Lower Plasma Melatonin in the Intervertebral Disk Degeneration Patients Was Associated with Increased Proinflammatory Cytokines

Determination of Melatonin ａnd Proinflammatory Factors Plasma melatonin concentrations of both IDD patients ａnd healthy controls were measured using human melatonin ELISA Kit (Cat#: 10,698, Glory Science, USA). IL-1β, IL6 ａnd TNF-α levels in the plasma were measured using IL-1β (Cat#:QLB00B, R&D, USA), IL-6 (Cat#: RJ11850, Renjie Bio, China) ａnd TNF-α (589,201–480, Cayman, USA) ELISA kit. All the measurements were conducted according to the manufacturer’s protocols. Three repeats for all the samples measurement were adopted ａnd the average value was used in final analyses. Statistical Analysis The continuous data were present as a mean ± standard deviation (SD) in this current study. The difference between two groups was analyzed with non-paired t-test, ａnd the difference among more than two groups were analyzed with one-way analysis of variance (ANOVA) followed by the newman-keuls method for multiple comparison analysis test. The difference of grouped data was analyzed with Chi-square analysis. The diagnostic effect of plasma melatonin for IDD would be detected using receiver operating characteristic curve. The linear correlation between two descriptive data was detected with the Pearson linear analyses. The alpha significance value was < 0.05. Results Participant Characteristics In this case–control study, the potential participants were screened for inclusions or exclusions based on the criteria for both IDD cases ａnd healthy controls. As showed in Figure 1, the after excluding the inappropriate participants, a total of 71 IDD cases ａnd 54 healthy controls were included in this study. The blood samples collections ａnd laboratory examination were conducted for advanced analyses. After analyzing the clinical characteristics, plasma melatonin levels ａnd the proinflammatory factors concentrations of the included participants in this study. The comparisons of these characteristics of the control ａnd IDD cases were presented in Table 1. There were no significant differences in smoking status, BMI levels as well as DM ａnd systemic hypertension histories between IDD cases ａnd healthy controls (P=0.081, 0.164, 0.458 ａnd 0.564, respectively). The mean symptom duration of the IDD cases was 30.00 ± 9.04 months ａnd there were 7, 10, 28 ａnd 26 IDD cases in Pfirmann Grade 2, 3, 4 ａnd 5, respectively. In the advanced analyses on the melatonin levels ａnd the proinflammatory factors concentrations, a higher IL-6 (0.601 ± 0.085 vs 0.507 ± 0.167 pg/mL, P<0.001) ａnd a higher TNF-α (2.523 ± 0.642 vs 1.975 ± 0.078 pg/mL, P<0.001) levels were detected in the IDD cases comparing with the control group. No significant difference was detected in the IL-1β between IDD cases ａnd healthy controls (P=0.850). Decreased Plasma Melatonin in IDD Cases As shown in Figure 2A, a significant decreased melatonin concentration was detected in the IDD cases in Pfirmann Grade 3, 4 ａnd 5, respectively (P=0.009, P<0.001 ａnd P<0.001, respectively). In advance, the diagnostic effect of plasma melatonin for IDD were detected using receiver operating characteristic curve with the plasma melatonin data in 71 IDD cases ａnd 54 controls. It was found that melatonin could be used as a diagnostic biomarker for IDD with an area under curve of 0.808 ａnd P<0.001 (Figure 2B).

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