Alzheimer's Update: 'Beeting' Alzheimer's Disease
Antioxidants have become favorable ingredients and supplements in food and nutrition industries. Although aerobic metabolism supports great and diverse life forms, misregulated oxidation can damage biomolecules and harm living organisms. To be oxidized, thus, is unavoidable for aerobic organisms. Nevertheless, living systems since the Great Oxygenation Event roughly 2 billion years ago have gradually evolved to cope with unnecessary oxidative damages by producing antioxidation agents and enzymes.
Foods rich in antioxidants such as beetroot and its products frequently are labeled as "superfoods" to boost sales. Despite extensive knowledge about oxidation chemistry in living systems, it's not clear whether additional antioxidants can ease the oxidative damages in vivo. It's an issue that deserves further discussion.
Since biological oxidative damage is a risk factor in Alzheimer's disease (AD) and many other disorders, antioxidant-rich foods may thus be helpful for human health. Our recent research further points to the possible benefits of antioxidants, including beetroots, for patients with AD.
Biochemical Imbalance and Oxidative Stress
These two side products, referred to as the reactive oxygen species (ROS), are relatively more reactive than O2 and can yield unnecessary oxidation of biomolecules. They can also cause the biochemical/physiological phenomenon dubbed "oxidative stress," which is associated with many disorders and diseases in humans, including arthritis, diabetes, heart diseases, aging, and neurodegenerative diseases such as Alzheimer's and Parkinson's.1-3 If the abnormal redox activities can be blocked, the disorders and diseases may be better prevented, controlled, and treated along with the use of existing clinical treatments.
Redox-active Fe and Cu ions in small biomolecules and proteins can potentially interact/bind with oxygen and produce ROS. Thus, antioxidants that can inhibit oxygen binding to the Fe and Cu centers can greatly prevent the formation of ROS and may be beneficial to health from a chemical viewpoint. Although chemical research cannot be translated directly to clinical use, some statistical analyses point to possible connections, such as the health benefits of Mediterranean diet4 and nuts5, which are widely accepted by biochemists and health professionals.
With a gradual increase in the average age of the population, age-dependent AD has become a significant public health issue that will become more serious with time. Currently, there are no drugs or treatments that can cure this disease, and available medications are prescribed only to ease the symptoms. Since the etiology of this disease has not been fully understood, there are no targets for its prevention and treatment. Nevertheless, some risk factors for the disease, such as environment, infections, inflammation, brain injury, brain activities, and oxidative stress, may serve as targets that everyone can pay attention to.
Antioxidants Against AD
The Aβ hypothesis is supported by the observation that Aβ plaques are toxic to neurons and some rat models and that the overexpression of Aβ in familial AD and Down's syndrome can result in early onset of the disease.8-11 Meanwhile, the presence of Aβ in healthy cerebrospinal fluid, the focal distribution of Aβ in the brains, and the presence of Aβ plaques associated with head injury that eventually disappear reflect that other factors may be involved and challenge the role of Aβ in AD.12-14
Despite the uncertainty, inhibition of Aβ toxicity can be a useful strategy for alleviating damages by Aβ if it is a cause of the disease, or preventing further damages by Aβ if it is a consequence of the disease.
Aβ peptide can bind transition metal iron, cobalt, copper, and zinc (Fe, Co, Cu, and Zn) ions. Of these, the redox-active Fe- and Cu-Aβ complexes can potentially render oxidative stress in vivo. Our research shows that several neurotransmitters, including dopamine, epinephrine, norepinephrine, and serotonin, can be oxidized by Cu-Aβ complexes with astonishing rate accelerations.
The oxidation of the neurotransmitters is notably enhanced under oxidative stress when hydrogen peroxide H2O2 is present.15-17 Since these neurotransmitters are involved in many brain functions, such as satisfaction, mood, sleep cycle, and alertness, their oxidation may disturb certain proper brain functions that are linked to the misbehaviors of AD patients. Whether there's any connection between the oxidation of neurotransmitters and AD symptoms and to what extent can these in vitro experimental results be translated into in vivo situations are questions requiring further extensive research, clinical trials, and broad statistical analyses. Regardless, if unregulated oxidations of neurotransmitters by metal-Aβ complexes can be prevented, possible benefits may be gained.
Flavonoids are ubiquitous antioxidants in plants (fruits, vegetables, green tea, and red wine) and have diverse bioactivities, showing antimicrobial, antifungal, antiviral, anticancer, antihepatotoxic, antiinflammatory, antiatherogenic, antiallergenic, antiosteoporotic, antibiotic, and neuroprotective properties.18,19 Moreover, flavonoids increase the lifespan of the worm Caenorhabditis elegans,20,21 protect the striatum in rat model of Parkinson's disease against oxidative stress and dopaminergic neuron loss,22 prevent Aβ plaque formation,23-25 and protect Aβ-induced cellular toxicity.26
Our research, which shows flavonoids can inhibit the oxidative activity of Cu-Aβ, also reveals different mechanisms for the inhibition by various flavonoids.27 The metal-chelating quercetin was quantified to be 10-fold more effective than the nonchelating catechin and epicatechin against Cu-Aβ oxidation activity.
Our most recent endeavor on the inhibition of the oxidative activity of Cu-Aβ was presented at the 255th National Meeting & Exposition of the American Chemical Society.28 Therein, we demonstrated that the red pigment betanin from beetroots is a potential metal-binding ligand and an excellent inhibitor against the oxidative activity of Cu-Aβ. Since betanin can pass the blood-brain barrier and inhibit the oxidation activity of Cu-Aβ, it can potentially lessen oxidative stress in the brains of AD patients.
Betanin belongs to the indole-derived betalain pigment family found in roughly a dozen plant families, including red beets (Beta vulgaris, from which the term betanin was coined), amaranth (such as colored quinoas of the genus Chenopodium), bougainvillea, Malabar spinach (Basella rubra L, which contains gomphrenin in its ripe fruits), and some cacti (such as red pitahaya, aka red dragonfruit Hylocereus costaricensis, which also contains indicaxanthin). Besides their antioxidation activity, betalains also exhibit anti-inflammatory, anticancer, antilipodemic, and antimicrobial activities, according to cellular studies.29
Clinical trials indicate that red beet exhibits some health benefits, including lowering blood pressure, improving athletic performance (which may be attributed to its nitrate content), and stimulating liver cell function (which awaits further explorations), and thus is a low-cost functional food for cardiovascular health.30
Those who consume betalain-containing foods should be aware that the pigments can pass through the digestive and urinary systems and appear in bowel movements and urine, causing unnecessary alarm.
Since fruits and vegetables are rich in antioxidants, they are chemically sound to be used against oxidative stress, including that caused by Cu- and Fe-Aβ in AD. Before strategies can be found for preventing the disease and drugs are developed for treating it, some potential tactics to protect against the devastation of AD are still the common sense practices of keeping the brain active, exercising, eating healthful diets, including eating plenty fruits and vegetables, and "beeting" it with beetroots.
— Li-June Ming, PhD, is a professor in the department of chemistry at the University of South Florida. He specializes in bioinorganic chemistry and inorganic medicinal chemistry through the use of nuclear magnetic resonance and kinetics as research tools.
Acknowledgments: Our research on oxidation chemistry of metallopeptides was partially supported by the National Science Foundation, the University of South Florida (USF), and the USF MetalloBiomolecule Interest Group Research Fund.
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