Phase I dose-escalation study to evaluate the safety, pharmacokinetics, and pharmacodynamics of CEP-9722 (a PARP1-2 inhibitor) as single‑agent and in combination with temozolomide in patients with advanced solid tumors (NCT00920595)

3052

Background: Poly-ADP-ribose (PAR) polymerases (PARPs) are essential in cellular processing of DNA damage via the base excision repair pathway. CEP-9722, an orally available PARP1-2 inhibitor, demonstrated single-agent antitumor activity and synergy with temozolomide (TMZ) in xenograft models. This phase I study evaluated the pharmacokinetics, pharmacodynamics, and the maximum tolerated dose (MTD) of CEP-9722 in monotherapy and combination with TMZ. Methods: Adult patients with advanced solid tumors were enrolled in cohorts of 3-6 patients to receive a 14-day cycle of CEP-9722 (days 1-5), followed by 28-day cycles of CEP-9722 (days 1-5) plus TMZ (150 mg/m2 days 1-5). The dose of CEP-9722 was 150 mg/day in the first cohort and was escalated depending on the occurrence of dose-limiting toxicities (DLTs) during cycles 1 and 2. The safety, pharmacokinetics, and pharmacodynamics (PAR levels in peripheral blood mononuclear cells) of CEP-9722 were analyzed. Results: Overall, 26 patients (18F,8 M) 18 to 71 years of age were enrolled in 5 cohorts of 3-9 patients and treated with CEP-9722 at 150-1000 mg/day. The MTD of CEP-9722 in combination with TMZ (150 mg/m2) was reached at 1000 mg/day. The recommended dose was 750 mg/day. A total of 9 patients were treated at the recommended dose. DLTs were observed in 2 patients during cycle 1 (1 grade 3 myositis at 750 mg/day and 1 grade 3 asthenia at 1000 mg/day) and 2 patients during cycle 2 (1 grade 3 asthenia at 300 mg/day and 1 persistent grade 2 weight loss at 1000 mg/day). Overall during this study, 4 grade 3 treatment-related adverse events were observed. The pharmacokinetics showed high intra- and inter-patient variability at all doses. The pharmacodynamic analysis demonstrated PARP inhibition at all doses, but the high inter- and intra-patient variability prevented any conclusion regarding a dose / PARP inhibition relationship. Conclusions: TheMTD of CEP-9722 when administered with TMZ was 1000 mg days 1-5 and the combination CEP-9722/TMZ was well tolerated. In addition, a clear signal of PARP inhibition was demonstrated.

Subcutaneous omacetaxine mepesuccinate in patients with chronic phase (CP) or accelerated phase (AP) chronic myeloid leukemia (CML) resistant/intolerant to two or three approved tyrosine-kinase inhibitors (TKIs)

6513

Background: Omacetaxine mepesuccinate (“omacetaxine”) is a first-in-class, reversible, transient inhibitor of protein elongation that facilitates tumor cell death without depending on BCR-ABL signaling. Clinical activity was shown in two phase 2, open-label, multicenter studies in treatment-resistant CML. Methods: A subset from the phase 2 studies included patients in CP or AP who were resistant/intolerant to ≥2 approved TKIs. Omacetaxine 1.25 mg/m2 was given SC twice daily: ≤14 consecutive days/28-day cycle for induction, ≤7 days/cycle as maintenance. Secondary results were calculated for responses by number of prior TKIs. Results: Of 122 patients (median age, 60 years), 62 had received 2 TKIs (100% imatinib; 76% dasatinib; 24% nilotinib) and 60 had received all 3 approved TKIs. Prior non-TKI therapies (eg, 52% hydroxyurea, 34% interferon) were common. Of 45 CP patients in the 2 TKI group, 12 (27%) had major cytogenetic response (MCyR; median duration of 17.7 mo), and of 36 in the 3 TKI group, 4 (11%) had MCyR (median duration not reached). Of 17 AP patients in the 2 TKI group, 6 (35%) had major hematologic response (MaHR; median duration, 13.4 mo), and of 24 in the 3 TKI group, 5 (21%) had MaHR (median duration, 6.4 mo). Median months of survival in the 2 and 3 TKI groups were 30.1 and not reached for CP and 12.0 and 24.6 for AP. Treatment-related grade 3/4 adverse events (AEs) occurred in 52 (84%) patients in the 2 TKI group and 42 (70%) in the 3 TKI group (most common: thrombocytopenia [71%, 48%]). Fifteen (24%) and 16 (27%) had an AE leading to discontinuation, primarily disease progression. There were 20 deaths (primarily disease progression), 11 in the 2 TKI group and 9 in the 3 TKI group; 4 were considered related to treatment (sepsis in 2, pancytopenia, febrile neutropenia). Conclusions: In patients with heavily pretreated CML, response to omacetaxine therapy occurred whether they had received 2 or 3 prior TKIs. The drug was well tolerated. Tolerability was similar across the TKI groups in both CP and AP patients. Support: Teva Pharmaceutical Industries Ltd.

The glucokinase activator GKA50 causes an increase in cell volume and activation of volume-regulated anion channels in rat pancreatic β-cells

Glucokinase plays a key role in the metabolism of glucose by pancreatic β-cells. In this study the effects of the glucokinase activator GKA50 on cell volume and electrical activity in rat β-cells were examined. One micro molar GKA50 caused an increase in β-cell volume in the presence of 4mM glucose. GKA50 also caused a depolarisation of β-cell membrane potential and increased electrical activity. These changes were associated with the activation of inward whole-cell currents, and were attenuated by the anion channel inhibitor 5-nitro-2-(3-phenylpropylamino) benzoic acid. In single channel experiments, the open probability of volume-regulated anion channels (VRAC) was increased from 0.03±0.01 to 0.19±0.04 (n=3) by the GKA50. The data suggest that a GKA50-evoked increase in glucose metabolism causes an increase in β-cell volume. This in turn activates VRAC leading to a depolarisation of the cell membrane potential.

Functional characterization of bestrophin-1 missense mutations associated with autosomal recessive bestrophinopathy

PURPOSE

Autosomal recessive bestrophinopathy (ARB) is a retinal dystrophy affecting macular and retinal pigmented epithelium function resulting from homozygous or compound heterozygous mutations in BEST1. In this study we characterize the functional implications of missense bestrophin-1 mutations that cause ARB by investigating their effect on bestrophin-1's chloride conductance, cellular localization, and stability.

METHODS

The chloride conductance of wild-type bestropin-1 and a series of ARB mutants were determined by whole-cell patch-clamping of transiently transfected HEK cells. The effect of ARB mutations on the cellular localization of bestrophin-1 was determined by confocal immunofluorescence on transiently transfected MDCK II cells that had been polarized on Transwell filters. Protein stability of wild-type and ARB mutant forms of bestrophin-l was determined by the addition of proteasomal or lysosomal inhibitors to transiently transfected MDCK II cells. Lysates were then analyzed by Western blot analysis.

RESULTS

All ARB mutants investigated produced significantly smaller chloride currents compared to wild-type bestrophin-1. Additionally, co-transfection of compound heterozygous mutants abolished chloride conductance in contrast to co-transfections of a single mutant with wild-type bestrophin-l, reflecting the recessive nature of the condition. In control experiments, expression of two dominant vitelliform macular dystrophy mutants was shown to inhibit wild-type currents. Cellular localization of ARB mutants demonstrated that the majority did not traffic correctly to the plasma membrane and that five of these seven mutants were rapidly degraded by the proteasome. Two ARB-associated mutants (p.D312N and p.V317M) that were not trafficked correctly nor targeted to the proteasome had a distinctive appearance, possibly indicative of aggresome or aggresome-like inclusion bodies.

CONCLUSIONS

Differences in cellular processing mechanisms for different ARB associated mutants lead to the same disease phenotype. The existence of distinct pathogenic disease mechanisms has important ramifications for potential gene replacement therapies since we show that missense mutations associated with an autosomal recessive disease have a pathogenic influence beyond simple loss of function.

A dual action of saturated fatty acids on electrical activity in rat pancreatic β-cells. Role of volume-regulated anion channel and KATP channel currents

Free fatty acids (FFAs) exert complex actions on pancreatic β-cells. Typically, an initial potentiation of insulin release is followed by a gradual impairment of β-cell function, the latter effect being of possible relevance to hyperlipidaemia in type 2 diabetes mellitus. The molecular actions of FFAs are poorly understood. The present study investigated the acute effects of saturated FFAs on electrophysiological responses of rat pancreatic β-cells. Membrane potential and KATP channel activity were recorded using the perforated patch technique. Volume-regulated anion channel (VRAC) activity was assessed from conventional whole-cell recordings. Cell volume regulation was measured using a video-imaging technique. Addition of octanoate caused a transient potentiation of glucose-induced electrical activity, followed by a gradual hyper-polarisation and a prolonged inhibition of electrical activity. Octanoate caused an initial increase in VRAC activity followed by a secondary inhibition coinciding with increased KATP channel activity. Similar effects were observed with palmitate and 2-bromopalmitate whereas butyrate was virtually ineffective. Octanoate and palmitate also exerted a dual effect on electrical activity evoked by tolbutamide. Octanoate significantly attenuated cell volume regulation in hypotonic solutions, consistent with VRAC inhibition. It is concluded that medium and long chain FFAs have a dual action on glucose-induced electrical activity in rat pancreatic β-cells: an initial stimulatory effect followed by a secondary inhibition. These effects appear to be the result of reciprocal actions on VRAC and KATP channel currents, and could contribute towards the stimulatory and inhibitory actions of FFAs on pancreatic β-cell function.

Environmental risk factors associated with leptospirosis among butchers and their associates in Jamaica

BACKGROUND

Leptospirosis, a spirochetal zoonosis, is considered an occupational disease of persons engaged in agriculture, sewage works, forestry, and butchery.

OBJECTIVE

To determine the environmental sources and the knowledge, attitude and practices for leptospirosis among butchers and slaughterhouse workers, as well as the seroprevalence of leptospirosis among cattle and pigs presented for slaughter.

METHODS

Using an interviewer administered questionnaire, all 110 butchers and other slaughterhouse workers in the parishes of Kingston and St. Andrew, Jamaica were surveyed. In addition, 179 blood samples from animals presented for slaughter were tested for anti-Leptospira antibodies using the microscopic agglutination test (MAT).

RESULTS

Analyses indicated that people with the studied occupations are at risk for developing leptospirosis due to several environmental risk factors that exist in slaughterhouses. Among the risk factors, limited knowledge of the disease and its transmission, lower educational level attained, younger age and unhealthy behaviors (e.g., hand washing and improper or lack of use of personal protective gears), presence of stray dogs and rodents, and inadequate maintenance of physical plants, were found to be important. Of the total number of animal samples tested, 20 (11%) were positive. Canicola and Hardjo (among cattle) and Bratislava (among pigs) were the major seroreactors.

CONCLUSION

Butchers and slaughterhouse workers engaged in animal handling and slaughtering could be frequently exposed to leptospirosis, and hence control strategies targeting at these populations should be implemented.

Comparison of antibiotic resistance and virulence factors in pigmented and non-pigmented Pseudomonas aeruginosa

OBJECTIVE

Pseudomonas aeruginosa produces multiple virulence factors that have been implicated in pathogenesis and quorum sensing. The aim of this study was to determine differences in the virulence factors of pigmented and non-pigmented P aeruginosa isolates.

METHODS

Associations were assessed between pigment production (pyocyanin and pyoverdin) and production of DNase, elastase, lipase, protease, siderophore, twitching motility, antibiotic resistance patterns and virulence-associated genes in 57 non-duplicate P aeruginosa isolates from wounds, sputum, urine, high vaginal swab (HVS), ear, eye and respiratory tract swabs and aspirates of peritoneum and ulcers.

RESULTS

Most (82.5%) of the isolates produced either pigment. Pigmented isolates produced more frequently and significant more (p < 0.05) DNase, elastase, lipase protease, and siderophore. Imipenem was the only antibiotic to which all isolates were susceptible (p < 0.05), while 93% and 32% were resistant to tetracycline and norfloxacin, respectively. There was however no significant difference between pigmented and non-pigmented isolates when antibiotic resistance was compared. While isolates had multiple virulence-associated genes, exoS (51%), rhlA (37%) and rhlB (46%) were the predominant genes detected. Except for exoY, genes were present in pigmented isolates more frequently than in non-pigmented isolates.

CONCLUSION

The results of this study suggest that antibiotic resistance per se might not be associated with the pigment production in P aeruginosa. However pigment production appeared to be more significantly associated with multi-drug resistance, presence of virulence-associated genes, and expression of certain virulence factors, most notably elastase, protease, siderophore and DNase activity. Since pigment production is easy to determine, this might to be a good starting point to identify the virulence status of an isolate.

Epithelial pathways in choroid plexus electrolyte transport

A stable intraventricular milieu is crucial for maintaining normal neuronal function. The choroid plexus epithelium produces the cerebrospinal fluid and in doing so influences the chemical composition of the interstitial fluid of the brain. Here, we review the molecular pathways involved in transport of the electrolytes Na+, K+, Cl-, and HCO3(-)across the choroid plexus epithelium.

The emergence of qnr-mediated quinolone resistance among Enterobacteriaceae in Jamaica

OBJECTIVE

Quinolone resistance is usually caused by various chromosomal mutations, but has been more recently associated with plasmids which carry the qnr determinant. The aim of this study is to investigate the prevalence of qnr genes in clinical isolates of Enterobacteriaceae in Jamaica.

METHODS

A total of 255 non-duplicate fluoroquinolone-resistant Enterobacteriaceae clinical isolates, comprising 232 Escherichia coli, 20 Klebsiella species and three Enterobacter spp were collected between October 2007 and November 2008 from hospitalized patients in Jamaica. The presence of the qnr gene was screened by PCR using specific primers for qnrA, qnrB and qnrS in extracted plasmid DNA.

RESULTS

Eighty-three (32.5%) of these isolates were qnr-positive, of which 47.0% housed the qnrA gene only, 1.2% qnrB and 9.6% qnrS only. Another 36.1% possessed both qnrA and qnrS genes. Approximately 30% of the quinolone-resistant E coli isolates harboured the qnr gene while 50% Klebsiella spp and all Enterobacter spp were positive.

CONCLUSION

The emergence of qnr-mediated quinolone resistance among clinical Enterobacteriaceae isolates is described for the first time in Jamaica.

Electrical activity in pancreatic islet cells: The VRAC hypothesis

A major aspect of stimulation of β-cell function by glucose is the induction of electrical activity. The ionic events that underlie β-cell electrical activity are understood in some detail. At sub-stimulatory glucose concentrations, the β-cell is electrically 'silent'. Increasing the glucose concentration to stimulatory levels results in a gradual depolarisation of the membrane potential to a threshold potential where 'spikes' or action potentials are generated. These action potentials represent the gating of voltage-sensitive Ca²(+) channels, leading to Ca²(+) entry into the cell, thus triggering the release of insulin. The stimulatory actions of glucose on the β-cell depend on the metabolism of the hexose. A major question concerns the molecular mechanism(s) whereby β-cell plasma membrane potential is regulated by changes in glucose metabolism in the cell. This article provides a brief summary of the evidence suggesting that, in addition to metabolically-regulated K(ATP) channels, β-cells are equipped with a volume-regulated anion channel that is activated by glucose concentrations within the range effective in modulating electrical activity and insulin release.

Opposing effects of tenidap on the volume-regulated anion channel and K(ATP) channel activity in rat pancreatic beta-cells

Tenidap (5-chloro-2-hydroxy-3-(thiophene-2-carbonyl)indole-1-carboxamide) is a non-steroidal anti-inflammatory and anti-rheumatic drug with several cellular actions including inhibition of anion transport processes. Since other anion transport inhibitors have been shown to inhibit activity of the volume-regulated anion channel (VRAC), the present study investigated the effects of tenidap on activity of this channel in pancreatic beta-cells. Membrane potential, VRAC currents and input conductance were recorded from single rat beta-cells in primary culture using perforated patch, conventional whole-cell and cell-attached configurations of the patch-clamp technique. Relative cell volume was measured using a video-imaging method. Tenidap (0.1mM) was found to rapidly hyperpolarise the beta-cell membrane potential and terminate glucose-induced electrical activity. This effect was associated with a pronounced outward current shift at a holding potential of -65mV. Tenidap was found to inhibit activity of the volume-regulated anion channel with IC(50) values of 31 and 43microM for outward and inward currents respectively. Tenidap also markedly increased beta-cell input conductance, representing an activation of the K(ATP) conductance. beta-cell regulatory volume decrease following hypotonically-induced cell swelling was sensitive to inhibition by 50microM tenidap. Tenidap is a potent inhibitor of the volume-regulated anion channel and K(ATP) channel activator in rat pancreatic beta-cells. These actions could at least in part explain the recently reported inhibitory actions of the drug on electrical and secretory activity in the beta-cell, and could also underlie other pharmacological actions of the drug.

Missense mutations in a retinal pigment epithelium protein, bestrophin-1, cause retinitis pigmentosa

Bestrophin-1 is preferentially expressed at the basolateral membrane of the retinal pigmented epithelium (RPE) of the retina. Mutations in the BEST1 gene cause the retinal dystrophies vitelliform macular dystrophy, autosomal-dominant vitreochoroidopathy, and autosomal-recessive bestrophinopathy. Here, we describe four missense mutations in bestrophin-1, three that we believe are previously unreported, in patients diagnosed with autosomal-dominant and -recessive forms of retinitis pigmentosa (RP). The physiological function of bestrophin-1 remains poorly understood although its heterologous expression induces a Cl--specific current. We tested the effect of RP-causing variants on Cl- channel activity and cellular localization of bestrophin-1. Two (p.L140V and p.I205T) produced significantly decreased chloride-selective whole-cell currents in comparison to those of wild-type protein. In a model system of a polarized epithelium, two of three mutations (p.L140V and p.D228N) caused mislocalization of bestrophin-1 from the basolateral membrane to the cytoplasm. Mutations in bestrophin-1 are increasingly recognized as an important cause of inherited retinal dystrophy.

Studies of the mechanism of activation of the volume-regulated anion channel in rat pancreatic beta-cells

There is evidence that depolarization of the pancreatic beta cell by glucose involves cell swelling and activation of the volume-regulated anion channel (VRAC). However, it is unclear whether cell swelling per se or accompanying changes in intracellular osmolality and/or ionic strength are responsible for VRAC activation. VRAC activity was measured in rat beta cells by conventional or perforated patch whole-cell recording. Cell volume was measured by video imaging. In conventional whole-cell recordings, VRAC activation was achieved by exposure of the cells to a hyposmotic bath solution, by application of positive pressure to the pipette, or by use of a hyperosmotic pipette solution. Increased concentrations of intracellular CsCl also caused channel activation, but with delayed kinetics. In perforated patch recordings, VRAC activation was induced by isosmotic addition of the permeable osmolytes urea, 3-O-methyl glucose, arginine, and NH4Cl. These effects were all accompanied by beta-cell swelling. It is concluded that increased cell volume, whether accompanied by raised intracellular osmolality or ionic strength, is a major determinant of VRAC activation in the beta cell. However, increased intracellular ionic strength markedly reduced the rate of VRAC activation. These findings are consistent with the hypothesis that the accumulation of glucose metabolites in the beta cell, and the resultant increase in cell volume, provides a signal coupling glucose metabolism with VRAC activation.

Contrasting effects of glycerol and urea transport on rat pancreatic beta-cell function

BACKGROUND/AIMS

Pancreatic beta-cell function is influenced by changes in cell volume. Such volume changes depend on water permeability of the plasma membrane, conferred in part by aquaporins. Islet cells express aquaporin 7 (AQP7), which is permeable to urea and glycerol in addition to water. We therefore investigated the effects of glycerol and urea on rat pancreatic beta-cell function.

METHODS

Electrical activity and whole-cell current were studied using the perforated patch technique. Cell volume was measured by video-imaging and insulin release by radioimmunoassay. Aquaporin 7 expression was studied by RT-PCR, Western blot and double fluorescent immunolabelling.

RESULTS

The isosmotic addition of glycerol and urea resulted in depolarization of the plasma membrane and electrical activity, accompanied by beta-cell swelling, activation of the volume-regulated anion channel (VRAC) and insulin release. However, the effects of glycerol, in contrast to urea, persisted throughout exposure to the osmolyte. Glycerol also caused beta-cell activation when added hyperosmotically. A non-metabolizable glycerol analogue had comparable effects to urea on beta-cells. The expression of AQP7 was demonstrated in rat beta-cells.

CONCLUSION

Glycerol and urea can activate beta-cells via their rapid uptake across the beta-cell plasma membrane, possibly via AQP7. This results in cell swelling, VRAC activation, electrical activity and insulin release. Glycerol appears to exert an additional effect, possibly related to its intracellular metabolism.

An appraisal of ultramicrotomy, FIBSEM and cryogenic FIBSEM techniques for the sectioning of biological cells on titanium substrates for TEM investigation

Ultramicrotomy, focused ion beam scanning electron microscopy (FIBSEM) and cryogenic FIBSEM (cryo-FIBSEM) techniques, as developed for the controlled cross-sectioning of mesenchymal stem cells (MSCs) and human osteoblasts (HObs) on titanium (Ti) substrates for transmission electron microscopy (TEM) investigation, are compared. Conventional ultramicrotomy has been used to section cells on Ti-foil substrates embedded in resin, but significant problems with cell detachment using this technique restricted its general applicability. Conventional FIBSEM 'lift-out' procedures were found to be effective for the preparation of uniform sections of fixed and dehydrated cell/Ti specimens, but the control of cell staining remains an issue. Cryo-FIBSEM procedures used with an 'H-bar' sample geometry enabled the sectioning of fixed and hydrated cell/Ti specimens, but issues remain over ion beam-induced artefacts and control of frost on the sample foils.

HCO 3--dependent volume regulation in alpha-cells of the rat endocrine pancreas

Ion transport activity in pancreatic α-cells was assessed by studying cell volume regulation in response to anisotonic solutions. Cell volume was measured by a video imaging method, and cells were superfused with either 4-(2-hydroxyethyl)piperazine-1-ethanesulfonic acid-buffered or HCO₃⁻-buffered solutions. α-Cells did not exhibit a regulatory volume increase (RVI) in response to cell shrinkage caused by hypertonic solutions. A RVI was observed, however, in cells that had first undergone a regulatory volume decrease (RVD), but only in HCO₃⁻-buffered solutions. RVI was also observed in response to a HCO₃⁻-buffered hypertonic solution in which the glucose concentration was increased from 4 to 20 mM. The post-RVD RVI and the glucose-induced RVI were both inhibited by 10 μM 5-(N-methyl-N-isobutyl) amiloride or 100 μM 2,2′-(1,2-ethenediyl) bis (5-isothio-cyanatobenzenesulfonic acid), but not by 10 μM benzamil nor 10 μM bumetanide. These data suggest that Na⁺–H⁺ exchangers and Cl⁻–HCO₃⁻ exchangers contribute to volume regulation in α-cells.

Domain walls in the (Ga,Mn)as diluted magnetic semiconductor

We report experimental and theoretical studies of magnetic domain walls in an in-plane magnetized (Ga,Mn)As dilute moment ferromagnetic semiconductor. Our high-resolution electron holography technique provides direct images of domain wall magnetization profiles. The experiments are interpreted based on microscopic calculations of the micromagnetic parameters and Landau-Lifshitz-Gilbert simulations. We find that the competition of uniaxial and biaxial magnetocrystalline anisotropies in the film is directly reflected in orientation dependent wall widths, ranging from approximately 40 to 120 nm. The domain walls are of the Néel type and evolve from near-90 degrees walls at low temperatures to large angle [11[over ]0]-oriented walls and small angle [110]-oriented walls at higher temperatures.

Biallelic mutation of BEST1 causes a distinct retinopathy in humans

We describe a distinct retinal disorder, autosomal-recessive bestrophinopathy (ARB), that is consequent upon biallelic mutation in BEST1 and is associated with central visual loss, a characteristic retinopathy, an absent electro-oculogram light rise, and a reduced electroretinogram. Heterozygous mutations in BEST1 have previously been found to cause the two dominantly inherited disorders, Best macular dystrophy and autosomal-dominant vitreoretinochoroidopathy. The transmembrane protein bestrophin-1, encoded by BEST1, is located at the basolateral membrane of the retinal pigment epithelium in which it probably functions as a Cl(-) channel. We sequenced BEST1 in five families, identifying DNA variants in each of ten alleles. These encoded six different missense variants and one nonsense variant. The alleles segregated appropriately for a recessive disorder in each family. No clinical or electrophysiological abnormalities were identified in any heterozygotes. We conducted whole-cell patch-clamping of HEK293 cells transfected with bestrophin-1 to measure the Cl(-) current. Two ARB missense isoforms severely reduced channel activity. However, unlike two other alleles previously associated with Best disease, cotransfection with wild-type bestrophin-1 did not impair the formation of active wild-type bestrophin-1 channels, consistent with the recessive nature of the condition. We propose that ARB is the null phenotype of bestrophin-1 in humans.

Ion channel diversity, channel expression and function in the choroid plexuses

Knowledge of the diversity of ion channel form and function has increased enormously over the last 25 years. The initial impetus in channel discovery came with the introduction of the patch clamp method in 1981. Functional data from patch clamp experiments have subsequently been augmented by molecular studies which have determined channel structures. Thus the introduction of patch clamp methods to study ion channel expression in the choroid plexus represents an important step forward in our knowledge understanding of the process of CSF secretion.

Two K⁺ conductances have been identified in the choroid plexus: Kv1 channel subunits mediate outward currents at depolarising potentials; Kir 7.1 carries an inward-rectifying conductance at hyperpolarising potentials. Both K⁺ channels are localised at the apical membrane where they may contribute to maintenance of the membrane potential while allowing the recycling of K⁺ pumped in by Na⁺-K⁺ ATPase. Two anion conductances have been identified in choroid plexus. Both have significant HCO₃^- permeability, and may play a role in CSF secretion. One conductance exhibits inward-rectification and is regulated by cyclic AMP. The other is carried by an outward-rectifying channel, which is activated by increases in cell volume. The molecular identity of the anion channels is not known, nor is it clear whether they are expressed in the apical or basolateral membrane. Recent molecular evidence indicates that choroid plexus also expresses the non-selective cation channels such as transient receptor potential channels (TRPV4 and TRPM3) and purinoceptor type 2 (P2X) receptor operated channels. In conclusion, good progress has been made in identifying the channels expressed in the choroid plexus, but determining the precise roles of these channels in CSF secretion remains a challenge for the future.

Curcumin induces electrical activity in rat pancreatic beta-cells by activating the volume-regulated anion channel

Curcumin, the principal active component of turmeric, is reported to exert a number of therapeutic actions, including a hypoglycaemic/antidiabetic action. The underlying mechanisms to this action are essentially unknown. We have investigated the hypothesis that a direct stimulatory action on the pancreatic beta-cell could contribute towards the hypoglycaemic activity of this compound. Electrical and ion channel activity were recorded in rat beta-cells using the patch-clamp technique. beta-Cell volume was measured using a video-imaging technique. Insulin release was measured from intact islets by radioimmunoassay. Curcumin (2-10 microM) activated the volume-regulated anion channel in beta-cells. Single channel studies indicated that activation was the result of increased channel open probability. This effect was accompanied by depolarisation of the cell membrane potential, the generation of electrical activity and enhanced insulin release. Curcumin also decreased beta-cell volume, presumably reflecting loss of Cl(-) (and hence water) as a result of anion channel activation. These findings are consistent with the suggestion that Cl(-) fluxes play an important role in regulating beta-cell function. The stimulation of beta-cell function by curcumin could contribute to the hypoglycaemic actions of this compound, and these findings identify a novel potential therapeutic target for the treatment of type 2 diabetes mellitus.

Glucose-induced swelling in rat pancreatic alpha-cells

Pancreatic beta-cells increase in volume when exposed to elevated concentrations of extracellular glucose. This study has examined the effects of glucose on the volumes of pancreatic alpha-cells, which like beta-cells are regulated by glucose, and intestinal epithelial Caco-2 cells which are unresponsive to glucose. Cell volume changes were monitored by a video-imaging method. Increasing the extracellular glucose concentration caused a concentration-dependent increase in alpha-cell volume over the range 1-20mM. Glucose-induced swelling was not, however, observed in Caco-2 cells. The glucose-induced swelling in both alpha- and beta-cells was abolished by 0.5mM phloretin, an inhibitor of the GLUT proteins, indicating that GLUT mediated glucose transport is a pre-requisite for swelling. Glucose metabolism also appears to be essential, as islet cell swelling was not observed with 16 mM 3-O-methyl glucose. These data suggest that glucose-induced swelling may be a property exclusive to glucose-regulated cells.