PM10 impairs the antioxidant defense system and exacerbates oxidative stress driven cell death

The aim of this study was to investigate the effect of airborne particulate matter with a mean aerodynamic diameter of ≤10 μm (PM₁₀) on oxidative stress markers and antioxidant enzymatic activity and its relevance in the face of acute oxidative challenge in a human lung epithelial cell line (A549). PM₁₀-induced reactive oxygen species (ROS) generation and oxidative damage with no changes in cellular viability. In addition, PM₁₀ decreased glutathione (GSH) levels (54.9%) and the activity of the antioxidant enzymes superoxide dismutase (65%), catalase (31.2%), glutathione reductase (61.5%) and glutathione-S-transferase (42.39%). Trolox, a scavenger of reactive species, prevented the increase of ROS generation and the decrease in GSH levels but partially prevented PM₁₀-induced oxidative damage. Interestingly, it was unable to avoid the decrease in the activity of antioxidant enzymes. Finally, the survival of the cells previously exposed to PM₁₀ and challenged with hydrogen peroxide was significantly lower. We conclude that the impairment in the antioxidant defense system induced by PM₁₀ weaken ROS detoxification which exacerbates cell death when these cells are exposed to an acute oxidative challenge.     

Altered oxidative status and integrin expression in cyclosporine A-treated oral epithelial cells

Abstract

Background and objective: Cyclosporine A (CsA) is an immunosuppressive agent administered to transplant patients. A well-known reported oral side effect of CsA consumption is gingival overgrowth (GO). Changes in the expression of integrins occurring in the gingiva following CsA treatment have been reported but these reports are mainly concerned with the connective tissue of the gingiva. In this study we targeted the alterations in the oral epithelium using KB cells, an oral epithelial cell line.

Methods: Cultured oral epithelial cells were treated with increasing concentrations of CsA (0.1, 1 and 10?µg/mL) and the molecular changes involving antioxidant enzymes [glutathione peroxidase (GPx) and glutathione reductase (GR)] and the level of reactive oxygen species (ROS) were measured. Quantitative real-time PCR was used to assess the expression of selected integrins (α₂, α₅ and β₁).

Results: At CsA concentration above 0.1?µg/mL GPx demonstrated an increase in activity while GR activity and the level of reduced glutathione were diminished (p?<?0.05). α₅ and β₁ integrin were downregulated at all treatment concentrations of CsA while α₂ integrin presented this effect at concentrations above 1?µg/mL (p?<?0.05).

Conclusion: The results suggest a possible role for oxidative stress and the altered expression of integrins in the pathology of CsA-induced gingival overgrowth.     

Dissolution and bandgap paradigms for predicting the toxicity of metal oxide nanoparticles in the marine environment: an in vivo study with oyster embryos

Dissolution and bandgap paradigms have been proposed for predicting the ability of metal oxide nanoparticles (NPs) to induce oxidative stress in different in vitro and in vivo models. Here, we addressed the effectiveness of these paradigms in vivo and under conditions typical of the marine environment, a final sink for many NPs released through aquatic systems. We used ZnO and MnO₂ NPs as models for dissolution and bandgap paradigms, respectively, and CeO₂ NPs to assess reactive oxygen radical (ROS) production via Fenton-like reactions in vivo. Oyster embryos were exposed to 0.5–500?μM of each test NP over 24?h and oxidative stress was determined as a primary toxicity pathway across successive levels of biological complexity, with arrested development as the main pathological outcome. NPs were actively ingested by oyster larvae and entered cells. Dissolution was a viable paradigm for predicting the toxicity of NPs in the marine environment, whereas the surface reactivity based paradigms (i.e. bandgap and ROS generation via Fenton-like reaction) were not supported under seawater conditions. Bio-imaging identified potential cellular storage-disposal sites of solid particles that could ameliorate the toxicological behavior of non-dissolving NPs, whilst abiotic screening of surface reactivity suggested that the adsorption-complexation of surface active sites by seawater ions could provide a valuable hypothesis to explain the quenching of the intrinsic oxidation potential of MnO₂ NPs in seawater.     

Antioxidant effects of the chestnut (Castanea crenata) inner shell extract in t-BHP-treated HepG2 cells,and CCl4- and high-fat diet-treated mice

The antioxidant effects of chestnut inner shell extract (CISE) were investigated in a tert-butylhydroperoxide (t-BHP)-treated HepG2 cells, and in mice that were administered carbon tetrachloride (CCl₄) and fed a high-fat diet (HFD). Pre-incubation with CISE significantly blocked the oxidative stress induced by t-BHP treatment in HepG2 cells (P < 0.05) and preserved the activities of catalase, superoxide dismutase, glutathione peroxidase, and glutathione reductase compared to group treated with t-BHP only. Similarly, the CCl₄- and HFD-induced reduction of antioxidant enzymes activities in liver was prevented by CISE treatment compared to control groups. Furthermore, hepatic lipid peroxidation were remarkably lower (P < 0.05) in the CISE-treated groups with t-BHP or HFD. To determine the active compound of CISE, the fractionation of CISE has been conducted and scoparone and scopoletin were identified as main compounds. These compounds were also shown to inhibit the t-BHP-induced ROS generation and reduction in antioxidant enzyme activity in an in vitro model system. From these results, it was demonstrated that CISE has the ability to protect against damage from oxidative stressors such as t-BHP, CCl₄ and HFD in in vitro and in vivo models. The CISE might be useful for the prevention of oxidative damage in liver cells and tissues.     

Effects of sub-acute exposure to TiO2, ZnO and Al2O3 nanoparticles on oxidative stress and histological changes in mouse liver and brain

Abstract

Nanomaterials are at the leading edge of the rapidly developing field of nanotechnology. However the information regarding toxicity of these nanoparticles on humans and environment is still deficient. The present study investigated the toxic effects of three metal oxide nanoparticles, TiO₂, ZnO and Al₂O₃ on mouse erythrocytes, brain and liver. Male mice were administered a single oral dose of 500?mg/kg of each nanoparticles for 21 consecutive days. The results suggest that exposure to these nano metallic particles produced a significant oxidative stress in erythrocyte, liver and brain as evident from enhanced levels of Reactive Oxygen Species (ROS) and altered antioxidant enzymes activities. A significant increase in dopamine and norepinephrine levels in brain cerebral cortex and increased brain oxidative stress suggest neurotoxic potential of these nanoparticles. Transmission electron microscopic (TEM) analysis indicated the presence of these nanoparticles inside the cytoplasm and nucleus. These changes were also supported by the inhibition of CuZnSOD and MnSOD, considered as important biomarkers of oxidative stress. The toxic effects produced by these nanoparticles were more pronounced in the case of zinc oxide, followed by aluminum oxide and titanium dioxide, respectively. The present results further suggest the involvement of oxidative stress as one of the main mechanisms involved in nanoparticles induced toxic manifestations.     

Influence of simulated gastrointestinal conditions on particle-induced cytotoxicity and interleukin-8 regulation in differentiated and undifferentiated Caco-2 cells

Abstract

Novel aspects of engineered nanoparticles offer many advantages for optimising food products and packaging. However, their potential hazards in the gastrointestinal tract require further investigation. We evaluated the toxic and inflammatory potential of two types of particles that might become increasingly relevant to the food industry, namely SiO₂ and ZnO. The materials were characterised for their morphology, oxidant generation and hydrodynamic behaviour. Cytotoxicity and interleukin-8 mRNA and protein expression were evaluated in human intestinal Caco-2 cells. Particle pretreatment under simulated gastric and intestinal pH conditions resulted in reduced acellular ROS formation but did not influence cytotoxicity (WST-1 assay) or IL-8 expression. However, the differentiation status of the cells markedly determined the cytotoxic potency of the particles. Further research is needed to determine the in vivo relevance of our current observations regarding the role of particle aggregation and the stage of intestinal epithelial cell differentiation in determining the hazards of ingested particles.     

Fullerene derivatives induce premature senescence: A new toxicity paradigm or novel biomedical applications

Engineered fullerenes (C₆₀) are extensively used for commercial and clinical applications based on their unique physicochemical properties. Such materials have also been recognized as byproducts of many industrial activities. Functionalization of C₆₀ may significantly influence the nature of its interactions with biological systems, impacting its applications and raising uncertainties about its health effects. In the present study, we compared the bioimpact of two chemically modified fullerene derivatives, hexa carboxyl fullerene adduct (Hexa-C₆₀) and tris carboxyl fullerene adduct (tris-C₆₀) to pristine fullerene C₆₀ encapsulated with gamma (γ)-cyclodextrin C₆₀ (CD-C₆₀), using human cutaneous epithelial cells (HEK) to simulate possible applications and occupational dermal exposure route. We report, for the first time, the discovery of premature senescence as a potential endpoint of nanomaterial elicited biological effects, providing a new paradigm for nanoparticle-induced toxicity in human cells. Moreover, this response appeared to be functionalization specific, in that, only tris-C₆₀ induced senescence. We investigated key biological responses, such as cellular viability, intracellular ROS generation, cell proliferation and cell cycle responses. Our results indicate that the often observed ‘anti-apoptotic’ function of fullerene derivatives may be independent of their ‘ROS scavenging’ role as previously reported. We discovered that the tris-C₆₀-induced responses were associated with G₀/G₁ cell cycle arrest and cellular senescence. On further evaluation of the molecular mechanisms underlying the senescent response, a significant decrease in the expression levels of HERC5 was noted. HERC5 is a ubiquitin ligase of the HERC family and is implicated to be involved in innate immune responses to viral and bacterial infections.     

Gene expression profiles in rat lung after inhalation exposure to C60 fullerene particles

Concern over the influence of nanoparticles on human health has risen due to advances in the development of nanotechnology. We are interested in the influence of nanoparticles on the pulmonary system at a molecular level. In this study, gene expression profiling of the rat lung after whole-body inhalation exposure to C₆₀ fullerene (0.12 mg/m³; 4.1 × 10⁴ particles/cm³, 96 nm diameter) and ultrafine nickel oxide (Uf-NiO) particles (0.2 mg/m³; 9.2 × 10⁴ particles/cm³, 59 nm diameter) as a positive control were employed to gain insights into these molecular events. In response to C₆₀ fullerene exposure for 6 h a day, for 4 weeks (5 days a week), C₆₀ fullerene particles were located in alveolar epithelial cells at 3 days post-exposure and engulfed by macrophages at both 3 days and 1 month post-exposures. Gene expression profiles revealed that few genes involved in the inflammatory response, oxidative stress, apoptosis, and metalloendopeptidase activity were up-regulated at both 3 days and 1 month post-exposure. Only some genes associated with the immune system process, including major histocompatibility complex (MHC)-mediated immunity were up-regulated. These results were significantly different from those of Uf-NiO particles which induced high expression of genes associated with chemokines, oxidative stress, and matrix metalloproteinase 12 (Mmp12), suggesting that Uf-NiO particles lead to acute inflammation for the inhalation exposure period, and the damaged tissues were repaired in the post-exposure period. We suggest that C₆₀ fullerene might not have a severe pulmonary toxicity under the inhalation exposure condition.     

Protection of l-methionine against H2O2-induced oxidative damage in mitochondria

Reactive oxygen species (ROS) is reported to be a critical pathogenic factor and mitochondria is one of the susceptible subcellular organs for oxidative damage. Methionine sulfoxide reductase A (MsrA) is a key anti-oxidant enzyme associated with cytoprotection and previous reports have revealed its importance in mitochondrial function. The anti-oxidation of MsrA is due to Met-centered redox cycle, suggesting that Met-centered redox cycle may play a critical role in mitochondrial protection. l-Methionine (l-Met), a natural amino acid with anti-oxidation activity, can mimic the effect of Met-centered redox cycle. Here, we investigated the protection of l-Met on H₂O₂-induced oxidative damage in mitochondria. Our study demonstrated that l-Met protected H₂O₂-induced injury in CHO cells. Cytoprotections of l-Met at low concentrations (1–5 mM) were abolished by dimethyl sulfoxide (DMSO), a competitive inhibitor of MsrA function, suggesting that these effects may involve the participation of MsrA. Overexpression of MsrA in CHO cells protected mitochondria from H₂O₂-induced downtrend of membrane potential and production of mitochondrial superoxide. Pre-treatment with l-Met (1 mM) produced a similar effect on the mitochondrial protection against H₂O₂. Furthermore, it was observed that topical application of l-Met can prevent 12-O-tetradecanoyl-phorbol-13-acetate (TPA)-induced oxidative damage in the skin of mice. These results suggest that anti-oxidation activity of l-Met may promise a new strategy for the prevention of oxidative stress-induced damage.     

Evaluation of an in vitro screening model to assess phosgene inhalation injury

Therapeutic development against exposure to toxic gases is hindered by the lack of appropriate models to evaluate candidate compounds prior to animal efficacy studies. In this study, an in vitro, air-liquid interface exposure model has been tested to examine its potential application for screening treatments for phosgene (carbonyl chloride)-induced pulmonary injury. Epithelial cultures on Transwell^® inserts, combined with a Vitrocell^® exposure apparatus, provided a physiologically relevant exposure environment. Differentiated human bronchial epithelial (16HBE) cultures were exposed for 8?min to phosgene ranging from 0 to 64?ppm and assessed for changes in transepithelial electrical resistance (TEER, epithelial barrier integrity), cellular viability (XTT) and post-exposure (PE) cellular metabolic energy status. Exposure to phosgene concentrations ≥8?ppm caused dose-dependent and significant decreases in TEER and XTT which did not recover within 24-h PE. In addition, at 64?ppm the rate of oxidative glutamine metabolism was significantly inhibited at 6 and 24?h after exposure. Glycolytic activities (glucose utilization and lactate production) were also inhibited, but to a lesser extent. Decreased glycolytic function can translate to insufficient energy sources to counteract barrier function failure. Consistent and sensitive markers of phosgene exposure were TEER, cell viability and decreased metabolism. As such, we have assessed an appropriate in vitro model of phosgene inhalation that produced quantifiable alterations in markers of lung cell metabolism and injury in human airway epithelial cells. Data indicate the suitability of this model for testing classes of anti-edemagenic compounds such as corticosteroids or phosphodiesterase inhibitors for evaluating phosgene therapeutics.     

Angiotensin II type 1 receptor blockade suppresses H2O2-induced retinal degeneration in photoreceptor cells

Exposure to reactive oxygen species (ROS) leads to the development and progression of retinal degenerative diseases. However, the exact mechanisms are not fully understood. In this article, the role of angiotensin II type 1 receptor (AT1R) signaling in H₂O₂-induced retinal damage was examined. Mouse photoreceptor-derived 661?W cells were treated with the AT1R blockers valsartan, losartan and candesartan before exposure to H₂O₂. Cell viability, intracellular ROS level, mitochondrial membrane potential (MMP), cytochrome-c level, DNA fragmentation, caspase activity and gene expression were detected. Pre-treatment of 661?W cells with AT1R blockers significantly decreased H₂O₂-mediated toxicity and reduced the ROS level. In addition, apoptosis-related biochemical indicators showed that pre-incubation of AT1R blockers would elevate the MMP, decrease the release of cytochrome-c and formation of DNA fragmentation, and inhibit activities of caspase-3 and caspase-9 in exogenous H₂O₂-treated 661?W cells. Moreover, treatment with AT1R blockers suppressed the expression of Egr1, Fosl1 and Lox12. These results suggest that AT1R signaling mediates H₂O₂-induced apoptosis, at least partially through generating the ROS and increasing the levels of proapoptotic molecules in 661?W cells. AT1R blockade may provide a new therapeutic approach for preventing oxidative stress-induced retinal neural damage.     

Comparison of protein, RNA, and DNA binding and cell-cycle-specific growth inhibitory effects of nickel compounds in cultured cells

Crystalline NiS particles are potent inducers of morphological transformation and are actively phagocytosed by cells. Water-soluble nickel compounds are less potent, possibly because the total amount of nickel that enters cells is less, and its subcellular distribution differs in a number of ways from that following the entry of NiS in the form of an internalized particle. To further study this problem, we have examined the binding of ⁶³Ni to DNA, RNA, and protein isolated from cultured Chinese hamster ovary cells treated with either crystalline ⁶³NiS or ⁶³NiCl₂. Treatment of cultured cells with ⁶³NiS at 10 μg/ml for 3 days resulted in binding of nickel to DNA, RNA, or protein in the range of 1 μg of nickel bound per milligram macromolecule. However, similar treatment of cells with ⁶³NiCl₂ at 10 μg/ml for 1 to 5 days resulted in approximately one to several orders of magnitude less nickel bound to DNA, RNA, and protein. In the case of ⁶³NiCl₂ treatment, cellular proteins contained about 100 times more ⁶³Ni bound than the respective RNA or DNA fractions. However, the protein fraction obtained from cells treated with crystalline NiS contained about 15 times more nickel bound than the same fraction isolated from cells that were similarly treated with ⁶³NiCl₂. RNA or DNA had 300 to 2000 times more bound nickel following crystalline NiS treatment compared to cells treated similarly with NiCl₂. In contrast to the selective binding of ⁶³NiCl₂ to protein, cultured cells treated with crystalline ⁶³NiS had equivalent levels of nickel associated with RNA, DNA, and protein. Since the interaction of ⁶³Ni with these macromolecules following crystalline ⁶³NiS treatment was not due to the binding of the actual particles, the dissolution of intracellular ⁶³NiS particles probably plays an important role in governing the distribution of ⁶³Ni ions available for binding. The greater intracellular macromolecular binding of ⁶³Ni resulting from treatment of cells with ⁶³NiS compared to cultures similarly exposed to ⁶³NiCl₂ paralleled the more potent effects of crystalline NiS in slowing and arresting cell proliferation. Crystalline NiS caused pronounced cell cycle specific blockage at a considerably lower concentration than was required for NiCl₂ to similarly arrest cell growth. Flow cytometry analysis showed that both compounds selectively blocked cell cycle progression in S phase (DNA synthetic stage). These results are suggestive of a common mechanism and site of toxicity inherent to both compounds and related to the cell growth phase during which DNA is replicated.     

Activation of endothelial cells after exposure to ambient ultrafine particles: The role of NADPH oxidase

Several studies have shown that ultrafine particles (UFPs) may pass from the lungs to the circulation because of their very small diameter, and induce lung oxidative stress with a resultant increase in lung epithelial permeability. The direct effects of UFPs on vascular endothelium remain unknown. We hypothesized that exposure to UFPs leads to endothelial cell O₂⁻ generation via NADPH oxidase and results in activation of endothelial cells. Our results showed that UFPs, at a non-toxic dose, induced reactive oxygen species (ROS) generation in mouse pulmonary microvascular endothelial cells (MPMVEC) that was inhibited by pre-treatment with the ROS scavengers or inhibitors, but not with the mitochondrial inhibitor, rotenone. UFP-induced ROS generation in MPMVEC was abolished by p67^phox siRNA transfection and UFPs did not cause ROS generation in MPMVEC isolated from gp91^phox knock-out mice. UFP-induced ROS generation in endothelial cells was also determined in vivo by using a perfused lung model with imaging. Moreover, Western blot and immunofluorescence staining results showed that MPMVEC treated with UFPs resulted in the translocation of cytosolic proteins of NADPH oxidase, p47^phox, p67^phox and rac 1, to the plasma membrane. These results demonstrate that NADPH oxidase in the pulmonary endothelium is involved in ROS generation following exposure to UFPs. To investigate the activation of endothelial cells by UFP-induced oxidative stress, we determined the activation of the mitogen-activated protein kinases (MAPKs) in MPMVEC. Our results showed that exposure of MPMVEC to UFPs caused increased phosphorylation of p38 and ERK1/2 MAPKs that was blocked by pre-treatment with DPI or p67^phox siRNA. Exposure of MPMVEC obtained from gp91^phox knock-out mice to UFPs did not cause increased phosphorylation of p38 and ERK1/2 MAPKs. These findings confirm that UFPs can cause endothelial cells to generate ROS directly via activation of NADPH oxidase. UFP-induced ROS lead to activation of MAPKs through induced phosphorylation of p38 and ERK1/2 MAPKs that may further result in endothelial dysfunction through production of cytokines such as IL-6. Our results suggest that endothelial oxidative stress may be an important mechanism for PM-induced cardiovascular effects.     

Large Porous Particle Impingement on Lung Epithelial Cell Monolayers—Toward Improved Particle Characterization in the Lung

Purpose. The ability to optimize new formulations for pulmonary delivery has been limited by inadequate in vitro models used to mimic conditions particles encounter in the lungs. The aim is to develop a physiologically-relevant model of the pulmonary epithelial barrier that would allow for quantitative characterization of therapeutic aerosols in vitro. Methods. Calu-3 human bronchial epithelial cells were cultured on permeable filter inserts under air-interfaced culture (AIC) and liquid-covered culture (LCC) conditions. Calu-3 cells grown under both conditions formed tight monolayers and appeared physiologically similar by SEM and immunocytochemical staining against cell junctional proteins and prosurfactant protein-C. Results. Aerosolized large porous particles (LPP) deposited homogeneously and reproducibly on the cell surface and caused no apparent damage to cell monolayers by SEM and light microscopy. However, monolayers initially grown under LCC conditions showed a significant decrease in barrier properties within the first 90 min after impingement with microparticles, as determined by transepithelial electrical resistance (TEER) measurements and fluorescein-sodium transport. Conversely, AIC grown monolayers showed no significant change in barrier properties within the first 90 min following particle application. A dense mucus coating was found on AIC grown Calu-3 monolayers, but not on LCC grown monolayers, which may protect the cell surface during particle impinging. Conclusions. This in vitro model, based on AIC grown Calu-3 cells, should allow a more relevant and quantitative characterization of therapeutic aerosol particles intended for delivery to the tracheo-bronchial region of the lung or to the nasal passages. Such characterization is likely to be particularly important with therapeutic aerosol particles designed to provide sustained drug release in the lung.     

Modulation of the Tight Junctions of the Caco-2 Cell Monolayers by H2-antagonists

Purpose. The tight junctions in the intestinal epithelium represent highly specialized intercellular junctions. Ranitidine, an H₂-antagonist, causes a tightening of the tight junctions. Hence, we have investigated the effect of ranitidine and other H₂-antagonists on the function of the intestinal tight junctions. Methods. Effect of the H₂-antagonists on the tight junctions has been investigated using the transepithelial electrical resistance (TEER) and the transport of mannitol across the Caco-2 cell monolayers. Results. Four different H₂-antagonists caused an increase in the TEER across the Caco-2 cell monolayers, accompanied by a decrease in the permeability for mannitol. The effect was concentration-dependent and saturable. Ranitidine and famotidine, caused a decrease in their own transport rate across the Caco-2 cells. Ranitidine competitively inhibited the increase in TEER caused by famotidine, whereas compounds which represent molecular fragments of ranitidine had no effect. The relative potency of the four H₂-antagonists in causing an increase in the TEER correlated inversely with the oral bioavailability of these compounds in humans. Conclusions. We hypothesize that the H₂-antagonists exert their effect on the tight junctions of Caco-2 cells by modulation of interactions among proteins associated with the tight junctional complex.     

Derivation of PM10 size-selected human equivalent concentrations of inhaled nickel based on cancer and non-cancer effects on the respiratory tract

Abstract

Nickel (Ni) in ambient air is predominantly present in the form of oxides and sulfates, with the distribution of Ni mass between the fine (particle aerodynamic diameter <?2.5?µm; PM_2.5) and coarser (2.5–10?µm) size-selected aerosol fractions of PM₁₀ dependent on the aerosol's origin. When deriving a long-term health protective reference concentration for Ni in ambient air, the respiratory toxicity and carcinogenicity effects of the predominant Ni compounds in ambient air must be considered. Dosimetric adjustments to account for differences in aerosol particle size and respiratory tract deposition and/or clearance among rats, workers, and the general public were applied to experimentally- and epidemiologically-determined points of departure (PODs) such as no(low)-effect concentrations, for both cancer and non-cancer respiratory effects. This approach resulted in the derivation of threshold-based PM₁₀ size-selected equivalent concentrations (modified PODs) of 0.5?µg Ni/m³ based on workers' cancer effects and 9–11?µg Ni/m³ based on rodent respiratory toxicity effects. Sources of uncertainty in exposure extrapolations are described. These are not reference concentrations; rather the derived PM₁₀ size-selected modified PODs can be used as the starting point for the calculation of ambient air reference concentrations for Ni. The described approach is equally applicable to other particulates.     

Arylamine N-acetyltransferase activity in bronchial epithelial cells and its inhibition by cellular oxidants

Bronchial epithelial cells express xenobiotic-metabolizing enzymes (XMEs) that are involved in the biotransformation of inhaled toxic compounds. The activities of these XMEs in the lung may modulate respiratory toxicity and have been linked to several diseases of the airways. Arylamine N-acetyltransferases (NAT) are conjugating XMEs that play a key role in the biotransformation of aromatic amine pollutants such as the tobacco-smoke carcinogens 4-aminobiphenyl (4-ABP) and β-naphthylamine (β-NA). We show here that functional human NAT1 or its murine counterpart Nat2 are present in different lung epithelial cells i.e. Clara cells, type II alveolar cells and bronchial epithelial cells, thus indicating that inhaled aromatic amines may undergo NAT-dependent biotransformation in lung epithelium. Exposure of these cells to pathophysiologically relevant amounts of oxidants known to contribute to lung dysfunction, such as H₂O₂ or peroxynitrite, was found to impair the NAT1/Nat2-dependent cellular biotransformation of aromatic amines. Genetic and non genetic impairment of intracellular NAT enzyme activities has been suggested to compromise the important detoxification pathway of aromatic amine N-acetylation and subsequently to contribute to an exacerbation of untoward effects of these pollutants on health. Our study suggests that oxidative/nitroxidative stress in lung epithelial cells, due to air pollution and/or inflammation, could contribute to local and/or systemic dysfunctions through the alteration of the functions of pulmonary NAT enzymes.     

In Vitro Drug Absorption Enhancement Effects of Aloe vera and Aloe ferox

The effect of whole leaf and gel materials from two aloe species (Aloe vera and A. ferox) was compared with that of the precipitated polysaccharides from these aloe materials on the transepithelial electrical resistance (TEER) as well as transport of a model compound (atenolol) in the apical-to-basolateral direction across rat intestinal tissue. All the aloe leaf materials and precipitated polysaccharides had a statistically significant effect of lowering the TEER (P < 0.05) compared to the control group, which indicates their ability to open tight junctions between adjacent epithelial cells. In contrast to the expectation from the TEER results, only the precipitated polysaccharides from dehydrated A. vera gel (Daltonmax 700^®) had a statistically significant effect of enhancing the transport of atenolol (P < 0.05). These in vitro results therefore indicate that A. vera gel polysaccharides have potential as drug absorption enhancing agents in novel pharmaceutical drug delivery systems.