Effects of hyperbaric oxygen therapy on the healing of thermal burns and its relationship with ICAM-1: A case-control study

Key pathways and genes that are altered during treatment with hyperbaric oxygen in patients with sepsis due to necrotizing soft tissue infection (HBOmic study)

BACKGROUND

For decades, the basic treatment strategies of necrotizing soft tissue infections (NSTI) have remained unchanged, primarily relying on aggressive surgical removal of infected tissue, broad-spectrum antibiotics, and supportive intensive care. One treatment strategy that has been proposed as an adjunctive measure to improve patient outcomes is hyperbaric oxygen (HBO2) treatment. HBO2 treatment has been linked to several immune modulatory effects; however, investigating these effects is complicated due to the disease's acute life-threatening nature, metabolic and cell homeostasis dependent variability in treatment effects, and heterogeneity with respect to both patient characteristics and involved pathogens. To embrace this complexity, we aimed to explore the underlying biological mechanisms of HBO2 treatment in patients with NSTI on the gene expression level.

METHODS

We conducted an observational cohort study on prospective collected data, including 85 patients admitted to the intensive care unit (ICU) for NSTI. All patients were treated with one or two HBO2 treatments and had one blood sample taken before and after the intervention. Total RNAs from blood samples were extracted and mRNA purified with rRNA depletion, followed by whole-transcriptome RNA sequencing with a targeted sequencing depth of 20 million reads. A model for differentially expressed genes (DEGs) was fitted, and the functional aspects of the obtained set of genes was predicted with GO (Gene Ontology) and KEGG (Kyoto Encyclopedia of genes and Genomes) enrichment analyses. All analyses were corrected for multiple testing with FDR.

RESULTS

After sequential steps of quality control, a final of 160 biological replicates were included in the present study. We found 394 protein coding genes that were significantly DEGs between the two conditions with FDR < 0.01, of which 205 were upregulated and 189 were downregulated. The enrichment analysis of these DEGs revealed 20 GO terms in biological processes and 12 KEGG pathways that were significantly overrepresented in the upregulated DEGs, of which the term; "adaptive immune response" (GO:0002250) (FDR = 9.88E-13) and "T cell receptor signaling pathway" (hsa04660) (FDR = 1.20E-07) were the most significant. Among the downregulated DEGs two biological processes were significantly enriched, of which the GO term "apoptotic process" (GO:0006915) was the most significant (FDR = 0.001), followed by "Positive regulation of T helper 1 cell cytokine production" (GO:2000556), and "NF-kappa B signaling pathway" (hsa04064) was the only KEGG pathway that was significantly overrepresented (FDR = 0.001).

CONCLUSIONS

When one or two sessions of HBO2 treatment were administered to patients with a dysregulated immune response and systemic inflammation due to NSTI, the important genes that were regulated during the intervention were involved in activation of T helper cells and downregulation of the disease-induced highly inflammatory pathway NF-κB, which was associated with a decrease in the mRNA level of pro-inflammatory factors.

TRIAL REGISTRATION

Biological material was collected during the INFECT study, registered at ClinicalTrials.gov (NCT01790698).

Correlation analysis of HIF-1α and Ca15-3 in response to neoadjuvant chemotherapy in locally advanced breast cancer: A cohort study in Indonesia

BACKGROUND

Breast cancer (BC) is the most common cancer among women worldwide and a leading cause of death in Indonesia. The primary treatment of locally advanced BC is neoadjuvant chemotherapy (NAC). The rapid proliferation of tumor cells in a neoplastic microenvironment is largely due to hypoxia, which also encourages the development of chemoresistant BC. The master regulator of the hypoxia response is hypoxia-inducible factor-1α (HIF-1α). The response evaluation criteria in solid tumors (RECIST) is an objective response metric that demonstrates the efficacy of a NAC based mostly on the size of the tumor. Ca15-3 is the protein product of the MUC1 gene and is the most widely used serum marker in BC. The purpose of this study is to investigate the relationship between HIF-1α and RECIST and between Ca15-3 and RECIST and to assess the relationship among all of them in BC.

METHODS

This observational study used the prospective cohort method included 11 patients with histopathologically confirmed BC, specifically invasive ductal carcinoma. We evaluated the changes in HIF-1α and Ca15-3 serum levels using ELISA and measured tumor lesions with RECIST. The procedure was carried out twice. Serum levels were measured at baseline, and after receiving two cycles of NAC (5 weeks).

RESULTS

Among the 11 patients included in this study, HIF-1α, Ca15-3, and RECIST decreased significantly after NAC. The changes in RECIST correlated with Ca15-3: each unit decrease in RECIST score was associated with a 0.3-unit decrease in Ca15-3 levels (p = 0.019).

CONCLUSIONS

There was a decrease in HIF-1α, followed by a decrease in Ca15-3 and RECIST in response to chemotherapy. There was a statistically significant correlation between Ca15-3 and response to chemotherapy. This study evidences the relationship between factors that shape the local tumor microenvironment.

Is There a Place for Hyperbaric Oxygen Therapy?

Hyperbaric oxygen therapy (HBOT) involves treating patients by providing 100% oxygen through inhalation while inside a treatment pressurized chamber. The oxygen acts as a drug and the hyperbaric chamber as the dosing device. The effect of hyperbaric hyperoxia is dose dependent and, therefore, treatment depth and duration are important when considering its use. HBOT can either be the primary method of treatment or used adjunctively to medications or surgical techniques. The underpinning physiology is to bring oxygen-rich plasma to hypoxic tissue, preventing reperfusion injury, strengthening immune responsiveness, and encouraging new collagen deposition as well as endothelial cell formation.

Correlation between Radiological Images and Histopathological Type of Meningioma: A Cohort Study

Background

Histologically affirmed meningiomas represent 37.6% of all essential central nervous system tumors and half of all types of critical central nervous system tumors. This study compares computed tomography (CT) scans of the head with histological findings to establish the characteristics of different types of meningiomas observed in eastern Indonesia.

Methods

This prospective study evaluated 224 patients by examining the correlation between histological and CT data collected from January to December 2020 at Wahidin Sudirohusodo Hospital, Makassar, Indonesia. We assessed data including the location of pre- and post-contrast CT scans, number of tumors, margin, density, contrast enhancement, bony reaction, calcification, and perifocal edema. Patients underwent biopsies followed by an examination of the anatomical pathology tissue.

Results

The female-to-male ratio of participants was 4.2 to 1, and the highest incidence was observed in participants of both genders aged 40-60 years. The most common meningioma subtype was meningothelial, while the most commonly observed locations involved the convexity and sphenoid regions. Most meningiomas had well-defined margins on CT imaging: 54.5% of patients exhibited isodense lesions on pre-contrast scans, and 64.7% exhibited high-contrast enhancement. Bone destruction developed in 4.1% of patients, while hyperostosis was observed in 17.4%, and calcification was present in 10.3% of the participants. Edema was identified in 65.2% of cases, of which moderate edema was the most common manifestation.

Conclusion

Meningioma should be highly suspected in female patients aged 40-60 with isodense lesions on pre-contrast CT scans and high-contrast enhancement on post-contrast CT scans. Meningiomas were primarily classified as convexity meningiomas with well-defined margins. The presence of hyperostosis, calcification, and brain edema supported the meningioma diagnosis.

Hyperbaric oxygen therapy in low extremity trauma: A case series

Introduction

Trauma to the extremities is a common major health problem that requires special attention because it can have a dangerous impact on both the viability of the limb and the patient's life. Hyperbaric oxygen therapy is an alternative therapy hypothesized to improve the prognosis in lower extremity trauma.

Case presentation

We present a series of 7 cases of lower extremity trauma treated with hyperbaric oxygen therapy: soft tissue loss, neglected chronic burn injury, high-voltage electrical burn, gas gangrene, crush injury, chemical burn, and excoriation with skin loss.

Discussion

Hyperbaric oxygen therapy involves giving 100% oxygen in a chamber at pressures above atmospheric pressure (2–3 atm absolute [ATA]). It can increase oxygen delivery to peripheral tissues with vascular compromise, cytogenic and vasogenic edema, and cellular hypoxia caused by limb trauma.

Conclusion

Hyperbaric oxygen therapy has many benefits in lower extremity trauma for wound recovery, preventing complications, and helping patients return to daily activities.

•

Hyperbaric oxygen therapy is an alternative therapy believed to improve the prognosis in cases of lower extremity trauma.

•

We present 7 cases: soft tissue loss, chronic burn, high-voltage burn, gangrene, crush, chemical burn, and excoriation.

•

Hyperbaric oxygen therapy has benefits for wound recovery, preventing complications, and return to daily activities.

Doxorubicin induced immune abnormalities and inflammatory responses via HMGB1, HIF1-α and VEGF pathway in progressive of cardiovascular damage

Background

Doxorubicin (DOX) is a commonly used treatment for cancer and the mechanism of DOX-induced cardiomyocyte damage in cardiovascular disease is not fully understood. High-mobility group box 1 (HMGB1), strong induce proinflammatory cytokines via damage associated molecular pattern (DAMP) which its interaction with the receptor of advanced glycation end products (RAGE), that affect cytokine release, and angiogenesis via the role of HMBG1, HIF-1α and VEGF as an important regulator in these cardiac failure processes. Hypoxia-inducible factor-1α (HIF-1α) is plays an important role in the cellular response to systemic oxygen levels of cells and VEGF is an angiogenic factor and can stimulate cellular responses on the surface of endothelial cells will be described

Objective

The aim of this article is to comprehensively review the role of HMGB1, HIF-1α, and VEGF in DOX-induced Cardiovascular Disease and its molecular mechanisms.

Methods

The data in this study were collect by search the keyword combinations of medical subject headings (MeSH) of “HMGB1”, “HIF-1 α”, “VEGF”, “DOX” and “Cardiovascular disease” and relevant reference lists were manually searched in PubMed, EMBASE and Scopus database. All relevant articles in data base above were included and narratively discussed in this review article.

Results

Several articles were revealed that molecular mechanisms of the DOX in cardiomyocyte damage and related to HMGB1, HIF-1α and VEGF and may potential treatment and prevention to cardiovascular disease in DOX intervention.

Conclusion

HMGB1, HIF-1α and VEGF has a pivotal regulator in DOX-induce cardiomyocyte damage and predominantly acts through different pathways. The role of HMGB1 in DOX-induced myocardial damage suggests that HMGB1 is a mediator of DOX-induced damage. In addition, DOX can inhibit HIF-1α activity where DOX can decrease HIF-1α expression and HIF-1α is also responsible for upregulation of several angiogenic factors, including VEGF. VEGF plays an important role in angiogenesis and anti-angiogenesis both in vitro and in vivo and reduces the side effects of DOX markedly. In addition, the administration of anti-angiogenesis will show an inhibitory effect on angiogenesis mediated by the VEGF signaling pathway and triggered by DOX in cells.

•

The effect of Doxorubicin (DOX) induced cardiovascular damage via several pathways.

•

Cardiovascular damage can involve HMGB1, HIF-1α, and VEGF.

•

HMGB1, HIF-1α, and VEGF as a pivotal regulator in DOX-induce cardiomyocyte damage.

•

HMGB1, HIF-1α, and VEGF in cardiovascular diseases will be predominantly acting through different pathways.

Oxygenation therapies for improved wound healing: Current trends and technologies

Degree of oxygenation is one of the important parameters governing various processes, including cell proliferation, angiogenesis, extracellular matrix production, and even combating the microbial burden at the wound site, all...

Fostering a faster post-operative wound healing process with hyperbaric oxygen therapy in a rare case of squamous odontogenic tumor

Introduction

The surgical removal of an intraoral tumor and preventing intraoral wound dehiscence are constant challenges faced by surgeons today. Hyperbaric oxygen therapy (HBOT), the inhalation of 100% oxygen at a greater atmospheric pressure, is often used in cases of wounds to induce a faster wound healing process, alongside other treatment modalities. We report a rare case of squamous odontogenic tumor (SOT) treated with HBOT after being surgically removed to foster an accelerated wound recovery.

Case presentation

A 39-year-old Asian male presented with an intraoral 3 × 4 cm tumor, accompanied by acute pain on the maxillary region. Biopsy results showed a solid, brown parenchyma with islands of mature squamous epithelial cells, confirming the diagnosis of an SOT. An intraoral surgical approach was performed to remove the tumor. The patient was then treated with prophylactic antibiotics and 5 consecutive, daily sessions of HBOT at 2.0 ATA as an adjuvant therapy. No further complaints and no abnormalities were found at the 2-week follow-up evaluation.

Discussion

In our case of SOT, HBOT plays a role to inhibiting the bacterial growth which could lead to post-operative wound infections. A number of studies have incorporated HBOT as an adjuvant therapy for post-operative intra oral wounds which has resulted in minimal wound complications.

Conclusion

The use of HBOT as an adjunctive therapy in managing possible wound complications after the resection of an intraoral tumor enables a faster angiogenesis process, reduces tissue hypoxia and minimizes the risk of post-operative wound infections; hence fostering the wound healing process.

•

Squamous odontogenic tumors (SOT) are very rare tumors.

•

SOTs are local infiltrating lesion described as aggressive, odontogenic, and epithelial.

•

HBOT can be used as supportive therapy in SOT.

•

Hyperbaric oxygen therapy (HBOT) can accelerate wound healing and minimize the possibility of postoperative infection.

Hyperbaric Oxygen Therapy for Reconstructive Urology Wounds: A Case Series

INTRODUCTION

Hyperbaric oxygen therapy (HBOT) has been applied to urological wound healing because it reduces inflammation, facilitates angiogenesis through endothelial proliferation, stimulates fibroblast, lymphocyte, and macrophage activity, and exerts bactericidal effects. Thus, we present a case series of reconstructive urology wounds treated adjunctively with HBOT.

CASE REPORT

Here, we present the cases of eight patients with urology wounds who underwent different forms of surgical reconstruction. Three patients received penile shaft silicone fluid injection with repeated infection, successful excision of a siliconoma mass, and defect closure with a full-thickness skin graft. One patient had hypospadias and multiple post-closure fistulae. Two patients had bilateral keystone flaps (post total penectomy, orchidectomy, perineotomy, and penile tumors) closed with a split-thickness skin graft (STSG). Two patients had Fournier's gangrene in their genital area, for which the wound was debrided and then closed with a STSG. All patients received HBOT after surgery with satisfying results.

CONCLUSION

HBOT promotes wound healing and improves graft integration in patients undergoing urological reconstructive surgery.

The effect of hyperoxia on the hemostasiological status of severely burned patients

The state of the hemostasis system was studied in 9 patients of the middle age group (44 ± 9.94 years) who received thermal trauma on an area of more than 32% (49.4 ± 18.3) of the body surface, accompanied by the development of burn shock. The standard therapy for burn injury was supplemented with HBO sessions. Treatment with hyperbaric oxygen was carried out in pressure chambers BLKS-307, BLKS-307/1. The state of the coagulation, anticoagulant and fibrinolytic links of the hemostasis system, as well as the viscoelastic properties of the blood, were assessed immediately before the HBO session and immediately after it. The total number of comparison pairs was 45. Under the influence of HBO therapy, there was an increase in the activity of antithrombin III (ATIII), protein C (PrS) and a decrease in the viscoelastic properties of blood (p <0.05). Positive deviations in the values of ATIII, Pr C, von Willebrand factor, APTT, prothrombin and thrombin time, fibrinogen, factor XIII, XIIa-dependent fibrinolysis, D-dimers and thromboelastography parameters were revealed. The maximum frequency of their occurrence was recorded for ATIII (95%), the minimum - for the D-dimer (62%). After HBO procedures, undesirable deviations of the hemostatic system parameters were also noted. They were chaotic, were compensated by an increase in the activity of physiological anticoagulants and were not accompanied by complications of a thrombogenic nature. Thus, conducting HBO therapy sessions in the acute period of burn disease increases the activity of physiological anticoagulants and stabilizes the viscoelastic properties of blood. There is a high frequency of occurrence of positive effects of hyperoxia on the components of the hemostasis system. The identification of its undesirable effects indicates the need to monitor the state of the hemostasis system during HBO procedures.

Therapeutic Outcome of Burn Patients Treated With Hyperbaric Oxygen

Amongst various interventions for burns and inhalation injuries, hyperbaric oxygen therapy (HBOT) has recently been widely integrated as an adjunctive management of care due to its therapeutic properties in reducing tissue hypoxia, pathological inflammation, and augmenting neovascularization. However, the limitation of human clinical trials and data undermines its efficacy to be implemented as an adjunctive therapeutic modality in burns. The purpose of the literature review is to determine the efficacy of HBOT as an adjunct to standard management in burns. A review of the literature was done by searching PubMed, Cochrane, Medline, EMBASE, and Google Scholar for papers addressing the comparison of therapeutic outcomes between HBOT and non-HBOT in burns. Current research findings are conflicting, and the use of HBOT as an adjunct in burns management is still controversial. Therefore there is still a need for more data and research on the therapeutic benefits of HBOT in burn management.

Predicting hyperbaric oxygen therapy success using the decision tree approach

Introduction

Hyperbaric oxygen therapy (HBOT), a procedure that involves the patient inhaling 100% oxygen gas under pressure, is currently used as an adjunctive treatment option for certain inflammatory conditions. HBOT can improve wound healing by increasing the rate of angiogenesis in injured tissue by increasing levels of vascular endothelial growth factor (VEGF). VEGF causes re-epithelialization, the migration of endothelial cells, and the formation of granulation tissue, which are involved in the wound healing process.

Methods

This study contains secondary data analyses of information previously collected in two separate studies, each concerning the effects of HBOT on diabetic foot ulcers and crush injury fractures at Prof. Dr. R. D. Kandou Hospital Manado and Siloam Hospital Manado from 2019 to early 2020.

Results

Based on the classification tree analysis, the predictors of HBOT success were leukocytes level (34%), platelet count (32%), and age (26%). The conditional inference tree analysis also indicated significant leukocyte levels, age, and platelet counts (p < 0.001), with which the interpretation of these results was the same as the classification tree analysis method. The results obtained from the random forest analysis revealed that the mean value of Gini reduction for leukocytes (207.3), platelets (110.2), age (97.9), and hemoglobin (57.9) can be used as indicators of successful HBOT. These three methods support that age, leukocytes, and platelets are determinants of HBOT success, while hemoglobin levels were only significant in one analysis method. Therefore, a new, proposed algorithm containing these factors was assembled from the results of this study.

Conclusion

HBOT cannot be separated from specific variables that contribute to and can predict its success.

Systemic lidocaine administration influences NF-kβ gene expression, NF-kβ and TNF- α protein levels on BALB/c mice with musculoskeletal injury

Background

The immune system can produce various inflammatory mediators to protect the body from stress and surgical trauma. However, this excessive inflammatory response will interfere with the body's immune system, causing systemic inflammatory response syndrome and multi-organ failure if allowed to continue. Lidocaine as an anti-inflammatory is used to treat surgical pain and pain arising from the disease process and treat ventricular arrhythmias. This study aims to prove the efficacy of systemic lidocaine injection as an anti-inflammatory drug in BALB/c mice with sterile musculoskeletal injuries.

Methods

This study used a prospective experimental laboratory study on experimental animals of BALB/c mice using a simple randomized design. Sixteen adult white BALB/c mice (male, healthy, 10-12 weeks old, 35-40 g body weight, and no disability) were selected and randomly divided into two groups: the group given lidocaine (2 mg/kg body weight) and a group that was given sterile distilled water. NF-kβ and TNF-α protein levels were detected by ELISA, while mRNA expression of NF-kβ was analyzed and determined by quantitative real-time PCR.

Results

Musculoskeletal injury significantly increased the expression of both mRNA and protein levels of NF-kβ and TNF-α protein level. In addition, the NF-kβ (protein and mRNA) and TNF-α (protein) levels in rats experiencing inflammation due to musculoskeletal injury were significantly decreased in the lidocaine group (p < 0.001).

Conclusions

The administration of systemic lidocaine injection was able to inhibit the expression of mRNA NF-kβ, the protein levels of NF-kβ, and protein levels of TNF-α in mice with musculoskeletal injuries.

Focused ultrasound ablation of a large canine oral tumor achieves efficient tumor remission: a case report

Purpose: Oral cancers are one of the commonly diagnosed tumors worldwide in human and veterinary patients. Most oral cancers are surgically resected; however, obtaining an adequate margin of safety in patients without compromising their quality of life is often challenging. Herein, we investigated the ability of non-invasive focused ultrasound (FUS) to thermally ablate a biopsy confirmed canine oral cancer. Materials and Methods: A male canine patient with a large neurilemmoma (schwannoma) mass on the left maxilla, with evidence of thinning and loss of alveolar bone and pressure necrosis, was treated with FUS ablation instead of the traditional maxillectomy procedure. FUS ablations were performed in three sessions over three weeks. Tumor remission was determined with computed tomography and histopathological examination of the treated site. Additionally, the anti-tumor immune effects of FUS were assessed by flow cytometry analysis of blood and tumor samples. Results: Complete tumor remission was noted at the treated site. Treatment related adverse events were primarily thermal burns of the buccal mucosa, which were managed with periodic hyperbaric oxygen therapy and surgical coverage of the underlying exposed bones with gingival flaps. Enhanced proliferation of adaptive immunity cells (e.g., T-cells) was observed in tumor and blood samples. Conclusion: Our limited investigation in a canine oral cancer patient suggests that FUS may avoid the need for large-scale resection of bony tissues, thus potentially improving quality of life.

Correlation of interleukin-6 and C-reactive protein levels in plasma with the stage and differentiation of colorectal cancer: A cross-sectional study in East Indonesia

Introduction

Tumors most often develop due to inflammatory factors, including inflammatory cells that produce cytokines and cytotoxic mediators that can stimulate malignant transformation. Knowing that interleukin-6 (IL-6) and C-reactive protein (CRP) factor into the development of colorectal cancer (CRC), we aimed to assess IL-6 and CRP's relationship with the stage and differentiation of CRC.

Methods

In a sample of 46 patients with CRC, as confirmed by histopathological examination, plasma levels of IL-6 and CRP were measured from peripheral venous blood samples before surgery and examined using enzyme-linked immunosorbent assay.

Results

Most patients were male (63.0%) and at least 50 years old (73.9%). A positive correlation emerged between stage of CRC and both plasma IL-6 (r = 0.396, p = .003) and CRP (r = 0.376, p = .005) levels, which the Kruskal–Wallis test indicated were highest in stage IV (IL-6: median = 25.80, p = .019; CRP: median = 34.10, p = .040). Plasma IL-6 levels (median = 25.80, p = .019) were higher in well-differentiated CRC, whereas plasma CRP levels (median = 34.10, p = .040] were higher in poorly differentiated tissue. Linear plotting revealed a linear relationship between plasma IL-6 and plasma CRP levels in patients with CRC.

Conclusion

Because the stage of CRC significantly correlates with plasma IL-6 and CRP levels, IL-6 and CRP can serve as diagnostic factors in assessing the progress and prognosis of CRC.

•

Interleukin-6 (IL-6) and C-reactive protein (CRP) levels can indicate inflammation.

•

Chronic inflammation affects the progression of colorectal cancer (CRC).

•

An association exists between IL-6, CRP, and stage of CRC.

•

IL-6 and CRP can be diagnostic factors in assessing CRC's progression.

Hyperbaric Oxygen Therapy Attenuates Burn-Induced Denervated Muscle Atrophy

Background: Neuronal apoptosis and inflammation in the ventral horn of the spinal cord contribute to denervated muscle atrophy post-burn. Hyperbaric oxygen therapy (HBOT) exerts anti-inflammation and neuroprotection. Furthermore, hypoxia-inducible factor (HIF)-1α has been reported to promote inflammation and apoptosis. We investigated the therapeutic potential of HBOT and the role of HIF-1α post-burn. Methods: Sprague-Dawley rats were divided into three groups: a control group, an untreated burn group receiving burn and sham treatment, and a HBOT group receiving burn injury and HBOT. The burn injury was induced with 75ºC ± 5ºC at the right hindpaw. HBOT (100% oxygen at 2.5 atmosphere, 90 min/day) and sham HBOT (21% oxygen at 1 atmosphere, 90 min/day) was started on day 28 after burn injury and continued for 14 treatments (days 28-41). Incapacitance (hind limb weight bearing) testing was conducted before burn and weekly after burn. At day 42 post-burn, the gastrocnemius muscle and the spinal cord ventral horn were analyzed. Results: HBOT improved burn-induced weight bearing imbalance. At day 42 post-burn, less gastrocnemius muscle atrophy and fibrosis were noted in the HBOT group than in the untreated burn group. In the ventral horn, HBOT attenuated the neuronal apoptosis and glial activation post-burn. The increases in phosphorylated AKT/mTOR post-burn were reduced after HBOT. HBOT also inhibited HIF-1α signaling, as determined by immunofluorescence and western blot. Conclusions: HBOT reduces burn-induced neuronal apoptosis in the ventral horn, possibly through HIF-1α signaling.