Increased cerebral infarct volumes in polyglobulic mice overexpressing erythropoietin.

There is increasing evidence that erythropoietin (Epo) has a protective function in cerebral ischemia. When used for treatment, high Epo plasma levels associated with increases in blood viscosity, however, may counteract beneficial effects of Epo in brain ischemia. The authors generated two transgenic mouse lines that overexpress human Epo preferentially, but not exclusively, in neuronal cells. In mouse line tg21, a fourfold increase of Epo protein level was found in brain only, whereas line tg6 showed a dramatic increase of cerebral and systemic transgene expression resulting in hematocrit levels of 80%. Cerebral blood flow (CBF), as determined by bolus tracking magnetic resonance imaging, was not altered in the tg6 line. The time-to-peak interval for the tracer, however, increased approximately threefold in polyglobulic tg6 mice. Immunohistochemical analysis revealed an increase in dilated vessels in tg6 mice, providing an explanation for unaltered CBF in polyglobulic animals. Permanent occlusion of the middle cerebral artery (pMCAO) led to similar perfusion deficits in wild-type, tg6, and tg21 mice. Compared with wild-type controls, infarct volumes were not significantly smaller (22%) in tg21 animals 24 hours after pMCAO, but were 49% enlarged (P < 0.05) in polyglobulic tg6 mice. In the latter animals, elevated numbers of Mac-1 immunoreactive cells in infarcted tissue suggested that leukocyte infiltration contributed to enlarged infarct volume. The current results indicate that moderately increased brain levels of Epo in tg21 transgenic mice were not sufficient to provide significant tissue protection after pMCAO. The results with tg6 mice indicate that systemic chronic treatment with Epo associated with elevated hematocrit might deteriorate outcome after stroke either because of the elevated hematocrit or other chronic effects.

Mammalian gene expression in hypoxic conditions.

Hypoxia induces gene expression of specific genes such as erythropoietin (Epo) and vascular endothelial growth factor (VEGF) that allow physiological adaptation to the environmental conditions at the cellular, local, and systemic levels. Reduced oxygenation is also a common precursor of many pathological processes, including coronary artery defects, ischemia, and malignant tumour formation. The hypoxia-inducible transcription factor HIF-1, a heterodimer consisting of the oxygen-regulated alpha-subunit and the constitutively expressed beta or ARNT-subunit, serves as a master regulator of oxygen-dependent gene expression. We observed that upon hypoxic exposure of HeLa cells in tonometer, accumulation of HIF-1alpha occurred within two minutes, while reoxygenation strongly reduced HIF-1alpha levels within four to eight minutes. Thus, hypoxia leads to a rapid cellular adaptation. In another line of investigation, we analysed the impact of hypoxia-independent overexpression of Epo in transgenic mice. Despite a hematocrit of about 80% the transgenic mice did not develop hypertension or thromboembolic complications.

Generation and application of chicken egg-yolk antibodies.

Despite the fact that the use of chicken as immunization host brings many advantages to the production of polyclonal antibodies, the generation of egg yolk immunoglobulins (IgY) is rarely chosen. In this review, we report on the fast and efficient method for generation and affinity purification of IgY, in this case raised against the alpha-subunit of hypoxia-inducible factor-1 (HIF-1). The IgY antibody was successfully applied in a variety of methods and a number of different species for HIF-1alpha detection. In electrophoretic mobility shift assays, the IgY antibody recognized the native HIF-1 complex. The IgY antibody also detected HIF-1alpha protein on Western blots with extracts derived from human, monkey, pig, dog and mouse cell lines grown under hypoxic conditions. Immunofluorescence and immunoprecipitation experiments using the IgY antibody allowed detection and subcellular localization of HIF-1alpha in the nuclei of hypoxic cells. Chicken antibody production brings great benefit concerning the welfare of the immunized animals, due to non-invasive antibody harvesting with the added convenience of simple egg collection. An additional advantage is the fast and simple IgY isolation from egg yolk. IgY technology is a great improvement and should be considered as a good alternative to conventional polyclonal antibody production in mammals.

Decreased alveolar oxygen induces lung inflammation.

Molecular mechanisms of the inflammatory reaction in hypoxia-induced lung injury are not well defined. Therefore, effects of alveolar hypoxia were studied in rat lungs, exposing rats to 10% oxygen over periods of 1, 2, 4, 6, and 8 h. An increase in the number of macrophages in bronchoalveolar lavage fluid of hypoxic animals was shown between 1 and 8 h. Extravasation of albumin was enhanced after 1 h and remained increased throughout the study period. NF-kappaB-binding activity as well as mRNA for TNF-alpha, macrophage inflammatory protein (MIP)-1beta, and monocyte chemoattractant protein (MCP)-1 were increased within the first 2 h of exposure to hypoxia. Hypoxia-inducible factor (HIF)-1alpha and intercellular adhesion molecule (ICAM)-1 mRNA were upregulated between 1 and 6 h. Elimination of alveolar macrophages by intratracheal application of liposome-encapsulated clodronate led to a decreased expression of NF-kappaB binding activity, HIF-1alpha, TNF-alpha, ICAM-1, and MIP-1beta. In summary, alveolar hypoxia induced macrophage recruitment, an increase in albumin leakage, and enhanced expression of inflammatory mediators, which were mainly macrophage dependent. Alveolar macrophages appear to have a prominent role in the inflammatory response in hypoxia-induced lung injury and the related upregulation of inflammatory mediators.