The role of proteolytic enzymes in demyelination in experimental allergic encephalomyelitis

Proteolysis of multiple myelin basic protein isoforms after neurotrauma: characterization by mass spectrometry

Neurotrauma, as in the case of traumatic brain injury, promotes protease over-activation characterized by the select fragmentation of brain proteins. The resulting polypeptides are indicators of biochemical processes, which can be used to study post-injury dynamics and may also be developed into biomarkers. To this end, we devised a novel mass spectrometry approach to characterize post-injury calpain proteolytic processing of myelin basic protein (MBP), a biomarker of brain injury that denotes white matter damage and recovery. Our approach exceeds conventional immunological assays in its deconvolution of multiple protein isoforms, its absolute quantification of proteolytic fragments and its polypeptide selectivity. We quantified and characterized post-injury proteolytic processing of all MBP isoforms identified in adult rat cortex. Further, the translation of calpain-cleaved MBP into CSF was verified following brain injury. We ascertained that the exon-6 sequence of MBP resulted in a characteristic shift in gel migration for intact and fragmented protein alike. We also found evidence for a second post-TBI cleavage event within exon-2 and for the dimerization of the post-TBI 4.3 kDa fragment. Ultimately, the novel methodology described here can be used to study MBP dynamics and other similar proteolytic events of relevance to brain injury and other CNS processes.

Increased calpain correlates with Th1 cytokine profile in PBMCs from MS patients

Multiple sclerosis (MS) is a devastating autoimmune demyelinating disease of the central nervous system (CNS). This study investigated whether expression and activity of the calcium-activated protease calpain correlated with Th1/Th2 dysregulation in MS patients during states of relapse and remission. Calpain expression and activity were significantly increased in peripheral blood mononuclear cells (PBMCs) from MS patients, compared to controls, with the highest expression and activity noted during relapse. Th1 cytokines were highest and Th2 cytokines were lowest in MS patients during relapse. Treatment with calpain inhibitor, calpeptin, decreased Th1 cytokines in PBMCs from MS patients. Calpain inhibitor also reduced degradation of myelin basic protein (MBP) by inhibiting the calpain secreted from MBP-specific T cells. Taken together, these results suggested calpain involvement in Th1/Th2 dysregulation in MS patients.

Mechanism of myelin breakdown in experimental demyelination: a putative role for calpain

Although calpain has been extensively studied, its physiological function is poorly understood. In contrast, its role in the pathophysiology of various diseases has been implicated, including that of experimental allergic encephalomyelitis (EAE), an animal model of the demyelinating disease multiple sclerosis (MS). In EAE, calpain degrades myelin proteins, including myelin basic protein (MBP), suggesting a role for calpain in the breakdown of myelin in this disease. Subsequent studies revealed increased calpain activity and expression in the glial and inflammatory cells concomitant with loss of axon and myelin proteins. This suggested a crucial role for calpain in demyelinating diseases.

A putative mechanism of demyelination in multiple sclerosis by a proteolytic enzyme, calpain

In autoimmune demyelinating diseases such as multiple sclerosis (MS), the degradation of myelin proteins results in destabilization of the myelin sheath. Thus, proteases have been implicated in myelin protein degradation, and recent studies have demonstrated increased expression and activity of a calcium-activated neutral proteinase (calpain) in experimental allergic encephalomyelitis, the corresponding animal model of MS. In the present study, calpain activity and expression (at translational and transcriptional levels) were evaluated in white matter from human patients with MS and Parkinson's and Alzheimer's diseases and compared with that of white matter from normal controls. Western blot analysis revealed that levels of the active form of calpain and calpain-specific degradation products (fodrin) were increased by 90.1% and 52.7%, respectively, in MS plaques compared with normal white matter. Calpain translational expression was up-regulated by 462.5% in MS plaques compared with controls, although levels of the specific endogenous inhibitor, calpastatin, were not altered significantly. At the transcriptional level, no significant changes in calpain or calpastatin expression were detected by reverse transcription-PCR. Using double immunofluorescent labeling, increased calpain expression was observed in reactive astrocytes, activated T cells, and activated mononuclear phagocytes in and adjacent to demyelinating lesions. Calpain activity and translational expression were not increased significantly in white matter from patients with Parkinson's or Alzheimer's diseases compared with that of normal controls. Because calpain degrades all major myelin proteins, the increased activity and expression of this proteinase may play a critical role in myelinolysis in autoimmune demyelinating diseases such as MS.

Macrophage and microglial responses to cytokines in vitro: phagocytic activity, proteolytic enzyme release, and free radical production

Certain cytokines are believed to play a key role in the development of autoimmune demyelinating diseases. Little is known, however, about the effects of these cytokines in the regulation of the key event in myelin destruction, the phagocytosis of myelin by phagocytic cells. We investigated the effects of certain cytokines and growth factors on cultured peritoneal macrophages and microglia in respect to their various functions, phagocytosis, secreted proteolytic activity, and oxidative activity. Interferon-gamma (IFN-gamma), tumor necrosis factor-alpha (TNF-alpha), and lipopolysaccharide (LPS), all proinflammatory factors, actually decreased (IFN-gamma and LPS), or had no effect (TNF-alpha) on myelin phagocytosis by macrophages, but substantially increased phagocytic activity by microglia. Surprisingly, interleukins 4 and 10 (IL-4 and IL-10), considered to be downregulating cytokines, increased phagocytic activity by macrophages, while with microglia, IL-4 had no effect, but IL-10 almost doubled myelin phagocytosis. Transforming growth factor-beta (TGF-beta) had no significant effect on either cell. These cytokines did not affect proteolytic secretion in microglia, while IFN-gamma and LPS induced a doubling of the secreted proteases. This proteolytic activity was almost completely suppressed by calpain inhibitors, although some gelatinase appeared to be present. Microglia exerted much more oxidative activity on the membranes than macrophages, and granulocyte-macrophage colony stimulating factor (GM-CSF) and interleukin 1beta (IL-1beta) significantly increased microglial oxidative activity. The pattern of responses of macrophages and microglia to the cytokine types indicate that in cytokine-driven autoimmune demyelinating disease, microglia may be the more aggressive cell in causing tissue injury by phagocytosis and oxidative injury, while infiltrating macrophages may produce most of the proteolytic activity thought to contribute to myelin destruction.

A new mechanism of methylprednisolone and other corticosteroids action demonstrated in vitro: inhibition of a proteinase (calpain) prevents myelin and cytoskeletal protein degradation

The affect of methylprednisolone (MP), an anti-inflammatory drug upon purified calpain and the Ca2+-mediated degradation of endogenous proteins of spinal cord homogenate in vitro has been examined. Activity of calpain purified from rabbit muscle was greatly inhibited in a dose-dependent fashion by MP. A 50% inhibition was obtained with 3.2 mM MP concentration and the activity was inhibited further (80%) at 8.1 mM. More potent inhibition of the purified enzyme (70-80%) was produced by dexamethasone (3.9 mM) and prednisolone (4.1 mM). Calpain-mediated degradation of myelin basic protein (MBP) was also inhibited by MP as was cathepsin B-mediated MBP breakdown. The effect of MP and other steroids upon calcium-mediated degradation of spinal cord homogenate was also evaluated. SDS-PAGE analysis revealed significant inhibition of neurofilament protein breakdown by MP and other corticosteroids. This inhibitory effect was much less than that exerted by the calpain inhibitors calpeptin and/or E64-d. These results indicate that MP acts as a proteinase (calpain) inhibitor and define a new mechanism for its actions.

Calpain secreted by activated human lymphoid cells degrades myelin

Calpain secreted by lymphoid (MOLT-3, M.R.) or monocytic (U-937, THP-1) cell lines activated with PMA and A23187 degraded myelin antigens. The degradative effect of enzymes released in the extracellular medium was tested on purified myelin basic protein and rat central nervous system myelin in vitro. The extent of protein degradation was determined by SDS-PAGE and densitometric analysis. Various proteinase inhibitors were used to determine to what extent protein degradation was mediated by calpain and/or other enzymes. Lysosomal and serine proteinase inhibitors inhibited 20-40% of the myelin-degradative activity found in the incubation media of cell lines, whereas the calcium chelator (EGTA), the calpain-specific inhibitor (calpastatin), and a monoclonal antibody to m calpain blocked myelin degradation by 60-80%. Since breakdown products of MBP generated by calpain may include fragments with antigenic epitopes, this enzyme may play an important role in the initiation of immune-mediated demyelination.

Electrolyte-induced demyelination in rats. 2. Ultrastructural evolution

This study presents the electron microscopic evolution of lesions in electrolyte-induced demyelination (EID) in rats, a lesion which bears striking histological and clinical similarity to central pontine myelinolysis. The earliest change was observed during the hyponatremic phase and consisted of minimal intracellular edema present throughout the brain. Following the injection of hypertonic saline, additional changes were observed which were restricted to sites previously reported to be frequently involved in EID. Early dilatation of the inner tongue of oligodendrocyte cytoplasm in myelinated nerve fibers was observed at 3 h post hypertonic saline injection (PHS). This was followed, at 48 h PHS, by the appearance of degenerative changes consistent with dying oligodendrocytes. Well-delineated, vacuolar and spongy lesions, seen by light microscopy, were present by 48 h PHS at the same sites as above. Electron microscopically, this appearance was found to be due to striking intramyelinic edema. By 96 h PHS, macrophages containing myelin and other cellular debris were frequently present at these sites. Concomitantly, myelin sheaths underwent vesicular disruption and disintegration. This sequence of events suggests a lesion of the oligodendrocyte-myelin complex, secondary to initial blood-brain barrier damage and edema.

Bovine brain cathepsin D: inhibition by pepstatin and binding to concanavalin A

1. Cathepsin D from bovine brain has been purified 1100-fold in 46% recovery. Three isozymes are present with pI (+/- 0.05) = 6.10, 6.30 and 6.40. 2. The isozymes are single polypeptide chains with apparent Mr = 42,000 and are similar with respect to substrate binding and cleavage; the pH-optimum is 3.5 with virtually no activity at neutral pH. 3. Pepstatin inhibits the enzyme and kinetic data are consistent with a "tight binding" mechanism. 4. The dissociation constant for the concanavalin A-enzyme complex is Kd = 19 nM at pH 5.0. 5. Under conditions where 90% of the enzyme is bound to soluble concanavalin A, full enzymatic activity is observed.

Binding of cathepsin D to the mannose receptor on rat peritoneal macrophages

Adherent cultures of rat peritoneal macrophages secrete lysozyme and the lysosomal marker enzymes beta-glucuronidase, beta-N-acetylglucosaminidase and acid phosphatase; the levels of secreted lysosomal cathepsin D, however, were found to be insignificant. Incubation of the cells at 4 degrees C for 15 min with yeast mannan or with 50 mM mannose, methyl alpha-glucopyranoside, or N-acetylglucosamine caused the concentration of cathepsin D in the culture medium to increase 30-40-fold; mannose-6-phosphate had no effect. 125I-labeled cathepsin D was prepared and the binding constant to the macrophage cell surface was determined to be KD = 27 nM. The data suggest that cathepsin D binds to the mannose receptor of macrophages and that binding to this receptor is not in equilibrium with the bulk medium.

Schwann cell plasminogen activator is regulated by neurons

The synthesis and release of plasminogen activators (PAs) in co-cultures of embryonic rat dorsal root ganglion nerve cells (NCs) and Schwann cells (SCs) were examined by metabolic labeling, immunoprecipitation, immunodepletion, SDS-PAGE, zymography, and a two-step esterolytic assay. Metabolic labeling of SC cultures followed by immunoprecipitation of the conditioned medium (CM) demonstrated that cultured SCs synthesized and released tissue type PA (tPA). Failure of amiloride to inhibit PA activity in SCCM indicated that urokinase PA (uPA) was unlikely to contribute significantly to PA activity in SCCM. Experimental manipulation of the NCs and SCs suggested that NCs regulated SC derived PA. Total PA activity increased in SCCM 10-14-fold by 6 days after removal of NCs. Multiple molecular weight forms of PAs were detected by SDS-PAGE followed by zymography. A PA approximately 95 kDa was absent in co-cultures of SCs + NCs but prominent by 4 days postdenervation; PA approximately 50-70 kDa increased through 8 days postdenervation and PA approximately 25 kDa, present in SC + NC cultures, was absent 8 days after removal of NCs. Upon reintroduction of NCs to denervated cultures (SCs), the pattern of PAs detected in culture medium was transitional between innervated and denervated cultures. Immunodepletion experiments using conditioned medium from denervated SC cultures indicated that various molecular weight forms of PA detected in SCCM by zymography were immunologically related to tPA. These studies demonstrate that SCs synthesized and released tPA in a tissue culture model of peripheral nerve and that one mechanism for regulation of PA released by SCs was by association with NCs. This regulation occurred in cultures of both myelinating and nonmyelinating Schwann cells and thus was not dependent on the state of myelination.

The acid instability of myelin. A model for myelin degeneration in multiple sclerosis

Electron micrographs of samples of bovine spinal cord which have been briefly acidified (10 mM lactate buffer, pH 5.5, 25 degrees C, 15 minutes) prior to being fixed for EM examination, reveal extensive vesicular disruption of the myelin lamellae; micrographs of control samples incubated under identical conditions at pH 7.0, show normal compact lamellae. Culture of thioglycollate-elicited rat peritoneal macrophages in the presence of derivatized, non-ingestible, bovine CNS material results in the secretion of lactic acid and the acidification of the culture medium to levels which are comparable to those which cause lamellae disruption in the tissue slices. Because of the sensitivity of the myelin lamellae to an acidic microenvironment, it is suggested that a local hyperlactemia, with the resulting decrease in interstitial pH, may be a major pathological process in cell-mediated inflammatory demyelination. Antihyperlactemics may therefore provide a new therapeutic approach to minimizing myelin degeneration in multiple sclerosis and in other CNS disorders characterized by inflammatory demyelination.

Suppressive effect of camostat mesilate (FOY 305) on acute experimental allergic encephalomyelitis (EAE)

Camostat mesilate (FOY305), a synthetic serine protease inhibitor and has been developed as a drug for pancreatitis, is effective in suppressing acute experimental allergic encephalomyelitis in Lewis rats. Loss of weight, clinical score and yield of myelin protein from brain stem were improved by daily injection of FOY305 compared with saline from day 6 after inoculation with homogenate of guinea pig spinal cord. A significant decrease of yield of myelin has been shown here for the first time in acute EAE in Lewis rat. This is in accord with myelin breakdown demonstrated morphologically. Our study also demonstrates a significant improvement of yield of myelin protein by FOY305. Our results suggest the possibility of a clinical application of this protease inhibitor for human demyelinating diseases such as multiple sclerosis.

Lysosomal enzymes in experimental allergic encephalomyelitis: time course and evidence of the source

The lysosomal enzymes acid proteinase and beta-glucuronidase, were assayed in spinal cords of rats during the course of experimental allergic encephalomyelitis (EAE). Histological and histochemical examination was carried out versus controls, in selected areas of the same cords biochemically assayed, to look at the distribution of the lysosomal enzyme acid phosphatase. The biochemical assay showed a significant increase of the enzyme activities during the disease and the increase was significantly correlated with the intensity of the disease. The distribution in the nervous tissue of the increase in acid phosphatase activity observed in animals with EAE, suggests that endogenous nervous cells may contribute to the lysosomal enzyme increase in EAE.

Characterization of astrocyte plasminogen activator

We have previously shown that astrocytes produce and secrete plasminogen activator (PA) and that this function is responsive to various modulating agents. When astrocyte conditioned medium (CM) is subjected to SDS-PAGE and PA activity localized by fibrin-agar gel overlay, the activity in the CM is found to comigrate with control t-PA. On affinity chromatography CM PA specifically binds to t-PA antibody. The latter also inhibits fibrinolytic activity of CM PA. When incubated with a fibrin clot, CM PA activity can be shown to bind to fibrin. These observations help identify the enzyme in astrocyte CM as t-PA. A possible role of astrocyte PA in myelin injury could provide an explanation for the previously observed correlation between fibrin deposition and demyelination as well as inhibition of demyelination by ancrod and heparin in experimental allergic encephalomyelitis.

Secretion of plasminogen activator by cerebral astrocytes and its modulation

Plasminogen activator (PA) has been related to the neuron migration during brain development. PA has also been shown to degrade myelin basic protein. We present data to show that neonatal Balb/c astrocytes show PA activity on 125I-fibrin coated plates. Secreted and cell associated fibrinolytic activity is detected only in the presence of plasminogen. Modulants like concanavalin A and phorbol myristate acetate enhance PA production and this function involves a transcriptional event. Dexamethasone inhibits baseline as well as concanavalin A induced enhancement of PA activity. These results raise the possibility that astrocytes may have an active role in myelinoclastic disorders and CNS developmental defects.

Secretion of lactic acid by peritoneal macrophages during extracellular phagocytosis. The possible role of local hyperacidity in inflammatory demyelination

Culture of thioglycollate-elicited rat peritoneal macrophages in the presence of derivatized, non-ingestible, bovine CNS material results in a release of the lysosomal marker enzyme beta-glucuronidase that is both dose- and time-dependent. Concomitant with enzyme secretion, lactic acid is secreted in a manner that is also dose- and time-dependent. The secretion of lactic acid represents an increased dependence on anaerobic glycolysis by the aerobic phagocyte cultures and is paralleled by an increase in cytoplasmic lactate dehydrogenase. When unbuffered media are used, the secretion of lactic acid is accompanied by a drop in the pH of the culture medium. Culture of the cells in the presence of the pyruvate dehydrogenase stimulator, dichloroacetate, inhibits the formation of lactic acid and the resulting drop in pH. Suspensions of multilamellar myelin undergo turbidity changes and aggregation in acidic media. Initial rates of turbidity changes follow a titration curve with an apparent pKa of 6.0. Because of the sensitivity of the myelin lamellae to an acidic microenvironment, it is suggested that a local hyperlactemia, with the resulting decrease in interstitial pH, may be a major pathological process in cell-mediated inflammatory demyelination. Antihyperlactemics, such as dichloroacetate, may therefore provide a new therapeutic approach to minimizing myelin degeneration in multiple sclerosis and in other CNS disorders characterized by inflammatory demyelination.

Proteolytic enzymes in experimental spinal cord injury

Experimental spinal cord injury was produced in rats by dropping a 10 g weight from 30 cm upon dura-invested exposed spinal cord. Proteolytic activities at neutral (pH 7.6) and acid (pH 5.5 and 3.6) pH were determined in whole homogenate and the cytosolic fraction of the lesion (lumbar) and cervical control segments. The enzyme activity was monitored by SDS-PAGE analysis of the extent of substrate myelin basic protein (MBP) degradation. Activities (neutral and cathepsin B-like) in the sham-operated spinal cord were lower than those of cervical autologous control at 24 h after injury. The increase in neutral proteinase activity was progressive and greater in the lesion than the autologous control. A 61.5% +/- 3.5 loss of MBP was observed at 2 h following injury and increased at 24 h (78.2% +/- 3.4). The loss of MBP coincided with the appearance of several low molecular weight peptides. The cathepsin B-like and cathepsin D activities were also increased in the lesion but to a lesser extent than the neutral proteinase. The neutral proteinase and cathepsin B-like activity were inhibited by leupeptin and not by pepstatin while the converse obtained for cathepsin D activity. The release of neutral proteolytic activity which is nonlysosomal in origin suggests a novel hypothesis for the mechanism of traumatic axon-myelin injury.

Ultrastructural sequence of myelin breakdown during Wallerian degeneration in the rat optic nerve

Adult albino rats were subjected to unilateral surgical removal of the eyeball. After survival times of 7-140 days, the numerical response of the neuroglial cells, and the progressive disintegration of the myelin sheaths in the optic nerves, were studied qualitatively and quantitatively in electron-microscopic montages. The distribution density of microglia and astroglia in degenerating optic nerve increased to peaks after 35 and 56 days respectively, whereas, the oligodendroglia gradually decreased. During the early stage of degeneration, microglial cells appeared and invaded the sheath at the intraperiod line, peeling off the outer lamellae, which were then engulfed by phagocytosis. Within the microglia, myelin sheath fragments were surrounded by a membrane curled to form a myelin ring. In the intermediate stage of degeneration, the paired electron-dense lines of the ring, made up of myelin basic protein, decomposed and formed a homogeneous or heterogeneous osmiophilic layered structure, the myelin body, which, in the final stages, disintegrated and transformed into globoid lipid droplets and needle shaped cholesterol crystals.

Calcium-stimulated proteolysis in myelin: evidence for a Ca2+-activated neutral proteinase associated with purified myelin of rat CNS

Incubation of myelin purified from rat spinal cord with CaCl2 (1-5 mM) in 10-50 mM Tris-HCl buffer at pH 7.6 containing 2 mM dithiothreitol resulted in the loss of both the large and small myelin basic proteins (MBPs), whereas incubation of myelin with Triton X-100 (0.25-0.5%) and 5 mM EGTA in the absence of calcium produced preferential extensive loss of proteolipid protein (PLP) relative to MBP. Inclusion of CaCl2 but not EGTA in the medium containing Triton X-100 enhanced degradation of both PLP and MBPs. The Ca2+-activated neutral proteinase (CANP) activity is inhibited by EGTA (5 mM) and partially inhibited by leupeptin and/or E-64c. CANP is active at pH 5.5-9.0, with the optimum at 7-8. The threshold of Ca2+ activation is approximately 100 microM. The 150K neurofilament protein (NFP) was progressively degraded when incubated with purified myelin in the presence of Ca2+. These results indicate that purified myelin is associated with and/or contains a CANP whose substrates include MBP, PLP, and 150K NFP. The degradation of PLP (trypsin-resistant) in the presence of detergent suggests either release of enzyme from membrane and/or structural alteration in the protein molecule rendering it accessible to proteolysis. The myelin-associated CANP may be important not only in the turnover of myelin proteins but also in myelin breakdown in brain diseases.

Effects of trypsin and plasmin treatment of myelin on the myelin-associated glycoprotein and basic protein

Human and rat myelin preparations were incubated with varying concentrations of trypsin and plasmin to determine the effects of these proteolytic enzymes on myelin-associated glycoprotein (MAG), basic protein, and other myelin proteins and to compare the effects with those of the neutral protease that was reported to be endogenous in myelin. Basic protein was most susceptible to degradation by both trypsin and plasmin, whereas MAG was relatively resistant to their actions. Under the assay conditions used, the highest concentrations of trypsin and plasmin degraded greater than 80% of the basic protein but less than 30% of the MAG, and lower concentrations caused significant loss of basic protein without appreciably affecting MAG. Neither trypsin nor plasmin caused a specific cleavage of MAG to a derivative of MAG (dMAG) in a manner analogous to the endogenous neutral protease. Thus the endogenous protease appears unique in converting human MAG to dMAG much more rapidly than it degrades basic protein. MAG is slowly degraded along with other proteins when myelin is treated with trypsin or plasmin, but it is less susceptible to their action than is basic protein.

Elevated neutral protease activity in myelin from brains of patients with multiple sclerosis

Incubation of human myelin at neutral pH resulted in the proteolytic conversion of the myelin-associated glycoprotein to a lower molecular weight derivative (dMAG) and the degradation of basic protein. The formation of dMAG occurred much more rapidly than the degradation of basic protein. The formation of dMAG and the degradation of basic protein both occurred significantly more rapidly in myelin preparations purified from brains of patients with multiple sclerosis than in preparations from control brain. The results suggest that this neutral protease associated with myelin may function in the pathogenesis of demyelinating diseases such as multiple sclerosis.

Regional studies of myelin proteins in human brain and spinal cord

The myelin specific proteins, myelin basic protein (MBP) and myelin proteolipid protein (PLP) were quantitated by radioimmunoassay (RIA) and the activity of the enzyme 2',3'-cyclic 3' phosphohydrolase (CNP) measured, in 27 regions of normal brain and spinal cord. Varying regional concentrations for each protein and regional variations for protein ratios were noted, supporting the concept of a varying chemical composition for myelin throughout the central nervous system (CNS). Variation was also noted among myelin subfractions from a single region. Regions with special sensitivity to the multiple sclerosis process had relatively lower proportions of CNP in several, but not all cases.

Lysosomal enzymes in ocular tissues and diseases

Lysosomal enzymes are distributed widely in various ocular tissues. Among these tissues, the uvea and retina show the higher enzyme activities of acid phosphates, beta-blucuronidase, alpha-fucosidase, alpha-mannosidase, arylsulfatase, cathepsin D, cathepsin B and others. The particular role of lysosomal enzymes in the pathogenic processes of ocular diseases such as storage disease, uveitis, retinal degeneration, retinal detachment, corneal dystrophy and glaucoma is strongly suggested. The enzymes also have additional importance in ocular physiopathology.

Observations on the effects of protease inhibitors on the suppression of experimental allergic encephalomyelitis

Inhibitors of proteolytic enzymes were tested for their ability to suppress the clinical signs and CNS lesions produced by injection of purified myelin in complete Freund's adjuvant into Lewis rats. Pepstatin or a series of neutral protease inhibitors including aprotinin, soybean trypsin inhibitor, leupeptin, antipain, trans-aminomethyl cyclohexane carboxylic acid (AMCA), epsilon-amino caproic acid (EACA) nitrophenyl guanidino benzoate (NPGB), D- and L-polylysine, or a new commercial protease inhibitor, dipropionyl Rhein (DPR) were injected daily beginning on day 7 after immunization of rats with myelin. Aprotinin and soybean trypsin inhibitor exacerbated the symptoms and lesions of experimental allergic encephalomyelitis (EAE), leupeptin and antipain had no effect, and the plasminogen activators AMCA, EACA, NPGB, as well as poly-L- and poly-D-lysine and DPR suppressed various aspects of EAE. The measurement of acid protease as a biochemical method for quantitation of the degree of cellular infiltration into the CNS is proposed, and the results with the various treatments presented. AMCA and NPGB may exert their effects at the site of entrance of the lymphoid cells into the CNS.

Partial purification and characterization of neutral proteases in lymph nodes of rats with experimental allergic encephalomyelitis

Two kinds of neutral protease activities in lymph nodes from Lewis rats with acute experimental allergic encephalomyelits (EAE) have been separated and partially purified and characterized. A soluble enzyme preparation enriched by gel filtration and ion-exchange chromatography hydrolyzes myelin basic protein, polylysine, and other basic proteins with an optimum pH at 6.0-6.5. It is inhibited by p-chloromercuribenzoate, and thus appears to be a mixture of thiol proteases. Another fraction containing proteolytic enzyme activity is strongly bound to the insoluble lymph node residue, and it also hydrolyzes myelin basic protein and histone, but not polylysine. It has a pH optimum above 7.5, is inhibited by phenylmethylsulfonyl fluoride, thus resembling elastase, but does not hydrolyze elastin-Congo red. The insoluble enzyme preparation hydrolyzes basic protein to 4-5 peptides in a pattern on polyacrylamide gels resembling that of the hydrolysis of basis protein by whole lymphocytes; the soluble enzyme mixture produces small fragments not retained on gels. Lymphocytes are a major component of the cells infiltrating the nervous system in experimental allergic encephalomyelitis, and neutral proteases contained in these cells may contribute to the degradation of myelin, especially of the basic protein.

Degradation of basic protein and Wolfgram protein in central nervous system by soluble enzymes of human peripheral polymorphonuclear leucocytes

The present communication describes the ability of soluble enzymes (SE) of peripheral polymorphonuclear leucocytes of control and multiple sclerosis (MS) patients to degrade major myelin proteins of MS and control myelin. MS and control SE degraded in situ both Wolfgram protein (WP) and basic protein (BP) of isolated myelin. No differences were found between the action of control and MS patients SE on myelin. However, significantly less degradation of BP and WP in control myelin compared to that in MS myelin was found. Only 30% of SE samples (both control and MS) degraded significant amounts of proteolipid protein in myelin. It is postulated that SE associated demyelination in MS may be a factor contributing to the demyelinating process.

Mitigation of experimental allergic encephalomyelitis by cathepsin D inhibition

Intraperitoneal treatment with the enzyme inhibitor, pepstatin, of BSVS mice, guinea pigs and Lewis rats which were sensitized with guinea pig spinal cord and pertussis vaccine resulted in complete or partial suppression of paralysis dependent on the species studied and alterations of histological signs of experimental allergic encephalomyelitis (EAE). The effect was dose-dependent but had no relationship to the age of the experimental animal at the time of the experiment.

Neutral protease activity in lymphocytes of Lewis rats with acute experimental allergic encephalomyelitis

Lymphocytes from popliteal and inguinal lymph nodes of Lewis rats with acute EAE as a result of injection of lyophilized guinea pig myelin in Freund's complete adjuvant exerted strong proteolytic activity at neutral pH toward myelin basic protein. After injection of myelin the level of proteolytic activity remained about the same as that in lymphocytes from Freund's adjuvant-injected controls until about day 10 after injection, just before the onset of paralytic symptoms; then the proteolytic activity increased to approximately double its former level. Myelin basic protein was hydrolyzed by whole lymphocytes, but more activity was unmasked by homogenization. Similar results were also obtained using lymphocytes from thymus of EAE and control animals. Lymphocytes with high levels of proteolytic activity were not absorbed by glass wool, did not stain with neutral red, nor did they phagocytose antibody-coated sheep red blood cells. Thymus and lymph node lymphocytes cleaved myelin basic protein to three major peptides and a fourth minor peptide, while spleen lymphocytes hydrolyzed basic protein at only one point resulting in two peptides whose molecular weights added up to that of myelin basic protein. The protease activity was inhibited by 5 X 10(-3) M p-chloromercuribenzoate and by phenylmethyl sulfonyl fluoride, TPCK, and soybean trypsin inhibitor, therefore the enzymatic activity probably depends on a serine residue and a sulfhydryl group. The bulk of the enzymatic activity is mostly membrane bound with the highest specific activity and total activity contained in a lysosomal-mitochondrial fraction. In view of the infiltration of lymphocytes into the brain substance in acute EAE, it is suggested that these cells may contribute to the destruction of myelin which is usually attributed to the monocyte or macrophage.

Degradation of myelin basic protein by cerebrospinal fluid: preservation of antigenic determinants under physiological conditions

Cerebrospinal fluid contains several proteolytic enzymes that can degrade myelin basic protein (BP) under physiological conditions into peptide fragments of various sizes which still contain antigenic determinants capable of binding antibodies to BP. These enzymes are optimally active in either acid (pH 4) or nuetral (pH 7 to 8) conditions and can be characterized by the nature of the BP peptide fragments produced. Proteinases resembling cathepsin D, thrombin, plasmin (fibrinolysin), or kallikrein are present in variable amounts in CSF. No relationship to any particular disease has yet been established.

Chronic relapsing experimental allergic encephalomyelitis: morphological sequence of myelin degradation

Myelin degradation in chronic relapsing experimental allergic encephalomyelitis was studied using light microscopic histochemistry and electron microscopy. In the earliest stages, a large number of myelin stripping macrophages were found. The Luxol fast blue positive degradation products were then gradually transformed into PAS positive material. No sudanophilic stage of myelin degradation was found in this model. In electron microscopy, the Luxol fast blue positive material was identified as uniformly layered lipid inclusions with a periodicity of 4.0--4.5 nm. During further digestion, this material was transformed into polymorph structured material, consisting of lamellar leaflets with a diameter of 7--10 nm, curved cylindrical profiles and granular osmiophilic material.

Activity of 2',3'-cyclic nucleotide 3'-phosphohydrolase in human cerebrospinal fluid

Activity of the myelin marker enzyme 2',3'-cyclic nucleotide 3'-phosphohydrolase (CNP) was assayed in cerebrospinal fluid samples obtained from patients with multiple sclerosis (MS) and other neurological diseases. The enzyme activity was found to be elevated in acute cases of MS and reduced during remission. It was present in other demyelinating diseases, and no activity was detected in normal CSF. CNP may be released into CSF from any insult to myelin. The level of activity appears to reflect demyelination and the rate of breakdown of the myelin sheath.

Treatment of experimental allergic encephalomyelitis with an inhibitor of cathepsin D (pepstatin)

Intraperitoneal administration of pepstatin (2 mg/day for 5 weeks) to Lewis rats subjected to experimental allergic encephalomyelitis (EAE) (induced by guinea pig spinal cord and pertussis vaccine) suppressed the appearance of clinical signs of disease, and reduced the severity and incidence of CNS lesions normally associated with this disease. Administration of pepstatin for shorter periods to Lewis rats, or BSVS mice, or guinea pigs challenged with myelin basic protein delayed, but did not prevent clinical signs of EAE, but was accompanied in all cases by a less severe histopathology.

Neutral proteinases secreted by macrophages degrade basic protein: a possible mechanism of inflammatory demyelination

In the inflammatory demyelinating diseases, such as multiple sclerosis, Landry-Guillain-Barré syndrome and experimental allergic encephalomyelitis, demyelination occurs in the vicinity of infiltrating mononuclear cells. Although the histopathology is characteristic of each disease, the general observation that myelin destruction in inflammatory lesions begins prior to phagocytosis suggests a common mechanism for myelinolysis in these diseases. Recent studies show that stimulated macrophages secrete several neutral proteinases, including plasminogen (Plg) activator. We have tested the possibility that these proteinases could, directly or indirectly, initiate myelin destruction. Isolated brain myelin was incubated with supernatant media from cultures of stimulated mouse peritoneal macrophages in the presence and absence of Plg. Cell supernatants alone caused some degradation of basic protein (BP) in myelin. The amount degraded was considerably enhanced in the presence of Plg. The other myelin proteins remained essentially intact. While the Plg-independent proteolytic activity in the supernatants was abolished by EDTA, known to inhibit the neutral proteinases, the Plg-dependent hydrolysis was inhibited by p-nitrophenylguanidinobenzoate, an inhibitor of Plg activator and plasmin. These results suggested that the Plg activator secreted by the macrophages generated plasmin, which selectively degraded BP. This interpretation was confirmed by the observation that urokinase, a Plg activator, plus Plg was effective in degrading BP in myelin. We propose that the action of neutral proteinases released by stimulated macrophages, and its amplification by the Plg-plasmin system, may play a significant role in several inflammatory demyelinating diseases; and that the relative specificity of these reactions for myelin lies in the extreme susceptibility of BP to proteolysis.