Inosine

Overview
Inosine is a nucleoside that is formed when hypoxanthine is attached to a ribose ring (also known as a ribofuranose) via a β-N9-glycosidic bond.

Inosine is commonly found in tRNAs and is essential for proper translation of the genetic code in wobble base pairs.

Knowledge of inosine metabolism has led to advances in immunotherapy in recent decades. Inosine monophosphate is oxidised by the enzyme inosine monophosphate dehydrogenase yielding xanthosine monophosphate, a key precursor in purine metabolism. Mycophenolate mofetil is an anti-metabolite, anti-proliferative drug, used in the treatment of a variety of autoimmune diseases including Wegener's granulomatosis. The uptake of purine by actively dividing B cells can exceed 8 times that of normal body cells and therefore this set of white cells (which cannot operate purine salvage pathways) is selectively targeted by the purine deficiency resulting from IMD inhibition.

Reactions
Adenine is converted to adenosine or IMP, either of which in turn is converted into inosine (I), which pairs with adenine (A), cytosine (C) and uracil (U).

Purine nucleoside phosphorylase intraconverts inosine and hypoxanthine.

Inosine is also an intermediate in a chain of purine nucleotides reactions required for muscle movements.

Clinical significance
It was tried in the seventies in eastern countries for improving athletic performance, based on the fact that is an intermediate compound used in the muscle movements. Nevertheless the clinical trials with this purpose showed no improvement.

Nowadays, it has been shown that inosine has neuroprotective properties. It has been proposed for administration after stroke, because observation has shown that axonal re-wiring is encouraged. It has been tried also for multiple sclerosis and is currently in phase II of the trials.

It produces uric acid after ingestion, which is a natural antioxidant and a peroxinitrite scavenger, which can explain the behaviour in multiple sclerosis (peroxynitrite has been correlated with the axons degeneration ).

Currently Boston Life Sciences holds the patent for treatment of stroke and this company is currently investigating its properties for MS under the name axosine for Multiple Sclerosis.

Biotechnology
When designing primers for polymerase chain reaction, inosine is useful in that it will indiscriminately pair with adenine, thymine, or cytosine. This allows one to design a primer that spans a single nucleotide polymorphism, without worry that the polymorphism will disrupt the primer's annealing efficiency.