Introduction

Hypertension affects roughly one billion individuals worldwide, making it a prevalent chronic disease1. As a major risk factor for cardiovascular diseases, it poses a threat to public health globally2. Current treatment strategies focus on comprehensive risk management beyond mere blood pressure control, emphasizing target organ protection and clinical event reduction3. Endothelial dysfunction is crucial in hypertension development, serving as both an early biomarker of elevated blood pressure and a warning for future cardiovascular events4,5. However, limited evidence exists on how early endothelial function improvement (EEFI) can prevent the progression of subclinical target organ damage (STOD) in hypertensive patients.

Flow-mediated dilation (FMD), a non-invasive technique, assesses endothelial function and accurately reflects vascular health. Using this technology, our prior research6,7,8,9,10 has investigated the link between endothelial function and hypertension, demonstrating that endothelial dysfunction correlates with a heightened risk of progression and complications in essential hypertension (EH). Based on these findings, we hypothesized that EEFI would reduce the incidence of STOD in EH patients. We aimed to explore this hypothesis through empirical research. This study sought to explore the potential of EEFI to prevent STOD in EH patients. The findings could enhance the understanding of EH progression and inform prevention and treatment strategies for hypertension.

Methods

Experimental protocol

This single-center retrospective cohort study drew from the Hypertension Target Organ Damage and Its Risk Factors—Fuzhou Study database. Ethical clearance was granted by the Ethics Committee of the First Affiliated Hospital of Fujian Medical University (Ref: MRCTA, ECFAH of FMU (2020) 306). Additionally, the study was registered with the China Clinical Trial Registry under registration number ChiCTR2000039448 (Dated: 28/10/2020), available at http://www.chictr.org.cn/index.aspx. The study conformed to the Declaration of Helsinki guidelines, with all participants having read and signed informed consent forms before participating.

Participants

This study analyzed EH patients from the First Affiliated Hospital of Fujian Medical University, with follow-up data spanning August 1, 2000, to May 31, 2016. Hypertension diagnosis followed the 2018 Chinese Guidelines for Prevention and Treatment of Hypertension11. STOD diagnostic criteria: (1) cardiac: echocardiography showing left ventricular mass index (LVMI) ≥ 115 g/m2 for males or ≥ 95 g/m2 for females; (2) renal: mildly elevated serum creatinine (males 115–133 μmol/L, females 107–124 μmol/L), reduced glomerular filtration rate [30–59 mL/(min·1.73 m2)], proteinuria-to-creatinine ratio ≥ 30 mg/g; (3) vascular: carotid intima-media thickness (CIMT) ≥ 0.9 mm or arterial plaques. Endothelial function improvement was defined as a return to normal for initially dysfunctional patients, and an enhancement beyond baseline for those initially normal, after three months of treatment. Inclusion criteria: (1) confirmed EH; (2) no evidence of STOD or any cardiovascular disease (e.g., myocardial infarction, stroke, or peripheral artery disease). Exclusion criteria were: secondary hypertension, presence of STOD or cardiovascular disease, heart failure, severe arrhythmias, hematologic or rheumatologic conditions, significant liver or kidney dysfunction, thyroid issues, cancer, recent serious infections, or immunosuppressant use7,8.

All patients received treatment as per the standards outlined in the Chinese guidelines for hypertension management11. Follow-up was conducted every 1 to 3 months by telephone appointment, encompassing both outpatient and inpatient visits. If patients did not comply, certain target organ assessments (e.g., CIMT) were postponed to a 6-month interval. The follow-up endpoint was the occurrence of STOD, with the interval from enrollment to STOD onset was defined as the survival period. The follow-up cut-off date was May 31, 2018, with a median follow-up time of 25 months (95%CI 10–63). Initially intended to follow 762 patients, the study ultimately included 456 due to exclusion criteria, losses to follow-up, and missing FMD data. Patients were categorized into groups based on initial endothelial function: impaired and normal. Within three months of enrollment, they were further subdivided into improved and unimproved groups based on improvement in endothelial function (Fig. 1).

Figure 1
figure 1

Flowchart for identifying study cohorts from the Hypertension Target Organ Damage and Its Risk Factors—Fuzhou Study database. EH essential hypertension, FMD flow-mediated dilation, CVD cardiovascular disease.

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Clinical data collection

Upon admission, data on participants’ age, gender, drinking and smoking habits, duration of hypertension and medical history were collected. Current smokers were defined as individuals who smoked at least one cigarette daily for over six months. Drinkers were defined as males consuming over 25 g and females over 15 g of alcohol per day10. Participants were required to abstain from coffee and strong tea for half an hour before the examination. Following a 5-min rest, blood pressure and heart rate were measured with a HEM-7052 automatic sphygmomanometer (Omron, Japan), averaging three readings10. Height and weight were measured, and then body mass index (BMI) was calculated as weight (kg) divided by the square of height (m2). Blood samples were drawn from the antecubital vein of all subjects in the morning after an 8-h fast. Subsequently, the samples were analyzed for total bilirubin, alanine aminotransferase, lactate dehydrogenase, uric acid, creatinine, total cholesterol (TC), high-density lipoprotein-cholesterol, low-density lipoprotein-cholesterol (LDL-C), and fasting serum glucose (FSG) using an ADVIA 2400 automatic analyzer (Siemens, Germany)10. Urinary albumin was assessed by immunoturbidimetry (Roche P800, USA), and urinary creatinine by colorimetric method (Boehringer Mannheim/Hitachi 717 system, Germany), to calculate the urine albumin-to-creatinine ratio (UACR)10. The estimated glomerular filtration rate (eGFR) was calculated using the Chronic Kidney Disease Epidemiology Collaboration equation12.

Flow-mediated dilation

This study adhered to international ultrasound guidelines for vascular function13 and integrated previous research6,7,8,9,10 to establish a standardized testing protocol. Patients were positioned supinely, with the target vessel, the brachial artery segment 5 cm above the right elbow crease, clearly marked. Following a 10-min rest, the basal inner diameter of the brachial artery was measured three times using a LOGIQ7 color doppler ultrasound (GE, USA), and the average was recorded as D0. A cuff was placed 5–17.5 cm above the elbow, inflated to 200 mmHg or 50 mmHg above systolic pressure, obstructing blood flow for 5 min, followed by rapid deflation. After 80–90 s of decompression, the diameter of the target vessel (D1) was measured6,7,8,9,10. Endothelial-dependent vascular function was calculated using the formula FMD = (D1 − D0) × 100%/D0, defining FMD ≤ 7.1% as endothelial dysfunction6,7,14. Vascular function was assessed by three researchers trained in the same standardized method, with an intra-operator coefficient of variation of 1.9% and an inter-operator coefficient of variation of 6.92%6,7,8,9,10.

Carotid ultrasound and echocardiography

The examination was performed using a LOGIQ7 color Doppler ultrasound (GE, USA) by an experienced physician unaware of the clinical details. During the carotid ultrasound, participants lay flat, without a pillow, turning their head towards the examined side. The ultrasound continuously scanned from the right brachiocephalic artery’s bifurcation to the left aortic arch’s origin, covering both carotid arteries and their branches. CIMT was measured five times 1.5 cm proximal to the common carotid artery bifurcation, and the average was taken as the result15. If plaques were present, measurements were taken at the same proximal location. During echocardiography, the physician measured left ventricular end-diastolic diameter (EDD), septal wall thickness (SWT), and posterior wall thickness (PWT) using M-mode tracing while participants rested. Left ventricular mass (LVM) was calculated with the formula: 0.8 × 1.04 × [(EDD + SWT + PWT)3 − EDD3] + 0.6. Body surface area (BSA) was calculated from height and weight, and LVMI was derived by dividing LVM by BSA16.

Statistical analyses

Data processing and analysis utilized SPSS version 22.0. Tests for normal distribution and homogeneity of variance preceded analysis of continuous variables. Normally distributed data were reported as mean ± standard deviation, while non-normally distributed data were reported as median and interquartile distance. Categorical data were expressed as frequencies (percentages). Group differences were assessed using Pearson or Fisher's chi-square tests, Student's t-test, and Mann–Whitney U test. Kaplan–Meier survival curves and cumulative hazard curve for the occurrence of outcome events in the two groups of patients were plotted using the "survival + survminer" package in R software (version 4.2.1), with group differences compared using the log-rank test. Finally, multivariate Cox regression analysis determined the effects of EEFI on STOD and identified additional potential risk factors. Subgroup analysis was performed, with results visualized using the "forestploter" package. Statistical significance was defined as a two-sided p-value < 0.05.

Results

Comparison of patient baseline characteristics

This study included 456 patients with EH, 180 with endothelial dysfunction, and 276 with normal endothelial function. Eventually, 177 patients developed STOD. All patients included in the study were free from any previous cardiovascular diseases at baseline. Compared to those with normal function, the endothelial dysfunction group featured a higher proportion of men, smokers, and individuals with diabetes, and displayed increased age as well as extended duration of EH (p < 0.05). Additionally, this group had lower levels of FMD, but higher uric acid levels (p < 0.05). In terms of medication, patients with initial endothelial impairment used more statins and fewer β-blockers than those with normal function (p < 0.05). No significant differences were observed in other baseline data between the two groups (Table 1).

Table 1 Clinical characteristics of hypertensives patients with and without initial endothelial impairment.
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Patients were categorized based on initial endothelial function for further analysis. In the impaired group, the improved subgroup had significantly fewer smokers than the unimproved subgroup (p < 0.05), with similar other baseline characteristics. Despite similar blood pressure control, the improved subgroup used more renin-angiotensin system (RAS) inhibitors and fewer diuretics than the unimproved subgroup (Table 2). In the normal group, those in the improved subgroup were younger with higher eGFR levels than the unimproved subgroup (p < 0.05). There were no significant abnormalities between the groups in terms of initial treatment medications and other baseline data (Table 3).

Table 2 Clinical characteristics of patients with initial endothelial impairment who improved vs. those who did not improve after 3 months of enrollment treatment.
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Table 3 Clinical characteristics of patients with initial normal endothelial function who improved vs. those who did not improve after 3 months of enrollment treatment.
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Relationship between EEFI and the incidence of STOD in EH patients

Kaplan–Meier survival curve analysis revealed a significantly higher incidence of STOD in EH patients with endothelial dysfunction than in those with normal function (Log-rank test, p < 0.001), as shown in Fig. S1 (Supplementary Fig. 1). Subsequent subgroup analysis with a cumulative hazard curve indicated that the group with improved endothelial function exhibited a significantly lower STOD incidence than the unimproved group (Log-rank test, p < 0.05) (Fig. 2).

Figure 2
figure 2

Cumulative hazard curves for STOD in the improved (dotted line) and unimproved (solid line) groups of EH patients with initial impaired (a) and unimpaired (b) endothelial function. EH essential hypertension, STOD subclinical target organ damage.

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Cox regression analysis of the incidence of STOD in EH patients

Multivariate Cox regression analysis was conducted with EEFI, factors with significant differences or trends in the univariate analysis, and traditional risk factors (age, gender, BMI, smoking, blood pressure, FSG, and LDL-C) as independent variables to examine their association with STOD incidence. In patients with initial endothelial impairment, age, female and LDL-C emerged as independent risk factors for STOD, whereas EEFI (HR = 0.53, 95% CI 0.35–0.79) served as a protective factor (Fig. 3a). Subgroup analysis showed that EEFI significantly reduced the risk of STOD in patients under 65, male, overweight, non-diabetic, non-smokers, with LDL-C below 3.4 mmol/L. Conversely, its impact was not significant in patients 65 or older, female gender, not overweight, diabetic, smokers, or with LDL-C at or above 3.4 mmol/L (Fig. 3b). As illustrated in Fig. 4a, for patients with normal endothelial function, EEFI (HR = 0.53, 95% CI 0.30–0.94) continued to act as a protective factor against STOD, whereas smoking was the sole independent risk factor. Notably, the subgroup analysis revealed similar results to those in patients with initially impaired endothelial function, except for gender, BMI, and diabetes, which were not yet statistically different, as shown in Fig. 4b.

Figure 3
figure 3

Cox regression analysis of STOD in patients with essential hypertension who had initial impaired endothelial function (a) and its subgroups (b). STOD subclinical target organ damage, BMI body mass index, LDL-C low-density lipoprotein-cholesterol, EEFI early endothelial function improvement.

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Figure 4
figure 4

Cox regression analysis of STOD in patients with essential hypertension who had initial normal endothelial function (a) and its subgroups (b). STOD subclinical target organ damage, BMI body mass index, LDL-C low-density lipoprotein-cholesterol, eGFR estimated glomerular filtration rate, EEFI early endothelial function improvement.

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Discussion

This retrospective cohort study analyzed 456 patients with EH over 16 years to evaluate the impact of EEFI on preventing STOD. Results showed that EH patients with endothelial dysfunction faced a significantly higher risk of developing STOD than those with normal function. More importantly, early improvement in endothelial function significantly lowered the cumulative incidence of STOD, particularly when blood pressure was maintained at target levels. Interestingly, the protective benefits of endothelial function improvement were more pronounced in certain groups, including patients under 65 years of age, nonsmokers, and with lower LDL-C levels.

Endothelial cells are crucial for vascular health, regulating vasodilation, vasoconstriction, anti-inflammatory responses, and anticoagulant functions17. In EH, endothelial dysfunction significantly increases the risk of developing STOD18,19. FMD is a well-established, accurate, and non-invasive indicator of peripheral endothelial function6,7,8,9,10,13 and is widely utilized in clinical research. Sun et al.19 found that adverse changes in FMD correlated with increases in LVH, UACR, and CIMT in a large cohort of EH patients. Furthermore, Yang et al.20 in a prospective study involving 199 EH patients, demonstrated that FMD was independently linked to the occurrence of STOD. This cohort study reaffirmed that EH patients who initially had endothelial dysfunction were much more likely to develop STOD compared to those with normal function. Mechanistically, endothelial dysfunction impairs nitric oxide (NO) production, leading to reduced vasodilation and increased vascular resistance, contributing to the advancement of hypertension4,17. Additionally, endothelial dysfunction is associated with increased oxidative stress and inflammation, further damaging vascular tissues and exacerbating blood pressure control18. Therefore, endothelial dysfunction is not only an independent predictor of STOD in EH patients but also a crucial target for clinical intervention.

This study showed that EEFI significantly reduced the cumulative incidence of STOD in EH patients, irrespective of their initial endothelial function. Studies have suggested that identifying and treating endothelial dysfunction can slow the progression of hypertension and decrease the risk of severe cardiovascular events19,21. Intervention studies have revealed that RAS inhibitors and statins not only provide foundational treatment but also enhance endothelial cell function, increase NO production, and improve vascular health22,23,24. After three months of consistent antihypertensive treatment, only a subset of patients experienced improvement in endothelial function, potentially due to the endothelial protective effects of RAS inhibitors and statins. Recent research has indicated that SIRT6, through epigenetic modulation, can prevent hypertension-induced endothelial dysfunction21. Non-pharmacological interventions, such as regular aerobic exercise25,26, dietary changes (e.g., mediterranean diet27, omega-3 fatty acids28), stress reduction techniques (e.g., yoga29), and lifestyle modifications like smoking cessation30, have been shown to improve endothelial function and promote vascular health in recent studies. However, reports on the early enhancement of endothelial function to reduce STOD in EH patients remain scarce. This study enhances our understanding that EEFI can serve as a preventive strategy to lower the risk of STOD in hypertensives.

This study also emphasized the importance of EEFI in specific populations. In hypertensive patients under 65 years, EEFI effects are more pronounced due to their greater vascular elasticity and stronger cellular regenerative capacity31. Male patients' positive response to EEFI may be due to their unique physiological and hormonal conditions. Research indicates that androgens may promote vasodilation in hypertensives by increasing the bioavailability of NO32. Overweight patients face a heightened risk of endothelial dysfunction, driven by elevated inflammation33. In this population, early intervention in endothelial function may reduce cardiovascular risks34. Hypertensive non-smokers typically exhibit lower oxidative stress35. Thus, they are better positioned to benefit from EEFI and show a stronger capacity for endothelial function recovery. Additionally, lower LDL-C and normal blood glucose support a healthy metabolic state, enhancing the endothelial cells' response to treatment and thereby promoting vascular health36,37. These findings underscore the need for targeted endothelial assessment and intervention in specific hypertensive subgroups to lower STOD risk and improve cardiovascular health, facilitating personalized treatment strategies.

However, this study had several limitations. The retrospective cohort design might have introduced information bias and missing variables, which were addressed through Cox regression analysis. Categorizing patients by endothelial function improvement within three months did not consider the effects of different medications or lifestyle changes. The single-center setting with a limited sample size, especially with few patients having initial endothelial dysfunction, may constrain the broader applicability. Importantly, we did not analyze major adverse cardiovascular events, which are essential for understanding long-term cardiovascular risks. We also did not measure endothelial glycocalyx biomarkers, which could have provided deeper insights into endothelial health. Although FMD is the gold standard for assessing endothelial function, it is time-consuming, expensive, and requires specialized equipment and personnel. Alternative methods like reactive hyperemia index, pulse wave velocity, and serum biomarkers (e.g., endothelin-1 and C-reactive protein) could be more practical38. Lastly, our study included only Asian patients, limiting our findings' applicability to other racial and geographic populations. Future research should include a more diverse patient population to validate and broaden these findings.

Conclusion

In summary, this study demonstrated that meeting blood pressure targets in EH patients, combined with early enhancement of endothelial function, significantly decreased the risk of subsequent STOD. The results provide clinicians essential insights into assessing and intervening in endothelial function, recommending their incorporation into standard EH management protocols, particularly for patients under 65 years old, non-smoking, and with LDL levels below 3.4 mmol/L.