Melatonin Protects Against Titanium Oxide-Induced Neurotoxicity: Neurochemical, Neurobehavioral, and Histopathological Evidences

Lycopene alleviates cognitive dysfunctions in an Alzheimer's disease rat model via suppressing the oxidative and neuroinflammatory signaling

Oxidative stress and neuroinflammation are key contributors to the development of neurodegenerative disorders, including Alzheimer's disease (AD). Lycopene (LYC) has demonstrated effectiveness in inhibiting inflammatory and oxidative stress markers and appears to exert a modulatory impact on several physiological pathways, behavioral manifestations, and cognitive symptoms associated with AD in animal models. In the present study, an AD model was established in male Wistar albino rats through daily oral administration of hydrated aluminum chloride (AlCl₃·6H₂O) at a dose of 75 mg/kg for six weeks. A Morris water maze (MWM) behavioral test was conducted to confirm memory impairment and cognitive deterioration in the treated rats. Animals exhibiting cognitive dysfunction were subsequently treated with LYC (5 mg/kg orally) for an additional six weeks, followed by a second MWM test before sacrifice. The findings revealed that LYC significantly enhanced performance and cognitive function in the AD model rats and markedly (p < 0.001) reduced the accumulation of amyloid β1-42, proinflammatory mediators [interleukin-1 beta (IL-1β) and tumor necrosis factor-alpha (TNF-α)], malondialdehyde (MDA), and nitrite levels. Furthermore, LYC significantly (p < 0.001) decreased the acetylcholine (ACh) concentration, monoamine oxidase (MAO), creatine kinase (CK), and lactate dehydrogenase (LDH) activites. Additionally, LYC significantly (p < 0.001) increased the acetylcholinesterase (AChE) activity, nuclear factor erythroid-2-related factor 2 (Nrf2), serotonin, anti-inflammatory mediators [transforming growth factor beta-1 (TGF-β1) and interleukin-10 (IL-10)] levels, superoxide dismutase (SOD), and glutathione peroxidase (GPx) activities. The therapeutic efficacy of LYC was further supported by improvements in the histopathological appearance of brain tissues, significant (p < 0.001) enhancement of synaptophysin immunohistochemical expression, and suppression of the immunohistochemical expression of cell cycle-related proteins (Ki67 and proliferating cell nuclear antigen [PCNA]). In conclusion, LYC may represent a promising therapeutic agent for AD by targeting multiple pathogenic mechanisms.

p-Coumaric acid potential in restoring neuromotor function and oxidative balance through the Parkin pathway in a Parkinson disease-like model in Drosophila melanogaster

p-Coumaric acid is a significant phenolic compound known for its potent antioxidant activity. Thus, this study investigated the effects of p-coumaric acid on the behavioral and neurochemical changes induced in Drosophila melanogaster by exposure to rotenone in a Parkinson disease (PD)-like model. The flies were divided into four groups and maintained for seven days on different diets: a standard diet (control), a diet containing rotenone (500 μM), a control diet to which p-coumaric acid was added on the fourth day (0.3 μM), and a diet initially containing rotenone (500 μM) with p-coumaric acid added on the fourth day (0.3 μM). Exposure to p-coumaric acid ameliorated locomotor impairment and reduced mortality induced by rotenone. Moreover, p-coumaric acid normalized oxidative stress markers (ROS, TBARS, SOD, CAT, GST, and NPSH), mitigated oxidative damage, and reflected in the recovery of dopamine levels, AChE activity, and cellular viability post-rotenone exposure. Additionally, p-coumaric acid restored the immunoreactivity of Parkin and Nrf2. The results affirm that p-coumaric acid effectively mitigates PD-like model-induced damage, underscoring its antioxidant potency and potential neuroprotective effect.

Effects of hippocampal damage on pain perception in a rat model of Alzheimer's disease induced by amyloid-β and ibotenic acid injection into the hippocampus

Patients with Alzheimer's disease (AD) present with a variety of symptoms, including core symptoms as well as behavioral and psychological symptoms. Somatosensory neural systems are generally believed to be relatively unaffected by AD until late in the course of the disease; however, somatosensory perception in patients with AD is not yet well understood. One factor that may complicate the assessment of somatosensory perception in humans centers on individual variations in pathological and psychological backgrounds. It is therefore necessary to evaluate somatosensory perception using animal models with uniform status. In the current study, we focused on the hippocampus, the primary site of AD. We first constructed a rat model of AD model using bilateral hippocampal injections of amyloid-β peptide 1-40 and ibotenic acid; sham rats received saline injections. The Morris water maze test was used to evaluate memory impairment, and the formalin test (1 % or 4 % formalin) and upper lip von Frey test were performed to compare pain perception between AD model and sham rats. Finally, histological and immunohistochemical methods were used to evaluate tissue damage and neuronal activity, respectively, in the hippocampus. AD model rats showed bilateral hippocampal damage and had memory impairment in the Morris water maze test. Furthermore, AD model rats exhibited significantly less pain-related behavior in phase 2 (the last 50 min of the 60-minute observation) of the 4 % formalin test compared with the sham rats. However, no significant changes were observed in the von Frey test. Immunohistochemical observations of the trigeminal spinal subnucleus caudalis after 4 % formalin injection revealed significantly fewer c-Fos-immunoreactive cells in AD model rats than in sham rats, reflecting reduced neuronal activity. These results indicate that AD model rats with hippocampal damage have reduced responsiveness to persistent inflammatory chemical stimuli to the orofacial region.

Melatonin is a Neuroprotective and Antioxidant Agent against Neurotoxicity Induced by an Intrahippocampal Injection of Nickel in Rats

The investigation into the hippocampal function and its response to heavy metal exposure is crucial for understanding the mechanisms underlying neurotoxicity, this can potentially inform strategies for mitigating the adverse effects associated with heavy metal exposure. Melatonin is an essential neuromodulator known for its efficacy as an antioxidant. In this study, we aimed to determine whether melatonin could protect against Nickel (Ni) neurotoxicity. To achieve this, we performed an intracerebral injection of Ni (300 µM NiCl2) into the right hippocampus of male Wistar rats, followed by melatonin treatment. Based on neurobehavioral and neurobiochemical assessments, our results demonstrate that melatonin efficiently enhances Ni-induced behavioral dysfunction and cognitive impairment. Specifically, melatonin treatment positively influences anxious behavior, significantly reduces immobility time in the forced swim test (FST), and improves learning and spatial memory abilities. Moreover, neurobiochemical assays revealed that melatonin treatment modulates the Ni-induced alterations in oxidative stress balance by increasing antioxidant enzyme activities, such as superoxide dismutase (SOD) and catalase (CAT). Additionally, we observed that melatonin significantly attenuated the increased levels of lipid peroxidation (LPO) and nitric oxide (NO). In conclusion, the data from this study suggests that melatonin attenuates oxidative stress, which is the primary mechanism responsible for Ni-induced neurotoxicity. Considering that the hippocampus is the main structure involved in the pathology associated with heavy metal intoxication, such as Ni, these findings underscore the potential therapeutic efficacy of melatonin in mitigating heavy metal-induced brain damage.

Melatonin: A Potential Regulator of DNA Methylation

The pineal gland-derived indoleamine hormone, melatonin, regulates multiple cellular processes, ranging from chronobiology, proliferation, apoptosis, and oxidative damage to pigmentation, immune regulation, and mitochondrial metabolism. While melatonin is best known as a master regulator of the circadian rhythm, previous studies also have revealed connections between circadian cycle disruption and genomic instability, including epigenetic changes in the pattern of DNA methylation. For example, melatonin secretion is associated with differential circadian gene methylation in night shift workers and the regulation of genomic methylation during embryonic development, and there is accumulating evidence that melatonin can modify DNA methylation. Since the latter one impacts cancer initiation, and also, non-malignant diseases development, and that targeting DNA methylation has become a novel intervention target in clinical therapy, this review discusses the potential role of melatonin as an under-investigated candidate epigenetic regulator, namely by modulating DNA methylation via changes in mRNA and the protein expression of DNA methyltransferases (DNMTs) and ten-eleven translocation (TET) proteins. Furthermore, since melatonin may impact changes in the DNA methylation pattern, the authors of the review suggest its possible use in combination therapy with epigenetic drugs as a new anticancer strategy.