Activity of melatonin against Leishmania infantum promastigotes by mitochondrial dependent pathway

The Role of Melatonin in the Inflammatory Process in Patients with Hyperglycemia and Leishmania Infection

Type 2 diabetes mellitus is a metabolic disorder that causes chronic high blood sugar levels, and diabetic patients are more susceptible to infections. American cutaneous leishmaniasis is an infectious disease caused by a parasite that affects the skin and mucous membranes, leading to one or multiple ulcerative lesions. Chronic inflammation and functional changes in various organs and systems, including the immune system, are the primary causes of both diseases. Melatonin, an essential immunomodulatory, antioxidant, and neuroprotective agent, can benefit many immunological processes and infectious diseases, including leishmaniasis. Although, limited reports are available on diabetic patients with leishmaniasis. The literature suggests that melatonin may play a promising role in inflammatory disorders. This study was designed to assess melatonin levels and inflammatory mediators in diabetic patients affected by leishmaniasis. Blood samples from 25 individuals were analyzed and divided into four groups: a control group (without any diseases), a Leishmania-positive group, patients with type 2 diabetes mellitus, and patients with a combination of both diseases. This study measured the serum levels of melatonin through ELISA, while IL-4 and TNF-α were measured using flow cytometry, and C-reactive protein was measured through turbidimetry. This study found that patients with leishmaniasis significantly increased TNF-α and decreased melatonin levels. However, the group of diabetic patients with leishmaniasis showed higher melatonin levels than the control group. These observations suggest that TNF-α may influence melatonin production in patients with American cutaneous leishmaniasis, potentially contributing to the inflammatory characteristics of both diseases.

Melatonin: A look at protozoal and helminths

Melatonin is a pleiotropic neurohormone found in different animal, plant, and microorganism species. It is a product resulting from tryptophan metabolism in the pineal gland and is widely known for its ability to synchronize the circadian rhythm to antitumor functions in different types of cancers. The molecular mechanisms responsible for its immunomodulatory, antioxidant and cytoprotective effects involve binding to high-affinity G protein-coupled receptors and interactions with intracellular targets that modulate signal transduction pathways. In vitro and in vivo studies have reported the therapeutic potential of melatonin in different infectious and parasitic diseases. In this review, the protective and pathophysiological roles of melatonin in fighting protozoan and helminth infections and the possible mechanisms involved against these stressors will be discussed.

Okra [Abelmoschus esculentus (L.) Moench] improved blood glucose and restored histopathological alterations in splenic tissues in a rat model with streptozotocin-induced type 1 diabetes through CD8+ T cells and NF-kβ expression

Diabetes mellitus is a complex metabolic syndrome that involves dysfunction of spleen and other lymphoid organs. Medicinal plants, including okra (Abelmoschus esculentus (L.) Moench), were used widely for diabetes treatment. Scarce data are available about the potential anti-diabetic effects of okra, the histopathological alterations in splenic tissues and the mechanistic pathways underlying this association. The current research investigated the effects of okra pod extract on the biochemical parameters and expression of CD8+ T cells and nuclear factor kappa (NF-k) B and releasing proinflammatory cytokines in spleen in streptozotocin (STZ)-induced diabetic rat models. A total of 50 mature male Wister albino rats were divided into five isolated groups; the first served as control (untreated) animals, the second (DM group) diabetes induced by STZ (at a dose of 45 mg/kg body weight, administered intraperitoneally), the third group (DM + Insulin): diabetic rats administered insulin subcutaneously (10 units/kg bw/day) daily for 4 weeks, the fourth group was administrated 400 mg/kg okra extract daily for 4 weeks, and diabetic induced rats in the fifth group were administrated 400 mg/kg okra extract daily for 4 weeks. The 2,2-diphenyl-1-picrylhydrazyl (DPPH) scavenging activity in Abelmoschus esculentus (L.) Moench was studied, and the content of phenolic compounds in okra pods was estimated using high-performance liquid chromatography. Diabetes induction led to decreased body weight, increased blood glucose levels. Capsular thickness was significantly increased, white pulp was widely dispersed, and mature lymphocytes in the periphery were also drastically decreased, with thick follicular arteries, necrosis, and depletion of lymphocytes in the germinal center. Red pulp revealed severe congestion and degenerative changes, deposition of hemosiderin granules and lymphocytic depletion. In addition, collagen fiber deposition was increased also in this group. The induction of diabetes exaggerated NF-kβ expression and mediated downregulation of the expression of CD8+ T cells in spleen tissue. Interestingly, oral administration of okra extracts post diabetes induction could mitigate and reverse such adverse effects. Altogether, our study points out the potential benefits of okra in improving blood glucose levels and restoring histopathological alterations in splenic tissues through CD8+ T cells and NF-kβ expression in a diabetic rat model.

Melatonin downregulates the increased hepatic alpha-fetoprotein expression and restores pancreatic beta cells in a streptozotocin-induced diabetic rat model: a clinical, biochemical, immunohistochemical, and descriptive histopathological study

Background

Diabetes mellitus (DM) is a chronic metabolic disorder. Hepatopathy is one of the serious effects of DM Melatonin (MT) is a potent endogenous antioxidant that can control insulin output. However, little information is available about the potential association between melatonin and hepatic alpha-fetoprotein expression in diabetes.

Objective

This study was conducted to assess the influence of MT on diabetes-related hepatic injuries and to determine how β-cells of the pancreas in diabetic rats respond to MT administration.

Materials and methods

Forty rats were assigned to four groups at random (ten animals per group). Group I served as a normal control group. Group II was induced with DM, and a single dose of freshly prepared streptozotocin (45 mg/kg body weight) was intraperitoneally injected. In Group III, rats received 10 mg/kg/day of intraperitoneal melatonin (IP MT) intraperitoneally over a period of 4 weeks. In Group IV (DM + MT), following the induction of diabetes, rats received MT (the same as in Group III). Fasting blood sugar, glycosylated hemoglobin (HbA1c), and serum insulin levels were assessed at the end of the experimental period. Serum liver function tests were performed. The pancreas and liver were examined histopathologically and immunohistochemically for insulin and alpha-fetoprotein (AFP) antibodies, respectively.

Results

MT was found to significantly modulate the raised blood glucose, HbA1c, and insulin levels induced by diabetes, as well as the decreased alanine aminotransferase (ALT) and aspartate aminotransferase (AST). Furthermore, MT attenuated diabetic degenerative changes in the pancreas and the hepatic histological structure, increased the β-cell percentage area, and decreased AFP expression in the liver tissue. It attenuated diabetes-induced hepatic injury by restoring pancreatic β-cells; its antioxidant effect also reduced hepatocyte injury.

Conclusion

Collectively, the present study confirmed the potential benefits of MT in downregulating the increased hepatic alpha-fetoprotein expression and in restoring pancreatic β-cells in a streptozotocin-induced diabetic rat model, suggesting its promising role in the treatment of diabetes.

Melatonin ameliorates serobiochemical alterations and restores the cardio-nephro diabetic vascular and cellular alterations in streptozotocin-induced diabetic rats

Melatonin possesses a wide range of pharmacological activities, including antidiabetic properties. Diabetes mellitus (DM) induces several physiopathological changes in body organs, which could be observed lately after systemic failure. In the current study, we aimed to investigate the serobiochemical changes and the histopathological picture in the diabetic heart and the kidney early before chronic complications and highlight the association between hyperglycemia, glomerular alterations, and cardiovascular changes. In addition, the role of melatonin in the treatment of cardio-nephro diabetic vascular and cellular adverse changes in streptozotocin-induced diabetic rats was also studied. A total of 40 mature Wistar albino rats were distributed into five groups; (1) control untreated rats, (2) diabetic mellitus untreated (DM) rats, in which DM was induced by the injection of streptozotocin (STZ), (3) control melatonin-treated (MLT), (4) melatonin-treated diabetic (DM + MLT) rats, in which melatonin was injected (10 mg/kg/day, i.p.) for 4 weeks, and (5) insulin-treated diabetic (DM + INS) rats. The serum biochemical analysis of diabetic STZ rats showed a significant (P < 0.05) increase in the concentrations of blood glucose, total oxidative capacity (TOC), CK-MB, endothelin-1, myoglobin, H-FABP, ALT, AST, urea, and creatinine as compared to control rats. In contrast, there was a significant (P < 0.05) decrease in serum concentration of insulin, total antioxidative capacity (TAC), total nitric oxide (TNO), and total protein level in DM rats vs. the control rats. Significant improvement in the serobiochemical parameters was noticed in both (DM + MLT) and (DM + INS) groups as compared with (DM) rats. The histological examination of the DM group revealed a disorder of myofibers, cardiomyocyte nuclei, and an increase in connective tissue deposits in between cardiac tissues. Severe congestion and dilation of blood capillaries between cardiac muscle fibers were also observed. The nephropathic changes in DM rats revealed various deteriorations in glomeruli and renal tubular cells of the same group. In addition, vascular alterations in the arcuate artery at the corticomedullary junction and interstitial congestion take place. Melatonin administration repaired all these histopathological alterations to near-control levels. The study concluded that melatonin could be an effective therapeutic molecule for restoring serobiochemical and tissue histopathological alterations during diabetes mellitus.

Melatonin ameliorates the adrenal and pancreatic alterations in streptozotocin-induced diabetic rats: Clinical, biochemical, and descriptive histopathological studies

Previous studies have demonstrated the beneficial effects of melatonin in diabetic rats. However, limited studies have been conducted on the potential effects of melatonin on the descriptive histopathological and morphometric findings in different compartments of the adrenal glands in diabetic animal models. In this study, using a streptozotocin (STZ)-induced diabetic rat model, we sought to examine histological alterations in the pancreas and adrenal glands and observe the effect of the administration of melatonin on the histopathology and morphology of the pancreas and the adrenal gland cortex and medulla that are altered by STZ-induced hyperglycemia. Rats were randomly assigned to four different groups: Group I, normal control; Group II, melatonin group (MT) (10 mg/kg/day); Group III, (diabetic STZ group), and Group IV, diabetic (STZ) + melatonin group (MT). Throughout the experiment, the animals' fasting blood sugar levels were measured. Blood was obtained to determine the animals' cumulative blood sugar levels after sacrification. For histological and morphometrical evaluations, the pancreatic and adrenal gland tissues were dissected and processed. Our results showed that diabetic rats receiving melatonin significantly (P < 0.05) improved their fasting blood sugar and cumulative blood sugar levels compared to the diabetic group not receiving melatonin. Furthermore, histopathological examinations of the pancreatic and adrenal tissues of the diabetic rats indicated the occurrence of severe histopathological and morphometric changes. Morphometric analysis of the adrenals indicated a significant increase (P < 0.05) in the thickness of the cortex zones [zona glomerulosa (ZG), zona fasciculata (ZF), and zona reticularis (ZR)] for the diabetic STZ group compared with other groups, and a significant decrease (P < 0.05) in the diameter of the in adrenal gland medullas in the diabetic STZ rats compared to the other groups. Furthermore, treatment with melatonin restored these changes in both the pancreatic and adrenal gland tissues and produced a significant (P < 0.05) improvement in the cortex and medulla thickness compared to the untreated diabetic rats. Overall, melatonin significantly reduced the hyperglycemic levels of glucose in diabetic rats and reversed the majority of histopathological alterations in the tissues of the pancreas and adrenals, demonstrating its anti-diabetic activity.

Acaricidal Properties of Four Neem Seed Extracts (Azadirachta indica) on the Camel Tick Hyalomma dromedarii (Acari: Ixodidae)

Tick infestation remains one of the major health problems that affect the productivity and comfort of camels. The control of ticks mainly relies on using chemical acaracides. Limited information is available on the potential benefits and activity of various neem extracts on Hyalomma ticks. The present study investigated the acaricidal activity of neem seed extracts at different concentrations against developmental stages of the camel tick Hyalomma dromedarii in comparison to Butox and diazinon. The acaricidal activity of three extracts, namely, hexane extract (HE), methyl chloride extract (MCE), and methanol extract (ME), of neem seeds (Azadirachta indica) were tested at varying concentrations of 5, 10, 15, and 20% on engorged H. dromedarii female ticks at days 1, 3, 5, 7, 12, 16, 20, 28, 37, and 43 after treatment (DPT). Interestingly, results of applying different neem seed extracts to engorged H. dromedarii female ticks showed that the most effective extract was hexane at concentration 20%, causing 100% mortality at 1st day post-application, while methanol extract at 20% and dichloromethane extract at 20% caused the death of all ticks at 28th day posttreatment as compared to Butox® 5.0 and Diazinon-60, which resulted in mortality of all ticks at 3 and 5 DPT, respectively. In addition, no mortality was reported with the application of aqueous extract (AE), which served as the control group. Furthermore, the neem hexane extract exhibited high efficacy against reproductive performance of female ticks, whereas no fertility or oviposition was reported at all of their concentrations. Additionally, no hatchability occurred using all neem extracts, except the aqueous extract, which showing no effect. In the present study, larvae responded more rapidly to the plant extracts, whereas mortality of all larvae was recorded at 24 h after treatment with 5% hexane. Taken together, this study pointed out that the acaricidal effect of hexane extract of neem seeds was more effective and could be economically used for controlling H. dromedarii ticks.

Insight into melatonin-mediated response and signaling in the regulation of plant defense under biotic stress

Melatonin plays a crucial role in the mitigation of plant biotic stress through induced defense responses and pathogen attenuation. Utilizing the current knowledge of signaling and associated mechanism of this phytoprotectant will be invaluable in sustainable plant disease management. Biotic stress in plants involves complex regulatory networks of various sensory and signaling molecules. In this context, the polyfunctional, ubiquitous-signaling molecule melatonin has shown a regulatory role in biotic stress mitigation in plants. The present review conceptualized the current knowledge concerning the melatonin-mediated activation of the defense signaling network that leads to the resistant or tolerant phenotype of the infected plants. Fundamentals of signaling networks involved in melatonin-induced reactive oxygen species (ROS) or reactive nitrogen species (RNS) scavenging through enzymatic and non-enzymatic antioxidants have also been discussed. Increasing evidence has suggested that melatonin acts upstream of mitogen-activated proteinase kinases in activation of defense-related genes and heat shock proteins that provide immunity against pathogen attack. Besides, the direct application of melatonin on virulent fungi and bacteria showed disrupted spore morphology, destabilization of cell ultrastructure, reduced biofilm formation, and enhanced mortality that led to attenuate disease symptoms on melatonin-treated plants. The transcriptome analysis has revealed the down-regulation of pathogenicity genes, metabolism-related genes, and up-regulation of fungicide susceptibility genes in melatonin-treated pathogens. The activation of melatonin-mediated systemic acquired resistance (SAR) through cross-talk with salicylic acid (SA), jasmonic acid (JA) has been essential for viral disease management. The high endogenous melatonin concentration has also been correlated with the up-regulation of genes involved in pathogen-associated molecular pattern (PAMP)-triggered immunity (PTI) and effector-triggered immunity (ETI). The present review highlights the versatile functions of melatonin towards direct inhibition of pathogen propagule along with active participation in mediating oxidative burst and simulating PTI, ETI and SAR responses. The hormonal cross-talk involving melatonin mediated biotic stress tolerance through defense signaling network suggests its suitability in a sustainable plant protection system.

Prognostic Value of Immunoglobulin G (IgG) Patterns by Western Blotting Immunodetection in Treated Dogs Previously Infected with Leishmania infantum

Leishmaniasis is a heterogeneous group of neglected tropical diseases with various clinical syndromes, which is caused by obligate intracellular protozoa of the genus Leishmania and transmitted by the bite of a female phlebotomine sandfly. Humans and several animal species are considered as reservoirs of the disease. Among other animal species, dogs are the most important reservoirs in a domestic environment, maintaining the endemic focus of the parasite. The behavior of the disease progression and the clinical symptoms of the disease in the infected dog is mainly associated with depressed cellular immunity and strong humoral response. This study aimed to assess the role of Western blotting in the analysis of the idiotype expression of the two main immunoglobulins (IgG1 and IgG2) in dogs that are naturally infected with Leishmania infantum (L. infantum) and treated with N-methyl meglumine antimoniate. Interestingly, for the first time, our study identified several L. infantum antigen polypeptides (14, 31, 33, 49, 64, 66, 99, and 169 kDa) that more frequently stimulate an immune reaction in recovered dogs after treatment, whereas in the non-recovered group of dogs, four antigen polypeptides of L. infantum with molecular weights of 31, 49, 66, and 115 kDa with unfavorable prognosis were identified. Clearly, these interesting findings confirm the strong association between the detected immunodominant bands and the successful recovery in treated dogs that can be used for differentiating the treated dogs from the untreated dogs, as well as the markers of a favorable or unfavorable prognosis and, as a consequence, the prediction of the clinical outcome of the disease. Likewise, these data could be helpful in the implementation of novel vaccines from the detected antigens.

Feline Leishmaniosis in Northwestern Italy: Current Status and Zoonotic Implications

Leishmaniasis remains one of the major neglected tropical diseases. The epidemiological profile of the disease comprises a wide range of hosts, including dogs and cats. Despite several studies about feline Leishmaniosis, the role of cats in disease epidemiology and its clinical impact is still debated. The present study raises awareness about the impact of leishmaniasis in cats from an endemic region in of Northwestern Italy (Liguria). A total number of 250 serum and 282 blood samples were collected from cats, then assessed for Leishmania infantum (L. infantum) serologically using western blot (WB) and molecularly using polymerase chain reaction (PCR). We also tested the association of Leishmania infection with some infectious agents like haemotropic Mycoplasma, Feline immunodeficiency virus (FIV) and Feline leukemia virus (FeLV) together with the hematobiochemical status of the examined animals. Interestingly, all tested animals were asymptomatic and out of 250 examined serum samples, 33 (13.20%) samples (confidence interval (CI) 95% 9.56-17.96%) were positive at WB for L. infantum, whereas of the 282 blood samples, 80 (28.36%) returned a positive PCR (CI 95% 23.43-33.89%). Furthermore, there was a statistical association between PCR positivity for L. infantum and some hematological parameters besides FIV infection as well as a direct significant correlation between Mycoplasma infection and WB positivity. Taken together, the present findings report high prevalence of L. infantum among cats, which reinforces the significance of such positive asymptomatic animals and confirms the very low humoral response in this species. In addition, the laboratory values provide evidence that infection by the parasite is linked to alteration of some hematological parameters and is correlated to some infectious agents. These data are of interest and suggest future research for accurate diagnosis of such zoonosis.

Melatonin Enhances the Mitochondrial Functionality of Brown Adipose Tissue in Obese-Diabetic Rats

Developing novel drugs/targets remains a major effort toward controlling obesity-related type 2 diabetes (diabesity). Melatonin controls obesity and improves glucose homeostasis in rodents, mainly via the thermogenic effects of increasing the amount of brown adipose tissue (BAT) and increases in mitochondrial mass, amount of UCP1 protein, and thermogenic capacity. Importantly, mitochondria are widely known as a therapeutic target of melatonin; however, direct evidence of melatonin on the function of mitochondria from BAT and the mechanistic pathways underlying these effects remains lacking. This study investigated the effects of melatonin on mitochondrial functions in BAT of Zücker diabetic fatty (ZDF) rats, which are considered a model of obesity-related type 2 diabetes mellitus (T2DM). At five weeks of age, Zücker lean (ZL) and ZDF rats were subdivided into two groups, consisting of control and treated with oral melatonin for six weeks. Mitochondria were isolated from BAT of animals from both groups, using subcellular fractionation techniques, followed by measurement of several mitochondrial parameters, including respiratory control ratio (RCR), phosphorylation coefficient (ADP/O ratio), ATP production, level of mitochondrial nitrites, superoxide dismutase activity, and alteration in the mitochondrial permeability transition pore (mPTP). Interestingly, melatonin increased RCR in mitochondria from brown fat of both ZL and ZDF rats through the reduction of the proton leak component of respiration (state 4). In addition, melatonin improved the ADP/O ratio in obese rats and augmented ATP production in lean rats. Further, melatonin reduced mitochondrial nitrosative and oxidative status by decreasing nitrite levels and increasing superoxide dismutase activity in both groups, as well as inhibited mPTP in mitochondria isolated from brown fat. Taken together, the present data revealed that chronic oral administration of melatonin improved mitochondrial respiration in brown adipocytes, while decreasing oxidative and nitrosative stress and susceptibility of adipocytes to apoptosis in ZDF rats, suggesting a beneficial use in the treatment of diabesity. Further research regarding the molecular mechanisms underlying the effects of melatonin on diabesity is warranted.

Hepatosplenic Protective Actions of Spirulina platensis and Matcha Green Tea Against Schistosoma mansoni Infection in Mice via Antioxidative and Anti-inflammatory Mechanisms

Schistosomiasis, a major parasitic illness, has high morbidity and negative financial effects in subtropical and tropical countries, including Egypt. The present study investigated the therapeutic effects of Spirulina platensis (SP) and matcha green tea (MGT) in Schistosoma mansoni-infected mice combined with tracing their possible antioxidant and anti-inflammatory impacts and their protective potency. A total of 60 Swiss albino mice were randomly allocated into six groups (n = 10): control group (CNT, received normal saline); SP–MGT group [received oral SP (3 g/kg bodyweight/day) plus MGT (3 g/kg bodyweight/day)]; S. mansoni group (infected with S. mansoni cercariae, 100 ± 10/mouse, using the tail immersion method); SP-infected group (infected with S. mansoni and received oral SP); MGT-infected group (received oral MGT after S. mansoni infection); and SP–MGT-infected group (received combined treatment of SP and MGT after S. mansoni infection). Treatment with SP and MGT started 4 weeks after S. mansoni infection and ended 10 weeks after. SP and MGT treatment (SP-infected and MGT-infected groups) and the combined treatment (SP–MGT-infected group) minimized the hepatic damage induced by S. mansoni; circulating alanine aminotransferase and aspartate transaminase decreased, and total protein, albumin, and globulin serum levels increased. The serum level of malondialdehyde significantly declined, and catalase, glutathione peroxidase, superoxide dismutase, and total antioxidant capacity increased in SP-infected, MGT-infected, and SP–MGT-infected groups compared with the infected group. Co-administration of SP and MGT reduced serum cytokine levels (tumor necrosis factor-alpha, interferon-gamma, and interleukin-13) and increased interleukin-10 levels after S. mansoni infection compared with the infected group. Moreover, treatment with SP and/or MGT decreased the number of granulomas in hepatic and splenic tissues compared with the infected group. Collectively, our results suggest that combined SP and MGT treatment is effective for S. mansoni infection. Liver and spleen tissue alterations were improved, the antioxidant systems were stimulated, and the inflammatory response was suppressed. Further research is recommended to investigate the mechanisms of the combined SP and MGT treatment effects to facilitate the development of novel therapies against this disease.

The emerging paradigm of calcium homeostasis as a new therapeutic target for protozoan parasites

Calcium channels (CCs), a group of ubiquitously expressed membrane proteins, are involved in many pathophysiological processes of protozoan parasites. Our understanding of CCs in cell signaling, organelle function, cellular homeostasis, and cell cycle control has led to improved insights into their structure and functions. In this article, we discuss CCs characteristics of five major protozoan parasites Plasmodium, Leishmania, Toxoplasma, Trypanosoma, and Cryptosporidium. We provide a comprehensive review of current antiparasitic drugs and the potential of using CCs as new therapeutic targets. Interestingly, previous studies have demonstrated that human CC modulators can kill or sensitize parasites to antiparasitic drugs. Still, none of the parasite CCs, pumps, or transporters has been validated as drug targets. Information for this review draws from extensive data mining of genome sequences, chemical library screenings, and drug design studies. Parasitic resistance to currently approved therapeutics is a serious and emerging threat to both disease control and management efforts. In this article, we suggest that the disruption of calcium homeostasis may be an effective approach to develop new anti-parasite drug candidates and reduce parasite resistance.

Molecular Mechanisms of Melatonin-Mediated Cell Protection and Signaling in Health and Disease

Melatonin, an endogenously synthesized indolamine, is a powerful antioxidant exerting beneficial action in many pathological conditions. Melatonin protects from oxidative stress in ischemic/reperfusion injury, neurodegenerative diseases, and aging, decreases inflammation, modulates the immune system, inhibits proliferation, counteracts the Warburg effect, and promotes apoptosis in various cancer models. Melatonin stimulates antioxidant enzymes in the cells, protects mitochondrial membrane phospholipids, especially cardiolipin, from oxidation thus preserving integrity of the membranes, affects mitochondrial membrane potential, stimulates activity of respiratory chain enzymes, and decreases the opening of mitochondrial permeability transition pore and cytochrome c release. This review will focus on the molecular mechanisms of melatonin effects in the cells during normal and pathological conditions and possible melatonin clinical applications.

Intracellular Ca2+ Signaling in Protozoan Parasites: An Overview with a Focus on Mitochondria

Ca²⁺ signaling has been involved in controling critical cellular functions such as activation of proteases, cell death, and cell cycle control. The endoplasmatic reticulum plays a significant role in Ca²⁺ storage inside the cell, but mitochondria have long been recognized as a fundamental Ca²⁺ pool. Protozoan parasites such as Plasmodium falciparum, Toxoplasma gondii, and Trypanosoma cruzi display a Ca²⁺ signaling toolkit with similarities to higher eukaryotes, including the participation of mitochondria in Ca²⁺-dependent signaling events. This review summarizes the most recent knowledge in mitochondrial Ca²⁺ signaling in protozoan parasites, focusing on the mechanism involved in mitochondrial Ca²⁺ uptake by pathogenic protists.

Treatment with melatonin induces a reduction of Toxoplasma gondii development in LLC-MK2 cells

It is known that the current treatment for toxoplasmosis causes side effects. Thus, it is essential to develop new therapies with reduced adverse effects while concurrently maintaining broad coverage and prophylactic therapy. Melatonin is a hormone that participates in the circadian cycle in vertebrates and has antioxidant, immunomodulatory, and antitumoral functions. In addition, it has been shown that melatonin can modulate immune responses and parasitic development during infection by Trypanosoma cruzi and Leishmania spp. Furthermore, studies indicate that melatonin increases the number of lymphocytes in rats infected by Toxoplasma gondii. However, there is no information on the possible effects of melatonin in T. gondii-infected host cells in vitro. This study analyzed the effects of melatonin treatment in the monkey kidney cell epithelial cell line, LLC-MK2, after infection with T. gondii. LLC-MK2 cells were infected and treated/not treated with melatonin, and the infection index was then quantified. Melatonin treatment did not alter host cell viability and was able to reduce parasite proliferation in LLC-MK2 cells at 24 and 48 h and at 6 days. Analysis by scanning electron microscopy confirmed reduction of parasite proliferation and alterations of tachyzoite shapes. Transmission electron microscopy images showed parasites with ruptured plasma membranes and cytoplasmic leakage. After treatment, parasites showed positive staining for apoptotic-like cell death. These results suggest that the use of melatonin as the lead compound for the synthesis of new compounds may constitute an alternative treatment for toxoplasmosis.

Melatonin and Leishmania amazonensis Infection Altered miR-294, miR-30e, and miR-302d Impacting on Tnf, Mcp-1, and Nos2 Expression

Leishmaniases are neglected diseases that cause a large spectrum of clinical manifestations, from cutaneous to visceral lesions. The initial steps of the inflammatory response involve the phagocytosis of Leishmania and the parasite replication inside the macrophage phagolysosome. Melatonin, the darkness-signaling hormone, is involved in modulation of macrophage activation during infectious diseases, controlling the inflammatory response against parasites. In this work, we showed that exogenous melatonin treatment of BALB/c macrophages reduced Leishmania amazonensis infection and modulated host microRNA (miRNA) expression profile, as well as cytokine production such as IL-6, MCP-1/CCL2, and, RANTES/CCL9. The role of one of the regulated miRNA (miR-294-3p) in L. amazonensis BALB/c infection was confirmed with miRNA inhibition assays, which led to increased expression levels of Tnf and Mcp-1/Ccl2 and diminished infectivity. Additionally, melatonin treatment or miR-30e-5p and miR-302d-3p inhibition increased nitric oxide synthase 2 (Nos2) mRNA expression levels and nitric oxide (NO) production, altering the macrophage activation state and reducing infection. Altogether, these data demonstrated the impact of melatonin treatment on the miRNA profile of BALB/c macrophage infected with L. amazonensis defining the infection outcome.

A Functional Analysis of the Cyclophilin Repertoire in the Protozoan Parasite Trypanosoma Cruzi

Trypanosoma cruzi is the etiological agent of Chagas disease. It affects eight million people worldwide and can be spread by several routes, such as vectorborne transmission in endemic areas and congenitally, and is also important in non-endemic regions such as the United States and Europe due to migration from Latin America. Cyclophilins (CyPs) are proteins with enzymatic peptidyl-prolyl isomerase activity (PPIase), essential for protein folding in vivo. Cyclosporin A (CsA) has a high binding affinity for CyPs and inhibits their PPIase activity. CsA has proved to be a parasiticidal drug on some protozoa, including T. cruzi. In this review, we describe the T. cruzi cyclophilin gene family, that comprises 15 paralogues. Among the proteins isolated by CsA-affinity chromatography, we found orthologues of mammalian CyPs. TcCyP19, as the human CyPA, is secreted to the extracellular environment by all parasite stages and could be part of a complex interplay involving the parasite and the host cell. TcCyP22, an orthologue of mitochondrial CyPD, is involved in the regulation of parasite cell death. Our findings on T. cruzi cyclophilins will allow further characterization of these processes, leading to new insights into the biology, the evolution of metabolic pathways, and novel targets for anti-T. cruzi control.

Synergistic anti-oomycete effect of melatonin with a biofungicide against oomycetic black shank disease

Human health, food safety, and agriculture have been threatened by oomycetic diseases caused by notorious pathogenic oomycetes. Chemical oomyceticides are the main approaches in control of pathogenic oomycetes. However, the overused chemical oomyceticides have resulted in serious environmental pollution and drug resistance. The eco-friendly bio-oomyceticides are required for sustainable development through screening synergistic drug combinations. In this study, Phytophthora nicotianae (P. nicotianae), as one of the most destructive oomycetic diseases in agriculture, was used as a model system to screen the novel bio-oomyceticides based on drug combination. The results showed that treatment of melatonin or ethylicin (IUPAC Name: 1-ethylsulfonylsulfanylethane) alone displayed similar phenotypes such as the inhibition of the hyphal growth, reduction of the cell viability, and suppression of the virulence of P. nicotianae. Importantly, melatonin and ethylicin shared the same targets of interfering with the amino acid metabolism, overexpressing apoptosis-inducing factor, and dysregulating the virulence-related genes. Furthermore, strong synergism against P. nicotianae was induced by combining melatonin with ethylicin. Under treatment of the combination of melatonin and ethylicin, the expression of genes associated with amino acid, the apoptosis-inducing factor, and the virulence-related genes was much more significantly dysregulated than that of single drug treatment. Thus, the tobacco black shank caused by P. nicotianae can be successfully controlled using the combination of melatonin and ethylicin. These observations suggest that the synergistic effect based on the combination of melatonin and ethylicin is an eco-friendly alternative for the control of the destructive oomycetic diseases.

Melatonin Attenuates Potato Late Blight by Disrupting Cell Growth, Stress Tolerance, Fungicide Susceptibility and Homeostasis of Gene Expression in Phytophthora infestans

Phytophthora infestans (P. infestans) is the causal agent of potato late blight, which caused the devastating Irish Potato Famine during 1845-1852. Until now, potato late blight is still the most serious threat to potato growth and has caused significant economic losses worldwide. Melatonin can induce plant innate immunity against pathogen infection, but the direct effects of melatonin on plant pathogens are poorly understood. In this study, we investigated the direct effects of melatonin on P. infestans. Exogenous melatonin significantly attenuated the potato late blight by inhibiting mycelial growth, changing cell ultrastructure, and reducing stress tolerance of P. infestans. Notably, synergistic anti-fungal effects of melatonin with fungicides on P. infestans suggest that melatonin could reduce the dose levels and enhance the efficacy of fungicide against potato late blight. A transcriptome analysis was carried out to mine downstream genes whose expression levels were affected by melatonin. The analysis of the transcriptome suggests that 66 differentially expressed genes involved in amino acid metabolic processes were significantly affected by melatonin. Moreover, the differentially expressed genes associated with stress tolerance, fungicide resistance, and virulence were also affected. These findings contribute to a new understanding of the direct functions of the melatonin on P. infestans and provide a potential ecofriendly biocontrol approach using a melatonin-based paradigm and application to prevent potato late blight.

The potential use of melatonin to treat protozoan parasitic infections: A review

Melatonin (N-acetyl-5-methoxytryptamine) is a circadian hormone produced in vertebrates by the pineal gland and other organs. Melatonin is believed to influence immune cells leading to modulation of the proliferative response of stimulated lymphocytes as well as cytokine production. Due to the antioxidant and immunomodulatory effects of melatonin, it is suggested that this molecule could be a therapeutic alternative agent to fight bacterial, viral, and parasitic infections by a variety of mechanisms. Herein, we review the effects of melatonin on the cell biology of protozoan parasites and host's immune response. In toxoplasmosis, African trypanosomiasis and Chagas' disease, melatonin enhances host's immune response against the parasite via regulating the secretion of inflammatory mediators. In amoebiasis, melatonin reduces the amoebic lesions as well as increasing the leukophagocytosis and the number of dead amoebae. In giardiasis, serum melatonin levels are elevated in these patients; this suggests a positive correlation between the level of melatonin and phagocytic activity in the G. duodenalis infected patients, possibly related to melatonin's immunomodulatory effect. In leishmaniasis, melatonin arrests parasite replication accompanied by releasing mitochondrial Ca²⁺ into the cytosol, increasing the level of mitochondrial nitrites as well as reducing superoxide dismutase (SOD) activity. In malaria, melatonin synchronizes the Plasmodium cell cycle via modulating cAMP-PKA and IP3-Ca²⁺ pathways. Thus, simultaneous administration of melatonin agonists or giving pharmacological doses of melatonin may be considered a novel approach for treatment of malarial infection.

Melatonin Modulates Neuronal Cell Death Induced by Endoplasmic Reticulum Stress under Insulin Resistance Condition

Insulin resistance (IR) is an important stress factor in the central nervous system, thereby aggravating neuropathogenesis and triggering cognitive decline. Melatonin, which is an antioxidant phytochemical and synthesized by the pineal gland, has multiple functions in cellular responses such as apoptosis and survival against stress. This study investigated whether melatonin modulates the signaling of neuronal cell death induced by endoplasmic reticulum (ER) stress under IR condition using SH-SY5Y neuroblastoma cells. Apoptosis cell death signaling markers (cleaved Poly [ADP-ribose] polymerase 1 (PARP), p53, and Bax) and ER stress markers (phosphorylated eIF2α (p-eIF2α), ATF4, CHOP, p-IRE1, and spliced XBP1 (sXBP1)) were measured using reverse transcription-PCR, quantitative PCR, and western blottings. Immunofluorescence staining was also performed for p-ASK1 and p-IRE1. The mRNA or protein expressions of cell death signaling markers and ER stress markers were increased under IR condition, but significantly attenuated by melatonin treatment. Insulin-induced activation of ASK1 (p-ASK1) was also dose dependently attenuated by melatonin treatment. The regulatory effect of melatonin on neuronal cells under IR condition was associated with ASK1 signaling. In conclusion, the result suggested that melatonin may alleviate ER stress under IR condition, thereby regulating neuronal cell death signaling.

Melatonin Receptor Agonists as the "Perioceutics" Agents for Periodontal Disease through Modulation of Porphyromonas gingivalis Virulence and Inflammatory Response

Aim

“Perioceutics” including antimicrobial therapy and host modulatory therapy has emerged as a vital adjunctive treatment of periodontal disease. Melatonin level was significantly reduced in patients with periodontal diseases suggesting melatonin could be applied as a potential “perioceutics” treatment of periodontal diseases. This study aims to investigate the effects of melatonin receptor agonists (melatonin and ramelteon) on Porphyromonas gingivalis virulence and Porphyromonas gingivalis-derived lipopolysaccharide (Pg-LPS)-induced inflammation.

Methods

Effects of melatonin receptor agonists on Porphyromonas gingivalis planktonic cultures were determined by microplate dilution assays. Formation, reduction, and viability of Porphyromonas gingivalis biofilms were detected by crystal violet staining and MTT assays, respectively. Meanwhile, biofilms formation was also observed by confocal laser scanning microscopy (CLSM). The effects on gingipains and hemolytic activities of Porphyromonas gingivalis were evaluated using chromogenic peptides and sheep erythrocytes. The mRNA expression of virulence and iron/heme utilization was assessed using RT-PCR. In addition, cell viability of melatonin receptor agonists on human gingival fibroblasts (HGFs) was evaluated by MTT assays. After pretreatment of melatonin receptor agonists, HGFs were stimulated with Pg-LPS and then release of cytokines (IL-6 and lL-8) was measured by enzyme-linked immunosorbent assay (ELISA).

Results

Melatonin and ramelteon did exhibit antimicrobial effects against planktonic culture. Importantly, they inhibited biofilm formation, reduced the established biofilms, and decreased biofilm viability of Porphyromonas gingivalis. Furthermore, they at sub-minimum inhibitory concentration (sub-MIC) concentrations markedly inhibited the proteinase activities of gingipains and hemolysis in a dose-dependent manner. They at sub-MIC concentrations significantly inhibited the mRNA expression of virulence factors (kgp, rgpA, rgpB, hagA, and ragA), while increasing the mRNA expression of ferritin (ftn) or hemolysin (hem). They did not show obvious cytotoxicity toward HGFs. They inhibited Pg-LPS-induced IL-6 and IL-8 secretion, which was reversed by luzindole, the melatonin receptor antagonist.

Conclusion

Melatonin receptor agonists can inhibit planktonic and biofilm growth of Porphyromonas gingivalis by affecting the virulent properties, as well as Pg-LPS-induced inflammatory response. Our study provides new evidence that melatonin receptor agonists might be useful as novel “perioceutics” agents to prevent and treat Porphyromonas gingivalis-associated periodontal diseases.

Melatonin as an antioxidant: under promises but over delivers

Melatonin is uncommonly effective in reducing oxidative stress under a remarkably large number of circumstances. It achieves this action via a variety of means: direct detoxification of reactive oxygen and reactive nitrogen species and indirectly by stimulating antioxidant enzymes while suppressing the activity of pro-oxidant enzymes. In addition to these well-described actions, melatonin also reportedly chelates transition metals, which are involved in the Fenton/Haber-Weiss reactions; in doing so, melatonin reduces the formation of the devastatingly toxic hydroxyl radical resulting in the reduction of oxidative stress. Melatonin's ubiquitous but unequal intracellular distribution, including its high concentrations in mitochondria, likely aid in its capacity to resist oxidative stress and cellular apoptosis. There is credible evidence to suggest that melatonin should be classified as a mitochondria-targeted antioxidant. Melatonin's capacity to prevent oxidative damage and the associated physiological debilitation is well documented in numerous experimental ischemia/reperfusion (hypoxia/reoxygenation) studies especially in the brain (stroke) and in the heart (heart attack). Melatonin, via its antiradical mechanisms, also reduces the toxicity of noxious prescription drugs and of methamphetamine, a drug of abuse. Experimental findings also indicate that melatonin renders treatment-resistant cancers sensitive to various therapeutic agents and may be useful, due to its multiple antioxidant actions, in especially delaying and perhaps treating a variety of age-related diseases and dehumanizing conditions. Melatonin has been effectively used to combat oxidative stress, inflammation and cellular apoptosis and to restore tissue function in a number of human trials; its efficacy supports its more extensive use in a wider variety of human studies. The uncommonly high-safety profile of melatonin also bolsters this conclusion. It is the current feeling of the authors that, in view of the widely diverse beneficial functions that have been reported for melatonin, these may be merely epiphenomena of the more fundamental, yet-to-be identified basic action(s) of this ancient molecule.

Melatonin attenuates Leishmania (L.) amazonensis infection by modulating arginine metabolism

Acute inflammatory responses induced by bacteria or fungi block nocturnal melatonin synthesis by rodent pineal glands. Here, we show Leishmania infection does not impair daily melatonin rhythm in hamsters. Remarkably, the attenuated parasite burden and lesion progression in hamsters infected at nighttime was impaired by blockage of melatonin receptors with luzindole, whereas melatonin treatment during the light phase attenuated Leishmania infection. In vitro studies corroborated in vivo observations. Melatonin treatment reduced macrophage expression of Cat-2b, Cat1, and ArgI, genes involved in arginine uptake and polyamine synthesis. Indeed, melatonin reduced macrophage arginine uptake by 40%. Putrescine supplementation reverted the attenuation of infectivity by melatonin indicating that its effect was due to the arrest of parasite replication. This study shows that the Leishmania/host interaction varies in a circadian manner according to nocturnal melatonin pineal synthesis. Our results provide new data regarding Leishmania infectiveness and show new approaches for applying agonists of melatonin receptors in Leishmaniasis therapy.

Melatonin: a well-documented antioxidant with conditional pro-oxidant actions

Melatonin (N-acetyl-5-methoxytryptamine), an indoleamine produced in many organs including the pineal gland, was initially characterized as a hormone primarily involved in circadian regulation of physiological and neuroendocrine function. Subsequent studies found that melatonin and its metabolic derivatives possess strong free radical scavenging properties. These metabolites are potent antioxidants against both ROS (reactive oxygen species) and RNS (reactive nitrogen species). The mechanisms by which melatonin and its metabolites protect against free radicals and oxidative stress include direct scavenging of radicals and radical products, induction of the expression of antioxidant enzymes, reduction of the activation of pro-oxidant enzymes, and maintenance of mitochondrial homeostasis. In both in vitro and in vivo studies, melatonin has been shown to reduce oxidative damage to lipids, proteins and DNA under a very wide set of conditions where toxic derivatives of oxygen are known to be produced. Although the vast majority of studies proved the antioxidant capacity of melatonin and its derivatives, a few studies using cultured cells found that melatonin promoted the generation of ROS at pharmacological concentrations (μm to mm range) in several tumor and nontumor cells; thus, melatonin functioned as a conditional pro-oxidant. Mechanistically, melatonin may stimulate ROS production through its interaction with calmodulin. Also, melatonin may interact with mitochondrial complex III or mitochondrial transition pore to promote ROS production. Whether melatonin functions as a pro-oxidant under in vivo conditions is not well documented; thus, whether the reported in vitro pro-oxidant actions come into play in live organisms remains to be established.