Up-regulation of central mu-opioid receptors in a model of hepatic encephalopathy: a potential mechanism for increased sensitivity to morphine in liver failure

Opioid use and risks in candidates and recipients of liver transplant

Opioid use is extremely prevalent among patients with cirrhosis and those who received liver transplant (LT), despite concerns regarding opioid-related risks in this population. While there are many theoretical risks of opioids in patients with hepatic dysfunction, there is limited evidence on the effect of opioid use on clinical outcomes in cirrhosis and patients before and after LT specifically. As a result, there is significant center-level variability in opioid-related practices and policies. The existing data-largely based on retrospective observational studies-do suggest that opioids are associated with increased health resource utilization pre-LT and post-LT and that they may precipitate HE in patients with cirrhosis and increase the risk of graft loss and death after LT. The strongest predictor of opioid use after LT is opioid use before transplant; thus, a focus on safe opioid use in the pretransplant and peritransplant periods is essential for minimizing opioid-related harms. We describe 3 strategies to guide LT providers including (1) improved characterization of pain, mental health symptoms, and opioid and polysubstance use; (2) minimization of opioid prescriptions for those at highest risk of adverse events; and (3) safe prescribing strategies for those who do use opioids and for the management of opioid use disorder. Ultimately, our goal is to improve the quality of life and transplant outcomes among patients with cirrhosis and those who received LT, particularly those living with concurrent pain, mental health, and substance use disorders.

Cirrhosis Inpatients Receive More Opioids and Fewer Nonopioid Analgesics Than Patients Without Cirrhosis

GOALS/BACKGROUND

Pain is common among cirrhosis patients, particularly those hospitalized with acute illness. Managing pain in this population is challenging due to concern for adverse events and lack of guidelines for analgesic use. We sought to characterize analgesic use among inpatients with cirrhosis compared with matched noncirrhosis controls, as well as hospital-level variation in prescribing patterns.

METHODS

We utilized the Vizient Clinical Database, which includes clinical and billing data from hospitalizations at >500 US academic medical centers. We identified cirrhosis patients hospitalized in 2017-2018, and a matched cohort of noncirrhosis patients. Types of analgesic given-acetaminophen (APAP), nonsteroidal anti-inflammatory drugs (NSAIDs), opioids, and adjuvants (eg, gabapentinoids, antidepressants) were defined from inpatient prescription records. Conditional logistic regression was used to associate cirrhosis diagnosis with analgesic use.

RESULTS

Of 116,363 cirrhosis inpatients, 83% received at least 1 dose of an analgesic and 58% had regular inpatient analgesic use, rates that were clinically similar to noncirrhosis controls. Cirrhosis inpatients were half as likely to receive APAP (26% vs. 42%, P <0.01) or NSAIDs (3% vs. 7%, P <0.01), but were more likely to receive opioids (59% vs. 54%, P <0.01), particularly decompensated patients (60%). There was notable variation in analgesic prescribing patterns between hospitals, especially among cirrhosis patients.

CONCLUSIONS

Analgesic use was common among inpatients, with similar rates among patients with and without cirrhosis. Cirrhosis patients-particularly decompensated patients-were less likely to receive APAP and NSAIDs and more likely to receive opioid analgesics. Because of lack of evidence-based guidance for management of cirrhosis patients with pain, providers may avoid nonopioid analgesics due to perceived risks and consequently may overutilize opioids in this high-risk population.

Using Intervention Mapping to Develop a Novel Pain Self-Management Intervention for People with Cirrhosis

BACKGROUND

Chronic pain is common among patients with cirrhosis and is challenging to treat. While promising, pain self-management (PSM) interventions have not been tailored to this population's needs.

AIMS

To design a PSM intervention for patients with cirrhosis.

METHODS

Semi-structured interviews with 17 patients with cirrhosis, 12 hepatologists, and 6 administrators from two medical centers were conducted to inform a rigorous, structured intervention mapping (IM) process. Qualitative content analysis was guided by social cognitive theory (SCT) and the Consolidated Framework for Implementation Research (CFIR) and incorporated into intervention development. A planning group met regularly throughout the intervention, to reach consensus about how to use data and theory to develop the intervention through IM.

RESULTS

Participants described barriers to PSM behaviors, including the absence of simple, evidence-based interventions for pain for patients with cirrhosis, inadequate provider knowledge, time, and training, and lack of champions, funding, and communication. Patients described high motivation to treat pain using behavioral methods including meditation, prayer, and exercise. The intervention was designed to address barriers to PSM behaviors for patients with cirrhosis, using behavior change methods that address knowledge, self-efficacy, and outcome expectations. The LEAP (Liver Education About Pain) intervention is a 12-week, modular intervention delivered by phone via individual and group sessions with a health coach.

CONCLUSIONS

People with cirrhosis, hepatologists, and administrators informed this theory-driven, tailored PSM intervention, which was designed to be implementable in the real world.

Casomorphins and Gliadorphins Have Diverse Systemic Effects Spanning Gut, Brain and Internal Organs

Food-derived opioid peptides include digestive products derived from cereal and dairy diets. If these opioid peptides breach the intestinal barrier, typically linked to permeability and constrained biosynthesis of dipeptidyl peptidase-4 (DPP4), they can attach to opioid receptors. The widespread presence of opioid receptors spanning gut, brain, and internal organs is fundamental to the diverse and systemic effects of food-derived opioids, with effects being evidential across many health conditions. However, manifestation delays following low-intensity long-term exposure create major challenges for clinical trials. Accordingly, it has been easiest to demonstrate causal relationships in digestion-based research where some impacts occur rapidly. Within this environment, the role of the microbiome is evidential but challenging to further elucidate, with microbiome effects ranging across gut-condition indicators and modulators, and potentially as systemic causal factors. Elucidation requires a systemic framework that acknowledges that public-health effects of food-derived opioids are complex with varying genetic susceptibility and confounding factors, together with system-wide interactions and feedbacks. The specific role of the microbiome within this puzzle remains a medical frontier. The easiest albeit challenging nutritional strategy to modify risk is reduced intake of foods containing embedded opioids. In future, constituent modification within specific foods to reduce embedded opioids may become feasible.

2020 Clinical Update in Liver Transplantation

The gold standard treatment of end-stage liver disease continues to be liver transplantation (LT). The challenges of LT require skilled anesthesiologists to anticipate physiologic changes associated with end-stage liver disease and surgical considerations that affect multiple organ systems. While on the waiting list, patients may be placed on new anticoagulation medications that can confound already complex coagulopathy in LT patients. Pain management often is an afterthought for such a complex procedure, but appropriate medications can help control pain while limiting opioid medications. Surgical stress and medications for immunosuppression can affect perioperative glucose management in ways that have implications for patient and graft survival. The coronavirus disease 2019 pandemic in 2020 provided a new challenge for anesthesiologists. The uncertainty of the novel respiratory virus challenged providers beyond just LT patients.

Opioid prescriptions are associated with hepatic encephalopathy in a national cohort of patients with compensated cirrhosis

BACKGROUND

Opioids are often prescribed for pain in cirrhosis and may increase the risk of hepatic encephalopathy (HE).

AIM

To assess the association between opioids and HE in patients with well-compensated cirrhosis.

METHODS

We used the IQVIA PharMetrics (Durham, NC) database to identify patients aged 18-64 years with cirrhosis. We excluded patients with any decompensation event from 1 year before cirrhosis diagnosis to 6 months after cirrhosis diagnosis. Over the 6 months after cirrhosis diagnosis, we determined the duration of continuous opioid use and classified use into short term (1-89 days) and chronic (90-180 days). We assessed whether patients developed HE over the subsequent year (ie 6-18 months after cirrhosis diagnosis). We used a landmark analysis and performed multivariable Cox proportional hazards regression to assess associations between opioid use and HE, adjusting for relevant confounders.

RESULTS

The cohort included 6451 patients with compensated cirrhosis, of whom 23.3% and 4.7% had short-term and chronic opioid prescriptions respectively. Over the subsequent year, HE occurred in 6.3% patients with chronic opioid prescriptions, 5.0% with short-term opioid prescriptions and 3.3% with no opioid prescriptions. In the multivariable model, an increased risk of HE was observed with short-term (adjusted hazard ratio, HR 1.44, 95% CI 1.07-1.94) and chronic opioid prescriptions (adjusted HR 1.83, 95% CI 1.07-3.12) compared to no opioid prescriptions.

CONCLUSION

In this national cohort of privately insured patients with cirrhosis, opioid prescriptions were associated with the risk of incident HE. Opioid use should be minimised in those with cirrhosis and, when required, limited to short duration.

In inpatients with cirrhosis opioid use is common and associated with length of stay and persistent use post-discharge

Background

Previous studies have demonstrated that opioids are often prescribed and associated with complications in outpatients with cirrhosis. Less is known about opioids among hospitalized patients with cirrhosis. We aimed to describe the patterns and complications of opioid use among inpatients with cirrhosis.

Methods

This retrospective cohort study included adult patients with cirrhosis admitted to a single hospital system from 4/4/2014 to 9/30/2015. We excluded hospitalizations with a surgery, invasive procedure, or palliative care/hospice consult in order to understand opioid use that may be avoidable. We determined the frequency, dosage, and type of opioids given during hospitalization. Using bivariable and multivariable analyses, we assessed length of stay, intensive care unit transfer, and in-hospital mortality by opioid use.

Results

Of 217 inpatients with cirrhosis, 118 (54.4%) received opioids during hospitalization, including 41.7% of patients without prior outpatient opioid prescriptions. Benzodiazepines or hypnotic sleep aids were given to 28.8% of opioid recipients. In the multivariable model, younger age and outpatient opioid prescription were associated with inpatient opioids. Hospitalization was longer among opioid recipients (median 3.9 vs 3.0 days, p = 0.002) and this difference remained after adjusting for age, cirrhosis severity, and medical comorbidities. There was no difference in intensive care unit transfers and no deaths occurred. At discharge, 22 patients were newly started on opioids of whom 10 (45.5%) had opioid prescriptions at 90 days post-discharge.

Conclusion

In non-surgical inpatients with cirrhosis, opioid prescribing was common and associated with prolonged length of stay. A high proportion of patients newly discharged with opioid prescriptions had ongoing prescriptions at 90 days post-discharge.

Characteristics of Opioid Prescriptions to Veterans With Cirrhosis

BACKGROUND & AIMS

Despite increased risks for adverse effects in patients with cirrhosis, little is known about opioid prescriptions for this population. We aimed to assess time trends in opioid prescribing and factors associated with receiving opioids among patients with cirrhosis.

METHODS

Among Veterans with cirrhosis, identified using national Veterans Health Administration data (2005-2014), we assessed characteristics of patients and their prescriptions for opioids. We calculated the annual proportion of patients receiving any opioid prescription. Among opioid recipients, we assessed prescriptions that were long-term (>90 days' supply), for high doses (>100 MME/day), or involved combinations of opioids and acetaminophen or benzodiazepine. We evaluated patient characteristics independently associated with long-term and any opioid prescriptions using mixed-effects regression models.

RESULTS

Among 127,239 Veterans with cirrhosis, 97,974 (77.0%) received a prescription for an opioid. Annual opioid prescriptions increased from 36% in 2005 to 47% in 2014 (P < .01). Among recipients of opioids, the proportions of those receiving long-term prescriptions increased from 47% in 2005 to 54% in 2014 (P < .01), and19%-21% received prescriptions for high-dose opioids. Prescriptions for combinations of opioids and acetaminophen decreased from 68% in 2005 to 50% in 2014 (P < .01) and for combinations of opioids and benzodiazepines decreased from 24% to 19% over this time (P < .01). Greater probability of long-term opioid prescriptions was independently associated with younger age, female sex, white race, hepatitis C, prior hepatic decompensation, hepatocellular carcinoma, mental health disorders, nicotine use disorders, medical comorbidities, surgery, and pain-related conditions.

CONCLUSION

Among Veterans with cirrhosis, 36%-47% were prescribed opioids in each year. Mental health disorders and hepatic decompensation were independently associated with long-term opioid prescriptions.

Chronic opioid use is associated with altered gut microbiota and predicts readmissions in patients with cirrhosis

BACKGROUND

Opioid use is epidemic in cirrhosis, which could precipitate hepatic encephalopathy (HE) potentially through gut dysbiosis and inflammation.

AIM

To define the effect of opioids on readmissions and on gut microbiota composition and functionality.

METHODS

Cohort 1 had 200 cirrhotic in-patients (with/without opioid use) followed prospectively through the index hospitalisation and 6 months post discharge. Readmissions (HE-related/unrelated) were compared between patients discharged on opioids compared to the rest, including using a multi-variable analysis. Cohort 2 consisted of 72 cirrhotics on chronic opioids who were age/model for end-stage liver disease (MELD) and prior HE-balanced with 72 cirrhotics not on opioids. Stool microbiota composition (multi-tagged sequencing), predicted functionality (PiCRUST), endotoxemia and systemic inflammation (IL-6, IL-17) were compared.

RESULTS

Cohort 1: Chronic opioid use was statistically similar between those admitted with/without HE, and was judged to be an HE precipitant in <5% of cases during the index hospitalisation. Of the 144 patients alive at 6 months, 82 were readmitted. The opioid users had a significantly higher all cause (69% vs. 48%, P = 0.008), but not HE-related readmissions (30% vs. 41%, P = 0.30). On regression, opioid therapy and female gender were predictive of readmission independent of MELD score and previous HE. Cohort 2: Significant dysbiosis was noted in the opioid cohort, especially in HE+opioid patients with lower autochthonous taxa and Bacteroidaceae relative abundance. PiCRUST showed highest aromatic amino acid and endotoxin production in opioid users. Opioid users also had higher endotoxemia and IL-6 but not IL-17.

CONCLUSION

Chronic opioid use in cirrhosis is associated with increased endotoxemia, dysbiosis and all-cause readmissions.

Analgesics in patients with hepatic impairment: pharmacology and clinical implications

The physiological changes that accompany hepatic impairment alter drug disposition. Porto-systemic shunting might decrease the first-pass metabolism of a drug and lead to increased oral bioavailability of highly extracted drugs. Distribution can also be altered as a result of impaired production of drug-binding proteins or changes in body composition. Furthermore, the activity and capacity of hepatic drug metabolizing enzymes might be affected to various degrees in patients with chronic liver disease. These changes would result in increased concentrations and reduced plasma clearance of drugs, which is often difficult to predict. The pharmacology of analgesics is also altered in liver disease. Pain management in hepatically impaired patients is challenging owing to a lack of evidence-based guidelines for the use of analgesics in this population. Complications such as bleeding due to antiplatelet activity, gastrointestinal irritation, and renal failure are more likely to occur with nonsteroidal anti-inflammatory drugs in patients with severe hepatic impairment. Thus, this analgesic class should be avoided in this population. The pharmacokinetic parameters of paracetamol (acetaminophen) are altered in patients with severe liver disease, but the short-term use of this drug at reduced doses (2 grams daily) appears to be safe in patients with non-alcoholic liver disease. The disposition of a large number of opioid drugs is affected in the presence of hepatic impairment. Certain opioids such as codeine or tramadol, for instance, rely on hepatic biotransformation to active metabolites. A possible reduction of their analgesic effect would be the expected pharmacodynamic consequence of hepatic impairment. Some opioids, such as pethidine (meperidine), have toxic metabolites. The slower elimination of these metabolites can result in an increased risk of toxicity in patients with liver disease, and these drugs should be avoided in this population. The drug clearance of a number of opioids, such as morphine, oxycodone, tramadol and alfentanil, might be decreased in moderate or severe hepatic impairment. For the highly excreted morphine, hydromorphone and oxycodone, an important increase in bioavailability occurs after oral administration in patients with hepatic impairment. Lower doses and/or longer administration intervals should be used when these opioids are administered to patients with liver disease to avoid the risk of accumulation and the potential increase of adverse effects. Finally, the pharmacokinetics of phenylpiperidine opioids such as fentanyl, sufentanil and remifentanil appear to be unaffected in hepatic disease. All opioid drugs can precipitate or aggravate hepatic encephalopathy in patients with severe liver disease, thus requiring cautious use and careful monitoring.

Theories of the pathogenesis of hepatic encephalopathy

The earliest hypothesis of the pathogenesis of HE implicated ammonia, although effects of appreciable concentrations of this neurotoxin did not resemble HE. Altered eurotransmission in the brain was suggested by similarities between increased GABA-mediated inhibitory neurotransmission and HE, specifically decreased consciousness and impaired motor function. Evidence of increased GABAergic tone in models of HE has accumulated; potential mechanisms include increased synaptic availability of GABA and accumulation of natural benzodiazepine receptor ligands with agonist properties. Pathophysiological concentrations of ammonia associated with HE, have the potential of enhancing GABAergic tone by mechanisms that involve its interactions with the GABAa receptor complex.

Abnormal nociception and opiate sensitivity of STOP null mice exhibiting elevated levels of the endogenous alkaloid morphine

BACKGROUND

Mice deficient for the stable tubule only peptide (STOP) display altered dopaminergic neurotransmission associated with severe behavioural defects including disorganized locomotor activity. Endogenous morphine, which is present in nervous tissues and synthesized from dopamine, may contribute to these behavioral alterations since it is thought to play a role in normal and pathological neurotransmission.

RESULTS

In this study, we showed that STOP null brain structures, including cortex, hippocampus, cerebellum and spinal cord, contain high endogenous morphine amounts. The presence of elevated levels of morphine was associated with the presence of a higher density of mu opioid receptor with a higher affinity for morphine in STOP null brains. Interestingly, STOP null mice exhibited significantly lower nociceptive thresholds to thermal and mechanical stimulations. They also had abnormal behavioural responses to the administration of exogenous morphine and naloxone. Low dose of morphine (1 mg/kg, i.p.) produced a significant mechanical antinociception in STOP null mice whereas it has no effect on wild-type mice. High concentration of naloxone (1 mg/kg) was pronociceptive for both mice strain, a lower concentration (0.1 mg/kg) was found to increase the mean mechanical nociceptive threshold only in the case of STOP null mice.

CONCLUSIONS

Together, our data show that STOP null mice displayed elevated levels of endogenous morphine, as well as an increase of morphine receptor affinity and density in brain. This was correlated with hypernociception and impaired pharmacological sensitivity to mu opioid receptor ligands.

Up-regulation of mu-opioid receptors in the spinal cord of morphine-tolerant rats

Though morphine remains the most powerful drug for treating pain, its effectiveness is limited by the development of tolerance and dependence. The mechanism underlying development of tolerance to morphine is still poorly understood. One of the factors could be an alteration in the number of micro-receptors within specific parts of the nervous system. However, reports on changes in the micro-opioid receptor density in the spinal cord after chronic morphine administration are conflicting. Most of the studies have used subcutaneously implanted morphine pellets to produce tolerance. However, it does not simulate clinical conditions, where it is more common to administer morphine at intervals, either by injections or orally. In the present study, rats were made tolerant to morphine by injecting increasing doses of morphine (10-50 mg/kg, subcutaneously) for five days. In vitro tissue autoradiography for localization of micro-receptor in the spinal cord was done using [3H]-DAMGO. As compared to the spinal cord of control rats, the spinal cord of tolerant rats showed an 18.8% increase or up-regulation in the density of micro-receptors in the superficial layers of the dorsal horn. This up-regulation of micro-receptors after morphine tolerance suggests that a fraction of the receptors have been rendered desensitized, which in turn could lead to tolerance

Cholestasis and endogenous opioids: liver disease and exogenous opioid pharmacokinetics

A class of endogenous opioids is upregulated in liver disease particular to cholestasis, which contributes to symptoms in liver disease such as pruritus, hypotension and encephalopathy. Symptoms associated with cholestasis are reversed or at least ameliorated by mu opioid receptor antagonists. Palliation of symptoms related to cholestatic liver disease also involves bile acid binding agents. Opioid receptor antagonists, unlike bile acid binding agents, have been reported to relieve multiple symptoms, except for pruritus, and improve liver function as demonstrated in experimental cholestasis. Exogenous opioid pharmacology is altered by liver disease. Dose reduction or prolongation of dose intervals is necessary depending on the severity of liver disease.

Endocannabinoids and liver disease--review

AIMS

Endocannabinoids are endogenous compounds that bind to the same receptors as tetrahydrocannabinol, the active component in marijuana and hashish. They have been found to have many physiological and patho-physiological functions, including mood alteration, control of feeding and appetite, motor and co-ordination activities, analgesia, immune modulation and gut motility. In this review we aim to elucidate current knowledge as to their role in liver physiology and disease.

METHODS

The major findings published to date concerning endocannabinoids and liver disease are described, and their implications with regard to understanding disease mechanisms, and the development of new treatments is considered.

RESULTS

Recently, endocannabinoids have been implicated in the hemodynamic alterations occurring in cirrhosis. These changes appear to be mediated via specific cannabinoid receptors (CB1) on splanchnic and hepatic vascular endothelium. Plasma levels of endocannabinoids also seem to be elevated in hepatitis, and are involved in apoptosis of hepatocytes by a membrane mechanism not related to a specific receptor. Other studies suggest a beneficial role for cannabinoids in reducing the inflammation of experimental hepatitis. In an animal model of acute hepatic failure, both endocannabinoids and the antagonist to the CB1 receptor have been found to have a beneficial effect on neurological and cognitive function.

CONCLUSIONS

Endocannabinoids appear to be involved in several aspects of acute and chronic liver disease, including vascular changes, modulation of inflammatory process and neurological function, Further research may provide new insights into the pathophysiology of liver disease, as well as a basis for novel treatment modalities.

Antineuropathic Effects of the Antibiotic Derivative Spicamycin KRN5500

Excellence in neuropathic pain management continues to challenge the ability of health care providers. Current medications are helpful but often create significant side effects or simply fail to provide adequate analgesia. We report here on a serendipitous finding of the successful attenuation of neuropathic pain in a patient with long-standing monoclonal gammopathy, Raynaud's disease, and neuropathic pain who received the trial chemotherapeutic agent KRN5500. This finding led to animal studies that have provided support for the possible use of KRN5500 in the treatment of neuropathic pain in humans as well as some insight into the possible mechanism(s) of action of this drug.

Endogenous opiates and behavior: 2002

This paper is the twenty-fifth consecutive installment of the annual review of research concerning the endogenous opioid system, now spanning over a quarter-century of research. It summarizes papers published during 2002 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 (Section 2), and the roles of these opioid peptides and receptors in pain and analgesia (Section 3); stress and social status (Section 4); tolerance and dependence (Section 5); learning and memory (Section 6); eating and drinking (Section 7); alcohol and drugs of abuse (Section 8); sexual activity and hormones, pregnancy, development and endocrinology (Section 9); mental illness and mood (Section 10); seizures and neurologic disorders (Section 11); electrical-related activity and neurophysiology (Section 12); general activity and locomotion (Section 13); gastrointestinal, renal and hepatic functions (Section 14); cardiovascular responses (Section 15); respiration and thermoregulation (Section 16); and immunological responses (Section 17).

Anticipating and treating opioid-associated adverse effects

Opioids are frequently avoided as viable tools in the management of pain due to perceived dangerous or untoward adverse drug events. Whilst they are relatively safe options for the treatment of pain, side effects and toxicities do exist and should be anticipated by the provider. The central nervous, gastrointestinal, genito-urinary, integumentary, metabolic/endocrine, cardiovascular, pulmonary, hepatic/renal, ocular and immune systems all manifest changes associated with opioid therapy. These adverse events, ranging from nuisance to therapy-limiting, are manageable when addressed quickly and appropriately. Opioids are safe and efficacious analgesics when these effects are considered.