Polished rice as natural sources of cancer-preventing geranylgeranoic acid

GGPPS Negatively Regulates the Formation of Neutrophil Extracellular Traps in Lipopolysaccharide-Induced Acute Lung Injury

Acute respiratory distress syndrome (ARDS) and acute lung injury (ALI) are life-threatening diseases. Neutrophil extracellular traps (NETs) play a key role in lung damage. Geranylgeranyl diphosphate synthase (GGPPS) is associated with the development of inflammatory diseases. We aimed to explore the role of GGPPS in NETs formation in ARDS/ALI. First, lung pathological changes in lipopolysaccharide (LPS)-induced ALI mice after myeloid-specific GGPPS deletion were evaluated. The level of NETs formation was analyzed by immunofluorescence, PicoGreen assay and Western blotting. Next, we determined the role of GGPPS in NETs formation and underlying mechanisms using immunofluorescence, flow cytometry, DCFH-DA, and SYTOX GREEN staining in vitro. Finally, the correlation between GGPPS expression incirculating neutrophils and dsDNA levels in plasma was evaluated. Myeloid-specific GGPPS deletion mice showed increased NETs deposition in lung tissue and aggravated histopathological damage of lung tissue. In vitro, GGPPS deficiency in neutrophils resulted in increased NETs formation by Phorbol-12-myristate-13-acetate (PMA), which was reversed by Geranylgeranyl diphosphate (GGPP). In addition, inhibitors blocking protein kinase C (PKC) and NADPH-oxidase (NOX) decreased NETs formation induced by GGPPS deletion. Importantly, GGPPS expression in circulating neutrophils was decreased in ARDS patients compared with the healthy control, and the level of dsDNA in plasma of ARDS patients was negatively correlated with the GGPPS expression. Taken together, GGPPS deficiency in neutrophils aggravates LPS-induced lung injury by promoting NETs formation via PKC/NOX signaling. Thus, neutrophil GGPPS could be a key therapeutic target for ARDS.

Geranylgeranoic acid, a bioactive and endogenous fatty acid in mammals: a review

Geranylgeranoic acid (GGA) was first reported in 1983 as one of the mevalonic acid (MVA) metabolites, but its biological significance was not studied for a long time. Our research on the antitumor effects of retinoids led us to GGA, one of the acyclic retinoids that induce cell death in human hepatoma-derived cell lines. We were able to demonstrate the presence of endogenous GGA in various tissues of male rats, including the liver, testis, and cerebrum, by LC-MS/MS. Furthermore, the biosynthesis of GGA from MVA in mammals including humans was confirmed by isotopomer spectral analysis using ¹³C-labeled mevalonolactone and cultured hepatoma cells, and the involvement of hepatic monoamine oxidase B (MAOB) in the biosynthesis of GGA was also demonstrated. The biological activity of GGA was analyzed from the retinoid (differentiation induction) and non-retinoid (cell death induction) aspects, and in particular, the non-retinoid mechanism by which GGA induces cell death in hepatoma cells was found to involve pyroptosis via ER-stress responses initiated by TLR4 signaling. In addition to these effects of GGA, we also describe the in vivo effects of GGA on reproduction. In this review, based mainly on our published papers, we have shown that hepatic MAOB is involved in the biosynthesis of GGA and that GGA induces cell death in human hepatoma-derived cell lines by non-canonical pyroptosis, one of the mechanisms of sterile inflammatory cell death.

Regulation of protein prenylation

Prenyltransferases (PTases) are known to play a role in embryonic development, normal tissue homeostasis and cancer by posttranslationally modifying proteins involved in these processes. They are being discussed as potential drug targets in an increasing number of diseases, ranging from Alzheimer's disease to malaria. Protein prenylation and the development of specific PTase inhibitors (PTIs) have been subject to intense research in recent decades. Recently, the FDA approved lonafarnib, a specific farnesyltransferase inhibitor that acts directly on protein prenylation; and bempedoic acid, an ATP citrate lyase inhibitor that might alter intracellular isoprenoid composition, the relative concentrations of which can exert a decisive influence on protein prenylation. Both drugs represent the first approved agent in their respective substance class. Furthermore, an overwhelming number of processes and proteins that regulate protein prenylation have been identified over the years, many of which have been proposed as molecular targets for pharmacotherapy in their own right. However, certain aspects of protein prenylation, such as the regulation of PTase gene expression or the modulation of PTase activity by phosphorylation, have attracted less attention, despite their reported influence on tumor cell proliferation. Here, we want to summarize the advances regarding our understanding of the regulation of protein prenylation and the potential implications for drug development. Additionally, we want to suggest new lines of investigation that encompass the search for regulatory elements for PTases, especially at the genetic and epigenetic levels.

Effect of Dietary Geranylgeraniol and Green Tea Polyphenols on Glucose Homeostasis, Bone Turnover Biomarkers, and Bone Microstructure in Obese Mice

Previously, we demonstrated that the administration of either geranylgeraniol (GGOH) or green tea polyphenols (GTP) improved bone health. This study examined the combined effects of GGOH and GTP on glucose homeostasis in addition to bone remodeling in obese mice. We hypothesized that GGOH and GTP would have an additive or synergistic effect on improving glucose homeostasis and bone remodeling possibly in part via suppression of proinflammatory cytokines. Forty-eight male C57BL/6J mice were assigned to a high-fat diet (control), HFD + 400 mg GGOH/kg diet (GG), HFD + 0.5% GTP water (TP), or HFD + GGOH + GTP (GGTP) diet for 14 weeks. Results demonstrated that GTP supplementation improved glucose tolerance in obese mice. Neither GGOH nor GTP affected pancreas insulin or bone formation procollagen type I intact N-terminal, bone volume at the lumbar vertebrae, or bone parameters at the trabecular bone and cortical bone of the femur. There was an interactive effect for serum bone resorption collagen type 1 cross-linked C-telopeptide concentrations, resulting in no-GGOH and no-GTP groups having the highest values. GGOH increased trabecular number and decreased trabecular separation at the lumbar vertebrae. GTP increased trabecular thickness at lumbar vertebrae. The GG group produced the greatest connectivity density and the lowest structure model index. Only GTP, not GGOH, decreased adipokines concentrations (resistin, leptin, monocyte chemoattractant protein-1, and interleukin-6). In an obese male mouse model, individual GGOH and GTP supplementation improved glucose homeostasis, serum CTX, and trabecular microstructure of LV-4. However, the combined GGOH and GTP supplementation compromises such osteoprotective effects on serum CTX and trabecular bone of obese mice.

Geranylgeraniol Inhibits Lipopolysaccharide-Induced Inflammation in Mouse-Derived MG6 Microglial Cells via NF-κB Signaling Modulation

Persistent inflammatory reactions in microglial cells are strongly associated with neurodegenerative pathogenesis. Additionally, geranylgeraniol (GGOH), a plant-derived isoprenoid, has been found to improve inflammatory conditions in several animal models. It has also been observed that its chemical structure is similar to that of the side chain of menaquinone-4, which is a vitamin K₂ sub-type that suppresses inflammation in mouse-derived microglial cells. In this study, we investigated whether GGOH has a similar anti-inflammatory effect in activated microglial cells. Particularly, mouse-derived MG6 cells pre-treated with GGOH were exposed to lipopolysaccharide (LPS). Thereafter, the mRNA levels of pro-inflammatory cytokines were determined via qRT-PCR, while protein expression levels, especially the expression of NF-κB signaling cascade-related proteins, were determined via Western blot analysis. The distribution of NF-κB p65 protein was also analyzed via fluorescence microscopy. Thus, it was observed that GGOH dose-dependently suppressed the LPS-induced increase in the mRNA levels of Il-1β, Tnf-α, Il-6, and Cox-2. Furthermore, GGOH inhibited the phosphorylation of TAK1, IKKα/β, and NF-κB p65 proteins as well as NF-κB nuclear translocation induced by LPS while maintaining IκBα expression. We showed that GGOH, similar to menaquinone-4, could alleviate LPS-induced microglial inflammation by targeting the NF-kB signaling pathway.

Age-Dependent Decrease in Hepatic Geranylgeranoic Acid Content in C3H/HeN Mice and Its Oral Supplementation Prevents Spontaneous Hepatoma

Geranylgeranoic acid (GGA) has been developed as a preventive agent against second primary hepatoma. Recently, GGA was reported to induce cell death in human hepatoma cells via TLR4-mediated pyroptosis. We have reported that GGA is enzymatically biosynthesized from mevalonic acid in human hepatoma-derived cells and that endogenous GGA is found in most organs of rats. In addition, we found that upregulation of endogenous GGA levels by zaragozic acid A (ZAA) induced cell death in human hepatoma-derived cells. Therefore, we investigated the age-related changes in hepatic GGA and the possibility of suppressing hepatocarcinogenesis by GGA supplementation using male C3H/HeN mice that spontaneously develop hepatoma. We measured endogenous GGA and mRNA of monoamine oxidase (BMAOB), a key enzyme of GGA biosynthesis, in the liver of male C3H/HeN mice aged 6–93 weeks. We also tried suppressing spontaneous hepatocarcinogenesis by a single administration of GGA to C3H/HeN mice. Hepatic GGA content and Maob mRNA expression level age-dependently decreased in male C3H/HeN mice; some of which produced spontaneous hepatoma in 2 years. A single oral administration of GGA at 11 months of age significantly prevented hepatoma in terms of the number and weight of tumors per mouse at 24 months. Oral supplementation with GGA or geranylgeraniol significantly increased endogenous hepatic GGA contents dose-dependently; and ZAA dramatically upregulated hepatic GGA. In this study; we found an age-dependent decrease in hepatic endogenous GGA in male C3H/HeN mice and efficient prevention of spontaneous hepatoma by a single administration of GGA at 11 months of age.

Natural Compounds Attenuate Denervation-Induced Skeletal Muscle Atrophy

The weight of skeletal muscle accounts for approximately 40% of the whole weight in a healthy individual, and the normal metabolism and motor function of the muscle are indispensable for healthy life. In addition, the skeletal muscle of the maxillofacial region plays an important role not only in eating and swallowing, but also in communication, such as facial expressions and conversations. In recent years, skeletal muscle atrophy has received worldwide attention as a serious health problem. However, the mechanism of skeletal muscle atrophy that has been clarified at present is insufficient, and a therapeutic method against skeletal muscle atrophy has not been established. This review provides views on the importance of skeletal muscle in the maxillofacial region and explains the differences between skeletal muscles in the maxillofacial region and other regions. We summarize the findings to change in gene expression in muscle remodeling and emphasize the advantages and disadvantages of denervation-induced skeletal muscle atrophy model. Finally, we discuss the newly discovered beneficial effects of natural compounds on skeletal muscle atrophy.

Oral Administration of Geranylgeraniol Rescues Denervation-induced Muscle Atrophy via Suppression of Atrogin-1

BACKGROUND/AIM

Geranylgeraniol (GGOH), a C20 isoprenoid naturally occurs in several foods. We previously reported that GGOH treatment reduced the expression levels of Atrogin-1 which is involved in skeletal muscle degradation and stimulates the myogenic differentiation of C2C12 myoblasts. However, the effect of GGOH supplementation on skeletal muscle metabolism in vivo is unknown.

MATERIALS AND METHODS

Skeletal muscle atrophy was induced by denervation. The expression levels of Atrogin-1 were assessed by western blotting or real time PCR.

RESULTS

Intraoral administration of GGOH reduced the decrease in the cross-sectional area of muscle fibers and also suppressed the expression levels of Atrogin-1 in denervation induced muscle atrophy. Also, GGOH treatment suppressed the expression of Atrogin-1 and the decrease in skeletal muscle fiber size by glucocorticoid in vitro.

CONCLUSION

Intraoral administration of GGOH rescues denervation-induced muscle atrophy via suppression of Atrogin-1.

Hepatic monoamine oxidase B is involved in endogenous geranylgeranoic acid synthesis in mammalian liver cells

Geranylgeranoic acid (GGA) originally was identified in some animals and has been developed as an agent for preventing second primary hepatoma. We previously have also identified GGA as an acyclic diterpenoid in some medicinal herbs. Recently, we reported that in human hepatoma-derived HuH-7 cells, GGA is metabolically labeled from ¹³C-mevalonate. Several cell-free experiments have demonstrated that GGA is synthesized through geranylgeranial by oxygen-dependent oxidation of geranylgeraniol (GGOH), but the exact biochemical events giving rise to GGA in hepatoma cells remain unclear. Monoamine oxidase B (MOAB) has been suggested to be involved in GGOH oxidation. Here, using two human hepatoma cell lines, we investigated whether MAOB contributes to GGA biosynthesis. Using either HuH-7 cell lysates or recombinant human MAOB, we found that: 1) the MAO inhibitor tranylcypromine dose-dependently downregulates endogenous GGA levels in HuH-7 cells; and 2) siRNA-mediated MAOB silencing reduces intracellular GGA levels in HuH-7 and Hep3B cells. Unexpectedly, however, CRISPR/Cas9-generated MAOB-KO human hepatoma Hep3B cells had GGA levels similar to those in MAOB-WT cells. A sensitivity of GGA levels to siRNA-mediated MAOB downregulation was recovered when the MAOB-KO cells were transfected with a MAOB-expression plasmid, suggesting that MAOB is the enzyme primarily responsible for GGOH oxidation and that some other latent metabolic pathways may maintain endogenous GGA levels in the MAOB-KO hepatoma cells. Along with the previous findings, these results provide critical insights into the biological roles of human MAOB and provide evidence that hepatic MAOB is involved in endogenous GGA biosynthesis via GGOH oxidation.

Rice Components with Immunomodulatory Function

Rice (Oryza sativa) is one of the most important food crops in the world, and the effect of its consumption on human health is of great concern. Evidence has accumulated that rice contains several components, such as γ-oryzanol and rice bran fibers, which modulate the immune system. In addition, rice has other immunologically beneficial characteristics. It has a low allergenic potential and is gluten-free, reducing the risk of development of food allergies and diseases related to gluten sensitivity such as coeliac disease. This review presents the recent advances in our understanding of the immunomodulatory function of rice components.

Geranylgeraniol Induces PPARγ Expression and Enhances the Biological Effects of a PPARγ Agonist in Adipocyte Lineage Cells

BACKGROUND

The global incidence of diabetes mellitus (DM) has risen precipitously, even in middle- and low-income countries. Peroxisome proliferator-activated receptor γ (PPARγ) plays an important role in the control of cellular glucose metabolism. Activation of PPARγ beneficially results in increased insulin sensitivity. However, the expression of PPARγ is reduced by obesity and several nutritional factors. Here we examined the effect of geranylgeraniol (GGOH), a bioactive compound found naturally in fruits, vegetables, and grains, on the expression and activation of PPARγ.

MATERIALS AND METHODS

C3H10T1/2 mouse embryonic fibroblasts and 3T3-L1 pre-adipocytes were used as in vitro models of adipocyte differentiation and function. Quantitative reverse-transcriptase polymerase chain reaction, western blotting, Oil Red O staining, and luciferase assay were performed to respectively assess mRNA expression, protein levels, lipid droplet formation and transcriptional activity.

RESULTS

GGOH increased the expression of PPARγ in adipocyte lineage cells. GGOH also enhanced adipogenesis induced by rosiglitazone, a thiazolidinedione class PPARγ agonist.

CONCLUSION

GGOH induces PPARγ expression and enhances the biological effects of a PPARγ agonist in adipocyte lineage cells.

Geranylgeraniol-induced Myogenic Differentiation of C2C12 Cells

BACKGROUND

Geranylgeraniol (GGOH) is a C20 isoprenoid found in fruits, vegetables, and grains, including rice. As a food substance, GGOH is categorized as 'Generally Recognized as Safe'. GGOH is an intermediate product in the mevalonate pathway and acts as a precursor to geranylgeranyl pyrophosphate.

MATERIALS AND METHODS

C2C12 mouse myoblasts derived from muscle satellite cells were used. Quantitative reverse-transcriptase polymerase chain reaction, western blotting analysis, and immunocytochemical analysis were performed to respectively assess mRNA expression, protein levels, and the number of myofibers.

RESULTS

GGOH reduced the expression levels of skeletal muscle atrophy-related ubiquitin ligases in myofibers derived from C2C12 cells. GGOH induced myogenic differentiation of C2C12 cells via geranylgeranylation. GGOH did not adversely affect the proliferation of C2C12 cells.

CONCLUSION

GGOH induces myoblast differentiation in C2C12 cells.

Unequivocal evidence for endogenous geranylgeranoic acid biosynthesized from mevalonate in mammalian cells

Geranylgeranoic acid (GGA) has been reported to induce autophagic cell death via upregulation of lipid-induced unfolded protein response in several human hepatoma-derived cell lines, and its 4,5-didehydro derivative has been developed as a preventive agent against second primary hepatoma in clinical trials. We have previously reported that GGA is a natural diterpenoid synthesized in several medicinal herbs. Here, we provide unequivocal evidence for de novo GGA biosynthesis in mammals. First, with normal male Wistar rats, the levels of GGA in liver were found to be far greater than those in other organs analyzed. Second, we demonstrated the metabolic GGA labeling from the ¹³C-labeled mevalonolactone in the human hepatoma-derived cell line, HuH-7. Isotopomer spectral analysis revealed that approximately 80% of the cellular GGA was newly synthesized from mevalonate (MVA) in 12 h and the acid picked up preexisting farnesyl diphosphate (FPP) and geranylgeranyl diphosphate (GGPP), suggesting that GGA is derived from FPP and GGPP through the MVA pathway. Third, zaragozic acid A, a squalene synthase inhibitor, induced dose-dependent upregulation of endogenous GGA content in HuH-7 cells and their concomitant cell death. These results strongly suggest that a cancer-preventive GGA is biosynthesized via the MVA pathway in mammals.

The poor design of clinical trials of statins in oncology may explain their failure - Lessons for drug repurposing

Statins are widely used to treat hypercholesterolaemia. However, by inhibiting the production of mevalonate, they also reduce the production of several isoprenoids that are necessary for the function of small GTPase oncogenes such as Ras. As such, statins offer an attractive way to inhibit an "undruggable" target, suggesting that they may be usefully repurposed to treat cancer. However, despite numerous studies, there is still no consensus whether statins are useful in the oncology arena. Numerous preclinical studies have provided evidence justifying the evaluation of statins in cancer patients. Some retrospective studies of patients taking statins to control cholesterol have identified a reduced risk of cancer mortality. However, prospective clinical studies have mostly not been successful. We believe that this has occurred because many of the prospective clinical trials have been poorly designed. Many of these trials have failed to take into account some or all of the factors identified in preclinical studies that are likely to be necessary for statins to be efficacious. We suggest an improved trial design which takes these factors into account. Importantly, we suggest that the design of clinical trials of drugs which are being considered for repurposing should not assume it is appropriate to use them in the same way as they are used in their original indication. Rather, such trials deserve to be informed by preclinical studies that are comparable to those for any novel drug.

A novel function of geranylgeraniol in regulating testosterone production

Isoprenoids play widely differing roles in various physiological processes in animals and plants. Geranylgeraniol (GGOH) is an isoprenoid found in plants, and is an important metabolic derivative in the isoprenoid/cholesterol synthesis pathway. Earlier studies focused on GGOH's ability to improve the side effects of bisphosphonate therapy by regulating the mevalonate pathway. More recently, the mevalonate pathway-independent effects of GGOH have been described, including anti-inflammatory, anti-tumorigenic, and neuroprotective activities. It is noteworthy that GGOH regulates the steroidogenesis pathway in testis-derived I-10 tumor cells. Testosterone is a hormone produced via steroidogenesis in testicles and plays a role in fetal development and the male reproductive system. GGOH enhanced testosterone and progesterone (its precursor) levels in I-10 cells by activating adenylate cyclase via cAMP/PKA signaling, without altering phosphodiesterase activity. These findings highlight the potential benefits of GGOH as a therapeutic agent for low testosterone levels, such as late-onset hypogonadism in men.

Dietary geranylgeraniol can limit the activity of pitavastatin as a potential treatment for drug-resistant ovarian cancer

Pre-clinical and retrospective studies of patients using statins to reduce plasma cholesterol have suggested that statins may be useful to treat cancer. However, prospective clinical trials have yet to demonstrate significant efficacy. We have previously shown that this is in part because a hydrophobic statin with a long half-life is necessary. Pitavastatin, the only statin with this profile, has not undergone clinical evaluation in oncology. The target of pitavastatin, hydroxymethylglutarate coenzyme-A reductase (HMGCR), was found to be over-expressed in all ovarian cancer cell lines examined and upregulated by mutated TP53, a gene commonly altered in ovarian cancer. Pitavastatin-induced apoptosis was blocked by geranylgeraniol and mevalonate, products of the HMGCR pathway, confirming that pitavastatin causes cell death through inhibition of HMGCR. Solvent extracts of human and mouse food were also able to block pitavastatin-induced apoptosis, suggesting diet might influence the outcome of clinical trials. When nude mice were maintained on a diet lacking geranylgeraniol, oral pitavastatin caused regression of Ovcar-4 tumour xenografts. However, when the animal diet was supplemented with geranylgeraniol, pitavastatin failed to prevent tumour growth. This suggests that a diet containing geranylgeraniol can limit the anti-tumour activity of pitavastatin and diet should be controlled in clinical trials of statins.

Synergistic Impact of d-δ-Tocotrienol and Geranylgeraniol on the Growth and HMG CoA Reductase of Human DU145 Prostate Carcinoma Cells

The growth-suppressive effect of d-δ-tocotrienol and geranylgeraniol is at least partially attributed to their impact on 3-hydroxy-3-methylglutaryl coenzyme A (HMG CoA) reductase, the rate-limiting enzyme in the mevalonate pathway that provides essential intermediates for the posttranslational modification of growth-related proteins including RAS. We hypothesize that these agents synergistically impact cell growth based on their complementary mechanisms of action with HMG CoA reductase. d-δ-tocotrienol (0-40 µmol/L; half maximal inhibitory concentration [IC₅₀] = 15 µmol/L) and geranylgeraniol (0-100 µmol/L; IC₅₀ = 60 µmol/L) each induced concentration-dependent suppression of the growth of human DU145 prostate carcinoma cells. Blends of the two agents synergistically suppressed the growth of DU145 cells, with combination index values ranging 0.67-0.75. While 7.5 µmol/L d-δ-tocotrienol and 30 µmol/L geranylgeraniol individually had no impact on cell cycle distribution in DU145 cells, a blend of the agents induced cell cycle arrest at the G1 phase. The synergistic downregulation of the expression of HMG CoA reductase by 7.5 µmol/L d-δ-tocotrienol and 30 µmol/L geranylgeraniol was accompanied by a reduction in membrane K-RAS protein. Our finding supports the cancer chemopreventive action of plant-based diets and their isoprenoid constituents. Properly formulated isoprenoids and derivatives may provide novel approaches in prostate cancer prevention and therapy.

Antitumor properties of two traditional aromatic rice genotypes (Kalijira and Chinigura)

OBJECTIVE

Methanol extract of bran and unpolished grain of two traditional aromatic rice genotypes viz. Kalijira and Chinigura were assayed for their activity on the growth and initiation of crown-gall tumors on potato disks.

MATERIALS AND METHODS

Three Agrobacterium tumefaciens (A. tumefaciens) strain AtSl0105, AtTa0112, and AtAc0114 were used as the tumor forming agent. Collected rice was separated to bran and unpolished grain by different milling processes and made into fine powder before extracting using methanol. Antitumor assay of plant extracts was performed according to standard potato disc bioassay. Disc diffusion assay (Kirby-Bauer Method) was used to screen A. tumefaciens sensitivity test.

RESULTS

The results demonstrated a high correlation between the ability of aromatic rice to inhibit the initiation and growth of crown-gall tumors on potato disks. Maximum tumor inhibitions were observed against the strain AtSl0105 by Kalijira bran (73.91%) and Chinigura bran (69.56%). Both unpolished grains showed significant effect (Kalijira 57.43%, Chinigura 55.53%) to inhibit the tumor.

CONCLUSION

It can be concluded that aromatic rice (Kalijira and Chinigura) might be a potential source of antitumor agent that can be used for further drug development for tumor treatment.

Dietary supplementation with geranylgeraniol suppresses lipopolysaccharide-induced inflammation via inhibition of nuclear factor-κB activation in rats

PURPOSE

The isoprenoid geranylgeraniol (GGOH) inhibits nuclear factor-kappa B (NF-κB) activation in the liver, yet the mechanism remains unclear. We investigated the modulation and inhibition of lipopolysaccharide (LPS)-induced NF-κB signaling in the liver of rats fed a GGOH-supplemented diet.

METHODS

Rats were fed a diet supplemented with or without GGOH for 10 days. Rats were then intraperitoneally injected with 0.5 mg/kg LPS or vehicle (sterilized saline) and fasted for 18 h. Plasma levels of the inflammatory cytokines tumor necrosis factor (TNF)-α, interleukin (IL)-1β, and IL-6, and the liver damage indicators alanine and aspartate aminotransferases (ALT and AST) were assessed. Liver mRNA and proteins were assayed for changes in NF-κB target genes and signal transduction genes.

RESULTS

Rats fed a high-dose, GGOH-supplemented diet showed significantly lower levels of plasma inflammatory cytokines and ALT and AST activities. In the liver, GGOH significantly suppressed NF-κB activation and mRNA expression of its pro-inflammatory target genes. Furthermore, GGOH supplementation substantially suppressed mRNA expression of signal transducer genes upstream of the IκB kinase complex. Western blotting of liver extracts further demonstrated the substantial decrease in total IL-1 receptor-associated kinase 1 (IRAK1) and TNF receptor-associated factor 6 (TRAF6), leading to lower signal transduction and inhibition of NF-κB after LPS.

CONCLUSION

A 10-day, high-dose, GGOH-supplemented diet was sufficient to inhibit LPS-induced inflammation and activation of NF-κB in rat livers. GGOH significantly modulated NF-κB signaling molecules, inhibiting its signal transduction and activation in the liver, thus protecting against liver damage.

Geranylgeraniol oxidase activity involved in oxidative formation of geranylgeranoic acid in human hepatoma cells

Geranylgeranoic acid (GGA), a 20-carbon acyclic polyprenoic acid (all-trans 3,7,11,15-tetramethyl- 2,4,6,10,14-hexadecatetraenoic acid) and its derivatives were developed as synthetic "acyclic retinoids" for cancer chemoprevention. Previously, we have shown the natural occurrence of GGA in various medicinal herbs and reported enzymatic formation of GGA from geranylgeraniol (GGOH) through geranylgeranial (GGal) by rat liver homogenates. Here, we present several lines of evidence that a putative GGOH oxidase is involved in GGA synthesis by human hepatoma cell lysates. First, conversion of GGOH to GGal did not require exogenous NAD(+), whereas the conversion from GGal to GGA absolutely required additional NAD(+). Second, GGal synthesis from GGOH was coupled with consumption of oxygen from the reaction mixture. Third, GGOH-dependent GGal synthesis activity was proteinase K-resistant and even enhanced by proteinase K treatment; GGOH oxidase activity was enriched in the mitochondrial fraction. Finally, recombinant human monoamine oxidase (MAO)-B, but not MAO-A catalyzed oxidation of GGOH to GGal. These data suggest that a putative mitochondrial GGOH oxidase is involved in the initial step of GGA synthesis from GGOH.