Biomimetic multilayer coatings deliver gentamicin and reduce implant-related osteomyelitis in rats

Implant-related infections like periprosthetic joint infections (PJI) are still a challenging issue in orthopedic surgery. In this study, we present a prophylactic anti-infective approach based on a local delivery of the antibiotic gentamicin. The local delivery is achieved via a nanoscale polyelectrolyte multilayer (PEM) coating that leaves the bulk material properties of the implant unaffected while tuning the surface properties. The main components of the coating, i.e. polypeptides and sulfated glycosaminoglycans (sGAG) render this coating both biomimetic (matrix mimetic) and biodegradable. We show how adaptions in the conditions of the multilayer assembly process and the antibiotic loading process affect the amount of delivered gentamicin. The highest concentration of gentamicin could be loaded into films composed of polypeptide poly-glutamic acid when the pH of the loading solution was acidic. The concentration of gentamicin on the surface could be tailored with the number of deposited PEM layers. The resulting coatings reveal a bacteriotoxic effect on Staphylococcus cells but show no signs of cytotoxic effects on MC3T3-E1 osteoblasts. Moreover, when multilayer-coated titanium rods were implanted into contaminated medullae of rat tibiae, a reduction in the development of implant-related osteomyelitis was observed. This reduction was more pronounced for the multifunctional, matrix-mimetic heparin-based coatings that only deliver lower amounts of gentamicin.

Radiographic and Histological Analysis of a Synthetic Bone Graft Substitute Eluting Gentamicin in the Treatment of Chronic Osteomyelitis

Introduction: Managing chronic osteomyelitis can be challenging and attention to the osseous dead-space left following resection is an important part of successful treatment. We assess radiographic bone healing following implantation of a gentamicin-eluting synthetic bone graft substitute (gBGS) used at chronic osteomyelitis (cOM) resection. We also describe histological carrier changes from biopsies in nine cases at various time points. Methods: This was a retrospective review of a prospectively collected consecutive series of 163 patients with Cierny-Mader Type III or IV cOM who underwent single-stage excision, insertion of gBGS and definitive soft-tissue closure or coverage. Bone defect filling was assessed radiographically using serial radiographs. Nine patients had subsequent surgery, not related to infection recurrence, allowing opportunistic biopsy between 19 days and two years after implantation. Results: Infection was eradicated in 95.7% with a single procedure. 138 patients had adequate radiographs for assessment with minimum one-year follow-up (mean 1.7 years, range 1.0-4.7 years). Mean void-filling at final follow-up was 73.8%. There was significantly higher void-filling in metaphyseal compared to diaphyseal voids (mean 79.0% versus 65.6%; p=0.017) and in cases with good initial interdigitation of the carrier (mean 77.3% versus 68.7%; p=0.021). Bone formation continued for more than two years in almost two-thirds of patients studied (24/38; 63.2%). Histology revealed active biomaterial remodelling. It was osteoconductive with osteoblast recruitment, leading to the formation of osteoid, then woven and lamellar bone on the substrate's surface. Immunohistochemistry demonstrated osteocyte specific markers, dentine matrix protein-1 and podoplanin within the newly formed bone. Conclusion: This antibiotic-loaded biomaterial is effective in managing dead-space in surgically treated cOM with a low infection recurrence rate (4.3%) and good mean bone void-filling (73.8%). The radiographic resolution of the bone defect is associated with bone formation, as supported by histological analysis.

Establishment and effects of allograft and synthetic bone graft substitute treatment of a critical size metaphyseal bone defect model in the sheep femur

Assessment of bone graft material efficacy is difficult in humans, since invasive methods like staged CT scans or biopsies are ethically unjustifiable. Therefore, we developed a novel large animal model for the verification of a potential transformation of synthetic bone graft substitutes into vital bone. The model combines multiple imaging methods with corresponding histology in standardized critical sized cancellous bone defect. Cylindrical bone voids (10 ml) were created in the medial femoral condyles of both hind legs (first surgery at right hind leg, second surgery 3 months later at left hind leg) in three merino‐wool sheep and either (i) left empty, filled with (ii) cancellous allograft bone or (iii) a synthetic, gentamicin eluting bone graft substitute. All samples were analysed with radiographs, MRI, μCT, DEXA and histology after sacrifice at 6 months. Unfilled defects only showed ingrowth of fibrous tissue, whereas good integration of the cancellous graft was seen in the allograft group. The bone graft substitute showed centripetal biodegradation and new trabecular bone formation in the periphery of the void as early as 3 months. μCT gave excellent insight into the structural changes within the defects, particularly progressive allograft incorporation and the bone graft substitute biodegradation process. MRI completed the picture by clearly visualizing soft tissue ingrowth into unfilled bone voids and presence of fluid collections. Histology was essential for verification of trabecular bone and osteoid formation. Conventional radiographs and DEXA could not differentiate details of the ongoing transformation process. This model appears well suited for detailed in vivo and ex vivo evaluation of bone graft substitute behaviour within large bone defects.

Single-stage treatment of chronic osteomyelitis with a new absorbable, gentamicin-loaded, calcium sulphate/hydroxyapatite biocomposite: a prospective series of 100 cases

AIMS

Chronic osteomyelitis may recur if dead space management, after excision of infected bone, is inadequate. This study describes the results of a strategy for the management of deep bone infection and evaluates a new antibiotic-loaded biocomposite in the eradication of infection from bone defects.

PATIENTS AND METHODS

We report a prospective study of 100 patients with chronic osteomyelitis, in 105 bones. Osteomyelitis followed injury or surgery in 81 patients. Nine had concomitant septic arthritis. 80 patients had comorbidities (Cierny-Mader (C-M) Class B hosts). Ten had infected nonunions. All patients were treated by a multidisciplinary team with a single-stage protocol including debridement, multiple sampling, culture-specific systemic antibiotics, stabilisation, dead space filling with the biocomposite and primary skin closure.

RESULTS

Patients were followed up for a mean of 19.5 months (12 to 34). Infection was eradicated in 96 patients with a single procedure and all four recurrences were successfully managed with repeat surgery. Adverse events were uncommon, with three fractures, six wound leaks and three unrelated deaths. Outcome was not dependant on C-M host class, microbial culture, wound leakage or presence of nonunion.

CONCLUSION

This single-stage protocol, facilitated by the absorbable local antibiotic, is effective in the treatment of chronic osteomyelitis. It offers a more patient-friendly treatment compared with other published treatment options. Cite this article: Bone Joint J 2016;98-B:1289-96.

Ceramic Biocomposites as Biodegradable Antibiotic Carriers in the Treatment of Bone Infections

Local release of antibiotic has advantages in the treatment of chronic osteomyelitis and infected fractures. The adequacy of surgical debridement is still key to successful clearance of infection but local antibiotic carriers seem to afford greater success rates by targeting the residual organisms present after debridement and delivering much higher local antibiotic concentrations compared with systemic antibiotics alone. Biodegradable ceramic carriers can be used to fill osseous defects, which reduces the dead space and provides the potential for subsequent repair of the osseous defect as they dissolve away. A dissolving ceramic antibiotic carrier also raises the possibility of single stage surgery with definitive closure and avoids the need for subsequent surgery for spacer removal.

In this article we provide an overview of the properties of various biodegradable ceramics, including calcium sulphate, the calcium orthophosphate ceramics, calcium phosphate cement and polyphasic carriers. We summarise the antibiotic elution properties as investigated in previous animal studies as well as the clinical outcomes from clinical research investigating their use in the surgical management of chronic osteomyelitis.

Calcium sulphate pellets have been shown to be effective in treating local infection, although newer polyphasic carriers may support greater osseous repair and reduce the risk of further fracture or the need for secondary reconstructive surgery. The use of ceramic biocomposites to deliver antibiotics together with BMPs, bisphosphonates, growth factors or living cells is under investigation and merits further study.

We propose a treatment protocol, based on the Cierny-Mader classification, to help guide the appropriate selection of a suitable ceramic antibiotic carrier in the surgical treatment of chronic osteomyelitis.

[Classification of haematogenous and post-traumatic osteomyelitis]

A classification of osteomyelitis must reflect the complexity of the disease and, moreover, provide conclusions for the treatment. The classification is based on the following eight parameters: source of infection (OM [osteomyelitis]/OT [post-traumatic OM]), anatomic region, stability of affected bone (continuity of bone), foreign material (internal fixation, prosthesis), range of infection (involved structures), activity of infection (acute, chronic, quiescent), causative microbes (unspecific and specific bacteria, fungi) and comorbidity (immunosuppressive diseases, general and local). In the long version of the classification, which was designed for scientific studies, the parameters are named by capital letters and specified by Arabic numbers, e.g., an acute, haematogenous osteomyelitis of a femur in an adolescent with diabetes mellitus, caused by Staphylococcus aureus, multi-sensible is coded as: OM2 Lo33 S1a M1 In1d Aa1 Ba2a K2a. The letters and numbers can be found in clearly arranged tables or calculated by a freely available grouper on the internet (www.osteomyelitis.exquit.net). An equally composed compact version of the classification for clinical use includes all eight parameters, but without further specification. The above-mentioned example in the compact version is: OM 3 S a Ba2 K2. The short version of the classification uses only the first six parameters and excludes causative microbes and comorbidity. The above mentioned example in the short version is: OM 3 S a. The long version of the classification describes an osteomyelitis in every detail. The complexity of the patient's disease is clearly reproducible and can be used for scientific comparisons. The for clinical use suggested compact and short versions of the classification include all important characteristics of an osteomyelitis, can be composed quickly and distinctly with the help of tables and provide conclusions for the individual treatment. The freely available grouper (www.osteomyelitis.exquit.net) creates all three versions of the classification in one step.

Surgical debridement to optimise wound conditions and healing

Different treatment strategies are available for bone, joint and soft tissue infections, including use of local antibiotics; negative pressure wound therapy; one-stage, two-stage or multi-stage revisions; or open wound therapy. All methods have one principle in common: adequate surgical debridement is the prerequisite for successful treatment of bone, joint and soft tissue infections. According to the different textures of healthy, infected or necrotic tissue, special techniques are used. In this article we will describe the clinical presentation of necrotic and non-vital tissue in skin, soft tissue and bone and appropriate techniques of debridement.

The effect of polyelectrolyte multilayer coated titanium alloy surfaces on implant anchorage in rats

Advances have been achieved in the design and biomechanical performance of orthopedic implants in the last decades. These include anatomically shaped and angle-stable implants for fracture fixation or improved biomaterials (e.g. ultra-high-molecular-weight polyethylene) in total joint arthroplasty. Future modifications need to address the biological function of implant surfaces. Functionalized surfaces can promote or reduce osseointegration, avoid implant-related infections or reduce osteoporotic bone loss. To this end, polyelectrolyte multilayer structures have been developed as functional coatings and intensively tested in vitro previously. Nevertheless, only a few studies address the effect of polyelectrolyte multilayer coatings of biomaterials in vivo. The aim of the present work is to evaluate the effect of polyelectrolyte coatings of titanium alloy implants on implant anchorage in an animal model. We test the hypotheses that (1) polyelectrolyte multilayers have an effect on osseointegration in vivo; (2) multilayers of chitosan/hyaluronic acid decrease osteoblast proliferation compared to native titanium alloy, and hence reduce osseointegration; (3) multilayers of chitosan/gelatine increase osteoblast proliferation compared to native titanium alloy, hence enhance osseointegration. Polyelectrolyte multilayers on titanium alloy implants were fabricated by a layer-by-layer self-assembly process. Titanium alloy (Ti) implants were alternately dipped into gelatine (Gel), hyaluronic acid (HA) and chitosan (Chi) solutions, thus assembling a Chi/Gel and a Chi/HA coating with a terminating layer of Gel or HA, respectively. A rat tibial model with bilateral placement of titanium alloy implants was employed to analyze the bones' response to polyelectrolyte surfaces in vivo. 48 rats were randomly assigned to three groups of implants: (1) native titanium alloy (control), (2) Chi/Gel and (3) Chi/HA coating. Mechanical fixation, peri-implant bone area and bone contact were evaluated by pull-out tests and histology at 3 and 8 weeks. Shear strength at 8 weeks was statistically significantly increased (p<0.05) in both Chi/Gel and Chi/HA groups compared to the titanium alloy control. No statistically significant difference (p>0.05) in bone contact or bone area was found between all groups. No decrease of osseointegration of Chi/HA-coated implants compared to non-coated implants was found. The results of polyelectrolyte coatings in a rat model showed that the Chi/Gel and Chi/HA coatings have a positive effect on mechanical implant anchorage in normal bone.

[Joint infections. Known facts and new trends]

Acute septic arthritis is a surgical emergency because rapid septic destruction of articular cartilage can lead to impairment or even loss of joint function. Diagnosis consists of patient history, clinical examination, laboratory results, (sonography- guided) joint aspiration and radiography. Emergency therapy is based on arthroscopic or open joint debridement and lavage combined with systemic antibiotic therapy. No data are available for the recommendation of local antibiotics but antiseptic solutions are not recommended because of cartilage damage. New trends in diagnostics are positron emission tomography/computed tomography (PET/CT), urine sticks for analysis of joint fluid and molecular pathology. Chronic joint empyema is more diagnostically demanding and is difficult to treat. In cases of necrotic and infected articular cartilage, joint resection has to be performed for quiescence of infection. Options following successful treatment of empyema are arthroplasty, arthrodesis or permanent resection.

Freezing of rat tibiae at -20°c does not affect the mechanical properties of intramedullary bone/implant-interface: brief report

Background:

The effects of freezing-thawing cycles on intramedullary bone-implant interfaces have been studied in a rat model in mechanical pull-out tests.

Implants:

Twenty TiAl6V4 rods (Ø 0.8 mm, length 10 mm) implanted in rat tibiae

Methods:

10 rats underwent bilateral tibial implantation of titanium rods. At eight weeks, the animals were sacrificed and tibiae harvested for biomechanical testing. Eight tibiae were frozen and stored at -20°C for 14 days, the remaining eight were evaluated immediately post-harvest. Pull-out tests were used to determine maximum force and interfacial shear strength.

Results:

There were no significant differences between fresh and those of the frozen-thawed group in maximum force or in interfacial shear strength.

Conclusion:

Frozen Storage of rat tibiae containing implants at -20° C has no effects on the biomechanical properties of Bone/ Implant interface.

[Definition of the Diagnosis Osteomyelitis-Osteomyelitis Diagnosis Score (ODS)]

AIM

The disease "osteomyelitis" is characterised by different symptoms and parameters. Decisive roles in the development of the disease are played by the causative bacteria, the route of infection and the individual defense mechanisms of the host. The diagnosis is based on different symptoms and findings from the clinical history, clinical symptoms, laboratory results, diagnostic imaging, microbiological and histopathological analyses. While different osteomyelitis classifications have been published, there is to the best of our knowledge no score that gives information how sure the diagnosis "osteomyelitis" is in general.

METHOD

For any scientific study of a disease a valid definition is essential. We have developed a special osteomyelitis diagnosis score for the reliable classification of clinical, laboratory and technical findings. The score is based on five diagnostic procedures: 1) clinical history and risk factors, 2) clinical examination and laboratory results, 3) diagnostic imaging (ultrasound, radiology, CT, MRI, nuclear medicine and hybrid methods), 4) microbiology, and 5) histopathology.

RESULTS

Each diagnostic procedure is related to many individual findings, which are weighted by a score system, in order to achieve a relevant value for each assessment. If the sum of the five diagnostic criteria is 18 or more points, the diagnosis of osteomyelitis can be viewed as "safe" (diagnosis class A). Between 8-17 points the diagnosis is "probable" (diagnosis class B). Less than 8 points means that the diagnosis is "possible, but unlikely" (class C diagnosis). Since each parameter can score six points at a maximum, a reliable diagnosis can only be achieved if at least 3 parameters are scored with 6 points.

CONCLUSION

The osteomyelitis diagnosis score should help to avoid the false description of a clinical presentation as "osteomyelitis". A safe diagnosis is essential for the aetiology, treatment and outcome studies of osteomyelitis.

[Preservation of hip prosthesis with local surgical revision and creation of a fistula persistens : an option for palliative treatment of periprosthetic infection in old, polymorbid patients?]

BACKGROUND

The number of implanted hip prostheses is increasing constantly. At the same time the patients are becoming older and older. Thus, also patients with periprosthetic infections are older and therefore sicker. Uniform guidelines for the treatment of infected arthroplasties are controversial. Empirical studies show that the explantation of the original prosthesis and implantation of a revision may be the option with the greatest chance of success. These very aggressive procedures may overburden the old, polymorbid patient. The aim of this study was to ascertain whether or not keeping the hip prosthesis in combination with local debridement, formation of a permanent fistula and long-term administration of antibiotics is a possible option for the treatment of infected hip prostheses in old and polymorbid patients.

PATIENTS

Between 01.01.2004 and 28.01.2007, 12 patients with periprosthetic infection after hip arthroplasty (PIH) were treated. Their average age was 79.8 years. Eleven patients were rated ASA III preoperatively. The prostheses were on average 23.8 weeks old when the first signs of infection occurred. In 10 cases the infection was caused by Staphylococcus (MRSA 3x). The main comorbidities were hypertension, diabetes, coronary heart disease and thyroid malfunction.

RESULTS

After a mean 8.83 months, six patients were deceased (average age 85.50 years). In five of the remaining six patients the fistula worked without any problem. In one case the fistula was occluded. None of the patients showed any sign of acute infection. All were able to walk with full weight-bearing on the affected hip.

CONCLUSION

Restricting the indication to old, polymorbid patients, preservation of the arthroplasty in combination with local surgical debridement, permanent fistula and long-term systemic administration of antibiotics seems to be an alternative to explantation of the prosthesis with consecutive revision arthroplasty or resection arthroplasty.

Outcome of allogeneic vascularized knee transplants

Transplantation of vascularized knee joints is a novel approach in Composite Tissue Allotransplantation (CTA). In 1996 our group started a clinical knee transplantation project and six transplantations have been performed since. Key problems identified early were the monitoring of acute rejection and choice of an immunosuppressive regime. One graft was lost due to postoperative infection and one due to of noncompliance where the patient discontinued the immunosuppressant regime. In three cases late rejection lead to necrosis and graft dysfunction after 15, 16 and 24 months, respectively. Exit-strategies were arthrodesis in one patient and Above Knee Amputation in two cases. With retrospective analysis after initial five cases the treatment protocol was improved. The immunosuppressive drug regime was altered, femoral diaphysis and knee joint grafting was combined and a vascularized block of donor skin and subcutaneous tissue was harvested with the graft (sentinel skin graft). The sentinel skin graft enabled us to monitor acute rejection by clinical and histological examination and avoid late rejection by rapid treatment with high dose steroids. In summary, over a four-year period, one of six allogeneic vascularized knee transplants has survived, one was lost from a surgical site infection, one by noncompliance and three by late rejection. Analysis of our data leads us to suggest that knee transplantation should be limited to a combined injury consisting of extensive loss of cartilage and bone, deficient extensor mechanism and soft tissue and skin defects without any signs of infection. Transplantation should only be taken into consideration as last option before Above Knee Amputation in an otherwise healthy patient under 35 years of age.

Prophylaxis and treatment of implant-related infections by local application of antibiotics

Despite the improvement in surgical technique and implant design in orthopedic and trauma surgery, implant-related infections are still a challenging problem for surgeons. The use of local prophylaxis to avoid infection, such as antibiotic-loaded cement in arthroplasty, gentamicin PMMA beads and gentamicin-collagen sponge in trauma surgery, and antibacterial coating of metal implants, is discussed in the first part of this article. The second part discusses the role of local antibiotics such as gentamicin PMMA beads, and gentamicin-collagen and antibiotic-loaded cement spacers in treating implant-related infections.

The effect of anti-L-selectin (aselizumab) in multiple traumatized patients--results of a phase II clinical trial

OBJECTIVE

The objectives of this study were to evaluate safety (primary) and clinical efficacy (secondary) of the humanized monoclonal anti-L-selectin antibody aselizumab in severely injured patients.

DESIGN

Prospective phase II, parallel group, double-blind, randomized, placebo-controlled clinical trial.

SETTING

Fourteen medical intensive care units or trauma units in level I trauma centers in Belgium, Germany, and Poland.

PATIENTS

Eighty-four patients with a sustained trauma due to a blunt or penetrating injury and a total Injury Severity Scale score of > or =25.

INTERVENTIONS

Patients received either aselizumab at dosages of 0.5, 1, or 2 mg/kg or placebo within 6 hrs of the traumatic event and were followed for 6 wks.

MEASUREMENTS AND MAIN RESULTS

The number of expeditable adverse events increased dose dependently over the aselizumab groups compared with placebo. There were no statistically significant differences between all groups regarding leukopenia and risk of infection. No immunologic response following infusion of aselizumab was noted. The number of patients with multiple organ failure, defined as a median value of the total Goris Multiple Organ Failure score of > or =5 on > or =2 consecutive days within 14 days, was not significantly different for the 0.5 mg/kg, 1 mg/kg, 2 mg/kg, and placebo groups. There were no statistically significant differences in time of mechanical ventilation, length of stay in an intensive care unit, and total duration of hospitalization between treatment groups.

CONCLUSIONS

Aselizumab was associated with a higher rate of infections and leucopenia; however, this difference was not significantly different compared with placebo. For all efficacy variables, aselizumab presented no significant trends but only a few scattered statistically significant differences between groups.

Behandlung der MRSA-Infektion in der septischen Extremit�tenchirurgie

INTRODUCTION

Infection with methicillin-resistant Staphylococcus aureus (MRSA) remains a major challenge both therapeutically and hygienically.

METHODS

Between January 2000 and January 2002, 27 patients with MRSA infections were treated and evaluated in a prospective clinical study. For effective wound management, operative revisions were performed every 3rd day. Following debridement, the wounds were vacuum sealed and specific i.v. antibiotics were administered. Wound closure was performed if three consecutive wound samples submitted for bacterial culture remained negative.

RESULTS

All patients with MRSA infections were treated successfully until signs of infection disappeared and bacterial cultures were negative. An average of 7.3 operations per patient was required to eradicate MRSA infection. Follow-up of patients revealed recurrence of infection in four patients.

CONCLUSION

Prevention of further spreading and successful treatment of MRSA infections in reconstructive orthopedic surgery is possible with appropriate surgical and hygienic concepts. In almost every second patient complex revision procedures were required.

Xenogeneic rejection mechanisms shown by intravital microscopy

The importance of this model is that it showed exactly where in the organ the xenogeneic damage occurred. The liver received the blood mainly via portal veins, which merge with the pulsatile arterioles in the Disse spaces. This periportal area is followed by the sinusoids and ends in the central or postsinusoidal vein. IVM enables us to differentiate between perfused and unperfused sinusoids and to calculate the ratio. Not all sinusoids are perfused at any time. It appears that 5% to 10% are unperfused. During xenoperfusion, only 65% of sinusoids show blood flow after a perfusion of 12 minutes. This is less than in hemorrhagic shock. Only the combined platelet inhibitors and apheresis resulted in remarkable improvement. The calculation of an index indicates the improvement of acinar perfusion. Thrombocytes and leukocytes remain, however, in the liver. In conclusion, the model used to analyze the dynamics of microvascular liver perfusion and sinusoidal perfusion is suitable for such investigations in a xenogeneic model. It has no major side effects, either on the perfusing blood or on the liver, as proved in the isogeneic control group. The important finding in our eyes is that the perfusion failure begins in the periportal fields, where the blood enters the foreign microvasculature and where the leukocytes first come in contact with the foreign endothelium. All previous manipulations had only a minor impact on this contact of cells with the foreign endothelium. The study indicates that the early events of xenogeneic hyperacute rejection are of unspecific character and involve leukocytes and thrombocytes to a major degree, thus being responsible for the dramatic decrease in the microcirculation in xenogeneic livers.

Intravital microscopic investigation of xenogeneic microcirculation and impact of complement depletion by cobra venom factor

Discordant xenografts are hyperacutely rejected within minutes. Disturbances in the microcirculation are considered to be the central mechanisms of hyperacute xenogeneic rejection (HXR). In this study intravital fluorescence microscopy was applied to investigate the dynamics of microcirculatory alterations in a setting in which HXR was inhibited by complement (C) depletion. Blood flow was measured as rat livers were perfused with isogeneic rat or xenogeneic human blood to assess the pattern of either physiological isogeneic hemoperfusion or in the course of HXR. Next, the complement system of the perfusate was inactivated by cobra venom factor (CVF) in order to inhibit HXR. Liver sinusoids of the isogeneic group were homogeneously perfused (sinusoidal perfusion rate 93.6+/-0.3%), whereas in the xenogeneic group the sinusoidal perfusion rate dropped to 67.1+/-3%. The perfusion in the periportal zone of an acinus was significantly lower ( 59.0+/-3.3%) than in the pericentral zone (76.2+/-3.1%). Treatment with CVF improved the sinusoidal perfusion to a value of 85.6+/-2.3%, physiological perfusion, however could not be reached. In contrast to the isogeneic group, massive white blood cell (WBC) and platelet accumulation was found in the xenogeneic group, especially in the terminal portal vessels and in the periportal zone of liver acini. WBC and platelet counts show that the adherence of these cells appears rapidly in the first 5 min after reperfusion as firm adherence. CVF was not able to inhibit WBC and platelet accumulation, indicating that WBC endothelial interactions do not require an intact complement system. Bile flow, a parameter of liver function, decreased only slightly during isogeneic perfusion. The addition of CVF to the rat blood reduced the bile flow to one half of the untreated isogeneic flow, indicating a hepatotoxic side-effect of CVF. In xenogeneic perfusion the bile flow dropped to 62.6% and with the addition of CVF to 37.5% in the first 15 min after reperfusion. The bile flow of the CVF treated groups recovered during the perfusion but could not reach isogeneic values.

Monitoring of microhemodynamic changes during ex vivo xenogeneic liver perfusion using intravital microscopy

The main targets of xenogeneic rejection mechanisms are the endothelial cells of the graft. Their activation and the consequent alteration of the organ's microcirculation lead to the destruction of the xenograft. Microhemodynamic changes occurring during this process are still poorly characterized. The aim of this study was to analyze the microcirculation during xenogeneic ex vivo hemoperfusion of rat livers and to monitor the impact of treatment strategies using intravital fluorescence microscopy. In contrast to the isogeneic control group, blood flow almost completely stopped within the first minutes of xenoperfusion. Simultaneously, perfusion pressure increased and bile production was reduced. Acetylsalicylate (Aspisol) and the platelet-activating factor antagonist WEB 2170 improved the microcirculation and function of the xenoperfused liver. The combination showed a synergistic effect. After apheresis of preformed xenogeneic antibodies, the parameters measured were comparable with those seen in isogeneic experiments. Complement degradation with cobra venom factor revealed a minor improvement in perfusion. A rapid, extensive, and irreversible leukocyte accumulation in terminal portal vessels was observed in all xenogeneic experiments. Blood counts of the perfusate confirmed the early trapping of leukocytes and platelets in the xenoperfused liver, indicating nonimmunological, cellular involvement in this rejection process.

Organs from animals for man

In the following review some of the problems of xenotransplantation shall be discussed, based on the few experimental data available so far and on reports in the literature describing investigations which may be of importance for xenotransplantation. The impact of gravity on the upright posture of man versus almost all other mammals, the dysfunction between enzymes and hormones in different species and the lack of interactions between interleukins, cytokines and vasoactive substances will be taken into consideration. The question must be asked whether different levels of carrier molecules or serum proteins play a role in the physiological network. Even though the development of transgenic animals or other imaginative manipulations may lead to the acceptance of any type of xenografted organ, it has to be established for how long the products of the xenografts are able to act in the multifactorial orchestra. We are far from understanding xenogeneic molecular mechanisms involved in toxicity, necrosis and apoptosis or even reperfusion injury and ischemia in addition to the immediate mechanisms of the hyperacute xenogeneic rejection. Here, cell adhesion, blood clotting and vasomotion collide and bring micro- and macrocirculation to a standstill. All types of xenogeneic immunological mechanisms studied so far were found to have a more serious impact than those seen in allogeneic transplantation. In addition we are now only beginning to understand that so-called immunological parameters in allogeneic mechanisms act also in a true physiological manner in the xenogeneic situation. These molecular mechanisms occur behind the curtain of hyperacute, accelerated, acute or chronic xenograft rejection of which only some folds have been lifted to allow glimpses of part of the total scene. Other obstacles are likely to arise when long-term survival is achieved. These obstacles include retroviral infections, transfer of prions and severe side effects of the massive immunosuppression which will be needed. Moral, ethical and religious concerns are under debate and the species-specific production of proteins of the foreign donor species developed for clinical use suddenly appears to be a greater problem than anticipated.