Renal involvement in urinary tract infection

Hyponatremia may reflect severe inflammation in children with febrile urinary tract infection

BACKGROUND

Hyponatremia is the most common electrolyte abnormality in clinical practice, but little is known about the association between febrile urinary tract infection (UTI) and hyponatremia or its significance to clinical outcomes.

METHODS

Data from 140 children with febrile UTI between 2000 and 2010 were retrospectively analyzed. Laboratory examinations [white blood cell (WBC) count, erythrocyte sedimentation rate (ESR), C-reactive protein (CRP), and serum sodium concentration], renal ultrasonography, (99m)Technetium-dimercaptosuccinic acid (DMSA) scintigraphy, and voiding cystourethrogram were performed. Culture growing >50,000 colonies of one single bacterial species on a urine sample obtained by catheter or >100,000 colonies on two clean-catch samples was required to establish diagnosis of UTI.

RESULTS

In children with renal cortical defects diagnosed after DMSA scintigraphy (group 1), duration of fever was significantly longer (P = 0.038) and WBC (P = 0.047) and CRP (P < 0.0001) levels significantly higher than in those without renal cortical defects (group 2). However, serum sodium levels were significantly lower in group 1 than group 2 (135.9 ± 2.4 vs 137.4 ± 2.7 mEq/L, P = 0.007). Hyponatremia (serum sodium ≤ 135 mEq/L) was also more frequent in group 1 than in group 2 (74.1 % vs 45.3 %, P = 0.012). Serum sodium concentration was negatively correlated with WBC count (r = -0.156, P = 0.011) and CRP levels (r = -0.160, P= 0.028).

CONCLUSIONS

Our study indicates that hyponatremia may be a substantial inflammatory marker and is significantly and independently associated with the degree of inflammation in children with febrile UTI.

Roles of toll-like receptors in C-C chemokine production by renal tubular epithelial cells

Pyelonephritis, in which renal tubular epithelial cells are directly exposed to bacterial component, is a major predisposing cause of renal insufficiency. Although previous studies have suggested C-C chemokines are involved in the pathogenesis, the exact source and mechanisms of the chemokine secretion remain ambiguous. In this study, we evaluated the involvement of Toll-like receptors (TLRs) in C-C chemokine production by mouse primary renal tubular epithelial cells (MTECs). MTECs constitutively expressed mRNA for TLR1, 2, 3, 4, and 6, but not for TLR5 or 9. MTECs also expressed MD-2, CD14, myeloid differentiation factor 88, and Toll receptor-IL-1R domain-containing adapter protein/myeloid differentiation factor 88-adapter-like. Synthetic lipid A and lipoprotein induced monocyte chemoattractant protein 1 (MCP-1) and RANTES production in MTECs, which strictly depend on TLR4 and TLR2, respectively. In contrast, MTECs were refractory to CpG-oligodeoxynucleotide in chemokine production, consistently with the absence of TLR9. LPS-mediated MCP-1 and RANTES production in MTECs was abolished by NF-kappaB inhibition, but unaffected by extracellular signal-regulated kinase inhibition. In LPS-stimulated MTECs, inhibition of c-Jun N-terminal kinase and p38 mitogen-activated protein kinase significantly decreased RANTES, but did not affect MCP-1 mRNA induction. Thus, MTECs have a distinct expression pattern of TLR and secrete C-C chemokines in response to direct stimulation with a set of bacterial components.

FcRn-mediated transcytosis of immunoglobulin G in human renal proximal tubular epithelial cells

In the kidney, proteins filtered through glomeruli are reabsorbed by endocytosis along the proximal tubules to avoid renal loss of large amounts of proteins. Recently, neonatal Fc receptor (FcRn), which is involved in the transport of IgG across several epithelial and endothelial cells, was reported to be expressed in renal proximal tubular epithelial cells (RPTECs). However, there has been no direct evidence for receptor-mediated endocytosis of IgG in human RPTECs. To explore physiological roles of FcRn in the proximal tubules, we used the human RPTECs to examine IgG transport. FcRn was expressed in RPTECs and physically associated with beta(2)-microglobulin, preserving the capacity of specific pH-dependent IgG binding. Human IgG was bound to the cell surface of RPTECs in a pH-dependent manner. The human IgG transport assay revealed that receptor-mediated transepithelial transport of intact IgG in RPTECs is bidirectional and that it requires the formation of acidified intracellular compartments. With the use of double immunofluorescence, the internalized human IgG was marked in cytoplasm of RPTECs and colocalized with FcRn. These data define the mechanisms of FcRn-associated IgG transport in RPTEC monolayers. It was suggested that the intact pathway for human IgG transepithelial transport may avoid lysosomal degradation of IgG.

Fever in the clinical diagnosis of acute pyelonephritis

Acute pyelonephritis is a clinical syndrome that can be confused with other conditions. To investigate this problem, a retrospective cohort study was conducted using two mutually exclusive sets of clinical criteria for acute pyelonephritis in women 15 years of age or older who presented to the emergency department of a university hospital. All patients had pyuria, and one group had documented fever (temperature of > or = 37.8 degrees C) while the other group had a temperature of < 37.8 degrees C but had other evidence of possible upper tract infection. The study cohort was comprised of 103 febrile and 201 afebrile patients. Afebrile hospitalized patients were ultimately found to have another diagnosis more often than were the febrile hospitalized patients (35% v 7%; P = .02), and the afebrile nonhospitalized patients were more likely to have another diagnosis than were the febrile nonhospitalized patients (13% v 0%; P = .004). Other diagnoses included cholecystitis, pelvic inflammatory disease, and diverticulitis. The positive predictive value of the definition of pyelonephritis in the febrile group was 0.98, and it was 0.84 for the afebrile group. Physicians examining patients with clinical evidence of acute pyelonephritis but without objective fever should be alert for alternative diagnoses.

Antibodies to Tamm-Horsfall protein in patients with acute pyelonephritis

The role of antibodies to Tamm-Horsfall protein in the diagnosis of acute pyelonephritis was studied. Antibodies to Tamm-Horsfall protein were also determined in a group of normal subjects. Patients with acute pyelonephritis were divided into subgroups according to the concurrent presence of vesicoureteral reflux or nephrolithiasis. No statistically significant differences (p > 0.05) were observed for any class of antibodies (IgG, IgA and IgM) between the groups of healthy subjects and patients with acute pyelonephritis, regardless of the presence or absence of vesicoureteral reflux or nephrolithiasis. Values for different antibody classes showed that IgM antibodies were the most abundant in all the groups examined. A difference in the values of IgM relative to IgA and IgG antibodies was found to be statistically significant in the patient group only (p < 0.05). In patients with vesicoureteral reflux, there was no statistically significant difference (p > 0.05) between the values of IgM and of other antibody classes. In these patients, however, the highest values of all the three antibody classes were obtained, although these differences were also not statistically significant (p > 0.05). The results pointed to the need of further studies of the role of antibodies to Tamm-Horsfall protein in the diagnosis and pathogenesis of tubulointerstitial nephritis.

Cellular biology of glomerulosclerosis

The burgeoning literature on glomerulosclerosis makes frequent review of the literature necessary. At this stage, the key processes involved have surely been defined. It is now appropriate to make deductions about possible therapies and to plan experiments and trials.

Urinary tract infection. How has its management changed?

In patients with apparent urinary tract infection, clinical presentation and results of physical examination and a few simple laboratory studies can identify patients who need urine culture and/or imaging studies and can guide initial therapy. A wide variety of effective antibiotics are available for various causes, and local patterns of microbial sensitivity and cost-effectiveness help govern drug selection. Response to therapy governs further treatment and follow-up. Exclusion of complicated infection and particular risk factors permits simplified but effective management of symptomatic recurrent infections.

Normokalaemic pseudohypoaldosteronism is present in children with acute pyelonephritis

The present study demonstrates that renal tubular unresponsiveness to aldosterone, without associated hyperkalaemia, is present in children with acute pyelonephritis. We studied 32 children with a diagnosis of acute pyelonephritis established by high fever, flank pain/tenderness, increased blood levels of C-reactive protein and significant Escherichia coli growth in the urine culture. Renal tubular function tests and determinations of plasma renin activity and aldosterone concentration were performed at diagnosis (study 1), after three days of iv gentamycin (study 2) and after 21 days of antibiotic therapy (study 3). Findings were compared to those present in 32 normal children of similar age. Despite normal plasma potassium concentration, fractional potassium excretion and transtubular potassium concentration gradient were significantly decreased in studies 1 and 2, becoming normal in study 3. Decreased renal potassium excretion coexisted with increased values for plasma renin activity and aldosterone concentration. In study 3 these hormones remained elevated only in patients with scarred kidneys. The functional alteration present in acute pyelonephritis may be directly caused by the interstitial inflammation or be mediated by some E. coli endotoxin.