## 4 Discussion
In general, acetylation neutralizes the positive charge of lysine residues, resulting in a weaker histone-DNA interaction, in a subsequent relaxation of the chromatin, and transcriptional activation [58]. In this context, FA may impact post-transcriptional modifications disturbing the recruitment of regulatory complexes and evolving into an aberrant chromatin assembly that may facilitate anchorage-independent growth of cells. These data suggest that compromising chromatin assembly, through inhibition of lysine acetylation, may dysregulate cancer-related gene expression, as a possible new mechanism underlying FA-induced carcinogenesis [31]. The identification of FA reactive sites on histones is an initial step in understanding additional mechanisms of FA toxicity and carcinogenicity [59]. However, many issues remain to be clarified concerning the structure and fate of FA lysine adducts, the biological impact of such modifications on lysine residues, which are the exact sites for the formation of adducts, and their exact modes of action as well as how these changes may be recovered. Overall, to fully understand these aspects may be important to define the role of such alterations as possible biomarkers of early effect or susceptibility to the adverse FA impact. MicroRNA alterations have been detected in both in vitro [33] and in vivo models [34; 35; 36]. From a biological monitoring perspective, some conclusions, emerged from the study by [PERSON] et al. [35], need to be carefully considered. In different, simultaneously analyzed tissues, in fact, the authors determined the greatest and more time-stable miRNA alterations (from 7 to 28 days of treatment) in the \"most directly exposed\" nose epithelium compared to the \"less directly exposed\" WBCs. Moreover, miRNA changes showed a tissue-specific expression as only a minimal part of the alterations overlapped between these two different target sites. This underlines the importance to preliminary evaluate the relevance of individual biological matrices in the assessment of epigenetic biomarkers in relation to the routes of exposure as well as to the biological cascade intended to be investigated. Most of the miRNAs affected in nose epithelium and WBCs, in fact, were related to the expression of genes involved in nasopharyngeal carcinomas as well as in inflammatory/immune responses. Comparably, miRNA alterations detected in nose-epithelium of nonhuman primates were predicted to affect the balance between cell death and survival-affecting apoptosis, cell cycle progression, inflammation, therefore being potentially implicated in cellular transformation and cancer development [34; 36]. Then, an altered expression of miRNAs may not only be useful as a biomarker, but also as an active component or tumor development. Evidence has been pointed out concerning the miRNAalterations in all types of human cancer, both induced by genotoxic carcinogens, i.e., polycyclic aromatic hydrocarbon, aflatoxin B1, n-nitroso compounds, as well as by not genotoxic carcinogens, i.e., arsenic [27]. However, the specific role of miRNA deregulation in the etiology of cancers remain to be elucidated. To establish a link between miRNAs and carcinogenesis, some essential issues need to be addressed, such as if the altered expression of miRNA occurs at the early stages of carcinogenesis in the target organ and if such early changes are also evident in full-fledged tumors; if a mechanistic link exists between aberrant miRNA expression and cancer development; and whether altered miRNA expression is sufficient to initiate neoplastic cell transformation and cancer development. Interestingly, it was estimated that between 7% and 35% of the FA-responsive transcripts were regulated by FA-associated miRNAs. These data, on the one side, suggest that the miRNAs may be operating through mechanisms other than mRNA degradation [46; 60], but also that, on the other side, other transcriptional regulators, such as DNA methylation and histone modifications [61], may play a role in FA-induced genomic responses.