ABSTRACT
Single-cell RNA sequencing (scRNA-seq) has contributed to understanding cellular heterogeneity and immune profiling in cancer. The aim of the study was to investigate gene expression and immune profiling in colorectal cancer (CRC) using scRNA-seq. We analyzed single-cell gene expression and T cell receptor (TCR) sequences in 30 pairs of CRC and matched normal tissue. Intratumoral lymphocytes were measured with digital image analysis. CRC had more T cells, epithelial cells, and myeloid cells than normal colorectal tissue. CRCs with microsatellite instability had more abundant T cells than those without microsatellite instability. Immune cell compositions of CRC and normal colorectal tissue were inversely correlated. CD4 + or CD8 + proliferating T cells, CD4 + effector memory T cells, CD8 + naïve T cells, and regulatory T cells of CRC showed higher TCR clonal expansion. Tumor epithelial cells interacted with immune cells more strongly than normal. T cells, myeloid cells, and fibroblasts from CRCs of expanded T cell clonotypes showed increased expression of genes related to TNF and NFKB signaling and T cell activation. CRCs of expanded T cell clonotypes also showed stronger cellular interactions among immune cells, fibroblasts, and endothelial cells. Pro-inflammatory CXCL and TNF signaling were activated in CRCs of expanded T cell clonotype. In conclusion, scRNA-seq analysis revealed different immune cell compositions, differential gene expression, and diverse TCR clonotype dynamics in CRC. TCR clonality expansion is associated with immune activation through T cell signaling and chemokine signaling. Patients with CRCs of expanded clonotype can be promising candidates for immunotherapy.
ABSTRACT
The lack of an appropriate preclinical model of metabolic dysfunction-associated steatotic liver disease (MASLD) that recapitulates the whole disease spectrum impedes exploration of disease pathophysiology and the development of effective treatment strategies. Here, we develop a mouse model (Streptozotocin with high-fat diet, STZ + HFD) that gradually develops fatty liver, metabolic dysfunction-associated steatohepatitis (MASH), hepatic fibrosis, and hepatocellular carcinoma (HCC) in the context of metabolic dysfunction. The hepatic transcriptomic features of STZ + HFD mice closely reflect those of patients with obesity accompanying type 2 diabetes mellitus, MASH, and MASLD-related HCC. Dietary changes and tirzepatide administration alleviate MASH, hepatic fibrosis, and hepatic tumorigenesis in STZ + HFD mice. In conclusion, a murine model recapitulating the main histopathologic, transcriptomic, and metabolic alterations observed in MASLD patients is successfully established.
Subject(s)
Carcinoma, Hepatocellular , Diet, High-Fat , Disease Models, Animal , Liver Neoplasms , Animals , Carcinoma, Hepatocellular/metabolism , Carcinoma, Hepatocellular/pathology , Carcinoma, Hepatocellular/genetics , Male , Liver Neoplasms/metabolism , Liver Neoplasms/pathology , Liver Neoplasms/genetics , Mice , Diet, High-Fat/adverse effects , Mice, Inbred C57BL , Humans , Liver/metabolism , Liver/pathology , Fatty Liver/metabolism , Fatty Liver/pathology , Streptozocin , Liver Cirrhosis/metabolism , Liver Cirrhosis/pathology , Transcriptome , Obesity/metabolism , Obesity/complications , Diabetes Mellitus, Type 2/complications , Diabetes Mellitus, Type 2/metabolism , Non-alcoholic Fatty Liver Disease/metabolism , Non-alcoholic Fatty Liver Disease/pathology , Non-alcoholic Fatty Liver Disease/complicationsABSTRACT
Our study aimed to expand tumor-infiltrating lymphocytes (TILs) from primary non-small cell lung cancers (NSCLCs) and evaluate their reactivity against tumor cells. We expanded TILs from 103 primary NSCLCs using histopathological analysis, flow cytometry, IFN-γ release assays, cell-mediated cytotoxicity assays, and in vivo efficacy tests. TIL expansion was observed in all cases, regardless of EGFR mutation status. There was also an increase in the median CD4+/CD8+ ratio during expansion. In post-rapid expansion protocol (REP) TILs, 13 out of 16 cases, including all three cases with EGFR mutations, exhibited a two-fold or greater increase in IFN-γ secretion. The cytotoxicity assay revealed enhanced tumor cell death in three of the seven cases, two of which had EGFR mutations. In vivo functional testing in a patient-derived xenograft model showed a reduction in tumor volume. The anti-tumor activity of post-REP TILs underscores their potential as a therapeutic option for advanced NSCLC, irrespective of mutation status.
Subject(s)
Carcinoma, Non-Small-Cell Lung , ErbB Receptors , Lung Neoplasms , Lymphocytes, Tumor-Infiltrating , Mutation , Carcinoma, Non-Small-Cell Lung/genetics , Carcinoma, Non-Small-Cell Lung/immunology , Carcinoma, Non-Small-Cell Lung/pathology , Humans , Lymphocytes, Tumor-Infiltrating/immunology , Lung Neoplasms/genetics , Lung Neoplasms/immunology , Lung Neoplasms/pathology , ErbB Receptors/genetics , ErbB Receptors/immunology , Animals , Female , Male , Middle Aged , Aged , Mice , Interferon-gamma/genetics , Interferon-gamma/immunology , AdultABSTRACT
BACKGROUND/AIM: Adoptive cell therapy using antigen-specific T cells is a promising treatment modality for cancer patients. Various methods to isolate specific T cells and identify corresponding T cell receptor (TCR) sequences are known. This study aimed to identify antigen-specific TCR from T cells isolated using carboxyfluorescein succinimidyl ester (CFSE), which marks proliferating activated T cells. MATERIALS AND METHODS: CFSE stained healthy donor peripheral blood mononuclear cells (PBMCs) were treated with cytomegalovirus (CMV) or Epstein-Barr virus (EBV) peptides for seven days. Then, proliferating T cells with decreased CFSE staining were isolated and single cell VDJ sequencing was performed on isolated T cells to identify antigen-specific TCRs. RESULTS: As antigen-specific TCR candidates, ten TCR clones were selected for the CMV antigen and five for the EBV antigen. The reactivity of ten CMV TCR-transduced T cells and one EBV TCR-transduced T cell toward T2 cells pulsed with CMV or EBV peptide was confirmed via NFAT-luciferase, IFN-γ ELISA, and cytotoxicity assays. CONCLUSION: Identification of antigen-specific TCRs with CFSE staining is a valid method for the development of effective immunotherapy. The identified CMV- or EBV-specific TCRs can be used for adoptive cell therapy to treat cancer.
Subject(s)
Cytomegalovirus Infections , Epstein-Barr Virus Infections , Fluoresceins , Neoplasms , Succinimides , Humans , T-Lymphocytes , Epstein-Barr Virus Infections/therapy , Herpesvirus 4, Human , Leukocytes, Mononuclear , Cytomegalovirus , Receptors, Antigen, T-CellABSTRACT
BACKGROUND: Patient-derived xenograft (PDX) models serve as a valuable tool for the preclinical evaluation of novel therapies. They closely replicate the genetic, phenotypic, and histopathological characteristics of primary breast tumors. Despite their promise, the rate of successful PDX engraftment is various in the literature. This study aimed to identify the key factors associated with successful PDX engraftment of primary breast cancer. METHODS: We integrated clinicopathological data with morphological attributes quantified using a trained artificial intelligence (AI) model to identify the principal factors affecting PDX engraftment. RESULTS: Multivariate logistic regression analyses demonstrated that several factors, including a high Ki-67 labeling index (Ki-67LI) (p < 0.001), younger age at diagnosis (p = 0.032), post neoadjuvant chemotherapy (NAC) (p = 0.006), higher histologic grade (p = 0.039), larger tumor size (p = 0.029), and AI-assessed higher intratumoral necrosis (p = 0.027) and intratumoral invasive carcinoma (p = 0.040) proportions, were significant factors for successful PDX engraftment (area under the curve [AUC] 0.905). In the NAC group, a higher Ki-67LI (p < 0.001), lower Miller-Payne grade (p < 0.001), and reduced proportion of intratumoral normal breast glands as assessed by AI (p = 0.06) collectively provided excellent prediction accuracy for successful PDX engraftment (AUC 0.89). CONCLUSIONS: We found that high Ki-67LI, younger age, post-NAC status, higher histologic grade, larger tumor size, and specific morphological attributes were significant factors for predicting successful PDX engraftment of primary breast cancer.
Subject(s)
Breast Neoplasms , Animals , Humans , Female , Breast Neoplasms/therapy , Breast Neoplasms/diagnosis , Heterografts , Artificial Intelligence , Disease Models, Animal , Xenograft Model Antitumor AssaysABSTRACT
BACKGROUND/AIM: The effectiveness of adoptive T cell therapy for solid tumors remains suboptimal, partly attributed to insufficient T cell infiltration into the tumor site. A promising strategy involves directing T cells towards the tumor utilizing tumor-specific chemokine receptors. MATERIALS AND METHODS: We analyzed chemokine receptor expression in activated T cells and chemokine expression in breast and lung cancer using The Cancer Genome Atlas (TCGA) data. Subsequently, we generated 1G4 T cell receptor-engineered T (TCR-T) cells with CCR10 and performed in vitro and in vivo efficacy tests. RESULTS: CCR10 exhibited insufficient expression in various human T cells. Analysis of TCGA RNA sequencing data revealed elevated expression of the chemokine CCL28, the corresponding chemokine for CCR10, in breast and lung cancer. Consequently, we generated CCR10-1G4 TCR-T cells. CCR10-1G4 dual expressing TCR-T cells exhibited comparable cellular cytotoxicity but increased mobility compared to 1G4 TCR-T cells in vitro. Furthermore, injecting CCR10-1G4 dual expressing TCR-T cells into a xenograft tumor model demonstrated enhanced in vivo trafficking and a greater reduction of tumor burden. CONCLUSION: This study highlights the potential of CCR10 for developing efficient adoptive T-cell treatments targeting solid tumors.
Subject(s)
Lung Neoplasms , T-Lymphocytes , Humans , T-Lymphocytes/metabolism , Chemokines/metabolism , Receptors, Chemokine , Immunotherapy , Lung Neoplasms/therapy , Receptors, Antigen, T-Cell/genetics , Receptors, CCR10/genetics , Receptors, CCR10/metabolismABSTRACT
Metabolic Dysfunction-Associated Steatotic Liver Disease (MASLD) is currently the leading cause of chronic liver disease worldwide. Metabolic Dysfunction-Associated Steatohepatitis (MASH), an advanced form of MASLD, can progress to liver fibrosis, cirrhosis, and hepatocellular carcinoma. Based on recent findings by our team that liver 5HT2A knockout male mice suppressed steatosis and reduced fibrosis-related gene expression, we developed a peripheral 5HT2A antagonist, compound 11c for MASH. It shows good in vitro activity, stability, and in vivo pharmacokinetics (PK) in rats and dogs. Compound 11c also shows good in vivo efficacy in a diet-induced obesity (DIO) male mice model and in a choline-deficient, L-amino acid-defined, high-fat diet (CDAHFD) male mice model, effectively improving histologic features of MASH and fibrosis. According to the tissue distribution study using [14C]-labeled 11c, the compound was determined to be a peripheral 5HT2A antagonist. Collectively, first-in-class compound 11c shows promise as a therapeutic agent for the treatment of MASLD and MASH.
Subject(s)
Fatty Liver , Liver Neoplasms , Musculoskeletal Physiological Phenomena , Male , Mice , Animals , Dogs , Rats , Fatty Liver/drug therapy , Liver Cirrhosis/drug therapy , Mice, KnockoutABSTRACT
We examined long-term response (2008-2017) of the macrobenthos to the Hebei Spirit oil spill that occurred around the Taean coast, Korea, in December 2007. Oil concentrations were below the Korea/US environmental standards as of January 2008. Organic matter, chlorophyll-a, and zooplankton abundance dominated by Noctiluca scintillans were higher after the spill. Macrobenthic diversity recovered to pre-incident (2007) level in 2011. Biomass exceeded that level in 2011 and the increase prolonged for 5 years. Cross-correlation and regression analyses showed that chlorophyll-a at year t and zooplankton abundance at t-2 had a significant relationship with macrobenthic biomass at t (p < 0.05 for both), suggesting the transfer of increased organic matter (transformed from crude oil within the pelagic ecosystem) into the benthic ecosystem. Coastal wetlands around the incident area, vulnerable to oil pollution and slowly remobilizing accumulated oil, seemed to affect pelagic ecosystem processes and the unexpectedly increased and sustained biomass.
Subject(s)
Petroleum Pollution , Petroleum , Petroleum Pollution/analysis , Ecosystem , Longitudinal Studies , Korea , Chlorophyll/analysis , Chlorophyll A/analysis , Petroleum/analysis , Republic of KoreaABSTRACT
Non-alcoholic fatty liver disease (NAFLD), attributed to excessive fat accumulation in the liver, is reportedly prevalent worldwide. NAFLD is one of the leading causes of chronic liver disease, including non-alcoholic steatohepatitis (NASH), cirrhosis, and hepatic cellular carcinoma (HCC). The peripheral roles of serotonin (5-hydroxytryptamine, 5HT) were found to regulate hepatic lipid metabolism. Among serotonin receptor subtypes, 5HT2A receptor is known to regulate hepatic lipid metabolism. Hepatic lipid accumulation and hepatic triglyceride (TG) were reduced in liver-specific 5HT2A receptor knockout (5HT2A receptor LKO) mice upon high-fat diet (HFD) feeding. In the present study, we explored a series of new peripherally acting 5HT2A receptor antagonists. Compound 14a displayed good in vitro activity, with an IC50 value of 0.17 nM. Compound 14a exhibited good microsomal stability, no significant CYP and hERG inhibition, and 5HT receptor subtype selectivity. The brain-to-plasma ratio of 14a was below the lower limit of quantification, indicating limited blood-brain barrier (BBB) penetration. HFD-fed 14a treated mice showed decreased liver steatosis and lobular inflammation. These results demonstrate the potential of newly synthesized peripheral 5HT2A receptor antagonists for treating NAFLD.
Subject(s)
Carcinoma, Hepatocellular , Liver Neoplasms , Non-alcoholic Fatty Liver Disease , Animals , Carcinoma, Hepatocellular/pathology , Diet, High-Fat/adverse effects , Liver/metabolism , Liver Neoplasms/pathology , Mice , Mice, Inbred C57BL , Non-alcoholic Fatty Liver Disease/drug therapy , Non-alcoholic Fatty Liver Disease/etiology , Serotonin/metabolism , Tyrosine/metabolismABSTRACT
BACKGROUND: Breast cancer treatment with selective estrogen receptor modulators (SERMs) increasesthe incidence of uterine malignant mixed Müllerian tumors (uMMMTs). We examine clinicopathologiccharacteristics and prognosis of SERM-associated uMMMTs (S-uMMMTs) and discusspossible pathogenetic mechanisms. METHODS: Among 28,104 patients with breast cancer, clinicopathologicfeatures and incidence of uMMMT were compared between patients who underwentSERM treatment and those who did not. Of 92 uMMMT cases that occurred during the same period,incidence, dose, and duration of SERM treatment, as well as overall survival rate, were comparedfor patients with breast cancer who underwent SERM treatment and those who did not (S-uMMMTvs NS-uMMMT) and for patients without breast cancer (de novo-uMMMT). Histopathologicalfindings and immunophenotypes for myogenin, desmin, p53, WT-1, estrogen receptor (ER) α, ERß,progesterone receptor, and GATA-3 were compared between S-uMMMT and de novo-uMMMT. RESULTS: The incidence of S-uMMMT was significantly higher than that of NS-uMMMT (6.35-fold).All patients with SERM were postmenopausal and received daily 20-40 mg SERM. CumulativeSERM dose ranged from 21.9 to 73.0 g (mean, 46.0) over 39-192 months (mean, 107). Clinicopathologicfeatures, such as International Federation of Gynecology and Obstetrics stage andoverall survival, were not significantly different between patients with S-uMMMT and NS-uMMMTor between patients with S-uMMMT and de novo-uMMMT. All 11 S-uMMMT cases available forimmunostaining exhibited strong overexpression/null expression of p53 protein and significantlyincreased ERß expression in carcinomatous and sarcomatous components. CONCLUSIONS: SERMtherapy seemingly increases risk of S-uMMMT development; however, clinicopathologic featureswere similar in all uMMMTs from different backgrounds. p53 mutation and increased ERß expressionmight be involved in the etiology of S-uMMMT.
ABSTRACT
Identifying the accurate origin of periampullary cancers is important because different origins may trigger different clinicopathological behaviors. The presence of intraepithelial precursor lesions, including high-grade pancreatic intraepithelial neoplasias (PanINs) and/or high-grade biliary intraepithelial neoplasias (BilINs), may be suggestive of the origin of the periampullary carcinoma in challenging cases. To prove the usefulness of high-grade intraepithelial precursor lesions in identifying the origin of ambiguous periampullary cancers, the status and grades of PanINs and BilINs were evaluated in 256 periampullary carcinomas with a well-defined cancer origin as a test set, including 114 pancreatic cancers, 82 distal bile duct cancers, 54 ampullary cancers, and 6 duodenal cancers. One hundred twelve periampullary carcinomas with clinically equivocal epicenter either by radiologic imaging or by endoscopic finding used as a validation set. High-grade PanINs were found more commonly in pancreatic cancers than in distal bile duct, ampullary, and duodenal cancers both in test (P = .002) and validation sets (P < .001). Similarly, high-grade BilINs were identified more frequently in distal bile duct cancers than in ampullary, pancreatic, and duodenal cancers both in test (P < .001) and validation sets (P = .039). High-grade PanINs were found most commonly in pancreatic cancers, whereas high-grade BilINs were seen most frequently in distal bile duct cancers. In addition, both high-grade PanINs and high-grade BilINs are uncommonly noted in ampullary or duodenal cancers. The recognition of high-grade intraepithelial lesions can help identify the primary origin of periampullary cancers, especially when the epicenter of the periampullary cancer is ambiguous.
Subject(s)
Ampulla of Vater/pathology , Carcinoma in Situ/pathology , Carcinoma, Pancreatic Ductal/pathology , Common Bile Duct Neoplasms/pathology , Duodenal Neoplasms/pathology , Adult , Aged , Aged, 80 and over , Female , Humans , Male , Middle AgedABSTRACT
We propose a theoretical framework to predict the deformation mechanism of the γ-TiAl single crystal without lattice defects by combining the generalized stacking fault energy and the Schmid factor. Our theory is validated against an excellent testbed, the single crystal nanowire, by correctly predicting four major deformation mechanisms, namely, ordinary slip, super slip, twinning, and mixed slip/fracture observed during the tensile and compressive tests along 10 different orientations using molecular dynamics simulations. Interestingly, although lattice defects are not taken into account, the theoretical predictions match well with existing experiments on bulk specimen with only a few exceptions; the exceptions are discussed based on the size-dependent deformation mechanism in the presence of preexisting dislocation sources. We expect that the method in this paper can be generalized to study various ductile intermetallic crystals where conventional Schmid law does not hold well.
ABSTRACT
BACKGROUND: BRAF mutation has been recognized as an important biomarker of colorectal cancer (CRC) for targeted therapy and prognosis prediction. However, sequencing for every CRC case is not cost-effective. An antibody specific for BRAF V600E mutant protein has been introduced, and we thus examined the utility of BRAF VE1 immunohistochemistry for evaluating BRAF mutations in CRC. METHODS: Fifty-one BRAF-mutated CRCs and 100 age and sexmatched BRAF wild-type CRCs between 2005 and 2015 were selected from the archives of Asan Medical Center. Tissue microarrays were constructed and stained with BRAF VE1 antibody. RESULTS: Forty-nine of the 51 BRAF-mutant CRCs (96.1%) showed more than moderate cytoplasmic staining, except for two weakly stained cases. Six of 100 BRAF wild-type cases also stained positive with BRAF VE1 antibody; four stained weakly and two stained moderately. Normal colonic crypts showed nonspecific weak staining, and a few CRC cases exhibited moderate nuclear reactivity (3 BRAF-mutant and 10 BRAF wild-type cases). BRAF-mutated CRC patients had higher pathologic stages and worse survival than BRAF wild-type patients. CONCLUSIONS: BRAF VE1 immunohistochemistry showed high sensitivity and specificity, but occasional nonspecific staining in tumor cell nuclei and normal colonic crypts may limit their routine clinical use. Thus, BRAF VE1 immunohistochemistry may be a useful screening tool for BRAF V600E mutation in CRCs, provided that additional sequencing studies can be done to confirm the mutation in BRAF VE1 antibody-positive cases.
ABSTRACT
This report describes a rare case of invasive extramammary Paget disease of the vulva with signet ring cell morphology in a 58-yr-old woman with a history of signet ring cell carcinoma of the stomach. This case was initially misinterpreted as a metastatic gastric carcinoma to the vulva because an initial small, superficial biopsy specimen showed infiltration of signet ring cells in the dermis without intraepidermal Paget cells. However, a surgically resected specimen showed concordant immunophenotypes in both intraepidermal Paget cells and intradermal signet ring cell components with immunoreactivity to cytokeratin (CK) 7, CEA, and gross cystic disease fluid protein-15, and immunonegativity for CK20, MUC5AC, and MUC6. Gastric signet ring cell carcinoma showed immunoreactivity to CK7, CEA, MUC5AC, and MUC6, and immunonegativity for gross cystic disease fluid protein-15 and CK20. The diagnosis of primary invasive extramammary Paget disease of the vulva was also supported by a long interval after gastrectomy (7.5 yr), the solitary involvement of the vulva, and the absence of lymphovascular invasion. This case demonstrates that invasive extramammary Paget disease may have a signet ring cell morphology and immunohistochemical profile similar to those of gastric signet ring cell carcinoma, but the addition of gross cystic disease fluid protein-15 immunostain in the panel of markers is helpful in the differential diagnosis.
Subject(s)
Biomarkers, Tumor/metabolism , Carcinoma, Signet Ring Cell/complications , Carrier Proteins/metabolism , Glycoproteins/metabolism , Paget Disease, Extramammary/diagnosis , Stomach Neoplasms/complications , Vulvar Neoplasms/diagnosis , Diagnosis, Differential , Female , Humans , Membrane Transport Proteins , Middle Aged , Paget Disease, Extramammary/complications , Paget Disease, Extramammary/metabolism , Paget Disease, Extramammary/pathology , Vulva/metabolism , Vulva/pathology , Vulvar Neoplasms/complications , Vulvar Neoplasms/metabolism , Vulvar Neoplasms/pathologyABSTRACT
Bioassay and gene expression experiments were conducted in order to evaluate the growth and physiology of Prorocentrum minimum isolated from a eutrophic coastal water in response to tannic acid. In the bioassay experiments, variations in abundance, chlorophyll (chl) a concentration, maximum fluorescence (in vivo Fm), and photosynthetic efficiency (Fv/Fm) were measured over the course of a seven-day incubation. Moreover, stress-related gene expression in both the control and an experimental (2.5 ppm TA treatment) group was observed for 24 h and 48 h. The molecular markers used in this study were the heat shock proteins (Hsp70 and Hsp90) and cyclophilin (CYP). The findings show that P. minimum can thrive and grow at low concentrations (<2.5 ppm) of tannic acid, and, above this concentration, cells begin to slow down development. In addition, TA concentration of 10 ppm halted photosynthetic activity. At the molecular level, treatment with tannic acid increased the expression of Hsp70, Hsp90, and CYP, and heat shock proteins are more upregulated than the cyclophilin gene. Exposure to tannic acid increased the expression of stress factors over time (48 h) by 10- to 27-fold the expression level of the control group. These results suggest that tannic acid can be used to control harmful algal blooms such as those containing P. minimum in eutrophic coastal waters.
Subject(s)
Dinoflagellida/drug effects , Harmful Algal Bloom/drug effects , Tannins/pharmacology , Algal Proteins/genetics , Chlorophyll/metabolism , Chlorophyll A , Cyclophilins/genetics , Dinoflagellida/genetics , Dinoflagellida/metabolism , Gene Expression/drug effects , HSP70 Heat-Shock Proteins/genetics , HSP90 Heat-Shock Proteins/genetics , Photosynthesis/drug effectsABSTRACT
Phytoplankton size structure and water properties in the Youngsan River estuary, which has been altered by a sea dike, were monitored over an annual cycle (2003-2004) to investigate the effects of freshwater inputs on their spatial and temporal variation. Trophic status was also evaluated using the trophic status index (TRIX). Freshwater was discharged from an artificial reservoir throughout the year, supplying nutrients (except for [Formula: see text] ) and low levels of dissolved oxygen to the estuary, which resulted in eutrophication ("greatest trophic level"). Turbidity increased, and density stratification developed in the water column. The density stratification in turn affected the reduction of dissolved oxygen concentration in the bottom water during the freshwater discharge. Chlorophyll a concentrations, dominated by nano-sized (<20 µm) particles, were generally much lower when the water column was stratified by freshwater discharge (.90-5.03 µg chl L(-1)) than when the water column was well-mixed with no freshwater inputs from the dike (3.42-47.0 µg chl L(-1)). The net-scale (>20 µm) decrease in phytoplankton biomass differed from that in tropical estuaries affected by monsoons and in other temperate estuaries. Temporal variations in water quality and phytoplankton size structure were more strongly influenced by artificial regulation of the freshwater discharge than by monsoon meteorological events. This study implies that a different paradigm than that for natural estuaries or larger estuaries with dams is required for the better understanding and management of ecosystems in estuaries altered by anthropogenic activities, such as the construction of sea dikes.
Subject(s)
Eutrophication , Phytoplankton , Estuaries , Fresh Water , Nitrates/analysis , Nitrites/analysis , Oxygen/analysis , Phosphates/analysis , Population Density , Quaternary Ammonium Compounds/analysis , Salinity , Silicon Dioxide/analysis , Temperature , Water QualityABSTRACT
A strong linear relationship was observed between the average double bond equivalence (DBE) and the ratio of carbon to oxygen atoms in oxygenated compounds of dissolved organic matter (DOM). Data were acquired by a Fourier transform ion cyclotron resonance mass spectrometer (FT-ICR MS), equipped with a negative-mode electrospray ionization source. The slope and y-intercepts extracted from the linear relationship can be used to compare DOM samples originating from different locations. Significant differences in these parameters were observed between inland riverine and offshore coastal DOM samples. Offshore coastal DOM molecules underwent a change of one DBE for each removal or addition of two oxygen atoms. This suggested the existence of multiple carboxyl groups, each of which contains a double bond and two oxygen atoms. Inland riverine samples exhibited a change of ~1.5 DBE following the addition or removal of two oxygen atoms. This extra change in DBE was attributed to cyclic structures or unsaturated chemical bonds. The DBE value with maximum relative abundance and the minimum DBE value for each class of oxygenated compounds showed that approximately two oxygen atoms contributed to a unity change in DBE. The qualitative analyses given here are in a good agreement with results obtained from analyses using orthogonal analytical techniques. This study demonstrates that DBE and the carbon number distribution, observed by high resolution mass spectrometry, can be valuable in elucidating and comparing structural features of oxygenated molecules of DOM.