Pain Comorbidities with Attention Deficit: A Narrative Review of Clinical and Preclinical Research.

A negative correlation exists between attention and pain. The cognitive impairments linked to pain can significantly impede a patient's healing process and everyday tasks, particularly for individuals experiencing persistent pain. Furthermore, it has been demonstrated that diversion can effectively decrease pain levels in individuals. The focus of this review is to analyze clinical trials and fundamental investigations regarding alterations in focus and persistent discomfort. Moreover, we investigated the common neuroanatomy associated with attention and pain. Furthermore, we examined the impact of various neuromodulators on the transmission of pain and processes related to attention, while also considering the potential neural mechanisms that contribute to the co-occurrence of pain and attention deficits. Further investigation in this field will enhance our comprehension of patient symptoms and the underlying pathophysiology, ultimately resulting in more objective approaches to treatment.

Painful Diabetic Neuropathy Is Associated with Compromised Microglial IGF-1 Signaling Which Can Be Rescued by Green Tea Polyphenol EGCG in Mice.

Background: Painful diabetic neuropathy (PDN) is a frequent and troublesome complication of diabetes, with little effective treatment. PDN is characterized by specific spinal microglia-mediated neuroinflammation. Insulin-like growth factor 1 (IGF-1) primarily derives from microglia in the brain and serves a vital role in averting the microglial transition into the proinflammatory M1 phenotype. Given that epigallocatechin-3-gallate (EGCG) is a potent anti-inflammatory agent that can regulate IGF-1 signaling, we speculated that EGCG administration might reduce spinal microglia-related neuroinflammation and combat the development of PDN through IGF-1/IGF1R signaling. Methods: Type 1 diabetes mellitus (T1DM) was established by a single intraperitoneal (i.p.) injection of streptozotocin (STZ) in mice. The protein expression level of IGF-1, its receptor IGF1R, interleukin 1ß (IL-1ß), tumor necrosis factor-α (TNF-α), and inducible nitric oxide synthase (iNOS) was determined by Western blot or immunofluorescence. Results: The spinal IGF-1 expression markedly decreased along with the presence of pain-like behaviors, the spinal genesis of neuroinflammation (increased IL-1ß, TNF-α, and Iba-1+ microglia), and the intensified M1 microglia polarization (increased iNOS+Iba-1+ microglia) in diabetic mice. IGF-1 could colocalize with neurons, astrocytes, and microglia, but only microglial IGF-1 was repressed in T1DM mice. Furthermore, we found that i.t. administration of mouse recombinant IGF-1 (rIGF-1) as well as i.t. or i.p. treatment with EGCG alleviated the diabetes-induced pain-like behaviors, reduced neuroinflammation (suppressed IL-1ß, TNF-α, and Iba-1+ microglia), prevented the M1 microglia polarization (less iNOS+Iba-1+ microglia), and restored the microglial IGF-1 expression. Conclusions: Our data highlighted the importance of maintaining spinal IGF-1 signaling in treating microglia-related neuroinflammation in PDN. This study also provides novel insights into the neuroprotective mechanisms of EGCG against neuropathic pain and neuroinflammation through IGF-1 signaling, indicating that this agent may be a promising treatment for PDN in the clinical setting.

Diabetic neuropathic pain induced by streptozotocin alters the expression profile of non-coding RNAs in the spinal cord of mice as determined by sequencing analysis.

Diabetic neuropathic pain (DNP) is one of the most serious complications of diabetes. Patients with DNP always exhibit spontaneous and stimulus-evoked pain. However, the pathogenesis of DNP remains to be fully elucidated. Non-coding RNAs (ncRNAs) serve important roles in several cellular processes and dysregulated expression may result in the development of several diseases, including DNP. Although ncRNAs have been suggested to be involved in the pathogenesis of DNP, their precise roles remain to be determined. In the present study, sequencing analysis was used to investigate the expression patterns of coding genes, microRNAs (miRNAs), long ncRNAs (lncRNAs) and circular RNAs (circRNAs) in the spinal cord of mice with streptozotocin (STZ)-induced DNP. A total of 30 mRNAs, 148 miRNAs, 9 lncRNAs and 135 circRNAs exhibited significantly dysregulated expression 42 days after STZ injection. Functional enrichment analysis indicated that protein digestion and absorption pathways were the most significantly affected pathways of the differentially expressed (DE) mRNAs. The Rap1 signaling pathway, human T-lymphotropic virus-I infection and the MAPK signaling pathway were the three most significant pathways of the DE miRNAs. A total of 2,118 distinct circRNAs were identified and the length of the majority of the circRNAs was <1,000 nucleotides (nt) (1,552 circRNAs were >1,000 nt) with a median length of 620 nt. In the present study, the expression characteristics of coding genes, miRNAs, lncRNAs and circRNAs in DNP mice were determined; it paves the road for further studies on the mechanisms associated with DNP and potentially facilitates the discovery of novel ncRNAs for therapeutic targeting in the management of DNP.

Abnormal Insulin-like Growth Factor 1 Signaling Regulates Neuropathic Pain by Mediating the Mechanistic Target of Rapamycin-Related Autophagy and Neuroinflammation in Mice.

Neuropathic pain is a chronic condition with little specific treatment. Insulin-like growth factor 1 (IGF1), interacting with its receptor, IGF1R, serves a vital role in neuronal and brain functions such as autophagy and neuroinflammation. Yet, the function of spinal IGF1/IGF1R in neuropathic pain is unclear. Here, we examined whether and how spinal IGF1 signaling affects pain-like behaviors in mice with chronic constriction injury (CCI) of the sciatic nerve. To corroborate the role of IGF1, we injected intrathecally IGF1R inhibitor (nvp-aew541) or anti-IGF1 neutralizing antibodies. We found that IGF1 (derived from astrocytes) in the lumbar cord increased along with the neuropathic pain induced by CCI. IGF1R was predominantly expressed on neurons. IGF1R antagonism or IGF1 neutralization attenuated pain behaviors induced by CCI, relieved mTOR-related suppression of autophagy, and mitigated neuroinflammation in the spinal cord. These findings reveal that the abnormal IGF1/IGF1R signaling contributes to neuropathic pain by exacerbating autophagy dysfunction and neuroinflammation.

Chemotherapy-induced peripheral neuropathy is promoted by enhanced spinal insulin-like growth factor-1 levels via astrocyte-dependent mechanisms.

BACKGROUND: Chemotherapy-induced peripheral neuropathy (CIPN) is a common and intractable complication in chemotherapy-receiving patients. Insulin-like growth factor-1 (IGF-1) is a popular neurotrophin with various functions, such as maintaining neuronal survival and synaptic functioning in the central nervous system. Therefore, we hypothesized that the IGF-1 signaling pathway could be a candidate target for treating CIPN. METHODS: We established the CIPN model by injecting mice intraperitoneally with oxaliplatin and assessed IGF-1 protein expression, its receptor IGF1R, phospho-IGF1R (p-IGF1R), interleukin-17A (IL-17A), tumor necrosis factor-α (TNF-α), and calcitonin gene-related peptide (CGRP) in the lumbar spinal cord with Western blot and immunofluorescence. To examine the effect of IGF-1 signaling on CIPN, we injected mice intrathecally or intraperitoneally with mouse recombinant IGF-1 (rIGF-1). RESULTS: IGF-1 protein expression decreased significantly in the spinal cord on D3 and D10 (the 3rd and 10th days after beginning oxaliplatin chemotherapy) and was co-localized with astrocytes primarily in the lumbar spinal cord, whereas IGF1R was predominantly expressed on neurons. Both intrathecally- and intraperitoneally-administered rIGF-1 relieved the chemotherapy-induced pain-like behavior and reduced IL-17A, TNF-α, and CGRP protein expressions in the spinal cord. CONCLUSION: Our results indicate a vital role for IGF-1 signaling in CIPN. Targeting IGF-1 signaling could be a potent therapeutic strategy for treating CIPN in clinical settings.

Ultrasound-Guided Transmuscular Quadratus Lumborum Block Reduces Postoperative Pain Intensity in Patients Undergoing Total Hip Arthroplasty: A Randomized, Double-Blind, Placebo-Controlled Trial.

Methods: Eighty-eight patients undergoing THA were randomized to receive 0.33% ropivacaine (Group QLB, n = 44) or saline (Group Con, n = 44) for QL3 block. Spinal anesthesia was then performed. Pain intensity was assessed using the visual analog scale (0: no pain to 10: worst possible pain). The primary outcome was pain scores recorded at rest at 3, 6, 12, 24, 36, and 48 h and on standing and walking at 24, 36, and 48 h postoperatively. Secondary outcomes were analgesic consumption, side effects, the 10-meter walking speed on day 6, and patient satisfaction after surgery. Results: Postoperative pain intensity was significantly lower in Group QLB compared to Group Con at rest after 3, 6, 12, 24, 36, and 48 h (p < 0.001) and during mobilization after 24, 36, and 48 h (p < 0.001). Morphine use was significantly lower in Group QLB compared to Group Con during 0-24 h (16.0 ± 7.1 vs. 34.1 ± 7.1 mg, p < 0.001) and during 24-48 h (13.0 ± 4.0 vs. 17.4 ± 4.6 mg, p < 0.001) postoperatively. The 10-meter walking speed was higher in Group QLB compared to Group Con, both at comfortable (0.79 ± 0.13 vs. 0.70 ± 0.14 m/s, p=0.012) and at maximum speeds (1.18 ± 0.26 vs. 1.06 ± 0.22 m/s, p < 0.001). Incidences of nausea (7.3% vs. 31%, p=0.006), vomiting (7.3% vs. 26.2%, p = 0.022), and urinary retention (9.8% vs. 28.6%, p=0.030) were lower in Group QLB than in Group Con. Conclusions: Ultrasound-guided QL3 block is an effective pain management technique after THA.

Contributions of mTOR Activation-Mediated Upregulation of Synapsin II and Neurite Outgrowth to Hyperalgesia in STZ-Induced Diabetic Rats.

Painful diabetic neuropathy (PDN) is among the common complications in diabetes mellitus (DM), with its underlying mechanisms largely unknown. Synapsin II is primarily expressed in the spinal dorsal horn, and its upregulation mediates a superfluous release of glutamate and a deficiency of GABAergic interneuron synaptic transmission, which is directly implicated in the facilitation of pain signals in the hyperalgesic nociceptive response. Recently, synapsin II has been revealed to be associated with the modulation of neurite outgrowth, whereas the process of this neuronal structural neuroplasticity following neuronal hyperexcitability still remains unclear. In this study, we found that under conditions of elevated glucose, TNF-α induced the activation of mTOR, mediating the upregulation of synapsin II and neurite outgrowth in dorsal horn neurons. In vivo, we demonstrated that mTOR and synapsin II were upregulated and coexpressed in the spinal dorsal horn neurons in rats with streptozotocin (STZ)-induced diabetes. Furthermore, the intrathecal administration of the mTOR inhibitor rapamycin or synapsin II shRNA significantly diminished the expression of synapsin II, effectively mitigating hyperalgesia in PDN rats. We are the first to discover that in STZ-induced diabetic rats the activation of mTOR mediates the upregulation of synapsin II and neurite outgrowth, both contributing to hyperalgesia. These findings may benefit the clinical therapy of PDN by provision of a novel target.

Intrathecal administration of rapamycin inhibits the phosphorylation of DRG Nav1.8 and attenuates STZ-induced painful diabetic neuropathy in rats.

The mammalian target of rapamycin (mTOR) is a key regulator of mRNA translation and protein synthesis, and it is specifically inhibited by rapamycin. In chronic pain conditions, mTOR-mediated local protein synthesis is crucial for neuronal hyperexcitability and synaptic plasticity. The tetrodotoxin-resistant (TTX-R) sodium channel Nav1.8 plays a major role in action potential initiation and propagation and cellular excitability in DRG (dorsal root ganglion) neurons. In this study, we investigated if mTOR modulates the phosphorylation of Nav1.8 that is associated with neuronal hyperexcitability and behavioral hypersensitivity in STZ-induced diabetic rats. Painful diabetic neuropathy (PDN) was induced in Sprague-Dawley rats by intraperitoneal injection with streptozotocin (STZ) at 60mg/kg. After the onset of PDN, the rats received daily intrathecal administrations of rapamycin (1µg, 3µg, or 10µg/day) for 7 days; other diabetic rats received the same volumes of dimethyl sulfoxide (DMSO). Herein, we demonstrate a marked increase in protein expression of total mTOR and phospho-mTOR (p-mTOR) together with the up-regulation of phosphor-Nav1.8 (p-Nav1.8) prior to the mechanical withdrawal threshold reaching a significant reduction in dorsal root ganglions (DRGs). Furthermore, the intrathecal administration of rapamycin, inhibiting the activity of mTOR, suppressed the phosphorylation of DRG Nav1.8, reduced the TTX-R current density, heightened the voltage threshold for activation and lowered the voltage threshold for inactivation and relieved mechanical hypersensitivity in diabetic rats. An intrathecal injection (i.t.) of rapamycin inhibited the phosphorylation and enhanced the functional availability of DRG Nav1.8 attenuated STZ-induced hyperalgesia. These results suggest that rapamycin is a potential therapeutic intervention for clinical PDN.

Curcumin ameliorated diabetic neuropathy partially by inhibition of NADPH oxidase mediating oxidative stress in the spinal cord.

Nicotinamide adenine dinucleotide phosphate (NADPH) oxidases are the main enzymes that produce oxidative stress, which plays an important role in painful diabetic neuropathy. Curcumin has been reported to exert an antinociceptive effect in a rat model of diabetic neuropathy by suppressing oxidative stress in the spinal cord. However, it remains unknown whether the mechanism by which curcumin ameliorates diabetic neuropathy can be attributed to spinal NADPH oxidases. This study was designed to determine the effect of curcumin on diabetic neuropathy and to investigate its precise mechanism in relation to NADPH oxidase-mediating oxidative stress in the spinal cord. Diabetic neuropathy was induced in Sprague-Dawley rats by intraperitoneal injection with 1% streptozotocin (STZ; 60 mg/kg). After the onset of diabetic neuropathy, a subset of the diabetic rats received daily intragastric administrations of curcumin (200mg/kg) or intraperitoneal injections of apocynin (2.5mg/kg) for 14 consecutive days, whereas other diabetic rats received equivalent volumes of normal saline (NS). STZ resulted in diabetic neuropathy with hyperglycemia and a lower paw withdrawal threshold (PWT), accompanied by elevations in the expression of the NADPH oxidase subunits p47(phox) and gp91(phox) and in the levels of hydrogen peroxide (H2O2) and malondialdehyde (MDA) and a reduction in superoxide dismutase (SOD) activity (P<0.05) in the spinal cord. Both curcumin and apocynin ameliorated diabetic neuropathy. In conclusion, curcumin attenuated neuropathic pain in diabetic rats, at least partly by inhibiting NADPH oxidase-mediating oxidative stress in the spinal cord.