Amino acid status in dogs with protein-losing nephropathy

Metabolic implications of amino acid metabolites in chronic kidney disease progression: a metabolomics analysis using OPLS-DA and MBRole2.0 database

BACKGROUND

As chronic kidney disease (CKD) progresses, metabolites undergo diverse transformations. Nevertheless, the impact of these metabolic changes on the etiology, progression, and prognosis of CKD remains uncertain. Our objective is to conduct a metabolomics analysis to scrutinize metabolites and identify significant metabolic pathways implicated in CKD progression, thereby pinpointing potential therapeutic targets for CKD management.

METHODS

We recruited 145 patients with CKD and determined their mGFR by measuring the plasma iohexol clearance, whereupon we partitioned them into four groups based on their mGFR values. Non-targeted metabolomics analysis was conducted using UPLC-MS/MS assays. Differential metabolites were identified via one-way ANOVA, PCA, PLS-DA, and OPLS-DA analyses employing the MetaboAnalyst 5.0 platform. Ultimately, we performed differential metabolite pathway enrichment analysis, using both the MetaboAnalyst 5.0 platform and the MBRole2.0 database.

RESULTS

According to the findings of the MBRole2.0 and MetaboAnalyst 5.0 enrichment analysis, six amino acid metabolism pathways were discovered to have significant roles in the progression of CKD, with the glycine, serine, and threonine metabolism pathway being the most prominent. The latter enriched 14 differential metabolites, of which six decreased while two increased concomitantly with renal function deterioration.

CONCLUSIONS

The metabolic analysis unveiled that glycine, serine, and threonine metabolism plays a pivotal role in the progression of CKD. Specifically, glycine was found to increase while serine decreased with the deterioration of CKD.

Essential and Non-Essential Amino Acids in Dogs at Different Stages of Chronic Kidney Disease

Abnormalities of serum amino acid profile, mostly characterized by a reduction in essential amino acids (EAAs) and an increase in non-essential amino acids (NEAAs), have been documented in human chronic kidney diseases (CKD). Amino acid disorders have been associated with CKD complications, such as metabolic acidosis and malnutrition. The aim of the present study was to evaluate EAAs and NEAAs in dogs affected by CKD at different IRIS stages, with particular reference to calcium−phosphate abnormalities, metabolic acidosis, and protein-energy wasting syndrome (PEW). Serum EAAs (L-histidine, L-isoleucine, L-leucine, L-lysine, methionine, L-phenylalanine, L-threonine, tryptophan, L-valine, and L-arginine) and serum NEAAs (L-alanine, L-aspartic acid, L-cysteine, L-glutamic acid, glycine, proline, L-serine, and L-tyrosine) were analyzed with HPLC in a group of dogs with CKD (n = 62), and in a group of healthy dogs (n = 25). CKD dogs showed significantly lower serum levels of histidine (p < 0.000), isoleucine (p < 0.000), tryptophan (p < 0.000), alanine (p = 0.013), cysteine (p < 0.000), and serine (p = 0.002), and significantly higher levels of proline (p < 0.000), leucine (p = 0.001), lysine (p < 0.000), valine (p < 0.000), arginine (p = 0.002), glutamic acid (p = 0.002), and glycine (p = 0.010) compared to healthy dogs. Dogs with abnormal calcium x phosphate values showed significantly higher levels of cysteine (p = 0.003), and lower levels of tryptophan (p = 0.025) compared to CKD dogs with normal CaxP. Dogs with metabolic acidosis showed significantly higher levels of phenylalanine (p = 0.035) and leucine (p = 0.034) compared to CKD dogs without metabolic acidosis. Dogs with PEW showed significantly lower levels for most of amino acids. In PEW dogs, the median distribution of both EAAs (p = 0.000) and NEAAs (p = 0.001) was significantly lower. The serum pattern of both EAAs and NEAAs was significantly different in CKD dogs compared to healthy dogs, although no association with the progression of the IRIS stage was found.

Serum and Fecal Amino Acid Profiles in Cats with Chronic Kidney Disease

The purpose of the study was to quantify serum and fecal amino acids (AA) in cats with chronic kidney disease (CKD) and compare to healthy cats. Thirty-five cats with International Renal Interest Society Stage 1–4 CKD and 16 healthy mature adult and senior client-owned cats were included in this prospective cross-sectional study. Sera were analyzed for 25 AA concentrations using an ion exchange chromatography AA analyzer with post column ninhydrin derivatization. Voided fecal samples were analyzed for 22 AA concentrations using liquid chromatography with tandem mass spectrometry. CKD cats had lower serum concentrations of phenylalanine (mean difference ± standard error of the mean: 12.7 ± 4.3 µM; p = 0.03), threonine (29.6 ± 9.2 µM; p = 0.03), tryptophan (18.4 ± 5.4 µM; p = 0.005), serine (29.8 ± 12.6 µM; p = 0.03), and tyrosine (11.6 ± 3.8 µM; p = 0.01) and higher serum concentrations of aspartic acid (4.7 ± 2.0 µM; p = 0.01), β-alanine (3.4 ± 1.2 µM; p = 0.01), citrulline (5.7 ± 1.6 µM; p = 0.01), and taurine (109.9 ± 29.6 µM; p = 0.01) when compared to healthy cats. Fecal AA concentrations did not differ between healthy cats and CKD cats. 3-Methylhistidine-to-creatinine did not differ between healthy cats with and without muscle loss. Cats with CKD IRIS Stages 1–4 have a deranged serum amino acid profile compared to healthy cats.

Evaluation of Serum and Urine Amino Acids in Dogs with Chronic Kidney Disease and Healthy Dogs Fed a Renal Diet

This observational study aimed to evaluate serum and urinary amino acid (AA) concentrations in healthy dogs and dogs with chronic kidney disease (CKD) fed a commercial therapeutic renal diet with reduced protein and phosphorus levels. Ten dogs with CKD stages 3 or 4 composed the study group and received the renal diet for 180 days (RG T180). A control group (CG T30) composed of seven healthy dogs was fed a renal diet for 30 days. When comparing serum AA between RG T180 and CG T30, histidine, isoleucine, leucine, lysine, phenylalanine, tryptophan, cysteine, citrulline, ornithine, taurine, branched-chain amino acids (BCAA), and total essential amino acids (EAA) were higher in RG T180. Meanwhile, arginine, asparagine, aspartate, glutamine, serine, and tyrosine were higher in CG T30. Serum phenylalanine, tryptophan, and hydroxyproline were higher in RG T0 (dogs with CKD before consuming a renal diet) when compared to RG T180. In addition, the serum ratios of arginine/citrulline, tyrosine/phenylalanine, and serine/glycine were higher in CG T30 than in RG T180. Concerning urinary AA concentrations in CKD dogs, isoleucine, phenylalanine, tryptophan, aspartate, cysteine, and BCAA were higher in RG T180. In urine, the total EAA/total non-essential AA ratio in RG T180 was higher than in CG T30 as well as tyrosine/phenylalanine ratio higher in CG T30. In conclusion, the combination of renal diet and conservative treatment over 6 months in dogs with CKD stages 3 or 4 affected the AAs metabolism when compared to healthy adult dogs.

Flaxseed Increases Animal Lifespan and Reduces Ovarian Cancer Severity by Toxically Augmenting One-Carbon Metabolism

We used an LC-MS/MS metabolomics approach to investigate one-carbon metabolism in the plasma of flaxseed-fed White Leghorn laying hens (aged 3.5 years). In our study, dietary flaxseed (via the activity of a vitamin B6 antagonist known as "1-amino d-proline") induced at least 15-fold elevated plasma cystathionine. Surprisingly, plasma homocysteine (Hcy) was stable in flaxseed-fed hens despite such highly elevated cystathionine. To explain stable Hcy, our data suggest accelerated Hcy remethylation via BHMT and MS-B12. Also supporting accelerated Hcy remethylation, we observed elevated S-adenosylmethionine (SAM), an elevated SAM:SAH ratio, and elevated methylthioadenosine (MTA), in flaxseed-fed hens. These results suggest that flaxseed increases SAM biosynthesis and possibly increases polyamine biosynthesis. The following endpoint phenotypes were observed in hens consuming flaxseed: decreased physiological aging, increased empirical lifespan, 9-14% reduced body mass, and improved liver function. Overall, we suggest that flaxseed can protect women from ovarian tumor metastasis by decreasing omental adiposity. We also propose that flaxseed protects cancer patients from cancer-associated cachexia by enhancing liver function.

Approach to the Diagnosis of Hepatocutaneous Syndrome in Dogs: A Retrospective Study and Literature Review

Superficial necrolytic dermatitis (SND) is a rare and often fatal disease in dogs that has been associated with pancreatic neuroendocrine neoplasia (SND/EN) and hepatocutaneous syndrome (SND/HCS). Although various combinations of diagnostics have been used to differentiate these two causes of SND, there are currently no data on which combination would enable the most timely and noninvasive way to diagnose HCS. Medical records were reviewed retrospectively (2004-2018) for dogs with SND/HCS (n = 24) and SND/EN (n = 1). These data were compared with cases found by review of the literature of dogs with SND/HCS (n = 105) and SND/EN (n = 13). The most consistent findings with SND were dermatological lesions affecting paw pads or mucocutaneous junctions (143/143, 100%) and marked plasma hypoaminoacidemia (58/58, 100%). On ultrasound, a honeycomb liver was seen in 62/63 (98%) dogs with SND/HCS but none with SND/EN. Six out of 23 (26%) dogs in the retrospective study with SND/HCS had marked keratinocyte apoptosis, a finding that was associated with diabetes mellitus. This study suggests that in dogs with characteristic skin lesions, an amino acid profile permits a noninvasive diagnosis of SND. An abdominal ultrasound can then assist in the differentiation of SND/HCS and SND/EN.

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.

Impact of storage temperature, storage duration, and deproteinization on plasma amino acid concentrations in dogs

Reliability of canine plasma amino acid analysis depends on sample stability which can be influenced by pre-analytical handling techniques, storage temperature, storage time, and deproteinization status. Extrapolating data to dogs from research in other species is limited given discordant methodology and interspecies differences. The present study investigated the effects of deproteinization status (non-deproteinized or deproteinized) and storage temperature (at -20 °C or - 80 °C) on the concentration of 22 canine plasma amino acids during a 300-day storage period. Storage time had a significant effect (p < 0.05) of overall declining concentration of most amino acids. Compared to non-deproteinized samples, deproteinization contributed to overall higher concentrations of cyst(e)ine and glutamic acid, and consistently modified the effect of storage time and temperature on cyst(e)ine, glutamic acid, and glutamine. Compared to -20 °C, storage at -80 °C contributed to a higher concentration of cyst(e)ine and glutamic acid, and modified the effect of storage time on arginine, glutamic acid, glutamine, and tryptophan. Storage time had a consistent, significant effect on amino acid concentrations in canine plasma samples. Although sample deproteinization and low storage temperature modified the effect of storage time, these interactions were variable among analyzed amino acids. Therefore, timely sample analysis is recommended. If delayed sample analysis is inevitable, deproteinization should be performed prior to sample banking to preserve amino acid stability.

High serum creatinine concentration is associated with metabolic perturbations in dogs

BACKGROUND

The kidneys have many essential metabolic functions, and metabolic disturbances during decreased renal function have not been studied extensively.

OBJECTIVES

To identify metabolic changes in blood samples with increased serum creatinine concentration, indicating decreased glomerular filtration.

ANIMALS

Clinical samples analyzed using a nuclear magnetic resonance (NMR) based metabolomics platform. The case group consisted of 23 samples with serum creatinine concentration >125 μmol/L, and the control group of 873 samples with serum creatinine concentration within the reference interval.

METHODS

Biomarker association with increased serum creatinine concentration was evaluated utilizing 3 statistical approaches: Wilcoxon rank-sum test, logistic regression analysis (false discovery rate (FDR)-corrected P-values), and random forest classification. Medians of the biomarkers were compared to reference intervals. A heatmap and box plots were used to represent the differences.

RESULTS

All 3 statistical approaches identified similar analytes associated with increased serum creatinine concentrations. The percentages of citrate, tyrosine, branched-chain amino acids, valine, leucine, albumin, linoleic acid and the ratio of phenylalanine to tyrosine differed significantly using all statistical approaches, acetate differed using the Wilcoxon test and random forest, docosapentaenoic acid percentage only using logistic regression (P < .05), and alanine only using random forest.

CONCLUSIONS AND CLINICAL IMPORTANCE

We identified several metabolic changes associated with increased serum creatinine concentrations, including prospective diagnostic markers and therapeutic targets. Further research is needed to verify the association of these changes with the clinical state of the dog. The NMR metabolomics test is a promising tool for improving diagnostic testing and management of renal diseases in dogs.

Association between vitamin D metabolites, vitamin D binding protein, and proteinuria in dogs

BACKGROUND

Proteinuria has been associated with progression of renal disease and increased morbidity and mortality in dogs and people. In people, proteinuria also has been associated with hypovitaminosis D. Little is known about the relationship between vitamin D metabolism and proteinuria in dogs.

OBJECTIVES

To further elucidate vitamin D status in dogs with protein-losing nephropathy (PLN) and minimal to no azotemia. We hypothesized that vitamin D metabolites would be lower in dogs with PLN compared to healthy dogs.

ANIMALS

Twenty-three client-owned adult dogs with PLN and 10 healthy control dogs.

METHODS

Serum 25-hydroxyvitamin D (25[OH]D), 1,25-dihydroxyvitamin D (1,25[OH]₂ D), 24,25-dihydroxyvitamin D (24,25[OH]₂ D), serum vitamin D binding protein (VDBP), and urine 25(OH)D concentrations were measured.

RESULTS

Compared to healthy dogs, dogs with PLN had lower concentrations of all vitamin D metabolites (P < .01). Correlations (rho; 95% confidence interval [CI]) in dogs with PLN are reported. Serum 25(OH)D and 24,25(OH)₂ D concentrations were positively correlated with albumin (r = 0.47; 0.07-0.74), and 24,25(OH)₂ D was negatively correlated with urine protein-to-creatinine ratio (UPC; r = -0.54; -0.78 to -0.16). Urine 25(OH)D-to-creatinine ratio was negatively correlated with serum albumin concentration (r = -0.77; -0.91 to -0.50) and positively correlated with UPC (r = 0.79; 0.53-0.91). Serum VDBP concentration was positively correlated with serum albumin concentration (r = 0.53; 0.05-0.81).

CONCLUSIONS AND CLINICAL IMPORTANCE

Dogs with PLN have decreased serum concentrations of vitamin D metabolites. Urine 25(OH)D-to-creatinine ratio and UPC are correlated in PLN dogs. Future studies are needed to assess additional management strategies for dogs with PLN.

Amino acid status in dogs with protein-losing nephropathy

Background

Proteinuria in dogs with kidney disease can contribute to protein‐energy wasting and malnutrition. Little is known about amino acid (AA) status in dogs with protein‐losing nephropathy (PLN).

Objectives

The purpose of our study was to further elucidate AA status in PLN dogs, with the hypothesis that PLN dogs would have altered AA status as compared to healthy dogs.

Animals

Thirty client‐owned PLN dogs were compared to 10 healthy control dogs.

Methods

Prospective observational study. Dogs with PLN that were presented to the teaching hospital were enrolled. Plasma AA profiles were measured using an automated high‐performance liquid chromatography AA analyzer.

Results

Compared to control dogs, PLN dogs had significantly lower concentrations of leucine, threonine, histidine, glycine, proline, asparagine, tyrosine, o‐hydroxyproline, and serine, as well as sums of both essential and nonessential AA (P < .05). Dogs with PLN had significantly lower ratios of tyrosine‐to‐phenylalanine and glycine‐to‐serine (P < .05), and a significantly greater ratio of valine‐to‐glycine (P < .05).

Conclusions and Clinical Importance

Dogs with PLN have altered AA status compared to healthy dogs. These findings could have therapeutic implications in determining optimal management of PLN dogs, such as providing AA supplementation along with other standard treatment.