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.

SignificanceThe 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

BackgroundMuscle mass is a balance between protein degradation and protein synthesis

Protein Degradation

MAFbxBNIP3

Muscle Mass

Protein Synthesis

MyoDIGF-1

BackgroundSerum 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.

BackgroundPatients 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.

PurposeThe 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.

MethodologyIn 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<.05Tumor-Drug interaction, p<.05

Results: Muscle expression of IL-6

* Tumor effect, p<.001+ Drug effect , p<.01Tumor-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

Time factor, p<.001 (within subjects)Tumor effect, p=.001 (between subjects)Tumor-time interaction, p=.004

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?