Distinct roles of N-acetyl and 5-methoxy groups in the antiproliferative and neuroprotective effects of melatonin

Effects of melatonin on planaria head regeneration are dependent on both timing and duration of exposure

Melatonin is a multifunctional biomolecule with demonstrated stimulatory, inhibitory, and antioxidant effects, including both receptor-mediated and receptor-independent mechanisms of action. One of its more perplexing effects is the disruption of regeneration in planaria. Head regeneration in planaria is a remarkable phenomenon in which stem cells (neoblasts) migrate to the wound site, proliferate, then differentiate into all functional tissue types within days of injury. We investigated how both the timing and duration of melatonin exposure affect head regeneration in the planaria Phagocata gracilis (Haldeman). Our results demonstrate that P. gracilis is capable of recovery from the melatonin-induced delay of regeneration and reveal the time required to recover to control levels. Further, we found evidence of regenerative stage-specific responses to discontinuous melatonin exposure, including non-inhibitory effects. Further exploration of melatonin's effects on regeneration can be targeted to specific regenerative processes, and the possibility of multiple mechanisms of action should be recognized.

Melatonin attenuates scopolamine-induced cognitive dysfunction through SIRT1/IRE1α/XBP1 pathway

BACKGROUND

The prevalence of dementia around the world is increasing, and these patients are more likely to have cognitive impairments, mood and anxiety disorders (depression, anxiety, and panic disorder), and attention deficit disorders over their lifetime. Previous studies have proven that melatonin could improve memory loss, but its specific mechanism is still confused.

METHODS

In this study, we used in vivo and in vitro models to examine the neuroprotective effect of melatonin on scopolamine (SCOP)-induced cognitive dysfunction. The behavioral tests were performed. 18F-FDG PET imaging was used to assess the metabolism of the brain. Protein expressions were determined through kit detection, Western blot, and immunofluorescence. Nissl staining was conducted to reflect neurodegeneration. MTT assay and RNAi transfection were applied to perform the in vitro experiments.

RESULTS

We found that melatonin could ameliorate SCOP-induced cognitive dysfunction and relieve anxious-like behaviors or HT22 cell damage. 18F-FDG PET-CT results showed that melatonin could improve cerebral glucose uptake in SCOP-treated mice. Melatonin restored the cholinergic function, increased the expressions of neurotrophic factors, and ameliorated oxidative stress in the brain of SCOP-treated mice. In addition, melatonin upregulated the expression of silent information regulator 1 (SIRT1), which further relieved endoplasmic reticulum (ER) stress by decreasing the expression of phosphorylate inositol-requiring enzyme (p-IRE1α) and its downstream, X-box binding protein 1 (XBP1).

CONCLUSIONS

These results indicated that melatonin could ameliorate SCOP-induced cognitive dysfunction through the SIRT1/IRE1α/XBP1 pathway. SIRT1 might be the critical target of melatonin in the treatment of dementia.

Cellular and molecular mechanisms of aflatoxin B1-mediated neurotoxicity: The therapeutic role of natural bioactive compounds

Aflatoxin B1 (AFB1), a dietary toxin from the mold Aspergillus species, is well acknowledged to elicit extra-hepatic toxicity in both animals and humans. The neurotoxicity of AFB1 has become a global public health concern. Contemporary research on how AFB1 enters the brain to elicit neuronal dysregulation leading to noxious neurological outcomes has increased greatly in recent years. The current review discusses several neurotoxic outcomes and susceptible targets of AFB1 toxicity at cellular, molecular and genetic levels. Specifically, neurotoxicity studies involving the use of brain homogenates, neuroblastoma cell line IMR-32, human brain microvascular endothelial cells, microglial cells, and astrocytes, as well as mammalian and non-mammalian models to unravel the mechanisms associated with AFB1 exposure are highlighted. Further, some naturally occurring bioactive compounds with compelling therapeutic effects on AFB1-induced neurotoxicity are reviewed. In conclusion, available data from literature highlight AFB1 as a neurotoxin and its possible pathological contribution to neurological disorders. Further mechanistic studies aimed at discovering and developing effective therapeutics for AFB1 neurotoxicity is warranted.

Melatonin and Mesenchymal Stem Cells as a Key for Functional Integrity for Liver Cancer Treatment

Hepatocellular carcinoma (HCC) is the most common hepatobiliary malignancy with limited therapeutic options. On the other hand, melatonin is an indoleamine that modulates a variety of potential therapeutic effects. In addition to its important role in the regulation of sleep–wake rhythms, several previous studies linked the biologic effects of melatonin to various substantial endocrine, neural, immune and antioxidant functions, among others. Furthermore, the effects of melatonin could be influenced through receptor dependent and receptor independent manner. Among the other numerous physiological and therapeutic effects of melatonin, controlling the survival and differentiation of mesenchymal stem cells (MSCs) has been recently discussed. Given its controversial interaction, several previous reports revealed the therapeutic potential of MSCs in controlling the hepatocellular carcinoma (HCC). Taken together, the intention of the present review is to highlight the effects of melatonin and mesenchymal stem cells as a key for functional integrity for liver cancer treatment. We hope to provide solid piece of information that may be helpful in designing novel drug targets to control HCC.

N-Heterocyclic Carbenes Derived from Guanosine: Synthesis and Evidences of Their Antiproliferative Activity

Palladium(II) and platinum(II) complexes bearing N-heterocyclic carbenes derived from guanosine are synthesized via oxidative addition, followed by protonation in the presence of acid. Cytotoxicity of the compounds is evaluated in several cell lines. Compounds 2a, 2b, and 3a are selective for glioblastoma U251 cells and are nontoxic toward healthy human embryonic kidney (HEK293) cells.

Metabolic Biomarkers for Prognostic Prediction of Pre-diabetes: results from a longitudinal cohort study

To investigate the metabolic biomarkers of predicting the transition from pre-diabetes (pre-DM) to normal glucose regulation (NGR) and diabetes (DM) in a longitudinal cohort study. 108 participants with pre-DM were followed up for ten years and divided into 3 groups according to different glycemic outcomes. 20 participants progressed to DM, 20 regressed to NGR, and 68 remained at pre-DM. Alterations in plasma metabolites in these groups were evaluated by untargeted ultra-performance liquid chromatography-quadrupole time-of-flight mass spectrometry (UPLC-QTOF-MS). Twenty three metabolites related to glycerophospholipid metabolism, oxidation and antioxidation were associated with the process from pre-DM to NGR, while twenty two metabolites related to amino acid metabolism, glycerophospholipid metabolism and mitochondrial β-oxidation played important roles in the progression to DM. Results from stepwise logistic regression analysis showed that five biomarkers (20-Hydroxy-leukotriene E4, Lysopc(20:4), 5-methoxytryptamine, Endomorphin-1, Lysopc(20:3)) were good prediction for the restoration to NGR, and five biomarkers (Iso-valeraldehyde, linoleic acid, Lysopc(18:1), 2-Pyrroloylglycine, Dityrosine) for the development of DM. The findings suggest that the combination of these potential metabolites may be used for the prognosis of pre-DM. Targeting the pathways that involved in these prognostic biomarkers would be beneficial for the regression to NGR and the early prevention of DM among pre-DM.

Dietary Sources and Bioactivities of Melatonin

Insomnia is a serious worldwide health threat, affecting nearly one third of the general population. Melatonin has been reported to improve sleep efficiency and it was found that eating melatonin-rich foods could assist sleep. During the last decades, melatonin has been widely identified and qualified in various foods from fungi to animals and plants. Eggs and fish are higher melatonin-containing food groups in animal foods, whereas in plant foods, nuts are with the highest content of melatonin. Some kinds of mushrooms, cereals and germinated legumes or seeds are also good dietary sources of melatonin. It has been proved that the melatonin concentration in human serum could significantly increase after the consumption of melatonin containing food. Furthermore, studies show that melatonin exhibits many bioactivities, such as antioxidant activity, anti-inflammatory characteristics, boosting immunity, anticancer activity, cardiovascular protection, anti-diabetic, anti-obese, neuroprotective and anti-aging activity. This review summaries the dietary sources and bioactivities of melatonin, with special attention paid to the mechanisms of action.