Modulation of fibroblast proliferation by postsurgical macrophages

Platelet-Rich Plasma Releasate Promotes Early Healing in Tendon After Acute Injury

Background

Acute tendon injury can limit motion and thereby inhibit tendon healing. Positive results have been found after the use of platelet-rich plasma (PRP) to treat tendon injury; however, the early effects of PRP on tendon regeneration are not known.

Purpose/Hypothesis

The purpose of this study was to evaluate the effects of PRP releasate (PRPr) on the early stages of tendon healing in a rat partial tenotomy model. It was hypothesized that PRPr can promote early healing of an Achilles tendon in rats.

Study Design

Controlled laboratory study.

Methods

PRP was prepared by a 2-step method of manual platelet concentration from 10 rats. PRPr was isolated from the clotted preparation after activation by thrombin and was applied to an Achilles tendon on 1 side of 30 rats on the second day after partial tenotomy, with normal saline used as the control on the other side. Achilles tendon samples were harvested 5 and 10 days after tenotomy. At each time point, 15 Achilles tendon samples were obtained, of which 5 samples were evaluated by Masson trichrome staining, apoptosis, and cell proliferation, while the other 10 samples were tested for tensile strength using a material testing machine.

Results

Compared with saline-treated control tendons, the PRPr-treated tendons showed increased collagen synthesis near the cut edge and fewer apoptotic cells (P = .01). An immunohistochemical analysis revealed more Ki-67-positive cells but fewer cluster of differentiation (CD) 68⁺ (ED1⁺) macrophages in PRPr tendons compared with saline-treated tendons (P < .01). Tendons treated with PRPr also showed higher ultimate tensile strength than those treated with saline (P = .03).

Conclusion

PRPr treatment promotes tissue recovery in the early phase of tendon healing by stimulating tendon cell proliferation and collagen production while inhibiting cell apoptosis and CD68⁺ (ED1⁺) macrophage infiltration.

Clinical Relevance

These findings suggest that with PRPr treatment, higher loads can be applied to the healing tendon at an earlier time, which can help the patient resume activity earlier.

The shift in macrophages polarisation after tendon injury: A systematic review

Background

The role of macrophages (Mφs) in tendon injury healing is controversy. The aims of this study were to determine whether there is a shift in Mφs polarisation after an acute and chronic tendon injury ​and to assess whether the Mφs polarisation between the partial and complete rupture is different.

Methods

This systematic review of the scientific literature was based on the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) and Cochrane guidelines. PubMed database and Excerpta Medica Database (EMBASE) were used for specific search criteria. Only studies measuring Mφs using specific cell markers in Achilles tendon tissue and rotator cuff tendon tissue were included, respectively.

Results

Five Achilles tendon injury studies and four rotator cuff injury studies were included. Expression of the pan Mϕs marker Cluster of Differentiation (CD) 68 was significantly upregulated in acute Achilles tendon ruptures compared to intact tendons, while no significant changes were found in Mφs polarisation markers CD80 (M1 Mφs) and CD206 (M2 Mφs). High levels of CD86 (M1 Mφs) and CD206 were observed in acute partial rupture. Expression of CD68 and CD206 were significantly upregulated in chronic rotator cuff tendinopathy and downregulated as structural failure increases. A low level of CD206 was observed in complete tendon rupture regardless of acute or chronic injury.

Discussion and conclusion

In spite of the limited number of articles included, findings from this study suggested that the process of inflammation plays an important role in acute Achilles tendon injuries, indicated by the increased expression of CD68+ Mφs. Low levels of CD206+ Mφs were constantly observed in complete Achilles tendon rupture, while high levels of CD80+ Mφs and CD206+ Mφs were observed in partial Achilles tendon rupture, which suggested the potential correlation between M2 Mφs and tendon structure. For chronic rotator cuff injury, CD68+ Mφs and CD206+ Mφs were higher in tendinopathic tissues in comparison to the intact control tissues. Both CD68+ Mφs and CD206+ Mφs has an inverse relation to the structural failure in the torn rotator cuff tendon. After tendon rupture, the time point of biopsy specimen collection is an important factor, which could occur in the acute phase or chronic phase. Collectively, the understanding of the roles in Mφs after tendon injury is inadequate, and more research efforts should be devoted to this direction.

The translational potential of this article

This article provided a potential implication on how pan Mφs or M2 Mφs might be associated with ruptured or torn tendon structure. Managing Mφs numbers and phenotypes may lead to possible novel therapeutic approaches to the management of early tendinopathy, early acute tendon rupture, hence, promote healing after restoration surgery.

Evaluation of microstructurally motivated constitutive models to describe age-dependent tendon healing

Tendon injuries are common to all ages. Injured tendons typically do not recover full functionality. The amount and organization of tendon constituents dictate their mechanical properties. The impact of changes in these constituents during (patho)physiologic processes (e.g., aging and healing) are not fully understood. Toward this end, microstructurally motivated strain energy functions (SEFs) offer insight into underlying mechanisms of age-dependent healing. Several SEFs have been adapted for tendon; however, most are phenomenological. Therefore, the aims of this study are: (1) evaluate the descriptive capability of SEFs in age-dependent murine patellar tendon healing and (2) identify a SEF for implementation in a growth and remodeling (G&R) model. To accomplish these aims, models were fitted to patellar tendon tensile data from multiple age groups and post-injury timepoints. Model sensitivity to parameters and the determinability of the parameters were assessed. A two-way analysis of variance was used to identify changes in parameters and the feasibility of implementing each model into a G&R model is discussed. The evaluated SEFs exhibited adequate descriptive capability. Parameter determinability and sensitivity analysis, however, highlighted the need for additional data to inform and validate the models to increase physiologic relevance and enable G&R model formulation to determine underlying mechanisms of age-dependent healing. This work, as a first, evaluated changes in tendon mechanical properties both as functions of age and injury in an age-dependent manner using microstructurally motivated models, highlights inherent dependencies between parameters of widely used hyperelastic models, and identified unique post-injury behavior by the aging group compared to the mature and aged groups.

Intratendinous Injection of Hyaluronate Induces Acute Inflammation: A Possible Detrimental Effect

Hyaluronate (HA) is therapeutic for tendinopathy, but an intratendinous HA injection is usually painful; thus, it is not suggested for clinical practice. However, there are no studies on the histopathological changes after an intratendinous HA injection. We hypothesized that an HA injection would induce more-acute inflammation than that induced by an injection of phosphate buffered saline (PBS). Thirty-two rats were randomly divided into 4 post-injection groups (n = 8): day 3, day 7, day 28, and day 42. HA (0.1 c.c.) was, using ultrasound guidance, intratendinously injected into each left Achilles tendon, and PBS (0.1 c.c.) into each right one. For each group, both Achilles tendons of 3 control-group rats (n = 6) were given only needle punctures. The histopathological score, ED1+ and ED2+ macrophage densities, interleukin (IL)-1β expression, and the extent of neovascularization were evaluated. In both experimental groups, each Achilles tendon showed significant histopathological changes and inflammation compatible with acute tendon injury until day 42. The HA group showed more-significant (p < 0.05) histopathological changes, higher ED1+ and ED2+ macrophage density, and higher IL-1β expression than did the PBS group. The neovascularization area was also significantly (p < 0.05) greater in the HA group, except on day 3. Both HA and PBS induced acute tendon injury and inflammation, sequential histopathological changes, ED1+ and ED2+ macrophage accumulation, IL-1β expression, and neovascularization until post-injection day 42.HA induced more-severe injury than did PBS. Therefore, an intratendinous HA injection should be avoided.

Use of ultra-high molecular weight polycaprolactone scaffolds for ACL reconstruction

Previously, we reported on the implantation of electrospun polycaprolactone (PCL) grafts for use in ACL tissue engineering in a small animal model. In the present study, we hypothesized that grafts fabricated from ultra-high molecular weight polycaprolactone (UHMWPCL) would have similarly favorable biologic properties but superior mechanical properties as compared to grafts fabricated from PCL. Two forms of polycaprolactone were obtained (UHMWPCL, MW = 500 kD, and PCL, MW = 80 kD) and electrospun into scaffolds that were used to perform ACL reconstruction in 7-8 week old male Lewis rats. The following groups were examined: UHMWPCL, PCL, flexor digitorum longus (FDL) allograft, native ACL, as well as sham surgery in which the ACL was transsected. At 16 weeks post-operatively, biomechanical testing, histology, and immunohistochemistry (IHC) were performed. Analysis of cellularity indicated that there was no significant difference among the UHMWPCL, PCL, and FDL allograft groups. Quantification of birefringence from picrosirius red staining demonstrated significantly more aligned collagen fibers in the allograft than the PCL group, but no difference between the UHMWPCL and allograft groups. The peak load to failure of the UHMWPCL grafts was significantly higher than PCL, and not significantly different from FDL allograft. This in vivo study establishes the superiority of the higher molecular weight version of polycaprolactone over PCL as a scaffold material for ACL reconstruction. By 16 weeks after implantation, the UHMWPCL grafts were not significantly different from the FDL allografts in terms of cellularity, peak load to failure, stiffness, and collagen fiber alignment. © 2015 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 34:828-835, 2016.

Evaluation of polycaprolactone scaffold with basic fibroblast growth factor and fibroblasts in an athymic rat model for anterior cruciate ligament reconstruction

Anterior cruciate ligament (ACL) rupture is a common ligamentous injury often necessitating surgery. Current surgical treatment options include ligament reconstruction with autograft or allograft, which have their inherent limitations. Thus, there is interest in a tissue-engineered substitute for use in ACL regeneration. However, there have been relatively few in vivo studies to date. In this study, an athymic rat model of ACL reconstruction was used to evaluate electrospun polycaprolactone (PCL) grafts, with and without the addition of basic fibroblast growth factor (bFGF) and human foreskin fibroblasts. We examined the regenerative potential of tissue-engineered ACL grafts using histology, immunohistochemistry, and mechanical testing up to 16 weeks postoperatively. Histology showed infiltration of the grafts with cells, and immunohistochemistry demonstrated aligned collagen deposition with minimal inflammatory reaction. Mechanical testing of the grafts demonstrated significantly higher mechanical properties than immediately postimplantation. Acellular grafts loaded with bFGF achieved 58.8% of the stiffness and 40.7% of the peak load of healthy native ACL. Grafts without bFGF achieved 31.3% of the stiffness and 28.2% of the peak load of healthy native ACL. In this in vivo rodent model study for ACL reconstruction, the histological and mechanical evaluation demonstrated excellent healing and regenerative potential of our electrospun PCL ligament graft.

Changes in macrophage phenotype and induction of epithelial-to-mesenchymal transition genes following acute Achilles tenotomy and repair

Tendon injuries occur frequently in physically active individuals, but the clinical outcomes for these injuries can be poor. In many injured tissues the repair process is orchestrated by two types of cells, macrophages and fibroblasts. Macrophages, which have both pro-inflammatory (M1) and anti-inflammatory (M2) phenotypes, can directly participate in tissue remodeling and direct the response of other cells through the secretion of cytokines and growth factors. In many organ systems, epithelial cells can trans-differentiate into fibroblasts, which can then regenerate damaged ECM. This process is triggered via activation of epithelial-to-mesenchymal transition (EMT) signaling programs. Most tendons are surrounded by sheets of epithelial cells, and these tissue layers could provide a source of fibroblasts to repair injured tendons. To gain greater insight into the biology of tendon repair, we performed a tenotomy and repair in Achilles tendons of adult rats and determined changes in macrophage phenotype, and ECM- and EMT-related genes over a 4-week time course. The results from this study suggest that changes in macrophage phenotype and activation of EMT-related programs likely contribute to the degradation and subsequent repair of injured tendon tissue.

Tendon healing

An understanding of the processes of tendon healing and tendon-to-bone healing is important for the intraoperative and postoperative management of patients with tendon ruptures or of patients requiring tendon transfers in foot and ankle surgery. Knowledge of the normal process allows clinicians to develop strategies when normal healing fails. This article reviews the important work behind the identification of the normal phases and control of tendon healing. It outlines the failed response in tendinopathy and describes tendon-to-bone healing in view of its importance in foot and ankle surgery.

Macrophages accumulate in the early phase of tendon-bone healing

A scar tissue interface forms rather than a normal ligament insertion site following attachment of a tendon graft to bone. The specific cell types that initiate the process of tendon-to-bone healing are unknown. We hypothesized that inflammatory cell accumulation following tendon-to-bone repair results in this scar interface. We used a rodent model to examine the temporal and spatial pattern of accumulation of hematopoietic lineage cells in the early phase of tendon-to-bone healing. Thirty-six Lewis rats underwent anterior cruciate ligament (ACL) reconstruction in the left knee using a flexor digitorum longus tendon graft. Six animals were sacrificed at 4, 7, 11, 14, 21, and 28 days after surgery. Serial sections were analyzed for proliferating cells (PCNA), recruited macrophages (ED1), resident macrophages (ED2), neutrophils, T-lymphocytes (CD3), mast cells, immature progenitor cells/pericytes (expressing the NG2 cell-surface chondroitin sulfate proteoglycan), and newly-formed blood vessels (Factor VIII). Neutrophils, ED1(+) and ED2(+) macrophages accumulated sequentially in the healing tendon graft, with progressive cell ingrowth from the interface towards the inner tendon. Neutrophils and ED1(+) cells were seen in the tendon-bone interface at 4 days after surgery, while ED2(+) macrophages were not identified until 11 days. These cells progressively repopulated the tendon graft. NG2-positive progenitor cells were found along the edge of the bone tunnel in the interface, but these cells did not invade the tendon. Occasional T-lymphocytes and mast cells were seen in the tendon-bone interface. There was no proliferation of intrinsic tendon cells, indicating that the tendon does not directly contribute to healing. We hypothesize that cytokines produced by infiltrating macrophages are likely to contribute to the formation of a fibrous scar tissue interface rather than a normal insertion site.

Insulin-dependent diabetes impairs the inflammatory response and delays angiogenesis following Achilles tendon injury

Although impaired wound healing associated with type 1 diabetes mellitus has been well studied in skin tissue, the influence of this metabolic disorder on tendon healing and recovery has not been extensively investigated. Because tendons are known to have limited repair potential, we studied the tendon-healing process by using a diabetic rat tendonitis model. We tested the hypothesis that diabetes influences the inflammatory response, cell proliferation, and angiogenesis in injured Achilles tendons. Diabetes was induced by injecting streptozotocin at 45 mg/kg body wt. Non-diabetic rats as well as diabetic and insulin-treated diabetic animals were then injected with collagenase. The accumulation of inflammatory cells was quantified in transversal sections of Achilles tendon by using immunohistochemical staining at days 0, 1, 3, 7, 14, and 28 posttrauma. The number of proliferative cells and the extent of neovascularization was also quantified in the paratenon and the core of the tendon at days 0, 3, 7, 14, and 28 posttrauma. Relative to nondiabetic and insulin-treated diabetic animals, the numbers of accumulated neutrophils and ED1(+) and ED2(+) macrophages in diabetic rats decreased by 46, 43, and 52%, respectively, in the first 3 days after injury compared with levels in nondiabetic and insulin-treated diabetic animals. The density of newly formed blood vessels decreased by 35 and 29% in the paratenon and the core of tendon, respectively, at days 3 and 7 after injury. Lastly, the concentration of proliferative cells decreased by 34% in the paratenon at day 7 posttrauma in injured tendons from diabetic rats relative to nondiabetic rats. These results indicate that alterations in inflammatory, angiogenic, and proliferative processes occurred in the diabetic state that might eventually perturb tendon healing and remodeling.

Stimulation of mesothelial cell proliferation by exudate macrophages enhances serosal wound healing in a murine model

Examination of thermally induced serosal lesions in mice displayed collections of inflammatory cells, predominantly macrophages, on and surrounding the wound within 48 hours of injury. Furthermore, by 2 days a large number of uninjured mesothelial cells adjacent to the wound were synthesizing DNA. From these findings, it was hypothesized that macrophages play a major role in serosal repair by stimulating mesothelial cell proliferation. Again, using a murine model of mesothelial regeneration, depletion of circulating monocytes significantly delayed serosal healing whereas addition of peritoneal exudate cells to the wound site 36 hours before injury increased the healing rate. In vivo assessment of mesothelial cell proliferation using tritiated thymidine incorporation and autoradiography demonstrated that peritoneal exudate cells stimulated mesothelial cell proliferation (12.44 +/- 1.63% labeling index, compared with controls in which medium only was used 4.48 +/- 0.71%). The mesothelial proliferation was predominantly because of macrophage-secreted products with molecular weights of 36 to 53 kd or 67 to 100 kd. These data support the hypothesis that macrophages play an important role in serosal healing by stimulating mesothelial cell proliferation.

Neutrophils and macrophages accumulate sequentially following Achilles tendon injury

Structural damage and inflammation occur following tendon injury. The purpose of this study was to determine the time course of inflammatory cell accumulation in two animal models of acute tendinopathy. In the first model, rat Achilles tendons were exposed by blunt dissection, injected with collagenase and sacrificed at 1, 3, 7, 14 and 28 days. In the second model, collagenase was injected percutaneously and rats were sacrificed after 1 and 3 days. Sham animals were sacrificed at 1 and 3 days in both models. Neutrophil and ED1 macrophage populations increased by 46- and 18-fold, respectively, after 1 day in surgically exposed Achilles tendons (EAT) injected with collagenase. Neutrophils dropped by 70% while the concentration of ED1 macrophages remained constant at day 3 post-injury. Neutrophils and ED1+ macrophages returned to control values after 7 and 14 days, respectively. ED2+ macrophages showed a tendency to increase at day 28 although no significant difference was observed relative to ambulatory controls. Collagenase injected percutaneously reduced the extent of inflammation compared with operated animals. Thus, injured tendons exhibited a specific sequence of inflammatory cell accumulation which varied in intensity according to the modality used for collagenase injection.

The role of the immune system in conjunctival wound healing after glaucoma surgery

The immune system has a fundamental role in the development and regulation of ocular healing, which plays an important role in the pathogenesis of most blinding diseases. This review discusses the mechanisms of normal wound healing, describing the animal and fetal wound healing models used to provide further insight into normal wound repair. In particular, conjunctival wound repair after glaucoma filtration surgery will be used to illustrate the contributions that the different components of the immune system make to the healing process. The potential role of macrophages, the possible regulatory effect of lymphocytes, and the important role of growth factors and cytokines in the wound healing reaction are discussed. The significance of the immune system in the pathogenesis of aggressive conjunctival scarring is addressed, particularly assessing the predisposing factors, including drugs, age, and ethnicity. The rationale behind the pharmacological agents currently used to modulate the wound healing response and the effects these drugs have on the function of the immune system are described. Finally, potential new therapeutic approaches to regulating the wound healing response are reported.

Identification of macrophages at the site of peritoneal injury: evidence supporting a direct role for peritoneal macrophages in healing injured peritoneum

OBJECTIVE

To determine if peritoneal macrophages are present at the site of a surgical injury to the peritoneum during wound healing.

DESIGN

Controlled research study.

SETTING

Academic research laboratory. EXPERIMENTAL MODEL: A murine model of peritoneal wound healing.

INTERVENTION(S)

Intraperitoneal injection of polystyrene beads 1 hour after a surgical peritoneal injury to identify peritoneal macrophages.

MAIN OUTCOME MEASURE(S)

Presence of peritoneal macrophages at the site of the healing wound as determined by intracellular polystyrene beads on transmission electron microscopy 1, 3, 7, and 14 days after injury.

RESULT(S)

Peritoneal macrophages were easily distinguished from other cell types by the phagocytosis of polystyrene beads. One day after injury, peritoneal macrophages were adherent to the wound surface. By 3 days, mesothelial cells began covering the peritoneal macrophages at the wound surface and peritoneal macrophages were identified deep within the wound. Seven days after injury, the mesothelial layer was completely reconstituted, but peritoneal macrophages persisted within the healing would below the surface mesothelium.

CONCLUSION(S)

These data indicate that peritoneal macrophages are present at the peritoneal injury site throughout the healing interval and are consistent with these macrophages having a critical role in peritoneal wound healing.

The peritoneal response to expanded polytetrafluoroethylene and oxidized regenerated cellulose surgical adhesion barriers

OBJECTIVE

To determine the peritoneal response to the surgical adhesion barriers expanded-polytetrafluoroethylene (ePTFE) and oxidized regenerated cellulose (ORC).

STUDY DESIGN

The barriers were retrieved from the peritoneal cavities of women and mice 2 hours to 14 days after insertion and subjected to histology and electronmicroscopy.

RESULTS

Macrophages and mesothelial cells rapidly appeared on the surface of both materials. ePTFE was covered by 3 days, with the macrophages gradually being replaced by mesothelium and disappearing thereafter. By 7 days, a delicate membrane with surface mesothelial cells completely enveloped the ePTFE, creating a "pseudoperitoneum". The membrane was difficult to recover as it was fragile and not adherent to the ePTFE. ORC was rapidly infiltrated and degraded by leukocytes and disappeared by 5 days in mice and from all but 1 of 20 women by 11 days.

CONCLUSIONS

ePTFE is rapidly encapsulated by a non-adherent membrane resembling peritoneum while ORC is rapidly infiltrated and degraded by peritoneal fluid leukocytes.

Identification of epidermal growth factor, transforming growth factor-alpha, and epidermal growth factor receptor in surgically induced pelvic adhesions in the rat and intraperitoneal adhesions in the human

OBJECTIVE

Our purpose was to determine the presence and cellular distribution of epidermal growth factor, transforming growth factor-alpha, and epidermal growth factor receptor in surgically induced pelvic fibrous adhesions in rat uterine horns subjected to burn, crush, and debridement injury and intraperitoneal fibrous adhesions formed to various organs in the human.

STUDY DESIGN

A total of 15 injured and five uninjured rats were used in this study, and fibrous adhesions and intact peritoneum were removed for processing 2 weeks after surgery. Fibrous adhesions formed to uterine, ovarian, and oviductal tissues and the peritoneal wall from eight patients who had gynecologic surgery were also collected. The tissues were processed for immunohistochemical localization of epidermal growth factor, transforming growth factor-alpha, and epidermal growth factor receptor with specific antibodies to human and rat epidermal growth factor and transforming growth factor-alpha and the extracellular binding domain of the epidermal growth factor receptor.

RESULTS

All the cell types in the rat fibrous adhesion immunostained for epidermal growth factor, transforming growth factor-alpha, and epidermal growth factor receptor. The highest immunostaining intensity for epidermal growth factor was associated with inflammatory cells infiltrated into the fibrous adhesion, followed by arteriole endothelial and smooth muscle cells, fascial striated muscle, and fibroblasts of the fibrous adhesion. In the uterine tissue at the site of injuries myometrial smooth muscle cells, in addition to inflammatory cells that migrated among stromal cells, also immunostained for epidermal growth factor. Fibrous adhesions also immunostained for transforming growth factor-alpha with three separate polyclonal antibodies to the amino and carboxy termini of transforming growth factor-alpha precursor and the mature transforming growth factor-alpha, with no substantial differences in their intensity and pattern compared with epidermal growth factor. The pattern and cellular distribution of epidermal growth factor receptor was similar to that seen for epidermal growth factor and transforming growth factor-alpha. Fibrous adhesions from patients with intraperitoneal adhesions immunostained for epidermal growth factor, transforming growth factor-alpha, and epidermal growth factor receptor with a pattern and intensity similar to that observed in fibrous adhesions in the rats.

CONCLUSIONS

The data suggest that epidermal growth factor and transforming growth factor-alpha may play a key role both in normal mechanism of peritoneal repair after injury and formation and maintenance of fibrous adhesions.

The formation of coalescing peritoneal adhesions requires injury to both contacting peritoneal surfaces

OBJECTIVE

To determine whether surgical trauma to one or both contacting peritoneal surfaces is necessary to cause coalescing adhesions.

SETTING

Research laboratory.

DESIGN

The abdominal wall peritoneum and one or both contacting medial peritoneal surfaces of surgically approximated uterine horns in mice were injured by electrocautery, cutting, scratching, or scraping. Adhesion formation was assessed visually and histologically 3 and 7 days later.

RESULTS

Regardless of the type of peritoneal injury, few adhesions resulted when only a single injury was made to the abdominal wall (< or = 6%) or to one uterine horn (< or = 13%). When both opposing uterine surfaces were injured, however, adhesions formed at 57% of the sites after electrocautery, 100% after cutting, 100% after scratching, but 0% after scraping. When previously created uterine adhesions were lysed, they reformed at 15 of 15 sites with and 12 of 13 (92%) sites without electrocautery for hemostasis at the time of lysis.

CONCLUSIONS

In this murine model, the development of postsurgical adhesions required surgical trauma to both contacting peritoneal sites, regardless of the type of injury, the mobility of the opposing peritoneal surfaces or whether hemostasis was achieved. The clinical implications are that more attention needs to be focused on protecting contacting normal peritoneal surfaces from inadvertent injury during surgery and that different therapeutic strategies may be required for prevention of adhesion formation and reformation because of the high probability of contact between injured peritoneal surfaces with the latter.

Function of peritoneal exudate cells after abdominal surgery

Peritoneal macrophages and polymorphonuclear neutrophils are key cells in the repair of postoperative injury. Increased numbers of macrophages migrate into the peritoneal cavity after operation and the function of these cells changes over the postoperative interval. Macrophage activities, such as respiratory burst, arachidonic acid metabolism, monokine secretion, and plasminogen activator inhibitory activity, are elevated by peritoneal operation. However, the secretion of plasminogen activator activity is decreased after operation. The kinetics with which each of these functions changes varies with the parameter examined, indicating a complex regulation of the differentiation of leukocytes after operation. In addition, the activity of postoperative macrophages can be modulated in vitro by exposure to cytokines and conditioned media from polymorphonuclear neutrophils and macrophages. Thus, cell-cell interactions and factors secreted within the peritoneal cavity may regulate the contribution of postoperative leukocytes to peritoneal repair after operation.

Modulation of peritoneal re-epithelialization by postsurgical macrophages

The studies reviewed here show that postsurgical macrophages are capable of modulating the proliferation of TRC. That is, macrophages either suppress or enhance the proliferation of TRC depending on the culture time and the medium used as a comparison, i.e., culture medium with only serum or spent medium from cultures of resident peritoneal macrophages. Postsurgical macrophages also modulate the morphology of (spindly or rounded appearance) and the secretion of extracellular matrices by TRC. The responsivity of TRC to control by postsurgical macrophage-spent media or growth factors changes as a function of postsurgical and/or culture time. In addition, cells harvested from the site of peritoneal trauma (TRC) did not respond to growth factors in a fashion entirely the same as fibroblasts. This indicates that cells harvested from the site of peritoneal injury are unique. Lastly, after removal of a suppressive factor from postsurgical macrophage-spent media by dialysis, the factors secreted by postsurgical macrophages are more potent in enhancing TRC proliferation than growth factors individually.

Modulation of postsurgical macrophage function by early postsurgical polymorphonuclear leukocytes

Surgical trauma to the peritoneum, in the absence of infection, elicits a rapid and transient influx of polymorphonuclear leukocytes (PMNs) into the peritoneal cavity prior to the accumulation of macrophages. The aim of this study was to characterize the effects of these PMNs on macrophage function in the early postsurgical period. Rabbits underwent intestinal reanastomosis and peritoneal exudate cells were collected at various times after surgery. Macrophage-enriched preparations were incubated with spent media from cultures of PMNs obtained at the corresponding times after surgery. Superoxide anion (O2-) release by macrophages in response to phorbol myristate acetate was determined by cytochrome c reduction. Fibrinolytic and protease inhibitory activities in macrophage-spent media were also evaluated. The release of O2- had already increased at 2 hr, reached peak levels at 6 hr, and decreased by 24 hr after surgery. Spent media from PMNs harvested 6 hr after surgery suppressed, whereas spent media from postsurgical 12- or 24-hr PMNs increased O2- release from macrophages harvested at 6 and 12 hr after surgery. PMN-spent media had no effect on the secretion of plasminogen activator (PA) from macrophages harvested within 12 hr after surgery. In contrast, PA activity in the spent media from macrophages harvested 24 hr after surgery was elevated after exposure to PMN-spent media. PA inhibitory activity was reduced in macrophage-spent media at 2 hr after surgery and increased by 24 hr, while PMN-spent media had no effect on the level of PA inhibitory activity. Thus, soluble factors secreted into the culture medium by PMNs modulate macrophage function as soon as 6-12 hr after surgery.

Identification of a novel cell population in nonhealing wounds in tumors

We have explored wound healing in tumors as a possible model for tumor-host interaction. This work demonstrated tumor wound healing failure to be the result of intense inhibition of fibroblasts although the tumor cells did not appear to be the direct source of the inhibitors. The inflammatory infiltrate found in tumor wounds was then examined for possible sources of the observed fibroblast suppression. Although the tumor wound infiltrate contains cell populations similar to a normal wound infiltrate, it also contains a large, vacuolated, nonadherent, phagocytic mononuclear cell which has morphologic and cytochemical characteristics of a lipid-laden macrophage. However, the cell also proliferates under normal culture conditions and has an immunophenotype more characteristic of lymphocytes than those of macrophages with striking expression of the CD8 surface antigen. Conditioned media from this cell population markedly inhibit fibroblast proliferation suggesting it is the source of fibroblast inhibitors within the tumor wound. Mechanical dissociation of non-wounded tumors yielded evidence that the tumor wound cell is normally present in small numbers within the tumor.

Effects of interleukin-1 (IL-1) on postsurgical macrophage secretion of protease and protease inhibitor activities

Although peritoneal macrophages secrete a variety of inflammatory mediators and proteases during postsurgical repair of the peritoneum, regulation of this secretion is poorly understood. Here, the responsivity of peritoneal macrophages to interleukin-1 (IL-1) stimulation in vitro, measured by the secretion of protease and protease inhibitor activities, was evaluated as a function of postsurgical time. Macrophages were harvested at various times after peritoneal sidewall abrasion, isolated by discontinuous density centrifugation and cultured with varying concentrations of IL-1. IL-1 increased the secretion of plasminogen activator (PA) activity by peritoneal macrophages in a concentration-dependent manner on postsurgical Days 0, 3, 10, and 14. Macrophages harvested on postsurgical Day 1 after surgery responded only to high concentration of IL-1, while on Days 5 and 7 all doses of IL-1 stimulate PA. On Days 7, 10, and 14 after surgery, the secretion of PA activity (after acid treatment) by postsurgical macrophages was generally high and increased with IL-1 treatment. The level of PA activity after inactivation of acid labile inhibitors (PAI) also increased in a dose-dependent manner on Days 0, 3, and 5. Although Day 1 macrophages expressed the highest PAI activity of all groups, they had relatively low responsivity to IL-1 with regards to PAI secretion. The level of elastase activity by postsurgical macrophages was lowest on Day 1, highest on Day 7, and decreased thereafter. All concentrations of IL-1 inhibited elastase activity of macrophages on Day 7.(ABSTRACT TRUNCATED AT 250 WORDS)

Kinetics of interleukin-1 and tumor necrosis factor secretion by rabbit macrophages recovered from the peritoneal cavity after surgery

Macrophages play a crucial role in wound healing after surgical injury, both as scavenger cells responsible for wound debridement and as cells that secrete soluble factors such as interleukin-1 (IL-1) and tumor necrosis factor (TNF). IL-1 and TNF alter many of the biological activities of cells that appear in postsurgical wounds. In this study, we determined the kinetics of IL-1 and TNF production by rabbit macrophages harvested from postsurgical peritoneal exudate (postsurgical macrophages) at several time points after peritoneal surgery. To further characterize the level of functional activities of postsurgical macrophages, the IL-1 and TNF levels were determined with or without stimulating the cells with lipopolysaccharide (LPS) and phorbol myristate acetate (PMA). After surgery, the number of macrophages harvested by peritoneal lavage increased, reached peak levels on postsurgical day 3, and then decreased. IL-1 levels secreted by macrophages cultured without stimuli were elevated on postsurgical day 14 compared to the values on day 3 and 7. TNF concentrations peaked on days 1 and 14. In the conditioned culture media from LPS-PMA-stimulated macrophages, the levels of both IL-1 and TNF peaked on postsurgical days 3 and 14. These data suggest that the susceptibility of postsurgical macrophages to stimuli changes during the wound healing process with maximum sensitivity to the stimuli present during the early phase of peritoneal repair (day 3).

Regulation of proliferation of peritoneal tissue repair cells by peritoneal macrophages

Macrophages produce soluble mediators which modulate fibroblast growth during tissue repair. Interaction between tissue repair fibroblasts (TRC) and regulatory proteins from surgically elicited macrophages is important for peritoneal reepithelialization. In this study, we compared the effects of an extract from postsurgical macrophage spent medium with those of known growth factors on TRC collected from injured peritoneum to evaluate certain characteristics of macrophage secretory products on peritoneal healing. Rabbits underwent a midline laparotomy followed by resection and reanastomosis of the ileum or abrasion of the abdominal wall. TRC were then collected at various times after surgery. Peritoneal macrophages recovered from nonsurgical or postsurgical rabbits were cultured for 2 days in vitro. The peak of thymidine incorporation by TRC occurred on day 5 after surgery; this gradually decreased with extended postsurgical times. Fibroblast growth factor and epidermal growth factor stimulated, whereas TGF-beta inhibited, [3H]thymidine incorporation into TRC. Maximal thymidine incorporation occurred when TRC from Postsurgical Day 5 were cultured with an extract from postsurgical macrophage spent medium. However, when TRC recovered from Postsurgical Days 2 and 10 were cultured with an extract of postsurgical macrophage spent medium, they showed greater stimulation than Day 5 TRC. These data suggest that postsurgical macrophages may produce an array of factors that stimulate fibroblast growth and differentiation and may in turn affect tissue repair throughout the wound healing process.

Kinetics of interleukin-1 secretion by murine macrophages recovered from the peritoneal cavity after surgery

Macrophages play a central role in wound healing after surgical injury possibly through the secretion of soluble factors like interleukin-1 (IL-1). IL-1 has many biological activities which regulate most of the cell types that appear in postsurgical wounds. In this study, we determined the levels of IL-1 production by murine macrophages harvested from postsurgical exudate at several time points after standardized peritoneal surgery. To further characterize the level of functional activities of postsurgical macrophages, the IL-1 levels were determined with or without stimulating the cells with lipopolysaccharide (LPS) and phorbol myristate acetate (PMA). After surgery, the number of macrophages harvested by peritoneal lavage increased, reached peak levels on Postsurgical Day 3, and then decreased. IL-1 levels secreted by macrophages cultured without stimuli gradually increased after surgery, reaching peak levels on Day 10. In conditioned media from LPS-PMA-stimulated macrophages, IL-1 levels were significantly greater than in media from unstimulated macrophages and peaked on Postsurgical Day 3. These data suggest that the susceptibility of postsurgical macrophages to stimuli changes during the postsurgical wound healing process. Accordingly, IL-1 may play an important role in the late rather than in the early phase of peritoneal repair.

The mitogenic activity of peritoneal tissue repair cells: control by growth factors

The purpose of this study was to determine the proliferative activity of tissue repair fibroblasts recovered directly from injured peritoneum at various times after surgery and to test the mitogenic response of tissue repair cells (TRC) to growth factors. Rabbits underwent bilateral peritoneal abrasion (5 X 5 cm) with sterile gauze until punctate bleeding developed. Postsurgical (Days 2, 5, 7, and 10) tissue repair cells were recovered from the injured peritoneum by scraping with a scalpel blade. Although tissue repair cells consisted of a mixed cell type after 4 days in culture, recovered cells were essentially fibroblasts. These TRC were then pulsed with [3H]thymidine after 4 days in culture. The incorporation of thymidine into Postsurgical Day 5 TRC increased significantly compared to that of Day 2 TRC (P less than 0.05). Incorporation then decreased with time following surgery. Fibroblast growth factor (FGF) and epidermal growth factor (EGF) stimulated the incorporation of thymidine into TRC. However, the response of Postsurgical Day 7 and 10 TRCs to 1 microgram/ml EGF was significantly greater than those of Postsurgical Day 2 and 5 TRCs (Day 2 TRC, 166 +/- 7.4; Day 10 TRC, 420 +/- 96% of control cells without EGF, P less than 0.05). Platelet-derived growth factor (PDGF, 10 ng/ml) also stimulated the incorporation of thymidine into Day 10 TRCs, but this stimulatory activity (129.9 +/- 8.5% of control) was less than EGF or FGF. IL-1 alpha and IL-2 did not stimulate the incorporation of thymidine into TRC at a concentration of 100 pg/ml, but these cytokines did stimulate protein synthesis by TRC.(ABSTRACT TRUNCATED AT 250 WORDS)

Production of protease inhibitors by postsurgical macrophages

The deposition and lysis of fibrin are important processes in normal peritoneal healing. Since macrophages secrete a neutral plasminogen activator, we studied the production of plasminogen-dependent, fibrinolytic activity by postsurgical macrophages. Peritoneal exudate macrophages were collected from rabbits after resection and reanastomosis of their ileum. Intracellular plasminogen activator (PA) activity of resident (nonsurgical) macrophages was 8.4 +/- 1.8 milli-Plough units (mPU)/10(6) cells. Postsurgical Day 1 macrophages had significantly less activity (0.33 +/- 0.056 mPU/10(6) cells) compared to resident cells. Thereafter, the PA activity gradually increased and reached control levels by Postsurgical Day 7. The PA activity secreted by postsurgical macrophages into serum-free medium after 48 hr of culture was also determined. Conditioned medium from macrophages collected on Postoperative Days 1-5 exhibited less PA activity than buffer controls. PA activity was detected after acid treatment of the conditioned medium to remove acid-labile inhibitors. The activities of PA in acid-treated conditioned medium increased gradually and reached nonsurgical levels by Postsurgical Day 7. In spent medium from macrophages collected on Postsurgical Days 1-3, high levels of urokinase inhibitory activities were secreted; production gradually decreased during the later postoperative period. This inhibitory activity of macrophage-conditioned medium on urokinase-like PA activity was partially diminished by acidification of the media. These results support the hypothesis that macrophages in the postsurgical exudate may play an important role in the fibrinolytic process during peritoneal wound healing, perhaps through production and secretion of plasminogen activator as well as acid-labile and resistant protease inhibitors.

Mitogenic and protein synthetic activity of tissue repair cells: control by the postsurgical macrophage

It is well known that fibroblasts are a main source of extracellular matrix synthesis necessary for tissue repair. In addition, macrophages secrete products that are known to modulate synthesis of extracellular matrix. Accordingly, we studied the incorporation of [3H]thymidine, [3H]proline, and [35S]sulfate into macromolecules produced by fibroblasts recovered from the site of peritoneal tissue repair cultured with and without spent media from postsurgical peritoneal macrophages. Rabbits underwent resection and reanastomosis of their small intestines. Peritoneal exudative cells (PEC) were then collected on postsurgical day 5 and day 10 as well as from nonsurgical controls, separated by discontinuous Percoll gradient centrifugation, and cultured for 48 h. A second group of rabbits underwent peritoneal wall abrasion from which fibroblast tissue repair cells (TRC) were collected from the site of injury at postsurgical day 7 and maintained in culture for varying times. Incorporation of radiolabeled precursors into DNA, collagen, and sulfated proteoglycans was determined. Incorporation of [3H]thymidine and [3H]proline into untreated TRC gradually decreased with culture duration. Conversely, [35S]sulfate incorporation gradually increased during prolonged culture. Macrophage spent media increased the levels of [3H]thymidine incorporation by the TRC. [3H]Proline and [35S]sulfate incorporation into TRC were also stimulated by macrophage spent media. However, this stimulation may be due to the enhanced proliferation of TRC by macrophage spent media. In conclusion, tissue repair fibroblasts are activated for postsurgical repair at the site of injury by many factors including secretory products from postsurgical macrophages.

Incorporation of thymidine by fibroblasts: evidence for complex regulation by postsurgical macrophages

Macrophages and fibroblasts are major components of the postsurgical repair process. In order to understand more fully the interaction between these two cell types, we studied the modulation by macrophages of the incorporation of [3H]thymidine into postsurgical fibroblasts recovered from the site of peritoneal injury. Peritoneal exudate cells (PEC):(greater than 95% macrophages) were collected from rabbits 4 and 7 days after resection and reanastomosis of the small intestine. PEC were suspended in Medium 199 (M-199) with 3% fetal calf serum (FCS) and incubated for 48 hr. Fibroblasts were obtained from rabbits that underwent abrasion of the parietal peritoneum 7 days previously, and were cultured for 7 days in M-199 with 3% FCS. Fibroblasts were then replated and incubated with macrophage-spent medium. Incorporation of [3H]thymidine into fibroblasts was significantly suppressed after 24 hr of incubation with macrophage-spent media compared to the incorporation by fibroblasts incubated with fresh medium (control). This suppression was most profound when fibroblasts were incubated with resident (nonsurgical) macrophage-spent medium. The incorporation of thymidine by macrophage-spent media groups then increased rapidly and reached control levels at 48 hr of incubation. After 54 hr of incubation, the incorporation of thymidine by fibroblasts incubated with media from postsurgical macrophages was significantly higher than that of control. Morphological changes in fibroblasts also appeared as the culture with macrophage-spent media progressed. Initially, fibroblasts were shaped like pine needles, but after 7 days of culture, fibroblasts assumed a spherical shape. Round-shaped fibroblasts returned to the original morphology (pine needle shape) after incubation for 48 hr with macrophage-spent medium.(ABSTRACT TRUNCATED AT 250 WORDS)

Superoxide anion production by postsurgical macrophages

In order to characterize further the metabolic activity of postsurgical macrophages, we examined their potential to produce superoxide anion (O2-) in response to phorbol myristate acetate. Rabbits underwent resection and reanastomosis of their ileum after which peritoneal exudative cells (PEC) were collected at various times after surgery. Macrophages were isolated from the PEC with a discontinuous Percoll gradient. Thereafter, O2- release by these cells in response to phorbol myristate acetate (PMA) was determined by cytochrome c reduction. Macrophages recovered on postsurgical Days 3-7 expressed three- to fourfold greater O2- release than resident (nonsurgical) macrophages (P less than 0.001). In a time-course study of O2- release, maximum release occurred at 6 hr postsurgery, dropped to half of peak levels by Day 1, increased to peak levels again on Day 4, and remained increased until Day 7. The ability of macrophages to release O2- than gradually decreased, reaching control levels by Day 13. These data suggest that resident peritoneal macrophages are rapidly primed to produce enhanced amounts of superoxide anion in response to appropriate stimuli after surgery, and that macrophages subsequently recruited into the peritoneal cavity as a result of surgical trauma may also be primed for enhanced O2- release as they differentiate into modulator macrophages for tissue repair.