Doxycycline inhibits type X collagen synthesis in avian hypertrophic chondrocyte cultures

Advances in biomimetic regeneration of elastic matrix structures

Elastin is a vital component of the extracellular matrix, providing soft connective tissues with the property of elastic recoil following deformation and regulating the cellular response via biomechanical transduction to maintain tissue homeostasis. The limited ability of most adult cells to synthesize elastin precursors and assemble them into mature crosslinked structures has hindered the development of functional tissue-engineered constructs that exhibit the structure and biomechanics of normal native elastic tissues in the body. In diseased tissues, the chronic overexpression of proteolytic enzymes can cause significant matrix degradation, to further limit the accumulation and quality (e.g., fiber formation) of newly deposited elastic matrix. This review provides an overview of the role and importance of elastin and elastic matrix in soft tissues, the challenges to elastic matrix generation in vitro and to regenerative elastic matrix repair in vivo, current biomolecular strategies to enhance elastin deposition and matrix assembly, and the need to concurrently inhibit proteolytic matrix disruption for improving the quantity and quality of elastogenesis. The review further presents biomaterial-based options using scaffolds and nanocarriers for spatio-temporal control over the presentation and release of these biomolecules, to enable biomimetic assembly of clinically relevant native elastic matrix-like superstructures. Finally, this review provides an overview of recent advances and prospects for the application of these strategies to regenerating tissue-type specific elastic matrix structures and superstructures.

Inhibitory action of minocycline on lipopolysaccharide-induced release of nitric oxide and prostaglandin E2 in BV2 microglial cells

Microglia are the major inflammatory cells in the central nervous system and become activated in response to brain injuries such as ischemia, trauma, and neurodegenerative diseases including Alzheimer's disease (AD). Moreover, activated microglia are known to release a variety of proinflammatory cytokines and oxidants such as nitric oxide (NO). Minocycline is a semisynthetic second-generation tetracycline that exerts anti-inflammatory effects that are completely distinct form its antimicrobial action. In this study, the inhibitory effects of minocycline on NO and prostaglandin E2 (PGE2) release was examined in lipopolysaccharides (LPS)-challenged BV2 murine microglial cells. Further, effects of minocycline on inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2) expression levels were also determined. The results showed that minocycline significantly inhibited NO and PGE2 production and iNOS and COX-2 expression in BV2 microglial cells. These findings suggest that minocycline should be evaluated as potential therapeutic agent for various pathological conditions due to the excessive activation of microglia.

A nonantibiotic chemically modified tetracycline (CMT-3) inhibits intimal thickening

Recent research has shown that the tetracycline antibiotics are pluripotent drugs that inhibit the activity of matrix metalloproteinases (MMPs) and affect many cellular functions including proliferation, migration, and matrix remodeling. We have shown that doxycycline inhibits MMP activity and intimal thickening after injury of the rat carotid artery, however we do not know whether these effects are because of the antibiotic, anti-MMP, or other actions of doxycycline. Recently, chemically modified tetracyclines have been synthesized that lack antibiotic activity but retain anti-MMP activity (CMT-3), or lack both antibiotic and anti-MMP activity (CMT-5). In the current study we have assessed the effects of treatment with CMT-3 or CMT-5 on intimal thickening after balloon catheter injury of the rat carotid artery. Rats were treated by oral gavage with 15 mg/kg/day CMT-3 or CMT-5. CMT-3 significantly reduced smooth muscle cell (SMC) proliferation in both the medial and intimal layers of the injured rat carotid artery compared to CMT-5. Furthermore, CMT-3 inhibited SMC migration from the media to the intima by 86% at 4 days after injury. CMT-3 also decreased MMP-2 activity. Finally, we found that CMT-3 treatment resulted in a significant reduction in intimal cross-sectional area from 0.23 +/- 0.01 mm(2) in the CMT-5 control group to 0.19 +/- 0.01 mm(2). There was also a reduction in elastin and collagen accumulation within the intima. We conclude that CMT-3 attenuated intimal thickening after arterial injury by inhibiting SMC proliferation, migration and MMP activity, and accumulation of extracellular matrix. The inhibitory effects of CMT-3 were independent of the antibiotic properties, but were dependent on the anti-MMP activity of the tetracycline family.

Proteolysis involving matrix metalloproteinase 13 (collagenase-3) is required for chondrocyte differentiation that is associated with matrix mineralization

Collagenases are involved in cartilage matrix resorption. Using bovine fetal chondrocytes isolated from physeal cartilages and separated into a distinct prehypertrophic subpopulation, we show that in serum-free culture they elaborate an extracellular matrix and differentiate into hypertrophic chondrocytes. This is characterized by expression of type X collagen and the transcription factor Cbfal and increased incorporation of 45Ca2+ in the extracellular matrix, which is associated with matrix calcification. Collagenase activity, attributable only to matrix metalloproteinase (MMP) 13 (collagenase-3), is up-regulated on differentiation. A nontoxic carboxylate inhibitor of MMP-13 prevents this differentiation; it suppresses expression of type X collagen, Cbfal, and MMP-13 and inhibits increased calcium incorporation in addition to inhibiting degradation of type II collagen in the extracellular matrix. General synthesis of matrix proteins is unaffected. These results suggest that proteolysis involving MMP-13 is required for chondrocyte differentiation that occurs as part of growth plate development and which is associated with matrix mineralization.

Doxycycline modulates smooth muscle cell growth, migration, and matrix remodeling after arterial injury

The tetracyclines function as antibiotics by inhibiting bacterial protein synthesis, but recent work has shown that they are pluripotent drugs that affect many mammalian cell functions including proliferation, migration, apoptosis, and matrix remodeling. Because all of these processes have been implicated in arterial intimal lesion development, the objective of these studies was to examine the effect of doxycycline treatment using a well-characterized model of neointimal thickening, balloon catheter denudation of the rat carotid artery. Rats were treated with 30-mg/kg/day doxycycline. Doxycycline reduced the activity of matrix metalloproteinase (MMP)-2 and MMP-9 in the arterial wall, and inhibited smooth muscle cell migration from media to intima by 77% at 4 days after balloon injury. Replication of smooth muscle cells in the intima at 7 days was reduced from 28.3 plus minus 2.5% in controls to 17.0 +/- 2.8% in doxycycline-treated rats. The synthesis of elastin and collagen was not affected, but accumulation of elastin was blocked in the doxycycline-treated rats. By contrast, collagen accumulation was not affected, which led to the formation of a more collagen-rich intima. At 28 days after injury, the intimal:medial ratio was significantly reduced from 1.67 +/- 0.09 in control rats to 1.36 +/- 0.06 in the doxycycline-treated rats. This study shows that doxycycline is an effective inhibitor of cell proliferation, migration, and MMP activity in vivo. Further study in more complicated models of atherosclerosis and restenosis is warranted.

Doxycycline-induced inhibition of prolidase activity in human skin fibroblasts and its involvement in impaired collagen biosynthesis

Several lines of evidence suggest that doxycycline, a semi-synthetic derivative of tetracycline, may be a useful agent in the treatment of osteoarthritis. It inhibits collagen synthesis and collagenase activity in hypertrophic chondrocytes, slowing the process of collagen turnover. However, the mechanism of doxycycline-induced inhibition of these processes has not been established. We considered prolidase, an enzyme involved in collagen metabolism, as a possible target for the doxycycline-induced inhibition of collagen synthesis. Cultured human skin fibroblasts, specialized for collagen synthesis, were used as model cells. Prolidase [E.C. 3.4.13.9] is a manganese-dependent cytosolic exopeptidase that cleaves imidodipeptides containing C-terminal proline, thus providing large amounts of proline for collagen resynthesis. Enzyme activity is regulated through the beta1 integrin receptor. Therefore, we compared the effect of doxycycline on prolidase activity and expression, collagen biosynthesis, gelatinolytic activity and beta1 integrin expression in 24-h treated cultured human skin fibroblasts. We found that doxycycline induced coordinately inhibition of prolidase activity and collagen biosynthesis (IC50 at about 150 microg/ml) and gelatinolytic activity in cultured human skin fibroblasts. The inhibitory effect of doxycycline on the processes was not due to the cytotoxicity of this drug, as shown in the cell viability tetrazoline test. However, an inhibitory effect of the drug on DNA synthesis was observed (IC50 at about 100 microg/ml). The decrease in prolidase activity in fibroblasts treated with doxycycline was not accompanied by any differences in the amount of prolidase or beta1 integrin recovered from these cells, as shown by Western immunoblot analysis. This suggests that the doxycycline-induced down-regulation of prolidase is a post-translational event. The data presented here raise the possibility that the doxycycline-induced decrease in collagen biosynthesis is mostly due to the inhibition of prolidase activity.

Specificity of inhibition of matrix metalloproteinase activity by doxycycline: relationship to structure of the enzyme

OBJECTIVE

To investigate the inhibition of matrix metalloproteinase 1 (MMP-1), MMP-8, and MMP-13 by doxycycline, and to determine whether the variable hemopexin-like domain of each MMP was responsible for the differences in susceptibility to doxycycline inhibition among these collagenases.

METHODS

Recombinant human MMP-1 (collagenase 1), MMP-8 (collagenase 2), and MMP-13 (collagenase 3), truncated forms of MMP-8 and MMP-13 lacking the hemopexin-like domain, and a mutant form of truncated MMP-13 were used in these studies. The activity of the full-length MMP in the presence of doxycycline was tested against type II collagen, a natural substrate for the enzymes. A small peptolide substrate was used to determine which structural features of the MMPs were related to sensitivity to doxycycline inhibition.

RESULTS

The activity of MMP-13 and MMP-8 against type II collagen was inhibited by 50-60% by 30 microM doxycycline, while that of MMP-1 was inhibited only 18% by 50 microM doxycycline. In contrast, in experiments with the peptolide substrate, neither full-length nor truncated MMP-13 was inhibited until the concentration of the drug exceeded 90 microM. MMP-8 and truncated MMP-8 were sensitive to inhibition by 30 microM doxycycline, while MMP-1 was slightly inhibited (14%) by 90 microM doxycycline. For MMP-8, inhibition was reversible upon dilution and was independent of the order in which the reagents were added. Kinetic analysis of the inhibition constant (K(i)) of MMP-8 (K(i) = 36 microM) and truncated MMP-8 (K(i) = 77 microM) indicated that inhibition was noncompetitive.

CONCLUSION

Significant inhibition of MMP-13 and MMP-8 activity against collagen occurred in vitro at concentrations that were near the concentrations achieved in serum after oral dosing. Studies with truncated enzymes and 2 substrates suggest that doxycycline disrupts the conformation of the hemopexin-like domain of MMP-13 and the catalytic domain of MMP-8.

Doxycycline inhibits collagen synthesis by differentiated articular chondrocytes

Doxycycline (DOX) profoundly inhibited collagen synthesis by differentiated articular chondrocytes. At 25 microM, the rate of collagen synthesis was suppressed by more than 50% without affecting cell proliferation (DNA levels) and general protein synthesis (35S-Met and 35S-Cys incorporation). Steady-state mRNA levels of type II collagen were also reduced, indicating that DOX may have an effect at the transcriptional level of type II collagen. The IC50 value of DOX to downregulate collagen synthesis (17 microM) is close to DOX levels attained in vivo (< 10 microM), and it is more than ten-fold lower than the IC50 values to inhibit the activity of most matrix metalloproteinases (MMPs). As such, these findings support the hypothesis that the reduced severity of OA observed in the dog anterior cruciate ligament model resulting from prophylactic treatment with DOX may involve mechanisms other than MMP inhibition alone. Our findings suggest that prevention of changes in the chondrocyte phenotype may be involved in the beneficial effect of doxycycline in experimental osteoarthritis, for differentiated chondrocytes in early stages of osteoarthritis exhibit elevated collagen synthesis.

Tetracycline derivatives inhibit cartilage degradation in cultured embryonic chick tibiae

Tetracyclines have been used extensively as antibiotics and growth promoters in the poultry industry. However, they can inhibit angiogenesis and matrix degradation, both of which are essential for normal growth plate cartilage development. The purpose of this research was to test the ability of several tetracyclines to inhibit cartilage degradation in cultured embryonic chick tibiae. Based on gross observations and biochemical quantitation of collagen release into the media, minocycline, doxycycline, oxytetracycline, and tetracycline inhibited cartilage degradation at 20, 40, 60, and 80 micrograms ml-1 respectively. Chlortetracycline did not inhibit cartilage degradation at concentrations tested. The ability of the tetracycline derivative to inhibit cartilage degradation was in general related to its hydrophobicity. Since a majority of the cartilage in the embryonic chick tibia will develop into the post hatched growth plate, it may be important to determine if any of the tetracyclines used as antibiotics could cause problems in in vivo growth plate cartilage development.