Sigma-1 Receptor Agonists Acting on Aquaporin-Mediated H2O2 Permeability: New Tools for Counteracting Oxidative Stress

Sigma receptor and aquaporin modulators: chiral resolution, configurational assignment, and preliminary biological profile of RC752 enantiomers

The key role of chiral small molecules in drug discovery programs has been deeply investigated throughout last decades. In this context, our previous studies highlighted the influence of the absolute configuration of different stereocenters on the pharmacokinetic, pharmacodynamic and functional properties of promising Sigma receptor (SR) modulators. Thus, starting from the racemic SR ligand RC752, we report herein the isolation of the enantiomers via enantioselective separation with both HPLC and SFC. After optimization of the eco-sustainable chiral SFC method, both enantiomers were obtained in sufficient amount (tens of mg) and purity (ee up to 95%) to allow their characterization and initial biological investigation. Both enantiomers a) displayed a high affinity for the S1R subtype (Ki = 15.0 ± 1.7 and 6.0 ± 1.2 nM for the (S)- and (R)-enantiomer, respectively), but only negligible affinity toward the S2R (> 350 nM), and b) were rapidly metabolized when incubated with mouse and human hepatic microsomes. Furthermore, the activity on AQP-mediated water permeability indicated a different functional profile for the enantiomers in terms of modulatory effect on the peroxiporins gating.

Neurodegeneration: can metabolites from Eremurus persicus help?

The number of patients affected by neurodegenerative diseases is increasing worldwide, and no effective treatments have been developed yet. Although precision medicine could represent a powerful tool, it remains a challenge due to the high variability among patients. To identify molecules acting with innovative mechanisms of action, we performed a computational investigation using SAFAN technology, focusing specifically on HuD. This target belongs to the human embryonic lethal abnormal visual-like (ELAV) proteins and plays a key role in neuronal plasticity and differentiation. The results highlighted that the molecule able to bind the selected target was (R)-aloesaponol-III-8-methyl ether [(R)-ASME], a metabolite extracted from Eremurus persicus. Notably, this molecule is a TNF-α inhibitor, a cytokine involved in neuroinflammation. To obtain a suitable amount of (R)-ASME to confirm its activity on HuD, we optimized the extraction procedure. Together with ASME, another related metabolite, germichrysone, was isolated. Both ASME and germichrysone underwent biological investigation, but only ASME confirmed its ability to bind HuD. Given the multifactorial nature of neurodegenerative diseases, we decided to investigate ASME as a proteasome activator, being molecules endowed with this kind of activity potentially able to counteract aggregations of dysregulated proteins. ASME was able to activate the considered target both in enzymatic and cellular assays. Therefore, ASME may be considered a promising hit in the fight against neurodegenerative diseases.

Activation of sigma-1 receptor ameliorates sepsis-induced myocardial injury by mediating the Nrf2/HO1 signaling pathway to attenuate mitochondrial oxidative stress

BACKGROUND

Sepsis is a condition that triggers the release of large amounts of reactive oxygen species and inflammatory factors in the body, leading to myocardial injury and cardiovascular dysfunction - an important contributor to the high mortality rate associated with sepsis. Although it has been demonstrated that the sigma-1 receptor (S1R) is essential for preventing oxidative stress, its effectiveness in treating sepsis is yet unknown.

AIM

This study aimed to investigate the role and mechanisms of S1R activation in sepsis-induced myocardial injury.

METHODS

A model of sepsis-induced myocardial injury was constructed by performing cecum ligation and puncture(CLP) surgery on rats. Flv or BD1047 were intraperitoneally injected into rats for one consecutive week before performing CLP, and then intraperitoneally injected into the rats again 1 h after the surgery.The effects of Flv and BD1047 were detected by HE staining, immunofluorescence staining, IHC staining, echocardiography measurements,TUNEL, oxidative stress detection, TEM, flow cytometry and western blot. We further validated the mechanism in vitro using neonatal rat cardiomyocites and H9C2 cells.

RESULTS

S1R protein level was reduced in the hearts of septic rats, whereas administration of Flv, an S1R activator, ameliorated myocardial injury, mitochondrial oxidative stress, and pathological manifestations of sepsis. On the other hand, administration of the S1R inhibitor BD1047 exacerbated the mitochondrial oxidative stress, and apoptosis, as well as symptoms and pathological manifestations of sepsis. In addition, we found that up-regulation of S1R activated the Nrf2/HO1 signaling pathway and promoted nuclear translocation of Nrf2, which activated downstream proteins to generate antioxidant factors, such as HO1, in turn alleviating oxidative stress and countering myocardial damage.

CONCLUSION

By scavenging ROS accumulation and reducing mitochondrial oxidative stress via the Nrf2/HO1 signaling pathway, activation of S1R improves cardiac function, mitigates death of cardiomyocytes, and attenuates sepsis-induced myocardial injury.

Gut Bacteria Promote Phosphine Susceptibility of Tribolium castaneum by Aggravating Oxidative Stress and Fitness Costs

Knowledge about resistance mechanisms can provide ideas for pesticide resistance management. Although several studies have unveiled the positive or negative impacts of gut microbes on host pesticide resistance, minimal research is available regarding the association between gut microbes and host phosphine resistance. To explore the influence of gut bacteria on host phosphine susceptibility and its molecular basis, mortality, fitness, redox responses, and immune responses of adult Tribolium castaneum were determined when it was challenged by phosphine exposure and/or gut bacteria inoculation. Five cultivable gut bacteria were excised from a population of phosphine-resistant T. castaneum. Among them, only Enterococcus sp. inoculation significantly promoted host susceptibility to phosphine, while inoculation of any other gut bacteria had no significant effect on host phosphine susceptibility. Furthermore, when T. castaneum was exposed to phosphine, Enterococcus sp. inoculation decreased the female fecundity, promoted host oxidative stress, and suppressed the expression and activity of host superoxide dismutase, catalase, and peroxidase. In the absence of phosphine, Enterococcus sp. inoculation also elicited overactive immune responses in T. castaneum, including the immune deficiency and Toll signaling pathways and the dual oxidase-reactive oxygen species system. These results indicate that Enterococcus sp. likely promotes host phosphine susceptibility by aggravating oxidative stress and fitness costs.

Discovery of RC-752, a Novel Sigma-1 Receptor Antagonist with Antinociceptive Activity: A Promising Tool for Fighting Neuropathic Pain

Neuropathic pain (NP) is a chronic condition resulting from damaged pain-signaling pathways. It is a debilitating disorder that affects up to 10% of the world's population. Although opioid analgesics are effective in reducing pain, they present severe risks; so, there is a pressing need for non-opioid pain-relieving drugs. One potential alternative is represented by sigma-1 receptor (S1R) antagonists due to their promising analgesic effects. Here, we report the synthesis and biological evaluation of a series of S1R antagonists based on a 2-aryl-4-aminobutanol scaffold. After assessing affinity toward the S1R and selectivity over the sigma-2 receptor (S2R), we evaluated the agonist/antagonist profile of the compounds by investigating their effects on nerve growth factor-induced neurite outgrowth and aquaporin-mediated water permeability in the presence and absence of oxidative stress. (R/S)-RC-752 emerged as the most interesting compound for S1R affinity (K_i S1R = 6.2 ± 0.9) and functional antagonist activity. Furthermore, it showed no cytotoxic effect in two normal human cell lines or in an in vivo zebrafish model and was stable after incubation in mouse plasma. (R/S)-RC-752 was then evaluated in two animal models of NP: the formalin test and the spinal nerve ligation model. The results clearly demonstrated that compound (R/S)-RC-752 effectively alleviated pain in both animal models, thus providing the proof of concept of its efficacy as an antinociceptive agent.

Identification of a novel extracellular inhibitor of FGF2/FGFR signaling axis by combined virtual screening and NMR spectroscopy approach

The aberrant activation of the fibroblast growth factor 2 (FGF2)/fibroblast growth factor receptor (FGFR) signalling pathway drives severe pathologies, including cancer development and angiogenesis-driven pathologies. The perturbation of the FGF2/FGFR axis via extracellular allosteric small inhibitors is a promising strategy for developing FGFR inhibitors with improved safety and efficacy for cancer treatment. We have previously investigated the role of new extracellular inhibitors, such as rosmarinic acid (RA), which bind the FGFR-D2 domain and directly compete with FGF2 for the same binding site, enabling the disruption of the functional FGF2/FGFR interaction. To select ligands for the previously identified FGF2/FGFR RA binding site, NMR data-driven virtual screening has been performed on an in-house library of non-commercial small molecules and metabolites. A novel drug-like compound, a resorcinol derivative named RBA4 has been identified. NMR interaction studies demonstrate that RBA4 binds the FGF2/FGFR complex, in agreement with docking prediction. Residue-level NMR perturbations analysis highlights that the mode of action of RBA4 is similar to RA in terms of its ability to target the FGF2/FGFR-D2 complex, inducing perturbations on both proteins and triggering complex dissociation. Biological assays proved that RBA4 inhibited FGF2 proliferative activity at a level comparable to the previously reported natural product, RA. Identification of RBA4 chemical groups involved in direct interactions represents a starting point for further optimization of drug-like extracellular inhibitors with improved activity.

Novel S1R agonists counteracting NMDA excitotoxicity and oxidative stress: A step forward in the discovery of neuroprotective agents

Sigma-1 receptor (S1R) has been considered a promising therapeutic target for several neurodegenerative diseases and S1R agonists have shown neuroprotective activity against glutamate excitotoxicity and oxidative stress. Starting from a previously identified low nanomolar S1R agonist, in this work we prepared and tested novel benzylpiperidine/benzylpiperazine-based compounds designed by applying a ring opening strategy. Among them, 4-benzyl-1-(2-phenoxyethyl)piperidine 6b (S1R Ki = 0.93 nM) and 4-benzyl-1-(3-phenoxypropyl)piperidine 8b (S1R Ki = 1.1 nM) emerged as high affinity S1R ligands and showed selectivity over S2R and N-methyl-d-aspartate receptor (NMDAR). Candidate compounds behaved as potent S1R agonists being able to enhance the neurite outgrowth induced by nerve growth factor (NGF) in PC12 cell lines. In SH-SY5Y neuroblastoma cell lines they exhibited a neuroprotective effect against rotenone- and NMDA-mediated toxic insults. The neuroprotective activity of 6b and 8b was reverted by co-treatment with an S1R antagonist, PB212. Compounds 6b and 8b were tested for cytotoxicity in-vitro against three human cancer cell lines (A549, LoVo and Panc-1) and in-vivo zebrafish model, resulting in a good efficacy/safety profile, comparable or superior to the reference drug memantine. Overall, these results encourage further preclinical investigations of 6b and 8b on in-vivo models of neurodegenerative diseases.

Cerium Oxide Nanoparticles Regulate Oxidative Stress in HeLa Cells by Increasing the Aquaporin-Mediated Hydrogen Peroxide Permeability

Some aquaporins (AQPs) allow the diffusion of hydrogen peroxide (H₂O₂), the most abundant ROS, through the cell membranes. Therefore, the possibility of regulating the AQP-mediated permeability to H₂O₂, and thus ROS scavenging, appears particularly important for controlling the redox state of cells in physiological and pathophysiological conditions. Several compounds have been screened and characterized for this purpose. This study aimed to analyze the effect of cerium oxide nanoparticles (CNPs) presenting antioxidant activity on AQP functioning. HeLa cells express AQP3, 6, 8, and 11, able to facilitate H₂O₂. AQP3, 6, and 8 are expressed in the plasma membrane and intracellularly, while AQP11 resides only in intracellular structures. CNPs but not cerium ions treatment significantly increased the water and H₂O₂ permeability by interacting with AQP3, 6, and especially with AQP8. CNPs increased considerably the AQP-mediated water diffusion in cells with oxidative stress. Functional experiments with silenced HeLa cells revealed that CNPs increased the H₂O₂ diffusion mainly by modulating the AQP8 permeability but also the AQP3 and AQP6, even if to a lesser extent. Current findings suggest that CNPs represent a promising pharmaceutical agent that might potentially be used in numerous pathologies involving oxidative stress as tumors and neurodegenerative diseases.

Repurposing the Antiplatelet Agent Ticlopidine to Counteract the Acute Phase of ER Stress Condition: An Opportunity for Fighting Coronavirus Infections and Cancer

Different pathological conditions, including viral infections and cancer, can have a massive impact on the endoplasmic reticulum (ER), causing severe damage to the cell and exacerbating the disease. In particular, coronavirus infections, including SARS coronavirus-2 (SARS-CoV-2), responsible for COVID-19, cause ER stress as a consequence of the enormous amounts of viral glycoproteins synthesized, the perturbation of ER homeostasis and the modification of ER membranes. Therefore, ER has a central role in the viral life cycle, thus representing one of the Achilles’ heels on which to focus therapeutic intervention. On the other hand, prolonged ER stress has been demonstrated to promote many pro-tumoral attributes in cancer cells, having a key role in tumor growth, metastasis and response to therapies. In this report, adopting a repurposing approach of approved drugs, we identified the antiplatelet agent ticlopidine as an interferent of the unfolded protein response (UPR) via sigma receptors (SRs) modulation. The promising results obtained suggest the potential use of ticlopidine to counteract ER stress induced by viral infections, such as COVID-19, and cancer.