Soluble Alpha Klotho in Acromegaly: Comparison With Traditional Markers of Disease Activity.

CONTEXT: Soluble alpha klotho (sαKL) has been linked to growth hormone (GH) action, but systematic evaluation and comparisons with traditional biomarkers in acromegaly are lacking. OBJECTIVE: To evaluate the potential of sαKL to aid classification of disease activity. METHODS: This retrospective study at 2 academic centers included acromegaly patients before surgery (A, n = 29); after surgery (controlled, discordant, or uncontrolled) without (B1, B2, B3, n = 28, 11, 8); or with somatostatin analogue treatment (C1, C2, C3, n = 17, 11, 5); nonfunctioning pituitary adenomas (n = 20); and healthy controls (n = 31). sαKL was measured by immunoassay and compared with traditional biomarkers (random and nadir GH, insulin-like growth factor I [IGF-I], IGF binding protein 3). Associations with disease activity were assessed. RESULTS: sαKL was correlated to traditional biomarkers, particularly IGF-I (rs=0.80, P <0.0001). High concentrations before treatment (A, median, interquartile range: 4.04 × upper limit of normal [2.26-8.08]) dropped to normal after treatment in controlled and in most discordant patients. A cutoff of 1548 pg/mL for sαKL discriminated controlled (B1, C1) and uncontrolled (B3, C3) patients with 97.8% (88.4%-99.9%) sensitivity and 100% (77.1%-100%) specificity. sαKL was below the cutoff in 84% of the discordant subjects. In the remaining 16%, elevated sαKL and IGF-I persisted, despite normal random GH. Sex, age, body mass index, and markers of bone and calcium metabolism did not significantly affect sαKL concentrations. CONCLUSION: Our data support sαKL as a biomarker to assess disease activity in acromegaly. sαKL exhibits close association with GH secretory status, large dynamic range, and robustness toward biological confounders. Its measurement could be helpful particularly when GH and IGF-I provide discrepant information.

Use of the metallothionein promoter-human growth hormone-releasing hormone (GHRH) mouse to identify regulatory pathways that suppress pituitary somatotrope hyperplasia and adenoma formation due to GHRH-receptor hyperactivation.

Hyperactivation of the GHRH receptor or downstream signaling components is associated with hyperplasia of the pituitary somatotrope population, in which adenomas form relatively late in life, with less than 100% penetrance. Hyperplastic and adenomatous pituitaries of metallothionein promoter-human GHRH transgenic (Tg) mice (4 and > 10 months, respectively) were used to identify mechanisms that may prevent or delay adenoma formation in the presence of excess GHRH. In hyperplastic pituitaries, expression of the late G(1)/G(2) marker Ki67 increased, whereas the proportion of 5-bromo-2'-deoxyuridine-labeled cells (S phase marker) did not differ from age-matched controls. These results indicate cell cycle progression is blocked, with further evidence suggesting that enhanced p27 activity may contribute to this process. For adenomas, formation was associated with loss of p27 activity (nuclear localization and mRNA). Increased endogenous somatostatin (SST) tone may also slow the conversion from hyperplastic to adenomatous state because mRNA levels for SST receptors, sst2 and sst5, were elevated in hyperplastic pituitaries, whereas adenomas were associated with a decline in sst1 and sst5 mRNA. Also, SST-knockout Tg pituitaries were larger and adenomas formed earlier compared with those of SST-intact Tg mice. Unexpectedly, these changes were independent of changes in proliferation rate within the hyperplastic tissue, suggesting that endogenous SST controls GHRH-induced adenoma formation primarily via modulation of apoptotic and/or cellular senescence pathways, consistent with the predicted function of some of the most differentially expressed genes (Casp1, MAP2K1, TNFR2) identified by membrane arrays and confirmed by quantitative real-time RT-PCR.

Tumor deletion mapping on chromosome 11q13 in eight families with isolated familial somatotropinoma and in 15 sporadic somatotropinomas.

CONTEXT: Isolated familial somatotropinoma (IFS) is a rare endocrine disease defined as the occurrence of at least two cases of acromegaly or gigantism in a family that does not exhibit features of Carney complex or multiple endocrine neoplasia type 1. Analysis of the multigenerational expression in families suggests that IFS is inherited as an autosomal dominant disease with incomplete penetrance. The association between the disease and loss of heterozygosity on chromosome 11q13 as well as its linkage to this region has been well established, but the IFS gene still remains unknown. OBJECTIVE: The aim of this report was to narrow the previously described chromosomal region (9.7 cM) to which the gene was previously localized and to evaluate potential candidates. DESIGN AND SETTING: Using haplotyping and allelotyping techniques, we studied eight new families (total of 14 tumors) with IFS and 15 sporadic somatotropinomas. Eighteen polymorphic markers spanning an approximately 9-Mb region on chromosome 11q12.2-11q13.3 were used. MAIN OUTCOME AND RESULTS: Loss of heterozygosity was found in all families and in 40% of sporadic tumors. Although multiple and frequently discontinuous, the presence of allelic loss limited by retentions at their boundaries suggests a new interval of approximately 2.21 Mb on chromosome 11q13.3. Three potential candidate genes (DOC-1R, LOC 399919, and LOC 440049) in this region were sequenced, although no mutations were found. CONCLUSIONS: Identification of the IFS gene is still necessary because it will not only provide insight into the molecular basis of IFS but may also elucidate the pathogenesis of sporadic somatotropinomas.