For a long time, lipoprotein(a) (Lp(a)) has not been as studied as low-density lipoprotein cholesterol (LDL-C), even though it contributes to a substantial share of residual cardiovascular risk [1, 2, 3]. Its ‘resurrection’ was fueled by genetic investigations supported by epidemiological, clinical, and experimental findings [4, 5, 6]. Its official inauguration in both European [7] and American guidelines [8] subsequently followed. Thus, owing to cardiological advancements, elevated lipoprotein(a) is now recognized as a global challenge for humankind, with a fifth—1.4 billion people—facing cardiovascular risk [9].

At the current stage, phase 3 studies of the antisense oligonucleotide (pelacarsen) [10] and phase 2 studies of small interfering ribonucleic acid (siRNA) (olpasiran) [11] are being completed. Simultaneously, the threshold levels for initiating treatment to mitigate cardiovascular risk and the necessary Lp(a) reduction for achieving clinically significant benefits are being determined [12]. Notably, recent analyses of the results from the EPIC-Norfolk [13] and Copenhagen General Population [14] studies have found sex differences in the impact of high lipoprotein(a) levels on increasing cardiovascular risk.

An analysis of the EPIC-Norfolk study revealed a higher association of Lp(a) levels with the risk of future coronary heart disease (CHD) in men compared to women. The risk of CHD incidence in men was statistically significant when Lp(a) levels were above the median, whereas for women, the risk of CHD incidence was statistically significant at Lp(a) levels above the 90th percentile [13]. In another large study, the Copenhagen General Population Study (CGPS), where the number of women (n = 37,545) slightly exceeded the number of men (n = 32,497), it was observed that even though Lp(a) levels increased by 27% in women over 50 years of age, this did not lead to an increased cardiovascular risk relative to the male cohort [14].

This study aimed to investigate major adverse cardiovascular events (MACE) over 5 years in patients with coronary artery disease (CAD), in general, and depending on sex, lipoprotein(a) level, and the kringle IV type 2 (KIV-2) repeat numbers in the Lipoprotein(A) (LPA) gene.

This study included 216 patients (120 women and 96 men) hospitalized with a diagnosis of ‘CAD, unstable angina (IIB class, Braunwald et al. [15], 1989)’ between 2016 and 2017. Patients with a history of myocardial infarction (MI) within the previous 3 months, type 2 diabetes requiring insulin therapy, atrial fibrillation, chronic heart failure above functional class I (New York Heart Association (NYHA)), chronic renal and hepatic insufficiency, long-term continuous use of lipid-lowering drugs, premenopausal hormone therapy, and early surgical menopause were excluded from the study. Women were considered post-menopausal if they had not experienced menstruation for at least 12 months due to natural menopause. Baseline treatment for the study group included statins, or a combination of statins and ezetimibe, to achieve target LDL-C levels. A recent meta-analysis of 24 eligible studies confirmed that hormone replacement therapy may significantly reduce Lp(a) concentrations [16] Early surgical menopause in women leads to a premature reduction in estrogen levels and an increase in Lp(a) levels.

Baseline treatment included statins or a combination of statins and ezetimibe to achieve target LDL-C levels. Over a five-year period, the three-point risk of MACEs, encompassing cardiovascular death, non-fatal myocardial infarction, and stroke, was assessed.

The following diagnostic and functional parameters were assessed in all patients to verify the CAD diagnosis and determine inclusion and exclusion criteria for the study: 12-lead electrocardiogram (ECG), echocardiography (EchoCG), ultrasound examination of the carotid arteries, 24-hour Holter monitoring, treadmill test, coronary angiography (if required), and biochemical tests.

In the cohort of patients randomized to the study (Table 2), there were 96 men and 120 women. Although the women with CAD were, on average, 3.5 years older (p 0.05), the comparison groups did not differ in terms of comorbidity, including hypertension (HT), body mass index (BMI), and type 2 diabetes mellitus (T2DM). Similarly, there were no significant differences in the severity of the clinical course of CAD, such as a history of myocardial infarction (MI), stroke, or revascularization.

Women exhibited slightly higher total cholesterol levels (p 0.05), which were associated with higher HDL-C levels (p 0.05). This occurred as HDL-C levels did not significantly differ between men and women. Additionally, women had slightly higher levels of ApoA-I (p 0.05) and PCSK9 (p 0.01). The lower ApoB:ApoA-I ratio in women can be attributed to their higher ApoA-I levels. Of the 120 women examined, 100 (83%) were postmenopausal due to age, and 20 (17%) were premenopausal. This was reflected in their blood estradiol levels. Expectedly, testosterone levels were higher in men.

In the studied CAD patient cohort, the Lp(a) distribution was right skewed, with a median value of 13.0 mg/dL and an average of 30.2 mg/dL. The median Lp(a) level was slightly higher in women at 14.0 mg/dL (interquartile range: 7.0–51.5) compared to men at 12.0 mg/dL (interquartile range: 5.0–41.5), though this difference was not statistically significant. Additionally, the 5-year risk of MACEs was not significantly different between women and men, with a RR of 0.71 and a 95% confidence interval (CI) of 0.44–1.15.

Among all patients, the first quartile (Q1) and fourth quartile (Q4) Lp(a) values were 6 mg/dL and $>$48 mg/dL, respectively (refer to Table 3). It is possible that due to postmenopausal status, the Q4 for Lp(a) distribution in women was $>$51.5 mg/dL, while in men, it was $>$41.5 mg/dL. As expected, the 2^{-Δ⁢Δ⁢Ct} value, which is associated with the size of apolipoprotein(a) isoforms, was significantly lower in Q4 than in Q1 among all patients (p 0.001), as well as separately among men (p 0.01) and women (p 0.01). In all quartiles for the Lp(a) distribution, the HDL-C and ApoA-I levels were higher, and the ApoB:ApoA-I ratio was lower in women than in men. The estradiol level in women was significantly lower in all Lp(a) quartiles, which may be attributed to postmenopausal age.

The relative risk of MACEs for patients with elevated Lp(a) (Fig. 1) was 2.0 (95% CI: 1.04–3.87, p 0.05) in Q4 ($\ge$48 mg/dL) versus Q1 ($\le$6 mg/dL). This increase was mainly observed in men, with a RR of 2.6 (95% CI: 1.10–6.16, p 0.05), but was not statistically significant in women, where the RR was 1.4 (95% CI: 0.50–3.92).

Fig. 1.

Risk of MACEs by quartiles of lipoprotein(a) (Lp(a)) in all patients (A), and men (B)and women (C) separately. Q1, Q2–3, Q4, quartiles of Lp(a); RR, relative risk; MACE, major adverse cardiovascular event.

When the examined patients were divided into quartiles based on the 2^{-Δ⁢Δ⁢Ct} value (see Table 4), the lower quartile (Q1) included patients with values 3.9, and the upper quartile (Q4) $>$6.1. For women, these values were 3.7 and $>$6.1, respectively, and 4.0 and $>$6.3 for men, respectively. In Q1, the median Lp(a) was higher compared to Q4: 42.5 mg/dL among all patients (p 0.01), 24.0 mg/dL in men (p 0.01), and 46.5 mg/dL in women (p 0.01). Additionally, the HDL-C and ApoA-I levels were consistently higher in all quartiles in women compared to men, while estradiol and testosterone levels were lower.

The RRs of MACEs for Q1 versus Q4 according to 2^{-Δ⁢Δ⁢Ct} (number of KIV-2 repeats) were as follows: 3.0 (95% CI: 1.48–6.08, p 0.001) for all patients; 3.0 (95% CI: 1.20–6.55, p 0.01) for men; 3.3 (95% CI: 1.02–10.4, p 0.05) for women (see Fig. 2).

Fig. 2.

Risk of MACEs by quartiles for 2^{-Δ⁢Δ⁢𝐂𝐭}* (number of KIV-2 repeats) in all patients (A) and men (B) and women (C) separately. Q1, Q2–3, Q4, quartiles of 2^{-Δ⁢Δ⁢Ct}* from quantitative real-time polymerase chain reaction (qPCR), as a genetic score for lipoprotein(a) concentration, associated with apolipoprotein(a) isoform size and LPA KIV-2 number of repeats. RR, relative risk; MACE, major adverse cardiovascular event; KIV-2, kringle IV type 2.

CAD is a leading cause of death in both men and women across developed and developing countries [19]. An analysis of the Women’s Health Study cohort involving female healthcare professionals revealed that in women under 55 years of age, premature CAD was more closely associated with diabetes mellitus, metabolic syndrome, hypertension, and smoking than LDL-C, non-HDL-C, and ApoB [20].

The estrogen level in women fluctuates cyclically at different periods of their lifetime, and this causes changes in the levels of lipids [21]. Additionally, decreased estradiol levels adversely affect postmenopausal lipid profiles, leading to a complex of pathogenetic issues, including endothelial dysfunction and inflammation, which in turn increase the risk of atherosclerotic cardiovascular disease (ASCVD) in women [22]. Population studies have shown that Lp(a) levels increase by 8–13% in postmenopausal women relative to premenopausal controls [12, 23, 24]. Lp(a) plasma levels are determined by the apolipoprotein(a) (apo(a)) levels, the expression of which is also modulated by estrogens [24]. The results of a recent meta-analysis [16] of 24 eligible studies confirmed that hormone replacement therapy (HRT) may significantly reduce Lp(a) concentrations compared with placebo or no treatment. In this case, oral estrogen causes a greater reduction in Lp(a) concentrations than transdermal estrogen.

Lp(a) has been recognized as an independent risk factor for cardiovascular morbidity and mortality. Recent findings from authoritative studies, including the Women’s Health Study (WHS), EPIC-Norfolk, and the CGPS—amounting to over 100,000 observations [13, 14, 25]—have highlighted sex-specific variations in its impact on cardiovascular risk.

Initially, results from three cohort studies [25] in women (WHS, n = 24,558; Women’s Health Initiative (WHI), n = 1815; Justification for the use of statins in prevention (JUPITER), n = 2569) demonstrated its limited effect on cardiovascular risk compared to the JUPITER study in men (n = 5161). Unlike men, elevated Lp(a) did not independently affect the development of endpoints in women but only in combination with an increased level of total cholesterol ($>$220 mg/dL).

Then, the results of the EPIC-Norfolk study [13], which investigated the association between Lp(a) levels and long-term CAD, IS, and calcific aortic valve stenosis (CAVS) in a population-based study of 25,663 men and women aged between 45 and 79 years residing in Norfolk (UK), demonstrated a link between high Lp(a) with prevalent CAD and CAVS in both men and women but not with ischemic stroke in women.

Finally, the CGPS with 37,545 women and 32,497 men aged 20–89 years, with a median age of 60 years (from 2003 to 2006 until the studied endpoint, death, or December 2018), showed that Lp(a) levels increased modestly to around age 50 in women (+27%); however, the risk of morbidity and mortality for high Lp(a) was similar in women and men above 50 [14].

The CGPS [14], which is the largest study in this context, found that Lp(a) levels increased with age in women due to decreased estradiol concentrations and estimated glomerular filtration rate (eGFR). However, despite higher levels of lipoprotein(a) in women relative to men, there was a similar risk for myocardial infarction, ischemic heart disease, ischemic stroke, aortic valve stenosis, heart failure, cardiovascular mortality, and all-cause mortality in women and men with lipoprotein(a) levels $>$40 mg/dL (83 nmol/L), overall and stratified for above and below age 50.

The authors believe that the modest increase in lipoprotein(a) levels selectively in women aged about 50 years observed in the CGPS challenges the current view that only one measurement of lipoprotein(a) in women and men is sufficient to determine the concentration of lipoprotein(a) over a lifetime [14]. This is especially important for women who had lipoprotein(a) measurements taken before age 50, where additional lipoprotein(a) measurements should be considered at a later stage. However, it has yet to be determined exactly how many measurements will be needed from the onset of post-menopause in women since it varies across the lifetime.

The kringle IV (KIV) repeat polymorphism explains approximately 30–70% of the variability [12] in Lp(a) concentration and allows the identification of patients with small apolipoprotein(a) isoforms. Most large-scale studies have demonstrated that apo(a) size is genetically determined and that predominantly small isoforms are associated with an increased cardiovascular risk [4, 26, 27]. In this regard, qPCR is a faster, more sensitive, and more reliable assay to detect the number of KIV2 repeats in LPA, which will facilitate risk stratification and decision-making on the initiation of therapy in women with difficult cases [28].

In our study, 100 out of 120 examined women (83%) were observed to be postmenopausal due to age. Furthermore, in the fourth quartile (Q4) of the Lp(a) distribution among women, the Lp(a) value exceeded 51.5 mg/dL, compared to $>$41.5 mg/dL in men (+19.4%, NS), but this did not correspond to an increased 5-year risk of MACEs in women. However, in the first quartile (Q1) of the 2^{-Δ⁢Δ⁢Ct} distribution in all patients and men and women separately, which included individuals with genetically determined pathogenic “small” apo(a) isoforms, the Lp(a) values were significantly higher than in Q4 for all cases (p 0.01). In our study, this combination of elevated Lp(a) and genetic risk factors increased MACEs in both men and women equally.

The quantification of kringle IV type 2 repeat copy number in the LPA gene through qPCR more accurately reflects the risk of MACE within 5 years in women with coronary artery disease. This sex-specific observation underscores the importance of personalized medical approaches in the management and risk assessment of CAD. Alternatively, this may necessitate, in some cases, the use of inexpensive and technically accessible genetic screening methods, such as qPCR, to tailor treatment more effectively.

Additional resources can be obtained from the corresponding author [Aleksandr Shek], with the consent of all authors of the article.

AS and RA designed the study. AA, KF, SK and GA performed the study and analyzed MACEs. DZ performed the genetic research. RK and AK performed and analyzed functional studies. LK performed and analyzed the biochemical studies. All authors contributed to editorial changes in the manuscript. All authors read and approved the final manuscript. All authors have participated sufficiently in the work and agreed to be accountable for all aspects of the work.

Our study was approved by the Ethics Committee of the Republican Specialized Scientific and Practical Medical Center of Cardiology No. 8 dated September 28, 2016. All subjects provided written informed consent before participating in the treatment.

Not applicable.

The study was supported by a research grant from the Ministry of Innovative Development of Uzbekistan (State Registration No. PZ-202007041).

The authors declare no conflict of interest.