Effect of hypoxia and exogenous IL-10 on the pro-inflammatory cytokine TNF-alpha and the anti-angiogenic molecule soluble Flt-1 in placental villous explants.

Background: The placenta plays a pivotal role in the pathophysiology of preeclampsia. Insufficient trophoblast invasion within the placenta can cause focal regions of ischaemia/hypoxia that, in turn, may stimulate the production of inflammatory cytokines. These cytokines are thought to cause endothelial cell activation and dysfunction, resulting in the clinical signs of preeclampsia. In addition to insufficient trophoblast invasion, the presence of inadequate maternal vasculature remodelling by trophoblasts also leads to changes in angiogenesis that may result from variations in the inflammatory cytokine profile.

Objective: This study examined changes in the protein levels of IL-10 (immunoregulatory), TNF-alpha (pro-inflammatory) and sFlt-1 (anti-angiogenic) in normal term placentas under different oxygen tensions. The second aim was to determine if the link between varying levels of the cytokine, IL-10, and the expression/release of TNF-alpha was oxygen dependent, and whether there was a concurrent change in sFlt-1.

Methods: Normal term placentas (n=6) were cultured at three different oxygen tensions (2%, 8% or 21%) in the presence or absence of exogenous IL-10. Protein (TNF-alpha and sFlt-1) secretion was measured using commercial ELISA kits, and qRT-PCR was used to examine gene expression.

Results: Placental IL-10 release was significantly reduced at 2% oxygen when compared to 8% (p=0.045) and 21% (p=0.013). Expression of TNF-alpha and sFlt-1 was not significantly different. Exogenous IL-10 significantly reduced TNF-alpha protein levels only when explants were cultured in 2% oxygen (p=0.05). Soluble Flt-1 protein secretion was unaffected by the addition of IL-10 at any of the oxygen tensions tested.

Conclusions: TNF-alpha release can be inhibited in vitro by IL-10 under hypoxic conditions. However, IL-10 has no affect on sFlt-1 in term placentas, suggesting that these molecules act either via different pathways, or if linked, may be so at different stages of placental development.