Efficacy and Mechanisms of GLN Dipeptide in the SICU

Overview: Relative deficiency of glutamine (GLN) appears to contribute to morbidity and mortality in surgical intensive care unit (SICU) patients, but conventional nutrition support does not repair this deficit. GLN requirements increase during critical illness when utilization by the immune system, gut mucosa and other tissues exceeds endogenous production. GLN depletion under these conditions may contribute to hospital morbidity and mortality. Conventional parenteral nutrition (PN) does not contain GLN and thus does not prevent GLN depletion in catabolic patients. However, a pilot study and other reports strongly suggest that GLN-supplemented PN improves metabolic and clinical outcomes in critically ill patients. Underlying mechanisms for GLN action are poorly understood, but may involve systemic upregulation of the cytoprotective molecules glutathione (GSH), specific heat shock proteins (HSP) and GLN itself, improved gut barrier defenses, and improved innate and/or adaptive immune function. Properties of L-GLN limit provision in PN, but the dipeptide alanyl-glutamine (AG) confers stability and solubility in PN solutions. The pilot study demonstrated a marked decrease in nosocomial infection, improved indices of organ function, and a possible decrease in hospital mortality in SICU patients receiving AG-supplemented PN (AG-PN) versus standard, GLN-free PN (STD-PN). Investigators propose a multi-center, double-blind, controlled, Phase III trial, based on a pilot study, that will determine the effect of parenteral GLN on important clinical outcomes in patients requiring SICU care and PN after cardiac, vascular or colonic surgery. Investigators also propose to obtain needed hypothesis-generating, descriptive data from the Aim 1 study subjects to inform subsequent, truly mechanistic studies of GLN action in animal and human models of surgical critical illness. Study subjects will be randomized on an intent-to-treat basis to receive AG-PN or isonitrogenous, isocaloric STD-PN until enteral feeding is established.

Hypotheses:

• SICU patients receiving PN supplemented with GLN dipeptide (AG-PN) will demonstrate improved clinical outcomes compared to patients receiving STD-PN.
• Administration of AG-PN in the Aim 1 study subjects: a) increases serial blood levels of specific cytoprotective molecules and improves systemic redox status; b) is associated with decreased serum positivity for the bacterial products flagellin and lipopolysaccharide ( LPS) and the adaptive immune response to these mediators; and c) improves key indices of innate/adaptive immunity.

Specific Aims:

Aim 1: To perform a Phase III randomized controlled trial (RCT) to determine whether AG-PN decreases hospital mortality, nosocomial infections, and other indices of hospital morbidity versus STD-PN in SICU patients. The study will test whether AG-PN: decreases hospital mortality and the incidence of nosocomial infection (primary endpoints) in SICU patients after cardiac, vascular or colonic surgery. We will also determine whether AG-PN decreases total hospital infections, bloodstream infections (BSI), infections due to Staphylococcus aureus or fungal species, the number of days patients require mechanical ventilation, the SICU and total hospital length of stay and the 6-month mortality rate (secondary endpoints).

Aim 2: To determine in the Aim 1 study subjects whether AG-PN: a) increases systemic blood concentrations of the cytoprotective molecules GSH, HSP-70, HSP-27 and GLN and improves systemic GSH and cysteine redox status; b) is associated with decreased serum positivity for the bacterial products flagellin and LPS and titers of anti-flagellin and anti-LPS immunoglobulin M (IgM), immunoglobulin A (IgA) and immunoglobulin G (IgG); and c) improves key indices of innate/adaptive immune cell function.

Inclusion criteria

1) A signed informed consent is in place on the patient's chart; 2) The patient is at least 18 but not more than 90 years of age at time of surgery; 3) The patient has a body mass index (BMI) < 40 kg/m2 prior to surgery; 4) The patient currently requires SICU care and is within 14 days postoperative from one of the following open (non-laparoscopic) surgical procedures: coronary artery bypass graft(CABG), cardiac valve, vascular (non-neurosurgical), or esophageal gastrointestinal resection of esophagus, stomach, small bowel, colon and/or rectum), or operation to identify the source of peritonitis when there is evidence of a bowel perforation (with or without bowel resection); 5) The patient will require central venous PN for 7+ subsequent days after entry on a clinical basis≠; 6) There is central venous access for administration of the study PN; and 7) The patient's primary physician(s) will allow the investigative team to manage the study PN and enteral feedings during the current hospitalization.

Exclusion criteria

1) The patient is pregnant; 2) The patient has clinical sepsis [defined as unstable blood pressure despite pressor support AND mean arterial pressure (MAP) < 60 mm Hg on at least 3 consecutive readings within a 3-hour period during the 24 hours prior to study entry; 3) a) The patient has a current malignancy requiring surgery as the GLND qualifying operation OR b) the patient is currently receiving an active regimen of chemotherapy and/or radiotherapy to treat a previously diagnosed malignancy†; 4) The patient has a history of seizures or pre-existing seizure disorder; 5) The patient has a current encephalopathy*; 6) The patient has a known history of cirrhosis OR a serum total bilirubin level ≥ 10.0 mg/dL); 7) The patient has a history of chronic renal failure requiring dialysis, or has significant renal dysfunction (defined as serum creatinine > 2.5 mg/dL and is not receiving continuous renal replacement therapy (CRRT) or the patient requires acute hemodialysis postoperatively; 8) The patient has a concomitant burn or trauma injury; 9) The patient has previously undergone an organ transplantation;10) the patient has a history of HIV/AIDS; 11) The patient has received any investigational drug within 60 days prior to study entry; 12) The patient has received enteral or parenteral enteral feedings enriched in arginine and/or glutamine within 30 days prior to study entry; and 13) The patient is unable or unwilling to participate in study procedures such as longitudinal blood draws and out patient follow-up visits, etc.

*Encephalopathy for GLND can be diagnosed only in non-chemically sedated patients by the primary critical care physicians or neurologist consultants and is defined as either a comatose state OR severe abnormalities diagnosed by electroencephalogram (EEG), OR if all of the following criteria are met: a) patient goes to sleep but is arousable to verbal and painful stimuli; does not open eyes spontaneously (decreased level of consciousness); b) patient exhibits severe confusion or complete disorientation when aroused (disorientation); c) patient exhibits severe lethargy or bizarre behavior (behavioral dysfunction); and d) patient exhibits inability to cooperate, asterixis, ataxia, clonus, decortication, decerebration, seizures, or rigidity (severe neuromuscular dysfunction).

† Patients with malignant metastasis and terminal untreatable carcinoma will be excluded as per the operational definition agreed upon by the Data Safety and Monitoring Board (DSMB).

≠ Please note that the patient should be in the SICU at the initial PN hang time.