Molecular composition of adiponectin in urine is a useful biomarker for detecting early stage of diabetic kidney disease.

We previously developed two immune complex transfer enzyme immunoassays (ICT-EIA) to measure total adiponectin (T-AN) and high molecular weight adiponectin (H-AN) in urine and have verified their usefulness as biomarkers for diabetic kidney disease. In this study, we developed T-AN and H-AN assays using the sandwich EIA (Sand-EIA). The reactivities of Sand-EIAs were compared with ICT-EIAs by measuring size exclusion chromatography (SEC) fractions of urine and adiponectin standard. As a result, ICT-EIAs showed higher macromolecular specificity. We then analyzed the molecular profile of adiponectin in the urine of 5 patients with different eGFR stages by measuring SEC fractions of urine. The results showed that smaller adiponectin correlated relatively well with eGFR stage. Finally, because SEC is time-consuming, we investigated that the ratio of T-ANs by Sand-EIA and ICT-EIA could be a good indicator of the monomer adiponectin. The ratio was evaluated using 77 urine samples from patients with diabetes and showed a significant decrease at an earlier stage compared with other biomarkers. In conclusion, we demonstrated a new index to estimate monomer adiponectin in urine by using Sand-EIA and ICT-EIA, and urinary monomer adiponectin can be a good early indicator of deterioration of renal function in diabetic patients. J. Med. Invest. 70 : 464-470, August, 2023.

Insulin receptor cleavage induced by estrogen impairs insulin signaling.

INTRODUCTION: Soluble insulin receptor (sIR), which is the ectodomain of insulin receptor (IR), is present in human plasma. Plasma sIR levels are positively correlated with blood glucose levels and negatively correlated with insulin sensitivity. An in vitro model of IR cleavage shows that extracellular calpain 2 directly cleaves IR, which generates sIR, and sequential cleavage of the IRß subunit by γ-secretase impairs insulin signaling in a glucose concentration-dependent manner. Nevertheless, sIR levels vary among subjects with normal glucose levels. RESEARCH DESIGN AND METHODS: We examined sIR levels of pregnant women throughout gestation. Using an in vitro model, we also investigated the molecular mechanisms of IR cleavage induced by estradiol. RESULTS: In pregnant women, sIR levels were positively correlated with estrogen levels and significantly increased at late pregnancy independent of glucose levels. Using an in vitro model, estrogen elicited IR cleavage and impaired cellular insulin signaling. Estradiol-induced IR cleavage was inhibited by targeting of calpain 2 and γ-secretase. Estrogen exerted these biological effects via G protein-coupled estrogen receptor, and its selective ligand upregulated calpain 2 expression and promoted exosome secretion, which significantly increased extracellular calpain 2. Simultaneous stimulation of estrogen and high glucose levels had a synergic effect on IR cleavage. Metformin prevented calpain 2 release in exosomes and restored insulin signaling impaired by estrogen. CONCLUSIONS: Estradiol-induced IR cleavage causes cellular insulin resistance, and its molecular mechanisms are shared with those by high glucose levels. sIR levels at late pregnancy are significantly elevated along with estrogen levels. Therefore, estradiol-induced IR cleavage is preserved in pregnant women and could be part of the etiology of insulin resistance in gestational diabetes mellitus and overt diabetes during pregnancy.

Urinary adiponectin excretion is an early predictive marker of the decline of the renal function in patients with diabetes mellitus.

AIMS: Since diabetes-associated kidney complication changes from diabetic nephropathy to diabetic kidney disease (DKD), more suitable biomarkers than urinary albumin are required. It has been hypothesized that urinary adiponectin (u-ADPN) is associated with the progression of DKD. We therefore evaluated the effectiveness of u-ADPN in predicting the decline of the renal function in patients with diabetes prior to end-stage renal disease. METHODS: An ultrasensitive immune complex transfer enzyme immunoassay (ICT-EIA) was used to measure total and high molecular weight (HMW) adiponectin separately. We evaluated the relationships between the creatinine-adjusted urinary total-ADPN and HMW-ADPN, albumin (UACR) and liver-type fatty acid binding protein (L-FABP) at baseline and the 2-year change of the estimated glomerular filtration rate (ΔeGFR). RESULTS: This 2-year prospective observational study included 201 patients with diabetes. These patients were divided into three groups according to their ΔeGFR: ≤-10 mL/min/1.73m2, >-10 and ≤0 mL/min/1.73m2, and >0 mL/min/1.73m2. Jonckheere-Terpstra test showed that lower ΔeGFR was associated with higher u-HMW-ADPN (p = 0.045). In logistic regression analysis, u-HMW-ADPN was associated with ΔeGFR after adjusted age, sex, and basal eGFR. CONCLUSION: Urinary HMW-ADPN could predict a declining renal function in patients with diabetes.

Development of fully automated and ultrasensitive assays for urinary adiponectin and their application as novel biomarkers for diabetic kidney disease.

Glomerular filtration rate (GFR) and urinary albumin excretion rate (UAER) are used to diagnose and classify the severity of chronic kidney disease. Total adiponectin (T-AN) and high molecular weight adiponectin (H-AN) assays were developed using the fully automated immunoassay system, HI-1000 and their significance over conventional biomarkers were investigated. The T-AN and H-AN assays had high reproducibility, good linearity, and sufficient sensitivity to detect trace amounts of adiponectin in the urine. Urine samples after gel filtration were analyzed for the presence of different molecular isoforms. Low molecular weight (LMW) forms and monomers were the major components (93%) of adiponectin in the urine from a diabetic patient with normoalbuminuria. Urine from a microalbuminuria patient contained both high molecular weight (HMW) (11%) and middle molecular weight (MMW) (28%) adiponectin, although the LMW level was still high (52%). The amount of HMW (32%) and MMW (42%) were more abundant than that of LMW (24%) in a diabetic patient with macroalbuminuria. T-AN (r = - 0.43) and H-AN (r = - 0.38) levels showed higher correlation with estimated GFR (eGFR) than UAER (r = - 0.23). Urinary levels of both T-AN and H-AN negatively correlated with renal function in diabetic patients and they may serve as new biomarkers for diabetic kidney disease.

Circulating osteocalcin as a bone-derived hormone is inversely correlated with body fat in patients with type 1 diabetes.

The objective of the present study was to investigate the correlations between serum undercarboxylated osteocalcin (ucOC) or osteocalcin (OC) concentrations and %body fat, serum adiponectin and free-testosterone concentration, muscle strength and dose of exogenous insulin in patients with type 1 diabetes. We recruited 73 Japanese young adult patients with childhood-onset type 1 diabetes. All participants were receiving insulin replacement therapy. The correlations between logarithmic serum ucOC or OC concentrations and each parameter were examined. Serum ucOC and OC concentrations were inversely correlated with %body fat (r = -0.319, P = 0.007; r = -0.321, P = 0.006, respectively). Furthermore, multiple linear regression analyses were performed to determine whether or not serum ucOC or OC concentrations were factors associated with %body fat. Serum ucOC and OC concentrations remained significant factors even after adjusting for gender, HbA1c, body weight-adjusted total daily dose of insulin and duration of diabetes (ß = -0.260, P = 0.027; ß = -0.254, P = 0.031, respectively). However, serum ucOC and OC concentrations were not correlated with serum adiponectin or free-testosterone concentrations, muscle strength or dose of exogenous insulin. In conclusion, our study demonstrates the inverse correlation between serum ucOC or OC concentrations and body fat in patients with type 1 diabetes.

The immune complex transfer enzyme immunoassay: Mechanism of improved sensitivity compared with conventional sandwich enzyme immunoassay.

Immune complex transfer enzyme immunoassay (ICT-EIA) is one of the technologies which enables ultrasensitive measurements of protein biomarkers. The ICT-EIA uses two types of beads and sandwich-shaped immune complexes are transferred from the 1st bead to the 2nd bead in the assay. The purpose of the study is to reveal the reason why the ICT-EIA achieves ultrasensitive measurements by making a detailed comparison between conventional sandwich enzyme immunoassay (Sand-EIA) and ICT-EIA. ICT-EIAs for cytokines were developed and the sensitivities were compared with the sandwich EIAs. ICT-EIAs had about 100 times higher sensitivities because of markedly decreased non-specific signals derived from non-specific binding of detection antibody conjugates onto the polystyrene bead. The results have enabled us to show the importance of reducing non-specific signals in EIAs to obtain higher sensitivities. This methodology should be more valuable if combined with a different label detection system such as digital counting or immuno-PCR, which may enable the detection of single target protein molecules in the near future.

A study of high-, middle- and low-molecular weight adiponectin in urine as a surrogate marker for early diabetic nephropathy using ultrasensitive immune complex transfer enzyme immunoassay.

Background For the early identification of patients at risk of developing diabetic nephropathy, we have developed an ultrasensitive immune complex transfer enzyme immunoassay to measure adiponectin in urine. Methods We developed immune complex transfer enzyme immunoassay for adiponectin and measured urinary adiponectin from 70 healthy subjects, 35 obese non-diabetic subjects and 20 patients with diabetes. Results The urinary adiponectin concentrations in patients with diabetes (3.3 ± 10.7 ng/mg creatinine) were significantly higher than those in obese subjects (0.54 ± 0.44; P < 0.01) and healthy subjects (0.46 ± 0.42; P < 0.001). The gel filtration elution profile of urine from healthy subjects showed traces of four immunoreactive peaks (high-, medium-, low-molecular weight and monomer molecules), despite the majority of blood adiponectin being high-molecular weight. However, urinary adiponectin molecules were more frequent in low-molecular weight as the estimate glomerular filtration rate decreased. Furthermore, as blood glucose concentrations rose, middle-molecular weight and high-molecular weight increased in urine. Further, urinary adiponectin concentrations correlated with estimate glomerular filtration rate ( r = -0.61, P < 0.001), but not urinary albumin. In addition, our analysis showed a significantly ( P < 0.001) higher value for urinary adiponectin in the G2 stage of chronic kidney disease classification where urinary albumin is not elevated. Conclusion Adiponectin increases in urine as renal function decreases, and urinary adiponectin may be useful as a surrogate marker for diabetic nephropathy risk.

Sequential cleavage of insulin receptor by calpain 2 and γ-secretase impairs insulin signalling.

AIMS/HYPOTHESIS: Soluble insulin receptor (sIR), the ectodomain of the insulin receptor (IR), has been detected in human plasma and its concentration paralleled that of blood glucose. We have previously developed an in vitro model using HepG2 liver-derived cells, which mimics changes in sIR levels in plasma from diabetic patients and shows that calcium-dependent proteases cleave IR extracellularly (a process known as shedding). The present study aimed to reveal the mechanisms of IR cleavage. METHODS: Using the in vitro model, we investigated the molecular mechanisms of IR cleavage, which is accelerated by high-glucose treatment. We also analysed the relationship between IR cleavage and cellular insulin resistance, and the correlation between plasma sIR levels and insulin sensitivity, which was assessed by the euglycaemic-hyperinsulinaemic clamp technique. RESULTS: Here, we determined that calpain 2, which is secreted into the extracellular space associated with exosomes, directly cleaved the ectodomain of the IRß subunit (IRß), which in turn promoted intramembrane cleavage of IRß by γ-secretase. IR cleavage impaired insulin signalling and the inhibition of IR cleavage (by knockdown of calpain 2 and γ-secretase), restored IR substrate-1 and Akt, independent of IR. Furthermore, the glucose-lowering drug, metformin, prevented IR cleavage accompanied by inhibition of calpain 2 release in exosomes, and re-established insulin signalling. In patients with type 2 diabetes, plasma sIR levels inversely correlated with insulin sensitivity. CONCLUSIONS/INTERPRETATION: Sequential cleavage of IR by calpain 2 and γ-secretase may contribute to insulin signalling in cells and its inhibition may be partly responsible for the glucose-lowering effects of metformin. Thus, IR cleavage may offer a new mechanism for the aetiology of insulin resistance.

Endoplasmic reticulum stress induced by tunicamycin increases resistin messenger ribonucleic acid through the pancreatic endoplasmic reticulum eukaryotic initiation factor 2α kinase-activating transcription factor 4-CAAT/enhancer binding protein-α homologous protein pathway in THP-1 human monocytes.

AIMS/INTRODUCTION: Resistin, secreted from adipocytes, causes insulin resistance in mice. In humans, the resistin gene is mainly expressed in monocytes and macrophages. Tunicamycin is known to induce endoplasmic reticulum (ER) stress, and reduce resistin gene expression in 3T3-L1 mouse adipocytes. The aim of the present study was to examine whether ER stress affects resistin gene expression in human monocytes. MATERIALS AND METHODS: The relationship between resistin messenger ribonucleic acid (mRNA) and ER stress markers mRNA was analyzed by reverse transcription polymerase chain reaction in isolated monocytes of 30 healthy volunteers. The effect of endotoxin/lipopolysaccharides or tunicamycin on resistin gene expression was analyzed in THP-1 human monocytes. Signaling pathways leading to resistin mRNA were assessed by the knockdown using small interfering RNA or overexpression of key molecules involved in unfolded protein response. RESULTS: Resistin mRNA was positively associated with immunoglobulin heavy chain-binding protein (BiP) or CAAT/enhancer binding protein-α homologous protein (CHOP) mRNA in human isolated monocytes. In THP-1 cells, lipopolysaccharides increased mRNA of BiP, pancreatic endoplasmic reticulum eukaryotic initiation factor 2α kinase (PERK) and CHOP, as well as resistin. Tunicamycin also increased resistin mRNA. This induction appeared to be dose- and time-dependent. Tunicamycin-induced resistin mRNA was inhibited by chemical chaperone, 4-phenylbutyric acid. The knockdown of either PERK, activating transcription factor 4 (ATF4) or CHOP reduced tunicamycin-induced resistin mRNA. Conversely, overexpression of ATF4 or CHOP increased resistin mRNA. CONCLUSIONS: Endoplasmic reticulum stress induced by tunicamycin increased resistin mRNA through the PERK-ATF4-CHOP pathway in THP-1 human monocytes. ER stress could lead to insulin resistance through enhanced resistin gene expression in human monocytes.

Development of a novel ultrasensitive enzyme immunoassay for human glutamic acid decarboxylase 65 antibody.

BACKGROUND: We developed a novel, ultrasensitive enzyme immunoassay (immune complex transfer enzyme immunoassay) for determination of glutamic acid decarboxylase autoantibody concentrations in serum samples from patients with type 2 diabetes. METHODS: We developed an immune complex transfer enzyme immunoassay for glutamic acid decarboxylase autoantibody and measured glutamic acid decarboxylase autoantibody from 22 patients with type 1 diabetes, 29 patients with type 2 diabetes, and 32 healthy controls. RESULTS: A conventional ELISA kit identified 10 patients with type 1 diabetes and one patient with type 2 diabetes as glutamic acid decarboxylase autoantibody positive, whereas 15 patients with type 1 diabetes and six patients with type 2 diabetes were identified as glutamic acid decarboxylase autoantibody positive using immune complex transfer enzyme immunoassay. CONCLUSIONS: Immune complex transfer enzyme immunoassay is a highly sensitive and specific assay for glutamic acid decarboxylase autoantibody and might be clinically useful for diabetic onset prediction and early diagnosis.

Immunoreactive insulin in diabetes mellitus patient sera detected by ultrasensitive ELISA with thio-NAD cycling.

To minimize patient suffering, the smallest possible volume of blood should be collected for diagnosis and disease monitoring. When estimating insulin secretion capacity and resistance to insulin in diabetes mellitus (DM), increasing insulin assay immunosensitivity would reduce the blood sample volume required for testing. Here we present an ultrasensitive ELISA coupled with thio-NAD cycling to measure immunoreactive insulin in blood serum. Only 5 µL of serum was required for testing, with a limit of detection (LOD) for the assay of 10(-16) moles/assay. Additional recovery tests confirmed this method can detect insulin in sera. Comparisons between a commercially available immunoreactive insulin kit and our ultrasensitive ELISA using the same commercially available reference demonstrated good data correlation, providing further evidence of assay accuracy. Together, these results demonstrate our ultrasensitive ELISA could be a powerful tool in the diagnosis and treatment of not only DM but also many other diseases in the future.

Subattomole detection of adiponectin in urine by ultrasensitive ELISA coupled with thio-NAD cycling.

Adiponectin is a hormone secreted from adipocytes, and it demonstrates antidiabetic, anti-atherosclerotic, antiobesity and anti-inflammatory effects. However, the patterns of change in urinary adiponectin levels in various diseases remain unknown, because only trace amounts of the hormone are present in urine. In the present study, we applied an ultrasensitive ELISA coupled with thio-NAD cycling to measure urinary adiponectin levels. Spikeand-recovery tests using urine confirmed the reliability of our ultrasensitive ELISA. The limit of detection for adiponectin in urine was 2.3×10(-19) moles/assay (1.4 pg/mL). The urinary adiponectin concentration ranged between 0.04 and 5.82 ng/mL in healthy subjects. The pilot study showed that the urinary adiponectin levels, which were corrected by the creatinine concentration, were 0.73±0.50 (ng/mg creatinine, N=6) for healthy subjects, versus 12.02±3.85 (ng/mg creatinine, N=3) for patients with diabetes mellitus (DM). That is, the urinary adiponectin levels were higher (P<0.05) in DM patients than in healthy subjects. Further, these urinary adiponectin levels tended to increase with the progression of DM accompanied with nephropathy. Our method is thus expected to provide a simple, rapid and reasonably priced test for noninvasive monitoring of the progression of DM without the requirement of special tools.

Development of in vitro model of insulin receptor cleavage induced by high glucose in HepG2 cells.

Soluble insulin receptor (sIR), the ectodomain of IR, has been detected in human plasma, and its concentration parallels that of blood glucose in patients with diabetes. IR has a pivotal role in glucose homeostasis and diabetes development; therefore, cleavage of IR promoted by hyperglycemia is involved in insulin resistance and glucose toxicity. To elucidate the physiology of sIR, we developed an in vitro model mimicking the changes in sIR levels in plasma from patients with diabetes. Among four human cell lines that expressed IR, spontaneous cleavage of IR occurred only in HepG2 cells. The molecular characteristics of sIR derived from HepG2 cells were similar to those of sIR detected in human plasma. The concentration of sIR in the medium did not differ between basal and high-glucose conditions in the initial 24-h period, but increasing the duration of pre-stimulation (>48 h) led to a significant increase in sIR levels in cells exposed to high glucose. Additionally, glucose-dependent increment of sIR was reversible in this model. These results are consistent with the observation of plasma sIR in patients with diabetes. Using this model, O-linked N-acetylglucosamine modification was determined to be involved in high-glucose-induced IR cleavage. A calcium-dependent protease was shown to cleave IR extracellularly. These findings show that this in vitro model could be useful for determining the molecular mechanism underlying IR cleavage.

Development of an ultra-sensitive enzyme immunoassay for human insulin autoantibodies.

OBJECTIVES: We developed an ultrasensitive enzyme immunoassay (ICT-EIA) for insulin autoantibody (IAA) measurements to better understand the pathophysiology of diabetes. DESIGN AND METHODS: We developed ICT-EIA for IAA and measured IAA in 24 patients with type 1 diabetes, 30 patients with type 2 diabetes, 30 patients with methimazole-treated Graves' disease, 20 patients with Hashimoto's disease, 9 patients with hyperinsulinemia, and 73 healthy control subjects. RESULTS: The conventional ELISA identified 3 patients with type 1 diabetes and 2 patients with type 2 diabetes as IAA positive, whereas 15 patients with type 1 diabetes, 7 patients with type 2 diabetes, and 4 patients with methimazole-treated Graves' disease were identified as IAA positive using ICT-EIA. CONCLUSIONS: The ICT-EIA is an ultrasensitive and specific assay for IAA, and its use may provide a better understanding of the role of IAA in diabetes onset and progression.

A novel ultra-sensitive enzyme immunoassay for soluble human insulin receptor ectodomain and its measurement in urine from healthy subjects and patients with diabetes mellitus.

OBJECTIVE: For the early identification of patients at risk of developing diabetes mellitus, and to prevent the onset of diabetes by performing dietary counseling and exercise guidance, we have developed an ultra-sensitive immune complex transfer enzyme immunoassay (ICT-EIA) to measure soluble human insulin receptor ectodomain (sIRalpha) in urine which is collected non-invasively. DESIGN AND METHODS: We developed ICT-EIA for sIRalpha and measured urinary sIRalpha from 106 healthy volunteers, 35 obese volunteers and 42 patients with diabetes. RESULTS: The detection limit of ICT-EIA (0.04 pg/mL), using a urine sample of as little as 100 microL, was a few hundred-fold higher than that of conventional ELISA. Using ICT-EIA, the urinary sIRalpha level in patients with diabetes (9.7+/-20.1 pg/mg creatinine) was significantly higher than those in healthy volunteers (1.4+/-0.9; P<0.001). CONCLUSION: ICT-EIA for sIRalpha may be useful as a good marker for evaluating diabetes risk.

Adrenomedullin release in the rat mesenteric resistance artery.

Adrenomedullin (AM) is a potent vasodilator peptide whose major source is the vascular wall. In the present study, the mechanism of release of AM was investigated in the rat mesenteric resistance artery. The isolated mesenteric vascular bed was perfused with Krebs solution at a constant flow rate (5 ml/min) and AM in the perfusate was measured by a highly sensitive enzyme immunoassay (Immunoenzymometric assay; IEMA) method. In preparations without endothelium, spontaneous release of AM was detected in the perfusate (68.7+/-5.8 fmol/ml, n=45). Periarterial nerve stimulation (PNS, 4 and 8 Hz) caused 11.4+/-3.9% (4 Hz) and 9.1+/-3.5% (8 Hz) decreases in the spontaneous release of AM. Removal of Ca2+ from the medium did not affect the spontaneous AM release, but abolished the PNS-induced inhibition of spontaneous AM release. Perfusion of 10nM calcitonin gene-related peptide (CGRP) or 0.1 microM capsaicin (inducer of CGRP release) inhibited significantly the spontaneous AM release. PNS (8 Hz)-induced inhibition of spontaneous AM release was antagonized by CGRP(8-37) (CGRP receptor antagonist). These results suggest that AM is mainly released from vascular smooth muscle cells of the rat mesenteric artery and endogenous or exogenous CGRP inhibits AM release.

Study of blood metabolism and urinary excretion of chymopapain following intradiscal injection using a high-sensitivity enzyme immunoassay.

To develop chymopapain-induced chemonucleolysis as an established treatment, it is necessary to determine the kinetics of chymopapain in blood and urine following intradiscal injection. To investigate the rate of blood metabolism and urinary excretion of chymopapain following intradiscal injection, we developed a high-sensitivity enzyme immunoassay for chymopapain. The sensitivity for this assay was 1 pg/tube (40 amol). After injecting chymopapain into the nucleus pulposus of humans, levels of blood chymopapain were measured by enzyme immunoassay. The level of chymopapain in blood decreased gradually, with a half-life of 2-3 days. The half-life for urinary excretion was a little longer, at 3 days. It was also found that chymopapain in blood was not present as a free molecule but formed a complex that had a molecular weight of about 120 kDa. These findings suggest that most chymopapain would not have activity in blood.

Disassociated increases of adrenomedullin in the rat cerebrospinal fluid and plasma after salt loading and systemic administration of lipopolysaccharide.

To determine the role of adrenomedullin (AM) in the fluid electrolyte homeostasis and endotoxin shock, cerebral spinal fluid (CSF) and plasma were sampled from rats after respective challenges. The AM levels were measured by a highly sensitive immunoassay. The AM levels in the CSF of the rats anesthetized with ether (10.7 +/- 0.60 fmol/ml) were significantly higher than those with isoflurane 5.17 +/- 0.70 fmol/ml, P < 0.01), while the plasma level did not differ significantly. The CSF levels of the rats received 2% saline drinking increased to 3 and 4 folds at day 5 and day 7, respectively, while the plasma levels did not differ from controls at both time points. The AM levels in CSF or plasma increased to 1.5 and 3 folds at 1.5 h after intraperitoneal (i.p.) administration of lipopolysaccharide (LPS, 5 mg/kg), reached 6.5 and 30 folds at 6 h, respectively, while no change was observed in the controls. The present findings suggest that AM in the CSF is regulated independently from that in the plasma, the centrally synthesized AM plays and important role in the regulation of the fluid electrolyte homeostasis. Furthermore, the circulatory AM plays an important role in the endotoxin shock.

Development of an ultrasensitive enzyme immunoassay for human proadrenomedullin N-terminal 20 peptide and direct measurement of two molecular forms of PAMP in plasma from healthy subjects and patients with cardiovascular disease.

OBJECTIVE: Proadrenomedullin N-terminal 20 peptide (PAMP) processed from an adrenomedullin precursor is a potent hypotensive peptide. It was anticipated that a mature form of PAMP (m-PAMP) and an intermediate PAMP-gly existed together in the blood. To measure concentrations of PAMPs in human plasma directly, we have developed a highly sensitive enzyme immunoassay (immune complex transfer enzyme immunoassay, ICT-EIA). DESIGN AND METHODS: PAMP was reacted simultaneously with 2,4-dinitrophenyl (DNP)-biotinyl-bovine serum albumin (BSA)-anti-PAMP Fab' conjugate and anti-PAMP Fab'-beta-D-galactosidase conjugate. The immune complex that was formed was initially trapped onto a polystyrene bead coated with anti-DNP IgG, and then transferred onto a second polystyrene bead coated with streptavidin. The resulting three-component complex was then assayed fluorometrically. RESULTS: The detection limits of ICT-EIA for both m-PAMP and PAMP-gly were 0.1 pmol/l with as little as 10 microl of plasma, and were a hundred times higher than with conventional radioimmunoassay (RIA). Using ICT-EIA, we determined that the plasma concentrations of m-PAMP and PAMP-gly in 51 healthy volunteers were 0.51 +/- 0.19 and 1.15 +/- 0.38 pmol/l (mean +/- SD), respectively. Both plasma m-PAMP and PAMP-gly concentrations in patients with a variety of diseases, including hypertension, heart failure, chronic renal failure, and hemodialysis, were significantly higher than those in healthy subjects. In addition, both plasma m-PAMP and PAMP-gly concentrations in patients with New York Heart Association (NYHA) class I-IV heart failure were increased in proportion to clinical severity. CONCLUSIONS: These sensitive and specific ICT-EIAs may be used as a powerful tool for investigating the cardiovascular system in patients with heart failure.

Glycine-extended adrenomedullin exerts vasodilator effect through amidation in the rat aorta.

Human adrenomedullin (hAM) is an endogenous peptide that has potent vasodilator activity. Mature AM is biosynthesized from its intermediate form, glycine-extended AM (AM-gly), by carboxy-terminal amidation. AM-gly is generally considered to be biologically inactive but is a major molecular form in human and rat plasma. The present study demonstrated that recombinant human AM-gly (hAM-gly) elicits potent vasodilator effect on isolated rat aorta. In aortic rings, hAM-gly produced dose-dependent (0.1-100 nM) relaxation in phenylephrine-precontracted strips (pD(2) 8.4+/-0.5). The vasorelaxant potency of hAM-gly was comparable to that of hAM (pD(2) 8.6+/-0.2) but hAM-gly took a significantly (P<0.01) longer time to reach the maximal relaxation compared with hAM (T(max) 23+/-4 vs. 5+/-2 min). Vasorelaxant responses to hAM-gly were abolished by endothelial removal. N(omega)-nitro-L-arginine (L-NNA) and AM(22-52) significantly (P<0.01) reduced the vasodilator effect of hAM-gly. Furthermore, 4-phenyl-3-butenoic acid (PBA), an alpha-amidation enzyme inhibitor, significantly (P<0.05) inhibited the vasorelaxant responses to hAM-gly without any effect on the hAM-induced relaxation, suggesting the possible process of amidation in the rat aorta. We further clarified that the aorta has the ability to convert exogenous hAM-gly to mature hAM and the conversion is inhibited by PBA. These results suggest that the circulating AM-gly may play a role in regulating vascular tone and increased plasma AM-gly may be involved in the pathophysiology of cardiovascular diseases.