Shifting Patterns of Nitrogen Excretion and Amino Acid Catabolism Capacity during the Life Cycle of the Sea Lamprey (Petromyzon marinus)

Evaluation of health benefits of sea lamprey (Petromyzon marinus) isolates using in vitro antiinflammatory and antioxidant assays

Sea lamprey (Petromyzon marinus), a parasitic fish which survives on blood of other fishes, is consumed as a delicacy in many countries. Our earlier studies on sea lamprey compounds that showed potential to deter adult sea lampreys yielded several sterols, glycerides, free fatty acids, amino acids, organic acids and nitrogenous compounds. Therefore, this study was to assess the health-benefits of these compounds including additional isolates from HPLC fractions that kept aside due to lack of activity in sea lamprey deterrent assays. In vitro cyclooxygenase enzymes (COX-1 and -2) and lipid peroxidation (LPO) inhibitory assays, respectively, were used to determine antiinflammatory and antioxidant activities. Among the tested sterols, cholesteryl eicosapentaenoate and cholesteryl arachidonate exhibited IC50 values of 14.6 and 17.7 μg/mL for COX-1 and 17.3 and 20.8 μg/mL for COX-2, respectively. Cholesteryl palmitate and cholesteryl oleate showed moderate COX-1 and COX-2 enzyme inhibition at 25 μg/mL. Amino acids arginine, tyrosine, glutamic acid, tryptophan and asparagine also showed moderate COX-1 and COX-2 inhibition at the same concentration. Among the twelve new isolates from fractions that we did not investigate earlier, a novel uracil derivative petromyzonacil showed COX-1 and COX-2 inhibition at 25 μg/mL by 35 and 15%, respectively. Cholesterol esters tested at 25 μg/mL exhibited LPO inhibition between 38 and 82 percent. Amino acids cysteine, methionine, aspartic acid, threonine, tryptophan, histidine, glutamic acid, phenylalanine and tyrosine at 25 μg/mL showed LPO inhibition between 37 and 58% and petromyzonacil by 32%. These assay results indicate that consumption of sea lamprey offer health-benefits in addition to nutritional benefits.

Functional re-organization of the gills of metamorphosing sea lamprey (Petromyzon marinus): preparation for a blood diet and the freshwater to seawater transition

Sea lamprey (Petromyzon marinus) begin life as filter-feeding larvae (ammocoetes) before undergoing a complex metamorphosis into parasitic juveniles, which migrate to the sea where they feed on the blood of large-bodied fishes. The greater protein intake during this phase results in marked increases in the production of nitrogenous wastes (N-waste), which are excreted primarily via the gills. However, it is unknown how gill structure and function change during metamorphosis and how it is related to modes of ammonia excretion, nor do we have a good understanding of how the sea lamprey's transition from fresh water (FW) to sea water (SW) affects patterns and mechanisms of N-waste excretion in relation to ionoregulation. Using immunohistochemistry, we related changes in the gill structure of larval, metamorphosing, and juvenile sea lampreys to their patterns of ammonia excretion (J_amm) and urea excretion (J_urea) in FW, and following FW to artificial seawater (ASW) transfer. Rates of J_amm and J_urea were low in larval sea lamprey and increased in feeding juvenile, parasitic sea lamprey. In freshwater-dwelling ammocoetes, immunohistochemical analysis revealed that Rhesus glycoprotein C-like protein (Rhcg-like) was diffusely distributed on the lamellar epithelium, but following metamorphosis, Rhcg-like protein was restricted to SW mitochondrion-rich cells (MRCs; ionocytes) between the gill lamellae. Notably, these interlamellar Rhcg-like proteins co-localized with Na⁺/K⁺-ATPase (NKA), which increased in expression and activity by almost tenfold during metamorphosis. The distribution of V-type H⁺-ATPase (V-ATPase) on the lamellae decreased following metamorphosis, indicating it may have a more important role in acid-base regulation and Na⁺ uptake in FW, compared to SW. We conclude that the re-organization of the sea lamprey gill during metamorphosis not only plays a critical role in allowing them to cope with greater salinity following the FW-SW transition, but that it simultaneously reflects fundamental changes in methods used to excrete ammonia.

Lipid and protein catabolism contribute to aerobic metabolic responses to exhaustive exercise during the protracted spawning run of the lamprey Geotria australis

This paper has integrated new and past data to elucidate how lipid, protein and glycogen metabolism contribute to generating the ATP required by the southern hemisphere lamprey Geotria australis during its ~ 13-15 months, non-trophic upstream spawning migration. Energy is required for maintenance, swimming, the development of gonads and secondary sexual characters and spawning and post-spawning activities. Plasma and muscle metabolites were measured in animals subjected to an exercise-recovery regime at the commencement and completion of the spawning run. The present study demonstrated the following. At all stages of the migration, plasma glucose and glycerol concentrations increased during exercise and then declined, whereas plasma FFAs exhibited the reverse trend. During exercise and recovery, alanine declined and ammonia increased in the plasma of early migrants, while the opposite occurred in mature males. Following exercise, muscle alanine rose and then declined in early migrants, but declined and then rose in mature males. The composite data emphasise that, while the same catabolic processes are employed by both sexes early in the migration, when animals are immature, they differ markedly between the sexes as they mature and then spawn, reflecting their different demands. Energy is supplied predominantly via anaerobic metabolism in early migrants, but by anaerobic and aerobic metabolism in prespawning females and by aerobic metabolism in mature males and spent females. Although proteolysis is limited early in the migration, it is employed extensively during maturation and particularly by females, which undergo a substantial reduction in length in the lead-up to spawning.

Control of invasive sea lampreys using the piscicides TFM and niclosamide: Toxicology, successes & future prospects

The invasion of the Laurentian Great Lakes of North America by sea lampreys (Petromyzon marinus) in the early 20th century contributed to the depletion of commercial, recreational and culturally important fish populations, devastating the economies of communities that relied on the fishery. Sea lamprey populations were subsequently controlled using an aggressive integrated pest-management program which employed barriers and traps to prevent sea lamprey from migrating to their spawning grounds and the use of the piscicides (lampricides) 3-trifluoromethyl-4-nitrophenol (TFM) and niclosamide to eliminate larval sea lampreys from their nursery streams. Although sea lampreys have not been eradicated from the Great Lakes, populations have been suppressed to less than 10% of their peak numbers in the mid-1900s. The ongoing use of lampricides provides the foundation for sea lamprey control in the Great Lakes, one of the most successful invasive species control programs in the world. Yet, significant gaps remain in our understanding of how lampricides are taken-up and handled by sea lampreys, how lampricides exert their toxic effects, and how they adversely affect non-target invertebrate and vertebrates species. In this review we examine what has been learned about the uptake, handling and elimination, and the mode of TFM and niclosamide toxicity in lampreys and in non-target animals, particularly in the last 10 years. It is now clear that the mode of TFM toxicity is the same in non-target fishes and lampreys, in which TFM interferes with oxidative phosphorylation by the mitochondria leading to decreased ATP production. Vulnerability to TFM is related to abiotic factors such as water pH and alkalinity, which we propose changes the relative amounts of the bioavailable un-ionized form of TFM in the gill microenvironment. Niclosamide, which is also a molluscicide used to control snails in areas prone to schistosomiasis infections of humans, also likely works by uncoupling oxidative phosphorylation, but less is known about other aspects of its toxicology. The effects of TFM include reductions in energy stores, particularly glycogen and high energy phosphagens. However, non-target fishes readily recover from sub-lethal TFM exposure as demonstrated by the rapid restoration of energy stores and clearance of TFM. Although both TFM and niclosamide are non-persistent in the environment and critical for sea lamprey control, increasing public and institutional concerns about pesticides in the environment makes it imperative to explore other means of sea lamprey control. Accordingly, we also address possible "next-generation" strategies of sea lamprey control including genetic tools such as RNA interference and CRISPR-Cas9 to impair critical physiological processes (e.g. reproduction, digestion, metamorphosis) in lamprey, and the use of green chemistry to develop more environmentally benign chemical methods of sea lamprey control.

Nitrogenous compounds characterized in the deterrent skin extract of migratory adult sea lamprey from the Great Lakes region

The sea lamprey (Petromzons marinus) is a devastating invasive species that represents a significant impediment to restoration of the Laurentian Great Lakes. There is substantial interest in developing environmentally benign control strategies for sea lamprey, and many other aquatic invasive species, that employ the manipulation of semiochemical information (pheromones and chemical cues) to guide the movements of invaders into control opportunities (e.g. traps, locations for safe pesticide application, etc.). A necessary precursor to the use of semiochemicals in conservation activities is the identification of the chemical constituents that compose the odors. Here, we characterize the major nitrogenous substances from the water-soluble fraction of a skin extract that contains the sea lamprey alarm cue, a powerful repellent that has proven effective in guiding the movements of migrating sea lamprey in rivers. Nitrogenous compounds are suspected components of fish alarm cues as the olfactory sensory neurons that mediate alarm responses transduce amino acids and related compounds. A laboratory assay confirmed the behavioral activity contained in the alarm cue resides in the water-soluble fraction of the skin extract. This water-soluble fraction consisted primarily of creatine (70%), heterocyclic nitrogenous compounds (4.3%) and free amino acids (18.4%), respectively. Among the free amino acids characterized in our study, essential amino acids constituted 13% of the water-soluble fraction. Free amino acids isolated from the water-soluble fraction composed of arginine, phenylalanine, threonine, and asparagine 3.9, 2.7, 2.6 and 2.4% of the water-soluble fraction, respectively. We discuss the implications of these findings for understanding the nature and use of the sea lamprey alarm cue in conservation activities.

Influence of body size, metabolic rate and life history stage on the uptake and excretion of the lampricide 3-trifluoromethyl-4-nitrophenol (TFM) by invasive sea lampreys (Petromyzon marinus)

Invasive sea lamprey (Petromyzon marinus) are controlled in the Great Lakes using the lampricide 3-trifluoromethyl-4-nitrophenol (TFM), which is applied to streams infested with larval lamprey. However, lamprey that survive treatments (residuals) remain a challenge because they may subsequently undergo metamorphosis into parasitic juvenile animals that migrate downstream to the Great Lakes, where they feed on important sport and commercial fishes. The goal of this study was to determine if body size and life stage could potentially influence sea lamprey tolerance to TFM by influencing patterns of TFM uptake and elimination. Because mass specific rates of oxygen consumption (M˙O₂) are lower in larger compared to smaller lamprey, we predicted that TFM uptake would be negatively correlated to body size, suggesting that large larvae would be more tolerant to TFM exposure. Accordingly, TFM uptake and M˙O₂ were measured in larvae ranging in size from 0.2-4.2g using radio-labelled TFM (¹⁴C-TFM) and static respirometry. Both were inversely proportional to wet mass (M), and could be described usingthe allometric power relationship: Y=aM^b, in which M˙O₂=1.86M^0.53 and TFM Uptake=7.24M^0.34. We also predicted that body size would extend to rates of TFM elimination, which was measured following the administration of ¹⁴C-TFM (via intraperitoneal injection). However, there were no differences in the half-lives of elimination of TFM (T _1/2-TFM). There were also no differences in M˙O₂ or TFM uptake amongst size-matched larval, metamorphosing (stages 6-7), or post-metamorphic (juvenile) sea lamprey. However, the T_1/2-TFM was significantly lower in larval than post-metamorphic lamprey (juvenile), indicating the larval lamprey cleared TFM more efficiently than juvenile lamprey. We conclude that larger larval sea lamprey are more likely to survive TFM treatments suggesting that body size might be an important variable to consider when treating streams with TFM to control these invasive species.

Rh glycoprotein immunoreactivity in the skin and its role in extrabranchial ammonia excretion by the sea lamprey (Petromyzon marinus) in fresh water

Aquatic organisms employ various strategies to excrete ammonia across the gills, skin, and (or) renal routes. During three different stages of their life cycle, we hypothesized that the basal vertebrate sea lamprey (Petromyzon marinus L., 1758) used the skin as a route for ammonia excretion. Measurements of ammonia excretion using divided flux chambers revealed that extrabranchial sites (skin plus renal) of ammonia excretion were quantitatively more important in larval sea lampreys, but following metamorphosis, the gills became the dominant route of excretion in juvenile sea lampreys. Despite the greater relative importance of the skin in the larval stage, Rh glycoprotein isoforms Rhbg, Rhcg1, and Rhcg2 were detected in the skin in all three sea lamprey life stages examined, but the patterns of expression were dependent on the life stage. We conclude that, during the relatively sedentary filter-feeding larval stage, extrabranchial routes play an equally important role as the gill in facilitating ammonia excretion. However, the gills by virtue of their extensive branchial vasculature become the dominant route of ammonia excretion following metamorphosis because of the need to offload greater amounts of ammonia arising from higher rates of basal ammonia production and the potential to excrete higher amounts of ammonia following ingestion of protein-rich blood in the parasitic stage.

Iso-petromyroxols: novel dihydroxylated tetrahydrofuran enantiomers from sea lamprey (Petromyzon marinus)

An enantiomeric pair of new fatty acid-derived hydroxylated tetrahydrofurans, here named iso-petromyroxols, were isolated from sea lamprey larvae-conditioned water. The relative configuration of iso-petromyroxol was elucidated with 1D and 2D NMR spectroscopic analyses. The ratio of enantiomers (er) in the natural sample was measured by chiral-HPLC-MS/MS to be ca. 3:1 of (–)- to (+)-antipodes.

Life stage dependent responses to the lampricide, 3-trifluoromethyl-4-nitrophenol (TFM), provide insight into glucose homeostasis and metabolism in the sea lamprey (Petromyzon marinus)

The primary method of sea lamprey (Petromyzon marinus) control in the Great Lakes is the treatment of streams and rivers with the pesticide 3-trifluoromethyl-4-nitrophenol (TFM), which targets larval sea lamprey. However, less is known about the effects of TFM on other stages of the sea lamprey's complex life cycle. The goal of this study was to determine how TFM affected internal energy stores, metabolites, and ion balance in larval, juvenile (parasitic) and adult sea lamprey. The larvae were more tolerant to TFM than the adults, with a 2-fold higher 12h TFM LC50 and a 1.5-fold higher LC99.9. Acute (3h) exposure of the larvae, parasites and adults to their respective 12h TFM LC99.9 led to marked reductions in glycogen and phosphocreatine in the adult brain, with lesser or no effect in the larvae and parasites. Increased lactate in the brain, at less than the expected stoichiometry, suggested that it was exported to the blood. Kidney glycogen declined after TFM exposure, suggesting that this organ plays an important role in glucose homeostasis. TFM-induced disturbances to ion balance were minimal. In conclusion, TFM perturbs energy metabolism in all major stages of the sea lamprey life cycle in a similar fashion, but the adults appear to be the most sensitive. Thus, the adult stage could be a viable and effective target for TFM treatment, particularly when used in combination with other existing and emerging strategies of sea lamprey control.

Adaptations of a deep sea scavenger: high ammonia tolerance and active NH₄⁺ excretion by the Pacific hagfish (Eptatretus stoutii)

The Pacific hagfish (Eptatretus stoutii) has an exceptional ability to both withstand and recover from exposure to high external ammonia (HEA). This tolerance is likely due to the feeding behavior of this scavenger, which feeds on intermittent food falls of carrion (e.g. fish, large marine mammals) during which time it may be exposed to high concentrations of total ammonia (T(Amm)=NH3+NH4(+)) while burrowed inside the decomposing carcass. Here we exposed hagfish to 20 mmol L(-1) T(Amm) for periods of up to 48 h and then let animals recover in ammonia-free seawater. During the 48 h HEA exposure period, plasma T(Amm) increased 100-fold to over 5000 μmol L(-1) while ammonia excretion (J(amm)) was transiently inhibited. This increase in plasma T(Amm) resulted from NH3 influx down massive inwardly directed ΔP(NH3) gradients, which also led to a short-lived metabolic alkalosis. Plasma [T(Amm)] stabilized after 24-48 h, possibly through a reduction in NH3 permeability across the body surface, which lowered NH3 influx. Ammonia balance was subsequently maintained through the re-establishment of J(amm) against an inwardly directed ΔP(NH3). Calculations of the Nernst potential for ammonia strongly indicated that J(amm) was also taking place against a large inwardly directed NH4(+) electrochemical gradient. Recovery from HEA in ammonia-free water was characterized by a large ammonia washout, and the restoration of plasma TAmm concentrations to near control concentrations. Ammonia clearance was also accompanied by a residual metabolic acidosis, which likely offset the ammonia-induced metabolic alkalosis seen in the early stages of HEA exposure. We conclude that restoration of J(amm) by the Pacific hagfish during ammonia exposure likely involves secondary active transport of NH4(+), possibly mediated by Na(+)/NH4(+) (H(+)) exchange.

Metabolic responses to exhaustive exercise change markedly during the protracted non-trophic spawning migration of the lamprey Geotria australis

Adults of the Southern hemisphere lamprey Geotria australis were subjected to an exercise/recovery regime at the commencement and end of their 12-15 month non-trophic, upstream spawning migration. In early (immature) migrants and pre-spawning females, muscle glycogen was markedly depleted during exercise, but became rapidly replenished. As muscle lactate rose during exercise and peaked 1-1.5 h into the recovery period, and therefore after muscle glycogen had become replenished, it cannot be the direct source for that replenishment. However, both plasma lactate and glycerol (but not muscle glycerol and glucose) rose sharply during exercise and then declined markedly during the first 0.5 h of recovery and thus exhibited the opposite trend to that of muscle glycogen, implying that these limited pools of glycogenic precursors contribute to glycogen replenishment. Although plasma glucose rose following exercise, and consequently could also be a precursor for muscle glycogen replenishment, it remained elevated even after muscle glycogen had become replenished. While resting pre-spawning females and mature males retained high muscle glycogen concentrations, this energy store became permanently depleted in females during spawning. In mature males, muscle glycogen remained high and lactate low during the exercise/recovery regime, whereas muscle glycerol declined precipitously during exercise and then rose rapidly. In summary, vigorous activity by G. australis is fuelled extensively by anaerobic metabolism of glycogen early in the spawning run and by pre-spawning females, but by aerobic metabolism of its energy reserves in mature males.

Failure of ATP supply to match ATP demand: the mechanism of toxicity of the lampricide, 3-trifluoromethyl-4-nitrophenol (TFM), used to control sea lamprey (Petromyzon marinus) populations in the Great Lakes

Although the pesticide, 3-trifluoromethyl-4-nitrophenol (TFM), has been extensively used to control invasive sea lamprey (Petromyzon marinus) populations in the Great Lakes, it is surprising that its mechanism(s) of toxicity is unresolved. A better knowledge of the mode of toxicity of this pesticide is needed for predicting and improving the effectiveness of TFM treatments on lamprey, and for risk assessments regarding potential adverse effects on invertebrate and vertebrate non-target organisms. We investigated two hypotheses of TFM toxicity in larval sea lamprey. The first was that TFM interferes with oxidative ATP production by mitochondria, causing rapid depletion of energy stores in vital, metabolically active tissues such as the liver and brain. The second was that TFM toxicity resulted from disruption of gill-ion uptake, adversely affecting ion homeostasis. Exposure of larval sea lamprey to 4.6 m gl(-1) TFM (12-h LC50) caused glycogen concentrations in the brain to decrease by 80% after 12h, suggesting that the animals increased their reliance on glycolysis to generate ATP due to a shortfall in ATP supply. This conclusion was reinforced by a 9-fold increase in brain lactate concentration, a 30% decrease in brain ATP concentration, and an 80% decrease in phosphocreatine (PCr) concentration after 9 and 12h. A more pronounced trend was noted in the liver, where glycogen decreased by 85% and ATP was no longer detected after 9 and 12h. TFM led to marginal changes in whole body Na(+), Cl(-), Ca(2+) and K(+), as well as in plasma Na(+) and Cl(-), which were unlikely to have contributed to toxicity. TFM had no adverse effect on Na(+) uptake rates or gill Na(+)/K(+)-ATPase activity. We conclude that TFM toxicity in the sea lamprey is due to a mismatch between ATP consumption and ATP production rates, leading to a depletion of glycogen in the liver and brain, which ultimately leads to neural arrest and death.

Ammonia and urea transporters in gills of fish and aquatic crustaceans

The diversity of mechanisms of ammonia and urea excretion by the gills and other epithelia of aquatic organisms, especially fish and crustaceans, has been studied for decades. Although the decades-old dogma of ;aquatic species excrete ammonia' still explains nitrogenous waste excretion for many species, it is clear that there are many mechanistic variations on this theme. Even within species that are ammonoteles, the process is not purely ;passive', often relying on the energizing effects of proton and sodium-potassium ATPases. Within the ammonoteles, Rh (Rhesus) proteins are beginning to emerge as vital ammonia conduits. Many fishes are also known to be capable of substantial synthesis and excretion of urea as a nitrogenous waste. In such species, members of the UT family of urea transporters have been identified as important players in urea transport across the gills. This review attempts to draw together recent information to update the mechanisms of ammonia and urea transport by the gills of aquatic species. Furthermore, we point out several potentially fruitful avenues for further research.