Two adaptation processes in auditory hair cells together can provide an active amplifier

The hair cells of the vertebrate inner ear convert mechanical stimuli to electrical signals. Two adaptation mechanisms are known to modify the ionic current flowing through the transduction channels of the hair bundles: a rapid process involves calcium ions binding to the channels; and a slower adaptation is associated with the movement of myosin motors. We present a mathematical model of the hair cell which demonstrates that the combination of these two mechanisms can produce `self-tuned critical oscillations', i.e. maintain the hair bundle at the threshold of an oscillatory instability. The characteristic frequency depends on the geometry of the bundle and on the calcium dynamics, but is independent of channel kinetics. Poised on the verge of vibrating, the hair bundle acts as an active amplifier. However, if the hair cell is sufficiently perturbed, other dynamical regimes can occur. These include slow relaxation oscillations which resemble the hair bundle motion observed in some experimental preparations.Comment: 13 pages, 6 figures,REVTeX 4, To appear in Biophysical Journa

Soluplus solutions as thermothickening materials for topical drug delivery.

Soluplus is a pharmaceutical excipient used primarily in the manufacture of solid dispersions. The polymer also exhibits interesting rheology in aqueous solution, increasing in viscosity as the solution is warmed. This material could have application topical drug delivery to sites including the skin, vagina, rectum or nasal mucosa, where the increase in viscosity allows for improved retention. However, there exists very little information surrounding this “thermothickening” phenomenon and the effect of solution composition on temperature-dependent rheology. In this study, the effect of soluplus concentration, salt inclusion, ethanol addition, and pH on temperature-dependent rheology was measured. The rheology of the solutions was unaffected by pH over the range tolerated by the skin (pH 4–7), but the inclusion of ethanol rapidly negated the thermothickening effect. “Salting out” of the solutions resulted in a depression of gelation temperatures, and an increase in both storage and loss moduli of the solutions. 30% (w/v) soluplus in 1 M NaCl or KCl was identified as a potential thermothickening agent for topical drug delivery.Peer reviewe

Multi-responsive microencapsulated nanogels for the oral delivery of small interfering RNA

Multi-responsive, anionic poly(methacrylic acid-co-N-vinyl-2-pyrrolidone) microscale hydrogels (microgels) encapsulating polycationic nanoscale hydrogels (nanogels) were synthesized with either degradable or nondegradable crosslinks. The pH-responsive volume phase transition of these formulations was consistent with the pH transition experienced during intestinal delivery, as the hydrogels swelled at pH values greater than pH 5. The physicochemical characteristics of the nondegradable formulations were evaluated by microscopy, potentiometric titration, Fourier transform infrared spectroscopy, and thermal gravimetric analysis. The nondegradable formulations successfully loaded and released a model protein in physiological buffers, but the ability of the microgels to release the nanogels upon exposure to intestinal conditions was inadequate. Therefore, microgels containing enzyme-degradable oligopeptide crosslinks were synthesized then characterized using Fourier transform infrared spectroscopy, electron microscopy, confocal microscopy, and ImageStream flow cytometry. Degradation of the microgels upon incubation in trypsin solutions, simulated gastric fluid, or simulated intestinal fluid was evaluated by measuring the change in relative turbidity over time. Microgels were degraded specifically by the enzyme trypsin, and the rate of degradation was dependent upon the microgel to trypsin concentration ratio; for all ratios tested, degradation was complete within 4 hours. The cytocompatibility of the enzyme-degraded microgels encapsulating nanogels was evaluated in both a human and a murine cell line; at microgel concentrations less than 0.4 mg/ml the cell viability was greater than 90%. Confocal microscopy was used to obtain Z-stack images of the cells following incubation with the microgels, confirming that nanogels were released from the degraded microgels and subsequently inteRNAlized by RAW 264.7 murine macrophage cells. The microencapsulated nanogels were able to load siRNA via electrostatic complexation with loading efficiencies ranging from 60-80%. Incubation of loaded microgels in simulated intestinal fluid with reduced trypsin concentrations or in rat intestinal fluid resulted in successful degradation of the microgel matrix and release of a detectable amount of viable siRNA. The degraded microgels with nanogels transfected the two different cell lines with up to 20% silencing efficiency. Though the knockdown efficiency is not as high as that of nanogels alone, the microgel results are consistent and reproducible across two cell lines.Chemical Engineerin

A pH-responsive amphiphilic hydrogel based on pseudopeptides and poly(ethylene glycol) for oral delivery of hydrophobic drugs

Oral administration is a noninvasive and convenient drug delivery route most preferred by patients. However, poor stability in the gastrointestinal tract and low bioavailability of hydrophobic drugs has greatly limited their oral administration. To address this problem, we report a pH-responsive, amphiphilic hydrogel drug carrier based on a pseudopeptide poly(l-lysine isophthalamide) (PLP) and poly(ethylene glycol) (PEG). The hydrogels were prepared by a simple N-(3-(dimethylamino)propyl)-N′-ethyl carbodiimide hydrochloride (EDC)/N-hydroxysuccinimide (NHS) coupling reaction, and the cross-linking was confirmed by infrared spectroscopy and differential scanning calorimetry analyses. Because of the pH-responsive conformational alteration of PLP, the hydrogels were relatively hydrophobic and collapsed at acidic pH, but became hydrophilic and swollen at neutral pH. The amphiphilicity enabled the hydrogels to well retain and protect hydrophobic model drugs in the simulated gastric fluid, but efficiently release them in the simulated intestinal fluid. These results suggested that the pH-responsive amphiphilic hydrogels are promising candidates for oral delivery of hydrophobic drugs

Synthesis and characterisation of stimuli-responsive amino acid-based polymeric materials for drug delivery

The delivery of cell-targeted therapeutics, particularly macrodrugs such as proteins and nucleic acids, is of great importance for modern therapy. However, there are many different barriers in the complex bio-environment, which significantly limit the drug availability and efficacy. Herein, this thesis presents the work on development of smart amino acid-based polymeric materials for drug delivery. Specifically, drug delivery vehicles at different length scales with different stimuli-responsive behaviour have been systematically investigated. A library of anionic, cell penetrating peptide-mimicking, lysine-based hyperbranched polymers have been developed for intracellular drug delivery. Results showed that these polymers destabilised membranes significantly at late endosomal pH, but remained non-lytic at physiological pH. The multivalency effect of the hyperbranched structure further effectively promoted the membrane interactions. Further investigation into endosomal release showed that the hyperbranched polymers could facilitate intracellular payload delivery in Hela cells. A series of amphiphilic hydrogels have been developed for oral drug delivery. The effects of crosslinking ratio, solid contents and molecular weights of crosslinkers on hydrogels’ behaviour were investigated. Also, the in vitro model drug loading and release was evaluated. Results suggested that hydrophobic payloads could be successfully incorporated into the hydrogels, and the release in biorelevant buffers was triggered by pH stimulus. Furthermore, by using disulfide-bond containing crosslinkers, the hydrogels responded to the redox trigger in the colon, which led to a faster and more efficient release. For intracellular drug delivery via an oral route, nanogels were prepared using membrane-active polymers by either physical or chemical crosslinking. The physically crosslinked nanogels were designed to have pH-responsive dissociation. So they could retain model drugs in the acidic gastric fluid, but release them in the neutral intestinal fluid. After dissociation, the polymers were membrane-lytic at slight acidic pH (5.5), which could probably permeabilise cell membranes for intracellular delivery.Open Acces

Modeling the interdependency of low-priority congestion control and active queue management

Recently, a negative interplay has been shown to arise when scheduling/AQM techniques and low-priority congestion control protocols are used together: namely, AQM resets the relative level of priority among congestion control protocols. This work explores this issue by (i) studying a fluid model that describes system dynamics of heterogeneous congestion control protocols competing on a bottleneck link governed by AQM and (ii) proposing a system level solution able to reinstate priorities among protocols.Comment: 9 page

pH and Reactive Oxygen Species-Sequential Responsive Nano-in-Micro Composite For Targeted Therapy of Inflammatory Bowel Disease

Oxidative stress and abnormally high levels of reactive oxygen species (ROS) play an essential role in the pathogenesis and progression of inflammatory bowel disease (IBD). Oxidation‐responsive nanoparticles (NPs) are formulated from a phenylboronic esters‐modified dextran (OxiDEX) that degrades selectively in response to hydrogen peroxide (H2O2). OxiDEX NPs are coated with chitosan and encapsulated in a pH‐sensitive polymer to produce nano‐in‐micro composites. The microparticles are spherical with homogeneous particle size (53 ± 3 µm) and maintain integrity at acidic pH, preventing the premature release of the NPs in gastric conditions. The degradation of NPs is highly responsive to the level of H2O2, and the release of the drug is sustained in the presence of physiologically relevant H2O2 concentrations. The presence of chitosan on the particles surface significantly enhances NPs stability in intestinal pH and their adhesion on the intestinal mucosa. Compared to a traditional enteric formulation, this formulation shows tenfold decreased drug permeability across C2BBe1/HT29‐MTX cell monolayer, implying that lower amount of drug would be absorbed to the blood stream and, therefore, limiting the undesired systemic side effects. Based on these results, a successful nano‐in‐micro composite for targeted therapy of IBD is obtained by combination of the responsiveness to pH and ROS.Peer reviewe

EFFECT OF LIPID SUPPLEMENTATION ON RUMINAL EPITHELIAL MEMBRANE FATTY ACID COMPOSITION AND SHORT-CHAIN FATTY ACID ABSORPTION

Inclusion of lipid into diets increases the energy density and, depending on the type of lipid, may alter the fatty acid (FA) composition of tissues. Effects of dietary lipid on the digestive and immune function gastrointestinal tract have been evaluated, but effects on how dietary FA affect short-chain fatty acid (SCFA) absorption have not been investigated. The objective of this study was to determine the effect of dietary lipid supply and lipid type on the FA composition of the ruminal epithelium and absorption of SCFA. Twenty-one Holstein steers (194.1 ± 26.77 kg) were randomly assigned to the control (CON; 2.2% ether extract) or 1 of 2 lipid supplementation treatments (5% ether extract) utilizing saturated (SAT) or unsaturated sources and protected fat (UNSAT). After 30 d, calves were killed and samples of ruminal digesta, blood, and ruminal tissue were collected for FA analysis, and ruminal tissue was used for ex vivo measurement of acetate, propionate, and butyrate uptake and flux. Data were analyzed as a randomized complete block design using the mixed model of SAS with the fixed effect of treatment and the random effect of block. Calves fed SAT and UNSAT had greater (P < 0.01) concentration of total FA in ruminal fluid than CON. Feeding UNSAT increased the monounsaturated (P < 0.001) and polyunsaturated (P = 0.002) FA content in ruminal fluid relative to SAT and CON. The concentration of FA in the ruminal epithelium did not differ among treatments but there was a tendency (P = 0.069) for SAT calves to have more total FA and saturated FA (P = 0.053) than UNSAT. Moreover, UNSAT calves had greater (P = 0.006) omega-3 FA concentration in the ruminal epithelium than CON and SAT calves. Calves fed SAT had greater (P = 0.038) total propionate uptake with greater passive diffusion (P = 0.015) than CON and UNSAT. Calves fed SAT also had greater total butyrate uptake (P = 0.008). However, there were no differences for acetate, propionate, or butyrate flux among treatments. Thus, it is concluded that the provision of dietary lipid alters the FA composition of the ruminal epithelium and the uptake of propionate and butyrate with the greatest response when saturated lipid sources are provided