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Department of Cell Biology, Bioceros BV, Yalelaan 46, 3584 CM Utrecht, The Netherlands
¹ Departments of Experimental and Internal Medicine and
² Medical Biochemistry, Academic Medical Center, University of Amsterdam, Meibergdreef 15, 1105 AZ Amsterdam, The Netherlands

(Requests for offprints should be addressed to P J Simons; Email: p.simons{at}bioceros.com)

Adiponectin and, especially, its oligomeric complex composition have been suggested to be critical in determining insulin sensitivity. Pro-inflammatory cytokines play an important role in the development of insulin resistance in obesity and associated diseases. Therefore, we investigated the effect of long-term exposure of tumour necrosis factor (TNF)-, interleukin (IL)-6, IL-1ß, and interferon (IFN)- on total insulin-sensitizing adiponectin secretion and adiponectin complex formation from human adipocytes. In parallel, adipocyte delipidation and leptin production levels were monitored. The present study demonstrates that TNF-, IL-1ß, and IFN- dose and time dependently suppressed total adiponectin secretion within 7 days (60, 70, and 35% reduction respectively). IL-6 was also able to reduce (50%) adiponectin production, although only in combination with exogenous soluble IL-6 receptors (sIL-6R). However, the oligomeric distribution (high, middle, and low molecular weight (HMW) complexes) of secreted adiponectin was not altered by any of these cytokines. All studied pro-inflammatory cytokines resulted in delipidation and reduction of lipid-laden adipocyte numbers. Despite this reduction of lipid-laden adipocytes, TNF-, IL-6/sIL-6R, and IL-1ß stimulated leptin release. Our data indicate that (i) long-term pro-inflammatory cytokine exposure downregulates total adiponectin secretion from delipidizing adipocytes and (ii) pro-inflammatory cytokines are not important regulators of adipocyte-derived adiponectin oligomerization. Hence, their individual contribution to low expression of HMW adiponectin found in insulin-resistant conditions seems unlikely. Furthermore, delipidizing adipocytes and preadipocytes are active leptin producers when stimulated by TNF-, IL-6/sIL-6R, and IL-1ß.

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