Associations of serum sclerostin with bone mineral density, markers of bone metabolism and thalassaemia characteristics in adult patients with transfusion-dependent beta-thalassaemia

Exogenous iron caused osteocyte apoptosis, increased RANKL production, and stimulated bone resorption through oxidative stress in a murine model

Iron overload is a risk factor for osteoporosis due to its oxidative toxicity. Previous studies have demonstrated that an excessive amount of iron increases osteocyte apoptosis and receptor activator of nuclear factor κ-B ligand (RANKL) production, which stimulates osteoclast differentiation in vitro. However, the effects of exogenous iron supplementation-induced iron overload on osteocytes in vivo and its role in iron overload-induced bone loss are unknown. This work aimed to develop an iron overloaded murine model of C57BL/6 mice by intraperitoneal administration of iron dextran for two months. The iron levels in various organs, bone, and serum, as well as the microstructure and strength of bone, apoptosis of osteocytes, oxidative stress in bone tissue, and bone formation and resorption, were assessed. The results showed that 2 months of exogenous iron supplementation significantly increased iron levels in the liver, spleen, kidney, bone tissue, and serum. Iron overload negatively affected bone microstructure and strength. Osteocyte apoptosis and empty lacunae rate were elevated by exogenous iron. Iron overload upregulated RANKL expression but had no significant impact on osteoprotegerin (OPG) and sclerostin levels. Static and dynamic histologic analyses and serum biochemical assay showed that iron overload increased bone resorption without significantly affecting bone formation. Exogenous iron promoted oxidative stress in osteocytes in vivo and in vitro. Additional supplementation of iron chelator (deferoxamine) or N-acetyl-l-cysteine (NAC) partially alleviated bone loss, osteocyte apoptosis, osteoclast formation, and oxidative stress due to iron overload. These findings, in line with prior in vitro studies, suggest that exogenous iron supplementation induces osteoclastogenesis and osteoporosis by promoting osteocyte apoptosis and RANKL production via oxidative stress.

Bone Mineral Density and Dickkopf-1 in Adolescents with Non-Deletional Hemoglobin H Disease

BACKGROUND

Low bone mineral density (BMD) is prevalent in individuals with β-thalassemia and is associated with increased circulating dickkopf-1 concentration. These data are limited in α-thalassemia. Therefore, we aimed to determine the prevalence of low BMD and the association between BMD and serum dickkopf-1 in adolescents with non-deletional hemoglobin H disease, a form of α-thalassemia whose severity is comparable to β-thalassemia intermedia.

METHODOLOGY

The lumbar spine and total body BMD were measured and converted into height-adjusted z-scores. Low BMD was defined as BMD z-score ≤ -2. Participant blood was drawn for measurement of dickkopf-1 and bone turnover marker concentrations.

RESULTS

Thirty-seven participants with non-deletional hemoglobin H disease (59% female, mean age 14.6 ± 3.2 years, 86% Tanner stage ≥2, 95% regularly transfused, 16% taking prednisolone) were included. Over one year prior to the study, mean average pretransfusion hemoglobin, ferritin and 25-hydroxyvitamin D concentrations were 8.8 ± 1.0 g/dL, and 958 ± 513 and 26 ± 6 ng/mL, respectively. When participants taking prednisolone were excluded, the prevalence of low BMD at the lumbar spine and total body was 42% and 17%, respectively. BMD at both sites was correlated positively with body mass index z-score, and negatively with dickkopf-1 (all p-values <0.05). There were no correlations among dickkopf-1, 25-hydroxyvitamin D, osteocalcin and C-telopeptide of type-I collagen. Multiple regression analysis showed dickkopf-1 inversely associated with total body BMD z-score adjusting for sex, bone age, body mass index, pre-transfusion hemoglobin, 25-hydroxyvitamin D, history of delayed puberty, type of iron chelator and prednisolone use (p-value = 0.009).

CONCLUSIONS

We demonstrated a high prevalence of low BMD in adolescents with non-deletional hemoglobin H disease. Moreover, dickkopf-1 inversely associated with total body BMD suggesting it may serve as a bone biomarker in this patient population.

New Entity-Thalassemic Endocrine Disease: Major Beta-Thalassemia and Endocrine Involvement

Beta-thalassemia (BTH), a recessively inherited haemoglobin (Hb) disorder, causes iron overload (IO), extra-medullary haematopoiesis and bone marrow expansion with major clinical impact. The main objective of this review is to address endocrine components (including aspects of reproductive health as fertility potential and pregnancy outcome) in major beta-thalassemia patients, a complex panel known as thalassemic endocrine disease (TED). We included English, full-text articles based on PubMed research (January 2017–June 2022). TED includes hypogonadism (hypoGn), anomalies of GH/IGF1 axes with growth retardation, hypothyroidism (hypoT), hypoparathyroidism (hypoPT), glucose profile anomalies, adrenal insufficiency, reduced bone mineral density (BMD), and deterioration of microarchitecture with increased fracture risk (FR). The prevalence of each ED varies with population, criteria of definition, etc. At least one out of every three to four children below the age of 12 y have one ED. ED correlates with ferritin and poor compliance to therapy, but not all studies agree. Up to 86% of the adult population is affected by an ED. Age is a positive linear predictor for ED. Low IGF1 is found in 95% of the population with GH deficiency (GHD), but also in 93.6% of persons without GHD. HypoT is mostly pituitary-related; it is not clinically manifested in the majority of cases, hence the importance of TSH/FT4 screening. HypoT is found at any age, with the prevalence varying between 8.3% and 30%. Non-compliance to chelation increases the risk of hypoT, yet not all studies confirmed the correlation with chelation history (reversible hypoT under chelation is reported). The pitfalls of TSH interpretation due to hypophyseal IO should be taken into consideration. HypoPT prevalence varies from 6.66% (below the age of 12) to a maximum of 40% (depending on the study). Serum ferritin might act as a stimulator of FGF23. Associated hypocalcaemia transitions from asymptomatic to severe manifestations. HypoPT is mostly found in association with growth retardation and hypoGn. TED-associated adrenal dysfunction is typically mild; an index of suspicion should be considered due to potential life-threatening complications. Periodic check-up by ACTH stimulation test is advised. Adrenal insufficiency/hypocortisolism status is the rarest ED (but some reported a prevalence of up to one third of patients). Significantly, many studies did not routinely perform a dynamic test. Atypical EM sites might be found in adrenals, mimicking an incidentaloma. Between 7.5–10% of children with major BTH have DM; screening starts by the age of 10, and ferritin correlated with glycaemia. Larger studies found DM in up to 34%of cases. Many studies do not take into consideration IGF, IGT, or do not routinely include OGTT. Glucose anomalies are time dependent. Emerging new markers represent promising alternatives, such as insulin secretion-sensitivity index-2. The pitfalls of glucose profile interpretation include the levels of HbA1c and the particular risk of gestational DM. Thalassemia bone disease (TBD) is related to hypoGn-related osteoporosis, renal function anomalies, DM, GHD, malnutrition, chronic hypoxia-induced calcium malabsorption, and transplant-associated protocols. Low BMD was identified in both paediatric and adult population; the prevalence of osteoporosis/TBD in major BTH patients varies; the highest rate is 40–72% depending on age, studied parameters, DXA evaluation and corrections, and screening thoracic–lumbar spine X-ray. Lower TBS and abnormal dynamics of bone turnover markers are reported. The largest cohorts on transfusion-dependent BTH identified the prevalence of hypoGn to be between 44.5% and 82%. Ferritin positively correlates with pubertal delay, and negatively with pituitary volume. Some authors appreciate hypoGn as the most frequent ED below the age of 15. Long-term untreated hypoGn induces a high cardiovascular risk and increased FR. Hormonal replacement therapy is necessary in addition to specific BTH therapy. Infertility underlines TED-related hormonal elements (primary and secondary hypoGn) and IO-induced gonadal toxicity. Males with BTH are at risk of infertility due to germ cell loss. IO induces an excessive amount of free radicals which impair the quality of sperm, iron being a local catalyser of ROS. Adequate chelation might improve fertility issues. Due to the advances in current therapies, the reproductive health of females with major BTH is improving; a low level of statistical significance reflects the pregnancy status in major BTH (limited data on spontaneous pregnancies and growing evidence of the induction of ovulation/assisted reproductive techniques). Pregnancy outcome also depends on TED approach, including factors such as DM control, adequate replacement of hypoT and hypoPT, and vitamin D supplementation for bone health. Asymptomatic TED elements such as subclinical hypothyroidism or IFG/IGT might become overt during pregnancy. Endocrine glands are particularly sensitive to iron deposits, hence TED includes a complicated puzzle of EDs which massively impacts on the overall picture, including the quality of life in major BTH. The BTH prognostic has registered progress in the last decades due to modern therapy, but the medical and social burden remains elevated. Genetic counselling represents a major step in approaching TH individuals, including as part of the pre-conception assessment. A multidisciplinary surveillance team is mandatory.