Chronic kidney disease in cats alters response of the plasma metabolome and fecal microbiome to dietary fiber

Insights into the gut-kidney axis and implications for chronic kidney disease management in cats and dogs

Chronic kidney disease (CKD) in cats and dogs presents significant clinical challenges, with emerging research highlighting the pivotal role of the gut-kidney axis in its pathogenesis and management. Gut dysbiosis, characterized by alterations in the gut microbiome composition and function, contributes to microbial dysmetabolism of key nutrients causing uremic toxin accumulation and disruptions in amino acid, bile acid and fatty acid profiles. These disturbances in turn exacerbate renal dysfunction and systemic inflammation. Recent research in veterinary medicine, particularly in cats, supports the gut microbiome and microbial-derived metabolites as novel therapeutic targets. Potential therapeutic strategies targeting the gut microbiome and microbial dysmetabolism, including dietary management, probiotics, adsorbents, and addressing constipation, offer promising avenues for intervention to restore metabolic balance and preserve renal function. This review highlights the microbial influence on renal health and focuses on potential therapeutic strategies available to veterinarians to optimize the management of CKD in cats and dogs.

Gut and Urinary Microbiota in Cats with Kidney Stones

Upper urinary tract urolithiasis is an emerging disease in cats, with 98% of kidney stones composed of calcium oxalate. In humans, disturbances in the intestinal and urinary microbiota are suspected to contribute to the formation of calcium oxalate stones. We hypothesized that similar mechanisms may be at play in cats. This study examines the intestinal and urinary microbiota of nine cats with kidney stones compared to nine healthy cats before, during, and after treatment with the antibiotic cefovecin, a cephalosporin. Initially, cats with kidney stones displayed a less diverse intestinal microbiota. Antibiotic treatment reduced microbiota diversity in both groups. The absence of specific intestinal bacteria could lead to a loss of the functions these bacteria perform, such as oxalate degradation, which may contribute to the formation of calcium oxalate stones. This study confirms the presence of a distinct urobiome in cats with kidney stones, characterized by greater richness and diversity compared to healthy cats. These findings highlight the potential of microbiota modulation as a strategy to prevent renal lithiasis in cats.

Description of the fasted serum metabolomic signature of lean and obese cats at maintenance and of obese cats under energy restriction

This study aimed to investigate the serum metabolomic profile of obese and lean cats as well as obese cats before and after energy restriction for weight loss. Thirty cats, 16 obese (body condition score 8 to 9/9) and 14 lean (body condition score 4 to 5/9), were fed a veterinary weight loss food during a 4-week period of weight maintenance (L-MAINT and O-MAINT). The 16 obese cats were then energy restricted by a 60% energy intake reduction with the same food for a 10-week period (O-RESTRICT). Fasted serum metabolites were measured using nuclear magnetic resonance and direct infusion mass spectrometry after the maintenance period for L-MAINT and O-MAINT cats and after the energy restriction period for O-RESTRICT and compared between groups using a two-sided t-test. Obese cats lost 672 g ± 303 g over the 10-week restriction period, representing a weight loss rate of 0.94 ± 0.28% per week. Glycine, l-alanine, l-histidine, l-glutamine, 2-hydroxybutyrate, isobutryric acid, citric acid, creatine, and methanol were greater in O-RESTRICT compared to O-MAINT. There was a greater concentration of long-chain acylcarnitines in O-RESTRICT compared to both O-MAINT and L-MAINT, and greater total amino acids compared to O-MAINT. Glycerol and 3-hydroxybutyric acid were greater in O-MAINT compared to L-MAINT, as were several lysophosphatidylcholines. Thus, energy restriction resulted in increased dispensable amino acids in feline serum which could indicate alterations in amino acid partitioning. An increase in lipolysis was not evident, though greater circulating acylcarnitines were observed, suggesting that fatty acid oxidation rates may have been greater under calorie restriction. More research is needed to elucidate energy metabolism and substrate utilization, specifically fatty acid oxidation and methyl status, during energy restriction in strict carnivorous cats to optimize weight loss.

A pilot study of alterations of the gut microbiome in canine chronic kidney disease

Introduction

Gut dysbiosis has been noted in humans and animals with chronic kidney disease (CKD). However, little is known about the gut microbiome in canine patients with CKD. This study aimed to analyze and compare the gut microbiome profiles of healthy and CKD dogs, including differences in the gut microbiome between each CKD stage.

Methods

The study was conducted on 29 client-owned dogs who underwent physical examination, complete blood count (CBC), serum biochemistry, and urinalysis. The gut microbiome profile of healthy dogs (n = 10) and dogs with CKD (n = 19) was analyzed employing 16S rRNA sequencing.

Results

Significant differences were seen in the composition of the gut microbiome, with increased operational taxonomic units from the phylum Proteobacteria (p = 0.035), family Enterobacteriaceae (p < 0.001), and genus Enterococcus (p = 0.002) in dogs with CKD, and a decrease in the genus Ruminococcus (p = 0.007). Furthermore, an increase in both the progression of CKD and abundance of genus Klebsiella (Jonckheere-Terpstra test statistic value (JT) = 2.852, p = 0.004) and Clostridium (JT = 2.018, p = 0.044) was observed.

Discussion

Our study demonstrated that in dogs with CKD, the composition of the gut microbiome varied depending on the stage of CKD. Alterations in gut microbiome composition observed in CKD patients are characterized by an increase in proteolytic bacteria and a decrease in saccharolytic bacteria. These findings suggest specific gut microbiota could be targeted for clinical management of uremic dogs with CKD.

Adding a polyphenol-rich fiber bundle to food impacts the gastrointestinal microbiome and metabolome in dogs

Introduction

Pet foods fortified with fermentable fibers are often indicated for dogs with gastrointestinal conditions to improve gut health through the production of beneficial post-biotics by the pet's microbiome.

Methods

To evaluate the therapeutic underpinnings of pre-biotic fiber enrichment, we compared the fecal microbiome, the fecal metabolome, and the serum metabolome of 39 adult dogs with well-managed chronic gastroenteritis/enteritis (CGE) and healthy matched controls. The foods tested included a test food (TF1) containing a novel pre-biotic fiber bundle, a control food (CF) lacking the fiber bundle, and a commercially available therapeutic food (TF2) indicated for managing fiber-responsive conditions. In this crossover study, all dogs consumed CF for a 4-week wash-in period, were randomized to either TF1 or TF2 and fed for 4 weeks, were fed CF for a 4-week washout period, and then received the other test food for 4 weeks.

Results

Meaningful differences were not observed between the healthy and CGE dogs in response to the pre-biotic fiber bundle relative to CF. Both TF1 and TF2 improved stool scores compared to CF. TF1-fed dogs showed reduced body weight and fecal ash content compared to either CF or TF2, while stools of TF2-fed dogs showed higher pH and lower moisture content vs. TF1. TF1 consumption also resulted in unique fecal and systemic metabolic signatures compared to CF and TF2. TF1-fed dogs showed suppressed signals of fecal bacterial putrefactive metabolism compared to either CF or TF2 and increased saccharolytic signatures compared to TF2. A functional analysis of fecal tryptophan metabolism indicated reductions in fecal kynurenine and indole pathway metabolites with TF1. Among the three foods, TF1 uniquely increased fecal polyphenols and the resulting post-biotics. Compared to CF, consumption of TF1 largely reduced fecal levels of endocannabinoid-like metabolites and sphingolipids while increasing both fecal and circulating polyunsaturated fatty acid profiles, suggesting that TF1 may have modulated gastrointestinal inflammation and motility. Stools of TF1-fed dogs showed reductions in phospholipid profiles, suggesting fiber-dependent changes to colonic mucosal structure.

Discussion

These findings indicate that the use of a specific pre-biotic fiber bundle may be beneficial in healthy dogs and in dogs with CGE.

Serum Metabolites Characterization Produced by Cats CKD Affected, at the 1 and 2 Stages, before and after Renal Diet

Utilizing metabolomics, a tool for measuring and characterizing low-molecular-weight substances (LMWs), to identify eventual changes in response to dietary intervention is novel in cats with chronic kidney disease (CKD), a condition characterized by retention of uremic solutes. This study aims to assess the serum metabolomic profile of cats in early stages of CKD and to compare the serum metabolomic of CKD cats after 60 days of a renal diet to evaluate the effect of dietary intervention on these metabolites. Twenty-five domestic cats were included in the study. Fifteen cats with CKD stages 1 (n = 6) and 2 (n = 9) according to the International Renal Interest Society (IRIS) were included in the renal groups, and a control group consisting of 10 cats was included. All animals were enrolled on a maintenance diet for 30 days before the experimental period. The metabolomics analysis was performed by gas chromatography-mass spectrometry (GC-MS). Partial least squares discriminant analysis (PLS-DA) was performed on Metaboanalyst 4.0 software. Forty-three metabolites were identified. Citric acid and monostearin were altered in the CKD2 group when compared to CKD1 and the control group at T0. A total of seven serum metabolites differed after 60 days of the renal diet: glycine, fructose, glutamic acid, arachidonic acid, stearic acid, creatinine, and urea. Changes were seen in the serum metabolomic profile after 60 days of the renal diet, and some of the metabolites that changed in response to the diet have beneficial effects on health. Overall, metabolomics markers have the potential to identify early stages of CKD, providing insights into the possible pathophysiologic processes that contribute to the development and progression of CKD.

Dietary enrichment of resistant starches or fibers differentially alter the feline fecal microbiome and metabolite profile

BACKGROUND

Cats are strict carnivores but possess a complex gastrointestinal (GI) microbial community that actively ferments dietary substrates that are not digested and reach the colon. The GI microbiota responses to dietary inclusion of resistant starches versus fibers have not been tested in cats. Thus, our objective was to evaluate the effects of diets enriched in resistant starch or fibers on the fecal characteristics, microbiome, and metabolite profiles of cats. Twelve healthy adult domestic shorthair cats (age = 9.6 ± 4.0 year; body weight = 3.9 ± 1.0 kg) were used in a replicated 3 × 3 Latin square design to test diets that were enriched with: (1) resistant starch (ERS), (2) a fiber-prebiotic-probiotic blend (FPPB), or (3) a fiber-prebiotic-probiotic blend + immune-modulating ingredients (iFPPB). In each 28-day period, 22 days of diet adaptation was followed by fecal and blood sample collection. Fecal samples were used for shotgun metagenomic sequencing. In addition, fecal and blood metabolite measurements and white blood cell stimulation was performed to assess immune function.

RESULTS

A total of 1690 bacterial species were identified, with 259 species differing between fiber-rich and ERS treatments. In comparison with fiber-rich treatments that increased diversity and promoted Firmicutes and Bacteroidetes populations, resistant starch reduced microbial diversity and fecal pH, led to a bloom in Actinobacteria, and modified Kyoto Encyclopedia of Genes and Genomes orthology (KO) terms pertaining to starch and sucrose metabolism, fatty acid biosynthesis and metabolism, epithelial cell signaling, among others. Resistant starch also differentially modified fecal metabolite concentrations with relevance to GI and overall host health (increased butyrate; decreased propionate and protein catabolites - branched-chain fatty acids; phenols and indoles; ammonia) and reduced blood cholesterol, which correlated strongly with microbial taxa and KO terms, and allowed for a high predictive efficiency of diet groups by random forest analysis.

CONCLUSION

Even though domestic cats and other carnivores evolved by eating low-carbohydrate diets rich in protein and fat, our results demonstrate that the feline microbiome and metabolite profiles are highly responsive to dietary change and in directions that are predictable.

Dietary Betaine Interacts with Very Long Chain n-3 Polyunsaturated Fatty Acids to Influence Fat Metabolism and Circulating Single Carbon Status in the Cat

Simple Summary

The domestic cat can metabolize and thrive on a range of intakes of different dietary polyunsaturated fatty acids (PUFA). However, changes in the intake of PUFA have relatively unknown effects on concentrations of other fatty acids and metabolites. Similarly, the effect of increasing dietary betaine (which is a single carbon donor) on circulating concentrations of metabolites and fatty acids is relatively unreported. As might be expected, increasing intake of specific dietary fatty acids resulted in an increased concentration of that fatty acid and moieties containing that fatty acid. Dietary betaine increased concentration of many compounds associated with single carbon metabolism (e.g., dimethyl glycine, sarcosine, methionine) and many PUFA such as the n-6 PUFA linoleic acid (LA) and arachidonic acid (ARA) and the n-3 fatty acids α-linolenic acid (αLA), and docosahexaenoic acid (DHA). Dietary betaine interacted with the addition of dietary fish oil to dampen diet-induced increase of ARA while potentiating the increase of circulating DHA occurring with increased DHA dietary intake. Dietary betaine and fish oil also combined to reduce the circulating concentration of the renal toxin 3-indoxyl sulfate, suggesting a positive effect on the gut microbiota. These data suggest a positive effect of a daily betaine intake which exceeds 60 mg per kg body weight. The data also support an added benefit of a combined EPA+DHA daily intake of greater than 26 mg/kg body weight as well as a daily intake of 75 mg/kg body weight of alpha linolenic acid.

Abstract

Six foods were used to evaluate the interaction of dietary betaine and n-3 PUFA in the cat. There was no ingredient added to the control food to specifically increase betaine or n-3 fatty acids. The experimental design was a 3 × 2 factorial (fatty acids were varied from the control food which had no added source of n-3 fatty acids, flax was included as a source of 18 carbon n-3, or menhaden fish oil as a source of EPA and DHA). Foods were then formulated using these three foods as a base with added betaine or without added betaine. Forty eight cats were used in this study. Equal numbers of cats were allotted by age and gender to each of the six dietary treatments. The cats were offered food amounts to maintain weight and consumed the food to which they were assigned for the length of the study (60 days). Metabolomics, selected circulating analytes and fatty acids were analyzed at the beginning and end of the feeding period. There was an increase in single carbon metabolites (betaine, dimethyl glycine, and methionine) with the consumption of dietary betaine. Betaine also increased the concentration of specific PUFA (ARA, αLA, DHA, and the sum of all circulating PUFA). The combination of dietary betaine and fish oil resulted in a reduction of circulating 3-indoxyl sulfate which suggests a renal benefit from their combined dietary presence.

Metabolomic changes in cats with renal disease and calcium oxalate uroliths

INTRODUCTION

There is a significant incidence of cats with renal disease (RD) and calcium oxalate (CaOx) kidney uroliths in domesticated cats. Foods which aid in the management of these diseases may be enhanced through understanding the underlying metabolomic changes.

OBJECTIVE

Assess the metabolomic profile with a view to identifying metabolomic targets which could aid in the management of renal disease and CaOx uroliths.

METHOD

This is a retrospective investigation of 42 cats: 19 healthy kidney controls, 11 with RD, and 12 that formed CaOx nephroliths. Cats were evaluated as adults (2 through 7 years) and at the end of life for plasma metabolomics, body composition, and markers of renal dysfunction. Kidney sections were assessed by Pizzolato stain at the end of life for detection of CaOx crystals. CaOx stone presence was also assessed by analysis of stones removed from the kidney at the end of life.

RESULTS

There were 791 metabolites identified with 91 having significant (p < 0.05, q < 0.1) changes between groups. Many changes in metabolite concentrations could be explained by the loss of renal function being most acute in the cats with RD while the cats with CaOx stones were intermediate between control and RD (e.g., urea, creatinine, pseudouridine, dimethylarginines). However, the concentrations of some metabolites differentiated RD from CaOx stone forming cats. These were either increased in the RD cats (e.g., cystathionine, dodecanedioate, 3-(3-amino-3-carboxypropyl) uridine, 5-methyl-2'-deoxycytidine) or comparatively increased in the CaOx stone forming cats (phenylpyruvate, 4-hydroxyphenylpyruvate, alpha-ketobutyrate, retinal).

CONCLUSIONS

The metabolomic changes show specific metabolites which respond generally to both renal diseases while the metabolomic profile still differentiates cats with RD and cats with CaOx uroliths.

A Diet Supplemented with Polyphenols, Prebiotics and Omega-3 Fatty Acids Modulates the Intestinal Microbiota and Improves the Profile of Metabolites Linked with Anxiety in Dogs

Simple Summary

This study used a nutrition-based approach to examine the effects of foods supplemented with fish oil and a polyphenol blend (citrus pulp, carrot, and spinach) with or without added tomato pomace on anxiety-related biomarkers in dogs. First, all dogs consumed the same initial food, then either the control or test (with tomato pomace) foods, then the washout food, then switched over to the test or control foods, each for 30-day periods. Many more changes in plasma and fecal metabolites were observed when comparing the washout food with the control or test foods than when the control and test foods were compared. Plasma levels of several metabolites that were previously associated with anxiety disorders, including 4-ethylphenyl sulfate, were decreased with the control or test foods compared with the washout food. In addition, bacterial genera that are decreased in the feces of those with anxiety-like disorders were increased following the consumption of the control or test foods. Overall, these data indicate that foods supplemented with omega-3 fatty acids and selected fiber and polyphenol sources lead to beneficial changes in anxiety-related metabolites and gut bacteria.

Abstract

A nutrition-based approach was utilized to examine the effects of fish oil and a polyphenol blend (with or without tomato pomace) on the fecal microbiota and plasma/fecal metabolomes. Forty dogs, aged 5–14 years, were fed a washout food, then randomized to consume a control (fish oil and polyphenol blend without tomato pomace) or test (fish oil and polyphenol blend with tomato pomace) food, then the washout food, and crossed over to consume the test or control food; each for 30 days. Several metabolites differed when comparing consumption of the washout with either the control or test foods, but few changed significantly between the test and control foods. Plasma levels of 4-ethylphenyl sulfate (4-EPS), a metabolite associated with anxiety disorders, demonstrated the largest decrease between the washout food and the control/test foods. Plasma 4-EPS levels were also significantly lower after dogs ate the test food compared with the control food. Other plasma metabolites linked with anxiety disorders were decreased following consumption of the control/test foods. Significant increases in Blautia, Parabacteroides, and Odoribacter in the fecal microbiota correlated with decreases in 4-EPS when dogs ate the control/test foods. These data indicate that foods supplemented with polyphenols and omega-3 fatty acids can modulate the gut microbiota to improve the profile of anxiety-linked metabolites.

Feeding Fiber-Bound Polyphenol Ingredients at Different Levels Modulates Colonic Postbiotics to Improve Gut Health in Cats

Simple Summary

Food eaten by humans or companion animals is broken down by enzymes produced by the host and also by bacteria present in the large intestine of the host. Many of the compounds produced can have beneficial effects on the host’s health. Previous studies in dogs evaluated changes after they ate food containing a fiber bundle made of pecan shells, flax seed, and powders from cranberry, citrus, and beet. These studies showed that bacteria in the large intestine switched from digesting mainly protein to digesting mainly carbohydrates resulting in production of compounds with beneficial properties. The study presented here tested this fiber bundle in cats to see which compounds and/or bacteria in the feces changed. After cats consumed food containing the fiber bundle, several compounds associated with beneficial health effects increased, and some compounds that indicate the breakdown of protein decreased. In contrast, little change in fecal bacteria was observed following consumption of food with the fiber bundle. Overall, these findings indicate that, similar to the dog studies, bacteria in the large intestine of cats were able to digest the fiber bundle to make compounds that may contribute to host health and also shifted to digestion of carbohydrates instead of protein.

Abstract

Consumption of fiber in its different forms can result in positive health effects. Prior studies in dogs found that addition of a fiber bundle (composed of pecan shells, flax seed, and powders of cranberry, citrus, and beet) to food resulted in a shift in fecal bacterial metabolism from proteolysis to saccharolysis. The present study evaluated the changes in fecal metabolites and microbiota in healthy cats following the consumption of this fiber bundle. Following a 28-day pre-feed period, 56 healthy adult cats received food with none or one of three concentrations (0%, 1%, 2%, and 4%) of the fiber bundle for a 31-day period. In cats that consumed the 4% fiber bundle, levels of ammonium and fecal branched-chain fatty acids (BCFAs) decreased from baseline and compared with the other groups. Addition of any level of the fiber bundle resulted in increases in beneficial metabolites: polyphenols hesperidin, hesperetin, ponciretin, secoisolariciresinol diglucoside, secoisolariciresinol, and enterodiol. Little change in fecal microbiota was observed. Since higher levels of ammonia and BCFAs indicate putrefactive metabolism, the decreases in these with the 4% fiber bundle indicate a shift toward saccharolytic metabolism despite little change in the microbiota composition.

Urinary and plasma metabolome of farm mink (Neovison vison) after an intervention with raw or cooked poultry offal: a 1H NMR investigation

The introduction of high amounts of cooked poultry offal in mink feed has been associated with health problems in growing mink. Cooking mink feed is a convenient way of reducing microbiological activity, but it may have a negative effect on raw material quality and animal welfare. This study investigates growth and health of mink fed raw or cooked poultry offal and describes urinary and blood plasma metabolic changes related to the feeding. A total of 65 male mink were divided in three feeding groups, two fed cooked offal and one group fed raw offal, and the plasma and urine samples were collected at 3 time points during the growth. Both bio-fluids and feed samples were measured by ¹H NMR spectroscopy and resulted metabolomics data were analysed using univariate and multivariate statistical methods that revealed dominating effect of the mink growth stages and to a less extent the feeding regime. Metabolome differences in relation to low body mass index (BMI) and kidney lesions were observed in plasma. Disease and decrease in BMI was associated with high creatinine and dimethylglycine content in plasma. These molecules were also particularly indicative of the cooked feeds. Moreover, low urinary taurine levels were also associated with disease and low BMI. Individual mink appeared to show negative effects of the cooked feed diet, including impaired growth and gross pathological lesions involving the kidneys. This may be related to the absorption of essential metabolites such as amino acids and fats, necessary for mink growth, that are negatively impacted by the cooking process.

The Serum and Fecal Metabolomic Profiles of Growing Kittens Treated with Amoxicillin/Clavulanic Acid or Doxycycline

Simple Summary

This study investigated the impact of antibiotic treatment οn the serum and fecal metabolome (the collection of all small molecules produced by the gut bacteria and the host) of young cats. Thirty 2-month-old cats with an upper respiratory tract infection were treated with either amoxicillin/clavulanic acid for 20 days or doxycycline for 28 days. In addition, another 15 control cats that did not receive antibiotics were included. Blood was collected on days 0 (before treatment), 20/28 (last day of treatment), and 300 (10 months after the end of treatment), while feces were collected on days 0, 20/28, 60, 120, and 300. Seven serum and fecal metabolites differed between cats treated with antibiotics and control cats at the end of treatment period. Ten months after treatment, no metabolites differed from healthy cats, suggesting that amoxicillin/clavulanic acid or doxycycline treatment only temporarily affects the abundance of the serum and fecal metabolome.

Abstract

The long-term impact of antibiotics on the serum and fecal metabolome of kittens has not yet been investigated. Therefore, the objective of this study was to evaluate the serum and fecal metabolome of kittens with an upper respiratory tract infection (URTI) before, during, and after antibiotic treatment and compare it with that of healthy control cats. Thirty 2-month-old cats with a URTI were randomly assigned to receive either amoxicillin/clavulanic acid for 20 days or doxycycline for 28 days, and 15 cats of similar age were enrolled as controls. Fecal samples were collected on days 0, 20/28, 60, 120, and 300, while serum was collected on days 0, 20/28, and 300. Untargeted and targeted metabolomic analyses were performed on both serum and fecal samples. Seven metabolites differed significantly in antibiotic-treated cats compared to controls on day 20/28, with two differing on day 60, and two on day 120. Alterations in the pattern of serum amino acids, antioxidants, purines, and pyrimidines, as well as fecal bile acids, sterols, and fatty acids, were observed in antibiotic-treated groups that were not observed in control cats. However, the alterations caused by either amoxicillin/clavulanic acid or doxycycline of the fecal and serum metabolome were only temporary and were resolved by 10 months after their withdrawal.

The Human Microbiome in Chronic Kidney Disease: A Double-Edged Sword

Chronic kidney disease (CKD) is an increasing global health burden. Current treatments for CKD include therapeutics to target factors that contribute to CKD progression, including renin–angiotensin–aldosterone system inhibitors, and drugs to control blood pressure and proteinuria control. Recently, associations between chronic disease processes and the human microbiota and its metabolites have been demonstrated. Dysbiosis—a change in the microbial diversity—has been observed in patients with CKD. The relationship between CKD and dysbiosis is bidirectional; gut-derived metabolites and toxins affect the progression of CKD, and the uremic milieu affects the microbiota. The accumulation of microbial metabolites and toxins is linked to the loss of kidney functions and increased mortality risk, yet renoprotective metabolites such as short-chain fatty acids and bile acids help restore kidney functions and increase the survival rate in CKD patients. Specific dietary interventions to alter the gut microbiome could improve clinical outcomes in patients with CKD. Low-protein and high-fiber diets increase the abundance of bacteria that produce short-chain fatty acids and anti-inflammatory bacteria. Fluctuations in the urinary microbiome are linked to increased susceptibility to infection and antibiotic resistance. In this review, we describe the potential role of the gut, urinary and blood microbiome in CKD pathophysiology and assess the feasibility of modulating the gut microbiota as a therapeutic tool for treating CKD.

Correlation between metabolomic profile constituents and feline pancreatic lipase immunoreactivity

Background

Feline pancreatic lipase immunoreactivity (fPLI) is commonly used to diagnose pancreatitis in cats (FP). Untargeted metabolomics has been extensively applied in human and veterinary medicine, but no metabolomic studies regarding FP have been conducted.

Objectives

To identify metabolites significantly associated with increased fPLI.

Animals

Forty‐nine client‐owned cats: 11 clinically healthy and 38 with various clinical conditions.

Methods

Analytical cross‐sectional study with convenience sampling. A panel of 630 metabolites belonging to 26 biochemical classes was quantified in plasma using a commercial metabolomic assay. The correlation between plasma metabolite concentrations and serum fPLI was evaluated using Spearman's rank correlation coefficient (R_s) with Bonferroni correction. Multivariable analysis then was performed to control for glomerular filtration rate, liver damage, and blood glucose concentration. The accuracy of selected metabolites in discriminating between cats with normal (≤3.5 μg/L) and increased (>5.3 μg/L) fPLI was estimated using the area under the receiver operating characteristic curve (AUROC).

Results

Four hundred and seven of 630 metabolites (64.6%) were quantified in all cats. When controlled for potential confounders only 3 sphingolipids were significantly positively correlated with fPLI: 2 cerebrosides: HexCer(d18:1/24:0); (R_s = .56), and HexCer(d18:1/24:1); (R_s = .58) and 1 sphingomyelin: SM C18:0 (R_s = .55). Their AUROCs in identifying cats with increased fPLI were 82% (95% confidence interval [CI 95%], 70%‐94%), 84% (CI 95%, 72%‐96%), and 78% (CI 95%, 65%‐92%), respectively.

Conclusions and Clinical Importance

Selected sphingolipids are moderately positively correlated with fPLI and appear to have fair to moderate diagnostic accuracy in discriminating between cats with normal and increased fPLI.

Preliminary demonstration of benchtop NMR metabolic profiling of feline urine: chronic kidney disease as a case study

Objective

The use of benchtop metabolic profiling technology based on nuclear magnetic resonance (NMR) was evaluated in a small cohort of cats with a view to applying this as a viable and rapid metabolic tool to support clinical decision making.

Results

Urinary metabolites were analysed from four subjects consisting of two healthy controls and two chronic kidney disease (CKD) IRIS stage 2 cases. The study identified 15 metabolites in cats with CKD that were different from the controls. Among them were acetate, creatinine, citrate, taurine, glycine, serine and threonine. Benchtop NMR technology is capable of distinguishing between chronic kidney disease case and control samples in a pilot feline cohort based on metabolic profile. We offer perspectives on the further development of this pilot work and the potential of the technology, when combined with sample databases and computational intelligence techniques to offer a clinical decision support tool not only for cases of renal disease but other metabolic conditions in the future.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13104-021-05888-y.

Application of Metabolomics to Identify Potential Biomarkers for the Early Diagnosis of Coronary Heart Disease

Coronary heart disease (CHD) is one of the leading causes of deaths globally. Identification of serum metabolic biomarkers for its early diagnosis is thus much desirable. Serum samples were collected from healthy controls (n = 86) and patients with CHD (n = 166) and subjected to untargeted and targeted metabolomics analyses. Subsequently, potential biomarkers were detected and screened, and a clinical model was developed for diagnosing CHD. Four dysregulated metabolites, namely PC(17:0/0:0), oxyneurine, acetylcarnitine, and isoundecylic acid, were identified. Isoundecylic acid was not found in Human Metabolome Database, so we could not validate differences in its relative abundance levels. Further, the clinical model combining serum oxyneurine, triglyceride, and weight was found to be more robust than that based on PC(17:0/0:0), oxyneurine, and acetylcarnitine (AUC = 0.731 vs. 0.579, sensitivity = 83.0 vs. 75.5%, and specificity = 64.0 vs. 46.5%). Our findings indicated that serum metabolomics is an effective method to identify differential metabolites and that serum oxyneurine, triglyceride, and weight appear to be promising biomarkers for the early diagnosis of CHD.

Effect of Nutrition on Age-Related Metabolic Markers and the Gut Microbiota in Cats

Age-related changes in the gut microbiota and metabolites are associated with the increased risk of detrimental conditions also seen with age. This study evaluated whether a test food with potential anti-aging benefits results in favorable changes in plasma and fecal metabolites and the fecal microbiota in senior cats. Forty healthy domestic cats aged 8.3–13.5 years were fed a washout food for 30 days, then control or test food for 30 days. After another 30-day washout, cats were switched to the other study food for 30 days. Assessment of plasma and fecal metabolites showed lower levels of metabolites associated with detrimental processes (e.g., uremic toxins) and higher levels of metabolites associated with beneficial processes (e.g., tocopherols) after cats consumed the test food compared with the control food. A shift toward proteolysis with the control food is supported by higher levels of amino acid metabolites and lower levels of carbohydrate metabolites. Operational taxonomic units of greater abundance with the test food positively correlated with carbohydrate and nicotinic acid metabolites, and negatively correlated with uremic toxins, amino acid metabolism, secondary bile salts, and branched-chain fatty acids. Taken together, the test food appears to result in greater levels of metabolites and microbiota associated with a healthier state.

The impact of periodontal disease and dental cleaning procedures on serum and urine kidney biomarkers in dogs and cats

The objective of this study was to evaluate the benefits and inherent risks of dental cleaning procedures, based on serum and urine biomarkers for kidney function and tissue damage, in dogs and cats. Thirty-one asymptomatic, mostly older dogs (14 neutered male and 17 ovariohysterectomized female dogs of various breeds between 3 and 14 years old) and cats (19 neutered male and 12 ovariohysterectomized female domestic short hair cats between 2 and 16 years old) diagnosed with periodontal disease on physical exam, and recommended by their veterinarian to have dental cleaning under general anesthesia were evaluated in a prospective study. Serum and urine samples were collected from dogs and cats 1 week before, 6 hours after, and again 1 week after the dental cleaning procedure. Samples were analyzed for biomarkers of kidney function [serum creatinine (Cr), symmetric dimethylarginine (SDMA), and blood urea nitrogen (BUN), and urine for specific gravity (USG) and protein:creatinine (UPC) ratio]. A panel of biomarkers for renal tissue damage was also assessed [serum β-aminoisobutyric acid (BAIB), and urine cystatin B and clusterin]. Samples collected one week before dental cleaning procedures showed that increased age and severity of dental disease were linked to abnormal kidney function biomarker values (age: elevated SDMA and Cr concentrations and isosthenuric USG values; disease severity: elevated UPC ratios) as well as elevated urine cystatin B and clusterin concentrations. Directly after the dental cleaning procedure, an increased number of cats with elevated SDMA concentrations was observed (specifically in cats with longer duration of dental procedures). Extended duration of dental procedures (≥60 min) was linked to increased urine cystatin B and clusterin concentrations, whereas shorter duration procedures was linked to decreased urine cystatin B and clusterin. Higher SDMA concentrations persisted in cats one week after the dental cleaning procedures and were linked to elevated UPC ratios one week before cleaning procedures. In conclusion, the results of this study indicate a link between severity of dental disease, renal tissue injury, and impaired renal function. Longer duration dental procedures in cats may carry inherent risks of kidney injury and impaired renal function.

Miscanthus Grass as a Novel Functional Fiber Source in Extruded Feline Diets

Although dietary fiber is not considered an essential nutrient in a complete and balanced diet for felines, it provides a substrate for fermentation by gut microbiota, thus promoting gastrointestinal health through the production of fermentative metabolites, as well as improving laxation. The aim of this research was to evaluate the novel fiber source, Miscanthus grass (Miscanthus giganteus), in comparison with traditional fiber sources and their effects on fecal quality, apparent total tract digestibility (ATTD), fecal fermentative end products, and microbiota of healthy adult cats. Four dietary treatments were evaluated, differing in dietary fiber source. The diets were formulated to meet or exceed the AAFCO (2018) nutritional profile for adult cats and contained either cellulose (CO), Miscanthus grass fiber (MF), a blend of Miscanthus fiber and tomato pomace (MF + TP), or beet pulp (BP). The study was conducted using a completely randomized design with 28 neutered adult, domesticated shorthair cats (19 females and 9 males, mean age 2.2 ± 0.03 years; mean body weight 4.6 ± 0.7 kg, mean body condition score 5.6 ± 0.6). The experimental period comprised 21 days, and a fresh fecal and a total fecal collection were performed during the last 4 days of the trial period. Daily food intake (DM basis) was similar across all groups (P > 0.05). Additionally, treatment did not affect fecal output (as-is or DM basis), fecal score, or fecal pH (P > 0.05). Cats fed BP had significantly higher total dietary fiber ATTD than all the other treatments (P < 0.05) and the highest concentrations of total short-chain fatty acid, acetate, and propionate (P < 0.05), while butyrate concentrations were similar for all treatments (P > 0.05). Inclusion of dietary fibers was effective in modulating gut microbiota. Cats fed diets containing Miscanthus grass had greater α-diversity than cats fed BP. As no adverse effects on health, fecal quality, or ATTD of macronutrients were observed with the inclusion of 9% Miscanthus grass fiber or fiber blend, the data suggest that Miscanthus grass fiber and fiber blends are viable alternatives to the traditional dietary fiber sources used in commercial extruded feline diets, being most comparable to cellulose.

Best Practices for Microbiome Study Design in Companion Animal Research

The gut microbiome is a community of microorganisms that inhabits an animal host's gastrointestinal tract, with important effects on animal health that are shaped by multiple environmental, dietary, and host-associated factors. Clinical and dietary trials in companion animals are increasingly including assessment of the microbiome, but interpretation of these results is often hampered by suboptimal choices in study design. Here, we review best practices for conducting feeding trials or clinical trials that intend to study the effects of an intervention on the microbiota. Choices for experimental design, including a review of basic designs, controls, and comparison groups, are discussed in the context of special considerations necessary for microbiome studies. Diet is one of the strongest influences on the composition of gut microbiota, so applications specific to nutritional interventions are discussed in detail. Lastly, we provide specific advice for successful recruitment of colony animals and household pets into an intervention study. This review is intended to serve as a resource to academic and industry researchers, clinicians, and veterinarians alike, for studies that test many different types of interventions.

Effect of Added Dietary Betaine and Soluble Fiber on Metabolites and Fecal Microbiome in Dogs with Early Renal Disease

Renal diets are recommended for dogs with chronic kidney disease (CKD). This study examined the effects of foods with added betaine and fiber on the plasma and fecal metabolome and fecal microbiome in dogs with early stage CKD. At baseline, several metabolites differed between healthy dogs and those with CKD. Dogs with CKD (n = 28) received a control food, low soluble fiber plus betaine food (0.5% betaine, 0.39% oat beta-glucan, and 0.27% short-chain fructooligosaccharides (scFOS)), or high soluble fiber plus betaine food (0.5% betaine, 0.59% oat beta-glucan, and 0.41% scFOS) each for 10 weeks in different sequences. Consumption of test foods led to several favorable, significant changes in the plasma metabolome, including decreases of several uremic toxins and other deleterious metabolites, and increases in favorable metabolites compared with the control food. Only 7 fecal metabolites significantly changed with consumption of the test foods compared with the control food, largely increases in polyphenols and lignans. Few changes were seen in the fecal microbiome, though some taxa that significantly changed in response to the test foods have beneficial effects on health, with some negatively correlating with uremic toxins. Overall, foods with added betaine and soluble fiber showed positive effects on the plasma and fecal metabolomes.

Changes in the Fecal Metabolome Are Associated with Feeding Fiber Not Health Status in Cats with Chronic Kidney Disease

The objective was to determine the effects of feeding different fiber sources to cats with chronic kidney disease (CKD) compared with healthy cats (both n = 10) on fecal metabolites. A cross-over within split-plot study design was performed using healthy and CKD cats (IRIS stage 1, 2, and 3). After cats were fed a complete and balanced dry food designed to aid in the management of renal disease for 14 days during a pre-trial period, they were randomly assigned to two fiber treatments for 4 weeks each. The treatment foods were formulated similar to pre-trial food and contained 0.500% betaine, 0.586% oat beta glucan, and either 0.407% short chain fructooligosaccharides (scFOS) fiber or 3.44% apple pomace. Both treatment foods had similar crude fiber (2.0 and 2.1% for scFOS and apple pomace, respectively) whereas soluble fiber was 0.8 and 1.6%, respectively. At baseline, CKD had very little impact on the fecal metabolome. After feeding both fiber sources, some fecal metabolite concentrations were significantly different compared with baseline. Many fecal uremic toxins decreased, although in healthy cats some increased; and some more so when feeding apple pomace compared with scFOS, e.g., hippurate, 4-hydroxyhippurate, and 4-methylcatechol sulfate; the latter was also increased in CKD cats. Changes in secondary bile acid concentrations were more numerous in healthy compared with CKD cats, and cats in both groups had greater increases in some secondary bile acids after consuming apple pomace compared with scFOS, e.g., tauroursodeoxycholate and hyocholate. Although changes associated with feeding fiber were more significant than changes associated with disease status, differential modulation of the gut-kidney axis using dietary fiber may benefit cats.