Jerome Rossert

Estimating GFR Using Serum Cystatin C Alone and in Combination With Serum Creatinine: A Pooled Analysis of 3,418 Individuals With CKD

BACKGROUND Serum cystatin C was proposed as a potential replacement for serum creatinine in glomerular filtration rate (GFR) estimation. We report the development and evaluation of GFR-estimating equations using serum cystatin C alone and serum cystatin C, serum creatinine, or both with demographic variables. STUDY DESIGN Test of diagnostic accuracy. SETTING & PARTICIPANTS Participants screened for 3 chronic kidney disease (CKD) studies in the United States (n = 2,980) and a clinical population in Paris, France (n = 438). REFERENCE TEST Measured GFR (mGFR). INDEX TEST Estimated GFR using the 4 new equations based on serum cystatin C alone, serum cystatin C, serum creatinine, or both with age, sex, and race. New equations were developed by using linear regression with log GFR as the outcome in two thirds of data from US studies. Internal validation was performed in the remaining one third of data from US CKD studies; external validation was performed in the Paris study. MEASUREMENTS GFR was measured by using urinary clearance of iodine-125-iothalamate in the US studies and chromium-51-EDTA in the Paris study. Serum cystatin C was measured by using Dade-Behring assay, standardized serum creatinine values were used. RESULTS Mean mGFR, serum creatinine, and serum cystatin C values were 48 mL/min/1.73 m(2) (5th to 95th percentile, 15 to 95), 2.1 mg/dL, and 1.8 mg/L, respectively. For the new equations, coefficients for age, sex, and race were significant in the equation with serum cystatin C, but 2- to 4-fold smaller than in the equation with serum creatinine. Measures of performance in new equations were consistent across the development and internal and external validation data sets. Percentages of estimated GFR within 30% of mGFR for equations based on serum cystatin C alone, serum cystatin C, serum creatinine, or both levels with age, sex, and race were 81%, 83%, 85%, and 89%, respectively. The equation using serum cystatin C level alone yields estimates with small biases in age, sex, and race subgroups, which are improved in equations including these variables. LIMITATIONS Study population composed mainly of patients with CKD. CONCLUSIONS Serum cystatin C level alone provides GFR estimates that are nearly as accurate as serum creatinine level adjusted for age, sex, and race, thus providing an alternative GFR estimate that is not linked to muscle mass. An equation including serum cystatin C level in combination with serum creatinine level, age, sex, and race provides the most accurate estimates.

Predictive Performance of the Modification of Diet in Renal Disease and Cockcroft-Gault Equations for Estimating Renal Function

Recent recommendations emphasize the need to assess kidney function using creatinine-based predictive equations to optimize the care of patients with chronic kidney disease. The most widely used equations are the Cockcroft-Gault (CG) and the simplified Modification of Diet in Renal Disease (MDRD) formulas. However, they still need to be validated in large samples of subjects, including large non-U.S. cohorts. Renal clearance of (51)Cr-EDTA was compared with GFR estimated using either the CG equation or the MDRD formula in a cohort of 2095 adult Europeans (863 female and 1232 male; median age, 53.2 yr; median measured GFR, 59.8 ml/min per 1.73 m(2)). When the entire study population was considered, the CG and MDRD equations showed very limited bias. They overestimated measured GFR by 1.94 ml/min per 1.73 m(2) and underestimated it by 0.99 ml/min per 1.73 m(2), respectively. However, analysis of subgroups defined by age, gender, body mass index, and GFR level showed that the biases of the two formulas could be much larger in selected populations. Furthermore, analysis of the SD of the mean difference between estimated and measured GFR showed that both formulas lacked precision; the CG formula was less precise than the MDRD one in most cases. In the whole study population, the SD was 15.1 and 13.5 ml/min per 1.73 m(2) for the CG and MDRD formulas, respectively. Finally, 29.2 and 32.4% of subjects were misclassified when the CG and MDRD formulas were used to categorize subjects according to the Kidney Disease Outcomes Quality Initiative chronic kidney disease classification, respectively.

Erythropoietic response and outcomes in kidney disease and type 2 diabetes

BACKGROUND Non–placebo-controlled trials of erythropoiesis-stimulating agents (ESAs) comparing lower and higher hemoglobin targets in patients with chronic kidney disease indicate that targeting of a lower hemoglobin range may avoid ESA-associated risks. However, target-based strategies are confounded by each patients individual hematopoietic response. METHODS We assessed the relationship among the initial hemoglobin response to darbepoetin alfa after two weight-based doses, the hemoglobin level achieved after 4 weeks, the subsequent darbepoetin alfa dose, and outcomes in 1872 patients with chronic kidney disease and type 2 diabetes mellitus who were not receiving dialysis. We defined a poor initial response to darbepoetin alfa (which occurred in 471 patients) as the lowest quartile of percent change in hemoglobin level (<2%) after the first two standardized doses of the drug. RESULTS Patients who had a poor initial response to darbepoetin alfa had a lower average hemoglobin level at 12 weeks and during follow-up than did patients with a better hemoglobin response (a change in hemoglobin level ranging from 2 to 15% or more) (P<0.001 for both comparisons), despite receiving higher doses of darbepoetin alfa (median dose, 232 μg vs. 167 μg; P<0.001). Patients with a poor response, as compared with those with a better response, had higher rates of the composite cardiovascular end point (adjusted hazard ratio, 1.31; 95% confidence interval [CI], 1.09 to 1.59) or death (adjusted hazard ratio, 1.41; 95% CI, 1.12 to 1.78). CONCLUSIONS A poor initial hematopoietic response to darbepoetin alfa was associated with an increased subsequent risk of death or cardiovascular events as doses were escalated to meet target hemoglobin levels. Although the mechanism of this differential effect is not known, these findings raise concern about current target-based strategies for treating anemia in patients with chronic kidney disease. (Funded by Amgen; ClinicalTrials.gov number, NCT00093015.)

Timing of Onset of CKD-Related Metabolic Complications

Chronic kidney disease (CKD) guidelines recommend evaluating patients with GFR <60 ml/min per 1.73 m(2) for complications, but little evidence supports the use of a single GFR threshold for all metabolic disorders. We used data from the NephroTest cohort, including 1038 adult patients who had stages 2 through 5 CKD and were not on dialysis, to study the occurrence of metabolic complications. GFR was measured using renal clearance of (51)Cr-EDTA (mGFR) and estimated using two equations derived from the Modification of Diet in Renal Disease study. As mGFR decreased from 60 to 90 to <20 ml/min per 1.73 m(2), the prevalence of hyperparathyroidism increased from 17 to 85%, anemia from 8 to 41%, hyperphosphatemia from 1 to 30%, metabolic acidosis from 2 to 39%, and hyperkalemia from 2 to 42%. Factors most strongly associated with metabolic complications, independent of mGFR, were younger age for acidosis and hyperphosphatemia, presence of diabetes for acidosis, diabetic kidney disease for anemia, and both male gender and the use of inhibitors of the renin-angiotensin system for hyperkalemia. mGFR thresholds for detecting complications with 90% sensitivity were 50, 44, 40, 39, and 37 ml/min per 1.73 m(2) for hyperparathyroidism, anemia, acidosis, hyperkalemia, and hyperphosphatemia, respectively. Analysis using estimated GFR produced similar results. In summary, this study describes the onset of CKD-related complications at different levels of GFR; anemia and hyperparathyroidism occur earlier than acidosis, hyperkalemia, and hyperphosphatemia.

Scleraxis and NFATc Regulate the Expression of the Pro-α1(I) Collagen Gene in Tendon Fibroblasts

The combinatorial action of separate cis-acting elements controls the cell-specific expression of type I collagen genes. In particular, we have shown that two short elements located between -3.2 and -2.3 kb and named TSE1 and TSE2 are needed for expression of the mouse COL1a1 gene in tendon fibroblasts. In this study, we analyzed the trans-acting factors binding to TSE1 and TSE2. Gel shift experiments showed that scleraxis (SCX), which is a basic helix-loop-helix transcription factor that is expressed selectively in tendon fibroblasts, binds TSE2, preferentially as a SCX/E47 heterodimer. In transfection experiments, overexpression of SCX and E47 strongly enhanced the activity of reporter constructs harboring either four copies of TSE2 cloned upstream of the COL1a1 minimal promoter or a 3.2-kb segment of the COL1a1 proximal promoter. Analysis of TSE1 showed that it contains a consensus binding site for NFATc transcription factors. This led us to show that the NFATc4 gene is expressed in tendons of developing mouse limbs and in TT-D6 cells, a cell line that has characteristics of tendon fibroblasts. In gel shift assays, TSE1 bound NFATc proteins present in nuclear extracts from TT-D6 cells. In transfection experiments, overexpression of NFATc transactivated a reporter construct harboring four copies of TSE1 cloned upstream of the COL1a1 minimal promoter. By contrast, inhibition of the nuclear translocation of NFATc proteins in TT-D6 cells strongly inhibited the expression of the COL1a1 gene. Taken together, these results suggest that SCX and NFATc4 cooperate to activate the COL1a1 gene specifically in tendon fibroblasts.

A Peptide-Based Erythropoietin-Receptor Agonist for Pure Red-Cell Aplasia

BACKGROUND We investigated whether a novel, synthetic, peptide-based erythropoietin-receptor agonist (Hematide, Affymax) can stimulate erythropoiesis in patients with anemia that is caused by antierythropoietin antibodies. METHODS In this open-label, single-group trial, we enrolled patients with chronic kidney disease who had pure red-cell aplasia or hypoplasia due to antierythropoietin antibodies and treated them with a synthetic peptide-based erythropoietin-receptor agonist. The agonist was administered by subcutaneous injection at an initial dose of 0.05 mg per kilogram of body weight every 4 weeks. The primary end point was a hemoglobin concentration above 11 g per deciliter without the need for transfusions. RESULTS We treated 14 patients with the peptide agonist for a median of 28 months. The median hemoglobin concentration increased from 9.0 g per deciliter (with transfusion support in the case of 12 patients) before treatment to 11.4 g per deciliter at the time of the last administration of the agonist; transfusion requirements diminished within 12 weeks after the first dose, after which 13 of the 14 patients no longer required regular transfusions. Peak reticulocyte counts increased from a median of 10x10(9) per liter before treatment to peak counts of greater than 100x10(9) per liter. The level of antierythropoietin antibodies declined over the course of the study and became undetectable in six patients. One patient who initially responded to treatment had a diminished hematologic response a few months later despite increased doses of the agonist and required transfusions again; this patient was found to have antibodies against the agonist. One patient died 4 months after the last dose of the agonist, and a grade 3 or 4 adverse event occurred in seven other patients during the study period. CONCLUSIONS This novel agonist of the erythropoietin receptor can correct anemia in patients with pure red-cell aplasia caused by antierythropoietin antibodies. (ClinicalTrials.gov number, NCT00314795.).

Epoetin-associated pure red cell aplasia: past, present, and future considerations.

BACKGROUND: Since 1988, millions of patients have received epoetin products intravenously (IV) and subcutaneously. In 1998, epoetin‐associated pure red cell aplasia (PRCA) was first reported and causation was attributed to formulations without human serum albumin (HSA), subcutaneous administration, and uncoated rubber stoppers.

Treatment of erythropoietin-induced pure red cell aplasia: a retrospective study

BACKGROUND Recombinant human erythropoietin is the standard treatment for anaemia related to chronic kidney disease, and its widespread use has been favoured by a very high therapeutic index. However, since 1998, more than 200 patients worldwide with chronic kidney disease treated in this way have developed neutralising antibodies to erythropoietin, causing pure red cell aplasia. We aimed to collate clinical and pathological features in patients unequivocally shown to have erythropoietin-induced pure red cell aplasia. METHODS We retrospectively obtained data from the files of 47 patients with pure red cell aplasia. We assessed treatment and outcome of patients and defined recovery from pure red cell aplasia as an increase in reticulocyte counts to more than 20 000 per microL in patients who were no longer transfusion-dependent. FINDINGS When patients developed pure red cell aplasia, all were receiving erythropoietin subcutaneously, and the product most typically prescribed was epoetin alfa (Eprex, Ortho Biotech). The median delay between start of erythropoietin treatment and occurrence of pure red cell aplasia was 11 months (IQR 7.5-14). Nine patients received no immunosuppressive treatment, and none of these recovered. Of 37 patients who received immunosuppressive therapy, 29 (78%) recovered. All six patients who received a kidney transplant recovered within 1 month, and recovery rates were between 56% and 88% in patients treated with corticosteroids, corticosteroids plus cyclophosphamide, or ciclosporin. No relapse of pure red cell aplasia happened after stopping immunosuppressive treatment, but no patient was rechallenged with erythropoietin. INTERPRETATION Immunosuppressive treatment accelerates recovery from erythropoietin-induced pure red cell aplasia.

Anti-Erythropoietin Antibodies and Pure Red Cell Aplasia

Eberhard Ritz More than twenty years ago, investigators who immunized rabbits against human erythropoietin (EPO) to generate polyclonal antibodies noted that the animals producing antibodies against this hormone became progressively anemic ([1][1]). Apparently human EPO was sufficiently different

EGR1 and EGR2 Involvement in Vertebrate Tendon Differentiation

The molecules involved in vertebrate tendon formation during development remain largely unknown. To date, only two DNA-binding proteins have been identified as being involved in vertebrate tendon formation, the basic helix-loop-helix transcription factor Scleraxis and, recently, the Mohawk homeobox gene. We investigated the involvement of the early growth response transcription factors Egr1 and Egr2 in vertebrate tendon formation. We established that Egr1 and Egr2 expression in tendon cells was correlated with the increase of collagen expression during tendon cell differentiation in embryonic limbs. Vertebrate tendon differentiation relies on a muscle-derived FGF (fibroblast growth factor) signal. FGF4 was able to activate the expression of Egr genes and that of the tendon-associated collagens in chick limbs. Egr gene misexpression experiments using the chick model allowed us to establish that either Egr gene has the ability to induce de novo expression of the reference tendon marker scleraxis, the main tendon collagen Col1a1, and other tendon-associated collagens Col3a1, Col5a1, Col12a1, and Col14a1. Mouse mutants for Egr1 or Egr2 displayed reduced amounts of Col1a1 transcripts and a decrease in the number of collagen fibrils in embryonic tendons. Moreover, EGR1 and EGR2 trans-activated the mouse Col1a1 proximal promoter and were recruited to the tendon regulatory regions of this promoter. These results identify EGRs as novel DNA-binding proteins involved in vertebrate tendon differentiation by regulating type I collagen production.