A search for synthetic peptides that inhibit soluble N-ethylmaleimide sensitive-factor attachment receptor-mediated membrane fusion.

Soluble N-ethylmaleimide sensitive-factor attachment receptor (SNARE) proteins have crucial roles in driving exocytic membrane fusion. Molecular recognition between vesicle-associated (v)-SNARE and target membrane (t)-SNARE leads to the formation of a four-helix bundle, which facilitates the merging of two apposing membranes. Synthetic peptides patterned after the SNARE motifs are predicted to block SNARE complex formation by competing with the parental SNAREs, inhibiting neuronal exocytosis. As an initial attempt to identify the peptide sequences that block SNARE assembly and membrane fusion, we created thirteen 17-residue synthetic peptides derived from the SNARE motifs of v- and t-SNAREs. The effects of these peptides on SNARE-mediated membrane fusion were investigated using an in vitro lipid-mixing assay, in vivo neurotransmitter release and SNARE complex formation assays in PC12 cells. Peptides derived from the N-terminal region of SNARE motifs had significant inhibitory effects on neuroexocytosis, whereas middle- and C-terminal-mimicking peptides did not exhibit much inhibitory function. N-terminal mimicking peptides blocked N-terminal zippering of SNAREs, a rate-limiting step in SNARE-driven membrane fusion. Therefore, the results suggest that the N-terminal regions of SNARE motifs are excellent targets for the development of drugs to block SNARE-mediated membrane fusion and neurotransmitter release.

Pharmacokinetics of clindamycin in the plasma and dialysate after intraperitoneal administration of clindamycin phosphoester to patients on continuous ambulatory peritoneal dialysis: an open-label, prospective, single-dose, two-institution study.

We evaluated the pharmacokinetics of clindamycin and the dose of clindamycin phosphate necessary to treat peritonitis after intraperitoneal administration of clindamycin phosphate to patients on continuous ambulatory peritoneal dialysis (CAPD). This was an open-label, prospective, single-dose study conducted at the two levels of institutional clinical care in South Korea. Twelve patients (six men and six women; all older than 25 years), mean CAPD duration of 38.2 months with various origins without peritonitis, received 600 mg clindamycin phosphate mixed with only the first 2-L dialysate (1.5% dextrose). The 1.5%, 1.5%, 2.5% and 1.5% dextrose dialysates were serially exchanged every 6 hr. If patients were non-anuric, 24-hr urine samples were also collected. Clindamycin phosphate was incompletely activated to clindamycin in the dialysate. The clindamycin concentration in the dialysate was greater than the effective concentration (5 µg/mL) at 6.87 µg/mL up to 6 hr. So, 600 mg clindamycin phosphate per every 6 hr dialysate is effective for treatment of peritonitis. It has been reported that the clindamycin concentrations in the dialysate may be higher in CAPD patients with peritonitis. Thus, we can expect that intraperitoneal administration of <600 mg clindamycin phosphate per every 6 hr dialysate could be maintained over 5 µg/mL in patients with peritonitis. The transfer of clindamycin was unidirectional from the dialysate to the plasma.

Pharmacokinetics of drugs in rats with diabetes mellitus induced by alloxan or streptozocin: comparison with those in patients with type I diabetes mellitus.

OBJECTIVES: In rats with diabetes mellitus induced by alloxan (DMIA) or streptozocin (DMIS), changes in the cytochrome P450 (CYP) isozymes in the liver, lung, kidney, intestine, brain, and testis have been reported based on Western blot analysis, Northern blot analysis, and various enzyme activities. Changes in phase II enzyme activities have been reported also. Hence, in this review, changes in the pharmacokinetics of drugs that were mainly conjugated and metabolized via CYPs or phase II isozymes in rats with DMIA or DMIS, as reported in various literature, have been explained. The changes in the pharmacokinetics of drugs that were mainly conjugated and mainly metabolized in the kidney, and that were excreted mainly via the kidney or bile in DMIA or DMIS rats were reviewed also. For drugs mainly metabolized via hepatic CYP isozymes, the changes in the total area under the plasma concentration-time curve from time zero to time infinity (AUC) of metabolites, AUC(metabolite)/AUC(parent drug) ratios, or the time-averaged nonrenal and total body clearances (CL(NR) and CL, respectively) of parent drugs as reported in the literature have been compared. KEY FINDINGS: After intravenous administration of drugs that were mainly metabolized via hepatic CYP isozymes, their hepatic clearances were found to be dependent on the in-vitro hepatic intrinsic clearance (CL(int)) for the disappearance of the parent drug (or in the formation of the metabolite), the free fractions of the drugs in the plasma, or the hepatic blood flow rate depending on their hepatic extraction ratios. The changes in the pharmacokinetics of drugs that were mainly conjugated and mainly metabolized via the kidney in DMIA or DMIS rats were dependent on the drugs. However, the biliary or renal CL values of drugs that were mainly excreted via the kidney or bile in DMIA or DMIS rats were faster. SUMMARY: Pharmacokinetic studies of drugs in patients with type I diabetes mellitus were scarce. Moreover, similar and different results for drug pharmacokinetics were obtained between diabetic rats and patients with type I diabetes mellitus. Thus, present experimental rat data should be extrapolated carefully in humans.

Pharmacokinetics of intravenous methotrexate in mutant Nagase analbuminemic rats.

It has been reported that the plasma (or serum) levels of albumin and globulins were lower and higher, respectively, than the serum levels in control rats. Hence, it could be expected that these changes could affect the renal clearance (Cl(r)) of methotrexate in Nagase analbuminemic rats (NARs) due to changes in plasma protein binding values. Therefore, methotrexate at a dose of 100 mg/kg was administered intravenously to control rats and NARs. The plasma protein binding of methotrexate in NARs was significantly greater (29.4% increase) than the controls, probably due to the considerable binding of the drug (34.2%) to 1.8% beta-plus 0.63% gamma-globulins. The Cl(r) of methotrexate in NARs was significantly slower (36.1% decrease) than the controls, due to the significantly smaller Ae(0-24h) (25.8% decrease). The smaller Ae(0-24h) could be due to the significantly smaller free (unbound to plasma proteins) fractions of methotrexate in plasma (13.8% decrease) in NARs, since methotrexate was mainly excreted in the urine via glomerular filtration. However, the Cl(nr) values were comparable between the control rats and NARs. This could be because methotrexate is not metabolized considerably via hepatic CYP isozymes based on control rats pretreated with SKF 525-A (a nonspecific inhibitor of hepatic CYP isozymes in rats).