Dextromethorphan efficiently increases bactericidal activity, attenuates inflammatory responses, and prevents group a streptococcal sepsis

The N-Methyl-D-Aspartate Receptor Antagonist Dextromethorphan Improves Glucose Homeostasis and Preserves Pancreatic Islets in NOD Mice

For treatment of type 1 diabetes mellitus, a combination of immune-based interventions and medication to promote beta-cell survival and proliferation has been proposed. Dextromethorphan (DXM) is an N-methyl-D-aspartate receptor antagonist with a good safety profile, and to date, preclinical and clinical evidence for blood glucose-lowering and islet-cell-protective effects of DXM have only been provided for animals and individuals with type 2 diabetes mellitus. Here, we assessed the potential anti-diabetic effects of DXM in the non-obese diabetic mouse model of type 1 diabetes. More specifically, we showed that DXM treatment led to five-fold higher numbers of pancreatic islets and more than two-fold larger alpha- and beta-cell areas compared to untreated mice. Further, DXM treatment improved glucose homeostasis and reduced diabetes incidence by 50%. Our data highlight DXM as a novel candidate for adjunct treatment of preclinical or recent-onset type 1 diabetes.

A mouse air pouch model for evaluating the anti-bacterial efficacy of phage MR-5 in resolving skin and soft tissue infection induced by methicillin-resistant Staphylococcus aureus

With the alarming rise in antimicrobial resistance, phage therapy represents a new paradigm for combating antibiotic-resistant infectious diseases that is worth exploring for its clinical success. With this scenario, the present study aimed at evaluating the in vivo potential of phage MR-5 (broad host range Staphylococcus aureus phage) against soft tissue infections induced by methicillin-resistant S. aureus (MRSA). Also, the usefulness of relatively simple murine air pouch as a dual-purpose model (to study both anti-bacterial and anti-inflammatory parameters) in the field of phage therapeutics has been put to test. Murine air pouch model was established with experimental skin infection induced by S. aureus ATCC 43,300 followed by subcutaneous administration of phage alone as well as along with linezolid. Phage MR-5 alone and in combination with linezolid (showing synergy) brought significant reduction in the bacterial load (both extracellular as well as intracellular) that led to faster resolution of pouch infection. The main conclusions surfaced from the present study include the following: (a) murine air pouch model represents a simple useful model (mimicking subcutaneous skin infection) for studying anti-bacterial potencies of drug candidates. Therefore, its use and further adaptations especially in field of phage therapeutics is highly advocated and (b) phage MR-5 proved to be a potential therapeutic candidate against treatment of MRSA-induced skin and soft tissue infections and use of combination therapy is strongly recommended.

Playing With Fire: Proinflammatory Virulence Mechanisms of Group A Streptococcus

Group A Streptococcus is an obligate human pathogen that is a major cause of infectious morbidity and mortality. It has a natural tropism for the oropharynx and skin, where it causes infections with excessive inflammation due to its expression of proinflammatory toxins and other virulence factors. Inflammation directly contributes to the severity of invasive infections, toxic shock syndrome, and the induction of severe post-infection autoimmune disease caused by autoreactive antibodies. This review discusses what is known about how the virulence factors of Group A Streptococcus induce inflammation and how this inflammation can promote disease. Understanding of streptococcal pathogenesis and the role of hyper-immune activation during infection may provide new therapeutic targets to treat the often-fatal outcome of severe disease.

Heterometrus Spinifer: An Untapped Source of Anti-Tumor Molecules

Despite intensive research, cancer incidence and mortality continue to rise. Consequently, the necessity to develop effective anti-cancer therapy is apparent. We have recently shown that the gut bacteria of animals living in polluted environments, such as crocodiles, are a potential source of novel anti-tumor molecules. To extend this work to other resilient species, we investigated the anti-tumor effects of gut bacteria of Heterometrus spinifer (a scorpion). Bacteria from the feces and gut were isolated, identified and evaluated for their anti-tumor effects. Bacterial-conditioned media was prepared in Roswell Park Memorial Institute (RPMI) 1640 media, and cytotoxicity and growth inhibitory properties were examined against cervical (HeLa) cancer cells. Liquid chromatography–mass spectrometry (LC-MS) was conducted to establish the identity of the molecules. Eighteen bacteria species from the gut (HSG01-18) and ten bacteria species from feces (HSF01-10) were tested for anti-tumor effects. Bacterial-conditioned media from scorpion gut and feces exhibited significant growth inhibitory effects against HeLa cells of 66.9% and 83.8%, respectively. Microscopic analysis of cancer cells treated with conditioned media HSG12 and HSG16 revealed apoptosis-like effects. HSG12 was identified as Pseudomonas aeruginosa and HSG16 was identified as Bacillus subtilis. Both conditioned media exhibited 100% growth inhibitory effects versus a selection of cancer cells, comprising cervical, breast and prostate cancer cells. LC–MS indicated the presence of 72 and 38 compounds, detected from HSG12 and HSG16, respectively. Out of these compounds, 47 were successfully identified while the remainder were unidentified and are possibly novel. This study suggests that the fecal and gut microbiota of scorpions might possess molecules with anti-cancer properties, however, further intensive research is needed to assess these expectations.

Dextromethorphan Analgesia in a Human Experimental Model of Hyperalgesia

Editor’s Perspective

What We Already Know about This Topic

What This Article Tells Us That Is New

Background

Central pain sensitization is often refractory to drug treatment. Dextromethorphan, an N-methyl-d-aspartate receptor antagonist, is antihyperalgesic in preclinical pain models. The hypothesis is that dextromethorphan is also antihyperalgesic in humans.

Methods

This randomized, double-blind, placebo-controlled, crossover study explores the antihyperalgesic effect of single and repeated 30-mg dose of oral dextromethorphan in 20 volunteers, using the freeze-injury pain model. This model leads to development of primary and secondary hyperalgesia, which develops away from the site of injury and is associated with central sensitization and activation of N-methyl-d-aspartate receptor in the spinal cord. The primary outcome was antihyperalgesia calculated with the area under the curve of the percentage change in mechanical pain threshold (electronic von Frey) on the area of secondary hyperalgesia. The secondary outcomes were mechanical pain threshold on the area of primary hyperalgesia and cognitive (reaction time) effect.

Results

Single 30-mg results are reported. Antihyperalgesia (% · min) is significantly higher on the area of secondary hyperalgesia with dextromethorphan than placebo (median [interquartile range]: 3,029 [746; 6,195] vs. 710 [–3,248; 4,439], P = 0.009, Hedge’s g = 0.8, 95% CI [0.1; 1.4]). On primary hyperalgesia area, mechanical pain threshold 2 h after drug intake is significantly higher with dextromethorphan (P = 0.011, Hedge’s g = 0.63, 95% CI [0.01; 1.25]). No difference in antinociception is observed after thermal painful stimuli on healthy skin between groups. Reaction time (ms) is shorter with placebo than with dextromethorphan (median [interquartile range]: 21.6 [–37.4; 0.1] vs. –1.2 [–24.3; 15.4], P = 0.015, Hedge’s g = 0.75, 95% CI [0.12; 1.39]). Nonserious adverse events occurrence (15%, 3 of 20 volunteers) was similar in both groups.

Conclusions

This study shows that low-dose (30-mg) dextromethorphan is antihyperalgesic in humans on the areas of primary and secondary hyperalgesia and reverses peripheral and central neuronal sensitization. Because dextromethorphan had no intrinsic antinociceptive effect in acute pain on healthy skin, N-methyl-d-aspartate receptor may need to be sensitized by pain for dextromethorphan to be effective.

Streptolysin S induces mitochondrial damage and macrophage death through inhibiting degradation of glycogen synthase kinase-3β in Streptococcus pyogenes infection

Group A Streptococcus (GAS) infection is associated with a variety of human diseases. Previous studies indicate GAS infection leads to RAW264.7 cell death, but the mechanism is unclear. Here, analyzing the timing of reactive oxygen species (ROS) production and using mitochondrial ROS scavenger, we found the wild type GAS-induced RAW264.7 cell death was associated with mitochondrial ROS. The wild type GAS infection could activate glycogen synthase kinase-3β (GSK-3β). Inhibition of GSK-3β activity by lithium chloride or decreasing GSK-3β expression by lentivirus-mediated short hairpin RNA for GSK-3β could not only decrease the wild type GAS-induced mitochondrial ROS generation, mitochondria damage and cell death, but also reduced GAS intracellular replication. Streptolysin S (SLS), a GAS toxin, played the important role on GAS-induced macrophage death. Compared to the wild type GAS with its isogenic sagB mutant (SLS mutant)-infected macrophages, we found sagB mutant infection caused less mitochondrial ROS generation and cell death than those of the wild type GAS-infected ones. Furthermore, the sagB mutant, but not the wild type or the sagB-complementary mutant, could induce GSK-3β degradation via a proteasome-dependent pathway. These results suggest that a new mechanism of SLS-induced macrophage death was through inhibiting GSK-3β degradation and further enhancing mitochondrial damage.

Ultralow doses of dextromethorphan protect mice from endotoxin-induced sepsis-like hepatotoxicity

Dextromethorphan, a wildly used over-the-counter antitussive drug, is reported to have anti-inflammatory effects. Previously, we and others have demonstrated that dextromethorphan at micromolar doses displays potent hepatoprotective effects and enhances mice survival in a sepsis model. Moreover, we also observed potent anti-inflammatory and neuroprotective effects of subpicomolar concentrations of dextromethorphan in rodent primary neuron-glial cultures. The purpose of this study was to provide a proof of principle that ultralow dose dextromethorphan displays anti-inflammatory and cytoprotective effects in animal studies. Here, we report that subpico- and micromolar doses of dextromethorphan showed comparable efficacy in protecting mice from lipopolysaccharide/d-galactosamine (LPS/GalN)-induced hepatotoxicity and mortality. Mice were given injections of dextromethorphan from 30 min before and 2, 4 h after an injection of LPS/GalN (20 μg/600 mg/kg). Our results showed that dextromethorphan at subpicomolar doses promoted survival rate in LPS/GalN-injected mice. Ultralow dose dextromethorphan also significantly reduced serum alanine aminotransferase activity, TNF-α level and liver cell damage of endotoxemia mice. Mechanistic studies using primary liver Kupffer cell cultures revealed that subpicomolar concentrations of dextromethorphan reduced the NADPH oxidase-generated superoxide free radicals from Kupffer cells, which in turn reduced the elevation of its downstream reactive oxygen species (iROS) to relieve the oxidative stress and decreased TNF-α production in Kupffer cells. Taken together, these findings suggest a novel therapeutic concept of using ultralow doses of dextromethorphan for the intervention of sepsis or septic shock.

Dextromethorphan Attenuates NADPH Oxidase-Regulated Glycogen Synthase Kinase 3β and NF-κB Activation and Reduces Nitric Oxide Production in Group A Streptococcal Infection

Group A Streptococcus (GAS) is an important human pathogen that causes a wide spectrum of diseases, including necrotizing fasciitis and streptococcal toxic shock syndrome. Dextromethorphan (DM), an antitussive drug, has been demonstrated to efficiently reduce inflammatory responses, thereby contributing to an increased survival rate of GAS-infected mice. However, the anti-inflammatory mechanisms underlying DM treatment in GAS infection remain unclear. DM is known to exert neuroprotective effects through an NADPH oxidase-dependent regulated process. In the present study, membrane translocation of NADPH oxidase subunit p47^phox and subsequent reactive oxygen species (ROS) generation induced by GAS infection were significantly inhibited via DM treatment in RAW264.7 murine macrophage cells. Further determination of proinflammatory mediators revealed that DM effectively suppressed inducible nitric oxide synthase (iNOS) expression and NO, tumor necrosis factor alpha, and interleukin-6 generation in GAS-infected RAW264.7 cells as well as in air-pouch-infiltrating cells from GAS/DM-treated mice. GAS infection caused AKT dephosphorylation, glycogen synthase kinase-3β (GSK-3β) activation, and subsequent NF-κB nuclear translocation, which were also markedly inhibited by treatment with DM and an NADPH oxidase inhibitor, diphenylene iodonium. These results suggest that DM attenuates GAS infection-induced overactive inflammation by inhibiting NADPH oxidase-mediated ROS production that leads to downregulation of the GSK-3β/NF-κB/NO signaling pathway.

Dextromethorphan Exhibits Anti-inflammatory and Immunomodulatory Effects in a Murine Model of Collagen-Induced Arthritis and in Human Rheumatoid Arthritis

Dextromethorphan (d-3-methoxy-17-methylmorphinan, DXM) is a commonly used antitussive with a favorable safety profile. Previous studies have demonstrated that DXM has anti-inflammatory and immunomodulatory properties; however, the effect of DXM in rheumatoid arthritis (RA) remains unknown. Herein, we found that DXM treatment attenuated arthritis severity and proinflammatory cytokine expression levels, including TNF-α, IL-6, and IL-17A, in paw tissues of CIA mice. DXM treatment also reduced serum TNF-α, IL-6, and IL-17A levels of CIA mice and patients with RA. DXM further decreased the production of anti-CII IgG, IFN-γ, and IL-17A in collagen-reactive CD4⁺ T cells extracted from the lymph nodes of CIA mice. In vitro incubation of bone marrow–derived dendritic cells with DXM limited CD4⁺ T-cell proliferation and inflammatory cytokine secretion. In conclusion, our results showed that DXM attenuated arthritis symptoms in CIA mice and significantly reduced proinflammatory cytokines in patients with RA, suggesting that it can be used as an anti-arthritic agent.

Effects of dextromethorphan and oxycodone on treatment of neuropathic pain in mice

Background

Neuropathic pain is a very troublesome and difficult pain to treat. Although opioids are the best analgesics for cancer and surgical pain in clinic, only oxycodone among opioids shows better efficacy to alleviate neuropathic pain. However, many side effects associated with the use of oxycodone render the continued use of it in neuropathic pain treatment undesirable. Hence, we explored whether dextromethorphan (DM, a known N-methyl-D-aspartate receptor antagonist with neuroprotective properties) could potentiate the anti-allodynic effect of oxycodone and underlying mechanisms regarding to glial cells (astrocytes and microglia) activation and proinflammatory cytokines release in a spinal nerve injury (SNL) mice model.

Results

Oxycodone produced a dose-dependent anti-allodynic effect. Co-administration of DM at a dose of 10 mg/kg (i.p.) (DM10) which had no anti-allodynic effect by itself enhanced the acute oxycodone (1 mg/kg, s.c.) effect. When the chronic anti-allodynic effects were examined, co-administration of DM10 also significantly enhanced the oxycodone effect at 3 mg/kg. Furthermore, oxycodone decreased SNL-induced activation of glial cells (astrocytes and microglia) and plasma levels of proinflammatory cytokines (IL-6, IL-1β and TNF-α). Co-administration of DM10 potentiated these effects of oxycodone.

Conclusion

The combined use of DM with oxycodone may have therapeutic potential for decreasing the effective dose of oxycodone on the treatment of neuropathic pain. Attenuation of the glial activation and proinflammatory cytokines in the spinal cord may be important mechanisms for these effects of DM.

Kallistatin modulates immune cells and confers anti-inflammatory response to protect mice from group A streptococcal infection

Group A streptococcus (GAS) infection may cause severe life-threatening diseases, including necrotizing fasciitis and streptococcal toxic shock syndrome. Despite the availability of effective antimicrobial agents, there has been a worldwide increase in the incidence of invasive GAS infection. Kallistatin (KS), originally found to be a tissue kallikrein-binding protein, has recently been shown to possess anti-inflammatory properties. However, its efficacy in microbial infection has not been explored. In this study, we transiently expressed the human KS gene by hydrodynamic injection and investigated its anti-inflammatory and protective effects in mice via air pouch inoculation of GAS. The results showed that KS significantly increased the survival rate of GAS-infected mice. KS treatment reduced local skin damage and bacterial counts compared with those in mice infected with GAS and treated with a control plasmid or saline. While there was a decrease in immune cell infiltration of the local infection site, cell viability and antimicrobial factors such as reactive oxygen species actually increased after KS treatment. The efficiency of intracellular bacterial killing in neutrophils was directly enhanced by KS administration. Several inflammatory cytokines, including tumor necrosis factor alpha, interleukin 1β, and interleukin 6, in local infection sites were reduced by KS. In addition, KS treatment reduced vessel leakage, bacteremia, and liver damage after local infection. Therefore, our study demonstrates that KS provides protection in GAS-infected mice by enhancing bacterial clearance, as well as reducing inflammatory responses and organ damage.

Dextromethorphan inhibits activations and functions in dendritic cells

Dendritic cells (DCs) play an important role in connecting innate and adaptive immunity. Thus, DCs have been regarded as a major target for the development of immunomodulators. In this study, we examined the effect of dextromethorphan (DXM), a common cough suppressant with a high safety profile, on the activation and function of DCs. In the presence of DXM, the LPS-induced expression of the costimulatory molecules in murine bone marrow-derived dendritic cells (BMDCs) was significantly suppressed. In addition, DXM treatment reduced the production of reactive oxygen species (ROS), proinflammatory cytokines, and chemokines in maturing BMDCs that were activated by LPS. Therefore, DXM abrogated the ability of LPS-stimulated DCs to induce Ag-specific T-cell activation, as determined by their decreased proliferation and IFN-γ secretion in mixed leukocyte cultures. Moreover, the inhibition of LPS-induced MAPK activation and NF-κB translocation may contribute to the suppressive effect of DXM on BMDCs. Remarkably, DXM decreased the LPS-induced surface expression of CD80, CD83, and HLA-DR and the secretion of IL-6 and IL-12 in human monocyte-derived dendritic cells (MDDCs). These findings provide a new insight into the impact of DXM treatment on DCs and suggest that DXM has the potential to be used in treating DC-related acute and chronic diseases.

Use of 3-hydroxy fatty acid concentrations in a murine air pouch infection model as a surrogate marker for LPS activity: a feasibility study using environmental Burkholderia cenocepacia isolates

Using a murine hypodermic air pouch infection model designed to mimic the release of bacterial products at physiological levels, 3-hydroxy fatty acid (3-OH FA) and endotoxin unit levels from Burkholderia cenocepacia isolates were assessed. The B. cenocepacia environmental isolates (n=35) survived in the hypodermic air pouch but did not invade across the peritoneal epithelial layer during a 72-h infection. For all 35 strains, when the molar ratio of C(14:0) 3-OH FA to C(16:0) 3-OH FA in the air pouch fluid wash samples was between 1.4 and 2.5, the concentrations of C(14:0) 3-OH FA were correlated with the endotoxin unit levels. However, both surrogate markers exhibited different correlations to the inflammatory response. The linear regression coefficient was 0.4234 for C(14:0) 3-OH FA concentrations vs. NO productions, 0.223 for endotoxin unit levels vs. NO productions, 0.5008 for C(14:0) 3-OH FA concentrations vs. TNF-alpha productions and 0.2869 for endotoxin unit levels vs. TNF-alpha productions. Therefore, C(14:0) 3-OH FA concentrations, rather than endotoxin unit levels, acted as an immunostimulatory indicator for LPS in the B. cenocepacia isolates.