Modern possibilities of neurosurgical treatment of brain metastases

Despite significant progress in neuroimaging and introduction of new combined treatments for solid tumors, brain metastases are still adverse factor for overall survival. Brain metastases are diagnosed in 8-10% of patients and associated with extremely poor prognosis. These lesions result focal and general cerebral symptoms. Literature review highlights the current principles of surgical treatment of metastatic brain lesions in patients with solid tumors.

Regulation of Thiamine (Vitamin B1)-Dependent Metabolism in Mammals by p53

Transcriptional factor p53 is a master regulator of energy metabolism. Energy metabolism strongly depends on thiamine (vitamin B1) and/or its natural derivatives. Thiamine diphosphate (ThDP), which is a major thiamine derivative, affects p53 binding to DNA. In order to elucidate the mechanism of regulation of thiamine-dependent metabolism by p53, we assessed putative p53-binding sites near transcription starting points in genes coding for transporters and enzymes, whose function is associated with thiamine and/or its derivatives. The predictions were validated by studying cell metabolic response to the p53 inducer cisplatin. Expression of p53 and its known target, p21, has been evaluated in cisplatin-treated and control human lung adenocarcinoma A549 cells that possess functional p53 pathway. We also investigated the activity of enzymes involved in the thiamine-dependent energy metabolism. Along with upregulating the expression of p53 and p21, cisplatin affected the activities of metabolic enzymes, whose genes were predicted as carrying the p53-binding sites. The activity of glutamate dehydrogenase GDH2 isoenzyme strongly decreased, while the activities of NADP+-dependent isocitrate dehydrogenase (IDH) and malic enzymes, as well as the activity of 2-oxoglutarate dehydrogenase complex at its endogenous ThDP level, were elevated. Simultaneously, the activities of NAD+-dependent IDH, mitochondrial aspartate aminotransferase, and two malate dehydrogenase isoenzymes, whose genes were not predicted to have the p53-binding sequences near the transcription starting points, were upregulated by cisplatin. The p53-dependent regulation of the assayed metabolic enzymes correlated with induction of p21 by p53 rather than induction of p53 itself.

Thiamine Mono- and Diphosphate Phosphatases in Bovine Brain Synaptosomes

Neurodegenerative diseases are accompanied by changes in the activity of thiamine mono- and diphosphate phosphatases, but molecular identification of these mammalian enzymes is incomplete. In this work, the protein fraction of bovine brain synaptosomes displaying phosphatase activity toward thiamine derivatives was subjected to affinity chromatography on thiamine-Sepharose. Protein fractions eluted with thiamine (pH 7.4 or 5.6), NaCl, and urea were assayed for the phosphatase activity against thiamine monophosphate (ThMP), thiamine diphosphate (ThDP), and structurally similar purine nucleotides. Proteins in each fraction were identified by mass spectrometry using the SwissProt database for all organisms because of insufficient annotation of the bovine genome. Peptides of two annotated bacterial phosphatases, alkaline phosphatase L from the DING protein family and exopolyphosphatase, were identified in the acidic thiamine eluate. The abundance of peptides of alkaline phosphatase L and exopolyphosphatase in the eluted fractions correlated with ThMPase and ThDPase activities, respectively. The elution profiles of the ThMPase and ThDPase activities differed from the elution profiles of nucleotide phosphatases, thus indicating the specificity of these enzymes toward thiamine derivatives. The search for mammalian DING phosphatases in the eluates from thiamine-Sepharose revealed X-DING-CD4, mostly eluted by the acidic thiamine solution (pH 5.6). The identified exopolyphosphatase demonstrated structural similarity with apyrases possessing the ThDPase activity. The obtained results demonstrate that mammalian DING proteins and apyrases exhibit ThMPase and ThDPase activity, respectively.

Mechanisms of Non-coenzyme Action of Thiamine: Protein Targets and Medical Significance

Thiamine (vitamin B1) is a precursor of the well-known coenzyme of central metabolic pathways thiamine diphosphate (ThDP). Highly intense glucose oxidation in the brain requires ThDP-dependent enzymes, which determines the critical significance of thiamine for neuronal functions. However, thiamine can also act through the non-coenzyme mechanisms. The well-known facilitation of acetylcholinergic neurotransmission upon the thiamine and acetylcholine co-release into the synaptic cleft has been supported by the discovery of thiamine triphosphate (ThTP)-dependent phosphorylation of the acetylcholine receptor-associated protein rapsyn, and thiamine interaction with the TAS2R1 receptor, resulting in the activation of synaptic ion currents. The non-coenzyme regulatory binding of thiamine compounds has been demonstrated for the transcriptional regulator p53, poly(ADP-ribose) polymerase, prion protein PRNP, and a number of key metabolic enzymes that do not use ThDP as a coenzyme. The accumulated data indicate that the molecular mechanisms of the neurotropic action of thiamine are far broader than it has been originally believed, and closely linked to the metabolism of thiamine and its derivatives in animals. The significance of this topic has been illustrated by the recently established competition between thiamine and the antidiabetic drug metformin for common transporters, which can be the reason for the thiamine deficiency underlying metformin side effects. Here, we also discuss the medical implications of the research on thiamine, including the role of thiaminases in thiamine reutilization and biosynthesis of thiamine antagonists; molecular mechanisms of action of natural and synthetic thiamine antagonists, and biotransformation of pharmacological forms of thiamine. Given the wide medical application of thiamine and its synthetic forms, these aspects are of high importance for medicine and pharmacology, including the therapy of neurodegenerative diseases.

Thiamine Induces Long-Term Changes in Amino Acid Profiles and Activities of 2-Oxoglutarate and 2-Oxoadipate Dehydrogenases in Rat Brain

Molecular mechanisms of long-term changes in brain metabolism after thiamine administration (single i.p. injection, 400 mg/kg) were investigated. Protocols for discrimination of the activities of the thiamine diphosphate (ThDP)-dependent 2-oxoglutarate and 2-oxoadipate dehydrogenases were developed to characterize specific regulation of the multienzyme complexes of the 2-oxoglutarate (OGDHC) and 2-oxoadipate (OADHC) dehydrogenases by thiamine. The thiamine-induced changes depended on the brain-region-specific expression of the ThDP-dependent dehydrogenases. In the cerebral cortex, the original levels of OGDHC and OADHC were relatively high and not increased by thiamine, whereas in the cerebellum thiamine upregulated the OGDHC and OADHC activities, whose original levels were relatively low. The effects of thiamine on each of the complexes were different and associated with metabolic rearrangements, which included (i) the brain-region-specific alterations of glutamine synthase and/or glutamate dehydrogenase and NADP+-dependent malic enzyme, (ii) the brain-region-specific changes of the amino acid profiles, and (iii) decreased levels of a number of amino acids in blood plasma. Along with the assays of enzymatic activities and average levels of amino acids in the blood and brain, the thiamine-induced metabolic rearrangements were assessed by analysis of correlations between the levels of amino acids. The set and parameters of the correlations were tissue-specific, and their responses to the thiamine treatment provided additional information on metabolic changes, compared to that gained from the average levels of amino acids. Taken together, the data suggest that thiamine decreases catabolism of amino acids by means of a complex and long-term regulation of metabolic flux through the tricarboxylic acid cycle, which includes coupled changes in activities of the ThDP-dependent dehydrogenases of 2-oxoglutarate and 2-oxoadipate and adjacent enzymes.