference in ERK1/2 expression and activation, as well as in SCD1 and IR expression in obese women is consistent with the hypothesis that they may predominantly develop SC fat, which could in turn help protect from metabolic disorders.

Figure 1

Comparison of dietary fatty acid content (left panel) and SC or OM adipose tissue fatty acid composition (right panel). Only fatty acids that were detected at a value higher than 0.5 g fatty acid per 100 g adipose tissue are represented.

Figure 2

Associations between SCD1 mRNA expression or SCD1 protein levels in SC adipose tissue (AT) and total BFM. Messenger RNA expression normalized according to ATP5O mRNA expression (similar results were obtained using other housekeeping genes, see Subjects and Methods); protein levels normalized with GAPDH. Pearson correlation coefficients are shown.

Figure 3

OM/SC ratios of SCD1 mRNA expression (a), SCD1 protein level (b), total ERK1/2 protein level, ERK 1/2 phosphorylation state (p-ERK 1/2) (c) and IR expression (d) in normal or overweight women (BMI<30 kg m⁻²) vs obese women (BMI⩾30 kg m⁻²). SCD1 mRNA expression values were normalized with G6PD whereas protein expressions were normalized by GAPDH (b–d). *P<0.05.