Cell-mediated contraction of collagen lattices in serum-free medium: effect of serum and nonserum factors

Entrapment of Cultured Pancreas Islets in Three-Dimensional Collagen Matrices

In vitro culture of islets of Langerhans decreases their immunogenecity, presumably by eliminating passenger leukocytes and other Ia+ presenting cells within the islets. Islets cultivated in petri dishes either at 37°C or at 25°C gradually disintegrate during culture in a time-dependent manner which is related to the free-floating condition of the islets. Also, a fraction of the islets disperse as single cells and beta-cell aggregates or adhere to the bottom of the culture dishes. Thus, the retrieval rate of transplantable islets is dampened due to their disintegration and spontaneous dispersion in conventional petri dish cultures.

Entrapment of freshly harvested islets of Langerhans in a three-dimensional collagen matrix was studied as an alternative method for islet cultivation. The contraction of collagen fibrils during in vitro culture counteracts the dispersion of islets and helps in maintaining their integrity while in culture. It was observed that the entrapped islets maintain satisfactory morphology, viability, and capability of glucose-dependent insulin secretion for over 2 wk. The oxygen consumption rate and glucose metabolism of these islets was not deranged when entrapped in collagen. Also, the retrieval of islets is easier and more efficient than that observed in conventional culture systems.

Our results indicate that culture of islets in three-dimensional collagen gels can potentially develop into an ideal system applicable to clinical transplantation of cultured islets or beta-cell aggregates.

Prostaglandin E2 differentially regulates contraction and structural reorganization of anchored collagen gels by human adult and fetal dermal fibroblasts

Contraction and remodeling of granulation tissue by fibroblasts is a crucial component of dermal wound healing. Postnatal wounds heal with imperfect repair and scar formation, whereas tissue repair in fetal wounds is regenerative. Prostaglandin E2 (PGE2) modulates the behavior of fibroblasts in the wound bed. This study was designed to investigate the mechanism by which PGE2 regulates an in vitro model of granulation tissue, anchored collagen gels, by human adult and fetal dermal fibroblasts. We hypothesized that PGE2 differentially regulates contraction and remodeling of anchored collagen gels by these fibroblast phenotypes. These results indicate that once tension was generated, fetal fibroblasts exerted lower contractile forces resulting in less collagen contraction. This coincided with less prominent stress fibers, yet fetal fibroblasts were able to substantially remodel the collagen architecture. This mechanism was differentially modulated by PGE2 and was mimicked with a PGE2 receptor agonist, indicating a cyclic adenosine monophosphate (cAMP)-dependent mechanism through the EP2 receptor. However, direct up-regulation of cAMP led to decreases in contraction and remodeling by both fibroblast phenotypes indicating an altered signaling pathway. Therefore, targeting cAMP via the EP2 receptor could potentially decrease adult fibroblast contractile forces to the levels of the fetal fibroblast phenotype in order to decrease dermal scarring.

Differential regulation of free-floating collagen gel contraction by human fetal and adult dermal fibroblasts in response to prostaglandin E2 mediated by an EP2/cAMP-dependent mechanism

In contrast to fetal wound healing, dermal adult wound healing results in imperfect repair and scar formation. Fibroblasts are responsible for the contraction and remodeling of the wound matrix, which is influenced by inflammatory mediators including prostaglandin E2 (PGE2). This study addresses the mechanism by which PGE2 regulates contraction of collagen gels by human fetal and adult dermal fibroblasts. We hypothesized that the intrinsic phenotypic properties of the two types of fibroblasts and their responses to PGE2 alter their contraction properties and contribute to different wound healing outcomes. Contraction was evaluated using free-floating fibroblast-populated collagen gels that contract by migratory forces. PGE2 was found to differentially inhibit collagen gel contraction by fetal and adult fibroblasts. This effect was mimicked by a specific PGE2 receptor agonist as well as by two pharmacological agents, indicating a cyclic adenosine monophosphate-dependent signaling pathway mediated through the EP2 receptor. Our results indicate that fetal fibroblast contraction is maintained by a more stable actin cytoskeleton. Therefore, the migratory phenotype may be sufficient for physical remodeling of the wound matrix leading to regenerative repair. Maintenance of this phenotype in the later stages of wound healing could potentially be achieved by targeting cyclic adenosine monophosphate via the EP2 receptor.

Collagen Gel Anisotropy Measured by 2-D Laser Trap Microrheometry

Collagen gels can serve as biomaterials ideal for tissue equivalents, especially if they are remodeled to have fibril anisotropy mimicking native tissue. Type I collagen gel remodeling was studied microscopically to investigate the changes caused by fibroblasts in collagen gel structures, with and without the growth factors PDGF-BB and TGF-beta1. A bidirectional laser trap microrheometry technique was developed that revealed a high degree of local heterogeneity and anisotropy in the structure of the collagen gels during active fibroblast contraction. The use of the growth factors increased not only the gel anisotropy, but the heterogeneity as well, indicating further changes in the collagen fibril orientations. This work shows the ability to influence the remodeling capabilities of fibroblasts by using growth factors in order to begin to elucidate the changes in the local mechanical environment of contracting collagen gels. We present this experimental technique as a method for probing changes in the fibroblast-driven anisotropy of collagen gels as a basis for understanding microstructural tissue organization important in the development of collagen-based tissue equivalents.

Prostaglandin E2 differentially modulates human fetal and adult dermal fibroblast migration and contraction: implication for wound healing

Cyclooxygenase-2 is up-regulated shortly after dermal injury and it has been shown to have important activity during the repair process. Its main product in the skin, prostaglandin E2 (PGE2), modulates both inflammatory and fibrotic processes during wound healing and partially dictates the overall outcome of wound healing. PGE2 signaling has been shown to be altered during fetal wound healing. This study was designed to examine the mechanism(s) by which PGE2 regulates fibroblast migration and contraction and to determine whether these mechanisms are conserved in fetal-derived dermal fibroblasts. Fetal and adult dermal fibroblasts express all four PGE2 receptors. PGE2 inhibits fetal and adult fibroblast migration in a dose-dependent manner through the EP2/EP4-cAMP-protein kinase A pathway. However, fetal fibroblasts appear to be refractory to this effect, requiring a 10-fold higher concentration of PGE2 to achieve a similar degree of inhibition as adult fibroblasts. Inhibition of adult fibroblast migration correlated with disruption of the actin cytoskeleton. In contrast, PGE2 or a cAMP analog did not disrupt the actin cytoskeleton of fetal dermal fibroblasts. These findings were extended using a modified free-floating, fibroblast-populated collagen lattice (FPCL) contraction assay designed to measure fibroblast contraction. PGE2-inhibited FPCL contraction by adult fibroblasts, but fetal fibroblasts exhibited higher rates of FPCL contraction and a blunted response to exogenous modulation by PGE2 or a cyclase activator (forskolin). These findings indicate that fetal dermal fibroblasts are partially refractory to the effects of PGE2, a major inflammatory mediator associated with dermal wound healing. This effect may have significant and specific relevance to the scarless fetal wound-healing phenotype.

The effect of the amelogenin fraction of enamel matrix proteins on fibroblast-mediated collagen matrix reorganization

Enamel matrix proteins (EMP), extracted from developing porcine teeth, promote not only periodontal regeneration but also cutaneous wound healing presumably via the amelogenin fraction. Because it is unclear whether the effect of EMP can be ascribed to amelogenins, we compared EMP with recombinant amelogenin in the relaxed dermal equivalent (DE) in vitro model for early wound contraction. EMP and recombinant porcine amelogenin (rP172) at 1 mg/ml were incorporated into DEs composed of human dermal fibroblasts and a type I collagen matrix. The area reduction, as a measure of contraction, as well as fibroblast numbers and TGF-beta1 levels, were quantified over 7 days in culture in the presence of 10% foetal bovine serum. Both EMP and recombinant amelogenin increased contraction (p < 0.005) and fibroblast numbers (p < 0.005) compared with controls (acetic acid vehicle and 1mg/ml porcine serum albumin) and the positive control TGF-beta1 added at 10 ng/ml. Increased contraction with EMP and recombinant amelogenin was most pronounced after the first day of incubation and was associated with elevated (p < 0.005) TGF-beta1 levels in conditioned medium. In conclusion, the amelogenin component of EMP augmented fibroblast-driven collagen matrix remodelling, at least partially, by increasing the endogenous production of TGF-beta1. These effects of EMP/amelogenin may be beneficial for cutaneous wound healing.

Gamma radiation inhibits fibroblast-mediated collagen gel retraction

Radiation exposure is known to impair healing in irradiated areas. Fibroblasts play a major role in the production and modification of extracellular matrix in wound repair. Since one important aspect of wound repair is the contraction of the wound, this study investigated the effects of radiation on the ability of fibroblasts to mediate collagen gel contraction in an in vitro model of wound retraction. After irradiation, the cells were detached and suspended in a solution of rat tail tendon collagen. Radiation exposure decreased retraction, and this effect was dose dependent. In order to define the mechanism of reduced gel retraction, we investigated alpha2beta1 cell surface integrin and fibronectin, which are thought to mediate contraction, and prostaglandin E2 (PGE2), which is known to inhibit this process. PGE2 release increased dose responsively following radiation. The cyclooxygenase inhibitor indomethacin could partially restore the contractile activity of irradiated fibroblasts. Fibronectin production in gel culture showed a significant decrease. In contrast, there was no decrease in alpha2beta1 integrin expression in radiated cells. In conclusion, radiation decreases fibroblast-mediated gel contraction. Increased PGE2 production and decreased fibronectin production by irradiated fibroblasts may contribute to this effect and may be in part responsible for poor healing of radiated tissue.

Differences in wound contraction between horses and ponies: the in vitro contraction capacity of fibroblasts

The contribution of wound contraction to wound closure determines the speed of second intention wound healing and it has been shown that significant differences exist with regard to both contraction and inflammatory response between horses and ponies and between various areas of the body. In this study, the contraction capacity of fibroblasts from limbs and buttocks of 4 Dutch Warmblood horses and 4 Shetland ponies was studied in vitro, in order to determine whether differences in wound contraction are due to differences in the inherent contraction capacity of the fibroblasts or to differences in tissue environmental factors, such as the inflammatory response. Fibroblasts were harvested from subcutaneous tissue, cultured and then suspended in both floating and anchored collagen gels. Contraction capacity was assessed by measuring the decrease in area of the floating gels and by measuring the microforces generated in the anchored gels using a custom-built measuring device. In the floating gels, no difference existed in the contraction capacity of fibroblasts from horses and ponies, or from limbs and buttocks. In the anchored gels, no differences existed between horse and pony fibroblasts, but the fibroblasts from the limbs started to contract significantly sooner and produced significantly higher forces than those from the buttocks. It is concluded that the in vivo differences in wound contraction between horses and ponies and between different sites of the body are not caused by differences in the inherent contraction capacity of fibroblasts. The in vitro differences between fibroblasts from limbs and buttocks are thought to be due to the lower proliferation rate and the longer culture time of the fibroblasts originating from the limbs, because mature fibroblasts can develop higher contraction forces than immature fibroblasts. This means that tissue environmental factors, such as cytokine profiles during the inflammatory response, determine the extent of contraction during wound healing. Further research should be directed towards the role of the inflammatory response in wound healing.

Mast cells enhance contraction of three-dimensional collagen lattices by fibroblasts by cell-cell interaction: role of stem cell factor/c-kit

Reorganization of the extracellular matrix is important in many biological and pathophysiological processes, including tissue remodelling, wound healing, or cancer metastasis. The ability of cultured fibroblasts to reorganize and contract three-dimensional type I collagen gels is regarded as an in vitro model for this process. In tissue fibrosis, complex interactions among fibroblasts, inflammatory cells and the extracellular matrix are taking place. Mast cells have often been discussed to play a role in several fibrotic conditions including scleroderma, scar formation, or wound healing. In this study, we examined the effects of mast cells on contraction of collagen lattices. The results demonstrate that co-culture of dermal fibroblasts with a human mast cell line (HMC-1) significantly enhanced contraction of the three-dimensional collagen lattices, whereas mast cells alone failed to contract the gel. Addition of culture supernatants of mast cells did not enhance the speed of gel contraction, indicating the importance of cell-cell contact. Morphological analysis showed that mast cells were incorporated into the lattices. Histological examination also demonstrated that within the lattices, mast cells were localized in close contact to, or attached to, fibroblasts. As fibroblasts and mast cells are known to attach via stem cell factor (SCF)/c-kit interaction when co-cultured in monolayers, we also examined the effect of antibodies against SCF and c-kit in this system. Addition of both antibodies inhibited gel contraction up to 70%. In contrast, antibodies against interleukin-4 (IL-4) and IL-4 receptor did not affect gel contraction. These results indicate that mast cells enhance fibroblast-mediated contraction of collagen lattices via direct cell-cell contact, mediated in part by SCF/c-kit interactions.

Cell interactions with collagen matrices in vivo and in vitro depend on phosphatidylinositol 3-kinase and free cytoplasmic calcium

We have investigated the role of phosphatidylinositol 3-kinase (PI3-kinase) in cellular interactions with collagenous matrices. Platelet-derived growth factor-BB (PDGF-BB) elicited a mobilization of intracellular Ca2+ in pig aortic endothelial (PAE) cells transfected with wild type PDGF beta-receptor. This response was greatly reduced in PAE cells transfected with PDGF beta-receptors mutated at positions Y740 and Y751 to prevent PI3-kinase binding. The experimental drug 1D-myo-inositol 1,2,6-trisphosphate (alpha-trinositol) induced a rapid increase and subsequent oscillations of the cytoplasmic Ca2+ concentration in cultured fibroblasts. This response was not due to an effect of alpha-trinositol on inositol 1,4,5-trisphosphate (IP3) receptors. alpha-Trinositol did not influence PDGF-BB elicited chemotaxis through collagen-coated membranes of PAE cells transfected with the wild-type PDGF beta-receptor, but restored PDGF-BB elicited chemotaxis of PAE cells transfected with the PI3-kinase binding-site mutated PDGF beta-receptor. Collagen gel contraction has been suggested to serve as a model for cellular control of interstitial fluid pressure (PIF) in dermis. The PI3-kinase inhibitors wortmannin (50 nM) and LY294002 (5 microM) inhibited the stimulation of fibroblast-mediated collagen gel contraction by 0.4 nM PDGF-BB. Injection of wortmannin in rat paw skin induced a lowering of PIF, and this effect was abolished in animals pre-treated with alpha-trinositol. Pretreatment of rats with alpha-trinositol abolished the decrease in PIF induced by injecting monoclonal anti-rat alpha 2 beta 1 integrin IgG in rat paw skin. Taken together our data indicate that cell-collagen interactions in vivo and in vitro depend on PI3-kinase, and that this dependence can be bypassed by a drug eliciting intracellular Ca2+ mobilization.

Cigarette smoke extract inhibits fibroblast-mediated collagen gel contraction

Cigarette smoking, the major cause of pulmonary emphysema, is characterized by destruction of alveolar walls. Because tissue destruction represents a balance between injury and repair, we hypothesized that cigarette smoke exposure may contribute to the development of emphysema through the inhibition of tissue contraction during the repair process. To partially evaluate this hypothesis, we investigated the effects of cigarette smoke extract (CSE) on the ability of cultured fibroblasts to mediate collagen gel contraction in vitro: CSE inhibited fibroblast-mediated gel contraction in a concentration-dependent manner (P < 0.01). Production of prostaglandin E2, a known inhibitor of fibroblast contraction, was unchanged by CSE as was cell surface integrin expression. In contrast, fibronectin production by fibroblasts was inhibited (P < 0.01), and addition of exogenous fibronectin partially restored the contractile activity, thus suggesting at least one mechanism to explain inhibition of gel contraction by CSE. When CSE was treated to remove volatile components, it showed less inhibitory activity on fibroblast-mediated gel contraction. Therefore, we also examined the effects of acrolein and acetaldehyde, two volatile components of cigarette smoke. Inhibition of contraction was observed at 5 microM acrolein and at 0.5 mM acetaldehyde. In conclusion, cigarette smoke inhibited fibroblast-mediated gel contraction, and this inhibition was due, at least in part, to the volatile components of cigarette smoke and may be mediated, at least in part, by a decrease in fibroblast fibronectin production. By inhibition of repair, these smoke components may contribute to the development of pulmonary emphysema.

Platelet derived growth factor and fibroblast growth factor basic levels in the vitreous of patients with vitreoretinal disorders

AIM

To determine the potential role of basic fibroblast growth factor (bFGF) and platelet derived growth factor (PDGF) in the pathogenesis of proliferative vitreoretinopathy (PVR).

METHODS

An enzyme linked immunosorbent assay technique was used to determine the quantities of bFGF and PDGF in 38 vitreous samples taken from patients undergoing trans pars plana vitrectomy (PPV) for a variety of vitreoretinal disorders.

RESULTS

bFGF levels ranged from undetectable to 318.7 pg/ml. The mean concentration was 27.57 pg/ml. PDGF levels ranged from undetectable to 160 pg/ml, the mean concentration being 40.06 pg/ml. Eight of 13 patients with clinical evidence of retinal detachment (RD) and PVR had significantly elevated bFGF concentrations, whereas only one of 11 patients with RD and no PVR had detectable bFGF; seven of eight patients with RD and PVR had elevated PDGF concentrations in the vitreous, whereas all 10 patients with RD and no PVR had no detectable vitreous PDGF. Eight patients with vitreous haemorrhage had raised PDGF concentrations, and the levels were particularly high (> 120 pg/ml) in those two patients with active neovascularisation. Two out of nine patients with vitreous haemorrhage had raised bFGF levels.

CONCLUSIONS

bFGF and PDGF concentrations are elevated in PVR even in the absence of vitreous haemorrhage, and not in patients with RD uncomplicated by PVR. This observation suggests that both cytokines may be involved in the pathogenesis of PVR.

Recombinant Human Albumin in Cell Culture: Evaluation of Growth-Promoting Potential for NRK and SCC-9 Cells In Vitro

Serum-derived albumin has for a long time been used in cell culture media, but the exact role of albumin and/or impurities bound to albumin has not been precisely defined. In this study, recombinant human albumin was evaluated for its growth-promoting activity on two cell lines, NRK and SCC-9. For NRK cells, the recombinant human albumin was found to exert an inhibitory effect. The fact that fatty acid free HSA was also inhibitory while HSA fraction V was stimulatory suggested a role for fatty acids or some other bound moieties in growth stimulation by HSA fraction V. Addition of oleic acid, cholesterol, phosphatidylcholine, phosphatidylserine or a combination of these lipids, however, did not significantly improve the growth stimulating activity of either fatty acid free HSA or the recombinant human albumin. For SCC-9 cells, both recombinant human albumin and fatty acid free HSA showed slight stimulation (although they were not as active as HSA fraction V), suggesting that in some cell systems, the albumin molecule per se may promote cell growth and survival.

Adhesion molecules in scleroderma: collagen binding integrins

In summary, adhesion molecules are likely to play a prominent role in scleroderma pathogenesis and evolution. Endothelial adhesion molecules required for leukocyte extravasation are upregulated in affected tissue, though the mechanism is unclear. Certainly, endothelial adhesion molecule expression is seen in the context of other diseases not characterized by fibrosis. Adhesion molecules on the fibroblast, particularly those that play a role in fibroblast collagen interactions, may be very important. The ability of fibroblasts to organize collagen fibrils, and to exert forces across collagenous tissue, is likely to involve a prominent role of alpha 2 beta 1 integrin. Enhanced organization and contraction of newly formed collagen, as well as unregulated procollagen production, may be intimately linked in this disease process. At least two factors that strongly enhance fibroblast force generation could potentially influence other aspects of scleroderma. TGF beta is a potent stimulus for collagen production and has been found to be elevated in lesional scleroderma. Endothelin 1 is also a potent vasoconstrictor and is elevated in scleroderma patient serum as well [60,62-65]. Its apparent role in other fibrocontractive diseases suggests that its potential role in the pathogenesis of scleroderma deserves additional attention.

Activation-dependent contractility of rat hepatic lipocytes in culture and in vivo

Hepatic lipocytes are perisinusoidal cells that have been thought to be analogous to tissue pericytes, a cell type with purported vasoregulatory properties. However, we and others have recently demonstrated that lipocytes acquire markers of smooth muscle cells or myofibroblasts only after liver injury, via a process termed "activation." In this study, we document lipocyte contractility on collagen lattices and examine the importance of activation in this process. In culture, lipocytes became contractile only after spreading and activating, coincident with expression of smooth muscle alpha actin, a marker of activation (1990. Virchows Arch. B Cell Pathol. 59:349). After 5 d in culture, lipocytes induced rapid and sustained contraction of collagen lattices (to 43.7 +/- 2.3% of their original size 24 h after detachment). There was no contraction of lattices containing hepatocytes. Scanning electron microscopy demonstrated intimate associations of lipocyte cell membranes and collagen fibrils. Reduction in cell volume during contraction was also prominent. Lattice contraction by lipocytes was proportional to cell number. Serum was a potent stimulator of lipocyte contraction, as were endothelin types 1, 2, and 3; the effect of serum and endothelin 1 were additive. Neither thrombin, angiotensin-II, serotonin, nor the cytokines PDGF and TGF beta induced contraction. Cytochalasin B treatment resulted in concentration-dependent inhibition of contraction. As a test of the in vivo relevance of the culture findings, lipocytes were isolated from fibrotic animals and examined immediately after adherence. Whereas lipocytes from normal liver were initially compact, smooth muscle alpha actin negative and noncontractile, cells from animals with hepatic injury due to CCl4 displayed an activated appearance, expressed smooth muscle alpha actin, and were contractile immediately after adherence. Additionally, IFN-gamma, an agent which blocks lipocyte activation (1992. Hepatology. 16:776), inhibited lipocyte contraction. The data document that normal (i.e., quiescent) lipocytes are not contractile, but that activation is associated with the development of contractility. These findings suggest that a role for lipocytes in organ contraction or vasoregulation may be confined to injured, not normal liver.

Fibroblast contraction of collagen gels requires activation of protein kinase C

Fibroblasts stimulated to contract collagen gels with serum were completely inhibited by staurosporine, a broad spectrum kinase inhibitor. Further analysis demonstrated that staurosporine is potent (IC50 17 nM), rapid in onset, and completely reversible. Complete inhibition of gel contraction was also observed with calphostin C (IC50 48 nM), an inhibitor specific for protein kinase C (PKC). Similar effects were not observed with KT5926 or KT5720, inhibitors for myosin light chain kinase and cAMP-dependent kinases, respectively. These data suggested that serum-stimulated fibroblast contraction is dependent upon activation of PKC. This was also observed with fibroblast contraction stimulated with endothelin-1, platelet-derived growth factor, and transforming growth factor beta. PKC activated directly with low concentrations of phorbol ester was observed to stimulate fibroblast contraction of collagen gels, in some cases within 30 minutes of exposure.

Cyclic AMP-induced inhibition of collagen lattice contraction by fibroblasts may be attenuated by both cyclic AMP dependent and independent mechanisms

The contraction of collagen lattices made with foreskin fibroblasts in medium containing 1% fetal bovine serum was inhibited by intracellular cyclic AMP-raising drugs including cholera toxin (CT), forskolin, and dibutyryl-cAMP. The inhibition by CT was attenuated by insulin, acidic fibroblast growth factor (aFGF), and transforming growth factor-beta (TGF-beta). All three peptide factors have previously been reported to promote collagen lattice contraction by arterial smooth muscle cells and/or fibroblasts. Incubation of cells suspended in collagen gels with CT and forskolin resulted in a transient rise of the intracellular cyclic AMP levels, which peaked at 2 hr and 30 min, respectively, after drug exposure. Cholera toxin-induced intracellular cyclic AMP increase was attenuated by TGF-beta, but not by aFGF and insulin, when added simultaneously. Thus, TGF-beta may attenuate CT's inhibition on collagen lattice contraction by attenuating CT-induced intracellular cyclic AMP increase, whereas the attenuation by insulin and aFGF on the inhibition of lattice contraction may be mediated by a cyclic AMP-independent mechanism.

Extracellular matrix contraction by fibroblasts: peptide promoters and second messengers

Cells contracting connective tissue matrices generate tractional forces in tissues. Studies of fibroblast contraction, using collagen gels in an in vitro model, demonstrate that it involves the actin cytoskeleton, specific extracellular matrix receptors and requires stimulation by exogenous promoters. Fibroblast contraction is stimulated by factors released by platelets and potentially secreted within the contracting tissue. Endothelial cells secrete a potent promoter of fibroblast contraction which has been identified as endothelin 1. The pathway through which fibroblast contraction is stimulated appears to require activation of protein kinase C. Tumor cells can also secrete endothelin. These mechanisms may be relevant to tumor progression.

Primary culture of rat hepatocytes entrapped in cylindrical collagen gels: An in vitro system with application to the bioartificial liver

A static culture model employing cylindrical collagen-hepatocyte gels is reported for large scale testing of conditions relevant to the three compartment hollow fiber bioartificial liver. High density hepatocyte cultivation was achieved by cell entrapment within the collagen-hepatocyte gel. Hepatocyte viability was assessed by vital staining, gel contraction, and insulin utilization. Measures of hepatocyte-specific function included albumin synthesis, ureagenesis, lidocaine biotransformation, and cholate conjugation. Although hepatocyte viability remained stable through the seven day incubation period, hepatocyte functions were not uniformly preserved. Albumin synthesis remained stable, while representative P-450 and conjugation activities decreased with time. This static culture system will facilitate the development of a hollow fiber bioartificial liver which utilizes cylindrical collagen-hepatocyte gels.

Endothelins produced by endothelial cells promote collagen gel contraction by fibroblasts

Endothelial 1 (E1) is identified as an endothelial cell secreted factor that stimulates collagen gel contraction by fibroblasts. This identification is based on (a) co-localization of stimulatory activity in endothelial cell conditioned media with synthetic E1 in reversed phase analysis; (b) removal of the activity from conditioned media with antiserum directed against E1; and (c) the activity of synthetic E1. Treatment of endothelial cell conditioned media with immobilized anti-E1 antibodies removed 59% of the activity from the pool suggesting that E1 is the major contraction promoter in endothelial cell conditioned medium. The mechanism of action of E1 is shown to be different from serum in that E1-promoted contraction is dependent upon the synthesis of an unknown effector protein. Synthetic E1 is shown to be a potent promoter of gel contraction with half-maximal activity occurring at 32 pM. Two other endothelins, E2 and VIC, are slightly less active than E1. A fourth endothelin species, E3, is substantially less active. A comparison of E1 with other contraction promoting peptides revealed that E1 and platelet-derived growth factor are essentially equal in specific activity, whereas TGF beta is approximately 50-fold more potent.