Free fatty acid storage in human visceral and subcutaneous adipose tissue: role of adipocyte proteins

Abstract

Objective: Because direct adipose tissue free fatty acid (FFA) storage may contribute to body fat distribution, we measured FFA (palmitate) storage rates and fatty acid (FA) storage enzymes/proteins in omental and abdominal subcutaneous fat.

Research design and methods: Elective surgery patients received a bolus of [1-(14)C]palmitate followed by omental and abdominal subcutaneous fat biopsies to measure direct FFA storage. Long chain acyl-CoA synthetase (ACS) and diacylglycerol acyltransferase activities, CD36, fatty acid-binding protein, and fatty acid transport protein 1 were measured.

Results: Palmitate tracer storage (dpm/g adipose lipid) and calculated palmitate storage rates were greater in omental than abdominal subcutaneous fat in women (1.2 ± 0.8 vs. 0.7 ± 0.4 μmol · kg adipose lipid(-1) · min(-1), P = 0.005) and men (0.7 ± 0.2 vs. 0.2 ± 0.1, P < 0.001), and both were greater in women than men (P < 0.0001). Abdominal subcutaneous adipose tissue palmitate storage rates correlated with ACS activity (women: r = 0.66, P = 0.001; men: r = 0.70, P = 0.007); in men, CD36 was also independently related to palmitate storage rates. The content/activity of FA storage enzymes/proteins in omental fat was dramatically lower in those with more visceral fat. In women, only omental palmitate storage rates were correlated (r = 0.54, P = 0.03) with ACS activity.

Conclusions: Some adipocyte FA storage factors correlate with direct FFA storage, but sex differences in this process in visceral fat do not account for sex differences in visceral fatness. The reduced storage proteins in those with greater visceral fat suggest that the storage factors we measured are not a predominant cause of visceral adipose tissue accumulation.

FIG. 1.

Comparison of regional difference in FA storage. A: SA (dpm/g lipid). B: FFA storage (μmol ⋅ kg lipid⁻¹ ⋅ min⁻¹). C: Percent storage. Open bars represent abdominal subcutaneous adipose tissue, and closed bars represent omental adipose tissue. †P < 0.05 vs. omental adipose tissue within same sex group. *P < 0.01 vs. omental adipose tissue within same sex group. ‡P < 0.03 vs. same depot in men.

FIG. 2.

Correlation between regional FA storage factors and regional fat mass. Left: Abdominal subcutaneous adipose tissue. A: Relationship between ACS and abdominal subcutaneous adipose tissue fat mass for women r = 0.18, P = 0.65 and for men r = 0.01, P = 0.82. B: Relationship between DGAT and abdominal subcutaneous adipose tissue fat mass for women r = 0.03, P = 0.58 and for men r = 0.07, P = 0.45. C: Relationship between CD36 and abdominal subcutaneous adipose tissue fat mass for women r = 0.12, P = 0.24 and for men r = 0.01, P = 0.78. D: Relationship between plasma membrane FABP(pm) and abdominal subcutaneous adipose tissue fat mass (r and P values for men and women). Right: Omental adipose tissue. E: Relationship between abdominal subcutaneous adipose tissue and omental fat mass for women r = 0.50, P = 0.002 and for men r = 0.88, P < 0.0001. F: Relationship between DGAT and omental fat mass for women r = 0.72, P < 0.0001 and for men r = 0.80, P < 0.0001. G: Relationship between CD36 and omental fat mass for women r = 0.52, P = 0.003 and for men r = 0.85, P < 0.0001. H: Relationship between FABP(pm) and omental fat mass (r and P values for men and women). Solid squares/solid line, men; open circles/dashed line, women; ASQ, abdominal subcutaneous adipose tissue.

FIG. 3.

Relationships between calculated palmitate storage rates and FA storage factors. A: Relationship between abdominal subcutaneous adipose tissue palmitate storage and ACS for women r = 0.66, P = 0.01 and for men r = 0.70, P = 0.01. B: Relationship between omental palmitate storage and ACS for women r = 0.54, P = 0.03 and for men r = 0.17, P = 0.57. C: Relationship between omental palmitate storage and CD36 for women r = 0.33, P = 0.20 and for men r = 0.67, P = 0.01. Solid squares/solid lines, men; open circles/dashed lines, women.