Activation of the inducible form of nitric oxide synthase in the brains of patients with multiple sclerosis

Control of nitric oxide production by transforming growth factor-beta1: mechanistic insights and potential relevance to human disease

Studies on the multifunctional nature of the transforming growth factor-beta (TGF-beta) family of cytokines and the enzyme nitric oxide synthase (NOS) have suggested that they mediate a wide variety of vital processes in evolutionarily divergent organisms. Numerous mechanistic studies have investigated the consequences of the regulation of NO by the TGF-beta's for mammalian physiology. Studies with several cell types in vitro indicate that TGF-beta1 negatively controls the expression of the enzyme responsible for the prolonged production of large amounts NO, the inducible nitric oxide synthase (NOS2; iNOS), by reducing the expression and activity of NOS2 at multiple levels. Recent studies with TGF-beta1 null mice or mice which overexpress TGF-beta1 suggest that this cytokine may be a primary negative regulator of NOS2 in vivo. The interaction between NOS2 and TGF-beta1 may represent a central homeostatic mechanism in mammalian physiology with implications for a variety of human diseases.

Raised serum nitrate and nitrite levels in patients with multiple sclerosis

Nitric oxide and its highly reactive derivative peroxynitrite have been implicated as non-specific inflammatory mediators of neuronal and oligodendrocyte damage and death in multiple sclerosis. In a cross-sectional study we found levels of the nitric oxide metabolites nitrate and nitrite to be raised in the serum of patients with demyelinating disease (65.6 microM (SD 32.9)), acquired immune deficiency syndrome (57.9 microM (SD 34.9)) and inflammatory neurological disease (57.5 microM (SD 31.3)), compared with normal control subjects (32.8 microM (SD 12.2)) and patients with non-inflammatory neurological disease (41.1 microM (SD 12.3), p < 0.001). Nitric oxide metabolites were raised in all clinical subtypes of multiple sclerosis, as well as in clinically isolated syndromes compatible with demyelination, and were not related to progressive disease or disability. This study provides further evidence for a role of nitric oxide in the immunopathogenesis of inflammatory diseases of the central nervous system, including multiple sclerosis.

Pathogenesis of immune-mediated demyelination in the CNS

Collective evidence from studies in the animal model experimental autoimmune encephalomyelitis and pathological and immunological studies on MS patients suggest that this most common inflammatory demyelinating disorder of the central nervous system results from primarily T-lymphocyte driven aberrant immune responses to a number of myelin and possibly non-myelin antigens. These include MBP, PLP, MOG, MAG, CNP and S 100. Autoreactive T-cells reactive with these antigens circulate in blood and upon activation can travel across the blood-brain-barrier to initiate a local immunoflammatory response provided they encounter a microglial cell that displays antigenic epitopes in the context of MHC class II gene products and accessory molecules. Demyelination probably results from antibody-induced complement activation. Repeated inflammatory episodes eventually exhaust the reparative capacities of oligodendrocytes and damage axons. As the disease evolves, an initialy focussed immune response may diversify due to a process termed epitope spreading. The initial event of T lymphocyte activation remains elusive, but molecular mimicry, cross-recognition of structures shared between microbes and myelin, appears to be crucial.