Molecular Mechanisms Responsible for Pharmacological Effects of Genipin on Mitochondrial Proteins

Inhibition of Mitochondrial Uncoupling Proteins Arrests Human Spermatozoa Motility without Compromising Viability

Mitochondrial uncoupling proteins (UCPs) are central in the regulation of mitochondrial activity and reactive oxygen species (ROS) production. High oxidative stress is a major cause of male infertility; however, UCPs expression and function in human spermatozoa are still unknown. Herein, we aimed to assess the expression and function of the different homologs (UCP1-6) in human spermatozoa. For this purpose, we screened for the mRNA expression of all UCP homologs. Protein expression and immunolocalization of UCP1, UCP2, and UCP3 were also assessed. Highly motile spermatozoa were isolated from human normozoospermic seminal samples (n = 16) and incubated with genipin, an inhibitor of UCPs (0, 0.5, 5, and 50 µM) for 3 h at 37 °C. Viability and total motility were assessed. Mitochondrial membrane potential and ROS production were evaluated. Media were collected and the metabolic profile and antioxidant potential were analyzed by ¹H-NMR and FRAP, respectively. The expression of all UCP homologs (UCP1-6) mRNA by human spermatozoa is herein reported for the first time. UCP1-3 are predominant at the head equatorial segment, whereas UCP1 and UCP2 are also expressed at the spermatozoa midpiece, where mitochondria are located. The inhibition of UCPs by 50 µM genipin, resulting in the UCP3 inhibition, did not compromise sperm cell viability but resulted in irreversible total motility loss that persisted despite washing or incubation with theophylline, a cAMP activator. These effects were associated with decreased mitochondrial membrane potential and lactate production. No differences concerning UCP3 expression, however, were observed in spermatozoa from normozoospermic versus asthenozoospermic men (n = 6). The inhibition of UCPs did not increase ROS production, possibly due to the decreased mitochondrial activity and genipin antioxidant properties. In sum, UCPs are major regulators of human spermatozoa motility and metabolism. The discovery and characterization of UCPs' role in human spermatozoa can shed new light on spermatozoa ROS-related pathways and bioenergetics physiology.

UCP2 as a Cancer Target through Energy Metabolism and Oxidative Stress Control

Despite numerous therapies, cancer remains one of the leading causes of death worldwide due to the lack of markers for early detection and response to treatment in many patients. Technological advances in tumor screening and renewed interest in energy metabolism have allowed us to identify new cellular players in order to develop personalized treatments. Among the metabolic actors, the mitochondrial transporter uncoupling protein 2 (UCP2), whose expression is increased in many cancers, has been identified as an interesting target in tumor metabolic reprogramming. Over the past decade, a better understanding of its biochemical and physiological functions has established a role for UCP2 in (1) protecting cells from oxidative stress, (2) regulating tumor progression through changes in glycolytic, oxidative and calcium metabolism, and (3) increasing antitumor immunity in the tumor microenvironment to limit cancer development. With these pleiotropic roles, UCP2 can be considered as a potential tumor biomarker that may be interesting to target positively or negatively, depending on the type, metabolic status and stage of tumors, in combination with conventional chemotherapy or immunotherapy to control tumor development and increase response to treatment. This review provides an overview of the latest published science linking mitochondrial UCP2 activity to the tumor context.

Design, synthesis, and characterization of a novel dual cross-linked gelatin-based bioadhesive for hard and soft tissues adhesion capability

Many surgical treatments require a suitable tissue adhesive that maintains its performance in wet conditions and can be applied simultaneously for hard and soft tissues. In the present study, a dual cross-linked tissue adhesive was synthesized by mixing the gelatin methacryloyl (Gel-MA) and gelatin-dopamine conjugate (Gel-Dopa). The setting reaction was based on a photopolymerization process in the presence of a combination of riboflavin and triethanolamine and a chemical cross-linking process attributed to the genipin as a natural cross-linker. Modified gelatin macromolecules were characterized and the best wavelength for free radical generation in the presence of riboflavin was obtained. Tissue adhesives were prepared with 30% hydrogels of Gel-MA and Gel-Dopa with different ratios in distilled water. The gelation occurred in a short time after light irradiation. The chemical, mechanical, physical, and cytotoxicity properties of the tissue adhesives were evaluated. The results showed that despite photopolymerization, chemical crosslinking with genipin played a more critical role in the setting process. Water uptake, degradation behavior, cytotoxicity, and adhesion properties of the adhesives were correlated with the ratio of the components. The SEM images showed a porous structure that could ensure the entry of cells and nutrients into the surgical area. While acceptable properties in most experiments were observed, all features were improved as the Gel-Dopa ratio increased. Also, the obtained hydrogels revealed excellent adhesive properties, particularly with bone even after wet incubation, and it was attributed to the amount of gelatin-dopamine conjugate. From the obtained results, it was concluded that a dual adhesive hydrogel based on gelatin macromolecules could be a good candidate as a tissue adhesive in wet condition.

Nanothermometer with Temperature Induced Reversible Emission for Evaluation of Intracellular Thermal Dynamics

Temperature dynamics reflect the physiological state of cells, and accurate measurement of intracellular temperature helps to understand the biological processes. Herein, we report a novel nanothermometer by conjugating a fluorescent probe 3-ethyl-2-[4-(1,2,2-triphenylvinyl)styryl]benzothiazol-3-ium iodide (TPEBT) with a thermoresponsive polymer poly(N-isopropylacrylamide-co-tetrabutylphosphonium styrenesulfonate) [P(NIPAM-co-TPSS)]. The derived nanoprobe TPEBT-P(NIPAM-co-TPSS) self-assembles into micelles with TPEBT as hydrophobic core and PNIPAM as hydrophilic shell. It exhibits aggregation-induced emission (AIE) at λ_ex/λ_em = 420/640 nm in aqueous medium with a quantum yield of Φ_F 11.9%. The rise in temperature transforms PNIPAM chains from linear to compact spheres to serve as the core of micelles, and meanwhile converts TPEBT from the state of aggregation to dispersion and redistributes in the micellar shell. Temperature-driven phase transition of P(NIPAM-co-TPSS) mediates the reversible aggregation and disaggregation of TPEBT and endows the nanothermometer with temperature-dependent AIE features and favorable sensitivity for temperature sensing in 32-40 °C. TPEBT-P(NIPAM-co-TPSS) is taken up by HeLa cells to distribute mainly in lysosomes. It enables quantitative visualization of in situ thermal dynamics in response to stimuli from carbonyl cyanide 4-(trifluoromethoxy)phenylhydrazone, oligomycin, genipin, and lipopolysaccharide. The real-time monitoring of photothermal-induced intracellular temperature variation is further conducted.

Genipin, an Inhibitor of UCP2 as a Promising New Anticancer Agent: A Review of the Literature

Genipin is a protein cross-linking agent extracted from Gardenia (Gardenia jasminoides Ellis) fruits. This fruit has conventionally been used as a Chinese herbal medicine for the treatment of inflammation and jaundice and as an edible colorant in oriental countries. Uncoupling protein (UCP)-2 is a member of the family of uncoupling proteins, which are anion transporters positioned in the mitochondrial inner membrane. Genipin has been shown to have hepatoprotective activity, acting as an effective antioxidant and inhibitor of mitochondrial UCP2, and is also reported to exert significant anticancer effects. In this review, the author presents the latest progress of genipin as an anticancer agent and concisely describes its various mechanisms of action. In brief, genipin inhibits UCP2 to attenuate generation of reactive oxygen species (ROS), leading to ROS/c-Jun N-terminal kinase-dependent apoptosis of cancer cells. Genipin also increases the tissue inhibitors of matrix metalloproteases (MMP)-2, a kind of tumor promoter in a variety of cancers, as well as induces caspase-dependent apoptosis in in vitro and in vivo models. These findings suggest that genipin can serve as a promising novel antitumor agent that could be applicable for chemotherapy and/or chemoprevention for cancers.

Novel Findings regarding the Bioactivity of the Natural Blue Pigment Genipin in Human Diseases

Genipin is an important monoterpene iridoid compound isolated from Gardenia jasminoides J.Ellis fruits and from Genipa americana fruits, or genipap. It is a precursor of a blue pigment which may be attractive alternative to existing food dyes and it possesses various potential therapeutic properties such as anti-cancer, anti-diabetic and hepatoprotective activity. Biomedical studies also show that genipin may act as a neuroprotective drug. This review describes new aspects of the bioactivity of genipin against various diseases, as well as its toxicity and industrial applications, and presents its potential mechanism of action.

Biomimetic matrix for the study of neuroblastoma cells: A promising combination of stiffness and retinoic acid

Neuroblastoma is the third most common pediatric cancer composed of malignant immature cells that are usually treated pharmacologically by all trans-retinoic acid (ATRA) but sometimes, they can spontaneously differentiate into benign forms. In that context, biomimetic cell culture models are warranted tools as they can recapitulate many of the biochemical and biophysical cues of normal or pathological microenvironments. Inspired by that challenge, we developed a neuroblastoma culture system based on biomimetic LbL films of physiological biochemical composition and mechanical properties. For that, we used chondroitin sulfate A (CSA) and poly-L-lysine (PLL) that were assembled and mechanically tuned by crosslinking with genipin (GnP), a natural biocompatible crosslinker, in a relevant range of stiffness (30-160 kPa). We then assessed the adhesion, survival, motility, and differentiation of LAN-1 neuroblastoma cells. Remarkably, increasing the stiffness of the LbL films induced neuritogenesis that was strengthened by the combination with ATRA. These results highlight the crucial role of the mechanical cues of the neuroblastoma microenvironment since it can dramatically modulate the effect of pharmacologic drugs. In conclusion, our biomimetic platform offers a promising tool to help fundamental understanding and pharmacological screening of neuroblastoma differentiation and may assist the design of translational biomaterials to support neuronal regeneration. STATEMENT OF SIGNIFICANCE: Neuroblastoma is one of the most common pediatric tumor commonly treated by the administration of all-trans-retinoic acid (ATRA). Unfortunately, advanced neuroblastoma often develop ATRA resistance. Accordingly, in the field of pharmacological investigations on neuroblastoma, there is a tremendous need of physiologically relevant cell culture systems that can mimic normal or pathological extracellular matrices. In that context, we developed a promising matrix-like cell culture model that provides new insights on the crucial role of mechanical properties of the microenvironment upon the success of ATRA treatment on the neuroblastoma maturation. We were able to control adhesion, survival, motility, and differentiation of neuroblastoma cells. More broadly, we believe that our system will help the design of in vitro pharmacological screening strategy.

Mitochondrial Uncoupling Proteins (UCPs) as Key Modulators of ROS Homeostasis: A Crosstalk between Diabesity and Male Infertility?

Uncoupling proteins (UCPs) are transmembrane proteins members of the mitochondrial anion transporter family present in the mitochondrial inner membrane. Currently, six homologs have been identified (UCP1-6) in mammals, with ubiquitous tissue distribution and multiple physiological functions. UCPs are regulators of key events for cellular bioenergetic metabolism, such as membrane potential, metabolic efficiency, and energy dissipation also functioning as pivotal modulators of ROS production and general cellular redox state. UCPs can act as proton channels, leading to proton re-entry the mitochondrial matrix from the intermembrane space and thus collapsing the proton gradient and decreasing the membrane potential. Each homolog exhibits its specific functions, from thermogenesis to regulation of ROS production. The expression and function of UCPs are intimately linked to diabesity, with their dysregulation/dysfunction not only associated to diabesity onset, but also by exacerbating oxidative stress-related damage. Male infertility is one of the most overlooked diabesity-related comorbidities, where high oxidative stress takes a major role. In this review, we discuss in detail the expression and function of the different UCP homologs. In addition, the role of UCPs as key regulators of ROS production and redox homeostasis, as well as their influence on the pathophysiology of diabesity and potential role on diabesity-induced male infertility is debated.

Mitochondrial Uncoupling Proteins (UCP1-UCP3) and Adenine Nucleotide Translocase (ANT1) Enhance the Protonophoric Action of 2,4-Dinitrophenol in Mitochondria and Planar Bilayer Membranes

2,4-Dinitrophenol (DNP) is a classic uncoupler of oxidative phosphorylation in mitochondria which is still used in “diet pills”, despite its high toxicity and lack of antidotes. DNP increases the proton current through pure lipid membranes, similar to other chemical uncouplers. However, the molecular mechanism of its action in the mitochondria is far from being understood. The sensitivity of DNP’s uncoupling action in mitochondria to carboxyatractyloside, a specific inhibitor of adenine nucleotide translocase (ANT), suggests the involvement of ANT and probably other mitochondrial proton-transporting proteins in the DNP’s protonophoric activity. To test this hypothesis, we investigated the contribution of recombinant ANT1 and the uncoupling proteins UCP1-UCP3 to DNP-mediated proton leakage using the well-defined model of planar bilayer lipid membranes. All four proteins significantly enhanced the protonophoric effect of DNP. Notably, only long-chain free fatty acids were previously shown to be co-factors of UCPs and ANT1. Using site-directed mutagenesis and molecular dynamics simulations, we showed that arginine 79 of ANT1 is crucial for the DNP-mediated increase of membrane conductance, implying that this amino acid participates in DNP binding to ANT1.

The Effects of Natural and Synthetic Blue Dyes on Human Health: A Review of Current Knowledge and Therapeutic Perspectives

Blue synthetic dyes are widely used in many industries. Although they are approved for use as food dyes and in cosmetics and some medicines, their impacts on consumer health remain unknown. Some studies indicate that 2 synthetic dyes, Blue No. 1 and Blue No. 2, may have toxic effects. It has therefore been suggested that these should be replaced with natural dyes; however, despite being nontoxic and arguably healthier than synthetic dyes, these compounds are often unsuitable for use in food or drugs due to their instability. Nevertheless, among the natural blue pigments, anthocyanins and genipin offer particular health benefits, as they are associated with the prevention of cardiovascular disease and have anticancer, neuroprotective, anti-inflammatory, and antidiabetic properties. This review summarizes the effects of blue food and drug colorings on health and proposes that synthetic colors should be replaced with natural ones.

Metabolomics based comprehensive investigation of Gardeniae Fructus induced hepatotoxicity

Gardeniae Fructus (Zhizi in Chinese, ZZ in brief), a commonly used herbal medicine, has aroused wide concern for hepatotoxicity, but the mechanism remains to be investigated. This study was aimed at investigating the mechanism of ZZ-induced liver injury in vivo and in vitro based on metabolomics and evaluating the hepatotoxicity prediction ability of the in vitro model. SD rats were administered with extracted ZZ and HepG2 cells were treated with genipin, the major hepatotoxic metabolite of ZZ. Liver, plasma, intracellular and extracellular samples were obtained for metabolomics analysis. As a result, ZZ caused plasma biochemical and liver histopathological alterations in rats, and induced purine and amino acid metabolism disorder in the liver and pyrimidine, primary bile acids, amino acid metabolism and pantothenate and CoA biosynthesis disorder in the plasma. Pyrimidine, purine, amino acid metabolism and pantothenate and CoA biosynthesis were also found to be disturbed in the genipin-treated HepG2 cells, which exhibited similarity with the result in vivo. This study comprehensively illustrates the underlying mechanism involved in ZZ-related hepatotoxicity from the aspect of metabolome, and provides evidence that identifying hepatotoxicity can be achieved in cells, representing a non-animal alternative for systemic toxicology.

Natural Products Targeting the Mitochondria in Cancers

There are abundant sources of anticancer drugs in nature that have a broad prospect in anticancer drug discovery. Natural compounds, with biological activities extracted from plants and marine and microbial metabolites, have significant antitumor effects, but their mechanisms are various. In addition to providing energy to cells, mitochondria are involved in processes, such as cell differentiation, cell signaling, and cell apoptosis, and they have the ability to regulate cell growth and cell cycle. Summing up recent data on how natural products regulate mitochondria is valuable for the development of anticancer drugs. This review focuses on natural products that have shown antitumor effects via regulating mitochondria. The search was done in PubMed, Web of Science, and Google Scholar databases, over a 5-year period, between 2015 and 2020, with a keyword search that focused on natural products, natural compounds, phytomedicine, Chinese medicine, antitumor, and mitochondria. Many natural products have been studied to have antitumor effects on different cells and can be further processed into useful drugs to treat cancer. In the process of searching for valuable new drugs, natural products such as terpenoids, flavonoids, saponins, alkaloids, coumarins, and quinones cover the broad space.

Assessment of Visual and Retinal Function Following In Vivo Genipin-Induced Scleral Crosslinking

Purpose

Genipin has been proposed as a possible neuroprotective therapy in myopia and glaucoma. Here, we aim to determine the effects of prolonged genipin-induced scleral stiffening on visual function.

Methods

Eyes from Brown Norway rats were treated in vivo with either a single 15 mM genipin retrobulbar injection or sham retrobulbar injection and were compared to naïve eyes. Intraocular pressure, optomotor response, and electroretinograms were repeatedly measured over 4 weeks following retrobulbar injections to determine visual and retinal function. At 4 weeks, we quantified retinal ganglion cell axon counts. Finally, molecular changes in gene and protein expression were analyzed via real-time polymerase chain reaction (RT-PCR) and proteomics.

Results

Retrobulbar injection of genipin did not affect intraocular pressure (IOP) or retinal function, nor have a sustained impact on visual function. Although genipin-treated eyes had a small decrease in retinal ganglion cell axon counts compared to contralateral sham-treated eyes (−8,558 ± 18,646; mean ± SD), this was not statistically significant (P = 0.206, n = 9). Last, we did not observe any changes in gene or protein expression due to genipin treatment.

Conclusions

Posterior scleral stiffening with a single retrobulbar injection of 15 mM genipin causes no sustained deficits in visual or retinal function or at the molecular level in the retina and sclera. Retinal ganglion cell axon morphology appeared normal.

Translational Significance

These results support future in vivo studies to determine the efficacy of genipin-induced posterior scleral stiffening to help treat ocular diseases, like myopia and glaucoma.

Effect of betulin and betulonic acid on isolated rat liver mitochondria and liposomes

The paper considers the effects of plant triterpenoid betulin and its derivative betulonic acid on rat liver mitochondria and liposomes. It was found that betulonic acid and, to a lesser extent, betulin, activate mitochondrial respiration in states 2 and 4 and inhibit ADP- and DNP-stimulated (uncoupled) respiration. The effect of betulonic acid resulted in a significant decrease of the respiratory control and ADP/O ratios and decrease in Δψ. The effects of both compounds were most pronounced in the case of succinate-fueled mitochondrial respiration. This may include both the possible protonophore effect of betulonic acid and the inhibition of respiratory chain complexes by both compounds. Both agents enhanced H₂O₂ production in succinate-fueled mitochondria, while betulonic acid exerted an antioxidant effect with NAD-dependent substrates. Betulin was found to induce mitochondrial aggregation, but had no effect on membrane permeability. A similar pattern was found on liposomes. As revealed by the laurdan generalized polarization (GP) technique, betulin increased laurdan GP in lecithin liposomes, indicating a decrease in membrane fluidity. Measurements of GP as a function of fluorescence excitation wavelength gave an ascending line for high concentrations of betulin, which can be interpreted as phase heterogeneity of the lipid/betulin system. High concentrations of betulin (> 60 mol%) was also demonstrated to cause permeabilization of lecithin liposomes. Betulonic acid was much less effective in inducing the aggregation of mitochondria and liposomes and had no effect on membrane permeability. The possible mechanisms of betulin and betulonic acid effect on rat liver mitochondria and liposomes are discussed.