The pathobiology of subclinical pyelonephritis--an experimental evaluation

Animal models in the pharmacokinetic/pharmacodynamic evaluation of antimicrobial agents

Animal infection models in the pharmacokinetic/pharmacodynamic (PK/PD) evaluation of antimicrobial therapy serve an important role in preclinical assessments of new antibiotics, dosing optimization for those that are clinically approved, and setting or confirming susceptibility breakpoints. The goal of animal model studies is to mimic the infectious diseases seen in humans to allow for robust PK/PD studies to find the optimal drug exposures that lead to therapeutic success. The PK/PD index and target drug exposures obtained in validated animal infection models are critical components in optimizing dosing regimen design in order to maximize efficacy while minimize the cost and duration of clinical trials. This review outlines the key components in animal infection models which have been used extensively in antibiotic discovery and development including PK/PD analyses.

Diagnosis of acute pyelonephritis by contrast-enhanced ultrasonography in kidney transplant patients

BACKGROUND

Diagnostic imaging of acute pyelonephritis (APN) in renal transplanted patients is an important clinical issue. While conventional ultrasonography (US) has a limited diagnostic role, contrast-enhanced computer tomography and magnetic resonance imaging (MRI) represent the gold standard diagnostic tests. However, nephrotoxicity of either iodinated or paramagnetic contrast medium limits their use, especially in patients with kidney disease. Contrast-enhanced US (CEUS) may detect poorly perfused parenchymal renal areas, a useful feature in the diagnosis of APN. The aim of this study was to evaluate the diagnostic value of CEUS in APN compared with MRI as the reference test.

METHODS

From a pool of 389 kidney transplant patients, we prospectively recruited 56 patients with clinical suspicion of APN of the transplanted kidney. They underwent both CEUS and MRI, performed in a blinded manner by two different operators. Sensitivity, specificity, accuracy, positive and negative predictive values, and K statistics were calculated.

RESULTS

Thirty-seven out of 56 patients (66.1%) resulted positive for APN with the reference test, gadolinium-enhanced MRI. Thirty-five out of these 37 patients showed positive results for APN with CEUS, and 19 patients showed negative results for APN with both MRI and CEUS: sensitivity 95% (CI 82-99), specificity 100% (CI 83-100), accuracy 96% (CI 88-99), positive predictive value 100% (CI 90-100), negative predictive value 90% (CI 71-97) and K statistics 0.92 (P<0.01).

CONCLUSIONS

Our results suggest, for the first time, the feasibility of CEUS, a low-cost and low-risk diagnostic procedure, in the diagnosis of APN in kidney transplant patients.

Imaging data suggesting acute pyelonephritis in the kidney graft: report of five cases with atypical clinical presentation

Acute pyelonephritis is a common complication of kidney transplantation, occurring in up to 1% of grafts. Diagnosis is mainly clinical and atypical presentations have seldom been reported. The diagnostic role of imaging techniques has not been defined. Five cases of acute graft pyelonephritis are reported (three kidney, two pancreas-kidney grafts). The patients (median age 48 years) comprised three females and two males. Median post-transplant follow-up was 3 months, with three patients having predisposing factors for diabetes and one for an enteric bladder. None of the patients presented the 'classic' diagnostic tetrad (i.e. fever, positive urine cultures, low urinary tract symptoms and serum creatinine increase); although, at diagnosis, two of five patients presented with fever, one had increased creatinine levels and one had positive urine cultures. Of note, three patients had leucocyte casts at urinary sediment analysis, thus raising clinical suspicion. Renal ultrasounds were negative in all patients. Renal (99m)Tc-MAG3 (mercaptoacetyltriglycine) scintigraphy, which was used for the definition of kidney function impairment (one patient) or because of the presence of urinary casts (three patients), or after the biopsy diagnosis to locate the parenchymal lesions (one patient), was positive in all patients. The presence and pyelonephritic origin of the parenchymal lesions was confirmed by nuclear magnetic resonance or computed tomography scans. Acute graft pyelonephritis may develop in the absence of a full-blown clinical picture. Smouldering symptoms may occur in the presence of large perfusion deficits. (99m)Tc-MAG3 scintigraphy could be an important diagnostic tool in such cases.

Oxygen-dependent and -independent mechanisms of renal injury in experimental ascending pyelonephritis

Pyelonephritis is the most common urinary tract infection affecting females of all age groups. Despite concerted efforts the mechanism of renal injury in pyelonephritis is not clearly understood. In the present study we have made an attempt to characterise the mediators of inflammatory insult in an experimental model of ascending pyelonephritis. Mice infected with Escherichia coli O6:K13:H1 were sacrificed at 2, 7 and 14 days post-infection. Luminol-dependent chemiluminescence response, NADPH oxidase, acid phosphatase, beta-glucuronidase and N-acetyl-beta-D-glucosaminidase activities were monitored in circulating as well as renal phagocytic cells in order to determine the role of reactive oxygen species and lysosomal enzymes in genesis of renal injury. We have demonstrated that reactive oxygen species are generated at the initiation of infection and the levels increase progressively during the course of infection. While intracellular release of lysosomal enzymes was seen in all groups, extracellular release was primarily observed at 7 and 14 days post-infection only. The results indicate that while reactive oxygen species play a significant role in tissue injury during all stages of infection, lysosomal enzyme release in extracellular milieu augments tissue destruction at later stages only.

Reactive oxygen species-mediated tissue injury in experimental ascending pyelonephritis

Pyelonephritis is the most common urinary tract infection in females, but the pathogenetic mechanisms are not well understood. Reactive oxygen species (ROS) have been implicated as cause of injury in several renal diseases. In this study, we have demonstrated the role of ROS in pathogenesis of pyelonephritis in Balb/c mice. A clear correlation between extent of ROS generation and subsequent lipid peroxidation and DNA damage in kidneys was observed during the course of infection, from 2 to 14 days. Activities of brush border membrane marker enzymes were also significantly altered. Administration of antioxidants, superoxide dismutase, catalase and dimethylsulfoxide significantly reversed the histopathological changes, reduced the extent of lipid peroxidation in renal brush border membrane, and also reversed the altered enzyme activities to near normal situation. These results clearly suggest that interaction of ROS with various cellular organelles in kidneys has a significant deleterious effect, and this could be the underlying mechanism for renal dysfunction in pyelonephritis.