Structural Impact of Selected Retinoids on Model Photoreceptor Membranes

Photoreceptor membranes have a unique lipid composition. They contain a high level of polyunsaturated fatty acids including the most unsaturated fatty acid in nature, docosahexaenoic acid (22:6), and are enriched in phosphatidylethanolamines. The phospholipid composition and cholesterol content of the subcellular components of photoreceptor outer segments enables to divide photoreceptor membranes into three types: plasma membranes, young disc membranes, and old disc membranes. A high degree of lipid unsaturation, extended exposure to intensive irradiation, and high respiratory demands make these membranes sensitive to oxidative stress and lipid peroxidation. Moreover, all-trans retinal (AtRAL), which is a photoreactive product of visual pigment bleaching, accumulates transiently inside these membranes, where its concentration may reach a phototoxic level. An elevated concentration of AtRAL leads to accelerated formation and accumulation of bisretinoid condensation products such as A2E or AtRAL dimers. However, a possible structural impact of these retinoids on the photoreceptor-membrane properties has not yet been studied. In this work we focused just on this aspect. The changes induced by retinoids, although noticeable, seem not to be significant enough to be physiologically relevant. This is, however, an positive conclusion because it can be assumed that accumulation of AtRAL in photoreceptor membranes will not affect the transduction of visual signals and will not disturb the interaction of proteins engaged in this process.

Comparison of photodynamic efficiency of cholesterol, selected cholesterol esters, metabolites and oxidation products on lipid peroxidation processes

Cholesterol (Ch) is one of the most important components of biological membranes, which has a significant impact on their biophysical properties. As a key component of lipid membranes, Ch along with other unsaturated lipids present in a biological membrane undergoes oxidation reaction during oxidative stress. Cholesterol oxidation products, cholesteryl esters and metabolites are also localise in lipid membranes, where they may modify membrane properties. In this work the impact of cholesterol, selected cholesteryl esters, cholesterol oxidation products and metabolites on lipid peroxidation induced by photodynamic action has been studied using EPR oximetry and direct detection of singlet oxygen phosphorescence at 1270 nm. The obtained rate constants values of interaction of selected lipids and sterols with singlet oxygen indicate that the tested compounds are not efficient singlet oxygen quenchers. Nevertheless, the presence of sterols modifies to different extend the oxygen photoconsumption rate in peroxidisable liposomes.

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

Tauroursodeoxycholic acid (TUDCA), a hydrophilic bile acid containing taurine conjugated with the ursodeoxycholic acid (UDCA), has been known and used from ancient times as a therapeutic compound in traditional Chinese medicine. TUDCA has recently been gaining significant interest as a neuroprotective agent, also exploited in the visual disorders. Among several mechanisms of TUDCA's protective action, its antioxidant activity and stabilizing effect on mitochondrial and plasma membranes are considered. In this work we investigated antioxidant activity of TUDCA and its impact on structural properties of model membranes of different composition using electron paramagnetic resonance spectroscopy and the spin labeling technique. Localization of TUDCA molecules in a pure POPC bilayer has been studied using a molecular dynamics simulation (MD). The obtained results indicate that TUDCA is not an efficient singlet oxygen (1O2 (1Δg)) quencher, and the determined rate constant of its interaction with 1O2 (1Δg) is only 1.9 × 105 M-1s-1. However, in lipid oxidation process induced by a Fenton reaction, TUDCA reveals substantial antioxidant activity significantly decreasing the rate of oxygen consumption in the system studied. In addition, TUDCA induces slight, but noticeable changes in the polarity and fluidity of the investigated model membranes. The results of performed MD simulation correspond very well with the experimental results.

Sclera as a surrogate marker for determining AGE-modifications in Bruch's membrane using a Raman spectroscopy-based index of aging

PURPOSE

Raman spectroscopy is an effective probe of advanced glycation end products (AGEs) in Bruch's membrane. However, because it is the outermost layer of the retina, this extracellular matrix is difficult to analyze in vivo with current technology. The sclera shares many compositional characteristics with Bruch's membrane, but it is much easier to access for in vivo Raman analysis. This study investigated whether sclera could act as a surrogate tissue for Raman-based investigation of pathogenic AGEs in Bruch's membrane.

METHODS

Human sclera and Bruch's membrane were dissected from postmortem eyes (n = 67) across a wide age range (33-92 years) and were probed by Raman spectroscopy. The biochemical composition, AGEs, and their age-related trends were determined from data reduction of the Raman spectra and compared for the two tissues.

RESULTS

Raman microscopy demonstrated that Bruch's membrane and sclera are composed of a similar range of biomolecules but with distinct relative quantities, such as in the heme/collagen and the elastin/collagen ratios. Both tissues accumulated AGEs, and these correlated with chronological age (R(2) = 0.824 and R(2) = 0.717 for sclera and Bruch's membrane, respectively). The sclera accumulated AGE adducts at a lower rate than Bruch's membrane, and the models of overall age-related changes exhibited a lower rate (one-fourth that of Bruch's membrane) but a significant increase with age (P < 0.05).

CONCLUSIONS

The results suggest that the sclera is a viable surrogate marker for estimating AGE accumulation in Bruch's membrane and for reliably predicting chronological age. These findings also suggest that sclera could be a useful target tissue for future patient-based, Raman spectroscopy studies.

Multiplex analysis of age-related protein and lipid modifications in human Bruch's membrane

Aging of the human retina is characterized by progressive pathology, which can lead to vision loss. This progression is believed to involve reactive metabolic intermediates reacting with constituents of Bruch's membrane, significantly altering its physiochemical nature and function. We aimed to replace a myriad of techniques following these changes with one, Raman spectroscopy. We used multiplexed Raman spectroscopy to analyze the age-related changes in 7 proteins, 3 lipids, and 8 advanced glycation/lipoxidation endproducts (AGEs/ALEs) in 63 postmortem human donors. We provided an important database for Raman spectra from a broad range of AGEs and ALEs, each with a characteristic fingerprint. Many of these adducts were shown for the first time in human Bruch's membrane and are significantly associated with aging. The study also introduced the previously unreported up-regulation of heme during aging of Bruch's membrane, which is associated with AGE/ALE formation. Selection of donors ranged from ages 32 to 92 yr. We demonstrated that Raman spectroscopy can identify and quantify age-related changes in a single nondestructive measurement, with potential to measure age-related changes in vivo. We present the first directly recorded evidence of the key role of heme in AGE/ALE formation.

Paraneoplastic intestinal pseudo-obstruction, mononeuritis multiplex, and sensory neuropathy/neuronopathy

A patient with diffuse intestinal pseudo-obstruction consisting of gastric paresis and impaired small and large bowel motility, mononeuropathy multiplex, and sensory neuropathy/neuronopathy was found to have small-cell carcinoma of the lung. The clinical symptoms were thought to be consistent with paraneoplastic neuropathy, and high antineuronal and anti-calcium channel antibodies led to the diagnosis of small-cell carcinoma of the lung. Identification of paraneoplastic neuropathy is important, because early treatment may halt the progression of the underlying carcinoma.

Oculofacial-skeletal myorhythmia in central nervous system Whipple's disease: additional case and review of the literature

A case of oculofacial-skeletal myorhythmia associated with cerebral Whipple's disease is presented. This peculiar abnormal movement disorder consists of a convergent-divergent pendular nystagmus associated with a synchronous, rhythmic movement of the mouth, jaw, and extremities. The movements in previous cases have responded inconsistently to a variety of broad-spectrum antibiotic drugs, and antiepileptic, muscle relaxant, antispastic, and psychotropic drugs. The current patient's mental status improved after starting intravenous ceftriaxone but improvement of the abnormal movements occurred only after the addition of oral valproate. Current treatment consists of intravenous trimethoprim-sulfamethoxazole for 2 weeks followed by oral trimethoprim-sulfamethoxazole twice daily for 1 year. Presented here is an alternative treatment of intravenous ceftriazone followed by oral trimethoprim-sulfamethoxazole in combination with valproate for abnormal movements not responsive to antibiotic drugs alone.

A variant of adrenomyeloneuropathy in a family with adrenoleukodystrophy and adrenomyeloneuropathy

A 31-year-old man was seen with addisonian crisis, followed by the abrupt onset of spastic paraparesis and peripheral neuropathy. A workup revealed adrenal insufficiency, for which the patient was aggressively treated. The workup also revealed an increase in very-long-chain fatty acids consistent with the diagnosis of adrenomyeloneuropathy. Abnormal pituitary dysfunction improved with treatment of the Addison's disease. A review of the patient's pedigree revealed two family members in whom multiple sclerosis had been diagnosed but which, in retrospect, was thought to be adrenomyeloneuropathy. No other family member was found to have Addison's disease. A sibling died at age 8 of Schilder's disease, confirming the presence of adrenoleukodystrophy as well as adrenomyeloneuropathy within this family.

An electromagnetically controllable heart valve suitable for chronic implantation

A controllable valve suitable for chronic implantation was designed, and preliminary performance tests were conducted. A Björk-Shiley monostrut valve with an 18 mm disk was modified so that permanent magnetic material was implanted in the disk and an electromagnet was fitted around the ring of the valve. The opening of the disk is controlled by the interaction of the magnetic field created by the permanent magnets, and the field created by the electromagnet. The coil can be activated intermittently so that the valve can be held in the closed position or allowed to open and close unimpeded. The unit was designed to hold a maximum hydrostatic pressure equivalent to 50 mmHg. Power consumption by the prototype, while holding a pressure of 50 mmHg, is less than 10 watts. The overall diameter of the valve and electromagnet is 27 mm. The design and test results indicate that it is feasible to develop a unit suitable for chronic implantation in experimental animals and, possibly, in prosthetic blood pumping devices.