In this study, we construct a retrospective, cohort study, and found a significantly positive correlation between IR indexes and all-cause mortality in PD patients. Compared to lower index group, higher TyG index, higher TyG-BMI index and higher TG/HDL-C ratio group had a 158.7%, 144.9% and 142.4% increased risk of occurring mortality, may be considered as a potential target for improving the survival of patients undergoing PD.
Previous studies have found strongly correlation between TyG index, TyG-BMI index and TG/HDL-C ratio and mortality in different populations. In a recent large cross-sectional study, TyG-BMI was found to be associated with CVD mortality among participants from the National Health and Nutrition Examination Survey (NHANES), and ROC analysis showed that the TyG index had better predictive ability for CVD mortality than the TyG-BMI index[21]. Similarly, in a large prospective cohort study, Lopez-Jaramillo et al. reveled the positive correlation between higher TyG index and cardiovascular mortality [22]. Furthermore, in a cohort study aimed at acute ischemic stroke population, a negative correlation between higher TG/HDL-C ratio and 3-month survival was found by Deng and his collaborators, and in the subsequent construction of the clinical prediction mode, model enrolled TG/HDL-C ratio presented a perfect match between predicted and observed values [23]. Additionally, in a cohort study enrolled 6697 patients with chronic heart failure, tertile 2 of the TyG index was associated with a 1.29-times higher risk of all-cause mortality, and tertiles 3 with at 1.84-times risk, compared with the lowest TyG index quartile[24]. Another retrospective cohort study, comprising 8835 critically ill patients, compared the association between the dynamic change of the TyG index and the baseline TyG index with 1-year all-cause mortality. Following propensity score matching, Cheng et al. demonstrated a linear association between TyG variability ratio and 1-year all-cause mortality. And they suggested that the dynamic change of the TyG index may offer a more reliable predictive value for all-cause mortality compared to the baseline TyG index[25]. Additionally, in the field of nephrology, levels of TG/HDL-C ratio were also found to have liner association with all-cause mortality, both in early CKD patients and in advanced CKD patients[26]. However, to date, the relationship between these indexes and all-cause mortality has not been evaluated in the same PD patients, and the linear or non-linear association has not assessed either. Our study filled these gaps.
Although our study demonstrated the positive relationship between TyG index, TyG-BMI index and TG/HDL-C ratio and all-cause mortality in PD patients, the specific biological mechanisms were unclear. TyG index, TyG-BMI index and TG/HDL-C ratio are simply calculated by TG, FBG, BMI and HDL-C. Earlier studies have demonstrated the strong positive correlation between these indexes and IR. For example, Fernando et al. suggested that the TyG index had a high sensitivity (96.5%) and specificity (85.0%) for diagnosing IR, with an area under the curve (AUC) of 0.858 [27]. The higher TyG-BMI index and TG/HDL-C ratio were also related to higher morbidity of type 2 diabetes[28, 29]. Thus, TyG index, TyG-BMI index and TG-HDL-C ratio were gradually considered as simple and reliable markers for assessing IR. Consequently, our speculation is that IR may play a significant role in linking these indexes with all-cause mortality.
As previously mentioned, IR is characterized by reduced sensitivity or responsiveness to the metabolic actions of insulin. Thus, accompanied by the decreased sensitivity to the insulin, β cells will compensatorily increase insulin secretion, leading hyperinsulinemia. Hyperinsulinemia, as a feature of IR, caused endothelial dysfunction, promoted inflammation, and associated with development of numerous chronic diseases[30–32], especially with CVD[33–35]. A study from Finland also indicated that high fasting serum insulin level was independent risk factor for cardiovascular mortality. Moreover, IR also played a significant role in progressing of atherosclerosis[36, 37]. A recent meta-analysis summarized the association between them and concluded that increased levels of HOMA-IR are associated with a higher risk of developing coronary heart disease [38]. The specific biological mechanisms through which IR contributes to atherosclerosis are not yet clear. However, numerous in vitro and in vivo studies have indicated potential mechanisms were as follows: (1) stimulating lipid synthesis and activating SREBP-C[39, 40]; (2) promoting vascular smooth muscle cell growth and proliferation[41]; (3) decreasing the activation of endothelial nitric oxide synthetase (eNOS) and nitric oxide (NO) production in endothelial cells by inhibiting the palmitoylation of eNOS and promoting the activation of the Endothelial cell Na+ channel (EnNaC), ultimately leading to endothelial dysfunction[7, 42]. All these changes may result in higher morbidity of CVD, and contribute to poor prognosis.
Interestingly, our study also indicated that among these three indexes, TyG index showed the highest predictive level and stability for all-cause mortality in PD patients. We assumed it may be related to the best predictive ability of TyG index of IR among these indexes[43, 44]. However, the specific mechanism remains to be studied further. This suggests that clinicians are encouraged to utilize TyG index to evaluate the risk of occurring all-cause mortality in PD patients and take appropriate measures.
There were limitations to the current research. Firstly, since this study was retrospective, we were unable to eliminate the effect of taking different medications on the results. Secondly, due to several relevant data were missed, we were unable to assess the relationship between these indexes and cardiovascular-related mortality. Thirdly, although we hypothesized that the potential mechanism linking these indexes and all-cause mortality may be related to IR, our study didn’t conduct the HEC. Thus, we were unable to evaluate the predictive effects of these indicators on IR in PD patients. Further studies are needed to explore the association between the IR indexes and the gold standard of IR in PD patients. Furthermore, we only analyzed baseline TyG index, TyG-BMI index and TG/HDL-ratio, dynamic changes in indexes were not included in present study. Therefore, future studies are more likely to explore the predictive power of changes in these indexes on all-cause mortality in PD patients.