Effects of recombinant human granulocyte colony-stimulating factor on neutrophil functions in aged animals

G-CSF enhances resolution of Staphylococcus aureus wound infection in an age-dependent manner

This study tested the hypothesis that heightened bacterial colonization and delayed wound closure in aged mice could be attenuated by granulocyte colony-stimulating factor (G-CSF) treatment. Previously, we reported that aged mice had elevated bacterial levels, protracted wound closure, and reduced wound neutrophil accumulation after Staphylococcus aureus wound infection relative to young mice. In aseptic wound models, G-CSF treatment improved wound closure in aged mice to rates observed in young mice. Given these data, our objective was to determine if G-CSF could restore age-associated differences in wound bacterial burden and closure by increasing wound neutrophil recruitment. Young (3- to 4-month) and aged (18- to 20-month) BALB/c mice received three dorsal subcutaneous injections of G-CSF (250 ng/50 μL per injection) or saline control (50 μL per injection) 30 min after wound infection. Mice were killed at days 3 and 7 after wound infection, and bacterial colonization, wound size, wound leukocyte accumulation, and peripheral blood were evaluated. At days 3 and 7 after wound infection, bacterial colonization was significantly reduced in G-CSF-treated aged mice to levels observed in saline-treated young animals. Wound size was reduced in G-CSF-treated aged animals, with no effect on wound size in G-CSF-treated young mice. Local G-CSF treatment significantly enhanced neutrophil wound accumulation in aged mice, whereas there was no G-CSF-induced change in young mice. These data demonstrate that G-CSF enhances bacterial clearance and wound closure in an age-dependent manner. Moreover, G-CSF may be of therapeutic potential in the setting of postoperative wound infection or chronic nonhealing wounds in elderly patients.

Reduced neutrophil chemotaxis and infiltration contributes to delayed resolution of cutaneous wound infection with advanced age

Advanced age is associated with alterations in innate and adaptive immune responses, which contribute to an increased risk of infection in elderly patients. Coupled with this immune dysfunction, elderly patients demonstrate impaired wound healing with elevated rates of wound dehiscence and chronic wounds. To evaluate how advanced age alters the host immune response to cutaneous wound infection, we developed a murine model of cutaneous Staphylococcus aureus wound infection in young (3-4 mo) and aged (18-20 mo) BALB/c mice. Aged mice exhibit increased bacterial colonization and delayed wound closure over time compared with young mice. These differences were not attributed to alterations in wound neutrophil or macrophage TLR2 or FcγRIII expression, or age-related changes in phagocytic potential and bactericidal activity. To evaluate the role of chemotaxis in our model, we first examined in vivo chemotaxis in the absence of wound injury to KC, a neutrophil chemokine. In response to a s.c. injection of KC, aged mice recruited fewer neutrophils at increasing doses of KC compared with young mice. This paralleled our model of wound infection, where diminished neutrophil and macrophage recruitment was observed in aged mice relative to young mice despite equivalent levels of KC, MIP-2, and MCP-1 chemokine levels at the wound site. This reduced leukocyte accumulation was also associated with lower levels of ICAM-1 in wounds from aged mice at early time points. These age-mediated defects in early neutrophil recruitment may alter the dynamics of the inflammatory phase of wound healing, impacting macrophage recruitment, bacterial clearance, and wound closure.

Peculiarities of bone marrow hemopoiesis in early aging OXYS rats

Colony-forming activity of bone marrow cells in 3- and 12-month-old Wistar rats does not differ by the number of early and erythroid precursors and by the formation of granulocyte-macrophage colonies. In senescence-accelerated OXYS rats, the number of early and erythroid precursors significantly increases by the age of 12 months and surpasses the corresponding values in Wistar rats. The number of granulocyte-macrophage colonies in OXYS rats does not change with age, but the numbers of these colonies formed at the age of 3 and 12 months in these animals are higher than in Wistar rats. As a result, the total number of hemopoietic colonies in 12-month-old OXYS rats 2-fold surpassed that in 12-month-old Wistar rats. Activation of granulopoiesis and increased numbers of early and erythroid precursors indicate deep changes in the functional status of the hemopoietic stem cell in 1-year-old OXYS rats in the direction characteristic of aging animals.

Circulating blood leukocyte gene expression profiles: effects of the Ames dwarf mutation on pathways related to immunity and inflammation

Aging is associated with a decline of immune competence and an increase in markers of inflammation. There is considerable evidence that inflammatory processes play a role in aging and the determination of lifespan. Hypopituitary Ames dwarf mice have extended longevity and exhibit many symptoms of delayed aging, although various aspects of immune function are suppressed in the mutants. In the present study, the expression of genes related to immunity and inflammation was compared in peripheral blood leukocytes (PBL) from Ames dwarf and normal mice using Affymetrix GeneChip arrays. Among the more than 3000 probe sets that were differentially expressed, 273 were identified as being associated with immunity and/or inflammation. Pathway analysis revealed interactions among 91 of these probe sets, centered on casp3, bcl2, il4, prkca, mapk14 and TGFbeta1. Ames dwarf mice had reduced leukocyte expression of casp3 and TGFbeta and increased expression of Bcl2. Alterations in the expression of these genes suggest likely functional changes in apoptosis, B and T cell homeostasis, prostaglandin synthesis, humoral immunity, chemokine activity, complement activation, hemostasis and wound healing pathways. Collectively, these results suggest that activation of both anti-inflammatory pathways and an anti-clotting mechanism combined with reduced turnover of leukocytes may contribute to delayed aging and extended longevity of Ames dwarf mice. We are also aware that alterations in gene expression in PBLs can be due to different composition of PBL populations when comparing Ames dwarf to WT animals, and it will be interesting to investigate these genes in particular PBL populations in the future. However, whole leukocytes population represents the function of immune system in these organisms.

Peritoneal macrophages function modulation by L-carnitine in aging rats

BACKGROUND AND AIMS

The aging process is associated with a progressive decline in physiological functions involving immune response in most species. The aim of the present study was to determine the effect of L-carnitine on impaired macrophages function in aged rats.

METHODS

Superoxide anion production, chemotaxis and phagocytic activity were studied in peritoneal macrophages obtained from young (2 months old) and aged (24 months old) rats. L-carnitine (50 mg/kg bw) or control vehicle was orally gavaged into young and aged rats for 30 consecutive days.

RESULTS

The peritoneal macrophages of the aged rats exhibited an increase in superoxide anion generation and a decline in chemotaxis and phagocytic index by comparison with the young rats. Superoxide anion production in aged rats was significantly reduced by L-carnitine treatment, as accompanied by a significant enhancement of chemotactic activity, which was restored to control levels observed in young rats. The age-related reduction in phagocytic index was only slightly, but not significantly, restored by L-carnitine administration, however.

CONCLUSION

The findings suggest that L-carnitine administration may be useful in reversing some age-related changes.

Evaluation of phagocytosis and arachidonate metabolism by alveolar macrophages and recruited neutrophils from F344xBN rats of different ages

The incidence of infectious respiratory diseases increases with aging. Resident alveolar macrophages (AMs) and recruited leukocytes (PMNL) mediate cellular defense against bacterial infections in the lung, and phagocytosis and lipid mediator synthesis are important components of their antimicrobial capacity. The objective of this study was to determine if either phagocytic capacity or lipid mediator generation declines with normal aging, in either AMs or PMNL recruited to a site of inflammation. The F344xBN rat hybrid has a lower incidence of pathologies associated with aging, particularly up to 20 months; animals aged 6,12 and 18 months were chosen to evaluate changes associated with normal aging. As previously reported for peripheral blood leukocytes, phagocytosis by recruited PMNL declined with aging: recruited PMNL from 18 months rats showed a significantly decreased capacity to phagocytose live Klebsiella pneumoniae bacteria, compared to PMNL from 6 months rats. Surprisingly, however, the phagocytic capacity of AMs increased with aging: the phagocytic index of AMs from 18 months rats was more than three times that of AMs from 6 months rats. The capacity of AMs and recruited PMNL to release arachidonic acid or synthesize leukotrienes or prostaglandins did not change with aging. This study demonstrates that, although phagocytosis by recruited PMNL declines with aging, other aspects of immune function do not decline, and may actually increase, with normal aging. These results suggest that impaired phagocytosis by recruited PMNL may be an important component of the increased susceptibility to infectious respiratory diseases during normal aging.

Programmed cell death of the normal human neutrophil: an in vitro model of senescence

The present study provides experimental data which indicate that the neutrophil is ideal for studying programmed cell death or apoptosis in vitro. Neutrophils can be obtained from human peripheral blood in large numbers with minimal experimental manipulation and are easily separated from other leukocytes, providing nearly pure cell suspensions. The neutrophil life span in vitro is sufficiently short to allow observations to be made within eight hours after experimental manipulation. Neutrophils can also be easily maintained in serum-free, chemically defined media which can be systematically altered, thereby defining specific variables that influence the apoptotic process. Since the neutrophils do not need an exogenous trigger to undergo programmed cell death, it is also an excellent model to study senescence. It was determined from this study that neutrophils undergo apoptosis most efficiently at 37 degrees C, a temperature requirement for physiologic cell death. Neutrophils undergo apoptosis at a slightly faster rate and maintain membrane integrity better when incubated in a tissue culture medium (e.g., RPMI 1640) compared with a balanced salt solution (e.g., HBBB). Cycloheximide, an inhibitor of protein synthesis, was shown to accelerate apoptosis in a dose-dependent manner. The presence of Zn++ significantly decreased the rate of apoptosis, whereas the presence of Ca++ and Mg++ had no apparent effect. These studies indicate that the process of senescence, culminating in cell death, is subject to modulation by a variety of agents and experimental conditions. In addition, the ultrastructural features of neutrophils undergoing programmed cell death in vitro were compared in detail to those occurring in vivo and were found to be comparable.