Heme Arginate in Cardiac Surgery Patients

AKI is a common condition which carries significant morbidity and mortality and has no current treatment except supportive care.

Cardiac surgery remains the standard of care for the revascularisation of the most severe coronary artery disease despite improvements in percutaneous coronary intervention. The nature of such surgery confers an ischaemic renal insult and it follows on that AKI is a relatively common complication. However, the reported incidence of AKI post cardiac surgery varies widely depending on the diagnostic criteria used. A recent retrospective analysis of 4572 cardiac surgical patients at the Royal Infirmary of Edinburgh over a 5 year period showed that 12.4% developed AKI by AKIN criteria post operatively. This was associated with an increased risk of death and prolonged inpatient stay.

Pre-clinical studies in murine models of ischaemia reperfusion injury (IRI) have demonstrated that the anti-inflammatory enzyme HO-1 is of interest as a potential target for therapeutic intervention. Heme arginate (HA) is a drug licensed for human use, as a treatment for acute porphyria. HA upregulates HO-1, and ameliorates IRI when given before injury in murine models of IRI. In Phase I clinical trials, HA has been shown to upregulate HO-1 and is well tolerated.

This is a single-blinded randomised trial of Heme arginate (HA) in patients who are due to have cardiac surgery. The aim of the study is to investigate the efficacy of HA in HO-1 upregulation and its safety in this patient cohort. This will inform a further clinical trial of HA as a preventative treatment for AKI in patients undergoing cardiac surgery.

Methods

Eligible patients will be those planned for elective cardiac surgery, identified at their Cardiothoracic outpatient clinic assessment, aged 60 or above.

HA (3mg/kg) upregulates HO-1 mRNA up to 2-fold at 24 hours post dose in healthy young volunteers. Power calculations based on an 80% power (at p<0.05) to detect at least 2 fold upregulation of HO-1 protein by western blot necessitate 2 groups of 10 (assuming standard deviation (SD) of ±1.5x). 20 patients will be recruited (10 per group).

Patients who agree to participate will be invited up for a study visit to the Clinical Research Facility at the Royal Infirmary of Edinburgh (RIE). If consent is given, participants will be randomised to receive HA at a dose of either 1 or 3mg/kg (maximum 250mg). Prior to the dose being given, routine observations (including blood pressure, pulse, respiratory rate, oxygen saturations and temperature) will be taken, and the trial team member will perform a routine examination of the cardiac and respiratory systems. An electrocardiogram (ecg) will be done for reference.

Blood samples to assess HO-1 expression in circulating monocytes will be taken prior to the administration of the study drug, and at 24 hours post dose. Samples for routine blood tests including full blood count (FBC), urea and electrolytes (U\&E), C-reactive protein (CRP), liver function tests (LFT), and ferritin will be taken alongside those for monocyte isolation, with a further set on day 7. Serum (and urine) will be frozen for batch analysis and monocytes will be isolated by in-house protocols. Routine blood tests will be processed at the biochemistry and haematology laboratories at the RIE as per their usual methods.

Urine samples will be collected before the study drug is given, and at 24 hours and 7 days post dose. Urinalysis will be performed, and microalbuminuria and urinary biomarkers of tubular injury neutrophil gelatinase associated lipocalin(NGAL), interleukin 18(IL-18) \& kidney injury molecule 1(KIM-1) will be quantified.

Routine clinical observations will be carried out for 6 hours post dose, at which time the patient will be allowed home in the absence of any adverse events. A second study visit at the Clinical Research Facility will be scheduled for 24 hours post dose (day 1), with a third study visit on day 7.

The second and third study visits will allow reporting of any adverse events, as well as an opportunity to perform routine observations and take further blood samples for HO-1 induction and in order to analyse safety.

All patients will be genotyped for the short or long repeat HO-1 promoter polymorphism (either homozygous or heterozygous) though this has not been shown to affect HO-1 induction by HA in previous studies.

The RIE cardiac surgery unit performs approximately 1000 cases per year, with just less than 80% aged 60 or over from our analysis of 4572 patients. A conservative estimate for time to meet recruitment to the study is 3 months.