Do Certain Flavonoid IMPS Have a Vital Function?

A Collection of Useful Nuisance Compounds (CONS) for Interrogation of Bioassay Integrity

High-throughput screening (HTS) is a crucial technique for identifying potential hits to fuel drug discovery pipelines. However, this process naturally concentrates nuisance compounds that are not optimizable yet signal positively in a convincing manner. To be able to understand what types of nuisance compounds a particular assay is sensitive to, would be of great utility in being able to prioritize progressable over nonprogressable screening hits. In this study, we present a carefully compiled set of over 100 nuisance compounds that are known to interfere with assay readouts in either phenotypic or target-based screenings. Readily accessible in an assay-ready screening plate, we believe this nuisance compound set will be of great interest to the research community, helping to establish high-quality HTS assays and identify promising, optimizable hits.

Gardenin A treatment attenuates inflammatory markers, synuclein pathology and deficits in tyrosine hydroxylase expression and improves cognitive and motor function in A53T-α-syn mice

Oxidative stress and neuroinflammation are widespread in the Parkinson's disease (PD) brain and contribute to the synaptic degradation and dopaminergic cell loss that result in cognitive impairment and motor dysfunction. The polymethoxyflavone Gardenin A (GA) has been shown to activate the NRF2-regulated antioxidant pathway and inhibit the NFkB-dependent pro-inflammatory pathway in a Drosophila model of PD. Here, we evaluate the effects of GA on A53T alpha-synuclein overexpressing (A53TSyn) mice. A53TSyn mice were treated orally for 4 weeks with 0, 25, or 100 mg/kg GA. In the fourth week, mice underwent behavioral testing and tissue was harvested for immunohistochemical analysis of tyrosine hydroxylase (TH) and phosphorylated alpha synuclein (pSyn) expression, and quantification of synaptic, antioxidant and inflammatory gene expression. Results were compared to vehicle-treated C57BL6J mice. Treatment with 100 mg/kg GA improved associative memory and decreased abnormalities in mobility and gait in A53TSyn mice. GA treatment also reduced pSyn levels in both the cortex and hippocampus and attenuated the reduction in TH expression in the striatum seen in A53Tsyn mice. Additionally, GA increased cortical expression of NRF2-regulated antioxidant genes and decreased expression of NFkB-dependent pro-inflammatory genes. GA was readily detectable in the brains of treated mice and modulated the lipid profile in the deep gray brain tissue of those animals. While the beneficial effects of GA on cognitive deficits, motor dysfunction and PD pathology are promising, future studies are needed to further fully elucidate the mechanism of action of GA, optimizing dosing and confirm these effects in other PD models.

Gardenin A improves cognitive and motor function in A53T-α-syn mice

Oxidative stress and neuroinflammation are widespread in the Parkinson's disease (PD) brain and contribute to the synaptic degradation and dopaminergic cell loss that result in cognitive impairment and motor dysfunction. The polymethoxyflavone Gardenin A (GA) has been shown to activate the NRF2-regulated antioxidant pathway and inhibit the NFkB-dependent pro-inflammatory pathway in a Drosophila model of PD. Here, we evaluate the effects of GA on A53T alpha-synuclein overexpressing (A53TSyn) mice. A53TSyn mice were treated orally for 4 weeks with 0, 25, or 100 mg/kg GA. In the fourth week, mice underwent behavioral testing and tissue was harvested for immunohistochemical analysis of tyrosine hydroxylase (TH) and phosphorylated alpha synuclein (pSyn) expression, and quantification of synaptic, antioxidant and inflammatory gene expression. Results were compared to vehicle-treated C57BL6 mice. Treatment with 100 mg/kg GA improved associative memory and decreased abnormalities in mobility and gait in A53TSyn mice. GA treatment also reduced cortical and hippocampal levels of pSyn and attenuated the reduction in TH expression in the striatum. Additionally, GA increased cortical expression of NRF2-regulated antioxidant genes and decreased expression of NFkB-dependent pro-inflammatory genes. GA was readily detectable in the brains of treated mice and modulated the lipid profile in the deep gray brain tissue of those animals. While the beneficial effects of GA on cognitive deficits, motor dysfunction and PD pathology are promising, future studies are needed to further fully elucidate the mechanism of action of GA, optimizing dosing and confirm these effects in other PD models.

Significance Statement

The polymethoxyflavone Gardenin A can improve cognitive and motor function and attenuate both increases in phosphorylated alpha synuclein and reductions in tyrosine hydroxylase expression in A53T alpha synuclein overexpressing mice. These effects may be related to activation of the NRF2-regulated antioxidant response and downregulation of NFkB-dependent inflammatory response by Gardenin A in treated animals. The study also showed excellent brain bioavailability of Gardenin A and modifications of the lipid profile, possibly through interactions between Gardenin A with the lipid bilayer, following oral administration. The study confirms neuroprotective activity of Gardenin A previously reported in toxin induced Drosophila model of Parkinson's disease.

Consideration for Flavonoid-Containing Dietary Supplements to Tackle Deficiency and Optimize Health

Randomized clinical trials (RCT) and observational studies have highlighted the importance of flavonoid consumption for human health. Several studies have associated a high intake of dietary flavonoids with (a) enhanced metabolic and cardiovascular health, (b) enhanced cognitive and vascular endothelial functions, (c) an improved glycemic response in type 2 diabetes mellitus, and (d) a reduced risk of breast cancer in postmenopausal women. Since flavonoids belong to a broad and diverse family of polyphenolic plant molecules-with more than 6000 compounds interspersed in the human diet-researchers are still uncertain whether the intake of single, individual polyphenols or a large combination of them (i.e., synergistic action) can produce the greatest health benefits for humans. Furthermore, studies have reported a poor bioavailability of flavonoid compounds in humans, which presents a major challenge for determining their optimal dosage, recommended intake, and, consequently, their therapeutic value. Especially because of their scarce bioavailability from foods-along with the overall declining food quality and nutrient density in foods-the role of flavonoid supplementation may become increasingly important for human health. Although research shows that dietary supplements can be a highly useful tool to complement diets that lack sufficient amounts of important nutrients, some caution is warranted regarding possible interactions with prescription and non-prescription drugs, especially when taken concurrently. Herein, we discuss the current scientific basis for using flavonoid supplementation to improve health as well as the limitations related to high intakes of dietary flavonoids.

Predicting structural features of selected flavonoids responsible for neuroprotection in a Drosophila model of Parkinson's disease

Nature-derived bioactive compounds have emerged as promising candidates for the prevention and treatment of diverse chronic illnesses, including neurodegenerative diseases. However, the exact molecular mechanisms underlying their neuroprotective effects remain unclear. Most studies focus solely on the antioxidant activities of natural products which translate to poor outcome in clinical trials. Current therapies against neurodegeneration only provide symptomatic relief, thereby underscoring the need for novel strategies to combat disease onset and progression. We have employed an environmental toxin-induced Drosophila Parkinson's disease (PD) model as an inexpensive in vivo screening platform to explore the neuroprotective potential of selected dietary flavonoids. We have identified a specific group of flavonoids known as flavones displaying protection against paraquat (PQ)-induced neurodegenerative phenotypes involving reduced survival, mobility defects, and enhanced oxidative stress. Interestingly, the other groups of investigated flavonoids, namely, the flavonones and flavonols failed to provide protection indicating a requirement of specific structural features that confer protection against PQ-mediated neurotoxicity in Drosophila. Based on our screen, the neuroprotective flavones lack a functional group substitution at the C3 and contain α,β-unsaturated carbonyl group. Furthermore, flavones-mediated neuroprotection is not solely dependent on antioxidant properties through nuclear factor erythroid 2-related factor 2 (Nrf2) but also requires regulation of the immune deficiency (IMD) pathway involving NFκB and the negative regulator poor Imd response upon knock-in (Pirk). Our data have identified specific structural features of selected flavonoids that provide neuroprotection against environmental toxin-induced PD pathogenesis that can be explored for novel therapeutic interventions.

Drug discovery from natural products - Old problems and novel solutions for the treatment of neurodegenerative diseases

The use of natural products has been shown to be a fruitful approach in the discovery of novel pharmaceuticals. In fact, many currently approved drugs originated from compounds that were first identified in nature. Chemical diversity of natural compounds cannot be matched by man-made libraries of chemically synthesized molecules. Many natural compounds interact with and modulate regulatory protein targets and can be considered evolutionarily-optimized drug-like molecules. Despite this, many pharmaceutical companies have reduced or eliminated their natural product discovery programs in the last two decades. Screening natural products for pharmacologically active compounds is a challenging task that requires high resource commitment. Novel approaches at the early stage of the drug discovery pipeline are needed to allow for rapid screening and identification of the most promising molecules. Here, we review the possible evolutionary roots for drug-like characteristics of numerous natural compounds. Since many of these compounds target evolutionarily conserved cellular signaling pathways, we propose novel, early-stage drug discovery approaches to identify drug candidates that can be used for the potential prevention and treatment of neurodegenerative diseases. Invertebrate in vivo animal models of neurodegenerative diseases and innovative tools used within these models are proposed here as a screening funnel to identify new drug candidates and to shuttle these hits into further stages of the drug discovery pipeline.