Mostafa Z. Badr

Immunotoxicity of perfluorooctanoic acid and perfluorooctane sulfonate and the role of peroxisome proliferator-activated receptor alpha.

Perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS) are environmentally widespread and persistent chemicals with multiple toxicities reported in experimental animals and humans. These compounds can trigger biological activity by activating the alpha isotype of peroxisome proliferator-activated receptors (PPARs), ligand-activated transcription factors that regulate gene expression; however, some biological effects may occur independently of the receptor. Activation of the peroxisome proliferator-activated receptor alpha (PPARα) modulates lipid and glucose homeostasis, cell proliferation and differentiation, and inflammation. Reported immunomodulation in experimental animals exposed to PFOA and PFOS has included altered inflammatory responses, production of cytokines and other proteins, reduced lymphoid organ weights, and altered antibody synthesis. Mounting experimental animal evidence suggests PPARα independence of some immune effects. This evidence originates primarily from studies with PPARα knockout models exposed to PFOA that demonstrate hepatic peroxisome proliferation, reduced lymphoid organ weights, and altered antibody synthesis. As human PPARα expression is significantly less than that of rodents, potential PPARα independence indicates that future research must explore mechanisms of action of these compounds, including PPARα -dependent and -independent pathways. This multiauthored review contains brief descriptions of current and recently published work exploring immunomodulation by PFOA and PFOS, as well as a short overview of other PPARα ligands of therapeutic and environmental interest.

Role of Peroxisome Proliferator-Activated Receptors in Inflammation Control

Peroxisome proliferator-activated receptors (PPARs) were discovered over a decade ago, and were classified as orphan members of the nuclear receptor superfamily. To date, three PPAR subtypes have been discovered and characterized (PPARα, β/δ, γ). Different PPAR subtypes have been shown to play crucial roles in important diseases and conditions such as obesity, diabetes, atherosclerosis, cancer, and fertility. Among the most studied roles of PPARs is their involvement in inflammatory processes. Numerous studies have revealed that agonists of PPARα and PPARγ exert anti-inflammatory effects both in vitro and in vivo. Using the carrageenan-induced paw edema model of inflammation, a recent study in our laboratories showed that these agonists hinder the initiation phase, but not the late phase of the inflammatory process. Furthermore, in the same experimental model, we recently also observed that activation of PPARδ exerted an anti-inflammatory effect. Despite the fact that exclusive dependence of these effects on PPARs has been questioned, the bulk of evidence suggests that all three PPAR subtypes, PPARα, δ, γ, play a significant role in controlling inflammatory responses. Whether these subtypes act via a common mechanism or are independent of each other remains to be elucidated. However, due to the intensity of research efforts in this area, it is anticipated that these efforts will result in the development of PPAR ligands as therapeutic agents for the treatment of inflammatory diseases.

Peroxisome proliferator-activated receptors and cancer: challenges and opportunities

Peroxisome proliferator‐activated receptors (PPARs), members of the nuclear hormone receptor superfamily, function as transcription factors and modulators of gene expression. These actions allow PPARs to regulate a variety of biological processes and to play a significant role in several diseases and conditions. The current literature describes frequently opposing and paradoxical roles for the three PPAR isotypes, PPARα, PPARβ/δ and PPARγ, in cancer. While some studies have implicated PPARs in the promotion and development of cancer, others, in contrast, have presented evidence for a protective role for these receptors against cancer. In some tissues, the expression level of these receptors and/or their activation correlates with a positive outcome against cancer, while, in other tissue types, their expression and activation have the opposite effect. These disparate findings raise the possibility of (i) PPAR receptor‐independent effects, including effects on receptors other than PPARs by the utilized ligands; (ii) cancer stage‐specific effect; and/or (iii) differences in essential ligand‐related pharmacokinetic considerations. In this review, we highlight the latest available studies on the role of the various PPAR isotypes in cancer in several major organs and present challenges as well as promising opportunities in the field.

Inhibition of rat mammary gland carcinogenesis by simultaneous targeting of cyclooxygenase-2 and peroxisome proliferator-activated receptor γ

We examined the effect of celecoxib, a cyclooxygenase-2 (COX-2) inhibitor, and N-(9-fluorenyl-methyloxycarbonyl)-l-leucine (F-l-Leu), a peroxisome proliferator-activated receptor γ (PPARγ) agonist, separately and combined, on the development of methylnitrosourea (MNU)-induced rat mammary gland carcinogenesis. Celecoxib and F-l-Leu significantly reduced tumor incidence and multiplicity (P < 0.05). Combining both agents exerted higher (synergistic) cancer inhibition than separate treatments (P < 0.05). The effects of the test drugs on COX-2 and PPARγ expression and on the synthesis of prostaglandin E2 (PGE2) and 15-deoxy-Δ12,14-PGJ2 (15d-PGJ2) were examined in rat mammary normal (MNU-untreated), uninvolved, and tumor (MNU-treated) tissues. Celecoxib and F-l-Leu, separately, inhibited COX-2 and up-regulated PPARγ expression. These effects were paralleled by inhibition of PGE2 synthesis and up-regulation of 15d-PGJ2. Combined treatment resulted in higher alterations in COX-2 and PPARγ transcripts and PG synthesis compared with separate administrations. The effect of the test agents on Bcl2, BAX, and protein kinase Cα expression levels were examined in the rat mammary gland and the pro-(BAX:Bcl2) and anti-[PKCα*(Bcl2/BAX)] apoptotic ratios were evaluated. Each drug increased the proapoptotic ratio by 2- to 7-fold and reduced the antiapoptotic ratio by 2- to >8-fold in all tissues. Combined treatment, however, resulted in >9- to 14-fold up-regulation in the proapoptotic processes and 15- to >30-fold down-regulation in the antiapoptotic ones. Analyses were also carried out on the drug-induced modulation of cell cycle regulators and proliferation markers (cyclin-dependent kinase 1 and proliferating cell nuclear antigen). F-l-Leu and celecoxib each reduced the cyclin-dependent kinase 1 and proliferating cell nuclear antigen expression in the tumor. Higher down-regulation was attained in all tissues by combined treatment where cyclin-dependent kinase 1 and proliferating cell nuclear antigen almost retained the expression levels observed in the normal glands. In conclusion, simultaneous targeting of COX-2 and PPARγ may inhibit mammary cancer development more effectively than targeting each molecule alone. COX-2 inhibitors and PPARγ agonists coordinately mediate their anticancer effect via both COX-dependent (inhibition of COX-2, activation of PPARγ, and modulation PG synthesis) and COX-independent (induction of proapoptotic factors and inhibition of cell proliferation) pathways.

Expression of cyclooxygenase‐2 and peroxisome proliferator‐activated receptor‐γ and levels of prostaglandin E2 and 15‐deoxy‐Δ12,14‐prostaglandin J2 in human breast cancer and metastasis

Cyclooxygenase‐2 (COX‐2) expression and peroxisome proliferator‐activated receptor‐γ (PPARγ) inactivation are linked to increased risk of human breast cancer. The purpose of our study was to examine the relationship between COX‐2 (with the resulting prostaglandins E2, PGE2) and PPARγ (and its natural endogenous ligand 15‐Deoxy‐Δ12,14‐prostaglandin J2, 15d‐PGJ2) at various stages during the development of human breast cancer and its progression to metastasis. Human breast tissue specimens were collected from normal breasts or from individuals with fibrocystic disease and served as controls (n = 22). Tissues were also collected from uninvolved (n = 25), tumor (n = 25) and lymph node metastasis (n = 15) regions from breast cancer patients. COX‐2 and PPARγ mRNA expression were increased and downregulated, respectively, in tissues from cancer patients compared to controls. Metastatic tissues tended to have higher alterations compared to non‐metastatic tissues (p < 0.05). These altered expressions in COX‐2 and PPARγ were paralleled by increases in the tissue levels of PGE2 and decreases in 15d‐PGJ2. A significant inverse correlation was found between PGE2 and 15‐d‐PGJ2 (r = −0.51, p < 0.05). Significant correlations (p < 0.05) were also obtained between COX‐2 and PPARγ mRNA (inverse, r = −0.72) and between COX‐2 and PGE2 (direct, r = 0.68). Increases in COX‐2 mRNA expression and levels of PGE2 and down‐regulation of PPARγ mRNA expression and 15d‐PGJ2 levels were characterized as predictors of breast cancer risk (p < 0.05). Our results suggest that the altered expression of COX‐2 and PPARγ and the subsequent modulation in the tissue levels of PGE2 and 15‐d‐PGJ2 may influence the development of human breast cancer and its progression to metastasis.

Activation of peroxisome proliferator-activated receptor γ in brain inhibits inflammatory pain, dorsal horn expression of Fos, and local edema

Systemic administration of thiazolidinediones reduces peripheral inflammation in vivo, presumably by acting at peroxisome proliferator-activated receptor gamma (PPARgamma) in peripheral tissues. Based on a rapidly growing body of literature indicating the CNS as a functional target of PPARgamma actions, we postulated that brain PPARgamma modulates peripheral edema and the processing of inflammatory pain signals in the dorsal horn of the spinal cord. To test this in the plantar carrageenan model of inflammatory pain, we measured paw edema, heat hyperalgesia, and dorsal horn expression of the immediate-early gene c-fos after intracerebroventricular (ICV) administration of PPARgamma ligands or vehicle. We found that ICV rosiglitazone (0.5-50 microg) or 15d-PGJ(2) (50-200 microg), but not vehicle, dose-dependently reduced paw thickness, paw volume and behavioral withdrawal responses to noxious heat. These anti-inflammatory and anti-hyperalgesia effects result from direct actions in the brain and not diffusion to other sites, because intraperitoneal and intrathecal administration of rosiglitazone (50 microg) and 15d-PGJ(2) (200 microg) had no effect. PPARgamma agonists changed neither overt behavior nor motor coordination, indicating that non-specific behavioral effects do not contribute to PPAR ligand-induced anti-hyperalgesia. ICV administration of structurally dissimilar PPARgamma antagonists (either GW9662 or BADGE) reversed the anti-inflammatory and anti-hyperalgesic actions of both rosiglitazone and 15d-PGJ(2). To evaluate the effects of PPARgamma agonists on a classic marker of noxious stimulus-evoked gene expression, we quantified Fos protein expression in the dorsal horn. The number of carrageenan-induced Fos-like immunoreactive profiles was less in rosiglitazone-treated rats as compared to vehicle controls. We conclude that pharmacological activation of PPARgamma in the brain rapidly inhibits local edema and the spinal transmission of noxious inflammatory signals.

Peroxisome proliferator-activated receptor agonists inhibit inflammatory edema and hyperalgesia

Previous studies have produced conflicting data on the contribution of the peroxisome proliferator-activated receptors (PPARs) to the inflammatory process. This study investigated the effects of several PPARα and PPARγ subtype-specific agonists on the inflammation and hyperalgesia produced by intraplantar carrageenan injection in unanesthetized male Sprague-Dawley rats. Intraperitoneal administration of PPARα agonists reduced edema in parallel to their potencies determined in vitro. Perfluorooctanoic acid (PFOA) inhibited carrageenan-induced edema in a dose-dependent manner, and also reduced thermal hypersensitivity. Furthermore, PFOA produced much more robust effects when administered 0.5–24 hrs before carrageenan, as compared to when it was administered 1.5 hrs after carrageenan. Intraperitoneal administration of similar doses of the PPARγ agonist rosiglitazone, but not the less potent agonist, troglitazone, reduced edema when administered before but not after carrageenan. We conclude that systemic administration of potent PPARα and PPARγ agonists exert anti-hyperalgesic and/or antiinflammatory actions in vivo, possibly by interfering with the initiation of inflammation.

Rotenone, an anticarcinogen, inhibits cellular proliferation but not peroxisome proliferation in mouse liver

In previous National Toxicology Program (NTP) studies, rotenone reduced the background incidence of hepatocellular carcinoma in male B6C3F1 mice. In the present studies, rotenone reduced the basal hepatic labeling index of male B6C3F1 mice in a dose-dependent fashion and inhibited hepatocellular proliferation, but not peroxisome proliferation, induced by the peroxisome proliferator Wy-14,643. These results indicate that reduction of hepatic tumors by rotenone may have been due to decreased liver cell replication, that peroxisome proliferation can be induced in the absence of hepatocellular proliferation and suggest rotenone as a potential tool in studies of relationships of cell proliferation, peroxisomal proliferation and hepatocarcinogenesis.

Suppression of nitric oxide induction and pro-inflammatory cytokines by novel proteasome inhibitors in various experimental models

BackgroundInflammation has been implicated in a variety of diseases associated with ageing, including cancer, cardiovascular, and neurologic diseases. We have recently established that the proteasome is a pivotal regulator of inflammation, which modulates the induction of inflammatory mediators such as TNF-α, IL-1, IL-6, and nitric oxide (NO) in response to a variety of stimuli. The present study was undertaken to identify non-toxic proteasome inhibitors with the expectation that these compounds could potentially suppress the production of inflammatory mediators in ageing humans, thereby decreasing the risk of developing ageing related diseases. We evaluated the capacity of various proteasome inhibitors to suppress TNF-α, NO and gene suppression of TNF-α and iNOS mRNA, by LPS-stimulated macrophages from several sources. Further, we evaluated the mechanisms by which these agents suppress secretion of TNF-α, and NO production. Over the course of these studies, we measured the effects of various proteasome inhibitors on the RAW 264.7 cells, and peritoneal macrophages from four different strains of mice (C57BL/6, BALB/c, proteasome double subunits knockout LMP7/MECL-1-/-, and peroxisome proliferator-activated receptor-α-/- (PPAR-α-/-) knockout mice. We also directly measured the effect of these proteasome inhibitors on proteolytic activity of 20S rabbit muscle proteasomes.ResultsThere was significant reduction of chymotrypsin-like activity of the 20S rabbit muscle proteasomes with dexamethasone (31%), mevinolin (19%), δ-tocotrienol (28%), riboflavin (34%), and quercetin (45%; P< 0.05). Moreover, quercetin, riboflavin, and δ-tocotrienol also inhibited chymotrypsin-like, trypsin-like and post-glutamase activities in RAW 264.7 whole cells. These compounds also inhibited LPS-stimulated NO production and TNF-α secretion, blocked the degradation of P-IκB protein, and decreased activation of NF-κB, in RAW 264.7 cells. All proteasome inhibitors tested also significantly inhibited NO production (30% to 60% reduction) by LPS-induced thioglycolate-elicited peritoneal macrophages derived from all four strains of mice. All five compounds also suppressed LPS-induced TNF-α secretion by macrophages from C57BL/6 and BALB/c mice. TNF-α secretion, however, was not suppressed by any of the three proteasome inhibitors tested (δ-tocotrienol, riboflavin, and quercetin) with LPS-induced macrophages from LMP7/MECL-1-/- and PPAR-α-/- knockout mice. Results of gene expression studies for TNF-α and iNOS were generally consistent with results obtained for TNF-α protein and NO production observed with four strains of mice.ConclusionsResults of the current study demonstrate that δ-tocotrienol, riboflavin, and quercetin inhibit NO production by LPS-stimulated macrophages of all four strains of mice, and TNF-α secretion only by LPS-stimulated macrophages of C57BL/6 and BALB/c mice. The mechanism for this inhibition appears to be decreased proteolytic degradation of P-IκB protein by the inhibited proteasome, resulting in decreased translocation of activated NF-κB to the nucleus, and depressed transcription of gene expression of TNF-α and iNOS. Further, these naturally-occurring proteasome inhibitors tested appear to be relatively potent inhibitors of multiple proteasome subunits in inflammatory proteasomes. Consequently, these agents could potentially suppress the production of inflammatory mediators in ageing humans, thereby decreasing the risk of developing a variety of ageing related diseases.

Inhibition of nitric oxide in LPS-stimulated macrophages of young and senescent mice by δ-tocotrienol and quercetin

BackgroundChanges in immune function believed to contribute to a variety of age-related diseases have been associated with increased production of nitric oxide (NO). We have recently reported that proteasome inhibitors (dexamethasone, mevinolin, quercetin, δ-tocotrienol, and riboflavin) can inhibit lipopolysaccharide (LPS)-induced NO production in vitro by RAW 264.7 cells and by thioglycolate-elicited peritoneal macrophages derived from four strains of mice (C57BL/6, BALB/c, LMP7/MECL-1-/- and PPAR-α-/- knockout mice). The present study was carried out in order to further explore the potential effects of diet supplementation with naturally-occurring inhibitors (δ-tocotrienol and quercetin) on LPS-stimulated production of NO, TNF-α, and other pro-inflammatory cytokines involved in the ageing process. Young (4-week-old) and senescent mice (42-week old) were fed control diet with or without quercetin (100 ppm), δ-tocotrienol (100 ppm), or dexamethasone (10 ppm; included as positive control for suppression of inflammation) for 4 weeks. At the end of feeding period, thioglycolate-elicited peritoneal macrophages were collected, stimulated with LPS, LPS plus interferon-β (IFN-β), or LPS plus interferon-γ (IFN-γ), and inflammatory responses assessed as measured by production of NO and TNF-α, mRNA reduction for TNF-α, and iNOS genes, and microarray analysis.ResultsThioglycolate-elicited peritoneal macrophages prepared after four weeks of feeding, and then challenged with LPS (10 ng or 100 ng) resulted in increases of 55% and 73%, respectively in the production of NO of 46-week-old compared to 8-week-old mice fed control diet alone (respective control groups), without affecting the secretion of TNF-α among these two groups. However, macrophages obtained after feeding with quercetin, δ-tocotrienol, and dexamethasone significantly inhibited (30% to 60%; P< 0.02) the LPS-stimulated NO production, compared to respective control groups. There was a 2-fold increase in the production of NO, when LPS-stimulated macrophages of quercetin, δ-tocotrienol, or dexamethasone were also treated with IFN-β or IFN-γ compared to respective control groups. We also demonstrated that NO levels and iNOS mRNA expression levels were significantly higher in LPS-stimulated macrophages from senescent (0.69 vs 0.41; P< 0.05), compared to young mice. In contrast, age did not appear to impact levels of TNF-α protein or mRNA expression levels (0.38 vs 0.35) in LPS-stimulated macrophages. The histological analyses of livers of control groups showed lesions of peliosis and microvesicular steatosis, and treated groups showed Councilman body, and small or large lymphoplasmacytic clusters.ConclusionsThe present results demonstrated that quercetin and δ-tocotrienols inhibit the LPS-induced NO production in vivo. The microarray DNA analyses, followed by pathway analyses indicated that quercetin or δ-tocotrienol inhibit several LPS-induced expression of several ageing and pro-inflammatory genes (IL-1β, IL-1α, IL-6, TNF-α, IL-12, iNOS, VCAM1, ICAM1, COX2, IL-1RA, TRAF1 and CD40). The NF-κB pathway regulates the production of NO and inhibits the pro-inflammatory cytokines involved in normal and ageing process. These ex vivo results confirmed the earlier in vitro findings. The present findings of inhibition of NO production by quercetin and δ-tocotrienol may be of clinical significance treating several inflammatory diseases, including ageing process.