RNA interference tolerates 2'-fluoro modifications at the Argonaute2 cleavage site

Short interfering RNA (siRNA) molecules with good gene-silencing properties are needed for drug development based on RNA interference (RNAi). An initial step in RNAi is the activation of the RNA-induced silencing complex RISC, which requires degradation of the sense strand of the siRNA duplex. Although various chemical modifications have been introduced to the antisense strand, modifications to the Argonaute2 (Ago2) cleavage site in the sense strand have, so far, not been described in detail. In this work, novel 2'-F-purine modifications were introduced to siRNAs, and their biological efficacies were tested in cells stably expressing human tartrate-resistant acid phosphatase (TRACP). A validated siRNA that contains both purine and pyrimidine nucleotides at the putative Ago2 cleavage site was chemically modified to contain all possible combinations of 2'-fluorinated 2'-deoxypurines and/or 2'-deoxypyrimidines in the antisense and/or sense strands. The capacity of 2'-F-modified siRNAs to knock down their target mRNA and protein was studied, together with monitoring siRNA toxicity. All 2'-F-modified siRNAs resulted in target knockdown at nanomolar concentrations, despite their high thermal stability. These experiments provide the first evidence that RISC activation not only allows 2'-F modifications at the sense-strand cleavage site, but also increase the biological efficacy of modified siRNAs in vitro.     

Novel strategies for inhibition of bacterial biofilm in chronic rhinosinusitis

An important role has been recently reported for bacterial biofilm in the pathophysiology of chronic diseases, such as chronic rhinosinusitis (CRS). CRS, affecting sinonasal mucosa, is a persistent inflammatory condition with a high prevalence around the world. Although the exact pathological mechanism of this disease has not been elicited yet, biofilm formation is known to lead to a more significant symptom burden and major objective clinical indicators. The high prevalence of multidrug-resistant bacteria has severely restricted the application of antibiotics in recent years. Furthermore, systemic antibiotic therapy, on top of its insufficient concentration to eradicate bacteria in the sinonasal biofilm, often causes toxicity, antibiotic resistance, and an effect on the natural microbiota, in patients. Thus, coming up with alternative therapeutic options instead of systemic antibiotic therapy is emphasized in the treatment of bacterial biofilm in CRS patients. The use of topical antibiotic therapy and antibiotic eluting sinus stents that induce higher antibiotic concentration, and decrease side effects could be helpful. Besides, recent research recognized that various natural products, nitric oxide, and bacteriophage therapy, in addition to the hindered biofilm formation, could degrade the established bacterial biofilm. However, despite these improvements, new antibacterial agents and CRS biofilm interactions are complicated and need extensive research. Finally, most studies were performed in vitro, and more preclinical animal models and human studies are required to confirm the collected data. The present review is specifically discussing potential therapeutic strategies for the treatment of bacterial biofilm in CRS patients.     

Identification and characterization of carbapenem binding sites within the RND-transporter AcrB

Understanding the molecular determinants for recognition, binding and transport of antibiotics by multidrug efflux systems is important for basic research and useful for the design of more effective antimicrobial compounds. Imipenem and meropenem are two carbapenems whose antibacterial activity is known to be poorly and strongly affected by MexAB-OprM, the major efflux pump transporter in Pseudomonas aeruginosa. However, not much is known regarding recognition and transport of these compounds by AcrAB-TolC, which is the MexAB-OprM homologue in Escherichia coli and by definition the paradigm model for structural studies on efflux pumps. Prompted by this motivation, we unveiled the molecular details of the interaction of imipenem and meropenem with the transporter AcrB by combining computer simulations with biophysical experiments. Regarding the interaction with the two main substrate binding regions of AcrB, the so-called access and deep binding pockets, molecular dynamics simulations revealed imipenem to be more mobile than meropenem in the former, while comparable mobilities were observed in the latter. This result is in line with isothermal titration calorimetry, differential scanning experiments, and binding free energy calculations, indicating a higher affinity for meropenem than imipenem at the deep binding pocket, while both sharing similar affinities at the access pocket. Our findings rationalize how different physico-chemical properties of compounds reflect on their interactions with AcrB. As such, they constitute precious information to be exploited for the rational design of antibiotics able to evade efflux pumps.     

Mechanisms by which resistant starches and non-starch polysaccharide sources affect the metabolism and disposition of the food carcinogen, 2-amino-3-methylimidazo[4,5-f]quinoline

Although both non-starch polysaccharides (NSP) and resistant starches (RS) are included in current definitions of dietary fibre, our previous work has suggested fundamental differences in the way in which these two classes of material affect the disposition and absorption of a dietary carcinogen. The present studies explore whether different effects on carcinogen metabolism could play a role in the contrasting patterns seen previously. Groups of female Wistar rats were pre-fed for 4 weeks one of five types of defined diet (AIN-76). The control diet contained 35% maize starch and no dietary fibre. The RS-containing diets had all the maize starch substituted with either Hi-maize or potato starch. In the NSP-containing diets, 10% of the maize starch was substituted with dietary fibre in the form of either lignified plant cell walls (wheat straw) or soluble dietary fibre (apple pectin). Pre-fed rats were gavaged with the food carcinogen, [2-14C] 2-amino-3-methylimidazo[4,5-f]quinoline (IQ), and plasma and urinary metabolites characterized using HPLC at various time intervals after administration. After 4 h gavage, plasma from rats on both RS-containing diets contained significantly higher levels of intact IQ and lower levels of the major metabolites, IQ-5-O-glucuronide and IQ-5-sulfate, as compared with plasma from the negative control group at this time. In contrast, plasma from animals on the NSP-containing wheat straw diet (and to a lesser extent the apple pectin diet) showed significantly lower levels of intact IQ, and significantly higher levels of the two major metabolites, as compared with those from the control rats. These different metabolite profiles were also reflected in different urinary excretion profiles. Urine from rats pre-fed RS-containing diets revealed significantly slower metabolite excretion as compared with urine from rats that had been given the NSP-containing diets. Western blotting methodologies also profiled differences between the effects of these two types of dietary fibre in the expression of xenobiotic metabolizing enzymes. We conclude that changes in activity and expression of xenobiotic metabolising enzymes could play a role in the contrasting effects of these two types of dietary fibre on carcinogen uptake and disposition.     

红豆杉抗苯丙氨酸细胞系的筛选及悬浮培养特性

通过胁迫筛选法筛选红豆杉抗－苯丙氨酸细胞变异系,并比较了该细胞系与同步培养的原型细胞系悬浮培养的几项生理指标,结果表明,抗苯丙氨酸细胞系的紫杉醇含量显著高于原型细胞系的3－5倍,并且抗性细胞系的生长速率,细胞活性,pH值,胞内可溶性糖含量及褐变强度均与原型细胞系存在显著差别。     

Circumvention of multidrug resistance and reduction of cardiotoxicity of doxorubicin in vivo by coupling it with low density lipoprotein

Doxorubicin (Dox) was coupled into human low density lipoprotein (LDL) to form a complex LDL-Dox. In in vitro studies, the accumulation of LDL-Dox in human resistant hepatoma (R-HepG2) cells was found to be higher than that of free Dox in the cells, resulting in an increase of the cytotoxic effect on the cells. Moreover, in in vivo studies, under the same dosage of drugs (1 mg/kg), the anti-proliferative effect on the tumor cells of LDL-Dox in nude mice bearing R-HepG2 cells was higher than that of free Dox as evidenced by the larger reduction in tumor volumes and tumor weights in LDL-Dox treated group. Histological studies showed that LDL-Dox treatment did not cause any heart damage when compared with the control group. In contrast, Dox treatment caused disruption and vacuolization of myocardial filament. Plasma lactate dehydrogenase activity and plasma creatine kinase activity in nude mice bearing R-HepG2 cells were found to be elevated in the Dox-treated group but remained unchanged in LDL-Dox-treated group. The present studies indicate that when Dox is coupled with LDL, the multidrug resistance can be circumvented and the cardiotoxicity can be reduced.     

Raw potato starch and short-chain fructo-oligosaccharides affect the composition and metabolic activity of rat intestinal microbiota differently depending on the caecocolonic segment involved

AIMS: In vitro studies have suggested that fructo-oligosaccharides (FOS) and resistant starch (two fermentable non-digestible carbohydrates) display different fermentation kinetics. This study investigated whether these substrates affect the metabolic activity and bacterial composition of the intestinal microflora differently depending on the caecocolonic segment involved. METHODS AND RESULTS: Eighteen rats were fed a low-fibre diet (Basal) or the same diet containing raw potato starch (RPS) (9%) or short-chain FOS (9%) for 14 days. Changes in wet-content weights, bacterial populations and metabolites were investigated in the caecum, proximal and distal colon and faeces. Both substrates exerted a prebiotic effect compared with the Basal diet. However, FOS increased lactic acid-producing bacteria (LAPB) throughout the caecocolon and in faeces, whereas the effect of RPS was limited to the caecum and proximal colon. As compared with RPS, FOS doubled the pool of caecal fermentation products, while the situation was just the opposite distally. This difference was mainly because of the anatomical distribution of lactate, which accumulated in the caecum with FOS and in the distal colon with RPS. Faeces reflected these impacts only partly, showing the prebiotic effect of FOS and the metabolite increase induced by RPS. CONCLUSIONS: This study demonstrates that FOS and RPS exert complementary caecocolonic effects. SIGNIFICANCE AND IMPACT OF THE STUDY: The RPS and FOS combined ingestion could be beneficial by providing health-promoting effects throughout the caecocolon.     

Effects of tungstosilicate on strains of methicillin-resistant Staphylococcus aureus with unique resistant mechanisms

In a previous study, it was found that polyoxotungstates such as undecatungstosilicate (SiW11) greatly sensitized strains of methicillin-resistant Staphylococcus aureus (MRSA) to beta-lactams. In this report, the effects of SiW11 on several MRSA strains with unique resistant mechanisms were studied. SiW11 was still effective to MRSA mutants with higher beta-lactam resistance due to reduced cell-lytic activity. Since the antimicrobial effect of TOC-39 (a cephem antibiotic with strong affinity to penicillin-binding protein (PBP) 2') was not strongly enhanced in any case, it was confirmed that the sensitizing effect of SiW11 is due to reduced expression of PBP2'. However, the sensitizing effect of SiW11 was relatively weak in MRSA strains with lowered susceptibility to glycopeptide antibiotics. A certain resistant mechanism other than the mecA-PBP2' system worked in such a strain. Interestingly, an MRSA mutant with the Eagle-type resistance was dramatically sensitized. This result suggests that SiW11 has another site of action besides reducing the expression of PBP2'.     

Public transport as a reservoir of methicillin‐resistant staphylococci

Aims: The aim of this study was to explore the occurrence of methicillin‐resistant staphylococci in a large urban public transport system. Methods and Results: Samples were taken from hand rails, which passengers hold onto when they are standing. In total, 1400 swabs taken from 55 vehicles (trolleybuses, trams and buses) were examined. As many as 30·1% samples were positive for the presence of methicillin‐resistant coagulase‐negative staphylococci (MRCoNS), but none for methicillin‐resistant Staphylococcus aureus (MRSA). MRCoNS were isolated from all 55 vehicles. Nearly 50% of MRCoNS isolates displayed resistance not only to beta‐lactams, but at least to two or more other classes of antimicrobials as well. Conclusions: This study demonstrated widespread occurrence of MRCoNS on hand rails in public transport vehicles. MRSA was not detected. Significance and Impact of the Study: The recovery of methicillin‐resistant staphylococci from public transport system implies a potential risk for transmission of these bacteria in an out‐hospital environment.