IDPN (chemical)

IDPN is a synthetic nitrile, which was firstly synthesized among other amino nitriles in 1934.^[6] In the mid-20^th century  IDPN was described as a chemical that caused rodents to develop a  permanent neurological syndrome. This syndrome was characterized by abnormal movement and balance deficits. Subsequent studies showed that IDPN produces degeneration of vestibular hair cells.^[6][7]

During the late 20^th century, IDPN became a widely used experimental vestibular toxin in neurotoxicology. The compound was used to study hair-cell degeneration, central nervous system damage, and the behavioral consequences of vestibular dysfunction. These results showed that the degeneration of vestibular sensory cells and the changes in motor behavior are dose dependent.^[8]

IDPN is now used in laboratory studies as a model for inner-ear injury and movement disorders. This helps researchers to investigate how vestibular damage influences balance, sensory processing, and neuroplasticity.^[9]

IDPN is an aliphatic aminonitrile, specifically a secondary aminonitrile consisting of two β-cyanoethyl groups bound to a central nitrogen atom. Nitrile groups are commonly robust groups that are not metabolised unless activated by adjecent groups.^[10]The nitrile groups can act as hydrogen bond acceptors meaning that it can form hydrogen bonds with water or hydrogen bond donating amino acid residues such as serine and arganine.^[10]

IDPN is commonly synthesised through two successive cyanoethylations of ammonia with acrylonitrile under basic conditions.^[11] In the first step, ammonia undergoes a Michael addition to acrylonitrile to form β-aminonitrile.

${\displaystyle {\ce {NH3 + CH2=CH-CN->NH2-CH2-CH2-CN}}}$

In the second step, the reaction intermediate again undergoes a Michael addition with acrylonitrile to form β,β-iminodipropanenitrile.

${\displaystyle {\ce {NH2-CH2-CH2-CN + CH2=CH-CN->NC-CH2-CH2-NH-CH2-CH2-CN}}}$

The exact molecular mechanism of IDPN is unknown. However, there has been hypothesises that the molecule interacts with neurofilaments and gives a direct covalent modification^[12][13] or the production of free radicals.^[14] What is known is that IDPN selectively disrupts the low anterograde transport and initiates a disorganization of the cytoskeleton. The disorganization causes the neurofilaments to dissociate from microtubules, the neurofilaments then segregate towards the perimeter of the axonal cross section and the microtubules move to the interior core.^[13][15] IDPN's neurotoxicity mainly affects neurons containing 5-hydroxytriptamine.

In rats, IDPN is metabolised inside the liver into several different metabolites. The compound is first oxidised at one of the β-carbons and then further hydrolysed, cleaving the amide bond to form β-aminopropionitrile and cyanoacetic acid.^[11] β-aminopropionitrile is then further metabolised to β-alanine, which is the major metabolic product from IDPN.^[17] All three major metabolites do not show major toxicity, showing that the intact IDPN or an activated form is the reactive species.^[17]