A yeast-based phenotypic screen for aquaporin inhibitors

Aquaporins mediate transport of water or small, uncharged solutes across cellular membranes according to the prevailing osmotic and chemical gradients. Because of their implication in human diseases and pathophysiological states, aquaporins are considered as potential drug targets. Yet, specific aquaporin inhibitors for in vivo studies are not available. Common functional aquaporin assays that monitor biophysical parameters related to volume changes, such as light scattering or fluorescence quenching, are time consuming and require costly equipment. Hence, they are not well geared for screening large numbers of compounds. In this paper, we describe a less demanding phenotypic yeast-based assay on 96-well microplates. The assay uses a methylamine-sensitive yeast strain in which a methylamine-permeable test aquaporin is expressed to rescue proliferation on selection plates. Specific inhibition of the aquaporin directly correlates to reduced cell proliferation.     

Development of a novel screen for protease inhibitors

We have developed a novel plasmid-based, quantitative, in vitro screen to test the protease-inhibiting activities of existing and newly discovered agents.     

Biology of human sodium glucose transporters

There are two classes of glucose transporters involved in glucose homeostasis in the body, the facilitated transporters or uniporters (GLUTs) and the active transporters or symporters (SGLTs). The energy for active glucose transport is provided by the sodium gradient across the cell membrane, the Na(+) glucose cotransport hypothesis first proposed in 1960 by Crane. Since the cloning of SGLT1 in 1987, there have been advances in the genetics, molecular biology, biochemistry, biophysics, and structure of SGLTs. There are 12 members of the human SGLT (SLC5) gene family, including cotransporters for sugars, anions, vitamins, and short-chain fatty acids. Here we give a personal review of these advances. The SGLTs belong to a structural class of membrane proteins from unrelated gene families of antiporters and Na(+) and H(+) symporters. This class shares a common atomic architecture and a common transport mechanism. SGLTs also function as water and urea channels, glucose sensors, and coupled-water and urea transporters. We also discuss the physiology and pathophysiology of SGLTs, e.g., glucose galactose malabsorption and familial renal glycosuria, and briefly report on targeting of SGLTs for new therapies for diabetes.     

I-E expression and susceptibility to parasite infection

In most inbred strains of mice, antigen-presenting cells express I-A and I-E antigens (class II major histocompatibility complex antigens), and these antigens are involved in antigen-recognition by T cells. In some strains I-E products are not expressed or aberrantly expressed, yet these mice seem to be immunologically normal. In this article, Don Wassom and his colleagues discuss reports that antigen presented in the context of I-E produces a response which suppresses I-A restricted T-cell proliferation, in relation to their own findings that mice which do express I-E molecules are more susceptible to certain nematode infections than mice which do not express I-E.     

An Xpert screen to identify carbapenemases

To prevent the spread of carbapenemases-producing Enterobacteriaceae (CPE) active surveillance, contact isolation and cohorting infected patients should be practiced. Rectal swabs for the Xpert MDRO-assay of 32 patients were included. 71.85% were positive for targets incorporated into the MDRO-assay; whereas 28% were phenotypically not CRE and Xpert negative (9.37% had different mechanism [bla_OXA]). The assay identified 59.3%, 9.37% and 3.1% as bla_NDM, bla_NDM+VIM and bla_VIM, respectively. The assay is a screening test that identifies CPE harbouring organism within an hour and can be installed at tertiary-care facilities to screen colonized patients.     

牛磺酸对弥漫性脑创伤大鼠脑葡萄糖转运体表达的影响

目的: 检测弥漫性脑创伤(DBI)大鼠脑内葡萄糖转运体1(GLUT1)和葡萄糖转运体3(GLUT3)的表达以及牛磺酸对其的影响。方法: SD雄性大鼠随机分为假手术组、脑创伤组、低剂量牛磺酸组(200 mg/kg)和高剂量牛磺酸组(300 mg/kg),连续灌胃给药7 d。建立大鼠DBI模型,脑创伤后24 h,免疫组化和Western blotting检测脑组织中GLUT1和GIUT3蛋白的表达;透射电镜观察大脑皮层神经元超微结构的变化。结果: 各组脑组织中均可见有GLUT1表达的阳性细胞,其表现为在微血管内皮细胞胞浆或胞膜呈棕黄色。与假手术组相比,脑创伤组大鼠脑GLUT1蛋白表达无显著差异;与脑创伤组相比,低、高剂量牛磺酸组脑GLUT1蛋白表达显著增多(P<0.01);且低剂量牛磺酸组脑GLUT1蛋白表达显著高于高剂量牛磺酸组(P<0.05)。各组仅在第三脑室周围可见GLUT3表达的阳性神经元,阳性细胞胞浆或胞膜呈棕黄色。与假手术组相比,脑创伤组大鼠脑GLUT3蛋白表达显著增多(P<0.01);与脑创伤组相比,低、高剂量牛磺酸组脑GLUT3蛋白表达显著增多(P<0.01);且高剂量牛磺酸组脑GLUT3蛋白表达显著高于低剂量牛磺酸组(P<0.01)。低剂量牛磺酸组大脑皮层神经元病理改变明显减轻。结论: 牛磺酸可对DBI大鼠发挥脑保护作用,其机制可能是上调GLUT1和GLUT3蛋白表达,维持脑组织的能量供给。     

An autosomal genomic screen for autism

Autism is a severe neurodevelopmental disorder defined by social and communication deficits and ritualistic-repetitive behaviors that are detectable in early childhood. The etiology of idiopathic autism is strongly genetic, and oligogenic transmission is likely. The first stage of a two-stage genomic screen for autism was carried out by the Collaborative Linkage Study of Autism on individuals affected with autism from 75 families ascertained through an affected sib-pair. The strongest multipoint results were for regions on chromosomes 13 and 7. The highest maximum multipoint heterogeneity LOD (MMLS/het) score is 3.0 at D13S800 (approximately 55 cM from the telomere) under the recessive model, with an estimated 35% of families linked to this locus. The next highest peak is an MMLS/het score of 2.3 at 19 cM, between D13S217 and D13S1229. Our third highest MMLS/het score of 2.2 is on chromosome 7 and is consistent with the International Molecular Genetic Study of Autism Consortium report of a possible susceptibility locus somewhere within 7q31-33. These regions and others will be followed up in the second stage of our study by typing additional markers in both the original and a second set of identically ascertained autism families, which are currently being collected. By comparing results across a number of studies, we expect to be able to narrow our search for autism susceptibility genes to a small number of genomic regions. Am. J. Med. Genet. (Neuropsychiatr. Genet.) 88:609–615, 1999. © 1999 Wiley-Liss, Inc.     

The tuberous sclerosis complex regulates trafficking of glucose transporters and glucose uptake

Human cancers often display an avidity for glucose, a feature that is exploited in clinical staging and response monitoring by using (18)F-fluoro-deoxyglucose (FDG) positron emission tomography. Determinants of FDG accumulation include tumor blood flow, glucose transport, and glycolytic rate, but the underlying molecular mechanisms are incompletely understood. The phosphoinositide-3 kinase/Akt/mammalian target of rapamycin complex (mTORC) 1 pathway has been implicated in this process via the hypoxia-inducible factor alpha-dependent expression of vascular endothelial growth factor and glycolytic enzymes. Thus, we predicted that tumors with elevated mTORC1 activity would be accompanied by high FDG uptake. We tested this hypothesis in eight renal angiomyolipomas in which the loss of tuberous sclerosis complex (TSC) 1/2 function gave rise to constitutive mTORC1 activation. Surprisingly, these tumors displayed low FDG uptake on positron emission tomography. Exploring the underlying mechanisms in vitro revealed that Tsc2 regulates the membrane localization of the glucose transporter proteins (Glut)1, Glut2, and Glut4, and, therefore, glucose uptake. Down-regulation of cytoplasmic linker protein 170, an mTOR effector, rescued Glut4 trafficking in Tsc2(-/-) cells, whereas up-regulation of Akt activity in these cells was insufficient to redistribute Glut4 to the plasma membrane. The effect of mTORC1 on glucose uptake was confirmed using a liver-specific Tsc1- deletion mouse model in which FDG uptake was reduced in the livers of mutant mice compared with wild-type controls. Together, these data show that mTORC1 activity is insufficient for increased glycolysis in tumors and that constitutive mTOR activity negatively regulates glucose transporter trafficking.     

An ornithine decarboxylase activity assay to screen for potential chemopreventive agents

A unique assay method to detect ornithine decarboxylase (ODC) activity in normal tracheal epithelial cells induced by a classic tumor promoter, 12-O-tetradecanoyl-phorbol-13-acetate (TPA) has been developed. Using this new assay, the inhibition of induced ODC activity is measured, thereby providing a screening system to identify potential chemopreventive or therapeutic agents. The assay is designed to be specific as it detects a radioactively labeled reaction product, putrescine from the decarboxylation of ornithine by ODC. As TPA is a classical tumor promoter, inhibition TPA-induced ODC activity can also be used to select antitumor promoter agents. Since the assay requires only 2 days to complete, it can be used to screen a large number of compounds for chemopreventive activity in a relatively short period of time.     

An insulin-releasing system responsive to glucose: thermodynamic evaluation of permeability properties.

Two weak poly(acid)s, poly(acrylic acid) (PAA) and poly(N-acryloyl-glycine) (P1), were graft-copolymerized onto porous cellulose membrane and their protonation behavior in aqueous media was studied by potentiometric techniques. Comparison with the corresponding free polymers in solution showed the same basicity constants during the protonation of ionized carboxyl groups, and the large potentiometric hysteresis loops observed for the grafts were indicative of specific interactions with the cellulose substrate. This was confirmed by FT-IR spectroscopic analysis at low pH. The polymeric membrane system, containing immobilized glucose oxidase, was synthesized for the purpose of insulin delivery in response to glucose concentration. The porosity of the membrane was controlled by the charge-state conformations of the grafted chains. The formation of gluconic acid in the presence of glucose caused a drop in pH which led to neutralization of the negatively charged carboxyl groups. The decrease in electrostatic repulsion caused the extended macromolecular chain to assume a coil-like form and opened the membrane pores to insulin.     

An enhanced 13-week bioassay: An alternative to the 2-year bioassay to screen for human carcinogenesis

The 2-year rodent bioassay has become the standard carcinogenicity screen for chemicals, despite concerns of costs, time, and excessive doses. More importantly, there are increasing concerns regarding its relevance to human carcinogenic risk, especially for non-DNA reactive chemicals. Cancer risk can be increased either by direct damage to DNA (DNA reactivity) or by increased cell proliferation. Utilizing the scientific basis for mode of action analysis in the framework that has been developed for extrapolating to human relevance, a short-term screen is proposed as a replacement for the 2-year bioassay. Chemicals are evaluated for DNA reactivity, immunosuppression, and estrogenic activity, known mechanisms of human carcinogenesis, by in vitro and/or in vivo tests. The chemical can then be evaluated for toxicity and/or increased cell proliferation in target tissues. This relies primarily on evaluation of organ weights and histopathology, and also utilizes data from blood and urine chemistries and DNA-labeling indices. Significant concern is raised regarding the relevance of evaluation of tissues that are present in rats or mice but not humans, and the relevance of proliferative responses in rodent endocrine tissues. In developing alternative procedures to evaluate chemicals for possible carcinogenic activity in humans, it is important not to rely on the 2-year rodent bioassay for validation of the new procedure. It is time to discontinue the performance of the 2-year rodent bioassay.     

An in vitro screen for new fasciolicidal agents

In vitro screens employing newly excysted, 6- and 12-week-old flukes, in a medium permitting the linear growth of the parasites, were assessed. When exposed to certain known fasciolicides, newly excysted flukes were susceptible only to diamphenethide, the free amine of diamphenethide, emetine hydrochloride and albendazole. Older flukes were affected by a much wider range of compounds including the chlorinated hydrocarbons, the substituted phenols and the salicylanilides. However their susceptibility to diamphenethide and its active metabolite was decreased significantly. The activity of fasciolicides in these in vitro assays therefore closely parallels their activity in vivo. When several broad spectrum anti-nematode agents were evaluated against newly excysted flukes in these screens the benzimidazole, isothiocyanate, pyrimidine and imidazothiazole anthelmintics showed activity but 12 potent antiprotozoal agents were all inactive. It is concluded that these in vitro assays were useful for detecting any intrinsic activity that a compound might possess against flukes. Such activity could often be missed in conventional in vivo screens because of problems associated with host pharmacokinetics. Negative results from such in vivo screens could preclude the development of more bioavailable derivatives or pro-drugs as novel and useful fasciolicidal agents.     

Multiple expression of glucose transporters in the lateral wall of the cochlear duct studied by quantitative real-time PCR assay

We have investigated the gene expression of the facilitated glucose transporter (GLUT), H⁺-coupled myo-inositol cotransporter (HMIT), and Na⁺ glucose cotransporter (SGLT) in the lateral wall of the cochlear duct by conventional RT-PCR and quantitative real-time PCR. The isoforms GLUT1, -3, -4, -5, -8, -10, -12 and HMIT were detected in both the stria vascularis and the spiral ligament, whereas no SGLT isoforms could be detected in these tissues. Quantitative real-time PCR analysis revealed significant differences in the gene expression of GLUT1, -4, -5, -10, and HMIT isoforms between the stria vascularis and the spiral ligament. This result reflects the tissue-dependent distributions of GLUT isoforms. These findings strongly suggest that a number of GLUT isoforms participate in glucose transport in the stria vascularis and the spiral ligament.     

Multiple expression of glucose transporters in the lateral wall of the cochlear duct studied by quantitative real-time PCR assay

The precedence effect (PE) is thought to be beneficial for proper localization and perception of sounds. The majority of recent physiological studies focus on the neural discharges correlated with PE in the inferior colliculus (IC). Pentobarbital anesthesia is widely used in physiological studies. However, little is known of the effect of pentobarbital on the discharge of neurons in PE. Neuronal responses in the IC from 23 male SD rats were recorded by standard extracellular recording techniques following presentation of 4 ms white noise bursts, presented from either or both of two loud speakers, at different interstimulus delays (ISDs). The neural responses were recorded for off-line analysis before or after intraperitoneal administration of pentobarbital at a loading or maintenance dose. Data were assessed by one-way repeated measures analysis of variance and pairwise comparisons. When the ipsilateral stimuli were leading, pentobarbital at a loading dose significantly increased normalized response to lagging stimuli during recovery from anesthesia. However, it was not the case when the contralateral stimuli were leading. At a maintenance dose, the normalized response to lagging stimuli were significantly reduced, independent of whether contralateral or ipsilateral stimuli were leading. These data show that pentobarbital have no effect on the normalized response of leading stimuli but can prolong the recovery time of lagging stimuli to paired sources produced PE illusions, which was gradually attenuated during recovery from anesthesia. Thus, extracellular recording immediately after administration of pentobarbital should be avoided in physiological studies of neural correlates of PE.     

Immunohistochemical localization and quantification of glucose transporters in the mouse brain

A family of seven facilitative glucose transporters (Glut1-5, 7 and 8) mediates the cellular uptake of glucose. In the brain, Glut2, Glut5 and Glut8 are found at relatively low levels whereas Glut1, Glut3 and Glut4 were reported in abundance in several brain regions. Using immunofluorescence, this study investigated, compared and quantified the localization of the brain major glucose transporters, Glut1, Glut3 and Glut4, in the different cerebral areas of CD1 mice. Most of the staining of Glut1, Glut3 and Glut4 in the mouse brain coincides with observations made in rats. The results confirm the cortical neuropil distribution of Glut3, the prominence of this transporter in the mossy fiber field of the hippocampus and the Glut3 and Glut4 immunostaining of the hippocampal pyramidal cell layer. The present study also reports novel localizations of the transporters such as the presence of Glut3 in neuronal perikarya, Glut4-labeled neurons in the CA3 of the hippocampus and the subiculum. In the cerebellum, Glut3 shows subcellular localization to the base of the Purkinje cell bodies near the axon hillock. Furthermore, an important population of Golgi cells was found to be strongly immunostained for Glut4 in the granular cell layer of the cerebellum. The quantification results suggest that the relative abundance of Glut1 in the frontal and motor cortices coincides well with the high-energy demands of these brain regions. However, the Glut4-selective abundance in cerebral motor areas supports its suggested role in providing the energy needed for the control of the motor activity. The reported neuropil distribution of Glut3 seems to uphold its suggested role in synaptic energy provision and neurotransmitter synthesis.We conclude that the cellular and regional distributions of the glucose transporters in the rodent brain seem to be relevant to their corresponding functions.     

EGFR inhibitors identified as a potential treatment for chordoma in a focused compound screen

Chordoma is a rare malignant bone tumour with a poor prognosis and limited therapeutic options. We undertook a focused compound screen (FCS) against 1097 compounds on three well‐characterized chordoma cell lines; 154 compounds were selected from the single concentration screen (1 µm ), based on their growth‐inhibitory effect. Their half‐maximal effective concentration (EC₅₀) values were determined in chordoma cells and normal fibroblasts. Twenty‐seven of these compounds displayed chordoma selective cell kill and 21/27 (78%) were found to be EGFR/ERBB family inhibitors. EGFR inhibitors in clinical development were then studied on an extended cell line panel of seven chordoma cell lines, four of which were sensitive to EGFR inhibition. Sapitinib (AstraZeneca) emerged as the lead compound, followed by gefitinib (AstraZeneca) and erlotinib (Roche/Genentech). The compounds were shown to induce apoptosis in the sensitive cell lines and suppressed phospho‐EGFR and its downstream pathways in a dose‐dependent manner. Analysis of substituent patterns suggested that EGFR‐inhibitors with small aniline substituents in the 4‐position of the quinazoline ring were more effective than inhibitors with large substituents in that position. Sapitinib showed significantly reduced tumour growth in two xenograft mouse models (U‐CH1 xenograft and a patient‐derived xenograft, SF8894). One of the resistant cell lines (U‐CH2) was shown to express high levels of phospho‐MET, a known bypass signalling pathway to EGFR. Neither amplifications (EGFR, ERBB2, MET) nor mutations in EGFR, ERBB2, ERBB4, PIK3CA, BRAF, NRAS, KRAS, PTEN, MET or other cancer gene hotspots were detected in the cell lines. Our findings are consistent with the reported (p‐)EGFR expression in the majority of clinical samples, and provide evidence for exploring the efficacy of EGFR inhibitors in the treatment of patients with chordoma and studying possible resistance mechanisms to these compounds in vitro and in vivo. © 2016 The Authors. The Journal of Pathology published by John Wiley & Sons Ltd on behalf of Pathological Society of Great Britain and Ireland.