Transcript TrT In Renal Failure- Does Myeloperoxidase have a role??

Biomarkers of CVD in Renal
Failure. Facts and ?Fiction
A biochemical detective story
ACB SW regional meeting July 4th
John O’Connor
Presentation includes:
• The scale of CVD in CKD patients.
The Facts
• Biochemical Markers of Myocycte
damage in CKD Patients
• An alternative hypothesis. The
?Fiction
• Diagnostic Dilemmas
• Practical Considerations
Scale of CVD in CKD. The Facts!!
• The 5 level staging system for CKD only
came into being in 2002 so outcome vs
stage data is still forthcoming
• The overall prognosis for patients with
stage 5 CKD is dismal, ACS accounts for
20% of cardiovascular deaths
• Worst still the event is likely to be
catastrophic
• Only 40% of Dialysis patients survive a
year, 27% Two years
• 40% of new dialysis patients have left
ventricular abnormalities
n = 1 120 295 between 1996 and 2000 in California (mean age 52
yrs) - Mean follow-up 2.84 yrs
AS Go et al., N Engl J Med 2004
Decreases in GFR influence survival rate in patients following
MI
(VALIANT STUDY)
Rates of Death at 3-years from Cardio-Vascular Causes after MI
alongside other adverse outcomes according to GFR at
baseline
AS Anavekar et al., N Engl J Med 2004
CKD Patients Have additional CVD Risk
Factors
•These include;
•abnormal calcium and phosphate metabolism,
•anaemia,
•Inflammation (CRP)
•oxidative stress,
•thrombogenic factors
•uraemic toxins
•homocystine
Biochemical Markers of Myocte damage
in CKD Patients
•T CK often elevated in Haemodialysis Patients
•Troponin T and I are also raised (why?)
Chemistry
Department at the RD&E carried out an
audit on 174 patients with an impaired GFR (<60).
Of
these, 75 had measurable cTnT (> 0.02 ng/ml)
in the absence of any appreciable cardiac damage.
Distribution of TrT
90
Number of patients
80
70
60
50
40
30
20
10
0
<0.01 0.02
0.03
0.04
0.05
0.06
0.07
TrT ng/ml
0.08
0.09
0.1
>0.1
Biochemical Markers of MI in CKD
Patients
Hennepin County Medical Center,
Minnesota
Cohort:
733 ESRD patients (largest study to date)
Aim
: to determined the prevalence of increased
cardiac Troponin I (cTnI) and T (cTnT) in ESRD
Results: A significant
increase in TnT (82%) and
TnI (6%) was observed in ESRD patients compared
to 99th percentile.
Biochemical Markers of MI in CKD
Patients
Differences between [TnT] and [TnI] not entirely clear
from the literature.

TnT is more consistently raised than I (about 5:1)
? Cytosolic

[TnT] is greater than [TnI] per gram weight of cardiac
muscle

[TnT] increase during dialysis [TnI] decreases
(absorption onto dialysis membranes)


TnI may undergo more significant proteolysis
in the circulation than TnT
Methodological Issues: Troponins
Different forms of troponin which are released from
necrosing myocytes.

Wu et al studied serum troponins separated by
gel filtration (Clin Chem 1998:44;6)

Troponin T are released as the intact TnT:I:C complex and free cTnT

One Assay one standard  not a problem

cTnI mainly released in complexed form following
MI (which most assays measure) but also free cTnI variably measured
by different assays
Added issue is TnI hydrophobicity

Free cTnI can bind to other proteins present in blood,
such as calmodulin, a structural analogue to Troponin C,
potentially obscuring its antigenic epitopes

It may be possible that free TnI is lost to the
surfaces of blood collection tubes, pipette tips,
sample cuvettes, and so forth.

Why are Troponins raised?

Renal clearance of Troponin may be impaired?

But !! Troponins are large molecules, not easily filtered
Kinetic studies (of Troponin fall) in patients with ESRD
compared to patients with normal GFR who have MI’s, show no
differences


Current theory is that these patients are having silent microinfarcts
Certainly having a elevated ventricular mass is an independent
variable in having raised levels

TnT vs GFR
0.25
TnT ng/ml
0.2
0.15
0.1
0.05
0
0
10
20
30
40
50
eGFR
TnT > 0.01 and < 0.25 ng/ml
R = 0.282
No significant correlation
Omitted any patients admitted via A+E
60
70
80
Uraemic-induced skeletal myopathy
? may be responsible
• Uraemic states may promote re-expression of cardiac
troponin isoforms from damaged or regenerating skeletal
muscle fibres.
• The uraemic-induced skeletal myopathy hypothesis is also
supported by the observation that skeletal muscle from
patients treated with maintenance haemodialysis, have
significant morphological changes observed by electron
and light microscopy 22.
• However, studies using highly specific antibodies have
demonstrated absence of cTnT in skeletal muscle
immunohistochemically and absence of cTnT mRNA in
adult skeletal muscles 23.
• Therefore, there is currently insufficient data to support a
skeletal muscle source for serum cardiac cTnT elevations
in patients with ESRD.
TnT vs Urea
0.25
TnT ng/ml
0.2
0.15
0.1
0.05
0
0
10
20
30
40
50
Urea mmol/L
Pearson Correlation TnT vs Urea (TnT > 0.01 and < 0.25ng/ml)
R = 0.349
P = 0.0073 (very significant)
Omitted any patients admitted via A+E
Pointers from Transplant Patients
• TrT was positive in
14 of 26 (54%) pre
transplant samples
but only 3 out of 26
(12%) post
transplant samples.
• But can we assume
its all down to
clearance??
Another Theory (Currently under
investigation at the RDE) ? The Fiction
The presenter gazed at the
audience
Will they spot it he mused
The EPO mystery
The EPO Hypothesis
• EPO A hypoxia induced hormone
produced by the kidney stimulating
hematopoiesis
The EPO Hypothesis
• Role is to inhibit Apoptosis of erythroid
precursors
• Clue to its pleiotrpoic cytokine status
• There are EPO receptors in the Cardiovascular
system, both in endothelial cells and
cardiomyocytes
• Anoxia causes a two fold increase in expression
of these receptors
• Apoptosis / mitosis is occurring all the time in
healthy individuals but is increased in the
absence of EPO as would be the case with CKD
• EPO also improves cardiac vascularity
Apoptosis in Myocytes is via the Mitochondrial pathway
Activated by Oxidative stress (toxic ureamic compounds in CKD)
and Hypoxia
Contain proapoptotic factors
CYT C
Release of CYT is controlled by Bci-2
Family members, can open pores
If released into cytoplasm
activate Caspase Cascade
Death
Antipoptotic factors EPO
Keep pores closed
Life
Stabilises mitochondrial
Membrane preventing the
Release of Cyt C
Blocks Caspase 9 protects
Genomic DNA
Activation of the Janus
Kinase 2 pathway
P I 3 Kinase
(AKT) Protein Kinase B
Upregulates BcL-x (Anti
Apoptotic)
Cell Death
To induce a local
inflammatory response
Not to induce a local
inflammatory response
Some more clues
REVIEW Elevation of cardiac troponin I indicates more than
myocardial ischemia John P. Higgins, MD, MPhil*Johanna
A. Higgins, MD†Clin Invest Med 2003;26(3):133-47.
Apoptosis in myocytes in endstage heart failure Narula J,
Haider N, Virmani R, DiSalvo TG, Kolodgie FD, Hajjar RJ,
et al.. N Engl J Med 1996;335:1182-9. Comments in: N
Engl J Med 1996;335:1224-6; N Engl J Med
1997;336:1025-6. 158.
Functional consequences of caspase activation in cardiac
myocytes Communal C, Sumandea M, de Tombe P, Narula
J, Solaro RJ, Hajjar RJ.. Proc Natl Acad Sci U S A
2002;99:6252-6. 159..
Release of cardiac troponin in acutecoronary syndromes:
ischemia or necrosis? Wu AH, Ford L Clin Chim Acta
1999;284:161-74.
Conclusions from review
• Apoptosis (preserved membrane integrity) in
addition to necrosis (loss of membrane integrity)
may lead to the release of cTnI.
• Apoptosis is associated with the activation of
caspases that mediate the cleavage of vital
structural proteins.
• In cardiac myocytes, apoptosis may not be
complete, allowing the cells to persist for a
prolonged period within the myocardium.
• Therefore, activation of apoptotic pathways may
lead to contractile dysfunction prior to cell death.
• Other animal studies suggest that release of
troponin I can occur in the absence of
irreversible ischemia
Further clues: A blast from the
past
• Prognostic value of mitochondrial aspartate
aminotransferase in acute myocardial infarction
Giorgio Annoni Clinical Biochemistry
Volume 19, Issue 4 , August 1986, Pages 235-239
• Demonstrated that 12 hours after admission, serum mAST and m-AST/AST ratio were significantly higher in
the group of non-survivors compared with patients
with a favourable prognosis
• ? A reflection of the degree of Apoptosis following MI
• Ischaemia, with mild to moderate hypoxia can
lead to apoptosis of myocytes during a MI. This
may result in a non-functional region of tissue,
which if it is sufficiently large may lead to organ
failure.
• Apoptosis following MI begins in endothelial cells
EPO has a crucial protective role in these cells
• EPO could be a major determinant in myocardial
size and preserving function
• Rats pretreated (24h) with 5000 Iu/Kg EPO and
then subjected to I/R showed increased
myocardial recovery
• It could be argued that the damage limitation
was due to having increased oxygenated blood,
but it was a further 48h before haematocrit
increased
• Potential role in treating patients with MI to
prevent CHF
• Bahlmann et al studied CRF patients treated with
EPO (Darbepoietin)
• Concluded that EPO conferred tissue protection
and preserved the capillary network in the
Kidney without raising heamatocrit
• Could the same be happening to the heart
• One could postulate that in CKD patient a low
level of EPO would lead to increased Apoptosis
• This could explain the release of biomarkers of
cardiac damage and could explain
(Contraversially) the disparity between the bigger
rise in Troponin T (Cytostolic) compared with
Troponin I. In necrosis caused by ischaemia one
would have thought they would be equal
HB vs TnT in Patients with GFR < 50
y = -12.114x + 11.585
R = -0.-33
N= 69
16
14
12
HB
10
8
6
4
2
0
0
0.05
0.1
0.15
0.2
0.25
0.3
TnT mg/L
In theory patients with low EPO levels should have lower HB levels
From the RDE data set Hb vs TnT
Pearson correlation N=69
R = -0.33
Two tailed P value = 0.0071 (highly significant)
Clinical Implications
• We know that in CKD patients, anaemia is an established
risk for Cardiovascular disease. (but is this because the
EPO levels are low)
• Naomichi et al studied patients who suffered their first MI
and who had high levels of endogenous EPO. He found
that following PCI the infarctions were smaller
• However, there are no RCT’s or other conclusive data for
treating CKD patients with EPO (probably explains why
only 50% are being prescribed it)
• The TREAT study has just begun to explore this, the
outcomes may yield more data about the pleiotropic effects
of EPO
• There may be a role for EPO following MI alongside
reperfusion therapy, to help avoid CHF
Pointers from Transplant Patients
• cTnT produced positive
results in 14 of 26 (54%)
pretransplant samples
and 3 of 26 (12%) post
transplant samples.
• This demonstrates the
effect of replacing a fully
functional endocrine
gland producing
Erythropoietin
Prognostic implications
• It may be that if the increased
Troponin T levels reflect apoptosis
then potentially they could be used
as markers of cardioprotection in
patients treated with EPO?
Therapeutic implications
• EPO promotes microvascular growth
in the heart, suggesting functional
cardiac recovery with the formation
of new blood vessels
• In patients with resistant CHF EPO
plus iv Fe showed a big increase in
LV function and a reduction in
hospitalization days of 80%
Diagnostic Dilemmas

In CKD patients with low GFR and
“Chest Pain ? Cause”

There is a danger that patients get
diagnosed NSTEMI on the basis of
having a raised Troponin
Solution
 Measure 2x Troponin on admission
and at 12 hours pocp and see if
there is a dynamic change in the
concentration
• Pre screen all peritoneal and
heamodialysis patients to establish
baseline TrT
Thanks for your attention
Any Questions