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The Role of Interleukin-1 in Wound Biology. Part II: In Vivo and Human Translational Studies

Hu, Yajing PhD*; Liang, Deyong PhD; Li, Xiangqi MD; Liu, Hong-Hsing MD, PhD*; Zhang, Xun PhD; Zheng, Ming PhD*; Dill, David PhD§; Shi, Xiaoyou MD; Qiao, Yanli MD, MS*; Yeomans, David PhD*; Carvalho, Brendan MD*; Angst, Martin S. MD*; Clark, J. David MD, PhD; Peltz, Gary MD, PHD*

doi: 10.1213/ANE.0b013e3181f691eb
Analgesia: Research Reports

BACKGROUND: In the accompanying paper, we demonstrate that genetic variation within Nalp1 could contribute to interstrain differences in wound chemokine production through altering the amount of interleukin (IL)-1 produced. We further investigate the role of IL-1 in incisional wound biology and its effect on wound chemokine production in vivo and whether this mechanism could be active in human subjects.

METHODS: A well-characterized murine model of incisional wounding was used to assess the in vivo role of IL-1 in wound biology. The amount of 7 different cytokines/chemokines produced within an experimentally induced skin incision on a mouse paw and the nociceptive response was analyzed in mice treated with an IL-1 inhibitor. We also investigated whether human IL-1β or IL-1α stimulated the production of chemokines by primary human keratinocytes in vitro, and whether there was a correlation between IL-1β and chemokine levels in 2 experimental human wound paradigms.

RESULTS: Administration of an IL-1 receptor antagonist to mice decreased the nociceptive response to an incisional wound, and reduced the production of multiple inflammatory mediators, including keratinocyte-derived chemokine (KC) and macrophage inhibitory protein (MIP)-1α, within the wounds. IL-1α and IL-1β stimulated IL-8 and GRO-α (human homologues of murine keratinocyte-derived chemokine) production by primary human keratinocytes in vitro. IL-1β levels were highly correlated with IL-8 in human surgical wounds, and at cutaneous sites of human ultraviolet B-induced sunburn injury.

CONCLUSIONS: IL-1 plays a major role in regulating inflammatory mediator production in wounds through a novel mechanism; by stimulating the production of multiple cytokines and chemokines, it impacts clinically important aspects of wound biology. These data suggest that administration of an IL-1 receptor antagonist within the perioperative period could decrease postsurgical wound pain.

Published ahead of print October 1, 2010 Supplemental Digital Content is available in the text.

From the *Department of Anesthesia, Stanford University, Stanford; Veterans Affairs Palo Alto Health Care System, Palo Alto; Department of Genetics & Genomics, Roche Palo Alto, Palo Alto; and §Department of Computer Science, Stanford University, Stanford, California.

Address correspondence to Gary Peltz, 800 Welch Road, Room 213, Palo Alto, CA 94304. Address e-mail to gpeltz@stanford.edu.

Accepted July 28, 2010

Published ahead of print October 1, 2010

In the accompanying paper,1 we provide evidence that genetic variation affecting interleukin (IL)-1 production contributed to murine interstrain differences in the amounts of 2 chemokines (keratinocyte-derived chemokine [KC] and macrophage inhibitory protein [MIP]-1α) produced after incisional wounding. In that study we demonstrated that IL-1 stimulated chemokine production by murine fibroblast and keratinocyte cell lines in vitro. To determine whether this mechanism affected the in vivo wound response, we studied a well-characterized murine model of incisional wounding to assess the in vivo role of IL-1 in wound biology.2 We examined the effect that systemic administration of anakinra, a recombinant 153 amino acid protein that inhibits IL-1 signaling and is used for the treatment of rheumatoid arthritis,3,4 had on the amount of 7 different cytokines/chemokines produced within an experimentally induced skin incision on a mouse paw. We also investigated the relationship between IL-1 and other cytokines and chemokines in 2 human experimental wound paradigms.

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METHODS

Postsurgical Nociceptive Response

All animal experiments were performed using a protocol that was approved by the Stanford University Institutional Animal Care and Use Committee. Eight-week-old male C57B6 mice were administered vehicle or 100 mg/kg anakinra (Amgen, Thousand Oaks, California) (i.p.), an IL-1 receptor antagonist, at −0.5, 22, and 46 hours after hindpaw incision, using published methods.2 Wound skin tissues were collected at 0, 2, 24, and 48 hours after incision. Tissue IL-1β, KC, MIP-1α, IL-6, tumor necrosis factor (TNF)-α, granulocyte colony stimulating factor (G-CSF), and RANTES was measured using the Bio-Rad Bio-Plex mouse cytokine assay kit according to the manufacturer's instructions. The lower limit of detection for all analytes varied between 0.08 to 0.46 pg/mL, the upper limit varied between 1247 and 7546 pg/mL, and the coefficient of variation was <5% for each assay. The incisional nociceptive response was measured using the von Frey method at 0, 0.5, 1, 2, 24, and 48 hours after wounding, using our previously described methods.5

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Primary Human Keratinocyte and Chemokine Measurements

We wanted to determine whether there also was a relationship between IL-1 and other inflammatory mediators within human skin wounds. We investigated whether human IL-1β or IL-1α stimulated chemokine production by primary human keratinocytes, which are more representative of the cells that are present in human tissue than are the transformed cell lines that we previously evaluated. There are 3 human C-X-C chemokines (growth-related oncogene α (GRO-α), IL-8, and ENA-78) that are homologous to murine KC. However, ENA-78 was not tested here, because it is not expressed in human cutaneous wounds.6 Primary human keratinocytes (CC-2501) were obtained from Lonza (Walkersville, Maryland) and cultured in Clonetics KGM-Gold medium supplemented with KGM-Gold BulletKit (Lonza). We added 10 ng/mL recombinant human IL-1β or IL-1α (R&D Systems, Minneapolis, MN) to stimulate chemokine production. After 4 hours of incubation, the amount of GRO-α, IL-8, or MIP-1α secreted into the supernatant was measured by enzyme immunoassay by using a commercial kit (R&D systems, Minneapolis, Minnesota) according to the manufacturer's instructions. The analyte concentrations were calculated in relation to a standard curve. The lower limit of detection for all analytes analyzed was 31.2 pg/mL, and the upper limit varied from 1000 to 2000 pg/mL.

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Human Cesarean Wound Analysis

The data used for this analysis were obtained from a randomized controlled study that enrolled 38 healthy women with term pregnancies undergoing elective cesarean delivery.7 The IRB of the Stanford University School of Medicine approved this study, and written informed consent was obtained from all study participants. All patients received spinal anesthesia with intrathecal hyperbaric bupivacaine 12 mg, intrathecal fentanyl 10 μg, and intrathecal morphine 200 μg and were randomized to receive either a subcutaneous infiltration of bupivacaine 0.5% or saline at 2 mL/h for 24 hours postcesarean delivery. Wound exudate was sampled at 1, 3, 5, 7, and 24 hours postcesarean incision. Wound exudates were secured using a subcutaneous wound drain technique that we recently developed, and 17 different mediators were measured in duplicates using a multiplex bead array immunoassay plate (Bio-PlexTM system, BioRad, Hercules, California) as described.8,9 The lower limit of detection for all analytes analyzed varied between 0.1 and 1.1 pg/mL. The upper limit of detection varied between 233 and 4286 pg/mL. Standard curves were included in each analysis and concentrations calculated with Bio-Plex Manager software (Minneapolis, Minnesota). The median coefficient of variation (CV) across the range of concentrations used to construct the calibration curves ranged between 0.1% and 23.1%. The CV was >10% close to the limit of detection for IL4, IL7, IL-17, TNF-α, and MCP-1. The area under the curve (AUC) for each analyte concentration over the entire time course was used for correlation analysis. IL-8 was the only human C-X-C chemokine measured in this study; ENA-78 mRNA is not expressed in human cutaneous wounds,6 and GRO-α levels were not measured in this study. To stabilize the variance across the whole range of analytes measured, all data were log-transformed (10 based) for this analysis. The extent of correlation was then determined using Pearson's correlation coefficient.10 The positive correlations remained significant even if the nonparametric Spearman's ρ was used,11 or if potential outliers (2 data points with lowest IL-8 values or 5 data points with the lowest MIP-1β values) were excluded. The calculation of the correlation coefficient and its statistical significance was performed in R (http://www.r-project.org). An ad priori sample size analysis was based on our previous study8 and predicted that 19 subjects were required per study arm to detect a 30% change in the area under the curve of IL-6 concentration versus time (β = 0.8, P < 0.01). The amount of IL-1β level in a human incisional wound is highly correlated with the amount of IL-8 or MIP-1β.

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Human Ultraviolet B-Induced Sunburns

The inflammasome was previously shown to mediate ultraviolet (UV) B-induced IL-1β secretion by human keratinocytes.12 Therefore, we examined the relationships among 36 analytes in interstitial wound fluid obtained from 12 healthy volunteers with first-degree experimental UVB-induced sunburn. The interstitial wound fluid was obtained from microdialysis catheters inserted into the skin 24 hours after experimentally induced UVB sunburn.13 The data used for this analysis were obtained from a randomized controlled study that enrolled 12 healthy volunteers undergoing femoral nerve and sham block procedures in a blinded, randomized, cross-over study examining the effects of a peripheral nerve block on wound hyperalgesia and cytokine production in experimentally inflamed skin (Carvalho et al., unpublished material, 2010). The sample size of 12 patients was based on a previous study13 using similar methodology indicating that 11 subjects would allow detecting a 33% difference in wound heat hyperalgesia, the primary outcome of this study (β = 0.8; P < 0.025). The IRB of the Stanford University School of Medicine approved the study, and written informed consent was obtained from all study participants. Data obtained during sham treatment were used for this analysis. In brief, 2 1.5- cm diameter UVB burns were induced on the thigh with a 5-cm separation using a calibrated UVB source (Saalmann Multitester SBB LT 400, Saalmann GmbH, Herford, Germany). The amount of UVB irradiation used to induce first-degree sunburns corresponded to 3 times the minimal erythemal dose (MED), which was determined during an initial screening visit by exposing a subject to 5 ascending UVB doses (40 to 100 mJ/cm2). The MED was defined as the lowest UVB dose causing a complete reddening of the irradiated skin. First-degree sunburn developed over the course of 24 hours and remained stable for up to 2 days. The day after UVB irradiation interstitial wound fluid was sampled from the UVB-irradiated skin with a microdialysis technique.13 In brief, 2 custom-made microdialysis catheters were inserted intracutaneously into the 2 UVB lesions, and the microdialysate was collected over a 40-minute period. The concentration of 36 inflammatory and nociceptive mediators was assayed as for human cesarean wound analysis. To stabilize the variance across the whole range of analytes measured, we log-transformed (10 based) all data for this analysis. Because zeros were present in the data, the data were first offset by 1 before the log-transformation, i.e., transformed data = log (1 + raw data). The extent of correlations between IL-8 and the other 35 analytes were then determined using Pearson's correlation coefficient.10 On the basis of the murine results, which indicated that IL-1β had a substantial effect on wound chemokine production, we wanted to identify factors affecting IL-8 production in the sunburns. Therefore, we examined the strength of the association between IL-8 and all other measured wound analytes. The statistical significance of the correlations was assessed and then adjusted for multiple testing using the Benjamini-Hochberg method.14 One volunteer had extremely high levels of wound fluid cytokines. When the values from this volunteer were included, the unadjusted P value for the correlation was 10−6. This outlier seriously impacted the P value, which provided an overly optimistic assessment. Therefore, the correlations were calculated in 2 different ways, with or without the data from this volunteer. The calculation of the correlation coefficient and its statistical significance was performed in R (http://www.r-project.org).

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RESULTS

IL-1 Inhibition Decreases Inflammatory Mediator Production and Nociceptive Responses In Vivo in a Murine Incisional Wound Model

The amount of KC and MIP-1α produced within a wound 2 hours after incision was significantly decreased by systemic IL-1 blockade (Fig. 1). The amount of TNF-α, IL-6, and G-CSF in the wound tissue was also reduced by IL-1 inhibition, but RANTES (Chemokine (C-C motif) ligand 5) production was not altered. IL-1β production was increased after IL-1 blockade. The IL-1 antagonist significantly inhibited KC, MIP-1α, TNF-α, IL-6, and G-CSF production 2 hours after incisional wounding, whereas the amount of RANTES was unchanged and IL-1β was significantly increased.

Figure 1

Figure 1

Figure 2 shows the effect of IL-1 blockade on murine postsurgical nociceptive response. Although there was no effect at 0.5 hour, IL-1 blockade markedly reduced the mechanical nociceptive response within 2 hours after incision. This strong analgesic effect is also evident 24 and 48 hours after incision. IL-1 blockade caused an incisional nociceptive response to return to baseline within 48 hours after the incision, whereas the untreated mice had increased residual nociceptive response at 48 hours.

Figure 2

Figure 2

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IL-1 and Human Chemokine Production in Vitro

Consistent with the findings in the murine cell lines, IL-1β or IL-1α stimulation induced primary human keratinocytes to produce very large amounts of 2 CXC chemokines, GRO-α and IL-8 (Fig. 3). However, the primary human keratinocytes did not produce MIP-1α after IL-1 stimulation (data not shown).

Figure 3

Figure 3

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IL-1 and Chemokines in Human Wounds

We next used a recently developed method, which enables inflammatory and nociceptive mediators produced within human surgical wounds to be reliably measured in real time,8 to determine whether there was any correlation between the levels of IL-1β and chemokines in human wound tissue. For this analysis, surgical wound exudates were sampled at multiple times within 24 hours after cesarean incision in 38 healthy women with term pregnancies who were undergoing elective cesarean delivery. The area-under-curve (AUC) for each measured analyte was calculated across the entire time course to provide a composite measure of analyte production after wounding. Figure 4 shows the relationship between AUC for IL-8 (graph A) and MIP-1β (graph B) and the AUC for IL-1β. Although MIP-1α levels were not measured in this study, MIP-1β is a closely related cytokine. There was a significant correlation between both cytokines and IL-1β (IL-8 vs. IL-1β: r = 0.78, P < 0.0001; MIP-1β vs. IL-1β: r = 0.75, P < 0.0001).

Figure 4

Figure 4

We also examined the relationships among 36 analytes in interstitial wound fluid obtained from 12 healthy volunteers with first-degree experimental UVB-induced sunburn. The interstitial wound fluid was obtained from microdialysis catheters inserted into the skin 24 hours after experimentally induced UVB sunburn. Figure 5 shows the amounts of IL-8 and IL-1β within the fluid obtained from UVB-induced sunburns. These were highly correlated (r = 0.90, P value = 0.0002). Moreover, when the amount of IL-8 was compared with that of the 37 other analytes measured in wound fluid, IL-1β was the analyte that was most strongly correlated (adjusted P value <0.01; Table 1).

Figure 5

Figure 5

Table 1

Table 1

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DISCUSSION

Systemic inhibition of IL-1 decreased nociceptive responses and the production of multiple inflammatory mediators in a murine in vivo model of surgical wounding. The increased amount of IL-1β within the wound after IL-1 receptor blockade probably resulted from inhibition of IL-1 consumption. It was also important to determine whether the murine findings would translate to human wound responses. Because results obtained using cultured cell lines can be misleading, our finding that IL-1 stimulated chemokine production by primary human keratinocytes in vitro provides important additional experimental evidence indicating that IL-1 can affect wound chemokine production. Furthermore, human IL-1β and IL-8 levels were highly correlated in human surgical wounds and at cutaneous sites of human sunburn injury. Clearly, a causal relationship cannot be inferred from these correlations. However, when coupled with the primary keratinocyte data and the results from the in vivo murine incisional model, these correlations in 2 different types of human wounds support our finding that IL-1 plays a major role in regulating the in situ production of inflammatory chemokines in human wound tissue and that it impacts clinically important aspects of wound biology.

These results are consistent with recent publications demonstrating that IL-1 signaling is an essential mediator of postoperative incisional pain15 and inflammatory hyperalgesia,16 and can also contribute to the development of a chronic pain syndrome (reviewed by Wolf et al., Binshtok et al., and Verri et al.1517). Peripheral or central nervous system stimulation by IL-1 increases nociceptor excitability and can alter neuronal membrane currents.16,17 There is also abundant evidence that chemokines, especially IL-8 in humans or KC in rodents, play a significant role in hypernociceptive states.17,18 However, the results described here indicate that IL-1 produced within the wound plays a major role in wound biology; it regulates the in situ production of multiple inflammatory mediators after a surgical incision, including chemokines (KC in the mouse and IL-8 in humans) that are key mediators of inflammatory cell infiltration and pain.

Within the context of other known information, these results lead to a 4-step model for postsurgical wound pain that is described in Figure 6. Immediately after an incision, neutrophil entry into a wound can be initiated by a H2O2 gradient,19 mitochondrial components,20 or possibly other (lipid) mediators that are produced by the wounded tissue (step 1). The fact that other mediators can induce neutrophil recruitment acutely explains why IL-1 inhibition did not decrease pain immediately after wounding in the in vivo murine model. However, neutrophils are not the only source of IL-1 in wound tissue. Because keratinocytes have been shown to produce IL-1α,21 the in situ production of IL-1α by keratinocytes could also promote wound chemokine production. After the initial period after wounding, IL-1α produced by keratinocytes, along with IL-1β and other mediators produced by the wound infiltrating phagocytes, promote continued leukocyte recruitment into the wound (step 2). In response to the IL-1, keratinocytes and fibroblasts within the wound are stimulated to produce KC (or IL-8 in humans) and other mediators (step 3). The inflammatory mediators produced by infiltrating phagocytes and resident cells promote the continued recruitment and activation of other leukocytes within the wound (step 4). This model explains why inhibition of IL-1 signaling had such a strong effect on the postsurgical pain response and decreased the production of other inflammatory mediators within the wound. It also explains the large variation in KC production after incisional wounding among the inbred strains and why chemokine production was correlated with Nalp1 alleles. It is striking that the mediators that are critical for postsurgical wound pain are also known to regulate hyperalgesic states,16 sunburn,12 contact hypersensitivity,22 and inflammatory injury.18

Figure 6

Figure 6

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Perspective

These data suggest that administration of an IL-1 receptor antagonist (IL-1ra) within the perioperative period could decrease postsurgical inflammation and wound pain. IL-1ra is a naturally occurring 153-amino-acid protein that binds to the IL-1 receptor and competitively inhibits IL-1 binding to its receptor. Most important, a recombinant nonglycosylated form of this protein has been approved for treatment of rheumatoid arthritis, and it has a very good safety record, even when administered for a period of 3 years.3,4 The usual dose of IL-1ra is 100 mg subcutaneously every day, its terminal half-life ranges from 4 to 6 hours, and it is primarily (∼80%) cleared through renal excretion.23 Thus, there is a readily available, approved medication that could be used for perioperative IL-1 inhibition. The potential anti-inflammatory and analgesic benefits of IL-1 inhibition for a several-day period in the perioperative setting are clear from the above results. However, 2 critical concerns about perioperative IL-1 inhibition that must be addressed are whether it could have an adverse effect on wound healing and whether it could have an adverse effect on infection. There is a substantial amount of animal model data indicating that wound healing will not be impaired, and may even be facilitated by IL-1 inhibition for a short period. The quality of wound healing in vivo was actually improved in IL-1 receptor (IL-1R) knockout mice,24 whereas wound healing was impaired in IL-1ra knockout mice.25 Moreover, administration of an IL-1 inhibitor for 3 or 14 days actually improved periodontal wound healing in an in vivo primate model.26 Although it is difficult to interpret the results of in vitro models, acute exposure to exogenous IL-1 for 1 or 3 days reduced the repair of an injured meniscus.27 All of these data suggest that IL-1 inhibition for a short period could have a beneficial effect on wound healing variables.

Although there is a slightly increased risk of infection associated with prolonged use of this agent, the infections often occurred in individuals receiving other immunosuppressive therapy. For example, the rate of serious infections was higher for rheumatoid arthritis patients treated with IL-1ra for up to 3 years (5.37 events per 100 patient-years) than it was for controls (1.65 events per 100 patient-years), but the serious infection rate was substantially lower (2.87 events per 100 patient-years) if the patient was not receiving corticosteroid treatment at baseline in 1 study of 1346 rheumatoid arthritis patients.4 In a meta-analysis of 5 trials covering 2846 patients, there were no statistically significant differences noted in the number of withdrawals, deaths, adverse events (total and serious), or infections (total and serious) between the IL-1ra treated group and a placebo group.3 Although it is important to monitor patients for infection, an increased risk of infection would not be expected to occur as a consequence of a very brief period of IL-1 inhibition in the immediate perioperative period. Prudence might dictate, however, that IL-1 inhibition should be avoided when dealing with potentially contaminated or infected wounds, when treating immunocompromised patients, if the patient is being treated with a TNF inhibitor,28 or if there is evidence of (or risk for) a serious infection such as tuberculosis.

Other benefits could also accrue as a consequence of IL-1 inhibition in the perioperative period (Fig. 7). The incidence of venous thrombosis is increased after surgery, because of the combination of stasis (caused by immobility) and hypercoagulability due in part by a local increase in tissue factor, which can activate the coagulation cascade (reviewed by Martinelli et al.29). It is noteworthy that tissue factor expression on the surface of monocytes,30 polymorphonuclear (neutrophil) cells,31 or endothelial cells is rapidly induced by multiple inflammatory mediators, including IL-1, IL-6, IL-8, and TNF-α (and reviewed by Martinelli et al. and Mackman29,32). Our studies in mice indicated that IL-1 blockade inhibited the production of IL-6, the murine homologue of IL-8, and TNF-α in wounds.1,33 Thus, perioperative IL-1 inhibition could also decrease the incidence of postoperative thrombosis. There is also evidence in a rat model that IL-1ra can reduce pain in a rat model of a complex regional pain syndrome that can develop after immobilization due to fracture.34 It has also been proposed that a hippocampal inflammatory response that is associated with the cytokine-dependent activation of glial cells may contribute to postoperative impairment of cognitive function.35 There are in vitro36 and in vivo37 experimental data indicating that IL-1ra can attenuate neuronal injury and can ameliorate microglial activation after brain injury, or reduce cognitive dysfunction after septic shock.38 Though not assessed in our studies, systemic IL-1 inhibition conceivably could reduce central nervous system inflammation.

Figure 7

Figure 7

Currently, we treat postoperative pain primarily by administering drugs that affect pain-signaling pathways. Local anesthetics temporarily reduce the propagation of action potentials, and opioids reduce nociceptive signal transmission within the central nervous system. Although these measures diminish the response to pain, they do not address the primary problem, which is the inflammation caused by the surgical incision. Although we know a great deal about the mediators of acute inflammation, we have done very little with this knowledge to alter the dynamics within an injured tissue, to reduce local edema, reduce pain, or promote wound healing.

Perioperative administration of an IL-1 inhibitor would represent an important step toward developing novel anti-inflammatory strategies to reduce incisional pain. Beyond its own inflammatory effects, IL-1β is a “master mediator” that induces the production of multiple other proinflammatory mediators that are linked to nociception, including TNF-α, IL-6, cyclooxygenase-2, other chemokines, substance P, and nerve growth factor.3942 Although we used IL-1ra to inhibit IL-1β signaling, this pathway could also be blocked through inhibition of caspase-1, which is a protease that converts pro-IL-1β to the active cytokine. Of note, small molecule caspase-1 inhibitors are under development for the control of inflammation in a variety of diseases,43 and additional antibody-based biologics that directly bind to IL-1β are also under development.

Our results suggest that the analgesic effects of IL-1 inhibition may not be seen immediately postoperatively, but would be observed within the subacute period (a day or so) after the incision. The slight delay in analgesic onset may be due to the fact that the inflammatory mediators released immediately after the incisional wound may be arachadonic acid, reactive oxygen species, or both,19 or even mitochondrial peptides or DNA,44 whose production or activity is not affected by IL-1 inhibition. However, there is a rapid change in the inflammatory mediators produced within the wound, and IL-1 quickly assumes an important role during the early phases of wound healing. In clinical trials designed to test the analgesic effect of IL-1ra, it may be best to start the therapy at least 1 hour before incision, and closely analyze the treatment effects 1 to 4 days after the surgery. It is probably best to administer IL-1ra for a 24- to 36-hour period after surgery. If an IL-1ra is to be administered to individuals with impaired renal function, the dose must be decreased.23 In addition to measuring the analgesic effect on incisional pain, measurement of inflammatory mediators in wound fluids9,45,46 should be used to assess the efficacy of this therapy. The effect of IL-1ra on the incidence of excess scar and keloid formation should also be monitored. Because our results were based on an analysis of skin mediators, the effects of IL-1ra should initially be assessed in surgeries involving primarily skin and soft tissue. However, it will be important in subsequent studies to determine whether other postoperative complications, such as hypercoagulability, were reduced.

Moreover, because of our genetic analysis, we focused on the effect of IL-1 inhibition. However, our experiments suggest that targeting other inflammatory mediators could also be considered for controlling postincisional pain, edema, or scaring. For example, analysis of wound edge tissue has shown that IL-6, G-CSF, KC, MIP-1α, TNF-α, and complement fragment C5a all have increased abundance after incision, and many are associated with pain. We may be able to favorably impact both pain and wound healing by targeting these mediators, which could also enhance patient comfort and improve surgical outcome. Thus, perioperative immunomodulation holds promise for improving surgical outcomes.

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