Control of the disposition profiles of proteins in the kidney via chemical modification

Pharmacokinetic considerations for targeted drug delivery

Drug delivery systems involve technology designed to maximize therapeutic efficacy of drugs by controlling their biodistribution profile. In order to optimize a function of the delivery systems, their biodistribution characteristics should be systematically understood. Pharmacokinetic analysis based on the clearance concepts provides quantitative information of the biodistribution, which can be related to physicochemical properties of the delivery system. Various delivery systems including macromolecular drug conjugates, chemically or genetically modified proteins, and particulate drug carriers have been designed and developed so far. In this article, we review physiological and pharmacokinetic implications of the delivery systems.

Extravasation of macromolecules

Macromolecules can extravasate across the normal endothelium by transcapillary pinocytosis as well as by passage through interendothelial cell junctions, gaps or fenestrae. The main biological factors that control extravasation of a solute include regional differences in the capillary structures, the disease state of the organ or tissue, and the rate of blood and lymph supply. Physicochemical properties that are of profound significance in the extravasation of macromolecules are molecular size, shape, charge and hydrophilic/lipophilic balance (HLB) characteristics. Extravasation of small drugs, proteins, oligonucleotides and genes can be controlled by conjugating or forming complexes with macromolecular carriers. This requires a thorough understanding of the relationship between the chemical structures, physicochemical properties and the pharmacokinetics of both carrier and active molecules. This review article discusses the extravasation of macromolecules from the view points of pharmacokinetics and drug delivery systems, with the main emphasis on the extravasation across the liver, kidney and tumor capillaries.

Augmented inhibitory effect of superoxide dismutase on superoxide anion release from macrophages by direct cationization

Superoxide dismutase (SOD) was modified into cationized form (Cat-SOD) in order to enhance its pharmacological efficacy based on an electrostatic interaction. The inhibitory effect of Cat-SOD on superoxide anion release from inflammatory macrophages and its cellular interaction were studied in vitro. Cat-SOD exhibited an excellent inhibitory effect on superoxide anion release from the macrophages, and this effect surpassed those of native SOD and SOD modified with mannose (Man-SOD) which is taken up via mannose receptor-mediated endocytosis by macrophages. In the presence of colchicine, a microtubule-disruptive agent, the inhibitory effect of Cat-SOD was slightly impaired, whereas the effect of Man-SOD completely disappeared. The intracellular localization of fluorescein isothiocyanate-labeled SOD, Cat-SOD and Man-SOD observed by confocal laser microscopy supported the difference in their abilities to eliminate superoxide anions. The different sensitivities of Cat-SOD and Man-SOD to colchicine were also confirmed by the confocal laser microscopic images, suggesting their distinct intracellular trafficking pathways in the macrophages. In conclusion, Cat-SOD is desirable for its pharmacological activity, which is probably the result of its ability to be delivered to the vicinity of NADPH-oxidase which locates in the cell membrane and generates superoxide anions.

Renal disposition characteristics of oligonucleotides modified at terminal linkages in the perfused rat kidney

To clarify the renal disposition characteristics of oligonucleotides at the organ level, the renal handling of model end-capped oligonucleotides, 3'-methoxyethylamine 5'-biotin-decathymidylic acid containing phosphoramidate modifications at 3'- and 5'-terminal internucleoside linkages (T10) and its phosphorothioate (Ts10), were studied in the perfused rat kidney. In a single-pass indicator dilution experiment, venous outflow and urinary excretion patterns and tissue accumulation of radiolabeled oligonucleotides were evaluated under filtering or nonfiltering conditions. No significant binding to bovine serum albumin (BSA) in the perfusate was observed for T10, whereas more than 90% of Ts10 bound to BSA. The steady-state distribution volume of T10 calculated from the venous outflow pattern was larger than that of inulin, which corresponds to the extracellular volume of the kidney, whereas the distribution volume of Ts10 was larger than that of BSA (the intravascular volume). These results suggested their interaction with the vascular wall. Rapid urinary excretion was observed for T10, similar to inulin used as a marker of golmerular filtration rate. On the other hand, urinary excretion of Ts10 was greatly restricted due to its high binding ability (> 90%) to BSA in the perfusate. A significant amount of T10 and Ts10 was accumulated in the kidney (T10, 1.8% of injected dose; Ts10, 1.3%) compared with inulin (0.2%) and BSA (< 0.1%). The accumulation of these oligonucleotides was ascribed to both tubular reabsorption and uptake from the capillary side. In addition, the uptake of T10 from the capillary side was significantly inhibited by simultaneous injection of dextran sulfate, suggesting that the oligonucleotide was taken up as an anionic molecule. These findings will be useful information for the development of delivery systems for antisense oligonucleotides.

Improvement of therapeutic effect of human recombinant superoxide dismutase on ischemic acute renal failure in the rat via cationization and conjugation with polyethylene glycol

Therapeutic effect of superoxide dismutase (SOD) and three derivatives: a conjugate with polyethylene glycol (SOD-PEG2), a cationized derivative (cSOD), and a mannosylated derivative (Man-SOD), on acute renal failure induced by ischemia/reperfusion was studied in rats. SOD and derivatives were administered intravenously to the rat after nephrectomy of the right kidney and before and after 60 min occlusion of the left renal artery. At 48 hr after reperfusion, the renal function was evaluated by determining the urinary excretion rate of 14C-inulin injected intravenously. No therapeutic effect on the impaired renal function was shown in the case of low dose SOD (2600 unit/kg) treatment. In contrast, administration of cSOD which was shown to be taken up by the isolated perfused kidney from its capillary side and SOD-PEG2 which maintained high plasma concentration exhibited significant therapeutic effect, as did SOD at ten-fold higher dose (26,000 unit/kg). On the other hand, renal damage was promoted by Man-SOD. Thus, the present study demonstrated that chemical modification may improve the therapeutic effect of SOD on the ischemic acute renal failure and increased SOD concentration in the renal vascular space is an important factor for the improved effect.