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Open access

Anouar Aznou, Rick I. Meijer, Dani�l H van Raalte, Martin den Heijer, Annemieke C Heijboer, and Renate T De Jongh

Objective

The mechanisms underlying the development of peripheral insulin resistance are complex.

Several studies have linked sclerostin, an osteocyte-derived inhibitor of the Wnt/β-catenin pathway, to obesity and insulin resistance. The aim of this study was to investigate 1) whether serum sclerostin is associated with insulin sensitivity in lean and/or obese women; and 2) whether hyperinsulinemia affects serum sclerostin concentrations.

Design

A cross-sectional study.

Methods

Insulin sensitivity was measured in lean (BMI<25 kg·m-2) and obese (BMI > 30 kg·m-2) women using a hyperinsulinemic-euglycemic clamp. Serum sclerostin was measured at baseline and during the clamp procedure.

Results

We studied 21 lean and 22 obese women with a median age of 40 and 43

years and a median BMI of 22.4 and 33.5 kg·m-2, respectively. Obese women had higher

serum sclerostin than lean women (122±33 vs 93±33 nmol/L, p<0.01). Higher serum

sclerostin was associated with lower insulin sensitivity in obese, but not in lean individuals

(difference in M value between highest and lowest quartile: -7.02 mg⋅kg−1⋅min−1, p =

0.03 and 1.59 mg⋅kg−1⋅min−1, p = 0.50, respectively). Hyperinsulinemia did not affect serum

sclerostin in lean nor obese women (p>0.5).

Conclusion

Serum sclerostin is negatively associated with insulin sensitivity as measured

with the hyperinsulinemic euglycemic clamp in obese, but not lean women. This indicates a potential role of the Wnt/β-catenin pathway in regulating insulin sensitivity particularly in obese individuals. Our findings remain hypothesis-generating and should be confirmed by additional studies.

Open access

Stan Ursem, Vito Francic, Martin Keppel, Verena Schwetz, Christian Trummer, Marlene Pandis, Felix Aberer, Martin R Grübler, Nicolas D Verheyen, Winfried März, Andreas Tomaschitz, Stefan Pilz, Barbara Obermayer-Pietsch, and Annemieke C Heijboer

Objective

PTH can be oxidised in vivo, rendering it biologically inactive. Non-oxidised PTH (n-oxPTH) may therefore give a better image of the hormonal status of the patient. While vitamin D supplementation decreases total PTH (tPTH) concentration, the effect on n-oxPTH concentration is unexplored. We investigated the effect of vitamin D on n-oxPTH concentration in comparison to tPTH and compared the correlations between parameters of calcium, bone and lipid metabolism with n-oxPTH and tPTH.

Methods

N-oxPTH was measured in 108 vitamin D-insufficient (25(OH)D <75 nmol/L) hypertensive patients, treated with vitamin D (2800 IE daily) or placebo for 8 weeks in the Styrian Vitamin D Hypertension Trial (NCT02136771). We calculated the treatment effect and performed correlation analyses of n-oxPTH and tPTH with parameters of calcium, bone and lipid metabolism and oxidative stress.

Results

After treatment, compared to placebo, 25(OH)D concentrations increased, tPTH decreased by 9% (P < 0.001), n-oxPTH by 7% (P = 0.025) and the ratio of n-oxPTH/tPTH increased (P = 0.027). Changes in phosphate and HDL concentration correlated with changes in n-oxPTH, but not tPTH.

Conclusions

tPTH and n-oxPTH decrease upon vitamin D supplementation. Our study suggests that vitamin D supplementation reduces the oxidation of PTH, as we observed a small but significant increase in the non-oxidised proportion of PTH upon treatment. In addition, we found that changes in phosphate and HDL concentration showed a relationship with changes in n-oxPTH, but not tPTH. This may be explained by the biological activity of n-oxPTH. Further research should be carried out to establish the clinical relevance of n-oxPTH.