Journal home page: REVIEW ARTICLE. Micronucleus Applications in non-communicable diseases

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1 Journal home page: INTERNATIONAL JOURNAL OF INNOVATIVE AND APPLIED RESEARCH REVIEW ARTICLE Micronucleus Applications in non-communicable diseases Dr. Kumaraswamy Kademane 1 and *Dr. Barani Karikalan 2 1. Department of Pathology, International Medical University, Malaysia. 2. Department of Pathology, Mahsa University, Malaysia. *Corresponding Author Abstract: Micronuclei (MN) are directly related to genetic damage caused by various reasons and involved in pathogenesis of many diseases. MN assay can be utilized in many settings like to evaluate association of a risk factor, to understand pathological mechanism, to estimate susceptibility of the disease occurrence, to estimate prognosis of the disease, to predict the occurrence of complications related to the disease, to test newer treatment options and to compare different treatment modalities for the disease. With the said knowledge, diseases can be managed more effectively. This review gives a brief idea on how MN levels can be used in the management of various non-communicable diseases like diabetes, cardiovascular diseases, neurological diseases, chronic obstructive pulmonary diseases, chronic kidney diseases and immunological diseases. Key Words:Micronucleus, non-communicable diseases, genetic damage Introduction Micronuclei (MN) were first described in erythrocytes, where they are called as Howell-Jolly bodies, were later identified in lymphocytes and other exfoliated cells and had been related to genetic damage caused by exposure to environmental agents, various diseases including cancers and lifestyle changes(1). MN looks similar to main nuclei but smaller, usually about 1/16 to 1/3 of the mean diameter of the main nuclei. They are round or oval, non-refractile structures seen adjacent to or touching the main nucleus but they are never seen connecting to or overlapping with the main nucleus(2). MN are formed by acentric chromosome/chromatid fragments that got segregated from the spindle during mitosis, displaced, enclosed by a nuclear membrane. Acentric chromosome and chromatid fragments are formed when there is a defect in the DNA repair mechanism or if there exists DNA damage that exceeds repair capacity. Whole chromosomes get malsegregated as MN when there are defective kinetochore proteins that help in assembly of mitotic spindle due to cytosine and histone hypomethylation. Mitosis check point defect and abnormal centromere amplification are other causes for whole chromosome malsegregation. MN originating from whole chromosome could be distinguished from MN originating from acentric chromosome fragments by using pancentromeric DNA probes(1). MN can be found in normal individuals, but in insignificant numbers. Significant increase in MN is known to found in individuals exposed to environmental toxins, biohazard substance, radiation, drugs, and in diseases including chronic inflammatory conditions, cancers and genetic syndromes. MN scoring is usually done as number of micronucleated cells per 100 or 1000 cells and used clinically to detect genotoxicityby pollutants, carcinogens and drugs. They are also used in cancer screening, differentiating malignant and benign lesions, disease monitoring during treatment and in genetic diseases(3). Studies have also shown increase in MN score in population with life style factors like smoking and alcohol that are well known cancer risk factors. In addition, micronutrients and vitamin supplements had been reported to reduce MN score in cancerous and precancerous patients(4). The most commonly used method for scoring MN is cytokinesis block micronucleus assay (CBMN)(5). CBMN method is recently made easy and more reliable by development of image analysis systems like IMSTAR(6) and MetaSystemsMetafer image cytometry system(7).the cytokinesis-block micronucleus cytome (CBMN Cyt) assayis another updated method that not only measures MN but also other structures like nucleoplasmic bridges and nuclear buds(8). Other recent methods used for MN assay are flowcytometry(9) and laser scanning cytometry(10). 32

2 Objective of the review The review is intended to give a brief overview of utilization of MN assay in the prediction, diagnosis and prognosis of non-communicable diseases. Results and Discussion Cardiovascular diseases Based on the hypothesis that cancer and atherosclerosis may have common pathological mechanisms involved and involvement of mutational changes in atherogenesis suggested by many studies, Botto et al studied genetic damage in peripheral lymphocytes of patients with coronary vascular disease using MN assay. Increased MN wasseen in patients with known coronary atherosclerosis when compared to the control group confirming involvement of genetic damage in atherosclerosis. In addition, increase in MN correlated positively with increase in number of coronary vessels involved(11). Andreasi et al used MN assay for risk factor evaluation and relating them to various genetic polymorphisms of Methylenetetrahydrofolatereductase (MTHFR) gene. Patients with TT genotype of MTHFR polymorphism had higher plasma homocystiene, a known risk factor for cardiovascular disease, than CT and CC genotypes. MN levels were higher in patients with TT genotype and also in patients with high plasma homocystiene levels. Also, Plasma Vitamin B12 levels correlated negatively with plasma homocystiene levels, TT genotypes and MN levels. Thus, MN index is related to MTFTR gene polymorphisms causing genetic instability in coronary vascular disease(12). Smolkova et al using MN assay studied the effect of anti oxidant supplementation in decreasing DNA damage in cardiovascular disease patients. Cardiovascular disease patients supplemented with anti-oxidants showed decrease in MN levels than the control group. But patients with low folate level didn t show any decrease in MN levels even after anti-oxidant supplementation. Thus, folate was found to influence the protective effect of anti-oxidant against DNA damage(13). Andreassi et al confirmed increased MN levels in multivesselcoronary vascular diseasefurthur. They also found a significant increase in MN levels in patients with concomitant diabetes and in individuals who are under chronic nitrate therapy confirming the additive effect of these factors in genetic damage leading to coronary atherosclerosis(14). MN assay can also be used to predict future adverse events in cardiovascular disease patients. Federici et al, in their followup prospective cohort study evaluated MN levels in peripheral lymphocytes of 178 coronary artery disease patients. 58 patients ended up in major cardiovascular events like cardiac death, stroke and myocardial infarction during a follow-up of around 6 years. The adverse outcomes were significantly associated with increased MN levels (15). Primary prevention of cardiovascular disease ideally starts in early life. Assessing circulating DNA damage by MN assay might be helpful in predicting cardiovascular disease in high-risk children and adolescents. But Klieman et al could not correlate MN levels in individuals with cardiovascular risk factors indicating there is no permanent DNA damage in younger individuals with high risk factors. However, they were able to see a positive correlation with single cell gel electrophoresis, which indicates primary DNA damage in them. On the other hand, Vitamin C intake and folate status correlated negatively with MN levels. Thus, the use of MN assay in young individuals regarding cardiovascular disease is limited(16). Diabetes Glycosylated hemoglobin level is a predictive factor for complications in diabetes mellitus. Formation of glycation end products results in oxidative stress and subsequent DNA damage. Shettigar et al studied MN levels in diabetic patients and correlated with glycosylated hemoglobin levels. They were able to positively correlate both the readings and suggest that MN index can be used as a biomarker to predict the occurrence of complications in diabetes mellitus(17). Hyperglycemia is known to cause DNA damage in pregnant women and their newborns, which can be evaluated by MN levels in lymphocytes from the peripheral blood and cord blood. Witczak et al demonstrated increased MN levels in diabetic pregnant women and their newborns compared to their controls, especially the newborns of diabetic mothers had three times higher MN levels than newborns of normal women. This could be the reason for increased frequency of congenital malformations in infants of diabetic mothers(18). Mullner et al not only found raised MN levels in diabetic individuals compared to non diabetics, but also positively correlated MN levels with waist circumference, fasting plasma glucose, glycated hemoglobin and also participants 33

3 with cardiovascular risk factors. They also tried to correlate MN levels after dietary intervention with vegetables and walnut oil, but where able to find only moderate decrease in MN levels after intervention probably due to short duration of the study (19). Ramos et al using MN assay evaluated the effect of folic acid in diabetic patients. After intake of folic acid for a month, diabetic patients showed a significant decrease in their MN levels. Thus, folic acid being an anti oxidant reduces DNA damage and thereby delay complications associated with diabetes (20). Genotoxicity of anti-diabetic drugs in the long term can be assessed by MN test. Shaik et al compared MN levels of diabetic patients taking combination therapy of pioglitazone and glimepiride for more than 5 years with normal healthy subjects. MN levels in patients taking combination therapy were higher than normal controls indicating genotoxicity of oral anti-diabetic drugs in the long run(21). Gul et al using MN assay demonstrated that the genotoxicity level in diabetic patients treated with medical nutrition therapy, sitaglipton and thiazolidinediones. Sitagliptin was found to be more genotoxic than medical nutritional therapy but less genotoxic than thiazolidinediones. Thus, MN assay can be used to detect the effect of long-term use of anti-diabetic drugs and how they influence development of complications (22). Neurodegenerative diseases Trippi et al evaluated cytogenetic alterations in peripheral lymphocytes and skin fibroblasts in both sporadic and familial form of Alzheimer s disease (AD) patients via micronucleus test. They found increase in MN levels in AD patients than the controls. They also evaluated the effect of chemicals like aluminium and griseofulvin (known to cause DNA damage and produce AD like symptoms and lesions in animals) on peripheral lymphocytes of these patients. These chemical treatments caused changes in MN levels of peripheral lymphocytes of AD patients confirming that the peripheral systems also share cytologic alterations of the original disease and can be used in disease diagnosis and prognosis(23). Petrozzi et al also confirmed chromosomal damage in both AD and Parkinson s disease (PD) patients by increase in MN levels in their peripheral lymphocytes. In addition they did fluorescent insitu hybridization (FISH) to find the composition of MN in both the diseases. MN of AD patients contained mainly whole chromosome indicating microtubule instability. MN of PD patients were composed of acentric fragments indicating oxidative stress. Thus, composition of MN may indicate the molecular mechanisms underlying the disease process (24). Thomas et al tried to evaluate DNA damage in AD patients by measuring MN in buccal cells. But they did not see significant rise in MN levels, the reasons being discussed as less number of dividing basal cells in older individuals(25). Francois et al evaluated DNA damage by MN levels in patients with Down s syndrome that correlated well. They also found increased MN levels in lymphocytes and fibroblasts of AD patients. Thus, MN levels in peripheral cells could be a possible biomarker for diagnosing neurodegenerative diseases(26). Chronic Obstructive Pulmonary Diseases DNA damage is associated with Chronic Obstructive Pulmonary Diseases (COPD), reasons being free radicles produced by lung cells that are under oxidative stress and skeletal muscles cells especially during exercise. Maluf et al, in a study conducted in 25 COPD patients found MN frequency to be 6.72 in comparison to control group, 4.20(27). Susceptibility and progression of COPD is related to various genetic polymorphisms. Silva et al used MN test to evaluate DNA damage in COPD patients and PCR to identify potential genetic polymorphisms. Their results suggested possible associations between polymorphisms in genes like XRCC1, OGG1, XRCC3 and XRCC4 are associated with DNA damage with increased susceptibility to COPD(28). In addition, MN test was also used to study the effect of various interventions like physical exercise in COPD. Silva et al studied the effect physical exercise on COPD patients. DNA damage measured by buccal cell MN assay was less in patients who had undergone physical exercise when to non-physical exercise COPD group. Also, COPD patients on physical exercise had decreased susceptibility to exogenous DNA damage. When their peripheral lymphocytes were exposed to alkylating agent methyl methanesulphonate, the cells showed less DNA damage than other non-physical exercise COPD patients(29). Chronic Kidney Diseases Genetic damage is seen in chronic kidney disease (CKD), which makes these patients more susceptible to cancer. Sandoval et al found that the genetic damage in CKD patients measured by MN test is proportional to glomerular filtration index that indicates disease progression. This concludes that the MN levels correlate with level of disease progression in CKD patients. In addition, in patients with lower stage of CKD who had higher MN levels might indicate genetic predisposition of CKD in these patients(30). In addition, Sandoval et al attributed genetic damage to 34

4 decreased DNA repair capacity in CKD patients, which they related to increased radio sensitivity of peripheral lymphocytes of CKD patients. They exposed lymphocytes of CKD patients to ionizing radiation,invitro and measured DNA damage by MN test to indicate genetic instability in these patients(31). Analysis of MN levels in CKD patients showed that increased genetic damage in these patients is influenced by gender, age, diabetes and type of dialysis/treatment. Increased MN level were found in CKD patients with increased cholesterol, triglycerides, advanced glycation end products and markers of oxidative stress(32). Measuring MN levels in CKD patients can be useful to evaluate the efficacy of different treatment modalities. Roth et al compared genetic damage in CKD patients undergoing peritoneal dialysis with those undergoing hemodialysis (33). Thus, genetic damage in CKD patients measured by MN levels in either peripheral lymphocytes or buccal cells can be used to evaluate disease progression and to compare different therapeutic modalities. Immunological diseases Genetic damage is known to have important role in pathogenesis of immunological diseases. Karaman et al studied genetic damage in rheumatoid arthritis patients by measuring MN levels in their peripheral lymphocytes. They had higher MN levels in comparison with control group. Also, markers of oxidative stress like malondialdehyde were higher indicating the role of oxidative stress and genetic damage in these patients. This understanding may help in emergence of newer therapeutic modalities for immunological diseases(34). Table 1. Applications of MN levels in non-communicable diseases Applications To evaluate association of a risk factor with the disease To understand pathological mechanism behind the disease To estimate susceptibility of the disease occurrence To estimate prognosis of the disease To predict the occurrence of complications related to the disease To test newer treatment options and to compare different treatment modalities for the disease Conclusion The review has summarized various applications of measuring MN levels in patients with non-communicable diseases (Table 1). Emphasis has been made on MN levels as an effective and comparatively cheaper method that can be used fairly in the management of non-communicable diseases. References (1) Fenech M, Kirsch-Volders M, Natarajan A, Surralles J, Crott J, Parry J, et al. Molecular mechanisms of micronucleus, nucleoplasmic bridge and nuclear bud formation in mammalian and human cells. Mutagenesis 2011;26: (2) Bolognesi C, Knasmueller S, Nersesyan A, Thomas P, Fenech M. The HUMNxl scoring criteria for different cell types and nuclear anomalies in the buccal micronucleus cytome assay An update and expanded photogallery. Mutation Research 2013;753: (3) Swapan Samanta S, Pranab Dey P. Micronucleus and Its Applications. Diagnostic Cytopathology 2011;40: (4) Kashyap B, Reddy P. Micronuclei assay of exfoliated oral buccal cells: Means to assess the nuclear abnormalities in different diseases. J Cancer Res Ther 2012;8(2):

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