Modeling Suggests a Mechanism of Synergy Between Hepatitis C Virus Entry Inhibitors and Drugs of Other Classes

Hepatitis C virus (HCV) entry inhibitors (EIs) act synergistically with drugs targeting other stages of the HCV lifecycle. The origin of this synergy remains unknown. Here, we argue that the synergy may arise from the complementary activities of the drugs across cell subpopulations expressing different levels of HCV entry receptors. We employ mathematical modeling of viral kinetics in vitro, where cells with a distribution of entry receptor expression levels are exposed to HCV with or without drugs. The drugs act independently in each cell, as expected in the absence of underlying interactions. Yet, at the cell population level our model predicts that the drugs exhibit synergy. EIs effectively block infection of cells with low receptor levels. With high receptor levels, where EIs are compromised, other drugs are potent. This novel mechanism of synergy, arising at the cell population level may facilitate interpretation of drug activity and treatment optimization.

Rescue of renal function in a 3-year-old girl with Goodpasture's syndrome with a brief review of literature

Goodpasture's syndrome has been documented in only a handful of children under the age of four. We describe a 3-year-old girl presenting with anaemia and renal failure whose kidney biopsy showed anti-glomerular basement membrane (GBM) disease. She was treated aggressively with pulse steroids, plasmapheresis and monthly infusions of cyclophosphamide. After months of aggressive immunosuppression, her renal function normalized, and her anti-GBM antibody disappeared. A year after the onset, she underwent a second kidney biopsy for persistent proteinuria and hypertension that surprisingly showed focal sclerosing glomerulonephritis, an unreported finding at this age. The biopsy showed deposition of antibody on the GBM despite the fact that anti-GBM antibody had normalized in the serum 5 months earlier. Mycophenolate mofetil was added to the immunosuppression at that point. At her 3-year follow-up, creatinine clearance was 88.4 mL/min/1.73 m(2), proteinuria was 408 mg/day and blood pressure was controlled with enalapril 0.2 mg/kg/day. She has not had a relapse or abnormal anti-GBM antibody for 30 months, but her renal prognosis remains guarded. To our knowledge, this is the youngest patient to have a successful rescue of renal function after isolated Goodpasture's syndrome.

Non-steroidal anti-inflammatory drugs-associated acute interstitial nephritis with granular tubular basement membrane deposits

Acute tubulo-interstitial nephritis (ATIN) is an important cause of acute renal failure resulting from a variety of insults, including immune complex-mediated tubulo-interstitial injury, but drugs such as non-steroidal anti-inflammatory drugs (NSAIDs) are a far more frequent cause. Overall, as an entity, ATIN remains under-diagnosed, as symptoms resolve spontaneously if the medication is stopped. We report on a 14-year-old boy who developed acute renal failure 2 weeks after aortic valve surgery. He was put on aspirin following surgery and took ibuprofen for fever for nearly a week prior to presentation. He then presented to the emergency department feeling quite ill and was found to have a blood urea nitrogen (BUN) concentration of of 147 mg/dl, creatinine of 15.3 mg/dl and serum potassium of 8.7 mEq/l. Dialysis was immediately initiated. A kidney biopsy showed inflammatory infiltrate consistent with ATIN. However, in the tubular basement membrane (TBM), very intense granular deposits of polyclonal IgG and C3 were noted. He needed dialysis for 2 weeks and was treated successfully with steroids for 6 months. His renal recovery and disappearance of proteinuria took a year. In conclusion, this is a first report of NSAIDs-associated ATIN, showing deposits of granular immune complex present only in the TBM and not in the glomeruli.

The metabolism, pharmacokinetics and mechanisms of antiviral activity of ribavirin against hepatitis C virus

Ribavirin, a broad spectrum antiviral agent, in conjunction with interferon forms the current standard of treatment for hepatitis C virus (HCV) infection in humans. While ribavirin alone fails to induce a significant antiviral response, in combination with interferon, ribavirin dramatically improves the long-term outcome of therapy. The predominant mechanism(s) of ribavirin action against HCV, are yet to be established. In this review, we examine the current status of our understanding of the metabolism, pharmacokinetics and mechanisms of the antiviral activity of ribavirin against HCV, all of which are central to the rational identification of improved treatment protocols.

Effects of angiotensin II on NaPi-IIa co-transporter expression and activity in rat renal cortex

The kidney plays a major role in reabsorption of phosphate with the majority occurring in the proximal tubule (PT). The type IIa sodium-phosphate co-transporter (NaPi-IIa) is the main player in PT. The purpose of current study was to determine the effect of angiotensin II (A-II) on membrane expression of NaPi-IIa in the rat renal cortex. A-II (500 ng/kg/min) was chronically infused into the Sprague-Dawley rats by miniosmotic pump for 7 days. The arterial pressure and circulating plasma A-II level along with urine output were markedly increased in A-II rats. There was diuresis but no natriuresis. The phosphate excretion increased sevenfold on day 4 and 5.7-fold on day 7. There was no change in Na-dependent Pi uptake in brush-border membrane (BBM) vesicles between A-II-treated group and control on day 4, however, there was a 43% increase on day 7. Western blot analysis of NaPi-IIa protein abundance showed a parallel pattern: no change after 4 days of treatment and a 48% increase after 7 days of treatment. However, Northern blot analysis of cortical RNA showed no change in NaPi-IIa mRNA abundance on day 7. A-II stimulation of Na/Pi co-transport activity is a result of increases in the expression of BBM NaPi-IIa protein level and that stimulation is most likely mediated by posttranscriptional mechanisms.

Kimura disease with advanced renal damage with anti-tubular basement membrane antibody

Kimura disease (KD) is an autoimmune eosinophilic granulomatous disorder with generalized lymphadenopathy. A handful of pediatric patients with renal disease have been described, none of whom have been African-American (AA). We present an AA boy with KD and nephrotic syndrome (NS). Two months after stopping steroids, fever, asthma, eczema, and proteinuria recurred. His NS did not relapse but his platelet count decreased to 51,000/microl (x10(6)/l). On restarting prednisone, his platelet count normalized. A kidney biopsy revealed 23 of 37 glomeruli obsolescent and advanced damage with over 50% of cortical tissue replaced by interstitial fibrosis and chronic inflammation. Glomerular immunofluorescence was largely negative; very intense linear anti-tubular basement membrane (TBM) deposits of IgA, IgG, C3, and C4 were noted. At present, 36 months from onset, serum creatinine is 1.2 mg/dl (106 micromol/l). We present a 4-year-old AA boy with KD, NS, relapsing thrombocytopenia, and renal damage with anti-TBM antibody.

Managing Henoch-Schonlein purpura in children with fish oil and ACE inhibitor therapy

BACKGROUND

Henoch-Schonlein purpura (HSP) is a vasculitic syndrome with palpable purpura and renal involvement. The treatment for HSP with persistent renal disease remains controversial. The kidney biopsy in HSP shows IgA deposits and fish-oil therapy has proven to be promising in halting the progression of IgA nephropathy.

METHODS

Five children with biopsy-proven HSP with repeated episodes of haematuria and proteinuria were treated with fish oil (1 g orally twice daily). In three of the five patients an angiotensin-converting enzyme inhibitor (ACEI) was added for hypertension.

RESULTS

The mean duration of follow up after starting fish-oil therapy was 49.2 weeks. The protein excretion rate prior to starting fish oil was 1041 mg/day and on the last follow-up visit the rate had decreased to 104 mg/day (P <0.05). The average blood pressure (BP) prior to therapy was 135/82. On the last follow-up visit the average BP off ACEI had decreased to 100/54 (P <0.05). After a year of follow up serum creatinine and glomerular filtration rates have remained stable at 51.2 micromol/L and 128 mL/min/1.73 m2, respectively.

CONCLUSION

This is the first report of abatement of HSP with fish oil and ACEI in children. There is a need for randomized prospective trials to confirm this observation.

Hyponatremic hypertensive syndrome (HHS) in an 18-month old-child presenting as malignant hypertension: a case report

Background

The combination of hyponatremia and renovascular hypertension is called hyponatremic hypertensive syndrome (HHS). Malignant hypertension as a presentation has been reported in adults with HHS but is rare in children.

Case presentation

An eighteen month-old male presented with drowsiness, sudden onset status epilepticus and blood pressure of 210/160. The electrolytes on admission revealed sodium of 120 mEq/L and potassium of 2.1 mEq/L. The peripheral renin activity (PRA) was 172 ng/ml/min (normal 3–11 ng/ml/min) and serum aldosterone level was 91 ng/dl (normal 4 to 16 ng/dl). Patient underwent angioplasty with no success, followed by surgical correction. Two years since the diagnosis, the blood pressure is controlled with labetolol and amlodipine (at less than sixth of the pre-operative dosages). The PRA is 2.4 ng/ml/min and aldosterone 15.5 ng/dl. The child not only had three renal arteries on left but all of them were stenosed which to best of our knowledge has not been described.

Conclusion

As uncommon as HHS with malignant hypertension may be in adults it is under-reported in children and purpose of the case report is to raise its awareness.

Transient hypothyroidism in a breastfed infant after maternal use of iodoform gauze

We describe transient hypothyroidism induced in a 2 week-old breastfed infant by maternal use of iodoform gauze for a perirectal abscess. The initial newborn thyroid screen was normal. Low levels of thyroid hormone were discovered during a routine second newborn screen. Thyroid function has since normalized with short-term therapy with thyroxine and after the mother discontinued use of the packing iodoform gauze. This case illustrates the need to avoid iodine-containing products in breastfeeding mothers.

Kinetics of crystallization in hard-sphere colloidal suspensions

We propose a kinetic model for describing crystal nucleation kinetics in hard-sphere colloidal suspensions. The model captures the interplay between the enhanced thermodynamic driving force and the reduced particle diffusivity in determining crystal nucleation rates as the particle density is increased in hard-sphere suspensions. Model calculations of nucleation rates and crystal growth velocities agree quantitatively with experimental observations. The dependence of the critical cluster size on volume fraction that emerges differs qualitatively from predictions of classical theories allowing for an experimental validation of the mechanism of crystal nucleation in colloidal suspensions.

Crystal Nucleation Rates for Particles Experiencing Short-Range Attractions: Applications to Proteins

A kinetic model for the nucleation of a crystalline phase consisting of particles experiencing short-range attractions is developed. Of particular significance is the proximity of the metastable fluid/fluid phase boundary. The model incorporates self-consistent thermodynamics, changes in gradient diffusivity, and density fluctuations in the vicinity of the critical point. Density fluctuations associated with the spinodal of this metastable phase transition greatly enhance nucleation rates, suggesting that experimental conditions may be found where rapid nucleation and slow crystal growth can be achieved by moving the metastable critical point relative to the solubility boundary. Copyright 2000 Academic Press.