The mechanisms underlying neurodegenerative disorders are complex and multifactorial; however, accumulating evidences suggest few common shared pathways. These common pathways include mitochondrial dysfunction, intracellular Ca2+ overload, oxidative stress and inflammation. Often multiple pathways co-exist, and therefore limit the benefits of therapeutic interventions. Nutraceuticals have recently gained importance owing to their multifaceted effects. These food-based approaches are believed to target multiple pathways in a slow but more physiological manner without causing severe adverse effects. Available information strongly supports the notion that apart from preventing the onset of neuronal damage, nutraceuticals can potentially attenuate the continued progression of neuronal destruction. In this article, we i) review the common pathways involved in the pathogenesis of the toxicants-induced neurotoxicity and neurodegenerative disorders with special emphasis on Alzheimer's disease (AD), Parkinson's disease (PD), Huntington's disease (HD), Multiple sclerosis (MS) and Amyotrophic lateral sclerosis (ALS), and ii) summarize current research advancements on the effects of nutraceuticals against these detrimental pathways.

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Phospholipase D4 (PLD4), a single-pass transmembrane glycoprotein, is among the most highly upregulated genes in murine kidneys subjected to chronic progressive fibrosis, but the function of PLD4 in this process is unknown. Here, we found PLD4 to be overexpressed in the proximal and distal tubular epithelial cells of murine and human kidneys after fibrosis. Genetic silencing of PLD4, either globally or conditionally in proximal tubular epithelial cells, protected mice from the development of fibrosis. Mechanistically, global knockout of PLD4 modulated innate and adaptive immune responses and attenuated the upregulation of the TGF- signaling pathway and 1-antitrypsin protein (a serine protease inhibitor) expression and downregulation of neutrophil elastase (NE) expression induced by obstructive injury., treatment with NE attenuated TGF--induced accumulation of fibrotic markers. Furthermore, therapeutic targeting of PLD4 using specific siRNA protected mice from folic acid-induced kidney fibrosis and inhibited the increase in TGF- signaling, decrease in NE expression, and upregulation of mitogen-activated protein kinase signaling. Immunoprecipitation/mass spectrometry and coimmunoprecipitation experiments confirmed that PLD4 binds three proteins that interact with neurotrophic receptor tyrosine kinase 1, a receptor also known as TrkA that upregulates mitogen-activated protein kinase. PLD4 inhibition also prevented the folic acid-induced upregulation of this receptor in mouse kidneys. These results suggest inhibition of PLD4 as a novel therapeutic strategy to activate protease-mediated degradation of extracellular matrix and reverse fibrosis.

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Preplacement of compensatory tissue repair (CTR) by exposure to a nonlethal dose of a toxicant protects animals against a lethal dose of another toxicant. Although CTR is known to heteroprotect, the underlying molecular mechanisms are not completely known. Here, we investigated the mechanisms of heteroprotection using thioacetamide (TA): acetaminophen (APAP) heteroprotection model. Male Swiss Webster mice received a low dose of TA or distilled water (DW) vehicle 24 hours prior to a lethal dose of APAP. Liver injury, tissue repair, and promitogenic signaling were studied over a time course of 24 hours after APAP overdose to the TA- and DW-primed mice (TA + APAP and DW + APAP, respectively). Thioacetamide pretreatment afforded 100% protection against APAP overdose compared to 100% lethality in the DW + APAP-treated mice. Although hepatic Cyp2e1 was similar at the time of APAP administration, immediate activation of hepatic c-Jun N-terminal kinases (JNK) was observed in the TA + APAP-treated mice compared to its delayed activation in the DW + APAP group. In contrast to the DW + APAP group, the TA + APAP-treated mice exhibited extensive CTR, which was secondary to the timely activation of Wnt/β-catenin pathway. Our data indicate that rapid activation and appropriate termination of Wnt/β-catenin signaling and modulation of JNK activity underlie TA + APAP heteroprotection.

Compensatory tissue repair (CTR) in thioacetamide (TA)-primed rats protects them against acetaminophen (APAP)-induced lethality. This study was aimed at investigating the mechanisms of CTR-mediated heteroprotection in mice. Male Swiss Webster mice received a priming dose of TA (40 mg/kg body weight [BW] in 10 mL distilled water [DW]/kg BW, intraperitoneally [IP]). Thioacetamide-induced liver injury, CTR, and expression of annexin A1 and A2 (ANX1 and ANX2), the endogenous inhibitors of the death protein secretory phospholipase A2 (sPLA), were measured over a time course of 84 hours after TA priming. Both centrilobular necrosis and CTR peaked at 36 hours after TA priming as indicated by significantly increased plasma alanine transaminase (ALT) and aspartate transaminase (AST) activities, liver histology, and proliferating cell nuclear antigen immunostaining. Thioacetamide priming resulted in the overexpression of ANX1 and ANX2 at 36 to 84 hours and 12 to 60 hours, respectively. A lethal dose of APAP (600 mg/kg BW in 10 mL 0.45% NaCl/kg BW, IP) was given at 12, 24, or 36 hours after TA-priming. Thioacetamide priming did not affect the rise in plasma ALT, AST, sPLA, and arachidonic acid levels seen at 2 hours after the APAP overdose. Neither these biochemical parameters nor histology suggested any escalation of hepatic injury at later time points (12 and 24 hours after APAP overdose), consistent with 100% survival of the TA + APAP-treated mice compared to DW + APAP-treated mice, which had 100% mortality. Inhibition of ANX1 and ANX2 biosynthesis using cycloheximide (40 mg/kg BW in 5 mL DW/kg BW, IP) abolished this heteroprotection. Our data indicate that hepatic overexpression of ANX1 and ANX2 inhibits APAP-induced expansion of liver injury.

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