Aerobic physical training restores biomechanical properties of Achilles tendon in rats chemically induced to diabetes mellitus

Patellar tendon biomechanical and morphologic properties and their relationship to serum clinical variables in persons with prediabetes and type 2 diabetes

Tendon biomechanical properties and fibril organization are altered in patients with diabetes compared to healthy individuals, yet few biomarkers have been associated with in vivo tendon properties. We investigated the relationships between in vivo imaging-based tendon properties, serum variables, and patient characteristics across healthy controls (n = 14, age: 45 ± 5 years, body mass index [BMI]: 24 ± 1, hemoglobin A1c [HbA1c]: 5.3 ± 0.1%), prediabetes (n = 14, age: 54 ± 5 years, BMI: 29 ± 2; HbA1c: 5.7 ± 0.1), and type 2 diabetes (n = 13, age: 55 ± 3 years, BMI: 33 ± 2, HbA1c: 6.7 ± 0.3). We used ultrasound speckle-tracking and measurements from magnetic resonance imaging (MRI) to estimate the patellar tendon in vivo tangent modulus. Analysis of plasma c-peptide, interleukin-1β (IL-1β), IL-6, IL-8, tumor necrosis factor-α (TNF-α), adiponectin, leptin, insulin-like growth factor 1 (IGF-1), and C-reactive protein (CRP) was completed. We built regression models incorporating statistically significant covariates and indicators for the clinically defined groups. We found that tendon cross-sectional area normalized to body weight (BWN CSA) and modulus were lower in patients with type 2 diabetes than in healthy controls (p < 0.05). Our regression analysis revealed that a model that included BMI, leptin, high-density lipoprotein (HDL), low-density lipoprotein (LDL), age, and group explained ~70% of the variability in BWN CSA (R2 = 0.70, p < 0.001). For modulus, including the main effects LDL, groups, HbA1c, age, BMI, cholesterol, IGF-1, c-peptide, leptin, and IL-6, accounted for ~54% of the variability in modulus (R2 = 0.54, p < 0.05). While BWN CSA and modulus were lower in those with diabetes, group was a poor predicter of tendon properties when considering the selected covariates. These data highlight the multifactorial nature of tendon changes with diabetes and suggest that blood variables could be reliable predictors of tendon properties.

Human Achilles tendon mechanical behavior is more strongly related to collagen disorganization than advanced glycation end-products content

Diabetes is associated with impaired tendon homeostasis and subsequent tendon dysfunction, but the mechanisms underlying these associations is unclear. Advanced glycation end-products (AGEs) accumulate with diabetes and have been suggested to alter tendon function. In vivo imaging in humans has suggested collagen disorganization is more frequent in individuals with diabetes, which could also impair tendon mechanical function. The purpose of this study was to examine relationships between tendon tensile mechanics in human Achilles tendon with accumulation of advanced glycation end-products and collagen disorganization. Achilles tendon specimens (n = 16) were collected from individuals undergoing lower extremity amputation or from autopsy. Tendons were tensile tested with simultaneous quantitative polarized light imaging to assess collagen organization, after which AGEs content was assessed using a fluorescence assay. Moderate to strong relationships were observed between measures of collagen organization and tendon tensile mechanics (range of correlation coefficients: 0.570-0.727), whereas no statistically significant relationships were observed between AGEs content and mechanical parameters (range of correlation coefficients: 0.020-0.210). Results suggest that the relationship between AGEs content and tendon tensile mechanics may be masked by multifactorial collagen disorganization at larger length scales (i.e., the fascicle level).

Irregularity in Plantar Fascia, Muscle Edema and Tendon Thickness in Patients with High-Risk for Diabetic Foot

AIM

To investigate the alterations in the plantar fascia (PF), intrinsic muscles, and tendons in the feet of patients at high risk for developing diabetic foot.

METHODS

The healthy feet of 22 patients with type 2 diabetes, who had developed diabetic foot ulcers on a single foot without any pathology on the contralateral extremity, and those of 22 healthy volunteers were evaluated by magnetic resonance imaging. The volume of the Achilles tendon (AT), the surface area of the PF, the thickness of AT, flexor hallucis longus, flexor digitorum longus, tibialis posterior, and peroneus longus tendons, irregularity in the PF, and edema of intrinsic foot muscles were examined.

RESULTS

Nineteen patients (86%) had irregularity in the PF, whereas none of the healthy controls had any (p<0.001). Intrinsic muscle edema was more common in the group with diabetes (p=0.006). The volume of AT and the surface area of PF were decreased in patients with peripheral arterial disease (PAD) (p<0.05). Patients with diabetes mellitus but without PAD had a larger surface area of PF than that of controls (p<0.05). There were no differences in the volume of AT, the surface area of the PF, and other tendon thickness between the groups.

CONCLUSION

Irregularity in the PF and muscle edema may indicate a high risk for the diabetic foot. The presence of PAD may lead to regression in the structure of AT and PF.

Comparison of the Effects of Pulsed Electromagnetic Field and Extracorporeal Shockwave Therapy in a Rabbit Model of Experimentally Induced Achilles Tendon Injury

Achilles tendon injuries are a common cause of complications including adhesions and tendon degeneration. As a result of these complications, the biomechanical properties are lost. Extracorporeal shockwave therapy (ESWT) and pulsed electromagnetic field (PEMF) recover the injured tendon structure; however, detailed studies of changes in tendon biomechanical properties are limited. We hypothesized that PEMF application would improve Achilles tendon biomechanical properties similar to ESWT. The curative effects of a PEMF 4-week application (15 Hz, 1 mT, 260 µs, 1 h/day) and ESWT (3 doses/28 days, 1st dose: 0.12 mJ/mm2 , 15 Hz, 300 impulses; 2nd dose: 0.14 mJ/mm2 , 15 Hz, 500 impulses; 3rd dose: 0.14 mJ/mm2 , 15 Hz, 500 impulses) on rabbits with Achilles tendon injury were investigated in terms of histopathological and biomechanical properties. The clinical feasibility of PEMF application was evaluated by comparing the results of both methods. Fifty New Zealand female rabbits were divided into two groups to be used in either biomechanical or immunohistochemical studies. Each of the two groups was further divided into five groups: C (Control), SH (Sham), TI (tendon injury), TI + ESWT, and TI + PEMF. Biomechanical evaluations revealed that maximum load, toughness, and maximum stress averages of the TI + PEMF group significantly increased (P < 0.05). When immunohistochemical images of the TI + PEMF group were compared with those of the TI group, the amount of fibrous tissue was less, the homogeneity of collagen fibers recovered, and collagen organization was more uniform. We conclude that both ESWT and PEMF are equally efficient for Achilles tendon recovery. PEMF application is effective and can be used in the clinic as a painless alternative treatment method. © 2020 Bioelectromagnetics Society.

The Structural Effects of Diabetes on Soft Tissues: A Systematic Review

Hyperglycemia, which is associated with diabetes, increases the production of advanced glycation end products. Advanced glycation end products lead to the structural degradation of soft tissues. The structural degradation of diabetic soft tissues has been investigated in humans, rodents, and canines. Therefore, the objective of this review is to unify the various contributions to diabetes research through the mechanical properties and geometric characteristics of soft tissues. A systematic review was performed and identified the effects of diabetes on mechanical and geometric properties of soft tissues via experimental testing or in vivo - driven finite element analysis. The literature concludes that diabetes contributes to major structural changes in soft tissues but does not cause the same structural changes in all soft tissues (e.g., diabetic tendons are weaker and diabetic plantar tissues are tougher). Diabetes stiffens and toughens soft tissues, thus altering viscoelastic behavior (e.g., poor strain and stress response). However, diabetes management routines can prevent or minimize the effects of diabetes on the mechanical and geometric properties of soft tissues. Unification of the structural effects of diabetes on soft tissues will contribute to the pathophysiology of diabetes.

Understanding cellular and molecular mechanisms of pathogenesis of diabetic tendinopathy

There is accumulating evidence of an increased incidence of tendon disorders in people with diabetes mellitus. Diabetic tendinopathy is an important cause of chronic pain, restricted activity, and even tendon rupture in individuals. Tenocytes and tendon stem/progenitor cells (TSPCs) are the dominant cellular components associated with tendon homeostasis, maintenance, remodeling, and repair. Some previous studies have shown alterations in tenocytes and TSPCs in high glucose or diabetic conditions that might cause structural and functional variations in diabetic tendons and even accelerate the development and progression of diabetic tendinopathy. In this review, the biomechanical properties and histopathological changes in diabetic tendons are described. Then, the cellular and molecular alterations in both tenocytes and TSPCs are summarized, and the underlying mechanisms involved are also analyzed. A better understanding of the underlying cellular and molecular pathogenesis of diabetic tendinopathy would provide new insight for the exploration and development of effective therapeutics.

Effect of photobiomodulation and exercise on early remodeling of the Achilles tendon in streptozotocin-induced diabetic rats

The aim of this study was to compare the treatment effects of laser photobiomodulation (LPBM) therapy and aerobic exercise on the biomechanical properties, tissue morphology and the expression of tendon matrix molecules during early remodeling of Achilles tendon (AT) injury in diabetic rats. Animals were randomly assigned to five groups: injured non diabetic (I, n = 15), injured diabetic (ID, n = 15), injured diabetic plus LPBM (IDL, n = 16), injured diabetic plus aerobic exercise (IDE, n = 16) and injured diabetic plus aerobic exercise and LPBM (IDEAL, n = 17). Type 1 diabetes was induced via a single intravenous injection of Streptozotocin at a dose of 40 mg/kg. A partial tenotomy was performed in the right AT. LPBM was performed with an indium-gallium-aluminum-phosphide 660 nm 10 mW laser device (spot size 0.04 cm2, power density 250 mW/cm2, irradiation duration 16 s, energy 0.16 J, energy density 4 J/cm2) on alternate days for a total of 9 sessions over 3 weeks (total energy 1.44 J), using a stationary contact technique to a single point over the dorsal aspect of the AT. Moderate aerobic exercise was performed on a motorized treadmill (velocity 9 m/min for 60 minutes). At 3 weeks post-injury, biomechanical analyzes as well as assessment of fibroblast number and orientation were performed. Collagen 1 (Col1) and 3 (Col3) and matrix metalloproteinases (MMPs) -3 and 13 protein distributions were studied by immunohistochemistry; while Col1 and Col3 and MMP-2 and 9 gene expression were assessed by quantitative RT-PCR (qRT-PCR). IDEAL exhibited significant increases in several biomechanical parameters in comparison to the other groups. Moreover, IDEAL presented stronger Col1 immunoreactivity when compared to ID, and weaker Col3 immunoreactivity than IDE. Both IDL and IDEAL demonstrated weaker expression of MMP-3 in comparison to I, while IDL presented no expression of MMP-13 when compared to ID. ID, IDL and IDE showed an increased number of fibroblasts in comparison to I, while IDEAL decreased the number of these cells in comparison to ID and IDE. IDL and IDEAL groups exhibited decreased angular dispersion among the fibroblasts when compared to I. The gene expression results showed that IDE demonstrated a downregulation in Col1 mRNA expression in comparison to I and ID. IDEAL demonstrated upregulation of Col1 mRNA expression when compared to IDL or IDE alone and increased MMP-2 expression when compared to IDL and IDE. MMP-9 expression was upregulated in IDEAL when compared to I, IDL and IDE. Our results suggest a beneficial interaction of combining both treatment strategies i.e., aerobic exercise and LPBM, on the biomechanical properties, tissue morphology and the expression of matrix molecules in diabetic tendons.

Resistance jump training may reverse the weakened biomechanical behavior of tendons of diabetic Wistar rats

ABSTRACT Background: resistance training is widely applied in non-diabetic physical protocol showing effectiveness in improving the tendon tissue. To address this gap, we assessed the effects of resistance training on aquatic environment, on the biomechanical properties of the calcaneal tendon of diabetic Wistar rats. Methods: 59 male Wistar rats were evaluated for 60 days, they were randomly divided into the following groups: Sedentary Control Group (SCG, n=15), Sedentary Diabetic Group (SDG, n=15), Trained Control Group (TCG, n=14) and Trained Diabetic Group (TDG, n=15). After randomization the animals from the SDG and the TDG were induced to Diabetes Mellitus by intraperitoneal injection of Streptozotocin (60 mg/kg). The animals on the trained groups performed resistance exercise that consisted of jumping in an aquatic environment. After nine weeks the calcaneal tendons were collected and tractioned on a conventional mechanical testing machine. Results: the analysis of biomechanical parameters showed lower values in elastic modulus (p=0.000), maximum strength tension (p=0.000) and energy/area (p=0.008) in TDG compared to SDG in addition to an increase on the cross-sectional area (p=0.002). There was no difference for the specific deformation variable. Conclusion: the training protocol used restored some biomechanical parameters of the calcaneal tendon in rats induced to diabetes, thus, resulting in an improvement of its mechanical efficiency.

Tendinopathy in diabetes mellitus patients-Epidemiology, pathogenesis, and management

Chronic tendinopathy is a frequent and disabling musculo-skeletal problem affecting the athletic and general populations. The affected tendon is presented with local tenderness, swelling, and pain which restrict the activity of the individual. Tendon degeneration reduces the mechanical strength and predisposes it to rupture. The pathogenic mechanisms of chronic tendinopathy are not fully understood and several major non-mutually exclusive hypotheses including activation of the hypoxia-apoptosis-pro-inflammatory cytokines cascade, neurovascular ingrowth, increased production of neuromediators, and erroneous stem cell differentiation have been proposed. Many intrinsic and extrinsic risk/causative factors can predispose to the development of tendinopathy. Among them, diabetes mellitus is an important risk/causative factor. This review aims to appraise the current literature on the epidemiology and pathology of tendinopathy in diabetic patients. Systematic reviews were done to summarize the literature on (a) the association between diabetes mellitus and tendinopathy/tendon tears, (b) the pathological changes in tendon under diabetic or hyperglycemic conditions, and (c) the effects of diabetes mellitus or hyperglycemia on the outcomes of tendon healing. The potential mechanisms of diabetes mellitus in causing and exacerbating tendinopathy with reference to the major non-mutually exclusive hypotheses of the pathogenic mechanisms of chronic tendinopathy as reported in the literature are also discussed. Potential strategies for the management of tendinopathy in diabetic patients are presented.

Experimental Diabetes Alters the Morphology and Nano-Structure of the Achilles Tendon

Although of several studies that associate chronic hyperglycemia with tendinopathy, the connection between morphometric changes as witnessed by magnetic resonance (MR) images, nanostructural changes, and inflammatory markers have not yet been fully established. Therefore, the present study has as a hypothesis that the Achilles tendons of rats with diabetes mellitus (DM) exhibit structural changes. The animals were randomly divided into two experimental groups: Control Group (n = 06) injected with a vehicle (sodium citrate buffer solution) and Diabetic Group (n = 06) consisting of rats submitted to intraperitoneal administration of streptozotocin. MR was performed 24 days after the induction of diabetes and images were used for morphometry using ImageJ software. Morphology of the collagen fibers within tendons was examined using Atomic Force microscopy (AFM). An increase in the dimension of the coronal plane area was observed in the diabetic group (8.583 ± 0.646 mm²/100g) when compared to the control group (4.823 ± 0.267 mm²/100g) resulting in a significant difference (p = 0.003) upon evaluating the Achilles tendons. Similarly, our analysis found an increase in the size of the transverse section area in the diabetic group (1.328 ± 0.103 mm²/100g) in comparison to the control group (0.940 ± 0.01 mm²/100g) p = 0.021. The tendons of the diabetic group showed great irregularity in fiber bundles, including modified grain direction and jagged junctions and deformities in the form of collagen fibrils bulges. Despite the morphological changes observed in the Achilles tendon of diabetic animals, IL1 and TNF-α did not change. Our results suggest that DM promotes changes to the Achilles tendon with important structural modifications as seen by MR and AFM, excluding major inflammatory changes.

Previous physical exercise slows down the complications from experimental diabetes in the calcaneal tendon

BACKGROUND

the complications caused by diabetes increase fragility in the muscle-tendon system, resulting in degeneration and easier rupture. To avoid this issue, therapies that increase the metabolism of glucose by the body, with physical activity, have been used after the confirmation of diabetes. We evaluate the biomechanical behavior of the calcaneal tendon and the metabolic parameters in rats induced to experimental diabetes and submitted to pre- and post-induction exercise.

METHODS

54-male-Wistar rats were randomly divided into four groups: Control Group (CG), Swimming Group (SG), Diabetic Group (DG), and Diabetic Swimming Group (DSG). The trained groups were submitted to swimming exercise, while unexercised groups remained restricted to the cages. Metabolic and biomechanical parameters were assessed.

RESULTS

the clinical parameters of DSG showed no change due to exercise protocol. The tendon analysis of the DSG showed increased values for the elastic modulus (p<0.01) and maximum tension (p<0.001) and lowest value for transverse area (p<0.001) when compared to the SG, however it showed no difference when compared to DG.

CONCLUSION

the homogeneous values presented by the tendons of the DG and DSG show that physical exercise applied in the pre- and post-induction wasn't enough to promote a protective effect against the tendinopathy process, but prevent the progress of degeneration.

Human Achilles tendon glycation and function in diabetes

Diabetic patients have an increased risk of foot ulcers, and glycation of collagen may increase tissue stiffness. We hypothesized that the level of glycemic control (glycation) may affect Achilles tendon stiffness, which can influence gait pattern. We therefore investigated the relationship between collagen glycation, Achilles tendon stiffness parameters, and plantar pressure in poorly (n = 22) and well (n = 22) controlled diabetic patients, including healthy age-matched (45-70 yr) controls (n = 11). There were no differences in any of the outcome parameters (collagen cross-linking or tendon stiffness) between patients with well-controlled and poorly controlled diabetes. The overall effect of diabetes was explored by collapsing the diabetes groups (DB) compared with the controls. Skin collagen cross-linking lysylpyridinoline, hydroxylysylpyridinoline (136%, 80%, P < 0.01) and pentosidine concentrations (55%, P < 0.05) were markedly greater in DB. Furthermore, Achilles tendon material stiffness was higher in DB (54%, P < 0.01). Notably, DB also demonstrated higher forefoot/rearfoot peak-plantar-pressure ratio (33%, P < 0.01). Overall, Achilles tendon material stiffness and skin connective tissue cross-linking were greater in diabetic patients compared with controls. The higher foot pressure indicates that material stiffness of tendon and other tissue (e.g., skin and joint capsule) may influence foot gait. The difference in foot pressure distribution may contribute to the development of foot ulcers in diabetic patients.

Influence of acute and chronic streptozotocin-induced diabetes on the rat tendon extracellular matrix and mechanical properties

Diabetes is a major risk factor for tendinopathy, and tendon abnormalities are common in diabetic patients. The purpose of the present study was to evaluate the effect of streptozotocin (60 mg/kg)-induced diabetes and insulin therapy on tendon mechanical and cellular properties. Sprague-Dawley rats (n = 40) were divided into the following four groups: nondiabetic (control), 1 wk of diabetes (acute), 10 wk of diabetes (chronic), and 10 wk of diabetes with insulin treatment (insulin). After 10 wk, Achilles tendon and tail fascicle mechanical properties were similar between groups (P > 0.05). Cell density in the Achilles tendon was greater in the chronic group compared with the control and acute groups (control group: 7.8 ± 0.5 cells/100 μm(2), acute group: 8.3 ± 0.4 cells/100 μm(2), chronic group: 10.9 ± 0.9 cells/100 μm(2), and insulin group: 9.2 ± 0.8 cells/100 μm(2), P < 0.05). The density of proliferating cells in the Achilles tendon was greater in the chronic group compared with all other groups (control group: 0.025 ± 0.009 cells/100 μm(2), acute group: 0.019 ± 0.005 cells/100 μm(2), chronic group: 0.067 ± 0.015, and insulin group: 0.004 ± 0.004 cells/100 μm(2), P < 0.05). Patellar tendon collagen content was ∼32% greater in the chronic and acute groups compared with the control or insulin groups (control group: 681 ± 63 μg collagen/mg dry wt, acute group: 938 ± 21 μg collagen/mg dry wt, chronic: 951 ± 52 μg collagen/mg dry wt, and insulin group: 596 ± 84 μg collagen/mg dry wt, P < 0.05). In contrast, patellar tendon hydroxylysyl pyridinoline cross linking and collagen fibril organization were unchanged by diabetes or insulin (P > 0.05). Our findings suggest that 10 wk of streptozotocin-induced diabetes does not alter rat tendon mechanical properties even with an increase in collagen content. Future studies could attempt to further address the mechanisms contributing to the increase in tendon problems noted in diabetic patients, especially since our data suggest that hyperglycemia per se does not alter tendon mechanical properties.

Alterations of tendons in diabetes mellitus: what are the current findings?

As a connective tissue, tendon connects the muscle and bone, and plays the key role in the locomotor system. Some previous studies have shown the pathological alternations in diabetic tendons, which might result in the structural and functional changes, and even accelerate the process of diabetic foot. In this review, we examined the current findings of the diabetic tendons in the form of various aspects, and summarized the clinical presentation, imaging, biomechanical, histopathological, cellular and molecular abnormalities in the diabetic tendons. The progress of diabetic tendon damage is complicated and the main hypotheses include the excessive accumulation of AGEs, the altered inflammatory response, neovascularization and insensitive neuropathy. However, the cellular and molecular mechanisms of these alterations are still ambiguous. Tendon stem/progenitor cells (TSPCs) have been discovered to play important roles in both tendon physiology and tendon pathology. Recently, we identified TSPCs from patellar tendons in our well-established diabetic rat model and found impaired tenogenic differentiation potential of these cells. We proposed a new hypothesis that the impaired cell functions of diabetic TSPCs might be the underlying cellular and molecular mechanism of the diabetic tendon alternations. These findings should be helpful to establish a better therapeutic strategy for diabetic tendon repair and regeneration.

The role of animal models in tendon research

Tendinopathy is a debilitating musculoskeletal condition which can cause significant pain and lead to complete rupture of the tendon, which often requires surgical repair. Due in part to the large spectrum of tendon pathologies, these disorders continue to be a clinical challenge. Animal models are often used in this field of research as they offer an attractive framework to examine the cascade of processes that occur throughout both tendon pathology and repair. This review discusses the structural, mechanical, and biological changes that occur throughout tendon pathology in animal models, as well as strategies for the improvement of tendon healing.

Cite this article: Bone Joint Res 2014;3:193–202.

Ultrasound morphology of the Achilles in asymptomatic patients with and without diabetes

BACKGROUND

The prevalence of tendinopathies is increased in subjects with diabetes mellitus. However, there are few data on the structural abnormalities of Achilles tendons in asymptomatic diabetic patients. The aim of the study was to assess the morphologic characteristics of the Achilles tendon in subjects with diabetes in comparison with controls without diabetes.

METHODS

Participants were consecutively recruited from an outpatient population. Ultrasound longitudinal and transverse scans were performed bilaterally along the full length of Achilles tendon from the musculotendinous junction to the insertion. Degenerative features (abnormal fibrillar pattern, hypo-hyperechoic areas), signs of enthesopathy (bony erosion, enthesophytes, and bursitis), and intratendinous neovessel formation were recorded.

RESULTS

Asymptomatic sonographic abnormalities (ASA) were significantly increased in subjects with diabetes (35/136 [25.7%] vs 32/273 [11.7%], P = .0003). Sixty tendons with ASA were observed in the first group and 45 in the latter because ASA were bilateral in 25 and in 13 subjects, respectively. ASA were more frequently localized at the enthesis (32/60 [53.3%] vs 9/45 [20%], P = .0005) in the diabetes group, whereas, on the contrary, they were more prevalent at the midportion in controls (38/45 [84.4%] vs 36/60 [60%], P < .006).

CONCLUSION

Diabetes may predispose to Achilles tendinopathy and particularly to Achilles enthesopathy. Longitudinal studies, evaluating the progression of the lesions not only in the midportion of the tendon but also at the insertion are needed to support this conclusion.

LEVEL OF EVIDENCE

Level III, comparative series.

Impact of diabetes mellitus on surgical outcomes in sports medicine

Diabetes mellitus (DM) affects a significant proportion of the patients evaluated and treated by orthopedic surgeons who specialize in sports medicine. Sports-medicine-related conditions associated with DM include tendinopathy, adhesive capsulitis of the shoulder, and articular cartilage disease. This article reviews the current literature adressing the effect of DM on surgical outcomes in sports medicine. In general, patients with DM undergo operations more frequently and experience inferior surgical outcomes compared with patients without DM. Diabetes mellitus is associated with increased rates of complications from sports medicine procedures, such as infection, delayed healing, and failure of the operation. However, additional research is needed to determine the full impact of DM on patient outcomes in sports medicine. Surgeons should be cognizant of special considerations in the population of patients with DM and aim to tailor the surgical management of this growing patient population.

Experimental diabetes induces structural, inflammatory and vascular changes of Achilles tendons

This study aims to demonstrate how the state of chronic hyperglycemia from experimental Diabetes Mellitus can influence the homeostatic imbalance of tendons and, consequently, lead to the characteristics of tendinopathy. Twenty animals were randomly divided into two experimental groups: control group, consisting of healthy rats and diabetic group constituted by rats induced to Diabetes Mellitus I. After twenty-four days of the induction of Diabetes type I, the Achilles tendon were removed for morphological evaluation, cellularity, number and cross-sectional area of blood vessel, immunohistochemistry for Collagen type I, VEGF and NF-κB nuclear localization sequence (NLS) and nitrate and nitrite level. The Achilles tendon thickness (µm/100g) of diabetic animals was significantly increased and, similarly, an increase was observed in the density of fibrocytes and mast cells in the tendons of the diabetic group. The average number of blood vessels per field, in peritendinous tissue, was statistically higher in the diabetic group 3.39 (2.98) vessels/field when compared to the control group 0.89 (1.68) vessels/field p = 0.001 and in the intratendinous region, it was observed that blood vessels were extremely rare in the control group 0.035 (0.18) vessels/field and were often present in the tendons of the diabetic group 0.89 (0.99) vessels/field. The immunohistochemistry analysis identified higher density of type 1 collagen and increased expression of VEGF as well as increased immunostaining for NFκB p50 NLS in the nucleus in Achilles tendon of the diabetic group when compared to the control group. Higher levels of nitrite/nitrate were observed in the experimental group induced to diabetes. We conclude that experimental DM induces notable structural, inflammatory and vascular changes in the Achilles tendon which are compatible with the process of chronic tendinopathy.

Recombinant human adiponectin as a potential protein for treating diabetic tendinopathy promotes tenocyte progenitor cells proliferation and tenogenic differentiation in vitro

Adiponectin is an adipocyte-secreting hormone that increases cell sensitivity to insulin. It has been previously demonstrated that this hormone protects against Type II Diabetes and, is found to concurrently promote cell proliferation and differentiation. It is postulated that diabetic patients who suffer from tendinopathy may benefit from using adiponectin, which not only improves the metabolism of diabetic ridden tenocytes but also promotes progenitor cell proliferation and differentiation in tendons. These changes may result in tendon regeneration, which, in diabetic tendinopathy, is difficult to treat. Considering that such findings have yet to be demonstrated, a study was thus conducted using diabetic ridden human tenocyte progenitor cells (TPC) exposed to recombinant adiponectin in vitro. TPC were isolated from tendons of diabetic patients and exposed to 10 μg/ml adiponectin. Cell proliferation rate was investigated at various time points whilst qPCR were used to determine the tenogenic differentiation potential. The results showed that adiponectin significantly reduced blood glucose in animal models. The proliferation rate of adiponectin-treated TPCs was significantly higher at 6, 8 and 10 days as compared to untreated cells (p<0.05). The levels of tenogenic genes expression (collagen I, III, tenomodulin and scleraxis) were also significantly upregulated; whilst the osteogenic (Runx2), chondrogenic (Sox9) and adipogenic (PPARУγ) gene expressions remained unaltered. The results of this study suggest that adiponectin is a potential promoter that not only improves diabetic conditions, but also increases tendon progenitor cell proliferation and differentiation. These features supports the notion that adiponectin may be potentially beneficial in treating diabetic tendinopathy.