Evaluation of the operational conditions of the glucose oxidase and catalase multienzymatic system through enzyme co-immobilization on amino hierarchical porous silica

Hexaric acids have attracted attention lately because they are platform chemicals for synthesizing pharmaceuticals. In particular, gluconic acid is one of the most studied because it is readily available in nature. In this work, operational conditions like temperature and pH were evaluated for the enzymatic production of gluconic acid. For this purpose, glucose oxidase (GOx) and catalase (CAT) were individually immobilized and co-immobilized using amino-silica as support. The catalytic performance of the enzymes both as separate biocatalysts (GOx or CAT) and as an enzymatic complex (GOx-CAT) was assessed in terms of enzymatic activity and stability at temperatures 45 °C and 50 °C and pH 6 to 8. The results show that CAT is a key enzyme for gluconic acid production as it prevents GOx from being inhibited by H2O2. However, CAT was found to be less stable than GOx. Therefore, different GOx to CAT enzymatic ratios were studied, and a ratio of 1-3 was determined to be the best. The highest glucose conversion conditions were 45 °C and pH 7.0 for 24 h. Regarding the biocatalyst reuse, GOx-CAT retained more than 70% of its activity after 6 reaction cycles. These results contribute to further knowledge and application of oxidases for hexaric acid production and shed greater light on the role of the glucose oxidase/catalase pair in better catalytic performance. Both enzymes were immobilized in one pot, which is relevant for their potential use in industry; an enzyme system was obtained in a single step.

Immobilized biocatalyst engineering: Biocatalytic tool to obtain attractive enzymes for industry

Biocatalysis can improve current bioprocesses by identifying or improving enzymes that withstand harsh and unnatural operating conditions. Immobilized Biocatalyst Engineering (IBE) is a novel strategy integrating protein engineering and enzyme immobilization as a single workflow. Using IBE, it is possible to obtain immobilized biocatalysts whose soluble performance would not be selected. In this work, Bacillus subtilis lipase A (BSLA) variants obtained through IBE were characterized as soluble and immobilized biocatalysts, and how the interactions with the support affect their structure and catalytic performance were analyzed using intrinsic protein fluorescence. Variant P5G3 (Asn89Asp, Gln121Arg) showed a 2.6-fold increased residual activity after incubation at 76 °C compared to immobilized wild-type (wt) BSLA. On the other hand, variant P6C2 (Val149Ile) showed 4.4 times higher activity after incubation in 75 % isopropyl alcohol (36 °C) compared to Wt_BSLA. Furthermore, we studied the advancement of the IBE platform by performing synthesis and immobilizing the BSLA variants using a cell-free protein synthesis (CFPS) approach. The observed differences in immobilization performance, high temperature, and solvent resistance between the in vivo-produced variants and Wt_BSLA were confirmed for the in vitro synthesized enzymes. These results open the door for designing strategies integrating IBE and CFPS to generate and screen improved immobilized enzymes from genetic diversity libraries. Furthermore, it was confirmed that IBE is a platform that can be used to obtain improved biocatalysts, especially those with an unremarkable performance as soluble biocatalysts, which wouldn't be selected for immobilization and further development for specific applications.

Modulating Substrate Specificity of Rhizobium sp. Histamine Dehydrogenase through Protein Engineering for Food Quality Applications

Histamine is a biogenic amine found in fish-derived and fermented food products with physiological relevance since its concentration is proportional to food spoilage and health risk for sensitive consumers. There are various analytical methods for histamine quantification from food samples; however, a simple and quick enzymatic detection and quantification method is highly desirable. Histamine dehydrogenase (HDH) is a candidate for enzymatic histamine detection; however, other biogenic amines can change its activity or produce false positive results with an observed substrate inhibition at higher concentrations. In this work, we studied the effect of site saturation mutagenesis in Rhizobium sp. Histamine Dehydrogenase (Rsp HDH) in nine amino acid positions selected through structural alignment analysis, substrate docking, and proximity to the proposed histamine-binding site. The resulting libraries were screened for histamine and agmatine activity. Variants from two libraries (positions 72 and 110) showed improved histamine/agmatine activity ratio, decreased substrate inhibition, and maintained thermal resistance. In addition, activity characterization of the identified Phe72Thr and Asn110Val HDH variants showed a clear substrate inhibition curve for histamine and modified kinetic parameters. The observed maximum velocity (V_max) increased for variant Phe72Thr at the cost of an increased value for the Michaelis-Menten constant (K_m) for histamine. The increased K_m value, decreased substrate inhibition, and biogenic amine interference observed for variant Phe72Thr support a tradeoff between substrate affinity and substrate inhibition in the catalytic mechanism of HDHs. Considering this tradeoff for future enzyme engineering of HDH could lead to breakthroughs in performance increases and understanding of this enzyme class.

Replicating endothelial shear stress in organ-on-a-chip for predictive hypericin photodynamic efficiency

Photodynamic therapy using Hypericin (Hy-PDT) is an alternative non-invasive treatment that enables selective tumor inhibition and angiogenesis derived from the differential recruitment of endothelial cells in the tumor microenvironment. Most PDT studies were performed on in vitro models without vascular biomechanical simulation. Our work strives to develop a microchip that generates a constant shear stress force to investigate the Hy-PDT efficiency on human umbilical vein endothelial cells (HUVECs). The microchip with a single straight microchannel was composed of the bottom layer (polystyrene), the middle layer (double-sided biocompatible adhesive tape), and the top layer (polyester film) and could produce shear stress in the range of 1.4 - 7.0 dyn cm^-2. The quantification of vascular endothelial growth factor (VEGF), cell viability, and activities of caspases 3 and 7 were assayed to validate the microchip and Hy-PDT efficacy. After the endothelization, static and dynamic cell incubations with Hy were conducted in microchips. Compared to static systems, the shear stress displayed its effect on the increasing release of VEGF and promoted more cell damage and cell death via necrosis during Hy-PDT. In conclusion, the expressive shear stress-dependent manner during PDT treatments suggests that the microchip could be an essential approach in preclinical tests to evaluate the therapeutic outcome considering the endothelial shear stress microenvironment.

Promoting physical activity among university students with a co-constructed program during Covid-19 pandemic

Introduction

Since the beginning of the COVID-19 pandemic, sanitary context and e-learning has greatly modified students’ lifestyles. An increase of sedentary behaviors, a reduction in physical activity (PA) and a stronger tendency to move towards unhealthy diet have been demonstrated. Most of the research is largely descriptive and to date, no interventional studies have been conducted to prevent the deterioration of students’ health.

Objectives

The objective of the present research aims to evaluate the effects of an intervention program on the lifestyle and psychological state of student. Its primary objective is to promote PA among students, to improve both physical condition and motivation to engage in physical activity for one’s health by promoting motivational levers. Its second objective is to reduce and/or prevent the deterioration of the health of university students.

Methods

Students from University of Nîmes were recruited and randomly assigned to one of the two following conditions: an experimental group and a control group. The experimental group participated to an 8-weeks program of PA (co-constructed by users during design-based innovative workshops) whereas the control group did not. For each group, measures of PA, sedentary time, anthropometric data, sleep, physical condition and psychological variables (anxiety, depression, motivation, body appreciation, perceived control, well-being, …) were carried out before (T1: october 2021) and after (T2: December 2021) these 8-weeks in order to evaluate the benefits from the PA program.

Results

These assessments were performed in October 2021 (T1) and December 2021 (T2).

Conclusions

Data are still being collected and will be presented in April 2022.

Disclosure

No significant relationships.

Production of bacterial cellulose tubes for biomedical applications: Analysis of the effect of fermentation time on selected properties

Biosynthesis of bacterial cellulose (BC) in cylindrical oxygen permeable molds allows the production of hollow tubular structures of increasing interest for biomedical applications (artificial blood vessels, ureters, urethra, trachea, esophagus, etc.). In the current contribution a simple set-up is used to obtain BC tubes of predefined dimensions; and the effects of fermentation time on the water holding capacity, nanofibrils network architecture, specific surface area, chemical purity, thermal stability, mechanical properties, and cell adhesion, proliferation and migration of BC tubes are systematically analysed for the first time. The results reported highlight the role of culture time on key properties of the BC tubes produced, with significant differences arising from the denser and more compact fibril arrangements generated at longer fermentation intervals.

Biosynthesis of a Novel Antibacterial Dipeptide, Using Proteases From South American Native Fruits, Useful as a Food Preservative

Antiacanthain and granulosain are the partially purified proteolytic extracts from the South American native fruits of Bromelia antiacantha (Bertol. ) and Solanum granuloso leprosum, respectively. The aim of this work was to compare the ability of both soluble and immobilized antiacanthain and granulosain f or the synthesis of Z-Tyr-Val-OH, a novel antibacterial dipeptide, in different reaction systems formed by almost anhydrous organic solvents (X_w: 1 × 10⁻⁵) and several percentages of immiscible organic solvents in 100 mM Tris(hydroxymethyl)aminomethane hydrochloride buffer pH 8.0. Soluble antiacanthain in half of the 24 different organic biphasic media showed higher catalytic potential than in 100 mM Tris(hydroxymethyl)aminomethane hydrolchloride buffer pH 8.0. Soluble granulosain showed lower catalytic potential in all liquid-liquid biphasic media than in the same buffer. However, 50% (v/v) ethyl ethanoate in 100 mM Tris(hydroxymethyl)aminomethane hydrolchloride buffer pH 8.0 allowed to express the highest catalytic potential of both soluble enzymes. In 50% v/v ethyl ethanoate, soluble antiacanthain and granulosain catalyzed the synthesis of Z-Tyr-Val-OH with 72 ± 0.15 and 60 ± 0.10% maximal peptide yields, respectively. Multi-point immobilization in glyoxyl-silica did not lead to better peptide yields than soluble enzymes, in that liquid-liquid biphasic medium under the same reaction conditions. Soluble and glyoxyl-silica immobilized antiacanthain in almost anhydrous ethyl ethanoate (X_w: 1 × 10⁻⁵) were able to retain 17.3 and 45% of the initial proteolytic activity of antiacanthain in 100 mM Tris hydrolchloride buffer pH 8.0, respectively, at 40°C under agitation (200 rpm). Soluble and glyoxyl-silica immobilized granulosain were inactivated under the same reaction conditions. Glyoxyl-silica immobilized antiacanthain showed to be a robust biocatalyst in almost anhydrous ethyl ethanoate (X_w: 1 × 10⁻⁵), eliciting the best peptide yield (75 ± 0.13%). The synthesis reaction of Z-Tyr-Val-OH could not proceed when soluble antiacanthain was used under the same conditions. Both peptidases only catalyzed the synthesis reaction under kinetic control, using activated acyl donor substrates. Finally, this work reports a novel broad-spectrum antibacterial peptide that significantly decreased (p ≤ 0.05) the specific growth rates of Gram positive and Gram negative microorganisms at very low concentrations (≥15 and 35 μg/ml, respectively); contributing with a new safe food preservative of applying for different food systems.

Immobilized Biocatalyst Engineering: High throughput enzyme immobilization for the integration of biocatalyst improvement strategies

The increasing use of sustainable manufacturing technologies in the industry presents a constant challenge for the development of suitable biocatalysts. Traditionally, improved biocatalysts are developed either using protein engineering (PE) or enzyme immobilization (EI). However, these approaches are usually not simultaneously applied. In this work, we designed and validated an enzyme improvement platform, Immobilized Biocatalyst Engineering (IBE), which simultaneously integrates PE and EI, with a unique combination of improvement through amino acid substitutions and attachment to a support material, allowing to select variants that would not be found through single or subsequent PE and EI improvement strategies. Our results show that there is a significant difference on the best performing variants identified through IBE, when compared to those that could be identified as soluble enzymes and then immobilized, especially when evaluating variants with low enzyme as soluble enzymes and high activity when immobilized. IBE allows evaluating thousands of variants in a short time through an integrated screening, and selection can be made with more information, resulting in the detection of highly stable and active heterogeneous biocatalysts. This novel approach can translate into a higher probability of finding suitable biocatalysts for highly demanding processes.

Enzymatic synthesis of 4-methoxycinnamoylglycerol Uv filter mediated by immobilized-lipase and nanoparticle formation on N-succinylchitosan

The synthesis of 4-methoxycinnamoylglycerol takes advantage of the biodiesel subproduct for obtaining a hydrophilic UV cinnamate derivate filter, useful in sunscreen formulations. The objective here was to demonstrate that esterification of 4-methoxycinnamic acid and glycerol mediated by immobilized-lipase from Thermomyces lanuginosus is selective towards 4-methoxycinnamoylglycerol monoester UV filter, whose chemical characteristics favor the nanoparticles formation by ionotropic gelation on N-Succinyl chitosan. A cinnamic acid conversion ~34% in hexane is higher than in other reports, without the presence of other sub-products or degradation products. This eases the purification process by liquid-liquid extraction. The free glyceryl entities favour its incorporation on N-Succinyl chitosan nanoparticles with size around 185±77nm, which are promissory for sunblock products.

Development of alginate-pectin microcapsules by the extrusion for encapsulation and controlled release of polyphenols from papaya (Carica papaya L.)

The papaya fruit (Carica papaya L.) contains a wide variety of bioactive compounds with potential applications in the food and nutraceutical industries. The entrapment and release of such bioactive compounds remain a critical step for the development of functional, stable, and cost-effective storage and delivery systems, since the interaction of polymers on capsules and the payload molecules can influence the performance of the capsule system under operational conditions. The present study describes the encapsulation of rutin and trans-ferulic acid-rich extracts from papaya exocarp in a pectin-alginate composite, evaluating the performance of gallic acid encapsulation obtained through in situ and two-step entrapment methods. The best alginate:pectin ratio for gallic acid encapsulation was 55:45 and 61:39, achieving 6.1 mg and 28.1 mg GAE/g capsules when the papaya exocarp extract was encapsulated by in situ and two-step, respectively. We also evaluated the payload release performance of the obtained capsules under in vitro conditions simulating gastrointestinal conditions. Our results indicate an increased protective effect at gastric pH and targeted release of polyphenols when in situ encapsulation is used to encapsulate the extracts. PRACTICAL APPLICATIONS: Currently, adding value to agroindustry processing waste is an important focus to achieve a more economically and environmentally sustainable food industry. The recovery of bioactive molecules such as polyphenols, for food supplements or formulation additives in the form of by-product extracts is gaining importance as novel sustainable processes in the agricultural industry. Thus, the encapsulation of such bioactive extracts for storage and consumption is an active research field, aiming to overcome the low storage stability and lability to gastric conditions, currently hindering their applications in food or pharmaceutical formulations. In this sense, capsule design and the development of efficient encapsulation methods are very important to obtain a suitable carrier and protector system for the capsulated bioactive extracts or molecules. This research aims to add value to papaya waste and potentially to other agroindustry wastes such as pectin and alginate, resulting in a polyphenol carrier with excellent encapsulation and targeted release properties under gastrointestinal conditions. In conclusion, this kind of works could allow to the application of the agroindustry byproducts to obtain high added-value products, in the form of polyphenol-loaded capsules.

Deletion and Randomization of Structurally Variable Regions in B. subtilis Lipase A (BSLA) Alter Its Stability and Hydrolytic Performance Against Long Chain Fatty Acid Esters

The continuous search for novel enzyme backbones and the engineering of already well studied enzymes for biotechnological applications has become an increasing challenge, especially by the increasing potential diversity space provided by directed enzyme evolution approaches and the demands of experimental data generated by rational design of enzymes. In this work, we propose a semi-rational mutational strategy focused on introducing diversity in structurally variable regions in enzymes. The identified sequences are subjected to a progressive deletion of two amino acids and the joining residues are subjected to saturation mutagenesis using NNK degenerate codons. This strategy offers a novel library diversity approach while simultaneously decreasing enzyme size in the variable regions. In this way, we intend to identify and reduce variable regions found in enzymes, probably resulting from neutral drift evolution, and simultaneously studying the functional effect of said regions. This strategy was applied to Bacillus. subtilis lipase A (BSLA), by selecting and deleting six variable enzyme regions (named regions 1 to 6) by the deletion of two amino acids and additionally randomizing the joining amino acid residues. After screening, no active variants were found in libraries 1% and 4%, 15% active variants were found in libraries 2% and 3%, and 25% for libraries 5 and 6 (n = 3000 per library, activity detected using tributyrin agar plates). Active variants were assessed for activity in microtiter plate assay (pNP-butyrate), thermal stability, substrate preference (pNP-butyrate, -palmitate), and compared to wildtype BSLA. From these analyses, variant P5F3 (F41L-ΔW42-ΔD43-K44P), from library 3 was identified, showing increased activity towards longer chain p-nitrophenyl fatty acid esters, when compared to BSLA. This study allowed to propose the targeted region 3 (positions 40-46) as a potential modulator for substrate specificity (fatty acid chain length) in BSLA, which can be further studied to increase its substrate spectrum and selectivity. Additionally, this variant showed a decreased thermal resistance but interestingly, higher isopropanol and Triton X-100 resistance. This deletion-randomization strategy could help to expand and explore sequence diversity, even in already well studied and characterized enzyme backbones such as BSLA. In addition, this strategy can contribute to investigate and identify important non-conserved regions in classic and novel enzymes, as well as generating novel biocatalysts with increased performance in specific processes, such as enzyme immobilization.

Synthesis with Immobilized Lipases and Downstream Processing of Ascorbyl Palmitate

Ascorbyl palmitate is a fatty acid ester endowed with antioxidant properties, used as a food additive and cosmetic ingredient, which is presently produced by chemical synthesis. Ascorbyl palmitate was synthesized from ascorbic acid and palmitic acid with a Pseudomonas stutzeri lipase immobilized on octyl silica, and also with the commercial immobilized lipase Novozym 435. The latter was selected for optimizing the reaction conditions because of its high reactivity and stability in the solvent 2-methyl-2-butanol used as reaction medium. The reaction of the synthesis was studied considering temperature and molar ratio of substrates as variables and synthesis yield as response parameter. The highest yield in the synthesis of ascorbyl palmitate was 81%, obtained at 55 °C and an ascorbic acid to palmitic acid molar ratio of 1:8, both variables having a strong effect on yield. The synthesized ascorbyl palmitate was purified to 94.4%, with a purification yield of 84.2%. The use of generally recognized as safe (GRAS) certified solvents with a polarity suitable for the solubilization of the compounds made the process a viable alternative for the synthesis and downstream processing of ascorbyl palmitate.

Impact of pretransplant CMV-specific T-cell immune response in the control of CMV infection after solid organ transplantation: a prospective cohort study

INTRODUCTION

Although solid organ transplant (SOT) recipients with pretransplant serology for cytomegalovirus (CMV-R+) are considered at intermediate risk for CMV infection post transplantation, CMV infection remains a major cause of morbidity in this population. We prospectively characterized whether having pretransplant CMV-specific cellular immunity is independently associated with controlling infection after transplantation in R + SOT recipients.

METHODS

A prospective cohort of consecutive R + SOT recipients that received pre-emptive treatment for CMV infection was monitored after transplantation and variables were recorded during the follow-up. The cytomegalovirus-specific T-cell immune response was characterized by intracellular cytokine staining and viral loads determined using real-time PCR.

RESULTS

One hundred and thirty-five R + SOT recipients were included (67 kidney, 64 liver, four liver-kidney). Only one-third of the patients (42; 31.85%) had CMV-specific T-cell immunity (CD8⁺CD69⁺INF-γ⁺ T cells >0.25%) before transplantation. Patients with negative pretransplant immunity had more CMV infection (49, 52.7% vs. 15, 35.7%; p 0.07) and received more antiviral therapy than those with immunity (32, 34.4% vs. 6, 14.3%, p 0.016). Having CMV specific immunity was an independent factor for protection from developing viraemia ≥2000 IU/mL (OR 0.276, 95% CI 0.105-0.725, p < 0.01) and lower administration of treatment (OR 0.398, 95% CI 0.175-0.905, p 0.028). Only patients with no pretransplant CMV-specific T-cell response were diagnosed with CMV-disease (8, 8.6% vs. 0, 0%, p 0.05).

DISCUSSION

Our results show that having a pretransplant CMV specific T-cell response may be associated with a lower rate of CMV viraemia and less antiviral treatment after transplantation; however, more prospective studies are needed to confirm these findings.

How the Triton X-100 modulates the activity/stability of the Thermomyces lanuginose lipase: Insights from experimental and molecular docking approaches

The lipase and Triton X-100 mixture is common for stabilization, immobilization and application processes of these kinds of enzymes. The objective of this article was to study the structural behavior and catalytic performance of Thermomyces lanuginose lipase in the presence of Triton X-100 at 25 °C and different pHs. The structural changes were followed by circular dichroism, correlating them with the catalytic performance, which is reported as the initial lipase activity in the hydrolysis of p‑nitro phenyl butyrate at zero time and residual activity after 48 h of incubation in the absence or presence of surfactant, at the selected pHs. Computational simulations allowed to explain the correlations between the physicochemical changes and the formation of surfactant protein complex, leading to the elucidation of the main interactions that drive activity and stability of this lipase in presence of the Triton X-100 surfactant. Main results showed the Triton X-100-enzyme complex modulates the site active geometry, favoring a better substrate-enzyme adjustment, which influences the activity and stability at evaluated pHs. This study contributes to understand the effect of some additives commonly used to improve the biocatalytic performance on several applications for different industrial fields.

Selective and eco-friendly synthesis of lipoaminoacid-based surfactants for food, using immobilized lipase and protease biocatalysts

Lipoaminoacids, as surfactants, are an excellent option for food industry due to the currently trends in consumption of functional and natural ingredients. Synthesis of lauroyl glycine lipoaminoacid was carried out with a lipase from Pseudomonas stutzeri and a protease from Bacillus subtilis, which were immobilized in octyl-glyoxyl silica and glyoxyl-silica supports, respectively, comparing their catalytic performance. The enzymatic selectivity towards the lipoaminoacid instead of the dipeptide glycylglycine and synthesis yield were evaluated with respect to the characteristics of the immobilized biocatalysts and synthesis conditions. Three solvents were tested as reaction media for evaluating the expressed activity, stability and catalytic behavior during synthesis. Results indicate that both enzymes favor the lauroyl glycine synthesis over the peptide synthesis, but the immobilized protease has the best balance between selectivity and yield: 40% yield for lauroyl glycine and less than 5% for dipeptide after 96h of synthesis, at 45°C and acetone as solvent.

Understanding the functional properties of bio-inorganic nanoflowers as biocatalysts by deciphering the metal-binding sites of enzymes

The biomineralisation of metal phosphates is a promising approach to develop more efficient nanobiocatalysts; however, the interactions between the protein and the inorganic mineral are poorly understood. Elucidating which protein regions most likely participate in the mineral formation will guide the fabrication of more efficient biocatalysts based on metal-phosphate nanoflowers. We have biomineralised the lipase from Thermomyces lanuginosus using three calcium, zinc and copper phosphates to fabricate different types of bio-inorganic nanoflowers. To better understand how the biomineralisation process affects the enzyme properties, we have computationally predicted the protein regions with a higher propensity for binding Ca²⁺, Cu²⁺ and Zn²⁺. These binding sites can be considered as presumable nucleation points where the biomineralisation process starts and explain why different metals can form bio-inorganic nanoflowers of the same enzyme with different functional properties. The formation of calcium, copper and zinc phosphates in the presence of this lipase gives rise to nanoflowers with different morphologies and different enzymatic properties such as activity, stability, hyperactivation and activity-pH profile; these functional differences are supported by structural studies based on fluorescence spectroscopy and can be explained by the different locations of the predicted nucleation sites for the different metals. Among the three metals used herein, the mineralisation of this lipase with zinc-phosphate enables the fabrication of bio-inorganic nanoflowers 34 times more stable than the soluble enzyme. These bio-inorganic nanoflowers were reused for 8 reaction cycles achieving 100% yield in the hydrolysis of p-nitrophenol butyrate but losing more than 50% of their initial activity after 6 operational cycles. Finally, this heterogeneous biocatalyst was more active and enantioselective than the soluble enzyme (ee = 79%(R)) towards the kinetic resolution of rac-1-phenylethyl acetate yielding the R enantiomer with ee = 84%.

Structure-activity relationships on the study of β-galactosidase folding/unfolding due to interactions with immobilization additives: Triton X-100 and ethanol

Improving the enzyme stability is a challenge for allowing their practical application. The surfactants are stabilizing agents, however, there are still questions about their influence on enzyme properties. The structure-activity/stability relationship for β-galactosidase from Bacillus circulans is studied here by Circular Dichroism and activity measurements, as a function of temperature and pH. The tendency of preserving the β-sheet and α-helix structures at temperatures below 65°C and different pH is the result of the balance between the large- and short-range effects, respecting to the active site. This information is fundamental for explaining the structural changes of this enzyme in the presence of Triton X-100 surfactant and ethanol. The enzyme thermal stabilization in the presence of this surfactant responds to the rearrangement of the secondary structure for having optimal activity/stability. The effect of ethanol is more related with changes in the dielectric properties of the aqueous solution than with protein structural transformations. These results contribute to understand the effects of surfactant-enzyme interactions on the enzyme behavior, from the structural point of view and to rationalize the surfactant-based stabilizing strategies for β-galactosidades.

Serologic control against hepatitis B virus among dental students of the University of Granada, Spain

Background

To evaluate the immunological situation against hepatitis B virus (HBV) of a cohort of dentistry students, to analyze the behavior of the levels of hepatitis B surface antigen (anti-HBs) after the administration of one or three vaccine doses, and to determine the influence of age and sex on the immune response.

Material and Methods

This retrospective cohort study included students attending the School of Dentistry of the institution where the study was performed from 2005 to 2012 who had completed the public health vaccination calendar for HBV at the age of 12-13. Data on age, sex, basal anti-HBs levels, post-vaccination anti-HBs results and final anti-HBs levels were collected. Comparisons of the basal and final levels, as well as associations regarding age and sex, were performed by means of the Student t and Chi-square tests.

Results

Of the 359 students, 97 (27.02%) had basal antibody concentrations <10 mIU/ml, whereas in 262 the levels of anti-HBs were ≥10 mIU/ml (72.98%). Of the 288 participating students who completed the School´s protocol for immunization, 287 (99.65%) attained a level of protection ≥10 mIU/ml. Globally, there were statistically significant differences between the basal antibody levels and those achieved after administration of the vaccine and booster, but no association with age or sex was observed.

Conclusions

About 70% of dental students vaccinated as preadolescents had serologic evidence of protection against HBV. Administering a booster is associated with the presence of an excellent immune memory. There is clearly a need to reinforce control of the antibody levels in groups at risk, such as Dentistry students.

Key words:Dental students, hepatitis B virus, serologic control.

Milk fatty acid profile from grazing buffaloes fed a blend of soybean and linseed oils

The aim of the study was to examine the changes in milk fatty acid (FA) profile of grazing buffaloes fed either low (L, 276g/d) or high (H, 572g/d) doses of a blend (70:30, wt/wt) of soybean and linseed oils. Fourteen multiparous Mediterranean buffaloes grazing on a native pasture were fed 4 kg/day of a commercial concentrate containing no supplemental oil over a pre-experimental period of ten days. The baseline milk production and composition and milk FA profile were measured over the last three days. After this pre-experimental period the animals received the same concentrate added with either the L or H oil doses for 26 additional days. Milk yield (g/animal/day) did not differ at the start (1776 ± 522 and 1662 ± 291 for L and H, respectively, P<0.622) or at the end of the trial (4590 ± 991 and 4847 ± 447 in L and H, respectively, P<0.543). Baseline milk fat content (g/kg) averaged 77.1 (±20.5) in L and 74.3 (±9.9) in H (P<0.10) and was reduced (P<0.031) to 60.7 (±23.6) and 49.4 (±11.2) (P<0.0031) respectively after L and H with no differences between treatments (P<0.277). Baseline milk protein content (L=43.2 ± 3.4 and H= 44.3 ± 6.9g/kg) increased after oil supplementation (P<0.0001) in both L (73.2 ± 6.0g/kg) and H (68.4 ± 4.9g/kg) without differences between oil doses (P<0.123). Milk fat content of 14:0 decreased after oil supplementation only in the H treatment (5.29 to 4.03, P<0.007) whereas that of 16:0 was reduced (P<0.001) at both L (24.49 to 19.75g/100g FA) and H (25.92 to 19.17g/100g FA) doses. The reduction of total content of 12:0 to 16:0 was higher (P<0.052) in H (32.02 to 23.93g/100g FA) than L (30.17 to 25.45g/100g FA). Vaccenic acid content increased (P<0.001) from 5.70 to 13.24g/100g FA in L and from 5.25 to 16.77 in H, with higher results in the in H treatment (P<0.001). Baseline rumenic acid was sharply increased (P<0.001) in L (1.80 to 4.09g/100g FA, +127%) and H (1.60 to 4.61g/100g FA, +187%) with no differences between L and H (P<0.19). Overall, these results indicate a pronounced improvement in the nutritional value of milk fat from grazing buffaloes fed little amounts (0.276g/day) of a blend of soybean and linseed oils.

Improvement of efficiency in the enzymatic synthesis of lactulose palmitate

Sugar esters are considered as surfactants due to its amphiphilic balance that can lower the surface tension in oil/water mixtures. Enzymatic syntheses of these compounds are interesting both from economic and environmental considerations. A study was carried out to evaluate the effect of four solvents, temperature, substrate molar ratio, biocatalyst source, and immobilization methodology on the yield and specific productivity of lactulose palmitate monoester synthesis. Lipases from Pseudomonas stutzeri (PsL) and Alcaligenes sp. (AsL), immobilized in porous silica functionalized with octyl groups (adsorption immobilization, OS) and with glyoxyl-octyl groups (both adsorption and covalent immobilization, OGS), were used. The highest lactulose palmitate yields were obtained at 47 °C in acetone, for all biocatalysts, while the best lactulose:palmitic acid molar ratio differed according to the immobilization methodology, being 1:1 for AsL-OGS biocatalyst (20.7 ± 3%) and 1:3 for the others (30-50%).

Improvement of chitosan derivatization for the immobilization of bacillus circulans β-galactosidase and its further application in galacto-oligosaccharide synthesis

Chitosan was derivatized by two methodologies to design a robust biocatalyst of immobilized Bacillus circulans β-galactosidase from a low-cost support for its further application in the synthesis of galacto-oligosaccharides (GOS). In the first one, chitosan was derivatized by cross-linking with glutaraldehyde and activated with epichlorohydrin; in the second one, cross-linking and activation were done with epichlorohydrin in a two-step process, favoring first support cross-linking and then support functionalization (C-EPI-EPI). Epoxy groups were hydrolyzed and oxidized, obtaining two supports activated with different aldehyde concentrations (100-250 μmol/g). The expressed activity and stability of the immobilized biocatalysts varied according to the derivatization methodology, showing that both the cross-linking agent and the activation degree are key parameters in the final biocatalyst performance. The best compromise between expressed activity and thermal stability was obtained using C-EPI-EPI with 200 μmol of aldehyde groups per gram of support. The immobilization conditions were optimized, obtaining a biocatalyst with 280 IU/g, immobilization yields in terms of activity and protein of 17.3 ± 0.4 and 61.5 ± 3.9%, respectively, and a high thermal stability, with a half-life of 449 times the value of the soluble enzyme. The biocatalyst was applied to the synthesis of GOS in repeated batch operation without affecting the product composition. Four successive batches were required for obtaining a cumulative specific productivity higher than the one obtained with the soluble enzyme.

Interplay of carbon-silica sources on the formation of hierarchical porous composite materials for biological applications such as lipase immobilization

The porous inorganic materials, with hierarchical structures, find application in many processes where the chemical stability and pore connectivity are key points, such as separation, adsorption and catalysis. Here, we synthesized carbon-silica composite materials, which combine hydrolytic stability of the carbon with the surface chemical reactivity of silica in aqueous media. The polycondensation of carbonaceous and siliceous species from sucrose, Triton X-100 surfactant and tetraethylortosilicate during the hydrothermal synthesis led to the formation of hydrochar composite materials. The subsequent carbonization process of these composite hydrochars gave carbon-silica hierarchical porous materials. The study of the micellar reaction system and the characterization of the derivate materials (carbon-silica composite, carbon and silica) were carried out. The results indicate that synthesis conditions allowed the formation of a silica network interpenetrated with a carbon one, which is produced from the incorporated organic matter. The control of the acidity of the reaction medium and hydrothermal conditions modulated the reaction yield and porous characteristics of the materials. The composite nature in conjunction with the hierarchical porosity increases the interest of these materials for future biological applications, such as lipase immobilization.

Is "intra-operating room" thromboelastometry useful in liver transplantation? A case-control study in 303 patients

Coagulation monitoring during liver transplantation (LT) is, even today, fundamental to reduce blood loss during surgery. Thromboelastometry (TEM) is a proven technique for controlling the various parameters that influence coagulation. However, there are no studies linking "intra-operating room" TEM (orTEM) with LT outcomes. We describe a case-control study in 303 liver graft recipients analyzing variables associated with operative complications and long-term LT outcomes. The results showed that orTEM reduced the use of blood products in patients with Model for End-Stage Liver Disease scores of ≥ 21, retransplantation, and high surgical difficulty and important intraoperative bleeding. In addition, results in survival and postoperative complications were better when orTEM was used. In conclusion, we confirm that use of orTEM is associated with less use of blood products and a lower rate of complications after LT.

Donor characteristics that are associated with survival in liver transplant recipients older than 70 years with grafts

INTRODUCTION

The use of grafts from donors older than 70 years of age is increasing due to the decrease in the number of donors and the increase in waiting list patients.

MATERIAL AND METHODS

We undertook a univariate and multivariate analysis of 980 adult recipients of whole liver grafts, 129 of them from donors aged 70 years or older.

RESULTS

No differences were found in patient survival compared with recipients of younger grafts. There were no higher rates of rejection, vascular or biliary complications, postoperative bleeding, or infections, but older grafts were associated with graft dysfunction (P = .01) and a higher frequency of postoperative refractory ascites (P = .007), but without a greater need for retransplantation. As graft-associated factors, the joint presence in the donor of diabetes (P = .00; confidence interval [CI] = 0.04-0.117), hypertension (P = .00; CI = 0.22-0.39), and weight of more than 90 kg (P = .031; CI = 0.05-0.104) were suggestive of poor prognostic factors in recipient survival. Survival in hepatitis C virus (HCV) recipients or recipients aged older than 60 years was worse with donors aged older than 70 years, although not significantly so. With grafts from donors aged older than 80 years (n = 15), although patient survival rate was good (70% at 10 years), there was a higher rate of retransplantation (20%) and the early mortality rate was 13.3%.

CONCLUSIONS

Use of grafts from donors aged older than 70 years is safe, with similar survival to patients with younger grafts. The appearance of initial dysfunction with prolonged ascites may be due to a delay in reaching a correct functionality, but was not associated with increased mortality, complications, or need for retransplantation. It should also be avoided in recipients older than 60 years or with HCV. Grafts older than 80 years were associated with a good long-term patient survival but at the expense of a higher rate of retransplantation. However, it helps to reduce the time on the waiting list and, thus, mortality. We noted decreased survival associated with donor hypertension, diabetes, and obesity, so these donors should be selected more rigorously.

Heterofunctional hydrophilic-hydrophobic porous silica as support for multipoint covalent immobilization of lipases: application to lactulose palmitate synthesis

Lipase-catalyzed synthesis of sugar esters, as lactulose palmitate, requires harsh conditions, making it necessary to immobilize the enzyme. Therefore, a study was conducted to evaluate the effect of different chemical surfaces of hierarchical meso-macroporous silica in the immobilization of two lipases from Pseudomonas stutzeri (PsL) and Alcaligenes sp. (AsL), which exhibit esterase activity. Porosity and chemical surface of silica supports, before and after functionalization and after immobilization, were characterized by gas adsorption and Fourier transform infrared (FTIR) spectroscopy. PsL and AsL were immobilized in octyl (OS), glyoxyl (GS), and octyl-glyoxyl silica (OGS). Hydrolytic activity, thermal and solvent stability, and sugar ester synthesis were evaluated with those catalysts. The best support in terms of expressed activity was OS in the case of PsL (100 IU g(-1)), while OS and OGS were the best for AsL with quite similar expressed activities (60 and 58 IU g(-1), respectively). At 60 °C in aqueous media the more stable biocatalysts were GS-PsL and OGS-AsL (half-lives of 566 and 248 h, respectively), showing the advantage of a heterofunctional support in the latter case. Lactulose palmitate synthesis was carried out in acetone medium (with 4% of equilibrium moisture) at 40 °C obtaining palmitic acid conversions higher than 20% for all biocatalysts, being the highest of those obtained with OGS-AsL and OS-PsL. Therefore, screening of different chemical surfaces on porous silica used as supports for lipase immobilization allowed obtaining active and stable biocatalyst to be employed in the novel synthesis of lactulose palmitate.

Antitumor efficacy of mammalian target of rapamycin inhibitor therapy in liver transplant recipients with oncological disease: a case-control study

INTRODUCTION

The reported incidences of de novo malignancy following orthotopic liver transplantation (OLT) are significantly greater than those in the general population. We have analyzed the efficacy of mammalian target of rapamycin inhibitor (mTORi) as immunosuppressant therapy in patients with de novo malignancies or those engrafted because of a primary liver cancer.

METHODS

We performed a case-control study of patients with hepatocellular carcinoma (HCC; n = 119), cholangiocarcinoma (n = 1) or de novo malignancies (n = 73). Thirty-seven patients with these tumors were treated with mTORi, and 167, with calcineurin inhibitors (CNI). Switching to mTORi was performed progressively, withdrawing the CNI over 15 days, until obtaining levels of 5-10 ng/dL.

RESULTS

No incidence of rejection, serious adverse events, or death was observed with an overall actuarial survival of 68.5% in the mTORi group versus 45.7% among the CNI group. Overall rates of tumor recurrence were 15.2% and 36.8%, respectively (P < .05). Among patients with HCC, survival was 100% of mTORi with and 61.5% among CNI patients, with tumor recurrence rates of 6.2% and 19.1%, respectively (P < .05).

DISCUSSION

Surprising differences in survival and tumor recurrence rates were observed among the mTORi-treated group compared with controls. Switching from CNI to mTORi immunosuppressant therapy appeared to be safe. It seems to be reasonable to employ this strategy in liver transplant patients with primary hepatic or "de novo" neoplasms.