Impact of Anesthesia, Analgesia, and Euthanasia Technique on the Inflammatory Cytokine Profile in a Rodent Model of Severe Burn Injury

Abstract

Background Anesthetics used in burn and trauma animal models may be influencing results by modulating inflammatory and acute-phase responses. Accordingly, we determined the effects of various anesthetics, analgesia, and euthanasia techniques in a rodent burn model. Methods Isoflurane, ketamine-xylazine (KX), or pentobarbital, with or without buprenorphine, were administered prior to scald-burn in 72 rats that were euthanized without anesthesia by decapitation after 24 hours, and compared to unburned shams. In a second experiment, 120 rats underwent the same scald-burn injury using KX, and 24 hours later were euthanized under anesthesia or carbon dioxide (CO2). Additionally, we compared euthanasia by exsanguination versus decapitation. Serum cytokine levels were determined by ELISA. Results In the first experiment, isoflurane was associated with elevation of cytokine-induced neutrophil chemoattractant (CINC)-2, and monocyte chemotactic protein-1 (MCP-1), and KX and pentobarbital with elevation of CINC-1 and 2, interleukin (IL)-6 and MCP-1. Pentobarbital also decreased IL-1β. Interleukin-6 increased significantly when isoflurane or pentobarbital were combined with buprenorphine. In the second experiment, euthanasia performed by exsanguination under isoflurane was associated with reduced levels of IL-1β, CINC-1 and 2, and MCP-1, while KX reduced CINC-2 and increased IL-6 levels. Meanwhile, pentobarbital reduced levels of IL-1β and MCP-1, and CO2 reduced CINC-2 and MCP-1. Additionally, decapitation following KX, pentobarbital or CO2 decreased IL-1β and MCP-1, whilst we found no significant difference between isoflurane and controls. Euthanasia by exsanguination compared to decapitation using the same agent also led to modulation of several cytokines. Conclusions Differential expression of inflammatory markers with the use of anesthetics and analgesics should be considered when designing animal studies and interpreting results, as these appear to have significant modulating impact. Our findings indicate a brief anesthesia with isoflurane immediately prior to euthanasia by decapitation exerted the least dampening effect on the cytokines measured. Conversely, KX with buprenorphine may offer a better balance during longer procedures to avoid significant modulation. Standardization across all experiments that are compared and awareness of these findings is essential for those investigating the pathophysiology of inflammation in animal models.

Combination of ketamine and xylazine exacerbates cardiac dysfunction in severely scalded rats during the shock stage

“…At first, we hypothesized that differences in the experimental systems may have caused this outcome; for example, the proportion of xylazine in the K/X combination in the present study (25/6 mg/kg) was higher than those in other studies [37/7 mg/kg (23), 80/10 mg/kg (39) and 100/4 mg/kg (40)], which may be an additional cardiac inhibitory factor. The K/X combination, however, has been used widely and safely, although K/X has been reported to be associated with more highly elevated levels of cytokines, such as IL-6, than are associated with isoflurane in rats with burn injury (39).…”

Novel Mechanisms of Sildenafil in Pulmonary Hypertension Involving Cytokines/Chemokines, MAP Kinases and Akt

“…Among them, CINC-1 and CINC-2α/β have neutrophil chemotactic activity and promote neutrophil-facilitated cell damage in the lungs [32], [33]. In previous studies using an acute lung injury model, serum CINC-1 levels correlated with the elevated lung CINC-1 levels suggesting that circulating CINC-1 levels could be used as an early marker for the subsequent development of organ inflammation and injury [34].…”

Buprenorphine does not impact the inflammatory response in haemophilia A mice with experimentally-induced haemarthrosis

“…Furthermore, a non-significant increase in IL-1b, CINC-2, TNF-a and MCP-1 plasma levels were determined in the buprenorphinetreated group. 42 By contrast Hugunin et al found no effects of buprenorphine on plasma levels of IL-1b, IL-6, TNF-a and IL-10 in a mouse cecal ligation and puncture model 12 h after treatment 40 and Martucci et al found no effects in normal mice (no inflammatory condition) on IL-2 and IFN-g levels 60 min, 1, 3 or 7 days after buprenorphine treatment. 41 Thus it is possible that the effect of buprenorphine is dependent on the underlying inflammatory condition.…”

“…[36][37][38][39] Buprenorphine however, has been found not to modify cytokine release in several models 40,41 but results are inconsistent. 42 As the inflammatory response is an important part of the pathogenesis of haemophilic arthropathy any administration of analgesics should ideally not alter this response. For animal welfare and ethical reasons however, the full analgesic protocol in this model should be continued and the response of buprenorphine on the inflammatory response should be evaluated.…”