Ewald methods for polarizable surfaces with application to hydroxylation and hydrogen bonding on the (012) and (001) surfaces of alpha-Fe2O3

We present a clear and rigorous derivation of the Ewald-like method for calculation of the electrostatic energy of the systems infinitely periodic in two-dimensions and of finite size in the third dimension (slabs) which is significantly faster than existing methods. Molecular dynamics simulations using the transferable/polarizable model by Rustad et al. were applied to study the surface relaxation of the nonhydroxylated, hydroxylated, and solvated surfaces of alpha-Fe2O3 (hematite). We find that our nonhydroxylated structures and energies are in good agreement with previous LDA calculations on alpha-alumina by Manassidis et al. [Surf. Sci. Lett. 285, L517, 1993]. Using the results of molecular dynamics simulations of solvated interfaces, we define end-member hydroxylated-hydrated states for the surfaces which are used in energy minimization calculations. We find that hydration has a small effect on the surface structure, but that hydroxylation has a significant effect. Our calculations, both for gas-phase and solution-phase adsorption, predict a greater amount of hydroxylation for the (012) surface than for the (001) surface. Our simulations also indicate the presence of four-fold coordinated iron ions on the (001) surface.Comment: 23 pages, REVTeX (LaTeX), 8 figures not included, e-mail to [email protected], paper accepted in Surface Scienc

Unexpected Widespread Hypophosphatemia and Bone Disease Associated with Elemental Formula Use in Infants and Children

OBJECTIVE: Hypophosphatemia occurs with inadequate dietary intake, malabsorption, increased renal excretion, or shifts between intracellular and extracellular compartments. We noticed the common finding of amino-acid based elemental formula [EF] use in an unexpected number of cases of idiopathic hypophosphatemia occurring in infants and children evaluated for skeletal disease. We aimed to fully characterize the clinical profiles in these cases. METHODS: A retrospective chart review of children with unexplained hypophosphatemia was performed as cases accumulated from various centres in North America and Ireland. Data were analyzed to explore any relationships between feeding and biochemical or clinical features, effects of treatment, and to identify a potential mechanism. RESULTS: Fifty-one children were identified at 17 institutions with EF-associated hypophosphatemia. Most children had complex illnesses and had been solely fed Neocate® formula products for variable periods of time prior to presentation. Feeding methods varied. Hypophosphatemia was detected during evaluation of fractures or rickets. Increased alkaline phosphatase activity and appropriate renal conservation of phosphate were documented in nearly all cases. Skeletal radiographs demonstrated fractures, undermineralization, or rickets in 94% of the cases. Although the skeletal disease had often been attributed to underlying disease, most all improved with addition of supplemental phosphate or change to a different formula product. CONCLUSION: The observed biochemical profiles indicated a deficient dietary supply or severe malabsorption of phosphate, despite adequate formula composition. When transition to an alternate formula was possible, biochemical status improved shortly after introduction to the alternate formula, with eventual improvement of skeletal abnormalities. These observations strongly implicate that bioavailability of formula phosphorus may be impaired in certain clinical settings. The widespread nature of the findings lead us to strongly recommend careful monitoring of mineral metabolism in children fed EF. Transition to alternative formula use or implementation of phosphate supplementation should be performed cautiously with as severe hypocalcemia may develop

Long-Term Follow-up of Hypophosphatemic Bone Disease Associated With Elemental Formula Use: Sustained Correction of Bone Disease After Formula Change or Phosphate Supplementation

In this article, we describe the long-term outcomes of children who were previously reported to have developed hypophosphatemic bone disease in association with elemental formula use. An extended chart review allowed for an updated report of 34 children with regard to severity/duration of bone disease, extent of recovery, and time to correction using radiology reports and biochemical data. After implementation of formula change and/or phosphate supplementation, we found that serum phosphorus concentration increased and serum alkaline phosphatase activity decreased in all patients, normalizing by 6.6 ± 4.0 (mean ± SD) months following diagnosis. The decrease in serum alkaline phosphatase from diagnosis to the time of correction was moderately correlated with the concurrent increase in serum phosphorus (R = 0.48, P < .05). Age at diagnosis significantly correlated with time to resolution (R = 0.51, P = .01). This study supports the earlier report that bone disease associated with hypophosphatemia during elemental formula use responds to formula change and/or phosphate supplementation

Intermachine differences in DXA measurements vary by skeletal site, and impact the assessment of low bone density in children.

BACKGROUND: Bone mineral content (BMC) and areal-bone mineral density (aBMD) measurements of the lumbar spine (LS) and whole body less head (WBLH) by dual energy X-ray absorptiometry (DXA) are recommended for bone health assessment in children. Intermachine differences were not considered previously in formulating these recommendations. METHODOLOGY: DXA measurements of the LS, WBLH, total hip, femoral neck and distal 1/3 radius from the Bone Mineral Density in Childhood Study were examined. Healthy children, ages 6 to 16&nbsp;years, from five clinical centers participated. The same spine, whole body, and femur phantoms were measured on each Centers DXA machine. Percentage of individuals with low BMC or aBMD (Z-score&nbsp;&lt;&nbsp;-1.5) was determined. Clinical center differences were evaluated by analysis of covariance adjusting for height and BMI Z-score, calcium intake, physical activity, Tanner stage and bone age. Logistic regression assessed odds of low BMC or aBMD across clinical centers. RESULTS: Significant differences among Clinical Centers (p&nbsp;&lt;&nbsp;0.05) were evident in adjusted mean BMC and aBMD Z-scores (n&nbsp;=&nbsp;1503) for all skeletal sites. WBLH BMC and aBMD Z-scores had the greatest range across centers (-0.13 to 0.24, and -0.17 to 0.56, respectively). The percentage of children with Z-scores less than -1.5 varied among Clinical Centers from 1.9 [95%CI 0.8, 4.5] to 8.1 [95%CI 5.7, 11.3] for WBLH BMC, 1.1 [95%CI 0.4, 3.5] to 6.3 [95%CI 3.8, 10.1] for WBLH aBMD, and from 4.4 [95%CI 2.8, 7.0] to 12.6 [95%CI 9.3, 16.9] for distal 1/3 radius aBMD. For each skeletal site except total hip aBMD and femoral neck BMC, at least one center had significantly lower odds of low bone density. CONCLUSIONS: By design, our reference ranges capture intermachine variability. Most clinical centers dont know where their machine falls within the range of intermachine variability, and this may affect diagnosis of children evaluated for conditions that threaten bone health. Total hip scans showed the least, and whole body scans showed the most intermachine variability. Pediatric bone health assessment recommendations should recognize intermachine differences and address this important issue

The Utility of DXA Assessment at the Forearm, Proximal Femur, and Lateral Distal Femur, and Vertebral Fracture Assessment in the Pediatric Population: The 2019 Official Pediatric Positions of the ISCD.

Dual-energy X-ray absorptiometry (DXA) is widely used in the evaluation of bone fragility in children. Previous recommendations emphasized total body less head and lumbar spine DXA scans for clinical bone health assessment. However, these scan sites may not be possible or optimal for all groups of children with conditions that threaten bone health. The utility of DXA scans of the proximal femur, forearm, and radius were evaluated for adequacy of reference data, precision, ability of predict fracture, and applicability to all, or select groups of children. In addition, the strengths and limitations of vertebral fracture assessment by DXA were evaluated. The new Pediatric Positions provide guidelines on the use of these additional measures in the assessment of skeletal health in children

Unexpected widespread hypophosphatemia and bone disease associated with elemental formula use in infants and children

Objective Hypophosphatemia occurs with inadequate dietary intake, malabsorption, increased renal excretion, or shifts between intracellular and extracellular compartments. We noticed the common finding of amino-acid based elemental formula [EF] use in an unexpected number of cases of idiopathic hypophosphatemia occurring in infants and children evaluated for skeletal disease. We aimed to fully characterize the clinical profiles in these cases. Methods A retrospective chart review of children with unexplained hypophosphatemia was performed as cases accumulated from various centres in North America and Ireland. Data were analyzed to explore any relationships between feeding and biochemical or clinical features, effects of treatment, and to identify a potential mechanism. Results Fifty-one children were identified at 17 institutions with EF-associated hypophosphatemia. Most children had complex illnesses and had been solely fed Neocate® formula products for variable periods of time prior to presentation. Feeding methods varied. Hypophosphatemia was detected during evaluation of fractures or rickets. Increased alkaline phosphatase activity and appropriate renal conservation of phosphate were documented in nearly all cases. Skeletal radiographs demonstrated fractures, undermineralization, or rickets in 94% of the cases. Although the skeletal disease had often been attributed to underlying disease, most all improved with addition of supplemental phosphate or change to a different formula product. Conclusion The observed biochemical profiles indicated a deficient dietary supply or severe malabsorption of phosphate, despite adequate formula composition. When transition to an alternate formula was possible, biochemical status improved shortly after introduction to the alternate formula, with eventual improvement of skeletal abnormalities. These observations strongly implicate that bioavailability of formula phosphorus may be impaired in certain clinical settings. The widespread nature of the findings lead us to strongly recommend careful monitoring of mineral metabolism in children fed EF. Transition to alternative formula use or implementation of phosphate supplementation should be performed cautiously with as severe hypocalcemia may develop