Study of pyruvate kinase activity in human astrocytomas - alanine-inhibition test revisted

BACKGROUND

Recent studies have confirmed that alterations in the isoenzyme of pyruvate kinase (PK) provide tumor cells with selective growth advantage.

AIMS

Our aim was to establish the mean activity of the enzyme PK in human astrocytomas and to look for any trends in the activity with relation to histological grade.

MATERIALS AND METHODS

The PK (EC 2.7.1.40) activity was measured in the tumor homogenate by spectrophotometric rate determination. DeltaAbsorbance at 340 nm (A 340 nm ) per minute was obtained using the maximal linear rate for both the test and the blank. Enzyme activity was estimated in the presence and absence of amino acid alanine.

RESULTS

The mean PK level in astrocytomas was 3.5 +/- 2.0 mmol/min/mg protein, which was significantly higher (24%; P < 0.001) when compared to 2.8 +/- 0.3 mmol/min/mg protein in control brain. Highest PK activity was noted in grade 2 astrocytomas. In controls there was no change in PK activity in the presence of alanine. In grade 2 astrocytomas there was 7% decrease in mean PK activity in the presence of alanine, this difference in grade 3 astrocytomas was 33% and in grade 4 astrocytomas it was 61%. As the tumors were becoming malignant there was a graded increase in the levels of PK inhibition.

CONCLUSIONS

Mean PK activity was significantly higher in astrocytomas. There was a graded increase in level of PK inhibition as the tumors were becoming more malignant.

Multiple schwannomas: report of two cases

In this paper authors present two cases of multiple schwannomas without the features of neurofibromatosis (NF). The authors retrospectively reviewed the hospital charts, radiology films, operative notes and pathology slides of these two patients. There was no family history of neurofibromatosis. The two patients had contrast enhanced MRI, which was negative for vestibular schwannomas. Both underwent surgical excision of symptomatic lesions. Histopathology confirmed these lesions as schwannomas. Molecular genetic analysis in case 1 demonstrated two distinct mutations of the NF2 gene in two different schwannomas, with concomitant loss of heterozygosity in both tumours. In contrast peripheral blood lymphocytes did not reveal mutations of NF2. The authors recommend surgery for symptomatic lesions. Asymptomatic tumours can be monitored. Regular follow up is essential as they may develop fresh lesions at any time. The relevant literature is discussed.