Signals from adipose tissue, such as interleukin-6 (IL-6) and asymmetric dimethyl
arginine (ADMA), an endogenous nitric oxide inhibitor, explain the link between
obesity and metabolic diseases. Previously published human studies have used
omental adipose tissue to study visceral depots, based on the assumption that all
visceral adipose tissues are similar. This study, for the first time, assessed the release
of five adipokines (adiponectin, leptin, IL-6, MCP-1 and RANTES) from the
subcutaneous and two omental depots. Components of the cyclooxygenase (COX)
and the nitric oxide (NO) pathways, that regulate cytokine release in other tissues,
were also investigated for their putative role(s) in mediating adipokine release.
RANTES release was greatest from the gastric fat pad. However, significantly higher
circulating RANTES levels suggest that adipose tissue is unlikely to be the main
source of RANTES release.
Inhibition of the COX pathway, especially COX-2, reduced IL-6 release from
subcutaneous adipose tissue. Prostacyclin synthase (PGI2S) activity was higher in the
omental tissue and its protein expression was elevated in the stromavascular fraction
from this depot. PGI2S activity appears to mainly reside in the non-adipocyte cells
and is more coupled to IL-6 production in adipose tissue.
Serum insulin and CRP levels, and systolic blood pressure, directly associated with
subcutaneous tissue ADMA content, while BMI correlated with omental ADMA
release. ADMA release was higher from the omental depot. However, while DDAH2
expression was higher compared to DDAH1 in adipose tissue, there was no depot
specific difference in the expression of either isoform.
In conclusion, this study showed adipose depot specific differences of RANTES
release, a novel adipokine, from a hitherto poorly studied depot, the gastric fat pad.
Characteristics of the omental adipose tissues differed depending on location and
paracrine factors that may mediate the adipokine release. These regulatory pathways
included components of the COX and NO pathways
