PTP1B inhibitors: synthesis and evaluation of difluoro-methylenephosphonate bioisosteres on a sulfonamide scaffold

We have synthesized and evaluated a series of triaryl sulfonamide-based PTP1B inhibitors in which a difluoro-methylenephosphonate group of a potent lead has been replaced by potential bioisosteric replacements. Several mono- or di-charged compounds (8a, 8b, and 15a) were shown exhibit inhibitory activity in the low micromolar range, demonstrating the feasibility of using this approach in identifying non-phosphonate pTyr mimetics in a small molecular scaffold. These results also provide a useful indication of the relative effectiveness of these pTyr mimetics.     

Antihyperglycaemic activity of aqueous extract of Embelia ribes Burm in streptozotocin-induced diabetic rats

Forty days of orally feeding the aqueous E. ribes extract (100 and 200 mg/kg) to streptozotocin (40 mg/kg, iv, single dose) induced diabetic rats produced significant decrease in heart rate, systolic blood pressure, blood glucose, blood glycosylated hemoglobin, serum lactate dehydrogenase, creatine kinase and increase in blood glutathione levels as compared to pathogenic diabetic rats. Further, the extract significantly decreased the levels of pancreatic lipid peroxides and increased the levels of pancreatic superoxide dismutase, catalase and glutathione. The results suggest that aqueous E. ribes extract exhibits a significant blood glucose and blood pressure lowering potential. Further, it enhances endogenous antioxidant defense against free radicals produced under hyperglycaemic conditions, thereby, seemingly protects the pancreatic beta-cells against loss in streptozotocin induced diabetic rats.     

Catecholaminergic microcircuitry controlling the output of airway-related vagal preganglionic neurons.

In this study, we have investigated the ultrastructure and function of the catecholaminergic circuitry modulating the output of airway-related vagal preganglionic neurons (AVPNs) in ferrets. Immunoelectron microscopy was employed to characterize the nature of catecholaminergic innervation of AVPN at the ultrastructural level. In addition, immunofluorescence was used to examine the expression of the alpha(2A)-adrenergic receptor (alpha(2A)-AR) on AVPNs, and norepinephrine release within the rostral nucleus ambiguous (rNA) was measured by using microdialysis. Physiological experiments were performed to determine the effects of stimulation of the noradrenergic locus coeruleus (LC) cell group on airway smooth muscle tone. The results showed that 1) catecholaminergic nerve endings terminate in the vicinity of identified AVPNs but very rarely form axosomatic or axodendritic synapses with the AVPNs that innervate the extrathoracic trachea; 2) AVPNs express the alpha(2A)-AR; 3) LC stimulation-induced norepinephrine release within the rNA region was associated with airway smooth muscle relaxation; and 4) blockade of alpha(2A)-AR on AVPNs diminished the inhibitory effects of LC stimulation on airway smooth muscle tone. It is concluded that a noradrenergic circuit originating within the LC is involved in the regulation of AVPN activity within the rNA, and stimulation of the LC dilates the airways by the release of norepinephrine and activation of alpha(2A)-AR expressed by AVPNs, mainly via volume transmission.     

Cross Talk between Receptor Guanylyl Cyclase C and c-src Tyrosine Kinase Regulates Colon Cancer Cell Cytostasis

Increased activation of c-src seen in colorectal cancer is an indicator of a poor clinical prognosis, suggesting that identification of downstream effectors of c-src may lead to new avenues of therapy. Guanylyl cyclase C (GC-C) is a receptor for the gastrointestinal hormones guanylin and uroguanylin and the bacterial heat-stable enterotoxin. Though activation of GC-C by its ligands elevates intracellular cyclic GMP (cGMP) levels and inhibits cell proliferation, its persistent expression in colorectal carcinomas and occult metastases makes it a marker for malignancy. We show here that GC-C is a substrate for inhibitory phosphorylation by c-src, resulting in reduced ligand-mediated cGMP production. Consequently, active c-src in colonic cells can overcome GC-C-mediated control of the cell cycle. Furthermore, docking of the c-src SH2 domain to phosphorylated GC-C results in colocalization and further activation of c-src. We therefore propose a novel feed-forward mechanism of activation of c-src that is induced by cross talk between a receptor GC and a tyrosine kinase. Our findings have important implications in understanding the molecular mechanisms involved in the progression and treatment of colorectal cancer.Colorectal carcinoma is one of the most common forms of cancer seen in the developed world (10). The incidence in developing countries appears to be somewhat lower, but with high rates of mortality similar to those seen in developed countries (43). Treatment usually involves surgery or palliative chemotherapy, and recent research focuses on investigating molecular signatures associated with colorectal tumorigenesis as well as means of early detection in order to avoid high and rapid fatalities (61). Increased activity and expression of the tyrosine kinase c-src is frequently seen in colorectal cancer (5, 12), and activation of c-src in early stages of neoplastic transformation (32) is an indicator of a poor clinical prognosis (26). In general, c-src activity is as much as 16-fold higher in cancerous cells than in the adjacent colonic mucosa (12). Information on potential molecular mechanisms for the role of c-src in colonic tumorigenesis includes evidence that c-src activity increases during mitosis of human colon carcinoma cells (39), and increased c-src activity promotes cell motility and invasion during intestinal cell migration (34).A large number of substrates for c-src have been identified in different cell types, and a consensus site for tyrosine phosphorylation by c-src has been defined (50). Prediction of these sites in proteins present in colorectal carcinoma cells may assist in identifying novel targets for c-src action. The modular structure of c-src and other members of the src family kinases (SFKs), consisting of the SH4, unique, SH3, SH2, and kinase domains, allows these kinases to interact with a diverse group of proteins, creating a highly complex signal transduction network (48, 52). Consequently, SFKs have been demonstrated to be key downstream elements in signaling pathways emerging from cell surface receptors (52).Guanylyl cyclase C (GC-C) plays an important role in maintaining fluid ion homeostasis (54) and genomic integrity in intestinal cells (29) and serves as the receptor for the diarrheagenic heat-stable enterotoxin (ST) as well as endogenous ligands guanylin and uroguanylin (57). Binding of ST to the receptor leads to increased intracellular cyclic GMP (cGMP) accumulation and activation of the cystic fibrosis transmembrane conductance regulator, resulting in fluid and ion efflux that manifests as traveler''s diarrhea (45, 54). Recently it has been noted that regions of the world with the highest incidence of enterotoxigenic Escherichia coli-associated diarrhea exhibit the lowest incidence of colon cancer (43). In this context, studies have shown that activation of GC-C by its ligands inhibits human colonic cell proliferation and adenoma formation in mice, demonstrating a critical role for GC-C in inhibiting colon cancer initiation and progression (29, 33). For example, uroguanylin treatment suppresses polyp formation in the Apc(Min/+) mouse and induces apoptosis in human colon carcinoma cells via cGMP produced by GC-C (46). Interestingly, expression of the endogenous paracrine hormones for GC-C, guanylin and uroguanylin, is lost at the initiation of transformation, and therefore this reduced signaling via GC-C may allow cells to proliferate more rapidly, thereby leading to carcinogenesis (14).Expression of GC-C is largely restricted to the luminal side of intestinal cells in humans, and consequently, monitoring GC-C expression in circulating tumor cells in the peripheral blood of patients has been suggested to be a good marker for early detection of the primary tumor and/or metastasis of colon cancer (11, 28, 36). The molecular mechanisms by which GC-C activity is regulated during the initiation and progression of carcinogenesis remain undefined, and studies to investigate whether signaling events prevalent in colorectal cancer can modulate GC-C function have not been performed. Human colorectal carcinoma cell lines express GC-C and can therefore be used to study these molecular aspects of GC-C regulation and downstream signaling events (3, 4, 22).Phosphorylation is a rapid and reversible form of covalent modification frequently found in signaling systems. In our earlier studies, we have coexpressed domains of GC-C with the tyrosine kinase EphB1/Elk and observed tyrosine phosphorylation of GC-C (7). We report here that GC-C is a substrate for c-src tyrosine kinase and identify Tyr820 as the site for phosphorylation in GC-C. Following phosphorylation, pTyr820 serves as a site for interaction with the SH2 domain of c-src, resulting in further activation of c-src. Most importantly, tyrosine phosphorylation of GC-C inhibits cGMP production and prevents the cytostatic effects of GC-C induced by ligand interaction. Our studies therefore show the existence of a new signal transduction cross talk between c-src and GC-C in colonic cells, resulting in a feed-forward mechanism to further activate c-src, with important implications in cancer cell proliferation and disease progression.     

Aryloxy cyclohexyl imidazoles: A novel class of antileishmanial agents

Thirteen novel aryloxy cyclohexane-based mono and bis imidazoles were synthesized and evaluated in vitro as antileishmanials against Leishmania donovani and cytotoxicity assessed. These compounds were better than the existing drugs, sodium stibogluconate and pentamidine in respect to IC₅₀ and SI values. Promising compounds were tested further in vivo. Among all, the bis methylimidazole with 2-fluoro, 4-nitro aryloxy group (9) exhibited significant in vivo inhibition of 77.9%, thus providing new structural lead for antileishmanials.     

Identification of the dipeptidyl aminopeptidase responsible for N-terminal clipping of recombinant Exendin-4 precursor expressed in Pichia pastoris

Exendin-4 is a naturally occurring 39 amino acid peptide that is useful for the control of Type 2 diabetes. Recombinant Exendin-4, with an extra glycine at the carboxy-terminus (Exdgly), was expressed in the methylotropic yeast Pichia pastoris. A high proportion of the Exdgly molecules secreted into medium were found to be clipped, lacking the first two amino acids (His–Gly) from the N-terminus. Disruption of the P. pastoris homolog of the Saccharomyces cerevisiae dipeptidyl aminopeptidase (STE13) gene in Pichia genome resulted in a clone that expressed N-terminally intact Exdgly. Elimination of N-terminal clipping enhanced the yield and simplified the purification of Exdgly from P. pastoris culture supernatant.     

Treatment of spentwash using chemically modified bagasse and colour removal studies

Studies were carried out on derivatisation of bagasse into an ion exchange material and application of this chemically modified bagasse in the treatment of distillery wastewater. It was found that CHPTAC bagasse with HCl treatment and DEAE-bagasse in its free base form were most effective in colour removal and the mechanism of colour removal indicated significant contribution of both, the conventional ion exchange and the chemical sorption.     

Synthesis and appetite suppressant activity of 1-aryloxy-2-substituted aminomethyltetrahydronaphthalenes as conformationally rigid analogues of fluoxetine

Several 1-aryloxy-2-substituted aminomethyltetrahydronaphthalenes (7-21) as conformationally rigid analogues of fluoxetine were synthesized and evaluated for their anorexigenic and antidepressant activities. For SAR studies the related acyclic analogues (22-27) were also prepared. Out of the 21 synthesized compounds, 10 compounds (9, 10, 11, 15, 16, 18, 21, 22, 23 and 27) exhibited significant anorexigenic activity (at 75 micromol/kg). Interestingly, all the compounds (7-20, 22-26) were devoid of antidepressant effect, except for compounds 21 and 27 in which the antidepressant activity was retained. Compound 16 emerged as the most active compound of the series with better anorexigenic activity (97.92%) compared to fluoxetine (76.25%) and even with a clinically used drug sibutramine, thus providing a new structural lead for appetite suppressants.     

Biofilm and metallo beta-lactamase production among the strains of <Emphasis Type="Italic">Pseudomonas aeruginosa</Emphasis> and <Emphasis Type="Italic">Acinetobacter</Emphasis> spp. at a Tertiary Care Hospital in Kathmandu,Nepal

Introduction

Pseudomonas aeruginosa and Acinetobacter spp. are found to be associated with biofilm and metallo-β-lactamase production and are the common causes of serious infections mainly in hospitalized patients. So, the main aims of this study were to determine the rates of biofilm production and metallo beta-lactamase production (MBL) among the strains of Pseudomonas aeruginosa and Acinetobacter spp. isolated from hospitalized patients.

Methods

A total of 85 P. aeruginosa isolates and 50 Acinetobacter spp. isolates isolated from different clinical specimens from patients admitted to Shree Birendra Hospital, Kathmandu, Nepal from July 2013 to May 2014 were included in this study. The bacterial isolates were identified with the help of biochemical tests. Modified Kirby-Bauer disc diffusion technique was used for antimicrobial susceptibility testing. Combined disc diffusion technique was used for the detection of MBL production, while Congo red agar method and tube adherence method were used for detection of biofilm production.

Results

Around 16.4% of P. aeruginosa isolates and 22% of the strains of Acinetobacter spp. were metallo β-lactamase producers. Out of 85 P. aeruginosa isolates, 23 (27.05%) were biofilm producers according to tube adherence test while, only 13 (15.29%) were biofilm producers as per Congo red agar method. Similarly, out of 50 Acinetobacter spp. 7 (14%) isolates were biofilm producers on the basis of tube adherence test, while only 5 (10%) were positive for biofilm production by Congo red agar method. Highest rates of susceptibility of P. aeruginosa as well as Acinetobacter spp. were seen toward colistin.

Conclusion

In our study, biofilm production and metallo beta-lactamase production were observed among Pseudomonas aeruginosa and Acinetobacter spp. However, no statistically significant association could be established between biofilm production and metallo beta-lactamase production.