Isolate High Molecular Weight DNA using the NEW Isohelix™ Mag-Filter HMW Clean Up Kit

Isolate High Molecular Weight DNA using the NEW Isohelix™ Mag-Filter HMW Clean Up Kit

High molecular weight (HMW) DNA is important for applications that require the use of very long DNA molecules, such as long read sequencing. Long-read sequencing enables the detection of variants that are often difficult to resolve with short reads, such as structural variants, complex rearrangements, and variants in highly repetitive regions.

In order to fully take advantage of long-read sequencing, high quality, high molecular weight (HMW) input DNA is required. Traditional DNA extraction methods often result in fragmented DNA samples. If these shorter fragments are not removed, the average length of sequencing reads, and subsequent effectiveness of long-read analyses are reduced.

To address this requirement, Isohelix has developed the Mag-Filter HMW Clean Up Kit, which employs magnetic beads alongside specialized size selection chemistry to isolate high molecular weight DNA fragments from extracted DNA samples, while removing smaller DNA fragments and other contaminants from samples.

Samples prepared using the Mag-Filter HMW Clean Up Kit are perfect for NGS and long-read sequencing applications.

HMW DNA Cleanup and Size Selection

The Mag-Filter HMW kit removes low molecular weight DNA while safeguarding high molecular weight DNA integrity. High purity HWM DNA is achieved through DNA sample cleanup and size selection.

Saliva DNA samples spiked with DNA ladder and processed using the Mag-Filter Clean-Up Kit demonstrate effective removal of small DNA fragments.

HMW DNA from saliva and buccal swab samples

The Mag-Filter HMW kit is optimized for use with extracted saliva samples but can be used on DNA from a variety of sample sources, such as buccal swabs. It can also be used to increase sample purity, allowing the use of valuable samples with initially low purity that might otherwise fail quality control checks.

GFX-01

Simple to Use HMW DNA Preparation

The kit is simple to use and can cleanup samples for library prep in less than one hour. All kit components are non-hazardous, and gel separation is not required. The kit protocol can also be easily adjusted to accommodate varying sample volumes; the protocol is fully scalable, from small manually processed sample batches up to plate-based high throughput automation.

How to increase the quality and yield of DNA and RNA from saliva

Introduction

With advanced genomic analysis applications becoming routine in many labs, the need for high purity, high quality DNA and RNA samples collected using non-invasive sampling methods, such as saliva, is becoming increasingly important.

Nucleic acid extraction from saliva can be challenging due to the presence of contaminants and inhibitors  that can interfere with downstream applications. However, in recent years significant improvements have been made with devices to collect, store, and process saliva to extract DNA and RNA. Good yields of high-quality nucleic acids can now be extracted for use in sensitive downstream applications.

Variations in sample collection and handling can dramatically affect data quality. This article explains how to get the best from your saliva samples by maximizing the purity and yields of DNA and RNA with information on:

  • Preventing sample contamination
  • Saliva collection from donors
  • Nucleic acid stabilization
  • Safely shipping saliva samples
  • Choosing your DNA/RNA isolation kit
  • Isolating high molecular weight (HMW) DNA from saliva   
  • Cleaning up your DNA after an initial extraction

Preventing sample contamination

The main sources of human DNA in saliva are epithelial cells and leukocytes. Saliva samples may also include bacterial DNA, allowing for DNA extraction and analysis of the oral microbiome. To prevent contamination from external nucleic acids and other factors that may interfere with the purity of samples, it is important to ensure that donors do not eat, drink, smoke, or chew gum for at least 30 minutes before providing a sample.

Saliva collection from donors

For collection by donors at home without medical supervision, kits such as the GeneFix Saliva DNA/RNA range include a simple to attach funnel that makes it easy to collect saliva in a tube prefilled with stabilization reagent for transport and storage of the sample. 

GFX-03

Traditionally, collection devices were designed to collect 1ml or 2ml saliva, but newer devices such as the GFX-03, can collect up to 3ml if higher yields (300μg+) are required, e.g., for biobanking. For maximum yields, donors must ensure that they don’t include bubbles when measuring the liquid level in the tube as this can result in overfilling, or not collecting enough saliva.

Some donors, e.g., children or elderly patients, may find it difficult to produce saliva. If this is the case, saliva production can be stimulated by gently rubbing the cheeks or using a kit such as the SaliFix Saliva Swab DNA Collection kit which contains absorbent swabs for easy collection of smaller volumes of saliva.

Nucleic acid stabilization

One of the key benefits of using saliva as a source of nucleic acids is that samples can be collected remotely and mailed for analysis. Stabilization reagents protect sample integrity by stabilizing DNA and RNA and preventing microbial growth. GeneFix saliva collection kit tubes are prefilled with a non-hazardous guanidium-free stabilization reagent that stabilizes DNA at room temperature for 5 years and RNA for 2 months. Samples can be shipped and stored at room temperature, removing the costs and logistical challenges associated with cold chain storage and transport. For longer term storage GeneFix kits are also suitable for freezing at temperatures down to -80°C.

Safely shipping saliva samples

Shipping packaging and collection tubes must be manufactured from robust materials that can withstand the rigors of the mailing process to ensure your saliva samples arrive at the lab intact. Isohelix sample collection tubes are pressure tested to 95kPa, and Isohelix TPS-50 transport packs are pressure-tested and adhere to UN3373 packaging standards – including secure sealing strips and absorbent material that retains samples leaking from the primary tube within further layers of packaging, preventing sample cross-contamination.

Choosing your DNA/RNA Isolation Kit

Precipitation methods of DNA isolation such as the GeneFix Saliva-Prep Kit, enable the rapid and efficient extraction of high yields of high molecular weight DNA and can be easily scaled to accommodate different sample volumes. As these kits don’t require additional solvents, columns, or filtration, workflows are easy to automate, with fast handling times and reduced sample steps. The unique precipitation chemistry maximizes recovery of high molecular weight DNA, while minimizing co-precipitation of RNA and degraded low-weight DNA.

Alternatively, silica membrane-based spin columns, such as those included in the Xtreme (XME) and Xtreme-RNA (XMR) kits, allow the purification of very high-purity, high molecular weight DNA or RNA for demanding downstream applications such as next generation sequencing or microarrays.

Isolating high molecular weight (HMW) DNA from saliva

Gentle handling is key to preserving the integrity of your DNA samples and isolating HMW DNA for more demanding applications such as whole genome sequencing (WGS) or microarrays. To prevent shearing, use wide bore tips and pipette slowly, avoiding vortexing or shaking tubes.

Cleaning up your DNA after initial extraction

If, despite your best efforts, your extracted DNA is not of a sufficient concentration or purity for your downstream applications, a DNA clean up kit can be used. The Isohelix DNA clean up kit uses a simple 30 minute protocol to reclaim a “failed” sample, preserving your DNA yields and giving High Purity DNA with 260/280 ratios to 1.8.

Nanodrop Scan Before & After DCU CleanUp

Summary

By following the advice given in this article, high yields of high purity DNA can be extracted from saliva for use in a number of sensitive downstream applications.

GeneFix offers superior performance and high yields when compared with alternative collectors :

Isohelix Sample Collection: Research highlights from 2023

2023 was a busy year for Isohelix and our customers. In this blog, we present examples of how studies reported in peer-reviewed publications used Isohelix products to solve their sampling challenges.

We’ve highlighted four studies where Isohelix technologies were used to make groundbreaking discoveries in the world of biomedical research. In each of these studies, Isohelix sample collection products were used to collect DNA samples which were then analyzed using highly sensitive genetic analyses such as single nucleotide polymorphism (SNP) genotyping, genome wide association studies (GWAS), and next generation sequencing (NGS) analyses.

  1. GeneFix Saliva Collection Devices are used to collect samples for a large population-based study in Australia
  2. The Hong Kong Genome Project uses GeneFix Saliva Collection Devices to collect saliva samples and the  RapiDri Pouch kit for buccal swabs.
  3. Isohelix saliva collection kits are used to collect saliva from a large cohort of children in the USA
  4. Isohelix Buccal Swabs are used to swab surfaces to collect DNA from bacterial communities in subway facilities

STUDY 1 : Preliminary results from the Australian Genetics of Bipolar Disorder Study: A nation-wide cohort[i]

The Australian Genetics of Bipolar Disorder (BD) Study investigates a nation-wide cohort of adults living with bipolar disorder. The study aims to identify genetic risk factors influencing BD, medication treatment response, and adverse drug reactions (ADRs). Key goals are to characterize the patterns and costs of healthcare usage in BD and to examine the relationship between genetic risk and symptom severity. This article describes the study design and sample characteristics and summarises data collected on BD symptoms, psychiatric comorbidities, and medication use. 

A significant strength of the study is its sample size; it’s the largest population-based study of adults living with BD in Australia. Study participants are based throughout Australia, with many living in rural or remote communities. Saliva samples are collected using Isohelix GeneFixGFX-02 2 mL Saliva Collection Devices which stabilize DNA and RNA at room temperature for up to 60 months,  then mailed to QIMR Berghofer via prepaid Australia Post. Following DNA extraction, genotyping is conducted using the Illumina Global Screening Array V.2.0.

GFX-02

The study demonstrates that Australians with BD are motivated to participate in genetically focused research studies if given the opportunity and provided with simple and effective sample donation protocols. GeneFix Saliva Collectors are ideal for this type of project as their reagents are non-toxic, and the collectors are easy to use as they have a unique funnel design that prevents buffer spillages or flow-back.

The results highlight the high rate of comorbidities and adverse drug reactions among adults living with bipolar disorder in the general Australian population and pave the way for future genomic analyses to identify genetic variants influencing pharmacotherapy treatment response and side effects.

STUDY 2 : The Hong Kong genome project: building genome sequencing capacity and capability for advancing genomic science in Hong Kong[ii]

The Hong Kong Genome Project (HKGP) is the first large-scale genome sequencing (GS) project in the Hong Kong Special Administrative Region. The project aims to sequence 45,000-50,000 genomes in five years, providing participants with diagnoses and personalized treatments and driving the application and integration of genomic medicine into routine clinical care.

For each participant, 6 mL of blood is obtained and stored in two 3-mL EDTA-containing anticoagulation tubes. For buccal swabs, the RapiDri Pouch kit is used to collect cells from inside the cheek, and saliva samples are collected using the GeneFix Saliva DNA Collection and Stabilization Kit. DNA from saliva samples has been shown to be comparable to DNA from blood in many downstream applications[iii] and DNA from saliva samples collected using GeneFix kits is stable at room temperature for over five years, avoiding the high cost and logistical challenges of cold chain transport.

RapiDri Swab

This paper describes the establishment of a robust genome sequencing workflow for the project. The laboratory analyses approximately 350-500 samples per week. During the first 24 months of the project, 12,937 participants and their family members were recruited, and the laboratory has been adapted to facilitate the latest technologies, e.g., long read sequencing and multi-omics.

STUDY 3 : Avoidant Restrictive Food Intake Disorder Genes and Environment (ARFID-GEN): study protocol[iv]

This paper describes the Avoidant Restrictive Food Intake Disorder – Genes and Environment study (ARFID-GEN), which is designed to expand the discovery of genetic and environmental contributions to ARFID risk. The goal of the study is to deliver actionable findings that can be transformed into clinically meaningful insights. This will be achieved by advancing the understanding of the genetic architecture of ARFID relative to other eating disorders and other psychiatric, neurodevelopmental, and metabolic disorders and traits.

3,000 children and adults with ARFID from the United States are included in the study. Efficient online phenotyping of children and adults with ARFID including environmental exposures is combined with at-home saliva sampling, and samples are genotyped to analyze single nucleotide polymorphism (SNP) – based heritability, genome wide association studies, genetic correlations (rgs), and copy number variations (CNVs).

SK-2S

Eligible children are asked to complete a questionnaire on their symptoms and provide a saliva sample using Isohelix saliva collection kits, which are non-toxic and easy for children to use at home as they have a unique funnel design that prevents buffer spillages or flow-back. The kits are provided with return packaging for mailing to the lab for analysis.

The aim is to identify genome-wide significant loci for ARFID, informative rgs, implicated CNVs, and environmental precipitants. Ultimately, the work will hopefully yield information on critical biological pathways that may point toward drug discovery or repurposing that could aid in reversing the tenacity and lethality of these illnesses.

STUDY 4 : Investigation of Surface Bacterial Diversities and Compositions in the Global Subway Facilities[v]

This study explored surface bacterial communities in four global subway facilities using 16S rRNA gene amplicon sequencing of DNA extracted from swabs.

Isohelix Buccal swabs can be used to collect surface DNA from environmental sources as well as from buccal samples. Indoor surface samples for Busan City were collected twice per site using Isohelix DNA/RNA buccal swabs (SK-2S, Isohelix) moistened with sterile 1 mL of phosphate-buffered saline. Samples were collected for 3 min from each site in a 100 cm2 area as recommended in a previous study[vi]. The microbiome was analysed based on the 16S rRNA gene.

SK-2S

Samples collected in Korea were analysed alongside comparable samples obtained from previous studies in Boston[vii], Moscow[viii], and Mexico City[ix].

The study showed that the surface bacterial diversities and taxonomic profiling of the studied subway station surface environments were similar. Most of the predominant phylotypes were Gram-positive microorganisms that probably originated from human and outdoor sources.

Summary

The above studies are just a few of the projects that have used Isohelix sample collection and stabilization products to collect samples from research study participants or the environment, for genomic analysis.


CLICK HERE TO READ MORE PUBLICATIONS FEATURING ISOHELIX PRODUCTS

Tell us about how Isohelix products helped your study by emailing us at info@isohelix.com!

References

[i] Lind, Penelope A., et al. “Preliminary results from the Australian Genetics of Bipolar Disorder Study: A nation-wide cohort.” Australian & New Zealand Journal of Psychiatry 57.11 (2023): 1428-1442. https://journals.sagepub.com/doi/epub/10.1177/00048674231195571

[ii] Chu, Annie TW, et al. “The Hong Kong genome project: building genome sequencing capacity and capability for advancing genomic science in Hong Kong.”  J Transl Genet Genom 2023;7:196-212 https://www.oaepublish.com/articles/jtgg.2023.22

[iii] “New Saliva-Prep2 Isolates High Purity Genomic DNA using GeneFixTM Collectors”, Isoghelix Application Note GSPN: January 2019

[iv] Bulik, Cynthia M., et al. “ARFID Genes and Environment (ARFID-GEN): study protocol.” BMC psychiatry 23.1 (2023): 863. https://bmcpsychiatry.biomedcentral.com/articles/10.1186/s12888-023-05266-x

[v] Kim J, Bae S, Park S, Shukla SK, Yoo K. Investigation of Surface Bacterial Diversities and Compositions in the Global Subway Facilities. Atmosphere. 2023; 14(1):140. https://doi.org/10.3390/atmos14010140

[vi] Jansson, L.; Akel, Y.; Eriksson, R.; Lavander, M.; Hedman, J. Impact of swab material on microbial surface sampling. J. Microbiol. Methods 2020

[vii] Hsu, T.; Joice, R.; Vallarino, J.; Abu-Ali, G.; Hartmann, E.M.; Shafquat, A.; DuLong, C.; Baranowski, C.; Gevers, D.; Green, J.L. Urban transit system microbial communities differ by surface type and interaction with humans and the environment. Msystems 2016, 1, e00018-16

[viii] Klimenko, N.S.; Tyakht, A.V.; Toshchakov, S.V.; Shevchenko, M.A.; Korzhenkov, A.A.; Afshinnekoo, E.; Mason, C.E.; Alexeev, D.G. Co-occurrence patterns of bacteria within microbiome of Moscow subway. Comput. Struct. Biotechnol. J. 2020, 18, 314–322

[ix] Hernández, A.M.; Vargas-Robles, D.; Alcaraz, L.D.; Peimbert, M. Station and train surface microbiomes of Mexico City’s metro (subway/underground). Sci. Rep. 2020, 10, 8798

Isohelix launches the SaliFix™ Saliva Swab DNA Collection Kit

Increasing numbers of saliva samples are being collected remotely from study participants for use in genetic testing, so the need for safe, simple and easy to use sample collection, stabilization and transportation is growing rapidly.

Studies have shown that DNA samples from swabs can degrade rapidly without the correct stabilization. SaliFix™ Collectors contain 1ml of preservation reagent that is designed to maintains DNA integrity and yields whilst preventing bacterial growth long term, yet provides easy and easy device for Saliva DNA collection, stabilization, and transport.

SaliFix™ Collectors are specifically designed for collecting Saliva samples in various environment including at home, in clinic or remotely. The foam swabs effectively maximizes saliva collection, even from donors who may find it difficult to produce saliva.

The SaliFix™ kit also includes the SwabCatcher format for improved Sample Handling

The NEW SwabCatcher tube simplifies sample processing and cuts down on cross-contamination as the cap holds the swab tightly after screwing the cap onto the tube. This removed the tedious process choice of having to cut the swab tip and or manually using tweezers to remove the swab prior to processing. This makes the tube ideal for high-throughput processing using automated instruments, and further the tubes are barcoded for easy sample tracking.

SwabCatcher tubes are leakproof and fully transport tested to 95kPa to allow mailing and storage, and the reagents are non-hazardous.

Agarose gel analyzed by electrophoresis. Saliva DNA isolated from SaliFixTM collection devices using the Isohelix Saliva-Prep-2 kit (GSPN-50), shows high quality DNA with no degradation.

DNA collected using SaliFix™ collectors is of high yield and purity, and suitable for all downstream analyses.

Saliva Swab DNA Collection Kit

  • All-in-one saliva DNA collection, stabilization, and transport device.
  • Uses the NEW Swab-Catcher for easy handling and automated-processing.
  • Simple collection at home, in clinic. a viable alternative to blood collection.
  • Instant stabilization maximises DNA yields allowing RT shipping and storage in a non-hazardous format.
  • Optimized for extraction using Isohelix DNA extraction and other kits.

Product Information

SFX/LS/1/50   SaliFix™ saliva collection tubes prefilled with 1ml SaliFix™ buffer and individually wrapped, foam saliva swabs.

Pack of 50 devices

Isohelix launches the ‘SwabCatcher’ Swab DNA/RNA Collection Kit

NEW SwabCatcher tubes are used alongside RapiDri DNA and RNA Swab Kits designed to simplify the swabs transition through sample processing. The Tubes are also available pre-filled with BuccaLyse DNA and RNA stabilization buffer for room temperature shipping.

  • No more Swab retrieval issues
  • Automation, HT and Manual compatible
  • Barcoded for traceability
  • CE-IVD Certified
  • Fully transport tested to 95kPa

Product Information

SwabCapture             L/00/50                        50 x SwabCatcher 5ml collection tubes and caps(empty)

RapiDri                        RD-01                                200 x RapiDri swabs SwabCatcher with drying pouch

BuccaLyse                  BEK/L/05/50                50 x BuccaLyse SwabCatcher collection tubes pre-filled with 0.5ml buffer

BuccalFix                    BFX/L/05/50                50 x BuccalFix SwabCatcher collection tubes pre-filled with 0.5ml buffer

At Isohelix we use our extensive knowledge in product design, regulatory, safety & commercial markets to design products that make it easy for our customers to collect high quality nucleic acid samples from saliva, buccal cells, and stool samples.

10 Top Tips for Working With RNA

Obtaining high-quality RNA is the first step for sensitive downstream applications such as RT-PCR, digital PCR, and RNA-seq. However, this can be tricky, as RNA is fragile and susceptible to both physical degradation and digestion by ubiquitous ribonuclease (RNAse) enzymes.

In this blog, we give you ten top tips to ensure success when working with RNA to help you get the best results from your samples.

1. Use an area of the lab dedicated to working with RNA​

RNases are ubiquitous in the environment and maintain their activity even after autoclaving, so make sure to decontaminate your reagents and equipment before using them. Set aside a separate area for working with RNA away from other work, and use separate pipettes, tips, and other consumables. Ideally, use a UV decontamination cabinet or laminar flow hood to prevent contamination from airborne micro-organisms. Your skin secretes RNases, so wear clean gloves and a clean lab coat and face mask while handling samples.

2. Decontaminate work surfaces and equipment​

Common disinfectants such as 70% Isopropanol may be insufficient for inactivating RNases. Wipe down all work surfaces, and clean pipettes with a 10% household bleach solution (or a commercially available RNAse decontamination solution), followed by wiping down with RNAse-free/DEPC-treated H2O to inactivate potential RNases. Use filtered pipette tips for liquid handling to prevent aerosols and the cross-contamination of samples. Where possible, use sterile, disposable plasticware . If you must use non-disposable plasticware, treat it with 0.1 M NaOH/1 mM EDTA and RNase-free water. Always use molecular biology grade consumables and reagents certified as RNAse/Nuclease free, as lower quality reagents may be contaminated with RNases. ISOHELIX PRODUCTS ARE PRODUCED IN A CLEAN ENVIRONMENT AND ARE CERTIFIED RNAse-FREE

3. Use an RNA stabilization reagent​

RNA collection and analysis from saliva and buccal swab samples is especially challenging, given the high quantities of enzymes in the oral cavity. To overcome this, Isohelix has developed unique, non-toxic RNA stabilization buffers and included them in RNA collection kits, immediately preserving RNA from the moment of collection :

Using an RNA stabilization reagent preserves the integrity of the RNA in your saliva and buccal swab samples during room-temperature storage and shipping.

4. Handle samples carefully

Many RNA extraction kits include guanidium isothiocyanate (GITC) during the lysis stage to denature proteins. However, GITC is a toxic reagent that can potentially react with bleach (sodium hypochlorite) to generate toxic gases.
Xtreme-RNA is free from toxic reagents such as phenol, chloroform, β-mercaptoethanol, & guanidine salts, so it is much safer to handle in the lab.

5. Choose an RNA Extraction Kit optimized for your sample type

Choose the most appropriate kit for your samples and downstream applications. For example, the Isohelix Xtreme-RNA kit is a spin column based RNA purification kit for the swift, simple preparation of total human, viral, or microbial RNA, optimized for extraction from saliva and swab samples. Extracted samples are of high purity (expected A260/280: >1.9), so they are ideal for use in downstream applications such as rt-qPCR, RNAseq and microRNA-seq. The kit is scalable and can accommodate various sample input volumes.

6. Avoid toxic reagents

Many RNA extraction kits include guanidium isothiocyanate (GITC) during the lysis stage to denature proteins. However, GITC is a toxic reagent that can potentially react with bleach (sodium hypochlorite) to generate toxic gases.
Xtreme-RNA is free from toxic reagents such as phenol, chloroform, β-mercaptoethanol, & guanidine salts, so it is much safer to handle in the lab.

7. Be aware of potential gDNA contamination

The similarity in physical and chemical properties of DNA and RNA makes gDNA contamination of isolated RNA a common problem, and non-specific amplification due to gDNA contamination of samples can lead to overestimates of transcript levels using RT-PCR gene expression analysis. Many RT-PCR assays can be designed to be gDNA insensitive using exon-spanning primers, but this is not always possible. If required, DNase digestion can be performed following the final elution of RNA using most commercially available DNAse kits.

8. Accurately quantify your RNA

Before proceeding with downstream applications, assess the quality and quantity of extracted RNA. Use spectrophotometry (e.g., NanoDrop) for concentration determination and electrophoresis or capillary electrophoresis (e.g., Agilent Bioanalyzer) to assess RNA integrity.

9. Work swiftly

RNA in inadequately maintained oral samples can be degraded by intracellular nucleases. Extract RNA as quickly as possible after taking samples, and once begun, work as fast as you can to complete sample purification. Purified samples should always be kept chilled or on ice.

10. Always freeze extracted RNA

Even trace amounts of RNase can degrade RNA in non-frozen samples. Store extracted RNA short-term at -20°C (weeks to months), but in the longer term, store RNA at -80°C (years) as the low temperature will inhibit enzyme activity, preventing sample degradation.

More Info

To find out more about Isohelix’ High Quality Products for Collecting, Stabilizing and Extracting RNA, click here RNA Products | Isohelix

Genomic Analysis with DNA from Saliva instead of blood

Blood samples have traditionally been considered the gold standard DNA source for genomic analysis, but obtaining blood samples is a painful, invasive, and costly procedure that must be performed by qualified personnel.

By contrast, saliva collection is safe and non-invasive, and saliva collection kits can be mailed to donors for self-collection at home. As well as the sample source, how the sample is collected, stabilized, stored, and purified is critical to the quality and quantity of DNA that can be extracted.

Previously, challenges with DNA extracted from saliva included microbial contamination and lower nucleic acid yields. However, there have been significant improvements in devices to collect saliva, and good yields of high-quality DNA can now be extracted

This article discusses the use of DNA extracted from saliva for a wide range of downstream applications

Saliva is much easier and cheaper to collect and transport than blood

Participants in large scale epidemiological studies may be reluctant to provide blood samples due to the need to travel to a health center or the painful nature of giving a sample. Recruitment and compliance rates are much higher when saliva samples are used, as saliva collection is painless and can done at home.

Traditionally blood samples were shipped and stored at -20 degrees before processing, but DNA stabilization reagents are now available for collecting, transporting, and storing whole blood. However, these reagents often contain hazardous substances such as guanidium, so care must be taken while handling them.

Saliva samples require no pre-processing and are commonly collected using non-hazardous reagents, so they can be sent via mail. Saliva collection kits can stabilize DNA at room temperature for over five years, avoiding the high cost and logistical challenges of cold chain transport.

Which cells provide the DNA extracted from saliva and blood samples?

High quality DNA extracted from peripheral blood originates from leukocytes.

Human DNA in saliva originates from epithelial cells or or leukocytes. Unlike DNA derived from blood, saliva samples can include bacterial DNA, allowing DNA extraction from the oral microbiome. If required, qPCR assays can be used to quantify either human or bacterial DNA and measure and normalize saliva DNA samples.

Isohelix estimated the relative quantities of human and microbial DNA found in samples stabilized using their GeneFix reagent, which were then stored at room temperature prior to DNA extraction [i]. Approximately 7.4% of DNA in the samples was found to be of microbial origin. In a follow up study {ii}, GeneFix saliva stability samples that had been stored for up to 48 months at room temperature were tested, and no change in the proportion of bacterial DNA in samples over the stability period was found, demonstrating the GeneFix collectors fully stabilize saliva samples, preserve DNA and prevent microbial growth.

DNA yield from saliva samples is comparable to blood for downstream applications

Figure 1 shows the DNA concentration, yield and purity from 0.5ml raw saliva isolated using the GeneFix Saliva-Prep2 DNA Kit [iii}

In a study comparing DNA extracted from saliva and blood, Looi et al [iv] (2012), the DNA yield from saliva of 7.8 µg/0.5 mL from a manual purification method was comparable to the DNA yield from blood using a salt precipitation method (7.4 µg/0.5 mL blood sample). DNA extracted from saliva and blood were both high purity (A260/280 > 1.70).

Downstream analysis using DNA from saliva

The quality and quantity of DNA required for a study depend on the downstream analysis that will be performed. Below are some recent studies demonstrating the successful use of DNA from saliva extracted using Isohelix kits.  For a more comprehensive list of publications please click here

Whole DNA on 2.2% Agarose FlashGel with 1kb markers

PCR and RT-PCR

DNA extracted from saliva is routinely used for PCR and qRT-PCR and became particularly important during the Covid 19 pandemic.

Some key examples are :

  • Potocka, Natalia, et al. “Association of ACTN3 Polymorphism with Body Somatotype and Cardiorespiratory Fitness in Young Healthy Adults.” International journal of environmental research and public health 16.9 (2019): 1489. https://doi.org/10.3390/ijerph16091489
  • Carter, Nikki, et al. “A novel automated SARS-CoV-2 saliva PCR test protects a global asymptomatic workforce.” Scientific Reports 11.1 (2021): 1-6. https://doi.org/10.1038/s41598-021-92070-w

Genotyping

The accuracy of genotyping with saliva-derived DNA has been reported as comparable to DNA derived from blood [v,vi]

There are many examples in the literature where saliva samples have been used for genotyping :

  • Campos, Adrian I., et al. “Impact of CYP2C19 metaboliser status on SSRI response: a retrospective study of 9500 participants of the Australian Genetics of Depression Study.” The Pharmacogenomics Journal 22.2 (2022): 130-135. https://doi.org/10.1038/s41397-022-00267-7
  • Potocka, Natalia, et al. “Effects of the Trp64Arg Polymorphism in the ADRB3 Gene on Body Composition, Cardiorespiratory Fitness, and Physical Activity in Healthy Adults.” Genes8 (2023): 1541. https://doi.org/10.3390/genes14081541

Next Generation Sequencing

Although the use of blood-derived DNA is the current standard for WGS, Wall et al [vii] reported no differences in sequencing quality or variant call error rate between blood and saliva samples for both whole exome sequencing (WES) and WGS.

There are several examples in the literature of DNA from saliva being used for NGS :

  • Hansen, Marcus Høy, and Charlotte Guldborg Nyvold. “Replicate whole-genome next-generation sequencing data derived from Caucasian donor saliva samples.” Data in Brief 38 (2021): 107349. https://doi.org/10.1016/j.dib.2021.107349
  • Gopinath, Divya, et al. “Salivary bacterial shifts in oral leukoplakia resemble the dysbiotic oral cancer bacteriome.” Journal of oral microbiology 13.1 (2021): 1857998. https://doi.org/10.1080/20002297.2020.1857998

Methylation-based studies

There are some challenges with using DNA extracted from saliva for methylation-based analyses, e.g., cellular heterogeneity in salivary DNA, saliva samples can include bacterial DNA, and saliva samples are fragmented making long-range PCR or long read sequencing difficult [viii].

However, there are several examples in the literature of DNA from saliva being used for methylation studies, e.g., :

  • Ruffell, Simon GD, et al. “Ceremonial Ayahuasca in Amazonian Retreats—Mental Health and Epigenetic Outcomes From a Six-Month Naturalistic Study.” Frontiers in Psychiatry 12 (2021): 898. https://doi.org/10.3389/fpsyt.2021.687615
  • Zhang, Jun, et al. “Exploring Effect of Postdischarge Developmental Support Program on Preterm Infant Neurodevelopment and BDNF Gene DNA Methylation.” Advances in Neonatal Care (2022): 10-1097i 

Summary

Saliva collection is a robust, non-invasive and low cost method of gathering samples that is particularly useful for large-scale epidemiological and other genetic studies where recruitment rates are much higher when saliva samples are used, rather than blood.
Saliva DNA can be used for a wide range of analyses, including PCR, RTPCR, Genotyping Arrays, and Next Generation Sequencing.

References

[i] “Existing Human and Bacterial DNA Content in Human Saliva Samples,”  March 2023

[ii] “Does Bacterial Growth Occur in Isohelix GeneFixTM stabilized Saliva Samples”  Tech Note January 2020

[iii] “New Saliva-Prep2 Isolates High Purity Genomic DNA using GeneFixTM Collectors”, Isoghelix Application Note GSPN: January 2019

[iv] Looi ML, Zakaria H, Osman J, Jamal R. Quantity and quality assessment of DNA extracted from saliva and blood. Clin Lab. 2012;58(3-4):307-12. PMID: 22582505

[v] Genetic epidemiology : Ng DP, Koh D, Choo S, Chia KS. Saliva as a viable alternative source of human genomic DNA in genetic epidemiology. Clin Chim Acta. 2006;367(1–2):81–5.

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