Pyelonephritis provokes growth retardation and apoptosis in infant rat renal cortex

Peculiarities of leukocyte apoptosis modulation in children with pyelonephritis

One of the leading places among inflammatory diseases of the urinary tract of children belongs to pyelonephritis, the course of which presents in most cases as a severe infectious disease threatening the patient’s life, which is the main reason for development of chronic kidney failure. This study was conducted to compare apoptosis stages in peripheral blood of children of different age categories with pyelonephritis depending on etiological factor and complications. The problem of mechanisms underlying immune system misregulation, especially functional activity of leukocytes in children with pyelonephritis, have not been explored in recent years. Assessment of leukocytes (neutrophils) apoptosis stages in peripheral blood of children of different age categories with pyelonephritis depending on complications and etiological factor was the aim of present study. The children's peripheral blood samples were analysed and assessed using a flow cytofluorimeter. The present study demonstrates an increase of the level of apoptotic cells at an early stage of apoptosis in children of all age categories with chronic pyelonephritis, which can be explained by associations of a wide range of pathogens and the presence of sequelae. An increase in the number of apoptotic cells in the late stage of apoptosis is observed in children aged 1 month – 8 years, in children 8–18 years, the amount of apoptotic cells is reduced by 1.5 times. The study of apoptosis stages allows complete characterization of the dynamics of the apoptotic process and supplementation of the pathogenesis of pyelonephritis in children. Such studies will make it possible to affect apoptosis modulation to regulate or correct it and encourage the finding of innovative solutions in the treatment related to influence on the immune response. We conclude that enhancement of peripheral blood leukocyte apoptosis in chronic form of pyelonephritis especially in young children is due to the polyetiology of this form of pyelonephritis and the development of complications.

Prevention of Renal Scarring in Acute Pyelonephritis by Probiotic Therapy: an Experimental Study

We evaluated the protective effects of probiotic administration as a prophylaxis treatment and immediately after fever onset in increasing the immune response and decreasing the renal scarring in a rat model of acute pyelonephritis. Twenty-four rats were apportioned to three groups. In GI (n = 8), the rats were injected with direct inoculation of Escherichia coli into the right kidney. In GII (n = 8), the rats received a probiotic regimen 1 month before E. coli injection and the probiotic regimen was continued for the next 2 months. In GIII (n = 8), the probiotic regimen was started just after E. coli injection and was continued for 2 months. Technetium-99m-DMSA renal scan, histopathological evaluations, concentrations of CA19-9, IgA, blood urea nitrogen (BUN), and creatinine were assessed 1 and 2 months post-injection. It took an average of 4.2 ± 1.1 h between the injection and onset of fever in GI and GII. In GIII, this period was longer (7.5 ± 1.4). Probiotic administration resulted in reduction of interstitial fibrosis and tubular and glomerular atrophy in GII in all follow-ups. Technetium-99m-DMSA renal scan showed that the right kidney reached near the normal cortical integrity (47%) in GII compared to GI (32%) after 2 months of injection. However, the renal integrity did not improve significantly in GIII (41%). In GII, CA19-9 was lower (p < 0.05), while the levels of serum and fecal IgA were higher (p < 0.05). Administration of the probiotic regimen in the rat model may decrease renal damage in pyelonephritis. In spite of better results in the prophylactic group compared to the treatment group, no strong evidence was found to prove the advantage of its prophylactic application over the treatment administration.

A Putative Role of Apolipoprotein L1 Polymorphism in Renal Parenchymal Scarring Following Febrile Urinary Tract Infection in Nigerian Under-Five Children: Proposal for a Case-Control Association Study

Background

Although urinary tract infection (UTI) resolves with prompt treatment in a majority of children, some children, especially those aged less than 5 years, also develop renal parenchymal scarring (RPS). RPS causes high blood pressure that may lead to severe chronic kidney disease and end-stage renal disease (ESRD). Although the risk of UTI is higher in white children than in black children, it is unknown whether RPS is more common in white children than in black children as data are scarce in this regard. A common genetic predisposition to kidney disease in African Americans and the sub-Saharan African blacks is the possession of apolipoprotein L1 (APOL1). APOL1 risk variants regulate the production of APOL1. APOL1 circulates in the blood, and it is also found in the kidney tissue. While circulating, APOL1 kills the trypanosome parasites; an increased APOL1 in kidney tissues, under the right environmental conditions, can also result in the death of kidney tissue (vascular endothelium, the podocytes, proximal tubules, and arterial cells), which, ultimately, is replaced by fibrous tissue. APOL1 may influence the development of RPS, as evidence affirms that its expression is increased in kidney tissue following UTI caused by bacteria. Thus, UTI may be a putative environmental risk factor responsible for APOL1-induced kidney injury.

Objective

The aim of this proposal was to outline a study that seeks to determine if the possession of two copies of either G1 or G2 APOL1 variant increases the risk of having RPS, 6 months following a febrile UTI among Nigerian under-five children.

Methods

This case-control association study seeks to determine whether the risk of RPS from febrile UTI is conditional on having 2 APOL1 risk alleles (either G1 or G2). Cases will be children with a confirmed RPS following a febrile UTI. Controls will be age-, gender-, and ethnic-matched children with a febrile UTI but without RPS. Children with vesicoureteral reflux and other congenital anomalies of the urinary tract are to be excluded. Association between predictor variables (ethnicity, APOL1 G1 or G2, and others) and RPS will be tested at bivariate logistic regression analyses. Predictors that attained significance at a P value of ˂.05 will be considered for multiple logistic regressions. Likelihood-based tests will be used for hypothesis testing. Estimation will be done for the effect size for each of the APOL1 haplotypes using a generalized linear model.

Results

The study is expected to last for 3 years.

Conclusions

The study is contingent on having a platform for undergoing a research-based PhD program in any willing university in Europe or elsewhere. The findings of this study will be used to improve the care of African children who may develop RPS following febrile UTI.

Registered Report Identifier

RR1-10.2196/9514

Uropathogenic Escherichia coli P and Type 1 fimbriae act in synergy in a living host to facilitate renal colonization leading to nephron obstruction

The progression of a natural bacterial infection is a dynamic process influenced by the physiological characteristics of the target organ. Recent developments in live animal imaging allow for the study of the dynamic microbe-host interplay in real-time as the infection progresses within an organ of a live host. Here we used multiphoton microscopy-based live animal imaging, combined with advanced surgical procedures, to investigate the role of uropathogenic Escherichia coli (UPEC) attachment organelles P and Type 1 fimbriae in renal bacterial infection. A GFP⁺ expressing variant of UPEC strain CFT073 and genetically well-defined isogenic mutants were microinfused into rat glomerulus or proximal tubules. Within 2 h bacteria colonized along the flat squamous epithelium of the Bowman's capsule despite being exposed to the primary filtrate. When facing the challenge of the filtrate flow in the proximal tubule, the P and Type 1 fimbriae appeared to act in synergy to promote colonization. P fimbriae enhanced early colonization of the tubular epithelium, while Type 1 fimbriae mediated colonization of the center of the tubule via a mechanism believed to involve inter-bacterial binding and biofilm formation. The heterogeneous bacterial community within the tubule subsequently affected renal filtration leading to total obstruction of the nephron within 8 h. Our results reveal the importance of physiological factors such as filtration in determining bacterial colonization patterns, and demonstrate that the spatial resolution of an infectious niche can be as small as the center, or periphery, of a tubule lumen. Furthermore, our data show how secondary physiological injuries such as obstruction contribute to the full pathophysiology of pyelonephritis.

When bacteria such as uropathogenic Escherichia coli (UPEC) infect a living kidney, they face numerous physiological challenges such as the flow of urine. Bacteria need to attach themselves to the epithelial linings of the kidney to withstand this flow. In this work we use a live animal imaging model to study how UPEC colonize a living kidney despite the physiological challenges they face. We show that P and Type 1 fimbriae, two of the most well described UPEC adhesion factors, work together to promote successful bacterial colonization. P fimbriae mediate binding between the bacteria and the epithelial cells lining the tubules, while Type 1 appears to play a role in inter-bacterial binding and biofilm formation in the center parts of the lumen. The heterogeneous bacterial community which filled the tubule was subsequently shown to effect nephron filtration and resulted in a total loss of filtrate flow i.e. obstruction. This work demonstrates the interplay between the bacterial and host aspects, indicating how factors such as filtration may affect bacterial adhesion and vice versa. It also highlights the multifactorial basis of kidney infection, demonstrating how physiological injuries such as obstruction may contribute towards the full pathophysiology of pyelonephritis.

Vitamin E administration at the onset of fever prevents renal scarring in acute pyelonephritis

We evaluated the protective effects of antioxidant at the onset of fever on renal damage in a rat model of acute pyelonephritis. Twenty rats were allocated to four groups. In groups 1 to 3, the animals were given direct inoculation of Escherichia coli into the right kidney, and group four served as control. All rats in groups 1 to 3 were given once-daily intraperitoneal injections of ceftriaxon for five consecutive days, beginning on the third day after inoculation. The animals' body temperatures were monitored; as soon as body temperature reaches 38 degrees C, the rats in group 2 were given allopurinol co-treatment, whereas, in group 3, vitamin E co-treatment was started at fever onset. Both kidneys were excised 6 weeks later, for the evaluation of histopathologic changes, apoptotic damage, and concentrations of transforming growth factor-beta (TGF-beta). Only minimal changes were found in control samples. Pathologic scores of inflammation and fibrosis in group 1 were higher than in the vitamin E and allopurinol groups (P < 0.05). Apoptosis index was also decreased in groups 2 and 3, compared to group 1 (P < 0.05). There was no significant difference in average TGF-beta levels between study groups. These findings suggest that administration of vitamin E or allopurinol following the onset of fever can reduce renal damage in pyelonephritis.

Urinary aquaporin-2 in children with acute pyelonephritis

Children with acute pyelonephritis develop polyuria and have reduced maximum urinary concentration capacity. We studied whether these abnormalities are associated with altered urinary excretion of the water channel aquaporin-2 (AQP2) in the renal collecting duct. AQP2 is the main target for antidiuretic action of arginine vasopressin (AVP), and the urinary excretion of this protein is believed to be an index of AVP signaling activity in the kidney. Children with acute pyelonephritis, aged 5-14 years, were examined for urinary flow rate, creatinine clearance, unchallenged urine osmolality, and urinary ion excretion. Urinary excretion of AQP2 was measured by dot immunoblotting technique. Studies were performed in the acute phase of pyelonephritis, in the same children after treatment, and in control patients. At the onset of pyelonephritis, urinary flow rate and solute excretion were increased, but the urinary osmolality was unchanged. The urinary level and urinary excretion of AQP2 was increased in acute pyelonephritis and decreased after treatment. Excretion of aquaporin-3 was unchanged, suggesting that the increase in AQP2 urinary excretion was not due to a shedding of collecting duct cells. The results suggest that a mechanism proximal to the collecting duct may be responsible for the polyuria observed in children with acute pyelonephritis. Increased urinary AQP2 levels suggest that a compensatory activation of apical plasma membrane targeting of AQP2 may occur in pyelonephritis.

Carbon monoxide prevents apoptosis induced by uropathogenic Escherichia coli toxins

Urinary tract infections (UTIs) are often caused by Escherichia coli (E. coli). Previous studies have demonstrated that up-regulation of heme oxygenase-1 (HO-1) may trigger a survival mechanism against renal cell death induced by E. coli toxins. The present study analyses the role of carbon monoxide (CO), an end product of HO-1, in the survival mechanism. Moreover, we identified hemolysin as a putative pro-apoptotic toxin in the E. coli supernatant. Tubular cells were incubated with CO in the presence or absence of E. coli toxins. Uropathogenic or transformants of non-pathogenic strains expressing hemolysin were used. We found that the survival pathway during E. coli infection might be activated by HO-1-derived production of CO. The protection by CO was also associated with up-regulation of p21 protein expression. Furthermore, we found that in children with pyelonephritis, all the E. coli strains expressing hemolysin induced apoptosis. In E. coli strains not expressing hemolysin, only 45% of the strains could induce apoptosis. In conclusion, generation of CO elicited by HO-1 could promote survival signaling in renal cells. Hemolysin is one of the secreted toxins that are involved in inducing apoptosis during UTI.

Prenatal exposure to high level of glucocorticoids increases the susceptibility of renal proximal tubular cells to apoptosis induced by uropathogenic Escherichia coli toxins

Prenatal exposure to excessive glucocorticoids may alter the developing fetus inducing metabolic and endocrine imbalance in various organs, including the kidney. This study aimed at evaluating whether prenatal exposure to high levels of glucocorticoids adversely affects renal cell survival and predisposes to renal cell death. Pregnant rats were injected with 0.1 mg/kg dexamethasone (DEX) i.p. from day 1 of gestation. Renal proximal tubular cells (PTCs) were prepared from 20-day-old offspring in the DEX (DEX cells) and control groups (CON cells). After 4 days' culture, cells were exposed to uropathogenic Escherichia coli ARD6 toxins at concentrations known to induce apoptotic cell death. We found that cell death rate was significantly higher in DEX than in CON cells. Cells exhibited morphological and biochemical features of apoptosis. Conversely, the activity of the antioxidant enzyme catalase was significantly increased in renal cortex homogenate from 20-day-old DEX rats. The antioxidant vitamin E did not prevent apoptosis. These results indicate that prenatal exposure to high levels of glucocorticoids induces alterations in renal PTCs rendering them more sensitive to E. coli toxins via nonoxidative stress. With the increasing use of multiple doses of glucocorticoids in preterm infants, the possibility that antenatal glucocorticoids may lead to renal adverse consequences is of clinical relevance.

Renal cytokine responses in acute Escherichia coli pyelonephritis in IL-6-deficient mice

The aim of this study was to investigate the influence of IL-6 on mortality, bacterial growth and cytokine expression in experimental acute pyelonephritis. Female IL-6-deficient mice and their wild-type counterparts, 8-10 weeks old, were infected with Escherichia coli CFT 073 or injected with NaCl 0.9% (w/v) via the urethra and thereafter obstructed for 6 h. Animals were killed at 48 h, 6 days or 8 weeks and cytokine and bacterial renal levels were assessed at each time point. We found that IL-6-deficient mice had increased mortality and extensive renal bacterial growth on day 6, compared with wild-type mice (P < 0.05) and the histopathological changes were generally more severe and widespread in the IL-6-deficient mice. Peak mRNA expression of IL-1beta, IL-4, IL-10, IL-12 and interferon-gamma (IFN-gamma) occurred 48 h after infection in both IL-6 knock out and wild-type mice. Transforming growth factor-beta (TGF-beta) levels also peaked at 48 h in E. coli-infected wild-type mice, while in the IL-6-deficient strain both TGF-beta mRNA and protein levels were significantly lower at 48 h than wild-type levels (P < 0.0008 and P < 0.03, respectively) and remained stationary throughout the study period. Animals injected with NaCl 0.9% (w/v) displayed a similar decrease in TGF-beta expression (P < 0.02). When splenocytes from the IL-6-deficient mice were incubated with murine recombinant IL-6, TGF-beta levels increased to those of wild-type mice. No increase was observed when splenocytes from wild-type mice were incubated with the same doses of rIL-6. We therefore conclude that IL-6 plays an important role in bacterial clearance and directly influences the TGF-beta levels in experimental acute pyelonephritis. We also demonstrate that urethral obstruction per se induces an increase in TGF-beta the magnitude of which is decreased in IL-6-deficient mice.

Alpha-haemolysin of uropathogenic E. coli induces Ca2+ oscillations in renal epithelial cells

Pyelonephritis is one of the most common febrile diseases in children. If not treated appropriately, it causes irreversible renal damage and accounts for a large proportion of end stage renal failures. Renal scarring can occur in the absence of inflammatory cells, indicating that bacteria may have a direct signalling effect on renal cells. Intracellular calcium ([Ca2+]i) oscillations can protect cells from the cytotoxic effects of prolonged increases in intracellular calcium. However, no pathophysiologically relevant protein that induces such oscillations has been identified. Here we show that infection by uropathogenic Escherichia coli induces a constant, low-frequency oscillatory [Ca2+]i response in target primary rat renal epithelial cells induced by the secreted RTX (repeats-in-toxin) toxin alpha-haemolysin. The response depends on calcium influx through L-type calcium channels as well as from internal stores gated by inositol triphosphate. Internal calcium oscillations induced by alpha-haemolysin in a renal epithelial cell line stimulated production of cytokines interleukin (IL)-6 and IL-8. Our findings indicate a novel role for alpha-haemolysin in pyelonephritis: as an inducer of an oscillating second messenger response in target cells, which fine-tunes gene expression during the inflammatory response.

[Parenchymatous cicatrix and urinary tract infection: physiopathology and clinical implications]

Renal scarring is the main long term complication of acute pyelonephritis in children. The prevalence rate is hazardous since data from the literature are confusing with respect to reflux nephropathy, chronic pyelonephritis and renal hypoplasia. The pathology of such lesions consists in focal interstitial fibrosis. When the first pyelonephritic attack occurs during infancy, renal growth may be compromised. The current approach of renal scar assessment is based on dimercaptosuccinic acid (DMSA) scan. Bilateral extensive lesions may be responsible for altered glomerular filtration rate (GFR) and/or arterial hypertension. The management of overt scarring is conservative and careful prevention must be based on early and aggressive treatment of acute pyelonephritis.

Unilateral ureteral obstruction impairs renal antioxidant enzyme activation during sodium depletion

BACKGROUND

Obstructive nephropathy leads to progressive renal tubular atrophy and interstitial fibrosis and is associated with sodium wasting and sodium depletion. Renal damage resulting from unilateral ureteral obstruction (UUO) may be aggravated by reactive oxygen species (ROS), which are produced by a variety of processes. Ideally, deleterious effects of ROS are attenuated by antioxidant enzymes, including the superoxide dismutases, glutathione peroxidases, catalase, and glutathione-S-transferases. The general paradigm is that tissue damage occurs when ROS production is greater than the protective capacity of the antioxidant enzymes.

METHODS

This study was designed to investigate the response of renal antioxidant enzymes to UUO and sodium depletion. Adult, male Sprague-Dawley rats received normal-sodium or sodium-depleted siets and were subjected to UUO or sham operation. Obstructed (UUO), intact opposite, or sham-operated kidneys were harvested after 14 days, and antioxidant enzyme activities were measured in kidney homogenates. Thiobarbituric acid reactive substances were measured in these homogenates at 3 and 14 days after UUO or sham operation as an index of ROS production.

RESULTS

Renal interstitial area, a measure of fibrosis, was increased by UUO and was doubled in sodium-depleted animals. Sodium depletion increased manganese superoxide dismutase, glutathione peroxidases, and glutathione-S-transferase activities in sham-operated kidneys but not in UUO kidneys. Relative to intact opposite kidneys, UUO kidneys had reduced activities of catalase, manganese superoxide dismutase, and glutathione-S-transferase in normal-sodium animals and all antioxidant enzymes tested in sodium-depleted animals. Renal thiobarbituric acid reactive substances were increased by three days of UUO and were increased further by 14 days of sodium depletion.

CONCLUSION

In summary, sodium depletion increased several renal antioxidant enzymes, consistent with a stress response to increased ROS production. Further, UUO not only reduced antioxidant enzyme activities but also inhibited increases seen with sodium depletion. We conclude that suppression of renal antioxidant enzyme activities by UUO contributes to the progression of renal injury in obstructive nephropathy, a process exacerbated by sodium depletion.

Prenatal dexamethasone causes oligonephronia, sodium retention, and higher blood pressure in the offspring

Recent reports have shown that low birth weight infants have a higher incidence of adult hypertension. These observations have stimulated a number of studies designed to evaluate the mechanisms of this phenomenon. In this study, fetal growth retardation was induced by treating pregnant rats with dexamethasone. After birth, pups whose mothers were treated with dexamethasone had a lower body and kidney weight and a lower number of glomeruli than control pups. Immunohistochemistry on treated kidneys demonstrated a marked reduction in the number of cells undergoing mitosis in the cortical nephrogenic zone. In the treated group, body and kidney weight normalized by 60 d of age, but blood pressure was significantly higher compared with controls (130+/-4 versus 107+/-1 mm Hg). In addition, GFR was significantly lower, albuminuria was higher, urinary sodium excretion rate and fractional sodium excretion were lower, and sodium tissue content was higher. In contrast, when pregnant rats were treated with a natural glucocorticoid (hydrocortisone) which is metabolized by the placenta, fetal development and adult blood pressure were normal. In conclusion, we found that high levels of maternal glucocorticoids impair renal development and lead to arterial hypertension in offspring. Even though renal mass eventually normalizes, glomerular damage as well as sodium retention occur and these factors may contribute to the development of hypertension.