A vicious cycle of neuropathological, cognitive and behavioural sequelae of repeated opioid overdose

Machine Learning Analysis of the Orbitofrontal Cortex Transcriptome of Human Opioid Users Identifies Shisa7 as a Translational Target Relevant for Heroin Seeking Leveraging a Male Rat Model

BACKGROUND

Identifying neurobiological targets predictive of the molecular neuropathophysiological signature of human opioid use disorder (OUD) could expedite new treatments. OUD is characterized by dysregulated cognition and goal-directed behavior mediated by the orbitofrontal cortex (OFC), and next-generation sequencing could provide insights regarding novel targets.

METHODS

Here, we used machine learning to evaluate human postmortem OFC RNA sequencing datasets from heroin users and control participants to identify transcripts that were predictive of heroin use. To determine a causal link to OUD-related behaviors, we examined the effects of overexpressing the top target gene in a translational rat model of heroin seeking and behavioral updating. Additionally, we determined the effects of overexpression on the rat OFC transcriptome compared with that of human heroin users. Co-immunoprecipitation/mass spectrometry (co-IP/MS) from the rat OFC elucidated the protein complex of the novel target.

RESULTS

Our machine learning approach identified SHISA7 as predictive of human heroin users. Shisa7 is understudied but appears to be an auxiliary protein of GABAA (gamma-aminobutyric acid A) or AMPA receptors. In rats, Shisa7 expression positively correlated with heroin-seeking behavior. Overexpressing Shisa7 in the OFC augmented heroin seeking and impaired behavioral updating for sucrose-based operant contingency. RNA sequencing of rat OFC revealed gene coexpression networks regulated by Shisa7 overexpression similar to human heroin users. Finally, co-IP/MS showed that heroin influenced Shisa7 binding to glutamatergic and GABAergic receptor subunits. Both gene expression signatures and Shisa7 protein complex emphasized perturbations of neurodegenerative and neuroimmune processes.

CONCLUSIONS

Our findings suggest that OFC Shisa7 is a critical driver of neurobehavioral pathology related to drug-seeking behavior and behavioral updating, thus identifying a potential therapeutic target for OUD.

Nalbuphine Potentiates Reversal of Fentanyl Overdose by Naloxone

Developing an effective antidote for fentanyl-induced overdose to achieve timely reversal is an unmet public health need. Previously, we found that naloxone derivative NX90 with mild κ-opioid agonistic properties was three-fold more effective than the parent naloxone in reversing a fentanyl overdose in rats. To investigate whether κ-agonistic properties could indeed augment the robustness of overdose reversal, we evaluated a κ-agonist/µ-antagonist nalbuphine (NB) as well as its combinations with naloxone (NX) in a fentanyl overdose model in rodents. An administration of either NB or NX as single agents at 0.1 mg/kg doses produced a full recovery in 90 ± 9.9 min and 11.4 ± 2.7 min, respectively. A higher dose of NX at 0.2 mg/kg reversed an overdose within 4.8 ± 1.0 min. In contrast to that, the coadministration of NB and NX at 0.1 mg/kg each produced a synergistic effect, with overdose reversal in 3.4 ± 0.2 min. The coadministration of NX and NB at sub-therapeutic doses of 0.05 mg/kg each was also 1.2-fold more effective than NX at 0.2 mg/kg. We further found that co-administration of NB at different doses (0.025, 0.05, 0.1 mg/kg) and ratios (1:4 and 1:1) with NX had differential effects on overdose reversal, cardiorespiratory liabilities, and analgesia.

Association between toxic drug events and encephalopathy in British Columbia, Canada: a cross-sectional analysis

BACKGROUND

Encephalopathy can occur from a non-fatal toxic drug event (overdose) which results in a partial or complete loss of oxygen to the brain, or due to long-term substance use issues. It can be categorized as a non-traumatic acquired brain injury or toxic encephalopathy. In the context of the drug toxicity crisis in British Columbia (BC), Canada, measuring the co-occurrence of encephalopathy and drug toxicity is challenging due to lack of standardized screening. We aimed to estimate the prevalence of encephalopathy among people who experienced a toxic drug event and examine the association between toxic drug events and encephalopathy.

METHODS

Using a 20% random sample of BC residents from administrative health data, we conducted a cross-sectional analysis. Toxic drug events were identified using the BC Provincial Overdose Cohort definition and encephalopathy was identified using ICD codes from hospitalization, emergency department, and primary care records between January 1st 2015 and December 31st 2019. Unadjusted and adjusted log-binomial regression models were employed to estimate the risk of encephalopathy among people who had a toxic drug event compared to people who did not experience a toxic drug event.

RESULTS

Among people with encephalopathy, 14.6% (n = 54) had one or more drug toxicity events between 2015 and 2019. After adjusting for sex, age, and mental illness, people who experienced drug toxicity were 15.3 times (95% CI = 11.3, 20.7) more likely to have encephalopathy compared to people who did not experience a drug toxicity event. People who were 40 years and older, male, and had a mental illness were at increased risk of encephalopathy.

CONCLUSIONS

There is a need for collaboration between community members, health care providers, and key stakeholders to develop a standardized approach to define, screen, and detect neurocognitive injury related to drug toxicity.

Accelerated brain aging with opioid misuse and HIV: New insights on the role of glially derived pro-inflammation mediators and neuronal chloride homeostasis

Opioid use disorder (OUD) has become a national crisis and contributes to the spread of human immunodeficiency virus (HIV) infection. Emerging evidence and advances in experimental models, methodology, and our understanding of disease processes at the molecular and cellular levels reveal that opioids per se can directly exacerbate the pathophysiology of neuroHIV. Despite substantial inroads, the impact of OUD on the severity, development, and prognosis of neuroHIV and HIV-associated neurocognitive disorders is not fully understood. In this review, we explore current evidence that OUD and neuroHIV interact to accelerate cognitive deficits and enhance the neurodegenerative changes typically seen with aging, through their effects on neuroinflammation. We suggest new thoughts on the processes that may underlie accelerated brain aging, including dysregulation of neuronal inhibition, and highlight findings suggesting that opioids, through actions at the μ-opioid receptor, interact with HIV in the central nervous system to promote unique structural and functional comorbid deficits not seen in either OUD or neuroHIV alone.

Tau protein plays a role in the mechanism of cognitive disorders induced by anesthetic drugs

Cognitive disorders are mental health disorders that can affect cognitive ability. Surgery and anesthesia have been proposed to increase the incidence of cognitive dysfunction, including declines in memory, learning, attention and executive function. Tau protein is a microtubule-associated protein located in the axons of neurons and is important for microtubule assembly and stability; its biological function is mainly regulated by phosphorylation. Phosphorylated tau protein has been associated with cognitive dysfunction mediated by disrupting the stability of the microtubule structure. There is an increasing consensus that anesthetic drugs can cause cognitive impairment. Herein, we reviewed the latest literature and compared the relationship between tau protein and cognitive impairment caused by different anesthetics. Our results substantiated that tau protein phosphorylation is essential in cognitive dysfunction caused by anesthetic drugs, and the possible mechanism can be summarized as "anesthetic drugs-kinase/phosphatase-p-Tau-cognitive impairment".

Modifying naloxone to reverse fentanyl-induced overdose

Developing an effective antidote for fentanyl-induced overdose (OD) is an unmet medical need that requires both lipophilicity comparable to fentanyl and fast onset of overdose reversal. We synthesized and evaluated a bioreversible derivative of naloxone (NX-90) in silico, in vitro and in vivo to yield a robust reversal of fentanyl-induced OD in rats. All monitored reflexes along with the heart rate (HR) and respiratory rate (RR) were fully restored faster in the NX-90 groups than in naloxone groups on equimolar bases when given intranasally. In NX-90 treated rats RR over the time of observation (RR AUC) was significantly higher at all respective doses with no re-narcotization observed. Apart from the enhanced pharmacodynamics profile, NX-90 was found to have lower circulating levels of naloxone, clean profile in in vitro selectivity panels, as well as Ames and CYP450 counter screens. Finally, we demonstrated a robust release of the parent naloxone in brain matrix, as well as lower peripheral naloxone levels after NX-90 iv administration. With the demonstrated pharmacological profile superior yet congruent to naloxone we nominated NX-90 for preclinical development as an effective intranasal fentanyl antidote.