Fish oil attenuates persistent inflammatory pain in rats through modulation of TNF-α and resolvins

The Effect of Aerobic Exercise With an Omega-3 Supplement on the Tendon Healing Process

BACKGROUND

An Achilles tendon rupture is a common orthopaedic injury in athletes and other people. Therefore, it is essential to investigate methods that may yield beneficial results for tendon healing by addressing the inflammatory and gene expression aspects of the healing process.

PURPOSE

The objective of this study was to examine the effect of combining aerobic exercise and omega-3 supplementation on the process of Achilles tendon healing in male Wistar rats.

STUDY DESIGN

Controlled laboratory study.

METHODS

For the purpose of this experiment, 50 male Wistar rats were randomly assigned to 5 groups, with each group containing 10 rats. These groups were identified as a sham group (surgery without tendon damage), a negative control group (tendon damage), and 3 experimental groups: exercise group (tendon damage + aerobic exercise), omega-3 group (tendon damage + omega-3 supplement), and exercise + omega-3 group (tendon damage + aerobic exercise + omega-3 supplement). The Achilles tendon was cut and subsequently repaired through a surgical intervention. Beginning the day after the injury, the groups receiving omega-3 received a dose of 4.6 g/kg EPA [eicosapentaenoic acid] and 3.8 g/kg DHA [docosahexaenoic acid] orally each day, and those in the exercise groups ran on a treadmill 6 days a week. At 48 hours after completing the protocol, both tissue and blood samples were taken and immediately sent for biochemical (TNF-α, IL-1β, MDA, and SOD), gene expression (MMP-3, MMP-9, and SCX), histological (hematoxylin and eosin and Masson trichrome staining), and tensile analyses. Rats were also administered the Achilles functional index at various time points.

RESULTS

The histological results revealed a marked improvement in the arrangement of cells and collagen in the extracellular matrix of the exercise + omega-3 group, displaying a notably uniform and condensed alignment of collagen fibers compared with the other groups, which exhibited a lack of organization. Biochemical results showed that TNF-α, IL-1β, and MDA levels were significantly reduced in the exercise + omega-3 group (P < .05). On the other hand, a significant increase in the Achilles functional index score was shown in the exercise + omega-3 group at all time points (P < .05). In the same group, real-time polymerase chain reaction results demonstrated that the expression of MMP-3 and SCX genes increased and that the expression of the MMP-9 gene decreased (P < .05).

CONCLUSION

Aerobic exercise with omega-3 supplementation was more beneficial for healing a surgically cut Achilles tendon in a rat model than aerobic exercise or omega-3 supplementation alone.

CLINICAL RELEVANCE

Our findings suggest that omega-3 supplementation combined with aerobic exercise after an Achilles tendon injury may be able to accelerate the process of Achilles tendon regeneration and healing.

TAM receptors mediate the Fpr2-driven pain resolution and fibrinolysis after nerve injury

Nerve injury causes neuropathic pain and multilevel nerve barrier disruption. Nerve barriers consist of perineurial, endothelial and myelin barriers. So far, it is unclear whether resealing nerve barriers fosters pain resolution and recovery. To this end, we analysed the nerve barrier property portfolio, pain behaviour battery and lipidomics for precursors of specialized pro-resolving meditators (SPMs) and their receptors in chronic constriction injury of the rat sciatic nerve to identify targets for pain resolution by resealing the selected nerve barriers. Of the three nerve barriers-perineurium, capillaries and myelin-only capillary tightness specifically against larger molecules, such as fibrinogen, recuperated with pain resolution. Fibrinogen immunoreactivity was elevated in rats not only at the time of neuropathic pain but also in nerve biopsies from patients with (but not without) painful polyneuropathy, indicating that sealing of the vascular barrier might be a novel approach in pain treatment. Hydroxyeicosatetraenoic acid (15R-HETE), a precursor of aspirin-triggered lipoxin A4, was specifically upregulated at the beginning of pain resolution. Repeated local application of resolvin D1-laden nanoparticles or Fpr2 agonists sex-independently resulted in accelerated pain resolution and fibrinogen removal. Clearing macrophages (Cd206) were boosted and fibrinolytic pathways (Plat) were induced, while inflammation (Tnfα) and inflammasomes (Nlrp3) were unaffected by this treatment. Blocking TAM receptors (Tyro3, Axl and Mer) and tyrosine kinase receptors linking haemostasis and inflammation completely inhibited all the effects. In summary, nanoparticles can be used as transporters for fleeting lipids, such as SPMs, and therefore expand the array of possible therapeutic agents. Thus, the Fpr2-Cd206-TAM receptor axis may be a suitable target for strengthening the capillary barrier, removing endoneurial fibrinogen and boosting pain resolution in patients with chronic neuropathic pain.

Docosahexaenoic acid and etanercept could reduce functional and metabolic alterations during collagen-induced arthritis in rats without any synergistic effect

AIMS

Rheumatoid arthritis is an autoimmune disease which induces chronic inflammation and increases the risk for sarcopenia and metabolic abnormalities. Nutritional strategies using omega 3 polyunsaturated fatty acids could be proposed to alleviate inflammation and improve the maintenance of lean mass. Independently, pharmacological agents targeting key molecular regulators of the pathology such as TNF alpha could be proposed, but multiple therapies are frequently necessary increasing the risk for toxicity and adverse effects. The aim of the present study was to explore if the combination of an anti-TNF therapy (Etanercept) with dietary supplementation with omega 3 PUFA could prevent pain and metabolic effects of RA.

MATERIALS AND METHODS

RA was induced using collagen-induced arthritis (CIA) in rats to explore of supplementation with docosahexaenoic acid, treatment with etanercept or their association could alleviate symptoms of RA (pain, dysmobility), sarcopenia and metabolic alterations.

KEY FINDINGS

We observed that Etanercept had major benefits on pain and RA scoring index. However, DHA could reduce the impact on body composition and metabolic alterations.

SIGNIFICANCE

This study revealed for the first time that nutritional supplementation with omega 3 fatty acid could reduce some symptoms of rheumatoid arthritis and be an effective preventive treatment in patients who do not need pharmacological therapy, but no sign of synergy with an anti-TNF agent was observed.

Omega-3 polyunsaturated fatty acids ameliorate PM2.5 exposure induced lung injury in mice through remodeling the gut microbiota and modulating the lung metabolism

Short-term or long-term exposure to fine particulate matter (PM2.5) is related to increased incidences of respiratory diseases. This study aimed to investigate the influences of omega-3 polyunsaturated fatty acids (ω-3 PUFAs) supplementation on oxidative stress, inflammation, lung metabolic profile, and gut microbiota in PM2.5-induced lung injury mice. Mice were divided into four groups (n = 15, per group): two unsupplemented groups, control group and PM2.5 group, and two supplemented groups with ω-3 PUFAs, ω-3 PUFAs group, and ω-3 PUFAs + PM2.5 group. Mice in the supplemented groups were placed on an ω-3 PUFAs-enriched diet (ω-3 PUFAs, 21 g/kg). During the 5th to 6th week of dietary supplementation, mice were exposed to PM2.5 by intra-tracheal instillation. ω-3 PUFAs ameliorate lung histopathological injury, reduce inflammatory responses and oxidative stress, affect lung metabolite profile, and modulate gut microbiota in PM2.5-induced lung injury mice. Thus, supplementary ω-3 PUFAs showed effectiveness in attenuation of PM2.5-induced lung injury, indicating that the interventions exhibited preventive and therapeutic potential.

Doxorubicin-induced hepatic toxicity in rats: Mechanistic protective role of Omega-3 fatty acids through Nrf2/HO-1 activation and PI3K/Akt/GSK-3β axis modulation

Doxorubicin (DOX), a common antibiotic used to treat a variety of tumors, has several substantial adverse effects that limit its clinical use. As a result, finding effective protective agents to combat DOX-induced organ damage is a necessity. The current study was set to delineate the hepatoprotective role of omega‐3 fatty acids (ω-3FA) against DOX-mediated acute liver damage in rats and the underlined mechanism of GSK-3β inhibition. Five groups of rats were orally received either saline (groups 1 & 2) or ω-3FA (25, 50 and 100 mg/kg/day; groups 3, 4 & 5, respectively) for 28 consecutive days. Single DOX intraperitoneal injection (20 mg/kg) was used to induce hepatic toxicity in all groups except group 1 (negative control). Blood samples and liver tissues were collected 48-hr after injection. Our results revealed that pre-administration of ω-3FA (25, 50 and 100 mg/kg) to DOX-induced hepatic injured rats showed a significant reduction in serum hepatic injury biomarkers (ALT, AST, total and direct bilirubin) as well as hepatic contents of MDA, GSH, Nrf2 and HO-1. Additionally, hepatic PI3K, pAkt and GSK-3β have been restored significantly in a dose-dependent manner. Furthermore, all the hepatic histopathological features have been retained upon ω-3FA treatment together with the immunostaining intensity of tumor necrosis factor-α and caspase-3. These results suggest that ω-3FA have shown a marked activation of the Nrf2/HO-1 signaling pathway and modulation of the PI3K/pAkt/GSK-3β axis against DOX-induced hepatotoxicity.

Preventive Supplementation of Omega-3 Reduces Pain and Pro-inflammatory Cytokines in a Mouse Model of Complex Regional Pain Syndrome Type I

Complex regional pain syndrome type I (CRPS-I) is a condition that responds poorly to treatments. The role of omega-3 fatty acids in the treatment of inflammatory disorders is well described in the literature; however, few studies have evaluated its therapeutic benefits in different types of pain. We evaluated the potential antihyperalgesic and anti-inflammatory effects of preventive omega-3 supplementation in an animal model of CRPS-I. In experiment 1, Swiss female mice were supplemented for 30 days with omega-3 before the induction of the CRPS-I model and 14 days after. Mechanical hyperalgesia was evaluated at baseline and from the 4th to the 14th day after CPRS-I induction along with open field locomotor activity after 30 days of supplementation. In experiment 2, Swiss female mice were supplemented for 30 days with omega-3 and then subjected to the CRPS-I model. Twenty-four hours later the animals were euthanized, and tissue samples of the spinal cord and right posterior paw muscle were taken to measure pro-inflammatory cytokine TNF and IL-1β concentrations. Omega-3 supplementation produced antihyperalgesic and anti-inflammatory effects, as well as reducing pro-inflammatory cytokine concentrations, without altering the animals’ locomotion. No open field locomotor changes were found. The 30-day supplementation at the tested dose was effective in the CRPS-I model.

Immunoregulatory Effect of Preventive Supplementation of Omega-3 Fatty Acid in a Complex Regional Pain Syndrome Type I Model in Mice

Objective

Complex regional pain syndrome (CRPS) is usually triggered by trauma or a surgical procedure, and it typically becomes an established one after an intense inflammatory process with chronic pain and edema as the main symptoms. Available treatments for CRPS have low efficacy. This study aimed to evaluate the clinical and immunoregulatory effects of omega-3 polyunsaturated fatty acid (PUFA) supplementation on paw edema and anti- and pro-inflammatory cytokines and macrophage phenotypes in the chronic post-ischemia pain (CPIP) preclinical model of CRPS-Type I.

Methods

Female Swiss mice were supplemented with omega-3, corn oil, or saline and then submitted to the CPIP model of ischemia/reperfusion (I/R) injury. Supplementation was carried out for 30 days prior to and up to 2 or 15 days after the induction of CPIP, according to experimental protocols. The supplementation protocol included 1,500 mg/kg of omega-3 or corn oil through an intragastric route (gavage). Paw edema, interleukin- (IL-) 4, IL-10, transforming growth factor-β1 (TGF-β1), monocyte chemotactic protein-1 (MCP-1), and tumor necrosis factor (TNF) were then measured in the paw skin and muscle by enzyme-linked immunosorbent assay (ELISA), and macrophage phenotypes (M1 and M2) assessed in the paw muscle by Western blotting.

Results

The CPIP model induced an increase in paw thickness up to 72 h post-I/R. Mice supplemented with omega-3 compared to the saline group displayed reduced edema but neither altered skin IL-4 or skin and muscle TGF-β1, TNF, and MCP-1 concentrations, nor did they exhibit significantly altered muscle macrophage phenotype on the 2nd-day post-CPIP. However, omega-3 supplementation reversed the I/R-related reduction in IL-4 in the paw muscle compared to groups supplemented with saline and corn oil. Furthermore, omega-3 promoted the reduction of IL-10 levels in the paw skin, compared to animals with lesions supplemented with saline, until the 2nd-day post-CPIP. On the 15th day post-CPIP, IL-10 was significantly increased in the muscle of animals supplemented with omega-3 compared to the saline group.

Conclusion

The results suggest that omega-3 PUFA supplementation has anti-inflammatory effects in the CPIP model of CRPS-Type I, significantly reducing paw edema and regulating concentrations of anti-inflammatory cytokines, including IL-4 and IL-10.

Short- and Long-Term Effects of Dietary Supplementation with Fish Oil on Inflammatory Pain in Rats

INTRODUCTION

Dietary supplementation with fish oil is promising as a complementary therapy for inflammatory pain. However, further studies are needed to support its therapeutic potential. For example, the antinociceptive effect of fish oil is widely suggested to be dependent on decreased prostaglandin E₂ (PGE₂) synthesis, but no previous study has investigated if it affects PGE₂-induced nociceptive response. Similarly, beneficial long-term effects on inflammatory response are related to early exposure to fish oil, however, whether these effects include decreased inflammatory pain throughout life is not known.

OBJECTIVE

The aim of this study was to investigate the short- and long-term effects of fish oil on inflammatory pain.

METHODS

Dietary fish oil supplementation was performed through two protocols: in adult rats, during 20 days, or in dams, during pregnancy and lactation, with tests performed in adult offspring. The hyperalgesic response induced by carrageenan and its final mediators PGE₂ and norepinephrine was used to model inflammatory pain.

RESULTS

The findings demonstrated for the first time that dietary fish oil (1) decreases the hyperalgesia induced by carrageenan; (2) but not that induced by its final mediator PGE₂ and norepinephrine; (3) increase omega-3 polyunsaturated fatty acids in peripheral neural tissue; and (4) attenuates inflammatory pain in individuals exposed to fish oil during pre-natal life and lactation.

CONCLUSION

Together, these findings support that fish oil decreases inflammatory pain either when consumed during adult life or during prenatal development. Future studies should confirm the therapeutic potential of fish oil in humans, which is essential for the development of public policies to encourage a fish oil richer diet.

Amelioration of PM2.5-induced lung toxicity in rats by nutritional supplementation with fish oil and Vitamin E

BACKGROUND

Exposure to fine particulate matter (PM_2.5) has been associated with respiratory morbidity and mortality. Identification of interventional measures that are efficacious against PM_2.5-induced toxicity may provide public health benefits. This study examined the inhibitory effects of nutritional supplementation with fish oil as a source of omega-3 fatty acids and vitamin E (Vit E) on PM_2.5-induced lung toxicity in rats.

METHOD

Sixty four male Sprague Dawley rats were gavaged with phosphate buffered saline (PBS), corn oil (5 ml/kg), fish oil (150 mg/kg), or Vit E (75 mg/kg), respectively, once a day for 21 consecutive days prior to intratracheal instillation of PM_2.5 (10 mg/kg) every other day for a total of 3 times. Serum and bronchoalveolar lavage fluids (BALFs) were collected 24 h after the last instillation of PM_2.5. Levels of total proteins (TP), lactate dehydrogenase (LDH), superoxide dismutase (SOD), 8-epi-prostaglandin F2α (8-epi-PGF2α), interleukin-1β (IL-1β), C-reactive protein (CRP), IL-6, and tumor necrosis factor-ɑ (TNF-ɑ) were analyzed for markers of cell injury and inflammation. Additionally, histological alterations of lung tissues were examined by hematoxylin-eosin staining.

RESULT

Exposure to PM_2.5 resulted in lung toxicity, represented as increased levels of total proteins, LDH, 8-epi-PGF2α, IL-1β and TNF-α, and increased infiltration of inflammatory cells, and decreased SOD in the BALFs, and systemic inflammation, as evinced by increased levels of CRP and IL-6 in serum. Strikingly, supplementation with fish oil but not Vit E significantly ameliorated PM_2.5-induced lung toxicity and systemic inflammation.

CONCLUSION

PM_2.5 exposure induces oxidative stress, lung injury and inflammation, which is ameliorated significantly by fish oil and partially by Vit E.

Stearidonic acid combined with alpha-linolenic acid improves lipemic and neurological markers in a rat model subject to a hypercaloric diet

In this study, we hypothesized that terrestrial plant oils, rich in alpha linolenic acid (ALA) and stearidonic acid (SDA) relative to fish oil, rich in eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), prevent negative effects on cardiovascular and neurological function using a rat model fed a hypercaloric diet. Results showed effects on the FA profile, namely, eicosapentaenoic, EPA, and docosahexaenoic, DHA, levels. There were also effects on neural aspects (cAMP response element-binding protein, CREB, gene expression, at least, doubled) and the pro-inflammatory/anti-inflammatory balance (TNF-α, tumor necrosis factor alpha reduced by 30-50%). The most positive impact of ALA and SDA was the beneficial reduction of total lipids (from 395 ± 3 to 352-361 mg/dL), VLDL-cholesterol (from 21.8 ± 0.2 to 14.1-17.8 mg/dL), and triacylglycerols (from 109 ± 1 to 71-89 mg/dL) in both LIN (diet enriched in linseed oil) and BUG (diet enriched in Buglossoides oil) groups. Overall, data indicate that ALA- and SDA-rich lipid sources may counteract the undesirable cardiovascular effects of a hypercaloric diet based on milk fat.

Antioxidant capacity of omega-3-fatty acids and vitamin E against imidacloprid-induced hepatotoxicity in Japanese quails

Imidacloprid (IM) is a neonicotinoid insecticide, used in a wide range of agricultural activities worldwide. However, it results in ecosystem disturbances and signs of toxicity in human and animals. The current study was designed to elucidate the protective effects of omega-3-fatty acids (OFAs) and vitamin E (Vit E) against IM hepatotoxicity in Japanese quails. Seventy male quails (30 days old) were divided into seven groups (n = 10); G1 -ve control; G2 received IM (+ve control); G3 received OFA; G4 received Vit E; and G5, G6, and G7 received OFA and/or Vit E with IM for 30 days, respectively. Blood and liver tissue samples were collected. Imidacloprid significantly (p < 0.05) increased serum levels of alanine transferase (ALT), aspartate transferase (AST), triglycerides (TGC), and low-density lipoprotein cholesterol (LDL-C), as well as liver tissue malondialdehyde (MDA) concentration. Moreover, IM caused a significant (p < 0.05) decrease in the levels of serum high-density lipoprotein cholesterol (HDL-C), as well as liver superoxide dismutase (SOD) enzyme activity and reduced-glutathione (GSH) concentration in comparison to the -ve control group. Histopathological changes in hepatocytes, including thick cell trabeculae with marked hydropic vacuolar degeneration of cytoplasm, were found in IM-treated group. Treatment with OFA and/or Vit E resulted in significant improvements in general body condition, serum HDL-C level, and liver tissue SOD enzyme activity and GSH concentration, as well as significant decreases in the levels of serum AST, ALT, TGC, LDL-C, and hepatic tissue MDA. In conclusion, OFA and Vit E have a protective effect against IM toxicity, especially in their combination.

Long-Chain Omega-3 Fatty Acids Supplementation Accelerates Nerve Regeneration and Prevents Neuropathic Pain Behavior in Mice

Fish oil (FO) is the main source of long chain omega-3 polyunsaturated fatty acids (ω-3 PUFAs), which display relevant analgesic and anti-inflammatory properties. Peripheral nerve injury is driven by degeneration, neuroinflammation, and neuronal plasticity which results in neuropathic pain (NP) symptoms such as allodynia and hyperalgesia. We tested the preventive effect of an EPA/DHA-concentrate fish oil (CFO) on NP development and regenerative features. Swiss mice received daily oral treatment with CFO 4.6 or 2.3 g/kg for 10 days after NP was induced by partial sciatic nerve ligation. Mechanical allodynia and thermal hypernociception were assessed 5 days after injury. CFO 2.3 g/kg significantly prevented mechanical and thermal sensitization, reduced TNF levels in the spinal cord, sciatic MPO activity, and ATF-3 expression on DRG cells. CFO improved Sciatic Functional Index (SFI) as well as electrophysiological recordings, corroborating the increased GAP43 expression and total number of myelinated fibers observed in sciatic nerve. No locomotor activity impairment was observed in CFO treated groups. These results point to the regenerative and possibly protective properties of a combined EPA and DHA oral administration after peripheral nerve injury, as well as its anti-neuroinflammatory activity, evidencing ω-3 PUFAs promising therapeutic outcomes for NP treatment.

Resolving inflammation by using nutrition therapy: roles for specialized proresolving mediators

PURPOSE OF REVIEW

Inflammation is a unifying component of many of the diseases that afflict Western civilizations. Nutrition therapy and, in particular, essential fatty acid supplementation is one of the approaches that is currently in use for the treatment and management of many inflammatory conditions. The purpose of the present review is to discuss the recent literature in light of the discovery that essential fatty acids are converted by the body to a novel genus of lipid mediators, termed specialized proresolving mediators (SPMs).

RECENT FINDINGS

The SPM genus is composed of four mediator families - the lipoxins, resolvins, protectins, and maresins. These molecules potently and stereoselectively promote the termination of inflammation, tissue repair, and regeneration. Recent studies indicate that in disease, SPM production becomes dysregulated giving rise to a status of failed resolution. Of note, several studies found that omega-3 fatty acid supplementation, at doses within the recommended daily allowance, led to increases in several SPM families that correlate with enhanced white blood cell responses in humans and reduced inflammation in mice.

SUMMARY

Given the potent biological actions of SPM in organ protection and promoting bacterial clearance, nutritional therapies enriched in omega-3 fatty acids hold promise as a potential co-therapy approach when coupled with functional lipid mediator profiling.

Prevention of Chronic Post-Thoracotomy Pain in Rats By Intrathecal Resolvin D1 and D2: Effectiveness of Perioperative and Delayed Drug Delivery

Thoracotomy results in a high frequency of chronic postoperative pain. Resolvins are endogenous molecules, synthesized and released by activated immune cells, effective against inflammatory and neuropathic pain. Different resolvins have differential actions on selective neuronal and glial receptors and enzymes. This article examines the ability of intrathecal resolvin D1 and resolvin D2 to reduce chronic post-thoracotomy pain in rats. Thoracotomy, involving intercostal incision and rib retraction, resulted in a decrease in the mechanical force threshold to induce nocifensive behavior, an enlargement of the pain-sensitive area, and an increase in the fraction of rats showing nocifensive behavior, all for at least 5 weeks. The qualitative nature of the behavioral responses to tactile stimulation changed dramatically after thoracotomy, including the appearance of vigorous behaviors, such as turning, shuddering, and squealing, all absent in naive rats. Intrathecal delivery of resolvin D1 (30 ng/30 μL), at surgery or 4 days later, halved the spread of the mechanosensitive area, lowered by 60% the percent of rats with tactile hypersensitivity, and reduced the drop in threshold for a nocifensive response, along with a reduction in the occurrence of vigorous nocifensive responses. Resolvin D2's actions on threshold changes were statistically the same. These findings suggest that intrathecal resolvins, delivered preoperatively or several days later, can prevent chronic postoperative hyperalgesia.

PERSPECTIVE

In studies of rats, the injection of the proresolving compounds of the resolvin-D series into spinal fluid, before or just after thoracotomy surgery, prevents the occurrence of acute and chronic pain. If these chemicals, which have shown no side-effects, were used in humans it might greatly reduce chronic postoperative pain.