Measurement of estrogen effect on bone turnover by 2H2O labeling

A collagen extraction and deuterium oxide stable isotope tracer method for the quantification of bone collagen synthesis rates in vivo

The development of safe and practical strategies to prevent weakening of bone tissue is vital, yet attempts to achieve this have been hindered by a lack of understanding of the short-term (days-weeks) physiology of bone collagen turnover. To address this, we have developed a method to quantify bone collagen synthesis in vivo, using deuterium oxide (D₂ O) tracer incorporation techniques combined with gas chromatography pyrolysis isotope-ratio mass spectrometry (GC-pyrolysis-IRMS). Forty-six male and female rats from a selectively bred model ingested D₂ O for 3 weeks. Femur diaphyses (FEM), tibia proximal (T-PRO), and distal (T-DIS) epiphyses-metaphyses and tibia mid-shaft diaphyses (T-MID) were obtained from all rats after necropsy. After demineralisation, collagen proteins were isolated and hydrolysed and collagen fractional synthetic rates (FSRs) determined by incorporation of deuterium into protein-bound alanine via GC-pyrolysis-IRMS. The collagen FSR for the FEM (0.131 ± 0.078%/day; 95% CI [0.106-0.156]) was greater than the FSR at T-MID (0.055 ± 0.049%/day; 95% CI [0.040-0.070]; p < 0.001). The T-PRO site had the highest FSR (0.203 ± 0.123%/day; 95% CI [0.166-0.241]) and T-DIS the lowest (0.027 ± 0.015%/day; 95% CI [0.022-0.031]). The three tibial sites exhibited different FSRs (p < 0.001). Herein, we have developed a sensitive method to quantify in vivo bone collagen synthesis and identified site-specific rates of synthesis, which could be applicable to studies of human bone collagen turnover.

Gene expression and distribution of key bone turnover markers in the callus of estrogen-deficient, vitamin D-depleted rats

An experimental rat model was used to test the hypothesis that in osteoporosis (OP) the molecular composition of the extracellular matrix in the fracture callus is disturbed. OP was induced at 10 weeks of age by ovariectomy and a vitamin D(3)-deficient diet, and sham-operated animals fed normal diet served as controls. Three months later a closed tibial fracture was made and stabilized with an intramedullary nail. After 3 and 6 weeks of healing, the animals were killed and the fracture calluses examined with global gene expression, in situ mRNA expression, and ultrastructural protein distribution of four bone turnover markers: osteopontin, bone sialoprotein, tartrate-resistant acid phosphatase, and cathepsin K. Global gene expression showed a relatively small number of differently regulated genes, mostly upregulated and at 3 weeks. The four chosen markers were not differently regulated, and only minor differences in the in situ mRNA expression and ultrastructural protein distribution were detected. Gene expression and composition of fracture calluses are not generally disturbed in experimental OP.

New approaches and recent results concerning human-tissue collagen synthesis

PURPOSE OF REVIEW

Knowledge of the physiological regulation of human-tissue collagen metabolism in vivo is poor, due to the lack of appropriately robust methods. Recent application of stable isotope tracer techniques to measure human collagen synthesis has provided some insights into the role of nutrition and exercise on collagen turnover in the extracellular matrix of the musculoskeletal system.

RECENT FINDINGS

Collagen turnover in the musculoskeletal system is faster than previously thought. Bone collagen synthesis is increased by feeding, whereas both muscle collagen and tendon are unresponsive. Exercise stimulates collagen synthesis in both muscle and tendon in an apparently coordinated manner. There are also sex differences and normal aging is associated with increased muscle collagen synthesis and reductions in bone collagen synthesis, particularly in mature bone collagen.

SUMMARY

Collagen turnover appears to be faster than previously thought and is regulated by feeding and exercise, in a tissue-specific manner. Further application of these approaches, coupled with measures of gene and protein expression, to measure the acute regulation of collagen, will lead to a better understanding of the physiology and pathophysiology of human collagen turnover. This is particularly important for developing new therapies to improve bone health and minimize tissue fibrosis.

Heavy water labeling method for measuring the effect of genistein on mammary gland carcinogenesis

Heavy water labeling method was applied to measure the effect of genistein on mammary gland carcinogenesis by incoporating (2)H from (2)H(2)O into the deoxyribose (dR) moiety of purine deoxyribonucleotides in dividing cells. In the present study, we followed the study design of Lamartiniere group to evaluate the efficacy of (2)H(2)O labeling on the measurement of mammary gland carconogenesis. Female Sprague-Dawley rats were fed estrogen-free AIN-93G diet starting 1 week before breeding and continuing through pregnancy and lactation. Female pups were assigned to the following groups on postnatal day 16 and fed AIN-93G diet: vehicle (dimethylsulfoxide) (DMSO), genistein, and estradiol benzoate (EB). On postnatal days 16, 18, and 20, female pups were injected subcutaneously with 500 mug genistein/g body wt, 500 ng EB/g body wt, or an equivalent volume of the vehicle. At day 50 postpartum, half of each group were gavaged with 60 mg dimethylbenz[a]anthracene (DMBA) in perila oil. After 1 week of DMBA treatment, all animals were labeled with (2)H(2)O by administration of 4% (2)H(2)O in drinking water after single intraperitonial bolus injection with 99.9% (2)H(2)O until sacrifice on postnatal day 81. The time-dependent weight gains were observed in all groups throughout the experimental period. The enrichment of body (2)H(2)O was attained at 1.84-2.47% through oral administration of (2)H(2)O. Mammary epithelial cell proliferation was measured by enrichment (EM1) of dA from rats. DMBA-treated groups showed higher fractional synthesis than DMBA non-treated groups. The group exposed only to genistein showed significantly lower EM1 (1.46 +/- 0.87%) than those of control groups, i.e., the DMBA non-treated group (2.28 +/- 0.29%) and the DMBA-treated group (2.32 +/- 0.28%). Bromodeoxyuridine (BrdU) immunostaining of mammary tissue revealed that genistein reduced proliferation of the mammary epithelial, and the number of cells stained positive for BrdU both in DMBA-treated groups and DMBA non-treated groups. H&E staining of mammary epithelium also showed that the exposure to genistein decreased proliferation of the mammary epithelium. The epithelium in the rats treated with DMBA showed mostly multiple cell layers, in contrast to the mostly double layer shown in the DMBA non-treated rats. The exposure to genistein in the prepubertal period inhibited mammary epithelial cell proliferation. In conclusion, the (2)H(2)O labeling results were in good agreement with the results of BrdU incorporation and histomorphometry, which demonstrates that (2)H(2)O labeling can be used as a tool to measure carcinogenesis.

Alcohol-induced bone degradation and its early detection in the alcohol-fed castrated rats

The objective of this study was to examine alcohol-induced changes of bone in hormone-deficient males using the developed method. In the process of bone resorption, type I collagen crosslinking molecules, pyridinoline (PYD), are released into the circulation and cleared by the kidneys. (2)H(2)O as a tracer has been applied to measure the synthesis rates of slow-turnover proteins and successfully applied to bone collagen synthesis in our hormone deficiency rats. This study demonstrated for the first time, the early changes of the femur bone degradation in hormone-deficient male individuals, more influenced by alcohol through histopathological study, serum PYD assay, and (2)H(2)O labeling. We also observed that serum PYD was a sensitive pathological marker of bone degradation in castrated osteoporosis males and the unique features of (2)H(2)O labeling to measure the bone turnover collagen synthesis rates were excellent markers of bone degradation and aging.