WO1991016631A1

WO1991016631A1 - Simplified solid-phase immunobead assay for detection of ciguatoxin and related polyethers

Info

Publication number: WO1991016631A1
Application number: PCT/US1991/002703
Authority: WO
Inventors: Yoshitsugi Hokama
Original assignee: Hawaii Chemtect International
Priority date: 1990-04-20
Filing date: 1991-04-19
Publication date: 1991-10-31
Also published as: EP0528895A4; AU7789191A; CA2080925A1; AU647125B2; JPH05507554A; BR9106366A; EP0528895A1

Abstract

The development of a highly-simplified solid-phase colored latex immunobead assay for the detection of ciguatoxin and related polyethers. This procedure was compared with a previously-reported stick enzyme immunoassay. Chi square analysis of two separate experiments 153 and 283 fish of various species gave X2 values of p < 0.001 and < 0.005, respectively. Agreement between the two procedures with 26 fish implicated in ciguatera poisoning was 100 %. A preliminary assessment in the field showed encouraging results. The procedure appears to be simple and applicable to field use. Furthermore, this procedure should be applicable for other antibody-antigen detections, especially low dalton determinants.

Description

SIMPLIFIED SOLID-PHASE IMMUNOBEAD ASSAY FOR DETECTION OF CIGUATOXIN AND RELATED POLYETHERS

Field of the Invention

The invention relates to the use of antibodies for the detection of ciguatoxin in fish.

Background of the Invention

Immunological analysis of ciguatoxin (CTS) and related polyethers by radioimmunoassay (RIA) using I¹²⁵-labelled sheep anti-CTX prepared by immunization of sheep with purified CTX coupled to human serum albumin (HSA) was initiated in 1977. (See Hokama et al., "A Radioimmunoassay for Detection of Ciguatoxin," Toxicon. 15, 317-215 (1977), incorporated herein by this reference). This RIA was used to screen several thousand Seriola dumerili (kahala, amberjack) in a two-year study with the United Fishing Agency in the State of Hawaii. No false hegatives were reported, with 15% of the total fishes examined rejected as potentially toxic. Subsequently, an enzyme immunoassay procedure was developed using the same sheep-anti-CTX labelled with horseradish peroxidase for testing fish tissues. (See Hokama et al., "A Rapid Enzyme Immunoassay (EIA) for the Detection of Ciguatoxin in Contaminated Fish Tissues," Toxicon. 21, 817-824 (1983) and "An Enzyme Immunoassay for the Detection of Ciguatoxin and Competitive Inhibition of Related Natural Polyether Toxins," Seafood Toxins, ACS Symposium Series 262, Washington, DC 307-320 (1984); Kimura et al., "Comparison of Three Different Assays for the Assess- ment of Ciguatoxin in Fish Tissue: Radioimmunoassay, Mouse Bioassay and in vitro Guinea Pig Atrium Assay," Toxicon. 20, 907-912 (1982), and U.S. Patent No. 4,816,392 to Hokama, all incorporated herein by this reference.) This procedure permitted the analysis of cross-reactivity of purified ciguatoxin with purified okadiac acid (OA), brevetoxin (PdTx), maitotoxin (MTX), and monensin. A radioimmunoassay procedure for PdTx also demonstrated the cross-reactivity of CTX and PdTx. (See Baden et al., "Cross-reactivity in Immunoassays Against Toxins Isolated from Ptychodiscus brecis, "Toxic Dinoflagellates, Elsevier Applied Science Publishers, NY, 363-368 (1985), incorporated herein by this reference.)

Development oa a simplified stick enzyme immuno- assay (S-EIA) was initially reported by Y. Hokama (see "A Rapid Simplified Enzyme Immunoassay Stick Test for the Detection of Ciguatoxin and Related Polyethers from Fish Tissues," Toxicon, 23, 939-946 (1985), incorporated herein by this reference), using the sheep-anti-CTX. An extensive study reported recently using the S-EIA procedure gave no false negatives in the test system using monoclonal antibody to CTX, MAb-CTX. This procedure proved useful inn the laboratory, but was found to be impractical in the field and onboard ships.

I have now developed a highly simplified method using colored latex beads to which the MAb-CTX is bound. Fish-tissue toxin bound to liquid-coated stick colors when immersed into suspensions of latex- MAb-CTX reagent. The present invention presents the initial development of the procedure and the examination of various toxic and non-toxic fishes in comparison with the stick enzyme immunoassay.

Detailed Description

Source of fish; Fish samples were obtained from various sources. The fishes implicated in ciguatera poisoning were obtained from outbreaks in the State of Hawaii, Philippines, CAlifornia, and Texas. The clinical symptoms of the patients invoked were characteristic of what is categorized as ciguatera poisoning. (See Bagnis et al., "Clinical Features on 12,890 Cases of Ciguatera Fish Poisoning in French Polynesia," Progress in Venom and Toxin Research, P. Gopalakrishnakone, C.K. Tan, eds., Kent Ridge, Singapore, 272-384 (1987); Hokama et al., "Ciguatera Poisoning: Clinical and Immunological Aspects," J. Toxicol: Toxin Review, 5, 25-53 (1986); and Kodama et al., "Ciguatera Poisoning: Variation in Symptomology," Toxicon, 27, 593-595 (1989), all incorporated herein by this reference.) Identification of the fishes were determined according to Tinker, S.P., "A Handbook of the Marine Fishes of Hawaii and the Central Pacific Ocean, Honolulu" Fishes of Hawaii, Hawaii Service, Inc., 1978, incorporated herein by this reference.

Monoclonal antibodies (MAbs): The method of Schrier et al., Hybridoma Techniques, Cold Harbor Laboratory, Cold Spring, NY, 1980, incorporated herein by this reference, based on the original report of Kohler et al., "Continuous Cultures of Fused Cells Secreting Antibody of Predefined Specificity," Nature, 156, 494-497 (1975), incorporated herein by this reference, was used. Hybridoma preparation for Mab-CTX was carried out using purified CTX according to methods of Hokama et al., "Assessment of a Rapid Enzyme Immunoassay Stick Test for the Detection of Ciguatoxin and Related Polyether Toxins in Fish Tissues," Biol. Bull, 172, 144-153 (1987; "Monoclonal Antibody (MAb) in Detection of Ciguatoxin (CTX) and Related Polyethers by the Stick Enzyme Immunoassay (S-EIA) in Fish Tissues Associated with Ciguatera Poisoning," Mycotoxins and Phycotoxins '88, The Netherlands, Elsevier Applied Publishers BV Amsterdam, 303-310 (1989); and "Monoclonal Antibodies in the Detection of Ciguatoxin and Other Toxic Polyethers in Fish Tissues by Rapid Poke Stick Test," Proc. 5th Int. Coral Reef Congress, 4,, 449-474 (1985), all incorporated herein by this reference.

Stick Enzyme Immunoassay (S-EIA): The method for assessment of the fish samples run in conjunction with the new procedure was the S-EIA previously reported.

Solid-phase Immunobead Assay: The solid phase consisted of a paddle made of a bamboo stick coated with organic base solvent correction fluid supplied by Pentel of America, Ltd., Torrance CA 905034. Immunobead consisted of blue colored latex, 0.314 μ in diameter, supplied by Seradyn, Inc., Particle Technology Division Ind., IN.

Optimization of SPI Assay: Various parameters were examined to eliminate non-specific binding of colored latex to a coated bamboo paddle. Various concentrations of MAb-CTX with a constant suspension of colored latex were attempted to give the best specificity and sensitivity. Experiments were performed with colored latex alone in suspension (1% wt/wt in PBS buffer). Various MAb-CTX concentrations ranging from 0.05, 0.075, 0.10, 0.13, 0.20, 0.45, 0.50, to 1.0 mg/ml were added to the 1% colored latex. The liquid-paper-coated sticks were examined as-is or were coated with a 1% wt/wt solution of Human Serum Albumin (HSA), then examined as non-Me- OH-fixed or MeOH-fixed with the MAb-CTX-colored late. MAb-CTX was coated onto liquid-paper sticks and then examined with MAb-CTX-color latex.

The optimum condition obtained from these experiments was used for examining toxic fish from the Department of Health (State of Hawaii) and toxicfish samples from elsewhere which had been implicated in ciguatera poisoning. Reef fishes from various sources were also examined. For the development of the optimum conditions, known toxic fishes implicated in ciguatera poisoning were employed (for the positives). Negative controls were protein-coated sticks fixed with MeOH or unfixed blank sticks. The method according to Singer et al., "The Latex Fixation Test: One Application to the Serological Diagnosis of the Rheumatoid Arthritis," Amer. J. Med.. 888-892, Dec. (1956), and incorporated herein by this reference,was used for the preparation of the immunobeads. The optimum concentration of MAb-CTX protein was 0.45 mg/ml of the 1% bead suspension. This is designated as the immunobead. The immunobead was mixed thoroughly before use.

Solid-phase Immunoassay (SPIA): An inch-deep incision is made into the filet portion of the fish near the head region, as shown below. The coated paddle end is inserted into the incision and pushed up and down to touch the fish tissue. The paddle is removed, air-dried, and fixed quickly (1-3 seconds) with absolute methanol. After air-drying, the coated methanol-fixed end of the paddle is immersed into 0.5 ml of the immunobead color suspension. After 2, 5, and 10 minutes, the stick is examined and washed in saline. Any fish giving the stick a distinct coloration after 5 minutes is considered positive. If negative, immersion is continued up to 10 minutes. After 10 minutes, no color, very diffuse color, or no distinct coloration of the paddle is read as negative. In this case, the same procedure is repeated with another stick from another area of the same fish. If the stick is negative after 10 minutes, the fish is considered safe to eat. A borderline reading (±, ±) in two sticks after their 10-minute readings should not be eaten. Similarly, any single stick reacting in 5 minutes or less, read as + +, should not be eaten. Examples are given in the results. Control blank sticks (untreated coated stick, negative) should be run in parallel with the fish sample sticks. Similarly, a known positive (implicated in toxicity) should be run with the unknowns. The concept and methodology are illustrated below.

h

Comparison of S-EIA with SPIA

a. Department of Health-implicated fish in ciguatera poisoning:

Table 1 shows the species, source and the test values given by the S-EIA and SPIA procedures for fish implicated in ciguatera poisoning. All samples were obtained from the Department of Health, State of Hawaii , except for two specimens (Antigua and California) . The S-EIA values were all in the rejection category and in complete agreement with the SPIA results . The majority of the toxic fishes were from the Big Island of Hawaii and associated with the Caranx sp.

Total of 26 implicated fish all shew rejection (± or +) in both S-EIA and SPIA. b. Results of Routine Runs Examined in Comparison with the Stick-Enzyme Immunoassay (S-EIA):

An initial study of 153 fish, mostly jacks

(ulua) and amberjacks (kahala) was compared by the S-

EIA and the newly-established SPIA. The chi square

(X²) for the 153 fish samples was p < 0.001, suggesting a good association between the two tests. Eighty percent of the 153 samples were in agreement between the two tests, and 20% were in disagreement. The

SPIA appeared to be more sensitive than the S-EIA.

That is, most of the samples (12%) were negative with the S-EIA and positive with the SPIA, while 8% represented the inverse (S-EIA+/SPIA-).

A second comparison of the S-EIA and SPIA on 283 fishes gave essentially the same X², which was equivalent to p < 0.005 for all fish. Eighty-three percent of the 283 samples were in agreement between the two tests, while 17% were in disagreement. Again, the SPIA appears to have a greater sensitivity than S- EIA, with many of the samples (15%) negative in the S-EIA, and positive with the SPIA, while 2% represented the inverse (S-EIA+/SPIA-). The X² value of p < 0.005 suggests a significant association between the two tests.

Analysis of some individual species from Study 2 is shown in Table 2 in the comparison of the S-EIA and SPIA tests. Fish giving good agreements between tests are generally carnivorous (ulua, kahala, Lutianus sp., and wahanui). The greatest disagreement is seen with the halalu (mackerel). In most of the disagreements, the SPIA appears top be the more sensitive (-S-EIA/+SPIA).

Table 3 summarizes the comparison of S-EIA and SPIA of the two studies, totalling 436 fishes .

There is an overall 80% agreement, with 20% disagreement (12% = -S-EIA/+SPIA, and 8%

+S-EIA/-SSPIA) . The 20% samples of fish in categories -/+ and +/- will be further examined following extraction and then chromatographed by silica gel , with final assessment of the fractions by guinea pig and mouse bioassay.

* Twelve percent of the disagreement is in the S-EIA negative and SPIA positive group, while the remainder is in the +/- group.

Table 4 shows the preliminary data obtained by a voluntary sportsfisherman assessing the solid- phase immunoassay presented earlier. A study by Mr. Dale Takata of the Honolulu City Water and Waste management is summarized. Mr. Takata volunteered to use the new SPIA test. Of the 55 fishes of various species caught, 37 negative and borderline fishes were eaten, and 18 were rejected as being positive. Consumption of two fishes (papio and kole) from the positive group caused ciguatera poisoning in two individuals who were warned of the fish's toxicity based on the SPIA test.

* 2 of the 18 positive category fish were consumed, and both individuals showed ciguatera poisoning symptoms in less than 2 hours after eating. The fishes involved were C. strigosus and Caranx sp. (Papio).

An encouraging preliminary study strongly suggests the applicability of the SPIA for field use. This would be a significant advancement for reef sportsfishermen, long-distance yachters, and perhaps in-shore commercial fishermen. Comparative assessment of the S-EIA and SPIA shows very good association, with the Department of Health-implicated fish showing a 100% agreement. However, comparison of a variety of fish in two separate studies demonstrated an agreement of 80% (with moderate) association between the two tests. This is in part due to major difference in some species. For example, a great discrepancy is shown for the mackerel (halalu). Fortunately, this species has not caused ciguatera poisoning in

Hawaii, and therefore, the differences may be due to non-specific binding on the part of non-specific binding on the part of the SPIA test. (In general, this test appears to be more sensitive than the S- EIA.) Nevertheless, in the two major species implicated in ciguatera poisoning, Caranx sp. and Caranx sp. (Papio). Seriola sp., the association appears to be very good between the two tests.

(See Table 2.) Similarly, the association of the two tests with other carnivorous species appears to be good. The S-EIA procedure has been thoroughly tested the past three years.

Further examination following extraction of the fish samples showing discrepancies such as S- EIA-/SPIA+ or S-EIA+/SPIA- will be attempted by the guinea pig atria (see Miyahara et al., "Pharmacological Characterization of the Toxins in Cugateric Fishes," Mycotoxins and Phycotoxins '88, Elsevier Science Publishers B V Amsterdam, The Netherlands, 399-406 (1989), incorporated herein by this reference) and mouse assay. The single volunteer study gave promising results, and several more individuals and fishing clubs are being mobilized for an extensive evaluation. Refinement of the SPIA is still in progress. It is hoped to achieve a goal for wide use of the SPIA where ciguatera poisoning is endemic.

Furthermore, the SPIA method described should be applicable to other antigen-antibody systems, especially when the antigen is an epitope or hapten of low molecular weight.

Claims

WHAT IS CLAIMED IS:

1. An improved method for detection of ciguatoxin and structurally-related polyether marine toxins in fish tissue, the improvement comprising exposing the toxin to a monoclonal antibody bound to a colored, latex immunobead.