**1. Introduction**

Maintaining a healthy gut microbiome and a noninflammatory state is key to avoiding metabolic syndrome. In the studies described here, we sought to understand how the gut microbiome is affected by ingesting a type of ulvan from the green seaweed *Ulva* sp. 84, and the effects it has on plasma lipids and inflammation markers. The ulvan is referred to as SXRG84.

The gut microbiome is a complex system of microbes necessary for digestion and homeostasis [1]. A dysregulated microbiome may lead to inflammation and gut permeability. The chronic low-grade inflammation that accompanies metabolic disorder [2] may

**Citation:** Roach, L.A.; Meyer, B.J.; Fitton, J.H.; Winberg, P. Improved Plasma Lipids, Anti-Inflammatory Activity, and Microbiome Shifts in Overweight Participants: Two Clinical Studies on Oral Supplementation with Algal Sulfated Polysaccharide. *Mar. Drugs* **2022**, *20*, 500. https://doi.org/10.3390/ md20080500

Academic Editors: Donatella Degl'Innocenti and Marzia Vasarri

Received: 6 July 2022 Accepted: 29 July 2022 Published: 2 August 2022

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also give rise to comorbidities such as cardiovascular disease [3], depression [4], and neuropathy [5]. Inflammatory biomarkers, such as interleukin-6 (IL-6) and high-sensitivity C-reactive protein (hsCRP) independently predict future cardiovascular events with a magnitude of effect comparable to that of low-density lipoprotein cholesterol (LDL-C). Treatments for atherosclerosis may require both inflammation inhibition and additional cholesterol reduction [6]. Gut florae respond directly and indirectly to dietary and intestinal glycans, and the microbiome is important to digestive enzyme activity, synthesis of vitamins, interaction with the immune system, interaction with pathogens, and control of inflammatory activity across the gut–blood barrier [7]. Consequently, glycans and the gut florae they support have a lifetime role on the status of the metabolic and immune system.

Seaweeds contain large amounts of resistant dietary glycan. These include the alginates, laminarin and fucoidan (from brown seaweeds), carrageenan and agar (from red seaweeds) and "ulvans"—a diverse group of high-rhamnose-content polysaccharides from green seaweeds. This has recently been well reviewed by Shannon et al. [8]. Seaweed glycans are highly diverse [9,10]. The specificity of bacterial enzymes to dietary glucans implies that each seaweed mucopolysaccharide will have distinct effects on the composition of the microbiome and its metabolic function [11]. Consequently, a response to dietary glycans will also be specific, reflecting individual microbiome profiles, although commonalities related to the microbiome and gut processes are predicted.

Whole *Ulva* sp. seaweeds have been shown to influence gut metabolic processes [12]. There is low toxicity in purified ulvans [13], with doses of up to 600 mg/kg of body weight over six months shown to be well tolerated in rats. *Ulva* sp. and ulvans show effective lipid-lowering qualities. More recent research has shown a consistency in these findings and a diversity in similar metabolic disease related effects from diverse algae [14,15].

In previous studies, brown seaweeds and their components have been shown to exert beneficial effects on allergy and inflammation [16]. The brown seaweed extract fucoidan restored gut lysozyme levels in athletes [17], but fucoidan did not affect metabolic markers in obese nondiabetic subjects [18]. Green seaweeds, including the Ulvacean species similar to the one used in this study, contain a class of polysaccharides known as "ulvans". These heterodisperse sulfated polymers are quite diverse, but generally contain rhamnose, xylose, galactose, and uronic acid. They exhibit lipid-lowering activity [13], protective effects in irritable bowel syndrome (IBD) models [19], and antioxidant and antihyperlipidemic effects [20–22]. A hyperlipidemic rat model showed reductions in non-HDL-cholesterol and increases in HDL-cholesterol and a corresponding improvement in the atherogenic index (log (triglycerides/HDL-cholesterol)) [21]. At 300 mg/kg body weight, hypolipidemic effects were observed in a dose-dependent manner in high-fat-fed mice—an effect comparable to the drug simvastatin [23]. These studies were conducted primarily in animal models and human studies are warranted.

This research presents two consecutive clinical trials investigating the effects of a specific type of ulvan, sulfated xylorhamnoglucuronan, or "SXRG-84", on the metabolic disease markers, the microbiota, and inflammation.

The aim of Study 1 was to investigate the effects of "SXRG84" on plasma lipid levels, glucose, and insulin levels in overweight and obese individuals and assess the impact on the gut microbiota. The primary outcome measures were changes in plasma lipid levels. Secondary outcomes were carbohydrate metabolism, gut microbiota, inflammation, and oxidative stress. It was hypothesized that SXRG84 would have a favorable effect on plasma lipid levels, measures of carbohydrate metabolism, inflammation, and oxidative stress and would result in shifts in the gut microbiota when compared to the placebo group.

The second study (Study 2) was powered on the change in non-HDL-C observed in Study 1, using a randomized placebo-controlled crossover design. The primary objective was to confirm the Study 1 findings that SXRG84 would reduce non-HDL cholesterol in overweight participants. Secondary objectives were to examine the effects of the SXRG84 on further metabolic, inflammatory, and gut microbiota measures.

In this paper, we describe two studies that recruited participants who had a high BMI, and therefore, who had the potential for being metabolically challenged. The BMIs extended from 24 to 40, implying a range of metabolic flexibility. Metabolic flexibility is basically defined as being able to switch between utilizing glucose and lipids as a source of energy during fasting and fed states, as well as during exercise and resting, in order to maintain energy homeostasis [24]. A recent systematic review has shown that metabolic flexibility to glucose and insulin stimulation is inversely associated with the total amount of adipose tissue, waist circumference, and visceral adipose tissue [25]. This suggests that as the weight of a person increases, the metabolic flexibility decreases. Therefore, an additional aim of the first study is to compare metabolic markers across people that were overweight versus those that were obese on the various metabolic outcome measures as the potential to respond to treatments would be affected by metabolic flexibility.
