CN111197073A

CN111197073A - Method for extracting DNA sample from excrement and methylation detection method of colorectal cancer related gene

Info

Publication number: CN111197073A
Application number: CN201911314364.6A
Authority: CN
Inventors: 张良禄; 吴志诚; 董兰兰; 甘甜; 陈玉珠; 李婷婷
Original assignee: Wuhan Aimisen Life Technology Co ltd
Current assignee: Wuhan Aimisen Life Technology Co ltd
Priority date: 2019-12-19
Filing date: 2019-12-19
Publication date: 2020-05-26
Also published as: CN112553302A; CN112553302B

Abstract

The invention discloses a method for extracting a DNA sample from excrement and a methylation detection method of colorectal cancer related genes, and relates to the technical field of gene detection. The method comprises the following steps: centrifuging the fecal diluent sample to obtain a first supernatant; the stool in the stool dilution is taken from a subject in need of colorectal cancer or pre-colorectal cancer lesion detection; during centrifugation, the volume of the fecal diluent sample in a single centrifuge tube is no higher than 2 mL. The extraction method is simple to operate, the using amount of the excrement is small, the excrement can be extracted without using large-scale centrifugal equipment, the extraction effect is good, and the extracted DNA sample has good sensitivity and specificity when being used for subsequent methylation detection.

Description

Method for extracting DNA sample from excrement and methylation detection method of colorectal cancer related gene

Technical Field

The invention relates to the technical field of gene detection, in particular to a method for extracting a DNA sample from excrement and a methylation detection method of colorectal cancer related genes.

Background

Colorectal cancer is the most common malignant tumor in China and even in the world, the number of newly increased diseases in China is about 40 thousands every year, and the incidence of the diseases is the third place of all malignant tumors. The 5-year survival rate of early colorectal cancer patients can reach more than 90 percent after operation, the 5-year survival rate of middle and late patients is only about 10 percent, and most colorectal tumors grow slowly, keep silent or have no symptoms until the colorectal tumors reach a certain size or development stage. Therefore, colorectal cancer is an ideal target that can intervene by screening.

Enteroscopy is the gold standard for colorectal cancer detection and diagnosis, but has low popularity among the general population because it requires a complex bowel preparation procedure, is somewhat invasive and requires specialized technicians. Noninvasive detection methods such as Fecal Occult Blood Test (FOBT) and Fecal Immunochemical Test (FIT) are not sensitive, especially in detecting stage I colorectal cancer and advanced adenomas. Methylation is an epigenetic modification, and abnormal changes can cause changes in DNA conformation, DNA-protein interaction pattern and the like, thereby controlling gene expression. DNA methylation plays an important role in gene expression regulation, cell proliferation and differentiation, development, gene imprinting and the like, and has close relation with the occurrence and development of tumors. Stool contains a certain amount of exfoliated cells from the intestine, and thus the health of the intestine can be subsequently assessed by detecting certain DNA targets in these exfoliated cells. More and more researches indicate that the fecal DNA methylation detection shows great advantages in noninvasive colorectal cancer screening, and the sensitivity and specificity of the detection are superior to those of blood methylation detection and fecal occult blood detection. In 2014, the FDA approved the first colon and rectum cancer fecal DNA detection kit, Cologuard, which can simultaneously detect heme, KRAS gene mutation and methylation of two other genes in feces, and the detection sensitivity and specificity for colon and rectum cancer are 92% and 87%, respectively.

Good fecal DNA detection depends on upstream fecal treatment techniques including fecal preservation and fecal DNA extraction, among others. The existing fecal DNA extraction technology is various in types, and can be divided into a method for extracting all DNA and a method for extracting specific DNA by targeted enrichment according to the range of extracting genome; according to the kind of extraction reagent, there are mechanical method, magnetic bead method, chemical method, and the like. It should be noted that different extraction methods are suitable for different application scenarios, and the generated detection effect is different.

The fecal matrix is very complex in composition, contains various bacterial genome DNA, plant-derived DNA and animal-derived DNA, has relatively low content of exfoliated cells in intestinal tracts or other digestive tract positions, and contains PCR inhibitors such as polysaccharide, bile salt, humus, cholic acid and the like, and at the moment, if a method for extracting all genomes from feces (such as the prior art CN201611113440) is adopted, the detection of the DNA of the tumor exfoliated cells is very unfavorable for the huge gene background and the PCR inhibitors; in the prior art, CN201710332851 enriches a human genome by using a probe, although the human genome is specifically distinguished from other genomes to a certain extent, the enrichment of specific human genes is still not realized, and DNA from some tumor sources is seriously fragmented, and the enrichment of specific tumor genes cannot be realized through the whole enrichment of the human genome; in addition, the prior art also has the problems of using a large amount of feces, using an organic solvent and the like, such as CN201811636712, although using a large amount of feces may increase the extraction amount of the target gene, this inevitably increases the complexity and cost of the steps: specific reagent consumables (e.g., 5mL, 15mL, and 50mL centrifuge tubes) and equipment (large centrifuges, etc.) are required.

In view of this, the invention is particularly proposed.

Disclosure of Invention

The invention aims to provide a method for extracting a DNA sample from excrement and a methylation detection method of colorectal cancer related genes. The extraction method is simple to operate, can extract without using large-scale centrifugal equipment, and has low extraction cost; the extracted DNA sample has better sensitivity and specificity and good extraction effect when used for subsequent detection.

The invention is realized by the following steps:

in a first aspect, embodiments of the present invention provide a method for extracting a DNA sample from stool, the DNA sample being suitable for methylation detection of a colorectal cancer-related gene, the method comprising:

a pretreatment step: centrifuging the fecal diluent sample to obtain a first supernatant; the stool in the stool dilution is taken from a subject in need of colorectal cancer or pre-colorectal cancer lesion detection;

during centrifugation, the volume of the stool diluent sample in a single centrifuge tube is not higher than 2mL, preferably 0.5-1.8mL, and more preferably 1.8 mL;

the sample diluent comprises 100-500mmol/L EDTA, 50-300mmol/L Tris-HCl and 50-200mmol/L NaCl; the excrement diluent sample is formed by mixing excrement and excrement storage fluid according to the mass-volume ratio of 1 (3-5), and the preferable ratio is 1: 3.

In the prior art, the fecal DNA extraction process usually uses a 5mL, 15mL or 25mL centrifuge tube to dilute the sample for centrifugal pretreatment, and further needs a large-scale centrifugal device. Therefore, the following disadvantages are present: (1) for large-volume samples, large-scale centrifugal equipment has low centrifugal force and long single centrifugation time; (2) the centrifugal process needs balancing, and if the centrifugal process cannot be well balanced, machine faults are easy to occur; (3) when large-scale centrifugal equipment is used, the number of centrifugal tubes is small each time, and the centrifugal flux is low; (4) the pretreatment process usually requires multiple centrifugations, and has complex operation, high labor cost and high equipment cost. In the extraction process, the volume of the excrement diluent sample is controlled to be not higher than 2mL, and then centrifugal tubes with the specifications of 2mL and 1.5mL can be selected for centrifugation, so that the use of large-scale centrifugal equipment is avoided, the extraction process is accelerated, the convenience in the extraction process is improved, although the excrement use amount is reduced compared with that of the existing extraction method, the extraction effect is good, the extracted DNA sample can be used in subsequent methylation detection, the main colorectal cancer diseased condition or the pre-colorectal cancer diseased condition can be reflected through the detection result, and the method has good sensitivity and specificity.

In an alternative embodiment, the parameters of centrifugation are set as follows:

the rotation speed is 10000-.

In an alternative embodiment, the method further comprises:

an adsorption step: and uniformly mixing an adsorbent with the first supernatant to remove impurities in the supernatant to obtain a first mixed solution, and centrifuging the first mixed solution to obtain a second supernatant.

The excrement contains more impurities, and the impurities in the excrement can be removed better through the use of the adsorbent, so that the enrichment of a probe on a DNA sample in subsequent steps such as a capturing step is facilitated.

In an alternative embodiment, the adsorbent is selected from cross-linked polyvinylpyrrolidone.

In an alternative embodiment, the crospovidone is a crospovidone powder or a crospovidone tablet.

In alternative embodiments, the mass to volume ratio of the adsorbent to the first supernatant is 1 (2-4); further preferably 1: 4.

The research of the invention finds that the dosage of the adsorbent is one of the factors influencing the extraction effect, and the better extraction effect is achieved when the mass-volume ratio of the adsorbent to the first supernatant is controlled to be 1 (2-4), preferably 1: 4.

In an alternative embodiment, the method further comprises:

a nucleic acid denaturation step: and (3) performing denaturation treatment on the second supernatant so as to enable the DNA double-stranded structure to form a single-stranded structure.

Through denaturation, the DNA double-chain structure forms a single-chain structure, and the subsequent capture step is favorable for the combination of the probe and the target DNA fragment, so that a large amount of single-chain DNA can be enriched, the extraction effect is better, and the subsequent methylation detection effect is also favorable for improving.

In an alternative embodiment, the temperature of the denaturation treatment is 85 to 95 ℃ and the time is 5 to 15min, more preferably 10 min.

The research of the invention finds that the time of denaturation treatment has influence on the subsequent detection effect, the denaturation time is controlled within the range of 5-15min, the extraction effect is better, preferably 10min, and the extraction effect is better.

In an alternative embodiment, in the nucleic acid denaturation step, guanidine isocyanate is added to the second supernatant prior to the denaturation treatment.

In an alternative embodiment, the method further comprises:

a capturing step: adding a capture agent into the second supernatant to obtain a second mixed solution; wherein the capture agent comprises magnetic beads coupled with probes, and the probes are complementary with a certain section of the gene sequence to be extracted.

It should be noted that the sequence of the probe is related to the colorectal cancer related gene to be detected, and those skilled in the art can select an appropriate colorectal cancer related gene according to the detection requirement, and the sequence of the probe is designed according to the selected colorectal cancer related gene.

It should be noted that there may be one or more colorectal cancer-related genes to be detected, and those skilled in the art can select a suitable kind of colorectal cancer-related genes according to the detection requirement.

It should be noted that the genes related to colorectal cancer methylation to be detected include, but are not limited to, SDC2, TFPI2, VIM, NDRG4, SFRP1, SFRP2, BMP3, MGMT, SPG20, and SEPT 9.

The DNA sample extracted by the method is suitable for methylation detection of various colorectal cancer methylation related genes, including but not limited to SDC2, TFPI2, VIM, NDRG4, SFRP1, SFRP2, BMP3, MGMT, SPG20 and SEPT 9.

In an alternative embodiment, the capture agent is prepared by the following method:

mixing a magnetic bead solution containing magnetic beads with a probe solution of the probe to obtain a magnetic bead-probe mixed solution, wherein the volume of the magnetic bead-probe mixed solution is marked as V1, uniformly mixing the magnetic bead-probe mixed solution to couple the probe with the magnetic beads, placing the magnetic bead-probe mixed solution on a magnetic frame for adsorption, discarding supernatant, and adding a buffer solution with the volume of V1 to resuspend the magnetic beads to obtain the capture agent; the buffer solution contains 200mmol/L Tris-HCl and 100mmol/L NaCl;

wherein the concentration of the magnetic beads in the magnetic bead solution is 9-11mg/mL, and the concentration of the probe in the probe solution is 9-11 uM; the dosage of the magnetic bead solution satisfies the following formula: v ═ N × M; in the formula, V represents the volume of the magnetic bead solution, N represents the number of types of genes to be extracted, and M is 3 to 7 in μ L, preferably, M is 5. M means the optimal volume of the bead solution for a single gene to be extracted.

For example, when one gene is to be extracted, the amount of the bead solution is 1 × M, that is, 3 to 7 μ L, and when two genes are to be extracted, the amount of the bead solution is 2 × M, that is, 6 to 14 μ L, and so on. Namely, the dosage of the magnetic bead solution is determined by the variety and the quantity of the genes to be extracted.

The research of the invention finds that the usage amount of the magnetic bead liquid has influence on the extraction effect, when the to-be-extracted gene is one, the usage amount of the 9-11mg/mL magnetic bead liquid is controlled in the range of 3-7 mu L, the extraction effect is higher, and particularly, the better extraction effect can be obtained in the usage amount of 5 mu L.

In an alternative embodiment, the volume ratio of the magnetic bead solution to the probe solution is 1 (1-1.5), preferably 1:1.

The research of the invention also finds that the volume ratio of the magnetic bead liquid to the probe liquid is one of the factors influencing the extraction effect, and the magnetic bead liquid to the probe liquid has better extraction effect when the volume ratio is controlled within the range of 1 (1-1.5), and particularly has higher extraction effect when the volume ratio is controlled within the range of 1:1.

In an alternative embodiment, the magnetic beads are labeled with streptavidin, and the probes are labeled with biotin.

It should be noted that streptavidin and biotin are commonly used coupling systems in the art, and those skilled in the art will understand that other coupling systems such as digoxin and digoxin antibody can be used to couple the magnetic beads to the probes, and the coupling system used to couple the probes to the magnetic beads is within the scope of the present invention.

In an alternative embodiment, the method further comprises:

an incubation step: and (3) standing and incubating the second mixed solution for 40-90min, preferably 40 min.

In the present invention, the incubation temperature is not limited, and incubation at room temperature is also possible.

The research of the invention finds that the incubation time has influence on the extraction effect, and the incubation time is controlled within the range of 40-90min, so that a better extraction effect can be obtained; preferably, the incubation is controlled at 40min, and the extraction effect is better.

In a second aspect, the embodiments of the present invention provide a method for detecting methylation of a gene associated with colorectal cancer, the method aiming at diagnosis of non-diseases, comprising: extracting a DNA sample suitable for methylation detection of a gene associated with colorectal cancer using the method of any one of the preceding embodiments.

In alternative embodiments, the colorectal cancer-associated gene is selected from the group consisting of: SDC2, TFPI2, VIM, NDRG4, SFRP1, SFRP2, BMP3, MGMT, SPG20, and SEPT 9.

Drawings

In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings needed to be used in the embodiments will be briefly described below, it should be understood that the following drawings only illustrate some embodiments of the present invention and therefore should not be considered as limiting the scope, and for those skilled in the art, other related drawings can be obtained according to the drawings without inventive efforts.

FIG. 1 is a diagram: methylation of the SDC2 gene distinguishes ROC curves for colorectal cancer from normal samples;

FIG. 2 is a diagram of: methylation of the SDC2 gene distinguishes ROC curves for colorectal adenomas from normal samples;

FIG. 3 is a diagram of: methylation of the TFPI2 gene distinguishes the ROC curve for colorectal cancer from normal samples;

FIG. 4 is a diagram of: methylation of the TFPI2 gene distinguishes the ROC curve for colorectal adenomas from normal samples.

Detailed Description

In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. The examples, in which specific conditions are not specified, were conducted under conventional conditions or conditions recommended by the manufacturer. The reagents or instruments used are not indicated by the manufacturer, and are all conventional products available commercially.

The features and properties of the present invention are described in further detail below with reference to examples.

Example 1

The method for extracting DNA sample suitable for methylation detection of colorectal cancer related gene from feces provided in this example comprises the following steps:

(1) collecting a fecal sample, adding a fecal preservative solution according to a proportion, fully oscillating and uniformly mixing to obtain a fecal diluent sample;

the mass volume ratio of the excrement to the excrement storage solution is 1:3(1 mg: 3 mL);

the feces preservation solution contains: 300mmol/L EDTA, 200mmol/L Tris HCl and 150mmol/L NaCl.

(2) A sample of 1.8mL of fecal diluent was placed in a clean 2mL centrifuge tube, centrifuged at 12000rpm for 2min, the tube was gently removed from the centrifuge, and 1.2mL of the supernatant was carefully pipetted into a clean 2mL centrifuge tube.

(3) Adding adsorbent into 1.2mL of sample supernatant, performing vortex oscillation at a mass-volume ratio of the adsorbent to the supernatant of 1:4(g: mL), mixing the mixture sufficiently, and centrifuging at 12000rpm for 2 min.

Wherein the adsorbent is crosslinked polyvinylpyrrolidone powder or crosslinked polyvinylpyrrolidone tablet.

(4) The supernatant was transferred to a clean 2mL centrifuge tube, 5mol/L guanidinium isothiocyanate was added in equal volume, and mixed by gentle inversion.

(5) And (5) placing the centrifuge tube containing the supernatant obtained in the step (4) at 90 ℃ for denaturation for 10 min.

(6) Preparing a trapping agent:

calculating the usage amount of the magnetic bead solution (the concentration of the magnetic bead is 10mg/mL and the usage amount of the capture agent can be determined after the usage amount of the magnetic bead solution is determined) according to the type and the number of the genes to be detected (namely, the number of the extracted genes), wherein when one gene to be detected is used, the usage amount of the magnetic bead solution (the concentration of the magnetic bead solution is 10mg/mL) is 3-7 muL, and the preferred embodiment is 5 muL;

namely, the dosage of the magnetic bead solution satisfies the following formula: v ═ N × M; in the formula, V represents the volume of magnetic bead liquid, and N represents the number of types of genes to be extracted; m ranges from 3 to 7 in μ L, and M is preferably 5 in this embodiment;

after the usage amount of the magnetic bead solution is calculated, mixing the magnetic bead solution and a probe solution (the probe concentration is 10uM and the probe solution is marked with biotin) according to a volume ratio of 1:1 to obtain a magnetic bead-probe mixed solution, recording the volume as V1, shaking and uniformly mixing to couple the probe and the magnetic bead, placing the magnetic bead-probe mixed solution on a magnetic frame for adsorption, discarding the supernatant, adding a buffer solution for resuspension, shaking and uniformly mixing for 30s, and instantly centrifuging for 1s to obtain the capture agent.

The probe is complementary with the sequence of the colorectal cancer related gene to be extracted, and the sequence of the probe is designed from the sequence of the colorectal cancer related gene to be extracted. The type number of colorectal cancer related genes and corresponding probe sequences can be determined according to actual requirements.

(7) And (3) hybridization incubation: and (4) quickly adding the resuspended capture agent prepared in the step (6) into the denatured supernatant obtained in the step (5), reversing and uniformly mixing, and incubating for 40 min.

(8) Magnetic attraction separation: and (5) magnetically absorbing the mixed solution obtained in the step (7) for 6min, discarding the supernatant, and taking magnetic beads for precipitation.

(9) Rinsing: and (3) adding 1mL of rinsing liquid (EDTA (PH8.0, 5mM) and Tris-HCl (PH8.0, 20mM)) into the 2mL centrifuge tube in the step (9), shaking and uniformly mixing for 5s, carrying out instantaneous centrifugation for 2-4 s, placing on a magnetic frame for magnetic attraction for 2min, and discarding the supernatant.

(10) And (5) repeating the step (9).

(11) And (3) elution: and (3) adding 40 mu L of eluent into the 2mL centrifuge tube in the step (10), lightly shaking and uniformly mixing, absorbing magnetism for 2min, transferring the supernatant into a clean centrifuge tube to obtain a required DNA sample, wherein the DNA can be used for subsequent methylation detection of genes related to colorectal cancer, and the colorectal cancer disease condition or the colorectal cancer pre-lesion condition of the main body can be reflected according to the methylation detection result.

Of course, it should be noted that the extracted DNA may also be subjected to other types of detection, not limited to methylation detection, such as mutation of some genes associated with the occurrence and development of colorectal cancer, including but not limited to KRAS and TP 53.

Of course, the extracted DNA can be used for detecting other tumors, such as digestive tract tumors, esophageal cancer, gastric cancer, pancreatic cancer, gallbladder cancer and the like.

Example 2

This example provides a method for detecting colorectal cancer, comprising the steps of:

(a) extraction of DNA samples from faeces

DNA samples were extracted from feces using the method of example 1, targeting SDC2 and TFPI2 genes, and the capture probe sequence at step (6) was as follows:

SDC2：TGCTTGCGGCACTCCCGTGTAACTCCTATG；

TFPI2：AAACTTTCTCCTGTAGTCCAGACGGGGACG。

DNA samples were obtained which were mainly tested for methylation of the SDC2 gene.

In addition, when the SDC2 and TFPI2 genes are detected, the housekeeping gene β -actin is required to be simultaneously detected as an internal reference, and β -actin is taken as a target to extract the genes, the capture probe sequence in the step (6) is as follows:

ATTGGCAAGAGCCCGGCTCAGACAAAGACCC。

(b) sulfite conversion

The differentiation of methylated and unmethylated sequences is achieved by the conversion of unmethylated cytosine to uracil by sulfite, while methylated cytosine remains unchanged, and the nucleic acid conversion kit used in this example is ZYMOREZ DNA Methylation-Gold of ESEARCH^TMKit, see manufacturer's instructions for specific experimental procedures.

In other embodiments, methylation of the marker can be detected by other methods, such as sulfite sequencing, sulfite pyrosequencing, microarrays, mass spectrometry, denaturing high liquid chromatography, pyrosequencing, methylated DNA immunoprecipitation and quantitative polymerase chain reaction, methylated DNA immunoprecipitation sequencing, or nanopore sequencing.

(c) Methylation Specific PCR (MSP)

Detecting methylation sensitive sites of SDC2 and TFPI2 genes by using an MSP method for DNA obtained after transformation in the step (b), taking β -actin as an internal reference gene, wherein primer and probe sequences of SDC2, TFPI2 and β -actin are shown in a table 1, PCR reaction systems are shown in a table 2, and PCR reaction conditions are shown in a table 3.

TABLE 1 SDC2, TFPI2 and β -actin primer and Probe sequences

primer/Probe name	Nucleotide sequence (5 '-3')	SEQ ID NO.
			SDC2 Forward primer	CGAGTTTGAGTCGTAATCGTTGC		1
SDC2 reverse primer	TCCGCCGACACGCAAACCACCAAACC	2
			SDC2 probe	AACAAAACGAAACCTCCTACCCAAC	3
TFPI2 forward primer	CGCGGAGATTTGTTTTTTGT	4
			TFPI2 reverse primer	AACAAACATCGTCGCAAACCTC	5
TFPI2 Probe	ATAAAACCCGACAAAATCCG	6
			β -actin forward primer	CAAGATGAGATTGGCATGGCT	7
β -actin reverse primer	TGTGAACTTTGGGGGATGCTC	8
			β -actin probe	CCAGTTTTTAAATCCTGAGTCAAGC	9

The 5 'end of the SDC2 probe, the TFPI2 probe and the β -actin probe is marked with a fluorescent group, the 3' end is marked with a quenching group, wherein the fluorescent group of the SDC2 probe is FAM, the quenching group is MGB-NFQ, the fluorescent group of the TFPI2 probe is ROX, the quenching group is MGB-NFQ, &lTtTtransition = beta "&gTt beta &lTt/T &gTt-actin probe is VIC, and the quenching group is MGB-NFQ.

TABLE 2 MSP reaction System

TABLE 3 MSP reaction conditions

Quality control, synchronously detecting negative control and positive control in each detection, wherein the negative control is ultrapure water, the positive control is a mixture of SDC2 methylated plasmid, TFPI2 methylated plasmid and β -actin plasmid, and the concentration of the three plasmids is 1 × 10⁴copies/. mu.L. Negative control has no obvious exponential increase, and the Ct value is Undet/NoCt or Ct>40, the positive control has obvious index increasing period, Ct values of SDC2, TFPI2 and β -actin meet Ct values of 26-30, except for the negative control and the positive control, Ct values of internal reference genes of a detection sample meet Ct values of 35, and if the Ct values are not more than>35, it indicates that the added sample DNA contains PCR inhibitor or the added amount of DNA is too small, and DNA needs to be prepared again or the amount of DNA sample is increased for detection. After the negative control, the positive control and the reference gene all meet the requirements, the experiment is effective, and the next step of sample result judgment can be carried out. Otherwise, when the experiment is invalid, the detection is required to be carried out again.

(d) And (4) judging a result: determining cut-off value of Ct value of the sample to be detected through the positive judgment value, and if Ct value of SDC2 gene of the sample to be detected meets Ct less than or equal to 38, determining that the sample is SDC2 methylation positive (SDC 2)⁺) (ii) a If Ct is>38, the sample is SDC2 methylation negative (SDC 2)^－) (ii) a If the Ct value of the TFPI2 gene of the sample to be detected meets the condition that the Ct is less than or equal to 38, the sample is positive for TFPI2 methylation (TFPI 2)⁺) (ii) a If Ct is>38, the sample is TFPI2 methylation negative (TFPI 2)^－). Of note, only when SDC2 and TFPI2 were both methylation negative (SDC 2)^-TFPI2^-) Then judgeNegative, when at least one of SDC2 and TFPI2 is methylation positive (SDC 2)⁺TFPI2^-/SDC2^-TFPI2⁺/SDC2⁺TFPI2⁺) If yes, the result is judged to be positive.

Experimental example 1

Verification of sensitivity and specificity of the method of example 2

696 stool samples were collected from southern hospital, Wuhan university, wherein 289 samples were colorectal cancer samples, 190 samples were colorectal adenoma samples, 217 samples were normal samples, clinical information of the stool samples is shown in Table 4, and results of methylation detection of SDC2 and TFPI2 of the stool samples are shown in Table 5.

Statistical analysis: according to the detection results of the SDC2 and the TFPI2, the sensitivity and the specificity are calculated according to the following formulas, statistical analysis is carried out by applying SPSS23.0 software, the grouping efficiency of the SDC2 and the TFPI2 is evaluated by utilizing a ROC (Receiver operating characteristics) curve according to the detection results of colorectal cancer stool samples, and the area, the sensitivity and the specificity under the AUC (area under the curve) are calculated.

Sensitivity (Sensitivity) is 100% of true positive population/(true positive population + false negative population);

specificity (Specificity) is 100% of true negative number/(true negative number + false positive number).

Table 4696 clinical information on stool samples

TABLE 5696 stool samples for SDC2 and TFPI2 methylation assay results

SDC 2A ROC curve for distinguishing colorectal cancer samples from normal samples is shown in FIG. 1, and a ROC curve for distinguishing colorectal adenoma samples from normal samples is shown in FIG. 2; the ROC curve of TFPI2 for distinguishing colorectal cancer samples from normal samples is shown in fig. 3, and the ROC curve for distinguishing colorectal adenoma samples from normal samples is shown in fig. 4.

The above results show that the method of example 2 has a higher AUC for both SDC2 and TFPI2, and can be used to diagnose colorectal cancer or precancerous lesions.

Example 3

The method for extracting DNA sample suitable for methylation detection of colorectal cancer-associated gene from stool provided in this example is substantially the same as in example 1, except that in step (3), the mass-to-volume ratio of the adsorbent to the supernatant is 1:2(g: mL).

Comparative example 1

The method for extracting a DNA sample suitable for methylation detection of a colorectal cancer-associated gene from feces provided in this comparative example is substantially the same as in example 1, except that in step (3), the mass-to-volume ratio of the adsorbent to the supernatant is 1:6(g: mL).

Comparative example 2

The method for extracting a DNA sample suitable for methylation detection of a colorectal cancer-associated gene from feces provided in this comparative example is substantially the same as in example 1, except that in step (3), the mass-to-volume ratio of the adsorbent to the supernatant is 1:8(g: mL).

Experimental example 2

The extraction effects of example 1, example 3, and comparative examples 1 and 2 were examined

Stool samples (sample information is shown in Table 6) of three colorectal cancers (samples 1, 2 and 3), three colorectal adenomas (samples 10, 11 and 12) and three healthy persons (samples 19, 20 and 21) were selected, DNA samples were extracted by the methods of example 1, example 3 and comparative examples 1 and 2, SDC2 and TFPI2 genes were used as detection genes, β -actin gene was used as an internal reference, and Ct values were detected by the methylation detection method of example 2, and the results are shown in Table 7 below.

TABLE 6 sample information

TABLE 7

As can be seen from the above table, the Ct values of the β -actin and SDC2 genes in example 3 and example 1 are lower and smaller than those in comparative example 1 and comparative example 2, wherein the Ct value of example 1 is the smallest (P <0.05), which indicates that the DNA sample content of the target genes in example 3 and example 1 is high and the extraction effect is good.

It should be noted that the content of the target gene is generally very small, and the concentration is not suitable for uv spectrophotometry, and in addition, the concentration is low, some genes are fragmented, agarose gel electrophoresis cannot distinguish concentration differences, and the residual trace amount of magnetic beads may influence the measured concentration value, and the use of these indexes to reflect the extraction effect is very inaccurate, and has no reference meaning. Therefore, the Ct value is adopted to reflect the advantages and disadvantages of the effects of different extraction methods, the method has a reference meaning, the larger the Ct value is, the lower the content of the target gene is, the extraction effect is poor, the smaller the Ct value is, the higher the content of the target gene is, and the extraction effect is good.

Example 4

The method for extracting DNA samples suitable for methylation detection of colorectal cancer-related genes from feces provided in this example is substantially the same as in example 1, except that the denaturation time in step (5) is 15 min.

Comparative example 3

The comparative example provides a method for extracting a DNA sample suitable for methylation detection of a colorectal cancer-related gene from feces, which is substantially the same as in example 1, except that the denaturation time in step (5) is 6 min.

Comparative example 4

The comparative example provides a method for extracting a DNA sample suitable for methylation detection of a colorectal cancer-related gene from feces, which is substantially the same as in example 1, except that the denaturation time in step (6) is 8 min.

Experimental example 3

The extraction effects of example 1, example 4, and comparative examples 3 and 4 were examined

Three colorectal cancers (samples 1, 2 and 3), three colorectal adenomas (samples 10, 11 and 12) and three healthy human (samples 19, 20 and 21) stool samples (sample information is shown in Table 6) were selected, DNA samples were extracted by the methods of example 1, example 4 and comparative examples 3 and 4, the SDC2 gene was used as a detection gene, the β -actin gene was used as an internal reference, and Ct values were detected by referring to the methylation detection method in example 2, and the results are shown in Table 8 below.

TABLE 8

The results in Table 8 show that the Ct values of examples 1 and 4 are smaller (P <0.05) compared to comparative examples 3 and 4, indicating that the extraction efficiency is better when the denaturation time is controlled to 10-15min, and that the denaturation time can be set to 10min in the range of 10-15min from the viewpoint of time and cost saving.

Example 5

This example provides a method for extracting DNA sample suitable for methylation detection of colorectal cancer related gene from feces, which is substantially the same as that of example 1, except that in step (6), the volume of the magnetic bead solution is 3 uL.

Example 6

This example provides a method for extracting DNA sample suitable for methylation detection of colorectal cancer-related gene from feces, which is substantially the same as that of example 1, except that in step (6), the volume of the magnetic bead solution is 7 uL.

Experimental example 4

Examination of the extraction effects of example 1, example 5 and example 6

Stool samples (see Table 6) from three colorectal cancers (samples 4, 5, 6), three colorectal adenomas (samples 13, 14, 15) and three healthy persons (samples 22, 23, 24) were selected, DNA samples were extracted by the methods of example 1, example 5 and example 6, SDC2 and TFPI2 genes were used as detection genes, β -actin gene was used as an internal reference, and Ct values were detected by the methylation detection method of example 2, and the results are shown in Table 9 below.

TABLE 9

As can be seen from table 9, example 1 has a smaller Ct value (P <0.05) than examples 5 and 6, indicating that the extraction effect of example 1 is higher.

Example 7

The method for extracting DNA sample suitable for methylation detection of genes related to colorectal cancer from feces provided in this example is substantially the same as in example 1, except that in step (6), the volume ratio of the magnetic bead solution to the probe solution is 1: 1.5.

Comparative example 5

The comparative example provides a method for extracting a DNA sample suitable for methylation detection of colorectal cancer related genes from feces, which is basically the same as that in example 1, except that the volume ratio of the magnetic bead solution to the probe solution is 1: 0.5.

Comparative example 6

The comparative example provides a method for extracting a DNA sample suitable for methylation detection of colorectal cancer related genes from feces, which is basically the same as that in example 1, except that the volume ratio of the magnetic bead solution to the probe solution is 1: 2.

Experimental example 5

The extraction effects of example 1, example 7 and comparative examples 5 to 6 were examined

Stool samples (see Table 6) from three colorectal cancers (samples 4, 5, 6), three colorectal adenomas (samples 13, 14, 15) and three healthy persons (samples 22, 23, 24) were selected, DNA samples were extracted by the methods of example 1, example 7 and comparative examples 5 to 6, SDC2 and TFPI2 genes were used as detection genes, β -actin gene was used as an internal reference, and Ct values were measured with reference to the methylation detection method of example 2, and the results are shown in Table 10 below.

Watch 10

The results in Table 10 show that the Ct values of examples 1 and 7 are smaller than those of comparative examples 5 and 6 (P <0.05), which indicates that controlling the volume ratio of the magnetic bead solution to the probe solution in the range of 1:1-1.5 provides better extraction effect, especially the Ct value of example 1 is the smallest, indicating that controlling the volume ratio of the magnetic bead solution to the probe solution in the range of 1:1 provides better extraction effect.

Example 8

The method for extracting DNA sample suitable for methylation detection of colorectal cancer related gene from feces provided in this example is substantially the same as in example 1, except that in step (7), hybridization incubation time is 60 min.

Example 9

The method for extracting DNA samples suitable for methylation detection of colorectal cancer-related genes from feces provided in this example is substantially the same as in example 1, except that in step (7), the hybridization incubation time is 90 min.

Comparative example 7

The comparative example provides a method for extracting a DNA sample suitable for methylation detection of a colorectal cancer-associated gene from feces, which is substantially the same as in example 1, except that in step (7), the hybridization incubation time is 20 min.

Experimental example 6

The extraction effects of example 1, example 8, example 9 and comparative example 7 were examined

Stool samples (see Table 6) from three colorectal cancers (samples 7, 8, 9), three colorectal adenomas (samples 16, 17, 18) and three healthy persons (samples 25, 26, 27) were selected, DNA samples were extracted by the methods of example 1, example 8, example 9 and comparative example 7, SDC2 and TFPI2 genes were used as detection genes, β -actin gene was used as an internal reference, and Ct values were measured by the methylation detection method of example 2, and the results are shown in Table 11 below.

TABLE 11

As can be seen from Table 11, the Ct values of examples 1, 8 and 9 are significantly lower than that of comparative example 7(P <0.05), which indicates that the extraction effect of examples 1, 8 and 9 is better, and it should be noted that the Ct value of example 1 is lower than that of examples 8 and 9, which indicates that the extraction effect is better when the incubation time is controlled at 40 min.

Example 10

This example provides a method for extracting DNA samples suitable for methylation detection of genes associated with colorectal cancer from stool that is substantially the same as in example 1, except that in step (2), the volume of the stool diluent sample is 1.5 mL.

Example 11

This example provides a method for extracting DNA samples suitable for methylation detection of genes associated with colorectal cancer from stool, which is substantially the same as that of example 1, except that in step (2), the volume of the stool diluent sample is 1 mL.

Example 12

This example provides a method for extracting DNA samples suitable for methylation detection of genes associated with colorectal cancer from stool, which is substantially the same as that of example 1, except that in step (2), the volume of the stool diluent sample is 0.5 mL.

Experimental example 7

Examination of the extraction Effect of example 1 and examples 10 to 12

Stool samples of three colorectal cancers (samples 7, 8, and 9), three colorectal adenomas (samples 16, 17, and 18), and three healthy persons (samples 25, 26, and 27) were selected and extracted by the methods of example 1 and examples 10 to 12, using SDC2 and TFPI2 genes as detection genes and β -actin genes as internal references, and detecting Ct values with reference to the methylation detection method of example 2, and the results are shown in table 12 below.

TABLE 12

As can be seen from table 12, the Ct values of a small amount of the stool diluent samples are small, and the colorectal cancer morbidity judged according to the methylation detection results of the DNA samples obtained in the embodiments is completely consistent with the expected result (i.e., the enteroscopy result of each sample in table 6).

Experimental example 8

Comparison of the extraction Effect of the extraction method of example 1 and the extraction method of the existing commercial kit

Three colorectal cancers (samples 7, 8 and 9), three colorectal adenomas (samples 16, 17 and 18) and three Stool samples (samples 25, 26 and 27) (see table 6) of healthy people are selected, two DNA extraction modes are adopted for the 9 Stool samples, one is the extraction method of the example 1, the other is the Stool whole genome extraction mode, the kit is QIAamp DNA pool Minikit (QIAGEN), the specific operation steps are shown in the manufacturer specification, SDC2 and TFPI2 genes are used as detection genes, β -actin genes are used as internal references, and the Ct value is detected by referring to the methylation detection method in the example 2, and the result is shown in the following table 13.

Watch 13

The results in Table 13 show that the Ct values of the β -actin gene and the SDC2 gene in example 1 are smaller (P <0.05), most of the Ct values of the β -actin gene obtained by the whole genome extraction method (7/9) are larger than 35 or cannot be detected, which is basically equivalent to the sample invalid detection, and more than 50% of positive samples cannot be detected for the SDC2 gene or the TFPI2 gene in the detection gene, which indicates that the extraction effect of example 1 is better and is obviously better than that of the whole genome extraction method.

In summary, the extraction method provided by the embodiment of the invention has the following advantages:

1. at present, most of methods for extracting fecal DNA are full DNA extraction, the background of DNA extracted by the method is complex, the specificity is poor, downstream analysis is not facilitated, experimental example 8 compares two methods of full genome extraction and specific gene enrichment extraction, and the result shows that the detection effect of the probe enrichment method on colorectal cancer is obviously superior to that of the full genome extraction method.

2. The extraction method provided by the embodiment of the invention achieves the aim of realizing early detection of colorectal cancer by only using a small amount of samples by optimizing important parameters in the DNA extraction process, and has high accuracy, wherein the sensitivity of the methylation of the SDC2 gene to the colorectal cancer is up to 86.9 percent, the detection sensitivity to the colorectal adenoma is 56.3 percent, and the specificity is up to 95.9 percent; the sensitivity of TFPI2 gene methylation to colorectal cancer is up to 90.3%, the detection sensitivity to colorectal adenoma is 62.1%, and the specificity is up to 94.0%.

3. Few prior arts adopt a mode of enriching target DNA by magnetic beads, but the volume of the used fecal solution is large, so that special consumables and equipment (such as 5mL, 15mL and 50mL centrifuge tubes and corresponding centrifuges) are needed, and the operation steps are complicated and time-consuming (such as only a small amount of samples can be centrifuged by one large centrifuge at a time). In addition, only 2mL and 1.5mL of EP tubes and a common small-sized centrifuge are needed in the extraction method provided by the embodiment of the invention, so that the cost is greatly saved, and the detection flux is obviously improved.

Taking the extraction experiments of 24 stool samples as an example, the advantage of small volume extraction compared to large volume extraction is illustrated, as shown in the following table:

as can be seen from the table, since 1 sample usually needs to be centrifuged at least 2-3 times in one experiment, when extracting 24 samples, the small volume extraction can save 2 hours of manpower and about 60 yuan of centrifuge tube cost compared with the large volume extraction, and when the sample size is expanded to hundreds of thousands or even millions of levels, the economic benefit generated by the small volume extraction method is huge.

4. The method provided by the invention can be used together with an automatic instrument or a platform, and can further improve the extraction efficiency of the DNA of the excrement.

5. In the prior art, an organic solvent is mostly used in the DNA extraction process, the extraction method provided by the invention is a magnetic bead method, does not relate to an organic solvent, is safe and simple to operate, and greatly improves the specificity of DNA extraction by enriching target genes.

The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention, and various modifications and changes may be made by those skilled in the art. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

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Claims

1. A method for extracting a DNA sample from stool, said DNA sample being suitable for methylation detection of genes associated with colorectal cancer or pre-colorectal lesion, comprising:

a pretreatment step: centrifuging the fecal diluent sample to obtain a first supernatant; the stool in the stool dilution sample is taken from a subject in need of colorectal cancer detection;

during centrifugation, the volume of the fecal diluent sample in a single centrifuge tube is no greater than 2mL, preferably 0.5-1.8mL, and more preferably 1.8 mL.

2. The method for extracting DNA samples from feces according to claim 1, characterized in that the parameters of centrifugation are set as follows:

the rotation speed is 10000-.

3. The method of claim 1, further comprising:

an adsorption step: uniformly mixing an adsorbent with the first supernatant to remove impurities in the supernatant to obtain a first mixed solution, and centrifuging the first mixed solution to obtain a second supernatant;

preferably, the adsorbent is selected from cross-linked polyvinylpyrrolidone;

preferably, the crospovidone is a crospovidone powder or a crospovidone tablet.

4. The method of extracting a DNA sample from feces according to claim 3,

the mass volume ratio of the adsorbent to the first supernatant is 1 (2-4), preferably 1: 4.

5. The method of claim 4, further comprising:

a nucleic acid denaturation step: performing denaturation treatment on the second supernatant to enable the DNA double-stranded structure to form a single-stranded structure;

preferably, the temperature of the denaturation treatment is 85-95 ℃ and the time is 5-15min, and more preferably 10 min.

6. The method of claim 5, further comprising:

7. The method of extracting a DNA sample from feces according to claim 6,

the trapping agent is prepared by the following method:

mixing a magnetic bead solution containing magnetic beads with a probe solution of the probe to obtain a magnetic bead-probe mixed solution, wherein the volume of the magnetic bead-probe mixed solution is marked as V1, uniformly mixing the magnetic bead-probe mixed solution to couple the probe with the magnetic beads, placing the magnetic bead-probe mixed solution on a magnetic frame for adsorption, discarding supernatant, and adding a buffer solution with the volume of V1 to resuspend the magnetic beads to obtain the capture agent;

wherein the concentration of the magnetic beads in the magnetic bead solution is 9-11mg/mL, and the concentration of the probe in the probe solution is 9-11 uM; the dosage of the magnetic bead solution satisfies the following formula: v ═ N × M; in the formula, V represents the volume of the magnetic bead solution, N represents the number of types of genes to be extracted, and M is 3 to 7 in μ L, preferably M is 5;

preferably, the volume ratio of the magnetic bead liquid to the probe liquid is 1 (1-1.5), preferably 1: 1;

preferably, streptavidin is labeled on the magnetic beads, and biotin is labeled on the probes;

preferably, the buffer comprises: 200mmol/LTris HCl and 100 mmol/LNaCl.

8. The method of extracting a DNA sample from a stool according to claim 6 or 7, further comprising:

9. A method for detecting methylation of a gene associated with colorectal cancer, the method being aimed at non-disease diagnosis, comprising: a DNA sample suitable for methylation detection of genes associated with colorectal cancer or pre-colorectal pathology is obtained by the method according to any one of claims 1 to 8.

10. The methylation detection method of claim 9, wherein the colorectal cancer-associated gene is selected from the group consisting of: SDC2, TFPI2, VIM, NDRG4, SFRP1, SFRP2, BMP3, MGMT, SPG20, and SEPT 9.