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Endothelial injury, F-actin and vitamin-D binding protein
Figure 3. Extracellular acidification rate in peripheral blood mononuclear cells incubated with serum collected from two transplant recipients prior to and 100 days after hematopoietic stem cell transplant. (Top panel) Significantly different extracellular acidification rate (ECAR) after incubation with serum collected prior to hematopoietic stem cell transplant (HSCT) day 100 compared with serum collected prior to HSCT. Vitamin D binding protein (VDBP) level 78 mg/mL prior to HSCT and 907 mg/mL at day 100, genotype Gc1F/Gc1F. (Lower panel) No change in ECAR after incubation with serum collected prior to HSCT day 100 compared with serum collected prior to HSCT (baseline VDBP level 681 mg/dL, day 100 level 727 mg/dL, genotype Gc1S/Gc2).
Circulating concentrations of vitamin D binding protein (VDBP) and VDBP genotype are associated with clinical outcomes of hematopoietic stem cell transplant
VBDP is known to function as an actin scavenger, removing angiopathic F-actin from the circulation. We measured VBDP levels at six timepoints after HSCT (base- line, days 0, 7, 14, 30 and 100) in an expanded cohort of 190 consecutive HSCT recipients. Demographics of the cohort are shown in Table 1.
VDBP levels prior to start of transplant, and at day 0 and day 7 had no impact on transplant outcomes. In contrast, a higher day 30 VDBP level was associated with lower occurrence of TA-TMA in the first year after HSCT (31% vs. 10%, P=0.01, Figure 1C, Table 2). Adjustment of the data for TA-TMA risk factors of race and diagnosis yielded a P-value of 0.005. The rate of GvHD at 1 year was also higher in those with a lower VDBP level, although this did not reach statistical significance (21% vs. 8%, P=0.09, Table 2). We then analyzed VDBP level at day 100, looking for associations with clinical events occurring between day 100 and 1 year (summarized in Table 2). NRM at 1 year was significantly higher in HSCT recipients with a VDBP level lower than the median at day 100 (15% vs. 0%, P=0.002, Table 2, Figure 1D). Adjustment of the data for NRM risk factors of age and HLA-match yielded a P-value of 0.015. Moreover, GvHD at 1 year was more fre- quent in HSCT recipients with a VDBP level lower than the median at day 100 (18% vs. 3%, P=0.04, Table 2). In contrast, rates of TA-TMA did not correlate with VDBP level at day 100.
VDBP is a highly polymorphic protein, with three major alleles (Gc1F, Gc1S and Gc2) and a large number of rare
Table 3. Outcomes of hematopoietic stem cell transplant.
Number TA-TMA P of cases
NRM P 12%
13% 0%
0.22
Gc1S/Gc1S
Gc1F/Gc1F Gc2/Gc2
57 33%
16 63% 17 6%
0.001
Outcomes of hematopoietic stem cell transplant according to host vitamin D binding protein, only in cases with a homozygous genotype. TA-TMA: transplant-associated thrombotic microangiopathy; NRM: non-relapse mortality.
minor alleles. We asked whether the VDBP genotype influenced transplant outcomes by comparing transplant outcomes in HSCT recipients with the three homozygous genotypes Gc1F/Gc1F, Gc1S/Gc1S and Gc2/Gc2 (Table 3). Genotyping was performed using host DNA stored prior to HSCT as VDBP is primarily synthesized in the liver. We analyzed homozygous cases only to maximize our chance of seeing biological differences related to the genotype (90 total cases, 57 Gc1s/Gc1S, 16 Gc1F/Gc1F and 17 Gc2/Gc2). The data show a significant difference in frequency of TA- TMA according to the genotype with the highest frequen- cy seen in Gc1F/Gc1F individuals and the lowest in those with a Gc2/Gc2 genotype. NRM frequencies were not sta- tistically different.
Actin-vitamin D binding protein complex formation in hematopoietic stem cell transplant patients
We next investigated the kinetics of actin-VDBP com- plexes in the circulation. Typically, F-actin is cleared rapid- ly from the circulation by depolymerization by gelsolin,
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