Difference in growth hormone response to growth hormone-releasing hormone (GHRH) testing following GHRH subacute treatment in normal aging and growth hormone-deficient adults: possible perspectives for therapeutic use of GHRH or its analogs in elderly subjects?

The somatotroph axis function shows a decline in the elderly (somatopause). In particular growth hormone (GH) response to GH-releasing hormone (GHRH) is reduced in aged man but less than that observed in GH-deficient adults (GHDAs). Plasma GH response to GHRH (1 µg/kg BW) was significantly lower in four GHDAs than in seven healthy aged men 30, 60, and 90 min after acute GHRH administration. To verify whether a priming regimen might be able to increase the reduced GH response to GHRH, both healthy aged men and GHDA patients underwent repetitive administration of GHRH (100 µg GHRH intravenously as a single morning dose, every 2 days for 12 days). After the GHRH-priming regimen, plasma GH values 30, 60, and 90 min after the acute GHRH test were significantly higher than values at the corresponding time points before priming regimen in healthy aged men but not in GHDA patients. These findings confirmed that somatotroph cells become less sensitive to GHRH with normal aging and demonstrate that repetitive administration of GHRH restores the attenuated response only in healthy aged men but not in GHDA patients. This could support the possible use of GHRH or its analogs instead of recombinant human GH in elderly patients with the advantage of preserving the endogenous pulses of GH with the secretion of the different isoforms of GH. However, concerns arise about the possible role of these molecules in tumorigenesis and tumor growth promotion.

An opsonic function of the neutrophil bactericidal/permeability-increasing protein depends on both its N- and C-terminal domains.

The host response to Gram-negative bacterial infection is influenced by two homologous lipopolysaccharide (LPS)-interactive proteins, LPS-binding protein (LBP) and the bacteridical/permeability-increasing protein (BPI). Both proteins bind LPS via their N-terminal domains but produce profoundly different effects: BPI and a bioactive N-terminal fragment BPI-21 exert a selective and potent antibacterial effect upon Gram-negative bacteria and suppress LPS bioactivity whereas LBP is not toxic toward Gram-negative bacteria and potentiates LPS bioactivity. The latter effect of LBP requires the C-terminal domain for delivery of LPS to CD14, so we postulated that the C-terminal region of BPI may serve a similar delivery function but to distinct targets. LBP, holoBPI, BPI-21, and LBP/BPI chimeras were compared for their ability to promote uptake by human phagocytes of an encapsulated, phagocytosis-resistant strain of Escherichia coli. We show that only bacteria preincubated with holoBPI are ingested by neutrophils and monocytes. These findings suggest that, when extracellular holoBPI is bound via its N-terminal domain to Gram-negative bacteria, the C-terminal domain promotes bacterial attachment to neutrophils and monocytes, leading to phagocytosis. Therefore, analogous to the role of the C-terminal domain of LBP in delivery of LPS to CD14, the C-terminal domain of BPI may fulfill a similar function in BPI-specific disposal pathways for Gram-negative bacteria.

Lipopolysaccharide (LPS)-binding proteins BPI and LBP form different types of complexes with LPS.

Lipopolysaccharide (LPS)-binding protein (LBP) and bactericidal/permeability-increasing protein (BPI) are closely related LPS-binding proteins whose binding to LPS has markedly different functional consequences. To gain better insight into the possible basis of these functional differences, the physical properties of LBP-LPS and BPI-LPS complexes have been compared in this study by sedimentation, light scattering, and fluorescence analyses. These studies reveal dramatic differences in the physical properties of LPS complexed to LBP versus BPI. They suggest that of the two proteins, only LBP can disperse LPS aggegates. However, BPI can enhance both the sedimentation velocity and apparent size of LPS aggregates while inhibiting LPS-LBP binding even at very low (1:40 to 1:20) BPI:LPS molar ratios.