Effect of oral contraceptive treatment on bone mass acquisition in skeletally immature young female rats

Simultaneous nicotine and oral contraceptive exposure alters brain energy metabolism and exacerbates ischemic stroke injury in female rats

Smoking-derived nicotine (N) and oral contraceptives (OC) synergistically exacerbate ischemic brain damage in the females and underlying mechanisms remain elusive. Our published study showed that N toxicity is exacerbated by OC via altered mitochondrial function owing to a defect in the activity of cytochrome c oxidase. Here, we investigated the global metabolomic profile of brains of adolescent female Sprague-Dawley rats exposed to N ± OC. Rats were randomly exposed to saline or N + /-OC for 16-21 days followed by random allocation into two cohorts. One cohort underwent transient middle cerebral artery occlusion and histopathology was performed 30 days later. From the second cohort, cortical tissues were collected for an unbiased global metabolomic profile. Pathway enrichment analysis showed significant decrease in glucose, glucose 6-phosphate and fructose-6-phosphate, along with a significant increase in pyruvate in the N + /-OC exposed groups when compared to saline (p < 0.05), suggesting alterations in the glycolytic pathway which were confirmed by Western blot analyses of glycolytic enzymes. Infarct volume quantification showed a significant increase following N alone or N + OC as compared to saline control. Because glucose metabolism is critical for brain physiology, altered glycolysis deteriorates neural function, thus exacerbating ischemic brain damage.

Nicotine Exposure Along with Oral Contraceptive Treatment in Female Rats Exacerbates Post-cerebral Ischemic Hypoperfusion Potentially via Altered Histamine Metabolism

Smoking-derived nicotine (N) and oral contraceptives (OCs) synergistically exacerbate ischemic brain damage in the female, and the underlying mechanisms remain elusive. Our published study showed that N toxicity is exacerbated by OC via altered mitochondrial electron transport chain function. Because mitochondria play an important role in cellular metabolism, we investigated the global metabolomic profile of brains of adolescent and adult female Sprague-Dawley rats exposed to N with or without OC (N+/-OC). Rats were randomly exposed to saline or N+/-OC for 16-21 days followed by random allocation into two cohorts. The first cohort was used to characterize the cortical metabolome. Pathway enrichment analysis showed a significant increase in several histamine metabolites including 1-methylhistamine, 1-methyl-4-imidazoleacetate, and 1-ribosyl-imidazleacetate, along with carnosine and homocarnosine in adolescent and adult animals treated with N and N+OC in relation to respective saline controls, which may be reflective of altered histamine metabolism with nicotine treatment. We also observed reduced levels of the neurotransmitters N-acetyl-aspartyl-glutamate (NAAG), gamma-aminobutyrate (GABA), and N-methyl-GABA in N+OC treatment in adolescent animals. The second cohort underwent bilateral carotid artery occlusion and hypotension followed by cerebral blood flow (CBF) assessment a day later. Autoradiographic images of the brain 24 h after ischemic episodes showed severe reduction in cortical and hippocampal local CBF in N+/-OC-exposed rats compared with saline treated. Because GABA and histamine are critical for CBF maintenance, altered metabolism of these neurotransmitters may be responsible for observed severe post-ischemic hypoperfusion, which in turn exacerbates ischemic brain damage.

Nicotine and estrogen synergistically exacerbate cerebral ischemic injury

The greater incidence of myocardial infarction, cardiac arrest, and ischemic stroke among women who smoke and use oral contraception (OC) compared to women who do not smoke and who do or do not use OC may be due in part to how nicotine influences endocrine function in women. For example, we recently demonstrated that chronic exposure to nicotine, the addictive agent in tobacco smoke responsible for the elevated risk of cardiac arrest, abolishes the endogenous or exogenous 17β-estradiol-conferred protection of the hippocampus against global cerebral ischemia (a potential outcome of cardiac arrest) in naive or ovariectomized female rats. In the current study we examined the hypotheses that (1) a synergistic deleterious effect of nicotine plus oral contraceptives exacerbates post-ischemic hippocampal damage in female rats, and (2) nicotine directly inhibits estrogen-mediated intracellular signaling in the hippocampus. To test first hypothesis and to simulate smoking behavior-induced nicotine levels in the human body, we implanted osmotic pumps containing nicotine in the female rats for 16 days. Furthermore, we mimicked the use of oral contraceptives in females by administering oral contraceptives orally to the rat. Rats exposed to either nicotine alone or in combination with oral contraceptives were subjected to an episode of cerebral ischemia and the resultant brain damage was quantified. These results showed for the first time that nicotine with oral contraceptives did indeed exacerbate post-ischemic CA1 damage as compared to nicotine alone in naive female rats. In ex vivo hippocampal slice cultures, we found that nicotine alone or with 17β-estradiol directly hinders estrogen receptors-mediated phosphorylation of cyclic-AMP element binding protein, a process required for neuronal survival and also exacerbates ischemic damage. Thus, nicotine can affect the outcome of cerebral ischemia by influencing brain endocrine function directly rather than through indirect systemic effects.

Multigenerational exposure to ethinyl estradiol affects bone geometry, but not bone mineral density in rats

Estrogenic compounds are known to prevent bone loss in ovariectomized adult rats; however, their effects on bone in developing and reproductively-intact rats are less well-understood. In a large multigenerational experiment 0, 2, 10, or 50 ppb ethinyl estradiol (EE) in the diet was fed to intact male and female rats from conception until either weaning, postnatal day 140, or continuously for 2 years. Vertebrae (lumbar and caudal) and femurs were collected from subsets of these animals at necropsy at 48 days, 70 days, 140 days, or 2 years of age and subjected to dual-energy X-ray absorptiometry (DXA) scanning to measure bone mineral density (BMD), bone mineral content (BMC), and bone area. In addition, the length, cross-sectional area, marrow area, and cortical bone area of the femurs were measured directly in all animals at PND 140 and 2 years. Continuous dietary intake of 50 ppb EE decreased body weight by 8-27%. BMD adjusted for body weight was not affected by EE, with the exception of an increase in the caudal vertebrae in males treated with 50 ppb EE. In female rats, continuous treatment with 50 ppb EE decreased length and cross-sectional area of the femur. The length of the femur was decreased in the first two generations following institution of a phytoestrogen-free diet at the initiation of the study in all animals, including controls, but returned to the original length by the third or fourth generation. The cross-sectional area of the femur also varied by generation. In conclusion, a high dose of EE throughout the lifespan resulted in decreased bone size in females, which could reduce the force required to break the bone. Furthermore, dietary changes may have epigenetic effects which persist for multiple generations.

Levetiracetam, Phenytoin, and Valproate Act Differently on Rat Bone Mass, Structure, and Metabolism

PURPOSE

Long-term treatment with antiepileptic drugs (AEDs) is associated with increased risk of fractures. Phenytoin (PHT) and valproate (VPA) have both been suggested to influence bone health, whereas levetiracetam (LEV) is scarcely studied. The present study compares the effect of these AEDs on bone mass, biomechanical strength, and bone turnover in rats.

METHODS

Female rats received PHT (50 mg/kg), VPA (300 mg/kg), or LEV (50 and 150 mg/kg) for 90 days. Dissected femurs were analyzed using dual energy x-ray absorptiometry (DXA), three-point cantilever bending, and histomorphological evaluation. Serum levels of biochemical bone turnover markers were monitored using immunoassay quantification.

RESULTS

PHT and VPA reduced bone mineral density (BMD) and content (BMC) in one or more bone compartments, whereas LEV did not. VPA induced increased bone turnover, whereas modest changes were observed for PHT. Interestingly, low-dose LEV was associated with reduced biomechanical strength of the femoral neck (mainly trabecular bone). In addition, low-dose LEV treatment resulted in significantly reduced levels of serum osteocalcin, a marker of bone formation. Histomorphological analyses indicated increased retention of cartilage remnants at the growth plate metaphysis of rats treated with low-dose LEV vs. controls.

CONCLUSIONS

PHT, VPA, and LEV exert differential effects on bone mass and strength, suggesting different mechanisms of action. The weakening effect of low-dose LEV on the femoral neck, despite a constant BMD, suggests a primary effect on bone quality. These findings warrant further human studies of possible adverse effects of LEV on bone development and growth, particularly in children and adolescents.