Use of tissue plasminogen activator for thrombolysis in occluded peritoneal dialysis catheters in children.

Peritoneal dialysis is often the renal replacement therapy of choice in pediatric patients, but the smaller catheters are at high risk for occlusion by fibrin clots. Tissue-type plasminogen activator (t-PA) is a recombinant protease specific for fibrin, and has been shown to be an effective thrombolytic for central venous catheters. The present study aimed to demonstrate the effectiveness of t-PA for thrombolysis in occluded peritoneal catheters. Six patients between 3 weeks and 15 years of age presented with 7 episodes of occluded peritoneal catheters. In all cases, t-PA (2 mg in 40 mL normal saline) was instilled into the catheter. Patency was assessed after 60 minutes by rapid instillation and drainage of 10 mL dialysis solution per kilogram patient body weight. Thrombolysis was effective in 4 of 7 attempts. In 2 cases, occlusion occurred in the setting of acute peritonitis. In 2 cases, catheters required surgical replacement. One child developed a leak at the catheter exit site within 24 hours after treatment. No intraperitoneal bleeding was observed, and no changes were observed in systemic coagulation indices [prothrombin time (PT), activated partial thromboplastin time (aPTT), fibrinogen degradation products (FDP), and fibrinogen] assessed pre- and post-thrombolysis. In cases of occluded PD catheters, t-PA appears to be an effective and safe treatment.

Ehrlichia ewingii, a newly recognized agent of human ehrlichiosis.

BACKGROUND: Human ehrlichiosis is a recently recognized tick-borne infection. Four species infect humans: Ehrlichia chaffeensis, E. sennetsu, E. canis, and the agent of human granulocytic ehrlichiosis. METHODS: We tested peripheral-blood leukocytes from 413 patients with possible ehrlichiosis by broad-range and species-specific polymerase-chain-reaction (PCR) assays for ehrlichia. The species present were identified by species-specific PCR assays and nucleotide sequencing of the gene encoding ehrlichia 16S ribosomal RNA. Western blot analysis was used to study serologic responses. RESULTS: In four patients, ehrlichia DNA was detected in leukocytes by a broad-range PCR assay, but not by assays specific for E. chaffeensis or the agent of human granulocytic ehrlichiosis. The nucleotide sequences of these PCR products matched that of E. ewingii, an agent previously reported as a cause of granulocytic ehrlichiosis in dogs. These four patients, all from Missouri, presented between May and August 1996, 1997, or 1998 with fever, headache, and thrombocytopenia, with or without leukopenia. All had been exposed to ticks, and three were receiving immunosuppressive therapy. Serum samples obtained from three of these patients during convalescence contained antibodies that reacted with E. chaffeensis and E. canis antigens in a pattern different from that of humans with E. chaffeensis infection but similar to that of a dog experimentally infected with E. ewingii. Morulae were identified in neutrophils from two patients. All four patients were successfully treated with doxycycline. CONCLUSIONS: These findings provide evidence of E. ewingii infection in humans. The associated disease may be clinically indistinguishable from infection caused by E. chaffeensis or the agent of human granulocytic ehrlichiosis.

Increased plasma leptin concentration in end-stage renal disease.

Leptin is a 16-kDa protein recently identified as the obese gene product involved in body weight regulation. Administration of recombinant leptin to ob/ob mice, which have a genetic defect in leptin production, reduces food intake and increases energy expenditure. Leptin is synthesized by fat cells, and in normal humans, plasma concentrations are proportional to adiposity. The physiological actions and the degradation pathways of leptin in humans are unknown. We investigated renal elimination of leptin by comparing plasma leptin concentrations in end-stage renal disease (ESRD) patients with normal controls. Our hypothesis was that if renal filtration is a significant route of elimination, the hormone would accumulate in ESRD patients. Mean plasma levels in 141 ESRD patients (26.8 +/- 5.7 and 38.3 +/- 5.6 micrograms/L for males and females, respectively) were significantly higher (P < 0.001) than mean values obtained in normal controls (11.9 +/- 3.1 and 21.2 +/- 3.0 micrograms/L for males and females, respectively). Leptin concentrations in ESRD patients correlated directly with body mass index (BMI; r = 0.77 for men and 0.78 for women). The rate of increase in leptin concentrations with BMI was significantly greater in ESRD patients (5.5 and 6.6 micrograms/L/U BMI for men and women, respectively) than in normal controls (1.4 and 2.6 micrograms/L/U for men and women, respectively). Pre- and postdialysis leptin levels in hemodialysis patients were similar. Western blot of plasma from ESRD patients with high leptin levels showed bands corresponding to the intact protein (16 kDa) with no lesser or greater molecular mass species observed. Leptin concentrations in patients with ESRD did not correlate with measures of residual renal function (serum creatinine, beta 2-microglobulin, PTH, or GH levels). Similarly, we found no correlation between leptin levels and the number of years patients had been on dialysis or with recent weight changes. We conclude that intact leptin is increased in ESRD patients, but does not appear to cause decreased weight. As leptin levels did not correlate with residual renal function, increased production may account for the high levels observed.

Magnesium transport in Salmonella typhimurium: genetic characterization and cloning of three magnesium transport loci.

Salmonella typhimurium strains lacking the CorA Mg2+ transport system retain Mg2+ transport and the ability to grow in medium containing a low concentration of Mg2+. Mutagenesis of a corA strain followed by ampicillin selection allowed isolation of a strain that required Mg2+-supplemented media for growth. This strain contained mutations in at least two loci in addition to corA, designated mgtA and mgtB (for magnesium transport). Strains with mutations at all three loci (corA, mgtA, and mgtB) exhibited no detectable Mg2+ uptake and required 10 mM Mg2+ in the medium for growth at the wild-type rate. A wild-type allele at any one of the three loci was sufficient to restore both Mg2+ transport and growth on 50 microM Mg2+. P22 transduction was used to map the mgt loci. The mgtA mutation was located to approximately 98 map units (cotransducible with pyrB), and mgtB mapped at about 80.5 map units (near gltC). A chromosomal library from S. typhimurium was screened for clones that complemented the Mg2+ requirement of a corA mgtA mgtB mutant. The three classes of plasmids obtained could each independently restore Mg2+ transport to this strain and corresponded to the corA, mgtA, and mgtB loci. Whereas the corA locus of S. typhimurium is analogous to the corA locus previously described for Escherichia coli, neither of the mgt loci described in this report appears analogous to the single mgt locus described in E. coli. Our data in this and the accompanying papers (M. D. Snavely, J. B. Florer, C. G. Miller, and M. E. Maguire, J. Bacteriol. 171:4752-4760, 4761-4766, 1989) indicate that the corA, mgtA, and mgtB loci of S. typhimurium represent three distinct systems that transport Mg2+.

Magnesium transport in Salmonella typhimurium: characterization of magnesium influx and cloning of a transport gene.

The influx of Mg2+ in Salmonella typhimurium LT-2 was studied by both kinetic and genetic techniques. Wild-type cells grown in a high MgSO4 concentration (10 mM) exhibited a Km of 15 microM for Mg2+ influx, with a Vmax of 0.25 nmol of Mg2+ per min per 10(8) cells. The apparent Km decreased to 3 microM, and the Vmax increased 60% after growth in a low MgSO4 concentration (10 microM). Co2+ was a simple competitive inhibitor (Ki = 30 microM) of Mg2+ influx in cells grown in high Mg2+ concentrations but blocked only a portion of the Mg2+ influx in cells grown in low Mg2+ concentrations. Co2+ influx exhibited kinetics similar to those of Mg2+ influx (Km = 30 microM; Vmax = 0.5 nmol of Co2+ per min per 10(8) cells) but was not affected by growth conditions. Co2+ influx was competitively inhibited by both Mg2+ and Mn2+. Mutations affecting Mg2+ uptake were isolated by selection for spontaneous resistance to toxic levels of Co2+. One class of mutants designated corA mapped at 84 min near metE with the following gene order: corA, metE, zie-3161::Tn10, pepQ. A second class designated corB mapped at 98 min near pyrB. Mg2+ influx was decreased in a corA mutant strain (relative to that of the wild type) when grown in high Mg2+ concentrations but was restored when grown in low Mg2+ concentrations. Co2+ transport was completely abolished by the corA mutation under all growth conditions. Recombinant plasmids carrying the corA region from either Escherichia coli K-12 or S. typhimurium complemented the corA mutation in S. typhimurium, restoring uptake of both Co2+ and Mg2+ and conferring sensitivity to Co2+. The S. typhimurium corA gene was localized to a restriction fragment of approximately 1.5 kilobases.