Cingulate glutamate levels associate with pain in chronic pancreatitis patients

Recent advances in the understanding and management of chronic pancreatitis pain

Abdominal pain is the most common symptom of chronic pancreatitis (CP) and is often debilitating for patients and very difficult to treat. To date, there exists no cure for the disease. Treatment strategies focus on symptom management and on mitigation of disease progression by reducing toxin exposure and avoiding recurrent inflammatory events. Traditional treatment protocols start with medical management followed by consideration of procedural or surgical intervention on selected patients with severe and persistent pain. The incorporation of adjuvant therapies to treat comorbidities including psychiatric disorders, exocrine pancreatic insufficiency, mineral bone disease, frailty, and malnutrition, are in its early stages. Recent clinical studies and animal models have been designed to improve investigation into the pathophysiology of CP pain, as well as to improve pain management. Despite the array of tools available, many therapeutic options for the management of CP pain provide incomplete relief. There still remains much to discover about the neural regulation of pancreas-related pain. In this review, we will discuss research from the last 5 years that has provided new insights into novel methods of pain phenotyping and the pathophysiology of CP pain. These discoveries have led to improvements in patient selection for optimization of outcomes for both medical and procedural management, and identification of potential future therapies.

White matter brain changes in chronic pancreatitis: A 7-year longitudinal follow-up study

BACKGROUND/OBJECTIVES

The progression of cerebral white matter changes over time has not been explored in chronic pancreatitis (CP). We aimed to characterize such alterations in individuals with CP at baseline and after 7-years as compared with controls and to explore associations to risk factors and clinical parameters.

METHODS

Diffusion tensor imaging was used to evaluate 20 individuals with CP and 13 healthy controls at baseline and after 7-years (CP: n = 9, controls: n = 11). Tract-based spatial statistics were used to assess whole-brain white matter structure, extract significant fractional anisotropy (FA) clusters between groups, mean FA skeleton, mean FA and mean diffusivity (MD). FA of the extracted significant clusters between groups were used for regression analyses with risk factors and clinical parameters, including duration of CP, smoking, and diabetes.

RESULTS

At baseline, widespread reductions in FA were found in CP compared to controls involving corpus callosum, the anterior, posterior thalamic radiation, and superior and posterior corona radiata (cluster volume: 49,431 mm³, all P < 0.05). At baseline, also the mean FA (P = 0.004) and FA skeleton (P = 0.002) were reduced in CP compared to controls. FA of the extracted significant cluster was associated with the daily tobacco use (P = 0.001) and duration of CP (P = 0.010). At follow-up, the whole-brain FA skeleton was reduced by 1.7% for both CP individuals and controls (P = 0.878).

CONCLUSION

Individuals with CP had widespread cerebral white matter alterations at baseline that can likely be explained by the CP disease and exposure to toxic substances. Otherwise, further progression resembles that in healthy controls.

Mechanisms underlying paclitaxel-induced neuropathic pain: Channels, inflammation and immune regulations

Paclitaxel is a chemotherapeutic agent widely used for many types of malignancies. However, when paclitaxel is used to treat tumors, patients commonly experience severe neuropathic pain that is difficult to manage. The mechanism underlying paclitaxel-induced neuropathic pain remains unclear. Evidence demonstrates correlations between mechanisms of paclitaxel-mediated pain and associated actions of ion channels, neuroinflammation, mitochondrial damage, and other factors. This review provides a comprehensive analysis of paclitaxel-induced neuropathic pain mechanisms and suggestions for effective interventions.

Pain, depression, and poor quality of life in chronic pancreatitis: Relationship with altered brain metabolites

BACKGROUND

To evaluate if altered brain metabolites are connected to pain, depression and affective responses in CP.

METHODS

In this prospective study we evaluated pain characteristics, QOL (EORTC QLQc30+PAN28), depression (Beck depression inventory [BDI] II) in 558 patients with CP and 67 healthy controls. Brain metabolites were evaluated using magnetic resonance spectroscopy (MRS) in 49 patients and 5 healthy controls. We measured plasma metabolites using gas chromatography-mass spectrometry (GC-MS/MS). Relationship between metabolomic alterations, pain, depression and QOL components were assessed using statistical/bioinformatics methods. Benjamini-Hochberg FDR correction was applied for multiple testing.

RESULTS

261 (46.8%) patients had depression compared to 5 (7.5%) among healthy controls [n = 67](p < 0.0001). Risk [OR (95% CI) of developing depression in the presence of pain was 1.9 (1.33-1.68); p = 0.0004. The depression scores correlated negatively with functional components and positively with symptom components of EORTC QLQ30. Significant negative correlation, though based on a small sample size, was observed between N-acetyl aspartate in the left hippocampus and choline in the left prefrontal cortex with emotional and cognitive functions. PLS-DA modelling revealed significant alteration in the plasma metabolomic profile among patients with CP who had depression. Six metabolites were significantly different between CP with depression and healthy controls, of which glycine contributed most significantly to the PLS-DA model (VIP score of 3.5).

CONCLUSIONS

A significant proportion of patients with CP develops depression that correlate with poor QOL functions. Pain, depression, and emotional components of QOL in patients with CP correlated with N-acetyl aspartate and choline in the left hippocampus and left prefrontal cortex of the brain.

Neurophysiological Effects of the Anterior Cingulate Cortex on the Exacerbation of Crohn’s Disease: A Combined fMRI-MRS Study

Background

Crohn’s disease (CD) is characterized by repetitive phases of remission and exacerbation, the quality of life of patients with CD is strongly influenced by disease activity, as patients in the active phase experience significantly worse symptoms. To investigate the underlying mechanism of how the course of CD is exacerbated based on the bi-directionality of the brain-gut axis (BGA), we conducted a multi-modality neuroimaging study that combined resting-state functional magnetic resonance imaging (rs-fMRI) with proton magnetic resonance spectroscopy (MRS) to detect abnormalities in the anterior cingulate cortex (ACC).

Materials and Methods

Clinical scales including Visual Analog Scale (VAS) and Hospital Anxiety and Depression Scale (HADS) were used to evaluate the degree of abdominal pain and mood state of participants. We made a comparison between CD patients in the active phase, the remission phase and healthy controls (HCs), not only employed the innovative wavelet-transform to analyze the amplitude of low frequency fluctuation (ALFF) but also compared the sensitivity of wavelet-transform and the traditional fast Fourier transform (FFT). Brain metabolites such as glutamate (Glu), myo-inositol (mIns) and gamma-aminobutyric acid (GABA) were also detected. Then correlation analysis was made to see whether changes in the ACC correlated with CD’s clinical symptoms.

Results

CD patients in the active phase showed higher VAS scores (p = 0.025), the scores of anxiety and depression were also higher (all p < 0.05). Wavelet-transform is slightly more sensitive in the current research. Patients in the active phase exhibited higher ALFF in the left ACC and the left superior frontal gyrus, medial (SFGmed). Patients in the active phase showed increased Glu levels in the ACC than patients in the remission phase or HCs (p = 0.039 and 0.034 respectively) and lower levels of mIns than HCs (p = 0.036). There was a positive correlation between mWavelet-ALFF values of the ACC and HADS-depression scores in CD patients (r = 0.462, p = 0.006). Besides, concentrations of Glu positively correlated with mWavelet-ALFF in the ACC in all participants (r = 0.367, p = 0.006).

Conclusion

Abnormal spontaneous activity and metabolic levels in the ACC were detected in CD patients in the active phase along with severer abdominal pain and worse mood state, these may contribute to the exacerbation of CD. Therefore, the ACC might be a potential neural alternative for managing the exacerbation of CD.

Upregulation of Striatal Metabotropic Glutamate Receptor Subtype 1 (mGluR1) in Rats with Excessive Glutamate Release Induced by N-Acetylcysteine

The aim of this study is to investigate the changes in expression of metabotropic glutamate (Glu) receptor subtype 1 (mGluR1), a key molecule involved in neuroexcitetoxicity, during excessive Glu release in the brain by PET imaging. An animal model of excessive Glu release in the brain was produced by intraperitoneally implanting an Alzet osmotic pump containing N-acetylcysteine (NAC), an activator of the cysteine/Glu antiporter, into the abdomen of rats. Basal Glu concentration in the brain was measured by microdialysis, which showed that basal Glu concentration in NAC-treated rats (0.31 µM) was higher than that in saline-treated rats (0.17 µM) at day 7 after the implantation of the osmotic pump. Similarly, PET studies with [¹¹C]ITDM, a useful radioligand for mGluR1 imaging exhibited that the striatal binding potential (BP_ND) of [¹¹C]ITDM for mGluR1 in PET assessments was increased in NAC-treated animals at day 7 after implantation (2.30) compared with before implantation (1.92). The dynamic changes in striatal BP_ND during the experimental period were highly correlated with basal Glu concentration. In conclusion, density of mGluR1 is rapidly upregulated by increases in basal Glu concentration, suggesting that mGluR1 might to be a potential biomarker of abnormal conditions in the brain.

Perineural Invasion and Associated Pain Transmission in Pancreatic Cancer

Pancreatic ductal adenocarcinoma (PDAC) is one of the cancers with the highest incidence of perineural invasion (PNI), which often indicates a poor prognosis. Aggressive tumor cells invade nerves, causing neurogenic inflammation; the tumor microenvironment also induces nerves to undergo a series of structural and functional reprogramming. In turn, neurons and the surrounding glial cells promote the development of pancreatic cancer through autocrine and/or paracrine signaling. In addition, hyperalgesia in PDAC patients implies alterations of pain transmission in the peripheral and central nervous systems. Currently, the studies on this topic are relatively limited. This review will elaborate on the mechanisms of tumor-neural interactions and its possible relationship with pain from several aspects that have been focused on in recent years.

Tapentadol and oxycodone reduce cingulate glutamate in healthy volunteers

Tapentadol and oxycodone are commonly used analgesics. Preclinical studies have shown that oxycodone modulates brain metabolites related to opioid pathways, whereas tapentadol also affects noradrenergic activity. However, knowledge about the function of the medications in the human brain is limited. The aim was to investigate effects of tapentadol and oxycodone on brain glutamate, the most important neurotransmitter in pain processing. Magnetic resonance spectroscopy was obtained in 21 healthy subjects from the anterior cingulate cortex, prefrontal cortex, and insula at baseline and after 14 days of treatment with either 50 mg tapentadol, 10 mg oxycodone (equipotent dose, both extended release) or placebo twice daily in a randomized double-blind cross-over study. Compared to baseline, decreased glutamate/creatine levels were identified in anterior cingulate cortex after tapentadol (1.26 ± 0.14 vs. 1.35 ± 0.18, P = .04) and oxycodone (1.26 ± 0.10 vs. 1.35 ± 0.12, P = .05) treatments, both with 7% reduction. This indicates that both analgesics modulate the glutamatergic system at the supraspinal level in humans.

Two-Week Cervical Vagus Nerve Stimulation in Chronic Pancreatitis Patients Induces Functional Connectivity Changes of Limbic Structures

OBJECTIVES

Noninvasive vagus nerve stimulation (nVNS) has not only shown antinociceptive effects, but also demonstrated anti-inflammatory and antidepressant effects. These effects could be beneficial in chronic pancreatitis (CP) patients suffering from chronic abdominal pain, even though the underlying central mechanisms remain unclear. The aim was to investigate the effect of cervical nVNS in patients with painful CP on brain functional connectivity and cerebral metabolites.

MATERIALS AND METHODS

In a randomized double-blind, sham-controlled crossover trial, we used resting-state functional magnetic resonance imaging to investigate functional connectivity changes of limbic structures (seed-based analysis) after two weeks cervical nVNS treatment (GammaCore) as compared with two weeks sham treatment. Similarly, magnetic resonance spectroscopy was performed in the anterior cingulate cortex (ACC) with assessment of glutamate/creatine (Glu/cre) and N-acetylaspartate/creatine (NAA/cre).

RESULTS

Sixteen CP patients (mean age 56.6 ± 9.4 years) completed the trial. nVNS induced reduced functional connectivity compared to sham treatment between 1) bilateral thalamus and bilateral superior frontal gyrus, 2) ACC and putamen, and 3) posterior cingulate cortex and right thalamus (all p < 0.05). No changes were observed in Glu/cre (p = 0.96) and NAA/cre (p = 0.43) levels between the nVNS and sham treatments.

CONCLUSION

In our population of CP patients, cervical nVNS compared with sham treatment induced reduced functional connectivity of limbic structures, as also observed in other patient groups. The findings are relevant, since we have previously demonstrated an effect on pain scores in CP patients for both nVNS and sham treatment. Our results elucidate the effects in the central nervous system following nVNS treatment of CP patients, pointing at potential beneficial effects in this patient group.