Diazepam effects on non-syndromic cleft lip with or without palate: epidemiological studies, clinical findings, genes and extracellular matrix

IMPORTANCE OF THE FIELD

This review analyses international studies investigating the combined genetic and environmental causes of cleft lip with or without cleft palate (CL/P) and describes successes and limitations in identifying underlying genetic and environmental factors. CL/P, the most common congenital facial malformation, is a major public health burden in terms of medical costs and emotional stress to patients and families. Because genetic and environmental factors determine risk of occurrence, CL/P has a complex, multifactor aetiology.

AREAS COVERED IN THIS REVIEW

English language reports from 1980 to 2010 were searched for in Medline, PubMed, Science Citation Index, textbooks and review articles on drugs and pregnancy. Key words were diazepam or benzodiazepine(s) combined with cleft lip, cleft palate, oral malformations, prenatal exposure, GABA, gene expression and extracellular matrix.

WHAT THE READER WILL GAIN

This review presents an updated assessment of the mutagenic and genotoxic effects of diazepam (DZ), one of the most commonly used benzodiazepines, on CL/P occurrence.

TAKE HOME MESSAGE

Data are divergent; more studies are needed for an in-depth picture of the effects of DZ during gestation on the child's development, particularly on orofacial clefts.

Effects of titanium surface roughness on mesenchymal stem cell commitment and differentiation signaling

PURPOSE

Human mesenchymal stem cells (hMSCs) are primary cells capable of differentiating to osteocytic lineage when stimulated under appropriate conditions. This study examined changes in hMSC morphology, proliferation, and gene expression after growth on machined or dual acid-etched (AE) titanium surfaces.

MATERIALS AND METHODS

hMSCs, isolated from adult human bone marrow, were cultured on titanium surfaces. The two specimens of titanium surfaces in this study included machined and AE titanium disks. Cell morphology was evaluated by scanning electron microscopy, and cell proliferation and collagen synthesis were estimated by measuring the amount of 3H-thymidine incorporation into DNA and 3H-proline incorporation into collagen fibers. Alkaline phosphatase (ALP) activity was determined by measuring the release of p-nitrophenol from disodium p-nitrophenyl phosphate. Changes in gene expression for bone morphogenetic protein-2 (BMP-2), Runx2 type II, Osterix (Osx), osteopontin, type I collagen, ALP, osteocalcin, and bone sialoprotein were determined by reverse-transcriptase polymerase chain reaction after 22 days of in vitro culture in osteogenic medium.

RESULTS

The two substrates had no significant effects on cell adhesion and proliferation. Morphologic characteristics were observed by scanning electron microscopy. hMSCs on the machined surface spread more and were flatter than cells cultured on the AE surface. Osteopontin mRNA expression was similar on all surfaces, and the other mRNA transcripts were increased in hMSC cultured on AE surface. In particular, BMP-2, Runx2, and Osx, three osteogenic factors that induce the progressive differentiation of multipotent mesenchymal cells into osteoblasts, were expressed more on AE titanium than on machined titanium. Collagen and ALP assays confirmed the highest level of mRNA transcripts correlated with increases in these proteins.

CONCLUSION

These results showed that an AE titanium surface stimulated the expression of markers of osteoblastic phenotype more than a machined titanium surface.

Toremifene decreases type I, type II and increases type III receptors in desmoid and fibroma and inhibits TGFbeta1 binding in desmoid fibroblasts

Tissue infiltration is different in desmoid and fibroma tumours. Both produce high levels of transforming growth factor beta1 (TGFbeta1), which is related to extracellular matrix (ECM) accumulation which in turn regulates cell function and cell migration. Interactions between collagen, proteoglycans and cell surface fibronectin are involved in the assembly and functions of the ECM. As toremifene inhibits collagen and TGFbeta1 synthesis, we tested it in normal, desmoid and fibroma fibroblasts. We will report the changes in glycosaminoglycan (GAG) and collagen synthesis, TGFbeta1 activity, fibronectin mRNA expression and TGFbeta1 receptors after toremifene treatment in normal, fibroma and desmoid fibroblasts. We evaluated GAG and collagen synthesis with 3H-glucosamine and 3H-proline incorporation, TGFbeta1 activity with the ELISA method, TGFbeta1 receptor affinity with 125I-TGFbeta1 binding and total RNA with Northern blot analysis. GAG and collagen synthesis, TGFbeta1 activity and fibronectin levels were higher in fibroma and desmoid than normal fibroblasts. The increase was greater in desmoid than fibroma tumour cells. Toremifene treatment reduced GAG and collagen synthesis, TGFbeta1 activity and fibronectin levels in all cell cultures. The percentage reduction in GAG was similar in all cultures; the reduction in collagen synthesis and TGFbeta1 activity was the highest in desmoid fibroblasts. TGFbeta1 receptors were higher in fibroma and desmoid cells than controls. Toremifene reduced TGFbeta1 receptors only in desmoid fibroblasts, with no effect on the changes in type I, II, and III receptors. Our data show that toremifene modifies the ECM components that regulate cytokine activity and cell migration. The reduction in receptor number only in desmoid cells suggests that toremifene may reduce TGFbeta1's affinity for its receptors. Synthesis of a substance regulating protein kinase activity, which is directly involved in the link between TGFbeta1 and its receptors, cannot be excluded.

Desmoid and fibroma tumors differently respond to TGFβ1 stimulus and ECM macromolecule accumulation

Desmoid and fibroma tumours are characterized by cell proliferation, glycosaminoglycan and collagen fibre accumulation, high levels of transforming growth factor beta(1) (TGFbeta(1)) and different patterns of tissue infiltration. TGFbeta(1) is related to extracellular matrix (ECM) composition which, in turn, regulates cell functions and cell migration. In this study we report changes in cell proliferation, glycosaminoglycan (GAG) and collagen synthesis, TGFbeta(1) mRNA expression and fibronectin levels in normal, desmoid and fibroma fibroblast cultures before and after TGFbeta(1) stimulation. Our data showed cell proliferation, GAG and collagen synthesis, transforming growth factor beta(1) mRNA expression and fibronectin levels were significantly higher in desmoid than in fibroma cultures. TGFbeta(1) treatment had no effect on cell proliferation, but increased TGFbeta(1) mRNA expression, GAG, fibronectin and collagen synthesis in desmoid and fibroma fibroblasts. Its effects were more marked in desmoid cells. Fibronectin favours cell migration, while changes in GAG composition alter cell behaviour and ECM organization. In conclusion our data suggest that the different patterns of infiltration in desmoid and fibroma tumours are due to changes in ECM components and cell-ECM interactions which can be ascribed to altered TGFbeta(1) mRNA expression and TGFbeta(1) activity.

Extracellular matrix and growth factors in the pathogenesis of some craniofacial malformations

The normal development of cranial primordia and orofacial structures involves fundamental processes in which growth, morphogenesis, and cell differentiation take place and interactions between extracellular matrix (ECM) components, growth factors and embryonic tissues are involved. Biochemical and molecular aspects of craniofacial development, such as the biological regulation of normal or premature cranial suture fusion, has just begun to be understood, thanks mainly to studies performed in the last decade. Several mutations has been identified in both syndromic and non-syndromic craniosynostosis patients throwing new light onto the etiology, classification and developmental pathology of these diseases. In the more common craniosynostosis syndromes and other skeletal growth disorders, the mutations were identified in the genes encoding fibroblast growth factor receptor types 1-3 (FGFR1, 2 and 3) where they are dominantly acting and affect specific and important protein binding domain. The unregulated FGF signaling during intramembranous ossification is associated to the Apert and Crouzon syndrome. The non syndromic cleft of the lip and/or palate (CLP) has a more complex genetic background if compared to craniosynostosis syndrome because of the number of involved genes and type of inheritance. Moreover, the influence of environmental factor makes difficult to clarify the primary causes of this malformation. ECM represents cell environment and results mainly composed by collagens, fibronectin, proteoglycans (PG) and hyaluronate (HA). Cooperative effects of ECM and growth factors regulate regional matrix production during the morphogenetic events, connective tissue remodelling and pathological states. In the present review we summarize the studies we performed in the last years to better clarify the role of ECM and growth factors in the etiology and pathogenesis of craniosynostosis and CLP diseases.

Effect of titanium surface roughness on human osteoblast proliferation and gene expression in vitro

PURPOSE

Cell proliferation and extracellular matrix formation are primary events in bone formation. At the dental implant-tissue interface, implant surface roughness modulates osteoblast functions. The aim of the present in vitro study was to investigate the effect of varying surface roughness of titanium implant material on cell proliferation and mRNA expression of specific markers of osteoblast phenotype.

MATERIALS AND METHODS

Primary cultures of osteoblasts derived from human mandibular bone were cultured on titanium surfaces. Three titanium surfaces were studied: machined titanium, microsandblasted titanium, and macro-sandblasted titanium (average surface roughnesses of 0.5 and 3 microm, respectively). Cell morphology was estimated by scanning electron microscope analysis and cell proliferation by measuring the amount of 3H-thymidine incorporation into DNA. mRNA expression of osteonectin, osteopontin, bone sialoprotein (BSP), and Runx2, which are markers of osteoblastic phenotype, were determined by reverse transcriptase polymerase chain reaction (RT-PCR) analysis.

RESULTS

Human osteoblasts cultured on machined titanium spread more and were flatter than cells cultured on rough titanium. All blasted surfaces showed significantly higher DNA synthesis than the machined surfaces. Osteonectin mRNA expression was similar on all surfaces. Other mRNA transcripts were increased in osteoblasts cultured on rough titanium surfaces, particularly the macrosandblasted surface.

CONCLUSIONS

An average surface roughness of 3 microm (macro-sandblasted titanium) is more suitable than an average surface roughness of 0.5 microm (micro-sandblasted titanium) in favoring osteoblast differentiation in vitro.

In vitro human osteoblast and extracellular matrix changes after transforming growth factor beta 1 treatment

AIMS

Normal bone tissue is characterised by a balancing of osteoblast and osteoclast activity. The activity and differentiation of these cells are regulated by vitamins, hormones and cytokines. The action of these factors on bone tissue cells depends on the composition and mineralisation of extracellular bone matrix. In particular, transforming growth factor beta 1 (TGFbeta1) acts on collagen fibres, glycosaminoglycan secretion and on the enzymes correlated to the turnover of glycosaminoglycans. The normal functions of bone tissue also depend on its mineralisation, which is highly altered in the process of uraemia.

METHODS

In this study, we analysed in vitro the effect of transforming growth factor beta on osteoblast proliferation, collagen synthesis and glycosaminoglycan secretion with 3H-thymidine, 3H-proline or 3H-glucosamine incorporation, and on enzymes, such as beta-N-acetyl-D-glucosaminidase and beta-glucuronidase, involved in extracellular matrix turnover. Moreover, phosphatase alkaline activity and osteocalcin related to mineralisation of extracellular matrix were determined.

RESULTS

Our data show that TGFbeta1 significantly decreases 3H-thymidine and 3H-proline incorporation and increases (p < or = 0.01) extracellular sulphated glycosaminoglycan synthesis. It also increases osteocalcin levels, phosphatase alkaline, beta-N-acetyl-D-glucosaminidase and beta-glucoronidase activities.

CONCLUSION

TGFbeta1 changes the synthesis of extracellular matrix components by osteoblasts. These variations favour the action of cytokine and osteoclasts. Since the TGFbeta1 accumulates in bone tissue and increases during uraemia, with due limitations this action leads to an imbalance between synthesis and degradation and could explain bone alterations in uraemic patients.

Apert and Crouzon syndromes: clinical findings, genes and extracellular matrix

Apert and Crouzon syndromes are well known craniostenosis. In the last 10 years several studies were performed to provide a better understanding of the etiology and pathogenesis of these diseases. Both have an autosomal dominant mode of transmission, and a mutation in the gene encoding for the fibroblast growth factor receptor 2 (FGFR2) is the cause in most patients. However, the fact that the same mutation can produce a wide range of phenotypic expression makes the mechanism of anomalous development more complex. The extracellular matrix (ECM) is composed of proteins, glycosaminoglycans, and cytokines that are secreted in an autocrine and paracrine manner and are able to modify the ECM. Fibroblast growth factors are complexed with heparan sulfate, a component of the ECM, before binding the FGFR2. Data exist about different expressions of cytokines and ECM macromolecule in craniostenosis-derived fibroblasts and osteoblasts. Changes in ECM composition could explain the altered osteogenic process and account for pathologic variations in cranial development in addition to the FGFR2 mutations.

Biocompatibility of collagen membranes crosslinked with glutaraldehyde or diphenylphosphoryl azide: Anin vitro study

Crosslinking of collagen biomaterials increases their resistance to degradation in vivo. Glutaraldehyde (GA) is normally used to crosslink collagen biomaterial, but is often cytotoxic. Diphenylphosphoryl azide (DPPA) has recently been proposed as reagent, but little is known about its effects on cell behavior. In this study, we determined which collagen membrane was the most biocompatible: Paroguide which is crosslinked with DPPA and contains chondroitin sulfate; Opocrin which is crosslinked with DPPA; Biomed Extend which is crosslinked with GA; and Bio-Gide which is left untreated. Cell proliferation and extracellular matrix macromolecule deposition were evaluated in human fibroblasts cultured on the membranes. The GA-crosslinked Biomed Extend membrane and the not-crosslinked Bio-Gide membrane reduced cell growth and collagen secretion compared with DPPA-crosslinked biomembranes. When Paroguide and Opocrin were compared, better results were obtained with Paroguide. The greatest amount of transforming growth factor beta1, a growth factor involved in extracellular matrix macromolecule accumulation and in tissue regeneration, was produced by cells cultured on Paroguide, with Opocrin second. Our data suggest that the DPPA method is more biocompatible than the GA for crosslinking collagen biomaterials and that membranes made of collagen plus chondroitin sulfate are better than membranes made of pure collagen.

Biomembranes enriched with TGFbeta1 favor bone matrix protein expression by human osteoblasts in vitro

The use of growth factors in oral tissue regeneration is currently under investigation. When growth factors are combined with commercial materials, the in vitro mechanisms of action still remain unclear. The present study first evaluated the capacity of barrier membranes, used in oral surgery, to sequester TGFbeta(1). Resorbable HYAFF, paroguide, poly DL-lactide and nonresorbable PTFE membranes were immersed in MEM containing 0.2 ng (125)I-TGFbeta(1) for different periods of time. It was found that HYAFF membrane and paroguide sequestered the most TGFbeta(1), which was then released in its active form (as shown by the CCL64 cell line bioassay). Untreated membranes and membranes enriched with TGFbeta(1) were then used as substrate for human bone cells to evaluate the synthesis of the osteoblast phenotype, as indicated by specific parameters. Results showed that membranes enriched with TGFbeta(1) increased alkaline phosphatase activity, collagen, and osteocalcin production more than untreated membranes. HYAFF and paroguide membranes, which sequestered the most of TGFbeta(1), were the most suitable for stimulating bone matrix proteins.

The effect of polyamines and dialysate fluid on extracellular matrix synthesis in VERO cell cultures

BACKGROUND

Polyamines are involved in normal and pathological cell proliferation and differentiation. Like acid radicals, they play an important role in remodelling the extracellular matrix and are considered "uremic toxins". Proteins and glycosaminoglycans are essential components of the extracellular matrix, and contribute to normal mature organ functions. The aim of this study was to analyse the effects of free polyamines, dialysate fluid components and dialysis fluid on protein and extracellular glycosaminoglycan synthesis in VERO cell cultures.

METHODS

The dialysate fluid components were separated with a Sephadex G15 column and the cultures were analysed after incorporation of 3H-leucine and 3H-glucosamine. Cultures were run at pH 7.0 and pH 7.4. The glycosaminoglycan classes were separated with a DEAE column, and polyamines were determined by high-performance liquid chromatography. Proteins and single glycosaminoglycan classes were quantified by a scintillator. DNA gel electrophoresis was done to detect chromatin fragmentation.

RESULTS

Dialysate contained putrescine, spermidine and spermine, chromatography showing four peaks; only peaks I and II indicated polyamines at respectively Da 5000 and 1500. Polyamines are therefore linked to different carriers. There was an increase of protein and glycosaminoglycan synthesis with dialysis fluid and polyamines, but inhibition with peak II or dialysate. DNA gel electrophoresis showed no chromatin fragmentation. Findings at pH 7.0 and 7.4 were similar.

CONCLUSIONS

It would appear that in uremic patients polyamines are conjugated to protein carriers of different molecular weights with different biological actions. As polyamines and dialysis fluid affect changes in extracellular matrix, they could be related to physiological organ functions. However, these in vitro data must be considered with the appropriate limitations when we try to extrapolate them to the in vivo situation.

Crouzon's syndrome: differential in vitro secretion of bFGF, TGFbeta I isoforms and extracellular matrix macromolecules in patients with FGFR2 gene mutation

In the Crouzon's syndrome the cranial morphogenic processes are altered due to the early fusion of cranial sutures. We analysed the phenotype of cultured fibroblasts from normal subjects and from Crouzon patients with a specific fibroblast growth factor receptor 2 mutation resulting in a Cys 342 Tyr substitution within the third immunoglobulin domain. Crouzon fibroblasts differed from normal fibroblasts in their extracellular matrix macromolecule accumulation. In Crouzon fibroblasts glycosaminoglycans and fibronectin were decreased and type I collagen increased. As transforming growth factors beta (TGF beta) and basic fibroblasts growth factor (bFGF) together regulate extracellular matrix deposition, we evaluated TGF beta(1), TGF beta(3) and bFGF production by Crouzon and normal fibroblasts. TGF beta(1), TGFb(3) and bFGF levels were lower while TGF beta(1) mRNA transcripts were higher in Crouzon cells. As the increased TGF beta(1) gene expression did not translate into a parallel increase of secreted TGF beta(1), control of TGF beta(1) secretion may be mainly post-transcriptional. Furthermore, adding bFGF increased TGF beta(1) and TGF beta(3) secretion, suggesting the drop may be due to the altered signal transduction of bFGF. These innovative data suggest the in vitro differences between normal and Crouzon fibroblasts may be due to an imbalance in TGF beta and bFGF levels which alters the microenvironment where morphogenesis takes place.

Cyclosporin A and transforming growth factor beta modify the pattern of extracellular glycosaminoglycans without causing cytoskeletal changes in human gingival fibroblasts

Cyclosporin A is a powerful immunosuppressive drug that has had a major impact on transplant therapy. It apparently links to different enzymatic pathways, and affects multiple enzymatic systems. Transforming growth factor beta induces the deposition of glycosaminoglycans, proteoglycans, and collagen fibers in the extracellular matrix. The aim of this study of normal and hypertrophic human gingival fibroblast cultures was to evaluate the cytoskeletal and extracellular changes in glycosaminoglycan secretion due to the presence of cyclosporin A and transforming growth factor beta. The results showed that there is an increase in total and individual classes of extracellular glycosaminoglycans in the presence of cyclosporin A and transforming growth factor beta, but the action of the latter was significantly greater. Immunohistochemical analysis of the cytoskeleton did not reveal any morphological differences between treated and control cells. Our data suggest that the biochemical changes in the extracellular matrix are caused more by cytokine, and that cyclosporin A does not induce any morphological changes in fibroblast cultures derived from hypertrophic and normal gingiva.

Effects of transforming growth factor-beta1 and tumour necrosis factor-alpha on cultured fibroblasts from skin fibroma as modulated by toremifene

To determine how toremifene, an anti-oestrogen triphenylethylene derivate, reduces tumour mass, we investigated its modulation of TGF-beta1 and TNF-alpha in fibroma fibroblasts. Normal and fibroma fibroblasts, isolated from patients affected by Gardner's syndrome without or with fibroma manifestation, were cultured in vitro. Secretion of GAG, collagen and TGF-beta1 was increased in fibroma fibroblasts compared to healthy cells. The increase in TGF-beta1 secretion into the medium was associated with a parallel increase in TGF-beta1 gene expression and receptor number. Receptor cross-linking studies using radiolabelled TGF-beta1 revealed more receptors, particularly types I and II, in fibroma fibroblasts than in normal cells. Normal and fibroma fibroblasts did not synthesise TNF-alpha, but they had TNF-alpha membrane receptors, as shown by TNF-alpha assay. TNF-alpha secreted by human monocytes, which may be present in the peritumoral area, increased cell proliferation and GAG accumulation and was, in turn, enhanced by TGF-beta1 treatment. Both growth factors increased angiogenesis, as shown by the CAM assay. Toremifene reduced TGF-beta1 secretion by fibroma fibroblasts and TNF-alpha secretion by monocytes, thus downregulating cell proliferation, ECM macromolecule accumulation and angiogenic progression. We hypothesise that increased TGF-beta1 gene expression and TGF-beta1 secretion in fibroma fibroblasts as well as the subsequent rise in TNF-alpha production by monocytes may facilitate fibroma growth and that toremifene inhibits autocrine and paracrine growth factor production.

Epithelial-mesenchymal interactions and lung branching morphogenesis. Role of polyamines and transforming growth factor beta1

Lung branching morphogenesis is a result of epithelial-mesenchymal interactions, which are in turn dependent on extracellular matrix composition and cytokine regulation. Polyamines have recently been demonstrated as able to modify chick embryo skin differentiation. In this work we have examined the effects of putrescine and spermidine during chick embryo lung morphogenesis in organotypic cultures by morphological, histochemical and biochemical examination. To verify the role of polyamines, we used specific inhibitors, such as bis-cyclohexylammonium sulphate and alfa-difluoromethylornithine, and transforming growth factor beta1, an ornithine decarboxylase and polyamine stimulator. Our data show that lung morphogenesis is significantly altered following the induced mesenchymal glycosaminoglycan changes. The increase of mesenchymal glycosaminoglycans is correlated with a stimulation of lung development in the presence of polyamines, and with its inhibition when transforming growth factor beta1 is added to the culture medium. The morphometric data show a uniform increase of both the mesenchyme and epithelial branching with spermidine and putrescine stimulus, whereas the mesenchymal substance alone is significantly increased in apical-median lung sections with transforming growth factor beta1 and transforming growth factor beta1 + spermidine lung cultures. Transforming growth factor beta1 and transforming growth factor beta1 + spermidine confirm the blocking of epithelial branching formations and fibroblast activation, and show that polyamines are unable to prevent the blocking of epithelial cells due to the inhibitory effect of transforming growth factor beta1.

Synthesis and secretion of transforming growth factor-beta1 by human desmoid fibroblast cell line and its modulation by toremifene

The present study provides evidence that the in vitro cultured fibroblast cell line from desmoid tumors differs from normal fibrobasts in its extracellular matrix (ECM) macromolecule composition and is modulated by treatment with toremifene, an antiestrogen that reduces tumor mass by an unknown mechanism. The results showed increased transforming growth factor-beta 1 (TGF-beta1) production, TGF-beta1 mRNA expression, and TGF-beta1 receptor number in desmoid fibroblasts compared with normal cells. As desmoid fibroblasts did not produce tumor necrosis factor-alpha (TNF-alpha) but were sensitive to it, which enhanced glycosaminoglycans (GAG) accumulation, we assessed the TGF-beta1 effects on TNF-alpha production by human monocytes. Our results showed TGF-beta1 significantly increased TNF-alpha secretion by monocytes. Toremifene mediated its effects in desmoid fibroblasts via an estrogen receptor-independent pathway. It inhibited GAG accumulation and the secretion of both latent and active forms of TGF-beta1 and had an inhibitory effect on TNF-alpha production by monocytes. Our results suggest that in reducing TGF-beta1 production by desmoid fibroblasts and TNF-alpha production by monocytes, toremifene may restore the balance between the two growth factors.

In vitro comparison of bioabsorbable and non-resorbable membranes in bone regeneration

BACKGROUND

Barrier membranes are used to prevent down-growth of the oral mucosa along the root surface and to allow alveolar bone regeneration in guided tissue regeneration. Several studies have demonstrated bone regenerates in the presence of bioabsorbable and non-resorbable membranes, but no studies have compared multiple bioabsorbable barriers to one another and to non-resorbable barriers. This study evaluated the in vitro influence of bioabsorbable and non-resorbable membranes on specific parameters of human osteoblast activity.

METHODS

Human osteoblasts were cultured on bioabsorbable membranes made of collagen, hyaluronic acid, and poly DL-lactide, and the most common non-resorbable membrane which is made of expanded polytetrafluoroethylene (ePTFE). The osteoblasts were cultured in vitro for 24 hours on barrier membranes in the presence of 3H-thymidine and 3H-proline to study cell proliferation and collagen synthesis. Transforming growth factor-beta1 (TGF-beta1) secretion was evaluated in conditioned media using an ELISA kit.

RESULTS

The results showed that collagen and poly DL-lactide stimulated DNA synthesis more than ePTFE and hyaluronic acid. All bioabsorbable membranes significantly increased collagen synthesis and alkaline phosphatase activity. Collagen and hyaluronic acid increased secretion of TGF-beta1, a growth factor involved in bone remodeling.

CONCLUSIONS

These data suggest bioabsorbable membranes, particularly collagen and hyaluronic acid, may promote bone regeneration through their activity on osteoblasts.

Biocompatibility of alloys used in orthodontics evaluated by cell culture tests

The cytotoxicity of the most common alloys used in orthodontic appliances was determined by cell culture testing. Human gingival fibroblasts were cultured on 304 and 316 stainless steel, on brazing alloy composed of palladium (Pd), copper (Cu), and silver (Ag), and on plastic substrate (control). Studies were carried out with SEM and radiolabeled precursor incorporation. Cells were cultured in MEM without serum but with the addition of (3)H-thymidine to evaluate cell proliferation and (3)H-glucosamine to evaluate glycosaminoglycan (GAG) synthesis and secretion in the culture medium. Moreover, gingival fibroblasts were cultured in the presence of some metal ions generally released by orthodontic appliances to evaluate the cytotoxic effects of single ions. Morphologic observations with SEM and radiolabeled incorporation studies showed that 304 and 316 stainless steel were more biocompatible than the brazing alloy. Among the metal ions tested, Ag and Pd, constituents of the brazing alloy, showed the highest cytotoxicity.

In vitro cytotoxic effects of orthodontic appliances

The objective of this study was to evaluate the effects of an orthodontic appliance and of its components (brackets, bands, and arch wires) on some cell functions. Fibroblasts were cultured either in the presence of one unwashed orthodontic appliance, or one orthodontic appliance immersed in MEM for 28 days before use (washed appliance), or in the presence of MEM in which the appliances had been immersed. At the end of in vitro maintenance, morphological studies were carried out with SEM and TEM. Cell proliferation and GAG synthesis and secretion by radio-labeled precursors were assessed. The data indicated that unwashed appliances were more cytotoxic than washed ones. Moreover, the arch wire was the most biocompatible component of the orthodontic appliance, and the bracket was the least biocompatible. A comparative study into the effects on cell proliferation of the most common metal ions released by the appliances was also carried out. At the concentration released by one orthodontic appliance immersed for 28 days, the highest reduction in DNA synthesis was observed in the presence of Cu(++).

Differential in vitro phenotype pattern, transforming growth factor-beta(1) activity and mRNA expression of transforming growth factor-beta(1) in Apert osteoblasts

The phenotype of Apert osteoblasts differs from that of normal osteoblasts in the accumulation of macromolecules in the extracellular matrix. Apert osteoblasts increase type I collagen, fibronectin and glycosaminoglycans secretion compared with normal osteoblasts. Because the extracellular matrix macromolecule accumulation is greatly modulated by transforming growth factor-beta(1), we examined the ability of normal and Apert osteoblasts to secrete transforming growth factor-beta(1) by CCL-64 assay and to produce transforming growth factor-beta(1 )by analysis of the mRNA expression of transforming growth factor-beta(1). Northern blot analysis revealed an increased amount of transforming growth factor-beta(1) mRNA expression in Apert osteoblasts compared with normal ones. Moreover, the level of the active transforming growth factor-beta(1) isoform was higher in Apert than in normal media. In pathologic cells, the increase in transforming growth factor-beta(1) gene expression was associated with a parallel increase in the factor secreted into the medium. The level of transforming growth factor-beta(1) was decreased by the addition of basic fibroblast growth factor. Transforming growth factor-beta(1) is controlled temporally and spatially during skeletal tissue development and produces complex stimulatory and inhibitory changes in osteoblast functions. We hypothesise that in vitro differences between normal and Apert osteoblasts may be correlated to different transforming growth factor-beta(1) cascade patterns, probably due to an altered balance between transforming growth factor-beta(1) and basic fibroblast growth factor.

Ion release from orthodontic appliances

OBJECTIVE

The microbiological and enzymatic characteristics of the oral cavity would seem to provide a suitable environment for the corrosion of metals. We assayed the release of metal ions from one orthodontic appliance which included two 304 and 316 steel molar bands, ten 316 steel brackets, one nickel-titanium archwire and a brazing alloy to connect the elements of molar bands and brackets.

METHODS

The orthodontic appliance was dipped in both inorganic (pH 3.5-6.5) and organic acid solutions (w/v 1% each of tartaric, citric and ascorbic acid at pH 2.2 or 1.5% each of lactic and acetic acid at pH 2.5). The release of nickel (Ni), chromium (Cr), copper (Cu), silver (Ag) and palladium (Pd) was determined using an atomic absorption spectrophotometer Varian AA 10.

RESULTS

The release of Ni, Cr and Cu was markedly less at pH 6.5 than at pH 3.5 at all time points in acid solution. Daily release/single appliance after the first day decreased. Contrary to expectations, appliances immersed in organic acid solutions at pH 2.2 or 2.5 after 28 days generally released an amount of ions similar to that observed in inorganic acid solution at pH 3.5, with the exception of Cu. Release of silver and palladium, two metals present in the brazing alloy, proved to be very low (approximately 0.2 microgram after 28 days).

CONCLUSIONS

The daily release of Ni, Cu and Cr by an orthodontic appliance in acid pH, particularly favourable to corrosion, was well below that ingested with a normal daily diet. It is therefore concluded that the quantities of metal ions released in our experimental conditions should not be cause for concern in utilising the appliance.

TGFbeta and TGFalpha, antagonistic effect in vitro on extracellular matrix accumulation by chick skin fibroblasts at two distinct embryonic stages

ECM macromolecules create a specific environment that participates in the control of cell proliferation and differentiation during embryogenesis. Quantitative and qualitative alterations in the ECM may depend on several growth factors that modify cell metabolism. Since transforming growth factor beta (TGFbeta) and alpha (TGFalpha) are abundantly expressed during embryonic development in organs in which epithelial-mesenchymal interactions occur, the aim of this study was to determine: a) the effect of TGFbeta on the phenotype of 7 and 14 day chick embryo back skin (CEBS) fibroblasts by evaluating the neosynthesis of GAG, collagen and fibronectin; b) whether TGFalpha and TGFbeta production, in particular TGFbeta3 and TGFbeta4, and the number of TGFbeta receptors change during these two stages of embryonic development. The results show that the neosynthesis of ECM macromolecules, tested using radiolabelled precursors, is increased by TGFbeta. The growth factor generally favours cellular accumulation more than secretion. As far as GAG is concerned, TGFbeta has a greater stimulatory effect on sulphated GAG than on HA. Specific bioassay shows that TGFbeta3 and TGFbeta4 activity is higher in 7 day than 14 day CEBS fibroblasts. Moreover, TGFbeta3 and TGFbeta4 mRNA expression is increased in the first stages of development. Instead, the level of TGFalpha increases in successive developmental stages. Since TGFalpha stimulates the synthesis and secretion of HA, and HA binds and inactivates TGFbeta, the greater quantity of HA in 14 day fibroblasts may contribute to reducing the TGFbeta effect. Overall our data suggest that the production of TGFbeta and TGFalpha are age-dependent and that the balance between the two growth factors may be a mechanism for controlling skin differentiation.

Phenotype expression of human bone cells cultured on implant substrates

Bone cells derived from the human jaw were cultured on titanium, titanium coated with hydroxyapatite (THA) or with plasma spray (TPS) to study the behaviour of the cells anchored to implant substrates. Bone cells were cultured in MEM with the addition of [3H]-thymidine to evaluate cellular proliferation, and [3H]-glucosamine to evaluate GAG synthesis and accumulation in the extra-cellular matrix (ECM). Moreover, to study the degradation of GAG bone cells were cultured in the presence of NH4Cl, an amine known to inhibit lysosomal activity. Our results show that TPS is the substrate that favours both cellular proliferation and the accumulation of GAG in the ECM.

Phenotype expression of gingival fibroblasts cultured on membranes used in guided tissue regeneration

Human gingival fibroblasts were cultured in vitro using as substrates an extracellular matrix (matrix) and polytetrafluoride (PTFE) membranes, which are used in guided tissue regeneration. To test the degree of biocompatibility of these membranes, the cellular proliferation and the accumulation of extracellular matrix (ECM) macromolecules were considered as parameters. The fibroblasts were cultured in vitro for 24 and 48 hours without serum on plastic, matrix, and PTFE membranes in the presence of 3H-thymidine, 3H-glucosamine, and 3H-proline to study the neo-synthesis of DNA, glycosaminoglycans (GAG), and collagen proteins, respectively. Studies on cell proliferation showed that fibroblasts grown on matrix membrane significantly increased 3H-thymidine incorporation, while fibroblasts grown on PTFE membrane decreased 3H-thymidine incorporation, compared to plastic used as a control. Moreover, the PTFE membrane induced a marked decrease of collagen and GAG accumulation both in the cellular and extracellular pool, while the matrix membrane provoked a decrease of the two macromolecules in the cellular pool and an increase in the extracellular one, compared to the control. The data we obtained demonstrate that matrix membranes are the most suitable to stimulate both cellular proliferation and ECM macromolecule accumulation.

Exogenous heparin induces fibronectin overexpression parallel to angiogenesis in the extracellular matrix of the chick embryo chorioallantoic membrane

Heparin (HE) was injected into the allantoic sac of chick embryo eggs on the 5th day of incubation. After 48 h, a morphometric analysis of angiogenic response and an immunohistochemical investigation of fibronectin (FN) and type IV collagen immunoreactivity in developing vasculature were performed in order to verify whether HE-related choriollantoic membrane (CAM) angiogenic activity was associated with overexpression of FN and/or type IV collagen changes in CAM extracellular matrix. Data to be presented show a close relationship between HE treatment, angiogenic processes, and overexpression of FN, but not of type IV collagen in CAM extracellular matrix. They agree with other studies proving a facilitating role of FN in angiogenic processes.

Metal substrates influence the release of glycosaminoglycan and transforming growth factor beta by human bone cells

Bone cells derived from human jaw were isolated from explants and grown in vitro. Subcultures were cultured on plastic (control) and metal substrates for 24 and 48 hours in medium containing 3H-glucosamine and labeled glycosaminoglycan (GAG) accumulation was measured. In bone cells cultured on metal substrates there was an evident reduction in the synthesis and secretion of radiolabeled macromolecules compared to bone cells cultured on plastic. Moreover, the accumulation of single GAG classes was specific for each substrate tested. The results showed that titanium was the only metal substrate studied in which the percentage of individual GAG classes remained the same as control cultures. GAG reduction was due to a decreased synthesis and not to an increased degradation as shown by the decrement of exoglycosidase activity. The metals also reduced the activity of transforming growth factor beta (TGF beta), measured using interleukin-1 assay method, a factor involved in the various phases of bone remodeling; in this case, too, cells grown on titanium showed the highest TGF beta activity compared to the other metal substrates studied. The results indicate that the substrate to which the cells adhere do exhibit specific differences in GAG composition and TGF beta activity. The differences observed may be important during in vivo events such as guided tissue regeneration and bone deposition.

Transforming growth factor beta 1-hyaluronic acid interaction

Chick embryo skin fibroblasts release transforming growth factor beta 1 that is able to modulate glycosaminoglycan synthesis and secretion. When incubated with individual classes of glycosaminoglycans, the factor's modulatory activity was altered. To determine whether direct interactions between transforming growth factor beta 1 and glycosaminoglycans occur, we have assessed the activity of the growth factor after pre-incubation with single classes of glycosaminoglycans by assaying its inhibitory effect upon the proliferative response of thymocytes stimulated with interleukin-1. Untreated transforming growth factor beta 1 suppressed the proliferative response of thymocytes to interleukin-1, as did transforming growth factor beta 1 pre-incubated with sulphated glycosaminoglycans. By contrast, transforming growth factor beta 1 lost its inhibitory capacity when preincubated with high molecular weight hyaluronic acid. Digestion of transforming growth factor beta 1-hyaluronic acid complex with hyaluronidase released active transforming growth factor beta 1. Trypsin degraded transforming growth factor beta 1 alone, but did not degrade the transforming growth factor beta 1-hyaluronic acid complex. These results suggest that hyaluronic acid interacts with transforming growth factor beta 1, thus protecting the factor from tryptic degradation and may be a means of concentrating growth factor activity.

Exogenous heparin induces an increase in glycosaminoglycans of the chick embryo chorioallantoic membrane: its possible role in the regulation of angiogenic processes

In this study heparin (HE) was injected into the allantoic sac of chick embryo eggs at 5, 9, 14 days of incubation. 48 h after injection glycosaminoglycan (GAG) concentration was measured in the chorioallantoic membrane (CAM) in order to verify if HE-related CAM angiogenic activity previously demonstrated [Ribatti et al: Acta Anat 1987; 130:257-263] might be correlated with changes in GAG concentration. The results showed that HE inoculation induced an increase of 3H-glucosamine incorporation into total GAGs in comparison to control CAMs. Furthermore, HE altered the balance between the GAG classes, and in particular it produced a significant increase in the accumulation of hyaluronic acid and heparan sulfate between 7 and 11 days of incubation in comparison to control CAMs.

Modulation of phenotypic expression of fibroblasts by alteration of the cytoskeleton

Several studies indicate that the cytoskeleton may be involved in modulating the cellular response to environmental signals. We have studied the role of the cytoskeleton in regulating glycosaminoglycan (GAG) synthesis and secretion, hyaluronate (HA) endocytosis, the activities of hexoglycosidases, protein synthesis and secretion. Fibroblasts were treated with colchicine (1-8 microM) and nocodazole (1 or 4 microM) to alter microtubules or cytochalasin B (0.5-4 microM) to alter microfilaments. Colchicine inhibited GAG synthesis and secretion in a concentration-dependent manner. It reduced protein and sulphated GAG secretion, while HA secretion was not affected. Concentration-dependent disruption of microtubules from the periphery toward the cellular centre with nocodazole inhibited only the secretion of GAG. Centrosomal microtubles appeared to be required to promote GAG synthesis; intact microtubules promoted the transport of secretory products, intercompatmental transport of lysosomal enzymes and lysosome maturation, but not protein synthesis and HA secretion. Cytochalasin B treatment inhibited, in a concentration-dependent manner, the synthesis and secretion of GAGs and proteins, and the endocytosis of HA. Intact microfilament meshworks appeared to be required to promote synthesis and secretion of proteins and proteoglycans and to contribute to the transmembrane control of receptor-mediated endocytosis. Drug treatment of concanavalin A (Con A)-stimulated fibroblasts inhibited the stimulation of GAG synthesis. It is probable that this effect may result, in part, from drug-induced effects on Con A-mediated endocytosis.

Age related effects of lectins on GAG metabolism in cultured embryonic fibroblasts

Lectins (WGA, SBA or PNA) were administered to 7 and 14 days chick embryo fibroblasts to evaluate their ability to influence GAG cellular and extracellular accumulation. HA and sulphated GAG were differently affected by lectins. WGA addition to culture medium enhanced HA and sulphated GAG in the two examined compartments. SBA and PNA increased sulphated GAG only in the cellular pool with a consequent reduction of secreted GAG. As far as HA is concerned, SBA and PNA promoted its accumulation in the extracellular compartment. NH4Cl administration indicated a decline of GAG degradation in the course of development in presence of lectins. Generally the effect of lectins was greater in the youngest stage: showing that lectins were able to bind 7 and 14 days-old fibroblasts differently.

Embryonic skin fibroblasts release TGF alpha and TGF beta able to influence synthesis and secretion of GAG

Conditioned medium (CM), collected from 7 and 14 days-old chick embryo skin fibroblasts and added to the same cells, increases glycosaminoglycans (GAG) intra- and extracellular accumulation. The factors responsible for GAG enhancement are TGF alpha and TGF beta because they are trypsin and dithiothreitol sensitive, stable or enhanced by heat and transient acidification. Moreover, Sephadex G-75 fractions of CM active on GAG synthesis contain, when analysed on SDS-polyacrylamide gel electrophoresis, two bands that comigrate with TGF alpha and TGF beta and induce NRK cells clone 49F to form large colonies of mean size > 8.000 microns 2 in soft agar. Since both the factors must be present to induce the formation of large colonies we come to the conclusion that CM contains TGF alpha and TGF beta. The two growth factors have different effects on the accumulation of individual classes of GAG in the ECM. In particular, TGF beta stimulates a marked increase of CS and DS, TGF alpha of HA and DS in the medium. The contemporaneous addition of TGF alpha and TGF beta to 7 days-old fibroblasts produces a pattern of GAG response similar to CM. These embryonic fibroblasts may control their own GAG synthesis and secretion through autocrine TGF alpha and beta activity.

Pregnancy modulates the expression of beta-N-acetylhexosaminidase in rat serum and tissues

1. beta-N-Acetylhexosaminidases in maternal rat serum were separated by DEAE-cellulose chromatography and compared with those of adult rat serum. 2. In pregnant serum there is an increase of the isoenzymes which are entirely composed of beta-subunits (B and intermediate forms). 3. These alterations could be compared to those already described in human pregnancy. 4. The levels of beta-N-acetylhexosaminidase and the relative expression of alpha- and beta-subunits in normal and pregnant serum correlate with the above isoenzyme expression. 5. The increase of B and intermediate forms as well as the increase of specific activity during pregnancy was not peculiar to maternal serum but was also demonstrated in several foetal tissues and in maternal tissues, in which cases the beta-N-acetylhexosaminidase isoenzyme patterns closely resemble the foetal ones rather than those of the adult rat tissues. 6. These analogies strongly suggest that the expression of beta-subunit of beta-N-acetylhexosaminidase is regulated by hormones or other factors related to pregnancy.

Synthesis and secretion of glycosaminoglycans and proteins in human normal and otosclerotic bone cells

Some biosynthetic activities of normal and otosclerotic temporal bone cultures have been studied. Bone cells were cultured for 24 hrs. in medium containing 3H-glucosamine, 35SO4 or 3H-proline. Labelled glycosaminoglycans (GAG) and proteins were precipitated from cells and media. In otosclerotic bone cells there was an evident reduction in the synthesis and secretion of radiolabelled macromolecules. The inhibitory effect was always greater in the extracellular than in the intracellular compartment. Some glycosidases were also studied. Otosclerosis decreased the activity of all enzymes examined, indicating that the lower GAG synthesis and secretion in otosclerotic bone cells were not due to an increased degradation.

An evaluation of the mechanisms developmentally involved on cellular and extracellular glycosaminoglycans accumulation in chick embryo skin fibroblasts

1. Ammonium chloride, a lysosomotropic amine known to inhibit lysosomal function, was administered to 7-day cultured and 14-day chick embryo skin fibroblasts to evaluate the relationship between synthesis, degradation and uptake of glycosaminoglycans (GAG). 2. Following amine treatment, the amount of 3H-glucosamine and 35SO4 labelled cellular GAG increased, was more at 14 days than at 7 days. Hyaluronic acid (HA) incorporation was mainly interested at 7 days and that of sulphated GAG at 14 days. 3. The extracellular accumulation declined proportionally to the cellular increase of undegraded GAG. HA was mainly affected at 7 days and sulphated GAG at 14 days. 4. The amine did not change 3H-HA uptake and it was unable to inhibit its degradation. 5. The products of degradation of uptaken 3H-HA were retained inside the cell. Those released by degradation of newly synthesized GAG flowed out of the cell.

Relation between hyaluronan and sulphated glycosaminoglycan synthesis and degradation in cultured embryonic fibroblasts. Effect of concanavalin A and ammonium chloride administration

In order to evaluate the relationship between glycosaminoglycan (GAG) synthesis and degradation, the effect of NH4Cl, which inhibits lysosomal degradation, on GAG production was analysed in vitro in concanavalin A (Con A) stimulated fibroblasts from 7 and 14-day-old chick embryos. 35SO4 incorporation into total proteoglycan (PG), 3H incorporation into individual GAG classes, beta-N-acetyl-D-glucosaminidase and beta-D-glucuronidase activity were determined. The results indicate a correlation between Con A and NH4Cl effects: NH4Cl induced a reduction principally in the GAG classes most stimulated by Con A. Thus HA and DS are much more stimulated by Con A and inhibited by NH4Cl than are CS and HS.

Increase of intermediate forms of beta-N-acetylhexosaminidase during rat liver development and regeneration

1. Rat liver beta-N-acetylhexosaminidase was separated into several different molecular forms by DEAE-cellulose chromatography. 2. The subunit composition of the isoenzymes, as well as the similarities to human hexosaminidases, were determined by using the specific active alpha subunit substrate 4-methylumbelliferyl-beta-N-acetylglucosamine-6-sulphate. 3. As in human tissues, the intermediate form lacked the active alpha subunit and resembled hexosaminidase B rather than A. 4. The intermediate form was markedly increased in foetal liver and in regenerating liver after partial hepatectomy. 5. The variations in isoenzyme expression were accompanied by variations in specific activity of hexosaminidase. 6. Sulphated substrate analysis and thermal stability experiments indicated that the rapid cell proliferation had a greater effect on the formation of beta-subunit of hexosaminidase than on that of alpha-subunit.

Concanavalin A affects glycosaminoglycans cellular and extracellular accumulation in cultured embryonic fibroblasts

Incorporation of 3H glucosamine and 35SO4 into glycosaminoglycans and proteoglycans produced and secreted by 7, 11 and 14 day chick embryo fibroblasts in vitro after concanavalin A treatment has been determined. Lectin differently affects 3H and 35SO4 incorporation. It enhances 3H labelled GAG accumulation in both cellular and extracellular compartments. Total incorporation of 35SO4 remains unchanged whereas the intracellular one is stimulated and the extracellular is reduced. All the effects are more relevant in the early stages of development. HA and PG cellular and extracellular accumulation seems to be independently regulated.

Possible role of certain antioxidant enzymes in dimethylnitrosamine-induced liver carcinogenesis

An investigation was carried out to establish whether the reduction in catalase, glutathione peroxidase and superoxide dismutase activity, normally observed in liver tumours, is an early event and therefore of pathogenetic importance, or whether it is a late occurrence. Experiments performed on dimethylnitrosamine-treated hepatectomized and non-hepatectomized rats show that the decrease in activity of these enzymes is entirely due to hepatectomy, since the tumour-inducing doses of dimethylnitrosamine failed to provoke variations in the activity of these enzymes, in either normal or regenerating liver.

Activity changes of glyoxalases I-II and glutathione reductase in regenerating rat liver

In regenerating rat liver Glyoxalase I activity shows a significant increase 24-48 hrs after partial hepatectomy. Glyoxalase II activity is significantly increased at 16, 48, and 72 hrs, and shows a transient decrease at 24 hrs after surgery. It is likely that the observed changes in Glyoxalases I and II activities during hepatic regeneration are correlated with the different roles of these enzymes. Glutathione reductase activity, significantly reduced within 8-72 hrs after surgery, does not show any correlation with Glyoxalases. These studied enzyme activities do not display significant changes in the sham-operated animals.

Inhibition of in vitro keratinization of chick embryo skin cultured with hepatectomized rat serum

In the present study organ cultures of 6 day-old chick embryo matatarsal skin were used to determine the effect of hepatectomized rat serum in modulating epithelial differentiation. Six day-old chick embryo skin, maintained in organ culture for 6-7 days with a medium containing adult rat serum, was seem to undergo differentiation and keratinization faster then in vivo. Epidermis cultured for 6-7 days with a medium containing partially hepatectomized rat serum does not differentiate and the squamous layer is absent. Studies with 3H-cystine show a sharp decrease in the labelled amino-acids incorporation in the cultures added with serum obtained after partial hepatectomy.

[Incorporation of H3 uridine in chick embryo skin cultured in media containing histones]

In this paper the authors have carried out further research on the differentiation of six-day limb skin from chick embryos cultured in vitro in mediam containing histones. When 3H-uridine is added to this modified medium, a decrease of 3H-uridine uptake and incorporation is observed. The authors conclude that in their system the histones not only interfere with the regulation of genetic transcription by inhibiting DNA-dependent RNA synthesis, but they also change cellular permeability.

Further researches on the action of hepatectomized rat serum on epithelial differentiation in chick embryo skin

Skin explants obtained from 12-day old chick embryos, maintained in organ culture containing adult rat serum, show a lower epidermal growth in comparison with skin explants cultured with other adult animal serum; nevertheless the keratogeneous differentiation of the epidermal cell is evident. When the cultures are incubated with medium containing partially hepatectomized rat serum epidermal-cell differentiation and proliferation are absent.

[Action of human serum on differentiation of skin in vitro. Morphological data and study of the incorporation of labeled amino acids]

Epithelial-mesodermal tissue interactions have been shown to be required for normal cytodifferentiation of chick embryo skin. Six-day limb skin does not develop in a protein free chemically defined medium, but keratinization has been observed in medium containing chicken serum. In the present study the authors show that the addition of human serum may stimulate the in vitro differentiation of explants of six-day chick embryo skin. Human serum is able to support skin keratinization and this finding has been confirmed by histological and histochemical criteria. Synthesis of proteins in tissue cultures supplemented with human serum has been studied by use of labeled amino acids such as H3-Leucine and C14-Cystine. These incorporation studies show the existence of macromolecular factors in human serum which may be responsible for the observed skin differentiation.