Histomorphometric analysis of the epiphyseal growth plate in rats after prenatal alcohol exposure

Phenotype and synthesis activity of joint chondrocytes extracted from newborn rats with prenatal ethanol exposure

Thirteen female Wistar rats were divided into two groups: one treated with ethanol and the other of untreated. Four newborns from each mother were selected and weighed, measured, and evaluated for physical characteristics. From these neonates, chondrocytes were extracted from the articular cartilages of the femur and tibia, and cultivated in a chondrogenic medium at 37^oC and 5% CO₂. At 7, 14, and 21 days of cultivation, alkaline phosphatase activity tests, MTT conversion to formazan, and percentage area covered by cells per field were performed. At 21 days, the percentage of PAS⁺ areas in 3D cultures was performed, as well as the evaluation of gene transcript expression for aggrecan, SOX-9, collagen type II, collagen X, Runx-2, and VEGF by real-time RT-PCR. The means were compared by Student's t-test. The weight of the ethanol group neonates was significantly lower than that of the controls. Chondrocyte cultures from the ethanol group showed significantly higher AP activity, MTT conversion, and cell percentage. There was higher expression of collagen type II and lower expression of SOX-9 in the ethanol group. There was no difference in the percentage of PAS⁺ areas in pellets and in expression of aggrecan, collagen X, Runx-2, or VEGF between groups. In conclusion, prenatal exposure to ethanol alters the phenotype and activity of offspring chondrocytes, which may be mechanisms by which endochondral bone formation is compromised by maternal ethanol consumption.

Disruption of Bone Zinc Metabolism during Postnatal Development of Rats after Early Life Exposure to Cadmium

This current study was conducted to investigate whether bone tissue impairment induced by early life exposure to cadmium (Cd) during postnatal development could result from disruption to zinc (Zn) metabolism. For this reason, the offspring from mothers receiving either tap water, Cd, Zn or Cd + Zn during gestation and lactation periods were euthanized at PND21 and PND70. At the end of the lactation period (PND21), our results showed that exposure to Cd increased Cd accumulation and Zn depletion in the femur. Furthermore, calcium (Ca) level was reduced. At the molecular level, Cd induced an increase of MT-1 expression and caused an upregulation of ZIP2 accompanied with a down-regulation of ZnT5. Runx2, ALP, colα-1 and Oc mRNA levels were also decreased. In plasma, IGF-1 and osteocalcin concentrations were decreased. Further, Cd altered femoral growth by generating changes in the growth plate. Consequently, the toxic effect of Cd persisted at adult age (PND70) by decreasing bone volume (%BV/TV), bone mineral density (BMD) and Ca content and by increasing trabecular separation (Tb.Sp) in the distal femur. Interestingly, Zn supply provided total or partial corrections of several toxic effects of Cd. These data suggest that the increases of Zn bioavailability as well as the reduction of Cd accumulation in the femur following the changes in ZIP2 and ZnT5 expression are part of the mechanism involved in Zn protection against Cd toxicity on bone tissue.

Involvement of Zn Depletion in Cd-Induced Toxicity on Prenatal Bone Formation in Rat

This study explored the potential toxicity of Cd on the Zn bone depletion in prenatal bone formation. Female rats received either tap water, Cd, Zn, or Cd + Zn in their drinking water during gestation, and some markers of bone formation were studied in their fetuses removed at the 20th day of pregnancy (GD20). Cd exposure induced maternal hypozincemia and Zn depletion in the femur of the fetuses. A striking inhibition of bone formation in fetuses, expressed by decreases in femur length, width, and area, by the shortening of diaphysis, and by a decrease in length and area of distal and proximal proliferative zones, was observed in fetuses from Cd-exposed mothers. At the molecular level, Cd caused upregulation of MT-1 and ZIP2 genes and significantly depressed the expression of the ZnT5, colα1, osteocalcin, and ALP genes in the femur. Interestingly, Zn treatment ameliorated the Cd-induced maternal hypozincemia and femoral changes and partially restored the normal histomorphometry of the femur. These results suggest that the observed toxic effects of Cd are, at least in part, mediated by the disruption of maternal Zn metabolism during pregnancy leading to Zn depletion and thus to perturbation of prenatal bone formation.

Prenatal ethanol exposure disrupts the histological stages of fetal bone development

Maternal ethanol intake during pregnancy results in impairments in general growth and skeletal development in the offspring. We have previously shown that ethanol retards skeletal ossification at doses lower than those that affect growth. Moreover, skeletal sites vary in their sensitivity to ethanol effects, with more severe effects occurring in bones that undergo a greater proportion of their development in utero. Taken together, these data suggest that ethanol has specific effects on bone development, and that later stages in the ossification process may be particularly affected. Such effects could have important implications for the offspring's long-term bone health, as studies suggest that the intrauterine environment can program the skeleton. The present study examined the histological stages of bone development to determine if prenatal ethanol exposure alters the morphological development of the growth plate in the fetal rat. Rats were fed a liquid diet containing ethanol (Ethanol, E group), or without ethanol (Pair-Fed, PF, or Control, C groups) for 6 weeks: 3 weeks prior to breeding and during 3 weeks of pregnancy. Fetal tibiae were fixed, decalcified and stained for histological analysis on day 21 of gestation. Maternal ethanol intake resulted in a significant decrease in fetal total bone and diaphysis lengths, compared with tibiae from PF and C fetuses. Although the lengths of the epiphyses were not affected, ethanol disrupted the organization of the histological zones within the epiphyses. Prenatal ethanol exposure decreased the length of the resting zone, but increased the length of the hypertrophic zone. Enlargement of the hypertrophic zone is consistent with an effect of ethanol on the later stages of bone development; however, ethanol's effect on the resting zone indicates that earlier stages of bone development may also be disrupted. The functional significance of these morphological changes to long-term bone health remains to be determined.

Prenatal ethanol exposure has differential effects on fetal growth and skeletal ossification

There is increasing evidence suggesting that the intrauterine environment may influence long-term bone health and the risk of developing osteoporosis in later life. Alcohol (ethanol) is one factor whose presence in the prenatal environment has long-term consequences for the offspring, including permanent growth retardation. Moreover, prenatal ethanol exposure retards both fetal and postnatal bone development. It is unknown if ethanol's effects on skeletal development result from generalized growth retardation or effects specific to skeletal development. Furthermore, the level of ethanol exposure required to produce skeletal effects is unknown. The objectives of this study were to determine (1) if ethanol exerts specific effects on fetal skeletal development that are independent from its effects on general growth, and (2) the level of prenatal ethanol exposure required to affect fetal growth and skeletal ossification. Rats were fed isocaloric diets with ethanol (15%, 25%, or 36% ethanol-derived calories (EDC), approximating low, moderate, and high exposure levels), or without ethanol (pair-fed, PF, or control, C groups), prior to and throughout 21 days of gestation. The degree of E-induced delay in development was determined by comparison of E fetuses on d21 gestation to C fetuses on d17-d21 gestation. Prenatal ethanol exposure at 36% EDC decreased fetal body weight, length, and skeletal ossification compared with PF and C fetuses on d21 gestation. Importantly, effects on ossification, but not body weight or length, were also seen at the more moderate dose of 25% EDC, and the number of bones affected and the severity of effects on ossification tended to increase with dose of ethanol. Comparison of E fetuses on d21 gestation with C fetuses from d17 to 21 gestation indicated that the ethanol-induced delay in development differed for weight and skeletal ossification, and was not uniform among skeletal sites. Taken together, these data suggest that prenatal ethanol exposure has effects on fetal skeletal development that are independent of those on overall fetal growth, and that these effects occur even at moderate levels of maternal drinking. Effects of prenatal ethanol exposure on fetal skeletal development could potentially increase the offspring's risk of osteoporosis later in life.

Effect of Duration of Maternal Alcohol Consumption on Calcium Metabolism and Bone in the Fetal Rat

BACKGROUND

Prenatal ethanol exposure can retard fetal growth and delay skeletal development. Ethanol also impairs maternal calcium (Ca) homeostasis and this impairment could mediate some of ethanol's effects on the fetal skeleton. Our previous studies suggest that the duration of maternal ethanol consumption may be an important factor for determining the severity of ethanol's effects on Ca homeostasis and fetal skeletal development. The purpose of this study was, therefore, to determine the effect of the duration of maternal ethanol consumption on fetal growth and skeletal development and to investigate the possibility that ethanol's effects may be related to perturbations in fetal/maternal Ca homeostasis.

METHODS

Rats were fed ethanol (36% ethanol-derived calories) in liquid diets for 3 weeks (days 1-21 of gestation) or 6 weeks (for 3 weeks before and throughout gestation). Fetuses were collected on day 21 of gestation, and body weight and length were measured. Fetuses were stained to determine the degree of skeletal ossification, and fetal blood was analyzed for ethanol, Ca (total and ionic Ca), albumin, parathyroid hormone (PTH), and osteocalcin.

RESULTS

Maternal ethanol consumption decreased fetal growth and delayed fetal skeletal development. Although there was a trend for fetal body length and serum osteocalcin levels to be more severely affected with an increased duration of maternal ethanol consumption, duration had no effect on fetal body weight or skeletal ossification. Fetal Ca homeostasis was also affected by ethanol exposure, with fetal hypocalcemia apparent after 6 weeks of maternal ethanol intake. A significant inverse relationship was found between fetal blood Ca levels and blood alcohol concentration (BAC), suggesting that the severity of the fetal hypocalcemia may have been related to differences in fetal BAC, rather than duration of maternal ethanol intake. Fetal serum PTH levels did not differ significantly among treatment groups indicating that the fetal hypocalcemia was not caused by a decrease in PTH levels.

CONCLUSIONS

Prenatal ethanol exposure impaired Ca homeostasis and skeletal development in the fetal rat. The severity of ethanol's effects was only marginally dependent on the duration of maternal ethanol consumption per se and seemed to be more related to the relative exposure of the fetus to ethanol (fetal BAC). The relationship between the ethanol-induced fetal hypocalcemia and skeletal effects remains to be determined.

Quantitative histomorphometric analysis of the human growth plate from birth to adolescence

Longitudinal bone growth occurs via the transformation of growth plate cartilage into bone through a series of cell and matrix changes, termed endochondral ossification. In this study, we characterize the development of trabecular bone from growth plate cartilage in the human rib from birth to adolescence. The height of the proliferative and hypertrophic zones within the growth plate and the primary bone spongiosa decreased with increasing age, with the greatest change observed in the first year of postnatal life. Within these zones, an internal rearrangement of tissue structure occurred. The matrix volume fraction (either cartilage or bone) increased with age in each of the zones. A concomitant increase in cartilage septae thickness and bone trabecular thickness was observed. A decrease in cartilage septae number was seen in the proliferative zone and a decrease in bone trabeculae number was also observed in the primary spongiosa. However, no difference in cartilage septae number was noted in the hypertrophic zone, the region at which cartilage is transformed into bone. Together the proliferative and hypertrophic regions of the growth plate and the bone primary spongiosa appear to constitute the active growth region, with concomitant changes observed that result in longitudinal growth. In contrast, bone mineral volume in the secondary spongiosa was stable over the ages examined; however, trabecular architecture underwent consolidation as trabecular number decreased and trabecular thickness increased. The integration of the structural transformation from cartilage to bone is crucial in achieving the dual purposes of longitudinal growth and peak bone mass. The structure developed during childhood will have an important bearing on the response to bone-altering disease in later life.

Quantitative analysis of trabecular morphogenesis in the human costochondral junction during the postnatal period in normal subjects

BACKGROUND

Quantitative histomorphometric features of the bone growth plate in the human rib have been investigated in infants, ranging in age from 3-36 weeks (mean 18.6 weeks) to provide data currently not available.

METHODS

Measurements were taken in each histological zone of the growth plate. Data from 20 cases were pooled and parameters describing the characteristic features of trabecular bone calculated using morphometric formulae. The measurements were made from the resting zone of the cartilage to the secondary spongiosa, 3.78 mm from the starting point.

RESULTS

Cartilage volume fraction decreased from 78% in the resting zone to a bone volume fraction of between 20% and 30% in the secondary cancellous bone. Cartilage matrix surface increased rapidly in the cartilage and bone mineral surface declined in correspondence with the development of primary bone. The distance between chondrocyte lacunae was observed to decrease throughout the cartilage to a transverse septa thickness of 18 microns in the hypertrophic zone. A rapid increase in trabecular thickness to 128 microns was observed in the primary spongiosa, the secondary spongiosa ranging between 137 microns and 168 microns. Spacing, chondrocyte profile transverse diameter, increased to 30 microns in the hypertrophic zone, following which an increase in trabecular separation to 347 microns was observed in the primary spongiosa. The number of transverse intervals between individual chondrocyte lacunae was observed to increase in the cartilage to a maximum of 21.3 cartilaginous or mineralised septa per mm of growth plate length in the hypertrophic zone. Trabeculae in the metaphysis then decreased in number to approximately 1.5 trabeculae per mm in the secondary spongiosa.

CONCLUSIONS

These data thus provide new insight into the development of trabecular structure during growth and normal values for the comparison of tissue from skeletal dysplasias and growth disorders.