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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 transloc...

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, PPARa, PPARb/d and PPARg, 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.

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.

Cyclooxygenase-2 (COX-2) expression and peroxisome proliferator-activated receptor-␥ (PPAR␥) 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 E 2 , PGE 2 ) and PPAR␥ (and its natural endogenous ligand 15-Deoxy-⌬ 12,14 -prostaglandin J 2 , 15d-PGJ 2 ) 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 PPAR␥ 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 PPAR␥ were paralleled by increases in the tissue levels of PGE 2 and decreases in 15d-PGJ 2 . A significant inverse correlation was found between PGE 2 and 15-d-PGJ 2 (r ‫؍‬ ؊0.51, p < 0.05). Significant correlations (p < 0.05) were also obtained between COX-2 and PPAR␥ mRNA (inverse, r ‫؍‬ ؊0.72) and between COX-2 and PGE 2 (direct, r ‫؍‬ 0.68). Increases in COX-2 mRNA expression and levels of PGE 2 and down-regulation of PPAR␥ mRNA expression and 15d-PGJ 2 levels were characterized as predictors of breast cancer risk (p < 0.05). Our results suggest that the altered expression of COX-2 and PPAR␥ and the subsequent modulation in the tissue levels of PGE 2 and 15-d-PGJ 2 may influence the development of human breast cancer and its progression to metastasis. © 2002 Wiley-Liss, Inc. Key words: breast cancer; cyclooxygenases; peroxisome proliferatoractivated receptors; chemopreventionThe high prevalence of breast cancer 1 and the limited options for treatment provide a strong rationale for identifying new, selective molecular targets that can be nutritionally or pharmacologically modulated and, thereby, offer a potential for chemoprevention. Among the regulatory molecules that have been characterized as holding great promise for breast cancer prevention are cyclooxygenase-2 (COX-2) and peroxisome proliferator-activated receptor-␥ (PPAR␥). 2 Cyclooxygenase is the rate-limiting enzyme in prostaglandin (PG) synthesis, of which 2 isoforms were identified: the constitutive COX-1 and the inducible COX-2. PGs produced by COX-1 mediate various physiological responses, whereas PGs produced by COX-2, predominantly PGE 2 , induce inflammation and are potent mediators of a number of signal transduction pathways that modulate cell adhesion and growth and are implicated in cancer development. 3 COX-1 and COX-2 are the primary targets of non-steroidal anti-inflammatory drugs (NSAIDs), which inhibit the activity of these enzymes as a major mode of their anti-tumorigenic action. 4 Recent findings, however, suggest ...