Impact of Hemoglobin Concentration and Affinity for Oxygen on Tissue Oxygenation: The Case of Hemoglobin-Based Oxygen Carriers

Hemoglobin extravasation in the brain of rats exchange-transfused with hemoglobin-based oxygen carriers

Haemoglobin (Hb)-based oxygen carriers are under consideration as oxygen therapeutics. Their effect on apoptosis is critical, because the onset of pro-apoptotic pathways may lead to tissue damage. MP4OX, a polyethylene glycol-conjugated human Hb preserves the baseline level of neuron apoptosis with respect to sham. Here we develop a method for measuring Hb extravasation in brain. We exchange transfused rats by haemorrhaging 50% of their blood with simultaneous, isovolemic replacement with Hextend (negative control), MP4OX, or αα-cross-linked Hb. Animals were sacrificed 2 h after transfusion, brain tissue was harvested and processed for double-staining immunofluorescence, whereby Hb ? chain and NeuN (a neuron protein) were stained and quantitated. Whereas Hextend did not induce Hb extravasation, in both MP4OX and ??Hb brains Hb molecules were detected outside neurons. The level of extravasated Hb chains was > 3-fold higher in Hb compared to MP4OX. Western blot analysis revealed that the expression levels of protein related to redox imbalance (e.g., Nrf2, iNOS and ERK phosphorylation) were higher in ααHb than MP4OX. In conclusions, higher Hb extravasation in ααHb than MP4OX induces redox imbalance, which causes higher anti-oxidant response. Whereas Nrf2 response may be considered protective, iNOS response appears damaging.

Effect of overexpression of hypoxia-inducible factor-1α induced by hyperoxia in vivo in LNCaP tumors on tumor growth rate

OBJECTIVE

To study effect of overexpression of hypoxia-inducible factor-1α induced by hyperoxia in vivo in LNCaP tumors on tumor growth rate.

METHODS

The prostate cancer LNCaP cells were inoculated in the abdomen of mice. All the mice were randomly placed in the gas chamber with different oxygen content. The groups were divided as follows: twelve mice in hypoxia group, sixteen mice in normoxia group, ten mice in hyperoxia group. After 28 d of treatment, the mice were weighed, the blood samples were taken from the left ventricle, and the tumor was isolated and weighed. Tumor growth, angiogenesis and vascularization, HIF-1α expression and intracellular signal transduction molecules expression in each group of xenografts were detected and analyzed by using Western blotting and immunofluorescence and determination of hemoglobin.

RESULTS

Comparison of the growth of xenografts in each group showed that, the xenografts growth of hypoxia group was more quickly than that of normoxia group. The difference was statistically significant (P = 0.004). The difference in xenografts growth between hyperoxia group compared and normoxia group was not statistically significant (P > 0.05). The expressions of HIF-1α, VEGF and VEGF-R of xenografts in hyperoxia group were significantly higher than those of normoxia group (P < 0.05). The expression of HIF-1α of xenografts in hypoxia group and normoxia group were similar. The blood growth rate of xenografts in hypoxia group (170%) was significantly higher than that of normoxia group (40%) (P < 0.05). The expression of Nrf2 of xenografts in hyperoxia group was significantly higher than that of normoxia group (P < 0.05).

CONCLUSIONS

When hyperoxia induces the overexpression of HIF-1α in LNCaP tumor, it will not affect tumor growth. It provides a new ideas and theoretical basis for the clinical treatment of prostate cancer.

Microengineered cell and tissue systems for drug screening and toxicology applications: Evolution of in-vitro liver technologies

The liver performs many key functions, the most prominent of which is serving as the metabolic hub of the body. For this reason, the liver is the focal point of many investigations aimed at understanding an organism's toxicological response to endogenous and exogenous challenges. Because so many drug failures have involved direct liver toxicity or other organ toxicity from liver generated metabolites, the pharmaceutical industry has constantly sought superior, predictive in-vitro models that can more quickly and efficiently identify problematic drug candidates before they incur major development costs, and certainly before they are released to the public. In this broad review, we present a survey and critical comparison of in-vitro liver technologies along a broad spectrum, but focus on the current renewed push to develop "organs-on-a-chip". One prominent set of conclusions from this review is that while a large body of recent work has steered the field towards an ever more comprehensive understanding of what is needed, the field remains in great need of several key advances, including establishment of standard characterization methods, enhanced technologies that mimic the in-vivo cellular environment, and better computational approaches to bridge the gap between the in-vitro and in-vivo results.

In vivo hyperoxia induces hypoxia-inducible factor-1α overexpression in LNCaP tumors without affecting the tumor growth rate

Hypoxia is a recognized cause for solid tumors malignancy and resistance, probably via hypoxia-induced overexpression of the hypoxia-inducible factor (HIF)-1α, major modulator of the cell response to oxygen deprivation. Although hyperoxia, the opposite condition, may represent a key issue to assess this paradigm, its effect on tumor growth and HIF-1α expression remains unclear. To test whether hyperoxia and hypoxia have divergent effects, and to better focus into the role of HIF-1α in vivo, athymic mice xenografted with LNCaP cells were exposed for 28 days to atmospheres containing 10, 21 or 30% O2. Whereas the xenografts grew twice faster in hypoxia, their growth rates in hyperoxia and normoxia were similar. To analyze the involved molecular mechanisms, we performed various assays in xenograft tissues. Faster xenografts growth in hypoxia was associated with higher phosphorylation of protein kinase B (Akt) and higher expression of Ki67, both related with pro-survival and cell proliferation pathways. By contrast, the expression level of HIF-1α was similar in normoxia and hypoxia, but paradoxically twice higher in hyperoxia. The protein level of the nuclear factor (erythroid-derived 2)-like 2 (Nrf2) was also higher in hyperoxia, suggesting marked cell response to redox imbalance. Whereas both the vascular-endothelial growth factor (VEGF) and its receptor VEGF-R2 were overexpressed in hyperoxia, the tissue hemoglobin content was not increased, despite a slight reduction in vascularization. As a whole, this data indicates that the xenografts growth rate was independent of HIF-1α expression level, suggesting that in an in vivo setting alternative more effective proliferative paths associated with the cell response to the redox imbalance may override the paths linked to HIF-1α signaling.

Impact of acellular hemoglobin-based oxygen carriers on brain apoptosis in rats

BACKGROUND

Extracellular hemoglobin (Hb)-based oxygen carriers (HBOCs) are under extensive consideration as oxygen therapeutics. Their effects on cellular mechanisms related to apoptosis are of particular interest, because the onset of proapoptotic pathways may give rise to tissue damage.

STUDY DESIGN AND METHODS

The objective was to assess whether the properties of the Hb that replaces blood during an isovolemic hemodilution would modulate apoptotic-response mechanisms in rat brain and whether such signaling favors cytoprotection or damage. We exposed rats to exchange transfusion (ET; 50% blood volume and isovolemic replacement with Hextend [negative colloid control], MP4OX [PEGylated HBOC with high oxygen affinity], and ααHb [αα-cross-linked HBOC with low oxygen affinity; n=4-6/group]). Sham rats acted as control. Animals were euthanized at 2, 6, and 12 hours after ET; brain tissue was harvested and processed for analysis.

RESULTS

In MP4OX animals, the number of neurons that overexpressed the hypoxia-inducible factor (HIF)-1α was higher than in ααHb, particularly at the early time points. In addition, MP4OX was associated with greater phosphorylation of protein kinase B (Akt), a well-known cytoprotective factor. Indeed, the degree of apoptosis, measured as terminal deoxynucleotidyl transferase-positive neurons and caspase-3 cleavage, ranked in order of MP4OX < Hextend < ααHb.

CONCLUSION

Even though both HBOCs showed increased levels of HIF-1α compared to shams or Hextend-treated animals, differences in signaling events resulted in very different outcomes for the two HBOCs. ααHb-treated brain tissue showed significant neuronal damage, measured as apoptosis. This was in stark contrast to the protection seen with MP4OX, apparently due to recruitment of Akt and neuronal specific HIF-1α pathways.