Antibiotic-Induced Changes to the Host Metabolic Environment Inhibit Drug Efficacy and Alter Immune Function

Abstract

Bactericidal antibiotics alter microbial metabolism as part of their lethality and can damage mitochondria in mammalian cells. In addition, antibiotic susceptibility is sensitive to extracellular metabolites, but it remains unknown whether metabolites present at an infection site can affect either treatment efficacy or immune function. Here, we quantify local metabolic changes in the host microenvironment following antibiotic treatment for a peritoneal Escherichia coli infection. Antibiotic treatment elicits microbiome-independent changes in local metabolites, but not those distal to the infection site, by acting directly on host cells. The metabolites induced during treatment, such as AMP, reduce antibiotic efficacy and enhance phagocytic killing. Moreover, antibiotic treatment impairs immune function by inhibiting respiratory activity in immune cells. Collectively, these results highlight the immunomodulatory potential of antibiotics and reveal the local metabolic microenvironment to be an important determinant of infection resolution.

Keywords: LC-MS/MS; antibiotic; germ-free; immunomodulation; metabolic environment; metabolomics; phagocytosis; respiration; systems biology.

Figure 1. Antibiotic treatment depletes central metabolism intermediates in the peritoneum

(A) Experimental design for metabolomic profiling. C57BL/6J mice were subjected to control conditions (CTL), antibiotic treatment with 100 μg/mL cipro (ABX), intraperitoneal infection with 10⁷ CFU E. coli (INF), or their combination (COMB). Peritoneal lavage, plasma and lung lavage samples were collected 24 h after infection. (B) Hierarchically clustered heatmap of metabolite concentrations from CTL, ABX, INF and COMB mice. (C) PCA projection of metabolomic profiles from peritoneal samples of all four treatment groups. (D) PLS-DA of peritoneal samples from ABX mice. Metabolites selected by elastic net regularization were depleted for central metabolism intermediates. (E) Concentrations for metabolites with large LV1-loadings in peritoneal samples from the ABX metabolite signature. Antibiotic treatment depleted uridine diphosphate (udp), glucose-6-phosphate (g6p) and ribulose-5-phosphate (r5p). Data are represented as mean ± SEM from n = 3 independent biological replicates. Significance reported as FDR-corrected p-values in comparison with corresponding CTL conditions: *: p ≤ 0.05, **: p ≤ 0.01, ****: p ≤ 0.0001.

Figure 2. Antibiotic treatment elicits microbiome-independent changes in host metabolites

(A) Experimental design for germ-free (GF) metabolomic profiling. GF mice were subjected to antibiotic treatment with 100 μg/mL cipro (ABX) and sampled 24 h later. (B) Hierarchically clustered heatmaps for changes in metabolite concentrations between ABX and control (CTL) mice, by tissue sampled. (C) PCA projection of metabolomic profiles from CTL and ABX conventional (CONV) and GF mice in the peritoneum (left). Concentrations for peritoneal metabolites with large peritoneal ABX LV1-loadings in CONV and GF mice (right). (D) PCA projection of metabolomic profiles from CTL and ABX conventional (CONV) and GF mice in the plasma (left). Concentrations for plasma metabolites with large plasma ABX LV1-loadings in CONV and GF mice (right). Data are represented as mean ± SEM from n = 3 independent biological replicates. Significance reported as FDR-corrected p-values in comparison with corresponding CTL conditions: **: p ≤ 0.01, ***: p ≤ 0.001, ****: p ≤ 0.0001.

Figure 3. Antibiotic treatment elicits unique metabolic changes in the presence of infection

(A) PLS-DA of peritoneal samples from INF mice. Metabolites selected by elastic net regularization were enriched for purine metabolites. (B) Concentrations for metabolites with large LV1-loadings in peritoneal samples from the INF metabolite signature. Peritoneal infection increased the abundance of guanine monophosphate (gmp) and depleted adenosine (adn) and adenosine monophosphate (amp). (C) PCA projection of peritoneal samples from all four treatment groups using metabolites from the ABX and INF metabolite signatures. (D) PLS-DA of peritoneal samples from COMB mice. Metabolites selected by elastic net regularization were enriched across diverse pathways. (E) Concentrations for metabolites with large LV1-loadings in peritoneal samples from the COMB metabolite signature. The combination treatment increased the abundance of thymine (thym) and depleted 3-phospho-D-glyceroyl phosphate (23dpg) and guanosine (gsn). Data are represented as mean ± SEM from n = 3 independent biological replicates. Significance reported as FDR-corrected p-values in comparison with corresponding CTL conditions: *: p ≤ 0.05, **: p ≤ 0.01, ***: p ≤ 0.001, ****: p ≤ 0.0001.

Figure 4. Metabolites altered by antibiotic treatment during infection inhibit drug efficacy

(A) Cipro MICs following supplementation with 10 mM of each metabolite from the COMB signature. (B) Dose-dependent reduction in cipro susceptibility by amp. E. coli were treated with 25 ng/mL ciprofloxacin, supplemented with increasing concentrations of amp. (C) Cipro MICs following supplementation with 10 mM of each metabolite from the ABX signature. (D) Cipro MICs following supplementation with 10 mM of each metabolite from the INF signature. Data are represented as mean ± SEM from n ≥ 3 independent biological replicates. Significance reported as FDR-corrected p-values in comparison with corresponding CTL conditions: *: p ≤ 0.05, **: p ≤ 0.01, ***: p ≤ 0.001, ****: p ≤ 0.0001.

Figure 5. Direct actions of antibiotic treatment on immune cells inhibit phagocytic killing

(A) Changes in macrophage oxygen consumption rate in control (CTL) and cells pre-treated for 3 h with cipro, following electron transport chain uncoupling by 2 μM oligomycin, 1 μM FCCP and 0.5 μM rotenone + antimycin A. (B) Changes in respiratory capacity following cipro pre-treatment. (C) Pathogen engulfment by control (CTL) or macrophages treated with 20 μg/mL cipro (ABX), 10 mM amp (amp) or their combination (ABX + amp). (D) Pathogen survival in CTL, ABX, amp or ABX + amp macrophages. (E) Phagocytic killing by CTL, ABX, amp or ABX + amp macrophages. Data are represented as mean ± SEM from n ≥ 3 independent biological replicates. Significance reported as FDR-corrected p-values within the indicated comparisons: *: p ≤ 0.05, **: p ≤ 0.01, ****: p ≤ 0.0001.

Figure 6. Metabolic effects of antibiotic treatment on host cells inhibit drug efficacy and impair immune function

During infection, antibiotics work in concert with immune cells to clear microbial pathogens (black). Meanwhile, antibiotics and pathogen cells metabolically remodel the local infectious microenvironment by acting on local host cells (dashed). Induced metabolites can inhibit drug efficacy and potentiate immune function (purple). Direct actions by antibiotics on immune cell metabolism can also impair immune cell phagocytic activity (red).