Chloride channel blockade attenuates the effect of angiotensin II on tubuloglomerular feedback in WKY but not spontaneously hypertensive rats

Bicarbonate-Based Solution for the Management of Established Acute Kidney Injury: A Pilot Open-Label Observation Study

Background Administration of intravenous (IV) solutions constitutes a key component of acute kidney injury (AKI) management. However, the optimal IV fluid solution in the setting of AKI remains uncertain. In this study, we assessed whether the use of bicarbonate-containing solution in patients with established AKI is associated with early renal recovery as compared to bicarbonate-free solutions. Methods We performed an open-label observational pilot study in 59 patients with established AKI. IV fluid solutions that were used include bicarbonate-based solution with low chloride content (80 mEq/L of 8% sodium bicarbonate in a solution that contains 77 mEq/L of sodium, 77 mEq/L of chloride and 25 g/L of glucose) or solutions without bicarbonate with high chloride content (0.9% normal saline, 0.45% half-saline, normal ringer, or 4% succinylated gelatine). We evaluated the association of IV fluids type with renal recovery. Results The median age of study participants was 66 years (inter-quartile range (IQR) 37-85), and 59% (n=35) were men. The prevalence of diabetes and chronic kidney disease (CKD) stages 1-3 were 34% (n=20) and 39% (n=23), respectively. Patients who received bicarbonate-based IV solutions had a greater reduction of serum creatinine (sCr) per day (delta sCr) as compared with patients who received bicarbonate-free solutions (-0.29±0.47 vs. 0.07±0.42; p=0.007). The renal recovery was faster in patients who received bicarbonate-based solutions as compared to the bicarbonate-free group (days from peak sCr to baseline sCr: 5.6±2.1 vs. 7.6±2.8; p < 0.001, respectively). Conclusions We observed faster renal recovery in patients with established AKI who received the bicarbonate-based solution with low chloride content. Our study findings require confirmation in larger cohorts.

Relationships of hyperchloremia with hypertension and proteinuria in patients with chronic kidney disease

BACKGROUND

A few previous clinical studies have shown that chloride (Cl) contributes to the progression and development of hypertension or proteinuria. Therefore, we aimed to determine whether hyperchloremia is associated with hypertension or proteinuria in patients with chronic kidney disease (CKD) and to define the relationships between the reduction in serum Cl concentration associated with CKD treatment and improvements in hypertension and/or proteinuria.

METHODS

We performed a retrospective observational study of new or referred patients with CKD who had hyperchloremia, moderate proteinuria, renal dysfunction, and hypertension. Patients taking medication for metabolic acidosis or with a history of dialysis were excluded. The participants' systolic and diastolic blood pressure (BP), serum sodium (Na) and Cl concentrations, and urinary protein (UP) concentration were measured at baseline and after 1 month of CKD treatment.

RESULTS

Fifty-one patients with CKD were included in the study. Their serum Cl concentration independently correlated with sBP and UP at baseline (P = 0.022 and P = 0.033, respectively). After 1 month's CKD treatment, their serum Na and Cl concentrations, sBP, and UP were significantly lower. The change in sBP during the month (ΔsBP) correlated with the change in serum Cl (ΔCl) (P = 0.012) but not with the change in serum Na. Multivariate analysis showed that ΔsBP was independently associated with ΔCl (P = 0.029).

CONCLUSIONS

Hyperchloremia is an independent predictor of hypertension and proteinuria for patients with CKD.

Normal Saline Versus Balanced Crystalloids in Renal Transplant Surgery: A Double-Blind Randomized Controlled Study

Background

The importance of optimal acid-base balance during renal transplant surgeries cannot be stressed enough. Optimal preload and electrolyte balance is important in maintaining this. There has been a debate on the choice of perioperative crystalloids in renal transplant surgeries over the past decades. Normal saline (0.9% saline) is more likely to cause hyperchloremic acidosis when compared to balanced salt solutions (BSS) with low chloride content whereas BSS may cause hyperkalemia. We aim to compare the safety and efficacy of normal saline (NS), Ringer’s lactate (RL) and Plasmalyte (PL) on acid-base balance and electrolytes during living donor kidney transplantation.

Materials and methods

Patients were randomized to NS group (n = 60), RL group (n = 60) and Plasmalyte group (n = 60). Arterial blood samples were collected for acid-base analysis after induction of anaesthesia (T0), prior to clamping the iliac vein (T1), 10 minutes after reperfusion of the donated kidney (T2) and at the end of surgery (T3). In addition, serum creatinine and 24-hour urine output were recorded on postoperative days one, two and seven.

Results

There was a statistically significant difference (p < 0.001) in the pH at the end of surgery between the three groups with the NS group being more acidotic (pH 7.29 ± 0.06, 95% CI 7.27-7.32), although this was not clinically relevant. This was explainable by the parallel increase in chloride in the NS group. Early postoperative graft functions in terms of serum creatinine, urine output and graft failure requiring dialysis were not significantly different between the groups.

Conclusion

Balanced salt solutions such as Plasmalyte and Ringer’s lactate are associated with better pH and chloride levels compared to normal saline when used intraoperatively in renal transplant patients. This difference, however, does not appear to have any bearing on graft function. Plasmalyte seems to maintain a better acid-base and electrolyte balance, especially during the postreperfusion period.

Plasma-Lyte 148: A clinical review

AIM

To outline the physiochemical properties and specific clinical uses of Plasma-Lyte 148 as choice of solution for fluid intervention in critical illness, surgery and perioperative medicine.

METHODS

We performed an electronic literature search from Medline and PubMed (via Ovid), anesthesia and pharmacology textbooks, and online sources including studies that compared Plasma-Lyte 148 to other crystalloid solutions. The following keywords were used: “surgery”, “anaesthesia”, “anesthesia”, “anesthesiology”, “anaesthesiology”, “fluids”, “fluid therapy”, “crystalloid”, “saline”, “plasma-Lyte”, “plasmalyte”, “hartmann’s”, “ringers”“acetate”, “gluconate”, “malate”, “lactate”. All relevant articles were accessed in full. We summarized the data and reported the data in tables and text.

RESULTS

We retrieved 104 articles relevant to the choice of Plasma-Lyte 148 for fluid intervention in critical illness, surgery and perioperative medicine. We analyzed the data and reported the results in tables and text.

CONCLUSION

Plasma-Lyte 148 is an isotonic, buffered intravenous crystalloid solution with a physiochemical composition that closely reflects human plasma. Emerging data supports the use of buffered crystalloid solutions in preference to saline in improving physicochemical outcomes. Further large randomized controlled trials assessing the comparative effectiveness of Plasma-Lyte 148 and other crystalloid solutions in measuring clinically important outcomes such as morbidity and mortality are needed.

Concurrent activation of multiple vasoactive signaling pathways in vasoconstriction caused by tubuloglomerular feedback: a quantitative assessment

Tubuloglomerular feedback (TGF) describes the negative relationship between (a) NaCl concentration at the macula densa and (b) glomerular filtration rate or glomerular capillary pressure. TGF-induced vasoconstriction of the afferent arteriole results from the enhanced effect of several vasoconstrictors with an effect size sequence of adenosine = 20-HETE > angiotensin II > thromboxane = superoxide > renal nerves > ATP. TGF-mediated vasoconstriction is limited by the simultaneous release of several vasodilators with an effect size sequence of nitric oxide > carbon monoxide = kinins > adenosine. The sum of the constrictor effects exceeds that of the dilator effects by the magnitude of the TGF response. The validity of the additive model used in this analysis can be tested by determining the effect of combined inhibition of some or all agents contributing to TGF. Multiple independent contributors to TGF are consistent with the variability of TGF and of the factors contributing to TGF resetting.

Effects of fluid resuscitation with 0.9% saline versus a balanced electrolyte solution on acute kidney injury in a rat model of sepsis*

OBJECTIVE

To compare the acute effects of 0.9% saline versus a balanced electrolyte solution on acute kidney injury in a rat model of sepsis.

DESIGN

Controlled laboratory experiment.

SETTING

University laboratory.

SUBJECTS

Sixty adult, male Sprague-Dawley rats.

INTERVENTIONS

We induced sepsis by cecal ligation and puncture and randomized animals to receive fluid resuscitation with either 0.9% saline or Plasma-Lyte solution for 4 hours after 18 hours of cecal ligation and puncture (10 mL/kg in the first hour and 5 mL/kg in the next 3 hr). Blood and urine specimens were obtained from baseline, 18 hours after cecal ligation and puncture, immediately after 4 hours fluid resuscitation, and 24 hours later. We measured blood gas, plasma electrolytes, creatinine, interleukin-6, cystatin C, and neutrophil gelatinase-associated lipocalin concentrations. We also analyzed urine for cystatin C and neutrophil gelatinase-associated lipocalin. We used Risk, Injury, Failure, Loss and End-stage criteria for creatinine to assess severity of acute kidney injury. We observed all animals for survival up to 1 day after resuscitation. Surviving animals were killed for kidney histology. Finally, we carried out an identical study in 12 healthy animals.

MEASUREMENTS AND MAIN RESULTS

Compared with Plasma-Lyte, 0.9% saline resuscitation resulted in significantly greater blood chloride concentrations (p < 0.05) and significantly decreased pH and base excess. Acute kidney injury severity measured by RIFLE criteria was increased with 0.9% saline compared with Plasma-Lyte resuscitation (p < 0.05), and these results were consistent with kidney histology and biomarkers of acute kidney injury. Twenty-four-hour survival favored Plasma-Lyte resuscitation (76.6% vs 53.3%; p = 0.03). Finally, in healthy animals, we found no differences between fluids and no evidence of acute kidney injury.

CONCLUSION

Volume resuscitation with Plasma-Lyte resulted in less acidosis and less kidney injury and improved short-term survival when compared with 0.9% saline in this experimental animal model of sepsis.

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.

Renal tubular transport and the genetic basis of hypertensive disease

Several monogenic hypertensive disorders are caused by genetic mutations leading to the deranged function and/or regulation of renal tubular NaCl transport, such as mutations of the renal epithelial Na+ channel (ENaC) in Liddle syndrome, of the kinase WNK1 (with no K) in Gordon syndrome, and of the mineralocorticoid receptor, or of 11beta-hydroxysteroid dehydrogenase. Moreover, excessive formation of aldosterone in glucocorticoid-remediable hypertension leads to severe hypertension. Conversely, impaired function of the Na+,K+,2Cl- cotransporter (NKCC2), the renal outer medullary K+ channel (ROMK1), and the renal epithelial Cl- channel ClCKb/Barttin causes Bartter syndrome and defective Na+,Cl+ cotransporter (NCCT) Gitelman syndrome, salt-wasting disorders with hypotension. These monogenic disorders are rare, but illustrate the significance of renal tubular transport in blood pressure regulation. There is little doubt, however, that deranged renal salt reabsorption significantly contributes to essential hypertension polymorphisms of several genes participating in the regulation of renal Na+ transport have been shown to be associated with blood pressure and prevalence of hypertension. Two common genes will be discussed in more detail. The first encodes the renal Cl- channel ClCKb. A gain-of-function mutation of ClCKb, increasing channel activity by 7- to 20-fold is found in approximately 20% of unselected Caucasians and 40% of an unselected African population. The second common gene variant (prevalence, 3%-5% in unselected Caucasians), to be discussed in more detail, affects the serum and glucocorticoid inducible kinase SGK1, a kinase upregulated by mineralocorticoids and enhancing the activity of ENaC, ROMK, and Na+/K+ATPase. Both gene variants are associated with slightly increased blood pressure. SGK1 further stimulates the glucose transporter SGLT1, and the SGK1 gene variant correlates, in addition, with increased body mass index.

Chloride channels and α1-adrenoceptor-mediated pulmonary artery smooth muscle contraction: effect of pulmonary hypertension

Noradrenaline induced concentration-dependent contractions of pulmonary artery segments from control and monocrotaline-treated rats. There was a significant decrease in the maximum response but not sensitivity in artery segments from monocrotaline-treated rats. At a concentration (10(-6) M) that abolished KCl-induced contraction, nifedipine attenuated but did not abolish, noradrenaline-induced contraction in both groups. However, noradrenaline-induced contraction in artery segments from pulmonary hypertensive rats was more susceptible to inhibition by nifedipine. Bumetanide (10(-4) M), a chloride transport inhibitor and niflumic acid, a chloride channel inhibitor, reduced noradrenaline-induced contraction of the pulmonary artery in control and pulmonary hypertensive groups. These compounds were more effective in ring segments from pulmonary hypertensive rats. It was concluded that activation of chloride channels was involved in noradrenaline-induced contraction and that the contribution of chloride channels was enhanced in pulmonary hypertensive rats.

Activating Mutation of the Renal Epithelial Chloride Channel ClC-Kb Predisposing to Hypertension

The chloride channel ClC-Kb is expressed in the basolateral cell membrane of the distal nephron and participates in renal NaCl reabsorption. Loss-of-function mutations of ClC-Kb lead to classic Bartter syndrome, a rare salt-wasting disorder. Recently, we identified the ClC-Kb T481S polymorphism, which confers a strong gain-of-function effect on the ClC-Kb chloride channel. The present study has been performed to explore the prevalence of the mutation and its functional significance in renal salt handling and blood pressure regulation. As evident from electrophysiological analysis with the 2-electrode voltage-clamp technique, heterologous expression of ClC-Kb T481S in Xenopus oocytes gave rise to a current that was 7-fold larger than the current produced by wild-type ClC-Kb. The prevalence of the mutant allele was significantly higher in an African population from Ghana (22%) than in whites (12%). As tested in 1 white population, carriers of ClC-Kb T481S were associated with significantly higher systolic (by ≈6.0 mm Hg) and diastolic (by ≈4.2 mm Hg) blood pressures and significantly higher prevalence (45% versus 25%) of hypertensive (≥140/90 mm Hg) blood pressure levels. Individuals carrying ClC-Kb T481S had significantly higher plasma Na + concentrations and significantly decreased glomerular filtration rate. In conclusion, the mutation ClC-Kb T481S of the renal epithelial Cl − channel ClC-Kb strongly activates ClC-Kb chloride channel function in vitro and may predispose to the development of essential hypertension in vivo.