Systematic Review and Metanalysis of the Expression of Blood-Based and Cerebrospinal Fluid-Based Biomarkers Related to Inflammatory Mediators in Neuropathic Pain.

BACKGROUND: The understanding of neuropathic pain remains incomplete, highlighting the need for research on biomarkers for improved diagnosis and treatment. This review focuses on identifying potential biomarkers in blood and cerebrospinal fluid for neuropathic pain in different neuropathies. METHODS: Searches were performed in six databases: PubMed, Web of Science, Scopus, Cochrane Library, EMBASE, and CINAHL. Included were observational studies, namely cross-sectional, cohort, and case-control, that evaluated quantitative biomarkers in blood or cerebrospinal fluid. Data were qualitatively synthesized, and meta-analyses were conducted using R. The study is registered with PROSPERO under the ID CRD42022323769. RESULTS: The literature search resulted in 16 studies for qualitative and 12 for quantitative analysis, covering patients over 18 years of age with painful neuropathies. A total of 1403 subjects were analyzed, identifying no significant differences in levels of C-Reactive Protein (CRP), Interleukin-6 (IL-6), and Tumor Necrosis Factor-alpha (TNF-alpha) between patients with and without pain. Despite the high inter-rater reliability and adequate bias assessment, the results suggest negligible differences in inflammatory biomarkers, with noted publication bias and heterogeneity among studies, indicating the need for further research. CONCLUSIONS: Our review underscores the complex nature of neuropathic pain and the challenges in identifying biomarkers, with no significant differences found in CRP, IL-6, and TNF-alpha levels between patients with and without pain. Despite methodological robustness, the results are limited by publication bias and heterogeneity. This emphasizes the need for further research to discover definitive biomarkers for improved diagnosis and personalized treatment of neuropathic pain.

Reply to Rossettini et al. "Do Not Mix Apples with Oranges" to Avoid Misinterpretation of Placebo Effects in Manual Therapy: The Risk Is Resulting in a Fruit Basket. Comment on "Molina-Álvarez et al. Manual Therapy Effect in Placebo-Controlled Trials: A Systematic Review and Meta-Analysis. Int. J. Environ. Res. Public Health 2022, 19, 14021".

We have thoroughly reviewed and carefully analyzed the points raised in the comment titled: "Do not mix apples with oranges" to avoid misinterpretation of placebo effects in manual therapy: the risk is resulting in a fruit basket [...].

Manual Therapy Effect in Placebo-Controlled Trials: A Systematic Review and Meta-Analysis.

PURPOSE: Background: Evaluate whether the design of placebo control groups could produce different interpretations of the efficacy of manual therapy techniques. METHODS: Nine databases were searched (EMBASE, CINAHL, PsycINFO, MEDLINE, PubMed, SCOPUS, WEB of SCIENCE, COCHRANE, and PEDro). Randomized placebo-controlled clinical trials that used manual therapy as a sham treatment on subjects suffering from pain were included. Data were summarized qualitatively, and meta-analyses were conducted with R. RESULTS: 53 articles were included in the qualitative analysis and 48 were included in the quantitative analyses. Manipulation techniques did not show higher effectiveness when compared with all types of sham groups that were analyzed (SMD 0.28; 95%CI [-0.24; 0.80]) (SMD 0.28; 95%CI [-0.08; 0.64]) (SMD 0.42; 95%CI [0.16; 0.67]) (SMD 0.82; 95%CI [-0.57; 2.21]), raising doubts on their therapeutic effect. Factors such as expectations of treatment were not consistently evaluated, and analysis could help clarify the effect of different sham groups. As for soft tissue techniques, the results are stronger in favor of these techniques when compared to sham control groups (SMD 0.40; 95%CI [0.19, 0.61]). Regarding mobilization techniques and neural gliding techniques, not enough studies were found for conclusions to be made. CONCLUSIONS: The literature presents a lack of a unified placebo control group design for each technique and an absence of assessment of expectations. These two issues might account for the unclear results obtained in the analysis.

Antinociceptive and modulatory effect of pathoplastic changes in spinal glia of a TLR4/CD14 blocking molecule in two models of pain in rat.

The role of spinal glia in the development and maintenance of chronic pain has become over the last years a subject of increasing interest. In this regard, toll-like receptor 4 (TLR4) signaling has been proposed as a major trigger mechanism. Hence, in this study we explored the implications of TLR4 inhibition in the periphery and primarily in the CNS, focusing on the impact this inhibition renders in pain development and glia activation in the dorsal horn in two models of pain. Making use of a synthetic cluster of differentiation 14 (CD14)/TLR4 antagonist, the effect of TLR4 blockade on tactile allodynia and heat hyperalgesia was evaluated in osteoarthritic and postoperative rat models. An in vitro parallel artificial membrane permeation assay was performed to determine the proneness of the drug to permeate the blood-brain barrier prior to systemic and central administration. Findings suggest a dominant role of peripheral TLR4 in the model of incisional pain, whilst both peripheral and central TLR4 seem to be responsible for osteoarthritic pain. That is, central and peripheral TLR4 may be differently involved in the etiopathology of diverse types of pain what potentially seems a promising approach in the management of pain.

Perinatal undernourishment provokes long-lasting alterations of clusterin and fumarate hydratase expression in the rat nucleus accumbens.

BACKGROUND: Background: Perinatal malnutrition seems to provoke important neurochemical alterations in the brain that lead to higher vulnerability to develop neuropsychiatric disorders in the adulthood. OBJECTIVES: We have examined the persistence and reversibility of the changes induced by perinatal undernourishment on the expression of fumarate hydratase in the rat nucleus accumbens, bearing in mind that this expression has been previously linked with addictive disorders. Clusterin, a multifunctional protein known to be neuroprotective and possibly related to addiction in humans, was studied in parallel. METHODS: Female Wistar rats underwent a severe restriction of food during gestation and lactation. Upon weaning, a subgroup of undernourished animals was switched to normal chow and another one continued under food restriction. Control rats and their mothers were fed on chow along the experiment. Fumarate hydratase and clusterin were quantified by western blot after five months of postnatal life in the three experimental groups. RESULTS: Food restriction along the whole experimental period provoked a marked upregulation of both clusterin and fumarate hydratase in the mitochondrial fraction of the nucleus accumbens. In the case of clusterin, this upregulation was also observed in the cytosolic fraction of the nucleus accumbens. When undernourishment was limited to gestation and lactation the two proteins appeared downregulated with respect to controls. CONCLUSION: The results are consistent with the idea that perinatal malnutrition provokes marked changes in brain neurochemistry that are not fully corrected by the rehabilitation of normal feeding and could be linked to behavioural disturbances in the adulthood, that is, increased vulnerability to addiction.

Plasma midkine levels in patients with cocaine use disorder during abstinence. / Plasma midkine levels in patients with cocaine use disorder during abstinence.

Preclinical evidence suggests that endogenous midkine could play a key modulatory role on the neurotoxic and addictive effects of different kinds of drugs of abuse, including psychostimulants. However, this hypothesis has not yet been explored in humans. As a first approach to progress in this knowledge, we have comparatively studied plasma midkine levels in 75 patients with cocaine use disorder under abstinence and 26 control subjects matched for sex, age and body mass index. Patients were further segmented into early-abstinent (up to one month of abstinence, n = 30) and late-abstinent (more than one month of abstinence, n = 45). Midkine levels were quantified in plasma samples of all the participants by enzyme-linked immunosorbent assays. Early-abstinent patients exhibited a 60% increase of midkine plasma concentration in comparison with the controls. This elevation tended to normalize upon the progression of abstinence. The results obtained demonstrate that peripheral midkine levels are closely related to cocaine use and are consistent with the idea that this cytokine could play a protective role by limiting the biological activity of psychostimulants.

Diversos estudios preclínicos han sugerido que la midkina endógena podría jugar un papel modulador clave sobre los efectos neurotóxicos y adictivos de distintas drogas, incluidos los psicoestimulantes. Esta hipótesis no ha sido aún explorada en humanos. Como primer paso en esta dirección, en el presente trabajo hemos medido los niveles plasmáticos de midkina en 75 pacientes con trastorno por uso de cocaína en abstinencia y 26 controles apareados con los anteriores por sexo, edad e índice de masa corporal. Los pacientes fueron además divididos en un grupo de abstinencia temprana (menos de un mes, n = 30) y otro de abstinencia tardía (más de un mes, n = 45). Se cuantificaron los niveles plasmáticos de midkina de todos los participantes mediante un ensayo por inmunoabsorción ligado a enzimas. Los pacientes en abstinencia temprana mostraron un incremento del 60% en su concentración plasmática de midkina con respecto a los controles que tendió a desaparecer en los pacientes con periodos de abstinencia más prolongados. Los resultados demuestran que los niveles periféricos de midkina están estrechamente relacionados con el uso de cocaína y apoyan la idea de que dicha citoquina podría jugar un papel protector limitando la actividad biológica de los psicoestimulantes.

Monoclonal Antibodies for Chronic Pain Treatment: Present and Future.

Chronic pain remains a major problem worldwide, despite the availability of various non-pharmacological and pharmacological treatment options. Therefore, new analgesics with novel mechanisms of action are needed. Monoclonal antibodies (mAbs) are directed against specific, targeted molecules involved in pain signaling and processing pathways that look to be very effective and promising as a novel therapy in pain management. Thus, there are mAbs against tumor necrosis factor (TNF), nerve growth factor (NGF), calcitonin gene-related peptide (CGRP), or interleukin-6 (IL-6), among others, which are already recommended in the treatment of chronic pain conditions such as osteoarthritis, chronic lower back pain, migraine, or rheumatoid arthritis that are under preclinical research. This narrative review summarizes the preclinical and clinical evidence supporting the use of these agents in the treatment of chronic pain.

Clusterin levels in undernourished SH-SY5Y cells.

Food-related disorders are increasingly common in developed societies, and the psychological component of these disorders has been gaining increasing attention. Both overnourishment with high-fat diets and perinatal undernourishment in mice have been linked to a higher motivation toward food, resulting in an alteration in food intake. Clusterin (CLU), a multifaced protein, is overexpressed in the nucleus accumbens (NAc) of over-fed rats, as well as in those that suffered chronic undernutrition. Moreover, an increase of this protein was observed in the plasma of obese patients with food addiction, suggesting the implication of CLU in this eating disorder. To characterize CLU's cellular mechanisms, in vitro experiments of undernutrition were performed using dopaminergic SH-SY5Y cells. To mimic in vivo dietary conditions, cells were treated with different fetal bovine serum (FBS) concentrations, resulting in control (C group) diet (10% FBS), undernourishment (U group) diet (0.5% FBS), and undernourishment diet followed by restoration of control diet (UC group) (0.5 + 10% FBS). Undernourishment compromised cell viability and proliferation, and concomitantly increased CLU secretion as well as the cytosolic pool of the protein, while decreasing the mitochondrial level. The restoration of normal conditions tended to recover cell physiology, and the normal levels and distribution of CLU. This research study is a step forward toward the characterization of clusterin as a potential marker for food addiction and nutritional status.

Clusterin overexpression as a potential neuroprotective response to the pathological effects of high fat dieting on the brain reward system.

High-fat diets (HFDs) can lead to pathological changes in the brain underlying several behavioral disturbances (e.g., reward deficiency). To further increase our knowledge of these associations, we studied the sucrose reward and the brain expression of clusterin, a protein that is overexpressed after several kind of brain damaging conditions. C57BL/6J male mice were differentially fed on an HFD or standard chow for 41 days and underwent 11 sucrose place conditioning sessions followed by 4 extinction sessions to monitor the effects of HFD on sucrose reward by means of free choice tests. We quantified clusterin expression by immunochemistry in the nucleus accumbens, dorsal striatum and cingulate cortex. HFD tended to provoke a transient potentiation in the acquisition of sucrose-conditioned place preference, but this effect was followed by a much more consistent reduction in sucrose preference, which spontaneously disappeared after 31 days of an HFD with no need for extinction learning. The HFD mice showed higher clusterin expression in the nucleus accumbens but not in the other brain areas studied. The results confirm that HFDs strongly influence the rewarding properties of palatable foods and suggest a direct connection with neurotoxic alterations in the brain reward system tagged by clusterin overexpression.

Undernutrition induces major alterations in the lipid droplets of white and brown adipose tissues in wistar rats.

Several studies have shown a relationship between the distribution of fat mass around the organism, metabolic disorders, and an increased risk of morbidity and mortality. It has been demonstrated that in obese animals there is a big rise in the white fat deposits due to hyperplasia and hypertrophy of the adipocytes. Studies related to weight and health have been more popular regarding obesity rather than extreme caquexia or calorico-proteic deficiencies, but these states are interesting from the point of view of the preferential atrophy of certain organs that may help us in the understanding of undernourishment. Moreover, the discovery of beige adipose tissue has instigated thoughts around the roles played by the different cells in the adipose tissue as well as its adaptability in pathological states. In our study we carried out morphometric, morphological, and quantitative measurements of the adipose tissue in an animal model based on a 40-50% diet restriction in comparison to control animals. We have found a decrease in the size of white adipocytes together with a variation in the lipid droplet size of brown adipocytes in undernourished animals, what may be considered as possible transformations between the types of adipose tissues, and that could be caused by an adaptive phenomenon to the undernourished state.

Clusterin: Always protecting. Synthesis, function and potential issues.

In the last years, clusterin, a challenging and paradoxical apolipoprotein, has been of growing interest amongst a rising number of scientists. This enigmatic protein is present in all fluids of the organism besides within the intracellular matrix, and it plays diverse, and at times contrary, roles in a growing number of pathologies. It seems to vary its location and function to assure cellular survival being cytoprotective hence its significance in neuroprotection and cancer along with chemotherapy resistance. However, it can also lead to cellular arrest and its modulation to apoptosis. Additionally, it has been described to modulate pain, as well as linked to inflammation, cardioprotection, satiety and hunger, and possibly to addictive behaviour development. Thus, it has been postulated to be used both as a biomarker and a very explorable new therapeutic target for several conditions.

Sciatic Nerve Ligation Downregulates Mitochondrial Clusterin in the Rat Prefrontal Cortex.

The concentration of the multifunctional protein clusterin is reduced in the plasma of subjects with degenerative scoliosis (DS) and carpal tunnel syndrome (CTS) but elevated in the cerebrospinal fluid of neuropathic pain patients successfully treated with spinal cord stimulation. The present work tries to increase the knowledge of pain-associated changes of plasma and brain clusterin by using an animal model of neuropathy. We studied the effects of sciatic nerve ligation on mechanical allodynia (von Frey test), anxiety (elevated plus maze test), plasma clusterin (enzyme-linked immunosorbent assay) and clusterin expression in the nucleus accumbens (NAC) and prefrontal cortex (PFC) of adult male Wistar rats (western blot). The possible modulatory role of high fat (HF) dieting was also studied, bearing in mind that obesity has been also reported to influence nociception, clusterin levels and prefrontal cortex activation. Animals with nerve ligation showed mechanical allodynia, anxiety and a marked downregulation of clusterin in the mitochondrial fraction of the prefrontal cortex. Animals fed on HF also exhibited a slight increase of the sensitivity to mechanical stimuli and anxiety; however, the diet did not potentiate the effects of nerve ligation. The results did not confirm a parallelism between neuropathy, obesity and alterations of plasma levels of clusterin, but strongly suggest that the protein could be involved in the functional reorganization of the prefrontal cortex which has been recently reported in chronic pain conditions.

Proteomic Identification of Biomarkers Associated with Eating Control and Bariatric Surgery Outcomes in Patients with Morbid Obesity.

BACKGROUND: The current therapeutics of morbid obesity could be significantly improved after the identification of novel biomarkers associated with the food addiction endophenotype of obesity and with bariatric surgery outcomes. METHODS: We applied differential expression proteomics and enzyme-linked immunosorbent confirmatory assays to identify (a) proteins that varied according to loss of control over eating in morbidly obese patients and (b) proteins that varied between normoweight controls and patients before and 1 year after bariatric surgery. RESULTS: Clusterin was the only protein that consistently varied according to eating control in patients. Patients showed increased levels of serum amyloid P protein, apolipoprotein A4, serotransferrin, complement factors B and C3 and haptoglobin with respect to controls; the levels of all these proteins tended to return to control values 1 year after surgery. In contrast, apolipoprotein A1 and transthyretin were initially downregulated in patients and were scarcely changed by surgery. Leucine-rich alpha-2-glycoprotein was markedly increased in patients only after surgery. CONCLUSIONS: Clusterin could be of interest as a putative biomarker for food addiction diagnosis in people with morbid obesity. In addition, postsurgical normalization of the proteins initially dysregulated in obese subjects might help monitor clinical improvements after surgery, while lasting or newly detected alterations (i.e., those affecting transthyretin and leucine-rich alpha-2-glycoprotein) could reflect partial refractoriness and/or contribute to the early prediction of clinical problems.