Comparative neurotoxicity and pyrrole-forming potential of 2,5-hexanedione and perdeuterio-2,5-hexanedione in the rat.
2,5-Hexanedione (2,5-HD), the neurotoxic metabolite of n-hexane, reacts with protein amines to form alkylpyrrole adducts. Pyrrolylation of neurofilament protein may be the initiating molecular event in 2,5-HD neuropathy. The present study compares the neurotoxic and pyrrole-forming potentials of 2,5-HD with those of perdeuterio-2,5-HD ([D10]-2,5-HD) in the rat. Due to a requirement for C-H bond breaking in the reaction mechanism, the latter derivative was expected to exhibit a primary isotope effect, thus forming the pyrrole at a slower rate. In vitro studies confirmed that [D10]-2,5-HD pyrrolylated protein at only one-third of the initial rate seen with native 2,5-HD. Prolonged incubation resulted in similar pyrrole concentrations with both derivatives. Adult, male Wistar rats were administered daily (5 days/week) ip doses of either 3.5 mmol 2,5-HD or [D10]-2,5-HD/kg/day for 17 days or 2.5 mmol/kg/day for 38 days. At termination, animals administered 2,5-HD and [D10]-2,5-HD exhibited 27 and 8% body weight loss, respectively. Moderate to severe hindlimb paralysis was present in the 2,5-HD groups while only mild effects were seen in [D10]-2,5-HD-dosed rats. Neuropathological changes were prominent in spinal cord sections from 2,5-HD-treated animals, while no effects were present in rats given the deuterated derivative. Pyrrole adduct concentrations in serum and axonal cytoskeletal proteins from 2,5-HD-treated animals were two- to threefold higher than in rats given equimolar doses of [D10]-2,5-HD. Levels of covalent crosslinking of axonal cytoskeletal proteins (assessed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis) appeared to correlate with pyrrole concentrations. Tissue concentrations of each diketone isomer were not significantly different, indicating similar uptake of native and deuterated 2,5-HD. Mass spectrometry revealed rapid back exchange of the terminal (methyl) but not of the internal (methylene) deuteriums of [D10]-2,5-HD in vivo. These findings support an absolute requirement for pyrrole formation in gamma-diketone neurotoxicity.
DeCaprio
A P
AP
Wadsworth Center for Laboratories and Research, New York State Department of Health, Albany 12201.
Briggs
R G
RG
Jackowski
S J
SJ
Kim
J C
JC
D000818:Animals; D001259:Ataxia / Q000139:chemically induced; D001369:Axons / Q000187:drug effects*; D001835:Body Weight / Q000187:drug effects; D003598:Cytoskeletal Proteins / Q000032:analysis*; D003903:Deuterium / Q000009:adverse effects*; D006588:Hexanones / Q000633:toxicity*; D007274:Injections, Intraperitoneal; D007659:Ketones / Q000633:toxicity*; D008297:Male; D011758:Pyrroles / Q000032:analysis / Q000096:biosynthesis*; D051381:Rats; D011919:Rats, Inbred Strains; D013116:Spinal Cord / Q000187:drug effects
D003598:Cytoskeletal Proteins; D006588:Hexanones; D007659:Ketones; D011758:Pyrroles; D003903:Deuterium; C011269:2,5-hexanedione