Process for estimating stable type glycated hemoglobin and the apparatus thereof

Abstract: The present invention relates to a process for rapidly estimating stable type glycated hemoglobin and an apparatus thereof to be used in clinical tests. The process comprises treating by heating a sample which is diluted with a hemolysis agent containing a removal re­ agent for unstable type glycated hemoglobin, to achieve removal of the unstable type glycated hemo­ globin. The apparatus comprises a heating device (8) for samples which functions before the sample is in­ jected into a separation column (14).

Description: The present invention relates to a process for rapidly estimating stable type glycated hemoglobin and an apparatus thereof to be used in clinical tests. Glycated hemoglobin is produced when a saccharide in blood, mostly glucose, enters an erythrocyte in an amount proportional to its concentration and combines with the hemoglobin. Concentration of the glycated hemoglobin is supposed to reflect the mean concentration of glucose in the blood through a few past months. Since the amount of glycated hemoglobin is less susceptible to physiological factors than those of glucose in blood and urine, it is a most suitable index to be estimated in the diagnosis of diabetes and the follow-up observation of diabetic patients. The main component of the glycated hemoglobin is a hemoglobin of which glucose is combined to the N-terminal of the β chain and the formation is performed in two steps of reactions involving a non-enzymatic reaction. Namely, in the first step reaction the glycated hemoglobin formed partly returns to the isolated form by a reversible reaction and forms so-called unstable type glycated hemoglobin, while the second step reaction is an irreversible one in which stable type glycated hemoglobin is formed. A more reliable index of diabetes is obtained of course by measuring the amount of the stable type glycated hemoglobin. The glycated hemoglobin can be separated from hemoglobin utilizing the differences particularly in their electrical properties. Methods of the separation include the electrophoresis and the ion exchange chromatography. An apparatus of high performance liquid chromatography for this particular purpose is alos commercially available. Glycated hemoglobin can be separated from ordinary hemoglobin in these methods, but glycated hemoglobins in their stable and unstable types cannot be distinguished from each other. Therefore, estimation of the stable type glycated hemoglobin requires a prior treatment in which to remove unstable type glycated hemoglobin. Prior methods concerned include one process in which erythrocytes are incubated in a physiological saline solution or in a buffer solution containing semicarbazide and aniline and another process in which whole blood is hemolyzed in a hemolysis solution containing boric acid before incubation. For example, erythrocytes need to be washed several times repeatedly with the physiological saline solution prior to the incubation and also the incubation at 37°C has to continue for more than 4 hours (P.A.Svensen et al., Diabetologia, 19 , 130(1980) ). On the other hand, the semicarbazide - aniline method involves unstable reagent solutions which therefore need to be freshly prepared immediately before use and the incubation time should continue for 30 min to an hour at 37°C (D.M.Nathan et al., Clin.Chem., 28 , 512(1982) ). On the other hand, commercial reagents with which to remove unstable type glycated hemoglobin, though no problem is involved with respect to stability, require an incubation time of about 30 min at 37°C as in the preceding example. Any of the methods contain either troublesome pretreatment or problems in the rapid treatment of samples. Furthermore, from "High Performance Liquid Chromatography in Biochemistry", VCH publishers, pp. 97 - 99, the combination of a separation column with a preheating device is known. Besides, in "Chemical Abstracts", Vol. 101 (1984), 20145 h, a method for eliminating labile glucated hemoglobin has been published. Thereby, most of the labile glucated hemoglobin is removed by incubation of hemolyzates with pH-7 borate buffer for 30 minutes at room temperature. The object of the present invention is to provide a process being simpler and requiring a shorter time than prior ones for estimating stable type glycated hemoglobin and an apparatus thereof. More particularly, the present invention intends to provide a process for estimating stable type of glycated hemoglobin in which a sample solution, diluted beforehand with a hemolysis solution containing a reagent to remove unstable type glycated hemoglobin (hereinafter designated as hemolysis solution with a removing reagent), is treated by heating to remove unstable type glycated hemoglobin before it is introduced into a separation column of a high performance liquid chromatography and an apparatus with which to estimate stable type glycated hemoglobin by the high performance liquid chromatography provided with a heating compartment for heating the sample solution. The reagents to be used in this invention for removing unstable type glycated hemoglobin are boric acid, potassium phthalate and other products generally obtained commercially for this end including surfactants and antiseptics. They may be used without any further purification or pretreatment. Hemolysis agents can also be obtained from common commercial products. Addition of boric acid or potassium phthalateis allowed as desired. Stable type glycated hemoglobin can be isolated by use of ion exchange chromatography. Chromatographic separation columns are packed with those cation or anion exchange resins which have been developed for the purpose, but a commercial product may also serve. A sample solution has to be heated before it is brought to the separation column, either on line or off line. The on-line heating can be carried out in a variety of situations; for example, heating a table as a whole of an auto-sampler on which sample bottles are arranged, heating a sample vessel by an inserted heating element and heating a sucked portion of a sample solution. The last mode of heating is preferred from the heating efficiency, stability of the sample, simpleness of the apparatus and easiness in following the process. Any mode of heating may serve, so long as the temperature of a sample solution is quickly elevated. The temperature should be preferably in the range between 45°C and 70°C. The higher the temperature is, the sooner the unstable type glycated hemoglobin is removed. But at a temperature higher than 70°C denaturation or decomposition of hemoglobin occurs in the sample and makes the separation incomplete. On the other hand, the removal of unstable type glycated hemoglobin takes a longer time as a temperature below 45°C, not exhibiting the efficacy of this invention. After the unstable type glycated hemoglobin being removed by the heating treatment, stable type glycated hemoglobin in the sample is estimated from the absorbance values measured at 415 and 690 nm for the components obtained on the chromatograph. Brief Explanation of the Drawings: Fig. 1 is a schematic diagram of an embodiment of the present invention, showing a measuring apparatus provided with a heating device. Fig. 2 graphically shows the relation between the removal of unstable type glycated hemoglobin and the heating time at different temperatures of heating. Fig. 3 shows the correlation existing between the processes of this invention and a prior art which comprises treatment with a physiological saline solution. An example of the apparatus of this invention is illustrated in Fig. 1. The apparatus is a modification of a high performance liquid chromatograph. There is installed a heating device between the sample suction-injection device of the autosampler and the separation colum. The apparatus of the present invention consists of an auto-sampler 5 with a sample table 6 on which are placed samples diluted with a hemolysis agent containing a removing reagent, a suction nozzle 7 through which a sample solution is sucked, a heat block 8 for heating the sample, a sample loop 11 for measuring samples and a sample delivery device 12 with which sample and eluent solutions 1 are injected to the separation column 14 enclosed in a column oven 15 and a detector 16; and further a number of peripheral devices that are usually employed in ordinary high performance liquid chromatographs such as a degasser 2 which serves to deliver an eluent 1 to the sample delivery device 12, valves 2 and 3, a pressure pump 4, prefilter 13, a data processor and a recorder 17. The heat block 8 is provided with a heater 9 adequately selected from a sandwich type plane heater, a plane heater with grooves and a rod heater. Heater materials are slected from those heat-conductive metals such as aluminum and copper without any particular limitation. In addition, a tmperature sensor 10 and a controller 18 are provided for contorlling the temperature. Samples are first set on the sample table 6, and then sucked by the sample suction nozzle 7 in such an amount that the sample delivery tube 20 is filled up to the heat block 8. The samples are treated in the heat block 8 and then a part of the treated sample is introduced in the sample loop 11 for measurement, transferred through the sample delivery device 12 and injected into a separation column 14. The series of operations can be managed by the controller 18. Subsequently the components separated in the separation column 14 are detected by the detector 16 and determined quantitatively. At last the measured sample part is supplied to a waste liquid tank 19. The sample delivery tube 20 extending from the sample suction nozzle 7 to the sample delivery device 12 is preferably made of a chemically resistant and thermally conductive material such as Teflon and stainless steel. When a Teflon tube is used, one having a small diameter and a thin wall may be desirable for the sake of high thermal effect, but practically an inner diameter 0.2 mm to 2.0 mm should be selected to maintain a small flow resistance and a sufficient mechanical strength on suction and also to reduce difficulties on manufacture. As can be evidently observed in the above description, performances of the present invention are reckoned as followings: (1) unstable type glycated hemoglobin can be removed in a simple treatment and in a short period of time, and (2) only a very simple heating device is needed to estimate stable type glycated hemoglobin as an index of diabetes. The following examples describe the apparatus and process of the present invention, but the invention is not limited to them. Example 1: (A) Two blood samples were employed. One was a fresh blood sample to which sodium salt of ethylene-diaminetetraacetic acid was added as anti-coagulation agent and the other was a fresh blood sample which glucose was added to (in an amount of 10 mg per ml of blood) and incubated for 30 min at 37°C, the latter being intended to produce unstable type glycated hemoglobin in vitro. The blood samples were diluted to 200 times as large volume with a hemolysis solution of a 0.1% polyoxyether-boric acid buffer solution where boric acid is a removal reagent, and the diluted blood samples were placed on the sample table 6 as shown in Fig. 1. TSKgel Glyco (Toyo Soda Manufacturing Co.,Ltd.) was placed in a separation column (4.0 mm id x 150 mm). A temperature of 23°C was selected for the separation. Separation by elution was achieved with an HLC-723GHb eluent (Nippon Chemifar Co.,Ltd.) with a speed of 1.6 ml/min in a stepwise gradient method at 1.1, 2.4 and 3.6 min. At the first step in the heating treatment, a 150 µℓ portion of a sample was sucked for each run and the sample delivery tube was a Teflon tube having an inner diameter of 0.6 mm and an outer diameter of 1,6 mm (1/16 inch). At the heating part, each about 20 cm long Teflon sample delivery tube was wound around an aluminum bar heater 9 (of a 1.6 cm outer diameter and 6 cm long) and the whole was covered with an aluminum block 8. After the heat treatment, a 20 µℓ portion of the resulting solution was sampled for the separation. Absorbance values at 415 and 690 nm (as background) were measured with the detector 16, to obtain the content of stable type glycated hemoglobin. The efficiency with which to remove unstable type glycated hemoglobin was estimated with the temperature and time of the heating treatment varied and the result obtained is summarized in Fig. 2. Values obtained when glucose was added and not added are indicated by solid and blank circles, respectively. Even for the samples in which unstable type glycated hemoglobin was formed in vitro in the presence of glucose, the unstable type glycated hemoglobin was removed in 8 min at 50°C and in 1 min at 65°C. With the fresh blood samples to which glucose was not added, a 2 min heating time sufficed even at 50°C in contrast to more than 30 min at 37°C in prior arts. Thus, it proved the treatment proceeded in a particularly shorter time. (B) Estimated values of the present invention were compared with those of previous processes which employ treatment with a physiological saline solution. Samples used were freshly taken blood samples from normal persons and diabetic patients and an anti-coagulation reagent was added to all samples. Conditions of measurement were the same as in (A) except the temperature of the heat block and the period of heating time being 65°C and 1.5 min, respectively. In a pretreatment of the physiological saline solution method, about 10 times as much physiological saline solution as the whole blood was added, agitated, centrifuged, and a supernatant liquid was discarded. After the procedure being repeated twice, about 10 times as much physiological saline solution was added and the whole mixture was incubated at 37°C for 4 hours. Then centrifugation followed and such an amount of excessive supernatant liquid was discarded so as to leave the same volume of supernatant liquid as that of the blood corpuscles. The whole blood was diluted up to 200 times as large volume with a hemolysis agent for HLC-723GHb (consisting of 0.1% of triton X-100, 0.1% of sodium salt of ethylenediaminetetraacetic acid and 0.1% of sodium azide) and the mixture was submitted to measurement. The procedure was carried out with an apparatus which was not provided with a heat block, but other conditions were the same as those with a heat block. Result of estimations with 63 samples is shown in Fig. 3. A very high value of correlation was obtained between the processes of this invention and the physiological saline solution method with a correlation factor 0.9940. A correlation formula was derived as follows: Y = 1.031 X - 0.308 where X and Y were values obtained by present invention and the physiological saline solution method, respectively. This result demonstrated that, in this invention, unstable type glycated hemoglobin was completely removed as in the previous process.

Claims: Method for estimating stable type glycated hemoglobin in a blood sample in which the unstable glycated hemoglobin is removed from the hemolysis agent by incubating said hemolysis agent with a removal reagent before chromatography, characterized in that the blood sample diluted with the hemolysis agent containing the removal agent is heated to a temperature in a range from 45°C to 70°C. Apparatus for estimating stable-type glycated hemoglobin, comprising an eluent solution flow path formed by connecting an eluent solution pump (4), a sample delivery device (12), a separation column (14) and a detector (16) arranged in the order as recited, and a sample solution flow path formed by connecting a sample suction device (7), a heating device (8) and the sample delivery device (12). Apparatus according to claim 2, wherein the heating device is controlled in a temperature range of from 45°C to 70°C.

Inventors: MATSUMOTO KATSUYA, OKADA HARUO, TAKAHASHI HIROAKI, UMINO MASUO, MATSUMOTO, KATSUYA, OKADA, HARUO, TAKAHASHI, HIROAKI, UMINO, MASUO
Applicants: TOSOH CORP, TOSOH CORPORATION
Application year: 1987
Main classification: G01N33
IPC codes: G01N33, G01N30