Patients with Active Acromegaly are at High Risk of 25(OH)D Deficiency

New insights into the vitamin D/PTH axis in endocrine-driven metabolic bone diseases

BACKGROUND

Endocrine regulation of bone metabolisms is the focus of the "Skeletal Endocrinology" series of meetings.

AIMS

To report on the outcome of the discussion on the role of vitamin D/PTH axis in endocrine osteopathies held during the 10th Skeletal Endocrinology Meeting which took place in Stresa (Italy) in March 2023.

OUTCOMES

Vitamin D/PTH axis has relevant influence on several outcomes in the general population and in patients affected by endocrinopathies such as hypoparathyroidism and secreting pituitary adenomas.

CONCLUSIONS

Assessing the status of the vitamin D/PTH axis and using vitamin D and PTH as therapeutic agents is mandatory in several endocrine-related bone metabolic conditions.

Cholecalciferol Use Is Associated With a Decreased Risk of Incident Morphometric Vertebral Fractures in Acromegaly

CONTEXT

Skeletal fragility is observed in 30% to 60% of acromegaly patients, representing an emerging complication of the disease that increases disability. Despite several studies having investigated the clinical and hormonal prognostic factors for the occurrence of vertebral fractures (VFs) in acromegaly, very few data are available on their prevention/treatment including the effect of vitamin D (VD) supplementation, which has been reported to have a fracture-protective effect in several studies in patients with osteoporosis.

OBJECTIVE

We aimed to investigate the role of cholecalciferol (D3) supplementation in the prevention of incident VFs (i-VFs) in acromegaly.

METHODS

A longitudinal, retrospective and multicenter study was performed on 61 acromegaly patients treated and untreated with D3 supplementation.

RESULTS

Twenty-six patients were treated with D3 supplementation according to clinical guidelines. The median D3 weekly dosage was 8500 IU (interquartile range [IQR]: 3900). The median duration of D3 supplementation was 94 months (IQR: 38). At last follow-up, i-VFs were diagnosed in 14 patients (23%). I-VFs were less prevalent in patients on D3 supplementation (14.3% of cases) compared to patients not treated with D3 (85.7%; P = .02). The final level of serum V25OH-D was significantly lower in patients who developed i-VFs (28.6 ng/mL, IQR: 4.1) compared to patients who did not develop i-VFs (34.2 ng/mL, IQR: 9.6; P = .05). The logistic regression confirmed the protective role of D3 supplementation on the occurrence of i-VFs (odds ratio: 0.16; 95% CI, 0.03-0.79; P = .01).

CONCLUSION

It is likely that D3 supplementation could lead to a reduction in i-VFs in acromegaly.

Acromegaly and Bone: An Update

Since our discovery in 2006 that acromegaly is associated with an increased risk of vertebral fractures, many authors have confirmed this finding in both cross-sectional and prospective studies. Due to the high epidemiological and clinical impact of this newly discovered comorbidity of acromegaly, this topic has progressively become more important and prominent over the years, and the pertinent literature has been enriched by new findings on the pathophysiology and treatment. The aim of this narrative review was to discuss these novel findings, integrating them with the seminal observations, in order to give the reader an updated view of how the field of acromegaly and bone is developing, from strong clinical observations to a mechanistic understanding and possible prevention and treatment.

Skeletal complications in acromegaly

Hypersecretion of growth hormone (GH) is rare and typically results from a pituitary functional tumor - somatotropinoma. It leads to excessive linear bone growth and manifests as gigantism if occurring in childhood and adolescence, before the closure of epiphyses or as a acromegaly in adulthood. The excess of GH impacts bone metabolism directly as well as indirectly through increased insulin-like growth factor 1 (IGF-1). In acromegaly as a consequence of overproduction of GH and IFG-1 and the influence of these hormones on bone osteoblasts, bone metabolism, growth and density increase. However, bone turnover is accelerated causing impaired bone microstructure and strength, which may lead to increased risk of vertebral fractures irrespective of normal bone mineral density. Apart from the changes in bone architecture, acromegaly also results in a degenerative joint disease of a different nature than primary osteoarthritis. Moreover, acromegaly leads to cardiovascular, metabolic and respiratory complications, and thus significantly impairs the quality of life. In this review, authors summarize the pathophysiology, diagnosis, and treatment of bone and joint disease in acromegaly.

Severe acute respiratory syndrome coronavirus 2 may cause liver injury via Na+/H+ exchanger

The liver has many significant functions, such as detoxification, the urea cycle, gluconeogenesis, and protein synthesis. Systemic diseases, hypoxia, infections, drugs, and toxins can easily affect the liver, which is extremely sensitive to injury. Systemic infection of severe acute respiratory syndrome coronavirus 2 can cause liver damage. The primary regulator of intracellular pH in the liver is the Na⁺/H⁺ exchanger (NHE). Physiologically, NHE protects hepatocytes from apoptosis by making the intracellular pH alkaline. Severe acute respiratory syndrome coronavirus 2 increases local angiotensin II levels by binding to angiotensin-converting enzyme 2. In severe cases of coronavirus disease 2019, high angi-otensin II levels may cause NHE overstimulation and lipid accumulation in the liver. NHE overstimulation can lead to hepatocyte death. NHE overstimulation may trigger a cytokine storm by increasing proinflammatory cytokines in the liver. Since the release of proinflammatory cytokines such as interleukin-6 increases with NHE activation, the virus may indirectly cause an increase in fibrinogen and D-dimer levels. NHE overstimulation may cause thrombotic events and systemic damage by increasing fibrinogen levels and cytokine release. Also, NHE overstimulation causes an increase in the urea cycle while inhibiting vitamin D synthesis and gluconeogenesis in the liver. Increasing NHE3 activity leads to Na⁺ loading, which impairs the containment and fluidity of bile acid. NHE overstimulation can change the gut microbiota composition by disrupting the structure and fluidity of bile acid, thus triggering systemic damage. Unlike other tissues, tumor necrosis factor-alpha and angiotensin II decrease NHE3 activity in the intestine. Thus, increased luminal Na⁺ leads to diarrhea and cytokine release. Severe acute respiratory syndrome coronavirus 2-induced local and systemic damage can be improved by preventing virus-induced NHE overstimulation in the liver.

Pathophysiology of growth hormone secretion disorders and their impact on bone microstructure as measured by trabecular bone score

This article is focused on endocrine-mediated osteoporosis caused by growth hormone (GH) disorders; adult GH deficiency and acromegaly. GH and insulin like growth factor-1 (IGF-1) stimulate linear bone growth through complex hormonal interactions and activates epiphyseal prechondrocytes. GH, via receptor activator of nuclear factor-kappaB (RANK), its ligand (RANK-L), and the osteoprotegerin system, stimulates production of osteoprotegerin and its accumulation in bone matrix. Malfunction of this mechanism, could lead to specific bone impairment. However, the primary problem of bone disease in GH secretion disorders is the primary prevention of osteoporotic fractures, so it is important to determine bone quality that better reflects the patient's actual predisposition to fracture. A method estimating bone quality from lumbar spine dual X-ray absorptiometry (DXA) scans is trabecular bone score (TBS). TBS in addition to bone mineral density (BMD) is a promising predictor of the osteoporotic fracture risk in women with postmenopausal osteopenia. In acromegaly TBS better defines risk of fracture because BMD is normal or even increased. TBS helps to monitor the effect of growth hormone therapy. Despite these findings, TBS should not be used alone, but a comprehensive consideration of all fracture risk factors, BMD and bone turnover markers is necessary.

Plasma 25-Hydroxyvitamin D Levels and VDR Gene Expression in Peripheral Blood Mononuclear Cells of Leukemia Patients and Healthy Subjects in Central Kazakhstan

Low blood levels of the vitamin D metabolite 25-hydroxyvitamin D [25(OH)D] have been associated with an increased risk and poorer outcomes of various cancers, including hematological malignancies. The Central Kazakhstan area has a relatively high incidence rate of leukemia. However, the relationship between vitamin D status and leukemia or other types of cancer in Kazakhstan has not yet been addressed. Therefore, in this first pilot single-center study conducted in Central Kazakhstan, we compared plasma levels of 25(OH)D and the vitamin D receptor (VDR) gene expression levels in peripheral blood mononuclear cells of patients with leukemia and demographically matching healthy volunteers. The levels of 25(OH)D in patients were found to be significantly lower (10.8 ± 7.0 ng/mL; n = 31) than in healthy subjects (21.6 ± 7.8 ng/mL; n = 34; p < 0.0001). A similar difference was observed in both younger (<60 years old) and older (>60 years old) participants, though there was no association between 25(OH)D concentration and age within the patient group. In female patients, 25(OH)D levels were significantly lower than in male patients (p = 0.04). No significant seasonal variations of 25(OH)D were observed in either the patient or the control group. VDR gene expression levels appeared to be similar in leukemia patients and healthy subjects, and no correlation between the cellular VDR expression and plasma 25(OH)D concentrations was observed in either group of participants. We did not observe a significant association of 25(OH)D or VDR levels and overall survival of leukemia patients. This observational study conducted for the first time in Kazakhstan supports previous findings demonstrating reduced blood 25(OH)D levels in cancer (leukemia) patients. Larger studies are required to determine whether low 25(OH)D plasma concentrations represent a risk factor for leukemia development and/or progression.

Association of Vitamin D Receptor Polymorphisms With Activity of Acromegaly, Vitamin D Status and Risk of Osteoporotic Fractures in Acromegaly Patients

Introduction: The vitamin D receptor (VDR) gene is one of the most widely studied tumorigenesis-related genes. The primary objective of this study was assessment of possible roles of VDR gene polymorphisms in acromegaly, with regard to the activity of the disease and compared them with a control group. Furthermore, we have assessed the associations between these polymorphisms with vitamin D status as well as with TBS (trabecular bone score) and risk for osteoporotic fracture in acromegaly patients. Materials and Methods: We studied 69 patients with acromegaly and 51 healthy controls (CG). Acromegaly patients were divided into three subgroups on the basis of disease activity (AA, active acromegaly; CD, controlled disease; CA, cured acromegaly). In all patients, blood samples were obtained to assess the hormonal and metabolic status as well as genetic analysis. VDR polymorphisms were determined by means of two methods, Polymerase Chain Reactions (PCR) and minisequencing (SNaPshot). Results: Genotype frequencies for VDR ApaI, TaqI, BsmI, and FokI polymorphisms did not deviate significantly from Hardy-Weinberg equilibrium (HWE) in the acromegaly group as well as in the control group. There was no statistically significant difference in distributions of these four VDR genotypes between acromegaly patients and the control group. This study revealed statistically significant negative correlation between risk of major osteoporotic fractures and genotypes tt (TaqI), aa (ApaI) and bb (BsmI) in acromegaly groups. Furthermore, the negative correlations were observed between TBS and risk for major osteoporotic fractures and hip fractures. Conclusions: Our study suggests that tt (TaqI), aa (ApaI) and bb (BsmI) of VDR gene may be associated with better bone quality and microarchitecture (higher TBS), which lead to a lower risk of osteoporotic fractures in acromegaly patients. TBS may be a useful tool for predicting risk of fractures in acromegaly patients.

Physiological regulation of phosphate by vitamin D, parathyroid hormone (PTH) and phosphate (Pi)

Inorganic phosphate (Pi) is an abundant element in the body and is essential for a wide variety of key biological processes. It plays an essential role in cellular energy metabolism and cell signalling, e.g. adenosine and guanosine triphosphates (ATP, GTP), and in the composition of phospholipid membranes and bone, and is an integral part of DNA and RNA. It is an important buffer in blood and urine and contributes to normal acid-base balance. Given its widespread role in almost every molecular and cellular function, changes in serum Pi levels and balance can have important and untoward effects. Pi homoeostasis is maintained by a counterbalance between dietary Pi absorption by the gut, mobilisation from bone and renal excretion. Approximately 85% of total body Pi is present in bone and only 1% is present as free Pi in extracellular fluids. In humans, extracellular concentrations of inorganic Pi vary between 0.8 and 1.2 mM, and in plasma or serum Pi exists in both its monovalent and divalent forms (H2PO4- and HPO42-). In the intestine, approximately 30% of Pi absorption is vitamin D regulated and dependent. To help maintain Pi balance, reabsorption of filtered Pi along the renal proximal tubule (PT) is via the NaPi-IIa and NaPi-IIc Na+-coupled Pi cotransporters, with a smaller contribution from the PiT-2 transporters. Endocrine factors, including, vitamin D and parathyroid hormone (PTH), as well as newer factors such as fibroblast growth factor (FGF)-23 and its coreceptor α-klotho, are intimately involved in the control of Pi homeostasis. A tight regulation of Pi is critical, since hyperphosphataemia is associated with increased cardiovascular morbidity in chronic kidney disease (CKD) and hypophosphataemia with rickets and growth retardation. This short review considers the control of Pi balance by vitamin D, PTH and Pi itself, with an emphasis on the insights gained from human genetic disorders and genetically modified mouse models.

Acromegalic osteopathy

Acromegalic osteopathy is an emerging complication of acromegaly characterized by increase in bone turnover, deterioration in bone microarchitecture and high risk of vertebral fractures. Vertebral fractures, as diagnosed by a radiological and morphometric approach, occur in about one-third of acromegaly patients in close relationship with duration of active disease. However, the prediction of vertebral fractures in this clinical setting is still a matter of uncertainty, since the pathogenesis of acromegalic osteopathy is multifactorial and fractures may occur even in presence of normal bone mineral density. In this narrative article, we summarize the pathophysiology and clinical aspects of acromegalic osteopathy.

Reduction of trabecular and cortical volumetric bone mineral density at the proximal femur in patients with acromegaly

OBJECTIVE

Data on dual energy absorptiometry (DXA)-measured bone mineral density (BMD) at the level of the total hip (TH) and femoral neck (FN) in patients with acromegaly (ACRO) are conflicting. Increase in bone size associated with ACRO may limit the reliability of DXA. Our objective is to evaluate trabecular and cortical volumetric BMD (vBMD) across the proximal femur in ACRO patients.

DESIGN

Cross sectional study in a clinical research center.

PATIENTS

Thirty-five ACRO patients (19 males; mean age, 48±7 years; BMI, 27.5±4.4 kg/m(2); 17 with active disease) and 35 age, gender, and BMI-matched controls.

RESULTS

vBMD was assessed by quantitative computed tomography at the level of the TH, FN, trochanter (TR), and intertrochanteric (IT). Trabecular vBMD was lower in both total and active ACRO as compared with controls (P<0.01). Cortical vBMD was lower in ACRO patients (active and controlled) vs controls at both TH and TR sites (P<0.05). These findings were confirmed when only eugonadal patients were analyzed. Both total cross sectional area (CSA) and average cortical thickness (ACT) were greater in ACRO patients vs controls (P<0.05). An inverse association between disease duration and trabecular vBMD at TH (r=-0.42, P=0.023) and IT (r=-0.41, P=0.026) was also found.

CONCLUSION

Both cortical and trabecular vBMD are reduced at the proximal femur in ACRO patients, regardless of gender, gonadal status, and disease activity. Disease duration is negatively associated with trabecular vBMD at the TH and IT.