Comparison of Six Methods for the Assessment of Ischemia-Reperfusion Injury in Skeletal Muscle following Composite Tissue Allotransplantation

Methods of ex vivo analysis of tissue status in vascularized composite allografts

Vascularized composite allotransplantation can improve quality of life and restore functionality. However, the complex tissue composition of vascularized composite allografts (VCAs) presents unique clinical challenges that increase the likelihood of transplant rejection. Under prolonged static cold storage, highly damage-susceptible tissues such as muscle and nerve undergo irreversible degradation that may render allografts non-functional. Skin-containing VCA elicits an immunogenic response that increases the risk of recipient allograft rejection. The development of quantitative metrics to evaluate VCAs prior to and following transplantation are key to mitigating allograft rejection. Correspondingly, a broad range of bioanalytical methods have emerged to assess the progression of VCA rejection and characterize transplantation outcomes. To consolidate the current range of relevant technologies and expand on potential for development, methods to evaluate ex vivo VCA status are herein reviewed and comparatively assessed. The use of implantable physiological status monitoring biochips, non-invasive bioimpedance monitoring to assess edema, and deep learning algorithms to fuse disparate inputs to stratify VCAs are identified.

Methane attenuates lung ischemia-reperfusion injury via regulating PI3K-AKT-NFκB signaling pathway

Objective: This study aims to investigate the protective effects and possible mechanism of methane-rich saline (MS) on lung ischemia-reperfusion injury (LIRI) in rats.Methods: MS (2 ml/kg and 20 ml/kg) was injected intraperitoneally in rats after LIRI. Lung injury was assayed by Hematoxylin-eosin (HE) staining and wet-to-dry weight (W/D). The cells in the bronchoalveolar lavage fluid (BALF) and blood were counted. Oxidative stress was examined by the level of malondialdehyde (MDA) and superoxide dismutase (SOD). Inflammatory factors including tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β), and interleukin-10 (IL-10) were determined by ELISA. Lung tissue apoptosis was detected by TUNEL staining and western blotting of Bcl-2, Bax, and caspase-3. The expressions of IкBα, p38, PI3K, AKT, and NF-κB were analyzed with Western blotting.Results: MS effectively decreased the lung W/D ratio as well as the lung pathological damage and reduced the localized infiltration of inflammatory cells. Methane suppressed the expression of the PI3K-AKT-NFκB signaling pathway during the lung IR injury, which inhibited the activation of NF-kB and decreased the level of inflammatory cytokines, such as TNF-α, IL-1β, and IL-10. Moreover, we found that MS treatment relieved reactive oxygen species (ROS) damage by downregulating MDA and upregulating SOD. MS treatment also regulated apoptosis-related proteins, such as Bcl-2, Bax, and caspase-3.Conclusions: MS could repair LIRI and reduce the release of oxidative stress, inflammatory cytokines, and cell apoptosis via the PI3K-AKT-NFκB signaling pathway, which may provide a novel and promising strategy for the treatment of LIRI.

Twenty-Four-Hour Ex Vivo Perfusion with Acellular Solution Enables Successful Replantation of Porcine Forelimbs

BACKGROUND

A critical barrier to successful limb replantation and allotransplantation is the maximum allowable limb ischemia time of 4 to 6 hours. The current gold standard is to preserve amputated limbs on an ice slurry. Experimental machine perfusion has yielded promising results as an alternative. In particular, hypothermic acellular perfusion has enabled preservation of amputated limbs for up to 12 hours thus far.

METHODS

Amputated forelimbs of Yorkshire pigs were preserved on static cold storage at 4°C for 4 hours (static cold storage group) or perfused at 8°C for 24 hours (perfusion group) with oxygenated modified STEEN Solution perfusate before replantation. Animals were followed up for 7 days after replantation.

RESULTS

Eight animals underwent replantation (cold storage group, n = 4; perfusion group, n = 4). Seventy-five and 100 percent of animals in the static cold storage and perfusion groups survived for 7 days, respectively. Glycogen and adenosine triphosphate remained stable throughout perfusion. Heart and respiratory rate after replantation were increased in the static cold storage group. There was increased damage in muscle biopsy specimens obtained from animals in the static cold storage group after 7 days when compared with those from animals in the perfusion group.

CONCLUSIONS

Hypothermic acellular ex vivo perfusion of limbs for up to 24 hours enables tissue preservation comparable to that obtained with conventional static cold storage for 4 hours and may reduce muscle damage and systemic reactions on limb replantation. Translation to human limbs may help improve limb replantation and allotransplantation outcomes.

Pretreatment of vitamin D3 ameliorates lung and muscle injury induced by reperfusion of bilateral femoral vessels in a rat model

BACKGROUND

Peripheral arterial occlusive disease (PAOD) is a challenge in peripheral vascular disease. Clinical observations show reperfusion of occluded vessels may cause compartment syndrome or remote organ injury. Less well known is the role of vitamin D3 in tissue injury; therefore, we attempted to determine whether vitamin D3 could alleviate local and remote organ injury induced by reperfusion of occluded vessels in animal models.

METHODS

Twenty-four male Sprague-Dawley rats were randomized into four groups: saline + sham, saline + I/R, vitamin D3 + sham, and vitamin D3 + I/R group. After pretreatment for 5 d, the animals designed to I/R injury were subjected to 3 h of ischemia induced by bilateral femoral arteries clamp, followed by reperfusion of the vessels for 3 h on d 6. Left lung and left anterior tibial muscle tissue were harvested for wet/dry weight ratio and histopathologic analysis. Blood was collected for analysis of urea nitrogen (BUN), creatinine (Cr), aspartate aminotransferase (AST), alanine aminotransferase (ALT), tumor necrosis factor-alpha (TNF-α), interleukin-6 (IL-6), ionized calcium levels, and heme oxygenase-1 (HO-1).

RESULTS

Compared with the saline + sham group, there was a significant increase in plasma IL-6 level in both saline + I/R and vitamin D3 + I/R groups and muscle, lung wet/dry weight ratio in the saline + I/R group (P < 0.05). Compared with the saline + I/R group, there was a significant decrease in plasma IL-6 level, muscle and lung wet/dry weight ratio in both vitamin D3 + sham and vitamin D3 + I/R groups, and leukocyte HO-1 expression in vitamin D3 + sham group (P < 0.05). Compared with the vitamin D3 + sham group, there was a significant increase in plasma IL-6 levels in the vitamin D3 + I/R group, and leukocyte HO-1 expression in vitamin D3 + sham group (P < 0.05). BUN, Cr, AST, ALT, TNF-α, ionized calcium levels did not differ significantly among the groups.

CONCLUSIONS

Pretreatment of vitamin D3 ameliorates the systemic IL-6 levels, lung and muscle injury induced by ischemia followed by reperfusion of bilateral occluded vessels in a rat model.

Sequential limb ischemia demonstrates remote postconditioning protection of murine skeletal muscle

BACKGROUND

Ischemic postconditioning, the process of exposing tissues to brief cycles of ischemia-reperfusion after critical ischemia, can mitigate local ischemia-reperfusion injury. Remote protection of skeletal muscle has never been demonstrated in postconditioning models of ischemia-reperfusion injury.

METHODS

Mice were subjected to 2 hours of ipsilateral hind limb ischemia followed by reperfusion. Contralateral limb ischemia was subsequently induced for 2 hours after either 0 (n = 6), 20 (n = 6), or 120 (n = 5) minutes of ipsilateral limb reperfusion. These groups were compared with animals subjected to bilateral simultaneous injury (n = 8) and sham animals that did not undergo ischemia (n = 6). The gastrocnemius muscles were harvested for histologic evaluation, and injury was recorded as the percentage of injured fibers.

RESULTS

The first limbs undergoing injury in the 20-minute interval group had a 59 percent injury reduction compared with contralateral limbs (16.0 +/- 2.4 percent versus 39.5 +/- 6.5 percent) after 24 hours of reperfusion and 62 percent reduction after 48 hours (24.4 +/- 3.0 percent versus 63.6 +/- 5.5 percent). In animals with no interval or a 120-minute interval between the onset of limb ischemia, there was no significant difference in injury between hind limbs. The injury in these groups was similar to that in hind limbs subjected to simultaneous bilateral ischemia.

CONCLUSIONS

A 20-minute reperfusion interval between hind limb ischemia significantly protects against injury in the initially ischemic limb, while similar injury is observed with simultaneous ischemia or an interval of 120 minutes. This study demonstrates remote postconditioning of skeletal muscle and may lead to the development of post hoc therapies.

Enoxaparin does not ameliorate limb ischemia-reperfusion injury

OBJECTIVE

Since low molecular weight heparin has greater bioavailability and sustained serum levels in vivo than unfractionated heparin, it has been used to supplant unfractionated heparin to achieve therapeutic anticoagulation in humans. These studies were designed to determine whether treatment with enoxaparin could protect murine skeletal muscle from ischemia reperfusion injury.

METHODS

C57BL6 mice were divided into four groups. Sham control animals underwent 90 min of anesthesia alone. All other groups underwent 90 min of unilateral hindlimb ischemia. At the onset of reperfusion, animals received either normal saline (control and saline) or 4 mg/kg of enoxaparin subcutaneously twice daily. Groups were followed for 24 or 48 h reperfusion. Hindlimb skeletal muscle blood flow was measured by laser Doppler, and muscle was removed for histological and protein analysis. Tissue thrombosis was evaluated by thrombin antithrombin III (TAT III), local inflammation by measurement of proinflammatory cytokines (macrophage inflammatory protein-2: MIP-2, monocyte chemoattractant protein-1: MCP-1), and neutrophil infiltration by myeloperoxidase (MPO) using enzyme-linked immunosorbent assay. Plasma levels of Factor Xa were measured during reperfusion to confirm therapeutic levels of anticoagulation. Comparisons were calculated using analysis of variance.

RESULTS

At 24 h reperfusion, there was increased expression of MIP-2, MCP-1, MPO, and TAT III in saline and enoxaparin treated mice compared with control (*P < 0.05). By 48 h reperfusion, all parameters measured remained greater than control except for the enoxaparin treated mice whose TAT III levels were significantly less than untreated mice (P < 0.05). Despite documented therapeutic anticoagulation and decreased levels of markers of thrombosis in enoxaparin treated mice, there was no difference in tissue cytokines, inflammatory markers, degree of muscle fiber injury (31% +/- 8% versus 30% +/- 5%) or muscle flow between ischemia-reperfusion groups (2447 +/- 141 versus 2475 +/- 74 flux units) at 48 h reperfusion.

CONCLUSIONS

Post hoc administration of enoxaparin did not affect local tissue thrombosis, inflammatory markers, or muscle necrosis. This suggests that despite its potent in vivo activity, enoxaparin did not modulate skeletal muscle injury, thrombosis, or inflammatory following ischemia reperfusion. enoxaparin may not be useful in mediating skeletal muscle injury when administered in a clinically relevant scenario.

Ischemic preconditioning of skeletal muscle mitigates remote injury and mortality

BACKGROUND

Ischemic preconditioning (IPC) mitigates ischemia-reperfusion (I/R) injury in experimental models. However, the clinical significance of this protection has been unclear and a mortality reduction has not been previously reported in noncardiac models. This study examined the local and remote protection afforded by skeletal muscle IPC and sought to determine the significance of this protection on mortality.

METHODS

Mice subjected to 2 h hindlimb ischemia/24 h reperfusion (standard I/R injury) were compared with those undergoing a regimen of two 20-min cycles of IPC followed by standard I/R injury. Local injury was assessed via gastrocnemius histology, and remote injury was evaluated via intestinal histology and pulmonary neutrophil infiltration (n = 7). Mortality was compared in parallel groups for 1 week (n = 6). Groups were analyzed using an unpaired Student's t-test for gastrocnemius and pulmonary injury, and a Mann-Whitney rank sum test for intestinal injury. Mortality differences were interpreted through a hazard ratio.

RESULTS

Significant protection was observed in preconditioned animals. There was a 35% local injury reduction in skeletal muscle (71.2% versus 46.0%, P < 0.01), a 50% reduction in remote intestinal injury (2.3 versus 1.1, P < 0.01), and a 43% reduction in remote pulmonary injury (14.9 versus 8.5, P < 0.01) compared with standard injury controls. Preconditioned animals were also significantly protected from mortality, demonstrating a 66.7% survival at 1 wk compared with 0% survival after standard injury alone (hazard ratio 0.20, 95% CI: 0.02-0.59).

CONCLUSIONS

We have developed a murine model of IPC that demonstrates local and remote protection against I/R injury, and exhibits significant mortality reduction. This model demonstrates the powerful effect of IPC on local and remote tissues and will facilitate further study of potential mechanisms and therapies.

Development of reproducible histologic injury severity scores: skeletal muscle reperfusion injury

BACKGROUND

Ischemia-reperfusion injury of skeletal muscle is a common clinical and experimental problem. To date, there has been no uniform and reproducible method to assess the extent of histologic injury. In this study, we developed a novel statistical methodology for evaluating injury in individual myocytes and 3 distinct methods for the interpretation of this data.

METHODS

C57/BL6 mice underwent 2 h of hindlimb ischemia followed by reperfusion for 3 (n = 11), 24 (n = 12), or 48 (n = 10) h. The gastrocnemius muscles were harvested, stained, and evaluated under microscopy. Standardized criteria were applied to score individual myocytes as healthy or injured, and injury score was expressed as injured fibers/total fibers %. Three methods of analyzing myocyte data were developed and evaluated with statistical Block-Random Sampling to determine the number of counted fibers required to represent accurately the total injury. The Full-Frame Counting, Fourfold Divided Counting, and Stratified Individual Counting methods differ in the random order in which fibers or microscopic fields are scored.

RESULTS

The 3 methods were found to be statistically sound at all experimental time points. Using the Full-Frame, Fourfold, and Stratified methods, the maximum number of required fibers at all time points was 600, 300, and 100, respectively, to obtain an estimation of injury with a 95% confidence interval.

CONCLUSIONS

These criteria and statistical methods for histologic evaluation of ischemia-reperfusion injury in skeletal muscle are accurate and reproducible. The Fourfold method is the most practical and technically efficient method of assessing injury. Such a quantitative, direct assessment of injury is important and will be useful for future studies.

Local administration of the Poly ADP-Ribose Polymerase (PARP) inhibitor, PJ34 during hindlimb ischemia modulates skeletal muscle reperfusion injury

BACKGROUND

PARP stabilizes DNA and modulates inflammation in murine models of sepsis, stroke, and myocardial infarction. Previous studies have shown that systemic PARP inhibition before hindlimb ischemia preserves tissue viability and modulates cytokine synthesis during reperfusion. The purpose of this study was to determine whether intra-muscular (IM) administration of PJ34, a potent inhibitor of PARP, after the onset of acute hindlimb ischemia (post hoc) modulates the local production of inflammatory mediators during ischemia/reperfusion (I/R).

MATERIALS AND METHODS

The control tension tourniquet was used to establish unilateral hindlimb ischemia in mice for 3 h followed by 48 h I/R. The treatment group (PJ) received IM PJ34 (10 mg/kg) in the affected hindlimb 90 min into ischemia whereas the control group (UN) received IM saline (150 uL) at the same time point. Skeletal muscle viability (MTT mitochondrial activity), local neutrophil chemoattractant protein (KC), Interleukin 6 (IL-6), Interleukin 1beta (IL-1beta), and Myeloperoxidase (MPO) levels were measured in protein extracts after the reperfusion period.

RESULTS

Muscle viability (102% +/- 10 PJ, 78% +/- 4 UN, P = 0.04), IL-B (21.1 +/- 1.3 PJ, 15.5 +/- 1.0 UN, P = 0.02), and IL-6 levels (16.3 +/- 1.2 PJ, 10.9 +/- 1.4 UN, P = 0.04) after 48 I/R were significantly higher in PJ. KC and MPO levels were higher in PJ but neither reached statistical significance.

CONCLUSIONS

Post hoc PJ34 therapy appears to protect skeletal muscle from I/R injury despite increased levels of local cytokines. These initial findings support the role of local post hoc therapy in the treatment of acute limb threatening ischemia suggesting that further study of this novel therapy is warranted.