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Endotoxemia-mediated inflammation potentiates aminoglycoside-induced ototoxicity

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Science Translational Medicine  29 Jul 2015:
Vol. 7, Issue 298, pp. 298ra118
DOI: 10.1126/scitranslmed.aac5546
  • Fig. 1. Cochlear lateral wall uptake of GTTR is enhanced by LPS.

    (A) In xz planes of the cochlear lateral wall 1 hour after GTTR injection, F-actin labeling (green) revealed tight junctions (arrowheads) between marginal cells (MC), with amorphous labeling in basal cells (BC; arrows). In DPBS-treated mice, intense GTTR fluorescence (red) distinguished strial capillaries (c), with less intense fluorescence in marginal cells, intrastrial layer (IS), and basal cells of the stria vascularis. The spiral ligament (SL) fibrocytes presented substantially less intense GTTR fluorescence compared to strial cells. LPS-treated mice displayed more intense GTTR fluorescence in the lateral wall (right panel) compared to DPBS-treated mice (left panel). (B) A focal series of xy planes through marginal cells, intrastrial tissues, basal cells, and fibrocytes at successively lower xy planes in the z axis, 1 hour after GTTR injection. LPS-treated mice exhibited more intense GTTR fluorescence in grayscale (right panels) compared to DPBS-treated mice (left panels). Scale bar, 50 μm. (C) Mean pixel intensities of GTTR fluorescence in lateral wall ROIs (excluding capillary structures) are dose-dependently increased with increasing doses of LPS at 1 and 3 hours after GTTR injection (relative to DPBS-treated mice at 1 hour), with statistical significance in every cell type at 1 hour of LPS (1 mg/kg or higher dose) (*P < 0.05, **P < 0.01, ***P < 0.001, Wilcoxon signed-rank test; error bars, SEM; n as in table S1).

  • Fig. 2. Low-dose LPS does not alter serum concentrations but does alter cochlear concentrations of aminoglycosides.

    (A) Using immunoturbidimetry, GTTR serum concentrations were significantly higher in LPS (2.5 and 10 mg/kg)–treated mice than in controls at 1 or 3 hours. There was no difference between DPBS-treated mice and those dosed with LPS at 0.1 and 1 mg/kg, nor between mice dosed with LPS at 2.5 and 10 mg/kg. Serum concentrations of GTTR in mice treated with LPS at 2.5 mg/kg were significantly higher than in those treated with LPS at 0.1 and 1 mg/kg at both time points (P < 0.05). Elevated serum GTTR concentrations in mice treated with LPS at 10 mg/kg showed borderline significance at 1 hour compared to those treated with LPS at 0.1 and 1 mg/kg (P = 0.087 and P = 0.053, respectively) and variable significance at 3 hours (P = 0.27 and P = 0.028, respectively; see also table S2; *P < 0.05, **P < 0.01, ***P < 0.005, Mann-Whitney U test; n as in table S1). (B and D) Using ELISA, serum concentrations of GTTR or gentamicin were not statistically different between DPBS-treated and LPS (1 mg/kg)–treated mice at 1 or 3 hours after injection. (C and E) Cochlear concentrations of GTTR or gentamicin (GT) were significantly increased in LPS (1 mg/kg)–treated mice compared to those in controls at 1 or 3 hours after injection (*P < 0.05, Student’s unpaired t test; n = 4 per group). Error bars, SEM; a.u., arbitrary units.

  • Fig. 3. LPS does not alter BLB permeability but vasodilates basal strial capillaries.

    (A) The relative mean intensities of hTR fluorescence in marginal cell (MC), intrastrial tissue (IS), basal cell (BC), and spiral ligament (SL) layers from P6 pups were significantly elevated compared to the same ROIs in adult mice. There was no difference in hTR fluorescence of lateral wall ROIs between DPBS- and LPS-treated adult mice [*P < 0.05, ***P < 0.001, two-way analysis of variance (ANOVA) with Bonferroni post hoc tests; n = 6 cochleae per group; error bars, SD]. Absolute fluorescence intensities are shown in fig. S5A. (B and C) In P6 mice, the lumen of strial capillaries, revealed by phalloidin labeling, was larger than in adult DPBS-treated mice (endothelial cells indicated by white arrowheads). (D) Twenty-five hours after LPS treatment, a subpopulation of strial capillaries were dilated compared to DPBS-treated mice (C). Scale bar, 20 μm. (E) Strial capillary diameters in P6 mice were wider than those in DPBS-treated adults (see also Table 1). LPS-treated adult mice had a subset of dilated strial capillaries, resulting in a bimodal distribution. (F) LPS also dilated a subset of strial capillaries in C3H/HeOuJ mice compared to DPBS-treated C3H/HeOuJ mice. (G) In TLR4-hyporesponsive C3H/HeJ mice, LPS dilated fewer strial capillaries compared to LPS-treated control C3H/HeOuJ mice (F), resulting in an asymmetrical bimodal distribution. A Gaussian regression curve fit was applied to obtain the bimodal peak means in Table 1.

  • Fig. 4. Low-dose LPS induced major inflammatory responses in serum and cochleae within 6 hours.

    (A) Significant increases in selected serum inflammatory proteins were observed 6 hours after LPS (±gentamicin) injection compared to DPBS-treated mice (±gentamicin; n = 10 per cohort). (B) Significant increases in cochlear inflammatory proteins were observed 6 hours after LPS (±gentamicin) injection for TNFα, IL-1α, IL-6, IL-8, MIP-1α, and MIP-2α (but not IL-1β and IL-10) compared to DPBS-treated mice [±gentamicin; n = 5 per cohort; 4 cochleae per sample; measured in duplicate; *, significant difference after one-way ANOVA with Bonferroni multiple comparison correction and a family-wise 95% confidence level; error bars, 95% confidence intervals (CIs) derived from Student’s t test]. (C) Significant increases in cochlear mRNA for selected inflammatory markers were observed 6 hours after LPS (±gentamicin) injection when normalized to DPBS-treated mice [n = 6 per cohort; 2 cochleae per sample; *, significant difference if the 95% CI does not overlap with 1 (that is, DPBS-treated mice baseline)]. Gentamicin did not modulate serum or cochlear expression of inflammatory proteins or mRNA for inflammatory markers.

  • Fig. 5. TLR4-mediated cochlear inflammatory markers are attenuated in C3H/HeJ mice.

    (A) All selected acute-phase inflammatory proteins (except for IL-10) were significantly elevated in cochleae from LPS-treated C57BL/6 and C3H/HeOuJ mice compared to those from DPBS-treated mice of the same strain. Several inflammatory proteins (TNFα, IL-6, IL-8, MIP-1α, and MIP-2α) were more elevated in C57BL/6 compared to those in C3H/HeOuJ mice after LPS. In TLR4-hyporesponsive cochleae from C3H/HeJ mice, only a subset of inflammatory proteins (IL-1α, IL-6, IL-8, and MIP-1α) were elevated after LPS, with small differences between the means for TNFα and IL-10. Expression of predominantly later-expressing inflammatory markers (IL-1α, IL-6, IL-8, and MIP-1α) was significantly attenuated in LPS-treated C3H/HeJ mice compared to that in LPS-treated C3H/HeOuJ and C57BL/6 mice (n = 4 per cohort; 6 cochleae from 3 mice per sample). (B) In C57BL/6 and C3H/HeOuJ mice, significant increases were observed in cochlear expression of Il-1β, Il-6, Il-8, Il-10, Mip-1α, and Mip-2α mRNA after LPS treatment when normalized to DPBS-treated mice. These increases were attenuated for Il-8, Mip-1α, and Mip-2α in LPS-treated C3H/HeJ mice compared to those in LPS-treated C3H/HeOuJ mice. Il-10 mRNA expression was significantly higher in C3H/HeJ mice compared to that in C3H/HeOuJ and C57BL/6 mice (n = 4 per cohort; 2 cochleae from 1 mouse per sample). Error bars, 95% CI derived from Student’s t test; *, significant difference compared to C3H/HeOuJ mice after one-way ANOVA with Dunnett’s post hoc tests and a family-wise 95% confidence level. See also fig. S6.

  • Fig. 6. LPS-induced GTTR uptake by lateral wall cells is attenuated in TLR4-hyporesponsive C3H/HeJ mice.

    The fold change in GTTR intensity in LPS-treated mice over DPBS-treated mice is shown. GTTR fluorescence was significantly enhanced in strial marginal (MC), intermediate (IC), and basal (BC) cells, as well as fibrocytes (FC) of LPS-treated C3H/HeOuJ mice compared to that in DPBS-treated C3H/HeOuJ mice. LPS also significantly enhanced GTTR fluorescence intensities in strial cells (but not fibrocytes) in LPS-treated C3H/HeJ mice compared to that in DPBS-treated C3H/HeJ mice. Note that LPS-induced GTTR uptake was significantly attenuated (P < 0.05) in marginal cells, intermediate cells, and fibrocytes in C3H/HeJ mice compared to that in C3H/HeOuJ mice (*P < 0.05; n = 8 per bar; error bars, 95% CI derived from Student’s t test; significance was determined if 95% CI did not overlap with 1; #P < 0.05, unpaired one-way t test between strains; see fig. S8 for raw data).

  • Fig. 7. Chronic endotoxemia potentiates kanamycin ototoxicity.

    (A) Three weeks after chronic LPS (or DPBS) exposure ± kanamycin (see fig. S13), ABR threshold shifts for LPS-only mice (n = 5) were not different from DPBS-treated mice (n = 4). Kanamycin alone (n = 5) induced a small but significant PTS at only 32 kHz (**P < 0.01) compared to DPBS-treated mice. Mice that received LPS + kanamycin (n = 6) had significant PTS at 16, 24 (##P < 0.01), and 32 kHz (#P < 0.05) compared to those treated with kanamycin, DPBS, or LPS only (**P < 0.01). Mice receiving LPS + kanamycin also had significant PTS at 12 kHz compared to those treated with DPBS or LPS only (фP < 0.05 and P < 0.01, respectively), or LPS-only mice at 8 kHz (P < 0.05). Error bars, SD. All statistical results were produced using two-way ANOVA with Bonferroni post hoc correction with 95% family-wise confidence intervals. (B) Cytocochleogram for mice in (A) revealed that OHC loss in the basal cochlear regions was greater and over a wider frequency range in LPS + kanamycin–treated mice compared to that in mice treated with LPS, DPBS, or kanamycin alone. Mean cochlear length = 6.84 (±0.79, SD) mm. Error bars, 95% CI derived from Student’s t test. See also figs. S9 to S11 and tables S5 and S7 for statistical comparisons using two-way ANOVA Bonferroni post hoc correction with 95% family-wise confidence intervals.

  • Table 1. Vasodilation of strial capillaries by LPS.

    In basal coils, strial capillary diameters in P6 pups were significantly larger than those in DPBS-treated C57BL/6 adult mice (****P < 0.0001). LPS dilated a subset (45%) of strial capillaries in adult mice. The population of capillary diameters in LPS-treated C57BL/6 mice was significantly greater compared to that in DPBS-treated C57BL/6 mice (P < 0.0001). LPS also dilated a subset (50%) of strial capillaries in C3H/HeOuJ mice. In TLR4-hyporesponsive C3H/HeJ mice, LPS dilated a smaller subset (22%) of strial capillaries. The population of capillary diameters in LPS-treated C3H/HeJ mice was significantly greater compared to that in DPBS-treated C3H/HeJ mice (P < 0.0001). The population of capillary diameters in LPS-treated C3H/HeJ mice was significantly smaller compared to that in LPS-treated C3H/HeOuJ mice (P < 0.0001, one-way ANOVA with Tukey post hoc tests). In apical coils, LPS dilated a subset (45%) of strial capillaries in C57BL/6 mice. The population of apical strial capillary diameters in LPS-treated C57BL/6 mice was significantly greater compared to that in DPBS-treated C57BL/6 adult mice (P < 0.0001). A Gaussian regression curve fit was applied to obtain the peak means of the bimodal distributions in Fig. 3.

    MouseLPSMean
    diameter
    (±SD)
    in μm
    Mean
    bimodal
    diameter
    (±SD) in μm
    [% of n]
    n
    (number
    of mice)
    Significance
    (versus
    in-strain
    DPBS-treated
    mice)
    Basal coils
    C57BL/6
    P6 pups
    13.8 (±1.5)300 (3)****
    C57BL/6
    adults
    5.1 (±1.0)300 (3)
    C57BL/6
    adults
    +5.3 (±0.9)8.6 (±1.1)
    [45.3%]
    300 (3)****
    C3H/HeOuJ
    adults
    5.3 (±0.8)480 (4)
    C3H/HeOuJ
    adults
    +5.7 (±0.8)8.6 (±0.9)
    [49.7%]
    480 (4)****
    C3H/HeJ
    adults
    5.3 (±0.9)480 (4)
    C3H/HeJ
    adults
    +5.4 (±0.8)8.1 (±0.9)
    [22.1%]
    480 (4)****
    Apical coils
    C57BL/6
    adults
    5.0 (±0.7)480 (4)
    C57BL/6
    adults
    +5.6 (±0.6)8.1 (±1.0)
    [59.8%]
    480 (4)****
  • Table 2. Effect of LPS on serum concentrations of histamine and serotonin.

    Serum histamine concentrations were not affected by increasing doses of LPS. Serum serotonin concentrations were significantly decreased at all LPS doses compared to DPBS-treated mice (*P < 0.05, **P < 0.001, Mann-Whitney U test; n in table S1 at 3 hours after GTTR injection).

    LPS dose
    (mg/kg)
    Histamine
    (ng/ml ± SEM)
    Serotonin
    (ng/ml ± SEM)
    033 (±2)2770 (±100)**
    0.125 (±3)2135 (±285)**
    1.024 (±4)579 (±157)**
    2.528 (±3)830 (±246)**
    1036 (±6)837 (±329)**

Supplementary Materials

  • www.sciencetranslationalmedicine.org/cgi/content/full/7/298/298ra118/DC1

    Materials and Methods

    Fig. S1. LPS treatment enhances cochlear lateral wall uptake of GTTR.

    Fig. S2. OHC uptake of GTTR is accelerated by LPS exposure.

    Fig. S3. Renal uptake of GTTR is reduced only at high doses of LPS.

    Fig. S4. LPS induces acute anorexia.

    Fig. S5. LPS does not alter BLB permeability yet vasodilates apical strial capillaries.

    Fig. S6. Serum serotonin, but not histamine, concentrations were decreased with increasing doses of LPS.

    Fig. S7. TLR4-mediated inflammatory markers are modulated by LPS.

    Fig. S8. LPS-induced GTTR uptake by cochlear lateral wall cells in control C3H/HeOuJ and TLR4-hyporesponsive C3H/HeJ mice.

    Fig. S9. Absolute ABR thresholds are elevated by chronic kanamycin, or kanamycin plus LPS, dosing.

    Fig. S10. Threshold shifts induced by chronic kanamycin, or kanamycin plus LPS, dosing.

    Fig. S11. Effect of chronic kanamycin treatment, with or without LPS, on ABRs, OHC survival and BLB permeability.

    Fig. S12. Absolute ABRs, threshold shifts and weight changes induced by chronic LPS, kanamycin, or LPS+kanamycin in C57BL/6 mice.

    Fig. S13. Acute LPS-induced endotoxemia does not alter ABR thresholds.

    Fig. S14. Schematic displaying potential mechanisms for aminoglycoside trafficking across the BLB.

    Fig. S15. Acute LPS and aminoglycoside dosing paradigm.

    Fig. S16. ELISA and qRT-PCR experimental designs for 6- and 24-hour LPS exposures.

    Fig. S17. Chronic LPS–induced endotoxemia and kanamycin ototoxicity protocol.

    Table S1. Number of mice in each condition for Figs. 1 and 2A and fig. S1.

    Table S2. Probability of significant difference in GTTR serum concentrations for Fig. 2A.

    Table S3. Probability of a significant difference in threshold shifts 1 day after chronic LPS–induced endotoxemia with or without kanamycin treatment.

    Table S4. Probability of a significant difference in threshold shifts 1.5 weeks after chronic LPS–induced endotoxemia with or without kanamycin treatment.

    Table S5. Probability of significant difference in threshold shifts 3 weeks after chronic LPS–induced endotoxemia with or without kanamycin treatment.

    Table S6. Probability of a significant difference in threshold shifts immediately after chronic LPS–induced endotoxemia with or without kanamycin treatment.

    Table S7. Probability of a significant difference in OHC survival 3 weeks after chronic LPS–induced endotoxemia with or without kanamycin treatment.

    Table S8. Probability of a significant difference in OHC survival immediately after chronic LPS–induced endotoxemia with or without kanamycin treatment.

    Table S9. Probability of decreasing OHC survival 3 weeks after chronic LPS–induced endotoxemia with or without kanamycin treatment compared to immediately after treatment.

  • Supplementary Material for:

    Endotoxemia-mediated inflammation potentiates aminoglycoside-induced ototoxicity

    Ja-Won Koo, Lourdes Quintanilla-Dieck, Meiyan Jiang, Jianping Liu, Zachary D. Urdang, Jordan J. Allensworth, Campbell P. Cross, Hongzhe Li, Peter S. Steyger*

    *Corresponding author. E-mail: steygerp{at}ohsu.edu

    Published 29 July 2015, Sci. Transl. Med. 7, 298ra118 (2015)
    DOI: 10.1126/scitranslmed.aac5546

    This PDF file includes:

    • Materials and Methods
    • Fig. S1. LPS treatment enhances cochlear lateral wall uptake of GTTR.
    • Fig. S2. OHC uptake of GTTR is accelerated by LPS exposure.
    • Fig. S3. Renal uptake of GTTR is reduced only at high doses of LPS.
    • Fig. S4. LPS induces acute anorexia.
    • Fig. S5. LPS does not alter BLB permeability yet vasodilates apical strial capillaries.
    • Fig. S6. Serum serotonin, but not histamine, concentrations were decreased with increasing doses of LPS.
    • Fig. S7. TLR4-mediated inflammatory markers are modulated by LPS.
    • Fig. S8. LPS-induced GTTR uptake by cochlear lateral wall cells in control C3H/HeOuJ and TLR4-hyporesponsive C3H/HeJ mice.
    • Fig. S9. Absolute ABR thresholds are elevated by chronic kanamycin, or kanamycin plus LPS, dosing.
    • Fig. S10. Threshold shifts induced by chronic kanamycin, or kanamycin plus LPS, dosing.
    • Fig. S11. Effect of chronic kanamycin treatment, with or without LPS, on ABRs, OHC survival and BLB permeability.
    • Fig. S12. Absolute ABRs, threshold shifts and weight changes induced by chronic LPS, kanamycin, or LPS+kanamycin in C57BL/6 mice.
    • Fig. S13. Acute LPS-induced endotoxemia does not alter ABR thresholds.
    • Fig. S14. Schematic displaying potential mechanisms for aminoglycoside trafficking across the BLB.
    • Fig. S15. Acute LPS and aminoglycoside dosing paradigm.
    • Fig. S16. ELISA and qRT-PCR experimental designs for 6- and 24-hour LPS exposures.
    • Fig. S17. Chronic LPS–induced endotoxemia and kanamycin ototoxicity protocol.
    • Table S1. Number of mice in each condition for Figs. 1 and 2A and fig. S1.
    • Table S2. Probability of significant difference in GTTR serum concentrations for Fig. 2A.
    • Table S3. Probability of a significant difference in threshold shifts 1 day after chronic LPS–induced endotoxemia with or without kanamycin treatment.
    • Table S4. Probability of a significant difference in threshold shifts 1.5 weeks after chronic LPS–induced endotoxemia with or without kanamycin treatment.
    • Table S5. Probability of significant difference in threshold shifts 3 weeks after chronic LPS–induced endotoxemia with or without kanamycin treatment.
    • Table S6. Probability of a significant difference in threshold shifts immediately after chronic LPS–induced endotoxemia with or without kanamycin treatment.
    • Table S7. Probability of a significant difference in OHC survival 3 weeks after chronic LPS–induced endotoxemia with or without kanamycin treatment.
    • Table S8. Probability of a significant difference in OHC survival immediately after chronic LPS–induced endotoxemia with or without kanamycin treatment.
    • Table S9. Probability of decreasing OHC survival 3 weeks after chronic LPS–induced endotoxemia with or without kanamycin treatment compared to immediately after treatment.

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