Pinealectomy or light exposure exacerbates biliary damage and liver fibrosis in cholestatic rats through decreased melatonin synthesis

Mapping the evolution of liver aging research: A bibliometric analysis

BACKGROUND

With the increasing of the global aging population, healthy aging and prevention of age-related diseases have become increasingly important. The liver, a vital organ involved in metabolism, detoxification, digestion, and immunity, holds a pivotal role in the aging process of organisms. Although extensive research on liver aging has been carried out, no bibliometric analysis has been conducted to evaluate the scientific progress in this area.

AIM

To analyze basic knowledge, development trends, and current research frontiers in the field via bibliometric methods.

METHODS

We conducted bibliometric analyses via a range of analytical tools including Python, the bibliometrix package in R, CiteSpace, and VOSviewer. We retrieved publication data on liver aging research from the Web of Science Core Collection Database. A scientific knowledge map was constructed to display the contributions from different authors, journals, countries, institutions, as well as patterns of co-occurrence keywords and co-cited references. Additionally, gene regulation pathways associated with liver aging were analyzed via the STRING database.

RESULTS

We identified 4288 articles on liver aging, authored by 24034 contributors from 4092 institutions across 85 countries. Notably, the years 1991 and 2020 presented significant bursts in publication output. The United States led in terms of publications (n = 1008, 25.1%), citations (n = 55205), and international collaborations (multiple country publications = 214). Keywords such as “lipid metabolism”, “fatty liver disease”, “inflammation”, “liver fibrosis” and “target” were prominent, highlighting the current research hotspots. Notably, the top 64 genes, each of which appeared in at least 8 articles, were involved in pathways essential for cell survival and aging, including the phosphatidylinositol 3-kinase/protein kinase B, Forkhead box O and p53 signaling pathways.

CONCLUSION

This study highlights key areas of liver aging and offers a comprehensive overview of research trends, as well as insights into potential value for collaborative pursuits and clinical implementations.

Hepatic inflammation, ballooning, and pyknosis caused by LED light exposure in a mouse model, with differential effects by age and gender

Light-emitting diode (LED) is commonly used in lighting and digital devices in modern life, which delivers higher levels of blue light than other light sources. Previous work indicated that exposure to blue lights increases serum oxidative stress and affects hepatic functions in animals. However, the detailed hepatic pathogenesis caused by blue lights remains largely elusive. This study investigated the characteristics of hepatic injuries caused by LED light exposure in a mouse model. C57BL/6 mice were exposed the LED lights at 1000 lux, 12 h per day for 45 days or at 4500 lux, 1 h per day for 7 days. The mice were aged 8 weeks or 36 weeks in both genders and maintained under a 12 h light/dark cycle without alteration of diet pattern. Liver tissue sections were obtained for hematoxylin and eosin (H&E) and immunohistochemical staining. The mice with 1000 lux exposure displayed severe liver injuries, including inflammation, ballooning, and pyknosis, which were found to a lesser extent in the 4500 lux mice, and aging aggravated the hepatic injuries. The hepatocellular ballooning was found more severe in the males than the females. In contrast, the females expressed the F4/80 and TNF-α inflammatory markers more evidently. Taken together, LED light exposure may have detrimental effects on liver health, particularly in vulnerable groups such as the elderly and the females with excessive exposure to LED lights, even if they maintain a normal diet and regular light/dark cycles. The potential risk should be considered by both the clinicians and the public.

Chronobiology of Cancers in the Liver and Gut

Circadian rhythms dictate the timing of cellular and organismal physiology to maintain homeostasis. Within the liver and gut, circadian rhythms influence lipid and glucose homeostasis, xenobiotic metabolism, and nutrient absorption. Disruption of this orchestrated timing is known to negatively impact human health and contribute to disease progression, including carcinogenesis. Dysfunctional core clock timing has been identified in malignant growths and may be used as a molecular signature of disease progression. Likewise, the circadian clock and its downstream effectors also represent potential for novel therapeutic targets. Here, the role of circadian rhythms in the pathogenesis of cancers of the liver and gut will be reviewed, and chronotherapy and chronopharmacology will be explored as potential treatment options.

Crocin treatment exerts anti-inflammatory and anti-oxidative effects in liver tissue damage of pinealectomized diabetic rats

Diabetes mellitus (DM) is a chronic metabolic disorder with an increasing global prevalence that leads to significant morbidity and mortality. The liver plays a vital role in glycemic regulation in physiological and pathological conditions such as DM. Free radical formation and inhibition of antioxidant defense systems play a role in the liver damage pathogenesis in diabetic patients The antioxidant, anti-diabetic, anti-inflammatory, and radical scavenging properties of crocin are known. This study was designed to determine the possible protective effects of crocin against liver tissue damage in pinealectomized diabetic rats. Sixty rats were divided into six groups: Control, Sham+streptozotocin (STZ), Pinealectomy (PINX), PINX+STZ, PINX+Crocin, and PINX+STZ+Crocin. PNX procedure was carried out on the first day of the experiment. Intraperitoneal (i.p.) injection of 50 mg/kg STZ was performed on the 30th day of the experiment to induce DM. Crocin (50 mg/kg; i.p.) was applied for 15 days after the pinealectomy procedure and induction of DM. Crocin decreased the markers (alanine aminotransferase (ALT), aspartate aminotransferase (AST), alkaline phosphatase (ALP), interleukin-1β (IL-1β), and malondialdehyde (MDA)) of liver damage and increased antioxidant enzyme levels and tissue total antioxidant status. Histological results showed that the administration of crocin exhibited a protective effect against liver damage caused by STZ. These results indicate that crocin evidence protection against liver injury caused by STZ.

The role of light pollution in mammalian metabolic homeostasis and its potential interventions: A critical review

Irregular or unnatural artificial light causes severe environmental stress on the survival and health of organisms, which is rapidly becoming a widespread new type of environmental pollution. A series of disruptive behaviors to body homeostasis brought about by light pollution, including metabolic abnormalities, are likely to be the result of circadian rhythm disturbances. Recently, the proposed role of light pollution in metabolic dysregulation has accelerated it into an emerging field. Hence, the regulatory role of light pollution in mammalian metabolic homeostasis is reviewed in this contribution. Light at night is the most widely affected type of light pollution, which disrupts metabolic homeostasis largely due to its disruption of daily food intake patterns, alterations of hormone levels such as melatonin and glucocorticoids, and changes in the rhythm of inflammatory factor production. Besides, light pollution impairs mammalian metabolic processes in an intensity-, photoperiod-, and wavelength-dependent manner, and is also affected by species, gender, and diets. Nevertheless, metabolic disorders triggered by light pollution are not irreversible to some extent. Potential interventions such as melatonin supplementation, recovery to the LD cycle, time-restricted feeding, voluntary exercise, wearing blue light-shied goggles, and bright morning light therapy open a bright avenue to prevent light pollution. This work will help strengthen the relationship between light information and metabolic homeostasis and provide new insights for the better prevention of metabolic disorders and light pollution.

Prolonged Administration of Melatonin Ameliorates Liver Phenotypes in Cholestatic Murine Model

BACKGROUND & AIMS

Primary sclerosing cholangitis (PSC) is characterized by biliary senescence and hepatic fibrosis. Melatonin exerts its effects by interacting with Melatonin receptor 1 and 2 (MT1/MT2) melatonin receptors. Short-term (1 wk) melatonin treatment reduces a ductular reaction and liver fibrosis in bile duct-ligated rats by down-regulation of MT1 and clock genes, and in multidrug resistance gene 2 knockout (Mdr2^-/-) mice by decreased miR200b-dependent angiogenesis. We aimed to evaluate the long-term effects of melatonin on liver phenotype that may be mediated by changes in MT1/clock genes/miR200b/maspin/glutathione-S transferase (GST) signaling.

METHODS

Male wild-type and Mdr2^-/- mice had access to drinking water with/without melatonin for 3 months. Liver damage, biliary proliferation/senescence, liver fibrosis, peribiliary inflammation, and angiogenesis were measured by staining in liver sections, and by quantitative polymerase chain reaction and enzyme-linked immunosorbent assay in liver samples. We confirmed a link between MT1/clock genes/miR200b/maspin/GST/angiogenesis signaling by Ingenuity Pathway Analysis software and measured liver phenotypes and the aforementioned signaling pathway in liver samples from the mouse groups, healthy controls, and PSC patients and immortalized human PSC cholangiocytes.

RESULTS

Chronic administration of melatonin to Mdr2^-/- mice ameliorates liver phenotypes, which were associated with decreased MT1 and clock gene expression.

CONCLUSIONS

Melatonin improves liver histology and restores the circadian rhythm by interaction with MT1 through decreased angiogenesis and increased maspin/GST activity.

Beneficial effects of melatonin on liver fibrosis: A systematic review of current biological evidence

Hepatic fibrosis is a reversible response to either acute or chronic cellular injury from a wide variety of etiologies, characterized by excessive deposition of extracellular matrix resulting in liver dysfunction and cirrhosis. Melatonin (N‐acetyl‐5‐methoxytryptamine), the main product secreted by the pineal gland, is a multitasking indolamine with important physiological functions such as anti‐inflammatory and antioxidant actions, modulation of circadian rhythms, and immune system enhancement. Among the numerous biological activities of melatonin, its antifibrotic effects have received increasingly more attention. In this study, we performed a systematic review of publications of the last 10 years evaluating the mechanisms of action of melatonin against liver fibrosis. The study protocol was registered at PROSPERO (CRD42022304744). Literature research was performed employing PubMed, Scopus, and Web of Science (WOS) databases, and after screening, 29 articles were included. Results from the selected studies provided denoted the useful actions of melatonin on the development, progression, and evolution of liver fibrosis. Melatonin antifibrotic effects in the liver involved the reduction of profibrogenic markers and modulation of several cellular processes and molecular pathways, mainly acting as an antioxidant and anti‐inflammatory agent. In addition, the indolamine influenced different molecular processes, such as hepatocyte apoptosis, modulation of autophagy and mitophagy, restoration of circadian rhythms, and modulation of microRNAs, among others. Although some limitations have been found regarding variability in the study design, the findings here summarized display the potential role of melatonin in ameliorating the development of liver fibrosis and its possible progression to liver cirrhosis and hepatocarcinoma.

Melatonin receptor 1A, but not 1B, knockout decreases biliary damage and liver fibrosis during cholestatic liver injury

BACKGROUND AND AIMS

Melatonin reduces biliary damage and liver fibrosis in cholestatic models by interaction with melatonin receptors 1A (MT1) and 1B (MT2). MT1 and MT2 can form heterodimers and homodimers, but MT1 and MT2 can heterodimerize with the orphan receptor G protein-coupled receptor 50 (GPR50). MT1/GPR50 dimerization blocks melatonin binding, but MT2/GPR50 dimerization does not affect melatonin binding. GPR50 can dimerize with TGFβ receptor type I (TGFβRI) to activate this receptor. We aimed to determine the differential roles of MT1 and MT2 during cholestasis.

APPROACH AND RESULTS

Wild-type (WT), MT1 knockout (KO), MT2KO, and MT1/MT2 double KO (DKO) mice underwent sham or bile duct ligation (BDL); these mice were also treated with melatonin. BDL WT and multidrug resistance 2 KO (Mdr2^-/- ) mice received mismatch, MT1, or MT2 Vivo-Morpholino. Biliary expression of MT1 and GPR50 increases in cholestatic rodents and human primary sclerosing cholangitis (PSC) samples. Loss of MT1 in BDL and Mdr2^-/- mice ameliorated biliary and liver damage, whereas these parameters were enhanced following loss of MT2 and in DKO mice. Interestingly, melatonin treatment alleviated BDL-induced biliary and liver injury in BDL WT and BDL MT2KO mice but not in BDL MT1KO or BDL DKO mice, demonstrating melatonin's interaction with MT1. Loss of MT2 or DKO mice exhibited enhanced GPR50/TGFβR1 signaling, which was reduced by loss of MT1.

CONCLUSIONS

Melatonin ameliorates liver phenotypes through MT1, whereas down-regulation of MT2 promotes liver damage through GPR50/TGFβR1 activation. Blocking GPR50/TGFβR1 binding through modulation of melatonin signaling may be a therapeutic approach for PSC.

Melatonin prevents oxidative stress, inflammatory activity, and DNA damage in cirrhotic rats

BACKGROUND

Cirrhosis is an important health problem characterized by a significant change in liver parenchyma. In animals, this can be reproduced by an experimental model of bile duct ligation (BDL). Melatonin (MLT) is a physiological hormone synthesized from serotonin that has been studied for its beneficial properties, including its antioxidant potential.

AIM

To evaluate MLT’s effects on oxidative stress, the inflammatory process, and DNA damage in an experimental model of secondary biliary cirrhosis.

METHODS

Male Wistar rats were divided into 4 groups: Control (CO), CO + MLT, BDL, and BDL + MLT. MLT was administered (20 mg/kg) daily beginning on day 15 after biliary obstruction. On day 29 the animals were killed. Blood samples, liver tissue, and bone marrow were collected for further analysis.

RESULTS

BDL caused changes in biochemical and histological parameters and markers of inflammatory process. Thiobarbituric acid (0.46 ± 0.01) reactive substance levels, superoxide dismutase activity (2.30 ± 0.07) and nitric oxide levels (2.48 ± 0.36) were significantly lower (P < 0.001) n the groups that received MLT. DNA damage was also lower (P < 0.001) in MLT-treated groups (171.6 ± 32.9) than the BDL-only group (295.5 ± 34.8). Tissue damage and the expression of nuclear factor kappa B, interleukin-1β, Nrf2, NQO1 and Hsp70 were significantly lower in animals treated with MLT (P < 0.001).

CONCLUSION

When administered to rats with BDL-induced secondary biliary cirrhosis, MLT effectively restored the evaluated parameters.

The Apelin-Apelin Receptor Axis Triggers Cholangiocyte Proliferation and Liver Fibrosis During Mouse Models of Cholestasis

BACKGROUND AND AIMS

Apelin (APLN) is the endogenous ligand of its G protein-coupled receptor, apelin receptor (APJ). APLN serum levels are increased in human liver diseases. We evaluated whether the APLN-APJ axis regulates ductular reaction and liver fibrosis during cholestasis.

APPROACH AND RESULTS

We measured the expression of APLN and APJ and serum APLN levels in human primary sclerosing cholangitis (PSC) samples. Following bile duct ligation (BDL) or sham surgery, male wild-type (WT) mice were treated with ML221 (APJ antagonist) or saline for 1 week. WT and APLN^-/- mice underwent BDL or sham surgery for 1 week. Multidrug resistance gene 2 knockout (Mdr2^-/- ) mice were treated with ML221 for 1 week. APLN levels were measured in serum and cholangiocyte supernatants, and cholangiocyte proliferation/senescence and liver inflammation, fibrosis, and angiogenesis were measured in liver tissues. The regulatory mechanisms of APLN-APJ in (1) biliary damage and liver fibrosis were examined in human intrahepatic biliary epithelial cells (HIBEpiCs) treated with APLN and (2) hepatic stellate cell (HSC) activation in APLN-treated human HSC lines (HHSteCs). APLN serum levels and biliary expression of APLN and APJ increased in PSC samples. APLN levels were higher in serum and cholangiocyte supernatants from BDL and Mdr2^-/- mice. ML221 treatment or APLN^-/- reduced BDL-induced and Mdr2^-/- -induced cholangiocyte proliferation/senescence, liver inflammation, fibrosis, and angiogenesis. In vitro, APLN induced HIBEpiC proliferation, increased nicotinamide adenine dinucleotide phosphate oxidase 4 (Nox4) expression, reactive oxygen species (ROS) generation, and extracellular signal-regulated kinase (ERK) phosphorylation. Pretreatment of HIBEpiCs with ML221, diphenyleneiodonium chloride (Nox4 inhibitor), N-acetyl-cysteine (NAC, ROS inhibitor), or PD98059 (ERK inhibitor) reduced APLN-induced cholangiocyte proliferation. Activation of HHSteCs was induced by APLN but reduced by NAC.

CONCLUSIONS

The APLN-APJ axis induces cholangiocyte proliferation through Nox4/ROS/ERK-dependent signaling and HSC activation through intracellular ROS. Modulation of the APLN-APJ axis may be important for managing cholangiopathies.

The Role of Melatonin, IL-8 and IL-10 in Intrahepatic Cholestasis of Pregnancy

INTRODUCTION

Intrahepatic cholestasis of pregnancy is a pregnancy-specific liver disease that usually emerges during the third trimester of pregnancy. It is characterized by itching and elevated serum total bile acid levels, and it may lead to severe fetal complications. This study aimed to investigate the role of interleukin-8, a pro-inflammatory cytokine; interleukin-10, an anti-inflammatory cytokine; and melatonin in intrahepatic cholestasis of pregnancy.

MATERIALS AND METHODS

This prospective, case-controlled study was conducted with 51 women with intrahepatic cholestasis of pregnancy (40 mild and 11 severe cases) and 43 healthy pregnant women. Serum interleukin-8, interleukin-10, and melatonin levels were evaluated.

RESULTS

Melatonin and interleukin -10 were significantly lower in subjects with intrahepatic cholestasis of pregnancy (p=0.001; p=0.001, respectively p<0.05). Interleukin-8 levels were found to be significantly higher in the cholestasis group than control group (p=0.001, p<0.05).

CONCLUSIONS

Because interleukin-8, interleukin-10, and melatonin were found to be significantly correlated with intrahepatic cholestasis of pregnancy, we believe this finding could shed light on the etiology of the disease.

Pineal gland protects against chemically induced oral carcinogenesis and inhibits tumor progression in rats

Clinical investigations suggest that melatonin suppression and circadian dysfunction may be related to cancer development in shift workers. Studies also show that melatonin suppression after pinealectomy increases cancer incidence in preclinical models. However, no study evaluated the influence of pinealectomy on oral cancer development. In the current study, we investigated the effects of pinealectomy on oral squamous cell carcinoma (OSCC) occurrence and progression in rats. Rats submitted to sham surgery were used as control. Pinealectomy promoted an increase of 140% in OSCC occurrence when compared to sham animals. Tumors from pinealectomized rats displayed a higher volume and thickness than the tumors from sham-operated animals. Pinealectomy induced atrophy of the epithelium adjacent to the oral lesions. Pinealectomized rats showed higher mean number of tumor-associated macrophages and eosinophils in the invasive front of OSCC. In addition, nuclear overexpression of ERK1/2 and p53 was also observed in the front of carcinomas from pinealectomized rats. These results reveal that pineal gland plays a protective role against oral carcinogenesis. The melatonin suppression caused by the pinealectomy might contribute to oral cancer development by acting on ERK1/2 and p53 pathways and regulating tumor inflammation.

Melatonin and alcohol-related disorders

This review concerns the current knowledge of melatonin and alcohol-related disorders. Chronobiological effects of ethanol are related to melatonin suppression and in relation to inflammation, stress, free radical scavenging, autophagy and cancer risk. It is postulated that both alcohol- and inflammation-induced production of reactive oxygen species (ROS) alters cell membrane properties leading to tissue dysfunction and, subsequent further ROS production. Lysosomal enzymes are often used to assess the relationships between intensified inflammation states caused by alcohol abuse and oxidative stress as well as level of tissue damage estimated by the increased release of cellular enzymes into the extracellular space. Studies have established a link between alcoholism and desynchronosis (circadian disruption). Desynchronosis results from the disorganization of the body's circadian time structure and is an aspect of the pathology of chronic alcohol intoxication. The inflammatory conditions and the activity of lysosomal enzymes in acute alcohol poisoning or chronic alcohol-dependent diseases are in most cases interrelated. Inflammation can increase the activity of lysosomal enzymes, which can be regarded as a marker of lysosomal dysfunction and abnormal cellular integrity. Studies show alcohol toxicity is modulated by the melatonin (Mel) circadian rhythm. This hormone, produced by the pineal gland, is the main regulator of 24 h (sleep-wake cycle) and seasonal biorhythms. Mel exhibits antioxidant properties and may be useful in the prevention of oxidative stress reactions known to be responsible for alcohol-related diseases. Naturally produced Mel and exogenous sources in food can act in free radical reactions and activate the endogenous defense system. Mel plays an important role in the normalization of the post-stress state by its influence on neurotransmitter systems and the synchronization of circadian rhythms. Acting simultaneously on the neuroendocrine and immune systems, Mel optimizes homeostasis and provides protection against stress. Abbreviations: ROS, reactive oxygen species; Mel, melatonin; SRV, resveratrol; NF-κB, nuclear factor kappa-light-chain-enhancer of activated B cells; ANT, arylalkylamine-N-acetyltransferase; EC cells, gastrointestinal enterochromaffin cells; MT1, melatonin high-affinity nanomolecular receptor site; MT2, melatonin low-affinity nanomolecular receptor site; ROR/RZR, orphan nuclear retinoid receptors; SOD, superoxide dismutase; CAT, catalase; GPx, glutathione peroxidase; GR, glutathione reductase; GSH, reduced form of glutathione; GSSG, oxidized form of glutathione; TAC, total antioxidant capacity; ONOO∙^-, peroxynitrite radical; NCAM, neural cell adhesion molecules; LPO, lipid peroxidation; α-KG, α-ketoglutarate, HIF-1α, Hypoxia-inducible factor 1-α, IL-2, interleukin-2; HPA axis, hypothalamic-pituitary-adrenal axis; Tph1, tryptophan hydroxylase 1; AA-NAT, arylalkylamine-N-acetyltransferase; AS-MT, acetylserotonin O-methyltransferase; NAG, N-acetyl-beta-D-glucosaminidase; HBA1c glycated hemoglobin; LPS, lipopolysaccharide; AAP, alanyl-aminopeptidase; β-GR, β-glucuronidase; β-GD, β-galactosidase; LAP, leucine aminopeptidase.

Melatonin and circadian rhythms in liver diseases: Functional roles and potential therapies

Circadian rhythms and clock gene expressions are regulated by the suprachiasmatic nucleus in the hypothalamus, and melatonin is produced in the pineal gland. Although the brain detects the light through retinas and regulates rhythms and melatonin secretion throughout the body, the liver has independent circadian rhythms and expressions as well as melatonin production. Previous studies indicate the association between circadian rhythms with various liver diseases, and disruption of rhythms or clock gene expression may promote liver steatosis, inflammation, or cancer development. It is well known that melatonin has strong antioxidant effects. Alcohol drinking or excess fatty acid accumulation produces reactive oxygen species and oxidative stress in the liver leading to liver injuries. Melatonin administration protects these oxidative stress-induced liver damage and improves liver conditions. Recent studies have demonstrated that melatonin administration is not limited to antioxidant effects and it has various other effects contributing to the management of liver conditions. Accumulating evidence suggests that restoring circadian rhythms or expressions as well as melatonin supplementation may be promising therapeutic strategies for liver diseases. This review summarizes recent findings for the functional roles and therapeutic potentials of circadian rhythms and melatonin in liver diseases.

Constant Light Exerted Detrimental Cardiovascular Effects Through Sympathetic Hyperactivity in Normal and Heart Failure Rats

It has been documented that constant light exposure exerts complicated cardiovascular effects. However, a mounting collection of conflicting results did not make it any easier for researchers and physicians to consider the role of light on cardiovascular function. This study was designed to investigate how constant light exposure (24 h light/day) influences the cardiac function in normal and heart-failure (HF) rats. In normal rats, two groups of SD rats were accustomed in 12 h light/12 h dark (LD) or 24 h light (constant light, CL) for 4 weeks. In HF rats which was induced by myocardial infarction (MI) was let recover in LD for 4 weeks. Interestingly, compared with rats in LD environment (ejection fraction, EF%: 93.64 ± 2.02 in LD, 14.62 ± 1.53 in HF-LD), constant light (2 weeks) weakened the cardiac function in normal and HF rats (EF%: 79.42 ± 2.91 in CL, 11.50 ± 1.08 in HF-CL). The levels of renal sympathetic nerve activity and c-fos expression in the rostral ventrolateral medulla (RVLM), a key region controlling sympathetic outflow, were significantly increased in normal and HF rats after constant light (RSNA, Max%: 8.64 ± 0.48 in LD, 20.02 ± 1.24 in CL, 20.10 ± 1.16 in HF-LD, 26.82 ± 1.69 in HF-CL). In conclusion, it is suggested that constant light exposure exerts detrimental cardiovascular effects, which may be associated with the RVLM-related sympathetic hyperactivity.

Melatonin decreases cocaine-induced locomotor activity in pinealectomized rats

Objective:

Several studies have shown that the time of day regulates the reinforcing effects of cocaine. Additionally, melatonin and its MT₁ and MT₂ receptors have been found to participate in modulation of the reinforcing effects of such addictive drugs as cocaine. Loss of the diurnal variation in cocaine-induced locomotor sensitization and cocaine-induced place preference has been identified in pinealectomized mice. In addition, several studies in rodents have shown that administration of melatonin decreased the reinforcing effects of cocaine. The objective of this study was to evaluate the effect of melatonin on cocaine-induced locomotor activity in pinealectomized rats at different times of day (zeitgeber time [ZT]4, ZT10, ZT16, and ZT22).

Methods:

Naïve, pinealectomized Wistar rats received cocaine at different times of day. Melatonin was administered 30 min before cocaine; luzindole was administered 15 min prior to melatonin and 45 min before cocaine. After administration of each treatment, locomotor activity for each animal was recorded for a total of 30 min. Pinealectomy was confirmed at the end of the experiment through melatonin quantitation by ELISA.

Results:

Cocaine-induced locomotor activity varied according to the time of day. Continuous lighting and pinealectomy increased cocaine-induced locomotor activity. Melatonin administration decreased cocaine-induced locomotor activity in naïve and pinealectomized rats at different times of day. Luzindole blocked the melatonin-induced reduction in cocaine-induced locomotor activity in pinealectomized rats.

Conclusion:

Given its ability to mitigate various reinforcing effects of cocaine, melatonin could be a useful therapy for cocaine abuse.

Possible application of melatonin treatment in human diseases of the biliary tract

Melatonin was discovered in 1958 by Aaron Lerner. Its name comes from the ability of melatonin to change the shape of amphibian melanophores from stellate to roundish. Starting from the 1980s, the role of melatonin in the regulation of mammalian circadian and seasonal clocks has been elucidated. Presently, several other effects have been identified in different organs. For example, the beneficial effects of melatonin in models of liver damage have been described. This review gives first a general background on experimental and clinical data on the use of melatonin in liver damage. The second part of the review focuses on the findings related to the role of melatonin in biliary functions, suggesting a possible use of melatonin therapy in human diseases of the biliary tree.