2,5-Hexanedione alters microtubule assembly. I. Testicular atrophy, not nervous system toxicity, correlates with enhanced tubulin polymerization.

Charles River CD rats (200 g) were divided into three groups receiving either 1% 2,5-hexanedione (2,5-HD) or 0.035% 3,4-dimethyl-2,5-hexanedione (DMHD) in the drinking water or water alone (control) for 4 weeks. The two treated groups experienced similar nervous system dysfunction and systemic toxicity. Testicular toxicity, as evidenced by histological changes and decreased testis weight, was present only in 2,5-HD-treated rats. Tubulin was purified from brain and testis and assembly properties were determined. Purified brain and testis tubulin derived from the 2,5-HD-intoxicated rats displayed altered assembly with a shortened nucleation phase and more rapid rate of elongation. Brain tubulin from DMHD-intoxicated rats displayed assembly behavior similar to controls, while testis tubulin from DMHD-intoxicated rats displayed assembly behavior intermediate between the control and 2,5-HD tubulin preparations. The presence of gamma-diketone-induced assembly alterations following in vivo intoxication was accompanied by the formation of a high-molecular-weight protein identified as crosslinked tubulin. From these data, we conclude that microtubule assembly alterations are not etiologic in the development of nervous system dysfunction following intoxication but may represent the biochemical mechanism of 2,5-HD-induced testicular atrophy.