Atrial natriuretic peptide increases albuminuria in type I diabetic patients: evidence for blockade of tubular protein reabsorption

Neprilysin Inhibitors in Heart Failure: The Science, Mechanism of Action, Clinical Studies, and Unanswered Questions

This article provides a contemporary review and a new perspective on the role of neprilysin inhibition in heart failure (HF) in the context of recent clinical trials and addresses potential mechanisms and unanswered questions in certain HF patient populations. Neprilysin is an endopeptidase that cleaves a variety of peptides such as natriuretic peptides, bradykinin, adrenomedullin, substance P, angiotensin I and II, and endothelin. It has a broad role in cardiovascular, renal, pulmonary, gastrointestinal, endocrine, and neurologic functions. The combined angiotensin receptor and neprilysin inhibitor (ARNi) has been developed with an intent to increase vasodilatory natriuretic peptides and prevent counterregulatory activation of the angiotensin system. ARNi therapy is very effective in reducing the risks of death and hospitalization for HF in patients with HF and New York Heart Association functional class II to III symptoms, but studies failed to show any benefits with ARNi when compared with angiotensin-converting enzyme inhibitors or angiotensin receptor blocker in patients with advanced HF with reduced ejection fraction or in patients following myocardial infarction with left ventricular dysfunction but without HF. These raise the questions about whether the enzymatic breakdown of natriuretic peptides may not be a very effective solution in advanced HF patients when there is downstream blunting of the response to natriuretic peptides or among post-myocardial infarction patients in the absence of HF when there may not be a need for increased natriuretic peptide availability. Furthermore, there is a need for additional studies to determine the long-term effects of ARNi on albuminuria, obesity, glycemic control and lipid profile, blood pressure, and cognitive function in patients with HF.

Effect of Sacubitril/Valsartan on renal function in patients with chronic kidney disease and heart failure with preserved ejection fraction: A real-world 12-week study

Patients with chronic kidney disease (CKD) are often complicated with heart failure with preserved ejection fraction (HFpEF). However, several drugs, including angiotensin-converting enzyme inhibitor (ACEI) and angiotensin receptor blocker (ARB), have not shown apparent benefits in terms of morbidity and mortality of HFpEF. PARAMOUNT and other studies have shown the potential benefits of Sacubitril/Valsartan on patients with HFpEF, but its effects on renal function and the effect of low-dose Sacubitril/Valsartan in actual clinical conditions have not been thoroughly evaluated. In our longitudinal and observational research, 353 patients were followed up for 12 weeks. We evaluated renal function [urinary protein, serum creatinine and estimated glomerular filtration rate (eGFR)] and cardiac function [NT-proBNP (brain natriuretic peptide), New York Heart Association (NYHA) classification, left ventricular ejection fraction (LVEF), left atrial width and left ventricular end-diastolic width] at baseline and during follow-up. Worsening renal function (WRF) was defined as an increased serum creatinine≥26.5umol/L or decreased eGFR≥20%. The decline of eGFR in the Sacubitril/Valsartan group was slower than that in the control group (p = 0.021). The outcome of proteinuria in the ACEI/ARB group was significantly better than that in the Sacubitril/Valsartan group (p = 0.001). In terms of echocardiogram, the average left atrial width in Sacubitril/Valsartan group decreased by 1.38 ± 3.02 mm, which was significantly lower than that in the ACEI/ARB group (p = 0.02). The increase of urine protein class in the ACEI/ARB group increased the risk of WRF with statistical significance (OR = 2.36, 95%CI 1.01-5.49, p = 0.047), but no statistical significance was found in all the patients or Sacubitril/Valsartan group. In conclusion, Sacubitril/Valsartan could more effectively slow down renal function decline and reverse myocardial remodeling in patients with CKD and HFpEF than ACEI/ARB, even at low doses, though its protective effect on urinary protein is not as good as that of ACEI/ARB.

Potential effects and application prospect of angiotensin receptor-neprilysin inhibitor in diabetic kidney disease

Diabetic kidney disease (DKD) is one of the main causes of end-stage renal disease (ESRD) and all-cause mortality in diabetic patients, despite the extensive use of angiotensin-converting enzyme inhibitor (ACEI) and angiotensin II receptor blocker (ARB). Angiotensin receptor-neprilysin inhibitor (ARNI), combining ARB and neutral endopeptidase inhibitor (NEPI), is likely to have potential favorable effects in DKD. This review summarizes existing preclinical and clinical studies on mechanism of ARNI and its potential effects on DKD. In preclinical studies, ARNI manifested its renoprotective effects by improving natriuresis, ameliorating inflammation, oxidative stress and renal dysfunction, and slowing down glomerulosclerosis and tubulointerstitial injury of kidney, but its effect on proteinuria is still controversial. Beneficial effects of ARNI on blood glucose regulation and glycometabolism have also been reported. There are no clinical studies of ARNI that specifically focus on DKD patients so far. ARNI has application potential in DKD, but there still need clinical studies that focus on DKD patients to determine its effectiveness, safety and underlying mechanism.

Angiotensin receptor-neprilysin inhibitors: Comprehensive review and implications in hypertension treatment

Angiotensin receptor-neprilysin inhibitors (ARNIs) are a new class of cardiovascular agents characterized by their dual action on the major regulators of the cardiovascular system, including the renin-angiotensin system (RAS) and the natriuretic peptide (NP) system. The apparent clinical benefit of one ARNI, sacubitril/valsartan, as shown in clinical trials, has positioned the drug class as a first-line therapy in patients with heart failure, particularly with reduced ejection fraction. Accumulating evidence also suggests that sacubitril/valsartan is superior to conventional RAS blockers in lowering blood pressure in patients with hypertension. To decide whether to apply an ARNI to treat hypertension clinically, it is important to understand the potential properties of the drug in modulating multiple factors inside and outside the cardiovascular system beyond its effect on reducing peripheral blood pressure. In this context, ARNIs are distinct from preexisting antihypertensive medications in terms of the multiple actions of NPs in various organs and the pharmacological potential of neprilysin inhibitors to modulate multiple cardiac and noncardiac peptides. In particular, analysis of the clinical trials of sacubitril/valsartan implies that ARNIs can provide additional clinical benefits independent of their original purpose, including alleviation of glycemic control and renal impairment in patients with heart failure. Understanding the potential mechanisms of action of ARNIs will help interpret the relevance of their additional benefits beyond lowering blood pressure in hypertension. This review summarizes the comprehensive clinical evidence and relevance of ARNIs by specifically focusing on the potential properties of this new drug class in treating patients with hypertension.

Effect of sacubitril/valsartan on renal function: a systematic review and meta-analysis of randomized controlled trials

A worsening renal function is prevalent among patients with cardiovascular disease, especially heart failure (HF). Sacubitril/valsartan appears to prevent worsening of renal function and progression of chronic kidney disease (CKD) as compared with renin-angiotensin system (RAS) inhibitors alone in HF patients. It is unclear whether these advantages are present in HF patients only, or can be extended to other categories of patients, in which this drug was studied. We performed a systematic review and meta-analysis to assess the consistency of effect size regarding renal outcome across randomized controlled trials (RCTs) that compared sacubitril/valsartan with RAS inhibitors in patients with or without HF. We searched Medline (PubMed), Scopus, and Thomson Reuters Web of Science databases until June 2020. We took into account RCTs that compared sacubitril/valsartan with a RAS inhibitor and reported data regarding renal function. We used random-effects models to obtain summary odds ratio (OR) with 95% confidence interval (CI). We extracted hazard ratios for renal outcomes, glomerular filtration rate slopes or rates of renal adverse events. Sensitivity analyses were performed by moderator analysis and random-effects meta-regression. The search revealed 10 RCTs (published between 2012 and 2019) on 16 456 subjects. Sacubitril/valsartan resulted in a lower risk of renal dysfunction as compared with RAS inhibitors alone [k = 10; pooled OR = 0.70 (95% CI 0.57-0.85); P < 0.001], with a moderate inconsistency between studies [Q(9) = 15.18; P = 0.086; I²  = 40.73%]. A stronger association was found in studies including older patients (k = 10; β = -0.047730; P = 0.020) or HF patients with preserved ejection fraction [pooled OR = 0.53 (0.41-0.68) vs. 0.76 (0.57-1.01) for studies on HF patients with reduced ejection fraction; P for comparison = 0.065]. The effect size did not change with different comparators (angiotensin-converting enzyme inhibitors vs. angiotensin II type 1 receptor blockers, P = 0.279). No significant association was found when the analysis was restricted to studies on non-HF patients [k = 3; pooled OR = 0.86 (0.61-1.22); P = 0.403] and studies with high risk of bias [k = 3; pooled OR = 0.34 (0.08-1.44); P = 0.143]. Our findings support the role of sacubitril/valsartan on preservation of renal function, especially in older patients and HF patients with preserved ejection fraction. However, evidence is currently limited to HF patients, while the renal outcome of sacubitril/valsartan therapy outside the HF setting needs to be further investigated.

Renal effects of Sacubitril/Valsartan in heart failure with reduced ejection fraction: a real life 1-year follow-up study

Real-life data confirming the favourable renal outcome in patients with heart failure (HF) treated with Sacubitril/Valsartan, previously found in several trials (RCTs), are still scant. We evaluated the renal effects of Sacubitril/Valsartan in a real-life sample of HF patients. Observational analysis of 54 consecutive outpatients affected by HF with reduced ejection fraction (HFrEF) and clinical indication for Sacubitril/Valsartan. Patients were evaluated at baseline (T0) and after six (T6) and twelve (T12) months after initiating Sacubitril/Valsartan and compared with a group of 30 historical controls. Mean age: 65.5 ± 11.7 years. Older patients: 29 (53.7%). Mean baseline estimated glomerular filtration rate (eGFR): 59.4 ± 19.2 ml/min/1.73 m². Patients with chronic kidney disease (CKD), defined by an eGFR < 60 ml/min/1.73 m², were 29 (53.7%). Sacubitril/Valsartan was less titrated in both older patients and patients with CKD. There were no changes in diuretics during follow-up. Systolic blood pressure (BP) decreased during follow-up (p = 0.014), while left ventricular ejection fraction (LVEF) slighly increased (p < 0.001). Renal function improved after 12 months compared to historical controls (p for interaction < 0.001) and a greater benefit was found in subjects aged < 65 years (p for interaction = 0.002) and patients with CKD (p for interaction = 0.009). A statistically (p = 0.009), but not clinically significant increase in serum potassium was also found, regardless of age and CKD. This is the first study focused on the renal effects of Sacubitril/Valsartan in HFrEF patients followed for 12 months in a real-life clinical context. The improved eGFR, despite lower BP, represents an important confirmation outside the peculiar world of RCTs.

Effect of neprilysin inhibition on renal function in patients with type 2 diabetes and chronic heart failure who are receiving target doses of inhibitors of the renin-angiotensin system: a secondary analysis of the PARADIGM-HF trial

BACKGROUND

Neprilysin inhibition has favourable effects on experimental diabetic nephropathy. We sought to assess the effects of neprilysin inhibition on the course of renal function in patients with type 2 diabetes.

METHODS

In the randomised, double-blind PARADIGM-HF trial, the effects of sacubitril/valsartan (97 mg/103 mg twice daily) were compared with enalapril (10 mg twice daily) in 8399 patients with mild-to-moderate chronic heart failure and systolic dysfunction. In this secondary intention-to-treat analysis, we assessed the change in estimated glomerular filtration rate (eGFR) over a 44-month follow-up period in patients with (n=3784) and those without (n=4615) diabetes. PARADIGM-HF is registered with ClinicalTrials.gov, number NCT01035255.

FINDINGS

eGFR decreased by 1·1 mL/min per 1·73 m² per year (95% CI 1·0-1·2) in patients without diabetes, but by 2·0 mL/min per 1·73 m² per year (1·9-2·1) in those with diabetes (p<0·0001). Compared with patients treated with enalapril, those treated with sacubitril/valsartan had a slower rate of decline in eGFR (-1·3 vs -1·8 mL/min per 1·73 m² per year; p<0·0001), and the magnitude of the benefit was larger in patients with versus those without diabetes (difference 0·6 mL/min per 1·73 m² per year [95% CI 0·4-0·8] in patients with vs 0·3 mL/min per 1·73 m² per year [0·2-0·5] in those without diabetes; p_interaction=0·038). The greater effect of neprilysin inhibition in patients with diabetes could not be explained by the effects of treatment on the course of heart failure or on HbA_1c. The incremental benefit of sacubitril/valsartan in patients with diabetes was no longer apparent when changes in eGFR were adjusted for urinary cyclic guanosine monophosphate (p=0·41).

INTERPRETATION

In patients in whom the renin-angiotensin system is already maximally blocked, the addition of neprilysin inhibition attenuates the effect of diabetes to accelerate the deterioration of renal function that occurs in patients with chronic heart failure.

FUNDING

Novartis.

Role of the sodium-hydrogen exchanger in mediating the renal effects of drugs commonly used in the treatment of type 2 diabetes

Diabetes is characterized by increased activity of the sodium-hydrogen exchanger (NHE) in the glomerulus and renal tubules, which contributes importantly to the development of nephropathy. Despite the established role played by the exchanger in experimental studies, it has not been specifically targeted by those seeking to develop novel pharmacological treatments for diabetes. This review demonstrates that many existing drugs that are commonly prescribed to patients with diabetes act on the NHE1 and NHE3 isoforms in the kidney. This action may explain their effects on sodium excretion, albuminuria and the progressive decline of glomerular function in clinical trials; these responses cannot be readily explained by the influence of these drugs on blood glucose. Agents that may affect the kidney in diabetes by virtue of an action on NHE include: (1) insulin and insulin sensitizers; (2) incretin-based agents; (3) sodium-glucose cotransporter 2 inhibitors; (4) antagonists of the renin-angiotensin system (angiotensin converting-enzyme inhibitors, angiotensin receptor blockers and angiotensin receptor neprilysin inhibitors); and (5) inhibitors of aldosterone action and cholesterol synthesis (spironolactone, amiloride and statins). The renal effects of each of these drug classes in patients with type 2 diabetes may be related to a single shared biological mechanism.

Augmentation of glucagon-like peptide-1 receptor signalling by neprilysin inhibition: potential implications for patients with heart failure

Augmentation of glucagon-like peptide-1 (GLP-1) receptor signalling is an established approach to the treatment of type 2 diabetes. However, endogenous GLP-1 and long-acting GLP-1 receptor analogues are degraded not only by dipeptidyl peptidase-4, but also by neprilysin. This observation raises the possibilities that endogenous GLP-1 contributes to the clinical effects of neprilysin inhibition and that patients concurrently treated with sacubitril/valsartan and incretin-based drugs may experience important drug-drug interactions. Specifically, potentiation of GLP-1 receptor signalling may underlie the antihyperglycaemic actions of sacubitril/valsartan. Neprilysin inhibitors may also be able to augment the effects of long-acting GLP-1 analogues to increase heart rate and myocardial cyclic AMP, and thus, potentiate these deleterious actions; if so, concomitant treatment with GLP-1 receptor agonists may limit the efficacy of neprilysin inhibitors in patients with both heart failure and diabetes. For patients not concurrently treated with GLP-1 analogues, the action of neprilysin to enhance the effects of GLP-1 may be particularly relevant in the brain, where augmentation of GLP-1 and other endogenous peptides may act to inhibit amyloid-induced neuroinflammation and cytotoxicity and improve memory formation and executive functioning. Experimentally, neprilysin inhibitors may also potentiate the effects of endogenous GLP-1 and GLP-1 receptor agonists on blood vessels and the kidney. The role of neprilysin in the metabolism of endogenous GLP-1 and long-acting GLP-1 analogues points to a range of potential pathophysiological effects that may be clinically relevant to patients with heart failure, with or without diabetes.

From ARB to ARNI in Cardiovascular Control

Coexistence of hypertension, diabetes mellitus and chronic kidney disease synergistically aggravates the risk of cardiovascular and renal morbidity and mortality. These high-risk, multi-morbid patient populations benefit less from currently available anti-hypertensive treatment. Simultaneous angiotensin II type 1 receptor blockade and neprilysin inhibition (‘ARNI’) with valsartan/sacubitril (LCZ696) might potentiate the beneficial effects of renin-angiotensin-aldosterone inhibition by reinforcing its endogenous counterbalance, the natriuretic peptide system. This review discusses effects obtained with this approach in animals and humans. In animal models of hypertension, either alone or in combination with myocardial infarction or diabetes, ARNI consistently reduced heart weight and cardiac fibrosis in a blood pressure-independent manner. Additionally, LCZ696 treatment reduced proteinuria, focal segmental glomerulosclerosis and retinopathy, thus simultaneously demonstrating favourable effects on microvascular complications. These results were confirmed in patient populations. Besides blood pressure reductions in hypertensive patients and greatly improved (cardiovascular) mortality in heart failure patients, ventricular wall stress and albuminuria were reduced particularly in diabetic patients. The exact underlying mechanism remains unknown, but may involve improved renal haemodynamics and reduced glomerulosclerosis, e.g. related to a rise in natriuretic peptide levels. However, the assays of these peptides are hampered by methodological artefacts. Moreover, since sacubitrilat is largely renally cleared, drug accumulation may occur in patients with impaired renal function and thus hypotension is a potential side effect in patients with chronic kidney disease. Further caution is warranted since neprilysin also degrades endothelin-1 and amyloid beta in animal models. Accumulation of the latter may increase the risk of Alzheimer’s disease.

Blood pressure-independent renoprotection in diabetic rats treated with AT1 receptor-neprilysin inhibition compared with AT1 receptor blockade alone

ARNI [dual AT1 (angiotensin II type 1) receptor-neprilysin inhibition] exerts beneficial effects on blood pressure and kidney function in heart failure, compared with ARB (AT1 receptor blockade) alone. We hypothesized that ARNI improves cardiac and kidney parameters in diabetic TGR(mREN2)27 rats, an angiotensin II-dependent hypertension model. Rats were made diabetic with streptozotocin for 5 or 12 weeks. In the final 3 weeks, rats were treated with vehicle, irbesartan (ARB) or irbesartan+thiorphan (ARNI). Blood pressure, measured by telemetry in the 5-week group, was lowered identically by ARB and ARNI. The heart weight/tibia length ratio in 12-week diabetic animals was lower after ARNI compared with after ARB. Proteinuria and albuminuria were observed from 8 weeks of diabetes onwards. ARNI reduced proteinuria more strongly than ARB, and a similar trend was seen for albuminuria. Kidneys of ARNI-treated animals showed less severe segmental glomerulosclerosis than those of ARB-treated animals. After 12 weeks, no differences between ARNI- and ARB-treated animals were found regarding diuresis, natriuresis, plasma endothelin-1, vascular reactivity (acetylcholine response) or kidney sodium transporters. Only ARNI-treated rats displayed endothelin type B receptor-mediated vasodilation. In conclusion, ARNI reduces proteinuria, glomerulosclerosis and heart weight in diabetic TGR(mREN2)27 rats more strongly than does ARB, and this occurs independently of blood pressure.

Increased plasma concentrations of midregional proatrial natriuretic Peptide is associated with risk of cardiorenal dysfunction in type 1 diabetes

BACKGROUND

To examine possible associations between midregional proatrial natriuretic peptide (MR-proANP) and diabetic complications at baseline and risk of mortality and end-stage renal disease (ESRD) during follow-up in type 1 diabetes.

METHODS

Observational study including 667 patients, with plasma MR-proANP measured at baseline. Complications were defined as micro- (n = 168) or macroalbuminuria (n = 190) (urinary albumin excretion rate (UAER) 30-299 or ≥ 300 mg/24h), previous cardiovascular disease (CVD) (n = 143), cardiac autonomic dysfunction (heart rate variability < 11 beats/min) (n = 369), and retinopathy (n = 523). Adjustments included gender, age, systolic blood pressure, estimated glomerular filtration rate (eGFR), UAER, HbA1c, total cholesterol, 24-hour urinary sodium excretion (24h-U(Na)), body mass index, daily insulin dose, antihypertensive treatment, and smoking in linear regression analyses and analysis of covariance models. Development of ESRD (dialysis, renal transplantation, or GFR/eGFR < 15 ml/min/1.73 m(2)) and mortality was recorded through national registers.

RESULTS

The cohort included 293 (44%) females, aged 55 ± 13 years. Plasma MR-proANP (median (interquartile)) was 74.7 (49.2-116.8) pmol/L. Adjusted, MR-proANP correlated positively with age and UAER and negatively with eGFR, 24h-U(Na), total cholesterol, and HbA1c (P < 0.05). Moreover, MR-proANP levels increased with albuminuria degree and were higher in patients with previous CVD (P ≤ 0.001), but similar in patients with or without autonomic dysfunction or retinopathy (P ≥ 0.076). During follow-up (3.5 (3.1-4.0) years), higher MR-proANP concentrations predicted ESRD and mortality combined (n = 35) adjusted for gender, age, systolic blood pressure, eGFR, and previous CVD (hazard ratio per 1SD increase in logANP: 2.8 (1.6-4.7; P < 0.001)).

CONCLUSIONS

Increased plasma MR-proANP was associated with impaired renal function, increased albuminuria, and previous CVD. Moreover, MR-proANP concentrations were associated with increased risk of development of ESRD and mortality combined during follow-up.

Characteristics of dendroaspis natriuretic peptide and its receptor in streptozotocin-induced diabetic rats

Dendroaspis natriuretic peptide (DNP) shares a functionally important sequence homology with other natriuretic peptides. However, the characteristics of DNP and its receptor in the context of diabetes remafin to be fully elucidated. In the present study, alterations in the plasma levels and tissue contents of DNP and the properties of its receptor in diabetic rats, induced by streptozotocin (STZ) injection, were investigated. The plasma levels of DNP were 90.01 ± 4.12 and 196.68 ± 5.60 pg/ml in the control and STZ-induced diabetic rats, respectively. The tissue contents of DNP in the cardiac atrium, ventricle, renal cortex and inner medulla of the STZ-induced diabetic rats were also significantly increased compared with the control rats. Specific (125)I-DNP-binding sites were located predominantly in the glomeruli and inner medulla of the rat kidney. In the glomeruli of the kidney, the apparent dissociation constants (Kd) of (125)I-DNP in the control and STZ-induced diabetic rats were 0.41 ± 0.03 and 0.56 ± 0.06 nM, respectively. The maximum binding capacities (Bmax) of (125)I-DNP in control and STZ-induced diabetic rats were 2.98 ± 0.21 and 6.22 ± 1.06 fmol/mg protein, respectively. However, no differences were observed in the apparent Kd and Bmax of (125)I-DNP in the inner medulla of the kidney between the control and STZ-induced diabetic rats. In the glomerular and inner medullary kidney membranes, DNP stimulated the production of cyclic guanosine monophosphate (cGMP) in a dose-dependent manner. The magnitude of cGMP production in glomerular membranes was greater in the STZ-induced diabetic rats, whereas the magnitude of cGMP production in the inner medullary membranes was lower in the STZ-induced diabetic rats compared with the control rats. These results indicated that STZ-induced diabetes modulate DNP and its receptor, and also suggested that modulation of the DNP system is involved in the renal function of diabetic animals via the intracellular domain of the kidney NP receptor.

Kidney injury molecule-1 and neutrophil gelatinase-associated lipocalin as prognostic markers in idiopathic membranous nephropathy

Background

Urinary excretion of alpha-1-microglobulin and beta-2-microglobulin reflects tubular damage and predicts outcome in patients with idiopathic membranous nephropathy with reasonable accuracy. Urinary kidney injury molecule-1 and neutrophil gelatinase-associated lipocalin are novel biomarkers of tubular damage. We investigated if these markers could improve prediction of outcome in idiopathic membranous nephropathy.

Methods

We measured kidney injury molecule-1 and neutrophil gelatinase-associated lipocalin in urine samples from patients with idiopathic membranous nephropathy, who had nephrotic proteinuria and normal renal function. Excretion of alpha-1-microglobulin and beta-2-microglobulin had been measured previously. Progression was defined as a serum creatinine rise >30%, a rise in serum creatinine to an absolute value of ≥135  µmol/L, or a clinical decision to start immunosuppressive therapy. Remission was defined as proteinuria <3.5 g/day and >50% reduction from baseline.

Results

Sixty-nine patients were included. Median follow-up was 35 months (interquartile range 18–63 months). Progression occurred in 30 patients (44%), and spontaneous remission in 36 (52%). Kidney injury molecule-1 and neutrophil gelatinase-associated lipocalin excretion rates were significantly correlated with each other, and with alpha-1-microglobulin and beta-2-microglobulin. The areas under the receiver operating characteristic curves for progression were 0.75 (0.62–0.87) for kidney injury molecule-1 and 0.74 (0.62–0.87) for neutrophil gelatinase-associated lipocalin. In multivariate analysis with either alpha-1-microglobulin and beta-2-microglobulin, kidney injury molecule-1 and neutrophil gelatinase-associated lipocalin did not independently predict outcome.

Conclusion

Kidney injury molecule-1 and neutrophil gelatinase-associated lipocalin excretion rates correlated with excretion rates of other tubular damage markers and predicted outcome in patients with idiopathic membranous nephropathy. They did not add prognostic value compared to measurement of either alpha-1-microglobulin or beta-2-microglobulin.

Prognostic value of risk score and urinary markers in idiopathic membranous nephropathy

BACKGROUND AND OBJECTIVES

Accurate prediction of prognosis may improve management of patients with idiopathic membranous nephropathy. This study compared the Toronto Risk Score and urinary low-molecular weight proteins.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

One hundred four patients with biopsy-proven idiopathic membranous nephropathy who presented between 1995 and 2008 with a well-preserved kidney function and nephrotic range proteinuria were included. Urinary β2-microglobulin and α1-microglobulin measurements were obtained by timed standardized measurements, and the Toronto Risk Score was calculated using data obtained from medical records. The endpoint was progression, which was defined as an increase in serum creatinine > 50% or > 25% with a concentration > 135 μmol/L.

RESULTS

Forty-nine patients showed progression. The area under the receiver-operating characteristics curve was 0.78 (95% confidence interval = 0.69-0.88) for the risk score versus 0.80 (0.71-0.89) and 0.79 (0.71-0.88) for urinary β2- and α1-microglobulin, respectively. Differences were not significant. Persistent proteinuria did not add accuracy to the Toronto Risk Score. Conversely, its accuracy was not reduced when data from the first 6 months of follow-up were used. Furthermore, a score based on GFR estimated with the six-variable Modification of Diet in Renal Disease equation, calculated in the first 6 months of follow-up, gave an area under the receiver-operating characteristics curve of 0.83 (0.74-0.92), which was not statistically different from other markers.

CONCLUSIONS

The prognostic accuracies of the Toronto Risk Score and urinary low-molecular weight proteins were not significantly different. The risk score can be calculated within 6 months of diagnosis, and a simplified risk score using estimated GFR-Modification of Diet in Renal Disease may be sufficient.

Low-molecular-weight proteins as prognostic markers in idiopathic membranous nephropathy

BACKGROUND

Accurate prediction of prognosis in idiopathic membranous nephropathy (iMN) allows restriction of immunosuppressive therapy to patients at high risk for ESRD. Here we re-evaluate urinary low-molecular-weight proteins as prognostic markers and explore causes of misclassification.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

In a cohort of 129 patients with serum creatinine concentration <135 μmol/L and proteinuria ≥3.0 g/10 mmol, urinary α1- (uα1m) and β2-microglobulin (uβ2m) excretion rate was determined. Urinary α1m and uβ2m-creatinine ratio was also obtained. We defined progression as a rise in serum creatinine ≥50% or ≥25% and an absolute level ≥135 μmol/L.

RESULTS

Median survival time was 25 months, and 47% of patients showed progression. The area under the receiver operating characteristic curve for uβ2m was 0.81 (95% CI: 0.73 to 0.89). Using a threshold value of 1.0 μg/min, sensitivity and specificity were 73% and 75%, respectively. Similar accuracy was observed for the uβ2m-creatinine ratio with sensitivity and specificity of 75% and 73%, respectively, at a threshold of 1.0 μg/10 mmol creatinine. Similar accuracy was found for uα1m and uα1m-creatinine ratio. Blood Pressure and cholesterol contributed to misclassification. Repeated measurements improved accuracy in patients with persistent proteinuria: the positive predictive value of uβ2m increased from 72% to 89% and the negative predictive value from 76% to 100%.

CONCLUSIONS

Urinary excretion of uα2m and uβ2m predict prognosis in iMN. A spot urine sample can be used instead of a timed sample. A repeated measurement after 6 to 12 months increases prognostic accuracy.

High urinary excretion of kidney injury molecule-1 is an independent predictor of end-stage renal disease in patients with IgA nephropathy

BACKGROUND

The variable course of immunoglobulin A nephropathy (IgAN) warrants accurate tools for the prediction of progression. Urinary kidney injury molecule-1 (KIM-1) and neutrophil gelatinase-associated lipocalin (NGAL) are markers for the detection of early tubular damage caused by various renal conditions. We evaluated the prognostic value of these markers in patients with IgAN.

METHODS

We included patients (n = 65, 72% male, age 43 ± 13 years) with biopsy-proven IgAN, who were evaluated for proteinuria. Urinary KIM-1 and NGAL were measured by enzyme-linked immunosorbent assay. We analysed data using Cox regression for the outcome end-stage renal disease (ESRD).

RESULTS

Median serum creatinine was 142 μmol/L and proteinuria 2.2 g/day. During follow-up (median 75 months), 23 patients (35%) developed ESRD. In patients with IgAN median urinary KIM-1 excretion was 1.7 ng/min and NGAL excretion was 47 ng/min, both significantly higher than in healthy controls. KIM-1 and NGAL were correlated with proteinuria (r = 0.40 and 0.34, respectively, P < 0.01) and each other (r = 0.53, P < 0.01) but not with estimated glomerular filtration rate (eGFR). Interestingly, KIM-1 was not significantly correlated with the excretion of α(1)-microglobulin (α(1)m) and β(2)-microglobulin (β(2)m), known markers of tubular injury. Univariate analysis showed that baseline serum creatinine and urinary excretion of total protein, α(1)m, β(2)m, immunoglobulin G, KIM-1 and NGAL were significantly associated with ESRD. By multivariate analysis, serum creatinine and KIM-1 excretion proved to be significant independent predictors of ESRD.

CONCLUSION

KIM-1 and NGAL excretion are increased in patients with IgAN and correlate with proteinuria but not with eGFR. Baseline serum creatinine and urinary KIM-1, but not proteinuria, are independent predictors of ESRD.

Renal proximal tubular dysfunction is a major determinant of urinary connective tissue growth factor excretion

Connective tissue growth factor (CTGF) plays a key role in renal fibrosis. Urinary CTGF is elevated in various renal diseases and may have biomarker potential. However, it is unknown which processes contribute to elevated urinary CTGF levels. Thus far, urinary CTGF was considered to reflect renal expression. We investigated how tubular dysfunction affects urinary CTGF levels. To study this, we administered recombinant CTGF intravenously to rodents. We used both full-length CTGF and the NH(2)-terminal fragment, since the NH(2)-fragment is the predominant form detected in urine. Renal CTGF extraction, determined by simultaneous arterial and renal vein sampling, was 18 +/- 3% for full-length CTGF and 21 +/- 1% for the NH(2)-fragment. Fractional excretion was very low for both CTGFs (0.02 +/- 0.006% and 0.10 +/- 0.02%, respectively), indicating that >99% of the extracted CTGF was metabolized by the kidney. Immunohistochemistry revealed extensive proximal tubular uptake of CTGF in apical endocytic vesicles and colocalization with megalin. Urinary CTGF was elevated in megalin- and cubilin-deficient mice but not in cubilin-deficient mice. Inhibition of tubular reabsorption by Gelofusine reduced renal uptake of CTGF and increased urinary CTGF. In healthy volunteers, Gelofusine also induced an increase of urinary CTGF excretion, comparable to the increase of beta(2)-microglobulin excretion (r = 0.99). Furthermore, urinary CTGF correlated with beta(2)-microglobulin (r = 0.85) in renal disease patients (n = 108), and only beta(2)-microglobulin emerged as an independent determinant of urinary CTGF. Thus filtered CTGF is normally reabsorbed almost completely in proximal tubules via megalin, and elevated urinary CTGF may largely reflect proximal tubular dysfunction.

Transgenic overexpression of brain natriuretic peptide prevents the progression of diabetic nephropathy in mice

AIMS/HYPOTHESIS

Brain natriuretic peptide (BNP) is a potent vasorelaxing and natriuretic peptide that is secreted from the heart and has cardioprotective properties. We have previously generated hypotensive transgenic mice (BNP-Tg mice) that overproduce BNP in the liver, which is released into the circulation. Using this animal model, we successfully demonstrated the amelioration of renal injury after renal ablation and in proliferative glomerulonephritis. Glomerular hyperfiltration is an early haemodynamic derangement, representing one of the key mechanisms of the pathogenesis of diabetic nephropathy. Based on the suggested involvement of increased endogenous natriuretic peptides, the aim of this study was to investigate their role in the development and progression of diabetic nephropathy.

MATERIALS AND METHODS

We evaluated the progression of renal injury and fibrogenesis in BNP-Tg mice with diabetes induced by streptozotocin. We also investigated the effect of BNP on high glucose-induced signalling abnormalities in mesangial cells.

RESULTS

After induction of diabetes, control mice exhibited progressively increased urinary albumin excretion with impaired renal function, whereas these changes were significantly ameliorated in BNP-Tg mice. Notably, diabetic BNP-Tg mice revealed minimal mesangial fibrogenesis with virtually no glomerular hypertrophy. Glomerular upregulation of extracellular signal-regulated kinase, TGF-beta and extracellular matrix proteins was also significantly inhibited in diabetic BNP-Tg mice. In cultured mesangial cells, activation of the above cascade under high glucose was abrogated by the addition of BNP.

CONCLUSIONS/INTERPRETATION

Chronic excess of BNP prevents glomerular injury in the setting of diabetes, suggesting that renoprotective effects of natriuretic peptides may be therapeutically applicable in preventing the progression of diabetic nephropathy.

Elevated plasma concentrations of atrial and brain natriuretic peptide in type 1 diabetic subjects

BACKGROUND

The intravenous infusion of atrial (ANP) and brain (BNP) natriuretic peptides have been shown to increase urinary albumin excretion in type 1 diabetes.

AIMS

To measure plasma ANP and BNP concentrations in patients with type 1 diabetes and to examine the parameters associated with elevated plasma concentrations. Methods We measured plasma ANP and BNP concentrations, UAER, HbA1C systolic blood pressure, and left ventricular mass index. Plasma ANP and BNP were also measured in non-diabetic control subjects for comparison.

RESULTS

Using multivariate regression analysis plasma ANP correlated positively with HbA1C (1.9 + 0.47, p = 0.0002), UAER (0.37 + 0.05, p = 0.00001), SBP (1.26 + 0.5, p = 0.01) and LVMI (00.46 + 0.25, p = 0.07). BNP was positively related with LVMI (0.95 + 0.4, p = 0.02), and UAER (0.56 + 0.08, p = 0.001).

CONCLUSIONS

Plasma concentrations of ANP and BNP are elevated in some patients with type 1 diabetes. Plasma ANP concentrations are closely related to UAER and elevated plasma concentrations are associated with poor glycaemic control and systemic hypertension. Plasma BNP concentration is related to LVMI.

Treatment-related changes in urinary excretion of high and low molecular weight proteins in patients with idiopathic membranous nephropathy and renal insufficiency

BACKGROUND

In patients with idiopathic membranous nephropathy, an increased urinary excretion of high (IgG) and low [beta(2)-microglobulin (beta(2)M), alpha(1)-microglobulin (alpha(1)M)] molecular weight proteins predicts prognosis and precedes renal insufficiency. We have studied the changes in the urinary excretion of these proteins in patients with idiopathic membranous nephropathy and renal insufficiency during and after treatment with cyclophosphamide and steroids, and investigated their value in predicting long-term outcome.

METHODS

Standardized measurements of urinary IgG, albumin, beta(2)M and alpha(1)M were performed at 0, 2, 6 and 12 months in 11 patients, at 12 months in 25 patients and in 17 of these last patients after 2-5 years.

RESULTS

We observed a rapid improvement of glomerular permselectivity and tubular protein reabsorption within 2 months after the start of therapy. Despite a partial remission of proteinuria within 12 months in most patients, evidence of tubulo-interstitial injury remained apparent. Neither absolute levels of urinary IgG, beta(2)M or alpha(1)M at baseline or at 12 months nor the percentage reduction between baseline and 12 months clearly predicted the occurrence of a remission or a relapse to nephrotic range proteinuria. In the case of a persistent stable remission, we observed a gradual decrease of urinary beta(2)M towards normal values.

CONCLUSIONS

In patients with idiopathic membranous nephropathy and renal insufficiency, treatment with cyclophosphamide and steroids resulted in an improvement of glomerular permeability and tubular proteinuria. Tubular proteinuria remained present for many years, even in patients with stable remission of proteinuria. Measurements of urinary proteins at 12 months after treatment start lacked predictive accuracy.

Urinary Excretion of β2-Microglobulin and IgG Predict Prognosis in Idiopathic Membranous Nephropathy: A Validation Study

An accurate prediction of the prognosis of patients with idiopathic membranous nephropathy (iMN) should allow restriction of immunosuppressive treatment to patients who are at highest risk for ESRD. On the basis of retrospective studies, it has previously been suggested that the urinary excretions of beta2-microglobulin (Ubeta2m) and IgG (UIgG) are useful predictors of renal insufficiency in patients with iMN. The threshold values of 0.5 micro/min (Ubeta2m) and 250 mg/24 h (UIgG) have been validated in a new and larger patient cohort. From 1995 onward, 57 patients with iMN (38 men, 19 women; age 48 +/- 16 yr), a nephrotic syndrome, and a serum creatinine level </=1.5 mg/dl were studied prospectively. At baseline, a standardized measurement was carried out to determine renal function and protein excretion. The end point renal death was defined as a serum creatinine exceeding 1.5 mg/dl or a rise of serum creatinine of >50%. Mean (+/-SD) follow-up was 53 +/- 23 mo. Thus far, 25 (44%) of the patients have reached the end point renal death. Multivariate analysis confirmed Ubeta2m as the strongest independent predictor for the development of renal insufficiency. Sensitivity and specificity were 88 and 91%, respectively, for Ubeta2m, and both were 88% for UIgG. When the excretions of both proteins were combined, specificity improved to 97%. It is concluded that the present data validate the accuracy of Ubeta2m and of UIgG in predicting renal outcome in patients with iMN. These markers can be used to guide decisions on the start of immunosuppressive treatment.

Investigation of the human ANP gene in type 1 diabetic nephropathy: case-control and follow-up studies

The atrial natriuretic peptide gene (PND) is a candidate gene for diabetic nephropathy. We systematically analyzed five nonsynonymous PND polymorphisms and tested the association of genotype and haplotype distributions with diabetic nephropathy in a cross-sectional study and a 6-year follow-up study (489 and 301 type 1 diabetic patients, respectively). For this purpose, a new maximum-likelihood method dealing with haplotype-based association analysis for survival data was developed. None of the genotypes or haplotypes were associated with the disease in the case-control study. In the follow-up study, C708T and T2238C showed a weak association with disease progression, but T2238C was strongly associated with progression in poorly controlled subjects (mean HbA(1c) during follow-up was more than the median value [8.5%]; log-rank [TC or CC versus TT], P = 0.007; adjusted hazard ratio, TC or CC versus TT, 2.28, 95% CI 1.10-4.74; P = 0.027). The raw effect of the 2238C allele (hazard risk ratio 1.93, 95% CI 1.15-3.24; P = 0.012) was further confirmed by the haplotype analysis, suggesting that the 2238C allele of PND may affect the course of nephropathy in inadequately controlled type 1 diabetic patients.

Low concentrations of intravenous polygelines promote low-molecular weight proteinuria

BACKGROUND

Previously we observed that atrial natriuretic peptide (ANP)-induced albuminuria was accompanied by an increase in urinary excretion of the low-molecular weight protein (LMW protein) beta2-microglobulin (beta2-m), suggesting that the albuminuria may at least partly be the result of blockade of tubular protein reabsorption. However, in our experiments ANP was dissolved in the polygeline Haemaccel (Hoechst, Behring-Werke, Marburg Germany) to prevent adhesion of ANP to the infusion system. Anecdotal reports have shown that high dosages of polygelines such as Haemaccel or Gelofusine (Braun NPBI Oss, the Netherlands) may influence tubular protein handling. In the present study we have evaluated the effect of a low and high doses of the polygeline Haemaccel on proteinuria. In addition, we have reassessed the effects of ANP.

MATERIALS AND METHODS

We measured urinary beta2-microglobulin (beta2-m) and albumin excretion in healthy volunteers after infusion of a high-dose pure Haemaccel (0.04 mL kg(-1) min(-1) for 60 min), a low-dose Haemaccel (0.01 mL kg(-1) min(-1) for 60 min followed by infusion of 0.02 mL kg(-1) min(-1) for 60 min) and a low-dose Gelofusine (dose comparable to the low-dose Haemaccel). In addition we performed similar studies using ANP dissolved in saline and Haemaccel.

RESULTS

Infusion of Haemaccel caused a dose-dependent increase in urinary excretion of beta2-m. There were no differences between Haemaccel and Gelofusine. After infusion of ANP dissolved in Haemaccel urinary beta2-m excretion increased from 0.05 +/- 0.03 microg min(-1) to 27 +/- 10 microg min(-1) and urinary albumin excretion increased from 4.5 +/- 1.1 microg min(-1) to 9.7 +/- 6.3 microg min(-1) (P<0.05). During ANP + saline infusion, urinary beta2-m excretion did not change, whereas the urinary albumin excretion increased from 5.3 +/- 1.5 microg min(-1) to 7.9 +/- 2.4 microg min(-1) (P<0.05).

CONCLUSIONS

Our study demonstrates that even low doses of the polygelines Haemaccel and Gelofusine profoundly attenuate the tubular reabsorption of the low-molecular weight protein beta2-m. Atrial natriuretic peptide does not affect tubular protein reabsorption. Therefore, the rise in albuminuria during ANP infusion most likely reflects alterations in glomerular permeability.

Urinary excretion of complement C3d in patients with renal diseases

INTRODUCTION

Complement-mediated tubular injury may play an important role in the progression of renal diseases. C3d is a presumed marker of complement activation. Its precursor C3dg has been detected in the urine of patients with membranous nephropathy. However, little is known of the renal handling of C3d or its excretion in other renal diseases.

METHODS

We measured the urinary excretion of albumin, IgG, beta2-microglobulin (beta2m), and of complement C3d in patients with tubulo-interstitial nephritis (TIN; n= 8), in patients with membranous nephropathy (n = 35) and in patients with nonmembranous glomerular diseases (23 nonproliferative and 21 proliferative). Fractional excretions (FE) were calculated using creatinine clearance as marker of GFR.

RESULTS

C3d was not measurable in the urine of the healthy controls, but was detectable in seven out of eight of the TIN patients (median excretion 0.11 mU min-1, range 0.006-2.4 mU min-1). In these patients the urinary excretion of beta2m was clearly elevated (median 26.6 micro g min-1, range 1.0-103 micro g min-1). The FE of C3d correlated with the FE of beta2microglobulin (r = 0.83, P = 0.01), and their ratio amounted to 0.03 (range 0.003-0.06), a value in agreement with the expected sieving coefficient. Urine C3d was detectable in all but three of the patients with glomerular diseases (median excretion 0.36 mU min-1, range 0.004-7.9 mU min-1); C3d-excretion did not differ between the three subgroups of patients with glomerular diseases. FEC3d correlated with FEIgG (r = 0.88, P < 0.01). The ratio FEC3d/FEbeta2m was 0.78 (range 0.04-9.99). Selected patients with membranous nephropathy were re-analyzed after (partial) remission of proteinuria. Reduction of proteinuria resulted in a decrease of C3d excretion.

CONCLUSION

Urinary excretion of C3d is elevated in patients with TIN, most likely as a mere consequence of decreased tubular reabsorption. In patients with glomerular diseases urinary excretion of C3d is increased and related to proteinuria, independent of the underlying glomerular disease. In these patients there is evidence of increased local formation of C3d.

Atrial natriuretic peptide-induced microalbuminuria is associated with endothelial dysfunction in noncomplicated type 1 diabetes patients

BACKGROUND

Microalbuminuria reflects widespread vascular dysfunction in type 1 diabetes mellitus and results from increased glomerular sieving caused by changes in transglomerular pressure and/or permselectivity characteristics of the glomerular basement membrane. Increased tubular reabsorption or degradation of albumin will offset an early increase in albuminuria. We hypothesized that the infusion of atrial natriuretic peptide (ANP) as a tool to increase glomerular permeability might uncover changes in permselectivity in patients with uncomplicated type 1 diabetes.

METHODS

We investigated whether these patients were characterized by endothelial and/or vascular dysfunction. We therefore studied 46 normoalbuminuric patients (urinary albumin excretion [UAE] < 10 microg/min) with type 1 diabetes and 44 healthy controls. Measurements of renal hemodynamics and albuminuria were performed before (baseline) and during the infusion of ANP (0.01 microg/kg/min). On a separate occasion, endothelial function was assessed by the intra-arterial infusion of acetylcholine (ACh), an endothelial-dependent vasodilator.

RESULTS

At baseline, glomerular filtration rate (GFR) and effective renal plasma flow (ERPF) were greater in patients with diabetes (GFR, 121 +/- 3 versus 106 +/- 2 mL/min/1.73 m(2); ERPF, 558 +/- 16 versus 527 +/- 13 mL/min/1.73 m(2); P < 0.001). The infusion of ANP increased filtration fraction. There were no differences in these responses between groups. UAE was significantly greater in patients with diabetes after the ANP infusion (15.8 +/- 1.4 [+183%] versus 9.5 +/- 1.3 microg/min [+96%]; P < 0.01). A subgroup of patients with diabetes with an enhanced albuminuric response (change in UAE > 2 SD of controls) to ANP infusion (mean UAE, 30.3 +/- 1.0 microg/min; 425% +/- 61%) was characterized by a diminished vasodilatory response to ACh (maximal forearm blood flow, 17.2 +/- 2.9 [+563%] versus 26.3 +/- 2.3 mL/min/dL [+800%] in patients with diabetes with a normal albuminuric response; P < 0.05).

CONCLUSIONS

In a subgroup of patients with uncomplicated type 1 diabetes, an increase in glomerular permselectivity can be unmasked by the infusion of ANP. These patients are characterized by a diminished vascular response to ACh.

Brain natriuretic peptide increases urinary albumin and alpha-1 microglobulin excretion in Type 1 diabetes mellitus

Atrial natriuretic peptide (ANP) increases urinary albumin excretion in Type 1 diabetes mellitus (DM). Brain natriuretic peptide (BNP) is structurally and functionally related to ANP, but its effect on urine albumin excretion rate (UAER) is unknown.

AIMS

To compare the albuminuric effects of intravenous infusion of ANP and BNP, and to assess the effect of both peptides on tubular protein excretion.

METHODS

Eight subjects with Type 1 DM were randomised to a three leg, double blind, and placebo controlled study. On each study day, subjects were euglycaemic clamped and subsequently water loaded (20 mL/kg orally, plus urine losses) to steady state diuresis. When in steady state, creatinine clearance was estimated in three separate 1 hour periods. At the end of the first period, a 1 hour intravenous infusion of either placebo, ANP 0.025 microg/kg/min, or BNP 0.025 microg/kg/min was administered. There followed a 1 hour recovery period. Urine was collected at 15 min intervals for estimation of urine albumin (ACR) and alpha1 microglobulin creatinine ratio (MCR). Results were analysed by anova.

RESULTS

Creatinine clearance was similar on the three study days, and was unaltered by any infusion. ACR was unaltered by placebo (1.3 +/- 0.5-1.2 +/- 0.4 mg/mmol, mean +/- SD, p = 0.81), but increased compared to placebo with infusion of both ANP (1.2 +/- 0.4-9.8 +/- 8.4 mg/mmol, P = 0.0004), and BNP (1.1 +/- 0.4-13.4 +/- 8.6 mg/mmol, P = 0.0001). The MCR was unaltered by placebo infusion (P = 0.89), but increased compared with placebo after infusion of ANP (5.4 +/- 0.9-12.3 +/- 4.2 mg/mmol, P < 0.0001), and BNP (5.4 +/- 0.8-12.1 +/- 2.5 mg/mmol, P < 0.0001).

CONCLUSIONS

Intravenous infusion of BNP and ANP both increase the urine excretion of albumin and the tubular protein alpha1 microglobulin, independent of creatinine clearance.

The gelatin-derived plasma substitute Gelofusine causes low-molecular-weight proteinuria by decreasing tubular protein reabsorption

PURPOSE

Proteinuria is frequently encountered in patients in the intensive care unit, most likely as a result of renal tubular cell injury. It has been reported that gelatin-derived plasma substitutes contribute to an increase in renal protein excretion. The aim of this study was to investigate the magnitude and the mechanism of the proteinuric effect of Gelofusine, a modified gelatin.

MATERIALS AND METHODS

In six healthy male subjects, renal hemodynamics and urinary protein excretion were measured before and after infusion of 330 mL of Gelofusine.

RESULTS

Gelofusine had a minor effect on blood pressure, glomerular filtration rate, effective renal plasma flow, and on urinary excretion of immunoglobulin, and albumin. In contrast, there was a major increase in the urinary excretion of the low-molecular-weight proteins beta2-microglobulin (from 0.06 +/- 0.04 to 43.52 +/- 11.75 microg/min; P <.01) and alpha1-microglobulin (from 11 +/- 8 to 72 +/- 24 microg/min; P <.01). The urinary excretion of N-acetyl-beta-D-glucosaminidase (beta-NAG) remained unchanged, suggesting that there was no significant renal tubular cell injury.

CONCLUSIONS

When analyzing proteinuria in patients in the intensive care unit it should be considered that Gelofusine increases the urinary excretion of proteins, in particular those of low molecular weight. This effect is most likely due to competitive inhibition of tubular protein reabsorption.

Long-acting natriuretic peptide, vessel dilator, and kaliuretic peptide enhance urinary excretion rate of albumin, total protein, and beta(2)-microglobulin in patients with congestive heart failure

BACKGROUND

Albumin excretion is increased in persons with congestive heart failure (CHF), but the mechanism of this increase is unknown. Atrial natriuretic peptide (ANP) does not correlate with this albumin excretion, but the other 3 cardiac hormones derived from the ANP prohormone have never been investigated as to whether they can enhance albumin and/or protein excretion in persons with CHF.

METHODS AND RESULTS

Long-acting natriuretic peptide (LANP), vessel dilator, and kaliuretic peptide (100 ng/kg body weight/min) given intravenously for 60 minutes to NYHA Class III CHF patients (n = 24) increased the albumin excretion rate 2- to 7-fold (P <.001) and total protein excretion rate 2- to 5-fold (P <.001). These peptide hormones similarly enhanced beta(2)-microglobulin, a specific marker of proximal tubular reabsorption, excretion rate 25- to 40-fold (P <.0005) at the end of their respective infusions. Three hours after stopping their respective infusions, the beta(2)-microglobulin excretion rate was still 11- to 33-fold (P <.0005) increased.

CONCLUSIONS

LANP, vessel dilator, and kaliuretic peptide each enhance albumin and total protein excretion in persons with CHF. Part of the mechanism of this enhanced protein excretion is the inhibition of proximal tubular reabsorption of protein as shown by the beta(2)-microglobulin data.

Familial nephropathy differing from minimal change nephropathy and focal glomerulosclerosis

BACKGROUND

Nephrotic syndrome in childhood is mainly due to minimal change nephropathy. In general, it is characterized by selective proteinuria, by steroid responsiveness, and histologically by podocytic foot process effacement. Familial presentation is rare and mainly restricted to one generation.

METHODS

We describe the occurrence of a familial nephropathy in a mother and two daughters. An initial diagnosis of minimal change nephropathy was made, but subsequently unique features became apparent. During follow-up, detailed studies of renal function and urinary protein excretion were performed. Available frozen renal biopsy material was revised and processed for immunofluorescence to detect abnormalities in the expression of heparan sulfate proteoglycans. The latter results were compared with renal biopsies of a control group composed of five adult patients with minimal change nephropathy.

RESULTS

The mother and two daughters were proteinuric since their early childhood. The mother revealed a persistent nephrotic syndrome for more than 20 years despite treatment with various immunosuppressive drugs. Likewise, treatment with prednisone was ineffective in the daughters. All three patients retained normal renal function during follow-up. Detailed measurements revealed that the proteinuria was incredibly selective (selectivity index approximately 0.01), and there was no evidence of tubulointerstitial damage, as reflected by a normal excretion of the low-molecular weight proteins beta(2)-microglobulin and alpha1-microglobulin. Renal biopsy performed in the mother and one daughter was thought to be compatible with minimal change nephropathy. However, histologically, two remarkable findings were made. By electron microscopy, there was no evidence of foot process retraction; specifically, the foot process width and slit pore diameter were normal. Furthermore, in contrast to the control patients, the expression of heparan sulfate polysaccharide side chains, as reflected by the staining with monoclonal antibody JM403, was normal.

CONCLUSIONS

We propose that this family represents a new familial nephropathy. The molecular basis of the permeability defect remains to be identified.

A novel cGMP-regulated K+ channel in immortalized human kidney epitheliall cells (IHKE-1)

1. K+ channels from the apical membrane of immortalized human kidney epithelial (IHKE-1) cells were investigated in the cell-attached membrane configuration as well as in excised membranes using the patch clamp technique. 2. In cell-attached membrane patches the open probability (Po) of the K+ channel was 0.42 +/- 0.06 (mean +/- s.e.m. , n = 22) and its conductance was 94 +/- 5 pS with 145 mM K+ in the pipette (n = 25). In excised membrane patches the Po of the channel was 0.55 +/- 0.03 (n = 86) and its conductance was 65 +/- 2 pS (n = 68) with 145 mM K+ on one side of the membrane and 3.6 mM K+ on the other. The I-V curve of the K+ channel was not rectifying. 3. The channel was inhibited by several blockers of K+ channels such as 1 mM Ba2+ (cell-attached membrane: 78 +/- 8 %, n = 9; excised: 80 +/- 4 %, n = 26), 10 mM TEA+ (excised inside-out: 48 +/- 5 %, n = 34; excised outside-out: 100 +/- 0 %, n = 26), 0.1 mM verapamil (excised: 73 +/- 9 %, n = 12), and 10 nM charybdotoxin (excised outside-out: 67 +/- 9 %, n = 9). 4. The K+ channel was activated by depolarization and rising cytosolic Ca2+. Half-maximal activity occurred at a cytosolic Ca2+ concentration of 200 nM. In the cell-attached membrane configuration the K+ channel was inhibited in a concentration-dependent manner by atrial natriuretic peptide (ANP). Powas blocked equally well by 10 nM ANP (52 +/- 7 %, n = 10), brain natriuretic peptide (BNP; 37 +/- 11 %, n = 6) and C-type natriuretic peptide (CNP; 44 +/- 13 %, n = 8). 8-Bromoguanosine 3',5' cyclic monophosphate (8-Br-cGMP, 0.1 mM) also inhibited Poof this K+ channel, by 70 +/- 10 % (n = 5). 5. In excised membrane patches cGMP inhibited Po of this K+ channel in a concentration-dependent manner. The first significant effects were measured at a concentration of 1 microM (22 +/- 7 %, n = 6), and greatest effects were obtained at 0.1 mM (34 +/- 5 %, n = 15). cAMP (0.1 mM, n = 5) as well as GTP (0.1 mM, n = 5) had no significant effects on Po of this K+ channel. ATP (0.1 mM) had a weak inhibitory effect (17 +/- 5 %, n = 14). Addition of Mg-ATP to cGMP did not increase the inhibitory effect (30 +/- 4 %, n = 14). KT5823 (1 microM), a specific inhibitor of cGMP-dependent protein kinases, did not significantly alter the cGMP-induced reduction in Po of the K+ channel in three excised membrane patches. 6. The results present the first electrophysiological characterization of a mammalian K+ channel that is directly regulated by cGMP.