Postbiotic

Postbiotics - also known as metabiotics, biogenics, or simply metabolites - are soluble factors (metabolic products or byproducts), secreted by live bacteria, or released after bacterial lysis providing physiological benefits to the host.

However, this term is sometimes also used with regards to paraprobiotics - immobilised probiotics, which when ingested, may have the ability to exert positive biological responses and restore intestinal homeostasis in a similar manner to probiotics.Popovic, N., et al, The Influence of Heat-Killed Enterococcus faecium BGPAS1-3 on the Tight Junction Protein Expression and Immune Function in Differentiated Caco-2 Cells Infected With Listeria monocytogenes ATCC 19111. Front Microbiol 2019, 10 pages412
Paraprobiotics are currently being referred to as modified,Zorzela, L., et al., Is there a role for modified probiotics as beneficial microbes: a systematic review of the literature. Benef Microbes, 2017. 8(5): p. 739-754. inactivated, non-viable, para- or ghost probiotics. Probiotics are widely used and accepted in many countries in clinical practice. Paraprobiotics, the immobilised version of probiotics are gaining traction in recent years due to the concerns about the possibility of low tolerance of probiotics, especially in paediatric populations and in severely ill or immunocompromised patients. Pique, N., M. Berlanga, and D. Minana-Galbis, Health Benefits of Heat-Killed (Tyndallized) Probiotics: An Overview. Int J Mol Sci, 2019. 20(10). Paraprobiotics seem to have similar beneficial properties as live probiotics with fewer of the constraints associated with unstable, diminishing bacteria.

Paraprobiotics types

Paraprobiotics could be generated using different methods:
* Heat-inactivation (also includes tyndallisation)
* Ultraviolet-inactivated
* Chemical treatment (e.g. formalin)
* Gamma-irradiation
* Sonication

In most cases heat treatment is considered the method of choice for deactivating probiotic strains. The effect that different types of inactivation have on bacterial structure and components as well as the maintenance of probiotic properties requires further research.{{citation needed, date=November 2019

Mechanism of action

The mechanisms of action for paraprobiotics is less understood, though the possible mechanisms include immune system regulation and interference with pathogen attachment to host cells. Limited research hypothesises that immobilised paraprobiotics release key bacterial components, such as lipoteichoic acids, peptidoglycans, or exopolysaccharides which exhibit key immunomodulating effects and antagonising properties against pathogens.

General paraprobiotics applications

As paraprobiotics are newly emerging, so is the evidence to support the use of paraprobiotics. Emerging clinical and pre-clinical studies have demonstrated that paraprobiotics play a role in general health and well-being and for improving host immune function like that of probiotics.Berni Canani, R., et al., Specific Signatures of the Gut Microbiota and Increased Levels of Butyrate in Children Treated with Fermented Cow's Milk Containing Heat-Killed Lactobacillus paracasei CBA L74. Appl Environ Microbiol, 2017. 83(19)Arai, S., et al., Orally administered heat-killed Lactobacillus paracasei MCC1849 enhances antigen-specific IgA secretion and induces follicular helper T cells in mice. PLoS One, 2018. 13(6): p. e0199018. Komano, Y., et al., Efficacy of heat-killed Lactococcus lactis JCM 5805 on immunity and fatigue during consecutive high intensity exercise in male athletes: a randomized, placebo-controlled, double-blinded trial. J Int Soc Sports Nutr, 2018. 15(1): p. 39. It is paraproulated that paraprobiotics induce changes in the gut microbiome and the altered gut microbial composition is associated with increased levels of innate and acquired immunity biomarkers.Lee, A., et al., Consumption of Dairy Yogurt Containing Lactobacillus paracasei ssp. paracasei, Bifidobacterium animalis ssp. lactis and Heat-Treated Lactobacillus plantarum Improves Immune Function Including Natural Killer Cell Activity. Nutrients, 2017. 9(6). paraprobiotics also seem to exhibit antioxidant effects and has indicated its potential applications in food and pharmaceutical industries. Jang, H.J., et al., Antioxidant effects of live and heat-killed probiotic Lactobacillus plantarum Ln1 isolated from kimchi. J Food Sci Technol, 2018. 55(8): p. 3174-3180.

Paraprobiotics applications in biotherapy

Paraprobiotics (mostly heat-killed) have been evaluated in small study sizes and seem to be beneficial for the following clinical applications:

* Gastrointestinal diseases (bloating, paediatric disorders, infantile colic, diarrhea, extra-intestinal diseases)
* Upper respiratory tract infections
* Ocular disorders including eye fatigueMorita, Y., et al., Effect of Heat-Killed Lactobacillus paracasei KW3110 Ingestion on Ocular Disorders Caused by Visual Display Terminal (VDT) Loads: A Randomized, Double-Blind, Placebo-Controlled Parallel-Group Study. Nutrients, 2018. 10(8).
* There is a growing body of pre-clinical evidence supporting the use of paraprobiotics for the following applications:
* AsthmaLiu, Y.W., et al., Oral administration of heat-inactivated Lactobacillus plantarum K37 modulated airway hyperresponsiveness in ovalbumin-sensitized BALB/c mice. PLoS One, 2014. 9(6): p. e100105.
* Inflammatory bowel diseases (ulcerative colitis)Sang, L.X., et al., Live and heat-killed probiotic: effects on chronic experimental colitis induced by dextran sulfate sodium (DSS) in rats. Int J Clin Exp Med, 2015. 8(11): p. 20072-8. Sang, L.X., et al., Heat-killed VSL#3 ameliorates dextran sulfate sodium (DSS)-induced acute experimental colitis in rats. Int J Mol Sci, 2013. 15(1): p. 15-28.
* Colitis-associated colorectal cancerChung, I.C., et al., Pretreatment with a Heat-Killed Probiotic Modulates the NLRP3 Inflammasome and Attenuates Colitis-Associated Colorectal Cancer in Mice. Nutrients, 2019. 11(3).
* Type 2 Diabetes (improved glycemic parameters)Gao, X., et al., Effect of heat-killed Streptococcus thermophilus on type 2 diabetes rats. PeerJ, 2019. 7: p. e7117.
* Liver injuryChuang, C.H., et al., Heat-Killed Lactobacillus salivarius and Lactobacillus johnsonii Reduce Liver Injury Induced by Alcohol In Vitro and In Vivo. Molecules, 2016. 21(11). Chen, X., et al., Hepatoprotective Effects of Lactobacillus on Carbon Tetrachloride-Induced Acute Liver Injury in Mice. Int J Mol Sci, 2018. 19(8).
* Atopic dermatitisChoi, C.Y., et al., Anti-inflammatory potential of a heat-killed Lactobacillus strain isolated from Kimchi on house dust mite-induced atopic dermatitis in NC/Nga mice. J Appl Microbiol, 2017. 123(2): p. 535-543.
* Influenza virusesPark, S., et al., Effects of heat-killed Lactobacillus plantarum against influenza viruses in mice. J Microbiol, 2018. 56(2): p. 145-149. Jung, Y.J., et al., Heat-killed Lactobacillus casei confers broad protection against influenza A virus primary infection and develops heterosubtypic immunity against future secondary infection. Sci Rep, 2017. 7(1): p. 17360. Kiso, M., et al., Protective efficacy of orally administered, heat-killed Lactobacillus pentosus b240 against influenza A virus. Sci Rep, 2013. 3: p. 1563.
* Cardiac injuryLiao, P.H., et al., Heat-killed Lactobacillus Reuteri GMNL-263 Prevents Epididymal Fat Accumulation and Cardiac Injury in High-Calorie Diet-Fed Rats. Int J Med Sci, 2016. 13(8): p. 569-77.

Species used as paraprobiotics

Many species of bacteria have been identified to have benefits as paraprobiotic strains:

* '' Bifidobacterium breve''
* ''Bifidobacterium infantis''
* ''Bifidobacterium longum''
* ''Enterococcus faecalis''
* ''Lactobacillus acidophilus''
* '' Lactobacillus brevis''Saito, H., et al., Oral administration of heat-killed Lactobacillus brevis SBC8803 elevates the ratio of acyl/des-acyl ghrelin in blood and increases short-term food intake. Benef Microbes, 2019: p. 1-8.
* ''Lactobacillus bulgaricus''
* ''Lactobacillus casei''Saito, Y., et al., Effects of heat-killed Lactobacillus casei subsp. casei 327 intake on defecation in healthy volunteers: a randomized, double-blind, placebo-controlled, parallel-group study. Biosci Microbiota Food Health, 2018. 37(3): p. 59-65.
* '' Lactobacillus delbrueckii subsp. Bulgaricus''Warda, A.K., et al., Heat-killed lactobacilli alter both microbiota composition and behaviour. Behav Brain Res, 2019. 362: p. 213-223.
* '' Lactobacillus fermentum''
* ''Lactobacillus johnsonii''
* ''Lactobacillus paracasei''
* ''Lactobacillus plantarum''
* '' Lactobacillus reuteri''Ting, W.J., et al., Heat Killed Lactobacillus reuteri GMNL-263 Reduces Fibrosis Effects on the Liver and Heart in High Fat Diet-Hamsters via TGF-beta Suppression. Int J Mol Sci, 2015. 16(10): p. 25881-96.
* ''Lactobacillus salivarius''
* ''Lactococcus lactis''
* ''Streptococcus salivarius subsp. thermophilus''

References

Probiotics