the Influence of Remote Ischemic Preconditioning on Inflammation During Human Endotoxemia
Condition: Autoimmune Diseases; Infection
MeSH terms: Endotoxemia; Autoimmune Diseases; Inflammation
Study type: Interventional
Phase: Early Phase 1

Summary: 
      In a wide range of auto-inflammatory and infectious diseases attenuation of the immune
      response could be beneficial. Remote ischemic preconditioning (RIPC) has been identified as a
      means of protecting patients undergoing cardiac surgery from perioperative myocardial
      ischemic damage. This protection can be divided in a 'first window of protection' directly
      after preconditioning and a 'second window' that protects patients 12-48 hour after
      preconditioning. Repeated RIPC might have additional value, possibly by combining beneficial
      effects of the first and second windows of protection. The mechanisms behind these effects
      are under investigation, but attenuation of the inflammatory response is a major candidate.
      However, this has not yet been demonstrated in the setting of systemic inflammation in humans
      in vivo. This study aims to investigate the effects of (repeated) ischemic preconditioning on
      inflammation during human endotoxemia.
    

Detailed description: 
      Although the immune system is essential to survival, a variety of diseases originate from
      inappropriate or excessive activation of the immune response. Examples include a wide range
      of auto-inflammatory disease, infectious diseases such as sepsis, but also after major
      surgery like cardiac artery bypass grafting, after radiation therapy in the treatment of
      cancer, or following organ transplantation. In these instances, attenuation of the immune
      response could be beneficial.

      The concept of ischemic preconditioning (IPC) was first described in the 1980's. Murry and
      colleagues showed a protective effect of preconditioning the heart with 4 cycles of 5-minute
      long ischemia on the extent of myocardial infarction in dog hearts. Follow-up animal studies
      showed the same protective effects on the heart by introducing the cycles of ischemia to
      distant, or 'remote', organs like the kidney or the gut. Furthermore, this principle of
      'remote ischemic preconditioning' (RIPC) was also shown to be effective in humans when using
      a tourniquet to temporary cut off blood supply to one of the limbs, either an arm or a leg.
      As such, RIPC has been identified as a cheap and easy method of protecting patients
      undergoing elective CABG surgery from perioperative myocardial ischemic damage. In recent
      studies, two different timeframes in which RIPC exerts its protective effects have been
      identified. The classical or 'early window of protection' protects in the 1-2 hour after the
      RIPC stimulus while a 'second window of protection' is evident 12-24 hours after RIPC and
      lasts for 48-72 hours. Multiple-dose RIPC may be of additional value, as 7 daily doses of
      RIPC in humans resulted in protection of endothelial dysfunction, with both the local and
      remote beneficial effects lasting for up to 8 days after the last RIPC dose. This could be
      due to additive or synergistic effects of combining the first and second windows of
      protection.

      The mechanisms behind the observed protective effects are however still subject of
      investigation. Several have been put forward, of which attenuation of the inflammatory
      response is a major candidate.

      For instance, recent animal work has shown that RIPC results in downregulation of
      pro-inflammatory cytokines such as TNF-α and IL-6 and upregulation of anti-inflammatory
      cytokines such as IL-10. In support of the latter, the cardioprotective effects of RIPC were
      absent in IL-10 knockout mice or in wild-type mice treated with a monoclonal antibody against
      the IL-10 receptor. Hypoxia-inducible factor (HIF) has been shown to be a major contributor
      to this RIPC-induced IL-10 response.

      Adenosine appears to be a major determinant of the anti-inflammatory and tissue-protective
      effects of RIPC. In a in vivo forearm model, adenosine and ischemic preconditioning both
      resulted in the same reduction in ischemia-reperfusion injury. Also, administration of
      exogenous adenosine can mimic the protective effects of IPC, and antagonizing the adenosine
      receptor with caffeine blocks the protective effects of RIPC and augments the
      anti-inflammatory IL-10 response to lipopolysaccharide (LPS). Interestingly, one of the
      pathways in which ischemia-reperfusion can increase adenosine levels is through upregulation
      of CD73, which is dependent on the aforementioned HIF.

      Another possible mechanism behind the anti-inflammatory effects of RIPC is release of
      Toll-like receptor (TLR) ligands, which in turn induce an endotoxin tolerance-like state.
      Endotoxin tolerance is a refractory state of the immune system after challenge with the TLR4
      ligand LPS, characterized by diminished cytokine production upon a subsequent LPS challenge.
      However, induction of endotoxin tolerance was found to occur not only after LPS challenge but
      also using other TLR(4)-ligands, so-called 'cross-tolerance'. A possible candidate to induce
      tolerance in RIPC is heat shock protein 70 (HSP70), as extracellular HSP70 has been shown to
      induce tolerance to LPS in monocytes in vitro. Furthermore, in rats receiving ischemic
      preconditioning of the lower extremity, HSP70 expression was increased in the spinal cord and
      myocardium, and HSP70 upregulation was found in cardiomyocytes after RIPC in infants
      undergoing cardiac surgery. However, other, yet unidentified TLR ligands could also be
      involved.

      From the abovementioned studies, it appears that RIPC exerts significant effects on the
      immune response. However, this has not yet been demonstrated in the setting of systemic
      inflammation in humans in vivo. Furthermore, the mechanisms behind the putative
      anti-inflammatory effects and possible additive or synergistic effects of repeated RIPC
      (thereby combining both the first and second windows of protection) are unknown as well. This
      study aims to investigate the effects of (repeated) ischemic preconditioning during human
      endotoxemia, a standardized controlled model of inflammation.
    

Intervention name(s): Multiple-dose Remote Ischemic Preconditioning; Single-dose Remote Ischemic Preconditioning; LPS infusion
Intervention type(s): Other; Other; Biological
Intervention description(s): A blood-pressure cuff with handheld rubber inflation balloon and manometer is placed on the non-dominant arm of the subject. The cuff will be placed proximally from the elbow with the most proximal part of the cuff placed in the armpit. The cuff will be inflated to 250 mmHg after which a 5 minute countdown is started. After 5 minutes the pressure is released and the 5 minute countdown for reperfusion is started. This concludes one cycle out of a total of four.
1 "RIPC-dose" consists of 4 cycles of 5 minute ischemia followed by 5 minute reperfusion as described above.
Multiple-dose RIPC consists of a daily dose of 1 RIPC as described above for 7 consecutive days.; A blood-pressure cuff with handheld rubber inflation balloon and manometer is placed on the non-dominant arm of the subject. The cuff will be placed proximally from the elbow with the most proximal part of the cuff placed in the armpit. The cuff will be inflated to 250 mmHg after which a 5 minute countdown is started. After 5 minutes the pressure is released and the 5 minute countdown for reperfusion is started. This concludes one cycle out of a total of four.
1 "RIPC-dose" consists of 4 cycles of 5 minute ischemia followed by 5 minute reperfusion as described above.
Single-dose RIPC consists of 1 dose of RIPC as described above; To achieve a controlled inflammatory state, 30 subjects (multiple-dose RIPC group [n=10], single-dose RIPC group [n=10] and control group [n=10]) will receive LPS intravenously. The LPS at a dose of 2 ng/kg iv will be injected in 1 minute.
Other intervention name(s): RIPC; RIPC; human endotoxemia
Allocation: Randomized
Intervention model: Parallel Assignment
Masking: None (Open Label)
Primary purpose: Basic Science
Keywords: inflammation; remote ischemic preconditioning