Multiple sclerosis: some possible therapeutic opportunities

Quantitative Evaluation of Leukocyte Infiltration into the Spinal Cord in a Model of Experimental Autoimmune Encephalomyelitis: Statistical-Analytical Techniques for Use in Evaluating Drugs

Experimental autoimmune encephalomyelitis (EAE) is considered a useful animal model for preclinical development of drugs to treat human multiple sclerosis. The relationship between clinical disease signs and leukocyte infiltration into the lower spinal cord was studied in EAE in order to assess analytical and statistical methods for evaluating drug candidates. As expected, the degree of clinical disease was correlated with the amount of leukocyte infiltration into the lower spinal cord. Additionally, we were able to distinguish patterns of clinical signs and leukocyte infiltration for classes of recurring-remitting and progressive forms of the disease. The distributions of leukocyte infiltration sites correspond to negative binomial distributions, and the parameters calculated from the respective distributions differ significantly among disease classes. We determined the sensitivity of histological measures of the leukocyte infiltration and calculated the magnitude of differences required in order to observe statistically significant changes in leukocyte infiltration. Using immunohistochemistry to assess cell surface markers of leukocytes in the lower spinal cord, we measured the infiltration of CD4+ and CD8+ lymphocytes and cells of the macrophage/microglial lineage stained with the monoclonal antibody, F4/80. Treatment with an anti-4 integrin monoclonal antibody, PS/2, served as an indicator of how we may expect to measure the effects of new pharmaceutical agents tested using our particular model of EAE. PS/2 treatment affected clinical signs of disease only when administered very early in the time course of the disease, despite a marked statistically significant decline in CD4+ cells regardless of when the PS/2 was administered. The analytical and statistical techniques applied here may be used to design efficient and sensitive assays for the evaluation of new drugs that may prove useful in the treatment of multiple sclerosis.

Influence of histocompatibility genes on disease susceptibility and treatment response in patients with relapsing-remitting multiple sclerosis treated with interferon β-1a

Multiple sclerosis (MS) is the most common, non-traumatic cause of neurological disability in young adults. The aim of this study was to investigate the influence of HLA class II alleles DRB1* and DQB1* on susceptibility to relapsing-remitting (RR) MS and response to interferon (IFN) β-1a treatment. A prospective observational study was conducted. Seventeen patients with clinically definite RRMS, attending a tertiary referral center for multiple sclerosis in Israel and receiving treatment with subcutaneous IFN β-1a, 22 mcg three times weekly were recruited between December 1998 and February 2000 and observed for 12 months. HLA genotyping was performed and clinical characteristics (relapse rate and disability progression) assessed at baseline and after 12 months. HLA data for a healthy control group were also used for comparison. HLA and the success of treatment with IFN β-1a in this group of RRMS patients were assessed. The frequency of DRB1*03 was six times higher in patients treated with IFN β-1a than in the healthy control group (n=100): 29% (5/17) versus 5% (5/100), respectively. Additionally, DQB1*03 and DQB1*02 were present in 82% (14/17) and 41% (7/17) of RRMS patients, but in only 33% (33/100) and 18% (18/100) of control patients, respectively. A better response to IFN β-1a treatment was seen in patients carrying these alleles than in patients without these alleles. Our results indicated that DRB1*03, DQB1*03 and DQB1*02 alleles may contribute to MS susceptibility and IFN β-1a responsiveness, and warrant further verification in a larger population.

Progesterone synthesis and myelin formation in peripheral nerves

Progesterone is synthesized in the nervous system by neurons and glial cells. Because of their simple structure, plasticity and capacity of regeneration, peripheral nerves are particularly well suited for studying the biosynthesis, mechanisms of action and effects of the hormone. Schwann cells, the myelinating glial cells in the peripheral nervous system, synthesize progesterone in response to a diffusible neuronal signal. In peripheral nerves, the local synthesis of progesterone plays an important role in the formation of myelin sheaths. This has been shown in vivo, after cryolesion of the mouse sciatic nerve, and in vitro, in cocultures of Schwann cells and sensory neurons. Schwann cells also express an intracellular receptor for progesterone, which thus functions as an autocrine signalling molecule. Progesterone may promote myelination by activating the expression of genes coding for transcription factors (Krox-20) and/or for myelin proteins (P0, PMP22). Recently, it has been proposed that progesterone may indirectly regulate myelin formation by influencing gene expression in neurons. Steroid hormones also influence the proliferation of Schwann cells: estradiol becomes a potent mitogen for Schwann cells when levels of cAMP are elevated and glucocorticosteroids have been shown to increase the mitogenic effects of peptide growth factors.

High-dose mouse immunoglobulin G administration suppresses Theiler's murine encephalomyelitis virus-induced demyelinating disease

We studied the effect of high-dose mouse IgG on TMEV-induced demyelinating disease (TMEV-IDD). We injected TMEV intracerebrally into susceptible SJL/J mice and induced TMEV-IDD. Mouse IgG were injected intraperitonealy, and clinical course and various immunological indicators were studied. The results show that TMEV-IDD was significantly suppressed both clinically and histologically (P<0.01) when IgG were administered in the effector phase. The delayed type hypersensitivity and T cell proliferative response specific for TMEV were decreased by this treatment. In an ELISPOT assay, the number of TNF-alpha producing lymphocytes in the spinal cords was low in high-dose IgG treated mice compared with PBS treated control mice. These data suggest that administration of IgG suppresses TMEV-IDD and may be promising treatment to prevent exacerbation of human multiple sclerosis.

Differential mechanisms of neutrophil and monocyte adhesion on neuroblastoma cells: CD18 and VLA-4 integrins mediate adhesion to SK-N-SH, but not to SK-N-MC cell line

We examined the adhesion of monocytes and polymorphonuclear leukocytes (PMNLs) to the neuroblastoma (NB) cell lines SK-N-SH and SK-N-MC, which have some distinct differentiation characteristics. Monocytes adhered to SK-N-SH and SK-N-MC to the same extent (20 +/- 1.4% and 24 +/- 0.8% of monocytes added). Monocyte adhesion to SK-N-SH but not SK-N-MC was partially inhibited by treating monocytes with a mAb to the CD18 (beta2) integrin chain. The adhesion was further inhibited when monocytes were treated with a combination of mAb to CD18 and VLA-4. Treatment of both NB cell lines with interleukin-1alpha (0.5 ng/ml), tumor necrosis factor alpha (100 U/ml), interferon gamma (200 U/ml), or their combinations increased monocyte adhesion to SK-N-SH and SK-N-MC. With each condition, monocyte adhesion to SK-N-SH was partially blocked by mAb to CD18. The inhibition of adhesion to IL-1alpha- or TNFalpha-treated SK-N-SH cells was greater when the monocytes were treated with mAb to both CD18 and VLA-4. In contrast, monocyte adhesion to IL-1alpha or IFNgamma treated SK-N-MC was only slightly inhibited with a combination of mAb to CD18 + VLA-4 and there was no inhibition at all to TNFalpha-treated SK-N-MC. Spontaneous PMNL adhesion to SK-N-SH was almost negligible but increased by treating the cell line with IL-1alpha, TNFalpha, IFNgamma or their combinations. A mAb to CD18 blocked this increase in each case. The pattern of adhesion of PMNLs to SK-N-MC was totally different. PMNL adhesion to unstimulated SK-N-MC was very high (24 +/- 1.3%), was not inhibited by mAb to CD18, and did not increase by stimulating the cell line with IL-1alpha, TNFalpha, IFNgamma or their combinations. Overall, these results suggest two distinct patterns of monocyte and PMNL interaction with neural cells, such as the SK-N-SH and MC cell lines. While monocyte and PMNL adhesion to SK-N-SH is mainly via CD18/VLA-4 or the CD18 mechanisms, respectively, leukocyte adhesion to SK-N-MC is CD18- and VLA-4-independent. Thus, leukocyte-neural cell interactions share some mechanisms common also to leukocyte-endothelium interaction, but there are also unique mechanisms which may be neural cell and differentiation specific.

Glucocorticosteroids stimulate the activity of the promoters of peripheral myelin protein-22 and protein zero genes in Schwann cells

To better understand the mechanism by which glucocorticosteroids (GLUC) could enhance myelination in the PNS, cultured rat Schwann cells were transiently transfected with reporter constructs in which luciferase expression was controlled by the promoter region of either the peripheral myelin protein-22 (PMP22) or the protein zero (P(0)) genes. GLUC stimulated the activity of the P(0) promoter and the PMP22 promoters 1 and 2. The effect of GLUC was specific as estradiol and testosterone did not activate the promoters. The antagonist RU486 did not abolish the effect of GLUC, but instead stimulated promoter activities by itself. In the mammary carcinoma cell line 34i, which expresses GLUC receptors, GLUC did not stimulate the P(0) and PMP22 promoters while the promoter of the mouse mammary tumor virus was strongly activated. Thus, the activation by GLUC of the promoter activities of two peripheral myelin protein genes is Schwann cell-specific.

Pharmacology of the biological response modifier bropirimine (PNU-54461) on experimental autoimmune encephalomyelitis (EAE) in mice

In murine severe experimental autoimmune encephalomyelitis (EAE), an animal model for the human disease multiple sclerosis (MS), we tested the efficacy of a 5-halo-6-phenyl pyrimidinone compound, bropirimine (PNU-54461). We observed that the compound is active in suppressing EAE when administered orally, a significant pharmacological advantage compared to some current therapies for the treatment of MS. Furthermore, bropirimine was most efficacious when dosing was begun 5-10 days after injection of myelin basic protein, the protein isolated from the central nervous system and used for inducing EAE in our model. This is a period of time following the initial immunological events leading to the disease, when large-scale leukocyte infiltration into the central nervous system begins. Following oral dosing, bropirimine peaked in the blood within 3 h and was cleared to undetectable concentrations within 16-18 h. Despite the pharmacokinetics in the blood, bropirimine was fully efficacious when dosed orally every two or three days. Surprisingly, bropirimine treatment did not result in a statistically significant decrease in leukocyte infiltration into the lower spinal cord, unless the compound was dosed daily at a high concentration. We also observed the concentration and time course of alpha-interferon in blood following oral dosing of bropirimine. The kinetics of interferon in the blood are similar to, but clearly distinguishable from, the pharmacokinetics of bropirimine in the blood. It is not clear whether or not the induction of interferon plays a key role in the efficacy of bropirimine. Nevertheless, the results using bropirimine in EAE suggest that the compound may be useful for the treatment of multiple sclerosis.

Lipopolysaccharide differentially regulates microglial trk receptor and neurotrophin expression

Activated brain microglia play a pivotal role in inflammatory and degenerative disorders, mediating immune function and producing toxic and trophic agents. We previously reported that microglia express neurotrophins and that neurotrophin-3 (NT-3) increases microglial proliferation and phagocytosis, processes associated with cellular activation. However, mechanisms regulating responsiveness to NT-3 and expression of NT-3 in activated microglia remain undefined. To investigate mechanisms governing microglial responsiveness to neurotrophins, we determined whether microglia express trk C, the high-affinity receptor for NT-3, and whether the inflammatory agent lipopolysaccharide (LPS) regulates receptor expression. Trk C mRNA was expressed by unstimulated microglia, and both trk C mRNA and protein were dramatically increased by LPS. In contrast, expression of trk A, the high-affinity receptor for nerve growth factor (NGF), was down-regulated by LPS. Consequently, the same stimulus differentially influences responsiveness of microglia to distinct trophins. In addition, LPS induced microglial NT-3 expression, suggesting that increases in both the ligand and receptor modulate NT-3 effects on microglia. Regulation was specific, since brain-derived neurotrophic factor (BDNF) and NT-4/5 expression were unaltered by LPS. In sum, our findings raise the possibility that microglial NT-3 regulates their response to inflammation through autocrine mechanisms: LPS modulates both trk C and NT-3 which, in turn, regulate microglial function.

Mast cell specific proteases in rat brain: changes in rats with experimental allergic encephalomyelitis

Mast cell populations were identified within brain parenchyma by their specific proteases, using antibodies for immunohistochemistry and ELISAs, and riboprobes were developed for in situ hybridisation. Connective tissue mast cells expressing rat mast cell protease I (RMCPI) mRNA and immunoreactivity were observed in thalamus and showed no degranulation at 3, 8 and 13 days after induction of experimental allergic encephalomyelitis (EAE). Mucosal-like mast cells were clearly demonstrated in control rats by measuring RMCPII and by visualising cells expressing RMCPII mRNA and immunoreactivity. At day 13, but not 3 and 8 post immunisation, the number of RMCPII-expressing cells markedly increased in the EAE-induced group, mainly within brainstem and spinal cord close to inflammed blood vessels. The markers of histaminergic neurons were marginally affected 13 days after immunisation and the increase of [3H] histamine synthesis elicited by the H3-receptor antagonist, thioperamide, was not modified in any region of the brain. It is concluded that the cerebral RMCPII-expressing mast cells could play a role during EAE.