Association of Dietary Inammatory Potential (DIP) and Endothelial Function Biomarkers among Female Nurses of Isfahan Hospitals

Background: Dietary inammatory index (DIP) is a new dietary index designed to evaluate individuals’ diets. In addition, adhesion molecules are important biomarkers for assessing endothelium inammation that they related to atherosclerosis and cardiovascular disease. Also, there is no study for assessing the association between adhesion molecules and DIP until now as well as other studies that assessed the relationship between dietary inammatory index or DIP have controversy. The purpose of this cross-sectional study was to determine the correlation between DII and endothelial markers such as E-selectin, intercellular adhesion molecule-1 (sICAM-1) and vascular cell adhesion molecule-1 (sVCAM-1) among female nurses from Isfahan. In this study, dietary inammatory potential (DIP) was used instead of DII. Methods: This study was performed on 420 healthy nurses. The nurses were selected by random cluster sampling method from private and public Isfahan hospitals. A validated food frequency questionnaire (FFQ) was applied to assess the dietary inammatory potential. A fasting blood sample was collected for measuring the plasma levels of the endothelial markers and other variables. Results: After adjusting different potential confounders, no statistical association was found between DIP and sICAM-1, E–selectin and sVCAM-1 in model I (P=0.57, 0.98 and 0.45), model II (P=0.57, 0.98 and 0.45) and model III (P=0.67, 0.92 and 0.50) in comparison to the crude group (P=0.35, 0.83 and 0.49, respectively). Conclusions: The results revealed that the plasma levels of endothelial markers including E-selectin, sICAM-1, and sVCAM-1 were not signicantly associated with DIP in female nurses.


Introduction
Atherosclerosis is a continuing in ammatory state of the vessels [1]. The progression of atherosclerosis leads to myocardial infarction and sudden death [2]. It is believed that atherosclerosis is an in ammatory condition that is largely responsible for cardiovascular disease (CVD) mortality [3,4]. Endothelial dysfunction contributes to the pathogenesis of vascular disease and plays an important role in CVD as well [5,6]. Endothelial dysfunction is characterized by impaired activity of endothelial derived relaxant factors and increased activity of vasoconstrictor factors. However, cell adhesion molecules (CAM) including E-selectin, intercellular adhesion molecule-1 (sICAM-1) and vascular cell adhesion molecule-1 (sVCAM-1) accelerate atherosclerosis [4,[7][8][9].
Adhesion molecules are normally expressed by the endothelium. They also play a role in leukocyte rolling, rm adhesion, and transmigration. Furthermore, they are associated with a variety of pathophysiological processes and in ammatory disorders. Atherosclerotic lesions and fatty streaks increase the expression of sICAM-1, sVCAM-1, and P-and E-selectin on the human endothelial cells [10,11]. E-selectin plays an important role in acute in ammation [12][13][14]. Moreover, sICAM-1 and sVCAM-1 are involved in chronic in ammation [15,16]. Leukocyte adhesion is an important component of some vascular diseases and atherogenesis. Leukocyte recruitment occurs in a multistep process and selectin, which is expressed on the activated endothelial cells, is involved in the initial rolling process of leukocytes [12,17]. The leukocyte surface has sites for selectin ligand [18]. β1 and β2 integrin are expressed on leukocytes and act as binding sites for sVCAM-1 or sICAM-1. Furthermore, selectin plays a role in the initial rolling process of leukocytes whereas sICAM-1 and sVCAM-1 mediate leukocyte arresting and rm adhesion [12,[18][19][20].
Dietary in ammatory potential (DIP) is a new dietary index designed to evaluate the individual's diets. DIP is a tool to assess the potential in ammatory and anti-in ammatory properties of a diet based on food elements. In this index, values of + 1, 0, and − 1 indicate pro-in ammation, indifferent and antiin ammation reactions, respectively [21]. Actually, DIP is a resource to assess pro-in ammatory effects of food ingredients based on anti-in ammatory functions [21,22]. DIP has been linked to a variety of systemic biomarkers such as interleukin 6 (IL-6), tumor necrosis factor alpha (TNF-α), C-reactive protein (CRP) and several metabolic diseases such as CVD, cancers, and diabetes. Many studies have found that DIP is associated with the risk of metabolic syndrome and cardiovascular diseases [23][24][25][26][27][28].
Many studies have reported a positive association between DIP and CVDs [29,30]. Due to the increase in the global risk of CVDs and related diseases in the world, it is important to nd healthy dietary patterns with low in ammatory scores to tackle in ammation and CVDs. The purpose of this study was to determine the association between DIP and endothelial markers such as sICAM, sVCAM, and E-selectin in female nurses working in Isfahan hospitals.

Participants
Four hundred and eighty healthy female nurses aged > 30 years participated in this cross-sectional study.
The participants were selected randomly from seven public and private hospitals in Isfahan, Iran. The female nurses with a history of diabetes, malignancy, infections, and CVDs were excluded. Furthermore, the subjects who did not complete the FFQ questionnaire were also excluded from the study. Finally, 420 nurses were enrolled in the study. The participants ll in a consent form based on Tehran university of medical sciences ethics rules for participating on this study.
The study protocol was approved by Tehran university of medical sciences (IR.TUMS.VCR.REC.1399.584).

Blood sampling
Blood samples were collected from the participants after 12 hours of fasting to measure the levels of endothelial markers, lipid pro le, and fasting blood glucose. Then, the sample were centrifuged for 30-45 minute and frozen at 70°C. The levels of sVCAM-1, sICAM-1, and E-selectin were measured using commercial ELISA kits (Biosource International and Bender MED Systems) according to the manufacturer's instructions. ELISA kits were also used to measure low-density lipoprotein (LDL) and highdensity lipoprotein (HDL).

Dietary in ammatory score
The method developed by Shivappa et al was applied to calculate the DIP scores of the diets. The Food Frequency Questionnaire (FFQ) was used to determine the dietary intake [21]. In the Iranian dietary pattern, 29 out of 45 items of DII are very common, including Macronutrients (energy, carbohydrates, fat, protein, ber), Fat (cholesterol, saturated fatty acids (SFA), monounsaturated fatty acids (MUFA), polyunsaturated fatty acids (PUFA)), Water-soluble vitamins (pyridoxine, folic acid, niacin, thiamin, ascorbic acid and ribo avin). Fat-soluble vitamins (A,D and E), Minerals (iron, magnesium, zinc, and selenium), as well as caffeine, β-carotene, onion, garlic, pepper, and black tea [31]. Other DIP items that were uncommon in the Iranian dietary regimen were omitted form the list of FFQ.
The intake of the above dietary items was adjusted according to the daily energy intake [32]. A z-score was generated for all of the 29 items of the FFQ list for each participant. For each subject, the "standard global mean" was subtracted from the mean consumed food and divided by "global standard deviation". The global means and standard deviations were obtained by the method developed by Shivappa et al [21]. To decrease the skewness of the variables, the variables were converted to a centered percentile score. This score was then extended by the impact for every item [21]. The DIP scores of all foods were summed to calculate the overall score. More positive values indicated a higher in ammatory dietary potential.

Assessment of other variables
A computerized scale was used for weight measurement (to the nearest 0.1 kg). The subjects were asked to wear light clothing with no shoes. The height was also measured on the same visit day. Finally, weight (kg) and height (m) were used to calculate the body mass index (BMI) according to the following formula: The International Physical Questionnaire was used to evaluate daily physical activity [33,34] as MET-hour per week. The factors such as education level, family size, and economic status were inquired from all the participants to determine their socioeconomic status. Moreover, covariate data including age, marital status, menopause situation, past medical history, smoking or medication/supplementation history were selfreported by all the participants.

Statistical analysis
The nal analysis was performed on 420 individuals. Energy adjustment of the variables was carried out using the residual method. After completing the FFQ, the data were entered into an Excel datasheet and daily dietary intakes were compared using the IBM SPSS version 26 (IBM SPSS Statistics for Win, Armonk, NY) and Nutritionist IV (N4) software. Since there were three DIP groups (tertiles), one-way ANOVA was used for continuous variables including age, body mass index (BMI), weight, waist circumference, physical activity, and systolic and diastolic blood pressure, and Pearson's chi-square test was applied to categorical variables such as oral contraceptive (OCP) use, current corticosteroid use, menopause, marital status, overweight/obesity and socioeconomic status. Similarities between the energy intakes of the participants were adjusted by linear regression. Finally, the associations between DIP and E-selectin, ICAM, and VCAM in three tertiles was analyzed using ANCOVA.

Results
The mean ± SD age of the participants was 34.44 ± 7.27, 34.59 ± 6.8 and 36.47 ± 7.4 years in the 1st, 2nd, and 3rd tertile, respectively. The demographic characteristics of the subjects are presented in Table 1. b) High socioeconomic status was de ned based on educational level, income, family size, being owner of the house or renting the house, house area, being owner of the car and number and kind of the car(s), number of bedrooms, and determination of who was in charge of the family.
In addition, no signi cant association was found between DIP and the plasma level of sVCAM-1 in the crude model compared to model I (P-value: 0.49), model II (P-value: 0.45) and model III (P-value: 0.50) after adjusting for potential confounders (Fig. 3).

Discussion
No association was observed between dietary in ammatory potential (DIP) and endothelial biomarkers including E-selectin, sVCAM-1 and sICAM-1 in the participants. This dissociation remained signi cant after adjusting for possible confounders. This is the rst study of the association between adhesion molecules and DIP. Other studies assessed the correlation between DIP and cardiovascular disease.
The results of the present study are consistent with a study by Imran khan et al who carried out a cohort study on 1111 subjects to evaluate the relationship between DIP and cardiovascular disease (CVD). The results showed no a signi cant correlation between DIP and CVD in females while a signi cant relationship was found in male subjects [42]. Similarly, Gabriela Pocovi-Gerardino et al conducted a crosssectional study on 105 women with a mean age of 45.4 years old and found no signi cant correlation between the DIP score and CVD markers [43]. A study of 585 women aged 50-55 years old by Linda E. T. Vissers et al failed to show any correlation between DIP and CVD, ischemic heart disease, and myocardial infarction (MI) [44]. Furthermore, a prospective case-control study of 100000 participants showed no signi cant relationship between DII and MI [45].
By contrast, Bondonno et al reported that a high DIP score was associated with atherosclerotic vascular disease in women aged over 70 although they did not nd any association between DIP and carotid plaque severity [46]. Moreover, Stefanos Tyrovolas et al carried out a dose-dependent study to assess the correlation between DIP and CVD risk factors. They found a signi cant correlation between DIP and CVD risk factors such as diabetes mellitus, obesity, hypertension, and hypercholesterolemia. In addition, the participants with a high DIP score in the 3rd and 4th quartile had at least one CVD risk factor in comparison to the participants in the 1st quartile [47].
It was di cult to sort out consistent results with our ndings because many studies were carried out on subjects with unhealthy conditions. Moreover, there were differences between the studies in terms of the sample size. The geographic dietary pattern may also affect the results. Furthermore, many studies did not measure the plasma levels of sICAM-1, sVCAM-1 and E-selectin directly. Therefore, more studies are required to assess the correlation between endothelial markers and the DIP score.
This study had some limitations. For example, it had a cross-sectional design and therefore no conclusions can be made regarding causality. Moreover, there were some unknown confounders including shift time, bias in reporting food items, and difference in the dietary pattern between nurses in private and public hospitals, which could affect the results. Studies with larger sample sizes are required to obtain concrete results.

Conclusion
In summary, the ndings suggest that the plasma levels of endothelial markers including E-selectin, ICAM-1 and sVCAM-1 have no signi cant correlation with dietary in ammatory potential in females. Ethics approval and consent to participate The study protocol was approved by Tehran university of medical sciences (IR.TUMS.VCR.REC.1399.584).

Consent for publication
The participants ll in a consent form based on Tehran university of medical sciences ethics rules for participating on this study.