A feline-focused review of chronic kidney disease-mineral and bone disorders - Part 1: Physiology of calcium handling.

Mineral derangements are a common consequence of chronic kidney disease (CKD). Despite the well-established role of phosphorus in the pathophysiology of CKD, the implications of calcium disturbances associated with CKD remain equivocal. Calcium plays an essential role in numerous physiological functions in the body and is a fundamental structural component of bone. An understanding of calcium metabolism is required to understand the potential adverse clinical implications and outcomes secondary to the (mal)adaptation of calcium-regulating hormones in CKD. The first part of this two-part review covers the physiology of calcium homeostasis (kidneys, intestines and bones) and details the intimate relationships between calcium-regulating hormones (parathyroid hormone, calcitriol, fibroblast growth factor 23, α-Klotho and calcitonin) and the role of the calcium-sensing receptor.

A feline-focused review of chronic kidney disease-mineral and bone disorders - Part 2: Pathophysiology of calcium disorder and extraosseous calcification.

Derangements in mineral metabolism are one of the main entities in chronic kidney disease-mineral and bone disorder (CKD-MBD). This is the second of a two-part review of the physiology and pathophysiology of calcium homeostasis in feline CKD-MBD. While dysregulation in calcium homeostasis is known to contribute to the development of vascular calcification in CKD, evidence characterising the relationship between serum calcium concentration and nephrocalcinosis and nephrolithiasis is limited. Recently, fibroblast growth factor 23 (FGF23) and α-Klotho have gained increased research interest and been shown to be important biomarkers for the prediction of CKD progression in human patients. However, conflicting evidence exists on their role in calcium homeostasis and vascular and soft tissue calcification. This review details the pathophysiology of calcium disorders associated with CKD-MBD and its implications on vascular and soft tissue mineralisation in human and feline patients. Further prospective studies investigating the clinical consequences of calcium disturbances in cats with CKD are warranted and this may provide additional insight into the pathophysiology of feline CKD-MBD.

Renal Osteodystrophy due to Secondary Hyperparathyroidism in a Cat.

A 6 yr old neutered male mixed-breed cat presented for renal transplantation (RTx) for chronic kidney disease. Severe periodontal disease was identified, and before initiation of immunosuppressive therapy, a comprehensive oral health assessment and treatment procedure was performed to reduce the burden of existing oral infection. Dental radiography revealed diffuse, severe bone demineralization across the mandible and maxilla, with thinning of the cortices. Nasal turbinates were easily visualized owing to the decreased opacity of maxillary bone. Generalized bone resorption left teeth to appear minimally attached. A Vitamin D panel revealed a severely elevated parathyroid hormone level. Full mouth extractions were performed. Seven days following this procedure, RTx was performed. Serum creatinine concentration was within normal limits by 48 hr after surgery and remained normal until discharge 12 days after RTx. At 3.5 mo after RTx, the cat was mildly azotemic, and the parathyroid hormone level was elevated but significantly decreased from the original measurement. Secondary hyperparathyroidism is a common abnormality in cats with chronic kidney disease. However, clinical manifestations of hyperparathyroidism are rare in this species. This is a novel presentation of a cat demonstrating bone loss in the oral cavity as a result of renal secondary hyperparathyroidism.

Effects of calcifediol supplementation on markers of chronic kidney disease-mineral and bone disorder in dogs with chronic kidney disease.

BACKGROUND: Chronic kidney disease-mineral and bone disorder (CKD-MBD) in dogs is associated with hypovitaminosis D, increased parathyroid hormone (PTH), and increased fibroblast growth factor-23 (FGF-23) concentrations. Best practice for vitamin D metabolite supplementation in CKD-MBD remains unknown. OBJECTIVE: To provide an extended-release calcifediol supplement to dogs with CKD and to measure its effects on variables indicative of CKD-MBD. ANIMALS: Ten dogs with International Renal Interest Society stages 2 and 3 CKD. METHODS: In a prospective study, dogs received a calcifediol supplement for 84 days. Serum 25-hydroxyvitamin D (25[OH]D), 1,25-dihydroxyvitamin D (1,25[OH]2 D), 24,25-dihydroxyvitamin D (24,25[OH]2 D), creatinine, calcium, phosphorus, PTH, plasma FGF-23 concentrations, and urine profiles were measured monthly during supplementation. Urine calcium to creatinine (UCa/Cr) ratios and fractional excretion of calcium, phosphorus, and sodium were determined. RESULTS: All serum vitamin D metabolite concentrations increased significantly by day 84 (P < .001): [25(OH)D (median 249.9 ng/mL; range, 149.7-469.9 ng/mL) compared to baseline (median 50.2 ng/mL; range, 31.3-66.0 ng/mL); 1,25(OH)2 D (median 66.1 pg/mL; range, 56.9-88.1 pg/mL) compared to baseline (median 37.3 pg/mL; range, 29.3-56.7 pg/mL); 24,25(OH)2 D (median 81.4 ng/mL; range, 22.1-151.7 ng/mL) compared to baseline (median 15.4 ng/mL; range, 6.9-40.6 ng/mL)]. There were no significant differences in calcium, phosphorus, PTH concentrations, UCa/Cr or fractional excretion of calcium. No dog developed ionized hypercalcemia. Plasma FGF-23 concentrations increased by day 84 (median 1219 pg/mL; range, 229-8824 pg/mL) compared to baseline (median 798 pg/mL; range, 103-4.145 pg/mL) (P < .01). CONCLUSIONS AND CLINICAL IMPORTANCE: Calcifediol supplementation for 84 days was well-tolerated in dogs with IRIS stages 2 and 3 CKD. It remains to be determined how long-term supplementation would affect CKD progression and QOL.

Associations between single nucleotide polymorphisms in the calcium sensing receptor and chronic kidney disease-mineral and bone disorder in cats.

Feline chronic kidney disease (CKD) is associated with high variability in severity of CKD-mineral and bone disorder (CKD-MBD). The calcium sensing receptor (CaSR) regulates circulating parathyroid hormone (PTH) and calcium concentrations. Single nucleotide polymorphisms (SNPs) in the CaSR are associated with severity of secondary renal hyperparathyroidism and total calcium concentrations in human patients receiving haemodialysis. The objective of this study was to explore associations between polymorphisms in the feline CaSR (fCaSR) and biochemical changes observed in CKD-MBD. Client owned cats (≥9years) were retrospectively included. SNP discovery was performed in 20 cats with azotaemic CKD and normal or dysregulated calcium concentrations. Non-pedigree cats (n=192) (125 with azotaemic CKD and 66 healthy), Persians (n=40) and Burmese (n=25) were genotyped for all identified SNPs using KASP. Biochemical parameters from the date of CKD diagnosis or from first visit to the clinic (healthy cats) were used. Associations between genotype and ionized calcium, total calcium, phosphate, PTH and FGF-23 were performed for non-pedigree cats using logistic regression. Sequence alignment against the fCaSR sequence revealed eight novel exonic SNPs. KASP genotyping had high accuracy (99.6%) and a low failure rate (<6%) for all SNPs. Allele frequencies varied between breeds. In non-pedigree cats, one synonymous SNP CaSR:c.1269G>A was associated with logPTH concentration (adjusted for plasma creatinine concentration), with a recessive model having the best fit (G/G vs A/A-G/A, P=0.031). Genetic variation in the fCaSR is unlikely to explain the majority of the variability in presence and severity of CKD-MBD in cats.

Update on Mineral and Bone Disorders in Chronic Kidney Disease.

The inappropriate phosphorus retention observed in chronic kidney disease is central to the pathophysiology of mineral and bone disorders observed in these patients. Subsequent derangements in serum fibroblast growth factor 23, parathyroid hormone, and calcitriol concentrations play contributory roles. Therapeutic intervention involves dietary phosphorus restriction and intestinal phosphate binders in order to correct phosphorus retention and maintain normocalcemia. Additional therapies may be considered to normalize serum fibroblast growth factor 23 and parathyroid hormone.

Does Secondary Renal Osteopathy Exist in Companion Animals?

Secondary renal hyperparathyroidism is an inevitable consequence of chronic kidney disease. In human patients, the disease is associated with decreased bone quality and increased fracture risk. Recent evidence suggests that bone quality is also decreased in companion animals, more pronouncedly in cats compared with dogs, likely because of a longer disease course. The clinical significance of these findings is yet to be determined. However, clinicians should keep in mind that animals with chronic kidney disease have decreased bone quality and increased fracture risk.

Oral Manifestations of Chronic Kidney Disease and Renal Secondary Hyperparathyroidism: A Comparative Review.

Recent epidemiological studies have demonstrated that significant associations exist between oral disease and diseases involving non-oral tissues. Occasionally, the roles may be reversed and the oral cavity can be severely affected by systemic disease originating in another part of the body. Renal secondary hyperparathyroidism is a common endocrinopathy that occurs as a consequence of chronic azotemic kidney disease. Renal osteodystrophy, the most dramatic clinical consequence of renal secondary hyperparathyroidism is uncommon, but can result in demineralization of maxillofacial bones, loosening of teeth, and pathological jaw fractures. The purpose of this report is to update the current understanding of the pathophysiology of this endocrine disease and to compare the oral manifestations of renal secondary hyperparathyroidism in humans and companion animals. A 50-year review of the veterinary literature was undertaken to examine the clinical presentation of renal osteodystrophy in dogs, and to determine what clinical consequences of renal secondary hyperparathyroidism have been reported in domestic cats.

Cadmium toxicity to ringed seals (Phoca hispida): an epidemiological study of possible cadmium-induced nephropathy and osteodystrophy in ringed seals (Phoca hispida) from Qaanaaq in Northwest Greenland.

The Greenland marine food chains contain high levels of cadmium, mercury and selenium. Concentrations of cadmium in the kidney of ringed seals (Phoca hispida) from the municipalities of Qaanaaq and Upernavik (Northwest Greenland) are among the highest recorded in the Arctic. The purpose of the study was to determine whether cadmium-induced damage in the kidneys and the skeletal system could be detected among 100 ringed seals from Northwest Greenland. The cadmium concentrations in the kidney cortex ranged from 0 to 248 microg/g wet weight (mean=44.5, N=100) in the 99 kidneys examined. Experience from cadmium-poisoned humans and laboratory mammals indicates that concentrations above 50-200 microg/g wet wt. may induce histopathological changes. Overall, 31 of the ringed seals had cadmium concentrations in the kidney cortex above 50 microg/g wet wt., 11 had concentrations above 100 and one had a concentration above 200 microg/g wet wt. Obvious histopathological changes (categorised mainly as glomerulonephritis) were found in 10 of the seals; however, none of these changes could be attributed to cadmium-induced renal damage (mainly tubulopathy) as described for other species. Damage to the proximal kidney tubules is known to induce demineralisation of the skeletal system (Fanconi's syndrome). Therefore, the three lowest lumbar vertebrae were scanned in 91 seals to measure the content of calcium. The 10 cases of nephropathy could neither be linked to the degree of mineralisation of the skeleton nor to the cadmium concentrations. Furthermore, the degree of mineralisation of the skeleton was not correlated with the cadmium concentration, age or sex. It can therefore be concluded that despite high levels of cadmium, none of the ringed seals showed any signs of cadmium-induced nephropathy or osteodystrophy. This might be explained by the composition of the ringed seals diet, which contains high levels of vitamin D, calcium, phosphorus, zinc, selenium and protein. These elements are all likely to counteract cadmium-induced damage. It is speculated that ringed seal are not particularly vulnerable to osteodystrophy, due to their continuous growth (bone mineralisation) throughout life and the oestrogen hormonal activity of females throughout life.

Unusual hyperparathyroidism in a cat.

A 5 month-old, male, domestic short hair cat was presented with inappetence and vomiting. it was depressed and reluctant to move. The cat had difficulties in keeping the standing position and grossly deformed thighs. Lytic changes and disruption of normal architecture of the bone were observed, involving mainly the femoral diaphyses. An inverse Ca/P ratio and kidney failure were diagnosed. The possibility of whether the bone changes could have been related to primary or secondary renal hyperparathyroidism is discussed.

Rat hypoplastic kidney (hpk/hpk) induces renal anemia, hyperparathyroidism, and osteodystrophy at the end stage of renal failure.

In rats with genetically hypoplastic kidneys (hpk/hpk) and associated hypogonadism (hgn/hgn), their kidneys contain only one-quarter the number of nephrons that are found in those of normal rats [26]. Not surprisingly, therefore, renal excretive function has been shown to be depressed in hpk/hpk rats [26]. In the study presented here, we have examined the process of the progression of renal failure and the development of renal secondary disease in hpk/hpk rats. The plasma concentrations of urea-nitrogen and creatinine were significantly higher in adult hpk/hpk rats than in normal rats. These values elevated gradually and the degree of renal histological damage also progressed with advancing age in the hpk/hpk rats. In addition, renal anemia appeared at 140 days of age or later in these rats, and hyperplasia of the parathyroid glands was visible macroscopically at 280 days of age. In the hpk/hpk rats plasma levels of calcium and phosphorus were significantly lower and higher than in normal rats, respectively, at 280 days of age. Pathologically, the left femora of hpk/hpk rats exhibited fibrous osteodystrophy at 280 days of age and the calcium content of the right femora (as a percentage of the dry weight of bone) was significantly lower than in normal rats at both 210 and 280 days of age. These results indicate that the reduced nephrogenesis of the hpk/hpk rats causes progressive renal failure, secondarily inducing anemia, hyperparathyroidism, and osteodystrophy.

Aspectos clínicos e radiográficos de osteodistrofias de origem nutricional no cäo jovem / Clinical and radiographic aspects of nutritional osteodystrophies in dogs

Foram analisadas radiografias de 634 animais de espécie canina, jovens, de ambos os sexos e raças variadas, encaminhados ao Serviço de Radiologia do Hospital Veterinário da Faculdade de Medicina Veterinária e Zootecnia da Universidade de Säo Paulo, no período de janeiro de 1982 a dezembro de 1991, com suspeitas clínicas de osteopatia metabólica. A interpretaçäo dos exames radiográficos possibilitou o diagnóstico de Hiperparatireoidismo Secundário Nutricional, Raquitismo ou Osteodistrofia Hipertrófica. O Hiperparatireoidismo Secundário Nutricional foi a patologia mais freqüente das 3; entre os cäes de raças puras acometeu mais aqueles de raças grandes e gigantes e também foi mais freqüente no sexo masculino. O mesmo observamos com a Osteodistrofia Hipertrófica, que também foi mais freqüente em machos e, entre as raças puras, nas grandes e gigantes. Apenas 11 casos de Raquitismo foram diagnosticados no período de estudo

Renal dysplasia with secondary hyperparathyroidism and loose teeth in a young dog.

In a dog with renal dysplasia and secondary hyperparathyroidism, loose teeth resulted from excessive resorption of alveolar bone. Sharpey's fibers, still anchored in the cementum, were lost in the replacing fibrous tissue and few fibers found their way to distant bone fragments. The alveolar bone is the site of predilection for the excessive, generalized resorption of bone in hyperparathyroidism. Clinical radiographic examination of the jaws is a valuable tool in the detection of the disease.

Jaw lesions resulting from renal hyperparathyroidism in a young dog--a case report.

A five-month-old male Labrador retriever presented with massive bilateral jaw and facial swelling. Ulcers were found on the buccal mucosa and palate, and the jaws were flexible on firm palpation. The dog could eat only soft food and was underweight. Renal hyperparathyroidism was diagnosed based on serum chemistry screen, parathormone concentration, radiological findings and histopathology. The dog was euthanatized because of an extremely poor prognosis.

Generalized fibrous osteodystrophy in weaned pigs

Descreve-se a ocorrência de osteodistrofia fibrosa generalizada em leitös desmamados, de duas granjas comerciais. Na granja A, foram afetados 26 animais e na B, 240. A idade dos leitös variava entre 45 e 65 dias, todos tinham sido alimentados por um período de, aproximadamente, 35 dias, com raçäo pré-inicial e inicial, cujos níveis de Ca e P estavam muito abaixo dos recomendados. Ao exame clínico, quase todos os animais apresentaram dificuldades de locomoçäo, deformidades diversas do esqueleto e, em alguns, paralisia posterior. A necropsia, observaram-se aumento näo inflamatório das articulaçöes, fraturas de costelas e vértebras, bem como excessiva diminuiçäo da resistência revelou excesso de reabsorçäo óssea com proliferaçäo de tecido conjuntivo na epífise-metáfise e no córtex. Havia osteoclasia evidente