Abstract
Toxoplasma gondii is an intracellular protozoan that can modulate the environment of the infected host. An unfavorable environment modulated by T. gondii in the brain includes tumor microenvironment. Literature has suggested that T. gondii infection is associated with development of brain tumors. However, in Korea, epidemiological data regarding this correlation have been scarce. In this study, in order to investigate the relationship between T. gondii infection and brain tumor development, we investigated the seroprevalence of T. gondii among 93 confirmed brain tumor patients (various histological types, including meningioma and astrocytoma) in Korea using ELISA. The results revealed that T. gondii seropositivity among brain tumor patients (18.3%) was significantly (P<0.05) higher compared with that of healthy controls (8.6%). The seropositivity of brain tumor patients showed a significant age-tendency, i.e., higher in younger age group, compared with age-matched healthy controls (P<0.05). In conclusion, this study supports the close relationship between T. gondii infection and incidence of brain tumors.
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Key words: Toxoplasma gondii, seroprevalence, brain tumor, ELISA
More than 14.1 million common cancer cases are estimated around the world in 2012, and this number is anticipated to increase to 24.0 million by 2035 [
1]. About 256,000 central nervous system tumors (1.8% of all tumors) are diagnosed each year worldwide [
1]. Previous studies have found that risk factors for brain tumors include diverse chemical products, family history, and ionizing radiation from therapeutic and diagnostic devices in the head [
2]. However, the exact causes of these malignancies are yet unclear. Approximately 20% of various malignancies worldwide are due to infectious agents, including viruses, bacteria, and parasites [
3,
4]. Infectious agents can interfere with the host cell genetic machinery, such as DNA repair and cell cycle, and can lead to chronic inflammation and immune system impairments [
5].
The infectious agents associated with human cancers are most commonly viral pathogens, including human papilloma virus and hepatitis B and C viruses [
6]. However, there are only a few studies on the association between parasites and human cancers. It has been suggested that several parasite species, namely,
Paragonimus westermani,
Plasmodium sp.,
Opisthorchis viverrini,
Clonorchis sinensis,
Schistosoma haematobium, and
Hymenolepis nana are related to development of various types of human cancers [
7,
8]. Many other species of parasites may also have potential roles in development of human cancers.
Toxoplasma gondii is an intracellular protozoan that can modulate the microenvironment of the infected host [
9].
T. gondii can invade vital organs, including the central nervous system (CNS); however, its infection in humans is usually mild and asymptomatic in immunocompetent individuals [
9]. In immunocompromised patients,
T. gondii infection may cause severe diseases in the brain, including fatal meningitis and encephalitis [
9]. In addition, a possible correlation was suggested between
T. gondii infection and brain tumor development [
10]. This suggestion has been supported by other authors [
11-
18]. The mechanisms of the brain tumor induction by
T. gondii need to be further studied. In this study, in order to estimate the possible relationship between
T. gondii infection and brain tumor development, we investigated the seroprevalence of
T. gondii among brain tumor patients diagnosed in Korea.
We used sera of 93 patients (44 men and 49 women) diagnosed with various types of brain tumors supplied by the Biobank of Chonnam National University Hwasun Hospital (Hwasun, Jeollanam-do Province, Korea), a member of the Korea Biobank Network. As the control group, sera of 93 randomly selected healthy volunteers (45 men and 48 women) who visited the Korea Association of Health Promotion for health check-up were included for the assay. The ages of the brain tumor patients were 18-82 years (52.9±14.8 years) and those of the healthy controls were 10-86 years (51.9±12.2 years). The sera and blood were stored at -80˚C until analyzed. This study protocol was approved by the Institutional Review Board of Seoul National University Hospital, Seoul, Korea (IRB no. E-1507-065-687). The purpose and procedures of this study were explained to all participants, and a written informed consent was obtained from each of them.
The process of preparation for
Toxoplasma lysate antigens (TLA) [
19] and the procedure of ELISA [
14] followed previous studies with slight modifications. Briefly, 96-well microtiter plates (Costar, Cambridge, Massachusetts, USA) coated with TLA were incubated at 4˚C overnight. After washing, each well was reacted with the test serum samples (1:100) at 37˚C for 1 hr, and horseradish peroxidase-conjugated goat anti-human IgG (1:10,000; Bethyl Laboratories, Montgomery, Texas, USA) was applied at 37˚C for 1 hr. After several washes, freshly prepared o-phenylenediamine dihydrochloride (Sigma-Aldrich, St. Louis, Illinois, USA) was added, and the reaction was stopped by adding 8 N H
2SO
4. IgG antibody titers were determined at the optical density of 490 nm. To analyze the risk factors for toxoplasmosis, the chi-square test was applied.
P<0.05 was considered statistically significant. Pearson’s chi-square and Fisher’s exact tests were used to investigate associations among qualitative categorical variables using SPSS (SPSS Inc., Chicago, Illinois, USA). All tests were 2-sided, and the level of significant difference was defined as
P<0.05.
The IgG seropositive rate for
T. gondii, as analyzed by ELISA, was 18.3% (17/93) among patients with variable types of brain tumors (
Table 1). The seropositivity among brain tumor patients was significantly (
P<0.05) higher than the one among healthy persons, 8.6% (6/93 sera). In particular, patients with meningioma (41.7%;
P<0.05), metastatic carcinoma (30.0%;
P<0.05), astrocytoma (21.4%;
P>0.05), and glioblastoma (16.1%;
P>0.05) showed remarkably higher seropositivity for
T. gondii than healthy controls (
Table 1). The seropositivity was significantly (
P<0.05) higher in men than in women both in the brain tumor patients and healthy controls (
Fig. 1A). The age-seropositivity curve in healthy controls generally showed a steady increasing pattern according to increase of the age (
Fig. 1B), whereas in brain tumor patients the younger age group, for example, 30-49 years, revealed a significantly (
P<0.05) higher seropositivity compared with other age groups (
Fig. 1B).
Previous studies have shown that meningioma and astrocytoma were positively linked to high serum
T. gondii IgG antibody levels [
10,
13]. Similarly, our study showed higher prevalence of
Toxoplasma specific IgG in patients with meningioma (41.7%;
P<0.05) and astrocytoma (21.4%;
P>0.05) (
Table 1). Furthermore, in healthy controls, the seropositivity of
T. gondii was increased with age [
19,
20]. However, in our study, the seropositivity in brain tumor patients showed a different tendency; a significantly higher rate was observed in younger aged patients (30-49 years) with brain tumors, compared with age-matched healthy controls. These results support strongly the close relationship between
Toxoplasma infection and brain tumor incidence.
Since the 1960s, quite a number of studies [
10-
18] reported correlations between
T. gondii infection and brain tumor incidence (
Table 2). Various types of brain and multiple organ tumors, including glioma, acoustic neuroma, meningioma, Hodgkin’s lymphoma, multiple myeloma, and leukemia, have been reported to be positively associated with chronic
T. gondii infection (
Table 2). In this study, we also observed a high prevalence of
T. gondii infection in sera of various brain tumor patients in Korea. Especially, our study supports the previous finding that IgG seropositivity to
T. gondii is a risk factor for meningioma [
13]. These findings provide a strong need for a further study to establish the precise correlation between meningioma incidence and
T. gondii infection. However, results in this study have limitation to precisely explain the relationship between
T. gondii infection and brain tumor.
To evade host immune responses,
T. gondii parasites transform themselves into tissue cysts, and they are parasitic on various tissues, including the brain, heart, and skeletal muscle for lifetime of the host modulating the host immune responses [
21]. Furthermore, they can also modulate the cell cycle and apoptosis of the host cells for their proliferation [
17,
22]. Such behavioral pathogenesis of
T. gondii infection may be linked to the related hallmarks of tumor development. The unfavorable environment modulated by
T. gondii may be similar to appropriate precancerous conditions. Thus, we can presume that
T. gondii infection should help to develop brain tumors. Hosts with chronic
T. gondii infections are also vulnerable to the attack by other pathogens such as viral pathogens. If such viral pathogens are associated with brain tumor development, it can be another oncogenic effect of
T. gondii and may synergistically act as a carcinogen. In this respect, it is noteworthy that
Plasmodium falciparum and Epstein-Barr virus contributed synergistically to the formation of Burkitt’s lymphoma [
23].
Despite the studies on the association of
T. gondii and brain tumors, we cannot conclude whether chronic
T. gondii infection, with seropositivity, is involved in causing these brain tumors, or reversely brain tumor patients are at risk of recrudescence and dissemination of
T. gondii to undergo a chronic infection [
14]. Researches are also needed to determine whether
T. gondii itself acts as a carcinogen or takes the role of a creator of a precancerous environment to develop into brain tumors.
Notes
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We have no conflict of interest related to this work.
The biospecimens and data used for this study were provided by the Biobank of Chonnam National University Hwasun Hospital, Hwasun, Jeollanam-do Province, Korea, a member of the Korea Biobank Network. We would like to thank staff of The Korea Association of Health Promotion for providing the healthy control sera used for this study.
Fig. 1.Gender (A) and age (B)-associated seroprevalence of T. gondii infection among brain tumor patients in Korea compared with healthy controls.
Table 1.Seropositivity of T. gondii by ELISA among brain tumor patients in Korea
Table 1.
|
Types of brain tumors |
Brain tumor patients
|
Healthy controls
|
|
No. tested |
No. positive (%) |
No. tested |
No. positive (%) |
|
Meningioma |
12 |
5 (41.7)a
|
|
|
|
Metastatic carcinoma |
10 |
3 (30.0)a
|
|
|
|
Astrocytoma (including pilocytic/oligo) |
14 |
3 (21.4) |
|
|
|
Glioblastoma |
31 |
5 (16.1) |
|
|
|
Ganglioglioma and othersb
|
26 |
1 (3.8) |
|
|
|
Total |
93 |
17 (18.3) |
93 |
8 (8.6) |
Table 2.Summary of previous studies on the association of T. gondii infection with tumor incidence
Table 2.
|
Year |
Country |
Tumor type |
Methods |
Results |
Reference |
|
1963-1964 |
USA |
Glioma, Acoustic neuroma, Meningioma, Others |
Sabin-Feldman dye-test |
Tumor patients (n = 126): 56.3% |
Schuman et al. [11] |
|
Healthy controls (n = 126): 41.3% |
|
1979-2007 |
France |
Brain tumor |
Database |
Brain tumor mortality rates increase with T. gondii seroprevalence in France. |
Vittecoq et al. [12] |
|
1987-1990 |
Australia |
Glioma, Meningioma |
ELISA (IgG) |
Tumor patients (n = 53): 47.0% |
Ryan et al. [13] |
|
Healthy controls (n = 348): 31.0% |
|
2000-2002 |
Turkey |
Hodgkin's lymphoma, Multiple myeloma, Leukemia, Others |
ELISA (IgG) |
Cancer patients (n = 108): 63.0% |
Yazar et al. [14] |
|
Healthy controls (n = 108): 19.4% |
|
2006 |
China |
Nasopharyngeal carcinoma, Rectal cancer, Others |
ELISA (IgG) |
Cancer patients (n = 267): 24.0% |
Yuan et al. [15] |
|
Healthy controls (n = 148): 6.1% |
|
2008 |
Korea |
Malignant neoplasms |
LAT, ELISA (IgG) |
Malignant neoplasms: 19.0% (16 cases/84 T. gondii positive cases) |
Shin et al. [16] |
|
2008 |
37 countries |
Brain tumor |
Database |
Infection with T. gondii was associated with a 1.8-fold increase in the risk of brain tumors. |
Thomas et al. [17] |
|
2012-2014 |
China |
Brain tumor, Lung cancer, Cervical cancer, Others |
ELISA (IgG) |
Tumor patients (n = 900): 35.6% |
Cong et al. [18] |
|
Healthy controls (n = 900): 17.4% |
References
- 1. Ferlay J, Soerjomataram I, Ervik M, Dikshit R, Eser S, Mathers C, Rebelo M, Parkin D, Forman D, Bray F. GLOBOCAN 2012 v1.0, cancer incidence and mortality worldwide: IARC cancer base no. 11 [Internet]. International Agency for Research on Cancer 2012, Lyon, France, 2013. http://globocan.iarc.fr
- 2. Fisher JL, Scharwtzbaum JA, Wrensch M, Wiemels JL. Epidemiology of brain tumors. Neurol Clin 2007;25:867-890.
- 3. Pagano JS, Blaser M, Buendia MA, Damania B, Khalili K, Raab-Traub N, Roizman B. Infectious agents and cancer: criteria for a causal relation. Semin Cancer Biol 2004;14:453-471.
- 4. Bouvard V, Baan R, Straif K, Grosse Y, Secretan B, El Ghissassi F, Benbrahim-Tallaa L, Guha N, Freeman C, Galichet L, Cogliano V; WHO International Agency for Research on Cancer Monograph Working Group. A review of human carcinogens. Part B: biological agents. Lancet Oncol 2009;10:321-322.
- 5. Alibek K, Kakpenova A, Baiken Y. Role of infectious agents in the carcinogenesis of brain and head and neck cancers. Infect Agent Cancer 2013;8:7.
- 6. Correia da Costa JM, Vale N, Gouveia MJ, Botelho MC, Sripa B, Santos LL, Santos JH, Rinaldi G, Brindley PJ. Schistosome and liver fluke derived catechol-estrogens and helminth associated cancers. Front Genet 2014;5:444.
- 7. Del Brutto OH, Dolezal M, Castillo PR, García HH. Neurocysticercosis and oncogenesis. Arch Med Res 2000;31:151-155.
- 8. Muehlenbachs A, Bhatnagar J, Agudelo CA, Hidron A, Eberhard ML, Mathison BA, Frace MA, Ito A, Metcalfe MG, Rollin DC, Visvesvara GS, Pham CD, Jones TL, Greer PW, Vélez Hoyos A, Olson PD, Diazgranados LR, Zaki SR. Malignant transformation of Hymenolepis nana in a human host. N Engl J Med 2015;373:1845-1852.
- 9. Tenter AM, Heckeroth AR, Weiss LM. Toxoplasma gondii: from animals to humans. Int J Parasitol 2000;30:1217-1258.
- 10. Schuman LM, Choi NW, Gullen WH. Relationship of central nervous system neoplasms to Toxoplasma gondii infection. Am J Public Health Nations Health 1967;57:848-856.
- 11. Thirugnanam S, Rout N, Gnanasekar M. Possible role of Toxoplasma gondii in brain cancer through modulation of host microRNAs. Infect Agent Cancer 2013;8:8.
- 12. Vittecoq M, Elguero E, Lafferty KD, Roche B, Brodeur J, Gauthier-Clerc M, Missé D, Thomas F. Brain cancer mortality rates increase with Toxoplasma gondii seroprevalence in France. Infect Genet Evol 2012;12:496-498.
- 13. Ryan P, Hurley SF, Johnson AM, Salzberg M, Lee MW, North JB, McNeil JJ, McMichael AJ. Tumours of the brain and presence of antibodies to Toxoplasma gondii. Int J Epidemiol 1993;22:412-419.
- 14. Yazar S, Yaman O, Eser B, Altuntas F, Kurnaz F, Sahin I. Investigation of anti-Toxoplasma gondii antibodies in patients with neoplasia. J Med Microbiol 2004;53:1183-1186.
- 15. Yuan Z, Gao S, Liu Q, Xia X, Liu X, Liu B, Hu R. Toxoplasma gondii antibodies in cancer patients. Cancer Lett 2007;254:71-74.
- 16. Shin DW, Cha DY, Hua QJ, Cha GH, Lee YH. Seroprevalence of Toxoplasma gondii infection and characteristics of seropositive patients in general hospitals in Daejeon, Korea. Korean J Parasitol 2009;47:125-130.
- 17. Thomas F, Lafferty KD, Brodeur J, Elguero E, Gauthier-Clerc M, Missé D. Incidence of adult brain cancers is higher in countries where the protozoan parasite Toxoplasma gondii is common. Biol Lett 2012;8:101-103.
- 18. Cong W, Liu GH, Meng QF, Dong W, Qin SY, Zhang FK, Zhang XY, Wang XY, Qian AD, Zhu XQ. Toxoplasma gondii infection in cancer patients: prevalence, risk factors, genotypes and association with clinical diagnosis. Cancer Lett 2015;359:307-313.
- 19. Lim H, Lee SE, Jung BK, Kim MK, Lee MY, Nam HW, Shin JG, Yun CH, Cho HI, Shin EH, Chai JY. Serologic survey of toxoplasmosis in Seoul and Jeju-do, and a brief review of its seroprevalence in Korea. Korean J Parasitol 2012;50:287-293.
- 20. Flegr J. Influence of latent toxoplasmosis on the phenotype of intermediate hosts. Folia Parasitol (Praha) 2010;57:81-87.
- 21. Dubey JP, Lindsay DS, Speer CA. Structures of Toxoplasma gondii tachyzoites, bradyzoites, and sporozoites and biology and development of tissue cysts. Clin Microbiol Rev 1998;11:267-299.
- 22. Molestina RE, El-Guendy N, Sinai AP. Infection with Toxoplasma gondii results in dysregulation of the host cell cycle. Cell Microbiol 2008;10:1153-1165.
- 23. Facer CA, Playfair JH. Malaria, Epstein-Barr virus, and the genesis of lymphomas. Adv Cancer Res 1989;53:33-72.
