Muscle apoptosis is induced in pressure-induced deep tissue injury

Nomogram model for predicting pressure injury in COPD patients using SII: a Chinese clinical study

Objectives

This study aims to investigate the association between the Systemic Immune-Inflammation Index (SII) and the development of pressure injuries (PI) in patients with chronic obstructive pulmonary disease (COPD). Additionally, a nomogram model based on the SII will be constructed to predict the probability of pressure injury (PI) occurrence in patients with COPD.

Methods

A retrospective analysis was performed on the clinical data of 844 patients with COPD who were admitted to the Affiliated Hospital of Guangdong Medical University between June 2018 and December 2019. Logistic regression analysis was employed to identify risk factors associated with the development of PI, and the Wald chi-square test was used to select variables for constructing a predictive nomogram. The performance of the nomogram was assessed, followed by internal validation. Additionally, clinical data from 452 patients with COPD admitted to the Second Affiliated Hospital of Guangdong Medical University between January 2024 and December 2024 were prospectively collected for external validation.

Results

A total of 844 patients with COPD were included in this study, with 590 cases in the training group and 254 cases in the internal validation group. The predictors included in the nomogram model were age, respiratory rate [Breathe (R)], duration of COPD history, Serum albumin (ALB), SII, paralysis, edema, and activities of daily living (ADL). The nomogram demonstrated strong predictive performance and calibration. The area under the curve and 95% confidence intervals were 0.77 (0.72-0.82) for the training group, 0.77 (0.70-0.85) for the internal validation group, and 0.73 (0.66-0.81) for the external validation group.

Conclusion

This study identified the SII, age, respiratory rate, duration of COPD history, ALB, paralysis, and ADL as independent risk factors for the development of PI in patients with COPD. A nomogram model was successfully developed based on SII and validated through both internal and external testing. The findings suggest that SII is a reliable predictor of PI development in patients with COPD, and the model demonstrates strong predictive performance.

Preliminary evidence for the presence of programmed cell death in pressure injuries

Pressure injuries (PIs) are a common healthcare problem worldwide and are considered to be the most expensive chronic wounds after arterial ulcers. Although the gross factors including ischemia-reperfusion (I/R) have been identified in the etiology of PIs, the precise cellular and molecular mechanisms contributing to PIs development remain unclear. Various forms of programmed cell death including apoptosis, autophagy, pyroptosis, necroptosis and ferroptosis have been identified in PIs. In this paper, we present a detailed overview on various forms of cell death; discuss the recent advances in the roles of cell death in the occurrence and development of PIs and found much of the evidence is novel and based on animal experiments. Herein, we also state critical evaluation of the existing data and future perspective in the field. A better understanding of the programmed cell death mechanism in PIs may have important implications in driving the development of new preventive and therapeutic strategies.

The potential role of ferroptosis in the physiopathology of deep tissue injuries

Deep tissue injuries (DTIs) are a serious type of pressure injuries that mainly occur at the bony prominences and can develop rapidly, making prevention and treatment more difficult. Although consistent research efforts have been made over the years, the cellular and molecular mechanisms contributing to the development of DTIs remain unclear. More recently, ferroptosis, a novel regulatory cell death (RCD) type, has been identified that is morphological, biochemical and genetic criteria distinct from apoptosis, autophagy and other known cell death pathways. Ferroptosis is characterized by iron overload, iron-dependent lipid peroxidation and shrunken mitochondria. We also note that some of the pathological features of DTI are known to be key features of the ferroptosis pathway. Numerous studies have confirmed that ferroptosis may be involved in chronic wounds, including DTIs. Here, we elaborate on the basic pathological features of ferroptosis. We also present the evidence that ferroptosis is involved in the pathology of DTIs and highlight a future perspective on this emerging field, desiring to provide more possibilities for the prevention and treatment of DTIs.

Jet Lavage Irrigation Resolves Stage 4 Pelvic Pressure Injury Undermining

OBJECTIVE

Patients with stage 4 pelvic pressure injuries that have large, undermined cavities are at high risk for treatment failure and often fall into the category of palliative care. This case series identified five cases where treatment had stalled, and surgical reconstructive options were limited. Jet lavage irrigation in the outpatient setting was assessed as a treatment alternative.

METHODS

From an investigational review board study assessing the use of low-pressure jet lavage irrigation in the outpatient setting for chronic wounds, five patients were identified where the wound dimension increased at least 50% resulting from undermined cavities. All were considered high risk with Charlson Comorbidity Index scores of 5 or greater, and their wound healing had stalled with extended treatments of topicals and medicated dressings. A team of physical therapists irrigated these patients' wounds at the bedside with 3 L of saline 3 to 5 days per week using a special long irrigation tip to reach the depth of the undermined cavity. Digital planimetry was used to assess healing with wound size as the outcome.

RESULTS

Reduction of the undermined cavities was seen early within the first 3 weeks. No patient developed wound sepsis, and bacterial contamination was determined by use of autofluorescence digital imaging. Undermining resolution occurred in four patients, and one patient with an improving wound died of COVID-19.

CONCLUSIONS

This simple method offered clear benefits in each patient, but only one patient survived to complete wound healing. Patient and family satisfaction were high regarding the treatment, which created a painless, odor-free wound.

Advance in topical biomaterials and mechanisms for the intervention of pressure injury

Pressure injuries (PIs) are localized tissue damage resulting from prolonged compression or shear forces on the skin or underlying tissue, or both. Different stages of PIs share common features include intense oxidative stress, abnormal inflammatory response, cell death, and subdued tissue remodeling. Despite various clinical interventions, stage 1 or stage 2 PIs are hard to monitor for the changes of skin or identify from other disease, whereas stage 3 or stage 4 PIs are challenging to heal, painful, expensive to manage, and have a negative impact on quality of life. Here, we review the underlying pathogenesis and the current advances of biochemicals in PIs. We first discuss the crucial events involved in the pathogenesis of PIs and key biochemical pathways lead to wound delay. Then, we examine the recent progress of biomaterials-assisted wound prevention and healing and their prospects.

Myoglobin-derived iron causes wound enlargement and impaired regeneration in pressure injuries of muscle

The reasons for poor healing of pressure injuries are poorly understood. Vascular ulcers are worsened by extracellular release of hemoglobin, so we examined the impact of myoglobin (Mb) iron in murine muscle pressure injuries (mPI). Tests used Mb-knockout or treatment with deferoxamine iron chelator (DFO). Unlike acute injuries from cardiotoxin, mPI regenerated poorly with a lack of viable immune cells, persistence of dead tissue (necro-slough), and abnormal deposition of iron. However, Mb-knockout or DFO-treated mPI displayed a reversal of the pathology: decreased tissue death, decreased iron deposition, decrease in markers of oxidative damage, and higher numbers of intact immune cells. Subsequently, DFO treatment improved myofiber regeneration and morphology. We conclude that myoglobin iron contributes to tissue death in mPI. Remarkably, a large fraction of muscle death in untreated mPI occurred later than, and was preventable by, DFO treatment, even though treatment started 12 hr after pressure was removed. This demonstrates an opportunity for post-pressure prevention to salvage tissue viability.

A new device for the combined measurement of friction and through-thickness deformation on ex vivo skin samples

Skin irritation is a common phenomenon that becomes a real concern when caused by the use of medical devices. Because the materials used for the design of these devices are usually carefully selected for chemical compatibility with the skin, it is reasonable to assume that the irritations result from the mechanical interaction between the devices and the skin. The aim of this work was to develop a new device to study both the shear strains in the layers of the skin, using Digital Image Correlation (DIC), and the friction behaviour of ex vivo skin interacting with objects. Pig skin samples with various surface preparations were tested in friction experiments involving different contacting materials encountered in the conception of medical devices. The measure of the static and dynamic coefficients of friction as well as the length of adhesion has highlighted the great influence of skin surface conditioning on friction properties. Strain maps obtained through DIC provided insights into the impact of friction and adhesion effects on shear strain distribution in the skin as a function of depth beneath its surface.

Myonuclear apoptosis via cleaved caspase-3 upregulation is related to macrophage accumulation underlying immobilization-induced muscle fibrosis

INTRODUCTION/AIMS

Although macrophage accumulation plays a key role in the development of immobilization-induced muscle fibrosis, the underlying mechanisms remain unclear. Therefore, we focused on the alterations of myonuclear apoptosis via cleaved caspase-3, and investigated whether these changes may be related to macrophage accumulation.

METHODS

Eight-week-old Wistar rats were divided into immobilization and control groups, and the soleus muscles were selected for analysis.

RESULTS

The mRNA and protein expression of collagen and the number of CD11b-positive cells were significantly higher in the immobilized rats than in the control rats at 1 and 2 weeks. TdT-mediated dUTP nick end-labeling (TUNEL)-positive myonuclei counts in 1- and 2-week control rats were 0.2 ± 0.1 and 0.2 ± 0.5, whereas they were 1.0 ± 0.6 and 1.1 ± 0.5 in 1- and 2-week immobilized rats. The cleaved caspase-3 protein expressions in 1- and 2-week control rats were 0.2 ± 0.1 and 0.2 ± 0.1, whereas they were 0.5 ± 0.1 and 0.4 ± 0.2 in 1- and 2-week immobilized rats. TUNEL-positive myonuclei counts and cleaved caspase-3 protein expression were significantly higher in immobilized rats than in control rats at 1 and 2 weeks. The numbers of myonuclei in 1- and 2-week control rats were 2.8 ± 0.1 and 2.6 ± 0.4, whereas they were 2.2 ± 0.4 and 2.2 ± 0.2 in 1- and 2-week immobilized rats. The numbers of myonuclei were significantly lower in immobilized than in control rats at both time-points.

DISCUSSION

Myonuclear apoptosis via the upregulation of cleaved caspase-3 might induce macrophage accumulation. These alterations are related to immobilization-induced muscle fibrosis.

Quantitative iTRAQ LC-MS/MS reveals muscular proteome profiles of deep pressure ulcers

Pressure ulcers (PUs) are a common clinical issue lacking effective treatment and validated pharmacological therapy in hospital settings. Ischemia-reperfusion injury of deep tissue, especially muscle, plays a vital role in the formation and development of the overwhelming majority of PUs. However, muscular protein expression study in PUs has not been reported. Herein, we aimed to investigate the muscular proteins profiles in PUs and to explore the pathological mechanism of PUs. The iTRAQ LC-MS/MS was conducted to detect the protein profiles in clinical muscle samples of PUs. The GO and KEGG pathways analyses were performed for annotation of differentially expressed proteins. Protein-protein interaction (PPI) network was constructed by STRING online database, and hub proteins were validated by the immunoblotting. Based on proteomics results, we found a number of proteins that were differentially expressed in PU muscle samples compared with the normal and identified unique proteins expression patterns between these two groups, suggesting that they might involve in pathological process of the disease. Importantly, cathepsin B and D, as well as other autophagy-lysosome and apoptosis associated proteins were identified. Further experiments characterize the expression of these proteins and their regulation in the process of apoptosis and autophagy. These findings may provide novel insights into the mechanisms of lysosome-associated pathways involved in the initiation of PUs. This is the first study linking proteomics to PUs muscle tissues, which indicated cathepsin B and D might be key drug target for PUs.

Development of an apoptosis-assisted decellularization method for maximal preservation of nerve tissue structure

Preservation of tissue structure is often a primary goal when optimizing tissue and organ decellularization methods. Many current protocols nonetheless rely on detergents that aid extraction of cellular components but also damage tissue architecture. It may be more beneficial to leverage an innate cellular process such as apoptosis and promote cell removal without the use of damaging reagents. During apoptosis, a cell detaches from the extracellular matrix, degrades its internal components, and fragments its contents for easier clearance. We have developed a method that leverages this process to achieve tissue decellularization using only mild wash buffers. We have demonstrated that treating peripheral nerve tissue with camptothecin induced both an early marker of apoptosis, cleaved caspase-3 expression, as well as a late stage marker, TUNEL⁺ DNA fragmentation. Clearance of the cellular components was then achieved in an apoptosis-dependent manner using a gentle wash in hypertonic phosphate buffered saline followed by DNase treatment. This wash paradigm did not significantly affect collagen or glycosaminoglycan content, but it was sufficient to remove any trace of the cytotoxic compound based on conditioned media experiments. The resulting acellular tissue graft was immunogenically tolerated in vivo and exhibited an intact basal lamina microarchitecture mimicking that of native, unprocessed nerve. Hence, ex vivo induction of apoptosis is a promising method to decellularize tissue without the use of harsh reagents while better preserving the benefits of native tissue such as tissue-specific composition and microarchitecture.

STATEMENT OF SIGNIFICANCE

Tissue decellularization has expanded the ability to generate non-immunogenic organ replacements for a broad range of health applications. Current technologies typically rely on the use of harsh agents for clearing cellular debris, altering the tissue structure and potentially diminishing the pro-regenerative effects. We have developed a method for effectively, yet gently, removing cellular components from peripheral nerve tissue while preserving the native tissue architecture. The novelty of this process is in the induction of programmed cell death - or apoptosis - via a general cytotoxin, thereby enabling antigen clearance using only hypertonic wash buffers. The resulting acellular nerve scaffolds are nearly identical to unprocessed tissue on a microscopic level and elicit low immune responses comparable to an isograft negative control in a model of subcutaneous implantation.

An advanced magnetic resonance imaging perspective on the etiology of deep tissue injury

Early diagnosis of deep tissue injury remains problematic due to the complicated and multifactorial nature of damage induction and the many processes involved in damage development and recovery. In this paper, we present a comprehensive assessment of deep tissue injury development and remodeling in a rat model by multiparametric magnetic resonance imaging (MRI) and histopathology. The tibialis anterior muscle of rats was subjected to mechanical deformation for 2 h. Multiparametric in vivo MRI, consisting of T2, T2*, mean diffusivity (MD), and angiography measurements, was applied before, during, and directly after indentation as well as at several time points during a 14-day follow-up. MRI readouts were linked to histological analyses of the damaged tissue. The results showed dynamic change in various MRI parameters, reflecting the histopathological status of the tissue during damage induction and repair. Increased T2 corresponded with edema, muscle cell damage, and inflammation. T2* was related to tissue perfusion, hemorrhage, and inflammation. MD increase and decrease was reported on the tissue’s microstructural integrity and reflected muscle degeneration and edema as well as fibrosis. Angiography provided information on blockage of blood flow during deformation. Our results indicate that the effects of a single damage-causing event of only 2 h of deformation were present up to 14 days. The initial tissue response to deformation, as observed by MRI, starts at the edge of the indentation. The quantitative MRI readouts provided distinct and complementary information on the extent, temporal evolution, and microstructural basis of deep tissue injury-related muscle damage.

NEW & NOTEWORTHY We have applied a multiparametric MRI approach linked to histopathology to characterize damage development and remodeling in a rat model of deep tissue injury. Our approach provided several relevant insights in deep tissue injury. Response to damage, as observed by MRI, started at some distance from the deformation. Damage after a single indentation period persisted up to 14 days. The MRI parameters provided distinct and complementary information on the microstructural basis of the damage.

[Effect of different time windows and interventions on skin pressure ulcers and ischemia-reperfusion injury in rats]

OBJECTIVE

To observe the effect of different time windows and interventions on skin pressure ulcers and ischemia-reperfusion (I/R) injury in rats.

METHODS

Sixty?eight SD rats were randomly divided into blank control group (n=4) and model group (n=64). The rats in the model group were randomly divided into group A (n=32) without intervention and group B (n=32) with post?conditioning. The degree of skin compression, neutrophil infiltration and serum levels of free radicals were observed in the rats after compression for 2, 4, 6, and 8 h (8 rats at each time point).

RESULTS

A significant difference was found in the severity of skin damage among the control group, group A, and group B (P=0.001), and the injury was milder in group B than in group A. Severe skin lesions occurred in 2 rats after skin compression for 6 h, as compared with 6 after compression for 8 h (P=0.043), but in none of the rats after compression for 2 or 4. Seventeen rats in group B and 15 in group A showed grade 1 neutrophil infiltration in the skin lesions, and 8 rats in group B and 10 in group A showed grade II neutrophil infiltration (P=0.002). Neutrophil infiltration was the mildest in rats with a 2?h compression, and exacerbated progressively and significantly as the compression time extended (P=0.027). With the prolongation of the intervention time, the rats in both groups A and B showed decreased SOD and increased MDA and NO levels, and overall the I/R injury was milder in 2? and 4?h compression groups than in 6? and 8?h compression groups. The level of serum SOD was significantly higher and MDA and NO levels were significantly higher in group B than in group A (P<0.05).

CONCLUSION

Ischemic post?conditioning can relieve I/R injury in acute pressure ulcer in rats. The effective time window for intervention is within 6 h of ischemia, and the effect of ischemic post-conditioning is optimal within 2 h. Ischemic post?conditioning can alleviate free radical injury and inflammation caused by I/R injury.

Protective Effect of Unacylated Ghrelin on Compression-Induced Skeletal Muscle Injury Mediated by SIRT1-Signaling

Unacylated ghrelin, the predominant form of circulating ghrelin, protects myotubes from cell death, which is a known attribute of pressure ulcers. In this study, we investigated whether unacylated ghrelin protects skeletal muscle from pressure-induced deep tissue injury by abolishing necroptosis and apoptosis signaling and whether these effects were mediated by SIRT1 pathway. Fifteen adult Sprague Dawley rats were assigned to receive saline or unacylated ghrelin with or without EX527 (a SIRT1 inhibitor). Animals underwent two 6-h compression cycles with 100 mmHg static pressure applied over the mid-tibialis region of the right limb whereas the left uncompressed limb served as the intra-animal control. Muscle tissues underneath the compression region, and at the similar region of the opposite uncompressed limb, were collected for analysis. Unacylated ghrelin attenuated the compression-induced muscle pathohistological alterations including rounding contour of myofibers, extensive nucleus accumulation in the interstitial space, and increased interstitial space. Unacylated ghrelin abolished the increase in necroptosis proteins including RIP1 and RIP3 and attenuated the elevation of apoptotic proteins including p53, Bax, and AIF in the compressed muscle. Furthermore, unacylated ghrelin opposed the compression-induced phosphorylation and acetylation of p65 subunit of NF-kB. The anti-apoptotic effect of unacylated ghrelin was shown by a decrease in apoptotic DNA fragmentation and terminal dUTP nick-end labeling index in the compressed muscle. The protective effects of unacylated ghrelin vanished when co-treated with EX527. Our findings demonstrated that unacylated ghrelin protected skeletal muscle from compression-induced injury. The myoprotective effects of unacylated ghrelin on pressure-induced tissue injury were associated with SIRT1 signaling.

Intensive Care Unit-Acquired Weakness: Implications for Case Management

PURPOSE

The purpose of this case study is to provide a specific example of the disease trajectory for one patient's experience with intensive care unit-acquired weakness (ICUAW). This case study provides those in case management with an overview of some of the common signs and symptoms of ICUAW, as well as the possible prognosis and recovery from ICUAW.

PRIMARY PRACTICE SETTING

The events in this case study take place in the acute care setting including the intensive care unit of a mid-sized health center, a general medical-surgical (med-surg) unit, and a long-term acute care facility.

CONCLUSIONS

ICUAW affects the clinical, functional, and financial outcomes of patients. If the patient survives, their quality of life and the quality of life of their family members could be severely impacted. Case management practice has a significant role in coordinating care for those diagnosed with ICUAW. Case managers can use knowledge about ICUAW to improve the patient's transition throughout the hospital stay, improve discharge recommendations, and improve the patient's short-term and long-term outcomes. This may reduce unnecessary utilization of health care resources.

Age-related effect of cell death on fiber morphology and number in tongue muscle

INTRODUCTION

Multiple pathways may exist for age-related tongue muscle degeneration. Cell death is one mechanism contributing to muscle atrophy and decreased function. We hypothesized with aging, apoptosis, and apoptotic regulators would be increased, and muscle fiber size and number would be reduced in extrinsic tongue muscles.

METHODS

Cell death indices, expression of caspase-3 and Bcl-2, and measures of muscle morphology and number were determined in extrinsic tongue muscles of young and old rats.

RESULTS

Significant increases in cell death, caspase-3, and Bcl-2 were observed in all extrinsic tongue muscles along with reductions in muscle fiber number in old rats.

DISCUSSION

We demonstrated that apoptosis indices increase with age in lingual muscles and that alterations in apoptotic regulators may be associated with age-related degeneration in muscle fiber size and number. These observed apoptotic processes may be detrimental to muscle function, and may contribute to degradation of cranial functions with age. Muscle Nerve 57: E29-E37, 2018.

Effects of Biowastes Released by Mechanically Damaged Muscle Cells on the Propagation of Deep Tissue Injury: A Multiphysics Study

Deep tissue injuries occur in muscle tissues around bony prominences under mechanical loading leading to severe pressure ulcers. Tissue compression can potentially compromise lymphatic transport and cause accumulation of metabolic biowastes, which may cause further cell damage under continuous mechanical loading. In this study, we hypothesized that biowastes released by mechanically damaged muscle cells could be toxic to the surrounding muscle cells and could compromise the capability of the surrounding muscle cells to withstand further mechanical loadings. In vitro, we applied prolonged low compressive stress (PLCS) and short-term high compressive stress to myoblasts to cause cell damage and collected the biowastes released by the damaged cells under the respective loading scenarios. In silico, we used COMSOL to simulate the compressive stress distribution and the diffusion of biowastes in a semi-3D buttock finite element model. In vitro results showed that biowastes collected from cells damaged under PLCS were more toxic and could compromise the capability of normal myoblasts to resist compressive damage. In silico results showed that higher biowastes diffusion coefficient, higher biowastes release rate, lower biowastes tolerance threshold and earlier timeline of releasing biowastes would cause faster propagation of tissue damage. This study highlighted the importance of biowastes in the development of deep tissue injury to clinical pressure ulcers under prolonged skeletal compression.

Myoprotective effects of bFGF on skeletal muscle injury in pressure-related deep tissue injury in rats

BACKGROUND

Pressure ulcers (PUs) are a major clinical problem that constitutes a tremendous economic burden on healthcare systems. Deep tissue injury (DTI) is a unique serious type of pressure ulcer that arises in skeletal muscle tissue. DTI arises in part because skeletal muscle tissues are more susceptible than skin to external compression. Unfortunately, few effective therapies are currently available for muscle injury. Basic fibroblast growth factor (bFGF), a potent mitogen and survival factor for various cells, plays a crucial role in the regulation of muscle development and homeostasis. The main purpose of this study was to test whether local administration of bFGF could accelerate muscle regeneration in a rat DTI model.

METHODS

Male Sprague Dawley (SD) rats (age 12 weeks) were individually housed in plastic cages and a DTI PU model was induced according to methods described before. Animals were randomly divided into three groups: a normal group, a PU group treated with saline, and a PU group treated with bFGF (10 μg/0.1 ml) subcutaneously near the wound.

RESULTS

We found that application of bFGF accelerated the rate of wound closure and promoted cell proliferation and tissue angiogenesis. In addition, compared to saline administration, bFGF treatment prevented collagen deposition, a measure of fibrosis, and up-regulated the myogenic marker proteins MyHC and myogenin, suggesting bFGF promoted injured muscle regeneration. Moreover, bFGF treatment increased levels of myogenesis-related proteins p-Akt and p-mTOR.

CONCLUSIONS

Our findings show that bFGF accelerated injured skeletal muscle regeneration through activation of the PI3K/Akt/mTOR signaling pathway and suggest that administration of bFGF is a potential therapeutic strategy for the treatment of skeletal muscle injury in PUs.

Pressure Combined with Ischemia/Reperfusion Injury Induces Deep Tissue Injury via Endoplasmic Reticulum Stress in a Rat Pressure Ulcer Model

Pressure ulcer is a complex and significant health problem in long-term bedridden patients, and there is currently no effective treatment or efficient prevention method. Furthermore, the molecular mechanisms and pathogenesis contributing to the deep injury of pressure ulcers are unclear. The aim of the study was to explore the role of endoplasmic reticulum (ER) stress and Akt/GSK3β signaling in pressure ulcers. A model of pressure-induced deep tissue injury in adult Sprague-Dawley rats was established. Rats were treated with 2-h compression and subsequent 0.5-h release for various cycles. After recovery, the tissue in the compressed regions was collected for further analysis. The compressed muscle tissues showed clear cellular degenerative features. First, the expression levels of ER stress proteins GRP78, CHOP, and caspase-12 were generally increased compared to those in the control. Phosphorylated Akt and phosphorylated GSK3β were upregulated in the beginning of muscle compression, and immediately significantly decreased at the initiation of ischemia-reperfusion injury in compressed muscles tissue. These data show that ER stress may be involved in the underlying mechanisms of cell degeneration after pressure ulcers and that the Akt/GSK3β signal pathway may play an important role in deep tissue injury induced by pressure and ischemia/reperfusion.

SIRT1-dependent myoprotective effects of resveratrol on muscle injury induced by compression

Our current understanding on the molecular mechanisms by which sustained compression induces skeletal muscle injury is very limited. This study aimed to test the hypothesis that activation of SIRT1 by the natural antioxidant resveratrol could deactivate apoptotic and catabolic signaling in skeletal muscle exposed to moderate compression. Two cycles of 6-h constant pressure at 100 mmHg was applied to the tibialis region of right, but not left hindlimbs of Sprague Dawley rats pre-treated with DMSO (vehicle control) or resveratrol with/without sirtinol. Skeletal muscle tissues lying underneath and spatially corresponding to the compressed sites were collected for analyses. Resveratrol prevented the compression-induced manifestations of pathohistological damages including elevations of the number of interstitial nuclei and area of interstitial space and ameliorated oxidative damages measured as 4-hydroxy-2-nonenal (4HNE) and nitrotyrosine in skeletal muscle. In parallel, resveratrol augmented the expression level and activity of SIRT1 and phosphorylation levels of Foxo3a and Akt while suppressed the increases in protein abundances of p53, Bax, MAFbx, and ubiquitin, enzymatic activities of caspase 3 and 20S proteasome, and apoptotic DNA fragmentation in the compressed muscle. These favorable myoprotective effects of resveratrol were diminished upon pharmacological blockade of SIRT1 by using sirtinol. These novel data support the hypothesis that the anti-apoptotic and anti-catabolic effects of resveratrol on compression injury in skeletal muscle required the action of SIRT1.

The effects of oxidative stress on the compressive damage thresholds of C2C12 mouse myoblasts: implications for deep tissue injury

Deep tissue injury (DTI) is a severe kind of pressure ulcers formed by sustained deformation of muscle tissues over bony prominences. As a major clinical issue, DTI affects people with physical disabilities, and is obviously related to the load-bearing capacity of muscle cells in various in vivo conditions. It has been hypothesized that oxidative stress, either induced by reperfusion immediately following tissue unloading or in chronic inflammatory conditions, may affect the cellular capacity against subsequent mechanical damages. In this study, we measured the compressive damage threshold of C2C12 mouse myoblasts with or without pre-treatment of hydrogen peroxide as an oxidative agent to understand how changes in the oxidative environment may contribute to the development of DTI. Spherical indentation was applied onto a layer of agarose gel (3 mm thick) covering a monolayer of C2C12 myoblasts. Cell damage was recognized by using a cell membrane damage assay, propidium iodide. The spatial profile of the measured percentage cell damage was correlated with the radially varying stress field as determined by finite element analysis to estimate the compressive stress threshold for cell damage. Results supported the hypothesis that chronic exposure to high-dosage oxidative stress could compromise the capability of muscle cells to withstand compressive damages, while short exposure to low-dosage oxidative stress could enhance such capability.

Acylated and unacylated ghrelin inhibit doxorubicin-induced apoptosis in skeletal muscle

AIM

Doxorubicin, a potent chemotherapeutic drug, has been demonstrated previously as an inducer of apoptosis in muscle cells. Extensive induction of apoptosis may cause excessive loss of muscle cells and subsequent functional decline in skeletal muscle. This study examined the effects of acylated ghrelin, a potential agent for treating cancer cachexia, on inhibiting apoptotic signalling in doxorubicin-treated skeletal muscle. Unacylated ghrelin, a form of ghrelin that does not bind to GHSR-1a, is also employed in this study to examine the GHSR-1a signalling dependency of the effects of ghrelin.

METHODS

Adult C57BL/6 mice were randomly assigned to saline control (CON), doxorubicin (DOX), doxorubicin with treatment of acylated ghrelin (DOX+Acylated Ghrelin) and doxorubicin with treatment of unacylated ghrelin (DOX+Unacylated Ghrelin). Mice in all groups that involved DOX were intraperitoneally injected with 15 mg of doxorubicin per kg body weight, whereas mice in CON group received saline as placebo. Gastrocnemius muscle tissues were harvested after the experimental period for analysis.

RESULTS

The elevation of apoptotic DNA fragmentation and number of TUNEL-positive nuclei were accompanied with the upregulation of Bax in muscle after exposure to doxorubicin, but all these changes were neither seen in the muscle treated with acylated ghrelin nor unacylated ghrelin after doxorubicin exposure. Protein abundances of autophagic markers including LC3 II-to-LC3 I ratio, Atg12-5 complex, Atg5 and Beclin-1 were not altered by doxorubicin but were upregulated by the treatment of either acylated or unacyated ghrelin. Histological analysis revealed that the amount of centronucleated myofibres was elevated in doxorubicin-treated muscle while muscle of others groups showed normal histology.

CONCLUSIONS

Collectively, our data demonstrated that acylated ghrelin administration suppresses the doxorubicin-induced activation of apoptosis and enhances the cellular signalling of autophagy. The treatment of unacylated ghrelin has similar effects as acylated ghrelin on apoptotic and autophagic signalling, suggesting that the effects of ghrelin are probably mediated through a signalling pathway that is independent of GHSR-1a. These findings were consistent with the hypothesis that acylated ghrelin inhibits doxorubicin-induced upregulation of apoptosis in skeletal muscle while treatment of unacylated ghrelin can achieve similar effects as the treatment of acylated ghrelin. The inhibition of apoptosis and enhancement of autophagy induced by acylated and unacylated ghrelin might exert myoprotective effects on doxorubicin-induced toxicity in skeletal muscle.

Low-intensity treadmill exercise enhances fast recovery from bupivacaine-induced muscle injury in rats

Background

Although bupivacaine has been used to study muscle degeneration and regeneration, the potential enhancement of muscle injury by exercise has not been well examined. The purpose of this study was to determine whether low-intensity treadmill exercise enhances fast recovery from bupivacaine-induced muscle injury and to examine concomitant changes in heat-shock protein 70 (HSP70) expression during regeneration process.

Methods

In this study, Sprague-Dawley rats were randomly divided into the following four groups: the control group (CON), the sham group (SHAM), the injury group (INJ), and the injury and exercise group (EX) (n = 14 in each group). Expressions of HSP70, inducible nitric oxide synthase (iNOS), and caspase-3 were determined at 1 and 7 days after bupivacaine-induced muscle injury in gastrocnemius.

Results

Results showed that bupivacaine-induced muscle injury (1 day) significantly increased the expressions of HSP70 and iNOS. At 7 days after the muscle injury, HSP70 expression was higher in the EX group compared with that in the INJ group and elevated level of HSP70 by exercise is concomitant with downregulation of iNOS and the decreased number of caspase-3-positive cells as a marker of apoptosis. Fewer necrosis of myofibers were also found in the EX group compared with the INJ group.

Conclusion

Our results suggest that low-intensity treadmill exercise may enhance fast recovery from bupivacaine-induced muscle injury in rat partly by HSP70 upregulation.

Establishment of a novel rat model for deep tissue injury deterioration

Deep tissue injuries (DTIs) can become significant problems because of their rapid deterioration into deep pressure ulcers. Presently, no animal model of DTI deterioration has been developed. By concentrating pressure and shear stress in deep tissues while minimising pressure and shear stress in the overlying skin, we produced an effective rat model of DTI deterioration. Two-dimensional finite element method (FEM) simulated the distribution of pressure and shear stress under several pressure-loading conditions. FEM showed that concentrated shear stress in deep tissue with minimum shear stress in the overlying skin could be created by using a prominence and a cushion, respectively. On the basis of the results of FEM analysis, we selected suitable conditions for testing the rat DTI deterioration model. The compressed area was macroscopically observed until day 13, and histopathologic analysis via haematoxylin and eosin (H&E) staining was performed on days 3, 7 and 13. H&E staining showed that the distribution of tissue damage was similar to the predicted FEM results. Deep ulceration and tissue damage extending from deep tissues to the overlying skin and surrounding tissues were observed in the DTI deterioration model, which are similar to the clinical manifestations of DTI deterioration. In conclusion, a representative DTI deterioration model was established by concentrating high shear stress in deep tissues while minimising shear stress in the overlying skin. This model will allow a better understanding of the mechanisms behind DTI deterioration and the development of preventative strategies.

Oxidative stress and DNA damage signalling in skeletal muscle in pressure-induced deep tissue injury

The molecular mechanisms that contribute to the pathogenesis of pressure-induced deep tissue injury are largely unknown. This study tested the hypothesis that oxidative stress and DNA damage signalling mechanism in skeletal muscle are involved in deep tissue injury. Adult Sprague Dawley rats were subject to an experimental protocol to induce deep tissue injury. Two compression cycles with a static pressure of 100 mmHg was applied to an area of 1.5 cm(2) over the mid-tibialis region of right limb of the rats. The left uncompressed limb served as intra-animal control. Muscle tissues underneath compression region were collected for examination. Our analyses indicated that pathohistological characteristics including rounding contour of myofibres and extensive nuclei accumulation were apparently shown in compressed muscles. The elevation of 8OHdG immunopositively stained nuclei indicated the presence of oxidative DNA damage. Increase in oxidative stress was revealed by showing significant elevation of 4HNE and decreases in mRNA abundance of SOD1, catalase and GPx, and protein content of SOD2 in compressed muscles relative to control muscles. Increase in nitrosative stress was demonstrated by significant elevation of nitrotyrosine and NOS2 mRNA content. The activation of tumor suppressor p53 signalling was indicated by the remarkable increases in protein contents of total p53 and serine-15 phosphorylated p53. The transcript expression of the DNA-repairing enzyme, Rad23A, was significantly suppressed in compressed muscles. Our time-course study indicated that increased oxidative/nitrosative stress and proapoptotic signalling were maintained in muscles receiving increasing amount of compression cycles and post-compression time. Furthermore, resveratrol was found to attenuate the histological damage, oxidative/nitrosative stress and proapoptotic signalling in response to prolonged moderate compression. In conclusion, our findings are consistent with the hypothesis that oxidative stress and DNA damage signalling in skeletal muscle are involved in the underlying mechanisms responsible for the pathogenesis of pressure-induced deep tissue injury.

Pressure ulcer staging revisited: superficial skin changes & Deep Pressure Ulcer Framework©

Deficiencies in the current pressure ulcer classification system create the impetus for the current discourse on the clinical, legal, and economic implications of staging and considering shifting the paradigm in pressure ulcer description and assessment.

Effects of non contact low-frequency ultrasound on healing of suspected deep tissue injury: a retrospective analysis

The purpose of this study was to assess the effectiveness of non contact low-frequency ultrasound on the healing of suspected deep tissue injury (SDTI). Participants were adults ranging in age from 28 to 93 years old, with multiple diagnoses including anaemia, diabetes mellitus and hypertension. Data were examined retrospectively on 85 patients (intervention group = 43 and non intervention group = 42) with 127 SDTI (intervention group = 64 and non intervention group = 63). Participants in both groups received standard of care for treating pressure ulcers. A severity score was used to assess SDTI severity before treatment and healing/progression after treatment. This scale measures surface area, wound colour/tissue assessment, and skin integrity with potential scores of 3 to 18 (higher scores indicate greater severity). A significant difference in changes in wound severity was found (t = 5·67, P < 0.000). Difference in mean change scores was 2·52 on the 3-18 severity scale. The decrease in wound severity for the intervention group was 1·45. Severity in the non intervention group increased by 1·06. This exploratory study of the effect of the non contact low-frequency ultrasound provides initial findings that support its use with SDTI.

Occlusal disharmony increases amyloid-β in the rat hippocampus

Amyloid-β plays a causative role in Alzheimer's disease. Occlusal disharmony causes chronic psychological stress, and psychological stress increases amyloid-β accumulation. The purpose of the present study was to investigate whether occlusal disharmony-induced psychological stress affects the accumulation of amyloid-β and its related gene expressions in the rat hippocampus. Eight-week-old male Wistar rats (n = 18) were divided into three groups of six rats each: (1) a control group that received no treatment for 8 weeks; (2) an occlusal disharmony group that underwent cutoff maxillary molar cusps for 8 weeks; and (3) a recovered group that underwent cutoff maxillary molar cusps for 4 weeks followed by recovery for 4 weeks. Occlusal disharmony increased plasma corticosterone levels in a time-dependent manner. Levels of amyloid-β 40 and 42, glucocorticoid receptor (Gr) protein, and cleaved caspase 3 (Casp3) as well as gene expressions of amyloid precursor protein, beta-secretase, Casp3, and Gr in the hippocampus in the occlusal disharmony group were significantly higher than those in the control group (P < 0.016). These findings were significantly improved by recovery of occlusion (P < 0.016). These results indicate that psychological stress induced by occlusal disharmony reversibly induces amyloid-β 40 and 42 in the rat hippocampus through the glucocorticoid signal.

Protective effect of caspase inhibition on compression-induced muscle damage

There are currently no effective therapies for treating pressure-induced deep tissue injury. This study tested the efficacy of pharmacological inhibition of caspase in preventing muscle damage following sustained moderate compression. Adult Sprague-Dawley rats were subjected to prolonged moderate compression. Static pressure of 100 mm Hg compression was applied to an area of 1.5 cm2 in the tibialis region of the right limb of the rats for 6 h each day for two consecutive days. The left uncompressed limb served as intra-animal control. Rats were randomized to receive either vehicle (DMSO) as control treatment (n =8) or 6 mg kg⁻¹ of caspase inhibitor (z-VAD-fmk; n =8) prior to the 6 h compression on the two consecutive days.Muscle tissues directly underneath the compression region of the compressed limb and the same region of control limb were harvested after the compression procedure.Histological examination and biochemical/molecular measurement of apoptosis and autophagy were performed. Caspase inhibition was effective in alleviating the compression-induced pathohistology of muscle. The increases in caspase-3 protease activity, TUNEL index, apoptotic DNA fragmentation and pro-apoptotic factors (Bax, p53 and EndoG) and the decreases in anti-apoptotic factors (XIAP and HSP70) observed in compressed muscle of DMSO-treated animals were not found in animals treated with caspase inhibitor. The mRNA content of autophagic factors (Beclin-1, Atg5 and Atg12) and the protein content of LC3, FoxO3 and phospho-FoxO3 that were down-regulated in compressed muscle of DMSO-treated animals were all maintained at their basal level in the caspase inhibitor treated animals. Our data provide evidence that caspase inhibition attenuates compression-induced muscle apoptosis and maintains the basal autophagy level. These findings demonstrate that pharmacological inhibition of caspase/apoptosis is effective in alleviating muscle damage as induced by prolonged compression.

Proteasome inhibition alleviates prolonged moderate compression-induced muscle pathology

BACKGROUND

The molecular mechanism initiating deep pressure ulcer remains to be elucidated. The present study tested the hypothesis that the ubiquitin proteasome system is involved in the signalling mechanism in pressure-induced deep tissue injury.

METHODS

Adult Sprague Dawley rats were subjected to an experimental compression model to induce deep tissue injury. The tibialis region of the right hind limb was subjected to 100 mmHg of static pressure for six hours on each of two consecutive days. The compression pressure was continuously monitored by a three-axial force transducer within the compression indentor. The left hind limb served as the intra-animal control. Muscle tissues underneath the compressed region were collected and used for analyses.

RESULTS

Our results demonstrated that the activity of 20S proteasome and the protein abundance of ubiquitin and MAFbx/atrogin-1 were elevated in conjunction with pathohistological changes in the compressed muscle, as compared to control muscle. The administration of the proteasome inhibitor MG132 was found to be effective in ameliorating the development of pathological histology in compressed muscle. Furthermore, 20S proteasome activity and protein content of ubiquitin and MAFbx/atrogin-1 showed no apparent increase in the MG132-treated muscle following compression.

CONCLUSION

Our data suggest that the ubiquitin proteasome system may play a role in the pathogenesis of pressure-induced deep tissue injury.

Opposing responses of apoptosis and autophagy to moderate compression in skeletal muscle

AIM

The molecular mechanism that contributes to the pathogenesis of deep pressure ulcer remains to be elucidated. This study tested the hypotheses that: (1) apoptosis and autophagy are activated in compression-induced muscle pathology and (2) apoptotic and autophagic changes precede pathohistological changes in skeletal muscle in response to prolonged moderate compression.

METHODS

  Adult Sprague-Dawley rats were subjected to an experimental model of pressure-induced deep tissue injury. Static pressure of 100 mmHg was applied to an area of 1.5 cm(2) over the mid-tibialis region of right limb of rats for one single session of 6-h compression (1D) or two sessions of 6-h compression over two consecutive days with rats sacrificed one day (2D) or immediately after (2D-IM) the compression. The left uncompressed limb served as the intra-animal control. Muscle tissues underneath compression region were collected for analysis.

RESULTS

Our histological analysis indicated that pathohistological characteristics including rounding contour of myofibres and massive nuclei accumulation were apparently demonstrated in muscles of 2D and 2D-IM. In contrast, these pathohistological changes were generally not found in muscle following 1D. Apoptotic DNA fragmentation, terminal dUTP nick-end labelling index and caspase-3 protease activity were significantly elevated in compressed muscles of all groups. Caspase-9 enzymatic activity was found to be significantly increased in compressed muscles of 2D and 2D-IM whereas increase in caspase-8 activity was exclusively found in compressed muscle of 1D. According to our immunoblot analysis, FoxO3 was significantly reduced in compressed muscles of all groups whereas Beclin-1 was decreased only in 2D. LC3-I was significantly reduced in compressed muscles of all groups while LC3-II was decreased in 2D and 1D. No significant differences were found in the protein abundance of Akt and phospho-Akt in muscles among all groups.

CONCLUSION

These data demonstrate the opposing responses of apoptosis and autophagy to moderate compression in muscle. Moreover, our findings suggest that cellular changes in apoptosis and autophagy have already taken place in the very early stage in which apparent histopathology has yet to develop in the process of compression-induced muscle pathology.

Biomechanics of Pressure Ulcer in Body Tissues Interacting with External Forces during Locomotion

Forces acting on the body via various external surfaces during locomotion are needed to support the body under gravity, control posture, and overcome inertia. Examples include the forces acting on the body via the seating surfaces during wheelchair propulsion, the forces acting on the plantar foot tissues via the insole during gait, and the forces acting on the residual-limb tissues via the prosthetic socket during various movement activities. Excessive exposure to unwarranted stresses at the body-support interfaces could lead to tissue breakdowns commonly known as pressure ulcers, often presented as deep-tissue injuries around bony prominences or as surface damage on the skin. In this article, we review the literature that describes how the involved tissues respond to epidermal loading, taking into account both experimental and computational findings from in vivo and in vitro studies. In particular, we discuss related literature about internal tissue deformation and stresses, microcirculatory responses, and histological, cellular, and molecular observations.

Evaluation of the effect of trunk tilt on compressive soft tissue deformations under the ischial tuberosities using weight-bearing MRI

BACKGROUND

Deep tissue injury is the new acceptable term for deep pressure ulcers. Deep tissue injury of the buttocks is typically caused by sustained soft tissue deformations under the ischial tuberosities. Wheelchair users are at high risk, and although usually laterally tilted, the effect of tilts on tissue deformations is unknown. This has brought us to investigate buttocks tissue compressive deformations between the ischial tuberosities and skin during sitting in various body tilts, utilizing weight-bearing Magnetic resonance imaging (MRI).

METHODS

Ten healthy volunteers underwent sitting MRI, in six postures including neutral with/without weight-bearing, 10 degrees and 20 degrees lateral-tilts, and 20 degrees and 40 degrees anterior tilts. Studies utilized a coronal T1-weighted sequence. Images were evaluated for thickness of tissues between the skin and the lowest point of the ischial tuberosity, of fat between the skin and the gluteus muscle and of muscle between the ischial tuberosity and fat. Measurements in weight-bearing positions were compared to the non-weight-bearing for calculation of compressive tissue deformations in each trunk tilt. Statistical analysis was obtained utilizing multiple pairwise t-tests with Bonferroni corrections.

FINDINGS

Muscle and soft tissue compressive deformations, from highest to lowest, were 20 degrees -lateral-tilt (87%, 72%), lateral-10 degrees (85%, 70%), anterior-20 degrees (79%, 67%), anterior-40 degrees (74%, 64%), and neutral (72%, 59%). For the fat, highest was anterior-tilts (42%), followed by lateral-20 degrees -tilt (41%), lateral-10 degrees (39%) and neutral (35%).

INTERPRETATION

For lateral tilts, the higher the angle was, the higher the compressive deformation was. However, the most profound change in compressive deformation occurred at the small angle tilts.

Deep tissue injury rat model for pressure ulcer research on spinal cord injury

Many rat/mouse pressure ulcer (PU) models have been developed to test different hypotheses to gain deeper understanding of various causative risk factors, the progress of PUs, and assessing effectiveness of potential treatment modalities. The recently emphasized deep tissue injury (DTI) mechanism for PU formation has received increased attention and several studies reported findings on newly developed DTI animal models. However, concerns exist for the clinical relevance and validity of these models, especially when the majority of the reported rat PU/DTI models were not built upon SCI animals and many of the DTI research did not simulate well the clinical observation. In this study, we propose a rat PU and DTI model which is more clinically relevant by including chronic SCI condition into the rat PU model and to simulate the role of bony prominence in DTI formation by using an implant on the bone-tissue interface. Histological data and imaging findings confirmed that the condition of chronic SCI had significant effect on pressure induced tissue injury in a rat PU model and the including a simulated bony prominence in rat DTI model resulted in significantly greater injury in deep muscle tissue. Further integration of the SCI condition and the simulated bony prominence would result a rat PU/DTI model which can simulate even more accurately the clinical phenomenon and yield more clinically relevant findings.