Oligodendroglia and neurotrophic factors in neurodegeneration

Myelination by oligodendroglial cells (OLs) enables the propagation of action potentials along neuronal axons, which is essential for rapid information flow in the central nervous system. Besides saltatory conduction, the myelin sheath also protects axons against inflammatory and oxidative insults. Loss of myelin results in axonal damage and ultimately neuronal loss in demyelinating disorders. However, accumulating evidence indicates that OLs also provide support to neurons via mechanisms beyond the insulating function of myelin. More importantly, an increasing volume of reports indicates defects of OLs in numerous neurodegenerative diseases, sometimes even preceding neuronal loss in pre-symptomatic episodes, suggesting that OL pathology may be an important mechanism contributing to the initiation and/or progression of neurodegeneration. This review focuses on the emerging picture of neuronal support by OLs in the pathogenesis of neurodegenerative disorders through diverse molecular and cellular mechanisms, including direct neuron-myelin interaction, metabolic support by OLs, and neurotrophic factors produced by and/or acting on OLs.     

Pilot study of the sensitivity and specificity of the DNA integrity assay for stool-based detection of colorectal cancer in Malaysian patients

Background: To assess the diagnostic potential of tumor-associated high molecular weight DNA in stoolsamples of 32 colorectal cancer (CRC) patients compared to 32 healthy Malaysian volunteers by means ofpolymerase chain reaction (PCR). Methods: Stool DNA was isolated and tumor-associated high molecularweight DNA (1.476 kb fragment including exons 6-9 of the p53 gene) was amplified using PCR and visualizedon ethidium bromide-stained agarose gels. Results: Out of 32 CRC patients, 18 were positive for the presenceof high molecular weight DNA as compared to none of the healthy individuals, resulting in an overall sensitivityof 56.3% with 100% specificity. Out of 32 patients, 23 had tumor on the left side and 9 on the right side, 16 and2 being respectively positive. This showed that high molecular weight DNA was significantly (p = 0.022) moredetectable in patients with left side tumor (69.6% vs 22.2%). Out of 32 patients, 22 had tumors larger than 1.0cm, 18 of these (81.8%) being positive for long DNA as compared to not a single patient with tumor size smallerthan 1.0 cm (p <0.001). Conclusion: We detected CRC-related high molecular weight p53 DNA in stool samplesof CRC patients with an overall sensitivity of 56.3% with 100% specificity, with a strong tumor size dependence.     

Location of KCNE1 relative to KCNQ1 in the IKS potassium channel by disulfide cross-linking of substituted cysteines

The cardiac-delayed rectifier K⁺ current (I_KS) is carried by a complex of KCNQ1 (Q1) subunits, containing the voltage-sensor domains and the pore, and auxiliary KCNE1 (E1) subunits, required for the characteristic I_KS voltage dependence and kinetics. To locate the transmembrane helix of E1 (E1-TM) relative to the Q1 TM helices (S1–S6), we mutated, one at a time, the first four residues flanking the extracellular ends of S1–S6 and E1-TM to Cys, coexpressed all combinations of Q1 and E1 Cys-substituted mutants in CHO cells, and determined the extents of spontaneous disulfide-bond formation. Cys-flanking E1-TM readily formed disulfides with Cys-flanking S1 and S6, much less so with the S3-S4 linker, and not at all with S2 or S5. These results imply that the extracellular flank of the E1-TM is located between S1 and S6 on different subunits of Q1. The salient functional effects of selected cross-links were as follows. A disulfide from E1 K41C to S1 I145C strongly slowed deactivation, and one from E1 L42C to S6 V324C eliminated deactivation. Given that E1-TM is between S1 and S6 and that K41C and L42C are likely to point approximately oppositely, these two cross-links are likely to favor similar axial rotations of E1-TM. In the opposite orientation, a disulfide from E1 K41C to S6 V324C slightly slowed activation, and one from E1 L42C to S1 I145C slightly speeded deactivation. Thus, the first E1 orientation strongly favors the open state, while the approximately opposite orientation favors the closed state.     

Incidental parathyroidectomy in thyroidectomy and central neck dissection

BackgroundAlthough higher thyroidectomy volume has been linked with lower complication rates, its association with incidental parathyroidectomy remains less studied. The volume relationship is even less clear for central neck dissection, where individual parathyroid glands are at greater risk.MethodsPatients undergoing thyroidectomy with or without central neck dissection were evaluated for incidental parathyroidectomy, hypoparathyroidism, and hypocalcemia. Univariate and multivariable analyses were performed using binary logistic regression.ResultsOverall, 1,114 thyroidectomies and 396 concurrent central neck dissections were performed across 7 surgeons. Incidental parathyroidectomy occurred in 22.4% of surgeries (range, 16.9%–43.6%), affecting 7.1% of parathyroids at risk (range, 5.8%–14.5%). When stratified by surgeon, lower incidental parathyroidectomy rates were associated with higher thyroidectomy volumes (R² = 0.77, P = .008) and higher central neck dissection volumes (R² = 0.93, P < .001). On multivariable analysis, low-volume surgeon (odds ratio 2.94, 95% confidence interval 2.06–4.19, P < .001), extrathyroidal extension (odds ratio 3.13, 95% confidence interval 1.24–7.87, P = .016), prophylactic central neck dissection (odds ratio 2.68, 95% confidence interval 1.65–4.35, P <.001), and therapeutic central neck dissection (odds ratio 4.44, 95% confidence interval 1.98–9.96, P < .001) were the most significant factors associated with incidental parathyroidectomy. In addition, incidental parathyroidectomy was associated with a higher likelihood of temporary hypoparathyroidism (odds ratio 2.79, 95% confidence interval 1.45–5.38, P = .002) and permanent hypoparathyroidism (odds ratio 4.62, 95% confidence interval 1.41–5.96, P = .025), but not permanent hypocalcemia (odds ratio 1.27, 95% confidence interval 0.48–3.35, P = .63). Higher lymph node yield in central neck dissection was not associated with higher incidental parathyroidectomy rates (odds ratio 1.13, 95% confidence interval 0.85–8.81, P = .82).ConclusionHigher surgical volume conferred a lower rate of incidental parathyroidectomy. Nonetheless, greater lymph node yield in central neck dissections did not result in greater parathyroid-related morbidity. Such findings support the value of leveraging surgical volume to both optimize oncologic resection and minimize complication rates.     

Molecular determinants of local anesthetic action of beta-blocking drugs: Implications for therapeutic management of long QT syndrome variant 3

The congenital long QT syndrome (LQTS) is a heritable arrhythmia in which mutations in genes coding for ion channels or ion channel associated proteins delay ventricular repolarization and place mutation carriers at risk for serious or fatal arrhythmias. Triggers and therapeutic management of LQTS arrhythmias have been shown to differ in a manner that depends strikingly on the gene that is mutated. Additionally, beta-blockers, effective in the management of LQT-1, have been thought to be potentially proarrhythmic in the treatment of LQT-3 because of concomitant slowing of heart rate that accompanies decreased adrenergic activity. Here we report that the beta-blocker propranolol interacts with wild type (WT) and LQT-3 mutant Na⁺ channels in a manner that resembles the actions of local anesthetic drugs. We demonstrate that propranolol blocks Na⁺ channels in a use-dependent manner; that propranolol efficacy is dependent on the inactivated state of the channel; that propranolol blocks late non-inactivating current more effectively than peak sodium current; and that mutation of the local anesthetic binding site greatly reduces the efficacy of propranolol block of peak and late Na⁺ channel current. Furthermore our results indicate that this activity, like that of local anesthetic drugs, differs both with drug structure and the biophysical changes in Na⁺ channel function caused by specific LQT-3 mutations.     

Structure and stoichiometry of an accessory subunit TRIP8b interaction with hyperpolarization-activated cyclic nucleotide-gated channels

Ion channels operate in intact tissues as part of large macromolecular complexes that can include cytoskeletal proteins, scaffolding proteins, signaling molecules, and a litany of other molecules. The proteins that make up these complexes can influence the trafficking, localization, and biophysical properties of the channel. TRIP8b (tetratricopetide repeat-containing Rab8b-interacting protein) is a recently discovered accessory subunit of hyperpolarization-activated cyclic nucleotide-gated (HCN) channels that contributes to the substantial dendritic localization of HCN channels in many types of neurons. TRIP8b interacts with the carboxyl-terminal region of HCN channels and regulates their cell-surface expression level and cyclic nucleotide dependence. Here we examine the molecular determinants of TRIP8b binding to HCN2 channels. Using a single-molecule fluorescence bleaching method, we found that TRIP8b and HCN2 form an obligate 4:4 complex in intact channels. Fluorescence-detection size-exclusion chromatography and fluorescence anisotropy allowed us to confirm that two different domains in the carboxyl-terminal portion of TRIP8b--the tetratricopepide repeat region and the TRIP8b conserved region--interact with two different regions of the HCN carboxyl-terminal region: the carboxyl-terminal three amino acids (SNL) and the cyclic nucleotide-binding domain, respectively. And finally, using X-ray crystallography, we determined the atomic structure of the tetratricopepide region of TRIP8b in complex with a peptide of the carboxy-terminus of HCN2. Together, these experiments begin to uncover the mechanism for TRIP8b binding and regulation of HCN channels.     

2-Acetylpyridine thiocarbonohydrazones. Potent inactivators of herpes simplex virus ribonucleotide reductase.

A series of 2-acetylpyridine thiocarbonohydrazones was synthesized for evaluation as potential antiherpetic agents. The compounds were prepared by the condensation of 2-acetylpyridine with thiocarbonohydrazide followed by treatment with isocyanates or isothiocyanates. Many were found that were potent inactivators of ribonucleotide reductase encoded by HSV-1 and weaker inactivators of human enzyme. Several thiocarbonohydrazones (e.g. 38 and 39) inactivated HSV-1 ribonucleotide reductase at rate constants as much as seven times that of lead compound 2. In general, those substituted with weak electron-attracting groups offered the best combination of potency and apparent selective activity against the HSV-1 enzyme. Seven new thiocarbonohydrazones (21, 25, 31, 36, 38, 39, and 40) were apparently greater than 50-fold more selective than 2 against HSV-1 ribonucleotide reductase versus human enzyme. The results indicated new compounds worthy of further study as potentiators of acyclovir in combination topical treatment of herpes virus infections.