Binge alcohol treatment of adolescent rats followed by alcohol abstinence is associated with site-specific differences in bone loss and incomplete recovery of bone mass and strength

The effects of low dose parathyroid hormone on lumbar vertebrae in a rat model for chronic alcohol abuse

This study evaluated the hypothesis that increased bone marrow adipogenesis is coupled to decreased bone formation in rats consuming alcohol. Parathyroid hormone (PTH) increased bone formation but had no effect on marrow adiposity. We conclude that increased adiposity does not prevent the bone anabolic response to PTH.

INTRODUCTION

Alcoholism results in decreased bone formation and increased bone marrow adiposity. The present study tested the hypothesis that these reciprocal changes are coupled by evaluating the effect of intermittent PTH on bone formation and bone marrow adiposity in a rat model for chronic alcohol abuse.

METHODS

Three-month-old male Sprague Dawley rats (n = 10-11/group) were fed the Lieber-DeCarli liquid diet with 35% of the calories derived from ethanol. Control rats were pair-fed an isocaloric alcohol-free diet. The rats were administered low dose PTH (1 µg/kg/day sc, 5 d/week) or vehicle for 6 weeks. Cancellous bone architecture in lumbar vertebrae was evaluated by micro-computed tomography followed by histomorphometric assessment of bone formation and marrow adiposity.

RESULTS

Alcohol increased bone marrow adiposity but reduced bone formation. The latter was due to decreases in mineralizing perimeter/bone perimeter, a surrogate measure of osteoblast number, and mineral apposition rate, a measure of osteoblast activity. PTH increased bone formation by increasing mineralizing perimeter/bone perimeter. In contrast, PTH had no effect on mineral apposition rate or bone marrow adiposity. Interactions between alcohol consumption and PTH treatment were not detected for any endpoints evaluated.

CONCLUSIONS

PTH treatment blunted the decrease in mineralizing perimeter/bone perimeter in alcohol-fed rats but was ineffective in preventing the increase in bone marrow adiposity. These findings suggest that the alcohol-induced increase in adipocytes is not directly responsible for the accompanying reduction in bone formation.

The effects of pre-pubertal gonadectomy and binge-like ethanol exposure during adolescence on ethanol drinking in adult male and female rats

The pubertal surge in gonadal hormones that occurs during adolescence may impact the long-term effects of early alcohol exposure and sex differences in drinking behavior in adulthood. We investigated this hypothesis by performing sham or gonadectomy surgeries in Long-Evans rats around post-natal day (P) 20. From P35-45, males and females were given saline or 3.0 g/kg ethanol using a binge-like model of exposure (8 injections total). As adults (P100), they were trained to self-administer ethanol via a sucrose-fading procedure and then given access to different unsweetened concentrations (5-20%, w/v) for 5 days/concentration. We found that during adolescence, ethanol-induced intoxication was similar in males and females that underwent sham surgery. In gonadectomized males and females, however, the level of intoxication was greater following the last injection compared to the first. During adulthood, females drank more sucrose per body weight than males and binge-like exposure to ethanol reduced sucrose consumption in both sexes. These effects were not seen in gonadectomized rats. Ethanol consumption was higher in saline-exposed females compared to males, with gonadectomy reversing this sex difference by increasing consumption in males and decreasing it in females. Exposure to ethanol during adolescence augmented ethanol consumption in both sexes, but this effect was statistically significant only in gonadectomized females. Together, these results support a role for gonadal hormones during puberty in the short- and long-term effects of ethanol on behavior and in the development of sex differences in consummatory behavior during adulthood.

Long-term modulations in the vertebral transcriptome of adolescent-stage rats exposed to binge alcohol

AIMS

Dangerous alcohol consumption practices are common in adolescents, yet little is known about their consequences on attainment of peak bone mass and long-term skeletal integrity. We previously demonstrated that binge alcohol-exposed adolescent rats showed site-specific reductions in accruement of bone mineral density and bone strength, which were incompletely recovered following prolonged alcohol abstinence. Currently, we analysed the vertebral transcriptome of adolescent rats following alcohol treatment and abstinence to identify long-term molecular changes in the lumbar spine.

METHODS

Sixty male adolescent Sprague-Dawley rats were assigned to one of six treatment groups receiving binge alcohol (3 g/kg) or saline i.p., 3 consecutive days (acute binge), 4 consecutive weekly (3-day) binge cycles (chronic binge) or 4 weekly binge cycles followed by a 30-day abstinence period (chronic binge with abstinence). Following treatment, lumbar vertebrae were assayed for global transcriptional changes using gene array technology.

RESULTS

Analysis of the adolescent rat vertebral transcriptome identified clusters of binge alcohol-sensitive genes displaying differential expression patterns starting before bone damage was seen and persisting after alcohol treatment was discontinued. Functional grouping of these gene clusters identified candidate cellular pathways affected following acute and chronic binge treatment, as well as pathways remaining modulated following abstinence.

CONCLUSIONS

These results demonstrate that binge alcohol exposure can produce disruptions of normal bone gene expression patterns in the adolescent rat that persist well beyond the period of active intoxication. This data may have relevance to peak bone mass attainment and future risk of skeletal disease in adolescents engaging in repeated binge-drinking episodes.

Image registration demonstrates the growth plate has a variable affect on vertebral strain

Characterizing the biomechanical behavior of the vertebrae is important in understanding the impact of structural and material changes on spinal growth and fracture risk. The growth plate is critical for the normal development of the skeleton, with abnormalities leading to uneven maturation. Little is known about how growth plates affect the stress and strain experienced by the surrounding bone. Concentrated strain within the growth plate may influence mechanical cell signaling during development, lead to increased fracture risk at this site and may influence average bone strain measures. It is hypothesized that the growth plates and adjacent bony areas will take up a large amount of the strain within rat-tail vertebrae under axial compressive loading, leading to increased average bone strain measures. The sixth caudal vertebrae of 8 rnu/rnu rats were muCT scanned in both loaded (20-32 N axial compression) and unloaded configurations. Image registration was used to calculate strain in the bone due to the applied load by finding a spatial mapping between the two scans. In seven of the eight rats, the majority of the strain measured within their vertebrae was concentrated in the growth plates. Five of the specimens had growth plates that demonstrated rigid behavior in contrast to compliant growth plate behavior seen in the other three rats. The presence of a compliant growth plate led to higher average (-0.03 vs. -0.01) and maximum (-0.13 vs. -0.02) strains. The strain within the growth plate is important to consider when interpreting apparent tissue level biomechanical data commonly reported in the literature as this study suggests strains are not uniformly distributed with high concentrations in and around the growth plate. This strain distribution may provide insight into the mechanical signals that cells experience during the formation of new bone, with the higher strains near the growth plate signaling cells to lay down more bone, while also leading to increased risk of fracture in this region.

Binge-pattern alcohol exposure during puberty induces sexually dimorphic changes in genes regulating the HPA axis

Maternal alcohol consumption during critical periods of fetal brain development leads to devastating long-term consequences on adult reproductive physiology, cognitive function, and social behaviors. However, very little is known about the long-term consequences of alcohol consumption during puberty, which is perhaps an equally dynamic and critical period of brain development. Alcohol abuse during adulthood has been linked with an increase in clinically diagnosed anxiety disorders, yet the etiology and neurochemical mechanisms of alcohol-induced anxiety behavior is unknown. In this study, we determined the effects of binge ethanol exposure during puberty on two critical central regulators of stress and anxiety behavior: corticotrophin-releasing hormone (CRH) and arginine vasopressin (AVP). Our results showed that ethanol increased plasma corticosterone (CORT) levels in both sexes, yet binge-treated animals had significantly lower CORT levels than animals exposed to a single dose, suggesting that the hypothalamo-pituitary-adrenal (HPA) axis habituated to the repeated stressful stimuli of ethanol. Binge ethanol exposure also significantly increased CRH and AVP gene expression in the paraventricular nucleus of males, but not females. Overall, our results demonstrate that binge ethanol exposure during puberty changes the central expression of stress-related genes in a sex-specific manner, potentially leading to permanent dysregulation of the HPA axis and long-term behavioral consequences.