Hormonal control of the replication of human fetal fibroblasts: role of somatomedin C/insulin-like growth factor I

The use of growth factors on tendon injuries

Tendon injuries continue to be a vexing clinical problem faced by the upper extremity surgeon. These injuries often lead to disability and dissatisfaction for both the patient and treating physician. Advances throughout the century have focused largely on improvements in surgical techniques and therapy protocols. Recently, attention has been turned to the biologic pathways by which tendons heal and the growth factors involved in this process have been identified. There is great hope that these growth factors may one day be used to treat tendon injuries. This article provides a summary of the use of growth factors on tendon injuries including contemporary research, delivery methods, and future directions in this field.

Epidermal homeostasis: the role of the growth hormone and insulin-like growth factor systems

GH and IGF-I and -II were first identified by their endocrine activity. Specifically, IGF-I was found to mediate the linear growth-promoting actions of GH. It is now evident that these two growth factor systems also exert widespread activity throughout the body and that their actions are not always interconnected. The literature highlights the importance of the GH and IGF systems in normal skin homeostasis, including dermal/epidermal cross-talk. GH activity, sometimes mediated via IGF-I, is primarily evident in the dermis, particularly affecting collagen synthesis. In contrast, IGF action is an important feature of the dermal and epidermal compartments, predominantly enhancing cell proliferation, survival, and migration. The locally expressed IGF binding proteins play significant and complex roles, primarily via modulation of IGF actions. Disturbances in GH and IGF signaling pathways are implicated in the pathophysiology of several skin perturbations, particularly those exhibiting epidermal hyperplasia (e.g., psoriasis, carcinomas). Additionally, many studies emphasize the potential use of both growth factors in the treatment of skin wounds; for example, burn patients. This overview concerns the role and mechanisms of action of the GH and IGF systems in skin and maintenance of epidermal integrity in both health and disease.

Successful six-day kidney preservation using trophic factor supplemented media and simple cold storage

This study examined the effect of trophic factor supplementation [TFS; bovine neutrophil peptide-1 (bactenecin), 1 mg/L; substance P, 2.5 mg/L; nerve growth factor, 20 microg/L; epidermal growth factor, 10 microg/L; insulin-like growth factor-1, 10 microg/L] during cold storage with UW lactobionate solution. Dogs transplanted with kidneys stored for 4days in TFS-UW had significantly lower peak serum creatinine values (mean 2.9 +/- 0.2mg/dL) and returned to normal values faster (6 days) than kidneys stored for 3days in unmodified UW solution (4.2 +/- 0.3 mg/dL and 14 days, respectively). Kidneys stored for 5days in TFS-UW (mean peak creatinine 3.7 +/- 0.3) functioned equivalently to kidneys stored for 3days and better than kidneys stored for 4 days in UW alone. Dogs with kidneys stored for 6days in TFS-UW had mean peak creatinines of 5.7 +/- 0.4 mg/dL. These returned to normal creatinine values in 14 days, equal to 3-day stored and significantly better than kidneys stored for 4days in UW alone (20days recovery time). This study shows trophic factor deprivation appears to be a critical mechanism of injury in organ preservation with current synthetic storage media, and marks the initial development of a synthetic biologically active preservation solution, the next generation of preservation media.

Inflammation. 1: Its role in the healing of acute wounds

The inflammatory response is an essential part of the wound-healing process. This article discusses inflammation in acute wounds and the part played by the migration of cells including neutrophils, macrophages and T-lymphocytes.

Dexamethasone-mediated androgen metabolism in human gingival and oral periosteal fibroblasts

Dexamethasone modulates the effects of other hormones and mediates cell function; the periodontium is a target tissue for androgens. It was therefore relevant to investigate the modulation of androgen metabolism by dexamethasone in cultured human gingival (HGF) and oral periosteal fibroblasts (HPF). Each cell line was incubated in Eagle minimum essential medium with [(14)C]testosterone/[(14)C]4-androstenedione as substrates and serial concentrations of dexamethasone (0.5-50 microg/ml), for 24h; the medium was solvent-extracted, analyzed and quantified for steroid metabolites. In response to dexamethasone, both HGF (n=6) and HPF (n=4) showed up to two-fold increases in the formation of 5alpha-dihydrotestosterone and 4-androstenedione (P<0.01, one-way ANOVA), and 3.6- to 5-fold increases in the formation of testosterone (P<0.001), from [(14)C]4-androstenedione, with some inhibition at higher concentrations. Dexamethasone stimulated the formation of physiologically active androgen metabolites in a dose-dependent manner. These metabolites might therefore contribute to dichotomous effects in connective tissues of the periodontium, dependent on effective concentrations of dexamethasone.

Activin stimulates proliferation of rat ovarian thecal-interstitial cells

There is growing evidence that the function of ovarian theca-interstitial (T-I) cells may be modulated by paracrine actions of activin, inhibin, and follistatin. Furthermore, either dysregulation, dysfunction, or both, of these peptides may play a role in conditions associated with T-I hyperplasia, such as polycystic ovary syndrome (PCOS) and hyperthecosis. This study was designed to evaluate the role of activin, inhibin, and follistatin in the modulation of T-I cell proliferation. Interaction of these peptides with insulin-like growth factor-I (IGF-I), a known stimulator of T-I cell proliferation, was also assessed. Purified rat T-I cells were cultured for 48 h in chemically defined media and with or without activin (3-30 ng/ml), inhibin (3-30 ng/ml), follistatin (100 ng/ml), and/or IGF-I (10 nM). T-I cell proliferation was assessed using radiolabeled thymidine incorporation assay. Activin alone stimulated proliferation of T-I cells in a dose-dependent fashion (by up to 320% above control; P < 0.001), whereas inhibin alone or follistatin alone had no significant effect. Inhibin had also no effect on activin-induced proliferation. Follistatin significantly reduced the stimulatory effects of activin and decreased proliferation by up to 46% (P < 0.01) below the level attained in the presence of activin alone. IGF-I (10 nM), at a dose producing a near-maximal effect, increased proliferation by 175% above control (P < 0.001); insulin (10 nM) increased proliferation by 52% above control (P < 0.03). A combination of IGF-I (10 nM) and activin (30 ng/ml) resulted in a 1090% increase of proliferation above control (P < 0.001); this stimulatory effect was significantly greater than that achieved in the presence of either activin alone or IGF-I alone (P < 0.001). Similarly, a combination of insulin (10 nM) and activin (30 ng/ml) increased proliferation by 506% above control levels. Flow cytometry evaluation revealed that activin increased the proportion of actively dividing cells (in S or G2/M phase of the cell cycle) by 42% (P < 0.02), whereas IGF-I had no effect on the proportion of actively dividing cells. The present findings indicate that an activin-follistatin system may be involved in the regulation of the size of ovarian thecal-stromal compartment. In view of the synergy between activin and IGF-I, and the difference in the effects on the cell cycle distribution, stimulation of T-I proliferation by these agents is likely to be mediated via separate transduction pathways. Excess activin or insufficient follistatin may contribute to T-I hyperplasia.

Long-term effect of recombinant human insulin-like growth factor I on metabolic and growth control in a patient with leprechaunism

Leprechaunism is the most severe form of insulin resistance, manifesting with abnormal glucose metabolism and retarded growth. In the present study, we investigated the biological actions of recombinant human insulin-like growth factor I (rhIGF-I) in fibroblasts derived from a patient with leprechaunism. In the same patient, we also investigated the pharmacokinetics of IGF-I and the long-term effect of rhIGF-I treatment on metabolic control and physical growth. The patient's fibroblasts showed normal binding of IGF-I, normal phosphorylation of the beta-subunit of the IGF-I receptor, and normal [3H]thymidine incorporation in response to IGF-I. The fibroblast studies suggested that the patient would respond to IGF-I therapy, but certainly did not exclude the possibility of IGF-I resistance in vivo. Administration of recombinant human GH at the dose of 2.0 IU/kg for 3 consecutive days induced a minimal response of serum total IGF-I and IGF-binding protein-3 (IGFBP-3), suggesting partial GH resistance. To increase the serum total IGF-I level, we administered rhIGF-I with combination therapy of intermittent and continuous s.c. injection. This sustained the serum total IGF-I level, but not the serum IGFBP-3 level, within the normal range. The patient was treated with combination therapy of rhIGF-I by both s.c. injection and continuous s.c. infusion for 6 yr and 10 months. Administration of rhIGF-I at total daily dose of 1.6 mg/kg maintained her growth rate and hemoglobin A1c level nearly within the normal range. These findings suggest 1) that this leprechaun patient has an IGF-I-deficient state and partial GH resistance, as reflected by impaired production of IGF-I and IGFBP-3; 2) that rhIGF-I treatment works effectively for preventing postnatal growth retardation and normalizing glucose metabolism in patients with extreme insulin resistance; 3) that this treatment requires relatively higher dose of rhIGF-I; and 4) that treatment appears to be safe and devoid of adverse effects.

Combined insulin-like growth factor-1 and growth hormone improves weight loss and wound healing in burned rats

The anabolic effects of growth hormone (GH) in burned patients appear to act both directly and through insulin-like growth factor-1 (IGF-1). We, therefore, hypothesize that exogenous GH plus IGF-1 will attenuate increases in metabolism and lean muscle wasting while promoting wound healing.

MATERIALS AND METHODS

Rats, each weighing 440-470 g, were given a 35% total body surface area, full-thickness scald burn and divided into four groups to receive placebo (burned controls), bovine GH (2.5 mg/kg/day), IGF-1 (2.0 mg/kg/day), or bovine GH plus rhIGF-1 (2.5 + 2.0 mg/kg/day), respectively, for 8 weeks.

RESULTS

Total body weight gain after 8 weeks averaged 110 g for GH plus IGF-1 compared with gains of 49 and 11 g for GH or IGF-1 alone, respectively. Burned controls lost 24 g. Metabolic rates were significantly reduced in all groups receiving growth hormones. Gastrocnemius muscle dry weight was significantly increased in those receiving GH plus IGF-1 compared with GH and IGF-1 alone or burned controls (p < .01).

CONCLUSIONS

Data show that GH plus IGF-1 synergistically increased lean muscle weight, total body weight, and was more effective in re-epithelialization of the burn wound than either GH or IGF-1 alone.

Role of growth factors in cutaneous wound healing: a review

The well-orchestrated, complex series of events resulting in the repair of cutaneous wounds are, at least in part, regulated by polypeptide growth factors. This review provides a detailed overview of the known functions, interactions, and mechanisms of action of growth factors in the context of the overall repair process in cutaneous wounds. An overview of the cellular and molecular events involved in soft tissue repair is initially presented, followed by a review of widely studied growth factors and a discussion of commonly utilized preclinical animal models. The article concludes with a summary of the preliminary results from human clinical trials evaluating the effects of growth factors in the healing of chronic skin ulcers. Throughout, the interactions among the growth factors in the wound-healing process are emphasized.

Platelet-derived growth factor and dexamethasone combined with a collagen matrix induce regeneration of the periodontium in monkeys

Platelet-derived growth factor (PDGF) and the glucocorticoid dexamethasone combined with a collagen carrier matrix (CM) induced regeneration of the periodontium in monkeys. Regeneration was stringently defined as: (1) new cementum, (2) new supra-crestal bone extending coronally from the residual alveolar interdental septum and (3) functionally-oriented periodontal ligament fibers attaching new cementum to new bone. A single application of PDGF/dexamethasone/CM or CM was placed in debrided lesions of experimental periodontitis displaying 3-5 mm of attachment loss associated with horizontal and angular bony defects. Regeneration, judged histologically by these criteria and quantified by computer assisted histomorphometry after 4 weeks, was present only in PDGF/dexamethasone/CM treated lesions and not in those treated with CM or debridement alone. PDGF/dexamethasone/CM induced 5-fold more new cementum and ligament, and 7-fold more supra-crestal bone than control treatments. The presence of substantial amounts of regenerated periodontium including increased height of the alveolar bone; fill of vertically resorbed interdental alveolar septa in PDGF/dexamethasone/CM treated lesions suggests that this combination may provide a new therapeutic agent for the regeneration of lesions of periodontitis associated with horizontal as well as angular bony defects.

Modulation of peritoneal re-epithelialization by postsurgical macrophages

The studies reviewed here show that postsurgical macrophages are capable of modulating the proliferation of TRC. That is, macrophages either suppress or enhance the proliferation of TRC depending on the culture time and the medium used as a comparison, i.e., culture medium with only serum or spent medium from cultures of resident peritoneal macrophages. Postsurgical macrophages also modulate the morphology of (spindly or rounded appearance) and the secretion of extracellular matrices by TRC. The responsivity of TRC to control by postsurgical macrophage-spent media or growth factors changes as a function of postsurgical and/or culture time. In addition, cells harvested from the site of peritoneal trauma (TRC) did not respond to growth factors in a fashion entirely the same as fibroblasts. This indicates that cells harvested from the site of peritoneal injury are unique. Lastly, after removal of a suppressive factor from postsurgical macrophage-spent media by dialysis, the factors secreted by postsurgical macrophages are more potent in enhancing TRC proliferation than growth factors individually.

Synergistic effects of dexamethasone on platelet-derived growth factor mitogenesis in vitro

Platelet-derived growth factor (PDGF) and insulin-like growth factor-I (IGF-I) interact to stimulate proliferation of fibroblasts in culture. Glucocorticoids variably effect the response of cultured fibroblasts to polypeptide growth factors. This study determined the effects of dexamethasone on growth-factor stimulation of gingival, periodontal ligament and pulp fibroblast proliferation in vitro. Cultures of quiescent, low-passage, human fibroblasts were treated for varying periods of time with transforming growth factor-beta 2 (TGF-beta 2), PDGF and IGF-I: (1) alone, (2) in combination with each other, (3) singly plus dexamethasone, (4) in combination plus dexamethasone. Combinations of human, recombinant PDGF and IGF-I (10-1000 ng/ml) induced significantly higher rates of cell proliferation than either factor alone. Dexamethasone at doses ranging from 10(-5) to 10(-8) M substantially enhanced cell proliferation induced by these combinations and by PDGF without IGF-I but not IGF-I alone. By 6 days after a single application, 2-3 times as many cells were present in the PDGF and dexamethasone cultures as compared to PDGF without IGF-I. TGF-beta 2 specifically blocked the effects of dexamethasone added to PDGF-stimulated cells. Collagen and non-collagenous protein synthesis was not affected by the addition of PDGF and IGF-I with or without dexamethasone. These data suggest that dexamethasone may substitute for IGF-I in PDGF stimulation of cell proliferation.

Regulation of proliferation of peritoneal tissue repair cells by peritoneal macrophages

Macrophages produce soluble mediators which modulate fibroblast growth during tissue repair. Interaction between tissue repair fibroblasts (TRC) and regulatory proteins from surgically elicited macrophages is important for peritoneal reepithelialization. In this study, we compared the effects of an extract from postsurgical macrophage spent medium with those of known growth factors on TRC collected from injured peritoneum to evaluate certain characteristics of macrophage secretory products on peritoneal healing. Rabbits underwent a midline laparotomy followed by resection and reanastomosis of the ileum or abrasion of the abdominal wall. TRC were then collected at various times after surgery. Peritoneal macrophages recovered from nonsurgical or postsurgical rabbits were cultured for 2 days in vitro. The peak of thymidine incorporation by TRC occurred on day 5 after surgery; this gradually decreased with extended postsurgical times. Fibroblast growth factor and epidermal growth factor stimulated, whereas TGF-beta inhibited, [3H]thymidine incorporation into TRC. Maximal thymidine incorporation occurred when TRC from Postsurgical Day 5 were cultured with an extract from postsurgical macrophage spent medium. However, when TRC recovered from Postsurgical Days 2 and 10 were cultured with an extract of postsurgical macrophage spent medium, they showed greater stimulation than Day 5 TRC. These data suggest that postsurgical macrophages may produce an array of factors that stimulate fibroblast growth and differentiation and may in turn affect tissue repair throughout the wound healing process.

Suppression of protein kinase C and the stimulation of glucocorticoid receptor synthesis by dexamethasone in human fibroblasts derived from tumor tissue

Exposure of fibroblasts derived from keloid tissues, desmoid and dermal tissue from individuals with Gardner's syndrome (GS) to dexamethasone resulted in the suppression of protein kinase C (PKC) activity and [3H]thymidine incorporation into DNA, and a 20-fold induction of glutamine synthetase activity. Treatment of GS and keloid fibroblasts with 0.1 microM dexamethasone for 36 h increased glucocorticoid receptor (GR) synthesis, as determined by [35S]methionine labeling and immunoprecipitation with a monoclonal antibody to the human GR. The suppression of PKC activity by dexamethasone was shown to result from a loss of protein mass as determined by immunoblotting using an antibody to PKC type III. In contrast to these results, exposure of fibroblasts isolated from normal tissues to dexamethasone did not result in the suppression PKC and [3H]thymidine incorporation, there was only a sixfold induction of glutamine synthetase, and a decrease of GR synthesis. As no primary receptor binding defect could be detected, the altered response of tumor cells to steroid-occupied receptor indicates a partial post-receptor binding defect in GS and keloid cells.

The mitogenic activity of peritoneal tissue repair cells: control by growth factors

The purpose of this study was to determine the proliferative activity of tissue repair fibroblasts recovered directly from injured peritoneum at various times after surgery and to test the mitogenic response of tissue repair cells (TRC) to growth factors. Rabbits underwent bilateral peritoneal abrasion (5 X 5 cm) with sterile gauze until punctate bleeding developed. Postsurgical (Days 2, 5, 7, and 10) tissue repair cells were recovered from the injured peritoneum by scraping with a scalpel blade. Although tissue repair cells consisted of a mixed cell type after 4 days in culture, recovered cells were essentially fibroblasts. These TRC were then pulsed with [3H]thymidine after 4 days in culture. The incorporation of thymidine into Postsurgical Day 5 TRC increased significantly compared to that of Day 2 TRC (P less than 0.05). Incorporation then decreased with time following surgery. Fibroblast growth factor (FGF) and epidermal growth factor (EGF) stimulated the incorporation of thymidine into TRC. However, the response of Postsurgical Day 7 and 10 TRCs to 1 microgram/ml EGF was significantly greater than those of Postsurgical Day 2 and 5 TRCs (Day 2 TRC, 166 +/- 7.4; Day 10 TRC, 420 +/- 96% of control cells without EGF, P less than 0.05). Platelet-derived growth factor (PDGF, 10 ng/ml) also stimulated the incorporation of thymidine into Day 10 TRCs, but this stimulatory activity (129.9 +/- 8.5% of control) was less than EGF or FGF. IL-1 alpha and IL-2 did not stimulate the incorporation of thymidine into TRC at a concentration of 100 pg/ml, but these cytokines did stimulate protein synthesis by TRC.(ABSTRACT TRUNCATED AT 250 WORDS)

Serum glucocorticoids have persistent and controlling effects on insulinlike growth factor I action under serum-free assay conditions in cultured human fibroblasts

The biological actions of insulinlike growth factor I (IGF-I) measured under serum-free assay conditions were found to be significantly influenced by prior subculture conditions for adult human fibroblasts. Glucocorticoids seemed to be the major medium variable affecting IGF-I action. IGF-I added to serum-free cultures had little or no effect on [14C]aminoisobutyric acid uptake or [3H]thymidine incorporation in human fibroblasts previously maintained in media containing serum with low glucocorticoid levels or in serum stripped of endogenous steroids. However, a 48-h preincubation with dexamethasone resulted in a marked synergistic increase in IGF-I stimulation of [14C]aminoisobutyric acid uptake and [3H]thymidine incorporation in these cultures. In contrast, IGF-I in serum-free medium seemed to be a potent mitogenic and metabolic stimulus for human fibroblasts which had been subcultured in media with a high glucocorticoid content, either endogenous or supplemented. After these culture conditions, a 48-h preexposure to dexamethasone had no further enhancing effect on IGF-I action. Dexamethasone also potentiated IGF-I, insulin, and epidermal growth factor stimulation of fibroblast replication depending on the earlier subcultivation conditions. Thus, glucocorticoids are important modulators of IGF-I bioactivity in cultured human fibroblasts. Serum glucocorticoids can exert a profound influence on the biological phenomena measured in cell culture, even when the serum has been removed before the actual experiment, and must be carefully taken into account for accurate evaluation of the biological function of IGF-I and other growth factors.

Sensitization of human fibroblasts to insulin-like growth factor I by serum deprivation and dexamethasone pretreatment

Pretreatment of confluent human fibroblast cultures for two days in dexamethasone, serum free medium increased 10-20 fold the sensitivity of the cells to insulin-like growth factor I (IGF I) stimulation of amino acid uptake using the amino acid analog alpha-aminoisobutyric acid (AIB). This increased sensitivity resulted both from the use of serum free medium and the addition of dexamethasone to the serum free media. Pretreatment of the cells for 1, 2, or 3 days before assay showed that the maximum increase in sensitivity was obtained after a two day pretreatment. Pretreatment of the cells also increased their sensitivity to insulin and bovine insulin-like growth factor II stimulation of AIB uptake similar to that seen for IGF I. No consistent effect of the pretreatment was observed on either the basal level of AIB uptake or the maximal hormonal stimulation of AIB uptake. Nor was any change noted in the shape of the dose response curves. Addition of IGF I to the pretreatment medium greatly reduced the sensitivity of pretreated cells. [125I]IGF I binding studies done on suspended fibroblasts indicated that there was up to a two fold increase in the number of receptors with no increase in their affinity for IGF I. Thus, pretreatment of fibroblasts with dexamethasone and serum free medium greatly enhances their sensitivity to IGF I stimulation of AIB uptake and makes this an excellent in vitro bioassay system for IGF I.

Mitogenic and protein synthetic activity of tissue repair cells: control by the postsurgical macrophage

It is well known that fibroblasts are a main source of extracellular matrix synthesis necessary for tissue repair. In addition, macrophages secrete products that are known to modulate synthesis of extracellular matrix. Accordingly, we studied the incorporation of [3H]thymidine, [3H]proline, and [35S]sulfate into macromolecules produced by fibroblasts recovered from the site of peritoneal tissue repair cultured with and without spent media from postsurgical peritoneal macrophages. Rabbits underwent resection and reanastomosis of their small intestines. Peritoneal exudative cells (PEC) were then collected on postsurgical day 5 and day 10 as well as from nonsurgical controls, separated by discontinuous Percoll gradient centrifugation, and cultured for 48 h. A second group of rabbits underwent peritoneal wall abrasion from which fibroblast tissue repair cells (TRC) were collected from the site of injury at postsurgical day 7 and maintained in culture for varying times. Incorporation of radiolabeled precursors into DNA, collagen, and sulfated proteoglycans was determined. Incorporation of [3H]thymidine and [3H]proline into untreated TRC gradually decreased with culture duration. Conversely, [35S]sulfate incorporation gradually increased during prolonged culture. Macrophage spent media increased the levels of [3H]thymidine incorporation by the TRC. [3H]Proline and [35S]sulfate incorporation into TRC were also stimulated by macrophage spent media. However, this stimulation may be due to the enhanced proliferation of TRC by macrophage spent media. In conclusion, tissue repair fibroblasts are activated for postsurgical repair at the site of injury by many factors including secretory products from postsurgical macrophages.

Comparison of the toxicity of orally administered L-triiodothyronine (T3) in rat and cynomolgus monkey

Oral administration of L-triiodothyronine (L-T3) (0.015-1 mg/kg) for 30 days to mature rats or cynomolgus monkeys resulted in both species in a high mortality at 1 mg/kg (after 2 weeks of treatment) and a progressive loss in body weight. Dose-related elevations in plasma marker enzymes occurred, mainly after 1-2 weeks of treatment. The approximate no-effect dose for these changes was around 0.015-0.020 mg/kg for both rat and primate. The large elevations of leucine aminopeptidase (LAP) at 1 mg/kg L-T3 in monkey indicated hepatocellular toxicity although in the rat such large increases in alanine aminotransferase (ALT) and glutamate dehydrogenase (GLDH) were not seen. L-T3 also showed little toxicity to rat hepatocytes in vitro. High concentrations of L-T3 (7 x 10(-9) to 7 x 10(-7) M) had minimal effects on parameters of cell viability such as lactate dehydrogenase (LDH) leakage, chromium-51 release and [3H]leucine incorporation. Urinary enzymes in the rat showed a similar profile to those in plasma. Large rises in alkaline phosphatase (AKP) and N-acetyl glucosaminidase (NAG) at 1 mg/kg indicated possible proximal tubular damage although this was not supported histologically. Clinically, in both species L-T3 appeared more toxic to males than females but this was not supported histologically. The histological lesions observed were different in the 2 species. In the monkeys there was extensive lipid vacuolation of hepatocytes and changes in thyroid and adrenal cortex. In the rat there was fine, non-lipid vacuolation of hepatocytes and thyroid changes. In the rat, 2 previously unreported lesions were also noted. There were multinucleated cells in the renal distal tubular epithelium, and focal fibroplasia of serosal surfaces of abdominal viscera.

Alveolar macrophages release an insulin-like growth factor I-type molecule

Human alveolar macrophages, when activated, release a progression-type growth factor for fibroblasts that signals "competent" fibroblasts to replicate. The present study demonstrates that this growth activity is an insulin-like growth factor I (IGF-I)-type molecule. Partial purification of medium conditioned by activated alveolar macrophages using ion exchange and gel filtration chromatography revealed an IGF-I molecule as detected by an anti-IGF-I polyclonal antibody and that the specific activity of the progression-type growth activity tracked with the amount of IGF-I present. In a serum-free complementation test, the increase in fibroblast proliferation by alveolar macrophage IGF-I was reduced in a dose-response manner with an anti-IGF-I monoclonal antibody. The alveolar macrophage IGF-I displaced 125I-IGF-I from its receptor in a binding assay utilizing human lung fibroblasts and it stimulated type I IGF receptors purified from human lung fibroblasts to phosphorylate a tyrosine-containing artificial substrate. In contrast to the 7.6-kD serum IGF-I, gel chromatography revealed that the alveolar macrophage IGF-I had an apparent molecular mass of 26 kD, similar to other tissue IGF-Is. Alveolar macrophages expressed IGF-I mRNA transcripts as detected by solution hybridization using a 32P-labeled riboprobe complementary to exons I-II-III of the IGF-I gene. In the context of the known functions of the family of IGF-I molecules in cell growth, IGF-I released by activated alveolar macrophages may play a role in acute and chronic inflammatory disorders.

Reduced growth-factor requirement of keloid-derived fibroblasts may account for tumor growth

Keloids are benign dermal tumors that form during an abnormal wound-healing process in genetically susceptible individuals. Although growth of normal and keloid cells did not differ in medium containing 10% (vol/vol) fetal bovine serum, keloid cultures grew to significantly higher densities than normal cells in medium containing 5% (vol/vol) plasma or 1% fetal bovine serum. Conditioned medium from keloid cultures did not stimulate growth of normal cells in plasma nor did it contain detectable platelet-derived growth factor or epidermal growth factor. Keloid fibroblasts responded differently than normal adult fibroblasts to transforming growth factor beta. Whereas transforming growth factor beta reduced growth stimulation by epidermal growth factor in cells from normal adult skin or scars, it enhanced the activity of epidermal growth factor in cells from keloids. Normal and keloid fibroblasts also responded differently to hydrocortisone: growth was stimulated in normal adult cells and unaffected or inhibited in keloid cells. Fetal fibroblasts resembled keloid cells in their ability to grow in plasma and in their response to hydrocortisone. The ability of keloid fibroblasts to grow to higher cell densities in low-serum medium than cells from normal adult skin or from normal early or mature scars suggests that a reduced dependence on serum growth factors may account for their prolonged growth in vivo. Similarities between keloid and fetal cells suggest that keloids may result from the untimely expression of a growth-control mechanism that is developmentally regulated.

Insulin-like growth factor II binding and action in human fetal fibroblasts

To investigate the role of insulin-like growth factor II (IGF-II) in human prenatal growth, IGF-II binding and biological action were studied in four lines of fetal and three lines of postnatal human fibroblasts. Specific binding of IGF-II was similar in both groups: 15.7% and 14.9% for fetal and postnatal fibroblasts, respectively. This was 5-10 times the amount of IGF-I binding found in these cells. IGF-I and IGF-II caused dose-dependent increases in [14C]aminoisobutyric acid (AIB) uptake. IGF-II was sevenfold less potent than IGF-I in stimulating this metabolic response in both fetal and postnatal fibroblasts. The maximal effect of IGF-II in stimulating [14C]AIB uptake approach that of IGF-I. Similar results were obtained when IGF-I and IGF-II stimulation of [3H]thymidine incorporation was compared in fetal and postnatal fibroblasts. Incubation in the presence of alpha IR-3, a monoclonal antibody to the type I IGF receptor, inhibited the ability of both IGF-I and IGF-II to stimulate [14C]AIB uptake and [3H]thymidine incorporation in fetal and postnatal cells. A monoclonal antibody to the insulin receptor did not affect IGF action. These data indicate that IGF-II is a potent metabolic and mitogenic stimulus for human fetal fibroblasts. However, despite the presence of abundant type II IGF receptors on both fetal and postnatal human fibroblasts, IGF-II stimulation of amino acid transport and DNA synthesis appears to be mediated through the type I rather than through its own type II IGF receptor.

Interaction between endocrine and paracrine peptides in prenatal growth control

The evidence reviewed here shows that the endocrinology of fetal growth is very different from that operating postnatally. Pituitary hormones play little part in stimulating growth of the lean body mass or skeleton although growth hormone (GH) may be involved, in some as yet ill defined way in the ontogeny of the fetal pancreatic islet and insulin secretion. Insulin is important because it stimulates fetal cellular anabolism but acts in a permissive manner: with too little insulin growth is inhibited, with too much growth proceeds at a genetically predetermined rate. Placental lactogen (PL), or other peptides within the GH/PL family, may act as a true growth-promoting hormone in the fetus; it stimulates both cellular metabolism and mitosis. The part played by endocrine control mechanisms in the fetus is set in context by an appreciation of the importance of locally acting tissue growth factors, and in particular the somatomedins. Their part in fetal growth control is intimately bound up with the plane of nutrition experienced by the fetus. It is concluded that the simplest analysis that makes biological sense involves a consideration of hormones, tissue growth factors and nutrition, not hierarchically but as mutually interacting variables.

Effect of an anti-insulin-like growth factor I receptor antibody on insulin-like growth factor II stimulation of DNA synthesis in human fibroblasts

To investigate the role of insulin-like growth factor II in the control of DNA synthesis in human fibroblasts, dose-response curves for insulin-like growth factor I and II stimulation of [3H]thymidine incorporation were compared in the absence and presence of alpha IR-3, a highly specific monoclonal antibody directed against the type I insulin-like growth factor receptor. Specific binding of [125I]insulin-like growth factor I to human fibroblast monolayer cultures was inhibited 60-70% in the presence of alpha IR-3. alpha IR-3 had no effect on [125I]insulin-like growth factor II binding to human fibroblasts. However, alpha IR-3 inhibited both insulin-like growth factor I and II stimulated [3H]thymidine incorporation. These data indicate that the type II insulin-like growth factor receptor does not function as a transducer of insulin-like growth factor II's mitogenic effect in human fibroblasts.