Abyssinone V, a prenylated flavonoid isolated from the stem bark of Erythrina melanacantha increases oxidative stress and decreases stress resistance in Caenorhabditis elegans

OBJECTIVES

Recent studies showed that distinct extracts of Erythrina species used in the traditional medicine of sub-Saharan Africa are protective against stress conditions. However, the underlying molecular mechanisms as well as relevant compounds remain unclear.

METHODS

We used the model organism Caenorhabditis elegans to investigate compounds isolated from the stem bark of Erythrina melanacantha (abyssinone V (1), abyssinon-4'O-methylether (2), sigmoidin B-4'O-methylether (3), glabranin (4), 8-prenylnaringenin (5), citflavanone (6), exiguaflavanone (7) and homoeriodictyol (8)). Antioxidative capacity in vitro (trolox equivalent antioxidative capacity assay) and modulation of oxidative stress in vivo (2', 7'-dichlorofluorescein assay) were investigated; stress resistance was analysed using the nucleic acid stain SYTOX green.

KEY FINDINGS

None of the prenylated flavonoids caused protection against thermal stress; in contrast, most of the compounds (1, 4, 5, 8) decreased stress resistance. None of the compounds decreased the accumulation of reactive oxygen species, but abyssinone V (1) caused an increase in oxidative stress. In line with these results, none of these compounds showed radical-scavenging effects in vitro.

CONCLUSIONS

The stem bark of E. melanacantha contains various prenylated flavonoids, but no compound protected C. elegans against stress conditions. In contrast, abyssinone V increases oxidative stress and reduces stress resistance in this model organism.

Hibiscus sabdariffa L. extract prolongs lifespan and protects against amyloid-β toxicity in Caenorhabditis elegans: involvement of the FoxO and Nrf2 orthologues DAF-16 and SKN-1

PURPOSE

Hibiscus sabdariffa L. is commonly used as an ingredient for herbal teas and food supplements. Several studies demonstrated the beneficial effects of Hibiscus sabdariffa L. extracts (HSE); however, the bioactive components and their mode of action still remain unclear. Caenorhabditis elegans (C. elegans) was used to study health-related effects and the underlying molecular mechanisms of HSE in this model organism as well as effects of hydroxycitric acid (HCA), a main compound of HSE, and its structural analogue isocitric acid (ICA).

METHODS

Survival and locomotion were detected by touch-provoked movement. Thermotolerance was analysed using the nucleic acid stain SYTOX green, and intracellular ROS accumulation was measured via oxidation of H₂DCF. Localisation of the transcription factors DAF-16 and SKN-1 was analysed in transgenic strains (DAF-16::GFP, SKN-1::GFP). The involvement of DAF-16 and SKN-1 was further investigated using loss-of-function strains as well as gene silencing by feeding RNAi-inducing bacteria. Protection against amyloid-β toxicity was analysed using a transgenic strain with an inducible expression of human amyloid-β peptides in body wall muscle cells (paralysis assay).

RESULTS

HSE treatment resulted in a prominent extension of lifespan (up to 24%) and a reduction of the age-dependent decline in locomotion. HCA, a main compound of HSE increased lifespan too, but to a lesser extent (6%) while ICA was not effective. HSE and HCA did not modulate resistance against thermal stress conditions and did not exert antioxidative effects: HSE rather increased intracellular ROS levels, suggesting a pro-oxidative effect of the extract in vivo. HSE and HCA increased the nuclear localisation of the pivotal transcription factors DAF-16 and SKN-1 indicating an activation of these factors. Consistent with this result, lifespan prolongation by HSE was dependent on both transcription factors. In addition to the positive effect on lifespan, HSE treatment also elicited a (strong) protection against amyloid-ß induced toxicity in C. elegans in a DAF-16- and SKN-1-dependent manner.

CONCLUSION

Our results demonstrate that HSE increases lifespan and protects against amyloid-β toxicity in the model organism C. elegans. These effects were mediated, at least in parts via modulation of pathways leading to activation/nuclear localisation of DAF-16 and SKN-1. Since HCA, a main component of HSE causes only minor effects, additional bioactive compounds like flavonoids or anthocyanins as well as synergistic effects of these compounds should be investigated.

The resveratrol derivatives trans-3,5-dimethoxy-4-fluoro-4'-hydroxystilbene and trans-2,4',5-trihydroxystilbene decrease oxidative stress and prolong lifespan in Caenorhabditis elegans

OBJECTIVES

Resveratrol (trans-3,4',5-trihydroxystilbene (1)) was previously shown to extend the lifespan of different model organisms. However, its pharmacological efficiency is controversially discussed. Therefore, the bioactivity of four newly synthesized stilbenes (trans-3,5-dimethoxy-4-fluoro-4'-hydroxystilbene (3), trans-4'-hydroxy-3,4,5-trifluorostilbene (4), trans-2,5-dimethoxy-4'-hydroxystilbene (5), trans-2,4',5-trihydroxystilbene (6)) was compared to (1) and pterostilbene (trans-3,5-dimethoxy-4'-hydroxystilbene (2)) in the established model organism Caenorhabditis elegans.

METHODS

Trolox equivalent antioxidant capacity (TEAC), 2',7'-dichlorofluorescein (DCF), thermotolerance assays, C. elegans lifespan analyses.

KEY FINDINGS

All compounds exert a strong in-vitro radical scavenging activity (6 > 1 > 5 > 2 = 3 = 4), but in vivo, only (3) and (6) reduce reactive oxygen species (ROS) accumulation. Furthermore, (3) and (6) increased the mobility of aged nematodes and prolonged their mean lifespans, while these compounds decreased the thermal stress resistance. Using daf-16 (FoxO), skn-1 (Nrf2) and sir-2.1 (sirtuin) loss-of-function mutant strains, the in vivo antioxidant effects of compounds (3) and (6) were abolished, showing the necessity of these evolutionary highly conserved factors. However, short-time treatment with stilbenes (3) and (6) did not modulate the cellular localization of the transcription factors DAF-16 and SKN-1.

CONCLUSION

In contrast to resveratrol, the synthetic stilbene derivatives (3) and (6) increase the lifespan of C. elegans, rendering them promising candidates for pharmacological anti-ageing purposes.

The Lignan Pinoresinol Induces Nuclear Translocation of DAF-16 in Caenorhabditis elegans but has No Effect on Life Span

The lignan pinoresinol is a constituent of flaxseed, sesame seeds and olive oil. Because of different molecular effects reported for this compound, e.g. antioxidative activity, pinoresinol is suggested to cause positive effects on humans. Because experimental data are limited, we have analysed the effects of the lignan on the nematode Caenorhabditis elegans: in spite of a strong antioxidative capacity detected in an in vitro assay, no antioxidative effects were detectable in vivo. In analogy to this result, no modulation of the sensitivity against thermal stress was detectable. However, incubation with pinoresinol caused an enhanced nuclear accumulation of the transcription factor DAF-16 (insulin/IGF-like signalling pathway). Using a strain with an enhanced oxidative stress level (mev-1 mutant), we clearly see an increase in stress resistance caused by this lignan, but no change in reactive oxygen species. Furthermore, we investigated the effects of pinoresinol on the life span of the nematode, but no modulation was found, neither in wild-type nor in mev-1 mutant nematodes. These results suggest that pinoresinol may exert pharmacologically interesting effects via modulation of the insulin-like signalling pathway in C. elegans as well as in other species like mammals due to the evolutionary conservation of this signalling pathway.

Methylated derivatives of myricetin enhance life span in Caenorhabditis elegans dependent on the transcription factor DAF-16

Methylated derivatives of myricetin enhance the life span of the nematodeCaenorhabditis eleganscomparable to the non-methylated flavonoid myricetin. The life-prolonging effects are dependent on the transcription factor DAF-16.

Myricetin-mediated lifespan extension in Caenorhabditis elegans is modulated by DAF-16

Myricetin is a naturally occurring flavonol found in many plant based food sources. It increases the lifespan of Caenorhabditis elegans, but the molecular mechanisms are not yet fully understood. We have investigated the impact of this flavonoid on the transcription factors DAF-16 (C. elegans FoxO homologue) and SKN-1 (Nrf2 homologue), which have crucial functions in the regulation of ageing. Myricetin is rapidly assimilated by the nematode, causes a nuclear translocation of DAF-16 but not of SKN-1, and finally prolongs the mean adult lifespan of C. elegans by 32.9%. The lifespan prolongation was associated with a decrease in the accumulation of reactive oxygen species (ROS) detected by DCF. Myricetin also decreases the formation of lipofuscin, a pigment consisting of highly oxidized and cross-linked proteins that is considered as a biomarker of ageing in diverse species. The lifespan extension was completely abolished in a daf-16 loss-of-function mutant strain (CF1038). Consistently with this result, myricetin was also not able to diminish stress-induced ROS accumulation in the mutant. These results strongly indicate that the pro-longevity effect of myricetin is dependent on DAF-16 and not on direct anti-oxidative effects of the flavonoid.