Modulation of paraoxonase-2 in human dermal fibroblasts by UVA-induced oxidative stress: A new potential marker of skin photodamage

Paraoxonase-2 (PON2) is an intracellular protein, that exerts a protective role against cell oxidative stress and apoptosis. Genetic and environmental factors (i.e. dietary factors, cigarette smoke, drugs) are able to modulate cellular PON2 levels. The effect of ultraviolet A radiation (UVA), the oxidizing component of sunlight, on PON2 in human dermal fibroblasts (HuDe) has not been previously explored. Excessive UVA radiation is known to cause direct and indirect skin damage by influencing intracellular signalling pathways through oxidative stress mediated by reactive oxygen species (ROS) that modulate the expression of downstream genes involved in different processes, e.g. skin photoaging and cancer. The aim of this study was, therefore, to investigate the modulation of PON2 in terms of protein expression and enzyme activity in HuDe exposed to UVA (270 kJ/m2). Our results show that PON2 is up-regulated immediately after UVA exposure and that its levels and activity decrease in the post-exposure phase, in a time-dependent manner (2-24 h). The trend in PON2 levels mirror the time-course study of UVA-induced ROS. To confirm this, experiments were also performed in the presence of a SPF30 sunscreen used as shielding agent to revert modulation of PON2 at 0 and 2 h post-UVA exposure where other markers of photo-oxidative stress were also examined (NF-KB, γH2AX, advanced glycation end products). Overall, our results show that the upregulation of PON2 might be related to the increase in intracellular ROS and may play an important role in mitigation of UVA-mediated damage and in the prevention of the consequences of UV exposure, thus representing a new marker of early-response to UVA-induced damage in skin fibroblasts.

Phytochemicals as Modulators of Paraoxonase-1 in Health and Diseases

Chronic diseases such as cardiovascular disease (CVD), atherosclerosis, chronic liver disease, and neurodegenerative diseases are major causes of mortality. These diseases have gained much attention due to their complications, and therefore novel approaches with fewer side effects are an important research topic. Free radicals and oxidative stress are involved in the molecular mechanisms of several diseases. Antioxidants can scavenge free radicals and mitigate their adverse effects. One of the most important antioxidant enzymes are paraoxonases (PONs). These enzymes perform a wide range of physiological activities ranging from drug metabolism to detoxification of neuroleptics. Paraoxonase-1 (PON1) is produced in the liver and then transferred to the bloodstream. It has been demonstrated that PON1 could have beneficial effects in numerous diseases such as atherosclerosis, CVD, diabetes mellitus, and neurodegenerative diseases by modulating relevant signalling pathways involved in inflammation and oxidative stress. These pathways include peroxisome proliferator-activated receptor gamma (PPAR-γ) and protein kinase B/nuclear factor kappa-light-chain-enhancer of activated B cells (AKT/NF-κB)-dependent signalling pathways. Increasing PON1 could potentially have protective effects and reduce the incidence of various diseases by modulating these signalling pathways. Several studies have reported that dietary factors are able to modulate PON1 expression and activity. This review aimed at summarizing the state of the art on the effects of dietary phytochemicals on PON1 enzyme activity and the relevant signalling pathways in different diseases.

The role of paraoxonase in cancer

The paraoxonase (PON) gene family includes three proteins, PON1, PON2 and PON3. PON1 and PON3 are both associated with high-density lipoprotein (HDL) particles and exert anti-oxidant and anti-inflammatory properties. PON2 and PON3 are intracellular enzymes which modulate mitochondrial superoxide anion production and endoplasmic reticulum (ER) stress-induced apoptosis. The pleiotropic roles exerted by PONs have been mainly investigated in cardiovascular and neurodegenerative diseases. In recent years, overexpression of PON2 and PON3 has been observed in cancer cells and it has been proposed that both enzymes could be involved in tumor survival and stress resistance. Moreover, a lower activity of serum PON1 has been reported in cancer patients. This review summarizes literature data on the role of PONs in human cancers and their potential role as a target for antitumor drugs.

The Search for Dietary Supplements to Elevate or Activate Circulating Paraoxonases

Low levels of paraoxonase 1 (PON1) have been associated with the development of several pathological conditions, whereas high levels have been shown to be anti-atherosclerotic in mouse models. These findings suggest that PON1 could be a good surrogate biomarker. The other members of the family, namely PON2 and PON3, the role of which has been much less studied, deserve more attention. This paper provides a systematic review of current evidence concerning dietary supplements in that regard. Preliminary studies indicate that the response to dietary supplements may have a nutrigenetic aspect that will need to be considered in large population studies or in clinical trials. A wide range of plant preparations have been found to have a positive action, with pomegranate and some of its components being the best characterized and Aronia melanocarpa one of the most active. Flavonoids are found in the composition of all active extracts, with catechins and genistein being the most promising agents for increasing PON1 activity. However, some caveats regarding the dose, length of treatment, bioavailability, and stability of these compounds in formulations still need to be addressed. Once these issues have been resolved, these compounds could be included as nutraceuticals and functional foods capable of increasing PON1 activity, thereby helping with the long-term prevention of atherosclerosis and other chronic ailments.

Anti-inflammatory effect of water extracts of Graptopetalum paraguayense supplementation in subjects with metabolic syndrome: a preliminary study

BACKGROUND

Many studies have demonstrated that Graptopetalum paraguayense has good antioxidant ability; however, few studies have examined its anti-inflammatory effect. The study aimed to investigate the anti-inflammatory effects of water extracts of G. paraguayense (WGP, 4 g day(-1)) in subjects with metabolic syndrome (MS). Intervention was administered for 12 weeks. Levels of inflammatory markers [high sensitivity C-reactive protein (CRP), tumour necrosis factor-α (TNF-α), and interleukin-6 (IL-6)] and antioxidant enzymes activities were measured.

RESULTS

Forty-two subjects completed the 12 week intervention study (placebo, n = 19; WGP, n = 23). After 12 weeks supplementation, subjects in WGP group had significantly lower levels of inflammatory markers than the baseline (P < 0.05) and the placebo group (CRP, P = 0.07; TNF-α, P = 0.04; IL-6, P = 0.03). The changes in levels of the inflammatory markers were significantly decreased in WGP group (CRP, P = 0.04; TNF-α, P = 0.06; IL-6, P = 0.01) compared to the placebo group. Levels of inflammatory markers were significantly negatively correlated with the antioxidant enzymes activities after supplementation.

CONCLUSION

This study demonstrated a significant reduction in inflammatory status in MS after WGP supplementation. WGP may exert an anti-inflammatory effect on MS in addition to its antioxidant ability.

Effects of water extracts of Graptopetalum paraguayense on blood pressure, fasting glucose, and lipid profiles of subjects with metabolic syndrome

This study was aimed to investigate the effects of water extracts of Graptopetalum paraguayense (WGP, 4 g/d) on blood pressure, blood glucose level, and lipid profiles in subjects with metabolic syndrome (MS). Participants with MS (n = 54) were randomly assigned to the placebo (n = 28) and WGP groups (n = 26), and the intervention was administered for 12 weeks. Systolic blood pressure (SBP), diastolic blood pressure (DBP), fasting glucose (FG), lipid profiles (total cholesterol (TC), triglyceride (TG), low density lipoprotein cholesterol (LDL-C), and high density lipoprotein (HDL-C)), and antioxidant enzymes activities (catalase (CAT), superoxide dismutase (SOD), and glutathione peroxidase (GPx)) were measured. Forty-two subjects completed the study (placebo, n = 19; WGP, n = 23). FG, SBP, and LDL-C levels were significantly lower and HDL-C level and antioxidant enzymes activities (CAT and SOD) were significantly higher after WGP supplementation. Blood pressure, FG, and lipid profiles were significantly correlated with antioxidant enzymes activities after supplementation (P < 0.05). The present study demonstrated a significant reduction in blood pressure, blood glucose, and lipid profiles and an increase in antioxidant enzymes activities in subjects with MS after WGP supplementation. Taken together, the antioxidative capacity of WGP might exert a beneficial effect on MS. This trial is registered with ClinicalTrials.gov NCT01463748.

Interleukin-6 upregulates paraoxonase 1 gene expression via an AKT/NF-κB-dependent pathway

The aim of this study is to investigate the relationship between paraoxonase 1 (PON1) and atherosclerosis-related inflammation. In this study, human hepatoma HepG2 cell line was used as a hepatocyte model to examine the effects of the pro-inflammatory cytokines on PON1 expression. The results showed that IL-6, but not TNF-α and IL-1β, significantly increased both the function and protein level of PON1; data from real-time RT-PCR analysis revealed that the IL-6-induced PON1 expression occurred at the transcriptional level. Increase of IκB kinase activity and IκB phosphorylation, and reduction of IκB protein level were also observed in IL-6-treated HepG2 cells compared with untreated culture. This event was accompanied by increase of NF-κB-p50 and -p65 nuclear translocation. Moreover, treatment with IL-6 augmented the DNA binding activity of NF-κB. Furthermore, pharmacological inhibition of NF-κB activation by PDTC and BAY 11-7082, markedly suppressed the IL-6-mediated PON1 expression. In addition, IL-6 increased the levels of phosphorylated protein kinase B (PKB, AKT). An AKT inhibitor LY294002 effectively suppressed IKK/IκB/NF-κB signaling and PON1 gene expression induced by IL-6. Our findings demonstrate that IL-6 upregulates PON1 gene expression through an AKT/NF-κB signaling axis in human hepatocyte-derived HepG2 cell line.