Mukundan Attur

Bio: Mukundan Attur is an academic researcher from New York University. The author has contributed to research in topics: Cartilage & Osteoarthritis. The author has an hindex of 46, co-authored 124 publications receiving 8326 citations. Previous affiliations of Mukundan Attur include Novartis & Beth Israel Deaconess Medical Center.

A novel mechanism of action of tetracyclines: Effects on nitric oxide synthases

Abstract: Tetracyclines have recently been shown to have "chondroprotective" effects in inflammatory arthritides in animal models. Since nitric oxide (NO) is spontaneously released from human cartilage affected by osteoarthritis (OA) or rheumatoid arthritis in quantities sufficient to cause cartilage damage, we evaluated the effect of tetracyclines on the expression and function of human OA-affected nitric oxide synthase (OA-NOS) and rodent inducible NOS (iNOS). Among the tetracycline group of compounds, doxycycline > minocycline blocked and reversed both spontaneous and interleukin 1 beta-induced OA-NOS activity in ex vivo conditions. Similarly, minocycline > or = doxycycline inhibited both lipopolysaccharide- and interferon-gamma-stimulated iNOS in RAW 264.7 cells in vitro, as assessed by nitrite accumulation. Although both these enzyme isoforms could be inhibited by doxycycline and minocycline, their susceptibility to each of these drugs was distinct. Unlike acetylating agents or competitive inhibitors of L-arginine that directly inhibit the specific activity of NOS, doxycycline or minocycline has no significant effect on the specific activity of iNOS in cell-free extracts. The mechanism of action of these drugs on murine iNOS expression was found to be, at least in part, at the level of RNA expression and translation of the enzyme, which would account for the decreased iNOS protein and activity of the enzyme. Tetracyclines had no significant effect on the levels of mRNA for beta-actin and glyceraldehyde-3-phosphate dehydrogenase nor on levels of protein of beta-actin and cyclooxygenase 2 expression. These studies indicate that a novel mechanism of action of tetracyclines is to inhibit the expression of NOS. Since the overproduction of NO has been implicated in the pathogenesis of arthritis, as well as other inflammatory diseases, these observations suggest that tetracyclines should be evaluated as potential therapeutic modulators of NO for various pathological conditions.

Decreased Bacterial Diversity Characterizes the Altered Gut Microbiota in Patients With Psoriatic Arthritis, Resembling Dysbiosis in Inflammatory Bowel Disease

Abstract: Objective To characterize the diversity and taxonomic relative abundance of the gut microbiota in patients with never-treated, recent-onset psoriatic arthritis (PsA). Methods High-throughput 16S ribosomal RNA pyrosequencing was utilized to compare the community composition of gut microbiota in patients with PsA (n = 16), patients with psoriasis of the skin (n = 15), and healthy, matched control subjects (n = 17). Samples were further assessed for the presence and levels of fecal and serum secretory IgA (sIgA), proinflammatory proteins, and fatty acids. Results The gut microbiota observed in patients with PsA and patients with skin psoriasis was less diverse when compared to that in healthy controls. This could be attributed to the reduced presence of several taxa. Samples from both patient groups showed a relative decrease in abundance of Coprococcus species, while samples from PsA patients were also characterized by a significant reduction in Akkermansia, Ruminococcus, and Pseudobutyrivibrio. Supernatants of fecal samples from PsA patients revealed an increase in sIgA levels and decrease in RANKL levels. Analysis of fatty acids revealed low fecal quantities of hexanoate and heptanoate in both patients with PsA and patients with psoriasis. Conclusion Patients with PsA and patients with skin psoriasis had a lower relative abundance of multiple intestinal bacteria. Although some genera were concomitantly decreased in both conditions, PsA samples had a lower abundance of reportedly beneficial taxa. This gut microbiota profile in PsA was similar to that previously described in patients with inflammatory bowel disease and was associated with changes in specific inflammatory proteins unique to this group, and distinct from that in patients with skin psoriasis and healthy controls. Thus, the role of the gut microbiome in the continuum of psoriasis–PsA pathogenesis and the associated immune response merits further study.

Periodontal disease and the oral microbiota in new‐onset rheumatoid arthritis

Abstract: Objective To profile the abundance and diversity of subgingival oral microbiota in patients with never-treated, new-onset rheumatoid arthritis (RA). Methods Periodontal disease (PD) status, clinical activity, and sociodemographic factors were determined in patients with new-onset RA, patients with chronic RA, and healthy subjects. Multiplexed-454 pyrosequencing was used to compare the composition of subgingival microbiota and establish correlations between the presence/abundance of bacteria and disease phenotypes. Anti–Porphyromonas gingivalis antibody testing was performed to assess prior exposure to the bacterial pathogen P gingivalis. Results The more advanced forms of periodontitis were already present at disease onset in patients with new-onset RA. The subgingival microbiota observed in patients with new-onset RA was distinct from that found in healthy controls. In most cases, however, these microbial differences could be attributed to the severity of PD and were not inherent to RA. The presence and abundance of P gingivalis were also directly associated with the severity of PD and were not unique to RA. The presence of P gingivalis was not correlated with anti–citrullinated protein antibody (ACPA) titers. Overall exposure to P gingivalis was similar between patients with new-onset RA and controls, observed in 78% of patients and 83% of controls. The presence and abundance of Anaeroglobus geminatus correlated with the presence of ACPAs/rheumatoid factor. Prevotella and Leptotrichia species were the only characteristic taxa observed in patients with new-onset RA irrespective of PD status. Conclusion Patients with new-onset RA exhibited a high prevalence of PD at disease onset, despite their young age and paucity of smoking history. The subgingival microbiota profile in patients with new-onset RA was similar to that in patients with chronic RA and healthy subjects whose PD was of comparable severity. Although colonization with P gingivalis correlated with the severity of PD, overall exposure to P gingivalis was similar among the groups. The role of A geminatus and Prevotella/Leptotrichia species in this process merits further study.

Superinduction of cyclooxygenase-2 activity in human osteoarthritis-affected cartilage. Influence of nitric oxide.

Abstract: Cartilage specimens from osteoarthritis (OA)-affected patients spontaneously released PGE2 at 48 h in ex vivo culture at levels at least 50-fold higher than in normal cartilage and 18-fold higher than in normal cartilage + cytokines + endotoxin. The superinduction of PGE2 production coincides with the upregulation of cyclooxygenase-2 (COX-2) in OA-affected cartilage. Production of both nitric oxide (NO) and PGE2 by OA cartilage explants is regulated at the level of transcription and translation. Dexamethasone inhibited only the spontaneously released PGE2 production, and not NO, in OA-affected cartilage. The NO synthase inhibitor HN(G)-monomethyl-L-arginine monoacetate inhibited OA cartilage NO production by > 90%, but augmented significantly (twofold) the spontaneous production of PGE2 in the same explants. Similarly, addition of exogenous NO donors to OA cartilage significantly inhibited PGE2 production. Cytokine + endotoxin stimulation of OA explants increased PGE2 production above the spontaneous release. Addition of L-NMMA further augmented cytokine-induced PGE2 production by at least fourfold. Inhibition of PGE2 by COX-2 inhibitors (dexamethasone or indomethacin) or addition of exogenous PGE2 did not significantly affect the spontaneous NO production. These data indicate that human OA-affected cartilage in ex vivo conditions shows (a) superinduction of PGE2 due to upregulation of COX-2, and (b) spontaneous release of NO that acts as an autacoid to attenuate the production of the COX-2 products such as PGE2. These studies, together with others, also suggest that PGE2 may be differentially regulated in normal and OA-affected chondrocytes.

Developments in the scientific understanding of osteoarthritis

Abstract: Osteoarthritis is often a progressive and disabling disease, which occurs in the setting of a variety of risk factors – such as advancing age, obesity, and trauma – that conspire to incite a cascade of pathophysiologic events within joint tissues. An important emerging theme in osteoarthritis is a broadening of focus from a disease of cartilage to one of the 'whole joint'. The synovium, bone, and cartilage are each involved in pathologic processes that lead to progressive joint degeneration. Additional themes that have emerged over the past decade are novel mechanisms of cartilage degradation and repair, the relationship between biomechanics and biochemical pathways, the importance of inflammation, and the role played by genetics. In this review we summarize current scientific understanding of osteoarthritis and examine the pathobiologic mechanisms that contribute to progressive disease.

“Bioinformatics” 특집을 내면서

Abstract: BIOE 402. Medical Technology Assessment. 2 or 3 hours. Bioentrepreneur course. Assessment of medical technology in the context of commercialization. Objectives, competition, market share, funding, pricing, manufacturing, growth, and intellectual property; many issues unique to biomedical products. Course Information: 2 undergraduate hours. 3 graduate hours. Prerequisite(s): Junior standing or above and consent of the instructor.

Nitric oxide synthases: structure, function and inhibition

Abstract: This review concentrates on advances in nitric oxide synthase (NOS) structure, function and inhibition made in the last seven years, during which time substantial advances have been made in our understanding of this enzyme family. There is now information on the enzyme structure at all levels from primary (amino acid sequence) to quaternary (dimerization, association with other proteins) structure. The crystal structures of the oxygenase domains of inducible NOS (iNOS) and vascular endothelial NOS (eNOS) allow us to interpret other information in the context of this important part of the enzyme, with its binding sites for iron protoporphyrin IX (haem), biopterin, L-arginine, and the many inhibitors which interact with them. The exact nature of the NOS reaction, its mechanism and its products continue to be sources of controversy. The role of the biopterin cofactor is now becoming clearer, with emerging data implicating one-electron redox cycling as well as the multiple allosteric effects on enzyme activity. Regulation of the NOSs has been described at all levels from gene transcription to covalent modification and allosteric regulation of the enzyme itself. A wide range of NOS inhibitors have been discussed, interacting with the enzyme in diverse ways in terms of site and mechanism of inhibition, time-dependence and selectivity for individual isoforms, although there are many pitfalls and misunderstandings of these aspects. Highly selective inhibitors of iNOS versus eNOS and neuronal NOS have been identified and some of these have potential in the treatment of a range of inflammatory and other conditions in which iNOS has been implicated.

American College of Rheumatology 2012 recommendations for the use of nonpharmacologic and pharmacologic therapies in osteoarthritis of the hand, hip, and knee

Abstract: Objective To update the American College of Rheumatology (ACR) 2000 recommendations for hip and knee osteoarthritis (OA) and develop new recommendations for hand OA. Methods A list of pharmacologic and nonpharmacologic modalities commonly used to manage knee, hip, and hand OA as well as clinical scenarios representing patients with symptomatic hand, hip, and knee OA were generated. Systematic evidence-based literature reviews were conducted by a working group at the Institute of Population Health, University of Ottawa, and updated by ACR staff to include additions to bibliographic databases through December 31, 2010. The Grading of Recommendations Assessment, Development and Evaluation approach, a formal process to rate scientific evidence and to develop recommendations that are as evidence based as possible, was used by a Technical Expert Panel comprised of various stakeholders to formulate the recommendations for the use of nonpharmacologic and pharmacologic modalities for OA of the hand, hip, and knee. Results Both “strong” and “conditional” recommendations were made for OA management. Modalities conditionally recommended for the management of hand OA include instruction in joint protection techniques, provision of assistive devices, use of thermal modalities and trapeziometacarpal joint splints, and use of oral and topical nonsteroidal antiinflammatory drugs (NSAIDs), tramadol, and topical capsaicin. Nonpharmacologic modalities strongly recommended for the management of knee OA were aerobic, aquatic, and/or resistance exercises as well as weight loss for overweight patients. Nonpharmacologic modalities conditionally recommended for knee OA included medial wedge insoles for valgus knee OA, subtalar strapped lateral insoles for varus knee OA, medially directed patellar taping, manual therapy, walking aids, thermal agents, tai chi, self-management programs, and psychosocial interventions. Pharmacologic modalities conditionally recommended for the initial management of patients with knee OA included acetaminophen, oral and topical NSAIDs, tramadol, and intraarticular corticosteroid injections; intraarticular hyaluronate injections, duloxetine, and opioids were conditionally recommended in patients who had an inadequate response to initial therapy. Opioid analgesics were strongly recommended in patients who were either not willing to undergo or had contraindications for total joint arthroplasty after having failed medical therapy. Recommendations for hip OA were similar to those for the management of knee OA. Conclusion These recommendations are based on the consensus judgment of clinical experts from a wide range of disciplines, informed by available evidence, balancing the benefits and harms of both nonpharmacologic and pharmacologic modalities, and incorporating their preferences and values. It is hoped that these recommendations will be utilized by health care providers involved in the management of patients with OA.

Cyclooxygenase in biology and disease

Abstract: Cyclooxygenase (COX), the key enzyme required for the conversion of arachidonic acid to prostaglandins was first identified over 20 years ago. Drugs, like aspirin, that inhibit cyclooxygenase activity have been available to the public for about 100 years. In the past decade, however, more progress has been made in understanding the role of cyclooxygenase enzymes in biology and disease than at any other time in history. Two cyclooxygenase isoforms have been identified and are referred to as COX-1 and COX-2. Under many circumstances the COX-1 enzyme is produced constitutively (i.e., gastric mucosa) whereas COX-2 is inducible (i.e., sites of inflammation). Here, we summarize the current understanding of the role of cyclooxygenase-1 and -2 in different physiological situations and disease processes ranging from inflammation to cancer. We have attempted to include all of the most relevant material in the field, but due to the rapid progress in this area of research we apologize that certain recent findings may have been left out.

Osteoarthritis: A Disease of the Joint as an Organ

Abstract: Osteoarthritis (OA) is the most common form of arthritis and a major cause of pain and disability in older adults (1) Often OA is referred to as degenerative joint disease “(DJD)” This is a misnomer because OA is not simply a process of wear and tear but rather abnormal remodeling of joint tissues driven by a host of inflammatory mediators within the affected joint The most common risk factors for OA include age, gender, prior joint injury, obesity, genetic predisposition, and mechanical factors, including malalignment and abnormal joint shape (2, 3) Despite the multifactorial nature of OA, the pathological changes seen in osteoarthritic joints have common features that affect the entire joint structure resulting in pain, deformity and loss of function The pathologic changes seen in OA joints (Figures 1 and ​and2)2) include degradation of the articular cartilage, thickening of the subchondral bone, osteophyte formation, variable degrees of synovial inflammation, degeneration of ligaments and, in the knee, the menisci, and hypertrophy of the joint capsule There can also be changes in periarticular muscles, nerves, bursa, and local fat pads that may contribute to OA or the symptoms of OA The findings of pathological changes in all of the joint tissues are the impetus for considering OA as a disease of the joint as an organ resulting in “joint failure” In this review, we will summarize the key features of OA in the various joint tissues affected and provide an overview of the basic mechanisms currently thought to contribute to the pathological changes seen in these tissues Open in a separate window Figure 1 Sagittal inversion recovery (A–C) and coronal fast spin echo (D–F) images illustrating the magnetic resonance imaging findings of osteoarthritis (A) reactive synovitis (thick white arrow), (B) subchondral cyst formation (white arrow), (C) bone marrow edema (thin white arrows), (D) partial thickness cartilage wear (thick black arrow), (E–F) full thickness cartilage wear (thin black arrows), subchondral sclerosis (arrowhead) and marginal osteophyte formation (double arrow) Image courtesy of Drs Hollis Potter and Catherine Hayter, Hospital for Special Surgery, New York, NY