Mean residence times of TF-TF and TF-miRNA toggle switches

Toggle switch networks are the simplest possible circuits with the ability of making a decision related to cell differentiation during embryonic development and disease progression. A common occurrence of toggle switch circuits is in the epithelial-mesenchymal transition (EMT) and its reverse, the mesenchymal-epithelial transition (MET), pathways which play key roles in phenotypic plasticity during cancer metastasis and therapy resistance. Recent studies have shown that the cells attaining one or more hybrid epithelial/mesenchymal (E/M) phenotypes during EMT/MET are more aggressive than those in either the epithelial or mesenchymal phenotype. In this work we studied the stability of each phenotype for different toggle switch circuits. We considered two-component toggle switch networks comprising either two mutually inhibiting transcription factors (TF-TF) or a TF-microRNA (TF-miR) chimera pair, and from Langevin dynamics, we determined the mean residence time (MRT) of cell phenotypes. MRT can be considered to be an indicator of stability in each cell phenotype and we showed that by replacing one of the TFs of the TF-TF toggle switch with miRNA generically stabilizes the hybrid phenotype. However, in the absence [presence] of a monostable hybrid state, the miRNA with faster [slower] degradation will make the hybrid state more probable. These results help to understand the implications of TF-TF and TF-miR circuits in the dynamics of cell fate decisions.

The in vitro efficacy of neutral electrolysed water and povidone-iodine against CRS-associated biofilms

BACKGROUND

Despite best medical and surgical practice, some cases of chronic rhinosinusitis (CRS) can remain recalcitrant. Bacterial biofilms have been associated with the recalcitrance of sinonasal inflammation. Biofilms are highly resistant to commonly prescribed antibiotics. Accordingly, more effective antimicrobial treatment options are needed to treat refractory CRS. The aim of this study was to determine the in vitro efficacy of neutral electrolysed water (NEW) and povidone-iodine (PVI) against CRS-associated Staphylococcus aureus biofilms.

METHODS

Mature S. aureus biofilms were grown in a Centre for Disease Control (CDC) biofilm reactor. The antimicrobial activity of NEW, PVI and doxycycline was determined for both planktonic and biofilm cultures of a clinical S. aureus isolate using minimum inhibitory concentration (MIC), minimum bactericidal concentration (MBC) and minimum biofilm eradication concentration (MBEC) assays.

RESULTS

MICs and MBCs were determined for all antimicrobials. MBC values were similar to MICs for both antiseptics, but doxycycline MBCs were significantly higher than the associated MICs. Biofilms were highly resistant to NEW and doxycycline. The MBEC for doxycycline was between 500 and 1000 µg/mL. NEW was ineffective against biofilms and no MBEC could be determined. In contrast, a concentration of 10% of the commercial PVI solution (10 mg/mL PVI) led to effective eradication of mature biofilms.

CONCLUSION

In this study, only PVI showed promising antibiofilm activity at physiological concentrations. The in vivo efficacy of PVI warrants further investigation of its potential as a treatment for recalcitrant CRS.

First passage time properties of miRNA-mediated protein translation

An important function of microRNAs in gene regulation is to repress the protein synthesis in a multi-step process with implications in timing efficiency of the regulatory network. We propose a stochastic description of translation-initiation mechanism and solve for the steady state distribution of protein number in the linear regime. The time-dependent moments have been approximately calculated and the role of miRNAs in determining the First Passage Time (FPT) properties of protein dynamics has been established. We analytically show that the modulation of slow rates of the translation process will result in efficient and robust timing mechanism. For a general nonlinear model our numerical simulation results are in qualitative agreement with the linear model.

First passage time in post-transcriptional regulation by multiple small RNAs

The post-transcriptional regulation of a protein by multiple small RNA molecules has been formulated as a stochastic process. An approximate solution of the master equation shows that the protein statistics can exhibit a generic form applicable for many regulatory scenarios. The first passage time (FPT) statistics has been obtained for regulation by single sRNA, with negative and positive regulations as limiting cases, as well as regulation by multiple sRNAs. The multiple sRNAs are able to independently control protein mean and variance, and we show that this is an advantageous mechanism to control FPT fluctuations in order to improve timing efficiency in post-transcriptional regulation.

A Computational Systems Biology Approach Identifies SLUG as a Mediator of Partial Epithelial-Mesenchymal Transition (EMT)

Epithelial-mesenchymal plasticity comprises reversible transitions among epithelial, hybrid epithelial/mesenchymal (E/M) and mesenchymal phenotypes, and underlies various aspects of aggressive tumor progression such as metastasis, therapy resistance, and immune evasion. The process of cells attaining one or more hybrid E/M phenotypes is termed as partial epithelial mesenchymal transition (EMT). Cells in hybrid E/M phenotype(s) can be more aggressive than those in either fully epithelial or mesenchymal state. Thus, identifying regulators of hybrid E/M phenotypes is essential to decipher the rheostats of phenotypic plasticity and consequent accelerators of metastasis. Here, using a computational systems biology approach, we demonstrate that SLUG (SNAIL2) - an EMT-inducing transcription factor - can inhibit cells from undergoing a complete EMT and thus stabilize them in hybrid E/M phenotype(s). It expands the parametric range enabling the existence of a hybrid E/M phenotype, thereby behaving as a phenotypic stability factor. Our simulations suggest that this specific property of SLUG emerges from the topology of the regulatory network it forms with other key regulators of epithelial-mesenchymal plasticity. Clinical data suggest that SLUG associates with worse patient prognosis across multiple carcinomas. Together, our results indicate that SLUG can stabilize hybrid E/M phenotype(s).

NFATc Acts as a Non-Canonical Phenotypic Stability Factor for a Hybrid Epithelial/Mesenchymal Phenotype

Metastasis remains the cause of over 90% of cancer-related deaths. Cells undergoing metastasis use phenotypic plasticity to adapt to their changing environmental conditions and avoid therapy and immune response. Reversible transitions between epithelial and mesenchymal phenotypes – epithelial–mesenchymal transition (EMT) and its reverse mesenchymal–epithelial transition (MET) – form a key axis of phenotypic plasticity during metastasis and therapy resistance. Recent studies have shown that the cells undergoing EMT/MET can attain one or more hybrid epithelial/mesenchymal (E/M) phenotypes, the process of which is termed as partial EMT/MET. Cells in hybrid E/M phenotype(s) can be more aggressive than those in either epithelial or mesenchymal state. Thus, it is crucial to identify the factors and regulatory networks enabling such hybrid E/M phenotypes. Here, employing an integrated computational-experimental approach, we show that the transcription factor nuclear factor of activated T-cell (NFATc) can inhibit the process of complete EMT, thus stabilizing the hybrid E/M phenotype. It increases the range of parameters enabling the existence of a hybrid E/M phenotype, thus behaving as a phenotypic stability factor (PSF). However, unlike previously identified PSFs, it does not increase the mean residence time of the cells in hybrid E/M phenotypes, as shown by stochastic simulations; rather it enables the co-existence of epithelial, mesenchymal and hybrid E/M phenotypes and transitions among them. Clinical data suggests the effect of NFATc on patient survival in a tissue-specific or context-dependent manner. Together, our results indicate that NFATc behaves as a non-canonical PSF for a hybrid E/M phenotype.

Timing effciency in small-RNA-regulated post-transcriptional processes

Gene regulation in a cellular environment is a stochastic phenomenon leading to a large variability in mRNAs and protein numbers that are often produced in bursts. The regulation leading to varied protein dynamics can be ascribed to transcriptional or post-transcriptional mechanisms. In transcriptional regulation, the gene dynamically switches between an active and an inactive state, while in the post-transcriptional regulation small RNAs tune the activity of mRNAs. In either scenario, it is possible to calculate the time-dependent probability distribution of proteins and address the interesting question pertaining to their first passage time statistics. The coefficient of variation of first passage time can be considered to be an indicator of efficiency in controlling regulatory pathways and we show that post-transcriptional regulation performs better than simple transcriptional regulation for comparable protein yields.

The sinonasal mycobiota in chronic rhinosinusitis and control patients

BACKGROUND

While bacterial associations with chronic rhinosinusitis (CRS) are increasingly well described, fewer studies have examined the fungal component of the sinonasal microbiota. Here we present a study of the sinonasal mycobiota in a cohort of 144 patients (106 patients with CRS and 38 controls).

METHODOLOGY

Fungal communities were characterised by analysis of mucosal swab samples of the left and right middle meatuses via ITS2 marker amplicon sequencing on the Illumina MiSeq platform. Fungal associations with previously published bacterial community and inflammatory cytokine and cell data for this cohort (collected at the same intra-operative time point) were also investigated.

RESULTS

Malassezia spp. were ubiquitous and often highly predominant. Season of sampling explained more of the variability in the data than any of the clinical parameters. The predominant Malassezia sp. was distinct in patients with cystic fibrosis compared to those without. However, distinctions in the mycobiota were not evident between any other patient groupings assessed, and few fungal-bacterial or fungal-inflammatory associations were observed.

CONCLUSIONS

This study confirms the prominent place of Malassezia spp. within the upper respiratory tract. Overall, few distinctions between patient groups were evident, and these data lend further support to the hypothesis that fungal community types may have no direct causative association with idiopathic CRS. Additional studies incorporating a broader array of inflammatory markers are required to assess whether these ubiquitous fungi nonetheless play an exacerbating role in some sensitive individuals.

Mechanical and Thermal Properties of Teak Wood Flour/Starch Filled High Density Polyethylene Composites

Teak wood flour (TWF) reinforced HDPE composites were prepared and characterized in terms of mechanical, morphological and thermal properties using 2% polyethylene grafted with maleic anhydride (PE-g-MAH) as compatibilizer. The composites were prepared by twin screw extrusion and samples were prepared by injection molding. Mechanical properties increased with the incorporation of TWF, Starch and PE-g-MAH. Tensile strength and Young's modulus increased by 96% and 207%, respectively for TWF (40%)-HDPE composite as compared to virgin matrix. Scanning electron microscopy revealed good interface between TWF and matrix. FT-IR spectra confirmed the esterification reaction and H-bond between anhydride group of PE-g-MAH and cellulose of TWF. The DSC results showed that the melting temperature increased from 129°C to 137°C while crystallization (%) decreased from 40.49% for HDPE to 34.77% for 40% TWF composites, respectively. The storage modulus increased for all the composites at low temperature. Glass transition temperature practically remained unaffected by filler loading.

First-passage time statistics of stochastic transcription process for time-dependent reaction rates

Transcription in gene expression is an intrinsically noisy process which involves production and degradation of mRNAs. An important quantity to describe this stochastic process is the first-passage time (FPT), i.e., the time taken by mRNAs to reach a particular threshold. The process of transcription can be modelled as a simple birth-death process, assuming that the promoter is always in an active state and to encode the stochastic environment we consider the transcription rate to be time dependent. This generalization is suitable to capture bursty mRNA dynamics usually modelled as an ON-Off model and simplifies the calculation of FPT statistics for a cell population. We study the role of periodic modulation of the transcription rate on different moments of FPT distribution of a population of cells. Our calculation shows that for sinusoidal modulation there exists an extremal value of mean FPT as a function of the time period and phase of the transcription signal. However, for the square wave modulation of transcription rates simulation results show that the extremal value of the MFPT behaves monotonically with the variation of the phase.

Stability and mean residence times for hybrid epithelial/mesenchymal phenotype

Cancer metastasis and drug resistance remain unsolved clinical challenges. A phenotypic transition that is often implicated in both these processes is epithelial-mesenchymal transition (EMT) during which epithelial cells weaken their cell-cell adhesion and gain traits of migration and invasion, typical of mesenchymal cells. However, recent studies indicate that apart from these two states, cells can also exist in one or more hybrid E/M state(s), which plays an aggressive role in progression of the disease. Furthermore, computational and experimental studies have identified a variety of phenotypic stability factors (PSFs) that stabilize the hybrid E/M state(s) and can increase disease aggressiveness. In this work, we study EMT regulatory networks, in the presence of different PSFs, as dynamical systems subjected to random fluctuations. The cells thus explore different stable E, M, E/M states in the potential landscape and our aim is to quantify the residence time in each of these states. Our stochastic simulations indicate an universal feature that the mean residence time (MRT) in the hybrid E/M state is enhanced in the presence of PSFs. We demonstrate that the feature is consistent for a variety of PSFs, namely, GRHL2, OVOL, ΔNp63α, miR-145/OCT4, participating in the core EMT regulatory network. Our results reveal potential targets for pushing cells out of a hybrid E/M state and thus halting metastatic progression.

Combinatorial Characterization of Saliva for Oral Precancer Diagnostics

Background: Saliva based diagnostic can play an important role in the translational research related to cancer diagnostics and treatment. It is easily available, noninvasive, low storage cost, has less contamination chances with simple collection procedure. Cancers related to tobacco use, including oral cancer account for about 30% of all cancers in males and females. Five years' survival rate remains the same even after decades of advancement of detection, prevention, and treatment of OSCC (oral squamous cell carcinoma) mainly due to late diagnosis of oral potentially malignant disorders (OPMDs). Aim: Combinatorial characterization of saliva, endorsing multidimensional spectroscopic signatures using suitably designed biochamber. Methods: Eighteen saliva samples (6 normal, 6 OSF [oral submucous fibrosis, a type of OPMD] and 6 confirmed OSCC) were collected from GNIDSR (Guru Nanak Institute of Dental Science and Research) Kolkata. Ethical approval was obtained for the study and all the participants were explained the objectives of the study and a written informed consent was obtained from them. Participant's demographic detail and clinical characteristics were also recorded. The participants were asked not to consume food 1 hour before sample collection and were suggested to rinse their mouth 30 minutes prior to saliva expectoration to minimize the contamination of food in saliva. Empty, sterile, graded tubes were used for this purpose. The subjects were asked not to clear nose or throat during the process of saliva expectoration to avoid forced phlegm from other part of the respiratory tract. The saliva samples were then immediately transferred to −20 degrees and later in −80 degrees for long storage. The electrical impedance (EI) of saliva was measured in custom made biochambers with copper electrodes. The EI was measured for the frequency sweep from 20 Hz to 2 MHz using an impedance analyzer. Apart from EI measurement, the corresponding samples were subjected to FTIR (Fourier-transform IR spectroscopy) analysis. SPSS and OMNIC software were used for the data analysis of EI and FTIR respectively. Results: [Table: see text][Table: see text][Table: see text][ Table A , B & C represents descriptive statistics, correlation matrix and component matrix respectively. The multivariate analysis of the FTIR data indicates the significant differences ( P < 0.005) among the different study groups such as normal, OSF and OSCC. The eigen values (normal 0.917, OSF 0.962, OSCC 0.975) from component matrix analysis also indicate the same. Conclusion: The spectroscopic characterization (EI and FTIR) of saliva was effective in evaluating normal and OPMD condition. This noninvasive paradigm can serve as a complimentary technique to the existing gold standard methods for the early detection of oral cancer.

Moving beyond descriptions of diversity: clinical and research implications of bacterial imbalance in chronic rhinosinusitis

Chronic rhinosinusitis (CRS) is a debilitating disease which affects 5-16% of the general population and involves long-term inflammation of the sinonasal cavity. While microbial involvement in the pathogenesis of CRS has long been suspected, the exact role of microbes remains unclear. Recent application of cultivation-independent, molecular methods has provided much new information, taking advantage of developments in both laboratory- and bioinformatics-based analyses. The aim of this mini-review is to present a variety of available bioinformatics approaches, such as data classification techniques and network analyses, with proven applications in other aspects of human microbiome health and disease research. The uses of molecular techniques in the clinical setting are still in its infancy, but these tools can further our understanding of microbial imbalance during chronic disease and help guide effective patient treatment. The mini-review emphasises ways in which CRS bacterial gene-targeted sequencing data can progress beyond descriptive summaries and toward unlocking the mechanisms by which bacterial communities can be markers for sinus health.

Toll-like receptor activation by sino-nasal mucus in chronic rhinosinusitis

BACKGROUND

The sino-nasal disease chronic rhinosinusitis (CRS) is primarily an inflammatory condition that manifests in several ways. However, the aetiology of this complex disease is poorly understood. The aim of this study was to explore the association between toll-like receptor (TLR) activation, host immune response and sino-nasal mucus in healthy and diseased patients.

METHODS

The activation of TLR2/1 and TLR4 by sino-nasal mucus from 26 CRS patients and 10 healthy controls was measured. In addition, 7 inflammatory cytokines, bacterial community composition and bacterial abundance within the sino-nasal mucus were measured using molecular and diagnostic tools.

RESULTS

TLR activity was observed in 9/36 samples, including 2 healthy controls. There was a strong, positive correlation between members of the Gammaproteobacteria (Haemophilus, Enterobacter, Pseudomonas) and TLR2/1 and TLR4 activity. Bacterial abundance and cytokine (tumour necrosis factor) abundance were also positively correlated with TLR activity.

CONCLUSIONS

These findings suggest that a small proportion (20-30%) of individuals in each sub-group are more predisposed to TLR activity, which may be related to bacterial composition, diversity and abundance in the sinuses.

The in vitro effect of xylitol on chronic rhinosinusitis biofilms

INTRODUCTION

Biofilms have been implicated in chronic rhinosinusitis (CRS) and may explain the limited efficacy of antibiotics. There is a need to find more effective, non-antibiotic based therapies for CRS. This study examines the effects of xylitol on CRS biofilms and planktonic bacteria.

METHODS

Crystal violet assay and spectrophotometry were used to quantify the effects of xylitol (5% and 10% solutions) against Staphylococcus epidermidis, Pseudomonas aeruginosa, and Staphylococcus aureus. The disruption of established biofilms, inhibition of biofilm formation and effects on planktonic bacteria growth were investigated and compared to saline and no treatment.

RESULTS

Xylitol 5% and 10% significantly reduced biofilm biomass (S. epidermidis), inhibited biofilm formation (S. aureus and P. aeruginosa) and reduced growth of planktonic bacteria (S. epidermidis, S. aureus, and P. aeruginosa). Xylitol 5% inhibited formation of S. epidermidis biofilms more effectively than xylitol 10%. Xylitol 10% reduced S. epidermidis planktonic bacteria more effectively than xylitol 5%. Saline, xylitol 5% and 10% disrupted established biofilms of S. aureus when compared with no treatment. No solution was effective against established P. aeruginosa biofilm.

CONCLUSIONS

Xylitol has variable activity against biofilms and planktonic bacteria in vitro and may have therapeutic efficacy in the management of CRS.

Al2O3 influence on structural, elastic, thermal properties of Yb(3+) doped Ba-La-tellurite glass: evidence of reduction in self-radiation trapping at 1μm emission

Ba-La-tellurite glasses doped with Yb(3+) ions have been prepared through melt quenching technique by modifying their composition with the inclusion of varied concentration of Al2O3 to elucidate its effects on glass structural, elastic, thermal properties and Yb(3+) ion NIR luminescence performance. The FTIR spectral analysis indicates Al2O3 addition is promoting the conversion of BOs from NBOs which have been generated during the process of depolymerisation of main glass forming TeO4 units. The elastic properties of the glass revealed an improved rigidity of the glass network on addition of Al2O3. In concurrence to this, differential thermal analysis showed an increase in glass transition temperature with improved thermal stability factor. Also, Yb(3+) fluorescence dynamics demonstrated that, Al2O3 inclusion helps in restraining the detrimental radiation trapping of ∼1μm emission.

Influence of increased environmental water salinity on gluconeogenesis in the air-breathing walking catfish, Clarias batrachus

The present study was aimed at determining the effect of hypertonicity due to increased environmental water salinity on gluconeogenesis in air-breathing walking catfish (Clarias batrachus). In situ exposure to hypertonic saline solution (150 mM NaCl) led to a significant stimulation of glucose efflux due to gluconeogenesis from the liver after 7 days with further elevation after 14 days in the presence of each of the three potential gluconeogenic substrates (lactate, pyruvate, and glutamate). This was accompanied by significant increase of activities of three key gluconeogenic enzymes, namely phosphoenolpyruvate carboxykinase (PEPCK), fructose 1,6-biphosphatase (FBPase), and glucose 6-phosphatase (G6Pase) in liver and kidney by about twofold to threefold. Environmental hypertonicity also led to a significant elevation in the levels of PEPCK, FBPase, and G6Pase enzyme proteins in both the tissues by about 2- to 2.75-fold, accompanied by a significant elevation in the level of PEPCK mRNA by about 2- to 2.5-fold after 7 days, and further enhancement to about 3.5- to 4-fold after 14 days. Thus, the upregulation of PEPCK, FBPase. and G6Pase activities appears to be a result of transcriptional regulation of these genes. The induction of gluconeogenesis under environmental hypertonicity, which this catfish faces regularly in its natural habitat, possibly occurs as a consequence of changes in hydration status/cell volume of different cell types. This would certainly assist in maintaining glucose homeostasis, and also for a proper energy supply to support metabolic demands for ion transport and other altered metabolic processes under various environmental hypertonic stress-related insults.

Influence of cell volume changes on protein synthesis in isolated hepatocytes of air-breathing walking catfish (Clarias batrachus)

The present study aimed at determining the effect of cell volume changes on protein synthesis, measured as the incorporation of [(3)H]leucine into acid-precipitable protein, in isolated hepatocytes of air-breathing walking catfish (Clarias batrachus). The rate of protein synthesis, which was recorded to be 10.02 +/- 0.10 (n = 25) nmoles mg(-1) cell protein h(-1) in isotonic incubation conditions, increased/decreased significantly by 18 and 48%, respectively, following hypo- (-80 mOsmol l(-1))/hypertonic (+80 mOsmol l(-1)) incubation conditions (adjusted with NaCl), with an accompanying increase/decrease of hepatic cell volume by 12 and 20%, respectively. Similar cell volume-sensitive changes of protein synthesis were also observed when the anisotonicity of incubation medium was adjusted with mannitol. Increase of hepatic cell volume by 9%, due to addition of glutamine plus glycine (5 mM each) to the isotonic control incubation medium, led to a significant increase of protein synthesis by 14%. Decrease of hepatic cell volume by 15 and 18%, due to addition of dibutyl-cAMP and adenosine in isotonic control incubation medium, led to a significant decrease of protein synthesis by 30 and 34%, respectively. Thus, it appears that the increase/decrease of hepatic cell volume, caused either by changing the extracellular osmolarity or by the presence of amino acids or certain other metabolites, leads to increase/decrease of protein synthesis, respectively, and shows a direct correction (r = 0.99) between the hepatic cell volume and protein synthesis in walking catfish. These cell volume-sensitive changes of protein synthesis probably help this walking catfish in fine tuning the different metabolic pathways for better adaptation during cell volume changes and also to avoid the adverse affects of osmotic stress. This is the first report of cell volume-sensitive changes of protein synthesis in hepatic cells of any teleosts.

Influence of cell volume changes on autophagic proteolysis in the perfused liver of air-breathing walking catfish (Clarias batrachus)

Exposure of perfused liver of walking catfish (Clarias batrachus) to hypotonicity (-80 mOsmol/L) caused swelling of liver cells as evidenced by the increase in liver mass by 11.5%, and inhibition of [(3)H]leucine release (as a measure of proteolysis) by 37% from the radiolabeled perfused liver. Whereas, exposure of perfused liver to hypertonicity (+80 mOsmol/L) caused shrinkage of liver cells as evidenced by the decrease in liver mass by 10.4%, and stimulation of [(3)H]leucine release by 24%. Infusion of amino acids such as glutamine plus glycine (2 mM each) also caused increase in liver cell volume as evidenced by the increase in liver mass by 8.9%, and inhibition of [(3)H]leucine release by 29%. Adjustment of anisotonicity of the media without changing the NaCl concentration in the media had almost similar effects on proteolysis in the perfused liver. A direct correlation of cell volume changes or hydration status of liver cells with that of proteolysis was observed in the perfused liver regardless of whether the cell volume increase/decrease was evoked by anisotonic perfusion media or by the addition of amino acids. Thus, it appears that the increase/decrease in hepatic cell volume could be one of the important modulators for adjusting the autophagic proteolysis in walking catfish probably to avoid the adverse affects of osmotically induced cell volume changes, to preserve the hepatic cell function and for proper energy supply under osmotic stress. This is the first report of cell volume-sensitive changes of autophagic proteolysis in hepatic cells of any teleosts.

A study of tubular potassium secretory capacity in older patients with hyperkalaemia

OBJECTIVES

Sustained hyperkalaemia usually indicates a defect in renal potassium (K+) excretion and can be due to severe impairment of glomerular filtration rate (GFR). The major determinants of renal K+ secretion were studied in hyperkalaemic and normokalaemic elderly subjects to probe the major determinants of hyperkalaemia in this setting.

DESIGN

The transtubular potassium gradient (TTKG) provides an index of tubular K+ secretion and normally rises in patients with significant hyperkalaemia. Both GFR(glomerular filtration rate) and TTKG were assessed at baseline and repeated after 3 hours following ingestion of 0.1mg of fludrocortisone in three groups.

SETTING

An acute general hospital in the West of Ireland.

PARTICIPANTS

23 subjects in total; 8 older patients with unexplained hyperkalaemia (OHK), 8 older patients with normokalaemia (ONK) and 9 young normokalaemic controls (YNK).

MEASUREMENTS

The GFR was either measured by 24 hour creatinine clearance estimation or calculated using the Cockroft and Gault formula.TTKG was calculated using a specific formula.

RESULTS

Mean baseline TTKG was similar in all three groups and consequently inappropriately low in hyperkalaemic subjects. Three hours post fludrocortisone, the TTKG had risen significantly from baseline levels in the young subjects only (from 7.5+/-0.09 to 11.6+/-1.1, p<0.05). No significant increase was noted in either older group at this timepoint.

CONCLUSIONS

The inappropriately low baseline TTKG in the OHK group as well as the absence of a response to fludrocortisone indicate tubular insensitivity to aldosterone. GFR values in both OHK (40.06+/-2.31) and ONK (55.58+/-6.1) groups were significantly lower than those in the YNK group (101.66+/-6.9). In aggregate, these findings indicate that older hyperkalaemic patients typically have both impairment of glomerular filtration and renal tubular K+ secretion and highlights the requirement for vigilance in elderly patients when using medications which interfere with tubular function.

Mitochondrial citrulline synthesis from ammonia and glutamine in the liver of ureogenic air-breathing catfish, Clarias batrachus (Linnaeus)

The possible synthesis of citrulline, a rate limiting step for urea synthesis via the ornithine-urea cycle (OUC) in teleosts was tested both in the presence of ammonia and glutamine as nitrogen-donating substrates by the isolated liver mitochondria of ureogenic air-breathing walking catfish, C. batrachus. Both ammonia and glutamine could be used as nitrogen-donating substrates for the synthesis of citrulline by the isolated liver mitochondria, since the rate of citrulline synthesis was almost equal in presence of both the substrates. The citrulline synthesis by the isolated liver mitochondria requires succinate at a concentration of 0.1 mM as an energy source, and also requires the involvement of intramitochondrial carbonic anhydrase activity for supplying HCO3 as another substrate for citrulline synthesis. The rate of citrulline synthesis was further stimulated significantly by the isolated liver mitochondria of the fish after pre-exposure to 25 mM NH4Cl for 7 days. Due to possessing this biochemical adaptational strategy leading to the amelioration of ammonia toxicity mainly by channeling ammonia directly and/or via the formation of glutamine to the OUC, this air-breathing catfish could succeed in surviving in high external ammonia, which it faces in its natural habitat in certain seasons of the year.

Recurrent lymphocytic hypophysitis in a woman 27 years after subtotal adrenalectomy for hypercortisolism possibly of autoimmune origin

Lymphocytic hypophysitis commonly occurs in females in peripartum period but several unusual presentations have been reported. Here we report a rare case of recurrent lymphocytic hypophysitis in a woman who had subtotal adrenalectomy for hypercortisolism 27 years back. Polyglandular autoimmune endocrinopathy with an uncommon combination of Cushing's syndrome and recurrent hypophysitis is a strong possibility in this case. Treatment with steroids has been found to have beneficial effect.

Expression of ornithine-urea cycle enzymes in early life stages of air-breathing walking catfish Clarias batrachus and induction of ureogenesis under hyper-ammonia stress

The air-breathing walking catfish Clarias batrachus is a potential ureogenic teleost with having a full complement of ornithine-urea cycle (OUC) enzymes expressed in various tissues. The present study was aimed at determining the pattern of nitrogenous waste excretion in the form of ammonia-N and urea-N along with the changes of tissue ammonia and urea levels, and the expression of OUC enzymes and glutamine synthetase (GSase) in early life stages of this teleost, and further, to study the possible induction of ureogenesis in 15-day old fry under hyper-ammonia stress. The ammonia and urea excretion was visible within 12 h post-fertilization (hpf), which increased several-fold until the yolk was completely absorbed by the embryo. Although all the early developing stages were primarily ammoniotelic, they also excreted significant amount of nitrogen (N) in the form of urea-N (about 35-40% of total N). Tissue levels of ammonia and urea also increased along with subsequent developmental stages at least until the yolk absorption stage. All the OUC enzymes and GSase were expressed within 4-12 hpf showing an increasing trend of activity for all the enzymes until 350 hpf. There was a significant increase of activity of GSase, carbamyl phosphate synthetase III (CPSase III) and argininosuccinate lyase enzymes (ASL), accompanied with significant increase of enzyme protein concentration of at least two enzymes (GSase and CPSase III) in the 15-day old fry following exposure to 10 mM NH4Cl as compared to respective controls kept in water over a period of 72 h. Thus, it appears that the OUC enzymes are expressed in early life stages of walking catfish like other teleosts, but at relatively high levels and remain expressed all through the life stages with a potential of stimulation of ureogenesis throughout the life cycle as a sort of physiological adaptation to survive and breed successfully under hyper-ammonia and various other environmental-related stresses.

Cell volume changes affect gluconeogenesis in the perfused liver of the catfish Clarias batrachus

In addition to lactate and pyruvate, some amino acids were found to serve as potential gluconeogenic substrates in the perfused liver of Clarias batrachus. Glutamate was found to be the most effective substrate, followed by lactate, pyruvate, serine, ornithine, proline, glutamine, glycine, and aspartate. Four gluconeogenic enzymes, namely phosphoenolpyruvate carboxykinase (PEPCK), pyruvate carboxylase (PC), fructose 1,6-bisphosphatase (FBPase) and glucose 6-phosphatase (G6Pase) could be detected mainly in liver and kidney, suggesting that the latter are the two major organs responsible for gluconeogenic activity in this fish. Hypo-osmotically induced cell swelling caused a significant decrease of gluconeogenic efflux accompanied with significant decrease of activities of PEPCK, FBPase and G6Pase enzymes in the perfused liver. Opposing effects were seen in response to hyperosmotically induced cell shrinkage. These changes were partly blocked in the presence of cycloheximide, suggesting that the aniso-osmotic regulations of gluconeogenesis possibly occurs through an inverse regulation of enzyme proteins and/or a regulatory protein synthesis in this catfish. In conclusion, gluconeogenesis appears to play a vital role in C. batrachus in maintaining glucose homeostasis, which is influenced by cell volume changes possibly for proper energy supply under osmotic stress.

A proteomic approach to understanding the development of multidrug-resistant Candida albicans strains

Resistance of the pathogenic yeast Candida albicans to the antifungal agent fluconazole is often caused by the overexpression of genes that encode multidrug efflux pumps ( CDR1, CDR2, or MDR1). We have undertaken a proteomic approach to gain further insight into the regulatory network controlling efflux pump expression and drug resistance in C. albicans. Three pairs of matched fluconazole-susceptible and resistant clinical C. albicans isolates, in which drug resistance correlated with stable activation of MDR1 or CDR1/2, were analyzed for differences in their protein expression profiles. In two independent, MDR1-overexpressing, strains, additional up-regulated proteins were identified, which are encoded by the YPR127 gene and several members of the IFD ( YPL088) gene family. All are putative aldo-keto reductases of unknown function. These proteins were not up-regulated in a fluconazole-resistant strain that overexpressed CDR1 and CDR2 but not MDR1, indicating that expression of the various efflux pumps of C. albicans is controlled by different regulatory networks. To investigate the possible role of YPR127 in the resistance phenotype of the clinical isolates, we constitutively overexpressed the gene in a C. albicans laboratory strain. In addition, the gene was deleted in a C. albicans laboratory strain and in one of the drug-resistant clinical isolates in which it was overexpressed. Neither forced overexpression nor deletion of YPR127 affected the susceptibility of the strains to drugs and other toxic substances, suggesting that the regulatory networks which control the expression of efflux pumps in C. albicans also control genes involved in cellular functions not related to drug resistance.

Role of ureogenesis in tackling problems of ammonia toxicity during exposure to higher ambient ammonia in the air-breathing walking catfishclarias batrachus

In the present study, the possible role of ureogenesis to avoid the accumulation of toxic ammonia to a lethal level under hyper-ammonia stress was tested in the air-breathing walking catfish Clarias batrachus by exposing the fish at 25 mM NH4Cl for 7 days. Excretion of ammonia by the NH4Cl-exposed fish was totally suppressed, which was accompanied by significant accumulation of ammonia in different body tissues. The walking catfish, which is otherwise predominantly ammoniotelic, turned totally towards ureotelism from ammoniotelism with a 5- to 6-fold increase of urea-N excretion during exposure to higher ambient ammonia. Stimulation of ureogenesis was accompanied with significant increase of some of the key urea cycle enzymes such as carbamyl phosphate synthetase (urea cycle-related), argininosuccinate synthetase and argininosuccinate lyase both in hepatic and non-hepatic tissues. Due to this unique physiological strategy of turning towards ureotelism from ammoniotelism via the induced urea cycle, this air-breathing catfish is able to survive in very high ambient ammonia, which they face in certain seasons of the year in the natural habitat.

The epothilones, eleutherobins, and related types of molecules

Taxol is currently one of the most effective anticancer agents available. However, limitations due to multidrug-resistance (MDR) susceptibility and lack of aqueous solubility render it less than an ideal drug. These limitations, coupled with taxol's unique mechanism of tumor inhibition, involving the stabilization of microtubule assembly, have spurred the search for more effective chemotherapeutic agents. This review will discuss the chemistry and biology of some of the most promising new molecules with "taxol-like" activity. The extended family of microtubule-stabilizing agents now includes the epothilones, eleutherobins, discodermolide, laulimalide and WS9885B. The epothilones have emerged as one of the most exciting new candidates for detailed structure-activity-related studies. A review of our efforts in the synthetic and biological aspects of this research is presented, as are the latest developments reported from other laboratories in academia and the pharmaceutical industry. The synthesis and structure-activity studies of eleutherobins, as well as recent progress with discodermolide, laulimalide and WS9885B are also reviewed. An abundance of exciting advances in chemistry and biology have emerged from these studies, and it is hoped that it will ultimately result in the development of new and more effective chemotherapeutic agents in the fight against cancer.

Gastric toxicity and mucosal ulceration induced by oxygen-derived reactive species: protection by melatonin

Uncontrolled hydrochloric acid secretion and ulceration of the stomach mucosa due to various factors are serious global problems. Although the mechanism of acid secretion from the parietal cell is now well understood, the processes involved in gastric ulceration are still not clear. Among various causes of gastric ulceration, lesions caused by stress, alcohol consumption, Helicobacter pylori infection and due to use of nonsteroidal antiinflammatory drugs have been shown to be mediated largely through the generation of reactive oxygen species, especially the hydroxyl radical. A number of excellent drugs have proven useful in controlling hyperacidity and ulceration but their long-term use is associated with disturbing side-effects. Hence, the search is still on to find a compound possessing antisecretory, antiulcer and antioxidant properties which will serve as a therapeutic agent to reduce gastric hyperacidity and ulcers. This article describes the role of reactive oxygen species in gastric ulceration, drugs controlling them with their merits and demerits and, the role of melatonin, a pineal secretory product, in protecting against gastric lesions. In experimental studies, melatonin has been shown to be effective in reducing mucosal breakdown and ulcer formation in a wide variety of situations. Additionally, the low toxicity of melatonin supports further investigation of this molecule as a gastroprotective agent. Finally, we include a commentary on how melatonin research with respect to gastric pathophysiology can move forward with a view of eventually using this indole as a therapeutic agent to control gastric ulceration in humans.

Melatonin protects against stress-induced gastric lesions by scavenging the hydroxyl radical

The antiulcer effect of melatonin on gastric lesions caused by restraint-cold stress or by indomethacin (IMN) was studied with the intent of determining the mechanism of action of the indole. Melatonin dose-dependently prevents both stress and IMN-induced gastric damage with around 90% inhibition at a dose of 60 mg per kg BW. When compared with already-marketed antiulcer drugs, such as ranitidine and omeprazole, melatonin was found to be more effective than ranitidine but less effective than omeprazole in preventing stress ulcer. When compared with other antioxidants, melatonin was more potent than glutathione and essentially equipotent to alpha-tocopherol in blocking stress-induced ulcer. As stress-induced gastric lesions are mainly caused by oxidative damage due to hydroxyl radicals (*OH), the effect of melatonin in scavenging the *OH generated during stress conditions, as well as in an in vitro model system, was studied. The results indicate that melatonin at the dose of 60 mg per kg BW caused an 88% reduction of endogenous *OH during stress. Melatonin was also highly effective in scavenging *OH generated in vitro by a Cu2+-ascorbate system. In this case, melatonin at 100 microM reduced *OH by 80%. Melatonin was also found to be a more potent radical scavenger than benzoate, a known *OH scavenger. The results indicate that melatonin prevents stress-induced gastric lesions by scavenging the endogenous *OH. As it also protects against IMN-induced gastric damage, it probably also offers gastroprotection by maintaining endogenous prostaglandin levels.

Hypothalamic hamartoma as a cause of precocious puberty in neurofibromatosis type 1: patient report

Precocious puberty resulting from hypothalamic hamartoma is well known. Neurofibromatosis type 1 can also present with precocious puberty. However, hypothalamic hamartoma as the cause of precocious puberty in patients with neurofibromatosis type 1 has never been described in the literature. This rare occurrence of these two together in a patient with precocious puberty is reported.

Dexamethasone makes the gastric mucosa susceptible to ulceration by inhibiting prostaglandin synthetase and peroxidase--two important gastroprotective enzymes

The plausible mechanism by which dexamethasone makes the gastric mucosa susceptible to ulceration has been studied. As acid aggravates ulcer, the role of dexamethasone on acid secretion was first investigated. Dexamethasone stimulates both basal and drug (mercaptomethylimidazole)-induced gastric acid secretion by 100 and 50% respectively in male Wister rats 24 h after intramuscular administration at the dose of 1 mg/kg body wt. This stimulated acid secretion is 93% blocked by cimetidine indicating increased liberation of histamine in the process. Pretreatment of dexamethasone before 24 h produces ulcer in 30% of the pylorus- ligated rats and aggravates the ulcer index by 82% in both pylorus and esophagus ligated rats. The incidence of ulceration in the latter cases is also increased by 25%. As mucosal prostaglandin synthetase and peroxidase play an important role in gastroprotection through biosynthesis of prostaglandin and by scavenging endogenous H2O2 respectively, the effect of dexamethasone on the activities of these gastroprotective enzymes were studied. Prostaglandin synthetase and peroxidase activities of the mucosa are significantly inhibited by 87 and 83% respectively by 24-h pretreatment with dexamethasone. The results indicate that dexamethasone makes the mucosa prone to ulceration by inhibiting the activity of prostaglandin synthetase to block the gastroprotective action of prostaglandin and also by inhibiting the peroxidase, thereby elevating the endogenous H2O2 level to generate more reactive hydroxyl radical responsible for the mucosal damage.

Study of portal hypertension in children with special reference to sclerotherapy

Portal Hypertension (PH) is the commonest cause of upper gastrointestinal bleeding in children. Most Indian studies have highlighted extrahepatic portal venous obstruction (EHPVO) as the major cause of PH in children. As there is paucity of data from the eastern part of the country we decided to study the major causes of PH in children in this region and to ascertain the efficacy of sclerotherapy for its management. Fifty children aged 14 months to 10 years with PH were studied from April 1990 to April 1995. Thorough examination and relevant investigations showed non-cirrhotic portal fibrosis (NCPF) in 24 (48%), EHPVO in 18 (36%) and cirrhosis of liver in 8 (16%) children. Forty six children had hematemesis and melaena of whom endoscopic sclerotherapy (EST) was done in 45 cases. One child having type 2 gastric varices was referred for surgery. Following eradication of varices the patients were followed-up at 3 monthly intervals. Number of sittings of sclerotherapy required for obliteration of varices was 5.9 +/- 1.6. A variceal state was achieved in 35 (78%) cases and varices were reduced to Grade I in 6 cases (13%). Two cases underwent surgery for EST failure. One patient of cirrhosis died within two weeks of bleeding episode due to hepatic encephalpathy. Rebleeding (13%) and recurrences (13%) were noted during the follow-up period. Retrosternal discomfort (22%), dysphagia (22%), stricture (13%), oesophageal ulceration (13%) and fever (11%) were the complications noted but these could be managed conservatively. The present study highlights that NCPF is an important cause of PH in eastern India. EST is useful in controlling variceal bleeding in children irrespective of their aetiology.

Parallel synthesis and screening of a solid phase carbohydrate library

A solid phase carbohydrate library was synthesized and screened against Bauhinia purpurea lectin. The library, which contains approximately 1300 di- and trisaccharides, was synthesized with chemical encoding on TentaGel resin so that each bead contained a single carbohydrate. Two ligands that bind more tightly to the lectin than Gal-beta-1,3-GalNAc (the known ligand) have been identified. The strategy outlined can be used to identify carbohydrate-based ligands for any receptor; however, because the derivatized beads mimic the polyvalent presentation of cell surface carbohydrates, the screen may prove especially valuable for discovering new compounds that bind to proteins participating in cell adhesion.