Melatonin prevents experimental preterm labor and increases offspring survival

Preterm delivery is the leading cause of neonatal mortality and contributes to delayed physical and cognitive development in children. At present, there is no efficient therapy to prevent preterm labor. A large body of evidence suggests that intra‐amniotic infections may be a significant and potentially preventable cause of preterm birth. This work assessed the effect of melatonin in a murine model of inflammation‐associated preterm delivery which mimics central features of preterm infection in humans. For this purpose, preterm labor was induced in BALB/c mice by intraperitoneal injections of bacterial lipopolysaccharide (LPS) at 10.00 hr (10 μg LPS) and 13.00 hr (20 μg LPS) on day 15 of pregnancy. On day 14 of pregnancy, a pellet of melatonin (25 mg) had been subcutaneously implanted into a group of animals. In the absence of melatonin, a 100% incidence of preterm birth was observed in LPS‐treated animals, and the fetuses showed widespread damage. By comparison, treatment with melatonin prevented preterm birth in 50% of the cases, and all pups from melatonin‐treated females were born alive and their body weight did not differ from control animals. Melatonin significantly prevented the LPS‐induced rises in uterine prostaglandin (PG) E₂, PGF_2α, and cyclooxygenase‐2 protein levels. In addition, melatonin prevented the LPS‐induced increase in uterine nitric oxide (NO) production, inducible NO synthase protein, and tumor necrosis factor‐alpha (TNFα) levels. Collectively, our results suggest that melatonin could be a new therapeutic tool to prevent preterm labor and to increase offspring survival.     

Melatonin improves mitochondrial function in inguinal white adipose tissue of Zücker diabetic fatty rats

Mitochondrial dysfunction in adipose tissue may contribute to obesity‐related metabolic derangements such as type 2 diabetes mellitus (T2DM). Because mitochondria are a target for melatonin action, the goal of this study was to investigate the effects of melatonin on mitochondrial function in white (WAT) and beige inguinal adipose tissue of Zücker diabetic fatty (ZDF) rats, a model of obesity‐related T2DM. In this experimental model, melatonin reduces obesity and improves the metabolic profile. At 6 wk of age, ZDF rats and lean littermates (ZL) were subdivided into two groups, each composed of four rats: control (C‐ZDF and C‐ZL) and treated with oral melatonin in the drinking water (10 mg/kg/day) for 6 wk (M‐ZDF and M‐ZL). After the treatment period, animals were sacrificed, tissues dissected, and mitochondrial function assessed in isolated organelles. Melatonin increased the respiratory control ratio (RCR) in mitochondria from white fat of both lean (by 26.5%, P < 0.01) and obese (by 34.5%, P < 0.01) rats mainly through a reduction of proton leaking component of respiration (state 4) (28% decrease in ZL, P < 0.01 and 35% in ZDF, P < 0.01). However, melatonin treatment lowered the RCR in beige mitochondria of both lean (by 7%, P < 0.05) and obese (by 13%, P < 0.05) rats by maintaining high rates of uncoupled respiration. Melatonin also lowered mitochondrial oxidative status by reducing nitrite levels and by increasing superoxide dismutase activity. Moreover, melatonin treatment also caused a profound inhibition of Ca‐induced opening of mPTP in isolated mitochondria from both types of fat, white and beige, in both lean and obese rats. These results demonstrate that chronic oral melatonin improves mitochondrial respiration and reduces the oxidative status and susceptibility to apoptosis in white and beige adipocytes. These melatonin effects help to prevent mitochondrial dysfunction and thereby to improve obesity‐related metabolic disorders such as diabetes and dyslipidemia of ZDF rats.     

Melatonin and Exposure to Constant Light/Darkness Affects Ovarian Follicular Kinetics and Estrous Cycle in Indian Desert GerbilMeriones hurrianae(Jerdon)

Melatonin mediates photoperiodic influence on reproduction and constant light and darkness affect pineal biosynthesis of melatonin. The present study was undertaken to assess the effects of melatonin and drastic photoperiodic changes on reproduction in a tropical desert species with a fossorial lifestyle. Ovarian follicular kinetics and estrous cycle were studied in the Indian desert gerbilMeriones hurrianae,after treatment with melatonin and exposure to constant light (LL) and darkness (DD) regimes. Melatonin treatment increased (P < 0.001) ovarian weights without changing the uterine weights. While exposure to LL decreased (P < 0.001) both ovarian and uterine weights, exposure to DD had no effect on these weights. Follicular kinetics of growing and regressing follicles revealed that ovaries of melatonin-treated and DD-exposed animals had significantly more growing follicles. Melatonin treatment increased all types of growing follicles, especially antral and Graafian follicles. Exposure to DD increased all types of growing follicles, with the medium sized antral and Graafian follicles being significant (P < 0.01). In contrast to stimulation of follicular growth by melatonin and DD, LL caused regression of all stages of follicular growth and also reduced the number of small preantral follicles. Melatonin treatment increased (P < 0.001) the length of estrous cycle (5.08 to 7.29 days). Gerbils treated with melatonin, exposed to LL and DD, had a longer (P < 0.001) metestrus. Animals held in LL, had the least number (P < 0.001) of estrous smears (1 in 30 days). The results suggest that melatonin is involved in growth of ovarian follicles in the Indian desert gerbil.     

Melatonin improves bone mineral density at the femoral neck in postmenopausal women with osteopenia: a randomized controlled trial

Melatonin is known for its regulation of circadian rhythm. Recently, studies have shown that melatonin may have a positive effect on the skeleton. By increasing age, the melatonin levels decrease, which may lead to a further imbalanced bone remodeling. We aimed to investigate whether treatment with melatonin could improve bone mass and integrity in humans. In a double‐blind RCT, we randomized 81 postmenopausal osteopenic women to 1‐yr nightly treatment with melatonin 1 mg (N = 20), 3 mg (N = 20), or placebo (N = 41). At baseline and after 1‐yr treatment, we measured bone mineral density (BMD) by dual X‐ray absorptiometry, quantitative computed tomography (QCT), and high‐resolution peripheral QCT (HR‐pQCT) and determined calciotropic hormones and bone markers. Mean age of the study subjects was 63 (range 56–73) yr. Compared to placebo, femoral neck BMD increased by 1.4% in response to melatonin (P < 0.05) in a dose‐dependent manner (P < 0.01), as BMD increased by 0.5% in the 1 mg/day group (P = 0.55) and by 2.3% (P < 0.01) in the 3 mg/day group. In the melatonin group, trabecular thickness in tibia increased by 2.2% (P = 0.04), and volumetric bone mineral density (vBMD) in the spine, by 3.6% (P = 0.04) in the 3 mg/day. Treatment did not significantly affect BMD at other sites or levels of bone turnover markers; however, 24‐hr urinary calcium was decreased in response to melatonin by 12.2% (P = 0.02). In conclusion, 1‐yr treatment with melatonin increased BMD at femoral neck in a dose‐dependent manner, while high‐dose melatonin increased vBMD in the spine. Further studies are needed to assess the mechanisms of action and whether the positive effect of nighttime melatonin will protect against fractures.     

Melatonin induces browning of inguinal white adipose tissue in Zucker diabetic fatty rats

Melatonin limits obesity in rodents without affecting food intake and activity, suggesting a thermogenic effect. Identification of brown fat (beige/brite) in white adipose tissue (WAT) prompted us to investigate whether melatonin is a brown‐fat inducer. We used Zücker diabetic fatty (ZDF) rats, a model of obesity‐related type 2 diabetes and a strain in which melatonin reduces obesity and improves their metabolic profiles. At 5 wk of age, ZDF rats and lean littermates (ZL) were subdivided into two groups, each composed of four rats: control and those treated with oral melatonin in the drinking water (10 mg/kg/day) for 6 wk. Melatonin induced browning of inguinal WAT in both ZDF and ZL rats. Hematoxylin–eosin staining showed patches of brown‐like adipocytes in inguinal WAT in ZDF rats and also increased the amounts in ZL animals. Inguinal skin temperature was similar in untreated lean and obese rats. Melatonin increased inguinal temperature by 1.36 ± 0.02°C in ZL and by 0.55 ± 0.04°C in ZDF rats and sensitized the thermogenic effect of acute cold exposure in both groups. Melatonin increased the amounts of thermogenic proteins, uncoupling protein 1 (UCP1) (by ~2‐fold, P < 0.01) and PGC‐1α (by 25%, P < 0.05) in extracts from beige inguinal areas in ZL rats. Melatonin also induced measurable amounts of UCP1 and stimulated by ~2‐fold the levels of PGC‐1α in ZDF animals. Locomotor activity and circulating irisin levels were not affected by melatonin. These results demonstrate that chronic oral melatonin drives WAT into a brown‐fat‐like function in ZDF rats. This may contribute to melatonin′s control of body weight and its metabolic benefits.     

Early changes in glial reactivity and lipid peroxidation in diabetic rat retina: effects of melatonin

Abstract. Diabetes mellitus, the most common serious metabolic disorder, is characterized by functional and structural changes in the peripheral and central nervous systems. Glial cells provide structural and metabolic support for retinal neurons. During diabetes, one of the early pathogenic events is retinal glial reactivity. We studied the effects of melatonin, which is known to reduce oxidationbased neurotoxicity, on glial reactivity and lipid peroxidation in the retina of diabetic rats. Diabetes was induced by a single injection of streptozotocin (STZ), and these diabetic rats were treated daily either with melatonin (10 mg/kg) or saline vehicle. After 6 weeks of diabetes, we determined the extents of lipid peroxidation and glial reactivity in retina. Lipid peroxidation, measured on the basis of malondialdehyde and 4-hydroxyalkenals concentrations, was increased in diabetic rats (p<0.01) and this increase was prevented by melatonin treatment (p<0.05). Furthermore, gial reactivity, determined immunohistochemically from the levels of glial fibrillary acid protein (GFAP), was also increased significantly (p<0.01). Melatonin administration partially prevented this increase in GFAP content (p<0.05). In conclusion, glial reactivity is an early pathogenic event in diabetic retina and both reactive gliosis and accumulation of malondialdehyde and 4-hydroxyalkenals are prevented by melatonin supplementation.     

Melatonin reduces median nerve injury‐induced mechanical hypersensitivity via inhibition of microglial p38 mitogen‐activated protein kinase activation in rat cuneate nucleus

In this study, we examined the relationships between p38 mitogen‐activated protein kinase (MAPK) activation in the cuneate nucleus (CN) and behavioral hypersensitivity after chronic constriction injury (CCI) of the median nerve. We further investigated effects of melatonin administration and pinealectomy on p38 MAPK activation and development of hypersensitivity. Using immunohistochemistry and immunoblotting, low levels of phosphorylated p38 (p‐p38) MAPK were detected in CN of normal rats. As early as 1 day after CCI, p‐p38 MAPK levels in the ipsilateral CN were significantly increased (1.4 ± 0.2‐fold, P < 0.05), which reached a maximum at 7 days (5.1 ± 0.4‐fold, P < 0.001). Double immunofluorescence labeling with cell‐specific markers showed that p‐p38 MAPK immunoreactive cells co‐expressed OX‐42, a microglia activation maker, suggesting the expression of p‐p38 MAPK in microglia. Microinjection of SB203580, a p38 MAPK inhibitor, into the CN 1 day after CCI attenuated injury‐induced behavioral hypersensitivity in a dose‐dependent manner. Furthermore, animals received melatonin treatment at daily doses of 37.5, 75, 150, or 300 mg/kg from 30 min before until 3 days after CCI. Melatonin treatment dose‐dependently attenuated p‐p38 MAPK levels, release of pro‐inflammatory cytokines, and behavioral hypersensitivity following CCI; conversely, pinealectomy that resulted in a reduction in endogenous melatonin levels exacerbated these effects. In conclusion, median nerve injury‐induced microglial p38 MAPK activation in the CN modulated development of behavioral hypersensitivity. Melatonin supplementation eased neuropathic pain via inhibition of p38 MAPK signaling pathway; contrarily, reducing endogenous blood melatonin levels by pinealectomy promoted phosphorylation of p38 MAPK and made rats more vulnerable to nerve injury‐induced neuropathic pain.     

Melatonin improves cerebrovascular function and decreases oxidative stress in chronically hypoxic lambs

Chronic hypoxia during gestation and delivery results in oxidative stress and cerebrovascular dysfunction in the neonate. We assessed whether melatonin, a potent antioxidant and potential vasodilator, improves the cerebral vascular function in chronically hypoxic neonatal lambs gestated and born in the highlands (3600 m). Six lambs received melatonin (1 mg/kg per day oral) and six received vehicle, once a day for 8 days. During treatment, biometry and hemodynamic variables were recorded. After treatment, lambs were submitted to a graded FiO₂ protocol to assess cardiovascular responses to oxygenation changes. At 12 days old, middle cerebral arteries (MCA) were collected for vascular reactivity, morphostructural, and immunostaining evaluation. Melatonin increased fractional growth at the beginning and improved carotid blood flow at all arterial PO₂ levels by the end of the treatment (P < 0.05). Further, melatonin treatment improved vascular responses to potassium, serotonin, methacholine, and melatonin itself (P < 0.05). In addition, melatonin enhanced the endothelial response via nitric oxide‐independent mechanisms in isolated arteries (162 ± 26 versus 266 ± 34 AUC, P < 0.05). Finally, nitrotyrosine staining as an oxidative stress marker decreased in the MCA media layer of melatonin‐treated animals (0.01357 ± 0.00089 versus 0.00837 ± 0.00164 pixels/μm², P < 0.05). All the melatonin‐induced changes were associated with no systemic cardiovascular alterations in vivo. In conclusion, oral treatment with melatonin modulates cerebral vascular function, resulting in a better cerebral perfusion and reduced oxidative stress in the neonatal period in chronically hypoxic lambs. Melatonin is a potential therapeutic agent for treating cerebrovascular dysfunction associated with oxidative stress and developmental hypoxia in neonates.     

Melatonin ameliorates cerulein‐induced pancreatitis by the modulation of nuclear erythroid 2‐related factor 2 and nuclear factor‐kappaB in rats

Abstract: Melatonin exhibits a wide variety of biological effects, including antioxidant and anti‐inflammatory functions. Its antioxidant role impedes the etiopathogenesis of pancreatitis, but little is known about the signaling pathway of melatonin in the induction of antioxidant enzymes in acute pancreatitis (AP). The aim of this study was to determine whether melatonin could prevent cerulein‐induced AP through nuclear factor erythroid 2‐related factor 2 (Nrf2) and curtail inflammation by inhibition of NF‐κB. AP was induced by two intraperitoneal (i.p.) injections of cerulein at 2 h intervals (50 μg/kg) in Sprague‐Dawley rats. Melatonin (10 or 50 mg/kg/daily, i.p.) was administered 24 h before each injection of cerulein. The rats were killed 12 h after the last injection. Acinar cell degeneration, pancreatic edema, and inflammatory infiltration were significantly different in cerulein‐ and melatonin‐treated rats. Melatonin significantly reduced amylase, lipase, MPO, and MDA levels, and increased antioxidant enzyme activities including SOD and GPx, which were decreased in AP (P < 0.05). Melatonin increased the expression of NQO1, HO‐1, and SOD2 when compared with the cerulein‐induced AP group (P < 0.05). In addition, melatonin increased Nrf2 expression, and reduced expressions of tumor necrosis factor‐alpha, IL‐1β, IL‐6, IL‐8, and iNOS. The elevated nuclear binding of NF‐κB in the cerulein‐induced pancreatitis group was inhibited by melatonin. These results show that melatonin increases antioxidant enzymes and Nrf2 expression, and limits inflammatory mediators in cerulein‐induced AP. It is proposed that melatonin may play an important role in oxidative stress via the Nrf2 pathway in parallel with reduction of inflammation by NF‐κB inhibition.     

The protective effect of melatonin on smoke‐induced vascular injury in rats and humans: a randomized controlled trial

Smoking is one of the most harmful lifestyles in the world. Very few studies have investigated the effects of melatonin in smoke‐induced vascular injury. This study was designed to investigate whether melatonin could protect rats and humans from smoke‐induced vascular injury. 32 male rats and a double‐blind randomized controlled trial (RCT) containing 63 participants formed the subjects of this study. In rats, 10 mg/kg of melatonin was intraperitoneally injected. Blood samples and abdominal artery were harvested two weeks later. Melatonin decreased the expression of platelet endothelial cell adhesion molecule‐1 (CD31), intercellular adhesion molecule‐1 (ICAM‐1), vascular cell adhesion molecule‐1 (VCAM‐1) and endothelin‐1 (ET‐1) compared with the smoke exposed group (P < 0.05), whereas endothelial nitric oxide synthase (eNOS), nuclear erythroid 2‐related factor 2 (Nrf2), NAD(P)H quinone oxidoreductase 1 (NQO‐1), catalytic glutamate cysteine ligase (GCLC) and heme oxygenase‐1 (HO‐1) recovered markedly (P < 0.05). In humans, 3 mg/day of melatonin was taken orally by the participants. Blood samples were drawn at baseline and after two weeks of treatment. Compared with the oral placebo group, melatonin decreased the concentration of fibrinogen (Fbg) (P = 0.04) and free fatty acids (FFA) (P = 0.04) in smokers, along with the decreased expression of ICAM‐1, VCAM‐1 and ET‐1 (P = 0.004, P = 0.001, P < 0.0001, respectively). In contrast, Nrf2 and HO‐1 expression were markedly increased (P = 0.0001, P = 0.0049, respectively) after smokers took melatonin orally. In summary, our present data suggest that melatonin could ameliorate smoke‐induced vascular injury.     

Melatonin: Antioxidant and modulatory properties in age‐related changes during Trypanosoma cruzi infection

The purpose of this study was to investigate the effects of melatonin on selected biomarkers of innate and humoral immune response as well as the antioxidant/oxidant status (superoxide dismutase—SOD and reduced glutathione levels (GSH) to understand whether age‐related changes would influence the development of acute Trypanosoma cruzi (T. cruzi) infection. Young‐ (5 weeks) and middle‐aged (18 months) Wistar rats were orally treated with melatonin (gavage) (05 mg/kg/day), 9 days after infection. A significant increase in both SOD activity and GSH levels was found in plasma from all middle‐aged melatonin‐treated animals. Melatonin triggered enhanced expression of major histocompatibility class II (MHC‐II) antigens on antigen‐presenting cell (APC) and peritoneal macrophages in all treated animals. High levels of CD4⁺CD28‐negative T cells (*P<.05) were detected in middle‐aged control animals. Melatonin induced a significant reduction (***P<.001) in CD28‐negative in CD4⁺ and CD8⁺ T cells in middle‐aged control animals. Contrarily, the same group displayed upregulated CD4⁺CD28⁺T and CD8⁺CD28⁺T cells. Melatonin also triggered an upregulation of CD80 and CD86 expression in all young‐treated groups. Significant percentages of B and spleen dendritic cells in middle‐aged infected and treated animals were observed. Our data reveal new features of melatonin action in inhibiting membrane lipid peroxidation, through the reduction in 8‐isoprostane, upregulating the antioxidant defenses and triggering an effective balance in the antioxidant/oxidant status during acute infection. The ability of melatonin to counteract the immune alterations induced by aging added further support to its use as a potential therapeutic target not only for T. cruzi infection but also for other immunocompromised states.     

Neuroprotective effect of melatonin against ischemia is partially mediated by alpha‐7 nicotinic receptor modulation and HO‐1 overexpression

Melatonin has been widely studied as a protective agent against oxidative stress. However, the molecular mechanisms underlying neuroprotection in neurodegeneration and ischemic stroke are not yet well understood. In this study, we evaluated the neuroprotective/antioxidant mechanism of action of melatonin in organotypic hippocampal cultures (OHCs) as well as in photothrombotic stroke model in vivo. Melatonin (0.1, 1, and 10 μm ) incubated postoxygen and glucose deprivation (OGD) showed a concentration‐dependent protection; maximum protection was achieved at 10 μm (90% protection). Next, OHCs were exposed to 10 μm melatonin at different post‐OGD times; the protective effect of melatonin was maintained at 0, 1, and 2 hr post‐OGD treatment, but it was lost at 6 hr post‐OGD. The protective effect of melatonin and the reduction in OGD‐induced ROS were prevented by luzindole (melatonin antagonist) and α‐bungarotoxin (α‐Bgt, a selective α7 nAChR antagonist). In Nrf2 knockout mice, the protective effect of melatonin was reduced by 40% compared with controls. Melatonin, incubated 0, 1, and 2 hr post‐OGD, increased the expression of heme oxygenase‐1 (HO‐1), and this overexpression was prevented by luzindole and α‐bungarotoxin. Finally, administration of 15 mg/kg melatonin following the induction of photothrombotic stroke in vivo, reduced infarct size (50%), and improved motor skills; this effect was partially lost in 0.1 mg/kg methyllycaconitine (MLA, selective α7 nAChR antagonist)‐treated mice. Taken together, these results demonstrate that postincubation of melatonin provides a protective effect that, at least in part, depends on nicotinic receptor activation and overexpression of HO‐1.     

Pre‐treatment neutrophil/lymphocyte ratio and platelet/lymphocyte ratio are prognostic of progression in early stage classical Hodgkin lymphoma

To determine whether pre‐treatment neutrophil/lymphocyte (NLR) or platelet/lymphocyte ratios (PLR) are predictive for progression in early‐stage classical Hodgkin lymphoma (cHL), we derived NLR and PLR values for 338 stage I/II cHL patients and appropriate cut‐off point values to define progression. Two‐year freedom from progression (FFP) for patients with NLR ≥6·4 was 82·2% vs. 95·7% with NLR <6·4 (P < 0·001). Similarly, 2‐year FFP was 84·3% for patients with PLR ≥266·2 vs. 96·1% with PLR <266·2 (P = 0·003). On univariate analysis, both NLR and PLR were significantly associated with worse FFP (P = 0·001). On multivariate analysis, PLR remained a significant, independent prognostic factor (P < 0·001).     

Melatonin reduces hepatic mitochondrial dysfunction in diabetic obese rats

Hepatic mitochondrial dysfunction is thought to play a role in the development of liver steatosis and insulin resistance, which are both common characteristics of obesity and type 2 diabetes mellitus (T2DM). It was hypothesized that the antioxidant properties of melatonin could potentially improve the impaired functions of hepatic mitochondria in diabetic obese animals. Male Zucker diabetic fatty (ZDF) rats and lean littermates (ZL) were given either melatonin (10 mg/kg BW/day) orally for 6 wk (M‐ZDF and M‐ZL) or vehicle as control groups (C‐ZDF and C‐ZL). Hepatic function was evaluated by measurement of serum alanine transaminase and aspartate transaminase levels, liver histopathology and electron microscopy, and hepatic mitochondrial functions. Several impaired functions of hepatic mitochondria were observed in C‐ZDF in comparison with C‐ZL rats. Melatonin treatment to ZDF rats decreases serum levels of ALT (P < 0.001), alleviates liver steatosis and vacuolation, and also mitigates diabetic‐induced mitochondrial abnormalities, glycogen, and lipid accumulation. Melatonin improves mitochondrial dysfunction in M‐ZDF rats by increasing activities of mitochondrial citrate synthase (P < 0.001) and complex IV of electron transfer chain (P < 0.05) and enhances state 3 respiration (P < 0.001), respiratory control index (RCR) (P < 0.01), and phosphorylation coefficient (ADP/O ratio) (P < 0.05). Also melatonin augments ATP production (P < 0.05) and diminishes uncoupling protein 2 levels (P < 0.001). These results demonstrate that chronic oral melatonin reduces liver steatosis and mitochondria dysfunction in ZDF rats. Therefore, it may be beneficial in the treatment of diabesity.     

Melatonin stabilizes rupture‐prone vulnerable plaques via regulating macrophage polarization in a nuclear circadian receptor RORα‐dependent manner

Rupture of vulnerable plaques is the main trigger of acute cardio‐cerebral vascular events, but mechanisms responsible for transforming a stable atherosclerotic into a vulnerable plaque remain largely unknown. Melatonin, an indoleamine hormone secreted by the pineal gland, plays pleiotropic roles in the cardiovascular system; however, the effect of melatonin on vulnerable plaque rupture and its underlying mechanisms remains unknown. Here, we generated a rupture‐prone vulnerable carotid plaque model induced by endogenous renovascular hypertension combined with low shear stress in hypercholesterolemic ApoE^?/? mice. Melatonin (10 mg/kg/d by oral administration for 9 weeks) significantly prevented vulnerable plaque rupture, with lower incidence of intraplaque hemorrhage (42.9% vs. 9.5%, P = 0.014) and of spontaneous plaque rupture with intraluminal thrombus formation (38.1% vs. 9.5%, P = 0.029). Mechanistic studies indicated that melatonin ameliorated intraplaque inflammation by suppressing the differentiation of intraplaque macrophages toward the proinflammatory M1 phenotype, and circadian nuclear receptor retinoid acid receptor‐related orphan receptor‐α (RORα) mediated melatonin‐exerted vasoprotection against vulnerable plaque instability and intraplaque macrophage polarization. Further analysis in human monocyte‐derived macrophages confirmed the role of melatonin in regulating macrophage polarization by regulating the AMPKα‐STATs pathway in a RORα‐dependent manner. In summary, our data provided the first evidence that melatonin‐RORα axis acts as a novel endogenous protective signaling pathway in the vasculature, regulates intraplaque inflammation, and stabilizes rupture‐prone vulnerable plaques.     

Systemic and transdermal melatonin administration prevents neuropathology in response to perinatal asphyxia in newborn lambs

Perinatal asphyxia remains a principal cause of infant mortality and long‐term neurological morbidity, particularly in low‐resource countries. No neuroprotective interventions are currently available. Melatonin (MLT), a potent antioxidant, anti‐inflammatory and antiapoptotic agent, offers promise as an intravenous (IV) or transdermal therapy to protect the brain. We aimed to determine the effect of melatonin (IV or transdermal patch) on neuropathology in a lamb model of perinatal asphyxia. Asphyxia was induced in newborn lambs via umbilical cord occlusion at birth. Animals were randomly allocated to melatonin commencing 30 minutes after birth (60 mg in 24 hours; IV or transdermal patch). Brain magnetic resonance spectroscopy (MRS) was undertaken at 12 and 72 hours. Animals (control n = 9; control+MLT n = 6; asphyxia n = 16; asphyxia+MLT [IV n = 14; patch n = 4]) were euthanised at 72 hours, and cerebrospinal fluid (CSF) and brains were collected for analysis. Asphyxia resulted in severe acidosis (pH 6.9 ± 0.0; lactate 9 ± 2 mmol/L) and altered determinants of encephalopathy. MRS lactate:N‐acetyl aspartate ratio was 2.5‐fold higher in asphyxia lambs compared with controls at 12 hours and 3‐fold higher at 72 hours (P < .05). Melatonin prevented this rise (3.5‐fold reduced vs asphyxia; P = .02). Asphyxia significantly increased brain white and grey matter apoptotic cell death (activated caspase‐3), lipid peroxidation (4HNE) and neuroinflammation (IBA‐1). These changes were significantly mitigated by both IV and patch melatonin. Systemic or transdermal neonatal melatonin administration significantly reduces the neuropathology and encephalopathy signs associated with perinatal asphyxia. A simple melatonin patch, administered soon after birth, may improve outcome in infants affected by asphyxia, especially in low‐resource settings.