Influence of PLGA End Groups on the Release Profile of Dexamethasone from Ocular Implants

The present study deals with the development of dexamethasone (DM)-loaded implants using ester end-capped Resomer RG 502 poly(lactic acid-co-glycolic acid) (PLGA) (502), acid end-capped Resomer RG 502H PLGA (502H), and a 502H:502 mixture (3:1) via hot melt extrusion (HME). The prepared intravitreal implants (20 and 40% DM loaded in each PLGA) were thoroughly investigated to determine the effect of different end-capped PLGA and drug loading on the long-term release profile of DM. The implants were characterized for solid-state active pharmaceutical ingredient (APIs) using DSC and SWAXS, water uptake during stability study, the crystal size of API in the implant matrix using hot-stage polarized light microscopy, and in vitro release profile. The kinetics of PLGA release was thoroughly investigated using quantitative ¹H NMR spectroscopy. The polymorph of DM crystal was found to remain unchanged after the extrusion and stability study. However, around 3 times reduction in API particle size was observed after the HME process. The morphology and content uniformity of the RT-stored samples were found to be comparable to the initial implant samples. Interestingly, the samples (mainly 502H) stored at 40 °C and 75% RH for 30 d demonstrated marked deformation and a change in content uniformity. The rate of DM release was higher in the case of 502H samples with a higher drug loading (40% w/w). Furthermore, a simple digital in vitro DM release profile derived for the formulation containing a 3:1 ratio of 502H and 502 was comparable with the experimental release profile of the respective polymer mixture formulation. The temporal development of pores and/or voids in the course of drug dissolution, evaluated using μCT, was found to be a precursor for the PLGA release. Overall, the release profile of DM was found to be dependent on the PLGA type (independent of subtle changes in the formulation mass and diameter). However, the extent of release was found to be dependent on DM loading. Thus, the present investigation led to a thorough understanding of the physicochemical properties of different end-capped PLGAs and the underlying formulation microstructure on the release profile of a crystalline water-insoluble drug, DM, from the PLGA-based implant.

Lactoferricins impair the cytosolic membrane of Escherichia coli within a few seconds and accumulate inside the cell

We report the real-time response of Escherichia coli to lactoferricin-derived antimicrobial peptides (AMPs) on length scales bridging microscopic cell sizes to nanoscopic lipid packing using millisecond time-resolved synchrotron small-angle X-ray scattering. Coupling a multiscale scattering data analysis to biophysical assays for peptide partitioning revealed that the AMPs rapidly permeabilize the cytosolic membrane within less than 3 s-much faster than previously considered. Final intracellular AMP concentrations of ∼80-100 mM suggest an efficient obstruction of physiologically important processes as the primary cause of bacterial killing. On the other hand, damage of the cell envelope and leakage occurred also at sublethal peptide concentrations, thus emerging as a collateral effect of AMP activity that does not kill the bacteria. This implies that the impairment of the membrane barrier is a necessary but not sufficient condition for microbial killing by lactoferricins. The most efficient AMP studied exceeds others in both speed of permeabilizing membranes and lowest intracellular peptide concentration needed to inhibit bacterial growth.

131 Effect of Oviductal Fluid During In Vitro Culture on Bovine Embryo Development and Quality

The aim of this work was to establish an in vitro culture approach using bovine oviducal fluid (OF) to improve embryo quality and to provide an in vitro system to study oviduct function. Bovine oviducts ipsilateral to ovulation were collected at the slaughterhouse, 1 to 4 days after ovulation. The OF was collected by flushing the oviducts with 1 mL of Charles Rosenkrans 1 medium (CR1). Samples from 21 oviducts were pooled and proteins were concentrated using centrifugal filter devices. Aliquots of 3 different protein concentrations, determined by Bradford assay, were prepared and stored at –20°C. Abattoir-retrieved cumulus–oocyte complexes were used for standard in vitro maturation (IVM) and IVF (Day 0). On Day 1, presumptive zygotes (n = 1498) were randomly allocated to 4 different culture groups and cultured up to Day 9. The presumptive zygotes of the control group (n = 364) were cultured in CR1 with 5% oestrous cow serum (OCS) supplemented with 1 mg mL−1 hyaluronan. In the experimental groups, OCS was replaced by OF, resulting in 3 groups with final protein concentrations of 0.1 mg mL−1 (n = 380), 0.5 mg mL−1 (n = 380) or 1 mg mL−1 (n = 374). Cleavage rate was recorded on Day 2 and blastocyst yield on Days 7, 8, and 9 after fertilization. On Day 7, blastocysts were removed and either stained (Hoechst 33342) for cell number or subjected to a slow freezing protocol using 1.5 M ethylene glycol. After thawing, the re-expansion and hatching rate of blastocysts were determined at 24, 48 and 72 h. Eight replicates were carried out and data were analysed by ANOVA. Cleavage rate increased with increasing protein concentration (0.1 mg mL−1: 80.9 ± 4.2%; P > 0.05; 0.5 mg mL−1: 83.4 ± 2.5%; P < 0.1) and was significantly higher in the 1 mg mL−1 group (84.5 ± 4.4%; P < 0.05) compared with the control group (79.7 ± 3.4%). The cumulative blastocyst rate on Day 9 was significantly lower (P < 0.05) in all experimental groups (0.1 mg mL−1: 15.8 ± 8.9%; 0.5 mg mL−1: 18.7 ± 12.0%; 1 mg mL−1: 17.0 ± 11.2%) compared with the control group (34.1 ± 5.4%). The total number of cells was not affected by OF (P > 0.05). There was no significant difference (P > 0.05) in the post-thaw re-expansion rate between the experimental groups (0.1 mg mL−1: n = 26 thawed blastocysts; 0.5 mg mL−1: n = 27; 1 mg mL−1: n = 23) and the control group (n = 58). The post-thaw hatching rate was significantly higher at 24 and 72 h, respectively, in the 0.5 mg mL−1 group (44.4% and 74.1%; P < 0.05) and the 1 mg mL−1 group (47.8%; P < 0.05; and 82.6%; P < 0.01) compared with the control group (18.9% and 44.8%). The replacement of serum with OF during in vitro culture of bovine embryos had a stage specific effect, resulting in higher cleavage rates but lower blastocyst rates. To address this issue, OF will be collected at different stages and applied in the matching in vitro culture phases in future studies. Interestingly, the post-thaw hatching rate was up to twice as high in the experimental groups, indicating better quality of those embryos developing to blastocyst stage.

Organic coating on biochar explains its nutrient retention and stimulation of soil fertility

Amending soil with biochar (pyrolized biomass) is suggested as a globally applicable approach to address climate change and soil degradation by carbon sequestration, reducing soil-borne greenhouse-gas emissions and increasing soil nutrient retention. Biochar was shown to promote plant growth, especially when combined with nutrient-rich organic matter, e.g., co-composted biochar. Plant growth promotion was explained by slow release of nutrients, although a mechanistic understanding of nutrient storage in biochar is missing. Here we identify a complex, nutrient-rich organic coating on co-composted biochar that covers the outer and inner (pore) surfaces of biochar particles using high-resolution spectro(micro)scopy and mass spectrometry. Fast field cycling nuclear magnetic resonance, electrochemical analysis and gas adsorption demonstrated that this coating adds hydrophilicity, redox-active moieties, and additional mesoporosity, which strengthens biochar-water interactions and thus enhances nutrient retention. This implies that the functioning of biochar in soil is determined by the formation of an organic coating, rather than biochar surface oxidation, as previously suggested.

Biochar promotes plant growth via a slow release of nutrients; however, a mechanistic understanding of nutrient storage in biochar is lacking. Here, using high-resolution spectromicroscopy and mass spectrometry, the authors identify an organic coating on co-composted particles that enhances nutrient retention.

An Esterase from Anaerobic Clostridium hathewayi Can Hydrolyze Aliphatic-Aromatic Polyesters

Recently, a variety of biodegradable polymers have been developed as alternatives to recalcitrant materials. Although many studies on polyester biodegradability have focused on aerobic environments, there is much less known on biodegradation of polyesters in natural and artificial anaerobic habitats. Consequently, the potential of anaerobic biogas sludge to hydrolyze the synthetic compostable polyester PBAT (poly(butylene adipate-co-butylene terephthalate) was evaluated in this study. On the basis of reverse-phase high-performance liquid chromatography (RP-HPLC) analysis, accumulation of terephthalic acid (Ta) was observed in all anaerobic batches within the first 14 days. Thereafter, a decline of Ta was observed, which occurred presumably due to consumption by the microbial population. The esterase Chath_Est1 from the anaerobic risk 1 strain Clostridium hathewayi DSM-13479 was found to hydrolyze PBAT. Detailed characterization of this esterase including elucidation of the crystal structure was performed. The crystal structure indicates that Chath_Est1 belongs to the α/β-hydrolases family. This study gives a clear hint that also micro-organisms in anaerobic habitats can degrade manmade PBAT.

Dissecting and reconstructing synergism: in situ visualization of cooperativity among cellulases

Cellulose is the most abundant biopolymer and a major reservoir of fixed carbon on earth. Comprehension of the elusive mechanism of its enzymatic degradation represents a fundamental problem at the interface of biology, biotechnology, and materials science. The interdependence of cellulose disintegration and hydrolysis and the synergistic interplay among cellulases is yet poorly understood. Here we report evidence from in situ atomic force microscopy (AFM) that delineates degradation of a polymorphic cellulose substrate as a dynamic cycle of alternating exposure and removal of crystalline fibers. Direct observation shows that chain-end-cleaving cellobiohydrolases (CBH I, CBH II) and an internally chain-cleaving endoglucanase (EG), the major components of cellulase systems, take on distinct roles: EG and CBH II make the cellulose surface accessible for CBH I by removing amorphous-unordered substrate areas, thus exposing otherwise embedded crystalline-ordered nanofibrils of the cellulose. Subsequently, these fibrils are degraded efficiently by CBH I, thereby uncovering new amorphous areas. Without prior action of EG and CBH II, CBH I was poorly active on the cellulosic substrate. This leads to the conclusion that synergism among cellulases is morphology-dependent and governed by the cooperativity between enzymes degrading amorphous regions and those targeting primarily crystalline regions. The surface-disrupting activity of cellulases therefore strongly depends on mesoscopic structural features of the substrate: size and packing of crystalline fibers are key determinants of the overall efficiency of cellulose degradation.

Cellulases dig deep: in situ observation of the mesoscopic structural dynamics of enzymatic cellulose degradation

Enzymatic hydrolysis of cellulose is key for the production of second generation biofuels, which represent a long-standing leading area in the field of sustainable energy. Despite the wealth of knowledge about cellulase structure and function, the elusive mechanism by which these enzymes disintegrate the complex structure of their insoluble substrate, which is the gist of cellulose saccharification, is still unclear. We herein present a time-resolved structural characterization of the action of cellulases on a nano-flat cellulose preparation, which enabled us to overcome previous limitations, using atomic force microscopy (AFM). As a first step in substrate disintegration, elongated fissures emerge which develop into coniform cracks as disintegration continues. Detailed data analysis allowed tracing the surface evolution back to the dynamics of crack morphology. This, in turn, reflects the interplay between surface degradation inside and outside of the crack. We observed how small cracks evolved and initially increased in size. At a certain point, the crack diameter stagnated and then started decreasing again. Stagnation corresponds with a decrease in the total amount of surface which is fissured and thus leads to the conclusion that the surface hydrolysis “around” the cracks is proceeding more rapidly than inside the cracks. The mesoscopic view presented here is in good agreement with various mechanistic proposals from the past and allows a novel insight into the structural dynamics occurring on the cellulosic substrate through cellulase action.