Environmental pollutants and type 2 diabetes: a review of human studies

In vivo glycation-interplay between oxidant and carbonyl stress in bone

Metabolic syndromes (eg, obesity, type 2 diabetes (T2D), atherosclerosis, and neurodegenerative diseases) and aging, they all have a strong component of carbonyl and reductive-oxidative (redox) stress. Reactive carbonyl (RCS) and oxidant (ROS) stress species are commonly generated as products or byproducts of cellular metabolism or are derived from the environment. RCS and ROS can play a dual role in living organisms. Some RCS and ROS function as signaling molecules, which control cellular defenses against biological and environmental assaults. However, due to their high reactivity, RCS and ROS inadvertently interact with different cellular and extracellular components, which can lead to the formation of undesired posttranslational modifications of bone matrix proteins. These are advanced glycation (AGEs) and glycoxidation (AGOEs) end products generated in vivo by non-enzymatic amino-carbonyl reactions. In this review, metabolic processes involved in generation of AGEs and AGOEs within and on protein surfaces including extracellular bone matrix are discussed from the perspective of cellular metabolism and biochemistry of certain metabolic syndromes. The impact of AGEs and AGOEs on some characteristics of mineral is also discussed. Different therapeutic approaches with the potential to prevent the formation of RCS, ROS, and the resulting formation of AGEs and AGOEs driven by these chemicals are also briefly reviewed. These are antioxidants, scavenging agents of reactive species, and newly emerging technologies for the development of synthetic detoxifying systems. Further research in the area of in vivo glycation and glycoxidation should lead to the development of diverse new strategies for halting the progression of metabolic complications before irreversible damage to body tissues materializes.

The aryl hydrocarbon receptor in β-cells mediates the effects of TCDD on glucose homeostasis in mice

OBJECTIVE

Chronic exposure to persistent organic pollutants (POPs) is associated with increased incidence of type 2 diabetes, hyperglycemia, and poor insulin secretion in humans. Dioxins and dioxin-like compounds are a broad class of POPs that exert cellular toxicity through activation of the aryl hydrocarbon receptor (AhR). We previously showed that a single high-dose injection of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD, aka dioxin; 20 μg/kg) in vivo reduced fasted and glucose-stimulated plasma insulin levels for up to 6 weeks in male and female mice. TCDD-exposed male mice were also modestly hypoglycemic and had increased insulin sensitivity, whereas TCDD-exposed females were transiently glucose intolerant. Whether these effects are driven by AhR activation in β-cells requires investigation.

METHODS

We exposed female and male β-cell specific Ahr knockout (βAhrKO) mice and littermate Ins1-Cre genotype controls (βAhrWT) to a single high dose of 20 μg/kg TCDD and tracked the mice for 6 weeks.

RESULTS

Under baseline conditions, deleting AhR from β-cells caused hypoglycemia in female mice, increased insulin secretion ex vivo in female mouse islets, and promoted modest weight gain in male mice. Importantly, high-dose TCDD exposure impaired glucose homeostasis and β-cell function in βAhrWT mice, but these phenotypes were largely abolished in TCDD-exposed βAhrKO mice.

CONCLUSION

Our study demonstrates that AhR signaling in β-cells is important for regulating baseline β-cell function in female mice and energy homeostasis in male mice. We also show that β-cell AhR signaling largely mediates the effects of TCDD on glucose homeostasis in both sexes, suggesting that the effects of TCDD on β-cell function and health are driving metabolic phenotypes in peripheral tissues.

Cellular and molecular effects of fipronil in lipid metabolism of HepG2 and its possible connection to non-alcoholic fatty liver disease

Nonalcoholic fatty liver disease (NAFLD) is a global public health problem that affects more than a quarter of the population. The development of this disease is correlated with metabolic dysfunctions that lead to lipid accumulation in the liver. Pesticides are one of etiologies that support NAFLD establishment. Therefore, the effects of the insecticide fipronil on the lipid metabolism of the human hepatic cell line, HepG2, was investigated, considering its widespread use in field crops and even to control domestic pests. To address the goals of the study, biochemical, cellular, and molecular analyses of different concentrations of fipronil in cell cultures were investigated, after 24 h of incubation. Relevant metabolites such as triglycerides, glucose levels, β-oxidation processes, and gene expression of relevant elements correlated with lipid and metabolism of xenobiotics were investigated. The results suggested that at 20 μM, the pesticide increased the accumulation of triglycerides and neutral lipids by reducing fatty acid oxidation and increasing de novo lipogenesis. In addition, changes were observed in genes that control oxidative stress and the xenobiotic metabolism. Together, the results suggest that the metabolic changes caused by the insecticide fipronil may be deleterious if persistent, favoring the establishment of hepatic steatosis.

Persistent organic pollutants and β-cell toxicity: a comprehensive review

Persistent organic pollutants (POPs) are a diverse family of contaminants that show widespread global dispersion and bioaccumulation. Humans are continuously exposed to POPs through diet, air particles, and household and commercial products; POPs are consistently detected in human tissues, including the pancreas. Epidemiological studies show a modest but consistent correlation between exposure to POPs and increased diabetes risk. The goal of this review is to provide an overview of epidemiological evidence and an in-depth evaluation of the in vivo and in vitro evidence that POPs cause β-cell toxicity. We review evidence for six classes of POPs: dioxins, polychlorinated biphenyls (PCBs), organochlorine pesticides (OCPs), organophosphate pesticides (OPPs), flame retardants, and per- and polyfluoroalkyl substances (PFAS). The available data provide convincing evidence implicating POPs as a contributing factor driving impaired glucose homeostasis, β-cell dysfunction, and altered metabolic and oxidative stress pathways in islets. These findings support epidemiological data showing that POPs increase diabetes risk and emphasize the need to consider the endocrine pancreas in toxicity assessments. Our review also highlights significant gaps in the literature assessing islet-specific endpoints after both in vivo and in vitro POP exposure. In addition, most rodent studies do not consider the impact of biological sex or secondary metabolic stressors in mediating the effects of POPs on glucose homeostasis and β-cell function. We discuss key gaps and limitations that should be assessed in future studies.

Phthalate exposure and risk of diabetes mellitus: Implications from a systematic review and meta-analysis

BACKGROUND

Epidemiologic studies indicated that phthalate exposure might be associated with diabetes mellitus (DM). However, discrepancies existed. The link between phthalate exposure and risk of DM remained unclarified.

METHODS

We conducted a meta-analysis to explore the association between phthalate exposure and risk of DM. Effects of phthalate exposure on insulin resistance were also evaluated by systematic review.

RESULTS

Seven studies involving 12,139 participants were included in this meta-analysis. Our results showed that urinary concentrations of phthalates were positively associated with risk of DM. The pooled ORs were 3.11 (95% CI: 1.16-8.37) for monomethyl phthalate (MMP), 1.27 (95% CI: 1.03-1.56) for mono-n-butyl phthalate (MnBP), 2.59 (95% CI: 1.10-6.10) for mono-isobutyl phthalate (MiBP), 1.99 (95% CI: 1.52-2.61) for mono-(2-ethyl-5-hydroxyhexyl) phthalate (MEHHP), 1.90 (95% CI: 1.40-2.57) for mono-(2-ethyl-5-oxohexyl) phthalate (MEOHP), 1.55 (95% CI: 1.10-2.20) for mono-(2-ethyl-5-carboxypentyl) phthalate (MECPP), and 2.39 (95% CI: 1.18-4.85) for mono-(3-carboxypropyl) phthalate (MCPP), respectively. Molar summation of di-2-ethylhexyl phthalate metabolites (∑DEHP) was also found to be correlated with risk of DM (OR 2.15, 95% CI: 1.48-3.13). No significant association with risk of DM was found regarding monoethyl phthalate (MEP), monobenzyl phthalate (MBzP) and mono(2-ethylhexyl) phthalate (MEHP). In literature review, most studies showed positive correlations of phthalates, especially ∑DEHP, with homeostasis model assessment of insulin resistance and fasting glucose.

CONCLUSION

Exposure to phthalates, especially MMP, MnBP, MiBP, MCPP and DEHP metabolites, might be a risk factor of DM. Our results should be interpreted with caution due to heterogeneous design of enrolled studies.

Human health impacts of exposure to phthalate plasticizers: An overview of reviews

In this review of reviews, we overview the current global body of available evidence from structured reviews of epidemiological studies that explore human health outcomes associated with exposure to phthalates (chemical plasticisers commonly found in plastics). We found robust evidence for an association with lower semen quality, neurodevelopment and risk of childhood asthma, and moderate to robust evidence for impact on anogenital distance in boys. We identified moderate evidence for an association between phthalates/metabolites and low birthweight, endometriosis, decreased testosterone, ADHD, Type 2 diabetes and breast/uterine cancer. There was some evidence for other outcomes including anofourchette distance, fetal sex hormones, pre-term birth, lower antral follicle count, reduced oestrodiol, autism, obesity, thyroid function and hearing disorders. We found no reviews of epidemiological human studies on the impact of phthalates from recycled plastics on human health. We recommend that future research should use urine samples as exposure measures, consider confounders in analyses and measure impacts on female reproductive systems. Our findings align with emerging research indicating that health risks can occur at exposure levels below the "safe dose" levels set out by regulators, and are of particular concern given potential additive or synergistic "cocktail effects" of chemicals. This raises important policy and regulatory issues for identifying and controlling plastics and health related impacts and highlights a need for more research into substances of concern entering plastics waste streams via recycling.

Cytotoxicity and changes in gene expression under aluminium potassium sulfate on Spodoptera frugiperda 9 cells

Aluminium, a substance found in large amounts in nature, has been widely used for various purposes, especially food additives. The effects of long-term and excessive exposure to aluminium on human health are receiving increasing attention. The extensive human use of aluminium food additives can also cause aluminium to enter the ecosystem, where it has significant impacts on insects. This study explored the cytotoxicity and changes in gene expression under aluminium potassium sulfate toward Spodoptera frugiperda 9 cells. We found that high concentrations of aluminium resulted in cell enlargement and cell membrane breakage, decreased cell vitality, and apoptosis. Through RNA-Seq transcriptomics, we found that aluminium ions may inhibit the expression of regulatory-associated protein of mTOR, tdIns-dependent protein kinase-1, and small heat shock proteins (heat shock 70 kDa protein and crystallin alpha B), leading to changes in mTOR-related pathways (such as the longevity regulation pathway and PI3K-Akt signalling pathway), and promoting cell apoptosis. On the other hand, aluminium ions lead to the overexpression of GSH S-transferase, prostaglandin-H2 D-isomerase and pyrimidodiazepine synthase, and induce intracellular oxidative damage, which ultimately affects cell growth and apoptosis through a series of cascade reactions.

Prolonged Low-Dose Dioxin Exposure Impairs Metabolic Adaptability to High-Fat Diet Feeding in Female but Not Male Mice

CONTEXT

Human studies consistently show an association between exposure to persistent organic pollutants, including 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD, aka "dioxin"), and increased diabetes risk. We previously showed that a single high-dose TCDD exposure (20 µg/kg) decreased plasma insulin levels in male and female mice in vivo, but effects on glucose homeostasis were sex-dependent.

OBJECTIVE

The current study assessed whether prolonged exposure to a physiologically relevant low-dose of TCDD impacts glucose homeostasis and/or the islet phenotype in a sex-dependent manner in chow-fed or high-fat diet (HFD)-fed mice.

METHODS

Male and female mice were exposed to 20 ng/kg/d TCDD 2×/week for 12 weeks and simultaneously fed standard chow or a 45% HFD. Glucose homeostasis was assessed by glucose and insulin tolerance tests, and glucose-induced plasma insulin levels were measured in vivo. Histological analysis was performed on pancreas from male and female mice, and islets were isolated from females for TempO-Seq transcriptomic analysis.

RESULTS

Low-dose TCDD exposure did not lead to adverse metabolic consequences in chow-fed male or female mice, or in HFD-fed males. However, TCDD accelerated the onset of HFD-induced hyperglycemia and impaired glucose-induced plasma insulin levels in females. TCDD caused a modest increase in islet area in males but reduced the percent beta cell area within islets in females. TempO-Seq analysis suggested abnormal changes to endocrine and metabolic pathways in female TCDDHFD islets.

CONCLUSION

Our data suggest that prolonged low-dose TCDD exposure has minimal effects on glucose homeostasis and islet morphology in chow-fed male and female mice but promotes maladaptive metabolic responses in HFD-fed females.

The potential ameliorative impacts of cerium oxide nanoparticles against fipronil-induced hepatic steatosis

Fipronil (FIP) is a phenylpyrazole insecticide that is commonly used in agricultural and veterinary fields for controlling a wide range of insects, but it is a strong environmentally toxic substance. Exposure to FIP has been reported to increase the hepatic fat accumulation through altered lipid metabolism, which ultimately can contribute to nonalcoholic fatty liver disease (NAFLD) development. The present study aimed to examine the function of cerium oxide nanoparticles (CeNPs) in protecting against hepatotoxicity and lipogenesis induced by FIP. Twenty-eight male albino rats were classified into four groups: FIP (5 mg/kg/day per os), CTR, CeNPs (35 mg/kg/day p.o.), and FIP + CeNPs (5 (FIP) + 35 (CeNPs) mg/kg/day p.o.) for 28 consecutive days. Serum lipid profiles, hepatic antioxidant parameters and pathology, and mRNA expression of adipocytokines were assessed. The results revealed that FIP increased cholesterol, height-density lipoprotein, triacylglyceride, low-density lipoprotein (LDL-c), and very-low-density lipoprotein (VLDL-c) concentrations. It also increased nitric oxide (NO) and malondialdehyde (MDA) hepatic levels and reduced glutathione peroxidase (GPx) and superoxide dismutase (SOD) enzyme activities. Additionally, FIP up-regulated the fatty acid-binding protein (FABP), acetyl Co-A carboxylase (ACC1), and peroxisome proliferator-activated receptor-alpha (PPAR-α). Immunohistochemically, a strong proliferation of cell nuclear antigen (PCNA), ionized calcium-binding adapter molecule 1 (Iba-1), cyclooxygenase-2 (COX-2) reactions in the endothelial cells of the hepatic sinusoids, and increased expression of caspase3 were observed following FIP intoxication. FIP also caused histological changes in hepatic tissue. The CeNPs counteracted the hepatotoxic effect of FIP exposure. So, this study recorded an ameliorative effect of CeNPs against FIP-induced hepatotoxicity.

Female mice exposed to low doses of dioxin during pregnancy and lactation have increased susceptibility to diet-induced obesity and diabetes

Objective

Exposure to persistent organic pollutants is consistently associated with increased diabetes risk in humans. We investigated the short- and long-term impact of transient low-dose dioxin (2,3,7,8-tetrachlorodibenzo-p-dioxin, TCDD) exposure during pregnancy and lactation on glucose homeostasis and beta cell function in female mice, including their response to a metabolic stressor later in life.

Methods

Female mice were injected with either corn oil (CO; vehicle control) or 20 ng/kg/d TCDD 2x/week throughout mating, pregnancy and lactation, and then tracked for 6–10 weeks after chemical exposure stopped. A subset of CO- and TCDD-exposed dams was then transferred to a 45% high-fat diet (HFD) or remained on a standard chow diet for an additional 11 weeks to assess the long-term effects of TCDD on adaptability to a metabolic stressor. To summarize, female mice were transiently exposed to TCDD and then subsequently tracked beyond when TCDD had been excreted to identify lasting metabolic effects of TCDD exposure.

Results

TCDD-exposed dams were hypoglycemic at birth but otherwise had normal glucose homeostasis during and post-TCDD exposure. However, TCDD-exposed dams on a chow diet were modestly heavier than controls starting 5 weeks after the last TCDD injection, and their weight gain accelerated after transitioning to a HFD. TCDD-exposed dams also had an accelerated onset of hyperglycemia, impaired glucose-induced plasma insulin levels, reduced islet size, increased MAFA^-ve beta cells, and increased proinsulin accumulation following HFD feeding compared to controls. Overall, our study demonstrates that low-dose TCDD exposure during pregnancy has minimal effects on metabolism during the period of active exposure, but has detrimental long-term effects on metabolic adaptability to HFD feeding.

Conclusions

Our study suggests that transient low-dose TCDD exposure in female mice impairs metabolic adaptability to HFD feeding, demonstrating that dioxin exposure may be a contributing factor to obesity and diabetes pathogenesis in females.

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Female mice exposed to TCDD during pregnancy are hypoglycemic at birth.

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TCDD exposure promotes weight gain long after exposure ceases.

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TCDD-exposed dams fed a high-fat diet have accelerated onset of glucose intolerance.

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TCDDHFD dams have defects in islet morphology and beta cell function.

Determination of bisphenol A in barreled drinking water by a SPE-LC-MS method

A quantitative method was established to determine the well-known endocrine disruptor bisphenol A (BPA) in barreled drinking water. Samples were pretreated by solid phase extraction (SPE), and then analyzed by liquid chromatography-mass spectrometry (LC-MS). Working standard solutions were obtained by pretreatment of a series of aqueous standard solutions over the concentration range of 122.9-1190.7 ng L^-1. The linear calibration curve was Y = 69.4X + 2206.2 with the correlation coefficient (R²) of 0.9929. The average recoveries from spiked samples were more than 91.6%. The relative standard deviations (n = 6) were less than 9.6%. The method allowed the detection of 7.0 ng L^-1 BPA in barreled drinking water. Typical barreled drinking water products in the market were detected. As results, thirty-five of fifty-two commercial samples were found to contain BPA with a maximum concentration of 898.7 ng L^-1. The occurrence of BPA in barreled drinking water may be due to the pollution of raw water, the inefficiency of purification processes and the migration of BPA from barrels. The daily exposure of adults to BPA through drinking barreled drinking water is far below the current human tolerable daily intake (TDI) set by European Food Safety Authority (EFSA).

Long-term metabolic consequences of acute dioxin exposure differ between male and female mice

Epidemiological studies have consistently shown an association between exposure to environmental pollutants and diabetes risk in humans. We have previously shown that direct exposure of mouse and human islets (endocrine pancreas) to the highly persistent pollutant TCDD (2,3,7,8-tetrachlorodibenzo-p-dioxin) causes reduced insulin secretion ex vivo. Furthermore, a single high-dose of TCDD (200 µg/kg) suppressed both fasting and glucose-induced plasma insulin levels and promoted beta-cell apoptosis after 7 days in male mice. The current study investigated the longer-term effects of a single high-dose TCDD injection (20 µg/kg) on glucose metabolism and beta cell function in male and female C57Bl/6 mice. TCDD-exposed males displayed modest fasting hypoglycemia for ~4 weeks post-injection, reduced fasting insulin levels for up to 6 weeks, increased insulin sensitivity, decreased beta cell area, and increased delta cell area. TCDD-exposed females also had long-term suppressed basal plasma insulin levels, and abnormal insulin secretion for up to 6 weeks. Unlike males, TCDD did not impact insulin sensitivity or islet composition in females, but did cause transient glucose intolerance 4 weeks post-exposure. Our results show that a single exposure to dioxin can suppress basal insulin levels long-term in both sexes, but effects on glucose homeostasis are sex-dependent.

Urinary concentrations and distribution profiles of 21 phthalate metabolites in pet cats and dogs

Phthalates are widely used in several consumer products, including plastics, toys, cosmetics, and medical devices. Little is known about phthalate exposure in pet animals, however, even though they share an indoor environment with humans; this is the first study to measure such exposure. We measured 21 phthalate monoester metabolites (PhMs) in the urine of pet cats (n = 50) and dogs (n = 50) collected from New York State, USA. PhMs were widely detected in all samples, and 12 of 21 PhMs had detection frequencies (Dfs) >80%. The median urinary concentrations of total PhMs in pet cats and dogs were 630 ng/mL and 186 ng/mL, respectively. Monoethyl phthalate (mEP) was the most abundant compound in both cats and dogs. Phthalic acid (PA; a non-specific metabolite of phthalates) was found at very high concentrations in cats (median: 520 ng/mL). The estimated daily intake (EDI) and hazard quotient (HQ) for major phthalates in pets showed that DEHP exposures in cats and dogs were only 2-fold less than the US Environmental Protection Agency suggested reference dose (RfD) for humans.

Mediation analysis for the relationship between urinary phthalate metabolites and type 2 diabetes via oxidative stress in a population in Jeddah, Saudi Arabia

Human exposure to phthalates is ubiquitous and has received considerable attention due to their association with adverse health outcomes, including type 2 diabetes mellitus (T2DM). Nevertheless, earlier studies that link phthalate exposure to T2DM yielded ambiguous results. Furthermore, studies that associate phthalate exposure with oxidative stress and then with T2DM are scant. In this diabetic case-control study, urine samples collected from 101 individuals aged 28-68 years from Jeddah, Saudi Arabia, were analyzed to determine 20 phthalate metabolites (PhMs) and seven oxidative stress biomarkers (OSBs). Unconditional logistic regression was used to estimate odds ratios for the association between diabetes and urinary PhMs and OSBs in participants, stratified by age, gender, nationality, smoking status, occupation, and urinary creatinine. Twelve PhMs and five OSBs were found at detection rates above 50%, with geometric mean concentrations of 0.61-100 and 0.35-10.7 ng/mL (1.04-171 and 0.61-18.6 μg/g creatinine), respectively. Almost all exposures were significantly higher in diabetic cases than in controls. The 12 PhMs were positively associated with higher urinary concentrations of 8-hydroxy-2'-deoxyguanosine (8-OHdG) and 8-iso-prostaglandin F_2α (8-PGF_2α). Individuals in the 3rd and/or 4th quartile(s) for urinary concentrations of PhMs and OSBs showed 3.7- and 7.3-fold increase, respectively, in the odds of having diabetes compared with those in the 1st quartile. The rank order of association of PhMs/OSBs with diabetes followed the order of: mEP ≈ mBP > mEHP > mCPP > mECPP ≈ mEOHP ≈ mEHHP ≈ mIBP ≈ mMP > mCMHP ≈ mBzP and 8-OHdG > 8-PGF_2α ≈ 15-PGF_2α. The relationship between phthalate exposure and risk of developing T2DM was mediated in part by phthalate-induced oxidative stress, especially 8-OHdG. Our study suggests that human exposure to phthalates is associated with increased oxidative stress which mediates the development of T2DM.

Permethrin and ivermectin modulate lipid metabolism in steatosis-induced HepG2 hepatocyte

Recent studies have reported the positive association between exposure to insecticides and increased risk of obesity and type 2 diabetes, which are closely associated with non-alcoholic fatty liver disease (NAFLD). However, it is not known if insecticide exposure can contribute to NAFLD. Thus, the goal of the current study was to determine if insecticide exposures can exacerbate the physiological conditions of NAFLD by modulating hepatic lipid metabolism. The effects of 12 insecticides on triglycerides (TG) accumulation were tested using palmitic acid (PA)-induced HepG2 hepatoma steatosis model. Results showed that among tested insecticides, permethrin and ivermectin significant interacted with palmitic acid to potentiate (permethrin) or decrease (ivermectin) TG accumulation. Further study showed that permethrin significantly promoted fatty acid synthesis, while suppressed lipid oxidation-related genes only under steatosis conditions. In comparison, ivermectin inhibited lipogenesis-related genes and promoted farnesoid X receptor, which upregulates fatty acid oxidation. Results in this study suggested that hepatic lipid metabolism may be more susceptible to insecticide exposure in the presence of excessive fatty acids, which can be associated with the development of NAFLD.

Permethrin, a pyrethroid insecticide, regulates ERK1/2 activation through membrane depolarization-mediated pathway in HepG2 hepatocytes

Permethrin is a pyrethroid insecticide that acts thru membrane depolarization and is known to disrupt calcium levels in neurons. Disrupted calcium homeostasis is linked to oxidative stress as well as many other cellular mis-functions and permethrin has been reported to disrupt lipid and glucose metabolism in animals and mammalian cell models. It is not known, however, if permethrin influences calcium levels and its associated cellular mechanisms in liver cells. Thus, the goal of the current study was to investigate the mechanisms of permethrin on calcium-mediated cellular signaling pathway, particularly on activation of extracellular signal-related kinase (ERK1/2 or p42/p44) using human hepatocytes, HepG2. The current results showed that permethrin treatment induced oxidative stress and phosphorylation of ERK1/2, which were dependent upon voltage-sensitive sodium channels (VSSC). It was further determined that permethrin-induced ERK1/2 activation was mediated by the metabotropic glutamate receptors (mGluRs)-phosphoinositide phospholipase C (PLC)-protein kinase C (PKC) pathway, but not by changes of intracellular calcium or ER stress-mediated mechanisms.