Benchmarking of protein carbonylation analysis in Caenorhabditis elegans: specific considerations and general advice

Caenorhabditis elegans as an in vivo model for the identification of natural antioxidants with anti-aging actions

Natural antioxidants have recently emerged as a highly exciting and significant topic in anti-aging research. Diverse organism models present a viable protocol for future research. Notably, many breakthroughs on natural antioxidants have been achieved in the nematode Caenorhabditis elegans, an animal model frequently utilized for the study of aging research and anti-aging drugs in vivo. Due to the conservation of signaling pathways on oxidative stress resistance, lifespan regulation, and aging disease between C. elegans and multiple high-level organisms (humans), as well as the low and controllable cost of time and labor, it gradually develops into a trustworthy in vivo model for high-throughput screening and validation of natural antioxidants with anti-aging actions. First, information and models on free radicals and aging are presented in this review. We also describe indexes, detection methods, and molecular mechanisms for studying the in vivo antioxidant and anti-aging effects of natural antioxidants using C. elegans. It includes lifespan, physiological aging processes, oxidative stress levels, antioxidant enzyme activation, and anti-aging pathways. Furthermore, oxidative stress and healthspan improvement induced by natural antioxidants in humans and C. elegans are compared, to understand the potential and limitations of the screening model in preclinical studies. Finally, we emphasize that C. elegans is a useful model for exploring more natural antioxidant resources and uncovering the mechanisms underlying aging-related risk factors and diseases.

Caernohabditis elegans as a Model Organism to Evaluate the Antioxidant Effects of Phytochemicals

The nematode Caenorhabditis elegans was introduced as a model organism in biological research by Sydney Brenner in the 1970s. Since then, it has been increasingly used for investigating processes such as ageing, oxidative stress, neurodegeneration, or inflammation, for which there is a high degree of homology between C. elegans and human pathways, so that the worm offers promising possibilities to study mechanisms of action and effects of phytochemicals of foods and plants. In this paper, the genes and pathways regulating oxidative stress in C. elegans are discussed, as well as the methodological approaches used for their evaluation in the worm. In particular, the following aspects are reviewed: the use of stress assays, determination of chemical and biochemical markers (e.g., ROS, carbonylated proteins, lipid peroxides or altered DNA), influence on gene expression and the employment of mutant worm strains, either carrying loss-of-function mutations or fluorescent reporters, such as the GFP.

Origin and pathophysiology of protein carbonylation, nitration and chlorination in age-related brain diseases and aging

Non-enzymatic protein modifications occur inevitably in all living systems. Products of such modifications accumulate during aging of cells and organisms and may contribute to their age-related functional deterioration. This review presents the formation of irreversible protein modifications such as carbonylation, nitration and chlorination, modifications by 4-hydroxynonenal, removal of modified proteins and accumulation of these protein modifications during aging of humans and model organisms, and their enhanced accumulation in age-related brain diseases.

Inhibition of amyloid-induced toxicity by ergothioneine in a transgenic Caenorhabditis elegans model

The abnormal accumulation of β-amyloid peptide (Aβ) is recognized as a central component in the pathogenesis of Alzheimer disease. While many aspects of Aβ-mediated neurotoxicity remain elusive, Aβ has been associated with numerous underlying pathologies, including oxidative and nitrosative stress, inflammation, metal ion imbalance, mitochondrial dysfunction, and even tau pathology. Ergothioneine (ET), a naturally occurring thiol/thione-derivative of histidine, has demonstrated antioxidant and neuroprotective properties against various oxidative and neurotoxic stressors. This study investigates ET's potential to counteract Aβ-toxicity in transgenic Caenorhabditis elegans overexpressing a human Aβ peptide. The accumulation of Aβ in this model leads to paralysis and premature death. We show that ET dose-dependently reduces Aβ-oligomerization and extends the lifespan and healthspan of the nematodes.

Interplay between ionizing radiation effects and aging in C. elegans

Living species are chronically exposed to environmental ionizing radiations from sources that can be overexpressed by nuclear accidents. In invertebrates, reproduction is the most radiosensitive studied endpoint, likely to be connected with aging. Surprisingly, aging is a sparsely investigated endpoint after chronic ionizing radiation, whereas understanding it is of fundamental interest in biology and medicine. Indeed, aging and aging-related diseases (e.g., cancer and degenerative diseases) cause about 90% of deaths in developed countries. Therefore, glp-1 sterile Caenorhabditis elegans nematode was used to assess the impact of chronic gamma irradiation on the lifespan. Analyses were performed, at the individual level, on aging and, in order to delve deeper into the mechanisms, at the molecular level, on oxidative damage (carbonylation), biomolecules (lipids, proteins and nucleic acids) and their colocalization. We observed that ionizing radiation accelerates aging (whatever the duration (3-19 days)/dose (0.5-24 Gy)/dose rate (7 and 52 mGy h^-1) tested) leading to a longevity value equivalent to that of wt nematode (∼25-30 days). Moreover, the level of protein oxidative damage (carbonylation) turned out to be good cellular biomarker of aging, since it increases with age. Conversely, chronic radiation treatments reduced carbonylation levels and induced neutral lipid catabolism whatever the dose rate and the final delivered dose. Finally, under some conditions a lipid-protein colocalization without any carbonyl was observed; this could be linked to yolk accumulation in glp-1 nematodes. To conclude, we noticed through this study a link between chronic gamma exposure, lifespan shortening and lipid level decrease associated with a decrease in the overall carbonylation.

Precoce and opposite response of proteasome activity after acute or chronic exposure of C. elegans to γ-radiation

Species are chronically exposed to ionizing radiation, a natural phenomenon which can be enhanced by human activities. The induced toxicity mechanisms still remain unclear and seem depending on the mode of exposure, i.e. acute and chronic. To better understand these phenomena, studies need to be conducted both at the subcellular and individual levels. Proteins, functional molecules in organisms, are the targets of oxidative damage (especially via their carbonylation (PC)) and are likely to be relevant biomarkers. After exposure of Caenorhabditis elegans to either chronic or acute γ rays we showed that hatching success is impacted after acute but not after chronic irradiation. At the molecular level, the carbonylated protein level in relation with dose was slightly different between acute and chronic exposure whereas the proteolytic activity is drastically modified. Indeed, whereas the 20S proteasome activity is inhibited by acute irradiation from 0.5 Gy, it is activated after chronic irradiation from 1 Gy. As expected, the 20S proteasome activity is mainly modified by irradiation whereas the 26S and 30S activity are less changed. This study provides preliminaries clues to understand the role of protein oxidation and proteolytic activity in the radiation-induced molecular mechanisms after chronic versus acute irradiation in C. elegans.

In situ visualization of carbonylation and its co-localization with proteins, lipids, DNA and RNA in Caenorhabditis elegans

All key biological macromolecules are susceptible to carbonylation - an irreparable oxidative damage with deleterious biological consequences. Carbonyls in proteins, lipids and DNA from cell extracts have been used as a biomarker of oxidative stress and aging, but formation of insoluble aggregates by carbonylated proteins precludes quantification. Since carbonylated proteins correlate with and become a suspected cause of morbidity and mortality in some organisms, there is a need for their accurate quantification and localization. Using appropriate fluorescent probes, we have developed an in situ detection of total proteins, DNA, RNA, lipids and carbonyl groups at the level of the whole organism. In C. elegans, we found that after UV irradiation carbonylation co-localizes mainly with proteins and, to a lesser degree, with DNA, RNA and lipids. The method efficiency was illustrated by carbonylation induction assessment over 5 different UV doses. The procedure enables the monitoring of carbonylation in the nematode C. elegans during stress, aging and disease along its life cycle including the egg stage.