Protective Effects of Arachidonic Acid Against Paraquat-Induced Pulmonary Injury

Deuterated Arachidonic Acid Ameliorates Lipopolysaccharide-Induced Lung Damage in Mice

Arachidonic acid (ARA) is a major component of lipid bilayers as well as the key substrate for the eicosanoid cascades. ARA is readily oxidized, and its non-enzymatic and enzymatic oxidation products induce inflammatory responses in nearly all tissues, including lung tissues. Deuteration at bis-allylic positions substantially decreases the overall rate of ARA oxidation when hydrogen abstraction is an initiating event. To compare the effects of dosing of arachidonic acid (H-ARA) and its bis-allylic hexadeuterated form (D-ARA) on lungs in conventionally healthy mice and in an acute lung injury model, mice were dosed with H-ARA or D-ARA for six weeks through dietary supplementation and then challenged with intranasal lipopolysaccharide (LPS) for subsequent analysis of bronchoalveolar lavage fluid and lung tissue. Dosing on D-ARA resulted in successful incorporation of D-ARA into various tissues. D-ARA significantly reduced LPS-induced adverse effects on alveolar septal thickness and the bronchoalveolar area. Oral deuterated ARA is taken up efficiently and protects against adverse LPS-induced pathology. This suggests novel therapeutic avenues for reducing lung damage during severe infections and other pathological conditions with inflammation in the pulmonary system and other inflammatory diseases.

The herbicide paraquat-induced molecular mechanisms in the development of acute lung injury and lung fibrosis

The herbicide paraquat (PQ; 1,1'-dimethyl-4,4'-bipyridylium dichloride) is a highly toxic organic heterocyclic herbicide that has been widely used in agricultural settings. Since its commercial introduction in the early 1960s, numerous cases of fatal PQ poisonings attributed to accidental and/or intentional ingestion of PQ concentrated formulations have been reported. The clinical manifestations of the respiratory system during the acute phase of PQ poisoning mainly include acute lung injury (ALI)/acute respiratory distress syndrome (ARDS), followed by pulmonary fibrosis in a later phase. The focus of this review is to summarize the most recent publications related to PQ-induced lung toxicity as well as the underlying molecular mechanisms for PQ-mediated pathologic processes. Growing sets of data from in vitro and in vivo models have demonstrated the involvement of the PQ in regulating lung oxidative stress, inflammatory response, epigenetics, apoptosis, autophagy, and the progression of lung fibrosis. The article also summarizes novel therapeutic avenues based on a literature review, which can be explored as potential means to combat PQ-induced lung toxicity. Finally, we also presented clinical studies on the association of PQ exposure with the incidence of lung injury and pulmonary fibrosis.

Protective effects of febuxostat against paraquat-induced lung toxicity in rats: Impact on RAGE/PI3K/Akt pathway and downstream inflammatory cascades

AIMS

The herbicide paraquat causes fatal lung toxicity by induction of xanthine oxidase, production of free radicals and inflammation. Febuxostat, a xanthine oxidase inhibitor and anti-gout has recently shown anti-inflammatory activity. Accordingly, this study was carried out to investigate whether febuxostat may attenuate paraquat-induced lung toxicity and to explore the possible underlying mechanisms.

MAIN METHODS

Rats were administered either vehicle, a single dose of paraquat (30 mg/kg, i.p.), febuxostat (15 mg/kg, oral), or both for 14 successive days. Serum LDH and sRAGE were estimated. Lung tissue xanthine oxidase activity, SOD, TAC, MDA, and RAGE, HMGB1 gene expression, PI3K/Akt and β-catenin protein expression, MMP-9, IL-8, VEGF and COX-2 gene expression were estimated.

KEY FINDINGS

Results showed that paraquat induced lung injury characterized by enhanced oxidative stress and inflammation, upregulated RAGE, HMGB1 gene expression, PI3K/Akt and β-catenin protein expression. Administration of febuxostat inhibited the deleterious effects of paraquat on lung through inhibition of xanthine oxidase activity and related oxidative stress, downregulation of RAGE/PI3K/Akt pathway, and suppression of β-catenin protein expression and its downstream inflammatory mediators.

SIGNIFICANCE

The present study showed that febuxostat may abrogate paraquat-induced lung toxicity and demonstrated a novel mechanism for its ameliorative effects.

Identification of potential serum biomarkers of acute paraquat poisoning in humans using an iTRAQ quantitative proteomic

Paraquat (PQ) poisoning has high mortality rates in many countries. Due to it readily being absorbed through the gastrointestinal tract and rapidly excreted in the urine, few biomarkers possess satisfactory specificity and sensitivity in diagnostic and forensic practices. To investigate serum biomarkers in patients with PQ poisoning, pooled sera was analyzed using a proteomic approach based on iTRAQ coupled LC-MS/MS. Of the 413 proteins identified with high confidence, 81 were found to be differentially expressed (1.5-fold change) in the sera of patients with PQ poisoning. The differential expression pattern of 4 of these proteins was validated by enzyme-linked immunosorbent assay (ELISA) in clinical samples. A sera sample from a PQ poisoning patient has shown relatively increased abundance of S100A8 and S100A9. The overexpression of S100A8 and S100A9 was further validated in the lung tissue of PQ-treated rat associated with lung damage. Meanwhile, we identified another two down-expressed proteins, transferrin receptor protein 1 (TfR1) and serum amyloid P-component (SAP), which may be also practicable in human clinical samples as PQ poisoning serum biomarkers. Furthermore, receiver operating characteristic curve analysis confirmed that the expression levels of S100 alarmins, TfR1 and SAP in patient serum could provide a discriminatory diagnostic test for predicting PQ poisoning in patients. Therefore, our results suggest that increased serum levels of S100 alarmins and decreased serum levels of TfR1 and SAP may constitute potential biomarkers for the prediction of PQ poisoning in humans, and might be novel therapeutic targets in PQ poisoning.

Soluble Epoxide Hydrolase Inhibitor Attenuates Lipopolysaccharide-Induced Acute Lung Injury and Improves Survival in Mice

Acute lung injury (ALI) is characterized by rapid alveolar injury, vascular leakage, lung inflammation, neutrophil accumulation, and induced cytokines production leading to lung edema. The mortality rate of patients suffering from ALI remains high. Epoxyeicosatrienoic acids (EETs) are cytochrome P450-dependent derivatives of polyunsaturated fatty acid with antihypertensive, profibrinolytic, and anti-inflammatory functions. EETs are rapidly hydrated by soluble epoxide hydrolase (sEH) to their less potent diols. The aim of this study was to investigate the role of sEH inhibitor trifluoromethoxyphenyl propionylpiperidin urea (TPPU) and EETs in lipopolysaccharide (LPS)-induced ALI of mice. Our studies revealed that inhibition of sEH with TPPU attenuated the morphological changes in mice, decreased the neutrophil infiltration to the lung, pro-inflammatory cytokine levels (IL-1β and TNF-α) in serum and bronchoalveolar lavage fluid (BALF), and alveolar capillary leakage (lung wet/dry ratio and total protein concentration in BALF). TPPU improved the survival rate of LPS-induced ALI. In addition, in vitro experiments revealed that both TPPU and EETs (11,12-EET and 14,15-EET) suppressed the expression of IL-1β and TNF-α, and LDH release in RAW264.7 cells. These results indicate that EETs play a role in dampening LPS-induced acute lung inflammation, and suggest that sEH could be a valuable candidate for the treatment of ALI.

Increased ω-3 polyunsaturated fatty acid/arachidonic acid ratios and upregulation of signaling mediator in individuals with autism spectrum disorders

AIMS

The investigation of links between the ratio of omega-3/omega-6 PUFAs and neuronal signaling is a research priority in autism spectrum disorders (ASD).

MAIN METHODS

We examine the relationships between the plasma ratios of docosahexaenoid acid (DHA)/arachidonic acid (AA) and eicopentaenoic acid (EPA)/AA and biomarkers of AA-related signaling mediators such as ceruloplasmin, transferrin and superoxide dismutase, in the behavioral symptoms of 28 individuals with ASD (mean age 13.5±4.6years) and 21 age- and gender-matched normal healthy controls (mean age 13.9±5.7years). Behavioral symptoms were assessed using the Aberrant Behavior Checklists (ABC). We conducted controlling for dietary intake and assessed the dietary intake of nutrients.

KEY FINDINGS

There were no significant differences in intake of nutrients such as omega-3 and omega-6 PUFAs, saturated and unsaturated fatty acid, DHA, AA, iron and copper. Plasma EPA, DHA, and arachidic acid levels, and plasma DHA/AA and EPA/AA ratios were significantly higher, while plasma AA and adrenic acid were significantly lower in the 28 individuals with ASD than in the 21 normal controls. The ABC scores were significantly higher in the ASD group compared to the control group. The plasma ceruloplasmin levels in the ASD group were significantly reduced compared to those in the control group.

SIGNIFICANCE

Increased plasma DHA/AA and EPA/AA ratios may be related to low plasma levels of ceruloplasmin which has neuroprotective properties. Reduced plasma ceruloplasmin levels may diminish the protective capacity against brain damage, and may contribute to the pathophysiology of behavioral symptoms in individuals with ASD.

Down-regulation of a signaling mediator in association with lowered plasma arachidonic acid levels in individuals with autism spectrum disorders

Previous studies have indicated that the altered composition of polyunsaturated fatty acids (PUFAs) might contribute to the pathophysiology of autism spectrum disorder (ASD). We examined the relationship between the plasma fatty acid levels, expressed as μg/ml, and the plasma levels of biomarkers of AA-related signaling mediators, such as ceruloplasmin, transferrin and superoxide dismutase, and assessed the behavioral symptoms of 30 individuals with ASD (mean age, 13.6 ± 4.3 years old) compared with 20 age- and gender-matched normal controls (mean age, 13.2 ± 5.4 years old) using Aberrant Behavior Checklists (ABC). The plasma levels of EPA and the plasma ratios of EPA/AA were significantly higher, while the plasma levels of AA and metabolites, such as 5,8,11,14-eicosatetraenoic acid, adrenic acid, and ceruloplasmin (Cp), were significantly lower in the 30 individuals with ASD compared with the 20 normal controls. The ABC scores were significantly increased in the ASD group compared with those of the control group. Thus, the results of the present study revealed that reduced plasma levels of AA and metabolites in association with high plasma EPA/AA ratios might down-regulate AA-related signaling mediators, such as Cp. Subsequently, reduced plasma Cp levels might reduce the protective capacity for brain damage, resulting in the pathophysiology underlying the behavioral symptoms in individuals with ASD. These findings suggest that reduced plasma AA levels may downregulate Cp.