Seaweed supplements normalise metabolic, cardiovascular and liver responses in high-carbohydrate, high-fat fed rats

Abstract

Increased seaweed consumption may be linked to the lower incidence of metabolic syndrome in eastern Asia. This study investigated the responses to two tropical green seaweeds, Ulva ohnoi (UO) and Derbesia tenuissima (DT), in a rat model of human metabolic syndrome. Male Wistar rats (330-340 g) were fed either a corn starch-rich diet or a high-carbohydrate, high-fat diet with 25% fructose in drinking water, for 16 weeks. High-carbohydrate, high-fat diet-fed rats showed the signs of metabolic syndrome leading to abdominal obesity, cardiovascular remodelling and non-alcoholic fatty liver disease. Food was supplemented with 5% dried UO or DT for the final 8 weeks only. UO lowered total final body fat mass by 24%, systolic blood pressure by 29 mmHg, and improved glucose utilisation and insulin sensitivity. In contrast, DT did not change total body fat mass but decreased plasma triglycerides by 38% and total cholesterol by 17%. UO contained 18.1% soluble fibre as part of 40.9% total fibre, and increased magnesium, while DT contained 23.4% total fibre, essentially as insoluble fibre. UO was more effective in reducing metabolic syndrome than DT, possibly due to the increased intake of soluble fibre and magnesium.

Figure 1

Effects of seaweeds treatment on systolic blood pressure. Values are mean ± SEM, n = 8–10. Endpoint means without a common letter differ, p < 0.05. C, corn starch fed rats; CUO, corn starch rats treated with Ulva ohnoi; CDT, corn starch rats treated with Derbesia tenuissima; H, high-carbohydrate, high-fat diet fed rats; HUO, high-carbohydrate, high-fat rats treated with Ulva ohnoi; HDT, high-carbohydrate, high-fat rats treated with Derbesia tenuissima.

Figure 2

Effects of seaweeds treatment on inflammation and fibrosis in the heart. Haematoxylin and eosin staining of left ventricle showing infiltration of inflammatory cells (A–F, inflammatory cells marked as “in”) (×20) from C (A); CUO (B); CDT (C); H (D); HUO (E) and HDT (F) rats. Picrosirius red staining of left ventricle showing collagen deposition (G–M, fibrosis marked as “fi”)(20×) from C (A); CUO (B); CDT (C); H (D); HUO (E) and HDT (F) rats. C, corn starch fed rats; CUO, corn starch rats treated with Ulva ohnoi; CDT, corn starch rats treated with Derbesia tenuissima; H, high-carbohydrate, high-fat diet fed rats; HUO, high-carbohydrate, high-fat rats treated with Ulva ohnoi; HDT, high carbohydrate, high fat rats treated with Derbesia tenuissima.

Figure 3

Effects of seaweeds treatment on noradrenaline-induced contraction (A); sodium nitroprusside-induced relaxation (B); and acetylcholine-induced relaxation (C) in thoracic aortic preparations from C, CUO, CDT, H, HUO and HDT rats. Values are mean ± SEM, n = 8–10. Endpoint means without a common letter differ, p < 0.05. C, corn starch fed rats; CUO, corn starch rats treated with Ulva ohnoi; CDT, corn starch rats treated with Derbesia tenuissima; H, high-carbohydrate, high-fat diet fed rats; HUO, high-carbohydrate, high-fat rats treated with Ulva ohnoi; HDT, high-carbohydrate, high-fat rats treated with Derbesia tenuissima.

Figure 4

Effects of seaweeds treatment on inflammation and fat deposition in the liver. Haematoxylin and eosin staining of liver showing enlarged fat vacuoles (A–F, marked as “fv”) (×20) and inflammatory cells (G–L, marked as “in”) (×20) from C (A,G); CUO (B,H); CDT (C,I); H (D,J); HUO (E,K) and HDT (F,L) rats. C, corn starch fed rats; CUO, corn starch rats treated with Ulva ohnoi; CDT, corn starch rats treated with Derbesia tenuissima; H, high-carbohydrate, high-fat diet fed rats; HUO, high-carbohydrate, high-fat rats treated with Ulva ohnoi; HDT, high-carbohydrate, high-fat rats treated with Derbesia tenuissima.

Figure 5

Outline of the experimental protocol for measurements on rats. SBP, systolic blood pressure; OGTT, oral glucose tolerance test; AC, abdominal circumference, ITT, insulin tolerance test; DEXA, dual energy X-ray absorptiometry; UO, Ulva ohnoi; DT, Derbesia tenuissima.