Sea grapes extract improves blood glucose, total cholesterol, and PGC-1α in rats fed on cholesterol- and fat-enriched diet

Editorial note

Editorial Note (20^th October 2023): The F1000 Editorial Team has not yet received a new version of this article, as detailed in the Editorial Notes published on 16^th June and 4^th August 2023. The F1000 Editorial Team will no longer be requesting a new version from the authors. Readers should be aware that there is key information missing from the article regarding fasting, euthanasia and blood drawing procedures, and ethical approval; this information had been previously given to and verified by the F1000 Editorial Team, but the authors have not yet updated their article, which was also requested to include a reanalysis.

Editorial Note (4^th August 2023): The F1000 Editorial Team has not yet received a new version of this article, as detailed in the Editorial Note published on 16^th June 2023. The F1000 Editorial Team is actively contacting the authors to request the new version of the article.

Editorial Note (16^th June 2023): Since publication, it has been brought to the attention of the Editorial Team that the article was missing key information regarding fasting, euthanasia and blood drawing procedures, and ethical approval. In addition, clarifications were sought regarding discrepancies in the data presented. The Editorial Team requested further detail and an explanation from the authors in March 2023. The authors provided an adequate response regarding the missing information and stated they would rerun their analysis. They were requested by the Editorial Team to create a new version of the article to include the additional details and reanalysis. A new version of the article has not yet been provided by the authors.

Introduction

Reactive Oxygen Species (ROS) are the amounts of reactive molecules and free radicals derived from oxygen in a molecule (i.e., superoxide, peroxide, hydrogen peroxide, hydroxyl radical, etc.) (Sies & Jones, 2020). Oxygen-based radicals are produced as a byproduct in the mitochondrial electron transport at the aerobic respiration performed by oxidoreductase enzymes and metal-catalyzed oxidation. A recent study has shown that ROS has a role in cell apoptosis that leads to organ dysfunction (Pizzino et al., 2017).

Peroxisome proliferator-activated receptor-gamma coactivator (PGC)-1α is a transcription coactivator that regulates the genes involved in energy metabolism. It is the main regulator of mitochondrial biogenesis (Liang &Ward, 2006). PGC-1α stimulates mitochondrial biogenesis and encourages the remodeling of muscle tissue to a fiber-type composition that is metabolically more oxidative and less glycolytic in nature, and it participates in the regulation of both carbohydrate and lipid metabolism (Puigserver & Spiegelman, 2003; S. Yang et al., 2020).

The ability of cell defense against ROS has been associated with aging and contributes to the increased oxidative stress state. This condition can disturb the enzyme activity, especially through the reversible oxidative reaction at the thiol functional group at the side chain of the enzyme structures (Birben et al., 2012). This can lead to the alteration of biomolecule structure and integrity, and enzyme dysfunction (Freitas et al., 2016). As a result, insulin resistance and Type 2 Diabetes can development (Facchini et al., 2001; Meigs et al., 2003). Additionally, the effect of aging on changes in liver mass can increase serum Low-Density Lipoprotein (LDL)-cholesterol level, due to the hepatocytes cell death caused by oxidative stress (Anantharaju et al., 2002; Miller, 1984). Hence, effective control of ROS levels is essential. The aging population tends to have a higher prevalence of chronic disease, thus there is a demand for health-improving foods (Park, 2013). The consumption and production of high-antioxidant as functional foods in recent years are popular due to their capability of reducing Reactive Oxygen Species (ROS), as well as having an impact on several aging and chronic related diseases (Park, 2013; Park et al., 2004). However, there are some challenges that are associated with the utilization of functional food. For example, specific functional foods need to be consumed in high concentrations in order to be biologically effective, therefore, this would require the nutritional facts such as the daily dose of the bioactive compound in each serving size to be determined (Kang et al., 2011). Preliminary studies are needed to determine which bioactive compound is the most beneficial, and what is the quantitative-activity relationship between the bioactive compounds contained in functional foods.

Sea grapes (Caulerpa racemosa) or lawi-lawi (Indonesia-local terminology) is a species of editable green alga, seaweed in the Caulerpaceae family found in waters surrounding Sulawesi (Pakki et al., 2020). Sea grapes are harvested intensively as they are an important source of macronutrients and micronutrients, especially in East and South-East Asia (grown commercially in ponds and consumed in the Philippines, Indonesia and Vietnam) as a major part of the traditional diet (Chen et al., 2019). Some studies showed that sea grapes contains several bioactive components, such as protein, polysaccharides, polyphenol, flavonoids, and antioxidants (P. Yang et al., 2015; Yep et al., 2019; Taslim & Fahrul, 2021). Moreover, sea grapes have a high antioxidant level, and they have the potential to act as functional food or nutraceuticals (Tanna et al., 2020; Yep et al., 2019; Nurkolis et al., 2021). The extract of sea grapes can reduce glucose level, aspartate aminotransferase (AST), alanine aminotransferase (ATL). Moreover, it appears to have a hepatoprotective activity in diabetic rats (Qudus B Aroyehun et al., 2020). Therefore, this study aims to evaluate the effects of Sea grapes extract on blood glucose levels, total cholesterol, and PGC-1α in male Wistar rats on cholesterol- and fat-enriched diets (CFED).

Methods

This in vivo study was conducted at the pharmacological laboratory, faculty of mathematics and natural sciences, Sam Ratulangi University.

Collection and preparation of plant material

Fresh sea grapes (Caulerpa racemosa) was collected from the shallow section (5-10 meters from the sea surface) of the Mantehage seawater, North Sulawesi, Indonesia. The botanical identification and authentication were confirmed at the department of pharmacology, faculty of mathematics and natural sciences, Sam Ratulangi University, Indonesia. The specimens were collected for feature references. The sea grapes were rinsed thoroughly with water, air-dried at room temperature and in an 40°C oven, then powdered by an electric mill.

Preparation of sea grapes extracts

Crude powder (one kg) was macerated in 96% ethanol for 72 hours with each extraction performed in triplicates, which resulted in 34% yield. The crude extracts were filtered by Whatman 41 filter paper. The total filtrate was concentrated and evaporated at 40°C with a rotary evaporator RV 8 IKA under reduced pressure (100 millibar) for 90 minutes, and evaporated in an 40°C oven to produce a thick extract. The extract was stored in a refrigerator at 10°C until used in the study.

Animal handling and ethical approval

All experimental rats were kept on standardized free access of feed and ad libitum of water. The study was conducted in the Laboratory of Pharmacology, Faculty of Mathematics and Natural Sciences, Sam Ratulangi University, Manado, Indonesia. Forty male Wistar albino rats (Rattus norvegicus) (4-5 weeks) weighing between 200 – 250 g were obtained from the Laboratory Animals Farming Makassar, Indonesia, and transported to the research site. The animals were grouped and housed in cages and maintained under standard laboratory conditions (temperature: 27 ± 2^oC), with light and dark cycles (12/12 hours). The rats were acclimatized to laboratory conditions for 10 days before the commencement of the experiment. The research protocol (use of experimental animals) refers to the Declaration of Helsinki. The Council for International Organizations of Medical Sciences (CIOMS) has approved the application of ethical health research protocols online (http://sim-epk.keppkn.kemkes.go.id) RSUP Prof. Dr. RD. Kandou, Manado with No. 086/EC/KEPK-KANDOU/VI/2021. Additionally, all experimental procedures were carried out according to the Institutional Animal Care and Usage Committee (ARRIVE guidelines) (Nurkolis et al., 2021).

In vivo studies of sea grapes extracts to evaluate blood glucose, total cholesterol, and PGC-1α levels

Data management and analysis

The data were statistically analyzed with the use of the MANOVA/Multivariate ANOVA test. The Levene’s test was used to determine which posthoc tests should be conducted. In cases where the Levene’s test p-value was <0.05 Games-Howell test (equal variances not assumed), and for p-value >0.05 Bonferroni test (equal variances assumed) was used. Statistical analyses were performed by using SPPS 26.0 for the Windows version.

Results

The Levene's Homogeneity test shows that the p-value for glucose and PGC-1α are <0.05, therefore equal variance cannot be assumed, while equal variances can be assumed for cholesterol as the p-value is >0.05.

The results indicate that blood glucose significantly increased in group B, compared to group A (p < 0.05) (Table 2). Blood glucose significantly decreased in both groups C and D (p < 0.05). The effect of sea grapes administration as much as 150 mg/kg BW is more effective than the sea grapes 450 mg/kg BW, in significantly decreasing blood glucose in rats (p < 0.05).

As expected the rats in group B had significantly increased blood cholesterol levels compared to group A (p < 0.05). In both groups A and B (p < 0.05), blood cholesterol significantly decreased in rats given CFED + sea grapes extract 150 mg/kg BW, and CFED treatment + sea grapes extract 450 mg/kg BW. There was no significant difference between the CFED treatment group + 150 mg/kg BW sea grapes extract, and the CFED treatment group + 450 mg/kg BW sea grapes extract, in reducing blood cholesterol (high dose of the extract did not result in significant effects (p > 0.05)).

Group B had a significantly decreased PGC-1α serum concentration. PGC-1α serum concentrations significantly increased in group C, as well in group D, compared to groups A and B. The effect of sea grapes administration as much as 150 mg/kg BW is more effective than that of sea grapes 450 mg/kg BW, in the significant increase of PGC-1α serum in rats.

Discussion

This study showed that the supplementation of sea grapes extract managed to lower blood glucose and serum cholesterol significantly in rats that were given cholesterol- and fat-enriched diets (Figure 1). Although compared to the control group, rats that were given cholesterol- and fat-enriched diets with sea grapes extract had lower levels of blood cholesterol and blood glucose.

Figure 1. Effects of sea grapes extract on subject rats.

The Results of this study indicate that sea grapes have the capability of reducing blood glucose levels (Table 2). Similarly, Aroyehun et al., have shown that sea grapes have antidiabetic activity (Qudus B Aroyehun et al., 2020). The plasma analysis in this study has also indicated that the sea grapes treated group had a significant decrease (p < 0.05) in their blood glucose levels compared to the untreated diabetic group (Qudus B Aroyehun et al., 2020). Sea grapes extract-treated group demonstrated similar efficacy in lowering blood glucose as Metformin (Qudus B Aroyehun et al., 2020), hence, sea grapes may have an hypoglycaemic effect. A hyperglycaemic state may induce oxidative stress that could be detrimental to insulin-sensitive tissues such as the liver, which may cause damage to the organ (Bugianesi, 2005; Manna, 2010; Palsamy, 2010).

This study showed that sea grapes reduce hyperlipidemia in rats, however this is not in line with the findings by Aroyehun et al., (Qudus B Aroyehun et al., 2020), which states that sea grapes extract has little to no effect on the cholesterol level of induced diabetic rats. In addition, the effect of lower doses of the extract (150 mg/kg BW) was better in lowering blood cholesterol than higher doses of sea grapes extract (450 mg/kg BW) (Figure 1, Table 3). This can be due to the saturated fatty acids content, especially palmitic acid, which dominates the composition of fatty acids, comprising 80% of the total fat in sea grapes (Qudus B Aroyehun et al., 2020). Studies have shown that palmitate acid may raise total cholesterol levels, specifically LDL-cholesterol levels (Clandinin et al. 2000; Mensink, 2013).

Levels of PGC-1α in rats significantly decreased after being given a CFED diet compared to the control group (Figure 1, Table 4). However, PGC-1α levels increased significantly in rats given sea grapes extract, even when compared to the control group. This suggests that PGC-1α, which is one of the major elements in mitochondrial biogenesis, is enhanced by the sea grapes extract. Perhaps the content of flavonoids as well as phenols in sea grapes extract can cause this effect. One study has shown that flavonoid supplementation increases the performance in endurance activities via an increase in expression of PGC-1α as the “master regulator” of biogenesis and skeletal muscle angiogenesis (Khani et al. 2017). In addition, other studies have also shown that antioxidant compounds can upregulate PGC-1α target genes, which not only play a role in preventing oxidative damage, but also reduce mitochondrial ROS levels, ensure mitochondrial integrity during cell differentiation (Beldelli et al. 2014), as well as avoiding the cytotoxic effects of ROS accumulation (St-Pierre et al. 2006).

Conclusion

Sea grapes extract is proven to improve blood glucose levels, total cholesterol, and PGC-1α in rats fed with cholesterol- and fat-enriched diets. The results of this study can be used as a reference for clinical trials to further research the beneficial effects of sea grapes for human consumption. However, it is necessary to do the same research with parameters other than blood sugar, cholesterol and PGC-1a, to expand its metabolic scope.

Data availability

Reporting guidelines

Harvard Dataverse: Arrive checklist for Sea grapes extract with blood glucose, total cholesterol, and PGC-1α in rats fed on cholesterol- and fat-enriched diet.

https://doi.org/10.7910/DVN/NXF0IW (Nurkolis et al., 2021).

Data are available under the terms of the Creative Commons Zero “No rights reserved” data waiver (CC0 1.0 Public domain dedication).

Author contributions

M.K and F.N. collated study ideas, designed and experiment, analyzed data, and compiled manuscripts. N.A.T, N. R, N. S, H.K.P, D.S.W and N. M analyzed and interpreted the data and critically revised the manuscript. F. N and F.M.I conducted experiments, analyzed biochemistry, and critically revised the manuscript. N. M, M.R.B, R. R, P.S.A and K.E.K.M, implemented experimental protocols, assisted in statistical analysis, interpreted data, and critically revised manuscripts. All writers read and approve the final manuscript.