Aquaporin 2 in Cerebral Edema: Potential Prognostic Marker in Craniocerebral Injuries.

Despite continuous medical advancements, traumatic brain injury (TBI) remains a leading cause of death and disability worldwide. Consequently, there is a pursuit for biomarkers that allow non-invasive monitoring of patients after cranial trauma, potentially improving clinical management and reducing complications and mortality. Aquaporins (AQPs), which are crucial for transmembrane water transport, may be significant in this context. This study included 48 patients, with 27 having acute (aSDH) and 21 having chronic subdural hematoma (cSDH). Blood plasma samples were collected from the participants at three intervals: the first sample before surgery, the second at 15 h, and the third at 30 h post-surgery. Plasma concentrations of AQP1, AQP2, AQP4, and AQP9 were determined using the sandwich ELISA technique. CT scans were performed on all patients pre- and post-surgery. Correlations between variables were examined using Spearman's nonparametric rank correlation coefficient. A strong correlation was found between aquaporin 2 levels and the volume of chronic subdural hematoma and midline shift. However, no significant link was found between aquaporin levels (AQP1, AQP2, AQP4, and AQP9) before and after surgery for acute subdural hematoma, nor for AQP1, AQP4, and AQP9 after surgery for chronic subdural hematoma. In the chronic SDH group, AQP2 plasma concentration negatively correlated with the midline shift measured before surgery (Spearman's ρ -0.54; p = 0.017) and positively with hematoma volume change between baseline and 30 h post-surgery (Spearman's ρ 0.627; p = 0.007). No statistically significant correlation was found between aquaporin plasma levels and hematoma volume for AQP1, AQP2, AQP4, and AQP9 in patients with acute SDH. There is a correlation between chronic subdural hematoma volume, measured radiologically, and serum AQP2 concentration, highlighting aquaporins' potential as clinical biomarkers.

Intrathrombotic appearances of AQP-1 and AQP-3 in relation to thrombus age in murine deep vein thrombosis model.

Aquaporins (AQPs) are membrane-bound proteins for water transportation and are useful for diagnosing drowning and wound vitality in forensic pathology. Here, we examined intrathrombotic expression of AQP-1 and AQP-3 using deep vein thrombosis models in mice. To perform immunohistochemical analyses, we used anti-AQP-1 and anti-AQP-3 antibodies. In thrombus samples with the post-ligation intervals of 1 to 5 days, AQP-1+ areas were over 70%. At 7 days after the IVC ligation, AQP-1+ areas became less than 50%, eventually decreasing to 11% at 21 days. At 3 days after the IVC ligation, AQP-3+ cells started to appear from the peripheral area. Thereafter, the positive cell number progressively increased and reached to a peak at 10 days after the IVC ligation. When the intrathrombotic AQP-1+ area was as large as the intrathrombotic collagen area or smaller, it would indicate a thrombus age of ≥ 10 days. AQP-3+ cell number of > 30 would indicate a thrombus age of 10-14 days. Collectively, our study implied that the detection of AQP-1 and AQP-3 would be useful for the determination of thrombus age.

Aquaporin 1 alleviates acute kidney injury via PI3K-mediated macrophage M2 polarization.

BACKGROUND: Lipopolysaccharide (LPS)-induced acute kidney injury (AKI) is associated with an abnormal immune response. Accumulating evidence has demonstrated that aquaporin 1 (AQP1) prevents kidney tissue injury in LPS-induced AKI by mediating immune response. However, the underlying mechanisms remain obscure. Macrophages as immune cells with multiple phenotypes are important mediators in tissue homeostasis and host defense. We propose that macrophage polarization is implicated in AQP1-mediated immune response. METHODS: Herein we established sepsis-induced AKI model rats through intraperitoneal injection of LPS into Wistar rats to reveal immune mechanism of damage. We also used LPS-induced mouse RAW264.7 cells to elucidate the molecular mechanism of macropage polarization. RESULTS: Histopathology showed that renal tubular epithelial cells in the model group were swollen, inflammatory exudation was obvious and the inflammatory factors, interleukin-6 (IL-6) and tumor necrosis factor α (TNF-α) were increased. Western blotting showed PI3K was upregulated in the model group. Serum creatinine and urea nitrogen increased after LPS injection. Renal AQP1 mRNA is downregulated and serum AQP1 protein increased first and then decreased in LPS-induced AKI rats. M2 macrophage markers (Arg-1, CD206) were increased in repair stage. In addition, treatment of murine macrophages (RAW264.7) with AQP1 siRNA resulted in decreased PI3K activation and M2 polarization, but increased IL-6 and TNF-α. Moreover, inhibiting PI3K with wortmannin imitated the results of AQP1 silencing. CONCLUSIONS: Macrophage M2 polarization is likely the cellular mechanism underlying the anti-AKI property of AQP1, and PI3K activation is involved in the AQP1-induced M2 phenotype switch.

Aquaporin-1 attenuates macrophage-mediated inflammatory responses by inhibiting p38 mitogen-activated protein kinase activation in lipopolysaccharide-induced acute kidney injury.

OBJECTIVE: This study was designed to investigate the role of AQP1 in the development of LPS-induced AKI and its potential regulatory mechanisms in the inflammatory responses of macrophages. METHODS: Male Wistar rats were injected intraperitoneally with LPS, and biochemical and histological renal damage was assessed. The levels of inflammatory mediators, macrophage markers and AQP1 in blood and kidney tissues were assessed by ELISA. RTPCR was used to assess changes in the relative levels of AQP1 mRNA induced by LPS. Western blot and immunofluorescence analyses were performed to assay the activation of the p38 MAPK and NF-κB pathways, respectively. The same detection methods were used in vitro to determine the regulatory mechanisms underlying AQP1 function. RESULTS: AQP1 mRNA levels were dramatically decreased in AKI rats following the increased expression of inflammatory factors. In vitro experiments demonstrated that silencing the AQP1 gene increased inflammatory mediator secretion, altered the classical activation of macrophages, greatly enhanced the phosphorylation of p38 and accelerated the translocation of NF-κB. Furthermore, these results were blocked by doramapimod, a p38 inhibitor. Therefore, these effects were mediated by the increased phosphorylation of p38 MAPK. CONCLUSION: Our results suggest that altered AQP1 expression may be associated with the development of inflammation in AKI. AQP1 plays a protective role in modulating acute renal injury and can attenuate macrophage-mediated inflammatory responses by downregulating p38 MAPK activity in LPS-induced RAW264.7 cells. The pharmacological targeting of AQP1-mediated p38 MAPK signalling may provide a novel treatment approach for AKI.

Red blood cell aquaporin-1 expression is decreased in hereditary spherocytosis.

Aquaporin-1 (AQP1) is the membrane water channel responsible for changes in erythrocyte volume in response to the tonicity of the medium. As the aberrant distribution of proteins in hereditary spherocytosis (HS) generates deficiencies of proteins other than those codified by the mutated gene, we postulated that AQP1 expression might be impaired in spherocytes. AQP1 expression was evaluated through flow cytometry in 5 normal controls, 1 autoimmune hemolytic anemia, 10 HS (2 mild, 3 moderate, 2 severe, and 3 splenectomized), and 3 silent carriers. The effect of AQP1 inhibitors was evaluated through water flow-based tests: osmotic fragility and hypertonic cryohemolysis. Serum osmolality was measured in 20 normal controls and 13 HS. The effect of erythropoietin (Epo) on AQP1 expression was determined in cultures of erythroleukemia UT-7 cells, dependent on Epo to survive. Independent of erythrocyte size, HS patients showed a lower content of AQP1 in erythrocyte membranes which correlated with the severity of the disease. Accordingly, red blood cells from HS subjects were less sensitive to cryohemolysis than normal erythrocytes after inhibition of the AQP1 water channel. A lower serum osmolality in HS with respect to normal controls suggests alterations during reticulocyte remodeling. The decreased AQP1 expression could contribute to explain variable degrees of anemia in hereditary spherocytosis. The finding of AQP1 expression induced by Epo in a model of erythroid cells may be interpreted as a mechanism to restore the balance of red cell water fluxes.

A new AQP1 null allele identified in a Gypsy woman who developed an anti-CO3 during her first pregnancy.

BACKGROUND AND OBJECTIVES: The Colton blood group antigens are carried by the AQP1 water channel. AQP1(-/-) individuals, also known as Colton-null since they express no Colton antigens, do not suffer any apparent clinical consequence but may develop a clinically significant alloantibody (anti-CO3) induced by transfusion or pregnancy. Identification and transfusion support of Colton-null patients are highly challenging, not only due to the extreme rarity of this phenotype, the lack of appropriate reagents in most laboratories, as well as the possibility of confusing it with the recently described CO:-1,-2,3,-4 phenotype where AQP1 is present. This study investigated a new Colton-null case and evaluated three commercially available anti-AQP1s to identify Colton-null red blood cell samples. METHODS: The Colton-null phenotype was investigated by standard serological techniques, AQP1 sequencing, immunoblot and flow cytometry analyses. RESULTS: We identified and characterized the Colton-null phenotype in a Gypsy woman who developed an anti-CO3 during her first pregnancy. After developing a simple and robust method to sequence AQP1, we showed that she was apparently homozygous for a new AQP1 null allele, AQP1 601delG, whose product is not expressed in her red blood cells. We also established the Colton specificity of three commercially available anti-AQP1s in immunoblot and/or flow cytometry analyses. CONCLUSION: This Gypsy woman represents the sixth Colton-null case characterized at the serological, genetic and biochemical levels. The validation here of new reagents and methods should facilitate the identification of Colton-null individuals.

Prognostic value of serum aquaporin-1, aquaporin-3 and galectin-3 for young patients with colon cancer.

BACKGROUND: This study aimed to investigate the long-term prognosis value of serum galectin-3, aquaporin (AQP)-1 and AQP-3 in young patients with colon cancer. METHODS: A total of 100 young patients with colon cancer, 100 cases of benign colon and 100 healthy people were collected. All colon cancer patients were followed up for 42 months. RESULTS: Compared with the benign lesion group and the control group, preoperative serum galectin-3, AQP-1 and AQP-3 concentrations were significantly increased in patients with colon cancer (P < 0.05). The immunohistochemistry scores of galectin-3, AQP-1 and AQP-3 in colon cancer patients were positively correlated with serum galectin-3, AQP-1 and AQP-3 concentrations (P < 0.05). Serum galectin-3, AQP-1 and AQP-3 concentrations were positively correlated with TNM staging (galectin-3: rPearson = 0.502, P < 0.001; AQP-1: rPearson = 0.415, P < 0.001; AQP-3: rPearson = 0.454, P < 0.001) and differentiation (galectin-3: rPearson = 0.377, P = 0.004; AQP-1: rPearson = 0.411, P = 0.001; AQP-3: rPearson = 0.483, P < 0.001). Receiver operator characteristic curve (ROC) analysis showed that the area under ROC curve (AUC) of the combination of galectin-3, AQP-1 and AQP-3 in distinguishing colon cancer was 0.907. The sensitivity in the parallel mode was 87.6%, and the specificity in the serial mode was 98.2%. Compared with the low galectin-3 group, low AQP-1 group and low AQP-3 group, the survival time of patients in the high galectin-3 group (χ2 = 13.929, P < 0.001), high AQP-1 group (χ2 = 10.157, P = 0.001) and high AQP-3 group (χ2 = 4.364, P = 0.037) were significantly shortened. CONCLUSION: Galectin-3 combined with AQP-1 and AQP-3 had important value in the identification of young patients with colon cancer and was of great value in evaluating long-term prognosis.

Expression of aquaporin-1 in normal, hyperplasic, and carcinomatous endometria.

OBJECTIVE: To explore the relationship between aquaporin-1 (AQP1) and endometrial adenocarcinoma. METHOD: Intratumoral microvessel density (IMD) was assessed as well as AQP1 and vascular endothelial growth factor expression in samples from 117 women, 75 with endometrioid adenocarcinoma, 17 with endometrial hyperplasia, and 25 with normal proliferative endometria. RESULTS: AQP1 was located in the epithelial cells of microvessels and small vessels in all samples. The AQP1/IMD ratio was highest in samples from the first, less in samples from the second, and least in samples from the third group. In samples from endometrioid adenocarcinoma, the AQP1/IMD ratio was significantly correlated with histologic grade, surgical stage, myometrial invasion, and extrauterine metastasis. There was a positive correlation between AQP1 expression and IMD and between AQP1/IMD ratio and VEGF expression. CONCLUSION: AQP1 may be involved in the tumorigenesis and progression of endometrioid adenocarcinoma by promoting angiogenesis, and AQP1 level may be both a tumor indicator and a new therapeutic target.

Effects of darbepoetin injections on erythrocyte membrane transport protein expressions in humans.

The present study investigated the effects of injected darbepoetin [novel erythropoietin stimulating protein (NESP)] on the density of three erythrocyte membrane transport proteins: the lactate-H+ cotransporter (monocarboxylate transporter 1), the chloride/bicarbonate exchanger 1 (anion exchanger 1), and the water channel aquaporin 1. Thirteen subjects were injected with NESP once a week for 4 wk. Blood samples were obtained before, during, and after the injection period, and the erythrocyte transport proteins were determined by Western blotting. The NESP injections induced a transient increase in hematocrit, red cell volume, and reticulocyte fraction. The density of aquaporin 1 protein was higher (maximal increase +59%) (P < 0.01) during the injection period compared with the preinjection value and lower (P < 0.01) after the injection period. The density of anion exchanger 1 protein was higher (maximal increase +15%) (P < 0.05) during the injection period compared with the preinjection value and tended (P = 0.06) to be lower after the injection period than before the injection period. The density of the erythrocyte monocarboxylate transporter 1 protein was higher (maximal increase +43%) (P < 0.05) during the injection period than in the preinjection period. Age separation experiments using self-creating Percoll gradients demonstrated a higher density of membrane transport proteins in young red blood cells. These data suggest that the NESP-induced increase in membrane transport proteins is caused by a higher fraction of newly formed erythrocytes (and reticulocytes), which have a higher density of membrane transport proteins. However, increased incorporation of membrane proteins during erythrocyte formation may also be involved. We suggest that NESP improves the quality of erythrocyte membrane transport through these mechanisms.

Aquaporin-1 expression in canine peripheral erythrocytes and its relation to cell volume.

To evaluate the relationship between aquaporin-1 (AQP1) expression and the cell volume of red blood cells (RBCs), canine peripheral RBCs were separated according to specific gravity, and expression of the AQP1 protein on the membrane of RBCs was compared using anti-dog AQP1 polypeptide serum. Western blot analysis indicated that there was no significant difference in AQP1 expression between large and small cell fractions. In addition, the AQP1 expression of inherited high K/low Na RBCs which are known to be 20% larger than normal RBCs, was comparable to that of normal RBCs. These results suggest that AQP1, the major water channel in RBCs, does not determine the cell volume of peripheral canine RBCs.

Aquaporins AQP1 and AQP4 in the cerebrospinal fluid of bacterial meningitis patients.

Aquaporins facilitate water transport through cell membranes. Due to the localization of AQP1 and AQP4 in the brain, they might contribute to cerebral edema. Our study aimed to determine whether AQP1 and AQP4 can be measured in cerebrospinal fluid (CSF), and whether there is a difference in AQP1 and AQP4 concentration between patients with bacterial meningitis (BM) and healthy controls. AQP1 and AQP4 concentrations in CSF from 35 patients with BM and 27 controls were analyzed using a commercial ELISA. The mean concentration of AQP1 in CSF was significantly elevated in patients with BM (BM: 3.8±3.4ng/ml, controls: 0.8±0.5ng/ml; p<0.001). AQP4 had a tendency to be increased, however the difference was not significant (BM: 1.8±3.1ng/ml, controls: 0.1±0.2ng/ml; p=0.092). AQP1 and AQP4 in CSF of BM patients were inversely correlated (r=-0.47, p=0.004). We could not find any other correlation between concentration of AQP1 or AQP4 in CSF and CSF leukocytes, lactate, protein, albumin CSF/serum ratio, age, a prediction score, an outcome score or the Glasgow Coma Scale at admission in patients with BM. Control patients displayed a correlation between AQP1 and the albumin CSF/serum ratio (r=0.390, p=0.040). This is the first study that detected AQP1 and AQP4 in CSF. Whether the significant elevation of AQP1 is due to a higher expression and subsequent shedding into CSF or a BM-induced cell damage needs to be determined.