Borrelia burgdorferi and Escherichia coli lipopolysaccharides induce nitric oxide and interleukin-6 production in cultured rat brain cells.

Borrelia burgdorferi, the spirochetal agent of Lyme disease, infects the central nervous system (CNS), but the factors that mediate inflammation and neurologic dysfunction are not known. Sonicated B. burgdorferi stimulated in a concentration-dependent manner the production of nitric oxide (NO) in glial-enriched primary cultures of neonatal rat brain cells via induction of NO synthase activity. Lipopolysaccharide (LPS) of Escherichia coli also stimulated nitrite accumulation in a concentration-dependent manner. Stimulation of NO production by B. burgdorferi sonicate and E. coli LPS was associated with increased levels of mRNA coding for the cytokine-inducible form of NO synthase. B. burgdorferi sonicate also stimulated release of interleukin-6, with a concentration-response relationship similar to that for its stimulation of nitrite production, as did E. coli LPS. A competitive antagonist of E. coli LPS, Rhodopseudomonas sphaeroides lipid A, inhibited LPS-induced stimulation of NO synthase activity but markedly potentiated that of B. burgdorferi, indicating that the initial triggering mechanism of B. burgdorferi is distinct from that of E. coli LPS. Induction of NO synthase by bacterial agents within the brain may represent a common pathway of CNS inflammation and neurotoxicity.