Dexamethasone-induced increase in platelet-derived growth factor (B) mRNA in human alveolar macrophages and myelomonocytic HL60 macrophage-like cells

Multiplicity of Glucocorticoid Action in Inhibiting Allograft Rejection

Glucocorticoids (GCs) are used as immunosuppressive and antiinflammatory agents in organ transplantation and in treating autoimmune diseases and inflammatory disorders. GCs were shown to exert their antiproliferative effects directly through blockade of certain elements of an early membrane-associated signal transduction pathway, modulation of the expression of select adhesion molecules, and by suppression of cytokine synthesis and action. GCs may act indirectly by inducing lipocortin synthesis, which in turn, inhibits arachidonic acid release from membrane-bound stores, and also by inducing transforming growth factor (TGF)-β expression that subsequently blocks cytokine synthesis and T cell activation. Furthermore, by preferentially inhibiting the production of Th1 cytokines, GCs may enhance Th2 cell activity and, hence, precipitate a long-lasting state of tolerance through a preferential promotion of a Th2 cytokine-secreting profile. In exerting their antiproliferative effects, GCs influence both transcriptional and posttranscriptional events by binding their cytosolic receptor (GR), which subsequently binds the promoter region of cytokine genes on select DNA sites compatible with the GCs responsible elements (GRE) motif. In addition to direct DNA binding, GCs may also directly bind to, and hence antagonize, nuclear factors required for efficient gene expression, thereby markedly reducing transcriptional rate. The pleiotrophy of the GCs action, coupled with the diverse experimental conditions employed in assessing the GCs effects, indicate that GCs may utilize more than one mechanism in inhibiting T cell activation, and warrant careful scrutiny in assigning a mechanism by which GCs exert their antiproliferative effects. © 1998 Elsevier Science Inc.

Platelet-derived growth factor: a key factor in the pathogenesis of graves' ophthalmopathy and potential target for treatment

Activation of orbital fibroblasts resulting in excessive proliferation, cytokine and hyaluronan production and differentiation into adipocytes, is a main determinant of orbital tissue inflammation and tissue expansion in Graves' ophthalmopathy (GO). During the last years we have shown that the platelet-derived growth factor (PDGF) isoforms PDGF-AA, PDGF-AB and PDGF-BB are increased in orbital tissue from GO patients with active and inactive disease. These PDGF isoforms exhibit the capacity to stimulate proliferation, hyaluronan and cytokine/chemokine production by orbital fibroblasts. Moreover, PDGF-AB and PDGF-BB increase thyroid stimulating hormone receptor (TSHR) expression by orbital fibroblasts, which enhances the orbital fibroblast activating capacity of the THSR stimulatory autoantibodies present in Graves' disease (GD) patients. Of these PDGF isoforms PDGF-BB exhibits the strongest orbital fibroblast activating effects, which is likely related to its ability to bind both the PDGF-receptor (PDGF-R)α and PDGF-Rβ chains. Thus the PDGF-system fulfills important roles in orbital fibroblast activation in both active and inactive GO, which supports a therapeutic rationale for blocking PDGF signaling in GO. Tyrosine kinase inhibitors (TKIs) may be candidates to target PDGF signaling. Of several TKIs tested dasatinib exhibited the highest potency to block PDGF-R signaling in orbital fibroblasts and may represent a promising compound for the treatment of GO as it was effective at low dosage and is associated with less side effects compared to imatinib mesylate and nilotinib. In this review the contribution of PDGF to the pathophysiology of GO as well as therapeutic approaches to target this PDGF-system will be addressed.

Contribution of lung fibroblast migration in the fibrotic process of airway remodeling in asthma

BACKGROUND

The fibrotic process in airway remodeling of asthma may be characterized by an exaggerated deposition of extracellular matrix (ECM) components such as fibronectin and type I, III and IV collagen. In the present study, we established airway remodeling model mice and examined the mechanism of fibrotic change by measuring chemotactic activity of lung fibroblasts and quantifying collagen content in lung tissues.

METHODS

Airway remodeling model mice were made by ovalbumin (OA) sensitization and inhalation. Bronchoalveolar lavage (BAL) and bronchial biopsy were performed. Cell migration was assessed by the Boyden's chamber technique. The collagen content of lung tissue was measured using ELISA.

RESULTS

The chemotactic activity in lung fibroblasts toward the mouse BAL fluid (BALF) was significantly increased in OA-inhaled mice. Total soluble collagen content was significantly increased in OA-inhaled mice. We observed markedly increased collagen deposition around the airway wall in OA-inhaled mice, which was not shown in saline-inhaled mice. Furthermore, fibronectin in the BALF of OA-inhaled mice was significantly higher than that in the control mice.

CONCLUSIONS

The total soluble collagen content increased during the fibrotic change of airway remodeling in asthma. Furthermore, migration of fibroblasts may play a key role in this remodeling process, and fibronectin and type I and IV collagen seem to be chemotactic factors for the fibroblasts.

The macrophage migration inhibitory factor-glucocorticoid dyad: regulation of inflammation and immunity

The cytokine macrophage migration inhibitory factor (MIF) occupies a unique position in physiology by its ability to directly regulate the immunosuppressive actions of glucocorticoids. We review herein the interactions between MIF and glucocorticoids within the immune system and discuss the relevance of the MIF-glucocorticoid regulatory dyad in physiology and immunopathology. Therapeutic antagonism of MIF may be an effective approach for steroid-sparing therapies in patients with refractory autoimmune or inflammatory diseases.

Regulation of Fibrosis by the Immune System

Inflammation and fibrosis are two inter-related conditions with many overlapping mechanisms. Three specific cell types, macrophages, T helper cells, and myofibroblasts, each play important roles in regulating both processes. Following tissue injury, an inflammatory stimulus is often necessary to initiate tissue repair, where cytokines released from resident and infiltrating leukocytes stimulate proliferation and activation of myofibroblasts. However, in many cases this drive stimulates an inappropriate pro-fibrotic response. In addition, activated myofibroblasts can take on the role of traditional APCs, secrete pro-inflammatory cytokines, and recruit inflammatory cells to fibrotic foci, amplifying the fibrotic response in a vicious cycle. Moreover, inflammatory cells have been shown to play contradictory roles in initiation, amplification, and resolution of fibrotic disease processes. The central role of the macrophage in contributing to the fibrotic response and fibrotic resolution is only beginning to be fully appreciated. In the following review, we discuss the fibrotic disease process from the context of the immune response to injury. We review the major cellular and soluble factors controlling these responses and suggest ways in which more specific and, hopefully, more effective therapies may be derived.

Regulation of PDGF and its receptors in fibrotic diseases

Platelet-derived growth factor (PDGF) isoforms play a major role in stimulating the replication, survival, and migration of myofibroblasts during the pathogenesis of fibrotic diseases. During fibrogenesis, PDGF is secreted by a variety of cell types as a response to injury, and many pro-inflammatory cytokines mediate their mitogenic effects via the autocrine release of PDGF. PDGF action is determined by the relative expression of PDGF alpha-receptors (PDGFRalpha) and beta-receptors (PDGFRbeta) on the surface of myofibroblasts. These receptors are induced during fibrogenesis, thereby amplifying biological responses to PDGF isoforms. PDGF action is also modulated by extracellular binding proteins and matrix molecules. This review summarizes the literature on the role of PDGF and its receptors in the development of fibrosis in a variety of organ systems, including lung, liver, kidney, and skin.

Pharmacology of airway inflammation in asthma and COPD

The current asthma therapies are not cures and symptoms return soon after treatment is stopped even after long term treatment. Although inhaled glucocorticoids are highly effective in controlling airway inflammation in asthma, they are ineffective in the small group of patients with glucocorticoid-dependent and -resistant asthma. With very few exceptions, COPD is caused by tobacco smoking, and smoking cessation is the only truly effective treatment of COPD available. Current pharmacological treatment of COPD is unsatisfactory, as it does not significantly influence the severity of the disease or its natural course. Glucocorticoids are scarcely effective in COPD patients without concomitant asthma. Bronchodilators improves symptoms and quality of life, in COPD patients, but, with the exception of tiotropium, they do not significantly influence the natural course of the disease. Theophylline is the only drug which has been demonstrated to have a significant effect on airway inflammation in patients with COPD. Here we review the pharmacology of currently used antiinflammatory therapies for asthma and COPD and their proposed mechanisms of action. Recent understanding of disease mechanisms in severe steroid-dependent and -resistant asthma and in COPD, has lead to the development of novel compounds, which are in various stages of clinical development. We review the current status of some of these new potential drugs.

Activated protein C inhibits the expression of platelet-derived growth factor in the lung

The natural anticoagulant-activated protein C may inhibit inflammation and fibrosis in the lung. Platelet-derived growth factor is involved in the pathogenesis of lung fibrosis. This study assessed the effect of activated protein C on platelet-derived growth factor expression in human cell lines and in an in vivo model of lung fibrosis. Activated protein C significantly inhibited the secretion and expression of platelet-derived growth factor in human lung cell lines, primary bronchial epithelial cells, and macrophages. In vitro studies also showed that the endothelial activated protein C receptor is expressed by lung epithelial cells and macrophages, and that this receptor and the proteolytic activity of activated protein are implicated in the inhibition of platelet-derived growth factor expression. In the in vivo model of lung fibrosis, intratracheal administration of activated protein C decreased the expression of platelet-derived growth factor and suppressed the development of lung fibrosis. Concomitant intratracheal administration of activated protein C and anti-endothelial activated protein C receptor or anti-platelet-derived growth factor suppressed the inhibitory activity of activated protein C in vivo. In brief, this study describes a novel biological function of activated protein C that may further explain its inhibitory activity on lung inflammation and fibrosis.

Regulation of macrophage migration inhibitory factor expression by glucocorticoids in vivo

Glucocorticoid hormones are important anti-inflammatory agents because of their anti-inflammatory and proapoptotic action within the immune system. Their clinical usefulness remains limited however by side effects that result in part from their growth inhibitory action on sensitive target tissues. The protein mediator, macrophage migration inhibitory factor (MIF), is an important regulator of the host immune response and exhibits both glucocorticoid-antagonistic and growth-regulatory properties. MIF has been shown to contribute significantly to the development of immunopathology in several models of inflammatory disease. Although there is emerging evidence for a functional interaction between MIF and glucocorticoids in vitro, little is known about their reciprocal influence in vivo. We investigated the expression of MIF in rat tissues after ablation of the hypothalamic-pituitary-adrenal axis and after high-dose glucocorticoid administration. MIF expression is constitutive and independent of the influence of adrenal hormones. Hypophysectomy and the attendent loss of pituitary hormones, by contrast, decreased MIF protein content in the adrenal gland. Administration of dexamethasone was found to increase MIF protein expression in those organs that are considered to be sensitive to the growth inhibitory effects of glucocorticoids (immune and endocrine tissues, skin, and muscle). This increase was most likely because of a posttranscriptional regulatory effect because tissue MIF mRNA levels were not influenced by dexamethasone treatment. Finally, MIF immunoneutralization enhanced lymphocyte egress from blood during stress-induced lymphocyte redistribution, consistent with a functional interaction between MIF and glucocorticoids on immune cell trafficking in vivo. These findings suggest a role for MIF in both the homeostatic and physiological action of glucocorticoids in vivo.

Transcriptional and post-transcriptional mechanisms of glucocorticoid antiproliferative effects

Glucocorticoids (GCs) are used as immunosuppressive and anti-inflammatory agents in treating organ transplantation rejection, autoimmune diseases, (hematological) cancers, and inflammatory disorders. GCs exert their effects through a multitude of mechanisms, the most significant of which is inhibition of cytokine production, and for some cytokines their effects on target cells. Paradoxically, GCs also upregulate the expression of (pro-inflammatory) high-affinity cytokine receptors on target cells in the face of lost ligand (cytokine) stimulation. GC inhibition of cytokine expression occurs at both transcriptional and post-transcriptional levels. GCs acted transcriptionally by binding their cytosolic receptor (GR), thereby facilitating its nuclear translocation and subsequent binding to the promoter region of cytokine genes on sites compatible with GC response element (GRE) motifs, which in turn directly or indirectly regulated gene expression. In addition to direct DNA binding, GCs acted post-transcriptionally by: (1) antagonism of nuclear factors required for efficient gene expression either directly or through induction of the expression of specific transcription factor antagonists, (2) altered Th lineage development by favouring the generation of (anti-inflammatory) Th2 cells and suppressing the induction or the activity of established (pro-inflammatory) Th1 cells, and (3) stimulating the expression of transforming growth factor (TGF)-beta, an immunosuppressive cytokine which inhibited cytokine production. However, these mechanisms are not mutually exclusive, since GCs may utilize more than one mechanism in exerting their anti-proliferative effect.

The anti-inflammatory effects of leukotriene-modifying drugs and their use in asthma

Asthma is a chronic inflammatory disease of the airways. Anti-inflammatory drug therapy, primarily using corticosteroids, is now considered the first-line treatment in the management of all grades of asthma severity. Although corticosteroids are believed to be the most potent anti-inflammatory agents available, they do not suppress all inflammatory mediators involved in the asthmatic response. Leukotrienes, which are lipid mediators generated from the metabolism of arachidonic acid, play an important role in the pathogenesis of asthma. They produce bronchospasm, increase bronchial hyperresponsiveness, mucus production, and mucosal edema, and enhance airway smooth muscle cell proliferation and eosinophil recruitment into the airways, and their synthesis or release is unaffected by corticosteroid administration. The use of leukotriene synthesis inhibitors or leukotriene receptor antagonists as anti-inflammatory therapies in asthma has therefore been investigated. Beneficial effects of leukotriene-modifying drugs have been demonstrated in the management of all grades of asthma severity, and there is evidence that certain patient groups (such as those with exercise-induced asthma or aspirin-induced asthma) may be particularly suitable for such therapy.

In vivo gene transfer of an extracellular domain of platelet-derived growth factor beta receptor by the HVJ-liposome method ameliorates bleomycin-induced pulmonary fibrosis

A number of investigators have reported augmented expression of PDGF in lungs with idiopathic pulmonary fibrosis (IPF) or with other types of pulmonary fibrosis. To accomplish such a regulation of PDGF activity, we constructed an expression plasmid of the extracellular domain of PDGF receptor beta chain (XR), which lacks intracellular tyrosine kinase domain and transmembrane portions, and estimated the therapeutic effects of XR gene transfer through the trachea on bleomycin-induced lung fibrosis of C57BL/6 mice using the hemagglutinating virus of Japan(HVJ)-liposome method. The XR gene transfer ameliorated the increases in the wet weight and hydroxyproline content and the histopathologic changes of the lung induced by bleomycin. These findings suggest that PDGF plays a crucial role in the pathogenesis of pulmonary fibrosis, and that XR gene transfer using the HVJ-liposome method may limit the progression of pulmonary fibrosis.

Mechanism of action and in vivo role of platelet-derived growth factor

Platelet-derived growth factor (PDGF) is a major mitogen for connective tissue cells and certain other cell types. It is a dimeric molecule consisting of disulfide-bonded, structurally similar A- and B-polypeptide chains, which combine to homo- and heterodimers. The PDGF isoforms exert their cellular effects by binding to and activating two structurally related protein tyrosine kinase receptors, denoted the alpha-receptor and the beta-receptor. Activation of PDGF receptors leads to stimulation of cell growth, but also to changes in cell shape and motility; PDGF induces reorganization of the actin filament system and stimulates chemotaxis, i.e., a directed cell movement toward a gradient of PDGF. In vivo, PDGF has important roles during the embryonic development as well as during wound healing. Moreover, overactivity of PDGF has been implicated in several pathological conditions. The sis oncogene of simian sarcoma virus (SSV) is related to the B-chain of PDGF, and SSV transformation involves autocrine stimulation by a PDGF-like molecule. Similarly, overproduction of PDGF may be involved in autocrine and paracrine growth stimulation of human tumors. Overactivity of PDGF has, in addition, been implicated in nonmalignant conditions characterized by an increased cell proliferation, such as atherosclerosis and fibrotic conditions. This review discusses structural and functional properties of PDGF and PDGF receptors, the mechanism whereby PDGF exerts its cellular effects, and the role of PDGF in normal and diseased tissues.

Inhaled corticosteroid reduced lamina reticularis of the basement membrane by modulation of insulin-like growth factor (IGF)-I expression in bronchial asthma

BACKGROUND

Pathological studies of bronchial biopsy specimens have confirmed the apparent thickening of lamina reticularis of the epithelial basement membrane. Corticosteroids have proven to be most effective in modifying airway inflammation. However, there is not much data on the effects of corticosteroid-treatment on the basement membrane.

OBJECTIVE

To investigate the effects of inhaled beclomethasone dipropionate (BDP) on the thickness of basement membrane and cellular infiltration into the bronchial mucosa, and the expression of growth factors in patients with asthma.

METHODS

We studied bronchial biopsies from 24 asthmatic patients before and after treatment with inhaled BDP, 400 microg twice a day or placebo, for 6 months in a double-blind manner. Each subject recorded daily asthma symptoms and peak expiratory flow (PEF). Lung function and bronchial responsiveness to methacholine were measured before and after treatment. The thickness of the basement membrane was determined by electron microscopy. Inflammatory cells and the expression of growth factors were examined by immunohistochemistry in endobronchial biopsy specimens.

RESULTS

After 6 months of treatment, we observed a significant improvement of asthma symptoms (P<0.01), PEF (P<0.01), diurnal variation of PEF (P<0.05), and airway responsiveness (P< 0.05) in the BDP group compared with the placebo group. This was accompanied by a significant decrease in the thickness of the lamina reticularis (P < 0.001), and in the number of activated eosinophils (P<0.01), T-lymphocytes (P<0.01), and fibroblasts (P < 0.05) in BDP-treated patients. There was also a reduction in the expression of insulin-like growth factor (IGF)-I (P < 0.01). Significant correlation was found between the IGF-I expression and collagen thickening (rs = 0.34, P<0.01), and the number of fibroblasts (rs = 0.45, P < 0.01).

CONCLUSION

These results suggest that corticosteroid treatment in asthma can reduce the lamina reticular thickness by modulation of IGF-I expression with consequent inhibition of the airway infiltration by inflammatory cells, and therefore may help to prevent remodelling of the airways.

Bronchoscopic evaluation of severe asthma. Persistent inflammation associated with high dose glucocorticoids

The role of inflammation in the pathogenesis of severe asthma chronically treated with high doses of glucocorticoids is poorly understood. Despite this, treatment has been aimed at advancing anti-inflammatory and immunomodulator therapy. This study was designed to evaluate both the presence and type of airway inflammation in patients with severe asthma. A prospective bronchoscopic study evaluated 14 severe, high-dose oral glucocorticoid dependent asthmatics. Bronchoalveolar lavage fluid was analyzed for cytology and inflammatory mediators. Endobronchial and transbronchial biopsies were performed in selected patients for morphometric evaluation of macrophage/monocytes, neutrophils, eosinophils and lymphocytes. These results were compared with lavage and endo- and transbronchial biopsy studies in normal controls and patients with moderate asthma. The concentration of eosinophils in bronchoalveolar lavage fluid was highest in the moderate asthmatics not on glucocorticoids, with very little difference between normal controls and severe asthmatics (significant difference among the groups, p = 0.007). In contrast, the severe asthmatics demonstrated a twofold higher concentration of neutrophils in lavage than either the mild-moderate asthmatics, or the normal controls (p = 0.032 among the groups, p < 0.05 between the severe asthmatics and both controls). Similar results were obtained in the endobronchial and transbronchial biopsy specimens, which consistently showed significantly higher numbers of neutrophils in the severe asthmatics than in the control groups. The eicosanoid mediators, thromboxane and leukotriene B4, were also highest in the severe asthma group (differences among the groups, p = 0.019 and p = 0.023, respectively). These findings suggest that inflammation remains in severe symptomatic asthmatics despite treatment with high dose glucocorticoids which may be due to the severity of disease, glucocorticoid treatment, or other as yet undefined factors.

Steroid therapy in obstructive airway diseases

Asthma and chronic obstructive pulmonary disease (COPD) are two common illnesses that cause significant morbidity and mortality. Steroids are widely used in both conditions. They act through steroid or glucocorticoid receptors (GR) causing up or down regulation of protein synthesis resulting in an increase in lipocortin 1 and beta 2 adrenergic receptors, and decreased levels and activities of cytokines or cytokine receptors, which reduces the inflammatory process in the airways and decreases bronchial hyperreactivity. Consequently symptoms of airway obstruction are alleviated and lung function is improved. In asthma, steroids have been convincingly shown to be effective in the treatment of both acute exacerbations and chronic condition. In COPD, however, only a subset of patients seem to respond favourably to steroid therapy. Therapeutic trials are therefore recommended before committing to a long-term treatment in order to determine this subset of patients, as no markers of steroid responsiveness can be identified. The inhaled steroids currently available have a good safety profile with significant side effects occurring only occasionally. Such side effects are usually confined to the oropharynx, causing local irritation, candidiasis and dysphonia, which can be easily overcome. Biochemical abnormalities involving bone, adrenal, carbohydrate and lipid profiles have been noted with high doses of inhaled steroids; however, these have no significant clinical effects.

Increase in interleukin (IL)-1 beta and IL-6 in bronchoalveolar lavage fluid obtained from infants with chronic lung disease of prematurity

Chronic lung disease (CLD) of prematurity is associated with an initial increase in pulmonary neutrophils followed by pulmonary fibrosis. We determined whether the proinflammatory cytokines, IL-1 beta and IL-6, were increased in the bronchoalveolar lavage fluid obtained from nine infants (median gestation 25 wk, birthweight 820 g) who developed CLD, seven (28 wk, 1110 g) who recovered from the respiratory distress syndrome (RDS), and four (38 wk, 2690 g) control infants. IL-1 beta and IL-6 protein were both increased in the bronchoalveolar lavage fluid from the CLD groups when compared with the RDS and control groups. This difference for both the cytokines was most marked on d 10 of age, when results from infants with and without CLD were compared (IL-1 beta, 4.6 versus 1.1 ng/mL, p < 0.05; and IL-6, 9.5 versus 1.5 ng/mL, p < 0.05). Immunocytochemistry of lavage cells for IL-1 beta, IL-6, and IL-8 protein showed alveolar macrophages to contain all three cytokines, with lesser staining evident in neutrophils, and in epithelial cells occasionally obtained by lavage. The contribution of alveolar macrophages and luminal cells to the increase in IL-6 and IL-1 was determined by performing semiquantitative reverse transcription-polymerase chain reactions on RNA extracted from lavage cells. IL-6 mRNA expression was increased in lavage cells from the CLD infants when compared with the RDS group. However, the expression for IL-1 beta and IL-8 mRNA was similar in both groups. These results suggest that IL-1 beta, IL-6, and IL-8 may contribute to the pathogenesis of CLD, and that, in CLD, IL-6 may be produced by cells within the air spaces.

Growth factor mRNA expression in normal colorectal mucosa and in uninvolved mucosa from ulcerative colitis patients

This study was carried out to investigate the expression of various growth factors (GFs) involved in mucosal healing and thereby to clarify whether there are potential differences in the expression of GFs between normal colonic mucosa and the uninvolved mucosa of ulcerative colitis (UC). GF mRNA was investigated by reverse transcription polymerase chain reaction in colorectal biopsies from 20 normal controls and 15 UC patients. The positive rates (%) for mRNA expression for normal/UC were: epidermal growth factor (EGF) 65/53, transforming growth factor (TGF)-alpha 100/87, TGF-beta 1 60/33, insulin like growth factor-I 45/33, platelet-derived growth factor-A 55/67, basic fibroblast growth factor 0/0, hepatocyte growth factor (HGF) 50/53, EGF receptor 20/27, erb-B2 75/73, and HGF receptor (c-MET) 55/67. Semiquantitation of mRNA showed significantly lower expression of TGF-beta 1 (P < 0.05) in UC. Differences in expression and mRNA levels were not statistically significant for any other GFs. Our results indicate that mucosa in chronic persistent UC has a low basal expression of TGF-beta 1 mRNA, and, since TGF-beta 1 is a multifunctional GF that plays important roles in regulating repair and regeneration following tissue injury, this low expression may be partially responsible for the intractability of the disease.

Signals controlling the expression of PDGF

PDGF is an important polypeptide growth factor that plays an essential role during early vertebrate development and is associated with tissue repair and wound healing in the adult vertebrate. Moreover, PDGF is thought to play a role in a variety of pathological phenomena, such as cancer, fibrosis and atherosclerosis. PDGF is expressed as a dimer of A and/or B chains, the precursors of which are encoded by two single copy genes. Although the PDGF genes are expressed coordinately in a number of cell types, they are independently expressed in a majority of cell types. The expression of either PDGF gene can be affected by very diverse extracellular stimuli and the type of response is dependent on the cell type that is exposed to the stimulus. Expression of the PDGF chains can be modulated at every imaginable level: by regulating accessibility of the transcription start site, by varying the transcription initiation rate, by using alternative transcription start sites, by alternative splicing, by using alternative polyadenylation signals, by varying mRNA decay rates, by regulating efficiency of translation, by protein modification, and by regulating secretion. Even upon secretion, the activity of PDGF can be modulated by non-specific or specific PDGF-binding proteins. This review provides an overview of the cell types in which the PDGF genes are expressed, of the factors that are known to affect the expression of PDGF, and of the various levels at which the expression of PDGF genes can be regulated.

Identification of M. tuberculosis ribosomal RNA in mouthwash samples from patients with tuberculosis

It is often not possible to obtain satisfactory sputum samples from patients suspected of having pulmonary tuberculosis. In this study, we asked whether it was possible to identify M. tuberculosis ribosomal RNA (rRNA) in mouthwash samples, and in a prospective clinical study, whether the presence of this rRNA correlated with clinical M. tuberculosis infection. Using a combination of reverse transcriptase and polymerase chain reaction amplification, it was possible to identify M. tuberculosis rRNA in mouthwash samples. M. tuberculosis rRNA was identified in mouthwash samples from patients with active tuberculosis more commonly than in samples from control subjects (P < 0.05). The test was positive in four of ten patients with active pulmonary tuberculosis, one of eight contacts, none of eight past cases of tuberculosis, two of eight patients with other diagnosis and one of five healthy volunteers. M. tuberculosis rRNA was identified in sputum from four of eight patients and in bronchoscopy trap samples from four of five patients with active tuberculosis. However, one of ten sputum samples and two of five bronchoscopy samples from subjects with a clinical diagnosis other than active tuberculosis were positive. These results indicate that although it is technically possible to identify M. tuberculosis on the basis of the presence of rRNA in mouthwash samples, the poor sensitivity and specificity of the technique suggest that it is unlikely to be useful clinically.

Apoptosis induced by DNA topoisomerase I and II inhibitors in human leukemic HL-60 cells

The induction of apoptosis following topoisomerase inhibitors proceeds in at least three distinct steps: (1) induction of cleavable complexes (potentially lethal damage), (2) topoisomerase-induced DNA damage, and (3) a presently unknown sequence of events that must either lead to cell cycle arrest (G2-block, differentiation) or apoptosis. DNA degradation provides a convenient way to quantify apoptosis in HL-60 cells. Extensive apoptosis can be induced rapidly in undifferentiated HL-60 cells without prevention by cycloheximide or actinomycin D. Therefore, HL-60 cells appear to express constitutively the apoptotic machinery that may be kept under control of a yet unknown repressor. The absence of the tumor suppressor p53 and the presence of bcl-2 are in contrast with the sensitivity of these cells to apoptosis. Agents that modify chromatin structure (zinc, poly[ADPribose] inhibitors, spermine) can block DNA fragmentation without affecting cell survival. By contrast macrophage-like differentiation by phorbol esters suppresses apoptosis without affecting topoisomerase-induced DNA damage. Better understanding of the apoptotic regulation in the widely used and characterized HL-60 cell line should allow the identification of new mechanisms and parameters of cellular sensitivity and resistance to the cytotoxic activity of anticancer agents.

Transforming growth factor beta 1 gene expression in human airways

BACKGROUND

Asthmatic airways have a characteristic deposition of connective tissue under the epithelial basement membrane, but the mediators involved in this alteration are unknown. Several authors have postulated that transforming growth factor beta 1 (TGF-beta 1) could be overexpressed in asthmatic airways.

METHODS

Lung samples from 16 asthmatic patients, six patients with chronic obstructive pulmonary disease (COPD), and six non-obstructed smokers were analysed. RNA was extracted from these tissues to measure expression of TGF-beta 1 by Northern blot analysis using a cDNA probe for TGF-beta 1. The level of expression was quantitated by densitometry using glyceraldehyde 3-phosphate dehydrogenase mRNA as a control. TGF-beta 1 was localised to specific cell types in these lungs by immunohistochemical analysis using polyclonal antibodies specific for intracellular and extracellular TGF-beta 1.

RESULTS

The 2.5 kb TGF-beta 1 mRNA was seen in all 18 samples analysed by Northern blotting and densitometric analysis showed no difference between the asthmatic group (mean (SD) 108% (43%)), the group with COPD (122% (33%)), and the non-obstructed group (100% (49%)). The TGF-beta 1 precursor was immunolocalised throughout the airway wall including the epithelium and in alveolar macrophages. The mature TGF-beta 1 was localised primarily within the connective tissue of the airway wall. These patterns of expression of both forms of TGF-beta 1 were similar in lungs from asthmatic patients, those with COPD, and controls.

CONCLUSIONS

While TGF-beta 1 mRNA and protein are abundantly expressed in human lungs, there is no clear difference in expression between the airways of asthmatic subjects and those of smokers with and without COPD.

Efficacy and safety of inhaled corticosteroids in asthma. Report of a workshop held in Eze, France, October 1992

Inhaled glucocorticosteroids have now become first-line therapy for the treatment of chronic asthma in many countries. They are the most effective asthma therapy currently available, and numerous studies have documented their long-term efficacy in asthma control in adults and in children. Inhaled steroids suppress inflammation in asthmatic airways, although their precise molecular mechanism of action is not yet certain. It is likely that steroids affect the transcription of several steroid-responsive genes, and, of particular importance, they may inhibit cytokine gene transcription and cytokine effects, thereby reducing the chronic inflammation in asthmatic airways. Inhaled steroids are now used at a much earlier stage in asthma therapy, and there is a strong argument for their early introduction in both adults and children to prevent asthma morbidity and mortality and possibly the structural changes resulting from uncontrolled chronic inflammation, which may lead to irreversible airflow obstruction in some patients. Of paramount importance is the question of safety as inhaled steroids are likely to be required for a long time. Local side effects caused by oropharyngeal deposition of the inhaled steroid may be reduced by the use of spacer devices and mouthwashing. Systemic side effects caused by gastrointestinal absorption of the fraction deposited in the oropharynx may also be reduced by these devices. There are differences in the systemic bioavailability of the different inhaled steroids currently in use, and inhaled steroids with the lowest bioavailability should be chosen when high doses of inhaled steroids are required for asthma control. Systemic side effects are usually observed only when daily doses of > 800 micrograms are inhaled, and whether effects on very sensitive biochemical indices are relevant to long-term deleterious effects is not yet certain. There is now overwhelming evidence that the doses of inhaled steroids required to control asthma in the majority of adults and children are safe and without systemic side effects. It is important to control asthma with the minimum dose of inhaled steroids possible, however. In the future it may be possible to develop inhaled steroids with even fewer systemic effects if the fraction absorbed from the respiratory tract can be rapidly metabolized in the bloodstream.

Up-regulation of alveolar macrophage platelet-derived growth factor-B (PDGF-B) mRNA by interferon-gamma from Mycobacterium tuberculosis antigen (PPD)-stimulated lymphocytes

Macrophage production of PDGF-B is believed to be important in the pathogenesis of diseases where chronic lung inflammation develops into fibrosis. Since tuberculosis is characterized by chronic inflammation and tissue fibrosis, we asked if lymphokines from lymphocytes stimulated by the Mycobacterium tuberculosis antigen PPD, contained factors capable of increasing human alveolar macrophage PDGF-B mRNA. Supernatants from both phytohaemagglutinin (PHA)- and purified protein derivative (PPD)-stimulated lymphocytes, when added to macrophages, induced an increase in the mRNA of PDGF-B, but not transforming growth factor-beta (TGF-beta). When lymphocytes from contacts of patients with tuberculosis, patients with tuberculosis, and normal subjects were compared following PPD stimulation, the lymphocytes from the contacts had the greatest proliferation response, the greatest production of interferon-gamma (IFN-gamma), and their lymphokines induced the greatest increase in PDGF-B mRNA in macrophages. Recombinant human IFN-gamma reproduced this ability of lymphokines to increase macrophage PDGF-B mRNA. Finally, the increase in macrophage PDGF-B mRNA following incubation with supernatants from PPD-stimulated lymphocytes was shown to be due to IFN-gamma, when the increase in macrophage PDGF-B mRNA was prevented by addition of anti-human IFN-gamma antibody to the lymphocyte supernatant. This study indicated that antigen-stimulated lymphocytes released IFN-gamma, which in turn resulted in an increase in PDGF-B mRNA in alveolar macrophages. Such a mechanism provides a link between the DTH response and the first stages of a fibrotic reaction, and may offer an explanation for the progression of chronic inflammation to fibrosis, as occurs in the lungs of patients with untreated pulmonary tuberculosis.