As a city,  Singapore’s main sources of particulate and benzene emission into the air are from industries and motor vehicles. Although our region’s air quality is considered acceptable for most individuals, transboundary smoke haze from land and forest fires in the region also affect Singapore’s air quality from time to time, particularly during the Southwest monsoon period from August to October. 

We all know about these air pollutants from the external environment. But what’s surprising is that the air inside our homes, schools, shopping malls and other indoor places can be even more polluted than the outdoors. 

Let’s name a few below.

Indoor stove cooking can release carbon monoxide, formaldehyde. Air fresheners and household cleaners can release volatile organic compounds. Dust harbors dust mites, pollen and even tiny plastic particles. Whiteboard markers used in classrooms can produce VOC like xylene. And if one uses scented candles and smoke indoors, the level of HAP would be higher. Our own personal skincare that contains solvent like benzene is also an indoor air pollutant.

While we always aim to reduce the exposure of air pollutants through the use of air purifiers, exhaust hood, and non-toxic cleaning agents, we can never avoid them completely. This low air quality can be an issue for vulnerable groups like toddlers, children, elderly and individuals with chronic respiratory issues.

Air pollution is a mixture of particulate matter (PM) and gases. It contains a mixture of organic materials (e.g. pollen, spores and microbial particles) and inorganic materials (e.g. polycyclic aromatic hydrocarbons, sulphates, nitrates, metals, mineral dust and ions) that can come from traffic and industrial emission to windblown soil and road dust. 

Small particulate matter can enter deep into our lungs leading to pollution-induced airway inflammation in more serious cases. Other short-term health impacts include eye, nose, throat and lung irritation, coughing, sneezing, runny nose and shortness of breath.

Our gut is also exposed to air pollutants

Air pollutants not only enter our lungs via inhalation which can eventually lead to them entering the blood circulation by crossing over the epithelial barrier, but also through ingestion of contaminated water and food where our gut is directly exposed to these pollutants.

Through the mucociliary clearance from the lungs and transported to the gut, a large proportion of particles, which do not enter the blood stream via the lungs, might still enter the blood via the GI tract. 

These pollutants do not just irritate our nose and eyes, but with the entry of pollutants into the bloodstream begins the onset of systemic inflammation. Because of the exposure and impacts  of air pollutants on our lungs and gut, more asthma attacks, decreased forced expiratory volume, increased lung infections, appendicitis, IBD, peptic ulcers have been reported.

Damages caused by air pollutants

1. A reduced gut biodiversity and changes in many bacterial gene pathways has been observed in young adults in South California due to air pollutants exposure from whole genome sequencing. This results in the change of gut microbial metabolites produced and gut microbial functionality. Short bouts of air pollution can also already be efficient in changing the gut microbiome as shown in children aged 5 to 12 years old from Beijing with the decline in relative abundance of phylum Firmicutes.
2. Particulate matter itself can cause oxidative stress due to the presence of organic and inorganic ROS and redox-active components. When there is excessive and prolonged air pollutants exposure, the body anti-oxidative defences can be overwhelmed which leads to destruction of cells and tissues in the epithelial of gut and endothelial of lungs.
3. Air pollution has also been found to cause a change in the profile of lipid-mediators and the occurrence of oxidized lipids. A clinical study with healthy adults in China, demonstrated that a two-fold increase in PM2.5 lead to a median increase of oxidized low-density lipoprotein levels. Elevated presence of oxidized lipids has also been associated with oxidative damage to epithelial cells and activation of innate immune cells that drive systemic pro-inflammatory responses.  
4. Air pollutants can perturb the barrier integrity by increasing the availability of inflammatory mediators and ROS, and by affecting gene transcription and expression of tight junction proteins, disrupting the epithelial and endothelial barrier by destabilizing the tight junctions in the GI and lungs
5. The combined effects of air pollution-induced loss of epithelial integrity, increased epithelial permeability, and changes in the mucosal barrier allows disease-causing germs to also enter into the circulation, resulting in the production and systemic release of proinflammatory mediators (TNF-α, IL- 6 and IL-1β) that can contribute to the further loss of barrier function and also induce a systemic inflammation affecting distant organs. 

Image: The association between air pollution exposure and effects in the gut and lungs during all stages of life (Keulers et al., 2022).

PM2.5, being the standard for measuring air pollution level, has been known to induce prooxidant and proinflammatory actions. But PM4.0 impacts have not been studied. Chen et. al. (2019) showed that PM4.0 exposure can lead to inflammatory responses in the lungs and systematic inflammation, resulting in the release of inflammatory cytokines, which can induce lung inflammation through mechanisms that are similar to those for PM2.5.

In this blog, we will be sharing the first study done on PM4.0 amd how kefir peptides have been demonstrated to mitigate the negative impacts.

Kefir grains is associated with broad health benefits as it is a complex of symbiotic components, including lactic acid, acetic bacteria, exopolysaccharide (EPS), and proteins with natural bioactive peptides with a variety of biological activities, such as antimicrobial, immunomodulatory, antiallergenic, antitumoral, antidiabetic, anti-inflammatory, anti-mutagenic activities and anti-oxidative effects. Its benefits aren't just limited to live microbial components. Kefir peptides in this study have been shown to mitigate lung inflammation caused by PM4.0 based on (1) pulmonary inflammation (2) inflammatory mediator expression (3) histopathogical references.

Pulmomary inflammation induced by PM4.0

Data showed that exposure to PM4.0 significantly increased the levels of inflammatory cytokines (IL-1β and TNF-α), in BALF (fluid collected in the airways) and serum, compared to those in the control group. An increase in the relative cell counts of macrophages and neutrophils, a significant increase in the generation of extracellular ROS  (reactive oxygen species) in the pulmonary tissue was observed in the PM4.0-induced groups.

The balance between the production of ROS and the antioxidant defense system, SOD (superoxide dismutase), determines the degree of oxidative stress. PM4.0 decreased the total SOD (superoxide dismutase) defense activity compared to those in the control group.

Inflammatory mediator expression  induced by PM4.0

The expression of NLRP3, p-NF-κB, caspase 1, IL-4 and TNF-α were significantly increased in the PM4.0 groups, without differences between them.

Histopathological changes induced by PM4.0

Mice displayed lung inflammation with pulmonary edema and alveolar infiltration of neutrophils in the PM4.0 groups. Lung histopathology also showed an increase in α-smooth muscle actin (α-SMA) in lung tissues exposed to PM4.0 compared to the control group, suggesting the presence of fibrosis.

Kefir peptides on PM4.0- induced NF-κB activation

Chen et al. (2019) demonstrated that oral consumption of kefir peptides reduce NF-κB activation of inflammation and the amount of PM4.0 particulate depositions in the pulmonary tissues and BALF.  

Kefir peptides on pulmonary inflammation and oxidative status induced by PM4.0

Kefir peptides treatment leads to a significant decrease in ROS, inflammatory cells and cytokines and a significant increase in total SOD (defence mechanism) activity.

Kefir peptides on inflammatory mediator expression induced by PM4.0

Kefir peptides treatment result in a significant decreased p-NF-κB level and p-NF-κB/NF-κB ratio which results in a subsequent drop in NLRP3, caspase-1, IL-1β, IL-6, TNF-α and IL-4 expression

Kefir peptides on histopathological changes induced by PM4.0

While pulmonary edema, alveolar infiltration of neutrophils and lung fibrosis were evident and significant higher levels of α-SMA protein were observed in the PM4.0 exposed group, there are lower amounts of neutrophil infiltration, lung edema and lung fibrosis, including collagen deposition and collagen fibers and decreased α-SMA level post PM4.0 exposure with kefir peptides treatment.

Conclusion

With particulate matter such as PM4.0 disrupting the balance of our gut microbiome which can further lead on to more serious complications and reduced resilience, it is always recommended to seed back the good microbes in balance back to our gut. With the strong co-relationship between gut and lungs, a balanced gut microbiome will aid in the rebalancing of lung microbiome and its health.

Upcoming blog on benzene toxicity and milk kefir

Benzene, a colourless or light yellow liquid chemical at room temperature, is commonly found in motor vehicle exhaust, tobacco smoke and even sunscreens. Many reports demonstrated that benzene presents a powerful inflammatory potential and suggest that this property could be the initial step towards its carcinogenic potential in both humans and animals (Ben Dhia et al., 2021). Because benzene evaporates into the air quickly, it calls for a huge concern as a toxic pollutant. In a study published in 2021, kefir milk has been demonstrated to alleviate immunotoxicity and hematotoxicity induced by exposure to benzene in rats. 

References

1. Ben Dhia, O., Lasram, M. M., Harizi, N., Doghri, R., Charfi, L., Souai, N., Najjari, A., Ouzari, H. I., & Ben-Hadj-Khalifa, S. (2021, April 2). Kefir milk alleviates benzene-induced immunotoxicity and hematotoxicity in rats. Environmental Science and Pollution Research, 28(31), 42230–42242. https://doi.org/10.1007/s11356-021-13569-3.

2. Chen, H.-L., Hung, K.-F., Yen, C.-C., Laio, C.-H., Wang, J.-L., Lan, Y.-W., Chong, K.-Y., Fan, H.-C., & Chen, C.-M. (2019). Kefir peptides alleviate particulate matter <4 μm (pm4.0)-induced pulmonary inflammation by inhibiting the NF-ΚB pathway using luciferase transgenic mice. Scientific Reports, 9(1). https://doi.org/10.1038/s41598-019-47872-4.

3. Keulers, L., Dehghani, A., Knippels, L., Garssen, J., Papadopoulos, N., Folkerts, G., Braber, S., & van Bergenhenegouwen, J. (2022). Probiotics, prebiotics, and synbiotics to prevent or combat air pollution consequences: The gut-lung axis. Environmental Pollution, 302, 119066. https://doi.org/10.1016/j.envpol.2022.119066

4. Salim SY, Kaplan GG, Madsen KL. Air pollution effects on the gut microbiota: a link between exposure and inflammatory disease. Gut Microbes. 2014 Mar-Apr;5(2):215-9. doi: 10.4161/gmic.27251. Epub 2013 Dec 20. PMID: 24637593; PMCID: PMC4063847.

5. Wang X, Hui Y, Zhao L, Hao Y, Guo H, Ren F. Oral administration of Lactobacillus paracasei L9 attenuates PM2.5-induced enhancement of airway hyperresponsiveness and allergic airway response in murine model of asthma. PLoS One. 2017 Feb 15;12(2):e0171721. doi: 10.1371/journal.pone.0171721. PMID: 28199353; PMCID: PMC5310903.