Bile acids with differing hydrophilic-hydrophobic properties do not influence cytokine production by human monocytes and murine Kupffer cells

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Abstract

Bile acids have been proposed to exert immunological effects of potential pathogenic or therapeutic relevance, yet the experimental evidence remains preliminary. We reexamined the effects of a variety of bile salts with differing hydrophilic-hydrophobic properties on the production of interleukin-6 (IL-6) and tumor necrosis factor alpha (TNF α) from monocytes and Kupffer cells. Monocytes from healthy human donors and Kupffer cells from 5-week-old mice were incubated for up to 18 hours with or without varying concentrations of bile salts and lipopolysaccharide (LPS). Monocyte viability was ≥ 95% with up to 250 μmol/L sodium ursodeoxycholate and ≤ 90% with 200 μmol/L chenodeoxycholate, decreasing sharply at higher concentrations. Kupffer cells were more vulnerable, particularly to chenodeoxycholate (viabilities of 25% and 0% at concentrations of 100 μmol/L and 200 μmol/L, respectively). In monocytes incubated in the presence of 20% fetal calf serum, neither ursodeoxycholate and chenodeoxycholate, nor a variety of other unconjugated and conjugated bile acids, tested up to their maximal noncytotoxic concentrations, influenced the IL-6 and TNF alpha production, at any level of LPS stimulation. Similar to monocytes, incubation of murine Kupffer cells with ursodeoxycholate and chenodeoxycholate did not influence cytokine release. In contrast, the addition of 10 nmol/L dexamethasone to monocytes significantly decreased TNF-alpha and IL-6 release (69 ± 11% and 48 ± 15%, respectively). When monocytes were incubated with 200 μmol/L chenodeoxycholate in the presence of lower concentrations of fetal calf serum (10% and 5%, respectively) a significant inhibition of cytokine release was observed, whereas incubation with ursodeoxycholate did not cause any effect. Flow cytometry using fluoresceinated LPS showed that chenodeoxycholate does not interact with the CD14 receptor, thus excluding the possibility of an interference with the LPS uptake by monocytes. Incubation with [14C]-chenodeoxycholate showed that the intracellular bile acid uptake was inversely related to the concentration of fetal calf serum, being negligible (< 3 fmol/cell) at the highest level. In conclusion, bile acids with widely different hydrophobicities are incapable of influencing the release of IL-6 and TNF alpha by monocytes and Kupffer cells, provided they are studied at noncytotoxic concentrations and in the presence of physiological amounts of proteins.

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