Characterization of poly-4-hydroxybutyrate mesh for hernia repair applications.

BACKGROUND: Phasix mesh is a fully resorbable implant for soft tissue reconstruction made from knitted poly-4-hydroxybutyrate monofilament fibers. The objectives of this study were to characterize the in vitro and in vivo mechanical and resorption properties of Phasix mesh over time, and to assess the functional performance in a porcine model of abdominal hernia repair. MATERIALS AND METHODS: We evaluated accelerated in vitro degradation of Phasix mesh in 3 mol/L HCl through 120 h incubation. We also evaluated functional performance after repair of a surgically created abdominal hernia defect in a porcine model through 72 wk. Mechanical and molecular weight (MW) properties were fully characterized in both studies over time. RESULTS: Phasix mesh demonstrated a significant reduction in mechanical strength and MW over 120 h in the accelerated degradation in vitro test. In vivo, the Phasix mesh repair demonstrated 80%, 65%, 58%, 37%, and 18% greater strength, compared with native abdominal wall at 8, 16, 32, and 48 wk post-implantation, respectively, and comparable repair strength at 72 wk post-implantation despite a significant reduction in mesh MW over time. CONCLUSIONS: Both in vitro and in vivo data suggest that Phasix mesh provides a durable scaffold for mechanical reinforcement of soft tissue. Furthermore, a Phasix mesh surgical defect repair in a large animal model demonstrated successful transfer of load bearing from the mesh to the repaired abdominal wall, thereby successfully returning the mechanical properties of repaired host tissue to its native state over an extended time period.

Fully resorbable poly-4-hydroxybutyrate (P4HB) mesh for soft tissue repair and reconstruction: A scoping review.

Background: Poly-4-hydroxybutyrate (P4HB) is a fully resorbable, biologically-produced polymer with a strength and flexibility comparable to permanent synthetic polymers. The objective was to identify/summarize all peer-reviewed publications involving P4HB mesh. Methods: A scoping review was conducted within PubMed and included articles published through October 2022. Results: A total of n = 79 studies were identified (n = 12 in vitro/bench; n = 14 preclinical; n = 6 commentaries; n = 50 clinical). Of the clinical studies, n = 40 reported results applicable to hernia and n = 10 to plastic/reconstructive surgery and involved patients of all Centers for Disease Control (CDC) wound classes and Ventral Hernia Working Group (VHWG) grades. Conclusion: P4HB mesh provides long-term hernia repair strength and exhibits promising clinical outcomes beyond its resorption period. Future studies should include randomized controlled trials comparing P4HB to other biomaterials, as well as optimal patient selection, operative technique, long-term outcomes, minimization of potential mesh-related complications, and potential contraindications/complications for P4HB in hernia/abdominal wall reconstruction.

Efficacy of Flowable Collagen Hemostat Evaluated in Preclinical Models of Liver Injury and Spinal Cord Exposure.

Introduction: Excessive bleeding in trauma and surgical settings leads to increased operative time, reoperation rates, and overall healthcare costs. A wide range of hemostatic agents have been developed to control bleeding that can vary considerably in type of hemostatic action, ease of application, cost, risk of infection, and dependence on patient coagulation. Microfibrillar collagen-based hemostatic materials (MCH) have yielded beneficial results in a variety of applications. Methods: A new flowable collagen product, containing a modified MCH flour, but in a more convenient flowable delivery system, was evaluated for hemostatic efficacy in preclinical models of solid organ injury and spinal cord exposure. The primary objective of this study was to compare the hemostatic potential and local tissue responses to this novel, flowable collagen-based hemostatic agent to the original flour formulation to confirm that the new method of delivery did not interfere with the hemostatic properties of the MCH flour. Results: When observed visually, the flowable MCH flour mixed with saline (FL) provided more precise application and uniform coverage to injured tissues compared to the dry MCH flour alone (F0). All of the treatments (FL, F0, and gauze) exhibited comparable Lewis bleed grade at all three time points evaluated in the capsular resection liver injury model (bleed grade: 1.0-1.3; p> 0.05 in all cases). FL and F0 exhibited comparable 100% acute hemostatic efficacy and similar long-term histomorphological properties (up to 120 days) in a capsular resection liver injury in pigs, while gauze resulted in significantly lower rates of acute hemostatic efficacy (8-42%, p<0.05 in all cases). In an ovine model of dorsal laminectomy and durotomy, FL and F0 again exhibited comparable results without any neurological effects. Conclusion: Flowable microfibrillar collagen was shown to yield favorable short- and long-term outcomes in two representative applications where hemostatic efficacy is critical to surgical success.

Early wound morbidity and clinical outcomes associated with P4HB mesh compared to permanent synthetic mesh in umbilical and small to medium, routine ventral hernia repairs.

Background: Permanent synthetic meshes such as polypropylene (PP) have been utilized for hernia repair for decades, but concerns remain regarding potential long-term, mesh-related complications. A resorbable polymer such as poly-4-hydroxybutyrate (P4HB) represents an alternative with high initial strength, that gradually resorbs, leaving an abdominal wall that is at least as strong as it would be in its native state. We aimed to compare early wound morbidity and clinical outcomes associated with P4HB to traditional, permanent PP in umbilical and small to medium, routine ventral hernias using data from the Abdominal Core Health Quality Collaborative (ACHQC). Methods: Inclusion criteria for the umbilical cohort included: all Centers for Disease Control and Prevention (CDC) wound classes, all Ventral Hernia Working Group (VHWG) hernia grades, and hernia defects <3 cm. The small to medium, routine ventral hernia cohort was limited to CDC class I wounds, VHWG hernia grades I and II, and hernia defects <5 cm. The study group was comprised of P4HB meshes; the comparator group was an aggregate of PP meshes. Clinical outcomes were assessed at 30 days. Results: There was no significant difference in early wound morbidity, readmission, or reoperation between the P4HB and PP cohorts. A small number of patients experienced SSO, with ≤4% requiring procedural intervention. None of the patients (0% in all cases) experienced skin/soft tissue necrosis, infected seroma, infected hematoma, exposed/contaminated/infected mesh, enterocutaneous fistula, graft failure, or pain requiring intervention at 30-days. However, P4HB was associated with significantly greater operative time, length of stay, and use of myofascial release compared to PP (p < 0.05 in all cases). Conclusions: Short-term clinical outcomes associated with resorbable P4HB mesh are comparable to permanent synthetic PP mesh in umbilical and small to medium, routine ventral hernia repairs, despite significant differences in operative time and length of stay. Longer-term follow-up is needed to expand on the clinical relevance of these short-term findings.

Mechanical and Histological Characteristics of Phasix™ ST Mesh in a Porcine Model of Hernia Repair.

PURPOSE: The objective of this study was to determine mechanical and histological properties of Phasix™ ST Mesh in various defect sizes and characterize the tissue replacing Phasix™ ST Mesh in a porcine model of ventral hernia repair. METHODS: Simulated hernia defects were surgically created in the midline of twenty-four (n = 24) Yucatan pigs. Treatment groups included 8 cm defect sutured closed (buttress) and unclosed 4 cm and 8 cm defect groups. Phasix™ ST Mesh (15 cm diameter circle) was implanted laparoscopically and fixated circumferentially with SorbaFix™ Absorbable Fixation System fasteners. The repair sites underwent mechanical, molecular weight, and histological evaluation at 48 and 72 weeks postimplantation. RESULTS: Mechanical testing of Phasix™ ST Mesh-repaired sites revealed similar strengths at both time points for all three repair types, p > 0.05 in all cases (48 weeks: 142.4 ± 6.0 N, 142.3 ± 16.5 N, and 168.8 ± 38.5 N; 72 weeks: 110.0 ± 18.3 N, 138.6 ± 42.2 N, and 160.6 ± 42.0 N for 4 cm defect, 8 cm defect, and 8 cm buttress, respectively. mean ± SEM) No significant differences were observed over time except at 72 weeks postimplantation when the 4 cm defect group exhibited significantly lower strength than the T0 strength of Phasix™ ST Mesh (204.6 ± 5.0 N, p < 0.05). The molecular weight of Phasix™ ST Mesh decreased over time, regardless of repair type. Histological analysis showed comparable mature collagen/fibrovascular tissue around and within the Phasix™ ST Mesh interstices, including the segment of mesh overlying the defect. CONCLUSION: Phasix™ ST Mesh-repaired sites exhibited similar mechanical strengths and histological properties across all defect sizes in this porcine model.

Long-Term, Prospective, Multicenter Study of Poly-4-Hydroxybutyrate Mesh (Phasix Mesh) for Hernia Repair in Cohort at Risk for Complication: 60-Month Follow-Up.

BACKGROUND: Long-term resorbable mesh represents a promising technology for ventral and incisional hernia repair (VIHR). This study evaluates poly-4-hydroxybutyrate mesh (P4HB; Phasix Mesh) among comorbid patients with CDC class I wounds. STUDY DESIGN: This prospective, multi-institutional study evaluated P4HB VIHR in comorbid patients with CDC class I wounds. Primary outcomes included hernia recurrence and surgical site infection. Secondary outcomes included pain, device-related adverse events, quality of life, reoperation, procedure time, and length of stay. Evaluations were scheduled at 1, 3, 6, 12, 18, 24, 30, 36, and 60 months. A time-to-event analysis (Kaplan-Meier) was performed for primary outcomes; secondary outcomes were reported as descriptive statistics. RESULTS: A total of 121 patients (46 male, 75 female) 54.7 ± 12.0 years old with a BMI of 32.2 ± 4.5 kg/m 2 underwent VIHR with P4HB Mesh (mean ± SD). Fifty-four patients (44.6%) completed the 60-month follow-up. Primary outcomes (Kaplan-Meier estimates at 60 months) included recurrence (22.0 ± 4.5%; 95% CI 11.7% to 29.4%) and surgical site infection (10.1 ± 2.8%; 95% CI 3.3 to 14.0). Secondary outcomes included seroma requiring intervention (n = 9), procedure time (167.9 ± 82.5 minutes), length of stay (5.3 ± 5.3 days), reoperation (18 of 121, 14.9%), visual analogue scale-pain (change from baseline -3.16 ± 3.35 cm at 60 months; n = 52), and Carolinas Comfort Total Score (change from baseline -24.3 ± 21.4 at 60 months; n = 52). CONCLUSIONS: Five-year outcomes after VIHR with P4HB mesh were associated with infrequent complications and durable hernia repair outcomes. This study provides a framework for anticipated long-term hernia repair outcomes when using P4HB mesh.

Compartment syndrome-induced microvascular dysfunction: an experimental rodent model.

BACKGROUND: Acute compartment syndrome (CS) is a limb-threatening disease that results from increased intracompartmental pressure. The pathophysiologic mechanisms by which this occurs are poorly understood. This study was designed to measure the effects of increased intracompartmental pressure on skeletal muscle microcirculation, inflammation and cellular injury using intravital videomicroscopy (IVVM) in a clinically relevant small animal model. METHODS: We induced CS in 10 male Wistar rats (175-250 g), using a saline infusion technique. Intracompartmental pressure was controlled between 30 and 40 mm Hg and maintained for 45 minutes. After fasciotomy, the extensor digitorum longus muscle was visualized using IVVM, and perfusion was quantified. We quantified leukocyte recruitment to measure the inflammatory response. We measured muscle cellular injury using a differential fluorescent staining technique. RESULTS: The number of nonperfused capillaries increased from 12.7 (standard error of the mean [SEM] 1.4 ) per mm in the control group to 30.0 (SEM 6.7) per mm following 45 minutes of elevated intracompartmental pressure (CS group; p = 0.031). The mean number of continuously perfused capillaries (and SEM) decreased from 78.4 (3.2) per mm in the control group to 41.4 (6.9) per mm in the CS group (p = 0.001). The proportion of injured cells increased from 5.0% (SEM 2.1%) in the control group to 16.3% (SEM 6.8%) in the CS group (p = 0.006). The mean number of activated leukocytes increased from 3.6 (SEM 0.7) per 100 µm(2) in the control group to 8.6 (SEM 1.8) per 100 µm(2) in the CS group (p = 0.033). CONCLUSION: Early CS-induced microvascular dysfunction resulted in a decrease in nutritive capillary perfusion and an increase in cellular injury and was associated with a severe acute inflammatory component.

Hindlimb ischemia/reperfusion-induced remote injury to the small intestine: role of inducible nitric-oxide synthase-derived nitric oxide.

Systemic inflammatory response syndrome, as a consequence of ischemia/reperfusion (I/R), negatively influences the function of the affected organs. The objective of this study was to assess the role of nitric oxide (NO) in remote intestinal inflammatory response elicited by hindlimb I/R. To this end, C57BL/6 (wild type; WT) and inducible nitric-oxide synthase (iNOS)-deficient mice were subjected to bilateral hindlimb ischemia (1 h) followed by 6 h of reperfusion. Some WT mice were injected with iNOS inhibitor N-[3-(aminomethyl)benzyl] acetamidine (1400W) (5 mg/kg s.c.) immediately before reperfusion, and proinflammatory response was assessed 6 h later. Hindlimb I/R resulted in dysfunction of the small intestine as assessed by the increase in permeability [blood-to-lumen clearance of Texas Red-dextran (molecular mass 3 kDa)] and an increase in the luminal levels of tumor necrosis factor (TNF)-alpha protein and nitrate/nitrite (NO(2)(-)/NO(3)(-)). The above-mentioned changes were accompanied by up-regulation of the proinflammatory phenotype in the mucosa of small intestine with respect to 1) an increase in TNF-alpha and iNOS protein expression, 2) leukocyte accumulation, 3) formation of edema, 4) an increase in leukocyte rolling/adhesion in the submucosal microvasculature, and 5) activation of transcription factor nuclear factor-kappaB and up-regulation of adhesion molecule expression. Interestingly, the most profound changes with respect to intestinal dysfunction were found in jejunum and ileum, whereas duodenum was affected the least. Interfering with iNOS activity (1400W and iNOS-deficient mice) significantly attenuated hindlimb I/R-induced inflammatory response and dysfunction of the small intestine with respect to the above-mentioned markers of inflammation. The obtained results indicate that hindlimb I/R induces remote inflammatory response in the small intestine through an iNOS-derived NO-dependent mechanism.

Contamination of hybrid hernia meshes compared to bioresorbable Phasix™ Mesh in a rabbit subcutaneous implant inoculation model.

BACKGROUND: Hybrid hernia meshes combine biological tissue-derived extracellular matrix with permanent or resorbable synthetic. The objective of this study was to evaluate hybrid meshes (Gore® Synecor, Zenapro™, Ovitex™ 1S Reinforced Bioscaffold Permanent, and Ovitex™ 1S Reinforced Bioscaffold Resorbable) compared to non-hybrid, bioresorbable synthetic mesh (Phasix™ Mesh) in a rabbit bacterial inoculation model. MATERIALS AND METHODS: Subcutaneous pockets were bilaterally created in male, New Zealand White rabbits (n = 25). Circular meshes (3.8 cm diameter) were implanted and inoculated with 1 × 106 colony forming units (CFU) of clinically-isolated methicillin-resistant Staphylococcus aureus (MRSA). A given animal received a single mesh type. Seven days post-inoculation, animals were euthanized and white material and microbial colonization were assessed by abscess scoring and CFU quantification, respectively. Non-parametric Kruskal-Wallis with Dunn's post-hoc tests compared results for different meshes. RESULTS: Phasix™ Mesh and Synecor exhibited significantly lower abscess scores than Zenapro™, Ovitex™ 1S Permanent, and Ovitex™ 1S Resorbable (p < 0.05). All pocket swabs for Zenapro™ and Ovitex™ meshes were positive for MRSA (100%), with 20% of Synecor and 0% Phasix™ Mesh. Microbial colonization was significantly lower for Phasix™ Mesh (0 CFU) relative to Zenapro™ (6.73 × 107 CFU (median)), Ovitex™ 1S Permanent (7.87 × 107 CFU) and Ovitex™ 1S Resorbable (1.45 × 108 CFU), and for Synecor (0 CFU) relative to both Ovitex™ meshes. Phasix™ Mesh was the only device with no detectable abscess or microbial colonization. CONCLUSION: Phasix™ Mesh demonstrated no detectable abscess or microbial colonization at 7-days post-implantation and inoculation, in contrast with four hybrid meshes, which all demonstrated colonization in a rabbit bacterial inoculation model.

Inhalation of carbon monoxide prevents liver injury and inflammation following hind limb ischemia/reperfusion.

The induction of heme oxygenase (HO), the rate limiting enzyme in the conversion of heme into carbon monoxide (CO) and biliverdin, limits liver injury following remote trauma such as hind limb ischemia/reperfusion (I/R). Using intravital video microscopy, we tested the hypothesis that inhaled CO (250 ppm) would mimic HO-derived liver protection. Hind limb I/R significantly decreased sinusoidal diameter and volumetric flow, increased leukocyte accumulation within sinusoids, increased leukocyte rolling and adhesion within postsinusoidal venules, and significantly increased hepatocyte injury compared with naive animals. Inhalation of CO alone did not alter any microcirculatory or inflammatory parameters. Inhalation of CO following I/R restored volumetric flow, decreased stationary leukocytes within sinusoids, decreased leukocyte rolling and adhesion within postsinusoidal venules, and significantly reduced hepatocellular injury following hind limb I/R. HO inhibition did not alter microcirculatory parameters in naive mice, but did increase inflammation, as well as increase hepatocyte injury following hind limb I/R. Inhalation of CO during HO inhibition significantly reduced such microcirculatory deficits, hepatic inflammation, and injury in response to hind limb I/R. In conclusion, these results suggest that HO-derived hepatic protection is mediated by CO, and inhalation of low concentrations of CO may represent a novel therapeutic approach to prevent remote organ injury during systemic inflammatory response syndrome, or SIRS.

A role for cyclic nucleotide monophosphates in synaptic modulation by a crayfish neuropeptide.

DF2 (DRNFLRFamide), a FMRFamide-like peptide, has been shown to increase the amount of transmitter released at crayfish neuromuscular junctions. Here, we examined a possible role for the cyclic nucleotide monophosphates, cAMP and cGMP, in DF2's effects on synaptic transmission. The effects of DF2 on synaptic transmission were monitored by recording excitatory postsynaptic potentials (EPSPs) in the deep abdominal extensor muscles of the crayfish, Procambarus clarkii. A number of activators and inhibitors were used to determine whether or not cAMP, cGMP, protein kinase A (PKA) and protein kinase G (PKG) mediate the effect of this neuropeptide. Phosphodiesterase inhibitors, known to inhibit the breakdown of cAMP (IBMX) and/or cGMP (mdBAMQ), potentiate the effect of DF2 on synaptic transmission. Activators of PKA (Sp-cAMPS) and PKG (8-pCPT-cGMP) increase EPSP amplitude, mimicking the effects of DF2. Inhibitors of PKA (Rp-cAMPS) and PKG (Rp-8-pCPT-cGMPS) each block a portion of the response to the peptide, and when applied together these two inhibitors completely block the response. Taken together, these results indicate that cyclic nucleotides and cyclic nucleotide-dependent protein kinases are necessary components of the pathway underlying modulation by this neuropeptide.

Histologic characterization of acellular dermal matrices in a porcine model of tissue expander breast reconstruction.

BACKGROUND: Acellular dermal matrices (ADMs) have been commonly used in expander-based breast reconstruction to provide inferolateral prosthesis coverage. Although the clinical performance of these biologic scaffold materials varies depending on a number of factors, an in-depth systematic characterization of the host response is yet to be performed. The present study evaluates the biochemical composition and structure of two ADMs, AlloDerm(®) Regenerative Tissue Matrix and AlloMax™ Surgical Graft, and provides a comprehensive spatiotemporal characterization in a porcine model of tissue expander breast reconstruction. METHODS: Each ADM was characterized with regard to thickness, permeability, donor nucleic acid content, (residual double-stranded DNA [dsDNA]), and growth factors (basic fibroblast growth factor [bFGF], vascular endothelial growth factor [VEGF], and transforming growth factor-beta 1 [TGF-ß1]). Cytocompatibility was evaluated by in vitro cell culture on the ADMs. The host response was evaluated at 4 and 12 weeks at various locations within the ADMs using established metrics of the inflammatory and tissue remodeling response: cell infiltration, multinucleate giant cell formation, extent of ADM remodeling, and neovascularization. RESULTS: AlloMax incorporated more readily with surrounding host tissue as measured by earlier and greater cell infiltration, fewer foreign body giant cells, and faster remodeling of ADM. These findings correlated with the in vitro composition and cytocompatibility analysis, which showed AlloMax to more readily support in vitro cell growth. CONCLUSIONS: AlloMax and AlloDerm demonstrated distinct remodeling characteristics in a porcine model of tissue expander breast reconstruction.

Protective mechanisms during ischemic tolerance in skeletal muscle.

The purpose of this study was to test specific mechanisms of protection afforded the rat extensor digitorum longus (EDL) muscle during ischemic tolerance. Two days following five cycles of 10 min ischemia and 10 min reperfusion, heme oxygenase (HO) and calcium-dependent nitric oxide synthase (cNOS) activities were increased 2- and 2.5-fold (p <.05), respectively. Interestingly, calcium-independent NOS (iNOS) activity was completely downregulated (p <.05). The levels of superoxide dismutase (SOD) and catalase were increased 2-fold (p <.05), while glutathione peroxidase activity remained unchanged from non-preconditioned controls. Using intravital microscopy combined with chromium mesoporphyrin (CrMP), a selective HO inhibitor, and l-NAME, a NOS inhibitor, the roles of HO and cNOS were evaluated. Ischemic tolerance in the EDL muscle, 48 h after the preconditioning stimulus, was characterized by complete protection from both microvascular perfusion deficits and tissue injury after a 2-h period of ischemia. Removal of NOS activity completely removed the benefit afforded microvascular perfusion, while inhibition of HO activity prevented the parenchymal protection. These data suggest that ischemic tolerance within skeletal muscle is associated with the upregulation of specific cytoprotective proteins and that the benefits afforded by cNOS and HO activity are spatially discrete to the microvasculature and parenchyma, respectively.

Endogenous heme oxygenase induction is a critical mechanism attenuating apoptosis and restoring microvascular perfusion following limb ischemia/reperfusion.

BACKGROUND: A protective role for endogenous heme oxygenase (HO) in the initiation of remote liver injury after limb ischemia/reperfusion has been established. This study expands on our previous work by investigating the role of endogenous HO on hepatocellular injury, hepatocyte death (necrotic and apoptotic), and microvascular perfusion at protracted post-reperfusion times. METHODS: Remote liver injury was studied after 1 hour of bilateral hind limb ischemia and 3, 6, or 24 hours of reperfusion in male C57BL6 mice. Inhibition of HO was achieved with the use of chromium mesoporphrin (CrMP). Established intravital videomicroscopy techniques were used to evaluate microvascular perfusion and hepatocyte death. Hepatocellular injury was quantified by serum alanine transaminase. Apoptosis was measured by using DNA laddering, Cell Death ELISA, and caspase-3 activity. RESULTS: Although significant perfusion deficits and hepatocellular injury/death occurred after 3 hours, progression of hepatocellular death beyond 6 hours was not observed. A transient increase in apoptosis was observed at 6 hours. By 24 hours, microvascular perfusion was completely restored. This lack of progression correlated with increased HO activity, observed throughout the protocol. Administration of CrMP reduced HO activity to sham nonstressed levels, and caused increased microvascular perfusion deficits, hepatocellular injury, and hepatocyte death over 24 hours. The transient increase in apoptosis was increased in duration and magnitude in CrMP-treated animals. CONCLUSIONS: These results suggest that endogenous HO activity prevents the progression of remote liver injury after limb ischemia/reperfusion.

Pulsatile versus nonpulsatile flow during cardiopulmonary bypass: microcirculatory and systemic effects.

BACKGROUND: Controversy exists regarding the optimal perfusion modality during cardiopulmonary bypass (CPB). Here we compare the effects of pulsatile versus nonpulsatile perfusion on microvascular blood flow during and after CPB. METHODS: High-risk cardiac surgical patients were randomly assigned to have pulsatile (n=10) or nonpulsatile (n=10) flow during CPB. The sublingual microcirculation was assessed using orthogonal polarization spectral imaging. Hemodynamic and microvascular variables were obtained after anesthesia (baseline), during CPB, and post-CPB. RESULTS: Compared with baseline, a normal microcirculatory blood flow pattern was accomplished at all time points under pulsatile flow conditions. Peaking 24 hours postoperatively, a higher proportion of normally perfused microvessels occurred under pulsatile versus nonpulsatile flow (56.0%±3.9% vs 33.3%±4.1%; p<0.05). Concurrently, pulsatility resulted in a reduction in the prevalence of pathologic hyper-dynamically perfused vessels (6.0%±3.4% vs 19.6%±8.8%; p<0.05). Leukocyte adherence decreased relative to the nonpulsatile group both during and after CPB. Furthermore, peak lactate levels were reduced under pulsatile flow conditions postoperatively. CONCLUSIONS: Pulsatile perfusion is superior to nonpulsatile perfusion at preserving the microcirculation, which may reflect attenuation of the systemic inflammatory response during CPB. We suggest the implementation of pulsatile flow can better optimize microvascular perfusion, and may lead to improved patient outcomes in high-risk cardiac surgical procedures requiring prolonged CPB time.

Remote inflammatory response in liver is dependent on the segmental level of spinal cord injury.

BACKGROUND: Traumatic spinal cord injury (SCI) triggers a systemic inflammatory response (SIR) that contributes to a high incidence of secondary organ complications, particularly after a cervical or high-level thoracic injury. Because liver plays a key role in initiating and propagating the SIR, the aim of this study was to assess the effects that SCI at differing segmental levels has on the intensity of the inflammatory response in the liver. METHODS: Using male Wistar rats, clip compression SCI was performed at the 4th thoracic (T4 SCI; high-level SCI) or the 12th thoracic (T12 SCI; low-level SCI) spinal cord segment. Sham-injured rats had a partial laminectomy, but no SCI. Leukocyte recruitment to the liver, hepatic blood flow, and hepatocellular injury/death were assessed using intravital microscopy and histology. Chemokine and cytokine concentrations were assessed in the liver. Outcomes were measured at 1.5 hours, 12 hours, and 24 hours after SCI. RESULTS: At 12 hours after injury, T4 SCI caused a threefold increase in hepatic leukocyte recruitment compared with T12 SCI (p < 0.05). T4 SCI induced 50% more hepatocyte injury than T12 SCI at 12 hours (p < 0.05). Hepatic blood flow decreased after SCI, but not after sham injury, and stayed decreased only after T4 SCI at 24 hours after injury. The T4 SCI-induced changes were accompanied by increases in the hepatic concentrations of interleukin-1ß, leptin, interleukin 10, and cytokine-induced neutrophil chemoattractant-1 at 1.5 hours. CONCLUSIONS: Our findings indicate that traumatic SCI triggers an acute SIR that contributes to hepatocellular injury. SCI-induced remote injury/dysfunction to the liver appears to be transient and is more robust after an upper thoracic SCI compared with a lower thoracic SCI.

Indomethacin reduces cell damage: shedding new light on compartment syndrome.

INTRODUCTION: Indomethacin may preserve tissue viability in compartment syndrome. The mechanism of improved tissue viability is unclear, but the anti-inflammatory effects may alter the relative contribution of tissue necrosis versus apoptosis to cellular injury. Existing studies have only considered indomethacin administration before induction of elevated intracompartment pressure. The purpose of this study was to determine the effect of timing of indomethacin administration on muscle damage in elevated intracompartment pressure and to assess apoptosis as a cause of tissue demise. METHODS: Twenty-four Wistar rats were randomized to elevated intracompartmental pressure (EICP) for either 45 or 90 minutes (30 mmHg). In the 45-minute cohort, indomethacin was withheld in Group 1 (CS45), given before induction of EICP in Group 2 (CS45Indo0), or given after 30 minutes of EICP/15 minutes before fasciotomy in Group 3 (CS45Indo30). In the 90-minute cohort, indomethacin was withheld in Group 4 (CS90) or given after 30 or 60 minutes of EICP in Groups 5 (CS90Indo30) and 6 (CS90Indo60). Intravital microscopy and fluorescent staining assessed capillary perfusion, cell damage, and inflammatory activation within extensor digitorum longus muscle. Apoptosis was assessed using spectrophotometric assessment of caspase levels. Groups 1 to 3 and 4 to 6 were compared using analysis of variance with P < 0.05 deemed significant. RESULTS: Perfusion and tissue viability improved in indomethacin-treated groups. Nonperfused capillaries decreased from Group 1 (CS45) (50.1 +/- 2.5) to Group 2 (CS45Indo0) (38.4 +/- 1.8) and Group 3 (CS45Indo30) (14.13 +/- 1.73) (P < 0.05). Similarly, Group 5 (CS90Indo30) and Group 6 (CS90Indo60) had 25% fewer nonperfused capillaries compared with Group 4 (CS90) (P < 0.0001). Group 2 (CS45Indo0) and Group 3 (CS45Indo30) showed fewer damaged cells (1% +/- 0.5% and 8.7% +/- 2%) compared with Group 1 (CS45) (20% +/- 14%) (P < 0.0001). Group 5 (CS90Indo30) showed decreased cell damage (13% +/- 1%) compared with Group 4 (CS90) (18% +/- 1%) (P < 0.01). Group 6 (CS90Indo60) also showed decreased cell damage (11% +/- 1%) compared with Group 4 (CS90) (18% +/- 1%); however, this difference was not significant (P > 0.05). Apoptotic activity was present with elevated intracompartment pressure. At 30 minutes, there were elevated caspase levels in Group 4 and Group 6 EICP groups (0.47 +/- 0.08) compared with control subjects (0.19 +/- 0.02) (P < 0.003). However, indomethacin-treated groups did not differ from control subjects with regard to caspase levels (P > 0.05). CONCLUSION: Indomethacin decreased cell damage and improved perfusion in elevated intracompartment pressure. The benefits of indomethacin were partially time-dependent; some improvement in tissue viability occurred regardless of timing of administration. Although apoptosis was common in elevated intracompartment pressure, the protective effect of indomethacin does not appear to be related to apoptosis. CLINICAL RELEVANCE: Adjuvant treatment with indomethacin may improve outcome in compartment syndrome.

Low-dose inhaled carbon monoxide attenuates the remote intestinal inflammatory response elicited by hindlimb ischemia-reperfusion.

Heme oxygenase (HO) represents the rate-limiting enzyme in the degradation of heme into carbon monoxide (CO), iron, and biliverdin. Recent evidence suggests that several of the beneficial properties of HO, may be linked to CO. The objectives of this study were to determine if low-dose inhaled CO reduces remote intestinal leukocyte recruitment, proinflammatory cytokine expression, and oxidative stress elicited by hindlimb ischemia-reperfusion (I/R). Male mice underwent 1 h of hindlimb ischemia, followed by 3 h of reperfusion. Throughout reperfusion, mice were exposed to AIR or AIR + CO (250 ppm). Following reperfusion, the distal ileum was exteriorized to assess the intestinal inflammatory response by quantifying leukocyte rolling and adhesion in submucosal postcapillary venules with the use of intravital microscopy. Ileum samples were also analyzed for proinflammatory cytokine expression [tumor necrosis factor (TNF)-alpha and interleukin (IL)-1beta] and malondialdehyde (MDA) with the use of enzyme-linked immunosorbent assay and thiobarbituric acid reactive substances assays, respectively. I/R + AIR led to a significant decrease in leukocyte rolling velocity and a sevenfold increase in leukocyte adhesion. This was also accompanied by a significant 1.3-fold increase in ileum MDA and 2.3-fold increase in TNF-alpha expression. Treatment with AIR + CO led to a significant reduction in leukocyte recruitment and TNF-alpha expression elicited by I/R; however, MDA levels remained unchanged. Our data suggest that low-dose inhaled CO selectively attenuates the remote intestinal inflammatory response elicited by hindlimb I/R, yet does not provide protection against intestinal lipid peroxidation. CO may represent a novel anti-inflammatory therapeutic treatment to target remote organs following acute trauma and/or I/R injury.

Microvascular changes in radiation-induced oral mucositis.

BACKGROUND: Mucositis is one of the most debilitating side effects of head and neck cancer therapy and is currently believed to arise from an inflammatory cascade leading to cellular damage. However, no effective treatment has been identified despite extensive attempts with anti-inflammatory medications. OBJECTIVE: To compare real-time microvascular inflammatory changes with oral mucositis levels in patients undergoing radiotherapy or chemoradiotherapy for head and neck tumours. DESIGN: Prospective, longitudinal, cohort, observational study. SETTING: Regional cancer program. METHODS: Twenty patients with head and neck tumours were assessed on a weekly basis throughout the course of radiotherapy. Levels of mucositis were graded objectively using the Oral Mucositis Assessment Scale and subjectively using a patient symptom questionnaire. Video imaging of the sublingual microcirculation was obtained using orthogonal polarized spectral imaging to quantify inflammatory markers such as microcirculatory velocity, white blood cell margination, and extravasation. RESULTS: Despite very high levels of objective and subjective mucositis, inflammatory changes were not present in the microcirculation. CONCLUSIONS: Typical microvascular inflammatory changes are not demonstrated in radiation-induced mucositis. These findings contradict the currently proposed mechanism of mucosal damage and may therefore have important implications in the development of novel therapeutic interventions.

Role of heme oxygenase in the protection afforded skeletal muscle during ischemic tolerance.

OBJECTIVE: Ischemic tolerance (IT) is known to improve resistance to ischemia/reperfusion (I/R)-induced injury; however, the mechanisms remain unknown. The authors hypothesized that induction of heme oxygenase (HO), a heat shock protein, would provide anti-inflammatory benefits during IT, thereby preventing leukocyte-derived I/R injury. METHODS: Male Wistar rats were randomly assigned to sham (n = 4), I/R (n = 9), preconditioning (PC)+I/R (n = 7), chromium mesoporphyrin, to inhibit HO (CrMP; n = 4), or PC+I/R+CrMP (n = 6) groups. PC consisted of 5 cycles of I/R, each lasting 10 min, induced by tightening a tourniquet placed above the greater trochantor of the hindlimb. Twenty-four hours later, the hindlimb underwent 2 h of no-flow ischemia followed by intravital microscopy during 90 min reperfusion to assess capillary perfusion (#/mm), tissue injury (ratio of ethidium bromide to bisbenzimide labeled cells/100 microm2), leukocyte rolling (Lr, #/1000 microm2), and adhesion (La, #/1000 microm2) in postcapillary venules of the extensor digitorum longus (EDL) muscle. RESULTS: In the I/R group, Lr was significantly increased (7.1 +/- 0.4) compared to sham (3.1 +/- 0.4). PC+I/R increased Lr (10.8 +/- 0.72), which was further exacerbated by the removal of HO (14.2 +/- 1.3). La (7.8 +/- 2.0) was significantly increased compared to sham (2.4 +/- 0.9), while PC returned La back to sham levels (1.9 +/- 0.7). Removal of HO activity, via CrMP, had no significant effect on La (3.9 +/- 0.7). However, CrMP removed the protection to microvascular perfusion (I/R = 9.4 +/- 1.1, PC = 16.6 +/- 1.8, sham = 20.5 +/- 2.8, PC+CrMP+I/R = 12.3 +/- 2.3) and prevented protection from ischemia-induced tissue injury. CONCLUSION: The data suggest that HO is an important protective mechanism during IT in skeletal muscle, but such protection was by mechanisms other than altered leukocyte-endothelial cell interaction.