**2. Biomarkers – General definitions**

Biomarkers have been defined by the National Academy of Sciences (USA) as an alteration in cellular or biochemical components, processes, structure or functions that is measurable

effect or susceptibility possibly resulting in health damage or disease. These signs are

There has been dramatic progress in the application of biomarkers to human studies of cancer causation. Progress has been made in the development and validation of biomarkers that are directly relevant to the carcinogenic process and that can be used in large-scale

There are many important aspects to consider when a biomonitoring study is designed. For instance, there is needed a detail information on genotoxin exposure, e.g. type of toxin, duration of exposure, commencing date of exposure relative to sampling date of buccal cells, in order to achieve a meaningful interpretation of data. It will also helps to identify key variables affecting the observed frequency of biomarkers, like age, gender, vitamin B status,

Based on the impact on genotoxicity biomarkers in peripheral blood lymphocytes on the design of biomonitoring studies, Battershill et al. (2008) study have considered a strong/sufficient correlation between micronucleus (MN) frequency and increasing age. The effect is more pronounced in females than in males, with the increase more marked after 30 years of age. There are studies that also demonstrated a strong correlation between age and MN frequency and suggested that chromosome loss is a determining factor in this increase. In what concern to gender, is also documented a gender difference in the background incidence of MN in peripheral blood lymphocytes (PBL), with the frequency being consistently higher in females. A study that assessed MN, chromosomal aberrations and sister chromatid exchange showed highly significant elevations in MN in lymphocytes of women (29% when adjusted for age and smoking) whereas chromosomal aberrations and sister chromatid exchange remained unchanged. This may reflect aneuploidy detected in

In respect to smoking, although the link between smoking and cancer is strong and exposure to genotoxic carcinogens present in tobacco smoke has been convincingly demonstrated, interestingly the same convincing association is less apparent when assessing biomonitoring studies of genotoxicity. HUMN project study about tobacco smoke, the majority of the laboratories showed no significant differences between smokers and nonsmokers and the pooled analysis, interestingly, indicated an overall decrease for all smokers

It was verified a weak/insufficient evidence for association with genotoxicity end points and alcohol consumption. Alcohol consumption has been causally associated with cancer at a number of sites (e.g. head and neck cancer). Alcoholic beverages have not been reported to induce mutagenic effects in rodents. The evidence regarding an effect of drinking alcoholic beverages on increased MN or substitute for chromosomal aberrations formation in PBL is

Biomarkers have been defined by the National Academy of Sciences (USA) as an alteration in cellular or biochemical components, processes, structure or functions that is measurable

referred to as biomarkers (Manno et al., 2010).

epidemiologic studies (Manno et al., 2010).

MN assays (Battershill et al., 2008).

compared to controls (Battershill et al., 2008).

inconclusive (Battershill et al., 2008).

**2. Biomarkers – General definitions** 

genotype and smoking status (Thomas et al., 2009).

in a biological system or sample. The traditional, generally accepted classification of biomarkers into three main categories - biomarkers of exposure, effect, and susceptibility; depending on their toxicological significance (Manno et al., 2010).

A biomarker can potentially be any substance, structure or process that could be monitored in tissues or fluids and that predicts or influences health, or assesses the incidence or biological behaviour of a disease. Identification of biomarkers that are on causal pathway, have a high probability of reflecting health or the progression to clinical disease, and have the ability to account for all or most of the variation in a physiological state or the preponderance of cases of the specified clinical outcome, have largely remained elusive (Davis et al., 2007).

A biomarker of exposure is a chemical or its metabolite or the product of an interaction between a chemical and some target molecule or macromolecule that is measured in a compartment or a fluid of an organism (Manno et al., 2010).

A biomarker of effect is a measurable biochemical, structural, functional, behavioural or any other kind of alteration in an organism that, according to its magnitude, can be associated with an established or potential health impairment or disease. A sub-class of biomarkers of effect is represented by biomarkers of early disease (Manno et al., 2010).

A biomarker of susceptibility may be defined as an indicator of an inherent or acquired ability of an organism to respond to the challenge of exposure to a chemical (Manno et al., 2010).

Although the different types of biomarkers are considered for classification purposes, as separate and alternative, in fact it is not always possible to attribute them to a single category. The allocation of a biomarker to one type or the other sometimes depends on its toxicological significance and the specific context in which the test is being used (Manno et al., 2010).
