Toxicokinetic study of pyrrole adducts and its potential application for biological monitoring of 2,5-hexanedione subacute exposure

Protein pyrrole adducts are associated with elevated glucose indices and clinical features of diabetic diffuse neuropathies

INTRODUCTION

Diabetic neuropathy is the most prevalent complication of diabetes mellitus. Although the precise etiology of this neurological disorder has yet to be defined, elevated blood glucose promotes anerobic glycolysis; this produces excess advanced glycation end-products, many of which have a pyrrole structure. Here, we test the hypothesis that protein pyrrole adducts are associated with elevated glucose indices and some clinical features of diabetic diffuse neuropathies.

METHOD

We investigated the levels of plasma pyrrole adducts and adjusted urinary pyrrole adducts in a group of elderly persons (n = 516, age 60-79) residing in the District of Luohu, Shenzhen, China between 2017 and 2018. Symptoms of distal symmetric polyneuropathy (DSPN) and resting heart rate, a measure of autonomic nervous system function, were collected from participants (n = 258) with elevated glucose indices.

RESULT

Protein pyrrole adducts showed a strong correlation with glucose indices before and after adjustment for age and estimated glomerular filtration rates. Stratified analysis showed that the medians and interquartile values of pyrrole adducts grew as glucose indices of the subgroups increased. Participants with symptoms of DSPN and sinus tachycardia presented elevated levels of plasma pyrrole adducts.

CONCLUSION

This study provides a novel link between glucose indices and the etiology of diabetic diffuse neuropathies.

No-observed-adverse-effect level of hair pyrrole adducts in chronic n-hexane intoxication in rats

n-Hexane has been reported to induce serious peripheral neuropathy in workers. Pyrrole adducts are the unique reaction products of n-hexane in organisms and have been demonstrated to be critical to n-hexane neuropathy. Our previous studies have demonstrated that pyrrole adducts could accumulate in hair and showed high correlation with neuropathy at the end of experiments in rat models. In the present study, we examined the time course of hair pyrrole adducts and behavioral changes in rats exposed to different dosages of n-hexane in both treatment (24 weeks) and recovery phases. Our results showed: 1. After treatment, 1.0, 2.0, and 4.0 g/kg dosage groups all lost weight, but the 0.5 g/kg dosage group showed no impairment; after recovery, all impaired rats regained weight. 2. After treatment, 1.0, 2.0, and 4.0 g/kg dosage groups all showed a rise in gait scores, decreased rotarod latency, and decreased motor nerve conduction velocity, whereas the 0.5 g/kg dosage group showed no impairment; after recovery, all impaired rats were completely rehabilitated. 3. After treatment, levels of pyrrole adducts in serum, urine, and hair of experimental groups increased; after recovery, serum and urine pyrrole adducts showed no difference from the control (P > 0.05), whereas hair pyrrole adducts were significantly different from the control (P < 0.01). 4. The half-lives of serum and urine pyrrole adducts were 47.8-78.0 h and 42.7-52.9 h, while the half-life of hair pyrrole adducts was 14-24 weeks. 5. During treatment and recovery, levels of serum, urine, and hair pyrrole adducts showed high correlation with gait scores (P < 0.01), and hair pyrrole adducts had the largest partial correlation coefficient. In conclusion, hair pyrrole adducts could serve as a stable and reliable biomarker for the prevention of n-hexane intoxication. Furthermore, the no-observed-adverse-effect level of hair pyrrole adducts in rats is 275.2 ± 61.5 nmol/g protein. Further studies are required for the definition of the biological exposure limit in humans.

Diallyl sulfide-induced attenuation of n-hexane-induced peripheral nerve impairment is associated with metabolic inhibition of n-hexane

Chronic exposure to n-hexane could induced serious peripheral nerve impairments. It has been well documented that the metabolic activation from n-hexane to 2,5-hexanedione (2,5-HD) is vital in the pathogenesis. Diallyl sulfide (DAS) is an extract of garlic and able to block the bioactivation of xenobiotic. The current study was designed to investigate whether DAS can attenuate n-hexane induced neuropathy. Male Wistar rats were pretreated with DAS (50 or 100 mg/kg.bw) and then n-hexane (3 g/kg.bw) for 7 weeks. Behavioral performance, biomarker measurement and toxicokinetic studies were performed. Enzymatic methods and western blotting analyses were also conducted to investigate the hepatic phase I enzymes (including cytochrome P450(CYP)2E1, CYP1A1 and CYP2B1) and phase II enzymes (including glutathione S transferase theta 1 (GSTT1) and NA(D)PH dehydrogenase quinone 1 (NQO1)). The results showed that DAS improved the behavioral performance while reducing the toxic metabolite: 2,5-HD and pyrrole adducts. Besides, DAS reduced the expression of CYP2E1 with a proportional decrease in activity, which largely decreased the bioactivation of n-hexane in vivo. The results suggested that DAS decreased the toxic metabolites of n-hexane to attenuate n-hexane-induced peripheral neuropathy.

Pyrrole adducts in globin and plasma of workers exposed to hexane

OBJECTIVES

Urinary excretion of 2,5-hexanedione is currently used to estimate the exposure levels of hexane occurring to an individual during the previous work shift. However, because hexane exposures and urinary 2,5-hexanedione levels can vary considerably from day to day, and subchronic to chronic exposures to hexane are required to produce neuropathy, this biomarker may not accurately reflect the risk of an individual for developing hexane neuropathy. This investigation examines the potential of hexane-derived pyrrole adducts produced on globin and plasma proteins as markers for integrating cumulative exposures. Because the pyrrole markers incorporate bioactivation of hexane to 2,5-hexandione and the initial step of protein adduction involved in hexane-induced neuropathy, they potentially can serve as biomarkers of effect through reflecting pathogenetic events within the nervous system. Additionally, pyrrole formation is an irreversible reaction suggesting that hexane-derived protein pyrroles can be used to assess cumulative exposures to provide a better characterization of individual susceptibilities.

METHODS

To examine the utility of the proposed markers, blood samples were obtained from eleven workers who used hexane for granulating metal powders in a slurry to produce metal machining die tools and four non-exposed volunteers. Globin and plasma were isolated, and the proteins were digested using pepsin, reacted with Ehrlich's reagent and the level of pyrrole adducts were determined by absorbance at 530 nm. To determine the dose-response curve and dynamic range of the assay, erythrocytes were incubated with a range of 2,5-hexanedione concentrations and the net absorbance at 530 nm of isolated globin was measured.

RESULTS

Pyrrole was detected in both the globin and plasma samples of the workers exposed to hexane and the levels of pyrroles in plasma were positively correlated with the levels of pyrroles in globin for most of the workers.

CONCLUSIONS

This investigation demonstrates that detectable levels of hexane-derived protein pyrrole adducts are produced on peripheral proteins following occupational exposures to hexane and supports the utility of measuring pyrroles for integrating cumulative exposures to hexane.

Hair pyrrole adducts serve as biomarkers for peripheral nerve impairment induced by 2,5-hexanedione and n-hexane in rats

Pyrrole adducts are specific reaction products of 2,5-hexadione (2,5-HD) in vivo and are considered highly relevant to the pathogenesis of peripheral nerve impairments after exposure to n-hexane, though the exact mechanism remains unclear. In this study, 40 male Wistar rats were randomly divided into three experimental groups and one control group, in which all rat’s hair were shaved completely at the beginning. The rats in three experimental groups were treated with 2,5-HD by gavage at dosages of 100, 200 and 300 mg/kg per day respectively, six times per week for 8 weeks. Abnormality of gait and changes in the rota-rod latency were surveilled. Pyrrole adducts in hair, urine and serum of all rats were measured at the endpoint. Results showed that the increased pyrrole adducts in hair, urine and serum accumulated in dose-response relationship. Spearman’s correlation analysis between pyrrole adducts and gait scores showed that hair pyrrole adducts were highly relevant to the gait scores. Moreover, we treated rats with n-hexane and succeed to verify the results aforesaid. Further, multiply linear regression analysis showed that hair pyrrole adducts have higher partial correlation coefficients than these in serum and urine in both 2,5-HD and n-hexane treated models. Our findings draw the conclusion that the hair pyrrole adducts might serve as a promising biomarker of n-hexane induced peripheral neuropathy.

2,5-hexanedione induced apoptosis of rat bone marrow mesenchymal stem cells by reactive oxygen species

Objectives:

n-Hexane, a common industrial organic solvent, causes multiple organ damage, especially neurotoxicity, which is proved to be caused by its metabolite 2,5-hexanedione (2,5-HD). We previously showed that 2,5-HD induced apoptosis of rat bone marrow mesenchymal stem cells (BMSCs). In the current study, we explored the mechanism of 2,5-HD-induced apoptosis, especially the role played by reactive oxygen species (ROS).

Methods:

Intracellular ROS levels after 2,5-HD treatment were measured by the dichloro-dihydro-fluorescein diacetate (DCFH-DA) method, and the antioxidant N-acetyl cysteine (NAC) was used to scavenge ROS. Apoptosis, mitochondrial membrane potential (MMP), and caspase-3 activity were measured after 2,5-HD exposure with or without NAC pretreatment.

Results:

In rat BMSCs, 20 mM 2,5-HD significantly increased ROS levels and apoptosis. In addition, MMP activity was decreased and caspase-3 activity was increased. With NAC pretreatment, ROS increases were prevented, cells were rescued from apoptosis, and both MMP and caspase-3 activity returned to normal levels. Western blotting analysis of malondialdehyde-modified proteins and superoxide dismutase (SOD) 1 showed that after 2,5-HD exposure, BMSCs had oxidative damage and abnormal SOD1 expression. These returned to normal when cells were pretreated with NAC in addition to 20 mM 2,5-HD. Furthermore, the expressions of NF-κB p65/RelA and phospho-NF-κB p65/RelA (Ser536) were suppressed after 2,5-HD exposure and restored by NAC pretreatment.

Conclusions:

2,5-HD-induced apoptosis in rat BMSCs is potentially mediated by excessive ROS production.