1. Biomarkers in the Cardiorenal Syndromes
Catherine Krawczeski, MD
Associate Professor of Pediatrics
University of Cincinnati College of Medicine
Cardiac Intensive Care
Co-Director, Center for Acute Care Nephrology
The Heart Institute
Cincinnati Children’s Hospital Medical Center

2. Cardiorenal Syndromes
Type I: Acute Cardiorenal Syndrome
Abrupt worsening of cardiac function (e.g. acute cardiogenic shock or acutely decompensated CHF) leading to acute kidney injury
Type II: Chronic Cardiorenal Syndrome
Chronic abnormalities in cardiac function (e.g. chronic CHF) causing progressive and potentially permanent chronic kidney disease
Type III: Acute Renocardiac Syndrome
Abrupt worsening of renal function (e.g. acute kidney ischemia or glomerulonephritis) causing acute cardiac disorder (e.g. heart failure, arrhythmia, ischemia)
Type IV: Chronic Renocardiac Syndrome
Chronic kidney disease (e.g. chronic glomerular or interstitial disease) contributing to decreased cardiac function, cardiac hypertrophy and/or increased risk of adverse cardiovascular events
Type V: Secondary Cardiorenal Syndrome
Systemic condition (e.g. diabetes mellitus, sepsis) causing both cardiac and renal dysfunction
Combined disorders of the heart and kidney are classified as cardiorenal syndromes.
The most recent definition includes 5 subtypes reflecting a variety of conditions where there primary failing organ can be either the heart or the kidney, and a timeframe of disease.

3. Cardiorenal Syndromes
Type I: Acute Cardiorenal Syndrome
Abrupt worsening of cardiac function (e.g. cardiac surgery, cardiogenic shock or acute decompensated HF) leading to acute kidney injury
Type II: Chronic Cardiorenal Syndrome
Chronic abnormalities in cardiac function (e.g. chronic CHF) causing progressive and potentially permanent chronic kidney disease
Type III: Acute Renocardiac Syndrome
Abrupt worsening of renal function (e.g. acute kidney ischemia or glomerulonephritis) causing acute cardiac disorder (e.g. heart failure, arrhythmia, ischemia)
Type IV: Chronic Renocardiac Syndrome
Chronic kidney disease (e.g. chronic glomerular or interstitial disease) contributing to decreased cardiac function, cardiac hypertrophy and/or increased risk of adverse cardiovascular events
Type V: Secondary Cardiorenal Syndrome
Systemic condition (e.g. diabetes mellitus, sepsis) causing both cardiac and renal dysfunction
I’m going to focus most of this talk on types 1 and 5 CRS.
Type 1 CRS is defined as an abrupt worsening of cardiac function (as occurs with cardiac surgery, cardiogenic shock or acute decompensated HF) leading to acute kidney injury. As you can imagine, as a cardiac intensivist, this is by far the largest group of AKI that I see.
Type 5 or secondary CRS occurs when a systemic disease (such as sepsis) causes both cardiac and renal dysfunction.

4. This schematic details the complex interplay between the heart and kidney.
In the face of acute heart disease, a combination of altered hemodynamics, immune mediated damage, activation of the sympathetic nervous system and renin-angiotensin system, and exogenous factors such as nephrotoxin lead to development of acute kidney injury.

5. Cardiorenal Syndromes
Impaired kidney function, or worsening kidney function, in the setting of acute decompensated heart failure, portends a significantly worse prognosis
Is it possible to prevent AKI in HF patients?
How do we manage these patients without damaging their kidneys?
Studies have demonstrated that ……
This leads to 2 important questions…

6. This demonstrates the delicate balance between volume depletion and acute decompensation in the diseased state.
In the normal heart and normal kidney….
Ronco, JACC, 2012 Epub

7. Diagnosing AKI
Diagnostic criteria not standard– over 30 definitions in literature- making comparisons between studies difficult
Inadequate “gold standard”
SCr is delayed and unreliable in the acute setting
Quest for biomarkers an intense area of research
Particularly important for CS-AKI, a planned ischemic event and in decompensated HF, where hydration status is often difficult to assess
Pediatric patients ideal population to study biomarkers
So why is it difficult to diagnose AKI and monitor patients for development of CRS?
As we’ve discussed, the current gold standard is woefully inadequate.
We know that creatinine is a very insensitive marker of AKI, varying widely with age, gender, diet, muscle mass, medications and hydration status.….
As such the quest for biomarkers has been an intense area of research
Biomarkers are particularly important for CS-AKI, which is a planned ischemic event where early detection and early therapy is possible and for decompensated HF, where hydration

8. Serum cystatin C, serum creatinine
Antecedents
Intermediate stage
AKI
Outcomes
Normal
↑Risk
Damage
↓ GFR
Kidney Failure
Death
Biomarkers of structural injury
Biomarkers of functional injury
NGAL, IL-18, L-FABP, KIM-1
Serum cystatin C, serum creatinine
Adapted from Murray, CJASN, 2008; 3:

9. Neutrophil Gelatinase-Associated Lipocalin (NGAL)
Sideraphore binding lipocalin, first identified in a neutrophils
Normally very small amounts in kidney tubules
Marked upregulation very early after ischemic or nephrotoxic AKI
May be measured in plasma or urine
May be influenced by other conditions such as systemic or urinary tract infections, inflammatory conditions, and malignancies
The most promising biomarker to date is Neutrophil Gelatinase-Associated Lipocalin or NGAL.
NGAL was first identified as a neutrophil granule. It is normally found in very small amounts in the kidney tubules and is markedly upregulated very quickly after kidney injury.
It may be measured in plasma or blood (which is advantageous in the case of anuria) but may be influenced by other conditions such as…..

10. Pilot study of NGAL
Landmark prospective study of 71 congenital heart patients undergoing CPB
20 (28%) developed AKI (defined as >50% increase in SCr from baseline)
SCr increase occurred 1-3 days after surgery
We investigated NGAL as an early biomarker for AKI after CPB.
We chose post-CPB kidney injury since this was a common cause of ischemic AKI and there was a temporally predictable injury, allowing us to collect baseline and post-injury specimens.
Our original study involved 71 prospectively enrolled patinets undergoing surgery for congenital heart disease. We defined AKI as a 50% or greater increase in SCr from baseline.

11. NGAL Both urine and plasma NGAL independent predictors of AKI
AUC 2h plasma NGAL 0.91
AUC 2h urine NGAL 0.998
Postoperative NGAL levels correlate with
Duration of AKI
Length of hospital stay
Length of mechanical ventilation
Mortality
Looking at their respective ROC curves, both urine and plasma NGAL are excellent predictors of AKI with AUCs of .91 to .998.
In our study, postoperative NGAL levels correlated with duration of AKI, length of hospital stay, length of mechanical ventilation and mortality.

12. NGAL
Validated in multiple adult and pediatric studies, with multiple etiologies of AKI (ischemic, nephrotoxic, sepsis, CIN, etc).
But…. AUC not as good in adult studies
Co-morbidities?
Inflammation, infection, malignancy, lung disease
NGAL Meta-analysis of Prospective CPB Studies
2538 cardiac surgical patients
Average sensitivity 76%
Average specificity 77%
Mean AUC 0.78
Studies in decompensated HF confirm elevations in NGAL associated with increase rate of adverse events and short tem mortality
NGAL has been validated in multiple adult and pediatric studies and with multiple etiologies of AKI (including ischemic, toxic, septic, and contrast nephropathy).
Unfortunately, however, the AUC’s have not been as good in adults studies, possible do to a increased incidence of co-morbidities in the adult population such as inflammation, infection, malignancy, and lung disease, all of which are know to increase baseline NGAL levels.
In recent meta-analysis of prospective CPB studies which involved 2538 cardiac surgical patients, average sensitivity was 76%, specificity 77% and AUC Notably this compares well with the iinitial studies of troponin, which had an AUC in a similar range.
Haase et al, AJKD 54: , 2009

13. Biomarkers as Endpoints
JACC 2011;57:
One of the difficulties we have with evaluating AKI biomarkers is that we have a flawed gold standard.
These are the results of a pooled analysis, looking specifically at outcomes in patients who demonstrate elevations in NGAL but do not have serum creatinine rise, shown here in this column. This subgroup of patients, who did not fit traditional AKI criteria, still had significantly higher mortality and ICU length of stay, than those who did not have NGAL rises.
Such results may influence our diagnostic criteria in the future.

14. Interleukin 18 (IL-18)
Pro-inflammatory cytokine, activating macrophages
Induced and cleaved in the proximal tubule
Low concentration at baseline
Easily detected in the urine after ischemic injury
Levels correlate with outcomes
A second promising biomarker is interleuking 18 or IL-18.
IL-18 is a pro-inflammatory cytokine which is induced an cleaved in the proximal tubule. IL-18 is in low concentration at baseline but in easily detected in the urine after ischemic injury.

15. Cystatin C
Endogenous cysteine proteinase inhibitor produced by nucleated cells at a constant rate
Used primarily as assessment of glomerular filtration
Serum levels readily measurable using standard laboratory platform
Significant rise at 12h after CPB with peak at 24h
Can be measured in urine or plasma
Cystatin C is an endogenous cysteine proteinase inhibitor. It is produced by nucleated cells at a constant rate. Multiple studies have determined the utility of cystatin C in the measure ment of GFR and unlike the other biomarkers cystatin c may be readily measured using standard current laboratory platforms. In one of our recent studies we found a significant rise in cystatin C at 12 hours after bypass in AKI patients with a peak at 24 hours. We determined that a cutoff value of 1.16 mg/dl at 12 h was predicitve of AKI.
Cut-off value of 1.16 mg/dL at 12h predictive of AKI
Krawczeski et al, CJASN 2010

16. Other Promising Biomarkers
Kidney Injury Molecule-1 (KIM-1):
Epithelial trans-membrane protein, cell-cell interaction.
Appears to have strong relationship with severity of renal injury
Later increase but perhaps higher specificity
Elevations noted in cardiac transplant patients with kidney injury
Liver-type Fatty Acid Binding Protein (L-FABP):
Member of lipocalin family- binds long-chain fatty acid oxidation products
Proximal tubular marker
Intermediate elevation after AKI
Under Investigation:
Monocyte Chemoattractant Protein-1 (MCP-1 )
Hepcidin
Alpha-1 Microglobulin (A1M)
Albumin -
IL-18, KIM-1 and L_FABP are 3 additional proteins which have emerged as promising early AKI biomarkers and are undergoing validation studies.
Given the multifactorial etiology of ischemic AKI it is likely that no single biomarker may be ideal and instead that combinations of biomarkers may prove best at identifying patients at risk. 16

17. Biomarker Combinations
AKI has multi-factorial etiology
Likely no single biomarker will be sufficient but that a biomarker “panel” may prove to be ideal
Variable rise in biomarker concentrations may allow timing of insult and direct appropriate therapy
Given the multi-factorial etiology of AKI, it is likely that no single biomarker will be sufficient but that a biomarker “panel” may prove to be ideal.

18. Biomarker Combinations
JACC 2011;58:
220 pediatric CPB patients
Evaluation of: Urine NGAL, IL-18, KIM-1, and L-FABP
Sequential pattern determined
Correlation with outcomes and severity of AKI
Combination of biomarkers was most predictive of AKI
Elevations able to predict “severe” AKI
Because of this, we recently looked at combinations of biomarkers in pediatric patients undergoing CPB.
In this study of 220 patients, NGAL, IL-18, KIM-1 and L-FABP were evaluated both alone and as a panel.
Since the results are being discussed at an upcoming session, I can’t go into too much detail but we determined a sequential pattern of elevation in these biomarkers, demonstrated their correlation with outcomes and severity of AKI and most importantly, demonstrated that using a combination or panel of biomarkers proved most predictive of AKI

20. Coupling Cardiac and AKI Biomarkers
Addition of NGAL to known cardiac biomarkers (such as BNP) may allow full interpretation of fluid status in decompensated HF and direct clinical care
Ronco, et al

21. Summary
Current diagnostic standard is inadequate and outdated and has limited potential therapeutic advances
Tools of modern science are providing us with highly promising candidates to improve the outcomes of AKI
What is needed:
Refinement of AKI definition
Evaluation of biomarker performance in all etiologies of CRS
Development of rapid diagnostic tests -- ? Biomarker “panels”
Therapeutic trials
In summary,