Changes in the nature of the collagen during development and resorption of granulatin tissue

Understanding the molecular mechanism associated with reversal of oral submucous fibrosis targeting hydroxylysine aldehyde-derived collagen cross-links

Fibrosis is a pathological state characterized by excessive deposition of the extracellular matrix components leading to impaired tissue function in the affected organ. It results in scarring of the affected tissue akin to an over-healing wound as a consequence of chronic inflammation and repair in response to injury. Persistent trauma of susceptible oral mucosa due to habitual chewing of betel quid resulting in zealous healing of the mucosal tissue is one plausible explanation for the onset of oral submucous fibrosis (OSF). The irreversibility and resistance of collagen to degradation and its high potential to undergo malignant change are a major reason for morbidity in OSF. Hence, early diagnosis and timely treatment are crucial to prevent the progression of OSF to malignancy. This review focuses on the mechanistic insight into the role of collagen cross-links in advancing fibrosis and possible therapeutic targets that bring about a reversal of fibrosis. These options may be beneficial if attempted as a specific therapeutic modality in OSF as is in organ fibrosis. The upregulation of lysyl oxidase and lysyl hydroxylase has been shown to exhibit the higher levels of the hydroxylysine aldehyde-derived cross-links in fibrosis and tumor stroma promoting the tumor cell survival, resistance, and invasion. The in silico analysis highlights the potential drugs that may target the genes regulating collagen crosslinking.

Collagen cross-linking mediated by lysyl hydroxylase 2: an enzymatic battlefield to combat fibrosis

The hallmark of fibrosis is an excessive accumulation of collagen, ultimately leading to organ failure. It has become evident that the deposited collagen also exhibits qualitative modifications. A marked modification is the increased cross-linking, leading to a stabilization of the collagen network and limiting fibrosis reversibility. Not only the level of cross-linking is increased, but also the composition of cross-linking is altered: an increase is seen in hydroxyallysine-derived cross-links at the expense of allysine cross-links. This results in irreversible fibrosis, as collagen cross-linked by hydroxyallysine is more difficult to degrade. Hydroxyallysine is derived from a hydroxylysine in the telopeptides of collagen. The expression of lysyl hydroxylase (LH) 2 (LH2), the enzyme responsible for the formation of telopeptidyl hydroxylysine, is universally up-regulated in fibrosis. It is expected that inhibition of this enzyme will lead to reversible fibrosis without interfering with the normal repair process. In this review, we discuss the molecular basis of collagen modifications and cross-linking, with an emphasis on LH2-mediated hydroxyallysine cross-links, and their implications for the pathogenesis and treatment of fibrosis.

Through gap junction communications, co-cultured mast cells and fibroblasts generate fibroblast activities allied with hypertrophic scarring

BACKGROUND

The prominent inflammatory cell identified in excessive scarring is the mast cell. Hypertrophic scar exhibits myofibroblasts derived from the transformation of fibroblasts, increased collagen synthesis, and stationary nonmigratory resident cells. The co-culture of fibroblasts with an established rat mast cell line (RMC-1) was used to explore the hypothesis of whether mast cells through gap junctional intercellular communications guide fibroblasts in promoting excessive scarring.

METHODS

Human dermal fibroblasts were cultured alone or co-cultured with RMC-1 cells as is or with either blocked gap junctional intercellular communications or devoid of cytoplasmic granules. Collagen synthesis was analyzed by dot blot analysis; immunohistology identified myofibroblasts, and a cell migration assay measured fibroblast locomotion.

RESULTS

Fibroblasts co-cultured with RMC-1 cells transformed into myofibroblasts, had increased collagen synthesis, and showed retarded cell migration. In contrast, RMC-1 cells unable to form gap junctional intercellular communications were similar to fibroblasts alone, failing to promote these activities. Degranulated RMC-1 cells were as effective as intact RMC-1 cells.

CONCLUSIONS

Mast cells induce fibroblast activities associated with hypertrophic scarring through gap junctional intercellular communications. Eliminating the mast cell or its gap junctional intercellular communications with fibroblasts may be a possible approach in preventing hypertrophic scarring or reducing fibrotic conditions.

Lysyl hydroxylase 3-mediated glucosylation in type I collagen: molecular loci and biological significance

Recently, by employing the short hairpin RNA technology, we have generated MC3T3-E1 (MC)-derived clones stably suppressing lysyl hydroxylase 3 (LH3) (short hairpin (Sh) clones) and demonstrated the LH3 function as glucosyltransferase in type I collagen (Sricholpech, M., Perdivara, I., Nagaoka, H., Yokoyama, M., Tomer, K. B., and Yamauchi, M. (2011) Lysyl hydroxylase 3 glucosylates galactosylhydroxylysine residues in type I collagen in osteoblast culture. J. Biol. Chem. 286, 8846-8856). To further elucidate the biological significance of this modification, we characterized and compared type I collagen phenotypes produced by Sh clones and two control groups, MC and those transfected with empty vector. Mass spectrometric analysis identified five glycosylation sites in type I collagen (i.e. α1,2-87, α1,2-174, and α2-219. Of these, the predominant glycosylation site was α1-87, one of the major helical cross-linking sites. In Sh collagen, the abundance of glucosylgalactosylhydroxylysine was significantly decreased at all of the five sites with a concomitant increase in galactosylhydroxylysine at four of these sites. The collagen cross-links were significantly diminished in Sh clones, and, for the major cross-link, dihydroxylysinonorleucine (DHLNL), glucosylgalactosyl-DHLNL was diminished with a concomitant increase in galactosyl-DHLNL. When subjected to in vitro incubation, in Sh clones, the rate of decrease in DHLNL was lower, whereas the rate of increase in its maturational cross-link, pyridinoline, was comparable with controls. Furthermore, in Sh clones, the mean diameters of collagen fibrils were significantly larger, and the onset of mineralized nodule formation was delayed when compared with those of controls. These results indicate that the LH3-mediated glucosylation occurs at the specific molecular loci in the type I collagen molecule and plays critical roles in controlling collagen cross-linking, fibrillogenesis, and mineralization.

Lymphocytes, cytokines and adhesion molecules in chronic graft versus host disease

Aims-To determine which inflammatory and immune pathways are implicated in the development of chronic graft versus host disease (GvHD) and whether differences between these pathways are responsible for the different presentations of chronic GvHD.Methods-Biopsy specimens of diseased and normal skin were obtained from patients presenting with lichen planus-like and sclerodermatous type chronic GvHD. Expression of epidermal cytokines, adhesion molecules and lymphoid surface markers was analysed by means of immunohistochemistry. Apoptosis was detected using the in situ nick endlabelling method.Results-In both GvHD lesion types, CD8+ cells predominated in the epidermis, whereas CD4+ cells were the most prevalentin the dermis. Apoptotickeratinocytes were found in diseased skin only and Fas antibodies labelled a considerable number of keratinocytes. The epidermis in both types of lesions expressed interleukin (IL) 1alpha, tumour necrosis factor (TNF) alpha and intercellular adhesion molecule (ICAM)-1, but dermal vascular cell adhesion molecule (VCAM)-1 expression was restricted to specimens of lichen planus-like GvHD. IL1alpha and E-selectin were expressed in normal looking skin of 55% and 80%, respectively, of patients with lichen planus-like GvHD.Conclusion-The similarity between expression of epidermal cytokines and adhesion molecules (with the exception of VCAM-1) and lymphocyte phenotype in lichen planus-like and sclerodermatous GvHD strongly suggests that the latter occurs as a consequence of the healing process. VCAM-1 distinguishes between lichen planus-like and sclerodermatous lesions. IL1alpha and E-selectin are potential early markers of chronic GvHD.

The effects of cyclophosphamide and azathioprine on collagen in skin and granulation tissue in rats, and the effects of cyclophosphamide on collagen in human skin

Granulation tissue was produced in rats by subcutaneous implantation of cellulose sponges. The effect of daily intraperitoneal injections of cyclophosphamide or azathioprine on rat skin and granulation tissue was examined after 14 and 42 days. Skin biopsies from patients with glomerulonephritis were analyzed before and after 42 days of treatment with cyclophosphamide or placebo. In the rats, cytostatic treatment caused an increase in the dry weight of the skin, and azathioprine increased the dry weight and the protein content of the granulomas. The increase in the dry weight was accompanied by a decrease in water percentage. The alpha-amino nitrogen/OH-proline ratio in purified acid soluble collagen from skin and granulation tissue increased with the dose and duration of cytostatic treatment. No effect on the aldehyde content was observed. Cyclophosphamide caused a decrease in the alpha/beta ratio in acid soluble collagen from granulation tissue, but not in the collagen from the skin. Salt soluble collagen was increased in the skin after 14 days of cytostatic treatment, but remained unchanged in the granulation tissue. In human skin cyclophosphamide caused no statistically significant changes in the amount of salt soluble or total collagen. It is concluded, that daily treatment of rats with cyclophosphamide or azathioprine from 14 to 42 days seems to inhibit the catabolic processes in the skin and granulation tissue, to decrease the hydroxylation of proline in collagen, and to inhibit the intermolecular cross-linking in collagen.?222

5-fluorouracil selectively inhibits collagen synthesis

BACKGROUND

Fibroproliferative disorders, such as Dupuytren's contracture of the hand, are characterized by excessive production of collagen. 5-Fluorouracil has been used to treat fibroproliferative disorders of the eye and skin and is thought to inhibit thymidylate synthetase blocking DNA replication. 5-Fluorouracil has been shown to down-regulate fibroblast proliferation and differentiation in vitro.

METHODS

This study investigated the dose-dependent effect of 5-fluorouracil on fibroblast extracellular matrix production. Fibroblasts were derived from tendon and primary Dupuytren's disease of the hand, a fibroproliferative disorder of the palmar aponeurosis (n = 4 patients). Total collagen synthesis was determined by means of the incorporation of radiolabeled proline. Fibroblast secretion of the profibrotic factor transforming growth factor-beta1 (TGF-beta1) was measured by a sandwich enzyme-linked immunosorbent assay. Gene expression of collagen types I and III and TGF-beta1 were quantified by means of reverse-transcriptase polymerase chain reaction assays.

RESULTS

The authors found that 5-fluorouracil caused a dose-dependent, selective, and specific decrease in collagen production by Dupuytren's fibroblasts compared with noncollagenous protein synthesis. By contrast, procollagen types I and III mRNA were unaffected by 5-fluorouracil treatment. These changes did not appear to be mediated by alterations in the endogenous secretion of TGF-beta1 or its autocrine effect on collagen metabolism.

CONCLUSIONS

The clinical implication is that 5-fluorouracil could possibly reduce extracellular matrix production and therefore reduce recurrence of Dupuytren's disease of the hand.

A histological and anatomical profile of pacinian corpuscles from Dupuytren's contracture and the expression of nerve growth factor receptor

The etiology of Dupuytren's disease is unknown. The causes of the fibroplastic response of nodules, fibrosis of cords, and prominence of pacinian corpuscles are not evident. Histological and immunohistology differences in pacinian corpuscles from the hands of five patients with Dupuytren's disease compared with 17 Dupuytren's-free patients are presented. Histological sections of pacinian corpuscle specimens were stained with hematoxylin and eosin and immunostained for nerve growth factor receptor. The length and width of intact pacinian corpuscles were measured, and the number of layers within each corpuscle was counted and recorded. Grossly, the pacinian corpuscles from Dupuytren's patients were larger and more numerous compared with those from unaffected patients. When measured microscopically, the pacinian corpuscles from Dupuytren's diseased fascia were significantly larger (2.0 x 1.1 mm) compared with controls (1.5 x 0.78 mm). The pacinian corpuscles from Dupuytren's-affected patients had significantly more layers (64 +/- 14) compared with those from control patients (40 +/- 9). Nerve growth factor receptor staining of pacinian corpuscles from patients affected with Dupuytren's disease showed greater intensity and more area stained compared with unaffected controls. It is suggested that nerve growth factor may be involved in the increased size of pacinian corpuscles in Dupuytren's-affected fascia. It is proposed that the cellular outgrowth from pacinian corpuscles may generate the cells that develop into Dupuytren's nodules.

Alterations in the organisation, ultrastructure and biochemistry of the myocardial collagen matrix in doberman pinschers with dilated cardiomyopathy

Remodelling of the collagen matrix of the myocardium has been implicated in the pathogenesis of dilated cardiomyopathy, a major cause of heart failure in Doberman pinschers. The aim of this study was to characterise the myocardial collagen matrix of Dobermans. In clinically normal Dobermans there was evidence of focal fibrosis. Collagen cross-links were altered in both diseased and clinically normal Doberman myocardium as compared with myocardium from control dogs. Extensive remodelling, in the form of a loss of collagen tethers, increased collagen synthesis and alterations in the collagen cross-links, occurs in diseased Doberman myocardium. Changes in the collagenous matrix are also present in apparently normal Dobermans. These changes are likely to be involved in the progression of the disease and may explain the predisposition of this breed to dilated cardiomyopathy.

Physicochemical properties of extracellular matrix proteins in post-burn human granulation tissue

Wound healing is a finely controlled biological process involving a series of complex cellular interactions. Following inflammation, the wound bed matrix is gradually replaced by granulation tissue followed by the long slow process where collagen accumulates and restores tensile strength. The studies revealed that human granulation tissue varied in many aspects in comparison with normal skin. In granulation tissue the molecular organization of collagen showed an increased amount of type III collagen resembling embryonic tissue. The presence of type V collagen with three distinct chains was the characteristic feature of granulation tissue. The physicochemical properties of collagen extracted from granulation tissue showed the influence of proteoglycans during collagen aggregation and these proteoglycans from the major non-collagenous proteins during the proliferative phase of healing.

Migration and healing of ligament cells under inflammatory conditions

It is well documented that the adult human medial collateral ligament has a functional healing response, whereas the anterior cruciate ligament does not. The differential healing responses of the medial collateral and anterior cruciate ligaments could be due to factors caused by different biological conditions and locations in vivo. In addition, different intrinsic properties of the constituent cells of these ligaments may contribute to their different healing abilities. Ligament healing follows an orderly process of hemorrhage, inflammation, proliferation, and remodeling. At the cellular level, healing involves a cell's detachment from and attachment to the matrix adjacent to the wound area, migration, and proliferation. This study sought to investigate whether, during migration, the responses of the medial collateral and anterior cruciate ligament fibroblasts are intrinsically different under the same inflammatory conditions. Human medial collateral and anterior cruciate ligament fibroblast cells were cultured, and in vitro wounds were simulated by streaking the cells with an inoculating loop, creating a cell-free area. The migration of the cells into this gap, thus filling the cell-free area, was observed. Two sets of experiments were conducted; one varied the wound width and the other added the inflammatory factors tumor necrosis factor-alpha, complement C5a, and lipopolysaccharide. As the width of the wound increased, the rate of recovery decreased for both types of ligament cells (slope: anterior cruciate ligament, 0.13 hour/micron and medial collateral ligament, 0.10 hour/micron). Also, the three inflammatory factors used all inhibited the recovery rates of both ligaments to ones that were 1.4-2.3 times slower than controls. However, in both sets of experiments, the anterior cruciate ligament fibroblasts were more sensitive to inflammatory factors, and the medial collateral ligament fibroblasts had faster recovery rates (anterior cruciate ligament, 1.2-3.4 times slower than rates for medial collateral ligament fibroblasts, excluding those under lipopolysaccharide treatment). The results showed that medial collateral and anterior cruciate ligament fibroblasts responded differently under the same inflammatory conditions. This may suggest that these differences in intrinsic properties contribute to their different healing responses and abilities.

The relationship between quantitative changes in collagen and formation of wrinkles on hairless mouse skin after chronic UV irradiation

Female albino hairless mice were irradiated chronically with sub-erythemal doses of UVB radiation. Collagen extracted from the irradiated or non-irradiated dorsal skin of mice was fractionated into neutral salt-soluble (NSC), acid-soluble (ASC) and insoluble fractions (ISC). An age-related exponential decrease in the content and proportion of acid-soluble collagen was found in each group. The contents and the proportions of ASC from irradiated mice were always significantly lower than those from age-matched control animals. Age-related slight decreases were observed in the contents (per fresh weight of tissues) of NSC, ISC and total collagen in the control group but decreases in these collagen contents after UVB irradiation were marked. A dramatic decrease in ASC occurred nearly concomitantly with wrinkle formation in the irradiated mice. The decrease of acid-soluble skin collagen in irradiated mice may play a role in the formation of wrinkles on hairless mouse dorsal skin.

The effects of early mobilisation and immobilisation on the healing process following muscle injuries

The biological processes following muscle injury include 2 competitive events; regeneration of muscle fibres and the simultaneous production of granulation tissue. We have studied the effects of early mobilisation and immobilisation on the healing of rat gastrocnemius muscle following partial rupture by a controlled contusion mechanism. Muscle fibre regeneration is inhibited by the formation of dense connective tissue scar. Immobilisation following injury limits the size of the connective tissue area formed within the site of injury; the penetration of muscle fibres through the connective tissue is prominent but their orientation is complex and not parallel with the uninjured muscle fibres. Immobilisation for longer than 1 week is followed by marked atrophy of the injured gastrocnemius muscle. Mobilisation started immediately after injury is followed by a dense scar formation in the injury area prohibiting muscle regeneration. When mobilisation is started after a short period of immobilisation a better penetration of muscle fibre through the connective tissue is found and the orientation of regenerated muscle fibres is aligned with the uninjured muscle fibres. Although a little delay in healing processes in muscles mobilised after short immobilisation was found morphologically, the gain in strength and energy absorption capacity was quite similar and as good as that of muscles treated by early mobilisation alone.

Histological and biochemical analysis of the fibrous tissue induced by implantation of synthetic ligament (Dacron): an experimental study in a rat model

We conducted a comparative study to evaluate the quality and true nature of the fibrous tissue formed around synthetic grafts when used in ligament replacement. In one group of Lewis rats, a patellar ligament was replaced with a Dacron prosthesis; the comparison group received a tail tendon isograft. Two-, 4-, 8-, 12-, and 24-week comparisons showed histological and biochemical changes in the Dacron group alone that were consistent with foreign-body reaction. Specifically, the Dacron group showed infiltration by large numbers of macrophages and foreign-body, multinucleated giant cells. In addition, the capsule of fibrous tissue that developed around the Dacron ligaments was characterized by lower collagen solubility, a higher content of noncollagenous protein, and a higher proportion of type III collagen than that comprising the isografted tendons. The results of this study call into question the suitability of synthetics for ligament replacement.

The effects of increased tension on healing medical collateral ligaments

The effects of motion and increased levels of stress on the biomechanical, biochemical, and morphological properties of healing medial collateral ligaments were assessed in a rabbit model. In one group, the medial collateral ligament of the left hindlimb was transected and allowed to heal with cage activity for either 6 or 12 weeks. In another group, the transected ligaments were permitted to heal for 4 weeks and then were placed under increased stress by inserting a stainless steel pin perpendicularly underneath the healing medial collateral ligament. The animals were allowed cage activity for an additional 2 or 8 weeks. The varus-valgus joint laxity and the stress-strain properties of the medical collateral ligament substance were obtained. Further, the quantity of total collagen, amount and ratio of the collagen cross-links, dihydroxylysinonorleucine and hydroxylysinonorleucine, and the histologic appearance of the healing medical collateral ligaments were evaluated for all groups. At 6 weeks, knees with a transected medial collateral ligament were twice as lax as the controls. However, joints with the stainless steel tension pin had varus-valgus values approximately 1.5 times those of the controls. At 12 weeks, joints with increased stress were not statistically different from the controls. The group that had healing with increased stress for 12 weeks produced the highest stress for a given strain compared to any other group. Also, the total collagen levels and the ratio of dihydroxylysinonorleucine/hydroxylysinonorleucine were the closest to normal of any transected group. Finally, qualitative histologic improvements were seen, including a more longitudinal arrangement of collagen fibers and decreased cellularity.

Alterations in dry mass content of collagen fibers in degenerative tendinopathy and tendon-rupture

The dry mass concentration and collagen fiber morphology of intact, as well as of degenerated and ruptured human Achilles, biceps brachii, extensor pollicis longus and quadriceps tendons, were determined by using the interference microscopical technique. The variation in the collagen fiber thickness was demonstrated in different intact tendons, the fibers being largest in the Achilles and smallest in the extensor pollicis longus tendons. However, the intact tendons exhibited only thick collagen fibers. In the degenerative tendinopathies an increase of the dry mass content was observed, being especially marked in calcifying tendinopathy. In the degenerated tendons the average collagen fiber diameter had decreased, and two clearly distinct populations of thick and thin fibers were observed. The dry mass content of the thick fibers was significantly greater than that of the thin fibers. The present results demonstrate striking changes in the collagen and its dry mass content in degenerative tendinopathy, thus also increasing the susceptibility to ruptures.

In vitro maturation of collagen fibrils modulates spreading, DNA synthesis, and collagenolysis of epidermal cells and fibroblasts

Collagen fibrils were maturated in vitro by incubating them in a serum-containing culture medium at 37 degrees C for varied lengths of time. Epidermal cells and fibroblasts were cultured on these maturated collagen gels to see the effects of maturation on cellular morphology and physiology. The spreading and DNA synthesis of both types of cells on the maturated collagen gels were significantly enhanced compared to those on fresh gels. The maturation did not affect the cellular adhesiveness to the substrate. The secretion of collagenase by epidermal cells was suppressed on the maturated collagen gels, the extent of the suppression being related to the length of maturation of the gels. These maturation-related effects of collagen were also observed when collagen was incubated in the medium without serum, indicating that the effects are not due to deposition of serum proteins to collagen gels during maturation. Physical and chemical characterizations of the maturated collagen were performed: the mechanical strength of collagen gels increased in maturated collagen gels, the amounts of insoluble collagen increased with the maturation. These changes in the chemical and physical nature of the maturated collagen gel strongly suggested that there was an increase in intermolecular crosslinks during the process of maturation. These maturation-induced changes in collagen were marked when collagen gels were incubated in the presence of glucose, indicating that a glucose-protein reaction such as the Maillard reaction is involved in this phenomenon.

Extracellular matrix in healing CO2 laser incision wound

Extracellular matrix components laminin, Type IV collagen, Type III collagen, and fibronectin, of laser-treated rat tongue mucosa were studied over a healing period of 28 days by using immunohistochemical and electron microscopic techniques. Their distribution and amount in laser wounds was compared with that in scalpel incisions and normal tongue mucosa. Laser treatment caused an extensive destruction of both epithelial and stromal cells but left much of the connective tissue matrix intact. Basement membranes, in particular, appeared to resist laser irradiation. During the study period the laser-induced lesions healed through reparative synthesis of matrix proteins which led to filling of the tissue defects. The regenerative processes with concomitant re-epithelialization took place more slowly in laser-treated than in scalpel incision wounds. The relative resistance of the matrix proteins against laser irradiation and the slow removal and replacement of the residual matrix is suggested to account at least partially for the lack of scarring and contraction frequently observed in laser-treated areas.

Basic mechanisms in the healing cutaneous wound

The process of wound healing can be divided into substrate, proliferative, and remodeling phases. The basic biologic and physiologic events which transpire during these stages are examined in detail. Particular emphasis is placed on the interactions between platelets, macrophages, and other inflammatory cells, and fibroblasts in the healing wound. Recent advances in the roles played by interleukins, fibronectin, and epidermal growth factor are discussed.

Skeletal muscle injury--molecular changes in the collagen during healing

Changes in the collagen types and cross-linking of granulation and scar tissue in the injured site of partially ruptured gastrocnemius muscle were studied after a reproducible contusion injury to the left calf of a rat. In normal i.m. collagen the proportion of Type I collagen was considerably higher than Type III. Following injury there was a rapid increase in the proportion of Type III collagen reaching a maximum at 5 days after injury. After a further 2 days the proportion of Type I had increased significantly resulting in a decrease of the Type III/I ratio to below that of the control. However, as healing progressed there was a gradual shift back to the Type III/I ratio for normal i.m. collagen. The collagen produced in response to an injury was initially stabilized by the stable keto-imine cross-link hydroxylysino-5-keto-norleucine, characteristic of embryonic collagenous tissues. The proportion of the stable keto-imine cross-link gradually decreased, and a reversion to the cross-link pattern of normal uninjured i.m. collagenous connective tissue occurred towards the end of the 42-day follow-up period. The present biochemical study demonstrates that during the early phases of the repair process there is a reversion to the collagens typically present in high proportions in embryonic dermal connective tissue. This suggests that the fibroblasts have the ability to modify their product expression under varying circumstances. The study also demonstrates the importance of collagen cross-linking in determining the tensile strength of collagen fibre during the repair process.

Tendons and ligaments: a morphological and biochemical comparison

The purpose of this study was to compare selected rabbit tendons and ligaments morphologically and biochemically. Five representative structures from each of six age- and sex-matched rabbits were compared. Biochemical analyses included total collagen, reducible collagen cross-links, quantitative collagen typing, DNA, and glycosaminoglycans. Histological and chemical differences were demonstrated between the tendons and the ligaments. Smaller differences were also found between the individual ligaments (collateral and cruciate) and between the two tendons (patellar and Achilles) that were examined. These findings suggest that ligaments are more metabolically active than tendons, having more plump cellular nuclei, higher DNA content, larger amounts of reducible cross-links, and the presence of more type III collagen, as compared with tendons. They also contain slightly less total collagen than tendons and more glycosaminoglycans. We conclude that the tendons and ligaments studied have unique histological and biochemical characteristics, despite their gross similarities. Relatively increased metabolic activity in ligaments, implied by our findings, may be species specific, age related (transient), or may truly represent a structural expression of functional need for more rapid adaptation. Further investigation of other similarities or differences between particular ligaments (or tendons) is indicated, and attention is directed toward the importance of such variables in development of models for tendon and ligament studies.

Effect of D-penicillamine pre- and post-implantation treatment on formation of sponge-induced granulation tissue in rats

DNA, collagen and sulfated glycosaminoglycans (GAGs) of rat sponge granulation tissue were studied after 42 days of D-penicillamine (D-pen) treatment at 100, 250 or 500 mg/kg/day, starting 10 days before or 28 days after induction of granulation tissue formation. The effects were compared with those observed when the same dosage was started at the onset of the granulation tissue formation and with pair-fed controls. D-pen stimulated the cell invasion into the sponge implants, as manifested by an increased DNA content, particularly with pre-treatment. Pre-treatment reduced the net deposition of of collagen per cell as assessed by the lower hydroxyproline/DNA ratio, at the lower dose leading to reduced collagen concentration. The total amount of granulation tissue collagen remained essentially unaffected within the observation period. Salt-soluble collagen was augmented in a dose-dependent manner, irrespective of treatment protocol, signifying decreased collagen cross-linking. Both pre- and post-implantation treatment enhanced the radiosulfate incorporation into sulfated GAGs, regardless of dose, whereas treatment from the day of sponge implantation had no effect. It is concluded that D-pen enhances the early connective tissue response to injury. Reduction of collagen cross-linking and net collagen deposition, concomitant with stimulation of the proteoglycan metabolism, may pertain to the antirheumatoid activity of D-pen. The observations suggest that long-term administration of D-pen, starting before new attacks of arthritis, may be most effective in controlling developing articular fibrosis.

Medial collateral ligament healing. A multidisciplinary assessment in rabbits

Medial collateral ligament healing without treatment has been studied in a rabbit model. Complete midsubstance gaps were found to heal by distinct scar formation over time. This healing process was fast since the gap was bridged quickly; however, more subtle changes in appearance of the healing tissue continued for many months. The ligament "scar" was found to be structurally abnormal chemically and mechanically even at long-term followup. A plateau in its improvement suggests that the scar may never approach normal ligament characteristics (without treatment). A baseline of ligament healing by scar formation has been established.

Type V collagen during granulation tissue development

The collagen content, as determined by hydroxyproline assay, of experimental granulation tissue in rats was observed to increase rapidly 21 days, and less rapidly to 90 days of tissue development. Resistance of the collagen to pepsin digestion reached a maximum at 21 days, suggesting more extensive or more stable crosslinking at that time. Type V collagen and the expected collagen types I and III were present in pepsin extracts of the granulation tissue as determined by SDS-polyacrylamide gel electrophoresis. Over 3 months of tissue development the relative quantity of type V collagen, as evidenced by changes in the alpha B chain, varied in parallel with the changing vascularity of the tissue, suggesting an association with capillary endothelial cells and angiogenesis.

Reversibility of D-penicillamine induced collagen alterations in rat skin and granulation tissue

Granulation tissue was produced in rats by subcutaneous implantation of Visella sponges. D-penicillamine (D-pen) 100 or 500 mg/kg was administered daily for 42 days by gastric tubing. Pairfed, placebo treated animals were included as controls. Half of the groups were kept for additionally 28 days without medication. The inhibitory effect of D-pen on cross-link formation in newly synthesized collagen was readily reversible. By contrast, cross-link deficiency lasting beyond the observation period was observed in the higher polymeric collagen variants released by dilute acid, heat exposure or limited pepsin proteolysis as estimated by solubility, alpha/beta chain ratio and/or aldehyde content. By SDS-polyacrylamide gel electrophoresis on gels containing 3.6 M urea it was shown that purified dermal acid soluble collagen from treated animals consisted of a mixture of type I and III collagen, whereas only type I collagen was detected in controls. The band pattern was identical in reduced and unreduced collagen samples. Four weeks after D-pen discontinuance type III collagen had disappeared from the acid extract. Moreover, the ratio of type III to type I collagen in the pepsin digest from both granulation tissue and skin showed a persistent rise with D-pen. These observations indicate that D-pen destabilized type III collagen in particular by interference with its disulfide linkages. The amount of granulation tissue remained unaffected throughout the experiment, whereas the skin collagen content decreased at the higher dose level. The regeneration was not completed by the end of the observation period. Modulation of the molecular stability of granuloma collagens may be of relevance for the antirheumatoid effect of D-pen, but the sustained effect on normal tissues may imply a long standing impairment of their supportive capacity.

Current concepts in soft connective tissue wound healing

The strength and integrity of intact soft connective tissues are related to the forces which exist between collagen fibrils and these in turn appear to depend on collagen fibril size, density and architecture en masse. The genetic type of collagen, enzymic modifications to the collagen monomer and the proteoglycan environment all affect fibril size. Current evidence suggests that the restoration of tissue continuity and the early redevelopment of tissue strength following wounding are initially achieved by the formation of a myofibroblast-reticulin network which eventually disappears as the healing wound ages. The extent of this network defines the area in which repair tissue will be laid down and the network is equipped with the sensory apparatus to monitor the physical and chemical environment where healing is taking place and thus to direct the various facets of connective tissue synthesis outlined above. The maturation of the scar connective tissue matrix and the development of attachment between new and original connective tissues are simultaneous, related but independent processes. It takes some time before the weld is achieved by the same forces that hold connective tissue fibres together in intact tissues and the myofibroblast-reticulin network is replaced.

Collagen metabolism and phenotype after prostaglandin E2 treatment of granuloma: direct and macrophage-modulated effects

Local administration of PGE2 (2 micrograms) to polyether sponges, implanted s.c. in rats, inhibited hydroxyproline and total protein accumulation, without altering relative amounts of collagen, when administered early during granuloma development. In contrast, while DNA as well as total protein accumulation was inhibited by local PGE2 treatment of established granuloma, hydroxyproline accumulation and the relative amounts of collagen were enhanced. This PGE2-induced collagen enhancement was associated with an increased type III : type I collagen ratio, possibly due to differential intracellular breakdown of newly synthesized collagen. The solubility of granuloma collagen was unaffected by PGE2. Impregnation of sponges with carrageenan before implantation, thereby giving macrophage-dominated granuloma, did not affect the changes in protein and DNA induced by later treatment with PGE2, but did reverse the PGE2-induced accumulation of hydroxyproline. This latter effect probably reflects macrophage-mediated, PGE2 enhancement of collagenolytic activity.

Keloids: a review

Keloids are predominantly fibrous tumors which appear as firm, variably pruritic or tender growths near a site of injury. Usually appearing between the ages of 10 and 30, most keloids are located on the upper back, shoulders, earlobes, and anterior portion of the chest. The etiology remains unknown, but the accumulated fibrous tissue is associated with increased cellularity and increased metabolic activity of keloid fibroblasts. Isolated keloid fibroblasts demonstrate normal growth characteristics along with increased collagen and proteoglycan synthesis. Numerous keloid treatments have been attempted, but variable success has followed either single use or combinations of intralesional corticosteroid injection, surgery, pressure devices, radiation, cryosurgery, and systemic chemotherapy.

Characterization of dermal collagen in systemic sclerosis

The amount of dermal collagen is increased in systemic sclerosis. However, unlike certain inflammatory conditions, the relative proportions of Type I and Type III collagens are closely similar to those found in normal adult dermis. Similarly, no change in the distribution of the collagen types could be detected by immunofluorescent staining, although a considerable thickening of the epidermis was clearly evident in all the sclerotic lesions examined.

The effects of dietary nitrogen level on the collagen of rat skin

1. Male rats of approximately 120 g body-weight were maintained on a commercial stock diet containing 204 g crude protein (nitrogen x 6.25)/kg, a hydroxyproline-free high-protein (HP) diet containing 200 g casein/kg as the only protein source, or a low-protein (LP) diet containing 40 g casein/kg. After 6 weeks on these diets half of each group was transferred to a non-protein (NP) diet and the experiment was continued for a further 6 weeks. Animals from each group were killed at 4 d, 3 weeks and 6 weeks after the transfer to the NP diet. 2. Throughout the experiment the urinary excretion of N, hydroxyproline and creatinine, and the content and solubility of the skin collagen were determined. 3. When compared with a control group killed at the beginning of the experiment the rats maintained on the LP diet showed an increase of 25% in total N content of the skin but collagen content increased by 100%. Rats transferred from the HP to the NP diet lost both N and collagen from the skin, but those transferred from the LP to the NP diet lost N but increased the collagen content by 42%. 4. Protein deprivation brought about marked changes in the solubility of the skin collagen, suggesting an increase in the rate of maturation of skin collagen.

Aging, and crosslinking in mammlian collagen

The amount and type of borohydride-reducible crosslinks in collagen have been examined as a function of animal age. In a variety of bovine, canine and human tissues the level of redicible crosslinks decreases with time and the ratios of individual compounds change. There is both tissue and species specificity in the extent of these changes. A decrease in the level of reducible crosslinks correlates with the cessation of growth. Loss of reducible crosslinks does not imply a small total number of crosslinks since physical changes with age imply the opposite. We conclude that reducible crosslinks are converted to a stable nonreducible state and the persistence of low levels of reducible crosslinks may be indicative of a low level of turnover in the tissue. Changes in ratios of reducible crosslinks are of doubtful functioal significance and may simply reflect variation in post-translational modification of lysine residues.

Isolation and purification of a small molecular weight hydroxyproline-containing structural glycopeptide from early mammalian granulation tissue

A small molecular weight structural glycopeptide was solubilized after collagenase digestion of the connective tissue capsule surrounding the 5-day sponge-implant of the rat. The major amino acids are one residue each of aspartic and glutamic acids, proline, hydroxyproline and alanine and two residues of glycine, and the carbohydrates are one residue each of glucose, xylose and hexosamine and two residues of mannose. The sum of the amino acid and carbohydrate residues gives a molecular weight of 1635. Dansylation of the glycopeptide produces a single strongly fluorescent yellow-orange amino-terminal spot, not positively identified. The solubilization of the granuloma glycopeptide by collagenase and its composition are suggestive of its association with an immature form of collagen in early granulation tissue.

Collagen and myofibroblasts of granulation tissue. A chemical, ultrastructural and immunologic study

In granulation tissue produced in the rat by subcutaneous injection of turpentine oil or polyvynile sponge implantation, the great majority of fibroblasts (myofibroblasts) possess a contractile apparatus which makes them similar to smooth-muscle cells. Chemical analysis shows that these granulation tissues contain a high proportion of Type III collagen, a genetically distinct collagen normally associated with embryonic dermal tissue. Type III collagen may persist up to 9 months after sponge implantation and myofibroblasts are seen in granulation tissue by means of electron microscopy and immunofluorescence. When granulation tissue is resorbed 50 days after turpentine oil injection, myofibroblasts disappear and the dermis contains Type I collagen. The concurrent presence of myofibroblasts and Type III collagen suggests that myofibroblasts, in addition to their contractile activity, synthetize, at least in part, type III collagen.