Skip to main content
NCBI home page
Journal of Diabetes Investigation logoLink to Journal of Diabetes Investigation
letter
. 2019 Jun 6;11(1):88–95. doi: 10.1111/jdi.13069

Circulating complement‐1q tumor necrosis factor‐α‐related protein isoform 5 levels are low in type 2 diabetes patients and reduced by dapagliflozin

Cheng Zhang 1, Yong Luo 1, Rui Liu 2, Xiaoqiang Li 3, Mengliu Yang 1, Yu Zhang 2, Ling Li 4, Huaming Mou 1, Lian Guo 1, Jing Li 1, Hua Liu 5, Gangyi Yang 1,2, Xianxiang Zhang 1,✉
PMCID: PMC6944827  PMID: 31070007

Abstract

Aims/Introduction

As a member of the tumor necrosis factor‐α‐related protein family, complement‐1q tumor necrosis factor‐α‐related protein isoform 5 (CTRP5) has been found to be associated with obesity and insulin resistance (IR). Previous studies in humans and animals have reported contradictory results related to the association between CTRP5 and IR. The purpose of the present study was to explore the relationship between CTRP5 and IR through a cross‐sectional study and drug intervention study of type 2 diabetes patients.

Materials and Methods

A cross‐sectional study was carried out with 118 newly diagnosed patients with type 2 diabetes and 116 healthy adults. In an interventional study, 78 individuals with newly diagnosed type 2 diabetes received sodium–glucose cotransporter 2 inhibitor (dapagliflozin) treatment for 3 months. Circulating CTRP5 concentrations were measured by enzyme‐linked immunosorbent assay.

Results

Serum CTRP5 concentrations were markedly reduced in patients with type 2 diabetes when compared with those of healthy individuals (P < 0.01). When considering the study population as a whole, individuals with IR (homeostasis model of assessment of IR ≥2.78) had lower CTRP5 concentrations than the individuals without IR (homeostasis model of assessment of IR <2.78; P < 0.01). Serum CTRP5 negatively correlated with age, body mass index, waist‐to‐hip ratio, Systolic blood pressure, triglyceride, total cholesterol, glycated hemoglobin, fasting blood glucose, 2‐h blood glucose, fasting insulin and homeostasis model of assessment of IR. After 12 weeks of sodium–glucose cotransporter 2 inhibitor treatment, serum CTRP5 levels in type 2 diabetes patients were significantly reduced accompanied with ameliorated glycometabolism and IR compared with before treatment (P < 0.01).

Conclusions

CTRP5 is likely a marker for type 2 diabetes in humans.

Keywords: Complement‐1q tumor necrosis factor‐α‐related protein isoform 5, Sodium–glucose cotransporter 2 inhibitor , Type 2 diabetes mellitus

The present study found that complement‐1q tumor necrosis factor‐α‐related protein isoform 5 (CTRP5) levels were reduced in type 2 diabetes patients and that plasma CTRP5 levels were related to insulin resistance. Furthermore, we found that plasma CTRP5 concentrations further decreased after dapaglifozin treatment, which showed that CTRP5 might play an important role in the development of type 2 diabetes.

graphic file with name JDI-11-88-g003.jpg

Introduction

The complement‐1q tumor necrosis factor‐α (TNF‐α)‐related protein family (CTRPs) includes 15 members that have similar structure and function to adiponectin (Adipoq)1. CTRPs are widely expressed in various tissues in animals and humans, and have important metabolic functions2, 3, 4, 5, 6, 7, 8. Because Adipoq is relative to energy homeostasis and insulin sensitivity in vivo, it is important to investigate the physiological function of each member of the CTRPs family and the changes in circulating levels in an insulin‐resistant state. Previous studies have shown that members of the CTRPs family5, 8, 9, 10 might be related to energy equilibrium and insulin resistance (IR). In addition, in individuals with obesity, metabolic syndrome and type 2 diabetes, plasma levels of some CTRPs, such as CTRP9, CTRP1and CTRP3, were found to increase or decrease11, 12, 13, 14. In mice, CTRP1, CTRP3 and CTRP9 have been found to be related to the onset of IR, obesity and hepatic steatosis3, 7.

CTRP5 is a 25 kDa secretory glycoprotein encoded by C1QTNF5. This cytokine is mainly expressed in adipose tissue, skeletal muscle, basal lamina, retinal epithelium and so on15, 16, 17. The CTRP5 deoxyribonucleic acid sequence is highly conserved and has three conserved domains: a signal peptide, a collagen and C1q domain17. Ten years ago, a genome‐wide association study reported that a polymorphism of CTRP5 gene was associated with the development of metabolic syndrome in a Japanese patient18. An increasing CTRP5 expression was found in subcutaneous fat in obese individuals using microarray analysis16. Park et al. found that serum CTRP5 levels were increased in IR‐related rat and mice, such as db/db mice and OLETF rats15. Furthermore, CTRP5 increased glucose uptake by increasing the activity of AMPK and promoted the translocation of glucose transporter‐4 in the cell membrane. In the in vitro study, CTRP5 was also found to increase the phosphorylation of acetyl coenzyme A carboxylase and stimulate the oxidation of fatty acids15. In the other study, CTRP5 treatment led to the inhibition of Adipoq release and secretion in fat cells19.

In recent years, it has been reported that insulin‐induced Akt phosphorylation (a key component of insulin signals) in fat and muscle tissues is inhibited by the treatment of CTRP5 protein20. Based on these findings, CTRP5, as a new secreted protein, might be involved in the incidence of IR and type 2 diabetes. However, data are lacking on the correlation between CTRP5 and type 2 diabetes in humans.

Sodium–glucose cotransporter 2 inhibitor (SGLT2i) is a newly discovered hypoglycemic drug. Recently, SGLT2i has been found to reduce weight gain by a high‐fat diet, increase lipolysis and fat browning, elevate the circulating levels of cytokines, such as fibroblast growth factor 21, and improve IR in vivo 21.

In the current study, we hypothesized that IR could alter circulating levels of CTRP5, and circulating CTRP5 might be regulated by dapagliflozin, a SGLT2i. Therefore, the objectives of the present study study were as follows: (i) to determine circulating levels of CTRP5 in newly diagnosed type 2 diabetes patients and healthy participants; (ii) to investigate the relationship between circulating CTRP5 and IR; (iii) to observe the effect of SGLT2i treatment on circulating CTRP5 in type 2 diabetes patients.

Methods

Study population

A total of 234 Chinese Han individuals participated in the current study, including 118 newly diagnosed type 2 diabetes patients and 116 healthy individuals, 78 type 2 diabetes patients received SGLT2i treatment, a detailed flow diagram is shown in Figure S1. The diagnosis of type 2 diabetes was based on a 75‐g oral glucose tolerance test according to the diagnostic criteria from the American Diabetes Association22. All patients were not treated with any antidiabetic agents, insulin, diet control or physical exercise. Type 1 diabetes patients and type 2 diabetes patients with acute and chronic complications, hypertension, liver cirrhosis, hepatic and renal failure, congestive heart failure or other major diseases were excluded from this study. Age‐ and sex‐matched healthy individuals without any clinical evidence of diseases (body mass index [BMI] ranged 18–24 kg/m2) were recruited from the community or schools through advertisement or routine medical checkup, and were used as the controls. The oral glucose tolerance test was carried out for the control individuals to exclude type 2 diabetes and impaired glucose tolerance, and individuals with a family history of type 2 diabetes were also excluded. None of these individuals used any medications that alter glucose and lipid metabolism. All individuals who participated the present study were asked to sign informed consent before the start of the experiment. This study was approved by the ethics committee of Chongqing Medical University in accordance with the World Medical Association Declaration of Helsinki23.

Measurements of anthropometric, biochemical and cytokine parameters

Bodyweight (kilograms) / height squared was used to calculate BMI. The waist‐to‐hip ratio (WHR) was calculated by the measurements of waist and hip circumferences. The percentage of fat in vivo was measured by bioelectrical impedance (BIA‐101; RJL Systems, Shenzhen, China). The equation used to calculate homeostasis model assessment of IR (HOMA‐IR) was fasting insulin (mU/L) × fasting blood glucose (FBG; mmol/L) / 22.524. The 75th percentile value of HOMA‐IR from the healthy individuals was selected as the cut‐off point to define IR25. Therefore, the IR was defined as HOMA‐IR ≥2.78. After a 10‐h overnight fast, blood samples were collected, and glucose and glycated hemoglobin (HbA1c) were immediately measured by the glucose‐oxidase method and anion‐exchange high‐performance liquid chromatography. Serum was separated and was stored at –80°C for the measurement of biochemical and cytokine parameters.

Human CTRP5 (Cat. #) enzyme‐linked immunosorbent assay kit was purchased from Aviscera Bioscience Inc. (CA, USA) with the following measurement index: intra‐ and interassay coefficients of variance were 6–8% and 8–12%, respectively. Linearity was in the range of 1.56–100 μg/L. The limit of detection for this assay was 0.5 μg/L. Insulin was measured with chemiluminescence. Blood fat, free fatty acids, alanine transaminase, aspartate transaminase and serum creatinine were measured with commercial kits (Roche, Shanghai, China), as previously described26.

Interventional study

A total of 78 patients with type 2 diabetes, including 38 women and 40 men, attended this self‐controlled clinical study of SGLT2i treatment without a placebo‐controlled group. The inclusion criteria included age 40–70 years; BMI of 25–35 kg/m2, and HbA1c levels between 6.5 and 9.0%. Patients with type 1 diabetes, ketoacidosis, a history of hypoglycemia unawareness, malignant disease or any other diseases were excluded. These patients were treated with dapaglifozin (AstraZeneca, Jiangsu, China) 10 mg once daily before breakfast for 12 weeks. All patients were asked to maintain their former lifestyle and dietary habits during the study. Patients with three FBG readings >14 mmol/L were withdrawn from the study to prevent acute complications. Blood samples were collected at 08.00 h on day 1 before treatment and on day 2 of the last treatment for the measurements of biochemical parameters and CTRP5. The study was approved by the ethics committee of Chongqing Medical University. All participants provided written informed consent.

Statistical analysis

The sample size is calculated as follows. N = [Zα/2σ/εμ]2 (σ, standard; μ, mean; Zα/2 = 1.96, α = 0.05, ε = 4%). The normal distribution of variables was evaluated by the Kolmogorov–Smirnov test. Data are the mean ± standard deviation or median (interquartile range). Differences between groups were assessed by anova, an unpaired t‐test or a paired t‐test. Spearman's correlation analysis was used to examine the association of CTRP5 levels with other parameters. Multiple stepwise regression analysis was used to investigate the relationship between CTRP5 and the other variables, with CTRP5 as a dependent variable. Multivariate logistic regression analysis was used to investigate the association of CTRP5 with type 2 diabetes. Row mean scores and Cochran–Armitage trend test of the impact of plasma CTRP5 level on type 2 diabetes were carried out. Receiver operating characteristic (ROC) curve analyses were used to evaluate the performance of CTRP5 in the diagnosis of type 2 diabetes by calculating the area under ROC curve (AUC). The maximum sensitivity and specificity of CTRP5 to predict type 2 diabetes were determined by the Youden Index. The comparison of the AUC was carried out by a P < 0.05. The greater AUC represents the higher diagnostic value for CTRP5 to differentiate the diseases. All data were based on two‐sided tests. All analyses were carried out by statistical software SAS version 22.0 (SAS Institute, Cary, NC, USA). P < 0.05 was considered statistically significant.

Results

Main clinical features and CTRP5 levels in study populations

The anthropometric, biochemical and cytokine parameters in study participants are shown in Table 1. Type 2 diabetes patients had higher BMI, WHR, systolic blood pressure, FBG, 2‐h blood glucose after glucose overload (2 h‐BG), HOMA‐IR, HbA1c, triglyceride and total cholesterol than controls (P < 0.01 or 0.05). In the current study, fasting CTRP5 concentrations were measured in 116 healthy adults (aged 40–70 years). Figure S2a shows the distribution of circulating CTRP5 concentrations in these participants. In healthy participants, the range of CTRP5 concentration was 85.11–235.16 μg/L. Circulating levels of CTRP5 were between 90.74–228.21 μg/L for 95% healthy participants. Importantly, circulating levels of CTRP5 were markedly lower in type 2 diabetes patients than in the controls (P < 0.01; Figure 1a), and the reduction of CTRP5 in type 2 diabetes patients remained significant after age, sex and BMI adjustment (P < 0.01; Table 1). However, there was no difference in serum CTRP5 levels between men and women (118.05 ± 34.87 vs 125.82 ± 35.05 μg/L). In addition, circulating levels of CTRP5 were also no different between overweight/obese (BMI ≥25 kg/m2) and lean individuals (BMI <25 kg/m2; 118.51 ± 38.36 vs 125.13 ± 33.35 μg/L). Intriguingly, individuals with IR (HOMA‐IR ≥2.78) had lower CTRP5 concentrations than individuals without IR (HOMA‐IR <2.78; (110.88 ± 31.97 vs 140.07 ± 32.25 μg/L, P < 0.01; Figure S2b).

Table 1.

Main clinical features and circulating complement‐1q tumor necrosis factor‐α‐related protein isoform 5 levels in the study participants

Variables NGT (n = 116) T2DM (n = 118) P
Age (years) 54 ± 12.7 56 ± 9.1 NS
BMI (kg/m2) 22.97 ± 2.35 24.87 ± 2.99 <0.01
FAT% (%) 28.45 ± 5.33 29.87 ± 6.24 NS
WHR 0.88 ± 0.09 0.92 ± 0.05 <0.01
SBP (mmHg) 119.23 ± 14.13 127.68 ± 11.24 <0.01
DBP (mmHg) 76.44 ± 10.19 76.25 ± 8.71 NS
FBG (mmol/L) 5.28 ± 0.42 8.66 ± 1.68 <0.01
2 h‐BG (mmol/L) 6.16 ± 0.99 14.41 ± 2.84 <0.01
FIns (mU/L) 8.98 ± 3.63 14.03 ± 5.54 <0.01
HOMA‐IR 2.01 (1.42–2.78) 5.21 (3.45–7.36) <0.01
HbA1c (%) 5.45 ± 0.37 8.30 ± 0.95 < 0.01
TG (mmol/L) 1.29 ± 0.53 1.95 ± 0.83 <0.01
TC (mmol/L) 4.74 ± 0.90 4.97 ± 0.85 <0.05
HDL (mmol/L) 1.21 ± 0.19 1.10 ± 0.18 <0.01
LDL (mmol/L) 2.74 ± 0.80 2.76 ± 0.77 NS
FFA (mmol/L) 0.44 ± 0.14 0.46 ± 0.13 NS
CTRP5 (μg/L) 142.72 ± 34.24 105.59 ± 25.39 <0.01
CTRP5 (μg/L)† 140.31 ± 3.08 106.58 ± 2.88 <0.01
Open in a new tab

Data are mean ± standard deviation or median (interquartile range).

†

Data are mean ± standard error, adjustment for age, sex and body mass index (BMI).

2 h‐BG, 2‐h blood glucose after glucose overload; CTRP5, complement‐1q tumor necrosis factor‐α‐related protein isoform 5; DBP, diastolic blood pressure; FAT%, the percentage of fat in vivo; FBG, fasting blood glucose; FFA, free fatty acid; FIns, fasting insulin; HbA1c, glycated hemoglobin; HDL‐C, high‐density lipoprotein cholesterol; HOMA‐IR, homeostasis model assessment of insulin resistance; LDL‐C, low‐density lipoprotein cholesterol; NGT, normal glucose tolerance; NS, not significant; SBP, systolic blood pressure; T2DM, type 2 diabetes mellitus; TC, total cholesterol; TG, triglyeride; WHR, waist‐to‐hip ratio.

Figure 1.

Figure 1

Open in a new tab

Concentrations of circulating complement‐1q tumor necrosis factor‐α‐related protein isoform 5 (CTRP5) in the study population. (a) Circulating CTRP5 levels in newly diagnosed type 2 diabetes and healthy participants. (b) Circulating CTRP5 levels pre‐ and post‐treatment with SGLT2i in type 2 diabetes patients. Data are the mean ± standard deviation. **P < 0.01 versus normal glucose tolerance (NGT) or pre‐treatment. T2DM, type 2 diabetes.

Correlation of CTRP5 with clinical and biochemical parameters

Next, we analyzed the association of CTRP5 with other parameters in the entire study population. We found that the CTRP5 concentrations of circulation correlated negatively with age, BMI, WHR, systolic blood pressure, triglyceride, total cholesterol, HbA1c, FBG, 2 h‐BG, fasting insulin and HOMA‐IR (Table S1). In multivariate regression analyses, the results showed that age and HOMA‐IR were two independent factors associated with circulating CTRP5, but there was no relationship between CTRP5 and other variables (Table S1). The multiple regression equation is YCTRP5 = 189.63 – 7.203XHbA1c – 32.749XHOMA‐IR.

Next, stepwise regression analyses were used to investigate the affecting factors of circulating CTRP5. When all study participants were included for analysis, the results showed that the main determinants of CTRP5 were HOMA‐IR and HbA1c (Figure S1c).

Association of CTRP5 levels with the prevalence of type 2 diabetes

Multivariate logistic regression showed that CTRP5 levels in the circulation also correlated with the occurrence of type 2 diabetes, even after controlling for clinical and biochemical parameters (Table S2). Furthermore, CTRP5 levels in the circulation presented a linear trend and were associated with type 2 diabetes (Table S3). When circulating CTRP5 was divided into three tertiles in all study participants (tertile 1, <105.01 μg/L; tertile 2, 105.01–130.41 μg/L; tertile 3, >130.41 μg/L), the prevalences of developing type 2 diabetes were 78.37% for tertile 1, 62.16 for tertile 2 and 18.91% for tertile 3 (vs tertile 1, P < 0.01 or 0.05; Figure S2d). Finally, to predict the odds of developing type 2 diabetes, we carried out the analyses of the ROC curves. As shown in Figure 2, the AUC was 0.82 for type 2 diabetes (AUCT2DM; sensitivity 75.0%, specificity 77.1%; Figure 2). The cut‐off value of CTRP5 for predicting type 2 diabetes was 117 μg/L.

Figure 2.

Figure 2

Open in a new tab

Receiver operating characteristic (ROC) curve analyses were carried out for the prediction of type 2 diabetes according to the complement‐1q tumor necrosis factor‐α‐related protein isoform 5 (CTRP5) levels. AUC, area under the receiver operating characteristic curve; T2DM, type 2 diabetes.

Effect of SGLTi treatment on CTRP5 levels in type 2 diabetes patients

As shown in Table S4, dapaglifozin administration for 3 months in type 2 diabetes patients led to a significant reduction in BMI, WHR, the percentage of body fat, blood pressure, HbA1c, FBG, 2 h‐BG, fasting insulin and HOMA‐IR (P < 0.01). However, after treatment, serum alanine transaminase, aspartate transaminase, serum creatinine, triglyceride, total cholesterol, high‐density lipoprotein cholesterol, low‐density lipoprotein cholesterol levels and free fatty acid showed no change in these patients (Table S4). Of note, CTRP5 levels in the circulation were significantly reduced after SGLT2i treatment (from 99.72 ± 19.31 to 67.49 ± 33.02 μg/L, P < 0.01; Figure 1b).

Discussion

The present study shows that circulating CTRP5 concentrations are markedly lower in newly diagnosed type 2 diabetes patients compared with controls. This result is analogous to the low Adipoq (a CTRP5 paralog) levels in type 2 diabetes patients, which have been widely acknowledged to be related to diabetes27. This finding is consistent with a recent study that reported the low levels of circulating CTRP5 in type 2 diabetes patients28. However, sample sizes in the study by Yan et al. were relatively small, and patients were treated with antidiabetic agents, insulin or other medications. In addition, patients with different disease durations and complications were included28. However, in a study of mice, Park et al. reported that obese and diabetic mice had higher circulating CTRP5 levels15 than lean mice, whereas another study found that CTRP5 levels were not changed in ob/ob mice20. The discrepancy between mice and human studies is unclear, and might be due to the following reasons: (i) CTRP5 might play different roles in humans and mice, just as resistin plays different roles in humans and mice29; and (ii) type 2 diabetes in humans is a disease associated with multiple genes and environmental factors, whereas ob/ob and db/db mice are only caused by leptin deficiency. Therefore, the phenotype might be different because of the different genetic qualities.

Furthermore, in healthy individuals, circulating CTRP5 concentrations in the present study are lower than that reported by Emamgholipour et al.30, but higher than that reported by Schwartze et al.1 The discrepancy might be attributable to differences of the ethnic cohort, sample sizes, age of participants and/or assay method. Importantly, in the present study, the participants were age‐ and sex‐matched, and a drug‐naive population. However, follow‐up studies are required to elucidate this issue.

Recently, CTRP5 has been found as a mediator of obesity, IR and metabolic syndrome 31. Thus, we also analyzed the association of circulating CTRP5 and other metabolic markers. We found that CTRP5 correlated negatively with HbA1c, FBG and 2 h‐BG, suggesting a link between CTRP5 and glucose metabolism, and a possible role for CTRP5 in the development of diabetes. In previous studies, it has been reported that some members of the CTRP5 family are involved in the regulation of glucose and fatty acid metabolism2, 4, 5, 10, 32, 33. Therefore, it is possible that CTRP5 serves as a regulator of glycometabolism.

Here, we also showed that CTRP5 concentrations were reduced in IR and type 2 diabetes states, and correlated negatively with HOMA‐IR and HbA1c; ROC curves analysis also showed that circulating CTRP5 has a moderate effect to predict type 2 diabetes, suggesting that CTRP5 is associated with IR and type 2 diabetes. The result is consistent with the report by Emamgholipour et al.30, but is inconsistent with that of Choi et al.33, who found that there is no relationship between circulating CTRP5 and IR. In a high‐fat diet‐induced IR mice study, CTRP5‐deficient mice showed attenuated hepatic steatosis and improved insulin action, suggesting a positive relationship between CTRP5 and IR20. In addition, IR is also affected by many other factors, including ethnicity, and genetic and nutritional status. Therefore, more studies of different populations are necessary to explore the association of CTRP5 with IR.

SGLT2i is a new class of antidiabetic agents with an insulin‐independent mechanism34. SGLT2i is a transport protein for sodium–glucose cotransport in the kidney proximal tubule35, 36, 37. Therefore, SGLT2i, as a novel antidiabetic agent has two mechanisms that decrease blood glucose levels without increasing insulin secretion38. It also leads to weight loss through osmotic diuresis39, 40. Recently, in a mice study, SGLT2i was found to improve IR in vivo 21. In a previous study, we also reported that dapaglifozin treatment of type 2 diabetes significantly raised plasma zinc‐alpha‐2‐glycoprotein and Adipoq (two insulin sensitizer) concentrations41. In addition, in an in vitro study, dapaglifozin treatment increased zinc‐alpha‐2‐glycoprotein expression and secretion in HepG2 cells, whereas peroxisome proliferator‐activated receptor‐γ inhibitor co‐treatment blocked the effects of dapaglifozin41. The present study showed that CTRP5 was closely correlated with IR. We thus investigated the impact of 12 weeks of dapaglifozin therapy on CTRP5 concentrations in type 2 diabetes patients. Consistent with previous reports, we showed that dapaglifozin reduced the HbA1c, FBG, 2 h‐BG and insulin levels, and HOMA‐IR, indicating improved glucose metabolism and increased insulin sensitivity in tissues. After SGLT2i administration for 12 weeks, circulating CTRP5 levels significantly decreased in type 2 diabetes patients, despite improving IR. Therefore, this result suggests that CTRP5 can only be used for the diagnosis of newly diagnosed type 2 diabetes patients, but not for the evaluation of the therapeutic effect. This fact might limit its possible clinical application value. We speculate that there are several explanations for this finding: (i) SGLT2i might inhibit CTRP5 expression and secretion in peripheral tissues; (ii) SGLT2i might promote the degradation or elimination of CTRP5; or (iii) SGLT2i treatment might increase other cytokines in circulation, such as Adipoq and fibroblast growth factor 2121, which inhibited CTRP5 secretion and release into circulation. In addition, SGLT2i improves the IR state, thereby reducing the compensatory secretion of CTRP5 under IR. However, the precise mechanism(s) by which SGLT2i increases insulin sensitivity and decreases circulating CTRP5 levels remains unclear.

Because the mechanism of the role of SGLT2i is different from other hypoglycemic drugs, it is not clear whether other drugs can lead to the decrease of circulating CTRP5 levels. Although bivariate correlation analyses showed that serum CTRP5 is negatively correlated with HOMA‐IR and blood glucose level, the decrease of HOMA‐IR and blood glucose after SGLT2i treatment indicates that these factors could not directly cause the increase of circulating CTRP5. Therefore, in diabetes patients, there might be other causes leading to decreased CTRP5 expression, such as lipid metabolism disorders or changes in other adipokines. Further in‐depth studies are necessary.

The present study had some limitations. First, the nature of a cross‐sectional study is not allowed to decide causation. Second, the interventional study was an open‐label, self‐controlled trial without a placebo‐controlled group, thus weakening the stringency of the results. Third, individuals recruited in the study came from routine medical checkups, so the participants did not fully represent the overall situation of type 2 diabetes and a healthy population. Therefore, a selective bias is noteworthy. Fourth, this study was carried out in a Chinese population. Therefore, the results might not apply to other ethnicities. Fifth, circulating CTRP5 concentrations were determined by a single measurement, and it might not reflect the alterations of CTRP5 from prediabetes to diabetes. Thus, it is important to measure CTRP5 levels at different stages of IR or type 2 diabetes. Nevertheless, data from the present study sufficiently show the relationship among CTRP5, IR and type 2 diabetes, and suggest that alterations in circulating CTRP5 levels might play a role in the development of IR and diabetes.

In conclusion, as a primary outcome of the present study, we showed that CTRP5 levels in circulation were markedly decreased in newly diagnosed type 2 diabetes patients and correlated with IR. As a secondary outcome, we found that after 12 weeks of SGLT2i treatment, serum CTRP5 levels in type 2 diabetes patients were significantly reduced accompanied with improved IR. Therefore, we conclude that CTRP5 is likely a marker for type 2 diabetes in humans.

Disclosure

The authors declare no conflict of interest.

Supporting information

Figure S1 Flow diagram.

Figure S2 (a) Distribution of circulating concentration of complement‐1q tumor necrosis factor‐α‐related protein isoform 5 (CTRP5) in 116 healthy individuals. (b) Circulating CTRP5 levels according to the homeostasis model of assessment of insulin resistance (HOMA‐IR). (c) All factors and stepwise multiple regression analyses of the circulating CTRP5 in the entire study population. The circles correspond to the regression coefficients (β) and the error bars indicate the 95% confidence interval of β. R 2, coefficient of determination. (d) Prevalence of elevated type 2 diabetes in different quartiles of CTRP5.

Table S1 Linear regression analysis of variables associated with circulating complement‐1q tumor necrosis factor‐α‐related protein isoform 5 levels in the study population.

Table S2 Association of circulating complement‐1q tumor necrosis factor‐α‐related protein isoform 5 with type 2 diabetes in fully adjusted models.

Table S3 Row mean scores and Cochran–Armitage trend test of the impact of plasma complement‐1q tumor necrosis factor‐α‐related protein isoform 5 level on type 2 diabetes.

Table S4 Clinical characteristics pre‐ and post‐treatment with dapaglifozin in type 2 diabetes patients.

Click here for additional data file. (3.9MB, docx)

Acknowledgments

The authors thank the patients and staff who participated in this study. This work was supported by research grants from the National Natural Science Foundation of China (81800755) to MY; and Chongqing Health and Family Planning Committee and Chongqing Health Science and Technology Committee Combined Project (2018QNXM029) to CZ.

J Diabetes Investig 2020; 11: 88–95

Clinical Trial Registry ClinicalTrials.gov ChiCTR‐OCC‐11001422

References

  • 1. Schwartze JT, Landgraf K, Spielau U, et al Adipocyte C1QTNF5 expression is BMI‐dependently related to early adipose tissue dysfunction and systemic CTRP5 serum levels in obese children. Int J Obes 2017; 41: 955–963. [DOI] [PubMed] [Google Scholar]
  • 2. Peterson JM, Aja S, Wei Z, et al C1q/TNF‐related protein‐1 (CTRP1) enhances fatty acid oxidation via AMPK activation and ACC inhibition. J Biol Chem 2012; 287: 1576–1587. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 3. Peterson JM, Seldin MM, Wei Z, et al CTRP3 attenuates diet‐induced hepatic steatosis by regulating triglyceride metabolism. Am J Physiol Gastro intest Liver Physiol 2013; 305: G214–G224. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 4. Peterson JM, Wei Z, Seldin MM, et al CTRP9 transgenic mice are protected from diet‐induced obesity and metabolic dysfunction. Am J Physiol Regul Integr Comp Physiol 2013; 305: R522–R533. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 5. Peterson JM, Wei Z, Wong GW. C1q/TNF‐related protein‐3 (CTRP3), a novel adipokine that regulates hepatic glucose output. J Biol Chem 2010; 285: 39691–39701. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 6. Seldin MM, Lei X, Tan SY, et al Skeletal muscle‐derived myonectin activates the mTOR pathway to suppress autophagy in liver. J Biol Chem 2013; 289: 36073–36082. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 7. Wei Z, Lei X, Petersen PS, et al Targeted deletion of C1q/TNF‐related protein 9 (CTRP9) increases food intake, decreases insulin sensitivity, and promotes hepatic steatosis in mice. Am J Physiol Endocrinol Metab 2014; 306: E779–E790. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 8. Wong GW, Krawczyk SA, Kitidis‐Mitrokostas C, et al Identification and characterization of CTRP9, a novel secreted glycoprotein, from adipose tissue that reduces serum glucose in mice and forms heterotrimers with adiponectin. FASEB J 2009; 23: 241–258. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 9. Kopp A, Bala M, Weigert J, et al Effects of the new adiponectin paralogous protein CTRP‐3 and of LPS on cytokine release from monocytes of patients with type 2 diabetes mellitus. Cytokine 2011; 49: 51–57. [DOI] [PubMed] [Google Scholar]
  • 10. Wei Z, Peterson JM, Lei X, et al C1q/TNF‐related protein‐12 (CTRP12), a novel adipokine that improves insulin sensitivity and glycemic control in mouse models of obesity and diabetes. J Biol Chem 2012; 287: 10301–10315. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 11. Chalupova L, Zakovska A, Adamcova K. Development of a novel enzyme‐linked immuno‐sorbent assay (ELISA) for measurement of serum CTRP1: a pilot study: measurement of serum CTRP1 in healthy donors and patients with metabolic syndrome. Clin Bio Chem 2013; 46: 73–78. [DOI] [PubMed] [Google Scholar]
  • 12. Choi KM, Hwang SY, Hong HC, et al C1q/TNF‐relatedprotein‐3 (CTRP‐3) and pigment epithelium‐derived factor (PEDF) concentrations in patients with type 2 diabetes and metabolic syndrome. Diabetes 2012; 61: 2932–2936. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 13. Hwang YC, Woo OHS, Park SW, et al Association of serum C1q/TNF‐related protein‐9 (CTRP9) concentration with visceral adiposity and metabolic syndromein humans. Int J Obes 2014; 38: 1207–1212. [DOI] [PubMed] [Google Scholar]
  • 14. Kim KY, Kim HY, Kim JH, et al Tumor necrosis factor‐alpha and interleukin‐1beta increases CTRP1 expression in adipose tissue. FEBS Lett 2006; 580: 3953–3960. [DOI] [PubMed] [Google Scholar]
  • 15. Park SY, Choi JH, Ryu HS, et al C1q tumor necrosis factor alpha‐related protein isoform 5 is increased in mitochondrial DNA‐depleted myocytes and activates AMP‐activated protein kinase. J Biol Chem 2009; 284: 27780–27789. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 16. Lee YH, Nair S, Rousseau E, et al Microarray profiling of isolated abdominal subcutaneous adipocytes from obese vs nonobese Pima Indians: increased expression of inflammation‐related genes. Diabetologia 2005; 48: 1776–1783. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 17. Mandal MN, Vasireddy V, Reddy GB, et al CTRP5 is a membrane‐associated and secretory protein in the RPE and ciliary body and the S163R mutation of CTRP5 impairs its secretion. Invest Opthalmol Vis Sci 2006; 47: 5505–5513. [DOI] [PubMed] [Google Scholar]
  • 18. Yamada Y, Ichihara S, Kato K, et al Genetic risk formetabolic syndrome: examination of candidate gene polymorphisms related to lipid metabolism in Japanese people. J Med Genet 2008; 45: 22–28. [DOI] [PubMed] [Google Scholar]
  • 19. Schmid A, Kopp A, Aslanidis C, et al Regulation and function of C1Q/TNF‐related protein‐5 (CTRP‐5) in the context of adipocyte biology. Exp Clin Endocrinol Diabetes 2013; 121: 310–317. [DOI] [PubMed] [Google Scholar]
  • 20. Lei X, Rodriguez S, Petersen PS, et al Loss of CTRP5 improves insulin action and hepatic steatosis. Am J Physiol Endocrinol Metab 2016; 310: E1036–E1052. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 21. Xu L, Nagata N, Nagashimada M, et al SGLT2 inhibition by empagliflozin promotes fat utilization and browning and attenuates inflammation and insulin resistance by polarizing m2 macrophages in diet‐induced obese mice. EBio Med 2017; 20: 137–149. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 22. American Diabetes Association . Diagnosis and classification of diabetes mellitus. Diabetes Care 2011; 34: S62–S69. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 23. World Medical Association . World medical association declaration of Helsinki ethical principles for medical research involving human subjects. JAMA 2013; 310: 2191–2194. [DOI] [PubMed] [Google Scholar]
  • 24. Matthews DR, Hosker JP, Rudenski AS, et al Homeostasis model assessment: insulin resistance and beta‐cell function from fasting plasma glucose and insulin concentrations in man. Diabetologia 1985; 28: 412–419. [DOI] [PubMed] [Google Scholar]
  • 25. Ascaso JF, Pardo S, Real JT, et al Diagnosing insulin resistance by simple quantitative methods in subjects with normal glucose metabolism. Diabetes Care 2003; 26: 3320–3325. [DOI] [PubMed] [Google Scholar]
  • 26. Luo Y, Li L, Xu X, et al Decreased circulating BMP‐9 levels in patients with Type 2 diabetes is a signature of insulin resistance. Clin Sci 2017; 131: 239–246. [DOI] [PubMed] [Google Scholar]
  • 27. hehzad A, Iqbal W, Shehzad O, et al Adiponectin: regulation of its production and its role in human diseases. Hormones 2012; 11: 8–20. [DOI] [PubMed] [Google Scholar]
  • 28. Yan Z, Zhao J, Gan L, et al CTRP3 is a novel biomarker for diabetic retinopathy and inhibits HGHL‐induced VCAM‐1 expression in an AMPK‐dependent manner. PLoS ONE 2017; 12: e0178253. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 29. Filková M, Haluzík M, Gay S, et al The role of resistin as a regulator of inflammation: implications for various human pathologies. Clin Immunol 2009; 133: 157–170. [DOI] [PubMed] [Google Scholar]
  • 30. Emamgholipour S, Moradi N, Beigy M, et al The association of circulating levels of complement‐C1qTNF‐related protein5 (CTRP5) with nonalcoholic fatty liver disease and type2 diabetes: a case‐control study. Diabetol Metab Syndr 2015; 7: 108. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 31. Schaffler A, Buechler C. CTRP family: linking immunity to metabolism. Trends Endocrinol Metab 2012; 23: 194–204. [DOI] [PubMed] [Google Scholar]
  • 32. Enomoto T, Ohashi K, Shibata R, et al Adipolin/C1qdc2/CTRP12 functions as an adipokine that improves glucose metabolism. J Biol Chem 2011; 286: 34552–34558. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 33. Choi HY, Park JW, Lee N, et al Effects of a combined aerobic and resistance exercise program on C1q/TNF‐related protein‐3(CTRP‐3) and CTRP‐5 levels. Diabetes Care 2013; 36: 3321–3327. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 34. List JF, Whaley JM. Glucose dynamics and mechanistic implications of SGLT2 inhibitors in animals and humans. Kidney Int Suppl 2011; 120: S20–S27. [DOI] [PubMed] [Google Scholar]
  • 35. Wright EM, Hirayama BA, Loo DF. Active sugar transport in health and disease. J Intern Med 2007; 261: 32–43. [DOI] [PubMed] [Google Scholar]
  • 36. Kanai Y, Lee WS, You G, et al The human kidney low affinity Na+/glucose co‐transporter SGLT2. Delineation of the major renal reabsorptive mechanism for D‐glucose. J Clin Invest 1994; 93: 397–404. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 37. Hediger MA, Rhoads DB. Molecular physiology of sodium‐glucose cotransporters. Physiol Rev 1994; 74: 993–1026. [DOI] [PubMed] [Google Scholar]
  • 38. Idris I, Fau‐Donnelly R, Donnelly R. Sodium‐glucose co‐transporter‐2 inhibitors: an emerging new class of oral anti‐diabetic drug. Diabetes Obes Metab 2009; 11: 79–88. [DOI] [PubMed] [Google Scholar]
  • 39. Komoroski B, Vachharajani N, Feng Y, et al Dapagliflozin, a novel, selective SGLT2 inhibitor, improved glycemic control over 2 weeks in patients with type2 diabetes mellitus. Clin Pharmacol Ther 2009; 85: 513–519. [DOI] [PubMed] [Google Scholar]
  • 40. de Wit HM, Te Groen M, Rovers MM, et al The placebo response of injectable GLP‐1 receptor agonists vs oral DPP‐4 inhibitors and SGLT‐2 inhibitors: a systematic review and meta‐analysis. Br J Clin Pharmacol 2016; 82: 301–314. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 41. Liao X, Wang X, Li H, et al Sodium‐glucose co‐transporter 2 (SGLT2) inhibitor increases circulating zinc‐ alpha2‐glycoprotein levels in patients with type 2 diabetes. Sci Rep 2016; 6: 32887. [DOI] [PMC free article] [PubMed] [Google Scholar]

Associated Data

This section collects any data citations, data availability statements, or supplementary materials included in this article.

Supplementary Materials

Figure S1 Flow diagram.

Figure S2 (a) Distribution of circulating concentration of complement‐1q tumor necrosis factor‐α‐related protein isoform 5 (CTRP5) in 116 healthy individuals. (b) Circulating CTRP5 levels according to the homeostasis model of assessment of insulin resistance (HOMA‐IR). (c) All factors and stepwise multiple regression analyses of the circulating CTRP5 in the entire study population. The circles correspond to the regression coefficients (β) and the error bars indicate the 95% confidence interval of β. R 2, coefficient of determination. (d) Prevalence of elevated type 2 diabetes in different quartiles of CTRP5.

Table S1 Linear regression analysis of variables associated with circulating complement‐1q tumor necrosis factor‐α‐related protein isoform 5 levels in the study population.

Table S2 Association of circulating complement‐1q tumor necrosis factor‐α‐related protein isoform 5 with type 2 diabetes in fully adjusted models.

Table S3 Row mean scores and Cochran–Armitage trend test of the impact of plasma complement‐1q tumor necrosis factor‐α‐related protein isoform 5 level on type 2 diabetes.

Table S4 Clinical characteristics pre‐ and post‐treatment with dapaglifozin in type 2 diabetes patients.

Click here for additional data file. (3.9MB, docx)

Articles from Journal of Diabetes Investigation are provided here courtesy of Wiley

RESOURCES