Geraniol attenuates oxidative stress by Nrf2 activation in diet-induced experimental atherosclerosis

Mechanism and Progress of Natural Products in the Treatment of NAFLD-Related Fibrosis

Nonalcoholic fatty liver disease (NAFLD) has emerged as the most prevalent chronic liver disorder worldwide, with liver fibrosis (LF) serving as a pivotal juncture in NAFLD progression. Natural products have demonstrated substantial antifibrotic properties, ushering in novel avenues for NAFLD treatment. This study provides a comprehensive review of the potential of natural products as antifibrotic agents, including flavonoids, polyphenol compounds, and terpenoids, with specific emphasis on the role of Baicalin in NAFLD-associated fibrosis. Mechanistically, these natural products have exhibited the capacity to target a multitude of signaling pathways, including Hedgehog, Wnt/β-catenin, TGF-β1, and NF-κB. Moreover, they can augment the activities of antioxidant enzymes, inhibit pro-fibrotic factors, and diminish fibrosis markers. In conclusion, this review underscores the considerable potential of natural products in addressing NAFLD-related liver fibrosis through multifaceted mechanisms. Nonetheless, it underscores the imperative need for further clinical investigation to authenticate their effectiveness, offering invaluable insights for future therapeutic advancements in this domain.

Natural Monoterpenes as Potential Therapeutic Agents against Atherosclerosis

Traditional herbal medicines based on natural products play a pivotal role in preventing and managing atherosclerotic diseases, which are among the leading causes of death globally. Monoterpenes are a large class of naturally occurring compounds commonly found in many aromatic and medicinal plants. Emerging evidence has shown that monoterpenes have many biological properties, including cardioprotective effects. Remarkably, an increasing number of studies have demonstrated the therapeutic potential of natural monoterpenes to protect against the pathogenesis of atherosclerosis. These findings shed light on developing novel effective antiatherogenic drugs from these compounds. Herein, we provide an overview of natural monoterpenes' effects on atherogenesis and the underlying mechanisms. Monoterpenes have pleiotropic and multitargeted pharmacological properties by interacting with various cell types and intracellular molecular pathways involved in atherogenesis. These properties confer remarkable advantages in managing atherosclerosis, which has been recognized as a multifaceted vascular disease. We also discuss limitations in the potential clinical application of monoterpenes as therapeutic agents against atherosclerosis. We propose perspectives to give new insights into future preclinical research and clinical practice regarding natural monoterpenes.

Anti-Inflammatory Activity of Geraniol Isolated from Lemon Grass on Ox-LDL-Stimulated Endothelial Cells by Upregulation of Heme Oxygenase-1 via PI3K/Akt and Nrf-2 Signaling Pathways

Among the world's leading causes of cardiovascular disease, atherosclerosis is a chronic inflammatory disorder that affects the arteries. Both vasodilation and vasoconstriction, low levels of nitric oxide and high levels of reactive oxygen species and pro-inflammatory factors characterize dysfunctional blood vessels. Hypertension, and atherosclerosis, all start with this dysfunction. Geraniol, a compound of acyclic monoterpene alcohol, found in plants such as geranium, lemongrass and rose, is a primary constituent of essential oils. It shows a variety of pharmacological properties. This study aimed to investigate the impact of geraniol on Ox-LDL-induced stress and inflammation in human umbilical vein endothelial cells. In this study, HUVECs were treated with Ox-LDL or geraniol at different dose concentrations. MTT assay, Western blot, ROS generation and DNA fragmentation were used to evaluate geraniol's effects on Ox-LDL-induced HUVECs inflammation. The results show that geraniol pre-incubation ameliorates Ox-LDL-mediated HUVECs cytotoxicity and DNA fragmentation. The geraniol inhibited the production of pro-inflammatory cytokines by Ox-LDL, including TNF-α, IL-6 and IL-1β. In Ox-LDL-stimulated HUVECs, geraniol suppresses the nuclear translocation and activity of NF-ᴋB as well as phosphorylation of IkBα. Moreover, geraniol activated the PI3K/AKT/NRF2 pathway in HUVECs, resulting in an increase in the expression of HO-1. Taking our data together, we can conclude that, in HUVECs, geraniol inhibits Ox-LDL-induced inflammation and oxidative stress by targeting PI3/AKT/NRF2.

Nutritional Health Perspective of Natto: A Critical Review

Natto, a traditional soy food fermented by Bacillus subtilis, is made by steaming or cooking soaked soybean seeds, inoculating them with the bacteria, and then letting them sit for an incubation period. Natto soya has grown popular because of its nutritional importance and health advantages. As a result, farmers have more opportunities, thanks to the natto soybean market. For the natto soybean market to remain stable and grow, improved soybean cultivars with enhanced natto quality traits are essential. Natto's high-quality attributes are influenced by the bacteria strain, processing parameters, and soybean variety. Natto has a specific flavor and aroma with a slimy, sticky consistency. Natto possesses various therapeutic potentials and contains a range of essential nutrients and bioactive compounds, i.e., nattokinase, soybean isoflavone, γ-polyglutamic acid, vitamin K₂, and biogenic amines. Bacterial species, processing conditions, and cultivars of soybean determine the quality characteristics of natto. Natto food is higher in menaquinone-7 and contains 100 times more menaquinone-7 than most cheeses. The present review highlights the production technology, microbiology, nutritional composition, and therapeutic potentials of natto.

Miso: A traditional nutritious & health-endorsing fermented product

Consumer demand for fermented foods with a well-balanced nutrient profile has been increasing owing to their ability to prevent chronic diseases as well as their functional, nutritional, and nutraceutical benefits. Among those functional foods, miso is a well-known traditional fermented food with a distinctive savory flavor and aroma that is most commonly used as a seasoning in miso soup. Among different fermented products, miso is derived from soybeans and grains as a result of the activities of Koji enzymes and beneficial microbes. Additionally, the microbial community of miso is thought to be crucial in enhancing its distinct flavor and texture as well as its nutritional properties. Despite the importance of microorganisms in the production of miso, there has been relatively little research done to characterize and describe the nutritional and medicinal potential of miso. In this review, the potential therapeutic properties, i.e., anticancer, antimicrobial, and antiobesity, of miso have been discussed comprehensively. This review envisions the production technology, its history, microbial population, nutritional properties, and the potential health benefits of miso associated with its consumption.

Renal Ischemia/Reperfusion Mitigation via Geraniol: The Role of Nrf-2/HO-1/NQO-1 and TLR2,4/MYD88/NFκB Pathway

BACKGROUND

Renal ischemia/reperfusion injury is a clinically recurrent event during kidney transplantation. Geraniol is a natural monoterpene essential oil component. This study aimed to inspect geraniol's reno-protective actions against renal I/R injury with further analysis of embedded mechanisms of action through scrutinizing the Nrf-2/HO-1/NQO-1 and TLR2,4/MYD88/NFκB signaling pathways.

METHODS

Wistar male rats were randomized into five groups: Sham, Sham + geraniol, Renal I/R, and two Renal I/R + geraniol groups representing two doses of geraniol (100 and 200 mg/kg) for 14 days before the renal I/R. Renal I/R was surgically induced by occluding both left and right renal pedicles for 45 min, followed by reperfusion for 24 h. A docking study was performed to anticipate the expected affinity of geraniol towards three protein targets: hTLR4/MD2, hTLR2, and hNrf2/Keap1.

RESULTS

Renal I/R rats experienced severely compromised renal functions, histological alteration, oxidative stress status, escalated Nrf-2/HO-1/NQO-1, and amplified TLR2,4/MYD88/NFκB. Geraniol administration ameliorated renal function, alleviated histological changes, and enhanced Nrf-2/HO-1/NQO-1 with a subsequent intensification of antioxidant enzyme activities. Geraniol declined TLR2,4/MYD88/NFκB with subsequent TNF-α, IFN-γ, MCP-1 drop, Bax, caspase-3, and caspase-9 reduction IL-10 and Bcl-2 augmentation. Geraniol exhibited good fitting in the binding sites of the three in silico examined targets.

CONCLUSIONS

Geraniol might protect against renal I/R via the inhibition of the TLR2,4/MYD88/NFκB pathway, mediating anti-inflammation and activation of the Nrf2 pathway, intervening in antioxidative activities.

Monoterpenes as Sirtuin-1 Activators: Therapeutic Potential in Aging and Related Diseases

Sirtuin 1 (SIRT) is a class III, NAD⁺-dependent histone deacetylase that also modulates the activity of numerous non-histone proteins through deacylation. SIRT1 plays critical roles in regulating and integrating cellular energy metabolism, response to stress, and circadian rhythm by modulating epigenetic and transcriptional regulation, mitochondrial homeostasis, proteostasis, telomere maintenance, inflammation, and the response to hypoxia. SIRT1 expression and activity decrease with aging, and enhancing its activity extends life span in various organisms, including mammals, and improves many age-related diseases, including cancer, metabolic, cardiovascular, neurodegenerative, respiratory, musculoskeletal, and renal diseases, but the opposite, that is, aggravation of various diseases, such as some cancers and neurodegenerative diseases, has also been reported. Accordingly, many natural and synthetic SIRT1 activators and inhibitors have been developed. Known SIRT1 activators of natural origin are mainly polyphenols. Nonetheless, various classes of non-polyphenolic monoterpenoids have been identified as inducers of SIRT1 expression and/or activity. This narrative review discusses current information on the evidence that supports the role of those compounds as SIRT1 activators and their potential both as tools for research and as pharmaceuticals for therapeutic application in age-related diseases.

Geraniol and β-citronellol participate in the vasorelaxant effects of Rosa damascena Miller essential oil on the rat thoracic aorta

AIM

This study aimed to investigate the vasoactive effects of Rosa damascena Miller essential oil and its major components, geraniol and β-citronellol, on the rat thoracic aorta.

METHODS

Isolated tissue bath model and Wistar rats were used to perform the experiments. Two-fold increasing concentrations (20-160 μg/mL) of rose oil were administered to determine its vasoactive effects. Submaximal contractions were induced by PE or KCl in both endothelium-intact and -denuded segments. Time-matched control groups were also formed. To evaluate the role of geraniol and β-citronellol, concentrations in the range of 0.4-3.2 μg/mL and 0.8-6.4 μg/mL were applied respectively. The statistical significance level was considered as p < 0.05.

RESULTS

All doses of rose oil applied led to vasorelaxation in thoracic aortas precontracted with PE. In precontracted thoracic aortas with KCl, the significant effect of rose oil persisted, albeit slightly diminished. When the endothelium was removed, the relaxant effect of rose oil was partially reduced, but still significant. Besides, although geraniol relaxed aortic segments at all concentrations (0.4 to 3.2 μg/mL), β-citronellol caused vasorelaxation at doses of 1.6, 3.2, and 6.4 μg/mL.

CONCLUSION

In conclusion, the first findings were obtained that rose oil can cause a vasorelaxant effect in a concentration-dependent manner in rat thoracic aorta. This effect substantially persisted in vascular segments without endothelium or precontracted with KCl. It was further shown for the first time that geraniol and β-citronellol exert vasodilatory effects on the rat thoracic aorta. These results suggest that rose oil exhibits its vasorelaxant effect through geraniol and β-citronellol.

Geraniol Averts Methotrexate-Induced Acute Kidney Injury via Keap1/Nrf2/HO-1 and MAPK/NF-κB Pathways

Objectives: Geraniol, a natural monoterpene, is an essential oil component of many plants. Methotrexate is an anti-metabolite drug, used for cancer and autoimmune conditions; however, clinical uses of methotrexate are limited by its concomitant renal injury. This study investigated the efficacy of geraniol to prevent methotrexate-induced acute kidney injury and via scrutinizing the Keap1/Nrf2/HO-1, P38MAPK/NF-κB and Bax/Bcl2/caspase-3 and -9 pathways. Methods: Male Wister rats were allocated into five groups: control, geraniol (orally), methotrexate (IP), methotrexate and geraniol (100 and 200 mg/kg). Results: Geraniol effectively reduced the serum levels of creatinine, urea and Kim-1 with an increase in the serum level of albumin when compared to the methotrexate-treated group. Geraniol reduced Keap1, escalated Nrf2 and HO-1, enhanced the antioxidant parameters GSH, SOD, CAT and GSHPx and reduced MDA and NO. Geraniol decreased renal P38 MAPK and NF-κB and ameliorated the inflammatory mediators TNF-α, IL-1β, IL-6 and IL-10. Geraniol negatively regulated the apoptotic mediators Bax and caspase-3 and -9 and increased Bcl2. All the biochemical findings were supported by the alleviation of histopathological changes in kidney tissues. Conclusion: The current findings support that co-administration of geraniol with methotrexate may attenuate methotrexate-induced acute kidney injury.

Geraniol isolated from lemon grass to mitigate doxorubicin-induced cardiotoxicity through Nrf2 and NF-κB signaling

BACKGROUND

Geraniol, a natural monoterpene, is a component of many plant essential oils. It contains many medicinal and pharmacological properties. Doxorubicin is an anticancer drug; however, its clinical usage is limited due to its cumulative and dose-dependent cardiotoxicity. This study investigates geraniol as a protective agent against doxorubicin-induced cardiotoxicity and explores possible underlying mechanisms of action.

METHODS

Male Sprague-Dawley rats were allocated into five groups. Groups 1 and 2 were administered saline and geraniol 200 mg/kg/day/orally, respectively, for 15 days. Group 3 was administered intraperitoneal doxorubicin (5 mg/kg/IP on the 5th, 10th and 15th days to achieve a cumulative dose of 15 mg/kg) to induce cardiotoxicity. The fourth and fifth groups were treated with either geraniol 100 mg/kg or 200 mg/kg orally and doxorubicin to equal the doxorubicin dose administered to Group 3.

RESULTS

Treatment with geraniol significantly ameliorated cardiac damage and restored serum cardiac injury marker levels in doxorubicin treated animals. Geraniol upregulated Nrf2 and HO-1 expression, elevated total antioxidant capacity, decreased the nuclear accumulation of kappa-light-chain enhancer of activated B cells (NF-κB), decreased the phosphorylation and degradation of nuclear factor of kappa light polypeptide gene enhancer in B-cells inhibitor, alpha (IκBα), suppressed tumor necrosis factor-alpha (TNF-α), interleukin 1 beta (IL-1β), and interleukin-18 (IL-18) levels, and restored the levels of Bax and caspase-3 and 9 in heart tissue.

CONCLUSION

Geraniol may function as a potential activator of nuclear factor erythroid 2-related factor 2 (Nrf2), which subsequently improves Nrf2-dependent antioxidative signaling, diminishes apoptosis and subdues the inflammatory response. The downstream result is protection of the heart from doxorubicin-induced cardiotoxicity.

Geraniol improved memory impairment and neurotoxicity induced by zinc oxide nanoparticles in male wistar rats through its antioxidant effect

AIMS

Zinc oxide nanoparticles (ZnO-NPs) are currently applied in food and pharmaceutical industries whose neurotoxic effect on the central nervous system (CNS) is a major concern. Considering the pharmacological properties (antioxidant, anti-inflammatory) of the geraniol (GE), we aimed to investigate the efficacy of geraniol on ZnO-NPs neurotoxicity.

MATERIALS AND METHODS

We used 32 male Wistar rats, randomly assigned to four groups (n = 8): Control, GE (daily received 100 mg/kg of GE by gavage), ZnO-NPs (received intraperitoneal injection of 75 mg/kg of ZnO-NPs twice a week), and ZnO-NPs + GE (received both GE and ZnO-NPs at same doses above during 4 weeks). Morris water maze (MWM) and Y-maze tasks were done to evaluate learning and memory function. Biochemical assays were done to measure total antioxidant capacity (TAC), malondialdehyde (MDA), superoxide dismutase (SOD), glutathione peroxidase (GPX) and ZnO-NPs bioaccumulation. Nissl and H&E staining were performed for histological evaluations.

KEY FINDINGS

The results of behavioral study revealed that GE improved learning and memory impairment induced by ZnO-NPs. Moreover, neuroprotective effect of GE significantly decreased pathological parameters such as necrosis and gliosis, and consequently increased the number of nerve cells in the cortex and different hippocampal areas. Furthermore, biochemical studies demonstrated that GE significantly increased antioxidant indices (namely, TAC, SOD, and GPX) and reduced oxidative stress marker (MDA) and Zn bioaccumulation in ZnO-NPs treated animals.

SIGNIFICANCE

Our results provide experimental evidence to further investigate the precise mechanisms underlying the geraniol as a promising therapeutic approach for improvement of cognitive function and neurotoxicity induce by ZnO-NPs.

A review on herbal Nrf2 activators with preclinical evidence in cardiovascular diseases

Cardiovascular diseases (CVDs) are an ever-growing problem and are the most common cause of death worldwide. The uncontrolled production of reactive oxygen species (ROS) and the activation of ROS associated with various cell signaling pathways with oxidative cellular damage are the most common pathological conditions connected with CVDs including endothelial dysfunction, hypercontractility of vascular smooth muscle, cardiac hypertrophy and heart failure. The nuclear factor E2-related factor 2 (Nrf2) is a basic leucine zipper redox transcription factor, together with its negative regulator, kelch-like ECH-associated protein 1 (Keap1), which serves as a key regulator of cellular defense mechanisms to combat oxidative stress and associated diseases. Multiple lines of evidence described here support the cardiac protective property of Nrf2 in various experimental models of cardiac related disease conditions. In this review, we emphasized the molecular mechanisms of Nrf2 and described the detailed outline of current findings on the therapeutic possibilities of the Nrf2 activators specifically from herbal origin in various CVDs. Based on evidence from various preclinical experimental models, we have highlighted the activation of Nrf2 pathway as a budding therapeutic option for the prevention and treatment of CVDs, which needs further investigation and validation in the clinical settings.

Geraniol attenuates oxidative stress, bioaccumulation, serological and histopathological changes during aluminum chloride-hepatopancreatic toxicity in male Wistar rats

Aluminum chloride (AlCl₃) has different industrial applications including manufacturing paint and water treatment. The present study was designed to evaluate the alleviating effect of geraniol against AlCl₃-induced hepatopancreatic toxicity. To this end, forty male Wistar rats were divided into control (0.9% NaCl, IP), geraniol (100 mg/kg orally), AlCl₃ (70 mg/kg, IP), and AlCl₃ (70 mg/kg, IP) plus geraniol (100 mg/kg orally) groups and then were treated daily for 28 days. Based on the results, serum cholesterol, triglyceride, as well as liver and pancreas enzymes increased significantly (P < 0.05) while the level of insulin significantly decreased in AlCl₃-treated rats compared to the control group (P < 0.05). The presence of geraniol relieved the toxic effects of AlCl₃ as well. On the other hand, the level of malondialdehyde (MDA) increased in the AlCl₃-treated group while the activities of glutathione peroxidase and the total antioxidant activity demonstrated a reduction. However, the MDA level decreased while the antioxidant enzymes increased in co-treated with geraniol group. Histopathological examination revealed that simultaneous treatment with geraniol in AlCl₃ intoxicated rats ameliorate the liver lesions such as necrosis, inflammatory cell infiltration, vacuolar degeneration, along with hyperemia and the cell density of the Langerhans islands. Finally, the results indicated that geraniol attenuated the side effect of AlCl₃-induced hepatopancreatic toxicity.

Geraniol activates Nrf-2/HO-1 signaling pathway mediating protection against oxidative stress-induced apoptosis in hepatic ischemia-reperfusion injury

Geraniol (GOH) is a natural essential oil that possesses antioxidant, anti-inflammatory, and antiapoptotic properties by various signaling pathways. Liver ischemia-reperfusion injury (IRI) is a serious event that triggers liver dysfunction or even failure. Nuclear factor erythroid 2-related factor 2 (Nrf2), a transcriptional factor, maintains cellular defense mechanism through antioxidant and anti-inflammatory properties. To detect GOH effect against liver IRI through the activation of the Nrf2/HO-1 antioxidant pathway, five groups of rats were randomized to normal, sham, IR, GOH, and GOH/IR. Blood samples and liver tissues were collected to measure various biochemical parameters related to liver function, and oxidative stress as well as inflammatory and apoptotic indicators besides liver tissue histopathology was evaluated by light microscopy. GOH induces activation of Nrf2 along with the upregulation of HO-1 expression. Also, the antioxidant activity of GOH was shown by the elevation of total antioxidant capacity and GSH levels, together with normalizing malondialdehyde. Regarding the anti-inflammatory effect of GOH, it suppresses the levels of TNF-α, iNOS, and COX-2. Additionally, the antiapoptotic effect of GOH, Bax, and caspase-3, 9 were reduced in liver tissue. GOH is a promising hepatoprotective agent in liver IRI through the activation of Nrf2/HO-1 antioxidant pathway.

Natural Monoterpenes: Much More than Only a Scent

Terpenes are a widespread group of secondary metabolites that can be found in various family plants such as the Lamiaceae. In view of their numerous valuable biological activities, the industrial production of concrete terpenes and essential oils rich in the substances is intensively studied. Monoterpenes constitute a significant part of the whole group of the aforementioned secondary metabolites. This is due to their numerous biological activities and their ability to permeate the skin. Despite the fact that these substances have gain popularity, they are not comprehensively characterized. The presented review is based on studies of the biological activities of the most important monoterpenes and the essential oils rich in these compounds. The authors focused attention on antioxidant activity, inhibition towards acetyl- and butyrylcholinesterase, and α-amylase and α-glucosidase, antifungal, hepatoprotective, sedative properties, and their skin permeation enhancement.

The Effects of Dimethyl Fumarate on Atherosclerosis in the Apolipoprotein E-Deficient Mouse Model with Streptozotocin-Induced Hyperglycemia Mediated By the Nuclear Factor Erythroid 2-Related Factor 2/Antioxidant Response Element (Nrf2/ARE) Signaling Pathway

Background

This study aimed to investigate the effects of dimethyl fumarate (DMF) on thoracic aortic atherosclerosis in the apolipoprotein E (apo-E)-deficient mouse model with streptozotocin (STZ)-induced hyperglycemia, and the signaling pathways involved.

Material/Methods

Eight-week-old ApoE−/− male mice (n=30) were randomly divided into three groups: the Control group (ApoE−/−) (n=10); the diabetic model (STZ) group (n=10); and the DMF-treated (25 mg/kg) diabetic model (DMF+STZ) group (n=10). The area of the thoracic aortic atherosclerosis was determined by histology. Reactive oxygen species (ROS) levels in mouse serum and homogenates of the thoracic aorta were determined by colorimetry. Levels of nicotinamide-adenine dinucleotide phosphate (NADPH) oxidase subunit gp91^phox were detected by immunological hybridization, and levels of heme oxygenase-1 (HO-1) were measured by enzyme-linked immunosorbent assay (ELISA).

Results

Compared with the Control group, in the STZ group, the area of aortic atherosclerosis was significantly increased, the levels of serum and aortic ROS, HO-1, nuclear factor-κB (NF-κB), intercellular adhesion molecule 1 (ICAM-1), and gp91^phox were increased, and nuclear factor erythroid 2-related factor 2 (Nrf2), endothelial nitric oxide synthase (eNOS), and phosphorylated eNOS (p-eNOS) were significantly reduced. Compared with the STZ group, in the DMF+STZ group, the area of aortic atherosclerosis was significantly reduced, the levels of serum and aortic ROS, HO-1, NF-κB, ICAM-1, and gp91^phox were significantly reduced, and Nrf2, eNOS, and p-eNOS were significantly increased.

Conclusions

In the apo-E-deficient mouse model with STZ-induced hyperglycemia, DMF reduced the development of atherosclerosis of the thoracic aorta through the nuclear factor erythroid 2-related factor 2/antioxidant response element (Nrf2/ARE) signaling pathway.

Contribution of Nrf2 to Atherogenic Phenotype Switching of Coronary Arterial Smooth Muscle Cells Lacking CD38 Gene

Background/Aims

Recent studies have indicated that CD38 gene deficiency results in dedifferentiation or transdifferentiation of arterial smooth muscle cells upon atherogenic stimulations. However, the molecular mechanisms mediating this vascular smooth muscle (SMC) phenotypic switching remain unknown.

Methods & Results

In the present study, we first characterized the phenotypic change in the primary cultures of coronary arterial myocytes (CAMs) from CD38^−/− mice. It was shown that CD38 deficiency decreased the expression of contractile marker calponin, SM22α and α-SMA but increased the expression of SMC dedifferentiation marker, vimentin, which was accompanied by enhanced cell proliferation. This phenotypic change in CD38^−/− CAMs was enhanced by 7-ketocholesterol (7-Ket), an atherogenic stimulus. We further found that the CD38 deficiency decreased the expression and activity of nuclear factor E2-related factor 2 (Nrf2), a basic leucine zipper (bZIP) transcription factor sensitive to redox regulation. Similar to CD38 deletion, Nrf2 gene silencing increased CAM dedifferentiation upon 7-Ket stimulation. In contrast, the overexpression of Nrf2 gene abolished 7-Ket-induced dedifferentiation in CD38^−/− CAMs. Given the sensitivity of Nrf2 to oxidative stress, we determined the role of redox signaling in the regulation of Nrf2 expression and activity associated with CD38 effect in CAM phenotype changes. It was demonstrated that in CD38^−/− CAMs, 7-Ket failed to stimulate the production of O₂^−., while in CD38^+/+ CAMs 7-Ket induced marked O₂^−. production and enhancement of Nrf2 activity, which was substantially attenuated by NOX4 gene silencing. Finally, we demonstrated that 7-Ket-induced and NOX4-dependent O₂^−. production was inhibited by 8-Br-cADPR, an antagonist of cADPR or NED-19, an antagonist of NAADP as product of CD38 ADP-ribosylcyclase, which significantly inhibited the level of cytosolic Ca²⁺ and the activation of Nrf2 under 7-Ket.

Conclusion

Taken together, these results suggest that CD38 activity is required for 7-Ket-induced Ca²⁺ and consequently O₂^−. production in CAMs, which increases Nrf2 activity to maintain their differentiated status. When CD38 gene expression and function are deficient, the Nrf2 activity is suppressed, thereby leading to phenotypic switching of CAMs.