Tissue plasminogen activator expression in meningiomas and glioblastomas

Enzyme-linked immunosorbent assay (ELISA) and Western blotting techniques were used to investigate and compare the expression of tissue plasminogen activator (tPA) in benign (meningioma) and malignant (glioblastoma) human brain tumours.

A total of 22 tumour samples comprising 11 meningiomas and 11 glioblastomas with adjacent peritumoural tissue were analysed.

The mean tPA content of meningiomas was approximately half that of glioblastomas (55.40 (S.D. 34.58) versus 106.98 (S.D. 43.82) ng/ml, p=0.006). Comparing tPA quantity in tumour and peritumoural tissue, there was a significant difference for meningiomas (55.40 (S.D. 34.58) versus 28.35 (S.D. 22.55) ng/ml, p=0.05), but no difference for glioblastomas (106.98 (S.D. 43.82) versus 84.23 (S.D. 57.39) ng/ml, p=0.32). Comparing tumour with normal brain tissue, there was no difference for meningiomas (55.40 (S.D. 34.58) versus 33.08 (S.D. 21.55) ng/ml, p=0.22), but a significant difference for glioblastomas (106.98 (S.D. 43.82) versus 33.08 (S.D. 21.55) ng/ml, p=0.004). Western blotting showed that in the meningioma group, the molecular weight pattern was constant with a dominant well-defined band at 41kD. Peritumoural tissue demonstrated two bands, with the stronger band at 41kD and a slightly weaker band at 71kD. In the glioblastoma group, there was more heterogeneity, with a dominant 41kD band found in all tumour and peritumoural samples, together with additional bands at 34, 58 and 66kD.

These results indicate that (1) tPA is present in larger quantities in glioblastoma compared to meningioma and normal brain, (2) tPA quantity is not significantly different in the peritumoural tissue adjacent to glioblastoma but is significantly less for meningioma, and (3) tPA is expressed in more heterogenous forms in glioblastoma. This present study therefore suggests that the expression of tPA in a brain tumour may be an additional prognostic factor in terms of its malignant and invasive potential.