Lipopolysaccharide-induced acute renal failure in conscious rats: effects of specific phosphodiesterase type 3 and 4 inhibition

Phosphodiesterase 4 inhibitors in diabetic nephropathy

Phosphodiesterase subtype 4 (PDE4) hydrolyzes cyclic AMP, a secondary messenger that mediates intracellular signaling, and plays key roles in inflammatory and fibrotic responses. Based on these significant anti-inflammatory effects, oral administration of PDE4 inhibitor is approved for the treatment of chronic obstructive pulmonary disease, atopic dermatitis, and psoriasis. However, PDE4 inhibition also has adverse effects, such as diarrhea, vomiting, dyspepsia, and headache. Therefore, the application of PDE4 inhibitors for chronic diseases, such as diabetes and its complications, has not yet been approved. Recent studies have reported the clinical benefits of pentoxifylline, a non-selective PDE inhibitor, in patients with kidney disease. The PDE4 inhibitor, roflumilast, also clearly ameliorates the symptoms of diabetes mellitus by improving hyperglycemia and insulin resistance. However, the beneficial effects of PDE4 inhibition on diabetic nephropathy have not yet been evaluated, and its potential mechanisms of action remain unknown. In this review, we discuss the beneficial effects of PDE4 inhibitors and their mechanisms of action using diabetes and DN models.

NCS 613, a PDE4 inhibitor, by increasing cAMP level suppresses systemic inflammation and immune complexes deposition in kidney of MRL/lpr lupus- prone mice

Nephritis remains the most common severe manifestation of systemic lupus erythematosus in which auto-antibodies mediate chronic inflammation and kidney damage. cAMP-phosphodiesterases regulate sodium excretion and inflammation in various tissues. How cAMP elevation can reduce systemic inflammation and suppress kidney inflammation and damage remains elusive. PDE4 signaling and cAMP metabolism were investigated along immune complex depositions in target tissues and kidney damage (histology). SLE disease progression is associated with changes in kidney PDE4 activity and expression. Moreover, lupus prone mice exhibit low kidney cAMP level which is associated to induction and relocation of nuclear and cytoskeleton PDE4 isoforms. Auto-antibodies-induced kidney damage was attested by mesangial proliferation and cellular infiltration. Interestingly, we reported that NCS 613 treatment decreases systemic auto-antibody secretion and their corresponding immune complex deposition in target tissues. Furthermore, NCS 613 is able to increase cAMP levels in the kidney; hence this compound rescues kidney PDE4 alterations in treated mice. NCS 613 overcomes disease progression in lupus prone mice by improving wellbeing and decreasing inflammation in treated mice. The PDE4 inhibitor, NCS 613, is a new anti-inflammatory compound that is believed to be a leading drug candidate for the treatment of inflammatory diseases such as lupus nephritis.

Cilomilast Ameliorates Renal Tubulointerstitial Fibrosis by Inhibiting the TGF-β1-Smad2/3 Signaling Pathway

Background: Renal tubulointerstitial fibrosis is the key pathological feature in chronic kidney diseases (CKDs) with no satisfactory therapies in clinic. Cilomilast is a second-generation, selective phosphodiesterase-4 inhibitor, but its role in renal tubulointerstitial fibrosis in CKD remains unclear.

Material and Methods: Cilomilast was applied to the mice with unilateral ureteric obstruction (UUO) and renal fibroblast cells (NRK-49F) stimulated by TGF-β1. Renal tubulointerstitial fibrosis and inflammation after UUO or TGF-β1 stimulation were examined by histology, Western blotting, real-time PCR and immunohistochemistry. KIM-1 and NGAL were detected to evaluate tubular injury in UUO mice.

Results:In vivo, immunohistochemistry and western blot data demonstrated that cilomilast treatment inhibited extracellular matrix deposition, profibrotic gene expression, and the inflammatory response. Furthermore, cilomilast prevented tubular injury in UUO mice, as manifested by reduced expression of KIM-1 and NGAL in the kidney. In vitro, cilomilast attenuated the activation of fibroblast cells stimulated by TGF-β1, as shown by the reduced expression of fibronectin, α-SMA, collagen I, and collagen III. Cilomilast also inhibited the activation of TGF-β1-Smad2/3 signaling in TGF-β1-treated fibroblast cells.

Conclusion: The findings of this study suggest that cilomilast is protective against renal tubulointerstitial fibrosis in CKD, possibly through the inhibition of TGF-β1-Smad2/3 signaling, indicating the translational potential of this drug in treating CKD.

PDE/cAMP/Epac/C/EBP-β Signaling Cascade Regulates Mitochondria Biogenesis of Tubular Epithelial Cells in Renal Fibrosis

AIMS

Cyclic adenosine 3'5'-monophosphate (cAMP) is a universal second messenger that plays an important role in intracellular signal transduction. cAMP is synthesized by adenylate cyclases from adenosine triphosphate and terminated by the phosphodiesterases (PDEs). In the present study, we investigated the role of the cAMP pathway in tubular epithelial cell mitochondrial biogenesis in the pathogenesis of renal fibrosis.

RESULTS

We found that the cAMP levels were decreased in fibrotic kidney tissues, and replenishing cAMP could ameliorate tubular atrophy and extracellular matrix deposition. The downregulation of cAMP was mainly attributed to the increased PDE4 expression in tubular epithelial cells. The inhibition of PDE4 by PDE4 siRNA or the specific inhibitor, rolipram, attenuated unilateral ureteral obstruction-induced renal interstitial fibrosis and transforming growth factor (TGF)-β1-stimulated primary tubular epithelial cell (PTC) damage. The Epac1/Rap1 pathway contributed to the main effect of cAMP on renal fibrosis. Rolipram could restore C/EBP-β and PGC-1α expression and protect the mitochondrial function and structure of PTCs under TGF-β1 stimulation. The antifibrotic role of rolipram in renal fibrosis relies on C/EBP-β and PGC-1α expression in tubular epithelial cells. Innovation and Conclusion: The results of the present study indicate that cAMP signaling regulates the mitochondrial biogenesis of tubular epithelial cells in renal fibrosis. Restoring cAMP by the PDE4 inhibitor rolipram may ameliorate renal fibrosis by targeting C/EBP-β/PGC1-α and mitochondrial biogenesis. Antioxid. Redox Signal. 29, 637-652.

The Effects of Extensive Glomerular Filtration of Thin Graphene Oxide Sheets on Kidney Physiology

Understanding how two-dimensional (2D) nanomaterials interact with the biological milieu is fundamental for their development toward biomedical applications. When thin, individualized graphene oxide (GO) sheets were administered intravenously in mice, extensive urinary excretion was observed, indicating rapid transit across the glomerular filtration barrier (GFB). A detailed analysis of kidney function, histopathology, and ultrastructure was performed, along with the in vitro responses of two highly specialized GFB cells (glomerular endothelial cells and podocytes) following exposure to GO. We investigated whether these cells preserved their unique barrier function at doses 100 times greater than the dose expected to reach the GFB in vivo. Both serum and urine analyses revealed that there was no impairment of kidney function up to 1 month after injection of GO at escalating doses. Histological examination suggested no damage to the glomerular and tubular regions of the kidneys. Ultrastructural analysis by transmission electron microscopy showed absence of damage, with no change in the size of podocyte slits, endothelial cell fenestra, or the glomerular basement membrane width. The endothelial and podocyte cell cultures regained their full barrier function after >48 h of GO exposure, and cellular uptake was significant in both cell types after 24 h. This study provided a previously unreported understanding of the interaction between thin GO sheets with different components of the GFB in vitro and in vivo to highlight that the glomerular excretion of significant amounts of GO did not induce any signs of acute nephrotoxicity or glomerular barrier dysfunction.

Blockade of the N-Methyl-D-Aspartate Glutamate Receptor Ameliorates Lipopolysaccharide-Induced Renal Insufficiency

N-methyl-D-aspartate (NMDA) receptor activation in rat kidney reduces renal perfusion and ultrafiltration. Hypoperfusion-induced ischemia is the most frequent cause of functional insufficiency in the endotoxemic kidney. Here, we used non-hypotensive rat model of lipopolysaccharide-induced endotoxemia to examine whether NMDA receptor hyperfunction contributes to acute kidney injury. Lipopolysaccharide-induced renal damage via increased enzymuria and hemodynamic impairments were ameliorated by co-treatment with the NMDA receptor blocker, MK-801. The NMDA receptor NR1 subunit in the rat kidney mainly co-localized with serine racemase, an enzyme responsible for synthesizing the NMDA receptor co-agonist, D-serine. The NMDA receptor hyperfunction in lipopolysaccharide-treated kidneys was demonstrated by NR1 and serine racemase upregulation, particularly in renal tubules, and by increased D-serine levels. Lipopolysaccharide also induced cell damage in cultured tubular cell lines and primary rat proximal tubular cells. This damage was mitigated by MK-801 and by small interfering RNA targeting NR1. Lipopolysaccharide increased cytokine release in tubular cell lines via toll-like receptor 4. The release of interleukin-1β from these cells are the most abundant. An interleukin-1 receptor antagonist not only attenuated cell death but also abolished lipopolysaccharide-induced NR1 and serine racemase upregulation and increases in D-serine secretion, suggesting that interleukin-1β-mediated NMDA receptor hyperfunction participates in lipopolysaccharide-induced tubular damage. The results of this study indicate NMDA receptor hyperfunction via cytokine effect participates in lipopolysaccharide-induced renal insufficiency. Blockade of NMDA receptors may represent a promising therapeutic strategy for the treatment of sepsis-associated renal failure.

Epithelial transport during septic acute kidney injury

A goal for scientists studying septic acute kidney injury (AKI) should be to formulate a conceptual model of disease that is able to coherently reconcile the molecular and inflammatory consequences of sepsis with impaired epithelial tubular function, diminished glomerular filtration rate (GFR) and ultimately kidney failure. Recent evidence has shed light on how sepsis modulates the tubular regulation of ion, glucose, urea and water transport and acid-base homeostasis in the kidney. The present review summarizes recent discoveries on changes in epithelial transport under septic and endotoxemic conditions as well as the mechanisms that link inflammation with impaired tubular membrane transport. This paper also proposes that the tubular dysfunction that is mediated by inflammation in sepsis ultimately leads to increased sodium and chloride delivery to the distal tubule and macula densa, contributing to tubuloglomerular feedback and impaired GFR. We feel that this conceptual model resolves many of the physiologic and clinical paradoxes that septic AKI presents to practicing researchers and clinicians.

Exogenous Vasopressin-Induced Hyponatremia in Patients With Vasodilatory Shock: Two Case Reports and Literature Review

Vasopressin has gained wide support as an adjunct vasopressor in patients with septic shock. This agent exerts its vasoconstriction effects through smooth muscle V1 receptors and also has antidiuretic activity via renal V2 receptors. This interaction with the renal V2 receptors results in the integration of aquaporin 2 channels in the apical membrane of the renal collecting duct leading to free water reabsorption. Thus, water intoxication with subsequent hyponatremia, although rare, is a potentially serious side effect of exogenous vasopressin administration. We present 2 patients who developed hyponatremia within hours of initiation of vasopressin infusion. Extensive diuresis followed its discontinuation with subsequent normalization of serum sodium. One of the patients required the use of hypertonic saline for more rapid normalization of serum sodium due to concerns for potential seizure activity. A review of the literature relevant to the incidence of vasopressin-induced hyponatremia is provided as well as discussion on additional factors relevant to septic shock that should be considered when determining the relative risk of hyponatremia in patients receiving vasopressin.

Effects of cytokines on potassium channels in renal tubular epithelia

Renal tubular potassium (K(+)) channels play important roles in the formation of cell-negative potential, K(+) recycling, K(+) secretion, and cell volume regulation. In addition to these physiological roles, it was reported that changes in the activity of renal tubular K(+) channels were involved in exacerbation of renal cell injury during ischemia and endotoxemia. Because ischemia and endotoxemia stimulate production of cytokines in immune cells and renal tubular cells, it is possible that cytokines would affect K(+) channel activity. Although the regulatory mechanisms of renal tubular K(+) channels have extensively been studied, little information is available about the effects of cytokines on these K(+) channels. The first report was that tumor necrosis factor acutely stimulated the single channel activity of the 70 pS K(+) channel in the rat thick ascending limb through activation of tyrosine phosphatase. Recently, it was also reported that interferon-γ (IFN-γ) and interleukin-1β (IL-1β) modulated the activity of the 40 pS K(+) channel in cultured human proximal tubule cells. IFN-γ exhibited a delayed suppression and an acute stimulation of K(+) channel activity, whereas IL-1β acutely suppressed the channel activity. Furthermore, these cytokines suppressed gene expression of the renal outer medullary potassium channel. The renal tubular K(+) channels are functionally coupled to the coexisting transporters. Therefore, the effects of cytokines on renal tubular transporter activity should also be taken into account, when interpreting their effects on K(+) channel activity.

Inhibition of NF-kappaB ameliorates sepsis-induced downregulation of aquaporin-2/V2 receptor expression and acute renal failure in vivo

Acute renal failure (ARF) is frequently associated with polyuria and urine concentration defects and it is a severe complication of sepsis because it increases the mortality rate. Inhibition of NF-kappaB activation has been suggested to provide a useful strategy for the treatment of septic shock. However, the impact on sepsis-induced ARF is still unclear. Therefore, we examined the effect of pyrrolidine dithiocarbamate (PDTC) and of small interfering RNA (siRNA) silencing NF-kappaB p50/p105 on sepsis-induced downregulation of vasopressin V(2) receptors and aquaporin (AQP)-2 channels using a cecal ligation and puncture (CLP) mouse model. CLP caused a time-dependent downregulation of renal vasopressin V(2) receptor and of AQP2 expression without alterations in plasma vasopressin levels. Renal activation of NF-kappaB in response to CLP was attenuated by PDTC pretreatment, which also attenuated the downregulation of V(2) receptor and AQP2 expression. Furthermore, a strong nuclear staining for the NF-kappaB p50 subunit throughout the whole kidney in response to CLP was observed. siRNA against NF-kappaB p50 attenuated the CLP-induced nuclear translocation of the p50 subunit and the CLP-induced downregulation of V(2) receptor and AQP2 expression. Additionally, PDTC and siRNA pretreatment inhibited the CLP-induced increase in renal TNF-alpha and IL-1beta concentration and NOS-2 mRNA abundance. Moreover, PDTC and siRNA pretreatment ameliorated CLP-induced hypotension and ARF. Our findings suggest that NF-kappaB activation is of importance for the downregulation of AQP2 channel and vasopressin V(2) receptor expression during sepsis. In addition, our data indicate that NF-kappaB inhibition ameliorates sepsis-induced ARF.

The role of phosphodiesterase 3 in endotoxin-induced acute kidney injury

Background

Acute kidney injury frequently accompanies sepsis. Endotoxin is known to reduce tissue levels of cAMP and low levels of cAMP have been associated with renal injury. We, therefore, hypothesized that endotoxin induced renal injury by activating phosphodiesterase 3 (PDE3) which metabolizes cAMP and that amrinone an inhibitor of PDE3 would prevent the renal injury.

Methods

Animals were divided into three groups (n = 7/group): 1) Control (0.9% NaCl infusion without LPS); 2) LPS (0.9% NaCl infusion with LPS); 3) Amrinone+LPS (Amrinone infusion with LPS). Either lipopolysaccharide (LPS) or vehicle was injected via the jugular vein and the rats followed for 3 hours. We explored the expression of PDE3 isoenzymes and the concentrations of cAMP in the tissue.

Results

The PDE3B gene but not PDE3A was upregulated in the kidney of LPS group. Immunohistochemistry also showed that PDE3B was expressed in the distal tubule in the controls and LPS caused PDE3B expression in the proximal as well. However, PDE3A was not expressed in the kidney either in the control or LPS treated groups. Tissue level of cAMP was decreased after LPS and was associated with an increase in blood urea nitrogen, creatinine, ultrastructural proximal tubular changes, and expression of inducible nitric oxide synthase (iNOS) in the endotoxemic kidney. In septic animals the phosphodiesterase 3 inhibitor, amrinone, preserved the tissue cAMP level, renal structural changes, and attenuated the increased blood urea nitrogen, creatinine, and iNOS expression in the kidney.

Conclusion

These findings suggest a significant role for PDE3B as an important mediator of LPS-induced acute kidney injury.

Modulation of aquaporin-2/vasopressin2 receptor kidney expression and tubular injury after endotoxin (lipopolysaccharide) challenge

OBJECTIVE

Sepsis-induced organ dysfunctions remain prevalent and account for >50% of intensive care unit admissions for acute renal failure with a mortality rate nearing 75%. In addition to the fact that the mechanisms underlying the pathophysiology of sepsis-related acute renal failure are unclear, the impact on septic-induced acute renal failure of either norepinephrine, a gold-standard vasopressor, and arginine vasopressin, a candidate alternative, are not well understood.

DESIGN

Randomized and controlled in vivo study.

SETTING

Research laboratory and animal facilities.

SUBJECTS

Adult rats treated with endotoxin (lipopolysaccharide) and/or vasopressors.

INTERVENTIONS

Rats were intraperitoneally injected with lipopolysaccharide (12 mg/kg) or saline and then infused with either saline, 0.375 microg/microL arginine vasopressin, or 32.5 microg/microL norepinephrine for 18 hrs. These vasopressor rates yielded respective targeted blood levels observed in human septic shock.

MEASUREMENTS AND MAIN RESULTS

Renal function, including glomerular filtration rate and fraction, renal blood flow, aquaporin-2, and arginine vasopressin-2 (V2 receptor) networking, water and salt handling, and urinary protein excretion, were evaluated. After lipopolysaccharide challenge arginine vasopressin infusion: 1) impaired creatinine clearance without affecting renal blood flow, glomerular filtration rate, and fraction but reduced free-water clearance, both of which being partially restored by the V2 receptor antagonist SR-121463B; 2) decreased the recognized ability of arginine vasopressin alone to recruit aquaporin-2 to the apical membrane increase its mRNA expression and urinary release; 3) increased urinary protein content but decreased specific kidney injury molecule-1, and Clara cell protein-16 release (p < 0.05 vs. lipopolysaccharide alone). Conversely, norepinephrine infusion did not add to lipopolysaccharide-induced alteration of urine biochemistry, except for improved creatinine clearance and increased microalbuminuria.

CONCLUSION

In this endotoxic model, dose-targeted arginine vasopressin infusion increased lipopolysaccharide-induced renal dysfunction without affecting renal blood flow and glomerular function, but with particular disruption of aquaporin-2/V2 receptor networking, consecutive decreased salt and water handling ability. This is in clear contrast with norepinephrine infusion and suggests specific arginine vasopressin-induced "tubular epithelial dysfunction."

Mechanisms of the urinary concentration defect and effect of desmopressin during endotoxemia in rats

Acute renal failure during human sepsis is often nonoliguric. To study the underlying mechanisms, renal function was assessed in endotoxic and control male Wistar rats during and after saline loading and treatment with the selective V2 receptor agonist desmopressin. Escherichia coli endotoxin (dose, 8 mg/kg) was administered from time (t)=0 to t=60 min; saline loading (rate, 5 mL/100 g per hour) was administered from t=0 to t=120 min. Thereafter, half of each group received desmopressin (dose, 10 microg) for 1 h. The inner medullary (IM) osmolality, hematocrit, plasma, and urinary concentrations of sodium, potassium, urea, and osmolality were measured; then, aquaporin 2 (AQP2) immunohistochemistry was performed. Plasma vasopressin concentrations were measured at t=180 min. Saline loading increased urine volume in all rats. In the endotoxic group, mean arterial pressure decreased when saline loading was stopped. Despite increased hematocrit and vasopressin levels (>16 pg/mL), the endotoxin group had a low IM osmolality (mean +/- SEM, 412+/-0.04 mOsm/kg H2O) in comparison with the control group (mean +/- SEM, 1,094+/-0.17 mOsm/kg H2O) and was not able to either decrease urine volume or raise urine osmolality. Desmopressin treatment in endotoxin-treated rats maintained mean arterial pressure, increased sodium reabsorption, IM osmolality, and urine osmolality, and decreased urine flow. The AQP2 intensity decreased in the endotoxin group, and the apical localization disappeared; both were not affected by desmopressin. Our results indicate that endotoxemia in rats acutely diminishes renal urinary concentration capacity and is associated with a decreased IM osmolality and diminished apical AQP2 localization. These findings may help to explain nonoliguric acute renal failure in human septic shock.

Proinflammatory cytokines cause down-regulation of renal chloride entry pathways during sepsis

OBJECTIVE

Sepsis is the most important trigger for acute renal failure, with tubular dysfunction and collapse in urine concentration. As chloride plays a major role in the urinary concentrating mechanisms, we aimed to investigate the regulation of renal chloride entry pathways, such as kidney-specific chloride channel 1, kidney-specific chloride channel 2, Barttin, thiazide-sensitive Na+-Cl- cotransporter, renal outer medullary potassium channel, and Na+/K+-adenosine triphosphatase during sepsis.

DESIGN

Prospective animal trial.

SETTING

Laboratory of the Department of Anesthesiology.

SUBJECTS

Male C57/BL6 and B6129SF2/J mice and mice deficient for tumor necrosis factor-alpha, interleukin-1-receptor-1, interferon-gamma, or interleukin-6.

INTERVENTIONS

Mice were injected with lipopolysaccharide (LPS) or proinflammatory cytokines. Hemodynamic and renal variables, cytokine concentrations, and expression of renal chloride-reabsorbing systems were investigated. Experiments with cytokine knockout mice, renal artery-clipped mice, and mice treated with glucocorticoids, low-dose LPS, and sodium nitroprusside were performed.

MEASUREMENTS AND MAIN RESULTS

LPS-injected mice presented with decreased blood pressure and glomerular filtration rate, increased fractional chloride excretion, and depressed expression of renal chloride transporters/channels. Similar alterations were observed after application of tumor necrosis factor-alpha, interleukin-1beta, interferon-gamma, or interleukin-6. LPS-induced down-regulation of chloride transporters/channels was not affected in cytokine knockout mice. Glucocorticoid treatment inhibited LPS-induced increase of cytokine concentrations, diminished LPS-induced renal dysfunction, and attenuated the down-regulation of renal chloride transporters/channels. Injection of low-dose LPS increased renal tissue cytokines and down-regulated chloride entry pathways without arterial hypotension, indicating that renal ischemia due to systemic hypotension does not mediate down-regulation of renal chloride transporters/channels. In addition, renal ischemia induced by renal artery clipping or sodium nitroprusside administration did not influence chloride transporter/channel expression.

CONCLUSIONS

Our results demonstrate down-regulation of renal chloride transporters/channels during sepsis, which is probably mediated by proinflammatory cytokines and accounts for the development of LPS-induced tubular dysfunction. Our findings contribute to the understanding, on one hand, the failure of single-anticytokine strategies and, on the other hand, the beneficial effects of glucocorticoids in the therapy of septic patients.

Losartan decreases vasopressin-mediated cAMP accumulation in the thick ascending limb of the loop of Henle in rats with congestive heart failure

INTRODUCTION

Vasopressin (AVP) stimulates sodium reabsorption and Na,K,2Cl-cotransporter (NKCC2) protein level in the thick ascending limb (TAL) of Henle's loop in rats. Rats with congestive heart failure (CHF) have increased protein level of NKCC2, which can be normalized by angiotensin II receptor type-1 (AT(1)) blockade with losartan.

AIM

In this study, we investigated whether CHF rats displayed changes in AVP stimulated cAMP formation in the TAL and examined the role of AT(1) receptor blockade on this system.

METHOD

CHF was induced by ligation of the left anterior descending coronary artery (LAD). SHAM-operated rats were used as controls. Half of the rats were treated with losartan (10 mg kg day(-1) i.p.).

RESULTS

CHF rats were characterized by increased left ventricular end diastolic pressure. Measurement of cAMP in isolated outer medullary TAL showed that both basal and AVP (10(-6) m) stimulated cAMP levels were significantly increased in CHF rats (25.52 +/- 4.49 pmol cAMP microg(-1) protein, P < 0.05) compared to Sham rats (8.13 +/- 1.14 pmol cAMP microg(-1) protein), P < 0.05). Losartan significantly reduced the basal level of cAMP in CHF rats (CHF: 12.56 +/- 1.93 fmol microg(-1) protein vs. Los-CHF: 7.49 +/- 1.08, P < 0.05), but not in Sham rats (SHAM: 4.66 +/- 0.59 vs. Los-SHAM: 4.75 +/- 0.71). AVP-mediated cAMP accumulation was absent in both groups treated with losartan (Los-SHAM: 4.75 +/- 0.71 and Los-CHF: 7.49 +/- 1.08).

CONCLUSION

The results indicate that the increased NKCC2 protein level in the mTAL from CHF rats is associated with increased cAMP accumulation in this segment. Furthermore, the finding that AT(1) receptor blockade prevents AVP-mediated cAMP accumulation in both SHAM and CHF rats suggests an interaction between angiotensin II and AVP in regulation of mTAL Na reabsorption.

A systematic review of urinary findings in experimental septic acute renal failure

OBJECTIVE

In experimental septic acute renal failure, urinary analysis is used to help diagnose and classify renal injury. However, the scientific basis for such use has not been systematically evaluated. Thus, we appraised the value of common urinary findings for the diagnosis and classification of experimental septic acute renal failure.

DESIGN

Systematic review.

SETTING

Academic medical center and university-based research laboratory.

SUBJECTS

Experimental studies describing urinary biochemistry, derived indexes, and microscopy in septic acute renal failure.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Twenty-seven articles fulfilled all inclusion criteria. Due to heterogeneity, no formal quantitative analysis was possible. The methods for induction of sepsis and models were variable. The urinary sodium, fractional excretion of sodium, and urine osmolality were reported in only four (15%), 21 (78%), and seven (26%) studies, respectively. The fractional excretion of sodium exhibited a decrease, no change, or an increase from baseline in 11 (52%), five (24%), and five (24%) studies, respectively. The urine osmolality decreased from baseline in all endotoxin-induced models but showed an early transient increase in six (22%) studies of cecal-ligation perforation. Proteinuria or urinary enzymuria was reported in only seven (26%) studies. Urinary microscopy was described in one study. Only ten studies (37%) simultaneously reported on histopathology. In all these studies, histology either was normal or showed minor ultrastructural changes on electron microscopy.

CONCLUSIONS

No conclusions are possible on how several urinary tests perform in diagnosing or classifying acute renal failure or in predicting the presence of acute tubular necrosis in experimental sepsis. Additional research is necessary to define the diagnostic and prognostic value of urinalysis in experimental sepsis.

Regulation of renal sodium transporters during severe inflammation

Sepsis-associated acute renal failure is characterized by decreased GFR and tubular dysfunction. The pathogenesis of endotoxemic tubular dysfunction with failure in urine concentration and increased fractional sodium excretion is poorly understood. This study investigated the regulation of renal sodium transporters during severe inflammation in vivo and in vitro. Injection of high-dosage LPS reduced BP and GFR, increased fractional sodium excretion, and strongly decreased the expression of Na(+)/H(+)-exchanger, renal outer medullary potassium channel, Na(+)-K(+)-2Cl(-) co-transporter, epithelial sodium channel, and Na(+)/K(+)-ATPase in mice. Also, injection of TNF-alpha, IL-1beta, or IFN-gamma decreased renal function and expression of renal sodium transporters. LPS-induced downregulation of sodium transporters was not affected in cytokine-knockout mice. However, supplementary glucocorticoid treatment, which inhibited LPS-induced increase of tissue cytokine concentrations, attenuated LPS-induced renal dysfunction and downregulation of tubular sodium transporters. Injection of low-dosage LPS increased renal tissue cytokines and downregulated renal sodium transporters without arterial hypotension. In vitro, in cortical collecting duct cells, cytokines also decreased expression of renal outer medullary potassium channel, epithelial sodium channel, and Na(+)/K(+)-ATPase. Renal hypoperfusion by renal artery clipping did not influence renal sodium transporter expression, in contrast to renal ischemia-reperfusion injury, which depressed transporter expression. These findings demonstrate downregulation of renal sodium transporters that likely accounts for tubular dysfunction during inflammation. These data suggest that alteration of renal sodium transporters during LPS-induced acute renal failure is mediated by cytokines rather than renal ischemia. However, in a complex in vivo model of severe inflammation, the possible presence and influence of renal hypoperfusion and reperfusion on the expression of renal sodium transporters cannot be completely excluded.

The effect of spironolactone on experimental periodontitis in rats

BACKGROUND

Elevated levels of tumour necrosis factor (TNF) have been found in patients with adult periodontitis. Animal studies have shown that TNF plays an important role in the pathogenesis of periodontitis. New findings suggest that the aldosterone-inhibitor spironolactone possesses an anti-TNF effect. The purpose of the study was to determine the anti-TNF effect of spironolactone in an endotoxic shock rat model and to disclose the effect of oral administration of spironolactone on the development of experimental periodontitis in rats.

METHODS

The study was divided in two parts. Part 1: oral administration of spironolactone (100 mg/kg) followed by intravenous lipopolysaccharide (1 mg/kg) infusion 45 min later. Blood samples were taken before and 90 min after lipopolysaccharide infusion to determine the TNF levels in spironolactone treated and non-treated rats. Part 2: oral administration of spironolactone [100 mg/(kg day)] starting 2 days prior to induction of experimental periodontitis established by peridental ligatures. Morphometrical and radiographical registrations of alveolar bone destruction were carried out to determine the effect of spironolactone on the progression of experimental periodontitis.

RESULTS

In part 1 the endotoxic shock model showed a significant reduction in TNF levels in the spironolactone-treated group compared to the non-treated group, suggesting that spironolactone acts as a TNF inhibitor. In part 2 spironolactone-treated rats did not demonstrate significantly less alveolar bone destruction compared to non-treated rats.

CONCLUSIONS

The insignificant effect of spironolactone treatment could be explained by the fast metabolism of spironolactone and that spironolactone does not completely inhibit TNF production in rats. Moreover, many other cytokines and mediators involved in alveolar bone destruction may account for the lacking response to spironolactone.

Acute endotoxemia in rats induces down-regulation of V2 vasopressin receptors and aquaporin-2 content in the kidney medulla

BACKGROUND

Endotoxemia can lead to fluid metabolism alterations despite unchanged or elevated plasma vasopressin (VP) levels, suggesting a refractoriness of the kidney to the effect of the peptide. To test this hypothesis, we examined the effect of lipopolysaccharide (LPS) injection on the expression of V2 receptors and aquaporin-2 in the kidney.

METHODS

Plasma VP and urine osmolality, and binding of [3H]VP to kidney membranes, Western blot, and immunohistochemical analysis of aquaporin-2, in situ hybridization for V2 VP receptors and cytokines mRNAs were measured in the kidney 3 to 24 hours after LPS injection, 250 microg/100 g, intraperitoneally.

RESULTS

LPS injection caused prolonged decreases in urine osmolality (up to 24 hours) without significant changes in plasma levels of sodium or VP. This was associated with marked decreases in V2 VP receptor mRNA and VP receptor number in the kidney, which were evident for up to 12 hours after LPS injection. Aquaporin-2 in kidney inner medulla was also reduced by about 50%. LPS induced interleukin (IL)-1beta in the kidney medulla by 3 hours, reached maximum at 6 hours, and started to decline by 12 hours, while it increased IL-6 mRNA significantly only at 3 hours. Interleukin mRNA expression was absent in kidneys of control rats. In vitro incubation of kidney medulla slices with IL-1beta reduced VP binding.

CONCLUSION

The inflammatory response to acute endotoxemia down regulates V2 VP receptors and aquaporin-2 of the kidney inner medulla resulting in prolonged impairment of the renal capacity to concentrate urine.

Effects of renal denervation on tubular sodium handling in rats with CBL-induced liver cirrhosis

This study was designed to examine the effect of bilateral renal denervation (DNX) on thick ascending limb of Henle's loop (TAL) function in rats with liver cirrhosis induced by common bile duct ligation (CBL). The CBL rats had, as previously shown, sodium retention associated with hypertrophy of the inner stripe of the outer medulla (ISOM) and increased natriuretic effect of furosemide in vivo, and semiquantitative immunoblotting showed increased expression of the furosemide-sensitive Na-K-2Cl cotransporter type 2 (NKCC2) in ISOM from CBL rats. DNX significantly attenuated the sodium retention in the CBL rats, which was associated with normalization of the natriuretic effect of furosemide, as well as a significant reduction in the expression of NKCC2 in the ISOM. However, the marked hypertrophy of the ISOM found in CBL rats was not reversed by DNX. Together, these data indicate that increased renal sympathetic nerve activity known to be present in CBL rats plays a significant role in the formation of sodium retention by stimulating sodium reabsorption in the TAL via increased renal abundance of NKCC2.