Interleukin-1 regulates multiple atherogenic mechanisms in response to fat feeding

Abstract

Background: Atherosclerosis is an inflammatory process that develops in individuals with known risk factors that include hypertension and hyperlipidaemia, influenced by diet. However, the interplay between diet, inflammatory mechanisms and vascular risk factors requires further research. We hypothesised that interleukin-1 (IL-1) signaling in the vessel wall would raise arterial blood pressure and promote atheroma.

Methodology/principal findings: Apoe(-/-) and Apoe(-/-)/IL-1R1(-/-) mice were fed high fat diets for 8 weeks, and their blood pressure and atherosclerosis development measured. Apoe(-/-)/IL-R1(-/-) mice had a reduced blood pressure and significantly less atheroma than Apoe(-/-) mice. Selective loss of IL-1 signaling in the vessel wall by bone marrow transplantation also reduced plaque burden (p < 0.05). This was associated with an IL-1 mediated loss of endothelium-dependent relaxation and an increase in vessel wall Nox 4. Inhibition of IL-1 restored endothelium-dependent vasodilatation and reduced levels of arterial oxidative stress.

Conclusions/significance: The IL-1 cytokine system links atherogenic environmental stimuli with arterial inflammation, oxidative stress, increased blood pressure and atherosclerosis. This is the first demonstration that inhibition of a single cytokine can block the rise in blood pressure in response to an environmental stimulus. IL-1 inhibition may have profound beneficial effects on atherogenesis in man.

Figure 1. Atherosclerosis formation in mice following feeding of a high fat diet.

Atherosclerotic lesion area in the aortic sinus of Apoe^−/− and Apoe^−/−/IL-R1^−/− mice (a) and chimeric mice (b) fed a high fat and chow diets. Apoe→DN denotes Apoe^−/−/IL-1R1^−/− (DN) mice receiving Apoe^−/− bone marrow (n = 3); DN→Apoe denotes Apoe^−/− mice receiving Apoe^−/−/IL-1R1^−/− marrow (n = 9).

Figure 2. Blood pressure of mice following feeding of a high fat diet.

Mean blood pressure in Apoe^−/−/IL-1R1^−/− (a) and Apoe^−/ (b) mice fed all 3 diets, and Apoe^−/−/IL-1R1^−/− compared to Apoe^−/− mice fed chow (c) Western (d) and WHC (e). (f) Mean blood pressure in Apoe^−/− mice administered with hrIL-1ra or placebo, fed WHC diet. n = 4 for all groups.

Figure 3. Vascular reactivity of arterioles from Apoe^−/− and Apoe^−/−/IL-R1^−/− mice.

(a–b) % maximum dilation of pre-constricted mesenteric arterioles (EC₈₀PE) to acetylcholine. (c) Endothelium-independent relaxation responses assessed by superfusion of sodium nitroprusside (SNP) were not different between Apoe^−/− and Apoe^−/−/IL-R1^−/− mice both fed a WHC diet (n = 6 per group).

Figure 4. NO activity, ROS and NOS expression in mice fed WHC diet.

(a) cGMP in lung homogenates (n = 14), (b) eNOS enzymatic activity (n = 6) and (c) in-situ ROS (white arrowhead) in Apoe^−/−/IL-R1^−/− and Apoe^−/− mice fed WHC. (Note: images chosen illustrate ROS levels not atherosclerotic lesion size). Chemiluminescent quantification of ROS in mice fed WHC (d) and Apoe^−/− mice fed WHC diet (n = 9) and administered hrIL-1ra (n = 4) (e).

Figure 5. Nox expression following feeding of WHC diet.

Expression of Nox is selectively reduced in Apoe^−/−/IL-R1^−/− mice fed WHC. (a) qRT-PCR shows reduced (p<0.05) levels of Nox 4 in the vascular wall of Apoe^−/−/IL-R1^−/− mice fed WHC diet. Levels of Nox 2 (b) and Nox 1 (c) do not differ. n = 12 per group.