A 3D bioprinted hydrogel gut-on-chip with integrated electrodes for transepithelial electrical resistance (TEER) measurements.

Conventional gut-on-chip (GOC) models typically represent the epithelial layer of the gut tissue, neglecting other important components such as the stromal compartment and the extracellular matrix (ECM) that play crucial roles in maintaining intestinal barrier integrity and function. These models often employ hard, flat porous membranes for cell culture, thus failing to recapitulate the soft environment and complex 3D architecture of the intestinal mucosa. Alternatively, hydrogels have been recently introduced in GOCs as ECM analogs to support the co-culture of intestinal cells inin vivo-like configurations, and thus opening new opportunities in the organ-on-chip field. In this work, we present an innovative GOC device that includes a 3D bioprinted hydrogel channel replicating the intestinal villi architecture containing both the epithelial and stromal compartments of the gut mucosa. The bioprinted hydrogels successfully support both the encapsulation of fibroblasts and their co-culture with intestinal epithelial cells under physiological flow conditions. Moreover, we successfully integrated electrodes into the microfluidic system to monitor the barrier formation in real time via transepithelial electrical resistance measurements.

Splice-Switching Antisense Oligonucleotides Correct Phenylalanine Hydroxylase Exon 11 Skipping Defects and Rescue Enzyme Activity in Phenylketonuria.

The PAH gene encodes the hepatic enzyme phenylalanine hydroxylase (PAH), and its deficiency, known as phenylketonuria (PKU), leads to neurotoxic high levels of phenylalanine. PAH exon 11 is weakly defined, and several missense and intronic variants identified in patients affect the splicing process. Recently, we identified a novel intron 11 splicing regulatory element where U1snRNP binds, participating in exon 11 definition. In this work, we describe the implementation of an antisense strategy targeting intron 11 sequences to correct the effect of PAH mis-splicing variants. We used an in vitro assay with minigenes and identified splice-switching antisense oligonucleotides (SSOs) that correct the exon skipping defect of PAH variants c.1199+17G>A, c.1199+20G>C, c.1144T>C, and c.1066-3C>T. To examine the functional rescue induced by the SSOs, we generated a hepatoma cell model with variant c.1199+17G>A using CRISPR/Cas9. The edited cell line reproduces the exon 11 skipping pattern observed from minigenes, leading to reduced PAH protein levels and activity. SSO transfection results in an increase in exon 11 inclusion and corrects PAH deficiency. Our results provide proof of concept of the potential therapeutic use of a single SSO for different exonic and intronic splicing variants causing PAH exon 11 skipping in PKU.

Pathogenic variants of the coenzyme A biosynthesis-associated enzyme phosphopantothenoylcysteine decarboxylase cause autosomal-recessive dilated cardiomyopathy.

Coenzyme A (CoA) is an essential cofactor involved in a range of metabolic pathways including the activation of long-chain fatty acids for catabolism. Cells synthesize CoA de novo from vitamin B5 (pantothenate) via a pathway strongly conserved across prokaryotes and eukaryotes. In humans, it involves five enzymatic steps catalyzed by four enzymes: pantothenate kinase (PANK [isoforms 1-4]), 4'-phosphopantothenoylcysteine synthetase (PPCS), phosphopantothenoylcysteine decarboxylase (PPCDC), and CoA synthase (COASY). To date, inborn errors of metabolism associated with all of these genes, except PPCDC, have been described, two related to neurodegeneration with brain iron accumulation (NBIA), and one associated with a cardiac phenotype. This paper reports another defect in this pathway (detected in two sisters), associated with a fatal cardiac phenotype, caused by biallelic variants (p.Thr53Pro and p.Ala95Val) of PPCDC. PPCDC enzyme (EC 4.1.1.36) catalyzes the decarboxylation of 4'-phosphopantothenoylcysteine to 4'-phosphopantetheine in CoA biosynthesis. The variants p.Thr53Pro and p.Ala95Val affect residues highly conserved across different species; p.Thr53Pro is involved in the binding of flavin mononucleotide, and p.Ala95Val is likely a destabilizing mutation. Patient-derived fibroblasts showed an absence of PPCDC protein, and nearly 50% reductions in CoA levels. The cells showed clear energy deficiency problems, with defects in mitochondrial respiration, and mostly glycolytic ATP synthesis. Functional studies performed in yeast suggest these mutations to be functionally relevant. In summary, this work describes a new, ultra-rare, severe inborn error of metabolism due to pathogenic variants of PPCDC.

Analysis and Molecular Determinants of HIV RNase H Cleavage Specificity at the PPT/U3 Junction.

HIV reverse transcriptases (RTs) convert viral genomic RNA into double-stranded DNA. During reverse transcription, polypurine tracts (PPTs) resilient to RNase H cleavage are used as primers for plus-strand DNA synthesis. Nonnucleoside RT inhibitors (NNRTIs) can interfere with the initiation of plus-strand DNA synthesis by enhancing PPT removal, while HIV RT connection subdomain mutations N348I and N348I/T369I mitigate this effect by altering RNase H cleavage specificity. Now, we demonstrate that among approved nonnucleoside RT inhibitors (NNRTIs), nevirapine and doravirine show the largest effects. The combination N348I/T369I in HIV-1BH10 RT has a dominant effect on the RNase H cleavage specificity at the PPT/U3 site. Biochemical studies showed that wild-type HIV-1 and HIV-2 RTs were able to process efficiently and accurately all tested HIV PPT sequences. However, the cleavage accuracy at the PPT/U3 junction shown by the HIV-2EHO RT was further improved after substituting the sequence YQEPFKNLKT of HIV-1BH10 RT (positions 342-351) for the equivalent residues of the HIV-2 enzyme (HQGDKILKV). Our results highlight the role of ß-sheets 17 and 18 and their connecting loop (residues 342-350) in the connection subdomain of the large subunit, in determining the RNase H cleavage window of HIV RTs.

3D printed polyamide macroencapsulation devices combined with alginate hydrogels for insulin-producing cell-based therapies.

Cell macroencapsulation has shown a great potential overcoming the low survival of the transplanted pancreatic islets in the Type 1 Diabetes Mellitus (T1DM) treatment, as it avoids the need for lifelong immunosuppression. It is still not completely known how these devices interact with the host immune system when implanted. However, their surface properties seem to be crucial factors for a successful implant. In this context, the hydrophilicity and porosity of the surface of the macrocapsules are two of the most important properties that can affect the functionality of the graft; hydrophilicity defines the interactions with the host's immune cells, while the porosity determines the biosafety of the device while conditioning the oxygen, nutrients and insulin diffusion. Here, we report a novel ß-cell macroencapsulation system that combines an injectable alginate hydrogel with an external 3D-printed implantable device. This external macrocapsule protects the inner hydrogel containing cells, while allowing the precise location of the implant in the body. In addition, it would allow the easy extraction of the grafted cells in the case the implant fails or the renewal of the therapeutic cells is required. This study evaluates the biological effect of the macroencapsulation devices' surface properties (hydrophilicity and porosity). We studied two different pore sizes and hydrophilicities in four different devices containing rat INS1E ß-cells embedded in alginate hydrogels. All the devices showed great biocompatibility, although the hydrophilic ones exhibited higher fibroblast adhesion, which could potentially enhance the fibrotic response when implanted. Importantly, INS1E cells did not escape from the devices, denoting high biosafety. Cells grown within all devices and maintained their insulin secretory function. However, the hydrophobic device with a smaller pore size showed better cell viability values and, therefore, it might be the best candidate for the development of a safe ß-cell replacement therapy in T1DM.

3D Printed porous polyamide macrocapsule combined with alginate microcapsules for safer cell-based therapies.

Cell microencapsulation is an attractive strategy for cell-based therapies that allows the implantation of genetically engineered cells and the continuous delivery of de novo produced therapeutic products. However, the establishment of a way to retrieve the implanted encapsulated cells in case the treatment needs to be halted or when cells need to be renewed is still a big challenge. The combination of micro and macroencapsulation approaches could provide the requirements to achieve a proper immunoisolation, while maintaining the cells localized into the body. We present the development and characterization of a porous implantable macrocapsule device for the loading of microencapsulated cells. The device was fabricated in polyamide by selective laser sintering (SLS), with controlled porosity defined by the design and the sintering conditions. Two types of microencapsulated cells were tested in order to evaluate the suitability of this device; erythropoietin (EPO) producing C2C12 myoblasts and Vascular Endothelial Growth Factor (VEGF) producing BHK fibroblasts. Results showed that, even if the metabolic activity of these cells decreased over time, the levels of therapeutic protein that were produced and, importantly, released to the media were stable.

Amino acid residues in HIV-2 reverse transcriptase that restrict the development of nucleoside analogue resistance through the excision pathway.

Nucleoside reverse transcriptase (RT) inhibitors (NRTIs) are the backbone of current antiretroviral treatments. However, the emergence of viral resistance against NRTIs is a major threat to their therapeutic effectiveness. In HIV-1, NRTI resistance-associated mutations either reduce RT-mediated incorporation of NRTI triphosphates (discrimination mechanism) or confer an ATP-mediated nucleotide excision activity that removes the inhibitor from the 3' terminus of DNA primers, enabling further primer elongation (excision mechanism). In HIV-2, resistance to zidovudine (3'-azido-3'-deoxythymidine (AZT)) and other NRTIs is conferred by mutations affecting nucleotide discrimination. Mutations of the excision pathway such as M41L, D67N, K70R, or S215Y (known as thymidine-analogue resistance mutations (TAMs)) are rare in the virus from HIV-2-infected individuals. Here, we demonstrate that mutant M41L/D67N/K70R/S215Y HIV-2 RT lacks ATP-dependent excision activity, and recombinant virus containing this RT remains susceptible to AZT inhibition. Mutant HIV-2 RTs were tested for their ability to unblock and extend DNA primers terminated with AZT and other NRTIs, when complexed with RNA or DNA templates. Our results show that Met73 and, to a lesser extent, Ile75 suppress excision activity when TAMs are present in the HIV-2 RT. Interestingly, recombinant HIV-2 carrying a mutant D67N/K70R/M73K RT showed 10-fold decreased AZT susceptibility and increased rescue efficiency on AZT- or tenofovir-terminated primers, as compared with the double-mutant D67N/K70R. Molecular dynamics simulations reveal that Met73influences ß3-ß4 hairpin loop conformation, whereas its substitution affects hydrogen bond interactions at position 70, required for NRTI excision. Our work highlights critical HIV-2 RT residues impeding the development of excision-mediated NRTI resistance.

Viral reverse transcriptases.

Reverse transcriptases (RTs) play a major role in the replication of Retroviridae, Metaviridae, Pseudoviridae, Hepadnaviridae and Caulimoviridae. RTs are enzymes that are able to synthesize DNA using RNA or DNA as templates (DNA polymerase activity), and degrade RNA when forming RNA/DNA hybrids (ribonuclease H activity). In retroviruses and LTR retrotransposons (Metaviridae and Pseudoviridae), the coordinated action of both enzymatic activities converts single-stranded RNA into a double-stranded DNA that is flanked by identical sequences known as long terminal repeats (LTRs). RTs of retroviruses and LTR retrotransposons are active as monomers (e.g. murine leukemia virus RT), homodimers (e.g. Ty3 RT) or heterodimers (e.g. human immunodeficiency virus type 1 (HIV-1) RT). RTs lack proofreading activity and display high intrinsic error rates. Besides, high recombination rates observed in retroviruses are promoted by poor processivity that causes template switching, a hallmark of reverse transcription. HIV-1 RT inhibitors acting on its polymerase activity constitute the backbone of current antiretroviral therapies, although novel drugs, including ribonuclease H inhibitors, are still necessary to fight HIV infections. In Hepadnaviridae and Caulimoviridae, reverse transcription leads to the formation of nicked circular DNAs that will be converted into episomal DNA in the host cell nucleus. Structural and biochemical information on their polymerases is limited, although several drugs inhibiting HIV-1 RT are known to be effective against the human hepatitis B virus polymerase. In this review, we summarize current knowledge on reverse transcription in the five virus families and discuss available biochemical and structural information on RTs, including their biosynthesis, enzymatic activities, and potential inhibition.

Effects of HIV-1 reverse transcriptase connection subdomain mutations on polypurine tract removal and initiation of (+)-strand DNA synthesis.

HIV-1 reverse transcriptase (RT) connection subdomain mutations at positions 348, 369 and 376 have been associated with resistance to non-nucleoside RT inhibitors (NNRTIs). N348I may interfere with the initiation of (+)-strand DNA synthesis by reducing polypurine tract (PPT) removal in the presence of nevirapine. The effect of NNRTIs on the RNase H-mediated cleavage of PPT-containing template-primers has been studied with wild-type HIV-1 RT and mutants N348I, T369I, T369V, T376S and N348I/T369I. In the presence of NNRTIs, all RTs were able to stimulate PPT cleavage after primer elongation. The enhancing effects of nevirapine and efavirenz were reduced in RTs carrying mutation N348I, and specially N348I/T369I. However, those mutations had no effect on rilpivirine-mediated cleavage. Prior to elongation, the PPT remains resilient to cleavage, although efavirenz and rilpivirine facilitate RNase H-mediated trimming of its 3'-end. The integrity of the 3'-end is essential for the initiation of (+)-strand DNA synthesis. In the presence of dNTPs, rilpivirine was the most effective inhibitor of (+)-strand DNA synthesis blocking nucleotide incorporation and preventing usage of available PPT primers. The N348I/T369I RT showed reduced ability to generate short RNA products revealing a cleavage window defect. Its lower RNase H activity could be attributed to enhanced rigidity compared to the wild-type enzyme.

Cell cycle control and HIV-1 susceptibility are linked by CDK6-dependent CDK2 phosphorylation of SAMHD1 in myeloid and lymphoid cells.

Proliferating cells are preferentially susceptible to infection by retroviruses. Sterile α motif and HD domain-containing protein-1 (SAMHD1) is a recently described deoxynucleotide phosphohydrolase controlling the size of the intracellular deoxynucleotide triphosphate (dNTP) pool, a limiting factor for retroviral reverse transcription in noncycling cells. Proliferating (Ki67(+)) primary CD4(+) T cells or macrophages express a phosphorylated form of SAMHD1 that corresponds with susceptibility to infection in cell culture. We identified cyclin-dependent kinase (CDK) 6 as an upstream regulator of CDK2 controlling SAMHD1 phosphorylation in primary T cells and macrophages susceptible to infection by HIV-1. In turn, CDK2 was strongly linked to cell cycle progression and coordinated SAMHD1 phosphorylation and inactivation. CDK inhibitors specifically blocked HIV-1 infection at the reverse transcription step in a SAMHD1-dependent manner, reducing the intracellular dNTP pool. Our findings identify a direct relationship between control of the cell cycle by CDK6 and SAMHD1 activity, which is important for replication of lentiviruses, as well as other viruses whose replication may be regulated by intracellular dNTP availability.

Nucleoside/nucleotide analog inhibitors of hepatitis B virus polymerase: mechanism of action and resistance.

Hepatitis B virus (HBV) polymerase and human immunodeficiency virus (HIV) reverse transcriptase are structurally related. However, the HBV enzyme has a protein priming activity absent in the HIV enzyme. Approved nucleoside/nucleotide inhibitors of the HBV polymerase include lamivudine, adefovir, telbivudine, entecavir and tenofovir. Although most of them target DNA elongation, guanosine and adenosine analogs (e.g. entecavir and tenofovir, respectively) also impair protein priming. Major mutational patterns conferring nucleoside/nucleotide analog resistance include the combinations rtL180M/rtM204(I/V) (for lamivudine, entecavir, telbivudine and clevudine) and rtA181V/rtN236T (for adefovir and tenofovir). However, development of drug resistance is very slow for entecavir and tenofovir. Novel nucleoside/nucleotide analogs in advanced clinical trials include phosphonates similar to adefovir or tenofovir, and new tenofovir derivatives with improved pharmacological properties.

Temperature effects on the fidelity of a thermostable HIV-1 reverse transcriptase.

Transcriptomics and gene expression analysis are largely dependent of the availability of efficient thermostable reverse transcriptases (RTs). However, the intrinsic fidelity of DNA synthesis catalyzed by retroviral RTs is low. Reported error rates are in the range 1.2 × 10(-5)-6.7 × 10(-4), with oncoretroviral RTs being the most faithful enzymes. Wild-type HIV-1 group O (HIV-1O) RT is a thermostable polymerase that is able to synthesize cDNA at temperatures as high as 70 °C. At 37 °C, its error rate has been estimated at 5.8 × 10(-5) in M13mp2 lacZ-based forward mutation assays. However, at higher temperatures (e.g. 50 and 55 °C), the accuracy of HIV-1O RT is increased by approximately two- to five-fold. At 55 °C, the HIV-1O RT error rate (1.3 × 10(-5)) was similar to that shown by the AffinityScript (Agilent Technologies Inc., La Jolla, CA, USA) RT, a commercially available thermostable murine leukaemia virus RT. At higher temperatures, the increased accuracy of the HIV-1 enzyme results from a lower base substitution error rate, although it shows a higher tendency to introduce frameshifts. Kinetic studies carried out with model template-primers suggest minor differences in nucleotide discrimination, although, at higher temperatures, HIV-1O RT showed a reduced ability to extend mispaired template-primers.

Effectiveness of regular reporting of spirometric results combined with a smoking cessation advice by a primary care physician on smoking quit rate in adult smokers: a randomized controlled trial. ESPIROTAB study.

BACKGROUND: Undiagnosed airflow limitation is common in the general population and is associated with impaired health and functional status. Smoking is the most important risk factor for this condition. Although primary care practitioners see most adult smokers, few currently have spirometers or regularly order spirometry tests in these patients. Brief medical advice has shown to be effective in modifying smoking habits in a large number of smokers but only a small proportion remain abstinent after one year. The aim of this study is to evaluate the effectiveness of regular reporting of spirometric results combined with a smoking cessation advice by a primary care physician on smoking quit rate in adult smokers. METHODS/DESIGN: Intervention study with a randomized two arms in 5 primary care centres. A total of 485 smokers over the age of 18 years consulting their primary care physician will be recruited.On the selection visit all participants will undergo a spirometry, peak expiratory flow rate, test of smoking dependence, test of motivation for giving up smoking and a questionnaire on socio-demographic data. Thereafter an appointment will be made to give the participants brief structured advice to give up smoking combined with a detailed discussion on the results of the spirometry. After this, the patients will be randomised and given appointment for follow up visits at 3, 6, 12 and 24 months. Both arms will receive brief structured advice and a detailed discussion of the spirometry results at visit 0. The control group will only be given brief structured advice about giving up smoking on the follow up. Cessation of smoking will be tested with the carbon monoxide test. DISCUSSION: Early identification of functional pulmonary abnormalities in asymptomatic patients or in those with little respiratory symptomatology may provide "ideal educational opportunities". These opportunities may increase the success of efforts to give up smoking and may improve the opportunities of other preventive actions to minimise patient risk. Comparing adult smokers in the intervention group with those in the control group, a minimum improvement expected with respect to the rates of smoking cessation would represent a large number of avoided morbimortality. TRIAL REGISTRATION: ClinicalTrials.gov: NCT01296295.

Thermostable HIV-1 group O reverse transcriptase variants with the same fidelity as murine leukaemia virus reverse transcriptase.

Wild-type HIV-1 group O RT (reverse transcriptase) shows increased thermostability in comparison with HIV-1 group M subtype B RT and MLV (murine leukaemia virus) RT. However, its utility in the amplification of RNA targets is limited by the reduced accuracy of lentiviral RTs compared with oncoretroviral RTs (i.e. MLV RT). The effects of the mutations K65R, R78A and K65R/V75I on the fidelity of HIV-1 group O RTs were studied using gel-based and M13mp2 lacZ forward-mutation fidelity assays. Forward-mutation assays demonstrated that mutant RTs K65R, R78A and K65R/V75I showed >9-fold increased accuracy in comparison with the wild-type enzyme and were approximately two times more faithful than the MLV RT. Compared with MLV RT, all of the tested HIV-1 group O RT variants showed decreased frameshift fidelity. However, K65R RT showed a higher tendency to introduce one-nucleotide deletions in comparison with other HIV-1 group O RT variants. R78A had a destabilizing effect on the RT, either in the presence or absence of V75I. At temperatures above 52 °C, K65R and K65R/V75I retained similar levels of DNA polymerase activity to the wild-type HIV-1 group O RT, but were more efficient than HIV-1 group M subtype B and MLV RTs. K65R, K65R/V75I and R78A RTs showed decreased misinsertion and mispair extension fidelity in comparison with the wild-type enzyme for most base pairs studied. These assays revealed that nucleotide selection is mainly governed by kpol (pol is polymerization) in the case of K65R, whereas both kpol and Kd affect nucleotide discrimination in the case of K65R/V75I.

Microcantilever-based platforms as biosensing tools.

The fast and progressive growth of the biotechnology and pharmaceutical fields forces the development of new and powerful sensing techniques for process optimization and detection of biomolecules at very low concentrations. During the last years, the simplest MEMS structures, i.e. microcantilevers, have become an emerging and promising technology for biosensing applications, due to their small size, fast response, high sensitivity and their compatible integration into "lab-on-a-chip" devices. This article provides an overview of some of the most interesting bio-detections carried out during the last 2-3 years with the microcantilever-based platforms, which highlight the continuous expansion of this kind of sensor in the medical diagnosis field, reaching limits of detection at the single molecule level.

Increased thermostability and fidelity of DNA synthesis of wild-type and mutant HIV-1 group O reverse transcriptases.

Reverse transcription coupled with DNA amplification has become a well-established and powerful molecular technique for studying ribonucleic acids. However, the efficiency of those reactions is largely dependent on the molecular properties of currently used reverse transcriptases (RTs). Engineered and natural RT variants with improved thermostability and fidelity of DNA synthesis should be of great utility in the amplification of RNA targets. In this study, we demonstrate that the wild-type (WT) HIV-1 group O (O_WT) RT shows increased thermostability in comparison with Moloney murine leukemia virus RT and a prototypic HIV-1 group M:subtype B (BH10_WT) RT, while rendering higher yields in reverse transcription PCRs that included a cDNA synthesis step performed at a high temperature range (57-69 degrees C). In addition, the O_WT RT showed 2.5-fold increased accuracy in M13 lacZalpha forward mutation assays in comparison with the BH10_WT RT. Unlike the BH10_WT enzyme, O_WT RT showed a very low error rate for frameshifts. Mutational hot spots induced by O_WT RT occurred at nucleotide runs, suggesting a dislocation-mediated mechanism for the generation of base substitutions. In HIV-1 group O RT, substituting Ile75 for Val rendered an enzyme that was 1.9 and 4.7 times more faithful than O_WT RT and BH10_WT RTs, respectively, in forward mutation assays. The mutant RT also showed increased misinsertion and mispair extension fidelity in kinetic assays. However, its mutational spectrum was similar to that obtained with the WT group O polymerase. V75I caused a loss of efficiency of reverse transcription PCR amplifications at 65 and 68 degrees C in comparison with O_WT RT. However, a double mutant devoid of RNase H activity (V75I/E478Q) was found to reverse-transcribe at temperatures as high as 68 degrees C, while maintaining the increased accuracy of the V75I mutant.