3.6 Blood calcium levels are negatively correlated with the severity of PQ poisoning in patients
As lysine suppresses PQ-induced pulmonary fibrosis by reducing STIM1-TRPC1 axis increased intracellular calcium levels and EMT process, we considered intracellular calcium homeostasis was critical for maintaining normal pulmonary functions. To further confirmed the importance of calcium signal during PQ-raised pulmonary fibrosis, we turned our sights into the clinical records. By carefully analyzing the laboratory blood tests, we found that the blood calcium levels of PQ-poisoned patients were significantly decreased compared to healthy volunteers. Further analysis revealed a negative correlation between the calcium levels and the PQ concentrations in blood (Fig. 5A&B). Importantly, no significant correlation was observed in potassium, sodium, or chlorine (Fig. 5C-E). We further tracked the records of each patient with little poisoning. These patients exhibited continuous reduction of blood calcium levels during the malignant progression indicated by the increased blood creatinine levels. Intriguingly, the blood calcium levels were restored, yet not fully, when patients were recovered from PQ poisoning indicated by the reduction of blood creatinine levels into normal range (Fig. 5F). Whereas, patients suffering high amount of PQ poisoning died accompanied with extremely high creatinine levels and low blood calcium levels (Fig. 5G). The reduction of blood calcium levels in PQ-poisoned patients could be due to multiple reasons, from which one of the possibilities could be due to the large usage of extracellular calcium pools by STIM1-mediated calcium entry as we previously reported (Yang et al., 2022). To address this possibility, we analyzed the blood calcium levels in two PQ-poisoned animal models with or without lysine treatment, and found that PQ-poisoned mice exhibited a significant reduction of blood calcium levels, which was dramatically restored by lysine treatment (Fig. 5H). Consistent with the observations in PQ-poisoned mice model, lysine treatment impressively alleviated the reduction of blood calcium levels in the PQ-poisoned cynomolgus model (Fig. 5I). Interestingly, PQ-poisoned group exhibited a recovery of blood calcium levels during daytime in the second and third days, which might be ascribed to a feedback regulation of blood calcium levels due to calcium absorption in the gut and calcium reabsorption in the kidney. Nevertheless, these results indicated the potential functions of calcium signaling in modulation of the pathogenesis in PQ-raised toxicity and pulmonary fibrosis.