[Effect of methylene blue and its metabolite - azure I - on bioenergetic parameters of intact mice brain mitochondria]

Clinical features of seven patients poisoned with a tolfenpyrad-based insecticide in Thailand

INTRODUCTION

Tolfenpyrad, a novel insecticide originating from Japan and first approved in 2002, has been marketed in numerous countries. Data on tolfenpyrad exposure in humans are limited. This study aimed to characterize the clinical features and outcomes of acute poisoning from tolfenpyrad-based insecticides in Thailand.

METHODS

This retrospective study analyzed cases of tolfenpyrad exposure reported to the Ramathibodi Poison Center from 2012 to 2022.

RESULTS

A total of seven patients were identified, with the majority being male (n = 5). Deliberate tolfenpyrad exposure accounted for three cases. The median age was 33 (range 1-46) years. Severe systemic effects were evident at presentation in the four patients ingesting tolfenpyrad. These included altered mental status (n = 4), mydriasis (n = 2), cardiac arrest (n = 1), hypotension (n = 4), bradycardia (n = 2), and high anion gap metabolic acidosis (n = 4). The median time from exposure to hospital presentation was 30 (range 15-60) minutes. All four patients ingesting tolfenpyrad died, whereas the three patients exposed via inhalation and dermally developed only mild clinical effects, and all were discharged following supportive care.

DISCUSSION

We observed many of the clinical features reported previously, including vomiting, mydriasis, altered mental status, metabolic acidosis, and hypotension. We also noted a combination of bradycardia and hypotension while not observing respiratory depression.

CONCLUSIONS

Tolfenpyrad insecticide poisoning has been reported infrequently. Rapid systemic toxicity can follow ingestion, resulting in a high mortality. Larger-scale studies are essential to identify predictors of severity and determine the optimal treatment for tolfenpyrad-poisoned patients.

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.

Methylene Blue Induces Antioxidant Defense and Reparation of Mitochondrial DNA in a Nrf2-Dependent Manner during Cisplatin-Induced Renal Toxicity

Cisplatin is a platinum-based cytostatic drug that is widely used for cancer treatment. Mitochondria and mtDNA are important targets for platinum-based cytostatics, which mediates its nephrotoxicity. It is important to develop therapeutic approaches to protect the kidneys from cisplatin during chemotherapy. We showed that the exposure of mitochondria to cisplatin increased the level of lipid peroxidation products in the in vitro experiment. Cisplatin caused strong damage to renal mtDNA, both in the in vivo and in vitro experiments. Cisplatin injections induced oxidative stress by depleting renal antioxidants at the transcriptome level but did not increase the rate of H₂O₂ production in isolated mitochondria. Methylene blue, on the contrary, induced mitochondrial H₂O₂ production. We supposed that methylene blue-induced H₂O₂ production led to activation of the Nrf2/ARE signaling pathway. The consequences of activation of this signaling pathway were manifested in an increase in the expression of some antioxidant genes, which likely caused a decrease in the amount of mtDNA damage. Methylene blue treatment induced an increase in the expression of genes that were involved in the base excision repair (BER) pathway: the main pathway for mtDNA reparation. It is known that the expression of these genes can also be regulated by the Nrf2/ARE signaling pathway. We can assume that the protective effect of methylene blue is related to the activation of Nrf2/ARE signaling pathways, which can activate the expression of genes related to antioxidant defense and mtDNA reparation. Thus, the protection of kidney mitochondria from cisplatin-induced damage using methylene blue can significantly expand its application in medicine.

Molecular Mechanisms of the Neuroprotective Effect of Methylene Blue

Methylene blue (MB) is the first fully synthetic compound that had found its way into medicine over 120 years ago as a treatment against malaria. MB has been approved for the treatment of methemoglobinemia, but there are premises for its repurposing as a neuroprotective agent based on the efficacy of this compound demonstrated in the models of Alzheimer's, Parkinson's, and Huntington's diseases, traumatic brain injury, amyotrophic lateral sclerosis, depressive disorders, etc. However, the goal of this review was not so much to focus on the therapeutic effects of MB in the treatment of various neurodegeneration diseases, but to delve into the mechanisms of direct or indirect effect of this drug on the signaling pathways. MB can act as an alternative electron carrier in the mitochondrial respiratory chain in the case of dysfunctional electron transport chain. It also displays the anti-inflammatory and anti-apoptotic effects, inhibits monoamine oxidase (MAO) and nitric oxide synthase (NOS), activates signaling pathways involved in the mitochondrial pool renewal (mitochondrial biogenesis and autophagy), and prevents aggregation of misfolded proteins. Comprehensive understanding of all aspects of direct and indirect influence of MB, and not just some of its effects, can help in further research of this compound, including its clinical applications.