Dr RG Wiseman Pinto
Nitric oxide is an important molecule that has attracted considerable attention in modern medical research. Today, medical research is going down to the level of molecules within cells and intercellular regions. Nitric oxide is one such molecule whose role has been revisited and redefined over the decades in the era of molecular medicine.
Nitric oxide (NO) was first synthesised by Joseph Priestley in 1772. Later, in 1998, three scientists, Dr F Murad, Dr R Furchgott and Dr L Ignarro, received the Nobel Prize in Physiology or Medicine for demonstrating that NO causes relaxation of vascular smooth muscle, resulting in dilation of blood vessels and contributing to cardiovascular physiology.
NO is a colourless gas in nature but, in the human body, it has tremendous useful effects on numerous systems and organs. It is produced in endothelial cells, macrophages and neurones from the amino acids arginine and citrulline. It requires the enzyme NOS, nitric oxide synthase.
NO is today regarded as a holy grail because of its numerous effects. It causes vasodilation of blood vessels by relaxing smooth muscles. In this way, it supplies abundant nutrition and oxygen to tissues and organs. It is useful in preventing Alzheimer's disease, diabetes mellitus and autoimmune diseases. It has anti-inflammatory effects and boosts immunity. It also functions as a brain neurotransmitter, reduces stress and lowers blood pressure.
NO helps in erectile function in both males and females, improves stamina, helps prevent strokes and may help reduce atherosclerosis. It also reduces oxidative stress, helping in anti-ageing, and acts on platelets, improving their function.
All organs benefit from NO, with important effects on the cardiovascular system, lungs, central nervous system and kidneys.
NO is present in certain dietary items and is also produced through different pathways. The first is the NOS pathway. As age increases, the level and activity of this enzyme decrease. The second is the enterosalivary pathway, in which nitrates in food are converted to NO in the posterior part of the tongue by anaerobic bacteria. A third pathway operates in hypoxic situations. There is also an alternative pathway in the paranasal sinuses.
Thus, the raw materials for NO include the amino acids arginine and citrulline.
Dietary items very rich in NO and its precursors include beetroot and beet juice, salads, green leafy vegetables, spinach, garlic and celery. Citrus fruits such as oranges, lemons, lime and grapes are rich in vitamin C. Watermelons and watermelon juice, dark chocolates, pomegranates, nuts and seeds and rhubarb are also included.
However, excess NO can be harmful because it can act as a free radical. Excess NO can cause respiratory irritation, eye and skin problems, lung damage and blood toxicity.
Many molecules are undergoing clinical trials and research to obtain adequate NO. However, natural fruits and vegetables consumed in abundant quantity, together with good lifestyle practices, will produce NO which can be beneficial to organs and systems and help in these lifestyle diseases.
Thus, NO is indeed a golden grail. The future holds optimistic times.
(The writer is a Professor of Pathology, former Head of Department at Goa Medical College, former Dean of Goa University, and the current President of the Asian Society of Cytopathology)
