The Role of PTHrP in Regulating Mineral Metabolism During Pregnancy, Lactation, and Fetal/Neonatal Development

The Molecular Biology of Placental Transport of Calcium to the Human Foetus

From fertilisation to delivery, calcium must be transported into and within the foetoplacental unit for intracellular signalling. This requires very rapid, precisely located Ca2+ transfers. In addition, from around the eighth week of gestation, increasing amounts of calcium must be routed directly from maternal blood to the foetus for bone mineralisation through a flow-through system, which does not impact the intracellular Ca2+ concentration. These different processes are mediated by numerous membrane-sited Ca2+ channels, transporters, and exchangers. Understanding the mechanisms is essential to direct interventions to optimise foetal development and postnatal bone health and to protect the mother and foetus from pre-eclampsia. Ethical issues limit the availability of human foetal tissue for study. Our insight into the processes of placental Ca2+ handling is advancing rapidly, enabled by developing genetic, analytical, and computer technology. Because of their diverse sources, the reports of new findings are scattered. This review aims to pull the data together and to highlight areas of uncertainty. Areas needing clarification include trafficking, membrane expression, and recycling of channels and transporters in the placental microvilli; placental metabolism of vitamin D in gestational diabetes and pre-eclampsia; and the vascular effects of increased endothelial Orai expression by pregnancy-specific beta-1-glycoproteins PSG1 and PSG9.

Comparison between surgical and non-surgical management of primary hyperparathyroidism during pregnancy: a systematic review

PURPOSE

The management of primary hyperparathyroidism (PHPT) during pregnancy may be surgical or conservative. This study compared adverse outcomes between surgical and non-surgical treatments. Additionally, the study investigated the correlation between serum calcium values and complication rates.

METHODS

A systematic review of retrospective studies, case series, and case reports. Biochemical parameters, interventions, and outcomes of each pregnancy were recorded. The study population comprised two groups: the non-surgical and surgical groups. Adverse outcomes were categorized as maternal, obstetric, or neonatal.

RESULTS

The surgical and non-surgical groups consisted of 163 and 185 patients, respectively. A positive correlation was observed between the mean maternal gestational calcium value and both maternal and obstetric complication. Neonatal complications were more prevalent in patients treated conservatively across all maternal calcium values (p < 0.001). No significant differences were observed in maternal outcomes and overall obstetric outcomes between the study groups, albeit a higher mean serum calcium value in the surgical group (12.3 mg/dL) compared with the non-surgical group (11.1 mg/dL).

CONCLUSIONS

Given the significantly lower neonatal adverse outcomes in the surgical group compared to the non-surgical group, along with non-inferior maternal and obstetric outcomes in the surgical group, the overall data of this study suggest that parathyroidectomy is favorable to non-surgical management even in cases of mild hypercalcemia.

Pregnancy- and lactation-induced osteoporosis: a social-media-based survey

BACKGROUND

Pregnancy- and lactation-induced osteoporosis (PLO) presenting as spinal fractures is rare, and the spectrum of clinical presentation, risk factors and pathophysiology are incompletely understood. The aim of this study was to delineate clinical parameters, risk factors and osteoporosis-related quality of life (QOL) of women with PLO.

METHODS

Participants of a social-media (WhatsApp) PLO group and mothers of a parents' WhatsApp group (control group) were offered to fill a questionnaire, including an osteoporosis-related QOL section. The groups were compared using the independent Students t test for numerical variables, and the Chi-square test or Fisher's exact test for categorical variables.

RESULTS

Twenty-seven women with PLO and 43 in the control group (aged 36.2 ± 4.7 and 38.8 ± 4.3 years, respectively, p = 0.04) participated. Among women with PLO, more than 5 vertebrae were involved in 13 (48%), 4 vertebrae in 6 (22%), and 3 or fewer vertebrae in 8 (30%). Among the 24 women with relevant data, 21 (88%) had nontraumatic fractures; 3 (13%) women had fractures during pregnancy, and the remaining during the early postpartum period. Diagnosis was delayed for over 16 weeks for 11 (41%) women; 16 (67%) received teriparatide. Significantly lower proportions of women in the PLO group engaged in physical activity over 2 hours/week, before and during pregnancy (37 vs. 67%, p < 0.015 and 11 vs. 44%, p < 0.003, respectively). A lower proportion of the PLO than the control group reported calcium supplementation during pregnancy (7% vs. 30%, p = 0.03) and a higher proportion reported treatment with low-molecular-weight-heparin during pregnancy (p = 0.03). Eighteen (67%) of the PLO group expressed fear of fractures and 15 (56%) fear of falls, compared to none and 2%, respectively, of the control group (p < 0.00001 for both).

CONCLUSIONS

Most of the women with PLO who responded to our survey reported spinal fractures involving multiple vertebrae, delayed diagnosis, and treatment with teriparatide. Compared to a control group, they reported less physical activity and impaired QOL. For this uncommon yet severe condition, a multidisciplinary effort should be exerted for early identification and treatment, to alleviate back pain, prevent subsequent fractures and improve QOL.

Effect of ethanol consumption during pregnancy and lactation on bone histomorphometry and in vitro osteogenic differentiation of bone marrow mesenchymal stem cells in maternal rats

This study aimed to evaluate the effect of maternal ethanol consumption during gestation and lactation on bone mass and osteogenic differentiation of mesenchymal stem cells of the bone marrow (BMMSCs) in rats. Thirteen adult Wistar rats were used. The rats were mated, and after confirmation of gestation, (day 0) they were distributed in two groups: the control group and the ethanol-treated group. From the ninth day of gestation, the rats of the ethanol and control groups were administered 40% alcoholic solution (4 g ethanol/kg) and distilled water, respectively, daily via gavage until the thirtieth day of lactation. The BMMSCs were extracted from the right femurs and tibiae and cultured using an osteogenic medium for 7, 14, and 21 days. The conversion of MTT to formazan crystals, alkaline phosphatase activity, and percentages of cells per field were analyzed. The number of mineralized nodules per field was examined, and quantification of the gene transcripts for osteopontin, osteocalcin, and BMP-2 was evaluated on day 21 by real-time RT-PCR. Morphometric evaluations of the percentage of trabecular bone and cortical thickness in the left femur and tibia were performed. The means were compared by the Student's t-test, and the differences were considered significant if p < 0.05. The BMMSCs of the rats that consumed ethanol during gestation and lactation, when subjected to osteogenic differentiation in vitro, demonstrated higher conversion of MTT to formazan, higher alkaline phosphatase activity, a higher percentage of cells per field, higher expression of BMP-2, and higher synthesis of mineralized nodules when compared to those of control rat cells. However, there was no significant difference in the percentage of trabecular bone or cortical thickness between both groups. Hence, the consumption of ethanol during pregnancy and lactation did not alter the trabecular and cortical bone tissues of the femur and tibia compared with that of pregnant and lactating control rats that did not consume alcohol, despite BMMSCs showing higher osteogenic differentiation under in vitro conditions.

Calcium restriction during lactation has minimal effects on post-weaning mineral metabolism and bone recovery

Dietary calcium (Ca) restriction during lactation in the rat, which induces intra-cortical and endocortical remodeling, has been proposed as a model to study bone matrix maturation in the adult skeleton. The purpose of this study was to assess the effects of dietary Ca restriction during lactation on post-weaning mineral metabolism and bone formation. Mated female Sprague-Dawley rats were randomized into groups receiving either 0.6% Ca (lactation/normal Ca) or 0.01% Ca (lactation/low Ca) diets during lactation. Virgin animals fed normal Ca were used as controls (virgin/normal Ca). At the time of weaning, animals on the low Ca diet were returned to normal Ca and cohorts of all three groups were sacrificed at days 0, 1, 2, 7, and 14 post-weaning. Lactation caused bone loss, particularly at the endocortical surface, but the amount was not affected by dietary Ca. Rats in the lactation/low Ca group had increased cortical porosity compared to the other groups, particularly within the size range of secondary osteons. Dietary Ca restriction during lactation did not affect post-weaning bone formation kinetics or serum Ca and phosphate levels. In both lactation groups, there was a transient increase in phosphate and fibroblast growth factor 23 (FGF23) post-weaning, which trended toward virgin/normal Ca levels over time. Thus, the additional challenge of low dietary Ca during lactation to induce intra-cortical remodeling in the rat has minimal effects on bone formation kinetics and mineral metabolism during the post-weaning period, providing further justification for this model to study matrix maturation in the adult skeleton.

Clinical characteristics and bisphosphonates treatment of rare pregnancy- and lactation-associated osteoporosis

Pregnancy- and lactation-associated osteoporosis (PLO) is a rare disorder with poorly known etiology, pathophysiology, and therapy. We aimed to investigate the clinical characteristics of PLO and evaluate the effectiveness and safety of bisphosphonates on it. A total of 12 patients were diagnosed with PLO on the basis of medical history, bone mineral density (BMD), and/or fragility fractures during pregnancy and lactation. We investigated the clinical, biochemical, and radiological characteristics of patients. We assessed the effects of alendronate or zoledronic acid through observing the changes of bone turnover biomarkers and BMD during the treatment. Secondary osteoporosis was excluded by comprehensive differential diagnosis. The mean age of these patients was 31 ± 5 years old. All of these patients presented severe back pain. Multiple vertebral compression fractures (VCFs) were found in 10 patients, and the median (P25th, P75th) number of compressed vertebra was 3 (3, 5). Ten patients had vitamin D insufficiency or deficiency. Serum level of bone resorption marker (β-CTX with mean of 0.68 ± 0.41 ng/ml) was moderately higher than the normal range. BMD at lumbar spine, femoral neck, and total hip were low as 0.894 ± 0.153 g/cm², 0.728 ± 0.090 g/cm², and 0.728 ± 0.080 g/cm², respectively. Either alendronate or zoledronic acid could effectively relieve bone pain, reduce β-CTX level, and increase BMD. PLO is a rare type of osteoporosis, which was characterized by increased bone resorption and decreased BMD, even VCFs. Bisphosphonate therapy was well tolerated and effective in management of PLO, but needed to be further verified in randomized controlled trial.

Could use of Selective Serotonin Reuptake Inhibitors During Lactation Cause Persistent Effects on Maternal Bone?

The lactating mammary gland elegantly coordinates maternal homeostasis to provide calcium for milk. During lactation, the monoamine serotonin regulates the synthesis and release of various mammary gland-derived factors, such as parathyroid hormone-related protein (PTHrP), to stimulate bone resorption. Recent evidence suggests that bone mineral lost during prolonged lactation is not fully recovered following weaning, possibly putting women at increased risk of fracture or osteoporosis. Selective Serotonin Reuptake Inhibitor (SSRI) antidepressants have also been associated with reduced bone mineral density and increased fracture risk. Therefore, SSRI exposure while breastfeeding may exacerbate lactational bone loss, compromising long-term bone health. Through an examination of serotonin and calcium homeostasis during lactation, lactational bone turnover and post-weaning recovery of bone mineral, and the effect of peripartum depression and SSRI on the mammary gland and bone, this review will discuss the hypothesis that peripartum SSRI exposure causes persistent reductions in bone mineral density through mammary-derived PTHrP signaling with bone.

Presentation and management of osteoporosis presenting in association with pregnancy or lactation

In this review, we summarize our current understanding of the pathophysiology of fragility fractures that occur for the first time during pregnancy and lactation, and provide guidance on appropriate investigations and treatment strategies. Most affected women will have had no prior bone density reading, and so the extent of bone loss that may have occurred during pregnancy or lactation is uncertain. During pregnancy, intestinal calcium absorption doubles in order to meet the fetal demand for calcium, but if maternal intake of calcium is insufficient to meet the combined needs of the mother and baby, the maternal skeleton will undergo resorption during the third trimester. During lactation, several hormonal changes, independent of maternal calcium intake, program a 5-10 % loss of trabecular mineral content in order to provide calcium to milk. After weaning the baby, the maternal skeleton is normally restored to its prior mineral content and strength. This physiological bone resorption during reproduction does not normally cause fractures; instead, women who do fracture are more likely to have additional secondary causes of bone loss and fragility. Transient osteoporosis of the hip may affect one or both femoral heads during pregnancy but it involves localized edema and not skeletal resorption. Case reports have described the use of calcitonin, bisphosphonates, strontium ranelate, teriparatide, vertebroplasty, and kyphoplasty to treat post-partum vertebral fractures. However, the need for such treatments is uncertain given that a progressive increase in bone mass subsequently occurs in most women who present with a fracture during pregnancy or lactation.

Effective treatment of severe pregnancy and lactation-related osteoporosis with teriparatide: case report and review of the literature

Pregnancy or lactation-related osteoporosis (PLO) is a very rare and debilitating condition which is usually diagnosed during the last trimester of the pregnancy or early postpartum period. Herein, we report a case with severe PLO and multiple vertebral compression fractures that were successfully treated with teriparatide. Twenty-three-year-old female patient was admitted to our clinic two months after her first spontaneous vaginal delivery with the complaint of severe back pain. Bone mineral density was measured using dual energy X-ray absorptiometry (DEXA), and low T- and Z-scores were observed in lumbar vertebrae. In vertebral MRI, severe height loss was detected in thoracic (T) 5,7,10,11,12 vertebrae. After exclusion of the other possible causes of OP, she was diagnosed to have PLO and the lactation was stopped. She was treated with calcium 1000 mg/day, cholecalciferol 800 mg/day and teriparatide 20 µg/day. At the 12th and 18th month of therapy, BMD was increased by 8% and 27%, respectively, at the lumbar spine and pain was completely relieved in few months. There are pharmacological therapy modalities that can be used in PLO. Bisphosphonates are effective, but there are some concerns that they accumulate in bone and may expose fetus in subsequent pregnancies. Teriparatide is a strong candidate to be the optimal medical therapy in severe cases since it is effective and safe.

Bone development and mineral homeostasis in the fetus and neonate: roles of the calciotropic and phosphotropic hormones

Mineral and bone metabolism are regulated differently in utero compared with the adult. The fetal kidneys, intestines, and skeleton are not dominant sources of mineral supply for the fetus. Instead, the placenta meets the fetal need for mineral by actively transporting calcium, phosphorus, and magnesium from the maternal circulation. These minerals are maintained in the fetal circulation at higher concentrations than in the mother and normal adult, and such high levels appear necessary for the developing skeleton to accrete a normal amount of mineral by term. Parathyroid hormone (PTH) and calcitriol circulate at low concentrations in the fetal circulation. Fetal bone development and the regulation of serum minerals are critically dependent on PTH and PTH-related protein, but not vitamin D/calcitriol, fibroblast growth factor-23, calcitonin, or the sex steroids. After birth, the serum calcium falls and phosphorus rises before gradually reaching adult values over the subsequent 24-48 h. The intestines are the main source of mineral for the neonate, while the kidneys reabsorb mineral, and bone turnover contributes mineral to the circulation. This switch in the regulation of mineral homeostasis is triggered by loss of the placenta and a postnatal fall in serum calcium, and is followed in sequence by a rise in PTH and then an increase in calcitriol. Intestinal calcium absorption is initially a passive process facilitated by lactose, but later becomes active and calcitriol-dependent. However, calcitriol's role can be bypassed by increasing the calcium content of the diet, or by parenteral administration of calcium.

Osteoporosis presenting in pregnancy, puerperium, and lactation

PURPOSE OF REVIEW

To describe our current state of knowledge about the pathophysiology, incidence, and treatment of osteoporosis that presents during pregnancy, puerperium, and lactation.

RECENT FINDINGS

When vertebral fractures occur in pregnant or lactating women, it is usually unknown whether the skeleton was normal before pregnancy. Maternal adaptations increase bone resorption modestly during pregnancy but markedly during lactation. The net bone loss may occasionally precipitate fractures, especially in women who have underlying low bone mass or skeletal fragility prior to pregnancy. Bone mass and strength are normally restored postweaning. Transient osteoporosis of the hip is a sporadic disorder localized to one or both femoral heads; it is not due to generalized skeletal resorption. Anecdotal reports have used bisphosphonates, strontium ranelate, teriparatide, or vertebroplasty/kyphoplasty to treat postpartum vertebral fractures, but it is unclear whether these therapies had any added benefit over the spontaneous skeletal recovery that normally occurs after weaning.

SUMMARY

These relatively rare fragility fractures result from multifactorial causes, including skeletal disorders that precede pregnancy, and structural and metabolic stresses that can compromise skeletal strength during pregnancy and lactation. Further study is needed to determine when pharmacological or surgical therapy is warranted instead of conservative or expectant management.