Molecular epidemiology of primary brain tumors

Heritability of nervous system tumors: a sibling-based design

Background

The contribution of genetic and environmental factors to susceptibility to nervous system tumors remains unclear. We performed a quantitative genetic study using a sibling design to estimate the heritability of nervous system tumors, as well as the proportion of the risk of these tumors, which is attributable to environmental factors.

Methods

We conducted a population-based cohort study using Swedish National Register data. All individuals born in Sweden during 1950-2010 with available information on both biological parents were included. A Multi-Generation Register was used to identify family clusters, including both full- and half-siblings. Initially, one index person was randomly selected from each cluster containing only full siblings and one sibling was randomly assigned to this index person. Subsequently, within each of the remaining clusters of full- and half-siblings, an index person was randomly selected, and a half-sibling was randomly assigned to this index person. Among the randomly selected siblings, cases of nervous system tumors were identified using the cancer registry. Quantitative genetic models were used to estimate the proportion of the variance in nervous system tumors attributable to additive genetic factors, shared environment, and individual-specific environment.

Results

The heritability of nervous system tumors was estimated to be 29% (95% confidence interval (CI) = 19%-39%), while the contribution of the non-shared environment to the variance of nervous system tumors was estimated to be 71% (95% CI = 61%-81%). The shared environmental parameter was estimated as zero in the full model.

Conclusion

The variation in susceptibility to nervous system tumors is predominantly attributable to non-shared environmental factors, followed by genetic factors.

Association of RNA m7G Modification Gene Polymorphisms with Pediatric Glioma Risk

Glioma stemming from glial cells of the central nervous system (CNS) is one of the leading causes of cancer death in childhood. The genetic predisposition of glioma is not fully understood. METTL1-WDR4 methyltransferase complex is implicated in tumorigenesis by catalyzing N7-methylguanosine (m⁷G) modification of RNA. This study is aimed at determining the association of glioma risk with three polymorphisms (rs2291617, rs10877013, and rs10877012) in METTL1 and five polymorphisms (rs2156315 rs2156316, rs6586250, rs15736, and rs2248490) in WDR4 gene in children of Chinese Han. We enrolled 314 cases and 380 controls from three independent hospitals. Genotypes of these polymorphisms were determined using the TaqMan assay. We found the WDR4 gene rs15736 was significantly associated with reduced glioma risk (GA/AA vs. GG: adjusted odds ratio = 0.63, 95%confidence interval = 0.42 - 0.94, P = 0.023) out of the eight studied polymorphisms. Stratified analyses showed that the association of rs15736 with the risk of glioma remained significant in children aged 60 months or older, girls, the subgroups with astrocytic tumors, or grade I + II glioma. We also found the combined effects of five WDR4 gene polymorphisms on glioma risk. Finally, expression quantitative trait locus (eQTL) analyses elucidated that the rs15736 polymorphism was related to the expression level of WDR4 and neighboring gene cystathionine-beta-synthase (CBS). Our finding provided evidence of a causal association between WDR4 gene polymorphisms and glioma susceptibility in Chinese Han children.

Identification of Prognostic LncRNAs Subtypes Predicts Prognosis and Immune Microenvironment for Glioma

Glioma is the most commonly occurring primary neuroepithelial neoplasm. Long noncoding RNAs (lncRNAs) are emerging as pivotal modulators of gene expression in the immune system and play critical roles in the growth, progression, and immune response of carcinomas. In this study, we performed univariate Cox regression analysis on survival data from TCGA and identified 20 prognostic lncRNAs. Moreover, we revealed that these prognosis-related lncRNAs (PRLnc) were dysregulated in glioma. Furthermore, we constructed a signature based on the expression levels of these prognosis-related lncRNAs based on 13 prognostic lncRNAs, including AGAP2-AS1, CYTOR, MIR155HG, LINC00634, HOTAIRM1, SNHG18, LINC01841, LINC01842, LINC01426, MIR9-3HG, TMEM220-AS1, LINC00641, LINC01270, and LINC01503. The Kaplan–Meier curves show that high-risk patients had a shorter survival time. Finally, the glioma samples were classified into 2 subgroups based on the median expression of prognosis-related lncRNAs in each sample. In summary, these findings suggest that PRLnc is associated with tumor-infiltrating immune cells in glioma and that subtype 2 patients may respond more positively to immunotherapy.

Association between human herpesvirus-6 and primary brain tumors: a systematic review and meta-analysis

Aim: The present study aimed to find out the prevalence and any possible association between human herpesvirus (HHV-6) and primary brain tumors. Materials & methods: The systematic literature search was performed by finding related articles from major databases. Analysis was performed by comprehensive meta-analysis software. Results: A total of 13 (25 datasets) articles were included in the study, seven (15 datasets) of which were case/control and the rest (ten datasets) were cross-sectional studies. The pooled prevalence of HHV-6 among primary brain cancer patients was 29% (95% CI: 24–33%; I2 = 97.89%). An association was found between HHV-6 and primary brain cancer (summary odds ratio: 3.77% [95% CI: 2.59–5.49%; I2 = 19.0%]). Conclusion: Our analysis demonstrated that HHV-6 is associated with primary brain cancer. Reactivation of the virus could be triggered by the tumor, therefore, we cannot be certain that the virus appeared before the cancer development.

The Effects of Sterol-Related Signaling Pathways on Glioma

Gliomas are considered as one of the important brain tumors in adults due to their impact on life quality and cognitive functions. Current methods that are used for treating glioma are not satisfying enough. Understanding cellular and molecular events underlying its pathogenesis and progression may lead to the discovery of novel therapeutic approaches. Sterols are a subtype of steroids and are essential for the physiologic functions of eukaryotic cells. Sterols can be produced by protozoans and microheterotrophs. Moreover, they are found in some natural sources, such as plants, animals, fungi, microalgae, and yeasts. Besides the roles of sterols in physiologic processes, studies have shown that they are involved in pathologic processes, including tumorigenesis and tumor progression. As investigations have revealed, sterol-related signaling pathways are involved in glioma and targeting them may result in new therapeutic options for patients. Thus, we summarized some of the sterol-related signaling pathways in glioma and how they can be associated with other signaling pathways, including EGFR/PI3K/Akt/mTOR, P53, and retinoblastoma protein.

Relationship Between Oral Contraceptives and the Risk of Gliomas and Meningiomas: A Dose-Response Meta-Analysis and Systematic Review

OBJECTIVE

Glioma and meningioma are the most common primary brain tumors in adults. Epidemiologic studies of the relationship between female hormone exposure and exogenous hormone use and the risk of meningioma and glioma in females have yielded inconsistent results.

METHODS

Two investigators comprehensively searched 3 electronic databases, including PubMed, Embase, and Cochrane Library. A total of 11 case-control studies were enrolled for meta-analysis. Dose-response meta-analyses were conducted.

RESULTS

Compared with the non-oral contraceptives (OCs) female users, the female OC users might have reduced risk of glioma (risk ratio [RR], 0.87; 95% confidence interval [CI], 0.77-0.97; I² = 42.6%). However, there was no obvious evidence of an association between OC use and the risk of meningioma in females (RR, 0.99; 95% CI, 0.87-1.13; I² = 42.7%). Using OCs for >10 years in females may significantly decrease the risk of glioma to 30% (RR, 0.7; 95% CI, 0.6-0.81; I² = 0%). The dose-response meta-analyses indicated that the risk of glioma in females significantly decreased when the duration of oral OC use was >7.5 years.

CONCLUSIONS

OC use may not increase the risks of glioma and meningioma in females. Instead, the long-term use of OCs may significantly decrease the risk of glioma, and the benefits are even more pronounced when the time window is >7.5 years. Nonetheless, the pooled results in this study suggest that OC use may not increase the risk of meningioma. Therefore, our conclusion should be validated and supplemented in future larger studies.

MicroRNA-16 inhibits the growth and metastasis of human glioma cells via modulation of PI3K/AKT/mTOR signalling pathway

Introduction

Gliomas are lethal cancers accounting for significant human mortality across the globe. MicroRNAs (miRs) have shown potential to act as therapeutic targets for the treatment of cancer. Herein the role and therapeutic implications of miR-16 in glioma were investigated.

Material and methods

Expression analysis was carried out by qRT-PCR. Cell-Titer-Glo assay (Promega) was used for the determination of cell proliferation. DAPI, AO/EB, and annexin V/PI assays were used to detect apoptosis. Wound healing and Transwell assays were used for cell migration and invasion, respectively. Western blot analysis was used for the determination of protein expression.

Results

The study revealed that miR-16 was significantly suppressed in the human glioma cells. Ectopic expression of miR-16 in U118 MG cells inhibited the proliferation via induction of apoptosis. The apoptosis induction was also accompanied by an upsurge of Bax and depletion of Bcl-2. The overexpression of miR-16 also inhibited the migration and invasion of the glioma U118 MG cells, as evident from the wound healing and transwell assays, which were accompanied by the inhibition of metalloproteinase-2 and -9 (MMP-2 and MMP-9). The effects of miR-16 overexpression were also examined on the PI3K/AKT/mTOR signalling pathway. The results showed that miR-16 overexpression inhibited the phosphorylation of the p70S6K, AKT, and mTOR at Ser473, Ser2448, and Thr389, respectively, with no apparent effects on the total PI3K and AKT.

Conclusions

miR-16 acts as tumour suppressor in glioma and may severe as therapeutic target for glioma treatment.

MicroRNA-181 inhibits the proliferation, drug sensitivity and invasion of human glioma cells by targeting Selenoprotein K (SELK)

Gliomas are aggressive type of brain tumors and cause significant human mortality world over. The frequent relapses, development of drug resistance, the adverse effects of the chemotherapy and dearth of the therapeutic targets form the major hurdles in glioma treatment. Several studies suggest that microRNAs (miRs) are involved in the development and progression of different cancers. Herein, the therapeutic potential of miR-181 was explored in human glioma cells. The results showed that miR-181 is significantly downregulated in human glioma cells. Overexpression of miR-181 caused significant inhibition in the proliferation of U87 and U118 glioma cells. The miR-181 triggered growth inhibition was found to be mainly due to the induction of apoptosis which was concomitant with increase in the Bax/Bcl-2 ratio. Additionally, miR-181 enhanced the chemosensitivity of the glioma cells to temozolomide and suppressed their invasion. Bioinformatic analysis showed that miR-181 exerts its effects by inhibiting the expression of Selenoprotein K (SELK). The expression of SELK was found to be significantly upregulated in glioma cells and silencing of SELK suppressed the proliferation of glioma cells. Nonetheless, overexpression of SELK could nullify the effects of miR-181 on the proliferation of the glioma cells. Taken together, miR-181 may exhibit therapeutic implications in the treatment of glioma.

Role of SOD2 Ala16Val polymorphism in primary brain tumors

The present study aimed to investigate the possible association between the genetic polymorphism of the enzyme superoxide dismutase 2 (SOD2, also known as manganese-dependent SOD), Ala16Val (rs4880), and primary brain tumor risk in the Turkish population. Frequency of the SOD2 gene rs4880 polymorphism was identified in 225 Turkish individuals (120 controls and 105 patients with primary brain tumor) by polymerase chain reaction-restriction fragment length polymorphism. Subject demographics and clinical characteristics were also recorded. The findings were evaluated using logistic regression and χ² tests. Logistic regression analysis indicated that smoking did not increase the risk for primary brain tumor [odds ratio (OR)=0.77, 95% confidence interval (CI)= 0.44-1.33, χ²=0.352, P=0.860]. Similarly, there was no statistically significant difference in the family history of cancer incidence between the control subjects and the primary brain tumor patients (OR=0.81, 95% CI=0.39-1.71, χ²=0.340, P=0.560). There was no significant association of the histopathological type, genotype/allele frequencies and inheritance models of tumor with the gene variants among the patients with primary brain tumor. In summary, the results of the present study indicated that the Ala16Val polymorphism of the SOD2 gene was not associated with primary brain tumor risk in the Turkish population studied.

The Application of FOXO1A Expression Predicts Aggressive Behavior and Poor Prognosis in Gliomas

Forkhead box, class O, 1A (FOXO1A) is an important factor related to some human malignancies. We tested the association between FOXO1A cytoplasmic expression and World Health Organization grading system in primary brain tumors (PBTs). First of all, Western blot analysis was also performed in normal brain tissue and U87MG, LN229, GBM8401, and U118MG glioma cell lines protein lysates. Then, in order to realize FOXO1A gene expression in gliomas, U87MG, LN229, GBM8401 mRNA were applied to performed quantitative reverse transcription polymerase chain reaction (RT-PCR). At last, the immunohistochemical (IHC) analysis of FOXO1A was performed in 8 non-neoplastic brain tissues and 126 PBTs. The immunostain scores were obtained as the degree of cytoplasmic FOXO1A intensity multiplied by the percentage of positively stained tumor area. On the basis of the results of these in vitro studies, marked increase FOXO1A protein and mRNA expressions in glioma cell lines than in normal human tissue. On the view point of IHC stains, the average immunostain score of FOXO1A in all PBTs was significantly higher than non-neoplastic brain tissues. In addition, the immunostain scores of FOXO1A in high grade were higher than low-grade gliomas. Furthermore, higher cytoplasmic expression of FOXO1A might indicate the shorter overall survival rate in gliomas. Furthermore, FOXO1A expression was associated with isocitrate dehydrogenase I /2, ATRX, and p53 mutation by IHC staining. Therefore, the application of FOXO1A IHC stain might have some benefits to improve diagnostic accuracy, predict tumor progression, and evaluate survival time in glioma patients.

Proteolipid Protein 2 Overexpression Indicates Aggressive Tumor Behavior and Adverse Prognosis in Human Gliomas

Proteolipid protein 2 (PLP2), a membrane protein of the endoplasmic reticulum, is related to tumor proliferation and metastasis in some human cancers, but not in gliomas. First, we performed western-blot analysis, real-time quantitative PCR and immunohistochemical stains to detect PLP2 expression in 4 glioma cell lines and human glioma tissues. In addition, we used small interfering RNA (SiPLP2) and short hairpin RNA (shPLP2) to knockdown PLP2 expression in GBM8401 and LN229 glioma cell lines. After then, the alteration of PLP2 suppressed glioma cells behavior were examined by cell proliferation, wound healing, cell invasion, and colonies formation assays. Finally, the possible mechanism of PLP2 was analyzed by detecting the expression of the proteins related to cell-cycle checkpoints, cell-proliferative signaling factors, and cell-matrix interaction. Compared with normal brain cell lysates and mRNA, all glioma cell lines displayed PLP2 protein and mRNA overexpression. Besides, higher PLP2 IHC staining significantly correlated with more advanced tumor grades and poorer prognosis in human gliomas. Both siPLP2 transfected gliomas showed a clear inhibition of glioma cell proliferation, migration, and invasion as well as down-regulating p-p38, p-ERK, MMP-2, and MMP-9 expression. In conclusion, we successfully demonstrated that PLP2 overexpression played an oncogenic role in glioma development and aggressive tumor behavior.

MDM4 contributes to the increased risk of glioma susceptibility in Han Chinese population

Recently, MDM4 gene has been reported to be a susceptibility gene for glioma in Europeans, but the molecular mechanism of glioma pathogenesis remains unknown. The aim of this study was to investigate whether common variants of MDM4 contribute to the risk of glioma in Han Chinese individuals. A total of 24 single-nucleotide polymorphisms (SNPs) of the MDM4 gene were assessed in a dataset of 562 glioma patients (non-glioblastoma) and 1,192 cancer-free controls. The SNP rs4252707 was found to be strongly associated with the risk of non-GBM (P = 0.000101, adjusted odds ratio (OR) = 1.34, 95% confidence interval (CI) = 1.16–1.55). Further analyses indicated that there was a significant association between A allele of rs4252707 associated with the increased non-GBM risk. Haplotype analysis also confirmed a result similar to that of the single-SNP analysis. Using stratification analyses, we found the association of rs4252707 with an increased non-GBM risk in adults (≥18 years, P = 0.0016) and individuals without IR exposure history (P = 0.0013). Our results provide strong evidence that the MDM4 gene is tightly linked to genetic susceptibility for non-GBM risk in Han Chinese population, indicating a important role for MDM4 gene in the etiology of glioma.

Height, waist circumference, body mass index, and body somatotype across the life course and risk of glioma

PURPOSE

Recent studies have suggested height as a risk factor for glioma, but less is known regarding body mass index (BMI) or other anthropomorphic measures. We evaluated the association between body habitus and risk of glioma.

METHODS

We evaluated the association of measures of height, BMI, waist circumference, and somatotypes with risk of glioma in two prospective cohorts, the Nurses' Health Study and the Health Professionals Follow-Up Study.

RESULTS

We documented 508 incident cases of glioma (321 glioblastoma [GBM]). In both cohorts, we found no significant association between adult BMI or waist circumference and risk of glioma, with pooled HR for BMI of 1.08 (95% CI 0.85-1.38 comparing ≥ 30 to < 25 kg/m²) and for waist circumference of 1.05 (95% CI 0.80-1.37 highest vs. lowest quintile). Higher young adult BMI (at age 18 in NHS and 21 in HPFS) was associated with modestly increased risk of glioma in the pooled cohorts (pooled HR 1.35, 95% CI 1.06-1.72 comparing ≥ 25 kg/m² vs. less; HR 1.34 for women and 1.37 for men). Analysis of body somatotypes suggested reduced risk of glioma among women with heavier body types at all ages this measure was assessed (HRs ranging from 0.52 to 0.65 comparing highest tertile to lowest tertile), but no significant association among men. Height was associated with increased risk of glioma among women (HR 1.09, 95% CI 1.04-1.14 per inch), but not significantly among men. Within the 8 years prior to diagnosis, cases had no material weight loss compared to non-cases. All results were similar when limited to GBM.

CONCLUSION

Adult BMI and waist circumference were not associated with glioma. Higher BMI at age 21 for men and at age 18 for women was modestly associated with risk in the pooled cohort. Based on body somatotypes, however, women with heavier body types during childhood and young adulthood may be at lower risk of glioma, although this association was not observed later in life with measurements of BMI. Greater height was associated with increased risk, and the trend was more pronounced in women.

Manganese-Induced Neurotoxicity and Alterations in Gene Expression in Human Neuroblastoma SH-SY5Y Cells

Manganese (Mn) is an essential trace element required for many physiological functions including proper biochemical and cellular functioning of the central nervous system (CNS). However, exposure to excess level of Mn through occupational settings or from environmental sources has been associated with neurotoxicity. The cellular and molecular mechanism of Mn-induced neurotoxicity remains unclear. In the current study, we investigated the effects of 30-day exposure to a sub-lethal concentration of Mn (100 μM) in human neuroblastoma cells (SH-SY5Y) using transcriptomic approach. Microarray analysis revealed differential expression of 1057 transcripts in Mn-exposed SH-SY5Y cells as compared to control cells. Gene functional annotation cluster analysis exhibited that the differentially expressed genes were associated with several biological pathways. Specifically, genes involved in neuronal pathways including neuron differentiation and development, regulation of neurogenesis, synaptic transmission, and neuronal cell death (apoptosis) were found to be significantly altered. KEGG pathway analysis showed upregulation of p53 signaling pathways and neuroactive ligand-receptor interaction pathways, and downregulation of neurotrophin signaling pathway. On the basis of the gene expression profile, possible molecular mechanisms underlying Mn-induced neuronal toxicity were predicted.

Common genetic variations in cell cycle and DNA repair pathways associated with pediatric brain tumor susceptibility

Knowledge on the role of genetic polymorphisms in the etiology of pediatric brain tumors (PBTs) is limited. Therefore, we investigated the association between single nucleotide polymorphisms (SNPs), identified by candidate gene-association studies on adult brain tumors, and PBT risk.The study is based on the largest series of PBT cases to date. Saliva DNA from 245 cases and 489 controls, aged 7-19 years at diagnosis/reference date, was genotyped for 68 SNPs. Data were analyzed using unconditional logistic regression.The results showed EGFRrs730437 and EGFRrs11506105 may decrease susceptibility to PBTs, whereas ERCC1rs3212986 may increase risk of these tumors. Moreover, stratified analyses indicated CHAF1Ars243341, CHAF1Ars2992, and XRCC1rs25487 were associated with a decreased risk of astrocytoma subtype. Furthermore, an increased risk of non-astrocytoma subtype associated with EGFRrs9642393, EME1rs12450550, ATMrs170548, and GLTSCRrs1035938 as well as a decreased risk of this subtype associated with XRCC4rs7721416 and XRCC4rs2662242 were detected.This study indicates SNPs in EGFR, ERCC1, CHAF1A, XRCC1, EME1, ATM, GLTSCR1, and XRCC4 may be associated with the risk of PBTs. Therefore, cell cycle and DNA repair pathways variations associated with susceptibility to adult brain tumors also seem to be associated with PBT risk, suggesting pediatric and adult brain tumors might share similar etiological pathways.

ARID4B is a good biomarker to predict tumour behaviour and decide WHO grades in gliomas and meningiomas

Aims

Although ARID4B is known to promote tumour metastasis in breast cancer and inhibit transformation and progression in leukaemia, the possible effect of ARID4B on primary brain tumours (PBTs) is not well characterised. We tested the hypothesis that expression of ARID4B correlates with WHO grade and survival in patients with PBTs.

Methods

Western blot analysis was performed on protein lysates prepared from normal brain tissue and glioma cell lines (U87MG, LN229, GBM8401 and U118MG). Subsequently, immunohistochemical analysis of ARID4B was performed on 2 tissue microarrays, including 12 normal brain tissues, 63 meningiomas with different subtypes, 232 gliomas of various grades and degrees of differentiation, 8 central neurocytomas and 4 chordomas. The ARID4B immunostaining score was calculated by multiplying the intensity score by the percentage of tumour cells expressing ARID4B.

Results

In vitro, ARID4B protein expression was increased in some glioma cell lines. In addition, the average ARID4B immunostaining score was 38.03, 79.09, 129.76 and 119.32, respectively, in gliomas of WHO grade I, II, III and IV. Higher ARID4B immunostaining score was significantly correlated with more advanced WHO grade of gliomas (p=7.4×10–6) and meningiomas. Finally, higher ARID4B expression tended to the shorter survival rates, but did not reach statistical significance.

Conclusions

ARID4B overexpression presented in most of PBTs, rather than non-neoplastic brain tissue, and correlated with WHO grades in meningiomas and gliomas. Therefore, ARID4B is a satisfactory biomarker to highlight tumour component and predict tumour behaviour in primary brain neoplasms.

Nrf2 Expressions Correlate with WHO Grades in Gliomas and Meningiomas

Background: Nuclear factor erythroid 2-related factor 2 (NFE2L2, also known as Nrf2) is associated with cellular progression and chemotherapeutic resistance in some human cancers. We tested the relationship between Nrf2 expression and survival of patients with primary brain tumors (PBTs). Methods: In order to realize Nrf2 protein expression in gliomas, Western blot analysis was performed in normal brain tissue and U87MG, LN229, GBM8401 and U118MG glioma cell lines protein lysates. Then, U87MG, LN229, and GBM8401 mRNA were applied to performed quantitative RT-PCR for detect Nrf2 gene expression in glioma cell lines. At last, immunohistochemical analysis was used to determine the expression of Nrf2 in samples from 178 PBTs and 10 non-neoplastic brain tissues. Results: In these included in vitro studies, both Nrf2 protein and mRNA expression in all human glioma cell lines were higher than normal brain tissue. Similarly, on the viewpoint of immunohistochemistry, Nrf2 expression in gliomas were positively correlated with World Health Organization (WHO) grades. Additionally, compared with the expression of Nrf2 in non-neoplastic brain tissue, expression in meningiomas was of a stronger intensity and was present in a higher percentage of cells. Furthermore, scores were significantly higher in WHO grade II than in WHO grade I meningiomas. Finally, overall survival tended to be shorter in patients whose PBTs had higher expression of Nrf2, although the correlation was not statistically significant. Conclusions: Nrf2 overexpression positively correlated with WHO grade in gliomas and meningiomas. On the other hand, Nrf2 immunohistochemical stain could help pathologists to differentiate atypical meningiomas from benign tumors. Therefore, Nrf2 expression may be a useful biomarker to predict WHO grade and cellular behavior of PBTs.

Association of the CCDC26 rs4295627 polymorphism with the risk of glioma: Evidence from 7,290 cases and 11,630 controls

Published data on the association between the coiled-coil domain-containing 26 (CCDC26) rs4295627 polymorphism and the risk of glioma have been inconclusive. To further investigate this association, a meta-analysis was performed. By a comprehensive literature search using PubMed and EMBASE databases, a total of 16 case-control studies were identified for inclusion in the meta-analysis. Odds ratios (ORs) with 95% confidence intervals (CIs) were calculated to assess this association. Our results confirmed that the risk with allele G was higher compared with that with allele T for glioma. The results indicated that the allele G of rs4295627 polymorphism in the CCDC26 gene was associated with increased risk of glioma in the homozygote model (GG vs. TT, OR=1.936, 95 %CI: 1.500-2.658, P<0.001), the heterozygote model (GT vs. TT, OR=1.323, 95% CI: 1.241-1.412, P=0.206), the dominant model (GG+GT vs. TT, OR=1.375, 95% CI: 1.256-1.505, P=0.026), the recessive model (GG vs. GT+TT, OR=1.769, 95% CI: 1.302-2.403, P<0.001) and the allele model (G vs. T, OR=1.310, 95% CI: 1.185-1.448, P<0.001). Current evidence suggests that the rs4295627 polymorphism in the CCDC26 gene may contribute to glioma susceptibility. However, further case-control studies are required to confirm our results.

Integrative genomic and proteomic profiling of human neuroblastoma SH-SY5Y cells reveals signatures of endosulfan exposure

Endosulfan, an organochlorine pesticide, is known to induce multiple disorders/abnormalities including neuro-degenerative disorders in many animal species. However, the molecular mechanism of endosulfan induced neuronal alterations is still not well understood. In the present study, the effect of sub-lethal concentration of endosulfan (3 μM) on human neuroblastoma cells (SH-SY5Y) was investigated using genomic and proteomic approaches. Microarray and 2D-PAGE followed by MALDI-TOF-MS analysis revealed differential expression of 831 transcripts and 16 proteins in exposed cells. A gene ontology enrichment analysis revealed that the differentially expressed genes and proteins were involved in variety of cellular events such as neuronal developmental pathway, immune response, cell differentiation, apoptosis, transmission of nerve impulse, axonogenesis, etc. The present study attempted to explore the possible molecular mechanism of endosulfan induced neuronal alterations in SH-SY5Y cells using an integrated genomic and proteomic approach. Based on the gene and protein profile possible mechanisms underlying endosulfan neurotoxicity were predicted.

Descriptive epidemiology and risk factors of primary central nervous system tumors: Current knowledge

Although comparisons are difficult due to differences in methodologies, the annual incidence rates of central nervous system (CNS) tumors range from 8.5 to 21.4/100,000 population according to cancer registries, with a predominance of neuroepithelial tumors in men and meningiomas in women. An increase in the incidence of CNS tumors has been observed during the past decades in several countries. It has been suggested that this trend could be due to aging of the population, and improvements in diagnostic imaging and healthcare access, but these factors do not explain differences in incidence by gender and histological subtypes. Several etiological hypotheses related to intrinsic (sociodemographic, anthropometric, hormonal, immunological, genetic) and exogenous (ionizing radiation, electromagnetic fields, diet, infections, pesticides, drugs) risk factors have led to analytical epidemiological studies to establish relationships with CNS tumors. The only established environmental risk factor for CNS tumors is ionizing radiation exposure. However, for other risk factors, studies have been inconsistent and inconclusive due to systematic differences in study design and difficulties in accurately measuring exposures. Thus, the etiology of CNS tumors is complex and may involve several genetic and/or environmental factors that may act differently according to histological subtype.

Genetic variant near TERC influencing the risk of gliomas with older age at diagnosis in a Chinese population

A recent genome-wide association study has identified an association between rs1920116 near TERC and high-grade glioma in populations of European ancestry. In order to evaluate the effect of the SNP rs1920116 near TERC in the Chinese population, we examined associations of this candidate SNP with glioma in a sample of 1970 Chinese Han individuals. SNP genotype data were available for 980 Chinese glioma patients and 990 healthy controls. Logistic regression analyses were performed to evaluate the association between rs1920116 and glioma risk adjusted for age, gender and stratified by tumor grade where appropriate. The allele G at TERC rs1920116 are risk factors for gliomas, and its association with glioma risk was consistent across tumor subgroups in the Chinese Han population (OR = 1.18-1.21). In order to assess variation in SNP effect size at different patient ages, glioma cases and controls were divided into 3 age strata, in years: <50, 50-59, and 60+. The results of multiple logistic regression analyses indicate that the SNP has age-specific effects on the risk of developing glioma. Our report confirmed the effects of rs1920116 near TERC on glioma occurring in older peoples in the Chinese Han population for the first time. As TERC is a candidate for inter-individual variation in telomere length, our study supports the hypothesis that telomerase-related mechanisms of telomere maintenance are more associated with gliomas that develop later in life.

Genetic Modulation of Neurocognitive Function in Glioma Patients

PURPOSE

Accumulating evidence supports the contention that genetic variation is associated with neurocognitive function in healthy individuals and increased risk for neurocognitive decline in a variety of patient populations, including cancer patients. However, this has rarely been studied in glioma patients.

EXPERIMENTAL DESIGN

To identify the effect of genetic variants on neurocognitive function, we examined the relationship between the genotype frequencies of 10,967 single-nucleotide polymorphisms in 580 genes related to five pathways (inflammation, DNA repair, metabolism, cognitive, and telomerase) and neurocognitive function in 233 newly diagnosed glioma patients before surgical resection. Four neuropsychologic tests that measured memory (Hopkins Verbal Learning Test-Revised), processing speed (Trail Making Test A), and executive function (Trail Making Test B, Controlled Oral Word Association) were examined.

RESULTS

Eighteen polymorphisms were associated with processing speed and 12 polymorphisms with executive function. For processing speed, the strongest signals were in IRS1 rs6725330 in the inflammation pathway (P = 2.5 × 10(-10)), ERCC4 rs1573638 in the DNA repair pathway (P = 3.4 × 10(-7)), and ABCC1 rs8187858 in metabolism pathway (P = 6.6 × 10(-7)). For executive function, the strongest associations were in NOS1 rs11611788 (P = 1.8 × 10(-8)) and IL16 rs1912124 (P = 6.0 × 10(-7)) in the inflammation pathway, and POLE rs5744761 (P = 6.0 × 10(-7)) in the DNA repair pathway. Joint effect analysis found significant gene polymorphism-dosage effects for processing speed (Ptrend = 9.4 × 10(-16)) and executive function (Ptrend = 6.6 × 10(-15)).

CONCLUSIONS

Polymorphisms in inflammation, DNA repair, and metabolism pathways are associated with neurocognitive function in glioma patients and may affect clinical outcomes.

Genetic Contribution of Polymorphisms in Glutathione S-Transferases to Brain Tumor Risk

Existing data have shown a major effect of glutathione S-transferase (GST) single-nucleotide polymorphisms on activities of detoxification-related enzymes, and it is the functional importance that leads to extensive research on the association of GST polymorphisms with the risk of developing brain tumor. Previously reported associations, nevertheless, remain inconsistent. This study aimed to reevaluate the association with new information from recent research articles. We weekly searched multiple databases, aiming to cover all studies looking at the associations being examined in this work. Eligibility of studies was evaluated based on predesigned inclusion criteria. To assess the association of GST polymorphisms with brain tumor risk, we calculated genotypic ORs by comparing the number of genotypes between cases and controls. We also detected interstudy heterogeneity, publication bias, and single studies' influence. A total of 13 research articles were identified through databases and hand search. We found significantly elevated risk of brain tumor associated with GSTT1 null status in individuals of European ethnicity (OR 1.46, 95% CI 1.12-1.92). In the analysis of GSTP1 I105V, we observed that Val/Val genotype compared to the Ile/Ile genotype was more prone to a reduced brain tumor risk (OR 0.77, 95% CI 0.64-0.93). Such major effects were similarly seen for GSTP1 A114V (OR 1.14, 95% CI 1.01-1.29 for Val/Val + Ala/Val vs. Ala/Ala). When data were limited to glioma, we found a significant elevation associated with the combination of Val/Val and Ala/Val genotypes (OR 1.18, 95% CI 1.01-1.37). However, no clear association was detected between other polymorphisms investigated and glioma. These statistical data suggest that some of the polymorphisms at GST loci are possibly associated with the genetic risk of brain tumor.

Cytomegalovirus and glioma: putting the cart before the horse

In 1908, Oluf Bang and Vilhelm Ellerman laid the foundation for theory of oncoviruses by demonstrating that the avian erythroblastosis (a form of chicken leukaemia) could be transmitted by cell-free extracts. Since then, it has been shown very convincingly that viruses can directly cause several human cancers by various mechanisms. Epidemiological data imply that viruses are the second most important risk factor for cancer development in humans, exceeded only by tobacco consumption. Although the ability of certain viruses (hepatitis B and C, human papillomavirus, etc) to cause cancer has been time tested and proven scientifically, there are several other potential viral candidates whose role in oncogenesis is more controversial. One such controversial scenario involves the role of cytomegalovirus (CMV) in malignant gliomas, the most common form of primary brain tumour. CMV first attracted attention about a decade ago when CMV gene products were found in glioma tissue but not in normal brain. Since this initial observation, several different groups have shown an oncomodulatory effect of CMV; however, direct association between CMV infection and incidence of glioma is lacking. In this review, we will evaluate the evidence, both preclinical and clinical, regarding the possible role of CMV in gliomagenesis and maintenance. We will also critically evaluate the rationale for using antiviral drugs in the treatment of patients with glioma.

Brain tumors: Special characters for research and banking

A brain tumor is an intracranial neoplasm within the brain or in the central spinal canal. Primary malignant brain tumors affect about 200,000 people worldwide every year. Brain cells have special characters. Due to the specific properties of brain tumors, including epidemiology, growth, and division, investigation of brain tumors and the interpretation of results is not simple. Research to identify the genetic alterations of human tumors improves our knowledge of tumor biology, genetic interactions, progression, and preclinical therapeutic assessment. Obtaining data for prevention, diagnosis, and therapy requires sufficient samples, and brain tumors have a wide range. As a result, establishing the bank of brain tumors is very important and essential.

Genetic variants in N-myc (and STAT) interactor and susceptibility to glioma in a Chinese Han population

Glioma is one of the most common and lethal brain tumors. N-myc (and STAT) interactor (NMI) gene has been reported in tumorigenesis, and our previous study further showed its implication in glioma progression. To elucidate its involvement in the etiology of glioma, we conducted a case-control study of 875 patients and 1040 controls in a Chinese Han population by genotyping 7 representative single nucleotide polymorphisms (SNPs) in NMI. Allele and genotype frequency distribution of five loci (rs2278089, rs2194492, rs6734376, rs3854012, and rs11730) were significantly different between the cases and controls. Unconditional logistic regression showed that the variant genotypes of rs2278089 [adjusted odds ratio (OR) = 1.57, P = 4.23 × 10(-6)], rs2194492 (adjusted OR = 1.49, P = 1.20 × 10(-4)), and rs6734376 (adjusted OR = 0.06, P = 8.65 × 10(-13)) significantly affected glioma risk compared with the major homozygotes, while the minor homozygotes of rs3854012 (adjusted OR = 0.54, P = 4.64 × 10(-6)) and rs11730 (adjusted OR = 0.60, P = 1.50 × 10(-4)) showed significant protective effects. Further stratified analyses indicated that these associations remained significant in subgroups of low-grade glioma (LGG) and high-grade glioma (HGG). Additionally, haplotype and diplotype analyses showed consistent results. The Bonferroni correction was applied for all these analyses. Moreover, luciferase reporter gene assays revealed enhanced promoter activity of the C risk allele of rs2194492 in several cell lines compared with the G major allele, suggesting its potential function in transcriptional activation of NMI. Taken together, these results revealed that NMI polymorphisms may contribute to genetic susceptibility to glioma.

XRCC1 gene polymorphisms and glioma risk in Chinese population: a meta-analysis

Background

Three extensively investigated polymorphisms (Arg399Gln, Arg194Trp, and Arg280His) in the X-ray repair cross-complementing group 1 (XRCC1) gene have been implicated in risk for glioma. However, the results from different studies remain inconsistent. To clarify these conflicts, we performed a quantitative synthesis of the evidence to elucidate these associations in the Chinese population.

Methods

Data were extracted from PubMed and EMBASE, with the last search up to August 21, 2014. Meta-analysis was performed by critically reviewing 8 studies for Arg399Gln (3062 cases and 3362 controls), 8 studies for Arg194Trp (3419 cases and 3680 controls), and 5 studies for Arg280His (2234 cases and 2380 controls). All of the statistical analyses were performed using the software program, STATA (version 11.0).

Results

Our analysis suggested that both Arg399Gln and Arg194Trp polymorphisms were significantly associated with increased risk of glioma (for Arg399Gln polymorphism: Gln/Gln vs. Arg/Arg, OR = 1.82, 95% CI = 1.46–2.27, P = 0.000; Arg/Gln vs. Arg/Arg, OR = 1.25, 95% CI = 1.10–1.42, P = 0.001 and for Arg194Trp polymorphism: recessive model, OR = 1.78, 95% CI = 1.44–2.19, P = 0.000), whereas the Arg280His polymorphism had no influence on the susceptibility to glioma in a Chinese population.

Conclusions

This meta-analysis suggests that there may be no association between the Arg280His polymorphism and glioma risk, whereas the Arg399Gln/Arg194Trp polymorphisms may contribute to genetic susceptibility to glioma in the Chinese population. Nevertheless, large-scale, well-designed and population-based studies are needed to further evaluate gene-gene and gene–environment interactions, as well as to measure the combined effects of these XRCC1 variants on glioma risk.

Association of leukocyte mitochondrial DNA content with glioma risk: evidence from a Chinese case-control study

Background

Increasing evidence suggests that alterations in mitochondrial DNA (mtDNA) content may be implicated in the tumorigenesis of several malignancies. However, the association between mtDNA content in peripheral blood lymphocytes (PBLs) and glioma risk has not been investigated.

Methods

Real-time PCR was used to examine the mtDNA content in PBLs of 414 glioma patients and 414 matched controls in a hospital-based case–control study. The association between mtDNA content and glioma risk was evaluated using an unconditional multivariate logistic regression model.

Results

We found that glioma patients exhibited a significantly higher median mtDNA content than healthy controls (0.99 vs. 0.71, P < 0.001). Unconditional multivariate logistic regression analysis adjusting for age, gender, smoking status, and family cancer history showed that there was an S-shaped association between mtDNA content and glioma risk. Higher mtDNA content was significantly associated with an elevated risk of glioma. Compared with the first quartile, the odds ratio (95% confidence interval) for subjects in the second, third, and fourth quartiles of mtDNA content were 0.90 (0.52-1.53), 3.38 (2.15-5.31), and 5.81 (3.74-9.03), respectively (P for nonlinearity = 0.009). Stratified analysis showed that the association between mtDNA content and glioma risk was not modulated by major host characteristics.

Conclusions

Our findings demonstrate for the first time that a higher mtDNA content in PBLs is associated with an elevated risk of glioma, which warrants further investigation in larger populations.

Association between the G870A polymorphism of Cyclin D1 gene and glioma risk

Previous studies have shown the association of the Cyclin D1 (CCND1) G870A polymorphism with glioma risk, but the findings are inconsistent and inconclusive. To shed some light on the findings across individual studies and acquire a quantitative assessment of this association, we conducted a meta-analysis of all published case-control studies thus far. Four independent studies with a total of 690 cases and 1,014 controls were identified after a systematic search of the PubMed, Embase, Web of Science, and Wanfang databases. The strength of the association between the CCND1 G870A polymorphism and glioma risk was estimated by the pooled odds ratios (ORs) with 95 % confidence intervals (95 %CIs). Subgroup analysis by ethnicity was also performed. Overall, a statistically significant association was found between the CCND1 G870A polymorphism and glioma risk in three genetic models (ORA vs. G = 1.178, 95 %CI 1.025-1.354, P OR = 0.021; ORAA vs. GG = 1.328, 95 %CI 1.007-1.750, P OR = 0.045; ORAA + AG vs. GG = 1.253, 95 %CI 1.006-1.516, P OR = 0.044). In subgroup analysis, the pooled ORs suggested that the CCND1 G870A polymorphism was associated with an increased risk of glioma in Caucasians under the heterozygote and dominant genetic models (ORAG vs. GG = 1.329, 95 %CI 1.001-1.766, P OR = 0.049; ORAA + AG vs. GG = 1.332, 95 %CI 1.019-1.740, P OR = 0.036). The meta-analysis suggests that the CCND1 G870A polymorphism is a risk factor for the development of glioma.

Reproductive factors and risk of primary brain tumors in women

Gender-specific incidence patterns and the presence of hormonal receptors on tumor cells suggest that sex hormones may play a role in the onset of primary brain tumors. However, epidemiological studies on the relation of hormonal risk factors to the risk of brain tumors have been inconsistent. We examined the role of reproductive factors in the onset of glioma and meningioma in a case-control study conducted in the Southeastern US that included 507 glioma cases, 247 meningioma cases, and 695 community-based and friend controls. Unconditional logistic regression was used to estimate odds ratios (ORs) and 95% confidence intervals (CI) adjusting for age, race, US state of residence, and education. An older age at menarche was associated with an increased risk of glioma (≥ 15 vs. ≤ 12 years: OR 1.65; 95% CI 1.11-2.45), with a stronger association observed in pre-menopausal (OR 2.22; 95% CI 1.12-4.39) than post-menopausal (OR 1.55; 95% CI 0.93-2.58) women. When compared to controls, meningioma cases were more likely to have undergone natural menopause (OR 1.52; 95% CI 1.04-2.21) whereas glioma cases were less likely to be long term users of oral contraceptives (OR 0.47; 95% CI 0.33-0.68). Increasing parity was not related to the risk of either tumor. Current findings are consistent with a limited role for hormones in the onset of brain tumors in women. Results contribute to a growing body of evidence that a later age at menarche increases the risk of glioma in women.

Cyclin D1 gene G870A variants and primary brain tumors

Alterations of cyclin D1, one of the main regulators of the cell cycle, are known to be involved in various cancers. The CCDN1 G870A polymorphism causes production of a truncated variant with a shorter half-life and thus thought to impact the regulatory effect of CCDN1. The aim of the present study was to contribute to existing results to help to determine the prognostic value of this specific gene variant and evaluate the role of CCDN1 G870A polymorphism in brain cancer susceptibility. A Turkish study group including 99 patients with primary brain tumors and 155 healthy controls were examined. Genotypes were determined by polymerase chain reaction-restriction fragment length polymorphism analysis. The CCDN1 genotype frequencies in meningioma, glioma and control cases were not significantly different (p>0.05). No significant association was detected according to clinical parameters or tumor characteristics; however, a higher frequency of AG genotype was recorded within patients with astrocytic or oligoastrocytic tumors. A significant association between AG genotype and gliobilastoma multiforme (GBM) was recorded within the patients with glial tumors (p value=0.048 OR: 1.87 CI% 1.010-3.463). According to tumor characteristics, no statistically significant difference was detected within astrocytic, oligoasltrocytic tumors and oligodentrioglias. However, patients with astrocytic astrocytic or oligoastrocytic tumors showed a higher frequency of AG genotype (50%) when compared to those with oligodendrioglial tumors (27.3%). Our results indicate a possible relation between GBM formation and CCDN1 genotype.

Association between leukocyte telomere length and glioma risk: a case-control study

BACKGROUND

Compelling epidemiological evidence indicates that alterations of telomere length are associated with risks of many malignancies in a tumor-specific manner, such as lung cancer, breast cancer, and non-Hodgkin's lymphoma. However, the association between leukocyte telomere length and glioma risk has not been investigated.

METHODS

Relative telomere length (RTL) of peripheral blood leukocytes from 467 glioma patients and 467 healthy controls, matched by age and sex, was measured using the real-time PCR-based method in a case-control study. An unconditional multivariate logistic regression model was applied to estimate the association between RTL and glioma risk.

RESULTS

Glioma patients showed notably longer RTL than controls (median, 0.555 vs 0.444; P > .04). RTL was negatively correlated with age in both cases (ρ = -0.430; P < .001) and controls (ρ = -0.388; P < .001). After adjusting for age, sex, smoking status and family history of cancer, multivariate logistic regression analysis showed that there was a U-shaped association between RTL and glioma risk (P for nonlinearity <.001). Compared with individuals in the second tertile of RTL, the odds ratios (95% CI) for participants in the first and third tertiles were 2.16 (range, 1.52-3.09) and 3.51 (range, 2.45-5.00), respectively. Stratified analysis showed that the association between RTL and glioma risk was not modulated by major host characteristics.

CONCLUSIONS

Our study demonstrates for the first time that either shorter or longer RTL in peripheral blood leukocytes is associated with increased glioma risk, which warrants further investigation in the future.

Investigation of ICAM-1 and β3 integrin gene variations in patients with brain tumors

BACKGROUND

Primary brain tumors constitute a small percent of all malignant cancers, but their etiology remains poorly understood. β3 integrin (ITGB3) has been recognized to play influential roles in angiogenesis, tumor growth and metastasis. Intercellular adhesion molecule-1 (ICAM-1) is a surface glycoprotein important for tumor invasion and angiogenesis. The aim of this study was to investigate whether specific genetic polymorphisms of ICAM-1 and ITGB3 could be associated with brain cancer development and progression in a Turkish population. Our study is the first to our knowledge to investigate the relationship between brain tumor risk and ICAM-1 and β3 integrin gene polymorphisms.

MATERIALS AND METHODS

The study covered 92 patients with primary brain tumors and 92 age-matched healthy control subjects. Evaluation of β3 integrin (Leu33Pro (rs5918)) and ICAM-1 (R241G (rs1799969) and K469E (rs5498)) gene polymorphisms was performed by polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP).

RESULTS

According to results of our research, the A allele of the ICAM-1 R241G gene polymorphism appeared to be a risk factor for primary brain tumors (p<0.001). Similarly, the frequency of the A mutant allele of ICAM-1 R241G was statistically significant in patients with brain tumors classified as glioma (p<0.001). When allele and genotype distributions of ICAM- 1 K469E, ICAM-1 R241G and β3 integrin Leu33Pro gene polymorphisms were evaluated with age, sex, and smoking, there were no statistically significant differences. Haplotype analysis revealed that the frequencies of GAC (rs1799969-rs5498-rs5918) and GAT (rs1799969-rs5498-rs5918) haplotypes were significantly lower in patients as compared with controls (p=0.001; p=0.036 respectively).

CONCLUSIONS

This study provides the first evidence that ICAM-1 R241G SNP significantly contributes to the risk of primary brain tumors in a Turkish population. In addition, our results suggest that ICAM-1 R241G in combination ICAM-1 K469E may have protective effects against the development of brain cancer.

Assessment of the association between XRCC1 Arg399Gln polymorphism and glioma susceptibility

The Arg399Gln polymorphism, located in the region of the BRCT-I interaction domain of XRCC1, has been extensively explored in its function and association with glioma risk. However, these studies generated contradictory instead of conclusive results. A meta-analysis was performed to derive a more precise evaluation of the relationship between XRCC1 Arg399Gln polymorphism and glioma risk. We searched the PubMed, EMBASE, and Web of Science and extracted 12 eligible studies with 4,062 glioma cases and 5,302 glioma-free controls for this meta-analysis. The pooled odds ratios (ORs) and 95% confidence intervals (CIs) were calculated to assess the strength of the association. In the overall analysis, we found that the XRCC1 Arg399Gln polymorphism was statistically associated with the risk of glioma (OR(GG vs. AG + AA) = 0.90, 95% CI = 0.84-0.97, P(heterogeneity) = 0.020; OR(allele G vs. allele A )= 0.96, 95% CI = 0.91-1.00, P(heterogeneity) = 0.110). We also observed significant association between this polymorphism and glioma risk in Asian populations. The results of the meta-analysis suggest a potential decreased susceptibility to glioma in association with the XRCC1 Arg399Gln polymorphism, especially in Asians. Yet, it is necessary to conduct future prospective explorations to gain a better insight into the impact of XRCC1 Arg399Gln polymorphism on glioma risk.

Association between XRCC3 Thr241Met polymorphism and risk of brain tumors: a meta-analysis

X-ray repair cross-complementing group 3 (XRCC3) plays an important role in the process of homologous recombination repair for DNA double-strand breaks which further maintains the stability of the genome. XRCC3 Thr241Met polymorphism has been indicated in the development of cancers, but the association of the XRCC3 Thr241Met polymorphism with risk of brain tumors is still unclear owing to the conflicting findings from previous studies. We performed a meta-analysis to provide a better understanding on the association between the XRCC3 Thr241Met polymorphism and risk of brain tumors. The pooled odds ratio (OR) with corresponding 95 % confidence interval (95 % CI) was used to assess the association. Thirteen case-control studies involving a total of 4,984 cases and 7,472 controls were included. Overall, there was no statistically significant association between the XRCC3 Thr241Met polymorphism and risk of brain tumors under all contrast models. Subgroup analysis by race suggested that the XRCC3 Thr241Met polymorphism was associated with increased risk of brain tumors in Asians under all four contrast models (Met vs. Thr: OR = 1.22, 95 % CI 1.09-1.36, P < 0.01; MetMet vs. ThrThr: OR = 1.89, 95 % CI 1.38-2.57, P < 0.01; MetMet vs. ThrThr/ThrMet: OR = 1.78, 95 % CI 1.31-2.40, P < 0.01; and MetMet vs. ThrThr/ThrMet: OR = 1.19, 95 % CI 1.04-1.36, P = 0.01). However, there was no significant association between the XRCC3 Thr241Met polymorphism and risk of brain tumors in Caucasians. Therefore, the XRCC3 Thr241Met polymorphism is associated with increased risk of brain tumors, especially in Asians.

Toenail iron, genetic determinants of iron status, and the risk of glioma

PURPOSE

Iron is essential for oxygen transport and oxidative metabolism; however, elevated iron stores can trigger overproduction of reactive oxygen species and induce DNA damage. Little is known about the association between body iron stores and glioma risk. This study examined the associations of iron levels measured in toenails and genetic variants linked to body iron stores with risk of glioma in a clinic-based case-control study.

METHODS

Samples were collected a median of 24 days following glioma diagnosis in the cases (10th-90th percentile, range: 10-44 days). Nail iron levels were measured in 300 cases and 300 controls using neutron activation analysis. A total of 24 genetic variants associated with iron status were genotyped in 622 cases and 628 controls. Logistic regression was used to estimate odds ratios (OR) and 95 % confidence intervals (CI) for glioma risk according to toenail iron and the examined genotypes.

RESULTS

No association was observed between toenail iron and glioma risk when restricting to cases with nails collected within ~3 weeks of diagnosis (OR = 0.93; 95 % CI 0.46, 1.87 comparing those with high (≥14 μg/g) vs. low (<6 μg/g) iron levels). In contrast, an inverse association with increasing iron was observed after restricting to cases with a delay of 3 weeks or greater (OR = 0.42; 95 % CI 0.19, 0.95), reflecting potentially insidious effects of advancing disease on iron levels among the cases. No associations were observed for any of the examined genetic variants.

CONCLUSION

The results do not support a role for body iron stores as a determinant of glioma risk.

Early life exposures and the risk of adult glioma

Exposure to common infections in early life may stimulate immune development and reduce the risk for developing cancer. Birth order and family size are proxies for the timing of exposure to childhood infections with several studies showing a reduced risk of glioma associated with a higher order of birth (and presumed younger age at infection). The aim of this study was to examine whether birth order, family size, and other early life exposures are associated with the risk of glioma in adults using data collected in a large clinic-based US case-control study including 889 glioma cases and 903 community controls. A structured interviewer-administered questionnaire was used to collect information on family structure, childhood exposures and other potential risk factors. Logistic regression was used to calculate odds ratios (OR) and corresponding 95% confidence intervals (CI) for the association between early life factors and glioma risk. Persons having any siblings were at significantly lower risk for glioma when compared to those reporting no siblings (OR=0.64; 95% CI 0.44-0.93; p=0.020). Compared to first-borns, individuals with older siblings had a significantly lower risk (OR=0.75; 95% CI 0.61-0.91; p=0.004). Birth weight, having been breast fed in infancy, and season of birth were not associated with glioma risk. The current findings lend further support to a growing body of evidence that early exposure to childhood infections reduces the risk of glioma onset in children and adults.

Four common polymorphisms in microRNAs and the risk of adult glioma in a Chinese case-control study

Emerging evidence has shown that microRNAs (miRNAs) participate in human carcinogenesis as tumor suppressors or oncogenes. It has been suggested that four common single nucleotide polymorphisms (SNPs; miR-146aG > C, 149C > T, 196a2C > T, and 499A > G) are associated with susceptibility to numerous malignancies. However, published results are inconsistent and inclusive. To further investigate the role of these loci, we examined the association of the miRNA polymorphisms with the risk of gliomas in a Han population in northeastern China. Both miR-146aG > C and 196a2C > T showed allelic differences between glioma patients and healthy controls in the studied population, with an OR of 1.30 (P = 0.0006) and an odds ratio (OR) of 1.25 (P = 0.003), respectively. Logistic regression analysis also revealed that the 146aG > C and 196a2C > T wild-type homozygous carriers had an increased glioma risk compared to the variant carriers. Besides, in pairwise comparisons two SNP combinations were associated with the risk of glioma. Among others, carriers of both homozygous risk genotypes, i.e., 146aGG and 196a2CC were associated with a nearly 4-fold increased risk of glioma (OR = 3.77, P = 1.3 × 10(-4)). Overall, glioma risk increased with increasing numbers of risk variant alleles. These results suggest that the miR-146aG > C and 196a2C > T might influence the risk of developing glioma in a northeastern Han Chinese population.

The role and clinical significance of DNA damage response and repair pathways in primary brain tumors

Primary brain tumors, in particular, glioblastoma multiforme (GBM), continue to have dismal survivability despite advances in treating other neoplasms. The goal of new anti-glioma therapy development is to increase their therapeutic ratios by enhancing tumor control and/or decreasing the severity and incidence of side effects. Because radiotherapy and most chemotherapy agents rely on DNA damage, the cell's DNA damage repair and response (DRR) pathways may hold the key to new therapeutic strategies. DNA double-strand breaks (DSBs) generated by ionizing radiation and chemotherapeutic agents are the most lethal form of damage, and are repaired via either homologous recombination (HR) or non-homologous end-joining (NHEJ) pathways. Understanding and exploitation of the differences in the use of these repair pathways between tumor and normal brain cells will allow for an increase in tumor cell killing and decreased normal tissue damage. A literature review and discussion on new strategies which can improve the anti-glioma therapeutic ratio by differentially targeting HR and NHEJ function in tumor and normal neuronal tissues is the focus of this article.

Anti-human-cytomegalovirus immunoglobulin G levels in glioma risk and prognosis

The role of human cytomegalovirus (HCMV) in glioma development and progression remains controversial. The purpose of our study was to assess the potential associations between anti-HCMV antibodies (immunoglobulin G [IgG] and immunoglobulin M [IgM]) and glioma risk and prognosis using data from the Harris County Case–Control Study. Multivariable logistic regression models were utilized to estimate odds ratios and 95% confidence intervals (CI) for the associations between glioma status and antibody levels among glioma cases (n = 362) and cancer-free controls (n = 462). Hazard ratios and 95% CIs were calculated using Cox proportional hazards regression, adjusting for age, race, and sex, to determine if antibody levels were associated with survival over time among cases. Among IgG-positive participants, increasing anti-HCMV IgG levels were associated with decreasing glioma risk (P for trend = 0.0008), and those with the lowest level of anti-HCMV IgG (<10 U/mL) had the highest glioma risk, controlling for age, sex, and race/ethnicity (OR: 2.51, 95% CI: 1.42–4.43). Antibody levels were not associated with survival among glioma cases. Our study contributes new evidence toward the potential importance of the direct and indirect effects of HCMV infection in gliomagenesis.

Inflammation and Gliomagenesis: Bi-Directional Communication at Early and Late Stages of Tumor Progression

Inflammation has been closely linked to various forms of cancer. Less is known about the role of inflammation in glioma, especially at the initiation stage. In this review, we first describe the unique features of the immune system in the brain. We then discuss the current understanding of the mechanisms by which glioma cells modulate the immune system, especially how bi-directional communications between immune cells and glioma cells create an immunosuppressed microenvironment that promotes tumor survival and growth. We also address the potential tumor-initiating roles of inflammation in glioma. Finally, we describe several immunotherapy approaches currently being developed to reverse these interactions and stimulate the immune system to eliminate glioma cells.

A functional polymorphism in XRCC1 is associated with glioma risk: evidence from a meta-analysis

Previous studies show that X-ray cross-complementing group 1 (XRCC 1) Arg399Gln may result in variations in repair efficiency of DNA damage, and this repair deficit may eventually cause individual susceptibility to glioma. However, published data regarding the association between XRCC 1 Arg399Gln polymorphism and glioma risk was contradictory. The aim of this study was to derive a more precise estimation of the association of XRCC 1 Arg399Gln polymorphism with glioma risk by performing a meta-analysis of eligible studies. Odds ratios (ORs) and 95 % confidence intervals (95 %CIs) were used to assess the strength of the association. We performed a meta-analysis of eleven published studies that included 2,808 glioma cases and 3,114 controls. Overall, there was a significant association between XRCC1 Arg399Gln polymorphism and glioma risk in two genetic models (for ArgGln vs ArgArg: OR = 1.30, 95 % CI 1.01-1.68; for GlnGln/ArgGln vs ArgArg: OR = 1.28, 95 % CI 1.01-1.62). In the stratified analysis by ethnicity, the XRCC1 Arg399Gln polymorphism had a higher risk of glioma development among Asians (for Gln vs Arg: OR = 1.34, 95 % CI 1.12-1.61; for GlnGln vs ArgArg: OR = 1.72, 95 % CI 1.18-2.51; for ArgGln vs ArgArg: OR = 1.31, 95 % CI 1.01-1.71; for GlnGln/ArgGln vs ArgArg: OR = 1.41, 95 % CI 1.10-1.80; for GlnGln vs ArgArg/ArgGln: OR = 1.48, 95 % CI 1.05-2.09)., but not among Caucasians. In conclusion, the results suggest that the XRCC 1 Arg399Gln polymorphism may contribute to the susceptibility of glioma in Asians.

Association of p53 Arg72Pro and MDM2 SNP309 polymorphisms with glioma

Epidemiological studies of the association of variants p53 Arg72Pro and MDM2 single-nucleotide polymorphism 309 (SNP309) with glioma risk have produced inconsistent results. The aim of the current study was to evaluate the association of these 2 variants with glioma susceptibility using a meta-analysis approach. For p53 Arg72Pro, 10 case-control studies including 2587 glioma patients and 4061 unrelated controls were identified. The pooled odds ratios (ORs) for Arg/Pro heterozygotes and Pro/Pro homozygotes were 1.08 [95% confidence interval (95%CI) = 0.85-1.37] and 1.08 (95%CI = 0.85-1.36), respectively, when compared to Arg/Arg carriers. Under the dominant effect model, Pro allele carriers also showed no significantly elevated glioma risk (pooled OR = 1.11, 95%CI = 0.90-1.38), and similar results were found under the recessive-effect model (pooled OR = 1.17, 95%CI = 0.85-1.61). For variant MDM2 SNP309, 3 case-control studies including 606 cases and 309 controls were identified. A marginal association with glioma risk was found for heterozygous G/T carriers (pooled OR = 1.95, 95%CI = 1.00- 3.81), whereas homozygous G/G carriers showed an increased but not significantly elevated risk of glioma (pooled OR = 2.14, 95%CI = 0.71-6.45) compared with that of T/T homozygotes. We also found no significant association between the MDM2 SNP309 polymorphism and glioma risk (pooled OR = 1.86, 95%CI = 0.94-3.67 and pooled OR = 1.25, 95%CI = 0.62-2.56, respectively) under the dominant and recessive models. Taken together, the current data suggested that the 2 polymorphisms may not contribute to glioma susceptibility.