Circulating Concentrations of Insulin Resistance-Associated Hepatokines, Selenoprotein P and Leukocyte Cell-Derived Chemotaxin 2, during an Oral Glucose Tolerance Test in Humans

Abstract

A hepatokine is a collective term for liver-derived secretory factors whose previously-unrecognized functions have been recently elucidated. We have rediscovered selenoprotein P (SeP) and leukocyte cell-derived chemotaxin 2 (LECT2) as hepatokines that are involved in the development of insulin resistance and hyperglycemia. The aim of this study was to determine whether and, if so, how oral glucose loading alters the two hepatokines in humans. We measured concentrations of serum SeP and plasma LECT2 during 75 g oral glucose tolerance test (OGTT) (n = 20) in people with various degrees of glucose tolerance. In OGTT, concentrations of both serum SeP and plasma LECT2 decreased at 120 min compared with the baseline values, irrespective of the severity of glucose intolerance. Decrement of serum SeP during OGTT showed no correlations to the clinical parameters associated with insulin resistance or insulin secretion. In multiple stepwise regression analyses, plasma cortisol was selected as the variable to explain the changes in plasma concentrations of LECT2. The current data reveal the acute inhibitory actions of oral intake of glucose on circulating SeP and LECT2 in humans, irrespective of the severity of glucose intolerance. This study suggests that circulating SeP is regulated by the unknown clinical factors other than insulin and glucose during OGTT.

INTRODUCTION

Hepatokine is a collective term for liver-derived secretory factors whose previously-unrecognized functions have been recently elucidated. Growing evidence indicates that hepatokines participate in regulation of glucose metabolism and insulin sensitivity as well as other tissue-derived factors such as adipokines.^1,2) Selenoprotein P (SeP) and leukocyte cell-derived chemotaxin 2 (LECT2), both of which were known to be secretory proteins mainly produced by the liver,^3,4) have been rediscovered as hepatokines that are involved in the development of insulin resistance and hyperglycemia.^5,6) Previous in vivo experiments using knockout mice indicate that genetic deletion of SeP or LECT2 improves insulin resistance and hyperglycemia in dietary obese mice.^5,6) These reports suggest that antagonism of these two hepatokines attenuates insulin resistance under over-nutritional conditions. Much attention has been paid to the hepatokines as therapeutic targets for insulin resistance-associated diseases such as type 2 diabetes.

We have rediscovered SeP as a hepatokine that induces insulin resistance and hyperglycemia in type 2 diabetic condition.⁵⁾ SeP emerged as a hepatokine whose hepatic expression levels positively correlate with the severity of insulin resistance in patients with type 2 diabetes.⁵⁾ SeP is a liver-derived secretory protein abundantly expressed in plasma.⁷⁾ SeP contains ten residues of selenocysteine and functions as a transport protein of selenium, an essential trace element.³⁾ Our experiments using purified SeP from human plasma have revealed that SeP directly reduces insulin signal transduction in cultured hepatocytes and myotubes.⁵⁾ A more recent report has shown that SeP impairs health-promoting effects of exercise training by suppressing exercise-induced molecular adaptation in the skeletal muscle through the receptor low density lipoprotein receptor-related protein 1 (LRP1).⁸⁾ Overproduction of SeP in the liver contributes to the pathogenesis of various kinds of lifestyle-related diseases, such as type 2 diabetes.^9,10)

Insulin negatively regulates gene expression for SeP (encoded by the Selenop gene in mice) in cultured hepatocytes.^5,11) Insulin suppresses transcriptional activity of Selenop in hepatocytes by inactivating Forkhead box protein O1 (FoxO1), a transcriptional factor that directly binds to and activates promoter region of Selenop.¹²⁾ Consistent with these reports in vitro, Selenop gene expression increases in the liver of mice under fasted states where blood concentrations of insulin are reduced.⁵⁾ However, it is still unknown whether oral glucose loading alters blood concentrations of SeP in humans.

We have rediscovered LECT2 as a hepatokine whose production is increased in people with obesity.⁶⁾ LECT2 emerged as a hepatokine whose hepatic expression levels positively correlate with body mass index in patients with type 2 diabetes.⁶⁾ LECT2 was originally cloned as a neutrophil chemotactic factor.¹³⁾ Gene expression for LECT2 (encoded by the Lect2 gene in mice) is selectively expressed by adult and fetal liver cells.¹⁴⁾ Our experiments using recombinant LECT2 have revealed that LECT2 impairs insulin signal transduction in cultured myotubes by activating Jun NH₂-terminal kinase (JNK). In contrast, genetic deletion of LECT2 attenuates skeletal muscle insulin resistance in dietary obese mice. This study reveals that LECT2 functions as a hepatokine that links obesity to skeletal muscle insulin resistance.⁶⁾

Gene expression for Lect2 in cultured hepatocytes is negatively regulated by adenosine monophosphate-activated protein kinase (AMPK), the energy depletion-sensing kinase.⁶⁾ Consistent with this finding in hepatocytes, feeding of high fat diet decreases AMPK activity and increases gene expression for Lect2 in the liver of mice.⁶⁾ Additionally, plasma LECT2 concentrations show the rapid response preceding body weight changes during diet-induced weight cycling in mice.¹⁵⁾ However, similar to SeP, few papers were available on blood concentrations of LECT2 in humans during oral glucose loading test or daily diet intake.

Because both SeP and LECT2 are hepatokines that have great impacts on whole body glucose metabolism, we hypothesized that circulating concentrations of the two hepatokines are regulated by oral intake of glucose, as well as those of gut-derived hormones such as glucagon-like peptide-1 (GLP-1) and gastric inhibitory polypeptide (GIP). In fact, many kinds of hormones, such as adiponectin, that play a major role in the regulation of glucose metabolism are known to be altered during oral glucose tolerance test.^16–18) Additionally, people with abnormal glucose tolerance might show different profiles of circulating SeP and LECT2 during glucose loading. To test this hypothesis, we measured concentrations of serum SeP and plasma LECT2 during 75 g oral glucose tolerance test in people with various degrees of glucose tolerance.

MATERIALS AND METHODS

Study Subjects and Protocol

For the study of oral glucose tolerance test (OGTT), the subjects were patients who visited outpatient department of Tsuruga Hospital. Twenty subjects were selected based on entry criteria and exclusion criteria. A total of 20 subjects (males/females: 10/10, mean age: 66 years) accepted the invitation. No subjects are treated with oral hypoglycemic agents, insulins nor GLP-1 therapy. After overnight fasting for at least 12 h, they underwent a 75 g OGTT. Peripheral venous blood samples were obtained for biochemical analyses and hepatokine measurement. In the OGTT, blood samples were collected before, at 30 min, 1 h and 2 h after ingestion of Trelan-G™ (75 g glucose in 225 mL water).

Hepatokine Measurement

Concentrations of serum SeP were measured by a sol particle homogeneous immunoassay as we previously reported. We assessed serum levels of full-length SeP selectively by using two types of SeP monoclonal antibodies, one recognizing N-terminal domain of SeP and another recognizing the C-terminal domain.¹⁹⁾ Plasma levels of LECT2 were measured by Ab-Match ASSEMBLY Mouse LECT2 kit (MBL).⁶⁾

Patient Eligibility

The eligibility criteria were as follows: > 20 years of age; patients with diabetes; patients with impaired glucose tolerance; patients with normal glucose tolerance who suspected to have metabolic diseases (BMI >25, fasting plasma glucose >100 mg/dL, postprandial plasma glucose >140 mg/dL, HbA1c > 6.0%, patients with dyslipidemia or fatty liver).

The exclusion criteria included: 1) poorly controlled unstable diabetes, 2) presence of a severe health problem and not suitable for the study, 3) pregnant, 4) patients taking corticosteroid treatments, 5) liver cirrhosis, 6) patients who were diagnosed as malignant diseases.

Human Rights Statement and Informed Consent

The current study was conducted in accordance with the principles in the Declaration of Helsinki of 1964 and later versions. The study protocol was approved by the Ethical Committee of Kanazawa University and the Ethical Committee of Municipal Tsuruga Hospital, respectively. All the people in current study provided written informed consent (date of the latest revision approved: 17 November 2014, approval no. 1592-2). The trial was registered with the University Hospital Medical Information Network (UMIN) Clinical Trials Registry (date of the latest revision approval at UMIN: 14 October 2016, approval no. UMIN000024411).

Statistical Analysis

Numeric variables are expressed as means ± standard errors of mean (S.E.M.). For testing differences in time course of parameters, one-way repeated measures ANOVA were used and post hoc test were performed using the Bonferroni correction (Figs. 1C, D). To analyze difference in mean of three groups, we performed one-way ANOVA and Tukey–Kramer post-hoc test (Figs. 2, 3). In the study of 75g OGTT, we used stepwise multiple regression models to estimate the relationships between baseline levels of plasma LECT2 and the different components of the variables.

Fig. 1. Time–Course of Plasma Glucose

Plasma glucose (A), serum insulin (B), serum SeP (C), and plasma LECT2 (D) during 75 g OGTT in all the participants (n = 20). Data are represented as mean ± S.E.M. DM: diabetes mellitus, IGT: impaired glucose tolerance, NGT: normal glucose tolerance. * p < 0.05, † p < 0.01.

Fig. 2. The Profiles of Blood Hepatokines during 75 g OGTT in the Participants Classified by the Severity of Glucose Tolerance

(A) Serum concentrations of SeP during 75 g OGTT in the participants classified by the severity of glucose intolerance (n = 7 for subjects with normal glucose tolerance, n = 6 for subjects with impaired glucose tolerance, n = 7 for subjects with type 2 diabetes). Serum concentration of SeP was decreased from 30 to 60 min in the impaired glucose tolerance subjects. * p < 0.05 (B) Plasma concentrations of LECT2 during 75 g OGTT in the participants classified by the severity of glucose intolerance (n = 7 for subjects with normal glucose tolerance, n = 6 for subjects with impaired glucose tolerance, n = 7 for subjects with type 2 diabetes). Data are represented as mean ± S.E.M.

Fig. 3. ΔSeP_120-0 and ΔLECT2_120-0 in the Participants Classified by the Severity of Glucose Tolerance

ns., not significant. DM: diabetes mellitus, IGT: impaired glucose tolerance, NGT: normal glucose tolerance.

A p value of less than 0.05 was considered statistically significant. All data were analyzed by using the Statistical Package for the Social Sciences version 22.0 (SPSS, Chicago, IL, U.S.A.).

RESULTS

Alteration of Blood Concentrations of SeP and LECT2 during OGTT

Basal characteristics of the subjects are shown in Table 1. After a loading of 75 g of glucose, concentrations of plasma glucose and serum insulin were altered as shown in Figs. 1A, B. No adverse effects associated with severe hyperglycemia were observed after 75 g OGTT. A repeated measures ANOVA with a Greenhouse–Geisser correction were performed and mean serum concentrations of SeP and plasma concentrations of LECT2 differed statistically significantly between time points (p < 0.05 and p < 0.05). Post hoc tests using the Bonferroni correction revealed that serum concentrations of SeP and plasma concentrations of LECT2 decreased at 120 min compared with those at 0 min, respectively (Figs. 1C, D p < 0.01 and p < 0.05,). Additionally, serum concentrations of SeP decreased at 60 min (p < 0.05) compared with those at 0 min (Fig. 1C). Among the three groups classified by the severity of glucose intolerance, there were no significant differences in SeP concentrations among the three groups (Fig. 2A). Plasma concentrations of LECT2 also showed no differences among the three groups (Fig. 2B). In addition, ΔSeP_120-0 and ΔLECT2_120-0, which were calculated by subtraction from blood concentrations of SeP or LECT2 at 120 min to those at 0 min, showed no significant differences among the three groups classified by the severity of glucose intolerance (Figs. 3A, B).

Table 1. Characteristics of Subjects in OGTT

n	20
Age	65 ± 1.4
Sex (male/female)	10/10
BMI (kg/m2)	24.2 ± 0.5
Waist circumference (cm)	86.2 ± 1.8
DM/IGT/NGT	7/6/7
Biochemical data
HbA1c (%)	6.1 ± 0.1
FPG (mg/dL)	110.2 ± 5.1
PPG 120 min (mg/dL)	186.4 ± 22.1
Total protein(g/dL)	7.5 ± 0.1
Albumin (g/dL)	4.4 ± 0.1
Aspartate transaminase (IU/L)	24.2 ± 2.8
Alanine transaminase (IU/L)	27.1± 4.9
Creatinine (mg/dL)	0.78 ± 0.1
Triglyceride (mg/dL)	120.6 ± 16.2
HDL-C (mg/d)	71.0 ± 4.4
LDL-C (mg/dL)	99.1 ± 8.0
ACTH (pg/mL)	28.3 ± 3.1
Cortisol (µg mL)	13.2 ± 0.8
HOMA-R	2.36 ± 0.37
HOMA-β	78.0 ± 15.5
Blood levels of hepatokines
Fasting serum levels of SeP (µg/mL)	3.98 ± 0.15
Fasting plasma levels of LECT2 (ng/mL)	58.1 ± 4.2

Variables are expressed as n or means ± S.E.M. Abbreviation: BMI: body mass index; DM: diabetes mellitus, IGT: impaired glucose tolerance, NGT: normal glucose tolerance; HbA1c: glycated hemoglobin A1c; FPG: fasting plasma glucose: PPG: postprandial plasma glucose; HDL-C: high density lipoprotein cholesterol; LDL-C: low density lipoprotein cholesterol (obtained by the Friedwald formula); ACTH: adrenocorticotropic hormone; HOMA-R: homeostasis model assessment of insulin resistance; HOMA-β: homeostasis model assessment of beta cell; SeP: selenoprotein P; LECT2: leukocyte cell-derived chemotaxin 2.

Correlations between Decrement of SeP or LECT2 and Clinical Parameters during OGTT

To understand what clinical factors contribute to the reduction of the two hepatokines during OGTT, we assessed the correlations between ΔSeP_120-0 or ΔLECT2_120-0 and the clinical other parameters (Tables 2, 3). There were no significant correlations between ΔSeP_120-0 and the other parameters (Table 2). ΔLECT2_120-0 correlated negatively with serum insulin (0, 60, 120 min), low density lipoprotein cholesterol (LDL-C), morning plasma concentrations of cortisol, baseline plasma concentrations of LECT2 and homeostasis model assessment of beta cell (HOMA-β) (Table 3).

Table 2. Correlation between ΔSeP_120-0 and the Other Parameters in OGTT

	R	p
Age	0.02	0.90
Hight	0.14	0.56
Body weight	0.33	0.15
BMI	0.39	0.09
Waist circumference	0.16	0.49
HbA1c	0.14	0.54
Plasma glucose 0 min	0.06	0.78
Plasma glucose 30 min	−0.21	0.37
Plasma glucose 60 min	−0.16	0.49
Plasma glucose 120 min	−0.1	0.65
Insulin 0 min	0.27	0.25
Insulin 30 min	0.19	0.41
Insulin 60 min	0.15	0.53
Insulin 120 min	0.20	0.40
LECT2 0 min	0.22	0.36
Total protein	0.33	0.20
Albumin	−0.12	0.65
Aspartate transaminase	−0.03	0.90
Alanine transaminase	0.10	0.66
Creatinine	0.09	0.69
Triglyceride	0.18	0.45
HDL-C	0.11	0.62
LDL-C	−0.03	0.90
Growth hormone	−0.36	0.16
Adrenocorticotropic hormone	0.09	0.72
Cortisol	−0.04	0.85
SeP 0 min	−0.10	0.67
SeP 30 min	0.09	0.69
SeP 60 min	0.15	0.52
SeP 120 min	0.23	0.33
HOMA-R	0.27	0.26
HOMA-β	0.28	0.22

Abbreviation: BMI: body mass index; HbA1c: glycated hemoglobin A1c; HDL-C: high density lipoprotein cholesterol; LDL-C: low density lipoprotein cholesterol (obtained by the Friedwald formula); HOMA-R: homeostasis model assessment of insulin resistance; HOMA-β: homeostasis model assessment of beta cell; SeP: selenoprotein P; LECT2: leukocyte cell-derived chemotaxin 2.

Table 3. Correlation between ΔLECT2_120-0 and the Other Parameters in OGTT

	R	p
Age	−0.07	0.76
Height	0.29	0.20
Body weight	0.02	0.90
BMI	−0.24	0.29
Waist circumference	−0.21	0.37
HbA1c	−0.02	0.91
Plasma glucose 0 min	0.10	0.66
Plasma glucose 30 min	−0.09	0.68
Plasma glucose 60 min	−0.23	0.32
Plasma glucose 120 min	−0.17	0.45
Insulin 0 min	−0.45	0.04*
Insulin 30 min	−0.02	0.94
Insulin 60 min	−0.51	0.02*
Insulin 120 min	−0.50	0.02*
SeP 0 min	0.30	0.20
Total protein	−0.34	0.19
Albumin	−0.14	0.95
Aspartate transaminase	0.12	0.58
Alanine transaminase	0.79	0.74
Creatinine	0.20	0.38
Triglyceride	−0.29	0.20
HDL-C	0.19	0.41
LDL-C	−0.48	0.03*
Growth hormone	0.20	0.93
Adrenocorticotropic hormone	−0.19	0.46
Cortisol	−0.50	0.04*
LECT2 0 min	−0.67	<0.0001*
LECT2 30 min	−0.36	0.12
LECT2 60 min	−0.35	0.13
LECT2 120 min	−0.37	0.11
HOMA-R	−0.41	0.07
HOMA-β	−0.56	0.01*

* p <0.05. Abbreviation: BMI: body mass index; HbA1c: glycated hemoglobin A1c; HDL-C: high density lipoprotein cholesterol; LDL-C: low density lipoprotein cholesterol (obtained by the Friedwald formula); HOMA-R: homeostasis model assessment of insulin resistance; HOMA-β: homeostasis model assessment of beta cell; SeP: selenoprotein P; LECT2: leukocyte cell-derived chemotaxin 2.

Models to Explain Decrement of LECT2 in OGTT

To further clarify the mechanisms by which OGTT decreases LECT2 concentrations, we selected 27 clinical variables and performed multivariable analyses using stepwise method to generate models to explain ΔLECT2_120-0. Plasma cortisol concentrations, height, and LDL-C were selected as the significant variables to explain ΔLECT2_120-0 (Table 4).

Table 4. Multivariate Regression Analyses on ΔLECT2_120-0

	Adjusted R2	β	Standardized β	VIF	p-Value	AIC
Model 1
Cortisol	0.255	−0.978	−0.559	1.000	0.038	40.420
Model 2
Cortisol	0.453	−1.406	−0.803	1.265	0.014	36.876
Height		0.283	0.533	1.265
Model 3
Cortisol	0.638	−1.496	−0.855	1.280		31.763
Height		0.396	0.745	1.508	0.004
LDL-C		−0.075	−0.471	1.203

Followed variables are included in multivariable regression analyses: Age, BMI, Waist circumstance, SeP 0 min, LECT2 0 min, Plasma glucose (0, 30, 60 and 120 min), Insulin (0, 30, 60 and 120 min), HbA1c, Growth hormone, Adrenocorticotropic hormone, Cortisol, Total protein, Albumin, Aspartate transaminase, Alanine transaminase, Triglyceride, HDL-C, LDL-C, Creatinine.

DISCUSSION

The current study shows the reduction of circulating hepatokines, SeP and LECT2, after the loading of glucose in humans. We have previously reported that both SeP and LECT2 attenuate insulin signal transduction in cultured myotubes, although the molecular mechanisms by which the two hepatokines induce insulin resistance are different. The degree of down-regulation of the two hepatokines after glucose intake was relatively small, but down-regulation of SeP and LECT2 might be beneficial because it might act postprandially to increase insulin signaling and enhance glucose uptake in the skeletal muscle.

The current findings reveal that oral glucose loading acutely suppresses circulating levels of SeP in humans within 120 min. We previously reported that glucose-induced upregulation and insulin-induced downregulation of Selenop gene expression, but it took more than six hours for glucose or insulin to alter levels of gene expression of Selenop in the cultured hepatocytes.⁵⁾ The current study raises the possibility that oral glucose loading may inhibit SeP secretion in the liver and/or may increase the degradation of circulating SeP in a short time, probably independently of gene expression of Selenop in the hepatocytes.

Oral glucose loading reduces serum concentrations of SeP in the participants, irrespective of the severity of glucose intolerance. We and the other groups have previously reported that insulin negatively and glucose positively regulate Selenop gene expression in cultured hepatocytes.^5,11,12) However, in the current study, ΔSeP_120-0 during OGTT showed no significant correlations with the insulin- and glucose-associated parameters. Additionally, the participants with type 2 diabetes or impaired glucose tolerance, who had hyperglycemia or hyperinsulinemia during OGTT, respectively, showed a similar descending pattern of circulating SeP. These findings suggest that circulating SeP during OGTT in humans is regulated by the unknown clinical factors other than insulin and glucose. After oral glucose loading, blood levels of secretory factors other than insulin, such as gut-derived incretins, and activity of sympathetic nerve system fluctuate dramatically in humans.^16,17,20) Further cellular or animal studies are needed to determine whether incretins and sympathetic nerve system regulate circulating levels of SeP during OGTT.

Multiple regression analysis reveals that fasting plasma cortisol is an independent explanatory variable of ΔLECT2_120-0 in the OGTT study. Notably, fasting plasma cortisol did not significantly correlate with fasting plasma LECT2, but the participants with high concentrations of fasting cortisol showed a large decrement in plasma LECT2 during OGTT. However, as far as we know, there are no reports regarding the crosstalk between cortisol and LECT2. Additional cellular experiments are needed to determine whether cortisol affects LECT2 gene expression or LECT2 secretion in cultured hepatocytes.

A limitation of the current study is small numbers of the human subjects. In particular, the numbers may be insufficient to detect a statistically significant difference in the analyses classified by the severity of glucose intolerance. Further large-scale clinical studies are needed to confirm whether glucose intolerance alters the response of SeP or LECT2 during OGTT.

In conclusion, the present data demonstrate the acute inhibitory actions of oral intake of glucose on circulating SeP and LECT2 in humans. Response of SeP and LECT2 to oral glucose loading shows a similar pattern in people, irrespective of the severity of glucose intolerance.

Acknowledgments

We thank for Mutsumi Tanaka (Alfresa Pharma Corporation) for technical assistance of SeP measurement. This work was supported by JSPS KAKENHI Grants 16K09740 (H.M.).

Conflict of Interest

The authors declare no conflict of interest.

REFERENCES

• 1) Stefan N, Haring HU. The role of hepatokines in metabolism. Nat. Rev. Endocrinol., 9, 144–152 (2013).
• 2) Stefan N, Haring HU. The metabolically benign and malignant fatty liver. Diabetes, 60, 2011–2017 (2011).
• 3) Burk RF, Hill KE. Selenoprotein P-expression, functions, and roles in mammals. Biochim. Biophys. Acta, 1790, 1441–1447 (2009).
• 4) Yamagoe S, Akasaka T, Uchida T, Hachiya T, Okabe T, Yamakawa Y, Arai T, Mizuno S, Suzuki K. Expression of a neutrophil chemotactic protein LECT2 in human hepatocytes revealed by immunochemical studies using polyclonal and monoclonal antibodies to a recombinant LECT2. Biochem. Biophys. Res. Commun., 237, 116–120 (1997).
• 5) Misu H, Takamura T, Takayama H, Hayashi H, Matsuzawa-Nagata N, Kurita S, Ishikura K, Ando H, Takeshita Y, Ota T, Sakurai M, Yamashita T, Mizukoshi E, Yamashita T, Honda M, Miyamoto K, Kubota T, Kubota N, Kadowaki T, Kim HJ, Lee IK, Minokoshi Y, Saito Y, Takahashi K, Yamada Y, Takakura N, Kaneko S. A liver-derived secretory protein, selenoprotein P, causes insulin resistance. Cell Metab., 12, 483–495 (2010).
• 6) Lan F, Misu H, Chikamoto K, Takayama H, Kikuchi A, Mohri K, Takata N, Hayashi H, Matsuzawa-Nagata N, Takeshita Y, Noda H, Matsumoto Y, Ota T, Nagano T, Nakagen M, Miyamoto K, Takatsuki K, Seo T, Iwayama K, Tokuyama K, Matsugo S, Tang H, Saito Y, Yamagoe S, Kaneko S, Takamura T. LECT2 functions as a hepatokine that links obesity to skeletal muscle insulin resistance. Diabetes, 63, 1649–1664 (2014).
• 7) Hill KE, Wu S, Motley AK, Stevenson TD, Winfrey VP, Capecchi MR, Atkins JF, Burk RF. Production of selenoprotein P (Sepp1) by hepatocytes is central to selenium homeostasis. J. Biol. Chem., 287, 40414–40424 (2012).
• 8) Misu H, Takayama H, Saito Y, Mita Y, Kikuchi A, Ishii KA, Chikamoto K, Kanamori T, Tajima N, Lan F, Takeshita Y, Honda M, Tanaka M, Kato S, Matsuyama N, Yoshioka Y, Iwayama K, Tokuyama K, Akazawa N, Maeda S, Takekoshi K, Matsugo S, Noguchi N, Kaneko S, Takamura T. Deficiency of the hepatokine selenoprotein P increases responsiveness to exercise in mice through upregulation of reactive oxygen species and AMP-activated protein kinase in muscle. Nat. Med., 23, 508–516 (2017).
• 9) Ishikura K, Misu H, Kumazaki M, Takayama H, Matsuzawa-Nagata N, Tajima N, Chikamoto K, Lan F, Ando H, Ota T, Sakurai M, Takeshita Y, Kato K, Fujimura A, Miyamoto K, Saito Y, Kameo S, Okamoto Y, Takuwa Y, Takahashi K, Kidoya H, Takakura N, Kaneko S, Takamura T. Selenoprotein P as a diabetes-associated hepatokine that impairs angiogenesis by inducing VEGF resistance in vascular endothelial cells. Diabetologia, 57, 1968–1976 (2014).
• 10) Misu H, Ishikura K, Kurita S, Takeshita Y, Ota T, Saito Y, Takahashi K, Kaneko S, Takamura T. Inverse correlation between serum levels of selenoprotein P and adiponectin in patients with type 2 diabetes. PLOS ONE, 7, e34952 (2012).
• 11) Speckmann B, Walter PL, Alili L, Reinehr R, Sies H, Klotz LO, Steinbrenner H. Selenoprotein P expression is controlled through interaction of the coactivator PGC-1alpha with FoxO1a and hepatocyte nuclear factor 4alpha transcription factors. Hepatology, 48, 1998–2006 (2008).
• 12) Walter PL, Steinbrenner H, Barthel A, Klotz LO. Stimulation of selenoprotein P promoter activity in hepatoma cells by FoxO1a transcription factor. Biochem. Biophys. Res. Commun., 365, 316–321 (2008).
• 13) Yamagoe S, Yamakawa Y, Matsuo Y, Minowada J, Mizuno S, Suzuki K. Purification and primary amino acid sequence of a novel neutrophil chemotactic factor LECT2. Immunol. Lett., 52, 9–13 (1996).
• 14) Yamagoe S, Mizuno S, Suzuki K. Molecular cloning of human and bovine LECT2 having a neutrophil chemotactic activity and its specific expression in the liver. Biochim. Biophys. Acta, 1396, 105–113 (1998).
• 15) Chikamoto K, Misu H, Takayama H, Kikuchi A, Ishii KA, Lan F, Takata N, Tajima-Shirasaki N, Takeshita Y, Tsugane H, Kaneko S, Matsugo S, Takamura T. Rapid response of the steatosis-sensing hepatokine LECT2 during diet-induced weight cycling in mice. Biochem. Biophys. Res. Commun., 478, 1310–1316 (2016).
• 16) Calanna S, Christensen M, Holst JJ, Laferrère B, Gluud LL, Vilsbøll T, Knop FK. Secretion of glucose-dependent insulinotropic polypeptide in patients with type 2 diabetes: systematic review and meta-analysis of clinical studies. Diabetes Care, 36, 3346–3352 (2013).
• 17) Calanna S, Christensen M, Holst JJ, Laferrère B, Gluud LL, Vilsbøll T, Knop FK. Secretion of glucagon-like peptide-1 in patients with type 2 diabetes mellitus: systematic review and meta-analyses of clinical studies. Diabetologia, 56, 965–972 (2013).
• 18) Ryan AS, Berman DM, Nicklas BJ, Sinha M, Gingerich RL, Meneilly GS, Egan JM, Elahi D. Plasma adiponectin and leptin levels, body composition, and glucose utilization in adult women with wide ranges of age and obesity. Diabetes Care, 26, 2383–2388 (2003).
• 19) Tanaka M, Saito Y, Misu H, Kato S, Kita Y, Takeshita Y, Kanamori T, Nagano T, Nakagen M, Urabe T, Takamura T, Kaneko S, Takahashi K, Matsuyama N. Development of a sol particle homogeneous immunoassay for measuring full-length selenoprotein P in human serum. J. Clin. Lab. Anal., 30, 114–122 (2016).
• 20) Kumakura A, Shikuma J, Ogihara N, Eiki J, Kanazawa M, Notoya Y, Kikuchi M, Odawara M. Effects of celiac superior mesenteric ganglionectomy on glucose homeostasis and hormonal changes during oral glucose tolerance testing in rats. Endocr. J., 60, 525–531 (2013).