TABLE 3.
The effects of IHNT and CHT on aging markers and age-related diseases using cell culture.
| Author, year (ref.) | Targeted conditions | Cell line | Study design | Type of hypoxia | Hypoxia protocol (for cases) | Aging markers | Results | Conclusion | Safety issues |
| Casciaro et al., 2020 | Cellular aging | hAFSCs | Non-RCT | CHT | 1% O2 for 5 weeks up to 8–9 passages. | Stemness properties (mRNA levels of Oct4 upregulation and protein expression of SSEA4) | 1% O2 extends stemness | Low oxygen concentrations might improve the generation of functional hAFSCs for therapeutic use by delaying the onset of cellular aging. | Not reported |
| Proliferative ability | 1% O2 extends proliferative features | ||||||||
| Induction of senescence-associated markers | 1% O2 delays induction of senescence-associated markers. | ||||||||
| Changes in metabolism and resistance to stress | Hypoxic hAFSCs activate a metabolic shift and increase resistance to pro-apoptotic stimuli. | ||||||||
| Osteogenic differentiation | Cells at low oxygen remain capable of osteogenesis for prolonged periods of time | ||||||||
| Damiani et al., 2021 | Skin aging | HDF | Non-RCT | CHT | 5% O2. HDF were passaged at 80% confluence. Cells were serially cultured until enough cells were obtained for all experiments. | Cellular proliferation rate | Increased cell proliferation under 21% O2 compared to 5% O2 | The 21% O2 impose a mild oxidative stress on HDF which accelerates the aging process in culture compared to 5% O2 where the underlying level of oxidative stress is reduced. cells grown under normoxia undergo a “stress-induced premature senescence” when compared to their matched counterparts grown under hypoxia. The modulation of miR-181a to different oxygen tensions and its potential role in altering the expression of antioxidant genes could represent an important molecular event in skin aging. |
Not reported |
| Intracellular ROS | Lower levels of intracellular ROS in cells at 21% O2 compared to those at 5% O2. | ||||||||
| Mitochondrial superoxide anion generation | Higher levels of mitochondrial superoxide anion in cells at 21% O2 compared to at 5% O2 | ||||||||
| CoQ10 level and oxidative status | Total coenzyme Q10 levels decrease with cell passages and increase with oxygen tension. | ||||||||
| Total glutathione (GSH + GSSG) |
Total glutathione levels reduce under Low oxygen tension | ||||||||
| Single and double-strand DNA damage | DNA damage increased under 21% O2 vs. 5% O2. | ||||||||
| β-galactosidase activity, p16, CAT, SOD1, SOD3, MMP1, and COL1A1 genes expression | Higher levels of SOD1 and SOD3, upregulation of MMP1 and downregulation of COL1A1 under 21% O2 vs. 5% O2. | ||||||||
| Minamino et al., 2001 | Vascular disorder | VSMC | Non-RCT | CHT | 1% O2 until 10 passages. | Telomerase activity | Chronic hypoxia can prolong the growth of human VSMC by inducing telomerase activity and telomere stabilization. Hypoxia induced phosphorylation of the telomerase catalytic component (TERT) and sustained high levels of TERT protein expression in VSMC compared to normoxia. | Hypoxic induction of telomerase activity could be involved in long-term growth of VSMC and may thus contribute to human vascular disorders. | Not reported |
| Tantingco and Ryou, 2020 | Ischemic stroke | Mice microglia, EOC20 cells | Non-RCT | IHNT | Three days IHT consisting of 5–8 daily, 5–10 min cycles of hypoxia (3.5–4% O2) with intervening 4-min re-oxygenation. | Cell viability | Intermittent hypoxic training protects the microglia from oxygen–glucose deprivation/re-oxygenation stress. | Due to the effect of intermittent hypoxic training on the microglia phenotype, intermittent hypoxic training could be considered as an effective intervention in the treatment or rehabilitation program for the ischemic stroke victims. | Not reported |
| TLR2 proteins content | The TLR2 protein content was significantly elevated in the oxygen–glucose deprivation and re-oxygenation group, and intermittent hypoxic training lowered it to normoxia level. | ||||||||
| Anti-inflammatory cytokines (IL-10 and IL-4) | IL-10 and IL-4 were significantly increased in the intermittent hypoxic training groups. | ||||||||
| Reactive oxygen species (ROS) | Intermittent hypoxic training lowers the ROS generation | ||||||||
| Phagocytic activity | Intermittent hypoxic training increases phagocytic activity (about 12-fold) vs. normoxia. | ||||||||
| Cell phenotype | Intermittent hypoxic training regulates the polarization of the microglial phenotype toward anti-inflammatory type M2. | ||||||||
| Polonis et al., 2020 | OSA | HWPs | Non-RCT | IHNT | 9 cycles of IH (30 min of 21% O2 followed by 30 min of 0.1% O2) per day for up to 7 days | Senescence in HWPs | A higher prevalence of cells positive for senescence-associated β-galactosidase activity was also evident with chronic IH exposure. | This study identifies chronic IH as a trigger of senescence-like phenotype in preadipocytes. | Not reported |
hAFSCs, human amniotic fluid stem cells; CHT, continuous hypoxia training; IHT, intermittent hypoxia training; IH, intermittent hypoxia; non-RCT, non-randomized controlled trial; HDF, human dermal fibroblasts; VSMC, vascular smooth muscle cell; HPLC, high performance liquid chromatography; qPCR, quantitative polymerase chain reaction; ELISA, enzyme linked immunosorbent assay; OSA, obstructive sleep apnea; HWPs, human white preadipocytes; ROS, reactive oxygen species; TLR2, toll-like receptor 2.