Insulin and bone health in young adults: The mediator role of lean mass

BACKGROUND

The positive relationship between lean mass (LM) and bone health is well known, but a positive association between insulin and LM has also been described. Insulin has some anabolic properties on bone through the stimulation of osteoblast differentiation, yet the role of LM as a confounder or mediator in this relationship remains uncertain.

OBJECTIVE

To examine whether the association between insulin levels and bone health is mediated by LM.

METHODS

A cross-sectional study was conducted at the Castilla La Mancha University (Spain) involving 466 young adults (113 young men; 19.5±2.3 years). LM and total-body bone mineral content (BMC) were measured by dual energy x-ray absorptiometry, and insulin was measured in fasting serum samples.

RESULTS

Young adults with high total LM had higher values of total-body BMC than their peers after controlling for age and sex, this relationship persisted after adjusting for insulin levels (p<0.001). In mediation analyses, insulin levels were positively associated with total-body BMC (b = 0.05; p<0.001) and total LM acted as an intermediate variable, attenuating the association between insulin levels and total-body BMC (b = -31.98; p>0.05) as indicated by Sobel test values for indirect effect (z = 4.43; p<0.001).

CONCLUSIONS

LM plays an important role in the relationship between insulin levels and bone health, in such a way that while increases in LM have a positive influence on bone health, they are also negatively associated with insulin levels.

Mouse Amelogenin Exons 8 and 9: Sequence Analysis and Protein Distribution

Amelogenin is the major protein of the developing enamel. Two additional exons, termed 8 and 9, have been characterized in the rat. Our aim was: to identify the mouse amelogenin exons 8/9 sequences; to investigate the potential presence of the alternative spliced isoforms of amelogenin exons 8/9; and to immunolocalize proteins containing sequences encoded by exons 8/9 during odontogenesis. RT-PCR analysis with exon 9 anti-sense primer generated 2 major amplicons with the use of a mouse tooth cDNA library and dental cell lines. DNA sequence analysis showed 93% identify with the rat exons 8/9 sequence. Alternative splicing of exon 3 was also found, but only in cDNAs lacking exons 8 and 9. Immunohistochemistry localized exons 8/9-encoded proteins in ameloblasts, young odontoblasts, and stratum intermedium cells. Analysis of our data supports the hypothesis that: (1) AMELX contains 2 additional exons; (2) ameloblasts and odontoblasts synthesize amelogenin 8/9; and (3) amelogenin splice variants may have unique functions during tooth formation.

An 18-month vitreous fluorophotometric follow-up study in juvenile diabetics

The authors assessed a fluorophotometry follow-up study of 18 months in 24 juvenile insulin-dependent diabetic patients with no retinopathy. The initial duration of diabetes was 5.96 +/- 3.44 years and the glycosylated hemoglobin (HbA1c) was 10.12 +/- 2.27%. The baseline Vitreous Penetration Ratio transmittance value (VPRt) was 4.13 +/- 1.31 x 10-6 min-1 and after 18 months was 5.36 +/- 1.85 x 10-6 min-1, yielding a statistically significant difference (p < 0.01). The average HbA1c during the follow-up term was 9.80 +/- 1.72%. VPRt values were significantly correlated with the duration of diabetes and HbA1c. During the follow-up 3 patients developed foveal background diabetic retinopathy with respect to a high initial VPRt value (6.22 +/- 0.27 x 10-6 min-1), nevertheless, the other 7 patients with high baseline VPRt did not do so. We suggest that vitreous fluorophotometry could be a beneficial procedure in the management of insulin-dependent diabetic patients; however, there is not a cut-off value for VPRt values to help distinguish patients prone to develop retinopathy.

Chemiluminescent immunoassay (CLIA) for urinary albumin

A simple chemiluminescent immunoassay (CLIA) for urinary albumin has been developed based on the use of a chemiluminescent acridinium ester-labelled human albumin and a commercially available antiserum. It includes two incubation steps and a second polyethylene glycol-assisted antibody separation. The sensitivity of detection is 0.016 mg/l, the assay working range is 0.1-5 mg/l, and the inter-assay CVs are less than or equal to 15%. Using 10- and 50-fold sample dilutions in assay buffer, a wide working range (1-250 mg/l) is obtained covering normal and pathological conditions. Timed overnight urine samples (bed rest conditions) were collected on three consecutive days for each patient. Albumin excretion rate (AER) was 4.7 +/- 2.7 micrograms/min (mean +/- SD), range 1-15.9 micrograms/min in 36 healthy subjects (17 male, 19 female, ages 4-56 years), with day-to-day variations of 28.5 +/- 20% (mean +/- SD), range 3.3-76.1%. The use of an acridinium ester as a chemiluminescent (CL) label overcomes the disadvantages of short shelf-life and health and safety hazards associated with radioisotopes. Results compare favourably with those obtained using a commercially available RIA kit.