Purinergic signalling at the plasma membrane: a multipurpose and multidirectional mode to deal with amyotrophic lateral sclerosis and multiple sclerosis

At endogenous brain concentrations, the neuroinhibitory tryptophan metabolite kynurenic acid (KYNA) is a preferential antagonist of the α7 nicotinic acetylcholine receptor (α7nAChR). In the present study, male Wistar rats were fed a high tryptophan diet (adding 0.1-1.5% tryptophan) for 24 h to examine (i) the effect of increased tryptophan on extracellular dopamine (DA) and KYNA levels and (ii) to determine any possible interactions between DA and KYNA. Brain KYNA levels were dose-dependently increased by tryptophan intake, and these increase were consistent with kynurenine (KYN), the precursor to KYNA, levels in the brain, plasma and liver. Administration of the 1.5% tryptophan added diet reduced the extracellular DA level to 60%, and increased the extracellular KYNA to 320% in the striatum. The DA reduction was attenuated through inhibiting KYNA synthesis with 2-aminoadipic acid. These results indicate that a high tryptophan diet can induce KYNA production and suppress DA release. One possible mechanism is that as more KYN is metabolized from the high doses of tryptophan in the liver and released into the blood stream, KYNA production in astrocytes is enhanced and the increased extracellular KYNA inhibits DA release by blocking α7nAChRs. Dietary manipulation of KYNA formation in astrocytes may offer a unique strategy to modulate DA.     

Production of human metabolites of the anti-cancer drug flutamide via biotransformation in <Emphasis Type="Italic">Cunninghamella</Emphasis> species

Fungi belonging to the genus Cunninghamella have enzymes similar to those employed by mammals for the detoxification of xenobiotics, thus they are useful as models of mammalian drug metabolism, and as a source for drug metabolites. We report the transformation of the anti-cancer drug flutamide in Cunninghamella sp. The most predominant phase I metabolites present in the plasma of humans, 2-hydroxyflutamide and 4-nitro-3-(trifluoromethyl)aniline, were also produced in Cunninghamella cultures. Other phase I and phase II metabolites were also detected using a combination of HPLC, GC–MS and ¹⁹F-NMR.     

Effects of different temperatures, velocities and loads on the gliding resistance of flexor digitorum profundus tendons in a human cadaver model

The purpose of this study was to investigate the effects of temperature, velocity and load on the gliding resistance (GR) of flexor digitorum profundus (FDP) tendons in a human cadaver model. A total of 40 FDP tendons from the index through small digits of ten human cadavers were tested to assess the effect of temperature (4, 23 or 36 °C), velocity (2, 4, 6, 8, 10 or 12 mm/s) and load (250, 500, 750, 1000, 1250 and 1500 g) on GR. The mean GR at 4 °C was significantly higher than the mean GR at 36 °C (p<0.0066). There was no significant difference in the mean GR of the tested velocities. The mean GR was proportional to load, with each successive load having significantly higher GR than the loads before it (all p<0.001). There was no significant difference in the mean GR by digit. In this in vitro model, we have demonstrated that tendon gliding resistance is proportional to load, independent of velocity and somewhat affected by temperature. We conclude that it is important to specify these conditions when reporting gliding resistance, especially load and temperature.     

Finite element model of subsynovial connective tissue deformation due to tendon excursion in the human carpal tunnel

Carpal tunnel syndrome (CTS) is a nerve entrapment disease, which has been extensively studied by the engineering and medical community. Although the direct cause is unknown, in vivo and in vitro medical research has shown that tendon excursion creates microtears in the subsynovial connective tissue (SSCT) surrounding the tendon in the carpal tunnel. One proposed mechanism for the SSCT injury is shearing, which is believed to cause fibrosis of the SSCT. Few studies have reported quantitative observations of SSCT response to mechanical loading. Our proposed model is a 2-D section that consists of an FDS tendon, interstitial SSCT and adjacent stationary tendons. We believe that developing this model will allow the most complete quantitative observations of SSCT response to mechanical loading reported thus far. Boundary conditions were applied to the FEA model to simulate single finger flexion. A velocity was applied to the FDS tendon in the model to match loading conditions of the documented cadaver wrist kinematics studies. The cadaveric and FEA displacement results were compared to investigate the magnitude of stiffness required for the SSCT section of the model. The relative motions between the model and cadavers matched more closely than the absolute displacements. Since cadaveric models do not allow identification of the SSCT layers, an FEA model will help determine the displacement and stress experienced by each SSCT layer. Thus, we believe this conceptual model is a first step in understanding how the SSCT layers are recruited during tendon excursion.     

A new testing device for measuring gliding resistance and work of flexion in a digit

In order to move the finger the tendon force must overcome the gliding resistance of the tendon as well as the forces to move the joints, finger inertias, and external load. These sources, combined, make up the work of flexion (WOF) which has been experimentally used to evaluate the finger function. In this study, we have designed a new device, which can measure the forces at the proximal and distal end of the tendon during finger flexion, so that gliding resistance can be isolated from the WOF. Two index fingers from a pair of human cadaver hands were used for testing this device. Preliminary data showed that internal resistance occupied about 10% of WOF with an intact tendon. However, after tendon repair, the gliding resistance increased 31% of WOF for a modified Kessler repair and 50% of WOF for a Becker repair compared to intact tendon. We simulated joint stiffness by injection of saline solution into the proximal interphalangeal joint. This increased the overall WOF but not the gliding resistance. We believe that this testing device provides a useful tool to evaluate finger function after tendon repair in an experimental model.     

MYCN sensitizes human neuroblastoma to apoptosis by HIPK2 activation through a DNA damage response

MYCN amplification occurs in approximately 20% of human neuroblastomas and is associated with early tumor progression and poor outcome, despite intensive multimodal treatment. However, MYCN overexpression also sensitizes neuroblastoma cells to apoptosis. Thus, uncovering the molecular mechanisms linking MYCN to apoptosis might contribute to designing more efficient therapies for MYCN-amplified tumors. Here we show that MYCN-dependent sensitization to apoptosis requires activation of p53 and its phosphorylation at serine 46. The p53(S46) kinase HIPK2 accumulates on MYCN expression, and its depletion by RNA interference impairs p53(S46) phosphorylation and apoptosis. Remarkably, MYCN induces a DNA damage response that accounts for the inhibition of HIPK2 degradation through an ATM- and NBS1-dependent pathway. Prompted by the rare occurrence of p53 mutations and by the broad expression of HIPK2 in our human neuroblastoma series, we evaluated the effects of the p53-reactivating compound Nutlin-3 on this pathway. At variance from other tumor histotypes, in MYCN-amplified neuroblastoma, Nutlin-3 further induced HIPK2 accumulation, p53(S46) phosphorylation, and apoptosis, and in combination with clastogenic agents purged virtually the entire cell population. Altogether, our data uncover a novel mechanism linking MYCN to apoptosis that can be triggered by the p53-reactivating compound Nutlin-3, supporting its use in the most difficult-to-treat subset of neuroblastoma.     

Cumulative effects of volcanic ash on the food preferences of two Orthopteran species

Inert dusts are an early form of insecticide which is still in use. One of the most common inert dusts is volcanic ash. In order to study the reaction of rangeland grasshoppers, Dichroplus vittigerum (Acrididae) and a katydid, Burgilis mendosensis (Phaneropteridae), to the presence of volcanic ash in their food sources and how this reaction changed as a function of time, we conducted paired preference tests between clean leaves of their preferred host plant and leaves exposed to volcanic ash of different grain size. The behavioral response was measured as the rating on the Thurstonian preference scale of leaves with ash in relation to clean leaves. The results showed that the avoidance of volcanic ash increased as a function of time in both species. Both species studied are occasionally exposed to volcanic activity, and come from an area in which a volcanic eruption had recently occurred. As their populations did not decrease after the ash fall, we propose that some behavioral responses such as avoidance of places with ash, works as tolerance mechanism to inert dusts exposure.