This Article Full Text Full Text (PDF) Submit a related Letter to the Editor Alert me when this article is cited Alert me when eLetters are posted Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Request Copyright Permission Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Wickman, S. Articles by Dunkel, L. Search for Related Content PubMed PubMed Citation Articles by Wickman, S. Articles by Dunkel, L.

Effects of Suppression of Estrogen Action by the P450 Aromatase Inhibitor Letrozole on Bone Mineral Density and Bone Turnover in Pubertal Boys

Hospital for Children and Adolescents, University of Helsinki, Helsinki, FIN-00029 HUS, Finland

Address all correspondence and requests for reprints to: Sanna Wickman, Hospital for Children and Adolescents, University of Helsinki, PL 281, FIN-00029 HUS, Finland. E-mail: sanna.wickman{at}helsinki.fi.

The essential role of estrogen (E) in regulation of developing peak bone mass in males was confirmed when young adult men were described who cannot respond to or produce E because of defective E receptor or P-450 aromatase enzyme, respectively. These men had significantly reduced bone mineral density (BMD) despite normal or supranormal androgen concentrations, and E administration improved BMD in the men with aromatase deficiency, whereas testosterone (T) was ineffective. Because new P450 aromatase inhibitors may prove to be potential drugs in various growth disorders, the effect of suppression of E action on developing peak bone mass has to be closely evaluated.

In this study, we explored the effects of suppression of E synthesis on bone metabolism in pubertal boys. A total of 23 boys with constitutional delay of puberty were randomized to receive T and placebo or T and a specific and potent P450 aromatase inhibitor, letrozole. We determined BMD in the lumbar spine and the femoral neck. Bone resorption was studied by measuring the serum concentration of cross-linked carboxyterminal telopeptide of type I collagen by two different methods (CTx and ICTP), and bone formation by determining the serum concentrations of carboxyterminal propeptide of type I procollagen (PICP), osteocalcin, and alkaline phosphatase.

We demonstrated previously that, during treatment with T and placebo, the concentrations of androgens and E increased. During treatment with T and letrozole, the E concentrations remained at the pretreatment level, but the androgen concentrations increased; the increase in the T concentration was more than 5-fold higher than during treatment with T and placebo. We did not observe any significant differences in the changes in bone mineral content, BMD, or bone mineral apparent density, an estimate of true volumetric BMD, between the treated groups. Lumbar spine bone mineral apparent density increased in both treated groups; but in the T- plus letrozole-treated group, the increase was statistically significant only 6 months after discontinuation of letrozole treatment. All bone resorption and formation markers increased during treatment with T and placebo. During treatment with T plus letrozole, CTx, PICP, and osteocalcin remained unchanged, whereas ICTP and alkaline phosphatase increased. Thus, 1-yr treatment with this new P450 aromatase inhibitor in pubertal boys is unlikely to be associated with any major harmful effect on developing peak bone mass. However, to convincingly exclude such effects, particularly rare or minor ones, will require a study with a larger sample size; and thus, close follow-up of bone metabolism during treatment with P450 aromatase inhibitors is still warranted.

This work was supported by the Foundation for Pediatric Research, Helsinki, Finland; the Helsinki University Central Hospital Research Fund; and Finska Läkaresällskapet.

Abbreviations: ALP, Alkaline phosphatase; BMAD, bone mineral apparent density; BMC, bone mineral content; BMD, bone mineral density; BMI, body mass index; DHT, dihydrotestosterone; E, estrogen; E2, estradiol; ER, estrogen receptor; IGFBP, IGF-binding protein; OC, osteocalcin; PICP, procollagen; T, testosterone.

This article has been cited by other articles:

				S. Loves, J. Ruinemans-Koerts, and H. de Boer Letrozole once a week normalizes serum testosterone in obesity-related male hypogonadism Eur. J. Endocrinol., May 1, 2008; 158(5): 741 - 747. [Abstract] [Full Text] [PDF]

				P. Zhou, B. Shah, K. Prasad, and R. David Letrozole Significantly Improves Growth Potential in a Pubertal Boy With Growth Hormone Deficiency Pediatrics, February 1, 2005; 115(2): e245 - e248. [Abstract] [Full Text] [PDF]

				L. Gennari, R. Nuti, and J. P. Bilezikian Aromatase Activity and Bone Homeostasis in Men J. Clin. Endocrinol. Metab., December 1, 2004; 89(12): 5898 - 5907. [Abstract] [Full Text] [PDF]

				T. Raivio, L. Dunkel, S. Wickman, and O. A. Janne Serum Androgen Bioactivity in Adolescence: A Longitudinal Study of Boys with Constitutional Delay of Puberty J. Clin. Endocrinol. Metab., March 1, 2004; 89(3): 1188 - 1192. [Abstract] [Full Text] [PDF]