Exosomes from human saliva as a source of microRNA biomarkers

OBJECTIVE

The aim of this study was to examine the presence of microRNAs (miRNAs) within exosomes isolated from human saliva and to optimize and test methods for successful downstream applications.

DESIGN

Exosomes isolated from fresh and frozen glandular and whole human saliva were used as a source of miRNAs. The presence of miRNAs was validated with TaqMan quantitative PCR and miRNA microarrays.

RESULTS

We successfully isolated exosomes from human saliva from healthy controls and a patient with Sjögren's syndrome. microRNAs extracted from the exosomal fraction were sufficient for quantitative PCR and microarray profiling.

CONCLUSIONS

The isolation of miRNAs from easily and non-invasively obtained salivary exosomes with subsequent characterization of the miRNA expression patterns is promising for the development of future biomarkers of the diagnosis and prognosis of various salivary gland pathologies.

AP214, an analogue of alpha-melanocyte-stimulating hormone, ameliorates sepsis-induced acute kidney injury and mortality

Sepsis remains a serious problem in critically ill patients with the mortality increasing to over half when there is attendant acute kidney injury. alpha-Melanocyte-stimulating hormone is a potent anti-inflammatory cytokine that inhibits many forms of inflammation including that with acute kidney injury. We tested whether a new alpha-melanocyte-stimulating hormone analogue (AP214), which has increased binding affinity to melanocortin receptors, improves sepsis-induced kidney injury and mortality using a cecal ligation and puncture mouse model. In the lethal cecal ligation-puncture model of sepsis, severe hypotension and bradycardia resulted and AP214 attenuated acute kidney injury of the lethal model with a bell-shaped dose-response curve. An optimum AP214 dose reduced acute kidney injury even when it was administered 6 h after surgery and it significantly improved blood pressure and heart rate. AP214 reduced serum TNF-alpha and IL-10 levels with a bell-shaped dose-response curve. Additionally; NF-kappaB activation in the kidney and spleen, and splenocyte apoptosis were decreased by the treatment. AP214 significantly improved survival in both lethal and sublethal models. We have shown that AP214 improves hemodynamic failure, acute kidney injury, mortality and splenocyte apoptosis attenuating pro- and anti-inflammatory actions due to sepsis.

Frequent Hemodialysis Network (FHN) randomized trials: Study design

Observational studies suggest improvements with frequent hemodialysis (HD), but its true efficacy and safety remain uncertain. The Frequent Hemodialysis Network Trials Group is conducting two multicenter randomized trials of 250 subjects each, comparing conventional three times weekly HD with (1) in-center daily HD and (2) home nocturnal HD. Daily HD will be delivered for 1.5-2.75 h, 6 days/week, with target eK(t)/V(n) > or = 0.9/session, whereas nocturnal HD will be delivered for > or = 6 h, 6 nights/week, with target stdK(t)/V of > or = 4.0/week. Subjects will be followed for 1 year. The composite of mortality with the 12-month change in (i) left ventricular mass index (LVMI) by magnetic resonance imaging, and (ii) SF-36 RAND Physical Health Composite (PHC) are specified as co-primary outcomes. The seven main secondary outcomes are between group comparisons of: change in LVMI, change in PHC, change in Beck Depression Inventory score, change in Trail Making Test B score, change in pre-HD serum albumin, change in pre-HD serum phosphorus, and rates of non-access hospitalization or death. Changes in blood pressure and erythropoiesis will also be assessed. Safety outcomes will focus on vascular access complications and burden of treatment. Data will be obtained on the cost of delivering frequent HD compared to conventional HD. Efforts will be made to reduce bias, including blinding assessment of subjective outcomes. Because no large-scale randomized trials of frequent HD have been previously conducted, the first year has been designated a Vanguard Phase, during which feasibility of randomization, ability to deliver the interventions, and adherence will be evaluated.

Exosomal Fetuin-A identified by proteomics: a novel urinary biomarker for detecting acute kidney injury

Urinary exosomes containing apical membrane and intracellular fluid are normally secreted into the urine from all nephron segments, and may carry protein markers of renal dysfunction and structural injury. We aimed to discover biomarkers in urinary exosomes to detect acute kidney injury (AKI), which has a high mortality and morbidity. Animals were injected with cisplatin. Urinary exosomes were isolated by differential centrifugation. Protein changes were evaluated by two-dimensional difference in gel electrophoresis and changed proteins were identified by mass spectrometry. The identified candidate biomarkers were validated by Western blotting in individual urine samples from rats subjected to cisplatin injection; bilateral ischemia and reperfusion (I/R); volume depletion; and intensive care unit (ICU) patients with and without AKI. We identified 18 proteins that were increased and nine proteins that were decreased 8 h after cisplatin injection. Most of the candidates could not be validated by Western blotting. However, exosomal Fetuin-A increased 52.5-fold at day 2 (1 day before serum creatinine increase and tubule damage) and remained elevated 51.5-fold at day 5 (peak renal injury) after cisplatin injection. By immunoelectron microscopy and elution studies, Fetuin-A was located inside urinary exosomes. Urinary Fetuin-A was increased 31.6-fold in the early phase (2-8 h) of I/R, but not in prerenal azotemia. Urinary exosomal Fetuin-A also increased in three ICU patients with AKI compared to the patients without AKI. We conclude that (1) proteomic analysis of urinary exosomes can provide biomarker candidates for the diagnosis of AKI and (2) urinary Fetuin-A might be a predictive biomarker of structural renal injury.

Simvastatin improves sepsis-induced mortality and acute kidney injury via renal vascular effects

Acute kidney injury (AKI) occurs in about half of patients in septic shock and the mortality of AKI with sepsis is extremely high. An effective therapeutic intervention is urgently required. Statins are 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors that also have pleiotropic actions. They have been reported to increase the survival of septic or infectious patients. But the effect of simvastatin, a widely used statin, on sepsis-induced AKI is unknown. The effects of simvastatin and tumor necrosis factor (TNF)-alpha neutralizing antibody were studied in a clinically relevant model of sepsis-induced AKI using cecal ligation and puncture (CLP) in elderly mice. Simvastatin significantly improved CLP-induced mortality and AKI. Simvastatin attenuated CLP-induced tubular damage and reversed CLP-induced reduction of intrarenal microvascular perfusion and renal tubular hypoxia at 24 h. Simvastatin also restored towards normal CLP-induced renal vascular protein leak and serum TNF-alpha. Neither delayed simvastatin therapy nor TNF-alpha neutralizing antibody improved CLP-induced AKI. Simvastatin improved sepsis-induced AKI by direct effects on the renal vasculature, reversal of tubular hypoxia, and had a systemic anti-inflammatory effect.

Sepsis-induced organ failure is mediated by different pathways in the kidney and liver: acute renal failure is dependent on MyD88 but not renal cell apoptosis

Toll-like receptors (TLRs) are important in sepsis. Myeloid differentiation factor 88 (MyD88) is a key molecule involved in signal transduction by multiple TLRs. The objective of this study was to investigate the contribution of TLR4 and MyD88 to acute renal failure (ARF) induced by polymicrobial sepsis. Liver dysfunction and apoptosis in the spleen contribute to sepsis severity after cecal ligation and puncture (CLP). Therefore, we also investigated liver injury and splenic apoptosis. We used a mouse model of sepsis-induced ARF using CLP to generate polymicrobial sepsis. Despite fluid and antibiotic resuscitation the mice developed multi-organ failure, including ARF, which resembles human sepsis. We investigated the role of the TLR4 receptor by comparing C3H/HeJ mice (which lack TLR4) with C3H/He0UJ normal controls. The role of MyD88 was investigated by comparing MyD88 knockout mice (MyD88(-/-)) with wild-type controls. Following CLP, mice lacking TLR4 and wild-type mice both developed comparable ARF. However, MyD88(-/-) mice did not develop ARF compared to wild-type controls. In contrast, MyD88(-/-) mice developed liver injury comparable to wild type. After CLP, MyD88(-/-) mice had significantly reduced apoptosis in the spleen compared with wild type. Apoptosis was not detected in the kidney of wild-type or MyD88(-/-) mice after CLP. In summary, ARF induced by polymicrobial sepsis is dependent on MyD88, but not TLR4. The absence of MyD88 dissociates ARF from liver injury; liver injury is MyD88-independent. There was MyD88-dependent apoptosis in the spleen, but no apoptosis in the kidney. MyD88 may be a good drug target for some, but not all, organ dysfunctions following sepsis.

Interleukin-10 inhibits ischemic and cisplatin-induced acute renal injury

BACKGROUND

Acute renal failure (ARF) is caused by ischemic and nephrotoxic insults acting alone or in combination. Anti-inflammatory agents have been shown to decrease renal ischemia-reperfusion and cisplatin-induced injury and leukocyte infiltration. Interleukin-10 (IL-10) is a potent anti-inflammatory cytokine that inhibits inflammatory and cytotoxic pathways implicated in acute renal injury. Therefore, we sought to determine if IL-10 inhibits acute renal injury.

METHODS

The effects of IL-10 were studied in mice following cisplatin administration and bilateral renal ischemia-reperfusion, in a rat model of renal transplantation, and in cultured mouse cortical tubule cells.

RESULTS

IL-10 significantly decreased renal injury following cisplatin administration and following renal ischemia/reperfusion. Delay of IL-10 treatment for one hour after cisplatin also significantly inhibited renal damage. IL-10 and alpha-melanocyte stimulating hormone (alpha-MSH) increased recovery following transplantation of a kidney subjected to warm ischemia. To explore the mechanism of action of IL-10, its effects were measured on mediators of leukocyte trafficking and inducible nitric oxide synthase (NOS-II). IL-10 inhibited cisplatin and ischemia-induced increases in mRNA for tumor necrosis factor-alpha (TNF-alpha), intercellular adhesion molecule-1 (ICAM-1), and NOS-II. IL-10 also inhibited staining for markers of apoptosis and cell cycle activity following cisplatin administration, and nitric oxide production in cultured mouse cortical tubules.

CONCLUSIONS

IL-10 protects against renal ischemic and cisplatin-induced injury. IL-10 may act, in part, by inhibiting the maladaptive activation of genes that cause leukocyte activation and adhesion, and induction of iNOS.

Intranephron localization and regulation of the V1a vasopressin receptor during chronic metabolic acidosis and dehydration in rats

The intrarenal localization and role of the V1a vasopressin receptor in body fluid homeostasis are unclear. We investigated the intranephron localization of V1a receptor mRNA and protein using reverse transcription (RT)-competitive polymerase chain reaction (PCR) and immunohistochemistry with a specific polyclonal antibody. To determine whether the V1a receptor is involved in the regulation of acid-base balance, we also examined the effects of acute and chronic metabolic acidosis and dehydration on V1a receptor expression. V1a mRNA was expressed most abundantly in the cortical collecting ducts (CCD) and decreased in the deeper CD. Expression in the glomeruli and thick ascending limbs was low. The immunohistochemical study revealed the presence of the V1a receptor in the glomeruli, the thick ascending limbs and the CD. Dehydration decreased V1a mRNA expression in the CD. Chronic metabolic acidosis increased V1a receptor mRNA expression in the CD but decreased V2 receptor mRNA expression. Western blot analysis revealed up-regulation of the V1a receptor protein in chronic metabolic acidosis. Incubation of microdissected CCD or outer medullary CD (OMCD) in a low-pH (or or low-HCO3-) medium increased the levels of V1a receptor mRNA but decreased V2 receptor mRNA expression. Incubating OMCD with arginine vasopressin (AVP) and the V1a receptor antagonist (OPC21268) increased V2 receptor mRNA expression compared with incubation with AVP alone. These data suggest that V1a receptors are present primarily in the principal and intercalated cells in the CD and that these receptors are involved in the regulation of water and acid-base balance.

Buprenorphine given after surgery does not alter renal ischemia/reperfusion injury

BACKGROUND AND PURPOSE

Potential drugs for human acute renal failure are often tested in an animal model of renal ischemia/reperfusion injury. Analgesics are often not given after surgery because of concerns that they would alter renal function. Therefore, we tested whether postoperative analgesia would alter animal health or affect the degree of renal injury.

METHODS

Mice were subjected to either 32 or 37 minutes of renal ischemia, given two or six doses of buprenorphine or vehicle at 12-hour intervals, and followed for 72 hours. In some animals, we measured body temperature and physical activity by use of telemetry.

RESULTS

Animals treated with buprenorphine recovered more rapidly from surgery based on postoperative activity, and had a small but not significant tendency for faster restoration of normal body temperature. Animals treated with buprenorphine had less weight loss after 37 minutes of ischemia. Buprenorphine given after surgery did not influence the degree of renal injury after ischemia/reperfusion.

CONCLUSIONS

Buprenorphine should be given after renal ischemia-reperfusion surgery because administration of the proper analgesic improved animal health without interfering with the renal ischemia/reperfusion model. Analgesic treatment at the time of the operation and 12 hours after was sufficient. Buprenorphine may reduce the post-surgical stress response, and thus potentially improve the specificity of testing for drugs that reduce or treat renal injury.

IF-LCM: laser capture microdissection of immunofluorescently defined cells for mRNA analysis rapid communication

BACKGROUND

The next phase of the molecular revolution will bring functional genomics down to the level of individual cells in a tissue. Laser capture microdissection (LCM) coupled with reverse transcription-polymerase chain reaction (RT-PCR) can measure gene expression in normal, cancerous, injured, or fibrotic tissue. Nevertheless, targeting of specific cells may be difficult using routine morphologic stains. Immunohistochemistry can identify cells with specific antigens; however, exposure to aqueous solutions destroys 99% of the mRNA. Consequently, there is an overwhelming need to identify specific tissue cells for LCM without mRNA loss. We report on a rapid immunofluorescent LCM (IF-LCM) procedure that allows targeted analysis of gene expression.

METHODS

A LCM microscope was outfitted for epifluorescence and light level video microscopy. Heat filters were added to shield the image intensifier from the laser. Frozen sections were fluorescently labeled by a rapid one minute incubation with anti-Tamm-Horsfall antibody and an ALEXA-linked secondary antibody. Fluorescently labeled thick ascending limb (TAL) cells were detected by low light level video microscopy, captured by LCM, and mRNA was analyzed by RT-PCR for basic amino acid transporter, Tamm-Horsfall protein, and aquaporin-2.

RESULTS

The immunofluorescently identified TAL could be cleanly microdissected without contamination from surrounding tubules. The recovery of RNA following rapid immunofluorescence staining was similar to that obtained following hematoxylin and eosin staining, as assessed by RT-PCR for malate dehydrogenase.

CONCLUSIONS

We conclude that the new apparatus and method for the immunofluorescent labeling of tissue cells targeted for LCM can isolate pure populations of targeted cells from a sea of surrounding cells with highly acceptable preservation of mRNA. Since the TAL is minimally injured following ischemia, identification of the different responses between TAL and surrounding tissue in damaged kidneys may provide new therapeutic targets or agents for the treatment of acute renal failure.

Analysis of segmental renal gene expression by laser capture microdissection

Analysis of segmental renal gene expression by laser capture microdissection.

BACKGROUND

The study of normal renal physiology has been greatly aided by microdissection techniques that have delineated the exceptional functional and cellular heterogeneity both along the nephron and between different nephron populations. These techniques are not widely used to study renal injury as microdissection is difficult because of tissue necrosis or fibrosis. We developed a procedure to detect specific gene expression in specific locations of the kidney in histologic sections.

METHODS

The anatomic specificity of laser capture microdissection (LCM) was employed with the sensitivity of reverse transcriptase-polymerase chain reaction (RT-PCR).

RESULTS

LCM/RT-PCR detected mRNA for podoplanin in 2% of a single glomerulus, rat basic amino acid transporter in 6% of a single cross-section of proximal straight tubule, and renin in eight proximal convoluted tubule cross-sections. LCM/RT-PCR could isolate pure populations of proximal convoluted tubules, proximal straight tubules, and thick ascending limbs from renal histologic sections, although pure collecting ducts could not be isolated. LCM/RT-PCR localized ischemia-reperfusion-induced induction of KC/interleukin-8 primarily to the medullary thick ascending limb, and detected transforming growth factor-beta (TGF-beta) mRNA in glomeruli of a patient with membranous glomerulonephropathy.

CONCLUSIONS

When used with an appropriate laser spot size, LCM/RT-PCR can measure gene expression in glomeruli or specific parts of the nephron and can study alterations in steady-state mRNA levels in animal models of renal disease. The applications, limitations, and refinements of this approach are discussed.

Relationship between apparent (single-pool) and true (double-pool) urea distribution volume

BACKGROUND

The volume of urea distribution (V) is usually derived from single-pool variable volume urea kinetics. A theoretical analysis has shown that modeled single-pool V (Vsp) is overestimated when the urea reduction ratio (URR) is greater than 65 to 70% and is underestimated when the URR is less than 65%. The "true" volume derived from double-pool kinetics (Vdp) does not exhibit this effect. An equation has been derived to adjust Vsp to the expected Vdp.

METHODS

To validate these theoretical predictions, we examined data from the Hemodialysis (HEMO) Study to assess the performance of Vdp as estimated from Vsp using the previously published prediction equation. For increased precision, both Vsp and Vdp were factored by anthropometric volume (Va). Patients were first dialyzed with a target equilibrated dialysis dose (eKt/V) of 1.45 during a baseline period and were then randomly assigned to eKt/V targets of either 1. 05 (a URR of approximately 67%) or 1.45 (a URR of approximately 75%). A blood sample was obtained one hour after starting dialysis during one dialysis in each patient.

RESULTS

Vsp/Va was (mean +/- SD) 1.014 +/- 0.127 in 795 patients during the baseline period when the URR was approximately 1.45. During the first modeled dialysis after randomization, the Vsp/Va fell to 0.961 +/- 0.138 in the group with an eKt/V target of 1.05, but did not change significantly under the high eKt/V goal. The correction of Vsp to Vdp using the prediction equation resulted in a Vdp/Va ratio of 0.96 to 0.98 in all three circumstances without significant differences. When a blood sample was drawn one hour after starting dialysis, the apparent Vsp/Va ratio at one hour was much lower at 0.708 +/- 0.139. However, the mean Vdp/Va ratio, computed using the correction equation, was 0.968 +/- 0.322, which was similar to the Vdp/Va ratio calculated from the postdialysis blood urea nitrogen.

CONCLUSIONS

These data suggest that the previously derived formula for adjusted Vsp is valid experimentally. The Vsp/Vdp correction should be useful for prescribing hemodialysis with either a very low Kt/V (for example, daily and early incremental dialysis) or a very high Kt/V.

Imprecision of the hemodialysis dose when measured directly from urea removal. Hemodialysis Study Group

BACKGROUND

The postdialysis blood urea nitrogen (BUN; Ct) is a pivotal parameter for assessing hemodialysis adequacy by conventional blood-side methods, but Ct is relatively unstable because of hemodialysis-induced disequilibrium. The uncertainty associated with this method is potentially reduced or eliminated by measuring urea removed on the dialysate side, a more direct approach that can determine adequacy from the fraction of urea removed and by substituting an estimate of the equilibrated postdialysis BUN (Ceq) for Ct. For a patient with a known urea volume (V), Ceq, the equilibrated Kt/V (eKt/V), and the solute removal index (SRI) can be calculated from the predialysis BUN (C0), total urea nitrogen removed (A), and V from simple mass balance calculations (dialysate/volume method). However, a theoretical error analysis showed that relatively small errors in A, C0, or V are magnified when SRI or eKt/V is calculated using this method, especially at higher eKt/V values (for example, if eKt/V = 1.4 per dialysis, a 7% dialysate collection error causes a 20% error in eKt/V).

METHODS

During three to four baseline dialyses in each of 39 patients enrolled in the pilot phase of the HEMO Study, "A" was measured using an instrument that sampled dialysate frequently (Biostat), and V was calculated from A, C0, and Ceq (median CV for V = 5.6%). The mean V was then applied to the dialysate/volume method to estimate eKt/V and SRI during two to five subsequent dialyses per patient (comparison dialyses). The accuracy and precision of these estimates were assessed by comparing them with eKt/V and SRI derived from a direct measurement of Ceq drawn 30 minutes after dialysis (reference method), from mathematical curve-fitting of sequential dialysate urea concentrations (dialysate curve-fit method), and from another blood-side method that estimates eKt/V from single pool Kt/V and the fractional rate of solute removal (rate method): eKt/V = spKt/V - 0.6.K/V + 0.03.

RESULTS

During 128 comparison dialyses, median absolute errors for calculated eKt/V compared with the reference method were 0.169, 0.061, and 0.071 for the dialysate/volume method, the rate method, and the dialysate curve-fitting method, respectively. The corresponding correlation coefficients were 0.47, 0.88, and 0.81. For SRI, median absolute errors were 0.044, 0.018, and 0.027, and the correlation coefficients were 0.54, 0.85, and 0.74 for the three methods.

CONCLUSIONS

The precision of eKt/V and SRI measurements was significantly lower for the dialysate/volume method compared with the blood-side methods. Inclusion of the dialysate curve analysis provided by the Biostat restored precision to the dialysate method to a level comparable to that of the blood-side methods. New techniques employing dialysate urea analysis should include a concentration profile to avoid these inherent methodological errors and assure the accuracy of eKt/V and SRI.

Treatment of acute renal failure

Acute renal failure is a life threatening illness whose mortality has remained high since the introduction of hemodialysis 25 years ago, despite advances in supportive care. Acute renal failure is an extremely morbid and costly disorder with a significant proportion of patients progressing to end-stage renal disease requiring dialysis. To the nephrologist, acute renal failure remains an extremely frustrating disease, because the pathophysiology is not well understood and the limited therapeutic options force the nephrologist to sit on the sidelines and wait for renal function to return. For example, dialysis remains the only FDA-approved treatment for acute renal failure, but dialysis may also cause renal injury that prolongs renal failure. The purpose of this perspective is to understand the results of the recent, largely negative, clinical trials in view of recent advances in the epidemiology of ARF. This review will also discuss diagnostic tools, strategies for improved design of clinical trials, and other therapeutic interventions that will be needed to properly treat acute renal failure in the 21st century.

Localization of the ROMK potassium channel to the apical membrane of distal nephron in rat kidney

BACKGROUND

The apical potassium (K+) channels mediate K+ recycling in thick ascending limb (TAL) and K+ secretion in cortical collecting duct (CCD). Recently, the cDNAs for a family of renal K+ channels, ROMK1, -2 and -3, were identified. Based on the biophysical properties and mRNA distribution, it is believed that these ROMK cDNAs encode the apical K+ channels of TAL and CCD. However, the information for cellular and subcellular localization of the ROMK proteins in these tubules is still not available.

METHODS

Paraffin or frozen kidney sections from adult Sprague-Dawley rats were stained by polyclonal antibodies against the N- and C-terminal domain of ROMK. Immunoreactive staining was visualized by color development from horseradish peroxidase reaction. Membrane homogenates from kidney were analyzed by Western blot analysis.

RESULTS

The polyclonal antibodies against cytoplasmic epitope of ROMK recognized a approximately 42 kD protein in the membrane homogenates from kidney, but not from liver. Staining by immunocytochemistry revealed that ROMK channels were localized to the apical membranes of the distal nephron in cortex and outer medulla, including thick ascending limb and collecting tubule. ROMK staining was absent in glomerulus, proximal tubule and inner medulla. Double staining of the tissue section with both ROMK-specific and H+-ATPase-specific antibodies revealed labeling of ROMK in the principal cells of the collecting tubules.

CONCLUSIONS

These results further strengthen the idea that ROMK channels play important roles in the recycling of K+ in TAL and the secretion of K+ in CCD.

Alpha-melanocyte-stimulating hormone inhibits renal injury in the absence of neutrophils

BACKGROUND

We previously showed that alpha-melanocyte stimulating hormone (alpha-MSH) decreases ischemia/reperfusion injury even when started six hours after ischemia. Alpha-MSH inhibits both neutrophil accumulation and nitric oxide production. To determine the relative importance of alpha-MSH on the neutrophil pathway, we examined the effects of alpha-MSH in injury models where neutrophil effects are minimal or absent.

METHODS

We studied the effects of alpha-MSH in (1) intercellular adhesion molecule-1 (ICAM-1) knock-out and background mice that were subjected to 40 minutes of ischemia and 24 hours reperfusion, and (2) isolated kidneys that were subjected to in vivo ischemia for 20 minutes and then perfused ex vivo for one hour without neutrophils. To begin to search for direct tubule effects of alpha-MSH, we studied the effect of alpha-MSH on nitric oxide (NO) in endotoxin/interferon-gamma-treated mouse cortical tubule cells.

RESULTS

ICAM-1 knock-out mice had 75% less neutrophil infiltration than background mice after ischemia. Despite the relative lack of neutrophils, alpha-MSH inhibited renal injury in ICAM-1 knock-out mice. Alpha-MSH also significantly preserved GFR and tubular sodium reabsorption in the isolated perfused ischemic kidney model. Alpha-MSH and a nitric oxide inhibitor did not exhibit synergy. Finally, alpha-MSH inhibited nitrite production by 20% in the mouse cortical tubule cells (MCT), similar to parallel observations in a cultured mouse macrophage line (RAW cells).

CONCLUSIONS

We conclude that alpha-MSH decreases renal injury when neutrophil effects are minimal or absent, indicating that alpha-MSH inhibits neutrophil-independent pathways of renal injury. The preservation of sodium absorption ex vivo and inhibition of nitrite production in cultured MCT cells suggests that alpha-MSH inhibits tubular injury by direct tubular effects.

alpha-Melanocyte-stimulating hormone and acute renal failure

alpha-Melanocyte-stimulating hormone (MSH) is an endogenous anti-inflammatory cytokine that inhibits all major forms of inflammation, alpha-MSH level is increased at sites of inflammation in humans, and is produced in the pituitary and in macrophages. The effects of alpha-MSH are mediated by melanocortin receptors found on macrophages, neutrophils, and renal tubules. alpha-MSH inhibited ischemic acute renal failure in mice and rats, even when started 6 h after injury. alpha-MSH acts, in part, by inhibiting the maladaptive activation of genes that cause inflammatory and cytotoxic renal injury. However, alpha-MSH is effective even in the absence of neutrophils, suggesting that alpha-MSH also acts directly on renal tubules.

Intrarenal localization of nitric oxide synthase isoforms and soluble guanylyl cyclase

1. Nitric oxide (NO) plays an important role in the regulation of renal function. To date, five isoforms of NO synthase (NOS) and four subunits of soluble guanylyl cyclase have been cloned. The kidney contains four isoforms of NOS and all subunits of soluble guanylyl cyclase. 2. This review focuses on the intrarenal location of the isoforms of NOS and the subunits of soluble guanylyl cyclase.

Alpha-melanocyte-stimulating hormone protects against renal injury after ischemia in mice and rats

Reperfusion after ischemia induces cytokines, chemoattractant chemokines, adhesion molecules, and nitric oxide (NO). The resultant neutrophil adherence and NO potentiates renal injury. alpha-Melanocyte-stimulating hormone (alpha-MSH) is a potent anti-inflammatory agent that inhibits neutrophil migration and production of neutrophil chemokines and NO. Since neutrophils and NO promote renal ischemic injury, we sought to determine if alpha-MSH inhibits renal injury in a model of bilateral renal ischemia. alpha-MSH significantly reduced ischemia-induced renal damage, measured by changes in renal histology and plasma blood urea nitrogen and creatinine in mice. alpha-MSH significantly decreased tubule necrosis, neutrophil plugging, and capillary congestion. Delay of alpha-MSH treatment for 6 h after ischemia also significantly inhibited renal damage. alpha-MSH also significantly inhibited ischemic damage in rats. To begin to determine the mechanism of action of alpha-MSH, we measured its effects on mediators of neutrophil trafficking and induction of the inducible isoform of NO synthase-II. alpha-MSH inhibited ischemia-induced increases in mRNA for the murine neutrophil chemokine KC/IL-8. alpha-MSH also inhibited induction of mRNA for the adhesion molecule ICAM-1, which is known to be critical in renal ischemic injury. alpha-MSH inhibited nitration of kidney proteins and induction of NO synthase-II. We conclude: (a) alpha-MSH protects against renal ischemia/reperfusion injury; and (b) it may act, in part, by inhibiting the maladaptive activation of genes that cause neutrophil activation and adhesion, and induction of NO synthase.

Differential regulation of rat glomerular and proximal tubular renin mRNA following uninephrectomy

Pages F776–F783: J. E. Tank, O. W. Moe, R. A. Star, and W. L. Henrich. “Differential regulation of rat glomerular and proximal tubular renin mRNA following uninephrectomy.” On p. F779, a registration error during printing caused the Southern blots of Fig. 2 to be misaligned with respect to the line graphs. The correct image of Fig. 2 is shown below.

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Alpha-melanocyte-stimulating hormone reduces endotoxin-induced liver inflammation

Alpha-Melanocyte-stimulating hormone (MSH) is a potent anti-inflammatory agent in many models of inflammation, suggesting that it inhibits a critical step common to different forms of inflammation. We showed previously that alpha-MSH inhibits nitric oxide (NO) production in cultured macro-phages. To determine how alpha-MSH acts in vivo, we induced acute hepatic inflammation by administering endotoxin (LPS) to mice pretreated with Corynebacterium parvum, alpha-MSH prevented liver inflammation even when given 30 min after LPS administration. To determine the mechanisms of action of alpha-MSH, we tested its influence on NO, infiltrating inflammatory cells, cytokines, and chemokines. Alpha-MSH inhibited systemic NO production, hepatic neutrophil infiltration, and increased hepatic mRNA abundance for TNF alpha, and the neutrophil and monocyte chemokines (KC/IL-8 and MCP-1). We conclude that alpha-MSH prevents LPS-induced hepatic inflammation by inhibiting production of chemoattractant chemokines which then modulate infiltration of inflammatory cells. Thus, alpha-MSH has an effect very early in the inflammatory cascade.

Differential regulation of rat glomerular and proximal tubular renin mRNA following uninephrectomy

Angiotensin II is thought to play a role in the renal adaptations to reduced renal mass, but earlier work has shown that plasma renin activity (PRA) does not increase in this setting. To examine this paradox, we studied the effect of uninephrectomy (UNX) on circulating, juxtaglomerular, glomerular, and proximal tubular (PT) renin. PRA was unchanged 2 wk following UNX and fell slightly at 6 wk. Single kidney renin secretory capacity and cortical renin mRNA, reflecting juxtaglomerular renin, were unchanged at 2 and 6 wk. With quantitative competitive reverse transcription-polymerase chain reaction, renin mRNA in microdissected glomeruli and PT were dramatically increased 2 wk post-UNIX (for glomeruli: sham, 1.2 +/- 0.3, vs. UNX, 8.8 +/- 1.9 x 10(5) copies/glomerulus; for PT: sham, 4.6 +/- 0.9, vs. UNX, 17.7 +/- 5.1 x 10(3) copies/mm). By 6 wk, glomerular renin was unchanged, and PT renin mRNA was markedly suppressed (for glomeruli; sham, 2.9 +/- 1.2, vs. UNX, 4.2 +/- 1.1 x 10(5) copies/glomerulus; for PT: sham, 7.5 +/- 2.1, vs. UNX, 1.0 +/- 0.3 x 10(3) copies/mm). These results demonstrate differential regulation of the circulating, juxtaglomerular, glomerular, and PT renin systems. Early activation of glomerular and PT renin may result in increased local generation of angiotensin II and thereby affect renal structural and functional adaptations following UNX.

Induction of inducible nitric-oxide synthase by the heterotrimeric G protein Galpha13

While the functions of several G protein alpha subunits such as alpha(s( and alpha(q) are relatively well understood, the action of others such as alpha13 remain largely undefined. Because of recent interest in regulation of nitric-oxide synthase (NOS) by G protein-coupled signaling systems and findings that receptors for two proinflammatory substances, thrombin and thromboxane couple to alpha13, we studied the effect of alpha13 on NOS activity in a renal epithelial cell line. We found that stable overexpression of alpha13 or its GTPase-deficient mutant, alpha13Q226L, in a continuous renal epithelial cell line (MCT) increased NOS activity. The increased NOS activity was due to increased expression of the macrophage-inducible form of NOS (iNOS). iNOS protein and activity were not increased in similar cells expressing an activated alpha(s) (alpha(s)Q227L) or were minimally increased in cells expressing activated alpha(i1) (alpha-i1Q204L) and alpha(q) (alpha(q)Q209L), members of the three other G protein alpha chain families. Transient co-expression of alpha13 or alpha13Q226L increased the activity of an iNOS promoter-CAT construct demonstrating that alpha13 increases iNOS expression through transcription. Consequently, alpha13 induces iNOS through a novel mechanism that is distinct from that of other G protein alpha chains and that may mediate the actions of G protein-dependent proinflammatory agents.

alpha-MSH production, receptors, and influence on neopterin in a human monocyte/macrophage cell line

alpha-Melanocyte-stimulating hormone (alpha-MSH), a tridecapeptide derived from pro-opiomelanocortin, has potent antiinflammatory activity in laboratory animals. alpha-MSH inhibits nitric oxide production by murine macrophages, an influence believed to reflect activation of an autocrine circuit in these cells, one that is based on production and release of alpha-MSH and subsequent stimulation of melanocortin receptors. We found that THP-1 cells, human monocytic cells, produced alpha-MSH; this production was increased by interleukin-6, tumor necrosis factor a, or concanavalin A. These cells also expressed the gene for the human alpha-MSH receptor MC1. Unlike murine macrophages, THP-1 cells produced little nitrite in response to interferon-gamma (IFN-gamma) and lipopolysaccharide, and a-MSH inhibited this production only slightly. However, production of neopterin, a presumed primate homologue of nitric oxide in lower animals, was increased in THP-1 cells stimulated with INF-gamma plus TNF-alpha and alpha-MSH significantly inhibited this production. The evidence indicates that an autocrine regulatory circuit based on alpha-MSH occurs in human monocyte/macrophages much as in murine macrophages. alpha-MSH-induced modulation of specific inflammatory mediators/cytotoxic agents appears to differ depending on the importance of the mediators in the myelomonocytic cells of different species.

The neuropeptide alpha-MSH has specific receptors on neutrophils and reduces chemotaxis in vitro

The proopiomelanocortin-derived peptide alpha-melanocyte stimulating hormone (alpha-MSH) has potent anti-inflammatory effects in all animal models of inflammation against which it has been tested. Understanding of the mechanism by which this occurs is incomplete, although there is recent evidence for alpha-MSH receptors in murine and human macrophages and for modulation of production of proinflammatory cytokines and related mediators by alpha-MSH. Because of the prominence of neutrophils in early stages of inflammatory reactions where alpha-MSH is effective, we examined human neutrophils for evidence of mRNA for alpha-MSH receptors and for inhibition of neutrophil chemotaxis. There was accumulation of mRNA for melanocortin receptor 1 (MC1) in RT/PCR product from neutrophils stimulated with interferon and LPS. In subsequent studies alpha-MSH inhibited migration of neutrophils from most normal volunteers when the cells were placed in FMLP or IL-8 gradients. The inhibition by alpha-MSH could be traced to alterations in cAMP in neutrophils. The presence of alpha-MSH receptor message in neutrophils is consistent with the established anti-inflammatory effects of the peptide. Direct inhibition of neutrophil chemotaxis likely contributes to the anti-inflammatory activity of alpha-MSH.

Accuracy of urea removal estimated by kinetic models

The most accurate method for assessing the dialysis dose delivered during high efficiency/flux hemodialysis has not been established. Most current indices of dialysis dose are based on blood-side urea measurements, and thus estimate urea removal. Unfortunately, these methods may lead to inappropriately short dialysis during high flux or high efficiency dialysis, perhaps because of inaccuracies in estimating the amount of urea removal. It is unknown whether these clearance-based approaches can accurately predict either absolute or fractional net urea removal, the latter being equivalent to the solute removal index (SRI). Therefore, we compared the urea removal calculated by five blood-side kinetic methods: (1) urea reduction ration, (2) 1-pool, (3) 2-pool models, and the (4) Smye and (5) Daugirdas formulae. These were compared with the gold standard measurement by direct dialysate quantification. Eight stable patients receiving high-flux hemodialysis were studied over four sessions each. BUN was measured at 0, 45 minutes, 90 minutes, end dialysis, one hour after dialysis (equilibrium value), and 48 hours later. Total body water was determined from the dialysate urea removal; the urea generation rate was calculated using one hour post-dialysis and 48-hour BUN values. Both the total body water and urea generation rate were provided to the 1- and 2-pool models to optimize accuracy. The urea reduction ratio overestimated SRI. The 1-pool model overestimated both absolute urea removal and SRI in 28 of 32 sessions. The 2-pool model slightly underestimated both absolute urea removal and SRI. In contrast, the Smye and Daugirdas formulas accurately estimated SRI.(ABSTRACT TRUNCATED AT 250 WORDS)

Evidence of autocrine modulation of macrophage nitric oxide synthase by alpha-melanocyte-stimulating hormone

alpha-Melanocyte-stimulating hormone (alpha-MSH) is a potent inhibitory agent in all major forms of inflammation. To identify a potential mechanism of antiinflammatory action of alpha-MSH, we tested its effects on production of nitric oxide (NO), believed to be a mediator common to all forms of inflammation. We measured NO and alpha-MSH production in RAW 264.7 cultured murine macrophages stimulated with bacterial lipopolysaccharide and interferon gamma. alpha-MSH inhibited production of NO, as estimated from nitrite production and nitration of endogenous macrophage proteins. This occurred through inhibition of production of NO synthase II protein; steady-state NO synthase II mRNA abundance was also reduced. alpha-MSH increased cAMP accumulation in RAW cells, characteristic of alpha-MSH receptors in other cell types. RAW cells also expressed mRNA for the primary alpha-MSH receptor (melanocortin 1). mRNA for proopiomelanocortin, the precursor molecular of alpha-MSH, was expressed in RAW cells, and tumor necrosis factor alpha increased production and release of alpha-MSH. These results suggest that the proinflammatory cytokine tumor necrosis factor alpha can induce macrophages to increase production of alpha-MSH, which then becomes available to act upon melanocortin receptors on the same cells. Such stimulation of melanocortin receptors could modulate inflammation by inhibiting the production of NO. The results suggest that alpha-MSH is an autocrine factor in macrophages which modulates inflammation by counteracting the effects of proinflammatory cytokines.

TNF-alpha and IFN-gamma induce expression of nitric oxide synthase in cultured rat medullary interstitial cells

Cytokines increase the expression of the inducible (type II) nitric oxide synthase (NOS) in macrophages, liver, and renal epithelial cells. Previously, we found that cultured rat medullary interstitial cells (RMIC) contain high levels of soluble guanylyl cyclase. To determine whether these cells can also produce NO, we studied the effects of tumor necrosis factor-alpha (TNF-alpha) and interferon-gamma (IFN-gamma) on NO production, NOS II mRNA, and NOS II protein expression. Both TNF-alpha and IFN-gamma, in the presence of a low concentration of the other cytokine, caused dose-dependent increases in NO production. Exposure to TNF-alpha and IFN-gamma stimulated the production of NOS II mRNA, as determined by Northern blotting. Restriction mapping of reverse transcription-polymerase chain reaction products indicated that normal cells contained macrophage NOS II, whereas cytokine-stimulated cells contained primarily vascular smooth muscle NOS II and some macrophage NOS II. The appearance of NOS II protein was demonstrated by Western blotting. RMIC cell guanosine 3',5'-cyclic monophosphate accumulation increased 129-fold in response to the cytokines. NOS inhibitors decreased nitrite production. We conclude that 1) TNF-alpha and IFN-gamma induce the expression of vascular smooth muscle NOS II and production of NO in RMIC, and 2) NO acts as an autocrine activator of the soluble guanylyl cyclase in RMIC.

Prolonged in vivo hypoxia enhances nitric oxide synthase type I and type III gene expression in adult rat lung

Prolonged hypoxia in the adult rat causes a decline in endothelium-derived nitric oxide (NO) production in the pulmonary circulation. To evaluate whether this is related to a decrease in endothelial NO synthase (NOS-III) expression, we determined the effects of hypobaric hypoxia (7 or 21 days) on NOS-III gene expression in adult rat lung. Neuronal NOS (NOS-I) expression was also examined; NOS-I has been immunohistochemically localized to rat bronchiolar epithelium. NOS-III and NOS-I mRNA abundance were assessed in reverse transcription-polymerase chain reaction assays and the proteins were evaluated by immunoblot analysis. After 7 and 21 days of hypoxia, there were increases in the steady-state levels of both NOS-III and NOS-I mRNA, rising 2.7- to 3.0-fold and 2.5- to 2.8-fold, respectively. These findings were confirmed by Northern analyses. In parallel, NOS-III and NOS-I protein abundance were also increased with hypoxia by 3.0- to 3.5-fold and 2.4- to 3.0-fold, respectively. NOS activity detected by [3H]arginine to [3H]citrulline conversion rose 109%. Thus, prolonged in vivo hypoxia causes enhancement of NOS-III and NOS-I gene expression in adult rat lung, indicating that the pulmonary expression of these genes is modulated in vivo. The increase in NOS-III expression does not explain the declines in pulmonary endothelial NO production previously observed following prolonged hypoxia in this model. Alternatively, the fall in NO production may be related to diminished NOS co-factor availability.

Endothelial nitric oxide synthase is expressed in cultured human bronchiolar epithelium

Nitric oxide (NO) is an important mediator of physiologic and inflammatory processes in the lung. To better understand the role of NO in the airway, we examined constitutive NO synthase (NOS) gene expression and function in NCI-H441 human bronchiolar epithelial cells, which are believed to be of Clara cell lineage. NOS activity was detected by [3H]arginine to [3H]citrulline conversion (1,070 +/- 260 fmol/mg protein per minute); enzyme activity was inhibited 91% by EGTA, consistent with the expression of a calcium-dependent NOS isoform. Immunoblot analyses with antisera directed against neuronal, inducible, or endothelial NOS revealed expression solely of endothelial NOS protein. Immunocytochemistry for endothelial NOS revealed staining predominantly in the cell periphery, consistent with the association of this isoform with the cellular membrane. To definitively identify the NOS isoform expressed in H441 cells, NOS cDNA was obtained by degenerate PCR. Sequencing of the H441 NOS cDNA revealed 100% identity with human endothelial NOS at the amino acid level. Furthermore, the H441 NOS cDNA hybridized to a single 4.7-kb mRNA species in poly(A)+ RNA isolated from H441 cells, from rat, sheep, and pig lung, and from ovine endothelial cells, coinciding with the predicted size of 4.7 kb for endothelial NOS mRNA. Guanylyl cyclase activity in H441 cells, assessed by measuring cGMP accumulation, rose 6.6- and 5.4-fold with calcium-mediated activation of NOS by thapsigargin and A23187, respectively. These findings indicate that endothelial NOS is expressed in select bronchiolar epithelial cells, where it may have autocrine effects through activation of guanylyl cyclase. Based on these observations and the previous identification of endothelial NOS in a kidney epithelial cell line, it is postulated that endothelial NOS may be expressed in unique subsets of epithelial cells in a variety of organs, serving to modulate ion flux and/or secretory function.

Transport and interaction of nitrogen oxides and NO2 with CO2-HCO3- transporters in pancreatic acini

Recently, we showed that NO2- increases gap junction (GJ) permeability and synchronizes intracellular Ca2+ concentration oscillations in pancreatic acini (Loessburg et al., J. Biol. Chem. 268: 19769-19775, 1993). NO2- is also an end product of nitric oxide (NO) production and metabolism. Because of the effect of NO2- on GJ permeability and the possible importance of NO2- in NO metabolism and cytotoxicity, we used pancreatic acinar cells and intracellular pH (pHi) measurements to study the interaction of nitrogen oxides and NO2- with cellular proteins. Exposing cells to NO2- resulted in a concentration-dependent cytosolic acidification. The acidification did not require the transport of NO2- and was not mediated by diffusion of HNO2. Because the acidification was prevented by CO2-HCO3- and inhibition of carbonic anhydrase, it is possible that other nitrogen oxides present in a solution containing NO2- enter the cells by diffusion and interact with OH- or H2O to stably acidify the cytosol. NO2- itself is shown to be transported by the HCO3- transporters present in the plasma membrane. Thus manipulation of the cellular Cl- gradient and 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS) were used to show Cl-/NO2- exchange, whereas stimulation of external Na(+)-dependent amiloride-insensitive and DIDS-sensitive pHi increase in acidified cells was used to demonstrate a Na(+)-(NO2-)n cotransport. Hence NO2- can be a convenient substitute for HCO3- when studying HCO3- transport in an open system. The studies also show that cellular levels of nitrogen oxides and NO2- can be modulated by the cellular HCO3(-)-buffering system.(ABSTRACT TRUNCATED AT 250 WORDS)

Localization and regulation of endothelial NO synthase mRNA expression in rat kidney

Nitric oxide (NO) has effects on renal blood flow, glomerular filtration rate, renin secretion, and renal sodium excretion. Four isoforms of nitric oxide synthase (NOS) have been cloned to date. However, the molecular identity of NOS present in the renal vasculature is unknown. Endothelial NOS (NOS-III) is regulated both acutely by cell calcium and chronically by shear stress. To determine if renal blood vessels and the glomerulus express NOS-III mRNA, we used degenerate polymerase chain reaction (PCR) to clone a portion of rat NOS-III. We then assayed NOS-III mRNA in microdissected renal structures by reverse transcriptase-PCR. NOS-III mRNA was expressed at high levels in glomeruli, arcuate vessels, and interlobular artery/afferent arterioles. NOS-III mRNA was detected inconsistently in proximal tubules, thick ascending limbs, and cortical and inner medullary collecting ducts. Previous studies have shown that chronic oral treatment with the NOS inhibitor N omega-nitro-L-arginine methyl ester (L-NAME) decreases NO synthesis and causes hypertension. To determine if the systemic blockade occurs only by competitive inhibition, we determined the effect of L-NAME on glomerular NOS-III mRNA. L-NAME administration (5 days) decreased NOS-III mRNA in the glomerulus to 25 +/- 12% of control levels. We conclude that endothelial NOS-III mRNA is preferentially expressed in the glomerulus and renal vasculature, where it can modulate renal blood flow and glomerular filtration rate. Furthermore, glomerular NOS-III may be modulated at the level of mRNA abundance in vivo by systemic L-NAME.(ABSTRACT TRUNCATED AT 250 WORDS)

Homologous and heterologous desensitization of a guanylyl cyclase-linked nitric oxide receptor in cultured rat medullary interstitial cells

Selected studies of nitroglycerin tolerance have demonstrated desensitization of the nitric oxide-stimulated guanylyl cyclase. To define the mechanism by which the response to nitric oxide becomes desensitized, we studied the effects of activating both nitric oxide and atrial natriuretic peptide-stimulated guanylyl cyclases in rat medullary interstitial cells. Cells were pretreated with the nitric oxide agonists nitroprusside (SNP) and SIN-1 for 18 hr before measuring SNP- or SIN-1-stimulated cyclic GMP (cGMP) accumulation in the presence of 3-isobutyl-1-methylxanthine. Pretreatment with SNP decreased SNP- and SIN-1-stimulated cGMP accumulation without altering the EC50 for SNP. Pretreatment with SIN-1 also inhibited SNP and SIN-1-stimulated cGMP accumulation. To rule out a nonspecific metabolic effect of SNP, we showed that SNP pretreatment decreased SIN-1-stimulated soluble guanylyl cyclase activity, but had no significant effect on forskolin-stimulated cyclic AMP accumulation. Pretreatment with SNP also decreased the mRNA abundance of the alpha 1- and beta 1-subunits of guanylyl cyclase. Pretreatment with either atrial natriuretic peptide or 8-chlorophenylthio-cGMP inhibited SNP-stimulated cGMP. We conclude that the soluble guanylyl cyclase-linked nitric oxide receptor exhibits homologous and heterologous desensitization in rat medullary interstitial cells. The site of regulation is unknown, but homologous desensitization may involve decreased abundance of soluble guanylyl cyclase.

Membrane localization of H+ and HCO3- transporters in the rat pancreatic duct

The pancreatic duct secretes alkaline fluid that is rich in HCO3- and poor in Cl-. The molecular mechanisms that mediate ductal secretion and are responsible for the axial gradients of Cl- and HCO3- along the ductal tree are not well understood because H+ and HCO3- transport by duct cells have not been characterized or localized. To address these questions, we microdissected the intralobular, main, and common segments of the rat pancreatic duct. H+ and HCO3- transporters were characterized and localized by following intracellular pH while perfusing the bath and the lumen of the ducts. In intralobular ducts, Na(+)-dependent and amiloride-sensitive recovery from acid load in the absence of HCO3- was used to localize a Na+/H+ exchanger to the basolateral membrane (BLM). Modification of Cl- gradients across the luminal (LM) and BLM in the presence of HCO3- showed the presence of Cl-/HCO3- exchangers on both membranes of intralobular duct cells. Measurement of the effect of Cl- on one side of the membrane on the rate and extent of pHi changes caused by removal and addition of Cl- to the opposite side suggested that both exchangers are present in the same cell. In the presence of HCO3-, intralobular duct cells used three separate mechanisms to extrude H+: (a) BLM-located Na+/H+ exchange, (b) Na(+)-independent vacuolar-type H+ pump, and (c) BLM-located, Na(+)-dependent, amiloride-insensitive, and 4',4'-diisothiocyanatostilbene-2,2'-disulfonic acid sensitive mechanism, possibly a Na(+)-dependent HCO3- transporter. The main and common segments of the duct displayed similar mechanisms and localization of H+ and HCO3- transporters to the extent studied in the present work. In addition to the transporters found in intralobular ducts, the main and common ducts showed Na+/H+ exchange activity in the LM. Three tests were used to exclude a significant luminal to basolateral Na+ leak as the cause for an apparent luminal Na+/H+ exchange in an HCO3- secreting cells: (a) addition of amiloride and removal of Na+ from the LM had a profound effect on Na+/H+ exchange activity on the BLM and vice versa; (b) inhibition of all transporters in the BLM by bathing the duct in the inert hydrocarbon Fluorinert FC-75 did not prevent cytosolic acidification caused by removal of luminal Na+; and (c) luminal Na+ did not activate the basolateral Na(+)-dependent HCO3- transporter. An Na(+)-independent, bafilomycin-sensitive H+ pumping activity was marginal in the absence of HCO3-.(ABSTRACT TRUNCATED AT 400 WORDS)

Nitric oxide synthase type I and type III gene expression are developmentally regulated in rat lung

The successful transition from fetal to neonatal life involves a marked decline in pulmonary vascular resistance which is modulated in part by endothelium-derived nitric oxide. To define the molecular processes which prepare the pulmonary circulation for nitric oxide mediation of vasodilatation at the time of birth, we determined the ontogeny of endothelial nitric oxide synthase (NOS-III) gene expression in lungs from fetal and newborn rats. Maturational changes in lung neuronal NOS (NOS-I) expression were also investigated; the latter isoform has been localized to rat bronchiolar epithelium. NOS proteins were examined by immunoblot analysis, and mRNA abundance was assessed in reverse transcription-polymerase chain reaction assays. Both NOS-III and NOS-I protein were detectable in 16-day fetal lung, they increased 3.8- and 3.1-fold, respectively, to maximal levels at 20 days of gestation (term = 22 day), and they fell postnatally (1-5 days). In parallel with the findings for NOS-III protein, NOS-III mRNA increased from 16 to 20 days gestation and fell after birth. In contrast, NOS-I mRNA abundance declined during late fetal life and rose postnatally. These findings were confirmed by Northern analyses. Thus NOS-III and NOS-I gene expression are developmentally regulated in rat lung, with maximal NOS-III and NOS-I protein present near term. The regulation of pulmonary NOS-III may primarily involve alterations in transcription or mRNA stability, whereas NOS-I expression in the maturing lung may also be mediated by additional posttranscriptional processes.

Depletion of intracellular Ca2+ stores activates nitric-oxide synthase to generate cGMP and regulate Ca2+ influx

The mechanism of activation of the agonist-stimulated Ca2+ entry pathway in the plasma membrane is not known. To determine the role of nitric-oxide synthase (NOS) and cGMP in the regulation of this pathway, we used intact and streptolysin O (SLO)-permeable pancreatic acini and measured the relationship between Ca2+ release from internal stores, the NO metabolic pathway, generation of cGMP, and activation of Ca2+ entry. We found that agonist- or thapsigargin (Tg)-activated Ca2+ entry is inhibited by L-NA, a specific inhibitor of NOS, and by LY83583, an inhibitor of guanylyl cyclase. Inhibition of Ca2+ entry by inhibition of NOS was reversed by the NO releasing molecules NO2- and sodium nitroprusside (SNP) and by Bt2cGMP. Inhibition of Ca2+ entry by inhibition of guanylyl cyclase was reversed by Bt2cGMP, but not by the NO releasing agents. The use of L-NA-treated cells and different concentrations of SNP revealed that cGMP has a dual effect on Ca2+ entry. Increasing cGMP up to 10-fold above control activated Ca2+ entry. Further increase in cGMP up to 80-fold above control inhibited Ca2+ entry in a concentration-dependent manner. Measurement of cellular cGMP in intact cells showed that carbachol, Tg, and NO2- increased cGMP to similar levels. The effects of carbachol and Tg were inhibited by L-NA and LY83586, whereas the effect of NO2- was inhibited only by LY83583. SLO-permeabilized cells were shown to be agonist-competent in that the agonist induced Ca2+ release from the inositol 1,4,5-trisphosphate (IP3) pool and activated a NO-dependent generation of cGMP. These cells were used to study the regulation of NOS by Ca2+ and by Ca2+ content of the internal stores. When internal stores were maintained loaded with Ca2+, increasing medium [Ca2+] up to 2.5 microM only modestly increased NOS activity. In contrast, the depletion of Ca2+ from internal stores markedly increased NOS activity independent of medium [Ca2+]. Thus, NOS senses both cytosolic [Ca2+]i and internal store Ca2+ load. We propose that activation of Ca2+ entry involves an agonist-mediated Ca2+ release from internal stores which activates a cellular pool of NOS to generate cGMP, which then modulates Ca2+ entry pathway in the plasma membrane. This mechanism can explain the capacitative nature of Ca2+ entry. The biphasic effect of cGMP provides the cells with a negative feedback mechanism which inhibits Ca2+ entry during periods of high cell [Ca2+]i. This could allow oscillatory behavior of Ca2+ entry.

Nitric oxide

Nitric oxide is a newly discovered gas that mediates communication between adjacent cells and signals inside cells. Defects in the nitric oxide signalling cascade have been found in patients with systemic hypertension, pulmonary hypertension, and coronary artery disease. High concentrations of nitric oxide are cytotoxic. Over-production of nitric oxide contributes to the pathogenesis of septic shock and uremic bleeding. This review focuses on the cardiovascular and platelet actions of nitric oxide, with emphasis on clinical studies of agents that modulate the nitric oxide signalling cascade.

Gap junction communication modulates [Ca2+]i oscillations and enzyme secretion in pancreatic acini

Global (all cells in an acinus) and focal (1-2 out of 10-15 cells) stimulation of pancreatic acini with bombesin or t-butyloxycarbonyl-Tyr(SO3)-Nle-Gly-Tyr-Asp-2-phenylethyl ester (CCKJ) together with modulation of gap junction (GJ) permeability by octanol and NO2- was used to study the role of GJ permeability in controlling [Ca2+]i oscillations and enzyme secretion. GJ permeability was quantitated by measuring fluorescence recovery after photobleaching. Octanol at 0.5 mM markedly reduced, whereas 15 mM NO2- increased GJ permeability. Focal application of bombesin caused synchronized oscillations in the entire acinus, whereas global stimulation resulted in asynchronous oscillations. Increasing GJ permeability with NO2- had no effect on bombesin-evoked [Ca2+]i oscillations. Octanol inhibited ongoing oscillations evoked by focal or global bombesin stimulation. However, when GJ were blocked prior to stimulation, subsequent global stimulation with bombesin induced long-lasting oscillations in all cells. Re-establishing GJ communication for as little as 37.5 s conferred GJ dependence on the order and time of [Ca2+]i spiking evoked by global bombesin stimulation. Focal and global stimulation with CCKJ gave different patterns of [Ca2+]i oscillations. However, in contrast to bombesin, inhibition of GJ with octanol had no effect on oscillations induced by global CCKJ stimulation. Increasing GJ permeability with NO2- synchronized CCKJ-stimulated oscillations by equalizing the amplitude and increasing the frequency in all cells within an acinus. These observations suggest that amplitude and frequency of [Ca2+]i oscillations can be regulated independently of each other, and that GJ permeable molecules modulate the frequency of [Ca2]i oscillation in an agonist-specific manner. Regardless of the agonist, increasing the frequency of oscillations by modulation of GJ permeability correlated with an increased enzyme secretion.

Characterization of soluble guanylyl cyclase in transformed human non-pigmented epithelial cells

Topical application of nitro vasodilators, such as sodium nitroprusside, reduces intraocular pressure. In brain and blood vessels, nitro vasodilators activate soluble guanylyl cyclases, producing cGMP. The location and molecular identity of ocular guanylyl cyclases are unknown. We studied transformed human non-pigmented ciliary epithelial cells, whose parental cells are responsible for the production of aqueous humor. Sodium nitroprusside increased cGMP 40 to 60 fold in a time and concentration dependent manner (EC50 40 to 100 microM). Methylene blue inhibited this effect (IC50 0.6 microM in the presence of 100 microM sodium nitroprusside). We also detected mRNA for the alpha 1 and beta 1, but not the beta 2, subunit isoforms of soluble guanylyl cyclase in these cells by Northern blotting. We conclude that transformed non-pigmented epithelial cells contain an active heterodimeric soluble guanylyl cyclase composed of at least alpha 1 and beta 1 subunits.

The urease inhibitor acetohydroxamic acid is transported by the urea pathway in rat terminal IMCD

Acetohydroxamic acid (AHA), a urea analogue, is used clinically to dissolve struvite stones because it inhibits the urease produced by Proteus mirabilis. To be effective, the concentration of AHA must be high in the collecting duct system and final urine. Because AHA is structurally similar to urea, we investigated whether AHA is transported by the urea carrier found in the terminal inner medullary collecting duct (IMCD) and the erythrocyte. We examined AHA transport under four conditions known to affect urea movement across the terminal IMCD, i.e., stimulation by vasopressin (AVP) and hyperosmolality, and inhibition by phloretin and urea analogues. The AHA permeability was determined with a 10 mM bath-to-lumen AHA gradient. AHA was measured by ultramicrocolorimetry. Addition of 1 nM AVP to the bath increased the AHA permeability of the perfused terminal IMCD. Increasing perfusate and bath osmolality from 290 to 690 mosmol/kgH2O (by adding NaCl) also increased tubule permeability to AHA. Addition of either 0.25 mM phloretin to the bath or 200 mM thiourea to the lumen reversibly inhibited the AVP-stimulated AHA permeability. AHA-induced osmotic lysis of erythrocytes was inhibited by phloretin or thionicotinamide; AHA inhibited the osmotic lysis induced by the urea analogue acetamide. Thus, in the rat terminal IMCD, both urea and AHA transport are stimulated by AVP and hyperosmolality, and both are inhibited by phloretin and thiourea. In erythrocytes, both urea and AHA transport are inhibited by phloretin or thionicotinamide. Thus AHA is transported by the urea carrier in the terminal IMCD and erythrocyte.(ABSTRACT TRUNCATED AT 250 WORDS)

Osmolarity-stimulated urea transport in rat terminal IMCD: role of intracellular calcium

We showed previously that both increasing osmolality by adding NaCl or manitol (hyperosmolarity) or adding vasopressin can stimulate urea permeability in rat terminal inner medullary collecting ducts (IMCD). Vasopressin acts via adenosine 3',5'-cyclic monophosphate (cAMP), but the mechanism by which hyperosmolarity acts is unknown. To study the mechanism, we determined the effect of varying osmolality (with NaCl) on two potential second messenger systems, i.e., cAMP and intracellular calcium. There was no significant difference in cAMP production among tubules incubated at 290, 490, 690, or 890 mosmol/kg. In contrast, cAMP did increase significantly after vasopressin (10(-8) M) addition. Intracellular calcium increased significantly when osmolality was increased from 290 to 490 mosmol/kg in the absence of vasopressin. To examine whether changes in intracellular calcium affect urea permeability, we added thapsigargin (and removed bath calcium) while maintaining osmolality at 290 mosmol/kg. Both intracellular calcium and urea permeability increased significantly. Next, we buffered intracellular calcium by pretreatment with the acetoxymethyl ester of 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid (BAPTA, 50 microM). BAPTA completely blocked the increase in urea permeability occurring when osmolality was increased from 290 to 490 mosmol/kg, but did not block the increase in urea permeability occurring when vasopressin (10(-8) M) was added. In summary, 1) hyperosmolarity increases intracellular calcium, but has no effect on cAMP accumulation; 2) thapsigargin increases intracellular calcium and urea permeability; and 3) BAPTA blocks the hyperosmolarity-stimulated increase in urea permeability, but not vasopressin-stimulated urea permeability.(ABSTRACT TRUNCATED AT 250 WORDS)

Renin expression in renal proximal tubule

Angiotensinogen, angiotensin-converting enzyme, and renin constitute the components of the renin-angiotensin system. The mammalian renal proximal tubule contains angiotensinogen, angiotensin-converting enzyme, and angiotensin receptors. Previous immunohistochemical studies describing the presence of renin in the proximal tubule could not distinguish synthesized renin from renin trapped from the glomerular filtrate. In the present study, we examined the presence of renin activity and mRNA in rabbit proximal tubule cells in primary culture and renin mRNA in microdissected proximal tubules. Renin activity was present in lysates of proximal tubule cells in primary culture. Cellular renin content in cultured proximal tubule cells was increased by incubation with 10(-5) M isoproterenol and 10(-5) M forskolin by 150 and 110%, respectively. In addition, renin transcripts were detected in poly(A)+ RNA from cultured proximal tubule cells by RNA blots under high stringency conditions. In microdissected tubules from normal rats, renin mRNA was not detectable with reverse transcription and polymerase chain reaction. However, in tubules from rats administered the angiotensinogen-converting-enzyme inhibitor, enalapril, renin was easily detected in the S2 segment of the proximal tubule. We postulate the existence of a local renin-angiotensin system that enables the proximal tubule to generate angiotensin II, thereby providing an autocrine system that could locally modulate NaHCO3 and NaCl absorption.

Differential expression of mRNA for guanylyl cyclase-linked endothelium-derived relaxing factor receptor subunits in rat kidney

Endothelium-derived relaxing factor (EDRF) has profound effects on the renal vasculature, the glomerular mesangium, and also affects renal salt excretion. EDRF stimulates guanylyl cyclases, which are thought to be heterodimers comprised of alpha and beta subunits. Two alpha and two beta isoforms have been identified thus far. However, the molecular composition of in vivo guanylyl cyclase-linked EDRF receptors is unknown. We used polymerase chain reaction to clone a portion of the rat alpha 2 subunit. Guanylyl cyclase-linked EDRF receptor mRNA was detected in microdissected renal structures using a reverse transcription/polymerase chain reaction assay. The interlobular artery/afferent arteriole contained mRNA for the alpha 1, alpha 2, and beta 1 subunits; a faint beta 2 band was found in 29% of experiments. In contrast, the cortical collecting duct contained mRNA only for alpha 1 and beta 2 subunits. We conclude that guanylyl cyclase-linked EDRF receptor subunit isoforms are independently and heterogeneously expressed in the renal vasculature and cortical collecting duct, suggesting that several different EDRF receptors exist in vivo. These data suggest that the tubule receptor is composed of alpha 1/beta 2. The vasculature may contain at least two different EDRF receptors (alpha 1/beta 1 and alpha 2/beta 1). Some beta 2 may also be expressed, allowing for even greater heterogeneity.

Simultaneous recording of cell volume changes and intracellular pH or Ca2+ concentration in single osteosarcoma cells UMR-106-01

We present a new technique for the simultaneous measurement of cell volume changes and intracellular ionic activities in single cells. The technique uses measurement of changes in the concentration of intracellularly trapped fluorescent dyes to report relative cell volume. By using pH- or Ca(2+)-sensitive dyes and recording at the ion-sensitive and -insensitive (isosbestic) wavelengths, the method can measure both cell volume changes and intracellular ionic activities. The technique was used to study the mechanisms of regulatory volume decrease (RVD) in the osteosarcoma cell line UMR-106-01 grown on cover slips. Swelling cells in 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid (HEPES)-buffered hypotonic medium was followed by stable cytosolic acidification and a decrease in cell volume back toward normal. The recovery of cell volume could be blocked by depolarization, treatment with ouabain, or depletion of cell Cl-. These suggest the conductive efflux of K+ and Cl- during RVD. The cytosolic acidification that accompanied cell swelling was not blocked by amiloride, bafilomycin A, or removal of Cl- and could not be reproduced by depletion of cellular ATP. These findings exclude Na+/H+ and Cl-/HCO-3 exchange, intracellularly generated acid, or increased metabolism, respectively, as the cause of the acidification. The cell swelling-induced acidification was inhibited by depolarization, suggesting the involvement of an electrogenic pathway. The acidification, as well as RVD, was inhibited by short incubation with deoxyglucose, and these effects could not be reversed by valinomycin. Thus, the anionic pathway(s) participating in RVD and the acidification are sensitive to the cellular level of ATP. Together, these studies indicate that RVD in UMR-106-01 cells in HEPES-buffered medium is mediated by the conductive efflux of K+, Cl-, and OH-.

Regulatory volume decrease in the presence of HCO3- by single osteosarcoma cells UMR-106-01

The technique for the simultaneous recording of cell volume changes and pHi in single cells was used to study the role of HCO3- in regulatory volume decrease (RVD) by the osteosarcoma cells UMR-106-01. In the presence of HCO3-, steady state pHi is regulated by Na+/H+ exchange, Na+ (HCO3-)3 cotransport and Na(+)-independent Cl-/HCO3- exchange. Following swelling in hypotonic medium, pHi was reduced from 7.16 +/- 0.02 to 6.48 +/- 0.02 within 3.4 +/- 0.28 min. During this period of time, the cells performed RVD until cell volume was decreased by 31 +/- 5% beyond that of control cells (RVD overshoot). Subsequently, while the cells were still in hypotonic medium, pHi slowly increased from 6.48 +/- 0.02 to 6.75 +/- 0.02. This increase in pHi coincided with an increase in cell volume back to normal (recovery from RVD overshoot or hypotonic regulatory volume increase (RVI)). The same profound changes in cell volume and pHi after cell swelling were observed in the complete absence of Cl- or Na+, providing HCO3- was present. On the other hand, depolarizing the cells by increasing external K+ or by inhibition of K+ channels with quinidine, Ba2+ or tetraethylammonium prevented the changes in pHi and RVD. These findings suggest that in the presence of HCO3-, RVD in UMR-106-01 cells is largely mediated by the conductive efflux of K+ and HCO3-. Removal of external Na+ but not Cl- prevented the hypotonic RVI that occurred after the overshoot in RVD. Amiloride had no effect, whereas pretreatment with 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS) strongly inhibited hypotonic RVI. Thus, hypotonic RVI is mediated by a Na+(out)-dependent, Cl(-)-independent and DIDS-inhibitable mechanism, which is indicative of a Na+(HCO3-)3 cotransporter. This is the first evidence for the involvement of this transporter in cell volume regulation. The present results also stress the power of the new technique used in delineating complicated cell volume regulatory mechanisms in attached single cells.

Water and nonelectrolyte permeabilities of apical membranes of toad urinary bladder granular cells

Certain types of epithelial cells such as those lining the toad urinary bladder have been classified as "tight" because their apical membranes exhibit low permeabilities to water, ions, and small nonelectrolytes. However, the permeability properties and structural features of these specialized apical membranes remain unclear because these membranes have never been purified. To isolate toad bladder granular cell apical membranes, we derivatized the bladder apical surface with the membrane-impermeant bifunctional reagent N-hydroxysulfosuccinimydyl-S,S-biotin (NHS-SS-biotin). After cell disruption, these derivatized apical membranes were purified using streptavidin-coated magnetic beads in a magnetic field. With the use of lactoperoxidase-mediated radioiodination as a marker for apical membrane, this preparative procedure purified apical membrane 48- or 72-fold as compared with homogenate. Thin section electron microscopy revealed unilamellar vesicles with some nonvesiculated membranes, while fragments of organelles such as mitochondria were absent. Water and nonelectrolyte permeabilities of purified apical membrane vesicles were similar to those obtained in intact bladders in the absence of antidiuretic hormone stimulation. The results demonstrate that isolated apical vesicles do not contain water channels and confirm the applicability of Overton's rule to the apical membrane of the toad urinary bladder. The technique has general applicability to isolation of other plasma membranes, and the apical membranes obtained are suitable for structural analysis.

Maple syrup urine disease in Mennonites. Evidence that the Y393N mutation in E1 alpha impedes assembly of the E1 component of branched-chain alpha-keto acid dehydrogenase complex

Maple Syrup Urine Disease (MSUD) in Mennonites is associated with homozygosity for a T to A transversion in the E1 alpha gene of the branched-chain alpha-keto acid dehydrogenase complex. This causes a tyrosine to asparagine substitution at position 393 (Y393N). To assess the functional significance of this missense mutation, we have carried out transfection studies using E1 alpha-deficient MSUD lymphoblasts (Lo) as a host. The level of E1 beta subunit is also greatly reduced in Lo cells. Efficient episomal expression in lymphoblasts was achieved using the EBO vector. The inserts employed were chimeric bovine-human cDNAs which encode mitochondrial import competent E1 alpha subunit precursors. Transfection with normal E1 alpha cDNA into Lo cells restored decarboxylation activity of intact cells. Western blotting showed that both E1 alpha and E1 beta subunits were markedly increased. Introduction of Y393N mutant E1 alpha cDNA failed to produce any measurable decarboxylation activity. Mutant E1 alpha subunit was expressed at a normal level, however, the E1 beta subunit was undetectable. These results provide the first evidence that Y393N mutation is the cause of MSUD. Moreover, this mutation impedes the assembly of E1 alpha with E1 beta into a stable alpha 2 beta 2 structure, resulting in the degradation of the free E1 beta subunit.