15 BEDREST: Targeting bed rest-induced adipose tissue dysfunction with anti-inflammatory & antioxidant nutrients

Bed rest is a useful experimental model of physiological deconditioning which is analogous to accelerated ageing in an increasingly sedentary population. As part of the ELIPS programme, the European Space Agency are planning a long-term bed rest study to determine the impact of a nutritional anti-inflammatory and antioxidant countermeasure (including resveratrol, vitamins E and C, lycopene and epigallocatechin). We hypothesise that bed rest will lead to inflammatory and metabolic disturbances in subcutaneous adipose tissue (fat) which mimic many of the changes in this tissue seen with ageing and physical inactivity - and that the planned countermeasures will offset the changes induced by bed rest.

Collectively, our understanding of adipose tissue has changed enormously in recent years and adipose tissue is clearly much more than a simple energy store. Adipose tissue is an active player in diverse physiological systems ranging from bone remodelling through to muscle substrate (fuel) utilisation. Adipose tissue communicates with other tissues via the secretion of archetypal 'adipokines' (e.g., adiponectin) but adipose tissue is also responsible for the secretion of many other proteins and mediators which have implications for other distant tissues including muscle and bone. We hypothesise that increased glucose uptake by adipose tissue in response to bed rest will provoke cellular and oxidative stress - causing adipocytes to secrete/express molecules designed in part to initiate an immune response but which then exacerbates adipose dysfunction.

We will take adipose tissue biopsies before and after 60-d bed rest in both control and intervention groups (n=8 to 12 in each group). We will determine changes in whole adipose tissue at both gene expression and protein levels. Since we cannot assume that bed rest and the anti-inflammatory and antioxidant countermeasures will elicit equal effects in the heterogeneous cells that comprise adipose tissue, we will separate adipocytes from non-adipocytes (e.g. immune cells) and examine adipocytes and immune cells separately. We will determine adipocyte glucose uptake in basal and insulin-stimulated conditions. We will examine changes in the number of specific immune cells that are resident within adipose (e.g. macrophages) and also whether these cells have a pro- or anti-inflammatory phenotype. We will culture small pieces of adipose tissue to examine changes in adipokine secretion - and whether the pattern and amount of selected adipokines is impacted upon by bed rest. Finally, we will undertake exploratory work to examine whether altered adipokine secretion with bed rest has the potential to impact upon bone and muscle cell models. Virtually all of the above work will be conducted in the UK using frozen samples.

Importantly, the planned countermeasures have the potential to positively impact upon adipose tissue function from the earliest mechanistic step (e.g., resveratrol and epigallocatechin decrease adipose tissue glucose uptake) all the way through to downstream consequences related to secondary oxidative stress and inflammation (e.g., all of the ingredients have been shown to target either oxidative stress and/or inflammation in adipose tissue). To date, most of these mechanisms have only been examined in rodent adipose tissue and thus the planned intervention represents an excellent opportunity to verify whether we can translate these exciting findings into humans.

Adipose tissue dysfunction has been implicated in the aetiology of ageing, diabetes, and cardiovascular disease - with physical inactivity being a potential common mediator. In this context, this research will (i) characterise bed rest-induced adipose tissue dysfunction, (ii) demonstrate whether these changes have implications for other tissues (i.e. muscle and bone) and (iii) determine whether the anti-inflammatory and antioxidant countermeasures successfully target adipose tissue dysfunction in humans.

The long-term bed rest planned in AO-13-BR will be conducted in males and will last 60 days. The planned countermeasures comprise an anti-inflammatory, anti-oxidant cocktail likely to include resveratrol, vitamins E and C, lycopene and epigallocatechin. There will be one intervention and one control group (n=8 to 12). The intervention and core measures are pre-defined.

We will collect subcutaneous adipose tissue before and after the period of bed rest coupled with synchronous blood and urine samples and continuous glucose monitoring over 5-7 days. We will determine the impact of bed rest and the anti-inflammatory and antioxidant countermeasures on adipose gene expression - prioritizing genes that target bed rest-induced mechanistic pathways plus those which will shed light on the impact of the countermeasures. These include adipocyte glucose metabolism as a key initiator of adipose dysfunction, inflammatory mediators and classical adipokines (e.g., IL-6, leptin) and those that have been specifically implicated as intermediate pathways invoked by the countermeasures (e.g., SIRT). We will assess cell-specific outcomes in adipocytes and adipose-resident immune cells. In adipocytes, this will include basal and insulin-stimulated glucose uptake and related pathways likely to be activated by bed rest and modified by the countermeasures. We will use flow cytometry to determine the number of immune cells (e.g., macrophages), whether these cells have a pro- or anti-inflammatory phenotype and activation status (e.g., pro- or anti-inflammatory macrophages), and whether bed rest-induced changes are positively impacted upon by the anti-inflammatory and antioxidant countermeasures. Using freshly-harvested tissue, we will culture whole adipose explants to determine adipokine secretion ex vivo. Finally, we will use an in vitro system to explore the potential impact of altered adipokine secretion on muscle and bone cell models.

WHO WILL BENEFIT FROM THIS RESEARCH?

The beneficiaries from this research are broad and include, the European Space Agency (ESA) and other space agencies around the world, commercial space flight (e.g., Virgin Galactic), organisations who manage people during long term bed rest (e.g., NHS), plus pharmaceutical and nutritional companies interested in developing new therapies, treatments and products targeting pathways induced by inactivity in adipose tissue.

HOW WILL THEY BENEFIT FROM THIS RESEARCH?

An improved understanding of the adipose tissue responses to bed rest - including whether these can be modulated using an anti-inflammatory/anti-oxidant cocktail - has implications for (i) prolonged space flight (ii) other contexts where there is a sustained period of relative inactivity (e.g., hospitalization, injury or illness) and (iii) the translation of knowledge towards new therapies, treatments and products. The benefits range from improved policy/practice and organizational effectiveness within specific user groups and stakeholders through to the development of therapies and nutritional interventions for commercialization and exploitation.

Briefly, these include:

SPACE: This research will provide the first comprehensive characterization of the changes within adipose tissue during prolonged bed rest as a surrogate of prolonged space flight. Thus, agencies involved in preparation for long-term space exploration will benefit from an improved understanding of the potential role for adipose tissue and whether these changes can be modified using a simple nutritional antioxidant/anti-inflammatory countermeasure. The UK is a leader in spaceflight and discovery and, thus, this research will impact policy and practice within space agencies and commercial ventures - as well as on the health of individuals who subsequently embark on long-term space flight.

BED REST: The adipose tissue responses to bed rest and the impact of the antioxidant/anti-inflammatory countermeasure have implications for policy and practice in terms of the management of people during long term bed rest (e.g., during hospitalization, injury or illness). This has the potential to impact upon organizational effectiveness, as well as the health, wellbeing and quality of life of patients.

INDUSTRY: Adipose tissue is a key player in ageing and chronic diseases such as type 2 diabetes and cardiovascular disease. Physical inactivity is a likely common mediator but the mechanisms are poorly understood. This research will characterize for the first time the changes in adipose tissue after a profound reduction in physical activity. The characterization of the molecular changes and cellular composition of adipose tissue will create an opportunity to develop drugs designed to target specific nodes. If successful, this has the potential to generate exploitable opportunities based on this new knowledge. Furthermore, given the nature of the antioxidant/anti-inflammatory countermeasure, this work has the potential to help generate new nutritional products and supplements which target adipose tissue dysfunction. This could have very broad implications - for example, by age 75 years, humans have not only doubled their adipose tissue mass but adipose has typically also become both pro-inflammatory and dysfunctional.