Activation of the newly discovered cyclostome renin-angiotensin system in the river lamprey Lampetra fluviatilis

The role of the renin-angiotensin system (RAS) in salinity adaptation in Pacific white shrimp (Litopenaeus vannamei)

The renin-angiotensin system (RAS) is a hormonal system that plays an important role in the regulation of blood pressure and cardiovascular homeostasis in mammals. In fishes, the RAS pathway participates in osmoregulation and salinity adaptation. However, the role of the RAS pathway in invertebrates, particularly in crustaceans, remains unknown. In this study, four key genes of the RAS pathway (LV-ACE, LV-APN, LV-AT1R, and LV-RR) were cloned, characterized, and their expression levels were detected in the eyestalk, hepatopancreas, and muscle of Litopenaeus vannamei during long-term and short-term low salinity stress. The results showed that LV-ACE, LV-APN, LV-AT1R, and LV-RR encode 666, 936, 175, and 323 amino acids, respectively. Low salinity stress downregulated the expression levels of LV-ACE, LV-APN, LV-AT1R, and LV-RR in L. vannamei, indicating that the RAS pathway was suppressed under low salinity. Moreover, these genes play important roles in the regulation of drinking rate, controlling urine output, blood glucose, and blood pressure, indicating that their downregulation probably affected the homeostasis of shrimps. These findings provide novel insights into the mechanism of salinity adaptation in L. vannamei.

Simultaneous determination of nine trace concentration angiotensin peptides in human serum using ultra high performance liquid chromatography with tandem mass spectrometry with sephadex LH-20 gel solid-phase extraction

The renin-angiotensin system is a highly complex enzymatic system consisting of multiple peptide hormones, enzymes, and receptors. Here, an assay to simultaneously quantify eight angiotensin peptides and bradykinin in human serum was developed and validated, using ultra high performance liquid chromatography coupled with tandem mass spectrometry. A pre-concentration method of Sephadex LH-20 gel solid-phase extraction was first applied for analysis of angiotensin peptides from serum sample. The triple quadrupole mass spectrometer was operated in the positive ion mode and multiple reaction monitoring was used for drug quantification. The analytical time was within 5 min, much raising the analysis efficiency. Limits of detection ranged from 0.9 to 1.3 pg/mL, and displayed the same level of sensitivity compared with radioimmunoassay. The method was successfully applied to 22 healthy human serum samples, giving the concentrations of angiotensin I, angiotensin II, angiotensin III, angiotensin IV, angiotensin 1-9, angiotensin 1-7, angiotensin 1-5, Asn¹ ,Val⁵ -Angiotensin II, and bradykinin for reference. This novel metabolic profile study of vasoactive peptides based on gel solid-phase extraction concentration provided not only an accurate quantitative assay of the serum concentrations, but also a promising methodology for evaluating the diagnostic values of the various peptides.

De novo assembly and transcriptome analysis of osmoregulation in Litopenaeus vannamei under three cultivated conditions with different salinities

Litopenaeus vannamei, one of the most important euryhaline crustaceans, is cultured in seawater, brackish water, and freshwater worldwide. We performed Illumina RNA sequencing of L. vannamei gills, generating 124,914,870; 119,250,450; and 105,487,350 raw reads from the shrimps cultured in seawater, brackish water, and freshwater, respectively. From these reads, 466,293 transcripts were de novo assembled and annotated. Comparative genomic analysis showed that 1752 genes were significantly differentially expressed in the freshwater group compared with the seawater group, including 1242 upregulated and 510 downregulated genes. In addition, 1246 genes were differentially expressed in the brackish group vs. the seawater water group, including 659 upregulated and 587 downregulated genes. These differentially expressed genes were mainly involved in energy metabolism, substance metabolism, ion transport and signal transduction, and genetic process. Gene Ontology and Kyoto Encyclopedia of Genes and Genomes pathway enrichment analysis were used to analyze the functional significance of the differentially expressed genes, included those responding to salinity through diverse biological functions and processes and numerous potential genes associated with the osmotic response. L. vannamei responses to the three cultivated salinities were analyzed using next-generation sequencing. The transcriptional database established from the current research adds to the information available on L. vannamei and the findings expand our knowledge of the molecular basis of osmoregulation mechanisms in this species.

Validating the relationship between 3-dimensional body acceleration and oxygen consumption in trained Steller sea lions

We tested the ability of overall dynamic body acceleration (ODBA) to predict the rate of oxygen consumption ([Formula: see text]) in freely diving Steller sea lions (Eumetopias jubatus) while resting at the surface and diving. The trained sea lions executed three dive types-single dives, bouts of multiple long dives with 4-6 dives per bout, or bouts of multiple short dives with 10-12 dives per bout-to depths of 40 m, resulting in a range of activity and oxygen consumption levels. Average metabolic rate (AMR) over the dive cycle or dive bout calculated was calculated from [Formula: see text]. We found that ODBA could statistically predict AMR when data from all dive types were combined, but that dive type was a significant model factor. However, there were no significant linear relationships between AMR and ODBA when data for each dive type were analyzed separately. The potential relationships between AMR and ODBA were not improved by including dive duration, food consumed, proportion of dive cycle spent submerged, or number of dives per bout. It is not clear whether the lack of predictive power within dive type was due to low statistical power, or whether it reflected a true absence of a relationship between ODBA and AMR. The average percent error for predicting AMR from ODBA was 7-11 %, and standard error of the estimated AMR was 5-32 %. Overall, the extensive range of dive behaviors and physiological conditions we tested indicated that ODBA was not suitable for estimating AMR in the field due to considerable error and the inconclusive effects of dive type.

Angiotensin AT2 receptor activates the cyclic-AMP signaling pathway in eel

A unique angiotensin type 2 receptor (AT2) that induces a cAMP signaling pathway was cloned and characterized for the first time in fish, Anguilla japonica. Phylogeny and synteny results showed that the AT2s among fishes and tetrapods share the same origin despite a sub-cluster formation among eel, salmon, and zebrafish. The eel AT2 was expressed abundantly in the spleen and localized at straight arterioles and ellipsoid regions prior to the sinusoid, suggesting a role in the regulation of microcirculation and/or immune response. Various angiotensin (Ang) peptides, including Ang II, Ang III, and Ang IV, were detected in the spleen by a radioimmunoassay coupled with HPLC separation, and these endogenous peptides stimulated a cAMP signaling, which has no crosstalk with cGMP pathway. The common and contrasting features of AT2 between fishes and mammals imply some ancestral characters of AT2, which are important information for receptor binding and evolutionary studies.

Presence of functional angiotensin II receptor and angiotensin converting enzyme in the aorta of the snake Bothrops jararaca

AIM

Angiotensin II (Ang II) interacts with AT(1) and AT(2) receptors and, in some vertebrates, with an Ang II binding site showing low affinity for AT(1) and AT(2) receptor antagonists. This study was carried out to characterize the Ang II receptor, and the presence of an angiotensin-converting enzyme (ACE) in the aorta of the Bothrops jararaca snake.

MAIN METHOD

Contraction induced by Ang I or II in aortic ring from the snake was evaluated in the absence or in the presence of ACE-blocker or Ang II antagonists.

KEY FINDINGS

Ang II analogs, modified at positions 1 and 5, induced vasoconstriction with differences in their potencies. The relative rank order was: [Asp(1), Val(5)] Ang II=[Asp(1), Ile(5)] Ang II>>>[Asn(1), Val(5)] Ang II. ACE-like activity was detected, as well as an Ang II receptor with low affinity for AT(1) and AT(2) selective receptor antagonists (pK(B) values of 5.62±0.23 and 5.08±0.25). A disulfide reducing agent almost abolished the Ang II effect, while an alpha adrenoceptor antagonist, or removing the endothelium, did not modify the Ang II effect. These results indicate that the B. jararaca aorta has an Ang II receptor pharmacologically distinct from AT(1) and AT(2) receptors, and the vasoconstrictor effect observed is independent of catecholamine or endothelium modulation. ACE and the AT receptor in the aorta of B. jararaca may be part of a tissue renin-angiotensin system.

SIGNIFICANCE

The data contribute to the knowledge of the renin-angiotensin system in vertebrate species, and provide insight into the understanding of snake Ang II receptor characteristics and diversity.

Changes in plasma angiotensin subtypes in Japanese eel acclimated to various salinities from deionized water to double-strength seawater

Our knowledge of complexity of the renin-angiotensin system (RAS) has grown in recent years and various angiotensin peptides including Ang II, Ang III, Ang IV, and Ang (1-7) were found to have specific functions. Using a combination of HPLC and radioimmunoassay (RIA), we established a high resolution method to quantify various angiotensin subtypes in the plasma of eel acclimated to deionized water (dW), freshwater (FW), seawater (SW), and double-strength seawater (DSW). [Asn(1), Val(5)]-Ang II, [Asp(1), Val(5)]-Ang II, [Val(4)]-Ang III, and [Val(3)]-Ang IV are all present in the circulation and both Ang II subtypes were significantly higher in DSW eel. When the eel was transferred from FW to SW, plasma immunoreactive (ir) Ang II concentration increased and its levels were highly correlated to plasma osmolality, suggesting that the elevated plasma osmolality is the major stimulus for activating the RAS during high salinity transfer. To examine the conversion of [Asn(1)] to [Asp(1)] residue in vivo and in vitro, synthetic [Asn(1), Val(5)]-Ang II was injected into the circulation or incubated with plasma, but the production of [Asp(1), Val(5)]-Ang II was insignificant, which implies that the conversion may occur at the angiotensinogen level. An asparaginase assay was further developed for measuring asparaginase activity and the highest activity was in liver in both FW and SW eel. This new method of analysis can be extended to study the endogenous angiotensin ligands in the local RAS. The potential significance of [Asn(1)] to [Asp(1)] conversion on Ang II metabolism and function is discussed.

Emergence and evolution of the renin-angiotensin-aldosterone system

The renin-angiotensin-aldosterone system (RAAS) is not the sole, but perhaps the most important volume regulator in vertebrates. To gain insights into the function and evolution of its components, we conducted a phylogenetic analysis of its main related genes. We found that important parts of the system began to appear with primitive chordates and tunicates and that all major components were present at the divergence of bony fish, with the exception of the Mas receptor. The Mas receptor first appears after the bony-fish/tetrapod divergence. This phase of evolutionary innovation happened about 400 million years ago. We found solid evidence that angiotensinogen made its appearance in cartilage fish. The presence of several RAAS genes in organisms that lack all the components shows that these genes have had other ancestral functions outside of their current role. Our analysis underscores the utility of sequence comparisons in the study of evolution. Such analyses may provide new hypotheses as to how and why in today's population an increased activity of the RAAS frequently leads to faulty salt and volume regulation, hypertension, and cardiovascular diseases, opening up new and clinically important research areas for evolutionary medicine.

Peptide and protein drugs: the study of their metabolism and catabolism by mass spectrometry

Peptide and protein drugs have evolved in recent years into mainstream therapeutics, representing a significant portion of the pharmaceutical market. Peptides and proteins exhibit highly diverse structures, broad biological activities as hormones, neurotransmitters, structural proteins, metabolic modulators and therefore have a significant role as both therapeutics and biomarkers. Understanding the metabolism of synthetic or biotechnologically derived peptide and protein drugs is critical for pharmaceutical development as metabolism has a significant impact on drug efficacy and safety. Although the same principles of pharmacokinetics and metabolism of small molecule drugs apply to peptide and protein drugs, there are few notable differences. Moreover, the study of peptide and protein drug metabolism is a rather complicated process which requires sophisticated analytical techniques, and mass spectrometry based approaches have provided the capabilities for efficient and reliable quantification, characterization, and metabolite identification. This review article will focus on the current use of mass spectrometry for the study of the metabolism of peptide and protein drugs.

An unexpected link between angiotensinogen and thrombin

Angiotensinogen is well known as source protein for a group of potent vasoactive hormones, however, a discrete biochemical activity of the angiotensinogen body is not known. Here we investigated angiotensinogen from the lamprey Lampetra fluviatilis (L. fluviatilis), an early-diverged vertebrate. The recombinantly produced protein showed progressive inhibitory activity towards human α-thrombin with a second-order rate constant of 2.6×10(4) M(-1) min(-1). Heparin enhanced the reaction rate >800-fold with a bell-shaped dose-response curve and a stoichiometry of inhibition (SI) of 1.3, revealing lamprey angiotensinogen as an effective α-thrombin inhibitor. Genomic, biochemical, and protein sequence data indicate that angiotensinogen and heparin cofactor II (HCII) originated from a common ancestral thrombin antagonist, thus providing insight into an early stage of thrombin control.

Local renin-angiotensin system and the brain--a continuous quest for knowledge

The ancient renin-angiotensin system (RAS) was discovered more than a hundred years ago by identifying the rate-limiting enzyme of the system and its relevance to blood pressure regulation. Forty years ago, Detlev Ganten et al. postulated the existence of a tissue RAS. In these forty years, he kept developing the knowledge of these systems either directly or by training or attracting the interest of many researchers. Through the present review, we try to highlight recent advancements that originated from the postulation of local brain RAS. Although a large amount of knowledge accumulated, this system continues to intrigue and stimulate the interest and imagination of many researchers.

Antidiuretic action of angiotensin II in the river lamprey Lampetra fluviatilis: evidence for endocrine control of kidney function in cyclostomes

Intravenous infusion of angiotensin II ([Asn¹ Val⁵]-Ang II) at 10⁻⁹ mol min⁻¹ kg⁻¹ body mass produced a significant antidiuresis in river lamprey Lampetra fluviatilis, captured during upstream migration and maintained in fresh water. Although the renin-angiotensin hormonal system (RAS) is now recognized in jawless fishes, until this study, the role of homologous Ang II in L. fluviatilis kidney function had not been examined. This study provides the first evidence for an antidiuretic action of Ang II in cyclostomes and, in evolutionary terms, suggests a renal function for the RAS in early vertebrates.

Stanniectomy attenuates the renin–angiotensin response to hypovolemic hypotension in freshwater eels (Anguilla rostrata) but not blood pressure recovery

Plasma Angiotensin II (ANG II) concentrations were measured in SHM (sham-operated 2 weeks) and CSX (corpuscles of Stannius removed 2 weeks) eels before and after the induction of hypovolemic hypotension (HH) by the rapid withdrawal of 8 ml kg bw(-1) of caudal venous blood. Baseline (before exsanguination) plasma ANG II concentrations were similar in SHM and CSX eels (81.3 +/- 18.8 fmol ml(-1) cf. 106 +/- 31.6 fmol ml(-1), respectively) but the elevation in plasma ANG II following HH (1,732 +/- 82 fmol ml(-1)) was attenuated by CSX (368 +/- 127 fmol ml(-1)) showing that the CS are linked to plasma ANG II concentrations. Plasma ANG II in both groups returned to baseline levels within 48 h. Dorsal aortic blood pressures (DABP) were measured in both experimental groups before, and during the 60 min after, blood withdrawal. A 44% decrease in mean DABP was observed in both SHM and CSX eels within 2 min and followed by similar rapid patterns of recovery of systolic, diastolic, and pulse pressures in both groups during the next 60 min showing that short-term recovery of DABP is not CS-dependent. Stanniectomy increased plasma Ca and K(+) and decreased plasma Mg, Na(+), Cl(-) and osmolality which confirms some earlier observations in eels and other freshwater teleosts.

Intestinal anion exchange in marine fish osmoregulation

Despite early reports, dating back three quarters of a century, of high total CO(2) concentrations in the intestinal fluids of marine teleost fishes, only the past decade has provided some insight into the functional significance of this phenomenon. It is now being recognized that intestinal anion exchange is responsible for high luminal HCO(3)(-) and CO(3)(2-) concentrations while at the same time contributing substantially to intestinal Cl(-) and thereby water absorption, which is vital for marine fish osmoregulation. In species examined to date, the majority of HCO(3)(-) secreted by the apical anion exchange process is derived from hydration of metabolic CO(2) with the resulting H(+) being extruded via a Na(+):H(+) exchange mechanism in the basolateral membrane. The basolateral H(+) extrusion is critical for the apical anion exchange and relies on the Na(+) gradient established by the Na(+)-K(+)-ATPase. This enzyme thereby ultimately fuels the secondary active transport of HCO(3)(-) and Cl(-) by the apical anion exchanger. High cellular HCO(3)(-) concentrations (>10 mmol l(-1)) are required for the anion exchange process and could be the result of both a high metabolic activity of the intestinal epithelium and a close association of the anion exchange protein and the enzyme carbonic anhydrase. The anion exchange activity in vivo is likely most pronounced in the anterior segment and results in net intestinal acid absorption. In contrast to other water absorbing vertebrate epithelia, the marine teleost intestine absorbs what appears to be a hypertonic fluid to displace diffusive fluid loss to the marine environment.

Evolutionary aspects of intestinal bicarbonate secretion in fish

Experiments compared intestinal HCO3- secretion in the intestine of marine teleost Gulf toadfish, Opsanus beta, to representatives of early chondrostean and chondrichthyan fishes, the Siberian sturgeon, Acipenser baerii, and white-spotted bamboo shark, Chiloscyllium plagiosum, respectively. As seen in marine teleosts, luminal HCO3- concentrations were 10-fold plasma levels in all species when exposed to hyperosmotic conditions. While intestinal water absorption left Mg2+ and SO4(2-) concentrated in intestinal fluids up to four-fold ambient seawater concentrations, HCO3- was concentrated up to 50 times ambient levels as a result of intestinal HCO3- secretion. Reduced luminal Cl- concentrations in the intestine of all species suggest that HCO3- secretion also occurs via Cl-/HCO3- exchange in chondrostean and chondrichthyan fishes. Sturgeon began precipitating carbonates from the gut after only 3 days at 14 per thousand, a mechanism utilized by marine teleosts to reduce intestinal fluid osmolality and maintain calcium homeostasis. Analysis of published intestinal fluid composition in the cyclostome Lampetra fluviatilis reveals that this species likely also utilize intestinal HCO3- secretion for osmoregulation. Analysis of existing cyclostome data and our results indicate that intestinal Cl-/HCO3- exchange plays an integral role in maintaining hydromineral balance not only in teleosts, but in all fish (and perhaps other animals) with a need to drink seawater.