Biological variation of major gut-derived uremic toxins in the serum of healthy adult cats

Impaired renal transporter gene expression and uremic toxin excretion as aging hallmarks in cats with naturally occurring chronic kidney disease

Aging leads to nephron senescence and chronic kidney disease (CKD). In cats, indoxyl sulfate (IxS) has been previously quantified and associated with CKD, and little is known about tubular transporters. Two cohorts of cats aged 6 to 21 years were enrolled. Cohort 1 included 41 colony cats with 28 control and 13 CKD cats. Cohort 2 had 30 privately-owned cats with 10 control and 20 CKD cats. In cohort 1, serum concentrations of IxS, trimethylamine N-oxide (TMAO), p-cresol sulfate (PCS), and phenyl sulfate were higher in CKD vs. control cats (all P<0.05). This observation was independently validated in cohort 2. Renal cortical and medullar tissues were collected from a third cohort of cats euthanized for humane reasons unrelated to the study. We provided the evidence that renal tubular transporter genes, OAT1, OAT4, OATP4C1, and ABCC2, but not OAT3, were expressed in the kidneys of cats, and their expressions were downregulated in CKD (all FDR<0.1). Cats and humans share 90.9%, 77.8%, and 82.5% identities in OAT1, OATP4C1, and ABCC2 proteins, respectively. In healthy cats, circulating TMAO and IxS are significantly correlated with age. Our study reveals impaired uremic toxin secretion and tubular transporter expression in cats with CKD.

The Effect of Renaltec on Serum Uremic Toxins in Cats with Experimentally Induced Chronic Kidney Disease

Serum uremic toxins markedly increase in cats with chronic kidney disease (CKD) and have deleterious consequences. Renaltec is an oral adsorbent that binds uremic toxin precursors in the gut. In this prospective cohort study utilizing 13 purpose-bred cats with remnant kidney model-induced CKD (12 IRIS Stage 2, 1 IRIS Stage 3) eating a standardized renal diet, we aimed to assess the effect of Renaltec administration on serum indoxyl sulfate (IDS) and p-cresol sulfate (pCS) concentrations. Cats were sequentially treated with standard of care for 56 days, 500 mg Renaltec orally once daily for 56 days, and then three months later, 500 mg Renaltec orally twice daily for 56 days. Serum IDS and pCS concentrations were measured 28 and 56 days after the administration of Renaltec. Blood pressure and kidney function were measured before and 56 days after the administration of Renaltec. Significant decreases in serum IDS and pCS concentrations were observed for both once- and twice-daily dosing, particularly during the first 28 days of administration. More cats with BID dosing had clinically significant reductions in serum IDS and pCS concentrations than with SID dosing. Renaltec can reduce the serum concentrations of deleterious gut-derived uremic toxins in cats with CKD.

The Effect of Dietary Protein Concentration on the Fecal Microbiome and Serum Concentrations of Gut-Derived Uremic Toxins in Healthy Adult Cats

The purpose of this study was to evaluate the effect of feeding healthy adult cats with foods containing variable protein concentrations on the fecal microbiome and serum concentrations of the gut-derived uremic toxins indoxyl sulfate, p-cresol sulfate (pCS), and trimethylamine-n-oxide. Twenty healthy young adult cats were randomized into two groups and fed either a low-protein diet (LPD; 7.4 g/100 kcal ME) or a high-protein diet (HPD; 11.0 g/100 kcal ME) for a 12-week period. Serum uremic toxin concentrations were measured via liquid chromatography tandem mass spectrometry, and the fecal microbiome was characterized using shallow sequence shotgun metagenomics. Cats that consumed the HPD had higher pCS concentrations at 8 weeks (p = 0.028) when compared to baseline. After 12 weeks, cats fed the HPD had higher fecal alpha diversity indices at both the taxonomic and functional levels and lower fecal Bifidobacterium relative abundance compared to those cats fed the LPD. In conclusion, a change in diet and dietary protein concentration shifted the fecal microbial community and microbial function. Feeding cats a high amount of protein increased serum concentrations of the uremic toxin pCS; however, the effect was short-lived.

Short-term postprandial changes in select serum biochemistry analytes in healthy adult cats

OBJECTIVES

The aim of this study was to evaluate the magnitude, duration and significance of postprandial changes to select serum biochemistry analytes in healthy adult cats in the 12 h period after a meal.

METHODS

Nine adult research cats fed commercial food were included. Blood samples were taken after a 12 h fast (hour 0), cats were offered and consumed a meal, and postprandial samples were obtained over a 12 h period starting 2 h after the baseline blood draw (hours 2, 4, 6, 8, 10 and 12). Serum samples were run on a Roche Cobas C501 chemistry analyzer to obtain concentrations of blood urea nitrogen (BUN), creatinine, phosphorus, total calcium, bicarbonate, cholesterol, magnesium, sodium, potassium and chloride. Serum concentrations of each analyte at hours 2, 4, 6, 8, 10 and 12 were compared with concentrations prior to feeding.

RESULTS

Serum concentration for at least one postprandial time point was different from baseline fasted concentration for BUN (hour 2, P = 0.006; hour 4, P <0.0001; hour 6, P = 0.002; hour 8, P = 0.026), phosphorus (hour 2, P = 0.019), bicarbonate (hours 2, 4, 6, 8 and 10; all P <0.01), glucose (hour 12, P = 0.014), magnesium (hour 10, P = 0.029) and chloride (hour 2, P = 0.026; hour 4, P = 0.044; hour 12, P = 0.019). No significant difference was seen at any postprandial sampling point compared with baseline for serum creatinine, total calcium, cholesterol, sodium or potassium concentrations.

CONCLUSIONS AND RELEVANCE

Short-term postprandial serum concentrations of BUN, phosphorus, bicarbonate and chloride differed at multiple time points within a 12 h period compared with the fasted state at baseline, with most values remaining within the reference intervals. Veterinarians should be aware of these alterations, though they are unlikely to be mistaken for pathological disease states in healthy adult cats.

Biological variation of major gut-derived uremic toxins in the serum of healthy adult cats

Background

Biological variation of serum indoxyl sulfate (IS), p‐cresol sulfate (pCS), and trimethylamine‐n‐oxide (TMAO) concentrations in cats is unknown.

Objectives

To determine short‐ and medium‐term biological variation, index of individuality (II), and reference change values for serum IS, pCS, and TMAO concentrations in healthy adult cats. To determine the effect of feeding on serum concentrations.

Animals

Twelve healthy adult cats.

Methods

Prospective, cohort study. Seven serum samples over a 12‐hour period (short‐term) and 5 serum samples over a 19‐day period (medium‐term) were collected. Serum concentrations of total IS, pCS, and TMAO were measured every 2 hours in a 12‐hour period (hours 0‐12) after a meal in 9 cats and compared to concentrations in a nonfed state.

Results

For IS, the II was high using short‐term (1.96) and low using medium‐term (0.65) biological variation estimates. Individuality was intermediate for pCS (short‐term, 0.98; medium‐term, 1.17) and TMAO (short‐term, 1.47; medium‐term, 0.83). Serum IS, pCS, and TMAO concentrations were significantly lower in a fed state compared to a nonfed state at hours 4, 6, 8, and 12; at hours 4 and 6; and at hours 2, 4, 6, 8, 10, 12, respectively.

Conclusion and Clinical Importance

Population‐based reference intervals with reference to the subject‐based interval can be used to monitor serum pCS and TMAO concentrations. For IS, a subject‐based and a population‐based reference interval is best for short‐term and medium‐term monitoring, respectively. To compare serial measurements, it would be prudent to collect samples at the same time of day and consistently in either a fed or nonfed state.