Relationship between endogenous opioid function and opioid analgesic adverse effects

Endogenous Opioid Function and Responses to Morphine: The Moderating Effects of Anger Expressiveness

Long-term use of opioid analgesics may be ineffective or associated with significant negative side effects for some people. At present, there is no sound method of identifying optimal opioid candidates. Individuals with chronic low back pain (n = 89) and healthy control individuals (n = 102) underwent ischemic pain induction with placebo, opioid blockade (naloxone), and morphine in counterbalanced order. They completed the Spielberger Anger-Out subscale. Endogenous opioid function × Anger-out × Pain status (chronic pain, healthy control) interactions were tested for morphine responses to ischemic threshold, tolerance, and pain intensity (McGill Sensory and Affective subscales) and side effects. For individuals with chronic pain and healthy control participants, those with low endogenous opioid function and low anger-out scores exhibited the largest morphine analgesic responses, whereas those with high anger-out and low endogenous opioid function showed relatively weaker morphine analgesic responses. Further, individuals with chronic pain with low endogenous opioid function and low anger-out scores also reported the fewest negative effects to morphine, whereas those with low endogenous opioid function and high anger-out reported the most. Findings point toward individuals with chronic pain who may strike a favorable balance of good analgesia with few side effects, as well as those who have an unfavorable balance of poor analgesia and many side effects.

PERSPECTIVE

We sought to identify optimal candidates for opioid pain management. Low back pain patients who express anger and also have deficient endogenous opioid function may be poor candidates for opioid therapy. In contrast, low back patients who tend not to express anger and who also have deficient endogenous opioid function may make optimal candidates for opioid therapy.

Anti-nerve growth factor antibody attenuates chronic morphine treatment-induced tolerance in the rat

Background

Nerve growth factor (NGF) is known to induce inflammation and pain; however its role in opioid-induced tolerance has not been studied. This study investigated the effects of an anti-NGF neutralizing antibody on the development of tolerance following chronic morphine treatment in naïve rats.

Methods

Four groups of rats were used in this study; one treated with saline alone, one with 10 mg/kg of morphine, one with 10 μg of anti-NGF and the other with 10 mg/kg of morphine + 10 μg of anti-NGF, twice per day for 5 days. The route of treatment was subcutaneous (S.C.) for morphine and saline, and intraperitoneal (i.p.) for anti-NGF. Response to a noxious thermal stimulus during the course of drug treatment was assessed (Hargreaves’ test). Further, the change in the NGF levels in the lumbar spinal cord was measured by ELISA.

Results

Our results showed that repeated administration of morphine produced an apparent tolerance which was significantly attenuated by co-administration of anti-NGF (P < 0.001). Additionally, the area under the curve (AUC) of the analgesic effect produced by the combination of morphine and anti-NGF was significantly (P < 0.001) greater than for saline controls and chronic morphine treated rats. Moreover, the level of NGF in the spinal cord of chronic morphine treated rats was significantly higher (P < 0.05) than in both the saline control group and the group receiving simultaneous administration of anti-NGF with morphine. These results indicate that anti-NGF has the potential to attenuate morphine-induced tolerance behavior by attenuating the effects of NGF at the spinal level.

Conclusion

Taken together, our study strongly suggests that the NGF signaling system is a potential novel target for treating opioid-induced tolerance.

Endogenous opiates and behavior: 2014

This paper is the thirty-seventh consecutive installment of the annual review of research concerning the endogenous opioid system. It summarizes papers published during 2014 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides, opioid receptors, opioid agonists and opioid antagonists. The particular topics that continue to be covered include the molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors related to behavior (endogenous opioids and receptors), and the roles of these opioid peptides and receptors in pain and analgesia (pain and analgesia); stress and social status (human studies); tolerance and dependence (opioid mediation of other analgesic responses); learning and memory (stress and social status); eating and drinking (stress-induced analgesia); alcohol and drugs of abuse (emotional responses in opioid-mediated behaviors); sexual activity and hormones, pregnancy, development and endocrinology (opioid involvement in stress response regulation); mental illness and mood (tolerance and dependence); seizures and neurologic disorders (learning and memory); electrical-related activity and neurophysiology (opiates and conditioned place preferences (CPP)); general activity and locomotion (eating and drinking); gastrointestinal, renal and hepatic functions (alcohol and drugs of abuse); cardiovascular responses (opiates and ethanol); respiration and thermoregulation (opiates and THC); and immunological responses (opiates and stimulants). This paper is the thirty-seventh consecutive installment of the annual review of research concerning the endogenous opioid system. It summarizes papers published during 2014 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides, opioid receptors, opioid agonists and opioid antagonists. The particular topics that continue to be covered include the molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors related to behavior (endogenous opioids and receptors), and the roles of these opioid peptides and receptors in pain and analgesia (pain and analgesia); stress and social status (human studies); tolerance and dependence (opioid mediation of other analgesic responses); learning and memory (stress and social status); eating and drinking (stress-induced analgesia); alcohol and drugs of abuse (emotional responses in opioid-mediated behaviors); sexual activity and hormones, pregnancy, development and endocrinology (opioid involvement in stress response regulation); mental illness and mood (tolerance and dependence); seizures and neurologic disorders (learning and memory); electrical-related activity and neurophysiology (opiates and conditioned place preferences (CPP)); general activity and locomotion (eating and drinking); gastrointestinal, renal and hepatic functions (alcohol and drugs of abuse); cardiovascular responses (opiates and ethanol); respiration and thermoregulation (opiates and THC); and immunological responses (opiates and stimulants).

The Contribution of Differential Opioid Responsiveness to Identification of Opioid Risk in Chronic Pain Patients

The Screener and Opioid Assessment for Patients with Pain-Revised (SOAPP-R) predicts increased risk of opioid misuse in chronic pain patients. We evaluated whether higher SOAPP-R scores are associated with greater opioid reinforcing properties, potentially contributing to their predictive utility. Across 2 counterbalanced laboratory sessions, 55 chronic low back pain sufferers completed the SOAPP-R at baseline and measures of back pain intensity, evoked pain responsiveness (thermal, ischemic), and subjective opioid effects after receiving intravenous morphine (.08 mg/kg) or saline placebo. Morphine effect measures were derived for all outcomes, reflecting the difference between morphine and placebo condition values. Higher SOAPP-R scores were significantly associated with greater desire to take morphine again, less feeling down and feeling bad, and greater reductions in sensory low back pain intensity following morphine administration. This latter effect was due primarily to SOAPP-R content assessing medication-specific attitudes and behavior. Individuals exceeding the clinical cutoff (18 or higher) on the SOAPP-R exhibited significantly greater morphine liking, desire to take morphine again, and feeling sedated; less feeling bad; and greater reductions in sensory low back pain following morphine. The SOAPP-R may predict elevated opioid risk in part by tapping into individual differences in opioid reinforcing effects.

PERSPECTIVE

Based on placebo-controlled morphine responses, associations were observed between higher scores on a common opioid risk screener (SOAPP-R) and greater desire to take morphine again, fewer negative subjective morphine effects, and greater analgesia. Opioids may provide the best analgesia in those patients at greatest risk of opioid misuse.

Therapeutic Basis of Clinical Pain Modulation

Pain is a hallmark of almost all bodily ailments and can be modulated by agents, including analgesics and anesthetics that suppress pain signals in the central nervous system. Defects in the modulatory systems, including the endogenous pain-inhibitory pathways, are a major factor in the initiation and chronicity of pain. Thus, pain modulation is particularly applicable to the practice of medicine. This review summarizes the existing literature on pain modulation. Here, we critically reviewed the literature from PubMed on pain modulation published primarily within the past 5 years in high impact journals. Specifically, we have discussed important anatomical landmarks of pain modulation and outlined the endogenous networks and underlying mechanisms of clinically relevant pain modulatory methods. The Gate Control Theory is briefly presented with discussion on the capacity of pain modulation to cause both hyper- and hypoalgesia. An emphasis has been given to highlight key areas in pain research that, because of unanswered questions or therapeutic potential, merit additional scientific scrutiny. The information presented in this paper would be helpful in developing novel therapies, metrics, and interventions for improved patient management.