**3. Potential uses of peripheral blood micronucleus test (PBMNE)**

The peripheral blood erythrocyte micronucleus test (PBMNE) is used for ecotoxicological studies, monitoring of health effects from anthropogenic contamination, and genotoxic evaluation of pharmacological therapy administered in patients with chronic diseases [1]. Regarding the experimental procedure, mice are the most commonly used animals [2]. However, there are more animal models such as the rat and hamster [3] and others not as common like primates [4], birds [5], reptiles [6, 7], amphibians [8, 9], embryos [10], and fish [11]. Peripheral blood is the most versatile tissue for genotoxic and cytotoxic analysis. It is possible to use polychromatic and normochromatic erythrocyte conditions to explain the effects of myelosuppression and DNA damage [12]. Like all diagnostic tests, it has its limitations, which must be considered to avoid false negatives. One of them is that it does not detect substances that do not produce fractures or anaphase lags (aberrations that do not imply the occurrence of acentric fragments, for example, translocations and inversions); it is also not valuable for cells exhibiting a low rate of cell division or when organ-specific or species-specific carcinogens are tested [13].

Therefore, if all industrialization processes have the potential to generate large amounts of genotoxic substances, it is necessary to implement new models, such as plants or animals, to evaluate whether a particular substance or agent is harmful in the short/long term due to its mutagenic, clastogenic or aneuploidogenic, and teratogenic properties. Furthermore, to define toxic doses with greater precision, studies in several bioindicator models and not only in one must be carried out [14]. For the selection of any organism (plant or animal) as a toxic biomonitor, its cost, convenience, sensitivity, and possible extrapolation to other organisms or situations must be justified [15].

#### **3.1 Peripheral red blood micronuclei assay**

Peripheral blood was selected as a non-invasive sample to perform the MNi assay considering the invasive procedure implicated in a bone marrow sample. MNi are characterized by having a round or almond shape, with a diameter that varies from 1/20 to 1/5 (0.4 to 1.6 μ) of the average erythrocyte size (6 to 8 μ in diameter). William Henry Howell and Justin Marie Jolly identified MNi in erythrocyte precursors at the end of the 19th century and described them as remnants of the nucleus of circulating erythrocytes. Therefore, they are called Howell-Jolly bodies [16]. Subsequently, Dawson described MNi in the bone marrow of patients with several pathologies, including deficiency of cobalamin and folates; thereafter, MNi were described in lymphocytes [17].

Young or polychromatic erythrocytes (EPC) lose ribosomes within 24 hours after enucleation but retain MNi; later, they reach maturity and are transformed into normochromatic erythrocytes (ENC). These are stained blue-gray with the Giemsa stain or red with acridine orange, facilitating their identification when they are counted in tests of short exposure periods [1, 18]. Under certain circumstances, micronucleated erythrocyte (MND) values are often altered. Regardless of the tissue that is used in the MNi test, the data obtained are highly informative since it is a diagnostic tool to detect the loss of genetic material when these structures are identified in the cytoplasm of cellular compartment of the analyzed sample [19, 20].

#### **3.2 Peripheral blood and mononuclear phagocytic system MNi test**

The mononuclear phagocytic system (MPS), formerly called the reticuloendothelial system, is responsible for eliminating old or altered red blood cells, including micronucleated cells. In addition, the MPS system plays a key role in regulating innate immunity and it is constituted by dendritic cells, macrophages, and monocytes. The spleen, which is rich in macrophages, is the most sensitive detector for any red blood cell abnormality. By filtering the blood, the spleen eliminates foreign particles through phagocytic cells and destroys old erythrocytes or their fragments caused by structural changes that reduce their flexibility, making it difficult to pass through the microcirculation, undergoing cell lysis and splenic clearance [14, 21].

In mammals, two types of spleen are described, "defensive" and "storage." The former is smaller in size, has less muscle, but is abundant in lymphatic tissue and sinusoids; the latter, is larger, scarce in sinusoids, rich in the red pulp, and stores a more significant amount of blood [21]. Nevertheless, some species have a "defensive" spleen, which eliminates the abnormal erythrocytes in their entirety, making it impossible to observe MNi in peripheral blood. On the other hand, species with "storage" spleen are deficient in their phagocytic function and allow MNi to be observed at any time during the life of the species, as in the case of mice [14].


*Genomic Instability and Cyto-Genotoxic Damage in Animal Species DOI: http://dx.doi.org/10.5772/intechopen.99685*


#### *Updates on Veterinary Anatomy and Physiology*


#### **Table 1.**

*Examples of experimental species used in the MNi erythrocyte test as environmental biomonitors.*
