Development of secondary hyperparathyroidism and bone disease in diabetic rats with renal failure

Pathophysiology of bone disease in chronic kidney disease: from basics to renal osteodystrophy and osteoporosis

Chronic kidney disease (CKD) is a highly prevalent disease that has become a public health problem. Progression of CKD is associated with serious complications, including the systemic CKD-mineral and bone disorder (CKD-MBD). Laboratory, bone and vascular abnormalities define this condition, and all have been independently related to cardiovascular disease and high mortality rates. The "old" cross-talk between kidney and bone (classically known as "renal osteodystrophies") has been recently expanded to the cardiovascular system, emphasizing the importance of the bone component of CKD-MBD. Moreover, a recently recognized higher susceptibility of patients with CKD to falls and bone fractures led to important paradigm changes in the new CKD-MBD guidelines. Evaluation of bone mineral density and the diagnosis of "osteoporosis" emerges in nephrology as a new possibility "if results will impact clinical decisions". Obviously, it is still reasonable to perform a bone biopsy if knowledge of the type of renal osteodystrophy will be clinically useful (low versus high turnover-bone disease). However, it is now considered that the inability to perform a bone biopsy may not justify withholding antiresorptive therapies to patients with high risk of fracture. This view adds to the effects of parathyroid hormone in CKD patients and the classical treatment of secondary hyperparathyroidism. The availability of new antiosteoporotic treatments bring the opportunity to come back to the basics, and the knowledge of new pathophysiological pathways [OPG/RANKL (LGR4); Wnt-ß-catenin pathway], also affected in CKD, offers great opportunities to further unravel the complex physiopathology of CKD-MBD and to improve outcomes.

Adynamic bone disease: Revisited

The bone and mineral disorders form an integral part of the management of a chronic kidney disease (CKD) patient. Amongst various types of bone pathologies in chronic kidney disease-mineral bone disorder (CKD-MBD), the prevalence of adynamic bone disease (ABD) is increasing. The present review discusses the updated pathophysiology, risk factors, and management of this disorder.

Adynamic bone disease: Revisited

The bone and mineral disorders form an integral part of the management of a chronic kidney disease (CKD) patient. Amongst various types of bone pathologies in chronic kidney disease-mineral bone disorder (CKD-MBD), the prevalence of adynamic bone disease (ABD) is increasing. The present review discusses the updated pathophysiology, risk factors, and management of this disorder.

Association of Insulin Glargine Treatment with Bone Mineral Density in Patients with Type 2 Diabetes Mellitus

PURPOSE

To assess the association of type 2 diabetes mellitus (T2DM) and insulin glargine treatment with bone mineral density (BMD) in Chinese people.

METHODS

This retrospective study included 50 subjects with T2DM: 25 received oral glucose-lowering medication (ORL group), and 25 received oral glucose-lowering medication in combination with insulin glargine injection (CGI group). Thirty non-diabetic control subjects were also included. BMD was measured at lumbar vertebrae 1-4 (L1-L4), spine bone mineral density (sBMD) results summary (L2-L4), femoral neck and trochanter by dual-energy x-ray absorptiometry.

RESULTS

Compared with non-diabetic controls, people with T2DM had significantly lower mean BMD at L2 (1.073±0.120 vs 0.984±0.158), L3 (1.094±0.129 vs 0.991±0.163) and L4 (1.089±0.130 vs 0.982±0.165) (all P<0.05), significantly lower levels of serum calcium (2.02±0.22 vs 2.27±0.17 mmol/L, P<0.05), PTH (24.19±9.71 vs 31.52±8.96 pg/mL, P<0.05), and higher serum phosphate levels (1.43±0.37 vs 1.20±0.15 mmol/L, P<0.05). The CGI group had higher L2, L3 and L4 BMD and sBMD (L2-L4) (P<0.05), higher serum calcium levels (2.19±0.11 vs 1.98±0.20 mmol/L, P<0.05) and lower serum phosphate levels (1.28±0.20 vs 1.58±0.43 mmol/L, P<0.05) versus the ORL group. BMD and serum calcium levels were associated with the application of insulin glargine.

CONCLUSION

These results suggest that insulin glargine may affect bone metabolism in patients diagnosed with T2DM. The study has implications for the selection of hypoglycemic agents for diabetic patients at risk of osteoporosis.

Understanding Bone Disease in Patients with Diabetic Kidney Disease: a Narrative Review

PURPOSE OF REVIEW

Both diabetes and kidney disease associate with the development of bone disease and an increased risk of fragility fractures. The etiologies of bone disease in patients with diabetic kidney disease (DKD) are multiple and complex. This review explores the association between DKD and bone disease and discusses how the presence of both diabetes and kidney disease may impair bone quality and increase fracture risk. Diagnostic tools as well as future research areas are also discussed.

RECENT FINDINGS

Patients with DKD have an increased risk of fragility fracture, most pronounced in patients with type 1 diabetes, and in DKD a high prevalence of adynamic bone disease is found. Recent studies have demonstrated disturbances in the interplay between bone regulating factors in DKD, such as relative hypoparathyroidism and alterations of bone-derived hormones including fibroblast growth factor-23 (FGF-23), sclerostin and klotho, which lead to bone disease. This review examines the current knowledge on bone disease in patients with DKD, clinical considerations for patient care, as well as subjects for future research.

Adynamic bone disease: from bone to vessels in chronic kidney disease

Adynamic bone disease (ABD) is a well-recognized clinical entity in the complex chronic kidney disease (CKD)-mineral and bone disorder. Although the combination of low intact parathyroid hormone (PTH) and low bone alkaline phosphatase levels may be suggestive of ABD, the gold standard for precise diagnosis is histomorphometric analysis of tetracycline double-labeled bone biopsies. ABD essentially is characterized by low bone turnover, low bone volume, normal mineralization, and markedly decreased cellularity with minimal or no fibrosis. ABD is increasing in prevalence relative to other forms of renal osteodystrophy, and is becoming the most frequent type of bone lesion in some series. ABD develops in situations with reduced osteoanabolic stimulation caused by oversuppression of PTH, multifactorial skeletal resistance to PTH actions in uremia, and/or dysregulation of Wnt signaling. All may contribute not only to bone disease but also to the early vascular calcification processes observed in CKD. Various risk factors have been linked to ABD, including calcium loading, ageing, diabetes, hypogonadism, parathyroidectomy, peritoneal dialysis, and antiresorptive therapies, among others. The relationship between low PTH level, ABD, increased risk fracture, and vascular calcifications may at least partially explain the association of ABD with increased mortality rates. To achieve optimal bone and cardiovascular health, attention should be focused not only on classic control of secondary hyperparathyroidism but also on prevention of ABD, especially in the steadily growing proportions of diabetic, white, and elderly patients. Overcoming the insufficient osteoanabolic stimulation in ABD is the ultimate treatment goal.

Calcium regulation and bone mineral metabolism in elderly patients with chronic kidney disease

The elderly chronic kidney disease (CKD) population is growing. Both aging and CKD can disrupt calcium (Ca2+) homeostasis and cause alterations of multiple Ca2+-regulatory mechanisms, including parathyroid hormone, vitamin D, fibroblast growth factor-23/Klotho, calcium-sensing receptor and Ca2+-phosphate product. These alterations can be deleterious to bone mineral metabolism and soft tissue health, leading to metabolic bone disease and vascular calcification and aging, termed CKD-mineral and bone disorder (MBD). CKD-MBD is associated with morbid clinical outcomes, including fracture, cardiovascular events and all-cause mortality. In this paper, we comprehensively review Ca2+ regulation and bone mineral metabolism, with a special emphasis on elderly CKD patients. We also present the current treatment-guidelines and management options for CKD-MBD.

Vitamin d and stage 5 chronic kidney disease: a new paradigm?

Vitamin D receptor agonists (VDRA) are currently recommended for the treatment of secondary hyperparathyroidism in stage 5 CKD. They are considered to be contraindicated in the presence of low or normal (for a dialysis patient) levels of PTH due to the risk of developing adynamic bone disease, with consequent vascular calcification. However, these recommendations are increasingly at odds with the epidemiological evidence, which consistently shows a large survival advantage for patients treated with low-dose VDRAs, regardless of plasma calcium, phosphate, or PTH. A large number of pleiotropic effects of vitamin D have been described, including inhibition of renin activity, anti-inflammation, and suppression of vascular calcification stimulators and stimulation of vascular calcification inhibitors present in the uremic milieu. Laboratory studies suggest that a normal cellular vitamin D level is necessary for normal cardiomyocyte and vascular smooth muscle function. While pharmacological doses of VDRA can be harmful, the present evidence suggests that the level of 1,25-dihydroxycholecalciferol should also be more physiological in stage 5 CKD, and that widespread use of low-dose VDRA would be beneficial. A randomized controlled trial to test this hypothesis is warranted.

Sevelamer hydrochloride improves hyperphosphatemia in hemodialysis patients with low bone turnover rate and low intact parathyroid hormone levels

Sevelamer improves hyperphosphatemia without increasing the calcium load. However, it remains unknown whether sevelamer restores bone metabolism in hemodialysis patients with low bone turnover osteodystrophy and hypoparathyroidism. We investigated the changes in serum intact parathyroid hormone (iPTH) and bone metabolic marker levels after replacing calcium carbonate with sevelamer in these patients. We also conducted stratified analysis based on patient background and multivariate analysis to determine the factors affecting these parameters. During sevelamer replacement therapy, serum calcium and phosphate concentrations, and the calcium phosphate product were measured at 0, 1, 3, and 6 months. Serum iPTH, bone alkaline phosphatase and osteocalcin concentrations were measured at 0 and 6 months. In hemodialysis patients (71 men and 46 women, 63 +/- 12 years old) serum calcium levels and the calcium phosphate product decreased significantly at 1 month. Serum iPTH, bone alkaline phosphatase and osteocalcin levels increased significantly at 6 months. Increases in serum iPTH concentrations were observed in all stratified groups. Significant increases in serum bone alkaline phosphatase and osteocalcin concentrations were found only in the relative hypoparathyroidism group (iPTH levels > or =51.5 pg/mL, the median pretreatment level). Multivariate analysis showed that the factors affecting change in serum iPTH level are baseline serum iPTH, baseline calcium level (> or =9.5 mg/dL), and dialysis duration of 10 years or longer. Sevelamer appears useful for the treatment of hyperphosphatemia in these patients. Particularly, in the relative hypoparathyroidism group, the iPTH secretory response is probably enhanced and bone turnover may have been improved as a result of reducing the calcium load.

Reversal of the adynamic bone disorder and decreased vascular calcification in chronic kidney disease by sevelamer carbonate therapy

A model of chronic kidney disease (CKD)-induced vascular calcification (VC) that complicates the metabolic syndrome was produced. In this model, the metabolic syndrome is characterized by severe atherosclerotic plaque formation, hypertension, type 2 diabetes, obesity, and hypercholesterolemia, and CKD stimulates calcification of the neointima and tunica media of the aorta. The CKD in this model is associated the adynamic bone disorder form of renal osteodystrophy. The VC of the model is associated with hyperphosphatemia, and control of the serum phosphorus both in this animal model and in humans has been preventive in the development of VC. This article reports studies that demonstrate reduction of established VC by the addition of sevelamer carbonate to the diets of this murine metabolic syndrome model with CKD. Sevelamer, besides normalizing the serum phosphorus, surprisingly, reversed the CKD-induced trabecular osteopenia. Sevelamer therapy increased osteoblast surfaces in the metaphyseal trabeculae of the tibia and femur. It also increased osteoid surfaces and, importantly, bone formation rates. In addition, sevelamer was found to be effective in decreasing serum cholesterol levels. These results suggest that sevelamer may have important actions in decreasing diabetic and uremic vasculopathy and that sevelamer carbonate may be capable of increasing bone formation rates that are suppressed by diabetic nephropathy.

Connections between vascular calcification and progression of chronic kidney disease: therapeutic alternatives

We have shown that renal injury and chronic kidney disease (CKD) directly inhibit skeletal anabolism, and that stimulation of bone formation decreases the serum phosphate. Most recently, these observations were rediscovered in low-density lipoprotein receptor null mice fed high-fat/cholesterol diets, a model of the metabolic syndrome (hypertension, obesity, dyslipidemia, and insulin resistance). We had demonstrated that these mice have vascular calcification (VC) of both the intimal atherosclerotic type and medial type. We have shown that VC is worsened by CKD and ameliorated by bone morphogenetic protein -7 (BMP-7). The finding that high-fat-fed low-density lipoprotein receptor null animals without CKD have hyperphosphatemia led us to examine the skeletons of these mice. We found significant reductions in bone formation rates, associated with increased VC and superimposing CKD results in the adynamic bone disorder (ABD), while VC was worsened and hyperphosphatemia persisted. A pathological link between abnormal bone mineralization and VC through the serum phosphorus was demonstrated by the partial effectiveness of directly reducing the serum phosphate by a phosphate binder that had no skeletal action. BMP-7 treatment corrected the ABD and corrected hyperphosphatemia, compatible with BMP-7-driven stimulation of skeletal phosphate deposition reducing plasma phosphate and thereby removing a major stimulus to VC. Thus, in the metabolic syndrome with CKD, a reduction in bone-forming potential of osteogenic cells leads to ABD producing hyperphosphatemia and VC, processes ameliorated by the skeletal anabolic agent BMP-7, in part through increased bone formation and skeletal deposition of phosphate, and in part through direct actions on vascular smooth muscle cells. We have demonstrated that the processes leading to vascular calcification begin with even mild levels of renal injury before demonstrable hyperphosphatemia, and they are preventable and treatable. Therefore, early intervention in CKD is warranted and may affect mortality of the disease.

Low turnover osteodystrophy and vascular calcification are amenable to skeletal anabolism in an animal model of chronic kidney disease and the metabolic syndrome

LDL receptor (LDLR)-null mice fed high-fat/cholesterol diets, a model of the metabolic syndrome, have vascular calcification (VC) worsened by chronic kidney disease (CKD) and ameliorated by bone morphogenetic protein-7 (BMP-7), an efficacious agent in treating animal models of renal osteodystrophy. Here, LDLR-/- high-fat-fed mice without CKD were shown to have significant reductions in bone formation rates, associated with increased VC and hyperphosphatemia. Superimposing CKD resulted in a low turnover osteodystrophy, whereas VC worsened and hyperphosphatemia persisted. BMP-7 treatment corrected the hyperphosphatemia, corrected the osteodystrophy, and prevented VC, compatible with skeletal phosphate deposition leading to reduced plasma phosphate and removal of a major stimulus to VC. A pathologic link between abnormal bone mineralization and VC through the serum phosphorus was supported by the partial effectiveness of directly reducing the serum phosphate by a phosphate binder that had no skeletal action. Thus, in this model of the metabolic syndrome with CKD, a reduction in bone-forming potential of osteogenic cells leads to low bone turnover rates, producing hyperphosphatemia and VC, processes ameliorated by the skeletal anabolic agent BMP-7, in part through deposition of phosphate and increased bone formation.

[Immunosuppressive therapy and bone metabolism after kidney transplantation]

The success of transplant medicine due to improvements of immunosuppressive therapy has led to a significant increase of patient and organ survival. With the increasing number of transplantations, however, long term complications, often affecting the skeletal system, are becoming more frequent. Bone alterations often exist prior to transplantation in patients with chronic renal failure. There are two types of renal osteopathy, including "low-turnover bone disease", consisting of osteomalacia, and adynamic bone disease, and "high-turnover bone disease" due to the development of secondary hyperparathyroidism. Many patients show evidence of both disorders (mixed bone disease). During the first months after transplantation patients lose bone mass rapidly. One of the major factors responsible for the development of osteoporosis is thought to be the intensive immunosuppressive therapy during that period, steroids in particular seem to play an important role. To what extent other medications influence bone metabolism has not been established. Currently there are no studies about a standardized therapy and treatment relies mainly on experience with other forms of osteoporosis.

Adynamic bone and chronic renal failure: an overview

Renal osteodystrophy may present with a wide spectrum of bone lesions, ranging from high bone turnover to low bone turnover. Decreased serum calcium and 1,25-dihydroxy vitamin D synthesis and retention of phosphate are involved in the pathogenesis of high bone turnover. However, several factors may influence the evolution of this disorder. The use of different therapeutic approaches (such as calcium supplements, phosphate binders, vitamin D metabolites, etc.), the type of treatment (either hemodialysis or continuous ambulatory peritoneal dialysis), and also the changes in the type of patients to whom we are offering dialysis (more diabetics and older patients are currently included in dialysis programs) may have introduced changes modifying the form of presentation of the bone metabolic disorders. As a result, recent studies reported a greater prevalence of adynamic forms of renal osteodystrophy. Patients with adynamic bone (with or without aluminum) would have more difficulties in handling and buffering calcium loads; consequently, they would have a higher risk of extraosseous calcifications.

Is aplastic osteodystrophy a disease of malnutrition?

Adynamic bone disease is emerging as a major type of renal osteodystrophy in chronic dialysis patients. Relative hypoparathyroidism is one of the important abnormalities underlying this disease. Recently, several reports have suggested that hypoparathyroidism reflects, at least in part, a state of malnutrition and contributes to the poor prognosis of patients on hemodialysis and chronic ambulatory peritoneal dialysis. Such a risk of survival may result not only from the malnutritional state, but also from unknown mechanisms resulting from parathyroid hormone (PTH) deficiency, or from other abnormalities that suppress PTH secretion. Another major abnormality underlying adynamic bone disease is the skeletal resistance to PTH in patients with uremia. Owing to the recent research on bone turnover at the molecular level, several new mechanisms for this abnormality have been elucidated. Correction of this 'skeletal resistance to PTH' will lead to the optimal management of parathyroid function and bone turnover in the future.

Effect of calcitriol and age on recovery from hypocalcemia in hemodialysis patients

Calcitriol is used to treat hyperparathyroidism in hemodialysis patients. Calcitriol treatment, either through a reduction in parathyroid hormone (PTH) levels or direct effect on bone, decreases the osteoblast and osteoclast surface and bone formation rate. Our study of 13 hemodialysis patients was designed to evaluate whether calcitriol treatment changed the rate of spontaneous recovery from hypocalcemia induced by a low-calcium dialysis. Calcitriol treatment decreased basal PTH levels from 614 +/- 84 to 327 +/- 102 pg/mL (P < 0.001) and maximal PTH levels from 1,282 +/- 157 to 789 +/- 161 pg/mL (P < 0.001), but the rate of serum ionized calcium recovery from hypocalcemia did not change. When the 13 patients were separated based on the median age of 64 years, the predialysis serum ionized calcium level was less in the younger (group I, 44 +/- 6 years; n = 6) than older (group II, 68 +/- 1 years; n = 7) patients (1.05 +/- 0.03 v 1.22 +/- 0.03 mmol/L, respectively; P < 0.01) despite similar basal (group I, 595 +/- 122 pg/mL v group II, 629 +/- 96 pg/mL) and maximal (group I, 1,114 +/- 299 pg/mL v group II, 1,425 +/- 141 pg/mL) PTH levels. Before calcitriol treatment, the rate of serum ionized calcium recovery from induced hypocalcemia was greater (P < 0.05) for similar PTH levels in the older than younger patients. After calcitriol treatment, despite a similar reduction in PTH levels, the rate of calcium recovery increased (P < 0.05) in the younger patients but did not change in the older patients. We also observed that toward the end of the low-calcium hemodialysis, PTH values decreased even though serum ionized calcium level continued to decline when the rate of calcium reduction slowed. In addition, hysteresis, defined as a lower PTH value during the recovery from hypocalcemia than during the induction of hypocalcemia for the same serum calcium concentration, was present during the spontaneous recovery from hypocalcemia. In conclusion, in the hemodialysis patient: (1) age appeared to affect the bone response to PTH and calcitriol treatment, (2) the PTH response to hypocalcemia was affected by a deceleration in the rate of calcium decrease, and (3) hysteresis of the PTH response to hypocalcemia occurred during the spontaneous recovery from hypocalcemia.

Serum levels of 1,25-dihydroxyvitamin D, 24,25-dihydroxyvitamin D, and 25-hydroxyvitamin D in nondialyzed patients with chronic renal failure

BACKGROUND

In patients with chronic renal failure (CRF), abnormalities in vitamin D metabolism are known to be present, and several factors could contribute to the abnormalities.

METHODS

We measured serum levels of three vitamin D metabolites, 1,25(OH)2D, 24, 25(OH)2D and 25(OH)D, and analyzed factors affecting their levels in 76 nondialyzed patients with CRF (serum creatinine> 1.6 and < 9.0 mg/dl), 37 of whom had diabetes mellitus (DM-CRF) and 39 of whom were nondiabetic (nonDM-CRF).

RESULTS

Serum levels of 1,25(OH)2D were positively correlated with estimated creatinine clearance (CCr; r = 0.429; P < 0.0001), and levels of 24,25(OH)2D were weakly correlated with CCr (r = 0.252, P < 0.05); no correlation was noted for 25(OH)D. Serum levels of all three vitamin D metabolites were significantly and positively correlated with serum albumin. Although there were no significant differences in age, sex, estimated CCr, calcium and phosphate between DM-CRF and nonDM-CRF, all three vitamin D metabolites were significantly lower in DM-CRF than in nonDM-CRF. To analyze factors influencing vitamin D metabolite levels, we performed multiple regression analyses. Serum 25(OH)D levels were significantly and independently associated with serum albumin, presence of DM and serum phosphate (R2 = 0.599; P < 0.0001). 24,25(OH)2D levels were significantly and strongly associated with 25(OH)D (beta = 0.772; R2 = 0.446; P < 0.0001). Serum 1,25(OH)2D levels were significantly associated only with estimated CCr (R2 = 0. 409; P < 0.0001).

CONCLUSIONS

These results suggest that hypoalbuminemia and the presence of DM independently affect serum 25(OH)D levels, probably via diabetic nephropathy and poor nutritional status associated with diabetes, and that 25(OH)D is actively catalyzed to 24,25(OH)2D in CRF, probably largely via extrarenal 24-hydroxylase. Serum levels of 1,25(OH)2D were significantly affected by the degree of renal failure. Thus, this study indicates that patients with CRF, particularly those with DM, should receive supplements containing the active form of vitamin D prior to dialysis.

Effect of thyroparathyroidectomy on urinary acidification in diabetic rats

In previous studies we have shown stimulation of renal acid excretion in the proximal tubules of rats with diabetes of short duration, with no important alterations in glomerular hemodynamics; on the other hand, in thyroparathyroidectomized rats (TPTX model), a significant decrease in renal acid excretion, glomerular filtration rate (GFR) and renal plasma flow (RPF) was detected. Since important changes in the parathyroid hormone-vitamin D-Ca axis are observed in the diabetic state, the present study was undertaken to investigate the renal repercussions of thyroparathyroidectomy in rats previously made diabetic by streptozotocin (45 mg/kg). Four to 6 days after the induction of diabetes (DM), a group of rats were thyroparathyroidectomized (DM + TPTX). Renal functional parameters were evaluated by measuring the inulin and sodium para-aminohippurate clearance on the tenth day. The decrease in the GFR and RPF observed in TPTX was not reversed by diabetes since the same alterations were observed in DM + TPTX. Net acid (NA) excretion was unchanged in DM (6.19 +/- 0.54), decreased in TPTX (3.76 +/- 0.25) and returned to normal levels in DM + TPTX (5.54 +/- 0.72) when compared to the control group (6.34 +/- 0.14 mumol min-1 kg-1). The results suggest that PTH plays an important vasodilator role regarding glomerular hemodynamics, since in its absence the impairment in GFR and RPF was not reversed by the diabetic state. However, with respect to acid excretion, the presence of diabetes was able to overcome the negative stimulus represented by TPTX.