CAPÍTULO II: FORMAS DE USO DEL ESPACIO EN EL HOGAR ACTUAL DEL CENTRO URBANO DE SANTA CLARA.
2.2 Resultados del trabajo de campo
The preceding chapter in this thesis demonstrated that cortisol concentrations were increased in the lungs of patients with ARDS. It also showed that the cortisol: cortisone ratio was increased in the alveolar space of patients with ARDS, suggesting increased local activity of 11β-‐HSD type 1 oxo-‐reduction of cortisone to cortisol. In this chapter we have demonstrated that the inflammatory mediators TNF-‐α and IL-‐1β, which have both previously been demonstrated to be key mediators in ARDS,10, 221 cause an up-‐regulation of 11β-‐HSD oxo-‐reductase activity in primary human alveolar macrophages.
The effect of the pro-‐inflammatory cytokines TNF-‐α and IL-‐1β on 11β-‐HSD activity has been observed previously in other cell types. Cooper et al. showed in osteoblasts that not only did these cytokines increase the 11β-‐HSD type 1 conversion of cortisone to cortisol, a suppression of the deactivation of cortisol to cortisone by 11β-‐HSD type 2 was also observed.64 Similar responses to these cytokines have been seen in many other cell types including adipocytes, hepatocytes,62 smooth muscle,65 and amnion and skeletal muscle fibroblasts. 54, 63
That LPS caused a decrease in the 11β-‐HSD oxo-‐reductase activity is unexpected given the finding that the other inflammatory molecules caused an up-‐regulation of this activity. We are unable to find any other reports of a similar response to LPS stimulation. Indeed, other investigators have demonstrated that human macrophage 11β-‐HSD type 1 mRNA and activity are up-‐regulated by LPS.210 Why we should have observed a different result is not clear, especially as the action of LPS on macrophages is to cause them to produce TNF-‐α, which we have shown to up-‐regulate rather than down-‐regulate oxo-‐ reductase activity. An altered response to LPS in these macrophages is a possibility, but further investigation is needed before such a finding should be accepted.
HMGB-‐1 is released from activated macrophages in response to pro inflammatory mediators such as TNF-‐α, IL-‐1β or LPS, and also causes the release of TNF-‐α and IL-‐1β from macrophages.223 It is thought to be a late mediator of sepsis and inflammation.224 We were not able to show any alteration in 11β-‐HSD activity induced by stimulation of the alveolar macrophages with this mediator. The absence of an increase in activity in response to HMGB-‐1, together with the declining increase in activity induced by BALF from day 4 of ARDS suggest therefore that the induction of 11β-‐HSD oxo-‐reductase
activity may be a phenomenon situated early, rather than late, in the signalling pathway of ARDS.
We were also unable to demonstrate a consistent effect of salbutamol on otherwise un-‐ stimulated alveolar macrophages. However, when co-‐stimulated with the pro-‐ inflammatory cytokine TNF-‐α, salbutamol caused a down-‐regulation of the induced increase in oxo-‐reductase activity, through the activation of the β-‐adrenoceptor. Why salbutamol should only cause such a response in co-‐stimulated cells is not clear: It is possible that the salbutamol induced changes are only detectable with greater activity, but also that the mechanism by which salbutamol acts is through a pathway activated only by the cytokines in question. In contrast to our findings Friedberg et al. demonstrated that although the 11β-‐HSD type 1 activity in adipocytes was increased by pro-‐inflammatory cytokines, it was also increased by salbutamol.56 That we showed an opposite effect is likely to represent phenotypic differences between the cells studied. A tissue specific response of 11β-‐HSD to similar stimulations has been demonstrated by Tomlinson et al. between adipocytes and hepatocytes.62
The experiments incubating alveolar macrophages with BALF from patients with ARDS were designed to approximate the conditions that alveolar macrophages might be exposed to in-‐vivo, and in so doing examine the mechanisms by which the observed enzyme activity develops. These experiments have many factors that require a caution to be used in their interpretation. The culture conditions consist of BALF mixed in a 1:1 ratio with the normal culture medium, leading to a less physiological environment for these cells. Despite these caveats the increase in the oxo-‐reductase activity of alveolar macrophages caused by incubation with ARDS BALF is nevertheless convincing. These
results are in keeping with our findings that pro-‐inflammatory cytokines up-‐regulate the 11β-‐HSD oxo-‐reductase activity.
Macrophage 11β-‐HSD type 1 activity is important in the host response to injury and the resolution of inflammation. Macrophages are responsible for the safe disposal of spent inflammatory cells that, and 11β-‐HSD activity promotes this process in animal models by increasing available intracellular cortisol.75 Failure of uptake of apoptotic cells leads these dying cells to undergo secondary necrosis and release further pro-‐inflammatory mediators,229 leading to further tissue damage and the perpetuation of the inflammatory process.230 Any failure of these mechanisms, and an insufficient up-‐ regulation of 11β-‐HSD oxo-‐reductase activity in alveolar macrophages would therefore be of functional importance in the resolution of inflammation in ARDS. If LPS were to be present in sufficient concentrations to suppress 11β-‐HSD oxo-‐reductase activity, this could lead to prolonged disease in ARDS.
One further consideration of the interpretation of these experiments is that in this only one cell type has been studied. Alveolar macrophages are essential effector cells in the resolution of ARDS, and 11β-‐HSD activity within these cells will influence their function. However, the total lung cortisol: cortisone ratio cannot be solely attributed to these cells. The response of other cell types within the lung to inflammatory stimuli should be further investigated. The histopathology study performed by Suzuki et al located an increase in 11β-‐HSD type 2 in the alveolar cell wall, as well as in CD68 positive cells in the alveolar lumen.69 Our results show that at least in these CD68 positive resident alveolar macrophages, inflammatory stimuli do not increase net local cortisol production. We cannot as yet inform on the activity present in other lung cells.
In conclusion, these experiments have shown that the 11β-‐HSD activity oxo-‐reductase activity of primary human alveolar macrophages is increased by pro-‐inflammatory cytokines, and in a BALF model of ARDS. LPS However decreases this activity. These findings provide a cellular mechanism for the increased cortisol: cortisone ratio present in the lungs of patients with ARDS that was identified in the previous chapter. This increase in 11β-‐HSD oxo-‐reduction of cortisone to cortisol amplifies the anti-‐ inflammatory signal by increasing available cortisol.