Inhibition of nitric oxide synthase-2 reduces the severity of mouse hepatitis virus-induced demyelination: implications for NOS2/NO regulation of chemokine expression and inflammation

Infection of C57BL/6 mice with mouse hepatitis virus strain V5A13.1 (MHV-V5 A13.1) results in an acute encephalitis followed by a chronic, progressive demyelinating disease with clinical and histological similarities to the hu man demyelinating disease Multiple Sclerosis (MS), Studies were undertaken to evaluate the contribution of NOSE generated NO in demyelination in MHV-i nfected mice. MHV-infected animals were treated daily with either 8 mg of a minoguanidine (AG), a selective inhibitor of NOS2 activity, or PBS by intra peritoneal (i.p.) injection. MHV-infection of mice resulted in 20% mortalit y in both groups with surviving mice clearing virus below levels of detecti on, as measured by plaque assay, by day 12 postinfection (p.i.). A signific ant decrease in the severity of clinical disease was observed in AG-treated animals as compared to mice receiving PBS at days 7 and 12 p.i. (P less th an or equal to 0.001 and 0.003, respectively) however, by day 21 p.i. AG-tr eated mice exhibited the same severity of clinical disease as control anima ls. Examination of brain and spinal cords from infected mice revealed a pro nounced reduction in the severity of inflammation at day 7 p.i. in mice tre ated with AG as compared to control mice. By day 12 p.i. there was a signif icant decrease (P less than or equal to 0.02) in the severity of demyelinat ion in AG-treated mice as compared to control animals yet both PBS and AG t reated mice had a similar degree of demyelination by day 21 p.i. Analysis o f chemokine mRNA transcripts by RNase protection assay revealed that AG-tre ated mice had significantly lower levels (P less than or equal to 0.007) of transcripts for the C-C chemokine monocyte chemoattractant protein-1 (MCP- 1) at day 7 p.i. as compared to control animals, By day 12 p.i., AG-treated mice and control mice had similar levels of chemokine transcripts. Togethe r, these data suggest that inhibition of NOS2/NO slows the progression of M HV-induced demyelination. One potential mechanism by which this may occur i s through controlling inflammation through modulation of chemokine expressi on in the CNS.