To the Editor: Oliveira et al. (1) published in 2004 an interesting article investigating the effects of external thermal injury on female sheep normal skin. External thermal injury induced skin nitric oxide synthase, nitric oxide production, and its metabolites whereas BBS-2, a specific inhibitor of nitric oxide synthase, counteracted these effects. The working hypothesis of Oliveira et al. has led us to conduct a similar study. To date, in fact, little is known about the cellular lesions of burned dermal tissue affecting patients with deep partial thickness and which factors regulate the transition into full thickness. In our study, we hypothesized that apoptosis could be present and play a dominant role in the pathogenesis of deep partial thickness burns because these areas are often ischemic and the persistent hypoxia can lead to programmed cellular death (2). Since September 2005, we began to gather skin biopsies of all thermal burns during the first week of recovery from a homogeneous group of patients regarding sex, age, associated diseases, and total burn and deep burn surface areas. We collected 15 biopsies for each type of burns (superficial, deep partial thickness, and full thickness), 45 in total. Immunohistochemistry analysis consisted in terminal deoxynucletidyl transferase-mediated deoxyuridine 5-triphosphate nick end labeling (TUNEL) and Fas antigen expression.We defined apoptotic cells as those with colocalization of markers of DNA markers (TUNEL) and Fas antigen expression.
Mean apoptotic death rate (the number of apoptotic cells out of the total cells per field) was 5.6% in superficial partial thickness burns (interquartile range, 0%-13%), 44.5% in deep partial thickness burns (interquartile range, 6.3%-90.5%) and 0% for full thickness burn (absence of nuclei caused by the coagulative necrosis) (Figs. 1, 2). The difference was highly significant (P = 0.0002). Interestingly, apoptotic cells were present also at 7 postburn days and affected both dermal cells and sweat glands (Fig. 2B).
Our study shows that, in deep partial thickness burns, after initial injury a significant cell loss derives from apoptosis. Apoptotic death is not present in other burn types probably because the ischemic zone is peculiar of the deep partial thickness. Notably, there is evidence that a prompt reperfusion of ischemic areas of acute myocardial infarction seems to impair or reverse apoptotic mechanisms of death in myocardiocytes (3). The presence of apoptosis until 7 postburn days would justify aggressive treatments aimed at restoring oxygenation in the dermal tissue. In this context, it is our working hypothesis that a prompt reperfusion of ischemic areas of patients with deep partial thickness burns would improve their clinical outcome. Reperfusion of ischemic areas may be achieved by the following: (1) increasing intravascular blood flow (2), (2) counteracting microvascular thrombosis (4), and (3) promoting vascular angiogenesis (5). Thus, it would be interesting to test the effect of such reperfusion strategies on dermal apoptosis and induced skin nitric oxide synthase expression in Oliveira's animal model of thermal injury.
We are especially grateful to Dr. G. F. Muschietti and the Biotest Italia for supplying the Apoptag Kit for TUNEL marker of DNA fragmentation and the FasL ligand CD95 antibody.
University of Tor Vergata in Rome
Ciampino (Roma), Italy
1. Oliveira GV, Shimoda K, Enkhbaatar P, Jodoin J, Burke AS, Chinkes DL, Hawkins HK, Herndon DN, Traber L, Traber D, et alet al: Skin nitric oxide and its metabolites are increased in nonburned skin after thermal injuries. Shock
2. Cassuto J, Tarnow P, Yregard L, Lindblom L, Rantfors J: Regulation of postburn ischemia by alpha- and beta-adrenoceptor subtypes. Burns
3. Baldi A, Abbate A, Bussani R, Patti G, Melfi R, Angelini A, Dobrina A, Rossiello R, Silvestri F, Baldi F, et al: Apoptosis and post-infarction left ventricular remodeling. J Mol Cell Cardiol
4. Saliba MJ Jr: Heparin in the treatment of burns: a review. Burns
5. Folkman J, Weisz PB, Joullie MM, Li WW, Ewing WR: Control of angiogenesis with synthetic heparin substitutes. Science