CYX-5, a G-protein biassed MOP receptor agonist, DOP receptor antagonist and KOP receptor agonist, evokes constipation but not respiratory depression relative to morphine in rats

BACKGROUND

Strong opioid analgesics such as morphine alleviate moderate to severe acute nociceptive pain (e.g. post-surgical or post-trauma pain) as well as chronic cancer pain. However, they evoke many adverse effects and so there is an unmet need for opioid analgesics with improved tolerability. Recently, a prominent hypothesis has been that opioid-related adverse effects are mediated by β-arrestin2 recruitment at the µ-opioid (MOP) receptor and this stimulated research on discovery of G-protein biassed opioid analgesics. In other efforts, opioids with MOP agonist and δ-opioid (DOP) receptor antagonist profiles are promising for reducing side effects c.f. morphine. Herein, we report on the in vivo pharmacology of a novel opioid peptide (CYX-5) that is a G-protein biassed MOP receptor agonist, DOP receptor antagonist and kappa opioid (KOP) receptor agonist.

METHODS

Male Sprague-Dawley received intracerebroventricular bolus doses of CYX-5 (3, 10, 20 nmol), morphine (100 nmol) or vehicle, and antinociception (tail flick) was assessed relative to constipation (charcoal meal and castor oil-induced diarrhoea tests) and respiratory depression (whole body plethysmography).

RESULTS

CYX-5 evoked naloxone-sensitive, moderate antinociception, at the highest dose tested. Although CYX-5 did not inhibit gastrointestinal motility, it reduced stool output markedly in the castor oil-induced diarrhoea test. In contrast to morphine that evoked respiratory depression, CYX-5 increased tidal volume, thereby stimulating respiration.

CONCLUSION

Despite its lack of recruitment of β-arrestin2 at MOP, DOP and KOP receptors, CYX-5 evoked constipation, implicating a mechanism other than β-arrestin2 recruitment at MOP, DOP and KOP receptors, mediating constipation evoked by CYX-5 and potentially other opioid ligands.

Finding the right spot: Where to measure airway parameters in patients with COPD

PURPOSE

The importance of spirometry for management of COPD was reduced in the 2017 revision of the GOLD report. CT derived airway measurements show strong correlations with lung function tests and symptoms. However, these correlations are specific to the airway localization, and currently there is no evidence for the ideal spot. Therefore, the aim of this prospective study was to systematically correlate CT derived airway measurements with extensive lung function testing.

METHODS AND MATERIALS

65 patients with diagnosed COPD underwent body plethysmography, impulse oscillometry and dose optimized qCT examination (Somatom Force, Healthineers, Germany) in inspiration and expiration. Eight airway parameters (e.g. outer diameter, maximal wall thickness) were acquired for both scans in every lobe for the third to fifth generation bronchus and correlated with the lung function tests.

RESULTS

The most significant correlations between airway parameters were found for the third generation bronchus of the upper left lobe during expiration (25 out of 48 correlation pairs, mean r = -0.39) and for the third generation bronchus of the upper right lobe during inspiration (9 out of 48 correlation pairs, mean r = -0.25). No significant correlations were for example found for the upper right lobe in expiration.

CONCLUSION

Correlations between airway parameters and lung function tests vary widely between lobes, bronchus generations and breathing states. Our work suggests that the third generation bronchus of the upper left lobe in expiration could be the preferred localization for airway quantification in future studies.

TRPA1 mediates the cardiac effects of acrolein through parasympathetic dominance but also sympathetic modulation in mice

Numerous studies have demonstrated that short-term air pollution exposure causes cardiac autonomic imbalance as measured by heart rate variability (HRV). We previously showed that a single exposure to acrolein, a ubiquitous gaseous component of air pollution, not only causes autonomic imbalance, but also increases arrhythmia through transient receptor potential A1 (TRPA1) cation channels. Thus, the goal of this study was to characterize acrolein-induced autonomic changes in both normal and TRPA1-knockout mice (KO). Conscious, unrestrained C57BL/6 (WT) and KO mice were exposed to 3 ppm acrolein for 3 h. Separate groups were treated with either atenolol (sympathetic blocker), atropine (parasympathetic blocker) or hexamethonium (autonomic neurotransmission blocker), immediately before exposure. Electrocardiogram (ECG) and heart rate (HR) were recorded continuously before, during and after exposure. Exposure to acrolein produced significant increases in standard deviation of normal-to-normal R-R intervals (SDNN), Root Mean Square of the Successive Differences (RMSSD) and Low-Frequency (LF), as well as an increase in arrhythmia in WT mice. Treatment with atenolol reduced this response while atropine enhanced it, and both drugs blocked the acrolein-induced increase in arrhythmia; hexamethonium had no effect. On the other hand, neither acrolein nor any drug had an effect in the KO mice. Thus, acrolein-induced HRV responses appear to be mediated by a combined parasympathetic and sympathetic modulation. KO mice did not demonstrate any increases in HRV with exposure to acrolein. These data demonstrate that the cardiac effects of irritant air pollutants likely involve disruption of homeostatic balance and altered regulation even in healthy animals.

Modification and Application of a Commercial Whole-body Plethysmograph to Monitor Respiratory Abnormalities in Neonatal Mice

Proper breathing is essential for mammals to acquire oxygen after birth and requires coordinated actions among several tissues, including diaphragm, intercostal muscles, trachea, bronchi, lung and respiration-regulating neurons located in the medulla oblongata. Genetically modified mice that die early postnatally may have respiratory defects caused by maldevelopment of any one of these tissues (Turgeon and Meloche, 2009). Because of the small body size of neonatal pups, whole-body plethysmography can be used to monitor their respiratory activities. In this protocol, we modified the commercial whole-body plethysmograph by increasing metal filters in the pneumotach, connecting an extension tube to the pneumotach and removing the bias flow supply. With these modifications, the sensitivity of this device is significantly increased to enable the detection of rhythmic respiration in neonatal mice as early as postnatal day 1 (P1).

Plethysmography measurements of respiratory function in conscious unrestrained mice

Whole body plethysmography (WBP) is used to quantify pulmonary function in conscious, unrestrained mice. We determined currently whether time of day and environmental lighting influence day-to-day reproducibility of pulmonary function, and quantifed the necessary habituation time in the WBP chamber. Two-month-old male C57BL6 and mdx mice (n = 8/group, reverse light cycle), were examined on consecutive days using a calibrated WBP chamber and manufacturer software was used to calculate respiratory measures. Respiratory data stabilized between 5-10 min for all variables. Mice exhibited time of day respiratory differences, performing more forceful and less frequent breaths midday (11:45 a.m. and 3:00 p.m.) compared to 7:30 a.m. WBP performed in darkened conditions elicited more forceful breathing than lit conditions. Day-to-day reproducibility during controlled conditions ranged from r(2) = 0.58 to 0.62 for the functional measures. Findings indicate reproducible respiratory data are obtainable following a 15-min chamber habituation and standardization of time of day and room lighting.

[Body plethysmography (I): Standardisation and quality criteria]

Whole body plethysmography is used to measure lung volumes, capacities and resistances. It is a well standardised technique, and although it is widely used in paediatric chest diseases units, it requires specific equipment, specialist staff, and some cooperation by the patient. Plethysmography uses Boyle's law in order to measure the intrathoracic gas volume or functional residual capacity, and once this is determined, the residual volume and total lung capacity is extrapolated. The measurement of total lung capacity is necessary for the diagnosis of restrictive diseases. Airway resistance is a measurement of obstruction, with the total resistance being able to be measured, which includes chest wall, lung tissue and airway resistance, as well as the specific airway resistance, which is a more stable parameter that is determined by multiplying the measured values of airway resistance and functional residual capacity. The complexity of this technique, the reference equations, the differences in the equipment and their variability, and the conditions in which it is performed, has led to the need for its standardisation. Throughout this article, the practical aspects of plethysmography are analysed, specifying recommendations for performing it, its systematic calibration and the calculations that must be made, as well as the interpretation of the results obtained. The aim of this article is to provide a better understanding of the principles of whole body plethysmography with the aim of optimising the interpretation of the results, leading to improved management of the patient, as well as a consensus among the speciality.