ANP is cleared much faster than BNP in patients with congestive heart failure

Objective To obtain a better understanding of the pharmacokinetics of atrial and brain natriuretic peptides (ANP and BNP, respectively), two peptide mediators used in the treatment of congestive heart failure (CHF). Although both peptides exert their effects by binding to a common receptor (natriuretic peptide receptor A) with about the same affinity, their respective loading and maintenance doses differ. Methods Sixteen CHF patients were randomized to be infused for 2 h with α-human ANP (0.05 μg/kg per minute) or BNP (0.01 μg/kg per minute). Plasma concentrations of both peptides were measured 0, 2, 5, 15, 30, 60 and 120 min post-infusion. The pharmacokinetic parameters were then calculated using a 1-compartment model. Results The plasma BNP concentrations in the ANP and BNP groups before infusion were 464.7 ± 339.8 and 506.8 ± 332.5 pg/ml, respectively. Following infusion, ANP disappeared from the circulation more rapidly than BNP: their plasma half-lives were 2.4 ± 0.7 and 12.1 ± 3.0 min, and their total body clearance volumes were 48.2 ± 24.1 and 10.1 ± 2.7 ml/min per kilogram, respectively. Conclusion ANP has a shorter half-life in the plasma of CHF patients than BNP, which suggests that it controls hemodynamics more readily than BNP.     

Clozapine: more than 900 mg/day may be needed

Patients may fail to respond to clozapine treatment despite use of the maximum licensed UK dosage (900 mg/day) because of ultra-rapid metabolism of the drug. We present the findings of a study of a national clozapine/norclozapine assay service for the period 1997-2005 and three individual case studies of patients treated with clozapine in doses greater than 900 mg/day. Clinicians should be alert to the possibility of treatment failure because of rapid clozapine clearance secondary to genetic factors and heavy cigarette consumption. This may necessitate the use of clozapine in doses up to 1400 mg/day, notably in young male smokers. Doses of greater than 900 mg/day are rarely justified in women. Anyone given relatively high-dose clozapine (600 mg/day or more) should be monitored regularly for adverse events and changes in smoking habit.     

RNA interference may be more potent than antisense RNA in human cancer cell lines

1. RNA interference (RNAi) is a newly discovered cellular pathway for the silencing of sequence-specific genes at the mRNA level by the introduction of the cognate double-stranded (ds) RNA. Because antisense (AS) mechanisms have similar effects, we compared these two effects in human cancer cell lines, considering a possible application of RNAi for cancer therapy. 2. We tested RNAi effects by transfecting human hepatoma and pancreatic cancer cell lines with AS and sense (S) RNA expression plasmids corresponding to the exogenous luciferase gene or the endogenous c-raf gene in the form of complexes with a cationic lipopolyamine or a tumour-targeting peptide vector we developed. In addition, we compared the effects of small interfering RNA and AS oligoDNA complexed with the peptide vector. 3. From the viewpoint of AS actions, the effect of the AS RNA may be cancelled by the S RNA, although, interestingly, we found that the combination of the AS and S RNA expression plasmids was more effective than the AS RNA expression plasmids alone in reducing target gene expression, whereas the S RNA expression plasmids had no effects. The combination of the luciferase AS and S RNA had no effects on the expression of either the beta-galactosidase gene or the c-raf gene. In the presence of 2-aminopurine (an inhibitor of dsRNA-activated protein kinase), the inhibitory effect of the combination of AS and S RNA on gene expression did not change in the case of the endogenous c-raf gene, but was reduced in the case of the exogenous luciferase gene. The effect of 22 nucleotide RNA duplexes corresponding to the luciferase gene was by one order stronger than that of the phosphorothioate AS DNA. 4. Thus, it is suggested that RNAi may be more potent than AS RNA in reducing target gene expression in human cancer cell lines, regardless of the length of dsRNA. With further studies on the RNAi phenomenon in cancer cells, RNAi could provide a novel approach for cancer gene therapy.     

Neutrophil activation during acetaminophen hepatotoxicity and repair in mice and humans

Following acetaminophen (APAP) overdose there is an inflammatory response triggered by the release of cellular contents from necrotic hepatocytes into the systemic circulation which initiates the recruitment of neutrophils into the liver. It has been demonstrated that neutrophils do not contribute to APAP-induced liver injury, but their role and the role of NADPH oxidase in injury resolution are controversial. C57BL/6 mice were subjected to APAP overdose and neutrophil activation status was determined during liver injury and liver regeneration. Additionally, human APAP overdose patients (ALT: > 800 U/L) had serial blood draws during the injury and recovery phases for the determination of neutrophil activation. Neutrophils in the peripheral blood of mice showed an increasing activation status (CD11b expression and ROS priming) during and after the peak of injury but returned to baseline levels prior to complete injury resolution. Hepatic sequestered neutrophils showed an increased and sustained CD11b expression, but no ROS priming was observed. Confirming that NADPH oxidase is not critical to injury resolution, gp91^phox−/− mice following APAP overdose displayed no alteration in injury resolution. Peripheral blood from APAP overdose patients also showed increased neutrophil activation status after the peak of liver injury and remained elevated until discharge from the hospital. In mice and humans, markers of activation, like ROS priming, were increased and sustained well after active liver injury had subsided. The similar findings between surviving patients and mice indicate that neutrophil activation may be a critical event for host defense or injury resolution following APAP overdose, but not a contributing factor to APAP-induced injury.