Bariatric Surgery Significantly Reduces Serum Concentration of Vascular Endothelial Growth Factor A and Increases Apelin-12 in Patients with Morbid Obesity

Abstract

Introduction and Purpose:

Obesity is widely known as a major health risk factor, and bariatric surgery has proved to be a sustainable and effective method to reduce body weight. The purpose of this study is to investigate whether bariatric surgery influences concentrations of vascular endothelial growth factor A (VEGF-A) and apelin-12 in the serum of obese patients and whether both hormones correlate with the body mass index (BMI).

Materials and Methods:

Thirty morbidly obese patients involved in the study underwent sleeve gastrectomy or gastric bypass surgery. Blood samples were obtained preoperatively, 6, 12, and 24 months after surgery. Levels of VEGF-A and apelin-12 in the sera were measured by the use of an enzyme-linked immunosorbent assay.

Results and Conclusions:

The BMI decreased after the bariatric procedure from 51.3 ± 9.1 to 37.5 ± 7.9 kg/m² (p < 0.0001). VEGF-A concentration significantly decreased from 189.5 ± 17.2 pg/mL preoperatively to 110.8 ± 19.1 pg/mL after 24 months (p < 0.05). The serum concentration of apelin-12 significantly increased from 482.6 ± 66.6 to 2458.3 ± 499.8 pg/mL 2 years after the surgery (p < 0.0001). VEGF-A is positively correlated with the BMI (r = 0.45, p < 0.0001), whereas apelin-12 has a negative correlation with the BMI (r = −0.28, p < 0.01).

Introduction

In recent years, obesity has rapidly developed to become a major health risk factor worldwide and it has already reached an epidemic level.^1,2 The continuous increase in the number of obese people is accompanied by an increase of obesity-related diseases, including type 2 diabetes, hypertension, lipid disorders, or ischemia disease.² In addition, overweight is associated with immunological and humoral disorders and an elevated tumor risk.^1,3 Besides storing lipids, the fat tissue acts as an endocrine organ by secreting a large number of hormones and cytokines called adipokines,⁴ thereby producing a proinflammatory environment.⁵

The vascular endothelial growth factor (VEGF)⁴ and apelin⁶ are two adipokines that are secreted by adipocytes. VEGF is a major proangiogenic factor that regulates the formation of blood vessels in the expanding fat tissue, and it can be detected in human plasma as well as in the serum.⁷ The VEGF production is, in part, regulated by the COP9 signalosome and the ubiquitin proteasome system in tumor cells⁸ as well as in preadipocytes.⁹ It stimulates tumor angiogenesis and is a risk factor for tumor growth in obesity.^4,8,10 Recently, a correlation between the VEGF and the body mass index (BMI) has been described.¹¹ Apelin is an adipokine with autokrine inhibitory effects on adipocyte differentiation.^6,12 Serum apelin concentration seems to increase after weight loss. However, in one study, it has been shown that it does not simply negatively correlate with the BMI, but depends on the diabetic status.¹²

The increasing number of patients with morbid obesity seeking treatment as well as the failure of conservative treatment modalities to achieve a desirable weight has led to the development of several surgical techniques to provide weight loss with the least possible morbidity. Despite modest weight loss after lifestyle modifications, bariatric surgery is the only evidence-based approach producing marked and sustainable weight loss in severely obese individuals. A number of meta-analyses have demonstrated the effectiveness of bariatric surgery in improving severe obesity and its associated comorbidities.¹³ Therefore, bariatric surgery is currently the most effective treatment for severe obesity.

In this study, we confirm the positive correlation between the BMI and the VEGF serum concentration both before and after bariatric surgery. In addition, we demonstrate an increase of apelin-12 in the serum of patients after laparoscopic gastric bypass (LGB) and laparoscopic sleeve gastrectomy (LSG) as well as a negative correlation with the BMI.

Materials and Methods

Participants

A total number of 30 morbidly obese patients (18 women, 12 men, age range 20–64 years, mean age 43.6 ± 11.7), with a BMI of more than 38 kg/m² (mean BMI 51.3 ± 9.1 kg/m²), were included in the study. All patients underwent laparoscopic bariatric surgery, LGB or LSG. Blood samples for later detection of VEGF-A and apelin-12 were obtained preoperatively as well as 6, 12, and 24 months after surgery, resulting in a total number of 88 serum samples. Thirty-two single-patient sera could not be collected due to nonattendance during follow-up. Fifteen patients were affected by type 2 diabetes, 25 patients had arterial hypertension, and 14 patients suffered from obstructive sleep apnea. The protocol was approved by the ethical committee of the Charité - Universitätsmedizin Berlin, and written informed consent was obtained from all suspects.

Blood sampling and blood analysis

Blood samples were taken from patients' arm veins into BD vacutainer serum tubes (6 mL). After 30 to 45 min coagulation time at room temperature, the blood was centrifuged at 4°C and 2,500 × g for 10 min. The serum was divided into separate aliquots and stored at −80°C. All determinations were performed in duplicate or triplicate. Serum VEGF-A was measured with an ELISA Kit for human VEGF-A that was purchased from Aviva Systems Biology with an intra- and interassay variation of less than 10%. Serum apelin-12 was measured with an ELISA Kit for human apelin-12 (Cloud-Clone), with an intraassay variation of less than 10% and an interassay variation of less than 12%. In all cases, measurements were conducted with original, undiluted serum.

Statistical analysis

The results are expressed as mean ± standard error of mean, except of the BMI being expressed as mean ± standard deviation. For a comparison of the patients' serum VEGF-A and apelin-12 concentrations preoperatively and after 6, 12, and 24 months of the surgery, Student's t-test was performed. For correlation of VEGF-A and apelin-12 concentrations with the BMI, the Pearson correlation coefficient was calculated. All statistical analyses were conducted with GraphPad Prism.

Results

In Table 1, patient data, including the comorbidities diabetes type 2, hypertension, and sleep apnea, are shown. In addition, Table 1 documents all individual results on BMI, circulating VEGF-A, and apelin obtained in this study for each patient. Later, we analyzed the data by using statistical methods.

Table 1.

Patient Data and Results of Body Mass Index, Vascular Endothelial Growth Factor, and Apelin Measurements for Each Patient

							BMI				VEGF				Apelin
				Comorbidities			Months
No.	Age	Gender	OP	DMT2	HTN	SA	0	6	12	24	0	6	12	24	0	6	12	24
1	28	F	LSG		×		42	29	25	25	162	34	88	97	478	2,988	319	2,763
2	48	F	LSG		×	×	69	n.d.	50	42	149	n.d.	81	66	704	n.d.	506	926
3	63	M	LSG	×			62	46	42	36	323	276	158	193	585	633	443	461
4	47	M	LSG		×	×	64	54	n.d.	n.d.	197	297	n.d.	n.d.	639	2,168	n.d.	n.d.
5	50	M	LSG		×	×	55	41	42	43	163	22	25	24	413	387	641	4,813
6	37	F	LGB	×		×	65	n.d.	49	58	144	n.d.	71	62	567	n.d.	667	671
7	55	M	LSG	×	×	×	54	n.d.	32	n.d.	145	n.d.	58	n.d.	394	n.d.	421	n.d.
8	51	F	LGB	×	×		47	n.d.	38	n.d.	234	n.d.	54	n.d.	95	n.d.	2,408	n.d.
9	40	F	LGB	×	×		47	36	32	34	137	32	63	78	90	3,618	894	999
10	26	F	LGB		×		48	n.d.	44	n.d.	174	n.d.	165	n.d.	134	n.d.	300	n.d.
11	43	M	LSG	×	×	×	67	52	42	40	339	109	163	137	104	2,230	624	6,170
12	48	F	LSG	×	×		46	36	36	37	112	63	74	59	283	553	1,486	3,450
13	64	F	LSG	×	×	×	40	32	30	34	106	38	62	57	583	629	3,099	2,105
14	30	M	LSG		×	×	61	41	36	34	341	207	163	134	412	279	754	1,682
15	57	F	LGB		×		44	37	37	38	305	207	227	184	372	1,528	928	2,590
16	47	M	LGB	×	×		39	34	33	32	217	214	273	238	502	259	694	2,870
17	50	F	LSG		×		42	28	n.d.	n.d.	116	84	n.d.	n.d.	413	2,148	n.d.	n.d.
18	43	F	LSG		×	×	56	45	n.d.	n.d.	241	173	n.d.	n.d.	554	2,812	n.d.	n.d.
19	53	M	LGB	×	×	×	43	32	31	n.d.	146	138	141	n.d.	674	788	834	n.d.
20	20	F	LSG		×		43	33	32	n.d.	95	44	83	n.d.	1,425	1,706	1,570	n.d.
21	43	F	LSG			×	49	38	n.d.	n.d.	199	218	n.d.	n.d.	1,804	1,940	n.d.	n.d.
22	27	F	LSG		×		60	51	n.d.	n.d.	513	425	n.d.	n.d.	571	2,811	n.d.	n.d.
23	56	M	LGB	×	×	×	46	37	n.d.	n.d.	176	144	n.d.	n.d.	209	543	n.d.	n.d.
24	36	F	LGB		×		52	40	n.d.	n.d.	115	158	n.d.	n.d.	464	498	n.d.	n.d.
25	42	F	LGB				43	36	n.d.	n.d.	103	78	n.d.	n.d.	175	385	n.d.	n.d.
26	28	F	LGB	×	×		54	43	n.d.	n.d.	112	91	n.d.	n.d.	333	396	n.d.	n.d.
27	28	M	LSG		×		51	39	26	n.d.	198	124	178	n.d.	82	1,226	1,014	n.d.
28	39	F	LGB	×			39	39	37	n.d.	174	80	77	n.d.	697	938	729	n.d.
29	56	M	LSG	×	×	×	65	57	55	n.d.	162	193	228	n.d.	413	126	1,178	n.d.
30	52	M	LSG	×	×	×	47	41	40	n.d.	86	74	85	n.d.	310	337	351	n.d.

BMI, body mass index; DMT2, diabetes mellitus type 2; F, female; HTN, hypertension; LGB, laparoscopic gastric bypass; LSG, laparoscopic sleeve gastrectomy; M, male; n.d., not determined; OP, operation; SA, sleep apnea; VEGF, vascular endothelial growth factor.

In this study, LGB and LSG were carried out. LGB is one of the first established procedures, and it is still one of the most popular bariatric procedures performed worldwide. By creating a small gastric pouch, a sensation of satiety is rapidly caused with food intake. This element is combined with a gastrointestinal bypass with a Roux-limb. LSG was originally performed in preparation for biliopancreatic diversion and duodenal switch in super-obese and high-risk patients.¹⁴ It is a simple, fast, effective, and less invasive procedure compared with LGB, which is characterized by constructing a narrow gastric sleeve by resecting the entire greater gastric curvature.

The BMI was determined before (0 month) and 6, 12, and 24 months after bariatric surgery. LGB as well as LSG caused a significant reduction of BMI by 22% from 51.3 ± 9.1 kg/m² preoperatively to 39.8 ± 7.6 kg/m² when measured 6 months after surgery (Fig. 1). Two years after surgery, there was no more significant decrease of BMI as compared with at 6 months. The 2-year BMI (37.5 ± 7.9 kg/m²) declined by more than 25% in comparison to the BMI before surgery (Fig. 1).

FIG. 1.

BMI values measured preoperatively (0 month) and 6, 12, and 24 months after bariatric surgery. BMI values are expressed as means ± standard deviation. p-Values and the number of patients (n) are indicated. BMI, body mass index.

VEGF-A was measured in the serum of obese patients by using a standard enzyme-linked immunosorbent assay. As shown in Figure 2, only 12 months after surgery, serum VEGF-A concentration was significantly reduced by more than 35% from 189.5 ± 17.2 pg/mL preoperatively to 119.9 ± 14.9 pg/mL. After 2 years, it even declined by 41% to a value of 110.8 ± 19.1 pg/mL as compared with the preoperative value. There was no difference on comparing LGB and LSG. Both bariatric surgery methods reduced serum VEGF-A concentrations of obese patients in a similar manner (data not shown).

FIG. 2.

Serum VEGF-A concentration estimated before (0 month) and 6, 12, and 24 months after bariatric surgery. VEGF-A was measured by an enzyme-linked immunosorbent assay, and data are expressed as mean ± standard error of mean. p-Values and the number of patients (n) are indicated. VEGF-A, vascular endothelial growth factor A.

The relationship between BMI and circulating levels of VEGF-A was estimated by Pearson correlation statistical analysis, as shown in Figure 4A. Data demonstrate that the BMI was directly associated with VEGF-A (r = 0.45, p < 0.0001).

Apelin-12 is produced by adipocytes,⁶ and it was measured in the circulating serum by an ELISA Kit. Our data summarized in Figure 3 demonstrate that apelin-12 was relatively low in obese patients before bariatric surgery. Already after 6 months, there was an ∼2.5-fold increase of serum apelin-12 concentration from 482.6 ± 66.6 pg/mL preoperatively to 1277.0 ± 207.1 pg/mL. Moreover, 2 years after surgery, the increase of apelin-12 in the circulating blood of patients was even fivefold compared with the apelin-12 level before bariatric surgery, amounting to 2458.3 ± 499.8 pg/mL. As shown in Figure 4B, the Pearson correlation coefficient revealed a negative correlation between the BMI and apelin-12 (r = −0.28, p < 0.01).

FIG. 3.

Serum apelin-12 concentration before (0 month) and 6, 12, and 24 months after bariatric surgery. Serum concentrations are expressed as mean ± standard error of mean. p-Values and the number of patients (n) are indicated.

FIG. 4.

Correlation between the BMI and serum VEGF-A concentration as well as between the BMI and serum apelin-12 concentration. (A) All BMI values and the corresponding VEGF concentrations both before and after surgery were analyzed by Pearson correlation analysis. (B) Calculation of a Pearson correlation factor by using all BMI values and the corresponding apelin-12 concentrations.

Discussion

At the moment, bariatric surgery is the only established treatment of obese individuals, thus allowing for significant and durable long-term weight loss, along with associated remission or sustained improvements in weight-related comorbidities (for review, see^15–17). In our study, bariatric surgery causes a loss of the average BMI by more than 25%, from 51.3 ± 9.1 kg/m² before surgery to 37.5 ± 7.9 kg/m² 2 years after surgery. There was no significant difference among surgical procedures, LGB or LSG (data not shown), thus confirming the data of Garcia de la Torre et al.⁷ In contrast to an earlier study,⁷ our results reveal a direct correlation between the BMI and the VEGF value in the serum of obese patients. Taking together all BMIs and VEGF data both before and after surgery, our Pearson correlation analysis revealed a significant positive correlation between the BMI and the VEGF serum concentration with a correlation factor of r = 0.45 (p < 0.0001). This confirms data obtained earlier in healthy male subjects under highly controlled conditions¹¹ and in childhood obesity.¹⁸ Our circulating VEGF concentration before surgery dropped down by more than 40% 2 years after bariatric surgery. Although the main decrease of the serum VEGF level can be measured already after 6 months, there is still a tendency for a continuous decrease after 12 and 24 months, indicating the long-term effect of the treatment.

VEGF is a major adipokine that promotes the expansion of adipose tissue.⁴ In addition, it is a major factor for the vascularization and expansion of solid tumors and anti-VEGF therapies are used for tumor treatment.^19,20 As demonstrated by our results, bariatric surgery can sustainably reduce the VEGF production by the fat tissue and may lower the tumor risk significantly. As recently shown, VEGF-A belongs to the cancer-associated circulating proteins that are involved in obesity-associated tumorigenesis and rapidly decrease after bariatric surgery.²¹

Circulating apelin level responses to bariatric surgery are controversial.^22–24 A study performed by Krist et al.²⁴ in 2013 showed that bariatric interventions (LGS with optional LGB) significantly lowered apelin-12 levels in obese patients 12 months after surgery. In this study, there was a positive correlation between apelin-12 levels and BMI in individuals with diabetes type 2.²⁴ A different study examined the effect of biliopancreatic diversion on plasma levels of apelin-12 and showed no influence of the procedure after 1 year.²³ Another study revealed that those patients suffering from diabetes type 2 had elevated serum levels of apelin-12 compared with nondiabetic subjects. However, these diabetic subjects showed no significant change in apelin-12 levels 6 months after LGS surgery.²⁵

Our study revealed a clear increase of circulating apelin-12 after bariatric surgery independently of the used procedure, LGB or LSG. Already 6 months after the operation, there is a significant increase of the apelin-12 level. Most interestingly is the long-term effect of bariatric surgery on the serum apelin-12 concentration. Here, we demonstrate for the first time a fivefold increase of apelin-12 after 2 years of surgery compared with the apelin-12 level in obese patients. Taking together all BMIs and apelin-12 data both before and after surgery, our Pearson correlation analysis revealed a significant negative correlation between the BMI and the apelin-12 serum concentration. Apelin inhibits adipogenesis by an autocrine mechanism⁶ and with regard to adipogenesis suppression, it is an antagonist of VEGF. In addition, apelin-deficient mice are insulin resistant²⁶ and administration of apelin increases glucose uptake and elevates insulin sensitivity.²⁷ Therefore, only an increase of apelin caused by bariatric surgery improves the diabetic status of obese patients, as demonstrated earlier.²⁸ The late increase of apelin-12 found by us might be an important sign of recovery from obesity. More studies are required to understand the role of apelin-12 in obesity and surgery-induced weight loss.

Conclusions

In conclusion, our data show that serum VEGF-A significantly decreases after bariatric surgery whereas serum apelin-12 increases. Both adipokines correlate significantly with the BMIs of obese patients. The decline of the BMI is associated with decreased VEGF-A and elevated apelin-12 levels in the serum, presumably indicating a possible mutual influence of both peptide hormones during weight loss. The reduction of VEGF decreases fat tissue angiogenesis and tumor risk. By blocking adipogenesis, apelin-12 could possibly have a lasting effect on obese patients after surgery.

Footnotes

Acknowledgment

The authors thank Kirsten Führer for the management of blood samples.

Ethical Approval

All procedures performed in this study were in accordance with the 1964 Helsinki Declaration and its later amendments or comparable ethical standards. The study was approved by the Bioethics Committee of the Charité - Universitätsmedizin Berlin.

Author Disclosure Statement

No competing financial interests exist.

References

Barness

, Opitz

, Gilbert-Barness

. Obesity: genetic, molecular, and environmental aspects. Am J Med Genet A, 2007; 143A:3016–3034.

Naser

, Gruber

, Thomson

. The emerging pandemic of obesity and diabetes: are we doing enough to prevent a disaster?. Int J Clin Pract, 2006; 60:1093–1097.

Byers

, Sedjo

. Does intentional weight loss reduce cancer risk?. Diabetes Obes Metab, 2011; 13:1063–1072.

Vona-Davis

, Rose

. Angiogenesis, adipokines and breast cancer. Cytokine Growth Factor Rev, 2009; 20:193–201.

Trayhurn

, Wood

. Adipokines: inflammation and the pleiotropic role of white adipose tissue. Br J Nutr, 2004; 92:347–355.

Than

, et al. Apelin inhibits adipogenesis and lipolysis through distinct molecular pathways. Mol Cell Endocrinol, 2012; 362:227–241.

Garcia de la Torre

, et al. Effects of weight loss after bariatric surgery for morbid obesity on vascular endothelial growth factor-A, adipocytokines, and insulin. J Clin Endocrinol Metab, 2008; 93:4276–4281.

Pollmann

, Huang

, Mall

, Bech-Otschir

, Naumann

, Dubiel

. The constitutive photomorphogenesis 9 signalosome directs vascular endothelial growth factor production in tumor cells. Cancer Res, 2001; 61:8416–8421.

Huang

, Ordemann

, Müller

, Dubiel

. The COP9 signalosome, cullin 3 and Keap1 supercomplex regulates CHOP stability and adipogenesis. Biology Open, 2012; 1:705–710.

10.

Hursting

, Hursting

. Growth signals, inflammation, and vascular perturbations: mechanistic links between obesity, metabolic syndrome, and cancer. Arterioscler Thromb Vasc Biol, 2012; 32:1766–1770.

11.

Loebig

, et al. Evidence for a relationship between VEGF and BMI independent of insulin sensitivity by glucose clamp procedure in a homogenous group healthy young men. PLoS One, 2010; 5:e12610.

12.

Goktas

, Moustaid-Moussa

, Shen

, Boylan

, Mo

, Wang

. Effects of bariatric surgery on adipokine-induced inflammation and insulin resistance. Front Endocrinol (Lausanne), 2013; 4:69.

13.

Gloy

, et al. Bariatric surgery versus non-surgical treatment for obesity: a systematic review and meta-analysis of randomised controlled trials. BMJ, 2013; 347:f5934.

14.

Cottam

, et al. Laparoscopic sleeve gastrectomy as an initial weight-loss procedure for high-risk patients with morbid obesity. Surg Endosc, 2006; 20:859–863.

15.

Pedersen

. The role of hormonal factors in weight loss and recidivism after bariatric surgery. Gastroenterol Res Pract, 2013; 2013:528450.

16.

Fobi

. Surgical treatment of obesity: a review. J Natl Med Assoc, 2004; 96:61–75.

17.

Biron

, et al. Twenty years of biliopancreatic diversion: what is the goal of the surgery?. Obes Surg, 2004; 14:160–164.

18.

Siervo

, et al. Body mass index is directly associated with biomarkers of angiogenesis and inflammation in children and adolescents. Nutrition, 2012; 28:262–266.

19.

Shi

, Siemann

. Simultaneous targeting of VEGF message and VEGF receptor signaling as a therapeutic anticancer approach. Anticancer Res, 2004; 24:213–218.

20.

Morabito

, Sarmiento

, Bonginelli

, Gasparini

. Antiangiogenic strategies, compounds, and early clinical results in breast cancer. Crit Rev Oncol Hematol, 2004; 49:91–107.

21.

Farey

, Fisher

, Levert-Mignon

, Forner

, Lord

. Decreased levels of circulating cancer-associated protein biomarkers following bariatric surgery. Obes Surg, 2016. [Epub ahead of print] DOI: 10.1007/s11695-016-2302-1.

22.

Castan-Laurell

, et al. Effect of hypocaloric diet-induced weight loss in obese women on plasma apelin and adipose tissue expression of apelin and APJ. Eur J Endocrinol, 2008; 158:905–910.

23.

Caron-Cantin

, et al. Acute and chronic effects of biliopancreatic diversion with duodenal switch surgery on plasma visfatin and apelin levels in patients with severe obesity. Obes Surg, 2013; 23:1806–1814.

24.

Krist

, et al. Effects of weight loss and exercise on apelin serum concentrations and adipose tissue expression in human obesity. Obes Facts, 2013; 6:57–69.

25.

Cavallo

, et al. Altered glucose homeostasis is associated with increased serum apelin levels in type 2 diabetes mellitus. PLoS One, 2012; 7:e51236.

26.

Yue

, et al. Apelin is necessary for the maintenance of insulin sensitivity. Am J Physiol Endocrinol Metab, 2010; 298:E59–E67.

27.

Dray

, et al. Apelin stimulates glucose utilization in normal and obese insulin-resistant mice. Cell Metab, 2008; 8:437–445.

28.

Buchwald

, et al. Weight and type 2 diabetes after bariatric surgery: systematic review and meta-analysis. Am J Med, 2009; 122:248.e5–256.e5.