Modification of cell vulnerability to oxidative stress by N-(3-oxododecanoyl)-L-homoserine-lactone, a quorum sensing molecule, in rat thymocytes.

N-(3-oxododecanoyl)-l-homoserine-lactone (ODHL), a quorum sensing molecule, affects intracellular Zn2+ concentration ([Zn2+]i) and cellular levels of nonprotein thiols ([NPT]i) of rat thymic lymphocytes, both of which are assumed to affect cell vulnerability to oxidative stress. Therefore, it is interesting to examine the effects of ODHL on the cells under oxidative stress. ODHL augmented the cytotoxicity of H2O2, but not calcium ionophore A23187. ODHL potentiated the H2O2-induced elevation of [Zn2+]i, wherein, it greatly attenuated the H2O2-induced increase in intracellular Ca2+ concentration. ODHL did not affect [NPT]i in the presence of H2O2. Therefore, we conclude that the elevation of [Zn2+]i is involved in the ODHL-induced potentiation of H2O2 cytotoxicity. Our findings suggest that ODHL modifies cell vulnerability to oxidative stress in host cells.

Hyperpolarization by N-(3-oxododecanoyl)-l-homoserine-lactone, a quorum sensing molecule, in rat thymic lymphocytes.

To study the adverse effects of N-(3-oxododecanoyl)-l-homoserine-lactone (ODHL), a quorum sensing molecule, on mammalian host cells, its effect on membrane potential was examined in rat thymic lymphocytes using flow cytometric techniques with a voltage-sensitive fluorescent probe. As 3-300 µM ODHL elicited hyperpolarization, it is likely that it increases membrane K+ permeability because hyperpolarization is directly linked to changing K+ gradient across membranes, but not Na+ and Cl- gradients. ODHL did not increase intracellular Ca2+ concentration. ODHL also produced a response in the presence of an intracellular Zn2+ chelator. Thus, it is unlikely that intracellular Ca2+ and Zn2+ are attributed to the response. Quinine, a non-specific K+ channel blocker, greatly reduced hyperpolarization. However, because charybdotoxin, tetraethylammonium chloride, 4-aminopyridine, and glibenclamide did not affect it, it is pharmacologically hypothesized that Ca2+-activated K+ channels, voltage-gated K+ channels, and ATP-sensitive K+ channels are not involved in ODHL-induced hyperpolarization. Although the K+ channels responsible for ODHL-induced hyperpolarization have not been identified, it is suggested that ODHL can elicit hyperpolarization in mammalian host cells, disturbing cellular functions.

N-(3-oxododecanoyl)-l-homoserine-lactone, a quorum sensing molecule, affects cellular content of nonprotein thiol content in rat lymphocytes: Its relation with intracellular Zn2.

Cellular actions of N-(3-oxododecanoyl)-l-homoserine-lactone (ODHL), a quorum sensing molecule of bacteria, were studied on rat thymocytes using a flow cytometer with appropriate fluorescent dyes to elucidate the effects of ODHL on host cells. A bell-shaped concentration-response relation was observed in the ODHL-induced changes in cellular glutathione content ([GSH]i). ODHL concentration-dependently increased intracellular Zn2+ levels ([Zn2+]i) and cellular O2- content ([O2-]i). The bell-shaped relation induced by ODHL can be explained as follows: a low concentration of ODHL is expected to induce moderate oxidative stress that intracellularly releases Zn2+ by converting thiols to disulfides. A slight elevation of [Zn2+]i may increase the [GSH]i. On the other hand, it is likely that a high concentration of ODHL causes severe oxidative stress that further causes both the decrease in [GSH]i and the increase in [Zn2+]i. Excessive increase in [Zn2+]i may augment oxidative stress that further decreases the [GSH]i. Other notable actions induced by ODHL included the elevation of [Zn2+]i by Zn2+ influx and the increase in [GSH]i under Zn2+-free conditions. Therefore, it is suggested that ODHL elicits diverse actions on host cells.

Cetylpyridinium chloride at sublethal levels increases the susceptibility of rat thymic lymphocytes to oxidative stress.

Cetylpyridinium chloride (CPC) is an antimicrobial agent used in many personal care products, with subsequent release into the environment. Since CPC is found at low concentrations in river and municipal wastewater, its influence on wildlife is of concern. Therefore, in this study, we used flow cytometry to examine the effects of sublethal concentrations of CPC on rat thymic lymphocytes in order to characterize the cellular actions of CPC at low concentrations in the presence and absence of H2O2-induced oxidative stress. CPC treatment increased the population of living cells with phosphatidylserine exposed on the outer surface of their plasma membranes (a marker of early stage apoptosis), elevated intracellular Zn2+ levels, and decreased the cellular content of nonprotein thiols. CPC also potentiated the cytotoxicity of H2O2. Our results suggest that, even at environmentally relevant sublethal concentrations, CPC exerts cytotoxic effects under oxidative stress conditions by increasing intracellular Zn2+ concentration and decreasing the cellular content of nonprotein thiols. These findings indicate that, under some in vitro conditions, CPC is bioactive at environmentally relevant concentrations. Therefore, CPC release from personal care products into the environment may need to be regulated to avoid its adverse effects on wildlife.

Chlorhexidine possesses unique cytotoxic actions in rat thymic lymphocytes: Its relation with electrochemical property of membranes.

Chlorhexidine (CHX) is an antibacterial agent used in various types of pharmaceutical products. Therefore, CHX is easily found around us. Owing to its positive charge, the electrochemical property of cell membranes was assumed to be a key point of cytotoxic action of CHX. Depolarization of membranes attenuated the cytotoxic action of CHX in rat thymic lymphocytes. CHX interfered with annexin V binding to membranes. Manipulations to induce exposure of phosphatidylserine on the outer membrane surface augmented the cytotoxic action of CHX, indicating that changes in the electrochemical property of membranes affected the cytotoxic action of CHX. Hence, CHX might kill cells physiologically undergoing apoptosis, resulting instead in necrotic cell death. However, the threshold CHX concentration in this in vitro study was slightly higher than blood CHX concentrations observed clinically. Therefore, these results may support the safety of CHX use although CHX possesses unique cytotoxic actions described in this study.