The mitochondrial protein Bak is pivotal for gliotoxin-induced apoptosis and a critical host factor of Aspergillus fumigatus virulence in mice.

Aspergillus fumigatus infections cause high levels of morbidity and mortality in immunocompromised patients. Gliotoxin (GT), a secondary metabolite, is cytotoxic for mammalian cells, but the molecular basis and biological relevance of this toxicity remain speculative. We show that GT induces apoptotic cell death by activating the proapoptotic Bcl-2 family member Bak, but not Bax, to elicit the generation of reactive oxygen species, the mitochondrial release of apoptogenic factors, and caspase-3 activation. Activation of Bak by GT is direct, as GT triggers in vitro a dose-dependent release of cytochrome c from purified mitochondria isolated from wild-type and Bax- but not Bak-deficient cells. Resistance to A. fumigatus of mice lacking Bak compared to wild-type mice demonstrates the in vivo relevance of this GT-induced apoptotic pathway involving Bak and suggests a correlation between GT production and virulence. The elucidation of the molecular basis opens new strategies for the development of therapeutic regimens to combat A. fumigatus and related fungal infections.

Proteins of Thermus thermophilus are resistant to glycation-induced protein precipitation: an evolutionary adaptation to life at extreme temperatures?

In thermophilic bacteria, formation of Maillard products may occur at increased rates because this reaction is favored at higher temperatures. Therefore, specific protective mechanisms against glycation-induced protein precipitation are likely to exist in thermophilic bacteria. Indeed, Thermus thermophilus proteins remained soluble when a cell-free extract of T. thermophilus was incubated at 37 degrees C in the presence of glucose, fructose, or methylglyoxal; whereas E. coli proteins precipitated. In E. coli cell-free extracts, sugar-induced precipitation was accelerated by the addition of 5 microM Fe2+ and inhibited by metal chelators, suggesting that glycoxidation processes are involved in the formation of the precipitate. A low lysine content, endogenous small scavenger molecules, or enzymatic "antiglycation" mechanisms for the degradation of AGEs or their precursors could be excluded as possible causes for the resistance to protein precipitation in T. thermophilus. Therefore, the resistance to glycation-mediated protein precipitation is an endogenous property of thermophilic proteins that was acquired during evolution in environments with high glycation activity.

The carbonyl scavengers aminoguanidine and tenilsetam protect against the neurotoxic effects of methylglyoxal.

Advanced glycation end products (AGEs) have been identified in age-related intracellular protein deposits of Alzheimer's disease (amyloid plaques and neurofibrillary tangles) and Parkinson disease (Lewy bodies), suggesting that these protein deposits have been exposed to AGE precursors such as the reactive dicarbonyl compound methylglyoxal. In ageing tissue and under diabetic pseudohypoxia, intracellular methylglyoxal levels rise through an impairment of triosephosphate utilization. Furthermore, methylglyoxal detoxification is impaired when reduced glutathione levels are low, conditions, which have all been described in Alzheimer's disease. However, there is less known about the toxicity of methylglyoxal, particularly about therapeutic strategies to scavenge such dicarbonyl compounds and attenuate their toxicity. In our study, extracellularly applied methylglyoxal was shown to be toxic to human neuroblastoma cells in a dose-dependent manner above concentrations of 150 microM with a LD50 of approximately 1.25 mM. Pre-incubation of methylglyoxal with a variety of carbonyl scavengers such as aminoguanidine or tenilsetam and the thiol antioxidant lipoic acid significantly reduced its toxicity. In summary, carbonyl scavengers might offer a promising therapeutic strategy to reduce the neurotoxicity of reactive carbonyl compounds, providing a potential benefit for patients with age-related neurodegenerative diseases.