Tauroursodeoxycholic Acid (TUDCA)-Lipid Interactions and Antioxidant Properties of TUDCA Studied in Model of Photoreceptor Membranes

Association of plasma metabolites with treatment response after intravitreal anti-vascular endothelial growth factor injections in treatment-naïve neovascular age-related macular degeneration

BACKGROUND/AIMS

To investigate the association between plasma metabolomic profiles and treatment response after intravitreal anti-vascular endothelial growth factor (VEGF) injections in treatment-naïve neovascular age-related macular degeneration (nAMD).

METHODS

This is part of a prospective longitudinal study that included patients with treatment-naïve nAMD who have undergone three loading intravitreal anti-VEGF injections. All patients underwent ophthalmological examinations including spectral domain optical coherence tomography (SD OCT). Fasting blood samples were collected at the time of study enrolment (not to first anti-VEGF injection) and metabolomic profiling was conducted using ultra-performance liquid chromatography-mass spectrometry. Treatment response was defined as no evidence of any subretinal and intraretinal fluid on SD OCT 4-6 weeks after the third injection. Multilevel mixed-effects linear modelling was used to assess associations between plasma metabolites and treatment response. Multiple comparisons were accounted for using the effective number of tests to explain 80% of the variance (ENT80), with a p value threshold of 0.0017.

RESULTS

We included 131 eyes of 101 patients, and 69 patients (68.3%) were female. 51 eyes (38.9%) were treatment responders. Taurodeoxycholate (TDCA) was the only plasma metabolite significantly associated with treatment response (β=1.6, ENT80=0.001).

CONCLUSION

In our study, TDCA was the most significant plasma metabolite associated with treatment response after three-loading dose of anti-VEGF therapy in patients with nAMD. Bile acids may have a beneficial impact on treatment response in nAMD through their neuroprotective property. Plasma metabolites may be used as biomarkers to predict responses to initial anti-VEGF therapy in patients with nAMD, providing a more individualised treatment plan.

TUDCA modulates drug bioavailability to regulate resistance to acute ER stress in Saccharomyces cerevisiae

Cells counter accumulation of misfolded secretory proteins in the endoplasmic reticulum (ER) through activation of the Unfolded Protein Response (UPR). Small molecules termed chemical chaperones can promote protein folding to alleviate ER stress. The bile acid tauroursodeoxycholic acid (TUDCA) has been described as a chemical chaperone. While promising in models of protein folding diseases, TUDCA's mechanism of action remains unclear. Here, we found TUDCA can rescue growth of yeast treated with the ER stressor tunicamycin (Tm), even in the absence of a functional UPR. In contrast, TUDCA failed to rescue growth on other ER stressors. Nor could TUDCA attenuate chronic UPR associated with specific gene deletions or overexpression of a misfolded mutant secretory protein. Neither pretreatment with nor delayed addition of TUDCA conferred protection against Tm. Importantly, attenuation of Tm-induced toxicity required TUDCA's critical micelle forming concentration, suggesting a mechanism where TUDCA directly sequesters drugs. Indeed, in several assays, TUDCA-treated cells closely resembled cells treated with lower doses of Tm. In addition, we found TUDCA can inhibit dyes from labeling intracellular compartments. Thus, our study challenges the model of TUDCA as a chemical chaperone and suggests that TUDCA decreases drug bioavailability, allowing cells to adapt to ER stress.

Microbiota mitochondria disorders as hubs for early age-related macular degeneration

Age-related macular degeneration (AMD) is a progressive neurodegenerative disease affecting the central area (macula lutea) of the retina. Research on the pathogenic mechanism of AMD showed complex cellular contribution governed by such risk factors as aging, genetic predisposition, diet, and lifestyle. Recent studies suggested that microbiota is a transducer and a modifier of risk factors for neurodegenerative diseases, and mitochondria may be one of the intracellular targets of microbial signaling molecules. This review explores studies supporting a new concept on the contribution of microbiota-mitochondria disorders to AMD. We discuss metabolic, vascular, immune, and neuronal mechanism in AMD as well as key alterations of photoreceptor cells, retinal pigment epithelium (RPE), Bruch's membrane, choriocapillaris endothelial, immune, and neuronal cells. Special attention was paid to alterations of mitochondria contact sites (MCSs), an organelle network of mitochondria, endoplasmic reticulum, lipid droplets (LDs), and peroxisomes being documented based on our own electron microscopic findings from surgically removed human eyes. Morphometry of Bruch's membrane lipids and proteoglycans has also been performed in early AMD and aged controls. Microbial metabolites (short-chain fatty acids, polyphenols, and secondary bile acids) and microbial compounds (lipopolysaccharide, peptidoglycan, and bacterial DNA)-now called postbiotics-in addition to local effects on resident microbiota and mucous membrane, regulate systemic metabolic, vascular, immune, and neuronal mechanisms in normal conditions and in various common diseases. We also discuss their antioxidant, anti-inflammatory, and metabolic effects as well as experimental and clinical observations on regulating the main processes of photoreceptor renewal, mitophagy, and autophagy in early AMD. These findings support an emerging concept that microbiota-mitochondria disorders may be a crucial pathogenic mechanism of early AMD; and similarly, to other age-related neurodegenerative diseases, new treatment approaches should be targeted at these disorders.

Melatonin and Indole-3-Propionic Acid Reduce Oxidative Damage to Membrane Lipids Induced by High Iron Concentrations in Porcine Skin

Iron excess in tissues results in increased oxidative damage. Among different tissues, the skin can particularly be severely damaged by oxidative stress, as it is exposed not only to endogenous but also directly to exogenous pro-oxidants. The skin is especially vulnerable to harmful oxidative stress. Melatonin and indole-3-propionic acid (IPA), two indole substances, are efficient antioxidants. This study aims to evaluate the potential protective effects of melatonin and IPA against oxidative damage to membrane lipids (lipid peroxidation (LPO)), induced in porcine skin homogenates by the Fenton reaction (Fe²⁺ + H₂O₂ → Fe³⁺ + ^•OH + OH⁻) when iron is used in extremely high concentrations. Skin homogenates were incubated in the presence of FeSO₄ (2400, 1200, 600, 300, 150 and 75 µM) + H₂O₂ (5 mM) with/without melatonin or IPA. LPO level (MDA + 4-HDA/mg protein) was measured spectrophotometrically. Melatonin, in its highest used concentration (5.0 mM), prevented FeSO₄ (1200 mM)-induced LPO, whereas it was effective in concentrations as low as 2.5 mM against all lower iron concentrations. IPA was protective in concentrations as low as 2.5 mM independently of FeSO₄ concentration. In conclusion, melatonin and IPA effectively protect against oxidative damage to membrane lipids induced by high concentrations of iron in porcine skin; therefore, both can be considered pharmacological agents in the case of disorders associated with excessive iron accumulation in the skin.