Western diet, but not high fat diet, causes derangements of fatty acid metabolism and contractile dysfunction in the heart of Wistar rats

Abstract

Obesity and diabetes are associated with increased fatty acid availability in excess of muscle fatty acid oxidation capacity. This mismatch is implicated in the pathogenesis of cardiac contractile dysfunction and also in the development of skeletal-muscle insulin resistance. We tested the hypothesis that 'Western' and high fat diets differentially cause maladaptation of cardiac- and skeletal-muscle fatty acid oxidation, resulting in cardiac contractile dysfunction. Wistar rats were fed on low fat, 'Western' or high fat (10, 45 or 60% calories from fat respectively) diet for acute (1 day to 1 week), short (4-8 weeks), intermediate (16-24 weeks) or long (32-48 weeks) term. Oleate oxidation in heart muscle ex vivo increased with high fat diet at all time points investigated. In contrast, cardiac oleate oxidation increased with Western diet in the acute, short and intermediate term, but not in the long term. Consistent with fatty acid oxidation maladaptation, cardiac power decreased with long-term Western diet only. In contrast, soleus muscle oleate oxidation (ex vivo) increased only in the acute and short term with either Western or high fat feeding. Fatty acid-responsive genes, including PDHK4 (pyruvate dehydrogenase kinase 4) and CTE1 (cytosolic thioesterase 1), increased in heart and soleus muscle to a greater extent with feeding a high fat diet compared with a Western diet. In conclusion, we implicate inadequate induction of a cassette of fatty acid-responsive genes, and impaired activation of fatty acid oxidation, in the development of cardiac dysfunction with Western diet.

Figure 1. Body weight is increased with Western and high fat diet feeding

Values are means±S.E.M. for 14–22 independent experiments per group. Open squares (□) represent low fat diet-fed rats, open circles (○) represent Western diet-fed rats and open triangles (Δ) represent high fat diet-fed rats. ***, P<0.001 compared with low fat diet for the entire feeding protocol.

Figure 2. Fed plasma NEFA concentrations are elevated in the acute to chronic stages of Western or high fat feeding with no net accumulation of myocardial triacylglycerols or protein carbonylation content

Fed plasma glucose concentration (A), plasma NEFA concentration (B), myocardial triacylglycerol content (C) and myocardial carbonylated protein content (D) after 1 day and 1 week (acute term, AT), 4 and 8 weeks (short term, ST), 16 and 24 weeks (intermediate term, IT), and 32 and 48 weeks (long term, LT) on low fat, Western or high fat diet. Values are means±S.E.M. for 12–27 independent experiments per group. Closed squares (■) represent low fat diet-fed rats, closed circles (●) represent Western diet-fed rats and closed triangles (▲) represent high fat-fed rats. *, P<0.05, **, P<0.01 and ***, P<0.001 compared with low fat diet at the same age.

Figure 3. Glucose oxidation flux is increased in response to an acute increase in work in the isolated perfused heart of the Wistar rat on low fat diet

Representative means±S.E.M. for cardiac power (closed squares, ■), oleate oxidation flux (open circles, ○) and glucose oxidation flux (closed circles, ●) of the Wistar rat on low fat diet (n=58) at baseline (perfusion time 0–20 min) and in response to an acute increase in work (shaded area, perfusion time 25–40 min). Values for subsequent heart perfusion data are presented as the representative value at 20 min of perfusion for baseline measures and at 40 min for measures at increased workload.

Figure 4. Cardiac power is decreased with Western diet in the long term

Cardiac power (A), MV˙O₂ (B), oleate oxidation (C) and glucose oxidation (D) at baseline (solid circles) and in response to an acute increase in work (open points) in the acute (AT), short (ST), intermediate (IT), and long term (LT) on low fat, Western or high fat diet. Values are means±S.E.M. for 12–18 independent experiments per group. Flux is represented per minute per gram dry weight (gdw). Closed squares (■) represent low fat diet-fed rats, closed circles (●) represent Western diet-fed rats and closed triangles (▲) represent high fat-fed rats at baseline. Open squares (□) represent low fat diet-fed rats, open circles (○) represent Western diet-fed rats and open triangles (△) represent high fat diet-fed rats after an acute increase in work. *, P<0.05, **, P<0.01 and ***, P<0.001 compared with low fat diet at the same age. $, P<0.05 compared with Western diet at the same age.

Figure 5. Cardiac expression of fatty acid-responsive genes involved in fatty acid futile cycling are increased to a greater extent by high fat diet compared with Western diet feeding

mRNA expression of pparα (A), ucp3 (B), cte1 (C), mte1 (D), pdhk4 (E) and glut4 (F) in the hearts of rats fed on low fat, Western or high fat diet in the acute (AT), short (ST), intermediate (IT) and long term (LT). Values are means±S.E.M. for 12–16 independent experiments per group. Closed squares (■) represent low fat diet-fed rats, closed circles (●) represent Western diet-fed rats and closed triangles (▲) represent high fat diet-fed rats. *, P<0.05, **, P<0.01 and ***, P<0.001 versus low fat at the same age. $, P<0.05, $$, P<0.01 and $$$, P<0.001 compared with Western at the same age.

Figure 6. Soleus muscle oleate oxidation maladapts earlier than cardiac oleate oxidation with Western or high fat diet

Isolated soleus oleate oxidation (A), radioactive lactate release (B), glucose oxidation flux (C) stimulated with 100 μU/ml insulin, and maximal glycogen production flux (D) stimulated with 1000 μU/ml insulin in the acute (AT), short (ST), intermediate (IT) and long term (LT) on low fat, Western or high fat diet. Values are means±S.E.M. for 12–16 independent experiments per group. Flux is represented per minute per gram wet weight (gww). Closed squares (■) represent low fat diet-fed rats, closed circles (●) represent Western diet-fed rats and closed triangles (▲) represent high fat diet-fed rats. *, P<0.05, **, P<0.01 and ***, P<0.001 compared with low fat diet at the same age.

Figure 7. Soleus mRNA expression of fatty acid-responsive genes involved in fatty acid futile cycling is increased to a greater extent by high fat diet feeding compared with Western diet feeding

mRNA expression of pparα (A), ucp3 (B), cte1 (C), mte1 (D), pdhk4 (E) and glut4 (F) in the soleus muscle of rats fed on low fat, Western or high fat diet in the acute (AT), short (ST), intermediate (IT) and long term (LT). Values are means±S.E.M. for 14–24 independent experiments per group. Closed squares (■) represent low fat diet-fed rats, closed circles (●) represent Western diet-fed rats and closed triangles (▲) represent high fat diet-fed rats. *, P<0.05, **, P<0.01 and ***, P<0.001 compared with low fat diet at the same age. $, P<0.05, $$, P<0.01 and $$$, P<0.001 compared with Western diet at the same age.

Figure 8. Putative role of the decrease in fatty acid-responsive genes in the development of contractile dysfunction with Western diet compared with high fat diet feeding

Fatty acid (FA) enters the cell through fatty acid transporters, fatty acid transport protein (FATP) and or fatty acid translocase (CD36), and is activated to fatty acyl-CoA (FA-CoA) by an isoform of acyl-CoA synthetase (ACS). The activated FA-CoA can undergo hydrolysis (at the indirect expense of ATP) via CTE1, which is decreased in the Western diet compared with the high fat diet, thus decreasing the capacity for fatty acid-mediated futile cycling. After entry of FA-CoAs into the mitochondrion via CPT and carnitine acyltransferase (CAT), there is a decrease in the capacity of MTE1 and UCP3 to ‘uncouple’ fat oxidation (indicated with dashed lines) with the Western diet compared with the high fat diet, which may result in a decreased free CoASH pool for complete β-oxidation and increased production of ROS by the electron transport chain (ETC). Therefore FA-CoAs accumulate and are shuttled into ‘lipotoxic pathways’.