Abstract
Vascular insulin resistance is a feature of obesity and type 2 diabetes that contributes to the genesis of vascular disease and glycemic dysregulation. Data from preclinical models indicate that vascular insulin resistance is an early event in the disease course, preceding the development of insulin resistance in metabolically active tissues. Whether this is translatable to humans requires further investigation. To this end, we examined if vascular insulin resistance develops when young healthy individuals (n = 18 men, n = 18 women) transition to an obesogenic lifestyle that would ultimately cause whole-body insulin resistance. Specifically, we hypothesized that short-term (10 days) exposure to reduced ambulatory activity (from >10 000 to <5000 steps/day) and increased consumption of sugar-sweetened beverages (6 cans/day) would be sufficient to prompt vascular insulin resistance. Furthermore, given that incidence of insulin resistance and cardiovascular disease is lower in premenopausal women than in men, we postulated that young females would be protected against vascular insulin resistance. Consistent with this hypothesis, we report that after reduced ambulation and increased ingestion of carbonated beverages high in sugar, young healthy men, but not women, exhibited a blunted leg blood flow response to insulin and suppressed skeletal muscle microvascular perfusion. These findings were associated with a decrease in plasma adropin and nitrite concentrations. This is the first evidence in humans that vascular insulin resistance can be provoked by short-term adverse lifestyle changes. It is also the first documentation of a sexual dimorphism in the development of vascular insulin resistance in association with changes in adropin levels.
Keywords: sedentary behavior, sugar-sweetened beverages, endothelial dysfunction, blood flow, sex differences, adropin
Beyond its role in cellular glucose uptake, insulin also exerts vasodilatory effects that increase delivery of insulin and glucose to target organs such as skeletal muscle (1‐3). In healthy individuals, insulin-induced and nitric oxide (NO)–mediated increases in leg blood flow account for as much as 35% of total insulin–stimulated leg glucose uptake (4). Conversely, insulin resistance in the vasculature diminishes insulin-induced vasodilation, thus limiting nutrient delivery and contributing to impaired glycemic control in obesity and type 2 diabetes (4‐6). Notably, endothelial insulin resistance not only contributes to impaired glucose metabolism but also represents a causal factor in the pathogenesis of cardiovascular disease (5‐14).
Previous work in genetic rodent models indicates that impairments in vascular insulin signaling are an early event in the disease course that precedes the appearance of insulin resistance in metabolically active tissues (eg, skeletal muscle, liver, adipose) and develops prior to manifestation of other indices of vascular dysfunction (15‐18). Whether these findings from preclinical models indicating that the vasculature is particularly vulnerable to insulin resistance can be translated to humans requires further investigation. We sought to determine if vascular insulin resistance develops when healthy individuals transition to an obesogenic lifestyle that would ultimately cause whole-body insulin resistance. Specifically, we hypothesized that a 10-day exposure to reduced ambulatory activity and increased consumption of sugar-sweetened beverages would be sufficient to instigate vascular insulin resistance (assessed via changes in leg blood flow and skeletal muscle perfusion in response to insulin), and that this effect would occur prior to overt weight gain. Furthermore, given that incidence of insulin resistance and cardiovascular disease is lower in premenopausal women than in men, we reasoned that young females would be, to a certain extent, protected against vascular insulin resistance.
Materials and Methods
Ethics Approval and Participants
The study was approved by the University of Missouri institutional review board (protocol 2012869), registered at ClinicalTrials.gov (NCT03785470), and conducted in accordance with the Declaration of Helsinki. Recreationally active men and women (age 18-45 years, body mass index <30 kg/m2) who regularly engaged in >10 000 steps of walking per day and consumed less than 2 nondiet carbonated soft drinks per day were recruited from the University of Missouri campus and surrounding Columbia, MO area. Exclusion criteria included diagnosis of cardiovascular disease, renal or hepatic diseases, active cancer, autoimmune diseases, immunosuppressant therapy, excessive alcohol consumption (>14 drinks/week for men, >7 drinks/week for women), current tobacco use, and pregnancy. Before participating in the study, all subjects provided written informed consent and completed a health history questionnaire, which also included a self-report of physical activity. Thereafter, subjects wore a pedometer (FITstep2 Pedometer, Gophersport, Owatonna, MN) for 3 days prior to the intervention, including 1 weekend day, for quantification of steps. During that time, subjects were instructed to follow their normal activity patterns. Only subjects that met the required number of steps per day were included in the study. Subject characteristics are provided in Table 1. Baseline data from a subset of participants were included in a previous publication (19) addressing an unrelated question (ie, the effects of aging on vascular function).
Table 1.
Participant characteristics, anthropometrics, hemodynamic measurements and blood profile before and after the obesogenic lifestyle (OL) intervention in females and males
| Females Mean ± SE (n = 18) | Males Mean ± SE (n = 18) | |||
|---|---|---|---|---|
| Race (n, %) | ||||
| Asian | (1, 5%) | (3, 16%) | ||
| Black | (3, 16%) | (2, 11%) | ||
| White/Hispanic | (0, 0%) | (2, 11%) | ||
| White/Non-Hispanic | (14, 78%) | (11, 61%) | ||
| Other | (0, 0%) | (0, 0%) | ||
| Before OL | After OL | Before OL | After OL | |
| Age (years) | 22 ± 1 | — | 25 ± 1 | — |
| Height (cm) | 165 ± 1 | — | 179 ± 1c | — |
| Body weight (kg) | 59.3 ± 1.9 | 59.7 ± 1.9a | 76.6 ± 2.1b | 77.1 ± 2.0a,b |
| Body mass index (kg/m2) | 21 ± 0.7 | 22 ± 0.7a | 23 ± 0.8 | 24 ± 0.8a |
| Body fat mass (%) | 35 ± 1 | 35 ± 1 | 26 ± 1b | 26 ± 1b |
| Lean body mass (kg/m2) | 13.4 ± 0.4 | 13.4 ± 0.3 | 17.2 ± 0.6b | 17.4 ± 0.6b |
| Systolic BP (mmHg) | 110 ± 1 | 109 ± 1 | 121 ± 2b | 119 ± 1b |
| Diastolic BP (mmHg) | 69 ± 1 | 68 ± 1 | 75 ± 2b | 74 ± 2b |
| cfPWV (m/s) | 5.09 ± 0.16 | 5.04 ± 0.12 | 5.76 ± 0.23b | 5.77 ± 0.21b |
| Fasted blood glucose (mg/dL) | 86 ± 2 | 85 ± 1 | 94 ± 3 | 90 ± 1 |
| Fasted insulin (µU/mL) | 6.5 ± 0.6 | 7.3 ± 0.6a | 4.8 ± 4.7b | 6.1 ± 1.9a,b |
| HOMA-IR (mg/dL) | 1.4 ± 0.1 | 1.6 ± 0.1a | 1.1 ± 0.1 | 1.3 ± 0.1a |
| Hemoglobin A1C (%) | 4.9 ± 0.06 | 4.9 ± 0.06 | 5.2 ± 0.05b | 5.1 ± 0.06b |
| Uric acid (mg/dL) | 3.8 ± 0.1 | 3.8 ± 0.1 | 5.2 ± 0.2b | 5.4 ± 0.2b |
| Total cholesterol (mg/dL) | 158.7 ± 7.7 | 156.6 ± 6.8 | 148.4 ± 6.7 | 149.7 ± 6.8 |
| LDL cholesterol (mg/dL) | 87.4 ± 6.9 | 85.6 ± 6.5 | 85.2 ± 6.9 | 86.3 ± 6.4 |
| HDL cholesterol (mg/dL) | 57.7 ± 2.4 | 55.9 ± 2.5a | 48.4 ± 2.9 | 45.3 ± 2.0a |
| Triglycerides (mg/dL) | 67.6 ± 5.7 | 75.8 ± 7.4a | 74.6 ± 7.8 | 90.6 ± 10.4a |
Abbreviations: BP, blood pressure; cfPWV, carotid-to-femoral pulse wave velocity; LDL, low-density lipoprotein; HDL, high-density lipoprotein; HOMA-IR, homeostatic model assessment for insulin resistance.
P < .05, main effect of OL.
P < .05, main effect of sex.
P < .05 vs Females (unpaired t-test).
10-Day Obesogenic Lifestyle Intervention
During the intervention, participants were instructed to reduce their daily activity such that the accumulation of steps per day was <5000. Throughout this period, subjects wore the pedometer during waking hours until just prior to sleep (ie, ∼15-18 hours of wear time per day). Furthermore, during the intervention, participants were asked to consume 6 cans of sugar-sweetened beverages (335 mL/can) of their choice per day. Drinks provided included Sprite, Coca-Cola, Pepsi, Mountain Dew, and Mug Root Beer. Subjects were otherwise allowed to eat ad libitum and contacted daily by the team to assess adherence to the protocol. Our experimental paradigm was intended to mimic 2 prevailing lifestyle behaviors that commonly coexist and contribute to the epidemic of obesity and type 2 diabetes; that is, sedentarism and excess consumption of sugary drinks (20‐27). It should be recognized that the study was not designed to pinpoint which of the 2 lifestyle factors is the main driver of vasculometabolic impairments, nor to determine if synergistic interactions exist between the 2 lifestyle factors.
Experimental Visit Procedures
On the experimental visit days, research subjects were admitted to the Clinical Research Center at the University of Missouri after an overnight fast and after refraining from caffeine for 12 hours. Prior to the baseline visit, subjects were also asked to abstain from vigorous physical activity for 24 hours. Scheduling of experimental visits in females was not controlled for the menstrual cycle given the duration of the intervention. Upon arrival, subjects underwent anthropometric measurements including height, weight, and body composition via dual-energy X-ray absorptiometry (QDR-4500A; Hologic, Shelby Township, MI). A negative pregnancy test was required for women. The primary outcome of the study was insulin-stimulated leg blood flow and skeletal muscle microvascular perfusion. For more complete characterization of the vascular phenotype, we also included measures of conduit artery function (ie, aortic stiffness and flow-mediated dilation (FMD) in the brachial and popliteal arteries).
Assessment of Carotid-to-Femoral Pulse Wave Velocity and FMD
Carotid-to-femoral pulse wave velocity (cfPWV) was measured using the cuff-based SphygmoCor XCEL system (AtCor Medical, Itasca, IL) for the assessment of aortic stiffness, as previously described (28).
FMD was assessed at the brachial and popliteal arteries via 2-dimensional Doppler ultrasound (iE33; Philips Medical Systems, Bethesda, MD) according to published guidelines and as previously described (29, 30). An independent investigator confirmed the quality of the videos and analysis.
Assessment of Insulin-stimulated Leg Blood Flow and Skeletal Muscle Microvascular Perfusion
Intravenous catheters were inserted into the antecubital veins of both arms for blood draws and infusion of insulin and dextrose as previously described (30). Approximately 20 minutes after placement of catheters, assessments of superficial femoral artery blood flow followed by quadriceps muscle (vastus lateralis) microvascular perfusion were obtained via 2-dimensional Doppler ultrasound and contrast-enhanced ultrasound, respectively, and as previously described (30). Then, insulin (Humulin R U-100) was prepared via dilution in 250 mL of 0.9% saline along with 5 mL of blood taken from the subject to a final concentration of 500 mU/mL. Two priming infusion rates (160-80 mU/m2/min) over 10 minutes were followed by a steady-state infusion of insulin at a constant dosage of 40 mU/m2/min, mimicking postprandial insulin levels. Femoral artery blood flow and quadriceps muscle microvascular perfusion were reassessed at the end of the 60-minute infusion, and data presented as percent of change from baseline (ie, pre-insulin) values. Whole blood glucose was determined every 5 minutes and maintained at fasting levels; this was achieved by variable infusion rates of a 20% dextrose solution. Plasma was obtained and stored at −80°C for later analysis.
Measurement of Fasting Plasma Nitrite, Adropin, and Other Biochemical Parameters
Nitrite concentrations were assessed using the method of ozone-based reductive chemiluminescence (CLD88, Eco Physics, Michigan, USA) according to the manufacturer guidelines and as previously described (31, 32). Adropin concentrations were measured via an enzyme-linked immunosorbent assay, in accordance with manufacturers guidelines (Phoenix Pharmaceuticals, Burlingame, CA, USA). Samples were also submitted to the Diabetes Diagnostic Laboratory, School of Medicine—University of Missouri, for insulin and hemoglobin A1c analyses, respectively. Fasted glucose, uric acid, and lipid profile were assessed at the University of Minnesota Advanced Research and Diagnostic Laboratory. Plasma samples obtained during the insulin infusion were assessed for insulin concentrations using a commercially available kit (ALPCO Cat. No. 80-INSHU-E10.1, Salem, NH).
Cell Culture Experiment and Immunoblotting
Human male donor derived aortic endothelial cells (Lonza, Cat# CC-2535; Morristown, NJ) were cultured in VascuLife® EnGS cell culture medium (2% fetal bovine serum) and incubated with vs without adropin (10 ng/mL, Phoenix Pharmaceuticals, 032-35, Burlingame, CA) for 24 hours. Thereafter, cells were stimulated with vs without insulin (100 nM, Humulin R U-100) for 30 minutes and collected. Cell lysates were prepared as previously described for immunoblotting (33). Membranes were probed for phosphorylated endothelial NO synthase (eNOS) activation Ser 1177 (1:1000, #ab184154, Abcam; AB_2768154) and total eNOS (1:1000, #610297, BD; AB_397691). Values are expressed as fold difference.
Statistical Analysis
Data are presented as mean ± SE. The Shapiro–Wilk test was performed for assessment of data distribution and statistically significant outliers were detected using the ROUT method (Q = 5%). Sex and/or intervention-related differences in outcomes were determined using unpaired t-test, 1-way analysis of variance (ANOVA), 2-way mixed-design ANOVA, and 2-way repeated measures ANOVA, as appropriate. The Holm–Sidak post hoc test was performed when significant interactions were found. The Pearson product–moment correlation coefficient was used to examine potential correlations between variables of interest. The results were considered statistically significant when P < .05. Statistical analyses were performed using GraphPad, Prism (version 9.0).
Results
Characteristics of the 10-day Obesogenic Lifestyle Intervention
Figure 1 depicts daily step counts and consumption of sugar, sodium, caffeine, and calories derived from the carbonated beverages in females and males. Both males and females achieved a similar significant reduction in daily steps (Fig. 1A), and no sex differences were noted in the depicted dietary variables (Fig. 1B).
Figure 1.
Daily step counts and sugar, sodium, caffeine, and calories added to the diet during the obesogenic lifestyle intervention. (A) Daily step counts before and after the obesogenic lifestyle (OL) intervention in females (n = 18) and males (n = 18). (B) Daily sugar, sodium, caffeine, and total calories derived from the intake of sweetened beverages during the OL intervention in females (n = 18) and males (n = 18). A 2-way mixed-design ANOVA (A) and unpaired t-test (B) were performed. †P < .05, main effect of OL.
Impact of the Obesogenic Lifestyle Intervention on Metabolic Outcomes and Measures of Conduit Artery Function
Table 1 shows the individuals’ characteristics, anthropometrics, metabolic profile, blood pressure, and cfPWV. The intervention resulted in increases in body weight, fasting triglycerides, and insulin levels along with worsening of insulin sensitivity in both females and males. In addition, high-density lipoprotein cholesterol decreased in both sexes. No differences were elicited in blood pressure or arterial stiffness. Popliteal and brachial artery FMD measures before and after the obesogenic lifestyle intervention are described in Table 2. As noted, the intervention significantly increased popliteal artery FMD in females, while there was a trend (P = .069) toward attenuation in males.
Table 2.
Popliteal and brachial artery characteristics during the flow-mediated dilation (FMD) assessments before and after the obesogenic lifestyle (OL) intervention in females and males
| Females Mean ± SE (n = 18) |
Males Mean ± SE (n = 18) |
|||
|---|---|---|---|---|
| Before OL | After OL | Before OL | After OL | |
| Popliteal artery | ||||
| Baseline diameter (mm) | 4.48 ± 0.1 | 4.46 ± 0.1 | 5.53 ± 0.1b | 5.56 ± 0.1b |
| Time-to-peak dilation (s) | 82 ± 12 | 102 ± 13 | 81 ± 14 | 102 ± 13 |
| Peak diameter (mm) | 4.69 ± 0.2 | 4.75 ± 0.1 | 5.77 ± 0.1b | 5.77 ± 0.1b |
| Absolute change in diameter (mm) | 0.19 ± 0.03 | 0.25 ± 0.03a | 0.22 ± 0.03 | 0.16 ± 0.02a |
| Mean shear (s−1) | 52 ± 7 | 68 ± 11 | 51 ± 4 | 49 ± 6 |
| Shear AUC (a.u.) | 6486 ± 2265 | 7132 ± 3234 | 5631 ± 1219 | 5743 ± 1803 |
| FMD (%) | 4.73 ± 0.75 | 6.44 ± 0.59a | 4.29 ± 0.50 | 3.00 ± 0.47 |
| Brachial artery | ||||
| Baseline diameter (mm) | 2.95 ± 0.1 | 3.04 ± 0.1 | 3.74 ± 0.1b | 3.73 ± 0.1b |
| Time-to-peak dilation (s) | 71 ± 11 | 65 ± 11 | 86 ± 13 | 70 ± 10 |
| Peak diameter (mm) | 3.23 ± 0.1 | 3.26 ± 0.1 | 3.98 ± 0.1b | 4.01 ± 0.1b |
| Absolute change in diameter (mm) | 0.28 ± 0.05 | 0.23 ± 0.03 | 0.22 ± 0.02 | 0.25 ± 0.03 |
| Mean shear (s−1) | 114 ± 16 | 133 ± 25 | 150 ± 26 | 148 ± 32 |
| Shear AUC (a.u.) | 36 832 ± 6852 | 27 697 ± 3077 | 24 010 ± 2392 | 27 163 ± 3090 |
| FMD (%) | 9.19 ± 1.73 | 7.53 ± 1.02 | 6.38 ± 0.73 | 6.86 ± 0.95 |
Abbreviations: AUC, area under the curve; OL, obesogenic lifestyle.
P < .05 vs Before OL (Holm–Sidak post hoc analysis).
P < .05, main effect of sex.
Females are Protected Against Vascular Insulin Resistance Induced by the Obesogenic Lifestyle Intervention
The effects of the intervention on vascular responses to insulin are depicted in Fig. 2. After 10 days, males exhibited a reduction in the leg blood flow and vascular conductance responses to insulin infusion compared with responses before the intervention. Notably, no significant changes in these variables were observed in females (Fig. 2A and 2B). Similarly, the obesogenic intervention suppressed skeletal muscle microvascular perfusion during insulin infusion in males but not females (Fig. 2C).
Figure 2.
Females are protected against vascular insulin resistance induced by the obesogenic lifestyle (OL) intervention. (A) Leg blood flow response to insulin infusion (percent change from baseline) before and after the OL intervention in females (n = 11) and males (n = 15). (B) Leg vascular conductance response to insulin infusion (percent change from baseline) before and after the OL intervention in females (n = 11) and males (n = 15). (C) Skeletal muscle perfusion response to insulin infusion (percent change from baseline) before and after the OL intervention in females (n = 13) and males (n = 15). (D and G) Plasma insulin concentrations during the 60-minute insulin infusion in females (n = 13) and males (n = 15). (E and H) Blood glucose concentrations during the 60-minute insulin infusion in females (n = 16) and males (n = 16). (F and I) Glucose infusion rates during the 60-minute insulin infusion in females (n = 15) and males (n = 17). BL, baseline. A 2-way mixed-design ANOVA (A, B, C) and 2-way repeated measures ANOVA (D-I) were performed. The Holm–Sidak post hoc test was performed when significant interactions were detected. *P < .05 vs Before OL.
Figure 2 also depicts plasma insulin and blood glucose levels, as well as glucose infusion rates during the 60-minute insulin infusion. In females, plasma insulin concentrations at 15 minutes of insulin infusion were significantly higher after the intervention, relative to preintervention (Fig. 2D). No differences between the pre- and postintervention glucose infusion rates or glucose concentrations were detected in females (Fig. 2E and 2F). Comparatively, males exhibited higher glucose values with an accompanying lower glucose infusion rate after the intervention, relative to preintervention (Fig. 2H and 2I). No differences in insulin levels during insulin infusion were detected between the 2 visits in males (Fig. 2G).
Protection Against Vascular Insulin Resistance Induced by the Obesogenic Lifestyle Intervention in Females Is Accompanied With Maintenance of Circulating Levels of Adropin and Nitrite
In parallel to the changes demonstrated in vascular insulin sensitivity, the intervention resulted in a decrease in plasma adropin and nitrite concentrations only in males (Fig. 3A and 3B). As a follow-up experiment, we examined if adropin exposure augments eNOS activation in response to insulin. As shown in Fig. 3C, we found that exposure of endothelial cells to adropin for 24 hours enhanced insulin-induced phosphorylation of eNOS.
Figure 3.
Protection against vascular insulin resistance induced by the obesogenic lifestyle (OL) intervention in females is accompanied with maintenance of circulating levels of adropin and nitrite. (A) Plasma adropin concentrations before and after the OL intervention in females (n = 18) and males (n = 18). (B) Plasma nitrite concentrations before and after the OL intervention in females (n = 16) and males (n = 18). A 2-way mixed-design ANOVA was performed. The Holm–Sidak post hoc test was performed when significant interactions were detected. *P < .05 vs Before OL. (C) Determination of eNOS (endothelial nitric oxide synthase) activation (p-Ser1177), relative to total eNOS, in human aortic endothelial cells treated with vs without adropin (24 hours) and insulin (30 minutes); representative Western blot images are also displayed; samples were loaded in random order; n = 9-10/group. One-way ANOVA followed by Holm–Sidak post hoc analysis was performed. *P < .05 Adropin + Insulin vs all other conditions.
Discussion
The main finding of the present investigation is that short-term adoption of an obesogenic lifestyle characterized by reduced ambulatory activity coupled with increased consumption of sugar-sweetened carbonated beverages results in vascular insulin resistance as demonstrated by decreased insulin-stimulated leg blood flow and skeletal muscle perfusion in young healthy men but not in women. This finding was accompanied by a decrease in plasma adropin and nitrite concentrations in men. To the best of our knowledge, this is the first evidence in humans that vascular insulin resistance can be provoked by short-term adverse lifestyle changes.
Insulin resistance in the vasculature, a distinctive feature of obesity and type 2 diabetes, contributes to impaired glucose disposal and to the pathogenesis of cardiovascular disease (9‐11, 13). Here we show that after 10 days of reduced ambulation and increased ingestion of carbonated beverages high in sugar, young healthy men exhibited a blunted leg blood flow response to insulin infusion and suppressed skeletal muscle microvascular perfusion. These findings were also accompanied with a trend towards a reduction in popliteal artery FMD and a significant decrease in circulating levels of nitrite, a surrogate index of NO bioavailability. Data from preclinical models indicate that reduced insulin sensitivity in the vasculature is an early event in the development of metabolic and vascular disease (15‐18). Notably, our data provide the first support towards this notion in humans in that we observed such vasculometabolic phenotypic characteristics shortly after men transitioned into an obesity/insulin resistance-promoting behavior.
A major finding of the present investigation is that vascular insulin sensitivity and endothelial function were preserved (or even enhanced) in women despite observed metabolic abnormalities. There is recent precedence in the literature for young females to be protected against vascular perturbations (34‐36). For example, evidence exists suggesting that young women are more protected than men against prolonged sitting-induced endothelial dysfunction in the popliteal artery (34). Similarly, young women also exhibit greater protection in the brachial artery against acute bouts of oscillatory shear stress and resistance exercise–induced impairments in endothelial function (35).
It is important to note that our intervention resulted in impaired popliteal but not brachial artery endothelial function. In this respect, we have previously reported that when active men adopt a sedentary behavior, without dietary modifications, endothelial dysfunction primarily manifests in the lower limbs (37). Even though our study was not designed to identify which of the 2 lifestyle factors is the main driver of vasculometabolic impairments in men, it is likely that reduced leg blood flow and shear stress owing to decreased locomotion is a key factor explaining the differential impact of our intervention on upper vs lower extremity endothelial function (37, 38).
Other factors beyond the reduction in leg shear stress may have also contributed to leg endothelial dysfunction and vascular insulin resistance. In this regard, we report that our intervention resulted in a decrease in circulating concentrations of adropin only in males. Adropin, a peptide primarily expressed in the liver, is known to have insulin sensitizing effects in metabolically active tissues (39), and its circulating levels can be suppressed by carbohydrate intake (40, 41). In particular, low plasma adropin has been shown to be associated with increased risk of obesity development and metabolic dysfunction in nonhuman male primates fed a high sugar diet (42). On the other hand, interventions known to improve vascular and metabolic outcomes such as increased physical activity (43‐45) and weight loss (46) result in higher adropin concentrations. Notably, here we show that exposure of endothelial cells to adropin augments insulin-induced activation of eNOS. It is therefore conceivable that the drop in plasma adropin concentrations elicited by the intervention may have contributed to the impaired blood flow responses to insulin in males. Recent work by Stokar et al demonstrated that hepatic production of adropin is regulated by estrogen receptor alpha signaling (47). Hence, it is tempting to speculate that greater estrogenic signaling in premenopausal women counterbalanced the decline in circulating levels of adropin induced by the obesogenic lifestyle intervention. However, further research is needed to test whether the mechanisms underlying adropin production are influenced by sex and if adropin is indeed a major contributor to vascular protection in females.
Several aspects of the present investigation warrant further consideration. First, we examined the immediate metabolic and vascular impact of an obesogenic lifestyle intervention in a cohort of young adults and, thus, future investigations are needed to determine the timeline for reversal of these vascular and metabolic changes. Second, we report that our intervention resulted in worsened insulin sensitivity, as revealed by an increase in homeostatic model assessment for insulin resistance (HOMA-IR). However, we recognize that changes in HOMA-IR values are closely dependent on insulin levels which are impacted by changes in body weight (Table 1), and insulin clearance (48, 49). In relation to this, we also documented higher plasma blood glucose during insulin infusion (accompanied by lower glucose infusion rates) in males, but not in females, at the postintervention visit. Conversely, at the postintervention visit, females showed higher circulating concentrations of insulin at minute 15 of insulin infusion. Although these findings are indicative of a potential sexual dimorphism in the development of whole-body insulin resistance and impairments in insulin clearance derived from the intervention, future studies are needed to definitively assess insulin sensitivity and clearance. Lastly, we found that plasma nitrite concentrations were decreased in males after the intervention, and we considered this suggestive of decreased bioavailable NO. Nevertheless, changes in plasma nitrite should be interpreted with caution as its concentration may also be influenced by inflammation and consumption of nitrate rich foods (50, 51).
In aggregate, we revealed that short-term obesogenic lifestyle typified by sedentarism and increased consumption of sugar-sweetened beverages is sufficient to negatively impact metabolic outcomes associated with glucose control in both young healthy males and females. However, impairments in vascular insulin sensitivity only occurred in men, underscoring a sexual dimorphism in the development of vascular insulin resistance induced by the adoption of such obesogenic lifestyle.
Acknowledgments
The authors appreciate the time and effort of all volunteer participants. We also acknowledge the nursing team at the Clinical Research Center and the assistance of Dr. Lauren Park, Dr. Allan Sales, Dr. Thaysa Ghiarone, and Makenzie Woodford at the onset of the project.
Abbreviations
- ANOVA
analysis of variance
- cfPWV
carotid-to-femoral pulse wave velocity
- eNOS
endothelial nitric oxide synthase
- FMD
flow-mediated dilation
- HOMA-IR
homeostatic model assessment for insulin resistance
- NO
nitric oxide
Contributor Information
James A Smith, Department of Nutrition and Exercise Physiology, University of Missouri, Columbia, MO, USA.
Rogerio N Soares, Department of Medicine, University of Missouri, Columbia, MO, USA.
Neil J McMillan, Department of Nutrition and Exercise Physiology, University of Missouri, Columbia, MO, USA.
Thomas J Jurrissen, Department of Nutrition and Exercise Physiology, University of Missouri, Columbia, MO, USA.
Luis A Martinez-Lemus, Department of Medicine, University of Missouri, Columbia, MO, USA; Dalton Cardiovascular Research Center, University of Missouri, Columbia, MO, USA; Department of Medical Pharmacology and Physiology, University of Missouri, Columbia, MO, USA.
Jaume Padilla, Department of Nutrition and Exercise Physiology, University of Missouri, Columbia, MO, USA; Dalton Cardiovascular Research Center, University of Missouri, Columbia, MO, USA; Harry S. Truman Memorial Veterans’ Hospital, Columbia, MO, USA.
Camila Manrique-Acevedo, Dalton Cardiovascular Research Center, University of Missouri, Columbia, MO, USA; Harry S. Truman Memorial Veterans’ Hospital, Columbia, MO, USA; Division of Endocrinology and Metabolism, Department of Medicine, University of Missouri, Columbia, MO 65212, USA.
Funding
This work was supported, in part, by the National Institutes of Health Grants R21 DK116081 (to C.M.-A.), R01 HL142770 (to C.M-A), R01 HL137769 (to J.P.), and R01 HL151384 (to L.A.M-L. and J.P.).
Author Contributions
J.P. and C.M.-A. conceived and designed research. J.A.S, R.S., N.J.M., T.J.J., and C.M.-A. performed the experiments. J.A.S., R.S., N.J.M., J.P., and C.M.-A. analyzed the data. All authors interpreted results of experiments. J.A.S., R.S., J.P., and C.M.-A. prepared figures. R.S., J.P., and C.M.-A. drafted the manuscript. All authors edited and revised the manuscript. All authors approved the final version of the manuscript. All authors herein listed agree to be accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved; and all persons designated as authors qualify for authorship, and all those who qualify for authorship are listed.
Disclosures
No conflicts of interest, financial or otherwise, are declared by the authors.
Data Availability
The data underlying this article will be shared on reasonable request to the corresponding author.
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Data Availability Statement
The data underlying this article will be shared on reasonable request to the corresponding author.