Palliative care pharmacotherapy literature summaries and analyses

Effect of captopril, an angiotensin-converting enzyme inhibitor, on morphine analgesia and tolerance in rats, and elucidating the inflammation and endoplasmic reticulum stress pathway in this effect

The purpose of current study was to examine the possible involvement of captopril, an angiotensin-converting enzyme inhibitor, on nociception, morphine analgesia and morphine tolerance development involving inflammation and ER-stress pathways in rats. In this study, thirty-six male Wistar rats were used. Animals were divided into six groups: Saline, 50 mg/kg captopril, 5 mg/kg morphine, morphine + captopril, morphine tolerance and morphine tolerance + captopril. The resulting analgesic effect was measured with hot plate and tail flick analgesia tests. The dorsal root ganglions (DRG) tissues were collected for inflammation parameters, endoplasmic reticulum (ER) stress and apoptosis proteins by using ELISA. Captopril showed anti-nociceptive effect when given alone (p < 0.05 to p < 0.01). In addition, captopril increased the analgesic effect of morphine (p < 0.05 to p < 0.001) and also decreased the tolerance to morphine at a significant level (p < 0.05 to p < 0.001). However, it decreased inflammation and ER-stress when applied with single-dose morphine and tolerance induction (p < 0.001). Moreover, captopril decreased apoptosis proteins after tolerance development (p < 0.001). In conclusion, captopril has antinociceptive properties, increasing analgesic effect of morphine, and preventing tolerance development. These effects may occur by suppressing inflammation and ER-stress pathways.

Bidirectional Action of Cenicriviroc, a CCR2/CCR5 Antagonist, Results in Alleviation of Pain-Related Behaviors and Potentiation of Opioid Analgesia in Rats With Peripheral Neuropathy

Clinical management of neuropathic pain is unsatisfactory, mainly due to its resistance to the effects of available analgesics, including opioids. Converging evidence indicates the functional interactions between chemokine and opioid receptors and their influence on nociceptive processes. Recent studies highlight that the CC chemokine receptors type 2 (CCR2) and 5 (CCR5) seem to be of particular interest. Therefore, in this study, we investigated the effects of the dual CCR2/CCR5 antagonist, cenicriviroc, on pain-related behaviors, neuroimmune processes, and the efficacy of opioids in rats after chronic constriction injury (CCI) of the sciatic nerve. To define the mechanisms of action of cenicriviroc, we studied changes in the activation/influx of glial and immune cells and, simultaneously, the expression level of CCR2, CCR5, and important pronociceptive cytokines in the spinal cord and dorsal root ganglia (DRG). We demonstrated that repeated intrathecal injections of cenicriviroc, in a dose-dependent manner, alleviated hypersensitivity to mechanical and thermal stimuli in rats after sciatic nerve injury, as measured by von Frey and cold plate tests. Behavioral effects were associated with the beneficial impact of cenicriviroc on the activation/influx level of C1q/IBA-1-positive cells in the spinal cord and/or DRG and GFAP-positive cells in DRG. In parallel, administration of cenicriviroc decreased the expression of CCR2 in the spinal cord and CCR5 in DRG. Concomitantly, we observed that the level of important pronociceptive factors (e.g., IL-1beta, IL-6, IL-18, and CCL3) were increased in the lumbar spinal cord and/or DRG 7 days following injury, and cenicriviroc was able to prevent these changes. Additionally, repeated administration of this dual CCR2/CCR5 antagonist enhanced the analgesic effects of morphine and buprenorphine in neuropathic rats, which can be associated with the ability of cenicriviroc to prevent nerve injury-induced downregulation of all opioid receptors at the DRG level. Overall, our results suggest that pharmacological modulation based on the simultaneous blockade of CCR2 and CCR5 may serve as an innovative strategy for the treatment of neuropathic pain, as well as in combination with opioids.

Metamizole relieves pain by influencing cytokine levels in dorsal root ganglia in a rat model of neuropathic pain

Background

Treatment of neuropathic pain is still challenging. Recent studies have suggested that dorsal root ganglia (DRG), which carry sensory neural signals from the peripheral nervous system to the central nervous system, are important for pathological nociception. A proper understanding of the significance and function of DRG and their role in pharmacotherapy can help to improve the treatment of neuropathic pain. Metamizole, also known as sulpyrine or dipyrone, is a non-opioid analgesic commonly used in clinical practice, but it is not used for neuropathic pain treatment.

Methods

Chronic constriction injury (CCI) of the sciatic nerve was induced in Wistar rats. Metamizole was administered intraperitoneally (ip) preemptively at 16 and 1 h before CCI and then twice a day for 7 days. To evaluate tactile and thermal hypersensitivity, von Frey and cold plate tests were conducted, respectively.

Results

Our behavioral results provide evidence that repeated intraperitoneal administration of metamizole diminishes the development of neuropathic pain symptoms in rats. Simultaneously, our findings provide evidence that metamizole diminishes the expression of pronociceptive interleukins (IL-1beta, IL-6, and IL-18) and chemokines (CCL2, CCL4, and CCL7) in DRG measured 7 days after sciatic nerve injury. These assays indicate, for the first time, that metamizole exerts antinociceptive effects on nerve injury-induced neuropathic pain at the DRG level.

Conclusions

Finally, we indicate that metamizole-induced analgesia in neuropathy is associated with silencing of a broad spectrum of cytokines in DRG. Our results also suggest that metamizole is likely to be an effective medication for neuropathic pain.

Graphic abstract

The 'mystery' of opioid-induced diarrhea

Bowel dysfunction, mainly constipation, is a well-known and anticipated side effect of opioids. The physician prescribing an opioid frequently confronts the challenge of preventing and treating bowel dysfunction. Different strategies have emerged for managing opioid-induced constipation. These strategies include physical activity, maintaining adequate fluid intake, adhering to regular daily bowel habits, using laxatives and other anticonstipation medications and, recently, using a peripheral opioid antagonist, either as a separate drug or in the form of an opioid agonistantagonist combination pill. What options exist for the physician when a patient receiving opioids complains of diarrhea, cramps and bloating, rather than the expected constipation? The present article describes a possible cause of opioid-induced diarrhea and strategies for management.