3D confocal microscope imaging of macromolecule uptake in the intact brachiocephalic artery

BACKGROUND AND AIMS

Elevated uptake of plasma macromolecules by the arterial wall is an early event in atherogenesis. Existing optical techniques for detecting macromolecular tracers in the wall have poor depth penetration and hence require en face imaging of flattened arterial segments. Imaging uptake in undistorted curved and branched vessels would be useful in understanding disease development.

METHODS

Depth penetration was increased by applying optical clearing techniques. The rat aorto-brachiocephalic junction was imaged intact by confocal microscopy after it had been exposed to circulating rhodamine-labelled albumin in vivo, fixed in situ, excised and then cleared with benzyl alcohol/benzyl benzoate. Tracer uptake was mapped onto a 3D surface mesh of the arterial geometry.

RESULTS

Tracer fluorescence was detectable throughout the wall closest to the objective lens and, despite a vessel diameter of c. 1 mm, in the wall on the other side of the artery, across the lumen. By tile scanning, tracer concentrations were mapped in the aorta, the brachiocephalic artery and their junction without opening or flattening either vessel. Optical clearing was also shown to be compatible with immunofluorescent staining and imaging of experimental atherosclerosis.

CONCLUSIONS

The technique obviates the need for labour-intensive sample preparation associated with standard en face imaging. More importantly, it preserves arterial geometry, facilitating co-localisation of uptake maps with maps of biomechanical factors, which typically exist on 3D surface meshes. It will permit the correlation of haemodynamic wall shear stress with macromolecule permeability more accurately in regions of high curvature or branching, such as in the coronary arteries.

Targeted Molecular Iron Oxide Contrast Agents for Imaging Atherosclerotic Plaque

Overview: Cardiovascular disease remains a leading cause of death worldwide, with vulnerable plaque rupture the underlying cause of many heart attacks and strokes. Much research is focused on identifying an imaging biomarker to differentiate stable and vulnerable plaque. Magnetic Resonance Imaging (MRI) is a non-ionising and non-invasive imaging modality with excellent soft tissue contrast. However, MRI has relatively low sensitivity (micromolar) for contrast agent detection compared to nuclear imaging techniques. There is also an increasing emphasis on developing MRI probes that are not based on gadolinium chelates because of increasing concerns over associated systemic toxicity and deposits¹. To address the sensitivity and safety concerns of gadolinium this project focused on the development of a high relaxivity probe based on superparamagnetic iron oxide nanoparticles for the imaging of atherosclerotic plaque with MRI. With development, this may facilitate differentiating stable and vulnerable plaque in vivo.

Aim: To develop a range of MRI contrast agents based on superparamagnetic iron oxide nanoparticles (SPIONs), and test them in a murine model of advanced atherosclerosis.

Methods: Nanoparticles of four core sizes were synthesised by thermal decomposition and coated with poly(maleicanhydride-alt-1-octadecene) (PMAO), poly(ethyleneimine) (PEI) or alendronate, then characterised for core size, hydrodynamic size, surface potential and relaxivity. On the basis of these results, one candidate was selected for further studies. In vivo studies using 10 nm PMAO-coated SPIONs were performed in ApoE^-/- mice fed a western diet and instrumented with a perivascular cuff on the left carotid artery. Control ApoE^-/- mice were fed a normal chow diet and were not instrumented. Mice were scanned on a 3T MR scanner (Philips Achieva) with the novel SPION contrast agent, and an elastin-targeted gadolinium agent that was shown previously to enable visualisation of plaque burden. Histological analysis was undertaken to confirm imaging findings through staining for macrophages, CX3CL1, elastin, tropoelastin, and iron.

Results: The lead SPION agent consisted of a 10 nm iron oxide core with poly(maleicanhydride-alt-1-octadecene), (-36.21 mV, r² 18.806 mmol^-1/s^-1). The irregular faceting of the iron oxide core resulted in high relaxivity and the PMAO provided a foundation for further functionalisation on surface -COOH groups. The properties of the contrast agent, including the negative surface charge and hydrodynamic size, were designed to maximise circulation time and evade rapid clearance through the renal system or phagocytosis. In vitro testing showed that the SPION agent was non-toxic.

In vivo results show that the novel contrast agent accumulates in similar vascular regions to a gadolinium-based contrast agent (Gd-ESMA) targeted to elastin, which accumulates in plaque. There was a significant difference in SPION signal between the instrumented and the contralateral non-instrumented vessels in diseased mice (p = 0.0411, student's t-test), and between the instrumented diseased vessel and control vessels (p = 0.0043, 0.0022, student's t-test). There was no significant difference between the uptake of either contrast agent between stable and vulnerable plaques (p = 0.3225, student's t-test). Histological verification was used to identify plaques, and Berlin Blue staining confirmed the presence of nanoparticle deposits within vulnerable plaques and co-localisation with macrophages.

Conclusion: This work presents a new MRI contrast agent for atherosclerosis which uses an under-explored surface ligand, demonstrating promising properties for in vivo behaviour, is still in circulation 24 hours post-injection with limited liver uptake, and shows good accumulation in a murine plaque model.

Influence of shear stress magnitude and direction on atherosclerotic plaque composition

The precise flow characteristics that promote different atherosclerotic plaque types remain unclear. We previously developed a blood flow-modifying cuff for ApoE^-/- mice that induces the development of advanced plaques with vulnerable and stable features upstream and downstream of the cuff, respectively. Herein, we sought to test the hypothesis that changes in flow magnitude promote formation of the upstream (vulnerable) plaque, whereas altered flow direction is important for development of the downstream (stable) plaque. We instrumented ApoE^-/- mice (n = 7) with a cuff around the left carotid artery and imaged them with micro-CT (39.6 µm resolution) eight to nine weeks after cuff placement. Computational fluid dynamics was then performed to compute six metrics that describe different aspects of atherogenic flow in terms of wall shear stress magnitude and/or direction. In a subset of four imaged animals, we performed histology to confirm the presence of advanced plaques and measure plaque length in each segment. Relative to the control artery, the region upstream of the cuff exhibited changes in shear stress magnitude only (p < 0.05), whereas the region downstream of the cuff exhibited changes in shear stress magnitude and direction (p < 0.05). These data suggest that shear stress magnitude contributes to the formation of advanced plaques with a vulnerable phenotype, whereas variations in both magnitude and direction promote the formation of plaques with stable features.

Low shear stress induces M1 macrophage polarization in murine thin-cap atherosclerotic plaques

Macrophages, a significant component of atherosclerotic plaques vulnerable to acute complications, can be pro-inflammatory (designated M1), regulatory (M2), lipid- (Mox) or Heme-induced (Mhem). We showed previously that low (LSS) and oscillatory (OSS) shear stress cause thin-cap fibroatheroma and stable smooth muscle cell-rich plaque formation respectively in ApoE-knockout (ApoE(-/-)) mice. Here we investigated whether different shear stress conditions relate to specific changes in macrophage polarization and plaque morphology by applying a shear stress-altering cast to the carotid arteries of high fat-fed ApoE(-/-) mice. The M1 markers iNOS and IRF5 were highly expressed in macrophage-rich areas of LSS lesions compared to OSS lesions 6weeks after cast placement, while the M2 marker Arginase-1, and Mox/Mhem markers HO-1 and CD163 were elevated in OSS lesions. Our data indicates shear stress could be an important determinant of macrophage polarization in atherosclerosis, with low shear promoting M1 programming.

Elevated uptake of plasma macromolecules by regions of arterial wall predisposed to plaque instability in a mouse model

Atherosclerosis may be triggered by an elevated net transport of lipid-carrying macromolecules from plasma into the arterial wall. We hypothesised that whether lesions are of the thin-cap fibroatheroma (TCFA) type or are less fatty and more fibrous depends on the degree of elevation of transport, with greater uptake leading to the former. We further hypothesised that the degree of elevation can depend on haemodynamic wall shear stress characteristics and nitric oxide synthesis. Placing a tapered cuff around the carotid artery of apolipoprotein E -/- mice modifies patterns of shear stress and eNOS expression, and triggers lesion development at the upstream and downstream cuff margins; upstream but not downstream lesions resemble the TCFA. We measured wall uptake of a macromolecular tracer in the carotid artery of C57bl/6 mice after cuff placement. Uptake was elevated in the regions that develop lesions in hyperlipidaemic mice and was significantly more elevated where plaques of the TCFA type develop. Computational simulations and effects of reversing the cuff orientation indicated a role for solid as well as fluid mechanical stresses. Inhibiting NO synthesis abolished the difference in uptake between the upstream and downstream sites. The data support the hypothesis that excessively elevated wall uptake of plasma macromolecules initiates the development of the TCFA, suggest that such uptake can result from solid and fluid mechanical stresses, and are consistent with a role for NO synthesis. Modification of wall transport properties might form the basis of novel methods for reducing plaque rupture.

Development of a bioassay system for human growth hormone determination with close correlation to immunoassay

Serum growth hormone (GH) level is measured largely through immunoassays in clinical practice. However, a few cases with bioinactive and immunoreactive GH have also been reported. We describe here a new bioassay system for GH determination using the BaF/GM cell line, which proliferates in a dose-dependent manner on hGH addition; cell proliferation was blocked by anti-hGH antibody. This bioassay had the lowest detection limit (∼0.02 ng/ml) reported thus far and the highest specificity for GH. The bioassay results were compared with those of an immunoradiometric assay across 163 patient samples in various endocrine states. A close correlation (the ratio of bioactivity/immunoreactivity was 1.04 ± 0.33, mean ± SD) was observed between bioactivity and immunoreactivity in these samples. The newly developed system is a specific, sensitive, easy, and fast bioassay system for GH determination; we consider it useful for evaluating GH bioactivity in various endocrine states.

High throughput en face mapping of arterial permeability using tile scanning confocal microscopy

Elevated uptake of plasma macromolecules by the arterial wall has been implicated in the initiation of atherosclerosis. Here we describe a new method for mapping such uptake in laboratory animals. Albumin was labelled with a fluorescent dye and administered intravenously. After 10 min, the aorta was fixed in situ, excised and opened. En face confocal microscopy employing a computer-controlled stage was used to obtain contiguous tiles, each consisting of a stack of images of fluorescence emission at different depths in the wall. To obtain two-dimensional maps, intensities were summed in each column of voxels starting at the endothelial surface and extending 10 μm into the wall. Variation in the sensitivity of the system with time and in all three spatial directions was assessed and corrected using calibration standards and model specimens. In immature rabbits, uptake around aorto-intercostal branches was greatest in an arrowhead-shaped region around the downstream half of each ostium, and at its lateral margins. Uptake around branches in mature rabbits was more uniform; it was highest upstream of the ostium. Patches and streaks of high uptake were also seen at non-branch locations in the descending thoracic aorta. Transport was more uniform around branches in mice, except for small regions of high uptake at the ostial rim and at the leading edge of an intimal cushion upstream of the ostium, where lesions develop. The technique provides accurate quantification in three dimensions over large areas; it has high throughput, sensitivity and resolution and is suitable for widespread use.

Molecular pharmacology of phosphatidylinositol 3-kinase inhibition in human glioma

Gliomas are primary brain tumors with poor prognosis that exhibit frequent abnormalities in phosphatidylinositol 3-kinase (PI3 kinase) signaling. We investigated the molecular mechanism of action of the isoform-selective class I PI3 kinase and mTOR inhibitor PI-103 in human glioma cells. The potent inhibitory effects of PI-103 on the PI3 kinase pathway were quantified. PI-103 and the mTOR inhibitor rapamycin both inhibited ribosomal protein S6 phosphorylation but there were clear differences in the response of upstream components of the PI3 kinase pathway, such as phosphorylation of Thr(308)-AKT, that were inhibited by PI-103 but not rapamycin. Gene expression profiling identified altered expression of genes encoding regulators of the cell cycle and cholesterol metabolism, and genes modulated by insulin or IGF1 signaling, rapamycin treatment or nutrient starvation. PI-103 decreased expression of positive regulators of G(1)/S phase progression and increased expression of the negative cell cycle regulator p27(kip1). A reversible PI-103-mediated G(1) cell cycle arrest occurred without significant apoptosis, consistent with the altered gene expression detected. PI-103 induced vacuolation and processing of LC-3i to LC-3ii, which are features of an autophagic response. In contrast to PI-103, LY294002 and PI-387 induced apoptosis, indicative of likely off-target effects. PI-103 interacted synergistically or additively with cytotoxic agents used in the treatment of glioma, namely vincristine, BCNU and temozolomide. Compared to individual treatments, the combination of PI-103 with temozolomide significantly improved the response of U87MG human glioma xenografts. Our results support the therapeutic potential for PI3 kinase inhibitors with a PI-103-like profile as therapeutic agents for the treatment of glioma.

Failure to generate atheroprotective apolipoprotein AI phenotypes using synthetic RNA/DNA oligonucleotides (chimeraplasts)

BACKGROUND

Elevated plasma high-density lipoprotein (HDL), and its major constituent apolipoprotein AI (apoAI), are cardioprotective. Paradoxically, two natural variants of apoAI, termed apoAI(Milano) and apoAI(Paris), are associated with low HDL, but nevertheless provide remarkable protection against heart disease for heterozygous carriers and may even lead to longevity. Both variants arise from point mutations and have Arg(173) and Arg(151) to Cys substitutions, respectively, which allow disulphide-linked dimers to form. Potentially, synthetic RNA/DNA oligonucleotides (chimeraplasts) can permanently correct single point mutations in genomic DNA. Here, we use a variation of such targeted gene repair technology, 'gain-of-function chimeraplasty', and attempt to enhance the biological activity of apoAI by altering a single genomic base to generate the atheroprotective phenotypes, apoAI(Milano) and apoAI(Paris).

METHODS

We targeted two cultured cell lines that secrete human apoAI, hepatoblastoma HepG2 cells and recombinant CHO-AI cells, using standard 68-mer chimeraplasts with polyethyleneimine (PEI) as carrier and then systematically varied several experimental conditions. As a positive control we targeted the dysfunctional APOE2 gene, which we have previously converted to wild-type APOE3.

RESULTS

Conversion of wild-type apoAI to apoAI(Milano) proved refractory, with limited correction in CHO-AI cells only. However, a successful conversion to apoAI(Paris) was achieved, as demonstrated by polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) analysis and direct genomic sequencing. Unexpectedly, attempts with a new batch of 68-mer chimeraplast to enhance conversion, by using different delivery vehicles, including chemically modified PEI, failed to show a base change; nor could conversion be detected with an 80-mer or a 52-76-mer series. In contrast, when a co-culture of CHO-E2 and CHO-AI cells was co-targeted, a clear conversion of apoE2 to apoE3 was seen, whereas no apoAI(Paris) could be detected. When the individual chimeraplasts were analysed by denaturing electrophoresis only the active apoE2-to-E3 chimeraplast gave a sharp band.

CONCLUSIONS

Our findings suggest that different batches of chimeraplasts have variable characteristics and that their quality may be a key factor for efficient targeting and/or base conversion. We conclude that, although an evolving technology with enormous potential, chimeraplast-directed gene repair remains problematical.

Inhibition of atherosclerosis in apolipoprotein-E-deficient mice following muscle transduction with adeno-associated virus vectors encoding human apolipoprotein-E

Apolipoprotein E (apoE) is a multifunctional plasma glycoprotein involved in lipoprotein metabolism and a range of cell signalling phenomena. ApoE-deficient (apoE(-/-)) mice exhibit severe hypercholesterolaemia and are an excellent model of human atherosclerosis. ApoE somatic gene transfer and bone marrow transplantation in apoE(-/-) mice results in reversal of hypercholesterolaemia, inhibition of atherogenesis and regression of atherosclerotic plaque density. Replication defective adeno-associated virus vectors (rAAVs) are an attractive system currently in clinical trial for muscle-based heterologous gene therapy to express secreted recombinant plasma proteins. Here we have applied rAAV transduction of skeletal muscle to express wild-type (epsilon3) and a defective receptor-binding mutant (epsilon2) human apoE transgene in apoE(-/-) mice. In treated animals, apoE mRNA was present in transduced muscles and, although plasma levels of recombinant apoE fell below the detection levels of our ELISA (ie <10 ng/ml), circulating antibodies to human apoE and rAAV were induced. Up to 3 months after a single administration of rAAV/apoE3, a significant reduction in atherosclerotic plaque density in aortas of treated animals was observed (approximately 30%), indicating that low-level rAAV-mediated apoE3 expression from skeletal muscle can retard atherosclerotic progression in this well-defined genetic model.

Enzyme immunoassay for oxytocin

A competitive, double antibody enzyme immunoassay for oxytocin in a heterologous system was developed. Horseradish peroxidase was conjugated with oxytocin using N-succinimidyl 3-(2-pyridyldithio) propionate, and rabbit anti-oxytocin serum was produced by immunization of oxytocin-bovine serum albumin complex which was prepared by the carbodiimide method. The sensitivity of the assay was 4 microIU/tube, which corresponded to 10 microIU per ml using 400 microliters of the sample which was extracted from the same volume of plasma by means of SEP-PAK C18 cartridges. The coefficients of variation for different levels of oxytocin ranged from 6.8-15.9% and 8.5-16.7%, for intra- and inter-assay. Recovery of oxytocin added to plasma after extraction was 99-117%. No or little cross-reaction with arginine- and lysine-vasopressin was found. Plasma oxytocin concentrations determined by the proposed enzyme immunoassay were well correlated with those determined by radioimmunoassay (r = 0.90).

A highly sensitive sandwich enzyme immunoassay of urinary growth hormone in children with short stature, Turner's syndrome, and simple obesity

GH values were determined by a highly sensitive sandwich enzyme immunoassay in the 1st morning and/or 24-h accumulated urine samples in 94 children (short stature 70, including 14 with complete GH deficiency, 9 with partial GH deficiency, and 47 with GH-normal short stature; Turner's syndrome, 10, and simple obesity, 14). GH values were also determined in the 2nd to 4th urine samples taken on the same day together with the 1st morning urine in 5 of them. GH values in the 1st morning urine correlated significantly with those of the 24-h urine and with serum peak and mean GH values during nocturnal sleep as a physiological GH secretion test. The 2nd to 4th urines had lower GH concentrations than the 1st morning urine. The GH value of the 1st morning urine in complete GH deficiency was significantly lower than those in GH-normal short stature, partial GH deficiency and Turner's syndrome. However, no significant difference was detected in urinary GH values between complete GH deficiency and simple obesity. We conclude that 1st morning urinary GH estimation may be useful for differentiation of complete GH deficiency from other causes of short stature, but may be difficult for the distinction between complete GH-deficiency and obesity with normal GH secretory ability.

Efficient high-performance liquid chromatographic system for protein purification

An efficient high-performance liquid chromatographic system, consisting of an affinity column and a high-performance size-exclusion column, was developed and applied to the purification of growth hormone receptors from rabbit livers. When a 6-ml sample of Triton X-100 extracts containing 16 mg of protein was applied to the system, 1200-fold purified receptor with a 10% recovery of binding activity from homogenates was obtained within 3-4 h. The purified receptor exhibited one main band on sodium dodecyl sulphate polyacrylamide gel electrophoresis, and the affinity constant (Ka = 6.0.10(9) M-1) was found to be comparable with that of 1% Triton X-100 extract (4.4.10(9) M-1). The injection of 1 ml of 3 M urea solution prior to receptor elution with 10 ml of 6 M urea solution was effective in removing non-specific binding proteins.

Measurement of nocturnal urinary growth hormone values

Nocturnal urinary growth hormone values were measured by a sensitive enzyme immunoassay in normal adults, patients with GH deficiency, patients with Turner's syndrome, normal but short children who had normal plasma GH responses to provocative tests, and patients with acromegaly. The mean nocturnal urinary GH values in patients with acromegaly were significantly greater than those in normal adults (1582.3 +/- 579.8 vs 53.5 +/- 8.6 pmol/mmol creatinine (+/- SEM); p less than 0.05). In the normal but short children and patients with Turner's syndrome, the mean nocturnal urinary GH values were 83.1 +/- 5.2 and 79.8 +/- 29.5 pmol/mmol creatinine, respectively. In patients with GH deficiency, the nocturnal urinary GH values were undetectable (less than 5.3 pmol/mmol creatinine) except in one patient where the value was 6.3 pmol/mmol creatinine. The nocturnal urinary GH values of the patients with GH deficiency were significantly lower than those of the other groups (p less than 0.05). In normal but short children, the nocturnal urinary GH values correlated significantly with mean plasma nocturnal GH concentrations (r = 0.76, p less than 0.001), and 24-hour urinary GH values (r = 0.84, p less than 0.001), respectively. In 4 patients with GH deficiency who had circulating anti-hGH antibody, the urinary GH values were also undetectable. These data indicate that nocturnal urinary GH value reflects endogenous GH secretion during collection time, and that measurement of the nocturnal urinary GH values is a useful method for screening of patients with GH deficiency and acromegaly.

Novel and sensitive noncompetitive enzyme immunoassay for kassinin in rat plasma

A novel and sensitive noncompetitive enzyme immunoassay for kassinin is described. Kassinin was biotinylated using sulfosuccinimidyl-6-(biotinamido)hexanoate. The biotinylated kassinin was trapped on anti-kassinin IgG-coated polystyrene balls and, after washing to eliminate other biotinylated substances, was eluted with HCl. The biotinylated kassinin eluted was reacted with anti-kassinin Fab'-peroxidase conjugate and trapped onto streptavidin-coated polystyrene balls. Peroxidase activity bound to the polystyrene balls was assayed by fluorimetry. The detection limit of kassinin was 0.13 pg (0.1 fmol)/tube or 0.065 microgram/l of rat plasma, which was 750-fold or 15-fold lower than that for competitive radioimmunoassay.

Urinary growth hormone (GH) measurements are useful for evaluating endogenous GH secretion

Daily (24-h) urinary GH excretion was measured using a highly sensitive sandwich enzyme immunoassay in 10 normal adults, 6 patients with hypopituitarism, 25 normal but short children who had normal plasma GH responses (peak plasma GH level, greater than 10 micrograms/L) to provocative tests, and 8 patients with acromegaly. The mean urinary GH values in the normal adults, patients with acromegaly, and patients with hypopituitarism were 13.8 +/- 4.0 (+/- SE) and 431.1 +/- 149.1 ng/g creatinine (Cr) (1.56 +/- 0.45 and 48.77 +/- 16.87 ng/mmol Cr) and undetectable, respectively; these mean values were significantly different from each other. In the normal but short children the urinary values ranged from undetectable to 55.8 ng/g Cr (6.31 ng/mmol Cr). All of the normal but short children and 4 patients with hypopituitarism participated in a 24-h endogenous GH secretion study. The urinary GH values correlated significantly with the mean 24-h plasma GH concentrations as an index of endogenous GH secretion (r = 0.81; P less than 0.001) and plasma somatomedin-C levels (r = 0.67; P less than 0.001), respectively. In 6 patients with acromegaly whose plasma GH levels were constant throughout a 4-h period, the urinary GH values also significantly correlated with the mean plasma GH levels (r = 0.95; P less than 0.01). These data indicate that urinary GH measurements reflect endogenous GH secretion and that measurement of urinary GH excretion is a useful, simple, and practical method for evaluating endogenous GH secretion.

Urinary growth hormone levels measured by ultrasensitive enzyme immunoassay in patients with renal insufficiency

An ultrasensitive enzyme immunoassay was used to measure urinary GH levels in patients with renal insufficiency and normal subjects. Urinary GH excretion varied widely, but was significantly higher (P less than 0.01) in patients with renal insufficiency (median, 339; range, 2-17,000 ng/day) than in normal subjects (5.4; 1.2-15 ng/day). Urinary GH excretion correlated positively with urinary beta 2-microglobulin excretion (r = 0.79; P less than 0.001) and negatively with creatinine clearance (r = -0.83; P less than 0.001). Gel chromatography of urine from patients with renal insufficiency revealed a major peak of urinary GH corresponding to a mol wt of 22K, that of pituitary GH. These findings suggest that the kidneys play an important role in the catabolism of GH and that urinary GH may reflect, at least in part, renal function as well as hypothalamo-pituitary function.

Sensitive sandwich enzyme immunoassay of human growth hormone (hGH) in serum and urine using monoclonal antibody-coated polystyrene balls

A sensitive sandwich enzyme immunoassay for human growth hormone (hGH) using monoclonal antibody is described. A monoclonal anti-hGH IgG-coated polystyrene ball was incubated with hGH and subsequently with affinity-purified rabbit anti-hGH Fab'-horseradish peroxidase conjugate. Peroxidase activity bound to the polystyrene ball was assayed by fluorimetry using 3-(4-hydroxyphenyl) propionic acid as a substrate. The detection limits of hGH in serum and urine were 1.5 ng/l using 20 microliters of serum and 0.2 ng/l using 0.15 ml of urine, respectively. The specificity and assay precision were satisfactory. hGH levels in serum and urine determined by the present sandwich enzyme immunoassay using monoclonal anti-hGH IgG-coated polystyrene balls were well correlated to those determined by the previous sandwich enzyme immunoassay using rabbit anti-hGH IgG-coated polystyrene balls. Levels of hGH in urine collected as first morning voids from healthy subjects aged 19-28 yr were 6.4 +/- 3.2 (SD) ng/g creatinine. However, the present assay gave lower hGH levels than the previous assay. This was at least partly explained by the fact that hGH in urine was less efficiently bound to monoclonal anti-hGH IgG-polystyrene balls than standard hGH, while the binding of hGH in urine and standard hGH to rabbit anti-hGH IgG-coated polystyrene balls was equally efficient. In addition, gel filtration showed that 22K hGH, a major component, in urine was less efficiently bound to monoclonal anti-hGH IgG-coated polystyrene balls than standard 22K hGH. The nature of hGH in serum and urine remains to be investigated.

Urine growth hormone determinations compared with other methods in the assessment of growth hormone secretion

Urinary excretion of hGH was studied in children with short stature using a sensitive sandwich enzyme immunoassay technique. Urinary hGH excretion, in terms of hGH: creatinine ratio, showed excellent correlation with the mean and peak hGH values during physiological and pharmacological tests. It seems that the urinary hGH levels reflect serum hGH profiles during the urine collection period. A border zone for the lower limits of normal hGH levels in the urine was 7.5-13.4 ng/g creatinine for the physiological test at night (from 2000 hours to 0600 hours) and 17.4-35.0 ng/g creatinine for the pharmacological tests. Assessment of hGH secretory status by the urinary hGH levels showed good agreement with the serum hGH response. Measurement of urinary hGH could be used as a diagnostic test for impaired hGH secretion, and the multiple blood drawing required in physiological and pharmacological tests might be replaced by urine sampling.