Cystatin c can be affected by nonrenal factors a preliminary study on leukemia

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Cystatin C can be affected by nonrenal factors: A preliminary

study on leukemia

Selda Demirta

ş

a

, Özay Akan

b

, Murat Can

c,

⁎

, Esra Elmali

b

, Hamdi Akan

d

a_{University of Ufuk, Faculty of Medicine, Department of Biochemistry, Ankara, Turkey} b_{University of Ankara, Faculty of Medicine, Ibn-I Sina Hospital Central Laboratory, Ankara, Turkey}

c_{University of Karaelmas, Faculty of Medicine, Department of Biochemistry, Zonguldak, Turkey} d_{University of Ankara, Faculty of Medicine, Department of Hematology, Ankara, Turkey}

Received 22 July 2005; received in revised form 5 September 2005; accepted 14 October 2005 Available online 6 December 2005

Abstract

Objective: The aim of this study was to evaluate the influence of malignancy and the impact of nephrotoxic drugs used in bone marrow transplantation (BMT) on the circulating levels of cystatin C in leukemia.

Methods: We studied nineteen patients (eleven men and eight women; mean age 30.1 ± 11.2, 27.9 ± 7.1 years) with acute lymphoblastic leukemia, acute myeloid leukemia and chronic myeloid leukemia. Cystatin C, urea, creatinine and creatinine clearance (CrCl) were measured 24 h before BMT, 1 week after BMT, 2 weeks after BMT and 3 weeks after BMT. The control group consisted of twenty healthy adults, and the mean age was 29.1 ± 8.9.

Results: At the pretransplantation period, values of cystatin C were significantly higher than in the control group (P b 0.05). Urea, creatinine and CrCl values were not statistically different from the controls. One week after BMT, the level of cystatin C was significantly low as compared to the levels measured 24 h before BMT, but was still significantly higher than the controls (Pb 0.05), whereas the levels of urea, creatinine and CrCl were in accordance with the levels of the controls. Two and three weeks after BMT, cystatin C values maintained the significant increase (Pb 0.05), whereas the values of urea, creatinine and CrCl still corresponded with those of the controls in both group.

Conclusions: Our preliminary data expose that cystatin C is not a reliable GFR marker in patients during leukemia or for monitoring nephrotoxic drugs used in BMT, but we can not reach definitive conclusion due to no gold standard for comparing the diagnostic accuracy of cystatin C. Further study is needed to elucidate the precise mechanism underlying this observation.

Keywords: Cystatin C; Leukemia; Creatinine; Creatinine clearance; Cancer; Bone marrow transplantation

Introduction

Cystatin C is a non-glycosylated low molecular weight protein (13,360 Da) that exists in all human tissues and has a widespread distribution in biological fluids[1]. It is a product of a housekeeper gene which is localized on chromosome 20 and has an inhibitor function on papain-like cysteine proteinases,

such as cathepsins B, H and L[2,3].

Recent evidence suggests that extracellular cathepsins degrade the components of the extracellular matrix and mediate

the invasion of cancer cells[4]. Based on its high extracellular

concentrations and inhibitory kinetics, cystatin C has been shown to be the most important extracellular inhibitor for several cathepsins. The loss or aberrant activity of a number of members of the cystatin superfamily has been shown to

correlate with the metastatic ability of some cancer cells [5–

7]. In several clinical studies, it has been observed that cystatin C levels significantly increased in malignant sera such as

melanoma, colorectal and hepatocellular carcinoma [8–10].

However, no information is available in the literature on the changes in the serum cystatin C concentration in patients with leukemia.

The serum concentration of cystatin C is constant because it is freely filtered in the renal glomeruli and almost completely rebsorbed and catabolized in the proximal tubules. Furthermore,

Clinical Biochemistry 39 (2006) 115–118

⁎ Corresponding author. Fax: +90 0372 2610155. E-mail address: drcanmurat@yahoo.com (M. Can).

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it was found that cystatin C is independent of nonrenal factors such as diet, age, sex, weight, muscle mass and gender [11,12]. Therefore, it is considered to be an ideal endogenous

marker of the GFR[13]and superior to other endogen markers

such as creatinine, urea and beta-2 microglobulin, which has been stated in the reference textbooks of Clinical Chemistry [14].

Nephrotoxic drugs used in bone marrow transplantation (BMT), including chemotherapeutics, antifungals, antibiotics and drugs used for the prophylaxis of graft versus host disease (GvHD) such as cyclosporine cause tubular cell damage; therefore, they may interfere with the tubular absorption and metabolism of cystatin C.

In the present study, we evaluated the influence of malignancy and the impact of nephrotoxic drugs used in BMT on the circulating levels of cystatin C in leukemia. For this purpose, cystatin C levels were monitored before and after BMT. To evaluate the change in cystatin C levels to see whether they result from renal factors or cancer, we have also compared cystatin C to serum creatinine and creatinine clearance (CrCl).

Materials and methods

We studied nineteen patients (eleven men and eight women; mean age 30.1 ± 11.2, 27.9 ± 7.1 years) with acute lymphoblastic leukemia, acute myeloid leukemia and chronic myeloid leukemia at the Hematology Department of Ankara University. The measurement of cystatin C, urea, creatinine and

CrCl was made at 24 h before BMT (point A), 1 week after BMT (point B), 2 weeks after BMT (point C) and 3 weeks after BMT (point D).

Nine patients received amphotericin B, and fifteen patients used amikacin antibiotics during the treatment. All of the patients received acyclovir and cyclosporine before, during and

after BMT (Table 1). The control group consisted of twenty

healthy adults, and the mean age was 29.1 ± 8.9.

Serum cystatin C was determined by latex particle enhanced immunoturbidimetry with a commercially available Dako cystatin C kit on a Roche Integra 800 automated analyzer. The serum and urine creatinine levels were detected with a kinetic Jaffé method, and CrCl was calculated using a standard formula: [CrCl = urine creatinine concentration (mg/dL) × urine volume measured from 24

h collection (mL/24 h) × 1.73 m2/serum creatinine (mg/

dL) × body surface area (m2) × 1440]. The reference range

of creatinine clearance was 71–151 mL/min/1.73 m2

. Urea values were measured with a kinetic method on a Roche Integra 800 automated analyzer. The study protocol was approved by the university ethics committee. Informed consent from the patients was obtained before the study.

Statistical analysis was performed using the Statistical Package for Social Sciences 11.0. Results were expressed as mean ± SD, and P values below 0.05 were reported as statistically significant. Differences between points and the

control group were evaluated by a Mann–Whitney test and

Wilcoxon test. Correlation between data was analyzed with Spearman correlation.

Results

The results are shown inTable 2. In point A

(pretransplanta-tion phase), the values of cystatin C were significantly higher

than the controls (P b 0.05), though the values of urea,

creatinine and CrCl were not statistically different from the controls.

In point B, the level of cystatin C was significantly decreased compared to the level of point A but was still significantly

higher than the controls (Pb 0.05), whereas the levels of urea,

creatinine and CrCl were in accordance with the levels of the controls.

In points C and D, the cystatin C values maintained a

significant increase (P b 0.05), whereas the values of urea,

Table 1

Patient and treatment characteristics

Characteristics Number of patients Sex and age (mean ± SD years)

Male 11 (30.1 ± 11.2) Female 8 (27.9 ± 7.1) Diagnosis ALL 3 AML 5 KML 11 Post BMT medication Cyclosporin 19 Acyclovir 19 Amikacin 9 Amphotericin 15 Table 2

The mean ± SD values of renal functional parameters before and after bone marrow transplantation

A B C D Control

Cystatin C (mg/L) 5.14 ± 4.16⁎ 3.39 ± 1.57 ⁎,⁎⁎ _{6.12 ± 4.40 ⁎} _{5.19 ± 3.36 ⁎} _{0.92 ± 0.18}

Creatinine (μmol/L) 59.2 ± 26.5 50.4 ± 30.0 57.5 ± 31.8 71.6 ± 38.0 86.6 ± 20.3 Creatinine clearance (mL/min/1.73 m2₎ _{148.4 ± 71.3} _{160.5 ± 67.7} _{131.3 ± 45.9} _{108.2 ± 37.4} _{118 ± 42.1}

Urea (mmol/L) 5.1 ± 3.0 4.2 ± 2.9 4.6 ± 3.8 5.1 ± 3.1 4.6 ± 3.2 A = 1 day before bone marrow transplantation.

B = 1 week after bone marrow transplantation. C = 2 weeks after bone marrow transplantation. D = 3 weeks after bone marrow transplantation.

⁎_{Significant difference between the values of the groups and the controls (P}_{b 0.05).} ⁎⁎_{Significant difference between the values of group B and groups A, C and D (P}_{b 0.05).}

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creatinine and CrCl were still in accordance with the those of the controls in both groups (Table 2,Fig. 1).

Discussion

The present findings demonstrate that serum levels of cystatin C are significantly higher than normal control levels in leukemia patients. Moreover, a transient decrease in cystatin C values (but higher than controls) was observed after the first week of BMT, and this decline reversed in the second week.

In malignancy, cysteine proteinases and their inhibitors have

an important role in cancer progression [15]. Cysteine

proteinases are known to have prognostic value in melanoma and colorectal cancer, and their enhancement was balanced with the increase of cystatin C[10,16]. Several studies have certainly shown that cystatin C is a more sensitive indicator for estimation of decreased GFR than serum creatinine and CrCl [17,18]. But, in recent investigations on cancer patients, there are conflicting results in the values of cystatin C. According to one study, cystatin C is superior to creatinine for detection of

decreased GFR in several cancer patients[19]. However, Kos et

al. found a poorer correlation between cystatin C and creatinine

in cancer patients [9]. In the current study, serum cystatin C

concentrations in leukemia patients before BMT were consis-tently higher than those in control subjects, but neither correlated with serum creatinine nor with CrCl, indicating that increased serum cystatin C concentrations were not due to decreased renal clearance but rather increased synthesis by the

malignant cells. These findings suggest that cystatin C can be affected from the nonrenal factors in leukemia.

In the present study, the nephrotoxic drugs such as amphotericin, amikacin, acyclovir and cyclosporine which were used in our patients do not seem to have an influence on renal functions. Based on the results of this study, cystatin C offers little value in the way of detecting renal toxicity in BMT. Thus, it does not warrant use in the monitoring of nephrotoxic drugs. After the first week following BMT, cystatin C concentrations significantly decreased compared to the pretreat-ment levels, whereas no difference was observed between the values of the pretreatment period and the second and the third week. This decline at the first week of BMT is most probably due to the early but transient effect of BMT on cystatin C synthesis. Tumor lysis syndrome associated renal dysfunction generally

occurs within 5 days after BMT[20]. It has also been reported

that GvHD is strongly related to the renal dysfunction after BMT

[21]. None of our patients developed tumor lysis syndrome.

Only one grade (1+) and two grade (2+) acute GvHD developed. We did not find any elevation in the data of renal function in these patients. This finding indicates that renal functional tests were less influenced by acute GvHD.

In summary, our preliminary data reveal that cystatin C is not a reliable GFR marker in patients with leukemia or for monitoring nephrotoxic drugs used in BMT, but we cannot reach definitive conclusions due to the lack of a gold standard for comparing the diagnostic accuracy of cystatin C. Further study is needed to elucidate the precise mechanism underlying this observation.

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