FES Helps Transplanted ES Cells Differentiate Into Neurons
Functional electrical stimulation (FES) appears to facilitate the differentiation of embryonic stem (ES) cells into neuronal phenotypes in rat models of spinal cord injury (SCI). The findings were reported by a team led by John W. McDonald III, MD, PhD--longtime physician of the late Christopher Reeve--this past September in San Diego at the 130th annual meeting of the American Neurological Association.
McDonald, who was recently named director of the International Center for Spinal Cord Injuries at the Kennedy Krieger Institute in Baltimore, has been a pioneer in using FES in the rehabilitation of patients with spinal cord injuries. He is credited for the advances Reeve made in recovery of function.
In his recent research with junior colleagues Daniel Becker, MD, of Vanderbilt University in Nashville and Carlo O. Martinez, PhD, of Washington University School of Medicine in St. Louis, McDonald demonstrated that transplanted ES-derived neural progenitor cells had a better chance of differentiating when target nerves in transplant recipients were exposed to FES.
The researchers implanted 2-channel FES electrodes that communicated with peroneal nerves in the hind limbs of 8 spinal cord-injured rats and then transplanted 100,000 green fluorescent protein-labeled neural stem cells above and below the SCI (T8/9). FES, which induced a steplike motion in the hind limbs, was activated for 3 hours per day for 15 days in 4 rats. The remaining 4 rats served as controls.
Histologic examination revealed that ES cells implanted below the SCI site were significantly more likely to differentiate into neural phenotypes in rats exposed to FES, compared with nonexposed rats (32% ± 4% vs 9% ± 1%). The researchers believe their findings will aid clinical researchers in developing techniques that maximize the therapeutic effectiveness of transplanted neural stem cells. *
EBIO Suppresses Epileptic Activity In Vitro
The agent 1-ethyl-2-benzimidazolinone (EBIO) blocked experimentally induced epileptiform activity in CA3 pyramidal neurons derived from rat hippocampal cells, reported a team of researchers from Instituto Cajal in Madrid. The primary mechanism of action is the chemical's ability to enhance medium afterhyperpolarization (mIAHP) related to calcium2+ (Ca2+) and potassium+ (K+) channel conductances, according to the investigators. This preliminary research may ultimately lead to the development of potent antiepileptic drugs that target certain Ca2+-mediated K+ channels.
The team, led by Washington Buño, MD, research professor in the Department of Neuronal Plasticity, reasoned that Ca2+ and K+ neuronal conductances that have medium and slow decay (ie, AHP) kinetics could be therapeutic targets for novel antiepileptic agents because these pathways impose negative-feedback regulation of neuronal excitability. The team induced epileptogenesis in rat hippocampal slices by superfusing the slices with magnesium2+ (Mg2+)-free artificial cerebrospinal fluid and either 4-aminopyridine (4-AP) or kainic acid.
Adding EBIO at doses ranging from 200 µM to 1 mM to the superfusions reduced the duration and frequency of epileptiform bursts, the number of spikes in interictal bursts, and the synchronization between bursts, and it ultimately silenced abnormal interictal activity. The researchers achieved the same results when they treated hippocampal slices superfused with 4-AP and Ringer solution containing 2 mM Mg2+ with EBIO, which confirmed other published research demonstrating that EBIO is not affected by Mg2+.
The researchers also showed that the effect of EBIO could be reversed by apamine, an mIAHP blocker. This particular experiment, according to the investigators, confirmed that EBIO inhibits epileptiform activity by enhancing Ca2+-mediated K+ channel conductance-associated mIAHP.
"Our results suggest that manipulations that enhance the mIAHP may prove adequate in the treatment of epilepsies; they also suggest that an abnormal down-regulation of the mIAHP may be a key factor in the genesis of hyperexcitable states," the team wrote in their study abstract. They concluded, "Therefore, the design of drugs that target and enhance the mIAHP may provide pharmacological tools in the treatment of epilepsies."
When asked about the clinical impact of his research, Buño commented in correspondence with Applied Neurology that although an agent that regulates Ca2+ and K+ may be curative, its possible harmful side effects must be investigated--and would be expected to occur, "especially because [the drug] would reduce excitability of neurons in neuronal circuits other than the ones showing abnormal activity. Experiments should be performed in in vivo models of epilepsy to test this possibility."
The citation for this research is Garduño J, Galván E, Fernández de Sevilla F, Buño W. 1-Ethyl-2-benzimidazolinone (EBIO) suppresses epileptiform activity in in vitro hippocampus. Neuropharmacology. 2005;49: 376-388. *
Generic Anti-inflammatory Promising as Glioma Drug
The "Achilles' heel" of glioma cells appears to have been discovered by researchers from the University of Alabama at Birmingham. What's more--metaphorically speaking--sulfasalazine, an anti-inflammatory used to treat Crohn disease and rheumatoid arthritis, may be the lethal arrow poised to pierce that heel.
An earlier study, conducted by a consortium of Belgian, French, and American investigators and published in Clinical Cancer Research in 2004, found that sulfasalazine induced cell death in several glioma cell lines and inhibited growth of human glioblastomas xenografted into mice. The international team treated experimental glioblastomas with sulfasalazine because the drug specifically inhibits transcription factor nuclear factor-kB, which the researchers proved is activated in glioblastomas. Indeed, the researchers used electrophoretic mobility shift analysis to demonstrate that nuclear factor-kB is active in several rat and human glioma cells and culture-derived nuclear extracts but not in astrocytes.
The team from the University of Alabama, led by Harald Sontheimer, PhD, professor in the Department of Neurobiology and director of the Civitan International Research Center, examined a different component of glioma cell growth that also was inhibited by sulfasalazine: system Xc2, an amino acid transporter that exchanges cystine--a glutathione precursor--for glutamate release within glioma cells.
The team theorized that glutamate is an "obligatory by-product" of cystine uptake--a hypothesis confirmed by their in vitro research. Furthermore, they unexpectedly found in their experiments that system Xc2 is the sole pathway for cystine uptake in glioma cells but not in neurons or astrocytes. Because of this, inhibition of the Xc2 pathway selectively results in caspase- mediated apoptosis of glioma cells.
To illustrate the clinical value of system Xc2 inhibitors in the treatment of brain cancer, the researchers xenografted human gliomas into the brains of mice and treated them with intraperitoneal injections of sulfasalazine (8 mg bid) for either 1 or 3 weeks. The results seen in the treated group were compared with those seen in a placebo control group. Tumor growth was slowed and, in those mice that were treated for 3 weeks, "near-complete inhibition" of tumor growth was achieved.
"Our animal data, albeit preliminary, suggest that sulfasalazine is well tolerated and may be effective in controlling glioma growth in an intracranial model of malignant melanoma," the team wrote. For more information, see:
• Chung WJ, Lyons SA, Nelson GM, et al. Inhibition of cystine update disrupts the growth of primary brain tumors. J Neurosci. 2005;25:7101-7110.
• Robe PA, Bentires-Alj M, Bonif M, et al. In vitro and in vivo activity of the nuclear factor-kB inhibitor sulfasalazine in human glioblastomas. Clin Can Res. 2004;10:5595-5603. *
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