Oxidative Stress Explained 

To understand oxidative stress better it is helpful to understand the chemistry of a free radical.

Atoms are surrounded by electrons that orbit the atom in layers called shells. Each shell needs to be filled by a set number of electrons. If the outer shell of an atom is not full, it is unstable and called a free radical. Atoms want to have a full outer shell so the free radicals react quickly with other substances to try attain another electron.

There are many types of free radicals, but the ones of most concern in biological systems are derived from oxygen, and these free radicals are known collectively as reactive oxygen species (ROS).

Oxygen has two unpaired electrons, one in each of the two outer shells. This structure makes oxygen especially susceptible to radical formation. Reactive oxygen species (ROS) are reactive forms of a standard oxygen molecule. High levels of ROS cause damage to cellular structures that leads to the process of oxidative stress.

Oxidative stress can damage the body’s cells, leading to a range of diseases and causes symptoms of aging, such as wrinkles.

Reactive Species Effects

Examples of reactive oxygen and nitrogen species

Enzymatic Antioxidants

Oxygen molecules in the body sometimes have an electron removed from its shell which makes it reactive species superoxide. Superoxide can be managed in a few ways.

1. One way is that a SOD enzyme changes superoxide to hydrogen peroxide and oxygen which is less reactive but still potentially harmful. Hydrogen peroxide is then neutralised by either GPx or CAT enzymes.

CAT enzyme converts the harmful hydrogen peroxide to neutral water and oxygen using iron as a cofactor.

GPx enzyme converts mildly harmful hydrogen peroxide to neutral water and oxygen using selenium and glutathione as a cofactor. During this process glutathione (GSH) is converted to glutathione disulfide (GSSG). The body wants more GSH to help convert more hydrogen peroxide so it needs to convert the GSSG back to GSH. Glutathione reductase enzyme converts GSSG back to GSH using vitamin B2 and NADPH.

2. Superoxide is sometimes also converted to other reactive species such as hydroxides. Metal ions are used as cofactors during this reaction. This is why one wants SOD enzymes to be working effectively to start the process of neutralising superoxides.

Exogenous Verses Endogenous Antioxidants

Endogenous antioxidants:

• Superoxide dismutase (SOD)
• Catalase (CAT)
• Glutathione peroxidase (GPx)
• Paraoxanase
• Glutathione S -transferase (GST)
• Glutathione
• Lipoic acid
• Bilirubin
• Melatonin
• Ubiquinol
• Uric acid
• Ferritin
• Transferrin

Interventions

• Ensure adequate intake of manganese, the cofactor for SOD2.
• As GPx1 uses selenium as a co-factor it is helpful to ensure adequate selenium intake. Brazil nuts are a rich source of selenium, and a regular intake has been shown to significantly increase the activity of the GPx1 enzyme in C allele carriers. One brazil nut contains approximately 70mcg of selenium, (providing over 100% RDA). Include brazil nuts in the diet and other food-rich sources of selenium, such as sardines and turkey. If selenium intake from food is poor, consider supplementation. 
• Provide adequate intake of glutathione precursors to support glutathione production. A diet should provide sulphur and building block amino acids. Eating beef, chicken and fish should supply adequate sulphur containing amino acids. For vegetarians and vegans the following may provide some sulphur but in smaller amounts: garlic, onion, broccoli, Brussels sprouts, cauliflower, kale, watercress and mustard greens. Some foods naturally contain glutathione however, it is poorly absorbed. Examples are spinach, avocados, and asparagus.