EVALUATION OF SYMMETRIC DIMETHYLARGININE AS AN EARLY BIOMARKER OF CHRONIC KIDNEY DISEASE IN CAPTIVE CHEETAHS (ACINONYX JUBATUS)

Glomerular filtration rate determined by measuring serum clearance of iohexol in unanesthetized cheetahs (Acinonyx jubatus) with comparison to serum symmetric dimethylarginine

One of the more common diseases affecting zoo-managed cheetahs (Acinonyx jubatus) is chronic renal disease, which can impact their welfare and ultimately shortens their lifespan. Early diagnosis, for which estimating Glomerular Filtration Rate (GFR) is one such tool, is imperative to help mitigate the negative impacts of this insidious disease. GFR was determined by measuring the serum clearance of iohexol in nine clinically normal, cheetahs managed under human care that presented for voluntary blood collection. A 2-sample iohexol clearance method was performed, along with serum symmetric dimethylarginine (SDMA) determination. SDMA has shown promise in humans, dogs, and cats, as an early biomarker of renal disease. Additionally, the relationship between GFR and SDMA, along with serum creatinine and BUN were analyzed. The mean values for the uncorrected GFR and corrected GFR were 2.08 ± 0.215 mL/min/kg body weight and 1.87 ± 0.173 mL/min/kg body weight, respectively. No significant correlations were observed between GFR, SDMA, serum creatinine, or BUN. Both the uncorrected and corrected iohexol-based GFR values were similar to an inulin-based GFR reference interval determined in zoo managed cheetahs and a reported domestic cat iohexol-based GFR reference interval. Serum SDMA values support previous research suggesting cheetahs have a separate reference interval from domestic cats (0-14 μg/dL). Measuring GFR by the serum clearance of iohexol shows promise as a readily available, cheap, and easily administered clearance marker that can be used in cheetahs trained for voluntary blood collection, thereby avoiding the need for anesthesia.

CYSTOCENTESIS AND URINALYSIS IN ZOOMEDICINE: AN UNDERESTIMATED TOOL FOR LARGE FELID STANDARD HEALTH CHECKS

Chronic kidney disease (CKD) is a prevalent disease among felids; yet its origin is still poorly understood, and the disease often remains asymptomatic for years, underscoring the need for early diagnosis. This study aimed to investigate the diagnostic value of urinalysis in accurately staging CKD, particularly as routine health checks in large felids often overlook its significance. In this research, ultrasound-guided cystocentesis (UGC) was performed on 50 captive nondomestic felids during routine veterinary health checks under general anesthesia. Urinalysis included microscopic examination of the sediment, measurement of urine specific gravity (USG) and protein to creatinine ratio (UPC). Additional serum kidney markers, such as creatinine and symmetric dimethylarginine, were compared with USG and UPC to assess their diagnostic value as urinary biomarkers. The results demonstrated proteinuria (UPC > 0.4) or borderline proteinuria (UPC 0.2-0.4) in 49% of the animals. Among these cases, 62% were of renal origin, and 38% were postrenal causes. USG was significantly higher in felids with borderline proteinuria compared to those with proteinuria. A moderate, but significant negative correlation between serum parameters and USG was observed, emphasizing the importance of assessing both diagnostic parameters during kidney evaluations. Additionally, felids with CKD have an increased risk of urinary tract infections, necessitating microscopic urinalysis and bacterial culture analysis. Abnormalities, including hematuria, pyuria, crystalluria, and bacteriuria, were found in approximately 38% of cases through microscopical examination of urine. No complications associated with UGC were observed and abnormal findings were detected in 60% of the cases. Based on these results, the authors recommend the inclusion of UGC and urinalysis as standard diagnostic tools in general health checks for nondomestic felids. This approach provides valuable insights into the early detection and staging of CKD, supporting early intervention and supportive medical care to prolong renal health in these animals.

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.

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.

USE OF SYMMETRIC DIMETHYLARGININE TO DETECT RENAL LESIONS IN FISH: A PRELIMINARY STUDY IN BROOK TROUT (SALVELINUS FONTINALIS)

Symmetric dimethylarginine (SDMA) is an early marker for renal lesions in mammals. The objectives of this study were 1) to establish a reference interval of SDMA in healthy brook trout, Salvelinus fontinalis (Mitchill, 1814), and 2) to assess its sensibility as a marker of renal pathology. Plasma SDMA was quantified by liquid chromatography-mass spectrometry in 25 adult brook trout, including 20 fish displaying no renal histologic lesions, and five fish displaying chronic nonactive microscopic granulomas. The fish size (P = 0.30) and weight (P = 0.12) were not statistically different among groups, nor were SDMA values (P = 0.22). However, brook trout without microscopic renal lesions tended to have lower SDMA values (no lesions: mean = 24.9 µg/dL; lesions: mean = 31.4 µg/dL). The reference interval (90% confidence interval [90% CI]) for SDMA concentration in brook trout ranged between 10.0 µg/dL (90% CI: 5.4-14.7) and 39.8 µg/dL (90% CI: 34.8-43.9). These values were higher than those previously reported in other vertebrate species. Further research is needed to evaluate the use of SDMA as a marker of renal function in fishes.

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

Chronic kidney disease (CKD) is a common cause of morbidity and mortality in captive tigers (Panthera tigris). Blood creatinine (Cr) and blood urea nitrogen measurements are inexpensive and common biomarkers used to evaluate renal function. However, several limitations have been reported regarding their sensitivity and interindividual variability. Symmetric dimethylarginine (SDMA) has been suggested to be a more sensitive biomarker that is less affected by extrarenal factors and has a strong correlation with glomerular filtration rate and blood Cr in several species. This project aimed to identify the usefulness of SDMA as an endogenous marker of kidney function in captive tigers. The hypothesis of this study is that increased circulating SDMA is positively associated with increased blood Cr. SDMA and Cr were measured in 65 banked samples (serum and plasma) from 30 individual captive tigers. The samples were collected over a 38-y period and stored at -21°C. SDMA and Cr concentrations were determined using the commercially available SDMA test and enzymatic colorimetric methods, respectively. SDMA had a significant positive association with Cr (for every 1 unit increase of log SDMA, Cr increased by 82%, P = 0.0002). Age and subspecies influenced Cr but not SDMA concentrations. In one animal, blood SDMA increased above the ZIMS reported range. approximately 3.6 mo before Cr increased. SDMA is currently indicated for the diagnosis of CKD in domestic felids and seems also promising in nondomestic felids. Further prospective studies might improve the understanding of the performance of this biomarker.

Quantitative Analysis of l-Arginine, Dimethylated Arginine Derivatives, l-Citrulline, and Dimethylamine in Human Serum Using Liquid Chromatography-Mass Spectrometric Method

ABSTRACT

Nitric oxide (NO) is a small molecule involved in the regulation of many physiological processes. It plays a crucial role in the regulation of nervous system, immune and inflammatory responses, and blood flow. NO is synthesized by nitric oxide synthase (NOS) during two-step oxidation of l-arginine to l-citrulline. Intermediates and derivatives of NO metabolism, such as l-arginine, l-citrulline, asymmetrical dimethylarginine (ADMA), symmetrical dimethylarginine (SDMA), and dimethylamine (DMA), are investigated as potential biomarkers. In this article, we present a novel analytical method that allowed for simultaneous analysis of l-arginine, ADMA, SDMA, l-citrulline, and DMA, in a single-step extraction and derivatization using benzoyl chloride. In brief, aliquots of serum were mixed with internal standard solution mixture (50 µM D6-DMA, 20 µM D7-ADMA, and 100 µM D7-arginine) and 0.025 M borate buffer, pH 9.2 (10:1:5). The derivatization process was performed at 25 °C for 5 min using 10% benzoyl chloride. A reverse phase column was used for chromatographic separation. Quantitation was performed using following ions (m/z): 279.1457, 286.1749, 307.1717, 314.2076, 280.1297, 150.0919, and 156.1113 for l-arginine, D7-arginine, ADMA, SDMA, D7-ADMA, l-citrulline, DMA, and D6-DMA, respectively. The method was validated, and its assay linearity, accuracy and precision, recovery, and limits of detection (1.7 µM l-arginine, 0.03 µM ADMA, 0.02 µM SDMA, 0.36 µM l-citrulline, 0.06 µM DMA) and quantification (3.2 µM l-arginine, 0.08 µM ADMA, 0.05 µM SDMA, 1.08 µM l-citrulline, 0.19 µM DMA) were determined. The method is sensitive, reliable, repeatable, and reproducible. It can be applied in the routine clinical/diagnostic laboratory.

GRAPHICAL ABSTRACT