Response: Increased Serum Angiopoietin-Like 6 Ahead of Metabolic Syndrome in a Prospective Cohort Study (Diabetes Metab J 2019;43:521-9)

Jun Namkung; Kyu-Sang Park

doi:10.4093/dmj.2019.0178

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Response Response: Increased Serum Angiopoietin-Like 6 Ahead of Metabolic Syndrome in a Prospective Cohort Study (Diabetes Metab J 2019;43:521-9): Jun Namkung^1,2, Kyu-Sang Park^2,3,4; Diabetes & Metabolism Journal 2019;43(5):729-730.
DOI: https://doi.org/10.4093/dmj.2019.0178
Published online: October 24, 2019

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¹Department of Biochemistry, Yonsei University Wonju College of Medicine, Wonju, Korea.

²Mitohormesis Research Center, Yonsei University Wonju College of Medicine, Wonju, Korea.

³Institute of Lifestyle Medicine, Yonsei University Wonju College of Medicine, Wonju, Korea.

⁴Department of Physiology, Yonsei University Wonju College of Medicine, Wonju, Korea.

Corresponding author: Jun Namkung. Department of Biochemistry, Yonsei University Wonju College of Medicine, 20 Ilsan-ro, Wonju 26426, Korea. junitive@yonsei.ac.kr

Corresponding author: Kyu-Sang Park. Department of Physiology, Yonsei University Wonju College of Medicine, 20 Ilsan-ro, Wonju 26426, Korea. qsang@yonsei.ac.kr

This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/4.0/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

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We really appreciate Dr. Kim for expressing interest and providing valuable comments on our recently published article, “Increased serum angiopoietin-like 6 ahead of metabolic syndrome in a prospective cohort study” which was published in Diabetes & Metabolism Journal [1].

Positive energy balance, increased adiposity, and inflammation are the major pathogenic components of metabolic syndrome [2]. Along with these metabolic stresses, anthropometric values and serum biomarker levels reflecting metabolic status alter, which can be used as predictors for metabolic syndrome [3 4]. These alterations are likely consequences of disease progression and participate in vicious cycles leading to aggravation of metabolic syndrome. However, a substantial portion of hepatokines, myokines, and adipokines shows increased expressions upon metabolic insult to attenuate disease progression. Their roles are concluded as a resilience against metabolic stress, which is opposite to conventional biomarkers. Angiopoietin-like 6 (ANGPTL6) is one example, since animal studies have demonstrated its beneficial influences on body metabolism including augmentation of energy expenditure and improvement of insulin sensitivity [5]. These actions of ANGPTL6 are required to relieve the burden of metabolic stress, and expression and secretion of ANGPTL6 might be induced by pathogenic components of metabolic disease. Therefore, an elevated ANGPTL6 level indicates the existence of metabolic stress requiring compensatory actions. Previously, we confirmed in mouse models that serum ANGPTL6 levels were increased by high fat diet and attenuated by exercise training [6]. Based on this, we interpreted our results in a prospective cohort study that upregulation of ANGPTL6 is a protective response alleviating metabolic stress [1]. We suggest that increased serum ANGPTL6 levels in a preclinical status reflect the increase in ongoing metabolic stress; thus, it could be used as a predictable biomarker of development of metabolic syndrome.

As the first prospective study, we provided evidence of a chronological relationship in which increased serum ANGPTL6 level precedes the onset of metabolic syndrome. As suggested by Dr. Kim, this study needs to be expanded to monitor ANGPTL6 levels during a follow-up period. We speculate the continuance of high ANGPTL6 level during the progression of metabolic syndrome and ANGPTL6 may work as a prognostic biomarker. This anticipation is also based on our previous observation in a cross-sectional study that showed a significantly increased serum level of ANGPTL6 in metabolic syndrome patients [7]. Nevertheless, we could not exclude the possibility that the increased ANGPTL6 level might be diminished at the late stage of metabolic deterioration. Hence, we are planning to compare the changes in ANGPTL6 according to disease severities as the progression of metabolic syndrome in the follow-up period. We definitely agree with Dr. Kim's suggestion to enlarge the cohort population size and to apply a risk-scoring system. In addition, further study is required to identify the mechanisms of ANGPTL6 upregulation including a sensing mechanism of metabolic stress and upstream signals of ANGPTL6. Previously, we had introduced leptin as an upstream regulator of ANGPTL6 [6], but more extensive identification of regulatory mechanisms for ANGPTL6 expression is needed. Finally, high ANGPTL6 level in metabolic syndrome patients can be interpreted as ANGPTL6 resistance, because increased ANGPTL6 failed to compensate for metabolic stress. To elucidate ANGPTL6 resistance, identification of ANGPTL6, which is still unknown, and its alteration in expression and signaling pathway upon metabolic stress are necessary in further study.

We thank Dr. Kim again for the thoughtful comments and welcome any further discussion.

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CONFLICTS OF INTEREST: No potential conflict of interest relevant to this article was reported.

REFERENCES

1. Namkung J, Sohn JH, Chang JS, Park SW, Kim JY, Koh SB, Kong ID, Park KS. Increased serum angiopoietin-like 6 ahead of metabolic syndrome in a prospective cohort study. Diabetes Metab J 2019;43:521-529. Article PubMed PMC PDF
2. Laclaustra M, Corella D, Ordovas JM. Metabolic syndrome pathophysiology: the role of adipose tissue. Nutr Metab Cardiovasc Dis 2007;17:125-139. Article PubMed
3. Wang H, Liu A, Zhao T, Gong X, Pang T, Zhou Y, Xiao Y, Yan Y, Fan C, Teng W, Lai Y, Shan Z. Comparison of anthropometric indices for predicting the risk of metabolic syndrome and its components in Chinese adults: a prospective, longitudinal study. BMJ Open 2017;7:e016062.Article PubMed PMC
4. Rao VS, Nagaraj RK, Hebbagodi S, Kadarinarasimhiah NB, Kakkar VV. Association of inflammatory and oxidative stress markers with metabolic syndrome in Asian indians in India. Cardiol Res Pract 2010;2011:295976Article PubMed PMC PDF
5. Oike Y, Akao M, Yasunaga K, Yamauchi T, Morisada T, Ito Y, Urano T, Kimura Y, Kubota Y, Maekawa H, Miyamoto T, Miyata K, Matsumoto S, Sakai J, Nakagata N, Takeya M, Koseki H, Ogawa Y, Kadowaki T, Suda T. Angiopoietin-related growth factor antagonizes obesity and insulin resistance. Nat Med 2005;11:400-408. Article PubMed PDF
6. Kim MJ, Namkung J, Chang JS, Kim SJ, Park KS, Kong ID. Leptin regulates the expression of angiopoietin-like 6. Biochem Biophys Res Commun 2018;502:397-402. Article PubMed
7. Namkung J, Koh SB, Kong ID, Choi JW, Yeh BI. Serum levels of angiopoietin-related growth factor are increased in metabolic syndrome. Metabolism 2011;60:564-568. Article PubMed

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Response: Increased Serum Angiopoietin-Like 6 Ahead of Metabolic Syndrome in a Prospective Cohort Study (Diabetes Metab J 2019;43:521-9)

Diabetes Metab J. 2019;43(5):729-730. Published online October 24, 2019

DOI: https://doi.org/10.4093/dmj.2019.0178

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Response: Increased Serum Angiopoietin-Like 6 Ahead of Metabolic Syndrome in a Prospective Cohort Study (Diabetes Metab J 2019;43:521-9)

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Namkung J, Park KS. Response: Increased Serum Angiopoietin-Like 6 Ahead of Metabolic Syndrome in a Prospective Cohort Study (Diabetes Metab J 2019;43:521-9). Diabetes Metab J. 2019;43(5):729-730.

DOI: https://doi.org/10.4093/dmj.2019.0178.

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