Dehydroepiandrosterone-induced changes in mitochondrial proteins contribute to phenotypic alterations in hepatoma cells

Inhibition of non-small cell lung cancer (NSCLC) proliferation through targeting G6PD

Background

Mounting evidence has linked cancer metabolic reprogramming with altered redox homeostasis. The pentose phosphate pathway (PPP) is one of the key metabolism-related pathways that has been enhanced to promote cancer growth. The glucose 6-phosphate dehydrogenase (G6PD) of this pathway generates reduced nicotinamide adenine dinucleotide phosphate (NADPH), which is essential for controlling cellular redox homeostasis.

Objective

This research aimed to investigate the growth-promoting effects of G6PD in non-small cell lung cancer (NSCLC).

Methods

Clinical characteristics and G6PD expression levels in lung tissues of 64 patients diagnosed with lung cancer at the King Chulalongkorn Memorial Hospital (Bangkok, Thailand) during 2009-2014 were analyzed. G6PD activity in NSCLC cell lines, including NCI-H1975 and NCI-H292, was experimentally inhibited using DHEA and siG6PD to study cancer cell proliferation and migration.

Results

The positive expression of G6PD in NSCLC tissues was detected by immunohistochemical staining and was found to be associated with squamous cells. G6PD expression levels and activity also coincided with the proliferation rate of NSCLC cell lines. Suppression of G6PD-induced apoptosis in NSCLC cell lines by increasing Bax/Bcl-2 ratio expression. The addition of D-(-)-ribose, which is an end-product of the PPP, increased the survival of G6PD-deficient NSCLC cell lines.

Conclusion

Collectively, these findings demonstrated that G6PD might play an important role in the carcinogenesis of NSCLC. Inhibition of G6PD might provide a therapeutic strategy for the treatment of NSCLC.

γ-Tocotrienol inhibits oxidative phosphorylation and triggers apoptosis by inhibiting mitochondrial complex I subunit NDUFB8 and complex II subunit SDHB

Tocotrienols (T3s) are a subgroup of vitamin E and they have been widely tested to inhibit cell growth in various tumor types. Previous studies have shown that T3s inhibit cancer cell growth by targeting multiple signaling transduction and cellular processes. However, the role of T3s in the regulation of cellular bioenergetic processes remains unclear. In this study, we found that γ-T3 interacts with mitochondrial electron transfer chain NDUFB8 (a subunit of complex I) and SDHB (a subunit of complex II) and inhibits oxidative phosphorylation (OXPHOS), and triggers the production of reactive oxygen species (ROS). In addition, we observed that γ-T3 upregulates the glycolytic capacity in cells, but it did not compensate for cellular ATP generation and decreased the ATP levels in cells. Furthermore, we performed western blots and RT-PCR to measure the mRNA and protein levels of mitochondrial electron transfer chain (ETC) proteins and complex V (ATP synthase), where the results indicated that γ-T3 specifically inhibited the levels of NDUFB8 and SDHB, whereas it had little effect on UQCRC2 (a subunit of complex III), COX4I1 (a subunit of complex IV), and ATP5F1A (a subunit of complex V). The inhibition of NDUFB8 and SDHB by γ-T3 led to the overproduction of ROS and the depletion of ATP, which may be responsible for inducing apoptosis in cancer cells. Our results suggest that mitochondrial respiration may be an effective target for anticancer treatments based on γ-T3.

Mechanisms of Action of Dehydroepiandrosterone

Dehydroepiandrosterone (3β-hydroxy-5-androsten-17-one, DHEA) and its sulfated metabolite DHEA-S are the most abundant steroids in circulation and decline with age. Rodent studies have shown that DHEA has a wide variety of effects on liver, kidney, adipose, reproductive tissues, and central nervous system/neuronal function. The mechanisms by which DHEA and DHEA-S impart their physiological effects may be direct actions on plasma membrane receptors, including a DHEA-specific, G-protein-coupled receptor in endothelial cells; various neuroreceptors, e.g., aminobutyric-acid-type A, N-methyl-d-aspartate (NMDA), and sigma-1 (S1R) receptors; by binding steroid receptors: androgen and estrogen receptors (ARs, ERα, or ERβ); or by their metabolism to more potent sex steroid hormones, e.g., testosterone, dihydrotestosterone, and estradiol, which bind with higher affinity to ARs and ERs. DHEA inhibits voltage-gated T-type calcium channels. DHEA activates peroxisome proliferator-activated receptor (PPARα) and CAR by a mechanism apparently involving PP2A, a protein phosphatase dephosphorylating PPARα and CAR to activate their transcriptional activity. We review our recent study showing DHEA activated GPER1 (G-protein-coupled estrogen receptor 1) in HepG2 cells to stimulate miR-21 transcription. This chapter reviews some of the physiological, biochemical, and molecular mechanisms of DHEA and DHEA-S activity.

Dehydroepiandrosterone and Experimental Osteoarthritis

Despite an increased understanding of the pathogenesis of osteoarthritis (OA) and the availability of a number of drugs designed to ameliorate its symptoms, a successful disease-modifying therapy remains elusive. Recent lines of evidence suggest that dehydroepiandrosterone (DHEA), a 19-carbon steroid hormone classified as an adrenal androgen, exerts a chondroprotective effect in OA patients, and it has been proven to be an effective DMOAD candidate that slows OA progression. However, the exact mechanisms underlying its anti-OA effect is largely unknown. This review summarizes emerging observations from studies of cell biology, preclinical animal studies, and preliminary clinical trials and describes the findings of investigations on this topic to develop an initial blueprint of the mechanisms by which DHEA slows OA progression. Presently, studies on DMOADs are increasing in importance but have met limited success. Encouragingly, the current data on DHEA are promising and may prove that DHEA-based treatment is efficacious for preventing and slowing human OA progression.