Roux-en-Y gastric bypass in rat reduces mu-opioid receptor levels in brain regions associated with stress and energy regulation

Utilization of a precision medicine genetic and psychosocial approach in outcome assessment of bariatric weight loss surgery: a narrative review

The obesity epidemic has become a global public health issue, impacting more than one billion people worldwide. 9% of the US population, or 28.8 million Americans will have an eating disorder in their lifetime. In fact, global eating disorder prevalence increased from 3.5% to 7.8% between 2000 and 2018. In spite of the fact that less than 6% of people with an eating disorder are medically underweight, it is indeed an important factor when considering issues related to obesity. This public health problem is often described as being caused by various genetic and psychosocial factors. One of the most effective strategies for treating morbid obesity and achieving significant weight loss is bariatric surgery. Recent focus on precision medicine approaches has expanded into bariatric surgery in an effort to better understand and achieve improved outcomes and reduce risk for post-operative weight regain and addiction transfers during the recovery process. Addiction transfers, including substance and non-substance addictions, are well established concerns for post-bariatric patients. This review details the genetic, molecular and psychosocial factors that can be utilized to inform and guide personalized treatment. Additionally, this review details some of the molecular mechanisms including dysregulation of catecholamine signaling as well as other neurotransmitter systems relevant to help further understand recovery science.

Chronic Δ9-tetrahydrocannabinol treatment has dose-dependent effects on open field exploratory behavior and [3H] SR141716A receptor binding in the rat brain

AIMS

Acute and chronic Δ9-THC exposure paradigms affect the body differently. More must be known about the impact of chronic Δ9-THC on cannabinoid-1 (CB1R) and mu-opioid (MOR) receptor levels in the brain. The present study examined chronic Δ9-THC's effects on CB1R and MOR levels and locomotor activity.

MAIN METHODS

Adolescent Sprague-Dawley rats were given daily intraperitoneal injections of Δ9-THC [0.75mg/kg (low dose or LD) or 2.0 mg/kg (high dose or HD)] or vehicle for 24 days, and locomotion in the open field was tested after the first and fourth weeks of chronic Δ9-THC exposure. Brains were harvested at the end of treatment. [3H] SR141716A and [3H] DAMGO autoradiography assessed CB1R and MOR levels, respectively.

KEY FINDINGS

Relative to each other, chronic HD rats showed reduced vertical plane (VP) entries and time, while LD rats had increased VP entries and time for locomotion, as assessed by open-field testing; no effects were found relative to the control. Autoradiography analyses showed that HD Δ9-THC significantly decreased CB1R binding relative to LD Δ9-THC in the cingulate (33%), primary motor (42%), secondary motor (33%) somatosensory (38%), rhinal (38%), and auditory (50%) cortices; LD Δ9-THC rats displayed elevated binding in the primary motor (33% increase) and hypothalamic (33% increase) regions compared with controls. No significant differences were observed in MOR binding for the LD or HD compared to the control.

SIGNIFICANCE

These results demonstrate that chronic Δ9-THC dose-dependently altered CB1R levels throughout the brain and locomotor activity in the open field.

Opioid Analgesics after Bariatric Surgery: A Scoping Review to Evaluate Physiological Risk Factors for Opioid-Related Harm

The persisting use of opioids following bariatric surgery has emerged as a prevalent complication, heightening the probability of opioid-related harm (ORM), such as opioid-related fatalities and prescription opioid use disorder (OUD). A comprehensive review of PubMed literature from 1990 to 2023 was conducted to pinpoint physiological influences on postoperative ORM. As a result, we found that patients undertaking bariatric operations often exhibit an inherently higher risk for substance use disorders, likely attributable to genetic predisposition and related neurobiological changes that engender obesity and addiction-like tendencies. Furthermore, chronic pain is a common post-bariatric surgery complaint, and the surgical type impacts opioid needs, with increased long-term opioid use after surgeries. Additionally, the subjective nature of pain perception in patients with obesity can distort pain reporting and the corresponding opioid prescription both before and after surgery. Furthermore, the postoperative alterations to the gastrointestinal structure can affect the microbiome and opioid absorption rates, resulting in fluctuating systemic exposure to orally ingested opioids. The prospect of ORM development post-bariatric surgery appears amplified due to a preexisting susceptibility to addictive habits, surgically induced pain, modified gut-brain interaction and pain management and the changed pharmacokinetics post-surgery. Further research is warranted to clarify these potential risk variables for ORM, specifically OUD, in the bariatric population.

Calorie restriction, but not Roux-en-Y gastric bypass surgery, increases [3 H] PK11195 binding in a rat model of obesity

Roux-en-Y gastric bypass surgery (RYGB) remains an effective weight-loss method used to treat obesity. While it is successful in combating obesity, there are many lingering questions related to the changes in the brain following RYGB surgery, one of them being its effects on neuroinflammation. While it is known that chronic high-fat diet (HFD) contributes to obesity and neuroinflammation, it remains to be understood whether bariatric surgery can ameliorate diet-induced inflammatory responses. To examine this, rats were assigned to either a normal diet (ND) or a HFD for 8 weeks. Rats fed a HFD were split into the following groups: sham surgery with ad libitum access to HFD (sham-HF); sham surgery with calorie-restricted HFD (sham-FR); RYGB surgery with ad libitum access to HFD (RYGB). Following sham or RYGB surgeries, rats were maintained on their diets for 9 weeks before being euthanized. [³ H] PK11195 autoradiography was then performed on fresh-frozen brain tissue in order to measure activated microglia. Sham-FR rats showed increased [³ H] PK11195 binding in the amygdala (63%), perirhinal (60%), and ectorhinal cortex (53%) compared with the ND rats. Obese rats who had the RYGB surgery did not show this increased inflammatory effect. Since the sham-FR and RYGB rats were fed the same amount of HFD, the surgery itself seems responsible for this attenuation in [³ H] PK11195 binding. We speculate that calorie restriction following obese conditions may be seen as a stressor and contribute to inflammation in the brain. Further research is needed to verify this mechanism.

Regulation of body weight: Lessons learned from bariatric surgery

BACKGROUND

Bariatric or weight loss surgery is currently the most effective treatment for obesity and metabolic disease. Unlike dieting and pharmacology, its beneficial effects are sustained over decades in most patients, and mortality is among the lowest for major surgery. Because there are not nearly enough surgeons to implement bariatric surgery on a global scale, intensive research efforts have begun to identify its mechanisms of action on a molecular level in order to replace surgery with targeted behavioral or pharmacological treatments. To date, however, there is no consensus as to the critical mechanisms involved.

SCOPE OF REVIEW

The purpose of this non-systematic review is to evaluate the existing evidence for specific molecular and inter-organ signaling pathways that play major roles in bariatric surgery-induced weight loss and metabolic benefits, with a focus on Roux-en-Y gastric bypass (RYGB) and vertical sleeve gastrectomy (VSG), in both humans and rodents.

MAJOR CONCLUSIONS

Gut-brain communication and its brain targets of food intake control and energy balance regulation are complex and redundant. Although the relatively young science of bariatric surgery has generated a number of hypotheses, no clear and unique mechanism has yet emerged. It seems increasingly likely that the broad physiological and behavioral effects produced by bariatric surgery do not involve a single mechanism, but rather multiple signaling pathways. Besides a need to improve and better validate surgeries in animals, advanced techniques, including inducible, tissue-specific knockout models, and the use of humanized physiological traits will be necessary. State-of-the-art genetically-guided neural identification techniques should be used to more selectively manipulate function-specific pathways.

Factors Predictive of Prolonged Postoperative Narcotic Usage Following Orthopaedic Surgery

BACKGROUND

The purpose of this comprehensive review was to investigate risk factors associated with prolonged opioid use after orthopaedic procedures. A comprehensive review of the opioid literature may help to better guide preoperative management of expectations as well as opioid-prescribing practices.

METHODS

A systematic review of all studies pertaining to opioid use in relation to orthopaedic procedures was conducted using the MEDLINE, Embase, and CINAHL databases. Data from studies reporting on postoperative opioid use at various time points were collected. Opioid use and risk of prolonged opioid use were subcategorized by subspecialty, and aggregate data for each category were calculated.

RESULTS

There were a total of 1,445 eligible studies, of which 45 met inclusion criteria. Subspecialties included joint arthroplasty, spine, trauma, sports, and hand surgery. A total of 458,993 patients were included, including 353,330 (77%) prolonged postoperative opioid users and 105,663 (23%) non-opioid users. Factors associated with prolonged postoperative opioid use among all evaluated studies included body mass index (BMI) of ≥40 kg/m (relative risk [RR], 1.06 to 2.32), prior substance abuse (RR, 1.08 to 3.59), prior use of other medications (RR, 1.01 to 1.46), psychiatric comorbidities (RR, 1.08 to 1.54), and chronic pain conditions including chronic back pain (RR, 1.01 to 10.90), fibromyalgia (RR, 1.01 to 2.30), and migraines (RR, 1.01 to 5.11). Age cohorts associated with a decreased risk of prolonged postoperative opioid use were those ≥31 years of age for hand procedures (RR, 0.47 to 0.94), ≥50 years of age for total hip arthroplasty (RR, 0.70 to 0.80), and ≥70 years of age for total knee arthroplasty (RR, 0.40 to 0.80). Age cohorts associated with an increased risk of prolonged postoperative opioid use were those ≥50 years of age for sports procedures (RR, 1.11 to 2.57) or total shoulder arthroplasty (RR, 1.26 to 1.40) and those ≥70 years of age for spine procedures (RR, 1.61). Identified risk factors for postoperative use were similar across subspecialties.

CONCLUSIONS

We provide a comprehensive review of the various preoperative and postoperative risk factors associated with prolonged opioid use after elective and nonelective orthopaedic procedures. Increased BMI, prior substance abuse, psychiatric comorbidities, and chronic pain conditions were most commonly associated with prolonged postoperative opioid use. Careful consideration of elective surgical intervention for painful conditions and perioperative identification of risk factors within each patient's biopsychosocial context will be essential for future modulation of physician opioid-prescribing patterns.

LEVEL OF EVIDENCE

Prognostic Level IV. See Instructions for Authors for a complete description of levels of evidence.

Endogenous opiates and behavior: 2019

This paper is the forty-second consecutive installment of the annual anthological review of research concerning the endogenous opioid system, summarizing articles published during 2019 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides and receptors as well as effects of opioid/opiate agonists and antagonists. The review is subdivided into the following specific topics: molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors (1), the roles of these opioid peptides and receptors in pain and analgesia in animals (2) and humans (3), opioid-sensitive and opioid-insensitive effects of nonopioid analgesics (4), opioid peptide and receptor involvement in tolerance and dependence (5), stress and social status (6), learning and memory (7), eating and drinking (8), drug abuse and alcohol (9), sexual activity and hormones, pregnancy, development and endocrinology (10), mental illness and mood (11), seizures and neurologic disorders (12), electrical-related activity and neurophysiology (13), general activity and locomotion (14), gastrointestinal, renal and hepatic functions (15), cardiovascular responses (16), respiration and thermoregulation (17), and immunological responses (18).

Preoperative brain μ-opioid receptor availability predicts weight development following bariatric surgery in women

Bariatric surgery is the most effective method for weight loss in morbid obesity. There is significant individual variability in the weight loss outcomes, yet factors leading to postoperative weight loss or weight regain remain elusive. Alterations in the μ-opioid receptor (MOR) and dopamine D₂ receptor (D₂R) systems are associated with obesity and appetite control, and the magnitude of initial brain receptor system perturbation may predict long-term surgical weight loss outcomes. We tested this hypothesis by studying 19 morbidly obese women (mean BMI 40) scheduled to undergo bariatric surgery. We measured their preoperative MOR and D₂R availabilities using positron emission tomography with [¹¹C]carfentanil and [¹¹C]raclopride, respectively, and then assessed their weight development association with regional MOR and D₂R availabilities at 24-month follow-up. MOR availability in the amygdala consistently predicted weight development throughout the follow-up period, but no associations were found for D₂R. This is the first study to our knowledge to demonstrate that neuroreceptor markers prior to bariatric surgery are associated with postoperative weight development. Postoperative weight regain may derive from dysfunction in the opioid system, and weight loss outcomes after bariatric surgery may be partially predicted based on preoperative brain receptor availability, opening up new potential for treatment possibilities.

Roux-en-Y gastric bypass increases GABA-A receptor levels in regions of the rat brain involved in object recognition memory and perceptual acuity

Roux-en-Y gastric bypass surgery (RYGB), one of the most common and successful procedures for combatting obesity, is associated with post-surgery substance use disorder (SUD) and other addictive behaviors in a subset of patients. We investigated the effects of RYGB on GABA-A receptor levels in the rat brain to identify potential mechanisms of this behavior. The GABAergic system is affected in addiction and has been implicated in the pathology of obesity. We assigned male Sprague-Dawley rats to four groups: standard, low fat diet with sham surgery (control), ad libitum HFD with sham surgery (Sham), calorie restricted HFD with sham surgery (Sham-FR), or HFD with RYGB surgery. Surgery was performed after 8 weeks on the control or HFD diet. Rats maintained their respective diets for 9 weeks post-surgery, then were sacrificed for GABA-A receptor autoradiography using the [³H] Flunitrazepam ligand. We identified increased GABA-A binding in the perirhinal cortex of ad-libitum HFD fed rats compared to normal diet controls. RYGB surgery increased GABA-A in the ectorhinal cortex compared to normal diet controls, and increased binding in the jaw region of the primary somatosensory cortex compared to food-restricted rats that received sham surgery. Hypothalamus GABA-A was also negatively correlated with body weight in the RYGB group, where GABA signaling may play a role in obesity regulation. These results suggest that HFD and RYGB modulate GABA signaling in regions important for object recognition memory, and that increased GABA-A levels in the jaw's perceptual field cortex arise from the surgery itself, independent of caloric restriction.

Chronic aerobic exercise: Autoradiographic assessment of GABA(a) and mu-opioid receptor binding in adult rats

Exercise programs have shown great potential for both the prevention and treatment of substance use disorder (SUD). As exercise has been shown to have potent effects on physical and psychological health, it is reasonable to examine the mechanism of how exercise can be used as an adjunct treatment for addiction. The present study examined the effects of chronic aerobic (treadmill) exercise on both GABA(a) and mu-opioid receptor levels in the brains of male and female rats. GABA(a) receptor binding, measured by [³H] Flunitrazepam, was increased in the cingulate cortex following exercise, but only in females. Mu-opioid receptor expression, measured by [³H] ([D-Ala², N-MePhe⁴, Gly-ol]-enkephalin) (DAMGO), showed no effect of exercise while showing an effect of sex, with increased [³H] DAMGO binding in the brains of sedentary males compared to that of sedentary females. Our findings support the potential role for GABA(a) signaling in the cingulate cortex as part of the mechanism of action of aerobic exercise. These data, along with prior reports, aid our understanding of the neurochemical impact and mechanism of chronic aerobic exercise on neuropsychiatric disease, particularly regarding addiction.

Chronic abdominal pain and persistent opioid use after bariatric surgery

Background and aims Bariatric surgery remains a mainstay for treatment of morbid obesity. However, long-term adverse outcomes include chronic abdominal pain and persistent opioid use. The aim of this review was to assess the existing data on prevalence, possible mechanisms, risk factors, and outcomes regarding chronic abdominal pain and persistent opioid use after bariatric surgery. Methods PubMed was screened for relevant literature focusing on chronic abdominal pain, persistent opioid use and pharmacokinetic alterations of opioids after bariatric surgery. Relevant papers were cross-referenced to identify publications possibly not located during the ordinary screening. Results Evidence regarding general chronic pain status after bariatric surgery is sparse. However, our literature review revealed that abdominal pain was the most prevalent complication to bariatric surgery, presented in 3-61% of subjects with health care contacts or readmissions 1-5 years after surgery. This could be explained by behavioral, anatomical, and/or functional disorders. Persistent opioid use and doses increased after bariatric surgery, and 4-14% initiated a persistent opioid use 1-7 years after the surgery. Persistent opioid use was associated with severe pain symptoms and was most prevalent among subjects with a lower socioeconomic status. Alteration of absorption and distribution after bariatric surgery may impact opioid effects and increase the risk of adverse events and development of addiction. Changes in absorption have been briefly investigated, but the identified alterations could not be separated from alterations caused solely by excessive weight loss, and medication formulation could influence the findings. Subjects with persistent opioid use after bariatric surgery achieved lower weight loss and less metabolic benefits from the surgery. Thus, remission from comorbidities and cost effectiveness following bariatric surgery may be limited in these subjects. Conclusions Pain, especially chronic abdominal, and persistent opioid use were found to be prevalent after bariatric surgery. Physiological, anatomical, and pharmacokinetic changes are likely to play a role. However, the risk factors for occurrence of chronic abdominal pain and persistent opioid use have only been scarcely examined as have the possible impact of pain and persistent opioid use on clinical outcomes, and health-care costs. This makes it difficult to design targeted preventive interventions, which can identify subjects at risk and prevent persistent opioid use after bariatric surgery. Future studies could imply pharmacokinetic-, pharmacodynamics-, and physiological-based modelling of pain treatment. More attention to social, physiologic, and psychological factors may be warranted in order to identify specific risk profiles of subjects considered for bariatric surgery in order to tailor and optimize current treatment recommendations for this population.