In vitro iron enrichment experiments in the Prydz Bay, the Southern Ocean: A test of the iron hypothesis

In "high nitrate, low chlorophyll" (HNLC) ocean regions, iron has been typically regarded as the limiting factor for phytoplankton production. This "iron hypothesis" needs to be tested in various oceanic environments to understand the role of iron in marine biological and biogeochemical processes. In this paper, three in vitro iron enrichment experiments were performed in Prydz Bay and at the Polar Front north of the Ross Sea, to study the role of iron on phytoplankton production. At the Polar Front of Ross Sea, iron addition significantly (P < 0.05, Student's t-test) stimulated phytoplankton growth. In Prydz Bay, however, both the iron treatments and the controls showed rapid phytoplankton growth, and no significant effect (P > 0.05, Student's t-test) as a consequence of iron addition was observed. These results confirmed the limiting role of iron in the Ross Sea and indicated that iron was not the primary factor limiting phytoplankton growth in Prydz Bay. Because the light environment for phytoplankton was enhanced in experimental bottles, light was assumed to be responsible for the rapid growth of phytoplankton in all treatments and to be the limiting factor controlling field phytoplankton growth in Prydz Bay. During the incubation experiments, nutrient consumption ratios also changed with the physiological status and the growth phases of phytoplankton cells. When phytoplankton growth was stimulated by iron addition, N was the first and Si was the last nutrient which absorption enhanced. The Si/N and Si/P consumption ratios of phytoplankton in the stationary and decay phases were significantly higher than those of rapidly growing phytoplankton. These findings were helpful for studies of the marine ecosystem and biogeochemistry in Prydz Bay, and were also valuable for biogeochemical studies of carbon and nutrients in various marine environments.

Preparation and in vitro antioxidant activity of kappa-carrageenan oligosaccharides and their oversulfated, acetylated, and phosphorylated derivatives

In order to study the relationship between chemical structure and properties of modified carrageenans versus antioxidant activity in vitro, K-carrageenan oligosaccharides were prepared through mild hydrochloric acid hydrolysis of the polysaccharide, and these were used as starting materials for the partial synthesis of their oversulfated, acetylated, and phosphorylated derivatives. The structure and substitution pattern of the oligosaccharides and their derivatives were Studied using FTIR and C-13 NMR spectroscopy, and their in vitro antioxidant activities were investigated. Certain derivatives of the carrageenan oligosaccharides exhibited higher antioxidant activity than the polysaccharides and oligosaccharides in certain antioxidant systems. The oversulfated and acetylated derivatives, which scavenge superoxide radicals, the phosphorylated and low-DS acetylated derivatives, which scavenge hydroxyl radicals, and the phosphorylated derivatives, which scavenge DPPH radicals, all exhibited significant antioxidant activities it, the systems examined. The effect of the molecular weight of the carrageenan on antioxidant activities, however, is not obvious from these studies. (c) 2005 Elsevier Ltd. All rights reserved.

Preparation, structural characterization and in vitro antitumor activity of kappa-carrageenan oligosaccharide fraction from Kappaphycus striatum

Oligosaccharides were prepared through mild hydrochloric acid hydrolysis of kappa-carrageenan from Kappaphycus striatum to compare the antitumor activity with carrageenan polysaccharides. Oligosaccharide fractions were isolated by gel permeation chromatography and the structure of fraction 1 (F1) was studied by using negative- ion electrospray ionization-mass spectrometry (ESI-MS), and H-1 and C-13-NMR spectrometry. The in vitro antitumor effects in three human neoplastic cell lines (KB, BGC, and Hela) of polysaccharides and F1 were investigated. The bioassay results showed that F1 exhibited relatively higher antitumor activity against the three cancer cells than polysaccharides.

In vitro determination of antioxidant activity of proteins from jellyfish Rhopilema esculentum

In this study, the antioxidant activity of proteins isolated from jellyfish, Rhopilema esculentum Kishinouye (R. esculentum), was determined by various antioxidant assays, including superoxide anion radical-scavenging, hydroxyl radical-scavenging, total antioxidant activity, reducing power and metal chelating activity. Butylated hydroxyanisole (BHA), butylated hydroxytoluene (BHT), alpha-tocopherol, vitamin C and mannitol were used as standards in those various antioxidant activities. The crude protein (CP) and the protein fractions isolated by Sephadex chromatography, first peak (FP) and second peak (SP), had very low reductive power and metal chelating abilities compared to EDTA, but they showed strong scavenging effects on the superoxide anion radical, hydroxyl radical and varying total antioxidant activity. FP and SP exhibited stronger scavenging effects on the superoxide anion radical than BHA, BHT or a-tocopherol. The EC50 values of FP and SP were 6.12 and 0.88 mu g/ml, respectively, while values EC50 of BHA, BHT and alpha-tocopherol were 31, 61 and 88 mu g/ml, respectively. CP, FP and SP showed far higher hydroxyl radical-scavenging activities than did vitamin C or mannitol. The EC50 values of CP, FP and SP were 48.76, 45.42 and 1.52 mu g/ml, but EC50 values of vitamin C and mannitol were 1907 and 4536 mu g/ml, respectively. In a beta-carotene-linoleate system, SP and CP showed antioxidant activity, but lower than BHA. Of the three samples, SP had the strongest antioxidant activity. So, SP may have a use as a possible supplement in the food and pharmaceutical industries. (c) 2005 Elsevier Ltd. All rights reserved.

Fucoidan protects against dopaminergic neuron death in vivo and in vitro

Parkinson's disease is a neurodegenerative disorder of uncertain pathogenesis characterized by a loss of dopaminergic neurons in substantia nigra pars compacta, and can be modeled by the neurotoxin 1-methyl-4-phenyl-1, 2, 3, 6-tetrahydropyridine (MPTP). Oxidative stress may contribute to MPTP- and Parkinson's disease-related neurodegeneration. Fucoidan is a sulfated polysaccharide extracted from brown seaweeds which possesses a wide variety of biological activities including potent antioxidative effects. Here we investigated the effect of fucoidan treatment on locomoter activities of animals, striatal dopamine and its metabolites and survival of nigral dopaminergic neurons in MPTP-induced animal model of Parkinsonism in C57/BL mice in vivo and on the neuronal damage induced by 1-methyl-4-phenylpyridinium (MPP+) in vitro, and to study the possible mechanisms. When administered prior to MPTP, fucoidan reduced behavioral deficits, increased striatal dopamine and its metabolites levels, reduced cell death, and led to a marked increase in tyrosine hydroxylase expression relative to mice treated with MPTP alone. Furthermore, we found that fucoidan inhibited MPTP-induced lipid peroxidation and reduction of antioxidant enzyme activity. In addition, pre-treatment with fucoidan significantly protected against MPP+-induced damage in MN9D cells. Taken together, these findings suggest that fucoidan has protective effect in MPTP-induced neurotoxicity in this model of Parkinson's disease via its antioxidative activity. (C) 2009 Elsevier B.V. All rights reserved.

Synthesized different derivatives of low molecular fucoidan extracted from Laminaria japonica and their potential antioxidant activity in vitro

Six low molecular fucoidan (DFPS) derivatives were synthesized successfully, and their potential antioxidant activities were investigated employing various established in vitro systems. All DFPS derivatives possessed considerable antioxidant activity, and had stronger antioxidant ability than DFPS in certain tests. The benzoylated DFPS (PHDF) showed strongest scavenging activity on superoxide, hydroxyl and 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical, however, DFPS exhibited greatest reducing power. Available data suggested that substituted groups of DFPS played an important role on antioxidant activity, and the mechanism on influence the antioxidant activity of samples of substituted group was indicated. (C) 2009 Elsevier B.V. All rights reserved.

Synthesized oversulphated, acetylated and benzoylated derivatives of fucoidan extracted from Laminaria japonica and their potential antioxidant activity in vitro

Three sulphated polysaccharide derivatives (oversulphated, acetylated and benzoylated fucoidan) were successfully synthesized, and their antioxidant activities were investigated employing various established in vitro systems. A novel catalyst N-bromosuccinimide (NBS) was used in acetylation and benzoylation reaction, and the degree of acetylation was evaluated using IR and NMR spectra. Both fucoidan derivatives possessed considerable antioxidant activity, and had stronger antioxidant ability than fucoidan in certain tests. The benzoylated fucoidan showed strongest superoxide and hydroxyl radical scavenging activity, however, the acetylated fucoidan exhibited strongest activity on scavenging DPPH radical and reducing power. Available data obtained with in vitro models suggested that substituted groups of fucoidan played an important role on antioxidant activity. The mechanism on the antioxidant activity of sulphonyl, acetyl and benzoyl group is different. (C) 2008 Elsevier Ltd. All rights reserved.

Synthesized phosphorylated and aminated derivatives of fucoidan and their potential antioxidant activity in vitro

Three sulfated polysaccharide derivatives (phosphorylated and aminated fucoidan) were synthesized, and their potential antioxidant activities were investigated employing various established in vitro systems. Two methods were used in phosphorylation fucoidan: polyphosphoric acid and POCl3 method. Aminated fucoidan was prepared using the epichlorohydrin and ammonia water. All fucoidan derivatives possessed considerable antioxidant activity, and exhibited stronger antioxidant ability than fucoidan in certain tests. The phosphorylated fucoidan showed stronger hydroxyl radical and 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging activity and reducing power. The mechanism on influence the antioxidant activity of samples of phosphate and amino group was indicated. (C) 2008 Elsevier B.V. All rights reserved.

In vitro antioxidant activities of acetylated, phosphorylated and benzoylated derivatives of porphyran extracted from Porphyra haitanensis

Porphyran extracted from red algae Porphyra haitanensis is a sulfated polysaccharide, which possesses excellent antioxidant activities. In this study, we prepared the acetylated, phosphorylated and benzoylated derivatives of porphyran. And then the antioxidant activities of all the samples were investigated including scavenging effects of superoxide and hydroxyl radicals and reducing power. The results of chemical analysis and FT-IR spectrum showed the modifications of porphyran were successful. And in addition, we found that certain derivative exhibited stronger antioxidant activity than raw material. And the mechanism of the structure-function relationship of these derivatives needs to be attended to. (C) 2009 Elsevier Ltd. All rights reserved.

Preparation of the different derivatives of the low-molecular-weight porphyran from Porphyra haitanensis and their antioxidant activities in vitro

Porphyran extracted from Porphyra haitanensis is a sulfated polysaccharide, which possesses excellent antioxidant activities. In this study, we prepared one low-molecular-weight porphyran and its sulfated, acetylated, phosphorylated and benzoylated derivatives. Their antioxidant activities were investigated including scavenging effect of superoxide, hydroxyl and 1,1-diphenyl-2-picrylhydrazyl radicals. The results of chemical analysis and FT-IR spectrums showed the modification was successful. And in addition, we found that certain derivative exhibited stronger antioxidant activity than low-molecular-weight porphyran. The benzoylated derivative showed the most excellent antioxidant activity in three assays, so this derivative needs to be attended to. (C) 2009 Elsevier B.V. All rights reserved.

Antioxidant activity of different sulfate content derivatives of polysaccharide extracted from Ulva pertusa (Chlorophyta) in vitro

Polysaccharide extracted from Ulva pertusa (Chlorophyta) is a group of sulfated heteropolysaccharide; for simplicity, the sulfated polysaccharide is referred to as ulvan in this paper. In this study, different sulfate content ulvans were prepared with sulfur trioxide/N,N-diinethylformamide (SO3-DMF) in formamide, and their antioxidant activities were investigated including scavenging activity of superoxide and hydroxyl radicals, reducing Power and metal chelating ability. As expected, we obtained several satisfying results, as follows: firstly, high sulfate content ulvans had more effective scavenging activity on hydroxyl radical than natural ulvan. Secondly, comparing with natural ulvan, high sulfate content ulvans exhibited stronger reducing power. Thirdly, HU4 (sulfate content, 30.8%) and HU5 (sulfate content, 32.8%) showed more pronounce chelating ability on ferrous ion at high concentration than other samples. (c) 2005 Elsevier B.V. All rights reserved.

Preparation of high-molecular weight and high-sulfate content chitosans and their potential antioxidant activity in vitro

The influence of molecular weight and substitution degree of sulfated polysaccharides on their biological activity is considered in majority of works involving the anticoagulant or antiviral properties of these substances. Therefore, the present paper describes the effect of preparation conditions of sulfated chitosans on their molecular weight and sulfur content, such as different reaction time, acid solvent and temperature. Foregoing literature expounded the action of dichloroacetic acid (DCAA) as acid solvent in homogeneous reaction. However, DCAA is expensive and noxious, therefore, in the present paper cheap and non-noxious formic acid (88%) was in place of DCAA. Furthermore, during reaction formic acid was not dehydrated. Under formic acid we obtained the satisfying results that was higher yield and equivalent sulfur contents compared to DCAA. IR and C-13 NMR spectrums proved the structure of the resultant obtained under formic acid or DCAA to be same. Now, it has not been reported for formic acid as acid solvent in homogeneous reaction of chitosan sulfatation. In this present paper, we also determined antioxidant activity of high-molecular weight and high-sulfate-content chitosans (HCTS). The results showed that HCTS could scavenge superoxide and hydroxyl radical. Its IC50 is 0.012 and 3.269 mg/mL, respectively. It had obviously reducing power and slight chelating activity. The data obtained in in vitro models clearly establish the antioxidant potency of HCTS. It is a potential antioxidant in vitro. (C) 2005 Elsevier Ltd. All rights reserved.

Preparation of low-molecular-weight and high-sulfate-content chitosans under microwave radiation and their potential antioxidant activity in vitro

In the present paper microwave radiation has been used to introduce N-sulfo and O-sulfo groups into chitosan with a thigh degree of substitution and low-molecular weight. The sulfation of chitosan was performed in microwave ovens. It was found that microwave heating is a convenient way to obtain a wide range of products of different degrees of substitution and molecular weight only by changing reaction time or/and radiation power. Moreover, microwave radiation accelerated the degradation of sulfated chitosan, and the molecular weight of sulfated chitosan was considerably lower than that obtained by traditional heating. There are no differences in the chemical structure of sulfated chitosan obtained by microwave and by conventional technology. FTIR and C-13 NMR spectral analyses demonstrated that a significantly shorter time is required to obtain a satisfactory degree of substitution and molecular weight by microwave radiation than by conventional technology. In this present paper, we also determined antioxidant activity of low-molecular-weight and high-sulfate-content chitosans (LCTS). The results showed LCTS could scavenge superoxide and hydroxyl radical. Its IC50 is 0.025 and 1.32mg/mL, respectively. It is a potential antioxidant in vitro. (C) 2004 Published by Elsevier Ltd.

Preparation of 1,3,5-thiadiazine-2-thione derivatives of chitosan and their potential antioxidant activity in vitro

Three new kinds of 1,3,5-thiadiazine-2-thi one derivatives of chitosan with two different molecular weight (SATTCS1, SATTCS2, TITTCS1, TITTCS2, CITTCS1 and CITTCS2) have been prepared. Their structures were characterized by IR spectroscopy. The substitution degree of derivatives calculated by elemental analyses was 0.47, 0.42, 0.41, 0.38, 0.41 and 0.36, respectively. The result shows that substitution degree of derivatives was higher with lower molecular weight. The antioxidant activity was studied using an established system, such as bydroxyl radical scavenging, superoxide radical scavenging and reducing power. Antioxidant activity of the 1,3,5-thiadiazine-2-thione derivatives of chitosan were stronger than that of chitosans and antioxiclant activity of low molecular weight derivatives were stronger than that of high molecular weight derivatives. It is a potential antioxidant in vitro. (c) 2007 Elsevier Ltd. All rights reserved.

Synthesis of acyl thiourea derivatives of chitosan and their antimicrobial activities in vitro

Three different acyl thiourea derivatives of chitosan (CS) were synthesized and their structures were characterized by FT-IR spectroscopy and elemental analysis. The antimicrobial behaviors of CS and its derivatives against four species of bacteria (Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus, and Sarcina) and four crop-threatening pathogenic fungi (Alternaria solani, Fusarium oxysporum f. sp. vasinfectum, Colletotrichum gloeosporioides (Penz.) Saec, and Phyllisticta zingiberi) were investigated. The results indicated that the antimicrobial activities of the acyl thiourea derivatives are much better than that of the parent CS. The minimum value of MIC and MBC of the derivatives against E coli was 15.62 and 62.49 mu g/mL, respectively. All of the acyl thiourea derivatives had a significant inhibitory effect on the fungi in concentrations of 50 - 500 mu g/mL; the maximum inhibitory index was 66.67%. The antifungal activities of the chloracetyl thiourea derivatives of CS are noticeably higher than the acetyl and benzoyl thiourea derivatives. The degree of grafting of the acyl thiourea group in the derivatives was related to antifungal activity; higher substitution resulted in stronger antifungal activity. (c) 2007 Elsevier Ltd. All rights reserved.