In silico characterization of the psilocybin biosynthesis pathway

Nearly all mushrooms of the Psilocybe genus contain the natural product psilocybin, which is a psychoactive alkaloid derived from l-tryptophan. Considering their use in ancient times, as well as their psychedelic properties, these mushrooms have re-emerged with psychotherapeutic potential for treating depression, which has triggered increased pharmaceutical interest. However, the psilocybin biosynthesis pathway was only recently defined and, as such, little exists in the way of structural data. Accordingly, the aim of this study was to structurally characterize this pathway by generating homology models for the four Psilocybe cubensis enzymes involved in psilocybin biosynthesis (PsiD, a decarboxylase; PsiH, a monooxygenase; PsiK, a phosphotransferase; PsiM, a methyltransferase). Following initial model generation and alignment with the identified structural templates, repeated refinement of the models was carried out using secondary structure prediction, geometry evaluation, energy minimization, and molecular dynamics simulations in water. The final models were then evaluated using molecular docking interactions with their substrates, i.e., psilocybin precursors (l-tryptophan, tryptamine, 4-hydroxytryptamine, and norbaeocystin/baeocystin), all of which generated feasible binding modes for the expected biotransformation. Further plausibility of the psilocybin → aeruginascin, 4-hydroxytryptamine → norpsilocin, and tryptamine → N,N-dimethyltryptamine conversions, all mediated by the generated model for PsiM, suggests valid routes of formation for these key secondary metabolites. The structural characterization of these enzymes and their binding modes which emerged from this study can lead to a better understanding of psilocybin synthesis, thereby paving the way for the development of novel substrates and selective inhibitors, as well as improved biotechnological manipulation and production of psilocybin in vitro.

In Silico Design and SAR Study of Dibenzyl Trisulfide Analogues for Improved CYP1A1 Inhibition

Dibenzyl trisulfide (DTS) is a natural compound with potential cancer‐preventive properties occurring in Petiveria alliacea L., an ethnomedicinal plant native to the Americas. Previous studies revealed its inhibitory activity toward cytochrome P450 (CYP)1 enzymes, key in the activation of environmental pollutants. Accordingly, the aim of this study was to design novel DTS analogues, aimed at improving not only inhibitory activity, but also specificity toward CYP1A1. This was achieved by targeting interactions with CYP1A1 residues of identified importance. Three‐dimensional structures for the novel analogues were subjected to molecular docking with several CYP isoforms, before being ranked in terms of binding affinity to CYP1A1. With three hydrogen bond donors, two hydrogen bond acceptors, a molecular mass of 361 Da, and a log P of 3.72, the most promising DTS analogue obeys Lipinski's rule of five. Following synthesis and in vitro validation of its CYP1A1‐inhibitory properties, this compound may be useful in future cancer‐preventive approaches.

Dibenzyl trisulfide binds to and competitively inhibits the cytochrome P450 1A1 active site without impacting the expression of the aryl hydrocarbon receptor

The toxicological manifestation of many pollutants relies upon their binding to the aryl hydrocarbon receptor (AHR), and it follows a cascade of reactions culminating in an elevated expression of cytochrome P450 (CYP) 1 enzymes. CYP1A1 and CYP1B1 are associated with enhanced carcinogenesis when chronically exposed to certain polyaromatic hydrocarbons, and their inhibition may lead to chemoprevention. We evaluated dibenzyl trisulfide (DTS), expressed in the ethnomedical plant, Petiveria alliacea, for such potential chemoprevention. Using recombinant human CYP1A1 and CYP1B1 bactosomes on a fluorogenic assay, we first demonstrated that DTS moderately inhibited both enzymes with half maximal inhibitory concentration (IC50) values of 1.3 ± 0.3 and 1.7 ± 0.3 μM, respectively. Against CYP1A1, DTS was a reversible, competitive inhibitor with an apparent inhibitory constant (Ki) of 4.55 ± 0.37 μM. In silico molecular modeling showed that DTS binds with an affinity of -39.8 kJ·mol-1, situated inside the binding pocket, approximately 4.3 Å away from the heme group, exhibiting interactions with phenylalanine residue 123 (Phe-123), Phe-224, and Phe-258. Lastly, zebrafish (Danio rerio) embryos were exposed to 0.08-0.8 μM DTS from 24 to 96 h post fertilization (hpf) with the in vivo ethoxyresorufin-O-deethylase (EROD) assay, and, at 96 hpf, DTS significantly suppressed EROD CYP1A activity in a dose-dependent manner, with up to 60% suppression in the highest 0.8 μM exposure group. DTS had no impact on gene transcription levels for cyp1a and aryl hydrocarbon receptor 2 (ahr2). In co-exposure experiments, DTS suppressed CYP1A activity induced by both B[a]P and PCB-126, although these reductions were not significant. Taken together, these results demonstrate that DTS is a direct, reversible, competitive inhibitor of the carcinogen-activating CYP1A enzyme, binding in the active site pocket close to the heme site, and shows potential in chemoprevention.

Best practice in primary care pathology: review 6

This sixth best practice review examines four series of common primary care questions in laboratory medicine: (1) laboratory monitoring in hypertension and heart failure abnormalities; (2) markers of inflammatory joint disease; (3) laboratory investigation of chronic diarrhoea; and (4) mumps and chickenpox. The review is presented in question-answer format, referenced for each question series. The recommendations represent a precis of guidance found using a standardised literature search of national and international guidance notes, consensus statements, health policy documents and evidence-based medicine reviews, supplemented by Medline Embase searches to identify relevant primary research documents. They are not standards but form a guide to be set in the clinical context. Most are consensus based rather than evidence based. They will be updated periodically to take account of new information.

Antigen-binding diversity of human hybridoma autoantibodies derived from splenocytes of patients with SLE

The antigen-binding specificity of human hybridoma-derived monoclonal autoantibodies (mAb) was analysed with mAbs derived from the spleens of two patients with active systemic lupus erythematosus (SLE). From one patient 72 mAbs (RSP clones) and from the other 173 mAbs (RT clones) were obtained. The binding specificity of these mAbs was analysed by solid- and fluid-phase ELISA against the autoantigens ssDNA, dsDNA, cardiolipin, SmRNP, histones, Sm-D and SS-B (La) synthetic peptides, and foreign antigens including bacterial polysaccharides. In addition, antinuclear antibody activity and anti-dsDNA binding were confirmed by fluorescence staining methods. Reflecting the patient's serological profile, none of the antibodies from the RSP clones reacted with ssDNA or dsDNA but 12 reacted with cardiolipin. In addition, three mAbs reacted with H4, five with U1 RNP, two with Sm-D peptides and 12 with SS-B peptides. In contrast, from the RT fusion, nine mAbs reacted with ssDNA, HI and SS-B peptides, seven with cardiolipin, four with dsDNA, two with Sm-D peptides and one each with H2A, H3 and H4. In many cases one mAb showed reactivity with more than one antigen: for example, mAb RT 72 binds to ssDNA, dsDNA, cardiolipin, H1, H4 and an Sm-D peptide; RT 6 binds to H1, SmRNP and ubiquitinated histone H2A. However, none of the antibodies showed 'across the board' polyreactivity; indeed, the selectivity of the reactions was notable and marked variation in antibody affinity was recorded. Eight of the mAbs bound to Salmonella typhimurium and two to the Klebsiella polysaccharide K-30.(ABSTRACT TRUNCATED AT 250 WORDS)

Reversible agranulocytosis related to azidothymidine therapy

Hematopoietic toxicity from Zidovudine (AZT) is fairly common, resulting in a requirement for red cell transfusions in up to 25% of patients. Reversible agranulocytosis occurred following approximately 1 week of AZT therapy in a man with AIDS. He recovered from the episode without incident. There was no evidence for underlying bone marrow dysfunction or an adverse drug reaction. Careful monitoring of AZT therapy continues to be of great importance.