Collagen: structure, function, and metabolism in normal and fibrotic tissues

Interosseous membrane anatomy and functional mechanics

Longitudinal forearm stability is maintained through the interaction of several anatomic structures. One such structure, the interosseous membrane, is a fibrous tissue with an oblique orientation from the radius to the ulna. The membrane maintains the interosseous space between the radius and ulna through forearm rotation and actively transfers forces from the radius to the ulna. The interosseous membrane's unique functional capabilities result from its anatomic and histologic organization, which produces a stiff structure with elastic properties capable of maintaining large loads. The interosseous membrane's load transferring ability reduces the forces placed on the radiocapitellar articulation, thereby protecting this joint. However, large chronic loading results in attenuation of the membrane fibers, thereby reducing longitudinal stability. Large sustained loads occur after radial head resection with concurrent interosseous membrane tears, resulting in the proximal migration of the radius and disruption of the distal radioulnar joint. Ultimately, the treatment option for severe membrane disruption combined with proximal migration of the radius is the creation of a single bone forearm.

Type I and type III procollagen gene expressions in the early phase of ligament healing in rabbits: an in situ hybridization study

The purpose of this study is to observe type I and type III procollagen gene expressions in the healing ligament using in situ hybridization histochemistry. The rabbit medial collateral ligaments were incised and harvested at 3, 7, 14, and 28 days postoperatively. The healing ligament showed increased expression of both procollagen genes through this period compared with the unoperated ligament. The peak expression level was observed at 7 or 14 days for type I and at 7 days for type III, respectively. The strongest expression of both genes was detected in the scar tissue created between the ends of the old ligament. Although type III procollagen gene expression was observed almost only in the newly created scar tissue, type I procollagen gene was expressed not only in the scar tissue, but also at the ends of the previously normal ligament. These results suggest that type I collagen synthesis begins shortly after ligament injury and occurs at the ends of the injured ligament as well as in the scar tissue, and that type III collagen is largely synthesized in the scar tissue around one week after injury but continues being synthesized for at least four weeks after injury.

Outgrowth of chondrocytes from human articular cartilage explants and expression of alpha-smooth muscle actin

The objectives of this study were to investigate the effect of various enzymatic treatments on the outgrowth of chondrocytes from explants of adult human articular cartilage and the expression of a specific contractile protein isoform, alpha-smooth muscle actin, known to facilitate wound closure in other connective tissues. Explants of articular cartilage were prepared from specimens obtained from patients undergoing total joint arthroplasty. The time to cell outgrowth in vitro was determined and the expression of alpha-smooth muscle actin shown by immunohistochemistry. Treatment of the explants with collagenase for 15 minutes reduced the time to outgrowth from more than 30 days to 3 days. Hyaluronidase, chondroitinase ABC, and trypsin applied for the 15-minute period had no effect on the time to cell outgrowth when compared with untreated controls. Pretreatment with hyaluronidase prior to collagenase reduced the time to outgrowth. A notable finding of this study was that the majority of chondrocytes in the adult human articular cartilage specimens and virtually all of the outgrowing cells contained alpha-smooth muscle actin. We conclude that human articular chondrocytes have the capability to migrate through enzymatically degraded matrix and express a contractile actin isoform. Collagenase treatment reduces the time required for cell outgrowth.

Characterization of dermal type I collagen of C3H mouse at different stages of the hair cycle

Hair follicles develop or regress in accordance with the hair cycle. In this study, we partially characterized fibrillar type I collagen, the predominant component in the dermis, at two stages of the hair cycle: anagen and telogen. Skin samples were obtained from the backs of two groups of 11-week-old C3H mice: one at anagen stage induced by shaving and the other at telogen stage. The amount of neutral salt-soluble (newly synthesized) collagen obtained from anagen skin was about twofold that from telogen skin, while the level of acid-soluble collagen was not significantly different between the two groups. The degree of lysine hydroxylation of pepsinized type I collagen obtained from anagen skin was significantly higher than that in telogen (5.0% higher in alpha1 chain, and 15.6% higher in alpha2 chain). Proline hydroxylation at the anagen stage was also slightly higher than in the telogen stage. Two major collagen cross-links were found in both groups of skin; dehydro-hydroxylysinonorleucine and dehydro-histidinohydroxymerodesmosine. The concentration of the latter, a complex tetravalent cross-link, was significantly lower in anagen skin when compared with telogen skin (mean +/- SD 0.64 +/- 0. 07 vs. 0.78 +/- 0.06 mol/mol collagen). The former showed no significant difference between the two groups. In addition, a significant amount of lysyl-aldehyde (a cross-link precursor) was found in anagen (0.16 +/- 0.02 mol/mol collagen), while it was 0.12 mol/mol collagen in telogen. These results indicate that the remodelling of collagen is more active in anagen skin than in telogen, and that characteristic post-translational modifications of dermal collagen seen in anagen may play a part in facilitating an environment around hair follicles for their migration and growth.

Adhesion strength differential of human ligament fibroblasts to collagen types I and III

Fibroblasts embedded in the amorphous healing tissue matrix of ligaments migrate into damaged sites during the inflammatory process that precedes the formation of new connective tissue after ligament injury. Cell motility involved in this migration is strongly influenced by cellular adhesion to proteins of the extracellular matrix. The adhesion mechanism of interest in this study is the attachment of fibroblasts from the anterior cruciate and medial collateral ligaments to types I and III collagen, two fibrillar collagens secreted by fibroblasts during tissue repair. Types I and III collagen constitute a major portion of these ligaments and are assembled by fibroblasts into long cable-like fibrils in the extracellular space. In this study, a micropipette aspiration technique was used to measure the force required to separate fibroblasts of the anterior cruciate and medial collateral ligaments from substrates composed of type I or III collagen, each at a concentration of 2 or 5 microg/ml. Approximately 1,200 fibroblasts from the anterior cruciate ligament and 1,600 from the medial collateral ligament were used, and the adhesion force and area of these cells were determined. Fibroblasts from the anterior cruciate ligament exhibited greater adhesion force than did those from the medial collateral ligament for all concentrations of types I and III collagen. In addition, the adhesiveness of fibroblasts from both ligaments was dependent on seeding time for all experimental conditions. To determine the adhesiveness per unit area, defined here as the adhesion strength, the adhesion force was normalized by the adhesion area. At early seeding times (15-45 minutes), fibroblasts from the anterior cruciate ligament exhibited greater adhesion strength on surfaces coated with type-I collagen than did those from the medial collateral ligament. However, for both collagen substrates, adhesion strength for fibroblasts from the anterior cruciate ligament decreased with seeding time whereas that for fibroblasts from the medial collateral ligament remained relatively constant for all seeding periods (15-75 minutes).

Lysylhydroxylation and non-reducible crosslinking of human supraspinatus tendon collagen: changes with age and in chronic rotator cuff tendinitis

OBJECTIVES

To investigate age related and site specific variations in turnover and chemistry of the collagen network in healthy tendons as well as the role of collagen remodelling in the degeneration of the supraspinatus tendon (ST-D) in rotator cuff tendinitis.

METHODS

Collagen content and the amount of hydroxylysine (Hyl), hydroxy-lysylpyridinoline (HP), lysylpyridinoline (LP), and the degree of non-enzymatic glycation (pentosidine) were investigated in ST-D and in normal human supraspinatus (ST-N) and biceps brachii tendons (BT-N) by high-performance liquid chromatography.

RESULTS

In BT-N, tendons that served as control tissue as it shows rarely matrix abnormalities, pentosidine levels rise linearly with age (20-90 years), indicating little tissue remodelling (resulting in an undisturbed accumulation of pentosidine). A similar accumulation was observed in ST-N up to 50 years. At older ages, little pentosidine accumulation was observed and pentosidine levels showed large interindividual variability. This was interpreted as remodelling of collagen in normal ST after age 50 years because of microruptures (thus diluting old collagen with newly synthesised collagen). All degenerate ST samples showed decreased pentosidine levels compared with age matched controls, indicating extensive remodelling in an attempt to repair the tendon defect. Collagen content and the amount of Hyl, HP, and LP of ST-N and BT-N did not change with age. With the exception of collagen content, which did not differ, all parameters were significantly (p < 0.001) lower in BT-N. The ST-D samples had a reduced collagen content and had higher Hyl, HP, and LP levels than ST-N (p < 0.001).

CONCLUSIONS

Inasmuch as Hyl, HP, and LP levels in ST-N did not change with age, tissue remodelling as a consequence of microruptures does not seem to affect the quality of the tendon collagen. On the other hand, the clearly different profile of post-translational modifications in ST-D indicates that the newly deposited collagen network in degenerated tendons is qualitatively different. It is concluded that in ST-D the previously functional and carefully constructed matrix is replaced by aberrant collagen. This may result in a mechanically less stable tendon; as the supraspinatus is constantly subjected to considerable forces this could explain why tendinitis is mostly of a chronic nature.

Evidence for altered synthesis of type II collagen in patients with osteoarthritis

There is evidence to suggest that the synthesis of type II collagen is increased in osteoarthritis (OA). Using an immunoassay, we show that the content of the C-propeptide of type II procollagen (CPII), released extracellularly from the newly synthesized molecule, is directly related to the synthesis of this molecule in healthy and osteoarthritic articular cartilages. In OA cartilage, CPII content is often markedly elevated (mean 7.6-fold), particularly in the mid and deep zones, reaching 29.6% of the content in newborn. Synthesis is also directly related to total collagen II content in OA, suggesting its importance in maintaining collagen content and cartilage structure. The release of CPII from cartilage is correlated directly with cartilage content. However, the increase in CPII in OA cartilage is not reflected in serum, where a significant reduction is observed. Together these studies provide evidence for alterations in procollagen II synthesis in vivo in patients with OA.

Quantitative magnetic resonance imaging in the assessment of degenerative disc disease

Understanding degenerative intervertebral disc diseases hinges on the ability to objectively and noninvasively assess the disc matrix composition and integrity. The potential of quantitative magnetic resonance imaging to meet these demands was evaluated. Analyzing the T1 and T2 signal patterns in the nucleus pulposus with increasing Thompson morphological grade revealed a significant reduction related to grade. This significant decrease in T1 and T2 in the nucleus pulposus with grade 4 degeneration and the corresponding low correlation coefficients with respect to the content of individual matrix molecules suggest that matrix integrity plays an important and distinct role in determining T1 and T2 signal. Similarly, the significant increase in magnetization transfer in the nucleus pulposus observed in grade 4 degeneration did not correlate with the changes in molecular content in these highly degenerated discs. Again, this lack of correlation clearly indicates that the tissue integrity and matrix composition independently contribute to the magnetization transfer signal. This study presents the first clear evidence that quantitative magnetic resonance analysis reflects not only the disc matrix composition, but also the structural integrity of the matrix of the disc.

How controlled stress affects healing tissues

Restoration of a patient's full range of motion, strength, and function are the primary goals of occupational and physical therapy. Immobilization of normal connective tissue leads to biochemical, biomechanical, and physiologic changes within a week. These changes are magnified in the presence of trauma or edema, and they may create permanent damage if not addressed swiftly and properly. This is best accomplished by applying specific types of stress to the involved and associated structures at optimal intervals during the rehabilitation process. Load must be applied at adequate intensity and duration to successfully affect the viscous property of connective tissue. This is necessary to effect permanent elongation of the restricted tissues. Early controlled motion is vital to prevent the negative changes associated with immobilization and to maintain normal viscoelasticity and homeostasis of connective tissue. Hand therapists must have a thorough understanding of the changes associated with injured structures. Only then can they provide optimal stress delivery to facilitate restoration of function.

Quantification of the N-terminal propeptide of human procollagen type I (PINP): comparison of ELISA and RIA with respect to different molecular forms

This paper compares the results of procollagen type I N-terminal propeptide (PINP) quantification by radioimmunoassay (RIA) and enzyme linked immunosorbent assay (ELISA). PINP in serum from a patient with uremic hyperparathyroidism was measured in RIA and ELISA to 20 micrograms l-1 and 116 micrograms l-1 and the corresponding concentrations in dialysis fluid were 94.5 micrograms l-1 and 140 micrograms l-1, respectively. PINP antigen appears in two distinct peaks following size chromatography and the two peak fractions display immunological identity and identical M(r)'s (27 kDa: SDS-PAGE). Analysis of fractions from size separated amniotic fluid, serum and dialysis fluid demonstrated that the RIA failed to measure the low molecular weight form of PINP. However, the anti-PINP supplied with the RIA-kit and the anti-PINP applied in the ELISA reacted equally well with both molecular forms of PINP when analysed in a direct ELISA. It is concluded that the major difference in the ELISA and RIA results is due to assay efficacy with respect to the low molecular weight form of PINP.

Pre-column derivatisation method for the measurement of glycosylated hydroxylysines of collagenous proteins

Measurement of the glycosylated hydroxylysines galactosyl- and glucosylgalactosylhydroxylysine (GH and GGH) in combination with other amino acids has been based on ion-exchange chromatography followed by reaction with ninhydrin. Here, a rapid and sensitive high-performance liquid chromatographic method with fluorimetric detection has been developed and employed to determine the glycosylated hydroxylysine residues in alkaline collagen hydrolysates. After hydrolysis, amino acids were derivatised with 9-fluorenylmethyl chloroformate and separated on a Micropak ODS-80TM reversed-phase column (150x4.6 mm). With a multistep gradient system all amino acids were separated in less than 30 min, including the collagen-specific hydroxylysine, hydroxyproline and the glycosylated hydroxylysines. The method was used to evaluate the glycosylation levels of human articular cartilage derived from femoral head, femoral condyle, tibial plateau and ankle. GGH was highest in cartilage from femoral head and ankle; GH showed no differences between the different sources of cartilage.

Doxyclycline inhibits collagen synthesis by bovine chondrocytes cultured in alginate

Doxycycline is known for its ability to inhibit matrix metalloproteinases (MMPs), a family of enzymes that play a role in cartilage breakdown in arthritides. Its prophylactic effect in reducing joint degradation in osteoarthritis is mainly attributed to this property. In this study, we show that doxycycline exhibits a profound inhibition of collagen synthesis by bovine articular chondrocytes cultured in alginate. At 25 microM doxycycline, collagen synthesis was decreased by 50%; no effect on cell proliferation (DNA levels) or general protein synthesis (35S-Met and 35S-Cys incorporation) was observed. Messenger RNA levels of type II collagen were also reduced, indicating an effect of doxycycline at the transcriptional level. The concentration of doxycycline needed to downregulate collagen synthesis was > 10-fold lower than that needed to inhibit most of the MMPs. Inasmuch as differentiated chondrocytes in the early stages of osteoarthritis exhibit increased collagen synthesis, the beneficial effect of doxycycline in vivo may involve prevention of changes in chondrocyte phenotype.

Injection techniques and use in the treatment of sports injuries

Corticosteroid injections are powerful, effective adjuncts in treating exercise-related musculoskeletal injuries. This article describes a variety of different injection techniques that can be applied to many types of injuries. Specific attention is placed on knowing the exact location of the injury, so the injection can be properly administered. The injections were applied to a variety of chronic conditions that 'seem to fail all the usual conservative measures'. The vast majority had an excellent response to the injections and were able to progress with the rehabilitation programme. The effectiveness of the injections is primarily dependent on 'hitting the target site', and following the injections with a comprehensive rehabilitation programme.

Shrinkage temperature versus protein extraction as a measure of stabilization of photooxidized tissue

A rise in thermal denaturation temperature has been utilized as an indication of stabilization of collagen-containing materials such as pericardial tissue and porcine heart-valve leaflets following treatment with glutaraldehyde, Denacol, or other chemical agents. In contrast, stabilization of bovine pericardial tissue by dye-mediated photooxidation does not result in a significant rise in shrinkage temperature comparable with these treated materials. It was therefore hypothesized that a rise in shrinkage temperature is not a necessary indication for tissue stabilization. A sensitive protein extraction assay has been developed which can be used to monitor the stabilization of pericardial tissue by a variety of treatment methods, including photooxidation. A reduction in extractable protein, as analyzed by polyacrylamide gel electrophoresis, is noted for pericardial tissue treated with photooxidation, glutaraldehyde, or Denacol. Loss of extractable protein, as a function of treatment time, correlates well with a significant rise in shrinkage temperature for pericardium treated with glutaraldehyde or Denacol but not with photooxidation. This difference is attributed to the stabilization processes of glutaraldehyde and Denacol, which involve extensive crosslinking and polymer formation within and in addition to the native pericardial matrix, leading to a rise in matrix complexity and thermal stability. In contrast, photooxidation is a catalytic process involving modification and crosslink formation within existing matrix components, resulting in a material with little added matrix complexity.

Laboratory assessment of nutritional metabolic bone disease in infants

OBJECTIVES

There are numerous laboratory investigations available for the assessment of an infant with suspected metabolic bone disease (MBD); thus, comprehensive laboratory investigations on every aspect of MBD would impose unnecessary stress to the infant and the costs involved would be prohibitive. An overview of the assessment of an infant with suspected MBD, in particular, nutrition-related bone disease, is presented. Our objectives include an understanding of: 1. the importance of appropriate information from history and physical examination to guide the laboratory investigations; 2. relevance and limitations of specific laboratory investigations: a. radiologic studies include diagnostic radiographs and quantitative bone mass determination by dual energy x-ray absorptiometry, b. biochemical measurements to determine mineral homeostasis and bone turnover, c. vitamin (vitamin D metabolites) and hormonal (parathyroid hormone and calcitonin) measurements; with respect to diagnosis and monitoring of the natural progress or response to therapy.

CONCLUSION

Relevant information from clinical history and physical examination, and an understanding of the role and limitations of various laboratory investigations, would allow the optimal utilization of laboratory tests in the assessment of an infant with MBD.

The human lumbar intervertebral disc: evidence for changes in the biosynthesis and denaturation of the extracellular matrix with growth, maturation, ageing, and degeneration

Very little is known about the turnover of extracellular matrix in the human intervertebral disc. We measured concentrations of specific molecules reflecting matrix synthesis and degradation in predetermined regions of 121 human lumbar intervertebral discs and correlated them with ageing and Thompson grade of degeneration. Synthesis in intervertebral discs, measured by immunoassay of the content of a putative aggrecan biosynthesis marker (846) and the content of types I and II procollagen markers, is highest in the neonatal and 2-5-yr age groups. The contents of these epitopes/molecules progressively diminished with increasing age. However, in the oldest age group (60-80 yr) and in highly degenerated discs, the type I procollagen epitope level increased significantly. The percentage of denatured type II collagen, assessed by the presence of an epitope that is exposed with cleavage of type II collagen, increased twofold from the neonatal discs to the young 2-5-yr age group. Thereafter, the percentage progressively decreased with increasing age; however, it increased significantly in the oldest group and in highly degenerate discs. We identified three matrix turnover phases. Phase I (growth) is characterized by active synthesis of matrix molecules and active denaturation of type II collagen. Phase II (maturation and ageing) is distinguished by a progressive drop in synthetic activity and a progressive reduction in denaturation of type 11 collagen. Phase III (degeneration and fibrotic) is illustrated by evidence for a lack of increased synthesis of aggrecan and type II procollagen, but also by an increase in collagen type II denaturation and type I procollagen synthesis, both dependent on age and grade of tissue degeneration.

The human lumbar endplate. Evidence of changes in biosynthesis and denaturation of the extracellular matrix with growth, maturation, aging, and degeneration

STUDY DESIGN

The authors measured concentrations of specific molecules reflecting matrix synthesis and degradation in 121 human endplates and correlated them with aging and grade of degeneration.

OBJECTIVES

Abnormal endplate development has been implicated in many spinal abnormalities, yet little is known about endplate matrix component turnover.

SUMMARY OF BACKGROUND DATA

Techniques are available to perform an in situ investigation of matrix component turnover with aging and degeneration.

METHODS

Newly synthesized aggrecan and Type I and Type II procollagens were measured with recently developed immunoassays. Percentage of denatured Type II collagen was assessed with a new enzyme-linked immunosorbent inhibition assay.

RESULTS

Synthesis in endplates, measured by content of an aggrecan marker (846) and content of Types I and II procollagen markers (CPI and CPII), is highest in the neonatal and 2- to 5-year age groups and steadily diminishes with increasing age. However, in the oldest age group and in highly degenerated discs, the CPI epitope level increased significantly. Percentage of denatured Type II collagen, assessed by the presence of an epitope exposed with the cleavage of Type II collagen, increased from the neonatal to the 2- to 5-year age groups. The percentage progressively decreased with increasing age. However, it significantly increased in endplates from highly degenerated discs.

CONCLUSIONS

The authors identified three matrix turnover phases, related to age and grade of degeneration. Phase I (growth) is characterized by active synthesis of matrix molecules and active denaturation of Type II collagen. Phase II (aging and maturation) is distinguished by a drop in synthetic activity and a reduction in denaturation of Type II collagen. Phase III (degenerative) is illustrated by an increase in Type II collagen denaturation and Type I procollagen synthesis, both related to grade of tissue degeneration.

Left ventricular perimysial collagen fibers uncoil rather than stretch during diastolic filling

The collagen fibers in the myocardium are initially wavy, suggesting that they may not be directly stretched for a portion of diastolic filling. To test whether the fibers gradually straighten and at what left ventricular (LV) pressure they become straight, 24 isolated, arrested rat hearts were fixed at physiologic diastolic LV pressures and changes in collagen structure were examined. As LV pressure increased, mean ( +/- SE) sarcomere length increased (1.80 +/- 0.02 to 1.88 +/- 0.02 from 0 mmHg to 26.3 +/- 4.1 mmHg) while the tortuosity of the perimysial fibers (fiber length/midline length) decreased (1.088 +/- 0.014 to 1.031 +/- 0.006 from 0 mmHg to 26.3 +/- 4.1 mmHg). Transmural variations in collagen structure paralleled the trends in sarcomere length (epicardial regions had longer sarcomeres and straighter collagen fibers than endocardial regions). These results indicate that there is a tight coupling between perimysial collagen fibers and myocytes, consistent with the nonlinear pressure-volume and pressure-sarcomere length relationships.

Molecular characteristics of dimethylnitrosamine induced fibrotic liver collagen

The molecular characteristics of purified pepsin solubilized collagen from rat liver was studied in control and dimethylnitrosamine administered animals. The alpha- and beta-chains of purified pepsin solubilized liver collagen were separated by subjecting the denatured collagen to SDS-polyacrylamide gel electrophoresis. The alpha 1(III) chains were resolved from the alpha 1(I) chains by interrupted electrophoresis with delayed reduction of the disulfide bonds of type III collagen. The aldehyde content of the purified pepsin solubilized collagen was estimated in control and experimental samples in order to assess the extent of collagen cross-links. Fibril formation curves were studied with purified pepsin solubilized collagen to see the rate of formation of cross-links within the fibrillar mesh. The results of the unreduced electrophoretic studies revealed a significant increase in the beta-subunit of type I collagen with a remarkable decrease of alpha/beta ratio in DMN treated animals. Reduction with beta-mercaptoethanol indicated the presence of type III collagen in the electrophoretic field with a proportionate increase on the 21st day. A significant increase in the aldehyde content and an increased rate of fibril formation were noticed in DMN induced fibrotic liver collagen. The data of the present investigation revealed that the DMN induced fibrotic liver collagen is more cross-linked than normal liver collagen and the deposition of type III collagen in more prominent than type I collagen in early fibrosis.

An immunohistochemical study of collagen types III, VI and IX in rabbit craniomandibular joint tissues following surgical induction of anterior disk displacement

The purpose of this study was to determine the effect of surgical induction of anterior disk displacement (ADD) on type-III, VI and IX collagens of the rabbit craniomandibular joint (CMJ) tissues using an immunohistochemical technique. The right joint was exposed surgically, all discal attachments were severed except for the posterior discal attachment (bilaminar zone). The disk was then repositioned anteriorly and sutured to the zygomatic arch. The left joint served as a sham-operated control. Ten additional joints were used as non-operated controls. Deeply anesthetized rabbits were perfused with 2% buffered formalin 2 weeks (10 rabbits) or 6 weeks (10 rabbits) following surgery. The articular disk, bilaminar zone, mandibular condyle and articular eminence were excised. The last two were decalcified in EDTA. All tissues were then sectioned at 10 microns in a cryostat. Sections were incubated with monoclonal antibodies directed against type-III, VI or IX collagens. Following incubation in the appropriate FITC-labelled secondary antibodies, all sections were studied under the fluorescence microscope. The results showed a reduction in immunostaining for type-VI and IX collagens in the condylar cartilage, disk and articular eminence at 2 weeks, followed by an increase in their immunostaining at 6 weeks and the appearance of a de novo type-III collagen in the condylar cartilage and the articular eminence. It is concluded that surgical induction of ADD in the rabbit CMJ leads to alterations in its type-III, VI and IX collagens.

Enhanced denaturation of the alpha (II) chains of type-II collagen in normal adult human intervertebral discs compared with femoral articular cartilage

The mechanical strength of connective tissues is dependent on the integrity of their fibrillar collagen frameworks. The objective of the present study was to assess type-II collagen damage (denaturation) in the adult human intervertebral disc compared with articular cartilage, in order to determine whether damage to this molecule may vary in different anatomical sites in the same person. A new immunochemical assay was used to measure the amounts of denatured and total type-II collagen in the annulus fibrosus and nucleus pulposus of the L5-S1 disc and in cartilage from the femoral condyles of the same individuals (n = 7). Denaturation of type-II collagen was significantly higher in both the annulus fibrosus and the nucleus pulposus than in articular cartilage. Such increased damage to type-II collagen in the adult disc may have relevance to the more pronounced degenerative changes observed in this tissue compared with articular cartilage.

The thermodynamic response of soft biological tissues to pulsed ultraviolet laser irradiation

The physical mechanisms that enable short pulses of high-intensity ultraviolet laser radiation to remove tissue, in a process known as laser ablation, remain obscure. The thermodynamic response of biological tissue to pulsed laser irradiation was investigated by measuring and subsequently analyzing the stress transients generated by pulsed argon fluorine (ArF, lambda = 193 nm) and krypton fluorine (KrF, lambda = 248 nm) excimer laser irradiation of porcine dermis using thin-film piezoelectric transducers. For radiant exposures that do not cause material removal, the stress transients are consistent with rapid thermal expansion of the tissue. At the threshold radiant exposure for ablation, the peak stress amplitude generated by 248 nm irradiation is more than an order of magnitude larger than that produced by 193 nm irradiation. For radiant exposures where material removal is achieved, the temporal structure of the stress transient indicates that the onset of material removal occurs during irradiation. In this regime, the variation of the peak compressive stress with radiant exposure is consistent with laser-induced rapid surface vaporization. For 193 nm irradiation, ionization of the ablated material occurs at even greater radiant exposures and is accompanied by a change in the variation of peak stress with radiant exposure consistent with a plasma-mediated ablation process. These results suggest that absorption of ultraviolet laser radiation by the extracellular matrix of tissue leads to decomposition of tissue on the time scale of the laser pulse. The difference in volumetric energy density at ablation threshold between the two wavelengths indicates that the larger stresses generated by 248 nm irradiation may facilitate the onset of material removal. However, once material removal is achieved, the stress measurements demonstrate that energy not directly responsible for target decomposition contributes to increasing the specific energy of the plume (and plasma, when present), which drives the gas dynamic expansion of ablated material. This provides direct evidence that ultraviolet laser ablation of soft biological tissues is a surface-mediated process and not explosive in nature.

Type II and type III collagen in mandibular condylar cartilage of patients with temporomandibular joint pathology

PURPOSE

This study was undertaken to examine the presence of type II and type III collagen in the cartilage of the mandibular condyle in different types of temporomandibular joint (TMJ) pathology, including rheumatoid arthritis (RA), to assess to what degree the newly formed tissue is cartilaginous.

PATIENTS AND METHODS

Tissue samples from 46 TMJ surgery patients (37 women and 9 men; mean age, 37 years; range, 14 to 76 years) were investigated. The samples were obtained at surgery mostly from anteriorly situated osteophytes or the anterosuperior uneven articular surface of the condyle. Tissue sections were stained with hematoxylin-eosin, toluidine blue, and Gomori's reticular stain. Type II and type III collagens were demonstrated by immunohistochemical staining.

RESULTS

The amount of type II collagen was variable in the mandibular condylar cartilage. Type III collagen was found in the new osteoid tissue as well as the new chondroid tissue that was synthesized in the most reactive situations.

CONCLUSIONS

Type II collagen synthesis occurred mainly in condylar hypertrophy and the intermediate stage of internal derangement of the TMJ. Type III collagen, which is found in fibrous repair tissue, was also found in sites of repair of mandibular condylar cartilage, including RA and osteomyelitis.

Treatment of superficial digital flexor tendinitis

This article reviews the research and clinical findings relevant to the treatment of acute tendinitis in the horse. The goals of treatment are to reduce inflammation, minimize scar tissue formation, and promote restoration of normal tendon function. A wide variety of treatments have and still are being used to treat tendinitis, which indicates that there is no uniformly successful way to return a horse to full athletic function after injury. Therapy depends on the severity of tendinitis and duration of injury and can be divided into treatment during the inflammatory, repair, and maturation phases of healing.

Stabilization of pericardial tissue by dye-mediated photooxidation

Bovine pericardial tissue was stabilized through a dye-mediated photooxidation reaction. Shrink temperature analysis of the stabilized tissue indicated a material with similar properties to untreated pericardial tissue and unlike identical tissue treated with glutaraldehyde. Photooxidized tissue was resistant to extraction when compared with untreated tissue or control tissues treated in the absence of light or dye. Photooxidized tissue was also resistant to enzymatic digestion by pepsin and to chemical digestion by cyanogen bromide (CNBr). In contrast, untreated or control treated tissues were readily digested by these reagents. Reduction of photooxidized tissue with beta-mercaptoethanol prior to CNBr digestion partially restored susceptibility of the tissue to CNBr digestion, indicating the photooxidation of methionine residues. Soluble collagen derived from bovine pericardium was used as a model compound for the photooxidation reaction. Polyacrylamide gel electrophoresis analysis indicated the photooxidative conversion of collagen into higher molecular weight aggregates consistent with intermolecular crosslink formation. Photooxidized tissue was stable to in vivo degradation when compared with control tissue. Results presented here indicate a crosslinked pericardial tissue produced by dye-mediated photooxidation possessing properties of chemical stability, enzymatic stability, in vivo stability, and biomechanical integrity suitable for use as a biomaterial.

Effects of lathyritic drugs and lathyritic demineralized bone matrix on induced and sustained osteogenesis

Demineralized bone matrix was implanted in normal and lathyritic rats. At 2 weeks, the bone that formed in the lathyritic animals had an elevated alkaline phosphatase activity and a reduced calcium content compared with the controls. Four weeks after implantation, these biochemical parameters were reversed, with a decrease in alkaline phosphatase activity and an increase in calcium content to control levels. The histology of the recovered implants revealed new bone formation. Lathyritic demineralized bone matrix was prepared from bones of rats fed beta-aminopropionitrile for 2 weeks (2-week BAPN-DBM) or 4 weeks (4-week BAPN-DBM), and was implanted in normal rats. Two weeks after implantation, both preparations of lathyritic demineralized bone matrix demonstrated early bone formation, although alkaline phosphatase activity and calcium content were reduced. By 4 weeks after implantation, no biochemical or histological evidence of bone formation remained at the site of the 4-week BAPN-DBM implants; continued but reduced bone formation was observed at the site of the 2-week BAPN-DBM implants. Reconstitution of inactivated normal demineralized bone matrix with the guanidine-soluble extracts restored the osteoinductive capacity. However, reconstitution of inactivated lathyritic demineralized bone matrix (4-week BAPN-DBM) failed to restore the osteoinductive capacity. These results indicate that the degree of crosslinking of the collagen matrix that acts as a carrier for osteoinductive proteins plays a key role in inducing and sustaining osteogenesis.

Increased damage to type II collagen in osteoarthritic articular cartilage detected by a new immunoassay

A new immunoassay was developed to detect denaturation of type II collagen in osteoarthritis (OA). A peptide, alpha 1 (II)-CB11B, located in the CB11 peptide of type II collagen, was synthesized and used to produce a monoclonal antibody (COL2-3/4m) of the IgG1 (kappa) isotype. This reacts with a defined epitope in denatured but not native type II collagen and the alpha 3 chain of type XI collagen. The latter is present in very small amounts (about 1% wt/wt) in cartilage relative to the alpha 1 (II) chain. By using an enzyme-linked immunosorbent assay, type II collagen denaturation and total type II collagen content were determined. The epitope recognized by the antibody was resistant to cleavage by alpha-chymotrypsin and proteinase K which were used to extract alpha 1 (II)-CB11B from the denatured (alpha-chymotrypsin soluble) and residual native (proteinase K soluble) collagen alpha-chains, respectively, present in human femoral articular cartilage. Type II collagen content was significantly reduced from a mean (range) of 14% (9.2-20.8%) of wet weight in 8 normal cartilages to 10.3% (7.4-15.0%) in 16 OA cartilages. This decrease, which may result in part from an increased hydration, was accompanied by an increase in the percent denaturation of type II collagen in OA to 6.0% of total type II collagen compared with 1.1% in normal tissue. The percent denaturation was ordinarily greater in the more superficial zone than in the deep zone of OA cartilage.

Anatomy of the anterior cruciate ligament: a blueprint for repair and reconstruction

The anterior cruciate ligament of the knee joint is a complex structure whose orientation, construct, and biology are directly related to its function as a constraint of knee joint motion. While the complexity of its design allows the ligament to function through the normal range of motion as a static stabilizer of the knee, it also makes the exact duplication of this structure very difficult. A fundamental knowledge of the functional anatomy of the anterior cruciate ligament provides the orthopaedic surgeon with an essential blueprint on which to base techniques of repair and reconstruction.

Healing characteristics of a type I collagenous structure treated with corticosteroids

One hundred twenty-eight skeletally mature New Zealand White rabbits were used to study the effect of a single corticosteroid injection on the biomechanical, biochemical, and histologic aspects of ligamentous healing. Two steroid dosages were used. The amount of the low-dose steroid was calculated by determining the corticosteroid concentration at which fibroblastic synthesis of collagen was inhibited in vitro. A human equivalent dose of betamethasone was used as the high-dose steroid injection. These two steroid doses and a saline control were injected around a transected medial collateral ligament. At 10 days all groups showed significantly inferior biomechanical properties relative to noninjected controls. By 3 weeks the human equivalent steroid dose group continued to demonstrate significantly inferior properties. Histologic and biochemical analyses confirmed the biomechanical results. The clinical relevance of the study was that the delivery of a human equivalent steroid dose into an acutely injured ligament significantly impairs the healing process relative to a noninjected ligament at 10 days and at 3 weeks after injury. This implies that a corticosteroid-treated injured ligament may not be able to withstand the mechanical loads of early vigorous rehabilitation.

Assessment of bone remodeling using biochemical indicators of type I collagen synthesis and degradation: relation to calcium kinetics

In this study, we investigated the relation between calcium kinetic indices of bone remodeling (resorption rate, r; and formation rate, m, respectively) and two serum markers of type I collagen turnover: the pyridinoline cross-linked carboxyterminal telopeptide domains of type I collagen (S-ICTP a marker of bone matrix degradation) and the carboxyterminal propeptide of human type I procollagen (S-PICP, a marker of bone matrix formation). We studied three groups: (i) healthy controls (n = 19), (ii) a mixed group of high and low-turnover bone diseases without mineralization defects (myxedema, thyrotoxicosis and primary hyperparathyroidism n = 38), and (iii) osteoporosis (n = 52). In healthy controls, a significant regression of S-PICP on m was obtained (R = 0.53, SEE/Y = 0.44, P < 0.02). Significant regressions were also demonstrable in high- and low-turnover bone disease (R = 0.50, P < 0.001), SEE/Y = 61%) and osteoporosis (R = 0.49, P < 0.001, SEE/Y = 50%). In controls the regression coefficient for the regression of S-ICTP on r was 0.19 (NS), in high and low turnover bone disease 0.66, (SEE/Y = 59%, P < 0.001) and in the osteoporotic group 0.40 (SEE/Y = 61%, P < 0.01). We conclude that S-PICP and S-ICTP reflect whole skeletal bone formation and resorption rates in a variety of metabolic bone diseases including osteoporosis.

Effects of hyaluronan on collagen fibrillar matrix contraction by fibroblasts

Hyaluronan, found in high concentrations in fetal tissues, appears to have a major role in preventing scar formation in fetal wounds. Nevertheless, its role in inhibiting wound contractures associated with scar formation has not been clearly demonstrated. Our current study evaluated the effects of hyaluronan using an in vitro floating collagen fibrillar matrix (CFM) contraction model. The results demonstrated that the contraction of CFM by fibroblasts was significantly reduced when high concentrations (> 1 mg/mL) of hyaluronan were present in the media. This phenomenon is unique to hyaluronan, because chondroitin sulfate was ineffective in this connection. Fibroblast migration and proliferation studies indicated that high concentrations of hyaluronan stimulated cell migration and had no cytotoxic effects. Some possible mechanisms by which high concentrations of hyaluronan reduced CFM contraction by fibroblasts were proposed. Because the viscosity of a hyaluronan solution is much greater than that of chondroitin sulfate, and this increases with concentration, we investigated whether this property in itself was an important factor in inhibiting CFM contraction. No direct correlation was found between the viscosity of glycosaminoglycans and their ability to reduce CFM contraction.

Serum type III procollagen peptide in patients with Pneumocystis carinii infection. The Copenhagen-Amsterdam PCP-Prednisolone Study Group

Inflammation may play a central role in the pathogenesis of HIV-related Pneumocystis carinii pneumonia (PCP). Serum levels of the amino-terminal propeptide of Type III procollagen (PIIINP) reflect inflammatory activity in granulation tissue and in chronic rheumatic and liver disorders. To investigate changes in PIIINP serum levels during an episode of HIV-related PCP, consecutive serum samples were taken from 48 HIV-infected patients with PCP in a randomized, placebo-controlled study of the effect of adjunctive methylprednisolone therapy (26 in corticosteroid [CS] group and 22 in control group). All patients were treated with co-trimoxazole. In the control group, PIIINP serum levels at day of initiation of therapy (Day 0) were significantly higher in patients requiring mechanical ventilation and/or dying during the course of the pneumonia, and serum levels of PIIINP higher than 5 ng/ml were associated with a higher mortality than levels below 5 ng/ml. The level of PIIINP increased from Day 0 to Day 5. There was a significant correlation between changes in PIIINP levels and changes in the alveolar-arterial oxygen gradient from Day 0 to Day 5. In the CS group, the PIIINP levels decreased while steroid was administered. At Days 21 to 28 there were no difference in the levels of PIIINP between the two groups. PIIINP serum levels may predict the clinical outcome of PCP. The antimicrobial therapy may exacerbate the inflammatory reaction in HIV-related PCP, leading to respiratory failure. CS prevents this increased inflammatory activity.

Whole organ evaluation of collagen in the developing human larynx and adjoining anatomic structures (hyoid and trachea)

The collagen composition (types I, II, and III) of the normal developing human larynx and trachea was examined by biochemical methods. Autopsy specimens of larynges with attached upper tracheal rings were obtained from 28 humans ranging in age from birth to 44 years. The specimens were randomly collected, but excluded if laryngeal disease existed. The age, sex, and cause of death were documented. Collagen is important in the growth, development, repair, regeneration, and structural and functional integrity of the laryngeal framework. A preliminary report of selected cartilaginous components of the larynx was previously published by the authors, which studied the changes in the phenotypic expression of the collagen genes in children from the newborn period to 5 years 10 months of age. The current study included all of the functioning components of the skeletal larynx and trachea. The results of biochemical examination of these tissues are reported, and the potential clinical significance of the results of the study is discussed.

Serum markers of type I collagen formation and degradation in metabolic bone disease: correlation with bone histomorphometry

Type I collagen makes up more than 90% of bone matrix. Therefore, analysis of antigens related to collagen formation and degradation in bone should provide good and specific estimates of both bone resorption and bone formation rates. In this study we measured serum levels of the pyridinoline cross-linked telopeptide domain of type I collagen (ICTP) as a marker of bone resorption and serum carboxy-terminal propeptide of type I procollagen (PICP) as a marker of bone formation. Serum levels of the two antigens were correlated to histomorphometric indices of bone resorption and bone formation calculated from iliac crest bone biopsies in a group of 18 individuals with high- and low-turnover bone disease (myxedema, primary hyperparathyroidism, and thyrotoxicosis). After logarithmic transformation the regression of S-ICTP on volume-referent resorption rate (BRs/R/BV) was significant (r = 0.61, p < 0.01, SEM/Y = 56%). S-ICTP also showed a significant regression on the volume-referent cancellous bone balance (r = -0.45, p < 0.05, SEM/Y = 412%). S-PICP was significantly correlated to the mineral appositional rate (r = 0.53, p < 0.05) and volume-referent bone formation rate (r = 0.61, p < 0.01, SEM/Y = 48%). The correlation to bone turnover as expressed in the activation frequency was also highly significant (r = 0.61, p < 0.01, SEM/Y = 51%). No significant correlation with wall thickness or bone balance was demonstrable per remodeling cycle. Thus, assays employing antigens that reflect collagen formation and degradation are useful instruments for the evaluation of rates of bone remodeling in metabolic bone disease.

Two cell lines from bone marrow that differ in terms of collagen synthesis, osteogenic characteristics, and matrix mineralization

Two cloned cell lines were isolated from cultures of mouse bone-marrow cells. One of the lines, D1, exhibited osteogenic properties and synthesized type-I collagen (alpha 1)2 alpha 2. The second cell line, D2, was not osteogenic and produced a collagen homotrimer (alpha 1)3. Whereas the extracellular matrix of the D1 cell cultures contained striated collagen fibrils, presumably composed of type-I collagen, the homotrimer-producing D2 cells did not demonstrate striated collagen fibrils. Instead, they had thin filaments without detectable striations. Sodium ascorbate stimulated collagen synthesis at the transcriptional level in both the D1 and the D2 cells. The bone-producing characteristics of D1 in vitro included high levels of alkaline phosphatase, increased cyclic adenosine monophosphate on treatment with parathyroid hormone, and expression of osteocalcin mRNA. The D1 cells, unlike the D2 cells, produced a mineralized matrix in vitro. Mineralization in the cultures of the D1 cells occurred in nodules of increased cell density, which also contained the cells with the highest concentrations of collagen mRNA, as shown by in situ hybridization. When the D1 cells were implanted in a diffusion chamber in vivo, a mixture of both osteogenic and adipogenic tissues was formed. This indicates that the D1 cell line is derived from an early marrow stromal precursor that is multipotential.

Chromosomal anomalies in radiation-induced fibrosis in the pig

R-banded karyotypes were established on fibroblasts from fibrotic tissues derived from experimental fibrosis induced in pigs, either surgically or by 64 Gy of gamma-rays from iridium-192. No chromosome aberrations were observed in the surgical fibrosis. In radiation-induced fibrosis, the high frequency of abnormal karyotypes and the frequent complexity of the chromosomal rearrangements suggest that the fibroblasts originated either from the 64-Gy area, or from the penumbra, but certainly not from non-irradiated areas. At early passages in vitro, almost all karyotypes were different, demonstrating a multiclonal origin of fibrotic tissue. At late passages (above 24), the situation was quite different, with the persistence of one or two clones only, demonstrating a strong selective pressure occurring in vitro.

Assessment of bone formation by biochemical markers in metabolic bone disease: separation between osteoblastic activity at the cell and tissue level

In this study , serum levels of classical serum markers of bone formation [carboxyterminal propeptide of procollagen type I (S-PICP), bone Gla protein (S-BGP)], and total alkaline phosphatase (S-AP)) were related to the calcium kinetic index of whole skeletal mineralization rate (m) by regression analysis in a variety of metabolic bone diseases. For each disease, the regression coefficient (r) as well as the fraction: standard error of estimate/mean dependent variable (SEE/Y) were determined. In a group of 19 normals, only the regression of S-PICP on m reached significance (r = 0.53, P < 0.02, SEE/Y = 0.44), whereas regressions of S-AP and S-BGP on m were nonsignificant. In a pooled material of high- and low-turnover bone diseases without mineralization defects or spinal fracture [myxedema, thyrotoxicosis, and primary hyperparathyroidism (n = 48)], a highly significant positive regression of S-PICP on m was demonstrable (r = 0.50, SEE/Y = 0.63, P < 0.001). The regression coefficients obtained for S-BGP and S-AP were 0.74 (P < 0.001, SEE/Y = 0.41) and 0.42 (P < 0.01, SEE/Y = 0.55), respectively. When analyzing individual diseases in this group, significant differences among the three markers were detectable. In a group of 52 osteoporotics, S-PICP correlated significantly to m (r = 0.49, P < 0.001, SEE/Y = 0.50). Corresponding r-values for S-BGP and S-AP were 0.21 (NS) and 0.48 (P < 0.001, SEE/Y = 0.61), respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Collagen in the developing larynx. Preliminary study

The primary purpose of this study was to determine the types of collagen in the developing human larynx that contribute to the structural framework and function of various components of this organ. The infant larynx is much more than a mere miniature of the adult "voice box." There are many age-related differences that occur in the larynx from the newborn period to the adult period of life. While collagen has been studied in numerous tissues, both normal and diseased, there have been no studies of the whole organ content, types, and/or changes of collagen in the developing human larynx that may account for many of the clinical findings. This study may at least in part explain whether collagen differences may account for the structural changes and responses that are seen in clinical practice.

The effect of gamma irradiation on a xenograft tendon bioprosthesis

Radiation sterilisation of xenograft prostheses has been shown to cause damage to the material. Such damage has been imputed to affect the mechanical and biological properties and may contribute to long-term failure. This study has examined the effect of 25 kGy (2.5 Mrad) of gamma radiation on the mechanical and physicochemical properties and the biological function of a xenograft tendon bioprosthesis derived from glutaraldehyde cross-linked kangaroo tail tendon. The ultimate tensile stress of nonirradiated glutaraldehyde cross-linked tendon was greater than that of fresh frozen tendon, but irradiated cross-linked tendon did not differ. Irradiation did not alter the response to prolonged collagenase exposure. There was a decrease in overall apparent cross-link density (as determined by thermal denaturation temperature). After 12 months implantation, there was a slightly more active cellular response around irradiated tendon and the very peripheral fibres were infiltrated, but the mechanical properties of the retrieved implants were the same for irradiated and nonirradiated material. Gamma irradiation would appear to be a satisfactory method of sterilisation for glutaraldehyde cross-linked tendon materials. However, as damage to the cross-linked structure was detected in this study, it may not be appropriate in other applications.

Differential patterns of PMN-elastase and type III procollagen peptide in knee joint effusions due to acute and chronic sports injuries

In 38 traumatic knee joint effusions the proteolytic enzyme PMN-elastase (PMN-E) and the repair marker procollagen III aminoterminal peptide (PIIINP) were determined. According to the period between trauma and first aspiration of the effusion, the patients were divided into 3 groups. Group I (17 patients; period between trauma and first aspiration not longer than 72 hours) showed high concentrations of PMN-E (up to 5400 ng/ml) and low concentrations of PIIINP (less than 13 U/ml). Group II (11 patients; aspiration within 4 to 14 days) had mean PMN-E and PIIINP concentrations of 125.6 ng/ml and 52.1 U/ml, respectively. In group III (10 patients, aspiration after 14 days) mean PMN-E concentration was 123.8 ng/ml and mean PIIINP concentration was 63.4 U/ml. Graphic depiction of PMN-E and PIIINP levels in each individual sample as a function of time between trauma and fluid collection revealed highly increasing PMN-E levels during the first 24 posttraumatic hours, followed by rapidly decreasing levels within 72 hours post trauma, and no change after the 4th posttraumatic day. In contrast, PIIINP increased continuously up to the first posttraumatic week and stayed at high levels up to 90 days (end of the observation period). The differential patterns of PMN-E and PIIINP concentration in knee joint effusions may be useful in estimating the period between trauma and first treatment (aspiration of effusion) and should, therefore, be helpful in detecting degenerative lesions, which seem to be characterized by low PMN-E concomitantly with high PIIINP levels.

Matrix in cartilage and bone development: current views on the function and regulation of major organic components

Study of the growth and development of cartilage and bone has been difficult because the structure of the tissues makes biological experiments hard to conduct. Recent advances in molecular biology have offered new possibilities for studying these processes. Many cartilage and bone specific cDNAs have been cloned and characterized and consequently used to localize the corresponding mRNAs in tissue sections. Developing cartilage and bone serve as a model for the study of extracellular matrix gene regulation during the proliferation, growth and differentiation of connective tissue cells. Normal skeletal growth and development are regulated by both systemic and local factors. The effects of many systemic hormones on bone metabolism have been studied extensively, but the pathways triggered by these hormones in the target cells are less well known. Recent evidence suggests that some growth factors, such as TGF-beta, IGFs and PDGF, act as local regulators of cartilage and bone metabolism. The different extracellular matrix components, e.g. collagens, are expressed differently in distinct cell types and developmental stages during cartilage and bone development. This model, therefore, facilitates the study of relations between the production of the various extracellular matrix components and the growth factors and the proto-oncogenes which may regulate them. Existing knowledge of the expression of major cartilage and bone components and their regulation during growth, differentiation and development is reviewed. An understanding of the normal growth and development of cartilage and bone is fundamental for elucidating the mechanisms underlying the various diseases -- both hereditary and acquired -- affecting the human skeleton.

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.

Age-related changes in collagen synthesis and degradation in rat tissues. Importance of degradation of newly synthesized collagen in regulating collagen production

During developmental growth, collagens are believed to be continuously deposited into an extracellular matrix which is increasingly stabilized by the formation of covalent cross-links throughout life. However, the age-related changes in rates of synthetic and degradative processes are less well understood. In the present study we measured rates of collagen synthesis in vivo using a flooding dose of unlabelled proline given with [14C]proline and determining production of hydroxy[14C]proline. Degradation of newly synthesized collagen was estimated from the amount of free hydroxy [14C]proline in tissues 30 min after injection. Collagen fractional synthesis rates ranged from about 5%/day in skeletal muscle to 20%/day in hearts of rats aged 1 month. At 15 months of age, collagen fractional synthesis rates had decreased markedly in lung and skin, but in skeletal muscle and heart, rates were unchanged. At 24 months of age, synthesis rates had decreased by at least 10-fold in all tissues, compared with rates at 1 month. The proportion of newly synthesized collagen degraded ranged from 6.4 +/- 0.4% in skin to 61.6 +/- 5.0% in heart at 1 month of age. During aging the proportion degraded increased in all tissues to maximal values at 15 months, ranging from 56 +/- 7% in skin to 96 +/- 1% in heart. These data suggest that there are marked age-related changes in rates of collagen metabolism. They also indicate that synthesis is active even in old animals, where the bulk of collagens produced are destined to be degraded.

Increased interleukin-2 production in response to human type I collagen stimulation in patients with systemic sclerosis

Peripheral blood mononuclear cells (PBMC) from patients with systemic sclerosis (SSc) produced increased amounts of interleukin-2 (IL-2), in a dose-dependent manner, in response to stimulation with human type I collagen, whereas PBMC from normal subjects did not. At a dose of 50 micrograms human type I collagen/10(6) PBMC, PBMC from SSc patients (n = 17) produced 8 times as much IL-2 as did PBMC from 16 normal subjects (P less than 0.005) and 3 times as much as did PBMC from a group of 13 rheumatoid arthritis patients (P less than 0.05). In contrast, IL-2 production by PBMC after nonspecific stimulation with the mitogen, phytohemagglutinin, did not differ among the SSc, rheumatoid arthritis, and normal control groups. Cell depletion experiments indicated that the IL-2-producing cells in SSc patients are CD4+. Thus, SSc patients have CD4 cells that are specifically sensitized to human type I collagen and can produce increased levels of IL-2. Measurement of IL-2 production stimulated by human type I collagen may be useful in evaluating disease activity, and further investigation of this process may contribute to the delineation of the pathogenesis of SSc.