[Estimation of glomerular filtration rate in children with chronic kidney disease (CKD) on the basis of cystatin C clearance]. / Ocena filtracji klebuszkowej u dzieci z przewleklq choroba nerek w oparciu o klirens cystatyny C.

UNLABELLED: Glomerular filtration rate (GFR) is the best marker of renal function. Creatinine and cystatin C are accepted as endogenous parameters of GFR. THE AIM: Comparison between cystatin C clearance and other methods used for estimation of GFR. MATERIAL AND METHODS: The study group consist of 73 children mean age 12.26 +/- 4.18, with CKD stage 1-4. We determined clearance of creatinine using Schwartz formule (Cl(Sch)), Counahan-Barratt formule (Cl(C-B)), cystatin C clearance (Cl(cystC)) and referred them for nuclear clearance investigations--technetium-diethylenetriamine pentaacetic acid (Cl(99m)Tc-DTPA). RESULTS: Mean values of GFR (ml/min/1.73 m2) amounted to: Cl(Sch) 113.87 +/- 36.98; Cl(C-B) 84.74 +/- 29.73; Cl(cystC) 89.55 +/- 25.87; Cl(99m)Tc-DTPA 87.28 +/- 30.71. Significant correlations were found (p < 0.00001) between Cl(99m)Tc-DTPA and Cl(Sch) r = 0.72; Cl(C-B) r = 0.71 and Cl(cystC) r = 0.72. Receiver-operating characteristics analysis showed that there where no significant differences between these methods for estimation GFR. CONCLUSION: Cystatin C clearance is an alternative method for determination of GFR.

Utilidad de la cistatina C en el ámbito hospitalario. Comparación con los distintos métodos de valoración renal / Utility of cystatin-C in hospitalized patients. Comparing with different methods of assessing renal fuction

La prueba utilizada habitualmente para valorar la función renal es la creatinina sérica, aunque por sus limitaciones, en muchas ocasiones es necesario recurrir a la medida del aclaramiento de creatinina en orina de 24 horas (Clcr), la fórmula de Cockroft-Gault (CG) o la fórmula de Levey (MDRD). Los distintos métodos pueden dar distintos resultados, creando una situación de confusión a los clínicos. La introducción de la Cistatina-C como nuevo marcador de función renal, podría suponer una mejora considerable. El objetivo de nuestro estudio fue comparar los distintos métodos de valoración renal y establecer la utilidad de la cistatina-C en el ámbito hospitalario. Fueron incluidos en el estudio 70 pacientes (44 hombres) seleccionados de manera aleatoria, predominando enfermos renales y pacientes diabéticos, a los que se les realizó el CLcr y se calculó CG y MDRD. La edad media de los pacientes fue 66 ± 14años, peso medio 73 ± 17Kg, creatinina 2,14 ± 1,77 mg/dL, cistatina-c 1,77 ± 1,18 mg/L, CLcr 54,39 ± 36,2 mL/min. La correlación entre 1/Crea con el Clcr, CG y MDRD fue respectivamente: 0,7735, 0,8269 y 0,9613, (p 0,05). En conclusión, la mayoría de las recogidas de orina podrían evitarse con la utilización de las fórmulas. La Cistatina es muy superior a la creatinina, sobre todo para detectar leve alteración renal (sensibilidad 80,4% vs 44,7% en hombres) convirtiéndose en una alternativa prometedora que reduciría a más de la mitad la IRC oculta generada por la creatinina, aunque se necesitan más estudios para confirmarlo

Serum creatinine is the most widely used parameter to assessing renal function, even though limitations, some time is necessary meassure 24 h creatinine clearance (CLcr), or estimate Cockroft-Gault (C-G) or MDRD formulas. Different methods can offer different results, and cause confusion in clinicians. Using Cystatin- C as new parameter of renal function could suppose an important improvement. The objective of our study was to compare the different methods from renal evaluation and establish the utility of cistatina-C in the hospital area. In the study were included 70 patients (44 men) selected of random way, predominate patients with kidney disease and diabetics, which was made CLcr and calculated CG and MDRD formulas. The mean age of the patients was 66 ± 14years, mean weight 73 ± 17Kg, creatinine 2,14 ± 1,77 mg/dL, cystatin-c 1,77 ± 1,18 mg/L, CLcr 54,39 ± 36,2 mL/min. The correlation of 1/Crea with the Clcr, C-G and MDRD formulas was respectively: 0,7735, 0.8269 and 0.9613, (p 0,05). In conclusion, most of the urine collections could be avoided with the use of the formulas. Cystatin-c is far beyond the creatinine, mainly to detect slight renal alteration (sensitivity 80,4% US 44,7% in men) becoming a promising alternative, that could reduce considerably hidden renal insufficiency (non detected by creatinine), although more studies are needed to confirm

Localization of tubular uptake segment of filtered Cystatin C and Aprotinin in the rat kidney.

AIM: The renal tubular uptake of 125I-Aprotinin (*Ap) is on average located more superficially than its filtration site, causing transfer of some of *Ap filtered in deep to more superficial cortical zones. 125I-Cystatin C (*Cy) showed less uptake in deep cortical zones than Ap, suggesting a longer and/or a more superficial tubular uptake site. To test that hypothesis and to quantify the outward transfer of the filtered polypeptides, we estimated the tubular uptake pattern of the tracers in perfusion fixed rat kidneys after intravenous injection of *Cy and *Ap. METHODS: Autoradiographs were made from 10 mum thick slices of Microfil nephron casts from outer (OC), middle (MC) and inner (IC) cortical zones to quantify cortical border-crossing *Ap transfer. Single nephron glomerular filtration rate (snGFR) was estimated as the zonal uptake of *Ap corrected for *Ap transfer, divided by its time-integrated plasma concentration and the zonal number of glomeruli. RESULTS: *Ap and *Cy uptake fell exponentially along the proximal convoluted tubule (PCT), indicating an uptake proportional to luminal concentration. Uptake in IC exceeded that in MC and OC nephrons. The per cent PCT length with *Cy uptake (67.2 +/- 1.6) exceeded that of *Ap (54.6 +/- 1.8). The zonal border-crossing PCT length (29-34% of total PCT) from deep to more superficial cortical zones transferred 4-6% more *Cy than *Ap. CONCLUSION: Greater tubular uptake length of *Cy than of *Ap causes more cortical border-crossing of *Cy. The zonal snGFR estimated from Aprotinin uptake corrected for border-crossing agreed well with that obtained with the Hanssen ferrocyanide technique.

Renal extraction of cystatin C vs 125I-iothalamate in hypertensive patients.

BACKGROUND: Several markers are available to estimate the glomerular filtration rate (GFR) in patients. Cystatin C is a relatively new marker and has been suggested as an alternative for creatinine. Numerous studies have been performed to evaluate the usefulness of cystatin C to estimate GFR. The aim of this study is to compare the renal extraction of cystatin C with that of 125I-iothalamate in hypertensive patients. METHODS: Forty hypertensive patients with unilateral renal artery stenosis, and who used at least two antihypertensive agents, were studied. For the determination of the renal extraction ratio, blood samples were drawn simultaneously from the renal vein and the abdominal aorta. The renal extraction ratio was calculated as ([A]-[V])/[A], in which A is the plasma concentration of the compound from the abdominal aorta, and V is the plasma concentration of the compound from the renal vein. RESULTS: The mean difference between the renal extraction ratio of cystatin C and that of 125I-iothalamate was 0.002. The 95% confidence interval (CI) for the mean difference was -0.036 to 0.032, which was not statistically significant. However, the limits of agreement were large (-0.271 and 0.267). CONCLUSIONS: Despite a lower reported glomerular sieving coefficient of cystatin C, the mean renal extraction of cystatin C was equal to the mean renal extraction of 125I-iothalamate in hypertensive patients, suggesting tubular secretion of cystatin C. Combined with the large variation in the renal extraction of cystatin C, these findings cast doubts on its usefulness as a glomerular filtration marker.

Calculation of glomerular filtration rate based on cystatin C in cirrhotic patients.

BACKGROUND: Plasma creatinine and creatinine clearance are of limited value for the estimation of renal function in cirrhotics. In these patients, cystatin C (Cys C) has been proposed as an alternative marker of glomerular filtration rate (GFR) and Cys C-based equations for calculation of GFR have been developed in non-cirrhotic patient cohorts. METHODS: We retrospectively analyzed correlation, bias, precision and accuracy of two Cys C-based formulae (Larsson and Hoek) for GFR estimation in comparison with two creatinine-based equations (Cockroft & Gault and MDRD). The Cys C was determined by an immunonephelometric method. The GFR was measured by means of inulin clearance in 44 consecutive patients with liver cirrhosis. RESULTS: On average, inulin clearance was 28.3 (95% CI: 29.2-41.3 ml/min/1.73 m2). Creatinine as well as Cys C-based equations overestimated the true GFR by 105-154%. However, Cys C-based equations showed significantly lower bias and higher precision than the creatinine-based formulae. Correlation and accuracy tended to be better with the Hoek and Larsson equation than with the Cockroft & Gault or MDRD formulae. Hoek and Larsson equations showed a similar diagnostic performance in all statistical procedures. CONCLUSION: Our data suggest a significant improvement of GFR estimation in liver cirrhotics by means of the Cys C-based Hoek and Larsson formulae. However, all estimates remain a crude approximation of true GFR and thus cannot replace gold standard methods.

Time course of low molecular weight proteins in the early kidney transplantation period--influence of corticosteroids.

BACKGROUND: Cystatin C (Cys C) is an established new marker of renal function in patients with various renal diseases and in kidney transplantation. However, few data are available for the early post-transplantation period. METHODS: Twenty-two patients who underwent renal transplantation (RTx) were evaluated for the kinetics of Cys C from day 0 to 14 in relation to creatinine and beta-2 microglobulin (B2MG). Blood samples were obtained immediately before and after transplantation and on a daily basis thereafter. Serum levels before transplantation (100%) were used to calculate reduction ratios. RESULTS: The decrease of the analytes differed considerably: immediately after RTx Cys C declined by 27.3% (P < 0.01). However, after 3 days, on average, all patients showed a significant increase in Cys C levels (15+/-2.5%; P < 0.01). B2MG levels fell quickly by 55.4 and 73.8% after days 1 and 7, respectively, and remained stable thereafter. In contrast, creatinine did not decrease immediately after RTx but fell slowly by 67.5% at the end of the study. Prior to rejection, all analytes showed a similar behaviour. Rejection treatment with high-dose methylprednisolone induced a significant increase in Cys C (+22.8+/-7.9%, P < 0.05), while in parallel, creatinine and B2MG decreased (-12.9+/-3.4 and -8.4+/-6.89%). CONCLUSIONS: Corticosteroid treatment for induction of immunosuppression or rejection therapy significantly induces Cys C, but decreases B2MG. Cys C and B2MG are not helpful in establishing the diagnosis of rejection earlier. Thus, our data indicate that Cys C and B2MG testing does not accurately reflect changes in the glomerular filtration rate early after transplantation.

Tubular absorption of filtered cystatin-C in the rat kidney.

As shown in previous studies, the two basic proteins aprotinin (Ap, 6.5 kDa) and cystatin (Cy, 13.3 kDa) can be used to estimate whole kidney glomerular filtration rate by measuring the renal cortical uptake relative to plasma concentration after i.v. injection. Local uptake of Ap can also be used to estimate local filtration rate, and the present experiments were undertaken to examine whether Cy would give a similar uptake pattern. Ap and Cy were labelled with 131I and 125I, respectively, and injected as an i.v. bolus. Frequent blood samples provided information on the filtered load. Five to 20 min after injection the kidney was clamped, frozen, and five tissue samples of 5-10 mg each were cut out from outer (OC), middle (MC) and inner cortex (IC) to be weighed and assessed for radioactivity. Five minute clearance ratios, Cy:Ap, were 1.36 +/- 0.04, 1.27 +/- 0.03 and 1.19 +/- 0.04 in OC, MC and IC, respectively. The higher Cy clearance was expected from a higher glomerular filtrate:plasma ratio of the less basic Cy (Donnan distribution). However, this does not explain the increase of Cy:Ap clearances going from IC to the OC. A surplus of extracellular uptake of Cy in superficial layers was excluded, leading to the following interpretation. In all cortical layers the proximal convoluted tubule, i.e. the protein uptake segment, is located more superficially than its parent glomerulus. A longer uptake segment for Cy than for Ap will therefore lead to a relative greater transfer of filtered Cy from IC to MC, and from MC to OC. Anatomical studies on single nephrons presented in another article lend strong support to this interpretation.

Multitrophic interactions involving genetically modified potatoes, nontarget aphids, natural enemies and hyperparasitoids.

Genetically modified (GM) potatoes expressing a cysteine proteinase inhibitor (cystatin) have been developed as an option for the management of plant parasitic nematodes. The relative impact of such plants on predators and parasitoids (natural enemies) of nontarget insects was determined in a field trial. The trial consisted of GM plants, control plants grown in soil treated with a nematicide and untreated control plants. The quantity of nontarget aphids and their quality as hosts for natural enemies were studied. Aphid density was significantly reduced by nematicide treatment and few natural enemies were recorded from treated potatoes during the study. In contrast, similar numbers of aphids and their more abundant predators were recorded from the untreated control and the GM potatoes. The size of aphids on GM and control plants was recorded twice during the study. During the first sampling period (2-9 July) aphids clip-caged on GM plants were smaller than those on control plants. During the second sampling period (23-30 July) there was no difference in aphid size between those from the GM and control plants. Host size is an important component of host quality. It can affect the size and fecundity of parasitoid females and the sex ratio of their offspring. However, neither the fitness of females of Aphidius ervi, the most prevalent primary parasitoid, nor the sex ratio of their progeny, were affected when the parasitoids developed on aphids feeding on GM plants. Two guilds of secondary parasitoid were also recorded during the study. The fitness of the most abundant species, Aspahes vulgaris, was not affected when it developed on hosts from GM plants. The transgene product, OC I Delta D86, was not detected in aphids that had fed on GM plants in the field, suggesting that there is minimal secondary exposure of natural enemies to the inhibitor. The results indicate that transgenic nematode resistance is potentially more compatible with aphid biological control than is current nematicide use.

Evaluation of cystatin C as an endogenous marker of glomerular filtration rate in dogs.

Cystatin C is a cysteine protease inhibitor produced by all nucleated cells. It is freely filtered by the glomerulus and is unaffected by nonrenal factors such as inflammation and gender. Because of greater sensitivity and specificity, cystatin C has been proposed to replace creatinine as a marker of glomerular filtration rate (GFR) in humans. The aims of this study were to validate an automated assay in canine plasma and to evaluate the usefulness of cystatin C as a marker of GFR in dogs. Western blotting was used to demonstrate cross-reactivity of an anti-human cystatin C antibody. An immunoturbidimetric assay was used to detect cystatin C in 25 clinically healthy dogs and 25 dogs with renal failure. Mean cystatin C concentration in the healthy dogs and the dogs with renal failure was 1.08 +/- 0.16 mg/L and 4.37 +/- 1.79 mg/L respectively. Intra- and interassay variability was <5%. The assay was linear (r = .974) between 0.14 and 7.53 mg/L. Both cystatin C and creatinine concentrations were measured in banked, frozen serum from 20 remnant kidney model dogs and 10 volume-depleted dogs for which GFR measurements by exogenous creatinine clearance had been determined previously. In the remnant kidney model, cystatin C was better correlated with GFR than creatinine (r = .79 versus .54) but was less well correlated with GFR in volume-depleted dogs (r = .54 versus .95). GFR measurements were repeated in the remnant kidney model dogs 60 days after initial GFR measurements. At this time, cystatin C and creatinine concentrations correlated equally well with GFR (r = .891 versus .894, respectively). Cystatin C concentration is a reasonable alternative to creatinine for screening dogs with decreased GFR due to chronic renal failure.

Renal handling of radiolabelled human cystatin C in the rat.

Serum cystatin C concentration correlates negatively with glomerular filtration rate as well as or better than that of serum creatinine, suggesting a constant formation, and elimination from extracellular fluid mainly by glomerular filtration. It is not known, however, how well the renal plasma clearance of this 13-kDa basic polypeptide matches the glomerular filtration rate. This was investigated in rats during control conditions and after reduced renal perfusion pressure. 125I-cystatin C and an indicator for glomerular filtration (51Cr-EDTA or 131I-aprotinin) were injected intravenously. The renal accumulation and urinary excretion of the tracers were recorded in periods of 2.5 to 20.0 min. The renal plasma clearance of 125I-cystatin C (Ccy) based on the renal content of 125I correlated well with the glomerular filtration rate (CCr-EDTA) in periods up to 6 min; i.e. Ccy = 0.94 x CCr-EDTA, r = 0.99. Less than 0.5% of the filtered amount appeared in the urine. During more prolonged periods, Ccy increasingly underestimated glomerular filtration rate, reaching about 0.4 x CCr-EDTA in a 20-min period. Free 125I relative to total plasma 125I activity increased from about 2% at 5 min to about 70% at 20 min. In nephrectomized rats, free 125I accumulated in plasma at a slower rate, accounting for about 15% of the total activity 20 min after injection of 125I-cystatin C. We conclude that cystatin C is (a) mainly removed from the extracellular fluid by the kidneys, (b) practically freely filtered in the glomeruli, and (c) completely absorbed and rapidly broken down by the proximal tubular cells.

Clearance of chicken cystatin from the rat circulation.

Chicken cystatin (mixed form) was prepared from egg white. Radioactively labeled preparations were administered intravenously to rats. 125I-cystatin disappeared from the rat circulation with a half-life of approximately 73 min. The radiolabeled inhibitor was rapidly taken up by the kidneys. Percoll density gradient analysis showed that it was incorporated into lysosomes. Within 24 hr after the injection of 125I-cystatin, 25% of the administered radioactivity was recovered in the urine, but only 2% was in the protein-bound form.

The effects of human salivary cystatins and statherin on hydroxyapatite crystallization.

The adsorption, at hydroxyapatite surfaces of neutral cystatin SN, acidic cystatin S and the phosphoserine-containing acidic cystatin S1 was compared to that of statherin. The effects of these adsorbed proteins on the constant-composition growth kinetics of hydroxyapatite were also studied. The neutral cystatin SN had a higher adsorption maximum than the acidic cystatins S and S1. Although the affinity of cystatin for hydroxyapatite surfaces was lower than that of statherin, their influence on the growth kinetics of hydroxyapatite was considerably greater, with the acidic cystatin S1 being the most active. At a surface concentration of 7.0 x 10(-8) mol m-2 hydroxyapatite, the cystatins decreased the rate of crystal growth by 80-95% as compared to that in the absence of protein. At this concentration, statherin showed a growth inhibition of 40%.