Bimodal effect of humic acids on the LPS-induced TNF-alpha release from differentiated U937 cells

Phytomedicine. 2009 May;16(5):470-6. doi: 10.1016/j.phymed.2008.10.003. Epub 2009 Jan 7.


Humic substances (HS) have been reported to possess anti-inflammatory as well as pro-inflammatory properties. The anti-inflammatory activity was demonstrated in the rat paw edema model and we found a preliminary explanation in the 5-lipoxygenase inhibitory effect of humic acids (HA). The pro-inflammatory activity is reflected by the production and release of pro-inflammatory cytokines in HA-treated neutrophilic granulocytes. With regard to the potential use of HA as antiviral and UV-protective agents it appears advisable to investigate the role of HS in the inflammation process in more detail. Hence we tested four different HS preparations - two naturally occurring HA from the Altteich peatland in Germany, one fulvic acid (FA) preparation from a Finnish spruce forest and a synthetic HA-like polymer (caffeic acid oxidation product, KOP) for their influence on the lipopolysaccharide (LPS)-induced TNF-alpha release in human U937 cells. In addition, the cytotoxicity of HS was determined. The results demonstrate a concentration-dependent bimodal effect of HA on the TNF-alpha release of differentiated LPS-stimulated U937 cells for both the natural black peat HA from the Altteich peatland and the HA-like polymer KOP. Low HA concentrations (10-80 microg/ml) enhanced the TNF-alpha release by up to threefold (pro-inflammatory activity), while HA concentrations >100 microg/ml reduced it about 10-fold (anti-inflammatory activity). FA failed to enhance TNF-alpha release, but reduced it at higher concentrations (>200 microg/ml) by the half. Brown water HA did not exert any significant effect on TNF-alpha release. No HS-stimulated TNF-alpha release was also observed in the absence of exogenously supplied LPS. This means that HS, unlike endotoxin, are no inflammation-causing agents for LPS-untreated cells. Differences in the effect of individual HS on TNF-alpha release are discussed in connection with the polyanionic character of HS, their molecular mass distribution and the hitherto imperfectly known chemical structure.

MeSH terms

  • Anti-Inflammatory Agents / adverse effects
  • Anti-Inflammatory Agents / pharmacology*
  • Benzopyrans / adverse effects
  • Benzopyrans / pharmacology*
  • Caffeic Acids / metabolism
  • Dose-Response Relationship, Drug
  • Humans
  • Humic Substances* / adverse effects
  • Lipopolysaccharides / toxicity
  • Plants
  • Soil
  • Tumor Necrosis Factor-alpha / metabolism*
  • U937 Cells


  • Anti-Inflammatory Agents
  • Benzopyrans
  • Caffeic Acids
  • Humic Substances
  • Lipopolysaccharides
  • Soil
  • Tumor Necrosis Factor-alpha
  • caffeic acid
  • fulvic acid