Joint Damage and Neuropathic Pain in Rats Treated With Lysophosphatidic Acid

The effects of the GLP1 analog liraglutide on allodynia and motor coordination in peripheral neuropathy induced by a chemotherapeutic agent, cisplatin

Peripheral neuropathy is one of the dose-limiting side effects of cisplatin (CIS) and still has no effective treatment. In this study, we aimed to investigate the potential protective effects of liraglutide, a Glucagon-like peptide-1 (GLP-1) analogue against CIS-induced peripheral neuropathy. For this purpose, female Sprague Dawley rats (n = 32) were randomly allocated into 4 groups: control, CIS, CIS + liraglutide (once weekly) and CIS + liraglutide (daily). Neuropathic pain was induced by CIS 3 mg/kg/week for 5 weeks. The potential effects of liraglutide were investigated by behavior tests (von Frey, tail flick and footprint analysis), biochemical analysis and histopathological analyses of sciatic nerves and dorsal root ganglions. In the von Frey and tail flick tests, liraglutide demonstrated anti-neuropathic effects. Liraglutide also ameliorated motor coordination which was impaired by CIS. Liraglutide was shown to have beneficial effects against CIS-induced peripheral neuropathy by parameters demonstrating reduction of histopathological damage (stained by toluidine blue) of the sciatic nerves and dorsal root ganglions, suppression of oxidative stress parameters (SOD, CAT and GPx), and inflammatory load (NO, IL-6 and IL-10). Weekly dosing regimen was more effective than daily administration of liraglutide in this study. As a result, liraglutide seems to be the candidate agent for the effective treatment of CIS-induced peripheral neuropathy.

Dysregulated ATX-LPA and YAP/TAZ signaling in dystrophic Sgcd-/- mice with early fibrosis and inflammation

BACKGROUND

Sarcoglycanopathies are muscle dystrophies caused by mutations in the genes encoding sarcoglycans (α, β, γ, and δ) that can destabilize the dystrophin-associated glycoprotein complex at the sarcolemma, leaving muscle fibers vulnerable to damage after contraction, followed by inflammatory and fibrotic responses and resulting in muscle weakness and atrophy. Two signaling pathways have been implicated in fibrosis and inflammation in various tissues: autotaxin/lysophosphatidic acid (ATX-LPA) and yes-associated protein 1/transcriptional co-activator with PDZ-binding motif (YAP/TAZ). LPA, synthesized by ATX, can act as a pleiotropic molecule due to its multiple receptors. Two Hippo pathway effectors, YAP/TAZ, can be dephosphorylated by LPA and translocated to the nucleus. They induce several target genes, such as CCN2/CTGF, involved in fibrosis and inflammation. However, no detailed characterization of these processes or whether these pathways change early in the development of sarcoglycanopathy has been evaluated in skeletal muscle.

METHODS

Using the δ-sarcoglycan knockout mouse model (Sgcd-/-), we investigated components of these pathways, inflammatory and fibrotic markers, and contractile properties of different skeletal muscles (triceps-TR, gastrocnemius-GST, diaphragm-DFG, tibialis anterior-TA, and extensor digitorum longus-EDL) at one and two months of age.

RESULTS

We found that Sgcd-/- mice show early dystrophic features (fiber damage/necrosis, centrally nucleated fibers, inflammatory infiltrate, and regenerated fibers) followed by later fiber size reduction in TR, GST, and DFG. These changes are concomitant with an early inflammatory and fibrotic response in these muscles. Sgcd-/- mice also have early impaired force generation in the TA and EDL, and resistance to mechanical damage in the EDL. In addition, an early dysregulation of the ATX-LPA axis and the YAP/TAZ signaling pathway in the TR, GST, and DFG was observed in these mice.

CONCLUSIONS

The ATX-LPA axis and the YAP/TAZ signaling pathway, which are involved in inflammation and fibrosis, are dysregulated in skeletal muscle from an early age in Sgcd-/- mice. These changes are concomitant with a fibrotic and inflammatory response in these mice. Unraveling the role of the LPA axis and YAP/TAZ in sarcoglycanopathy holds great promise for improving our understanding of disease pathogenesis and identifying novel therapeutic targets for this currently incurable group of muscle disorders.

Phospholipids and Sphingolipids in Osteoarthritis

Many studies now emphasize the intricate relationship between lipid metabolism and osteoarthritis (OA), a leading cause of disability. This narrative review examines alterations in the levels of phospholipids (PLs) and sphingolipids (SLs) in synovial fluid (SF), plasma, serum, and articular tissues; discusses their role in joint lubrication, inflammation, and cartilage degradation; and describes their potential as diagnostic markers and therapeutic targets. Key findings include stage-dependent elevated levels of specific PLs and SLs in the SF, blood, and tissue of OA patients, implicating them as possible biomarkers of disease severity and progression. Studies suggest that beyond the involvement of these lipids in joint lubrication, individual species, such as lysophosphatidylcholine (LPC) 16:0, lysophosphatidic acid (LPA), ceramide-1-phosphate (C1P), and sphingosine-1-phosphate (S1P), contribute to pain, inflammation, and degradation of joints through various signaling pathways. Cross-species comparisons suggest that dogs and mice experience similar lipidomic changes during OA as humans, rendering them valuable models for studying lipid-related mechanisms. PLs and SLs in SF appear to originate primarily from the synovial blood capillaries through diffusion. In addition, lipids that are produced locally by fibroblast-like synoviocytes (FLSs) are influenced by cytokines and growth factors that regulate the biosynthesis of PLs for joint lubrication. Emerging research has identified genes such as UGCG and ESYT1 as regulators of lipid metabolism in OA. Further, we examine the suitability of lipids as biomarkers of OA and the potential of targeting the PL and SL pathways to treat OA, emphasizing the need for further research to translate these findings into clinical applications.

Comparison of nociceptor properties using electrophysiology in preclinical models of osteoarthritis

Osteoarthritis (OA) pain originates in the joint by sensitization of articular nociceptors. While behavioural assessments provide valuable information regarding pain symptoms, the techniques are subjective and open to interpretation by the experimenter. This study used in vivo electrophysiological approaches to measure objectively joint nociceptor properties in three rodent models of OA. Single unit extracellular recordings of joint mechanosensitive afferents were carried out in male and female rats following either (1) transection of the medial meniscus (MMT: post-traumatic OA), (2) intra-articular injection of sodium monoiodoacetate (MIA: chemically-induced OA), or (3) intra-articular injection of lysophosphatidic acid (LPA: neuropathic OA). In naïve male control rats, the mechanical threshold of joint mechanonociceptors (23.5 ± 1.8 mNm) was significantly reduced with MMT (9.4 ± 1.1 mNm) and MIA (15.1 ± 1.6 mNm). In females, the mechanical threshold of naïve rats (23.2 ± 3.1 mNm) was reduced following induction of MMT (8.3 ± 1.0 mNm) and LPA (10.6 ± 2.2 mNm). Afferent firing frequency increased in male MMT (∼275 %), LPA (∼175 %), MIA (225 %), and female MMT (∼146 %), LPA (∼200 %), and MIA (∼192 %). Mechanical threshold and evoked firing were negatively correlated in all models for both sexes except LPA rats (male + female) and female MMT. These data indicate that MMT, MIA, and LPA induce peripheral sensitization of joint afferents thereby validating their use in OA pain studies.

Changes in serum levels of pain mediators in hemiplegic shoulder pain

OBJECTIVE

To provide a new insight into the diagnosis and treatment of hemiplegic shoulder pain (HSP) by investigating changes in serum pain mediators.

DESIGN

Cross-sectional study.

SUBJECTS/PATIENTS

Shoulder pain group (n = 34) and control group (n = 21).

METHODS

Pain-free shoulder mobility, anxiety status, depression status, and shoulder pain were measured by passive range of motion (PROM), self-rating anxiety scale, self-rating depression scale (SDS), and visual analog scale, respectively. The enzyme-linked immunosorbent assay was used to test the serum pain mediators, including interleukin (IL)-1β, IL-2, IL-6, IL-10, nerve growth factor (NGF), tumor necrosis factor-α (TNF-α), substance P (SP), calcitonin gene-related peptide (CGRP), bradykinin (BK), 5-hydroxytryptamine (5-HT), prostaglandin E2 (PGE2), and lysophosphatidic acid (LPA).

RESULTS

Shoulder pain group pain-free PROM significantly lower than control (p < .01), and SDS index score of shoulder pain group was significantly higher than control (p < .05). The rate of spasticity in the flexor elbow muscles is higher in shoulder pain group (p < .01). CGRP, IL-10, and IL-2 were significantly upregulated in shoulder pain group compared with control (p < .01), whereas NGF, TNF-α, IL-6, 5-HT, PGE2, SP, LPA, BK, and IL-1β were significantly decreased (p < .01).

CONCLUSION

Patients with HSP have a higher risk of joint mobility disorders and depression; spasticity may be an important factor in the development of shoulder pain; CGRP is thought to be the major pain mediator in HSP, and HSP may not be inflammatory.

Lysophosphatidic Acid Induced Apoptosis, DNA Damage, and Oxidative Stress in Spinal Cord Neurons by Upregulating LPA4/LPA6 Receptors

Lysophosphatidic acid (LPA) has disruptive effects on lumbar spinal stenosis (LSS). Recently, LPA has been reported to be involved in spinal cord neuronal injury and toxicity, promoting the pathogenesis of LSS. However, the exact effects of LPA on spinal cord neurons remain unknown. The purpose of this study is to investigate the effects of LPA (18 : 1) on spinal cord neuronal cytotoxicity, apoptosis, DNA damage, and oxidative stress. After clinical detection of LPA secretion, spinal cord neurons were treated with LPA (18 : 1); cell viability was analyzed by MTT assay, and LDH leakage was detected by LDH kit; cell apoptosis was detected by flow cytometry; ROS production was measured by DCFDA staining and MitoSOX Red Staining; the activation of the Gα12/Gα13 signaling pathway was detected by serum response factor response element (SRF-RE) luciferase reporter gene; the relationship among LPA, LPA4/6, and ROCK was examined by western blotting. In spinal cord neurons treated with LPA (18 : 1), cellular activity decreased and LDH release increased. The Rho kinase inhibitor (Y-27632) can attenuate LPA-induced apoptosis, DNA damage, and oxidative stress in spinal cord neurons. Moreover mechanistic investigation indicated that LPA (18 : 1) activates Gα12/13–Rho–ROCK2-induced apoptosis, DNA damage, and oxidative stress in spinal cord neurons by upregulating LPA4/LPA6 receptors. Further, the Rho kinase inhibitor Y-27632 attenuates the effects of LPA by downregulating LPA4/LPA6 receptors. Taken together, the possible mechanism by which LPA secretion in LSS patients aggravates patient injury was further elucidated using an LPA-induced spinal cord neuronal injury cell model in vitro.