Purple Sweet Potato Powder Containing Anthocyanin Mitigates High-Fat-Diet-Induced Dry Eye Disease

Abstract

Purple sweet potato (PSP) powder with anthocyanins possesses the ability to reduce oxidative stress and inflammation. Studies have presumed a positive correlation between body fat and dry eye disease (DED) in adults. The regulation of oxidative stress and inflammation has been proposed as the mechanism underlying DED. This study developed an animal model of high fat diet (HFD)-induced DED. We added 5% PSP powder to the HFD to evaluate the effects and underlying mechanisms in mitigating HFD-induced DED. A statin drug, atorvastatin, was also added to the diet separately to assess its effect. The HFD altered the structure of lacrimal gland (LG) tissue, reduced LG secretory function, and eliminated the expression of proteins related to DED development, including α-smooth muscle actin and aquaporin-5. Although PSP treatment could not significantly reduce body weight or body fat, it ameliorated the effects of DED by preserving LG secretory function, preventing ocular surface erosion, and preserving LG structure. PSP treatment increased superoxide dismutase levels but reduced hypoxia-inducible factor 1-α levels, indicating that PSP treatment reduced oxidative stress. PSP treatment increased ATP-binding cassette transporter 1 and acetyl-CoA carboxylase 1 levels in LG tissue, signifying that PSP treatment regulated lipid homeostasis maintenance to reduce the effects of DED. In conclusion, PSP treatment ameliorated the effects of HFD-induced DED through the regulation of oxidative stress and lipid homeostasis in the LG.

Keywords: anthocyanin; dry eye disease; high-fat diet; lacrimal gland; obesity; oxidative stress; purple sweet potato.

Figure 1

PSP treatment preserved tear secretion capacity in HFD-treated rats. The animals were treated with a high-fat diet (HFD) alone or supplemented with PSP (5%) or atorvastatin (S) for 19 weeks. Before sacrifice, 12 eyes in each group were performed Schirmer’s test to measure the tear secretion. Results were represented as the mean ± SD; p values were denoted to show the significant differences.

Figure 2

PSP reduced the erosion of ocular surface in HFD-treated rats. The animals were treated with a high-fat diet (HFD) alone or supplemented with PSP (5%) or atorvastatin (S) for 19 weeks. Before sacrifice, both eyes of each rat were stained with 1% (w/w) of lissamine green. Positive staining area indicated epithelial erosion was labeled with black arrow as shown in (A); the counts of positive signal were shown in (B). The chi-square test was conducted to analyze the results; p values were denoted to show the significant differences.

Figure 2

PSP reduced the erosion of ocular surface in HFD-treated rats. The animals were treated with a high-fat diet (HFD) alone or supplemented with PSP (5%) or atorvastatin (S) for 19 weeks. Before sacrifice, both eyes of each rat were stained with 1% (w/w) of lissamine green. Positive staining area indicated epithelial erosion was labeled with black arrow as shown in (A); the counts of positive signal were shown in (B). The chi-square test was conducted to analyze the results; p values were denoted to show the significant differences.

Figure 3

PSP reduced LG atrophy in HFD-treated rats. After sacrifice, one eye of each rat was obtained to perform histological examination. (A), the atrophy characterized by focal to confluent areas of shrunken and atrophied acini lined by small, low to flattened cuboidal cells as black arrows pointed; (B), the results were represented as the mean ± SD to indicate the pixel density of LG atrophy area; p values were denoted to show the significant differences.

Figure 3

PSP reduced LG atrophy in HFD-treated rats. After sacrifice, one eye of each rat was obtained to perform histological examination. (A), the atrophy characterized by focal to confluent areas of shrunken and atrophied acini lined by small, low to flattened cuboidal cells as black arrows pointed; (B), the results were represented as the mean ± SD to indicate the pixel density of LG atrophy area; p values were denoted to show the significant differences.

Figure 4

PSP increased α-SMA level in HFD-treated rats. Immunohistological examination was carried out to detect α-SMA level. (A), α-SMA-positive area were showed as brown color; (B), mean ± SD was represented to indicate the α-SMA-positive area. p values were denoted to show the significant differences.

Figure 4

PSP increased α-SMA level in HFD-treated rats. Immunohistological examination was carried out to detect α-SMA level. (A), α-SMA-positive area were showed as brown color; (B), mean ± SD was represented to indicate the α-SMA-positive area. p values were denoted to show the significant differences.

Figure 5

PSP treatment increased AQP5 level. Immunoblot examination was carried out to detect AQP5 level. The β-actin was used as the loading control. The relative image density was quantified by the densitometer. Ratio values calculated from triplicate experiments were represented as the mean ± SD shown in lower panel.

Figure 6

PSP treatment increased SOD-1 and IkB levels but reduced HIF-1α levels. Immunoblot examination was carried out to detect SOD-1, HIF-1α, IkB levels. The β-actin or α-tubulin was used as the loading control. The relative image density was quantified by the densitometer. Ratio values calculated from triplicate experiments were represented as the mean ± SD shown in lower panel.

Figure 7

PSP treatment increased ABCA1 and ACC-1 levels. Immunoblot examination was performed to detect ABCA1 and ACC-1 levels. The β-actin or α-tubulin was used as the loading control. The relative image density was quantified by the densitometer. Ratio values calculated from triplicate experiments were represented as the mean ± SD shown in lower panel.

Figure 8

Underlying mechanisms of PSP treatment in ameliorating HFD-induced DED. A, HFD is highly related to accumulation of intracellular oxidative stress, which was a crucial contributing factor toward DED [9,59]. B, Accumulation of oxidative stress leads to LGs atrophy [31], and LGs atrophy area in HFD-fed rats is significantly larger than those of PSP-fed rats. C, Oxidative stress may decrease SMA expression in LGs [60], and α-SMA is lower in HFD-fed rats compared with those with PSP supplement. D, Decrease in AQP-5 mRNA has been found in DED [28]. LGs of HFD-fed rats have lower AQP-5 expression level than that of PSP treatment. E, SOD-1 is preserved more in LGs of PSP-treated rats than that of HFD-fed rats, implying that PSP treatment reduces oxidative stress. F, PSP treatment reduces HIF-1α levels of LGs. G, PSP treatment increases IκBα levels to suppress inflammation. H, PSP treatment increases ABCA1 level.