Treatment effects of drotrecogin alfa (activated) in patients with severe sepsis with or without overt disseminated intravascular coagulation.

Disseminated intravascular coagulation (DIC) is a serious condition associated with sepsis. Clinical management of DIC is hampered by lack of clear diagnostic criteria. The International Society on Thrombosis and Haemostasis (ISTH) has proposed a diagnostic scoring algorithm for overt DIC based on routine laboratory tests. The objective was to assess a modified version of the ISTH scoring system and determine the effect of drotrecogin alfa (activated) (DrotAA, recombinant human activated protein C) on patients with DIC. The large database from the PROWESS clinical trial in severe sepsis was retrospectively used to assess a modified ISTH scoring system. Baseline characteristics and treatment effects of DrotAA were evaluated. At baseline, 29% (454/1568) of patients had overt DIC. Overt DIC was a strong predictor of mortality, independent of APACHE II score and age. Placebo-treated patients with overt DIC had higher mortality than patients without (43 vs. 27%). DrotAA-treated patients with overt DIC had a trend towards greater relative risk reduction in mortality than patients without (29 vs. 18%, P = 0.261) but both groups had greater relative risk reduction than placebo-treated patients. Serious bleeding rates during DrotAA infusion in patients with and without overt DIC were slightly increased (P = 0.498), compared with placebo, while clinically overt thrombotic events during the 28-day period were slightly reduced (P = 0.144). Modified ISTH overt DIC scoring may be useful as an independent assessment for identifying severe sepsis patients at high risk of death with a favorable risk/benefit profile for DrotAA treatment. Patients without overt DIC also received significant treatment benefit.

Cellular mechanism of aminoglycoside tolerance in long-term gentamicin treatment.

In the rat, nephrotoxicity results from uptake of gentamicin at the apical membrane of proximal tubule (PT) cells. However, during continuous gentamicin treatment, the PT epithelium has been shown to recover. The mechanism(s) of cellular recovery and development of tolerance remains unknown. Therefore, we undertook studies designed to characterize cellular adaptations that occur during long-term gentamicin (LTG) treatment. After 19 days of gentamicin treatment, electron microscopy morphological evaluation revealed cellular recovery with an apparent mild decrease in height and number of microvilli. Enzymatic analysis of LTG PT membranes showed that apical and basolateral membranes had essentially returned to normal. Analysis of apical membrane lipid content revealed persistent statistically significant (P < 0.01) elevations in phosphatidylinositol (PI). In vivo immunogold morphological studies and biochemical studies in LTG rats revealed that endocytosis of gentamicin was selectively reduced, whereas the markers of fluid-phase (horseradish peroxidase) and receptor-mediated (beta2-microglobulin) endocytoses were unaffected or increased. Biochemical analysis showed that, although gentamicin binding to apical membranes isolated from LTG rats increased greater than twofold (P < 0.05) over membranes from untreated rats, in vivo cellular uptake, quantified with [3H]gentamicin, was reduced. Western blot analysis of LTG apical membranes and immunofluorescent staining of perfusion-fixed LTG kidneys showed no change in megalin levels or its apical membrane localization. These data imply that recovery of PT cells from and tolerance to LTG treatment involve a selective inhibition of gentamicin uptake across the apical membrane. They indicate that the mediators of gentamicin endocytosis were affected differently: PI levels increased, whereas megalin levels did not change. We conclude that selective inhibition of gentamicin uptake during LTG treatment is not affected by a reduction in PI or megalin levels. We postulate that trafficking of gentamicin and/or gentamicin-containing endocytic structures is reduced in LTG rats, allowing cells to develop tolerance to gentamicin.

Convergence of apical and basolateral endocytic pathways for beta 2-microglobulin in LLC-PK1 cells.

Polarized epithelial cells internalize molecules from both apical and basolateral (BL) plasma membrane (PM) domains via receptor-mediated endocytosis. In the kidney, low-molecular-weight proteins (LMWP) are internalized across the apical membrane of proximal tubule cells and degraded in lysosomes. Although indirect evidence suggests some uptake may occur at the BL surface, in vivo studies performed in rats suggest little if any LMWP uptake occurs at the BL surface. The studies presented here showed that native human beta 2-microglobulin (beta 2M) was internalized across the apical surface and followed the same intracellular pathway in the proximal tubule-derived cell line LLC-PK1 as that described in vivo. Either 125I- or gold-labeled beta 2M (125I-beta 2M and gold-beta 2M) bound specifically and reversibly to the apical surface of confluent LLC-PK1 cells. These results were qualitatively similar to previously documented in vivo results. Subsequently, using gold-beta 2M and LLC-PK1 cells grown on porous supports, we showed that a functional uptake system for the LMWP beta 2M was present at the BL surface. Finally, using different-size gold particles conjugated to beta 2M applied simultaneously to the apical and BL surfaces, we observed that apical and BL endocytic routes converged in multivesicular acid phosphatase-negative endosomal structures. Taken together, these data imply that beta 2M can be internalized across both apical and BL domains and that the two pathways converge at a multivesicular level within the endosomal pathway.

Characterization of the beta 2-microglobulin endocytic pathway in rat proximal tubule cells.

The uptake mechanism(s) of low-molecular-weight proteins by proximal tubule cells remains incompletely characterized. We utilized a biochemical and semiquantitative morphological approach to better characterize the endocytic pathway of an anionic protein, beta 2-microglobulin (beta 2M), in the rat proximal tubule. Indirect immunogold techniques revealed beta 2M was taken up via a classic receptor-mediated endocytic pathway. In vitro biochemical and morphological characterization of iodinated beta 2M and gold-conjugated beta 2M (gold-beta 2M) binding to isolated brush-border membrane vesicles (BBMV) documented specific and quantitatively similar binding interactions of the modified beta 2M with BBMV. Kinetic characterization of the in vivo endocytic pathway of gold-beta 2M was undertaken using microinfusion of individual tubules. beta 2M initially bound at the apical surface, was internalized into subapical coated vesicles and delivered to endosomal-like structures within 5 min, and, finally, was concentrated in lysosomal-like structures within 15 min. This uptake was inhibited by excess unconjugated beta 2M. In addition, we directly showed that uptake did not occur across the basolateral surface. Finally, by passing solubilized BBMV over beta 2M affinity columns we were able to isolate binding activity.

Analysis of the nucleoside moiety of cobalamin and cobalamin analogues using gas chromatography-mass spectrometry.

Existing techniques for identification of cobalamin and cobalamin analogues generally use the intact molecule during characterization with somewhat ambiguous results. In this study a method is described for the identification of the nucleoside in the lower axial ligand of cobalamin and a variety of naturally occurring cobalamin analogues that differ from cobalamin in the base that is present in the nucleoside. Cobalamin and cobalamin analogues were isolated from biological samples by affinity chromatography using R-protein-Sepharose columns. The nucleosides of the lower axial ligand were then hydrolyzed and isolated by column chromatography using a mixed bed column. Nucleosides were oxidized with periodate and reduced with borohydride. After reisolation, the t-butyldimethylsilyl derivatives were prepared and analyzed using gas chromatography/mass spectrometry with selected ion monitoring. A stable isotope internal standard of cobalamin was biosynthetically produced and used to quantitate cobalamin in rabbit kidney. Cobalamin analogues were also shown to be present in rabbit kidney, but they contain the 5,6-dimethylbenzimidazole nucleoside (alpha-ribazole) in the lower axial ligand, indicating that these analogues differ from cobalamin in the corrin ring region of the molecule.