Peptide attachment to extremities of liposomal surface grafted PEG chains: preparation of the long-circulating form of laminin pentapeptide, YIGSR.

Poly(ethylene glycol) (PEG)-grafted liposomes offer new opportunities as long-circulating platforms presenting biologically relevant ligands. In pursuit of this goal, liposomal conjugates of YIGSR were prepared by mild periodate oxidation of TYIGSR-NH2 and incubation of the product with hydrazide-PEG-(distearoylphosphatidyl)ethanolamine-containing liposomes. The peptide-carrying liposomes, with up to 500 YIGSR residues per vesicle, despite exhibiting faster blood clearance rates than the parent liposomes in rats, remained in circulation for extended periods of time. Mean residence times for the parent liposomal formulation and conjugated preparations containing 200 and 500 YIGSR residues per vesicle were 28, 25, and 23 h, respectively. The results have important implications for systemic delivery of peptides and for their use as targeting moieties for PEG-grafted liposomes.

Increase in histone poly (ADP-ribosylation) in mitogen-activated lymphoid cells.

Poly (ADP-ribosylated) histones appear to be intermediates in nuclear processes that involve DNA strand breaks. We have studied histone ADP-ribosylation in cellular lysates from activated human lymphoid cells in culture. Modified histones differing in the number of ADP-ribose groups gave separate bands upon two-dimensional gel electrophoresis. Cellular lysates from control cells contained histones modified with 1 to 15 ADP-ribose groups. Stimulation of the cells during culture with phytohemagglutinin (PHA) or a phorbol ester (TPA) as well as combinations of these two reagents led to a significant increase in the upper limit number of ADP-ribose groups attached to histones in the presence of divalent metal ions. Hyper (ADP-ribosylated) H2B carrying at least 32 ADP-ribose groups gave a distinctly characteristic pattern on two-dimensional gels showing that highly ordered enzymatic steps are followed for its synthesis. Moreover, it was found that PHA and/or TPA induces branching of the poly (ADP-ribose) on H2B. The increase in histone poly (ADP-ribosylation) following lymphocyte activation was less dramatic during incubation of cellular lysates in the absence of divalent metal ions. The increased histone modification observed in this study may result from an increase in cell proliferation during activation of lymphoid cells. The finding that the number of ADP-ribose groups on H4 equals or exceeds by one the number of acetyl groups suggests that the two modifications may share common functions.