Extracellular Acetylated Histone 3.3 Induces Inflammation and Lung Tissue Damage

Extracellular histones, part of the protein group known as damage-associated molecular patterns (DAMPs), are released from damaged or dying cells and can instigate cellular toxicity. Within the context of chronic obstructive pulmonary disease (COPD), there is an observed abundance of extracellular histone H3.3, indicating potential pathogenic implications. Notably, histone H3.3 is often found hyperacetylated (AcH3.3) in the lungs of COPD patients. Despite these observations, the specific role of these acetylated histones in inducing pulmonary tissue damage in COPD remains unclear. To investigate AcH3.3’s impact on lung tissue, we administered recombinant histones (rH2A, rH3.3, and rAcH3.3) or vehicle solution to mice via intratracheal instillation. After 48 h, we evaluated the lung toxicity damage and found that the rAcH3.3 treated animals exhibited more severe lung tissue damage compared to those treated with non-acetylated H3.3 and controls. The rAcH3.3 instillation resulted in significant histological changes, including alveolar wall rupture, epithelial cell damage, and immune cell infiltration. Micro-CT analysis confirmed macroscopic structural changes. The rAcH3.3 instillation also increased apoptotic activity (cleavage of caspase 3 and 9) and triggered acute systemic inflammatory marker activation (TNF-α, IL-6, MCP-3, or CXCL-1) in plasma, accompanied by leukocytosis and lymphocytosis. Confocal imaging analysis confirmed lymphocytic and monocytic/macrophage lung infiltration in response to H3.3 and AcH3.3 administration. Taken together, our findings implicate extracellular AcH3.3 in inducing cytotoxicity and acute inflammatory responses, suggesting its potential role in promoting COPD-related lung damage progression

Ribosome-Templated Azide–Alkyne Cycloadditions: Synthesis of Potent Macrolide Antibiotics by In Situ Click Chemistry

Over half of all antibiotics target the bacterial ribosomenature’s complex, 2.5 MDa nanomachine responsible for decoding mRNA and synthesizing proteins. Macrolide antibiotics, exemplified by erythromycin, bind the 50S subunit with nM affinity and inhibit protein synthesis by blocking the passage of nascent oligopeptides. Solithromycin (<b>1</b>), a third-generation semisynthetic macrolide discovered by combinatorial copper-catalyzed click chemistry, was synthesized in situ by incubating either <i>E. coli</i> 70S ribosomes or 50S subunits with macrolide-functionalized azide <b>2</b> and 3-ethynylaniline (<b>3</b>) precursors. The ribosome-templated in situ click method was expanded from a binary reaction (i.e., one azide and one alkyne) to a six-component reaction (i.e., azide <b>2</b> and five alkynes) and ultimately to a 16-component reaction (i.e., azide <b>2</b> and 15 alkynes). The extent of triazole formation correlated with ribosome affinity for the <i>anti</i> (1,4)-regioisomers as revealed by measured <i>K</i>_d values. Computational analysis using the site-identification by ligand competitive saturation (SILCS) approach indicated that the relative affinity of the ligands was associated with the alteration of macrolactone+desosamine-ribosome interactions caused by the different alkynes. Protein synthesis inhibition experiments confirmed the mechanism of action. Evaluation of the minimal inhibitory concentrations (MIC) quantified the potency of the in situ click products and demonstrated the efficacy of this method in the triaging and prioritization of potent antibiotics that target the bacterial ribosome. Cell viability assays in human fibroblasts confirmed <b>2</b> and four analogues with therapeutic indices for bactericidal activity over in vitro mammalian cytotoxicity as essentially identical to solithromycin (<b>1</b>)