Structure-activity relationships of dimeric PPAR agonists

A series of dimeric PPAR agonists were designed and tested for PPAR activity in vitro. The SAR showed that dimeric ligands with a common group or full dimeric ligands had retained or even increased PPARgamma potency. The dimeric agonist concept can be used to fine tune the subtype selectivity of PPAR agonists. The PPARgamma potency could, at least partly, be explained using molecular modeling.     

Gallamine triethiodide selectively blocks voltage-gated potassium channels in Ranvier nodes

The effects of gallamine on ionic currents in single intact Ranvier nodes of the toad Xenopus were investigated. The following fully reversible effects were observed: 1. With a test concentration of 1 mmol/l the current-voltage relation of steady-state potassium currents, IK ss exhibited a complete block of IK ss up to about V = 110 mV; with stronger depolarisations the block was incomplete. The peak sodium currents, in contrast, were not affected. 2. At the same test concentration the potassium permeability constant PK was reduced by 92% from its normal value, while the sodium permeability constant PNa decreased by only 8%. 3. Concentration-response relations of the block of PK yielded an apparent dissociation constant of 30 micromol/l and a steepness parameter of unity. Patch-clamp experiments on cloned Kv1.1, Kv1.2, Kv1.3 and Kv3.1 channels yielded apparent dissociation constants of 86, 19, >100 and 121 micromol/l, respectively. Our findings show that gallamine is particularly well suited for separating potassium and sodium currents in axonal current ensembles. They also strongly suggest that potassium currents in Ranvier nodes of Xenopus are mainly carried by an ensemble of Kv1.1 and 1.2 channels.     

Design and characterization of a highly selective peptide inhibitor of the small conductance calcium-activated K+ channel, SkCa2

Apamin-sensitive small conductance calcium-activated potassium channels (SKCa1-3) mediate the slow afterhyperpolarization in neurons, but the molecular identity of the channel has not been defined because of the lack of specific inhibitors. Here we describe the structure-based design of a selective inhibitor of SKCa2. Leiurotoxin I (Lei) and PO5, peptide toxins that share the RXCQ motif, potently blocked human SKCa2 and SKCa3 but not SKCa1, whereas maurotoxin, Pi1, Tskappa, and PO1 were ineffective. Lei blocked these channels more potently than PO5 because of the presence of Ala(1), Phe(2), and Met(7). By replacing Met(7) in the RXCQ motif of Lei with the shorter, unnatural, positively charged diaminobutanoic acid (Dab), we generated Lei-Dab(7), a selective SKCa2 inhibitor (K(d) = 3.8 nm) that interacts with residues in the external vestibule of the channel. SKCa3 was rendered sensitive to Lei-Dab(7) by replacing His(521) with the corresponding SKCa2 residue (Asn(367)). Intracerebroventricular injection of Lei-Dab(7) into mice resulted in no gross central nervous system toxicity at concentrations that specifically blocked SKCa2 homotetramers. Lei-Dab(7) will be a useful tool to investigate the functional role of SKCa2 in mammalian tissues.     

Long-term acclimation to elevated pCO2 alters carbon metabolism and reduces growth in the Antarctic diatom Nitzschia lecointei

Increasing atmospheric CO₂ levels are driving changes in the seawater carbonate system, resulting in higher pCO₂ and reduced pH (ocean acidification). Many studies on marine organisms have focused on short-term physiological responses to increased pCO₂, and few on slow-growing polar organisms with a relative low adaptation potential. In order to recognize the consequences of climate change in biological systems, acclimation and adaptation to new environments are crucial to address. In this study, physiological responses to long-term acclimation (194 days, approx. 60 asexual generations) of three pCO₂ levels (280, 390 and 960 µatm) were investigated in the psychrophilic sea ice diatom Nitzschia lecointei. After 147 days, a small reduction in growth was detected at 960 µatm pCO₂. Previous short-term experiments have failed to detect altered growth in N. lecointei at high pCO₂, which illustrates the importance of experimental duration in studies of climate change. In addition, carbon metabolism was significantly affected by the long-term treatments, resulting in higher cellular release of dissolved organic carbon (DOC). In turn, the release of labile organic carbon stimulated bacterial productivity in this system. We conclude that long-term acclimation to ocean acidification is important for N. lecointei and that carbon overconsumption and DOC exudation may increase in a high-CO₂ world.     

Removal of GABA(A) receptor γ2 subunits from parvalbumin neurons causes wide-ranging behavioral alterations

We investigated the behavioral significance of fast synaptic inhibition by αβγ2-type GABA(A) receptors on parvalbumin (Pv) cells. The GABA(A) receptor γ2 subunit gene was selectively inactivated in Pv-positive neurons by Cre/loxP recombination. The resulting Pv-Δγ2 mice were relatively healthy in the first postnatal weeks; but then as Cre started to be expressed, the mice progressively developed wide-ranging phenotypic alterations including low body weight, motor deficits and tremor, decreased anxiety levels, decreased pain sensitivity and deficient prepulse inhibition of the acoustic startle reflex and impaired spatial learning. Nevertheless, the deletion was not lethal, and mice did not show increased mortality even after one year. Autoradiography with t-butylbicyclophosphoro[(35)S]thionate suggested an increased amount of GABA(A) receptors with only α and β subunits in central nervous system regions that contained high levels of parvalbumin neurons. Using BAC-transgenesis, we reduced some of the Pv-Δγ2 phenotype by selectively re-expressing the wild-type γ2 subunit back into some Pv cells (reticular thalamic neurons and cerebellar Pv-positive neurons). This produced less severe impairments of motor skills and spatial learning compared with Pv-Δγ2 mice, but all other deficits remained. Our results reveal the widespread significance of fast GABAergic inhibition onto Pv-positive neurons for diverse behavioral modalities, such as motor coordination, sensorimotor integration, emotional behavior and nociception.     

KCa3.1 channels are involved in the infiltrative behavior of glioblastoma in vivo

Glioblastoma multiforme (GBM) is a diffuse brain tumor characterized by high infiltration in the brain parenchyma rendering the tumor difficult to eradicate by neurosurgery. Efforts to identify molecular targets involved in the invasive behavior of GBM suggested ion channel inhibition as a promising therapeutic approach. To determine if the Ca²⁺-dependent K⁺ channel KCa3.1 could represent a key element for GBM brain infiltration, human GL-15 cells were xenografted into the brain of SCID mice that were then treated with the specific KCa3.1 blocker TRAM-34 (1-((2-chlorophenyl) (diphenyl)methyl)-1H-pyrazole). After 5 weeks of treatment, immunofluorescence analyses of cerebral slices revealed reduced tumor infiltration and astrogliosis surrounding the tumor, compared with untreated mice. Significant reduction of tumor infiltration was also observed in the brain of mice transplanted with KCa3.1-silenced GL-15 cells, indicating a direct effect of TRAM-34 on GBM-expressed KCa3.1 channels. As KCa3.1 channels are also expressed on microglia, we investigated the effects of TRAM-34 on microglia activation in GL-15 transplanted mice and found a reduction of CD68 staining in treated mice. Similar results were observed in vitro where TRAM-34 reduced both phagocytosis and chemotactic activity of primary microglia exposed to GBM-conditioned medium. Taken together, these results indicate that KCa3.1 activity has an important role in GBM invasiveness in vivo and that its inhibition directly affects glioma cell migration and reduces astrocytosis and microglia activation in response to tumor-released factors. KCa3.1 channel inhibition therefore constitutes a potential novel therapeutic approach to reduce GBM spreading into the surrounding tissue.     

The de-guanidinylated derivative of peramivir remains a potent inhibitor of influenza neuraminidase

The guanidine function in the potent neuraminidase inhibitor peramivir was included early on in the drug design process, and examination of X-ray structural data for the enzyme-inhibitor complex would seem to indicate that the guanidine plays a critical role in promoting binding. However, this functional group may also contribute to the poor oral availability of the drug. Given that the relative stereochemistry on the guanidine-bearing carbon in peramivir is opposite to that in zanamivir (a related neuraminidase inhibitor, for which the guanidine function is known to contribute substantially to the potency), we sought to determine the importance of the guanidine group to peramivir's overall potency. Here we report that the de-guanidinylated analogue of peramivir is only ca. 1-order of magnitude less potent than peramivir itself in two in vitro inhibition assays. This suggests that next-generation inhibitors designed to improve on peramivir's properties might profitably dispense with the guanidine function.     

The FXIIIVal34Leu, common and risk factors of venous thrombosis in early middle-age Costa Rican patients

In this study, eight common polymorphisms associated with venous thrombosis (VT) and thrombophilia factors were analyzed in a Costa Rican case-control study. With the use of polymerase chain reaction (PCR) methods the polymorphisms were detected in 120 patients and 133 controls (mean age <40 years old). It was concluded that a high level of fibrinogen, antiphospholipid antibodies, family history, and the genotype 34LeuLeu of FXIII OR 0.42 (0.20-0.89) showed a significant effect on the risk of VT.Associations between the risk of VT and genetic polymorphisms have been established. Some of these polymorphisms are highly prevalent in Caucasians, but there is a significant geographic variation in their prevalence among different populations. The results of this study support the protective effect of FXIII Val34Leu polymorphism in VT. These findings are consistent with previous reports that included other populations.