Identification, isolation, and characterization of daintain (allograft inflammatory factor 1), a macrophage polypeptide with effects on insulin secretion and abundantly present in the pancreas of prediabetic BB rats

A bioactive macrophage factor, the polypeptide daintain/allograft inflammatory factor 1 (AIF1), has been isolated from porcine intestine. It was discovered when searching for intestinal peptides with effects on insulin release, and its purification was monitored by the influence of the peptide fractions on pancreatic glucose-induced insulin secretion. Daintain/AIF1 is a 146-aa residue polypeptide with a mass of 16,603 Da and an acetylated N terminus. An internal 44-residue segment with the sequence pattern –KR–KK–GKR– has a motif typical of peptide hormone precursors, i.e., dibasic sites for potential activation cleavages and at the sequentially last such site, the structure GKR. The latter is a signal for C-terminal amide formation in the processing of peptide hormones. Daintain/AIF1 is immunohistochemically localized to microglial cells in the central nervous system and to dendritic cells and macrophages in several organs. A particularly dense accumulation of daintain/AIF1-immunoreactive macrophages was observed in the insulitis affecting the pancreatic islets of prediabetic BB rats. When injected intravenously in mice, daintain/AIF1 at 75 pmol/kg inhibited glucose (1 g/kg)-stimulated insulin secretion, with a concomitant impairment of the glucose elimination, whereas at higher doses (7.5 and 75 nmol/kg), daintain/AIF1 potentiated glucose-stimulated insulin secretion and enhanced the glucose elimination. Its dual influence on insulin secretion in vivo at different peptide concentrations, and the abundance of macrophages expressing daintain/AIF1 in the pancreatic islets of prediabetic rats, suggest that daintain/AIF1 may have a role in connection with the pathogenesis of insulin-dependent diabetes mellitus.

Platelet-derived growth factor BB induces functional vascular anastomoses in vivo.

Neovascularization that generates collateral blood flow can limit the extent of tissue damage after acute ischemia caused by occlusion of the primary blood supply. The neovascular response stimulated by the BB homodimeric form of recombinant platelet-derived growth factor (PDGF-BB) was evaluated for its capacity to protect tissue from necrosis in a rat skin flap model of acutely induced ischemia. Complete survival of the tissue ensued, when the original nutritive blood supply was occluded, as early as 5 days after local PDGF-BB application, and the presence of a patent vasculature was evident compared to control flaps. To further evaluate the vascular regenerative response, PDGF-BB was injected into the muscle/connective tissue bed between the separated ends of a divided femoral artery in rats. A patent new vessel that functionally reconnected the ends of the divided artery within the original 3- to 4-mm gap was regenerated 3 weeks later in all PDGF-BB-treated limbs. In contrast, none of the paired control limbs, which received vehicle with an inactive variant of PDGF-BB, had vessel regrowth (P < 0.001). The absence of a sustained inflammatory response and granulation tissue suggests locally delivered PDGF-BB may directly stimulate the angiogenic phenotype in endothelial cells. These findings indicate that PDGF-BB can generate functional new blood vessels and nonsurgically anastomose severed vessels in vivo. This study supports the possibility of a therapeutic modality for the salvage of ischemic tissue through exogenous cytokine-induced vascular reconnection.