Fluoride and strontium accumulation in bone does not correlate with osteoid tissue in dialysis patients

Microelement strontium and human health: comprehensive analysis of the role in inflammation and non-communicable diseases (NCDs)

Strontium (Sr), a trace element with a long history and a significant presence in the Earth's crust, plays a critical yet often overlooked role in various biological processes affecting human health. This comprehensive review explores the multifaceted implications of Sr, especially in the context of non-communicable diseases (NCDs) such as cardiovascular diseases, osteoporosis, hypertension, and diabetes mellitus. Sr is predominantly acquired through diet and water and has shown promise as a clinical marker for calcium absorption studies. It contributes to the mitigation of several NCDs by inhibiting oxidative stress, showcasing antioxidant properties, and suppressing inflammatory cytokines. The review delves deep into the mechanisms through which Sr interacts with human physiology, emphasizing its uptake, metabolism, and potential to prevent chronic conditions. Despite its apparent benefits in managing bone fractures, hypertension, and diabetes, current research on Sr's role in human health is not exhaustive. The review underscores the need for more comprehensive studies to solidify Sr's beneficial associations and address the gaps in understanding Sr intake and its optimal levels for human health.

Monitoring bone strontium intake in osteoporotic females self-supplementing with strontium citrate with a novel in-vivo X-ray fluorescence based diagnostic tool

Ten female volunteers were recruited as part of the Ryerson and McMaster University Strontium (Sr) in Bone Research Study to have their bone Sr levels measured as they self-supplemented with Sr supplements of their choice. Of the ten volunteers, nine were suffering from osteopenia and/or osteoporosis. Non-invasive bone Sr measurements were performed using an in vivo x-ray fluorescence (IVXRF) I-125 based system. Thirty minute measurements were taken at the finger and ankle, representing primarily cortical and trabecular bone, respectively. For analysis, the 14.2keV Sr K-alpha peak normalized to the Coherent peak at 35.5keV was used. Baseline readings, representing natural bone Sr levels were acquired since all volunteers had no previous intake of Sr based supplements or medications. Once Sr supplements were started, a 24h reading was taken, followed by frequent measurements ranging from weekly, biweekly to monthly. The longest volunteer participation was 1535days. The mean baseline Sr signal observed for the group was 0.42±0.13 and 0.39±0.07 for the finger and ankle, respectively. After 24h, the mean Sr signal rose to 1.43±1.12 and 1.17±0.51, for the finger and ankle, respectively, representing a statistically significant increase (p=0.0043 & p=0.000613). Bone Sr levels continued to increase throughout the length of the study. However the Sr signal varied widely between the individuals such that after three years, the highest Sr signal observed was 28.15±0.86 for the finger and 26.47±1.22 for the ankle in one volunteer compared to 3.15±0.15 and 4.46±0.36, for the finger and ankle, respectively in another. Furthermore, while it was previously reported by our group, that finger bone Sr levels may plateau within two years, these results suggest otherwise, indicating that bone Sr levels will continue to rise at both bone sites even after 4years of Sr intake.

Association between blood cadmium levels and malnutrition in peritoneal dialysis

Background

Malnutrition is associated with an increased risk of cardiovascular death and may cause protein-energy wasting in individuals with chronic kidney disease. A previous study demonstrated that blood cadmium levels (BCLs) were associated with malnutrition in maintenance hemodialysis (MHD) patients. However, the correlation between cadmium exposure and malnutrition remains unclear in chronic peritoneal dialysis (CPD) patients. This study examined the possible adverse effects of environmental cadmium exposure in CPD patients.

Methods

A total of 301 CPD patients were enrolled and divided into 3 study groups based on the following BCL tertiles: low (<0.19 μg/L), middle (0.19–0.39 μg/L), and high (>0.39 μg/L). Demographic, hematological, biochemical, and dialysis-related data were obtained for analysis. The analysis also included values of nutritional and inflammatory markers.

Results

The BCLs of CPD patients were lower than those of MHD patients. At baseline, patients in the high BCL group were older and had a higher prevalence of diabetes mellitus but lower serum albumin, creatinine, and phosphate levels than the patients in the other 2 groups. After adjusting for potential variables, stepwise backward multiple linear regression analysis revealed that age and alanine aminotransferase levels were positively associated with logarithmic transformation of BCLs (log BCLs), while serum albumin levels were negatively associated with log BCLs in CPD patients. The log BCLs were a significant determinant (beta coefficient ± standard error = -0.185 ± 0.074; P = 0.013) of nutritional status and significantly associated with the presence of malnutrition (odds ratio = 2.64; 95% confidence interval: 1.07–6.48; P = 0.035) in CPD patients after adjustment for related variables.

Conclusions

BCL is significantly associated with nutritional status and malnutrition in CPD patients. Therefore, it is important for CPD patients to avoid environmental exposure to cadmium such as through smoking and consumption of cadmium-rich foods.

Monitoring bone strontium levels of an osteoporotic subject due to self-administration of strontium citrate with a novel diagnostic tool, in vivo XRF: a case study

A previously developed in vivo X-ray fluorescence (IVXRF) I-125 based system was used to measure bone strontium levels non-invasively in an osteoporotic female volunteer. The volunteer was recruited in December 2008, as part of the Ryerson and McMaster University Strontium in Bone Research Study and measured at twice weekly, weekly and monthly intervals. Thirty minute measurements were taken at the finger and ankle bone sites, representing primarily cortical and trabecular bone, respectively and the strontium K-alpha X-ray peak at 14.16 keV was used in the analysis. Since the volunteer had no prior history of strontium based medications or supplementation, baseline natural strontium levels were obtained followed by a 24h measurement of first intake of strontium citrate supplements (680 mg Sr/day). While the baseline levels of 0.38 ± 0.05 and 0.39 ± 0.10 for the finger and ankle, respectively, were on par with those previously reported in Caucasians among twenty-two healthy non-supplementing strontium individuals by our group, an increase began to be seen after 24 hrs of 0.62 ± 0.14 and 0.45 ± 0.12 for the finger and ankle, respectively. By 120 h, the increase was statistically significant at 0.68 ± 0.07 and 0.93 ± 0.05, respectively. Further increases occurred within an interval of 90-180 days, with the most recent, after 800 days, at the finger and ankle being 7 and 15 times higher than the initial baseline reading. The intriguing results show bone strontium incorporation and retention follow a pattern, suggesting strontium levels, at least in the ankle, do not plateau within two to three years and will continue to increase over time, as an individual takes strontium supplements. The ability of this IVXRF system to monitor and measure bone strontium levels over time provides a useful diagnostic tool to help gain insight into strontium bone kinetics.

Trace minerals in patients with end-stage renal disease

The kidneys are famously responsible for maintaining external balance of prevalent minerals, such as sodium, chloride, and potassium. The kidney's role in handling trace minerals is more obscure to most nephrologists. Similarly, the impact of kidney failure on trace mineral metabolism is difficult to anticipate. The associated dietary modifications and dialysis create the potential for trace mineral deficiencies and intoxications. Indeed, there are numerous reports of dialysis-associated mishaps causing mineral intoxication, notable for the challenge of assigning causation. Equally challenging has been the recognition of mineral deficiency syndromes, amid what is often a cacophony of multiple comorbidities that vie for the attention of clinicians who care for patients with chronic kidney disease. In this paper, I review a variety of minerals, some of which are required for maintenance of normal human physiology (the U.S. Food and Drug Administration's list of essential minerals), and some that have attracted attention in the care of dialysis patients. For each mineral, I will discuss its role in normal physiology and will review reported deficiency and toxicity states. I will point out the interesting inter-relationships between several of the elements. Finally, I will address the special concerns of aluminum and magnesium as they pertain to the dialysis population.

Dialysis water as a determinant of the adequacy of dialysis

Hemodialysis patients are exposed to large volumes of water in the form of dialysate. Contaminants from the dialysate may cross the dialyzer membrane into the blood and have the potential to compromise the adequacy of dialysis. Several chemicals found commonly in drinking water have long been known to be toxic to hemodialysis patients. More recently, it has become apparent that even low levels of bacterial products in dialysate may adversely impact dialysis adequacy through their ability to stimulate an inflammatory response. Minimum levels of water and dialysate quality have been recommended to protect patients from chemical and microbiologic contaminants. Complying with these recommendations requires an appropriately designed water purification and distribution system, combined with a surveillance program designed to maintain dialysate quality.

Changes of bone remodeling immediately after parathyroidectomy for secondary hyperparathyroidism

BACKGROUND

Successful parathyroidectomy for secondary hyperparathyroidism alleviates bone pain and is followed by the development of hypophosphatemia and hypocalcemia, as well as an increase in bone mineral density. An increase in osteoblast surface (Ob.S/BS) is not observed several months after surgery. In this study, we investigated early bone changes at 1 week after parathyroidectomy and the mechanism underlying an increase in bone mineral density.

METHODS

Fourteen patients with severe secondary hyperparathyroidism underwent iliac bone biopsy before and 1 week after parathyroidectomy. Changes in histomorphometric parameters, including osteoclast surface (Oc.S/BS), eroded surface (ES/BS), erosion depth (E.De), fibrosis volume (Fb.V/TV), Ob.S/BS, osteoid volume (OV/BV), osteoid surface (OS/BS), and osteoid thickness (O.Th), were investigated. Changes in texture of mineralized bone and osteoid seams were also investigated.

RESULTS

Oc.S/BS (P < 0.001), ES/BS (P < 0.01), and E.De (P < 0.001) decreased, but Fb.V/TV did not change at 1 week postoperatively. In particular, osteoclasts disappeared in almost all patients. Ob.S/BS (P < 0.001) increased, and cuboidal osteoblasts were proliferating on the trabecular surface where osteoclasts had existed before parathyroidectomy. As a result, newly developed osteoblasts coexisted with fibrous tissue after surgery. OV/BV (P < 0.005), OS/BS (P < 0.005), and O.Th (P < 0.005) increased, with lamellar osteoid volume showing a particular increase. Bone mineralization continued despite the low postoperative serum parathyroid hormone level.

CONCLUSION

A rapid decrease in serum parathyroid hormone level after parathyroidectomy appears to suppress bone resorption, as well as cause a transient marked increase in bone formation and an increase in normal lamellar osteoid seams.

Dose-dependent effects of strontium on osteoblast function and mineralization

BACKGROUND

Strontium-ranelate is now being used in the treatment of osteoporosis in elderly patients. As the majority of these patients already have a decreased renal function they are at an increased risk for accumulation of the element. Recent findings from epidemiologic studies in dialysis patients and experimental data obtained in a chronic renal failure (CRF) rat model established a dose-related multiphasic effect of strontium (Sr) on bone formation. To confirm these in vivo findings an in vitro set-up, consisting of primary rat osteoblast cultures, was applied. Sr was added to the culture medium at concentrations of 0, 0.5, 1.0, 2.0, 5.0, 20, and 100 microg/mL, respectively.

METHODS

Calcium incorporation (index of mineralization) and alkaline phosphatase activity were determined in the medium during the culture period, while at the end of the experiment, nodule formation (mineralized + unmineralized area) was quantified using a digital imaging system. mRNA synthesis of various osteoblast specific genes was assessed by means of reverse transcription polymerase chain reaction (RT-PCR).

RESULTS

Compared to the control group (0 microg/mL Sr), a significantly reduced nodule formation in the presence of an intact mineralization was found for the lowest 0.5 and 1 microg/mL Sr doses, suggesting an impaired in vitro osteoblast differentiation. Both nodule formation and mineralization were normal for the 2 and 5 microg/mL doses. For the highest Sr doses (20 and 100 microg/mL) a reduced mineralization was observed in the presence of an intact nodule formation indicating an inhibitory effect on the hydroxyapatite formation. The alkaline phosphatase activity reflected the multiphasic pattern of the nodule formation while the calcium incorporation corresponded with the pattern of nodular mineralization. No variations in cell proliferation were found. RT-PCR revealed that Sr interfered with the osteoblast at the level of the mRNA synthesis of several relevant genes.

CONCLUSION

Using the proposed in vitro model we confirmed the multiphasic effect of Sr on bone formation previously demonstrated in a CRF rat model. The data presented allow us to suggest that at low concentrations Sr interferes with the bone formation at the level of cell differentiation, whereas at high concentrations the disturbed mineralization in the presence of an intact nodule formation is indicative for a physicochemical interference of Sr with the hydroxyapatite formation.

Dose-dependent effects of strontium on bone of chronic renal failure rats

BACKGROUND

We previously reported on increased bone strontium (Sr) levels in dialysis patients with osteomalacia versus those presenting other types of renal osteodystrophy. A causal role of strontium in the development of osteomalacia was established in a chronic renal failure (CRF) rat model.

METHODS

In the present study we investigated whether the effect of Sr on bone was related to dosage. Four groups of CRF rats were studied: a control group (control-CFR; N=6) not receiving strontium and three groups of animals loaded orally with Sr during 18 weeks by adding the element as the SrCl2. H20 compound to the drinking water at concentrations of 0.03 g/100mL (Sr-30; N=6), 0.075 g/100mL (Sr-75; N=6), or 0.15 g/100mL (Sr-150; N=6) respectively. A fifth group consisting of seven animals with intact renal function (control-NRF), not receiving Sr served as controls for the effect of CRF on bone histology.

RESULTS

As compared to the control-NRF and control-CRF groups, Sr administration resulted in a dose-dependent increase in bone and serum Sr levels. No difference in body weight and biochemical serum and urinary parameters [i.e., calcium (Ca), phosphorus (P), and creatinine] was noted between the various CRF groups. At sacrifice, intact parathyroid hormone (iPTH) levels of CRF groups were significantly (P < 0.05) higher than the values measured in the control-NRF group indicating the development of hyperparathyroidism secondary to the installation of the CRF. This is further supported by the differences in bone histomorphometry between the control-CRF and control-NRF animals, which, respectively, showed an increased amount of osteoid (mean +/- SEM 3.4 +/- 1.2% vs. 0.37 +/- 0.14%, P < 0.05) in combination with a distinct osteoblastic activity (35 +/- 11% vs. <2%, P < 0.05) and an increased bone formation rate [(BFR), 677 +/- 177 microm 2/mm2/day vs. 130 +/- 50 microm 2/mm2/day, P < 0.05]. Bone surface area and erodic perimeter did not differ between the various study groups. In the Sr-30 group, Sr loading went along with a dramatic reduction of the BFR as indicated by the total absence of double tetracyclin labels and osteoblastic activity, which in the presence of a low to normal amount of osteoid (2.7 +/- 1.9%) points to the development of the adynamic type of renal osteodystrophy. Interestingly, compared to the control-CRF group, histodynamic and histologic parameters of the Sr-75 group did not differ significantly and a substantial osteoblastic activity (7.6 +/- 4.0%) was seen also. In the Sr-150 group, the various osteoid parameters were significantly (P < 0.05) increased vs. all other groups and were accompanied by a reduced BFR and mineral apposition rate (MAR) and an increased mineralization lag time (MLT), indicating a mineralization defect and the development of osteomalacia.

CONCLUSIONS

Our findings indicate that the role of Sr in the development of bone lesions in renal failure is complex and that, depending on the dose, the element may act via multiple pathways.