Brigitte Pittet

Infection in breast implants

Infection is the leading cause of morbidity that occurs after breast implantation and complicates 2.0-2.5% of interventions in most case series. Two-thirds of infections develop within the acute post-operative period, whereas some infections may develop years or even decades after surgery. Infection rates are higher after breast reconstruction and subsequent implantation than after breast augmentation. Risk factors for infection associated with breast implantation have not been carefully assessed in prospective studies with long-term follow-up. Surgical technique and the patients underlying condition are the most important determinants. In particular, breast reconstruction after mastectomy and radiotherapy for cancer is associated with a higher risk for infection. The origin of infection in women with implants remains difficult to determine, but potential sources include a contaminated implant, contaminated saline, the surgery itself or the surgical environment, the patients skin or mammary ducts, or, as suggested by many reports, seeding of the implant from remote infection sites. Late infection usually results from secondary bacteraemia or an invasive procedure at a location other than breasts. Diagnostic and management strategies are proposed and the value of peri-operative surgical prophylaxis is revisited. The current hypothesis of the possible role of low-grade or subclinical infection in the origin of capsular contracture is also reviewed.

Hypoxia-Inducible Angiopoietin-2 Expression Is Mimicked by Iodonium Compounds and Occurs in the Rat Brain and Skin in Response to Systemic Hypoxia and Tissue Ischemia

Angiopoietins are ligands for the endothelial cell tyrosine kinase receptor Tie-2. Ang-1, the major physiological activator of Tie-2, promotes blood vessel maturation and stability. Ang-2 counteracts this effect by competitively inhibiting the binding of Ang-1 to Tie-2. Using a combined RNase protection/semiquantitative reverse transcriptase-polymerase chain reaction approach, we demonstrate that hypoxia up-regulates Ang-2 mRNA levels by up to 3.3-fold in two human endothelial cell lines. In bovine microvascular endothelial (BME) cells, the flavoprotein oxidoreductase inhibitor diphenylene iodonium (DPI) and the related compound iodonium diphenyl mimic induction of Ang-2 but not vascular endothelial growth factor (VEGF) by hypoxia; in combination with hypoxia, DPI further increases Ang-2 expression but has no effect on the induction of VEGF by hypoxia. Neither Ang-2 or VEGF was increased by cyanide or rotenone, suggesting that failure in mitochondrial electron transport is not involved in the oxygen-sensing system that controls their expression. In ischemic rat dorsal skin flaps or in the brain of rats maintained for 12 hours under conditions of hypoxia, Ang-2 mRNA was up-regulated 7.5- or 17.6- fold, respectively. VEGF was concomitantly increased, whereas expression of Ang-1, Tie-2, and the related receptor Tie-1 was unaltered. In situ hybridization localized Ang-2 mRNA to endothelial cells in hypoxic skin. These findings 1) show that up-regulation of Ang-2 by hypoxia occurs widely in endothelial cells in vitro and in vivo; 2) suggest that induction of Ang-2, but not VEGF, by hypoxia in BME cells is controlled by a flavoprotein oxidoreductase that is sensitive to iodonium compounds; and 3) point to Ang-2 and VEGF as independently regulated and selective effectors of hypoxia-induced vascular sprouting.

Delivery of FGF-2 but not VEGF by encapsulated genetically engineered myoblasts improves survival and vascularization in a model of acute skin flap ischemia

Stimulating angiogenesis by gene transfer approaches offers the hope of treating tissue ischemia which is untreatable by currently practiced techniques of vessel grafting and bypass surgery. Vascular endothelial growth factor (VEGF) and basic fibroblast growth factor (FGF-2) are potent angiogenic molecules, making them ideal candidates for novel gene transfer protocols designed to promote new blood vessel growth. In this study, an ex vivo gene therapy approach utilizing cell encapsulation was employed to deliver VEGF and FGF-2 in a continuous and localized manner. C2C12 myoblasts were genetically engineered to secrete VEGF121, VEGF165 and FGF-2. These cell lines were encapsulated in hollow microporous polymer membranes for transplantation in vivo. Therapeutic efficacy was evaluated in a model of acute skin flap ischemia. Capsules were positioned under the distal, ischemic region of the flap. Control flaps showed 50% necrosis at 1 week. Capsules releasing either form of VEGF had no effect on flap survival, but induced a modest increase in distal vascular supply. Delivery of FGF-2 significantly improved flap survival, reducing necrosis to 34.2% (P < 0.001). Flap vascularization was significantly increased by FGF-2 (P < 0.01), with numerous vessels, many of which had a large lumen diameter, growing in the proximity of the implanted capsules. These results demonstrate that FGF-2, delivered from encapsulated cells, is more efficacious than either VEGF121 or VEGF165 in treating acute skin ischemia and improving skin flap survival. Furthermore, these data attest to the applicability of cell encapsulation for the delivery of angiogenic factors for the treatment and prevention of tissue ischemia.

Noma: an “infectious” disease of unknown aetiology

Noma (cancrum oris) is a devastating gangrenous disease that leads to severe tissue destruction in the face and is associated with high morbidity and mortality. It is seen almost exclusively in young children living in remote areas of less developed countries, particularly in Africa. The exact prevalence of the disease is unknown, but a conservative estimate is that 770000 people are currently affected by noma sequelae. The cause remains unknown, but a combination of several elements of a plausible aetiology has been identified: malnutrition, a compromised immune system, poor oral hygiene and a lesion of the gingival mucosal barrier, and an unidentified bacterial factor acting as a trigger for the disease. This review discusses the epidemiology, clinical features, current understanding of the pathophysiology, and treatment of the acute phase and sequelae requiring reconstructive surgery. Noma may be preventable if recognised at an early stage. Further research is needed to identify more exactly the causative agents.

Hypoxia Impairs Skin Myofibroblast Differentiation and Function

Ischemic wounds are characterized by oxygen levels lower than that of healthy skin (hypoxia) and poor healing. To better understand the pathophysiology of impaired wound healing, we investigated how switching from high (21%) to low (2%) oxygen levels directly affects cultured skin myofibroblasts, essential cells for the normal wound repair process. Myofibroblast differentiation and function were assessed by quantifying α-smooth muscle actin expression and cell contraction in collagen gels and on wrinkling silicone substrates. Culture for 5 days at 2% oxygen is perceived as hypoxia and significantly reduced myofibroblast differentiation and contraction despite high levels of the profibrotic transforming growth factor-β1. Analysis of α-smooth muscle actin expression on wrinkling substrates over time showed that reduced myofibroblast contraction preceded α-smooth muscle actin disassembly from stress fibers after switching from 21 to 2% oxygen. These effects were reversible by restoring high oxygen conditions and by applying mechanical stress. We suggest that mechanical challenge is a clinical relevant strategy to improve ischemic and chronic wound healing by supporting myofibroblast formation.

Skin flap-induced regression of granulation tissue correlates with reduced growth factor and increased metalloproteinase expression.

Previous studies have shown that covering granulation tissue of a full‐thickness skin wound by a vascularized skin flap induces tissue remodeling, with a rapid loss of granulation tissue cells by apoptosis. In the present study, in situ hybridization has been used to examine mRNA expression for several factors that may be implicated in the apoptosis seen in this tissue. Skin wounds were made on the dorsal skin of 8‐week‐old rats. Ten days after wounding, skin flaps were created surgically and sutured over the granulation tissue. Tissue sections of granulation tissue from various times after addition of the skin flap were hybridized with 33P‐labelled cRNA probes for transforming growth factor‐β1 (TGF‐β1), beta‐inducible gene H3 (β‐ig‐h3), α1 (I) procollagen, α‐smooth muscle actin, matrix metalloproteinase‐13 (MMP‐13) and ‐2 (MMP‐2), tissue inhibitor of metalloproteinase‐1 (TIMP‐1), and inducible nitric oxide synthase (iNOS). Control granulation tissue prior to addition of the skin flap showed high levels of TGF‐β1, β‐ig‐h3, α1 (I) procollagen, α‐smooth muscle actin, and TIMP‐1 expression. MMP‐13, MMP‐2, and iNOS mRNA were low in 10‐day granulation tissue. Addition of a skin flap resulted in a decrease in the expression of TGF‐β1, β‐ig‐h3, α1 (I) procollagen, α‐smooth muscle actin, and TIMP‐1, but increased expression of MMP‐13 and MMP‐2. Similarly, an increase in iNOS mRNA expression was observed in the granulation tissue after addition of the skin flap. Addition of a vascularized skin flap may result in rapid remodelling of granulation tissue due to a decrease in expression ofthe trophic growth factor TGF‐β1 and increased degradation of extracellular matrix due to an alteration in the balance between MMPs and their inhibitor, TIMP‐1. Additionally, increased iNOS expression may also favour apoptosis through the generation of free radicals. The additive effect of reduced growth factor expression, increased extracellular matrix turnover, and nitric oxide generation may result in the fibroblast and vascular cell apoptosis seen during the rapid remodelling of this tissue. Copyright

Nonactivated versus thrombin-activated platelets on wound healing and fibroblast-to-myofibroblast differentiation in vivo and in vitro.

Background: Platelet preparations for tissue healing are usually preactivated before application to deliver concentrated growth factors. In this study, the authors investigated the differences between nonactivated and thrombin-activated platelets in wound healing. Methods: The healing effects (i.e., wound closure, myofibroblast formation, and angiogenesis) of nonactivated and thrombin-activated platelets were compared in experimental wounds in diabetic (db/db) animals. In vitro, fibroblast phenotype and function were tested in response to platelets and activated platelets. No treatment served as a negative control. Results: Wounds treated with platelets reached 90 percent closure after 15 days, faster than activated platelets (26 days), and with higher levels of myofibroblasts and angiogenesis. In vitro, platelets enhanced cell migration and induced two-fold higher myofibroblast differentiation and contraction compared with activated platelets. Conclusions: Platelets stimulate wound healing more efficiently compared with activated platelets by enhancing fibroblast differentiation and contractile function. Similar levels of growth factors may induce different biological effects when delivered “on demand” rather than in an initial bolus.

Covering by a flap induces apoptosis of granulation tissue myofibroblasts and vascular cells.

It has recently been shown that during the healing of an open wound, apoptosis mediates the decrease in cellularity during the transition between granulation tissue and scar. Because reduced contraction and a decrease in the number of fibroblastic cells have been described in wounds covered with a successful skin graft, we hypothesized that apoptosis could be responsible for these phenomena. Using in situ labeling of fragmented DNA, immunohistochemistry for α‐smooth muscle actin, and electron microscopy, we have studied in rats the evolution of 10‐day‐old wound tissue covered with a total skin flap (containing epidermis, dermis, and the cutaneous muscle). In 10‐day‐old wound tissue, few apoptotic vascular cells and rare apoptotic myofibroblasts were present; the number of apoptotic cells increased slightly 72 hours later. In wounds covered with total skin flaps, the number of apoptotic vascular and myofibroblastic cells increased drastically 6 hours after flap application with a maximum at 24 and 48 hours, respectively. A decrease of apoptotic cell number was noted at 72 hours; at this time, the size of the granulation tissue was greatly reduced and showed extracellular matrix remodeling. Total flaps were more efficient in the induction of granulation tissue cell apoptosis compared with dermo‐epidermal flaps. Moreover, the control application of full‐thickness skin autografts, which were not viable 7 days later, did not induce apoptosis 24 hours after implantation. Our results indicate that covering granulation tissue with a skin flap results in a massive apoptotic process, possibly by means of a (some) locally released substance(s).

Nasal reconstruction in children: a review of 29 patients

SUMMARYAcquired large nasal defects are much more common in adulthood than in childhood because of the frequency of skin tumors after a certain age. However, from their experience in treating a number of children with sequelae of noma and burns, the authors have collected a series of 17 total and 12 partial nasal reconstructions in children aged 1 to 15 years. After reviewing the various methods used for recreating the lining, the support, and the skin cover in the whole series, three cases are reported in detail. A 1-year-old patient received a tempororetroauricular flap after total amputation of the nose and was observed for 17 years. Another patient, who was burned as a baby, underwent reconstruction at age 10 with a deltopectoral flap and was observed for 7 years. The third patient underwent total nose reconstruction at age 12 with an Indian forehead flap. From their experience, the authors conclude that, for psychosocial reasons, nasal reconstruction should be started early, despite possible reoperation at a later age. The best results are certainly obtained at the end of growth or at least after the age of 12. Adjacent bone or soft tissue defects further enhance the difficult challenge of restoring a satisfactory aesthetic appearance in these children.

The sandwich epicranial flaps.

&NA; Sandwich epicranial flaps are prefabricated composite flaps that have multiple uses in reconstructing the middle and the lower facial region. Sandwich epicranial flaps always comprise the galea and a full‐thickness skin graft; they may, in addition, include the temporal muscle and a fragment of parietal bone. According to their composition, four types of sandwich epicranial flaps are described. Experience with a use of 36 sandwich epicranial flaps (13 with vascularized bone) is reported. A few examples demonstrate the use of sandwich epicranial flaps in dramatic facial mutilation following noma in children. The sandwich epicranial flap can be performed at any age, does not require microsurgical anastomoses, and has a low complication rate. It is particularly useful for major reconstructive procedures in children. (Plast. Reconstr. Surg. 97: 302, 1996.)