Enzyme-linked immunoassay for midkine, and its application to evaluation of midkine levels in developing mouse brain and sera from patients with hepatocellular carcinomas

Proangiogenic factor midkine is increased in melanoma patients with sleep apnea and induces tumor cell proliferation

Midkine (MDK) might mediate the proangiogenic effect of intermittent hypoxia (IH) in patients with obstructive sleep apnea (OSA) and cutaneous melanoma (CM). We compare circulating MDK in CM patients with and without OSA, and their relationship with tumor aggressiveness, while exploring in vitro effects of soluble MDK on human lymphatic endothelial (HLEC) and melanoma cell proliferation. In 360 CM patients, sleep studies and MDK serum level measurements were performed. The effect of MDK on cell proliferation was assessed using HLEC and melanoma cell lines with patient sera under both normoxia and IH. MDK levels were higher in severe OSA compared to mild OSA or non-OSA patients, whereas no differences in VEGF levels emerged. In OSA patients, MDK levels correlated with nocturnal hypoxemia and CM mitotic rate. In vitro, MDK promotes HLEC proliferation under IH conditions. Moreover, cultures of the human melanoma cell line C81-61 with sera from patients with the highest MDK levels promoted tumor cell proliferation, which was attenuated after the addition of MDK antibody. These responses were enhanced by IH exposures. In conclusion, in CM patients, OSA severity is associated with higher MDK levels, which, appear to enhance both the lymphangiogenesis as the intrinsic aggressiveness of CM tumor cells.

Serum Midkine is a clinical significant biomarker for colorectal cancer and associated with poor survival

Colorectal carcinoma (CRC) is one of the most common carcinomas worldwide. Early detection is crucial for reducing morbidity and mortality. Several promising studies described the use of midkine (MK) as a tumor marker. This study aimed to investigate a larger collective to ascertain if the preoperative serum midkine level (S‐MK) is suitable as a marker for screening and if S‐MK correlates with tumor progression and localization. It was also investigated for the first time whether patients with high S‐MK show poor survival. This prospective single‐center study included 299 patients with CRC. The preoperative serum midkine level (S‐MK) was determined using ELISA. Established tumor markers Carcinoembryonic antigen (CEA) and Carbohydrate antigen 19‐9 (CA 19‐9) were collected for comparison. The median follow‐up period was 65 months. S‐MK was significantly elevated in patients with CRC (P < .001). The receiver operation characteristic (ROC) curve has an area under the curve (AUC) of 0.868 (P < .001). A cut‐off value of 56.42 pg/mL results in a sensitivity of 84.3% and a specificity of 75.4%. In the one‐way analysis of variance (ANOVA), there were no significant correlations between S‐MK and tumor progression, localization. Furthermore, no significant correlation to CEA und CA 19‐9 could be found. Kaplan‐Meier survival analysis was able to show for the first time that patients with S‐MK of more than 225 pg/mL have a significantly shorter survival. Multivariate Cox regression showed that only CEA was an independent prognostic factor for survival. S‐MK helps estimate the prognosis for CRC and is a valuable component for developing a multimarker panel for screening and surveillance.

Midkine (MDK) growth factor: a key player in cancer progression and a promising therapeutic target

Midkine is a heparin-binding growth factor, originally reported as the product of a retinoic acid-responsive gene during embryogenesis, but currently viewed as a multifaceted factor contributing to both normal tissue homeostasis and disease development. Midkine is abnormally expressed at high levels in various human malignancies and acts as a mediator for the acquisition of critical hallmarks of cancer, including cell growth, survival, metastasis, migration, and angiogenesis. Several studies have investigated the role of midkine as a cancer biomarker for the detection, prognosis, and management of cancer, as well as for monitoring the response to cancer treatment. Moreover, several efforts are also being made to elucidate its underlying mechanisms in therapeutic resistance and immunomodulation within the tumor microenvironment. We hereby summarize the current knowledge on midkine expression and function in cancer development and progression, and highlight its promising potential as a cancer biomarker and as a future therapeutic target in personalized cancer medicine.

Diagnostic accuracy of midkine on hepatocellular carcinoma: A meta-analysis

OBJECTIVE

To evaluate the dependability and accuracy of midkine (MK) in the diagnosis of hepatocellular carcinoma (HCC).

METHODS

PubMed, EMBASE, Web of Science, China Biology Medicine disc and grey literature sources were searched from the date of database inception to January 2019. Two authors (B-H.Z. and B.L.) independently extracted the data and evaluated the study quality using the Quality Assessment of Diagnostic Accuracy Studies-2 tool. The sensitivity, specificity, positive likelihood ratio (LR+) and negative likelihood ratio (LR-) were estimated using a bivariate model. Moreover, hierarchical summary receiver operating characteristic curves were generated. The diagnostic odds ratio (DOR) and area under the curve (AUC) were pooled using a univariate model.

RESULTS

Nine articles (11 studies) were included (1941 participants). The bivariate analysis revealed that the sensitivity and specificity of MK for HCC diagnosis were 0.85 (95% CI 0.78-0.91) and 0.83 (95% CI 0.76-0.88), respectively. We also found a LR+ of 5.05 (95% CI 3.33-7.40), a LR- of 0.18 (95% CI 0.11-0.28), a DOR of 31.74 (95% CI 13.98-72.09) and an AUC of 0.91 (95% CI 0.84-0.99). Subgroup analyses showed that MK provided the best efficiency for HCC diagnosis when the cutoff value was greater than 0.5 ng/mL.

CONCLUSIONS

MK has an excellent diagnostic value for hepatocellular carcinoma.

Diagnostic impact of high serum midkine level in patients with gastric cancer

AIM

We evaluated the diagnostic impact of serum midkine (s-MK) levels in patients with gastric cancer using a monoclonal antibody enzyme-linked immunosorbent assay system (ELISA) to detect s-MK levels.

METHODS

Serum samples were obtained from 131 patients with gastric cancer including stage I (n = 71), stage II (n = 28), stage III (n = 16), and stage IV (n = 16) before surgery. Serum samples were analyzed using ELISA to detect soluble midkine. A cut-off value was fixed at 421 pg/mL, and the sample divided into two groups: a high s-MK group and a low s-MK group. Clinicopathological factors and prognosis were compared between these two groups using univariate and multivariate analyses. Comparison of two groups was analyzed by Fisher's exact probability test. Statistical significance was considered at P < 0.05.

RESULTS

High s-MK was significantly associated with high carcinoembryonic antigen (CEA) (P < 0.01). Positive rate of s-MK was higher than the positive rates of CEA in patients with stage I/II gastric cancer. Combination with CEA + CA19-9 + s-MK increased the positive rates of patients with stage I/II gastric cancer. No other clinicopathological factors were associated with s-MK. Although the high s-MK group showed worse overall survival than the low s-MK group, the difference was not statistically significant.

CONCLUSION

s-MK level is increased even during early-stage gastric cancer. Combined with s-MK, the positive rate of CEA + CA19-9 was increased in patients with stage I/II gastric cancer.

Serum midkine as a prognostic biomarker for patients with hepatocellular carcinoma

Gene expression profiles of paired hepatocellular carcinoma (HCC) and adjacent noncancerous liver tissue samples revealed preferential expression of midkine in HCC. This finding suggested the clinical usefulness of midkine measurement in serum for monitoring HCC treatment response, recurrence, and progression. A prospective study in 285 patients, 144 in complete remission and 141 at risk for developing de novo HCC, was conducted. The changes in serum midkine level were in parallel with disease activity in about 81% of patients with HCC. The study also revealed that rapidly rising serum midkine levels occurred in patients in the terminal stage of HCC. The rising rate of serum midkine levels was inversely correlated with remaining survival days. However, serum midkine measurement did not detect emergence of new HCC in most patients in complete remission and in high-risk people without a history of HCC. Serum midkine levels can be useful to monitor HCC progression, and a sharp rise signals the approach of end of life in patients with HCC.

Preparation and preliminary characterization of rabbit monoclonal antibodies against human midkine

We prepared rabbit monoclonal antibodies that target human midkine (MK). The MK gene was amplified by PCR from the plasmid pEGFP-MK and subcloned into the prokaryotic expression vector pGEX-1λT to generate an N-terminally glutathione S-transferase (GST)-tagged fusion protein construct. Expression of the GST-MK fusion protein was achieved by IPTG induction in Escherichia coli cells. The expressed protein was purified using the GST system. After verifying purification, the fusion protein was used to immunize rabbits to prepare monoclonal antibodies against human MK by the rabbit hybridoma technique. The hybridomas generated were screened by an enzyme-link immunoassay (ELISA) for specificity, which was further characterized by Western blotting and ELISA. SDS-PAGE analysis showed that the purified protein corresponds to the calculated molecular weight. The GST-MK fusion protein was prepared. At least one hybridoma cell line secreting anti-MK MAb was obtained. Western blotting analysis confirmed the identity of the MAb. The titer of the MAbs measured by an indirect ELISA was 1:64,000. The affinity constant, which was measured by a non-competitive ELISA, was found to be 3.0 × 10(9) M(-1). Western blotting and immunohistochemistry analysis showed that the produced MAbs bind to the MK protein in cancerous tissues. The GST-MK fusion protein was successfully expressed and purified. The MAbs against MK were subsequently prepared, which should further aid research and the application of MK MAbs in clinical settings.

Midkine as a factor to counteract the deposition of amyloid β-peptide plaques: in vitro analysis and examination in knockout mice

Background

Midkine is a heparin-binding cytokine involved in cell survival and various inflammatory processes. Midkine accumulates in senile plaques of patients with Alzheimer's disease, while it counteracts the cytotoxic effects of amyloid β-peptide and inhibits its oligomerization. The present study was conducted to understand the role of midkine upon plaque formation of amyloid β-peptide.

Methods

A surface plasmon assay was performed to determine the affinity of midkine for amyloid β-peptide. The deposition of amyloid β-peptide was compared in the brain of wild-type and midkine-deficient mice. An effect of midkine to microglias was examined by cell migration assay.

Results

Midkine bound to amyloid β-peptide with the affinity of 160 nM. The C-terminal half bound to the peptide more strongly than the N-terminal half, and heparin inhibited midkine from binding to the peptide. Pleiotrophin, which has about 50% sequence identity with midkine also bound to amyloid β-peptide. The deposition of amyloid β-peptide plaques in the cortex and hippocampus was more intense in 15-month-old midkine-deficient mice, compared to the corresponding wild-type mice. Midkine promoted migration of microglias in culture.

Conclusions

These results are consistent with the view that midkine attenuates the deposition of amyloid β-peptide plaques, and thus progression of Alzheimer's disease, by direct binding and also by promoting migration of microglias.

Midkine: a promising molecule for drug development to treat diseases of the central nervous system

Midkine (MK) is a heparin-binding cytokine, and promotes growth, survival, migration and other activities of target cells. After describing the general properties of MK, this review focuses on MK and MK inhibitors as therapeutics for diseases in the central nervous system. MK is strongly expressed during embryogenesis especially at the midgestation period, but is expressed only at restricted sites in adults. MK expression is induced upon tissue injury such as ischemic brain damage. Since exogenously administered MK or the gene transfer of MK suppresses neuronal cell death in experimental systems, MK has the potential to treat cerebral infarction. MK might become important also in the treatment of neurodegenerative diseases such as Alzheimer's disease. MK is involved in inflammatory diseases by enhancing migration of leukocytes, inducing chemokine production and suppressing regulatory T cells. Since an aptamer to MK suppresses experimental autoimmune encephalitis, MK inhibitors are promising for the treatment of multiple sclerosis. MK is overexpressed in most malignant tumors including glioblastoma, and is involved in tumor invasion. MK inhibitors may be of value in the treatment of glioblastoma. Furthermore, an oncolytic adenovirus, whose replication is under the control of the MK promoter, inhibits the growth of glioblastoma xenografts. MK inhibitors under development include antibodies, aptamers, glycosaminoglycans, peptides and low molecular weight compounds. siRNA and antisense oligoDNA have proved effective against malignant tumors and inflammatory diseases in experimental systems. Practical information concerning the development of MK and MK inhibitors as therapeutics is described in the final part of the review.

Midkine: a novel prognostic biomarker for cancer

Since diagnosis at an early stage still remains a key issue for modern oncology and is crucial for successful cancer therapy, development of sensitive, specific, and non-invasive tumor markers, especially, in serum, is urgently needed. Midkine (MK), a plasma secreted protein, was initially identified in embryonal carcinoma cells at early stages of retinoic acid-induced differentiation. Multiple studies have reported that MK plays important roles in tumor progression, and is highly expressed in various malignant tumors. Because increased serum MK concentrations also have been reported in patients with various tumors, serum MK may have the potential to become a very useful tumor marker. Here, we review and discuss the possibility and usefulness of MK as a novel tumor marker.

Midkine, a heparin-binding cytokine with multiple roles in development, repair and diseases

Midkine is a heparin-binding cytokine or a growth factor with a molecular weight of 13 kDa. Midkine binds to oversulfated structures in heparan sulfate and chondroitin sulfate. The midkine receptor is a molecular complex containing proteoglycans. Midkine promotes migration, survival and other activities of target cells. Midkine has about 50% sequence identity with pleiotrophin. Mice deficient in both factors exhibit severe abnormalities including female infertility. In adults, midkine is expressed in damaged tissues and involved in the reparative process. It is also involved in inflammatory reactions by promoting the migration of leukocytes, induction of chemokines and suppression of regulatory T cells. Midkine is expressed in a variety of malignant tumors and promotes their growth and invasion. Midkine appears to be helpful for the treatment of injuries in the heart, brain, spinal cord and retina. Midkine inhibitors are expected to be effective in the treatment of malignancies, rheumatoid arthritis, multiple sclerosis, renal diseases, restenosis, hypertension and adhesion after surgery.

Midkine in plasma as a novel breast cancer marker

Midkine, a heparin-binding growth factor, is up-regulated in many types of cancer. The aim of this study was to measure plasma midkine levels in patients with breast cancer and to assess its clinical significance. We examined plasma midkine levels in 95 healthy volunteers, 11 patients with ductal carcinoma in situ (DCIS), 111 patients with primary invasive breast cancer without distant metastasis (PIBC), and 25 patients with distant metastatic breast cancer (MBC), using an automatic immunoasssay analyzer (TOSOH AIA system). In PIBC, we studied the correlation between plasma midkine levels and clinicopathological factors. Immunoreactive midkine was detectable in the plasma of healthy volunteers, and a cut-off level of 750 pg/mL was established. In breast cancer patients, plasma midkine levels were increased above normal values. These elevated levels of midkine were seen in one (9.1%) of 11 patients with DCIS, 36 (32.4%) of 111 patients with PIBC, and 16 (64.0%) of 25 patients with MBC. Increased levels of midkine were correlated with menopausal status (P = 0.0497) and nuclear grade (P = 0.0343) in PIBC. Cancer detection rates based on midkine levels were higher than those based on three conventional markers including CA15-3 (P < 0.0001), CEA (P = 0.0077), and NCCST-439 (P < 0.0001). Detection rates of breast cancer using a combination of two conventional tumor markers (CA15-3/CEA, CA15-3/NCCST-439, or CEA/NCCST-439) with midkine is significantly higher than those using combination of three conventional tumor markers. Midkine may be a useful novel tumor marker for detection of breast cancer, superior to conventional tumor markers.

Midkine as a prognostic biomarker in oral squamous cell carcinoma

The aim of this study was to evaluate serum midkine (S-MK) concentrations as a prognostic tumour marker in oral squamous cell carcinoma (OSCC). We measured S-MK concentrations in patients with OSCC and healthy volunteers. In addition, we performed real-time quantitative reverse transcription-PCR analysis and immunohistochemistry with fresh tumour samples. To determine whether S-MK concentrations have prognostic value, we performed survival analyses with clinical information by using the log-rank test. Serum midkine concentrations were significantly higher in patients with OSCC than in healthy controls (P<0.001). Serum midkine concentrations were also significantly increased in early-stage OSCC compared with those of healthy individuals (P<0.001). In addition, immunohistochemistry allowed identification of overexpressed MK protein in OSCC tissues. MK mRNA showed higher expression in OSCC samples compared with normal mucosal samples. Patients in high S-MK groups showed a significantly lower 5-year survival rate compared with patients in low S-MK groups (P<0.05). The increased S-MK concentrations in early-stage OSCC were strongly associated with poor survival. Serum midkine concentrations may thus be a useful marker not only for cancer screening but also for predicting prognosis of OSCC patients.

Increased midkine gene expression in childhood B-precursor acute lymphoblastic leukemia

Midkine (MK) is a heparin-binding growth factor that is overexpressed in a number of solid cancers. However, expression in acute leukemia has not been clarified. We examined MK gene expression using real-time PCR in 94 children with acute leukemia. In 30 of the 41 patients with B-precursor ALL, MK gene expression was overexpressed than normal BM. MK gene was also overexpressed in more than half of patients with FAB M1 and M2 types of AML. Quantification of MK gene by real-time PCR offers particular promise as a prognostic marker and a marker for minimal residual disease in children with B-precursor ALL.

Evaluation of expression of midkine in oral squamous cell carcinoma and its correlation with tumour angiogenesis

Midkine, a new member of the heparin-binding growth factor family, was found recently to have a high expression level in many carcinoma specimens, including oesophagus, gall, bladder, pancreas, colorectum, breast and lung carcinomas, but few relevant studies have been performed. The aim of this study was to investigate the expression of midkine in oral squamous cell carcinoma (OSCC) and its correlation with tumour angiogenesis. Surgical specimens from 62 cases of OSCC and 10 cases of normal oral mucosa were examined by immunohistochemistry. The relationship between expression of midkine and the clinicopathological data and tumour angiogenesis was analysed. Midkine proteins were overexpressed in OSCC. The level of midkine expression was found to be significantly correlated with tumour size (P = 0.01), clinical stage (P = 0.002) and prognosis (P = 0.038). High midkine expression was associated with higher tumour angiogenesis as reflected by increased vascular endothelial growth factor expression (P = 0.005) and higher microvessel density (P = 0.004). These results indicate that midkine may be of great value in assessing the development and prognosis of OSCC, and could be taken as a new target for OSCC therapy.

Increased midkine levels in sera from patients with Alzheimer's disease

Midkine (MK) is a heparin binding growth factor and promotes growth, survival and migration of various cells including neurons. It is also known to accumulate in senile plaques of patients with Alzheimer's disease (AD). To investigate the involvement of serum MK in the pathophysiology of AD, serum MK levels were determined in patients with AD (n=36) and age- and sex-matched healthy controls (n=32), using an enzyme-linked immunosorbent assay (ELISA). The serum MK values of the patients with AD (median 560 and interquartile range (500-755) pg/ml) were significantly (U=278.5, P=0.0003, Mann-Whitney U-test) higher than those of the controls (median 500 and interquartile range (385-520) pg/ml). Moreover, 17 patients (47.2%) had abnormally high values of more than 600 pg/ml, but no controls (0%) did. There was no correlation between serum MK level and the mini mental state examination (MMSE) score in the patients. The demonstration of elevated MK levels in sera of patients with AD may contribute toward an understanding the pathophysiology of this disease, and provide a novel potential therapeutic strategy for decreasing neuronal damages in patients with AD. We found that serum MK levels in patients with AD were increased in comparison with those of normal controls.

Serum midkine concentrations and gastric cancer

Midkine (MK) is one of a family of heparin-binding growth factors, and increased MK expression is reported in various types of human carcinomas. To clarify the association between serum MK (S-MK) concentrations and gastric cancer, we examined S-MK concentrations of gastric cancer patients (n=275) and healthy controls (n=275). S-MK concentrations of all subjects were measured by enzyme-linked immunosorbent assay (elisa). The medians (25th and 75th percentiles) of S-MK were 192 (123 and 314) pg/mL in the cases and 170 (81 and 273) pg/mL in the controls (P <0.01). We also compared S-MK concentrations in each group divided by the progression stage or histological type of cancer. A difference was observed in the median S-MK concentrations between early and advanced cancers [182 (105 and 301) pg/mL vs 203 (139 and 331) pg/mL, P=0.07], but not between intestinal and diffuse type cancers [185 (121 and 306) pg/mL vs 198 (127 and 323) pg/mL, P=0.51]. We found that those progression stages affect S-MK concentration more strongly than the histological types in gastric cancer patients. Because S-MK seems to reflect the progression stage of gastric cancer, it may serve as a useful marker in the clinical follow-up of gastric cancer patients.

The role of midkine and pleiotrophin in liver regeneration

BACKGROUND/PURPOSE

We studied roles of two closely related heparin-binding growth factors, midkine (MK) and plieotrophin (PTN) in the processes of liver regeneration after partial hepatectomy.

METHODS

Liver regeneration was comparatively analyzed using mice deficient in the MK gene (Mdk), mice deficient in the pleiotrophin gene (Ptn) and wild-type mice.

RESULTS

Migration of neutrophils and macrophages to the liver 1-5 days after partial hepatectomy was suppressed in Mdk (-/-) mice. Liver damage as assessed by serum aspartate aminotransferase was also less severe in the deficient mice. On the other hand, cell growth in the liver was generally suppressed in the deficient mice 3-14 days after partial hepatectomy. The weight of the liver 7 and 14 days after partial hepatectomy was significantly less in Mdk (-/-) mice than wild-type mice. Very similar results were obtained using Ptn (-/-) mice except that a significant difference in the repaired liver weight was not observed between Ptn (-/-) mice and wild-type mice.

CONCLUSIONS

MK and PTN are involved both in the inflammatory and reparative processes after partial hepatectomy, and as a whole are beneficial for liver regeneration.

Midkine, a heparin-binding growth factor, is fundamentally involved in the pathogenesis of rheumatoid arthritis

OBJECTIVE

Midkine (MK), a heparin-binding growth factor, promotes growth, survival, and migration of various cells. The essential role of MK in migration of inflammatory cells has been shown using mice deficient in the MK gene (Mdk(-/-) mice). We undertook this study to investigate the role of MK in the pathogenesis of rheumatoid arthritis (RA).

METHODS

MK levels in specimens from patients were determined by enzyme-linked immunosorbent assay, and localization of MK was revealed by immunohistochemical analysis. Susceptibility to antibody-induced arthritis was compared between Mdk(-/-) and wild-type (WT) mice. Osteoclast differentiation was monitored using macrophage-like cells isolated from human synovial tissue and macrophages from mouse bone marrow.

RESULTS

MK levels in sera and synovial fluid were increased in most RA patients, indicating a strong correlation between MK expression and RA. MK was expressed in macrophage-like cells and fibroblast-like cells in synovial membranes from the patients. In antibody-induced arthritis, Mdk(-/-) mice seldom developed the disease, while most of the WT mice did. Administration of MK to the Mdk(-/-) mice increased the frequency of antibody-induced arthritis. Migration of inflammatory leukocytes to the synovial membranes in the disease model was suppressed in the Mdk(-/-) mice. Furthermore, MK was found to promote the differentiation of osteoclasts from macrophages.

CONCLUSION

MK participates in each of the two distinct phases of RA development, namely, migration of inflammatory leukocytes and osteoclast differentiation, and is a key molecule in the pathogenesis of RA.

Midkine and pleiotrophin in neural development and cancer

The midkine (MK) family consists of only two members, namely heparin-binding growth factors MK and pleiotrophin (PTN). During embryogenesis, MK is highly expressed in the mid-gestational period, whereas PTN expression reaches the maximum level around birth. Both proteins are localized in the radial glial processes of the embryonic brain, along which neural stem cells migrate and differentiate. Zebrafish and Xenopus MK can induce neural tissues. In addition, deposits of MK and/or PTN are found in neurodegenerative diseases, such as Alzheimer's disease and multiple system atrophy. Both molecules are induced in reactive astrocytes by ischemic insults. In this context, it is interesting that LDL receptor-related protein is a receptor for MK and PTN, and this receptor has been implicated in the pathogenesis of Alzheimer's disease. MK and PTN share receptors, and show similar biological activities that include fibrinolytic, anti-apoptotic, mitogenic, transforming, angiogenic, and chemotactic ones. These activities explain how these molecules are involved in carcinogenesis. MK is detected in human carcinoma specimens from pre-cancerous stages to advanced stages. Strong expression of PTN is also detected in several carcinomas, although, in general, MK is expressed more intensely and in a wide range of carcinomas than PTN. The blood MK level is frequently elevated in advanced human carcinomas, decreases after surgical removal of the tumors, and is correlated with prognostic factors. Thus, it is a good market for evaluating the progress of carcinomas. Furthermore, antisense oligonucleotides for MK and ribozymes for PTN show anti-tumor activity. Therefore, MK and PTN are candidate molecular targets for therapy for human carcinomas.

Correlation of elevated plasma levels of two structurally related growth factors, heparin affin regulatory peptide and midkine, in advanced solid tumor patients

Heparin affin regulatory peptide (HARP) and midkine (MK) are growth factors, expressed in carcinomas, neuroblastomas and gliomas. In this study, we measured the levels of HARP and MK in plasma samples from 77 cancer patients. The patients had advanced tumors with loco-regional (n=18) or metastatic (n=49) diseases and 10 patients have their diseases limited to the primary site. HARP and MK plasma concentrations were significantly higher in all of these different subgroups of cancer patients (P<0.05 in all cases), when compared to healthy controls (n=30). Neither HARP nor MK levels were significantly different between patients with loco-regional and metastatic tumors (P=0.203 and 0.242, respectively). Moreover, a strong correlation between the elevations of the plasma levels of these two proteins (r2=0.546) in these cancer patients was found. Measurements of these secreted angiogenic growth factors may be useful for evaluation of cancer diagnosis.

Preoperative serum midkine concentration is a prognostic marker for esophageal squamous cell carcinoma

High preoperative serum midkine concentration is associated with poor survival in patients with esophageal cancer, even after radical surgery, and thus may have prognostic value. Midkine (MK), a heparin-binding growth factor, is expressed in numerous cancer tissues, and serum MK (S-MK) concentrations are increased in patients with various neoplasms. The aim of this study is to evaluate the clinical significance of S-MK in patients with esophageal squamous cell cancer (SCC). S-MK was measured by enzyme-linked immunosorbent assay in 135 healthy controls, 16 patients with benign esophageal disease, and 93 patients with primary esophageal SCC before surgery. The serum concentrations of carcinoembryonic antigen (CEA), SCC antigen (SCC-Ag), and cytokeratin 19 fragment (CYFRA21-1) were also evaluated. All patients with esophageal SCC underwent radical esophagectomy. Tumor MK expression was assessed by immunohistochemistry in 14 fresh tumor specimens. To determine whether S-MK is of value as a prognostic factor, the authors conducted a survival analysis using Cox's proportional hazards model. S-MK values in patients with esophageal SCC were significantly higher than those in healthy controls (417 +/- 342 pg/ml vs. 154 +/- 76 pg/ml, P < 0.001). Using 300 pg/ml as the cut-off value (representing the mean + 2 standard deviations of the S-MK of healthy controls), 61% of patients with esophageal SCC were classified as positive. MK expression by the tumor was significantly associated with high level of S-MK. High S-MK (>/= 300 pg/ml) was associated with tumor size, immunoreactivity and poor survival. Multivariate analysis indicated that S-MK was an independent prognostic factor. S-MK may be a useful tumor marker for esophageal SCC. Increased preoperative S-MK in patients with esophageal SCC is associated with poor survival.

High levels of urinary midkine in various cancer patients

Midkine (MK) is a heparin-binding growth factor, which promotes growth, migration, and survival of various cells, and MK expression is increased in many human carcinomas. We determined the urinary MK level by enzyme-linked immunoassay. Taking 311pg/mg creatinine as a cut-off level, 70% of patients with various carcinomas (n=142) gave positive values, while only 5.5% of healthy volunteers (n=330) did. In case of gastric carcinoma, 17 out of 21 patients with stage 1 tumor were positive. Urinary MK levels are expected to become a convenient marker as an aid in detection of tumors.

Two clusters of serum midkine levels in drug-naive patients with schizophrenia

Midkine (MK) is a heparin-binding growth factor implicated in various biological phenomena such as development of the hippocampus and anxiety. We evaluated serum MK levels of drug-naive (n=15) and medicated (n=25) patients with schizophrenia, and age- and sex-matched normal controls (n=38). The patients showed two clusters in the levels. Four drug-naive patients (26.7%) and two medicated patients (8.0%) had abnormally high values, but no controls did, there being a significant difference in the numbers (P=0.003, Fisher's exact test). Furthermore, in other patients, the mean MK levels in drug-naive schizophrenia (0.30+/-0.10 ng/ml) were significantly (P=0.018, Fisher's protected least significant difference test) decreased than those in the controls (0.40+/-0.12 ng/ml). These suggest that there are two clusters of serum MK abnormalities in drug-naive patients with schizophrenia.

Immunoassay for measuring the heparin-binding growth factors HARP and MK in biological fluids

Heparin-affin regulatory peptide (HARP) and Midkine (MK) belong to a family of growth/differentiation factors that have a high affinity for heparin. The involvement of these molecules in various proliferative diseases prompted us to develop an assay for measuring the concentrations of these factors in biological fluids and culture media. This report describes an immunoassay that uses only commercially available materials, based on the high affinity of certain molecules for heparin. It consists of adsorbing heparin-BSA covalent complexes to microtiter plate wells and to quantify the heparin bound HARP or MK by using appropriate antibody. The method is specific and measures concentrations ranging from 40-1200 pg/mL HARP and from 25-1200 pg/mL MK and various parameters are investigated. The within-assay coefficient of variation was less than 5% for both assays. The method was checked by measuring the concentrations of these growth factors in the sera of healthy humans and in patients with cancer. As previously reported, we confirmed that the serum concentrations of MK are higher in patients with tumours (n = 139) than in controls (n = 19). The synthesis of HARP and MK by various cells in culture was also analysed.

Midkine, a heparin-binding growth factor, promotes growth and glycosaminoglycan synthesis of endothelial cells through its action on smooth muscle cells in an artificial blood vessel model

To study the interactions between smooth muscle cells and endothelial cells in vitro, we developed an artificial blood vessel model, which consisted of collagen gel containing human aortic smooth muscle cells and human umbilical vein endothelial cells grown on the gel. The blood vessel model was utilized to investigate the role of midkine, a heparin-binding growth factor, in the intercellular interactions that are important in angiogenesis. In the blood vessel model, midkine induced stratification of the endothelial cells and increased their proliferation and glycosaminoglycan synthesis. However,midkine had no effect on the smooth muscle cells or endothelial cells when they were cultured separately. Increased proliferation of the endothelial cells was also attained by coculturing them with smooth muscle cells in the presence of midkine or culturing endothelial cells with the conditioned medium of the smooth muscle cells, which had been treated with midkine. These experiments indicate that the target of midkine was smooth muscle cells, which secreted factor(s) acting on the endothelial cells. We identified interleukin-8 as one such factor; the synthesis of interleukin-8 by the smooth muscle cells was increased by exposure to midkine, and anti-interleukin-8 inhibited the midkine action. Furthermore, interleukin-8 caused stratification of the endothelial cells in the blood vessel model. These results provided evidence that midkine is one of the factors involved in epithelial-mesenchymal interactions.

Targeting antigen-specific receptors on B lymphocytes to generate high yields of specific monoclonal antibodies directed against biologically active lower antigenic peptides within presenilin 1

We describe a targeting technique that selects antigen-specific receptors on B lymphocytes using antigen driven selective production of monoclonal antibodies which are directed against functional peptide sequences within the presenilin 1 molecule that is believed to be related to the early-onset of familial Alzheimer's disease. Three different peptide sequences of presenilin 1 were constructed, one including the region around the amino acid position 300, where the putative cleavage site exists and the other two present in the N- and C-terminal regions of that site. The efficiency in production of the desired monoclonal antibodies was at least 5-40-fold that obtained with the poly(ethylene glycol) (PEG)-mediated method. In addition, monoclonal antibodies directed against each of the peptide sequence displayed a high specificity for the corresponding peptide, in contrast to the lack of success using the PEG method. Also, the selection of surface immunoglobulin receptors on B lymphocytes by the peptides of interest was confirmed by immunofluorescent analysis. Here we demonstrate that targeting B lymphocytes results in the successful and efficient production of highly specific monoclonal antibodies against the lower antigenic peptide sequences.

Expression of herpes simplex virus-thymidine kinase gene controlled by a promoter region of the midkine gene confers selective cytotoxicity to ganciclovir in human carcinoma cells

A selective expression of suicide gene(s) in tumor cells should produce a preferential cytotoxic effect on tumors. Promoter region(s) of a gene that is expressed in tumors but not in normal tissues can be useful for tumor-specific transcription of a suicide gene. Midkine (MK), a growth/differentiation factor, is expressed predominantly in various types of human tumors, whereas its expression in adult normal tissues is highly restricted. In our study, we showed that a 2.3-kb fragment of genomic DNA in the 5' upstream region of the MK gene could activate transcription of a fused reporter gene in MK-positive cells but not in MK-negative cells. Efficiency of the cis-acting sequence to permit expression of an exogenous gene in tumor cells was comparable with that of the SV40 promoter. Regulated expression of the herpes simplex virus-thymidine kinase (HSV-TK) gene under the control of the MK promoter conferred increased sensitivity to ganciclovir (GCV) on MK-positive tumor cells. Administration of GCV into nude mice that were implanted with MK-positive tumor cells that expressed the HSV-TK gene under the control of the MK promoter could suppress the subsequent tumor growth. Expression of therapeutic genes restricted to tumors can be achieved by the use of the putative cis-acting MK promoter.

Serum midkine levels are increased in patients with various types of carcinomas

The level of expression of midkine (MK), a heparin-binding growth factor, is increased in many types of human carcinomas. An enzyme-linked immunoassay, which utilizes a combination of rabbit and chicken antibodies revealed that serum MK level in the controls (n = 135) was 0.154 +/- 0.076 (mean +/- SD) ng ml(-1)with an apparent cut-off value as 0.5 ng ml(-1). Serum MK level was significantly elevated in the cancer patients (n = 150) (P< 0.001); 87% of the patients showed levels of more than 0.5 ng ml(-1). All ten types of cancer examined showed a similar profile of serum MK level. There was no or weak correlation between C-reactive protein level, a marker of inflammation, and serum MK level. Furthermore, in case of gastric carcinoma and lung carcinoma, patients with stage I carcinoma already showed elevated serum MK levels. The present results indicated that serum MK could serve as a general tumour marker with a good potential for clinical application.

Midkine is expressed during repair of bone fracture and promotes chondrogenesis

Midkine (MK) is a heparin-binding growth/differentiation factor implicated in the control of development and repair of various tissues. Upon fracture of the murine tibia, MK was found to be transiently expressed during bone repair. MK was immunohistochemically detected in spindle-shaped mesenchymal cells at the fracture site on day 4 after fracture and in chondrocytes in the area of endochondral ossification on day 7. MK expression was decreased on day 14 and scarcely seen on day 28 when bone repair was completed. This mode of MK expression is reminiscent of MK expression during development. MK was expressed in hypertrophic chondrocytes of the prebone cartilage rudiments on embryonic day 14 in mouse embryos. MK was also strongly expressed in the epiphyseal growth plate. MK was localized intracellularly during both bone repair and development, and this localization was confirmed by immunoelectron microscopy for embryonic chondrocytes. When MK cDNA was transfected into ATDC5 chondrogenic cells and overexpressed, the majority of transfected cells with strong MK expression showed enhanced chondrogenesis as revealed by increased synthesis of sulfated glycosaminoglycans, aggrecan, and type II collagen. These results suggest that MK plays important roles in chondrogenesis and contributes to bone formation and repair.

Midkine, a retinoic acid-inducible heparin-binding cytokine, is a novel regulator of intracellular calcium in human neutrophils

Midkine (MK), which induces chemotaxis of human neutrophils, was found to trigger mobilization of intracellular calcium of these cells. The maximum response was observed 150 sec after exposure to MK, suggesting a complex mechanism in the process. The calcium mobilization was inhibited by herbimycin A, Bordetella pertussis toxin and wortmannin, suggesting that a tyrosine kinase, a G protein-linked receptor and phosphatidyl inositol 3 kinase are involved in the process.

Evaluation of heparin-binding growth factors in rescuing morphogenesis of heparitinase-treated mouse embryonic lung explants

In vitro development of embryonic mouse lung explants was hindered by digestion with heparitinase, which removed about 40% of [35S] sulfate-labeled heparan sulfate synthesized. The enzyme-treated explants were inhibited in branching morphogenesis and the mesenchymal tissue was thin. Addition of basic fibroblast growth factor (bFGF), a typical heparin-binding growth factor, restored the inhibition caused by heparitinase in branching morphogenesis. Addition of midkine (MK), another heparin-binding growth factor, showed a weak effect on branching morphogenesis, but exhibited an effect in restoring development of mesenchymal tissue. These data together with the distribution of the factors indicate that both are involved in development of the lung. Heparitinase-treated explants can be useful models for evaluating roles played by various heparin-binding growth factors.