Skeletal and mineral metabolic effects of risedronate in a rat model of high-turnover renal osteodystrophy.

INTRODUCTION: High-turnover bone disease is a major consequence of SHPT and may explain the high risk for fracture in patients with advanced chronic kidney disease (CKD). Bisphosphonates suppress bone turnover and improve bone strength, but their effects have not been fully characterized in advanced CKD with severe SHPT. Bisphosphonates also increase 1,25-dihydroxyvitamin D levels in normal and uremic rats, but the underlying mechanism remains to be determined. MATERIALS AND METHODS: We investigated the skeletal and mineral metabolic effects of RIS, a pyridinyl bisphosphonate, in rats with severe SHPT induced by 5/6 nephrectomy plus a high phosphate diet. RESULTS: Nephrectomized rats developed severe SHPT, along with hyperphosphatemia, low 1,25-dihydroxyvitamin D, and markedly increased FGF23. Moreover, these rats exhibited characteristic features of high-turnover renal osteodystrophy, including increased indices of trabecular bone turnover, decreased cortical bone thickness, inferior cortical biomechanical properties, and a prominent increase in peritrabecular fibrosis. RIS treatment increased bone volume and partially attenuated trabecular bone remodeling, cortical bone loss, and mechanical properties, whereas it produced a marked improvement in peritrabecular fibrosis along with a corresponding decrease in osteogenic gene markers. RIS treatment also suppressed the elevation of FGF23, which was associated with increased 1,25-dihydroxyvitamin D. CONCLUSIONS: In a rat model of severe SHPT, treatment with RIS partially attenuated histological manifestations of high-turnover bone disease. RIS treatment also suppressed the elevation of FGF23, which may explain the increased 1,25-dihydroxyvitamin D production during the treatment.

TGF-Beta Signaling in Bone with Chronic Kidney Disease.

Transforming growth factor (TGF)-ß signaling is not only important in skeletal development, but also essential in bone remodeling in adult bone. The bone remodeling process involves integrated cell activities induced by multiple stimuli to balance bone resorption and bone formation. TGF-ß plays a role in bone remodeling by coordinating cell activities to maintain bone homeostasis. However, mineral metabolism disturbance in chronic kidney disease (CKD) results in abnormal bone remodeling, which leads to ectopic calcification in CKD. High circulating levels of humoral factors such as parathyroid hormone, fibroblast growth factor 23, and Wnt inhibitors modulate bone remodeling in CKD. Several reports have revealed that TGF-ß is involved in the production and functions of these factors in bone. TGF-ß may act as a factor that mediates abnormal bone remodeling in CKD.

The effect of Mg and Sr on the crystallinity of bones evaluated through Raman spectroscopy and laser ablation-ICPMS analysis.

We investigated the possible linkage between the crystallinity and elemental ratios (Mg/Ca and Sr/Ca) of the femoral cortical bones of rats with chronic kidney disease (CKD) or diabetes mellitus (DM). The Mg/Ca and Sr/Ca ratios were measured by using the laser ablation-inductively coupled plasma mass spectrometry (LA-ICPMS) technique and the crystallinity was evaluated by Raman spectroscopy on the same sample slice. The measured crystallinity varied significantly along the radial direction, reflecting the heterogeneities in the Mg/Ca ratio for the bone samples. For the endosteal cortical bone of CKD rats, the Mg/Ca ratio became higher. This is explained by the increase of the abundance of Mg in the bone, possibly due to the higher absorption efficiency of Mg in the intestine or due to the lower excretion efficiency of Mg from the kidney. For areas with a higher Mg/Ca ratio, the crystallinity of the bone was significantly more degraded than that for areas with a lower Mg/Ca ratio, suggesting that the substitution of Ca by Mg induced the deterioration of the crystallinity of hydroxyapatite (HAp). In addition, the measured Mg/Ca and Sr/Ca ratios of the bone were positively correlated with those found in serum samples. The data obtained here demonstrated that the metabolic alterations for inorganic elements caused the ionic substitutions of Ca by foreign cationic ions, and that the contents of foreign ions in the bone greatly affected the crystallinity of HAp.

Cardiac remodeling associated with protein increase and lipid accumulation in early-stage chronic kidney disease in rats.

Chronic kidney disease (CKD) is associated with increased risks of cardiovascular morbidity and mortality. Cardiac remodeling including myocardial fibrosis and hypertrophy is frequently observed in CKD patients. In this study, we investigate the mechanism involved in cardiac hypertrophy associated with CKD using a rat model, by morphological and chemical component changes of the hypertrophic and non-hypertrophic hearts. Sprague-Dawley rats were 4/5 nephrectomized (Nx) at 11 weeks of age and assigned to no treatment and treatment with AST-120, which was reported to affect the cardiac damage, at 18 weeks of age. At 26 weeks of age, the rats were euthanized under anesthesia, and biochemical tests as well as analysis of cardiac condition were performed by histological and spectrophotometric methods. Cardiac hypertrophy and CKD were observed in 4/5 Nx rats even though vascular calcification and myocardial fibrosis were not detected. The increasing myocardial protein was confirmed in hypertrophic hearts by infrared spectroscopy. The absorption of amide I and other protein bands in hypertrophic hearts increased at the same position as in normal cardiac absorption. Infrared spectra also showed that lipid accumulation was also detected in hypertrophic heart. Conversely, the absorptions of protein were obviously reduced in the myocardium of non-hypertrophic heart with CKD compared to that of hypertrophic heart. The lipid associated absorption was also decreased in non-hypertrophic heart. Our results suggest that cardiac remodeling associated with relatively early-stage CKD may be suppressed by reducing increased myocardial protein and ameliorating cardiac lipid load.

[New Developments in CKD-MBD. Bone quality and fracture in patients with chronic kidney disease].

Chronic kidney disease (CKD) patients have an extremely increased risk of fragility fractures, but the underling pathophysiological mechanisms remain obscure. Recently, the progresses of analysis technology have revealed the changes of bone quality in CKD condition. In particular, we can observe the characteristic changes of bone microarchitecture and bone chemical compositions in both human bone biopsy samples and experimental animal bones. Here, I will provide a short review on these bone quality factors and discuss on the relationship between bone quality and fracture in CKD patients.

Influence of food restriction combined with voluntary running on bone morphology and strength in male rats.

Athletes, in particular endurance athletes and dancers, are chronically exposed to a state of low energy availability due to insufficient dietary energy intake and massive exercise energy expenditure. Low energy availability sometimes causes bone fragility, thereby increasing the risk of bone disorders. Although the decrease in energy availability shows no sexual dimorphism, epidemiological studies have reported that bone disorders are less frequent in male athletes than in female athletes. We hypothesized that bone tissue was not affected by low energy availability in males. The purpose of this study was to examine the influence of food restriction combined with voluntary running training on bone morphology and strength in adult male rats. Fourteen-week-old male Sprague-Dawley rats were divided randomly into four groups: control (C) group, food restriction (R) group, exercise (Ex) group, and food restriction plus exercise (REx) group. For the R and REx groups, 30 % food restriction was carried out in comparison with the C group. Bone strength, bone mineral density (BMD), bone architecture, and bone turnover rate were measured after a 13-week experimental period. Bone strength was not significantly lower in the REx group compared with the C group. BMD and trabecular bone volume showed no difference among groups. These findings indicate that bone morphology and strength were little affected by food restriction combined with exercise training in adult male rats.

Dietary inorganic phosphorus regulates the intestinal peptide transporter PepT1.

BACKGROUND: Both organic and inorganic phosphorus (Pi) are present in regularly consumed foods, such as meats, eggs, and dairy products. Pi is often included in foods as an additive (as hidden phosphorus). The intestinal peptide transporter PepT1 mediates protein absorption, which is disturbed in renal insufficiency. Our aim was to determine the effects of dietary Pi content on the peptide transport activity and expression of PepT1. METHODS: The following animal models were used: (1) 7-week-old male Wistar rats; and (2) rats that underwent 3/4 nephrectomy to induce chronic kidney disease (CKD). The rats were fed a normal-protein (20%) diet containing low (0.02%), normal (0.6%), or high (1.2%) Pi levels. They were also fed diets containing varying amounts of protein and either low or normal Pi levels as follows: (1) low Pi/normal protein, (2) low Pi/high (50%) protein, (3) normal Pi/normal protein, and (4) normal Pi/high protein. RESULTS: Intestinal peptide transport activity and PepT1 expression levels were significantly higher in the CKD rats than in sham-operated control ones. Compared with the normal-protein diet, the high-protein diet increased PepT1 expression in the CKD rats. Intestinal dipeptide transport activity and PepT1 protein levels did not increase in the rats fed the low-Pi/high-protein diet. In contrast, intestinal dipeptide transport activity and PepT1 protein expression were markedly increased in the rats fed the normal-Pi/high-protein diet. CONCLUSION: Dietary Pi levels regulate intestinal peptide transport activity through PepT1.

Carvedilol ameliorates low-turnover bone disease in non-obese type 2 diabetes.

BACKGROUND: Diabetic bone disease is a major complication in diabetes mellitus and is characterized by low-turnover bone formation. Recent studies have demonstrated that oxidative stress could be associated with diabetic bone disease and that ß-adrenergic antagonists could increase bone formation. Our study investigated the effect of carvedilol (ß-blocker), possessing an antioxidant effect, on diabetic bone disease. METHODS: We used the non-obese, type 2 diabetes model Spontaneously Diabetic Torii (SDT) rats in this study. Sprague-Dawley rats were used as controls (control, n = 6). SDT rats were divided into four groups: diabetic (DM, n = 8), DM+insulin (DM+I, n = 7), DM+carvedilol (DM+C, n = 8), and DM+N-acetylcysteine (DM+N, n = 10) at 20 weeks. The rats were sacrificed at 30 weeks, after which blood and urine samples, bone mineral density, histomorphometry, and oxidative stress were evaluated. RESULTS: The number of 8-hydroxydeoxyguanosine-positive cells in bone tissue was significantly lower in the DM+C and DM+N groups than in the DM group. Mineral apposition rate and bone formation rate per bone surface in the DM+C and DM+N groups were significantly higher than those in the DM group, and these parameters were better in the DM+C group than in the DM+N group. CONCLUSION: Our data suggest that carvedilol has stronger effects on diabetic low-turnover bone disease beyond that which can be attributed to its antioxidative stress mechanism.

A novel underuse model shows that inactivity but not ovariectomy determines the deteriorated material properties and geometry of cortical bone in the tibia of adult rats.

Our goal in this study was to determine to what extent the physiologic consequences of ovariectomy (OVX) in bones are exacerbated by a lack of daily activity such as walking. We forced 14-week-old female rats to be inactive for 15 weeks with a unique experimental system that prevents standing and walking while allowing other movements. Tibiae, femora, and 4th lumbar vertebrae were analyzed by peripheral quantitative computed tomography (pQCT), microfocused X-ray computed tomography (micro-CT), histology, histomorphometry, Raman spectroscopy, and the three-point bending test. Contrary to our expectation, the exacerbation was very much limited to the cancellous bone parameters. Parameters of femur and tibia cortical bone were affected by the forced inactivity but not by OVX: (1) cross-sectional moment of inertia was significantly smaller in Sham-Inactive rat bones than that of their walking counterparts; (2) the number of sclerostin-positive osteocytes per unit cross-sectional area was larger in Sham-Inactive rat bones than in Sham-Walking rat bones; and (3) material properties such as ultimate stress of inactive rat tibia was lower than that of their walking counterparts. Of note, the additive effect of inactivity and OVX was seen only in a few parameters, such as the cancellous bone mineral density of the lumbar vertebrae and the structural parameters of cancellous bone in the lumbar vertebrae/tibiae. It is concluded that the lack of daily activity is detrimental to the strength and quality of cortical bone in the femur and tibia of rats, while lack of estrogen is not. Our inactive rat model, with the older rats, will aid the study of postmenopausal osteoporosis, the etiology of which may be both hormonal and mechanical.

[Morphological analysis of bone dynamics and metabolic bone disease. Bone histomorphometry for laboratory animals].

The bone histomorphometry is well-known as the histological evaluation method for the investigation of the efficacy of various kinds of medicine on bone metabolism disorder. Recently, in addition, it is indispensable for bone researchers to clarify characteristic of bone metabolism in genetically-modified mice by means of bone histomorphometry. Thus, bone histomorphometry has broad utility. However, it would not be an exaggeration to say that researchers are interested in only numerical value of various kinds of parameters without understanding lots of information obtained from morphological observation. Especially, we have to pay attention to measurement and interpretation of parameters of bone histomorphometry in case of growing bone, because growing bone is changing its size of longitudinal and width. In this review, we would like to explain how to measure with bone histomorphometry for modeling bone in growing animals.

Type I Angiotensin II Receptor Blockade Reduces Uremia-Induced Deterioration of Bone Material Properties.

Chronic kidney disease (CKD) is associated with a high incidence of fractures. However, the pathophysiology of this disease is not fully understood, and limited therapeutic interventions are available. This study aimed to determine the impact of type 1 angiotensin II receptor blockade (AT-1RB) on preventing CKD-related fragility fractures and elucidate its pharmacological mechanisms. AT-1RB use was associated with a lower risk of hospitalization due to fractures in 3276 patients undergoing maintenance hemodialysis. In nephrectomized rats, administration of olmesartan suppressed osteocyte apoptosis, skeletal pentosidine accumulation, and apatite disorientation, and partially inhibited the progression of the bone elastic mechanical properties, while the bone mass was unchanged. Olmesartan suppressed angiotensin II-dependent oxidation stress and apoptosis in primary cultured osteocytes in vitro. In conclusion, angiotensin II-dependent intraskeletal oxidation stress deteriorated the bone elastic mechanical properties by promoting osteocyte apoptosis and pentosidine accumulation. Thus, AT-1RB contributes to the underlying pathogenesis of abnormal bone quality in the setting of CKD, possibly by oxidative stress. © 2020 The Authors. Journal of Bone and Mineral Research published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research (ASBMR).

Spherical carbon adsorbent (AST-120) protects deterioration of renal function in chronic kidney disease rats through inhibition of reactive oxygen species production from mitochondria and reduction of serum lipid peroxidation.

BACKGROUND/AIM: An imbalance in renal redox status contributes to progression of renal dysfunction. We investigated the effects of an oral charcoal adsorbent (AST-120) on renal redox status, superoxide production from renal mitochondria, and serum lipid peroxidation using chronic kidney disease (CKD) model rats. METHODS: CKD was induced by 5/6 nephrectomy. CKD rats were divided into 2 groups: controls, and those treated with AST-120 for 20 weeks. We evaluated: (1) renal redox status by in vivo low-frequency electron spin resonance imaging (EPRI); (2) renal superoxide scavenging activity (SSA); (3) superoxide production from renal mitochondria; (4) immunostaining for Cu-Zn superoxide dismutase (SOD), and (5) oxidative stress markers including LDL-negative charge (LDL-CMF), serum lipid peroxide (LPO) and urinary hexanoyl-lysine (HEL). The effect of indoxyl sulfate, a uremic toxin, on mitochondrial superoxide production was also investigated. RESULTS: AST-120 treatment improved renal function, renal SSA, renal mitochondrial superoxide production, renal SOD expression, renal redox status by EPRI, and oxidative stress profiles by LDL-CMF, LPO and urinary HEL. Addition of indoxyl sulfate increased mitochondrial superoxide production and AST-120 also decreased this. CONCLUSIONS: Improvements in the redox status and lipid peroxidation induced by AST-120 may delay the progression of CKD.

Oral charcoal adsorbent (AST-120) prevents progression of cardiac damage in chronic kidney disease through suppression of oxidative stress.

BACKGROUND: Chronic kidney disease (CKD) is an important risk factor for cardiovascular disease (CVD). Increased oxidative stress plays a role in the pathogenesis of CVD in CKD patients. The oral charcoal adsorbent AST-120 attenuates the progression of CKD possibly by removing uraemic toxins such as indoxyl sulfate (IS), and reduces oxidative stress. We investigated the relationship between oxidative stress and cardiac damage in CKD and its prevention by AST-120. METHODS: Male Lewis rats were administered adriamycin at 8 weeks of age, and the right kidney was removed at 12 weeks of age. From 14 weeks of age, the rats were treated daily with AST-120 (n = 8) or were untreated (control group, n = 8). At 34 weeks of age, the rats were killed and urinary and blood biochemical tests as well as cardiac histological analyses were performed. RESULTS: At 14 weeks of age, there were no significant differences in blood pressure, renal function (creatinine clearance: 1.54 +/- 0.28 mL/min versus 1.60 +/- 0.22 mL/min), oxidative stress markers or other biochemical data between the control and AST-120 groups. At 34 weeks, despite similar blood pressure and renal function (creatinine clearance: 0.78 +/- 0.46 mL/min versus 0.75 +/- 0.54 mL/min), serum concentrations of IS and urinary excretion of 8-hydroxydeoxyguanosine (8-OHdG), acrolein and IS were significantly lower in the AST-120 group than in the control group. Heart volume, left ventricular volume and cardiac fibrosis were significantly smaller in the experimental AST-120 group than in the control group. Immunohistological analysis revealed that the numbers of 8-OHdG- and acrolein-positive cardiomyocytes and the degrees of myocardial and perivascular fibrosis were ameliorated by AST-120 administration. The myocardial fibrosis score was significantly associated with the 8-OHdG- (r = 0.848, P < 0.001) and acrolein-positive (r = 0.812, P < 0.001) cell scores. The perivascular fibrosis score was also significantly associated with the 8-OHdG- (r = 0.906, P < 0.0001) and acrolein-positive (r = 0.789, P < 0.001) cell scores. CONCLUSIONS: Oxidative stress is suggested to play a key role in the development of cardiac hypertrophy and fibrosis in CKD. AST-120 may suppress oxidative stress and reduce cardiac damage in CKD.

A Highly Efficient Adsorbent Cu-Perusian Blue@Nanodiamond for Cesium in Diluted Artificial Seawater and Soil-Treated Wastewater.

A new adsorbent Cu-Perussian blue@Nanodiamond (Cu-PB@DND) for Cs+ removal was prepared and characterized with IR, SEM, X-ray diffraction, particle size analysis, and zeta-potential. The adsorbent consists of a core of aggregated detonation nanodiamond (DND) particles with the surface treated with Cu-PB. Cesium adsorption was studied in two modes; a co-precipitation mode and a batch mode. In the co-precipitation mode, DND, CuCl2, and K4[Fe(CN)6] were added sequentially to a Cs+ solution in diluted artificial seawater. In the batch mode, adsorbent Cu-PB@DND was dispersed into a Cs+ solution with stirring. The distribution coefficient (Kd) of the co-precipitation mode was 8.8 × 107 (mL/g) at Cs+ 6.6 ppm in 0.07% seawater. The Kd value of the batch mode was 1.3 × 106 (mL/g). Precipitation of Cs+-incorporated particles was complete, and post filtration was not necessary. Excess copper and iron ions were completely removed and were not detected in the supernatant. The adsorption data for Cu-PB@DND were analyzed by assuming Langmuir isotherm and a good fit was obtained with a maximum adsorption capacity Qmax of 759 mg/g. The co-precipitation method was also applied to soil-treated wastewater.

Calcium isotope signature: new proxy for net change in bone volume for chronic kidney disease and diabetic rats.

Herein, we measure the Ca isotope ratios (44Ca/42Ca and 43Ca/42Ca) in serum and bone samples collected from rats with chronic kidney disease (CKD) or diabetes mellitus (DM). For the serum samples, the isotope ratios are lower for the CKD (δ44Ca/42Caserum = 0.16 ± 0.11‰; 2SD, n = 6) and the DM (δ44Ca/42Caserum = -0.11 ± 0.25‰; 2SD, n = 7) rats than that for the control rats (δ44Ca/42Caserum = 0.25 ± 0.04‰; 2SD, n = 7). Bone samples from two distinct positions of 20 rats in total, namely, the center and proximal parts of the tibial diaphysis, are subject to Ca isotope analysis. The resulting δ44Ca/42Ca values for the bone of the proximal part are about 0.3‰ lower than that for the serum samples from the same rats. The larger isotope fractionations between the serum and bone are consistent with previously reported data for vertebrate animals (e.g., Skulan and DePaolo, 1999), which suggests the preferential incorporation of lighter Ca isotopes through bone formation. For the bones from the control and CKD rats, there were no differences in the δ44Ca/42Ca values between the positions of the bone. In contrast, the δ44Ca/42Ca values of the bone for the DM rats were different between the positions of the bone. Due to the lower bone turnover rate for the DM rats, the δ44Ca/42Ca for the middle of the diaphysis can reflect the Ca isotopes in the bone formed prior to the progression of DM states. Thus, the resulting δ44Ca/42Ca values show a clear correlation with bone mineral density (BMD). This can be due to the release of isotopically lighter Ca from the bone to the serum. In the present study, our data demonstrate that the δ44Ca/42Ca value for serum can be used as a new biomarker for evaluating changes in bone turnover rate, followed by changes in bone volume.

High-fat diet in low-dose-streptozotocin-treated heminephrectomized rats induces all features of human type 2 diabetic nephropathy: a new rat model of diabetic nephropathy.

BACKGROUND AND AIM: We have developed a new rat model that mimics the natural course of diabetic nephropathy seen in type 2 diabetes. METHODS: Nine days after intravenous injection of streptozotocin (STZ) (40 mg/kg) or vehicle to 8-week-old male Sprague-Dawley rats, the animals' right kidneys were surgically removed. Two weeks after surgery, the STZ-injected rats were fed on either a high-fat (ST+HF) or a normal (ST) diet, while the vehicle-injected rats were fed on the high-fat diet (HF). RESULTS: Baseline biochemical markers did not differ between the three groups. Only the ST+HF group showed a significant increase in plasma glucose levels after 15 weeks, and simultaneously plasma insulin levels started to decrease, followed by an increase in plasma total cholesterol and triglyceride levels at 25 weeks and slightly later by an increase in blood pressure. In the ST+HF group, significant microalbuminuria was detected at 15 weeks followed by overt proteinuria, both of which were absent in the other two groups. Also in ST+HF, the creatinine clearance rate increased until week 15, and then gradually decreased. Histologically, ST+HF rats showed mesangial expansion at week 25, and diffuse glomerular sclerosis at the end of the experiments. CONCLUSION: The chronological changes in biochemical, physiological and histological markers in ST+HF rats are reminiscent of human type 2 diabetes and nephropathy. Our new model of type 2 diabetic nephropathy should help us to understand the pathophysiology of the disease and serve to explore measures to prevent and treat diabetic nephropathy.

Proteomic analysis of rat plasma by SELDI-TOF-MS under the condition of prevention of progressive adriamycin nephropathy using oral adsorbent AST-120.

AIMS: To determine changes in relative peak intensities of mass-to-charge ratio (m/z) between 2,000 and 15,000, which are difficult to evaluate by 2-dimensional gel electrophoresis, SELDI-TOF-MS (surface-enhanced laser desorption/ionization time of flight-mass spectrometry) proteomic changes in rat models of adriamycin nephropathy with or without AST-120 were investigated. METHODS: A normal group (n = 5), an adriamycin nephropathy group (n = 9), and an adriamycin nephropathy + AST-120 group (4 g/head/day) (n = 9) were established in SD rats. Anion exchange chips, Q10, washed by 50 mM Tris-HCl pH 8 as a ProteinChip and sinapinic acid were used. The mass range between 2,000 and 15,000 Da was measured. Twenty to 34 weeks after adriamycin 3 mg/kg injection, the adriamycin nephropathy + AST-120 group (plasma creatinine value: 2.1 +/- 0.8 mg/dl) clearly demonstrated slight renal dysfunction compared with that in the adriamycin nephropathy group (5.4 +/- 2.0 mg/dl). RESULTS: The relative intensities in the adriamycin nephropathy group were significantly higher in 7 peaks (such as 8,640, and 8,822 Da) and lower in 8 peaks (such as 4,188, and 8,358 Da) than those in the normal group. The relationship between the relative intensity of peaks and the plasma creatinine value demonstrated a positive correlation in 11 peaks (such as 8,640, and 8,822 Da), and a negative correlation in 6 peaks (such as 4,188 and 8,358 Da). Although the relative intensities of peaks in the adriamycin nephropathy + AST-120 group were between that of the adriamycin nephropathy group and that of the normal group, the relative intensities of 4 peaks (such as 3,664 and 5,179 Da) in the adriamycin nephropathy + AST-120 group demonstrated higher values than in the two other groups. The m/z 3,664 peak was purified and identified as a C-terminal fragment of apolipoprotein C-III. CONCLUSION: Low-molecular proteins and peptides in plasma in this chronic renal failure model showed not only increases but also decreases in some peaks. The relative intensities in some peaks increased in the adriamycin nephropathy + AST-120 group more than in the two other groups. One of these peaks was identified as the apolipoprotein C-III fragment. The relationship between these changes and the prevention of progression of chronic renal failure by AST-120 remains to be established.

Menatetrenone rescues bone loss by improving osteoblast dysfunction in rats immobilized by sciatic neurectomy.

Menatetrenone (MK-4) is a vitamin K2 homologue that has been used as a therapeutic agent for osteoporosis in Japan. However, there is no far any reported evidence that MK-4 ameliorates a pre-existing condition of reduced bone mineral density (BMD) in vivo. In this study, we evaluated the effect of MK-4 in a rat model of established bone loss through immobilization caused by sciatic neurectomy. Unilateral sciatic neurectomy (SNx) was performed in rats, and 10 or 30 mg/kg of MK-4 or vehicle was administered to the rats three weeks after operation. Seven weeks after operation, the rats were sacrificed and BMD and bone histomorphometric parameters were measured to assess the effects of MK-4. While BMD of the distal femoral metaphysis was significantly decreased after SNx, MK-4 administration increased BMD in the neurectomized rats. Bone formation was decreased continuously and bone resorption was initially increased in SNx rats. Four weeks treatment of MK-4 increased bone formation and suppressed bone resorption. In addition, increased carboxylated osteocalcin and decreased undercarboxylated osteocalcin in serum were observed in MK-4-administered rats. These results indicated that MK-4 rescued bone volume by improving osteoblast dysfunction and accelerating gamma carboxylation of osteocalcin. MK-4 may be useful for treating disuse osteopenia.

Altered material properties are responsible for bone fragility in rats with chronic kidney injury.

Chronic kidney disease (CKD) is associated with an increased risk of fragility fractures, but the underlying pathophysiological mechanism remains obscure. We performed an in vivo experimental study to examine the roles of uremia and abnormal mineral/parathyroid metabolism in the development of bone metabolic abnormalities in uremic rats. Male Sprague-Dawley rats were divided into four groups, comprising sham operation (high turnover bone control=HTB-Cont), 5/6-nephrectomy (high turnover bone nephrectomized=HTB-Nx), thyroparathyroidectomy (low turnover bone control=LTB-Cont), and thyroparathyroidectomy plus 5/6 nephrectomy (low turnover bone nephrectomized=LTB-Nx), and maintained for 16 weeks. Uremia was successfully created in the LTB-Nx and HTB-Nx groups, while hyperparathyroidism was only found in the HTB-Nx group. Cancellous bone histomorphometry revealed significantly higher bone turnover in the HTB-Nx group than in the LTB-Nx group. Storage modulus at 1 Hz and tan delta in cortical bone of the femur, which represent the viscoelastic mechanical properties, were significantly lower in both Nx groups than in the Cont groups regardless of bone metabolism. Pentosidine-to-matrix ratio was increased and crystallinity was decreased in both Nx groups regardless of bone turnover. Mineral-to-matrix ratio was significantly decreased in the HTB-Nx group, but increased in the LTB-Nx group. Enzymatic collagen crosslinks were decreased in the HTB-Nx group. The degree of orientation of the c-axis in carbonated hydroxyapatite (biological apatite=BAp) crystallites was decreased in both Nx groups regardless of bone metabolism. Stepwise multivariate regression revealed that pentosodine-to-matrix ratio and BAp preferential c-axis orientation were significantly associated with storage modulus and tan delta. In conclusion, bone elastic mechanical properties deteriorated regardless of bone metabolism or bone mass in rats with chronic kidney injury. Various changes in bone mineral properties were associated with CKD, including abnormal parathyroid function, impaired bone turnover, and uremia associated with the accumulation of uremic toxins, were responsible for these changes. Pentosidine-to-matrix ratio and BAp orientation at position 5 were the two meaningful determinants of elastic bone mechanical strength, and both factors were associated with the severity of uremia, but not parathyroid function or bone metabolism. These two factors may account for the increased bone fragility among CKD patients.

Indoxyl sulfate exacerbates low bone turnover induced by parathyroidectomy in young adult rats.

Low-turnover bone disease is one of the bone abnormalities observed in patients with chronic kidney disease (CKD) and is recognized to be associated with low serum parathyroid hormone (PTH) level and skeletal resistance to PTH. Indoxyl sulfate (IS) is a representative uremic toxin that accumulates in the blood as renal dysfunction progresses in CKD patients. A recent in vitro study using an osteoblastic cell culture system suggests that IS has an important role in the pathogenesis of low bone turnover through induction of skeletal resistance to PTH. However, the effects of IS on the progression of low bone turnover have not been elucidated. In the present study, we produced rats with low bone turnover by performing parathyroidectomy (PTX) and fed these rats a diet containing indole, a precursor of IS, to elevate blood IS level from indole metabolism. Bone metabolism was evaluated by measuring histomorphometric parameters of secondary spongiosa of the femur. Histomorphometric analyses revealed significant decreases in both bone formation-related parameters and bone resorption-related parameters in PTX rats. In indole-treated PTX rats, further decreases in bone formation-related parameters were observed. In addition, serum alkaline phosphatase activity, a bone formation marker, and bone mineral density of the tibia tended to decrease in indole-treated PTX rats. These findings strongly suggest that IS exacerbates low bone turnover through inhibition of bone formation by mechanisms unrelated to skeletal resistance to PTH.