In December 2019, a new infectious respiratory disease (Coronavirus disease 2019, COVID-191) caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) emerged2,3, quickly becoming a pandemic and a global threat to public health. The virus has a single-stranded RNA with a 30 kb genome, which encodes the spike (S) protein that expresses a receptor-binding domain (RBD) for the angiotensinconverting enzyme 2 (ACE2) receptor4. In addition, S protein contains cleavage sites for cell proteases FURIN and transmembrane serine protease 2 (TMPRSS2) that allow viral cell entrance5. Cells from the alveoli, GI tract, and cornea epithelium, among others, co-expressed Ace2 and Tmprss2 genes6.
The eye surface, particularly the cornea, is a route of SARS-CoV-2 entrance6,7. Also, the nasolacrimal duct could leak virus-containing tears into the upper respiratory tract. Several lipid mediators modulate in ammatory responses and have been hypothesized to counteract COVID-19 pathology8,9. Lipid mediators facilitate debris clearance and antagonize pro-in ammatory cytokines by fostering in ammation resolution10,11. Here, we study lipoxin A4 (LXA4) derived from the ω-6 arachidonic acid12, the R,R stereoisomers Neuroprotectin D1 (NPD1) 13 and Resolvin D6-isomer (RvD6i)14 called docosanoids since they are derived from ω-3 docosahexaenoic acid and Elovanoid (ELV)-N32 that belongs to a new lipid mediator class discovered in our laboratory -the elovanoids15, 16 . These lipids are di-hydroxylated derivatives of very long chain polyunsaturated fatty acids (>28C, VLC-PUFAs) with prohomeostatic and neuroprotective bioactivity11, 15,16. Here, we show that ELV-N32 and RvD6i selectively decrease ACE2 receptor expression and binding of RBD of the S protein in the cornea stroma in an in vivo rat model of cornea injury. We con rm that Ace2 is an interferon-stimulated gene in HCEC, a mechanism that would enhance SARS-CoV-2 infectivity17. Therefore, we use HCEC in culture challenged with IFNγ to demonstrate that ELV-N32 or RvD6i exert blockage of ACE2 receptor expression, binding of RBD, hyperin ammation, senescence programming, and components of the cytokine storm.
Lipid mediators decrease cornea injury-induced expression of ACE2 and binding of Alexa 594-RBD.
Host proteases for S protein: FURIN5, TMPRSS2 and dipeptidyl peptidase 4 (DPP4)18 are expressed in the cornea (Fig. 1a) , indicating that it is a potential site for SARS-CoV-2 entrance, in agreement with clinical studies showing infected patients' epiphora, conjunctival congestion, or chemosis19. SARS-CoV-2 triggers lung injury and a systemic dysfunction of the in ammatory-immune system re ected in the cytokine storm20,21. We found that our cornea injury model recapitulates in ammatory-immune system dysfuctions22, including ACE2 receptor expression upon injury. To identify mediators that modulate these responses and to understand consequent mechanisms, we tested the following lipid mediators: LXA4, ELV-N32, RvD6i, and NPD1 (Fig. 1b,c) . LXA4, ELV-N32, and RvD6i decrease ACE2 abundance and gene expression levels ( Supplementary Fig. S1 ) to non-injured tissue, while NPD1 had no effect (Fig. 1d) . Alexa 594-RBD displayed remarkable binding to injured cornea stroma, and LXA4, ELV-N32, and RvD6i counteracted these injury-induced effects. Again, NPD1 did not have an effect. Thus, there is a correlation between changes in the ACE2 receptor and RBD binding in the cornea after injury and lipid treatment. Interestingly, most of the RBD was detected in the stroma, and in ammatory cells labeled with CD68 showed co-localization with RBD ( Supplementary Fig. S2a-b) .
Lipid mediators disrupt the ACE2 upregulation, hyper-in ammation, senescence, and cytokine storm components in the injured cornea in vivo.
RNA-seq analysis 14 days after injury with and without treatment (Fig. 1b) revealed well-clustered transcriptional pro les in each treated group (Fig. 2a) . In PCA plots, the transcriptomic pro le of noninjured corneas, control (red), and injured corneas treated with vehicle (green) were well separated.
Topical treatment with lipid mediators shows pro les closer to control corneas than to vehicle-treated corneas. ELV-N32 (pink) and RvD6i (cyan) were the nearest to the normal cornea. DEseq2 analysis allows comparison of all treated groups as well as control corneas to vehicle as a reference. Upregulated genes in vehicle-treated injury corneas revealed differences among treatment with lipid mediators, as depicted in Venn diagrams (Fig. 2b ). Since NPD1 failed to decrease the ACE2 expression and RBD binding upon injury ( Fig. 1d-h) , we focused on the groups of shared genes between control-LXA4-ELV-N32-RvD6i (450 genes including Ace2) and control-ELV-N32-RvD6i (737 genes). KEGG pathway analysis of these two data sets revealed cytokines and senescence-related pathways ( Fig. 2c) with signi cant false discover rate (FDR) values. On the other hand, IPA analysis predicted several cytokines as upstream regulators of Ace2 increased expression after injury. Interestingly, in addition to cytokines, the CDKN2A (p16/INK4) and NFkB (complex) and its correlated genes were predicted as inducers of Ace2 (Fig. 2d) . The RNA-seq analysis of Cdkn2a gene (Fig. 2e ) and the IPA inhibition score and p-value of this gene (Fig. 2f ) and the NFKB complex (Fig. 2g) con rm the prediction.
Lipid mediators counter-regulate cytokine storm components, NFkB/in ammation, and senescenceassociated secretory phenotype after cornea injury.
Since Ace2 gene activation is caused by the action of cytokines, p16INK4a and NFkB, we targeted genes regulated by those inducers. Thus, we explored in the injured cornea: (i) activated cytokines found in the serum of SARS-CoV-2 patients20, (ii) senescence-associated secretory phenotype (SASP) genes23, and (iii) NFkB/in ammation genes found in lung biopsies of SARS-CoV-224. The Venn diagram showed several shared genes by the three inducers (Fig. 3a) . Fifty-one injury-upregulated genes were counteracted by the lipid mediators (Fig. 3b) . The plot for each speci c gene is provided in Supplementary Figs Using the KEGG pathway analysis, we found similar pathways to those found in the entire transcriptome ( Fig. 2c and Supplementary Fig. S3a ). Employing the EnrichR -Archs4 human analysis tissue database, the 51 genes are more abundant in the omentum and lung (bulk tissue) (Fig. 3c) . This suggests that genes detected in the injured cornea might recapitulate changes in gene expression that occur in lung injury. Three targeted cytokines Il1b, Il6, and Vegfa genes are plotted in Fig. 3d . Our data showed that Il6 and Vegfa were upregulated by the injury, and the administration of LXA4, ELV-N32, or RvD6i reduced their expression (Fig. 3d) . We also focused on integrin genes since the spike protein contains an RGD motif in the RBD site that is recognized by some integrins as a potential receptor of SARS-CoV-229,30. Six integrins, which have the RGD binding domain in the heterodimer con rmation, are increased after injury and decreased by some of the lipid mediators (Fig. 3e ). Among these genes, Itga5 and Itgb1 are of interest since their speci c blocker ATN-161 greatly attenuates the SARS-CoV-2 infection in vitro31, and their expression is signi cantly decreased by ELV-N32 and RvD6i.
Lipid mediators attenuate IFNγ-speci c induction of ACE2 expression, Alexa 594-RBD binding, and senescence programming in human corneal epithelial cells.
Based on the IPA prediction of upstream regulators of Ace2 targeted cytokines, we treated HCEC with IL1β, IL2, IL6, IL8, IFNγ, IFNα, IFNε or TNFα at 1, 10, and 100 ng/mL. IFNγ or IFNα were the only cytokines to activate Ace2 expression, with IFNγ being the more potent of the two ( Fig. 4a and Supplementary Fig.  S6 ). We followed Ace2 expression by dd-PCR that provides absolute quanti cation. ELV-N32 or RvD6i markedly attenuated IFNγ-triggered Ace2 activation (Fig. 4b ). In addition, IFNγ stimulates the overexpression of senescence programming genes Cdkn2a (p16INK4a) and Mmp1. ELV-N32, RvD6i, and NPD1 decrease Cdkn2a activation to control values, but LXA4 does not. IFNγ-stimulated Alexa 594-RBD binding (Fig. 4c ) correlates with increased ACE2 expression (Fig. 4b) . ELV-N32, RvD6, and NPD1 decrease IFNγ-stimulated RBD binding (Fig. 4c) . Therefore, our data show that following IFNγ-stimulated RBD binding to ACE2, induction of senescence programming genes Cdkn2a (p16INK4a) and Mmp1 as well as SASP secretome activation takes place. These events are blocked by ELV-N32, RvD6i, and NPD1 but not by LXA4 (Fig. 4d ).
Here, we discern bioactivity among a group of lipid mediators on critical targets related to SARS-CoV-2 entrance and deleterious consequences of this viral infection. We uncover that the lipid mediators ELV-N32 and RvD6i decrease ACE2 receptor expression, binding of RBD of the S protein, in ammatory responses, and senescence programming using the rat cornea in vivo model. In addition, we demonstrate using HCEC in culture challenged with IFNγ that ELV-N32 and RvD6i exert similar effects. ELV-N32 remarkably decreases Furin expression, a protease that cleaves the S1/S2 site required for SARS-CoV-2 entry in lung cells5.
A key cytokine responding to viral infections is IFNγ32 that increases in the serum of severely affected COVID-19 patients20,33. We found that IFNγ induces Ace2 expression in HCEC at a much lower dose than INFα. Moreover, IFNγ activates cellular senescence re ected in enhanced Cdkn2a expression and SASP secretome release. This observation could contribute to explain why aging populations are more susceptible to COVID-1934. ELV-N32 does bear senolytic activity16, and both, ELV-N32 and RvD6i suppressed senescence genes and the SASP secretome in HCEC (Fig. 4d) . Therefore, S protein internalization may lead to IFNγ secretion, which would synergize with an integrin-rich environment amplifying the IFNγ effect35 and stimulating Ace2 overexpression. As a result, the higher ACE2, the higher SARS-CoV-2 binding would be possible. ELV-N32 and RvD6i suppressed the IFNγ stimulation of Ace2 expression as well as the IFNγ-induced senescence, where many SASP components are proin ammatory cytokines. PEDF+DHA (the precursor of RvD6i) and RvD1 suppress type 1 proin ammatory macrophages (induced by IFNγ) while increasing the type 2 anti-in ammatory macrophage phenotype36,37. Interestingly, ELV-N32, RvD6i, and NPD1 attenuated ACE2-RBD in the IFNγ-treated cells in culture (Fig. 4c) , while in the rat injured cornea, LXA4 displayed a signi cant effect on preventing ACE2-RBD interaction (Fig. 1f-h) . Of the lipid mediators studied, ELV-N32 and RvD6i consistently displayed protective bioactivity. RvD6i was recently identi ed in mouse tears as related to corneal nerve regeneration14,38. ELV-N32 is a powerful neuroprotective and anti-in ammatory lipid mediator16.
ELV-N32 and RvD6i also decrease integrins expression. The S protein contains an RGD motif in the RBD site that recognizes integrins and stimulates virus internalization by activation PI-3K, a pathway predicted to increase along with ACE2 enhanced expression (Fig. 2c) 29, 30 . Inhibition of integrin α5β1 by a non-RGD peptide derived from bronectin, inhibit the binding of the S protein to ACE2 and decrease virus infection in in vitro31.
In conclusion, our data demonstrate that ELV-N32 or RvD6i diminish ACE2 expression and binding of the S protein RBD and, consequently, activate pro-homeostatic signaling and reduce tissue damage.
The application of these lipid mediators could be of therapeutic use alone or as a complement with current antiviral strategies for COVID-19. Moreover, the lipid mediators identi ed here might work by similar mechanisms in other cell types and further expand the scope of their therapeutic applications beyond the eye.
Limitations of this study.
Additional research will be needed to fully elucidate the molecular mechanisms used by the lipid mediators that elicit downregulation of ACE2 and the genes encoding in ammatory/senescence proteins. The use of the entire S protein in the models studied here will provide the connection between lipid mediators acting on cell attachment and cell entrance, particularly since ELV-N32 remarkably reduces furin expression correlated with ACE2 downregulation. Moreover, the use of the intact virus would offer a direct demonstration of the signi cance of the effects of the lipid mediators studied here. 
The rats were anesthetized by intraperitoneal injection of Ketamine (50-100 mg/kg) plus xylazine (5-10 mg/kg). A 4 mm diameter lter paper soaked in 1 N NaOH was placed on the central cornea of the right eye for 45 seconds, and then the eye was thoroughly washed with 10 mL of saline. After injury, the rats were randomly divided into ve treatment groups: vehicle; lipoxin A4 (LXA4) from Cayman Chemical (Ann Arbor, MI, USA); R,R Resolvin D6 isomer (RvD6i), R,R neuroprotection D (NPD1), and elovanoid (ELV)-N32 synthesized by Dr. R. Nshimiyimana and Prof. N. Petasis. All lipid solutions were prepared at the nal concentration of 10 μM using PBS with the minimal contamination of ethanol by evaporating the ethanol and immediately dissolve the lipids in PBS, then vortex well for 2 min. Topical administration (20 μl) was done 3x/day for 14 days. The experiments were double-blinded with the lipid mediators coded during the whole experiments. At the end of the study, when all data was collected, the code was opened.
Corneal RNA-sequencing Injured corneas (n = 5/condition) were harvested and homogenized with TRIzol (Thermo Fisher Scienti c) on ice with a glass Dounce homogenizer. RNA sequencing was performed as described14. Brie y, after mRNA extraction and determination of purity, 8 ng of total RNA was reverse transcribed, and total cDNAs were ampli ed using ISPCR primer, and the library was made with the Nextera XT DNA library preparation kit (Illumina, San Diego, CA, USA). The libraries were pooled with the same molarity and sequenced using the NextSeq 500/550 High Output Kit v2 (75 cycles, Illumina). After demultiplexing, RNA-seq data were aligned to the Rattus Norvegicus reference genome (ftp://ftp.ensembl.org/pub/release-98/fasta/rattus_norvegicus/dna/) using the Subread package v2.0.1 alignment function39. The BAM les for sequencing data alignment were counted using featureCounts function of Subread tool40 using the macOS Catalina. The raw count data were subjected to differential gene expression analysis using DESeq2 package for R41 with the vehicle group as reference. The adjusted p-values were named as the false discover rate (FDR). Signi cantly changed genes (FDR < 0.05) between each treatment vs. vehicle were subjected to the enrichment analysis using EnrichR42 and NetworkAnalyst 3.043, and pathway analysis using the IPA (QIAGEN Inc., https://www.qiagenbioinformatics.com/products/ingenuitypathway-analysis).
Preparation of Alexa 594-conjugated RBD fragment of S protein RBD fragment of the Spike protein belonging to SARS-CoV-2 (Raybiotech, Peachtree Corners GA. Cat. 230-30162-1000) was labeled using Alexa Fluor™ 594 Protein Labeling Kit (ThermoFisher, Waltham, MA. Cat. A10239) following the manufacturer's directions. Brie y, 1 mg of protein was dissolved in 0.1 M bicarbonate and then incubated with the Alexa Fluor 594 dye for one hour. The dye was washed using an Amicon-Ultra centrifugal lter cutoff 10KDa (Merck, Millipore Carrigtwohill, CO. Cat. UFC201024). To assess the e ciency of the label, the protein was measured at 280 nm and 590 nm absorbance using NanoDrop One (Thermo Scienti c). There was a ratio of 0.4 moles of dye/mole of protein and a recovery of about 80%. For screening the stimulation of receptor ACE2 by cytokines, the HCEC were cultured with KGM until 50-60% con uence. Then, changed to KBM containing IL-1β, -2, -6 and 8, IFN-α, -ε, and -γ or TNFα at 1, 10 or 100 ng/ml. The cells were harvested after 6 hours and analyze for the gene expression of Ace2. In other experiments, HCEC were stimulated with IFNγ, and thereafter, lipid mediators were added. For the Alexa 594-conjugated RBD binding, IFNγ was used as a cytokine trigger. At 12 hours after cytokine exposure and lipid mediator treatments, 0.5 μg of labeled RBD was added to the medium. The evaluation of RBD binding was conducted 24 hours after.
Corneal tissue was xed in Zamboni xative (MasterTech Scienti c, Lodi, CA USA) for 2 hours immediately after euthanasia. After thoroughly washing with PBS, the corneas were embedded in optimal cutting temperature compound, and serial 10-μm cryostat sections were obtained, dried at room temperature for 2 hours, and stored at -20 °C until use. For immuno uorescence, the sections were incubated with primary antibodies at the concentration described in Table 1 in a wet chamber at 4 °C overnight. The sections were washed 3 x/5 min with PBS following by incubation for 1 hour at RT with Alexa Fluor-conjugated secondary antibodies (1:1000 dilution). All sections were counterstained with DAPI (ThermoFisher Scienti c, Cat. D1306), and images of rat corneal samples were acquired with an Olympus IX71 uorescent microscope.
Twenty-four hours after Alexa 594-RBD was added to the HCEC, the cells were washed with PBS (3x/5min) and xed with 4% paraformaldehyde for 30 minutes at RT. The HCEC were washed 2x with PBS and stained with Hoechst 33342 Solution (ThermoFisher Scienti c, Cat. 62249) for 30 minutes at RT. Next, the HCEC were washed 2x with PBS before imaging. For unbiased data collection, 7 designated areas were de ned in each well ( Supplementary Fig. S7 ) and captured with an Olympus FV3000 confocal laser scanning microscopy under "Multi Area Time Lapse" (MATL) mode. All images were acquired with the same parameters and Z-section range, converted and inputted in the Imaris software version 9.5.1. The threshold for the control images was de ned by the HCEC without Alexa 594-conjugated RBD of S protein and using it as a threshold lter for the Imaris batch image processing function. The sum of total intensity for each image was used to evaluate the binding e ciency. The whole process was summarized in the Supplementary Fig. S7b ,c.
Total RNA was isolated using RNeasy Plus Mini Kit (Qiagen, Germany), and 1 µg of total RNA was reverse transcribed using an iScript cDNA Synthesis Kit (Bio-Rad, Cat. 170-8841). For ddPCR, 10 ng of cDNA was multiplexed with Ace2 and phosphoglycerate kinase 1 (Pgk1) probes (Bio-Rad, Cat. qHSACEP005-1563 and dHSACPE503-3809) using dd-PCR Supermix for Probes No dUTP (Bio-Rad, Cat. 1863024). Then, 20 µL of the reaction was mixed with 70 µL of Droplet Generation Oil (Bio-Rad Cat:1863005) to make the reaction droplets. The emulsi ed samples were carefully transferred to PCR plates (Bio-Rad, Cat. 12001925) and ampli ed using the cycling: 95 °C for 10 minutes, 40 cycles of a two-step cycling protocol (94 °C for 30 seconds and 60 °C for 1 minute), and 98 °C for 10 minutes. Next, the post-cycling plate was placed into the QX200 Droplet Reader with the FAM/HEX setting. The absolute quantity of DNA per sample (copies/µL) was processed using QuantaSoft Analysis Pro Software. For the data analysis, the ratio of quanti ed Ace2 to Pgk1 was used.
The capillary-based western assay was performed using a Jess Protein Simple system (San Jose, CA, USA) as manufacture suggested protocol. Brie y, samples were lysed with RIPA buffer containing a protease inhibitor cocktail (Sigma, Cat. P8340). Cell debris was removed after 10 min centrifugation at 16,000 x g. Protein concentration was determined by BCA assay (Thermo Fisher Scienti c, Cat. 23225) and 1 µg used/ reaction. Fluorescent Master Mix was mixed with 40 mM DTT, and the mixture was added to each sample to provide a denaturing and reducing environment. Samples were heated at 95 °C/5 min, and 3 µL of each sample were loaded. The 12-230 kDa cartridge (Protein Simple -#SM-W004) was used. Primary antibodies were diluted in antibody diluent 2 buffer (Protein Simple, #042-203) while the working solution of secondary antibodies was provided by the company (Protein Simple, #042-206) . Then, the lled plate was spin-down for 10 min at 1,000 x g to remove bubbles and plate, and capillaries were loaded into the Jess machine. For data analysis, the area of spectra that matched the molecular weight of the target protein was used. To reduce the coe cient variant, we analyzed the GAPDH for each capillary. The ratio of the targeted protein to GAPDH was used for statistical comparisons. For visualization, the arti cial lanes generated from spectra volume was used.
High-throughput qPCR using Biomark™ HD Quantitative PCR was performed with the Biomark HD system (Fluidigm, San Francisco, CA, USA). Brie y, 200 ng of RNA was reverse-transcribed using iScript Reverse Transcription Supermix (Bio-Rad), and the cDNA was pre-ampli ed using the PreAmp Master Mix (PN 100-5580; Fluidigm) . The cDNA was then subjected to Exonuclease I treatment and diluted 5 times in TE Buffer. The qPCR reaction mixture and primer reaction mixture were made and loaded into the Biomark 96.96 IFC™ (Integrated Fluidic Circuit). The enzyme reaction was mixed using Juno™ Controller (Fluidigm) and run using the cycling program of (i) 70 °C for 40 minutes followed by 60 °C for 30 seconds, (ii) hot start for 1 minute at 95 °C, (iii) 30 cycles of denaturation at 96 °C for 5 seconds, and annealing at 60 °C for 20 seconds, and (iv) melting curves between 60 °C and 95 °C with 1 °C increments/3 seconds. The Ct value of target genes was normalized to the house-keeping genes Gapdh, Hprt1, and Tfrc before normalized to the vehicle group. Relative fold changes from the ΔΔCT calculation was used to make the graph. Primersequences are provided in Table  2 .
Data are expressed as mean ± SD. The data were analyzed by 1-way ANOVA followed by Dunnett's multiple comparisons post hoc test at 95% con dence level with the vehicle as reference. All graphs were made using GraphPad Prism 7 (GraphPad Software, La Jolla, CA, USA) with the mean ± SD while all statistical analyses were done using built-in function of Prism 7.
The data that support the ndings of this study are available from the corresponding authors upon reasonable request. Selective lipid mediators disrupt ACE2 upregulation and injury-mediated hyper-in ammation, senescence, and cytokine storm components. a, PCA plot of RNA-seq data. Rat corneas were analyzed at day 14 after injury +/-treatments (Fig. 1b) . Each data point represents one animal (N = 5/group, except LXA4 with N = 3 and control with N = 6). The eclipse of 95% con dence interval was used to group data points from the same set of treatment. b, Venn diagram of signi cant genes (FDR < 0.05) upregulated by the vehicle treatment of injured corneas (RNA-seq data set was analyzed using DEseq2 with vehicle injured corneas as reference). The negative log2 fold change genes (upregulated by vehicle) with FDR < 0.05 were used.
We excluded NPD1 because it failed to decrease Ace2 expression upon injury (Fig. 1d) . The groups of shared genes between control-LXA4-ELV-N32-RvD6i and control-ELV-N32-RvD6i are depicted. c, The KEGG-pathway enrichment networks of selected genes from b. Bars were sorted by p-value. The length of the bar represents the signi cance of the pathway, while the lighter the color, the higher the signi cance. The number shows amount of genes from denoted group that are enriched in each pathway. d, IPA upstream regulator analysis of signi cant genes vs. vehicle (injury) group. There are proteins with negative activation z-score compared to vehicle group (blue color). Among those are CDKN2A and NFkB (complex). e, RNA-seq normalized counts of Cdkn2a gene that encodes the senescence key-marker p16INK4a; ELV-N32 decrease its expression. Data correspond to one cornea for each data point and is presented as mean ±SD. The p-values were analyzed by ANOVA-post hoc Dunnett's multiple comparisons test with vehicle as reference. The normalized counts were used for analysis. IPA scores for CDKN2A (f) and NFkB (complex) (g) upstream regulators. The left y-axis is the inhibition z-score, while the right y-axis e is -log10 of p-value. The cutoff line for p-value is <0.05. Lipid mediators down-regulate injury-induced gene expression of NFkB/in ammation, senescenceassociated secretory phenotype, and cytokine storm markers after cornea injury. a, Venn diagram of cytokines, SASP, and NFkB in ammatory genes upregulated by injury. b, Heatmap of normalized counts data. Each small square represents data from one cornea. There are 51 genes increased by injury, and most are inhibited by ELV-N32 and RvD6i treatment. c, The ArchS4 human tissue analysis prediction for the 51 genes. The length of the bar represents the signi cance of the gene set in the tissues, while the lighter the color, the higher the signi cance. The number shows the amount of genes from the denoted group enriched in each pathway. d, Scatter plots of Il1b, Il6, and Vegfa genes. e, Scatter plots of genes that encode proteins that target RGD. The p-value of ANOVA-post hoc Dunnett's multiple comparisons test with vehicle as reference are shown. Mean and SD are depicted as the lines. The normalized counts were used for analysis. Figure 4 