Immunoperoxidase techniques: the deleterious effect of sodium azide on the activity of peroxidase conjugates

Loss of anti-AT1R reactivity in ELISA post-adsorption - False reactivity or interference in the assay?

Autoantibodies to Angiotensin II type 1 receptor (AT1R) are associated with detrimental outcomes in organ transplants. However, reports showed that adsorption with latex beads reduced positive anti-AT1R antibodies, suggesting possible false reactivity. To investigate this conundrum, we studied 11 samples positive for AT1R antibodies with an ELISA kit before and after adsorption. Adsorption significantly reduced the measurable level of AT1R antibodies (28.3 ± 9.8 vs. 6.3 ± 3.0 U/ml, p < 0.001). AT1R antibodies were lower when post-adsorption serum was added back at 1:1 ratio to the neat serum compared to the diluent control (8.6 ± 4.2 vs. 18.1 ± 10.3 U/ml, p = 0.02). Sham adsorption with the buffer from Adsorb Out™ kit without beads also suppressed the detection of anti-AT1R antibodies (32.7 ± 9.1 vs. 8.1 ± 3.9 U/ml, p < 0.001). Thus, rather than actively removing nonspecific antibodies by the beads, the adsorption process introduces soluble factors that interfere with the detection of anti-AT1R antibodies with the ELISA kit.

A colorimetric alkaline phosphatase biosensor based on p-aminophenol-mediated growth of silver nanoparticles

Alkaline phosphatase (ALP) is an enzyme that catalyzes the dephosphorylation of proteins, nucleic acids, and biomolecules. It is a potential biomarker for diverse diseases such as breast cancer, osteopenia, and hepatobiliary. Herein, we developed a colorimetric sensor for the ALP assay based on its enzymatic activity to dephosphorylate the p-aminophenol phosphate (pAPP) into pAP. In a solution containing silver nanoparticles (AgNPs) and Ag⁺ ions prepared using a low concentration of NaBH₄, pAP mediates the growth of AgNPs by reducing the concentration of Ag⁺ ions to enhance the intensity of localized surface plasmon resonance as the pAPP cannot induce a reduction of the remaining Ag⁺ due to the masking of the hydroxyl with phosphate. The quantitative assay of the ALP was demonstrated via the colorimetric detection of the pAP-mediated growth of AgNPs in the presence of an ALP. The highly sensitive enzymatic growth of AgNPs provided a wider dynamic linear range of 0.5-225 U/L with a lower limit of detection of 0.24 U/L than that previously reported. The use of pAP resulted in excellent selectivity of the sensor for the ALP assay in human serum, yielding a high recovery rate and a high precision of 99.2 ± 1.5 % for the standard addition method.

A new methodology for optical biosensing with drop-casting fabrication of sensor chips and irradiation/detection of a single laser beam

The mechanism of glucose sensing based on the laser-induced morphology change.

Sodium azide induces necrotic cell death in rat squamous cell carcinoma SCC131

Sodium azide (NaN(3)) is widely used in industry and agriculture, and also in laboratories as a potent preservative. NaN(3) induces cell death when applied to cultured cells. However, whether the mode of cell death is apoptosis or necrosis remains a subject of debate. There have been no previous reports on NaN(3)-induced cell death in squamous cell carcinoma (SCC), and so we studied the mode of cell death induced by NaN(3) using the rat SCC cell line, SCC131. In this experiment, SCC131 cells died 48-72 h after NaN(3) treatment with concentrations greater than 5 mM. The NaN(3) treatment reduced the mitochondrial membrane potential and ATP content. Terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling and DNA ladder detection assay indicated that no DNA fragmentation occurred. In addition, phosphatidyl serine did not appear on the cell surface, according to the findings of dye-uptake bioassay and flow cytometric analysis of Annexin V labeling. Electron microscopic analysis revealed that the NaN(3)-treated cells showed mitochondrial swelling and rupture of the cell membrane. In conclusion, NaN(3) induces necrotic cell death in SCC131. This experimental model may be used in the study of necrotic cell death.

Acidosis causes endoplasmic reticulum stress and caspase-12-mediated astrocyte death

Endoplasmic reticulum (ER) stress leads to activation of caspase-12, which in turn can lead to activation of caspase-3 and cell death. Here we report that transient acidosis induces ER stress and caspase-12-mediated cell death in mouse astrocytes. After a 3-hour incubation at pH 6.0, astrocytes exhibited delayed cell death associated with nuclear condensation and fragmentation. Cell death was reduced by the protein synthesis inhibitor cycloheximide, further suggesting an active cell death program. Acidosis increased the expression of the ER chaperone protein GRP-78, indicative of ER stress. Acidosis also increased caspase-12 mRNA expression, caspase-12 protein expression, cleavage of caspase-12 to its active form, and activation of caspase-3. Each of these effects was suppressed in astrocytes pretreated with caspase-12 antisense phosphorodiamidate morpholino oligodeoxynucleotides (PMOs). Caspase-12 antisense PMOs also reduced the cell death induced by acidosis. Immunoprecipitation studies showed dissociation of both caspase-12 and Ire1-alpha from GRP-78, thereby suggesting a mechanism by which acidosis can initiate the ER stress response. To evaluate caspase-12 activation in vivo, rats were subjected to middle cerebral artery ischemia-reperfusion. Immunostaining of brain sections harvested 24 hours later showed increased caspase-12 expression and nuclear condensation in astrocytes of the periinfarct region exposed to acidosis during ischemia. These findings suggest that acidosis induces ER stress and caspase-12 activation, and that these changes may contribute to delayed cell death after ischemia.

Role of sodium azide in reducing nonspecific color development in enzyme immunoassays

Improved enzyme immunoassay (EIA) procedures achieved by incorporating sodium azide during predilution of serum samples in a solid-phase EIA for the detection of anti-Toxoplasma antibody in swine using a peroxidase conjugate and in all washes of a bovine brucellosis rapid card test EIA using alkaline phosphatase conjugate are reported. Without this modification, substantial background interference was encountered that showed direct correlation with the degree of hemolysis of the serum samples. Anti-Toxoplasma gondii antibody-negative samples, separated by subjective groupings based on degree of hemolysis, into "clear", "slight", and "gross/total" samples, had a mean +/- standard deviation of 0.150 +/- 0.072, 0.187 +/- 0.105, and 0.232 +/- 0.108, respectively. The incorporation of sodium azide during the initial step of serum dilution dramatically eliminated the background, giving a mean +/- standard deviation of 0.079 +/- 0.029, 0.076 +/- 0.022, and 0.081 +/- 0.029, respectively. The level of endogenous peroxidase activity, a possible factor for this nonspecific interference, was considerably elevated in some of the swine sera. The clear, slight, and gross/total categories had relative levels of 1%, 2%, and 51% peroxidase activity compared to the conjugate peroxidase activity of 100%. Whereas sodium azide could be used only in sample predilution in the swine toxoplasmosis peroxidase-conjugate test, in the bovine brucellosis alkaline phosphatase-conjugate card test it could be used in all wash cycles. Many brucellosis card test results were visually uninterpretable because of significant background color when the manufacturer's wash reagent was used. The substitution of a wash reagent containing sodium azide eliminated background color, giving a visually unambiguous test.

Immunocytochemical evidence for neuroendocrine differentiation in human breast carcinomas

Normal and neoplastic human breast tissues have been stained with antibodies recognizing neuroendrocrine differentiation. Fifteen out of 44 (34 per cent), breast carcinomas stained positively with monoclonal antibody LICRLON-E36, and 11 out of 44 (25 per cent) of these tumours stained with an antibody raised against neuron-specific enolase (NSE). Eight tumours stained positively with both antibodies. No correlation was observed between staining with these antibodies and the tumour histology, nor with the degree of cellular differentiation as indicated by staining with several cell surface directed monoclonal antibodies. Ultrastructural analysis of a series of breast tumours showed the presence of membrane-bound dense-core vesicles in almost all tumours, including E36 and NSE positive and negative tumours. The presence of these structures appears to be of little value in predicting neuroendocrine differentiation.

Human chorionic gonadotropin and human placental lactogen in extragonadal tumors. An immunoperoxidase study of ten non-germ cell neoplasms

The immunoperoxidase localization of the alpha and beta subunits of human chorionic gonadotropin (hCG) and of human placental lactogen (hPL) was studied in ten extragonadal nontrophoblastic tumors associated with raised serum levels of one or more of these placental proteins. Three of the tumors were bronchial carcinomas, one was a gastric carcinoma, two were malignant carcinoids (one bronchial and one gastric), two were pancreatic islet cell carcinomas, and two were metastatic carcinomas with an unknown primary site. The maximum alpha subunit serum level was 33,000 ng/ml (gastric carcinoid), the maximum hCG/hCG-beta level was 705,000 ng/ml, and the maximum hPL level was 50 ng/ml (both in the gastric carcinoma). An indirect immunoperoxidase technique and rabbit polyclonal affinity-purified antibodies and peroxidase conjugates were used on formalin-fixed, paraffin-embedded sections. Five blocks (eight cases) or six blocks (two cases) from various sites were obtained from each patient at surgery and/or autopsy. Positive stains for hCG/hCG-beta were seen in six of seven tumors (25/37 blocks) with raised levels, for the alpha subunit in nine of nine tumors (30/47 blocks), and for hPL in two of five tumors (4/26 blocks). Only a relatively minor number of the cells were positive, and within the same case, there was considerable site-to-site variation in the number of positive cells. Large bizarre cells contained hCG/hCG-beta as well as the alpha subunit, if it was demonstrated in the same tumor as the beta subunit. Otherwise, the alpha subunit was found in small unremarkable cells. Giant cells that were smaller than those positive for hCG/hCG-beta contained in hPL. In some serial sections, hCG-alpha, hCG/hCG-beta, and hPL were segregated in different cell populations, supporting the concepts of their separate genetic control.

A new monoclonal antibody to epithelial membrane antigen (EMA)-E29. A comparison of its immunocytochemical reactivity with polyclonal anti-EMA antibodies and with another monoclonal antibody, HMFG-2

Two polyclonal rabbit antibodies to epithelial membrane antigen (EMA), two mouse monoclonal antibodies (E29 and HMFG-2), and a "cocktail" of these two monoclonals have been compared using an indirect immunoperoxidase technique. Sections from 25 tissues (17 malignant and 8 benign), were examined. The distribution of staining with each of these reagents was similar, but the polyclonal antibodies produced stronger staining in colorectal carcinomas and lactating breast, whereas staining with the monoclonal antibodies was stronger in non-neoplastic pleural mesothelium and in pulmonary alveolar cells. When the two monoclonals were mixed there was no increase in staining intensity. E29 gave a "cleaner" result than HMFG-2, with better discrimination between cells and stroma, and is highly suitable for routine diagnostic histopathology.

Intercellular canaliculi in eccrine sweat glands: an immunoperoxidase study

Using an indirect immunoperoxidase technique, both epithelial membrane antigen and carcinoembryonic antigen were identified within the ducts and secretory coils of the eccrine sweat gland. Antibodies to epithelial membrane antigen stained the intercellular canaliculi of the secretory coils, as did those antisera to CEA which showed activity against normal cross-reacting antigen (CEX, NCA). Those without such activity showed minimal or no staining of intercellular canaliculi. There is a difference in antigenic expression between the acinar cells and their intercellular canaliculi, and the cells of eccrine ducts.

Epithelial markers in primary skin cancer: an immunoperoxidase study of the distribution of epithelial membrane antigen (EMA) and carcinoembryonic antigen (CEA) in 65 primary skin carcinomas

Sixty-five primary malignant skin tumours have been stained for carcinoembryonic antigen (CEA) and epithelial membrane antigen (EMA) using rabbit polyclonal affinity-purified antibodies and an indirect immunoperoxidase technique. The tumours consisted of 15 invasive squamous carcinomas, 23 basal cell carcinomas, 16 malignant eccrine poromas (porocarcinomas), and 11 sebaceous carcinomas. The basal cell carcinomas were negative for CEA and EMA except where there was keratotic or sebaceous differentiation. All the sebaceous and squamous carcinomas and 15/16 porocarcinomas contained EMA. 12/15 squamous carcinomas were positive for CEA. The malignant poromas were negative for CEA except on the ulcerated surface of two. In tumours classified as sebaceous carcinomas there was positive staining for CEA in some cells, cyst contents and/or keratotic foci. These findings have implications for the use of immunoperoxidase localization of epithelial markers in the differential diagnosis of primary and metastatic skin cancer.