Effects of short-term dry immersion on bone remodeling markers, insulin and adipokines

Abstract

BackgroundDry immersion (DI), a ground-based model of microgravity previously used in Russia, has been recently implemented in France. The aim of this study was to analyze early events in a short-term DI model in which all conditions are met to investigate who is first challenged from osteo- or adipo-kines and to what extent they are associated to insulin-regulating hormones.MethodsTwelve healthy men were submitted to a 3-day DI. Fasting blood was collected during pre-immersion phase for the determination of the baseline data collection (BDC), daily during DI (DI24h, DI48H and DI72h), then after recovery (R+3h and R+24h). Markers of bone turnover, phosphocalcic metabolism, adipokines and associated factors were measured.ResultsBone resorption as assessed by tartrate-resistant acid phosphatase isoform 5b and N-terminal crosslinked telopeptide of type I collagen levels increased as early as DI24h. At the same time, total procollagen type I N- and C-terminal propeptides and osteoprotegerin, representing bone formation markers, decreased. Total osteocalcin [OC] was unaffected, but its undercarboxylated form [Glu-OC] increased from DI24h to R+3h. The early and progressive increase in bone alkaline phosphatase activities suggested an increased mineralization. Dickkopf-1 and sclerostin, as negative regulators of the Wnt-β catenin pathway, were unaltered. No change was observed either in phosphocalcic homeostasis (calcium and phosphate serum levels, 25-hydroxyvitamin D, fibroblast growth factor 23 [FGF23]) or in inflammatory response. Adiponectemia was unchanged, whereas circulating leptin concentrations increased. Neutrophil gelatinase-associated lipocalin [lipocalin-2], a potential regulator of bone homeostasis, was found elevated by 16% at R+3h compared to DI24h. The secretory form of nicotinamide phosphoribosyl-transferase [visfatin] concentrations almost doubled after one day of DI and remained elevated. Serum insulin-like growth factor 1 levels progressively increased. Fasting insulin concentrations increased during the entire DI, whereas fasting glucose levels tended to be higher only at DI24h and then returned to BDC values. Changes in bone resorption parameters negatively correlated with changes in bone formation parameters. Percent changes of ultra-sensitive C-reactive protein positively correlated with changes in osteopontin, lipocalin-2 and fasting glucose. Furthermore, a positive correlation was found between changes in FGF23 and Glu-OC, the two main osteoblast-/osteocyte-derived hormones.ConclusionOur results demonstrated that DI induced an unbalanced remodeling activity and the onset of insulin resistance. This metabolic adaptation was concomitant with higher levels of Glu-OC. This finding confirms the role of bone as an endocrine organ in humans. Furthermore, visfatin for which a great responsiveness was observed could represent an early and sensitive marker of unloading in humans.

The Effects of Spaceflight Factors on the Human Plasma Proteome, Including Both Real Space Missions and Ground-Based Experiments

“…Any dissimilarity in the lists of significantly changed proteins could be explained by the differences in the dynamics of the development of effects in the ground-based experiments. The changes occurring during the dry immersion experiment develop rather quickly [9]—faster than during HDBR. Therefore, on the 21st day of the experiments, the physiological systems of the organism are in different states.…”

“…However, there are certain ethical restrictions that allow only experiments with physical inactivity and diet modification, in particular, modification of the composition of basic nutrients, as well as exercise tests. Some experiments were specifically designed to simulate physiological changes under the influence of separate factors of spaceflight such as head-down bed rest, dry immersion, and isolation in sealed chambers [8,9]. Head down bed rest (HDBR) is one of the experimental models that limits the mobility of a person to strict bed rest, while the head of the bed is lowered relative to the horizontal axis [8].…”

“…During the experiment, volunteers are immersed in thermoneutral water covered with a special elastic waterproof fabric. It is known that this model accurately reproduces the cardiovascular, motor, and other changes observed during spaceflight [9].…”

The Interplay Between Bone and Glucose Metabolism

“…Hence, such conflicting results may be ascribed to measurement bias in humans. In this context, interesting data were reported by Linossier et al who assessed the effect of the acute increase in bone resorption on glucose metabolism in 12 healthy men exposed to microgravity (35). Authors observed that the onset of insulin-resistance was in response to increased bone resorption and concomitant to the increase of uOC (35).…”

Dry Immersion as a Ground-Based Model of Microgravity Physiological Effects

“…There were no effects of 7-day DI on bone formation or increase of bone resorption in the study of Kopp (2008). A recent study performed during 3-day DI, however, revealed significant decrement of bone formation markers, namely total procollagen type I N- and C-terminal propetides and osteoprotegerin (Linossier et al, 2017).…”