Streptococcal infection as possible trigger for dense deposit disease (C3 glomerulopathy)

Dense deposit disease (DDD, formerly known as membranoproliferative glomerulonephritis (MPGN) type II) is a subtype of C3 glomerulopathy (C3G). Electron-dense deposits in the glomerular basement membrane characterize this glomerulonephritis. DDD typically presents with a nephritic syndrome that progresses to end-stage renal failure in 50 % of patients despite treatment. The pathogenic basis of DDD is uncontrolled activation of the alternative complement cascade although the potential triggering events that precipitate the development of complement dysregulation are typically unknown. There are isolated reports of an apparent association between streptococcal infection and DDD, as well as with MPGN types I and III. However, this association has not been deemed compelling, perhaps because so few cases have been reported or because of a current lack of evidence for a plausible hypothesis to connect a streptococcal infection with subsequent disease. In this report, we describe two patients with DDD who definitely had an antecedent streptococcal infection with the phenotype of acute post-streptococcal glomerulonephritis and whose initial kidney biopsy findings on light microscopy were indistinguishable from acute post-streptococcal glomerulonephritis. These patients had additional points of interest: recurrence of gross hematuria with recurrent streptococcal infections, slowly progressive course, persistently low serum C3 concentration, positive C3 nephritic factor, and positive risk alleles in the complement factor H (CFH) gene. Conclusion: We suggest that streptococcal infection may trigger DDD in individuals genetically predisposed by virtue of a disorder in complement regulation.     

Left atrial volume determination by echocardiography

To validate echocardiographic left atrial volume measurements, 25 patients with mitral stenosis were studied before and after mitral balloon valvuloplasty. Seven normals served as controls. The modified Simpson's rule was used for echocardiographic and angiographic left atrial volume determination from two orthogonal planes. Left atrial antero-posterior diameter was measured from parasternal long axis view and supero-inferior and medio-lateral diameters from apical four-chamber view. Transthoracic echocardiographic left atrial volume correlated well, but systematically underestimated angiographic left atrial volume (y=0.4x+27, r=0.92). Monoplane transesophageal echocardiography did not improve correlation, nor the underestimation. Out of the several left atrial diameters, antero-posterior dimension showed the closest correlation with angiographic volume (r=0.91), which persisted after exclusion of patients with atria >400 ml (r=0.84). Futhermore, relative changes of antero-posterior diameter after mitral valvuloplasty were closely related to the relative changes observed in left atrial volume (r=0.82). Our results suggest that, in spite of a consistent underestimation, bidimensional, transthoracic echocardiographic and angiographic left atrial assessment correlate closely. Moreover, it is suggested that the mere antero-posterior diameter from transthoracic two-dimensional image is sufficient in clinical practice for routine follow-op of left atrial volume.     

Use of adenovirus protein IX (pIX) to display large polypeptides on the virion--generation of fluorescent virus through the incorporation of pIX-GFP.

The adenovirus (Ad) protein IX (pIX) is a minor component of the Ad capsid and associates with the hexons that make up the facets of the icosahedron. In this study, we investigated whether a large protein tag could be fused to pIX without compromising the Ad vector itself. As proof-of-principle, we generated a pIX-green fluorescent protein (GFP) fusion protein. We show that a virus encoding the pIX-GFP can be generated and that pIX-GFP fusion protein was incorporated into the Ad capsid as efficiently as native pIX. In tissue culture, translocation of Ad/pIX-GFP from the outside of the cell to the nucleus could be followed using fluorescence microscopy, and the timing of migration to the nucleus was similar to that previously reported for Ad. We also could track the virus after injection into the tibialis anterior muscle of mice. Shortly after injection, the majority of the Ad/pIX-GFP accumulated in pockets adjacent to the muscle fibers, with some migration of the virus between fibers. Our ability to attach GFP to the Ad virion, through fusion to pIX, provides a valuable tool for virus tracking in vitro and in vivo. Moreover, our data indicate that pIX can be used as a platform to anchor proteins to the Ad capsid, such as large ligands for cell-type-specific targeting of the vector.     

Delayed presentation of thoracic esophageal perforation after blunt trauma

Thoracic esophageal perforation after blunt trauma is a rare injury with high mortality. Prompt recognition and aggressive treatment are paramount to survival. We report a case of delayed presentation that emphasizes the diagnostic difficulties in this traumatic injury. A review of the prevalence, diagnosis, and management is also discussed.     

Reemergence of macrolide resistance in pharyngeal isolates of group a streptococci in southwestern Pennsylvania

We previously reported on the emergence of macrolide-resistant pharyngeal isolates of group A streptococci (GAS) in our community. The purpose of the present study was to track longitudinal trends in macrolide resistance in these isolates in southwestern Pennsylvania. Testing for susceptibility to erythromycin and clindamycin was performed for all pharyngeal GAS isolates recovered at the Children's Hospital of Pittsburgh and a local pediatric practice between September 2001 and May 2002. Macrolide resistance phenotypes and genotypes were determined by double-disk diffusion and PCR, respectively. Strain relatedness was determined by field inversion gel electrophoresis and emm gene sequence typing. A total of 708 isolates of GAS were recovered during the study period; 68 (9.6%) were macrolide resistant, while all isolates were sensitive to clindamycin. The monthly prevalence of macrolide resistance ranged from 0 to 41%. Only 21 of 573 (3.7%) strains recovered from September 2001 through March 2002 were macrolide resistant. A sudden increase in the rate of macrolide resistance (47 of 135 isolates [35%]) was seen in April and May 2002. Sixty-two isolates demonstrated the M phenotype (resistance to macrolide antibiotics), and six isolates demonstrated the MLS(B) phenotype (resistance to most macrolide, lincosamide, and streptogramin B antibiotics); these isolates were confirmed to be mef(A) and erm(A), respectively. Three unique mef(A) clones and four unique erm(A) clones were identified among the resistant isolates. The MIC at which 50% of isolates are inhibited (MIC(50)) for the mef(A) strains was 16 micro g/ml, while the MIC(50) for erm(A) strains was 8 micro g/ml. The finding of high levels of macrolide resistance among pharyngeal isolates of GAS for a second successive year in our community raises the concern that this problem may be more common in the United States than was previously appreciated. Longitudinal surveillance of isolates from multiple centers is needed to define the prevalence of antimicrobial agent-resistant GAS in the United States.     

Prostaglandins mediate the vasodilatory effect of mannitol in the hypoperfused rat kidney.

We have previously reported that mannitol strikingly increases blood flow to rat kidneys hypoperfused at 35-40mm Hg. This vasodilator effect is not due to volume expansion or alterations in plasma osmolality. We have tested the hypothesis that the vasodilatory effect of mannitol in the ischemic rat kidney is mediated by one of the vasoactive renal hormone systems: renin-angiotension, kallikrein-kinin, or prostaglandins. Rats were infused with 5% mannitol in 0.9% saline to 3-5% of body weight. In agreement with our previous studies, RBF increased 1.3 +/- 0.1 ml/min despite maintenance of perfusion pressure at 35-40 mm Hg. The cyclooxygenase inhibitors, meclofenamate and indomethacin had no effect on renal blood flow (RBF) in hypoperfused kidneys. However, in rats pretreated with these inhibitors, expansion with mannitol increased RBF by only 0.37 +/- 0.02 ml/min, 28% of the response in the untreated group (p less than 0.001). Infusion of prostacyclin (PGI2) into the renal artery during reduced perfusion resulted in an increase in RBF of 1.0 +/- 0.1 ml/min. Subsequent expansion with mannitol increased RBF by only 0.5 +/- 0.1 ml/min more, less than one-half of the effect of mannitol in a concurrent group of rats not treated with PGI2. Unlike PGI2 prostaglandin E2 had only a minimal vasodilator effect during hyperperfusion. Imidazole, an inhibitor of thromboxane synthesis, did not alter RBF or renal vascular resistance during hypoperfusion. Treatment of rats during hypoperfusion. with the angiotensin-converting enzyme (kininase II) inhibitor teprotide increased RBF by 1.1 +/- 0.3 ml/min. However, teprotide did not alter the vascular response to mannitol: RBF increased 1.2 +/- 0.1 ml/min more when mannitol was infused into teprotide-treated rats. The renal vascular response to mannitol was not altered by treatment with aprotinin, an inhibitor of the kallikrein-kinin system. Aprotinin was ineffective whether given before or after the vascular response to mannitol was established. We conclude that the vasodilator response to mannitol in the ischemic rat kidney is mediated in large part by increased prostaglandin (PGI2) activity. The failure of converting enzyme inhibition and aprotinin to block the vasodilator response to mannitol is evidence against a role for the renin-angiotension or kallikreinkinin systems in mediating the vasodilator response.     

Myc confers androgen-independent prostate cancer cell growth

Prostate cancer is one of the most diagnosed and mortal cancers in western countries. A major clinical problem is the development of androgen-independent prostate cancer (AIPC) during antihormonal treatment. The molecular mechanisms underlying the change from androgen dependence to independence of these tumors are poorly understood and represent a challenge to develop new therapies. Based on genetic data showing amplification of the c-myc gene in AIPC, we studied the ability of c-myc to confer AIPC cell growth. Human androgen-dependent prostate cancer cells overexpressing c-myc grew independently of androgens and presented tumorigenic properties in androgen-depleted conditions. Analysis of signalling pathways by pharmacological inhibitors of the androgen receptor (AR) or by RNA interference directed against AR or c-myc showed that c-myc acted downstream of AR through multiple growth effectors. Thus c-myc is required for androgen-dependent growth and following ectopic expression can induce androgen-independent growth. Moreover, RNA interference directed against c-myc showed that growth of human AIPC cells, AR-positive or -negative, required c-myc expression. Furthermore, we showed that c-myc-overexpressing cells retain a functional p53 pathway and thus respond to etoposide.