Establishing an Animal Model to Investigate Depression with Coronary Heart Disease

Coronary heart disease (CHD) and depression are two prevalent conditions that often coexist in patients worldwide. The comorbidity of these conditions is associated with higher incidence and mortality rates, as well as worse prognoses. Research has established a bidirectional relationship between CHD and depression, suggesting that depression can increase the long-term risk of CHD, and CHD can exacerbate depressive symptoms. To better understand the interplay between these conditions and to facilitate future research, it is essential to establish a reliable animal model that mimics the clinical manifestations of depression with CHD. This study aimed to explore whether chronic unpredictable mild stress (CUMS) combined with a high-fat diet (HFD) could establish a representative and reliable rat model of depression with CHD.

Background and Rationale

Depression and CHD are major public health concerns globally. Studies have shown that depression is a significant risk factor for the development of CHD, and patients with CHD are more likely to experience depressive symptoms. The bidirectional relationship between these conditions complicates their management and treatment. Animal models are crucial for studying the underlying mechanisms and developing therapeutic interventions. CUMS is a widely used method to induce depression-like behaviors in animals, while feeding a HFD is a common approach to induce atherosclerosis and CHD. Previous studies have demonstrated that housing cynomolgus monkeys in single cages and feeding them an atherogenic diet could establish a model of depression combined with CHD. Additionally, CUMS combined with HFD in rats has been shown to mimic vascular depression in humans. However, it remains unclear whether CUMS combined with HFD can establish a comprehensive rat model of depression with CHD. This study sought to address this gap by investigating the effects of CUMS combined with HFD in rats.

Methods

Animal Groups and Treatment

After a one-week adaptation period, Wistar rats were randomly assigned to three groups: the CUMS with normal feed group (CUMS, n = 8), the CUMS combined with HFD group (CUMS + HFD, n = 8), and the normal control group (NC, n = 8). The rats in the CUMS group were housed individually and subjected to various stressors, including cage tilting for 24 hours, wet bedding for 24 hours, swimming in 5°C cold water for 3 minutes, swimming in 45°C hot water for 5 minutes, fasting for 24 hours, water deprivation for 24 hours, level shaking for 10 minutes, tail nip for 1 minute, and inversion of the light/dark cycle for 24 hours. These stressors were applied over 21 days, with each stressor applied 2 to 3 times. The same stressor was not applied consecutively over two days to prevent the animals from predicting the stimulation. The rats in the CUMS + HFD group were subjected to the same stressors as the CUMS group but were also fed a HFD. The HFD consisted of 3% cholesterol, 0.5% sodium cholate, 0.2% propylthiouracil, 5% sugar, 10% lard, and 81.3% normal feed. Before administering the HFD, a vitamin D3 injection was administered into the rat’s abdominal cavity at 600,000 U/kg once. All rats were maintained on the schedule for 8 weeks.

Behavioral Tests

After 8 weeks of modeling, the rats were subjected to an open field test and a forced swimming test to assess depression-like behaviors. The open field test measured the total distance traveled by the rats, while the forced swimming test measured the immobility time, which is indicative of depressive behavior.

Pathological and Biochemical Analyses

Pathological sectioning of the heart, cardiac vessels, and cerebral vessels was performed using oil red O-staining and hematoxylin-eosin (HE) staining to assess atherosclerosis and myocardial damage. Serum lipid levels, including triglycerides (TC) and total cholesterol (TG), were measured to evaluate hyperlipidemia. The expression of brain-derived neurotrophic factor (BDNF) in the brain tissue was assessed using Western blot analysis.

Statistical Analysis

All data were analyzed using the SPSS Graduate Pack 17.0 statistical software package. Data were expressed as the mean ± standard deviation. One-way analysis of variance was used to analyze differences in the parameters, with a P < 0.05 considered statistically significant.

Results

Behavioral Tests

Compared with the NC group, the CUMS and CUMS + HFD groups exhibited a shorter total distance in the open field test (CUMS: 1603.2 ± 361.0 cm vs. NC: 821.3 ± 303.2 cm, P < 0.01; CUMS + HFD: 1603.2 ± 361.0 cm vs. NC: 806.6 ± 347.0 cm, P < 0.01) and increased immobility times in the forced swimming test (CUMS: 9.7 ± 7.9 s vs. NC: 23.9 ± 10.47 s, P < 0.01; CUMS + HFD: 9.7 ± 7.9 s vs. NC: 24.4 ± 11.1 s, P < 0.01). These results indicated successful induction of depression-like behaviors in the CUMS and CUMS + HFD groups.

BDNF Expression

The CUMS and CUMS + HFD groups displayed a marked decrease in BDNF expression in the hippocampus compared with the NC group (CUMS: 0.9 ± 0.1 vs. NC: 0.8 ± 0.1, P < 0.01; CUMS + HFD: 0.9 ± 0.1 vs. NC: 0.7 ± 0.1, P < 0.01), further supporting the induction of depression-like behaviors.

Pathological Changes

Pathological sectioning of cardiac and cerebral vessels using oil red O-staining revealed no obvious abnormalities in the NC and CUMS groups. In contrast, the CUMS + HFD group exhibited diffuse intimal thickening and focal fat deposition in the cardiac and cerebral vessels, indicating atherosclerosis. HE staining of myocardial tissue showed no significant changes in the NC and CUMS groups. However, the CUMS + HFD group exhibited evidence of myocyte swelling, rupture, degeneration, necrosis, and inflammatory cell infiltration, indicating myocardial damage.

Serum Lipid Levels

The CUMS + HFD group showed increased serum levels of TC (1.1 ± 0.2 mmol/L vs. NC: 1.6 ± 0.3 mmol/L, P < 0.01; CUMS: 1.1 ± 0.3 mmol/L vs. CUMS + HFD: 1.6 ± 0.3 mmol/L, P < 0.01) and TG (0.4 ± 0.1 mmol/L vs. NC: 1.1 ± 0.2 mmol/L, P < 0.01; CUMS: 0.5 ± 0.2 mmol/L vs. CUMS + HFD: 1.1 ± 0.2 mmol/L, P < 0.01) compared with the NC and CUMS groups, indicating hyperlipidemia.

Discussion

This study demonstrated that CUMS combined with HFD could establish a rat model of depression with CHD. The CUMS and CUMS + HFD groups exhibited depression-like behaviors, as evidenced by the shorter total distance in the open field test, increased immobility time in the forced swimming test, and decreased BDNF expression. Additionally, the CUMS + HFD group exhibited atherosclerosis of cardiac and cerebral vessels, myocardial damage, and hyperlipidemia. These findings suggest that CUMS combined with HFD can induce symptoms of depression, atherosclerosis, myocardial damage, and hyperlipidemia in rats, providing a comprehensive model for studying the comorbidity of depression and CHD.

The establishment of this composite model is significant because it mimics the clinical manifestations of depression with CHD more closely than previous models that used CUMS or HFD alone. The CUMS + HFD model provides a better experimental tool for basic research and drug development for CHD with depression. However, further verification of this animal model is necessary, and the relationship between CHD and depression needs to be studied in greater depth.

Conclusion

In conclusion, this study demonstrated that CUMS combined with HFD in rats could establish a representative and reliable model of depression with CHD. The findings of this study provide an ideal animal model for future research on the comorbidity of CHD and depression, offering insights into the underlying mechanisms and potential therapeutic interventions.

doi.org/10.1097/CM9.0000000000000561

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