Biology subjects

Schmidt, H. H. H. W.

Publications and source records attributed to Schmidt, H. H. H. W..

4 recordsLinked to original sources

bioRxiv2018

A non-canonical chemical feedback self-limits nitric oxide-cyclic GMP signaling in health and disease

Nitric oxide (NO)-cyclic GMP (cGMP) signaling is a vasoprotective pathway therapeutically targeted for example in pulmonary hypertension. Its dysregulation in disease is incompletely understood. Here we show in pulmonary artery endothelial cells that feedback inhibition by NO of the NO receptor, the cGMP forming soluble guanylate cyclase (sGC), may contribute to this. Both endogenous NO from endothelial NO synthase or exogenous NO from NO donor compounds decreased sGC protein and activity. This was not mediated by cGMP as the NO-independent sGC stimulator or direct activation of cGMP-dependent protein kinase did not mimic it. Thiol-sensitive mechanisms were also not involved as the thiol-reducing agent, N-acetyl-L-cysteine did not prevent this feedback. Instead, both in-vitro and in-vivo and in health and acute respiratory lung disease, chronically elevated NO led to the inactivation and degradation of sGC whilst leaving the heme-free isoform, apo-sGC, intact or even increasing its levels. Thus, NO regulates sGC in a bimodal manner, acutely stimulating and chronically inhibiting, as part of self-limiting direct feedback that is cGMP-independent. In high NO disease conditions, this is aggravated but can be functionally recovered in a mechanism-based manner by apo-sGC activators that re-establish cGMP formation.

pharmacology and toxicology↗

bioRxiv2018

Isoform-specific NADPH oxidase inhibition for pharmacological target validation

Unphysiological reactive oxygen species (ROS) formation is considered an important pathomechanism for several disease phenotypes with high unmet medical need. Therapeutically, antioxidants have failed multiple times. Instead, focusing on only disease-relevant, enzymatic sources of ROS appears to be a more promising and highly validated approach. Here the family of five NADPH oxidases (NOX) stands out as drug targets. Validation has been restricted, however, mainly to genetically modified rodents and is lacking in other species including human. It is thus unclear whether the different NOX isoforms are sufficiently distinct to allow selective pharmacological modulation. Here we show for five of the most advanced NOX inhibitors that indeed isoform selectivity can be achieved. NOX1 was most potently (IC50) targeted by ML171 (0.1 M); NOX2, by VAS2870 (0.7 M); NOX4, by M13 (0.01 M) and NOX5, by ML090 (0.01 M). Conditions need to be carefully controlled though as previously unrecognized non-specific antioxidant and assay artefacts may limit the interpretation of data and this included, surprisingly, one of the most advanced NOX inhibitors, GKT136901. As proof-of-principle that now also pharmacological and non-rodent target validation of different NOX isoforms is possible, we used a human blood-brain barrier model and NOX inhibitor panel at IC50 concentrations. The protective efficacy pattern of this panel confirmed the predominant role of NOX4 in stroke from previous genetic models. Our findings strongly encourage further lead optimization efforts for isoform-selective NOX inhibitors and clinical development and provide an experimental alternative when genetic validation of a NOX isoform is not an option.\n\nO_FIG O_LINKSMALLFIG WIDTH=193 HEIGHT=200 SRC=\"FIGDIR/small/382226v2_ufig1.gif\" ALT=\"Figure 1\">\nView larger version (26K):\norg.highwire.dtl.DTLVardef@1708996org.highwire.dtl.DTLVardef@15909daorg.highwire.dtl.DTLVardef@960159org.highwire.dtl.DTLVardef@328083_HPS_FORMAT_FIGEXP M_FIG Graphical abstract C_FIG

pharmacology and toxicology↗

bioRxiv2018

Protein nitration is a physiological regulator of cardiac lactate dehydrogenase active site loop mobility and activity

Protein tyrosine nitration is a hallmark of oxidative stress related disease states, commonly detected as anti-nitrotyrosine immunoreactivity. The precise reactive oxygen sources, mechanisms of nitration as well as the modified target proteins and functional consequences, however, remain often unclear. Here we explore protein tyrosine nitration under basal conditions and find surprisingly physiologically nitrated proteins. Upon purifying a prominent physiologically nitrotyrosine immunopositive in hearts from mouse, rat and pig, we identify it as lactate dehydrogenase (LDH). Mechanistically, LDHs degree of basal nitration depended on two canonical sources, NO synthase (NOS) and myeloperoxidase (MPO), respectively. When validating the nitrated amino acid by MALDI-TOF mass spectrometry, we, surprisingly, located LDH nitration not to a tyrosine but the C-terminal tryptophan, Trp324. Molecular dynamics simulations suggested that Trp324 nitration restricts the interaction of the active site loop with the C-terminal -helix essential for activity. This prediction was confirmed by enzyme kinetics revealing an apparent lower Vmax of nitrated LDH, although yet unidentified concurrent oxidative modifications may contribute. Protein nitration is, thus, not a by definition disease marker but reflects also physiological signaling by eNOS/NO, MPO/nitrite and possibly other pathways. The commonly used assay of anti-nitrotyrosine immunoreactivity is apparently cross-reactive to nitrotryptophan requiring a reevaluation of the protein nitration literature. In the case of LDH, nitration of Trp324 is aggravated under cardiac metabolic stress conditions and functionally limits maximal enzyme activity. Trp324-nitrated LDH may serve both as a previously not recognized disease biomarker and possibly mechanistic lead to understand the metabolic changes under these conditions.

biochemistry↗

bioRxiv2018

Targeting comorbid diseases via network endopharmacology

The traditional drug discovery paradigm has shaped around the idea of \"one target, one disease\". Recently, it has become clear that not only it is hard to achieve single target specificity but also it is often more desirable to tinker the complex cellular network by targeting multiple proteins, causing a paradigm shift towards polypharmacology (multiple targets, one disease). Given the lack of clear-cut boundaries across disease (endo)phenotypes and genetic heterogeneity across patients, a natural extension to the current polypharmacology paradigm is targeting common biological pathways involved in diseases, giving rise to \"endopharmacology\" (multiple targets, multiple diseases). In this study, leveraging powerful network medicine tools, we describe a recipe for first, identifying common pathways pertaining to diseases and then, prioritizing drugs that target these pathways towards endopharmacology. We present proximal pathway enrichment analysis (PxEA) that uses the topology information of the network of interactions between disease genes, pathway genes, drug targets and other proteins to rank drugs for their interactome-based proximity to pathways shared across multiple diseases, providing unprecedented drug repurposing opportunities. As a proof of principle, we focus on nine autoimmune disorders and using PxEA, we show that many drugs indicated for these conditions are not necessarily specific to the condition of interest, but rather target the common biological pathways across these diseases. Finally, we provide the high scoring drug repurposing candidates that can target common mechanisms involved in type 2 diabetes and Alzheimers disease, two phenotypes that have recently gained attention due to the increased comorbidity among patients.

systems biology↗