The osteogenic response to distant skeletal injury

We tested the hypothesis that when one bone of the skeleton is injured, others experience an osteogenic response. Although similar or related phenomena have been observed previously, the purposes of the study were to determine if this response was reproducible, to characterize it in terms of its magnitude and duration, and to show how it is related to the type of injury sustained. To obtain this information, a model was used in which an intramedullary nail was implanted in the femur and a standard closed fracture was subsequently produced. The osteogenic response was measured by histomorphometry. Eight-four nine-week-old male Sprague-Dawley rats were divided into seven groups of twelve animals each. Groups I and II consisted of control animals in which no injury was produced. In Group-III rats, cortical drilling of the intercondylar notch and piriformis fossa of the right femur was performed, without intramedullary nailing. In Groups IV through VII, half of each group received intramedullary nails only, and in the other half intramedullary nailing was done and a closed transverse diaphyseal fracture was produced. With two different fluorochrome labels, rates of mineral apposition were measured in the left and right tibiae of all animals. The labeling periods differed in each group and were designed to determine when the peak response occurred, how long it lasted, and whether aging during the course of the experiment affected the response.(ABSTRACT TRUNCATED AT 250 WORDS)     

The adaptive intestinal response to massive enterectomy is preserved in c-SRC-deficient mice.

BACKGROUND/PURPOSE: The Src family of protein tyrosine kinases has been implicated in the downstream mitogenic signaling of several ligands including epidermal growth factor (EGF). Because EGF likely plays a role in adaptation after massive small bowel resection (SBR), we tested the hypothesis that c-src is required for this important response. METHODS: A 50% proximal SBR or sham operation (bowel transection or reanastomosis alone) was performed on c-src-deficient (n = 14) or wild-type (C57bl/6) mice (n = 20). The ileum was harvested on postoperative day 3 and adaptive parameters determined as changes in ileal wet weight, protein and DNA content, proliferation index, villus height, and crypt depth. Comparisons were done using analysis of variance (ANOVA), and a Pvalue less than .05 was considered significant. Values are presented as mean +/- SEM. RESULTS: The activity of c-src was increased in the ileum of wild-type mice after SBR but remained unchanged in c-src-deficient mice. Despite this lack of increase, adaptation occurred after SBR in the c-src-deficient mice as demonstrated by increased ileal wet weight, protein and DNA content, proliferation index, villus height, and crypt depth similar to wild-type mice. CONCLUSIONS: The adaptive response of the intestine to massive SBR is preserved despite reduced activity of the c-src protein. The mitogenic signaling that characterizes intestinal adaptation and is associated with receptor activation by EGF or other growth factors probably occurs by mechanisms independent of c-src protein tyrosine kinase.     

MMP9 regulates the cellular response to inflammation after skeletal injury

Like other tissue injuries, bone fracture triggers an inflammatory response, which plays an important role in skeletal repair. Inflammation is believed to have both positive and negative effects on bone repair, but the underlying cellular mechanisms are not well understood. To assess the role of inflammation on skeletal cell differentiation, we used mouse models of fracture repair that stimulate either intramembranous or endochondral ossification. In the first model, fractures are rigidly stabilized leading to direct bone formation, while in the second model, fracture instability causes cartilage and bone formation. We compared the inflammatory response in these two mechanical environments and found changes in the expression patterns of inflammatory genes and in the recruitment of inflammatory cells and osteoclasts. These results suggested that the inflammatory response could influence skeletal cell differentiation after fracture. We then exploited matrix metalloproteinase 9 (MMP9) that is expressed in inflammatory cells and osteoclasts, and which we previously showed is a potential regulator of cell fate decisions during fracture repair. Mmp9^?/? mice heal stabilized fractures via endochondral ossification, while wild type mice heal via intramembranous ossification. In parallel, we observed increases in macrophages and T cells in the callus of Mmp9^?/? compared to wild type mice. To assess the link between the profile of inflammatory cells and skeletal cell fate functionally, we transplanted Mmp9^?/? mice with wild type bone marrow, to reconstitute a wild type hematopoietic lineage in interaction with the Mmp9^?/? stroma and periosteum. Following transplantation, Mmp9^?/? mice healed stabilized fractures via intramembranous ossification and exhibited a normal profile of inflammatory cells. Moreover, Mmp9^?/? periosteal grafts healed via intramembranous ossification in wild type hosts, but healed via endochondral ossification in Mmp9^?/? hosts. We observed that macrophages accumulated at the periosteal surface in Mmp9^?/? mice, suggesting that cell differentiation in the periosteum is influenced by factors such as BMP2 that are produced locally by inflammatory cells. Taken together, these results show that MMP9 mediates indirect effects on skeletal cell differentiation by regulating the inflammatory response and the distribution of inflammatory cells, leading to the local regulation of periosteal cell differentiation.     

Monitoring the response to injury.

Tissue trauma leads to a severity-dependent activation of plasma and cellular systems. This response can be recorded by determining parameters which represent the activation state of these systems. In severely injured patients with multiple trauma three out of 14 parameters measured at the time of admission proved to be indicators of subsequent septic complications with a high degree of accuracy: Fibrinopeptide A (FPA--the first split product of fibrinogen), the C3 split product C3a, and the elastase-alpha 1 proteinase inhibitor-complex (E alpha 1 PI). In a second series of multiple-injured patients with femoral fractures who did not develop clinical sepsis (N = 25) these parameters were measured continuously to evaluate the influence of injury severity and of therapeutic strategy on the further course. We found a strong correlation between injury severity (ISS) and the degree of activation. The signs of activation decreased rapidly following immediate operative fixation, and remained elevated or even increased after primary femoral traction and secondary stabilization. The operative procedure did not cause any additional activation. Complications such as infection or the formation of haematomas were reflected by raised parameter levels.     

Circulating angiogenic biomolecules at rest and in response to upper-limb exercise in individuals with spinal cord injury

Abstract

Objective

Individuals with spinal cord injury (SCI) show structural and functional vascular maladaptations and muscle loss in their lower limbs. Angiogenic biomolecules play important roles in physiological and pathological angiogenesis, and are implicated in the maintenance of muscle mass. This study examined the responses of angiogenic molecules during upper-limb aerobic exercise in patients with SCI and in able-bodied (AB) individuals.

Methods

Eight SCI patients with thoracic lesions (T₆–T₁₂, ASIA A) and eight AB individuals performed an arm-cranking exercise for 30 minutes at 60% of their VO_2max. Plasma concentrations of vascular endothelial growth factor (VEGF-A₁₆₅), VEGF receptor 1 (sVEGFr-1), VEGF receptor 2 (sVEGFr-2), metalloproteinase 2 (MMP-2), and endostatin were measured at rest, after exercise, and at 1.5 and 3.0 hours during recovery.

Results

The two-way analysis of variance showed non-significant main effects of “group” and significant main effects of “time/exercise” for all angiogenic biomolecules examined (P < 0.01–0.001). The arm-cranking exercise significantly increased plasma concentrations of VEGF, sVEGFr-1, sVEGFr-2, MMP-2, and endostatin in both groups (P < 0.001–0.01). The magnitude of the increase was similar in both patients with SCI and AB individuals, as shown by the non-significant group × time interaction for all angiogenic parameters.

Conclusions

Upper-limb exercise (arm-cranking for 30 minutes at 60% of VO_2max) is a sufficient stimulus to trigger a coordinated circulating angiogenic response in patients with SCI. The response of angiogenic molecules to upper-limb aerobic exercise in SCI appears relatively similar to that observed in AB individuals.     

Circulating angiogenic biomolecules at rest and in response to upper-limb exercise in individuals with spinal cord injury

Objective

Individuals with spinal cord injury (SCI) show structural and functional vascular maladaptations and muscle loss in their lower limbs. Angiogenic biomolecules play important roles in physiological and pathological angiogenesis, and are implicated in the maintenance of muscle mass. This study examined the responses of angiogenic molecules during upper-limb aerobic exercise in patients with SCI and in able-bodied (AB) individuals.

Methods

Eight SCI patients with thoracic lesions (T₆–T₁₂, ASIA A) and eight AB individuals performed an arm-cranking exercise for 30 minutes at 60% of their VO_2max. Plasma concentrations of vascular endothelial growth factor (VEGF-A₁₆₅), VEGF receptor 1 (sVEGFr-1), VEGF receptor 2 (sVEGFr-2), metalloproteinase 2 (MMP-2), and endostatin were measured at rest, after exercise, and at 1.5 and 3.0 hours during recovery.

Results

The two-way analysis of variance showed non-significant main effects of “group” and significant main effects of “time/exercise” for all angiogenic biomolecules examined (P < 0.01–0.001). The arm-cranking exercise significantly increased plasma concentrations of VEGF, sVEGFr-1, sVEGFr-2, MMP-2, and endostatin in both groups (P < 0.001–0.01). The magnitude of the increase was similar in both patients with SCI and AB individuals, as shown by the non-significant group × time interaction for all angiogenic parameters.

Conclusions

Upper-limb exercise (arm-cranking for 30 minutes at 60% of VO_2max) is a sufficient stimulus to trigger a coordinated circulating angiogenic response in patients with SCI. The response of angiogenic molecules to upper-limb aerobic exercise in SCI appears relatively similar to that observed in AB individuals.     

Humoral response to SARS-CoV-2 is well preserved and symptom dependent in kidney transplant recipients

Data on the immune response to SARS-CoV-2 in kidney transplant recipients are scarce. Thus, we conducted a single-center observational study to assess the anti-SARS-CoV-2 IgG seroprevalence in outpatient kidney transplant recipients (KTR; n = 1037) and healthcare workers (HCW; n = 512) during the second wave of the COVID-19 pandemic in fall 2020 and evaluated the clinical variables affecting antibody levels. Antibodies against S1 and S2 subunit of SARS-CoV-2 were evaluated using immunochemiluminescent assay (cut off 9.5 AU/ml, sensitivity of 91.2% and specificity of 90.2%). Anti-SARS-CoV-2 IgG seroprevalence was lower in KTR than in HCW (7% vs. 11.9%, p = .001). Kidney transplant recipients with SARS-CoV-2 infection were younger (p = .001) and received CNI-based immunosuppression more frequently (p = .029) than seronegative KTR. Anti-SARS-CoV-2 IgG positive symptomatic KTR had a higher BMI (p = .04) than asymptomatic KTR. Interestingly, anti-SARS-CoV-2 IgG levels were higher in KTR than in HCW (median 31 AU/ml, IQR 17–84 vs. median 15 AU/ml, IQR 11–39, p < .001). The presence of moderate to severe symptoms in KTR was found to be the only independent factor affecting IgG levels (Beta coefficient = 41.99, 95% CI 9.92–74.06, p = .011) in the multivariable model. In conclusion, KTR exhibit a well-preserved symptom-dependent humoral response to SARS-CoV-2 infection.     

The systemic angiogenic response during bone healing

Introduction  Angiogenesis is known to be a critical and closely regulated step during bone formation and fracture healing driven by a complex interaction of various cytokines. Delays in bone healing or even nonunion might therefore be associated with altered concentrations of specific angiogenic factors. These alterations might in turn be reflected by changes in serum concentrations. Method  To determine physiological time courses of angiogenic cytokines during fracture healing as well as possible changes associated with failed consolidation, we prospectively collected serum samples from patients who had sustained surgical treatment for a long bone fracture. Fifteen patients without fracture healing 4 months after surgery (nonunion group) were matched to a collective of 15 patients with successful healing (union group). Serum concentrations of angiogenin (ANG), angiopoietin 2 (Ang-2), basic fibroblast growth factor (bFGF), platelet derived growth factor AB (PDGF-AB), pleiotrophin (PTN) and vascular endothelial growth factor (VEGF) were measured using enzyme linked immunosorbent assays over a period of 24 weeks. Results  Compared to reference values of healthy uninjured controls serum concentrations of VEGF, bFGF and PDGF were increased in both groups. Peak concentrations of these cytokines were reached during early fracture healing. Serum concentrations of bFGF and PDGF-AB were significantly higher in the union group at 2 and 4 weeks after the injury when compared to the nonunion group. Serum concentrations of ANG and Ang-2 declined steadily from the first measurement in normal healing fractures, while no significant changes over time could be detected for serum concentrations of these factures in nonunion patients. PTN serum levels increased asymptotically over the entire investigation in timely fracture healing while no such increase could be detected during delayed healing. Conclusion  We conclude that fracture healing in human subjects is accompanied by distinct changes in systemic levels of specific angiogenic factors. Significant alterations of these physiologic changes in patients developing a fracture nonunion over time could be detected as early as 2 (bFGF) and 4 weeks (PDGF-AB) after initial trauma surgery. Authors Stefan Weiss and Gerald Zimmermann contributed equally to this work.     

Cell-mediated immune response is better preserved by laparoscopy than laparotomy

BACKGROUND: This study compares the effects of carbon dioxide pneumoperitoneum versus laparotomy on cellular-mediated immune response in a murine model. METHODS: Sixty-eight female C3H/He mice were sensitized to keyhole limpet hemocyanin (KLH) and to a mouse mammary carcinoma cell line (MC2) before surgery. Animals were randomized into 4 groups: group I, anesthesia (control); group II, pneumoperitoneum with carbon dioxide; group III, extraperitoneal wound; group IV, laparotomy. All animals were challenged subsequently with KLH and MC2 tumor cells. Delayed-type hypersensitivity skin reaction (DTH) to KLH was measured on postoperative days (PODs) 1, 2, 4, and 5. Tumor growth was assessed weekly as an indicator of postoperative cellular immune response. RESULTS: Compared with preoperative values, postoperative DTH skin reactions were significantly less for all PODs in groups III and IV (P < .05), on POD 1 and 4 in group II (P < .05) and POD 4 for group I (P < .05). Group IV showed significantly fewer DTH skin reactions for all PODs compared with groups I and II (P < .05) and all PODs except on day 2 compared with group III (P < .05). Tumor growth was significantly increased at postoperative week 2 (n = 3/17 mice) and 3 (n = 4/17 mice) in group IV, when compared with groups I and II (P < .05). CONCLUSIONS: Cellular immunity is preserved after carbon dioxide pneumoperitoneum compared with extraperitoneal incisions and laparotomy as measured by DTH and the ability to reject an immunogenictumor.     

Endothelial response to venous injury.

This investigation characterized venous endothelial healing after surgical manipulation. Procedures were performed on jugular and femoral veins in 21 mongrel dogs without systemic anticoagulation. Veins were harvested at varying intervals and vessel structure evaluated with light, transmission, and scanning electron microscopy. Veins that were mobilized or stripped of adventitia demonstrated 25% to 50% endothelial loss at one hour. Endothelial damage was rapidly repaired with complete healing observed in some veins at 48 hours. Tourniquets and clamps resulted in prominent medial and endothelial injury at occlusion sites. Eighteen of 24 transected veins remained patent for the study period. Endothelial healing was unaffected by tension at anastomoses. These observations confirm that venous endothelium receives nutrition by luminal diffusion. The healing process of venous anastomoses is characterized by an early fibrin sleeve sealing the anastomotic site; endothelial bridging of defects can be noticeably delayed by excessive fibrin deposition.     

The nonspecific inflammatory response to injury

Purpose

The role of the nonspecific inflammatory response in causing injury related to surgery has become better understood over the last decade. There are complex interactions between neutrophils, cytokines and nitric oxide metabolites that may cause organ injury following surgery. The purpose of this review is to summarize some of the processes causing injury through these nonspecific pathways.

Methods

A review of the medical and anaesthetic literature related to inflammation, neutrophils and pro-inflammatory cytokines were performed using Medline. Bibliographies of relevant articles were searched and additional articles were then selected and reviewed.

Results

Pro-inflammatory cytokines, such as tumour necrosis factor, are released in response to a variety of noxious stimuli (e.g. burns, sepsis, or CABG surgery). These cytokines cause activation of neutrophils with increased upregulation of adhesion complexes on neutrophils and vascular endothelium. Nitric oxide synthase activity is also increased with a resultant increased production of nitric oxide. The increased nitric oxide concentration in the presence of Superoxide free radicals secreted by activated neutrophils forms peroxynitrite, a more reactive and toxic molecule. Once this process is initiated, diffuse organ injury can result. Although some information related to specific anaesthetics is available, firm recommendations related to clinical practice cannot be made.

Conclusions

There is a complex interplay of inflammatory mediators that can cause injury. Although specific clinical applications for manipulating these pathways are not yet generally available, this area holds promise to develop new techniques to improve outcomes following surgery.     

The immunologic response to thermal injury

Thermal injury is associated with altered immune defense. Extensive and deep thermal injuries lead to depressed immune defense function with both cellular and humoral defense affected. There is an intricate interaction between various components of the immune system. The altered specific immune response is seen as a depressed ability to produce active rosette-forming cells. Depressed stimulation of lymphocyte proliferation as well as the mixed lymphocyte response have also been recorded following burns. These effects are modulated by the release of kinins, prostaglandins, anaphylatoxins, superoxides, and leukotrienes, all of which can influence the inflammatory response following thermal injury. The humoral immunity is altered as seen by decreased levels of immunoglobulins, activation of complement with release of anaphylatoxins, and formation of membrane attacking complexes leading to inflammation and cytolysis. The immune response to burns is also affected by factors other than this injury, such as nutrition or diseases such as diabetes mellitus or disorders of the lymphoproliferative type. The immune response is also influenced by some drugs used for other reasons such as steroids, chemotherapeutic agents, and topical agents used for burn wound care. The immune reaction to a burn is also influenced by the additive effect of superimposed infections. Removal of injured tissue without the need for extensive transfusion will improve the ability of the burned patients to use their immune defense system in a fruitful way.

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Resumen La lesión térmica se asocia con una alteración en la defensa inmunitaria. Las lesiones térmicas extensas y profundas inducen depresión de la función de defensa inmunitaria, afectando tanto los mecanismos de defensa celular como los de defensa humoral. Existe una compleja interacción entre los varios componentes del sistema inmune. La alteración de la respuesta inmunitaria específica se observa como una disimunción de la habilidad para producir células conformadoras de rosetas. Una disminuida estimulación de la proliferación linfocitaria, así como la respuesta linfocítica mixta también han sido registradas en pacientes quemados. Tales efectos son modulados por la liberación de citocinas, prostaglandinas, anafilatoxinas, superóxides y leucotrienos, agentes todos que pueden influenciar la respuesta inflamatoria a la quemadura. La inmunidad humoral resulta alterada a juzgar por niveles disminuidos de inmunoglobulinas, activación del complemento con liberación de anafilatoxinas y formación de complejos que atacan las membranas, lo cual lleva a la inflamación y la citolisis. La respuesta inmunitaria en las quemaduras también resulta afectada por factores diferentes tales como desnutrición, ciertas enfermedades como la diabetes mellitus o entidades de tipo linfoproliferativo. La respuesta inmunitaria también es influenciada por ciertas drogas que se utilizan para otros propósitos, tales como esteroides, algunos agentes quimioterapéuticos y agentes de uso tópico usados para el cuidado de la herida, así como por el efecto aditivo de una infección superpuesta. La remoción de los tejidos lesionados sin la necesidad de grandes transfusiones mejora la capacidad del paciente quemado para utilizar su sistema de defensa inmunitaria en una forma fructífera.

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Résumé Les brûlures s'accompagnent d'une altération des mécanismes de défense immunologique. En effet, les brûlures profondes et étendues provoquent une diminution des fonctions cellulaires et humorales, avec des interactions entre les différentes composantes du système immunitaire. Une des traductions de cette dépression de la fonction immunologique est l'incapacité de produire des rosettes. Chez les brûlés, on a décrit également une diminution de la prolifération lymphocytaire et une réponse lymphocytaire mixte. Ces effets sont induits par la libération des kinines, des prostaglandines, des anaphylatoxines, des superoxydes et des leukotriènes, substances qui peuvent influencer la réponse inflammatoire après une agression thermique. L'immunité humorale est altérée comme en attestent la diminution du taux des immunoglobulines, l'activation du complément avec libération des anaphylatoxines et la formation de complexes qui attaquent la membrane cellulaire, entraînant inflammation et cytolyse. La réponse immune aux brûlures est également affectée par d'autres facteurs tel que l'état nutritionnel, certaines pathologies comme le diabète et les maladies lymphoprolifératives. La réponse immune est également influencée par certains médicaments comme les corticoïdes, les antibiotiques et produits à usage local employés dans les soins des brûlures. La réaction immune des brûlures est également perturbée par les surinfections. L'excision des tissus ne s'accompagnant pas de transfusions importantes aidera ces patients à garder leur capital immun.

     

The hypothalamo-pituitary-adrenal axis response to experimental traumatic brain injury.

Alterations in the hypothalamo-pituitary-adrenal (HPA) axis following traumatic brain injury have not been documented in detail. We used fluid percussion injury (FPI) to evaluate the early changes in components of the HPA axis following experimental traumatic brain injury. Wistar rats were sacrificed at 2 or 4 h following sham or FPI surgery. In situ hybridization histochemistry was used to determine the expression of mRNAs of corticotrophin releasing hormone (CRH) and arginine vasopressin (AVP) in the hypothalamus and pro-opiomelanocortin (POMC) in the pituitary. A group of animals undergoing no surgery were used as control. Repeated blood sampling from an indwelling catheter demonstrated that plasma corticosterone (CORT) levels peaked 30 min following surgery in sham and FPI animals but there was no significant difference in CORT concentration between these groups at any time. Pituitary POMC expression was increased following sham and FPI surgery (compared with control non-operated animals) but with no significant difference between the two groups undergoing surgery. Hypothalamic CRH mRNA expression was significantly higher in animals undergoing FPI compared with sham surgery. Hypothalamic AVP mRNA expression was not significantly increased when compared with control nonoperated animals. These data indicate that the anaesthesia and/or surgery associated with FPI or sham surgery induces a generalised activation of the HPA axis. The selective increase in CRH mRNA in animals undergoing FPI may be due to specific effects of traumatic brain injury rather than a general stress response and may suggest an additional neurotransmitter role for CRH following head injury. The absence of an AVP response suggests that the effects of FPI may be mediated through the CRH-alone-containing subpopulation of neurons.     

The cardiovascular response to burn injury

Severe burn injury has a profound and widespread effect on an individuals cardiovascular system. Early features include myocardial contractile dysfunction and increased vascular permeability. This progresses to a hyperdynamic/hypermetabolic state with oxygen consumption increasing by up to 200%. Animal studies have suggested that pro-inflammatory mediators may in part be responsible, with TNF alpha, nuclear factor-kappa B, p38 activated protein kinase, macrophage inhibitory factor and high mobility group box 1 all playing a role. Traditional markers of myocardial injury are often unreliable in the presence of severe burn injury, either being too non-specific or having uncertain clinical significance.The restoration of adequate organ perfusion without the development of significant peripheral oedema is one of the primary goals of cardiovascular resuscitation in the burn patient. Despite the use of resuscitation formulae and various methods of assessing cardiac output and perfusion to aid resuscitation, the burn patient is often over or under resuscitated. Over resuscitation has led to severe tissue oedema resulting in impaired tissue perfusion and complications including compartment syndromes in unburned limbs and abdominal compartment syndrome.Vasopressors have a role in supporting the circulation, particularly during septic episodes, although caution must be taken as progression of burn wound depth may occur. B-Blockers are being increasingly used to attenuate the hypermetabolic state in burn patients with some promising results, particularly in the paediatric population.This review will focus on the cardiovascular responses to burn injury and discuss early fluid resuscitation and pharmacological support.