Hydrogen peroxide-induced cytotoxicity in cultured epithelial cells (WISH): A functional and morphological study

Reverse Ordered Sequential Mechanism for Lactoperoxidase with Inhibition by Hydrogen Peroxide

Lactoperoxidase (LPO, Fe^III in its resting state in the absence of substrates)—an enzyme secreted from human mammary, salivary, and other mucosal glands—catalyzes the oxidation of thiocyanate (SCN⁻) by hydrogen peroxide (H₂O₂) to produce hypothiocyanite (OSCN⁻), which functions as an antimicrobial agent. The accepted catalytic mechanism, called the halogen cycle, comprises a two-electron oxidation of LPO by H₂O₂ to produce oxoiron(IV) radicals, followed by O-atom transfer to SCN⁻. However, the mechanism does not explain biphasic kinetics and inhibition by H₂O₂ at low concentration of reducing substrate, conditions that may be biologically relevant. We propose an ordered sequential mechanism in which the order of substrate binding is reversed, first SCN⁻ and then H₂O₂. The sequence of substrate binding that is described by the halogen cycle mechanism is actually inhibitory.

Inorganic chemistry of defensive peroxidases in the human oral cavity

The innate host response system is comprised of various mechanisms for orchestrating host response to microbial infection of the oral cavity. The heterogeneity of the oral cavity and the associated microenvironments that are produced give rise to different chemistries that affect the innate defense system. One focus of this review is on how these spatial differences influence the two major defensive peroxidases of the oral cavity, salivary peroxidase (SPO) and myeloperoxidase (MPO). With hydrogen peroxide (H(2)O(2)) as an oxidant, the defensive peroxidases use inorganic ions to produce antimicrobials that are generally more effective than H(2)O(2) itself. The concentrations of the inorganic substrates are different in saliva vs. gingival crevicular fluid (GCF). Thus, in the supragingival regime, SPO and MPO work in unison for the exclusive production of hypothiocyanite (OSCN(-), a reactive inorganic species), which constantly bathes nascent plaques. In contrast, MPO is introduced to the GCF during inflammatory response, and in that environment it is capable of producing hypochlorite (OCl(-)), a chemically more powerful oxidant that is implicated in host tissue damage. A second focus of this review is on inter-person variation that may contribute to different peroxidase function. Many of these differences are attributed to dietary or smoking practices that alter the concentrations of relevant inorganic species in the oral cavity (e.g.: fluoride, F(-); cyanide, CN(-); cyanate, OCN(-); thiocyanate, SCN(-); and nitrate, NO(3)(-)). Because of the complexity of the host and microflora biology and the associated chemistry, it is difficult to establish the significance of the human peroxidase systems during the pathogenesis of oral diseases. The problem is particularly complex with respect to the gingival sulcus and periodontal pockets (where the very different defensive stratagems of GCF and saliva co-mingle). Despite this complexity, intriguing in vitro and in vivo studies are reviewed here that reveal the interplay between peroxidase function and associated inorganic chemistry.

Multilayer primary epithelial cell culture from bovine conjunctiva as a model for in vitro toxicity tests

OBJECTIVE

The purpose of this study was to obtain a primary cell culture of bovine origin similar to the conjunctiva in terms of morphology and cell types, which could be of use for in vitro toxicity studies.

METHODS

After separation from the stroma by enzymatic treatment, conjunctival epithelial cells were dissociated and plated onto collagen-coated Transwell filters (1.13 cm(2) area). One group of plates was maintained in immersion and another was cultured under air-lifted conditions. Anti-epithelial keratin antibodies (AE1/AE3, K4) and antidesmoplakin 1 and 2 were used to characterize the cells by indirect immunofluorescence. The cell layer was examined after histological processing of the Transwell filter. Ultrastructural analysis was carried out by scanning electron microscopy (SEM). The bioelectric parameters transepithelial electrical resistance (TEER), potential difference (PD), short circuit current and paracellular permeability profile of carboxyfluorescein were monitored as indices of the functional characteristics of these cultures. Cytotoxicity was evaluated on morphological and functional (TEER) grounds after treating the cultures with several test substances.

RESULTS

Morphological studies showed pure and homogeneous cell cultures. In the SEM analysis, we observed contiguous polygonal cells with numerous short microvilli, a characteristic proportion of light, medium and dark cells and a sparse population of rounded PAS-positive cells, i.e. resembling goblet cells. Air-lifted cultures also showed a tissue-like cellular organization (8-9 layers). Immersion cultures reached a maximum TEER value of around 2.95 kOmega x cm(2) 7 days after plating while in air-lifted cultures TEER peaked up to 5.59 komega x cm(2) 11 days after plating. With regard to the use of bovine conjunctival epithelial cells (BCECs) for cytotoxicity screening, the system responded finely to the insults and yielded morphological and functional results in accordance with data obtained in vivo.

CONCLUSIONS

BCECs reproduce cell morphology and differentiation of the original tissue and should prove a useful tool for initial studies of drug toxicity.

Cytotoxicity of lazaroid U-75412E in human epithelial cell line (Wish)

The 21-aminosteroids (or lazaroids) are a recently synthesized class of compounds demonstrated to protect tissue against damage induced by trauma and/or ischemia. Currently, very little is known about the biological effects of lazaroids. In this work the action of lazaroid U-75412E on a human epithelial cell line (Wish) was evaluated. The data obtained showed an inhibition of cell growth and a dose- and time-dependent decrease of cell viability. Furthermore, a dose- and time-dependent increase of cells in the G2/M phase with the appearance of apoptotic cells was observed by flow cytometric analysis. Nuclear fragmentation was also evident. Lactate dehydrogenase release and scanning electron microscopy experiments suggested that plasma membrane integrity was altered by this compound. The immunofluorescence technique and transmission electron microscopy images also showed intracellular damage, such as alteration of microtubular arrangement, mitochondrial swelling and the presence of vacuoles. This study demonstrated that 1 microM U-75412E was unable to modify these parameters, while higher concentrations (6-75 microM) had a cytotoxic effect on Wish cells.