Defective mitophagy and induction of apoptosis by the depleted levels of PINK1 and Parkin in Pb and ß-amyloid peptide induced toxicity.

Exposure to lead (Pb), an environmental pollutant, is closely associated with the development of neurodegenerative disorders through oxidative stress induction and alterations in mitochondrial function. Damaged mitochondria could be one of the reasons for the progression of Alzheimer's Disease (AD). Mitophagy is vital in keeping the cell healthy. To know its role in Pb-induced AD, we investigated the PINK1/Parkin dependent pathway by studying specific mitophagy marker proteins such as PINK1 and Parkin in differentiated SH-SY5Y cells. Our data have indicated a significant reduction in the levels of PINK1 and Parkin in cells exposed to Pb and ß-amyloid peptides, both Aß (25-35) and Aß (1-40) individually and in different combinations, resulting in defective mitophagy. Also, the study unravels the status of mitochondrial permeability transition pore (MPTP), mitochondrial mass, mitochondrial membrane potential (MMP) and mitochondrial ROS production in cells treated with individual and different combination of Pb and Aß peptides. An increase in mitochondrial ROS production, enhanced MPTP opening, depolarization of membrane potential and reduced mitochondrial mass in the exposed groups were observed. Also, in the present study, we found that Pb and ß-amyloid peptides could trigger apoptosis by activating the Bak protein, which releases the cytochrome c from mitochondria through MPTP that further activates the AIF (apoptosis inducing factor) and caspase-3 proteins in the cytosol. The above findings reveal the potential role of mechanisms like PINK1/Parkin mediated mitophagy and dysfunctional mitochondria mediated apoptosis in Pb induced neurotoxicity.

Mechanisms associated with the dysregulation of mitochondrial function due to lead exposure and possible implications on the development of Alzheimer's disease.

Lead (Pb) is a multimedia contaminant with various pathophysiological consequences, including cognitive decline and neural abnormalities. Recent findings have reported an association of Pb toxicity with Alzheimer's disease (AD). Studies have revealed that mitochondrial dysfunction is a pathological characteristic of AD. According to toxicology reports, Pb promotes mitochondrial oxidative stress by lowering complex III activity in the electron transport chain, boosting reactive oxygen species formation, and reducing the cell's antioxidant defence system. Here, we review recent advances in the role of mitochondria in Pb-induced AD pathology, as well as the mechanisms associated with the mitochondrial dysfunction, such as the depolarisation of the mitochondrial membrane potential, mitochondrial permeability transition pore opening; mitochondrial biogenesis, bioenergetics and mitochondrial dynamics alterations; and mitophagy and apoptosis. We also discuss possible therapeutic options for mitochondrial-targeted neurodegenerative disease (AD).

Mitochondria-Mediated Moderation of Apoptosis by EGCG in Cytotoxic Neuronal Cells Induced by Lead (Pb) and Amyloid Peptides.

The developmental, epigenetic, and epidemiological studies on lead (Pb) toxicity have reported a strong connection between lead exposure and the progression of Alzheimer's disease (AD). The amyloid peptides were the main triggering elements, in the generation of extracellular plaques through which multiple cellular signaling events such as apoptosis and primarily oxidant-antioxidant balancing system will be affected, which leads to neuronal cell death. Our previous studies indicated that epigallocatechin gallate (EGCG), abundantly present in green tea, was found to be effective in alleviating the metal-induced neurotoxicity at the cellular level in terms of cell viability and apoptosis The aim of this study was to explore the protective mechanism of EGCG on the markers of oxidant-antioxidant system and mitochondria, which are involved in metal-induced neuronal cell death. Initially, the IC50 values for lead(Pb-5 µM), amyloid peptides (AP(1-40)-60 µM; AP(1-40)-8 µM), and EC50 value for EGCG(50 µM) were determined by both time- (12 h, 24 h, 48 h) and concentration-dependent manner and analyzed by MTT assay. The experimental groups were designed initially by treating with Pb and APs individually and in different combinations along with the presence of EGCG and are compared to the Pb and AP treated group without EGCG exposure. The cell lysates were used for analyzing oxidative stress markers by standardized laboratory protocol and the expression of mitochondrial markers such as VDAC and cytochrome C which were analyzed by both western blot and real-time PCR. Our results indicate that the EGCG-treated group has shown a significant increase in antioxidant marker expression levels (GSH, SOD, catalase, vitamin C) and a decrease in oxidative stress marker (NOS, MDA) levels when compared to the group without EGCG treatment (p < 0.05). Similarly, a significant decrease in expression levels of VDAC and cytochrome c were observed in the EGCG-treated group when compared to the group without EGCG treatment (p < 0.05). Our approach revealed that EGCG protects SH-SY5Y cells from Pb- and AP-induced cytotoxicity by regulating voltage-dependent anion channel (VDAC) expression and oxidant-antioxidant system and inhibits neuronal cell death.

Inactivation of GAP-43 due to the depletion of cellular calcium by the Pb and amyloid peptide induced toxicity: An in vitro approach.

Environmental pollutant, Lead (Pb) is known to induce neurotoxicity in human. The central nervous system is the most vulnerable to the minute levels of Pb induced toxicity. Pb has been linked to Alzheimer's disease (AD) as a probable risk factor, as it shows epigenetic and developmental link associated with Alzheimer's disease-like pathology. Beta amyloid peptides were considered as the crucial factors in the beta amyloid plaque formation in Alzheimer's disease brain. In this context, we investigated the molecular mechanism involved in the development of Pb induced Alzheimer's disease in in vitro. Previous data from our studies have reported that Pb in the presence of beta Amyloid peptide (1-40) and (25-35) induces more apoptosis than individual exposures. Here, to further evaluate the molecular mechanism underlying Pb induced Alzheimer's disease; we focussed on the involvement of calcium signalling in inducing cell death. Our experimental observations suggesting that Pb in the presence of beta amyloid peptide alters intracellular calcium levels, which leads to the increased beta-secretase activity, which further promotes the generation of beta amyloid peptides. It also showed depression in the levels of GAP-43 expression, inhibition of PKC activity and altering synaptic activity further leads to cell death.

Mitigative effects of epigallocatechin gallate in terms of diminishing apoptosis and oxidative stress generated by the combination of lead and amyloid peptides in human neuronal cells.

Environmental exposure to lead (Pb) is reported to associate with the development of Alzheimer's disease, where the formation of ß-amyloid peptides (APs) of (1-40), (1-42), and (25-35) is considered as the major risk factor. In this context, we aimed at investigating the effect of epigallocatechin gallate (EGCG), a major flavonoid polyphenol available in green tea, in mitigating the individual and combined toxicity generated by Pb and ß-APs in terms of oxidative stress and apoptosis in human neuronal cells. SH-SY5Y cells were exposed to Pb and ß-APs of (1-40) and (25-35) individually and in different combinations in the presence and absence of EGCG. The results indicated that EGCG mitigated both Pb- and ß-AP-induced oxidative stress in scavenging reactive oxygen species and apoptosis by improving the expression levels of Bax and bcl2 and inhibiting annexin V and caspase-3. Thus, our study shows that EGCG protects SH-SY5Y cells against the cytotoxicity induced by Pb and ß-APs by decreasing oxidative stress and inhibiting apoptosis.

Mechanistic comparison of current pharmacological treatments and novel phytochemicals to target amyloid peptides in Alzheimer's and neurodegenerative diseases.

The formation of ß amyloid plaques is one of the pathological hallmarks of Alzheimer's disease (AD). The process of accumulation of extracellular deposits of amyloid plaques occurs by the abnormal proteolysis of amyloid precursor protein, resulting in the formation of ß amyloid peptides which further aggregates and results in the formation of oligomers, protofibrils, fibrils, and plaques. The complexity in understanding the aggregation process has provided avenues for identifying potential targets against amyloid toxicity in the treatment of AD. The therapeutic approach mainly focuses on reducing the toxicity by halting the ß amyloid fibril formation. Besides conventional medicine, several naturally available compounds were shown to reduce the toxicity of amyloid plaques in the current scenario. This review provides a comprehensive account on recent updates of FDA-approved and naturally available compounds against toxicity of amyloid peptides and plaques both in vitro and in vivo.