Introduction of psoriasis

Psoriasis is a common, immunologically mediated, inflammatory disease characterized by scaly erythematous plaques on the skin and have comorbidities such as arthritis and cardiovascular disease. Pathogenesis of psoriasis involves polygenic predisposition and multiple environmental factors. Our team has collaborated with University of California Davis to investigate the effects of diets on psoriasis.

Obesity, diets, and psoriasis

The relationship between obesity and psoriasis is well known. Obesity exacerbates psoriasis while body weight reduction ameliorates psoriasis. However, both fat and sugars (ex. sucrose) induces obesity, and general people more often eats the Western diet (WD, high-fat and high-sugar content), which not only contains excessive fat but has excessive sugars from sugary drinks. On the other hand, the high-fat diet (HFD, high-fat and normal sugar content) is also used in animal experiments to investigate the relationship between obesity and disease. In this research, we aim at investigating if there is difference in psoriasiform inflammation between WD and HFD, both induce obesity. 

WD, HFD, and psoriasis

For study design, mice were classified into four groups based on the diets: WD, control diet (CD, a control recipe of WD), HFD, low-fat diet (LFT, a control recipe of HFD). After feeding them for 3 months, we applied imiquimod cream on ears of mice for 5 consecutive days to induce psoriasiform dermatitis, and measure ear thickness as an indicator of inflammation during the course. After applying imiquimod cream for 5 days, mice were sacrificed and their ears were harvested to examine histological change, RT-qPCR and immunohistochemistry specific to psoriasis-related inflammatory mediators.

After feeding for 3 months, mice fed with HFD had significantly more body weight than other groups. This is, mice fed with HFD had more severe obese than mice fed with WD. After applying imiquimod cream for 5 consecutive days to induce psoriasiform dermatitis, however, mice fed with WD had more severe ear swelling after day 4. Histological analysis also demonstrated that mice fed with WD had more neutrophils and higher density of Munromicroabscess as well as higher expression levels of IL-17A, Ly6g, IL-6 than mice fed with HFD.

Conclusion: WD induces psoriasis, and the high-sugar content may play a crucial role.

Taken together, while HFD induced more obesity than WD in these recipes, it was WD group that had more severe psoriasiform inflammation in terms of the murine imiquimod model. According to this finding, health education for patients with psoriasis should not only focus on body weight control but avoid excessive sugar intake. Further translational medicine investigation and human database research are need to verify these experimental results.