Gliomas: Role of Monoamine Oxidase B in Diagnosis

Abstract

Glioma is the most common type of brain tumour in humans. These tumours account for high morbidity and mortality because therapies are largely ineffective. A higher histologic grade of the glioma corresponds to increasing malignancy and reduced survival of the patient. Therefore, tumour classification and grading represent key factors for patient management. However, current grading schemes are still limited by subjective histological criteria. In this context, the enhancement in the glial content of the brain that appears during gliosis has been linked to increases in monoamine oxidase B (MAO-B) activity. In consequence, we decided to assess the hypothesis that MAO-B activity may be also increased in human glial tumours. Thus, we quantified MAO-B activity in membranes of low-grade astrocytomas (WHO grade I-II; n = 3), anaplastic astrocytomas (WHO grade III; n = 6), glioblastoma multiformes (WHO grade IV; n = 11), meningiomas (n = 12) and non-pathological human brains (n = 15) by [14C]PEA oxidation. MAO-B activity was significantly greater in glioblastoma multiformes than in postmortem control brains (p < 0.01) or meningiomas (p < 0.001). There were no significant differences in MAO-B activity between glioblastoma multiformes (WHO grade IV n = 11) and anaplastic astrocytomas (WHO grade III; n = 6) or low-grade astrocytomas (WHO grade I-II, n = 3). In conclusion, our results demonstrate a significant and selective increase in MAO-B activity in human gliomas when compared with meningiomas or non-tumoural tissue. These results suggest that the quantification of MAO-B activity may be a useful diagnostic tool for differentiating glial tumours from other types of brain tumours or surrounding normal brain tissue.