Serum apolipoprotein-A1 as a possible biomarker for monitoring treatment of canine leishmaniosis

Characterization of the plasma proteome from healthy adult dogs

Introduction

Bloodwork is a widely used diagnostic tool in veterinary medicine, as diagnosis and therapeutic interventions often rely on blood biomarkers. However, biomarkers available in veterinary medicine often lack sensitivity or specificity. Mass spectrometry-based proteomics technology has been extensively used in the analysis of biological fluids. It offers excellent potential for a more comprehensive characterization of the plasma proteome in veterinary medicine.

Methods

In this study, we aimed to identify and quantify plasma proteins in a cohort of healthy dogs and compare two techniques for depleting high-abundance plasma proteins to enable the detection of lower-abundance proteins via label-free quantification liquid chromatography-mass spectrometry. We utilized surplus lithium-heparin plasma from 30 healthy dogs, subdivided into five groups of pooled plasma from 6 randomly selected individuals each. Firstly, we used a commercial kit to deplete high-abundance plasma proteins. Secondly, we employed an in-house method to remove albumin using Blue-Sepharose.

Results and discussion

Among all the samples, some of the most abundant proteins identified were apolipoprotein A and B, albumin, alpha-2-macroglobulin, fibrinogen beta chain, fibronectin, complement C3, serotransferrin, and coagulation factor V. However, neither of the depletion techniques achieved significant depletion of highly abundant proteins. Despite this limitation, we could detect and quantify many clinically relevant proteins. Determining the healthy canine proteome is a crucial first step in establishing a reference proteome for canine plasma. After enrichment, this reference proteome can later be utilized to identify protein markers associated with different diseases, thereby contributing to the diagnosis and prognosis of various pathologies.

Changes of the salivary and serum proteome in canine hypothyroidism

In this study, changes in salivary and serum proteome of dogs with hypothyroidism were studied using tandem mass tags (TMT) labelling and liquid chromatography-mass spectrometry (LC-MS/MS). Saliva and serum proteome from 10 dogs with hypothyroidism were compared with 10 healthy dogs. In saliva, a total of seven proteins showed significant changes between the two groups, being six downregulated and one upregulated, meanwhile, in serum, a total of six proteins showed significant changes, being five downregulated and one upregulated. The altered proteins reflected metabolic and immunologic changes, as well as, skin and coagulation alterations, and these proteins were not affected by gender. One of the proteins that were downregulated in saliva, lactate dehydrognease (LDH), was measured by a spectrophotometric assay in saliva samples from 42 dogs with hypothyroidism, 42 dogs with non-thyroid diseases and 46 healthy dogs. The activity of LDH was lower in the saliva of hypothyroid dogs when compared to non-thyroid diseased dogs and healthy controls. This study indicates that canine hypothyroidism can produce changes in the proteome of saliva and serum. These two sample types showed different variations in their proteins reflecting physiopathological changes that occur in this disease, mainly related to the immune system, metabolism, skin and coagulation. In addition, some of the proteins identified in this study, specially LDH in saliva, should be further explored as potential biomarkers of canine hypothyroidism.

Serum proteome profiling of naturally acquired Babesia rossi infection in dogs

Babesiosis is a disease of significant medically and veterinary importance with worldwide distribution. It is caused by intra-erythrocyte protozoal parasites, with Babesia rossi causing the most severe clinical signs of all the large Babesia parasites infecting dogs. The disease can be clinically classified into uncomplicated and complicated forms with a wide range of clinical presentations from a mild, subclinical illness to complicated forms and death. The aim of this study was to assess serum proteomic profiles from dogs with babesiosis and healthy dogs using a label-based proteomics approach. Altogether 32 dogs naturally infected with B. rossi (subdivided into 18 uncomplicated cases and 14 complicated cases of babesiosis) and 20 healthy dogs were included. There were 78 proteins with significantly different abundances between the three groups of dogs. Elucidation of proteins and pathways involved in canine babesiosis caused by B. rossi have revealed key differences associated with haemostasis, innate immune system, lipid metabolism and inflammation. Shotgun proteomic profiling allowed identification of potential serum biomarkers for differentiation of disease severity in canine babesiosis caused by B. rossi. These findings may be applicable to the study of host-parasite interactions and the development of novel therapeutic targets.

Generating Detailed Spectral Libraries for Canine Proteomes Obtained from Serum and Urine

Domestic dogs (Canis lupus familiaris) are popular companion animals. Increase in medical expenses associated with them and demand for extending their lifespan in a healthy manner has created the need to develop new diagnostic technology. Companion dogs also serve as important animal models for non-clinical research as they can provide various biological phenotypes. Proteomics have been increasingly used on dogs and humans to identify novel biomarkers of various diseases. Despite the growing applications of proteomics in liquid biopsy in veterinary medicine, no publicly available spectral assay libraries have been created for the proteome of canine serum and urine. In this study, we generated spectral assay libraries for the two-representative liquid-biopsy samples using mid-pH fractionation that allows in-depth understanding of proteome coverage. The resultant canine serum and urine spectral assay libraries include 1,132 and 4,749 protein groups and 5,483 and 25,228 peptides, respectively. We built these complimentary accessible resources for proteomic biomarker discovery studies through ProteomeXchange with the identifier PXD034770.

Characterization and Proteomic Analysis of Plasma EVs Recovered from Healthy and Diseased Dogs with Canine Leishmaniosis

Dogs are highly valued companions and work animals that are susceptible to many life-threatening conditions such as canine leishmaniosis (CanL). Plasma-derived extracellular vesicles (EVs), exploited extensively in biomarker discovery, constitute a mostly untapped resource in veterinary sciences. Thus, the definition of proteins associated with plasma EVs recovered from healthy and diseased dogs with a relevant pathogen would be important for biomarker development. For this, we recovered, using size-exclusion chromatography (SEC), EVs from 19 healthy and 20 CanL dogs’ plasma and performed proteomic analysis by LC-MS/MS to define their core proteomic composition and search for CanL-associated alterations. EVs-specific markers were identified in all preparations and also non-EVs proteins. Some EVs markers such as CD82 were specific to the healthy animals, while others, such as the Integrin beta 3 were identified in most samples. The EVs-enriched preparations allowed the identification of 529 canine proteins that were identified in both groups, while 465 and 154 were only identified in healthy or CanL samples, respectively. A GO enrichment analysis revealed few CanL-specific terms. Leishmania spp. protein identifications were also found, although with only one unique peptide. Ultimately, CanL-associated proteins of interest were identified and a core proteome was revealed that will be available for intra- and inter-species comparisons.

Apolipoprotein A1 and serum amyloid A in dogs with sepsis and septic shock

Introduction

Apolipoprotein-A1 (Apo-A1) acts as a negative acute phase protein (APP) during inflammatory states, and has a potential prognostic value in people and dogs with sepsis. The aim of this retrospective study was to investigate the association of serum Apo-A1 concentration with disease severity, multiorgan dysfunction syndrome (MODS) and outcome in a population of dogs with sepsis, and to assess its correlation with major canine APPs.

Methods

Ninety-nine dogs with uncomplicated sepsis (n = 78) or septic shock (n = 21) were included. The serum concentration of Apo-A1, C-reactive protein (CRP) and serum amyloid A (SAA) were recorded, alongside the canine acute patient physiologic and laboratory evaluation fast (APPLE_fast) score and the presence of MODS.

Results

Dogs with septic shock had significantly lower serum Apo-A1 concentrations (106.3 ± 22.7 mg/dl; reference interval: 123.0-142.3 mg/dl), higher APPLE_fast score (30, 13-38) and greater frequency of MODS (67%) compared to those with uncomplicated sepsis (117.9 ± 19.3 mg/dl; 25, 6-33 and 8%, respectively) (P = 0.0201; P = 0.0005; P < 0.0001, respectively). Similarly, dogs with MODS had significantly lower serum Apo-A1 concentrations (104.1 ± 4.6 mg/dl) and higher APPLE_fast score values (31, 13-38) compared to those without MODS (118.32 ± 2.1 mg/dl and 26, 6-33, respectively) (P = 0.0050 and P = 0.0038, respectively). Conversely, neither CRP nor SAA were different between these groups. No difference in serum APPs concentrations was detected between survivors and non-survivors. Significant negative correlations were detected between serum Apo-A1 and SAA (P = 0.0056, r = -0.277), and between serum Apo-A1 and the APPLE_fast score (P = 0.0027, r = -0.3). In this population, higher values of the APPLE_fast score and the presence of MODS were independently associated with a higher risk of death.

Discussion

Our study shows that Apo-A1 is a useful biomarker of sepsis severity in dogs, since it is decreased in those with septic shock and MODS. Further prospective investigations are deemed to evaluate the applicability of Apo-A1 to predict sepsis course and response to treatment in septic dogs.

The Future of Biomarkers in Veterinary Medicine: Emerging Approaches and Associated Challenges

Simple Summary

In this review we seek to outline the role of new technologies in biomarker discovery, particularly within the veterinary field and with an emphasis on ‘omics’, as well as to examine why many biomarkers-despite much excitement-have not yet made it to clinical practice. Further we emphasise the critical need for close collaboration between clinicians, researchers and funding bodies and the need to set clear goals for biomarker requirements and realistic application in the clinical setting, ensuring that biomarker type, method of detection and clinical utility are compatible, and adequate funding, time and sample size are available for all phases of development.

Abstract

New biomarkers promise to transform veterinary practice through rapid diagnosis of diseases, effective monitoring of animal health and improved welfare and production efficiency. However, the road from biomarker discovery to translation is not always straightforward. This review focuses on molecular biomarkers under development in the veterinary field, introduces the emerging technological approaches transforming this space and the role of ‘omics platforms in novel biomarker discovery. The vast majority of veterinary biomarkers are at preliminary stages of development and not yet ready to be deployed into clinical translation. Hence, we examine the major challenges encountered in the process of biomarker development from discovery, through validation and translation to clinical practice, including the hurdles specific to veterinary practice and to each of the ‘omics platforms–transcriptomics, proteomics, lipidomics and metabolomics. Finally, recommendations are made for the planning and execution of biomarker studies with a view to assisting the success of novel biomarkers in reaching their full potential.

Proteomics in dogs: a systematic review

Proteomic analysis is having a rapid development as a method for the detection of biomarkers of diseases in dogs. Dogs in addition to their importance as companion animals, serve as important animal models for research. This study aims to systematically review evidence regarding the studies performed in proteomics in dogs, and specifically those made in serum, saliva, urine and/or plasma. Information searched in October 2020, January 2021 and August 2021, for English language publications of the last decade (2010-2020) were obtained from electronic databases. Screening, data extraction and risk of bias assessment were undertaken by two investigators. The risk of bias was evaluated using the Review Manager (RevMan 5) tool. Meta-analysis and case report studies were not included in this review. Through the screening process a total of 557 publications were identified after the removal of duplicates. Out of these, 65 were fully evaluated and 44 of these were included in the review. Most studies evaluated the proteome of disease and compared it with a healthy population, and most of the articles included were made on serum, followed by saliva. The overall risk of bias for all studies was high, due to an absence in the generation of random sequence. Overall proteomic analysis has allowed the discovery of new physiopathological pathways of diseases and potential biomarkers in the dog, which are addressed in this review.

Leishmanial apolipoprotein A-I expression: a possible strategy used by the parasite to evade the host's immune response

Apolipoprotein A-I (apo A-I) represents the main component of the Trypanosome lytic factor (TLF) which contributes to the host innate immunity against Trypanosoma and Leishmania. These parasites use complex and multiple strategies such as molecular mimicry to evade or subvert the host immune system. Previous studies have highlighted the adaptation mechanisms of TLF-resistant Trypanosoma species. These data might support the hypothesis that Leishmania parasites (amastigote forms in macrophages) might express apo A-I to bypass and escape from TLF action as a component of the host innate immune responses. The anti-inflammatory property of apo A-I is another mechanism that supports our idea that apo A-I may play a role in Leishmania parasites allowing them to bypass the host innate immune system.

Evaluation of Serum Apolipoprotein A1 in Canine Sepsis

Decreased serum apolipoprotein A1 (Apo-A1) concentration is associated with mortality in human sepsis. The diagnostic and prognostic role of serum Apo-A1 concentrations in canine sepsis was evaluated. Serum samples from septic dogs (n = 91) and healthy controls (n = 15) were retrospectively analyzed. According to the sepsis origin, four categories were identified: parvoviral enteritis (n = 26), pyometra (n = 20), septic peritonitis (n = 19), and miscellanea (n = 26). The canine acute patient physiologic and laboratory evaluation fast score (APPLE_fast), serum C-reactive protein (CRP) and albumin concentrations were reviewed in all enrolled dogs. Increased CRP (252.6 ± 119.2 mg/L; Reference Interval: 0–8.5 mg/L) and significant lower serum albumin and Apo-A1 concentrations were documented in dogs with sepsis (22.8 ± 5.3 g/L and 1.17 ± 0.27 g/L, respectively) compared to healthy ones (33.1 ± 2.5 g/L and 1.32 ± 0.05 g/L, respectively) (P < 0.0001). According to the origin of sepsis, only the subgroup of dogs with septic peritonitis had significantly lower Apo-A1 (1.03 ± 0.26 g/L) concentrations compared to healthy dogs (P < 0.001). No significant differences were found in serum albumin and CRP concentrations, and in APPLE_fast score values among the different subgroups of sepsis. Diagnosis of septic peritonitis was associated with a higher frequency of death (P = 0.006). In septic dogs, significant lower Apo-A1 concentrations were detected in non-survivors (1.02 ± 0.28 g/L; n = 27) compared to survivors (1.23 ± 0.24 g/L; n = 64; P = 0.0007). Moreover, significant higher values of the APPLE_fast score were calculated in non-survivors (26 ± 4; n = 19) compared to survivors (23 ± 4; n = 51) (P = 0.0114). According to the area under the ROC curve analysis, Apo-A1 <96 mg/dl had a fair accuracy (AUC = 0.72) to correctly predict mortality (P = 0.0004). Apo-A1 might support a diagnosis of canine septic peritonitis with a potential prognostic significance. Further prospective studies are warranted.

Serum proteome of dogs at subclinical and clinical onset of canine leishmaniosis

The objective of this study was to identify changes in serum proteome in dogs that may occur after an experimental infection at subclinical and clinical stages of canine leishmaniosis (CanL). For this purpose, canine pre- and post-infection with Leishmania infantum serum proteomes in the same dogs were analysed by a high-throughput label-based quantitative LC-MS/MS proteomic approach. A total of 169 proteins were identified, and 74 of them including complement C8 alpha chain, adiponectin, transferrin, sphingomyelin phosphodiesterase acid-like 3A and immunoglobulins showed different modulation between the different stages of CanL. These proteins could be considered as potential serum biomarkers of early diagnostic or disease progression in CanL. Additionally, biological pathways modulated during CanL such as blood coagulation or gonadotropin-releasing hormone receptor were revealed, which could help to understand the pathological mechanisms of the disease.

Changes in saliva of dogs with canine leishmaniosis: A proteomic approach

In the present study, a quantitative proteomic approach to study changes in saliva proteins associated with canine leishmaniosis (CanL) was performed. For this, canine salivary proteins were analysed and compared between dogs before (T0) and after (T1) experimental infection with Leishmania infantum by high-throughput label-based quantitative LC-MS/MS proteomic approach and bioinformatic analysis of the in silico inferred interactome protein network was created from the initial list of differential proteins. More than 2000 proteins were identified, and of the 90 differentially expressed proteins between T0 and T1, 12 were down-regulated with log2 fold change lower than -0.5849, and 19 were up-regulated with log2 fold change greater than 0.5849. This study provides evidence of changes in salivary proteome that can occur in canine leishmaniosis and revealed biological pathways in saliva modulated in canine leishmaniosis with potential for further targeted research.

Association of acute Babesia canis infection and serum lipid, lipoprotein, and apoprotein concentrations in dogs

BACKGROUND

Babesia canis infection induces a marked acute phase response (APR) that might be associated with alteration in lipid and lipoprotein metabolism and disease prognosis.

HYPOTHESIS

Dogs with B. canis-induced APR develop dyslipidemia with altered lipoprotein concentration and morphology.

ANIMALS

Twenty-nine client-owned dogs with acute B. canis infection and 10 clinically healthy control dogs.

METHODS

Observational cross-sectional study. Serum amyloid A (SAA) was measured using ELISA. Cholesterol, phospholipids, and triglycerides were determined biochemically. Lipoproteins were separated using agarose gel electrophoresis. Lipoprotein diameter was assessed by polyacrylamide gradient gel electrophoresis; correlation with ApoA-1 (radioimmunoassay) and SAA was determined.

RESULTS

Dogs with B. canis infection had a marked APR (median SAA, 168.3 μg/mL; range, 98.1-716.2 μg/mL) compared with controls (3.2 μg/mL, 2.0-4.2 μg/mL) (P < .001). Dogs with B. canis infection had significantly lower median cholesterol (4.79 mmol/L, 1.89-7.64 mmol/L versus 6.15 mmol/L, 4.2-7.4 mmol/L) (P = .02), phospholipid (4.64 mmol/L, 2.6-6.6 mmol/L versus 5.72 mmol/L, 4.68-7.0 mmol/L) (P = .02), and α-lipoproteins (77.5%, 27.7%-93.5% versus 89.2%, 75.1%-93.5%) (P = .04), and higher ApoA-1 (1.36 U, 0.8-2.56 U versus 0.95 U, 0.73-1.54 U) concentrations (P = .02). Serum amyloid A correlated with high-density lipoproteins (HDLs) diameter (rho = .43; P = .03) and ApoA-1 (rho = .63, P < .001).

CONCLUSIONS AND CLINICAL IMPORTANCE

Major changes associated with B. canis-induced APR in dogs are related to concentration, composition, and morphology of HDL particles pointing to an altered reverse cholesterol transport. Parallel ApoA-1 and SAA concentration increase is a unique still unexplained pathophysiological finding.

Changes in salivary analytes in canine parvovirus: A high-resolution quantitative proteomic study

The present study evaluated the changes in salivary proteome in parvoviral enteritis (PVE) in dogs through a high-throughput quantitative proteomic analysis. Saliva samples from healthy dogs and dogs with severe parvovirosis that survived or perished due to the disease were analysed and compared by Tandem Mass Tags (TMT) analysis. Proteomic analysis quantified 1516 peptides, and 287 (corresponding to 190 proteins) showed significantly different abundances between studied groups. Ten proteins were observed to change significantly between dogs that survived or perished due to PVE. Bioinformatics' analysis revealed that saliva reflects the involvement of different pathways in PVE such as catalytic activity and binding, and indicates antimicrobial humoral response as a pathway with a major role in the development of the disease. These results indicate that saliva proteins reflect physiopathological changes that occur in PVE and could be a potential source of biomarkers for this disease.

Use of acute phase proteins for the clinical assessment and management of canine leishmaniosis: general recommendations

BACKGROUND

Dogs with canine leishmaniosis (CanL) due to Leishmania infantum can show a wide spectrum of clinical and clinicopathological findings at the time of diagnosis. The aim of this paper is to describe the possible application of acute phase proteins (APPs) for the characterization and management of this disease, based on previously published information on the utility of APPs in CanL and the experience of the authors in using APPs as analytes in the profiling of canine diseases.

MAIN BODY

Dogs diagnosed with L. infantum infection by serology, polymerase chain reaction, cytological or histopathological identification, can be divided into three groups based on their clinical condition at physical examination and their APPs concentrations: Group 1: dogs with no clinical signs on physical examination and APPs in reference range; Group 2: dogs with changes in APPs but no clinical signs on physical examination; Group 3: dogs with clinical signs and changes in APPs. This report describes the main characteristics of each group as well as its association with the clinical classification schemes of CanL.

CONCLUSION

APPs concentration can be a useful clinical tool to characterize and manage CanL.

Changes in serum proteins in dogs with Ehrlichia canis infection

The aim of this study was the identification of proteins differentially represented in the serum proteome of seropositive dogs with (Group 1) and without (Group 2) clinical-pathologic signs consistent with ehrlichiosis compared to healthy control dogs. Serum samples were collected from 20 dogs of various breeds with naturally occurring ehrlichiosis (10 dogs belonged to Group 1 and 10 to Group 2) and 10 healthy dogs. Two-dimensional electrophoresis (2DE) of pooled serum for each of the group of dogs were run in triplicate. 2D image analysis showed 39 spots differently expressed between Group 1 and Group 2 compared with healthy ones. Mass spectrometry analysis allowed identification of 6 proteins: albumin, haptoglobin (Hp), alpha-1-antitrypsin (AAT), Retinol Binding Protein 4 (RBP-4), alpha-1-acid glycoprotein (AGP) and vitamin D-binding protein (VDBP). When a confirmatory study was performed for albumin, Hp, AAT and RBP-4 by using different assays, significant differences (P < 0.05) between diseased and healthy groups were observed. It can be concluded that there are significant changes in the serum proteome of dogs with ehrlichiosis with modifications in proteins related with the acute phase response such as Hp, albumin and AGP, with vitamin A transport such as RBP-4, with inhibitors of serine proteases and anti-inflammatory proteins such as AAT, and vitamin D metabolism and actin scavengers such as VDBP.

Identification of novel biomarkers for treatment monitoring in canine leishmaniosis by high-resolution quantitative proteomic analysis

The objective of this study was to use the Tandem Mass Tag (TMT) isobaric label-based proteomic approach, in order to identify new potential biomarkers for the treatment monitoring of canine leishmaniosis that could not be identified by the use of gel-based techniques. For this purpose serum samples were obtained from 5 clinically diseased dogs before and one month after the treatment of canine leishmaniosis. The non-depleted serum samples were subjected to reduction, alkylation and trypsin digestion, and the resulting peptides were labeled using 6-plex TMT reagents. To obtain information about protein identities and relative quantification, liquid chromatography-MS analysis of multiplexed TMT-labeled peptides was employed. This gel-free, label-based quantitative proteomic approach enabled identification of 117 canine proteins. Among these, 23 showed significant difference (p<0.05) in expression (two downregulated and 21 upregulated ranging from 1.25 to 2.5 fold change). Comparison of gel-free TMT-based quantification and a gel-based approach previously applied to the same samples resulted in the identification of some common markers (Apo-A1, vitamin D binding protein and RBP4). However, 20 additional differentially represented proteins were highlighted by the gel-free approach, 13 of which have not been previously reported in canine leishmaniosis. In conclusion, the TMT-based proteomic approach allowed identification of new serum proteins that significantly change in concentration after canine leishmaniosis treatment. These proteins are involved in various physiopathological processes such as inflammatory, coagulation or defense mechanisms, and could potentially be suitable biomarkers for treatment monitoring of this parasitic disease.