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Figure 5. PCA score results for differentiation of the human kidney stones. a1: score plot PC1-PC2 based on
positive ESI; a2: score plot PC2-PC3 based on positive ESI; b1: score plot PC1-PC2 under negative ESI ion
mode; b2: score plot PC2-PC3 under negative ESI ion mode. c1: 3D-score plot PC1-PC2 under positive ESI
c2: 3-D score plot under negative ESI.
(uric acid induced stones) and 3 (melamine-induced
stones) has been achieved. On the other hand, the
distribution of signs in each cluster from samples 4 to 6 is
restricted in a narrow scope. Thus, the PCs show strong
ability for differentiation of melamine and uric acid induced
stones from the other types of kidney stones. Although, a
few data points of sample 5 were mixed together with
samples 4 and 6 in the PC1 and PC2 plane (Figure 5a1),
all the data points of sample 5 were completely separated
from the other samples in PC3, as shown in Figure 5a2.
However, upon the negative ion detection mode, the six
different types of kidney stones were differentiated from
each other in the PC1 and PC2 plane (Figure 5b1), and
this could be clearly visualized in the corresponding 3-D
space (Figure 5c2). Therefore, negative ESI-MS is
proposed for differentiation of the kidney stone samples
without CID experiments, although the melamine induced
stones have been differentiated from the others under the
positive ion mode.
As shown in the clinical data (Table 1), the different
X-ray imaging properties (both the stone location and
transparency) of sample 1 from sample 5 might explain
the separation of samples 1 and 5 in the PCA score plots.
Zhou et al. 2023
In both Figure 5b1 and 5b2, 1.5-year history of powdered
milk intake was most likely to be the only factor for
differentiating sample 4 from sample 6 in the PCA score
plots, since the stones in patients 4 and 6 were both
located in the left kidney pelvis and were all radiopaque in
the X-ray imaging studied in the clinical examination.
Although, the stones in patient 5 were also radiopaque,
the location of the stone 5 was at the right ureter instead
of the left kidney pelvis. This could be the important factor
for differentiating sample 5 from either sample 4 or
sample 6. Similar to sample 5, the stone in sample 1 was
also located in the ureter (the left ureter), but it was
radiolucent in the X-ray imaging study, indicating that the
chemical composition of sample 1 should be different from
the opaque samples. In the PCA score plots, sample 2
was located remarkably far from the sample 3, because
sample 2 was uric acid induced kidney stones, which
should be chemically different from the melamine induced
kidney stones. Conclusively, the location and imaging
property of kidney stones are two of the most important
factors used to distinguish these kidney stones and
they play important roles in differentiating different types
of kidney stones after performing PCA.