Geert Dams

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.

Does the Phosphate Binder Lanthanum Carbonate Affect Bone in Rats with Chronic Renal Failure

Adequate control of phosphate levels remains an important issue in patients with chronic renal failure (CRF). Lanthanum carbonate has been proposed as a new phosphate binder. Previous studies have shown a high phosphate binding capacity (>97%) and low gastrointestinal absorption of lanthanum, without serious toxic side effects in the presence of a normal renal function (NRF). Because of lanthanums physicochemical resemblance to calcium, the possible effects of it on bone have to be considered. The aim of this study was to investigate the effects of lanthanum carbonate on bone histology in NRF and CRF rats after oral administration of the compound with doses of 100, 500, or 1000 mg/kg per d for 12 wk. Bone histomorphometry showed that CRF animals that received vehicle developed secondary hyperparathyroidism. Urinalysis of lanthanum-loaded CRF animals showed a dose-dependent decrease in urinary phosphorus excretion, which was clearly more pronounced in the CRF groups compared with NRF animals. Phosphatemia, however, remained normal. Lanthanum carbonate administration induced a dose-dependent decrease in bone formation rate and increase in osteoid area in CRF animals. Three of seven animals in the CRF-1000 group and one of eight animals in the NRF-100 group were classified as having a mineralization defect. The number of cuboidal osteoblasts, however, was not affected, indicating that bone changes were not due to a toxic effect of lanthanum on the osteoblast. Furthermore, lanthanum concentrations in the femur remained low and did not correlate with histomorphometric parameters. These findings suggest that the administration of high doses of phosphate binder (1000 mg/kg per d lanthanum carbonate), in combination with decreased 25-(OH) vitamin D(3) in the uremic state, resulted in phosphate depletion and followed by an increased mobilization of phosphorus out of bone and/or reduced incorporation into bone. There was no evidence that lanthanum had a direct toxic effect on osteoblasts.

Adequate phosphate binding with lanthanum carbonate attenuates arterial calcification in chronic renal failure rats

BACKGROUND Hyperphosphataemia is a risk factor for arterial calcification contributing to the high cardiovascular mortality in patients with chronic kidney disease. Calcium-based phosphate binders can induce hypercalcaemia and are associated with progression of vascular calcification. Therefore, the effect of lanthanum carbonate, a non-calcium phosphate binder, on the development of vascular calcification was investigated in uraemic rats. METHODS Chronic renal failure (CRF) was induced by feeding rats an adenine-enriched diet for 4 weeks. After 2 weeks, 1% or 2% lanthanum carbonate was added to the diet for 6 weeks. Calcification in the aorta, carotid and femoral arteries was evaluated histomorphometrically, biochemically and by ex vivo micro-CT. Chondro-/osteogenic conversion of vascular smooth muscle cells was also analysed in the rat aorta. RESULTS Treatment with 1% lanthanum carbonate (1% La) did not reduce vascular calcification, but in the 2% lanthanum carbonate (2% La) group vascular calcium content and area% Von Kossa positivity were decreased compared with control CRF rats. The aortic calcified volume measured with ex vivo micro-CT was significantly reduced in rats treated with 2% La. Although calcification was inhibited by treatment with 2% La, the chondrocyte transcription factor sox-9 was abundantly expressed in the aorta. CONCLUSION Treatment of CRF rats with 2% La reduces the development of vascular calcification by adequate phosphate binding resulting in a decreased supply of phosphate as a substrate for vascular calcification.

High-Resolution X-Ray Microtomography Is a Sensitive Method to Detect Vascular Calcification in Living Rats With Chronic Renal Failure

Objective—Chronic renal failure (CRF) is associated with a 10- to 20-fold increase in cardiovascular risk. Vascular calcification is a prominent feature of cardiovascular disease in patients with end-stage renal failure and contributes to the excess mortality in this population. In this study, we explored in vivo X-ray microtomography (micro-CT) as a tool to detect and follow-up vascular calcifications in the aorta of living rats with adenine-induced CRF. Methods and Results—With in vivo micro-CT, calcification of the aorta in uremic rats was clearly discernible on transversal virtual cross-sections. Micro-CT findings correlated well with tissue calcium content and histology. Repetitive scans in animals with light, moderate, and severe vascular calcification showed good reproducibility with minimal interference of motion artifacts. Moreover, both calcified volume and area could be quantified with this method. Conclusions—In vivo micro-CT scanning is a sensitive method to detect vascular calcifications in CRF rats, allowing follow-up and quantification of the development, and potential reversal during treatment, of vascular calcifications in living animals.

Effects of efficient phosphate binding on bone in chronic renal failure rats

Background. We recently reported that administration of high doses of lanthanum carbonate (1000 mg/kg/day) to chronic renal failure (CRF) rats can result in a mineralization defect. Our results suggested, however, that the impaired mineralization was not due to a direct toxic action of lanthanum on the bone, but rather was an indirect consequence of a phosphate depletion resulting from the compounds high phosphate-binding capacity. To further substantiate these results, in the present study, the effects of lanthanum carbonate on bone were compared to the effects of sevelamer, a nonabsorbed, non-metal-containing polymeric phosphate-binding agent. Methods. Male Wistar rats underwent a 5/6th nephrectomy to induce chronic renal failure, after which they were treated with either sevelamer (500 or 1000 mg/kg/day) or lanthanum carbonate (1000 mg/kg/day) by oral gavage for 12 weeks. Results. CRF animals treated with either sevelamer (500 or 1000 mg/kg/day) or lanthanum carbonate (1000 mg/kg/day) developed a phosphate depletion after 4 weeks of treatment, as evidenced by a marked reduction in phosphaturia. At sacrifice after 12 weeks of treatment, bone histomorphometry showed that a mineralization defect had developed in two out of six animals in the lanthanum-carbonate-treated group, in four out of seven animals in the 1000 mg/kg/day sevelamer group, and in one out of nine animals in the 500 mg/kg/day sevelamer group. Conclusions. These results corroborate our previous findings that the administration of a powerful phosphate-binding agent to CRF rats can induce phosphate depletion, resulting in a mineralization defect.

Role of Dietary Phosphorus and Degree of Uremia in the Development of Renal Bone Disease in Rats

The remnant kidney rat model has been extensively used for the evaluation of bone changes due to uremia. The present study aimed to assess the effect of the dietary phosphorus availability and of the severity of renal failure on bone histomorphometric changes and various biochemical markers over time in this model. Chronic renal failure (CRF) was induced in male Wistar rats by 5/6th nephrectomy. Half of the number of animals received a standard rat diet (STD) (0.67% P, containing low bioavailable phosphorus of plant origin); the other animals were fed a high phosphorus diet (HPD) (0.93% P, containing inorganic phosphorus with high bioavailability). Every two weeks, blood and urine samples were collected. At sacrifice after 6 or 12 weeks, bone samples were taken for the measurement of histological and histodynamic parameters. Serum creatinine measurements indicated the development of mild to moderate renal failure in both diet groups. Phosphaturia was unexpectedly low in all animals that received the STD, indicating relative phosphorus depletion despite the normal dietary phosphorus content. In the HPD CRF group, a decrease in calcemia and a rise in phosphatemia were seen after 12 weeks of CRF, which were more pronounced in animals with higher serum creatinine. Serum iPTH levels were distinctly increased in CRF rats fed a HPD, especially those with more pronounced renal failure. Serum osteocalcin and to a lesser extend tartrate-resistant acid phosphatase and urinary pyridinoline and deoxypyridinoline crosslinks were higher in the CRF animals compared to the shams, particularly in the animals of the HPD group with more pronounced CRF. In both diet groups, the CRF animals had significantly higher amounts of osteoid compared to shams. Only the animals that received a HPD developed distinct histological signs of secondary hyperparathyroidism (sHPTH), that is, an increased bone formation rate, mineral apposition rate, osteoblast perimeter, and eroded perimeter. Again, this effect was most prominent in rats with more severe CRF. In conclusion, data of the present study indicate that in experimental studies using the remnant kidney rat model, both the dietary phosphorus bioavailability and the degree of renal failure in the development of hyperparathyroidism should be considered.

A Magnesium Based Phosphate Binder Reduces Vascular Calcification without Affecting Bone in Chronic Renal Failure Rats

The alternative phosphate binder calcium acetate/magnesium carbonate (CaMg) effectively reduces hyperphosphatemia, the most important inducer of vascular calcification, in chronic renal failure (CRF). In this study, the effect of low dose CaMg on vascular calcification and possible effects of CaMg on bone turnover, a persistent clinical controversy, were evaluated in chronic renal failure rats. Adenine-induced CRF rats were treated daily with 185 mg/kg CaMg or vehicle for 5 weeks. The aortic calcium content and area% calcification were measured to evaluate the effect of CaMg. To study the effect of CaMg on bone remodeling, rats underwent 5/6th nephrectomy combined with either a normal phosphorus diet or a high phosphorus diet to differentiate between possible bone effects resulting from either CaMg-induced phosphate deficiency or a direct effect of Mg. Vehicle or CaMg was administered at doses of 185 and 375 mg/kg/day for 8 weeks. Bone histomorphometry was performed. Aortic calcium content was significantly reduced by 185 mg/kg/day CaMg. CaMg ameliorated features of hyperparathyroid bone disease. In CRF rats on a normal phosphorus diet, the highest CaMg dose caused an increase in osteoid area due to phosphate depletion. The high phosphorus diet combined with the highest CaMg dose prevented the phosphate depletion and thus the rise in osteoid area. CaMg had no effect on osteoblast/osteoclast or dynamic bone parameters, and did not alter bone Mg levels. CaMg at doses that reduce vascular calcification did not show any harmful effect on bone turnover.

Disturbances in Bone Largely Predict Aortic Calcification in an Alternative Rat Model Developed to Study Both Vascular and Bone Pathology in Chronic Kidney Disease

Because current rat models used to study chronic kidney disease (CKD)‐related vascular calcification show consistent but excessive vascular calcification and chaotic, immeasurable, bone mineralization due to excessive bone turnover, they are not suited to study the bone‐vascular axis in one and the same animal. Because vascular calcification and bone mineralization are closely related to each other, an animal model in which both pathologies can be studied concomitantly is highly needed. CKD‐related vascular calcification in rats was induced by a 0.25% adenine/low vitamin K diet. To follow vascular calcification and bone pathology over time, rats were killed at weeks 4, 8, 10, 11, and 12. Both static and dynamic bone parameters were measured. Vascular calcification was quantified by histomorphometry and measurement of the arterial calcium content. Stable, severe CKD was induced along with hyperphosphatemia, hypocalcemia as well as increased serum PTH and FGF23. Calcification in the aorta and peripheral arteries was present from week 8 of CKD onward. Four and 8 weeks after CKD, static and dynamic bone parameters were measurable in all animals, thereby presenting typical features of hyperparathyroid bone disease. Multiple regression analysis showed that the eroded perimeter and mineral apposition rate in the bone were strong predictors for aortic calcification. This rat model presents a stable CKD, moderate vascular calcification, and quantifiable bone pathology after 8 weeks of CKD and is the first model that lends itself to study these main complications simultaneously in CKD in mechanistic and intervention studies.

Differences in gastrointestinal calcium absorption after the ingestion of calcium-free phosphate binders

Both calcium-containing and noncalcium-containing phosphate binders can increase gastrointestinal calcium absorption. Previously, we observed that lanthanum carbonate administration to rats with renal failure is not associated with increased calciuria. Additionally, lanthanum carbonate treatment in dialysis patients has been associated with a less pronounced initial decrease in serum parathyroid hormone compared with other phosphate binders. For 8 days, male Wistar rats received a diet supplemented with 2% lanthanum carbonate, 2% sevelamer, 2% calcium carbonate, or 2% cellulose. Calciuria was found to be increased in animals with normal renal function treated with sevelamer or calcium carbonate but not with lanthanum carbonate. In animals with renal failure, cumulative calcium excretion showed similar results. In rats with normal renal function, serum ionized calcium levels were increased after 2 days of treatment with sevelamer, while calcium carbonate showed a smaller increase. Lanthanum carbonate did not induce differences. In animals with renal failure, no differences were found between sevelamer-treated, calcium carbonate-treated, and control groups. Lanthanum carbonate, however, induced lower ionized calcium levels within 2 days of treatment. These results were confirmed in normal human volunteers, who showed lower net calcium absorption after a single dose of lanthanum carbonate compared with sevelamer carbonate. In conclusion, these two noncalcium-containing phosphate-binding agents showed a differential effect on gastrointestinal calcium absorption. These findings may help to improve the management of calcium balance in patients with renal failure, including concomitant use of vitamin D.