Urinary biomarkers in assessing the nephrotoxic potential of gentamicin in solitary kidney patients after 7 days of therapy

Abstract

Introduction: The solitary kidney (SK) may present increased vulnerability to nephrotoxicity because of adaptive phenomena. Aims: Assessing the vulnerability of the SK with urinary tract infections (UTI) to gentamicin by means of urinary biomarkers (N-acetyl-beta-D-glucosaminidase (NAG) and urinary alpha-1-microglobulin), as well as glomerular filtration rate (GFR). Methods: We studied 14 patients with SK with UTI (group A) (mean age 58.07 ± 13.61 years, mean duration of SK 13.55 ± 12.33 years) who were administered gentamicin for 7 days. Group B consisted by 17 patients with SK without any other associated renal pathology (average age 51.17 ± 9.39 years, average existence period of a single kidney 33.23 ± 21.73 years). We also included a third group (group C) represented by nine healthy individuals, with two kidneys. Results: Increased values of urinary NAG were found in group B as compared to group C and alpha-1 microglobulin in group A as compared to group B. During treatment with gentamicin, increased values of both NAG and alpha-1-microglobulin in group A were found on day 7 as compared to values before treatment (day 7 NAG = 18.99 ± 14.07 U/g creat versus day 0, NAG = 5.15 ± 6.54 U/g creat, p = 0.004; day 7 alpha-1-microglobulin = 20.88 ± 18.84 mg/g creat versus day 0, urinary alpha-1-microglobulin = 4.96 ± 6.57 mg/g creat, p = 0.003). No statistically significant alterations of GFR were noticed after 7 days of treatment. Conclusions: We found the nephrotoxic effects of gentamicin at tubular level, but not at glomerular level. The nephrotoxic potential of gentamicin in patients with a SK can be monitored by assessing urinary biomarkers during treatment of UTI.

• Biomarkers
• gentamicin
• nephrotoxicity
• solitary kidney

Introduction

In clinical practice, there occur special situations when drugs with potential nephrotoxicity have to be administered to high-risk patients. Such a situation is to be met in the case of solitary kidney (SK).

The SK suffers adaptive processes of hypertrophy and hyperfiltration. These processes become maladaptive in time and can be accompanied by lesional processes, affecting the glomeruli, like focal and segmental glomerulosclerosis, or the tubes, like tubular-interstitial lesions.1,2 Therefore, the SK becomes vulnerable to nephrotoxic agents and represents for clinicians a therapeutic challenge with regard to nephrotoxicity. This situation can be assessed by measuring the glomerular filtration rate (GFR) and by means of urinary biomarkers.

Gentamicin is an aminoglycoside widely used in clinical practice, either in monotherapy or in association with other antibiotics or chemotherapeutics which exert synergistic action. It possesses nephrotoxic and ototoxic potential requiring caution in administration of this drug.

The main sites of nephrotoxicity are proximal tubular epithelial cells (PTECs), which requires gentamicin therapy to be monitored by urinary biomarkers that assess the proximal tubule (PT). Due to the fact that the SK can present tubulointerstitial lesions and gentamicin can exert nephrotoxic effects at tubular level, the problem arises whether gentamicin treatment could be beneficial for SK patients. At the same time, it is necessary to assess this potential nephrotoxicity.

Our article intends to evaluate this process by means of urinary biomarkers.

In clinical practice, there are situations that require gentamicin use in patients with SK:

• Sensitivity of germs to gentamicin only is rare, but possible in clinical practice. Gentamicin can constitute the only therapeutic alternative in case of germs resistant to other drugs.

• Aminoglycosides are used as first or second choice drugs in a vast variety of clinical situations.3

Aminoglycoside remains the choice in many circumstances, including septicaemiae or other serious infections due to Gram-negative bacilli and bacterial endocarditis.4 In severe Gram-negative infections, aminoglycosides generally remain the first-line antibiotics. Post-antibiotic effects of aminoglycosides are also of importance.5

It is to be noted that specialized literature (Pub Med) does not mention gentamicin used in SK patients.

Gentamicin remains an efficient antibiotic with a very good cost/efficiency rate. We consider it is not beneficial to give up, on grounds of prudence, its use in SK patients, especially in particular cases, when it represents a good solution. That is why we consider that presenting our observations is useful.

Urinary tract infections (UTI) are frequently present in patients with SK.6 Some of these cases benefit from treatment with gentamicin. Since UTI associates tubulointerstitial lesions in patients with SK who can present themselves such lesions consecutive to its adaptive processes, the use of gentamicin in these patients is to be carefully analyzed. It can have beneficial effects by the bactericide action on the pathological germs that produce tubulointerstitial lesions. In other situations, gentamicin might intensify tubular lesions consecutive to UTI and to adaptive phenomena of SK.

Taking into account these considerations, the article aims at assessing by means of urinary biochemical markers the evolution of tubular lesions in patients with SK and UTI during treatment with gentamicin. The objective of the article is to assess the nephrotoxicity of gentamicin in patients with SK and UTI.

Methods

Of the 295 patients hospitalized in the Department of nephrology between 2002 and 2010, we studied 84 SK patients for urinary biomarkers of tubular lesions. These 84 SK patients were admitted to the Department of nephrology between 2008 and 2010. The inclusion criteria consisted of history of unilateral nephrectomy in the group of patients with surgically-acquired SK and the presence of a single kidney confirmed by at least two imaging methods in patients with congenital SK. Patients with nephrotoxic consumption, tumors and other renal diseases superimposed on the SK were excluded.

Further on, the 84 SK patients were analyzed from clinical, biological, imaging points of view. Urinary biomarkers were also assessed. After investigation, in 47 patients with SK, we found UTI.

Of these, in 14 patients, representing our study group, clinical situation, antibiogram sensitivity, and disponibility imposes gentamicin treatment. The group under study was made of 14 patients (males—3p (21.42%), females—11p (78.57%), average age 58.7 ± 13.61 years), average existence period of a single kidney 13.55 ± 12.33 years (group A). The control group was represented by 17 patients with SK without any other associated renal pathology, males—7 p (41.17%), females—10 p (58.82%), average age 51.17 ± 9.39 years, average existence period of a single kidney 33.23 ± 21.73 years (group B).

For correct assessment of the data we obtained, we also included in the study a third group, made of nine healthy individuals, with two kidneys (males—2p (22.22%, females—7p (77.77%, average age 54.77 ± 12.74 years (group C).

The gentamicin dosage was 160 mg/day in two doses.

All patients were assessed with regard to the following parameters: serum creatinine, GFR, glycemia, cholesterol, triglycerides, serum uric acid, fibrinogen, hemoglobin, N-acetyl-beta-d-glucosaminidase (NAG) and urinary alpha-1-microglobulin. Urinary biomarkers were determined in specimens frozen at −80 °C and thawed before assay.

NAG was determined in the second morning urine specimen using the Roche colorimetric assay kit (cat. No. 875-406). The reference interval was 1.22–2.24 U/g creatinine (this interval of values was obtained in our laboratory from a healthy group). NAG is a lysosomal enzyme present in the proximal tubular cells, with a molecular weight of 130 kDa. It is a marker of established PT cell injury in the course of numerous renal diseases.7

Urinary alpha-1-microglobulin was evaluated in the second morning urine specimen using alpha-1-microglobulin ELISA kit K 6710 (Immundiagnostik AG, Benshaim, Germany). The reference value was < 15 mg/g creatinine.8 Alpha-1-microglobulin is a marker of early tubular dysfunction and it is used in the diagnosis and follow-up of tubulointerstitial diseases.9 It is freely filtered by the glomeruli and reabsorbed by PTs.

Chronic kidney disease (CKD) was defined as either kidney damage (pathological abnormalities or markers of damage including abnormalities in blood or urine samples) or GFR <60 mL/min for more than 3 months. (MDRD formula for estimated GFR: 186 × (SC in mg/dL)—1.154 × (age in years)—0.203 × (0.742 if female – K/DOQI 2002; KDIGO 2005).10 Presence of uropathy was assessed using abdominal ultrasound. In some cases, i.v. urography and/or CT scan were used.

Statistical analysis

Analyses were performed with SPSS version 16.0 (SPSS, Chicago, IL). Clinical and biological parameters are presented as means ± standard deviations or proportions. Normal distribution of the values was verified by the Smirnov–Kolmogorov test. To investigate the significance of the relation between individual damage urinary marker and eGFR, we performed a linear regression analysis (Pearson’s correlation analysis) by using eGFR as an independent variable and the urinary biomarker as a dependent variable. The relationship between variables was assessed using R² values. p Values for all hypothesis tests were two-sided, and statistical significance was set at p < 0.05.

Results

The comparative study on SK patients without other pathology (group A) versus the group of healthy individuals with two kidneys (group B), with similar ages, showed significant statistic differences between urinary elimination of NAG (group A NAG = 2.89 ± 2.10 U/g creat vs. group B NAG = 1.61 ± 0.82 U/g creat, p = 0.038, the t-unpaired test), respectively urinary albumin (group A, urinary albumin = 17.27 ± 14.88 mg/g creat vs. group B, urinary albumin = 5.56 ± 3.58 mg/g creat, p = 0.006, the t-unpaired test) (Table 1).

Table 1. Comparative assessment of SK patients without other pathology (group A) versus healthy individuals with two kidneys (group B).

Parameter	SK patients without other pathology (n = 17) (group A)	Healthy individuals with two kidneys (n = 9) (group B)	p
Age, years	51.17 ± 9.39	54.77 ± 12.74	0.42
Sex
Male (%)	41.17 (n = 7)	22.22 (n = 2)	NS
Female (%)	58.82 (n = 10)	77.77 (n = 7)	NS
GFR, ml/min/1.73 m^2	71.01 ± 11.31	69.94 ± 13.92	0.83
Albumin urin/creat urine (mg/g)	17.27 ± 14.88	5.56 ± 3.38	0.006
NAG/creat urine (U/g)	2.89 ± 2.108	1.61 ± 0.82	0.038
Alfa-1-microglobulin urin/creat urine (mg/g)	2.88 ± 5.57	2.09 ± 1.09	0.096

Notes: The data are presented as average value ± standard deviation or number (%) of patients. Average values were compared using the Student’s t-test (parametric variables) or the Mann–Whitney U test (non-parametric variables); proportions were compared using the chi-squared test; we considered statistically significant p < 0.05; NS—non-significant.

The comparative study on SK with UTI patients (group C) versus SK patients without other pathology (group A) regarding renal function determined by eGFR, and the dysfunction of the PT, monitored by urinary biomarkers, showed significant statistic differences between elimination of urinary alpha-1-microglobulin (group C, urinary alpha-1-microglobulin = 4.96 ± 6.57 mg/g creat vs. group A, urinary alpha-1-microglobulin = 2.88 ± 5.57 mg/g creat, p = 0.032, the U-Mann–Whitney test).

Regarding renal function assessed by eGFR, we did not find statistically significant differences between the groups under study, neither on day 0 of study, nor on day 7. These data are presented in Table 2.

Table 2. Comparative assessment of SK patients with UTI (group C) versus SK patients without other pathology (group A).

Parameter	Group C (n = 14)	Group A (n = 17)	p
Age, years	58.07 ± 13.61	51.17 ± 9.39	NS
Sex
Male (%)	21.42 (n = 3)	41.17 (n = 7)	NS
Female (%)	78.58 (n = 11)	58.82 (n = 10)	NS
Duration of existence of a SK, years	13.55 ± 12.33	33.23 ± 21.73	0.005
Serum creatinine, mg/dL (day 0)	1.17 ± 0.25	1.01 ± 0.15	NS
Serum creatinine, mg/dL (day 7)	1.16 ± 0.28	1.01 ± 0.15	NS
Urine albumin/creat urine (mg/g) (day 0)	36.29 ± 43.49	17.27 ± 14.88	NS
GFR, ml/min/1.73 m^2 (day 0)	56.78 ± 10.85	71.01 ± 11.31	0.0013
NAG/creat urine (U/g) (day 0)	5.15 ± 6.54	2.89 ± 2.108	NS
Alpha-1-microglobulin urine/creat urine (mg/g) (day 0)	4.96 ± 6.57	2.88 ± 5.57	0.032

Notes: The data are presented as average value ± standard deviation or number (%) of patients. Average values were compared using the Student’s t-test (parametric variables) or the U Mann–Whitney test (non-parametric variables); proportions were compared using the chi-squared test; we considered statistically significant p < 0.05; NS—non-significant.

After 7 days of treatment with gentamicin of the group under study (group C), we noticed significant increases of urinary elimination of NAG (day 7 NAG = 18.99 ± 14.07 U/g creat vs. day 0, NAG = 5.15 ± 6.54 U/g creat, p = 0.004, t-paired test), and of urinary alpha-1-micrglobulin (day 7 alpha-1-micrglobulin = 20.88 ± 18.84 mg/g creat vs. day 0 urinary alpha-1-micrglobulin = 4.96 ± 6.57 mg/g creat, p = 0.003, t-paired test), as compared to urinary eliminations previous to the antibiotic administration, without the renal function monitored by eGFR being significantly altered under treatment with gentamicin (Table 3).

Table 3. Comparative assessment of SK patients with UTI (group C) on study day 7 versus study day 0.

Parameter	Group under study, day 0 (n = 14)	Group under study, day 7 (n = 14)	p
GFR, ml/min/1.73 m^2	56.78 ± 10.85	57.49 ± 11.73	0.868
NAG/creat urine (U/g)	5.15 ± 6.54	18.99 ± 14.07	0.004
Alpha-1-microglobulin  urine/creat urine (mg/g)	4.96 ± 6.57	20.88 ± 18.84	0.003

Notes: The data are presented as average value ± standard deviations. Average values were compared using the Student’s t paired test. We considered statistically significant p < 0.05.

During treatment with gentamicin, we noticed an increased number of patients having urinary elimination of NAG, and of urinary alpha-1-microglobulin above reference limits. Thus, on study day 7, 12 patients (85.71%) had NAG eliminations above the reference limit, as compared to 9 patients (64.28%) on day 0. Urinary alpha-1-microglobulin was higher on day 7 in six patients (42.85%) as compared to two patients (14.28%) on study day 0.

On day 7, we noticed a strong correlation between NAG and urinary alpha-1-microglobulin (r = 0.727, 95% CI [0.320–0.907], R²= 0.529, p = 0.003).

Discussion

The objective of studying biomarkers under treatment with gentamicin was to assess the nephrotoxic potential of this antibiotic in patients with SK and UTI, having in mind the increased vulnerability of such patients.

The study showed in the investigated patients with SK and UTI treated with gentamicin increased values of biomarkers such as NAG and alpha-1-microglobulin as compared to their values before therapy was instituted. Thus, the values of urinary NAG in the group under study at the beginning of treatment were 5.15 ± 6.54 U/g creat and 18.99 ± 14.07 U/g creat after 7 days of treatment with gentamicin (p = 0.004). The values of urinary alpha-1-microglobulin were 4.96 ± 6.57 at the beginning of treatment and after 7 days of treatment with gentamicin 20.88 ± 18.44 mg/g urinary creatinine (p = 0.003).

The tubular lesions that occur during adaptative phenomena of the SK confer it vulnerability to external factors, including toxic ones. Under these conditions, administration of gentamicin might associate with increased risks of side effects of nephrotoxic type. Moreover, associations of SK with UTI bring about increased lesional risks since UTI produces tubulointerstitial injuries.

Under these conditions, we have at the level of the group under study at least three types of tubulointerstitial lesions. Some of them can occur during the evolution of SK, others are secondary to UTI and the third category of injuries is produced by tubular nephrotoxic effects of gentamicin.

An assessment of each of the three types of lesions, as well as global evaluation, can be made using markers of tubular lesion–urinary NAG and urinary alpha-1-microglobulin.

Thus, in a first stage, we analyzed in patients with SK tubular dysfunctions associated with adaptive phenomena. We did this by comparing the biochemical markers of the SK patients without other superposed pathologies, with the values of these markers obtained from the group of healthy persons with two kidneys. In a second stage, we studied the tubular injury of the patients with SK and UTI in comparison with the tubular injury of SK patients without other associated pathologies. In a third stage, we assessed the nephrotoxic lesion of gentamicin comparing the values of tubular injury biomarkers in patients with SK and UTI after 7 days of treatment with gentamicin with the values of these biomarkers obtained from the same patients before administration of gentamicin.

Urinary elimination of NAG and alpha-1-microglobulin in healthy persons with SK

The objective of the study was to determine whether people with SK present increased elimination of urinary NAG and alpha-1-microglobulin together with tubular lesions consecutive to adaptative phenomena of hypertrophy and hyperfiltration. To this effect, we analyzed eliminations of urinary NAG and, respectively, of alpha-1-microglobulin in apparently healthy persons with SK as compared to healthy individuals with two kidneys.

Our study found significantly higher values of urinary NAG in persons with SK as compared to persons with two kidneys. The values of urinary alpha-1-microglobulin were higher in individuals with SK versus persons with two kidneys, but this difference was not statistically significant.

Tekin et al. also pointed out high values of NAG elimination both in patients with childhood surgically acquired SK and in individuals with congenital SK.11

Gadalean et al. also draw attention to high values of urinary NAG both in individuals with surgical SK and in persons with congenital SK.12 Similar observations are reported by Stefanowicz et al.13

The SK undergoes hypertrophy and hyperfiltration adaptative phenomena, thus ensuring homeostasis under conditions of a limited number of nephrons. When the adaptative phenomena are surpassed there occur renal lesions manifested by proteinuria, hypertension and diminution of GFR. Histopathological examinations can detect segmental and focal glomerulosclerosis injuries.1

During adaptative phenomena, the tubes undergo hypertrophy processes, reaching dimensions up to 95% higher than those in persons with two kidneys.2 The tubes can present lesional alterations in their evolution. These lesional alterations can be evaluated by urinary biomarkers, such as urinary NAG and urinary alpha-1-microglobulin.

NAG is an enzyme that cannot pass through the glomerular filter because of its molecular weight (130 kDa). It appears in urine in higher quantities as a consequence of lesional processes affecting PT, being a sensitive marker for tubular injury.

Urinary alpha-1-microglobulin, another tubular lesion marker, also presented increased values in persons with SK, as compared to persons with two kidneys, but this difference was not statistically significant. Alpha-1-microglobulin is a protein that passes through the glomerular filter, being reabsorbed at PT level by means of a complex receptor (megalin--cubilin). In case of injuries of the PT, eliminations of urinary alpha-1-microglobulin are higher.

We consider that increased values of urinary NAG and of urinary alpha-1-microglobulin found in persons with SK can be related to the adaptative phenomena of SK.

Tubular injuries of SK associated with UTI

During its evolution, SK can get associated with UTI. Gluhovschi et al. identified this association in 49.5% cases.6

As pointed above, during the adaptative phenomena of SK tubular lesions can occur and UTI is associated with tubulointerstitial lesions. As a consequence of this association, the tubular lesions of SK can be more evident.

In the patients with SK and UTI, eliminations of urinary NAG and alpha-1-microglobulin were higher in patients with SK and UTI than in patients with SK without UTI, significant differences existing only for urinary releases of urinary alpha-1-microglobulin. This aspect could plead for that tubulointerstitial injuries consecutive to UTI are diverse: urinary NAG consecutive to lysosomal injury at PT level and urinary alpha-1-microglobulin coming from blood is filtered through the glomerular filter and reabsorbed at tubular level: the tubular injury associated with UTI would affect mainly the reabsorption processes, a fact determining significantly higher urinary elimination of urinary alpha-1-microglobulin.

We did not find in specialized literature papers to address the study of biochemical markers of tubular lesions associated with UTI in patients with SK. On the other hand, these tubular injuries associated with UTI were frequently described in literature in patients with two kidneys.

Thus, Gluhovschi et al. found in patients with two kidneys and UTI higher values of urinary NAG. These would be related to tubulointerstitial injuries.14,15 Urinary NAG as a marker of tubular injuries in UTI would allow differentiation between high and low localization of UTI.16,17

Urinary NAG in a patient with high localization UTI (as compared to low localization UTI) would have higher values because of tubular lesions associated with the kidneys affected by UTI.

In fact, high urinary NAG, as a biochemical marker of tubular lesions was detected in several situations:

• during glomerular nephropathies—in patients with chronic glomerulonephritis18

• in idiopathic nephrotic syndromes19

• in lupus nephropathy20

• after treatment with antiepileptic drugs – valproate21

• after administration of contrast substances22

• after administration of some antibiotics—amikacin, tobramycin14

• after administration of cytostatic medication of cisplatin type23

• after metals (cadmium, lead)24

• in diabetic nephropathy NAG has similar sensitivity that of albumin in early detection of renal impairment25

• in detecting renal diseases in hypertensive patients26

• in transplant rejection27

These observations highlight the multifactor origin of lesions of the PT in renal pathology that can be assessed by enzymatic methods, and by determination of urinary NAG, an important biochemical marker used in numerous studies regarding renal pathology and in assessments of the nephrotoxicity of antibiotics and of other medications with nephrotoxic potential.

In our study, we found significantly higher values of urinary alpha-1-microglobulin in patients with SK and UTI than in patients with SK without other pathologies. Specialized literature points out increased values of alpha-1-microglobulin in children with pyelonephritis.28

This biomarker was also used in assessing tubular lesions in acute kidney injury, and in non-oliguric acute tubular necrosis.29

Tubular injuries consecutive to gentamicin administration in patients with SK and UTI

Gentamicin is an antibiotic with well-known nephrotoxic potential. Its nephrotoxicity is complex, affecting mainly tubular structures and also acting at glomerular and vascular level.

Gentamicin alters membrane permeability and membrane aggregation,30 it produces lysosomal phospholipidosis,31 apoptosis and necrosis of tubular cells.31

At glomerular level, gentamicin stimulates mesangial proliferation which is associated with increased processes of apoptosis, it reduces the filtration coefficient by diminishing the number and size of pores on the glomerular filtration area.3

Gentamicin diminishes the renal flow by vasoconstricting effects. The GFR is reduced.3

The nephrotoxicity of gentamicin is related to several factors, among which we mention volemic depletion, electrolytic dysfunctions, dosage, and association with other drugs with nephrotoxic potential.32 It is to be noted that we did not find these facilitating factors in the patients under study.

For assessing the tubular nephrotoxicity of gentamicin, we used determinations of injury markers of the PT, namely NAG and alpha-1-microglobulin, and for assessing glomerular nephrotoxicity we used monitoring the GFR.

We have to take into account the participation of three factors in the production of tubular lesions:

• the above-discussed possible nephrotoxic action of gentamicin

• tubulointerstitial lesions consecutive to urinary infection, all the investigated patients presenting UTI, reason for which they were administered treatment with antibiotics

• tubular lesions consecutive to hypertrophy and hyperfiltration phenomena related to adaptative phenomena of SK

After 7 days of treatment, we found in the patients under study (group C) values of urinary NAG and of urinary alpha-1-microglobulin significantly higher than those before treatment was started. In specialized literature, there are few references to the assessment by biochemical markers of SK with UTI lesions under treatment with aminoglycosides.33 On the other hand, tubular injuries secondary to nephrotoxic effects of aminoglycosides were widely studied in patients with two kidneys.

Increased urinary elimination of NAG as an expression of tubular injuries secondary to nephrotoxic effects of aminoglycosides was described both in experimental studies and in studies on human subjects. Thus, experimental studies conducted by Whiting and Brown detected a relationship between the action of gentamicin on the tubes and enzymuria, analyzing the evolution of urinary NAG in experiment animals under treatment with gentamicin. They found that maximal values of urinary NAG were present after 7–10 days of treatment. The values of NAG return to the initial values at the end of the treatment, which lasted for 14 days. It is to be noted that the values of NAG diminished after cessation of treatment.34

In our study, we could observe the patients undergoing treatment only for 7 days, since after this interval their hospitalization was finished because of favorable evolution. Their family doctor continued their follow up, but they did not come back to the clinic in due time for being examined by means of urinary biochemical markers.

Increased values of urinary NAG were found in patients with two kidneys treated with gentamicin were reported by Wiland et al.35

Chapelsky et al. report early increases, starting with the second day of treatment, of the values of urinary NAG. Monitoring of NAG releases would allow identification of patients who present nephrotoxicity and whose treatment is to be interrupted.36 Unlike gentamicin, clarithromycin does not cause significant increases of urinary NAG.36

Carver et al. appreciate that there is correlation between the doses of gentamicin administered to rats and enzymuria, such as urinary NAG.37 The nephrotoxicity of other aminoglycosides, assessed by determination of urinary NAG, is to be mentioned as well. Gluhovschi et al. found increased values of urinary NAG in patients with UTI under treatment with amikacin.17 Administration of amikacin to children with cystic fibrosis presented increased values of urinary NAG.38 In fact, determination of NAG is considered to be an indicator of tubular dysfunctions both in renal disease and in toxic lesions.39

In literature, numerous authors also reported increased urinary elimination of alpha-1-microglobulin during treatment with aminoglycosides. Thus, Hugli et al. noted increased urinary elimination of alpha-1-microglobulin after 14-day administration of amikacin in patients with cystic fibrosis for respiratory infection with Pseudomonas aeruginosa.38 High values of urinary alpha-1-microglobulin were found by Wiesmann et al. after administration of gentamicin to patients under the age of 15. Concomitantly, they also found increased values of urinary NAG. Restoration of normal values of these parameters after cessation of treatment is to be noted.40

The utility of these markers in monitoring the nephrotoxicity of aminoglycosides is appreciated. Thus, Coscia et al. monitored the nephrotoxicity of the treatment with netilmicin in newborns by means of urinary alpha-1-microglobulin.41

However, our study also found some differences regarding the two biochemical markers related to the number of affected persons. Thus, NAG was high in 9/14 (64.28%) patients before treatment started, and when it stopped, their number increased to 12/14 (85.71) patients. Alpha-1-microglobulin presented high values in 2/24 (14.28%) patients with SK, to increase to 6/14 (42.85) patients after 7 days of treatment. The phenomenon is remarkable, because the megalin–cubilin receptor is interested both in the process of pinocytosis that takes part in the passage of gentamicin into the tubular cell, and in the reabsorption of alpha-1-microglobulin.

The assessment of the nephrotoxicity of gentamicin by means of biochemical markers of NAG and alpha-1-microglobulin type is significant. Only two patients did not present increased elimination of NAG. The determination of urinary alpha-1-microglobulin in relation with that of NAG highlighted the complexity of the nephrotoxicity of gentamicin at tubular level.

After 7 days of treatment, we found a strong direct correlation between urinary NAG and urinary alpha-1-microglobulin (R²= 0.529, p = 0.003).

The GFR did not reveal in the patients with SK and UTI treated with gentamicin statistically significant alterations as compared to the initial values. It is known that gentamicin acts at glomerular level reducing the filtration area and diminishing the size and number of its pores.3

No significant glomerular impairment (unlike tubular impairment) was found in the group under study. This reflects a dissociation of glomerular nephrotoxic effects and tubular nephrotoxic effects of gentamicin.

Likewise, Wiland and Szechinski did not find significant differences between GFR values before and after treatment, in the whole group under study, made of 25 patients with two kidneys.35 However, some of them presented increased serum creatinine values, the level of serum creatinine exceeding 0.4 mg/dL. The authors found transient renal insufficiency in 12–16% patients.35 We also found in our study diminution of GFR in 6 (42.86%) patients, although this diminution was not statistically significant and did not meet the AKI criteria.

Our study presents some limitations. Thus, because of the favorable evolution of the patients, on the one hand, and because of administrative limitation of periods of hospitalization and limited compliance of the patients after leaving the hospital, on the other hand, we could not assess the effects of gentamicin on patients with SK after they left the clinic.

In spite of these limitations, the study presents, for the first time in specialized literature, an observation at kidney level, by means of urinary biochemical markers, of an antibiotic with nephrotoxic potential administered to vulnerable patients, such as patients with SK.

Conclusions

The 7-day administration of gentamicin to patients with SK and urinary infection was accompanied by:

• favorable clinical evolution

• increased values of urinary markers: NAG and alpha-1-microglobulin, these reflecting lesions located at the PT level. Alterations of these urinary biochemical markers reflect the complexity of tubular lesions produced by gentamicin. The SK represents a risk factor for the therapeutic option of gentamicin. The investigated biomarkers (NAG and alpha-1-microglobulin) present increased values in apparently healthy patients with SK as compared to healthy individuals with two kidneys and could be related to the adaptative phenomena of SK. The vulnerability of the SK increases if the SK is associated with UTI, a situation in which the tubular injuries consecutive to adaptative phenomena of hypertrophy and hyperfiltration are intensified by tubulointerstitial lesions secondary to the infectious process.

GFR did not present significant alterations after treatment with gentamicin. The presence of tubular injuries in the absence of glomerular lesions pleads for a dissociation of the nephrotoxic effects of gentamicin.

The treatment with gentamicin in patients with SK, who present increased vulnerability, respectively nephrotoxic risk, can be monitored by means of urinary biochemical markers.

Declaration of interest

The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the article.