The term flavonoid describes all polyphenolic plant constituents that have a carbon skeleton analogous to that of the flavones -that is, two substituted benzene rings connected a 3-carbon chain. All of the approximately 4000 flavonoids that have been identified possess this same basic structural makeup. They are nearly ubiquitous secondary metabolites found especially in leafs, fruits & flowers. The are water soluble and occur both in free state and as glycosides.

Their molecular classification can be broken down as follows:

  • Degree of saturation of heterocyclic ring
  • Biosynthetic origin (ie. those that are intermediate steps vs. end products)
  • Molecular size (ie. mono, di, tri, and polymeric structures)
  • Conjugates (ie. whether bound to a sugar unit or hydroxyl group)

Their major role in plants is to function as growth regulators, and protect the plant from UV radiation by scavenging free radicals produced by the photosynthetic electron transport system. The also act as pigments, imparting colour to flowers & fruits.

Major Flavonoids Classes Include:

  • Flavonols (Quercitin)
  • Flavones (Apigenin)
  • Flavonones (Naringin)
  • Isoflavones (Genistein)
  • Catechins
  • Anthocyanidins/Proanthocyanidins  (Aka. Condensed tannins)

In the body they have a wide range of actions and many medicinal uses. Being potent antioxidants, they have been referred to as “nature’s biological response modifiers” or Redox Regulators, since they modify the body’s reaction to compounds such as allergens, viruses and carcinogens as evidenced by their anti-inflammatory, anti-allergic, antiviral and anticancer properties. Additionally they will strengthen vascular capillaries to prevent leakage of body fluids into surrounding tissues, and some will have phytoestrogenic, and liver-protective activity.

In summary the major actions of flavonoids include:

  • Antioxidant or Redox regulators, permitting resonance stabilization and rending potentially damaging molecules relatively unreactive
  • Smooth muscle relaxation (antispasmodics & hypotensives)
  • Reduced platelet aggregation & blood vessel protectants
  • Improved hypoxic tolerance
  • Enhanced neural transmission & Neuro-protective effects
  • Inhibition of mast cell lysis
  • Reduced capillary fragility via ability to crosslink collagen fibers
  • Increased intra-cellular vitamin C
  • Reduced allergic responses
  • Reduction of inflammatory leukotrienes
  • Mediate prevention of LDL oxidation
  • Bind metal ions (which prevent them from acting as ROS catalysts)

Pharmacology of Flavonoids

  • Inhibit the reduction of dehydroascorbic acid via glutathione by acting as H+ donors.
  • Inhibit catechol-O-methyltransferase → increased availability of catecholamines
  • Stimulate proline hydroxylase → formation of cross links between collagen fibers reinforces tensile strength of connective tissue and cell structures
  • Are synergists for Vitamin C, and will increase the amount of available in tissues by preventing it’s breakdown and up regulating it’s absorption

Herbal examples:

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