Transcript Tumor effect , p<.001

The Effect of Losartan on Skeletal Muscle
Wasting in a Mouse Model of Cancer-Related
Fatigue
Yvonne Clark, Runfeng Jing, Loren Wold, Donna
McCarthy Beckett
Significance
• 75-90% of patients with incurable cancer
complain of fatigue and 41% describe their
fatigue as severe.
• Cancer related fatigue (CRF) is more
distressing than pain, nausea, or vomiting.
• Symptoms of weakness and reduced effort
tolerance often co-occur with CRF.
Significance
The causes of CRF are multimodal and not clearly
understood. Several proposed mechanisms include
•
•
•
•
•
•
•
disturbances in HPA activity,
decreased serotonin synthesis,
altered circadian rhythms,
sleep disturbances
anemia
Increased serum levels of pro-inflammatory cytokines
loss of skeletal muscle mass
Background
Muscle mass is a balance between protein
degradation and protein synthesis
Protein
Degradation
Protein
Synthesis
MAFbx
BNIP3
MyoD
IGF-1
Muscle Mass
Background
Serum levels of pro-inflammatory cytokines,
such as IL-6, are increased in patients with
CRF and in mouse models of tumor-induced
muscle wasting.
IL-6 increases muscle expression of
biomarkers of metabolic pathways associated
with muscle protein degradation.
•
•
MAFbx
BNIP3.
Background
Patients with congestive heart failure, COPD,
and renal disease also often have muscle
wasting and fatigue and elevated serum levels
of IL-6 and……. Angiotensin II.
Infusion of Angiotensin II increases serum IL-6,
increases muscle expression of MAFbx and
suppresses serum levels of IGF-1 causing
muscle wasting in otherwise healthy animals.
Angiotensin II
• Angiotensin II exerts most of its biological
effects through binding AT1 or AT2
receptors.
• The AT1 receptor blocker Losartan
prevented skeletal muscle wasting in a
mouse model of disuse atrophy.
Purpose
The purpose of this study was to determine if
Losartan would reduce skeletal muscle wasting,
symptoms of fatigue, and biomarkers of muscle
metabolism in tumor bearing mice.
Methodology
In mice, fatigue is
modeled as
decreased
voluntary wheel
running activity
(VWRA).
Methodology
In mice, weakness is modeled as decreased
grip strength.
Methodology
•
•
•
•
Adult female mice were acclimated to the running
wheels before being inoculated subcutaneously with
C26 tumor cells.
One half of control and tumor bearing mice received
Losartan 10mg/kg/day in their drinking water.
VWRA was monitored over the course of tumor
growth.
Grip strength was measured before sacrifice .
Methodology
• Mice were euthanized on day 19 and the
gastrocnemius muscles were removed and
weighed. Muscles were homogenized in
Trizol for extraction of total RNA.
• Expression of IL-6, MAFbx, BNIP3, MyoD,
and IGF-1 mRNA was determined using
real-time PCR. Expression of each gene was
normalized to mean expression of the
house-keeping gene GAPDH.
Methodology
•
•
•
•
Muscle mass is reported as grams muscle
weight normalized to body weight.
Grip strength is reported as the average of 3
tests to determine grams of force needed to
dislodge the mouse from the wire mesh
normalized to body weight.
VWRA is reported as total wheel turns/24 hours.
Data was analyzed using two-way (tumor, drug)
and repeated measures analysis of variance.
Results: Gastroc Muscle Weight
(normalized to body weight)
* Tumor effect, p=.001
+ Drug effect, p<.05
Tumor-Drug interaction, p<.05
Results: Muscle expression of IL-6
* Tumor effect, p<.001
+ Drug effect , p<.01
Tumor-Drug interaction, p<.05
Results: Muscle Expression of MAFbx
* Tumor effect, p<.001
Results: Muscle Expression of BNIP3
* Tumor effect , p<.001
Results: Muscle Expression of MyoD
Results: Muscle Expression of IGF-1
* Tumor effect, p=.01
+ Drug effect, p=.05
Results: VWRA
6000
Control
5000
Control+10 mg Losartan
Tumor
4000
Tumor + 10 mg Losartan
3000
2000
1000
0
Day 1
Time factor, p<.001 (within subjects)
Tumor effect, p=.001 (between subjects)
Tumor-time interaction, p=.004
Day 7
Day15
Day 19
Results: Grip Strength
+ Drug effect, p=<.05
Conclusion
•
•
•
VWRA progressively declined and skeletal muscle
mass was significantly reduced in the tumor bearing
mice.
Tumor growth significantly increased expression of
IL-6, MAFbx, BNIP3 and IGF-1 mRNA in the
gastrocnemius muscle, but did not affect
expression of MyoD.
Treatment with 10mg/kg Losartan preserved muscle
mass and grip strength in tumor bearing mice but
did not affect VWRA in this mouse model of CRF.
Conclusion
•
•
•
Losartan reduced expression of IL-6 and IGF-1,
but did not affect expression of MAFbx, BNIP3, or
MyoD mRNA in the gastrocnemius muscle.
Because Losartan improved muscle mass and
grip strength, but did not affect VWRA, we
conclude that SMW may not be a major factor in
the fatigue that occurs with incurable cancer.
The data also suggest that Losartan warrants
further study in the treatment of tumor-induced
SMW.
Questions?