Next Article in Journal
The Nuclear Lamina: Protein Accumulation and Disease
Previous Article in Journal
The Role of Cutibacterium acnes in Intervertebral Disc Inflammation
 
 
Search for Articles:
Title / Keyword
Author / Affiliation / Email
Journal
Article Type
 
 
Advanced Search
 
Section
Special Issue
Volume
Issue
Number
Page
 
Journals
Biomedicines
Volume 8
Issue 7
10.3390/biomedicines8070187
biomedicines-logo
Submit to this Journal Review for this Journal Propose a Special Issue
► Article Menu

Article Menu

share Share announcement Help format_quote Cite question_answer Discuss in SciProfiles thumb_up
...
Endorse textsms
...
Comment
first_page
settings
Order Article Reprints
Font Type:
Arial Georgia Verdana
Font Size:
Aa Aa Aa
Line Spacing:
Column Width:
Background:
Article

Regulatory Effects of Skate Skin-Derived Collagen Peptides with Different Molecular Weights on Lipid Metabolism in the Liver and Adipose Tissue

by
Minji Woo
1,2 and
Jeong Sook Noh
3,*
1
Busan Innovation Institute of Industry, Science & Technology Planning (BISTEP), Busan 48058, Korea
2
Department of Food Science and Nutrition and Kimchi Research Institute, Pusan National University, Busan 46241, Korea
3
Department of Food Science and Nutrition, Tongmyong University, Busan 48520, Korea
*
Author to whom correspondence should be addressed.
Biomedicines 2020, 8(7), 187; https://doi.org/10.3390/biomedicines8070187
Submission received: 20 May 2020 / Revised: 27 June 2020 / Accepted: 29 June 2020 / Published: 30 June 2020
(This article belongs to the Section Drug Discovery and Development)
Browse Figures
Review Reports Versions Notes

Abstract

:
This study investigated the effects of skate skin collagen peptide (SSCP) with different molecular weights (MWs) on the lipid metabolism in the liver and adipose tissue. Male db/db mice were orally administered with water (control group) or low SSCP (LCP group) or high SSCP (HCP group) MW for 8 weeks whereas male m/m mice were used for comparison (normal group) (n = 10 each group). Compared to the control group, the LCP and HCP groups had lower adipose tissue mass, plasma and hepatic lipid concentrations, and plasma leptin levels (p < 0.05). Protein expression levels of lipogenesis-related protein were reduced in both liver and adipose tissues of SSCP-fed groups whereas those for lipolysis were elevated (p < 0.05). In particular, the LCP had the higher effects relative to the HCP. The above results were supported by histological analysis, revealing that SSCP administration decreased the size of adipose droplets and suppressed hepatic lipid accumulation. Our results showed that SSCP has potential antiobesity properties through the improvement of lipid metabolism in the liver and adipose tissue; in particular, the lower MW of collagen peptide had the greater effects.

1. Introduction

During the processing of fish, byproducts are generated from the skin, bones, fins, heads, and scales, in which the collagen-containing materials account for up to 30% of the total byproducts [1]. Collagen is a major component of animal-derived proteins, and has a wide range of applications, including the cosmetic, pharmaceutical, and food industries, due to its numerous beneficial effects, including antioxidative, lipid lowering, and so on [1,2,3,4,5,6]. A series of studies have verified the beneficial antioxidative effects of marine collagen peptides [2,3], the improvement of glucose/lipid metabolism [2,4,5], and the facilitation of learning and memory function [6]. The bioactivity of collagen is suggested to be directly correlated with its molecular weight (MW) [7]. Some reports suggest that small peptides (composed of 2–10 amino acids) possess more potent therapeutic effects than their parent native proteins or polypeptides (composed of 10–50 amino acids or more) [8]. Antioxidative activities of collagen peptides with a lower MW were greater than those with a higher MW [9]. However, the effect of different MWs of skate skin collagen peptide on lipid metabolism and the related mechanisms of action have not been elucidated.
Obesity is a multifactorial disease that is considered the most challenging public health problem [10,11,12,13]. In obesity, excessive lipid accumulation in the liver and adipose tissue occurs due to the dysregulation of key transcription factors and related enzymes [11,12,13]. At the molecular level, sterol regulatory element-binding protein (SREBP)-1 and -2 stimulate fatty acid and cholesterol synthesis by regulating fatty acid synthase (FAS), acetyl-CoA carboxylase (ACC), and 3-hydroxy-3-methylglutaryl-CoA reductase (HMGCR), respectively [14]. Moreover, adipocyte protein 2 (AP2), a fatty acid-binding protein, regulates the terminal differentiation of adipocytes. In contrast, peroxisome proliferator-activated receptor α (PPARα) upregulates genes involved in fatty acid oxidation, such as carnitine palmitoyltransferase 1A (CPT1) and acyl-CoA oxidase 1 (ACOX1) [15]. In addition, lipolysis, one of the most important processes to reduce fat mass, is regulated by lipases, such as hormone-sensitive lipase (HSL), particularly in triglyceride (TG)-rich adipose tissue [16,17]. These factors coordinately modulate lipid metabolism.
Skate (Raja kenojei) is a cartilaginous fish that is currently drawing much attention as a health marine product. Almost all studies on skate skin collagen have focused on the processing conditions [18], purification, and characterization [18,19]. Our previous study demonstrated that skate skin collagen peptide (without ultrafiltration, MW 1050 Da) prevents an increased hepatic lipid concentration in high-fat diet (HFD)-induced obese mice [20] and improves lipid profiles in the plasma and liver of db/db mice [21,22]. We hypothesized that collagen peptides with different MWs will have different effects in obese mice. Therefore, the present work evaluated the effect of two skate skin-derived collagen peptides with different MWs on plasma and hepatic lipid profiles, as well as lipogenesis and lipolysis-related markers in the liver and adipose tissue.

2. Materials and Methods

2.1. Preparation of the Collagen Hydrolysate Sample

Skate skin collagen peptides were hydrolyzed using enzymes, such as alcalase® and protamex® (Novozymes, Bagsvaerd, Denmark), for 2 or 6 h and separated by MW cut-off membranes (1 kDa), LCP (MW < 1 kDa), and HCP (MW > 1 kDa). The average MWs of LCP and HCP were 687 and 1442 Da, respectively. The compositions of both samples were similar. The amino acid constituents were as follows: LCP (aspartic acid 7.11%, hydroxy proline 6.85%, threonine 3.42%, serine 5.71%, glutamic acid 10.78%, proline 9.02%, glycine 22.09%, alanine 7.66%, valine 3.34%, methionine 2.15%, isoleucine 2.45%, leucine 3.67%, tyrosine 0.91%, phenylalanine 2.23%, ammonia 0.74%, lysine 3.22%, histidine 1.26%, arginine 7.05%, and others 0.34%) and HCP (aspartic acid 6.46%, hydroxy proline 6.15%, threonine 3.29%, serine 5.38%, glutamic acid 9.93%, proline 8.28%, glycine 19.97%, alanine 6.92%, valine 2.93%, methionine 1.72%, isoleucine 2.20%, leucine 3.32%, tyrosine 0.82%, phenylalanine 2.02%, ammonia 0.72%, lysine 3.49%, histidine 1.38%, arginine 7.84%, and others 7.23%). All collagen peptide samples were provided by Yeongsan Skate Co., Ltd. (Naju, Jeollanam-do, Korea).

2.2. Animal Study

C57BLKS/J db/db mice and m/m mice (male, 7 weeks old) were purchased from Dooyeol Biotech (Seoul, Korea). db/db mice are a leptin-deficient animal model, in which deficiency confers susceptibility to obesity, insulin resistance, and type 2 diabetes mellitus whereas m/m mice are widely used as a normal control. Animals were raised under controlled room temperature (23 ± 1 °C) and humidity (50 ± 5%) with a 12/12-h light-dark cycle and fed a standard laboratory pellet chow diet and water ad libitum. After an acclimatization period of 1 week, mice were divided into four groups based on body weight. db/db mice were orally administered LCP (LCP group) or HCP (HCP group) at a dose of 200 mg·kg bw−1·day−1 or water (control group, CON) for 8 weeks, and m/m mice were orally administered water as a vehicle (NOR group) using a zonde (n = 10 per group). The volume of oral administration was 100 µL. Each sample was prepared by dissolving in water and the concentration for oral administration was based on our previous study [21]. Dietary intake was checked daily and body weight was measured every week. After 8 weeks, the mice were subjected to a 12-h fasting period and sacrificed with CO2. Blood was collected by cardiac puncture into heparin tubes and the organs were collected after perfusion with ice-cold phosphate-buffered saline (PBS, 10 mM, pH 7.2). Plasma was separated immediately after blood was drawn and the organs, including liver and adipose tissues (visceral, subcutaneous, and epididymis), were stored at −80 °C until use. The animal study was conducted in accordance with the Guidelines for Animal Experiments approved by the University Institutional Animal Care and Use Committee (Approval number: PNU-2016-1354).

2.3. Plasma Lipid, Aminotransferase, and Adipokine Levels

TG (AM157S-K), TC (AM202-K), HDL-C (AM202-K), AST (AM203-K), and ALT (AM101-K) levels were measured using commercially available kits (Asan Pharmaceutical Co., Seoul, Korea). Adipokines, such as leptin (#ADI-900-019A, Enzo Life Sciences AG, Lausen, Switzerland), adiponectin (LF-EK0239; AbFrontier, Seoul, Korea), and FFAs (ab65341; Abcam Inc., Cambridge, MA, USA), were evaluated using commercial kits.

2.4. Hepatic Lipid Concentration

The liver tissue was homogenized with 10 volumes (w/v) of PBS (pH 7.4) using a polytron homogenizer (PT-MR 3100; Kinematica Inc., Lucerne, Switzerland). Hepatic lipids were extracted from liver homogenates using chloroform:methanol (2:1, v/v) solvent according to a previously described method [23]. Hepatic TG and TC concentrations were evaluated with the same commercially available kit used for the plasma lipid concentration.

2.5. Histological Analysis

The liver and adipose tissues were fixed in 4% formalin. Fixed liver and adipose tissue were used in frozen and paraffin blocking, respectively. Frozen-blocked liver tissues were cut (3 μm thick) with a microtome (CM1510S-3; Leica, Wetzlar, Germany) and stained with Oil Red O. Paraffin-blocked adipose tissue was sectioned (3 μm thick) using a microtome (Microm HM 325; Thermo Fisher Scientific, Waltham, MA, USA) and stained with hematoxylin and eosin on a coating glass slide. Slides were observed under a light microscope (×100 magnification; Nikon ECLIPSE Ti; Nikon Corp., Tokyo, Japan).

2.6. Western Blot Analysis

The protein expression was measured by the Western blot assay, which was performed as previously described using SDS-PAGE [24]. In brief, liver and epididymis adipose tissue liver tissues were homogenized with lysis buffer containing a protease inhibitor cocktail and the protein concentration was determined using the Bio-Rad protein assay kit (Bio-Rad, Hercules, CA, USA). An equal amount of protein was resolved on 10% SDS-PAGE. The separated proteins were electrophoretically transferred to a nitrocellulose membrane, blocked with 5% (w/v) skim milk solution, and then incubated with primary and secondary antibodies. Protein expression was visualized by enhanced chemiluminescence, detected using the CAS-400 (Core Bio, Seoul, Korea), and calculated using ImageJ software (National Institutes of Health, Bethesda, MD, USA). Protein expression was normalized to that of α-tubulin or β-actin. The primary antibodies used in this study, α-tubulin (ab52866), beta-actin (ab8227), and FAS (ab22759), were purchased from Abcam Inc. (Cambridge, UK), and AP2 (#3208) was purchased from Cell Signaling Technology (Beverly, MA, USA). The following were purchased from Santa Cruz Biotechnology (Santa Cruz, CA, USA): SREBP-1 (sc-8984), ACCα (sc-26817), PPARα (sc-9000), CPT1 (sc-139482), ACOX1 (sc-98499), SREBP-2 (sc-5603), HMGCR (sc-33827), CYP7A1 (sc-25536), and HSL (sc-74489). The dilution ration of primary antibody was 1:500 to 1:1000. The secondary horseradish peroxidase-conjugated antibodies (all from Abcam Inc.) were rabbit anti-goat IgG H & L (ab6741), donkey anti-rabbit IgG H & L (ab6802), and rabbit anti-mouse IgG H & L (ab6728).

2.7. Statistical Analysis

Statistical analysis was performed using SPSS version 23 (SPSS Inc., Chicago, IL, USA). Values are presented as the mean ± standard deviation. Statistical significance of differences was assessed by one-way analysis of variance (ANOVA) followed by Duncan’s multiple-range test at p < 0.05.

3. Results

3.1. Body Weight Gain, Organ Weight, Food Intake, and Aminotransferase Activity

As shown in Figure 1, there were no significant differences in the initial body weight and daily food intake among db/db mice (Figure 1a,b). The final body weights were significantly increased in db/db mice, relative to m/m mice, which were reduced by collagen supplements (Figure 1a, p < 0.05). The weight of visceral and subcutaneous adipose tissue increased in db/db mice but was reduced in the low-MW collagen peptide (LCP) (by 21.0% and 17.4%) and high-MW collagen peptide (HCP) groups (by 19.6% and 13.5%, respectively, Figure 1e,f, p < 0.05). However, those of the liver and epididymis adipose tissue were not significantly different among db/db mice (Figure 1c,d). The aminotransferase activities were elevated in db/db mice in which aspartic acid transaminase (AST) and alanine transaminase (ALT) activity in the LCP and HCP groups (Figure 1g,h, p < 0.05) but activity was not significantly different among db/db mice.

3.2. Effects of Skate Skin Collagen Peptides on Plasma Lipid, Adiponectin, and Leptin Levels, and Lipid Droplets in Adipose Tissue

Compared to m/m mice, the plasma lipid concentration that was elevated in db/db mice was reduced by collagen treatment (Figure 2). Compared to the CON group, plasma TG, total cholesterol (TC), and low-density lipoprotein cholesterol (LDL-C) levels were significantly lower in the LCP (29.3%, 35.2%, and 66.5%, respectively) and in the HCP groups (26.8%, 35.2%, and 66.8%, respectively) (Figure 2a–c, p < 0.05). Therefore, the atherogenic index was significantly reduced in collagen-fed mice by 45.0% and 46.3% in the LCP and HCP groups, respectively (Figure 2d, p < 0.05). Plasma free fatty acid (FFA) levels were reduced in collagen-fed mice, but there was no significant difference among db/db mice (Figure 2e). In contrast, plasma high-density lipoprotein cholesterol (HDL-C) levels in collagen-fed mice were lower in the CON group, whereas only the LCP-fed mice were significantly elevated by 41.0% (Figure 2f, p < 0.05). Compared to m/m mice, plasma adiponectin levels were lower in db/db mice (Figure 2g), whereas leptin and insulin levels were higher (Figure 2h,i). However, these levels were reversed by collagen supplementation, in which adiponectin levels in the LCP group were significantly elevated by 52.3% and both leptin and insulin levels in the LCP and HCP groups were diminished in the LCP group (by 33.0% and 44.1%, respectively) and the HCP group (by 49.2% and 46.6%, respectively), relative to the CON group (p < 0.05).
As shown in the adipose tissue histological results (Figure 2j), the differentiation of lipid droplets was observed in the CON group, relative to m/m mice. In contrast, collagen intake suppressed the enlargement of adipocytes; in particular, the degree of lipid droplet size was smaller in the LCP group than in the HCP group. The histological results were in line with the reduced plasma lipid levels in the collagen-fed groups.

3.3. Effects of Skate Skin Collagen Peptides on Hepatic Lipid Levels and the Degree of Lipid Accumulation in Liver Tissue

Hepatic TG and TC levels that were elevated in db/db mice were significantly decreased in collagen-fed groups (Figure 3a,b, p < 0.05). Compared to the CON group, the hepatic TG level in the LCP group was lower by 28.1% and hepatic TC levels in the LCP and HCP groups were reduced by 10.5% and 11.8%, respectively (p < 0.05).
Histological analysis of the liver showed that hepatic lipid deposition was prominent in the CON group, relative to m/m mice (Figure 3c), whereas collagen intake suppressed lipid accumulation in the liver. In particular, the degree of hepatic lipid accumulation was less severe in the LCP group than in the HCP group, which was consistent with the decreased hepatic TG and TC levels in the collagen-fed groups.

3.4. Protein Expression of Fatty Acid Synthesis in the Liver

Compared to the CON group, protein expression levels of SREBP-1 were significantly lower in the LCP and HCP groups by 42.8% and 41.6%, respectively, which was similar to that in the normal (NOR) group mice (Figure 4, p < 0.05). As expected, protein expression levels for FAS were significantly lower in the LCP group by 48.6%, and those for ACCα were significantly reduced in the LCP and HCP groups by 32.5% and 29.2%, respectively (p < 0.05).

3.5. Protein Expression of Beta-Oxidation in the Liver

Protein expression levels of PPARα were significantly elevated in the LCP group by 163.6%, compared to that in the CON group (Figure 5, p < 0.05). Similarly, protein expression levels of CPT1 and ACOX1 in the LCP group were higher by 168.5% and 153.9%, respectively (p < 0.05).

3.6. Protein Expression of Cholesterol Metabolism in the Liver

Compared to the CON group, the protein expression levels of cholesterol metabolism were significantly different only in the LCP group. The levels of SREBP-2 and its target gene, HMGCR, in the LCP group were significantly lower by 42.7% and 42.1%, respectively (Figure 6, p < 0.05). In contrast, protein expression of microsomal cytochrome P450 family 7 subfamily A member 1 (CYP7A1) in the LCP group was significantly elevated by 108.2% (p < 0.05).

3.7. Protein Expression of Lipogenesis-Related Molecules in Adipose Tissue

Compared to the CON group, protein expression levels involved in lipogenesis were significantly different only in the LCP group (Figure 7). The levels of SREBP-1, FAS, and AP2 in the LCP group were significantly lower by 43.7%, 51.0%, and 49.8%, respectively (p < 0.05).

3.8. Protein Expression of Lipolysis-Related Molecules in Adipose Tissue

Protein expression levels of PPARα in the LCP and HCP groups were significantly higher by 103.1% and 86.0%, respectively, compared to those in the CON group (Figure 8, p < 0.05). Protein expression levels of HSL and ACOX1 were significantly higher (by 110.9% and 120.1%, respectively) only in the LCP group (p < 0.05). Although the CPT1 level was elevated by collagen intake, there was no significant difference among db/db mice.

4. Discussion

Fish collagen peptides are widely used in the food, biomedical, and cosmetic industries because of their good biosafety and excellent bioavailability [25,26]. Skate skin is recognized as a potential source of collagen. Peptide MW is the most important factor that exerts functional properties because MW is highly associated with bioavailability [27,28]. Lower peptide MW is reported to reveal a wide range of biological activities than peptides with higher MW [27]. This study evaluated the effect of two different skate skin collagen peptides of different MWs (high and low) on liver and adipose lipid metabolism in obese mice.
Hyperlipidemia is a characteristic feature in an obese state through excessive fat accumulation in major organs, such as the liver and adipose tissue. In contrast, a reduction in body weight is associated with an improvement in the plasma lipid profile [29,30]. In the current study, the collagen-fed groups had lower plasma TG, TC, and LDL-C levels than the CON group, whereas the plasma HDL-C level was higher in the LCP group. The improvement of plasma lipid profiles in the collagen-fed groups might be associated with elevated adiponectin and reduced leptin levels, accompanied by a reduction in body weight gain and visceral and subcutaneous adipose tissue weights. The reduction in plasma lipid levels and adipose tissue weight was higher in the LCP group than in the HCP group, but a large difference between the LCP and HCP groups was not shown. These results are consistent with previous studies showing that fish collagen peptides decreased serum levels of TC, TG, and LDL-C, and increased serum HDL-C levels [25], as well as reduced body weight [25,29]. Similarly, the collagen derived from salmon [31], gray mullet [5], and skate [22] exert plasma lipid-lowering effects. In addition, chum salmon skin-derived collagen peptide increases adiponectin and decreases leptin levels in rats [32]. Similarly, the results of this study indicate that SSCP could have partial effects on regulation of the leptin level, indicating that both LCP and HCP lowers leptin levels. The preventive effect against hyperlipidemia was also observed in a human study, where marine collagen peptides reduced the levels of TG, FFA, TC, and LDL-C, and increased HDL-C levels [2]. Similarly, a recent clinical study shows that the percentage of body fat and body fat mass were found to be significantly better in the intervention group (2 g of skate skin collagen peptide per day) than those of control subjects [33]. These previous results are in good agreement with those of this study. Moreover, the most abundant amino acids in skate collagen are glycine, alanine, and proline [34]. Glycine supplementation is known to be largely effective in reducing weight in overweight and obese individuals by enhancing white-fat loss [10,35,36]. In addition, glycine elevated adiponectin levels and decreased TG plasma concentrations, resulting in the reduction of the adipose cell size in obese animal models [10,37,38]. These results support the hypolipidemic effects of skate skin collagen peptides rich in glycine.
Lipid metabolism is modulated by several transcription factors that target gene expression. In the present study, the hepatic expression levels of proteins involved in fatty acid synthesis (SREBP-1, ACC, and FAS) and cholesterol synthesis (SREBP-2 and HMGCR) were suppressed in the LCP group, relative to the CON group. However, fatty acid oxidation (PPARα, CPT1, and ACOX1) was enhanced by LCP supplementation. As a result, the LCP-fed groups had lower hepatic TG and TC levels, as evidenced by the histological results, demonstrating that hepatic lipid deposits were suppressed. These results are consistent with a previous study showing that collagen peptide derived from chum salmon skin prevented liver steatosis by upregulating PPARα expression in rats [32]. Our previous study demonstrated the dose-dependent effects of skate skin collagen peptide (without ultrafiltration) on the reduction of the hepatic lipid concentration mediated through the regulation of lipid metabolism-related genes in diet-induced obese mice [20]. Likewise, fish collagen peptides suppress palmitate-induced accumulation of lipid vacuoles in hepatocytes [25]. This phenomenon was confirmed in the current study. These results indicate that skate skin collagen peptide may act by reducing lipid synthesis and cholesterol uptake from the liver and facilitating liver fatty acid oxidation.
Consistent with the present observations in the liver, LCP supplementation significantly decreased lipogenesis and lipolysis in adipose tissue. LCP administration downregulated protein expression levels of fatty acid synthesis-related genes (SREBP-1, FAS, and AP2) and elevated the expression of fatty acid oxidation-related genes (PPARα, HSL, CPT1, and ACOX1) in the adipose tissue, as demonstrated by histological analysis of the adipose tissue showing that the LCP-fed mice had smaller adipocytes. Similarly, fish collagen peptides hydrolyzed from significantly inhibited lipid accumulation suppress adipocyte differentiation [7,21]. In addition, in epididymal adipose tissue of HFD-fed mice, the expression of key regulators of adipocyte differentiation, such as CCAAT-enhancer-binding protein (C/EBPα), PPAR-γ, and AP2 genes, is decreased by fish collagen peptide [25]. These observations suggested that skate skin collagen peptide inhibited adipocyte differentiation through a mechanism involving transcriptional repression of the major regulators.
As expected, the effects of LCP were greater than those of HCP. Our results are in agreement with many other studies that reported that the average collagen MW influences functional properties [39]. Peptides with smaller MW have more favorable bioactivities than peptides with higher MW, thereby enzymatic and chemical modifications have been extensively used to improve the functional properties of peptides [40]. Emerging evidence demonstrates that a lower collagen MW shows greater reducing powers, while a higher collagen MW shows lower effects [9]. In addition, peptides from marine species by-products (blue whiting and brown shrimp) suppress appetite by stimulating cholecystokinin secretion, in which small peptides (<1500 Da) exert a higher effect than larger MW peptides [41]. These results were in line with those of another fish peptide study, in which the peptide with the lowest MW from conger eel showed the highest antioxidative activities among peptides with different MWs [27]. These studies indicate that an increase in the collagen MW reduces functional properties. The higher biological effects of low-MW peptides are associated with increased absorption of smaller peptides that can easily cross the intestinal barrier and react in the body [25,40]. In addition, solubility is also an important factor in determining the functional properties of collagen [39]. The reduction in MW considerably improves the solubility of collagens. Because smaller peptides are more polar and form stronger hydrogen bonds with water, these peptides are more soluble [42,43]. Consistent with previous findings, our results showed that the lower collagen peptide MW had a larger effect on the improvement of lipid metabolism in the liver and adipose tissue.

5. Conclusions

To identify the potential antiobesity properties of collagen peptide, we report here that skate skin collagen peptide improved lipid metabolism in the liver and adipose tissue. These effects were mediated through the regulation of key transcription factors and enzymes related to lipogenesis and lipolysis. In particular, the low collagen peptide MW augmented larger effects relative to the high collagen peptide MW. Our results are important to broaden the applications of skate skin collagen peptides. Furthermore, advanced studies for metabolic changes by collagen peptide or amino acids are needed to uncover the effects of skate skin collagen peptide.

Author Contributions

Conceptualization, J.S.N. and M.W.; investigation, M.W.; resources, J.S.N.; writing—original draft preparation, M.W.; writing—review and editing, J.S.N.; project administration, J.S.N.; funding acquisition, J.S.N. All authors have read and agreed to the published version of the manuscript.

Funding

This work was supported by the Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education (NRF-2017R1D1A3B03034845).

Acknowledgments

This work was supported by the Technological Innovation R&D Program (S2409860) funded by the Small and Medium Business Administration (SMBA, Korea) and supported by the Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education (NRF-2017R1D1A3B03034845).

Conflicts of Interest

The authors declare no conflict of interest.

Abbreviations

MWMolecular weight
SREBPSterol regulatory element binding protein
FASFatty acid synthase
ACCAcetyl-CoA carboxylase
HMGCR3-hydroxy-3-methylglutaryl-CoA reductase
AP2Adipocyte protein 2
PPARαPeroxisome proliferator activated receptor α
CPT1Carnitine palmitoyltransferase 1A
ACOX1Acyl-CoA oxidase 1
HSLHormone-sensitive lipase
TGTriglyceride
HFDHigh fat diet
LCPLow MW collagen peptide
HCPHigh MW collagen peptide
ASTAspartic acid transaminase
CONControl
ALTAlanine transaminase
TCTotal cholesterol
LDL-CLow-density lipoprotein cholesterol
FFAFree fatty acid
HDL-CHigh-density lipoprotein cholesterol
NORNormal
CYP7A1Microsomal cytochrome P450 family 7 subfamily A member 1
PBSPhosphate-buffered saline
ANOVAOne-way analysis of variance

References

  1. Blanco, M.; Vázquez, J.; Pérez-Martín, R.; Sotelo, C. Hydrolysates of fish skin collagen: An opportunity for valorizing fish industry byproducts. Mar. Drugs 2017, 15, 131. [Google Scholar] [CrossRef] [Green Version]
  2. Wang, J.; Xie, Y.; Pei, X.; Yang, R.; Zhang, Z.; Li, Y. The lipid-lowering and antioxidative effects of marine collagen peptides. Chin. J. Prev. Med. 2008, 42, 226–230. [Google Scholar]
  3. Pan, X.; Zhao, Y.-Q.; Hu, F.-Y.; Wang, B. Preparation and identification of antioxidant peptides from protein hydrolysate of skate (Raja porosa) cartilage. J. Funct. Foods 2016, 25, 220–230. [Google Scholar] [CrossRef]
  4. Zhu, C.-F.; Li, G.-Z.; Peng, H.-B.; Zhang, F.; Chen, Y.; Li, Y. Treatment with marine collagen peptides modulates glucose and lipid metabolism in Chinese patients with type 2 diabetes mellitus. Appl. Physiol. Nutr. Metab. 2010, 35, 797–804. [Google Scholar] [CrossRef] [PubMed]
  5. Kim, H.-S.; Yoon, H.-D.; Seong, J.-H.; Lee, Y.-G.; Xie, C.-L.; Kim, S.-H.; Choi, W.-S. Effects of soluble collagen peptides extract derived from Mugil cephalus scale on the blood glucose and lipid metabolism in diabetic rats. J. Life Sci. 2009, 19, 1794–1801. [Google Scholar]
  6. Pei, X.; Yang, R.; Zhang, Z.; Gao, L.; Wang, J.; Xu, Y.; Zhao, M.; Han, X.; Liu, Z.; Li, Y. Marine collagen peptide isolated from Chum Salmon (Oncorhynchus keta) skin facilitates learning and memory in aged C57BL/6J mice. Food Chem. 2010, 118, 333–340. [Google Scholar] [CrossRef]
  7. Liu, J.; Si, S.; Qin, Y.; Zhang, B.; Song, S.; Guo, Y. The effect of different molecular weight collagen peptides on MC3T3-E1 cells differentiation. Bio-Med. Mater. Eng. 2015, 26, S2041–S2047. [Google Scholar] [CrossRef] [Green Version]
  8. Erdmann, K.; Cheung, B.W.; Schröder, H. The possible roles of food-derived bioactive peptides in reducing the risk of cardiovascular disease. J. Nutr. Biochem. 2008, 19, 643–654. [Google Scholar] [CrossRef] [PubMed]
  9. Jeevithan, E.; Jingyi, Z.; Bao, B.; Shujun, W.; JeyaShakila, R.; Wu, W.H. Biocompatibility assessment of type-II collagen and its polypeptide for tissue engineering: Effect of collagen’s molecular weight and glycoprotein content on tumor necrosis factor (Fas/Apo-1) receptor activation in human acute T-lymphocyte leukemia cell line. RSC Adv. 2016, 6, 14236–14246. [Google Scholar]
  10. Chen, J.; Ma, X.; Yang, Y.; Dai, Z.; Wu, Z.; Wu, G. Glycine enhances expression of adiponectin and IL-10 in 3T3-L1 adipocytes without affecting adipogenesis and lipolysis. Amino Acids 2018, 50, 629–640. [Google Scholar] [CrossRef]
  11. Abranches, M.V.; de Oliveira, F.C.E.; da Conceição, L.L.; Peluzio, M.d.C.G. Obesity and diabetes: The link between adipose tissue dysfunction and glucose homeostasis. Nutr. Res. Rev. 2015, 28, 121–132. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  12. Hardie, D. AMPK: A key regulator of energy balance in the single cell and the whole organism. Int. J. Obes. 2008, 32, S7–S12. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  13. Fu, L.; Bruckbauer, A.; Li, F.; Cao, Q.; Cui, X.; Wu, R.; Shi, H.; Zemel, M.B.; Xue, B. Interaction between metformin and leucine in reducing hyperlipidemia and hepatic lipid accumulation in diet-induced obese mice. Metabolism 2015, 64, 1426–1434. [Google Scholar] [CrossRef]
  14. Eberlé, D.; Hegarty, B.; Bossard, P.; Ferré, P.; Foufelle, F. SREBP transcription factors: Master regulators of lipid homeostasis. Biochimie 2004, 86, 839–848. [Google Scholar] [CrossRef]
  15. Jump, D.B. N-3 polyunsaturated fatty acid regulation of hepatic gene transcription. Curr. Opin. Lipidol. 2008, 19, 242. [Google Scholar] [CrossRef] [Green Version]
  16. Duncan, R.E.; Ahmadian, M.; Jaworski, K.; Sarkadi-Nagy, E.; Sul, H.S. Regulation of lipolysis in adipocytes. Annu. Rev. Nutr. 2007, 27, 79–101. [Google Scholar] [CrossRef] [Green Version]
  17. Zechner, R.; Zimmermann, R.; Eichmann, T.O.; Kohlwein, S.D.; Haemmerle, G.; Lass, A.; Madeo, F. FAT SIGNALS-lipases and lipolysis in lipid metabolism and signaling. Cell Metab. 2012, 15, 279–291. [Google Scholar] [CrossRef] [Green Version]
  18. Shon, J.; Eo, J.-H.; Hwang, S.J.; Eun, J.-B. Effect of processing conditions on functional properties of collagen powder from skate (Raja kenojei) skins. Food Sci. Biotechnol. 2011, 20, 99–106. [Google Scholar] [CrossRef]
  19. Hwang, J.-H.; Mizuta, S.; Yokoyama, Y.; Yoshinaka, R. Purification and characterization of molecular species of collagen in the skin of skate (Raja kenojei). Food Chem. 2007, 100, 921–925. [Google Scholar] [CrossRef]
  20. Woo, M.; Song, Y.; Kang, K.-H.; Noh, J. Anti-Obesity Effects of Collagen Peptide Derived from Skate (Raja kenojei) Skin Through Regulation of Lipid Metabolism. Mar. Drugs 2018, 16, 306. [Google Scholar] [CrossRef] [Green Version]
  21. Lee, H.; Woo, M.; Song, Y.; Noh, J. Inhibitory effect of skate skin collagen on hepatic lipid accumulation through regulation of lipid metabolism. J. Korean Soc. Food Sci. Nutr. 2018, 47, 235–242. [Google Scholar] [CrossRef]
  22. Baek, J.-M.; Kang, K.-H.; Kim, S.-H.; Noh, J.-S.; Jeong, K.-S. Development of high functional collagen peptide materials using skate skins. J. Environ. Sci. Int. 2016, 25, 579–588. [Google Scholar] [CrossRef]
  23. Folch, J.; Lees, M.; Sloane-Stanley, G. A simple method for the isolation and purification of total lipids from animal tissues. J. Biol. Chem. 1957, 226, 497–509. [Google Scholar]
  24. Park, C.H.; Xu, F.H.; Roh, S.-S.; Song, Y.O.; Uebaba, K.; Noh, J.S.; Yokozawa, T. Astaxanthin and Corni Fructus protect against diabetes-induced oxidative stress, inflammation, and advanced glycation end product in livers of streptozotocin-induced diabetic rats. J. Med. Food 2015, 18, 337–344. [Google Scholar] [CrossRef]
  25. Lee, E.J.; Hur, J.; Ham, S.A.; Jo, Y.; Lee, S.; Choi, M.-J.; Seo, H.G. Fish collagen peptide inhibits the adipogenic differentiation of preadipocytes and ameliorates obesity in high fat diet-fed mice. Int. J. Biol. Macromol. 2017, 104, 281–286. [Google Scholar] [CrossRef] [PubMed]
  26. Berillis, P. Marine collagen: Extraction and applications. In Research Trends in Biochemistry, Molecular Biology and Microbiology, Madhukar, S., Ed.; SM Group: Dover, DE, USA, 2015; pp. 1–13. [Google Scholar]
  27. Ranathunga, S.; Rajapakse, N.; Kim, S.-K. Purification and characterization of antioxidative peptide derived from muscle of conger eel (Conger myriaster). Eur. Food Res. Technol. 2006, 222, 310–315. [Google Scholar] [CrossRef]
  28. Deeslie, W.D.; Cheryan, M. Fractionation of soy protein hydrolysates using ultrafiltration membranes. J. Food Sci. 1992, 57, 411–413. [Google Scholar] [CrossRef]
  29. Astre, G.; Deleruyelle, S.; Dortignac, A.; Bonnet, C.; Valet, P.; Dray, C. Diet-induced obesity and associated disorders are prevented by natural bioactive type 1 fish collagen peptides (Naticol®) treatment. J. Physiol. Biochem. 2018, 74, 647–654. [Google Scholar] [CrossRef] [PubMed]
  30. Van Gaal, L.F.; Wauters, M.A.; De Leeuw, I.H. The beneficial effects of modest weight loss on cardiovascular risk factors. Int. J. Obes. Relat. Metab. Disord. 1997, 21, S5–S9. [Google Scholar]
  31. Saito, M.; Kiyose, C.; Higuchi, T.; Uchida, N.; Suzuki, H. Effect of collagen hydrolysates from salmon and trout skins on the lipid profile in rats. J. Agric. Food Chem. 2009, 57, 10477–10482. [Google Scholar] [CrossRef]
  32. Zhu, C.; Zhang, W.; Mu, B.; Zhang, F.; Lai, N.; Zhou, J.; Xu, A.; Liu, J.; Li, Y. Effects of marine collagen peptides on glucose metabolism and insulin resistance in type 2 diabetic rats. J. Food Sci. Technol. 2017, 54, 2260–2269. [Google Scholar] [CrossRef] [PubMed]
  33. Tak, Y.J.; Kim, Y.J.; Lee, J.G.; Yi, Y.H.; Cho, Y.H.; Kang, G.H.; Lee, S.Y. Effect of Oral Ingestion of Low-Molecular Collagen Peptides Derived from Skate (Raja Kenojei) Skin on Body Fat in Overweight Adults: A Randomized, Double-Blind, Placebo-Controlled Trial. Mar. Drugs 2019, 17, 157. [Google Scholar] [CrossRef] [Green Version]
  34. Mizuta, S.; Hwang, J.-H.; Yoshinaka, R. Molecular species of collagen in pectoral fin cartilage of skate (Raja kenojei). Food Chem. 2003, 80, 1–7. [Google Scholar] [CrossRef]
  35. Wijekoon, E.P.; Skinner, C.; Brosnan, M.E.; Brosnan, J.T. Amino acid metabolism in the Zucker diabetic fatty rat: Effects of insulin resistance and of type 2 diabetes. Can. J. Physiol. Pharmacol. 2004, 82, 506–514. [Google Scholar] [CrossRef]
  36. Takashina, C.; Tsujino, I.; Watanabe, T.; Sakaue, S.; Ikeda, D.; Yamada, A.; Sato, T.; Ohira, H.; Otsuka, Y.; Oyama-Manabe, N. Associations among the plasma amino acid profile, obesity, and glucose metabolism in Japanese adults with normal glucose tolerance. Nutr. Metab. 2016, 13, 5. [Google Scholar] [CrossRef] [PubMed]
  37. Yue, J.T.; Mighiu, P.I.; Naples, M.; Adeli, K.; Lam, T.K. Glycine normalizes hepatic triglyceride-rich VLDL secretion by triggering the CNS in high-fat fed rats. Circ. Res. 2012, 110, 1345–1354. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  38. Hafidi, M.E.; Pérez, I.; Zamora, J.; Soto, V.; Carvajal-Sandoval, G.; Banos, G. Glycine intake decreases plasma free fatty acids, adipose cell size, and blood pressure in sucrose-fed rats. Am. J. Physiol. 2004, 287, R1387–R1393. [Google Scholar] [CrossRef] [Green Version]
  39. Li, Z.; Wang, B.; Chi, C.; Gong, Y.; Luo, H.; Ding, G. Influence of average molecular weight on antioxidant and functional properties of cartilage collagen hydrolysates from Sphyrna lewini, Dasyatis akjei and Raja porosa. Food Res. Int. 2013, 51, 283–293. [Google Scholar] [CrossRef]
  40. Jeon, Y.-J.; Byun, H.-G.; Kim, S.-K. Improvement of functional properties of cod frame protein hydrolysates using ultrafiltration membranes. Process Biochem. 1999, 35, 471–478. [Google Scholar] [CrossRef]
  41. Cudennec, B.; Ravallec-Plé, R.; Courois, E.; Fouchereau-Peron, M. Peptides from fish and crustacean by-products hydrolysates stimulate cholecystokinin release in STC-1 cells. Food Chem. 2008, 111, 970–975. [Google Scholar] [CrossRef]
  42. Roberts, P.R.; Burney, J.; Black, K.W.; Zaloga, G.P. Effect of chain length on absorption of biologically active peptides from the gastrointestinal tract. Digestion 1999, 60, 332–337. [Google Scholar] [CrossRef]
  43. Gbogouri, G.; Linder, M.; Fanni, J.; Parmentier, M. Influence of hydrolysis degree on the functional properties of salmon byproducts hydrolysates. J. Food Sci. 2004, 69, C615–C622. [Google Scholar] [CrossRef]
Biomedicines 08 00187 g001 550
Figure 1. Effects of two skate skin-derived collagen peptides with different molecular weights on body weight (a), food intake (b), organ weight (c–f), and aminotransferase activity (g,h). Data are mean ± standard deviation (SD) (n = 10 per group). Experimental groups were divided into four groups; m/m mice were orally administered water as a vehicle (NOR group) whereas db/db mice were orally administered water (control group, CON), LCP (LCP group), or HCP (HCP group) at a dose of 200 mg·kg bw−1·day−1 for 8 weeks. a–c Different letters mean significant differences to one-way analysis of variance (ANOVA), followed by Duncan’s multiple-range test at p < 0.05.
Figure 1. Effects of two skate skin-derived collagen peptides with different molecular weights on body weight (a), food intake (b), organ weight (c–f), and aminotransferase activity (g,h). Data are mean ± standard deviation (SD) (n = 10 per group). Experimental groups were divided into four groups; m/m mice were orally administered water as a vehicle (NOR group) whereas db/db mice were orally administered water (control group, CON), LCP (LCP group), or HCP (HCP group) at a dose of 200 mg·kg bw−1·day−1 for 8 weeks. a–c Different letters mean significant differences to one-way analysis of variance (ANOVA), followed by Duncan’s multiple-range test at p < 0.05.
Biomedicines 08 00187 g001
Biomedicines 08 00187 g002 550
Figure 2. Effects of two skate skin-derived collagen peptides with different molecular weights on plasma lipid (a–f), adiponectin (g), leptin (h), and insulin levels (i), and lipid droplets in adipose tissue (j). Data are mean ± standard deviation (SD) (n = 10 per group). Experimental groups were divided into four groups; m/m mice were orally administered water as a vehicle (NOR group) whereas db/db mice were orally administered water (control group, CON), LCP (LCP group), or HCP (HCP group) at a dose of 200 mg·kg bw−1·day−1 for 8 weeks. a–c Different letters mean significant differences to one-way analysis of variance (ANOVA), followed by Duncan’s multiple-range test at p < 0.05. The atherogenic index (AI) was calculated as (TC - HDL-C) / HDL-C. Histological analysis of adipose tissue was performed using hematoxylin and eosin staining, magnification: 200×, bar: 50 μm.
Figure 2. Effects of two skate skin-derived collagen peptides with different molecular weights on plasma lipid (a–f), adiponectin (g), leptin (h), and insulin levels (i), and lipid droplets in adipose tissue (j). Data are mean ± standard deviation (SD) (n = 10 per group). Experimental groups were divided into four groups; m/m mice were orally administered water as a vehicle (NOR group) whereas db/db mice were orally administered water (control group, CON), LCP (LCP group), or HCP (HCP group) at a dose of 200 mg·kg bw−1·day−1 for 8 weeks. a–c Different letters mean significant differences to one-way analysis of variance (ANOVA), followed by Duncan’s multiple-range test at p < 0.05. The atherogenic index (AI) was calculated as (TC - HDL-C) / HDL-C. Histological analysis of adipose tissue was performed using hematoxylin and eosin staining, magnification: 200×, bar: 50 μm.
Biomedicines 08 00187 g002
Biomedicines 08 00187 g003 550
Figure 3. Effects of two skate skin-derived collagen peptides with different molecular weights on hepatic lipid levels (a,b) and lipid accumulation in the liver (c). Data are mean ± standard deviation (SD) (n = 10 per group). Experimental groups were divided into four groups; m/m mice were orally administered water as a vehicle (NOR group) whereas db/db mice were orally administered water (control group, CON), LCP (LCP group), or HCP (HCP group) at a dose of 200 mg·kg bw-1·day-1 for 8 weeks. a–c Different letters mean significant differences to one-way analysis of variance (ANOVA), followed by Duncan’s multiple-range test at p < 0.05. Histological analysis of liver tissue was performed using oil red O staining, magnification: 100×, bar: 100 μm.
Figure 3. Effects of two skate skin-derived collagen peptides with different molecular weights on hepatic lipid levels (a,b) and lipid accumulation in the liver (c). Data are mean ± standard deviation (SD) (n = 10 per group). Experimental groups were divided into four groups; m/m mice were orally administered water as a vehicle (NOR group) whereas db/db mice were orally administered water (control group, CON), LCP (LCP group), or HCP (HCP group) at a dose of 200 mg·kg bw-1·day-1 for 8 weeks. a–c Different letters mean significant differences to one-way analysis of variance (ANOVA), followed by Duncan’s multiple-range test at p < 0.05. Histological analysis of liver tissue was performed using oil red O staining, magnification: 100×, bar: 100 μm.
Biomedicines 08 00187 g003
Biomedicines 08 00187 g004 550
Figure 4. Effects of two skate skin-derived collagen peptides with different molecular weights on hepatic protein expression of fatty acid synthesis. Data are mean ± standard deviation (SD) (n = 10 per group). Experimental groups were divided into four groups; m/m mice were orally administered water as a vehicle (NOR group) whereas db/db mice were orally administered water (control group, CON), LCP (LCP group), or HCP (HCP group) at a dose of 200 mg·kg bw−1·day−1 for 8 weeks. a,b Different letters mean significant differences to one-way analysis of variance (ANOVA), followed by Duncan’s multiple-range test at p < 0.05.
Figure 4. Effects of two skate skin-derived collagen peptides with different molecular weights on hepatic protein expression of fatty acid synthesis. Data are mean ± standard deviation (SD) (n = 10 per group). Experimental groups were divided into four groups; m/m mice were orally administered water as a vehicle (NOR group) whereas db/db mice were orally administered water (control group, CON), LCP (LCP group), or HCP (HCP group) at a dose of 200 mg·kg bw−1·day−1 for 8 weeks. a,b Different letters mean significant differences to one-way analysis of variance (ANOVA), followed by Duncan’s multiple-range test at p < 0.05.
Biomedicines 08 00187 g004
Biomedicines 08 00187 g005 550
Figure 5. Effects of two skate skin-derived collagen peptides with different molecular weights on hepatic protein expression of beta-oxidation. Data are mean ± standard deviation (SD) (n = 10 per group). Experimental groups were divided into four groups; m/m mice were orally administered water as a vehicle (NOR group) whereas db/db mice were orally administered water (control group, CON), LCP (LCP group), or HCP (HCP group) at a dose of 200 mg·kg bw−1·day−1 for 8 weeks. a-–c Different letters mean significant differences to one-way analysis of variance (ANOVA), followed by Duncan’s multiple-range test at p < 0.05.
Figure 5. Effects of two skate skin-derived collagen peptides with different molecular weights on hepatic protein expression of beta-oxidation. Data are mean ± standard deviation (SD) (n = 10 per group). Experimental groups were divided into four groups; m/m mice were orally administered water as a vehicle (NOR group) whereas db/db mice were orally administered water (control group, CON), LCP (LCP group), or HCP (HCP group) at a dose of 200 mg·kg bw−1·day−1 for 8 weeks. a-–c Different letters mean significant differences to one-way analysis of variance (ANOVA), followed by Duncan’s multiple-range test at p < 0.05.
Biomedicines 08 00187 g005
Biomedicines 08 00187 g006 550
Figure 6. Effects of two skate skin-derived collagen peptides with different molecular weights on hepatic protein expression of cholesterol metabolism. Data are mean ± standard deviation (SD) (n = 10 per group). Experimental groups were divided into four groups; m/m mice were orally administered water as a vehicle (NOR group) whereas db/db mice were orally administered water (control group, CON), LCP (LCP group), or HCP (HCP group) at a dose of 200 mg·kg bw−1·day−1 for 8 weeks. a–-c Different letters mean significant differences to one-way analysis of variance (ANOVA), followed by Duncan’s multiple-range test at p < 0.05.
Figure 6. Effects of two skate skin-derived collagen peptides with different molecular weights on hepatic protein expression of cholesterol metabolism. Data are mean ± standard deviation (SD) (n = 10 per group). Experimental groups were divided into four groups; m/m mice were orally administered water as a vehicle (NOR group) whereas db/db mice were orally administered water (control group, CON), LCP (LCP group), or HCP (HCP group) at a dose of 200 mg·kg bw−1·day−1 for 8 weeks. a–-c Different letters mean significant differences to one-way analysis of variance (ANOVA), followed by Duncan’s multiple-range test at p < 0.05.
Biomedicines 08 00187 g006
Biomedicines 08 00187 g007 550
Figure 7. Effects of two skate skin-derived collagen peptides with different molecular weights on protein expression of lipogenesis-related molecules in adipose tissue. Data are mean ± standard deviation (SD) (n = 10 per group). Experimental groups were divided into four groups; m/m mice were orally administered water as a vehicle (NOR group) whereas db/db mice were orally administered water (control group, CON), LCP (LCP group), or HCP (HCP group) at a dose of 200 mg·kg bw−1·day−1 for 8 weeks. a–c Different letters mean significant differences to one-way analysis of variance (ANOVA), followed by Duncan’s multiple-range test at p < 0.05.
Figure 7. Effects of two skate skin-derived collagen peptides with different molecular weights on protein expression of lipogenesis-related molecules in adipose tissue. Data are mean ± standard deviation (SD) (n = 10 per group). Experimental groups were divided into four groups; m/m mice were orally administered water as a vehicle (NOR group) whereas db/db mice were orally administered water (control group, CON), LCP (LCP group), or HCP (HCP group) at a dose of 200 mg·kg bw−1·day−1 for 8 weeks. a–c Different letters mean significant differences to one-way analysis of variance (ANOVA), followed by Duncan’s multiple-range test at p < 0.05.
Biomedicines 08 00187 g007
Biomedicines 08 00187 g008 550
Figure 8. Effects of two skate skin-derived collagen peptides with different molecular weights on protein expression of lipolysis-related molecules in adipose tissue. Data are mean ± standard deviation (SD) (n = 10 per group). Experimental groups were divided into four groups; m/m mice were orally administered water as a vehicle (NOR group) whereas db/db mice were orally administered water (control group, CON), LCP (LCP group), or HCP (HCP group) at a dose of 200 mg·kg bw−1·day−1 for 8 weeks. a–c Different letters mean significant differences to one-way analysis of variance (ANOVA), followed by Duncan’s multiple-range test at p < 0.05.
Figure 8. Effects of two skate skin-derived collagen peptides with different molecular weights on protein expression of lipolysis-related molecules in adipose tissue. Data are mean ± standard deviation (SD) (n = 10 per group). Experimental groups were divided into four groups; m/m mice were orally administered water as a vehicle (NOR group) whereas db/db mice were orally administered water (control group, CON), LCP (LCP group), or HCP (HCP group) at a dose of 200 mg·kg bw−1·day−1 for 8 weeks. a–c Different letters mean significant differences to one-way analysis of variance (ANOVA), followed by Duncan’s multiple-range test at p < 0.05.
Biomedicines 08 00187 g008

Share and Cite

MDPI and ACS Style

Woo, M.; Noh, J.S. Regulatory Effects of Skate Skin-Derived Collagen Peptides with Different Molecular Weights on Lipid Metabolism in the Liver and Adipose Tissue. Biomedicines 2020, 8, 187. https://doi.org/10.3390/biomedicines8070187

AMA Style

Woo M, Noh JS. Regulatory Effects of Skate Skin-Derived Collagen Peptides with Different Molecular Weights on Lipid Metabolism in the Liver and Adipose Tissue. Biomedicines. 2020; 8(7):187. https://doi.org/10.3390/biomedicines8070187

Chicago/Turabian Style

Woo, Minji, and Jeong Sook Noh. 2020. "Regulatory Effects of Skate Skin-Derived Collagen Peptides with Different Molecular Weights on Lipid Metabolism in the Liver and Adipose Tissue" Biomedicines 8, no. 7: 187. https://doi.org/10.3390/biomedicines8070187

Note that from the first issue of 2016, this journal uses article numbers instead of page numbers. See further details here.

Article Metrics

Back to TopTop