Immunoassay and other ligand assays: present status and future trends

Immunoassay and other ligand assays have made a major impact on medical research and diagnosis since the first modern (radioisotopically-based) methods emerged. These ubiquitous microanalytic techniques are broadly classifiable as first generation (generally of "competitive" design, e.g., radioimmunoassay), and second generation (generally "noncompetitive," and relying on nonisotopic labels) these (often described as "ultrasensitive") being distinguished by dramatic improvements in sensitivity and performance time. A third generation is now in prospect (based on microarrays of antibody microspots) capable of ultrasensitive determination of hundreds of analytes in a drop of blood. Analogous technology (based on oligonucleotide arrays) is under intensive development for DNA analysis. Array technologies are likely to transform diagnostic medicine in the next decade.

Effects of gender, body composition, and menopause on plasma concentrations of leptin

Circulating concentrations of leptin ([leptin]) vary directly with body mass index and percentage body fat, and may thus constitute an afferent limb of a system regulating body fatness. We tested the hypotheses that: 1) Plasma [leptin] vary more directly with absolute fat mass than with fractional body fatness per se: and 2). The relationship between fat mass and [leptin] is significantly affected by gender and by menopausal status. [Leptin] in the post-absorptive state was examined in 67 subjects (26 male, 20 premenopausal female, 21 postmenopausal females; 43 never-obese, 24 obese) at usual body weight. Body composition was determined by hydrodensitometry, and [leptin] was determined by a double antibody ELISA assay. In male and pre-menopausal female subjects, subcutaneous adipose tissue aspirations were performed for determination of adipocyte volume by the osmium fixation method, and a 3 hour oral glucose tolerance tests was performed. At usual body weight, ([leptin]) was better correlated with absolute fat mass than with body mass index (BMI) or percentage body fat. BMI and % body fat did not account for any of the variance in [leptin] beyond that attributable to FM, per se. The regression equations relating FM to [leptin] did not differ significantly between obese and never-obese subjects. [Leptin] and fasting serum insulin concentrations were significantly correlated in males only. [Leptin] was significantly higher in pre- and post-menopausal females compared to males, even when [leptin] was corrected for differences in body composition (pre-menopausal females > post-menopausal females > males). While plasma [leptin], corrected for FM, declines significantly in women post-menopause, this decline is not sufficient to account for the striking sexual dimorphism in the relationship of leptin to fat mass. This sexual dimorphism is apparently also due, in part, to a suppressive effect of circulating androgens on [leptin].

Fibroblasts are in a position to provide directional information to migrating neutrophils during pneumonia in rabbit lungs

Previous findings have shown that pulmonary fibroblasts are associated with preexisting holes in the endothelial and epithelial basal laminae through which neutrophils appear to enter and leave the interstitium as they migrate from capillaries to alveoli. To determine their role in neutrophil migration, fibroblast organization within the interstitium was assessed by transmission electron microscope observations of serial-sectioned rabbit lung tissue. Interstitial fibroblasts were found to physically interconnect the endothelial basal lamina holes to epithelial basal lamina holes. Morphometric assessment of rabbit lung tissue instilled with Streptococcus pneumoniae revealed that approximately 70% of the surface area density of migrating neutrophils is in close contact (15 nm or less) with interstitial fibroblasts and extracellular matrix elements (30 and 40%, respectively). Although migrating neutrophils were close enough to adhere to both fibroblasts and extracellular elements, the interstitial fibroblasts are organized in a manner that would allow them to provide directional information to the neutrophils. A model illustrating this process is proposed.

Manual and automated (robotic) high-performance liquid chromatography methods for the determination of mycophenolic acid and its glucuronide conjugate in human plasma

A manual and an automated (Zymark PyTechnology robot) HPLC method for simultaneous determination of plasma mycophenolic acid (MPA) and its glucuronide conjugate (MPAG) are described here. Both methods are reproducible and accurate, and both are equivalent in all respects, including quantification limits (MPA, 0.100 microgram/ml; MPAG, 4.00 micrograms/ml), range (using 0.05-0.5 ml of plasma: MPA, 0.0500-20.0 micrograms/aliquot; MPAG, 2.00-200 micrograms/aliquot), precision, and accuracy. MPA and MPAG were stable under the conditions used with both methods. Results from aliquots of paired control samples, analyzed by the manual method over three years at six analytical laboratories, showed excellent agreement in precision and accuracy.

Neutrophil migration through preexisting holes in the basal laminae of alveolar capillaries and epithelium during streptococcal pneumonia

The purpose of this study was to determine whether or not there are preexisting holes in the endothelial and epithelial basal laminae of alveolar walls and to determine the path taken by neutrophils as they migrate from the capillaries to the airspace of the alveoli during inflammation. Using transmission electron microscopy and serial thin sections of normal rabbit and mouse lung, we have demonstrated the presence of slit-like holes in the capillary basal laminae and round holes in the basal laminae of type 2 pneumocytes. The slits in the capillary basal laminae were observed at the intersection of the thick and thin walls where endothelium, pericytes, and fibroblasts make close contact. The round holes in the type 2 cell basal laminae were observed at sites of close contact with fibroblasts. Neutrophils were observed to migrate through these slits and holes during streptococcal pneumonia in rabbit lungs. We conclude that during inflammation in the lung, migrating neutrophils displace pericytes and fibroblasts from the slits in the capillary basal lamina and then crawl through these slits into the alveolar interstitium. We postulate that neutrophils find their way to type 2 pneumocytes by following interstitial fibroblasts. We believe that neutrophils displace fibroblasts from their close contacts with the type 2 cells and then crawl through the holes in the basal lamina into the basal lateral space of the type 2 cells. From there, neutrophils migrate into the alveolar airspace.

Expression of the plasmodial pfmdr1 gene in mammalian cells is associated with increased susceptibility to chloroquine

Chloroquine (CQ)-resistant (CQR) Plasmodium falciparum malaria parasites show a strong decrease in CQ accumulation in comparison with chloroquine-sensitive parasites. Controversy exists over the role of the plasmodial pfmdr1 gene in the CQR phenotype. pfmdr1 is a member of the superfamily of ATP-binding cassette transporters. Other members of this family are the mammalian multidrug resistance genes and the CFTR gene. We have expressed the pfmdr1-encoded protein, Pgh1, in CHO cells and Xenopus oocytes. CHO cells expressing the Pgh1 protein demonstrated an increased, verapamil-insensitive susceptibility to CQ. Conversely, no increase in drug susceptibility to primaquine, quinine, adriamycin, or colchicine was observed in Pgh1-expressing cells. CQ uptake experiments revealed an increased, ATP-dependent accumulation of CQ in Pgh1-expressing cells over the level in nonexpressing control cells. The increased CQ accumulation in Pgh1-expressing cells coincided with an enhanced in vivo inhibition of lysosomal alpha-galactosidase by CQ. CHO cells expressing Pgh1 carrying two of the CQR-associated Pgh1 amino acid changes (S1034C and N1042D) did not display an increased CQ sensitivity. Immunofluorescence experiments revealed an intracellular localization of both mutant and wild-type forms of Pgh1. We conclude from our results that wild-type Pgh1 protein can mediate an increased intracellular accumulation of CQ and that this function is impaired in CQR-associated mutant forms of the protein. We speculate that the Pgh1 protein plays an important role in CQ import in CQ-sensitive malaria parasites.

Developing multianalyte assays

Multianalyte 'binding' assays represent a major advance in microanalytical technology for the measurement of substances of biological importance. Their further development should facilitate sensitive and reproducible quantification of analytes in many areas that are currently problematic, including diagnostic medicine and the standardization of biologicals.

Radioimmunoassay of ganirelix in plasma or serum

A procedure for the radioimmunoassay (RIA) of ganirelix in plasma or serum at concentrations as low as 0.050 ng/ml is described. Antiserum was produced by coupling the N-terminus glycyl analog of ganirelix to BSA by a carbodiimide reaction and immunizing rabbits with this conjugate. The antiserum did not crossreact with LHRH or with various ganirelix peptide fragments. For RIA, 125I labeled ganirelix was used as the tracer and a double antibody procedure was used to separate the free and bound fractions. No purification of the analyte was required prior to RIA. Accuracy of the method was assessed by adding known quantities of ganirelix to ganirelix-free plasma and determining the ratio of measured to added analyte. Linear regression analysis for the concentration range 0.050-50.0 ng/ml yielded a regression equation of y = 0.97x + 0.18, r = 0.999, where x is the amount added and y is the amount measured. Additional validation was obtained from an in vivo study in which [3H]-ganirelix was administered to monkeys and plasma clearance profiles were determined by RIA and an HPLC-radiochemical method. The results were in agreement within experimental error of the two methods. Linear regression analysis of the comparative data gave the equation y = 0.92x + 33.7, r = 0.980, where x is the amount measured by RIA and y is the amount measured by HPLC-radiochemical analysis.

Sonographic heat generation in vivo in the gravid long-tailed macaque (Macaca fascicularis)

Temperature elevations that occur during diagnostic ultrasonic exposure were assessed in vivo in gravid macaques after 10, 20, or 30 min (scan mode; N = 30) or 5, 10, or 15 min (pulsed Doppler; N = 32). Five time points were assessed during the second and third trimesters (gestational days 70 to 150 +/- 2; term, approximately 165 days) using a transient thermocouple technique. Measurements were obtained intracranially or at the muscle-bone interface using a commercial sector scanner (ATL MK 600, 7.5 MHz scanhead; scan mode, ISPTA) = 27 mW/cm2, ISPPA = 85 W/cm2, pulse repetition frequency (PRF) = 1 kHz; pulsed Doppler - ISPTA = 54 mW/cm2, ISPPA = 1.5 W/cm2, PRF = 18.5 kHz). Overall, the greatest temperature elevation achieved with either modality or location was 0.6 degrees C.

Studies on antipeptic ulcer agents: the quantitative structure-activity relationship analysis of heterocyclic aldehyde N4-substituted phenyl (thio) semicarbazones

Forty-five condensation products of furan-, pyrrole- and N-methyl pyrrole-alpha-carboaldehyde with N4-3- or N4-4-substituted phenyl semicarbazones and thiosemicarbazones were designed to optimize the antiulcer activity of a previously derived lead structure, formula II. Quantitative structure-activity relationships revealed that among the series of semicarbazones, increasing hydrophobicity and the introduction of electron-donating groups into the phenyl ring raise the antiulcer activity. Generally, semicarbazones are more active than the corresponding thiosemicarbazones. The wide gulf between the activity and toxicity of two derivatives (Compounds III and IV) necessitates further investigation of their pharmacological effects.

High specific activity chemiluminescent and fluorescent markers: their potential application to high sensitivity and 'multi-analyte' immunoassays

The sensitivities of immunoassays relying on conventional radioisotopic labels (i.e. radioimmunoassay (RIA) and immunoradiometric assay (IRMA) permit the measurement of analyte concentrations above ca 10(7) molecules/ml. This limitation primarily derives, in the case of 'competitive' or 'limited reagent' assays, from the 'manipulation errors arising in the system combined with the physicochemical characteristics of the particular antibody used; however, in the case of 'non-competitive' systems, the specific activity of the label may play a more important constraining role. It is theoretically demonstrable that the development of assay techniques yielding detection limits significantly lower than 10(7) molecules/ml depends on: (1) the adoption of 'non-competitive' assays designs; (2) the use of labels of higher specific activity than radioisotopes; (3) highly efficient discrimination between the products of the immunological reactions involved. Chemiluminescent and fluorescent substances are capable of yielding higher specific activities than commonly used radioisotopes when used as direct reagent labels in this context, and both thus provide a basis for the development of 'ultra-sensitive', non-competitive, immunoassay methodologies. Enzymes catalysing chemiluminescent reactions or yielding fluorescent reaction products can likewise be used as labels yielding high effective specific activities and hence enhanced assay sensitivities. A particular advantage of fluorescent labels (albeit one not necessarily confined to them) lies in the possibility they offer of revealing immunological reactions localized in 'microspots' distributed on an inert solid support. This opens the way to the development of an entirely new generation of 'ambient analyte' microspot immunoassays permitting the simultaneous measurement of tens or even hundreds of different analytes in the same small sample, using (for example) laser scanning techniques. Early experience suggests that microspot assays with sensitivities surpassing that of isotopically based methodologies can readily be developed.

Combination chemotherapy with mastectomy or radiotherapy for stage III breast carcinoma: a Cancer and Leukemia Group B study

One hundred thirteen evaluable patients with previously untreated stage III breast carcinoma were treated with three monthly cycles of cyclophosphamide (CYC), doxorubicin (DOX), 5-fluorouracil (5-FU), vincristine (VCR), and prednisone (PRED) (CAFVP). Subsequently, 91 (81%) were deemed operable. Patients were then randomized to receive surgery or radiotherapy (RT) to determine which of these modalities afforded better local tumor control. All patients also received 2 additional years of CAFVP in a further attempt to eradicate local disease and systemic micrometastases. Forty-one of the randomized patients have relapsed. Approximately half of the initial relapses in each arm were local. The overall duration of disease control was similar following either modality, with a median of 29.2 months for surgery patients and 24.4 months for RT patients. Similarly, there was no major difference in survival related to randomized treatment with an overall median of 39 months (median follow-up 37 months). Pre- or perimenopausal status and inflammatory disease were associated with shorter disease control and survival. Treatment was generally well tolerated and toxicity was acceptable. This study demonstrates that prolonged control of stage III breast carcinoma can be achieved with combined modality therapy in which cytotoxic chemotherapy precedes and follows treatment directly primarily at the breast tumor, using either surgery or RT. Nevertheless, new regimens must be designed if significant advances that may lead to the cure of this disease are to be achieved.