Carcinogênese de pele e pulmão em linhagens de camundongos selecionados segundo a reatividade inflamatória aguda.

Abstract

SOUZA, V. R. C. de. Skin and Lung Carcinogenesis in Mice Selected for Acute Inflammatory Response (AIR) 2007. 102 f. Doctor thesis (Immunology) Instituto de Ciencias Biomedicas, Departamento de Imunologia, Universidade de Sao Paulo, Sao Paulo, 2007. Two lines of mice were genetically selected for the maximal (AIRmax) or minimal (AIRmin) local acute inflammatory reactions (AIR) to non immunogenic polyacrilamide beads (Biogel). These lines greatly differed in susceptibility to two stage skin carcinogenesis induced by the epicutaneous administration of dimethylbenzo[a]anthracene and repeated doses of phorbol miristate acetate (DMBA/TPA) and for lung cancer induced by the ip injection of urethane. AIRmax were resistant and AIRmin susceptible, demonstrating an association between the predisposition to chemical carcinogenesis and the genetic control of inflammatory reactivity. In this work, we used two polycyclic aromatic hydrocarbon (PAH) carcinogenic compounds in these mouse lines: 3-methylcholanthrene (3-MCA) and DMBA. 3-MCA was injected im and 50% of AIRmin and AIRmax mice developed local tumor (≥ 0,5 cm) between 19 and 23 weeks after treatment, respectively. However, after 45 weeks, about 90% of all animals developed fibrosarcomas but at this time, AIRmin mice only, showed multiple lung adenomas and large adenocarcinomas. DMBA was applied in 5 repeated 50μg epicutaneous doses. AIRmax mice were resistant but AIRmin mice developed skin reaction, followed by the appearance of skin and lung tumors. Total RNA was extracted from skin fractions at 48 h after the last dose and expression levels of cytokines and P450 enzymes mRNA were scored by realtime PCR In AIRmin mice DMBA induced significantly up regulated levels of IL-1β (46x), TNF-α (6x), IL-6 (7x), TGF-β1 (5x) and CYP1B1 (7x) mRNA. In AIRmax, the results were similar to controls. The aryl hydrocarbon receptor (Ahr) plays an important role in polyaromatic hydrocarbon (PAH) metabolism. Upon binding to agonist this transcription factor increases the expression of CYP 450 enzymes. An allelic polymorphism was found in Ahr gene between inbred mouse lines which correlated to a decrease in binding affinity of the receptor to DMBA and a decrease in carcinogenesis susceptibility. All AIRmax are homozygous for the Ahr allele encoding the low affinity receptor whereas all AIRmin bear the high affinity related allele. The allelic segregation in these two lines indicates Ahr as a genetic marker or a gene target involved in inflammatory response control. This was confirmed by a linkage analysis or the co-inheritance of Ahr parental genotypes with the degree of acute inflammation to Biogel in a heterogeneous F2 (AIRmax X AIRmin) intercross population. Conclusions: AIRmax mice are resistant and AIRmin mice are susceptible to the induction of skin tumors by continuous application of DMBA. Late after treatment with DMBA and 3-MCA, AIRmin were also significantly more susceptible than AIRmax to develop lung tumors. AIRmin mice presented a precocious skin reaction to DMBA which was correlated to tumor development susceptibility. This reaction was contemporary to the upregulation of the expression in the skin of cytokine genes such as IL-1β, IL-6, TNF-α and TGF-β and of cytochrome P450 Cyp1b enzyme. The profile of cytokines induced in AIRmin mice is coherent with the elicitation of contact hypersensitivity reaction by DMBA. The increase in Cyp1b1 enzyme correlates with the cutaneous bioactivation of DMBA which in turn depends on high affinity binding to AHR. The results point to mechanisms and genetic factors underlying the differential susceptibility of AIRmax and AIRmin mice to carcinogenesis induced by PAHs.