Analyses and Insights into Genetic Reassortment and Natural Selection as Key Drivers of Piscine orthoreovirus Evolution.

Piscine orthoreovirus (PRV) is a pathogen that causes heart and skeletal muscle inflammation in Salmo salar and has also been linked to circulatory disorders in other farmed salmonids, such as Oncorhynchus kisutch and Oncorhynchus mykiss. The virus has a segmented, double-stranded RNA genome, which makes it possible to undergo genetic reassortment and increase its genomic diversity through point mutations. In this study, genetic reassortment in PRV was assessed using the full genome sequences available in public databases. This study used full genome sequences that were concatenated and genome-wide reassortment events, and phylogenetic analyses were performed using the recombination/reassortment detection program version 5 (RDP5 V 5.5) software. Additionally, each segment was aligned codon by codon, and overall mean distance and selection was tested using the Molecular Evolutionary Genetics Analysis X software, version 10.2 (MEGA X version 10.2). The results showed that there were 17 significant reassortment events in 12 reassortant sequences, involving genome exchange between low and highly virulent genotypes. PRV sequences from different salmonid host species did not appear to limit the reassortment. This study found that PRV frequently undergoes reassortment events to increase the diversity of its segmented genome, leading to antigenic variation and increased virulence. This study also noted that to date, no reassortment events have been described between PRV-1 and PRV-3 genotypes. However, the number of complete genomic sequences within each genotype is uneven. This is important because PRV-3 induces cross-protection against PRV-1, making it a potential vaccine candidate.

Effect of a Diet-Induced Obesity on the Progeny Response in a Murine Model.

Diet-induced obesity could have detrimental effects on adults and their progeny. The aim of this study was to determine the effect of a high-energy diet on both F1 mice body weight and tissue/organ weight and F2 offspring growth. A simple murine model for obesity was developed using a high-energy diet and mice reared in litters of five or ten, from 30 dams receiving a cafeteria diet of either commercial chow (low energy), or a mixture of commercial chow, chocolate (50% cacao), and salty peanuts (high energy). This diet continued from mating until weaning, when the pups were allocated according to sex into eight groups based on maternal diet, litter size, and post-weaning diet. On day 74, the males were slaughtered, and the females were bred then slaughtered after lactation. As a result, the high-energy maternal diet increased the F1 offspring growth during lactation, while the high-energy post-weaning diet increased the F1 adult body weight and tissue/organ weight. The high-energy maternal diet could negatively affect the onset of the F1 but not the maintenance of breastfeeding of F1 and F2 offspring. For F2 offspring growth, the high energy overlapped the low-energy post-weaning diet, due to problems of gaining weight during lactation.

Epigenetic reprogramming around IFN1 and IFNy2 promoters in rainbow trout cells inoculated with infectious pancreatic necrosis virus (IPNV).

Infectious pancreatic necrosis virus (IPNV) has proven to effectively evade the host antiviral responses. This study clarifies whether the modulation of the antiviral immune response exerted by IPNV involves epigenetic mechanisms. An in-silico characterization of the rainbow trout IFN1 and IFNγ2 promoters was performed, identifying the islands or sequences rich in CpG dinucleotides and the putative transcription factor binding sites (TBS) for both gene promoters. RTS11 cells (rainbow trout monocyte/macrophage) were infected with IPNV, and the course of viral infection was followed up to 48 h post infection (hpi). Infected cells showed increased IFN1 and IFNγ2 transcriptional expression at 6 and 24 hpi, respectively. IPNV infection caused increases and decreases in global IFNγ2 promoter methylation at 6 and 24 hpi, respectively. The CpG dinucleotides at positions -392 and + 38 of this promoter were the most sensitive to methylation changes. The IFN1 promoter remained fully unmethylated during the course of the infection, similar to the control. The changes in the methylation pattern observed for the IFNγ2 promoter were coincident with the changes in DNA methyltransferase (DNMT) expression levels, increasing at 6 hpi and decreasing below basal level at 24 hpi. Similarly, the H4 histones associated with the IFN1 and IFNγ2 promoters were hyperacetylated at 6 hpi, subsequently decreasing their acetylation below basal levels at 24 hpi, in both promoters. Coincidentally with the above, overexpression of histone acetyltransferase (HAT) was observed at 6 hpi and of histone deacetylase (HDAC) at 24 hpi, with return to baseline of HAT. These results suggest that IPNV would epigenetically modulate the expression of IFN1 by changing acetylation levels of the histones H4 associated with its promoter. Also, the modulation of the expression of IFNy2 would be by switching methylation/demethylation levels of its promoter, in addition to changes in acetylation levels of histones H4 associated with this promoter. This study is the first to demonstrate the effect of epigenetic reprogramming after IPNV infection in salmonid cells, demonstrating that promoter methylation/demethylation level and changes in the histone code associated with promoters may play a role in the modulation of the immune response induced by the virus.

Microcystin-LR modulates multixenobiotic resistance proteins in the middle intestine of rainbow trout, Oncorhynchus mykiss.

Global climate change favors explosive population growth events (blooms) of phytoplanktonic species, often producing toxic products, e.g., several genera of cyanobacteria synthesize a family of cyanotoxins called microcystins (MCs). Freshwater fish such as the rainbow trout Oncorhynchus mykiss can uptake MCs accumulated in the food chain. We studied the toxic effects and modulation of the activity and expression of multixenobiotic resistance proteins (ABCC transporters and the enzyme glutathione S-transferase (GST) in the O. mykiss middle intestine by microcystin-LR (MCLR). Juvenile fish were fed with MCLR incorporated in the food every 12 h and euthanized at 12, 24, or 48 h. We estimated the ABCC-mediated transport in ex vivo intestinal strips to estimate ABCC-mediated transport activity. We measured total and reduced (GSH) glutathione contents and GST and glutathione reductase (GR) activities. We studied MCLR cytotoxicity by measuring protein phosphatase 1 (PP1) activity and lysosomal membrane stability. Finally, we examined the relationship between ROS production and lysosomal membrane stability through in vitro experiments. Dietary MCLR had a time-dependent effect on ABCC-mediated transport, from inhibition at 12 h to a significant increase after 48 h. GST activity decreased only at 12 h, and GR activity only increased at 48 h. There were no effects on GSH or total glutathione contents. MCLR inhibited PP1 activity and diminished the lysosomal membrane stability at the three experimental times. In the in vitro study, the lysosomal membrane stability decreased in a concentration-dependent fashion from 0 to 5 µmol L - 1 MCLR, while ROS production increased only at 5 µmol L - 1 MCLR. MCLR did not affect mRNA expression of abcc2 or gst-π. We conclude that MCLR modulates ABCC-mediated transport activity in O. mykiss's middle intestine in a time-dependent manner. The transport rate increase does not impair MCLR cytotoxic effects.

The insecticide chlorpyrifos modifies the expression of genes involved in the PXR and AhR pathways in the rainbow trout, Oncorhynchus mykiss.

Chlorpyrifos (CPF) is an organophosphate pesticide, commonly detected in water and food. Despite CPF toxicity on aquatic species has been extensively studied, few studies analyze the effects of CPF on fish transcriptional pathways. The Pregnane X receptor (PXR) is a nuclear receptor that is activated by binding to a wide variety of ligands and regulates the transcription of enzymes involved in the metabolism and transport of many endogenous and exogenous compounds. We evaluated the mRNA expression of PXR-regulated-genes (PXR, CYP3A27, CYP2K1, ABCB1, UGT, and ABCC2) in intestine and liver of the rainbow trout, Oncorhynchus mykiss, exposed in vivo to an environmentally relevant CPF concentration. Our results demonstrate that the expression of PXR and PXR-regulated genes is increased in O. mykiss liver and intestine upon exposure to CPF. Additionally, we evaluated the impact of CPF on other cellular pathway involved in xenobiotic metabolism, the Aryl Hydrocarbon Receptor (AhR) pathway, and on the expression and activity of different biotransformation enzymes (CYP2M1, GST, FMO1, or cholinesterases (ChEs)). In contrast to PXR, the expression of AhR, and its target gene CYP1A, are reduced upon CPF exposure. Furthermore, ChE and CYP1A activities are significantly inhibited by CPF, in both the intestine and the liver. CPF activates the PXR pathway in O. mykiss in the intestine and liver, with a more profound effect in the intestine. Likewise, our results support regulatory crosstalk between PXR and AhR pathways, where the induction of PXR coincides with the downregulation of AhR-mediated CYP1A mRNA expression and activity in the intestine.

Exposure to hydrocarbons and chlorpyrifos alters the expression of nuclear receptors and antioxidant, detoxifying, and immune response proteins in the liver of the rainbow trout, Oncorhynchus mykiss.

The development of oil and gas production together with the fruit production in nearby areas of North Patagonia, Argentina, suggests aquatic pollution scenarios which include permanent oil pollution combined with short events of pesticides application. It has been reported that oil hydrocarbons activate the aryl hydrocarbon receptor (AhR) pathway in the rainbow trout, Oncorhynchus mykiss, and that the insecticide Chlorpyrifos (CPF) interacts with these effects. Thus, it is interesting to investigate whether hydrocarbons and insecticides, applied by separate or combined, can affect fish health and reproductive signaling by acting on different nuclear receptors' regulatory pathways. To study this kind of interactions, we exposed juvenile rainbow trout to water accommodated fraction (WAF) of crude oil (62 µg L-1 TPH) for 48 h and subsequently exposed the livers ex vivo to the insecticide Chlorpyrifos (CPF) (20 µg L-1) for 1 h. We analyzed the mRNA expression of nuclear receptors and proteins involved in detoxifying, antioxidant, immune and apoptosis responses by qRT-PCR. We also performed histopathological analysis. WAF induced the expression of the androgen (AR) and the Liver X receptor (LXR) by 8- and 3-fold, respectively. AR induction was reversed by subsequent exposure to CPF. The progesterone receptor (PR) and glucocorticoid receptor (GR) were increased 2-fold and 3-fold by WAF respectively, while estrogen and mineralocorticoid receptors were not affected. GR was also induced by CPF with an additive effect in the WAF-CPF treatment. The antioxidant genes, gamma glutamyl transferase (GGT), superoxide dismutase (SOD1) were induced by WAF (2-3-fold). WAF upregulated the ATP Binding Cassette Subfamily C Member 2 (ABCC2, MRP2) (4-fold) and downregulated alkaline phosphatase. WAF also induced the inflammatory interleukins (IL) IL-8, and IL-6 and the anti-inflammatory IL-10, while CPF induced the inflammatory tumor necrosis factor (-α) and IL-6, and activated the intrinsic apoptotic pathway through the induction of caspases 3 and 9. Both, WAF and CPF downregulated the expression of the extrinsic apoptosis initiator caspase 8 and the inflammatory caspase 1. In conclusion, WAF hydrocarbons alter O. mykiss endocrine regulation by inducing AR, PR and GR. The subsequent exposure to CPF reverses AR, suggesting a complex interaction of different pollutants in contaminated environments, WAF hydrocarbons alter liver metabolism by inducing the expression of LXR, GR, antioxidant and detoxifying enzymes, and both inflammatory and anti-inflammatory cytokines, and causing mild hepatic steatosis. CPF activates inflammatory and stress responses associated with the induction of inflammatory cytokines together with apoptosis initiator and executioner caspases.

Effect of Diet and Type of Pregnancy on Transcriptional Expression of Selected Genes in Sheep Mammary Gland.

These trials were carried out to determine firstly the effect of diet and type of pregnancy on the transcriptional expression of genes involved in angiogenesis and cell turnover/lactogenesis inside the sheep mammary gland from late gestation to late lactation. Eighteen Ile de France sheep, 8 twin- and 10 single-bearing ewes were alloted into two groups according to their diet, either based on ad libitum naturalized pasture or red clover hay plus lupine from day -45 pre-partum until day +60 post-partum. Samples from diets and mammary glands were collected at day -10 pre partum (time 1), day +30 (time 2) and day +60 post-partum (time 3) and analyzed by qRT-PCR. Additionally, samples from longissimus dorsi muscle were taken from lambs twice, at weaning and 45 days later, to determine the effect of the maternal treatment with regard to diet and type of pregnancy, on the mRNA expression of genes involved in lipid metabolism. The data was processed using the lme4 package for R, and SPSS Statistics 23.0 for Windows®. The results showed that the group of twin-bearing ewes fed red clover showed a higher expression of genes involved in angiogenesis before lambing and in cell turnover/lactogenesis during late lactation, explained by a lamb survival mechanism to delay apoptosis as a way to keep a secretory cells population and boosted by the diet quality, assuring a longer milk production potential during late lactation. Regarding lambs, apparently the maternal diet would influence the transcriptional expression of lipogenic enzymes in the longissimus dorsi muscle after weaning, but further studies are necessary to validate these results. In summary, Twin-bearing ewes fed red clover performed best at increasing the expression of genes associated with angiogenesis and cell turnover/lactogenesis in the mammary gland.

Comparative Pan-Genome Analysis of Piscirickettsia salmonis Reveals Genomic Divergences within Genogroups.

Piscirickettsia salmonis is the etiological agent of salmonid rickettsial septicemia, a disease that seriously affects the salmonid industry. Despite efforts to genomically characterize P. salmonis, functional information on the life cycle, pathogenesis mechanisms, diagnosis, treatment, and control of this fish pathogen remain lacking. To address this knowledge gap, the present study conducted an in silico pan-genome analysis of 19 P. salmonis strains from distinct geographic locations and genogroups. Results revealed an expected open pan-genome of 3,463 genes and a core-genome of 1,732 genes. Two marked genogroups were identified, as confirmed by phylogenetic and phylogenomic relationships to the LF-89 and EM-90 reference strains, as well as by assessments of genomic structures. Different structural configurations were found for the six identified copies of the ribosomal operon in the P. salmonis genome, indicating translocation throughout the genetic material. Chromosomal divergences in genomic localization and quantity of genetic cassettes were also found for the Dot/Icm type IVB secretion system. To determine divergences between core-genomes, additional pan-genome descriptions were compiled for the so-termed LF and EM genogroups. Open pan-genomes composed of 2,924 and 2,778 genes and core-genomes composed of 2,170 and 2,228 genes were respectively found for the LF and EM genogroups. The core-genomes were functionally annotated using the Gene Ontology, KEGG, and Virulence Factor databases, revealing the presence of several shared groups of genes related to basic function of intracellular survival and bacterial pathogenesis. Additionally, the specific pan-genomes for the LF and EM genogroups were defined, resulting in the identification of 148 and 273 exclusive proteins, respectively. Notably, specific virulence factors linked to adherence, colonization, invasion factors, and endotoxins were established. The obtained data suggest that these genes could be directly associated with inter-genogroup differences in pathogenesis and host-pathogen interactions, information that could be useful in designing novel strategies for diagnosing and controlling P. salmonis infection.

Molecular characterization of infectious pancreatic necrosis virus strains isolated from the three types of salmonids farmed in Chile.

BACKGROUND: The infectious pancreatic necrosis virus (IPNV) causes significant economic losses in Chilean salmon farming. For effective sanitary management, the IPNV strains present in Chile need to be fully studied, characterized, and constantly updated at the molecular level. METHODS: In this study, 36 Chilean IPNV isolates collected over 6 years (2006-2011) from Salmo salar, Oncorhynchus mykiss, and Oncorhynchus kisutch were genotypically characterized. Salmonid samples were obtained from freshwater, estuary, and seawater sources from central, southern, and the extreme-south of Chile (35° to 53°S). RESULTS: Sequence analysis of the VP2 gene classified 10 IPNV isolates as genogroup 1 and 26 as genogroup 5. Analyses indicated a preferential, but not obligate, relationship between genogroup 5 isolates and S. salar infection. Fifteen genogroup 5 and nine genogroup 1 isolates presented VP2 gene residues associated with high virulence (i.e. Thr, Ala, and Thr at positions 217, 221, and 247, respectively). Four genogroup 5 isolates presented an oddly long VP5 deduced amino acid sequence (29.6 kDa). Analysis of the VP2 amino acid motifs associated with clinical and subclinical infections identified the clinical fingerprint in only genogroup 5 isolates; in contrast, the genogroup 1 isolates presented sequences predominantly associated with the subclinical fingerprint. Predictive analysis of VP5 showed an absence of transmembrane domains and plasma membrane tropism signals. WebLogo analysis of the VP5 BH domains revealed high identities with the marine birnavirus Y-6 and Japanese IPNV strain E1-S. Sequence analysis for putative 25 kDa proteins, coded by the ORF between VP2 and VP4, exhibited three putative nuclear localization sequences and signals of mitochondrial tropism in two isolates. CONCLUSIONS: This study provides important advances in updating the characterizations of IPNV strains present in Chile. The results from this study will help in identifying epidemiological links and generating specific biotechnological tools for controlling IPNV outbreaks in Chilean salmon farming.

Resistance-nodulation-division efflux pump acrAB is modulated by florfenicol and contributes to drug resistance in the fish pathogen Piscirickettsia salmonis.

Piscirickettsia salmonis is a fastidious intracellular pathogen responsible for high mortality rates in farmed salmonids, with serious economic consequences for the Chilean aquaculture industry. Oxytetracycline and florfenicol are the most frequently used antibiotics against P. salmonis, but routine use could contribute to drug resistance. This study identified differentiated florfenicol susceptibilities in two P. salmonis strains, LF-89 and AUSTRAL-005. The less susceptible isolate, AUSTRAL-005, also showed a high ethidium bromide efflux rate, indicating a higher activity of general efflux pump genes than LF-89. The P. salmonis genome presented resistance nodulation division (RND) family members, a family containing typical multidrug resistance-related efflux pumps in Gram-negative bacteria. Additionally, efflux pump acrAB genes were overexpressed in AUSTRAL-005 following exposure to the tolerated maximal concentration of florfenicol, in contrast to LF-89. These results indicate that tolerated maximum concentrations of florfenicol can modulate RND gene expression and increase efflux pump activity. We propose that the acrAB efflux pump is essential for P. salmonis survival at critical florfenicol concentrations and for the generation of antibiotic-resistant bacterial strains.

Characterization and pathogenic role of outer membrane vesicles produced by the fish pathogen Piscirickettsia salmonis under in vitro conditions.

Piscirickettsia salmonis is one of the major fish pathogens affecting Chilean aquaculture. This Gram-negative bacterium is highly infectious and is the etiological agent of Piscirickettsiosis. Little is currently known about how the virulence factors expressed by P. salmonis are delivered to host cells. However, it is known that several Gram-negative microorganisms constitutively release outer membrane vesicles (OMVs), which have been implicated in the delivery of virulence factors to host cells. In this study, OMVs production by P. salmonis was observed during infection in CHSE-214 cells and during normal growth in liquid media. The OMVs were spherical vesicles ranging in size between 25 and 145 nm. SDS-PAGE analysis demonstrated that the protein profile of the OMVs was similar to the outer membrane protein profile of P. salmonis. Importantly, the bacterial chaperonin Hsp60 was found in the OMVs of P. salmonis by Western-blot and LC-MS/MS analyses. Finally, in vitro infection assays showed that purified OMVs generated a cytopathic effect on CHSE-214 cells, suggesting a role in pathogenesis. Therefore, OMVs might be an important vehicle for delivering effector molecules to host cells during P. salmonis infection.

Subunit interactions in pig-kidney fructose-1,6-bisphosphatase: binding of substrate induces a second class of site with lowered affinity and catalytic activity.

BACKGROUND: Fructose-1,6-bisphosphatase, a major enzyme of gluconeogenesis, is inhibited by AMP, Fru-2,6-P2 and by high concentrations of its substrate Fru-1,6-P2. The mechanism that produces substrate inhibition continues to be obscure. METHODS: Four types of experiments were used to shed light on this: (1) kinetic measurements over a very wide range of substrate concentrations, subjected to detailed statistical analysis; (2) fluorescence studies of mutants in which phenylalanine residues were replaced by tryptophan; (3) effect of Fru-2,6-P2 and Fru-1,6-P2 on the exchange of subunits between wild-type and Glu-tagged oligomers; and (4) kinetic studies of hybrid forms of the enzyme containing subunits mutated at the active site residue tyrosine-244. RESULTS: The kinetic experiments with the wild-type enzyme indicate that the binding of Fru-1,6-P2 induces the appearance of catalytic sites with lower affinity for substrate and lower catalytic activity. Binding of substrate to the high-affinity sites, but not to the low-affinity sites, enhances the fluorescence emission of the Phe219Trp mutant; the inhibitor, Fru-2,6-P2, competes with the substrate for the high-affinity sites. Binding of substrate to the low-affinity sites acts as a "stapler" that prevents dissociation of the tetramer and hence exchange of subunits, and results in substrate inhibition. CONCLUSIONS: Binding of the first substrate molecule, in one dimer of the enzyme, produces a conformational change at the other dimer, reducing the substrate affinity and catalytic activity of its subunits. GENERAL SIGNIFICANCE: Mimics of the substrate inhibition of fructose-1,6-bisphosphatase may provide a future option for combatting both postprandial and fasting hyperglycemia.

Use of reverse transcription-real time polymerase chain reaction (real time RT-PCR) assays with Universal Probe Library (UPL) probes for the detection and genotyping of infectious pancreatic necrosis virus strains isolated in Chile.

Reverse transcription-real time polymerase chain reaction (real time RT-PCR) assay with Universal Probe Library (UPL) probes has been developed for the detection and genotyping of Chilean infectious pancreatic necrosis virus (IPNV) isolates from infected cell culture. Partial nucleotide sequences (1175 bp) of the VP2 coding region from a selection of 7 Chilean IPNV isolates showed that they clustered into two main groups strongly correlated with Genogroups 1 and 5 proposed by Blake et al. (2001), corresponding to types West Buxton (WB) and Spajarup (Sp), respectively. Based on the VP2 gene sequences of those 7 Chilean isolates and different reference IPNV strains, 2 sets of candidate primer/UPL probes (# 8 and # 117) were designed and evaluated with a total of 32 field isolates isolated from Atlantic salmon (Salmo salar), rainbow trout (Oncorhynchus mykiss) and Pacific salmon (Oncorhynchus kisutch) farms from 2006 to 2010 in Chile. The UPL probes clearly differentiated the same two major Genogroups that those recognized by sequencing analysis. Among the Chilean isolates examined, 18 yielded amplification with UPL probe # 8, and 14 with probe # 117, respectively corresponding to types Sp and WB, as demonstrated by typing by sequencing. Based on the findings reported below, it has been demonstrated that the combined real time RT-PCR protocol with UPLs approach was efficient in discriminating distinct Genogroups of IPNV cultured in fish cell lines and, therefore, recommended its use for detection and typing of IPN viruses. The study also confirmed the existence of two IPNV type strains in Chilean salmonid aquaculture.

Essential role of intracellular glutathione in controlling ascorbic acid transporter expression and function in rat hepatocytes and hepatoma cells.

Although there is in vivo evidence suggesting a role for glutathione in the metabolism and tissue distribution of vitamin C, no connection with the vitamin C transport systems has been reported. We show here that disruption of glutathione metabolism with buthionine-(S,R)-sulfoximine (BSO) produced a sustained blockade of ascorbic acid transport in rat hepatocytes and rat hepatoma cells. Rat hepatocytes expressed the Na(+)-coupled ascorbic acid transporter-1 (SVCT1), while hepatoma cells expressed the transporters SVCT1 and SVCT2. BSO-treated rat hepatoma cells showed a two order of magnitude decrease in SVCT1 and SVCT2 mRNA levels, undetectable SVCT1 and SVCT2 protein expression, and lacked the capacity to transport ascorbic acid, effects that were fully reversible on glutathione repletion. Interestingly, although SVCT1 mRNA levels remained unchanged in rat hepatocytes made glutathione deficient by in vivo BSO treatment, SVCT1 protein was absent from the plasma membrane and the cells lacked the capacity to transport ascorbic acid. The specificity of the BSO treatment was indicated by the finding that transport of oxidized vitamin C (dehydroascorbic acid) and glucose transporter expression were unaffected by BSO treatment. Moreover, glutathione depletion failed to affect ascorbic acid transport, and SVCT1 and SVCT2 expression in human hepatoma cells. Therefore, our data indicate an essential role for glutathione in controlling vitamin C metabolism in rat hepatocytes and rat hepatoma cells, two cell types capable of synthesizing ascorbic acid, by regulating the expression and subcellular localization of the transporters involved in the acquisition of ascorbic acid from extracellular sources, an effect not observed in human cells incapable of synthesizing ascorbic acid.

Increased expression of the multidrug resistance-associated protein 1 (MRP1) in kidney glomeruli of streptozotocin-induced diabetic rats.

Oxidative stress has been linked to the podocytopathy, mesangial expansion and progression of diabetic nephropathy. The major cell defence mechanism against oxidative stress is reduced glutathione (GSH). Some ABC transporters have been shown to extrude GSH, oxidised glutathione or their conjugates out of the cell, thus implying a role for these transporters in GSH homeostasis. We found a remarkable expression of mRNA for multidrug resistance-associated proteins (MRP/ABCC) 1, 3, 4 and 5 in rat glomeruli. Three weeks after induction of diabetes in glomeruli of streptozotocin-treated rats, we observed a decline in reduced GSH levels and an increase in the expression and activity of MRP1 (ABCC1). These lower GSH levels were improved by ex vivo treatment with pharmacological inhibitors of MRP1 activity (MK571). We conclude that increased activity of MRP1 in diabetic glomeruli is correlated with an inadequate adaptive response to oxidative stress.

Endofacial competitive inhibition of the glucose transporter 1 activity by gossypol.

Gossypol is a natural disesquiterpene that blocks the activity of the mammalian facilitative hexose transporter GLUT1. In human HL-60 cells, which express GLUT1, Chinese hamster ovary cells overexpressing GLUT1, and human erythrocytes, gossypol inhibited hexose transport in a concentration-dependent fashion, indicating that blocking of GLUT1 activity is independent of cellular context. With the exception of red blood cells, the inhibition of cellular transport was instantaneous. Gossypol effect was specific for the GLUT1 transporter since it did not alter the uptake of nicotinamide by human erythrocytes. Gossypol affects the glucose-displaceable binding of cytochalasin B to GLUT1 in human erythrocyte ghost in a mixed noncompetitive way, with a K(i) value of 20 microM. Likewise, GLUT1 fluorescence was quenched approximately 80% by gossypol, while Stern-Volmer plots for quenching by iodide displayed increased slopes by gossypol addition. These effects on protein fluorescence were saturable and unaffected by the presence of D-glucose. Gossypol did not alter the affinity of D-glucose for the external substrate site on GLUT1. Kinetic analysis of transport revealed that gossypol behaves as a noncompetitive inhibitor of zero-trans (substrate outside but not inside) transport, but it acts as a competitive inhibitor of equilibrium-exchange (substrate inside and outside) transport, which is consistent with interaction at the endofacial surface, but not at the exofacial surface of the transporter. Thus, gossypol behaves as a quasi-competitive inhibitor of GLUT1 transport activity by binding to a site accessible through the internal face of the transporter, but it does not, in fact, compete with cytochalasin B binding. Our observations suggest that some effects of gossypol on cellular physiology may be related to its ability to disrupt the normal hexose flux through GLUT1, a transporter expressed in almost every kind of mammalian cell and responsible for the basal uptake of glucose.

Vitamin C is an essential antioxidant that enhances survival of oxidatively stressed human vascular endothelial cells in the presence of a vast molar excess of glutathione.

Cellular glutathione levels may exceed vitamin C levels by 10-fold, generating the question about the real antioxidant role that low intracellular concentrations of vitamin C can play in the presence of a vast molar excess of glutathione. We characterized the metabolism of vitamin C and its relationship with glutathione in primary cultures of human endothelial cells oxidatively challenged by treatment with hydrogen peroxide or with activated cells undergoing the respiratory burst, and analyzed the manner in which vitamin C interacts with glutathione to increase the antioxidant capacity of cells. Our data indicate that: (i) endothelial cells express transporters for reduced and oxidized vitamin C and accumulate ascorbic acid with participation of glutathione-dependent dehydroascorbic acid reductases, (ii) although increased intracellular levels of vitamin C or glutathione caused augmented resistance to oxidative stress, 10-times more glutathione than vitamin C was required, (iii) full antioxidant protection required the simultaneous presence of intracellular and extracellular vitamin C at concentrations normally found in vivo, and (iv) intracellular vitamin C cooperated in enhancing glutathione recovery after oxidative challenge thus providing cells with enhanced survival potential, while extracellular vitamin C was recycled through a mechanism involving the simultaneous neutralization of oxidant species. Therefore, in endothelial cells under oxidative challenge, vitamin C functions as an essential cellular antioxidant even in the presence of a vast molar excess of glutathione.

Mechanistic insights and functional determinants of the transport cycle of the ascorbic acid transporter SVCT2. Activation by sodium and absolute dependence on bivalent cations.

We characterized the human Na(+)-ascorbic acid transporter SVCT2 and developed a basic model for the transport cycle that challenges the current view that it functions as a Na(+)-dependent transporter. The properties of SVCT2 are modulated by Ca(2+)/Mg(2+) and a reciprocal functional interaction between Na(+) and ascorbic acid that defines the substrate binding order and the transport stoichiometry. Na(+) increased the ascorbic acid transport rate in a cooperative manner, decreasing the transport K(m) without affecting the V(max), thus converting a low affinity form of the transporter into a high affinity transporter. Inversely, ascorbic acid affected in a bimodal and concentration-dependent manner the Na(+) cooperativity, with absence of cooperativity at low and high ascorbic acid concentrations. Our data are consistent with a transport cycle characterized by a Na(+):ascorbic acid stoichiometry of 2:1 and a substrate binding order of the type Na(+):ascorbic acid:Na(+). However, SVCT2 is not electrogenic. SVCT2 showed an absolute requirement for Ca(2+)/Mg(2+) for function, with both cations switching the transporter from an inactive into an active conformation by increasing the transport V(max) without affecting the transport K(m) or the Na(+) cooperativity. Our data indicate that SVCT2 may switch between a number of states with characteristic properties, including an inactive conformation in the absence of Ca(2+)/Mg(2+). At least three active states can be envisioned, including a low affinity conformation at Na(+) concentrations below 20 mM and two high affinity conformations at elevated Na(+) concentrations whose Na(+) cooperativity is modulated by ascorbic acid. Thus, SVCT2 is a Ca(2+)/Mg(2+)-dependent transporter.

Novel expression of liver FBPase in Langerhans islets of human and rat pancreas.

Several reports have indicated the absence of gluconeogenic enzymes in pancreatic islet cells. In contrast, here we demonstrate that liver fructose-1,6-bisphosphatase (FBPase) is highly expressed both in human and rat pancreas. Interestingly, pancreatic FBPase is active and functional, and is inhibited by AMP and fructose-2,6-bisphosphate (Fru-2,6-P2). These results suggest that FBPase may participate as a component of a metabolic sensing mechanism present in the pancreas. Immunolocalization analysis showed that FBPase is expressed both in human and rat Langerhans islets, specifically in beta cells. In humans, FBPase was also located in the canaliculus and acinar cells. These results indicate that FBPase coupled with phosphofructokinase (PFK) plays a crucial role in the metabolism of pancreatic islet cells. The demonstration of gluconeogenic recycling of trioses as a new metabolic signaling pathway may contribute to our understanding of the differences between the insulin secretagogues trioses, fructose, and glucose in pancreas.

Up-regulation and polarized expression of the sodium-ascorbic acid transporter SVCT1 in post-confluent differentiated CaCo-2 cells.

Human cells acquire vitamin C using two different transporter systems, the sodium-ascorbic acid co-transporters with specificity for ascorbic acid, and the facilitative glucose transporters with specificity for dehydroascorbic acid. There is no information on the mechanism of vitamin C transport across the intestinal barrier, a step that determines the bioavailability of vitamin C in humans. We used the colon carcinoma cell line CaCo-2 as an in vitro model for vitamin C transport in enterocyte-like cells. The results of transport kinetics, sodium dependence, inhibition studies, and reverse transcriptase-PCR analysis indicated that CaCo-2 cells express the sodium-ascorbate co-transporters SVCT1 and SVCT2, the dehydroascorbic acid transporters GLUT1 and GLUT3, and a third dehydroascorbic acid transporter with properties expected for GLUT2. Analysis by real time quantitative PCR revealed that the post-confluent differentiation of CaCo-2 cells was accompanied by a marked increase (4-fold) in the steady-state level of SVCT1 mRNA, without changes in SVCT2 mRNA levels. Functional studies revealed that the differentiated cells expressed only one functional ascorbic acid transporter having properties expected for SVCT1, and transported ascorbic acid with a V(max) that was increased at least 2-fold compared with pre-confluent cells. Moreover, post-confluent Caco-2 cells growing as monolayers in permeable filter inserts showed selective sorting of SVCT1 to the apical membrane compartment, without functional evidence for the expression of SVCT2. The identification of SVCT1 as the transporter that allows vectorial uptake of ascorbic acid in differentiated CaCo-2 cells has a direct impact on our understanding of the mechanism for vitamin C transport across the intestinal barrier.