Hyperosmotic stress as a stimulant for proinflammatory cytokine production

The synthesis of proinflammatory cytokines involves members of the mitogen-activated protein (MAP) kinase stress pathway, particularly p38 MAP kinase and c-jun NH2-terminal kinase. In this report we used hyperosmotic stress to study changes in steady-state mRNA levels and synthesis of proinflammatory cytokines in freshly obtained human peripheral blood mononuclear cells (PBMC) in vitro. There was no evidence of interleukin (IL)-8 gene expression in freshly obtained human blood despite 30 cycles of amplification of reverse-transcribed mRNA using the polymerase chain reaction. In contrast, exposure of PBMC to hyperosmotic conditions (330-410 mOsM) by the addition of NaCl to tissue culture medium induced gene expression for IL-1 alpha, IL-1 beta, and IL-8. Routine tissue culture medium is hyperosmotic (305 mOsM) compared to human plasma (280-295 mOsM), but decreasing the osmolarity to the physiological range resulted in a 50% reduction in baseline IL-8 synthesis (P < 0.001). Although hyperosmotically induced accumulation of steady-state mRNA levels for IL-1 alpha and IL-1 beta increased 50- and 7-fold over control, respectively, these were poorly translated into each respective cytokine. However, in PBMC stimulated by hyperosmotic stress, the addition of femtomolar concentrations of bacterial lipopolysaccharide, IL-1, or 1% normal human serum resulted in a synergistic synthesis (at least twice that expected) of IL-1 alpha, IL-1 beta, TNF-alpha, and IL-8.