3.1 Clinical characteristics of the patients
A total of 58 children with HSP (28 males, 30 females) and 28 healthy children (14 males, 14 females) were recruited for this study. The mean age of the patients with HSP was 9.17±3.08 years, and that of the CON group was 10.60±3.66 years (Table 1). There was no significant difference in age between the two groups (p=0.061), while there was a significant difference in body mass index (BMI) between HSP group and healthy controls (p=0.03). The HSP patients were divided into three groups, including the untreated group (diagnosed as HSP for the first time and has not been treated with any immunotherapy drugs, includes glucocorticoids, 25.86%), the regular treated group (single or combined treated with immunotherapy drugs, 51.72%), and the withdrawal group (completely discontinued with any drugs for at least 3 months and currently without any clinical symptoms, 22.41%). The main clinical symptoms in patients with HSP included palpable rashes in the extremities (48.28%), arthritis (20.70%), gastrointestinal symptoms (20.70%) and renal damage (53.45%). 17 of total HSP patients did the renal biopsy (29.31%). And the results of blood routine and renal function in all patients were collected for correlation analysis.
3.2 The compositions of serum fatty acids in children with HSP and the healthy controls
40 fatty-acid methyl ester standards were analyzed using the established fatty acid analysis method, and a total of 37 fatty acids were detected and quantified in this experiment (Table 2), of which 1 fatty acid was not separated due to its isomers, and 2 were not detected. The internal standard was separated from each standard, and the chromatographic separation of each metabolite is good. The peak shape is sharp and symmetrical, which can quantify each metabolite by mass spectrometry. The linearity and correlation coefficient for each component according to the proportion of each component in the total concentration showed that the linearity of each analyte in the linear range is good, and the correlation coefficients are greater than 0.99. The results of our study showed that contents of all detected fatty acids in HSP patients upregulated comparing with the healthy children. Among them, 31 of total fatty acids had significant differences between HSP group and CON group (p<0.05), which includes 11 kinds of SFAs, 8 kinds of MUFAs and 12 kinds of PUFAs.
3.3 Correlation analysis with laboratory test results of HSP
The correlation between plasma metabolites and clinical indicators of HSP was shown in Figure 1. Heat map summarizing level fold changes of significantly Fatty acids metabolites in GC-MS Analysis of blood samples. Red and blue represent positive and negative correlations of metabolite in the HSP group comparing with healthy controls. The results show that many blood cell components are related to different kinds of free fatty acids.
3.4 Compositions of fatty acids in different groups of HSP
The distribution of serum fatty acids in the three groups of HSP (the regular treated group, the untreated group and the withdrawal group) was shown in Figure 2(a) using a barplot picture. It showed that palmitate (C16:0) and C18 were abundant in all three groups. Docosahexaenoic acid (DHA, C22:6) was significantly upregulated in the untreated group contrast with the regular treated group in figure 2(b). Palmitoleate (C16:1) and linolelaidate (C18:2TT) were significantly upregulated in the regular treated group compared with the withdrawal group in figure 2(c). Undecanoate (C11:0), myristoleate (C14:1), cis-11,14-Eicosadienoic acid ester (C20:2), cis-11,14,17-Eicosatrienoic acid ester (C20:1), docosapentaenoate (C22:5N6) and erucate (C22:1) were significantly upregulated in the untreated group compared with withdrawal group in figure 2(d).
3.5 Relationship between serum fatty acids and renal damage of HSP
The patients of HSP were divided into two groups according to whether have proteinuria or (and) hematuria. Wherein, group A represents there was no manifestation of kidney damage; and group B showing there were observed renal damage including proteinuria and hematuria. Figure 3(a) showed the compositions of fatty acids in the two groups. And we found there were significant differences in C18:1T, C20:1 and C24:1 between the two groups showing in Figure 3(b). Moreover, the three fatty acids, which are all MUFAs, were significantly higher in the group with renal impairment than that in the group without renal impairment.