Title: Engineering hydrophilic/amphiphilic Vitamin B6-based super antioxidant dendrimers for
controlling chronic inflammation
Project Summary/Abstract
Free radicals produced during chronic inflammation can damage cellular materials and cause oxidative stress,
which can intensify pathogenesis of various irreversible human diseases. Many studies report that naturally
occurring antioxidants such as vitamins C and E and quercetin are beneficial for prevention of a variety of
human ailments including asthma and cancer, but some studies are contradictory. Many natural antioxidants in
the presence of transition metal ions, like copper and iron, generate more free radicals (pro-oxidant effect). The
pro-oxidant effect is more severe with antioxidants that can directly coordinate with the metal ions through their
phenolic hydroxyl (OH) groups, such as catechol or gallol. We believe that this pro-oxidant action of
antioxidants explains the detrimental health effects reported for antioxidant supplements in clinical studies. We
previously synthesized large dendritic antioxidants with multiple phenolic units on the surface and interior with
metal chelating capability. These dendritic antioxidants showed much higher antioxidant activities over
naturally occurring popular antioxidants. For example, the dendrimer with 8 syringol units had 18-fold lower
IC50 in the DPPH assay than that of vitamin C. More importantly, they are devoid of harmful pro-oxidant
effects. We believed that the absence of pro-oxidant effects was achieved by entrapping metal ions within their
interior as well as using hindered phenolic units whose OH do not chelate transition metal ions. A major
drawback of the antioxidant dendrimers was their poor water-solubility. These antioxidants were highly
effective in quenching organic radicals and protecting non-polar biomolecules such as membrane lipids and
lipoproteins. However, their ability to quench water-soluble radicals such as OH· was limited. Various attempts
to increase the aqueous solubility of these compounds by incorporation of cores and branches rich in polar
groups were unsuccessful. In this proposal, we plan to develop a new class of hydrophilic/amphiphilic
antioxidant dendrimers with built-in potent antioxidant activity as well as metal chelating ability by synthesis
and assembly of pie-shaped dendritic segments known as dendrons (convergent method). A dendron with
metal chelating ability will be synthesized and its surface will be modified with three different classes of building
blocks (BBs) that are hydrophilic, hydrophobic, and amphiphilic. Water-soluble Vitamin B6 molecules (pyridoxal
and pyridoxal-5’-phosphate) will be used to form hydrophilic BBs and syringaldehyde, a hydrophobic BB. The
focal point of dendrons will be attached to a chemical carrying either an azido or alkynyl group. Attachment of
the properly matched dendrons via their focal points would yield hydrophilic/amphiphilic dendrimers with potent
antioxidant activities and devoid of any pro-oxidant actions. High potency will be achieved by attaching
numerous hindered antioxidant units to the surface of the dendron. The efficient metal chelation that helps
prevent the pro-oxidant effect will be achieved by embedding the N and O atoms to the interior of dendron.
Conjugation of BBs to the dendron surface and dendrons to dendrons will be done by “alkyne-azide click”
chemistry. The synthesized dendrimers will be tested for antioxidant activities (using chemical assays and the
biomolecules DNA and LDL) and pro-oxidant potential (using DNA). Cell toxicity will be assessed by the MTT
assay. Anti-inflammatory action on cytokine production will also be evaluated using RAW 264.7 macrophage
cells. Potent hydrophilic/amphiphilic antioxidant dendrimers free from pro-oxidant effects are potential
therapeutic agents for controlling chronic inflammation, and thus preventing/treating diseases strongly
associated with oxidative stress caused by free radicals. The availability of these antioxidants will also help
resolve the controversy associated with antioxidant supplementation in disease prevention/treatment.
