Amino acid and protein targets of 1,2-diacetylbenzene, a potent aromatic γ-diketone that induces proximal neurofilamentous axonopathy

The γ-diketone analogs 1,2-diacetylbenzene (1,2-DAB) and 2,5-hexanedione (2,5-HD), but not the δ-diketone 1,3-diacetylbenzene (1,3-DAB) or the β-diketone 2,4-hexanedione, induce neuropathological changes in the rodent central and peripheral nervous systems. The molecular targets of these neurotoxic aromatic and aliphatic γ-diketones, and of their nonneurotoxic structural analogs and ninhydrin, are examined by assessing their differential reactivity with neural and nonneural amino acids and proteins in vitro and in vivo. Whereas 1,2-DAB is chromogenic and forms polymers with amino acids (notably lysine) and proteins (especially lysine-rich proteins), 1,3-DAB lacks these properties. Ninhydrin forms a chromophore without evidence of protein polymerization. 1,2-DAB preferentially targets neurofilament over microtubule protein in vitro and in situ. Based on protein reactivity, 1,2-DAB is three orders of magnitude more reactive than 2,5-HD. Lysine-rich neurofilament protein subunits NF-H and NF-M are more susceptible than lysine-poor NF-L and β-tubulin to 1,2-DAB. These observations correlate with the development of proximal (1,2-DAB) and distal (2,5-HD) neurofilament-filled axonal swellings and segregated intact microtubules observed during systemic treatment with aromatic and aliphatic γ-diketones.