Implications of a Soy-Based Diet for Animal Models

Abstract

The use of animal models in fundamental or pre-clinical research remains an absolute requirement for understanding human pathologies and developing new drugs. In order to transpose these results into clinical practice, many parameters must be taken into account to limit bias. Attention has recently been focused on the sex, age or even strain of each animal, but the impact of diet has been largely neglected. Soy, which is commonly used in the diet in varying quantities can affect their physiology. In order to assess whether the presence of soy can impact the obtained results, we studied the impact of a soy-based diet versus a soy-free diet, on diastolic function in a rat model based on transgenic overexpression of the β₃-adrenergic receptors in the endothelium and characterized by the appearance of diastolic dysfunction with age. Our results show that the onset of diastolic dysfunction is only observed in transgenic male rats fed with a soy-free diet in the long term. Our study highlights the importance of the diet's choice in the study design process, especially regarding the proportion of soy, to correctly interpret the outcome as low-cost diets are more likely to be highly concentrated in soy.

Keywords: diastolic function; endothelium; phytoestrogen; sex; soy-based diet.

Figure 1

Echocardiography study at 15, 30 and 45 weeks of age and invasive hemodynamic study at 45 weeks of age depending on the rodent diet; with or without soy. We evaluated the ejection fraction on male (A), female (B) and ovariectomized (OVX) female (C) rats and the E/A ratio, on male (D), female (E) and OVX female (F) rats. Left ventricle (LV) and end-diastolic pressure (LVEDP) was evaluated at 45 weeks on male (G), female (H) and OVX female (I) rats. Data are expressed as mean ± SEM ***: p < 0.001. Echocardiography study at 15, 30 and 45 weeks of age and invasive hemodynamic study at 45 weeks of age depending on the rodent diet; with or without soy. We evaluated the ejection fraction on male (A), female (B) and OVX female (C) rats and the E/A ratio, on male (D), female (E) and OVX female (F) rats. LVEDP was evaluated at 45 weeks on male (G), female (H) and OVX female (I) rats. Male—WT—15 w—soy, n = 16; Male—WT—15 w—soyfree, n = 11; Male—WT—30 w—soy, n = 10; Male—WT—30 w—soyfree, n = 8; Male—WT—45 w—soy, n = 12; Male—WT—45 w—soyfree, n = 14; Male—Tgβ₃—15 w—soy, n = 13; Male—Tgβ₃—15 w—soyfree, n = 9, Male—Tgβ₃—30 w—soy, n = 7; Male—Tgβ₃—30 w—soyfree, n = 7, Male—Tgβ₃—45 w—soy, n = 7; Male—Tgβ₃—45 w—soyfree, n = 22; Female—WT—15 w—soy, n = 10; Female—WT—15 w—soyfree, n = 6; Female—WT—30 w—soy, n = 10; Female—WT—30 w—soyfree, n = 8; Female—WT—45 w—soy, n = 3; Female—WT—45 w—soyfree, n = 9; Female—Tgβ₃—15 w—soy, n = 5; Female—Tgβ₃—15 w—soyfree, n = 6; Female—Tgβ₃—30 w—soy, n = 5; Female—Tgβ₃—30 w—soyfree, n = 6; Female—Tgβ₃—45 w—soy, n = 3; Female—Tgβ₃—45 w—soyfree, n = 7; Female OVX—WT—15 w—soy, n = 3; Female OVX—WT—15 w—soyfree, n = 4; Female OVX—WT—30 w—soy, n = 3; Female OVX—WT—30 w—soyfree, n = 5; Female OVX—WT—45 w—soy, n = 6; Female OVX—WT—45 w—soyfree, n = 5; Female OVX—Tgβ₃—15 w—soy, n = 6; Female OVX—Tgβ₃—15 w—soyfree, n = 5; Female OVX—Tgβ₃—30 w—soy, n = 6; Female OVX—Tgβ₃—30 w—soyfree, n = 6; Female OVX—Tgβ₃—45 w—soy, n = 5; Female OVX—Tgβ₃—45 w—soyfree, n = 6. Data are expressed as mean ± SEM.

Figure 2

Changes in ^•NO synthases (NOS) protein expression was performed by Western blot analysis for neuronal NOS (nNOS) protein expression. Male—WT—Soy, n = 12; Male—WT—Soyfree, n = 8; Male—Tgβ₃—Soy, n = 6; Male—Tgβ₃—Soyfree, n = 11 (A), eNOS protein expression. Male—WT—Soy, n = 11; Male—WT—Soyfree, n = 8; Male—Tgβ₃—Soy, n = 6; Male—Tgβ₃—Soyfree, n = 11 (B) and iNOS protein expression. Male—WT—Soy, n = 3; Male—WT—Soyfree, n = 3; Male—Tgβ₃—Soy, n = 3; Male—Tgβ₃—Soyfree, n = 3 (C) on LV from male rats depending on the rodent diet (with or without soy at 45 weeks). n = Data are expressed as mean ± SEM *: p < 0.05, ***: p < 0.001.