Melatonin reduces hyperalgesia associated with inflammation

Melatonin modulates TLR4-mediated inflammatory genes through MyD88- and TRIF-dependent signaling pathways in lipopolysaccharide-stimulated RAW264.7 cells

Increasing evidence demonstrates that melatonin has an anti-inflammatory effect. Nevertheless, the molecular mechanisms remain obscure. In this study, we investigated the effect of melatonin on toll-like receptor 4 (TLR4)-mediated molecule myeloid differentiation factor 88 (MyD88)-dependent and TRIF-dependent signaling pathways in lipopolysaccharide (LPS)-stimulated macrophages. RAW264.7 cells were incubated with LPS (2.0 μg/mL) in the absence or presence of melatonin (10, 100, 1000 μm). As expected, melatonin inhibited TLR4-mediated tumor necrosis factor alpha (TNF-α), interleukin (IL)-1β, IL-6, IL-8, and IL-10 in LPS-stimulated macrophages. In addition, melatonin significantly attenuated LPS-induced upregulation of cyclooxygenase (COX)-2 and inducible nitric oxide synthase (iNOS) in macrophages. Further analysis showed that melatonin inhibited the expression of MyD88 in LPS-stimulated macrophages. Although it had no effect on TLR4-mediated phosphorylation of c-Jun N-terminal kinase (JNK), p38, and extracellular regulated protein kinase (ERK), melatonin significantly attenuated the activation of nuclear factor kappa B (NF-κB) in LPS-stimulated macrophages. In addition, melatonin inhibited TLR4-mediated Akt phosphorylation in LPS-stimulated macrophages. Moreover, melatonin significantly attenuated the elevation of interferon (IFN)-regulated factor-3 (IRF3), which was involved in TLR4-mediated TRIF-dependent signaling pathway, in LPS-stimulated macrophages. Correspondingly, melatonin significantly alleviated LPS-induced IFN-β in macrophages. In conclusion, melatonin modulates TLR4-mediated inflammatory genes through MyD88-dependent and TRIF-dependent signaling pathways.

Cytoprotective and anti-inflammatory effects of melatonin in hydrogen peroxide-stimulated CHON-001 human chondrocyte cell line and rabbit model of osteoarthritis via the SIRT1 pathway

Melatonin has potent antioxidant, analgesic, and antinociceptive properties. However, the effects of melatonin against oxidative stress-induced cytotoxicity and inflammatory mediators in human chondrocytes remain poorly understood. This study examined the effects and underlying mechanism of melatonin in hydrogen peroxide (H(2) O(2) )-stimulated human chondrocytes and rabbit osteoarthritis (OA) model. Melatonin markedly inhibited hydrogen peroxide (H(2) O(2) )-stimulated cytotoxicity, iNOS, and COX-2 protein and mRNA expression, as well as the downstream products, NO and PGE(2) . Incubation of cells with melatonin decreased H(2) O(2) -induced Sirtuin 1 (SIRT1) mRNA and protein expression. SIRT1 inhibition by sirtinol or Sirt1 siRNA reversed the effects of melatonin on H(2) O(2) -mediated induction of pro-inflammatory cytokines (NO, PGE(2) , TNF-α, IL-1β, and IL-8) and the expression of iNOS, COX-2, and cartilage destruction molecules. Melatonin blocked H(2) O(2) -induced phosphorylation of PI3K/Akt, p38, ERK, JNK, and MAPK, as well as activation of NF-κB, which was reversed by sirtinol and SIRT1 siRNA. In rabbit with OA, intra-articular injection of melatonin significantly reduced cartilage degradation, which was reversed by sirtinol. Taken together, this study shows that melatonin exerts cytoprotective and anti-inflammatory effects in an oxidative stress-stimulated chondrocyte model and rabbit OA model, and that the SIRT1 pathway is strongly involved in this effect.

Melatonin administration reduces inflammatory pain in rats

In view of the broad range of effects attributed to melatonin, this study evaluated its analgesic effect on inflammatory pain induced by complete Freund’s adjuvant (CFA) in Wistar rats. Inflammation was induced by intradermal CFA injection in the hind paw of all animals, which were then divided into two groups that received either 60 mg/kg of melatonin or vehicle (1% alcohol in saline), intraperitoneally, for three days. The analgesic effect of melatonin was assessed by the hot-plate test, immediately and thereafter at 30, 60, 90, and 120 minutes after the first administration and 24 hours after once-daily administration for 2 more days. After CFA injection, melatonin administration increased withdrawal latency at 60 minutes after the first dose. After the end of treatment, melatonin showed a significant analgesic effect on inflammatory pain. This study paves the way for exploration of how brief courses of treatment could improve this analgesic effect in the late phases of inflammatory pain.

Melatonin inhibits matrix metalloproteinase-9 (MMP-9) activation in the lipopolysaccharide (LPS)-stimulated RAW 264.7 and BV2 cells and a mouse model of meningitis

We explored anti-inflammatory potential of melatonin against the lipopolysaccharide (LPS)-induced inflammation in vivo and in vitro. RAW 264.7 and BV2 cells were stimulated by LPS, followed by the treatment with melatonin or vehicle at various time intervals. In a mouse model of meningitis induced by LPS, melatonin (5mg/kg) or vehicle was intravenously injected at 30min postinsult. The activity of matrix metalloproteinase-2 (MMP-2) and metalloproteinase-9 (MMP-9) was determined by gelatin zymography. Nuclear factor-kappa B (NFκB) translocation and binding activity were determined by immunocytochemistry and electrophoretic mobility shift assay (EMSA). Our results showed that either pretreatment or cotreatment with melatonin at 50-500 μm effectively inhibited the LPS-induced proMMP-9 activation in the RAW 264.7 and BV2 cells, respectively (P<0.05). This melatonin-induced proMMP-9 inhibition remained effective when treatment was delayed up to 2 and 6hr postinsult for RAW 264.7 and BV2 cells, respectively (P<0.05 for both groups). Additionally, melatonin significantly attenuated the rises of circulatory and cerebral MMP-9 activity, respectively (P<0.05) and reduced the loss of body weight (P<0.05) in mice with meningitis. Moreover, melatonin (50μm) effectively inhibited nuclear factor-kappa B (NFκB) translocation and binding activity in the LPS-treated RAW 264.7 and BV2 cells, respectively (P<0.05). These results demonstrate direct inhibitory actions of melatonin against postinflammatory NFκB translocation and MMP-9 activation and highlight its ability to inhibit systemic and cerebral MMP-9 activation following brain inflammation.

Melatonin in antinociception: its therapeutic applications

The intensity of pain sensation exhibits marked day and night variations. Since the intensity of pain perception is low during dark hours of the night when melatonin levels are high, this hormone has been implicated as one of the prime antinociceptive substances. A number of studies have examined the antinociceptive role of melatonin in acute, inflammatory and neuropathic pain animal models. It has been demonstrated that melatonin exerts antinociceptive actions by acting at both spinal cord and supraspinal levels. The mechanism of antinociceptive actions of melatonin involves opioid, benzodiazepine, α(1)- and α(2)-adrenergic, serotonergic and cholinergic receptors. Most importantly however, the involvement of MT(1)/MT(2) melatonergic receptors in the spinal cord has been well documented as an antinociceptive mechanism in a number of animal models of pain perception. Exogenous melatonin has been used effectively in the management of pain in medical conditions such as fibromyalgia, irritable bowel syndrome and migraine and cluster headache. Melatonin has been tried during surgical operating conditions and has been shown to enhance both preoperative and post-operative analgesia. The present review discusses the available evidence indicating that melatonin, acting through MT(1)/MT(2) melatonin receptors, plays an important role in the pathophysiological mechanism of pain.

Pain in neonatal intensive care: role of melatonin as an analgesic antioxidant

Endotracheal intubation is a common painful procedure in newborn care. Neonates are more sensitive to pain than older infants, children, and adults, and this hypersensitivity is further exacerbated in preterm neonates. The aim of this study was to evaluate the analgesic activity of melatonin during endotracheal intubation of the newborn by using the Neonatal Infant Pain Scale (NIPS) and Premature Infant Pain Profile (PIPP) score. Secondary outcome was an evaluation of melatonin as inflammatory responses. This was performed by measuring the levels of pro- and anti-inflammatory cytokines implicated in the pain. Sixty preterm infants were enrolled in the study and were randomly divided into two groups: 30 infants treated with melatonin plus common sedation and analgesia recommended by Italian Society of Neonatology (group 1) and 30 infants treated with only common sedation and analgesia. The sedative and analgesic drugs included atropine, fentanyl, and vecuronium. The reduction in pain score (NIPS) was similar in both groups at an early phase, while it (PIPP score) was lower in melatonin-treated group infants than the other newborns at a late phase, during intubation and mechanical ventilation. The differences were statistically significant at 12, 24, 48, and 72 hr (P < 0.001). Pro-inflammatory and anti-inflammatory cytokines (IL-6, IL-8, IL-10 and IL-12) were higher in the common sedation and analgesia group than in melatonin-treated infants at 24, 48, 72 hr and 7 days (P < 0.001). This study suggests the use of melatonin as an adjunct analgesic therapy during procedural pain, especially when an inflammatory component is involved.

Therapeutic benefit of melatonin in experimental feline uveitis

Uveitis is a frequent ophthalmic disorder which constitutes one of the main causes of blindness in domestic cats. The aim of this report was to analyze the effect of melatonin on experimentally induced uveitis in cats. Bacterial lipopolysaccharide (LPS) was injected intravitreally into one eye from intact cats, while the contralateral eye was injected with vehicle. Melatonin was orally administered every 24 hr to a group of ten cats, from 24 hr before until 45 days after intravitreal injections. Eyes were evaluated by means of clinical evaluation, intraocular pressure (IOP), blood-ocular barrier integrity (via measurement of protein concentration and cell content in samples of aqueous humor [AH]), electroretinogram (ERG), and histological examination of the retinas. In LPS-treated eyes, several clinical signs were observed until day 45 postinjection. The treatment with melatonin significantly decreased clinical signs and prevented the reduction in IOP induced by LPS. In LPS-injected eyes, melatonin significantly preserved the blood-ocular barrier integrity, as shown by a decrease in the number of infiltrating cells and protein concentration in the AH. Mean amplitudes of scotopic ERG a- and b-waves were significantly reduced in eyes injected with LPS, whereas melatonin significantly prevented the effect of LPS. At 45 days after injection, LPS induced alterations in photoreceptors and at the middle portion of the retina, whereas melatonin preserved the retinal structure. These results indicate that melatonin prevented clinical, biochemical, functional, and histological alterations induced by LPS injection. Thus, melatonin might constitute a useful tool for the treatment of feline uveitis.

A case-control study of melatonin receptor type 1A polymorphism and acute myocardial infarction in a Spanish population

Coronary artery disease (CAD) is a complex disease with genetic and environmental determinants. Although a large number of genetic polymorphisms involved in the pathogenesis of atherosclerosis have been identified, there is still no evidence of a genetic association with CAD. As melatonin might play a role in the pathogenesis of atherosclerosis through its anti-inflammatory and antioxidant properties, we tested whether the expression of six single nucleotide polymorphisms (SNPs) of the melatonin receptor differs in acute myocardial infarction (AMI) patients with acute myocardial infarction (n = 300) compared with healthy age- and sex-matched controls (n = 250). Finally, only MEL1A receptor SNP rs28383653 was selected because of Hardy-Weinberg equilibrium (χ(2) = 0.49). The distribution of genotype frequencies for this SNP showed that the unfavourable CT genotype was significantly more frequent in patients with AMI than in controls (4.5% versus 1.3%; P = 0.006). Multivariable analysis showed a significantly higher frequency of the unfavourable CT genotype in AMI patients with peripheral arteriopathy (28% versus 10%; P = 0.01). This finding suggests a synergism effect between the unfavourable genotype (CT) of the MELIA receptor SNP and the vascular disease in this subgroup of patients. To our knowledge, this is the first study to report an association between a genetic polymorphism of the melatonin receptor 1A and CAD.