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Biomedical subjects

R A Greenwald

Publications and source records attributed to R A Greenwald.

At least 19 recordsLinked to original sources
PubMed1992

Tetracyclines inhibit intracellular muscle proteolysis in vitro.

Tetracycline antibiotics (TETs) have a recently discovered novel action: inhibition of extracellular metalloproteinase activity, especially that of collagenase and gelatinase. This property, now confirmed in 8 different laboratories using > 40 tissue sources, includes natural and semi-synthetic TETs as well as a chemically modified TET (CMT) devoid of antimicrobial activity. We have used 14C-Tyr biosynthetically labelled intracellular proteins in L-6 myoblast culture as a test system to assess intracellular proteolysis. Starvation accelerates proteolysis, which can be suppressed by agents such as insulin or serum. Minocycline, doxycycline, and CMT all retarded the rate of intracellular protein degradation in a dose dependent manner. These agents also demonstrated marked synergism with insulin. A CMT derivative (pyrazole) stripped of one of its metal chelation sites and lacking anti-collagenase activity, also lost its antiproteolytic effect. CMT at physiologic concentrations (< or = 5 micrograms/ml) had no effect on protein synthesis, but at 15 micrograms/ml (pharmacologic), a suppressive effect was noted. These findings demonstrate that TETs can inhibit protein degradation as well as synthesis in a mammalian muscle-derived cell line.

Animals↗
PubMed1992

Inhibition of enzymatic activity of phospholipases A2 by minocycline and doxycycline.

Extracellular phospholipases A2 play an important role in articular and extra-articular inflammatory processes. Secretory non-pancreatic phospholipase A2 (PLA2) has been implicated in the pathogenesis of articular inflammation in rheumatoid arthritis, whereas pancreatic PLA2 contributes to the tissue damage associated with acute pancreatitis. Since in experimental models lipophilic tetracyclines such as minocycline and doxycycline are antiinflammatory, we examined their effects on PLA2 activity using two assay systems in vitro. We found that minocycline and to a lesser degree doxycycline were markedly inhibitory to both pancreatic and non-pancreatic PLA2. Using [14C]oleic acid labeled Escherichia coli membrane phospholipids as substrate, the IC50 values for minocycline and doxycycline were 3.6 x 10(-5) M (18 micrograms/mL) and 0.98 x 10(-4) M (47 micrograms/mL), respectively. In a scooting mode assay using the synthetic phospholipid 1-palmitoyl-2-(10-pyrenedecanoyl)-3-L-phosphatidylmethanol as substrate, IC50 values for minocycline were 5 microM (2.47 micrograms/mL) for non-pancreatic PLA2 and 8 microM (3.95 micrograms/mL) for pancreatic PLA2. Addition of excess calcium up to 50 mM did not reverse the inhibitory activity of tetracyclines. We conclude that lipophilic tetracyclines inhibit PLA2, probably by interaction with the substrate, and may be a useful adjunct in the therapy of inflammatory conditions in which PLA2 is implicated pathogenetically.

Animals↗
PubMed1992

Tetracyclines suppress matrix metalloproteinase activity in adjuvant arthritis and in combination with flurbiprofen, ameliorate bone damage.

Tetracyclines are potent inhibitors of 2 major matrix metalloproteinases which have been implicated in connective tissue degradation: collagenase and Type IV collagenase/gelatinase. We directly identified these enzyme activities in extracts of inflamed paw tissue from rats with adjuvant arthritis. Oral tetracycline therapy suppressed metalloproteinase activity in arthritic tissue, but even very high doses failed to exhibit substantial antiinflammatory efficacy (reduced joint swelling and paw diameter). Flurbiprofen, a conventional nonsteroidal antiinflammatory drug, reduced inflammatory indices as expected. The combination of the 2 agents administered orally completely inhibited collagenase activity, significantly inhibited gelatinase activity and produced substantial normalization of radiographic joint damage, far greater than either drug alone. Tetracycline inhibition curves in vitro suggest that the collagenase in this tissue is not of fibroblast origin. Tetracycline derivatives might be useful adjuncts to prevention of tissue damage in chronic inflammatory arthritides.

Administration, Oral↗
PubMed1992

The philatelic rheumatologist.

Many postage stamps illustrate themes, persons, or topics with rheumatologic connections. Examples include scientists from related disciplines, victims of rheumatic diseases, drugs used for arthritis, and stamps commemorating events such as World Rheumatism Year. A brief orientation to postage stamps and philately is given, and a small collection of rheumatologically related stamps is illustrated.

Global Health↗
PubMed1991

Oxygen radicals, inflammation, and arthritis: pathophysiological considerations and implications for treatment.

A vast amount of circumstantial evidence implicates oxygen-derived free radicals, especially superoxide and hydroxyl radical (and to lesser extent, hydrogen peroxide), as mediators of inflammation and/or tissue destruction in inflammatory and arthritic disorders. The substrates for radical generation, namely properly stimulated phagocytic cells, transition metal catalysts, and (to a limited extent) ischemia, are all amply present, although there is no particular rheumatic disease in which a consistent abnormality of radical generation has been identified. These radical species can clearly degrade hyaluronic acid, modify collagen and perhaps proteoglycan structure and/or synthesis, alter and interact with immunoglobulins, activate enzymes and inactivate their inhibitors, and possibly participate in chemotaxis. In most situations, however, there is ample scavenging ability to detoxify these radicals before they hit their target, and many rheumatic disease drugs can decrease their production and/or effects. Despite the apparent sufficiency of natural scavengers and the lack of direct evidence that oxygen radicals are pathogenetically important, substantial pharmaceutical effort is still being made to develop free radical scavengers as therapeutic agents. Although individual free radicals die out quickly, rheumatologic interest in them has been sustained for nearly two decades.

Arthritis↗
PubMed1991

Tetracyclines inhibit connective tissue breakdown: new therapeutic implications for an old family of drugs.

Tetracyclines have long been considered useful adjuncts in peridontal therapy based on their antimicrobial efficacy against putative periodontopathogens. However, recently these drugs were found to inhibit mammalian collagenases and several other matrix metalloproteinases (MMPs) by a mechanism independent of their antimicrobial activity. Evidence is presented that this property may be therapeutically useful in retarding pathologic connective tissue breakdown, including bone resorption. The experiments leading to this discovery are described and possible mechanisms are addressed, including the specificity of tetracyclines' anti-collagenase activity, the role of the drugs' metal ion (Zn2+, Ca2+)-binding capacity, and the site on the tetracycline molecule responsible for this nonantimicrobial property. Of extreme interest, the tetracycline molecule has been chemically modified in multiple ways, generating a new family of compounds called CMTs (chemically modified tetracyclines) that lack antimicrobial but still retain anti-collagenase activity. The first of these CMTs, 4-de-di-methylaminotetracycline, was found not to produce a major side-effect of antimicrobial tetracycline therapy--its administration to experimental animals did not result in the emergence of tetracycline-resistant microorganisms in the oral flora and gut. Numerous examples of the clinical potential of this non-antimicrobial property of tetracyclines in the treatment of periodontal and several medical diseases (e.g., sterile corneal ulcers, rheumatoid arthritis, skin bullous lesions, tumor-induced angiogenesis and metastasis) are discussed.

Animals↗
PubMed1991

Therapeutic usages of oxygen radical scavengers in human diseases: myths and realities.

Some distinct advances in pharmacologic manipulation of oxygen radical scavengers have been made which could ultimately greatly enhance the use of these reagents as drugs, as well as some innovative techniques for drug delivery. Unfortunately, most of the therapeutic reports in the literature, almost all of which are based on usage of standard (native) SOD and/or catalase, are still anecdotal and/or uncontrolled. A review of the human disease/treatment literature suggests that further tightening of the scientific design of such trials is still badly needed; hopefully better experimental design will be applied when products such as PEG conjugates or genetically engineered polymers are ready for testing.

Animals↗
PubMed1990

Superoxide dismutase and catalase as therapeutic agents for human diseases. A critical review.

The list of human and animal diseases for which oxygen radical scavenging therapy is being recommended continues to grow, based primarily on inferential evidence suggesting a potential role for oxygen-derived free radicals in various types of pathophysiology. Some distinct advances in pharmacologic manipulation of protein scavengers have been made which could ultimately greatly enhance the use of these reagents as drugs, as well as some innovative techniques for drug delivery (direct injection via endoscopy, iontophoresis). Unfortunately, most of the therapeutic reports in the literature, almost all of which are based on usage of standard (native) SOD and/or catalase, are still anecdotal and/or uncontrolled. A review of the human disease/treatment literature suggests that further tightening of the scientific design of such trials is still badly needed; hopefully better experimental design will be applied when products such as PEG conjugates or genetically engineered polymers are ready for testing.

Catalase↗
PubMed1989

Conversion of superoxide generated by polymorphonuclear leukocytes to hydroxyl radical: a direct spectrophotometric detection system based on degradation of deoxyribose.

Hydroxyl radical is produced secondarily after phagocytic cells have been stimulated to generate superoxide anion. The systems used most commonly for detection of cell-generated hydroxyl radical are often inconvenient for routine biomedical research. We have modified an assay used heretofore in cell-free systems, that is, the degradation of deoxyribose, and adapted it for use with neutrophils. The time and dose responses of the system, requirement for chelated iron, inhibition profiles with various scavengers, and correlation with superoxide production have been ascertained. The method correlated strongly with a standard but more cumbersome technique. Values for a normal population are provided. The method can readily be used to study the parameters of superoxide-hydroxyl radical conversion by cells in various disease or treatment states.

Deoxyribose↗
PubMed1988

Inhibition of epiphyseal cartilage collagenase by tetracyclines in low phosphate rickets in rats.

Drugs in the tetracycline family can inhibit mammalian tissue collagenase both in vitro and in vivo by a mechanism that is independent of antibiotic action. The epiphyseal cartilages of rachitic rats contain extremely high levels of collagenase (CGase), and we have used this model to study further the phenomenon of tetracycline inhibition of tissue CGase. Rickets was induced in rats by phosphate/vitamin D deficiency and parameters of gross bone morphology, bone chemistry, and serum chemistry were evaluated in both rachitic and nonrachitic animals with and without treatment with oral tetracyclines (TETs). Minocycline (or doxycycline) partially suppressed the appearance of many of the expected changes in the rachitic animals, including gross bone hardness, growth plate widening, long bone length, suppression of weight gain, and decreased bone ash content. The effects were dose dependent and were associated with marked suppression of the enhanced CGase activity. Examination of collagen breakdown products by SDS-PAGE documented that the rachitic enzyme behaved like other mammalian collagenases including in vitro inhibition with minocycline 10-20 micrograms/ml and with a nonantibiotic tetracycline. No evidence of TET osseous toxicity was noted, and, in fact, administration of TET to nonrachitic animals had a mildly favorable effect on growth and development. TET suppression of CGase can be demonstrated in a well defined model system and this form of pharmacologic enzyme inhibition can be a useful probe for delineating the role of the enzyme in connective tissue pathology.

Animals↗
PubMed1988

Degradation of hyaluronic acid by neutrophil derived oxygen radicals is stimulus dependent.

A disparity has been noted between the flux of superoxide generated by neutrophils and the effects of those radicals on a typical macromolecular substrate, hyaluronic acid (HA). To further investigate this phenomenon, comparative degradation studies were conducted using phorbol myristate acetate (PMA), which caused neutrophils to readily degrade HA, and digitonin, a stimulus which, like PMA, produced a sustained superoxide flux but which did not affect HA. The differential effects of the 2 stimuli could be related to concomitant release of peroxidase activity. The implications of this mechanism for in vivo oxygen radical effects are discussed.

Digitonin↗
PubMed1987

A non-antibacterial chemically-modified tetracycline inhibits mammalian collagenase activity.

Tetracyclines (including the semi-synthetic analogues, minocycline and doxycycline) are considered useful adjuncts in periodontal therapy because they suppress Gram-negative periodontopathogens. Recently, these antibiotics were found to inhibit mammalian collagenase activity, a property which may also be of therapeutic value. It has been suggested that the anti-collagenase properties of the tetracyclines are independent of their antibiotic efficacy. To advance this hypothesis further, we chemically converted tetracycline hydrochloride to its non-antimicrobial analogue, de-dimethylaminotetracycline. This chemically-modified tetracycline (CMT), although no longer an effective antibiotic, was found to inhibit the in vitro activity of collagenase from partially purified extracts of human rheumatoid synovial tissue and rachitic rat epiphysis. In a preliminary in vivo study, pathologically-excessive collagenase in skin and gingiva was induced by rendering adult male rats diabetic, and the oral administration of CMT to these rats significantly reduced the excessive collagenase activity in both tissues. Moreover, CMT administration did not affect the severe hyperglycemia in these rats but did prevent, at least in part, the diabetes-induced loss of body weight, skin weight, and skin collagen mass; these effects suggest a lack of toxicity in this animal model. A proposed clinical advantage of CMT over conventional tetracyclines, in the treatment of diseases characterized by excessive collagenolytic activity, is the lack of development of antibiotic-resistant micro-organisms during prolonged use. However, the consideration of clinical trials to support this hypothesis must await further laboratory and extensive toxicity tests.

Animals↗