Biomarker analysis of liver cells exposed to surfactant-wrapped and oxidized multi-walled carbon nanotubes (MWCNTs)

Carbon nanotubes (CNTs) have great potential in industrial, consumer, and mechanical applications, based partly on their unique structural, optical and electronic properties. CNTs are commonly oxidized or treated with surfactants to facilitate aqueous solution processing, and these CNT surface modifications also increase possible human and ecological exposures to nanoparticle-contaminated waters. To determine the exposure outcomes of oxidized and surfactant-wrapped multiwalled carbon nanotubes (MWCNTs) on biochemical processes, metabolomics-based profiling of human liver cells (C3A) was utilized. Cells were exposed to 0, 10, or 100ng/mL of MWCNTs for 24 and 48h; MWCNT particle size distribution, charge, and aggregation were monitored concurrently during exposures. Following MWCNT exposure, cellular metabolites were extracted, lyophilized, and buffered for (1)H NMR analysis. Acquired spectra were subjected to both multivariate and univariate analysis to determine the consequences of nanotube exposure on the metabolite profile of C3A cells. Resulting scores plots illustrated temporal and dose-dependent metabolite responses to all MWCNTs tested. Loadings plots coupled with t-test filtered spectra identified metabolites of interest. XPS analysis revealed the presence of hydroxyl and carboxyl functionalities on both MWCNTs surfaces. Metal content analysis by ICP-AES indicated that the total mass concentration of the potentially toxic impurities in the exposure experiments were extremely low (i.e. [Ni]≤2×10(-10)g/mL). Preliminary data suggested that MWCNT exposure causes perturbations in biochemical processes involved in cellular oxidation as well as fluxes in amino acid metabolism and fatty acid synthesis. Dose-response trajectories were apparent and spectral peaks related to both dose and MWCNT dispersion methodologies were determined. Correlations of the significant changes in metabolites will help to identify potential biomarkers associated with carbonaceous nanoparticle exposure.

The outcome of fistulotomy for anal fistula at 1 year: a prospective multicentre French study

AIM

The study aimed to evaluate outcome at 1 year of one- and two-stage fistulotomy for anal fistula in a large group of patients.

METHOD

A prospective multicentre observational study was designed to include patients with anal fistula treated by one- or two-stage fistulotomy. Data were collected using a self-administered questionnaire before surgery, during healing and at 1 year after surgery.

RESULTS

Group A (133 patients) with a low anal fistula underwent a one-stage fistulotomy. The median Wexner scores before and after surgery were 1.0 (0-11) and 2.0 (0-18) (P = 0.032) and the median Vaizey scores were 2.0 (0-14) and 3.0 (0-21) (P = 0.055). The Wexner scores and percentage of patients before and after fistulotomy were as follows: 0-5: 88%, 86%; 6-10: 10.7%, 10.7%; 11-15: 1.0%, 2.6%; and 16-20: 0%, 2%. Eighty-seven per cent of the patients were satisfied. Group B (62 patients) underwent two-stage fistulotomy for a high transsphincteric fistula. The Wexner scores and percentage of patients before the first stage and 1 year after the second stage were as follows: 0-5: 86%, 66%; 6-10: 4.5%, 20%; 11-15: 9%, 11%; and 16-20: 0%, 2%. The median Wexner scores before the first stage and after the second stage were 1 (0-14) vs. 4 (0-19) (P < 0.001), and the median Vaizey scores were 1.5 (0-11) vs. 4 (0-20) (P < 0.001). Eighty-eight per cent of the patients were satisfied.

CONCLUSION

Low transsphincteric anal fistula can be treated by fistulotomy without clinically significant continence disturbance. Treating high transsphincteric anal fistulae with two-stage fistulotomy is followed by mild continence disturbance. Satisfaction rates were high.

Aggregation and Stability of Reduced Graphene Oxide: Complex Roles of Divalent Cations, pH, and Natural Organic Matter

The aggregation and stability of graphene oxide (GO) and three successively reduced GO (rGO) nanomaterials were investigated. Reduced GO species were partially reduced GO (rGO-1h), intermediately reduced GO (rGO-2h), and fully reduced GO (rGO-5h). Specifically, influence of pH, ionic strength, ion valence, and presence of natural organic matter (NOM) were studied. Results show that stability of GO in water decreases with successive reduction of functional groups, with pH having the greatest influence on rGO stability. Stability is also dependent on ion valence and the concentration of surface functional groups. While pH did not noticeably affect stability of GO in the presence of 10 mM NaCl, adding 0.1 mM CaCl2 reduced stability of GO with increased pH. This is due to adsorption of Ca(2+) ions on the surface functional groups of GO which reduces the surface charge of GO. As the concentration of rGO functional groups decreased, so did the influence of Ca(2+) ions on rGO stability. Critical coagulation concentrations (CCC) of GO, rGO-1h, and rGO-2h were determined to be ∼ 200 mM, 35 mM, and 30 mM NaCl, respectively. In the presence of CaCl2, CCC values of GO and rGO are quite similar, however. Long-term studies show that a significant amount of rGO-1h and rGO-2h remain stable in Call's Creek surface water, while effluent wastewater readily destabilizes rGO. In the presence NOM and divalent cations (Ca(2+), Mg(2+)), GO aggregates settle from suspension due to GO functional group bridging with NOM and divalent ions. However, rGO-1h and rGO-2h remain suspended due to their lower functional group concentration and resultant reduced NOM-divalent cation bridging. Overall, pH, divalent cations, and NOM can play complex roles in the fate of rGO and GO.

Sunlight affects aggregation and deposition of graphene oxide in the aquatic environment

In this study, we investigate the role of simulated sunlight on the physicochemical properties, aggregation, and deposition of graphene oxide (GO) in aquatic environments. Results show that light exposure under varied environmental conditions significantly impacts the physicochemical properties and aggregation/deposition behaviors of GO. Photo-transformation has negligible effects on GO surface charge, however, GO aggregation rates increase with irradiation time for direct photo-transformation under both aerobic and anaerobic conditions. Under anaerobic conditions, photo-reduced GO has a greater tendency to form aggregates than under aerobic conditions. Aggregation of photo-transformed GO is notably influenced by ion valence, with higher aggregation found in the presence of divalent ions versus monovalent, but adding natural organic matter (NOM) reduces it. QCM-D studies show that deposition of GO on surfaces coated with organic matter decreases with increased GO irradiation time, indicating a potential increase in GO mobility due to photo-transformation. General deposition trends on Suwannee River Humic Acid (SRHA)-coated surfaces are control GO > aerobically photo-transformed GO ≈ anaerobically photo-transformed GO. The release of deposited GO from SRHA-coated surfaces decreases with increased irradiation time, indicating that photo-transformed GO is strongly attached to the NOM-coated surface.

Photochemical transformation of graphene oxide in sunlight

Graphene oxide (GO) is promising in scalable production and has useful properties that include semiconducting behavior, catalytic reactivity, and aqueous dispersibility. In this study, we investigated the photochemical fate of GO under environmentally relevant sunlight conditions. The results indicate that GO readily photoreacts under simulated sunlight with the potential involvement of electron-hole pair creation. GO was shown to photodisproportionate to CO2, reduced materials similar to reduced GO (rGO) that are fragmented compared to the starting material, and low molecular-weight (LMW) species. Kinetic studies show that the rate of the initially rapid photoreaction of GO is insensitive to the dissolved oxygen content. In contrast, at longer time points (>10 h), the presence of dissolved oxygen led to a greater production of CO2 than the same GO material under N2-saturated conditions. Regardless, the rGO species themselves persist after extended irradiation equivalent to 2 months in natural sunlight, even in the presence of dissolved oxygen. Overall, our findings indicate that GO phototransforms rapidly under sunlight exposure, resulting in chemically reduced and persistent photoproducts that are likely to exhibit transport and toxic properties unique from parent GO.

Interactions of graphene oxide nanomaterials with natural organic matter and metal oxide surfaces

Interactions of graphene oxide (GO) nanomaterials with natural organic matter (NOM) and metal oxide surfaces were investigated using a quartz crystal microbalance with dissipation monitoring (QCM-D). Three different types of NOM were studied: Suwannee River humic and fulvic acids (SRHA and SRFA) and alginate. Aluminum oxide surface was used as a model metal oxide surface. Deposition trends show that GO has the highest attachment on alginate, followed by SRFA, SRHA, and aluminum oxide surfaces, and that GO displayed higher interactions with all investigated surfaces than with silica. Deposition and release behavior of GO on aluminum oxide surface is very similar to positively charged poly-L-lysine-coated surface. Higher interactions of GO with NOM-coated surfaces are attributed to the hydroxyl, epoxy, and carboxyl functional groups of GO; higher deposition on alginate-coated surfaces is attributed to the rougher surface created by the extended conformation of the larger alginate macromolecules. Both ionic strength (IS) and ion valence (Na(+) vs Ca(2+)) had notable impact on interactions of GO with different environmental surfaces. Due to charge screening, increased IS resulted in greater deposition for NOM-coated surfaces. Release behavior of deposited GO varied significantly between different environmental surfaces. All surfaces showed significant release of deposited GO upon introduction of low IS water, indicating that deposition of GO on these surfaces is reversible. Release of GO from NOM-coated surfaces decreased with IS due to charge screening. Release rates of deposited GO from alginate-coated surface were significantly lower than from SRHA and SRFA-coated surfaces due to trapping of GO within the rough surface of the alginate layer.

Deposition and release of graphene oxide nanomaterials using a quartz crystal microbalance

Interactions of graphene oxide (GO) with silica surfaces were investigated using a quartz crystal microbalance with dissipation monitoring (QCM-D). Both GO deposition and release were monitored on silica- and poly-l-lysine (PLL) coated surfaces as a function of GO concentration and in NaCl, CaCl2, and MgCl2 as a function of ionic strength (IS). Under favorable conditions (PLL-coated positive surface), GO deposition rates increased with GO concentration, as expected from colloidal theory. Increased NaCl concentration resulted in a greater deposition attachment efficiency of GO on the silica surface, indicating that deposition of GO follows Derjaguin-Landau-Verwey-Overbeek (DLVO) theory; GO deposition rates decreased at high IS, however, due to large aggregate formation. GO critical deposition concentration (CDC) on the silica surface is determined to be 40 mM NaCl which is higher than the reported CDC values of fullerenes and lower than carbon nanotubes. A similar trend is observed for MgCl2 which has a CDC value of 1.2 mM MgCl2. Only a minimal amount of GO (frequency shift <2 Hz) was deposited on the silica surface in CaCl2 due to the bridging ability of Ca(2+) ions with GO functional groups. Significant GO release from silica surface was observed after adding deionized water, indicating that GO deposition is reversible. The release rates of GO were at least 10-fold higher than the deposition rates under similar conditions indicating potential high release and mobility of GO in the environment. Under favorable conditions, a significant amount of GO was released which indicates potential multilayer GO deposition. However, a negligible amount of deposited GO was released in CaCl2 under favorable conditions due to the binding of GO layers with Ca(2+) ions. Release of GO was significantly dependent on salt type with an overall trend of NaCl > MgCl2 > CaCl2.