Food Quality Affects Secondary Consumers Even at Low Quantities: An Experimental Test with Larval European Lobster

The issues of food quality and food quantity are crucial for trophic interactions. Although most research has focussed on the primary producer – herbivore link, recent studies have shown that quality effects at the bottom of the food web propagate to higher trophic levels. Negative effects of poor food quality have almost exclusively been demonstrated at higher food quantities. Whether these negative effects have the same impact at low food availability in situations where the majority if not all of the resources are channelled into routine metabolism, is under debate. In this study a tri-trophic food chain was designed, consisting of the algae Rhodomonas salina, the copepod Acartia tonsa and freshly hatched larvae of the European lobster Homarus gammarus. The lobster larvae were presented with food of two different qualities (C∶P ratios) and four different quantities to investigate the combined effects of food quality and quantity. Our results show that the quality of food has an impact on the condition of lobster larvae even at very low food quantities. Food with a lower C∶P content resulted in higher condition of the lobster larvae regardless of the quantity of food. These interacting effects of food quality and food quantity can have far reaching consequences for ecosystem productivity

Protection from ultraviolet damage and photocarcinogenesis by vitamin d compounds

© Springer Nature Switzerland AG 2020. Exposure of skin cells to UV radiation results in DNA damage, which if inadequately repaired, may cause mutations. UV-induced DNA damage and reactive oxygen and nitrogen species also cause local and systemic suppression of the adaptive immune system. Together, these changes underpin the development of skin tumours. The hormone derived from vitamin D, calcitriol (1,25-dihydroxyvitamin D3) and other related compounds, working via the vitamin D receptor and at least in part through endoplasmic reticulum protein 57 (ERp57), reduce cyclobutane pyrimidine dimers and oxidative DNA damage in keratinocytes and other skin cell types after UV. Calcitriol and related compounds enhance DNA repair in keratinocytes, in part through decreased reactive oxygen species, increased p53 expression and/or activation, increased repair proteins and increased energy availability in the cell when calcitriol is present after UV exposure. There is mitochondrial damage in keratinocytes after UV. In the presence of calcitriol, but not vehicle, glycolysis is increased after UV, along with increased energy-conserving autophagy and changes consistent with enhanced mitophagy. Reduced DNA damage and reduced ROS/RNS should help reduce UV-induced immune suppression. Reduced UV immune suppression is observed after topical treatment with calcitriol and related compounds in hairless mice. These protective effects of calcitriol and related compounds presumably contribute to the observed reduction in skin tumour formation in mice after chronic exposure to UV followed by topical post-irradiation treatment with calcitriol and some, though not all, related compounds

Biliary phospholipid secretion is not required for intestinal absorption and plasma status of linoleic acid in mice

Biliary phospholipids have been hypothesized to be important for essential fatty acid homeostasis. We tested this hypothesis by investigating the intestinal absorption and the status of linoleic acid in mdr2 Pgp-deficient mice which secrete phospholipid-free bile. In mice homozygous (-/-) for disruption of the mdr2 gene and wild-type (+/+) mice, dietary linoleic acid absorption was determined by 72 h balance techniques. After enteral administration, [C-13]-linoleic acid absorption was determined by measuring [C-13]-linoleic acid concentrations in feces and in plasma. The status of linoleic acid was determined in plasma and in liver by calculating the molar percentage of linoleic acid and the triene:tetraene ratio. Although plasma concentration of [C-13]-linoleic acid at 2 h after enteral administration was significantly lower in (-/-) compared to (+/+) mice (P less than or equal to 0.05), net intestinal absorption of dietary linoleic acid or of [C-13]-linoleic acid was similar in (+/+) and (-/-) mice. Molar percentage of linoleic acid and the triene:tetraene ratio were not different in whole plasma or in liver of (-/-) compared to (+/+) mice. Present data indicate that biliary phospholipids are involved in the rate of appearance in plasma of enterally administered linoleic acid, but are not required for net intestinal absorption or plasma status of linoleic acid. (C) 1999 Elsevier Science B.V. All rights reserved

Postprandial chylomicron formation and fat absorption in multidrug resistance gene 2 P-glycoprotein-deficient mice

Background & Aims: It has been proposed that biliary phospholipids fulfill specific functions in the absorption of dietary fat from the intestine, but the physiological significance has not been established. The aim of this study was to evaluate the role of biliary phospholipids in dietary fat absorption in vivo by using mice homozygous or heterozygous for disruption of the Mdr2 gene (Mdr2((-/-)), Mdr2((+/-)) and control (Mdr2((+/+))) mice. Mdr2((-/-)), mice do not secrete phospholipids and cholesterol into bile, and bile salt secretion is not impaired, Mdr2((+/-)), mice show only impaired (-40%) phospholipid secretion. Methods: Methods included an analysis of time dependency of intestinal uptake and plasma appearance of intragastrically administered (radiolabeled) triglycerides and measurement of 3-day fecal fat balance with low- and high-fat diets. Results: Intragastric administration of olive oil resulted in a rapid increase in plasma triglycerides in Mdr2((+/+)), and Mdr2((+/-)), but not in Mdr2((-/-)), mice. The "postprandial response" of plasma triglycerides could be partially restored in Mdr2((-/-)), mice by intraduodenal infusion of whole rat bile. After intragastric [H-3]triolein administration in Triton WR1339-pretreated animals, the appearance of H-3-triglycerides in plasma was reduced by 70% in Mdr2((-/-)), compared with Mdr2((+/+)), mice, excluding accelerated lipolysis as the cause of defective triglyceride response in Mdr2((-/-)), mice, H-3-triglycerides accumulated in enterocytes in Mdr2((-/-)), mice. Surprisingly, the efficacy of fat absorption as derived from balance studies was not affected and was only minimally affected in Mdr2((-/-)), mice fed low (14 energy percent)and high (35 energy percent)-fat diets, respectively tall >95%), Conclusions: The results show that biliary lipid secretion is necessary for postprandial appearance in plasma of chylomicrons in vivo but not for quantitative absorption of dietary lipids

Reduced plasma cholesterol and increased fecal sterol loss in multidrug resistance gene 2 P-glycoprotein-deficient mice

Background & Aims: mdr2 P-glycoprotein (Pgp) deficiency in mice leads to the absence of biliary phospholipids and cholesterol in the presence of normal bile salt secretion. The aim of this study was to evaluate the importance of the biliary pathway in cholesterol homeostasis by determining the effects of mdr2 Pgp deficiency on; hepatic and plasma lipid levels and cholesterol kinetics in chow-fed mice. Methods: Hepatic lipid content, enzyme activities, plasma lipoprotein levels, and fecal sterol excretion were measured in wild-type (+/+) and mdr2 Pgp-deficient (-/-) mice. Cholesterol kinetics were determined using radiotracer techniques. Results: No differences in hepatic lipid content were observed between (-/-) and (+/+) mice. Plasma high-density lipoprotein cholesterol and apolipoprotein A-I levels were strongly reduced in (-/-) mice compared with controls, whereas the apolipoprotein B contents of very-low-density lipoprotein and low-density lipoprotein were increased. Hepatic activity of 3-hydroxy-3-methylglutaryl-coenzyme A reductase was threefold greater in (-/-) mice than in controls; however, compartmental analysis of plasma cholesterol decay showed no differences in cholesterol synthesis between (-/-) and (+/+) mice. A dual isotope approach for estimating cholesterol absorption yielded similar to 50% lower values in (-/-) mice than in controls. Surprisingly, (-/-) mice showed a fourfold increase in fecal neutral sterol secretion. Conclusions: This study unequivocally establishes the important direct role of biliary lipids in the regulation of plasma lipid levels in mice