Algae provide options for improved treatment of metabolic syndrome

Algae provide options for improved treatment of metabolic
syndrome

Metabolic syndrome is a clustering of cardiometabolic risk factors including central obesity, hypertension, dyslipidaemia, glucose intolerance and non-alcoholic fatty liver disease which increases the risk of cardiovascular diseases and type 2 diabetes. Metabolic syndrome prevalence is increasing in all countries, for example in Australia, prevalence was 19% in 2000 and 29% in 2017 with an annual incidence of 3%. The continuing increase of incidence suggests that current treatment options are insufficient.

Seaweeds are part of the staple diet in south-east Asian countries and their intake correlates with a lower prevalence of metabolic syndrome. Seaweeds provide polysaccharides, vitamins, minerals, peptides, amino acids, polyphenols, carotenoids and omega-3 polyunsaturated fatty acids. This thesis investigated the physiological and metabolic responses to the whole biomass from species of red, green and brown macroalga (Kappaphycus alvarezii and Sarconema filiforme, Caulerpa lentillifera, and Sargassum siliquosum respectively) and microalgae (Nannochloropsis oceanica). Studies were performed in rats using a validated high-carbohydrate, high-fat diet with increased fructose and saturated/trans fats that induced cardiovascular, liver and metabolic signs, including obesity, hypertension, glucose/insulin intolerance and fatty liver, due to chronic low-grade inflammation. This diet induced changes that closely mimic the signs of human metabolic syndrome. The main components of interest in the seaweeds were the sulphated polysaccharides such as K- and t-carrageenans and non-sulphated polysaccharides such as fucoidans and alginates. As pigments often have low bioavailability, the advantage of nanoparticles was tested in curcumin.

Chapter 1 is a literature review of the therapeutic potential of macroalgae and microalgae as functional foods for metabolic syndrome. It also reviews curcumin and the application of nanoparticles to overcome low bioavailability. Chapter 2 determined that K. alvarezii, a red seaweed containing -carrageenan, normalised body weight and adiposity, lowered systolic blood pressure, improved heart and liver structure, and lowered plasma lipids in rats. In Chapter 3, S. filiforme, a red seaweed containing t- carrageenan, decreased body weight by ~10%, abdominal fat deposits by ~30%, reduced systolic blood pressure by 13 mmHg, and reduced plasma liver enzyme activities. These red seaweeds have carrageenans which most likely act as prebiotics to attenuate symptoms of metabolic syndrome. Chapter 4 investigated S. siliquosum, a brown seaweed, with alginate, fucoidans and laminarans as polysaccharides contributing to the 41.4% of dietary fibre in the biomass. It decreased body weight by ~12% but did not change other parameters. In Chapter 5, C. lentillifera, a green seaweed, decreased body weight by ~22%, reduced systolic blood pressure by 17 mmHg and reduced total plasma cholesterol and non-esterified fatty acids. The sulphated polysaccharides are the most likely compounds producing these physiological and metabolic actions. In Chapter 6, N. oceanica, a microalgae, was used as a source of eicosapentaenoic acid, up to ~9% dry weight for potential health benefits. A limiting factor was the intactness of the cell wall which may have decreased the bioavailability of eicosapentaenoic acid and hence optimal biological activity was not observed. In Chapter 7, a curcumin nanoparticle formulation was used to determine whether nanoparticles increase the low bioavailability of about 1% by 20-fold which may have future applications for other compounds with low bioavailability such as carotenoids from seaweeds.

Overall, this thesis found that seaweeds contain multiple compounds which attenuate obesity, hypertension, dyslipidaemia and inflammation, and therefore may be useful for further studies into functional foods for metabolic syndrome. A combination of seaweeds can be incorporated into the human diet to confer health benefits. Biotechnology applications such as nanoparticles can overcome low bioavailability which will lead to improved biological activity.