Plasma levels of OLFM4 in normals and patients with gastrointestinal cancer.

Olfactomedin 4 (OLFM4) is a secreted glycoprotein predominantly expressed in bone marrow and gastrointestinal tissues. Aberrant expression of OLFM4 has been shown in several cancers. However, the clinical significance hereof is currently controversial. OLFM4 has been proposed as a candidate biomarker of gastrointestinal cancers. To address this, we developed monoclonal antibodies against synthetic peptides representing various segments of OLFM4. We examined expression of OLFM4 in epithelial cells by immunohistochemistry and found that OLFM4 is highly expressed in proliferating benign epithelial cells and in some carcinoma cells. We developed an Enzyme Linked Immunosorbent Assay for OLFM4 and investigated whether plasma levels of OLFM4 reflect colorectal malignancies, but were unable to see any such association. Instead, we observed two populations of individuals with respect to OLFM4 levels in plasma, the majority with OLFM4 in plasma between 0 and 0.1 µg/ml, mean 0.028 µg/ml while 10% of both normals and patients with cancers had OLFM4 between 4 and 60 µg/ml, mean 15 µg/ml. The levels were constant over time. The background for this high plasma level is not known, but must be taken into account if OLFM4 is used as biomarker for GI cancers.

ProHNPs are the principal α-defensins of human plasma.

BACKGROUND: Human neutrophil peptides (HNPs) were discovered as abundant antimicrobial peptides of azurophil granules. Later studies revealed that most HNPs were produced by myelocytes and metamyelocytes and secreted into the bone marrow plasma as the inert proforms, proHNPs. Despite the vast amounts of proHNPs released into bone marrow plasma, little has been done to characterize these. Numerous studies have investigated HNPs in plasma, linking them to a variety of diseases, but without distinguishing between HNPs and their proforms. MATERIALS AND METHODS: We used an antibody with specificity against the propiece of proHNPs to investigate proHNPs in plasma and tissue. RESULTS: In contrast to previous studies using HNP antibodies, we found proHNPs to be many-fold more abundant than HNPs in plasma with a mean concentration of 2 µg/mL. The concentration was substantially higher in bone marrow plasma in accordance with the bone marrow being the site of origin of plasma proHNPs. ProHNPs were not bound to high molecular weight plasma proteins. Accordingly, proHNPs were filtered in the kidneys and resorbed in the proximal tubules. CONCLUSIONS: Most HNPs in plasma are in fact proHNPs, which is important given the differences in their origin and biological activities.