Strain and tumour specific variations in the effect of hypoxia on osteopontin levels in experimental models

Association between decreased osteopontin and acute mountain sickness upon rapid ascent to 3500 m among young Chinese men

BACKGROUND

Hypoxia causes oxidative stress and a decrease in osteopontin (OPN) in rats; however, little is known about the change in OPN in lowlander humans during hypobaric hypoxia. We explore the role of the predicted decrease in plasma OPN levels in humans upon high-altitude exposure and its relationship with acute mountain sickness (AMS), as well as superoxide dismutase (SOD) and malondialdehyde (MDA).

METHODS

Before and during acute altitude exposure, 261 men's plasma OPN, SOD, MDA, heart rate and pulse oximeter saturation (SpO2) were measured. AMS as assessed using the Lake Louise score (LLS) was defined as headache with a total LLS ≥3. Subjects were divided into AMS-0 (non-AMS subjects), mild AMS (headache with total LLS = 3 or 4) and severe AMS groups (headache with total LLS ≥5).

RESULTS

At 600 m, no difference in plasma OPN, SOD and MDA was observed between groups. At 3500 m, plasma OPN in severe AMS group was significantly decreased as compared with 600 m. Plasma SOD showed a tendency to decrease during altitude exposure. The opposite trend was observed for plasma MDA. Correlation analysis showed that total LLS was significantly correlated with OPN (ρ = -0.247, P < 0.001) and SOD (ρ = -0.224, P < 0.001). OPN showed significant correlation with SOD (r = 0.235, P < 0.001). Multivariate logistic regression analysis showed that higher plasma OPN was a protective factor for AMS [adjusted odds ratio (OR) 0.924, 95% confidence interval (CI) 0.884-0.966, P < 0.01].

CONCLUSION

Our results suggest that decreased plasma OPN is correlated with AMS, and oxidative stress may be implicated in this phenomenon. Decreased plasma SOD is also correlated with AMS.

Identifying pH independent hypoxia induced genes in human squamous cell carcinomas in vitro

BACKGROUND

Genes upregulated by low oxygen have been suggested as endogenous markers for tumor hypoxia. Yet, most of the genes investigated have shown inconsistent results, which have led to concerns about their ability to be true hypoxia makers. Previous studies have demonstrated that expression of hypoxia induced genes can be affected by extracellular pH (pH(e)).

METHODS

Five different human cell lines (SiHa, FaDu(DD), UTSCC5, UTSCC14 and UTSCC15) were exposed to different oxygen concentrations and pH (7.5 or 6.3), and gene expression analyzed with microarray (Affymetrix - Human Genome U133 Plus 2.0 Array).

RESULTS

An analysis of two of the cell lines using SAM identified 461 probesets that were able to separate the four groups "Normal oxygen, normal pH", "Low oxygen, normal pH", "Normal oxygen, low pH" and "Low oxygen, low pH". From here it was possible to identify a fraction of probesets induced at low oxygen independent of pH in these two cell lines, this fraction included HIG2, NDRG1, PAI1 and RORA. Further verification by qPCR highlighted the necessity of using more cell lines to obtain a robust gene expression profiles. To specifically select pH independent hypoxia regulated genes across more cell lines, data for FaDu(DD), UTSCC5, UTSCC14 and UTSCC15 were analyzed to identify genes that were induced by hypoxia in each cell line, where the induction was not affected by low pH, and where the gene was not significantly induced by low pH alone. Each cell line had 65-122 probesets meeting these criteria. For genes to be considered as target genes (hypoxia inducible pH independent), genes had to be present in three of four cell lines.

CONCLUSION

The result is a robust hypoxia profile unaffected by pH across cell lines consisting of 27 genes. This study demonstrates a way to identify hypoxia markers by microarray, where other factors in the tumor microenvironment are taken into account.

The impact of hypoxia on the activity of lactate dehydrogenase in two different pre-clinical tumour models

AIM

To investigate the direct relationship between tumour hypoxia and lactate dehydrogenase (Ldh) levels in serum and tumour in two different pre-clinical murine models.

MATERIALS AND METHODS

Experiments were performed in CDF1 or C3H/ Km mice implanted with a C3H mammary carcinoma and SCCVII squamous cell carcinoma, respectively. Low oxygen breathing for 1-72 h was used to increase tumour hypoxia. Ldh activity was measured in the serum and tumour cytosole with a colorimetric method. Tumour Ldha mRNA levels were assessed with RT-PCR. RESULTS; The serum Ldh in non-tumour bearing CDF1 mice and C3H/km mice was 10.592 U/ml and 1292 U/ml, respectively. For C3H mammary carcinoma bearing mice, a positive correlation between tumour volume and tumour and serum Ldh was found. Tumour Ldh in SCCVII carcinomas also increased with increasing tumour volume, but no volume dependence of serum Ldh was found. Low oxygen breathing caused a 2-3 fold increase in tumour Ldha mRNA in both tumour models. In C3H mammary carcinoma bearing mice, serum and tumour Ldh significantly increased after 48 and 72 hours of hypoxia, respectively. Low oxygen breathing did not change serum and tumour Ldh in SCCVII carcinoma bearing mice. Reoxygenation for 4 or 24 hours had no additional effect on Ldh activity in any of the models.

DISCUSSION

Serum Ldh activity can be a marker for tumour burden in certain types of cancer. The relationship between serum and tumour Ldh and tumour hypoxia has not been confirmed. However, Ldha mRNA may be a potential new marker of tumour hypoxia and should be further investigated.

Proteomic analysis of gene expression following hypoxia and reoxygenation reveals proteins involved in the recovery from endoplasmic reticulum and oxidative stress

BACKGROUND AND PURPOSE

Human tumors are characterized by large variations in oxygen concentration and hypoxic tumors are associated with poor prognosis. In addition, tumors are subjected to periodic changes in oxygenation characterized by hypoxia followed by reoxygenation. Cellular adaptation to hypoxia is well documented, nevertheless little is known about adaptive mechanisms to reoxygenation. Here, we investigate the changes in protein expression during reoxygenation using proteomics.

MATERIALS AND METHODS

HeLa cervix carcinoma cells were exposed to 4h of hypoxia (<0.01% O(2)) followed by 1h of reoxygenation. The cellular proteome was examined using 2D gel electrophoresis coupled with mass spectrometry. Validation and investigation of the underlying basis for induced protein expression was investigated using Western blot analysis and quantitative RT-PCR.

RESULTS

We identified proteins involved in several cellular processes that are responsible for regulating RNA metabolism, protein synthesis and degradation, including ribosomal protein P0, VCP/p97 and FUSE binding protein 2.

CONCLUSIONS

Our results suggest that these newly identified proteins function in pathways that may assist in the recovery of ER stress and protein synthesis during reoxygenation. These proteins may thus be important determinants of the behaviour and survival of tumor cells to transient hypoxic exposures.

Hypoxia induced expression of endogenous markers in vitro is highly influenced by pH

BACKGROUND

Genes such as carbonic anhydrase IX (Ca9), glucose transporter 1 (Glut1), lactate dehydrogenase A (LDH-A), osteopontin (OPN) and lysyl oxidase (LOX) have been suggested as hypoxic markers, but inconsistent results suggest that factors other than oxygen influence their expression. The current study is a detailed investigation using a range of pH values from 6.3 to 7.5 in two human cell lines to establish the pH dependency of hypoxia induced gene expression.

METHODS

Human tumour cell lines (uterine cervix squamous cell carcinoma (SiHa) and pharyngeal squamous cell carcinoma [FaDu(DD)]) were used. Hypoxia was induced by gassing cells in airtight chambers with various oxygen concentrations (21%, 1%, 0.1%, 0.01% and 0%) for up to 24h. The media were titrated to a range of pH values (7.5, 7.0, 6.7, 6.5 and 6.3). Gene expression was determined by real-time PCR.

RESULTS

In both SiHa and FaDu(DD) cells Ca9 and LOX reached the highest level of expression at 1% oxygen. In FaDu(DD) cells, a pH of 6.5 had a medium suppression effect on the hypoxia induced expression of Ca9. pH 6.3 resulted in severe suppression of expression for Ca9 and LOX in both SiHa and FaDu(DD). Glut1 and LDH-A had a similar expression pattern to each other, with a maximum expression at 0.01% oxygen, in both cell lines. For these genes pH 6.5 and 6.3 changed the expression pattern in SiHa cells. OPN was up regulated at low oxygen in SiHa cells, but was not induced by hypoxia in FaDu(DD) cells.

CONCLUSION

As tumour hypoxia occurs in a deprived microenvironment, other environmental factors, for example low pH, might interact with the effect of low oxygen concentration on gene expression. This study shows that pH in two cell lines has a profound influence on the oxygen dependent induction of certain endogenous hypoxic markers.