Citrulline: A potential immunomodulator in sepsis

Background: Sepsis leads to a complex systemic response of cytokines (both pro- and anti-inflammatory) and more recently recognized adipokine mediators. Endothelial nitric oxide (NO) may be a key component in regulating this response, but the pharmacologic manipulation of endothelial NO via L-arginine supplementation or inhibitors has provided inconsistent clinical data related to outcomes. These failures are related to the metabolism of L-arginine in the liver, toxicity of L-arginine, and asymmetric dimethylarginine inhibition, all of which may explain the "arginine paradox." L-citrulline (CIT) offers a potentially valuable means of supplementing arginine and therefore impacting favorably NO availability. The goal of this study was to determine whether CIT supplementation altered the systemic response of mediators and cytokines in a rat model of sepsis with varying degrees of severity. Methods: Sepsis was induced with 2 models of cecal ligation and puncture (CLP) of varying severity in Wistar rats. CIT supplementation was provided to half the animals as 8% CIT-supplemented feed for 3 weeks. Baseline mediator levels were assessed in the Wistar rats followed by comparison of the following groups at days 0, 1, and 3: sham-operated; CLP 8-mm (localized); and CLP 12-mm (extensive). The following analyses were performed in the groups: interleukin-6 (IL-6), IL-8, IL-10, resistin, and adiponectin levels (enzyme-linked immunosorbent assay performed in duplicate). L-arginine and CIT were measured with high-performance liquid chromatography combined with mass spectrometry. Results: Ninety-eight Wistar rats were evaluated, and survival was similar in both sepsis models with and without CIT. Serum IL-6 levels were lower in the CIT/CLP 8-mm group compared to the standard rat chow (STD)/CLP 8-mm group (41 vs 117 pg/mL; P =.011) on postoperative day 3. Serum IL-8 and IL-10 responses were similar across all groups. Serum resistin levels were lower in the CIT/CLP 12-mm group compared to the STD/CLP 12-mm group in the more severe sepsis model on day 3 (19 vs 38 ng/mL; P <.0001). The levels of serum L-arginine were greater in the CIT-supplemented animals compared to STD rodent diet animals before surgical insult (86.3 vs 294.0 μM; P =.004). Adiponectin was not affected by CIT supplementation. Conclusion: CIT may decrease the proinflammatory mediator response (IL-6 and resistin) without impairing the secretion of anti-inflammatory mediators (IL-10 and adiponectin) and thereby provide a safe means of immunomodulation that preserves the anti-inflammatory mediator response.