Acetylcholinesterase inhibitory activity of pigment echinochrome A from sea urchin Scaphechinus mirabilis

Multi-omic analysis reveals genes and proteins integral to bioactivity of Echinochrome A isolated from the waste stream of the sea urchin industry in Aotearoa New Zealand

Evechinus chloroticus (commonly known as kina) is a sea urchin species endemic to New Zealand. Its roe is a culinary delicacy to the indigenous Māori and a globally exported food product. Echinochrome A (Ech A) is a bioactive compound isolated from the waste product of kina shells and spines; however, the molecular mechanisms of Ech A bioactivity are not well understood, partly due to Ech A never being studied using unbiased genome-wide analysis. To explore the high-value pharmaceutical potential of kina food waste, we obtained unbiased functional genomic and proteomic profiles of yeast cells treated with Echinochrome A. Abundance was measured for 4100 proteins every 30 min for four hours using fluorescent microscopy, resulting in the identification of 92 proteins with significant alterations in protein abundance caused by Ech A treatment that were over-represented with specific changes in DNA replication, repair and RNA binding after 30 min, followed by specific changes in the metabolism of metal ions (specifically iron and copper) from 60-240 min. Further analysis indicated that Ech A chelated iron, and that iron supplementation negated the growth inhibition caused by Ech A. Via a growth-based genome-wide analysis of 4800 gene deletion strains, 20 gene deletion strains were sensitive to Ech A in an iron-dependent manner. These genes were over-represented in the cellular response to oxidative stress, suggesting that Ech A suppressed growth inhibition caused by oxidative stress. Unexpectedly, genes integral to cardiolipin and inositol phosphate biosynthesis were required for Ech A bioactivity. Overall, these results identify genes, proteins, and cellular processes mediating the bioactivity of Ech A. Moreover, we demonstrate unbiased genomic and proteomic methodology that will be useful for characterizing bioactive compounds in food and food waste.

Neuroprotective compounds from marine invertebrates

Background

Neuroinflammation is a key pathological feature of a wide variety of neurological disorders, including Parkinson’s, multiple sclerosis, Alzheimer’s, and Huntington’s disease. While current treatments for these disorders are primarily symptomatic, there is a growing interest in developing new therapeutics that target the underlying neuroinflammatory processes.

Main body

Marine invertebrates, such as coral, sea urchins, starfish, sponges, and sea cucumbers, have been found to contain a wide variety of biologically active compounds that have demonstrated potential therapeutic properties. These compounds are known to target various key proteins and pathways in neuroinflammation, including 6-hydroxydopamine (OHDH), caspase-3 and caspase-9, p-Akt, p-ERK, p-P38, acetylcholinesterase (AChE), amyloid-β (Aβ), HSF-1, α-synuclein, cellular prion protein, advanced glycation end products (AGEs), paraquat (PQ), and mitochondria DJ-1.

Short conclusion

This review focuses on the current state of research on the neuroprotective effects of compounds found in marine invertebrates and the potential therapeutic implications of these findings for treating neuroinflammatory disorders. We also discussed the challenges and limitations of using marine-based compounds as therapeutics, such as sourcing and sustainability concerns, and the need for more preclinical and clinical studies to establish their efficacy and safety.

Graphical abstract

Development of Novel Pharmaceutical Forms of the Marine Bioactive Pigment Echinochrome A Enabling Alternative Routes of Administration

Echinochrome A (EchA), a marine bioactive pigment isolated from various sea urchin species, is the active agent of the clinically approved drug Histochrome^®. EchA is currently only available in the form of an isotonic solution of its di- and tri-sodium salts due to its poor water solubility and sensitivity to oxidation. Electrospun polymeric nanofibers have lately emerged as promising drug carriers capable of improving the dissolution and bioavailability of drugs with limited water solubility. In the current study, EchA isolated from sea urchins of the genus Diadema collected at the island of Kastellorizo was incorporated in electrospun micro-/nanofibrous matrices composed of polycaprolactone and polyvinylpyrrolidone in various combinations. The physicochemical properties of the micro-/nanofibers were characterized using SEM, FT-IR, TGA and DSC analyses. The fabricated matrices exhibited variable dissolution/release profiles of EchA, as evidenced in in vitro experiments using gastrointestinal-like fluids (pH 1.2, 4.5 and 6.8). Ex vivo permeability studies using the EchA-loaded micro-/nanofibrous matrices showed an increased permeation of EchA across the duodenum barrier. The results of our study clearly show that electrospun polymeric micro-/nanofibers represent promising carriers for the development of new pharmaceutical formulations with controlled release, as well as increased stability and solubility of EchA, suitable for oral administration, while offering the potential for targeted delivery.

Marine Natural Products from the Russian Pacific as Sources of Drugs for Neurodegenerative Diseases

Neurodegenerative diseases are growing to become one of humanity's biggest health problems, given the number of individuals affected by them. They cause enough mortalities and severe economic impact to rival cancers and infections. With the current diversity of pathophysiological mechanisms involved in neurodegenerative diseases, on the one hand, and scarcity of efficient prevention and treatment strategies, on the other, all possible sources for novel drug discovery must be employed. Marine pharmacology represents a relatively uncharted territory to seek promising compounds, despite the enormous chemodiversity it offers. The current work discusses one vast marine region-the Northwestern or Russian Pacific-as the treasure chest for marine-based drug discovery targeting neurodegenerative diseases. We overview the natural products of neurological properties already discovered from its waters and survey the existing molecular and cellular targets for pharmacological modulation of the disease. We further provide a general assessment of the drug discovery potential of the Russian Pacific in case of its systematic development to tackle neurodegenerative diseases.

In vitro inhibition of acetylcholinesterase activity by yellow field pea (Pisum sativum) protein-derived peptides as revealed by kinetics and molecular docking

Compounds with structural similarities to the neurotransmitter (acetylcholine) are mostly used to inhibit the activity of acetylcholinesterase (AChE) in Alzheimer’s disease (AD) therapy. However, the existing drugs only alleviate symptoms of moderate to mild conditions and come with side effects; hence, the search is still on for potent and safer options. In this study, High performance liquid chromatography (HPLC) fractionations of AChE-inhibitory pea protein hydrolysates obtained from alcalase, flavourzyme and pepsin digestions were carried out followed by sequence identification of the most active fractions using mass spectrometry. Subsequently, 20 novel peptide sequences identified from the active fractions were synthesized and five peptides, QSQS, LQHNA, SQSRS, ETRSQ, PQDER (IC₅₀ = 1.53 – 1.61 μg/mL) were selected and analyzed for ability to change AChE protein conformation (fluorescence emission and circular dichroism), kinetics of enzyme inhibition, and enzyme-ligand binding configurations using molecular docking. The kinetics studies revealed different inhibition modes by the peptides with relatively low (<0.02 mM and <0.1 mM) inhibition constant and Michaelis constant, respectively, while maximum velocity was reduced. Conformational changes were confirmed by losses in fluorescence intensity and reduced α-helix content of AChE after interactions with different peptides. Molecular docking revealed binding of the peptides to both the catalytic anionic site and the peripheral anionic site. The five analyzed peptides all contained glutamine (Q) but sequences with Q in the penultimate N-terminal position (LQHNA, SQSRS, and PQDER) had stronger binding affinity. Results from the different analysis in this study confirm that the peptides obtained from enzymatic digestion of pea protein possess the potential to be used as novel AChE-inhibitory agents in AD management.

Neuroprotective Effect of 1,4-Naphthoquinones in an In Vitro Model of Paraquat and 6-OHDA-Induced Neurotoxicity

Targeted screening using the MTT cell viability test with a mini-library of natural and synthetic 1,4-naphthoquinones and their derivatives was performed in order to increase the survival of Neuro-2a neuroblastoma cells in in vitro paraquat and 6-hydroxydopamine models of Parkinson’s disease. As a result, 10 compounds were selected that could protect neuronal cells from the cytotoxic effects of both paraquat and 6-hydroxydopamine. The five most active compounds at low concentrations were found to significantly protect the activity of nonspecific esterase from the inhibitory effects of neurotoxins, defend cell biomembranes from lytic destruction in the presence of paraquat and 6-hydroxydopamine, and normalize the cell cycle. The protective effects of these compounds are associated with the suppression of oxidative stress, decreased expression of reactive oxygen species and nitric oxide formation in cells and normalization of mitochondrial function, and restoration of the mitochondrial membrane potential altered by neurotoxins. It was suggested that the neuroprotective activity of the studied 1,4-NQs is attributable to their pronounced antioxidant and free radical scavenging activity and their ability to reduce the amount of reactive oxygen species formed by paraquat and 6-hydroxydopamine action on neuronal cells. The significant correlation between the neuroprotective properties of 1,4-naphthoquinones and Quantitative Structure–Activity Relationship descriptors describing the physicochemical properties of these compounds means that the hydrophobicity, polarity, charge, and shape of the molecules can be of decisive importance in determining the biological activity of studied substances.

Sea Urchin Pigments: Echinochrome A and Its Potential Implication in the Cytokine Storm Syndrome

Background: Echinochrome A (EchA) is a pigment from sea urchins. EchA is a polyhydroxylated 1,4-naphthoquinone that contains several hydroxyl groups appropriate for free-radical scavenging and preventing redox imbalance. EchA is the most studied molecule of this family and is an active principle approved to be used in humans, usually for cardiopathies and glaucoma. EchA is used as a pharmaceutical drug. Methods: A comprehensive literature and patent search review was undertaken using PubMed, as well as Google Scholar and Espacenet search engines to review these areas. Conclusions: In the bloodstream, EchA can mediate cellular responses, act as a radical scavenger, and activate the glutathione pathway. It decreases ROS imbalance, prevents and limits lipid peroxidation, and enhances mitochondrial functions. Most importantly, EchA contributes to the modulation of the immune system. EchA can regulate the generation of regulatory T cells, inhibit pro-inflammatory IL-1β and IL-6 cytokine production, while slightly reducing IL-8, TNF-α, INF-α, and NKT, thus correcting immune imbalance. These characteristics suggest that EchA is a candidate drug to alleviate the cytokine storm syndrome (CSS).

Isolation and Structure Determination of Echinochrome A Oxidative Degradation Products

Echinochrome A (Ech A, 1) is one of the main pigments of several sea urchin species and is registered in the Russian pharmacopeia as an active drug substance (Histochrome®), used in the fields of cardiology and ophthalmology. In this study, Ech A degradation products formed during oxidation by O2 in air-equilibrated aqueous solutions were identified, isolated, and structurally characterized. An HPLC method coupled with diode-array detection (DAD) and mass spectrometry (MS) was developed and validated to monitor the Ech A degradation process and identify the appearing compounds. Five primary oxidation products were detected and their structures were proposed on the basis of high-resolution electrospray ionization mass spectrometry (HR-ESI-MS) as 7-ethyl-2,2,3,3,5,7,8-heptahydroxy-2,3-dihydro-1,4-naphthoquinone (2), 6-ethyl-5,7,8-trihydroxy-1,2,3,4-tetrahydronaphthalene-1,2,3,4-tetraone (3), 2,3-epoxy-7-ethyl-2,3-dihydro-2,3,5,6,8-pentahydroxy-1,4-naphthoquinone (4), 2,3,4,5,7-pentahydroxy-6-ethylinden-1-one (5), and 2,2,4,5,7-pentahydroxy-6-ethylindane-1,3-dione (6). Three novel oxidation products were isolated, and NMR and HR-ESI-MS methods were used to establish their structures as 4-ethyl-3,5,6-trihydroxy-2-oxalobenzoic acid (7), 4-ethyl-2-formyl-3,5,6-trihydroxybenzoic acid (8), and 4-ethyl-2,3,5-trihydroxybenzoic acid (9). The known compound 3-ethyl-2,5-dihydroxy-1,4-benzoquinone (10) was isolated along with products 7-9. Compound 7 turned out to be unstable; its anhydro derivative 11 was obtained in two crystal forms, the structure of which was elucidated using X-ray crystallography as 7-ethyl-5,6-dihydroxy-2,3-dioxo-2,3-dihydrobenzofuran-4-carboxylic acid and named echinolactone. The chemical mechanism of Ech A oxidative degradation is proposed. The in silico toxicity of Ech A and its degradation products 2 and 7-10 were predicted using the ProTox-II webserver. The predicted median lethal dose (LD50) value for product 2 was 221 mg/kg, and, for products 7-10, it appeared to be much lower (≥2000 mg/kg). For Ech A, the predicted toxicity and mutagenicity differed from our experimental data.

Cytoprotective Effect of Echinochrome A in Primary Culture of Pulmonary Fibroblasts from Albino Rats under Conditions of Oxidative Stress

We studied the effect of echinochrome A on the primary culture of pulmonary fibroblasts under normal conditions and under oxidative stress. Exposure to echinochrome A (100 μM, 6 h) did not affect the production of superoxide radical by fibroblasts, area of their nuclei, and number of nucleoli, but reduced the total area of nucleolar organizer regions against the background of stable proliferative activity of the culture. Two-hour oxidative stress induced by hydrogen peroxide solution (60 μM) increased the generation of superoxide radical, decreased DNA-synthetic activity of fibroblasts, area of fibroblast nuclei, and total area of nucleolar organizer regions. Preliminary administration of echinochrome A significantly attenuated the damaging effect of oxidative stress: the intensity of production of superoxide radicals decreased, DNA-synthetic activity and nucleus area of fibroblasts partially recovered; normalization of the total area of nucleoli was accompanied by an increase in their number.

Marine Pharmacology in 2014-2015: Marine Compounds with Antibacterial, Antidiabetic, Antifungal, Anti-Inflammatory, Antiprotozoal, Antituberculosis, Antiviral, and Anthelmintic Activities; Affecting the Immune and Nervous Systems, and Other Miscellaneous Mechanisms of Action

The systematic review of the marine pharmacology literature from 2014 to 2015 was completed in a manner consistent with the 1998-2013 reviews of this series. Research in marine pharmacology during 2014-2015, which was reported by investigators in 43 countries, described novel findings on the preclinical pharmacology of 301 marine compounds. These observations included antibacterial, antifungal, antiprotozoal, antituberculosis, antiviral, and anthelmintic pharmacological activities for 133 marine natural products, 85 marine compounds with antidiabetic, and anti-inflammatory activities, as well as those that affected the immune and nervous system, and 83 marine compounds that displayed miscellaneous mechanisms of action, and may probably contribute to novel pharmacological classes upon further research. Thus, in 2014-2015, the preclinical marine natural product pharmacology pipeline provided novel pharmacology as well as new lead compounds for the clinical marine pharmaceutical pipeline, and thus continued to contribute to ongoing global research for alternative therapeutic approaches to many disease categories.

Natural cholinesterase inhibitors from marine organisms

Covering: Published between 1974 up to 2018Inhibition of cholinesterases is a common approach for the management of several disease states. Most notably, cholinesterase inhibitors are used to alleviate the symptoms of neurological disorders like dementia and Alzheimer's disease and treat myasthenia gravis and glaucoma. Historically, most drugs of natural origin have been isolated from terrestrial sources and inhibitors of cholinesterases are no exception. However, the last 50 years have seen a rise in the quantity of marine natural products with close to 25 000 reported in the scientific literature. A number of marine natural products with potent cholinesterase inhibitory properties have also been reported; isolated from a variety of marine sources from algae to ascidians. Representing a diverse range of structural classes, these compounds provide inspirational leads that could aid the development of therapeutics. The current paper aims to, for the first time, comprehensively summarize the literature pertaining to cholinesterase inhibitors derived from marine sources, including the first papers published in 1974 up to 2018. The review does not report bioactive extracts, only isolated compounds, and a specific focus lies on compounds with reported dose-response data. In vivo and mechanistic data is included for compounds where this is reported. In total 185 marine cholinesterase inhibitors and selected analogs have been identified and reported and some of the compounds display inhibitory activities comparable or superior to cholinesterase inhibitors in clinical use.

Free Radical Scavenging Activity of Synthetic and Naturally Occurring Polyhydroxy-, Aminohydroxynaphthazarins and Related Compounds

Fifty natural and synthetic hydroxy-, aminohydroxynaphthazarins and related quinones were tested for their antiradical activities using 2,2'-azinobis(3-ethylbenzothiazoline-6-sulfonate) (ABTS) scavenging assay. The main features of structure-antiradical activity relationship of amino- and hydroxyquinones were determined for the first time. It was found that naphthazarins (5,8-dihydroxy-1,4-naphthoquinones) are much more active against ABTS-radical than related 1,4-naphthoquinones and 5-hydroxy-1,4-naphthoquinones. Natural aminonaphthazarins (spinamine E, echinamine A) and polyhydroxylated naphthazarins (spinazarin, echinochrome, spinochrome D and E) revealed high antiradical properties. In most cases, the presence of long chained O-alkoxy substituent in benzenoid part of naphthazarin core enhanced their antiradical activity.

Naphthoquinones of the spinochrome class: occurrence, isolation, biosynthesis and biomedical applications

Quinones are widespread in nature and have been found in plants, fungi and bacteria, as well as in members of the animal kingdom. More than forty closely related naphthoquinones have been found in echinoderms, mainly in sea urchins but occasionally in brittle stars, sea stars and starfish. This review aims to examine controversial issues on the chemistry, biosynthesis, functions, stability and application aspects of the spinochrome class, a prominent group of secondary metabolites found in sea urchins. The emphasis of this review is on the isolation and structure of these compounds, together with evaluation of their relevant biological activities, source organisms, the location of origin and methods used for isolation and identification. In addition, the studies of their biosynthesis and ecological function, stability and chemical synthesis have been highlighted. This review aims to establish a focus for future spinochrome research and its potential for benefiting human health and well-being.

Marine Waste Utilization as a Source of Functional and Health Compounds

Consumer demand for convenience has led to large quantities of seafood being value-added processed before marketing, resulting in large amounts of marine by-products being generated by processing industries. Several bioconversion processes have been proposed to transform some of these by-products. In addition to their relatively low value conventional use as animal feed and fertilizers, several investigations have been reported that have demonstrated the potential to add value to viscera, heads, skins, fins, trimmings, and crab and shrimp shells by extraction of lipids, bioactive peptides, enzymes, and other functional proteins and chitin that can be used in food and pharmaceutical applications. This chapter is focused on reviewing the opportunities for utilization of these marine by-products. The chapter discusses the various products and bioactive compounds that can be obtained from seafood waste and describes various methods that can be used to produce these products with the aim of highlighting opportunities to add value to these marine waste streams.

The Roles of Spinochromes in Four Shallow Water Tropical Sea Urchins and Their Potential as Bioactive Pharmacological Agents

Spinochromes are principally known to be involved in sea urchin pigmentation as well as for their potentially interesting pharmacological properties. To assess their biological role in sea urchin physiology, experiments are undertaken on crude extracts from four species and on four isolated spinochromes in order to test their antibacterial, antioxidant, inflammatory and cytotoxic activities. First, the antibacterial assays show that the use of crude extracts as representatives of antibacterial effects of spinochromes are inaccurate. The assays on purified spinochromes showed a decrease in the growth of four strains with an intensity depending on the spinochromes/bacteria system, revealing the participation of spinochromes in the defense system against microorganisms. Secondly, in the 2,2-diphenyl-1-picrylhydrazyl antioxidant assays, spinochromes show an enhanced activity compared to the positive control. This latter observation suggests their involvement in ultraviolet radiation protection. Third, spinochromes present a pro-inflammatory effect on lipopolysaccharide-stimulated macrophages, highlighting their possible implication in the sea urchin immune system. Finally, cytotoxicity assays based on Trypan blue exclusion, performed in view of their possible future applications as drugs, show a weak cytotoxicity of these compounds against human cells. In conclusion, all results confirm the implication of spinochromes in sea urchin defense mechanisms against their external environment and reveal their potential for pharmacological and agronomical industries.

Inhibitory Effects of Echinochrome A, Isolated from Shell of the Sea Urchin Anthocidaris crassispina, on Antigen-Stimulated Degranulation in Rat Basophilic Leukemia RBL-2H3 Cells through Suppression of Lyn Activation

Echinochrome A (Echi-A) was isolated from the sea urchin Anthocidaris crassispina and its structure determined using 1D and 2D-NMR. In the present study, we examined the inhibitory effect of Echi-A on antigen-stimulated degranulation in rat basophilic leukemia RBL-2H3 cells, which were suppressed in a dose dependent manner. The antigens bind to the high affinity immunoglobulin E receptor, which is expressed on the surface of mast cells and basophils and activate intracellular signal transduction, resulting in the release of biologically active mediators such as histamine. In order to disclose the inhibitory mechanisms of degranulation by Echi-A, we examined the elevation in intracellular Ca2+ concentration ([Ca2+]i), production levels of intracellular reactive oxygen species (ROS) and early intracellular signaling events. Both elevation of [Ca2+]i and intracellular ROS production were markedly suppressed in cells treated with Echi-A. Echi-A also suppressed the activation of Lyn, Syk, and PLCγ1/2 in antigen-stimulated cells. These results indicated that inhibition of antigen-stimulated degranulation in RBL-2H3 cells by Echi-A is mainly due to the inactivation of Lyn/Syk/PLCγ signaling pathways. Our findings suggest that Echi-A could be a beneficial agent for alleviating the symptoms of type I allergy.

New Aminonaphthoquinone from the Sea Urchins Strongylocentrotus pallidus and Mesocentrotus nudus

The aminonaphthoquinone, spinamine E (5), was isolated for the first time from the sea urchins Strongylocentrotus pallidus (Sars G.O., 1872) and Mesocentrotus nudus (A. Agassiz, 1864). The structure of 5 was elucidated as 2-amino-3,5,6,7,8-pentahydroxy-l,4-naphthoquinone using 1D 1H-, 13C- and 2D NMR procedures, and HR-ESI mass-spectrometric data of 5 and its trimethyl ether. Spinamine E, as well as two other aminonaphthoquinones of sea urchins, echinamines A (2) and B (3), along with their hydroxylated analogues, spinochrome E (4) and echinochrome A (1), were tested for their ability to scavenge the stable DPPH radical and to inhibit lipid peroxidation. All investigated naphthoquinones obtained from the sea urchins showed a high antiradical activity, which was up to 1.5 times higher than that of α-tocopherol. Echinamine B showed the highest scavenging effect (EC50 = 6.5-10−6 M); this effect decreases in the series 3>5>1>2>4>α-tocopherol. In a lipid peroxidation inhibition testing model, echinamine B and spinamine E showed the highest inhibitory effect. The stability of compounds 1-5 in weakly alkaline solutions was evaluated.

Marine natural products

This review covers the literature published in 2014 for marine natural products (MNPs), with 1116 citations (753 for the period January to December 2014) referring to compounds isolated from marine microorganisms and phytoplankton, green, brown and red algae, sponges, cnidarians, bryozoans, molluscs, tunicates, echinoderms, mangroves and other intertidal plants and microorganisms. The emphasis is on new compounds (1378 in 456 papers for 2014), together with the relevant biological activities, source organisms and country of origin. Reviews, biosynthetic studies, first syntheses, and syntheses that lead to the revision of structures or stereochemistries, have been included.

Echinochrome A Improves Exercise Capacity during Short-Term Endurance Training in Rats

Echinochrome A (Echi A) improves mitochondrial function in the heart; however, its effects on skeletal muscle are still unclear. We hypothesized that Echi A administration during short-term exercise may improve exercise capacity. Twenty-four male Sprague-Dawley rats were randomly divided into the following groups: control group (CG), Echi A-treated group (EG), aerobic exercise group (AG), and aerobic exercise treated with Echi A group (AEG) (n = 6 per group). Echi A was administered intra-peritoneally (0.1 mg/kg of Echi A in 300 µL phosphate-buffered saline) daily 30 min before each exercise training. The AG and AEG groups performed treadmill running (20 m/min, 60 min/day) five days/week for two weeks. The exercise capacity was significantly higher in the AG and AEG groups compared to other groups. Interestingly, the exercise capacity increased more effectively in the AEG group. The body weight in the EG tended to be slightly lower than that in the other groups. There were no significant changes in the plasma lipids among the groups. However, the gastrocnemius muscle mitochondria content was greater in the EG and AEG groups. These findings show that Echi A administration after short-term endurance training enhances exercise capacity, which was associated with an increase in skeletal muscle mitochondrial content.

Echinochrome A regulates phosphorylation of phospholamban Ser16 and Thr17 suppressing cardiac SERCA2A Ca²⁺ reuptake

Echinochrome A (Ech A), a marine bio-product isolated from sea urchin eggs, is known to have cardioprotective effects through its strong antioxidant and ATP-sparing capabilities. However, the effects of Ech A on cardiac excitation-contraction (E-C) are not known. In this study, we investigated the effects of Ech A on cardiac contractility and Ca(2+) handling in the rat heart. In ex vivo Langendorff hearts, Ech A (3 μM) decreased left ventricular developing pressure to 77.7 ± 6.5 % of basal level. In isolated ventricular myocytes, Ech A reduced the fractional cell shortening from 3.4 % at baseline to 2.1 %. Ech A increased both diastolic and peak systolic intracellular Ca(2+) ([Ca(2+)]i). However, the ratio of peak [Ca]i to resting [Ca]i was significantly decreased. Ech A did not affect the L-type Ca(2+) current. Inhibiting the Na(+)/Ca(2+) exchanger with either NiCl2 or SEA400 did not affect the Ech A-dependent changes in Ca(2+) handling. Our data demonstrate that treatment with Ech A results in a significant reduction in the phosphorylation of phospholamban at both serine 16 and threonine 17 leading to a significant inhibition of SR Ca(2+)-ATPase 2A (SERCA2A) and subsequent reduced Ca(2+) uptake into the intracellular Ca(2+) store. Taken together, our data show that Ech A negatively regulates cardiac contractility by inhibiting SERCA2A activity, which leads to a reduction in internal Ca(2+) stores.