Robert Terkeltaub - US grants

Lipoproteins have been found to have a number of influences on inflammation. The apo B-containing lipoproteins bind to monosodium urate crystals, the etiologic agent of gout, and are major, specific inhibitors of neutrophil responses to the crystals in vitro. The mechanism and structural requirements for the inhibitory effect of the predominant apo B lipoprotein, low density lipoprotein (LDL), will be analyzed. To establish the mechanism of LDL inhibition, its effects on physical association of neutrohils and crystals will first be evaluated using phase separation of crystal-cell suspensions in oils. Second, the effect of LDL on phagocytosis of the crystals will be quantitated and compared to concurrently measured effects on cytolysis. This will establish whether LDL acts by prevention of delivery of crystals to phagolysosomes or by inhibition of cytolysis, which is known to be initiated by phagolysosomal membranolysis. LDL effects on urate-induced membranolysis will also be directly addressed by quantitating 1) hemolysis of erythrocyte suspensions and 2) lactic dehydrogenase loss from neutrophils in the presence of cytochalasin B to block phagocytosis. Determination of the mechanism(s) responsible for LDL's effects will be followed by experiments to address the consequences of modifications of LDL structure. In this way, the structural requirements for lipoprotein inhibition of crystal-cell interaction will be ascertained. A number of LDL-related moieties will be evaluated: 1) LDL depleted of neutral lipids by starch-heptane extraction; 2) liposomes containing the major LDL lipids phosphatidyl choline, cholesterol and sphingomyelin at different molecular ratios; 3) core LDL and water soluble LDL peptides derived via limited digestion with trypsin and elastase, and 4) LDL modified by nonenzymatic glycosylation, acetylation and cationization. Modifications of LDL in this last fashion alter its high affinity apo B receptor-mediated cellular uptake and may inhibit or enhance cellular LDL degradation. The ability to bind to urate crystals will be quantitated, as a control, for each alteration of LDL which is associated with a loss of inhibitory activity for crystal-neutrophil interaction. These studies will address both the biologic effects of lipoproteins on neutrophil responses and the pathogenesis of crystal-induced inflammation and may point the way to a novel therapeutic approach.

The major objective of this proposal is to further define how crystal-cell interactions which mediate gouty inflammation are regulated. The adhesive platelet membrane glycoprotein GpIIb- IIIa, a member of a widely distributed family of heterodimeric "cytoadhesins", directly modulates secretion in response to urate crystals. Crystal surface-bound LDL,via apolipoprotein B-100, suppresses cell stimulation by inhibiting physical crystal-cell association, and directly diminishes soluble GpIIb-IIIa binding to urate crystals. We propose to: 1) Test the biologic relevance of the in vitro inhibitory effects of LDL on crystal-cell interaction in an animal model of urate crystal-induced synovial inflammation in rabbits; 2) Define the epitopes on platelet GpIIb-IIIa mediating binding to urate crystals, using purified, solubilized GpIIb-IIIa and a panel of monoclonal GpIIb-IIIa-specific antibodies. Fab fragments of inhibitory antibodies will be prepared and we will evaluate their effects, and the effects of synthetic peptides constructed from deduced sequences of their epitopes, on platelet secretion induced by urate crystals; 3) Define by similar means to the above, the domains of apo B-100 mediating both LDL binding to urate crystals and the inhibitory effect of LDL on crystal- induced cell stimulation; 4) Compare the LDL isolated from acute gouty fluids vs. noninflammatory osteoarthritic fluids for the ability to suppress urate crystal-induced cell stimulation. In addition we will define the physical, biochemical and relevant functional properties of synovial fluid apo E, as apo E appears to share the inhibitory activity of apo B in vitro. Results of these studies will enhance understanding of crystal- induces inflammation. Definition of the structural bases for direct adhesion of GpIIb-IIIa to crystal surfaces, and the inhibitory effect of apo B-100 on inflammatory cell adhesion to certain surfaces, may lead to novel therapeutic approaches for particulate-induced inflammation.

DESCRIPTION (Adapted from the applicant's abstract): Oxidized LDL is detected at inflammatory loci and activates proinflammatory cytokine release from monocytes and macrophages. Extensively oxidized LDL also can induce acute inflammation in vivo. The investigators propose to define further the physiologic significance and mechanism of these observations. To do so: (1) The investigators will define the properties of oxidized LDL in inflammatory human synovial fluids (SFs). To determine the nature and extent of oxidative LDL modification in human SFs the investigators will evaluate SF LDLs for apo B degradation, the degree of apo B lysyl residue modification, enhanced recognition by macrophages, and the ability to complete in solid-phase RIAs for three epitopes present in oxidized LDL: (malondialdehyde(MDA)-lysine, 4-hydroxynonenal(HNE)-lysine, and a unique apo B epitope). Certain new apo B epitopes in oxidized LDL are highly immunogenic, e.g., autoantibodies (autoAbs) to MDA-lysine are commonly detected in vivo. Thus, the investigators will quantify such autoAbs in SFs. The effects of the isolated autoAbs on phagocyte activation and inflammation induced by oxidized LDL will then be assessed, as described below. Last, the investigators will determine the extent of modification of oxidized LDL required for it to be proinflammatory in a rat model of acute synovitis (injection into subcutaneous air pouches). (2) The investigators will define the mechanism of mononuclear phagocyte activation by oxidized LDL. The investigators will determine the extent of modification of SF LDL required to induce proinflammtory cytokines (IL-1, and the major neutrophil chemotaxin, IL-8) in freshly isolated adherent human monocytes, well-differentiated monocyte-derived macrophages (MDM), and interferon-activated MDM. The modified apo B of oxidized LDL appears to be recognized both by a scavenger receptor and a putative oxidized LDL receptor on macrophages. Thus, the investigators will define the potential ability of the following to induce these cytokines, and cytosolic calcium mobilization, or to inhibit the ability of oxidized LDL to do so: (i) Other scavenger receptor ligands (fucoidin, acetylated(Ac)-LDL, and Ac-albumin); (ii) oxidized forms of LDL that appear to bind both, or neither receptor (Ac-LDL, and reductively methylated LDL, respectively); (iii) delipidated apo B extracted from modified LDLs. Last, the investigators will assess the potential roles in activation of polar and neutral lipids extracted from oxidized LDL, of receptor-mediated endocytosis and lysosomal degradation of oxidized LDL, and of oxidized LDL-induced enhancement of arachidonate metabolism in monocyte/macrophages.

We have determined a role of chondrocyte mitochondrial oxidative phosphorylation (OXPHOS) in matrix synthesis and mineralizing activity. Chondrocyte respiration was inhibited by the NO donor Sin-1. Chondrocyte mitochondrial reserve, as OXPHOS-induced ATP production, supported matrix synthesis and basal and TGFbeta-induced Ppi elaboration, and regulated MV composition and mineralizing activity. Because altered chondrocyte OXPHOS could modulate matrix loss and secondary cartilage mineralization in osteoarthritis (OAO, we propose a limited feasibility study to first assess if experimental OA in rabbit knees can be studied for, and is associated with, mitochondrial OXPHOS impairment. We will also carry out a clinical pilot study to quantify OXPHOS (and identify OXPHOS impairment including deficiency of the mitochondrial protective agent coenzyme Q10 (CoQ10), on an existing panel of isolated primary chondrocytes from human knee OA. Results of this pilot project could determine if OXPHOS preservation is a therapeutic target in OA.

DESCRIPTION (provided by applicant): The proposed program is designed to train postdoctoral researchers, at the level of MDs, MD/PhDs, and PhD scientists, interested in biomedical research in the area of rheumatic diseases. The training program will consist of a bench research laboratory experience of 12-36 months, under the close supervision of a mentor working on immunologic, molecular biologic, or biochemical problems relevant to the rheumatoid diseases, with an emphasis on generating novel research-based translational approaches to rheumatic diseases and ultimately, potential new targeted therapeutic interventions. Co-mentoring and team mentoring are features of the program, to mesh complementary skills and resources of more than one preceptor, in an individualized manner appropriate to the trainee and research project. All trainees will take courses in scientific ethic and scientific methodology. Other formal academic course work is available for those interested, at the discretion of the trainee and mentor. Training will be physicians, and MD/PhDs, who have completed one year of internship and two or more years of house staff training, usually in general internal medicine, or PhD scientists with an interest in devoting research efforts to subjects relevant to rheumatic diseases. Trainees will be chosen on the basis of their prior academic performance, research experience, publications, interviews, and recommendations from supervisors. Preference will be given to those with acknowledged research interests in rheumatologic and immunologic diseases, and demonstrated capacities in research. Four postdoctoral fellows will be selected to participate in the three-year fellowship. At the completio of the training, they will be prepared to compete successfully for full-time academic positions in medical schools or research institutes. We anticipate that the majority of the physicians and MD/PhDs will operate as rheumatologists within Departments of Medicine or as research scientists in academic centers or industry. The primary training unit will be the Rheumatology, Allergy and Immunology Division, in the Department of Medicine, University of California, San Diego, School of Medicine. At UCSD, training can be obtained in research laboratories located at the Biomedical Science, Leichtag, and Clinical Sciences Building located in La Jolla, or the San Diego Veterans Administration Medical Center also located adjoining the UCSD campus in La Jolla. Additional training is available in the UCSD Departments of Pediatrics, Bioengineering and Pharmacology, Genetics, and at nearby research institutions in the La Jolla research hub (i.e., the Scripps Research Institute, the La Jolla Institute of Allergy and Immunology, and the Sanford-Burnham Institute). Abundant patient sample resources and clinical research consultative resources are also available through the UCSD Clinical and Translational Research Institute, the UCSD Center for Innovative Therapy clinical research unit, and clinical facilities a UCSD Medical Center and the VA Medical Center.