Direct evidence that bacterial lipopolysaccharides elevate cyclic GMP levels in rat fetal liver cells

We have previously shown that crude bacterial lipopolysaccharide (LPS) preparations markedly increase cGMP levels in rat fetal liver cells in a time- and dose-dependent manner. To provide evidence that this effect was due to LPS and not an impurity in the preparations, three series of experiments were undertaken. First, LPS was prepared from Escherichia coli 055:B5 cells and its cGMP potency assessed at various stages of purification; second, the cGMP activity of three highly purified LPS preparations of known chemical structure was measured, and third, a well characterized LPS was broken into its lipid A and polysaccharide fractions and the cGMP activity of each fraction determined. The results showed that the cGMP stimulatory activity in E. coli 055:B5 cells co-purified in a parallel fashion with the LPS molecule derived from those cells, that the three chemically defined, highly purified LPS preparations were all very potent stimulators of cGMP levels, and that the ability to increase cGMP levels of lipid A prepared from a highly purified LPS was comparable in potency to the intact LPS, whereas the polysaccharide portion of the molecule was without activity. These findings indicate that the cGMP effect of LPS preparation is due to LPS and not a contaminant and that the activity resides within the lipid A moiety of the molecule.