Hepatic activities of thiamine-dependent enzymes, glucose-6-phosphate dehydrogenase and cytochrome P4501A in Baltic salmon (Salmo salar) yolk-sac fry after thiamine treatment

Multi-level assessment of the origin, feeding area and organohalogen contamination on salmon from the Baltic Sea

The Atlantic salmon (Salmo salar) population in the Baltic Sea consists of wild and hatchery-reared fish that have been released into the sea to support salmon stocks. During feeding migration, salmon migrate to different parts of the Baltic Sea and are exposed to various biotic and abiotic stressors, such as organohalogen compounds (OHCs). The effects of salmon origin (wild or hatchery-reared), feeding area (Baltic Main Basin, Bothnian Sea, and Gulf of Finland), and OHC concentration on the differences in hepatic proteome of salmon were investigated. Multi-level analysis of the OHC concentration, transcriptome, proteome, and oxidative stress biomarkers measured from the same salmon individuals were performed to find the key variables (origin, feeding area, OHC concentrations, and oxidative stress) that best account for the differences in the transcriptome and proteome between the salmon groups. When comparing wild and hatchery-reared salmon, differences were found in xenobiotic and amino acid metabolism-related pathways. When comparing salmon from different feeding areas, the amino acid and carbohydrate metabolic pathways were notably different. Several proteins found in these pathways are correlated with the concentrations of polychlorinated biphenyls (PCBs). The multi-level analysis also revealed amino acid metabolic pathways in connection with PCBs and oxidative stress variables related to glutathione metabolism. Other pathways found in the multi-level analysis included genetic information processes related to ribosomes, signaling and cellular processes related to the cytoskeleton, and the immune system, which were connected mainly to the concentrations of Polychlorinated biphenyls and Dichlorodiphenyltrichloroethane and their metabolites. These results suggest that the hepatic proteome of salmon in the Baltic Sea, together with the transcriptome, is more affected by the OHC concentrations and oxidative stress of the feeding area than the origin of the salmon.

Dietary factors potentially impacting thiaminase I-mediated thiamine deficiency

Fish population declines from thiamine (vitamin B1) deficiency have been widespread in ecologically and economically valuable organisms, ranging from the Great Lakes to the Baltic Sea and, most recently, the California coast. Thiamine deficiencies in predatory fishes are often attributed to a diet of prey fishes with high levels of thiamine-degrading (e.g., thiaminase) enzymes, such as alewives, rainbow smelt, and anchovies. Since their discovery, thiaminase I enzymes have been recognized for breaking down thiamine into its pyrimidine and thiazole moieties using various nucleophilic co-substrates to afford cleavage, but these studies have not thoroughly considered other factors that could modify enzyme activity. We found the thiaminase I enzyme from Clostridium botulinum efficiently degrades thiamine in the presence of pyridoxine (vitamin B6) as a co-substrate but has relatively limited activity in the presence of nicotinic acid (vitamin B3). Using fluorescence measurements, thiamine degradation in an over-the-counter complete multivitamin formulation was inhibited, and a B-complex formulation required co-substrate supplementation for maximal thiamine depletion. These studies prompted the evaluation of specific constituents contributing to thiaminase I inhibition by both chromatography and fluorescence assays: Cu²⁺ potently and irreversibly inhibited thiamine degradation; ascorbic acid was a strong but reversible inhibitor; Fe²⁺, Mn²⁺ and Fe³⁺ modulated thiamine degradation to a lesser degree. The enhancement by pyridoxine and inhibition by Cu²⁺ extended to thiaminase-mediated degradation from Burkholderia thailandensis, Paenibacillus thiaminolyticus, and Paenibacillus apiarius in tryptic soy broth supernatants. These co-substrate limitations and the common presence of inhibitory dietary factors complement recent studies reporting that the intended function of thiaminase enzymes is to recycle thiamine breakdown products for thiamine synthesis, not thiamine degradation.

Physiological changes and reproductive performance of Sterlet sturgeon Acipenser ruthenus injected with thiamine

To evaluate the effects of thiamine on physiological changes and spawning performance of Sterlet sturgeon Acipenser ruthenus, 45 farmed female fish (698.6±8.9g) were randomly distributed in 9 tanks (1000L) and fed a diet with 1g/kg of an anti-thiamine drug. This was provided for 5 months prior to spawning. Thiamine hydrochloride was intraperitoneally injected to fish at three different doses: 0 (T₀, as control), 5 (T₅) and 50 (T₅₀) mg/kg body weight at days 30, 90 and 150 after the experiment started. After five months, the results showed no significant differences in weight gain and hemoglobin level, but hematocrit significantly increased in T₅ group. There was no significant difference in glucose-6-phosphate dehydrogenase and estradiol-17β, but testosterone was significantly increased in the T₅₀ group. Total thiamine concentration in the eggs was significantly higher in T₅₀ than that detected in the control group. Fecundity and larval mortality at 6day post hatch (dph) showed no significant differences among treatments, while the number of eggs per gram was significantly lower in T₀ than that observed in T₅₀. Larval weights at 1 (11.6mg) and 6 (23.1mg) dph and larval lengths at 6 (15.6mm) dph were significantly affected by the treatment with the highest level of thiamine injection (T₅₀). Diseases symptoms such as yolk sac deformation, erratic pattern of swimming, and loss of equilibrium were observed at 4 dph in T₀ and T₅ groups. The overall results revealed that thiamine injection has positive effects on reproductive performance in the sturgeon and the negative impacts of anti-thiamine in the offspring can be reduced by the injection of this vitamin to the broodstock.

In vitro immune functions in thiamine-replete and -depleted lake trout (Salvelinus namaycush)

In this study we examined the impacts of in vivo thiamine deficiency on lake trout leukocyte function measured in vitro. When compared outside the context of individual-specific thiamine concentrations no significant differences were observed in leukocyte bactericidal activity or in concanavalin A (Con A), and phytohemagglutinin-P (PHA-P) stimulated leukocyte proliferation. Placing immune functions into context with the ratio of in vivo liver thiamine monophosphate (TMP--biologically inactive form) to thiamine pyrophosphate (TPP--biologically active form) proved to be the best indicator of thiamine depletion impacts as determined using regression modeling. These observed relationships indicated differential effects on the immune measures with bactericidal activity exhibiting an inverse relationship with TMP to TPP ratios, Con A stimulated mitogenesis exhibiting a positive relationship with TMP to TPP ratios and PHA-P stimulated mitogenesis exhibiting no significant relationships. In addition, these relationships showed considerable complexity which included the consistent observation of a thiamine-replete subgroup with characteristics similar to those seen in the leukocytes from thiamine-depleted fish. When considered together, our observations indicate that lake trout leukocytes experience cell-type specific impacts as well as an altered physiologic environment when confronted with a thiamine-limited state.

Impact of thiamine deficiency on T-cell dependent and T-cell independent antibody production in lake trout

Lake trout Salvelinus namaycush on thiamine-replete and thiamine-depleted diets were evaluated for the effects of thiamine status on in vivo responses to the T-dependent antigen trinitophenol (TNP)-keyhole limpet hemocyanin (TNP-KLH), the T-independent antigen trinitrophenol-lipolysaccaharide (TNP-LPS), or Dulbecco's phosphate-buffered saline (DPBS; negative control fish). Plasma antibody concentrations were evaluated for possible differences in total anti-TNP activity as well as differences in response kinetics. Associations between anti-TNP activity and muscle and liver thiamine concentrations as well as ratios of muscle-to-liver thiamine to anti-TNP activity were also examined. Thiamine-depleted lake trout that were injected with TNP-LPS exhibited significantly more anti-TNP activity than thiamine-replete fish. The depleted fish injected with TNP-LPS also exhibited significantly different response kinetics relative to thiamine-replete lake trout. No differences in activity or kinetics were observed between the thiamine-replete and -depleted fish injected with TNP-KLH or in the DPBS negative controls. Anti-TNP activity in thiamine-depleted lake trout injected with TNP-KLH was positively associated with muscle thiamine pyrophosphate (thiamine diphosphate; TPP) concentration. A negative association was observed between the ratio of muscle-to-liver TPP and T-independent responses. No significant associations between anti-TNP activity and tissue thiamine concentration were observed in the thiamine-replete fish. We demonstrated that thiamine deficiency leads to alterations in both T-dependent and T-independent immune responses in lake trout.

Wild birds of declining European species are dying from a thiamine deficiency syndrome

Wild birds of several species are dying in large numbers from an idiopathic paralytic disease in the Baltic Sea area. Here, we demonstrate strong relationships between this disease, breeding failure, and thiamine (vitamin B(1)) deficiency in eggs, pulli, and full-grown individuals. Thiamine is essential for vertebrates, and its diphosphorylated form functions as a cofactor for several life sustaining enzymes, whereas the triphosphorylated form is necessary for the functioning of neuronal membranes. Paralyzed individuals were remedied by thiamine treatment. Moreover, thiamine deficiency and detrimental effects on thiamine-dependent enzymes were demonstrated in the yolk, liver, and brain. We propose that the mortality and breeding failure are part of a thiamine deficiency syndrome, which may have contributed significantly to declines in many bird populations during the last decades.

A new erythrose 4-phosphate dehydrogenase coupled assay for transketolase

The standard assay for transketolase (E.C 2.2.1.1) has depended upon the use of D-xylulose 5-phosphate as the ketose donor substrate since the production of D-glyceraldehyde 3-phosphate can be readily coupled to a reaction that consumes NADH allowing the reaction to be followed spectrophotometrically. Unfortunately, commercial supplies of D-xylulose 5-phosphate recently became unavailable. In this article we describe the coupling of a transketolase reaction (using Leishmania mexicana transketolase) that converts D-fructose 6-phosphate to D-erythrose 4-phosphate. D-Erythrose 4-phosphate can then be converted to 4-phosphate D-erythronate using erythrose-4-phosphate dehydrogenase (E.C 1.2.1.72), a reaction that reduces NAD+ to NADH and can be easily followed spectrophotometrically. D-Ribose 5-phosphate and D-glyceraldehyde 3-phosphate can both be used as ketol acceptor substrates in the reaction although D-ribose 5-phosphate is also a substrate for the coupling enzyme.

The physiology and toxicology of salmonid eggs and larvae in relation to water quality criteria

The purpose of this review is to collate physiological knowledge on salmonid eggs and larvae in relation to water quality criteria. Salmonid genera reviewed include Coregonus, Thymallus, Salvelinus, Salmo, and Oncorhynchus spp. When physiological data for salmonids are lacking, the zebrafish and medaka models are included. The primary focus is on the underlying mechanisms involved in the hydro-mineral, thermal, and respiratory biology with an extended section on the xenobiotic toxicology of the early stages. Past and present data reveal that the eggs of salmonids are among the largest shed by any broadcast spawning teleost. Once ovulated, the physicochemical properties of the ovarian fluid provide temporary protection from external perturbations and maintain the eggs in good physiological condition until spawning. Following fertilisation and during early development the major structures protecting the embryo from poor water quality are the vitelline membrane, the enveloping layer and the chorion. The vitelline membrane is one of the least permeable membranes known, while the semi-permeable chorion provides both physical and chemical defense against metals, pathogens, and xenobiotic chemicals. In part these structures explain the lower sensitivity of the eggs to chemical imbalance compared to the larvae, however the lower metabolic rate and the chronology of gene expression and translational control suggest that developmental competence also plays a decisive role. In addition, maternal effect genes provide a defense potential until the mid-blastula transition. The transition between maternal effect genes and zygotic genes is a critical period for the embryo. The perivitelline fluids are an important trap for cations, but are also the major barrier to diffusion of gases and solutes. Acidic environmental pH interferes with acid-base and hydromineral balance but also increases the risk of aluminium and heavy metal intoxication. These risks are ameliorated somewhat by the presence of ambient humic acid. High temperatures during development may be teratogenic, cause sexual bias, or long-term effects on muscle cellularity. Xenobiotics cause inhibition of neural acetylcholine esterase and carboxylases and disrupt the normal signalling pathways of hormones by binding to relevant receptors and mimicking their actions. A complex suite of genes is activated in response to environmental or parentally transmitted xenobiotics. The primary defense mechanism in embryos involves resistance to uptake but later biotransformation via the aryl hydrocarbon receptor (AHR)-mediated activation of members of the cytochrome mixed-function mono-oxygenase superfamily (CYP1A, CYP2B, and CYP3A) and subsequent glucuronidation or glutathionation. Due to the number of duplicate or triplicate genes coding for intermediates in the signalling pathways, and cross-talk between nuclear orphan receptors and steroid hormone receptors, a large number of complications arise in response to xenobiotic intoxicaton. One such syndrome, known as blue-sac disease causes an anaphylactoid response in hatched larvae due to increased permeability in the vascular endothelium that coincides with AHR-mediated CYP induction. Early embryos also respond to such xenobiotic insults, but apparently have an immature translational control for expression of CYP proteins, which coincides with a lack of excretory organs necessary for the end-point of biotransformation. Other syndromes (M74 and Cayuga) are now associated with thiamine deficiency. Where possible guidelines for water quality criteria are suggested.

Pharmacokinetics of thiamine in female Baltic salmon (Salmo salar L.) broodfish

A thiamine deficiency disease termed M74 syndrome affects the yolk-sac fry of wild and feral Baltic salmon. However, very little is known about the pharmacokinetics of thiamine in salmon. This study examined the pharmacokinetics of thiamine hydrochloride injected intraperitoneally into feral and farmed Baltic salmon females preparing for spawning. The total thiamine concentrations in the eggs and white muscle of feral females were only half of those in the farmed fish after injection. The relative inefficiency of the incorporation of thiamine into the eggs in feral Baltic salmon may be a predisposition factor for M74 syndrome. The relative bioavailability of intraperitoneally-injected thiamine hydrochloride was shown to be ca. 94% of that administered intra-aortically. A far lower intraperitoneal dose (ca. 20mgkg(-1) fish) than currently used was shown to elevate the total thiamine concentration in the eggs above the critical threshold of M74 syndrome.

Baltic salmon (Salmo salar) yolk-sac fry mortality is associated with disturbances in the function of hypoxia-inducible transcription factor (HIF-1alpha) and consecutive gene expression

Baltic salmon (Salmo salar) suffer from abnormally high yolk-sac fry mortality designated as M74-syndrome. In 1990s, 25-80% of salmon females, which ascended rivers to spawn, produced yolk-sac fry suffering from the syndrome. Symptoms of M74-affected fry include neurological disturbances, impaired vascular development and abnormal haemorrhages. The latter symptoms are observed in mammalian embryos if the function of hypoxia inducible transcription factor (HIF-1alpha), its dimerization partner aryl hydrocarbon nuclear translocator (ARNT) or target gene vascular endothelial growth factor (VEGF) is disturbed. To study the possible involvement of HIF-1alpha and its target gene VEGF in the development of the syndrome, we collected healthy and M74-affected wild Baltic salmon yolk-sac fry and analyzed HIF-1alpha mRNA and protein expression, HIF-1alpha DNA-binding, target gene VEGF protein expression, and blood vessel density in both groups at different stages of yolk-sac fry development. In addition, since Baltic salmon females contain organochlorine contaminants, which have been suggested to be the cause of M74 syndrome via the aryl hydrocarbon receptor (AhR)-dependent gene expression pathway, we studied AhR protein expression, AhR DNA-binding and target gene CYP1A protein expression. Since the parents of both healthy and M74-affected wild fry will have experienced the organochlorine load from the Baltic Sea, hatchery-reared fry were included in the studies as an additional control. The results show that the vascular defects observed in fry suffering from M74 are associated with reduced DNA-binding activity of HIF-1alpha and subsequent downregulation of its target gene vascular endothelial growth factor (VEGF). In addition, also AhR function is decreased in diseased fry making it unlikely that symptoms of M74-affected fry would be caused by an upregulation of xenobiotically induced AhR-dependent gene expression pathway.

Proteomic sensitivity to dietary manipulations in rainbow trout

Changes in dietary protein sources due to substitution of fish meal by other protein sources can have metabolic consequences in farmed fish. A proteomics approach was used to study the protein profiles of livers of rainbow trout that have been fed two diets containing different proportions of plant ingredients. Both diets control (C) and soy (S) contained fish meal and plant ingredients and synthetic amino acids, but diet S had a greater proportion of soybean meal. A feeding trial was performed for 12 weeks at the end of which, growth and protein metabolism parameters were measured. Protein growth rates were not different in fish fed different diets; however, protein consumption and protein synthesis rates were higher in the fish fed the diet S. Fish fed diet S had lower efficiency of retention of synthesised protein. Ammonia excretion was increased as well as the activities of hepatic glutamate dehydrogenase and aspartate amino transferase (ASAT). No differences were found in free amino acid pools in either liver or muscle between diets. Protein extraction followed by high-resolution two-dimensional electrophoresis, coupled with gel image analysis, allowed identification and expression of hundreds of protein. Individual proteins of interest were then subjected to further analysis leading to protein identification by trypsin digest fingerprinting. During this study, approximately 800 liver proteins were analysed for expression pattern, of which 33 were found to be differentially expressed between diets C and S. Seventeen proteins were positively identified after database searching. Proteins were identified from diverse metabolic pathways, demonstrating the complex nature of gene expression responses to dietary manipulation revealed by proteomic characterisation.

Paraquat and menadione exposure of rainbow trout (Oncorhynchus mykiss)--studies of effects on the pentose-phosphate shunt and thiamine levels in liver and kidney

Possible xenobiotic interactions with thiamine were studied in salmonid fish, by repeatedly injecting two model substances, paraquat and menadione, into juvenile rainbow trout (Oncorhynchus mykiss). These two substances were chosen because of their well-known ability to redox-cycle and cause depletion of NADPH in several biological systems. Depletion of NADPH increases metabolism through the pentose-phosphate shunt and may thereby increase the need for thiamine diphosphate by heightened transketolase activity. A special food was produced with lower thiamine content than commercial food, usually enriched with thiamine, which could mask an effect on the thiamine level. After 9 weeks of exposure, glucose-6-phosphate dehydrogenase, transketolase, glutathione reductase and ethoxyresorufin O-deethylase were analysed in liver and kidney cellular sub-fractions as well as analysis of total thiamine concentrations in liver, kidney and muscle. The results showed that paraquat caused a large increase in hepatic glutathione reductase activity and induced hepatic glucose-6-phosphate dehydrogenase activity, i.e., the rate-limiting enzyme in the oxidative part of the pentose-phosphate shunt. Despite this paraquat exposure did not affect transketolase activity and total thiamine concentration.

Physiological, biochemical and morphological studies of Baltic salmon yolk-sac fry with an experimental thiamine deficiency: relations to the M74 syndrome

Sea-run Baltic salmon (Salmo salar) populations are suffering from the M74 syndrome, a reproduction disorder affecting both broodfish and their progeny. The syndrome is usually manifested during the middle part of the yolk-sac fry stage and has been shown to be associated with a thiamine (vitamin B(1)) deficiency. Development of the disease is reversible by thiamine treatments of broodfish or progeny. This study aimed at investigating the ability of the thiamine antagonist pyrithiamine, administered by microinjections 3 days after hatch, to cause M74-like signs i.e. typical clinical symptoms, high mortality rates and histopathological changes. Furthermore, the effects of pyrithiamine on hepatic activities of the thiamine-dependent enzyme transketolase (TK), the glucose-6-phosphate dehydrogenase (G6PDH) and the cytochrome P4501A (CYP1A) were evaluated. Six family groups with differing thiamine status were sampled on three occasions during the yolk-sac fry stage. All pyrithiamine exposed groups, with the exception of the one with the highest thiamine concentration, showed M74-like symptoms and suffered from high mortality. Enzyme activities were not different in pyrithiamine groups as compared with controls. However, the TK-activities were strongly associated with the thiamine concentrations. The G6PDH-activity demonstrated small variations with the highest activities in the M74-groups. The [TK]/[G6PDH]-ratios were considerably lower in the M74-groups than in the healthy controls, indicating an imbalance between the oxidative and the non-oxidative part of the pentose-phosphate shunt due to a deficit in thiamine. The pyrithiamine-injections induced several M74-like symptoms including incoordination, lethargy, whitened liver and yolk-sac precipitates. They also caused high mortality rates, in addition to lowered glycogen levels and increased prevalence of necrotic brain cells. Moreover, the study demonstrates that the TK, G6PDH and CYP1A-activities are associated with the thiamine content.

Effects of furazolidone, PCB77, PCB126, Aroclor 1248, paraquat and p,p'-DDE on transketolase activity in embryonal chicken brain

The effect of in ovo exposure to PCBs, DDE and paraquat on transketolase activity was measured in 19-day-old chicken embryos. Furazolidone was used as a positive control for decreased activity of the enzyme. The potency of contaminants to interact with transketolase was also tested in an in vitro system, using control brain 7000xg supernatants containing the enzyme. No effects were found on transketolase activity after in ovo or in vitro exposure to PCB126, Aroclor, DDE or paraquat. PCB77 decreased transketolase activity in vitro, but only at concentrations that, extrapolated to in ovo exposure, would be lethal to the embryo. Furazolidone decreased transketolase activity both in ovo and in vitro. For this contaminant, thiamine residues were analysed in the yolk sacs, but no differences were found between exposed and non-exposed eggs. Transketolase is dependent on thiamine pyrophosphate as a cofactor, and therefore, the decreased enzyme activity could be the result of an interaction between furazolidone and thiamine metabolism. Since thiamine residues were not affected by furazolidone and transketolase inhibition in vitro was similar to the inhibition after in ovo exposure, it was concluded that furazolidone interacted with transketolase on the enzymatic level rather than by a depletion of thiamine.