On the repair of oxidative damage to apoferritin: a model study with the flavonoids quercetin and rutin in aerated and deaerated solutions

The Role of Quercetin as a Plant-Derived Bioactive Agent in Preventive Medicine and Treatment in Skin Disorders

Quercetin, a bioactive plant flavonoid, is an antioxidant, and as such it exhibits numerous beneficial properties including anti-inflammatory, antiallergic, antibacterial and antiviral activity. It occurs naturally in fruit and vegetables such as apples, blueberries, cranberries, lettuce, and is present in plant waste such as onion peel or grape pomace which constitute good sources of quercetin for technological or pharmaceutical purposes. The presented study focuses on the role of quercetin in prevention and treatment of dermatological diseases analyzing its effect at a molecular level, its signal transduction and metabolism. Presented aspects of quercetin potential for skin treatment include protection against aging and UV radiation, stimulation of wound healing, reduction in melanogenesis, and prevention of skin oxidation. The article discusses quercetin sources (plant waste products included), methods of its medical administration, and perspectives for its further use in dermatology and diet therapy.

Quercetin and iron metabolism: What we know and what we need to know

Iron is a life-supporting micronutrient that is required in the human diet, and is essential for maintaining physiological homeostasis. Properly harnessing a redox-active metal such as iron is a great challenge for cells and organisms because an excess of highly reactive iron catalyzes the formation of reactive oxygen species and can lead to cell and tissue damage. Quercetin is a typical flavonoid that is commonly found in fruits and vegetables and has versatile biological effects. From a classical viewpoint, owing to its unique chemical characteristics, quercetin has long been associated with iron metabolism only in the context of its iron-chelating and ROS-scavenging activities. However, within the field of human iron biology, expanding concepts of the roles of quercetin are flourishing, and great strides are being made in understanding the interactions between quercetin and iron. This progress highlights the varied roles of quercetin in iron metabolism, which involve much more than iron chelation alone. A review of these studies provides an ideal context to summarize recent progress and discuss compelling evidence for therapeutic opportunities that could arise from a better understanding of the underlying mechanisms.

Chemistry of free radicals produced by oxidation of endogenous α-aminoketones. A study of 5-aminolevulinic acid and α-aminoacetone by fast kinetics spectroscopy

BACKGROUND

Excess 5-aminolevulinic acid (ALA) and α-aminoacetone (AA) are implicated in ketosis, porphyrinpathies and diabetes. Pathologic manifestations involve O₂⁻, H₂O₂, OH, enoyl radicals (ALA and AA) and their oxidation end products.

METHODS

To characterize enoyl radicals resulting from reaction of OH radicals with ALA and AA, micromolar OH concentrations were produced by pulse radiolysis of ALA and AA in aqueous solutions.

RESULTS

ALA and AA react with OH at k=1.5 × 10⁹ M⁻¹s⁻¹. At pH7.4, the ALA absorbance spectrum has a maximum at 330 nm (ε=750 M⁻¹cm⁻¹). This band appears as a shoulder at pH8.3 where two ALA species are present: (NH3)⁺-CH₂-CO-CH₂-CH₂-COO⁻ and NH₂-CH₂-CO-CH₂-CH₂-COO⁻ (pKa=8.3). At pH8.3, ALA reacts with oxygen (k=1.4 × 10⁸ M⁻¹s⁻¹) but not with O₂⁻. At pH8.3, AA oxidation produces two AA species characterized by an absorbance spectrum with maxima at 330 and 450 nm. ALA and AA are repaired by antioxidants (quercetin (QH), catechin, trolox, ascorbate) which are semi-oxidized (k>10(8)M⁻¹s⁻¹). QH bound to HSA or to apoferritin and ferritin repairs ALA and AA. In O₂-saturated apoferritin solutions, Q, O₂⁻, AA and reaction product(s) react with QH.

CONCLUSIONS

The optical absorption properties and the time evolution of ALA and AA were established for the first time. These radicals and their reaction products may be neutralized by antioxidants free in solution or bound to proteins.

GENERAL SIGNIFICANCE

Adjuvant antioxidant administration may be of interest in pathologies related to excess ALA or AA production.