Effect of an inapparent viral encephalitis on the levels of lysosomal glycosidases in mouse brain

Inapparent Tick-Borne Orthoflavivirus Infection in Macaca fascicularis: A Model for Antiviral Drug and Vaccine Research

Tick-borne encephalitis virus (TBEV) and Powassan virus (POWV) are neurotropic tick-borne orthoflaviviruses. They cause mostly asymptomatic infections in hosts, but severe forms with CNS involvement can occur. Studying the early stages of viral infections in humans is challenging, and appropriate animal models are essential for understanding the factors determining the disease severity and for developing emergency prophylaxis and treatment options. In this work, we assessed the model of the early stages of TBEV and POWV mono- and co-infections in Macaca fascicularis. Serological, biochemical, and virological parameters were investigated to describe the infection, including its impact on animal behavior. Viremia, neutralizing antibody dynamics, and viral load in organs were chosen as the main parameters distinguishing early-stage orthoflavivirus infection. Levels of IFNα, monocyte count, and cognitive test scores were proposed as additional informative indicators. An assessment of a tick-borne encephalitis vaccine using this model showed that it provided partial protection against POWV infection in Macaca fascicularis without signs of antibody-dependent enhancement of infection.

The relationship between axonal transport of protein and demyelination in the optic nerves of mice infected with Semliki Forest virus

Fast and slow axonal transport of protein have been studied in the optic nerves of mice infected with Semliki Forest Virus (SFV) that causes patchy demyelination throughout the CNS. Intravitreal injections of [3H]proline were given at regular intervals after virus inoculation, the labelled protein in the superior colliculi was then measured after survival periods of 18 h or 10 days, for fast and slow axonal transport studies, respectively. Fast transport studies showed an enhanced amount of protein arriving at the optic nerve terminals (superior colliculus) of the SFV-infected mice prior to the onset of demyelination. In contrast, the slow transport studies showed an enhanced amount of protein at the superior colliculus of the SFV-infected mice during the demyelination period. There was no concomitant increase in labelled protein in the retina at any time after the SFV infection. It is proposed that alteration in the transport of the protein constituents other than major myelin specific components may cause disruption of myelin maintenance in SFV infection.

Subcellular pathology of human neurodegenerative disorders: Alzheimer-type dementia and Huntington's disease

Activities of enzyme markers of subcellular organelles have been measured in brain tissue from subjects with Alzheimer-type dementia (ATD) and Huntington's disease (HD). Significant increases in the activity of the lysosomal enzyme beta-glucuronidase were observed in both ATD temporal cortex and HD putamen. It is suggested that beta-glucuronidase activity may be a useful biochemical indicator of cellular damage in the CNS. A significant reduction in neutral alpha-glucosidase activity was observed in ATD temporal cortex and HD putamen. This change may reflect an alteration in glycoconjugate processing and may relate to the susceptibility of neurones to the degenerative processes of ATD and HD.

Brain glycosidases in Creutzfeldt-Jakob disease

Several glycosidase activities were measured in frontal gray matter of 4 brains from subjects affected by Creutzfeldt-Jakob disease. The changes of N-acetyl-beta-glucosaminidase, N-acetyl-beta-galactosaminidase, beta-glucosidase, alpha-fucosidase and alpha-mannosidase were not statistically significant but significant increases of beta-glucuronidase and beta-galactosidase activities were found. These results are in accordance with several reports on brain glycosidases in scrapie and Semliki Forest virus-infected brain and could explain some changes in brain glycoconjugate content previously observed in human and experimental Creutzfeldt-Jakob disease.

Neurochemical changes in Creutzfeldt-Jakob disease

A biochemical study of a case affected by Creutzfeldt-Jakob disease is reported. Changes were found in soluble and insoluble proteins, glycoproteins and mucopolysaccharides and in total lipids, glycolipids, phospholipids and gangliosides. Also CNPase, choline acetyltransferase, 5'-nucleotidase and several glycosidases have an altered activity. All these data give a complete neurochemical pattern of the changes underlying the morphological and functional alterations in this disease.

The fragility of cerebral lysosomes in multiple sclerosis

The possibility that cerebral lysosomes in the white matter from patients with multiple sclerosis (MS) are more fragile than in normal controls was investigated in tissue obtained at necropsy. In the MS cases no differences were found in results from samples obtained from histologically distinct areas of white matter, i.e. plaque, periplaque and macroscopically normal white matter. However, in comparison to white matter from a group of controls, certain differences were found. Firstly, the cerebral lysosomes in MS white matter appeared to be more fragile than those in the control cases. Secondly, the remaining intact lysosomes in MS cases showed different characteristics from those obtained in control cases. These results, in the light of earlier experiments in rat brain, were interpreted as further evidence of a greater fragility in the cerebral lysosomes from MS cases. The implications of these results in relation to current thinking on the aetiology of MS are discussed.

Lethal encephalitis in 14-day-old mice given avirulent Semliki forest virus

Avirulent Semliki Forest Virus when inoculated intracerebrally and intraperitoneally into 14-day-old Swiss A2G mice induced a lethal encephalitis. There was destruction of neurones, especially pyramidal cells of the hippocampus, despite a rising serum antibody titer.

Ganglioside alterations in guinea pig brains at end stages of experimental Creutzfeldt-Jakob disease

Gangliosides were isolated from guinea pig brains at the end stages of experimental Creutzfeldt-Jakob disease. Quantitative analyses revealed marked decreases of ganglioside levels in pathologically devastated tissues such as cerebral cortex (-21%), basal ganglia and thalamus (-18%), and brain stem (-23%). The cerebellum revealed only minor pathological abnormalities and its ganglioside level remained unchanged. Thin-layer chromatography of the Creutzfeldt-Jakob brain gangliosides showed aberrant ganglioside patterns in all regions studied, including the cerebellum. With some exceptions, a trend in ganglioside pattern changes was detected which consisted of proliferation of GM3, GD3, GD2 and loss of GM1, GD1a, GD1b and GT1b.

Brain lysosomal glycosidase activity in immunosuppressed mice infected with avirulent Semliki forest virus

Mice infected with an avirulent strain of Semliki forest virus show an increase in the activity of some of the brain lysosomal glycosidases. The increase in activity of these enzymes has been correlated with the histological, virological, and serological changes that result from the infection in the presence and absence of immunosuppression. Semliki forest virus alone caused the development of a mild encephalitis with perivascular infiltration, microgliosis, astrocyte hypertrophy, and a focal spongiform encephalopathy, together with an increased activity of brain N-acetyl-beta-D-glucosaminidase and beta-glucuronidase. Antilymphocyte serum given after infection marginally affected the course of the disease. Cyclophosphamide markedly delayed the development of the spongy changes in the increase in enzyme activities, but not the perivascular infiltration. It is suggested that the increased activity of the lysosomal glycosidases studied may be linked both to the development of a successful immune response and to the focal spongiform changes produced by the infection.