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Saudi Journal of Kidney Diseases and Transplantation
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Table of Contents   
ORIGINAL ARTICLE  
Year : 2015  |  Volume : 26  |  Issue : 5  |  Page : 947-952
Renal inflammatory response to urinary tract infection in rat neonates


1 Jahrom University of Medical Sciences, Jahrom, Iran
2 Department of Pediatrics, Jahrom University of Medical Sciences, Jahrom, Iran
3 Department of Pathology, Shiraz University of Medical Sciences, Shiraz, Iran
4 School of Pharmacy, Shiraz University of Medical Sciences, Shiraz, Iran

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Date of Web Publication7-Sep-2015
 

   Abstract 

Urinary tract infection (UTI) is one of the most common bacterial infections. Maternal UTI is a risk factor for neonatal UTI. The aim of the present study was to determine the severity of renal inflammation in neonate rats born from mothers with induced UTI. Twelve pregnant rats (Sprague-Dawley) were included in study. The rats were divided into two groups (six rats in each group). In the first group, pyelonephritis was induced in the third trimester of pregnancy and the second group was used as a control group. After delivery, the neonates were divided into three groups based on days after birth (the 1 st, 3 rd and 7 th days after birth). In each group, two neonates of each mother were killed and a midline abdominal incision was made and both kidneys were aseptically removed. On the 7 th day, rat mothers were killed and their kidneys were removed. The preparations were evaluated with a bright field microscope for inflammatory response. Renal pathology showed inflammation in all UTI-induced mothers, but only two cases of neonates (2.1%) showed inflammation in the renal parenchyma. There was no relation between the positive renal culture and the pathological changes. We conclude that neonates with UTI born to UTI-induced mothers showed a lesser inflammatory response.

How to cite this article:
Zarepour M, Moradpoor H, Emamghorashi F, Owji S M, Roodaki M, Khamoushi M. Renal inflammatory response to urinary tract infection in rat neonates. Saudi J Kidney Dis Transpl 2015;26:947-52

How to cite this URL:
Zarepour M, Moradpoor H, Emamghorashi F, Owji S M, Roodaki M, Khamoushi M. Renal inflammatory response to urinary tract infection in rat neonates. Saudi J Kidney Dis Transpl [serial online] 2015 [cited 2019 Sep 20];26:947-52. Available from: http://www.sjkdt.org/text.asp?2015/26/5/947/164575

   Introduction Top


Urinary tract infection (UTI) is one of the most common bacterial infections. It affects 17.9-26% of pregnant women. There is also a high incidence of infection in the third trimester of pregnancy. [1],[2] The exact rate of UTI in newborns is not known, but studies have found that from about 1 in 1000 to 1 in 100 in full-term infants, and up to 1 in 10 premature infants, will have a UTI during the first month of life, and higher incidence of UTI in the Neonatal Intensive Care Unit has been detected in 15.05%. [3] A study showed that 5% of neonates with sepsis developed UTI. [4] Our previous work found maternal UTI as a risk factor for neonatal UTI. [5]

Host factors play a vital role in protection from UTI. Natural host defense factors include unidirectional flow of urine from the kidney to the bladder, secretion of glycosamines by bladder transitional cells, Tamm-Horsfall protein and defensins. Once the bacteria come into contact with urothelial cells, an innate immune response is started. [6] Neonatal inflammatory response has been considered to be intrinsically hyporesponsive. [7],[8] A study showed that an immature compensatory anti-inflammatory response syndrome (CARS) in pre-term infants predisposes them to the harmful effects of the pro-inflammatory cytokines, resulting in severe organ damage during infection. [9] Neonates and infants are at a higher risk for UTI during their first few months of life. This susceptibility has been attributed to an incomepletely developed immune system. [10] It is suggested that renal damage in adequately treated infants is probably due to a reflux-associated, pre-existing, congenital renal parenchymal pathology and not to the inflammatory process. [11]

The aim of the present study was the determination of severity of renal inflammation in neonate rats born to mothers with induced UTI.


   Materials and Methods Top


We studied 12 Sprague-Dawley pregnant rats weighing 244 ± 41.0 g obtained from the Laboratory Animal House of the Shiraz University of Medical Sciences, Shiraz, Iran. The experiment was performed in the Laboratory Animal House of the Jahrom University of Medical Sciences with cooperation of the Laboratory Animal House of the Shiraz University of Medical Sciences during the summer of 2012. The rats had free access to food and water throughout the experiment. They were maintained in terms of 12-h light, 12-h dark, temperature 24°C and humidity of 40-60% based on standard guidelines. They were divided into two groups (six rats in each group). In the first group, pyelonephritis was induced during the third trimester of pregnancy and the second group without infection was used as the control group.

The bacterial strain used to induce pyelonephritis was Escherichia coli (E. coli) (H2O6, pap+); it was obtained from a patient with pyelonephritis. The animals were anesthetized before induction of pyelonephritis. The side of the animals was shaved and rendered aseptic by an intraperitoneal injection of ketamine and xalazine. Then, a small incision was made at the level of the kidney. The left kidney was exposed and 0.05 mL of an inoculum containing 10 9 bacteria was injected through the upper pole of the left kidney. This technique, described previously by Kaye, produces pyelonephritis. [12]

After the induction of pyelonephritis, the animals were locked up in separate cages. After delivery, the neonates were divided into three groups based on days after birth (1 st , 3 rd and 7 th days after birth). In each group, two neonates from each mother were killed and a midline abdominal incision was made, and both kidneys were aseptically removed. Each kidney was divided into two parts by a sagittal incision and one half was sent in a sterile container for microbiologic study. In positive cases of kidney culture, types of infectioncausing organisms were defined. Other halves were fixed in 10% neutral formalin solution and stained with hematoxylin and eosin (HE). The preparations were evaluated with a bright field microscope and were photographed. Microscopic renal lesions were scored on plastic sections at a magnification of ×400. Each slide was coded such that identification of the groups was not possible for the observer. Slices came from three different pieces of renal cortex for each rat. The cortex and medulla, including glomerulus, tubules, vessels and interstitium, were evaluated. The percentage of cellular infiltration in each section was considered as severity of inflammation [interstitial inflammatory cells (IIC)].

For the microbiology study, half of each kidney was homogenized in 3 mL of sterile saline at 4°C. Appropriate dilutions of homogenized kidneys were made and 10-μL samples were placed in triplicate on MacConkey agar. The numbers of colony-forming units (CFUs) of E. coli in the kidneys were determined after an incubation of 18 h at 37°C (the CFU per milliliter of homogenate was transformed into CFU per gram of tissue).

The design of this experiment was approved by the ethic committee of the Jahrom University of Medical Sciences.


   Statistical Analyses Top


All statistical analyses were performed with SPSS version 11.5. The data were analyzed by ANOVA to determine the statistical significance of the difference between groups. A Pvalue less than 0.05 (P <0.05) was considered to be significant.


   Results Top


One hundred and eight kidney samples were obtained from mother rats and their neonates. [Table 1] shows the results of cultures and pathology of the kidneys. Cultures of eight kidney samples of 12 mothers were positive; 50% of the samples showed a positive culture. Overall, 56 (51.9%) of the kidney cultures were positive. [Table 2] shows the relationship between positive kidney cultures in mothers and their neonates. The kidney cultures were positive in all UTI-induced mother rats. Two mother rats in the control group also had a positive kidney culture, which was not related to the induction of infection.
Table 1: Frequency of positive kidney cultures in mother rats and their neonates.

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Table 2: Results of kidney cultures in mother rats and their neonates.

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E. coli was the causal agent in the UTIinduced group and non-hemolytic streptococci was the causal agent in one case of the control group. There was a correlation between the positive kidney cultures in mothers and neonates (58.8% vs. 40%, P = 0.05). However, there was no difference in the incidence of UTI in the neonates according to days after birth.

The renal pathology showed inflammation in all the UTI-induced mothers, but only 2/96 (2.1%) of neonate kidney cultures showed inflammation in the renal parenchyma; one of these two neonates belonged to mothers without infection and another neonate had a mother with a positive kidney culture and inflammation. There was no correlation between positive renal culture and inflammatory response in renal pathology. Our data showed that neonates have reduced inflammation in the kidney compared with adults during UTI, even though both adult and neonatal kidneys had a similar bacterial load [Figure 1].
Figure 1:

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   Discussion Top


In this study, we developed a neonatal model of UTI. In spite of positive kidney culture in neonates of UTI-induced mother, the pathology showed a low inflammatory response in neonates with UTI. Neonatal inflammatory response has been considered to be intrinsically hyporesponsive. [7],[8] Infiltration of neutrophils into the uro-epithelium and bladder lumen of mice has been observed as early as 6 h after inoculation with uropathogenic E. coli (UPEC). [13] Neutrophils are essential for bacterial clearance from the urinary tract, [14] and defects in neutrophil recruitment or function increase susceptibility to UTI. Uropathogenic E. coli suppress the host inflammatory response. [15] It has been suggested that the inflammatory process causes irreversible renal parenchymal scarring. The study could not confirm that younger children are at a greater risk for developing renal sequelae following pyelonephritis. [16]

A central element of innate immunity to bacterial infection is the neutrophil-a cell that contains cytoplasmic granules replete with antibiotic proteins and peptides. The activity of adult neutrophils against gram-negative bacteria is believed to depend, to a significant degree, on the presence of bactericidal/permeability-increasing protein (BPI), which binds with high affinity to bacterial lipopolysaccharides and kills gram-negative bacteria. This study showed that the neutrophils of newborns are selectively deficient in BPI. BPI deficiency correlates with decreased antibacterial activity of the newborn neutrophil extracts against serum-resistant E. coli and could contribute to the increased incidence of gram-negative infection. [17],[18] Clinical evidence of the pre-term neonates' immune incompetence includes the frequent development of neutropenia in response to bacterial sepsis. [19],[20] The immediate fall in neutrophil count that accompanies neonatal sepsis may be due to more than an inability to increase the proliferation of early progenitors. Studies in newborn rats have demonstrated that their absolute neutrophil cell mass per gram of body weight is only onequarter of that of adult animals. After birth, the neutrophil cell mass per gram of body weight expands to reach adult levels after about four weeks. [21] Neonatal neutrophils display less interaction with endothelial monolayers in conditions of flow than adult cells. Rolling adhesion is diminished, fewer cells attach to the activated endothelium and fewer cells migrate to the sub-endothelial tissue. [22]

The inflammatory response in the urinary tract presents as pyuria in urinalysis. Less inflammatory response results in less pyuria in neonates with UTI. However, pyuria is not a useful marker for the diagnosis of cultureproven UTI in neonates. [23]

Variability in inflammatory response in neonates has been observed in other infections. Neonatal mice developed similar SeV titers and cleared the virus with similar efficiency despite developing a dramatically lower degree of pulmonary inflammation compared with adults. [24] Pulmonary virus of the mouse (PVM) infection presented in an atypical fashion in neonatal mice; chemokine production is minimal in the lung tissue of neonatal mice and recruitment of pro-inflammatory leukocytes is diminished when compared with older mice. [25] A whole blood lipopolysaccharide stimulation assay showed significantly lower tumor necrosis factor-α values in preterm neonates who subsequently developed sepsis, indicating a degree of immunoparalysis. [26]

We conclude from our study that neonate rats with UTI showed less inflammatory response than adult rats. Further studies are warranted to evaluate whether intrauterine-acquired UTI in neonates can cause renal injury or scar.

Conflict of interest: None.

 
   References Top

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Kawser P, Afroza M, Arzumath AB, et al. Prevalence of urinary tract infection during pregnancy. J Dhaka Natl Med Coll Hos 2011;17:8-12.  Back to cited text no. 1
    
2.
Masinde A, Gumodoka B, Kilonzo A, Mshana SE. Prevalence of urinary tract infection among pregnant women at Bugando Medical Centre, Mwanza, Tanzania. Tanzan J Health Res 2009;11:154-9.  Back to cited text no. 2
    
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Youssef DM, Elfateh HA, Sedeek R, Seleem S. Epidemiology of urinary tract infection in neonatal intensive care unit: A single center study in Egypt. J Acad Med Sci 2012;2:25-9.  Back to cited text no. 3
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Milani Hosseini S, Ataei N, Khalafi F, Sheikhvatan M. Incidence of urinary tract infection in neonates with septicemia: a prospective study. Minerva Pediatr 2011;63:369-73.  Back to cited text no. 4
    
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Emamghorashi F, Mahmoodi N, Tagarod Z, Heydari ST. Maternal urinary tract infection as a risk factor for neonatal urinary tract infection. Iran J Kidney Dis 2012;6:178-80.  Back to cited text no. 5
    
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Kucheria R, Dasgupta P, Sacks SH, Khan MS, Sheerin NS. Urinary tract infections: new insights into a common problem. Postgrad Med J 2005;81:83-6.  Back to cited text no. 6
    
7.
Rowen JL, Smith CW, Edwards MS. Group B streptococci elicit leukotriene B4 and interleukin-8 from human monocytes: neonates exhibit a diminished response. J Infect Dis 1995;172:420-6.  Back to cited text no. 7
    
8.
Schibler KR, Liechty KW, White WL, Rothstein G, Christensen RD. Defective production of interleukin-6 by monocytes: a possible mechanism underlying several host defense deficiencies of neonates. Pediatr Res 1992;31:18-21.  Back to cited text no. 8
    
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Schultz C, Temming P, Bucsky P, Göpel W, Strunk T, Härtel C. Immature anti-inflammatory response in neonates. Clin Exp Immunol 2004;135:130-6.  Back to cited text no. 9
    
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Chang SL, Shortliffe LD. Pediatric urinary tract infections. Pediatr Clin North Am 2006;53:379-400, vi.  Back to cited text no. 10
    
11.
Goldman M, Bistritzer T, Horne T, Zoareft I, Aladjem M. The etiology of renal scars in infants with pyelonephritis and vesicoureteral reflux. Pediatr Nephrol 2000;14:385-8.  Back to cited text no. 11
    
12.
Kaye D. The effect of water diuresis on spread of bacteria through the urinary tract. J Infect Dis 1971;124:297-305.  Back to cited text no. 12
    
13.
Mulvey MA, Schilling JD, Martinez JJ, Hultgren SJ. Bad bugs and beleaguered bladders: interplay between uropathogenic Escherichia coli and innate host defenses. Proc Natl Acad Sci U S A 2000;97:8829-35.  Back to cited text no. 13
    
14.
Haraoka M, Hang L, Frendéus B, et al. Neutrophil recruitment and resistance to urinary tract infection. J Infect Dis 1999;180:1220-9.  Back to cited text no. 14
    
15.
Lloyd AL, Smith SN, Eaton KA, Mobley HL. Uropathogenic Escherichia coli Suppresses the host inflammatory response via pathogenicity island genes sisA and sisB. Infect Immun 2009;77:5322-33.  Back to cited text no. 15
    
16.
Benador D, Benador N, Slosman D, Mermillod B, Girardin E. Are younger children at highest risk of renal sequelae after pyelonephritis? Lancet 1997;349:17-9.  Back to cited text no. 16
    
17.
Levy O, Martin S, Eichenwald E, et al. Impaired innate immunity in the newborn: Newborn neutrophils are deficient in bactericidal/permeability-increasing protein. Pediatrics 1999;104:1327-33.  Back to cited text no. 17
    
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Cuenca AG, Wynn JL, Moldawer LL, Levy O. Role of innate immunity in neonatal infection. Am J Perinatol 2013;30:105-12.  Back to cited text no. 18
    
19.
Gessler P, Lüders R, König S, Haas N, Lasch P, Kachel W. Neonatal neutropenia in low birthweight premature infants. Am J Perinatol 1995;12:34-8.  Back to cited text no. 19
    
20.
Tissières P, Ochoda A, Dunn-Siegrist I, et al. Innate immune deficiency of extremely premature neonates can be reversed by interferon-? PLoS One 2012;7:e32863.  Back to cited text no. 20
    
21.
Erdman SH, Christensen RD, Bradley PP, Rothstein G. Supply and release of storage neutrophils. A developmental study. Biol Neonate 1982;41:132-7.  Back to cited text no. 21
    
22.
Anderson DC, Abbassi O, Kishimoto TK, Koenig JM, McIntire LV, Smith CW. Diminished lectin-, epidermal growth factor-, complement binding domain-cell adhesion molecule-1 on neonatal neutrophils underlies their impaired CD18-independent adhesion to endothelial cells in vitro. J Immunol 1991;146:3372-9.  Back to cited text no. 22
    
23.
Rahman AJ, Naz F, Ashraf S. Significance of pyuria in the diagnosis of urinary tract infections in neonates. J Pak Med Assoc 2011;61:70-3.  Back to cited text no. 23
    
24.
Bhattacharya S, Beal BT, Janowski AM, Shornick LP. Reduced inflammation and altered innate response in neonates during paramyxoviral infection. Virol J 2011;8:549.  Back to cited text no. 24
    
25.
Bonville CA, Ptaschinski C, Percopo CM, Rosenberg HF, Domachowske JB. Inflammatory responses to acute pneumovirus infection in neonatal mice. Virol J 2010;7:320.  Back to cited text no. 25
    
26.
Azizia M, Lloyd J, Allen M, Klein N, Peebles D. Immune status in very preterm neonates. Pediatrics 2012;129:e967-74.  Back to cited text no. 26
    

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Correspondence Address:
F Emamghorashi
Pediatric Nephrology, Motahary Hospital, Jahrom
Iran
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DOI: 10.4103/1319-2442.164575

PMID: 26354566

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