4'-Ethynyl-2-fluoro-2'-deoxyadenosine (EFdA) inhibits HIV-1 reverse transcriptase with multiple mechanisms

4'-Ethynyl-2-fluoro-2'-deoxyadenosine (EFdA) is a nucleoside analog that, unlike approved anti-human immunodeficiency virus type 1 (HIV-1) nucleoside reverse transcriptase inhibitors, has a 3'-OH and exhibits remarkable potency against wild-type and drug-resistant HIVs. EFdA triphosphate (EFdA-TP) is unique among nucleoside reverse transcriptase inhibitors because it inhibits HIV-1 reverse transcriptase (RT) with multiple mechanisms. (a) EFdA-TP can block RT as a translocation-defective RT inhibitor that dramatically slows DNA synthesis, acting as a de facto immediate chain terminator. Although non-translocated EFdA-MP-terminated primers can be unblocked, they can be efficiently converted back to the EFdA-MP-terminated form. (b) EFdA-TP can function as a delayed chain terminator, allowing incorporation of an additional dNTP before blocking DNA synthesis. In such cases, EFdA-MP-terminated primers are protected from excision. (c) EFdA-MP can be efficiently misincorporated by RT, leading to mismatched primers that are extremely hard to extend and are also protected from excision. The context of template sequence defines the relative contribution of each mechanism and affects the affinity of EFdA-MP for potential incorporation sites, explaining in part the lack of antagonism between EFdA and tenofovir. Changes in the type of nucleotide before EFdA-MP incorporation can alter its mechanism of inhibition from delayed chain terminator to immediate chain terminator. The versatility of EFdA in inhibiting HIV replication by multiple mechanisms may explain why resistance to EFdA is more difficult to emerge.

Biochemical mechanism of HIV-1 resistance to rilpivirine

Rilpivirine (RPV) is a second generation nonnucleoside reverse transcriptase (RT) inhibitor (NNRTI) that efficiently inhibits HIV-1 resistant to first generation NNRTIs. Virological failure during therapy with RPV and emtricitabine is associated with the appearance of E138K and M184I mutations in RT. Here we investigate the biochemical mechanism of RT inhibition and resistance to RPV. We used two transient kinetics approaches (quench-flow and stopped-flow) to determine how subunit-specific mutations in RT p66 or p51 affect association and dissociation of RPV to RT as well as their impact on binding of dNTP and DNA and the catalytic incorporation of nucleotide. We compared WT with four subunit-specific RT mutants, p66(M184I)/p51(WT), p66(E138K)/p51(E138K), p66(E138K/M184I)/p51(E138K), and p66(M184I)/p51(E138K). Ile-184 in p66 (p66(184I)) decreased the catalytic efficiency of RT (k(pol)/K(d)(.dNTP)), primarily through a decrease in dNTP binding (K(d)(.dNTP)). Lys-138 either in both subunits or in p51 alone abrogated the negative effect of p66(184I) by restoring dNTP binding. Furthermore, p51(138K) reduced RPV susceptibility by altering the ratio of RPV dissociation to RPV association, resulting in a net reduction in RPV equilibrium binding affinity (K(d)(.RPV) = k(off.RPV)/k(on.RPV)). Quantum mechanics/molecular mechanics hybrid molecular modeling revealed that p51(E138K) affects access to the RPV binding site by disrupting the salt bridge between p51(E138) and p66(K101). p66(184I) caused repositioning of the Tyr-183 active site residue and decreased the efficiency of RT, whereas the addition of p51(138K) restored Tyr-183 to a WT-like conformation, thus abrogating the Ile-184-induced functional defects.

HIV-1 and HIV-2 Vif interact with human APOBEC3 proteins using completely different determinants

Human APOBEC3 (A3) restriction factors provide intrinsic immunity against zoonotic transmission of pathogenic viruses. A3D, A3F, A3G, and A3H haplotype II (A3H-hapII) can be packaged into virion infectivity factor (Vif)-deficient HIVs to inhibit viral replication. To overcome these restriction factors, Vif binds to the A3 proteins in viral producer cells to target them for ubiquitination and proteasomal degradation, thus preventing their packaging into assembling virions. Therefore, the Vif-A3 interactions are attractive targets for novel drug development. HIV-1 and HIV-2 arose via distinct zoonotic transmission events of simian immunodeficiency viruses from chimpanzees and sooty mangabeys, respectively, and Vifs from these viruses have limited homology. To gain insights into the evolution of virus-host interactions that led to successful cross-species transmission of lentiviruses, we characterized the determinants of the interaction between HIV-2 Vif (Vif2) with human A3 proteins and compared them to the previously identified HIV-1 Vif (Vif1) interactions with the A3 proteins. We found that A3G, A3F, and A3H-hapII, but not A3D, were susceptible to Vif2-induced degradation. Alanine-scanning mutational analysis of the first 62 amino acids of Vif2 indicated that Vif2 determinants important for degradation of A3G and A3F are completely distinct from these regions in Vif1, as are the determinants in A3G and A3F that are critical for Vif2-induced degradation. These observations suggest that distinct Vif-A3 interactions evolved independently in different SIVs and their nonhuman primate hosts and conservation of the A3 determinants targeted by the SIV Vif proteins resulted in successful zoonotic transmission into humans.

IMPORTANCE

Primate APOBEC3 proteins provide innate immunity against invading pathogens, and Vif proteins of primate lentiviruses have evolved to overcome these host defenses by interacting with them and inducing their proteasomal degradation. HIV-1 and HIV-2 are two human pathogens that induce AIDS, and elucidating interactions between their Vif proteins and human A3 proteins could facilitate the development of novel antiviral drugs. Furthermore, understanding Vif-A3 interactions can provide novel insights into the cross-species transmission events that led to the HIV-1 and HIV-2 pandemics and evolution of host-virus interactions. We carried out mutational analysis of the N-terminal 62 amino acids of HIV-2 Vif (Vif2) and analyzed A3G/A3F chimeras that retained antiviral activity to identify the determinants of the Vif2 and A3 interaction. Our results show that the Vif2-A3 interactions are completely different from the Vif1-A3 interactions, suggesting that these interactions evolved independently and that conservation of the A3 determinants resulted in successful zoonotic transmission into humans.

Evaluation of Multiwavelength Culture Fluorescence for Monitoring the Aroma Compound 4-Hydroxy-2(or 5)-ethyl-5(or 2)-methyl-3(2H)-furanone (HEMF) Production

Fluorescence spectra of a 4-hydroxy-2(or 5)-ethyl-5(or 2)-methyl-3(2H)-furanone (HEMF) fermentation culture broth were combined with measurable process variables for off-line and on-line process monitoring. Culture broth fluorescence in UV and visible ranges was acquired by a fiber optic LCD array spectrometer. Process dynamics was followed on-line using a fiber optic probe attached to an external recirculation loop of the bioreactor. Partial least squares and stepwise regression methods were used to correlate measurable process parameters with the components of the fluorescence spectra. Both methods provided adequate approximation of yeast density, HEMF, glucose, and ethanol concentrations from fluorescence spectra. HEMF production was observed during the oxido-reductive growth phase when there was a lack of measurable oxygen in the culture broth and an excess of glucose. The addition of glucose resulted in the rapid production of HEMF and other metabolite intermediates such as ethanol, acetate, and glycerol.

Immunohistochemical study about the Flt-1/VEGFR1 expression in the gastrointestinal tract of mouse, rat, dog, swine and monkey

Fms-like tyrosine kinase 1 (Flt-1) performs a subordinate effector role in mesenchymal angiogenesis and potentially serves an equally important functional role as a self-contained receptor in epithelial cells. In both endothelial cells and epithelial cells, Flt-1/vascular endothelial growth factor receptor 1 (VEGFR1) downstream signalling is involved in regulating cellular processes such as cytoskeletal changes and cellular survival protection. Cellular renewal of the gastrointestinal mucosa is based on these processes and might involve Flt-1/VEGFR1 pathway activities; the molecular mechanisms regulating these cellular dynamics remain unclear. This study was performed to investigate the presence and distribution of Flt-1/VEGFR1 in epithelial cells of the gastrointestinal tract by immunohistochemistry (IHC). Gastrointestinal tissues were taken from eight anatomical sites from mouse, rat, dog, swine and monkey. Present results revealed a cytosolic Flt-1/VEGFR1 staining pattern in mucosal epithelial cells for all investigated species. Non-epithelial structures also displayed a distinct Flt-1/VEGFR1 positivity and included vascular smooth muscle walls, enteric smooth muscle layers, the enteric nervous system and capillary endothelial cells. Diverse intensities of the Flt-1/VEGFR1 binding reaction within each species were observed in the intestinal mucosa with a strong immunoreaction in enterocytes and with a low protein expression in the ileum in most species. Crypt cells in the large intestine were mostly negative for Flt-1/VEGFR1. A peculiar and mainly intranuclear antibody binding reaction was found in Brunner's gland epithelial cells of mouse and rat whereas Brunner's glands of dog, swine and monkey remained completely negative. These results indicate a potential involvement of Flt-1/VEGFR1 in normal restitution of gastrointestinal structures in the species studied. Additionally, intranuclear Flt-1/VEGFR1 antibody binding in Brunner's glands of rodents may suggest a nuclear translocation of the transmembrane VEGFR1 which has not previously been described.

[External anal sphincter repair using the overlapping technique in patients with anal incontinence and concomitant pudendal nerve damage]

BACKGROUND

No single surgical technique has so far emerged as the optimal approach to treat defects of the anal sphincter in patients with postpartum fecal incontinence. Our approach is to repair the external sphincter using the overlapping technique to optimize morphological and clinical outcome. The results were correlated with preoperatively determined pudendal nerve function.

METHODS

Thirty-five patients were followed up for three years after repair of the external anal sphincter. The patients had grade 2 (n = 29) or grade 3 (n = 6) fecal incontinence. Nineteen (54 %) patients had a concomitant defect of the internal anal sphincter and 28 (80 %) had abnormal pelvic floor EMG findings. Before surgery, all patients underwent conservative treatment with biofeedback and electrostimulation. The muscle ends were overlapped with Vicryl 4-0 sutures. A standardized protocol was used for the perioperative management in all patients.

RESULTS

Of the 35 patients who underwent overlapping repair of the external anal sphincter, 32 (91 %) had a satisfactory result at 3-year follow-up based on sonomorphological criteria. These 32 patients were continent for solid and liquid stools. Six of the 35 patients (17 %) continued to have flatus incontinence. Two (6 %) patients were improved and one patient (3 %) had unchanged incontinence. Pudendal nerve damage had no effect on the outcome of surgery.

CONCLUSIONS

Our findings at 3-year follow-up show good results for the overlapping repair of the external anal sphincter in terms of morphology and clinical symptoms. This outcome depends on an adequate preoperative pelvic floor conditioning, optimal perioperative management, and use of a standardized operative technique. Surgical repair of the morphological defect is recommended even in patients with pudendal nerve damage.