Biology subjects

Henderson, G.

Publications and source records attributed to Henderson, G..

6 recordsLinked to original sources

bioRxiv2024

Potency, dissociation kinetics and reversibility of fentanyls and nitazenes by naloxone at the μ opioid receptor

Background and PurposeFentanyls and nitazenes are opioid receptor agonists responsible for a large number of opioid overdose deaths. Here, we compared the potency, dissociation kinetics and antagonism by naloxone at the receptor of several fentanyl and nitazene analogues and compared them to morphine and DAMGO. Experimental ApproachIn vitro assays of G protein activation and signalling and arrestin recruitment were performed. AtT20 cells expressing receptors were loaded with a membrane potential dye and changes in fluorescence used to determine agonist potency, dissociation kinetics and susceptibility to antagonism by naloxone. BRET experiments were undertaken in HEK293T cells expressing opioid receptors, to assess Gi protein activation and {beta}-arrestin 2 recruitment. Key ResultsThe rate of agonist dissociation from the receptor varied, with morphine, DAMGO, alfentanil and fentanyl dissociating rapidly whereas isotonitazene, etonitazene, ohmefentanyl and carfentanil dissociated slowly. Slowly dissociating agonists were more resistant to antagonism by naloxone. For carfentanil, the slow rate of dissociation was not due to G protein receptor kinase-mediated arrestin recruitment as its rate of dissociation was not affected by inhibition of GRKs with Compound 101. The in vitro relative potencies of fentanyls and nitazenes compared to morphine were much lower than that previously observed in in vivo experiments. Conclusions and ImplicationsWith fentanyls and nitazenes, that slowly dissociate from the opioid receptor, antagonism by naloxone is pseudo competitive. In overdoses involving fentanyls and nitazenes higher doses of naloxone may be required for reversal than those normally used to reverse heroin overdose. What is already knownO_LI"Fentanyls" and "nitazenes" are potent agonists at the opioid receptor. C_LI What does this study addO_LISome fentanyls and nitazenes dissociate slowly and are less sensitive to naloxone antagonism C_LI What is the clinical significanceO_LIMore naloxone may be required to reverse overdoses involving fentanyls and nitazenes C_LI

pharmacology and toxicology↗

bioRxiv2024

Ultra-efficient, unified discovery from microbial sequencing with SPLASH and precise statistical assembly

Bacteria comprise > 12% of Earths biomass and profoundly impact human and planetary health.1 Many key biological functions of microbes, and functions differentiating strains, are conferred or modified by genome plasticity including mobilization of genetic elements, phage integration, and CRISPR arrays. Characterizing each of these processes is time-consuming and requires custom bioinformatic workflows ill-suited to enable discovery of new sources of genetic diversity or to uncover which elements are active. Further, strain typing of bacterial species and approaches to discriminate sub-populations remain time-consuming and resource intensive. Here, we show that SPLASH, our published approach for reference-free discovery and analysis directly from raw reads, and an improved statistical assembly algorithm, compactors, unify diverse tasks in microbial sequence analysis: discovering new mobile elements and CRISPR arrays missing from any reference, and generating rapid, metadata-free strain typing of diverse bacteria. SPLASH and compactors together constitute a new general discovery tool for biological discovery in the microbial world.

bioinformatics↗

bioRxiv2023

SPLASH: a statistical, reference-free genomic algorithm unifies biological discovery

The authors have withdrawn this manuscript due to a duplicate posting of manuscript number BIORXIV/2022/497555. Therefore, the authors do not wish this work to be cited as reference for the project. If you have any questions, please contact the corresponding author. The correct preprint can be found at doi: https://doi.org/10.1101/2022.06.24.497555

genomics↗

bioRxiv2022

Unsupervised reference-free inference reveals unrecognized regulated transcriptomic complexity in human single cells

Myriad mechanisms diversify the sequence content of eukaryotic transcripts at both the DNA and RNA levels, leading to profound functional consequences. Examples of this diversity include RNA splicing and V(D)J recombination. Currently, these mechanisms are detected using fragmented bioinformatic tools that require predefining a form of transcript diversification and rely on alignment to an incomplete reference genome, filtering out unaligned sequences, potentially crucial for novel discoveries. Here, we present SPLASH+, significantly advancing biological discovery possible with SPLASH, our recently introduced efficient, reference-free statistical approach. Integrating a micro-assembly and biological interpretation framework, SPLASH+ enables new discoveries including broad and novel examples of transcript diversification in single cells de novo, without the need for cell type metadata, which is impossible with current algorithms. Applied to 10,326 primary human single cells across 19 tissues profiled with SmartSeq2, SPLASH+ discovers a set of splicing and histone regulators with highly conserved intronic regions that are themselves subject to complex splicing regulation. Additionally, it reveals unreported transcript diversity in the heat shock protein HSP90AA1, as well as diversification in centromeric RNA expression, V(D)J recombination, RNA editing, and repeat expansion, all missed by existing methods. SPLASH+ is highly efficient, enabling the discovery of an unprecedented breadth of RNA regulation and diversification in single cells through a new automated paradigm of unbiased transcriptomic analysis.

bioinformatics↗

bioRxiv2021

Fentanyl binds to the mu-opioid receptor via the lipid membrane and transmembrane helices

Overdose deaths from synthetic opioids, such as fentanyl, have reached epidemic proportions in the USA and are increasing worldwide. Fentanyl is a potent opioid agonist, that is less well reversed by naloxone than morphine. Due to fentanyls high lipophilicity and elongated structure we hypothesised that its unusual pharmacology may be explained by a novel binding mode to the -opioid receptor (MOPr). By employing coarse-grained molecular dynamics simulations and free energy calculations, we determined the routes by which fentanyl and morphine access the orthosteric pocket of MOPr. Morphine accesses MOPr via the aqueous pathway; first binding to an extracellular vestibule, then diffusing into the orthosteric pocket. In contrast, fentanyl takes a novel route; first partitioning into the membrane, before accessing the orthosteric site by diffusing through a ligand-induced gap between the transmembrane helices. This novel lipophilic route may explain the high potency and lower susceptibility of fentanyl to reversal by naloxone.

pharmacology and toxicology↗

bioRxiv2019

Fentanyl depression of respiration: comparison with heroin and morphine

Background and PurposeFentanyl overdose deaths have reached epidemic levels in North America. Death in opioid overdose invariably results from respiratory depression. In the present work we have characterized how fentanyl depresses respiration and by comparing fentanyl with heroin and morphine, the active breakdown product of heroin, we have sought to determine whether there are factors, in addition to high potency, that contribute to the lethality of fentanyl.\n\nExperimental ApproachRespiration (rate and tidal volume) was measured in awake, freely moving mice by whole body plethysmography\n\nKey ResultsIntravenously administered fentanyl produced more rapid depression of respiration than equipotent doses of heroin or morphine. Fentanyl depressed both respiratory rate and tidal volume, the effect on tidal volume may reflect increased respiratory muscle stiffness. Fentanyl did not depress respiration in opioid receptor knock-out mice. Naloxone, the opioid antagonist widely used to treat opioid overdose, reversed the depression of respiration by morphine more readily than that by fentanyl whereas diprenorphine, a more lipophilic antagonist, was equipotent in reversing fentanyl and morphine depression of respiration. Prolonged treatment with morphine induced tolerance to respiratory depression but the degree of cross tolerance to fentanyl was less than the tolerance to morphine itself.\n\nConclusion and ImplicationsWe propose that several factors (potency, rate of onset, muscle stiffness, lowered sensitivity to naloxone and lowered cross tolerance to morphine) combine to make fentanyl more likely to cause opioid overdose deaths than other commonly abused opioids.

pharmacology and toxicology↗