ADR induces cardiac injury in mice
To establish experimental AIC in mice, 15 mg/kg ADR was injected intraperitoneally [15]. Echocardiographic analysis was performed on the sixth day after ADR treatment. The representative echocardiographic images are presented in Fig. 1A. We found that ADR induced a significant decrease of the ejection fraction (EF%), demonstrating that the mouse model was successfully established. In addition, we observed that the left ventricular fractional shortening (LVFS) was significantly lower in the ADR group than in the control group, suggesting that ADR treatment impaired cardiac systolic function (Fig. 1B). The left ventricular posterior wall thickness at end diastole (LVPWd) and systole (LVPWs) and the left ventricular anterior wall thickness at end diastole (LVAWd) and systole (LVAWs) were remarkably lower in the ADR group than in the control group, indicating that cardiac structural remodeling was induced by ADR (Fig. 1B).
Identification of differential AA metabolites in mice
AA profiles were obtained using validated and robust methodology, enabling the quantitation of 62 analytes from serum samples. In all analyzed samples, there were 51 detectable analytes. The concentrations of the remaining nine analytes were below the limit of quantitation (LOQ) or they exceeded the LOQ for some of the samples; thus, they were excluded from statistical analyses. The AA levels were compared between the ADR and control groups using Student’s t-test (Supplementary Table S1). We identified 14 differential metabolites (p < 0.01) in mice, including 10 metabolites with increased levels (l-lysine, l-serine, 5-aminovaleric acid, l-asparagine, O-phosphorylethanolamine, l-glutamic acid, l-methionine, l-histidine, l-tyrosine, l-tryptophan) and 4 metabolites with decreased levels (ethanolamine, cystathionine, 2-AA, l-glutathione oxidized) (Fig. 2).
Among these differential metabolites, we found that the levels of 2-AA, an intermediate compound in lysine metabolism, were significantly decreased. Recently, 2-AA was identified as a biomarker of insulin resistance, obesity, and diabetes [17, 18]. To explore the role of 2-AA in AIC, mice were fed with 2-AA daily for 1 week prior to ADR treatment. Data from echocardiography revealed that ADR treatment caused significant decreases of EF%, FS%, LVAWs, and LVPWs (Fig. 3B). However, EF%, FS%, and LVPW were not altered by 2-AA treatment in AIC mice, whereas LVAWs and LVAWd were lower in the ADR + 2-AA group than in the ADR group, suggesting that 2-AA treatment exacerbates AIC in mice.
Bioinformatic analysis of AA metabolites in mice
We then processed the 51 analyzed metabolites using PCA to obtain an overview of the data and identify potential severe outliers between the ADR and control groups regarding the metabolic profiles (Fig. 4A; principal component 1 [PC1], 49.9%; PC2, 18.3%). The distribution of metabolites in the control group was more compact, whereas that in the ADR group was more dispersed. However, the PCA score plot failed to reveal clear separation between the analyzed groups. The results demonstrated that the PCA-X model could not completely distinguish the ADR and control groups. A supervised OPLS-DA model was then established to acquire clustering information and differential metabolites to differentiate the ADR and control groups. The variables significant at VIP > 1.0 and p < 0.05 in the OPLS-DA model were considered as biomarker candidates. We used the parameters R2 and Q2 to assess the fitness and prediction capabilities of the OPLS-DA model, respectively. The OPLS-DA model resulted in two predictive components with R2X (cum) = 0.742, R2Y (cum) = 0.931, Q2 (cum) = 0.776. Meanwhile, coefficient variability analysis of variance (CV-ANOVA) and permutation testing were further used to validate the OPLS-DA model. The p value of CV-ANOVA in this established model was 0.025, and the plot of permutation testing with 200 permutations is presented in Fig. S1A. The OPLS-DA score plots of serum samples are presented in Fig. 4B, in which clear separation between the two groups is observed. The result suggests that the model has good practicability and predictability, and the separation reveals fundamental metabolic differences between the two groups. The plot of the predictive VIP values is presented in Fig. S2A. Metabolites in the serum samples that satisfied both VIP > 1.0 and p < 0.05 are listed in Table 1. Nine metabolites including l-glutamic acid, l-lysine, l-serine, l-tryptophan, l-methionine, l-histidine, l-asparagine, l-tyrosine, and O-phosphorylethanolamine comprised the signature of AIC in ADR-treated mice. Furthermore, MetaboAnalyst 5.0 was applied to analyze the data of differential metabolites to find the potential metabolic pathways based on Kyoto Encyclopedia of Genes and Genomes database, and the result is presented in Fig. 4C. Multiple metabolic pathways were perturbed by AIC, especially d-glutamine and d-glutamate metabolism; histidine metabolism; alanine, aspartate, and glutamate metabolism; aminoacyl-tRNA biosynthesis; and arginine biosynthesis. Detailed pathway results are summarized in Table S2.
Table 1
Amino acid metabolic signature of Adriamycin-induced cardiotoxicity in mice
Amino Acid
|
VIP value
|
p value
|
l -Glutamic acid
|
3.70606
|
p<0.0001
|
l -Lysine
l -Serine
l -Tryptophan
l -Methionine
l -Histidine
l -Asparagine
l -Tyrosine
O-Phosphorylethanolamine
|
2.87705
1.82098
1.80749
1.57079
1.36099
1.16729
1.1004
1.08842
|
0.039
0.023
0.024
0.003
0.010
0.012
0.028
p<0.0001
|
Variable importance for projection (VIP) from the orthogonal partial least squares discriminant analysis model constructed with the control and model groups.
Considering that the in vivo model might reflect the global AA metabolic status, we established an in vitro model using ADR-treated cardiomyocytes to specifically focus on the AA metabolic signature in AIC. H9c2 cells were treated with ADR at various concentrations for 24 h. Data from the CCK-8 assay indicated that treating H9c2 cells with 1 μM ADR significantly induced cytotoxicity (Fig. 5). Therefore, this concentration was selected for the AA metabolism study. Using UPLC-MS/MS, we identified 15 AA metabolites with significantly different levels among 44 detected metabolites in the conditioned medium of ADR-treated H9c2 cells (Table S3). The levels of 10 AA metabolites (hypotaurine, d-homoserine, 2-AA, ethanolamine, taurine, l-asparagine, l-glutamic acid, l-serine, l-glutamine, l-tyrosine) were increased in the ADR group, whereas those of five AA metabolites (cadaverine, l-homocystine, l-aspartic acid, l-ornithine, l-alanine) were decreased (Fig. 6). The 44 analyzed metabolites were processed by PCA to characterize the metabolic profile of the cellular model (PC1, 60.5%; PC2, 24.6%, Fig. 7A). The PCA score plot revealed clear separation between the analyzed data groups, indicating that two groups had different metabolic profiles.
Supervised OPLS-DA was also performed within the in vitro model. The OPLS-DA score plots of culture medium supernatant samples are presented in Fig. 7B, and the plot of the predictive VIP values is presented in Fig. S2B. The OPLS-DA model revealed clear separation between the analyzed data groups, indicating that significant changes of AA metabolism occurred after ADR treatment. Five metabolites (l-tyrosine, l-alanine, l-glutamine, l-serine, l-glutamic acid) satisfying both VIP > 1.0 and p < 0.05 were identified as the signature of AIC in the cellular injury model (Table 2). Five important pathways including phenylalanine, tyrosine, and tryptophan biosynthesis; alanine, aspartate, and glutamate metabolism; glycine, serine, and threonine metabolism; aminoacyl-tRNA biosynthesis; and tyrosine metabolism were perturbed in the in vitro AIC model (Fig. 7C and Table S4).
Table 2
Amino acid metabolic signature in Adriamycin-induced H9c2 cell injury models
Amino Acid
|
VIP value
|
p value
|
l -Tyrosine
|
3.63705
|
p<0.0001
|
l -Alanine
|
2.76496
|
p<0.0001
|
l -Glutamine
|
2.60996
|
0.025
|
l -Serine
|
2.54653
|
p<0.0001
|
l -Glutamic acid
|
2.11724
|
p<0.0001
|
Pathway analysis
Via an overlap analysis, we found that the levels of three AAs, namely l-glutamate, l-serine, and L-tyrosine, were increased in both the in vivo and in vitro models (Fig. 8A), suggesting AA utilization impairment in AIC. Furthermore, we found the aminoacyl-tRNA biosynthesis and alanine, aspartate, and glutamate metabolism were both involved in the two models (Fig. 8B), suggesting the two pathways might be associated with AIC.