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Biomedical subjects

S Chandrasekhar

Publications and source records attributed to S Chandrasekhar.

At least 55 records · Page 3Linked to original sources
PubMed1994

Osteonectin/SPARC is a product of articular chondrocytes/cartilage and is regulated by cytokines and growth factors.

Rabbit articular chondrocytes maintained in monolayer, synthesized and secreted a 46 kDa protein into the culture medium. N-terminal sequence analysis and immunoprecipitation of the radiolabeled material revealed this protein to be osteonectin (ON)/SPARC, a protein previously shown to be present in bone. When chondrocytes were exposed to interleukin-1, a cytokine with matrix degradative properties, ON synthesis and secretion was greatly inhibited. However, this was specific to IL-1 since two other pro-inflammatory cytokines (tumor-necrosis factor-alpha and interleukin-6) with properties similar to IL-1, failed to cause any discernible effect on ON synthesis. Several growth factors (TGF-beta, PDGF, and IGF-1), that have been shown to stimulate other cartilage matrix macromolecular synthesis, also stimulated ON synthesis and were also able to reverse the inhibitory effect of IL-1 on ON synthesis. These observations were also demonstrated in explant cultures of cartilage. Our studies suggest that ON is a biosynthetic product of articular cartilage and could play a role in cartilage structure and/or function.

Amino Acid Sequence↗
PubMed1994

Inhibition of IL-1 induced articular inflammation of rats by 4-aminothiazolidines, LY 221068 and LY 269415.

LY 221068 and LY 269415 are representative compounds from a chemical series of 4-aminothiazolidines, with potent antioxidant properties in vitro. We have evaluated these two compounds in a rat model of articular inflammation caused by the administration of recombinant human IL-1 beta into the knee joints. IL-1 injection into the knee joints has been shown to cause a complex series of changes resulting in synovitis, mesenchymal proliferation, and subchondral bone and cartilage erosion. The inflammatory response of the knee joint was measured by determining the changes in the joint swelling and also by histological evaluation of the knee joints. Rats pretreated (p.o.) with 10-25 mg/kg of either of these compounds (4 h prior to IL-1 injection) displayed greatly reduced soft tissue swelling with an IC50 of 7.5 mg/kg. Evaluation of histological lesions revealed, however, that LY 269415 (IC50 of 10 mg/kg) was more potent than LY 221068 (IC50 of 25 mg/kg) in reducing the severity of histological changes. The results demonstrate that antioxidants of this chemical series either directly or indirectly display anti-inflammatory properties and could be beneficial as therapeutic agents in inflammatory arthritis.

Animals↗
PubMed1993

Differential modulation of degradative and repair responses of interleukin-1-treated chondrocytes by platelet-derived growth factor.

Interleukin 1 (IL-1) plays a dual role in cartilage matrix degeneration by promoting extracellular proteinase action such as the matrix metalloproteinases (increased degradation) and by suppressing the synthesis of extracellular matrix molecules (inhibition of repair). Platelet-derived growth factor (PDGF) is a wound-healing hormone which is released along with IL-1 during the inflammatory response. Since previous studies have shown that PDGF enhances IL-1 alpha effects on metalloproteinase activity, in this report, we have examined whether PDGF modifies IL-1 beta effects on cartilage proteoglycan synthesis. Initially, we confirmed that rabbit articular chondrocytes treated with IL-1 beta + PDGF induced higher proteinase activity, in comparison with IL-1-treated cells. We further observed that the increased proteinase activity correlated with an increase in the synthesis of collagenase/stromelysin proteins and a corresponding increase in the steady-state mRNA levels for both the enzymes. Studies on IL-1 receptor expression suggested that PDGF caused an increase in IL-1 receptor expression which, by augmenting the IL-1 response, may have led to the increase in proteinase induction. Analysis of proteoglycan synthesis confirmed that IL-1 reduced the incorporation of sulphated proteoglycan, aggrecan, into the extracellular matrix of chondrocytes, whereas PDGF stimulated it. However, cells treated with IL-1 + PDGF synthesized normal levels of aggrecan. This is in contrast with cells treated with IL-1 + fibroblast growth factor, in which case only proteinase activity was potentiated. The results allow us to conclude that (a) the two effector functions that play a role in matrix remodelling, namely matrix lysis (proteinase induction) and matrix repair (proteoglycan synthesis), occur via distinct pathways and (b) PDGF may play a crucial role in cartilage repair by initially causing matrix degradation followed by promoting new matrix synthesis.

Animals↗
PubMed1993

Degradative and repair responses of cartilage to cytokines and growth factors occur via distinct pathways.

Cartilage destruction mediated by IL-1 is due to increased matrix lysis and decreased matrix repair. To determine whether the two processes are linked, we studied the influence of growth factors on IL-1 induced neutral protease induction, proteoglycan synthesis inhibition and IL-1 receptor expression. With respect to neutral protease induction, FGF and PDGF potentiated IL-1 activity, TGF-beta inhibited, while EGF, IGF-1 and -2 had no effect. With respect to IL-1 receptor expression, FGF and PDGF induced more IL-1 receptors, TGF-beta inhibited, while IGF-1, and 2 had no effect. Finally, with respect to proteoglycan synthesis, TGF-beta, PDGF and IGF-1 reversed IL-1 induced PG suppression to different extents, while FGF slightly potentiated IL-1 induced suppression of aggrecan synthesis. The results suggest that while IL-1 affects both increased aggrecan loss and decreased synthesis, the pathways leading to the effector functions are not necessarily linked and are likely to be distinct.

Animals↗
PubMed1993

A birth control vaccine is on the horizon for family planning.

Vaccines for control of fertility are likely to have an important impact on family planning methods. They are designed to act by mobilization of an internal physiological process and do not require external medication on a continuous basis. A number of birth control vaccines are at different stages of development, the most advanced being a vaccine inducing antibodies against human chorionic gonadotrophin (hCG). This vaccine consists of a heterospecies dimer (HSD, beta hCG associated with alpha-subunit of ovine luteinizing hormone, beta hCG:alpha oLH) linked to tetanus toxoid (TT) or diphtheria toxoid (DT) as carriers. The vaccine has recently passed an important milestone; it has completed the first leg of phase II efficacy trials. Women of proven fertility leading active sexual life were protected from becoming pregnant at antibody titres > or = 50 ng of hCG bioneutralization capacity per ml. This vaccine has previously been demonstrated to be reversible in its effect. It is free from any notable side-effects on endocrine, cardiovascular and other body functions. Ovulation was not disturbed and menstrual regularity was maintained. A logistic disadvantage of the present vaccine is the requirement for multiple injections. This is expected to be overcome by encapsulation of the requisite doses of the vaccine in biodegradable microspheres, which could be given at a single contact point for sustained antibody titres lasting over a year. A live recombinant vaccine has also been made that elicits high anti-hCG titres in monkeys for nearly 2 years following primary immunization and a booster at 8-9 months.

Adult↗
PubMed1992

Differential regulation of metalloprotease steady-state mRNA levels by IL-1 and FGF in rabbit articular chondrocytes.

The expression of collagenase and stromelysin is believed to be coordinately regulated. In this report however, we provide evidence that suggests subtle differences may exist in the early events of the induction of these enzymes. Rabbit articular chondrocytes treated with interleukin-1, either alone or in combination with fibroblast growth factor, accumulated steady-state mRNA levels for both the enzymes, with the latter treatment more effective in inducing greater levels and within a shorter time. Further, the induction of the enzymes by either protocol was blocked by cycloheximide co-treatment. Cycloheximide added 1 h post-stimulation with interleukin-1 + fibroblast growth factor failed to block stromelysin mRNA expression, but was able to block collagenase steady-state mRNA levels. Transforming growth factor-beta, another inhibitor of metallprotease induction, showed no such differential activity. The results suggest that collagenase and stromelysin may have subtle variations in their induction pathways. Our studies further show that the enzyme induction by interleukin-1 alone or in combination with fibroblast growth factor occurs through different, but related mechanisms.

Animals↗
PubMed1992

Studies on cell-wall deficient non-acid fast variants of Mycobacterium tuberculosis.

While the host-parasite relationship in tuberculosis still remains incompletely understood, there has been recent renewed interest in indications that tubercle bacilli are converted into metabolically inactive, non-acid fast (NAF) granular forms in the presence of host defence mechanisms and antituberculosis drugs. The present study investigates the mechanism of induction of these NAF variants in vitro and in vivo, and their ultimate pathogenicity. Evidence is provided that appears to clearly indicate that acid-fast mycobacteria are converted into NAF, cell wall deficient variants which remain dormant, only to revert to the parent, acid-fast bacilli in immune-compromised hosts, thence ultimately producing disease. It is then suggested that this may be one of the causes of the observed persistence of the bacilli in hosts in spite of chemotherapy. In a typical study in experimental animals in the present investigation, NAF variants were separated from lung lavage by differential centrifuging. When these were then injected into animals made immune-deficient with Freund's adjuvant or cyclophosphamide, they reverted to parent acid-fast forms. The presence of these NAF forms as variants of M. tuberculosis, and not merely contaminants, was clearly established by a number of methods. These included phase contrast and electron microscopy, immunological studies employing antiserum and comparison with the parent organisms, and gel electrophoresis of the proteins of the parent organisms. Other evidence is also offered confirming the hypothesis of reversion of NAF forms. It is also shown in this study that NAF forms can be induced in vitro by hydrolases.

Animals↗
PubMed1992

Intra-articular administration of interleukin-1 causes prolonged suppression of cartilage proteoglycan synthesis in rats.

The effect of IL-1 on proteoglycan synthesis was studied after intraarticular injection of IL-1 into the knee joints of rats. IL-1 reduced the sulfated glycosaminoglycan synthesis in the articular cartilage of rats in a dose-dependent fashion. Analysis of the sulfated molecules by chondroitinase ABC digestion followed by composite agarose/acrylamide gel electrophoresis confirmed the proteoglycan nature of the molecules. Immunoprecipitation of the methionine-labeled extracts with a polyclonal antibody against the core protein indicated that the reduction in glycosaminoglycan synthesis was due to an inhibition of the core protein synthesis after IL-1 treatment. IL-1 induced inhibition occurred in both young and old rats and was independent of the prostaglandin pathway, as non-steroidal anti-inflammatory drugs failed to block the inhibition of proteoglycan synthesis by IL-1. The cartilage of rats injected with IL-1 was able to recover with time and synthesize normal amounts of total proteoglycan. However, administration of successive doses resulted in a much delayed return to normal synthesis. These results suggest that IL-1, if available locally in a cyclical fashion, could significantly interfere with the ability of cartilage to repair by causing a prolonged suppression of proteoglycan synthesis.

Age Factors↗
PubMed1991

Effects of anti-arthritic drugs on IL-1 induced inflammation in rats.

Intra-articular injection of IL-1 in rats results in profound changes in the synovial joints including edema, synovitis, cartilage degeneration and fibroblast proliferation. We have tested the efficacy of several anti-arthritic drugs in this model to characterize the mechanism of IL-1 induced inflammatory lesions. The response to IL-1 was evaluated by measurement of soft-tissue swelling and by histological scoring. Dexamethasone, and several NSAIDS were effective in reducing the soft tissue swelling but only some were effective in improving the histological lesions. The slow-acting antirheumatic D-penicillamine and immunosuppressive agents such as cyclosporine A were ineffective. These observations provide further evidence that in vivo, at least some aspects of IL-1 induced changes in rat knee joints are likely to be prostaglandin mediated.

Animals↗
PubMed1991

Transforming growth factor-beta inhibition of interleukin-1 activity involves down-regulation of interleukin-1 receptors on chondrocytes.

Interleukin-1 (IL-1) plays an important role in cartilage destruction associated with inflammatory and degenerative arthritis because of its ability to induce matrix degrading enzymes. Previously, we have shown that the IL-1-induced chondrocyte protease activity was inhibited by transforming growth factor-beta (TGF-beta). In this paper, we show that TGF-beta inhibits the IL-1-induced synthesis of collagenase and stromelysin by reducing the steady-state mRNA levels in rabbit articular chondrocytes. We further demonstrate that TGF-beta-treated chondrocytes show reduced 125I-IL-1 binding that returns to a normal level when TGF-beta is removed from the culture medium. The inhibitory effect of TGF-beta is observed for both naturally occurring as well as fibroblast growth factor (FGF)-inducible binding sites (receptors). Scatchard analysis of receptor-ligand interactions demonstrate that the reduced binding is due to a reduction in the number of receptors for IL-1 and is not due to changes in affinity. Affinity cross-linking studies suggest that control chondrocytes contain two major cross-linked bands of Mr = 116 and 80 kDa and a minor band of Mr = 100 kDa. FGF-treated cells show enhanced levels of all the bands, plus an additional 200-kDa band. TGF-beta treatment of chondrocytes results in the reduction of all of these bands in both control as well as FGF-induced cells. These observations suggest that the ability of TGF-beta to down-regulate the IL-1 receptor may be a mechanism by which it exerts its effects in antagonizing the IL-1 activity on chondrocytes.

Animals↗
PubMed1991

Association of increased mycobacterium growth inhibitory factor with antituberculous immunity.

Cell-mediated immune mechanisms (CMI) were studied in 51 patients of pulmonary tuberculosis to evaluate the role of mycobacterium growth inhibitory factor in prognosis of the infection, before and after the administration of anti-tubercular drugs. Twenty five Mantoux negative individuals who were subsequently bacille Calmette-Guérin (BCG) vaccinated and 25 Mantoux positive, non-tuberculous controls were included in the study. Their clinical assessment was compared with skin sensitivity (Mantoux); lymphocyte transformation (LT) after stimulation with phytohaemagglutinin (PHA) and purified protein derivative (PPD); macrophage migration inhibitory factor (MIF), mycobacteria growth inhibitory factor (Myco IF) and listerial growth inhibitory factor (List IF). The tests were carried out at the beginning of the treatment and at intervals of three months, extending to one year. In the case of Mantoux positive controls, tests were carried out only once. It was found that Mantoux reaction had no correlation with LT, MIF, Myco IF and List IF. Both MIF and Myco IF, were significantly elevated in improving patients, whereas increase in List IF was not significant. An important finding was that Myco IF was at a higher level in improving patients whereas in those not responding to chemotherapy it was low.

Adult↗
PubMed1990

Interleukin-1-induced suppression of type II collagen gene transcription involves DNA regulatory elements.

Interleukin-1 is a proinflammatory polypeptide that influences cartilage macromolecular degradation and synthesis. Since previous studies have suggested that interleukin-1 may inhibit type II collagen synthesis, we have studied the mechanism of inhibition of type II collagen synthesis by interleukin-1. When rabbit articular chondrocytes were treated with purified recombinant interleukin-1 beta or macrophage-conditioned medium, the synthesis and assembly of type II collagen into the extracellular matrix were greatly reduced. The inhibition was concentration-dependent and occurred within 10 h of treatment with interleukin-1, with greater inhibition occurring at 30 h. The reduced level of collagen synthesis correlated with a reduction in the steady-state mRNA levels coding for type II collagen, as measured by a Northern blot analysis. This further correlated with a reduction in the transcription of type II collagen gene, as determined by nuclear run-on experiments. Finally, transfection studies using plasmid constructs containing DNA regulatory sequences from the type II gene, coupled to a reporter gene (CAT), revealed that in comparison to control chondrocytes, interleukin-1 treated cells showed a reduced level of CAT activity. These studies demonstrate that the inhibition of collagen type II synthesis by interleukin-1 is due to a reduction in the transcription of the type II collagen gene and that the reduction in gene transcription involves DNA regulatory sequences that determine type II collagen gene expression.

Animals↗
PubMed1990

Arthritis induced by interleukin-1 is dependent on the site and frequency of intraarticular injection.

Intraarticular injection of recombinant human interleukin-1 (IL-1) in rats resulted in varying degrees of inflammatory changes depending on the site and frequency of injections. (i) Much lower amounts of IL-1 were required to elicit an inflammatory response in the ankle joints (15-3000 ng) than the knee joints (90-150 micrograms). (ii) The inflammatory response was much greater if IL-1 was administered in multiple doses as compared to a single dose injection. One day after a single injection of IL-1 (90-150 micrograms), knee joints exhibited a mild increase in volume as a consequence of edema, but at the end of 1 week, no discernible change in volume was observed. However, when the same total amount of IL-1 was injected in three doses, there was a dramatic increase in joint volume at the end of 1 week that persisted for at least 3 weeks. The increase was dose dependent. (iii) The inflammatory response was dependent on the age/weight of the rats: the older the animals the greater the response. (iv) Under conditions where IL-1 induced inflammatory changes in knee joints, recombinant tumor necrosis factor failed to induce any significant response. (v) Histological examination of the knee joints revealed distinct differences in the pathological response to the two different protocols of IL-1 administration in the knee joints. The animals injected with a single dose of IL-1 showed a mild and transient inflammation that was resolved by 2 weeks postinjection, but exhibited degenerative changes associated with focal loss of chondrocytes and proteoglycan of the knee joint cartilage, which became progressively severe. The knee joints of animals given three injections of IL-1 showed evidence of marked acute synovitis, fibroplasia, loss of proteoglycan and chondrocytes, resorption of subchondral bone, and transition of hematopoeitic marrow cells into cells of mesenchymal morphology. (vi) Examination of proteoglycan synthesis by cartilage of IL-1-injected rats revealed that within 1 day after injection, a dramatic reduction in synthesis occurred which persisted for at least 2 weeks. These studies suggest that intraarticular injection of IL-1 provides a useful rodent model for the investigation of pathological changes occurring within a localized joint as a result of acute and chronic inflammatory stimuli. Relevant aspects of the pathology of joint erosion can be demonstrated depending on the frequency of IL-1 injection.

Aging↗
PubMed1990

Intracellular tubercle bacilli-alveolar macrophage lysosomal enzymes interaction in experimental tuberculosis.

This study is an attempt to understand the mechanism of macrophage activation and its effect on the microbicidal properties of the macrophage. Alveolar macrophages (AM) from normal and BCG-vaccinated guinea pigs were harvested at intervals of 1, 7, 14, 21, and 28 days. Half of the guinea pigs from each group were challenged intratracheally with Mycobacterium tuberculosis H37Rv. In AM, the levels of three lysosomal enzymes, beta-galactosidase (beta-gal), N-acetylglucosaminidase (N-ac), and lysozyme (lyso), were measured histochemically. The percentage of AM staining positively for these enzymes and the intensity of this staining were estimated as parameters of AM activation, along with the number of intracellular bacilli in these cells. Histochemical methods are preferred to biochemical methods as only the former indicate activation in individual cells. The enzymatic responses of AM depend on the type of vaccination and infection. Thus, beta-gal activity was significantly enhanced in immune animals whereas no such enhancement of activity was observed in the case of N-ac and lyso. The N-ac content was higher in infected animals and in the immune group, whereas lyso fluctuated at different time intervals after infection.

Acetylglucosaminidase↗
PubMed1990

Passive role of articular chondrocytes in quinolone-induced arthropathy in guinea pigs.

The role of articular chondrocytes and matrix degrading enzymes such as collagenase and neutral protease in the pathogenesis of quinolone-induced cartilage degeneration was investigated in immature guinea pigs. Articular cartilage from nalidixic acid (NA) treated guinea pigs was examined for the presence of protease activity or the ex vivo synthesis of collagenase at various times post-treatment. Histologic evaluation of knee joints confirmed the presence of degenerative changes in the matrix, but increased collagenase synthesis or protease activity were not detected. A separate group of animals was used to determine the importance of articular chondrocytes in the lesion generation. These cells were killed by intra-articular injection of the glycolysis inhibitor iodoacetic acid (IA) prior to treatment of the animals with NA. Typical "blister-like" their presence was not required for lesion development. Cartilage exposed to IA only did not exhibit "blister-like" lesions indicating that chondrocyte death and proteoglycan loss in conjunction with frictional forces associated with load-bearing were not sufficient to induce major matrical disruptive changes during the period of this study. These results indicate that articular chondrocytes are not actively involved in inducing the degenerative changes and provide no evidence for involvement of collagenase or neutral protease in the pathogenesis of the lesion.

Animals↗
PubMed1990

Extracellular enzymes of pulmonary fluid and their bactericidal effects on Mycobacterium tuberculosis.

The enzyme activity and bacillary content of cell free pulmonary lavage fluid has been compared in infected and immunized infected animals. Increased enzyme production was found as a result of macrophage activation. Marked decrease in the number of tubercle bacilli was observed in immunized infected animals. The active enzyme production is considered to be the impact of availability of enzyme specific substrate, particularly cell wall components of tubercle bacilli viz. arabinogalactan, arabinomannan and sulphatides. These macromolecules are considered as active substrates for the action of arabinosidase (EC:3.2.1.55), mannosidase (EC:3.2.1.24) and sulphatase-C (EC:3.1.6.1).

Animals↗
PubMed1989

Induction of interleukin-1 receptors on chondrocytes by fibroblast growth factor: a possible mechanism for modulation of interleukin-1 activity.

Interleukin-1 is a polypeptide factor with profound effects on several cell types, such as chondrocytes, fibroblasts, and T-cells. The ability of interleukin-1 to induce the synthesis of matrix-degradative enzymes, as well as prostaglandin E2, suggests a pivotal role for this mediator in chronic inflammation. Previous studies have shown that the effect of human monocyte interleukin-1 on the synthesis of collagenase and neutral proteases by chondrocytes was enhanced by basic fibroblast growth factor. Using recombinant human interleukin-1B, we have examined whether the potentiation of interleukin-1 effects by fibroblast growth factor is related to changes in the number or affinity of interleukin-1 receptors. Our studies confirm that rabbit articular chondrocytes in culture contain a single class of high-affinity receptors for interleukin-1 with a Ka of 0.9-1.1 x 10(-13) M-1. While the untreated chondrocytes contain approximately 1,620 receptors per cell, fibroblast growth factor-treated cells exhibit a higher number of receptors (approximately 2,960 per cell) with no apparent change in the affinity. The increase in receptor number can be abolished by inhibitors of lysosomal function, indicating a requirement for intracellular processing of the fibroblast growth factor. Our results suggest that the potentiation of interleukin-1 catabolic effects by fibroblast growth factor may be related to its ability to induce additional interleukin-1 receptors on the chondrocyte cell surface.

Animals↗