Experimental autoimmune encephalomyelitis is exacerbated in mice lacking the NOS2 gene.

Nitric oxide is believed to be a prominent mediator of inflammation based in part on the correlative expression of the inducible nitric oxide synthase (iNOS) gene in various pathologies. The resulting high output of the highly reactive molecule nitric oxide is then believed to play an important role in the evolving inflammatory response. Studies have shown that iNOS and nitric oxide are present in the tissues of patients with multiple sclerosis (MS). In rodent models of MS, experimental autoimmune encephalomyelitis (EAE), it has been shown that nonspecific NOS inhibitors partially ameliorate the disease. To determine the importance of iNOS in this model of MS, we induced EAE in mice containing a disrupted iNOS (NOS2) gene. Surprisingly, by day 24, the NOS2 knockout mice had a greater incidence of EAE than wild-type control mice (75 vs 12%), and had a higher average severity score (2.42 vs 0.44). These differences appear to result largely from the failure of the disease to remit in NOS2 KO mice. Wild-type mice have a profound ability to reverse EAE (82%) compared with the knockout mice (19%). This result implies that iNOS may in some instances play a protective role in autoimmune-mediated tissue destruction.

Aggrecan degradation in human cartilage. Evidence for both matrix metalloproteinase and aggrecanase activity in normal, osteoarthritic, and rheumatoid joints.

To examine the activity of matrix metalloproteinases (MMPs) and aggrecanase in control and diseased human articular cartilage, metabolic fragments of aggrecan were detected with monospecific antipeptide antibodies. The distribution and quantity of MMP-generated aggrecan G1 fragments terminating in VDIPEN341 were compared with the distribution of aggrecanase-generated G1 fragments terminating in NITEGE373. Both types of G1 fragments were isolated from osteoarthritic cartilage. The sizes were consistent with a single enzymatic cleavage in the interglobular domain region, with no further proteolytic processing of these fragments. Both neoepitopes were also detected by immunohistochemistry in articular cartilage from patients undergoing joint replacement for osteoarthritis (OA), rheumatoid arthritis (RA), and in cartilage from adults with no known joint disease. In control specimens, the staining intensity for both G1 fragments increased with age, with little staining in cartilage from 22-wk-old fetal samples. There was also an increase with age in the extracted amount of MMP-generated neoepitope in relation to both aggrecan and collagen content, confirming the immunohistochemical results. After the age of 20-30 yr this relationship remained at a steady state. The staining for the MMP-generated epitope was most marked in control cartilage exhibiting histological signs of damage, whereas intense staining for the aggrecanase-generated fragment was often noted in adult cartilage lacking overt histological damage. Intense staining for both neoepitopes appeared in the more severely fibrillated, superficial region of the tissue. Intense immunostaining for both VDIPEN- and NITEGE- neoepitopes was also detected in joint cartilage from patients with OA or RA. Cartilage in these specimens was significantly more degraded and high levels of staining for both epitopes was always seen in areas with extensive cartilage damage. The levels of extracted VDIPEN neoepitope relative to collagen or aggrecan in both OA and RA samples were similar to those seen in age-matched control specimens. Immunostaining for both types of aggrecan fragments was seen surrounding the cells but also further removed in the interterritorial matrix. In some regions of the tissue, both neoepitopes were found while in others only one was detected. Thus, generation and/or turnover of these specific catabolic aggrecan fragments is not necessarily coordinated. Our results are consistent with the presence in both normal and arthritic joint cartilage of proteolytic activity against aggrecan based on both classical MMPs and "aggrecanase."

Aggrecanase and metalloproteinase-specific aggrecan neo-epitopes are induced in the articular cartilage of mice with collagen II-induced arthritis.

OBJECTIVE: To analyze the roles of two classes of proteinases, 'aggrecanase', and matrix metalloproteinases (MMPs), in chondrodestruction during murine collagen-induced arthritis (CIA). METHODS: Generation of the 'aggrecanase' neo-epitope (NITEGE373), and the MMP neo-epitope (VDIPEN341) within aggrecan was studied by immunoperoxidase microscopy using specific anti-peptide antibodies in normal and stromelysin-1 (SLN-1) deficient knockout mice with CIA. RESULTS: High levels of NITEGE373 and VDIPEN341 neo-epitopes were observed in foci within CIA paw articular cartilage exhibiting depletion of glycosaminoglycans, in advance of significant cartilage erosion. The highest concentrations of NITEGE373 and VDIPEN341 labeling were observed and often co-distributed in the chondrocyte pericellular matrix, suggesting that stimulated chondrocytes can synthesize and/or activate both enzymes. Other regions of the cartilage frequently exhibited either NITEGE373 or VDIPEN341 labeling, but not both neo-epitopes simultaneously, suggesting that 'aggrecanase' and MMP cleavages of aggrecan may be generated independently. No detectable differences were observed in expression or distribution of either neo-epitope in SLN-1 knockout versus wild-type mice. In addition, in vitro digestion of joint sections with SLN-1 did not alter the expression of cartilage NITEGE373, while markedly increasing VDIPEN341 labeling. Peripheral nerves and brains of naive mice also exhibited intense anti-NITEGE373 labeling. CONCLUSIONS: These data indicate that NITEGE373 and VDIPEN341 aggrecan neo-epitopes are sensitive and specific markers of early joint pathology, and are consistent with the hypothesis that SLN-1 does not have 'aggrecanase' activity, and that 'aggrecanase' is distinct from the MMPs which cleave aggrecan at the MMP site.

Expression and immunoaffinity purification of human inducible nitric-oxide synthase. Inhibition studies with 2-amino-5,6-dihydro-4H-1,3-thiazine.

Recombinant human inducible nitric-oxide synthase (rH-iNOS) was expressed in the baculovirus system and purified by a novel immunoaffinity column. rH-iNOS and its native counterpart from cytokine-stimulated primary hepatocytes exhibited similar molecular mass of 130 kDa on SDS-polyacrylamide gel electrophoresis, recognition by antipeptide antibodies, specific activities, and IC50 values for inhibitors. The active dimeric form exhibited a specific activity range of 114-260 nmol/min/mg at 37 degrees C and contained 1.15 +/- 0.04 mol of calmodulin/monomer. The enzyme exhibited a Soret lambdamax at 396 nm with a shoulder at 460 nm and contained 0. 28-0.64 mol of heme/monomer. Dithionite reduction under CO yielded an absorbance maximum at 446 nm, indicating a P450-type heme. Imidazole induced a type II difference spectrum, reversible by L-Arg. 2-Amino-5,6-dihydro-4H-1,3-thiazine (ADT) was competitive versus L-Arg (Ki = 22.6 +/- 1.9 nM), reversed the type II difference spectrum induced by imidazole (Kd = 17.7 nM), and altered the CO-ferrous absorbance of rH-iNOS. L-Arg did not perturb the CO-ferrous adduct directly, but it partially reversed the ADT-induced absorbance shift, indicating that both bind similarly to the protein but interact differently with the heme.

Expression of inducible nitric oxide synthase and nitrotyrosine in colonic epithelium in inflammatory bowel disease.

BACKGROUND & AIMS: Inducible nitric oxide synthase (iNOS) is generated in several cell types by treatment with lipopolysaccharides or cytokines. Earlier studies suggested that ulcerative colitis is associated with increased NO produced by iNOS; however, the cellular source of the NO synthesis was not identified. A possible mechanism of NO-induced cellular damage is through its interaction with superoxide to produce peroxynitrite, which reacts with tyrosine to form nitrotyrosine in cellular proteins. METHODS: Using immunoperoxidase microscopy with a new monospecific human iNOS antibody (NO-53), the cellular distribution of iNOS and nitrotyrosine was examined using human colonic mucosa from normal bowel, ulcerative colitis, Crohn's disease, and diverticulitis. RESULTS: Intense focal iNOS labeling was localized to the inflamed colonic epithelium in ulcerative colitis, Crohn's disease, and diverticulitis but was not detectable in the uninflamed epithelium. Nitrotyrosine labeling was also observed in the inflamed colonic epithelium and was associated with nearby iNOS staining; nitrotyrosine was undetectable in normal mucosal epithelium. iNOS and nitrotyrosine were also detected in lamina propria mononuclear cells and neutrophils. CONCLUSIONS: These findings suggest that iNOS is induced in the inflamed human colonic epithelium and is associated with the formation of peroxynitrite and the nitration of cellular proteins.

Inducible nitric oxide synthase in pulmonary alveolar macrophages from patients with tuberculosis.

The high-output pathway of nitric oxide production helps protect mice from infection by several pathogens, including Mycobacterium tuberculosis. However, based on studies of cells cultured from blood, it is controversial whether human mononuclear phagocytes can express the corresponding inducible nitric oxide synthase (iNOS;NOS2). The present study examined alveolar macrophages fixed directly after bronchopulmonary lavage. An average of 65% of the macrophages from 11 of 11 patients with untreated, culture-positive pulmonary tuberculosis reacted with an antibody documented herein to be monospecific for human NOS2. In contrast, a mean of 10% of bronchoalveolar lavage cells were positive from each of five clinically normal subjects. Tuberculosis patients' macrophages displayed diaphorase activity in the same proportion that they stained for NOS2, under assay conditions wherein the diaphorase reaction was strictly dependent on NOS2 expression. Bronchoalveolar lavage specimens also contained NOS2 mRNA. Thus, macrophages in the lungs of people with clinically active Mycobacterium tuberculosis infection often express catalytically competent NOS2.

VDIPEN, a metalloproteinase-generated neoepitope, is induced and immunolocalized in articular cartilage during inflammatory arthritis.

The destruction of articular cartilage in immune inflammatory arthritic disease involves the proteolytic degradation of its extracellular matrix. The role of activated matrix metalloproteinases (MMPs) in the chondrodestructive process was studied by identifying a selective cleavage product of aggrecan in murine arthritis models initiated by immunization with either type II collagen or proteoglycan. We conducted semiquantitative immunocytochemical studies of VDIPEN341 using a monospecific polyclonal antibody requiring the free COOH group of the COOH-terminal Asn for epitope detection. This antibody recognizes the aggrecan G1 domain fragment generated by MMP [i.e., stromelysin (SLN) or gelatinase A] cleavage of aggrecan between Asn341-Phe342 but does not recognize intact aggrecan. VDIPEN was undetectable in normal mouse cartilage but was observed in the articular cartilage (AC) of mice with collagen-induced arthritis 10 d after immunization, without histological damage and clinical symptoms. This aggrecan neoepitope was colocalized with high levels of glycosaminoglycans (GAGs) in pericellular matrices of AC chondrocytes but was not seen at the articular surface at this early time. Digestion of normal (VDIPEN negative) mouse paw cryosections with SLN also produced heavy pericellular VDIPEN labeling. Computer-based image analysis showed that the amount of VDIPEN expression increased dramatically by 20 d (70% of the SLN maximum) and was correlated with GAG depletion. Both infiltration of inflammatory cells into the synovial cavity and early AC erosion were also very prominent at this time. Analysis of adjacent sections showed that both induction of VDIPEN and GAG depletion were strikingly codistributed within sites of articular cartilage damage. Similar results occurred in proteoglycan-induced arthritis, a more progressive and chronic model of inflammatory arthritis. These studies demonstrate for the first time the MMP-dependent catabolism of aggrecan at sites of chondrodestruction during inflammatory arthritis.

Cell-mediated catabolism of aggrecan. Evidence that cleavage at the "aggrecanase" site (Glu373-Ala374) is a primary event in proteolysis of the interglobular domain.

A rat chondrosarcoma cell line and primary bovine chondrocytes have been used to study cell-mediated aggrecan catabolism. Addition of 1 microM retinoic acid to chondrosarcoma cultures resulted in aggrecan proteolysis with the release of greater than 90% of the cell layer aggrecan into the medium within 4 days. NH2-terminal sequencing of chondroitin sulfate-substituted catabolic products gave a single major NH2-terminal sequence of ARGNVILTXK, initiating at Ala374. This showed that the proteinase, commonly referred to as "aggrecanase," which cleaves the Glu373-Ala374 bond of the interglobular domain of aggrecan (Sandy, J. D., Neame, P. J., Boynton, R. E., and Flannery, C. R. (1990) J. Biol. Chem. 266, 8683-8685), is active in this cell system. Aggrecan G1 domain, generated by cleavage of the interglobular domain, was also liberated during catabolism and this was characterized with three antipeptide antisera. Anti-CDAGWL was used as a general probe for G1 domain. Anti-FVDIPEN was used to specifically detect G1 domain with COOH terminus of Asn341, the form which is readily generated by cleavage of aggrecan by a wide range of matrix metalloproteinases. Anti-NITEGE antiserum was used to specifically detect G1 domain with COOH terminus of Gln373, the form which is the expected product of "aggrecanase"-mediated cleavage of aggrecan. Western blot analysis indicated that a single form of G1 domain of about 60 kDa was formed. G1 domain of this size reacted with both anti-CDAGWL and anti-NITEGE but not with anti-FVDIPEN. Similar experiments with primary bovine chondrocyte cultures, treated with either retinoic acid or interleukin 1, showed that two forms of catabolic G1 domain, of about 62 and 66 kDa, were formed. Both of these forms reacted on Western blots with anti-CDAGWL and also with anti-NITEGE. It is suggested that cell-mediated catabolism of the aggrecan interglobular domain in these culture systems, whether promoted by retinoic acid or interleukin 1, primarily involves cleavage of the Glu373-Ala374 bond by aggrecanase. The accumulation of G1 domain with a COOH-terminal of Glu373 shows that such aggrecanase-mediated cleavage can occur independent of the cleavage of the Asn341-Phe342 bond by matrix metalloproteinases.

Carboxyl terminus of inducible nitric oxide synthase. Contribution to NADPH binding and enzymatic activity.

Cloning of a nitric oxide synthase (NOS) from RAW 264.7 mouse macrophages (Xie, Q.-w., Cho, H. J., Calaycay, J., Mumford, R. A., Swiderek, K. M., Lee, T. D., Ding, A., Troso, T., and Nathan, C. (1992) Science 256, 225-228) yielded two sets of cDNA: one with a longer coding region of 1144 amino acids, whose sequence matched that of the purified protein, and another with a shorter coding region of 1122 amino acids, in which the last 10 carboxyl-terminal amino acids differed completely from those of the long form. We have now found that the short form lacks NOS activity. To determine the basis of this defect, we prepared recombinant chimeric, deletional, and point mutants of the long and short NOS variants, monitored their expression by immunoblot, and tested their enzymatic activity. By itself, lack of the 22-carboxyl-terminal residues of the long form NOS was scarcely consequential. Mutation of Phe1122, the only aromatic residue within one of the longest conserved regions shared by all NOSs of reported sequence, reduced enzymatic activity by 41%. Deletion of 23 carboxyl-terminal amino acids (including Phe1122) reduced activity by 71%. Further loss of Ile1121, another completely conserved residue, reduced activity by 95%, and with the deletion of the rest of the conserved region, NOS activity was undetectable. Normal dimerization and binding of heme and calmodulin by the short variants militated against distortions of tertiary structure affecting the amino-terminal half or middle portion of the protein. In contrast, the short variants were deficient in binding to NADPH, as predicted by a model of tertiary structure based on that of spinach ferredoxin-NADP+ reductase. This is the first demonstration that the carboxyl terminus of NOS is a functionally critical region.

A novel heterodimeric cysteine protease is required for interleukin-1 beta processing in monocytes.

Interleukin-1 beta (IL-1 beta)-converting enzyme cleaves the IL-1 beta precursor to mature IL-1 beta, an important mediator of inflammation. The identification of the enzyme as a unique cysteine protease and the design of potent peptide aldehyde inhibitors are described. Purification and cloning of the complementary DNA indicates that IL-1 beta-converting enzyme is composed of two nonidentical subunits that are derived from a single proenzyme, possibly by autoproteolysis. Selective inhibition of the enzyme in human blood monocytes blocks production of mature IL-1 beta, indicating that it is a potential therapeutic target.

Development of synthetic peptide substrates for the poliovirus 3C proteinase.

Picornaviruses, such as polio, translate their entire genome as a single polyprotein which must be proteolytically processed to produce the mature viral proteins. A majority of these cleavages are catalyzed by the virus-encoded cysteine proteinase, 3C. We report here the design and synthesis of a series of oligopeptide substrates, based upon native 3C cleavage sites, for an HPLC assay of poliovirus 3C proteinase activity. A similar series of peptides based upon human rhinovirus 3C cleavage sites was also examined. The enzyme shows a marked preference for those peptides with a proline in the P'2 position. A quenched fluorescent substrate suitable for continuous assay of 3C proteinase activity was also synthesized. Both the HPLC assay and the fluorescence assay were used to evaluate a number of potential 3C proteinase inhibitors.