Published Time: 2023-06-02
Obesity and type 2 diabetes are characterized by low-grade systemic inflammation and glucose intolerance, which can be partially controlled with nutritional interventions. Protein-containing nutritional supplements possess health-promoting benefits. Herein, we examined the effect of dietary supplementation with protein hydrolysates derived from fish sidestreams on obesity and diabetes, utilizing a mouse model of High-Fat Diet-induced obesity and type 2 diabetes. We examined the effect of protein hydrolysates from salmon and mackerel backbone (HSB and HMB, respectively), salmon and mackerel heads (HSH and HMH, respectively), and fish collagen. The results showed that none of the dietary supplements affected weight gain, but HSH partially suppressed glucose intolerance, while HMB and HMH suppressed leptin increase in the adipose tissue. We further analyzed the gut microbiome, which contributes to the metabolic disease implicated in the development of type 2 diabetes, and found that supplementation with selected protein hydrolysates resulted in distinct changes in gut microbiome composition. The most prominent changes occurred when the diet was supplemented with fish collagen since it increased the abundance of beneficial bacteria and restricted the presence of harmful ones. Overall, the results suggest that protein hydrolysates derived from fish sidestreams can be utilized as dietary supplements with significant health benefits in the context of type 2 diabetes and diet-induced changes in the gut microbiome.
Modern lifestyle changes have contributed to the increasing prevalence of a variety of chronic diseases, including metabolic syndrome and type 2 diabetes mellitus. At the basis of the latter typically stand obesity and insulin resistance, the incidence of which has been growing into a pandemic since the early 1980s. A number of factors may be implicated with varying significance, including genetics. However, lifestyle choices, such as dietary habits and physical (in)activity, heavily determine the likelihood of developing the above conditions.
Interestingly, the gut microbiome has recently been shown to actively modulate the host’s metabolism, probably playing a crucial role in the emergence and pathogenesis of obesity and insulin resistance. It may also modify the levels of inflammation, which contributes to metabolic dysregulation, through a number of mechanisms, including metabolite-mediated host immune system modulation and maintenance of the gut’s barrier integrity.
Dietary interventions are at the forefront of managing and combating obesity, diabetes, and metabolic syndrome. Nutritional supplements play a useful and supportive part in dietary interventions for reasons that include their content of bioactive compounds, nutrients, minerals, and essential trace elements. Fish are rich in proteins and bioactive peptides, minerals, vitamins, as well as omega-3 fatty acids and phospholipids, just to name a few, rendering them an appealing source of high-quality nutrition. Indeed, dietary supplements of fish origin have been suggested to exert a positive effect on conditions such as obesity and diabetes. Fish-derived oil, being a great source of ω-3 polyunsaturated fatty acids (ω-3-PUFAs), has been exhibited to ameliorate the obese phenotype, whereas a variety of fish extracts developed from tuna, Tapra fish or Masou salmon, also indicate an anti-obesity action. However, the knowledge regarding whether and in which way the gut microbiome is shaped by fish extracts is very sparse. Furthermore, the potential contribution of fish-derived collagen in suppressing weight gain and ameliorating obesity has been noted in mice, partially through inhibiting differentiation of preadipocytes to mature adipocytes. Notably, fish collagen is an attractive alternative to mammalian, as the latter might present some drawbacks, such as concerns related to disease transmission and allergic reactions, while vegan collagen does not have the original structure of the naturally produced complex protein. However, no data exist on the possible synergistic action of fish-derived collagen with fish protein hydrolysates on obesity and diabetes.
Each year, large amounts of sidestreams are generated by the fish industry. It is estimated that more than 50% of fish biomass is widely considered “waste”, including fins, heads, skins, and viscera, or used for low-value applications, such as animal nutrition and fertilizers. In addition, by-catch products, fish species, and undersized or damaged fish with low or no commercial value are considered fish waste, not only reducing economic growth but also posing a threat to aquatic ecosystems. Efforts to reduce bio-waste led to the valorization of fish sidestreams in order to produce high-value commercial compounds such as enzymes, peptides, collagen, chitin, polyunsaturated fatty acids (PUFAs), and bioactive compounds. Among valorization methods, the generation of bioactive peptides through fish sidestream protein hydrolysis has gained great interest in recent years, releasing bioactive peptides with anti-microbial, antiproliferative, and antioxidant properties.
The aim of the present study was to investigate the potential effects of fish-derived protein hydrolysates used as dietary supplements, including fish collagen, on obesity and insulin resistance, using the murine model of diet-induced obesity and type 2 diabetes, while also considering the impact of these dietary supplements on the composition of the gut microbiome.
Fish-derived hydrolysates were generated using mackerel and salmon sidestreams aiming to investigate their possible bioactivity in high-fat-induced obesity in mice and their potential use as nutritional supplements in obese-related pathological conditions. The composition of the different supplements and their organoleptic properties have been recently described.
It has been previously reported that fish-derived supplements exhibit beneficial properties, helping in the management of chronic diseases such as cardiovascular disease, type 2 diabetes, and autoimmunity by ameliorating insulin resistance, obesity, inflammation, and muscle damage as well as modulating gut microbiota. The majority of basic and clinical research has been focused on the extraction and administration of fish-derived oils containing high amounts of omega-3 fatty acids, eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA). In this study, we aim to investigate the potential beneficial role of nutritional supplements containing fish sidestream-derived protein hydrolysates, which are rich in bioactive peptides. To test the bioactivity of the aforementioned fish-derived supplements in High-Fat Diet-induced (HFD) insulin resistance, we treated mice for 3.5 weeks with HFD supplemented with 5% w/w of each protein hydrolysate. In each diet group, 5 mice of both sexes were randomly allocated. As a control, a 5% soy protein supplement was used to simulate protein intake levels, as fish supplements contain large amounts of protein. Additionally, a group of mice consuming a control diet (lean) supplemented with 5% of soy protein was used to monitor the progress of the experiment. Animal weight was monitored weekly, and a glucose tolerance test was performed at the end of the experiment. Interestingly, the group consuming the HSH nutritional supplement exhibited decreased glucose intolerance; in fact, 30 min post the dextrose injection, glucose levels in blood highly resembled those consuming a lean diet. Moreover, it is worth noting that both sexes were present in this study, as it is known that sex-related differences concerning insulin sensitivity may occur. Notably, when only male mice were considered, the HMB diet-consuming group exhibited significantly reduced insulin resistance compared to high-fat diet mice. The number of animals in each gender was small and, therefore, solid conclusions cannot be drawn. The results suggest that gender differences may be worth exploring concerning the effect of diet supplementation with protein hydrolysates on glucose intolerance.
Animals rapidly gain weight when they follow a diet rich in fat. When mice were fed a high-fat diet for 3.5 weeks, they indeed put on considerably more weight than the lean diet group. The supplemented HFD groups show similar weight gain compared to the HFD control group or a non-statistically significant tendency towards elevated weight accumulation, especially at the very start of the feeding period. That could be explained by the slightly higher calorie number of the extracts compared to the soy supplement of the control group due to their high protein content. Nevertheless, glucose tolerance was not affected, as none of the somewhat fattier groups exhibited any effect in GTT. Animal feed consumption was nearly identical between the HFD groups and lower than the lean-diet group, probably because of the calorie-denser and more fulfilling diet of the former. The final measurement was made on the day of sacrifice, for which the animals had to fast in order to undergo the GTT test, which explains the slight weight loss at the end of the experiment in some of the groups. Interestingly, the HSH group, which exhibited increased insulin sensitivity, accumulated almost as much fat or slightly more than the other HFD groups; therefore, an improvement in insulin sensitivity can be noted independently of an anti-obesity effect of the HSH extract.
During excess weight gain, abdominal adipose tissue accumulates fat and may contribute to insulin resistance. Male epididymal and female perigonadal adipose tissues were extracted and weighed at the end of the experiment. All animals following the HFD had significantly increased visceral fat accumulation compared to the lean diet control group. No statistically significant effect concerning abdominal fat accumulation was observed among the different nutritional supplement-consuming groups compared to the HFD control group.
Leptin is an important adipokine with a central homeostatic role, as it regulates, among other, satiety by acting in the brain, energy balance, and insulin sensitivity. A common trait of diet-induced obesity is leptin resistance, characterized by increased circulating levels of leptin to compensate for the deteriorated leptin sensitivity. In a state of obesity, the inhibitory leptin-induced signals on the appetite are diminished, consequently leading to hyperphagia, even in the presence of high circulating leptin levels. As expected, when obese individuals were injected with additional leptin, obesity was not reversed. Since leptin is primarily synthesized and secreted by the white adipose tissue, the excised male epididymal and female perigonadal fat tissues were homogenized to measure mRNA levels of leptin. The obese HFD groups exhibited considerably higher leptin gene expression compared to the lean diet control group, as expected. The expression of leptin is analogous to the energy stores, as enlarged adipocytes would express more leptin. Therefore, reduced leptin levels in the HMB and HMH groups that were observed independently of abdominal fat mass may be due to changes in adipocyte size and amelioration of glucose intolerance.
While the role of leptin in obesity is highly complicated and has not yet been completely elucidated, it is quite possible that leptin resistance is not only an important consequence of obesity, but also a serious risk factor for it. Therefore, the significantly decreased levels of leptin expression of the HMB and the HMH groups could indicate higher leptin sensitivity and possibly leptin-mediated protection from obesity. Whereas the HMH group had a tendency for improved glucose tolerance, it is likely that a longer supplementation period was needed for a robust physiological effect to emerge.
Urine pH is affected by diet and related metabolites, and supplementation with HFD resulted in a significant increase
