Characterization of serum metabolome in cats with chronic kidney disease

A Doença Renal Crônica (DRC) é uma enfermidade comum entre os felinos e um dos maiores desafios é a identificação precoce de possíveis distúrbios estruturais e/ou funcionais que ocorrem nos estadios iniciais da doença, quando o animal ainda não apresenta sinais clínicos. A etiologia da DRC é heterogênea e geralmente a causa de base não é identificada devido ao curso adaptativo da doença, sendo que as manifestações clínicas são apenas observadas nos estadios mais avançados, o que evidencia que pelo menos 66% dos néfrons sofreram lesão ou já foram perdidos. Novas estratégias para o diagnóstico precoce da DRC estão surgindo na medicina veterinária visando a implementação de intervenções terapêuticas a fim de retardar a progressão da doença. A metabolômica é o estudo que envolve a identificação e quantificação de pequenas moléculas presentes em amostras biológicas e tem como objetivo demonstrar alterações no metabolismo do indivíduo sob diferentes condições, assim como elucidar o mecanismo fisiopatológico de doenças crônicas, como a DRC. O presente estudo teve como objetivos caracterizar a metabolômica sérica de gatos diagnosticados com DRC estadios 1 e 2, visando a melhor compreensão dos padrões metabólicos presentes em cada fase da doença, bem como comparar a metabolômica do soro dos animais antes e após a introdução do manejo alimentar com um alimento coadjuvante renal. A hipótese firma-se de acordo com estudos prévios com outras espécies que demonstraram variação no perfil de metabólitos em indivíduos submetidos à diferentes estímulos fisiopatológicos, modificações ambientais, dietéticas e/ou modificações genéticas. Foram incluídos 25 gatos domésticos (fêmeas e machos), 15 diagnosticados com DRC nos estadios 1 (Grupo DRC1, n= 6) e 2 (Grupo DRC2, n= 9), de acordo com a IRIS (Sociedade Internacional de Interesse Renal), e o grupo controle foi composto por 10 gatos saudáveis. Todos os animais, de todos os grupos, foram submetidos a um período de 30 dias em dieta de manutenção (alimento basal). Após esta etapa inicial, foram iniciadas as coletas das amostras. Os períodos de coleta foram divididos em tempos, sendo T0 antes dos animais receberem a dieta coadjuvante renal e 30 dias após receberem o alimento basal (padronização dietética), seguidos dos tempos subsequentes T30 (30 dias após T0) e T60 (60 dias após T0). A caracterização da metabolômica foi realizada em T0 e T60 por espectrometria de massa/cromatografia gasosa (MS-GC). A análise discriminante de mínimos quadrados parciais (PLS-DA) e a análise de componentes principais (PCA) foram realizadas para avaliar as diferenças nos perfis metabolômicos entre os grupos e antes (DRC T0) e após a instituição do manejo dietético com o alimento coadjuvante renal (DRC T60) por meio do software Metaboanalyst 4.0. Gatos saudáveis e gatos com DRC estadios 1 e 2 apresentaram diferenças no perfil de metabólitos séricos quando avaliados já no tempo zero e após a padronização da dieta. O ácido cítrico e a monostearina foram os metabólitos que se diferenciaram entre os grupos de animais doentes renais quando comparados ao grupo controle. Após 60 dias de ingestão do alimento coadjuvante renal, outros metabólitos apresentaram diferença, dentre eles a glicina, frutose, ácido glutâmico, ácido araquidônico, ácido esteárico, creatinina e ureia. No geral, o emprego da metabolômica como ferramenta diagnóstica, tem o potencial de identificar complicações correlacionadas com a DRC ainda quando em condições subclínicas, o que pode auxiliar em elucidações de processos fisiopatológicos relacionados ao desenvolvimento e progressão da doença.Chronic kidney disease (CKD) it is a common disease in cats and one of the major challenges is the early identification of structural and/or functional disorders that occur in the early stages of the disease when the animal presents no clinical signs. The etiology of CKD is heterogeneous and usually the first causes are not identified due to the adaptive course of disease evolution, and clinical manifestations are only observed in the most advanced stages, which shows that at least 66% of nephrons have been injured or have already been lost. New strategies for early diagnosis of CKD are emerging in veterinary sciences to implement therapeutic interventions to decrease disease progression. Metabolomics is the study that involves the identification and quantification of small molecules present in biological samples and aims to show changes in individual metabolism under different conditions, as well as to elucidate the pathophysiological mechanism of chronic diseases, such as CKD. The present study has the goal to define the serum metabolomic of cats with different stages of CKD, to better understand the metabolic patterns present in each phase of the disease, and to compare the serum metabolomics of the animals before and after renal diet. The hypothesis is based on previous studies with other species that demonstrated variation of the metabolomic profile of individuals submitted to different pathophysiological stimuli, environmental, dietary and/or genetic modifications. The study was conducted using 25 domestic cats (females and males), 15 diagnosed with CKD stage 1 (CKD1, n= 6) and 2 (CKD2, n= 9), according to IRIS (International Renal Interest Society), and the control group was composed of 10 healthy cats. All animals, from all groups, were submitted to a period of 30 days on a maintenance diet. After this period, the samples started to be collected. Sample collections were conducted in periods, labeled as times, with T0 being collection before animals received the renal diet, and 30 days after a maintenance diet, followed by subsequent times T30 (30 days after T0) and T60 (60 days after T0). The metabolomics analysis was performed on T0 and T60 by mass spectrometry/gas chromatography (MS-GC). Partial least squares discriminant analysis (PLS-DA) and Principal component analysis (PCA) were performed to assess differences in metabolomic profiles between groups and before (CKD T0) and after renal diet (CKD T60). Data analysis was performed on Metaboanalyst 4.0 software. Healthy cats and CKD cats stages 1 and 2 showed differences in serum metabolic profile at T0 and after diet standardization. Citric acid and monostearin differed between CKD and control groups. After 60 days of renal diet consumption, other 7 serum metabolites differed, including glycine, fructose, glutamic acid, arachidonic acid, stearic acid, creatinine, and urea. Overall, metabolomics markers have the potential to identify complications correlated with CKD already in subclinical conditions, and these can provide insights into the possible pathophysiologic processes that contribute to the development and progression of CKD

The Role of Vitamin D in Small Animal Bone Metabolism

Dogs and cats have differences in vitamin D metabolism compared to other mammalian species, as they are unable to perform vitamin D cutaneous synthesis through sun exposure. Therefore, they are dependent on the dietary intake of this nutrient. The classic functions of vitamin D are to stimulate intestinal calcium and phosphate absorption, renal calcium and phosphate reabsorption and regulate bone mineral metabolism. Thus, it is an important nutrient for calcium and phosphorus homeostasis. This review highlights the evidence of the direct and indirect actions of vitamin D on bone mineral metabolism, the consequences of nutritional imbalances of this nutrient in small animals, as well as differences in vitamin D metabolism between different size dogs

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

Body Composition of Healthy Cats and Cats with Chronic Kidney Disease Fed on a Dry Diet Low in Phosphorus with Maintenance Protein

The aim was to evaluate the effect of feeding a low-phosphorus and maintenance protein diet in healthy cats and cats with chronic kidney disease (CKD) with IRIS stages 1 (CKD-1) and 2 (CKD-2). Cats were initially fed a senior diet (30 days) followed by the renal diet (60 days). Body composition, body weight (BW), muscle mass score (MMS), and body condition score (BCS) were assessed before (T30) and after renal diet intake (T60). General mixed linear models were used to assess the effects of fixed groups and moments (T30 × T60), as well as their interaction, in addition to the random effects of animals within each group. Unlike healthy cats and cats with CKD-1, cats with CKD-2 had a loss of BW, lower BCS (p < 0.005), and lower MMS (p = 0.0008) after 60 days of consuming the renal diet. The fat mass and lean body mass (LBM), determined by the deuterium isotopes method, did not change in all cats between T0 and T60. In healthy cats and cats with CKD-1, the renal diet resulted in maintenance of BW, BCS and MMS; but cats with CKD-2 presented lower BCS and did not reduce phosphatemia after consumption

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