A Correlative Relationship Between Chronic Pain and Insulin Resistance in Zucker Fatty Rats: Role of Downregulation of Insulin Receptors

Impaired Carbohydrate Metabolism among Women with Chronic Low Back Pain and the Role of Dietary Carbohydrates: A Randomized Controlled Cross-Over Experiment

Background: Impaired glucose regulation is suggested to be related to chronic low back pain (CLBP), although it is not clear how they interact with each other. Thus, the primary aim of this study was to investigate differences in postprandial glycemic responses (PPGRs) (the first sign of impaired glucose metabolism) to high- (sucrose) and low-glycemic index (GI) (isomaltulose) beverages in normoglycemic women with CLBP and healthy controls (HCs) and explore whether any group that showed greater PPGRs to high-GI beverage intake would benefit when the high-GI beverage was replaced with a low-GI beverage. Secondly, this study aimed to explore the association between PPGR and pain in patients with CLBP. Methods: This study was registered at clinicaltrials.org (NCT04459104) before the start of the study. In this study, 53 CLBP patients and 53 HCs were recruited. After 11-12 h of fasting, each participant randomly received isomaltulose or sucrose. Blood glucose levels were measured during the fasting state and 15, 30, 45, 60, 90, and 120 min after the beverage intake, and each participant underwent experimental pain measures. Results: Compared to the HCs, the CLBP group showed significantly higher PPGRs to sucrose (p < 0.021). Additionally, the CLBP group showed a significantly higher decrease in PPGR (p = 0.045) when comparing PPGR to sucrose with PPGR to isomaltulose. Correlation analysis revealed a positive association between self-reported pain sensitivity and PPGR to sucrose, while there was no association found between any experimental pain measures and glycemic responses. Conclusions: Overall, these findings suggest that normoglycemic CLBP patients might have a higher risk of developing impaired glucose tolerance than the HCs and might benefit more when high-GI foods are replaced with low-GI ones.

The analgesic effects of insulin and its disorders in streptozotocin-induced short-term diabetes

Evidence suggests that insulin resistance plays an important role in developing diabetes complications. The association between insulin resistance and pain perception is less well understood. This study aimed to investigate the effects of peripheral insulin deficiency on pain pathways in the brain. Diabetes was induced in 60 male rats with streptozotocin (STZ). Insulin was injected into the left ventricle of the brain by intracerebroventricular (ICV) injection, then pain was induced by subcutaneous injection of 2.5% formalin. Samples were collected at 4 weeks after STZ injection. Dopamine (DA), serotonin, reactive oxygen species (ROS), and mitochondrial glutathione (mGSH) were measured by ELISA, and gene factors were assessed by RT-qPCR. In diabetic rats, the levels of DA, serotonin, and mGSH decreased in the nuclei of the thalamus, raphe magnus, and periaqueductal gray, and the levels of ROS increased. In addition, the levels of expression of the neuron-specific enolase and receptor for advanced glycation end genes increased, but the expression of glial fibrillary acidic protein expression was reduced. These results support the findings that insulin has an analgesic effect in non-diabetic rats, as demonstrated by the formalin test. ICV injection of insulin reduces pain sensation, but this was not observed in diabetic rats, which may be due to cell damage ameliorated by insulin.

Enhanced pain sensitivity in obese patients with obstructive sleep apnoea syndrome is partially reverted by treatment: An exploratory study

BACKGROUND

Obesity is frequently associated with obstructive sleep apnoea syndrome (OSA) and chronic pain. OSA as well as continuous positive airway pressure (CPAP) treatment may modulate the pain perception threshold (PT) in patients with obesity.

METHODS

In this prospective, longitudinal study, all patients admitted for obesity assessment were screened for OSA by nocturnal polygraphy (SOMNOcheck^® , IAH ≥10) and performed mechanical (Von Frey electronic device) and electrical (PainMatcher^® ) pain tests. Those with severe OSA were retested for PT 1 month after initiation of CPAP therapy. Newly diagnosed patients with severe OSA (hypopnea apnoea index >30) have been offered to start CPAP treatment.

RESULTS

Among 85 patients, there were 27 OSA patients, aged between 40 ± 13.2 years with a BMI of 42 ± 7.2 kg/m² . Severe OSA patients (N = 11) showed a lower PT than non-OSA patients (N = 58) during mechanical (177 ± 120 vs. 328 ± 136 g, p < 0.01) and electrical methods (7.4 ± 6.4 vs. 12.9 ± 6.7 stimulation duration steps; p = 0.03). In the severe OSA group (N = 7), an increased PT was observed 1 month after CPAP treatment during mechanical pain testing (298 ± 69 vs. 259 ± 68 g, p < 0.05), but not during electrical pain testing (11.5 ± 3.0 vs. 12.4 ± 3.8 stimulation duration steps, p = 0.50).

CONCLUSION

In patients with obesity, this exploratory study showed that the presence of an OSA is associated with a decreased PT, whereas implantation of a CPAP device tends to normalize pain perception.

Evaluation of Bodily Pain Associated with Polycystic Ovary Syndrome: A Review of Health-Related Quality of Life and Potential Risk Factors

Polycystic ovary syndrome (PCOS) is the most common reproductive disease affecting the hormone and metabolic status of women. Its associated symptoms are diverse among the patients, including hyperandrogenism, insulin resistance, anovulation, infertility, obesity, hirsutism, acne, and more. In addition, PCOS can potentially increase the risk of dysmenorrhea, endometriosis, endometrioma, and irritable bowel syndrome, which are highly related to pelvic pain and sexual difficulty. However, little known is whether PCOS exacerbates other chronic bodily pain or contributes to hyperalgesia. Health-related quality of Life (HRQoL) reflects the life satisfaction and quality derived by an individual from mental, physical, emotional, and social activities under specific conditions. In this study, we reviewed pain perception from HRQoL of PCOS patients (SF-36). The review data evidently indicated that pain perception is significantly more prevalent in patients with PCOS than in healthy controls, and obesity and infertile status could be the rationales associated with pain development. Nevertheless, underlying causes remain undetermined due to the limited information from SF-36. Furthermore, we reviewed pathophysiologic factors to pain development or exacerbation, such as the deregulation of inflammation levels, adipokines, and insulin resistance. Although current evidence of pain perception and pathophysiologic risk factors are solid in PCOS, patients' pain perception is often ignored in clinical settings. Clinicians should note the perception and treatment of pain in PCOS patients. The correlation or causality between pain and PCOS warrants further clinical examination and basic studies, thereby providing new insights into this topic in the context of clinical diagnosis and health care.

A network pharmacology approach to predict potential targets and mechanisms of "Ramulus Cinnamomi (cassiae) - Paeonia lactiflora" herb pair in the treatment of chronic pain with comorbid anxiety and depression

BACKGROUND

Traditional Chinese medicine (TCM) prescriptions have multiple bioactive properties. "Gui Zhi-Shao Yao" herb pair is widely used to treat chronic pain (CP), as well as anxiety and depression. However, its related targets and underlying mechanisms have not been deciphered.

METHODS

In this study, the network pharmacology method was used to explore the bioactive components and targets of "Gui Zhi-Shao Yao" herb pair and further elucidate its potential biological mechanisms of action in the treatment of CP with comorbid anxiety disorder (AD) and mental depression (MD).

RESULTS

Following a series of analyses, we identified 15 active compounds, hitting 130 potential targets. After the intersections the targets of this herb pair and CP, AD and MD - sorted by the value of degree - nine targets were identified as the vital ones: Akt1, IL6, TNF, PTGS2, JUN, CASP3, MAPK8, PPARγ and NOS3. Gene ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis results demonstrated 11 pathways, such as AGE-RAGE signalling pathway, IL-17 signalling pathway, TNF signalling pathway, which primarily participate in the pathological processes.

CONCLUSIONS

This study preliminarily predicted and verified the pharmacological and molecular mechanisms of "Gui Zhi-Shao Yao" herb pair for treating CP with comorbid AD and MD from a holistic perspective. In vivo and in vitro experiments will be required to further investigate the mechanisms.KEY MESSAGEA network pharmacology approach was applied to identify key targets and molecular mechanisms.Nine targets were regarded as the vital targets for chronic pain with comorbid anxiety and depression.Predicted 11 pathways were the potential therapy targets and pharmacological mechanism of "Gui Zhi-Shao Yao" herb pair.

Is metformin a possible treatment for diabetic neuropathy?

Metformin is a hypoglycemic drug widely used in the treatment of type 2 diabetes. It has been proven to have analgesic and neuroprotective effects. Metformin can reverse pain in rodents, such as diabetic neuropathic pain, neuropathic pain caused by chemotherapy drugs, inflammatory pain and pain caused by surgical incision. In clinical use, however, metformin is associated with reduced plasma vitamin B12 levels, which can further neuropathy. In rodent diabetes models, metformin plays a neuroprotective and analgesic role by activating adenosine monophosphate-activated protein kinase, clearing methylgloxal, reducing insulin resistance, and neuroinflammation. This paper also summarized the neurological adverse reactions of metformin in diabetic patients. In addition, whether metformin has sexual dimorphism needs further study.

Estrogen modulation of the pronociceptive effects of serotonin on female rat trigeminal sensory neurons is timing dependent and dosage dependent and requires estrogen receptor alpha

ABSTRACT

The role of the major estrogen estradiol (E2) on orofacial pain conditions remains controversial with studies reporting both a pronociceptive and antinociceptive role of E2. E2 modulation of peripheral serotonergic activity may be one mechanism underlying the female prevalence of orofacial pain disorders. We recently reported that female rats in proestrus and estrus exhibit greater serotonin (5HT)-evoked orofacial nocifensive behaviors compared with diestrus and male rats. Further coexpression of 5HT 2A receptor mRNA in nociceptive trigeminal sensory neurons that express transient receptor potential vanilloid 1 ion channels contributes to pain sensitization. E2 may exacerbate orofacial pain through 5HT-sensitive trigeminal nociceptors, but whether low or high E2 contributes to orofacial pain and by what mechanism remains unclear. We hypothesized that steady-state exposure to a proestrus level of E2 exacerbates 5HT-evoked orofacial nocifensive behaviors in female rats, explored the transcriptome of E2-treated female rats, and determined which E2 receptor contributes to sensitization of female trigeminal sensory neurons. We report that a diestrus level of E2 is protective against 5HT-evoked orofacial pain behaviors, which increase with increasing E2 concentrations, and that E2 differentially alters several pain genes in the trigeminal ganglia. Furthermore, E2 receptors coexpressed with 5HT 2A and transient receptor potential vanilloid 1 and enhanced capsaicin-evoked signaling in the trigeminal ganglia through estrogen receptor α. Overall, our data indicate that low, but not high, physiological levels of E2 protect against orofacial pain, and we provide evidence that estrogen receptor α receptor activation, but not others, contributes to sensitization of nociceptive signaling in trigeminal sensory neurons.

Peripheral Neuropathy Phenotyping in Rat Models of Type 2 Diabetes Mellitus: Evaluating Uptake of the Neurodiab Guidelines and Identifying Future Directions

Diabetic peripheral neuropathy (DPN) affects over half of type 2 diabetes mellitus (T2DM) patients, with an urgent need for effective pharmacotherapies. While many rat and mouse models of T2DM exist, the phenotyping of DPN has been challenging with inconsistencies across laboratories. To better characterize DPN in rodents, a consensus guideline was published in 2014 to accelerate the translation of preclinical findings. Here we review DPN phenotyping in rat models of T2DM against the 'Neurodiab' criteria to identify uptake of the guidelines and discuss how DPN phenotypes differ between models and according to diabetes duration and sex. A search of PubMed, Scopus and Web of Science databases identified 125 studies, categorised as either diet and/or chemically induced models or transgenic/spontaneous models of T2DM. The use of diet and chemically induced T2DM models has exceeded that of transgenic models in recent years, and the introduction of the Neurodiab guidelines has not appreciably increased the number of studies assessing all key DPN endpoints. Combined high-fat diet and low dose streptozotocin rat models are the most frequently used and well characterised. Overall, we recommend adherence to Neurodiab guidelines for creating better animal models of DPN to accelerate translation and drug development.

Transcutaneous Auricular Vagus Nerve Stimulation at 20 Hz Improves Depression-Like Behaviors and Down-Regulates the Hyperactivity of HPA Axis in Chronic Unpredictable Mild Stress Model Rats

Transcutaneous auricular vagus nerve stimulation (taVNS) has gained growing interest as a non-invasive and non-pharmacologic treatment option in various neurological and psychiatric disorders. Animal experiments and clinical trials confirm that taVNS at the auricular concha region has beneficial effects on depression. However, stimulation frequencies are selected empirically, and there is no evidence showing that any frequency is superior to the others. This study explores antidepressant-like effects of three frequencies of taVNS on rats subjected to chronic unpredictable mild stress (CUMS). Sprague-Dawley rats were randomly divided into five groups, i.e., the control, CUMS, 5 Hz-taVNS, 20 Hz-taVNS, and 100 Hz-taVNS groups. The three different frequencies were administered during the 30-min taVNS procedure once a day for 28 consecutive days. Rats exposed to CUMS showed signs of depression-like behaviors, including reduction in sucrose preference and increased immobility time in forced swimming and open field tests as well as significant dysfunction of the hypothalamic-pituitary-adrenal (HPA) axis as detected by plasma corticosterone and adrenocorticotropic hormone concentration. The 28 days’ taVNS sessions with three frequencies elicited quite different consequences. Although 20 Hz taVNS significantly reversed the depression-like behaviors and downregulated the hyperactivity of the HPA axis, neither 5 nor 100 Hz showed any antidepressant-like effect on CUMS-induced rat behavior. Based on these results, we propose that, out of the three frequencies for taVNS intervention on depression, 20 Hz may be the optimized frequency to have a better modulation effect on HPA axis function by activating the auricular vagus nerve.

Insulin Resistance in Osteoarthritis: Similar Mechanisms to Type 2 Diabetes Mellitus

Osteoarthritis (OA) and type 2 diabetes mellitus (T2D) are two of the most widespread chronic diseases. OA and T2D have common epidemiologic traits, are considered heterogenic multifactorial pathologies that develop through the interaction of genetic and environmental factors, and have common risk factors. In addition, both of these diseases often manifest in a single patient. Despite differences in clinical manifestations, both diseases are characterized by disturbances in cellular metabolism and by an insulin-resistant state primarily associated with the production and utilization of energy. However, currently, the primary cause of OA development and progression is not clear. In addition, although OA is manifested as a joint disease, evidence has accumulated that it affects the whole body. As pathological insulin resistance is viewed as a driving force of T2D development, now, we present evidence that the molecular and cellular metabolic disturbances associated with OA are linked to an insulin-resistant state similar to T2D. Moreover, the alterations in cellular energy requirements associated with insulin resistance could affect many metabolic changes in the body that eventually result in pathology and could serve as a unified mechanism that also functions in many metabolic diseases. However, these issues have not been comprehensively described. Therefore, here, we discuss the basic molecular mechanisms underlying the pathological processes associated with the development of insulin resistance; the major inducers, regulators, and metabolic consequences of insulin resistance; and instruments for controlling insulin resistance as a new approach to therapy.

Prevalence of the Effects of Anxiety and Depression on People with Type 2 Diabetes Mellitus: An Analysis of Health Policy Studies in Improving the Quality of Life of Poor Families in the Urban Areas of West Lombok, Indonesia

BACKGROUND

To explore the tendency of the effects of anxiety and depression that occur in type 2 diabetes patients, especially poor patients who live in the urban areas with poor economic conditions, who do not have health access from the government, and live away from the hospitals.

METHODS

It is a cross-sectional study which aimed to determine the number of patients who experienced anxiety and depression problems due to the declining health conditions caused by diabetes. A sample size of 98 diabetics experiencing anxiety and depression when the treatment was carried out was included. The study design included a qualitative study with in-depth interviews with respondents who were at risk of diabetes, as well as to determine the level of anxiety and depression that occurred when medical care was provided and the feelings experienced by the respondents after the completion of treatment.

RESULTS

Diabetic patients are generally unaware that their illness is a chronic disease that takes a long time to treat. When the patients are sick, most of them do not immediately go to the hospital or a specialist to get their health examination and treatment, because the hospital is far from the patients' residence. Furthermore, some patients still use traditional medicine and non-medical treatment, so when the patients with critical conditions are taken to the hospital, they already have chronic diabetes.

CONCLUSION

The lack of access to health for chronic patients with poor economic conditions who live far from the hospitals and the scarcity of medical staff to carry out treatment of chronic diseases such as diabetes for poor patients in urban areas certainly have an impact on increasing the number of patients with chronic diseases. Therefore, the government is expected to be able to provide easy health policies to remote rural communities in order to achieve optimal community welfare and health.

Diabetic Peripheral Neuropathy Is Associated With Higher Systolic Blood Pressure in Adults With Type 2 Diabetes With and Without Hypertension in the Chinese Han Population

OBJECTIVES

Our aim in this study was to investigate the association between diabetic peripheral neuropathy (DPN) and above-normal blood pressure in nonhypertensive adult patients with type 2 diabetes mellitus (T2DM). We also compared achievement of clinical targets for DPN and non-DPN with T2DM.

METHODS

A retrospective survey was administered to 3,810 patients with T2DM. Cases were grouped according to the Toronto Clinical Scoring System as follows: non-DPN, mild DPN, moderate DPN and severe DPN. A total of 1,835 patients (hypertensive, 1,247; nonhypertensive, 588) also underwent nerve conduction velocity testing, and then was divided into quartile groups.

RESULTS

Irrespective of hypertension, systolic blood pressure (SBP) and glycated hemoglobin levels in the DPN group were higher than those in the non-DPN group (p<0.001). In hypertensive patients, blood pressure goal achievement was lower in the DPN group compared with the non-DPN group (31.1% vs 40.5%, p<0.05). Compared with the nerve conduction velocity Q1 (<P25%) group, optimal SBP of the Q2 (P25% to P50%), Q3 (P50% to P75%) and Q4 (>P75%) groups decreased by 62.2%, 68.2% and 78.0%, respectively. In the nonhypertensive patients, detection of optimal SBP was lower in the DPN group than in the non-DPN group (p<0.05). After adjusting for age, sex and diabetes duration (model 2), a 3-point higher DPN score on the Toronto Clinical Scoring System was associated with an SBP level of 4.2 mmHg higher (95% confidence interval, 0.01 to 0.17; p<0.01) in nonhypertensive patients with diabetes.

CONCLUSIONS

DPN is associated with difficulty in hypertension management in T2DM. It is also associated with elevated systolic blood hypertension, even in nonhypertensive patients with diabetes. Elevated SBP in nonhypertensive T2DM may be also worthy of further attention.

Enhancement of spinal dorsal horn neuron NMDA receptor phosphorylation as the mechanism of remifentanil induced hyperalgesia: Roles of PKC and CaMKII

Background

Modulation of N-methyl-D-aspartate receptor subunits NR1 and NR2 through phosphorylation mediates opioid-induced hyperalgesia, and activations of protein kinase C and extracellular signal-regulated kinase 1/2 potentiate while activation of calcium/calmodulin-dependent protein kinase II inhibits opioid-induced hyperalgesia. However, the mechanism of opioid-induced hyperalgesia development and in particular the potential interplay between N-methyl-D-aspartate receptors and protein kinase C or calcium/calmodulin-dependent protein kinase II or extracellular signal-regulated kinase 1/2 in the development of remifentanil-induced hyperalgesia is unclear.

Methods

Remifentanil (1 µg ċ kg−1 ċ min−1) was given intravenously over 60 min in rats, followed by the infusion of either vehicle solution or the respective inhibitors of protein kinase C (chelerythrine), extracellular signal-regulated kinase II (KN93), or extracellular signal-regulated kinase 1/2 (PD98059). Thereafter, the pain behaviors were evaluated by the paw withdrawal mechanical threshold and paw withdrawal thermal latency. In in vitro studies, fetal spinal cord dorsal horn neurons were primary cultured in the presence of 4 nM remifentanil for 60 min, and then the remifentanil was washed out and replaced immediately by culturing in the absence or presence of chelerythrine, KN93 or PD98059, respectively for up to 8 h. The expressions of N-methyl-D-aspartate receptors subunits and their phosphorylation (NR1, NR2B, p-NR1, p-NR2B) were analyzed by Western blotting after the completion of treatments. Functional changes of N-methyl-D-aspartate receptors were evaluated by electrophysiologic recordings of N-methyl-D-aspartate currents.

Results

Remifentanil induced significant thermal and mechanical hyperalgesia, which were significantly attenuated by Chelerythrine or KN93 but not PD98059. The expressions of NR1, NR2B, p-NR1, and p-NR2B were increased significantly and progressively over time after remifentanil administration, and these increases were all significantly attenuated by either chelerythrine or KN93 but not PD98059. Intriguingly, N-methyl-D-aspartate receptor functional enhancement induced by remifentanil was attenuated by Chelerythrine, KN93, and PD98059.

Conclusions

It is concluded that the enhancements in function and quantity of N-methyl-D-aspartate receptor via phosphorylation of its subunits through protein kinase C and calcium/calmodulin-dependent protein kinase II activation may represent the major mechanism whereby remifentanil induced hyperalgesia.

Auricular vagus nerve stimulation enhances central serotonergic function and inhibits diabetic neuropathy development in Zucker fatty rats

Painful neuropathy is a frequent comorbidity in diabetes. Zucker diabetic fatty (fa/fa) rats develop type 2 diabetes spontaneously with aging and show nociceptive hypersensitivity at the age of 13 weeks. In preclinical and clinical studies, the treatment of diabetic neuropathy is challenging, but complementary medicine such as transcutaneous auricular vagus nerve stimulation (taVNS) appears beneficial to the relief of neuropathic pain. However, the mechanism behind the effectiveness of taVNS remains unclear. In this study, we show that daily 30-min taVNS (2/15 Hz, 2 mA) for consecutive 27 days effectively inhibited the development of nociceptive hypersensitivity in Zucker diabetic fatty rats as detected by thermal hyperalgesia and mechanical allodynia in hindpaw. We also demonstrated that this beneficial effect in nociceptive behavior is related to an elevated serotonin (5-HT) plasma concentration and an upregulated expression of 5-HT receptor type 1A (5-HT1AR) in hypothalamus. We conclude that daily 30-min taVNS sessions lessen diabetic neuropathy development by enhancing serotonergic function in genetically diabetes prone individuals.

Perspective

This article presents taVNS as a new approach to inhibit the development of diabetic neuropathy in genetically prone individuals. This approach could potentially help clinicians who seek to avoid the complication of neuropathic pain in diabetic patient or to relieve the pain if there was one.

Acupuncture for chronic pain: an update and critical overview

PURPOSE OF REVIEW

Acupuncture is now recommended for several chronic pain conditions. Despite supportive evidence of its effectiveness, this ancient approach is often misunderstood, and may still be underused in mainstream practice. A critical review on its effectiveness and practice integration, and mechanisms of action is essential to the medical community that is continuing to seek nonopioid therapies for chronic pain.

RECENT FINDINGS

Mounting evidence supports the effectiveness of acupuncture to treat chronic low back, neck, shoulder, and knee pain, as well as headaches. Additional data are emerging that support the use of acupuncture as an adjunct or alternative to opioids, and in perioperative settings. Findings related to its mechanisms of action include transient receptor potential cation channel vanilloid 1 activation in the periphery, microglial suppression in the cerebral cortex and spinal cord, and regulation of cytokines and other key inflammatory factors in the spinal cord. Incremental integration of acupuncture into pain medicine practices and training programmes continues to grow.

SUMMARY

Acupuncture is effective, safe, and cost-effective for treating several chronic pain conditions when performed by well-trained healthcare professionals. Further studies on its use as an adjunct or alternative to opioids, and in perioperative settings are needed.