Deterioration of bio-based polylactic acid plastic teabags under environmental conditions and their associated effects on earthworms.

In response to the plastic waste crisis, teabag producers have substituted the petrochemical-plastic content of their products with bio-based, biodegradable polymers such as polylactic acid (PLA). Despite widespread use, the degradation rate of PLA/PLA-blended materials in natural soil and their effects on soil biota are poorly understood. This study examined the percentage mass deterioration of teabags with differing cellulose:PLA compositions following burial (-10 cm depth) in an arable field margin for 7-months, using a suite of analytical techniques, such as size exclusion chromatography, 1H nuclear magnetic resonance, dynamic scanning calorimetry, and scanning electron microscopy. The effect of 28-d exposure to teabag discs at environmentally relevant concentrations (0.02 %, 0.04 % and 0.07 % w/w) on the survival, growth and reproduction (OECD TG 222 protocol) of the key soil detritivore Eisenia fetida was assessed in laboratory trials. After 7-month burial, Tbag-A (2.4:1 blend) and Tbag-B (3.5:1 cellulose:PLA blend) lost 66 ± 5 % and 78 ± 4 % of their total mass, primarily attributed to degradation of cellulose as identified by FTIR spectroscopy and a reduction in the cellulose:PLA mass ratio, while Tbag-C (PLA) remained unchanged. There were clear treatment and dose-specific effects on the growth and reproductive output of E. fetida. At 0.07 % w/w of Tbag-A adult mortality marginally increased (15 %) and both the quantity of egg cocoons and the average mass of juveniles also increased, while at concentrations ≥0.04 % w/w of Tbag-C, the quantity of cocoons was suppressed. Adverse effects are comparable to those reported for non-biodegradable petrochemical-based plastic, demonstrating that bio-based PLA does not offer a more 'environmentally friendly' alternative. Our study emphasises the necessity to better understand the environmental fate and ecotoxicity of PLA/PLA-blends to ensure interventions developed through the UN Plastic Pollution Treaty to use alternatives and substitutes to conventional plastics do not result in unintended negative consequences.

Graphene oxide biopolymer aerogels for the removal of lead from drinking water using a novel nano-enhanced ion exchange cascade.

Potable water in developing countries often contains levels of toxic metals that exceed the recommended international limits, with impacts on human health. The aim of the present study was to develop a low cost aerogel synthesised from graphene oxide (GO) cross-linked with alginate to remove Pb2+ from potable water. Aerogels were made by a sol-gel of the composite materials followed by a freeze drying method. The shape of the aerogels were 50 mm diameter disks, 5 mm deep and characterised by an open porous network of 50 to 150 micrometres which are mechanically robust upon hydration. Firstly, the study was conducted using a batch adsorption method from a starting concentration 0.48 mM (100 mg/l) of Pb2+ in ultrapure water over 240 min, n = 4 with controls. A second series of experiments compared the adsorption of different competing ions at different valencies (Na+, Ca2+, Cu2+, La3+) in an equivalent media. A third series of experiments explored Pb2+ desorption from the aerogel at low pH and in highly acidic conditions. This simple filter system, based on a batch adsorption methodology expresses a high affinity for Pb2+ resulting in an ultra-high mean maximum adsorption capacity of 504 mg/g of Pb2+ within 240 mins at pH 5. The aerogel can also adsorb other toxic metal salts such as La3+ and Cu2+ with a capacity of 146 and 193 mg/g respectively. Furthermore, the aerogel structure can be acid washed removing 98% of the Pb2+ from the structure within three minutes. Overall, the data shows that GO alginate aerogels are highly effective at removing Pb2+ from water and the primary mechanism involved is ion exchange, although other phenomenon such as proton tunnelling may be a contributing factor to the ultra-high efficiency of the aerogel for Pb2+ remediation.

The minimum inhibitory concentration (MIC) assay with Escherichia coli: An early tier in the environmental hazard assessment of nanomaterials?

There are now over a thousand nano-containing products on the market and the antibacterial properties of some nanomaterials has created interest in their use as cleaning agents, biocides and disinfectants. Engineered nanomaterials (ENMs) are being released into the environment and this raises concerns about their effects on microbes in the receiving ecosystems. This study evaluated the bacterial toxicity of a wide range of nanomaterials with different surface coatings on Escherichia coli K-12 MG1655. The minimum inhibitory concentration (MIC) assay, which quantifies the threshold for growth inhibition in suspensions of bacteria, was used to rank the toxicity of silver (Ag), cupric oxide (CuO), cadmium telluride (CdTe) quantum dots, titanium dioxide (TiO2), nanodiamonds and multi-walled carbon nanotubes (MWCNTs). Bacteria were exposed for 12 h at 37 °C to a dilution series of the test suspensions in 96-well plates. The precision and accuracy of the method was good with coefficients of variation < 10%. In terms of the measured MIC values, the toxicity order of the ENMs was as follows: CdTe quantum dots ammonium-coated, 6 mg L-1 > Ag nanoparticles, 12 mg L-1 > CdTe quantum dots carboxylate-coated, 25 mg L-1 > CdTe quantum dots polyethylene glycol-coated, 100 mg L-1. The MIC values were above the highest test concentration used (100 mg L-1) for CuO, TiO2, nanodiamonds and MWCNTs, indicating low toxicity. The MIC assay can be a useful tool for the initial steps of ENMs hazard assessment.

Antibacterial activity and biofilm inhibition by surface modified titanium alloy medical implants following application of silver, titanium dioxide and hydroxyapatite nanocoatings.

One of the most common causes of implant failure is peri-implantitis, which is caused by bacterial biofilm formation on the surfaces of dental implants. Modification of the surface nanotopography has been suggested to affect bacterial adherence to implants. Silver nanoparticles are also known for their antibacterial properties. In this study, titanium alloy implants were surface modified following silver plating, anodisation and sintering techniques to create a combination of silver, titanium dioxide and hydroxyapatite (HA) nanocoatings. Their antibacterial performance was quantitatively assessed by measuring the growth of Streptococcus sanguinis, proportion of live/dead cells and lactate production by the microbes over 24 h. Application of a dual layered silver-HA nanocoating to the surface of implants successfully inhibited bacterial growth in the surrounding media (100% mortality), whereas the formation of bacterial biofilm on the implant surfaces was reduced by 97.5%. Uncoated controls and titanium dioxide nanocoatings showed no antibacterial effect. Both silver and HA nanocoatings were found to be very stable in biological fluids with material loss, as a result of dissolution, to be less than 0.07% for the silver nanocoatings after 24 h in a modified Krebs-Ringer bicarbonate buffer. No dissolution was detected for the HA nanocoatings. Thus, application of a dual layered silver-HA nanocoating to titanium alloy implants creates a surface with antibiofilm properties without compromising the HA biocompatibility required for successful osseointegration and accelerated bone healing.

Sub-lethal effects of titanium dioxide nanoparticles on the physiology and reproduction of zebrafish.

There are limited data on the sub-lethal physiological effects of titanium dioxide nanoparticles (TiO(2) NPs) in adult fishes, and the consequences of TiO(2) NP exposure on reproductive success are also unclear. This study aimed to examine the sub-lethal effects of a 14-d aqueous TiO(2) (TiO(2) NP, 0.1 or 1.0 mg l(-1); TiO(2) bulk, 1.0 mg l(-1)) exposure on the physiology and reproductive health of zebrafish. After the 14-d exposure, fish were examined for haematology, whole body electrolyte and trace metal profiles, biochemistry, and histopathology. Then, during a 21-d post exposure recovery period, effects of the TiO(2) exposure on reproductive success were evaluated. Whole body Ti concentrations increased significantly in fish exposed to both the 1.0 mg l(-1) TiO(2) NP and bulk TiO(2) compared to controls, but concentrations returned to control levels by the end of the recovery period. No change in erythrocyte counts were observed, but there was a two-fold decline in leukocyte counts in all TiO(2) treatment groups relative to time-matched controls. Whole body electrolyte and trace metal profiles were not affected by exposure to TiO(2), and there were no changes in Na(+)K(+)-ATPase activity in brain, gill or liver tissues. Total glutathione (GSH) levels in brain, gill and liver tissues were higher in fish exposed to TiO(2) NP (both 0.1 and 1.0 mg l(-1)) compared to bulk TiO(2) and control fish. Histological examination of gill, liver, brain and gonad tissues showed little evidence of treatment-related morphological change. At the end of the 14-d exposure adult zebrafish were able to reproduce; however, the cumulative number of viable embryos produced was lower in fish exposed to 1.0 mg l(-1) TiO(2) (both NP and bulk) by the end of the 21-d recovery period. Overall, this study showed limited toxicity of bulk or nano scale TiO(2) during the exposure; however reproduction was affected in both bulk and NP 1.0 mg l(-1) groups.

Dietary preference and feeding selectivity of common dragonet Callionymus lyra in U.K.

The gut contents of 90 individuals of common dragonet Callionymus lyra were analysed, of which 76 contained prey, along with 100 corresponding benthic grab samples in order to assess the diet of C. lyra in relation to the availability of its prey in the environment. Forty-five prey taxa were identified in the diet from 350 potential prey taxa identified in the environment. Calculation of the index of relative importance (I(RI)) found the main food components were crustaceans (%I(RI) = 86·3), mostly the porcelain crab Pisidia longicornis (%I(RI) = 43) and other decapods (%I(RI) = 18). Polychaetes played only a supplementary role in the overall diet (%I(RI) = 12·5). This study demonstrated that C. lyra is predominantly an opportunistic feeder that can modify its feeding behaviour to exploit alternative, more abundant prey.

Effects of manufactured nanomaterials on fishes: a target organ and body systems physiology approach.

Manufactured nanomaterials (NM) are already used in consumer products and exposure modelling predicts releases of ng to low µg l(-1) levels of NMs into surface waters. The exposure of aquatic ecosystems, and therefore fishes, to manufactured NMs is inevitable. This review uses a physiological approach to describe the known effects of NMs on the body systems of fishes and to identify the internal target organs, as well as outline aspects of colloid chemistry relevant to fish biology. The acute toxicity data, suggest that the lethal concentration for many NMs is in the mg l(-1) range, and a number of sublethal effects have been reported at concentrations from c. 100 µg to 1 mg l(-1). Exposure to NMs in the water column can cause respiratory toxicity involving altered ventilation, mucus secretion and gill pathology. This may not lead, however, to overt haematological disturbances in the short term. The internal target organs include the liver, spleen and haematopoietic system, kidney, gut and brain; with toxic effects involving oxidative stress, ionoregulatory disturbances and organ pathologies. Some pathology appears to be novel for NMs, such as vascular injury in the brain of rainbow trout Oncorhynchus mykiss with carbon nanotubes. A lack of analytical methods, however, has prevented the reporting of NM concentrations in fish tissues, and the precise uptake mechanisms across the gill or gut are yet to be elucidated. The few dietary exposure studies conducted show no effects on growth or food intake at 10-100 mg kg(-1) inclusions of NMs in the diet of O. mykiss, but there are biochemical disturbances. Early life stages are sensitive to NMs with reports of lethal toxicity and developmental defects. There are many data gaps, however, including how water quality alters physiological responses, effects on immunity and chronic exposure data at environmentally relevant concentrations. Overall, the data so far suggest that the manufactured NMs are not as toxic as some traditional chemicals (e.g. some dissolved metals) and the innovative, responsible, development of nanotechnology should continue, with potential benefits for aquaculture, fisheries and fish health diagnostics.

Limited DNA damage in human endothelial cells after hyperbaric oxygen treatment and protection from subsequent hydrogen peroxide exposure.

BACKGROUND: In vitro studies on hyperbaric oxygen (HBO) therapy suggest that HBO may cause DNA damage, but this has not been evaluated using endothelial cells. METHODS: Human umbilical cord endothelial cells (HUVECs) were exposed either to H(2)O(2) or to HBO for 90 min, with or without subsequent H(2)O(2) exposure. Measurements included the comet assay for DNA damage, and reduced and oxidised glutathione levels. RESULTS: HUVECs showed sensitivity to H(2)O(2) (EC(50) of 0.2mM for DNA migration). A single 90 min HBO treatment at 2.2 ATA caused a statistically significant (ANOVA, P<0.05) increase of DNA migration in HUVECs to 6.8 ± 0.3% (mean ± SEM, n=8), which returned to normal levels (4.9 ± 0.1%, n=6) after 24h. Further exposure to 0.2mM H(2)O(2) after HBO treatment significantly increased the DNA migration in HBO-treated cells immediately post-treatment; but 24h later the cells showed 22% less DNA damage and higher glutathione than controls. CONCLUSION: A single HBO exposure causes limited DNA damage to HUVECs, which repairs quickly. HBO treatment protects against H(2)O(2)-induced DNA damage and involves cellular glutathione. SIGNIFICANCE: Endothelial cells are unlikely to be compromised during HBO therapy.

Tissue injury and cellular immune responses to cadmium chloride exposure in the common mussel Mytilus edulis: modulation by lipopolysaccharide.

The immunotoxic effects of cadmium (Cd) exposure in bivalves are poorly understood and whether or not stimulation of the immune system exacerbates Cd toxicity is unclear. The mussel Mytilus edulis was exposed to 20 or 50 µg/l total Cd for up to 11 days compared to no added Cd controls to assess immune and other physiological responses. Selected experiments were then repeated in the presence of a lipopolysaccharide (LPS) challenge with and without subsequent Cd exposure. Immune functions of hemocytes, hematology, hemolymph glucose and ion content, as well as superoxide dismutase (SOD) activity and organ pathology were measured. Cd accumulated mainly in digestive gland and gills and to a lesser extent in the adductor muscle. Exposure to 20 µg/l Cd alone caused a transient modulated of phagocytosis and increased neutral red retention (Kruskal-Wallis, p = 0.002). The higher Cd concentration also increased cytotoxicity, and decreased hemocyte count. Changes in hemolymph Na(+), K(+), and glucose were small or negligible. Histopathological examination showed tissue injuries consistent with inflammation and necrosis in the gills, digestive gland, and adductor muscle during Cd exposure alone. LPS injection alone and LPS + Cd caused an increase in the number of circulating hemocytes by the end of the experiment (Kruskal-Wallis, p = 0.01) and a transient rise in phagocytosis at day 4 (analysis of variance (ANOVA), p = 0.001). The LPS + Cd treatment also caused transient changes in neutral red retention and in the cytotoxicity of hemocytes compared to controls. Intracellular SOD activity did not change in hemocytes under any treatment. Tissue inflammation and pathology was greatly increased by the effect of Cd exposure with an LPS injection compared to either treatment alone. We conclude that immunostimulation with LPS can greatly increase Cd-related organ pathologies but does not necessarily alter the responses of hemocytes.

Response of blood vessels in vitro to hyperbaric oxygen (HBO): modulation of VEGF and NO(x) release by external lactate or arginine.

Hyperbaric oxygen therapy (HBO) is suggested to promote angiogenesis during wound healing, but the mechanisms involved are not understood. This study used a novel isolated blood vessel preparation to explore the effects of air, normobaric oxygen or hyperbaric oxygen (2.2 ATA for 90 min) on the angiogenesis factor, vascular endothelial growth factor (VEGF), nitrite and nitrate (NO(x)), lactate dehydrogenase (LDH) and lactate release from the tissue in normal Krebs Ringer, and the Ringer supplemented with either l-arginine, or 15 mM lactate to mimic a wound environment, or both (l-arginine+lactate). The in vitro blood vessel preparation remained viable during all experiments. There were no effects of HBO treatment on any of the parameters measured in normal Krebs Ringer, but some treatment-dependent effects were observed in supplemented Krebs Ringer. In the lactate supplemented Krebs Ringer, medium LDH levels increased in response to either normobaric oxygen (NBO) or HBO, compared to air alone. There were also small, but statistically significant increases in total glutathione due to HBO treatment, compared to NBO or air in the lactate supplemented medium, and in the combined supplement. There were no effects of HBO on NO(x), changes in external medium lactate levels, or tissue VEGF in any of the Krebs Ringers tested. However, post treatment increases in VEGF were observed in the lactate supplemented medium, and for lactate release into the medium for the combined supplement. We conclude that HBO does not cause NO or VEGF production from the blood vessel in normal Krebs Ringer, but the data from supplemented medium show that the response of the tissue is subtly affected by the chemical environment around the blood vessel, and the tissue is more responsive to HBO when wound conditions are mimicked.

Prey selection and functional response of juvenile lemon sharks Negaprion brevirostris.

Prey preference of juvenile lemon sharks Negaprion brevirostris was examined in experiments conducted in field-based pens where the fish were offered meals of live teleosts: grey snapper Lutjanus griseus and yellow fin majorra Gerres cinereus in ratios of L. griseus:G. cinereus varying from 10:0 to 2:8. Relative electivity indices for each treatment showed that N. brevirostris preyed on G. cinereus rather than L. griseus. They showed a prey preference relating to density of G. cinereus (type II functional response) but not to L. griseus.

The haemolytic effect of verapamil on erythrocytes exposed to varying osmolarity.

The haemolytic effect of verapamil on red blood cells (RBCs) exposed to varying osmolarity was investigated. The experimental approach used a modified red cell haemolysis assay with concentrations of verapamil ranging from 50-1500 microM compared to drug free controls. The time-course of haemolytic effects was also investigated. We also briefly determined the haemolytic effects of verapamil in Ca2+-free conditions (with added EGTA). In conditions representing decreasing osmolarity (dilution from 140-0 mM NaCl) there was a significant increase in erythrocyte haemolysis that was also dependent on verapamil concentration (ANOVA, p<0.05). The red cells also showed a significantly increased rate of haemolysis over 5 h with increasing verapamil concentration (ANOVA, p<0.05). The degree of RBC hypotonic haemolysis was significantly increased in a Ca2+-free medium (+EGTA) compared to normal saline and this effect was exacerbated by additions of verapamil (ANOVA, p<0.05). Overall the data suggested that verapamil can cause haemolysis of RBCs in a predictable time- and concentration-dependent manner, and that verapamil increases the fragility of the erythrocytes further during hypotonic osmotic stress and Ca2+-free conditions. The mechanism of verapamil-dependent haemolysis could be directly related to the observed biphasic concentration-effect and could consequently involve several ion transport pathways.

Dietary copper exposure in the African walking catfish, Clarias gariepinus: transient osmoregulatory disturbances and oxidative stress.

There are few dietary Copper (Cu) toxicity studies on warm water fish. We used the African walking catfish (Clarias gariepinus) to perform the first in vivo dietary Cu toxicity study on this species. We measured end points normally associated with metal toxicity (nutritional performance, haematology, histology, tissue Cu, Na(+), and K(+), Na(+)K(+)-ATPase activity) and add to the limited data on oxidative stress during dietary Cu exposure (thiobarbituric acid reactive substances or TBARS, and total glutathione). Clarias gariepinus were fed to satiation on a Cu-loaded diet (1500 mg Cu kg(-1)dw feed), or a control diet (15 mg Cu kg(-1) dw feed), for 30 days. Dietary copper exposure caused elevated Cu concentrations in the intestine (20 fold), liver (5 fold) and gills (4 fold) of Cu-exposed fish compared to controls after 30 days (ANOVA, P<0.05). Copper-exposed fish showed a reduction in food intake and specific growth rate (SGR), but only very modest reductions in mean body mass at the end of the experiment (the latter not statistically significant). There were no treatment-dependent effects on food conversion ratio or proximate composition, and only transient disturbances to tissue electrolytes and Na(+)K(+)-ATPase activity. Haematology was normal throughout the experiment. Cu-exposed fish showed an increase in TBARS in the gill (1.5 fold) and intestine (2 fold increase) compared to the controls (ANOVA or Kruskal-Wallis, P<0.05). Total glutathione content in the intestine of Cu-exposed fish doubled by the end of the experiment compared to controls, reaching 12.7+/-2.85 micromol g(-1) wet weight (mean+/-S.E.M., n=6, Student's t-test, P<0.05). The liver showed some glycogen depletion consistent with reduced food intake, but no overt pathologies in the gills, liver or intestine were observed.

The effects of dietary iron concentration on gastrointestinal and branchial assimilation of both iron and cadmium in zebrafish (Danio rerio).

Zebrafish (Danio rerio) were fed either a diet containing 33mgFekg(-1) (low) or 95mgFekg(-1) (normal) for 10 weeks, after which short-term Cd and Fe uptake by the gastrointestinal tract and gill was assessed. Carcass metal content and transcript levels of the iron importer, Divalent Metal Transporter 1 (DMT1) and an iron exporter, ferroportin1, in both the gastrointestinal tract and gill were also measured. Fish fed the low Fe diet accumulated 13 times more Cd into their livers via the gastrointestinal tract than those fed the normal Fe diet. However, no significant increase in liver Fe accumulation was measured. Concomitantly, when exposed to 48nmolCdL(-1) fish fed the low Fe diet exhibited a approximately 4-fold increase in Cd accumulation on the gill and in the liver, compared to those fed a normal diet. In addition, fish fed the low Fe diet also significantly accumulated more Fe on the gill (nine-fold increase) and into the carcass (four-fold increase) when exposed to 96nmolFeL(-1), compared to fish fed a normal diet. Surprisingly, carcass Fe, Ca and Mg concentrations were increased in fish fed the low Fe diet, which suggests that Fe body levels may not be a good indicator of whether a fish is more or less susceptible to increased non-essential metal accumulation via an Fe uptake pathway. However, significantly elevated transcript levels of DMT1 and ferroportin1 (2.7- and 3.8-fold induction, respectively) were seen in the gastrointestinal tract, and DMT1 in the gills (1.8-fold induction) of zebrafish fed a low Fe diet. The correlation between Cd uptake and DMT1 expression suggests that one route of uptake of Cd, either from the diet or from the water, could be via DMT1.

Shifts in a fish's resource holding power during a contact paired interaction: the influence of a copper-contaminated diet in rainbow trout.

The influence of sublethal chronic dietary copper (Cu) exposure on the dominant-subordinate relationship between pairs of juvenile rainbow trout (Oncorhynchus mykiss) was examined. Fish were fed either a normal (11 mg Cu kg(-1) food) or Cu-contaminated (721 mg Cu kg(-1) food) diet for 8 wk. Paired interactions were observed--control versus control, Cu-exposed versus Cu-exposed, and control versus Cu-exposed fish--using a computer-aided video tracking system to measure duration of interactions, total distance moved, and the number of encounters during each contest. In concurrence with game theory, each interaction became escalated with a lesser size disparity between contestants. However, in Cu-exposed versus Cu-exposed fish interactions, the dominant-subordinate relationship was decided sooner and with less aggression than a control versus control fish interaction with fish of a similar relative body mass disparity. During control versus Cu-exposed fish interactions, control fish would normally dominate interactions (12 out of 16 bouts) unless the Cu-exposed fish had a 15% body mass advantage. Muscle glycogen and lactate levels after each contest reflected the duration of bouts and winners of the contests, irrespective of Cu exposure. We conclude that Cu-contaminated fish are less able to compete and have lower resource holding power than controls and will withdraw from a contest at a lower level of interaction, unless a size advantage in the Cu-exposed fish increases the probability of winning.

Dose-dependent inorganic mercury absorption by isolated perfused intestine of rainbow trout, Oncorhynchus mykiss, involves both amiloride-sensitive and energy-dependent pathways.

The trophic transfer and nutritional toxicity of mercury (Hg) in aquatic food chains is well known, but there is limited information on the mechanism of mercury uptake across the gut. In this study, isolated whole gut sacs from rainbow trout were used to identify the regions of the gut involved in Hg absorption, and then perfused intestines were used to investigate Hg uptake. Exposure of whole gut sacs to 100 micromol l(-1) Hg as HgCl2 in the luminal solution caused Hg accumulation primarily in the mucosa (78% or more), with the intact mid and hind gut supporting 59% of the accumulated Hg. Luminal exposure to [Hg] between 0 and 100 micromol l(-1) for 4 h in perfused trout intestines showed a non-linear dose-dependent accumulation with a maximum Hg uptake rate of about 103 nmol g(-1) h(-1), and suggests carrier mediated transport into the gut cells and the blood. Additions of 2 mmol l(-1) amiloride depressed Hg accumulation by the mid and hind gut by 40-50%, whilst additions of the Ca chelator 1 mmol l(-1) EGTA increased Hg levels in the tissue. Symmetrical additions of 10 mmol l(-1) cyanide did not prevent tissue accumulation of Hg, but caused a 3.4-fold decline in net Hg flux to the serosal compartment. We conclude that Hg absorption across the gut is partly carrier mediated and involves both amiloride sensitive, and energy-dependent pathways.

Sodium-sensitive and -insensitive copper accumulation by isolated intestinal cells of rainbow trout Oncorhynchus mykiss.

The pathway for copper (Cu) uptake across the mucosal membrane into intestinal cells has not been elucidated in fish. Copper accumulation in freshly isolated intestinal cells from rainbow trout Oncorhynchus mykiss was measured after exposure to 0-800 micromol l(-1) CuSO(4) for 15 min. With external Cu concentration (Cu(o)) of 800 micromol l(-1), the rate of Cu accumulation by cells was 1.88+/-0.52 nmol Cu mg(-1) cell protein h(-1) compared to 0.05+/-0.01 nmol Cu mg(-1) cell protein h(-1) with no added Cu(o) (means +/- s.e.m., N=6). Deduction of a rapid Cu accumulation measured on/in cells at time zero (about 12% of the total Cu uptake when Cu(o) was 800 micromol l(-1)) revealed a saturable uptake curve, which reached a plateau at 400 micromol l(-1) Cu(o) (K(m)=216 micromol l(-1) Cu(o); V(max)=1.09 nmol Cu mg(-1) cell protein h(-1); 140 mmol l(-1) NaCl throughout). Incubation of cells at 4 degrees C did not prevent Cu accumulation. Lowering external [Na(+)] to 11 mmol l(-1) (low Na(+)(o)) generally did not alter the rate of Cu accumulation into the cells over a 15 min period. Under low Na(+)(o) conditions Cu accumulation was exponential (non-saturable). Na(+)-insensitive Cu accumulation dominated (59% of total Cu accumulation) when Cu(o) was 400 micromol l(-1) or less. At high Cu(o) (800 micromol l(-1)), removal of Na(+) caused a 45% increase in Cu accumulation. Pre-incubation of cells with blocking agents of epithelial Na(+) channel (ENaC) for 15 min (normal [NaCl] throughout) caused Cu accumulation rates to increase by 40-fold (100 micromol l(-1) phenamil), 21-fold (10 micromol l(-1) CDPC) or 12-fold (2 mmol l(-1) amiloride) when Cu(o) was 800 micromol l(-1) compared to those in drug-free controls. Lowering the external chloride concentration [Cl(-)](o) from 131.6 to 6.6 mmol l(-1) (replaced by sodium gluconate) caused the rate of Cu accumulation to increase 11-fold when Cu(o) was 800 micromol l(-1). Application of 0.1 mmol l(-1) DIDS (normal Cl(-)(o)) caused a similar effect. Lowering external pH from 7.4 to pH 5.5 produced a 17-fold, saturable, increase in Cu accumulation rate, which was not explained by increased instantaneous Cu accumulation on/in cells at low pH. We conclude that Cu accumulation by intestinal cells is mainly Na(+)-insensitive and more characteristic of a pH- and K(+)-sensitive Ctr1-like pathway than Cu uptake through ENaCs.

Oxidative metabolism in platelets, platelet aggregation, and hematology in patients undergoing multiple hyperbaric oxygen exposures.

Repeated hyperbaric oxygen (HBO2) treatments at 2.2 ATA for 90 minutes each are used to treat chronically ill patients with problem wounds, but there are concerns about the cytotoxicity of oxygen to blood cells and platelet function during prolonged HBO2 therapy. We recruited 31 consenting patients scheduled for multiple HBO2 treatments to evaluate oxidative metabolism in platelets, platelet aggregation, and hematology (mean age +/- standard error, 61 +/- 2.6 years, 20 males, 11 females). Venous blood was collected before and after the 1st and 20th HBO2 treatments. No effect of HBO2 was observed on red cell counts, hematocrit, hemoglobin, mean red cell volume (MCV), platelet counts, basal levels of lactate production by platelets, ferric reducing ability of plasma (FRAP), or plasma protein. The capacity for oxidative metabolism (lactate ratio) in platelets was not affected by HBO2, except in smokers where it increased by the 20th HBO2 treatment. Mean lymphocyte count was increased by 38% after the 20th treatment. There was also a 23% increase in platelet protein content, and a 24% increase in arachidonic acid-dependent platelet activation. Collagen-dependent platelet aggregation was unaffected. Blood glucose showed HBO2-dependent variability, but remained in the normal range. Plasma lactate levels decreased significantly from 3.2 to 2.5 mmol/l by the end of the study. Overall, we found no evidence that 20 HBO2 sessions caused adverse effects on platelet aggregation or oxidative metabolism in platelets, red or white cell counts, or total antioxidant status of the plasma.

Physiological modulation of iron metabolism in rainbow trout (Oncorhynchus mykiss) fed low and high iron diets.

Iron (Fe) is an essential element, but Fe metabolism is poorly described in fish and the role of ferrireductase and transferrin in iron regulation by teleosts is unknown. The aim of the present study was to provide an overview of the strategy for Fe handling in rainbow trout, Oncorhynchus mykiss. Fish were fed Fe-deficient, normal and high-Fe diets (33, 175, 1975 mg Fe kg(-1) food, respectively) for 8 weeks. Diets were chosen so that no changes in growth, food conversion ratio, haematology, or significant oxidative stress (TBARS) were observed. Elevation of dietary Fe caused Fe accumulation particularly in the stomach, intestine, liver and blood. The increase in total serum Fe from 10 to 49 micro mol l(-1) over 8 weeks was associated with elevated total Fe binding capacity and decreased unsaturated Fe binding capacity, so that in fish fed a high-Fe diet transferrin saturation increased from 15% at the start of the experiment to 37%. Fish on the high-Fe diet increased Fe accumulation in the liver, which was correlated with elevation of hepatic ferrireductase activity and serum transferrin saturation. Conversely, fish on the low-Fe diet did not show tissue Fe depletion compared with normal diet controls and did not change Fe binding to serum transferrin. Instead, these fish doubled intestinal ferrireductase activity which may have contributed to the maintenance of tissue Fe status. The absence of clear treatment-dependent changes in branchial Fe accumulation and ferrireductase activity indicated that the gills do not have a major role in Fe metabolism. Some transient changes in Cu, Zn and Mn status of tissues occurred.

Sodium-dependent copper uptake across epithelia: a review of rationale with experimental evidence from gill and intestine.

The paper reviews the evidence for apparent sodium-dependent copper (Cu) uptake across epithelia such as frog skin, fish gills and vertebrate intestine. Potential interactions between Na(+) and Cu during transfer through epithelial cells is rationalized into the major steps of solute transfer: (i) adsorption on to the apical/mucosal membrane, (ii) import in to the cell (iii) intracellular trafficking, and (iv) export from the cell to the blood. Interactions between Na(+) and Cu transport are most likely during steps (i) and (ii). These ions have similar mobilities (lambda) in solution (lambda, Na(+), 50.1; Cu(2+), 53.6 cm(2) Int. ohms(-1) equiv(-1)); consequently, Cu(2+) may compete equally with Na(+) for diffusion to membrane surfaces. We present new data on the Na(+) binding characteristics of the gill surface (gill microenvironment) of rainbow trout. The binding characteristics of Na(+) and Cu(2+) to the external surface of trout gills are similar with saturation of ligands at nanomolar concentrations of solutes. At the mucosal/apical membrane of several epithelia (fish gills, frog skin, vertebrate intestine), there is evidence for both a Cu-specific channel (CTR1 homologues) and Cu leak through epithelial Na(+) channels (ENaC). Cu(2+) slows the amiloride-sensitive short circuit current (I(sc)) in frog skin, suggesting Cu(2+) binding to the amiloride-binding site of ENaC. We present examples of data from the isolated perfused catfish intestine showing that Cu uptake across the whole intestine was reduced by 50% in the presence of 2 mM luminal amiloride, with 75% of the overall inhibition attributed to an amiloride-sensitive region in the middle intestine. Removal of luminal Na(+) produced more variable results, but also reduced Cu uptake in catfish intestine. These data together support Cu(2+) modulation of ENaC, but not competitive entry of Cu(2+) through ENaC. However, in situations where external Na(+) is only a few millimoles (fish gills, frogs in freshwater), Cu(2+) leak through ENaC is possible. CTR1 is a likely route of Cu(2+) entry when external Na(+) is higher (e.g. intestinal epithelia). Interactions between Na(+) and Cu ions during intracellular trafficking or export from the cell are unlikely. However, effects of intracellular chloride on the Cu-ATPase or ENaC indicate that Na(+) might indirectly alter Cu flux. Conversely, Cu ions inhibit basolateral Na(+)K(+)-ATPase and may increase [Na(+)](i).