Anti-oxidative hormetic effects of cellular autophagy induced by nutrient deprivation in a molluscan animal model

This investigation using a molluscan animal model tested the hypothesis that experimentally induced lysosomal autophagy protects against oxidative cell injury. Induction of augmented lysosomal autophagy has previously been implicated in this protective process. Four treatment groups of blue mussels (Mytilus galloprovincialis) were used: Group 1 (fed - control), Group 2 (fasted), Group 3 (copper + fed) and Group 4 (copper + fasted). Groups 2 and 4 were fasted in order to trigger autophagy; and samples of hepatopancreas (liver analogue or digestive gland) from all 4 groups were taken at 3, 6 and 15 days. Treatment with copper provided a positive reference for oxidative stress: Groups 3 and 4 were treated with copper (10 μg Cu²⁺/animal/day) for three days only. Oxidative damage and cellular injury in hepatopancreatic digestive cells was found to decrease in Group 2 (fasted) compared to Group 1 (fed - control). Group 3 (fed + copper) showed clear evidence of oxidative stress and cell injury, as well as induction of antioxidant activities. Group 4 (copper + fasted) had a reduced uptake of copper and toxicity of copper was also reduced, compared with Group 3. It was concluded that augmented autophagy had a hormetic cytoprotective anti-oxidant effect.

Oxidative stress, lysosomal damage and dysfunctional autophagy in molluscan hepatopancreas (digestive gland) induced by chemical contaminants

Autophagy is a highly conserved evolutionary survival or defence process that enables cells and organisms to survive periods of environmental stress by breaking down cellular organelles and macromolecules in autolysosomes to provide a supply of nutrients for cell maintenance. However, autophagy is also a part of normal cellular physiology that facilitates the turnover of cellular constituents under normal conditions: it can be readily augmented by mild environmental stress; but becomes dysfunctional with severe oxidative stress leading to cellular pathology. The molluscan hepatopancreas or digestive gland provides a versatile and environmentally relevant model to investigate lysosomal autophagy and stress-induced dysfunctional autophagy. This latter process has been implicated in many animal and human disease conditions, including degenerative and neurodegenerative diseases, as well as obesity related conditions. Many environmental pollutants have also been found to induce dysfunctional autophagy in molluscan hepatopancreatic digestive cells, and in this study, the marine blue mussel Mytilus galloprovincialis was exposed for 7 days to: 0.1 μM, 1 μM and 10 μM concentrations of fluoranthene and phenanthrene (PAHs); chlorpyrifos and malathion (organophosphorus compounds); atrazine (triazine herbicide); copper (transition metal) and dodecylbenzene sulphonic acid (LAS, surfactant). The marine snail or periwinkle, Littorina littorea, was also exposed to phenanthrene, chlorpyrifos and copper. Indices of oxidative stress, cell injury and dysfunctional autophagy were measured (i.e., lysosomal membrane stability, protein carbonyls, lipofuscin, and lysosomal accumulation of lipid or lipidosis). Evidence of oxidative stress, based on the elevation of lipofuscin and protein carbonyls, was found for all compounds tested; with chlorpyrifos being the most toxic to both species. Dysfunctional autophagy was induced by all of the compounds tested in both species, except for atrazine in mussels. This failure of normal autophagy was consistently associated with oxidative stress. Autophagic dysfunction is an important emerging feature in the aetiology of many disease conditions in animals and humans; and an explanatory conceptual mechanistic model has been developed for dysregulation of autophagy in response to oxidative stress.

Impact of elevated levels of CO2 on animal mediated ecosystem function: the modification of sediment nutrient fluxes by burrowing urchins

A mesocosm experiment was conducted to quantify the relationships between the presence and body size of two burrowing heart urchins (Brissopsis lyrifera and Echinocardium cordatum) and rates of sediment nutrient flux. Furthermore, the impact of seawater acidification on these relationships was determined during this 40-day exposure experiment. Using carbon dioxide (CO2) gas, seawater was acidified to pHNBS 7.6, 7.2 or 6.8. Control treatments were maintained in natural seawater (pH≈8.0). Under normocapnic conditions, burrowing urchins were seen to reduce the sediment uptake of nitrite or nitrate whilst enhancing the release of silicate and phosphate. In acidified (hypercapnic) treatments, the biological control of biogeochemical cycles by urchins was significantly affected, probably through the combined impacts of high CO2 on nitrifying bacteria, benthic algae and urchin behaviour. This study highlights the importance of considering biological interactions when predicting the consequences of seawater acidification on ecosystem function.

Integration of biochemical, histochemical and toxicogenomic indices for the assessment of health status of mussels from the Tamar Estuary, U.K

The aim of this study was to examine whether a combination of biochemical, histopathological and toxicogenomic data could be used as a valuable tool for the assessment of biological risk associated with pollutants within the Tamar River and Estuary, S.W. England, U.K. Accordingly, biochemical and histopathological biomarkers (protein carbonyls, lipofuscin, neutral lipids, lysosomal stability [N-acetyl-β-hexosaminidase and neutral red], lysosomal volume, ferric reducing antioxidant power [FRAP] and malonaldehyde [MDA]) and gene expression profiles were assessed in 5 sites from the Tamar River and Estuary (Neal Point, Town Quay, Wilcove, Cremyll Ferry and Whitsand; and a reference site, Trebarwith Strand, N. Cornwall). PAHs were measured in mussel tissue and sediment and metals were measured in mussel tissue only. Data from the biomarkers was integrated into a Mussel Expert System (MES) model to produce a simple assessment of mussel stress. Clear gradients of mussel toxicity were identified by the biomarkers (with the exception of neutral lipids) with the highest impacted animals found furthest up the Tamar, whilst the MES was unable to identify a gradient of effect. Gene expression profiles also indicated a gradient of stress with the greatest number of significantly up- or down- regulated genes found at the uppermost 2 sites. The MES did, however, determine that mussels from all sites, except the reference site, were highly stressed; a conclusion that could not be inferred from the biomarker data alone. It is concluded that the MES is a valuable tool that permits integration and interpretation of complex sets of biomarker data by identifying the biological meaning of biomarker changes.

Histopathology of the skin of UV-B irradiated sole (Solea solea) and turbot (Scophthalmus maximus) larvae

Larval stages of two economically important flatfish, the sole (Solea solea) and turbot (Scophthalmus maximus) were exposed to ambient and elevated levels of UV-B. Sole larvae, which naturally occur in the plankton in early spring, demonstrated skin lesions at elevated levels of UV-B. Histopathology of the sole revealed cellular changes in the integument, characteristic of sunburn damage, with a reduction in the size of mucus-secreting cells and an increased epidermal thickening, especially at the highest doses of UV-B (2.15 KJ bio eff/m2). Pigmentation in the sole is restricted to a few isolated melanocytes. The integrity of the heavily pigmented skin of turbot appeared to be unaffected by comparable doses of UV-B. Both species have protective mechanisms, which minimize the effects of naturally-occurring levels of UV-B. However, sole appear to be poorly adapted to accommodate any further increase in solar radiation.

Influence of peppermint oil on absorptive and secretory processes in rat small intestine

BACKGROUND

Peppermint oil is used to relieve the symptoms of irritable bowel syndrome, relaxing intestinal smooth muscle by reducing the availability of calcium, but its effects on intestinal transport are unknown.

AIMS

To determine the effect of peppermint oil on intestinal transport processes.

METHODS

The influence of peppermint oil on intestinal transport was investigated in rat jejunum using both intestinal sheets mounted in Ussing chambers and brush border membrane vesicles.

RESULTS

Mucosal peppermint oil (1 and 5 mg/ml) had no significant effect on basal short circuit current, but inhibited the increase associated with sodium dependent glucose absorption. The increased short circuit current induced by serosal acetylcholine, a reflection of calcium mediated electrogenic chloride secretion, was unaffected by mucosal peppermint oil (5 mg/ml). In contrast, serosal peppermint oil (1 mg/ml) inhibited the response to acetylcholine without reducing the effect of mucosal glucose. In brush border membrane vesicles active glucose uptake was inhibited by extravesicular peppermint oil at concentrations of 0.5 and 1 mg/ml.

CONCLUSIONS

Peppermint oil in the intestinal lumen inhibits enterocyte glucose uptake via a direct action at the brush border membrane. Inhibition of secretion by serosal peppermint oil is consistent with a reduced availability of calcium.

5-Hydroxytryptamine induces electrogenic secretion and simultaneously activates a modulating inhibitory neural circuit in rat small intestine in vitro

5-Hydroxytryptamine (5-HT) induces electrogenic secretion across rat jejunum and ileum in vitro expressed as an increase in the short-circuit current. Enhancement of this secretory response by previous serosal addition of atropine (1 microM), hexamethonium (0.2 microM) or yohimbine (0.2 microM), especially in the ileum, indicated that 5-HT simultaneously activates an anti-secretory, inhibitory, enteric, neural, cholinergic-adrenergic pathway (ENCAP). A similar inhibitory ENCAP activated by 5-HT has previously been characterized in rat colon in vitro.