Dihydrolipoic but not alpha-lipoic acid affects susceptibility of eukaryotic cells to bacterial invasion.

Sensitivity of eukaryotic cells to facultative pathogens can depend on physiological state of host cells. Previously we have shown that pretreatment of HeLa cells with N-acetylcysteine (NAC) makes the cells 2-3-fold more sensitive to invasion by the wild-type Serratia grimesii and recombinant Escherichia coli expressing gene of actin-specific metalloprotease grimelysin [1]. To evaluate the impact of chemically different antioxidants, in the present work we studied the effects of α-Lipoic acid (LA) and dihydrolipoic acid (DHLA) on efficiency of S. grimesii and recombinant E. coli expressing grimelysin gene to penetrate into HeLa and CaCo cells. Similarly to the effect of NAC, pretreatment of HeLa and CaCo cells with 0.6 or 1.25 mM DHLA increased the entry of grimelysin producing bacteria by a factor of 2.5 and 3 for the wild-type S. grimesii and recombinant E. coli, respectively. In contrast, pretreatment of the cells with 0.6 or 1.25 mM LA did not affect the bacteria uptake. The increased invasion of HeLa and CaCo cells correlated with the enhanced expression of E-cadherin and ß-catenin genes, whereas expression of these genes in the LA-treated cells was not changed. Comparison of these results suggests that it is sulfhydryl group of DHLA that promotes efficient modification of cell properties assisting bacterial uptake. We assume that the NAC- and DHLA-induced stimulation of the E-cadherin-catenin pathway contributes to the increased internalization of the grimelysin producing bacteria within transformed cells.

N-acetylcysteine increases susceptibility of HeLa cells to bacterial invasion.

Serratia grimesii are non-pathogenic bacteria capable, however, to invade eukaryotic cells provided that they synthesize intracellular metalloprotease grimelysin (Bozhokina et al. [2011] Cell. Biol. Int. 35: 111-118). To elucidate how invasion of grimelysin containing bacteria depends on physiological state of host cells, we studied the effect of N-acetylcysteine (NAC) on susceptibility of HeLa cells to invasion by the wild-type S. grimesii and recombinant E. coli expressing grimelysin gene. Incubation of HeLa cells with 10 mM NAC resulted in changes of cell morphology and disassembly of actin cytoskeleton that were reversed when NAC was removed from the culture medium. Both in the presence of NAC and upon its removal, the entry of grimelysin producing bacteria increased by a factor of 1.5-2 and 3-3.5 for wild-type S. grimesii and recombinant E. coli, respectively. This effect does not correlate with cytoskeleton rearrangements but may be due to the NAC-induced up-regulation of cell surface receptors playing a role in cell adhesion and cell-cell junctions. A twofold difference in the efficiency of S. grimesii and recombinant E. coli to enter the NAC-treated cells suggests that the entry of the wild-type and recombinant bacteria occurs via different receptors which activity is differently affected by NAC.

Telomere shortening is a sole mechanism of aging in mammals.

We adduce proof that telomere shortening is the sole mechanism of aging. All apparent contradictions, particularly the absence of an inverse correlation between residual telomere length and donor age, are explained within the bounds of telomere theory. We explain in what way telomere shortening might be the cause of aging and lifespan restriction. We also show the inability of the oxidative theory to explain a number of indisputable (and easily explained by telomere theory) facts, such as malignant growth of tumor cells and why children begin aging not from the level reached by the cells of their parents at the moment of conception but from nothing. We postulate that if oxidative damage was entirely absent, telomeres would, nevertheless, shorten with each mitotic cycle because this is the mechanism of DNA replication. Aging would occur all the same, and it is the very thing we can observe under the effect of any antioxidants. If telomeres do not shorten, as is the case in transformed cells in which telomerase is working, aging will do stop and transformed cells will show no senescence. We also observe this in spite of the damaging effect of reactive oxygen species, which is even more intensive in transformed cells than in normal cells.

N-acetylcysteine-induced changes in susceptibility of transformed eukaryotic cells to bacterial invasion.

The effect of N-acetylcysteine (NAC) on morphological and physiological properties of "normal" 3T3 and 3T3-SV40 fibroblasts was studied. Incubation of the cells with 10 and 20 mM NAC for 20 h resulted in a reversible increase in the intracellular level of reduced glutathione and disorganization of actin cytoskeleton. Surprisingly, upon removal of NAC, 3T3-SV40 fibroblasts demonstrated formation of well-adhered cells with structured 3T3-like stress-fibers. Neither changes in glutathione levels, nor cytoskeleton disorganization/assembly abolished resistance of 3T3 cells to invasion by the bacterium Escherichia coli A2. On the other hand, pretreatment with NAC converted bacteria-susceptible 3T3-SV40 cells into resistant ones. These results show that NAC can induce partial reversion of transformed phenotype. We suggest that this effect is due to NAC-induced modifications of cell surface proteins rather than to changes in the level of intracellular glutathione.