Arginine and nitric oxide (NO) metabolism in sepsis: L-Citrulline enteral supplementation for the normalisation of the Arginine-NO metabolism.

Sepsis can be defined as an overwhelming systemic response to an infection
leading to
disturbed organ function, i.e. multiple organ dysfunction or failure (MOF).
Mortality rates of patients with sepsis vary from 40-70% and are determined by
the degree of organ failure.
During sepsis NO synthesis is compromised and contributes to impaired
microcirculation and organ disfunction. The cause for this compromised NO
production seems to be an impaired arginine metabolism, as plasma arginine
levels are reduced in sepsis.
Our recent data showed for the first time that arginine de novo synthesis
(citrulline converted back into arginine) cannot compensate these decreased
arginine levels in patients with severe sepsis, with decreased citrulline
plasma concentrations as underlying cause.
Therefore, reduced arginine de novo synthesis, through a decreased NO
production, may lead to a
decreased organ perfusion. Several mechanism may cause a reduced arginine
synthesis. Improving specifically the arginine de novo synthesis
(supplementation of L-citrulline) may thus be a possibility to improve NO
synthesis (by either enzyme), and may subsequently improve organ perfusion.
since the citrulline plasma concentrations are decreased in these patients
during sepsis, suppletion is the only option to normalise these concentrations.

Primary Objective: To study stimulating effects of prolonged (8h) enteral
L-citrulline supplementation on the normalisation of the Arginine-NO metabolism.

Secondary Objective: To study stimulating effects of prolonged (8h) enteral
L-citrulline supplementation on the microcirculation, systemic hemodynamics,
and organ function and disease severity scores.

Research questions:
1. What are the effects of prolonged (8h) L-citrulline supplementation on whole
body arginine de novo nitric oxide metabolism in septic patients, after
normalization of the citrulline levels?
2. Can prolonged L-citrulline supplementation improve microcirculation,
vascular reactivity and permeability in sepsis?
3. Does this prolonged L-citrulline supplementation subsequently result in
improved organ function and disease score?

Hypothesis
NO synthesis is compromised during sepsis through lack of arginine de novo
synthesis and may thereby contribute to impaired microcirculation and organ
dysfunction. Supplementation of L-citrulline in septic patients will normalize
the plasma citrulline concentrations and increase the NO production without
increased arginase activity and will improve organ function, vascular
permeability and microcirculation.

Open label supplementation study.
Duration: 2-year period
Setting: Intensive Care Units Maastricht University Medical Center (MUMC+)


The experimental phase is conducted in 24 patients with severe sepsis or septic
shock to study the effect of 8h enteral L-citrulline supplementation on the
normalisation of the plasma citrulline concentrations and the whole body nitric
oxide (NO) production, whole body arginine de novo metabolism, arginase
activity and microcirculation.
The L-citrulline dose (1.8 micromol.kg-1.min-1) will be based on:
1) the dosage used in the arginine clinical suppletion study
2) The dosage used in the previous pig studies,
2) a comparable increase in plasma citrulline with immunonutrition.
The experiment involves 8 hours and is designed as an open label feeding
supplementation study. L
-alanine (3.6 micromol.kg-1.min-1; isocaloric) is used as an alternative
suppleted amino acid during the study, based on our experience in healthy
subjects on the metabolic ward and in the pig studies in our lab. An
alternative suppletion is chosen to maintain equal isocaloric energy intake
during the experiment.
During the study period, metabolism is measured at 2 time points (T0
(=baseline), T8h), using a 2 x 2h stable isotopes protocol. Organ function is
monitored at regular intervals and microcirculation are performed during the
study period.

The experiment involves 8 hours during which L-citrulline-HCl (dose 1.8
micromol.kg-1.min-1) is supplemented enteral continuously (duodenal gauge)
together with the standard enteral nutrition provided through an enteral
canula. L-alanine-HCl (isocaloric dose: 3.6 micromol.kg-1.min-1) is used as an
alternative amino acid during the study.

In general, no side effects were observed regarding hemodynamics, and plasma
electrolytes with L-arginine infusion (MEC 03-139). These side effects are also
not expected from the L-citrulline supplementation. L-alanine is an amino acid,
which showed no side effects in previous patient (MEC 02-010) and animal
studies. Blood sampling is limited as much as possible by combining the blood
sampling in the protocol with the routine blood sampling for patient care.
During the study 10-ml blood samples are taken at regular intervals for
additional laboratory analyses (115 ml in total). These samples are drawn from
an indwelling arterial line already in place for standard treatment purposes.
The gastric tonometry catheter will replace the normal gastric catheter in the
patients. During standard endoscopic placement of a jejunal feeding tube,
microscopic images of the intestinal villi will be recorded. All other
measurements are non-invasive and are harmless.
Clinical side effects will be controlled intensively during the study, by
continuous hemodynamic observation. Changes in the patient*s profile are
treated according to standard ICU practice. The protocol will not interfere
with the patient care and treatment; when necessary due to surgical need or
other care, measurements will be postponed. No benefits are to be expected for
the individual patient in this studie.