Nutrition- and virus-induced stress represses the expression of manganese superoxide dismutase in vitro.

The relationship between oxidative stress and neuronal cell death has been suggested for many years. To understand the influence of oxidative stress on neuronal cell death, we investigated the influence of oxidative stress on DEV cells, a human glial cell line. Using enterovirus infection and/or malnutrition to induce oxidative stress, our results demonstrate that those stressors severely influence the antioxidant defense system in DEV cells. Although the expression of mitochondrial manganese superoxide dismutase (MnSOD) in DEV cells was significantly increased in acute infection with viral and nutritional stress, in persistent infection and nutritional stress, the expression of the MnSOD was drastically downregulated. We believe that this downregulation of MnSOD expression in the chronic stress model is due to repression of antioxidant defense. The downregulation of the MnSOD expression may lead to an increase of free-radical production and thus explain why the cells in the chronic stress model were more vulnerable to other oxidative stress influences. The vulnerability of DEV cells to additional stress factors resulted in progressive cell death, which may be analogous to the cell death in neurodegenerative diseases.

Detection of influenza viruses resistant to neuraminidase inhibitors in global surveillance during the first 3 years of their use.

Emergence of influenza viruses with reduced susceptibility to neuraminidase inhibitors (NAIs) develops at a low level following drug treatment, and person-to-person transmission of resistant virus has not been recognized to date. The Neuraminidase Inhibitor Susceptibility Network (NISN) was established to follow susceptibility of isolates and occurrence of NAI resistance at a population level in various parts of the world. Isolates from the WHO influenza collaborating centers were screened for susceptibilities to oseltamivir and zanamivir by a chemiluminescent enzyme inhibition assay, and those considered potentially resistant were analyzed by sequence analysis of the neuraminidase genes. During the first 3 years of NAI use (1999 to 2002), 2,287 isolates were tested. Among them, eight (0.33%) viruses had a >10-fold decrease in susceptibility to oseltamivir, one (0.22%) in 1999 to 2000, three (0.36%) in 2000 to 2001, and four (0.41%) in 2001 to 2002. Six had unique changes in the neuraminidase gene compared to neuraminidases of the same subtype in the influenza sequence database. Although only one of the mutations had previously been recognized in persons receiving NAIs, none were from patients who were known to have received the drugs. During the 3 years preceding NAI use, no resistant variants were detected among 1,054 viruses. Drug use was relatively stable during the period, except for an approximate 10-fold increase in oseltamivir use in Japan during the third year. The frequency of variants with decreased sensitivity to the NAIs did not increase significantly during this period, but continued surveillance is required, especially in regions with higher NAI use.

Impaired glutamate uptake and EAAT2 downregulation in an enterovirus chronically infected human glial cell line.

Rapid and efficient uptake of glutamate via the high-affinity glutamate transporter EAAT2 is important for limiting glutamate-mediated excitotoxicity involved in neuronal death. Furthermore, there is evidence of altered glutamate uptake and catabolism in motor neuron diseases. Such a defect has been reported in amyotrophic lateral sclerosis, the major motor neuron disease, and was associated with impairment in EAAT2 processing. We recently reported the presence of enterovirus genome specifically in the anterior horn of amyotrophic lateral sclerosis cases, suggesting the involvement of a chronic/persistent enterovirus infection in amyotrophic lateral sclerosis. To investigate a putative link between enterovirus infection and the glutamate-mediated excitotoxicity observed in amyotrophic lateral sclerosis, we developed an in vitro model consisting of a human glial cell line infected with ECHOvirus 6, one of the enteroviruses with sequences closely related to those detected in patients with amyotrophic lateral sclerosis. In these glial cells, an ECHOvirus 6 chronic infection was established, resulting in altered extracellular glutamate uptake. This correlated with an aberrant splicing of the EAAT2 pre-messenger ribonucleic acid and a significant loss of EAAT2 protein expression, similar to that observed in patients with amyotrophic lateral sclerosis. These results provide convincing evidence that an enterovirus chronic/persistent infection may alter glial glutamate uptake and catabolism. As enteroviruses are extremely common human pathogens, they may act as a trigger in the development of certain motor neuron diseases, such as amyotrophic lateral sclerosis.