Cinnamic acid, ferulic acid, and the flavonoids quercetin and taxifolin (dihydroquercetin) are naturally occurring compounds found in plants. They are often referred to as polyphenols and are known, among others, for their pharmacological effects supporting health through the inhibition of aging processes and oxidative stress. To improve their bioavailability, pharmacological activities, and safety, the creation of novel flavonoid–phenolic acid hybrids is an area of active research. Previous work showed that such hybridization products of phenolic acids and flavonoids enhanced the resilience of neuronal cells against oxidative stress in vitro, and attenuated cognitive impairment in a mouse model of Alzheimer’s disease (AD) in vivo. Notably, the therapeutic effects of the hybrid compounds we obtained were more pronounced than the protective activities of the respective individual components. The underlying mechanisms mediated by the flavonoid–phenolic acid hybrids, however, remained unclear and may differ from the signaling pathways activated by the originating structures of the respective individual phenolic acids or flavonoids. In this study, we characterized the effects of four previously described potent flavonoid–phenolic acid hybrids in models of oxidative cell death through ferroptosis. Ferroptosis is a type of iron-dependent regulated cell death characterized by lipid peroxidation and mitochondrial ROS generation and has been linked to neurodegenerative conditions. In models of ferroptosis induced by erastin or RSL3, we analyzed mitochondrial (lipid) peroxidation, mitochondrial membrane integrity, and Ca²⁺ regulation. Our results demonstrate the strong protective effects of the hybrid compounds against ROS formation in the cytosol and mitochondria. Importantly, these protective effects against ferroptosis were not mediated by radical scavenging activities of the phenolic hybrid compounds but through inhibition of mitochondrial complex I activity and reduced mitochondrial respiration. Our data highlight the effects of flavonoid–phenolic acid hybrids on mitochondrial metabolism and further important mitochondrial parameters that collectively determine the health and functionality of mitochondria with a high impact on the integrity and survival of the neuronal cells.

Cimicifuga racemosa extracts (CREs) have gained well-established use for the treatment of menopausal symptoms such as hot flushes and excessive sweating, and weight gain. While the clinical effects of CREs have been well documented, the mechanisms underlying these effects are largely unknown. More recently, the metabolic effects of the CRE Ze 450 were demonstrated in cultured cells in vitro and in mouse models of obesity in vivo. At the molecular level, metabolic regulation, enhanced insulin sensitivity, and increased glucose uptake were linked to the activation of AMP-activated protein kinase (AMPK). Therefore, we tested the effects of Ze 450 on AMPK phosphorylation and thus activation in cells from different tissues, i.e., murine C2C12 myoblast cells, human HEPG2 liver cells, mouse HT22 neuronal cells, and in murine 3T3L1 adipocytes. Using a FRET-based HTRF-assay, we found that Ze 450 induced AMPK phosphorylation and the activation of this key enzyme of metabolic regulation in cells from various different tissues including C2C12 (muscle), HEPG2 (liver), HT22 (hippocampal), and 3T3-L1 (adipocyte) cells. In C2C12 muscle cells, enhanced AMPK activation was accompanied by reduced mitochondrial respiration and enhanced glucose uptake. Further, Ze 450 enhanced the resilience of the cells against oxidative death induced by ferroptosis inducers erastin or RSL3. Our findings suggest a general effect of Cimicifuga racemosa on AMPK activation in different tissues and across species. This may have a significant impact on expanded therapeutic applications of Ze 450, since AMPK activation and the related metabolic effects have been previously associated with anti-aging effects and the prevention of the metabolic syndrome.