Endogenous transient receptor vanilloid 1 activation is protective during sepsis

Natalie Clark, Julie Keeble & Susan Brain, Cardiovascular Division, New Hunts House, King’s College, University of London. SE1 IUL.

Sepsis is a potentially life threatening systemic inflammatory response syndrome evoked by infection by pathogenic micro-organisms. Systemic conditions during sepsis favour both sensitisation and activation of the transient receptor potential vanilloid 1 (TRPV1) receptor, present on Aδ and C-fibers and best known for its ability to release neuropeptides. The current study has used genetically modified mice in which TRPV1 is deleted in a lipopolysaccharide (LPS) model of sepsis to explore whether endogenous TRPV1 receptors are implicated in the pathogenesis of sepsis.

Age- and sex-matched homozygous TRPV1 knockout (KO) and wildtype (WT) control mice, generated as described by Caterina et al. (2000), were used in the following studies. Mean arterial blood pressure (MAP) was measured by means of tail cuff plethysmography (Coda 6, Kent Scientific, USA). Rectal temperature was recorded using a rectal probe (Harvard). Basal measurements of MAP and temperature were obtained. Subsequently, mice received either LPS (5 mg/kg, for batches containing 2.25 million endotoxin units/mg, 10 ml/kg, serotype 0127:B8, i.p) or vehicle (saline, 10 ml/kg, i.p.). Rectal temperature was then re-measured 0.5 h later, and together with MAP, 1.5 and 4 h later. Animals were then culled and cardiac plasma and peritoneal exudate lavage fluid (PELF) were obtained and their nitric oxide (NO) content was assessed by using the Griess assay. Plasma levels of aspartate amino transferase (AST), creatinine and lipase were measured via Nationwide Laboratories (UK) to assess possible heart/liver, kidney and pancreatic dysfunction, respectively. Additionally, liver, kidney and spleens were excised to compare wet versus dry weight in order to gauge possible oedema. A subgroup of studies were terminated at 1.5 h to collect cardiac plasma and PELF for measurement of TNFα levels using a TNFα ELISA kit ( Tebu Bio, France).

LPS-evoked hypotension was significantly potentiated (p<0.05) in TRPV1 KO mice 4 h after administration of LPS (% change in MAP from baseline: WT= -38±6 mmHg, KO= -52±2 mmHg, n=10-11), as was hypothermia (% change in rectal temperature from baseline: WT= -7±1 ˚C, KO= -13±3 ˚C, n=6). In addition, LPS-induced increases in PELF TNFα were significantly (p<0.05) potentiated in KO mice (WT= 0.38±0.07 ng/ml, KO= 0.78±0.15 ng/ml, n=8), as were nitrite ( NO ) levels (WT= 15±3, KO= 35±10 ng/ml, n=8-9), although increases observed in the plasma were unaltered by TRPV1 deletion. LPS-induced oedema was only evident in KO liver tissue but . However, this was not significantly different from that observed in WT tissue. Interestingly, organ dysfunction was only evident in the heart/liver of TRPV1 KO mice.

These data demonstrate that TRPV1 KO mice exhibit a more severe septic phenotype than their WT counterparts, suggesting that the TRPV1 receptor is endogenously activated during sepsis with the effect of exerting a protective role. Thus, although TRPV1 antagonists have been developed for inflammatory pain states, the TRPV1 receptor may also be protective in certain inflammatory states.

Caterina M et al ., (2000) Science. 288 : 306-313.

Supported by the British Heart Foundation and Arthritis Research Campaign