Simple liquid chromatography method for the quantification of irinotecan and SN38 in sheep plasma: Application to in vivo pharmacokinetics after pulmonary artery chemoembolization using drug eluting beads

A rapid and simple liquid chromatography–fluorescence detection (LC–FD) method was developed and validated for the simultaneous quantification of irinotecan (CPT11) and SN38 in sheep plasma. Camptothecin (CPT) was used as the internal standard. A single step protein precipitation with acetonitrile was used for sample preparation. The separation was achieved using a 5 μm C18 column (250 mm × 4.5 mm, 5 μm) with a mobile phase composed of 36 mM sodium dihydrogen phosphate dehydrate and 4 mM sodium 1 heptane sulfonate–acetonitrile (72:28), the pH of the mobile phase was adjusted to 3. The flow rate was 1.45 mL/min and the fluorescence detection was operated at 355/515 nm (excitation/emission wavelengths). The run time was 13 min. The method was validated with respect to selectivity, extraction recovery, linearity, intra- and inter-day precision and accuracy, limit of quantification and stability. The method has a limit of quantification of 5 ng/mL for both CPT11 and SN38. The assay was linear over concentrations ranging from 5 to 5000 ng/mL and to 240 ng/mL for CPT11 and SN38, respectively. This method was used successfully to perform plasma pharmacokinetic studies of CPT11 after pulmonary artery embolization (PACE) in a sheep model. It was also validated for CPT11 and SN38 analysis in sheep lymph and human plasma.     

Ecdysteroid Titres and Cuticle Depositions in Embryos of the Dipteran Calliphora erythrocephala

Summary

Before the shortening of the germ band, embryos of Calliphora erythrocephala secrete an electron dense layer which resembles a thin atypical cuticle. After completion of the dorsal closure, a second, typical, cuticle is deposited. It is characterized by a thick procuticle and by the presence of hooked setae. This cuticle develops into the larval cuticle of the first instar.

We did not find in newly-laid eggs of Calliphora detectable amounts of either free or hydrolysable conjugated ecdysteroids. A marked rise in ecdysteroid concentrations, essentially attributable to free ecdysone and 20- hydroxyecdysone, occurs shortly before the deposition of the typical cuticle. After a transient decrease, the ecdysteroid titre rises again before hatching.

When eggs are mid-ligatured at blastula or early gastrula stages, the posterior embryonic half is able to build up a typical cuticle with hooked setae. This cuticulogenesis is therefore not dependent on the presence of the embryonic ring glands.     

Phosphorylation controls the interaction of the connexin43 C-terminal domain with tubulin and microtubules

Connexins are structurally related transmembrane proteins that assemble to form gap junction channels involved in the mediation of intercellular communication. It has been shown that the intracellular tail of connexin43 (Cx43) interacts with tubulin and microtubules with putative impacts on its own intracellular trafficking, its activity in channel communication, and its interference with specific growth factor signal transduction cascades. We demonstrate here that the microtubule binding of Cx43 is mainly driven by a short region of 26 amino acid residues located within the intracellular tail of Cx43. The nuclear magnetic resonance structural analysis of a peptide (K26D) corresponding to this region shows that this peptide is unstructured when free in solution and adopts a helix conformation upon binding with tubulin. In addition, the resulting K26D-tubulin molecular complex defines a new structural organization that could be shared by other microtubule partners. Interestingly, the K26D-tubulin interaction is prevented by the phosphorylation of K26D at a src kinase specific site. Altogether, the results elucidate the mechanism of the interaction of Cx43 with the microtubule cytoskeleton and propose a pathway for understanding the microtubule-dependent regulation of Cx43 gap junctional communications and the involvement of Cx43 in TGF-β signal transduction.     

Optimization of culture conditions for the production of Pleuromutilin from Pleurotus Mutilus using a hybrid method based on central composite design, neural network, and particle swarm optimization

This study aims at optimizing the culture conditions (agitation speed, temperature and pH) of the Pleuromutilin production by Pleurotus mutilus. A hybrid methodology including a central composite design (CCD), an artificial neural network (ANN), and a particle swarm optimization algorithm (PSO) was used. Specifically, the CCD and ANN were used for conducting experiments and modeling the non-linear process, respectively. The PSO was used for two purposes: Replacing the standard back propagation in training the ANN (PSONN) and optimizing the process. In comparison to the response surface methodology (RSM) and to the Bayesian regularization neural network (BRNN), PSONN model has shown the highest modeling ability. Under this hybrid approach (PSONN-PSO), the optimum levels of culture conditions were: 242 rpm agitation speed; temperature 26.88 and pH 6.06. A production of 10,074 ± 500 ??g/g, which was in very good agreement with the prediction (10,149 ??g/g), was observed in verification experiment. The hybrid PSONN-PSO gave a yield of 27.5% greater than that obtained by the hybrid BRNN-PSO. This work shows that the combination of PSONN with the generic PSO algorithm has a good predictability and a good accuracy for bio-process optimization. This hybrid approach is sufficiently general and thus can be helpful for modeling and optimization of other industrial bio-processes.     

RNase L mediates transient control of the interferon response through modulation of the double-stranded RNA-dependent protein kinase PKR

The transient control of diverse biological responses that occurs in response to varied forms of stress is often a highly regulated process. During the interferon (IFN) response, translational repression due to phosphorylation of eukaryotic initiation factor 2alpha, eIF2alpha, by the double-stranded RNA-dependent protein kinase, PKR, constitutes a means of inhibiting viral replication. Here we show that the transient nature of the IFN response against acute viral infections is regulated, at least in part, by RNase L. During the IFN antiviral response in RNase L-null cells, PKR mRNA stability was enhanced, PKR induction was increased, and the phosphorylated form of eIF2alpha appeared with extended kinetics compared with similarly treated wild type cells. An enhanced IFN response in RNase L-null cells was also demonstrated by monitoring inhibition of viral protein synthesis. Furthermore, ectopic expression of RNase L from a plasmid vector prevented the IFN induction of PKR. These results suggest a role for RNase L in the transient control of the IFN response and possibly of other cytokine and stress responses.     

FrzS acts as a polar beacon to recruit SgmX,a central activator of type IV pili during Myxococcus xanthus motility

In rod‐shaped bacteria, type IV pili (Tfp) promote twitching motility by assembling and retracting at the cell pole. In Myxococcus xanthus, a bacterium that moves in highly coordinated cell groups, Tfp are activated by a polar activator protein, SgmX. However, while it is known that the Ras‐like protein MglA is required for unipolar targeting, how SgmX accesses the cell pole to activate Tfp is unknown. Here, we demonstrate that a polar beacon protein, FrzS, recruits SgmX at the cell pole. We identified two main functional domains, including a Tfp‐activating domain and a polar‐binding domain. Within the latter, we show that the direct binding of MglA‐GTP unveils a hidden motif that binds directly to the FrzS N‐terminal response regulator (CheY). Structural analyses reveal that this binding occurs through a novel binding interface for response regulator domains. In conclusion, the findings unveil the protein interaction network leading to the spatial activation of Tfp at the cell pole. This tripartite system is at the root of complex collective behaviours in this predatory bacterium.     

Effects of oxidative and nitrosative stress on Tetrahymena pyriformis glyceraldehyde-3-phosphate dehydrogenase

Previous reports showed that hydrogen peroxide and the NO-generating reagent sodium nitroprusside (SNP)-modulated enzymatic activity of animal glyceraldehyde-3-phosphate dehydrogenase (GAPDH, EC 1.2.1.12). These modifications are suggested to have a physiological regulatory role. To gain further insight into this regulatory process the model ciliated protozoan Tetrahymena pyriformis was chosen. Both reagents inhibited growth of T. pyriformis cultures and produced a specific increase of GAPDH protein but only NO seemed to reduce GAPDH activity in cell-free extracts. Both specific activity and pI were found to be altered in the in vivo NO-treated purified enzyme, but no effect was detected by the in vivo H(2)O(2) treatment. Analytical chromatofocusing showed a single basic isoform (pI 8.8) in enzyme preparations from control and H(2)O(2)-treated cells. In contrast to this, three more acidic isoforms (pIs, 8.6, 8.0 and 7.3) were resolved in purified fractions from SNP-treated cells, suggesting post-translational modification of the enzyme by NO. Nevertheless, a decrease of GAPDH activity by H(2)O(2) and NO, mainly due to a decrease in its V(max) without apparent change in substrate affinity, was observed in vitro in the whole enzyme population. The increase of GAPDH protein level found in vivo suggests a cell response in order to compensate for the inhibitory effect on activity observed in the purified enzyme. This is the first report of NO- and H(2)O(2)-dependent effects on GAPDH of T. pyriformis, and identifies this key protein of central carbon metabolism as a physiological target of oxidative and nitrosative stress in this ciliated protozoan.     

Production of ethanol from starch by free and immobilized Candida tropicalis in the presence of alpha-amylase

Candida tropicalis is a potentially useful organism for the commercial production of ethanol as it is capable of fermenting starch at a low rate. To enhance this carbon source utilization and increase the rate of alcohol production, we pretreated corn soluble starch with alpha-amylase. Starch liquefaction was sufficient to drive the fermentation and to convert 96% substrate to ethanol. Indeed, in the presence of exogenous alpha-amylase, 9% (w/v) soluble starch was converted to 43.1g ethanol/l in 65 h with a productivity of 0.65 g/l h. Thus, bio-ethanol production using free and calcium alginate-immobilized C. tropicalis does not require the saccharification step. Furthermore, fed-batch fermentation by free C. tropicalis cells increased the final concentration to 56 g ethanol/l, reaching published values for Saccharomyces cerevisiae recombinant strains expressing both alpha-amylase and glucoamylase.