Inflammatory response to acute hypoxia in humans

Non-pharmacological interventions for vascular health and the role of the endothelium

The most common non-pharmacological intervention for both peripheral and cerebral vascular health is regular physical activity (e.g., exercise training), which improves function across a range of exercise intensities and modalities. Numerous non-exercising approaches have also been suggested to improved vascular function, including repeated ischemic preconditioning (IPC); heat therapy such as hot water bathing and sauna; and pneumatic compression. Chronic adaptive responses have been observed across a number of these approaches, yet the precise mechanisms that underlie these effects in humans are not fully understood. Acute increases in blood flow and circulating signalling factors that induce responses in endothelial function are likely to be key moderators driving these adaptations. While the impact on circulating factors and environmental mechanisms for adaptation may vary between approaches, in essence, they all centre around acutely elevating blood flow throughout the circulation and stimulating improved endothelium-dependent vascular function and ultimately vascular health. Here, we review our current understanding of the mechanisms driving endothelial adaptation to repeated exposure to elevated blood flow, and the interplay between this response and changes in circulating factors. In addition, we will consider the limitations in our current knowledge base and how these may be best addressed through the selection of more physiologically relevant experimental models and research. Ultimately, improving our understanding of the unique impact that non-pharmacological interventions have on the vasculature will allow us to develop superior strategies to tackle declining vascular function across the lifespan, prevent avoidable vascular-related disease, and alleviate dependency on drug-based interventions.

Is Biochemical Follow Up Possible in Peripheral Arterial Disease Treatment: Hypoxia Inducible Factor-1 Alpha?

Purpose

The hypoxia inducible factor (HIF)-1 is a dimeric protein complex that plays an integral role in the body’s response to hypoxia. This study aimed to analyze the regulation of HIF-1α following vascular and/or endovascular surgery in peripheral arterial disease (PAD) patients.

Methods

Materials and A total of 40 patients with PAD (≥Rutherford category 3) were included in this prospective study. The mean age was 61.9±9.2 years. Open surgery was performed in 16 patients, and endovascular intervention was performed in 34 patients. At preoperative (T1), postoperative day 1 (T2), and month 3 (T3), the serum HIF-1α levels were checked using the ELISA technique.

Results

At T3, the ankle-brachial index was significantly higher than the preoperative value (P<0.001). Serum HIF-1α levels at T1, T2, and T3 were 2.0±1.7 ng/mL, 1.9±1.7 ng/mL, and 1.6±1.4 ng/mL, respectively. Serum HIF-1α levels between T1 and T3 and between T2 and T3 were significantly different (P<0.05). The preoperative HIF-1α levels were lowest in iliac lesions compared to femoropopliteal or tibial lesions.

Conclusion

The HIF-1α levels were decreased in all patients on postoperative days, T2 and T3, compared with the preoperative values. Our results indicated that HIF-1α may be a surrogate marker after revascularization in patients with PAD. Further studies are needed to analyze the sensitivity, specificity, and cut-off values of HIF-1α in patients with PAD.

The Effects of Acute Hypoxia on Tissue Oxygenation and Circulating Alarmins in Healthy Adults

The binding of high-mobility group box-1 (HMGB-1) to the membrane receptor for advanced glycation end-products (mRAGE) is a key early mediator of non-infectious inflammation and its triggers include ischaemia/hypoxia. The effects of acute hypoxia on soluble RAGE (sRAGE) are unknown. Fourteen healthy adults (50 % women; 26.6±3.8 years) were assessed at baseline normoxia (T0), followed by four time-points (T90, 95, 100 and 180 min) over three hours of continuous normobaric hypoxia (NH, 4,450 m equivalent) and again 60 min after return to normoxia (T240). A 5-min exercise step test was performed during NH at T90. Plasma concentrations of HMGB-1, sRAGE VCAM-1, ICAM-1, VEGF IL-8 and IL-13 were measured using venous blood. Arterial and tissue oxygen saturations were measured using pulse oximetry (SpO2) and near-infrared spectroscopy (StO2), respectively. NH led to a significant reduction in SpO2, StO2, sRAGE and VEGF, which was compounded by exercise, before increasing to baseline values with normoxic restoration (T240). NH-exercise led to a paired increase in HMGB-1. sRAGE inversely correlated with HMGB-1 (r=-0.32; p=0.006), heart rate (r=-0.43; p=0.004) but was not linked to SpO2 or StO2. In conclusion, short-term NH leads to a fall in sRAGE and VEGF concentrations with a transient rise post NH-exercise in HMGB-1.

Immunologic Consequences of Hypoxia during Critical Illness

Hypoxia and immunity are highly intertwined at clinical, cellular, and molecular levels. The prevention of tissue hypoxia and modulation of systemic inflammation are cornerstones of daily practice in the intensive care unit. Potentially, immunologic effects of hypoxia may contribute to outcome and represent possible therapeutic targets. Hypoxia and activation of downstream signaling pathways result in enhanced innate immune responses, aimed to augment pathogen clearance. On the other hand, hypoxia also exerts antiinflammatory and tissue-protective effects in lymphocytes and other tissues. Although human data on the net immunologic effects of hypoxia and pharmacologic modulation of downstream pathways are limited, preclinical data support the concept of tailoring the immune response through modulation of the oxygen status or pharmacologic modulation of hypoxia-signaling pathways in critically ill patients.