Fentanyl-induced hyperalgesia and analgesic tolerance in male rats: common underlying mechanisms and prevention by a polyamine deficient diet

Treating chronic stress and chronic pain by manipulating gut microbiota with diet: can we kill two birds with one stone?

Background: Chronic stress and chronic pain are closely linked by the capacity to exacerbate each other, sharing common roots in the brain and in the gut. The strict intersection between these two neurological diseases makes important to have a therapeutic strategy aimed at preventing both to maintain mental health in patients. Diet is an modifiable lifestyle factor associated with gut-brain axis diseases and there is growing interest in its use as adjuvant to main therapies. Several evidence attest the impact of specific diets or nutrients on chronic stress-related disorders and pain with a good degree of certainty. A daily adequate intake of foods containing micronutrients such as amino acids, minerals and vitamins, as well as the reduction in the consumption of processed food products can have a positive impact on microbiota and gut health. Many nutrients are endowed of prebiotic, anti-inflammatory, immunomodulatory and neuroprotective potential which make them useful tools helping the management of chronic stress and pain in patients. Dietary regimes, as intermittent fasting or caloric restriction, are promising, although further studies are needed to optimize protocols according to patient's medical history, age and sex. Moreover, by supporting gut microbiota health with diet is possible to attenuate comorbidities such as obesity, gastrointestinal dysfunction and mood disorders, thus reducing healthcare costs related to chronic stress or pain.Objective: This review summarize the most recent evidence on the microbiota-mediated beneficial effects of macro- and micronutrients, dietary-related factors, specific nutritional regimens and dietary intervention on these pathological conditions.

Chronic inflammatory pain promotes place preference for fentanyl in male rats but does not change fentanyl self-administration in male and female rats

The current opioid epidemic is a national health crisis marked by skyrocketing reports of opioid misuse and overdose deaths. Despite the risks involved, prescription opioid analgesics are the most powerful and effective medications for treating pain. There is a clear need to investigate the risk of opioid misuse liability in male and female adults experiencing chronic pain. In the present study, we tested the hypothesis that chronic inflammatory pain would increase fentanyl intake, motivation to acquire fentanyl, and drug seeking in the absence of fentanyl in rats. Fentanyl intake, motivation for fentanyl, and drug seeking were tested under limited and extended access conditions using intravenous fentanyl self-administration. Fos activity in ventral tegmental area (VTA) dopamine neurons following intravenous fentanyl challenge (35 μg/kg) was examined using immunohistochemistry. Finally, we tested whether low-dose fentanyl supports development of conditioned place preference under an inflammatory pain state in rats. Contrary to our hypothesis, fentanyl self-administration and VTA Fos activity were unaffected by inflammatory pain status. During acquisition, males exhibited increased fentanyl intake compared to females. Animals given extended access to fentanyl escalated fentanyl intake over time, while animals given limited access did not. Males given extended access to fentanyl demonstrated a greater increase in fentanyl intake over time compared to females. During the dose-response test, females given limited access to fentanyl demonstrated increased motivation to acquire fentanyl compared to males. Both sexes displayed significant increases in responding for fentanyl as unit fentanyl doses were lowered. Following fentanyl challenge, females exhibited higher numbers of Fos-positive non-dopaminergic VTA neurons compared to males. Using conditioned place preference, we found that chronic inflammatory pain promotes fentanyl preference in males, but not females. These findings suggest that established fentanyl self-administration is resistant to change by inflammatory pain manipulation in both sexes, but chronic inflammatory pain increases the rewarding properties of low-dose fentanyl in males.

Pharmacological Interventions for Opioid-Induced Hyperalgesia: A Scoping Review of Preclinical Trials

BACKGROUND

Opioid analgesics are the most effective pharmacological agents for moderate and severe pain. However, opioid use has several limitations such as opioid-induced hyperalgesia (OIH), which refers to the increased pain sensitivity that occurs once analgesia wears off after opioid administration. Several pharmacological interventions have been suggested for OIH, but the current literature does not provide guidelines on which interventions are the most effective and whether they differ depending on the opioid that induces hyperalgesia. This scoping review aimed to identify and describe all the preclinical trials investigating pharmacological interventions for OIH caused by remifentanil, fentanyl, or morphine as the first step towards evaluating whether the most effective OIH interventions are different for different opioids.

METHODS

Electronic database searches were carried out in Embase, PubMed, and Web of Science. Detailed data extraction was conducted on the eligible trials.

RESULTS

72 trials were eligible for the review. Of these, 27 trials investigated remifentanil, 14 trials investigated fentanyl, and 31 trials investigated morphine. A total of 82 interventions were identified. The most studied interventions were ketamine (eight trials) and gabapentin (four trials). The majority of the interventions were studied in only one trial. The most common mechanism suggested for the interventions was inhibition of N-methyl-D-aspartate (NMDA) receptors.

CONCLUSION

This scoping review identified plenty of preclinical trials investigating pharmacological interventions for OIH. Using the current literature, it is not possible to directly compare the effectiveness of the interventions. Hence, to identify the most effective interventions for each opioid, the interventions must be indirectly compared in a meta-analysis.

Effect of different doses of esketamine compared with fentanyl combined with propofol on hypotension in patients undergoing painless abortion surgery: a prospective, randomized, double-blind controlled clinical trial

Background

Opioids analgesics commonly used in abortion procedures are associated with respiratory and circulatory depression. Esketamine is a N-methyl-D-aspartate receptor (NMDA) antagonist and a common analgesic. The drug has several advantages including rapid onset and offset and it causes minimal cardiorespiratory depression. However, studies have not explored the effects of esketamine in patients undergoing painless abortion surgery. Therefore, the present study sought to evaluate the effect of different doses of esketamine compared with the effect of fentanyl on incidence of perioperative hypotension in patients undergoing painless abortion surgery and to explore the optimal esketamine dose for this population.

Methods

A total of 178 female patients undergoing painless abortion surgery were enrolled to the current study. The patients were aged 18–45 years, had a body mass index (BMI) of 18–28 kg m^− 2 and a class I or II physical status as determined using the American Society of Anesthesiologists (ASA) system. Patients were randomly assigned to four groups as follows: group F (n = 45) in which patients underwent intravenous (IV) administration of 1 μg kg^− 1 fentanyl followed by IV administration of 2 mg kg^− 1 propofol, and group EL, group EM and group EH (n = 45, 44, 44) with patients receiving IV administration of 0.2 mg kg^− 1, 0.25 mg kg^− 1, 0.3 mg kg^− 1 esketamine, respectively, followed by IV administration of 2 mg kg^− 1 propofol. The primary outcome of the study was the incidence of hypotension whereas secondary outcomes included incidence of adverse events, perioperative changes of vital signs, anesthesia induction time, recovery time and dischargeable time, propofol addition, as well as patient, surgeon and anesthesiologist satisfaction levels.

Results

The findings showed that the incidence of hypotension was significantly lower in subjects in group EL, group EM and group EH (0, 0, 0%) relative to the incidence in patients in group F (20%) (χ² = 19.648; P = 0.000). In this study, the incidence of hypoxia of subjects in group EL, group EM and group EH (0, 2.3, 2.3%) was significantly lower compared with that of patients in group F (11.1%) (χ² = 8.622; P = 0.035). The findings indicated that the incidence of somatic motor reactions was significantly lower in participants in group EM and group EH (9.1, 4.5%) relative to that of patients in group F and group EL (26.7, 15.6%) (χ² = 10.254; P = 0.016). The results showed that the incidence of nausea and vomiting and potential psychiatric symptoms were significantly higher in patients in group EH (15.9, 11.4%) compared with that of participants in group F (2.2, 0%), group EL (4.4, 0%) and group EM (2.3, 2.3%) (χ² = 7.493; P = 0.038 and χ² = 8.248; P = 0.003). In this study, the mean arterial pressure (MAP) and heart rate (HR) of subjects in group EL, group EM and group EH were more stable compared with that of patients in group F. Frequency of the additional propofol dose was markedly less in group EM and EH (26.7%, 17,8%) compared with that in group F and EL (9.1, 4.5%) (χ² = 10.254; P = 0.016). The findings indicated that the dischargeable time was significantly shorter for patients in group EM compared with that of subjects in group F, group EL and group EH.

Conclusions

The findings of the present study showed that single-dose esketamine (0.25 mg kg^− 1) effectively decreased incidence of hypotension and total adverse events and reduced the frequency of additional propofol dose required for patients undergoing painless abortion with preservation of physician-patient satisfaction.