Physiological parameters regulating circulating levels of the IGFBP-4/Stanniocalcin-2/PAPP-A axis

BACKGROUND

Insulin Growth Factor Binding Protein 4 (IGFBP-4), Stanniocalcin-2 (STC-2) and Pregnancy-Associated Plasma Protein-A (PAPP-A) have a well-documented involvement in several physiological functions in humans but predictors of their circulating levels remain largely unknown. We aimed to identify anthropometric and biochemical parameters associated with circulating levels of IGFBP-4/STC-2/PAPP-A axis (ISPa) cross-sectionally and to study their day-night variation and their regulation in response to mixed meal and exercise.

METHODS

One hundred twenty two healthy individuals were evaluated cross-sectionally. Subgroups were subjected to standardized mixed meal ingestion in increasing quantities of 125mL or 250mL, or aerobic exercise for 30min, or day-night rhythm study. Main outcome measurements were circulating IGFBP-4 (total and intact), STC-2 and PAPP-A levels.

RESULTS

In multivariate models, the main predictors of serum total IGFBP-4 were PAPP-A and female gender. Intact IGFBP-4 was positively associated with serum creatinine. Height was inversely and female gender and % of total body fat were positively correlated with STC-2. PAPP-A decreased after ingesting both the 125mL (p=0.03) and 250mL quantities (p=0.001), while total IGFBP-4 was reduced after the 250mL quantity (p=0.001). Exercise increased STC-2 and PAPP-A levels (p<0.001 for both). Intact, and to a lesser extent total, IGFBP-4 displayed a cortisol-like day/night variation.

CONCLUSIONS

We report for the first time anthropometric and physiological modulators of ISPa serum levels in healthy humans.

Circulating follistatin displays a day-night rhythm and is associated with muscle mass and circulating leptin levels in healthy, young humans

PURPOSE

Follistatin may affect lean and fat mass and be implicated in metabolic diseases. We aimed to elucidate physiological predictors of circulating follistatin variation in healthy young humans.

PROCEDURES

This was an observational, cross-sectional study with two additional prospective observational arms (circadian, seasonal sub-studies) and one prospective interventional arm (mixed meal sub-study). Healthy, young individuals of both sexes (n=122) were subjected to anthropometric and body composition measurements and their eating and exercise behavior profiles were assessed by validated questionnaires. Sub-groups were subjected to standardized meal ingestion (n=36), day-night rhythm (n=20) and seasonal variation (n=20) studies. Main outcome of the study were circulating follistatin levels.

RESULTS

At baseline follistatin levels were correlated with creatinine (r=0.24; p=0.01), creatine phosphokinase (rs=0.22; p=0.02), and with lean body mass (rs=0.19; p=0.04) and were higher in males than females (p=0.004) after adjustment for leptin, which was its major predictor. Follistatin levels showed a circadian (p<0.001), but not a seasonal, variation, and were also affected by the phase of menstrual cycle in females (p=0.034). Follistatin levels were not affected by dietary or exercise habits but levels increased after a standardized meal ingestion (250kcal) (p=0.002).

CONCLUSIONS

In healthy young individuals circulating follistatin levels are correlated with muscle mass. Follistatin levels are associated with circulating leptin levels and display a day-night rhythm and a menstrual cycle, but not a seasonal, variation.

Circulating irisin in healthy, young individuals: day-night rhythm, effects of food intake and exercise, and associations with gender, physical activity, diet, and body composition

CONTEXT

The myokine irisin may increase energy expenditure and affect metabolism.

OBJECTIVE

The objective of the study was to elucidate predictors of irisin and study whether circulating irisin may have day-night rhythm in humans.

DESIGN

This was an observational, cross-sectional study with an additional 24-hour prospective observational arm (day-night rhythm substudy) and two prospective interventional arms (mixed meal substudy and exercise substudy).

SETTING

The study was conducted at the Hellenic Military School of Medicine (Thessaloniki, Greece).

PATIENTS AND INTERVENTIONS

One hundred twenty-two healthy, young individuals were subjected to anthropometric and body composition measurements, and their eating and exercise behavior profiles were assessed with validated questionnaires. Subgroups were subjected to day-night rhythm, standardized meal ingestion, and 30-minute aerobic exercise studies.

MAIN OUTCOME MEASURES

Circulating irisin levels were measured.

RESULTS

Ιrisin levels were lower in males than females (P = .02) after adjustment for lean body mass, which was its major determinant. Irisin levels followed a day-night rhythm (P < .001) with peak at 9:00 pm. Irisin levels were increased at the end of exercise (84.1 ± 10.0 vs 105.8 ± 14.3 ng/mL; P < .001). Irisin levels were not affected by intake of a standardized meal and were not associated with caloric intake or diet quality.

CONCLUSIONS

In healthy, young individuals, circulating irisin displays a day-night rhythm, is correlated with lean body mass, and increases acutely after exercise.