Mechanisms by Which Flavonoid Natural Products Regulate the Oxidative Stress-Inflammation Axis

Flavonoid natural products are not merely general free-radical-scavenging constituents, but important regulatory molecules capable of acting simultaneously on reactive oxygen species generation, redox buffering, inflammatory sensing, signal transduction, and inflammatory execution. In multiple stress and pathological contexts, oxidative stress and inflammation are not two independent categories of change, but instead form a continuously amplified positive-feedback network through processes such as mitochondrial damage, membrane lipid peroxidation, inflammasome assembly, and transcription-factor activation. The significance of flavonoid natural products therefore does not lie merely in single labels such as “antioxidant” or “anti-inflammatory,” but in their capacity to intervene at multiple levels of the oxidative stress-inflammation axis and alter the way cells and tissues respond to injurious stimuli. Analysis centered on the oxidative-stress initiation layer, antioxidant transcription layer, inflammatory transcription layer, inflammatory execution layer, and cellular-state layer is more helpful for understanding the true mechanistic positioning and research value of flavonoid natural products.

Keywords: flavonoids; oxidative stress; inflammation; reactive oxygen species; NF-kappaB; Nrf2; NLRP3; natural products

1. Biological Positioning of the Oxidative Stress-Inflammation Axis

1.1 Signaling properties of oxidative stress

(1) Reactive oxygen species generation layer

Reactive oxygen species are not merely byproducts of cellular injury. Within the physiological range, reactive oxygen species themselves are important signaling molecules involved in metabolic sensing, cell proliferation, and regulation of adaptive transcription. However, when their rate of generation continuously exceeds the capacity for clearance and buffering, reactive oxygen species are transformed from controllable signals into pro-damage factors, thereby inducing lipid peroxidation, oxidative protein modification, DNA damage, and organelle dysfunction.

(2) Redox homeostasis layer

Cellular control of reactive oxygen species does not depend on a single scavenging reaction, but on maintenance of redox balance through glutathione, thioredoxin, SOD, CAT, GPx, and Nrf2-related transcriptional responses. Once the reductive buffering system becomes insufficient, cells may still enter a state of stress amplification even when the absolute ROS level is not extremely elevated. Therefore, oxidative stress is fundamentally not a question of whether ROS exist, but whether ROS generation and clearance are out of balance.

1.2 Oxidation dependence of inflammatory responses

(1) Pro-inflammatory transcription initiation layer

Many inflammatory pathways are not initiated independently of an oxidative background. Membrane-receptor activation, mitochondrial injury, and metabolic stress can all be accompanied by elevated reactive oxygen species, which further promote activation of pro-inflammatory signaling pathways such as NF-kappaB, AP-1, MAPK, and JAK/STAT, thereby increasing expression of TNF-alpha, IL-1beta, IL-6, COX-2, and iNOS. Accordingly, oxidative stress often serves as the condition layer that allows inflammatory transcription to be continuously amplified.

(2) Inflammatory execution amplification layer

Once inflammation is established, it can further increase ROS and RNS burden through immune-cell recruitment, activation of NADPH oxidases, aggravation of mitochondrial damage, and inflammasome assembly, driving local tissues into a closed loop in which oxidation promotes inflammation and inflammation aggravates oxidation. In other words, oxidative stress and inflammation are not two separable groups of indicators, but one continuously amplifying coupled network.

Table 1. Major regulatory levels at which flavonoid natural products act on the oxidative stress-inflammation axis

Regulatory level	Representative nodes	Major actions of flavonoids	Mechanistic positioning
Oxidative-stress initiation layer	ROS, mitochondrial damage, lipid peroxidation	Reduce oxidative burden and buffer early injury	Upstream triggering layer of the axis
Antioxidant transcription layer	Nrf2/Keap1, HO-1, NQO1, GSH-related systems	Enhance endogenous defense and detoxification capacity	Negative regulatory layer of the axis
Inflammatory transcription layer	NF-kappaB, MAPK, TNF-alpha, IL-6, COX-2, iNOS	Downregulate pro-inflammatory gene expression	Transcriptional amplification layer of the axis
Inflammasome layer	NLRP3, ASC, caspase-1, IL-1beta	Suppress inflammatory escalation and pyroptotic amplification	Execution amplification level of the axis
Cellular-state layer	Autophagy, mitochondrial homeostasis, macrophage polarization	Reduce sustained injury and chronic inflammatory tendency	Outcome-regulatory layer of the axis

2. Structural Basis and Reaction Characteristics of Flavonoid Natural Products

2.1 Redox basis of the flavonoid scaffold

(1) Phenolic hydroxyl distribution

The characteristic redox-regulatory potential of flavonoid natural products is closely related to their polyphenolic skeleton. The catechol structure on the B ring, the conjugated system formed by the C2-C3 double bond and 4-oxo group, and the degree of hydroxylation at different positions together determine their electron-delocalization ability, radical-stabilizing capacity, and metal-ion-chelating capacity. Therefore, different flavonoids cannot simply be generalized as “all antioxidant,” because they exhibit obvious structural differences in reactivity.

(2) Substituent-modification characteristics

Natural flavonoids often occur as glycosides, methoxylated derivatives, or more complex conjugated forms. Glycosylation usually alters polarity, absorption, and cellular accessibility, whereas methoxylation may affect membrane permeability and metabolic stability. Accordingly, the in vivo effects of flavonoids do not always correspond directly to the in vitro activity of their corresponding aglycones, but instead must be evaluated in the combined context of absorption, biotransformation, and tissue exposure.

2.2 Multilevel properties of flavonoid action

(1) Direct reactive oxygen species scavenging

Flavonoids can directly participate in scavenging reactive oxygen and reactive nitrogen species through hydrogen donation, electron donation, or stabilization of radical intermediates. This level reflects mainly chemical reactivity and represents the initiation layer by which flavonoid natural products participate in regulation of oxidative stress, rather than their full biological significance.

(2) Signaling-network regulation

In vivo, the more important significance of flavonoids often lies in their regulation of signaling layers such as Nrf2, NF-kappaB, MAPK, JAK/STAT, and NLRP3, as well as in remodeling of mitochondria, the NOX system, antioxidant-enzyme networks, and inflammatory mediator expression profiles. For this reason, flavonoid natural products should be regarded as multilevel regulatory molecules that possess both chemical buffering capacity and signaling-regulatory capacity.

3. Regulation of the Oxidative Stress Layer by Flavonoid Natural Products

3.1 Regulation of the reactive oxygen species generation layer

(1) Regulation of mitochondria-derived ROS

Mitochondria are one of the major intracellular sources of ROS. When the electron transport chain is imbalanced, membrane potential becomes abnormal, or mitochondrial dynamics are disturbed, ROS generation rises markedly. Multiple classes of flavonoids can reduce mitochondria-derived ROS burden by improving mitochondrial membrane stability, maintaining membrane potential, reducing electron leakage, and buffering mitochondria-related oxidative stress. Their significance lies not in completely blocking oxidation, but in lowering the probability that mitochondria shift from signaling organelles to damage amplifiers.

(2) Regulation of NADPH oxidase-related ROS

In addition to mitochondria, the NADPH oxidase system is another major source of ROS under inflammatory conditions. Flavonoids can, to some extent, inhibit activation of the NOX system and reduce membrane-associated oxidative bursts, thereby decreasing oxidative burden in inflammatory cells and damaged tissues. This is particularly important in vascular inflammation, metabolic inflammation, and conditions involving excessive immune-cell activation.

3.2 Regulation of the antioxidant defense layer

(1) Nrf2-ARE response layer

One of the most representative mechanisms by which flavonoids regulate oxidative stress is promotion of the Nrf2-mediated antioxidant response. After translocation into the nucleus, Nrf2 can upregulate expression of antioxidant- and detoxification-related genes such as HO-1, NQO1, GCLC, GCLM, SOD, CAT, and GPx, thereby enhancing the cellular buffering capacity against persistent oxidative stimulation. Compared with direct ROS scavenging, this type of regulation is more oriented toward increasing overall system resilience.

(2) Glutathione and enzyme-maintenance layer

Many flavonoids can also indirectly maintain the GSH/GSSG balance, improve the operational efficiency of glutathione-dependent antioxidant systems, and reduce accumulation of terminal products of lipid peroxidation. In other words, flavonoids do not merely remove ROS that have already formed, but also support continued operation of antioxidant systems so that cells do not rapidly enter a state of oxidative exhaustion.

4. Regulation of the Inflammatory Signaling Layer by Flavonoid Natural Products

4.1 Regulation of the pro-inflammatory transcription layer

(1) NF-kappaB signaling layer

NF-kappaB is the core transcriptional hub linking inflammatory input to inflammatory output. Flavonoids can weaken expression of pro-inflammatory molecules such as TNF-alpha, IL-1beta, IL-6, COX-2, and iNOS by inhibiting IkappaBalpha degradation, reducing nuclear translocation of p65, or suppressing activation of upstream kinases. Their significance lies not only in lowering inflammatory mediators, but in reducing the tendency of tissues to enter a sustained inflammatory transcriptional state.

(2) MAPK and AP-1 signaling layer

In addition to NF-kappaB, flavonoids commonly affect ERK, JNK, p38 MAPK, and their related AP-1 signaling outputs. Because the MAPK system occupies a key intermediate position between receptor activation, stress sensing, and inflammatory transcription, flavonoid-mediated regulation of this system often simultaneously influences inflammatory amplification, stress responses, and cell-fate decisions.

4.2 Regulation of the inflammatory execution layer

(1) NLRP3 inflammasome layer

The NLRP3 inflammasome is an important point of convergence between oxidative stress and inflammatory execution. Mitochondrial ROS, abnormal ionic fluxes, lysosomal damage, and redox imbalance can all promote its assembly. Many flavonoids can reduce caspase-1 activation and mature IL-1beta release by lowering ROS, stabilizing mitochondrial function, reducing TXNIP-related amplification, and suppressing inflammasome assembly, thereby weakening the strength of the inflammatory execution layer.

(2) Immune-cell recruitment layer

Inflammation is not reflected only in cytokine expression, but also in upregulation of adhesion molecules, recruitment of immune cells, and increased tissue infiltration. Flavonoids can reduce expression of ICAM-1, VCAM-1, MCP-1, and related molecules, weaken accumulation of inflammatory cells in local tissues, and thereby limit the progression of inflammation from local signaling to tissue-level injury.

Table 2. Major directions of action of flavonoid natural products within the oxidative stress-inflammation axis

Direction of action	Main manifestation	Effect on host status
Inhibition of ROS generation	Reduces mitochondrial ROS and suppresses NOX-related oxidative bursts	Lowers the initiation strength of oxidative stress
Enhancement of antioxidant defense	Increases Nrf2-related antioxidant-enzyme expression and maintains stability of the GSH system	Improves cellular stress resistance and recovery capacity
Suppression of pro-inflammatory signaling	Inhibits NF-kappaB, MAPK, and expression of related pro-inflammatory mediators	Weakens inflammatory transcriptional amplification
Inhibition of inflammatory execution	Suppresses the NLRP3 inflammasome, caspase-1 activation, and IL-1beta maturation	Blocks inflammatory escalation and expansion of tissue injury
Maintenance of cellular homeostasis	Improves mitochondrial function, maintains autophagic flux, and optimizes immune-cell status	Reduces chronic inflammation and prolonged tissue injury tendency

5. Intervention of Flavonoid Natural Products at the Oxidative Stress-Inflammation Coupling Layer

5.1 Mitochondria-inflammation coupling layer

(1) Maintenance of mitochondrial homeostasis

An important basis for coupling between oxidative stress and inflammation is that mitochondrial damage can simultaneously release ROS and damage-associated signals, thereby triggering inflammasome activation and amplification of pro-inflammatory transcription. By maintaining mitochondrial membrane potential, reducing oxidative injury, and improving metabolic coupling, flavonoids can weaken this amplification pathway at its source.

(2) Interruption of the translation of oxidative damage into inflammatory output

When flavonoids reduce mitochondrial ROS and membrane lipid peroxidation, their role is not merely to reduce injury indicators, but to interrupt at an earlier stage the translation of oxidative damage into the inflammatory execution layer. Therefore, regulation at this level is closer to “breaking the coupling relationship” than to simply lowering terminal inflammatory readouts.

5.2 Layer of weakening the positive-feedback amplification loop

(1) Intervention in the bidirectional amplification loop

An important value of flavonoid natural products lies in the fact that they often act simultaneously at the oxidative layer and the inflammatory layer. That is, they can both reduce ROS generation and strengthen antioxidant buffering, while also weakening inflammatory outputs such as NF-kappaB, MAPK, and NLRP3. This bidirectional regulation makes them especially suitable for interrupting the positive-feedback loop between oxidative stress and inflammation.

(2) Reconstruction of the adaptive state

When the oxidative stress-inflammation axis is continuously activated, cells more readily shift from transient responses into sustained injury states. The multilevel regulatory actions of flavonoids essentially pull cells back from a trajectory of “damage amplification” toward one of “adaptive maintenance.” Therefore, the significance of flavonoid regulation is closer to improving system-level homeostatic capacity than to producing improvement in only a single endpoint indicator.

6. Structural Differences and Functional Stratification of Flavonoids

6.1 Differences among flavonoid subclasses

(1) Advantages of flavonols and catechol structures

Flavonols with a catechol structure on the B ring and a strongly conjugated system usually display more pronounced advantages in radical stabilization, metal-ion chelation, and antioxidant signaling regulation. Such structures are more likely to exert both direct buffering effects at the oxidative stress layer and indirect signaling-regulatory effects.

(2) Distribution advantages of methoxylated flavonoids

Some methoxylated flavonoids may not possess the strongest direct free-radical-scavenging ability, but because of altered lipophilicity and membrane permeability, they may exhibit different advantages in intracellular distribution, metabolic stability, and regulation of specific signaling pathways. Therefore, flavonoid activity cannot be judged linearly only by the number of phenolic hydroxyl groups, but instead must be understood in a combined framework of structure, exposure, and target layer.

6.2 Parent compound-metabolite differences

(1) Characteristics of glycosylated precursors

In vitro, glycosylated flavonoids often show activity strengths different from those of their aglycones, but in vivo their significance depends more on gastrointestinal hydrolysis, microbiota transformation, and absorption pathways. In other words, glycosylated forms do not simply represent “lower activity,” but often represent “requiring prior conversion before exerting effects.”

(2) Contribution layer of in vivo metabolites

The parent flavonoid compound and its in vivo metabolites often do not act at the same level. The former may be more biased toward local chemical buffering, whereas the latter may be more biased toward systemic signaling regulation. Therefore, flavonoid research that remains only at the level of the parent structure often cannot fully explain the complexity of actual host effects.

Table 3. Major functional emphases of different flavonoid subclasses within the oxidative stress-inflammation axis

Flavonoid subclass	Representative compounds	Common functional emphasis	Mechanistic characteristics
Flavonols	Quercetin, kaempferol, myricetin	Antioxidation, regulation of defense transcription, suppression of inflammatory transcription	Rich in polyphenolic hydroxyl groups and capable of both direct scavenging and signal regulation
Flavones	Luteolin, apigenin, chrysin	NF-kappaB/MAPK inhibition and downregulation of inflammatory transcription	More commonly act at the inflammatory transcription layer and inflammatory output layer
Flavanones	Hesperetin, naringenin, eriodictyol	Buffering of oxidative burden and regulation of metabolic inflammation	Commonly associated with metabolic stress and lipid-inflammatory backgrounds
Isoflavones	Genistein, daidzein, puerarin	Inflammatory regulation, hormone-like signaling, and metabolic homeostasis regulation	More pronounced effects at receptor and metabolic layers
Polymethoxyflavones	Nobiletin, tangeretin	Regulation of inflammatory transcription and membrane-permeability-related effects	Structurally more stable, with distinct cellular accessibility and distribution features

7. Related Research Products

Table 4. Product table related to flavonoid natural products and the oxidative stress-inflammation axis

Name	CAS No.	Experimental Stage	Key Use	Use Notes
Quercetin	117-39-5	Parent flavonoid intervention	Used as a representative flavonol to evaluate ROS buffering, Nrf2 activation, and NF-kappaB inhibition	Suitable as a benchmark parent flavonoid for comparison with glycosylated or methoxylated flavonoids
Luteolin	491-70-3	Oxidation-inflammation coupling intervention	Commonly used to examine MAPK-, NF-kappaB-, and NLRP3-related inhibitory effects	Suitable for combined validation in pro-inflammatory stimulation models and ROS models
Apigenin	520-36-5	Inflammatory transcription layer research	Suitable for evaluation of pro-inflammatory cytokine expression, COX-2/iNOS regulation, and suppression of signaling transcription	Suitable for use with LPS- and TNF-alpha-stimulated systems
Kaempferol	520-18-3	Antioxidant signaling regulation	Used to analyze Nrf2-ARE responses, mitochondrial homeostasis, and inflammatory buffering effects	Suitable for comparison with quercetin to examine structural differences caused by absence of the catechol moiety
Myricetin	529-44-2	Strong redox intervention	Used to study inhibition of ROS, metal chelation, and inflammatory amplification by polyhydroxylated flavonoids	Oxidation-sensitive, so protection from light and low-temperature handling are required during solution preparation and storage
Fisetin	528-48-3	Stress-inflammation axis research	Commonly used in studies of senescence-related inflammation, ROS accumulation, and cellular protection	Suitable for chronic oxidative-stress and inflammatory models
Isorhamnetin	480-19-3	Structural-modification comparison	Used to analyze the influence of methylation on flavonoid anti-inflammatory and antioxidant behavior	Suitable for parent-methylated derivative comparison with quercetin
Galangin	548-83-4	Flavonoid scaffold comparison	Used to study differences in regulation of inflammatory transcription and oxidative responses by low-hydroxyl flavonoids	More suitable as a structure-function comparison molecule
Chrysin	480-40-0	Inflammatory signaling research	Used to evaluate buffering of NF-kappaB-, MAPK-, and oxidative-stress-related injury	Suitable for basic intervention in inflammation-induced cell models
Hesperetin	520-33-2	Flavanone-effect research	Suitable for studies of regulation of inflammatory cytokines, endothelial stress, and ROS by flavanones	Can be paired with hesperidin for comparison of glycosylation effects
Naringenin	480-41-1	Flavanone intervention research	Used to analyze oxidative stress, lipid-metabolic inflammation, and cytoprotective effects	Suitable for metabolic-inflammation and lipotoxicity models
Hesperidin	520-26-3	Glycosylated flavonoid research	Used to analyze the role and transformation potential of glycosylated flavonoids in the oxidation-inflammation axis	Suitable for comparison with hesperetin
Naringin	10236-47-2	Glycosylated flavonoid research	Used to study regulation of inflammation and oxidative responses by glycosylated flavanones	Suitable for paired design with naringenin
Rutin	153-18-4	Barrier and vascular oxidative-stress research	Commonly used in studies of vascular protection, capillary stabilization, and ROS buffering	Suitable for comparison between conjugated and aglycone forms with quercetin
Isoquercitrin	482-35-9	Flavonoid glycoside comparison	Used to analyze the effects of quercetin glycosylation on absorption and functional layer	Suitable for serial comparison with quercetin and rutin
Kaempferol-3-O-glucoside	480-10-4	Glycosylated flavonoid research	Used to compare differences between kaempferol and its glycoside in inflammatory and oxidative regulation	More suitable for structure-exposure-function relationship studies
Hyperoside	482-36-0	Oxidative-injury protection research	Commonly used in models of cardiovascular and epithelial oxidative injury protection	Suitable for comparison with the quercetin glycoside family
Myricitrin	17912-87-7	Research on glycosylated polyhydroxylated flavonoids	Used to study the antioxidant and anti-inflammatory potential of highly hydroxylated flavonoid glycosides	Suitable for comparison with myricetin to examine combined hydroxylation and glycosylation effects
Genistein	446-72-0	Isoflavone signaling regulation	Commonly used in studies of inflammatory regulation, hormone-related signaling, and oxidative injury	Suitable for comparison with daidzein and their glycosides
Daidzein	486-66-8	Isoflavone-effect research	Used to analyze regulation of oxidative stress and inflammatory pathways by parent isoflavones	Suitable for precursor-parent comparison with daidzin
Genistin	529-59-9	Glycosylated isoflavone research	Used to investigate transformation and host-effect differences of glycosylated isoflavones	Suitable for microbiota-transformation or hydrolysis-related designs
Daidzin	552-66-9	Glycosylated isoflavone research	Suitable for studying differences in in vitro and in vivo exposure of glycosylated isoflavones	Can be used with daidzein in comparative studies
Biochanin A	491-80-5	Methoxylated isoflavone research	Used to evaluate the influence of methoxylation on inflammatory and oxidative regulation by isoflavones	Suitable for studies of structure-modification differences
Formononetin	485-72-3	Methoxylated isoflavone research	Commonly used in studies of inflammatory regulation, metabolic signaling, and tissue protection	Can be grouped with daidzein and genistein for comparative isoflavone studies
Puerarin	3681-99-0	Glycosylated isoflavone research	Used to study vascular oxidative stress, inflammatory injury, and metabolic protective effects	Suitable for cardiovascular and ischemia-reperfusion-related models
Baicalein	491-67-8	Dual intervention on oxidation and inflammation	Commonly used for ROS inhibition, downregulation of inflammatory transcription, and cell protection	Suitable for comparison of parent compound-glycoside differences with baicalin
Baicalin	21967-41-9	Glycosylated flavonoid research	Used to study the role of glycosylated flavonoids in inflammation and barrier homeostasis	Can be used with baicalein to analyze deglycosylation effects
Wogonin	632-85-9	Methoxylated flavone research	Used to study regulation related to inflammasomes, NF-kappaB, and oxidative stress	Suitable for stratified comparison within the Scutellaria flavone series
Oroxylin A	480-11-5	Methoxylated flavone research	Commonly used in studies of inflammation inhibition, barrier protection, and signaling pathways	More suitable for comparison of permeability differences introduced by methoxylation
Cynaroside	5373-11-5	Glycosylated flavonoid research	Used to analyze the effects of luteolin glycosylation on oxidative stress and inflammatory regulation	Suitable for paired design with luteolin
Apigetrin	578-74-5	Glycosylated flavonoid research	Used to compare the effects of apigenin and its glycoside derivative	Suitable for comparison between absorption precursors and active parent compounds
Taxifolin	480-18-2	Flavanonol-type flavonoid research	Used to analyze the influence of a saturated C ring on oxidative-stress and inflammatory regulation	Suitable for scaffold-difference comparison with quercetin
Dihydromyricetin	27200-12-0	Polyhydroxylated flavonoid research	Commonly used in studies of oxidative injury, inflammatory mediators, and buffering of metabolic abnormalities	Suitable for high oxidative-stress models
Epigallocatechin gallate	989-51-5	Strong antioxidant intervention	Used as a representative tea polyphenol to study regulation of ROS, Nrf2, and inflammatory transcription layers	Easily oxidized, so freshly prepared solutions and protection from light are recommended
Catechin	154-23-4	Flavan-3-ol research	Used to analyze the effects of tea catechins on oxidative stress and inflammation	Suitable for stereoisomeric comparison with epicatechins
Epicatechin	490-46-0	Flavan-3-ol research	Commonly used in studies of vascular protection, ROS inhibition, and inflammatory buffering	Suitable for endothelial and metabolic-inflammation models
Epicatechin gallate	1257-08-5	Catechin-derivative research	Used to compare the effects of galloylation on oxidation-inflammation regulation	Can be compared with epigallocatechin gallate and catechin
Nobiletin	478-01-3	Polymethoxyflavone research	Commonly used in studies of metabolic inflammation, adipose inflammation, and oxidative-stress regulation	Suitable for high-fat inflammatory backgrounds
Tangeretin	481-53-8	Polymethoxyflavone research	Used to study inflammatory transcription, oxidative stress, and metabolic reprogramming	Suitable for paired comparison with nobiletin
Diosmetin	520-34-3	Methoxylated flavone research	Used to analyze effects related to the oxidation-inflammation axis and vascular protection	Can be compared with hesperetin and nobiletin
Acacetin	480-44-4	Flavone-structure comparison	Used to study regulation of inflammation and oxidative signaling by low-hydroxyl methoxylated flavones	More suitable for structure-function stratification studies

The relationship between flavonoid natural products and the oxidative stress-inflammation axis is not adequately described by the linear logic that “after free radicals are scavenged, inflammation then declines.” More fundamentally, flavonoids can act simultaneously on reactive oxygen species generation, antioxidant defense, inflammatory transcription, and inflammatory execution, thereby interrupting at multiple points the continuously amplified feedback loop between oxidative stress and inflammation. For this reason, the research value of flavonoids should not remain limited to traditional antioxidant labels, but should instead be understood in terms of their network-level role as multilevel regulators of the stress-inflammation axis.

For more related articles, please see below:

[1] Determination of the content of plant flavonoid compounds

[2] Flavones: Structural Features, Physicochemical Properties, and Key Points for Research and Applications