COMPARISON OF BLOOD SYMMETRIC DIMETHYLARGININE AND CREATININE AS ENDOGENOUS MARKERS OF KIDNEY FUNCTION IN CAPTIVE TIGERS (PANTHERA TIGRIS)

Reference Interval Creation for Symmetric Dimethylarginine (SDMA) in Healthy Hispaniolan Amazon Parrots (Amazona ventralis) and Quaker Parrots (Myiopsitta monachus)

Renal disease is often identified as a cause of morbidity and mortality in avian patients. However, currently, early antemortem detection of renal disease in avian patients is difficult. Anatomical and physiological differences between mammals and birds mean the use of commonly employed diagnostic testing (ie, measurement of blood urea nitrogen [BUN] and serum creatinine, urinalysis, and ultrasonography) are either nondiagnostic or difficult to achieve. Symmetric dimethylarginine (SDMA) is considered a more sensitive marker for renal disease in humans, dogs, and cats. However, SDMA has not yet been assessed for diagnostic use in any psittacine species. In this study, we establish reference ranges for SDMA in both Hispaniolan Amazon parrots (Amazona ventralis, HAP) and Quaker parrots (Myiopsitta monachus, QP). Blood was collected from 23 Amazon parrots and 32 Quaker parrots maintained in research facilities. Measurement of SDMA through a commercially available immunoassay (IA-SDMA) as well as creatinine, BUN, uric acid, phosphorus, calcium, sodium, potassium, and chloride were determined through IDEXX Laboratories. Plasma SDMA concentrations ranged from 6 to 15 µg/dL and 3 to 15 µg/dL for the HAP and QP, respectively. Sex was a confounding factor for the QP population, but sex did not have a significant effect on SDMA for the HAP population. No significant correlations were identified between SDMA concentrations and other parameters in either psittacine species. Our results show proof of concept for the IA-SDMA and provide reference intervals for SDMA in HAP and QP. Further investigation is required to determine the validity of this assay and the predictive power of SDMA in the detection of renal impairment for parrots and other common companion birds.

Investigation of symmetric dimethylarginine as a serologic marker for kidney function in striped skunks (Mephitis mephitis)

IMPORTANCE

Kidney disease is prevalent among veterinary species, including zoo animals; however, investigations into this condition in striped skunks (Mephitis mephitis) are scarce. Diagnostic tools for kidney diseases in this species also remain limited.

OBJECTIVE

This study aimed to assess the utility of symmetric dimethylarginine as a biomarker for kidney disease in captive striped skunks in Korea.

METHODS

This retrospective study analysed 11 striped skunks housed at the Everland Zoo between 2017 and 2021. Blood samples were collected during health checks. Kidney function was assessed through blood analysis and diagnostic ultrasound, with necropsies conducted on deceased animals. Symmetric dimethylarginine levels were measured in 27 plasma samples collected from 11 skunks.

RESULTS

Over the study period, seven skunks were diagnosed with kidney disease. Analysis of 27 blood samples revealed a concurrent increase in SDMA levels with concentrations of blood urea nitrogen and blood creatinine. In 3 of the 7 skunks with kidney disease, symmetric dimethylarginine exceeded 14 µg/dL prior to the elevation of blood urea nitrogen and blood creatinine above the upper reference limit.

CONCLUSIONS AND RELEVANCE

To our knowledge, this is the first study investigating symmetric dimethylarginine in captive striped skunks in Korea. Our findings suggest that symmetric dimethylarginine may serve as an early and consistent biomarker for renal dysfunction in striped skunks. Further studies with larger clinical sample size from striped skunks are needed to validate the clinical utility of blood symmetric dimethylarginine concentration.

PRELIMINARY EVALUATION OF SYMMETRIC DIMETHYLARGININE AS A BIOMARKER OF RENAL INSUFFICIENCY IN WILD AND REHABILITATED FLORIDA MANATEES (TRICHECHUS MANATUS LATIROSTRIS)

Currently, there are limited antemortem tests available to evaluate renal function in Florida manatees (Trichechus manatus latirostris). Although few reports of renal pathology in manatees exist in the veterinary literature, debilitated animals that present to rehabilitation centers are frequently dehydrated, may have sustained renal trauma secondary to watercraft injury, and may experience ischemic events related to coagulation disorders leading to renal compromise. Clinicians remain limited to the analysis of blood urea nitrogen, creatinine levels, and urinalysis (if urine is obtained) to determine the extent of renal insufficiency, which may not accurately reflect renal function. This poses a diagnostic challenge for clinicians in discerning how critical renal compromise is to the animal's overall health and prognosis. For the first phase of this study, retrospective symmetric dimethylarginine (SDMA) values were determined from banked serum or plasma samples from 14 wild Florida manatees that had been collected while the animals were under rehabilitation in zoological institutions prior to their deaths. Values of SDMA for nine samples from eight manatees with known renal disease, as determined by histopathology, were compared to SDMA values for seven samples from six manatees with no reported renal lesions on histopathology. Values of SDMA from wild Florida manatees with known renal disease (mean 33.56 µg/dl ± 13.15, P= 0.017) were statistically significantly elevated when compared to SDMA values from manatees with no reported renal lesions (mean = 18.71 µg/dl ± 6.9) on histopathology. For the second phase of the study, serum or plasma samples were obtained from wild manatee populations from two geographically separate presumed-healthy wild manatee populations (n = 57). Although the upper limit was higher, serum SDMA concentrations from presumed-healthy wild manatees were comparable to those reported in small animal and equine medicine at 5.88-16.97 µg/dl.

EVALUATION OF SYMMETRIC DIMETHYLARGININE AS AN ENDOGENOUS MARKER OF RENAL DISEASE IN GREATER FLAMINGOS (PHOENICOPTERUS ROSEUS)

Detection of renal disease in birds is currently reliant on biochemical measures such as uric acid, which is only elevated after significant renal compromise has occurred. Symmetric dimethylarginine (SDMA) production has not been previously evaluated in birds and no reference intervals (RI) for measurement exist in avian species. This study aimed to develop an RI for SDMA in greater flamingos (Phoenicopterus roseus) and evaluate the association between SDMA levels and renal disease. Blood from 60 flamingos was collected for RI development and the RI of SDMA was found to be 11.8-34.2 µg/dl. Symmetric dimethylarginine showed a strong positive correlation with uric acid, a moderate positive correlation with creatine kinase, and moderate negative correlations with total protein, albumin, and glucose. No correlation was found with pododermatitis score or body condition. Using the SDMA RI, six clinical cases were included for assessment of the clinical relevance of SDMA in renally compromised patients. All birds that were euthanized had elevated SDMA levels and severe renal or systemic pathology on necropsy.

Symmetric Dimethylarginine is a Promising Biomarker for the Early Detection of Age-Related Kidney Dysfunction in Zoo Felids

Chronic renal failure is one of the leading causes of death in African lions, cheetahs, and tigers. Conventional methods to measure renal dysfunction include measuring serum creatinine and blood urea nitrogen (BUN). Symmetric dimethylarginine (SDMA) measurement is a reliable predictor of renal dysfunction in the domestic cat because SDMA serum levels increase early when the kidneys are damaged. Serum SDMA levels were assessed and correlated with creatinine as well as BUN from healthy captive Bengal tigers and lions at the Everland Zoo in Korea. Serum SDMA concentrations were increasingly associated with increased age in lions. However, SDMA concentrations were higher in some young Bengal tigers than in older ones, which may allow for earlier renal dysfunction detection in these young cats than would be BUN and creatinine alone. In Bengal tigers, the correlation between the SDMA and BUN was slightly higher than that between SDMA and creatinine. In lions, SDMA correlated better with creatinine than with BUN concentration. These results show that serum SDMA concentration can be used as a biomarker for age-associated renal dysfunction. SDMA measurement may be an essential preventive management method in zoos.

Blood concentration of symmetric dimethylarginine correlates with kidney damage as assessed with a proposed histologic grading system for chronic kidney disease in tigers (Panthera tigris)

OBJECTIVE

To determine the utility of blood symmetric dimethylarginine (SDMA) concentration measurement as a diagnostic tool for chronic kidney disease (CKD) in tigers (Panthera tigris) by comparing results for SDMA with those for traditional renal biomarkers and investigating correlations between these biomarkers and histopathologic kidney changes in tigers with CKD.

SAMPLE

Blood, urine, and kidney samples from 35 tigers with CKD from 2 sanctuaries.

PROCEDURES

Blood (serum or plasma) and urine samples were collected antemortem. Necropsy, including gross and histologic assessment, was performed for tigers that died or were euthanized for quality-of-life reasons. Results for CKD biomarkers in blood (BUN, creatinine, phosphorus, and SDMA concentrations) and urine (protein concentration, urine protein-to-creatinine ratio, and urine specific gravity) were evaluated for correlation with histologic kidney damage scored with an objective grading scale defined by percentage of inflammation, fibrosis, and tubular atrophy.

RESULTS

Symmetric dimethylarginine had the strongest significant correlation (ρ = 0.667) with histologic kidney damage score, followed by urine specific gravity (ρ = -0.639), blood creatinine concentration (ρ = 0.624), and BUN (ρ = 0.588). No significant correlation with kidney score was identified for blood phosphorus concentration, urine protein concentration, or the urine protein-to-creatinine ratio.

CLINICAL RELEVANCE

We recommend SDMA be prioritized as a renal biomarker in tigers, with SDMA results considered in addition to those of other traditional renal biomarkers when assessing kidney function in tigers. Additionally, the grading scale we developed could be replicated across patients and pathologists for more consistent postmortem assessment of CKD in tigers.