Neuroinflammation and adult hippocampal neurogenesis in neuropathic pain and alkyl glycerol ethers treatment in aged mice

Identification and validation of aging-related genes in neuropathic pain using bioinformatics

Background

Neuropathic pain (NP) is a debilitating and refractory chronic pain with a higher prevalence especially in elderly patients. Cell senescence considered a key pathogenic factor in NP. The objective of this research is to discover genes associated with aging in peripheral blood of individuals with NP using bioinformatics techniques.

Methods

Two cohorts (GSE124272 and GSE150408) containing peripheral blood samples of NP were downloaded from the GEO database. By merging the two cohorts, differentially expressed aging-related genes (DE-ARGs) were obtained by intersection with aging-related genes. The potential biological mechanisms of DE-ARGs were further analyzed through GO and KEGG. Three machine learning methods, namely, LASSO, SVM-RFE, and Random Forest, were utilized to identify diagnostic biomarkers. A Nomogram model was developed to assess their diagnostic accuracy. The validation of biomarker expression and diagnostic effectiveness was conducted in three distinct pain cohorts. The CIBERSORT algorithm was employed to evaluate the immune cell composition in the peripheral blood of patients with NP and investigate its association with the expression of diagnostic biomarkers.

Results

This study identified a total of 24 DE-ARGs, mainly enriched in "Chemokine signaling pathway," "Inflammatory mediator regulation of TRP channels," "HIF-1 signaling pathway" and "FOXO signaling pathway". Three machine learning algorithms identified a total of four diagnostic biomarkers (CEBPA, CEACAM1, BTG3 and IL-1R1) with good diagnostic performance and the similar expression difference trend in different types of pain cohorts. The expression levels of CEACAM1 and IL-1R1 exhibit a positive correlation with the percentage of neutrophils.

Conclusion

Using machine learning techniques, our research identified four diagnostic biomarkers related to aging in peripheral blood, providing innovative approaches for the diagnosis and treatment of NP.

Chronic Pain-Related Cognitive Deficits: Preclinical Insights into Molecular, Cellular, and Circuit Mechanisms

Cognitive impairment is a common comorbidity of chronic pain, significantly disrupting patients' quality of life. Despite this comorbidity being clinically recognized, the underlying neuropathological mechanisms remain unclear. Recent preclinical studies have focused on the fundamental mechanisms underlying the coexistence of chronic pain and cognitive decline. Pain chronification is accompanied by structural and functional changes in the neural substrate of cognition. Based on the developments in electrophysiology and optogenetics/chemogenetics, we summarized the relevant neural circuits involved in pain-induced cognitive impairment, as well as changes in connectivity and function in brain regions. We then present the cellular and molecular alternations related to pain-induced cognitive impairment in preclinical studies, mainly including modifications in neuronal excitability and structure, synaptic plasticity, glial cells and cytokines, neurotransmitters and other neurochemicals, and the gut-brain axis. Finally, we also discussed the potential treatment strategies and future research directions.

Marine Natural Products from the Russian Pacific as Sources of Drugs for Neurodegenerative Diseases

Neurodegenerative diseases are growing to become one of humanity's biggest health problems, given the number of individuals affected by them. They cause enough mortalities and severe economic impact to rival cancers and infections. With the current diversity of pathophysiological mechanisms involved in neurodegenerative diseases, on the one hand, and scarcity of efficient prevention and treatment strategies, on the other, all possible sources for novel drug discovery must be employed. Marine pharmacology represents a relatively uncharted territory to seek promising compounds, despite the enormous chemodiversity it offers. The current work discusses one vast marine region-the Northwestern or Russian Pacific-as the treasure chest for marine-based drug discovery targeting neurodegenerative diseases. We overview the natural products of neurological properties already discovered from its waters and survey the existing molecular and cellular targets for pharmacological modulation of the disease. We further provide a general assessment of the drug discovery potential of the Russian Pacific in case of its systematic development to tackle neurodegenerative diseases.

1-O-Alkylglycerol Ethers from the Marine Sponge Guitarra abbotti and Their Cytotoxic Activity

The cytotoxicity-bioassay-guided fractionation of the ethanol extract from the marine sponge Guitarra abbotti, whose 1-O-alkyl-sn-glycerol ethers (AGEs) have not been investigated so far, led to the isolation of a complex lipid fraction containing, along with previously known compounds, six new lipids of the AGE type. The composition of the AGE fraction as well as the structures of 6 new and 22 previously known compounds were established using ¹H and ¹³C NMR, GC/MS, and chemical conversion methods. The new AGEs were identified as: 1-O-(Z-docos-15-enyl)-sn-glycerol (1), 1-O-(Z-docos-17-enyl)-sn-glycerol (2), 1-O-(Z-tricos-15-enyl)-sn-glycerol (3), 1-O-(Z-tricos-16-enyl)-sn-glycerol (4), 1-O-(Z-tricos-17-enyl)-sn-glycerol (5), and 1-O-(Z-tetracos-15-enyl)-sn-glycerol (6). The isolated AGEs show weak cytotoxic activity in THP-1, HL-60, HeLa, DLD-1, SNU C4, SK-MEL-28, and MDA-MB-231 human cancer cells. A further cytotoxicity analysis in JB6 P⁺ Cl41 cells bearing mutated MAP kinase genes revealed that ERK2 and JNK1 play a cytoprotective role in the cellular response to the AGE-induced cytotoxic effects.

Natural and Enantiopure Alkylglycerols as Antibiofilms Against Clinical Bacterial Isolates and Quorum Sensing Inhibitors of Chromobacterium violaceum ATCC 12472

Resistance mechanisms occur in almost all clinical bacterial isolates and represent one of the most worrisome health problems worldwide. Bacteria can form biofilms and communicate through quorum sensing (QS), which allow them to develop resistance against conventional antibiotics. Thus, new therapeutic candidates are sought. We focus on alkylglycerols (AKGs) because of their recently discovered quorum sensing inhibition (QSI) ability and antibiofilm potential. Fifteen natural enantiopure AKGs were tested to determine their effect on the biofilm formation of other clinical bacterial isolates, two reference strains and their QSI was determined using Chromobacterium violaceum ATCC 12472. The highest biofilm inhibition rates (%) and minimum QS inhibitory concentration were determined by a microtiter plate assay and ciprofloxacin was used as the standard antibiotic. At subinhibitory concentrations, each AKG reduced biofilm formation in a concentration-dependent manner against seven bacterial isolates, with values up to 97.2%. Each AKG displayed QSI at different levels of ability without affecting the growth of C. violaceum. AKG (2S)-3-O-(cis-13’-docosenyl)-1,2-propanediol was the best QS inhibitor (20 μM), while (2S)-3-O-(cis-9’-hexadecenyl)-1,2-propanediol was the least effective (795 μM). The results showed for the first time the QSI activity of this natural AKG series and suggest that AKGs could be promising candidates for further studies on preventing antimicrobial resistance.

Chronic nanocurcumin treatment ameliorates pain-related behavior, improves spatial memory, and reduces hippocampal levels of IL-1β and TNFα in the chronic constriction injury model of neuropathic pain

BACKGROUND

Memory deficit is a common cognitive comorbid in patients with neuropathic pain that need better treatment. Recent research revealed that nanocurcumin has an antinociceptive action and a protective effect against memory disorders, suggesting its possible effectiveness for the treatment of neuropathic pain and its comorbidity.

METHODS

Adult male albino Wistar rats (n = 32) were randomly divided into four experimental groups: CCI+ nanocurcumin, CCI + vehicle, sham + nanocurcumin, and sham + vehicle. Neuropathic pain induced by a chronic constriction injury of the sciatic nerve. Nanocurcumin or vehicle was injected intraperitoneally for 10 days. Behavioral assessment achieved to evaluate pain threshold in the von Frey test and radiant heat test, also spatial learning and memory examined by the Morris water maze (MWM) test. To explore the possible relation, IL-1β, and TNF-α levels of the hippocampus measured by enzyme-linked immunosorbent assay (ELISA).

RESULTS

Our data showed that CCI caused neuropathic pain-related behaviors and spatial learning and memory disorders in rats. Chronic treatment with nanocurcumin significantly increased pain threshold (P < 0.001; F = 27.63, F = 20.58), improved spatial memory (P < 0.01; F = 47.37), and decreased the hippocampal levels of IL-1β (P < 0.001; F = 33.57) and TNF-α (P < 0.01; F = 7.25) in CCI rats.

CONCLUSION

Chronic nanocurcumin can ameliorate pain-related behavior, improve spatial learning and memory deficits, and is associated with the reduction of IL-1β and TNF-α levels in the hippocampus in CCI rats. Nanocurcumin may be potentially providing a therapeutic alternative for the treatment of neuropathic pain and its memory impairment comorbidity.

Role of Microglia in Modulating Adult Neurogenesis in Health and Neurodegeneration

Microglia are the resident immune cells of the brain, constituting the powerhouse of brain innate immunity. They originate from hematopoietic precursors that infiltrate the developing brain during different stages of embryogenesis, acquiring a phenotype characterized by the presence of dense ramifications. Microglial cells play key roles in maintaining brain homeostasis and regulating brain immune responses. They continuously scan and sense the brain environment to detect any occurring changes. Upon detection of a signal related to physiological or pathological processes, the cells are activated and transform to an amoeboid-like phenotype, mounting adequate responses that range from phagocytosis to secretion of inflammatory and trophic factors. The overwhelming evidence suggests that microglia are crucially implicated in influencing neuronal proliferation and differentiation, as well as synaptic connections, and thereby cognitive and behavioral functions. Here, we review the role of microglia in adult neurogenesis under physiological conditions, and how this role is affected in neurodegenerative diseases.

Neuropathic Pain Causes a Decrease in the Dendritic Tree Complexity of Hippocampal CA3 Pyramidal Neurons

The International Pain Association defines neuropathic pain as “an unpleasant sensory and emotional experience associated with actual or potential tissue damage.” Recent studies show that chronic neuropathic pain causes both morphological and functional changes within brain structures. Due to the impact of supraspinal centers on pain signal processing, patients with chronic pain often suffer from depression, anxiety, memory impairment, and learning disabilities. Changes in hippocampal neuronal and glial plasticity can play a substantial role in the development of these symptoms. Given the special role of the CA3 hippocampal area in chronic stress reactions, we suggested that this region may undergo significant morphological changes as a result of persistent pain. Since the CA3 area is involved in the implementation of hippocampus-dependent memory, changes in the neuronal morphology can cause cognitive impairment observed in chronic neuropathic pain. This study aimed to elucidate the structural and plastic changes within the hippocampus associated with dendritic tree atrophy of CA3 pyramidal neurons in mice with chronic sciatic nerve constriction. Behavioral testing revealed impaired working and long-term memory in mice with a chronic constriction injury. Using the Golgi-Cox method, we revealed a decrease in the number of branches and dendritic length of CA3 pyramidal neurons. The dendritic spine number was decreased, predominantly due to a reduction in mushroom spines. An ­immunohistochemical study showed changes in astro- and microglial activity, which could affect the morphology of neurons both directly and indirectly via the regulation of neurotrophic factor synthesis. Using ELISA, we found a decrease in brain-derived neurotrophic factor production and an increase in neurotrophin-3 production. Morphological and biochemical changes in the CA3 area are accompanied by impaired working and long-term memory of animals. Thus, we can conclude that morphological and biochemical changes within the CA3 hippocampal area may underlie the cognitive impairment in neuropathic pain.