Endothelial cells regulate proximal tubule epithelial cell sodium transport

Core fucosylation involvement in the paracrine regulation of proteinuria-induced renal interstitial fibrosis evaluated with the use of a microfluidic chip

Proteinuria is a clinical manifestation of chronic kidney disease that aggravates renal interstitial fibrosis (RIF), in which injury of peritubular microvessels is an important event. However, the changes in peritubular microvessels induced by proteinuria and their molecular mechanisms remain unclear. Thus, we aimed to develop a co-culture microfluidic device that contains renal tubules and peritubular microvessels to create a proteinuria model. We found that protein overload in the renal tubule induced trans-differentiation and apoptosis of endothelial cells (ECs) and pericytes. Moreover, profiling of secreted proteins in this model revealed that a paracrine network between tubules and microvessels was activated in proteinuria-induced microvascular injury. Multiple cytokine receptors in this paracrine network were core-fucosylated. Inhibition of core fucosylation significantly reduced ligand-receptor binding ability and blocked downstream pathways, alleviating trans-differentiation and apoptosis of ECs and pericytes. Furthermore, the protective effect of genetic FUT8 deficiency on proteinuria overload-induced RIF and pericyte-myofibroblast trans-differentiation was validated in FUT8 knockout heterozygous mice. In conclusion, we constructed and used a multiple-unit integrated microfluidic device to uncover the mechanism of proteinuria-induced RIF. Furthermore, FUT8 may serve as a hub-like therapeutic target to alleviate peritubular microvascular injury in RIF. STATEMENT OF SIGNIFICANCE: In this study, we constructed a multiple-unit integrated renal tubule-vascular chip. We reproduced human proteinuria on the chip and found that multiple receptors were modified by FUT8-catalyzed core fucosylation (CF) involved in the cross-talk between renal tubules and peritubular microvessels in proteinuria-induced RIF, and inhibiting the FUT8 of receptors could block the tubule-microvessel paracrine network and reverse the damage of peritubular microvessels and renal interstitial fibrosis. This tubule-vascular chip may provide a prospective platform to facilitate future investigations into the mechanisms of kidney diseases, and target-FUT8 inhibition may be an innovative and potential therapeutic strategy for RIF induced by proteinuria.

Urolithiasis Develops Endothelial Dysfunction as a Clinical Feature

An increased risk of cardiovascular morbidity has been reported in lithiasic patients. In this context, endothelial dysfunction (ED), an earlier status of atherogenesis, has been identified in hyperoxaluria rat models of urolithiasis. Objective: The purpose of this study was to determine the endothelial vascular function in patients with urolithiasis in relation to systemic inflammatory, oxidative stress, and vascular function serum markers. Methods: A cross-sectional study was performed between 27 urolithiasic patients, matched for age and sex, with 27 healthy patients. Endothelial function was assessed by measuring flow-mediated dilation (Celermajer method). Fasting blood was collected to determine metabolic parameters (glucose and lipid profile), along with serum CRP, IL-6, MDA, ADMA, and VCAM-1. Results: Both the control and urolithiasis groups were homogenous in anthropometric, exploration, and general laboratory measures. Flow-mediated dilation (%FMD) was 11.85% (SE: 2.78) lower in the lithiasis group (p < 0.001). No significant differences were achieved between groups when CRP, IL-6, MDA, ADMA, and VCAM-1 were compared, although slightly higher values of CRP, ADMA, and VCAM-1 were detected in the lithiasic group. A correlation was not reached in any of the serum markers when they were related to flow-mediated values, although a slight negative correlation trend was observed in MDA, VCAM-1, and IL-6 values. Conclusions: Endothelial dysfunction constitutes an important disorder related to urolithiasis patients. It must be considered as an early feature responsible for future cardiovascular events. Our study did not find a significant association between inflammatory, oxidative stress, endothelial serum markers, and flow-mediated dilation.

Effect of endothelial dysfunction on the pathogenesis of urolithiasis in patients with metabolic syndrome

OBJECTIVE

The aim of the present prospective clinical study was to investigate the possible effect of endothelial dysfunction in urolithiasis.

METHODS

The study included 92 patients older than 18 years. The patients were divided into 4 groups with 23 patients each as group 1: metabolic sydrome (MetS) (-) stone disease (SD) (-), group 2: MetS (-) SD (+), group 3: MetS (+) SD (-) and group 4: MetS (+) SD (+). C-reactive protein, homocysteine, uric acid, and creatinine levels were evaluated between the groups. Endothelial (dys)function was evaluated based on the brachial artery flow-mediated dilation (FMD) measurement.

RESULTS

The mean age was 41.9 ± 10.2 (range, 18-62) years. Mean FMD value was 15.9 ± 18.2% (range, 24.0-68.5%). A strong significant difference was found between group 1 and 2 (p < .001); group 1 and 3 (p < .001) and group 1 and 4 (p < .001) with regard to FMD.

CONCLUSION

These results suggest that endothelial dysfunction plays an important role in the pathogenesis of urolithiasis in patients with MetS.

Co-cultures of renal progenitors and endothelial cells on kidney decellularized matrices replicate the renal tubular environment in vitro

AIM

Herein we propose creating a bilayer tubular kidney in-vitro model. It is hypothesized that membranes composed of decellularized porcine kidney extracellular matrix are valid substitutes of the tubular basement membrane by mimicking the physiological relevance of the in vivo environment and disease phenotypes.

METHODS

Extracellular matrix was obtained from decellularized porcine kidneys. After processing by lyophilization and milling, it was dissolved in an organic solvent and blended with poly(caprolactone). Porous membranes were obtained by electrospinning and seeded with human primary renal progenitor cells to evaluate phenotypic alterations. To create a bilayer model of the in vivo tubule, the same cells were differentiated into epithelial tubular cells and co-cultured with endothelial cells in opposite sites.

RESULTS

Our results demonstrate increasing metabolic activity, proliferation and total protein content of renal progenitors over time. We confirmed the expression of several genes encoding epithelial transport proteins and we could also detect tubular-specific proteins by immunofluorescence stainings. Functional and transport assays were performed trough the bilayer by quantifying both human serum albumin uptake and inulin leakage. Furthermore, we validated the chemical modulation of nephrotoxicity on this epithelium-endothelium model by cisplatin exposure.

CONCLUSION

The use of decellularized matrices in combination with primary renal cells was shown to be a valuable tool for modelling renal function and disease in vitro. We successfully validated our hypothesis by replicating the physiological conditions of an in vitro tubular bilayer model. The developed system may contribute significantly for the future investigation of advanced therapies for kidney diseases.

Fluoride Exposure Induces Inhibition of Sodium-and Potassium-Activated Adenosine Triphosphatase (Na+, K+-ATPase) Enzyme Activity: Molecular Mechanisms and Implications for Public Health

In this study, several lines of evidence are provided to show that Na + , K + -ATPase activity exerts vital roles in normal brain development and function and that loss of enzyme activity is implicated in neurodevelopmental, neuropsychiatric and neurodegenerative disorders, as well as increased risk of cancer, metabolic, pulmonary and cardiovascular disease. Evidence is presented to show that fluoride (F) inhibits Na + , K + -ATPase activity by altering biological pathways through modifying the expression of genes and the activity of glycolytic enzymes, metalloenzymes, hormones, proteins, neuropeptides and cytokines, as well as biological interface interactions that rely on the bioavailability of chemical elements magnesium and manganese to modulate ATP and Na + , K + -ATPase enzyme activity. Taken together, the findings of this study provide unprecedented insights into the molecular mechanisms and biological pathways by which F inhibits Na + , K + -ATPase activity and contributes to the etiology and pathophysiology of diseases associated with impairment of this essential enzyme. Moreover, the findings of this study further suggest that there are windows of susceptibility over the life course where chronic F exposure in pregnancy and early infancy may impair Na + , K + -ATPase activity with both short- and long-term implications for disease and inequalities in health. These findings would warrant considerable attention and potential intervention, not to mention additional research on the potential effects of F intake in contributing to chronic disease.

Enhancement of HGF-induced tubulogenesis by endothelial cell-derived GDNF

Tubulogenesis, the organization of epithelial cells into tubular structures, is an essential step during renal organogenesis as well as during the regeneration process of renal tubules after injury. In the present study, endothelial cell-derived factors that modulate tubule formation were examined using an in vitro human tubulogenesis system. When human renal proximal tubular epithelial cells (RPTECs) were cultured in gels, tubular structures with lumens were induced in the presence of hepatocyte growth factor (HGF). Aquaporin 1 was localized in the apical membrane of these tubular structures, suggesting that these structures are morphologically equivalent to renal tubules in vivo. HGF-induced tubule formation was significantly enhanced when co-cultured with human umbilical vein endothelial cells (HUVECs) or in the presence of HUVEC-conditioned medium (HUVEC-CM). Co-culture with HUVECs did not induce tubular structures in the absence of HGF. A phospho-receptor tyrosine kinase array revealed that HUVEC-CM markedly enhanced phosphorylation of Ret, glial cell-derived neurotrophic factor (GDNF) receptor, in HGF-induced tubular structures compared to those without HUVEC-CM. HUVECs produced GDNF, and RPTECs expressed both Ret and GDNF family receptor alpha1 (co-receptor). HGF-induced tubule formation was significantly enhanced by addition of GDNF. Interestingly, not only HGF but also GDNF significantly induced phosphorylation of the HGF receptor, Met. These data indicate that endothelial cell-derived GDNF potentiates the tubulogenic properties of HGF and may play a critical role in the epithelial-endothelial crosstalk during renal tubulogenesis as well as tubular regeneration after injury.

Reconstructing the Human Renal Vascular-Tubular Unit In Vitro

Engineered human kidney-on-a-chip platforms show tremendous promise for disease modeling and drug screening. Outstanding challenges exist, however, in reconstructing the complex architecture, cellular make-up, and matrix composition necessary for the proper modeling of kidney function. Herein, the first fully tunable human kidney-on-a-chip platform is reported that allows the reconstruction of the native architecture of the renal endothelial-epithelial exchange interface using entirely cell-remodelable matrix and patient-derived kidney cells. This platform consists of a double-layer human renal vascular-tubular unit (hRVTU) enabled by a thin collagen membrane that replicates the kidney exchange interface. It is shown that endothelial and epithelial cells lining their respective lumens remodel the membrane in culture into a ≈1 µm thick exchange interface composed of native basement membrane proteins. This interface displays sufficient mechanical integrity for media flow and blood perfusion. As a proof of principle, it is demonstrated that the hRVTU performs kidney-specific functions including reabsorption of albumin and glucose from the epithelial channel. By incorporating multiple cell populations from single donors, it is demonstrated that the hRVTU may have utility for future precision medicine applications. The success of the system provides new opportunities for the next generation of organ-on-a-chip models.

A microfluidic renal proximal tubule with active reabsorptive function

In the kidney, the renal proximal tubule (PT) reabsorbs solutes into the peritubular capillaries through active transport. Here, we replicate this reabsorptive function in vitro by engineering a microfluidic PT. The microfluidic PT architecture comprises a porous membrane with user-defined submicron surface topography separating two microchannels representing a PT filtrate lumen and a peritubular capillary lumen. Human PT epithelial cells and microvascular endothelial cells in respective microchannels created a PT-like reabsorptive barrier. Co-culturing epithelial and endothelial cells in the microfluidic architecture enhanced viability, metabolic activity, and compactness of the epithelial layer. The resulting tissue expressed tight junctions, kidney-specific morphology, and polarized expression of kidney markers. The microfluidic PT actively performed sodium-coupled glucose transport, which could be modulated by administration of a sodium-transport inhibiting drug. The microfluidic PT reproduces human physiology at the cellular and tissue levels, and measurable tissue function which can quantify kidney pharmaceutical efficacy and toxicity.

Directional Fluid Transport across Organ-Blood Barriers: Physiology and Cell Biology

Directional fluid flow is an essential process for embryo development as well as for organ and organism homeostasis. Here, we review the diverse structure of various organ-blood barriers, the driving forces, transporters, and polarity mechanisms that regulate fluid transport across them, focusing on kidney-, eye-, and brain-blood barriers. We end by discussing how cross talk between barrier epithelial and endothelial cells, perivascular cells, and basement membrane signaling contribute to generate and maintain organ-blood barriers.

Hyponatremia in patients with systemic lupus erythematosus

The aim of this study was to determine whether decreased serum sodium concentration could be associated with the disease activity in SLE. We retrospectively analyzed the data of the two independent cohorts of children and adults with SLE in two centers. Hyponatremia was associated with serum chloride (p = 0.004), albumin (p = 0.002) and SLE disease activity index (SLEDAI) (p = 0.026) in children with SLE. Serum sodium levels were correlated negatively with ESR (p =0.001) and positively with serum albumin levels (p < 0.0001) and C3 (p = 0.008) in children with SLE and those levels were correlated negatively with serum interleukin-6 levels (p = 0.003) in adults with SLE. Independent risk factors for the development of hyponatremia were the decreased serum C3 levels (OR 1.069, p = 0.031), the decreased serum chloride levels (OR 2.054, p = 0.006) and increased erythrocyte sedimentation rate (ESR) (OR 1.066, p = 0.03) in children with SLE and increased C-reactive protein (CRP) (OR 1.480, p = 0.023) in combined cohorts with SLE by multiple logistic regression analyses. Our study firstly showed that hyponatremia could reflect a disease activity and severe inflammation of SLE.

Kidney-on-a-Chip Technology for Drug-Induced Nephrotoxicity Screening

Improved model systems to predict drug efficacy, interactions, and drug-induced kidney injury (DIKI) are crucially needed in drug development. Organ-on-a-chip technology is a suitable in vitro system because it reproduces the 3D microenvironment. A kidney-on-a-chip can mimic the structural, mechanical, transport, absorptive, and physiological properties of the human kidney. In this review we address the application of state-of-the-art microfluidic culturing techniques, with a focus on culturing kidney proximal tubules, that are promising for the detection of biomarkers that predict drug interactions and DIKI. We also discuss high-throughput screening and the challenges for in vitro to in vivo extrapolation (IVIVE) that will need to be overcome for successful implementation.

Gasotransmitters: novel regulators of epithelial na(+) transport?

The vectorial transport of Na(+) across epithelia is crucial for the maintenance of Na(+) and water homeostasis in organs such as the kidneys, lung, or intestine. Dysregulated Na(+) transport processes are associated with various human diseases such as hypertension, the salt-wasting syndrome pseudohypoaldosteronism type 1, pulmonary edema, cystic fibrosis, or intestinal disorders, which indicate that a precise regulation of epithelial Na(+) transport is essential. Novel regulatory signaling molecules are gasotransmitters. There are currently three known gasotransmitters: nitric oxide (NO), carbon monoxide (CO), and hydrogen sulfide (H(2)S). These molecules are endogenously produced in mammalian cells by specific enzymes and have been shown to regulate various physiological processes. There is a growing body of evidence which indicates that gasotransmitters may also regulate Na(+) transport across epithelia. This review will summarize the available data concerning NO, CO, and H(2)S dependent regulation of epithelial Na(+) transport processes and will discuss whether or not these mediators can be considered as true physiological regulators of epithelial Na(+) transport biology.

Human umbilical vein endothelial cells accelerate oxalate-induced apoptosis of human renal proximal tubule epithelial cells in co-culture system which is prevented by pyrrolidine dithiocarbamate

Oxalate is the most common component of kidney stones and elevated urinary levels induce renal tubular cell toxicity and death which is essential for crystal attachment. Endothelial cells, in some studies have been shown to regulate certain functions of renal proximal tubule cells. The aim of this study was to evaluate the effect of endothelial cells on tubular cell apoptosis in a co-culture system mimicking the in vivo renal physiological settings. The human umbilical vein endothelial cells (HUVEC) and human renal proximal tubule epithelial cells (RPTEC) were exposed to increasing concentrations (0-1.0 mM) of oxalate with or without 10 μM PDTC pretreatment for 24 h. In HUVEC, RPTEC and HUVEC-RPTEC co-cultures, the cell viability was measured using the WST-1 assay and cell death with the TUNEL analysis using the flow cytometry. The treatment of RPTECs with oxalate lead to 8.9-26.2% cell death which was reduced to 0-1.6% with the PDTC pretreatment. The death rate of RPTECs was significantly increased by 15-19% at different oxalate concentrations when co-cultured with HUVECs. In contrast, cell viability was not substantially altered in PDTC pretreated RPTECs that were co-cultured with HUVECs. Apoptosis was the way of cell death as similar rate of apoptosis was observed in cell culture systems. Although cell viability of RPTECs was further reduced when co-cultured with HUVECs, it was restored with the pretreatment of PDTC. This is the first study focusing on the role of endothelial cells on RPTEC apoptosis following hyperoxaluria.

Ion channels in inflammation

Most physical illness in vertebrates involves inflammation. Inflammation causes disease by fluid shifts across cell membranes and cell layers, changes in muscle function and generation of pain. These disease processes can be explained by changes in numbers or function of ion channels. Changes in ion channels have been detected in diarrhoeal illnesses, pyelonephritis, allergy, acute lung injury and systemic inflammatory response syndromes involving septic shock. The key role played by changes in ion transport is directly evident in inflammation-induced pain. Expression or function of all major categories of ion channels like sodium, chloride, calcium, potassium, transient receptor potential, purinergic receptor and acid-sensing ion channels can be influenced by cyto- and chemokines, prostaglandins, leukotrienes, histamine, ATP, reactive oxygen species and protons released in inflammation. Key pathways in this interaction are cyclic nucleotide, phosphoinositide and mitogen-activated protein kinase-mediated signalling, direct modification by reactive oxygen species like nitric oxide, ATP or protons and disruption of the cytoskeleton. Therapeutic interventions to modulate the adverse and overlapping effects of the numerous different inflammatory mediators on each ion transport system need to target adversely affected ion transport systems directly and locally.

Ethylene glycol induced hyperoxaluria increases plasma and renal tissue asymmetrical dimethylarginine in rats: a new pathogenetic link in hyperoxaluria induced disorders

PURPOSE

The pathogenesis of kidney stones remains elusive. There is some evidence that hyperoxaluria may effect vascular endothelium and many studies link renal stones to atherosclerosis. Also, renal vascular endothelial cells regulate proximal tubular epithelial cell function. We determined the effect of hyperoxaluria on plasma and tissue levels of asymmetrical dimethylarginine. The secondary aim was to determine the effect of verapamil on asymmetrical dimethylarginine.

MATERIALS AND METHODS

A total of 42 Sprague-Dawley rats were included in the study. In groups 1A, 1B and 1C hyperoxaluria was induced with ethylene glycol for 2 weeks. Groups 2A, 2B and 2C received ethylene glycol for 14 days and verapamil for 28 days. Control group 3 received no specific medication but distilled water. Blood samples were obtained at 24 hours and at study end, and kidney samples were obtained at 24 hours, and 7 and 28 days for histopathological evaluation.

RESULTS

Plasma asymmetrical dimethylarginine increased early in the hyperoxaluric group (p = 0.0002). The effect was retained at the end of the study period (p = 0.01). There was no increase in asymmetrical dimethylarginine in the verapamil group on short-term and long-term followup. Hyperoxaluria induced a significantly dense staining pattern in renal tissue asymmetrical dimethylarginine vs controls (p = 0.01). Asymmetrical dimethylarginine staining did not differ in the control and verapamil groups.

CONCLUSIONS

Increased systemic and local tissue asymmetrical dimethylarginine may help explain the pathogenetic mechanisms of hyperoxaluria induced disorders such as nephrolithiasis and atherosclerosis.

Development of Severe Hyponatremia due to Salt-Losing Nephropathy after Esophagectomy for Esophageal Cancer

A 72-year-old woman was admitted to our hospital for esophagectomy for esophageal cancer. On the third postoperative day, she developed polyuria (3.8 L/day), massive natriuresis, hyponatremia (112 mEq/L), hyperkalemia (5.6 mEq/L), and decreased central venous pressure, which was refractory to isotonic saline infusion. Laboratory findings indicated proximal tubular injury (high urinary β2-microglobulin, coexistence of hypouricemia) together with reduced aldosterone action at the cortical collecting duct. A diagnosis of salt-losing nephropathy was made and sodium correction was done with 3% saline and fludrocortisone. She responded well to therapy. The cause of hyponatremia was considered renal tubular dysfunction together with elevated antidiuretic hormone level. Postoperatively, it is important to look for the development of salt-losing nephropathy.

Influence of microvascular endothelial cells on transcriptional regulation of proximal tubular epithelial cells

In the renal cortex the peritubular capillary network and the proximal tubular epithelium cooperate in solute and water reabsorption, secretion, and inflammation. However, the mechanisms by which these two cell types coordinate such diverse functions remain to be characterized. Here we investigated the influence of microvascular endothelial cells on proximal tubule cells, using a filter-based, noncontact, close-proximity coculture of the human microvascular endothelial cell line HMEC-1 and the human proximal tubular epithelial cell line HK-2. With the use of DNA microarrays the transcriptomes of HK-2 cells cultured in mono- and coculture were compared. HK-2 cells in coculture exhibited a differential expression of 99 genes involved in pathways such as extracellular matrix (e.g., lysyl oxidase), cell-cell communication (e.g., IL-6 and IL-1β), and transport (e.g., GLUT3 and lipocalin 2). HK-2 cells also exhibited an enhanced paracellular gating function in coculture, which was dependent on HMEC-1-derived extracellular matrix. We identified a number of HMEC-1-enriched genes that are potential regulators of epithelial cell function such as extracellular matrix proteins (e.g., collagen I, III, IV, and V, laminin-α IV) and cytokines/growth factors (e.g., hepatocyte growth factor, endothelin-1, VEGF-C). This study demonstrates a complex network of communication between microvascular endothelial cells and proximal tubular epithelial cells that ultimately affects proximal tubular cell function. This coculture model and the data described will be important in the further elucidation of microvascular endothelial and proximal tubular epithelial cross talk mechanisms.

Extracellular renal guanosine cyclic 3'5'-monophosphate modulates nitric oxide and pressure-induced natriuresis

This study addresses the hypothesis that NO- and pressure-induced natriuresis are inhibited when guanosine cyclic 3',5'-monophosphate (cGMP) is prevented from being transported outside its renal synthesizing cells in vivo. Rats received a renal interstitial (RI) infusion of NO donor S-nitroso-N-acetylpenicillamine (SNAP) or SNAP+organic anion transporter inhibitor probenecid (PB) or SNAP+PB+cGMP. SNAP alone increased U(Na)V (P<0.05 at 1 hour and P<0.005 at 2 hours). In contrast, SNAP failed to increase U(Na)V when coinfused with PB, but cGMP coinfused with SNAP+probenecid restored the natriuretic response. SNAP alone increased RI cGMP (P<0.05) during the second experimental period. PB abolished the increase in RI cGMP in response to SNAP (P<0.01), but cGMP levels were restored by coinfusion with cGMP. PB also abolished SNAP-induced increases in fractional excretion of Na(+) (FE(Na)) and lithium (FE(Li)) (both P<0.01). PB also abolished the rise in RI cGMP and natriuresis induced by raising renal perfusion pressure (RPP) from 100 to 160 mm Hg in rats subjected to a standard pressure-natriuresis protocol and the natriuretic response was rescued by coinfusion with cGMP. RI administration of phosphodiesterase type V (PDE V) reduced both RIcGMP and U(Na)V in parallel (both P<0.01) without altering RIcAMP. The data demonstrate that export of cGMP from its renal synthesizing cells into the extracellular RI compartment is critical for the natriuretic action of NO donor SNAP or increased RPP and that RI cGMP controls basal Na(+) excretion. Extracellular cGMP modulates NO- and pressure-induced natriuresis.

Migration of leukocytes across an endothelium-epithelium bilayer as a model of renal interstitial inflammation

Interstitial inflammation has emerged as a key event in the development of acute renal failure. To gain better insight into the nature of these inflammatory processes, the interplay between tubular epithelial cells, endothelial cells, and neutrophils (PMN) was investigated. A coculture transmigration model was developed, composed of human dermal microvascular endothelial (HDMEC) and human renal proximal tubular cells (HK-2) cultured on opposite sides of Transwell growth supports. Correct formation of an endoepithelial bilayer was verified by light and electron microscopy. The model was used to study the effects of endotoxin (LPS), tumor necrosis factor (TNF)-α, and α-melanocyte-stimulating hormone (α-MSH) by measuring PMN migration and cytokine release. To distinguish between individual roles of microvascular endothelial and epithelial cells in transmigration processes, migration of PMN was investigated separately in HK-2 and HDMEC monolayers. Sequential migration of PMN through endothelium and epithelium could be observed and was significantly increased after proinflammatory stimulation with either TNF-α or LPS (3.5 ± 0.58 and 2.76 ± 0.64-fold vs. control, respectively). Coincubation with α-MSH inhibited the transmigration of PMN through the bilayer after proinflammatory stimulation with LPS but not after TNF-α. The bilayers produced significant amounts of IL-8 and IL-6 mostly released from the epithelial cells. Furthermore, α-MSH decreased LPS-induced IL-6 secretion by 30% but had no significant effect on IL-8 secretion. We established a transmigration model showing sequential migration of PMN across microvascular endothelial and renal tubular epithelial cells stimulated by TNF-α and LPS. Anti-inflammatory effects of α-MSH in this bilayer model are demonstrated by inhibition on PMN transmigration and IL-6 secretion.

Nitric oxide production by mouse renal tubules can be increased by a sodium-dependent mechanism

Renal tubules process large amounts of NaCl that other investigators indicate increases tubular generation of nitric oxide. We questioned whether medullary or superficial cortical tubules would have the greater increase in nitric oxide concentration, [NO], when stressed by sodium and if the sodium/calcium exchanger was involved. Sodium stress in proximal tubules is due to the large amount of sodium absorbed and medullary tubules exist in a hypertonic sodium environment. To sodium stress the tissue, mouse kidney slices were exposed to monensin to allow passive entry of sodium ions from isotonic media and in separate studies, 400 and 600 mOsm NaCl was used. [NO] was measured with microelectrodes. Monensin (10 microM) caused a sustained increase in medullary and cortical [NO] to approximately 180% of control and 400 mOsm NaCl caused a similar initial increase in [NO] that then subsided. 600 mOsm NaCl caused a more sustained increase in [NO] of >250% of control. L-NAME strongly attenuated the increased [NO] during sodium stress. The increase in [NO] during NaCl elevation was due to sodium ions because mannitol hyperosmolarity caused approximately 20% of the increase in [NO]. Entry of sodium during NaCl hyperosmolarity was through bumetanide sensitive channels because the drug suppressed increased [NO]. Blockade of the sodium/calcium ion exchanger strongly suppressed the increased [NO] during monensin, to increase sodium entry into cells, and the elevated NaCl concentration. The data support a sodium-NO linkage that increased NO signaling in proportion to sodium stress by cortical tubules and was highly dependent upon sodium-calcium exchange.

Evidence for the role of reactive nitrogen species in polymicrobial sepsis-induced renal peritubular capillary dysfunction and tubular injury

Acute kidney injury (AKI) remains a frequent and serious complication of human sepsis that contributes significantly to mortality. For better understanding of the development of AKI during sepsis, the cecal ligation and puncture (CLP) murine model of sepsis was studied using intravital video microscopy (IVVM) of the kidney. IVVM with FITC-dextran was used to determine the percentage of capillaries with continuous, intermittent or no flow at 0 (sham), 10, 16, and 22 h after CLP. There was a dramatic fall in capillary perfusion as early as 10 h after CLP that persisted through 22 h. The percentage of vessels with continuous flow at 16 h decreased from 73 +/- 2% in shams to 16 +/- 2% (P < 0.05), whereas the percentage of vessels with no flow increased from 4 +/- 1% in shams to 42 +/- 2% (P < 0.05). The capillary perfusion defect preceded the rise in serum creatinine. IVVM with dihydrorhodamine-123 was used to quantify in real time reactive nitrogen species (RNS) generation by renal tubules, and the inducible nitric oxide synthase inhibitor L-iminoethyl-lysine (mg/kg) was used to examine the role of inducible nitric oxide synthase inhibitor on capillary dysfunction and RNS generation. Tubular generation of RNS was significantly elevated at 10 h after CLP and was associated with tubules that were bordered by capillaries with reduced perfusion. L-iminoethyl-lysine significantly reversed the capillary perfusion defect, blocked RNS generation, and reduced AKI. These data show that capillary dysfunction and RNS generation contribute to tubular injury and suggest that RNS should be considered a potential therapeutic target in the treatment of sepsis-induced AKI.

Effects of the inducible nitric-oxide synthase inhibitor L-N(6)-(1-iminoethyl)-lysine on microcirculation and reactive nitrogen species generation in the kidney following lipopolysaccharide administration in mice

The mortality rate for septic patients with acute renal failure is approximately doubled compared with patients with sepsis alone. Unfortunately, the treatment for sepsis-induced renal failure has advanced little during the last several decades. Because sepsis is often caused by lipopolysaccharide (LPS), a mouse model of LPS challenge was used to study the development of kidney injury. We hypothesized that inducible nitric-oxide synthase (iNOS)-catalyzed nitric oxide production and that generation of reactive nitrogen species (RNS) might play a role in the microcirculatory defect and resulting tubular injury associated with LPS administration. Fluorescent intravital videomicroscopy was used to assess renal peritubular capillary perfusion and document RNS generation by renal tubules in real time. As early as 6 h after LPS administration (10 mg/kg i.p.), RNS generation (rhodamine fluorescence), redox stress [NAD(P)H autofluorescence], and the percentage of capillaries without flow were each significantly increased compared with saline-treated mice (p < 0.05). The generation of RNS was supported by the detection of nitrotyrosine-protein adducts in the kidney using immunohistochemistry. The iNOS inhibitor l-N(6)-(1-iminoethyl)-lysine (l-NIL; 3 mg/kg i.p.) completely blocked the increase in rhodamine fluorescence and NAD(P)H autofluorescence and prevented the capillary defects at 6 h after LPS administration. These results suggest that iNOS-derived RNS is an important contributor to the peritubular capillary perfusion defects and RNS generation that occur during sepsis and emphasize that pharmacological inhibition of iNOS may provide beneficial effects during sepsis by improving renal capillary perfusion and reducing RNS generation in the kidney.

Metabolic Alkalosis, Bedside and Bench

Although significant contributions to the understanding of metabolic alkalosis have been made recently, much of our knowledge rests on data from clearance studies performed in humans and animals many years ago. This article reviews the contributions of these studies, as well as more recent work relating to the control of renal acid-base transport by mineralocorticoid hormones, angiotensin, endothelin, nitric oxide, and potassium balance. Finally, clinical aspects of metabolic alkalosis are considered.

Changes in ion transport in inflammatory disease

Ion transport is essential for maintenance of transmembranous and transcellular electric potential, fluid transport and cellular volume. Disturbance of ion transport has been associated with cellular dysfunction, intra and extracellular edema and abnormalities of epithelial surface liquid volume. There is increasing evidence that conditions characterized by an intense local or systemic inflammatory response are associated with abnormal ion transport. This abnormal ion transport has been involved in the pathogenesis of conditions like hypovolemia due to fluid losses, hyponatremia and hypokalemia in diarrhoeal diseases, electrolyte abnormalities in pyelonephritis of early infancy, septicemia induced pulmonary edema, and in hypersecretion and edema induced by inflammatory reactions of the mucosa of the upper respiratory tract. Components of membranous ion transport systems, which have been shown to undergo a change in function during an inflammatory response include the sodium potassium ATPase, the epithelial sodium channel, the Cystic Fibrosis Transmembrane Conductance Regulator and calcium activated chloride channels and the sodium potassium chloride co-transporter. Inflammatory mediators, which influence ion transport are tumor necrosis factor, gamma interferon, interleukins, transforming growth factor, leukotrienes and bradykinin. They trigger the release of specific messengers like prostaglandins, nitric oxide and histamine which alter ion transport system function through specific receptors, intracellular second messengers and protein kinases. This review summarizes data on in vivo measurements of changes in ion transport in acute inflammatory conditions and in vitro studies, which have explored the underlying mechanisms. Potential interventions directed at a correction of the observed abnormalities are discussed.

A method for the isolation of glomerular and tubulointerstitial endothelial cells and a comparison of characteristics with the human umbilical vein endothelial cell model

BACKGROUND

Abnormalities in the structure and function of glomerular endothelial cells play a pivotal role in the development of progressive renal disease. The vascular abnormalities observed in the renal tubulointerstitium, however, correlate more strongly with progressive renal failure. Therefore, the successful isolation and culture of human renal microvascular endothelial cells from both the glomerulus and tubulointerstitium are paramount in studying renal disease models.

METHODS AND RESULTS

This study describes a simple and reproducible method for the isolation of human tubulointerstitial and glomerular endothelial cells by using immunomagnetic separation with anti-platelet endothelial-cell adhesion (anti-PECAM-1) Dyna beads, followed by manual weeding of mesangial and fibroblast contamination. No significant changes in morphological or immunohistochemical characteristics were observed up to passage two of culture. The in vitro characteristics of the endothelial cells were compared to the renal cortical endothelial cells in vivo and the standard human umbilical vein endothelial cell model (HUVECs). Similar to HUVECs, both populations of renal microvascular endothelial cells had a classical cobblestone appearance, stained positively for von Willebrand Factor and PECAM-1 and negatively for antifibroblast surface antigen and anticytokeratin. Differences in the expression of von Willebrand Factor, Wiebel Palade bodies and Flk-1 staining were observed between glomerular and tubulointerstitial endothelial cells. These immunohistochemical characteristics suggested that tubulointerstital endothelial cells were more closely aligned to HUVECS than to the glomerular endothelial cells. This observation indicated that HUVECs may be a suitable model for determining the tubulointerstitial endothelial response to systemic injury.

CONCLUSION

In conclusion, a unique and novel method for the differential isolation of both glomerular and tubulointerstitial endothelial cells has been developed. Significantly, characterization of these populations suggests a role for HUVECS in the study of renal tubulointerstitial disease.

Effect of acute hyperglycaemia on sodium handling and excretion of nitric oxide metabolites, bradykinin, and cGMP in Type 1 diabetes mellitus

AIMS

The aim of this study was to evaluate the effect of acutely induced hyperglycaemia on renal sodium handling and to explore the role of the bradykinin-nitric oxide-cGMP signalling pathway.

PATIENTS AND METHODS

We compared 20 Type 1 diabetic (DM1) patients without microalbuminuria with 15 weight-, age-, and sex-matched healthy controls (C). Clearances of para-aminohippuric acid (CPAH), inulin (Cin), lithium, sodium, and urinary nitrite/nitrate (NOx), cGMP and bradykinin excretion rates were measured in two 90-min periods: a glycaemic clamp-induced euglycaemia (5 mmol/l-period I) and hyperglycaemia (12 mmol/l-period II) (Study 1) and during time-controlled euglycaemia (5 mmol/l-period I and 5 mmol/l-period II) to avoid the effects of time and volume load (Study 2).

RESULTS

Cin and CPAH were not significantly different during euglycaemia (period I of Study 1) in DM1 and controls, whereas fractional excretion of sodium was decreased in DM1 (1.84 +/- 0.75 vs. 2.36 +/- 0.67%; P < 0.05) due to an increase in fractional distal tubular reabsorption of sodium (94.01 +/- 1.94 vs. 92.24 +/- 2.47%; P < 0.05). A comparison of changes during Study 1 and Study 2 revealed acute hyperglycaemia did not change renal haemodynamics significantly, while fractional distal tubular reabsorption of sodium increased (DM1: P < 0.05; C: P < 0.01) and fractional excretion of sodium decreased (P < 0.01) in both groups. The urinary excretion rates of NOx were comparable during euglycaemia in DM1 and C. While in C, they significantly increased during Study 1 (period I: 382 +/- 217 vs. period II: 515 +/- 254 nmol/min; P < 0.01) and Study 2 (period I: 202.9 +/- 176.8 vs. period II: 297.2 +/- 267.5 nmol/min; P < 0.05) as a consequence of the water load, no changes were found in DM1. The urinary excretion of bradykinin was lower in DM1 compared with C (0.84 +/- 0.68 vs. 1.20 +/- 0.85 micro g/min; P < 0.01) during euglycaemia; it was not affected by hyperglycaemia. There were no significant differences between DM1 and C and in cGMP urinary excretion rates following hyperglycaemia.

CONCLUSION

This study demonstrates that DM1 without renal haemodynamic alterations is associated with impaired renal sodium handling. Moreover, we did not find a relationship between the renal excretion rates of vasoactive mediators and sodium handling due to hyperglycaemia.

Nitric oxide synthesis in the kidney: isoforms, biosynthesis, and functions in health

Nitric oxide (NO) is a gaseous free radical that serves cell signaling, cellular energetics, host defense, and inflammatory functions in virtually all cells. In the kidney and vasculature, NO plays fundamental roles in the control of systemic and intrarenal hemodynamics, the tubuloglomerular feedback response, pressure natriuresis, release of sympathetic neurotransmitters and renin, and tubular solute and water transport. NO is synthesized from L-arginine by NO synthases (NOS). Because of its high chemical reactivity and high diffusibility, NO production by each of the 3 major NOS isoforms is regulated tightly at multiple levels from gene transcription to spatial proximity near intended targets to covalent modification and allosteric regulation of the enzyme itself. Many of these regulatory mechanisms have yet to be tested in renal cells. The NOS isoforms are distributed differentially and regulated in the kidney, and there remains some controversy over the specific expression of functional protein for the NOS isoforms in specific renal cell populations. Mice with targeted deletion of each of the NOS isoforms have been generated, and these each have unique phenotypes. Studies of the renal and vascular phenotypes of these mice have yielded important insights into certain vascular diseases, ischemic acute renal failure, the tubuloglomerular feedback response, and some mechanisms of tubular fluid and electrolyte transport, but thus far have been underexploited. This review explores the collective knowledge regarding the structure, regulation, and function of the NOS isoforms gleaned from various tissues, and highlights the progress and gaps in understanding in applying this information to renal and vascular physiology.

Regulation of an inwardly rectifying K+ channel by nitric oxide in cultured human proximal tubule cells

We investigated the effects of nitric oxide (NO) on activity of the inwardly rectifying K(+) channel in cultured human proximal tubule cells, using the cell-attached mode of the patch-clamp technique. An inhibitor of NO synthases, N(omega)-nitro-L-arginine methyl ester (L-NAME; 100 microM), reduced channel activity, which was restored by an NO donor, sodium nitroprusside (SNP; 10 microM) or 8-bromo-cGMP (8-BrcGMP; 100 microM). However, SNP failed to activate the channel in the presence of an inhibitor of soluble guanylate cyclase, 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (10 microM). Similarly, the SNP effect was abolished by a protein kinase G (PKG)-specific inhibitor, KT-5823 (1 microM), but not by a protein kinase A-specific inhibitor, KT-5720 (500 nM). Another NO donor, S-nitroso-N-acetyl-D,L-penicillamine (10 microM), mimicked the SNP-induced channel activation. In contrast to the stimulatory effect of SNP at a low dose (10 microM), a higher dose of SNP (1 mM) reduced channel activity, which was not restored by 8-BrcGMP. Recordings of membrane potential with the slow whole cell configuration demonstrated that l-NAME (100 microM) and the high dose of SNP (1 mM) depolarized the cell by 10.1 +/- 2.6 and 9.2 +/- 1.0 mV, respectively, whereas the low dose of SNP (10 microM) hyperpolarized it by 7.1 +/- 0.7 mV. These results suggested that the endogenous NO would contribute to the maintenance of basal activity of this K(+) channel and hence the potential formation via a cGMP/PKG-dependent mechanism, whereas a high dose of NO impaired channel activity independent of cGMP/PKG-mediated processes.

Overexpression of placenta growth factor contributes to the pathogenesis of pulmonary emphysema

To examine the role of placenta growth factor (PlGF) in the pathogenesis of pulmonary emphysema, we generated PlGF-transgenic (TG) mice using a phosphoglycerate kinase promoter. This resulted in constitutive overexpression of PlGF. In these TG mice, pulmonary emphysema, with enlarged air spaces and enhanced pulmonary compliance, first appeared at 6 months of age and became prominent at 12 months. Increased alveolar septal cell apoptosis was noted in their lungs. Fluorescence-activated cell sorter analysis suggests that these apoptotic septal cells are type II pneumocytes. At the same time, the messenger RNA of vascular endothelial growth factor and platelet-endothelial cell adhesion molecule-1, an endothelial cell marker, were downregulated indicating a reduced number of endothelial cells and its survival factor VEGF. In vitro, exogenous PlGF can inhibit the proliferation and promote the cell death of mouse type II pneumocytes. In normal newborn mice, abundant expression of PlGF messenger RNA was detected in the lungs during saccular division but was rapidly downregulated after alveolarization was complete. Thus, a persistently elevated PlGF was detrimental to the developed lung and causes the emphysematous change seen in our TG mice. Our study suggests that PlGF plays an important role in the pathogenesis of pulmonary emphysema via its action on type II pneumocytes.

Chronic nitric oxide synthase inhibition exacerbates renal dysfunction in cirrhotic rats

The present study investigated sodium balance and renal tubular function in cirrhotic rats with chronic blockade of the nitric oxide (NO) system. Rats were treated with the nonselective NO synthase inhibitor NG-nitro-l-arginine methyl ester (l-NAME) starting on the day of common bile duct ligation (CBL). Three weeks of daily sodium balance studies showed that CBL rats developed sodium retention compared with sham-operated rats and that l-NAME treatment dose dependently deteriorated cumulative sodium balance by reducing urinary sodium excretion. Five weeks after CBL, renal clearance studies were performed, followed by Western blotting of the electroneutral type 3 sodium/proton exchanger (NHE3) and the Na-K-ATPase present in proximal tubules. Untreated CBL rats showed a decreased proximal reabsorption with a concomitant reduction of NHE3 and Na-K-ATPase levels, indicating that tubular segments distal to the proximal tubules were responsible for the increased sodium reabsorption. l-NAME-treated CBL rats showed an increased proximal reabsorption measured by the lithium clearance method and showed a marked increase in NHE3 and Na-K-ATPase protein levels. Our results show that chronic l-NAME treatment exacerbates the sodium retention found in CBL rats by a significant increase in proximal tubular reabsorption.

Endothelial signaling during development

Blood vessels perfuse all tissues in the body and mediate vital metabolic exchange between tissues and blood. Increasing evidence, however, points to a direct role for paracrine signaling between blood vessel cells and surrounding target organ cells, during embryonic development and cell differentiation. Understanding the nature of this signaling and its heterogeneity, both in the embryo and in adult tissues, may not only provide insights into mechanisms for normal developmental cell fate decisions, but could also lead to novel targeted therapeutic approaches for a variety of diseases such as heart disease, diabetes or cancer.

Lipopolysaccharide induces biochemical alterations in chicks trained on the passive avoidance learning task

We have recently shown that activation of the immune system with lipopolysaccharide (LPS) results in memory-processing deficits for the passive avoidance learning task in the day-old chick. The current study examined two important issues in understanding the mechanisms underlying these memory deficits associated with immune system activation, namely, whether LPS (1) impairs Na(+)/K(+)-ATPase functioning and (2) increases corticosterone (CORT) concentrations in chicks trained on the task. As the effects of LPS on sickness behavior have only previously been characterized in older chickens, this study also tested whether LPS is able to produce similar alterations in day-old chicks. LPS decreased brain Na(+)/K(+)-ATPase activity and increased plasma concentrations of CORT in chicks trained on the passive avoidance learning task. These findings give an insight into some of the mechanisms that may be responsible for the LPS-induced memory-processing deficits. Consistent with previous research in older chickens, LPS increased body temperature in a dose-dependent manner, however, only the lowest dose of LPS tested significantly decreased food intake in the day-old chicks.

Effects of dopamine and nitric oxide on arterial pressure and renal function in volume expansion

1. The aim of the present study was to investigate the role of dopamine (DA) in the hypotensive and renal effects of L-arginine during extracellular fluid volume expansion (10% bodyweight). 2. Animals were randomized to non-expanded and expanded groups. Both groups received different treatments: L-arginine (250 mg/kg, i.v.), N(G)-nitro-L-arginine methyl ester (L-NAME; 1 mg/kg, i.v.), haloperidol (3 mg/kg, i.p.) and L-arginine + haloperidol (n = 8). Mean arterial pressure (MAP), diuresis, natriuresis, kaliuresis, glomerular filtration rate, renal plasma flow (RPF) and nitrite and nitrate (NO(x)) excretion were determined. 3. The increase in MAP induced by L-NAME was greater in expanded than in non-expanded rats (42 +/- 3 vs 32 +/- 3 mmHg, respectively; P < 0.01). Administration of haloperidol did not modify the L-arginine hypotensive effect. 4. Blockade of nitric oxide synthase diminished urine flow in non-expanded (4.15 +/- 0.56 vs 0.55 +/- 0.11 microL/min per 100 g; P < 0.01) and expanded animals (24.42 +/- 3.67 vs 17.85 +/- 2.16 microL/min per 100 g; P < 0.01). Diuresis induced by L-arginine was reduced by DA blockade in both non-expanded (17.15 +/- 2.11 vs 6.82 +/- 0.61 microL/min per 100 g; P < 0.01) and expanded animals (44.26 +/- 8.45 vs 25.43 +/- 5.12 microL/min per 100 g; P < 0.01). 5. Sodium excretion decreased with L-NAME treatment in non-expanded (0.22 +/- 0.03 vs 0.06 +/- 0.01 microEq/min per 100 g; P < 0.01) and expanded animals (3.72 +/- 0.70 vs 1.89 +/- 0.23 microEq/min per 100 g; P < 0.01). Natriuresis induced by L-arginine was diminished by haloperidol both in non-expanded (0.94 +/- 0.13 vs 0.43 +/- 0.04 microEq/min per 100 g; P < 0.01) and expanded rats (12.77 +/- 0.05 vs 3.53 +/- 0.75 microEq/min per 100 g; P < 0.01). Changes in kaliuresis changes seen following treatment with L-arginine, L-NAME and L-arginine + haloperidol followed a pattern similar to that observed for sodium excretion in both groups of rats. 6. L-arginine enhanced RPF in non-expanded animals (11.96 +/- 0.81 vs 14.52 +/- 1.05 mL/min per 100 g; P < 0.01). Glomerular filtration rate was increased by extracellular volume expansion (3.08 +/- 0.28 vs 5.42 +/- 0.46 mL/min per 100 g; P < 0.01). 7. The increase in NOx induced by acute volume expansion (0.18 +/- 0.03 vs 0.52 +/- 0.08 nmol/min per 100 g; P < 0.01) was diminished following the administration of haloperidol (0.52 +/- 0.08 vs 0.26 +/- 0.06 nmol/min per 100 g; P < 0.01). 8. Although DA does not participate in the actions of nitric oxide on vascular tone, both systems would play an important role in renal function adaptation during extracellular fluid volume expansion.

Glucose stimulates O2 consumption, NOS, and Na/H exchange in diabetic rat proximal tubules

Endothelial nitric oxide synthase (NOS) and neuronal NOS protein increased in proximal tubules of acidotic diabetic rats 3-5 wk after streptozotocin injection. NOS activity (citrulline production) was similar in nondiabetic and diabetic tubules incubated with low glucose (5 mM glucose + 20 mM mannitol); but after 30 min with high glucose (25 mM), Ca-sensitive citrulline production had increased 23% in diabetic tubules. Glucose concentration did not influence citrulline production in nondiabetic tubules. High glucose increased carboxy-2-phenyl-4,4,5,5,-tetramethylimidazoline 1-oxyl-3-oxide (cpt10)-scavenged NO sevenfold in a suspension of diabetic tubules but did not alter NO in nondiabetic tubules. Diabetes increased ouabain-sensitive 86Rb uptake (141 +/- 9 vs. 122 +/- 6 nmol x min(-1) x mg(-1)) and oligomycin-sensitive O2 consumption (QO2; 16.0 +/- 1.7 vs. 11.3 +/- 0.7 nmol x min(-1) x mg(-1)). Ethylisopropyl amiloride-inhibitable QO2 (6.5 +/- 0.6 vs. 2.4 +/- 0.3 nmol x min(-1) x mg(-1)) accounted for increased oligomycin-sensitive QO2 in diabetic tubules. N(G)-monomethyl-L-arginine methyl ester (L-NAME) inhibited most of the increase in 86Rb uptake and QO2 in diabetic tubules. L-NAME had little effect on nondiabetic tubules. Inhibition of QO2 by ethylisopropyl amiloride and L-NAME was only 5-8% additive. Uncontrolled diabetes for 3-5 wk increases NOS protein in proximal tubules and makes NOS activity sensitive to glucose concentration. Under these conditions, NO stimulates Na-K-ATPase and QO2 in proximal tubules.

Role of nitric oxide in the regulation of nephron transport

Nitric oxide (NO) plays an important role in various physiological processes in the kidney. In vivo experiments first suggested that the natriuretic and diuretic effects caused by NO may be due to decreased NaCl and fluid absorption by the nephron. In the last 10 years, several reports have directly demonstrated a role for NO in modulating transport in different tubule segments. The effects of NO on proximal tubule transport are still controversial. Both stimulation and inhibition of net fluid and bicarbonate have been reported in this segment, whereas only inhibitory effects of NO have been found in Na/H exchanger and Na/K-ATPase activity. The effects of NO in the thick ascending limb are more homogeneous than in the proximal tubule. In this segment, NO decreases net Cl and bicarbonate absorption. A direct inhibitory effect of NO on the Na-K-2Cl cotransporter and the Na/H exchanger has been reported, while NO was found to stimulate apical K channels in this segment. In the collecting duct, NO inhibits Na absorption and vasopressin-stimulated osmotic water permeability. An inhibitory effect of NO on H-ATPase has also been reported in intercalated cells of the collecting duct. Overall, the reported effects of NO in the different nephron segments mostly agree with the natriuretic and diuretic effects observed in vivo. However, the net effect of NO on transport is still controversial in some segments, and in cases like the distal tubule, it has not been studied.

Nitric oxide synthase blockade and body fluid volumes

The influence of chronic nitric oxide synthase inhibition with N G-nitro-L-arginine methyl ester (L-NAME) on body fluid distribution was studied in male Wistar rats weighing 260-340 g. Extracellular, interstitial and intracellular spaces, as well as plasma volume were measured after a three-week treatment with L-NAME (approximately 70 mg/kg per 24 h in drinking water). An increase in extracellular space (16.1 +/- 1.1 vs 13.7 +/- 0.6 ml/100 g in control group, N = 12, P<0.01), interstitial space (14.0 +/- 0.9 vs 9.7 +/- 0.6 ml/100 g in control group, P<0.001) and total water (68.7 +/- 3.9 vs 59.0 +/- 2.9 ml/100 g, P<0.001) was observed in the L-NAME group (N = 8). Plasma volume was lower in L-NAME-treated rats (2.8 +/- 0.2 ml/100 g) than in the control group (3.6 +/- 0.1 ml/100 g, P<0.001). Blood volume was also lower in L-NAME-treated rats (5.2 +/- 0.3 ml/100 g) than in the control group (7.2 +/- 0.3 ml/100 g, P<0.001). The increase in total ratio of kidney wet weight to body weight in the L-NAME group (903 +/- 31 vs 773 +/- 45 mg/100 g in control group, P<0.01) but not in total kidney water suggests that this experimental hypertension occurs with an increase in renal mass. The fact that the heart weight to body weight ratio and the total heart water remained constant indicates that, despite the presence of high blood pressure, no modification in cardiac mass occurred. These data show that L-NAME-induced hypertension causes alterations in body fluid distribution and in renal mass.

Protective effect of ischemic preconditioning on cold preservation and reperfusion injury associated with rat intestinal transplantation

OBJECTIVE

To define the protective effect of ischemic preconditioning on cold ischemia and reperfusion injury associated with intestinal transplantation, and the role of nitric oxide in this process.

SUMMARY BACKGROUND DATA

Ischemia/reperfusion injury continues to be a significant obstacle in small bowel transplantation. Preconditioning is a mechanism that protects against this injury.

METHODS

To study the capacity of preconditioning to prevent cold ischemia-associated injury and the inflammatory response associated with intestinal transplantation, the authors studied a control group of animals, cold ischemia groups with or without previous preconditioning and with or without previous administration of L-NAME or NONOS, and intestinal transplantation groups with or without previous preconditioning and with or without previous administration of L-NAME or NONOS.

RESULTS

Histologic findings and the release of lactate dehydrogenase into the preservation solution showed that preconditioning protects against cold ischemic preservation-associated injury. Preconditioning also prevented the inflammatory response associated with intestinal transplantation, measured by the above parameters and by neutrophil recruitment in the intestine. Inhibition of nitric oxide eliminates the protective effect.

CONCLUSIONS

Preconditioning protects the intestinal grafts from cold preservation and reperfusion injury in the rat intestinal transplantation model. Nitric oxide is involved in this protection.

Effects of L-arginine and furosemide on blood pressure and renal function in volume-expanded rats

1. The aim of the present study was to investigate the effects of L-arginine (L-Arg) on blood pressure and water and electrolyte excretion in control and extracellular fluid volume-expanded rats (10% bodyweight with 0.9% NaCl) and to determine whether diuretic treatment with furosemide (FUR) can be optimized by the administration of L-Arg in this model. 2. Both groups of animals were anaesthetized, divided into groups and treated with either 7.5 mg/kg FUR, 250 mg/kg L-Arg, 1 mg/kg NG-nitro-L-arginine methyl ester (L-NAME), FUR + L-NAME or FUR + L-Arg. Mean arterial pressure (MAP), diuresis, natriuresis and kaliuresis were determined. 3. Extracellular fluid volume expansion induced no changes in MAP in control and volume-expanded rats (92+/-6 vs 100+/-8 mmHg, respectively). The hypotension induced by FUR in control and volume-expanded rats (69+/-7 and 76+/-5 mmHg, respectively) was significantly (P < 0.01) enhanced by the administration of L-Arg (54+/-3 and 64+/-3 mmHg, respectively). 4. Injection of L-NAME increased MAP and diminished diuresis, natriuresis and kaliuresis in both groups. 5. Furosemide-induced water and electrolyte excretion was blunted by the administration of L-NAME. 6. The combination of L-Arg + FUR increased diuresis induced by FUR alone (control rats: 29.33+/-1.68 vs 12.91+/- 0.41 microL/min per 100 g, respectively; volume-expanded rats: 248.5+/-25.4 vs 112,6+/-8.3 microL/min per 100 g, respectively; P < 0.01). 7. The administration of the combination of L-Arg + FUR promoted a decrease in the sodium/water excretion ratio compared with the administration of FUR alone (control rats: 0.230+/-0.018 vs 0.45+/-0.03, respectively, P < 0.001; volume-expanded rats: 0.091+/-0.010 vs 0.22+/-0.03, respectively, P < 0.01). 8. The potassium/water excretion rate induced by FUR alone and in the presence of L-Arg followed a pattern similar to that seen for natriuresis (control rats: 0.35+/-0.05 vs 0.20+/-0.05 microEq/min per 100 g, respectively; volume-expanded rats: 0.045+/-0.008 vs 0.014+/-0.003 microEq/min per 100 g, respectively; P < 0.01). 9. The decrease in the electrolyte/water excretion ratio observed with FUR + L-Arg in volume-expanded rats was greater than in control animals. 10. The results of the present study show that the administration of FUR with L-Arg contributes to enhanced hypotensive and diuretic effects of FUR, thus diminishing the relative electrolyte excretion in normal conditions and in extracellular fluid volume expansion.

Peritubular fluid viscosity modulates H+ flux in proximal tubules through NO release

We evaluated the effects of increasing the viscosity (eta) in peritubular capillary perfusates (PCP; 20 mM HNaPO4--Ringer, pH 7.4) on proximal convoluted tubule (PCT) acidification. Micropuncture experiments were performed with simultaneous luminal and peritubular perfusion. Changes in pH of a 20 mM HNaPO4--Ringer (pH 7.4 at t = 0) droplet placed in PCT lumen were measured with H+-sensitive microelectrodes. By adding neutral dextran (molecular wt 300,000-400,000) to the PCP, eta was increased. The effect of 10(-5) M ATP added to normal-eta PCP was evaluated. High eta increased H+ flux (85 and 97% when eta was increased 20 and 30%, respectively, above the control value). This increase was abolished by adding the nitric oxide antagonist N(omega)-nitro-L-arginine (L-NNA; 10(-4) M) or the purinoreceptor antagonists suramin (10(-4) M) and reactive blue 2 (3 x 10(-5) M). Addition of 5 x 10(-3) M L-arginine to the peritubular perfusate overcame the inhibitory effect of L-NNA on high-eta-induced increase in H+ flux. ATP increased H+ flux (80%), and this effect was blocked by L-NNA. These results suggest that changes in eta can modulate proximal H+ flux, at least in part, through ATP-dependent nitric oxide release from the endothelial cells of the peritubular capillaries.

Production and functional roles of nitric oxide in the proximal tubule

A significant role for nitric oxide (NO) in proximal tubule physiology and pathophysiology has been revealed by a series of in vivo and in vitro studies. Whether the proximal tubule produces NO under basal conditions is still controversial; however, evidence suggests that the proximal tubule is constantly exposed to NO that might include NO from nonproximal tubule sources. When challenged with a variety of stimuli, including hypoxia, the proximal tubule is able to produce large quantities of NO. In vivo studies generally indicate that NO inhibits fluid and sodium reabsorption by the proximal tubule. However, the final effect of NO on proximal tubular reabsorption appears to depend on the concentration of NO and involve interaction with other regulatory mechanisms. NO regulates Na(+)-K(+)-ATPase, Na(+)/H(+) exchangers, and paracellular permeability of proximal tubular cells, which may contribute to its effect on proximal tubular transport. Enhanced production of NO, perhaps depending on macrophage type inducible NO synthase, participates in hypoxic/ischemic proximal tubular injury. In conclusion, NO plays a fundamental role in both physiology and pathophysiology of the proximal tubule.

Chemical hypoxia-induced increases in dopamine D1A receptor mRNA in renal epithelial cells are mediated by nitric oxide

Nitric oxide (NO) and dopamine (DA) have similar effects on renal function, with both having natriuretic and diuretic effects mediated by vascular and tubular mechanisms. Renal ischaemia or hypoxia have been shown to influence the activity of both systems. However, it is not known whether there is any crosstalk between the NO and dopaminergic systems in the kidney. Here using the porcine proximal tubule-like renal epithelial LLC-PK1 cell line as a model system, we determined whether exposure of cells to chemical hypoxia altered the steady-state levels of D1A receptor mRNA and whether the changes involved the NO system. Exposure of LLC-PK1 cells to chemical hypoxia resulted in a marked increase in D1A receptor mRNA levels as measured by reverse transcription-polymerase chain reaction (RT-PCR). The increased levels of D1A receptor mRNA following hypoxia were blocked by the NO synthase inhibitors NG-nitro-L-arginine methylester (L-NAME) or NG-monomethyl-L-arginine (L-NMMA). Further evidence that the NO system exerted positive effects on D1A receptor gene expression came from finding that the NO donor sodium nitroprusside, the NO precursor L-arginine and the guanosine 3', 5'-cyclic monophosphate (cyclic GMP) analogue 8-Br-cGMP all increased D1A receptor mRNA levels in LLC-PK1 cells. These results indicate that expression of the D1A receptor in LLC-PK1 cells can be positively regulated by the NO system. Such an interaction between the renal NO and DA systems may contribute to the reported protective effects that NO and DA exert upon the kidney under conditions of ischaemia.