Fish oil mitigates myosteatosis and improves chemotherapy efficacy in a preclinical model of colon cancer

<div><p>Background</p><p>This study aimed to assess whether feeding a diet containing fish oil was efficacious in reducing tumor- and subsequent chemotherapy-associated myosteatosis, and improving tumor response to treatment.</p><p>Methods</p><p>Female Fischer 344 rats were fed either a control diet for the entire study (control), or switched to a diet containing fish oil (2.0 g /100 g of diet) one week prior to tumor implantation (long term fish oil) or at the start of chemotherapy (adjuvant fish oil). Chemotherapy (irinotecan plus 5-fluorouracil) was initiated 2 weeks after tumor implantation (cycle-1) and 1 week thereafter (cycle-2). Reference animals received no tumor or treatment and only consumed the control diet. All skeletal muscle measures were conducted in the gastrocnemius. To assess myosteatosis, lipids were assessed histologically by Oil Red O staining and total triglyceride content was quantified by gas chromatography. Expression of adipogenic transcription factors were assessed at the mRNA level by real-time RT-PCR.</p><p>Results</p><p>Feeding a diet containing fish oil significantly reduced tumor- and subsequent chemotherapy-associated increases in skeletal muscle neutral lipid (p<0.001) and total triglyceride content (p<0.03), and expression of adipogenic transcription factors (p<0.01) compared with control diet fed animals. The adjuvant fish oil diet was as effective as the long term fish oil diet in mitigating chemotherapy-associated skeletal muscle fat content, and in reducing tumor volume during chemotherapy compared with control fed animals (p<0.01).</p><p>Conclusion</p><p>Long term and adjuvant fish oil diets are equally efficacious in reducing chemotherapy-associated myosteatosis that may be occurring by reducing expression of transcription factors involved in adipogenesis/lipogenesis, and improving tumor-response to chemotherapy in a neoplastic model.</p></div

Total triglyceride content in the rat gastrocnemius muscle quantified using gas chromatography.

<p>Values are means ± SD. Statistical symbols indicate: *different from Reference; ^‡different from tumor-bearing and cycle-1 control diet groups; ^§different from relative control diet group (p<0.05).</p

Relative tumor volume of tumor-bearing rats who underwent one or two cycles of CPT-11/5-FU treatment.

<p>Relative tumor volume was compared to the baseline volume when chemotherapy was initiated (Day 0). Black arrows show the days when single CPT-11 injections (50 mg/kg) occurred (Days 0, 7); white arrows show the days when single 5-FU injections (50 mg/kg) occurred (Days 1, 8). Values are means ± SD. *Indicates significant differences between the control and each fish oil diet group at each time point (p<0.01).</p

Experimental study design.

<p>Bars show the length of time each group was in the study. Dashed lines show when indicated interventions occurred.</p

Oil Red O staining and analysis of neutral lipid localization in rat gastrocnemius muscle.

<p>(A) Representative photomicrographs of Oil Red O stained skeletal muscle. Solid arrow shows an example of a positive fiber expressing Oil Red O; dashed arrow shows an example of Oil Red O staining between muscle fibers. Scale bar represents 100 μm. (B) Proportion of positive fibers expressing Oil Red O staining. Values are means ± SD. Statistical symbols indicate: *different from Reference; ^†different amongst the indicated control diet groups; ^§different from relative control diet group (p<0.05).</p

Patterns of adipogenic transcription factor mRNA expression in the rat gastrocnemius muscle.

<p>(A) Relative changes in <i>C/EPBδ</i>, <i>C/EBPα</i> and <i>PPARγ</i> mRNA expression levels as determined by the 2^−ΔΔCT method of analysis. Values are means ± SD. Statistical symbols indicate: *different from Reference; ^‡different from tumor-bearing and cycle-1 control diet groups; ^†different from tumor-bearing and cycle-2 control diet groups; ^§different from relative control diet group (p<0.05). (B) The correlation between each gene and the total triglyceride content.</p

EPA and DHA content within the rat gastrocnemius muscle tryglyceride fraction.

<p>EPA and DHA content within the rat gastrocnemius muscle tryglyceride fraction.</p