Serum deprivation and NGF induce and modulate voltage-gated Na(+) currents in human astrocytoma cell lines

Nerve growth factor improves visual loss in childhood optic gliomas: a randomized, double-blind, phase II clinical trial

Paediatric optic pathway gliomas are low-grade brain tumours characterized by slow progression and invalidating visual loss. Presently there is no strategy to prevent visual loss in this kind of tumour. This study evaluated the effects of nerve growth factor administration in protecting visual function in patients with optic pathway glioma-related visual impairment. A prospective randomized double-blind phase II clinical trial was conducted in 18 optic pathway glioma patients, aged from 2 to 23 years, with stable disease and severe visual loss. Ten patients were randomly assigned to receive a single 10-day course of 0.5 mg murine nerve growth factor as eye drops, while eight patients received placebo. All patients were evaluated before and after treatment, testing visual acuity, visual field, visual-evoked potentials, optic coherence tomography, electroretinographic photopic negative response, and magnetic resonance imaging. Post-treatment evaluations were repeated at 15, 30, 90, and 180 days Brain magnetic resonance imaging was performed at baseline and at 180 days. Treatment with nerve growth factor led to statistically significant improvements in objective electrophysiological parameters (electroretinographic photopic negative response amplitude at 180 days and visual-evoked potentials at 30 days), which were not observed in placebo-treated patients. Furthermore, in patients in whom visual fields could still be measured, visual field worsening was only observed in placebo-treated cases, while three of four nerve growth factor-treated subjects showed significant visual field enlargement. This corresponded to improved visually guided behaviour, as reported by the patients and/or the caregivers. There was no evidence of side effects related to nerve growth factor treatment. Nerve growth factor eye drop administration appears a safe, easy and effective strategy for the treatment of visual loss associated with optic pathway gliomas.

The role of ion channels in malignant brain tumors

Malignant gliomas are the most common primary brain tumors and have poor clinical prognosis, despite multimodal therapeutic strategies. In recent years, ion channels have emerged as major players in tumor pathophysiology regarding all hallmarks of cancer. Since ion channels are easily accessible structures, they may prove to be effective targets for canner therapy, although their broad expression pattern and role in physiological processes should be taken into consideration. This review summarizes the current knowledge on the role of ion channels in the pathophysiology of malignant gliomas, especially glioblastoma, and evaluates their potential role in targeted antiglioma therapy.

Peritumoral epilepsy: relating form and function for surgical success

Seizures are a prominent symptom in patients with both primary and secondary brain tumors. Medical management of seizure control in this patient group is problematic as the mechanisms linking tumorigenesis and epileptogenesis are poorly understood. It is possible that several mechanisms contribute to tumor-associated epileptic zone formation. In this review, we discuss key candidates that may be implicated in peritumoral epileptogenesis and, in so doing, hope to highlight areas for future research. Furthermore, we summarize the current role of antiepileptic medications in this type of epilepsy and examine the changes in surgical practice which may lead to improved seizure rates after tumor surgery. Lastly, we speculate on possible future preoperative and intraoperative considerations for improving seizure control after tumor resection.

The pathogenesis of tumor-related epilepsy and its implications for clinical treatment

Approximately 30-50% of patients with brain tumors present with seizures as the initial symptom. Seizures play a very important role in the quality of life, particularly in patients with slow-growing primary brain tumors. Tumor-related seizures are often refractory to antiepileptic treatment. Despite the importance of this subject to the fields of neurology, neurosurgery and neurooncology, the pathogenesis of tumor-related epilepsy remains poorly understood. This review summarizes possible mechanisms underlying the pathogenesis of tumor-related epilepsy, including both tumoral and peri-tumoral aspects. Tumor cells themselves may create intrinsic epileptogenicity, and inadequate homeostasis in the peri-tumoral tissues may lead to seizure susceptibility. Other local changes in electrolytes, perfusion, metabolism, and enzymes could also contribute. It is generally accepted that changes in amino acid neurotransmission are the most important mechanism underlying tumor-related seizures, and changes in extracellular ions also play an important role. Hypoxia, acidosis, and metabolic, immunological, and inflammatory changes may also be involved in the occurrence of seizures. Knowledge of these mechanisms may provide guidance in the search for new strategies for the surgical and medical treatment of tumor-related epilepsy.

Ion channels and the hallmarks of cancer

Plasma membrane (PM) ion channels contribute to virtually all basic cellular processes and are also involved in the malignant phenotype of cancer cells. Here, we review the role of ion channels in cancer in the context of their involvement in the defined hallmarks of cancer: 1) self-sufficiency in growth signals, 2) insensitivity to antigrowth signals, 3) evasion of programmed cell death (apoptosis), 4) limitless replicative potential, 5) sustained angiogenesis and 6) tissue invasion and metastasis. Recent studies have indicated that the contribution of specific ion channels to these hallmarks varies for different types of cancer. Therefore, to determine the importance of ion channels as targets for cancer diagnosis and treatment their expression, function and regulation must be assessed for each cancer.

Functional characterization of two isoforms of the P2Y-like receptor GPR17: [35S]GTPgammaS binding and electrophysiological studies in 1321N1 cells

The previously "orphan" G protein-coupled receptor GPR17 is structurally related to both P2Y nucleotide receptors and to receptors for cysteinyl leukotrienes. Genomic analysis revealed two putative open reading frames encoding for a "short" and a "long" receptor isoform of 339- and 367-amino acids, respectively, with the latter displaying a 28-amino acid longer NH(2) terminus. The short isoform has been recently "deorphanized," revealing dual responses to uracil nucleotides and cysteinyl leukotrienes. No information regarding the ligand specificity, tissue distribution, or pathophysiological roles of the long receptor isoform is available. In the present study, we cloned human long-GPR17, determined its tissue distribution, and characterized its pharmacological specificity in 1321N1 cells by [35S]GTPgammaS binding (which measures the ability of G protein-coupled receptor agonists to increase GTP binding to G proteins) and whole cell patch-clamp recording measuring receptor coupling to K+ channels. [35S]GTPgammaS binding in long-GPR17-expressing 1321N1 cells revealed concentration-dependent responses to uracil nucleotides (UDP-galactose = UDP > UDP-glucose) and cysteinyl leukotrienes (LTC4 > LTD4), which were counteracted by a purinergic (cangrelor) and a cysteinyl leukotriene antagonist (montelukast), respectively. The nonhydrolyzable ATP analog ATPgammaS also acted as an antagonist. GPR17 coupled to Gi and, to a lesser extent, Gq proteins. UDP-glucose and LTD(4) also induced increases in overall outward K+ currents, which were antagonized by the purinergic antagonists MRS2179 and cangrelor and by montelukast. We conclude that the previously uncharacterized long-GPR17 isoform is a functional receptor that is stimulated by both uracil nucleotides and cysteinyl leukotrienes. We also show that the signaling pathway of GPR17 involves the generation of outward K+ currents, an important protective mechanism that, in brain, is specifically aimed at reducing neuronal hyperexcitability and resultant neuronal injury.

Brain tumors and epilepsy: pathophysiology of peritumoral changes

Epilepsy commonly develops among patients with brain tumors, frequently even as the presenting symptom, and such patients consequently experience substantial morbidity from both the seizures and the underlying disease. At clinical presentation, these seizures are most commonly focal with secondary generalization and conventional medical management is often met with less efficacy. The molecular pathophysiology of these seizures is being elucidated with findings that both the tumoral and peritumoral microenvironments may exhibit epileptogenic phenotypes owing to disordered neuronal connectivity and regulation, impaired glial cell function, and the presence of altered vascular supply and permeability. Neoplastic tissue can itself be the initiation site of seizure activity, particularly for tumors arising from neuronal cell lines, such as gangliogliomas or dysembryoblastic neuroepithelial tumors. Conversely, a growing intracranial lesion can both structurally and functionally alter the surrounding brain tissue with edema, vascular insufficiency, inflammation, and release of metabolically active molecules, hence also promoting seizure activity. The involved mechanisms are certain to be multifactorial and depend on specific tumor histology, integrity of the blood brain barrier, and characteristics of the peritumoral environment. Understanding these changes that underlie tumor-related epilepsy may have roles in both optimal medical management for the seizure symptom and optimal surgical objective and management of the underlying disease.

Epidermal growth factor potentiates in vitro metastatic behaviour of human prostate cancer PC-3M cells: involvement of voltage-gated sodium channel

Background

Although a high level of functional voltage-gated sodium channel (VGSC) expression has been found in strongly metastatic human and rat prostate cancer (PCa) cells, the mechanism(s) responsible for the upregulation is unknown. The concentration of epidermal growth factor (EGF), a modulator of ion channels, in the body is highest in prostatic fluid. Thus, EGF could be involved in the VGSC upregulation in PCa. The effects of EGF on VGSC expression in the highly metastatic human PCa PC-3M cell line, which was shown previously to express both functional VGSCs and EGF receptors, were investigated. A quantitative approach, from gene level to cell behaviour, was used. mRNA levels were determined by real-time PCR. Protein expression was studied by Western blots and immunocytochemistry and digital image analysis. Functional assays involved measurements of transverse migration, endocytic membrane activity and Matrigel invasion.

Results

Exogenous EGF enhanced the cells' in vitro metastatic behaviours (migration, endocytosis and invasion). Endogenous EGF had a similar involvement. EGF increased VGSC Nav1.7 (predominant isoform in PCa) mRNA and protein expressions. Co-application of the highly specific VGSC blocker tetrodotoxin (TTX) suppressed the effect of EGF on all three metastatic cell behaviours studied.

Conclusion

1) EGF has a major involvement in the upregulation of functional VGSC expression in human PCa PC-3M cells. (2) VGSC activity has a significant intermediary role in potentiating effect of EGF in human PCa.

Influences of brain tumor-associated pH changes and hypoxia on epileptogenesis

OBJECTIVE

The pathophysiological changes related to epileptic activity in peri- and intra-tumoral tissue are complex and have been only partly understood until now; possible mechanisms involve different structural, biochemical and histological tumor-related alterations.

METHODS

Medical databases were searched for evidence on influence of brain tumor-associated pH changes and hypoxia on epileptogenesis.

RESULTS

During the perioperative period, tumor-related hypoxia and acidity related to tumor neovascularization by vascular endothelial growth factor (VEGF) in combination with angiopoietins 1/2 (ang 1/2), may be a major factor contributing to outcomes involving epileptic activity after surgical tumor removal. Because anaerobic fermentation produces far less ATP than oxidative phosphorlyation per molecule of glucose, increased activity of the glycolytic pathway is necessary to maintain free ATP levels in the hypoxic cell. In mammalian cells, this metabolic switch is regulated by the transcription factor hypoxia-inducible factor-1.

CONCLUSIONS

From the molecular point of view, therapeutic implications for the perioperative period may have relevance for the future.

Serum concentration modifies amplitude and kinetics of voltage-gated Na+ current in the Mat-LyLu cell line of rat prostate cancer

Voltage-gated Na+ channel (VGSC) expression has previously been shown to be upregulated in strongly metastatic prostate cancer cells (rat and human) and its activity shown to potentiate a variety of cellular behaviours integral to the metastatic cascade. However, the mechanism(s) responsible for the Na+ channel upregulation is not known. As a step towards evaluating the role of the extracellular biochemical environment in this regard, we have determined the effects of serum concentration on characteristics of Na+ channel expressed in the strongly metastatic Mat-LyLu rat prostate cancer cell line. Whole-cell patch-clamp recording techniques were used to study the effects of serum concentrations, above and below the normal 1%. Both the amplitude and the kinetics of the currents were analysed. The following results were obtained: (1) Adding 1% foetal calf serum to cells starved of serum for 24h increased Na+ current density; however, increasing serum concentration further (to 5%) caused a reduction. (2) Serum-free medium produced Na+ currents with slower kinetics of activation (time to peak) and inactivation (exponential decay). (3) Increased serum concentration (a) shifted steady-state inactivation to more positive potentials without affecting conductance and (b) increased tetrodotoxin sensitivity. It is concluded that serum concentration is an important determinant of the Na+ channel characteristics leading to possible transcriptional and post-translational modifications of channel expression and/or activity. Experiments are now needed to determine which constituents (protein hormones, growth factors, etc.) are responsible for these effects.

BK channel openers inhibit migration of human glioma cells

Large-conductance Ca(2+)-activated K(+) channels (BK channels) are highly expressed in human glioma cells. However, less is known about their biological function in these cells. We used the patch-clamp technique to investigate activation properties of BK channels and time-lapse microscopy to evaluate the role of BK channel activation in migration of 1321N1 human glioma cells. In whole cells, internal perfusion with a solution containing 500 nM free Ca(2+) and external application of the BK channel opener phloretin (100 micro M) shifted the activation threshold of BK channel currents toward more negative voltages of about -30 mV, which is close to the resting potential of the cells. The concentration of intracellular Ca(2+) in fura-2-loaded 1321N1 cells was measured to be 235+/-19 nM and was increased to 472+/-25 nM after treatment with phloretin. Phloretin and another BK channel opener NS1619 (100 micro M) reduced the migration velocity by about 50%. A similar reduction was observed following muscarinic stimulation of glioma cells with acetylcholine (100 micro M). The effects of phloretin, NS1619 and acetylcholine on cell migration were completely abolished by co-application of the specific BK channel blockers paxilline (5 micro M) and iberiotoxin (100 nM). The phloretin-induced increase in intracellular Ca(2+) was unaffected by the removal of extracellular Ca(2+) and co-application of paxilline. These findings indicate that glioma cell migration was inhibited through BK channel activation, independent of intracellular Ca(2+).

BK channel blockers inhibit potassium-induced proliferation of human astrocytoma cells

The functional role of BK channels, which are consistently expressed in glioma cells, is not clear. Here we show that the BK channels are regularly active in human 1321N1 astrocytoma cells at physiological membrane potentials. The proliferation of the cells at the physiological external [K+] of 5 mM is compared with that at the elevated external [K+] of 20 mM, simulating the situation in rapidly growing, necrotic tumours in vivo. High extracellular [K+] in the range 10-30 mM significantly increases the proliferation of 1321N1 cells. This K+ induced proliferation can be completely abolished by applying the specific BK channel blockers iberiotoxin (IBTX) or 1 mM tetraethylammonium (TEA). Neither blocker has any effect on cell growth at 5 mM [K+]e. These findings indicate a particular role of BK channels in astrocytoma cell proliferation.