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Thyroxine 5-deiodinase in human brain tumors
1Second Department of Internal Medicine, Tohoku University School of Medicine, Sendai, Japan.
The Journal of Clinical Endocrinology and Metabolism
|November 1, 1993
Summary
Human brain tumors, particularly gliomas, exhibit T4 5-monodeiodinase (5-D) activity, suggesting a role in regulating thyroid hormone levels within these tumors.
Area of Science:
- Endocrinology
- Neuroscience
- Oncology
Background:
- Thyroid hormone metabolism is crucial for normal brain function.
- The presence and role of deiodinating pathways in human brain tumors remain largely uncharacterized.
Purpose of the Study:
- To investigate the existence and characteristics of T4 5-monodeiodinase (5-D) activity in human brain tumors.
- To determine if this activity could play a role in thyroid hormone regulation within gliomas.
Main Methods:
- Analyzed 20 human brain tumors (astrocytomas, meningiomas, oligodendrogliomas, glioblastomas, medulloblastomas, lymphomas) for T4 5-D activity.
- Utilized mitochondrial-microsomal fractions and measured T4 5-D activity via radioimmunoassay (RIA) by quantifying rT3 production.
- Characterized enzyme kinetics, including heat lability and inhibition patterns.
Main Results:
- T4 5-D activity was detected in astrocytomas, oligodendrogliomas, glioblastomas, and malignant lymphoma.
- Enzyme activity demonstrated dependence on protein concentration, incubation time, temperature, and pH, and was heat labile.
- Activity was not inhibited by propylthiouracil but was dose-dependently inhibited by iopanoic acid and aurothioglucose.
Conclusions:
- Human gliomas and potentially malignant lymphomas possess T4 5-D activity, resembling type III deiodinase in rats.
- This enzyme activity may be involved in regulating intracellular thyroid hormone concentrations within gliomas.