METABOLISM OF OPIOIDS IS ALTERED IN LIVER MICROSOMES OF SICKLE CELL TRANSGENIC MICE

An alcohol dehydrogenase 7 gene polymorphism associates with both acute and chronic pain in sickle cell disease

Introduction: As the most distressing complication of sickle cell disease (SCD), pain is marked by considerable heterogenicity. In this study we explored the potential association of alcohol dehydrogenase 7 gene (ADH7) polymorphism rs971074 with sickle cell pain. Methods: We analyzed clinical phenotypes and the rs971074 single-nucleotide polymorphism in ADH7 by MassARRAY-iPlex analysis in a cohort of SCD patients. Results: The synonymous rs971074 was significantly associated with both acute and chronic pain in SCD. Patients with the minor T allele(s) recorded significantly more crisis episodes and severe chronic pain symptoms. Conclusion: Our study has identified the rs971074 minor T allele as a genetic biomarker potentially influencing acute and chronic pain. These findings may ultimately help inform strategies to develop precision pain therapies in SCD.

Sensitization of nociceptors and dorsal horn neurons contributes to pain in sickle cell disease

Sickle cell disease (SCD) describes a group of disorders associated with a point mutation in the beta chain of hemoglobin. The mutation leads to the creation of sickle hemoglobin (HbS) and causes distortion of erythrocytes through polymerization under low oxygen, resulting in characteristic sickle red blood cells. Vaso-occlusion episodes caused by accumulation of sRBCs results in ischemia-reperfusion injury, reduced oxygen supply to organs, oxidative stress, organ damage and severe pain that often requires hospitalization and opioid treatment. Further, many patients suffer from chronic pain, including hypersensitivity to heat and cold stimuli. Progress towards the development of novel strategies for both acute and chronic pain in patients with SCD has been impeded by a lack of understanding the mechanisms underlying pain in SCD. The purpose of this review is to highlight evidence for the contribution of peripheral and central sensitization that leads to widespread, chronic pain and hyperalgesia. Targeting the mechanisms that initiate and maintain sensitization in SCD might offer effective approaches to manage the severe and debilitating pain associated with this condition.

Effect of chronic opioid therapy on pain and survival in a humanized mouse model of sickle cell disease

Chronic morphine treatment leads to decreased survival in control mice, but not in sickle mice. Chronic morphine treatment leads to hyperalgesia in sickle mice, but does not lead to analgesic tolerance.

Sensitization of C-fiber nociceptors in mice with sickle cell disease is decreased by local inhibition of anandamide hydrolysis

Chronic pain and hyperalgesia, as well as pain resulting from episodes of vaso-occlusion, are characteristic features of sickle cell disease (SCD) and are difficult to treat. Since there is growing evidence that increasing local levels of endocannabinoids can decrease hyperalgesia, we examined the effects of URB597, a fatty acid amide hydrolase (FAAH) inhibitor, which blocks the hydrolysis of the endogenous cannabinoid anandamide, on hyperalgesia and sensitization of cutaneous nociceptors in a humanized mouse model of SCD. Using homozygous HbSS-BERK sickle mice, we determined the effects of URB597 on mechanical hyperalgesia and on sensitization of C-fiber nociceptors in vivo. Intraplantar administration of URB597 (10 μg in 10 μL) decreased the frequency of withdrawal responses evoked by a von Frey monofilament (3.9 mN bending force) applied to the plantar hind paw. This was blocked by the CB1 receptor antagonist AM281 but not by the CB2 receptor antagonist AM630. Also, URB597 decreased hyperalgesia in HbSS-BERK/CB2R sickle mice, further confirming the role of CB1 receptors in the effects produced by URB597. Electrophysiological recordings were made from primary afferent fibers of the tibial nerve in anesthetized mice. The proportion of Aδ- and C-fiber nociceptors that exhibited spontaneous activity and responses of C-fibers to mechanical and thermal stimuli were greater in HbSS-BERK sickle mice as compared to control HbAA-BERK mice. Spontaneous activity and evoked responses of nociceptors were decreased by URB597 via CB1 receptors. It is suggested that enhanced endocannabinoid activity in the periphery may be beneficial in alleviating chronic pain associated with SCD.

Transient receptor potential polymorphism and haplotype associate with crisis pain in sickle cell disease

AIM

Episodes of acute pain crisis contribute to considerable morbidity and mortality in sickle cell disease (SCD). Incomprehensive understanding of the underlying pain heterogeneity results in inadequate pain management. The transient receptor potential (TRP) family of voltage-gated ion channels acts as sensory transducers of diverse noxious stimuli. We performed an association study of polymorphisms in candidate genes TRPV1 and TRPA1 with pain in SCD patients.

METHODS

Utilization rate, in other words, number of emergency department/acute care center admissions over 12 months as a result of pain crisis, served as a marker for acute pain.

RESULTS & CONCLUSION

We identified that rs920829 (incident rate ratio = 1.44, p = 0.027 additive; IRR=1.68, p=0.008 recessive models of negative binomial regression) and the CGAGG haplotype of TRPA1 (odds ratio = 0.218, p = 0.009) were significantly associated with utilization rate, suggesting that TRPA1 gene polymorphisms may influence acute pain crisis in SCD.

Population Pharmacokinetics of Cefotaxime and Dosage Recommendations in Children with Sickle Cell Disease

The pharmacokinetic profile of most drugs is dependent on the patient's covariates and may be influenced by the disease. Cefotaxime is frequently prescribed in pediatric patients with sickle cell disease (SCD), characterized by vaso-occlusive complications, chronic hemolytic anemia, and a defective immunological function predisposing the individual to severe infection. Data on the impact of the disease on the disposition of cefotaxime are missing. In the present study, our aims were to determine cefotaxime pharmacokinetics when prescribed to children with SCD for suspected or proven bacterial infection, identify significant covariates, and perform Monte Carlo simulations to optimize the drug dosage. Cefotaxime serum concentrations were measured in 78 pediatric SCD patients receiving cefotaxime intravenously at a daily dose of 200 mg/kg of body weight in three or four divided doses over 30 min. A total of 107 concentrations were available for pharmacokinetic analysis. A population pharmacokinetic model was developed with NONMEM software and used for Monte Carlo simulations. Cefotaxime concentrations ranged from 0.05 to 103.7 mg/liter. Cefotaxime pharmacokinetics were best described by a one-compartment model: the median estimated weight-normalized volume of distribution and clearance were 0.42 liter/kg (range, 0.2 to 1.1 liter/kg) and 0.38 liter/h/kg (range, 0.1 to 1.2 liter/h/kg). Cefotaxime clearance increased by 22% in patients with acute chest syndrome. Dosing optimization, performed using EUCAST MIC susceptibility breakpoints, showed that a dose of 100 mg/kg/6 h should be used, depending on the patient's characteristics and clinical presentation, in order to reach a value of the percentage of time that the drug concentration exceeded the MIC under steady-state pharmacokinetic conditions of 80% in 80% of the patients when targeting sensitive Gram-positive cocci and Gram-negative bacilli with MICs of 1 mg/liter or below.

Fentanyl Buccal Tablet: A New Breakthrough Pain Medication in Early Management of Severe Vaso-Occlusive Crisis in Sickle Cell Disease

BACKGROUND

Sickle cell disease (SCD) is a worldwide distributed hereditary red cell disorder. The principal clinical manifestations of SCD are the chronic hemolytic anemia and the acute vaso-occlusive crisis (VOCs), which are mainly characterized by ischemic/reperfusion tissue injury. Pain is the main symptom of VOCs, and its management is still a challenge for hematologists, requiring a multidisciplinary approach.

METHODS

We carried out a crossover study on adult SCD patients, who received two different types of multimodal analgesia during two separate severe VOCs with time interval between VOCs of at least 6 months. The first VOC episode was treated with ketorolac (0.86 mg/kg/day) and tramadol (7.2 mg/kg/day) (TK treatment). In the second VOC episode, fentanyl buccal tablet (FBT; 100 μg) was introduced in a single dose after three hours from the beginning of TK analgesia (TKF treatment). We focused on the first 24 hours of acute pain management. The primary efficacy measure was the time-weighted-sum of pain intensity differences (SPID24). The secondary efficacy measures included the pain intensity difference (PID), the total pain relief (TOTPAR), and the time-wighted sum of anxiety (SAID24).

RESULTS

SPID24 was significantly higher in TKF than in TK treatment. All the secondary measures were significantly ameliorated in TKF compared to TK treatment, without major opioid side effects. Patients satisfaction was higher with TKF treatment than with TK one.

CONCLUSIONS

We propose that VOCs might require breakthrough pain drug strategy as vaso-occlusive phenomena and enhanced vasoconstriction promoting acute ischemic pain component exacerbate the continuous pain of VOCs. FBT might be a powerful and feasible tool in early management of acute pain during VOCs in emergency departments.

Buprenorphine and norbuprenorphine determination in mice plasma and brain by gas chromatography-mass spectrometry

A gas chromatography tandem mass spectrometry method for quantification of buprenorphine (BUP) and norbuprenorphine (NBUP) in brain and plasma samples from mice was developed and validated. Analytes were extracted from the brain or plasma by solid phase extraction and quantified within 20 minutes. Calibration was achieved by linear regression with a 1/x weighting factor and d₄-buprenorphine internal standard. All products were linear from 1 to 2000 ng/mL with a correlation of determination >0.99. Assay accuracy and precision of back-calculated standards were within ±10%. The lower limit of quantification for both BUP and NBUP from the brain and plasma was 1 ng/mL. This sensitive and specific method can be used for the investigation of BUP mechanism of action and clinical profile.

Respiratory toxicity of buprenorphine results from the blockage of P-glycoprotein-mediated efflux of norbuprenorphine at the blood-brain barrier in mice

OBJECTIVES

Deaths due to asphyxia as well as following acute poisoning with severe respiratory depression have been attributed to buprenorphine in opioid abusers. However, in human and animal studies, buprenorphine exhibited ceiling respiratory effects, whereas its metabolite, norbuprenorphine, was assessed as being a potent respiratory depressor in rodents. Recently, norbuprenorphine, in contrast to buprenorphine, was shown in vitro to be a substrate of human P-glycoprotein, a drug-transporter involved in all steps of pharmacokinetics including transport at the blood-brain barrier. Our objectives were to assess P-glycoprotein involvement in norbuprenorphine transport in vivo and study its role in the modulation of buprenorphine-related respiratory effects in mice.

SETTING

University-affiliated research laboratory, INSERM U705, Paris, France.

SUBJECTS

Wild-type and P-glycoprotein knockout female Friend virus B-type mice.

INTERVENTIONS

Respiratory effects were studied using plethysmography and the P-glycoprotein role at the blood-brain barrier using in situ brain perfusion.

MEASUREMENTS AND MAIN RESULTS

Norbuprenorphine(≥ 1 mg/kg) and to a lesser extent buprenorphine (≥ 10 mg/kg) were responsible for dose-dependent respiratory depression combining increased inspiratory (TI) and expiratory times (TE). PSC833, a powerful P-glycoprotein inhibitor, significantly enhanced buprenorphine-related effects on TI (p < .01) and TE (p < .05) and norbuprenorphine-related effects on minute volume (VE, p < .05), TI, and TE (p < .001). In P-glycoprotein-knockout mice, buprenorphine-related effects on VE (p < .01), TE (p < .001), and TI (p < .05) and norbuprenorphine-related effects on VE (p < .05) and TI (p < .001) were significantly enhanced. Plasma norbuprenorphine concentrations were significantly increased in PSC833-treated mice (p < .001), supporting a P-glycoprotein role in norbuprenorphine pharmacokinetics. Brain norbuprenorphine efflux was significantly reduced in PSC833-treated and P-glycoprotein-knockout mice (p < .001), supporting P-glycoprotein-mediated norbuprenorphine transport at the blood-brain barrier.

CONCLUSIONS

P-glycoprotein plays a key-protective role in buprenorphine-related respiratory effects, by allowing norbuprenorphine efflux at the blood-brain barrier. Our findings suggest a major role for drug-drug interactions that lead to P-glycoprotein inhibition in buprenorphine-associated fatalities and respiratory depression.

Increased clearance of morphine in sickle cell disease: implications for pain management

Acute vaso-occlusive painful episodes associated with sickle cell disease (SCD) are frequently treated with morphine. Many SCD individuals require relatively higher doses of morphine to achieve optimal analgesia. We studied pharmacokinetics of morphine in SCD to explore if altered disposition could be a factor contributing to increased requirement of morphine in this population. The study subjects were in steady state of health to avoid the effect of hemodynamic changes associated with vaso-occlusion on morphine disposition. The plasma concentrations of morphine and its major metabolites were measured at timed intervals in 21 SCD subjects after they received a single .1 mg/Kg infusion of morphine sulfate. USCPACK software was used to fit candidate pharmacokinetic models. Noncompartmental pharmacokinetic parameters for morphine were calculated. Morphine clearance was 2.4-3.6 L/h, half-life was .3-.7 hours, AUC(0-∞) was 27.7-42.5 ng∗h/mL, and volume of distribution was .96-3.38 L/kg. Clearance of morphine in the study population was 3-10 folds higher than published estimates in the non-SCD population, with correspondingly lower AUC and half-life. Volume of distribution was similar. This observation suggests that due to increased clearance SCD individuals may require higher dose and frequency of morphine to achieve comparable plasma levels.

PERSPECTIVE

Accelerated clearance of morphine likely related to increased hepatic and renal blood flow may be responsible for increased requirement of morphine in SCD. Although SCD individuals may require higher and more frequent doses of morphine, inter-individual variability of morphine disposition highlights the importance of individualization of the therapy.

Pain-related behaviors and neurochemical alterations in mice expressing sickle hemoglobin: modulation by cannabinoids

Sickle cell disease causes severe pain. We examined pain-related behaviors, correlative neurochemical changes, and analgesic effects of morphine and cannabinoids in transgenic mice expressing human sickle hemoglobin (HbS). Paw withdrawal threshold and withdrawal latency (to mechanical and thermal stimuli, respectively) and grip force were lower in homozygous and hemizygous Berkley mice (BERK and hBERK1, respectively) compared with control mice expressing human hemoglobin A (HbA-BERK), indicating deep/musculoskeletal and cutaneous hyperalgesia. Peripheral nerves and blood vessels were structurally altered in BERK and hBERK1 skin, with decreased expression of mu opioid receptor and increased calcitonin gene-related peptide and substance P immunoreactivity. Activators of neuropathic and inflammatory pain (p38 mitogen-activated protein kinase, STAT3, and mitogen-activated protein kinase/extracellular signal-regulated kinase) showed increased phosphorylation, with accompanying increase in COX-2, interleukin-6, and Toll-like receptor 4 in the spinal cord of hBERK1 compared with HbA-BERK. These neurochemical changes in the periphery and spinal cord may contribute to hyperalgesia in mice expressing HbS. In BERK and hBERK1, hyperalgesia was markedly attenuated by morphine and cannabinoid receptor agonist CP 55940. We show that mice expressing HbS exhibit characteristics of pain observed in sickle cell disease patients, and neurochemical changes suggestive of nociceptor and glial activation. Importantly, cannabinoids attenuate pain in mice expressing HbS.

Lack of interaction between metoclopramide and morphine in vitro and in mice

1. This study examined interactions via common metabolism or via common pharmacodynamic pathways between frequently co-prescribed metoclopramide (a prokinetic) and morphine (an opioid analgesic). 2. In human liver microsomes, morphine 3-glucuronide and morphine 6-glucuronide formation had V(max) estimates of 6.2 +/- 0.07 and 0.75 +/- 0.01 (nmole min(-1) mg(-1) protein) and K(m) estimates of 1080 +/- 37 and 665 +/- 55 (microM), respectively. The in vitro K(i) for morphine 3-glucuronide formation in the presence of metoclopramide in human liver microsomes or recombinant uridine diphosphoglucuronosyltransferase 2B7 predicted a lack of in vivo interaction. 3. Morphine (2 mg kg(-1) subcutaneously) delayed gastrointestinal meal transit in mice, metoclopramide (10 mg kg(-1) subcutaneously) had no effect on meal transit, and metoclopramide did not alter this effect of morphine. 4. Morphine (2 or 5 mg kg(-1) subcutaneously) was antinociceptive in mice (hot plate test) and metoclopramide (10 mg kg(-1) subcutaneously) did not alter the antinociceptive effects of morphine. 5. Together, the data suggest a lack of interaction between morphine and metoclopramide.

Pharmacogenetics of morphine: Potential implications in sickle cell disease

Morphine is frequently used to treat painful episodes associated with sickle cell disease (SCD) but may fail to provide adequate analgesia in many patients. This concise review focuses on unique disease related changes in physiologic variables associated with SCD that impacts pharmacokinetics and pharmacodynamics of morphine and may contribute to the variability in analgesia. Emerging evidence suggests that the allelic variants in the genes involving the opioid (UGT2B7, OPRM1, and ABCB1 genes) and nonopioid system (COMT gene) can alter the efficacy of morphine.

Treatment and prevention of pain due to vaso-occlusive crises in adults with sickle cell disease: an educational void

Pain due to vaso-occlusive crisis is the major cause of hospital use in sickle cell disease. Although available guidelines provide recommendations for opioid administration in this setting, only 4 (21%) of 19 medical textbooks present treatment regimens that are consistent with them. Moreover, only 7 texts (37%) note that addiction is infrequent in this population, while 11 (92%) of 12 texts provide such reassurance for cancer-related pain (P < .005). Finally, hydroxyurea use to decrease the frequency of vaso-occlusive crises is completely defined only in 2 textbooks. Thus, most medical texts provide neither adequate information for the treatment or prevention of pain due to vaso-occlusive crisis in sickle cell disease nor reassurance of the unlikelihood of addiction in this population. In contrast, treatment recommendations for less common hematologic disorders are consistent with current standards in 53% to 84% of appropriate texts (P < .05). Limited knowledge regarding the principles and appropriateness of opioid therapy; a lack of evidence-based research on pain control; and misconceptions and prejudices about drug abuse and addiction contribute to this educational void. Thus, research and training on pain control in sickle cell disease are needed to parallel studies of environmental and genetic factors contributing to the known clinical heterogeneity of this disorder.

Variable sulfation of dietary polyphenols by recombinant human sulfotransferase (SULT) 1A1 genetic variants and SULT1E1

Human cytosolic sulfotransferases (SULTs) catalyze the sulfate conjugation of several important endo- and xenobiotics. Among the superfamily of SULT enzymes, SULT1A1 catalyzes the sulfation of small planar phenolic compounds, whereas SULT1E1 has a major role in estrogen conjugation. The human SULT1A1 gene has common single nucleotide polymorphisms that define three allozymes, SULT1A1*1, *2, and *3. The enzyme kinetics of SULT1A1 allozymes and SULT1E1 were characterized for the polyphenolic substrates apigenin, chrysin, epicatechin, quercetin, and resveratrol. Purified recombinant SULT proteins were generated in a baculoviral-insect cell system, and incubated in vitro with each substrate to determine catalytic activity. The effect of polyphenol sulfation was examined in mammalian cell lines stably expressing SULT1E1. For all polyphenols investigated, "normal-activity" SULT1A1*1 allozyme had significantly greater Vmax estimates than SULT1E1, and allele-specific differences in SULT1A1-mediated sulfation were observed. The polymorphic SULT1A1*2 allozyme exhibited low activity toward apigenin, epicatechin, and resveratrol. SULT1A1*1 and *3 acted as normal-activity allozymes for these substrates. Altered cellular proliferation was observed in MCF-7 cells stably expressing SULT1E1 upon treatment with chrysin, quercetin, or resveratrol, thus suggesting inactivation of these compounds by SULT1E1. These results suggest an important role for SULT isozymes and their pharmacogenetics in polyphenol disposition.

Sulfotransferase (SULT) 1A1 Polymorphic Variants *1, *2, and *3 Are Associated with Altered Enzymatic Activity, Cellular Phenotype, and Protein Degradation

The superfamily of sulfotransferase (SULT) enzymes catalyzes the sulfate conjugation of several pharmacologically important endo- and xenobiotics. SULT1A1 catalyzes the sulfation of small planar phenols such as neurotransmitters, steroid hormones, acetaminophen, and p-nitrophenol (PNP). Genetic polymorphisms in the human SULT1A1 gene define three alleles, SULT1A1*1, *2, and *3. The enzyme activities of the SULT1A1 allozymes were studied with a variety of substrates, including PNP, 17beta-estradiol, 2-methoxyestradiol, catecholestrogens, the antiestrogen 4-hydroxytamoxifen (OHT), and dietary flavonoids. Using purified recombinant SULT1A1 protein, marked differences in *1, *2, and *3 activity toward every substrate studied were noted. Substrate inhibition was observed for most substrates. In general, the trend in V(max) estimates was *1 > *3 > *2; however, V(max)/K(m) estimate trends varied with substrate. In MCF-7 cells stably expressing either SULT1A1*1 or *2, the antiestrogenic response to OHT was found to be allele-specific: the cells expressing *2 exhibited a better antiproliferative response. The intracellular stability of the *1 and *2 allozymes was examined in insect as well as mammalian cells. The SULT1A1*2 protein had a shorter half-life than the *1 protein. In addition, the *2 protein was ubiquitinated to a greater extent than *1, suggesting increased degradation via a proteasome pathway. The results of this study suggest marked differences in activity of polymorphic SULT1A1 variants, including SULT1A1*3, toward a variety of substrates. These differences are potentially critical for understanding interindividual variability in drug response and toxicity, as well as cancer risk and incidence.

Endogenous opiates and behavior: 2004

This paper is the 27th consecutive installment of the annual review of research concerning the endogenous opioid system, now spanning over 30 years of research. It summarizes papers published during 2004 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, and the roles of these opioid peptides and receptors in pain and analgesia; stress and social status; tolerance and dependence; learning and memory; eating and drinking; alcohol and drugs of abuse; sexual activity and hormones, pregnancy, development and endocrinology; mental illness and mood; seizures and neurologic disorders; electrical-related activity and neurophysiology; general activity and locomotion; gastrointestinal, renal and hepatic functions; cardiovascular responses; respiration and thermoregulation; and immunological responses.