Controlled release of thyrotropin releasing hormone from microspheres: evaluation of release profiles and pharmacokinetics after subcutaneous administration.

The drug-release kinetics of thyrotropin releasing hormone (TRH) containing copoly(dl-lactic/glycolic acid) (PLGA) microspheres were evaluated both in vitro and in vivo. The drug was encapsulated in PLGA using an in-water drying method through a water in oil in water emulsion. The drug release from the PLGA microspheres in vitro correlated well with that in vivo, and pseudo-zero-order release kinetics were observed. The pharmacokinetics of TRH following administration of this controlled-release parenteral dosage form have been also examined in rats. Following a transient increase in the plasma level due to an initial burst, steady-state plasma levels were observed. The duration of drug release estimated from the plasma level was comparable with the results in the in vitro and in vivo release studies. The steady-state plasma levels correlated well with the levels predicted from the pharmacokinetic parameters following a single subcutaneous or intravenous injection of TRH solution. The results of this study confirm the previously reported in vivo sustained release of TRH achieved with this drug-delivery system.

Multiple and irreversible binding of cis-diamminedichloroplatinum(II) to human serum albumin and its effect on warfarin binding.

Irreversible bindings of cis-diamminedichloroplatinum(II) (cis-DDP) to human serum albumin (HSA) were investigated in a pH 7.4 buffer containing 0.1 M NaCl at various molar ratios (cis-DDP/HSA) up to 60 over a 14 d period (37 degrees C). The metal binding seemed to reach a plateau when incubated at less than 10 times excess of cis-DDP. As the molar ratio increased, the reaction rate was relatively fast within the first day, followed by a moderate increase in the metal binding. When incubated at 60 times excess of cis-DDP, the metal bound as much as 20 mol per mol of HSA in 14 d. Fluorescence quenching of the metal-bound protein suggested that the tryptophan residue was gradually exposed to a hydrophilic environment as the metal binding increased. Furthermore, cis-DDP cleaved disulfide bonds at the ratio of 1 mol of disulfide bond per 5.3 mol of the metal binding. It was therefore suggested that the metal binding also occurred at several sites other than the disulfide bond. Warfarin binding to the metal-bound protein, examined by fluorescence changes, also decreased with increasing metal binding or cleavage of the disulfide bonds. Thus, cis-DDP bound to multiple sites in addition to the lone sulfhydryl group (Cys-34), suggesting that massive conformational changes of the protein took place.

Fatty acid composition of lipids in tongue and hindleg muscles of muscular dystrophic mice.

In order to understand the pathogenesis of mouse muscular dystrophy, fatty acid and lipid compositions in tongue and hindleg muscles of dystrophic mice were analyzed. The phospholipid contents in tongue and hindleg muscles were 71-73% and 23-24% of the total lipids, respectively. The content of triglyceride in tongue and hindleg muscles was 8% and 66% of the total lipids, respectively. There were no significant differences in the phospholipid content of the tongue or hindleg muscles between normal and dystrophic mice. However, analyses of the fatty acid composition in phospholipids showed that the content of 16:0 and 22:6 in the hindleg muscles of dystrophic mice decreased significantly, while the content of C-18 fatty acids (18:0, 18:1 and 18:2) increased. In addition, the fatty acid composition in phospholipids of tongues of dystrophic mice was identical to that of normal mice. This latter result supports the bone-muscle imbalance hypothesis for the pathogenesis of mouse muscular dystrophy.