Methylene blue as an antimalarial agent

Working towards the development of vaccines and chemotherapeutics against neosporosis-With all of its ups and downs-Looking ahead

Neospora caninum is an apicomplexan and obligatory intracellular parasite, which is the leading cause of reproductive failure in cattle and affects other farm and domestic animals, but also induces neuromuscular disease in dogs of all ages. In cattle, neosporosis is an important health problem, and has a considerable economic impact. To date there is no protective vaccine or chemotherapeutic treatment on the market. Immuno-prophylaxis has long been considered as the best control measure. Proteins involved in host cell interaction and invasion, as well as antigens mediating inflammatory responses have been the most frequently assessed vaccine targets. However, despite considerable efforts no effective vaccine has been introduced to the market to date. The development of effective compounds to limit the effects of vertical transmission of N. caninum tachyzoites has emerged as an alternative or addition to vaccination, provided suitable targets and safe and efficacious drugs can be identified. Additionally, the combination of both treatment strategies might be interesting to further increase protectivity against N. caninum infections and to decrease the duration of treatment and the risk of potential drug resistance. Well-established and standardized animal infection models are key factors for the evaluation of promising vaccine and compound candidates. The vast majority of experimental animal experiments concerning neosporosis have been performed in mice, although in recent years the numbers of experimental studies in cattle and sheep have increased. In this review, we discuss the recent findings concerning the progress in drug and vaccine development against N. caninum infections in mice and ruminants.

Methylene blue in anticancer photodynamic therapy: systematic review of preclinical studies

Background: Methylene blue has a long history of clinical application. Thanks to phenothiazine chromophore, it has potential in photodynamic anticancer therapy. In spite of the growing body of literature that has evaluated the action of this dye on different types of cancer, the systematic understanding of this problem is still lacking. Therefore, this systematic review was performed to study the efficacy of methylene blue in photodynamic anticancer therapy. Methods: This systematic review was carried out in accordance with the PRISMA guidelines, and the study protocol was registered in PROSPERO (CRD42022368738). Articles for the systematic review were identified through the PubMed database. SYRCLE's risk of bias tool was used to assess the studies. The results of systematic analysis are presented as narrative synthesis. Results: Ten studies met the inclusion criteria and these full texts were reviewed. In the selected articles, the dosage of dye infusion ranged from 0.04 to 24.12 mg/kg. The effectiveness of photodynamic therapy with methylene blue against different types of cancer was confirmed by a decrease in tumor sizes in seven articles. Conclusion: The results of the systematic review support the suggestions that photodynamic therapy with methylene blue helps against different types of cancer, including colorectal tumor, carcinoma, and melanoma. In cases of nanopharmaceutics use, a considerable increase of anticancer therapy effectiveness was observed. The further research into methylene blue in photodynamic anticancer therapy is needed. Systematic Review Registration: (https://www.crd.york.ac.uk/prospero/display_record.php?RecordID=368738), identifier (CRD42022368738).

Cardioprotection by methylene Blue Against Epinephrine-Induced Cardiac Arrhythmias and Myocardial Injury

Methylene blue is used in the treatment of vasoplegic syndrome after cardiac surgery, anaphylaxis, and septic shock refractory to epinephrine and fluid resuscitation. In this study, we investigated the potential protective effect of methylene blue on the development of cardiac arrhythmias after injection of epinephrine in rats. Methylene blue was given intraperitoneally at doses of 50 or 100 mg/kg. Cardiac arrhythmia was then induced with 10 μg/kg of epinephrine intravenously. In untreated, control rats, epinephrine caused bradycardia (96.48 ± 1.06 vs. 365.03 ± 0.68 beats/min), increased PR interval (0.54 ± 0.04 vs. 0.039 ± 0.004), RR interval (0.64 ± 0.003 vs. 0.16 ± 0.004 sec), shortened QTc interval (0.067 ± 0.05 vs. 0.1 ± 0.004 sec), increased QRS duration (0.048 ± 0.005 vs. 0.028 ± 0.002 sec), decreased R wave amplitude (0.3 ± 0.03 vs. 0.49 ± 0.04 mv), decreased the height of the ST segment (-0.0696 ± 0.004 vs. -0.0054 ± 0.003 mv), and caused ventricular extrasystoles (7.92 ± 0.56 vs. 0.5 ± 0.5). Methylene blue given at 50 or 100 mg/kg increased the heart rate, decreased RR interval, QRS duration and the drop in the ST height, increased duration of QTc interval and R wave amplitude and decreased the number of extrasystoles. The histological study showed that methylene blue protected against myocardial structural disorganization, cellular damage, necrosis, and haemorrhage between muscle fibres induced by epinephrine injection. We conclude that methylene blue dose-dependently prevented epinephrine-induced arrhythmias and cardiac muscle injury.

Neuroprotective effects of methylene blue in streptozotocin-induced model of Alzheimer's disease

Methylene blue (MB) can be used as a multidirectional neuroprotector to stop the development of multiple cascades of neuron damage during neurodegenerative processes. This study assesses a protective effect of MB, using an experimental simulation of sporadic Alzheimer's disease by intracerebroventricular administration of streptozotocin (STZ) in rats. It was found that a STZ-induced impairment of memory can be partially mitigated with intravenous injections of MB after the administration of STZ. The treatment of animals with MB prevented the STZ-induced increase in the number and density of microglial and GFAP-positive cells in the brain cortex. In addition, it was shown that the expression of the LC3B protein, an indicator of autophagy, increases in the hippocampus of animals treated with STZ. In the hippocampus of animals treated with MB, an increase in the expression of the LC3B protein was prevented. Using the Griess reaction assay and immunocytochemical study was found that MB reduces lipopolysaccharide-induced NO-production and the expression of iNOS in cultured neurons. In conclusion, our data demonstrate that MB has neuroprotective and anti-inflammatory effects and is able to prevent autophagy. These effects have important therapeutic implications, so MB could potentially play a role in the treatment of neurodegenerative processes.

Synthetic Small Molecule Modulators of Hsp70 and Hsp40 Chaperones as Promising Anticancer Agents

A class of chaperones dubbed heat shock protein 70 (Hsp70) possesses high relevance in cancer diseases due to its cooperative activity with the well-established anticancer target Hsp90. However, Hsp70 is closely connected with a smaller heat shock protein, Hsp40, forming a formidable Hsp70-Hsp40 axis in various cancers, which serves as a suitable target for anticancer drug design. This review summarizes the current state and the recent developments in the field of (semi-)synthetic small molecule inhibitors directed against Hsp70 and Hsp40. The medicinal chemistry and anticancer potential of pertinent inhibitors are discussed. Since Hsp90 inhibitors have entered clinical trials but have exhibited severe adverse effects and drug resistance formation, potent Hsp70 and Hsp40 inhibitors may play a significant role in overcoming the drawbacks of Hsp90 inhibitors and other approved anticancer drugs.

The activity of methylene blue against asexual and sexual stages of Plasmodium vivax

Methylene blue (MB) is an alternative for combating drug-resistant malaria parasites. Its transmission-blocking potential has been demonstrated in vivo in murine models, in vitro, and in clinical trials. MB shows high efficacy against Plasmodium vivax asexual stages; however, its efficacy in sexual stages is unknown. In this study, we evaluated the potential of MB against asexual and sexual forms of P. vivax isolated from the blood of patients residing in the Brazilian Amazon. An ex vivo schizont maturation assay, zygote to ookinete transformation assay, direct membrane feed assay (DMFA), and standard membrane feed assay (SMFA) using P. vivax gametocytes with MB exposure were performed. A cytotoxicity assay was also performed on freshly collected peripheral blood mononuclear cells (PBMCs) and the hepatocyte carcinoma cell line HepG2. MB inhibited the P. vivax schizont maturation and demonstrated an IC₅₀ lower than that of chloroquine (control drug). In the sexual forms, the MB demonstrated a high level of inhibition in the transformation of the zygotes into ookinetes. In the DMFA, MB did not considerably affect the infection rate and showed low inhibition, but it demonstrated a slight decrease in the infection intensity in all tested concentrations. In contrast, in the SMFA, MB was able to completely block the transmission at the highest concentration (20 µM). MB demonstrated low cytotoxicity to fresh PBMCs but demonstrated higher cytotoxicity to the hepatocyte carcinoma cell line HepG2. These results show that MB may be a potential drug for vivax malaria treatment.

Rapid and Specific Action of Methylene Blue against Plasmodium Transmission Stages

Methylene blue (MB) is the oldest synthetic anti-infective. Its high potency against asexual and sexual stages of malaria parasites is well documented. This study aimed to investigate possible additional activities of MB in interfering with parasite transmission and determine target stages in Anopheles vectors and humans. MB's transmission-blocking activity was first evaluated by an ex vivo direct membrane feeding assay (DMFA) using Plasmodium falciparum field isolates. To investigate anti-mosquito stage activity, Plasmodium berghei-infected Anopheles stephensi mosquitoes were fed a second blood meal on mice that had been treated with methylene blue, 3, 6- and 15-days after the initial infectious blood meal. Anti-sporozoite and liver stage activities were evaluated in vitro and in vivo via sporozoite invasion and liver stage development assays, respectively. MB exhibited a robust inhibition of P. falciparum transmission in An. gambiae, even when added shortly before the DMFA but only a moderate effect against P. berghei oocyst development. Exposure of mature P. berghei and P. falciparum sporozoites to MB blocked hepatocyte invasion, yet P. berghei liver stage development was unaffected by MB. Our results indicate previously underappreciated rapid specific activities of methylene blue against Plasmodium transmission stages, preventing the establishment of both mosquito midgut and liver infections as the first essential steps in both hosts.

Investigation of Sonosensitizers Based on Phenothiazinium Photosensitizers

The main advantage of sonodynamic therapy (SDT), the combining of ultrasound with a sonosensitizer, over photodynamic therapy (PDT) is that ultrasound penetrates deeper into tissues to activate the sonosensitizer, which offers noninvasive therapy for tumors in a site-oriented approach. In this study, we synthesized two symmetrical phenothiazine derivatives in which the methyl groups of MB (methylene blue) have been replaced by a hexyl and hydroxyethyl chains, named 3,7-bis(dihexylamino)-phenothiazin-5-ium iodide (MB6C) and 3,7-bis(di(2-hydroxyethyl)amino)-phenothiazin-5-ium iodide (MBOH), respectively. We explore the efficiency differences between PDT and SDT induced by these phenothiazine derivatives based on the standard of methylene blue (MB). Spectral studies indicate that these MB analogs exhibit sonosensitization ability with a similar tendency to the photosensitization ability. This means that MB, MBOH, and MB6C can be potential photosensitizers and sonosensitizers. After biological evaluation, we conclude that compound MB6C is a potential PDT and SDT candidate because it exhibits higher uptake, efficient intracellular phototoxicity and sonotoxicity over MB and MBOH, with IC50 values of ~2.5 µM and ~5 µM, respectively.

Foreign body removal with the assistance of ultrasound guidance and methylene blue staining in children-a cohort study

BACKGROUND

Soft tissue foreign bodies (FBs) are very commonly observed in paediatric emergency departments. Not all FBs can be removed effectively, even via open surgery and image intensifier guidance. In the current study, we evaluated the efficiency of FB removal with the assistance of ultrasound (US) and methylene blue (MB) staining.

METHODS

We enrolled 80 patients at our clinical center between May 2016 and December 2020. Eleven patients were operated upon with the assistance of US guidance and MB and were defined as group A; the other 69 patients were defined as group B. For the patients in group A, US was first used to locate the FB; MB was then injected next to the FB. Open surgery was subsequently performed. For group B, the FBs were removed by conventional methods. The surgical outcomes were evaluated according to surgical duration, incision infection rates, radiograph exposure times, and FB residue rates.

RESULTS

The average surgery time for group A was 0.35 ± 0.10 hours; the corresponding time was 0.49 ± 0.50 hours in group B and there was a significant difference between the groups (p = 0.032). The radiograph exposure times were 1.33 ± 0.34 in group A and 4.65 ± 1.81 times in group B (p = 0.021).

CONCLUSIONS

This study demonstrates that assistance of US and MB staining is a more efficient approach compared with traditional methods for FB removal, and this surgical method can be used effectively for FB removal in children.

Resistance to artemisinin in falciparum malaria parasites: A redox-mediated phenomenon

Malaria remains a major public health disease due to its high yearly mortality and morbidity. Resistance to the gold standard drug, artemisinin, is worrisome and needs better understanding in order to be overcome. In this work, we sought to study whether redox processes are involved in artemisinin resistance. As artemisinin is known to act among others via production of reactive species, we first compared the production of reactive oxygen species and concomitant protein oxidation in artemisinin-sensitive and artemisinin-resistant parasites when treated with artemisinin. The results undoubtedly demonstrated, using different original methods, that the level of ROS, including superoxide production, and oxidized protein were lower in the resistant strain. Interestingly, the major in-between strain difference was reported at the earlier ring stages, which are the forms able to enter in a quiescence state according to the ART resistance phenomenon. Moreover, we demonstrated a better homeostasis regulation in relation with higher expression of antioxidants in the artemisinin-resistant parasites than their sensitive counterparts after artemisinin exposure, notably, superoxide dismutase and the glutathione (GSH) system. These findings enrich the body of knowledges about the multifaceted mechanism of artemisinin resistance and will help in the design and development of newer antimalarials strategies active against resistant parasites.

Identification of broad anti-coronavirus chemical agents for repurposing against SARS-CoV-2 and variants of concern

Endemic human coronaviruses (hCoVs) 229E and OC43 cause respiratory disease with recurrent infections, while severe acute respiratory syndrome (SARS)-CoV-2 spreads across the world with impact on health and societies. Here, we report an image-based multicycle infection procedure with α-coronavirus hCoV-229E-eGFP in an arrayed chemical library screen of 5440 clinical and preclinical compounds. Toxicity counter selection and challenge with the β-coronaviruses OC43 and SARS-CoV-2 in tissue culture and human airway epithelial explant cultures (HAEEC) identified four FDA-approved compounds with oral availability. Methylene blue (MB, used for the treatment of methemoglobinemia), Mycophenolic acid (MPA, used in organ transplantation) and the anti-fungal agent Posaconazole (POS) had the broadest anti-CoV spectrum. They inhibited the shedding of SARS-CoV-2 and variants-of-concern (alpha, beta, gamma, delta) from HAEEC in either pre- or post exposure regimens at clinically relevant concentrations. Co-treatment of cultured cells with MB and the FDA-approved SARS-CoV-2 RNA-polymerase inhibitor Remdesivir reduced the effective anti-viral concentrations of MB by 2-fold, and Remdesivir by 4 to 10-fold, indicated by BLISS independence synergy modelling. Neither MB, nor MPA, nor POS affected the cell delivery of SARS-CoV-2 or OC43 (+)sense RNA, but blocked subsequent viral RNA accumulation in cells. Unlike Remdesivir, MB, MPA or POS did not reduce the release of viral RNA in post exposure regimen, thus indicating infection inhibition at a post-replicating step as well. In summary, the data emphasize the power of unbiased, full cycle compound screens to identify and repurpose broadly acting drugs against coronaviruses.

Review on Methylene Blue: Its Properties, Uses, Toxicity and Photodegradation

The unavailability of clean drinking water is one of the significant health issues in modern times. Industrial dyes are one of the dominant chemicals that make water unfit for drinking. Among these dyes, methylene blue (MB) is toxic, carcinogenic, and non-biodegradable and can cause a severe threat to human health and environmental safety. It is usually released in natural water sources, which becomes a health threat to human beings and living organisms. Hence, there is a need to develop an environmentally friendly, efficient technology for removing MB from wastewater. Photodegradation is an advanced oxidation process widely used for MB removal. It has the advantages of complete mineralization of dye into simple and nontoxic species with the potential to decrease the processing cost. This review provides a tutorial basis for the readers working in the dye degradation research area. We not only covered the basic principles of the process but also provided a wide range of previously published work on advanced photocatalytic systems (single-component and multi-component photocatalysts). Our study has focused on critical parameters that can affect the photodegradation rate of MB, such as photocatalyst type and loading, irradiation reaction time, pH of reaction media, initial concentration of dye, radical scavengers and oxidising agents. The photodegradation mechanism, reaction pathways, intermediate products, and final products of MB are also summarized. An overview of the future perspectives to utilize MB at an industrial scale is also provided. This paper identifies strategies for the development of effective MB photodegradation systems.

Reactive Oxygen Species as the Brainbox in Malaria Treatment

Several measures are in place to combat the worldwide spread of malaria, especially in regions of high endemicity. In part, most common antimalarials, such as quinolines and artemisinin and its derivatives, deploy an ROS-mediated approach to kill malaria parasites. Although some antimalarials may share similar targets and mechanisms of action, varying levels of reactive oxygen species (ROS) generation may account for their varying pharmacological activities. Regardless of the numerous approaches employed currently and in development to treat malaria, concerningly, there has been increasing development of resistance by Plasmodium falciparum, which can be connected to the ability of the parasites to manage the oxidative stress from ROS produced under steady or treatment states. ROS generation has remained the mainstay in enforcing the antiparasitic activity of most conventional antimalarials. However, a combination of conventional drugs with ROS-generating ability and newer drugs that exploit vital metabolic pathways, such antioxidant machinery, could be the way forward in effective malaria control.

Methylene Blue-Based Nano and Microparticles: Fabrication and Applications in Photodynamic Therapy

Methylene blue (MB) has been used in the textile industry since it was first extracted by the German chemist Heinrich Caro. Its pharmacological properties have also been applied toward the treatment of certain diseases such as methemoglobinemia, ifosfamide-induced encephalopathy, and thyroid conditions requiring surgery. Recently, the utilization of MB as a safe photosensitizer in photodynamic therapy (PDT) has received attention. Recent findings demonstrate that photoactivated MB exhibits not only anticancer activity but also antibacterial activity both in vitro and in vivo. However, due to the hydrophilic nature of MB, it is difficult to create MB-embedded nano- or microparticles capable of increasing the clinical efficacy of the PDT. This review aims to summarize fabrication techniques for MB-embedded nano and microparticles and to provide both in vitro and in vivo examples of MB-mediated PDT, thereby offering a future perspective on improving this promising clinical treatment modality. We also address examples of MB-mediated PDT in both cancer and infection treatments. Both in-vitro and in-vivo studies are summarized here to document recent trends in utilizing MB as an effective photosensitizer in PDT. Lastly, we discuss how developing efficient MB-carrying nano- and microparticle platforms would be able to increase the benefits of PDT.

Glutathione reductase: A cytoplasmic antioxidant enzyme and a potential target for phenothiazinium dyes in Neospora caninum

Neospora caninum causes heavy losses related to abortions in bovine cattle. This parasite developed a complex defense redox system, composed of enzymes as glutathione reductase (GR). Methylene blue (MB) impairs the activity of recombinant form of Plasmodium GR and inhibits the parasite proliferation in vivo and in vitro. Likewise, MB and its derivatives inhibits Neospora caninum proliferation, however, whether the MB mechanism of action is correlated to GR function remains unclear. Therefore, here, N. caninum GR (NcGR) was characterized and its potential inhibitors were determined. NcGR was found in the tachyzoite cytosol and has a similar structure and sequence compared to its homologs. We verified the in vitro activity of rNcGR (875 nM) following NADPH absorbance at 340 nM (100 mM KH2PO4, pH 7.5, 1 mM EDTA, ionic strength: 600 mM, 25 °C). rNcGR exhibited a Michaelian behavior (Km(GSSG):0.10 ± 0.02 mM; kcat(GSSG):0.076 ± 0.003 s-1; Km(NADPH):0.006 ± 0.001 mM; kcat(NADPH): 0.080 ± 0.003 s-1). The IC50 of MB,1,9-dimethyl methylene blue, new methylene blue, and toluidine blue O on rNcGR activity were 2.1 ± 0.2 μM, 11 ± 2 μM, 0.7 ± 0.1 μM, and 0.9 ± 0.2 μM, respectively. Our results suggest the importance of NcGR in N. caninum biology and antioxidant mechanisms. Moreover, data presented here strongly suggest that NcGR is an important target of phenothiazinium dyes in N. caninum proliferation inhibition.

Radical Scavenging Potential of the Phenothiazine Scaffold: A Computational Analysis

The reactivity of phenothiazine (PS), phenoselenazine (PSE), and phenotellurazine (PTE) with different reactive oxygen species (ROS) has been studied using density functional theory (DFT) in combination with the QM‐ORSA (Quantum Mechanics‐based Test for Overall Free Radical Scavenging Activity) protocol for an accurate kinetic rate calculation. Four radical scavenging mechanisms have been screened, namely hydrogen atom transfer (HAT), radical adduct formation (RAF), single electron transfer (SET), and the direct oxidation of the chalcogen atom. The chosen ROS are HO^., HOO^., and CH₃OO^.. PS, PSE, and PTE exhibit an excellent antioxidant activity in water regardless of the ROS due to their characteristic diffusion‐controlled regime processes. For the HO^. radical, the primary active reaction mechanism is, for all antioxidants, RAF. But, for HOO^. and CH₃OO^., the dominant mechanism strongly depends on the antioxidant: HAT for PS and PSE, and SET for PTE. The scavenging efficiency decreases dramatically in lipid environment and remains only significant (via RAF) for the most reactive radical (HO^.). Therefore, PS, PSE, and PTE are excellent antioxidant molecules, especially in aqueous, physiological environments where they are active against a broad spectrum of harmful radicals. There is no advantage or significant difference in the scavenging efficiency when changing the chalcogen since the reactivity mainly derives from the amino hydrogen and the aromatic sites.

Repurposing methylene blue in the management of COVID-19: Mechanistic aspects and clinical investigations

The severe acute respiratory syndrome-coronavirus 2 (SARS-CoV-2) is the most recent coronaviruses, which has infected humans, and caused the disease COVID-19. The World Health Organization has declared COVID-19 as a pandemic in March 2020. The SARS-CoV-2 enters human hosts majorly via the respiratory tract, affecting the lungs first. In few critical cases, the infection progresses to failure of the respiratory system known as acute respiratory distress syndrome acute respiratory distress syndrome may be further associated with multi-organ failure and vasoplegic shock. Currently, the treatment of COVID-19 involves use of antiviral and anti-cytokine drugs. However, both the drugs have low efficacy because they cannot inhibit the production of free radicals and cytokines at the same time. Recently, some researchers have reported the use of methylene blue (MB) in COVID-19 management. MB has been used since a long time as a therapeutic agent, and has been approved by the US FDA for the treatment of other diseases. The additional advantage of MB is its low cost. MB is a safe drug when used in the dose of < 2 mg/kg. In this review, the applicability of MB in COVID-19 and its mechanistic aspects have been explored and compiled. The clinical studies have been explained in great detail. Thus, the potential of MB in the management of COVID-19 has been examined.

Spectroscopic Measurement of Methylene Blue Distribution in Organs and Tissues of Hamadryas Baboons during Oral Administration

New research on Methylene Blue (MB), carried out in 2020, shows that it can be an effective antiviral drug as part of COVID-19 treatment. According to the research findings, MB has potential as a direct antiviral drug for the prevention and treatment of COVID-19 in the first stages of the disease. However, the MB accumulation by various types of tissues, as well as by immune cells, has not been previously studied. Therefore, the objective of this study was to obtain spectral data on the interstitial distribution of the administered drug in endothelial tissues in primates. The data on interstitial MB distribution obtained by spectroscopic measurement at both macro- and microlevels during oral administration to Hamadryas baboon individuals demonstrate that MB accumulates in mucous membranes of gastrointestinal tract and the tissues of the respiratory, cardiovascular, immune, and nervous systems. Additionally, it was found that MB was present in lung and brain myeloid cells in significant concentrations, which makes it potentially useful for protection from autoimmune response (cytokine storm) and as a tool for the correction of immunocompetent cells’ functional state during laser irradiation. Since the cytokine storm starts from monocytic cells during SARS-CoV-2 cellular damage and since tumor-associated macrophages can significantly alter tumor metabolism, accumulation of MB in these cells provides a reason to conclude that the immune response correction in COVID-19 patients and change in macrophages phenotype can be achieved by deactivation of inflammatory macrophages in tissues with MB using laser radiation of red spectral range.

Chemical Biology Tools To Investigate Malaria Parasites

Parasitic diseases like malaria tropica have been shaping human evolution and history since the beginning of mankind. After infection, the response of the human host ranges from asymptomatic to severe and may culminate in death. Therefore, proper examination of the parasite's biology is pivotal to deciphering unique molecular, biochemical and cell biological processes, which in turn ensure the identification of treatment strategies, such as potent drug targets and vaccine candidates. However, implementing molecular biology methods for genetic manipulation proves to be difficult for many parasite model organisms. The development of fast and straightforward applicable alternatives, for instance small-molecule probes from the field of chemical biology, is essential. In this review, we will recapitulate the highlights of previous molecular and chemical biology approaches that have already created insight and understanding of the malaria parasite Plasmodium falciparum. We discuss current developments from the field of chemical biology and explore how their application could advance research into this parasite in the future. We anticipate that the described approaches will help to close knowledge gaps in the biology of P. falciparum and we hope that researchers will be inspired to use these methods to gain knowledge - with the aim of ending this devastating disease.

Evidence for in vitro and in vivo activity of the antimalarial pyronaridine against Schistosoma

Background

Schistosomiasis is highly prevalent in Africa. Praziquantel is effective against adult schistosomes but leaves prepatent stages unaffected—which is a limit to patient management and elimination. Given the large-scale use of praziquantel, development of drug resistance by Schistosoma is feared. Antimalarials are promising drugs for alternative treatment strategies of Schistosoma infections. Development of drugs with activity against both malaria and schistosomiasis is particularly appealing as schistosome infections often occur concomitantly with malaria parasites in sub-Saharan Africa. Therefore, antiplasmodial compounds were progressively tested against Schistosoma in vitro, in mice, and in a clinical study.

Results

Amongst 16 drugs and 1 control tested, pyronaridine, methylene blue and 5 other antimalarials were highly active in vitro against larval stage schistosomula with a 50% inhibitory concentration below 10 μM. Both drugs were lethal to ex vivo adult worms tested at 30 μM with methylene blue also active at 10 μM. Pyronaridine treatment of mice infected with S. mansoni at the prepatent stage reduced worm burden by 82% and cured 7 out of 12 animals, however in mice adult stages remained viable. In contrast, methylene blue inhibited adult worms by 60% but cure was not achieved. In an observational pilot trial in Gabon in children, the antimalarial drug combination pyronaridine-artesunate (Pyramax) reduced S. haematobium egg excretion from 10/10 ml urine to 0/10 ml urine, and 3 out of 4 children were cured.

Conclusion

Pyronaridine and methylene blue warrant further investigation as candidates for schistosomiasis treatment. Both compounds are approved for human use and evidence for their potential as antischistosomal compounds can be obtained directly from clinical testing. Particularly, pyronaridine-artesunate, already available as an antimalarial drug, calls for further clinical evaluation.

Trial registration

ClinicalTrials.gov Identifier NCT03201770.

Praziquantel is still the only drug in use for the treatment of all Schistosoma spp. and is exclusively active against the adult life cycle stage, since schistosomes in the prepatent period of up to eight weeks are not affected by the drug. Although resistance to praziquantel has not been confirmed and its existence remains controversial, some countries have identified clinical schistosome isolates with reduced sensitivity to praziquantel, after deployment in mass drug administration programs. The need for a new antischistosomal compound is urgent, ideally exhibiting broad activity against all stages of the parasite’s life cycle present in humans. After testing a series of antiplasmodial compounds, the authors found that several compounds also exhibited antischistosomal activity at various life cycle stages of the worms, including pyronaridine and methylene blue, both compounds already approved for human use. A pilot trial with pyronaridine-artesunate done in Gabon showed the first promising results against Schistosoma infections.

A Comparative Review on Current and Future Drug Targets Against Bacteria & Malaria

Long before the discovery of drugs like 'antibiotic and anti-parasitic drugs', the infectious diseases caused by pathogenic bacteria and parasites remain as one of the major causes of morbidity and mortality in developing and underdeveloped countries. The phenomenon by which the organism exerts resistance against two or more structurally unrelated drugs is called multidrug resistance (MDR) and its emergence has further complicated the treatment scenario of infectious diseases. Resistance towards the available set of treatment options and poor pipeline of novel drug development puts an alarming situation. A universal goal in the post-genomic era is to identify novel targets/drugs for various life-threatening diseases caused by such pathogens. This review is conceptualized in the backdrop of drug resistance in two major pathogens i.e. "Pseudomonas aeruginosa" and "Plasmodium falciparum". In this review, the available targets and key mechanisms of resistance of these pathogens have been discussed in detail. An attempt has also been made to analyze the common drug targets of bacteria and malaria parasite to overcome the current drug resistance scenario. The solution is also hypothesized in terms of a present pipeline of drugs and efforts made by scientific community.

Methylene Blue Application to Lessen Pain: Its Analgesic Effect and Mechanism

Methylene blue (MB) is a cationic thiazine dye, widely used as a biological stain and chemical indicator. Growing evidence have revealed that MB functions to restore abnormal vasodilation and notably it is implicated even in pain relief. Physicians began to inject MB into degenerated disks to relieve pain in patients with chronic discogenic low back pain (CDLBP), and some of them achieved remarkable outcomes. For osteoarthritis and colitis, MB abates inflammation by suppressing nitric oxide production, and ultimately relieves pain. However, despite this clinical efficacy, MB has not attracted much public attention in terms of pain relief. Accordingly, this review focuses on how MB lessens pain, noting three major actions of this dye: anti-inflammation, sodium current reduction, and denervation. Moreover, we showed controversies over the efficacy of MB on CDLBP and raised also toxicity issues to look into the limitation of MB application. This analysis is the first attempt to illustrate its analgesic effects, which may offer a novel insight into MB as a pain-relief dye.

New methylene blue derivatives suggest novel anti-orthopoxviral strategies

Decades after the eradication of smallpox and the discontinuation of routine smallpox vaccination, over half of the world's population is immunologically naïve to variola virus and other orthopoxviruses (OPXVs). Even in those previously vaccinated against smallpox, protective immunity wanes over time. As such, there is a concomitant increase in the incidence of human OPXV infections worldwide. To identify novel antiviral compounds with potent anti-OPXV potential, we characterized the inhibitory activity of PAV-866 and other methylene blue derivatives against the prototypic poxvirus, vaccinia virus (VACV). These compounds inactivated virions prior to infection and consequently inhibited viral binding, fusion and entry. The compounds exhibited strong virucidal activity at non-cytotoxic concentrations, and inhibited VACV infection when added before, during or after viral adsorption. The compounds were effective against other OPXVs including monkeypox virus, cowpox virus and the newly identified Akhmeta virus. Altogether, these findings reveal a novel mode of inhibition that has not previously been demonstrated for small molecule compounds against VACV. Additional studies are in progress to determine the in vivo efficacy of these compounds against OPXVs and further characterize the anti-viral effects of these derivatives.

Effect of long-term methylene blue treatment on the composition of mouse gut microbiome and its relationship with the cognitive abilities of mice

In recent years, methylene blue (MB) has attracted considerable interest as a potential drug for the treatment of methemoglobinemia and neurodegenerative diseases. MB is active against microorganisms from various taxonomic groups. However, no studies have yet been conducted on the effect of MB on the intestinal microbiome of model animals. The aim of this work was to study the effect of different concentrations of MB on the mouse gut microbiome and its relationship with the cognitive abilities of mice. We showed that a low MB concentration (15 mg/kg/day) did not cause significant changes in the microbiome composition. The Bacteroidetes/Firmicutes ratio decreased relative to the control on the 2nd and 3rd weeks. A slight decrease in the levels Actinobacteria was detected on the 3rd week of the experiment. Changes in the content of Delta, Gamma, and Epsilonproteobacteria have been also observed. We did not find significant alterations in the composition of intestinal microbiome, which could be an indication of the development of dysbiosis or other gut dysfunction. At the same time, a high concentration of MB (50 mg/kg/day) led to pronounced changes, primarily an increase in the levels of Delta, Gamma and Epsilonproteobacteria. Over 4 weeks of therapy, the treatment with high MB concentration has led to an increase in the median content of Proteobacteria to 7.49% vs. 1.61% in the control group. Finally, we found that MB at a concentration of 15 mg/kg/day improved the cognitive abilities of mice, while negative correlation between the content of Deferribacteres and cognitive parameters was revealed. Our data expand the understanding of the relationship between MB, cognitive abilities, and gut microbiome in respect to the antibacterial properties of MB.

Protein kinase inhibitors in traumatic brain injury and repair: New roles of nanomedicine

Traumatic brain injury (TBI) causes physical injury to the cell membranes of neurons, glial and axons causing the release of several neurochemicals including glutamate and cytokines altering cell-signaling pathways. Upregulation of mitogen associated protein kinase (MAPK) and extracellular signal-regulated kinase (ERK) occurs that is largely responsible for cell death. The pharmacological blockade of these pathways results in cell survival. In this review role of several protein kinase inhibitors on TBI induced oxidative stress, blood-brain barrier breakdown, brain edema formation, and resulting brain pathology is discussed in the light of current literature.

The ameliorative effects of methylene blue on testicular damage induced by cisplatin in rats

Cisplatin, a common chemotherapeutic drug, can induce testicular toxicity. Methylene blue, a potent antioxidant, can inhibit the generation of free radicals. This research aimed to study the protective effect of methylene blue against the cisplatin-induced toxicity of the reproductive system in rats. 35 male Wistar rats were divided into five groups: the control group, the cisplatin group (a single dose of 5 mg/kg cisplatin), the low-dose and high-dose methylene blue + cisplatin (2 and 4 mg/kg of methylene blue, respectively, for 7 days) and the methylene blue group (4 mg/kg of methylene blue, for 7 days). The treatments were applied through intraperitoneal injection. Cisplatin treatment reduced the sperm parameters and serum testosterone levels significantly. Methylene blue treatment increased the sperm count (p < .001), viability (p < .001) and motility (p < .001) compared to the cisplatin group. The methylene blue group showed a significant increase in the levels of testosterone compared to the cisplatin group (p < .001) and reverted histopathological changes in cisplatin-treated groups. Immunohistochemical evaluation of the caspase-3 protein revealed that the treatment with methylene blue has significant anti-apoptotic effects on testicular tissue damage. In conclusion, methylene blue can attenuate the cisplatin-induced histological damages and improve the sperm parameters.

Pharmacokinetics and Ex Vivo Antimalarial Activity of Artesunate-Amodiaquine plus Methylene Blue in Healthy Volunteers

High rates of artemisinin-based combination therapy (ACT) failures in the treatment of Plasmodium falciparum malaria in Southeast Asia have led to triple-drug strategies to extend the useful life of ACTs. In this study, we determined whether methylene blue [MB; 3,7-bis(dimethylamino)phenothiazin-5-ium chloride hydrate] alters the pharmacokinetics of artesunate-amodiaquine (ASAQ) and enhances the ex vivo antimalarial activity of ASAQ. In an open-label, randomized crossover design, a single oral dose of ASAQ (200 mg AS/540 mg AQ) alone or with MB (325 mg) was administered to 15 healthy Vietnamese volunteers. Serial blood samples were collected up to 28 days after dosing. Pharmacokinetic properties of the drugs were determined by noncompartmental analysis. After drug administration, plasma samples from seven participants were assessed for ex vivo antimalarial activity against the artemisinin-sensitive MRA1239 and the artemisinin-resistant MRA1240 P. falciparum lines, in vitro MB significantly increased the mean area under the curve of the active metabolite of AS, dihydroartemisinin (1,246 ± 473 versus 917 ± 405 ng·h/ml, P = 0.009) but did not alter the pharmacokinetics of AQ, AS, or desethylamodiaquine. Comparing the antimalarial activities of the plasma samples from the participants collected up to 48 h after ASAQ plus MB (ASAQ+MB) and ASAQ dosing against the MRA1239 and MRA1240 lines, MB significantly enhanced the blood schizontocidal activity of ASAQ by 2.0-fold and 1.9-fold, respectively. The ring-stage survival assay also confirmed that MB enhanced the ex vivo antimalarial activity of ASAQ against MRA1240 by 2.9-fold to 3.8-fold, suggesting that the triple-drug combination has the potential to treat artemisinin-resistant malaria and for malaria elimination. (This study has been registered in the Australian New Zealand Clinical Trials Registry [https://anzctr.org.au/] under registration number ACTRN12612001298808.).

Antimicrobial Activity of Lignin-Derived Polyurethane Coatings Prepared from Unmodified and Demethylated Lignins

Due to global ecological and economic challenges that have been correlated to the transition from fossil-based to renewable resources, fundamental studies are being performed worldwide to replace fossil fuel raw materials in plastic production. One aspect of current research is the development of lignin-derived polyols to substitute expensive fossil-based polyol components for polyurethane and polyester production. This article describes the synthesis of bioactive lignin-based polyurethane coatings using unmodified and demethylated Kraft lignins. Demethylation was performed to enhance the reaction selectivity toward polyurethane formation. The antimicrobial activity was tested according to a slightly modified standard test (JIS Z 2801:2010). Besides effects caused by the lignins themselves, triphenylmethane derivatives (brilliant green and crystal violet) were used as additional antimicrobial substances. Results showed increased antimicrobial capacity against Staphylococcus aureus. Furthermore, the coating color could be varied from dark brown to green and blue, respectively.

Hydrogel Nanofibers from Carboxymethyl Sago Pulp and Its Controlled Release Studies as a Methylene Blue Drug Carrier

The potential use of carboxymethyl sago pulp (CMSP) extracted from sago waste for producing hydrogel nanofibers was investigated as a methylene blue drug carrier. Sago pulp was chemically modified via carboxymethylation reaction to form carboxymethyl sago pulp (CMSP) and subsequently used to produce nanofibers using the electrospinning method with the addition of poly(ethylene oxide) (PEO). The CMSP nanofibers were further treated with citric acid to form cross-linked hydrogel. Studies on the percentage of swelling following the variation of citric acid concentrations and curing temperature showed that 89.20 ± 0.42% of methylene blue (MB) was loaded onto CMSP hydrogel nanofibers with the percentage of swelling 4366 ± 975%. Meanwhile, methylene blue controlled release studies revealed that the diffusion of methylene blue was influenced by the pH of buffer solution with 19.44% of MB released at pH 7.34 within 48 h indicating the potential of CMSP hydrogel nanofibers to be used as a drug carrier for MB.

The past, present and future of anti-malarial medicines

Great progress has been made in recent years to reduce the high level of suffering caused by malaria worldwide. Notably, the use of insecticide-treated mosquito nets for malaria prevention and the use of artemisinin-based combination therapy (ACT) for malaria treatment have made a significant impact. Nevertheless, the development of resistance to the past and present anti-malarial drugs highlights the need for continued research to stay one step ahead. New drugs are needed, particularly those with new mechanisms of action. Here the range of anti-malarial medicines developed over the years are reviewed, beginning with the discovery of quinine in the early 1800s, through to modern day ACT and the recently-approved tafenoquine. A number of new potential anti-malarial drugs currently in development are outlined, along with a description of the hit to lead campaign from which it originated. Finally, promising novel mechanisms of action for these and future anti-malarial medicines are outlined.

Study of Methylene Blue Interaction with Human Serum Albumin

The thiosine dye methylene blue (MB) interaction with human serum albumin (HSA) has been studied. MB was revealed to stabilize the native structure of HSA, since the denaturation temperature of the complexes is shifted to higher values in relation to that of the pure protein. It was also revealed that the absorption spectra of the complexes do not change noticeably, while in the fluorescence spectra the maximal intensity of MB decreases with the albumin concentration enhancement. Analysis of the obtained data allows to conclude that the main binding mode of MB to HSA, providing the stabilization of the protein native structure, is the electrostatic mechanism.

Nucleoside-lipid-based nanocarriers for methylene blue delivery: potential application as anti-malarial drug

Nucleolipid supramolecular assemblies are promising Drug Delivery Systems (DDS), particularly for nucleic acids. Studies based on negatively and positively charged nucleolipids (diC16dT and DOTAU, respectively) demonstrated appropriate stability, safety, and purity profile to be used as DDS. Methylene Blue (MB) remains a good antimalarial drug candidate, and could be considered for the treatment of uncomplicated or severe malaria. However, the development of MB as an antimalarial drug has been hampered by a high dose regimen required to obtain a proper effect, and a short plasmatic half life. We demonstrated that nanoparticles formed by nucleolipid encapsulation of MB using diC16dT and DOTAU (MB-NPs) is an interesting approach to improve drug stability and delivery. MB-NPs displayed sizes, PDI, zeta values, and colloidal stability allowing a possible use in intravenous formulations. Nanoparticles partially protected MB from oxido-reduction reactions, thus preventing early degradation during storage, and allowing prolongated pharmacokinetic in plasma. MB-NPs' efficacy, tested in vitro on sensitive or multidrug resistant strains of Plasmodium falciparum, was statistically similar to MB alone, with a slightly lower IC₅₀. This nucleolipid-based approach to protect drugs against degradation represents a new alternative tool to be considered for malaria treatment.

Nucleolipids protects methylene blue against reduction (induced by light and chemical reductants) and do not impair antimalarial activity.

A Mechanistic Investigation of Methylene Blue and Heparin Interactions and Their Photoacoustic Enhancement

We recently reported a real-time method to measure heparin in human whole blood based on the photoacoustic change of methylene blue (MB). Intriguingly, the MB behaved unlike other "turn on" photoacoustic probes-the absorbance decreased as the photoacoustic signal increased. The underlying mechanism was not clear and motivated this study. We studied the binding mechanism of MB and heparin in water and phosphate buffer saline (PBS) with both experimental and computational methods. We found that the photoacoustic enhancement of the MB-heparin mixture was a result of MB-heparin aggregation due to charge neutralization and resulting sequestration of MB in these aggregates. The sequestration of MB in the MB-heparin aggregates led to decreased absorbance-there was simply less free dye in solution to absorb light. The highest photoacoustic signal and aggregation occurred when the number of negatively charged sulfate groups on heparin was approximately equal to the number of positively charged MB molecule. The MB-heparin aggregates dissociated when there were more sulfated groups from heparin than MB molecules because of the electrostatic repulsion between negatively charged sulfate groups. PBS facilitated MB dimer formation regardless of heparin concentration and reprecipitated free MB in aggregates due to ionic strength and ionic shielding. Further molecular dynamics experiments found that binding of heparin occurred at the sulfates and glucosamines in heparin. Phosphate ions could interact with the heparin via sodium ions to impair the MB-heparin binding. Finally, our model found 3.7-fold more MB dimerization upon addition of heparin in MB solution confirming that heparin facilitates MB aggregation. We conclude that the addition of heparin in MB decreases the absorbance of the sample because of MB-heparin aggregation leading to fewer MB molecules in solution; however, the aggregation also increases the PA intensity because the MB molecules in the MB-heparin aggregate have reduced degrees of freedom and poor heat transfer to solvent.

Influence of phenothiazines, phenazines and phenoxazine on cation transport in Candida albicans

AIMS

(i) To analyse the increase in calcium ion uptake caused by several cationic dyes on Candida albicans, (ii) to postulate a mechanism, (iii) to define the effects of Zn ions on the phenomenon, and (iv) to propose the use of the dyes or their derivatives against C. albicans.

METHODS AND RESULTS

Cells were grown in yeast peptone dextrose medium and starved. We measured the hydrophobic solvent/water partition coefficients and the dyes uptake by the cells and found no correlation with their hydrophobicity. Most of the dyes caused an increase in K+ efflux (in correlation with a decrease in 86 Rb+ uptake), and a raise in Ca2+ uptake except for those used as Zn salts, but not of their HCl salts. Respiration and acidification of the medium were modified only with few dyes and interestingly, when exposing cultures to nile blue, neutral red and toluidine blue ZnCl2 a decrease in C. albicans growth was observed.

CONCLUSIONS

We propose a general mechanism for the stimulation of Ca2+ uptake by the dyes used. Some of the dyes tested might be used as agents against C. albicans, probably combined with other agents. Moreover, the effects of Zn ions on Ca2+ uptake and on cell growth open possibilities of further studies, not only of their effects, but also of the mechanism of Ca2+ transport in C. albicans and other yeasts.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study, in conjunction with previously published results, contribute to the basic research regarding ion transport in C. albicans and the role of zinc in this process. Besides, suggests the additional use of dyes, along with other antifungals agents, as combined therapy against candidiasis. Derived dyes from those used also might be possible therapeutic agents against this disease.

Artemisone and Artemiside Are Potent Panreactive Antimalarial Agents That Also Synergize Redox Imbalance in Plasmodium falciparum Transmissible Gametocyte Stages

The emergence of resistance toward artemisinin combination therapies (ACTs) by the malaria parasite Plasmodium falciparum has the potential to severely compromise malaria control. Therefore, the development of new artemisinins in combination with new drugs that impart activities toward both intraerythrocytic proliferative asexual and transmissible gametocyte stages, in particular, those of resistant parasites, is urgently required. We define artemisinins as oxidant drugs through their ability to oxidize reduced flavin cofactors of flavin disulfide reductases critical for maintaining redox homeostasis in the malaria parasite. Here we compare the activities of 10-amino artemisinin derivatives toward the asexual and gametocyte stages of P. falciparum parasites. Of these, artemisone and artemiside inhibited asexual and gametocyte stages, particularly stage V gametocytes, in the low-nanomolar range. Further, treatment of both early and late gametocyte stages with artemisone or artemiside combined with the pro-oxidant redox partner methylene blue displayed notable synergism. These data suggest that modulation of redox homeostasis is likely an important druggable process, particularly in gametocytes, and this finding thereby enhances the prospect of using combinations of oxidant and redox drugs for malaria control.

Lipophilic methylene blue analogues enhance mitochondrial function and increase frataxin levels in a cellular model of Friedreich's ataxia

Friedreich's ataxia (FRDA) is an autosomal recessive neurodegenerative disorder resulting from reduced expression of the protein frataxin (FXN). Although its function is not fully understood, frataxin appears to help assemble iron sulfur clusters; these are critical for the function of many proteins, including those needed for mitochondrial energy production. Finding ways to increase FXN levels has been a major therapeutic strategy for this disease. Previously, we described a novel series of methylene violet analogues and their structural optimization as potential therapeutic agents for neurodegenerative and mitochondrial disorders. Presently, a series of methylene blue analogues has been synthesized and characterized for their in vitro biochemical and biological properties in cultured Friedreich's ataxia lymphocytes. Favorable methylene blue analogues were shown to increase frataxin levels and mitochondrial biogenesis, and to improve aconitase activity. The analogues were found to be good ROS scavengers, and able to protect cultured FRDA lymphocytes from oxidative stress resulting from inhibition of complex I and from glutathione depletion. The analogues also preserved mitochondrial membrane potential and augmented ATP production. Our results suggest that analogue 5, emerging from the initial structure of the parent compound methylene blue (MB), represents a promising lead structure and lacks the cytotoxicity associated with the parent compound MB.

Efficacy and safety of methylene blue in the treatment of malaria: a systematic review

BACKGROUND

Methylene blue (MB) was the first synthetic antimalarial to be discovered and was used during the late 19th and early 20th centuries against all types of malaria. MB has been shown to be effective in inhibiting Plasmodium falciparum in culture, in the mouse model and in rhesus monkeys. MB was also shown to have a potent ex vivo activity against drug-resistant isolates of P. falciparum and P. vivax. In preclinical studies, MB acted synergistically with artemisinin derivates and demonstrated a strong effect on gametocyte reduction in P. falciparum. MB has, thus, been considered a potentially useful partner drug for artemisinin-based combination therapy (ACT), particularly when elimination is the final goal. The aim of this study was to review the scientific literature published until early 2017 to summarise existing knowledge on the efficacy and safety of MB in the treatment of malaria.

METHODS

This systematic review followed PRISMA guidelines. Studies reporting on the efficacy and safety of MB were systematically searched for in relevant electronic databases according to a pre-designed search strategy. The search (without language restrictions) was limited to studies of humans published until February 2017.

RESULTS

Out of 474 studies retrieved, a total of 22 articles reporting on 21 studies were eligible for analysis. The 21 included studies that reported data on 1504 malaria patients (2/3 were children). Older studies were case series and reports on MB monotherapy while recent studies were mainly controlled trials of combination regimens. MB was consistently shown to be highly effective in all endemic areas and demonstrated a strong effect on P. falciparum gametocyte reduction and synergy with ACT. MB treatment was associated with mild urogenital and gastrointestinal symptoms as well as blue coloration of urine. In G6PD-deficient African individuals, MB caused a slight but clinically non-significant haemoglobin reduction.

CONCLUSIONS

More studies are needed to define the effects of MB in P. falciparum malaria in areas outside Africa and against P. vivax malaria. Adding MB to ACT could be a valuable approach for the prevention of resistance development and for transmission reduction in control and elimination programs.

SYSTEMATIC REVIEW REGISTRATION

This study is registered at PROSPERO (registration number CRD42017062349 ).

Differential activity of methylene blue against erythrocytic and hepatic stages of Plasmodium

BACKGROUND

In the context of malaria elimination/eradication, drugs that are effective against the different developmental stages of the parasite are highly desirable. The oldest synthetic anti-malarial drug, the thiazine dye methylene blue (MB), is known for its activity against Plasmodium blood stages, including gametocytes. The aim of the present study was to investigate a possible effect of MB against malaria parasite liver stages.

METHODS

MB activity was investigated using both in vitro and in vivo models. In vitro assays consisted of testing MB activity on Plasmodium falciparum, Plasmodium cynomolgi and Plasmodium yoelii parasites in human, simian or murine primary hepatocytes, respectively. MB in vivo activity was evaluated using intravital imaging in BALB/c mice infected with a transgenic bioluminescent P. yoelii parasite line. The transmission-blocking activity of MB was also addressed using mosquitoes fed on MB-treated mice.

RESULTS

MB shows no activity on Plasmodium liver stages, including hypnozoites, in vitro in primary hepatocytes. In BALB/c mice, MB has moderate effect on P. yoelii hepatic development but is highly effective against blood stage growth. MB is active against gametocytes and abrogates parasite transmission from mice to mosquitoes.

CONCLUSION

While confirming activity of MB against both sexual and asexual blood stages, the results indicate that MB has only little activity on the development of the hepatic stages of malaria parasites.

Comparative Study of Toluidine Blue O and Methylene Blue Binding to Lysozyme and Their Inhibitory Effects on Protein Aggregation

A comparative binding interaction of toluidine blue O (TBO) and methylene blue (MB) with lysozyme was investigated by multifaceted biophysical approaches as well as from the aspects of in silico biophysics. The bindings were static, and it occurred via ground-state complex formation as confirmed from time-resolved fluorescence experiments. From steady-state fluorescence and anisotropy, binding constants were calculated, and it was found that TBO binds more effectively than MB. Synchronous fluorescence spectra revealed that binding of dyes to lysozyme causes polarity changes around the tryptophan (Trp) moiety, most likely at Trp 62 and 63. Calorimetric titration also depicts the higher binding affinity of TBO over MB, and the interactions were exothermic and entropy-driven. In silico studies revealed the potential binding pockets in lysozyme and the participation of residues Trp 62 and 63 in ligand binding. Furthermore, calculations of thermodynamic parameters from the theoretical docking studies were in compliance with experimental observations. Moreover, an inhibitory effect of these dyes to lysozyme fibrillogenesis was examined, and the morphology of the formed fibril was scanned by atomic force microscopy imaging. TBO was observed to exhibit higher potential in inhibiting the fibrillogenesis than MB, and this phenomenon stands out as a promising antiamyloid therapeutic strategy.

Risk factors and treatment of refractory anaphylaxis - a review of case reports

INTRODUCTION

Patients experiencing anaphylaxis who do not recover after treatment with intramuscular adrenaline are regarded as suffering from refractory anaphylaxis. The incidence of refractory anaphylaxis is estimated to range between 3-5% of anaphylaxis cases. The risk factors for refractory anaphylaxis are unknown. Areas covered: In the present analysis, we aimed to evaluate the management and risk factors of refractory anaphylaxis to highlight possible clinical implications for updating current management algorithms. Expert commentary: According to international guidelines, adrenaline given through the intramuscular (i.m.) route is a rapid and safe treatment but may be insufficient. Therefore, defined standardized treatment protocols for such cases of refractory anaphylaxis are needed to optimize the treatment. Point-of-care diagnostics may enable doctors to identify patients experiencing severe, refractory anaphylaxis early in order to initiate intensified critical care treatment.

After Treatment with Methylene Blue is Effective against Delayed Encephalopathy after Acute Carbon Monoxide Poisoning

Delayed encephalopathy after acute carbon monoxide (CO) poisoning (DEACMP) is the most severe and clinically intractable complication that occurs following acute CO poisoning. Unfortunately, the mechanism of DEACMP is still vague. Growing evidence indicates that delayed cerebral damage after CO poisoning is related to oxidative stress, abnormal neuro-inflammation, apoptosis and immune-mediated injury. Our recent report indicated that methylene blue (MB) may be a promising therapeutic agent in the prevention of neuronal cell death and cognitive deficits after transient global cerebral ischaemia (GCI). In this study, we aimed to investigate the potential of MB therapy to ameliorate the signs and symptoms of DEACMP. Rats were exposed to 1000 ppm CO for 40 min. in the first step; CO was then increased to 3000 ppm, which was maintained for another 20 min. The rats were implanted with 7-day release Alzet osmotic mini-pumps subcutaneously under the back skin, which provided MB at a dose of 0.5 mg/kg/day 1 hr after CO exposure. The results showed that MB significantly suppressed oxidative damage and expression of pro-inflammatory factors, including tumour necrosis factor-α and interleukin (IL)-1β. MB treatment also suitably modulated mitochondrial fission and fusion, which is helpful in the preservation of mitochondrial function. Furthermore, MB dramatically attenuated apoptosis and neuronal death. Lastly, behavioural studies revealed that MB treatment preserved spatial learning and memory in the Barnes maze test. Our findings indicated that MB may have protective effects against DEACMP.