Comparison of the Effects of Daily and Intermittent-Dose Calcitriol on Serum Parathyroid Hormone and Ionized Calcium Concentrations in Normal Cats and Cats with Chronic Renal Failure

Dietary 25-hydroxyvitamin D3 effects on vitamin D status, plasma metabolites and urine mineral excretion in adult cats

OBJECTIVES

The study aimed to evaluate the safety and effectiveness of vitamin D supplementation with dietary 25-hydroxyvitamin D3 (25[OH]D3) in adult cats.

METHODS

Three levels of dietary 25(OH)D3 concentrations (4.9, 8.4, 11.8 µg/kg as fed) were received by five adult cats for 9 weeks, each in a randomized complete block design. Effects were determined on plasma or serum concentrations of 25(OH)D3, 24,25-dihydroxyvitamin D3, calcitriol, parathyroid hormone, ionized calcium, urinary excretions of phosphorus, calcium and magnesium, and clinical hematology and chemistry panels.

RESULTS

The lowest concentration of dietary 25(OH)D3 supported elevation of vitamin D status, with no adverse effects. Supplementation of 8.4 µg/kg 25(OH)D3 had significant effects on the urinary magnesium: creatinine ratio. Increasing supplementation up to 11.8 µg/kg 25(OH)D3 had significant effects on plasma concentrations of calcium and magnesium, and vitamin D metabolites.

CONCLUSIONS AND RELEVANCE

Dietary supplementation with approximately 5.0 µg/kg of 25(OH)D3 or the ingested equivalence of 0.09 µg of 25(OH)D3 per metabolic body weight (kg0.67) is a safe, potent and effective means for raising vitamin D status in cats. A higher dose with approximately 11.8 µg/kg of 25(OH)D3 resulted in elevation in C-3 epimers of 25(OH)D3 and slight elevation in plasma magnesium and calcium concentrations above their respective reference intervals.

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.

Nutritional Management for Dogs and Cats with Chronic Kidney Disease

The nutritional management of canine and feline chronic kidney disease and protein-losing nephropathy is discussed. Special attention is paid to assessment of body composition (body weight, body condition score, and muscle condition score) and the dysrexia that often occurs with kidney disease. Various nutrients of concern are discussed and specific dietary options are provided.

Vitamin D Metabolism and Its Role in Mineral and Bone Disorders in Chronic Kidney Disease in Humans, Dogs and Cats

Some differences regarding Vitamin D metabolism are described in dogs and cats in comparison with humans, which may be explained by an evolutionary drive among these species. Similarly, vitamin D is one of the most important regulators of mineral metabolism in dogs and cats, as well as in humans. Mineral metabolism is intrinsically related to bone metabolism, thus disturbances in vitamin D have been implicated in the development of chronic kidney disease mineral and bone disorders (CKD-MBD) in people, in addition to dogs and cats. Vitamin D deficiency may be associated with Renal Secondary Hyperparathyroidism (RSHPT), which is the most common mineral disorder in later stages of CKD in dogs and cats. Herein, we review the peculiarities of vitamin D metabolism in these species in comparison with humans, and the role of vitamin D disturbances in the development of CKD-MBD among dogs, cats, and people. Comparative studies may offer some evidence to help further research about vitamin D metabolism and bone disorders in CKD.

The Role of Vitamin D in Small Animal Bone Metabolism

Dogs and cats have differences in vitamin D metabolism compared to other mammalian species, as they are unable to perform vitamin D cutaneous synthesis through sun exposure. Therefore, they are dependent on the dietary intake of this nutrient. The classic functions of vitamin D are to stimulate intestinal calcium and phosphate absorption, renal calcium and phosphate reabsorption and regulate bone mineral metabolism. Thus, it is an important nutrient for calcium and phosphorus homeostasis. This review highlights the evidence of the direct and indirect actions of vitamin D on bone mineral metabolism, the consequences of nutritional imbalances of this nutrient in small animals, as well as differences in vitamin D metabolism between different size dogs.

Vitamin D metabolism in dogs and cats and its relation to diseases not associated with bone metabolism

Due to the presence of receptors in the cells of numerous body tissues, vitamin D is associated with several physiological functions that go beyond calcium and phosphorus homoeostasis and control of bone metabolism in the body. In humans, several studies have associated lower vitamin D concentrations with numerous diseases, such as cancer, heart disease, autoimmune diseases and infectious diseases, and also with an increase in the total mortality rate of the population. Recently, this nutrient started to gain importance in veterinary medicine, and several articles have shown a correlation between low vitamin D status and diseases unrelated to bone metabolism. The present review aims to highlight the recent publications that investigated this relationship, bringing the evidence that exists so far in dogs and cats.

Beyond the skeleton: the role of vitamin D in companion animal health

While the role of vitamin D in the maintenance of skeletal health has been well-established for many years, the discovery that many non-skeletal tissues express the vitamin D receptor stimulated renewed interest in vitamin D and its wider physiological roles. Subsequently, a vast literature has emerged over the past three decades which has linked vitamin D deficiency to the development of many human diseases including cancer, autoimmune, infectious and cardiovascular disorders. In contrast, the role vitamin D plays in the physiology of non-skeletal tissues in cats and dogs has received little attention. The situation is now starting to change with the publication of several studies that have indicated that vitamin D metabolism is deranged in numerous companion animal disorders. This article reviews the biology of vitamin D in companion animals and highlights some of the recent studies which have advanced understanding of vitamin D homeostasis in cats and dogs. Finally, the essay discusses how a "One Health" approach could further the understanding of vitamin D metabolism in mammals. Investigating vitamin D homoeostasis in companion animals offers many advantages compared to human studies in which vitamin D status is influenced by many more variables.

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.

ISFM Consensus Guidelines on the Diagnosis and Management of Feline Chronic Kidney Disease

PRACTICAL RELEVANCE

Chronic kidney disease (CKD) is one of the most commonly diagnosed diseases in older cats. In most cats, CKD is also a progressive disease and can be accompanied by a wide range of clinical and clinicopathological changes. These ISFM Consensus Guidelines have been developed by an independent panel of clinicians and academics to provide practical advice on the diagnosis and management of this complex disease.

CLINICAL CHALLENGES

Although CKD is a common clinical problem in cats, the manifestations of disease vary between individuals. Thus there is a need for careful and repeat evaluation of cats with CKD and adjustment of therapy according to individual needs. In addition to addressing problems arising from CKD and improving quality of life (QoL) for the patient, therapy may also target slowing the underlying progression of disease and hence prolonging life. While maintaining QoL is of paramount importance in our patients, this can be challenging when multiple therapies are indicated. In some cases it is necessary to prioritise therapy, given an understanding of what is likely to most benefit the individual patient.

EVIDENCE BASE

In preparing these Guidelines, the Panel has carefully reviewed the existing published literature, and has also graded the quality of evidence for different interventions to help to provide practical recommendations on the therapeutic options for feline CKD. This is a field of veterinary medicine that has benefited from some excellent published clinical research and further research findings will undoubtedly modify the recommendations contained in these Guidelines in the future.

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.

Feline hyperparathyroidism: pathophysiology, diagnosis and treatment of primary and secondary disease

PRACTICAL RELEVANCE

Hyperparathyroidism exists in primary and secondary forms. Primary hyperparathyroidism has typically been considered a disease that uncommonly affects cats, but this condition is more prevalent than previous diagnoses would suggest. Secondary hyperparathyroidism may be caused by either nutritional influences (ie, nutritional secondary hyperparathyroidism) or chronic kidney disease (ie, renal secondary hyperparathyroidism). Tertiary hyperparathyroidism has yet to be documented in veterinary medicine, but it is possible that this condition occurs in some cats following longstanding renal secondary hyperparathyroidism.

CLINICAL CHALLENGES

Diagnosis of this group of calcium metabolic disorders presents a number of challenges for the clinician. For example, clinical signs can be non-specific and, especially in the case of primary hyperparathyroidism, there is often a low index of suspicion for the disease; careful sample handling is required for testing of parathyroid hormone (PTH) and ionized calcium levels; and there is currently no feline-specific assay for PTH, which has implications for test sensitivity and interpretation of results.

AIMS

This article briefly outlines PTH and calcium physiology by way of introduction to a review of PTH measurement and interpretation. Various forms of feline hyperparathyroidism are then described, encompassing diagnosis and treatment options.

Calcitriol, calcidiol, parathyroid hormone, and fibroblast growth factor-23 interactions in chronic kidney disease

Objective

To review the inter-relationships between calcium, phosphorus, parathyroid hormone (PTH), parent and activated vitamin D metabolites (vitamin D, 25(OH)-vitamin D, 1,25(OH)₂-vitamin D, 24,25(OH)₂-vitamin D), and fibroblast growth factor-23 (FGF-23) during chronic kidney disease (CKD) in dogs and cats.

Data Sources

Human and veterinary literature.

Human Data Synthesis

Beneficial effects of calcitriol treatment during CKD have traditionally been attributed to regulation of PTH but new perspectives emphasize direct renoprotective actions independent of PTH and calcium. It is now apparent that calcitriol exerts an important effect on renal tubular reclamation of filtered 25(OH)-vitamin D, which may be important in maintaining adequate circulating 25(OH)-vitamin D. This in turn may be vital for important pleiotropic actions in peripheral tissues through autocrine/paracrine mechanisms that impact the health of those local tissues.

Veterinary Data Synthesis

Limited information is available reporting the benefit of calcitriol treatment in dogs and cats with CKD.

Conclusions

A survival benefit has been shown for dogs with CKD treated with calcitriol compared to placebo. The concentrations of circulating 25(OH)-vitamin D have recently been shown to be low in people and dogs with CKD and are related to survival in people with CKD. Combination therapy for people with CKD using both parental and activated vitamin D compounds is common in human nephrology and there is a developing emphasis using combination treatment with activated vitamin D and renin-angiotensin-aldosterone-system (RAAS) inhibitors.

Feline CKD: New horizons - where do we go from here?

PRACTICAL RELEVANCE

Chronic kidney disease (CKD) is common in humans as well as in cats, and is a significant human health problem. In feline medicine, despite recent research and improvements in our understanding of the condition, management remains limited by late diagnosis and an inadequate ability to prevent progression of disease. Investigation of future treatments that both delay the progression of CKD and manage clinical signs, and that are also easy and cost effective to administer, is desirable. To this end, we may learn from our colleagues in the medical profession.

AUDIENCE

CKD is commonly encountered in general practice and so all practitioners dealing with cats will benefit from understanding future treatment possibilities and interventions in the management of CKD.

EVIDENCE BASE

Large-scale medical studies have been performed to provide an evidence base for treatment decisions in human CKD. Several studies in cats have looked at various aspects of treatment and prognosis, but large-scale studies are needed to assess the benefits of treatments such as angiotensin-converting enzyme inhibitors and angiotensin receptor blockers.

CLINICAL CHALLENGES

Providing treatment that is effective, easy to administer and not cost-prohibitive is the challenge currently faced by clinicians in the management of feline CKD.

Feline CKD: Current therapies - what is achievable?

PRACTICAL RELEVANCE

Treatment of feline chronic kidney disease (CKD) tends to focus on minimising the adverse effects of reduced renal function, rather than addressing an underlying cause. Despite this, and the progressive nature of CKD, treatment can improve quality of life and enable many cats to have long survival times.

EVIDENCE BASE

Strong evidence supports the provision of renal diets, which are protein and phosphorus restricted; compliance is improved by gradual dietary transition. Additional phosphorus restriction is achieved by the use of phosphate binding agents, although it is unknown if these yield similar survival benefits to those provided by renal diets. Interventions to control hypokalaemia and hypertension in affected cats are important to prevent serious complications. Administration of benazepril to cats with proteinuric kidney disease has been shown to significantly improve their appetite but not their survival. As CKD progresses, many cats will benefit from treatment to control clinical signs of uraemic gastroenteritis and anaemia.

Urinary calcium and oxalate excretion in healthy adult cats are not affected by increasing dietary levels of bone meal in a canned diet

This study aimed to investigate the impact of dietary calcium (Ca) and phosphorus (P), derived from bone meal, on the feline urine composition and the urinary pH, allowing a risk assessment for the formation of calcium oxalate (CaOx) uroliths in cats. Eight healthy adult cats received 3 canned diets, containing 12.2 (A), 18.5 (B) and 27.0 g Ca/kg dry matter (C) and 16.1 (A), 17.6 (B) and 21.1 g P/kg dry matter (C). Each diet was fed over 17 days. After a 7 dayś adaptation period, urine and faeces were collected over 2×4 days (with a two-day rest between), and blood samples were taken. Urinary and faecal minerals, urinary oxalate (Ox), the urinary pH and the concentrations of serum Ca, phosphate and parathyroid hormone (PTH) were analyzed. Moreover, the urine was microscopically examined for CaOx uroliths. The results demonstrated that increasing levels of dietary Ca led to decreased serum PTH and Ca and increased faecal Ca and P concentrations, but did not affect the urinary Ca or Ox concentrations or the urinary fasting pH. The urinary postprandial pH slightly increased when the diet C was compared to the diet B. No CaOx crystals were detected in the urine of the cats. In conclusion, urinary Ca excretion in cats seems to be widely independent of the dietary Ca levels when Ca is added as bone meal to a typical canned diet, implicating that raw materials with higher contents of bones are of subordinate importance as risk factors for the formation of urinary CaOx crystals.

Chronic kidney disease in dogs and cats

Chronic kidney disease (CKD) occurs commonly in older dogs and cats. Advances in diagnostics, staging, and treatment are associated with increased quality and quantity of life. Dietary modification has been shown to increase survival and quality of life and involves more than protein restriction as diets modified for use with CKD are lower in phosphorous and sodium, potassium and B-vitamin replete, and alkalinizing, and they contain n3-fatty acids. Additionally, recognition and management of CKD-associated diseases such as systemic arterial hypertension, proteinuria, and anemia benefit patients. This article summarizes staging and management of CKD in dogs and cats.

Chronic kidney disease in small animals

Chronic kidney disease (CKD) affects multiple body systems and presents with a wide variety of clinical manifestations. Proper application of conservative medical management can profoundly affect the clinical course of CKD. Diagnosis and management is facilitated by staging CKD and applying therapies that are appropriate for the patient's stage of CKD. Therapy and follow-up of CKD are described, with emphasis on stage-based therapy to ameliorate clinical signs and slow progression.

Therapies for feline chronic kidney disease. What is the evidence?

Practical relevance Successful treatment and prevention of kidney disease in pet animals requires a multidimensional approach to identify and eliminate causes or exacerbating factors, provide professional examination and care on a regular basis, and plan and implement a comprehensive treatment program when necessary.

Evidence base Over the years, many therapeutic and preventive interventions have been developed or advocated for chronic kidney disease (CKD), but evidence of efficacy or effectiveness is often lacking or highly variable. Accordingly, the main objective of this systematic review was to identify and critically appraise the evidence supporting various approaches to managing feline CKD; namely, fluid therapy, calcitrioi therapy, antihypertensive therapy, ACE inhibitor therapy, erythropoietic hormone replacement therapy, potassium supplementation, antioxidant supplementation, alkalinization therapy, dietary phosphorus restriction and intestinal phosphate binders, therapeutic renal foods, assisted feeding, dialysis and renal transplantation.