Ferrous and ferric differentially deteriorate proliferation and differentiation of osteoblast-like UMR-106 cells

Abstract

The association between iron overload and osteoporosis has been found in many diseases, such as hemochromatosis, β-thalassemia and sickle cell anemia with multiple blood transfusion. One of the contributing factors is iron toxicity to osteoblasts. Some studies showed the negative effects of iron on osteoblasts; however, the effects of two biological available iron species, i.e., ferric and ferrous, on osteoblasts are elusive. Since most intracellular ionized iron is ferric, osteoblasts was hypothesized to be more responsive to ferric iron. Herein, ferric ammonium citrate (FAC) and ferrous ammonium sulfate (FAS) were used as ferric and ferrous donors. Our results showed that both iron species suppressed cell survival and proliferation. Both also induced osteoblast cell death consistent with the higher levels of cleaved caspase 3 and caspase 7 in osteoblasts, indicating that iron induced osteoblast apoptosis. Iron treatments led to the elevated intracellular iron in osteoblasts as determined by atomic absorption spectrophotometry, thereby leading to a decreased expression of genes for cellular iron import and increased expression of genes for cellular iron export. Effects of FAC and FAS on osteoblast differentiation were determined by the activity of alkaline phosphatase (ALP). The lower ALP activity from osteoblast with iron exposure was found. In addition, ferric and ferrous differentially induced osteoblastic and osteoblast-derived osteoclastogenic gene expression alterations in osteoblast. Even though both iron species had similar effects on osteoblast cell survival and differentiation, the overall effects were markedly stronger in FAC-treated groups, suggesting that osteoblasts were more sensitive to ferric than ferrous.

The Risk of Developing Osteoporosis in Hemolytic Anemia—What Aggravates the Bone Loss?

“…With decreased osteoblast activity, calcium deposition decreases as well ( Figure 3 a) [ 30 , 35 , 36 ]. Several studies also indicate that serum iron will induce cleaved caspase 3 and caspase 7 of osteoblasts, inducing cell apoptosis [ 37 ]. Furthermore, oxidative stress (e.g., H 2 O 2 , ROS) produced by iron can inhibit osteoblast activity.…”

“…The crucial transcription pathways for osteoblastogenesis, including RUNX2, Wnt-βcatenin, and ERK, are regulated by oxidative stress [ 39 ]. In one dose-dependent manner in vitro study, ferric (III) iron and ferrous (II) iron both decreased osteoblast cell survival rate, but osteoblast was more sensitive to ferric (III) than ferrous (II) [ 37 ]. However, many studies have pointed out that iron promotes osteoclast differentiation, activation, and bone resorption.…”

“…In other words, the patient increases intestinal iron uptake and serum ferric (III) concentration sequentially rises without blood transfusion [ 42 ]. Ferric (III) iron increases by iron supplements intake, but ferrous (II) iron increases by blood transfusion therapy in thalassemia patients [ 37 ]. These phenomena are consistent with our finding that the iron supplements group and the nonblood transfusion therapy group have higher incidences of osteoporosis by increasing serum ferric (III) iron ( Table 4 ).…”

Hepcidin induces intestinal calcium uptake while suppressing iron uptake in Caco-2 cells

“…Iron overload-associated osteopenia and bone fracture are found in several diseases, such as thalassemia, which is an inherited anemia disease caused by underproduction of globin proteins [ 5 – 7 , 33 ]. Previous study suggested that extracellular iron inhibited osteoblast cell survival and induced osteoblast cell death [ 2 , 4 , 34 , 35 ]. In addition to the direct deleterious effects of iron on bone cells and bone remodeling process, intestinal calcium malabsorption has also been reported in thalassemia [ 1 , 8 , 9 , 11 ].…”

“…While normal serum iron levels have been reported to be 10–30 μM, the concentration over 50 μM was detected in iron overload patients [ 36 , 37 ]. Therefore, FAC in a range of 100–200 μM was used to represent iron overload condition in previous studies [ 2 , 4 ]. The normal extracellular calcium levels are within the range of 2.1–2.6 mM [ 38 ].…”