Nicotine and its metabolite cotinine target MD2 and inhibit TLR4 signaling

Nicotine Enantioselectively Targets Myeloid Differentiation Protein 2 and Inhibits the Toll-like Receptor 4 Signaling

Psychoactive substances, including morphine and methamphetamine, have been shown to interact with the classic innate immune receptor Toll-like receptor 4 (TLR4) and its partner protein myeloid differentiation protein 2 (MD2) in a nonenantioselective manner. (-)-Nicotine, the primary alkaloid in tobacco and a key component of highly addictive cigarettes, targets the TLR4/MD2, influencing TLR4 signaling pathways. Existing as two enantiomers, the stereoselective recognition of nicotine by TLR4/MD2 in the context of the innate immune response remains unclear. In this study, we synthesized (+)-nicotine and investigated its effects alongside (-)-nicotine on lipopolysaccharide (LPS)-induced TLR4 signaling. (-)-Nicotine dose-dependently inhibited proinflammatory factors such as tumor necrosis factor α (TNF-α), interleukin 6 (IL-6), and cyclooxygenase-2 (COX-2). In contrast, (+)-nicotine showed no such inhibitory effects. Molecular dynamics simulations revealed that (-)-nicotine exhibited a stronger affinity with the TLR4 coreceptor MD2 than (+)-nicotine. Additionally, in silico simulations revealed that both nicotine enantiomers initially attach to the entrance of the MD2 cavity, creating a metastable state before they fully enter the cavity. In the metastable state, (-)-nicotine established more stable interactions with the surrounding residues at the entrance of the MD2 cavity compared to those of (+)-nicotine. This highlights the crucial role of the MD2 cavity entrance in the chiral recognition of nicotine. These findings provide valuable insights into the distinct interactions between nicotine enantiomers and the TLR4 coreceptor MD2, underscoring the enantioselective effect of nicotine on modulating TLR4 signaling.

Dissecting the Role of the Hydroxyl Moiety at C14 in (+)-Opioid-Based TLR4 Antagonists via Wet-Lab Experiments and Molecular Dynamics Simulations

Toll-like receptor 4 (TLR4) is pivotal as an innate immune receptor, playing a critical role in mediating neuropathic pain and drug addiction through its regulation of the neuroinflammatory response. The nonclassical (+)-opioid isomers represent a unique subset of TLR4 antagonists known for their effective blood-brain barrier permeability. Despite growing interest in the structure-activity relationship of these (+)-opioid-based TLR4 antagonists, the specific impact of heteroatoms on their TLR4 antagonistic activities has not been fully explored. This study investigated the influence of the hydroxyl group at C14 in six (+)-opioid TLR4 antagonists (1-6) using wet-lab experiments and in silico simulations. The corresponding C14-deoxy derivatives (7-12) were synthesized, and upon comparison with their corresponding counterparts (1-6), it was discovered that their TLR4 antagonistic activities were significantly diminished. Molecular dynamics simulations showed that the (+)-opioid TLR4 antagonists (1-6) possessed more negative binding free energies to the TLR4 coreceptor MD2, which was responsible for ligand recognition. This was primarily attributed to the formation of a hydrogen bond between the hydroxyl group at the C-14 position of the antagonists (1-6) and the R90 residue of MD2 during the binding process. Such an interaction facilitated the entry and subsequent binding of these molecules within the MD2 cavity. In contrast, the C14-deoxy derivatives (7-12), lacking the hydroxyl group at the C-14 position, missed this crucial hydrogen bond interaction with the R90 residue of MD2, leading to their egression from the MD2 cavity during simulations. This study underscores the significant role of the C14 hydroxyl moiety in enhancing the effectiveness of (+)-opioid TLR4 antagonists, which provides insightful guidance for designing future (+)-isomer opioid-derived TLR4 antagonists.

Exploring the Function of (+)-Naltrexone Precursors: Their Activity as TLR4 Antagonists and Potential in Treating Morphine Addiction

Disruptions in the toll-like receptor 4 (TLR4) signaling pathway are linked to chronic inflammation, neuropathic pain, and drug addiction. (+)-Naltrexone, an opioid-derived TLR4 antagonist with a (+)-isomer configuration, does not interact with classical opioid receptors and has moderate blood-brain barrier permeability. Herein, we developed a concise 10-step synthesis for (+)-naltrexone and explored its precursors, (+)-14-hydroxycodeinone (1) and (+)-14-hydroxymorphinone (3). These precursors exhibited TLR4 antagonistic activities 100 times stronger than (+)-naltrexone, particularly inhibiting the TLR4-TRIF pathway. In vivo studies showed that these precursors effectively reduced behavioral effects of morphine, like sensitization and conditioned place preference by suppressing microglial activation and TNF-α expression in the medial prefrontal cortex and ventral tegmental area. Additionally, 3 displayed a longer half-life and higher oral bioavailability than 1. Overall, this research optimized (+)-naltrexone synthesis and identified its precursors as potent TLR4 antagonists, offering potential treatments for morphine addiction.

Surface decoration with leucine tetrapeptide: An antibacterial strategy against Gram-negative bacteria

Surface-associated microbe contamination by Gram-negative bacteria poses a serious problem in medical care. Cationic peptides or polymers are the main materials used for antibacterial surface coating, but the positive charge may lead to blood coagulation. Therefore, exploiting surface coating which is free of positive charge and is effective for Gram-negative bacteria inactivation is in urgent need. In this study, inspired by the affinity between lipopolysaccharides of Gram-negative bacteria and Toll-like receptors of immune cells, we develop a leucine-based tetrapeptide coating strategy for combating Gram-negative bacteria. The obtained surface has excellent bactericidal activity against Gram-negative bacteria like Pseudomonas aeruginosa and Escherichia coli. A 1 mm² coated glass surface could kill > 9.9 × 10⁴ CFU bacteria in 1 h and has nearly no damage to mammal cells. Moreover, this surface coating strategy could be applied on various surfaces like glass slices, glass capillary cavity and thermoplastic polyurethane slices. And the coated surface could largely mitigate the microbe contamination in an in vivo subcutaneous implantation. This work paves a new way for antibacterial surface-coating which is behaving no positive charge and is of great importance for biomedical devices.

One-Dimensional Rod-like Tobacco Mosaic Virus Promotes Macrophage Polarization for a Tumor-Suppressive Microenvironment

The phenotype of tumor-associated macrophages plays an important role in their function of regulating the tumor immune microenvironment. The M1-phenotype macrophages display tumor-killing and immune activating functions. Here we show that the tobacco mosaic virus (TMV), a rod-like plant virus, can polarize macrophages to an M1 phenotype and shape a tumor-suppressive microenvironment. RAW 264.7 cells and bone marrow derived-macrophages (BMDMs) can recognize TMV via Toll-like receptor-4, and then the MAPK and NF-κB signaling pathways are activated, leading to the production of pro-inflammatory factors. Furthermore, the in vivo assessments on a subcutaneous co-injection tumor model show that the TMV-polarized BMDMs shape a tumor-suppressive microenvironment, resulting in remarkable delay of 4T1 tumor growth. Another in vivo assessment on an established tumor model indicates the high tumor-metastasis-inhibiting capacity of TMV-polarized BMDMs. This work suggests a role for this plant virus in macrophage-mediated therapeutic approaches and provides a strategy for tumor immunotherapy.

Differential Effects of Nicotine, Alcohol, and Coexposure on Neuroimmune-Related Protein and Gene Expression in Corticolimbic Brain Regions of Rats

Nicotine and alcohol co-use is extremely common and their use constitutes two of the most common causes of preventable death, yet the underlying biological mechanisms are largely understudied. Activation of neuroimmune toll-like receptors (TLRs) promotes the induction of proinflammatory cascades and increases alcohol intake in rodents, which further promotes TLRs in the brain; nicotine may decrease central proinflammatory signaling. The current studies sought to determine the effects of nicotine ± alcohol (alone or in combination) on circulating blood plasma and TLR protein/gene expression in addiction-associated corticolimbic brain regions, including the prefrontal cortex-prelimbic (mPFC-PL) and nucleus accumbens core (AcbC). Adult rats were treated with alcohol (0 or 2 g/kg, IG) and exposed to nicotine vapor (0 or 30 mg/mL solution) daily for 2, 14, or 28 days. Plasma studies indicated no effects of independent exposure or coexposure in males. Coexposure decreased plasma nicotine levels versus nicotine-only treated females, yet alcohol and cotinine concentrations were unchanged. By 28 days, the anti-inflammatory cytokine IL-13 was decreased in alcohol-only females. Divergent changes in TLR3 (but not TLR4) protein occurred for independent-drug exposed males (but not coexposure), with reductions in the mPFC-PL after 14 days and increases in the AcbC by 28 days. Gene expression following chronic coexposure suggests nicotine may regionally counteract alcohol-induced inflammation, including increased AcbC-TLR3/4/7 and several downstream markers in females and increased mPFC-PL-TLR3 and -STAT3 (but not IRF3) evident in males with exposure to either drug alone. These findings give further insight into the role of sex and the neuroimmune system in independent exposure and coexposure to nicotine ± alcohol.

Dithymoquinone Analogues as Potential Candidate(s) for Neurological Manifestation Associated with COVID-19: A Therapeutic Strategy for Neuro-COVID

The COVID-19 era has prompted several researchers to search for a linkage between COVID-19 and its associated neurological manifestation. Toll-like receptor 4 (TLR-4) acts as one such connecting link. spike protein of SARS-CoV-2 can bind either to ACE-2 receptors or to TLR-4 receptors, leading to aggregation of α-synuclein and neurodegeneration via the activation of various cascades in neurons. Recently, dithymoquinone has been reported as a potent multi-targeting candidate against SARS-CoV-2. Thus, in the present study, dithymoquinone and its six analogues were explored to target 3CL^pro (main protease of SARS-CoV-2), TLR4 and PREP (Prolyl Oligopeptidases) by using the molecular docking and dynamics approach. Dithymoquinone (DTQ) analogues were designed in order to investigate the effect of different chemical groups on its bioactivity. It is noteworthy to mention that attention was given to the feasibility of synthesizing these analogues by a simple photo-dimerisation reaction. The DTQ analogue containing the 4-fluoroaniline moiety [Compound (4)] was selected for further analysis by molecular dynamics after screening via docking-interaction analyses. A YASARA structure tool built on the AMBER14 force field was used to analyze the 100 ns trajectory by taking 400 snapshots after every 250 ps. Moreover, RMSD, RoG, potential energy plots were successfully obtained for each interaction. Molecular docking results indicated strong interaction of compound (4) with 3CL^pro, TLR4 and PREP with a binding energy of -8.5 kcal/mol, -10.8 kcal/mol and -9.5 kcal/mol, respectively, which is better than other DTQ-analogues and control compounds. In addition, compound (4) did not violate Lipinski's rule and showed no toxicity. Moreover, molecular dynamic analyses revealed that the complex of compound (4) with target proteins was stable during the 100 ns trajectory. Overall, the results predicted that compound (4) could be developed into a potent anti-COVID agent with the ability to mitigate neurological manifestations associated with COVID-19.

ACT001 Inhibits TLR4 Signaling by Targeting Co-Receptor MD2 and Attenuates Neuropathic Pain

Neuropathic pain is a common and challenging neurological disease, which renders an unmet need for safe and effective new therapies. Toll-like receptor 4 (TLR4) expressed on immune cells in the central nervous system arises as a novel target for treating neuropathic pain. In this study, ACT001, an orphan drug currently in clinical trials for the treatment of glioblastoma, was identified as a TLR4 antagonist. In vitro quenching titrations of intrinsic protein fluorescence and saturation transfer difference (STD)-NMR showed the direct binding of ACT001 to TLR4 co-receptor MD2. Cellular thermal shift assay (CETSA) showed that ACT001 binding affected the MD2 stability, which implies that MD2 is the endogenous target of ACT001. In silico simulations showed that ACT001 binding decreased the percentage of hydrophobic area in the buried solvent-accessible surface areas (SASA) of MD2 and rendered most regions of MD2 to be more flexible, which is consistent with experimental data that ACT001 binding decreased MD2 stability. In keeping with targeting MD2, ACT001 was found to restrain the formation of TLR4/MD2/MyD88 complex and the activation of TLR4 signaling axes of NF-κB and MAPKs, therefore blocking LPS-induced TLR4 signaling downstream pro-inflammatory factors NO, IL-6, TNF-α, and IL-1β. Furthermore, systemic administration of ACT001 attenuated allodynia induced by peripheral nerve injury and activation of microglia and astrocyte in vivo. Given the well-established role of neuroinflammation in neuropathic pain, these data imply that ACT001 could be a potential drug candidate for the treatment of chronic neuropathic pain.

Poly(I:C) attenuates myocardial ischemia/reperfusion injury by restoring autophagic function

Polyinosinic-polycytidylic acid (poly(I:C)) is the agonist of Toll-like receptor 3 (TLR3), which participates in innate immune responses under the condition of myocardial ischemia/reperfusion injury (MIRI). It has been shown that poly(I:C) exhibited cardioprotective activities through the PI3K/Akt pathway, which is the main signal transduction pathway during autophagy. However, the precise mechanism by whether poly(I:C) regulates autophagy remains poorly understood. Thus, this study was designed to investigate the therapeutic effect of poly(I:C) against MIRI and the underlying pathway connection with autophagy. We demonstrated that 1.25 and 5 mg/kg poly(I:C) preconditioning significantly reduced myocardial infarct size and cardiac dysfunction. Moreover, poly(I:C) significantly promoted cell survival by restoring autophagy flux and then regulating it to an adequate level Increased autophagy protein Beclin1 and LC3II together with p62 degradation after additional chloroquine. In addition, mRFP-GFP-LC3 adenoviruses exhibited autophagy activity in neonatal rat cardiac myocytes (NRCMs). Mechanistically, poly(I:C) activated the PI3K/AKT/mTOR pathway to induce autophagy, which was abolished by LY294002 (PI3K antagonist), rapamycin (autophagy activator and mTOR inhibitor), or 3-methyladenine (autophagy inhibitor), suggesting either inhibition of the PI3K/Akt/mTOR pathway or autophagy activity interrupt the beneficial effect of poly(I:C) preconditioning. In conclusion, poly(I:C) promotes cardiomyocyte survival from ischemia/reperfusion injury by regulating autophagy via the PI3K/Akt/mTOR pathway.

Cotinine: Pharmacologically Active Metabolite of Nicotine and Neural Mechanisms for Its Actions

Tobacco use disorder continues to be a leading public health issue and cause of premature death in the United States. Nicotine is considered as the major tobacco alkaloid causing addiction through its actions on nicotinic acetylcholine receptors (nAChRs). Current pharmacotherapies targeting nicotine's effects produce only modest effectiveness in promoting cessation, highlighting the critical need for a better understanding of mechanisms of nicotine addiction to inform future treatments. There is growing interest in identifying potential contributions of non-nicotine components to tobacco reinforcement. Cotinine is a minor alkaloid, but the major metabolite of nicotine that can act as a weak agonist of nAChRs. Accumulating evidence indicates that cotinine produces diverse effects and may contribute to effects of nicotine. In this review, we summarize findings implicating cotinine as a neuroactive metabolite of nicotine and discuss available evidence regarding potential mechanisms underlying its effects. Preclinical findings reveal that cotinine crosses the blood brain barrier and interacts with both nAChRs and non-nAChRs in the nervous system, and produces neuropharmacological and behavioral effects. Clinical studies suggest that cotinine is psychoactive in humans. However, reviewing evidence regarding mechanisms underlying effects of cotinine provides a mixed picture with a lack of consensus. Therefore, more research is warranted in order to provide better insight into the actions of cotinine and its contribution to tobacco addiction.

Molecular Basis of Artemisinin Derivatives Inhibition of Myeloid Differentiation Protein 2 by Combined in Silico and Experimental Study

Artemisinin (also known as Qinghaosu), an active component of the Qinghao extract, is widely used as antimalarial drug. Previous studies reveal that artemisinin and its derivatives also have effective anti-inflammatory and immunomodulatory properties, but the direct molecular target remains unknown. Recently, several reports mentioned that myeloid differentiation factor 2 (MD-2, also known as lymphocyte antigen 96) may be the endogenous target of artemisinin in the inhibition of lipopolysaccharide signaling. However, the exact interaction between artemisinin and MD-2 is still not fully understood. Here, experimental and computational methods were employed to elucidate the relationship between the artemisinin and its inhibition mechanism. Experimental results showed that artemether exhibit higher anti-inflammatory activity performance than artemisinin and artesunate. Molecular docking results showed that artemisinin, artesunate, and artemether had similar binding poses, and all complexes remained stable throughout the whole molecular dynamics simulations, whereas the binding of artemisinin and its derivatives to MD-2 decreased the TLR4(Toll-Like Receptor 4)/MD-2 stability. Moreover, artemether exhibited lower binding energy as compared to artemisinin and artesunate, which is in good agreement with the experimental results. Leu61, Leu78, and Ile117 are indeed key residues that contribute to the binding free energy. Binding free energy analysis further confirmed that hydrophobic interactions were critical to maintain the binding mode of artemisinin and its derivatives with MD-2.

Nicotine prevents in vivo Aβ toxicity in Caenorhabditis elegans via SKN-1

OBJECTIVE

Nicotine, a main active compound in tobacco, has been shown to attenuate amyloid-β (Aβ) mediated neurotoxicity. However, the detailed underlying mechanisms remains to be elucidated. In this study, nematode Caenorhabditis elegans (C. elegans) had been chosen as the model animal for dissecting the role of nicotine in the prevention of Aβ-induced toxicity in vivo.

METHODS

CL2120 and CL4176 transgenic worms of Alzheimer's disease (AD) models were treated with different concentrations of nicotine, and worm paralysis was monitored. Next, the effects of nicotine on Aβ deposits, Aβ oligomers, reactive oxygen species (ROS) and the oxidative stress resistance in worms were measured. Moreover, the pathway responsible for nicotine alleviating Aβ-induced toxicity in vivo was explored by observing the oxidative stress resistance of skn-1 or daf-16 mutants in the presence of nicotine. Furthermore, the worm paralysis and Aβ deposits were further checked in CL4176 worms with skn-1 RNA interference under the condition of nicotine.

RESULTS

Nicotine (5 μM) attenuated AD-like symptoms of worm paralysis in CL2120 and CL4176 transgenic C. elegans. Nicotine did not inhibit Aβ aggregation in vitro, however it suppressed Aβ deposits and reduced the Aβ oligomers to alleviate the toxicity induced by Aβ overexpression in C. elegans. Although nicotine did not possess apparent intrinsic anti-oxidative activity, it decreased in vivo reactive oxygen species (ROS). Nicotine enhanced the oxidative stress resistance of C. elegans, which was mediated by SKN-1 but not DAF-16 signaling. Furthermore, skn-1 RNAi abrogated the effect of nicotine reducing Aβ deposits in vivo and completely blocked nicotine preventing Aβ induced worm paralysis.

CONCLUSIONS

Nicotine reduces Aβ oligomer formation and alleviates Aβ-induced paralysis of C. elegans, which is mediated by SKN-1 signaling.