Early in vivo MR spectroscopy findings in organophosphate-induced brain damage-potential biomarkers for short-term survival

Associations of Depression Score with Dialkyl Phosphate Metabolites in Urine: A Cross-Sectional Study

OBJECTIVES

Growing evidence suggests a link between organophosphate insecticides and depression disorder. These chemicals are metabolized and subsequently expelled through the urinary tract. The present study aims to investigate whether dialkyl phosphate metabolites associate with depression score and severity among the general population.

METHODS

This cross-sectional study used data from the National Health and Nutrition Examination Survey (NHANES). Depression was evaluated by the Patient Health Questionnaire-9 (PHQ-9). All urinary dialkyl phosphate metabolites were quantitatively analyzed. The survey's complex design parameters and sampling weights were considered.

RESULTS

3035 eligible individuals were included. The estimated prevalence of mild and major depression was 18.3% (95% confidence interval [CI]: 16.9-19.7%) and 9.9% (95% CI: 8.7-11.0%). For each incremental unit in the level of urinary dimethyl phosphate (DMP), individuals were found to have a higher depression score of 0.77 and a significantly increased odds ratio (OR) of 1.13 (95% CI: 1.12-1.13) for mild depression and 2.75 (95% CI: 2.74-2.76) for major depression.

CONCLUSIONS

Our findings indicate positive and independent associations between urinary dialkyl phosphate metabolites and an elevated risk of depression among the general population.

A longitudinal MRI and TSPO PET-based investigation of brain region-specific neuroprotection by diazepam versus midazolam following organophosphate-induced seizures

Acute poisoning with organophosphorus cholinesterase inhibitors (OPs), such as OP nerve agents and pesticides, can cause life threatening cholinergic crisis and status epilepticus (SE). Survivors often experience significant morbidity, including brain injury, acquired epilepsy, and cognitive deficits. Current medical countermeasures for acute OP poisoning include a benzodiazepine to mitigate seizures. Diazepam was long the benzodiazepine included in autoinjectors used to treat OP-induced seizures, but it is now being replaced in many guidelines by midazolam, which terminates seizures more quickly, particularly when administered intramuscularly. While a direct correlation between seizure duration and the extent of brain injury has been widely reported, there are limited data comparing the neuroprotective efficacy of diazepam versus midazolam following acute OP intoxication. To address this data gap, we used non-invasive imaging techniques to longitudinally quantify neuropathology in a rat model of acute intoxication with the OP diisopropylfluorophosphate (DFP) with and without post-exposure intervention with diazepam or midazolam. Magnetic resonance imaging (MRI) was used to monitor neuropathology and brain atrophy, while positron emission tomography (PET) with a radiotracer targeting translocator protein (TSPO) was utilized to assess neuroinflammation. Animals were scanned at 3, 7, 28, 65, 91, and 168 days post-DFP and imaging metrics were quantitated for the hippocampus, amygdala, piriform cortex, thalamus, cerebral cortex and lateral ventricles. In the DFP-intoxicated rat, neuroinflammation persisted for the duration of the study coincident with progressive atrophy and ongoing tissue remodeling. Benzodiazepines attenuated neuropathology in a region-dependent manner, but neither benzodiazepine was effective in attenuating long-term neuroinflammation as detected by TSPO PET. Diffusion MRI and TSPO PET metrics were highly correlated with seizure severity, and early MRI and PET metrics were positively correlated with long-term brain atrophy. Collectively, these results suggest that anti-seizure therapy alone is insufficient to prevent long-lasting neuroinflammation and tissue remodeling.

Quantitative T2 mapping-based longitudinal assessment of brain injury and therapeutic rescue in the rat following acute organophosphate intoxication

Acute intoxication with organophosphate (OP) cholinesterase inhibitors poses a significant public health risk. While currently approved medical countermeasures can improve survival rates, they often fail to prevent chronic neurological damage. Therefore, there is need to develop effective therapies and quantitative metrics for assessing OP-induced brain injury and its rescue by these therapies. In this study we used a rat model of acute intoxication with the OP, diisopropylfluorophosphate (DFP), to test the hypothesis that T2 measures obtained from brain magnetic resonance imaging (MRI) scans provide quantitative metrics of brain injury and therapeutic efficacy. Adult male Sprague Dawley rats were imaged on a 7T MRI scanner at 3, 7 and 28 days post-exposure to DFP or vehicle (VEH) with or without treatment with the standard of care antiseizure drug, midazolam (MDZ); a novel antiseizure medication, allopregnanolone (ALLO); or combination therapy with MDZ and ALLO (DUO). Our results show that mean T2 values in DFP-exposed animals were: (1) higher than VEH in all volumes of interest (VOIs) at day 3; (2) decreased with time; and (3) decreased in the thalamus at day 28. Treatment with ALLO or DUO, but not MDZ alone, significantly decreased mean T2 values relative to untreated DFP animals in the piriform cortex at day 3. On day 28, the DUO group showed the most favorable T2 characteristics. This study supports the utility of T2 mapping for longitudinally monitoring brain injury and highlights the therapeutic potential of ALLO as an adjunct therapy to mitigate chronic morbidity associated with acute OP intoxication.

Biochemical responses as early and reliable biomarkers of organophosphate and carbamate pesticides intoxication: A systematic literature review

Inhibition of cholinesterase (ChE) activity has been long considered as the main diagnostic method of organophosphate (OP) and carbamate pesticides poisoning; however, it has been shown that ChE activity may also be altered due to exposure to other non-organophosphorus toxicants and variety of different medical conditions. Hence, to avoid misdiagnosis, we aimed to systematically review available documents to look for additional biomarkers of OP and carbamate poisoning. The electronic databases in addition to Google scholar were searched for eligible articles on March 2022 using "organophosphate," "carbamate," and "biomarker" including all their similar terms. After collecting the relevant documents, the data were extracted and described qualitatively. In total, data of 66 articles from 51 human and 15 animal studies were extracted. Findings demonstrated that enzymes such as β-glucuronidase, neuropathy target esterase, amylase, and lipase, in addition to hematological indicators such as CBC, CRP, lactate dehydrogenase, and CPK have high sensitivity and accuracy in the diagnosis of OP poisoning. Findings suggest that using various markers for diagnosis of OP intoxication is helpful for appropriate management, and early identifying the patients at risk of death. The suggested biomarkers also help to avoid misdiagnosis of OP poisoning with other similar conditions.

Noninvasive Tracking of Anesthesia Neurotoxicity in the Developing Rodent Brain

BACKGROUND

Potential deleterious effect of multiple anesthesia exposures on the developing brain remains a clinical concern. We hypothesized that multiple neonatal anesthesia exposures are more detrimental to brain maturation than an equivalent single exposure, with more pronounced long-term behavioral consequences. We designed a translational approach using proton magnetic resonance spectroscopy in rodents, noninvasively tracking the neuronal marker N-acetyl-aspartate, in addition to tracking behavioral outcomes.

METHODS

Trajectories of N-acetyl-aspartate in anesthesia naïve rats (n = 62, postnatal day 5 to 35) were determined using proton magnetic resonance spectroscopy, creating an "N-acetyl-aspartate growth chart." This chart was used to compare the effects of a single 6-h sevoflurane exposure (postnatal day 7) to three 2-h exposures (postnatal days 5, 7, 10). Long-term effects on behavior were separately examined utilizing novel object recognition, open field testing, and Barnes maze tasks.

RESULTS

Utilizing the N-acetyl-aspartate growth chart, deviations from the normal trajectory were documented in both single and multiple exposure groups, with z-scores (mean ± SD) of -0.80 ± 0.58 (P = 0.003) and -1.87 ± 0.58 (P = 0.002), respectively. Behavioral testing revealed that, in comparison with unexposed and single-exposed, multiple-exposed animals spent the least time with the novel object in novel object recognition (F(2,44) = 4.65, P = 0.015), traveled the least distance in open field testing (F(2,57) = 4.44, P = 0.016), but exhibited no learning deficits in the Barnes maze.

CONCLUSIONS

Our data demonstrate the feasibility of using the biomarker N-acetyl-aspartate, measured noninvasively using proton magnetic resonance spectroscopy, for longitudinally monitoring anesthesia-induced neurotoxicity. These results also indicate that the neonatal rodent brain is more vulnerable to multiple anesthesia exposures than to a single exposure of the same cumulative duration.

A magnetic resonance imaging study of early brain injury in a rat model of acute DFP intoxication

Current treatments for seizures induced by organophosphates do not protect sufficiently against progressive neurodegeneration or delayed cognitive impairment. Developing more effective therapeutic approaches has been challenging because the pathogenesis of these delayed consequences is poorly defined. Using magnetic resonance imaging (MRI), we previously reported brain lesions that persist for months in a rat model of acute intoxication with the OP, diisopropylfluorophosphate (DFP). However, the early spatiotemporal progression of these lesions remains unknown. To address this data gap, we used in vivo MRI to longitudinally monitor brain lesions during the first 3 d following acute DFP intoxication. Adult male Sprague Dawley rats acutely intoxicated with DFP (4mg/kg, sc) were MR imaged at 6, 12, 18, 24, 48, 72h post-DFP, and their brains then taken for correlative histology to assess neurodegeneration using FluoroJade C (FJC) staining. Acute DFP intoxication elicited moderate-to-severe seizure activity. T2-weighted (T2w) anatomic imaging revealed prominent lesions within the thalamus, piriform cortex, cerebral cortex, hippocampus, corpus striatum, and substantia nigra that corresponded to neurodegeneration, evident as bands of FJC positive cells. Semi-quantitative assessment of lesion severity demonstrated significant regional variation in the onset and progression of injury, and suggested that lesion severity may be modulated by isoflurane anesthesia. These results imply that the timing of therapeutic intervention for attenuating brain injury following OP intoxication may be regionally dependent, and that longitudinal assessment of OP-induced damage by MRI may be a powerful tool for assessing therapeutic response.

From the Cover: MagneticResonance Imaging Reveals Progressive Brain Injury in Rats Acutely Intoxicated With Diisopropylfluorophosphate

Acute intoxication with organophosphates (OPs) can trigger seizures that progress to status epilepticus, and survivors often exhibit chronic neuropathology, cognitive impairment, affective disorders, and/or electroencephalographic abnormalities. Understanding how acute injury transitions to persistent neurological sequelae is critical to developing medical countermeasures for mitigating damage following OP-induced seizures. Here, we used in vivo magnetic resonance imaging (MRI) to monitor the spatiotemporal patterns of neuropathology for 1 month after acute intoxication with diisopropylfluorophosphate (DFP). Adult male Sprague Dawley rats administered pyridostigmine bromide (0.1 mg/kg, im) 30 min prior to successive administration of DFP (4 mg/kg, sc), atropine sulfate (2 mg/kg, im), and 2-pralidoxime (25 mg/kg, im) exhibited moderate-to-severe seizure behavior. T2-weighted and diffusion-weighted MR imaging prior to DFP exposure and at 3, 7, 14, 21, or 28 days postexposure revealed prominent lesions, tissue atrophy, and ventricular enlargement in discrete brain regions. Lesions varied in intensity and/or extent over time, with the overall magnitude of injury strongly influenced by seizure severity. Importantly, lesions detected by MRI correlated spatially and temporally with histological evidence of brain pathology. Analysis of histogram parameters extracted from frequency distributions of regional apparent diffusion coefficient (ADC) values identified the standard deviation and 90th percentile of the ADC as robust metrics for quantifying persistent and progressive neuropathological changes. The interanimal and interregional variations observed in lesion severity and progression, coupled with potential reinjury following spontaneous recurrent seizures, underscore the advantages of using in vivo imaging to longitudinally monitor neuropathology and, ultimately, therapeutic response, following acute OP intoxication.

MRS of brain metabolite levels demonstrates the ability of scavenging of excess brain glutamate to protect against nerve agent induced seizures

This study describes the use of in vivo magnetic resonance spectrocopy (MRS) to monitor brain glutamate and lactate levels in a paraoxon (PO) intoxication model. Our results show that the administration of recombinant glutamate-oxaloacetate transaminase (rGOT) in combination with oxaloacetate (OxAc) significantly reduces the brain-accumulated levels of glutamate. Previously we have shown that the treatment causes a rapid decrease of blood glutamate levels and creates a gradient between the brain and blood glutamate levels which leads to the efflux of excess brain glutamate into the blood stream thereby reducing its potential to cause neurological damage. The fact that this treatment significantly decreased the brain glutamate and lactate levels following PO intoxication suggests that it could become a new effective neuroprotective agent.