Tenomodulin knockout mice exhibit worse late healing outcomes with augmented trauma-induced heterotopic ossification of Achilles tendon

Heterotopic ossification (HO) represents a common problem after tendon injury with no effective treatment yet being developed. Tenomodulin (Tnmd), the best-known mature marker for tendon lineage cells, has important effects in tendon tissue aging and function. We have reported that loss of Tnmd leads to inferior early tendon repair characterized by fibrovascular scaring and therefore hypothesized that its lack will persistently cause deficient repair during later stages. Tnmd knockout (Tnmd-/-) and wild-type (WT) animals were subjected to complete Achilles tendon surgical transection followed by end-to-end suture. Lineage tracing revealed a reduction in tendon-lineage cells marked by ScleraxisGFP, but an increase in alpha smooth muscle actin myofibroblasts in Tnmd-/- tendon scars. At the proliferative stage, more pro-inflammatory M1 macrophages and larger collagen II cartilaginous template were detected in this group. At the remodeling stage, histological scoring revealed lower repair quality in the injured Tnmd-/- tendons, which was coupled with higher HO quantified by micro-CT. Tendon biomechanical properties were compromised in both groups upon injury, however we identified an abnormal stiffening of non-injured Tnmd-/- tendons, which possessed higher static and dynamic E-moduli. Pathologically thicker and abnormally shaped collagen fibrils were observed by TEM in Tnmd-/- tendons and this, together with augmented HO, resulted in diminished running capacity of Tnmd-/- mice. These novel findings demonstrate that Tnmd plays a protecting role against trauma-induced endochondral HO and can inspire the generation of novel therapeutics to accelerate repair.

Imbalanced cellular metabolism compromises cartilage homeostasis and joint function in a mouse model of mucolipidosis type III gamma

Mucolipidosis type III (MLIII) gamma is a rare inherited lysosomal storage disorder caused by mutations in GNPTG encoding the γ-subunit of GlcNAc-1-phosphotransferase, the key enzyme ensuring proper intracellular location of multiple lysosomal enzymes. Patients with MLIII gamma typically present with osteoarthritis and joint stiffness, suggesting cartilage involvement. Using Gnptg knockout (Gnptgko ) mice as a model of the human disease, we showed that missorting of a number of lysosomal enzymes is associated with intracellular accumulation of chondroitin sulfate in Gnptgko chondrocytes and their impaired differentiation, as well as with altered microstructure of the cartilage extracellular matrix (ECM). We also demonstrated distinct functional and structural properties of the Achilles tendons isolated from Gnptgko and Gnptab knock-in (Gnptabki ) mice, the latter displaying a more severe phenotype resembling mucolipidosis type II (MLII) in humans. Together with comparative analyses of joint mobility in MLII and MLIII patients, these findings provide a basis for better understanding of the molecular reasons leading to joint pathology in these patients. Our data suggest that lack of GlcNAc-1-phosphotransferase activity due to defects in the γ-subunit causes structural changes within the ECM of connective and mechanosensitive tissues, such as cartilage and tendon, and eventually results in functional joint abnormalities typically observed in MLIII gamma patients. This idea was supported by a deficit of the limb motor function in Gnptgko mice challenged on a rotarod under fatigue-associated conditions, suggesting that the impaired motor performance of Gnptgko mice was caused by fatigue and/or pain at the joint.This article has an associated First Person interview with the first author of the paper.

Spin locking in liquid entrapped in nanocavities: Application to study connective tissues

Study of the spin-lattice relaxation in the spin-locking state offers important information about atomic and molecular motions, which cannot be obtained by spin lattice relaxation in strong external magnetic fields. The application of this technique for the investigation of the spin-lattice relaxation in biological samples with fibril structures reveals an anisotropy effect for the relaxation time under spin locking, T_1ρ. To explain the anisotropy of the spin-lattice relaxation under spin-locking in connective tissue a model which represents a tissue by a set of nanocavities containing water is used. The developed model allows us to estimate the correlation time for water molecular motion in articular cartilage, τ_c=30μs and the averaged nanocavity volume, V≃5400nm³. Based on the developed model which represents a connective tissue by a set of nanocavities containing water, a good agreement with the experimental data from an articular cartilage and a tendon was demonstrated. The fitting parameters were obtained for each layer in each region of the articular cartilage. These parameters vary with the known anatomic microstructures of the tissue. Through Gaussian distributions to nanocavity directions, we have calculated the anisotropy of the relaxation time under spin locking T_1ρ for a human Achilles tendon specimen and an articular cartilage. The value of the fitting parameters obtained at matching of calculation to experimental results can be used in future investigations for characterizing the fine fibril structure of biological samples.

An epigenetic bioactive composite scaffold with well-aligned nanofibers for functional tendon tissue engineering

Poor tendon repair is often a clinical challenge due to the lack of ideal biomaterials. Electrospun aligned fibers, resembling the ultrastructure of tendon, have been previously reported to promote tenogenesis. However, the underlying mechanism is unclear and the aligned fibers alone are not capable enough to commit teno-differentiation of stem cells. Here, based on our observation of reduced expression of histone deacetylases (HDACs) in tendon stem/progenitor cells (TSPCs) cultured on aligned fibers, we proposed a strategy to enhance the tenogenesis effect of aligned fibers by using a small molecule Trichostatin A (TSA), an HDAC inhibitor. Such a TSA-laden poly (l-lactic acid) (PLLA) aligned fiber (A-TSA) scaffold was successfully fabricated by a stable jet electrospinning method, and demonstrated its sustained capability in releasing TSA. We found that TSA incorporated aligned fibers of PLLA had an additive effect in directing tenogenic differentiation. Moreover, the in situ implantation study in rat model further confirmed that A-TSA scaffold promoted the structural and mechanical properties of the regenerated Achilles tendon. This study demonstrated that HDAC was involved in the teno-differentiation with aligned fiber topography, and the combination of HDAC with aligned topography might be a more efficient strategy to promote tenogenesis of stem cells.

STATEMENT OF SIGNIFICANCE

Electrospun aligned fibers, resembling the ultrastructure of tendon, have been previously reported to promote tenogenesis. However, the underlying mechanism is unclear and the aligned fibers alone are not capable enough to commit teno-differentiation of stem cells. The uniqueness of our studies are as follows, based on our observation of reduced expression of histone deacetylases (HDACs) in tendon stem/progenitor cells (TSPCs) cultured on aligned fibers, we proposed a strategy to enhance the tenogenesis effect of aligned fibers by using a small molecule Trichostatin A (TSA), a HDAC inhibitor. Such a TSA-laden poly (l-lactic acid) (PLLA) aligned fiber (A-TSA) scaffold was successfully fabricated by a stable jet electrospinning method, and demonstrated its sustained capability in releasing TSA. The incorporation and subsequent release of bioactive small molecule TSA into electrospun aligned fibers allows a controllable manner for both biochemical and physical regulation of tenogenesis of stem cells both in vitro and in vivo. Collectively, the present study provides a model of "translating the biological knowledge learned from cell-material interaction into optimizing biomaterials (from Biomat-to-Biomat)".

Calcaneal Tendon Collagen Fiber Morphometry and Aging

Fibrillar collagen in tendons and its natural development in rabbits are discussed in this paper. Achilles tendons from newborn (~7 days) to elderly (~38 months) rabbits were monitored in intact (n tendons=24) and microtome sectioned (n tendons=11) states with label-free second harmonic generation microscopy. After sectioning, the collagen fiber pattern was irregular for the younger animals and remained oriented parallel to the load axis of the tendon for the older animals. In contrast, the collagen fiber pattern in the intact samples followed the load axis for all the age groups. However, there was a significant difference in the tendon crimp pattern appearance between the age groups. The crimp amplitude (A) and wavelength (Λ) started at very low values (A=2.0±0.6 µm, Λ=19±4 µm) for the newborn animals. Both parameters increased for the sexually mature animals (>5 months old). When the animals were fully mature the amplitude decreased but the wavelength kept increasing. The results revealed that the microtome sectioning artifacts depend on the age of animals and that the collagen crimp pattern reflects the physical growth and development.

High-resolution study of the 3D collagen fibrillary matrix of Achilles tendons without tissue labelling and dehydrating

Knowledge of the collagen structure of an Achilles tendon is critical to comprehend the physiology, biomechanics, homeostasis and remodelling of the tissue. Despite intensive studies, there are still uncertainties regarding the microstructure. The majority of studies have examined the longitudinally arranged collagen fibrils as they are primarily attributed to the principal tensile strength of the tendon. Few studies have considered the structural integrity of the entire three-dimensional (3D) collagen meshwork, and how the longitudinal collagen fibrils are integrated as a strong unit in a 3D domain to provide the tendons with the essential tensile properties. Using second harmonic generation imaging, a 3D imaging technique was developed and used to study the 3D collagen matrix in the midportion of Achilles tendons without tissue labelling and dehydration. Therefore, the 3D collagen structure is presented in a condition closely representative of the in vivo status. Atomic force microscopy studies have confirmed that second harmonic generation reveals the internal collagen matrix of tendons in 3D at a fibril level. Achilles tendons primarily contain longitudinal collagen fibrils that braid spatially into a dense rope-like collagen meshwork and are encapsulated or wound tightly by the oblique collagen fibrils emanating from the epitenon region. The arrangement of the collagen fibrils provides the longitudinal fibrils with essential structural integrity and endows the tendon with the unique mechanical function for withstanding tensile stresses. A novel 3D microscopic method has been developed to examine the 3D collagen microstructure of tendons without tissue dehydrating and labelling. The study also provides new knowledge about the collagen microstructure in an Achilles tendon, which enables understanding of the function of the tissue. The knowledge may be important for applying surgical and tissue engineering techniques to tendon reconstruction.

Are Sport-Specific Profiles of Tendon Stiffness and Cross-Sectional Area Determined by Structural or Functional Integrity?

The present study aimed to determine whether distinct sets of tendon properties are seen in athletes engaged in sports with contrasting requirements for tendon function and structural integrity. Patellar and Achilles tendon morphology and force-deformation relation were measured by combining ultrasonography, electromyography and dynamometry in elite ski jumpers, distance runners, water polo players and sedentary individuals. Tendon cross-sectional area normalized to body mass^2/3 was smaller in water polo players than in other athletes (patellar and Achilles tendon; -28 to -24%) or controls (patellar tendon only; -9%). In contrast, the normalized cross-sectional area was larger in runners (patellar tendon only; +26%) and ski jumpers (patellar and Achilles tendon; +21% and +13%, respectively) than in controls. Tendon stiffness normalized to body mass^2/3 only differed in ski jumpers, compared to controls (patellar and Achilles tendon; +11% and +27%, respectively) and to water polo players (Achilles tendon only; +23%). Tendon size appears as an adjusting variable to changes in loading volume and/or intensity, possibly to preserve ultimate strength or fatigue resistance. However, uncoupled morphological and mechanical properties indicate that functional requirements may also influence tendon adaptations.

Structural and Ultrastructural Characteristics of Bone-Tendon Junction of the Calcaneal Tendon of Adult and Elderly Wistar Rats

Tendons are transition tissues that transfer the contractile forces generated by the muscles to the bones, allowing movement. The region where the tendon attaches to the bone is called bone-tendon junction or enthesis and may be classified as fibrous or fibrocartilaginous. This study aims to analyze the collagen fibers and the cells present in the bone-tendon junction using light microscopy and ultrastructural techniques as scanning electron microscopy and transmission electron microscopy. Forty male Wistar rats were used in the experiment, being 20 adult rats at 4 months-old and 20 elderly rats at 20 months-old. The hind limbs of the rats were removed, dissected and prepared to light microscopy, transmission electron microscopy and scanning electron microscopy. The aging process showed changes in the collagen fibrils, with a predominance of type III fibers in the elderly group, in addition to a decrease in the amount of the fibrocartilage cells, fewer and shorter cytoplasmic processes and a decreased synthetic capacity due to degradation of the organelles involved in synthesis.

Automatic Evaluation of Collagen Fiber Directions from Polarized Light Microscopy Images

Mechanical properties of the arterial wall depend largely on orientation and density of collagen fiber bundles. Several methods have been developed for observation of collagen orientation and density; the most frequently applied collagen-specific manual approach is based on polarized light (PL). However, it is very time consuming and the results are operator dependent. We have proposed a new automated method for evaluation of collagen fiber direction from two-dimensional polarized light microscopy images (2D PLM). The algorithm has been verified against artificial images and validated against manual measurements. Finally the collagen content has been estimated. The proposed algorithm was capable of estimating orientation of some 35 k points in 15 min when applied to aortic tissue and over 500 k points in 35 min for Achilles tendon. The average angular disagreement between each operator and the algorithm was -9.3±8.6° and -3.8±8.6° in the case of aortic tissue and -1.6±6.4° and 2.6±7.8° for Achilles tendon. Estimated mean collagen content was 30.3±5.8% and 94.3±2.7% for aortic media and Achilles tendon, respectively. The proposed automated approach is operator independent and several orders faster than manual measurements and therefore has the potential to replace manual measurements of collagen orientation via PLM.

Analysis of collagen organization in mouse achilles tendon using high-frequency ultrasound imaging

Achilles tendon ruptures are traumatic injuries, and techniques for assessing repair outcomes rely on patient-based measures of pain and function, which do not directly assess tendon healing. Consequently, there is a need for a quantitative, in vivo measure of tendon properties. Therefore, the purpose of this study was to validate ultrasound imaging for evaluating collagen organization in tendons. In this study, we compared our novel, high-frequency ultrasound (HFUS) imaging and analysis method to a standard measure of collagen organization, crossed polarizer (CP) imaging. Eighteen mouse Achilles tendons were harvested and placed into a testing fixture where HFUS and CP imaging could be performed simultaneously in a controlled loading environment. Two experiments were conducted: (1) effect of loading on collagen alignment and (2) effect of an excisional injury on collagen alignment. As expected, it was found that both the HFUS and CP methods could reliably detect an increase in alignment with increasing load, as well as a decrease in alignment with injury. This HFUS method demonstrates that structural measures of collagen organization in tendon can be determined through ultrasound imaging. This experiment also provides a mechanistic evaluation of tissue structure that could potentially be used to develop a targeted approach to aid in rehabilitation or monitor return to activity after tendon injury.

Tendon tissue engineering and its role on healing of the experimentally induced large tendon defect model in rabbits: a comprehensive in vivo study

Healing of large tendon defects is challenging. We studied the role of collagen implant with or without polydioxanone (PDS) sheath on the healing of a large Achilles tendon defect model, in rabbits. Sixty rabbits were divided into three groups. A 2 cm gap was created in the left Achilles tendon of all rabbits. In the control lesions, no implant was used. The other two groups were reconstructed by collagen and collagen-PDS implants respectively. The animals were clinically examined at weekly intervals and their lesions were observed by ultrasonography. Blood samples were obtained from the animals and were assessed for hematological analysis and determination of serum PDGF level, at 60 days post injury (DPI). The animals were then euthanized and their lesions were assessed for gross and histopathology, scanning electron microscopy, biomechanical testing, dry matter and hydroxyproline content. Another 65 pilot animals were also studied grossly and histopathologically to define the host implant interaction and graft incorporation at serial time points. The treated animals gained significantly better clinical scoring compared to the controls. Treatment with collagen and collagen-PDS implants significantly increased the biomechanical properties of the lesions compared to the control tendons at 60DPI (P<0.05). The tissue engineered implants also reduced peritendinous adhesion, muscle fibrosis and atrophy, and increased ultrasonographical echogenicity and homogenicity, maturation and differentiation of the collagen fibrils and fibers, tissue alignment and volume of the regenerated tissue compared to those of the control lesions (P<0.05). The implants were gradually absorbed and substituted by the new tendon. Implantation of the bioimplants had a significant role in initiating tendon healing and the implants were biocompatible, biodegradable and safe for application in tendon reconstructive surgery. The results of the present study may be valuable in clinical practice.

The role of collagen arrangement change during tendon healing demonstrated by scanning electron microscopy

The dry weight of tendon tissue is accounted for mainly by collagen fibers. Accordingly, the tendon-healing process primarily involves repair of collagen fibers. During the remodeling phase of tendon healing, newly proliferating collagen fibers are transformed into a mature repaired tendon. Despite the importance of this phenomenon, the details of fibrous rebuilding have not been reported previously. The aim of this study was to visualize the ultrastructural changes and to obtain a clear understanding of the reorganization of the collagen fibers in the tendon repair site, using rat Achilles tendons. We used scanning electron microscopy (SEM) with cell maceration as the main method of analysis. Pretreatment with cell maceration removed the cellular components successfully. This allowed precise visualization of each collagen fiber and the three-dimensional network of the fibers. This study was the first to apply the cell-maceration/SEM method to observe tendon tissue. Seven days after surgery, new collagen fibers grew extensively in the repair site in a random arrangement. Fourteen days after surgery, the collagen fibers began to form an axial arrangement. Near the tendon stump, this change progressed from the outer layer to the core region. On the other hand, in the middle of the repair site, it progressed from the core to the outer layer. Change in the axial arrangement of collagen fibers contributes to the connection between the repair site and the tendon stump and to the separation of the repair site from the paratenon.

[Research on influence of repair with tissue engineered tendon of vitreous cryopreservation on ultrastructure of Achilles tendon defect]

By observations of the features of ultrastructure changes in the tissue engineered artificial tendon of vitreous cryopreservation, we investigated the repairing effect of tendon after an in-vivo implantation and hence we provided an important theoretical and experimental basis for the vitreous cryopreservation and application of tissue engineered artificial tendon. After vitreous cryopreservation, the implantation materials of tissue engineered artificial tendon dynamically constructed in vitro were implanted in rats for reparation of the tendon defect. A scanning electron microscope was used. At the 2nd week, the materials presented a reticular formation and there were juvenile tendon cells among materials. At the 6th week, materials were already degraded and absorbed, and then were substituted by neonatal tendon cells and collagen fibers. At the 8th week, dense tendon tissues containing uniform tendon cells and collagen fibers were found already formed; the density of collagen fibers significantly increased with time. Using a transmission electron microscope at the 2nd week, we found active proliferation of tendon cells; most of them were immature cells with a complete nuclear membrane, clear nucleolus and little collagen fibers. At the 6th week, tendon cells were more mature with a little-sized, deep-stained nucleolus surrounded by plenty of collagen fibers with complete fiber structure and clear cross striation. There was no significant difference between the two groups. Using an electron microscope, we found a very good agreement in observation of the tissue engineered artificial tendon after the in-vivo implantation in two groups. Neonatal tendon cells and collagen fiber tissues grew well and are in a similar form and order when compared versus normal tendon tissues. This proved that vitreous cryopreservation has no significant influence on the function of tendon cells. The neonatal tissue-engineered tendon exerts good function of growth and repair.

[Age-related changes in light microscopy with Sirius red technique in rat Achilles tendon]

OBJECTIVES

In this study, age-related morphological changes in intact rat Achilles tendon was investigated.

MATERIALS AND METHODS

Thirty Wistar albino rats of 2-3 weeks, six months and 12 months old groups 10 animal in each group were examined with Sirius red light microscobic staining.

RESULTS

The Sirius red light microscobic staining revealed that red stained collagen fibers have a decreased waviness with more rounded appearence of tenocyte nuclei, extracellular matrix along a increased vascularity and the number of tenocytes decreased with age was statistically meaningfull.

CONCLUSION

The possible causes of the spontaneously Achilles tendon rupture in adult ages group was investigated with Sirius red light microscopic technique. In this age group, initiation of the degenerative changes are decreasing the elasticity thus function of this tendon.

The effects of long-term low-dose cyclosporin A treatment on muscles and tendons: an experimental study

BACKGROUND

Limited studies report that patients receiving immunosuppressive therapy, including cyclosporin A (CsA), face muscle and/or tendon pathologies. The current study aimed (i) to investigate if CsA cause changes in the microscopic structure of striated muscle tissues and tendons after long-term low-dose therapy and (ii) to examine if the vehicle of CsA, Cremophor EL, or steroid administration might cause additional effects.

METHODS

Twenty-four adult female Sprague-Dawley rats weighing 230-300 g were divided at random into four groups. Group 1 served as the control. Groups 2-4 received CsA intraperitoneally for 2.5 months: Group 2 received the oral form of CsA, Group 3 received the intravenous form of CsA, which contains Cremophor EL, and Group 4 received the intravenous form of CsA and prednisolone. Samples from the Achilles tendons and triceps surae muscles were examined at light microscope level.

RESULTS

Focal necrotic areas, enlargement of connective tissue and increase in mononuclear cells were clear on muscles in the experimental groups. No morphologic effects were observed on tendons.

CONCLUSION

Long-term low-dose CsA therapy causes focal microscopic changes in muscles but not in tendons. No additional effects were demonstrated with Cremophor EL or steroids. It should be noted that muscle tissue damage after trauma or surgeries in patients receiving CsA might be more dramatic due to the pathologic changes already caused by CsA, as supported by several case reports.

Thermal (in)stability of type I collagen fibrils

We measured the Young's modulus at temperatures ranging from 20 to 100 degrees C for a collagen fibril that is taken from a rat's tendon. The hydration change under heating and the damping decrement were measured as well. At physiological temperatures 25 to 45 degrees C, the Young's modulus decreases, which can be interpreted as an instability of the collagen. For temperatures between 45 and 80 degrees C, the Young's modulus first stabilizes and then increases when the temperature is increased. The hydrated water content and the damping decrement have strong maximums in the interval 70 to 80 degrees C indicating complex intermolecular structural changes in the fibril. All these effects disappear after heat-denaturation of the sample at 120 degrees C. Our main achievement is a five-stage mechanism by which the instability of a single collagen at physiological temperatures is compensated by the interaction between collagen molecules.

High-intensity focused ultrasound ablation of ex vivo bovine achilles tendon

Small tears in tendons are a common occurrence in athletes and others involved in strenuous physical activity. Natural healing in damaged tendons can result in disordered regrowth of the underlying collagen matrix of the tendon. These disordered regions are weaker than surrounding ordered regions of normal tendon and are prone to re-injury. Multiple cycles of injury and repair can lead to chronic tendinosis. Current treatment options either are invasive or are relatively ineffective in tendinosis without calcifications. High-intensity focused ultrasound (HIFU) has the potential to treat tendinosis noninvasively. HIFU ablation of tendons is based on a currently-used surgical analog, viz., needle tenotomy. This study tested the ability of HIFU beams to ablate bovine tendons ex vivo. Two ex vivo animal models were employed: a bare bovine Achilles tendon (deep digital flexor) on an acoustically absorbent rubber pad, and a layered model (chicken breast proximal, bovine Achilles tendon central and a glass plate distal to the transducer). The bare-tendon model enables examination of lesion formation under simple, ideal conditions; the layered model enables detection of possible damage to intervening soft tissue and consideration of the possibly confounding effects of distal bone. In both models, the tissues were degassed in normal phosphate-buffered saline. The bare tendon was brought to 23 degrees C or 37 degrees C before insonification; the layered model was brought to 37 degrees C before insonification. The annular array therapy transducer had an outer diameter of 33 mm, a focal length of 35 mm and a 14-mm diameter central hole to admit a confocal diagnostic transducer. The therapy transducer was excited with a continuous sinusoidal wave at 5.25 MHz to produce nominal in situ intensities from 0.23-2.6 kW/cm(2). Insonification times varied from 2-10 s. The focus was set over the range from the proximal tendon surface to 7 mm deep. The angle of incidence ranged from 0 degrees (normal to the tissue surface) to 15 degrees . After insonification, tendons were dissected and photographed, and the dimensions of the lesions were measured. Transmission electron micrographs were obtained from treated and untreated tissue regions. Insonification produced lesions that mimicked the shape of the focal region. When lesions were produced below the proximal tendon surface, no apparent damage to overlying soft tissue was apparent. The low intensities and short durations required for consistent lesion formation, and the relative insensitivity of ablation to small variations in the angle of incidence, highlight the potential of HIFU as a noninvasive treatment option for chronic tendinosis.

The effect of therapeutic ultrasound intensity on the ultrastructural morphology of tendon repair

This study evaluated the effects of ultrasound intensity on the ultrastructural morphology of Achilles tendon healing. Twenty Sprague-Dawley rats with surgically hemi-transected Achilles tendons were randomly assigned into four groups of 0, 0.5, 1.2 and 2 W/cm(2) for ultrasound treatment, with five rats in each group. The treatments were administered with 1 MHz continuous ultrasound daily starting from day 5 after injury. On day 30, ultrathin slides of the Achilles tendons were prepared and examined with transmission electron microscopy. Results showed that the mean collagen fibril size of all treatment groups was higher than the control (p < 0.05). There was no significant difference in the collagen fibril size among the treatment groups. These findings suggest that therapeutic ultrasound can enhance the maturation of collagen fibrils of repairing tendons, and this was not dependent on the intensity of ultrasound applied.

Quantitative histology and ultrastructure fail to explain weakness of immobilized rabbit Achilles' tendons

OBJECTIVE

To test the hypothesis that mechanical weakness caused by immobilization is the result of characteristic histologic and ultrastructural changes in rabbit Achilles' tendons.

DESIGN

Single-blind, randomized controlled trial.

SETTING

University animal care facility.

ANIMALS

Twenty-three New Zealand rabbits.

INTERVENTION

Twenty weight-matched rabbits underwent unilateral hind leg immobilization. The Achilles' tendons of immobilized and contralateral legs were harvested after 4 or 8 weeks. For ultrastructural outcomes, 6 normal Achilles' tendons of 3 rabbits served as controls.

MAIN OUTCOME MEASURES

Light microscopic assessments were made on the tendons for cross-sectional area of the tendon, number of tenocytes, adipocytes and blood vessels, roundness of nuclei, area of intense metachromasia, and area of spatially aligned collagen fibers. Transmission electron microscopy (TEM) measured mean collagen fibril diameter and density.

RESULTS

Light microscopic assessment failed to reveal a statistical difference in any of the outcome measures between immobilized and contralateral tendons. TEM did not show a statistical difference in mean fibril diameter between the immobilized groups (4 wk, 113.8+/-1.6 nm; 8 wk, 113.5+/-1.4 nm) compared with their respective contralateral tendons (4 wk, 111.4+/-1.4 nm; 8 wk, 116.2+/-1.8 nm) and normal controls (111.8+/-2.0 nm). Eight-week contralateral fibrils were statistically larger than 4-week contralateral fibrils, which was attributed to a training effect of the leg opposite of the casted leg.

CONCLUSIONS

Our results add to the recent literature about the absence of characteristic histologic or collagen fibril size markers that could explain the mechanical weakness of immobilized tendons. Further research using biochemical, gene expression, and functional imaging markers of tendon is needed to pinpoint the alterations responsible for the mechanical weakness. Such markers would be crucial for the rehabilitation and secondary prevention of tendon injuries.

Crimp morphology in relaxed and stretched rat Achilles tendon

Fibrous extracellular matrix of tendon is considered to be an inextensible anatomical structure consisting of type I collagen fibrils arranged in parallel bundles. Under polarized light microscopy the collagen fibre bundles appear crimped with alternating dark and light transverse bands. This study describes the ultrastructure of the collagen fibrils in crimps of both relaxed and in vivo stretched rat Achilles tendon. Under polarized light microscopy crimps of relaxed Achilles tendons appear as isosceles or scalene triangles of different size. Tendon crimps observed via SEM and TEM show the single collagen fibrils that suddenly change their direction containing knots. The fibrils appear partially squeezed in the knots, bent on the same plane like bayonets, or twisted and bent. Moreover some of them lose their D-period, revealing their microfibrillar component. These particular aspects of collagen fibrils inside each tendon crimp have been termed 'fibrillar crimps' and may fulfil the same functional role. When tendon is physiologically stretched in vivo the tendon crimps decrease in number (46.7%) (P<0.01) and appear more flattened with an increase in the crimp top angle (165 degrees in stretched tendons vs. 148 degrees in relaxed tendons, P<0.005). Under SEM and TEM, the 'fibrillar crimps' are still present, never losing their structural identity in straightened collagen fibril bundles of stretched tendons even where tendon crimps are not detectable. These data suggest that the 'fibrillar crimp' may be the true structural component of the tendon crimp acting as a shock absorber during physiological stretching of Achilles tendon.

Tendon crimps and peritendinous tissues responding to tensional forces

Tendons transmit forces generated from muscle to bone making joint movements possible. Tendon collagen has a complex supramolecular structure forming many hierarchical levels of association; its main functional unit is the collagen fibril forming fibers and fascicles. Since tendons are enclosed by loose connective sheaths in continuity with muscle sheaths, it is likely that tendon sheaths could play a role in absorbing/transmitting the forces created by muscle contraction. In this study rat Achilles tendons were passively stretched in vivo to be observed at polarized light microscope (PLM), scanning electron microscope (SEM) and transmission electron microscope (TEM). At PLM tendon collagen fibers in relaxed rat Achilles tendons ran straight and parallel, showing a periodic crimp pattern. Similarly tendon sheaths showed apparent crimps. At higher magnification SEM and TEM revealed that in each tendon crimp large and heterogeneous collagen fibrils running straight and parallel suddenly changed their direction undergoing localized and variable modifications. These fibril modifications were named fibrillar crimps. Tendon sheaths displayed small and uniform fibrils running parallel with a wavy course without any ultrastructural aspects of crimp. Since in passively stretched Achilles tendons fibrillar crimps were still observed, it is likely that during the tendon stretching, and presumably during the tendon elongation in muscle contraction, the fibrillar crimp may be the real structural component of the tendon crimp acting as shock absorber. The peritendinous sheath can be stretched as tendon, but is not actively involved in the mechanism of shock absorber as the fibrillar crimp. The different functional behaviour of tendons and sheaths may be due to the different structural and molecular arrangement of their fibrils.

Ultrastructural immunolocalization of cartilage oligomeric matrix protein, thrombospondin-4, and collagen fibril size in rodent achilles tendon in relation to exercise

Fourteen 3-week-old Sprague-Dawley rats were housed in pairs in standard cages (5 controls) and in individual cages with a running wheel. Four of these rats had run 27-36 km/week (low training - LT) and 5 had run 56-92 km/week (high training - HT). After 4 weeks, the rats were euthanized and Achilles tendons were fixed for electron microscopy. The ultrastructural distribution of cartilage oligomeric matrix protein (COMP) and thrombospondin (TSP)-4 and collagen fibril thickness in two different extracellular compartments were studied. The immunolabeling of COMP decreased with longer running distance and was significantly lower in both the pericellular (p = 0.009) and interterritorial (p = 0.03) compartments of the HT rats compared with the controls. TSP-4 immunolabeling was higher in the pericellular compared with the interterritorial compartments in all rats (p = 0.013) but was not correlated with COMP immunolabeling. No alterations in collagen fibril size were found in relation to running; however, the gold markers representing COMP and TSP-4 were mostly found at the dark bands, representing the gap region of the fibril.

The effect of subcutaneously injected nicotine on achilles tendon healing in rabbits

The objective of this study was to evaluate the effect of subcutaneously injected nicotine on transversely transected and sutured achilles tendon healing in an experimental rabbit model. Adult New Zealand rabbits (n=22) weighting 3,000-3,500 g were used in this experimental study. Rabbits were randomly divided into two groups. Achilles tendon was transversely incised and repaired in all animals. In the experiment group subcutaneous injection of Nicotine tartrate 3 mg/kg/day was done. In the control group Serum physiologic injection was done at the same dosage. The injections were made three times a day in equal dosages. Nicotine and SF injections were made until the end of the 8-week, and then all animals were euthanized. Both light microscopic and electron microscopic evaluations were made on 14 animals. In N group light microscopic evaluation showed a visible gap in repair site. The total tendon score represented in N group was less than in SF group. The statistical analysis of the groups was significantly different for total tendon scores (P=0.002). Beside this electron microscopic examination showed inactive and degenerated fibroblasts and irregular collagen fibrils around them as well as collagen synthesis interruption in N group. Biomechanical evaluation was made on eight animals. The average tensile strength values in Group N (139.47+/-44.55 N) were significantly lower than those in Group SF (265.9+/-39.01 N) (z=2.309, P=0.029). Nicotine is the major chemical component common to all cigarettes and previously has been shown to affect wound and fracture healing adversely. The results of this study show that nicotine impairs achilles tendon healing after a surgical repair.

The COL5A1 gene and Achilles tendon pathology

PURPOSE

There is an increase in the incidence of Achilles tendon injuries as a result of the participation in physical activity. It has been suggested that some individuals have a genetic predisposition to Achilles tendon pathology (ATP). The aim of this study was to determine whether the alpha 1 type V collagen (COL5A1) gene, which encodes for a tendon protein, is associated with the symptoms of ATP.

METHODS

One-hundred and eleven Caucasian subjects diagnosed with ATP and 129 Caucasian control (CON) subjects were genotyped for the BstUI and DpnII restriction fragment length polymorphisms (RFLPs) within the COL5A1 gene.

RESULTS

There was a significant difference in the allele frequencies of the COL5A1 BstUI RFLP between the ATP and CON subjects (P=0.006). The frequency of the A2 allele was significantly higher in the CON group (29.8%) than in the ATP group (18.0%) (odds ratio of 1.9; 95% confidence interval (CI) 1.3-3.0; P=0.004). This allele had a stronger protective role when only the 72 patients diagnosed with chronic Achilles tendinopathy were analyzed (odds ratio of 2.6; 95% CI 1.5-4.5).

CONCLUSIONS

The COL5A1 BstUI RFLP is associated with ATP and more specifically, chronic Achilles tendinopathy. Individuals with an A2 allele of this gene are less likely of developing symptoms of chronic Achilles tendinopathy.

Structure and component alteration of rabbit Achilles tendon in tissue culture

The aim of this study was to investigate alterations of cultured tendon tissues to determine whether tissue culture is a useful method for biological analyses of the tendon. Tendon tissues for tissue culture were isolated from Achilles tendons of rabbits. The tendon segments were placed one segment per well and incubated in growth medium consisting of Dullbecco's modified Eagle's medium supplemented with 5% fetal bovine serum at 37 degrees C in a humidified atmosphere with 5% CO(2) for various periods. The alignment of collagen fibrils was preserved for 48 h, but tendon structure has disintegrated at 96 h. Alcian blue staining and gelatine zymography revealed that proteoglycan markedly diminished and that matrix metalloproteinase (MMPs) activity was upregulated sharply at 72 and 96 h. The ratio of collagen fibrils with large diameter had increased and the mean diameter and mass average diameter value had reached maximum at 48 h. The values then decreased and mean diameters at 72 and 96 h were significantly different from that at 48 h. At 96 h, the ratio of collagen fibrils with small diameters had increased and collagen fibrils with large diameters had disappeared. These findings indicate that structural alteration is possible to be induced by disintegration of collagen fibrils and disappearance of glycosaminoglycans from extracellular matrix (ECM), subsequent of upregulation of MMPs activity. Although the study period is limited, the tissue culture method is available for investigating cell-ECM interaction in tendons.

Ultrastructural changes of the gemifloxacin on Achilles tendon in immature rats: comparison with those of ciproxacin and ofloxacin

Gemifloxacin is a synthetic fluoroquinolone antimicrobial agent that exhibits potent activity against most Gram-negative and Gram-positive organisms, and has a comparatively low chondrotoxic potential in immature animals. This study examined the effects of gemifloxacin on the Achilles tendons in immature Sprague-Dawley rats treated by oral intubation once daily for 5 consecutive days from postnatal week 4 onward at doses of 0 (vehicle), and 600 mg/kg body weight. Ofloxacin or ciprofloxacin were used for comparison. The Achilles tendon specimens were examined by electron microscopy. In comparison with the vehicle-treated controls, there were ultrastructural changes in all samples from the gemifloxacin-, ofloxacin-, and ciprofloxacin-treated rats. Degenerative changes were observed in the tenocytes, and the cells that detached from the extracellular matrix were recognizable. The degree of degenerative changes and the number of degenerated cells in the Achilles tendon were significantly higher in the treated group than in the control group. Moreover, among the quinolone-treated groups, these findings were most significant in the ofloxacin-treated group, and least significant in the gemifloxacin-treated group. It is unclear what these findings mean with respect to the possible risk in juvenile patients treated with gemifloxacin or other quinolones. However, these results show that gemifloxacin causes less changes in the connective tissue structures.

Achilles tendon characterization in GDF-7 deficient mice

Growth/differentiation factors (GDFs) play a significant role in numerous skeletal tissues and processes. Previous work using the brachypod mouse has suggested that GDF-5 affects Achilles tendon composition, ultrastructure, and material behavior, as well as tendon repair. The aim of the present study was to examine the role of a related GDF family member, GDF-7 (BMP-12), in intact tendon by studying the Achilles tendon of genetically engineered knockout mice. Achilles tendons from 16-week-old GDF-7 -/- mice contained 14% less GAG/DNA than did wild type littermates (p = 0.0481), although collagen content was comparable to controls. Quantitative reverse transcriptase-polymerase chain reaction (QRT-PCR) results show that GDF-5 was upregulated two-threefold in response to the absence of GDF-7 protein. GDF-6 was also upregulated in knockouts, but to a lesser extent (twofold, p = 0.0013). On an ultrastructural level, GDF-7 deficient Achilles tendons exhibited a shift towards smaller diameter fibrils which resulted in a small but significant reduction in mean fibril diameter (-8%, p = 0.05). GDF-7 deficiency did not noticeably affect the expression of fibrillar collagens (I, III, V) or tendon proteoglycans (decorin, fibromodulin, lumican, biglycan, versican, aggrecan). Differences in tendon composition and ultrastructure were not biologically significant enough to have a noticeable effect on the structural or material behavior of the tendons. These results demonstrate that GDF-7 deficiency has a subtle effect on the composition and ultrastructure of murine Achilles tendon. The small magnitude of the observed differences may be due to overcompensation by related GDF family members.

The 3D structure of crimps in the rat Achilles tendon

The ultrastructure of crimps of the Achilles tendon of rat, excised and processed in a slack condition, was investigated by atomic force microscopy in air, in fluid and by scanning electron microscopy and stereo reconstruction. The tendon was made of distinct fascicles, each comprising a succession of straight segments connected by sharp angles. The length of the segments and the interposed angles varied widely. In particular, the angles ranged from almost zero to over 135 degrees . We did not observe a unique structure for the hinge regions, but rather a variety of gradations of buckling and/or torsion with no evident correlation with other features of tendon. A constant hallmark was the local loss of regular molecular packing, as revealed by the disappearance of the D-banding. Our results do not support recent reports of a helical structure or smooth sinusoidal waves in tendons. Such structures may nonetheless exist in other non-tensile structures whose collagen fibrils exhibit a helical inner architecture and are able to follow a highly convoluted course without buckling or crimping.

Age-related changes in human tendo calcaneus collagen fibrils

OBJECTIVE

The ruptures of tendo calcaneus often occur between the age of 30-45 years as described by several textbooks. It is also described that some diseases and drugs are said to be responsible in the etiology; however, there are no studies related with the detailed histological structure of collagen fibrils found in the tendon in the age groups of humans. In view thereof, this study was aimed to obtain further information on the etiology and to find an answer regarding the frequency of the ruptures occurring between the age of 30-45 years in humans.

METHODS

In the study, the biopsy specimens taken from 28 patients (ages 1-68 year) who had undergone surgery due to tendo calcaneus ruptures or achilloplasty operation were examined by transmission electron microscope. All the specimens were prepared according to routine electron microscopic tissue preparation technique. The patients were divided into 7 age groups (1-9, 10-19, 20-29, 30-39, 40-49, 50-59, >60 years) and there were 4 patients in each group. The transverse diameters of collagen fibers were measured from the ultra thin sections and statistical analysis of the results were performed. The study was carried out in the electron microscopy laboratory of the Anatomy Department of Hacettepe University, Ankara, Turkey between January 2004 and September 2004.

RESULTS

The diameters of the collagen fibers were higher in the 20-29 year-old group compared to other groups and it showed a statistically significant difference. In patients who were in the 30-39 year-old group or older, the diameters of the collagen fibers were lesser than the 20-29 year-old group. However, an increase was observed in the collagen fibril concentration of these groups. In examination of the specimens of patients who were under 20-year-old, the diameter of the collagen fibers were less than the 20-29 year-old group. The electron microscopic appearance of the tissue sample of a one-year-old patient had a specific organization and in this patient, both the diameters and concentration of collagen fibers were less.

CONCLUSION

We believe that the decrease in the diameters of collagen fibers of 30-45 year-old patients who are in the active period of their life, can play a role in the etiology of the frequency of tendo calcaneus ruptures similar to other etiologic factors.

Dynamic Changes Appearing in Collagen Fibers During Intrinsic Tendon Repair

Intrinsic healing of severed tendons shows a delay in a gain in breaking strength and the tendon becomes translucent. The cause of tendon translucence was investigated in suture-repaired rat Achilles tendon. The repair site with adjacent translucent tendon were evaluated histologically on day 10 by immunofluorescence and transmission electron microscopy. The healing tendon translucent region by hematoxylin-eosin staining had few inflammatory cells, polarized light birefringence showed thinner collagen fibers, immunofluorescence showed few myofibroblasts, and transmission electron microscopy revealed frayed, irregular thin collagen fibers. During embryogenesis, tendon fibers grow by the addition of discreet collagen fibril segment structures. The speculation is that collagen fibril segment structures are released from collagen fibers within the translucent tendon region for reuse during the regeneration of tendon collagen fibers during intrinsic tendon repair. Healing tendon translucence is related to a decrease in the diameter of collagen fibers by the release of collagen fibril segments within tendon bundles/fascicles.

Collagen fibres of the spontaneously ruptured human tendons display decreased thickness and crimp angle

PURPOSE

To study collagen fibre thickness and crimp formation in healthy and ruptured human tendons.

METHODS

The thickness, crimp angle and wavelength of the collagen fibres were analyzed by interference and polarization microscopy and the samples were studied by transmission and scanning electron microscopy in four different healthy human tendons (Achilles, Quadriceps, Biceps brachii and Extensor pollicis longus) and in 66 spontaneously ruptured tendons.

RESULTS

In the normal (healthy) tendons, the diameter and crimp angle of the collagen fibres varied greatly between the four different tendons, the thickest fibres with the largest crimp angle being in the Achilles and Quadriceps tendons, whereas the Biceps brachii and Extensor pollicis longus, tendons that bear lighter strains but carry functions of high specificity, were found to have substantially smaller collagen fibres with lower crimp angle. Ruptured tendons had significantly smaller collagen fibre diameter than the normal tendons, the fibre diameter being -36% in comparison to their healthy counterparts in the Achilles tendons (P < 0.0001), -24% in the Quadriceps tendons (P < 0.0001), -37% in the Biceps brachii (P < 0.0001) and -14% in the Extensor pollicis longus (P = 0.10), respectively. Similarly, the crimp angle of the collagen fibres was also found to be lower in the ruptured tendons than in healthy, normal tendons. Further, the collagen fibres in the ruptured human tendons showed great variation in the crimp angle between the adjacent fibres and in the successive crimps of the same fibre.

CONCLUSION

Our results show that spontaneously ruptured tendons display focal regions with decreased collagen fibre thickness, decreased crimp angle and disrupted crimp continuity, microscopic alterations that possibly result in reduced strength of the tendons being less resistant to tensile forces, and thus, place them at increased risk of ruptures.

Histologic findings of anterior cruciate ligament reconstruction with Achilles allograft

The purpose of the current study was to evaluate the remodeling process of Achilles allograft for anterior cruciate ligament reconstruction under light microscopic and electron microscopic evaluations. In 12 patients, histologic examinations were done preoperatively and during arthroscopy at 6, 12, and 24 months. Gross observations were made with respect to width, vascularity, elasticity, and stability of the Achilles allograft. Biopsy specimens were obtained at the followup arthroscopic study. Light microscopic examinations done at 6 months showed many fibroblasts with spindle-shaped nuclei and hypercellularity. At 12 months, the small folds pattern of collagen bundles and decreased cellularity were observed. At 24 months, gross and findings of the light microscopic evaluations of the allograft tendons were similar to those of the normal anterior cruciate ligaments. On electron microscopic examinations done at 24 months, the allograft had fibroblasts with much cytoplasm and densely packed parallel-laid collagen fibrils, which showed the characteristic cross striations, but the Achilles allograft ligaments did not show similar findings compared with biopsy samples from normal anterior cruciate ligaments.

Eccentric training in patients with chronic Achilles tendinosis: normalised tendon structure and decreased thickness at follow up

OBJECTIVE

To prospectively investigate tendon thickness and tendon structure by ultrasonography in patients treated with eccentric calf muscle training for painful chronic Achilles tendinosis located at the 2-6 cm level in the tendon.

METHODS

The patients were examined with grey scale ultrasonography before and 3.8 years (mean) after the 12 week eccentric training regimen. At follow up, a questionnaire assessed present activity level and satisfaction with treatment.

RESULTS

Twenty six tendons in twenty five patients (19 men and six women) with a mean age of 50 years were followed for a mean of 3.8 years (range 1.6-7.75). All patients had a long duration of painful symptoms (mean 17.1 months) from chronic Achilles tendinosis before treatment. At follow up, 22 of 25 patients were satisfied with treatment and active in Achilles tendon loading activities at the desired level. Ultrasonography showed that tendon thickness (at the widest part) had decreased significantly (p<0.005) after treatment (7.6 (2.3) v 8.8 (3) mm; mean (SD)). In untreated normal tendons, there was no significant difference in thickness after treatment (5.3 (1.3) mm before and 5.9 (0.8) mm after). All tendons with tendinosis had structural abnormalities (hypoechoic areas and irregular structure) before the start of treatment. After treatment, the structure was normal in 19 of the 26 tendons. Six of the seven patients with remaining structural abnormalities experienced pain in the tendon during loading.

CONCLUSIONS

Ultrasonographic follow up of patients with mid-portion painful chronic Achilles tendinosis treated with eccentric calf muscle training showed a localised decrease in tendon thickness and a normalised tendon structure in most patients. Remaining structural tendon abnormalities seemed to be associated with residual pain in the tendon.

[Experimental study on basic fibroblast growth factor combined slow-releasing degradable membrane to prevent tendon adhesion]

OBJECTIVE

To study the adhesion-preventing effect of basic fibroblast growth factor (bFGF) combined slow-releasing degradable membrane.

METHODS

The bFGF combined slow-releasing degradable membrane was made from bFGF and the reagent which could promote fibrinogen synthesize. Sixty-six SD rats were divided into groups A, B, C randomly (22 rats each group). In group A, sutured achilles tendon were encapsulated with bFGF combined slow-releasing degradable membrane; in group B, sutured achilles tendon were encapsulated with degradable membrane without any drug; in group C, achilles tendon were only sutured. Ninety days later, light-microscope, electron-microscopoe, figure-analysing, hydroxyproline content, extent of peritendon adhesion and biomechanic test were evaluated.

RESULTS

1. The amount of fibroblast and fibrinogen inside the sutured tendon in group A was larger than that in its peripheral connective tissue and in groups B and C (P < 0.05). The content of hydroxyproline and the ultimate tensile strength in group A was higher than those in groups B and C (P < 0.01). 2. The peripheral tissue in group A almost remains the formal loose connective tissue, but it became dense connective tissue in groups B and C and grew into the tendon. Moreover, the extent of adhesion in group A was lesser than that in groups B, C according to the mensuration of peritendon adhesion.

CONCLUSION

The bFGF combined slow-releasing degradable membrane can make the intrinsic healing of tendon faster than peripheral connective tissue proliferation, so it can prevent the formation of adhesion.

Order parameters of the orientation distribution of collagen fibers in Achilles tendon by 1H NMR of multipolar spin states

The angular distribution function of collagen fibrils in a sheep Achilles tendon was investigated by (1)H NMR of multipolar spin states represented by dipolar-encoded longitudinal magnetization and double-quantum filtered signals. For the first time the angular distribution function based on the Legendre moment expansion is used. Order parameters were obtained from the anisotropy of (1)H residual dipolar couplings of bond water, which were determined model-free from the excitation efficiency of the multipolar spin states and from double-quantum filtered line splitting. The orientation distribution function of collagen fibrils in Achilles tendon measured from the anisotropy of the residual dipolar couplings is characterized by the average values of beta0 = 1.8+/-0.2 degrees and order parameters [P2] = 0.93+/-0.04, [P4] = 0.78+/-0.04 and [P6] = 0.58+/-0.04. The order of many biological tissues in the presence of ageing, injuries or regeneration can be quantified by the order parameters of the angular distribution function.

GDF-5 deficiency in mice delays Achilles tendon healing

The aim of this study was to examine the role of one of the growth/differentiation factors, GDF-5, in the process of tendon healing. Specifically, we tested the hypothesis that GDF-5 deficiency in mice would result in delayed Achilles tendon repair. Using histologic, biochemical, and ultrastructural analyses, we demonstrate that Achilles tendons from 8-week-old male GDF-5 -/- mice exhibit a short-term delay of 1-2 weeks in the healing process compared to phenotypically normal control littermates. Mutant animals took longer to achieve peak cell density, glycosaminoglycan content, and collagen content in the repair tissue, and the time course of changes in collagen fibril size was also delayed. Revascularization was delayed in the mutant mice by 1 week. GDF-5 deficient Achilles tendons also contained significantly more fat within the repair tissue at all time points examined, and was significantly weaker than control tissue at 5 weeks after surgery, but strength differences were no longer detectable by 12-weeks. Together, these data support the hypothesis that GDF-5 may play an important role in modulating tendon repair, and are consistent with previously posited roles for GDF-5 in cell recruitment, migration/adhesion, differentiation, proliferation, and angiogenesis.

Ultrastructural changes induced by the des-F(6)-quinolone garenoxacin (BMS-284756) and two fluoroquinolones in Achilles tendon from immature rats

Garenoxacin is a des-(6)-fluoroquinolone exhibiting a comparatively low chondrotoxic potential in juvenile animals. We studied the effects of the drug on Achilles tendons in immature Wistar rats treated by oral intubation once daily (1) for 5 consecutive days from postnatal week 4 onward at doses of 0 (vehicle), 200 and 600 mg/kg body weight (b wt), and (2) for 21 consecutive days from postnatal day 4 onward at doses of 0 (vehicle), 80, 240 or 300 mg/kg b wt; ofloxacin or ciprofloxacin were used as comparators. Achilles tendon specimens were studied by electron microscopy. In comparison with vehicle-treated controls, ultrastructural changes were detectable in all samples from the garenoxacin-, ofloxacin-, or ciprofloxacin-treated rats (one animal per group). We found degenerative changes such as multiple vacuoles and large vesicles in the cytoplasm of tenocytes that resulted from swelling and dilatation of cell organelles (mitochondria, endoplasmic reticulum), densified nuclei and clumped chromatin; furthermore, cells that detached from the extracellular matrix, a general decrease of the fibril diameter and an increase in the distance between the collagenous fibrils were recognizable. The degree of changes increased with increasing doses. It remains unclear what these findings mean with respect to a possible risk in juvenile patients treated with garenoxacin or the other quinolones, but our results underline the fact that, in principle, this des-(6)-fluoroquinolone also has the potential to cause changes in connective tissue structures.

Systemic vanadate ingestion modulates rat tendon repair

The chronic ingestion of vanadate prevents the appearance of myofibroblasts within granulation tissue of full excision wounds in rats, yet these wounds close at an optimal rate. Myofibroblasts are reported in the repair of transected tendons. Here we investigate tendon repair in the absence of myofibroblasts. Vanadate in saline drinking water was given to rats in the experimental group, while rats in the control group received saline alone. The Achilles tendon of the left leg of each rat was transected and suture repaired. On day 10, both repaired tendons and uninjured tendons from the right leg were harvested and processed for histology. By immunohistology the repaired tendons of control rats had myofibroblasts (fibroblasts with alpha smooth muscle actin positive stress fibers), while myofibroblasts were absent in healing tendons from vanadate-treated rats. By transmission electron microscopy and polarized light optics, repaired tendons of control rats demonstrated thin, loosely packed, immature collagen fiber bundles. Collagen fiber bundles from healing tendons of the vanadate-treated group were thicker, uniformly packed, and more mature. The chronic ingestion of vanadate promotes the more rapid organization of collagen fiber bundles of healing transected tendons in the absence of myofibroblasts.

Anisotropy of collagen fiber orientation in sheep tendon by 1H double-quantum-filtered NMR signals

The anisotropy of the angular distribution of collagen fibrils in a sheep tendon was investigated by 1H double-quantum (DQ) filtered NMR signals. Double-quantum build-up curves generated by the five-pulse sequence were measured for different angles between the direction of the static magnetic field and the axis of the tendon plug. Proton residual dipolar couplings determined from the DQ build-up curves in the initial excitation/reconversion time regime which mainly represent the bound water are interpreted in terms of a model of spin-1/2 pairs with their internuclear axes oriented on average along the fibril direction in the presence of proton exchange. The angular distribution of collagen fibrils around the symmetry axis of the tendon measured by the anisotropy of the residual dipolar couplings was described by a Gaussian function with a standard deviation of 12 degrees +/-1 degrees and with the center of the distribution at 4 degrees +/-1 degrees. The existence of this distribution is directly reflected in the finite value of the residual dipolar couplings at the magic angle, the value of the angular contrast, and the oscillatory behavior of the DQ build-up curves. The 1H residual dipolar couplings were also measured from the doublets recorded by the DQ-filtered signals. From the angular dependence of the normalized splitting the angular distribution of the collagen fibrils was evaluated using a Gaussian function with a standard deviation of 19 degrees +/-1 degrees and with the center of distribution at 2 degrees +/-1 degrees. The advantages and disadvantages of these approaches are discussed.

Quantitative determination of the mineral distribution in different collagen zones of calcifying tendon using high voltage electron microscopic tomography

High voltage electron microscopic tomography was used to make the first quantitative determination of the distribution of mineral between different regions of collagen fibrils undergoing early calcification in normal leg tendons of the domestic turkey, Meleagris gallopavo. The tomographic 3-D reconstruction was computed from a tilt series of 61 different views spanning an angular range of +/- 60 degrees in 2 degrees intervals. Successive applications of an interactive computer operation were used to mask the collagen banding pattern of either hole or overlap zones into separate versions of the reconstruction. In such 3-D volumes, regions specified by the mask retained their original image density while the remaining volume was set to background levels. This approach was also applied to the mineral crystals present in the same volumes to yield versions of the 3-D reconstructions that were masked for both the crystal mass and the respective collagen zones. Density profiles from these volumes contained a distinct peak corresponding only to the crystal mass. A comparison of the integrated density of this peak from each profile established that 64% of the crystals observed were located in the collagen hole zones and 36% were found in the overlap zones. If no changes in crystal stability occur once crystals are formed, this result suggests the possibilities that nucleation of mineral is preferentially and initially associated with the hole zones, nucleation occurs more frequently in the hole zones, the rate of crystal growth is more rapid in the hole zones, or a combination of these alternatives. All lead to the conclusion that the overall accumulation of mineral mass is predominant in the collagen hole zones compared to overlap zones during early collagen fibril calcification.

pN collagen type III within tendon grafts used for anterior cruciate ligament reconstruction

This study measured the amount of immature collagen type III present in tendon rafts obtained from anterior cruciate ligament (ACL) reconstructions. These values were compared with those obtained from control grafts typically used for reconstruction--Achilles, patellar, and fascia lata--and also to the normal ACL. Analyses were performed using a commercially available radioimmunoassay (RIA). The RIA made use of a rabbit polyclonal antibody specific to the amino terminus of procollagen type III. The specificity of the Ab was confirmed by a western blot. Fibril diameter of each of the above samples was measured by transmission electron microscopy (TEM). We thus were able to determine if there was a relationship between pN collagen III content and fibril diameter. The mean amount of pN collagen type III in the normal tendon control group was 0.8 +/- 0.3 ng/microg total protein (range 0.0-2.5 ng/microg). There was significantly greater pN collagen III (16 +/- 3.7 ng/microg total protein) in the grafts containing an average fibril diameter <55 nm than in the normal tendons or ACL (P < 0.05). Grafts with an average fibril diameter >55 nm had similar levels of pN collagen III (1.0 +/- 0.79 ng/microg) as the controls. There was also significantly less pN-collagen III within the functional grafts (5.3 +/- 1.9 ng/microg) as compared to failed grafts, (21.6 +/- 5.1 ng/microg, P < 0.05). These results indicate that incomplete processing of procollagen III may be responsible for some of the ultrastructural alterations seen in tendon grafts. Since ultrastructural organization is believed to influence mechanical properties of these tissues. pN collagen III levels may be a possible indicator of ligament or tendon weakness.

Biochemical changes in Achilles tendon from juvenile dogs after treatment with ciprofloxacin or feeding a magnesium-deficient diet

Quinolones are antibacterial agents that have the potential to induce Achilles tendon disorders - such as tendinitis or even ruptures - in patients treated with these drugs. We studied the effects of ciprofloxacin on several proteins of Achilles tendons from immature dogs, 10- to 11-weeks-old. The dogs were treated orally for 5 days with 30 or 200 mg ciprofloxacin/kg body weight or with the vehicle alone. Since quinolone-like alterations in joint cartilage were observed in magnesium-deficient animals, another group was fed a magnesium-deficient diet for 6 weeks. At necropsy, tendons (n=3 from each group) were frozen and stored until analysis when they were homogenized in a lysis buffer to release a soluble fraction of the tendon proteins. Densitometric analysis of the immunoblots with anticollagen type I, anti-elastin, anti-fibronectin, and antiintegrin antibodies showed a significant reduction of all proteins. For example, collagen type I concentrations (mean +/-SD, arbitrary densitometric units) were 3190+/-217 (controls), 1890+/-468 (30mg/kg), 1695+/-135 (200mg/kg) and 2053+/-491 in the magnesium-deficient dogs. The differences between concentrations in controls and all treated groups were statistically significant (P<0.01, t-test). Similarly, compared with control samples, relative concentrations of other proteins in tendons from ciprofloxacin-treated dogs (30 mg/kg) decreased by 73% (elastin), 88% (fibronectin), and 96% (beta1 integrin) (data from low-dose group only). A very similar pattern of protein alterations was detected in samples from magnesium-deficient dogs. In conclusion, rather low doses of a fluoroquinolone or a diet-induced magnesium deficiency caused similar biochemical alterations in the soluble fraction of proteins from canine tendons. These findings support our hypothesis that quinolone-induced toxic effects on connective tissue structures are due to the magnesium-antagonistic effects of these antibacterial agents. They also indicate that patients with a latent magnesium deficiency could be at an increased risk of quinolone-induced tendon disorders.

GDF-5 deficiency in mice alters the ultrastructure, mechanical properties and composition of the Achilles tendon

Acromesomelic dysplasia of the Hunter-Thompson and Grebe types are rare human disorders based on growth/differentiation factor (GDF)-5/CDMP-1 genetic mutations. Numerous skeletal abnormalities are present in these individuals, including shortened limb bones and severe dislocations of the knee. In the GDF-5 deficient brachypodism mouse, similar, although less severe, phenotypes are observed. It is unknown whether the joint dislocations observed in these disorders are due to a defect in the original formation of joints such as the knee, or to abnormalities in the tendons and ligaments themselves. We hypothesized that tendons from GDF-5 deficient mice would exhibit altered composition, mechanical properties, and ultrastructure when compared with heterozygous control littermates. GDF-5 deficient Achilles tendons were structurally weaker than controls, and structural strength differences appeared to be caused by compromised material properties: after normalizing by collagen per unit length, mutant tendons were still 50% weaker (P < 0.0001) and 50% more compliant (P < 0.001) than controls. Despite comparable levels of skeletal maturity in the two cohorts, the majority of mutant tendon failures occurred in the mid-substance of the tendon (64% of all failures), whereas the majority of control failures occurred via avulsion (92% of all failures). Mutant Achilles tendons contained 40% less collagen per microgram of DNA when compared to controls (P = 0.004). No significant difference in glycosaminoglycan (GAG)/DNA was detected. Ultrastructural analyses indicated a slight trend toward increased frequency of small diameter (30-100 nm) collagen fibrils in the mutant Achilles. Our findings suggest that increased tendon and ligament laxity may be the cause of the joint dislocations seen in patients with Hunter-Thompson and Grebe type dysplasia, rather than developmental abnormalities in the joints themselves.

Ultrastructure of Achilles tendon from rats after treatment with fleroxacin

Quinolone therapy can be associated with tendon disorders (tendinitis, ruptures), but little is known about possible ultrastructural changes in tendons after exposure to these antimicrobials. We studied the Achilles tendons from fleroxacin-treated adult rats by electron microscopy. Wistar rats were treated orally with single oral doses of 0, 30, 100, 300 or 600 mg fleroxacin/kg body weight (n = 6 per group). The animals were killed 4 weeks after treatment. Achilles tendon samples were collected and tangential sections were made from the distal part of the tendon. Subsequently, tendons were cut crosswise for preparation of ultrathin sections. Samples were fixed by using glutaraldehyde, osmium tetroxide, tannic acid and finally contrasted with uranyl acetate/lead citrate before they were examined by transmission electron microscopy. The rats did not show any general effects such as behavioural changes or body weight changes which could be attributed to the treatment. However, we were able to detect pathological changes even at the lowest dose level (30 mg/kg), which increased in incidence and severity with increasing doses. Tenocytes exhibited degenerative changes such as multiple vacuoles and large vesicles in the cytoplasm that resulted from swelling and dilatation of cell organelles (mitochondria, endoplasmic reticulum). The nucleus became dense and the chromatin had clumped to form rough plaques. The cells detached from the extracellular matrix. Other important findings were a general decrease of the fibril diameter and an increase in the distance between the collagenous fibrils. The finding that these rather low single dose of a fluoroquinolone induce ultrastructural changes in Achilles tendons from rats, which were not associated with clinical symptoms and which were still present 4 weeks after treatment, is of concern. Further toxicological as well as clinical studies are needed to characterize the conditions under which quinolone-induced tendon lesions develop.

Changes in ADC caused by tensile loading of rabbit achilles tendon: evidence for water transport

Water diffusion measurements were performed on rabbit Achilles tendons during static tensile loading and tendons in an unloaded state. The apparent diffusion coefficient (ADC) was measured along two directions: parallel and perpendicular to the long axis of the tendon. Tendons were studied after being prepared in two ways: (a) after being stored frozen in phosphate-buffered saline (PBS) and (b) freshly isolated. Statistically significant directional anisotropy was observed in the ADC in all tendons. The ADC was significantly greater in the direction parallel to the long axis of the tendon than in the perpendicular direction. The anisotropy is attributed to the greater restrictions seen by the water molecules in the perpendicular direction and is consistent with the known geometry of the tendon. Storage in PBS caused tendons to swell. This increased the ADC measured along both directions and reduced the anisotropy. The existence of anisotropy in the ADC was not related to the orientation of the specimen in the magnet. The ADC increased along both directions following the application of a 5-N tensile load; the increase was greatest along the perpendicular axis of the tendon. In order to determine whether load-related changes in the ADC reflected changes in interfibrilar spacing, we used electron microscopy to measure load-related changes in fibril spacing. Load-related changes in fiber spacing could not account for the observed changes in the ADC. The increase in ADC caused by loading was attributed to the extrusion of tendon water into a bulk phase along the outside surface of the tendon. In PBS-stored samples, enough fluid was extruded that it could be visualized. The transient response of the ADC to a 5-N tensile load was also studied. The absolute ADC in both directions increased with loading and recovered to baseline upon unloading. The transient changes in ADC, for both loading and unloading, had a mean time constant of approximately 15 min. The magnitude of the load-induced transient ADC changes was comparable to that seen in the static-loading experiments.

Ultrastructure of Achilles tendons of rats treated with ofloxacin and fed a normal or magnesium-deficient diet

Fluoroquinolones can cause tendinitis and tendon rupture. However, toxicological as well as clinical information on quinolone-induced tendopathy is scarce. We performed extensive electron microscopic studies with Achilles tendon specimens from ofloxacin-treated rats. The drug was given at a dose of 1,200 mg/kg (body weight) orally. Juvenile Wistar rats received one or three oral doses each of 1,200 mg of ofloxacin/kg (body weight)/day. Three days after treatment, the tenocytes of their Achilles tendons showed degenerative alterations, such as multiple vacuoles and vesicles in the cytoplasm that had developed due to swellings and dilatations of cell organelles. Other indications of cell degradation were the occurrence of cell debris and cell detachment from the extracellular matrix accompanied by a loss of cell-matrix interaction. The tenocytes of juvenile Wistar rats that had been treated at day 36 with a single oral dose of 1,200 mg of ofloxacin/kg (body weight) and sacrificed either 3 or 6 months later exhibited similar degenerative alterations. The number of degenerative alterations of tenocytes after ofloxacin treatment was considerably higher in rats that had received a magnesium-deficient diet than in rats with normal magnesium status. Of the adult rats that had been treated once, 5 times, and 10 times with ofloxacin and killed 1 day later, only those with the 10-times treatment showed a significantly increased number of degeneratively altered tenocytes. In summary, effects observed in tendons show similar pathological features as described earlier in cartilage, indicating that quinolone-induced arthropathy and quinolone-induced tendopathy probably are different clinical manifestations of the same toxic effect on cellular components of connective tissue structures.

Matrix remodeling in healing rabbit Achilles tendon

Biochemical, biomechanical and ultrastructural properties of the connective tissue matrix were investigated during the early remodeling phase of tissue repair in experimentally tenotomized and repaired rabbit Achilles tendons. Sterile surgical tenotomy was performed on the right Achilles tendons of 14 rabbits and allowed to heal for 15 days. The animals were euthanized and the Achilles tendons excised from both limbs. The left contralateral Achilles tendon of each rabbit was used as a control in the experiments. Prior to biochemical analysis, both intact and healing tendons were tested for their biomechanical integrity. The results revealed that the healing tendons had regained some of their physicochemical characteristics, but differed significantly from the intact left tendons. The healing tendons regained 48% tensile strength, 30% energy absorption, 20% tensile stress, and 14% Young's modulus of elasticity of intact tendons. In contrast, biochemical analysis showed that the healing tendons had 80% of the collagen and 60% of the collagen crosslinks (hydroxypyridinium) of normal tendons. Sequential extraction of collagen from the tissues yielded more soluble collagen in the healing tendons than intact tendons, suggesting either an increase in collagen synthesis and/or enhanced resorption of mature collagen in healing tendons compared to intact tendons. Electron microscopic studies revealed remarkable differences in the ultrastructure between intact and healing tendons. These observations could explain, in part, the connective tissue response to healing during the early phases of tissue remodeling.

A study of dipolar interactions and dynamic processes of water molecules in tendon by 1H and 2H homonuclear and heteronuclear multiple-quantum-filtered NMR spectroscopy

The effect of proton exchange on the measurement of 1H-1H, 1H-2H, and 2H-2H residual dipolar interactions in water molecules in bovine Achilles tendons was investigated using double-quantum-filtered (DQF) NMR and new pulse sequences based on heteronuclear and homonuclear multiple-quantum filtering (MQF). Derivation of theoretical expressions for these techniques allowed evaluation of the 1H-1H and 1H-2H residual dipolar interactions and the proton exchange rate at a temperature of 24 degrees C and above, where no dipolar splitting is evident. The values obtained for these parameters at 24 degrees C were 300 and 50 Hz and 3000 s-1, respectively. The results for the residual dipolar interactions were verified by repeating the above measurements at a temperature of 1.5 degrees C, where the spectra of the H2O molecules were well resolved, so that the 1H-1H dipolar interaction could be determined directly from the observed splitting. Analysis of the MQF experiments at 1.5 degrees C, where the proton exchange was in the intermediate regime for the 1H-2H dipolar interaction, confirmed the result obtained at 24 degrees C for this interaction. A strong dependence of the intensities of the MQF signals on the proton exchange rate, in the intermediate and the fast exchange regimes, was observed and theoretically interpreted. This leads to the conclusion that the MQF techniques are mostly useful for tissues where the residual dipolar interaction is not significantly smaller than the proton exchange rate. Dependence of the relaxation times and signal intensities of the MQF experiments on the orientation of the tendon with respect to the magnetic field was observed and analyzed. One of the results of the theoretical analysis is that, in the fast exchange regime, the signal decay rates in the MQF experiments as well as in the spin echo or CPMG pulse sequences (T2) depend on the orientation as the square of the second-rank Legendre polynomial.