Transglutaminase 2 is involved in homocysteine-induced activation of human THP-1 monocytes.

Aberrant transglutaminase 2 (TG2) expression and protein cross-linking activity have been associated with several chronic neurodegenerative disorders in which inflammatory processes triggered by activated microglia and monocytes play a key role, such as Alzheimer's disease, Parkinson's disease, amyotrophic lateral sclerosis, and multiple sclerosis. Interestingly, mild-to-moderate hyperhomocysteinemia (HHcy), corresponding to increased plasma homocysteine (Hcy) concentrations in the range 16-60 µM, have recently been associated with the above-cited diseases. Using THP-1 monocytes, here we investigated the role of TG2 in cell response to mildly elevated Hcy concentrations. A five-day incubation with Hcy (∼25 µM) increased reactive oxygen species, peroxide lipids, as well as 8-hydroxyguanosine levels by twofold, and decreased the endogenous cell antioxidant defenses, that is reduced glutathione, by 50% in Hcy-exposed cultures compared with controls (p < 0.01). Hcy-induced oxidative stress was associated with increases in TG2 expression and activity, as well as nuclear factor kappa B activation. Notably, the latter was reduced in the presence of the TG-specific inhibitor R283. Hcy exposure also significantly increased the mRNA levels of tumor necrosis factor alpha, interleukin (IL)-6, and IL-1ß, as well as the level of Hcy-inducible endoplasmic reticulum (ER) stress protein, a marker of ER stress, in Hcy-exposed cultures compared with controls. Notably, these effects were dramatically reduced by R283. These preliminary findings indicate that TG2 plays a key role in Hcy-induced activation of THP-1 monocytes, involving oxidative as well as ER stress and inflammation. This underlines the potential of TG2 inhibition in the therapeutic management of inflammatory processes contributing to neurodegenerative disorders associated with mild HHcy.

CO(2) pneumoperitoneum induces in vitro hypoxic response culminating in apoptosis of human neuroblastoma cells.

The ablative role of minimally invasive surgery (MIS) in neuroblastoma (NB) is still controversial due to the possible CO2 pneumoperitoneum side-effects on tumor aggressiveness. It is known that CO2 produces hypoxic condition with changes in tumor microenvironment influencing cell functions. Here we investigated whether CO2 exposure affects the transcription factor HIF-1α and the apoptotic signalling pathway in SH-SY5Y NB cells. SH-SY5Y cells were exposed to a pressure of 15 mmHg CO2 (100%) for 4 h (T0) and then moved to normal condition for 24 h (T24). In control and CO2 -exposed cells, we analyzed the mRNA levels and DNA binding activity of HIF-1α. We also evaluated the proliferative activity and cell viability as well as caspase-9/3 cleavage and nuclear fragmentation. A significant increase in HIF- 1α activation was observed in SH-SY5Y cells exposed to CO2 compared to control cells. CO2 treatment also decreased the proliferation rate and the percentage of viable cells. In addition, the expression and cleavage of caspase-9 and -3 were significantly increased in NB cells exposed to CO2. These data correlated with apoptotic feature observed in CO2 -treated NB cells. Our findings show that CO2 -induced hypoxic condition exerts cytotoxic effects on NB cells by eliciting mitochondrial apoptotic pathway and thereby improving the understanding of the possible clinical impact of CO2 pneumoperitoneum on NB behaviour.

Toxic effects of mildly elevated homocysteine concentrations in neuronal-like cells.

Epidemiological and experimental evidence indicated that hyperhomocysteinemia is associated with neurodegeneration. However, homocysteine neurotoxic effects have been so far investigated mostly by employing homocysteine concentrations (≥100 µM) much higher than homocysteine mean plasma levels (20 µM) observed in patients with neurodegenerative disorders. While evaluating the effects of a prolonged exposure to ~20 µM homocysteine in neuronal-like differentiated SH-SY5Y cells, we observed a 35% loss of cell viability and a four-fold increase in reactive oxygen species levels in cells incubated with homocysteine for five days compared with controls. Moreover, homocysteine increased by 30% and around two-fold, respectively, the Comet-positive cell number and DNA damage indexes (tail length, T-DNA, olive tail moment) compared with controls. Cell response to homocysteine-induced DNA damage involved the up-regulation of Bax and, at a greater extent, Bcl-2, but not caspase-3, in association with a p53-independent increase of p21 levels; concomitantly, also p16 levels were increased. When looking at time-dependent changes in cyclin expression, we found that a significant up-regulation of cyclins D1, A1, E1, but not B1, concomitant with p21 down-regulation, occurred in cells incubated with homocysteine for three days. However, in line with the observed increase of p21 and p16 levels, a five days incubation with homocysteine induced cyclin down-regulation accompanied by a strong reduction of phosphorylated pRB amounts. These results suggest that, when prolonged, the exposure of neuronal-like cells to mildly elevated homocysteine concentrations triggers oxidative and genotoxic stress involving an early induction of cyclins, that is late repressed by G1-S check-point regulators.