Pet Wellness and Vitamin A: A Narrative Overview

The health of companion animals, particularly dogs and cats, is significantly influenced by nutrition, with vitamins playing a crucial role. Vitamin A, in particular, is indispensable, with diverse roles ranging from vision to immune modulation and reproduction. Despite its importance, the metabolism and dietary requirements of vitamin A in companion animals remain complex and not fully understood. This review provides a comprehensive overview of the historical perspective, the digestion, the metabolism, the physiological roles, the deficiency, the excess, and the interactions with other micronutrients of vitamin A in companion animals. Additionally, it highlights future research directions and gaps in our understanding. Insights into the metabolism of vitamin A in companion animals, personalized nutrition strategies based on genetic variability, longitudinal studies tracking the status of vitamin A, and investigations into its immunomodulatory effects are crucial for optimizing pet health and wellness. Furthermore, understanding the stability and bioavailability of vitamin A in pet food formulations is essential for ensuring the provision of adequate micronutrients. Overall, this review underscores the importance of vitamin A in companion animal nutrition and the need for further research to enhance our understanding and to optimize dietary recommendations for pet health and well-being.

Renal biomarkers in cats: A review of the current status in chronic kidney disease

Serum creatinine concentration, the classical biomarker of chronic kidney disease (CKD) in cats, has important limitations that decrease its value as a biomarker of early CKD. Recently, serum symmetric dimethylarginine concentration was introduced as a novel glomerular filtration rate biomarker for the early detection of CKD in cats. However, data on its specificity are still limited. The limitations of conventional biomarkers and the desire for early therapeutic intervention in cats with CKD to improve outcomes have prompted the discovery and validation of novel renal biomarkers to detect glomerular or tubular dysfunction. Changes in the serum or urinary concentrations of these biomarkers may indicate early kidney damage or predict the progression of kidney before changes in conventional biomarkers are detectable. This review summarizes current knowledge on renal biomarkers in CKD in cats, a field that has progressed substantially over the last 5 years.

Urinary proteome and metabolome in dogs (Canis lupus familiaris): The effect of chronic kidney disease

Chronic kidney disease (CKD) is a progressive and irreversible disease. Although urine is an ideal biological sample for proteomics and metabolomics studies, sensitive and specific biomarkers are currently lacking in dogs. This study characterised dog urine proteome and metabolome aiming to identify and possibly quantify putative biomarkers of CKD in dogs. Twenty-two healthy dogs and 28 dogs with spontaneous CKD were selected and urine samples were collected. Urinary proteome was separated by SDS-PAGE and analysed by mass spectrometry, while urinary metabolome was analysed in protein-depleted samples by 1D ¹H NMR spectra. The most abundant proteins in urine samples from healthy dogs were uromodulin, albumin and, in entire male dogs, arginine esterase. In urine samples from CKD dogs, the concentrations of uromodulin and albumin were significantly lower and higher, respectively, than in healthy dogs. In addition, these samples were characterised by a more complex protein pattern indicating mixed glomerular (protein bands ≥65 kDa) and tubular (protein bands <65 kDa) proteinuria. Urine spectra acquired by NMR allowed the identification of 86 metabolites in healthy dogs, belonging to 49 different pathways mainly involved in amino acid metabolism, purine and aminoacyl-tRNA biosynthesis or tricarboxylic acid cycle. Seventeen metabolites showed significantly different concentrations when comparing healthy and CKD dogs. In particular, carnosine, trigonelline, and cis-aconitate, might be suggested as putative biomarkers of CKD in dogs. SIGNIFICANCE: Urine is an ideal biological sample, however few proteomics and metabolomics studies investigated this fluid in dogs and in the context of CKD (chronic kidney disease). In this research, applying a multi-omics approach, new insights were gained regarding the molecular changes triggered by this disease in canine urinary proteome and metabolome. In particular, the involvement of the tubular component was highlighted, suggesting uromodulin, trigonelline and carnosine as possible biomarkers of CKD in dogs.

Utility of Urinary Markers in the Assessment of Renal Dysfunction in Familial Glomerulonephritis in Dobermann Dogs

Introduction

Dobermann dogs are reportedly predisposed to familial glomerulonephropathy. Proteinuria is a hallmark of canine familial glomerular diseases. The identification of glomerular abnormalities in breeds so predisposed is of great importance in improving breeding policy. Therefore, markers that allow the detection and localisation of renal damage are needed. The purpose of this study was to investigate the urinary concentrations of immunoglobulin G (uIgG), retinol-binding protein (uRBP), and Tamm–Horsfall protein (uTHP) in a family of Dobermanns with proteinuria and compare these concentrations with the corresponding values in healthy controls.

Material and Methods

Ten dogs of the Dobermann breed with proteinuria (five with a urine protein-to-creatinine ratio (UPC) of 0.5–1 and five with a UPC >1) and twelve healthy dogs were enrolled. An ELISA was performed to measure uIgG, uRBP, and uTHP, and these proteins were quantified in relation to urinary creatinine (uCrea).

Results

uIgG/uCr and uRBP/uCr were significantly higher in the family of Dobermanns than in the healthy dogs. A significant difference in the uTHP/uCr value was found only in dogs with a UPC of >1.

Conclusion

IgG seems to facilitate the diagnosis of primary hereditary glomerulopathy in Dobermanns. Moreover, in affected dogs, proteinuria characterisation seems to be a promising alternative option for the detection and localisation of renal lesions.

Assessment of acute kidney injury in canine parvovirus infection: Comparison of kidney injury biomarkers with routine renal functional parameters

Dogs with naturally occurring canine parvovirus (CPV) infection are at risk of developing acute kidney injury (AKI) due to several factors, including severe dehydration, hypotension and sepsis. Serum creatinine (sCr) and serum urea are insensitive markers for the assessment of early kidney injury. Therefore, the aim of this study was to investigate potential kidney injury in dogs with CPV infection using both routine renal functional parameters and several kidney injury biomarkers. Twenty-two dogs with CPV infection were prospectively enrolled and compared with eight clinically healthy control dogs. Urinary immunoglobulin G (uIgG) and C-reactive protein (uCRP) were measured to document glomerular injury, whereas urinary retinol-binding protein (uRBP) and neutrophil gelatinase-associated lipocalin (uNGAL) served as markers for tubular injury. These biomarkers were compared to routine renal functional parameters, including sCr, serum urea, urinary protein:creatinine ratio (UPC) and urine specific gravity (USG). Dogs with CPV infection had significantly higher concentrations of uIgG, uCRP, uRBP and uNGAL compared to healthy dogs. In contrast, sCr was significantly lower in dogs with CPV infection compared to controls, while serum urea was not significantly different. UPC and USG were both significantly higher in CPV-infected dogs. This study demonstrated that dogs with CPV infection had evidence of AKI, which remained undetected by the routine functional markers sCr and serum urea, but was revealed by UPC, uIgG, uCRP, uRBP and uNGAL. These results emphasize the added value of novel urinary kidney injury biomarkers to detect canine patients at risk of developing AKI.

Variability of serum concentrations of cystatin C and urinary retinol-binding protein, neutrophil gelatinase-associated lipocalin, immunoglobulin G, and C-reactive protein in dogs

Background

Markers of kidney dysfunction and damage have potential to detect chronic kidney disease (CKD) in early stages. However, data on long‐term variation of these markers in healthy dogs is lacking and is crucial for the interpretation of results.

Hypothesis/Objectives

To determine temporal variations of serum cystatin C (sCysC) and urinary retinol‐binding protein (uRBP), neutrophil gelatinase‐associated lipocalin (uNGAL), immunoglobulin G (uIgG), and C‐reactive protein (uCRP) in healthy dogs.

Animals

Eight clinically healthy adult Beagles were evaluated.

Methods

Longitudinal observational study. Serum cystatin C was determined by particle‐enhanced nephelometric immunoassay. Urinary retinol‐binding protein, uNGAL, uIgG and uCRP were determined by ELISA and concentrations were indexed to urinary creatinine. Within‐ and between‐dog variance components (VC) and within‐dog coefficients of variation (CV) were determined from blood and urine collected at eight time points over 1.5 years.

Results

Urinary C‐reactive protein (uCRP) concentrations were consistently below the detection limit (5.28 ng/mL). Mean ± within‐dog standard deviation for sCysC, uRBP/c, uNGAL/c and uIgG/c was 0.15 ± 0.01 mg/L, 0.09 ± 0.03 mg/g, 2.32 ± 2.03 μg/g and 12.47 ± 10.98 mg/g, respectively. Within‐dog CV for sCysC, uRBP/c, uNGAL/c and uIgG/c was 8.1%, 33.7%, 87.2% and 88.1%, respectively.

Conclusions and clinical importance

Serum cystatin C, uRBP/c, uNGAL/c and uIgG/c exhibit a wide range of long‐term within‐dog variability. Researchers and veterinarians might need to take this into account when interpreting their results. To assess their diagnostic and predictive ability, future studies need to establish reference ranges for healthy dogs and dogs with CKD.

Is Progressive Chronic Kidney Disease a Slow Acute Kidney Injury?

International Renal Interest Society chronic kidney disease Stage 1 and acute kidney injury Grade I categorizations of kidney disease are often confused or ignored because patients are nonazotemic and generally asymptomatic. Recent evidence suggests these seemingly disparate conditions may be mechanistically linked and interrelated. Active kidney injury biomarkers have the potential to establish a new understanding for traditional views of chronic kidney disease, including its early identification and possible mediators of its progression, which, if validated, would establish a new and sophisticated paradigm for the understanding and approach to the diagnostic evaluation, and treatment of urinary disease in dogs and cats.

Advances in the evaluation of canine renal disease

Many recent advances in the evaluation of dogs with kidney disease have improved our diagnostic algorithms and have impacted our therapeutic strategies. Non-invasive techniques, such as urinary and serologic biomarker evaluation, can help a clinician diagnose and treat a patient that cannot undergo a renal biopsy for clinical or financial reasons. Some biomarkers might help localize the affected structure (glomerulus vs. tubule) and indicate the type or severity of injury present. Although more research is needed, studies indicate that some biomarkers (e.g. urine protein to creatinine ratio and urinary immunoglobulins) can be useful in predicting adverse outcomes. Importantly, the sensitivity and specificity of biomarkers for renal injury should be established and clinicians need to understand the limitations of these assays. If a renal biopsy is performed, then it should be evaluated by a specialty diagnostic service with expertise in nephropathology. A panel of special stains, immunofluorescence for the detection of immunoglobulins and complement factors, and transmission electron microscopy can be routinely employed in cases of glomerular disease. These advanced diagnostics can be used to detect immune deposits in order to definitively diagnose immune complex mediated glomerular disease. Integrating the results of biomarker assays and comprehensive renal biopsy evaluation, the clinician can make informed therapeutic decisions, such as whether or not to immunosuppress a patient.

Correlation of Urine and Serum Biomarkers with Renal Damage and Survival in Dogs with Naturally Occurring Proteinuric Chronic Kidney Disease

Background

Urine protein loss is common in dogs with chronic kidney disease (CKD).

Hypothesis/Objectives

To evaluate new biomarkers of glomerular and tubulointerstitial (TI) damage compared with histology and as survival indicators in dogs with naturally occurring, proteinuric CKD.

Animals

One hunderd and eighty dogs with naturally occurring kidney disease.

Methods

Retrospective study using urine, serum, and renal biopsies from dogs with kidney disease, 91% of which had proteinuric CKD. Biomarkers were evaluated and correlated with pathologic renal damage, and significant associations, sensitivities, and specificities of biomarkers for renal disease type were determined.

Results

Fractional excretions of immunogloblin M (IgM_FE) and immunoglobulin G (IgG_FE) correlated most strongly with glomerular damage based on light microscopy (r = 0.58 and 0.56, respectively; P < .01). Serum creatinine (SCr) correlated most strongly with TI damage (r = 0.70, P < .01). Urine IgM/creatinine and urine NAG/creatinine had the highest sensitivity (75%) and specificity (78%) for detection of immune complex‐mediated glomerulonephritis. Although individually most biomarkers were significantly associated with decreased survival time (P < .05), in a multivariate analysis, SCr, IgM_FE, and glomerular damage based on transmission electron microscopy (TEM) were the only biomarkers significantly associated with survival time (SCr: P = .001; IgM_FE: P = .008; TEM: P = .017).

Conclusions and Clinical Importance

Novel urine biomarkers and FEs are useful for detection of glomerular and TI damage in dogs with proteinuric CKD and might predict specific disease types and survival.

Characterization of Proteinuria in Dogue de Bordeaux Dogs, a Breed Predisposed to a Familial Glomerulonephropathy: A Retrospective Study

Dogue de Bordeaux dog has been reported to be predisposed to a familial glomerulonephropathy that displays some morphological modifications reported in focal and segmental glomerulosclerosis. Prevalence of quantitatively abnormal renal proteinuria was recently reported to be 33% in this breed. The nature of the proteinuria was assessed by sodium dodecyl sulfate-agarose gel electrophoresis and determinations of urinary markers (urinary retinol-binding protein, urinary N-acetyl-β-glucosaminidase, urinary albumin and urinary immunoglobulin G) on stored specimens. Diagnostic performances of sodium dodecyl sulfate-agarose gel electrophoresis to identify dogs with elevated urinary biomarkers were assessed. Samples from 102 adult Dogue de Bordeaux dogs (47 non-proteinuric [urine protein-to-creatinine ratio ≤ 0.2], 20 borderline-proteinuric [0.2< urine protein-to-creatinine ratio ≤ 0.5] and 35 proteinuric dogs [urine protein-to-creatinine ratio >0.5]) were used, of which 2 were suffering from familial glomerulonephropathy. The electrophoretic protein patterns, for all but one proteinuric dog, were indicative of a glomerular origin and, in all dogs, the urinary albumin concentration related to creatinine concentration and the urinary immunoglobulin G concentration related to creatinine concentration were above the upper limit of the reference interval established for the breed. Sensitivity and specificity of sodium dodecyl sulfate-agarose gel electrophoresis identifying dogs with elevated urinary albumin concentration were 94% and 92%, respectively, while diagnostic performance of sodium dodecyl sulfate-agarose gel electrophoresis in detecting dogs with elevated urinary immunoglobulin G concentration yielded sensitivity and specificity of 90% and 74%, respectively. These results suggest that all proteinuric and some borderline-proteinuric Dogue de Bordeaux dogs likely have underlying glomerular lesions and that sodium dodecyl sulfate-agarose gel electrophoresis and urinary markers might be useful to screen dogs with borderline-proteinuria. Additional investigations are warranted to assess if these findings are related to the familial glomerulonephropathy.

Relationship between urinary Tamm-Horsfall protein excretion and renal function in dogs with naturally occurring renal disease

BACKGROUND

Tamm-Horsfall protein (THP) is physiologically excreted in urine, but little is known about the role of THP in the diagnosis of renal disease in dogs.

OBJECTIVE

The aim of this study was to evaluate to which extent naturally occurring renal disease affects the urinary excretion of THP.

METHODS

Dogs were divided into 5 groups according to plasma creatinine concentration, urinary protein-to-creatinine ratio (UP/UC), and exogenous plasma creatinine clearance (P-ClCr ) rates: Group A (healthy control dogs; n = 8), nonazotemic and nonproteinuric dogs, with P-ClCr rates > 90 mL/min/m(2) ; group B (n = 25), nonazotemic and nonproteinuric dogs with reduced P-ClCr rates (51-89 mL/min/m(2) ); group C (n = 7), nonazotemic but proteinuric dogs with P-ClCr rates 53-98 mL/min/m(2) ; group D (n = 8), azotemic and borderline proteinuric dogs (P-ClCr rates: 22-45 mL/min/m(2) ); and group E (n = 15), azotemic and proteinuric dogs (not tested for P-ClCr ). THP was measured by quantitative Western blot analysis, and the ratio of THP-to-urinary creatinine (THP/UC) was calculated.

RESULTS

The THP/UC concentrations were not different among dogs of groups A-D, but were reduced in dogs of group E (P < .001). THP/UC correlated negatively with serum creatinine (P < .01) and UP/UC (P < .01), but was not significantly associated with P-ClCr .

CONCLUSIONS

Decreased levels of THP/UC were present in moderately to severely azotemic and proteinuric dogs. This suggests tubular injury in these dogs and that THP might be useful as urinary marker to study the pathogenesis of renal disease.

Biomarkers in the assessment of acute and chronic kidney diseases in the dog and cat

In both human and veterinary medicine, diagnosing and staging renal disease can be difficult. Measurement of glomerular filtration rate is considered the gold standard for assessing renal function but methods for its assessment can be technically challenging and impractical. The main parameters used to diagnose acute and chronic kidney disease include circulating creatinine and urea concentrations, and urine-specific gravity. However, these parameters can be insensitive. Therefore, there is a need for better methods to diagnose and monitor patients with renal disease. The use of renal biomarkers is increasing in human and veterinary medicine for the diagnosis and monitoring of acute and chronic kidney diseases. An ideal biomarker would identify site and severity of injury, and correlate with renal function, among other qualities. This article will review the advantages and limitations of renal biomarkers that have been used in dogs and cats, as well as some markers used in humans that may be adapted for veterinary use. In the future, measuring a combination of biomarkers will likely be a useful approach in the diagnosis of kidney disorders.

Urinary biomarkers for acute kidney injury in dogs

Routinely, kidney dysfunction and decreased glomerular filtration rate (GFR) are diagnosed by the evaluation of changes in the serum creatinine (SCr) and blood urea nitrogen (BUN) concentrations. However, neither of these tests is sensitive or specific enough for the early diagnosis of impaired kidney function because they are both affected by other renal and nonrenal factors. Furthermore, kidney injury can be present in the absence of kidney dysfunction. Renal reserve enables normal GFR even when nephrons are damaged. Renal biomarkers, especially those present in urine, may be useful for the study of both acute and chronic nephropathies. The aim of this review is to describe the current status of urinary biomarkers as diagnostic tools for kidney injury in dogs with particular focus on acute kidney injury (AKI). The International Renal Interest Society (IRIS) canine AKI grading system and the implementation of urinary biomarkers in this system also are discussed. The discovery of novel urinary biomarkers has emerged from hypotheses about the pathophysiology of kidney injury, but few proteomic urine screening approaches have been described in dogs. Lack of standardization of biomarker assays further complicates the comparison of novel canine urinary biomarker validation results among studies. Future research should focus on novel biomarkers of renal origin and evaluate promising biomarkers in different clinical conditions. Validation of selected urinary biomarkers in the diagnosis of canine kidney diseases must include dogs with both renal and nonrenal diseases to evaluate their sensitivity, specificity as well as their negative and positive predictive values.

Serum and urinary adiponectin in dogs with renal disease from leishmaniasis

The objective of this study was to perform an analytical validation of a commercially available ELISA kit (human adiponectin) for urinary adiponectin determination in dogs, and to evaluate urinary adiponectin in dogs with glomerular injury. For this purpose, urine samples from three healthy dogs and three dogs with diagnosed kidney disease were used for analytical validation of the method. In order to evaluate possible influence of kidney damage on urinary adiponectin, serum and urine samples from six healthy and 58 dogs with leishmaniasis were included. The diseased dogs were allocated to three groups according to their urine protein/creatinine (UPC) ratio as non-proteinuric (NP), borderline proteinuric (BP), and proteinuric (P). Intra- and inter-assay coefficients of variation (CV) were lower than 10 per cent and 12 per cent, respectively. Dilutions of canine urine samples resulted in linear regression equations close to 1. Mean recovery was of 112 per cent. The detection limit was 0.75 ng/ml. Urinary adiponectin and urinary adiponectin/creatinine (UAC) ratio showed significantly higher values in urine of P group dogs compared with healthy, NP and BP dogs. In conclusion, an ELISA kit can be used for precise and accurate urinary adiponectin measurement in dogs. Urinary adiponectin is increased in dogs with proteinuria suggesting its possible use as a marker of kidney damage.

Renal function and morphology in aged Beagle dogs before and after hydrocortisone administration

Objectives of this study were to evaluate glomerular filtration rate (GFR), renal structural changes and proteinuria in aged Beagle dogs before and after hydrocortisone (HC) administration. Eleven Beagle dogs ≥10 years old were treated with either hydrocortisone (HC group, n = 6) or placebo (control group, n = 5). Urinary markers, GFR and kidney biopsies were evaluated before (T0), during (T16 wks) and after discontinuing HC administration (T24 wks). Results indicate that HC administration causes a significant increase in GFR. At all time points except T16 wks, proteinuria was higher in the control group than in the HC group, and there was no significant difference in urinary markers between groups. At T16 wks, proteinuria, urinary albumin-to-creatinine (c) ratio, immunoglobulin G/c and retinol-binding protein/c were higher compared to baseline in the HC group. At T0, rare to mild renal lesions were detected in all HC dogs and rare to moderate changes in all control dogs. Glomerulosclerosis progressed in both groups until T24 wks. Tubular atrophy was detected in three HC dogs at T16 wks and T24 wks, but also in five control dogs throughout the study. At every time point, five HC dogs and all control dogs had rare to moderate interstitial inflammation. Rare to mild interstitial fibrosis was found in up to three HC dogs at T16 wks and T24 wks, and severe fibrosis in one HC dog at T24 wks. Up to four control dogs had rare to mild fibrosis at all time points. These findings indicate that clinically healthy, aged Beagle dogs may have considerable renal lesions and proteinuria, which could have implications for experimental or toxicological studies. Additional research is needed to elucidate glucocorticoid effects on renal structure, but functional changes such as hyperfiltration and proteinuria warrant attention to kidney function of canine patients with Cushing's syndrome or receiving exogenous glucocorticoids.

C-reactive protein concentrations in serum of dogs with naturally occurring renal disease

The current study was undertaken to investigate the relation between serum C-reactive protein (CRP) concentrations and parameters of renal function in dogs with naturally occurring renal disease. Dogs were assigned to groups according to plasma creatinine concentration, urinary protein-to-creatinine ratio (UP/UC), and exogenous plasma creatinine clearance (P-ClCr) rates. Group A (healthy control dogs; n = 8): non-azotemic (plasma creatinine <125 µmol/l) and nonproteinuric (UP/UC <0.2), with P-ClCr rates >90 ml/min/m2; group B (n = 11): non-azotemic, nonproteinuric dogs with reduced P-ClCr rates (50–89 ml/min/m2); group C (n = 7): azotemic, borderline proteinuric dogs (P-ClCr rates: 22–67 ml/min/m2); and group D (n = 6): uremic, proteinuric dogs (not tested for P-ClCr). The serum CRP concentrations were measured via commercial enzyme-linked immunosorbent assay. The CRP concentrations in the clinically healthy dogs (group A) ranged from 2.09 mg/l to 8.60 mg/l (median: 3.21 mg/l). In comparison with dogs of group A, median CRP concentrations were significantly ( P < 0.01) elevated in dogs of group B (17.6 mg/l, range: 17.0–19.2 mg/l), group C (24.8 mg/l, range: 18.0–32.5 mg/l), and group D (59.7 mg/l, range: 17.7–123 mg/l). Serum CRP was significantly related to P-ClCr ( r = –0.83; P < 0.001), plasma creatinine ( r = 0.81; P < 0.001), UP/UC ( r = 0.70; P < 0.001), and leukocytes ( r = 0.49; P < 0.01). The significant relations between serum CRP concentrations and biochemical parameters of kidney function in plasma and urine suggest that a stimulation of the acute phase response is implicated in the pathogenesis of canine renal disease.