Diet-induced obesity causes cerebral vessel remodeling and increases the damage caused by ischemic stroke

Abstract

Hypertension, elevated fasting blood glucose and plasma insulin develop in rats fed a high fat (HF) diet. Our goal was to assess the effects of obesity, beginning in childhood, on the adult cardiovascular system. We hypothesized that rats fed a HF diet would have larger ischemic cerebral infarcts and middle cerebral artery (MCA) remodeling. Three-week-old male Sprague Dawley rats were fed a HF (obese) or control diet for 10 weeks. Cerebral ischemia was induced by MCA occlusion (MCAO). MCA structure was assessed by pressure myography and cerebral vessel matrix metalloproteinase (MMP) activity and expression and collagen levels were measured in vessels from rats that did not undergo MCAO. The cerebral infarct was greater in the obese rats than the control (46.0+/-2.1 vs 28.0+/-7.5% of the hemisphere infarcted, obese vs control p<0.05). The MCAs from obese rats had smaller lumens (232+/-7.2 vs 254+/-7.8 microm obese vs control p<0.05) and thicker walls (19.6+/-0.8 vs 17.8+/-0.9 microm obese vs control p<0.05) and were less compliant than MCAs from control rats. MMP-2 activity and collagen I expression were increased in vessels from obese rats and MMP-13 expression was reduced. These results suggest that obesity, beginning in childhood, causes inward vessel remodeling with a concomitant increase in vessel stiffness due to increased collagen deposition. These changes in MCA structure may be responsible for the increase in the ischemic damage after MCAO.

Figure 1. The obese have larger ischemic infarcts than control rats

Rats were fed the HF or control diets for 10 weeks beginning at 3 week of age. Cerebral ischemia was induced by MCAO and the size of the resultant infarct was assessed after 24 hours. The upper panel shows representative brain slices, the grey tissue is viable and the white tissue is tissue damaged by ischemia. The lower panel shows the percentage of the hemisphere infarcted (n=6 for obese and n=8 for control, *=p<0.05 compared to control by t-test).

Figure 2. Obesity has no effect on the response of the MCA to 5-HT or ADP

Rats were fed the HF or control diets for 10 weeks beginning at 3 weeks of age. 5-HT (A) and ADP (B) concentration response curves were generated using a small vessel arteriograph. The ability of the MCA to generate tone was also assessed using the pressure myograph (C) (n=8 for both groups).

Figure 3. Obesity reduces the MCA lumen and outer diameters and increases wall thickness and wall/lumen ratio

Rats were fed the HF or control diets for 10 weeks beginning at 3 weeks of age, MCA lumen (A) and outer diameter (B), wall thickness (C) and wall/lumen ratio (D) was assessed over a range of intralumenal pressures using a small vessel arteriograph under zero flow and calcium free conditions (n=15 for obese and n=16 for control, #=p<0.05 by ANOVA, *=p<0.05 compared to control in post-hoc analysis).

Figure 4. Obesity reduces vessel compliance and increases vessel stiffness

Rats were fed the HF or control diet for 10 weeks from 3 week of age. At the end of the treatment the MCA structure was assessed using a small vessel arteriograph. Vessel compliance was assessed by plotting a stress/strain curve (A) a leftward shift in the curve indicates a less complaint vessel. The β-coefficient (B) was calculated from the individual stress/strain curves (n=15 for obese and n=16 for control *=p<0.05 compared to control by t-test).

Figure 5. Obesity increases the activity of MMP-2 and collagen I expression and reduces MMP-13 expression

Rats were fed the HF or control diet for 10 week from 3 weeks of age, at the end of the treatment the rats were euthanized and the cerebral vessels were collected. MMP-2 activity was measured in cerebral vessels by gelatin zymography (A) (n=4 for each group, *=p<0.05 compared to control by t-test). MMP-13 expression was measured Western blot analysis (B), collagen I (C), and collagen IV (D) were measured by slot-blot analysis (n=7–8 for each group, *=p<0.05 compared to control by t-test). Representative zymograms and Western Blotts and slot blots are shown above the quantitative data.