High-Intensity Interval Training, but Not Whole-Body Cryostimulation, Affects Bone-Mechanosensing Markers and Induces the Expression of Differentiation Markers in Osteoblasts Cultured with Sera from Overweight-to-Obese Subjects

Abstract

Background/Objectives: Although there have been some clinical observations made, the mechanistic effects on bone metabolism of whole-body cryostimulation and high-intensity interval training (HIIT), either alone or in combination, are still debated. Here, we have investigated their effects on circulating osteo-immune and bone metabolic markers (osteopontin, osteocalcin, sclerostin, dikkopf-related protein 1, and fibroblast-growth factor 23) and their potential effects on osteoblast differentiation and function, in vitro, by treating SaOS-2 osteoblast-like cells with the sera obtained from the subjects who had undergone the different interventions or untreated control subjects. Methods: Sixty-seven inactive, overweight-to-obese participants (body mass index = 31.9 ± 5.0 kg·m^-2, 42 ± 13 years old) were recruited and randomly assigned to one group: control (CTRL, n = 14), training (HIIT, 6 sessions, n = 13), WBC (CRYO, 10 sessions, n = 17) or training combined with WBC (CRYO-HIIT, n = 23). The interventions lasted 14 days. Results: While circulating markers analysis revealed more protective potential against resorption in HIIT than in WBC alone or combined, gene expression from in vitro analysis showed an induction of late bone metabolic markers in the HIIT group. Conclusions: These data suggest a potentially protective effect of HIIT in bone against resorption, while WBC maintains homeostasis by preventing any resorptive phenomena and limiting any anabolic activity even when stimulated by intensive exercise.

Keywords: bone markers; cryostimulation; obesity; osteogenic differentiation; physical activity; resistance training.

Figure 1

Study design. Scheme of the three intervention groups with indicated the type (HIIT, CRYO or combination of CRYO-HIIT) and frequency of interventions. HIIT was performed 6 times over two weeks (every second day), CRYO was performed 10 times a week over two weeks, while in the combined intervention group, CRYO was performed 5 times a week with combination of CRYO every second day over two weeks. On days 6 and 7 no intervention was performed. Time points of blood collection are also indicated.

Figure 2

Circulating levels of bone markers in the entire cohort (A) and in obese subjects only (B). The differences were considered significant when p < 0.05. Asterisks indicate significant differences (* p < 0.05).

Figure 3

Circulating levels of osteo-immunological markers in the entire cohort (A) and in obese subjects only (B). The differences were considered significant when p < 0.05. Asterisks indicate significant differences (* p < 0.05, ** p < 0.01, *** p < 0.001).

Figure 4

Effect of sera treatment on osteoblast-like cell function. (I) Cell proliferation (a) and ALP enzymatic activity (b) after 48 h and 7 days of treatment with subjects’ sera, respectively. (II) Gene expression of significant bone-related genes after 48 h treatment with subjects’ sera, considering the entire cohort (a–c) or obese subjects only (d–f). The differences were considered significant when p < 0.05. Asterisks indicate significant differences (* p < 0.05, ** p < 0.01, *** p < 0.001, **** p < 0.0001).

Figure 5

Effect of interventions on osteoblast-like cells under differentiating conditions. Analysis of proliferation (A) and alkaline phosphatase (ALP) enzymatic activity (B), after 7 days of differentiation, and quantification of calcified extracellular matrix after 10 days of differentiation (C,D).

Figure 6

Effect of interventions on bone-related gene expression in osteoblast-like cells treated with subjects’ sera in differentiating conditions. Gene expression of significant bone-related genes after 7 days of differentiation, considering the entire cohort (A,B) or obese subjects only (C,D). The differences were considered significant when p < 0.05. Asterisks indicate significant differences (* p < 0.05, ** p < 0.01).