Bone aluminum and histomorphometric features of renal osteodystrophy

Interest of Bone Histomorphometry in Bone Pathophysiology Investigation: Foundation, Present, and Future

Despite the development of non-invasive methods, bone histomorphometry remains the only method to analyze bone at the tissue and cell levels. Quantitative analysis of transiliac bone sections requires strict methodologic conditions but since its foundation more 60 years ago, this methodology has progressed. Our purpose was to review the evolution of bone histomorphometry over the years and its contribution to the knowledge of bone tissue metabolism under normal and pathological conditions and the understanding of the action mechanisms of therapeutic drugs in humans. The two main applications of bone histomorphometry are the diagnosis of bone diseases and research. It is warranted for the diagnosis of mineralization defects as in osteomalacia, of other causes of osteoporosis as bone mastocytosis, or the classification of renal osteodystrophy. Bone biopsies are required in clinical trials to evaluate the safety and mechanism of action of new therapeutic agents and were applied to anti-osteoporotic agents such as bisphosphonates and denosumab, an anti-RANKL, which induces a marked reduction of the bone turnover with a consequent elongation of the mineralization period. In contrast, an increased bone turnover with an extension of the formation site is observed with teriparatide. Romosozumab, an anti-sclerostin, has a dual effect with an early increased formation and reduced resorption. Bone histomorphometric studies allow us to understand the mechanism of coupling between formation and resorption and to evaluate the respective role of bone modeling and remodeling. The adaptation of new image analysis techniques will help bone biopsy analysis in the future.

Newcastle Bone Disease in Hong Kong: A Study of Aluminium Associated Osteomalacia

We measured serum aluminium concentrations in 104 haemodialysis patients from 3 centres in Hong Kong. We found that the 52 patients dialyzed in unit A had much higher mean aluminium levels (100 μg/L) than those from the other two units (61 and 39 μg/L respectively). In unit A, where water treatment by reverse osmosis had been introduced only recently, 30.8% of patients had fractures/looser zones, 46.2% had rugger-jersey spine and 28.8% had skeletal erosions. When these patients were divided into two groups according to whether their serum aluminium concentration was below or above 100 μg/l, the latter patients had significantly lower alkaline phosphatase, serum phosphate, and higher total prescribed dose of aluminium hydroxide. It was concluded that both dialysate aluminium and oral aluminium intake seemed to have contributed to the high incidence of osteomalacic fractures among Unit A patients. In eight of these patients serum aluminium increased by more than 150 μg/L after four weeks of receiving 1.5 g desferrioxamine twice weekly. Serial X-rays showed that the mean time after dialysis for the appearance of fractures/Looser zones was 72 months. Three patients developed fractures/Looser zones after successful renal transplantation; and it was postulated that the prompt excretion of aluminium permitted increased osteoclastic activity, resulting in fractures in these patients.

Inhibition of bone formation in rats by aluminum exposure via Wnt/β-catenin pathway

The previous research found that aluminum trichloride (AlCl₃) inhibited rat osteoblastic differentiation through inactivation of Wnt/β-catenin signaling pathway in vitro. On that basis, the experiment in vivo was conducted in this study. Rats were orally exposed to 0 (control group) and 0.4 g/L AlCl₃ (AlCl₃-treated group) for 30, 60, 90 or 120 days, respectively. We found that mRNA expressions of type I collagen and insulin-like growth factor-1, mRNA and protein expressions of Runx2 and survivin, ratio of p-GSK3β/GSK3β and protein expression of β-catenin were all decreased, whereas the mRNA and protein expressions Dkk1 and sFRP1 and the mRNA expressions and activity of Caspase-3 were increased in the AlCl₃-treated group compared with the control group with time prolonged. These results suggest that AlCl₃ inhibits bone formation and induces bone impairment by inhibiting the Wnt/β-catenin signaling pathway in young growing rats.

Renal Osteodystrophy-Time for Common Nomenclature

PURPOSE OF REVIEW

The term renal osteodystrophy has been used to describe a wide variety of bone problems facing patients with chronic kidney disease (CKD). Here, we review the history of the use of this term.

RECENT FINDINGS

Bone disease resulting from CKD was first noticed in 1890. The term "renal osteodystrophy" was used to define the bone disease in 1942. Since then, important discoveries have increased our knowledge of the complexities of bone physiology in these patients. At the same time, secular changes in the disease have occurred. The terms used to describe the bone histological findings have changed as well, reflecting new understanding of the physiological processes. However, since different investigators used the terms in different ways, the need to standardize the nomenclature has become increasingly important. Ongoing international collaboration about nosography will allow more optimal communication among scientists and clinicians as we continue to make new discoveries.

Effects of aluminum trichloride on the cartilage stimulatory growth factors in rats

Aluminum (Al) is considered to be a potentially toxic metal and inhibits cartilage formation. Transforming growth factor β1 (TGF-β1) and bone morphogenetic protein 2 (BMP-2) are cartilage stimulatory growth factors, which play important roles in regulating the cartilage formation. To investigate the effects of aluminum trichloride (AlCl₃) on the regulation of cartilage formation. Eighty Wistar rats were orally exposed to 0 (control group), 0.4 g/L (low-dose group), 0.8 g/L (mid-dose group) and 1.6 g/L (high-dose group) AlCl₃ for 120 days, respectively. The rats body weight were decreased, the cartilage histological structure were disrupted, the cartilage and serum contents of Al and the serum level of C-telopeptide of type II collagen were all increased, the serum level of type II collagen (Col II) and alkaline phosphatase (ALP), and the mRNA expressions of TGF-β1, BMP-2, ALP and Col II were all decreased in the AlCl₃-treated groups compared with those in control group. These results indicate that AlCl₃ inhibits the cartilage formation through inhibition of the cartilage stimulatory growth factors expressions.

Effects of Aluminum Exposure on the Bone Stimulatory Growth Factors in Rats

Aluminum (Al) is considered to be a potentially toxic metal and inhibits bone formation. Transforming growth factor β1 (TGF-β1) and bone morphogenetic protein 2 (BMP-2) play an important role in regulating the bone formation. Therefore, this study aimed to investigate the effects of Al on the TGF-β1 and BMP-2 in rats. In this study, Wistar rats were randomly divided into Al-treated group and control group. The Al-treated rats were provided with drinking water containing 100 mg/L AlCl3, and the control rats were given distilled water for 30, 60, and 90 days, respectively. Ten rats were sacrificed in each group every 30 days. The Al-treated rats showed lower body weight and higher serum and bone levels of Al compared with the control rats. The expression levels of TGF-β1 and BMP-2 were also significantly decreased in the Al-treated rats. Serum levels of bone gamma-carboxyglutamic acid protein (BGP), carboxy-terminal propeptide of type I procollagen (PICP), and bone alkaline phosphatase (B-ALP) were markedly lower in the Al-treated groups than in the control group. These results indicate that Al inhibits the expression of TGF-β1 and BMP-2 in bone, which inhibits the activity of osteoblasts and reduces the synthesis of BGP, B-ALP, and type I collagen, thereby inhibiting bone formation.

Hypercalcemia in the Critically Ill Patient

Hypercalcemia is now frequently recognized in hospitalized patients, including those who are critically ill. Hypercalcemia in critically ill patients may be life threatening or an indication of an underlying but unsuspected disease process. All of the common causes of hypercalcemia can occur in the critically ill patient and are reviewed here. As in the general patient population, the two most common causes are probably malignant disease and primary hyperparathyroidism. Hypercalcemia is now readily reversible in most patients, particularly when the underlying pathophysiologic mechanisms responsible are recognized, and it should be treated actively.

Aluminum trichloride inhibits osteoblastic differentiation through inactivation of Wnt/β-catenin signaling pathway in rat osteoblasts

Exposure to aluminum (Al) suppresses bone formation. Osteoblastic differentiation plays a key role in the process of bone formation. However, the effect of Al on osteoblastic differentiation is still controversial, and the mechanism remains unclear. To investigate the effect of Al on osteoblastic differentiation and whether Wnt signaling pathway was involved in it, the primary rat osteoblasts were exposed to 1/40 IC50, 1/20 IC50 and 1/10 IC50 of aluminum trichloride (AlCl3) for 24h, respectively. The activity analysis of alkaline phosphate, qRT-PCR analysis of type I collagen, alkaline phosphate, Wnt3a and Dkk-1, Western blot analysis of p-GSK3β, GSK3β and β-catenin protein and Immunofluorescence staining for β-catenin suggested that AlCl3 inhibited osteoblastic differentiation and Wnt/β-catenin pathway. Moreover, we found exogenous Wnt3a application reversed the inhibitory effect of AlCl3 on osteoblastic differentiation, accompanied by activating the Wnt/β-catenin pathway. Taken together, these findings suggest that AlCl3 inhibites osteoblastic differentiation through inactivation of Wnt/β-catenin pathway in osteoblasts.

PHOSPHORUS METABOLISM AND MANAGEMENT IN CHRONIC KIDNEY DISEASE: Renal Osteodystrophy, Phosphate Homeostasis, and Vascular Calcification

New advances in the pathogenesis of renal osteodystrophy (ROD) change the perspective from which many of its features and treatment are viewed. Calcium, phosphate, parathyroid hormone (PTH), and vitamin D have been shown to be important determinants of survival associated with kidney diseases. Now ROD dependent and independent of these factors is linked to survival more than just skeletal frailty. This review focuses on recent discoveries that renal injury impairs skeletal anabolism decreasing the osteoblast compartment of the skeleton and consequent bone formation. This discovery and the discovery that PTH regulates the hematopoietic stem cell niche alters our view of secondary hyperparathyroidism in chronic kidney disease (CKD) from that of a disease to that of a necessary adaptation to renal injury that goes awry. Furthermore, ROD is shown to be an underappreciated factor in the level of the serum phosphorus in CKD. The discovery and the elucidation of the mechanism of hyperphosphatemia as a cardiovascular risk in CKD change the view of ROD. It is now recognized as more than a skeletal disorder, it is an important component of the mortality of CKD that can be treated.

Development of renal bone disease

Renal osteodystrophy (ROD) develops as the early stages of chronic renal failure (CRF) and covers a spectrum of bone changes observed in the uraemic patient, which extend from high remodelling bone disease (frequently known as osteitis fibrosa) to low turnover, or adynamic disease. Between these two extremes there are also cases of bone mineralization compromised in variable degrees, as is the case of 'mixed bone disease' and osteomalacia. The dynamic process of bone remodelling is compromised in CRF, and a positive or negative bone balance can be observed in uraemic patients. In addition to the classic modulators of bone remodelling, like parathyroid hormone, calcitriol and calcitonin, other factors were recently identified as significant modulators of osteoblast and osteoclast activation in uraemic patients. In fact, different cytokines and growth factors, acting at an autocrine or paracrine level, seem to play a relevant role in the bone and mineral changes observed in uraemia. Recently, observations have been made of the development of more sensitive and specific techniques to assay different biochemical markers of bone turnover and mineral metabolism. Analogously, new contributions of conventional bone histology, bone immunocytochemistry and molecular biology, which enabled the understanding of some etiopathogenic mechanisms of ROD, were observed.

Cinacalcet HCl: a novel therapeutic for hyperparathyroidism

Hyperparathyroidism (HPT) is a significant clinical concern for patients with a variety of diseases, notably the secondary HPT associated with chronic kidney disease requiring dialysis. Secondary HPT is associated with elevated para-thyroid hormone (PTH) levels, decreased levels of 1,25 dihydroxyvitamin D, and disordered mineral levels (usually high calcium and phosphorus). If not controlled, secondary HPT can result in bone disease, vascular calcification, and ultimately, patient mortality. Established, conventional therapies, such as 1,25dihydroxyvitamin D analogues (vitamin D analogues) and phosphate binders, have proven to be inadequate in enabling patients to meet the National Kidney Foundation's-Kidney Disease Outcomes Quality Initiative (NKF-K/DOQI) treatment goals for PTH, calcium and phosphorus levels. A novel therapeutic, cinacalcet HCl (formerly AMG 073; Sensipar in the US and Mimpara in Europe; Amgen, Inc.), binds directly to the calcium-sensing receptor (CaR) on the cells of the parathyroid gland, increasing the receptor's sensitivity to calcium and reducing PTH, serum calcium and phosphorus levels. Treatment with cinacalcet in clinical trials has safely and effectively improved achievement of the NKF-K/DOQI goals. Cinacalcet has also reduced serum calcium levels in patients with primary HPT, including parathyroid carcinoma, in the clinical trial setting. Evidence suggesting the utility of cinacalcet in these diseases and the potential for additional therapeutic applications will be discussed.

Intracapsular hip fractures in end-stage renal failure

Patients with end-stage renal failure (ESRF) have metabolic bone disease. This increases the risk of femoral neck fracture and increases the risk of complications associated with fracture fixation such as non-union and avascular necrosis (AVN). We report the results of treatment in a consecutive series of 15 intracapsular fractures of the hip occurring in 13 patients with ESRF over a 5-year period. Six intracapsular hip fractures (of which five were undisplaced) were treated by internal fixation. Five out of these six (mean=83.3%) required conversion to total hip arthroplasty because of non-union or AVN. In all six of these patients, internal fixation was considered adequate post operatively. Of the remaining nine intracapsular hip fractures treated by hemiarthroplasty, only one required conversion to total hip arthroplasty because of stem subsidence (mean=11%). The difference in the revision rate for the two groups i.e. primary fixation versus primary hemiarthroplasty was statistically significant (p-value=0.01). The six patients with undisplaced intracapsular fractures treated by internal fixation required a total of 14 major operations, at an average rate (including initial fracture fixation and revision surgery) of 2.3 per patient. The 9 displaced fractures treated by hemiarthroplasty required just 10 operations in total, at an average rate of 1.1 per patient. (The difference was significant; p-value=0.006.) The 1-year mortality in the whole group (13 patients with 15 fractures) was 44.4%. We suggest that patients with ESRF with an intracapsular fracture of the neck of femur should be treated by replacement arthroplasty irrespective of femoral head displacement because of the high risk of revision surgery associated with internal fixation.

Iron lactate-induced osteomalacia in association with osteoblast dynamics

Osteomalacia was induced in rats fed a diet containing 50,000 ppm (5%) iron lactate for 13 weeks. The histopathology and histomorphometrical dynamics of osteoblasts under this condition were examined. Bone histomorphometry of the proximal tibial metaphysis revealed that the osteoblast surface, osteoid volume, osteoid surface and labeled surface ratio, which are the parameters of bone formation had increased. The blood chemistry revealed the greatest elevation in the osteocalcin level; however, the parathyroid hormone (PTH) secretion and inorganic phosphorus level were very low. From the serum biochemical, histopathological and histomorphometrical findings, the bone lesion in iron lactate-overloaded rats was considered to be similar to low turnover osteomalacia showing decreased trabeculae in secondary spongiosa and increased lamellar osteoid. Furthermore, an iron-positive reaction was detected at the interface between osteoid and mineralized bone. In the bone lesions induced by chronic iron overload, osteoblast recruitment exceeded that of mineralization or, alternatively, the iron within osteoblasts along the trabecular bone suppressed the remodeling and led to an increase in osteoid thickness.

The biological behaviour and bioavailability of aluminium in man, with special reference to studies employing aluminium-26 as a tracer: review and study update

Until 1990 biokinetic studies of aluminium metabolism and biokinetics in man and other animals had been substantially inhibited by analytical and practical difficulties. Of these, the most important are the difficulties in differentiating between administered aluminium and endogenous aluminium-especially in body fluids and excreta and the problems associated with the contamination of samples with environmental aluminium. As a consequence of these it was not possible to detect small, residual body burdens of the metal following experimental administrations. Consequently, many believed aluminium to be quantitatively excreted within a short time of uptake in all, but renal-failure patients. Nevertheless, residual aluminium deposits in a number of different organs and tissues had been detected in normal subjects using a variety of techniques, including histochemical staining methods. In order to understand the origins and kinetics of such residual aluminium deposits new approaches were required. One approach taken was to employ the radioisotope (67)Ga as a surrogate, but this approach has been shown to be flawed-a consequence of the different biological behaviours of aluminium and gallium. A second arose from the availability, in about 1990, of both (26)Al-a rare and expensive isotope of aluminium-and accelerator mass spectrometry for the ultra-trace detection of this isotope. Using these techniques the basic features of aluminium biokinetics and bioavailability have been unravelled. It is now clear that some aluminium is retained in the body-most probably within the skeleton, and that some deposits in the brain. However, most aluminium that enters the blood is excreted in urine within a few days or weeks and the gastrointestinal tract provides an effective barrier to aluminium uptake. Aspects of the biokinetics and bioavailability of aluminium are described below.

Contemporary understanding and management of reflux and constipation in the general population and pregnancy: a consensus meeting

BACKGROUND

Gastro-oesophageal reflux disease (GERD) and constipation have a major impact on public health; however, the wide variety of treatment options presents difficulties for recommending therapy. Lack of definitive guidelines in pharmacy and general practice medicine further exacerbates the decision dilemma.

AIMS

To address these issues, a panel of experts discussed the principles and practice of treating GERD and constipation in the general population and in pregnancy, with the aim of developing respective treatment guidelines.

RESULTS

The panel recommended antacids 'on-demand' as the first-line over-the-counter treatment in reflux, and as rescue medication for immediate relief when reflux breaks through with proton pump inhibitors. Calcium/magnesium-based antacids were recommended as the treatment of choice for pregnant women because of their good safety profile. In constipation, current data do not distinguish a hierarchy between polyethylene glycol (PEG)-based laxatives and other first-line treatments, although limitations are associated with stimulant- and bulk-forming laxatives. Where data are available, PEG is superior to lactulose in terms of efficacy. In pregnancy, PEG-based laxatives meet the criteria for the ideal treatment.

CONCLUSIONS

The experts developed algorithms that present healthcare professionals with clear treatment options and management strategies for GERD and constipation in pharmacy and general practice medicine.

Renal bone disease: a new conceptual framework for the interpretation of bone histomorphometry

My purpose in this article is to restore the histologic appraisal of renal bone disease to the mainstream of bone and mineral metabolism from which it has been separated for many years. Historically, both the two major components were found in varying degrees in most patients, although one or other of them often predominated. For more than 15 years bone biopsy has been used almost exclusively to classify individual patients into hyperparathyroid, osteomalacic, mixed and adynamic categories according to rigid non-overlapping criteria, and remarkably few histologic data have been reported. All metabolic bone diseases result from disordered bone remodeling, the physiologic mechanism for replacing bone that has become too old to carry out its mechanical or metabolic functions. Bone remodeling is not directly concerned with the regulation of plasma calcium, which reflects the level of equilibration at quiescent bone surfaces between systemic and bone extracellular fluid set by parathyroid hormone. The separation of remodeling from homeostasis explains the concurrence of increased turnover and decreased plasma calcium in chronic renal failure; it is the homeostatic system, rather than the remodeling system, which is resistant to parathyroid hormone. The effect of mild hyperparathyroidism is a nonspecific increase in bone turnover, of which the best index is the bone formation rate measured by double tetracycline labeling expressed per unit of bone surface. Increased turnover is always accompanied by increased reversible mineral deficit. In prolonged hyperparathyroidism there is also accelerated irreversible bone loss manifested mainly as thinning of cortical bone, detectable in chronic renal failure before any symptoms, due to increased resorption depth on the endocortical surface. In severe hyperparathyroidism resorbed bone is replaced, not by a lesser quantity of normal bone, but by a mixture of vascular fibrous tissue and woven bone, referred to as osteitis fibrosa. In osteomalacia there is increased accumulation of osteoid, due not to increased turnover, but to prolongation of mineralization lag time, which in conjunction with increased thickness, surface and volume of osteoid is diagnostic. Converting histomorphometric data into category assignment discards most of the useful information, which can be retained by two-dimensional representation of severity. For the hyperparathyroid dimension, bone formation rate measured by double tetracycline labeling expressed per unit of bone surface is the most useful although not ideal. For the osteomalacic dimension a mineralization index was constructed that is unaffected by age or race. In patients with osteitis fibrosa, bone formation rate per unit of bone surface and mineralization index were inversely correlated. For the third dimension a structure/formation index was constructed which increases with age in healthy women and shows weak inverse correlation with bone formation rate. The structure/formation index is lower than normal in patients with osteitis fibrosa, and should be useful in the study of osteopenia in chronic renal failure. Bone formation rate is low in osteomalacia, but some patients have subnormal rates through quite a different mechanism. The frequency of this finding has been overestimated for several reasons: failure to exclude atypical osteomalacia (increased surface and volume but not thickness of osteoid), use of inappropriate reference values, and failure to measure the bone formation rate on endocortical and intracortical surfaces. In healthy women bone formation rate can be zero on the cancellous surface alone. Low bone formation rate is sometimes due to diabetes but most often is the expected response to subnormal parathyroid hormone secretion accompanying an excess of calcium, a situation recognized only recently because of improvement in parathyroid hormone assay methodology. Low cancellous bone formation rate should not increase fracture risk because turnover is much lower in the peripheral than in the central skeleton, and all reports of increased fracture risk are flawed or open to different interpretation. Low bone formation rate is associated with reduced skeletal buffering of calcium and increased soft tissue calcification. This is not a new disease needing its own treatment, however, but represents the final stage of skeletal adaptation to a surfeit of calcium. The concept of adynamic bone disease has been harmful by directing attention away from the most important consequence of over-treatment of hyperparathyroidism.

Treatment of hyperphosphatemia with sevelamer hydrochloride in hemodialysis patients: a comparison with calcium acetate

BACKGROUND

Sevelamer hydrochloride is a recently approved calcium- and aluminium-free phosphate binder. A randomized study comparing sevelamer and calcium acetate was performed to assess the control of hyperphosphatemia in hemodialysis patients.

METHODS

Administration of phosphate binders was discontinued during a two-week washout period. The patients were then randomized to receive sevelamer or calcium acetate. The laboratory tests were performed monthly for 34 weeks.

RESULTS

There was a statistically significant decrease of serum phosphorus in both sevelamer and calcium acetate treatments. In addition, sevelamer improved the lipid profile.

CONCLUSION

This study confirms that sevelamer is effective at lowering serum phosphorus in hemodialysis patients and that it has several striking properties that could be beneficial in atherosclerosis in dialysis patients.

Useful biochemical markers for diagnosing renal osteodystrophy in predialysis end-stage renal failure patients

BACKGROUND

Various biochemical markers have been evaluated in dialysis patients for the diagnosis of renal osteodystrophy (ROD). However, their value in predialysis patients with end-stage renal failure (ESRF) is not yet clear.

METHODS

Bone histomorphometric evaluation was performed and biochemical markers of bone turnover were determined in serum of an unselected predialysis ESRF population (N = 84).

RESULTS

Significant (P < 0.005) differences between the five groups with ROD (ie, normal bone [N = 32], adynamic bone [ABD; N = 19], hyperparathyroidism [N = 8], osteomalacia [OM; N = 10], and mixed lesion [N = 15]) were noted for intact parathyroid hormone, total (TAP) and bone alkaline phosphatase (BAP), osteocalcin (OC), and serum calcium levels. Serum creatinine and (deoxy)pyridinoline levels did not differ between groups. For the diagnosis of ABD, an OC level of 41 microg/L or less (< or =7.0 nmol/L) had a sensitivity of 83% and specificity of 67%. The positive predictive value (PPV) for the population under study was 47%. The combination of an OC level of 41 ng/L or less (< or =7.0 nmol/L) with a BAP level of 23 U/L or less increased the sensitivity, specificity, and PPV to 72%, 89%, and 77%, respectively. ABD and normal bone taken as one group could be detected best by a BAP level of 25 U/L or less and TAP level of 84 U/L or less, showing sensitivities of 72% and 88% and specificities of 76% and 60%, corresponding with PPVs of 89% and 85%, respectively. In the absence of aluminum or strontium exposure, serum calcium level was found to be a useful index for the diagnosis of OM.

CONCLUSION

OC, TAP, BAP, and serum calcium levels are useful in the diagnosis of ABD, normal bone, and OM in predialysis patients with ESRF.

Is there an optimal parathyroid hormone level in end-stage renal failure: the lower the better?

Skeletal resistance to parathyroid hormone is well defined in patients with chronic renal failure. In recent years, with the increased frequency of development of adynamic bone disease, it has been recognized that secondary hyperparathyroidism must exist as a 'trade off' mechanism to maintain skeletal bone remodeling in this patient population. An optimal level of intact parathyroid hormone to maintain the normal skeletal bone turnover is believed to be between 2.0 and 2.5 times the upper limit of normal parathyroid hormone. It has very recently been argued that the optimal parathyroid hormone level for maintenance of skeletal bone remodeling may be insufficient to prevent the extraskeletal complications of coronary artery calcifications, calcific valvular heart disease, and cardiac death. To provide optimal health care for these patients several new treatments have been developed, including use of new vitamin D analogs, calcimimetic agents, and noncalcium-based phosphorus binders. It is anticipated that with lower suppression of parathyroid hormone by these vitamin D analogs, intermittent suppression of parathyroid hormone with calcimimetic agents, and the use of noncalcium phosphorus binders (Renageltrade) by regulating serum calcium, the resultant phosphorus concentrations will provide an optimal parathyroid hormone activity to maintain skeletal bone remodeling, while preventing extraskeletal complications.

Bioactivity of sol-gel bioactive glass coated alumina implants

Alumina on alumina total hip arthroplasty has been in use for more than 25 years with encouraging results. However, an improvement of the alumina/bone interface still is required. The objective of this study was to investigate the in vitro and in vivo osteoconductive properties of sol-gel bioactive glass coated alumina implants. Two sol-gel glass compositions (58S Bioglass(R) and 77S Bioglass(R)) were used as coatings on alumina substrates and implanted in a rabbit model. The 58S sol-gel coating was employed in two configurations, single (A58S1) and double layer (A58S2). SEM analysis after one week in simulated body fluid revealed small crystals assumed to represent the initial phase of hydroxyapatite formation, whereas no clear conclusion could be drawn from Fourier transform infrared spectroscopy data. The percentage of bone in direct contact was greater for coated implants when compared to bulk alumina implants (p <0.001). In the case of A58S1 implants, bone percentage significantly increased from 45.1% after 3 weeks up to 87. 8% after 24 weeks of implantation (p = 0.0004). The presence of osteoid tissue, related to an aluminum release from the alumina substrates, was greatly diminished when compared to melt-derived glass-coated alumina implants.

Oral phosphate binders: phosphate binding capacity of iron (III) hydroxide complexes containing saccharides and their effect on the urinary excretion of calcium and phosphate in rats

Phosphate binders that contain aluminum or calcium are frequently prescribed to treat hyperphosphatemia in patients with end-stage renal disease (ESRD), but an accumulation of aluminum can lead to encephalopathy, aluminum-related bone disease (ARBD) such as osteomalacia, anaemia, and resistance to erythropoietin, and calcium accumulation can lead to hypercalcaemia. High phosphate concentrations are reduced in vitro and in vivo by a phosphate adsorption pill, which is synthesized by hydrolyzing ferrous sulfate in the presence of saccharides, to form an iron (III)-saccharide complex that is acid resistant and binds phosphate greater than iron (III) hydroxide alone. Under in vitro conditions, containing 3.26 mg P/dL, the iron (III)-sucrose complex showed the highest phosphate adsorption capacity at pH 2 with artificial gastric juice, 58.9 mg P/g binder. For the 7 day in vivo study, 0% (Group 1), 1% (Group 2), 4% (Group 3), and 8% (Group 4) iron (III)-sucrose complex was admixed into the rodent chow by weight and fed to 15 male Wistar rats. The weight and volume of the feces and urine, and the calcium, iron, and phosphorus excretions in the feces and urine samples were monitored for any signs of irregularity. Total urine outflow was collected during a 24-h period to determine the amount of phosphate recovered, which indicates the ability of the phosphate binder to reduce gastrointestinal phosphate absorption. The fecal iron excretion was significantly effected by the amount of binder ingested throughout the study for Group 2 (p < 0.001), Group 3 (p < 0.01), and Group 4 (p < 0.001). The urinary calcium excretion (mg/rat/24-h) significantly increased by the 7th day for Group 2 (p < 0.05) and Group 4 (p < 0.01) in comparison to the control. Finally, after 7 days, there was a significant drop in the urinary phosphorus levels (mg P/rat/24-h) in a dose dependent manner for Group 2: from 7.82 +/- 1.46 to 1.98 +/- 0.10 mg P/rat/24-h (102 mg P/dL/24-h; p < 0.05); Group 3: from 6.70 +/- 1.14 to 0.16 +/- 0.09 mg P/rat/24-h (6.0 mg P/dL/24-h; p < 0.01); and Group 4: from 8.25 +/- 0.67 to 0.04 +/- 0.01 mg P/rat/24-h (0.9 mg P/dL/24-h; p < 0.01). The results show that this new adsorbent might provide an alternative to conventional aluminum and calcium containing phosphate-binding agents for combating hyperphosphataemia.

Effect of histamine H2-receptor antagonist on the phosphorus-binding abilities of calcium carbonate and calcium lactate in hemodialysis patients

The effect of histamine H2-receptor antagonist (famotidine) on the phosphorus-binding abilities of calcium carbonate and calcium lactate were examined in 13 chronic hemodialysis patients. In seven patients receiving calcium carbonate, famotidine (20 mg/d) was given because of gastroduodenal disorders, and calcium carbonate was replaced with calcium lactate as a phosphorus binder after 4 wk of treatment with famotidine. With the 4-wk administration of famotidine accompanied by calcium carbonate, the serum phosphorus level increased from 6.3+/-0.9 to 7.1+/-0.5 mg/dl (P<0.05). However, with the substitution of calcium lactate, the serum phosphorus level decreased significantly when compared to that before substitution (6.3+/-0.2 and 6.0+/-0.9 mg/dl after 4 and 8 wk of substitution, respectively), despite continued administration of famotidine. Serum calcium, creatinine, alkaline phosphatase, high sensitive parathyroid hormone, blood urea nitrogen, arterial blood pH, and bicarbonate were not significantly altered during the trial period. In six control patients treated with calcium carbonate alone, there were no statistical changes in serum calcium and phosphorus levels after substitution of calcium lactate for calcium carbonate. These results suggest that famotidine significantly affects the phosphorus-binding ability of calcium carbonate, but not that of calcium lactate. A careful observation of changes in the serum phosphorus level should be required in hemodialysis patients receiving calcium carbonate and histamine H2-receptor antagonists. Calcium lactate may be useful as a phosphorus binder in such hemodialysis patients.

RenaGel, a nonabsorbed calcium- and aluminum-free phosphate binder, lowers serum phosphorus and parathyroid hormone. The RenaGel Study Group

BACKGROUND

This multicenter, open-label, dose-titration study assessed the safety and efficacy of RenaGel(R), a nonabsorbed calcium- and aluminum-free phosphate binder, in lowering serum phosphorus. Secondary outcomes were its effects on serum intact parathyroid hormone (iPTH) and serum lipids.

METHODS

Phosphate binders were discontinued during a two-week washout period. Patients whose serum phosphorus was more than 6.0 mg/dl during washout were eligible for treatment. RenaGel(R), at starting doses of two, three, or four 440 mg capsules three times per day with meals, was administered to 172 hemodialysis patients for eight weeks. RenaGel(R) could be increased by one capsule per meal every two weeks as necessary to achieve serum phosphorus control. A second two-week washout period followed.

RESULTS

Mean serum phosphorus rose from 6.8 +/- 2.0 mg/dl at prewashout to 9.1 +/- 2.4 mg/dl at the end of the washout period. It then declined to 6.6 +/- 1.9 mg/dl by the end of the eight-week RenaGel(R) treatment period (P < 0. 0001). Serum phosphorus increased to 8.0 +/- 2.2 mg/dl at the end of the second washout period. The mean dose at the end of RenaGel(R) treatment was 5.4 g per day. Eighty-four percent of the patients previously used calcium-based phosphate binders. As expected, calcium declined during the initial washout period when calcium-based phosphate binders were discontinued. Mean serum calcium declined from 9.6 +/- 1.0 mg/dl at prewashout to 9.1 +/- 0.8 mg/dl after washout. It then increased to 9.4 +/- 0.9 mg/dl by the end of RenaGel(R) treatment. Median serum iPTH increased during the two-week washout from 208 pg/ml to 316 pg/ml and then declined to 224 pg/ml at the end of the eight-week treatment period (P < 0.0001 vs. end of initial washout). After eight weeks of treatment, RenaGel(R) reduced mean serum total cholesterol from 171.0 +/- 43.1 mg/dl to 145.0 +/- 38.7 mg/dl (P < 0.0001) and mean serum low-density lipoprotein cholesterol from 102.0 +/- 34.9 mg/dl to 75. 6 +/- 29.4 mg/dl (P < 0.0001). High-density lipoprotein cholesterol, triglycerides, and serum albumin did not change.

CONCLUSIONS

RenaGel(R), a novel and calcium- plus aluminum-free effective phosphate binder, can control serum phosphorus and reduce the levels of PTH and cholesterol without inducing hypercalcemia or other side effects. Thus, this new phosphate binder may be effective in the treatment of renal osteodystrophy in uremic patients.

The spectrum of bone disease in 200 chronic hemodialysis patients: a correlation between clinical, biochemical and histological findings

INTRODUCTION

Renal osteodystrophy includes the complete range of mineral metabolism disorders that affect the skeleton in patients with chronic renal failure.

PATIENTS AND METHODS

200 patients with end-stage renal disease and on dialysis were investigated regarding the clinical, biochemical and histological findings of bone disease.

RESULTS

The spectrum of renal osteodystrophy consisted mainly of high turnover bone lesions (74.5%), including osteitis fibrosa in 57.5%. Patients with mild bone disease were on dialysis for shorter periods of time and were mostly asymptomatic. Patients with aluminum-related bone disease (16.5%) had the greatest aluminum exposure, either orally or parenterally, and together with patients with high turnover mixed disease, were the most symptomatic. Although on a non-regular basis, the vast majority of the patients (82.5%) had been receiving vitamin D. The incidence of adynamic bone disease was high (n = 8) among parathyroidectomized patients (n = 12). Significantly higher serum levels of alkaline phosphatase were observed in osteitis fibrosa.

CONCLUSIONS

The use of calcitriol and phosphate-binding agents on a non-regular basis seems to be the reason for the apparent reduced response to the treatment of secondary hyperparathyroidism. Alkaline phosphatase has been shown to be a fair marker for bone turnover in patients with osteitis fibrosa. The severity of the clinical manifestations of bone disease correlates with the histological features of bone lesion and to the time spent on dialysis.

Renal osteodystrophy

Renal osteodystrophy is a general complication of chronic renal failure and end-stage renal disease. The nature of renal osteodystrophy has changed since osteomalacia due to aluminum intoxication has become less prevalent. Osteomalacia has been replaced by the adynamic bone disorder. Suppression of osteitis fibrosa, calcitrol and control of secondary hyperparathyroidism has been shown to produce the adynamic bone disorder. Thus, many other factors besides secondary hyperparathyroidism and calcitrol deficiency contribute to the pathogenesis of renal osteodystrophy. Some of these factors, according to our current state of knowledge, are discussed in this chapter along with the presentation and treatment of renal osteodystrophy.

Bone disease in moderate renal failure: cause, nature and prevention

There are two primary types of bone disorders observed in patients with end-stage renal disease: a high-turnover osteodystrophy characterized by osteitis fibrosa, and a low-turnover osteodystrophy characterized initially by osteomalacia and, more recently, by adynamic or aplastic bone disease. This article reviews the clinical presentation, pathogenesis, and laboratory findings of patients with these two disorders. It discusses the important roles of phosphorous binding, vitamin D administration, and correction of acidosis in prevention and treatment of bone disease in patients with moderate renal insufficiency.

Distribution of aluminum in different brain regions and body organs of rat

In the present study, an attempt has been made to investigate the distribution of aluminum in different regions of brain and body organs of male albino rats, following subacute and acute aluminum exposure. Aluminum was observed to accumulate in all regions of the brain with maximum accumulation in the hippocampus. Subcellular distribution of aluminum indicated that there was maximum localization in the nucleus followed by cytosolic, microsomal, and mitochondrial deposition. Elution profile of cytosolic proteins on G-75 Sephadex column revealed a substantial amount of aluminum bound to high-mol-wt protein fraction. Aluminum was also seen to compartmentalize in almost all the tissues of the body to varying extents, and the highest accumulation was in the spleen.

Aluminium-induced bone disease in uremic rats: effect of deferoxamine

We have previously established a rat model of chronic uremia, which is suitable to investigate the effect of various treatment modalities on renal osteodystrophy [1]. After four months subsequent to 5/6 nephrectomy, some animals were treated by gavage for 9 weeks with tap water (controls), or with aluminium (Al-citrate) 3 x 25 mg/week/kg b.wt +/- subsequent deferoxamine (DFO) 3 x 50 mg/week/kg b.wt. for 4 weeks. At termination of the study, serum clinical chemistry, femoral chemical composition and mechanical properties, calvarial parathyroid hormone (PTH)-elicited adenylate cyclase (AC) and phospholipase C (PLC) activities, cross-sectional femoral area, as well as bone histomorphometry, were analyzed. Animals given Al displayed moderately enhanced serum Al and bone Al accumulation, however, DFO-treatment did not fully alleviate bone Al retainment. A small increase in serum PTH was seen in all animals rendered uremic. Furthermore, a marked fall in serum alkaline phosphatase (ALP) below normal controls was observed in Al +/- DFO-treated animals compared with uremic controls. The uremic condition led to reduced femoral ratios of hydroxyproline (HYP) over Ca(2+) and phosphate (P(i)), while Al-intoxication alone enhanced femoral Hyp contents above values seen for normal controls. The protracted ureamia caused a deterioration of long bone resilience and brittleness, however, Al +/- DFO-treatment seemed to normalize the latter. Contrastingly, Al +/- DFO-gavage enhanced time to fracture. Uremic rats intoxicated with Al showed a complete loss of calvarial PTH-sensitive AC and PLC activities. DFO-treatment normalized PTH-elicited PLC, while PTH-susceptible AC remained super-normal. Al apparently exerts a long term down-regulation of both PTH-sensitive signaling systems as evidenced by studies of rat UMR 106 osteosarcoma cells in culture. The uremic condition enhanced endosteal bone resorption as shown by femoral shaft dimension analysis, while Al +/- DFO-treatment insignificantly reversed the condition. Finally, histomorphometrical analyses showed that DFO-administration tended to normalize aberrant trabecular bone volume, while rectifying both bone resorption and degree of mineralization. In conclusion, we assert that Al-intoxication hampers both processes (i.e. formation and resorption) of bone turnover, and that DFO-treatment to a certain extent prevents the uremia- and Al-induced bone disease in rats.

Effects of aluminum on bone surface ion composition

Aluminum induces net calcium efflux from cultured bone. To determine whether aluminum alters the bone surface ion composition in a manner consistent with predominantly cell-mediated resorption, a combination of cell-mediated resorption and physicochemical dissolution or physicochemical dissolution alone, we utilized an analytic high-resolution scanning ion microprobe with secondary ion mass spectroscopy to determine the effects of aluminum on bone surface ion composition. We cultured neonatal mouse calvariae with or without aluminum (10(-7) M) for 24 h and determined the relative ion concentrations of 23Na, 27Al, 39K, and 40Ca on the bone surface and eroded subsurface. Control calvariae have a surface (depth approximately 6 nm) that is rich in Na and K compared with Ca(Na/Ca) = 24.4 + 1.4, mean + 95% confidence limit of counts per second of detected secondary ions, K+Ca = 13.2 + 0.9). Aluminum is incorporated into the bone and causes a depletion of surface Na and K relative to Ca (Na/Ca = 9.6 + 0.7, K/Ca = 4.9 + 0.4; each p < 0.001 versus control). After erosion (depth approximately 50 nm), control calvariae have more Na and K than Ca (Na/Ca = 16.0 + 0.1, K/Ca = 7.5 + 0.1); aluminum again depleted Na and K relative to Ca (Na/Ca = 4.1 + 0.1 K/Ca = 1.9 + 0.1; each p < 0.001 versus control). Aluminum produced a greater net efflux of Ca (362 +/- 53, mean +/- SE, nmol/bone/24 h) than control (60 +/- 30, p < 0.001). With aluminum, the fall in the ratios of both Na/Ca and K/Ca coupled with net Ca release from bone indicates that aluminium induces a greater efflux of Na and K than Ca from the bone surface and is consistent with an aluminum-induced removal of the bone surface. This alteration in surface ion concentration and calcium efflux is consistent with that observed when calcium is lost from bone through a combination of cell-mediated resorption and physicochemical dissolution.

Bone and mineral metabolism in childhood end-stage renal disease

Renal osteodystrophy represents a spectrum from high to low turn-over lesions of bone, and the specific pattern may change during the evolution of chronic renal failure and as a consequence of specific therapeutic interventions. Although secondary hyperparathyroidism remains the predominant histologic lesion in patients undergoing maintenance dialysis, recent evidence indicates higher frequency of adynamic lesion not associated with aluminum intoxication. The different factors involved in the development of each of the histologic subtypes have been described together with the clinical manifestations of renal bone disease in childhood. Avoidance of aluminum-containing medications and the intermittent administration of calcitriol are effective approaches for the management of the renal bone diseases. The long-term consequences of the adynamic lesion remain to be determined.

Aluminum content of infant formulas used in Turkey

In the past few years, there has been an upsurge of interest in aluminum (Al) and human health. The well-recognized manifestations of systemic Al toxicity include fracturing osteomalacia, dialysis encephalopathy, and microcytic hypochromic anemia. The role of Al in causing childhood diseases is also becoming clearer, but the safe plasma level still remains to be determined in newborns, especially in premature newborns, implying that it should be kept low. Premature infants receiving iv fluid therapy show evidence of Al loading. Additionally, the infant-feeding mixtures, especially the soy-based infant formulas, tested may be a significant additional source of Al in the diet of infants with low birthweights, and in infants and in young children with impaired renal function. Careful clinical and biochemical monitoring is warranted to determine whether it will be necessary to eliminate Al contamination of both oral and parenteral preparations used in infants and children who may be at risk for Al intoxication. In this present study, the Al content of infant feeds was measured by electrothermal atomic absorption spectrophotometry, and also compared with those of breast milk, cow's milk, milk powder, and some starches that are commonly used for preparation of infant feed in Turkey. Our results show that Al content of commercially available powdered infant formulas, most of which are imported from Europe, ranged from 1.211 to 10.925 micrograms/g. The mean value was higher than that of breast milk. It was also found that the Al content of cow's milk in various containers was higher than that of breast milk. The highest Al level among cow's milk samples was in the aluminized carton box.

Experimental osteodystrophy of chronic renal failure induced by aluminum- and ferric-nitrilotriacetate in Wistar rats

The aluminum (AI) and iron (Fe) chelate complexes of nitrilotriacetate (NTA) cause renal insufficiency when they are administered intraperitoneally to rats. Their effects on bone metabolism were studied in 4 week old Wistar rats. Daily intraperitoneal administration of AI-NTA (3mg AI/kg for 11 weeks) induced osteomalacia, impaired bone growth, decreased bone mineral density, lower serum PTH levels than normal as well as renal insufficiency. Al staining showed diffuse deposition in the trabecula and a strong linear band of aluminum deposited at the mineralization front and along the cement line. The osteoid seen markedly within the trabecula was probably the decalcified portion of the bone, the calcium apatite of which was defectively fabricated because of diffuse Al deposition in the trabecula. Al deposition along the cement line would make it much more susceptible to external shear stress than normal. Although daily intraperitoneal administration of Fe-NTA (6 mg Fe/kg for 11 weeks) caused impaired bone growth, decreased bone mineral content and renal insufficiency, the osteoid volume did not increase. Fe staining showed that Fe was deposited diffusely in the cytoplasm of osteoblasts. The results of this study demonstrated that during renal insufficiency, different minerals exhibit different modes of action on bone metabolism, and that Al-NTA is useful for experimental animal models of Al-induced osteomalacia in renal insufficiency.

Reduction of aluminium concentration in albumin products

The aluminium concentration in albumin products has been reduced to < or = 100 ppb by an anion exchanger treatment. Furthermore, we have found that this low aluminium concentration in a albumin products has been maintained for extensive periods of time, when they are stored in de-alkalized soft glass containers.