In this study, we applied ICP-MS to measure the plasma concentrations of 21 elements in the CAD patients and the healthy subjects. Unlike previous studies, we did not focus on the associations between the individual elements and CAD prevalence. Instead, a multi-element approach was implemented to explore the relationships between the ionomic profiles and CAD, which is more reliable and precise than examining individual elements. Firstly, we found that, in our study population, Sb, Ti, Fe, and Se may play a protective role in CAD, while Ba, Li, and Pb may have a detrimental influence on CAD. These results demonstrate that the status of elements in the human body may partly change when physiological conditions alter, as reported in other studies. For instance, accumulating evidence highlights the function of Se in the cardiovascular system, owing to its role in regulating the inflammatory response and antioxidant properties, as well as the importance of Se supplementation for patients undergoing cardiac surgery [25, 26]. On the contrary, Pb was widely interpreted as a harmful factor in CAD due to its role in inducing oxidative stress [27, 28]. However, certain contradictions exist. Specifically, it has been reported that both iron excess and deficiency may be positively associated with CAD [3, 29] or may not be related [5]. This conflict may be attributed to differences in sample size, ethnic groups, complications like anemia, lifestyle, and living environment, which may result in discrepant exposure to ions. Nevertheless, larger sample sizes and further research are needed to validate the relationship between iron and clinical outcome, verify its functions, and unveil mechanisms in CAD.
Subsequently, the PCA and OPLS-DA models revealed a distinct differentiation between patients with coronary artery disease (CAD) and healthy individuals based on their ionomic profiles. These results may suggest that elements with different physiological statuses may have distinguishable ionomic profiles, potentially aiding in the diagnosis of diseases such as CAD. More importantly, Li, Pb, Ni, Fe, and Sb were found to be the more important elements in the model according to VIP and S-plot analyses. This implies that simplifying the detection process by focusing on these five elements instead of the original 21 could potentially reduce time and cost in clinical diagnosis. Increasing studies took advantage of the prosperity of the ionomic profile to assist clinical work. For example, Sun et al. first utilized the ionomic profile to investigate associations between ion modules and networks and metabolic disorders [30]. Another study showed that the plasma ionomic profile may serve as a quick and convenient tool to reflect the therapeutic effect of cisplatin-based chemoradiotherapy in cervical cancer patients [31]. These results all indicate that it is possible to use the characteristics of an ionomic profile to identify patients and healthy individuals or evaluate treatment efficacy.
Furthermore, we found that the interaction network of ions in the CAD group was more intricate than in the healthy group, along with alterations in the correlations between elements. A notable example is the relationship of Sb, which is positively related to Zn and Fe in the healthy group while negatively associated with Ba, Mn, B, Sr, and Al in the CAD group (Fig. 2A-B). Simultaneously, it is worth noting that the level of Sb was lower in the CAD group than the healthy group, which may result from the fluctuation of other elements like Ba, Mn, B, Sr, or Al. These results imply that some ions may share similar uptake or transport mechanisms. For instance, Collins et al. summarized the possible mechanisms for iron-copper interactions, mainly involving ATPase, hephaestin, ceruloplasmin, and the transferrin-induced transport process [32]. Another study demonstrated that exposure to zinc sulfate increases iron uptake by respiratory epithelial cells, leading to the up-regulation of divalent metal transporter 1 (DMT1) and ferritin [33]. Given the intricate nature of the relationships and underlying mechanisms among multiple ions within organisms, it is both challenging and imperative to illuminate these complexities in future research.
Finally, some differences in ionomic profiles were also observed in CAD patients with complications like diabetes, hypertension, and hyperlipidemia, highlighting the significance of elements in regulating bodily functions. Understanding the ionomic profile could potentially aid in uncovering the association between elements and the disease, and clinicians may consider utilizing it as a supplementary biochemical indicator for diagnosing CAD.
It is undeniable that several limitations existed in this study. Firstly, the sample size is relatively small, which may impair the statistical power of these findings. Secondly, biological experiments should be conducted to explain the mechanisms of interactions among ions involved in our research in CAD. Thirdly, the study only measured plasma concentrations of elements at a single timepoint, thus lacking information on the dynamic changes in ionomic profiles. Future research should focus on monitoring element levels over extended periods and conducting multi-dimensional analysis of the elements in the body, including samples from urine, saliva, and hair. Despite tremendous efforts to explore the diagnostic and prognostic value of elements in CAD, the relationships between elements and CAD are complex and multifactorial. Therefore, a shift from single to multiple elements is necessary to gain a better understanding of the occurrence and progression of CAD, identify potential biomarkers, and potentially develop intervention therapies involving elements in the future.