**1. Introduction**

Hyperbaric oxygen therapy (HBOT) is a state-of-the-art medical treatment, which has advantageous therapeutic effects in wide range of pathologies. Despite its high therapeutic potential, its availability is still restricted, and the use of hyperbaric oxygen requires significant organizing steps in most health care systems. Thus, emergent or urgent utilization is very limited.

© 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2018 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

HBOT may be used by pulmonologists, internal medicine specialists, surgeons and obstetrics as well. Evidence-based medicine recommends its use in decompression sickness to protect severe lung injury and to enhance recompression [1]. Carbon monoxide intoxication is another severe, life-threatening emergency scenario, where HBOT enhances CO discard and saves lives [2]. HBOT is recommended in severe carbon monoxide intoxication when conservative ventilation techniques are not efficient to eliminate CO, linked with hemoglobin. These time-sensitive conditions shout for widely available HBOT; however, in low-income countries, its use is still optional.

cell culture conditions for short- or long-term maintenance. Cells are usually exposed to 100% oxygen in these chambers; however, some studies comprise 98% oxygen and 2%

replacing oxygen with nitrogen in cell culture incubators. Mostly, 5 or 10% oxygen levels are investigated in cell culture studies. The same cell culture media and culturing surface

More detailed studies comprise direct quantification of oxygen consumption levels in cellular cultures. These data provide information also on metabolomics status, indirectly on cellular energy homeostasis and metabolic activity of the investigated cultures [14]. Planning studies with direct measurement of oxygen consumption levels enable investigation of cellular func-

It is widely accepted that endothelial cells play a key role in a number of important physiological conditions and in pathological steps as well. Endothelial functions comprise regulation of blood flow via regulating vascular tone, vasodilation or vasocontraction. Furthermore, endothelial cells and their expressed factors are cornerstones in initiating or inhibiting platelet activation and blood clotting. Next role is inflammatory mechanisms, white blood cell rolling and diapedesis. Furthermore, special sites of endothelial barriers are the blood–brain barrier, the renal glomeruli and the portal endothelial cells. All these sites have complex barrier and gating functions. All endothelial functions can be modeled *in vitro* and may be investigated

Additionally, endothelial cells regulate and are involved in embryonic vasculogenesis and somatic angiogenesis as well. Neo-angiogenesis is a key pathological step in tumorous proliferation and metastases development as well. To fulfill these tasks, endothelial cells produce and secrete wide range of angiogenesis-related proteins and small molecules. These may be

Endothelial cells are keen to proliferate *in vitro*, wide range of cell lines and primary cultures are also available commercially. Widely used endothelial lines *in vitro* are the human umbilical vein endothelial cells (HUVEC), the human coronary arterial endothelial cell (HCAEC), capillary endothelial cells and others from human and animal sources as well. Arterial and venous endothelial cells can be divided via cell surface markers and genotype properties. Arterial and venous endothelial phenotypes differ also *in vitro* because the arterial and venous vessels have largely different functional tasks *in vivo*. As an example, arterial endothelial cells are the major regulators of peripheral vascular resistance, while venous capillary endothelium is the localization for white blood cells' rolling and diapedesis [15]. Furthermore, venous endothelial junctions are thinner, and vessels have greater compliance. Interestingly, arterial and venous plasticity exists *in vitro*, for example, HUVEC surprisingly express arterial markers *in vitro* [16].

and modified via changing oxygen levels or by application of HBOT for cultures.

investigated on gene expression or on the translational (protein) level.

for normal or low oxygen (hypoxic) conditions. For normoxic treatment (21% O<sup>2</sup>

can be used in altered oxygen levels, HBOT and in normal conditions [12, 13].

cell culture conditions are suitable (5% CO<sup>2</sup>

tion keep with oxygen consumption.

**2.2. Endothelial cells, angiogenesis**

 [11]. The level of hyperbaric pressure varies between 1.5 and 3 atmospheres absolute. Compression and decompression times may be applied according to focus of interest and study protocol. Standardization of basic research protocols is key to move the latest investigations with HBOT to clinical translation. Besides HBOT, oxygen levels may be modified

), general

69

, 95% normal air). Hypoxia can be induced by

http://dx.doi.org/10.5772/intechopen.75378

Cell Culture Effects of Altered Oxygen Levels and Hyperbaric Treatment *In Vitro*

CO2

Interestingly, HBOT proved to be effective in wound healing applications, for example, ulcers, scar formation after burn injury or plastic surgery operations [3]. Cardiovascular diseases are the leading cause of death in industrialized countries. Peripheral atherosclerotic diseases and diabetes often go side-by-side. Additionally, venous circulation may also be impaired in these patients. Considering the high burden of cardiovascular diseases, number of patients suffering from not-healing ulcers is constantly increasing. Furthermore, retinal arterial stenosis severely impairs vision, in which condition HBOT is on the palette of treatment applications. Wound healing and scar formation in plastic surgery have a huge esthetic impact and because of this, HBOT draws significant attention from cosmetic companies as well [5, 6].

Next argument for HBOT is that recent publications suggest its beneficial role in neurodegenerative diseases, such as multiple sclerosis [6]. Latest treatment options, for instance mesenchymal stem cell (MSC) implantation, also comprise hyperbaric treatment or preconditioning. Therapeutic potency of MSC improves after hyperbaric modification [8–10].

Other clinical applications of HBOT are severe anemia, crush injury and gas embolism, necrotizing fasciitis, osteomyelitis, brain abscesses and delayed radiation injury. Evidence is lacking in application for Parkinson's disease and autism.

*In vitro* models of HBOT utilize wide range of cell lines and tissue cultures [9]. HBOT can be combined with modification of cell culture circumstances, for example, adding active drugs, small molecules, growth factors or signaling drives, according to the focus of interest of the study protocol. Mostly, hyperbaric treatments are applied in parallel with normoxic and hypoxic conditions to implicate useful comparative data. Importantly, *in vitro* models have severe limitations as they are not capable to model the whole pathology and tissue characteristics treated with HBOT. *In vitro* models usually follow the clinical protocols of HBOT, regarding timing and incubation periods [10]. In this chapter, altered oxygen levels of human endothelial cell cultures, fibroblasts cultures, human MSC and pluripotent stem cell (PSC) cultures will be discussed, mirroring the effects of HBOT on angiogenesis, blood clotting, wound healing and future cell therapy/tissue engineering issues.
