Palmatine is a naturally occurring isoquinoline alkaloid that has been reported to display neuroprotective effects against amyloid‐β‐ (Aβ‐) induced neurotoxicity. However, the mechanisms underlying the neuroprotective activities of palmatine remain poorly characterized in vivo. We employed transgenic Caenorhabditis elegans models containing human Aβ_1-42 to investigate the effects and possible mechanisms of palmatine‐mediated neuroprotection. Treatment with palmatine significantly delayed the paralytic process and reduced the elevated reactive oxygen species levels in Aβ‐transgenic C. elegans. In addition, it increased oxidative stress resistance without affecting the lifespan of wild‐type C. elegans. Pathway analysis suggested that the differentially expressed genes were related mainly to aging, detoxification, and lipid metabolism. Real‐time PCR indicated that resistance‐related genes such as sod-3 and shsp were significantly upregulated, while the lipid metabolism‐related gene fat-5 was downregulated. Further studies demonstrated that the inhibitory effects of palmatine on Aβ toxicity were attributable to the free radical‐scavenging capacity and that the upregulated expression of resistance‐related genes, especially shsp, whose expression was regulated by HSF‐1, played crucial roles in protecting cells from Aβ‐induced toxicity. The research showed that there were significantly fewer Aβ deposits in transgenic CL2006 nematodes treated with palmatine than in control nematodes. In addition, our study found that Aβ‐induced toxicity was accompanied by dysregulation of lipid metabolism, leading to excessive fat accumulation in Aβ‐transgenic CL4176 nematodes. The alleviation of lipid disorder by palmatine should be attributed not only to the reduction in fat synthesis but also to the inhibition of Aβ aggregation and toxicity, which jointly maintained metabolic homeostasis. This study provides new insights into the in vivo neuroprotective effects of palmatine against Aβ aggregation and toxicity and provides valuable targets for the prevention and treatment of AD.

The hard clam Meretrix meretrix, which has been traditionally used as medicine and seafood, was used in this study to isolate antioxidant peptides. First, a peptide-rich extract was tested for its protective effect against paraquat-induced oxidative stress using the nematode model Caenorhabditis elegans. Then, three novel antioxidant peptides; MmP4 (LSDRLEETGGASS), MmP11 (KEGCREPETEKGHR) and MmP19 (IVTNWDDMEK), were identified and were found to increase the resistance of nematodes against paraquat. Circular dichroism spectroscopy revealed that MmP4 was predominantly in beta-sheet conformation, while MmP11 and MmP19 were primarily in random coil conformation. Using transgenic nematode models, the peptides were shown to promote nuclear translocation of the DAF-16/FOXO transcription factor, a pivotal regulator of stress response and lifespan, and induce the expression of superoxide dismutase 3 (SOD-3), an antioxidant enzyme. Analysis of DAF-16 target genes by real-time PCR reveals that sod-3 was up-regulated by MmP4, MmP11 and MmP19 while ctl-1 and ctl-2 were also up-regulated by MmP4. Further examination of daf-16 using RNA interference suggests that the peptide-increased resistance of C. elegans to oxidative stress was DAF-16 dependent. Taken together, these data demonstrate the antioxidant activity of M. meretrix peptides, which are associated with activation of the stress response factor DAF-16 and regulation of the antioxidant enzyme genes.

The hydrolysate of golden cuttlefish (Sepia esculenta) was prepared by using papain, and then, it was further separated by ultrafiltration, gel filtration chromatography, and reverse-phase high-performance liquid chromatography (RP-HPLC). The peptide components of the active fraction were identified by liquid chromatography-tandem mass spectrometry (LC-MS/MS), and then two novel peptides, SeP2 (DVEDLEAGLAK, 1159.27 Da) and SeP5 (EITSLAPSTM, 1049.22 Da), were obtained and displayed significant alleviation effects on oxidative stress in Caenorhabditis elegans. Studies indicated that S. esculenta antioxidant peptides (SePs) increase superoxide dismutase (SOD) activity but reduce reactive oxygen species (ROS) and malondialdehyde (MDA) levelsin oxidation-damaged nematodes. Using transgenic CF1553 nematodes, the sod-3p::GFP expression in the worms treated with SePs was significantly higher than that of the control nematodes. Real-time PCR also demonstrated that the expression of stress-related genes such as sod-3 is up-regulated by SePs. Furthermore, studies showed that SePs could obviously decrease fat accumulation as well as reduce the elevated ROS and MDA levels in high-fat nematodes. Taken together, these results indicated that SePs are capable of the activation of antioxidant defense and the inhibition of free radicals and lipid peroxidation, play important roles in attenuating oxidative stress and fat accumulation in C. elegans, and might have the potential to be used in nutraceutical and functional foods.

Matrine, a quinoline alkaloid, possesses lipid-regulating effects, but the underlying mechanisms are rarely characterized in vivo. With a fat-accumulating Caenorhabditis elegans model, we show that matrine reduces the fat content and the DHS-3::GFP-labeled lipid droplets in high-glucose-diet N2 and transgenic LIU1 nematodes, respectively. Based on RNA-seq, this study demonstrates that a loss of AAK-2 function suppresses the fat-lowering effects of matrine, and the hyperactivated AAK-2 strain has a relatively lower fat content than N2. The involvement of NHR-49 in matrine’s fat-lowering effects further suggests that matrine impacts fat breakdown and storage via the AAK-2/NHR-49-governed pathway. Using the transgenic SJ4143 (ges-1::GFP(mit)) and VS10 (vha-6p::mRFP-PTS1), we show that matrine activates the AAK-2/NHR-49 pathway, coupling the alteration of mitochondrial and peroxisomal functions. Studies of aak-2 and nhr-49 mutants reveal that AAK-2 and NHR-49 modulate lipid metabolic homeostasis; meanwhile, matrine increases physical fitness and lifespan through activating the AAK-2/NHR-49 pathway in high-glucose-diet nematodes. Surprisingly, we found that β-amyloid (Aβ) induces lipid metabolic disorder in an Alzheimer’s disease (AD) C. elegans model, but matrine not only reduces Aβ aggregation but also alleviates Aβ-mediated lipid metabolic disorder. Our data suggest that matrine has promise as a fat-lowering agent, and also offer new insights into its therapeutic potential for AD.