Humidifier disinfectant-associated specific diseases should be called together as "humidifier disinfectant syndrome"

Association between humidifier disinfectant use and development of lung cancer: A nested case-cohort study

OBJECTIVE

The outbreak of lung disease among humidifier disinfectants (HDs) users lead to the identification of humidifier disinfectants-associated lung injury (HDLI) cases. Subsequent research highlighted the respiratory health risks associated HDs but the connection to lung cancer remained uncertain. To assess the risk of lung cancer development among individuals exposed to HDs and to investigate the characteristics of HDs exposure influencing the occurrence of lung cancer.

MATERIALS AND METHODS

A cohort study was conducted using the national database, encompassing 7343 claimants exposed to HDs. The study focused on 195 confirmed lung cancer cases, employing the standardized incidence ratio (SIR) for comparisons with the general population, and the odds ratio (OR) using propensity score matching for internal comparisons.

RESULTS

The study found a significantly higher incidence of lung cancer among individuals exposed to HDs compared to the general Korean population, with elevated SIRs observed in both men and women (SIR = 3.43, 95 % CI = 2.81-4.13 for men; SIR = 11.19, 95 % CI = 8.95-13.82 for women). In the propensity score-matched case-control design, a longer duration of HDs use was associated with an increased risk of lung cancer (OR = 2.48, 95 % CI = 1.35-4.56 for using HDs for more than 49 months and OR = 1.02, 95 % CI = 1.01 - 1.03 for every one month).

CONCLUSION

The findings suggest a potential association between HDs exposure and an increased risk of lung cancer.

Polyhexamethylene guanidine phosphate induces epithelial-to-mesenchymal transition and cancer stem cell-like properties via Wnt/β-catenin signaling in human bronchial epithelial cells

Inhalation exposure to polyhexamethylene guanidine phosphate (PHMG-p), a primary component of humidifier disinfectants, has been linked to interstitial lung disease and potential carcinogenic effects. This study aimed to investigate epithelial cell transformation and the underlying molecular mechanisms by examining the properties of epithelial-mesenchymal transition (EMT) and cancer stem cells (CSCs) following prolonged exposure to PHMG-p. Beas-2B human bronchial epithelial cells were treated with 0.125-0.5 µg/ml PHMG-p for over 55 passages, resulting in approximately a 1.2-fold increase in proliferation and a 2-fold enhancement in wound healing, migration, and invasion. Long-term exposure induced morphological changes in Beas-2B, which adopted a spindle-shaped appearance, and displayed enhanced expression of EMT markers, including N-cadherin, Vimentin, Twist, and Snail (approximately 1.5- to 3.5-fold). Culturing these cells in a cancer stem cell medium further confirmed neoplastic transformation and the induction of CSC properties in long-term PHMG-p-treated cells. Additionally, expression levels of CSC phenotypic markers (CD44, CD133, ABCG2, and ALDH1A1) and stemness markers (SOX2, OCT4, Nanog, and KLF4) increased during PHMG-p-induced carcinogenesis. Moreover, increased reactive oxygen species (ROS) production and expression of β-catenin indicated the involvement of these signaling molecules during carcinogenesis. Collectively, our findings suggest that chronic exposure to PHMG-p, even at relatively low concentrations, can induce neoplastic transformation through the acquisition of EMT, stemness, and CSC phenotypes, potentially linked to the endogenous ROS and Wnt/β-catenin signaling pathway.

Longitudinal long term follow up investigation on the carcinogenic impact of polyhexamethylene guanidine phosphate in rat models

Polyhexamethylene guanidine phosphate (PHMG-p) is a major component in humidifier disinfectants, which cause life-threatening lung injuries. However, to our knowledge, no published studies have investigated associations between PHMG-p dose and lung damage severity with long-term follow-up. Therefore, we evaluated longitudinal dose-dependent changes in lung injuries using repeated chest computed tomography (CT). Rats were exposed to low (0.2 mg/kg, n = 10), intermediate (1.0 mg/kg, n = 10), and high (5.0 mg/kg, n = 10) doses of PHMG-p. All rats underwent repeated CT scans after 10 and 40 weeks following the first exposure. All CT images were quantitatively analyzed using commercial software. Inflammation/fibrosis and tumor counts underwent histopathological evaluation. In both radiological and histopathologic results, the lung damage severity increased as the PHMG-p dose increased. Moreover, the number, size, and malignancy of the lung tumors increased as the dose increased. Bronchiolar-alveolar hyperplasia developed in all groups. During follow-up, there was intergroup variation in bronchiolar-alveolar hyperplasia progression, although bronchiolar-alveolar adenomas or carcinomas usually increase in size over time. Thirty-three carcinomas were detected in the high-dose group in two rats. Overall, lung damage from PHMG-p and the number and malignancy of lung tumors were shown to be dose-dependent in a rat model using repeated chest CT scans during a long-term follow-up.

Exposures to humidifier disinfectant and various health conditions in Korean based on personal exposure assessment data of claimants for compensation

BACKGROUND

Humidifier disinfectants (HDs) were commonly used household chemicals to prevent microbial growth in a humidifier water tank in South Korea. A growing body of evidence has indicated that its airborne exposure can induce severe lung injury. However, there has been low awareness of other health outcomes in HD users. This study aimed to evaluate health conditions appealed by claimants for compensation in relation with an increased exposure to HD.

METHODS

From survey data of personal HD exposure assessment of claimants for compensation in Korea, we included a total of 4,179 subjects [cases in each dataset were defined by nine reported health conditions, i.e., pneumonia, asthma, cardiovascular disease, respiratory disease, otorhinolaryngologic disease, brain disease (including cerebrovascular disease), dermatological disease, lung cancer, and all cancers]. HD exposures was considered as the following exposure criteria: exposure duration, exposure proximity, exposure direction, chemical type, cumulative exposure time, indoor air concentration, and cumulative exposure level. Logistic regression models were used to evaluate the associations between HD exposure and health conditions.

RESULTS

After adjusting for sociodemographic and health behavioral factors and other chemical exposures (households, environmental, and occupational exposures), an increase in cumulative HD exposure time was significantly associated with risks of all nine diseases (all p-trends < 0.05). An increase in HD exposure duration was associated with asthma, respiratory disease, otorhinolaryngologic disease, dermatological disease, all cancers, and lung cancer (p-trends < 0.05). Indoor HD concentration was associated with only pneumonia (p-trend = 0.015).

CONCLUSIONS

Our findings suggest that cumulative exposures to airborne HD might potentially increase the risk of various reported health outcomes.

Reduced Diffusing Capacity in Humidifier Disinfectant-Associated Asthma Versus Typical Asthma: A Retrospective Case Control Study

BACKGROUND

Humidifier disinfectant-related lung injury (HDLI) is a severe form of toxic inhalational pulmonary parenchymal damage found in residents of South Korea previously exposed to specific guanidine-based compounds present in humidifier disinfectants (HD). HD-associated asthma (HDA), which is similar to irritant-induced asthma, has been recognized in victims with asthma-like symptoms and is probably caused by airway injury. In this study, diffusing capacity of the lung for carbon monoxide (DL_CO) in individuals with HDA was compared to that in individuals with pre-existing asthma without HD exposure.

METHODS

We retrospectively compared data, including DL_CO values, of 70 patients with HDA with that of 79 patients having pre-existing asthma without any known exposure to HD (controls). Multiple linear regression analysis and logistic regression analysis were performed to confirm the association between HD exposure and DL_CO after controlling for confounding factors. The correlation between DL_CO and several indicators related to HD exposure was evaluated in patients with HDA.

RESULT

The mean DL_CO was significantly lower in the HDA group than in the control group (81.9% vs. 88.6%; P = 0.021). The mean DL_CO of asthma patients with definite HD exposure was significantly lower than that of asthma patients with lesser exposure (P for trend = 0.002). In multivariable regression models, DL_CO in the HDA group decreased by 5.8%, and patients with HDA were 2.1-fold more likely to have a lower DL_CO than the controls. Pathway analysis showed that exposure to HD directly affected DL_CO values and indirectly affected its measurement through a decrease in the forced vital capacity (FVC). Correlation analysis indicated a significant inverse correlation between DL_CO% and cumulative HD exposure time.

CONCLUSION

DL_CO was lower in patients with HDA than in asthma patients without HD exposure, and decreased FVC partially mediated this effect. Therefore, monitoring the DL_CO may be useful for early diagnosis of HDA in patients with asthma symptoms and history of HD exposure.

Health Effects Associated With Humidifier Disinfectant Use: A Systematic Review for Exploration

BACKGROUND

It has been 10 years since the outbreak of lung disease caused by humidifier disinfectants in Korea, but the health effects have not yet been summarized. Therefore, this study aims to systematically examine the health effects of humidifier disinfectants that have been discovered so far.

METHODS

All literature with humidifier disinfectants and their representative components as the main words were collected based on the web, including PubMed, Research Information Sharing Service, and government publication reports. A total of 902 studies were searched, of which 196 were selected. They were divided into four groups: published human studies (group 1), published animal and cytotoxicology studies (group 2), technical reports (group 3), and gray literature (group 4).

RESULTS

Out of the 196 studies, 97 (49.5%) were published in peer-reviewed journals as original research. Group 1 consisted of 49 articles (50.5%), while group 2 consisted of 48 articles (49.5%). Overall, respiratory diseases such as humidifier disinfectant associated lung injury, interstitial lung disease, and asthma have a clear correlation, but other effects such as liver, heart, thymus, thyroid, fetal growth, metabolic abnormalities, and eyes are observed in toxicological experimental studies, but have not yet been identified in epidemiologic studies.

CONCLUSION

The current level of evidence does not completely rule out the effects of humidifier disinfectants on extrapulmonary disease. Based on the toxicological evidence so far, it is required to monitor the population of humidifier disinfectant exposure continuously to see if similar damage occurs.

Assessment of agonistic and antagonistic properties of humidifier disinfectants to the estrogenic and androgenic receptors by transactivation assay

Before being recalled and banned from the Korean market, humidifier disinfectants (HDs) were added to the humidifier water tank to prevent microbial growth. The known HDs active ingredients included the are oligo(2-(2-ethoxy)ethoxyethyl guanidine (PGH), polyhexamethylene guanidine (PHMG), a mixture of methylisothiazolinone (MIT) and chloromethylisothiazolinone (CMIT), didecyldimethyl ammonium chloride (DDAC), Sodium dichloroisocyanurate (NaDCC), and alkyldimethylbenzyl ammonium chloride (BAC). Previous epidemiological studies have suggested that PHMG induces fatal lung disease in pregnant, post-partum women, and young children. In an animal study, a mixture of DDAC and BAC exhibited decreased fertility and fecundity; increased time to first litter, longer pregnancy intervals, fewer pups per litter, and fewer pregnancies. In this study, endocrine-disrupting effects of HDs were investigated using estrogen receptor (ER) and androgen receptor (AR) transactivation assay based on OECD Test guidelines. Unexpectedly, unlike the previously reported reproductive toxicity data, in the present study, HDs did not show ER and AR transcriptional activation agonist and/or antagonist effects. However, it is difficult to conclude that HDs has no endocrine disruption effects, and further research on the effects of HDs mixtures, and in vivo tests including Uterotrophic bioassay and Hershberger bioassay would be necessary.

Need for individual-based evaluation to determine the association between humidifier disinfectants and health injuries

Background

Injuries caused by humidifier disinfectants (HDs) can no longer be grouped under the concept of HD lung injury. Focusing on individual cases, we were able to evaluate the relevance not only of diseases for which epidemiological correlation is recognized but also all diseases and symptoms that the victims complain of.

Methods

In-depth interviews and reassessment of 113 HD-exposed patients who had not been acknowledged as victims by the government were conducted, and their medical records were reviewed. Based on these processes, an assessment questionnaire for the injuries related to HDs was completed and the involvement of HDs was assessed either as “strong association,” “association,” or “no association.”

Results

In this study, of the 113 patients included who claimed damages, 78 (69.0%) had HD-related injuries. Among the cases of 22 patients who applied for injury acknowledgment due to upper respiratory inflammation that was not included among the acknowledged diseases, 17 (77.3%) were judged to be HD-related injuries (strong association vs. association: 10 [45.5%] vs. 7 [31.8%]). When the cases of 12 rhinitis patients were reassessed, 9 were HD-related injuries (strong association vs. association: 4 [33.3%] vs. 5 [41.7%]). When the cases of 18 asthma patients unacknowledged as a victim were reassessed, 17 (94.4%) were humidifier-related injuries (strong association vs. association: 12 [66.6%] vs. 5 [27.8%]). Among 4 interstitial lung disease patients unacknowledged as a victim, 2 (50.0%) were HD-related injuries.

Conclusions

HD-related health injuries should be assessed through both individual interviews and detailed chart reviews for more accurate injury acknowledgment. In the future, efforts should go beyond existing methods based on the adherence to acknowledgment criteria to directly listen to the victims.

A comprehensive study of deaths due to exposure to humidifier disinfectant in Korea: focusing on medical records, assessment of exposure to humidifier disinfectants, and causes of death

OBJECTIVES

We aimed to determine the characteristics of the deceased victims of deaths caused by exposure to humidifier disinfectants, and present the distribution of the victims’ data submitted for damage application, demographic characteristics, imaging findings, characteristics of humidifier disinfectant exposure, and distribution of the causes of death.

METHODS

An integrated database of victims was established using the medical records data of 1,413 victims submitted during the application for death damage caused by exposure to humidifier disinfectants, and the demographic characteristics, medical records, imaging findings, exposure characteristics, and cause of death were examined.

RESULTS

The average numbers of data submissions of each applicant for death damage were 3.0 medical use records. A total of 608 (43.0%) victims had more than one finding of acute, subacute, or chronic interstitial lung diseases. The average daily and cumulative use times of the victims were 14.40 and 24,645.81 hours, respectively, indicating greater exposure in this group than in the survivors. The humidifier disinfectants’ components comprised polyhexamethylene guanidine (72.8%), chloromethylisothiazolinone/methylisothiazolinone (10.5%), other components (15.0%), and oligo-[2-(2-ethoxy)-ethoxyethyl] guanidine chloride (1.5%). The components’ distribution was 67.8% for single-component use, which was higher than that in the survivors (59.8%). The distribution of the causes of death were: respiratory diseases (54.4%), neoplasms (16.8%), and circulatory diseases (6.3%). Other interstitial lung diseases (65.5%) were the most common cause of death among those who died due to respiratory diseases.

CONCLUSIONS

Careful discussions of appropriate remedies should be conducted based on a comprehensive understanding of the characteristics of the deceased victims, considering their specificities and limitations.

Evaluation of the long-term effect of polyhexamethylene guanidine phosphate in a rat lung model using conventional chest computed tomography with histopathologic analysis

There have been no studies on the effects of polyhexamethylene guanidine phosphate (PHMG) after a long period of exposure in the rodent model. We aimed to evaluate long-term lung damage after PHMG exposure using conventional chest computed tomography (CT) and histopathologic analysis in a rat model. A PHMG solution was intratracheally administrated to 24 male rats. At 8, 26, and 52 weeks after PHMG instillation, conventional chest CT was performed in all rats and both lungs were extracted for histopathologic evaluation. At 52 weeks after PHMG instillation, four carcinomas had developed in three of the eight rats (37.5%). Bronchiolo-alveolar hyperplasia and adenoma were found in rats at 8, 26, and 52 weeks post-instillation. The number of bronchiolo-alveolar hyperplasia significantly increased over time (P-value for trend< 0.001). The severity of lung fibrosis and fibrosis scores significantly increased over time (P-values for trend = 0.002 and 0.023, respectively). Conventional chest CT analysis showed that bronchiectasis and linear density scores suggestive of fibrosis significantly increased over time (P-value for trend < 0.001). Our study revealed that one instillation of PHMG in a rat model resulted in lung carcinomas and progressive and irreversible fibrosis one year later based on conventional chest CT and histopathologic analysis. PHMG may be a lung carcinogen in the rat model.

Fibrosis as a result of polyhexamethylene guanide exposure in cultured Statens Seruminstitut Rabbit Cornea (SIRC) cells

Previous research studies on the toxicity of polyhexamethylene guanidine (PHMG) as a humidifier disinfectant majorly focused on lung fibrosis. Considering that disinfectants in humidifiers are released in aerosol form, the eyes are directly exposed and highly vulnerable to the detrimental effects of the PHMG. Therefore, in the present study we investigated the adverse effects of PHMG on the eyes; considering fibrosis as a manifestation of PHMG toxicity in the eye, we evaluated fibrosis-related biomarkers in cultured Statens Seruminstitut Rabbit Cornea (SIRC) cells. Cell viability was measured using 3-(4,5-dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide (MTT) assay, fibrosis-related biomarkers were evaluated through polymerase chain reaction (PCR) and immunoblotting, and oxidative stress was evaluated using 2',7'-dichlorodihydrofluorescein diacetate (H2DCFDA). Polyhexamethylene guanidine showed cytotoxicity in a time and concentration-dependent manner. Fibrosis related biomarkers including transforming growth factor-β (TGF-β), α-smooth muscle actin (α-SMA), matrix metalloproteinase (MMP), tissue inhibitor of metalloproteinase (TIMP) and hemeoxygenase-1 (HO-1) increased in both gene and protein levels. Oxidative stress also increased in the PHMG-treated cultured cells. The findings of the present study suggest that PHMG could cause toxicity in the eye as manifested by fibrosis.

Different Characteristics of Childhood Asthma Related to Polyhexamethylene Guanidine Hydrochloride (PHMG) Exposure

RATIONALE

Exposure to humidifier disinfectants (HDs) can increase the risk of asthma but the characteristics of HD-related asthma are currently unclear. Polyhexamethylene guanidine hydrochloride (PHMG)-containing HD was the most commonly used and the most frequently associated with HD-associated lung injury.

OBJECTIVES

To investigate the characteristics of PHMG-induced asthma.

METHODS

This general population-based birth cohort study utilized data from the Panel Study of Korean Children from 2008 (n = 846). Spirometry, bronchial provocation tests, detailed history recording, and physical examinations were performed on seven-year-old patients (n=362). Exploratory analysis of plasma proteomics was performed.

RESULTS

Compared with healthy control, FEV1 was the lowest in PHMG-exposed asthma group. (z score = -0.806; 95% CI, -1.492 to -0.119) The positive rate of bronchial hyperresponsiveness was lower in children with PHMG-exposed asthma compared to children with asthma without HD exposure (13.3% vs. 47.4%). Long-term exposure to low-intensity PHMG before age three was associated with asthma symptoms. Periostin was higher in asthma without HD exposure compared to the healthy control. The inducible T cell costimulator ligand and hepatocyte growth factor activator were lower in PHMG-exposed asthma compared to asthma without exposure. Hepatocyte growth factor activator a positive correlation with FVC (z-score) in asthma with PHMG exposure (r=0.78, P<0.01).

CONCLUSIONS

The asthma associated with low intensity exposure to PHMG is characterized by lower lung function, lower positive rates of bronchial hyperresponsiveness, and varied distributions of plasma proteins. These findings suggest that asthma related to PHMG exposure may constitute a different mechanism of asthma pathophysiology.

Comparison of Long Term Follow-up Chest CT Imaging in Adult and Pediatric Patients with Humidifier Disinfectant-related Lung Injury

BACKGROUND

To compare the chest computed tomography (CT) images of children and adults in families with clusters of humidifier disinfectant-related lung injury (HDLI) after cessation of exposure to humidifier disinfectant (HD).

METHODS

We reviewed medical records of 19 families with 43 patients (21 adults, 22 children) among families, which had at least one adult and one child with HDLI. Each family was exposed to the same HD exposure environment.

RESULTS

In adults, centrilobular nodules were predominant (95.2%) in chronic HDLI findings after cessation of exposure to HD, however, in children, normal pattern was most prevalent on chest CT (45.5%), followed by centrilobular nodule (36.4%), bizarre lung cysts (36.4%), and reticulation (13.6%).

CONCLUSION

Unlike the known chronic HDLI finding of adults, centrilobular nodules were only present in 36.4% of children. The frequency of bizarre lung cysts were significantly greater in children than that in adults after cessation of similar exposure to HD. Thus, bizarre lung cysts may be useful as another novel finding of chronic HDLI in children who have no history of pulmonary infection or other perinatal disorder such as hyaline membrane disease or other interstitial lung disease.

Formation of lamellar body-like structure may be an initiator of didecyldimethylammonium chloride-induced toxic response

Due to the pandemic of coronavirus disease 2019, the use of disinfectants is rapidly increasing worldwide. Didecyldimethylammonium chloride (DDAC) is an EPA-registered disinfectant, it was also a component in humidifier disinfectants that had caused idiopathic pulmonary diseases in Korea. In this study, we identified the possible pulmonary toxic response and mechanism using human bronchial epithelial (BEAS-2B) cells and mice. First, cell viability decreased sharply at a 4 μg/mL of concentration. The volume of intracellular organelles and the ROS level reduced, leading to the formation of apoptotic bodies and an increase of the LDH release. Secretion of pro-inflammatory cytokines (IL-1β, IL-6, and TNF-α) and matrix metalloproteinase-1 also significantly increased. More importantly, lamellar body-like structures were formed in both the cells and mice exposed to DDAC, and the expression of both the indicator proteins for lamellar body (ABCA3 and Rab11a) and surfactant proteins (A, B, and D) was clearly enhanced. In addition, chronic fibrotic pulmonary lesions were notably observed in mice instilled twice (weekly) with DDAC (500 μg), ultimately resulting in death. Taken together, we suggest that disruption of pulmonary surfactant homeostasis may contribute to DDAC-induced cell death and subsequent pathophysiology and that the formation of lamellar body-like structures may play a role as the trigger. In addition, we propose that the cause of sudden death of mice exposed to DDAC should be clearly elucidated for the safe application of DDAC.

Mitochondria disease due to humidifier disinfectants: diagnostic criteria and its evidences

Humidifier disinfectant damages caused by the misuse of humidifier disinfects, such as polyhexamethylene guanidine (PHMG), resulted in chemical disasters in South Korea in 2011. About four million people were exposed to humidifier disinfectants (HDs) in the 17 years between 1994 and 2011. Although fatal lung damage was initially reported, investigations into the victims’ injuries revealed that the damage was not limited to the lungs, but that systemic damage was also confirmed. Considering the spread of HD from the lungs to the whole body, the toxic effects of PHMG from reactive oxygen species (ROS), NOTCH signaling pathways, and mitochondrial dysfunction resulted in endothelial damage in the lungs, blood vessels, liver, kidneys, bone marrow, nerves, and muscles. The main toxic mechanisms involved in HD damage may be the NOTCH pathway and mitochondrial damage. There are many case reports which include neurologic disorders (ADHD, depression, posttraumatic stress disorder), muscular disorder (exercise intolerance, myalgia), energy metabolism disorder (chronic fatigue syndrome), and immunologic disorder (rheumatoid arthritis) in HDs victims. These case reports involve multi-system involvement in HDs victims. Further well-designed study is needed to clarify whether mitochondrial dysfunction is associated with multi-organs involvement in HDs victims.

Eye irritation tests of polyhexamethylene guanidine phosphate (PHMG) and chloromethylisothiazolinone/methylisothiazolinone (CMIT/MIT) using a tissue model of reconstructed human cornea-like epithelium

Disinfectants including polyhexamethylene guanidine phosphate (PHMG) and mixtures of chloromethylisothiazolinone/ methylisothiazolinone (CMIT/MIT) have been widely used in Korea to prevent microbial growth in the humidifier water, which triggered an outbreak of serious respiratory diseases. In addition to the respiratory syndrome, disease-related symptoms including liver toxicity, asthma, and skin allergies were also found after extensive survey of people exposed to the humidifier disinfectants (HDs). In this study, eye irritation tests were performed based on the Organization for economic co-operation and development (OECD) test guidelines 492 using EpiOcularTM which is a tissue model of reconstructed human cornea-like epithelium. As results, the raw materials of PHMG (26% as active ingredient) and CMIT/MIT (1.5% as active ingredient) were classified under UN globally harmonized system of classification and labeling of chemical (GHS) category 1 or category 2. However, aqueous dilutions of raw materials such as market products of HDs that contain 0.13% of PHMG and 0.03% of CMIT/MIT or further dilutions of the market products for humidifier that contain 0.0013% of PHMG and 0.0003% of CMIT/MIT were classified under any category, which suggested absence of eye irritation at the test concentration.