Stimulation of bone collagen and non-collagenous protein synthesis by products of 5- and 12-lipoxygenase: determination by use of a simple quantitative assay

Matrix stiffness regulates bone repair by modulating 12-lipoxygenase-mediated early inflammation

Lipid metabolism in macrophages has been increasingly emphasized in exerting an anti-inflammatory effect and accelerating fracture healing. 12-lipoxygenase (12-LOX) is expressed in several cell types, including macrophages, and oxidizes polyunsaturated fatty acids (PUFAs) to generate both pro- and anti-inflammatory lipid mediators, of which the n-3 PUFAs play an important part in tissue homeostasis/fibrosis. Although mechanical factor regulates the lipid metabolic axis of inflammatory cells, specifically matrix stiffness influences macrophages metabolic responses, little is known about how matrix stiffness affects the 12-LOX-mediated early inflammation in bone repair. In the present study, demineralized bone matrix (DBM) scaffolds with different matrix stiffness were constructed by controlling the duration of decalcification (0 h (control), 1 h (high), 12 h (medium), and 5 d (low)) to repair the defected rat skull. The expression of inflammatory cytokines and macrophages polarization were analyzed. The lipid metabolites and lipid mediators' biosynthesis by matrix stiffness-regulated were further detected. The results showed that the low matrix stiffness could polarize macrophages into an anti-inflammatory phenotype, promote the expression of anti-inflammatory cytokines and specialized pro-resolving lipid mediators (SPMs) biosynthesis beneficial for the osteogenesis of mesenchymal stem cells (MSCs). After treated with ML355, the expression of anti-inflammatory cytokines/proteins and SPMs biosynthesis in macrophages cultured on low-matrix stiffness scaffolds were repressed, and there were almost no statistical differences among all groups. Findings from this study support that matrix stiffness regulates bone repair by modulating 12-LOX-mediated early inflammation, which suggest a direct mechanical impact of matrix stiffness on macrophages lipid metabolism and provide a new insight into the clinical application of SPMs for bone regeneration.

Retinoic acids exhibit anti-fibrotic activity through the inhibition of 5-lipoxygenase expression in scleroderma fibroblasts

The pathogenesis of systemic sclerosis (SSc) is not fully understood and there is no effective treatment for this disease. Retinoic acid (RA) can modulate connective tissue metabolism, exhibit anti-fibrotic activity, and improve the clinical symptoms of SSc. However, the mechanisms by which RA elicits its anti-fibrotic actions remain to be determined. The aim of this study was to elucidate the underlying mechanisms by which RA exerts beneficial effects on scleroderma. Cultured skin fibroblasts from patients with scleroderma were treated with RA and their effect on the expression of 5-lipoxygenase (LOX), transforming growth factor (TGF)-β1, connective tissue growth factor (CTGF), type I and type III collagen was tested by reverse transcription polymerase chain reaction (RT-PCR) and western immunoblotting. The effect of MK886, a 5-LOX-specific inhibitor, on the expression of TGF-β1, CTGF, type I and type III collagen was also examined by RT-PCR. In cultured scleroderma fibroblasts, the expression of 5-LOX was elevated compared with normal human dermal fibroblasts. RA significantly inhibited the expression of 5-LOX and of TGF-β1, CTGF, type I and type III collagen. We further found that the expression of TGF-β1, CTGF and type I and type III collagen mRNA was inhibited by MK886 in scleroderma fibroblasts. In vitro, RA reduced 5-LOX expression in scleroderma fibroblasts and downregulated TGF-β1 and CTGF expression, leading to the inhibition of type I and type III collagen synthesis. Our results indicate that the clinical effects of RA on scleroderma are, at least in part, attributable to the reduction of 5-LOX expression and the subsequent suppression of TGF-β1 and CTGF expression that results in the blockade of collagenogenesis.

Cartilage-derived biomarkers and lipid mediators of inflammation in horses with osteochondritis dissecans of the distal intermediate ridge of the tibia

OBJECTIVE

To assess whether reported alterations in metabolism of cartilage matrix in young (0 to 24 months old) horses with osteochondritis dissecans (OCD) may also be found in older (24 to 48 months old) horses with clinical signs of OCD and to investigate the role of eicosanoids in initiating these clinical signs.

SAMPLE POPULATION

Synovial fluid was collected from 38 tarsocrural joints of 24 warmblood horses with (22 joints of 16 horses) or without (16 joints of 8 horses) clinical signs and a radiographic diagnosis of OCD of the distal intermediate ridge of the tibia.

PROCEDURES

Turnover of type II collagen was investigated by use of specific immunoassays for synthesis (carboxypropeptide of type II collagen [CPII]) and degradation (collagenase-cleaved fragments of type II collagen [C2C]) products. Furthermore, glycosaminoglycan (GAG), leukotriene (LT) B(4), cysteinyl LTs, and prostaglandin (PG) E(2) concentrations were determined, and concentrations in joints with OCD were compared with those in joints without OCD.

RESULTS

Concentrations of CPII, C2C, and GAG did not differ significantly between affected and nonaffected joints. Fluid from joints with OCD had significantly higher LTB(4) and PGE(2) concentrations than did fluids from nonaffected joints.

CONCLUSIONS AND CLINICAL RELEVANCE

Altered collagen or proteoglycan turnover was not detected in 24- to 48-month-old horses at the time they developed clinical signs of OCD of the distal intermediate ridge of the tibia. However, increased concentrations of LTB(4) and PGE(2) in fluid of joints with OCD implicate these mediators in the initiation of clinical signs of OCD.

Elevated levels of leukotriene B4 and leukotriene E4 in bronchoalveolar lavage fluid from patients with scleroderma lung disease

OBJECTIVE

The leukotrienes are a family of arachidonic acid-derived lipid mediators with proinflammatory and profibrotic properties. The aim of this study was to analyze the role of leukotriene B(4) (LTB(4)) and LTE(4) in the pathogenesis of scleroderma lung disease (SLD).

METHODS

Nineteen systemic sclerosis (SSc) patients with SLD, 11 SSc patients without SLD, and 10 healthy controls were studied. Bronchoalveolar lavage (BAL) fluid was obtained during routine bronchoscopy of the right middle lobe in all study subjects. Levels of LTB(4) and LTE(4) were measured using enzyme immunoassay kits.

RESULTS

Levels of LTB(4) and LTE(4) were significantly higher in SSc patients with SLD (251 +/- 170 pg/ml and 479 +/- 301 pg/ml, respectively), than those in patients without SLD (114 +/- 86 and 159 +/- 149 pg/ml) and those in normal controls (86 +/- 49 and 110 +/- 67 pg/ml). In the total group of patients with SSc, levels of both leukotrienes correlated positively with the total number of cells in the BAL fluid and correlated negatively with the forced vital capacity. After intravenous pulse therapy with cyclophosphamide in 6 patients, there was a significant reduction in the concentration of LTB(4) (from 380 +/- 196 pg/ml to 155 +/- 123 pg/ml) but no significant difference in the levels of LTE(4) (from 697 +/- 325 pg/ml to 418 +/- 140 pg/ml).

CONCLUSION

Our findings show that LTB(4) and LTE(4) levels are elevated in SSc patients with SLD and correlate with parameters of inflammation in the lungs. These results indicate that leukotrienes may contribute to the pathogenesis of SLD and may represent a new therapeutic target.

Roles of cysteinyl leukotrienes in airway inflammation, smooth muscle function, and remodeling

A new paradigm for asthma pathogenesis is presented in which exaggerated inflammation and remodeling in the airways are a consequence of abnormal injury and repair responses arising from a subject's susceptibility to components of the inhaled environment. An epithelial-mesenchymal trophic unit becomes activated to drive pathologic remodeling and smooth muscle proliferation through complex cytokine interactions. Histamine, prostanoids, and cysteinyl leukotrienes (CysLTs) are potent contractile agonists of airway smooth muscle (ASM). The CysLTs appear to play a central role in regulating human ASM motor tone and phenotypic alterations, manifested as hypertrophy and hyperplasia in chronic severe asthma. The CysLTs augment growth factor-induced ASM mitogenesis through activation of CysLT receptors. Although they mediate their contractile effects by increasing phosphoinositide turnover and inducing increased cytosolic calcium, new data suggest that part of the contractile effect may be independent of calcium mobilization. Prostaglandin E(2), the predominant eicosanoid product of the airway epithelium, is a potent inhibitor of mitogenesis, collagen synthesis, and mesenchymal cell chemotaxis and therefore can suppress inflammation and fibroblast activation. The capacity of the epithelium for CysLT synthesis is inversely related to its ability to make PGE(2). The ASM is capable of expressing both leukotriene-synthesizing enzymes and CysLT receptors, and cytokines upregulate the receptor expression. This may be an explanation for the CysLTs promoting airway hyperresponsiveness in asthma. The CysLTs play an important role in the airway remodeling seen in persistent asthma that includes increases of airway goblet cells, mucus, blood vessels, smooth muscle, myofibroblasts, and airway fibrosis. Evidence from a mouse model of asthma demonstrated that CysLT(1) receptor antagonists inhibit the airway remodeling processes, including eosinophil trafficking to the lungs, eosinophil degranulation, T(H)2 cytokine release, mucus gland hyperplasia, mucus hypersecretion, smooth muscle cell hyperplasia, collagen deposition, and lung fibrosis.

Therapeutic ultrasound for osteoradionecrosis: an in vitro comparison between 1 MHz and 45 kHz machines

Mandibular osteoradionecrosis is a serious chronic complication which may follow radiotherapy. Therapeutic ultrasound is a highly effective, inexpensive and readily available means of promoting revascularisation and healing. 'Long wave' ultrasound increases penetration depth and, therefore, seems to be more appropriate than traditional high frequency ultrasound. The aim of this study was to compare a new treatment using 45 kHz with the current standard 1 MHz machine. A traditional 1 MHz machine, pulsed 1:4, at intensities of 0.1, 0.4, 0.7 and 1.0 W/cm2(SAPA) was compared with a long wave machine, 45 kHz, at intensities of 5, 15, 30 and 50 mW/cm2(SA). The ultrasound was applied to human gingival fibroblasts and mandibular osteoblasts in vitro. Cell proliferation (DNA synthesis) and collagen and non-collagenous protein synthesis assays were performed, using radiolabelled thymidine and proline, respectively. Controls were sham-insonated and all readings were given as a percentage of controls. Fibroblast proliferation increased by 47% at 0.7 W/cm2 (1 MHz) and by 43% at 50 mW/cm2 (45 kHz), and osteoblast proliferation increased by 52% at 1.0 W/cm2 (1 MHz), and by 35% at 30 mW/cm2 (45 kHz). Fibroblast collagen production increased by 48% at 0.1 W/cm2 (1 MHz), and by 44% at 15 mW/cm2 (45 kHz) and osteoblast collagen production increased by 55% at 0.1 W/cm2 (1 MHz) and by 112% at 30 mW/cm2 (45 kHz). Long wave ultrasound was, therefore, capable of inducing a comparable or even higher enhancement of bone formation compared with traditional ultrasound, which, with its greater penetration, may accelerate the healing effect of ultrasound on osteoradionecrosis. The suggested intensity for 45 kHz ultrasound is 30 mW/cm2.

Effects of LTD4 on human airway smooth muscle cell proliferation, matrix expression, and contraction In vitro: differential sensitivity to cysteinyl leukotriene receptor antagonists

The cysteinyl leukotrienes (CysLTs) mimic many of the features of asthma and are implicated in its pathophysiology. Little, however, is known about the effects of the CysLTs on airways remodeling. In this study the effects of leukotriene D4 (LTD4) on human airway smooth muscle (HASM) cell proliferation and expression of extracellular matrix proteins were investigated. LTD4 (0.1-10 microM) alone had no effect on DNA synthesis in HASM. LTD4, however, markedly augmented proliferation induced by the mitogen, epidermal growth factor (EGF, 1 ng/ml). The potentiating effect of LTD4 (1 microM) on EGF-induced DNA synthesis was abolished by pranlukast (1 microM) or pobilukast (30 microM), but unaffected by zafirlukast (1 microM). In contrast, pranlukast (pKB = 6.9), pobilukast (pKB = 7.0), and zafirlukast (pKB = 6.5) had equivalent potencies for inhibition of LTD4-induced contraction in human bronchus. LTD4 (0.1 or 10 microM) did not increase the total messenger RNA expression of the extracellular matrix proteins (pro-alpha[I] type I or alpha1[IV] type IV collagen), elastin, biglycan, decorin, and fibronectin, and did not influence tumor growth factor-beta (10 ng/ml)-induced effects on the expression of these proteins in HASM cells. These data indicate that LTD4 augments growth factor-induced HASM proliferation but does not alter the expression of various extracellular matrix components. The observed differences in sensitivity to the antagonists suggests that the former phenomenon may be mediated by a CysLT receptor distinct from that which mediates LTD4-induced HASM contraction. Collectively, these results provide preliminary evidence that CysLTs may play a role in airways remodeling in asthma.

Enhancement by sex hormones of the osteoregulatory effects of mechanical loading and prostaglandins in explants of rat ulnae

Explants of ulnae from 5-week-old male and female rats were cleaned of marrow and soft tissue and, in the presence and absence of 10(-8) M 17 beta-estradiol (E2) or 5 alpha-dihydrotestosterone (DHT), mechanically loaded or treated with exogenous prostanoids previously shown to be produced during loading. Over an 18-h period, mechanical loading (peak strain 1300 mu epsilon, 1 Hz, 8 minutes, maximum strain rate 25,000 mu epsilon/s), prostaglandin E2 (PGE2) and prostacyclin (PGI2) (10(-6) M), each separately produced quantitatively similar increases in cell proliferation and matrix production in bones from males and females, as indicated by incorporation of [3H]thymidine into DNA and [3H]proline into collagen. E2 and DHT both increased [3H]thymidine and [3H]proline incorporations, E2 producing greater increases in females than in males. Indomethacin abrogated the effects of loading, but had no effects on those of sex hormones. Loading, or prostanoids, together with sex hormones, produced responses generally equal to or greater than the addition of the individual influences acting independently. In females there was a synergistic response in [3H]thymidine incorporation between loading and E2, which was quantitatively similar to the interaction between E2 and PGE2 or PGI2. The interaction between loading and E2 for [3H]proline incorporation was not mimicked by these prostanoids. In males the synergism in [3H]proline incorporation seen between loading and DHT was mimicked by that between PGI2 and DHT. We conclude that loading stimulates increased bone cell proliferation and matrix production in situ through a prostanoid-dependent mechanism. This response is equal in size in males and females. Estrogen and testosterone increase proliferation and matrix production through a mechanism independent of prostanoid production. The interactions between loading and hormones are reproduced in some but not all cases by E2 and prostaglandins. E2 with loading and prostaglandins has greater effects in female bones, while DHT with loading and prostaglandins has greater effects in males.

The stimulation of bone formation in vitro by therapeutic ultrasound

A controlled study was performed to evaluate the effects of different ultrasound (US) intensities on 5-day-old mouse calvaria bone in tissue culture. A special technique to apply the US was developed, and the following parameters were measured: collagen and noncollagenous protein (NCP) synthesis (bone formation), and temperature change. It was found that ultrasound at 0.1 W/cm2 (SATA), pulsed 1:4, 3 MHz, 5 min, significantly stimulates bone formation (i.e., the synthesis of collagen and NCP) (p < 0.001 and p < 0.01). However, pulsed ultrasound at higher doses (1.0-2.0 W/cm2 (SATA), pulsed 1:4, 3 MHz, 5 min) significantly inhibited the synthesis of both collagen and NCP (p < 0.05). The temperature measurements showed a maximum rise of 1.8 degrees C [at 2.0 W/cm2 (SATA)] and no detected rise at 0.1 W/cm2 (SATA), suggesting that the effects in this study were primarily nonthermal. These results may reflect the healing effect of US on fractures and osteoradionecrosis and reinforces the use of low intensity US regimens [0.1 W/cm2 (SATA)] in clinical practice.

Mechanical loading and sex hormone interactions in organ cultures of rat ulna

The separate and combined effects of loading and 17 beta-estradiol (E2) or 5 alpha-dihydrotestosterone (DHT) on [3H]thymidine and [3H]proline incorporation were investigated in cultured ulna shafts from male and female rats. Ulnae were cultured and loaded to produce physiological strains in the presence or absence of 10(-8) M E2 or DHT. Loading engendered similar increases in incorporation of [3H]thymidine and [3H]proline in male and female bones. E2 engendered greater increases in incorporation in females than in males, and DHT greater increases in males than in females. In males E2 with loading produced increases in both [3H]thymidine and [3H]proline incorporation, which approximated to the arithmetic addition of the increases due to E2 and loading separately. In females E2 with loading produced increases greater than those in males, and substantially greater than the addition of the effects of E2 and loading separately. Loading with DHT in males also showed additional [3H]thymidine and [3H]proline incorporation. In females there was additional incorporation of [3H]proline, but not [3H]thymidine. The location of incorporation of [3H]thymidine and [3H] proline was consistent with their level of incorporation reflecting periosteal osteogenesis, in which case the early osteogenic effects of sex hormones are gender-specific when acting alone and in combination with loading. In males the effects of estrogen and testosterone add to, but do not enhance, the osteogenic responses to loading. In females testosterone with loading produces an additional effect on [3H]proline incorporation but no greater effect than loading alone on that of [3H]thymidine. In contrast, estrogen and loading together produce a greater effect than the sum of the two influences separately. Because premenopausal bone mass will have been achieved under the influence of loading and estrogen acting together, these findings suggest that the bone loss which follows estrogen withdrawal may result, at least in part, from reduction in the effectiveness of the loading-related stimulus on bone cell activity. This stimulus is normally responsible for maintaining bone mass and architecture.

Estrogen enhances the stimulation of bone collagen synthesis by loading and exogenous prostacyclin, but not prostaglandin E2, in organ cultures of rat ulnae

The shafts of ulnae from 110 g male rats were cultured, and after a period of 5 h preincubation one of each pair of bones was either loaded cyclically (500 g, 1 Hz, 8 minutes) to produce physiologic strains (-1300 mu epsilon) or treated with exogenous prostacyclin (PGI2) or prostaglandin E2 (10(-6) M, 8 minutes) in the presence or absence of 17 beta-estradiol (10(-8) M). PGI2, PGE2, and loading stimulated almost immediate increases in glucose 6-phosphate dehydrogenase (G6PD) activity in osteocytes and osteoblasts. This increase was uniform throughout the section with exogenous PGs in the medium but was related to local strain magnitude in loading. Elevated G6PD levels in response to loading and PGI2 persisted for 18 h, by which time, ALP activity in surface osteoblasts was elevated and [3H]proline incorporation into collagen increased. PGE2 produced similar immediate and sustained increases in G6PD activity and [3H]proline incorporation after 18 h but no change in ALP activity. Bones cultured for 18 h with 17 beta-estradiol increased their [3H]proline incorporation, as did those loaded, and treated with PGI2 and PGE2. Loading and PGI2 but not PGE2 produced similar proportional increases in [3H]proline incorporation above the increased baseline of estradiol alone. These results suggest that estrogen and loading together produce a greater osteogenic response than either separately. If so, estrogen withdrawal would result in a rapid fall in bone mass to establish a new equilibrium appropriate to the reduced effectiveness of the loading-related stimulus. Such a fall in bone mass is a characteristic feature of estrogen withdrawal at the menopause.