Amyloid precursor protein, A beta and amyloid-associated proteins involved in chloroquine retinopathy in rats--immunopathological studies

Systemic toxicity of chloroquine and hydroxychloroquine: prevalence, mechanisms, risk factors, prognostic and screening possibilities

Chloroquine (CQ) and its hydroxylated analog, hydroxychloroquine (HCQ), are 4-aminoquinoline initially used as an antimalarial treatment. CQ and HCQ (4-aminoquinoline, 4-AQ) are today used in rheumatology, especially to treat rheumatoid arthritis and systemic lupus erythematosus. Their mechanism of action revolves around a singular triptych: 4-AQ acts as alkalizing agents, ionized amphiphilic molecules, and by binding to numerous targets. 4-AQ have so pleiotropic and original mechanisms of action, providing them an effect at the heart of the regulation of several physiological functions. However, this broad spectrum of action is also at the origin of various and original side effects, notably a remarkable chronic systemic toxicity. We describe here the 4-AQ-induced lesions on the eye, the heart, muscle, the nerves, the inner ear, and the kidney. We also describe their prevalence, their pathophysiological mechanisms, their risk factors, their potential severity, and the means to detect them early. Most of these side effects are reversible if treatment is stopped promptly. This 4-AQ-induced toxicity must be known to prescribing physicians, to closely monitor its appearance and stop treatment in time if necessary.

Absence of histopathological changes in the retina of zebrafish treated with sodium iodate

In ophthalmological research, the use of zebrafish to investigate visual behaviors has been increasing, but can produce misleading, false-positive results if compounds adversely affect their motor functions or central nervous system. Therefore, histological analysis to identify a target organ is important in zebrafish toxicity assay. We investigated the retinal degeneration in zebrafish, using typical retinal toxicants, mainly sodium iodate and N-methyl-N-nitrosourea (MNU). No histopathological changes were found after sodium iodate exposure at 1.0 mM for 5 or 7 days in the retina of larval, juvenile, and adult zebrafish. There were also no obvious histopathological changes in the retina of adult zebrafish at 0.1 mM, even after 30 days treatment with sodium iodate. In addition, many proliferating cell nuclear antigen-positive cells were found not only in the ciliary marginal zone, but also in the outer nuclear layer, especially in larval and juvenile zebrafish with or without sodium iodate exposure. However, the concentrations of iodine in the blood and the eyeballs of adult zebrafish increased remarkably after the treatment. General retinal damage emerged after MNU exposure at 150 mg/l for 60 min in adult zebrafish, but first pyknotic cells appeared in the inner nuclear layer and the ganglion cell layer. Our findings indicate that zebrafish retina have a different reactivity pattern from mammalian animals against some retinal toxicants, and in them it is difficult to detect histopathological changes.

Chloroquine causes similar electroretinogram modifications, neuronal phospholipidosis and marked impairment of synaptic vesicle transport in albino and pigmented rats

Retinal toxicity of chloroquine has been known for several years, but the mechanism(s) of toxicity remain controversial; some author support the idea that the binding of chloroquine to melanin pigments in the retinal pigmented epithelium (RPE) play a major toxic role by concentrating the drug in the eye. In our study, 12 albinos Sprague-Dawley (SD) and 12 pigmented Brown Norway (BN) rats were treated orally for 3 months with chloroquine to compare functional and pathological findings. On Flash electroretinograms (ERG) performed in scotopic conditions, similar and progressive (time-dependent) delayed onset and decreased amplitudes of oscillatory potentials (from Day 71) and b-waves (on Day 92) were identified in both BN and SD rats. In both strains, identical morphological changes consisted of neuronal phospholipidosis associated with UV auto-fluorescence without evidence of retinal degeneration and gliosis; the RPE did not show any morphological lesions or autofluorescence. IHC analyses demonstrated a decrease in GABA expression in the inner nuclear layer. In addition, a marked accumulation of synaptic vesicles coupled with a marked disruption of neurofilaments in the optic nerve fibers was identified. In conclusion, ERG observations were very similar to those described in humans. Comparable ERG modifications, histopathology and immunohistochemistry findings were observed in the retina of both rat strains suggesting that melanin pigment is unlikely involved. chloroquine-induced impairment of synaptic vesicle transport, likely related to disruption of neurofilaments was identified and non-previously reported. This new mechanism of toxicity may also be responsible for the burry vision described in humans chronically treated with chloroquine.

The ubiquitin-proteasome system in retinal health and disease

The ubiquitin-proteasome system (UPS) is the main intracellular pathway for modulated protein turnover, playing an important role in the maintenance of cellular homeostasis. It also exerts a protein quality control through degradation of oxidized, mutant, denatured, or misfolded proteins and is involved in many biological processes where protein level regulation is necessary. This system allows the cell to modulate its protein expression pattern in response to changing physiological conditions and provides a critical protective role in health and disease. Impairments of UPS function in the central nervous system (CNS) underlie an increasing number of genetic and idiopathic diseases, many of which affect the retina. Current knowledge on the UPS composition and function in this tissue, however, is scarce and dispersed. This review focuses on UPS elements reported in the retina, including ubiquitinating and deubiquitinating enzymes (DUBs), and alternative proteasome assemblies. Known and inferred roles of protein ubiquitination, and of the related, SUMO conjugation (SUMOylation) process, in normal retinal development and adult homeostasis are addressed, including modulation of the visual cycle and response to retinal stress and injury. Additionally, the relationship between UPS dysfunction and human neurodegenerative disorders affecting the retina, including Alzheimer's, Parkinson's, and Huntington's diseases, are dealt with, together with numerous instances of retina-specific illnesses with UPS involvement, such as retinitis pigmentosa, macular degenerations, glaucoma, diabetic retinopathy (DR), and aging-related impairments. This information, though still basic and limited, constitutes a suitable framework to be expanded in incoming years and should prove orientative toward future therapy design targeting sight-affecting diseases with a UPS underlying basis.

Roles for the ubiquitin-proteasome pathway in protein quality control and signaling in the retina: implications in the pathogenesis of age-related macular degeneration

The accumulation of damaged or postsynthetically modified proteins and dysregulation of inflammatory responses and angiogenesis in the retina/RPE are thought be etiologically related to formation of drusen and choroidal neovascularization (CNV), hallmarks of age-related macular degeneration (AMD). The ubiquitin-proteasome pathway (UPP) plays crucial roles in protein quality control, cell cycle control and signal transduction. Selective degradation of aberrant proteins by the UPP is essential for timely removal of potentially cytotoxic damaged or otherwise abnormal proteins. Proper function of the UPP is thought to be required for cellular function. In contrast, age--or stress induced--impairment the UPP or insufficient UPP capacity may contribute to the accumulation of abnormal proteins, cytotoxicity in the retina, and AMD. Crucial roles for the UPP in eye development, regulation of signal transduction, and antioxidant responses are also established. Insufficient UPP capacity in retina and RPE can result in dysregulation of signal transduction, abnormal inflammatory responses and CNV. There are also interactions between the UPP and lysosomal proteolytic pathways (LPPs). Means that modulate the proteolytic capacity are making their way into new generation of pharmacotherapies for delaying age-related diseases and may augment the benefits of adequate nutrition, with regard to diminishing the burden of AMD.

Role of the ubiquitin-proteasome in protein quality control and signaling: implication in the pathogenesis of eye diseases

The ubiquitin-proteasome pathway (UPP) plays important roles in many cellular functions, such as protein quality control, cell cycle control, and signal transduction. The selective degradation of aberrant proteins by the UPP is essential for the timely removal of potential cytotoxic damaged or otherwise abnormal proteins. Conversely, accumulation of the cytotoxic abnormal proteins in eye tissues is etiologically associated with many age-related eye diseases such as retina degeneration, cataract, and certain types of glaucoma. Age- or stress-induced impairment or overburdening of the UPP appears to contribute to the accumulation of abnormal proteins in eye tissues. Cell cycle and signal transduction are regulated by the conditional UPP-dependent degradation of the regulators of these processes. Impairment or overburdening of the UPP could also result in dysregulation of cell cycle control and signal transduction. The consequences of the improper cell cycle and signal transduction include defects in ocular development, wound healing, angiogenesis, or inflammatory responses. Methods that enhance or preserve UPP function or reduce its burden may be useful strategies for preventing age-related eye diseases.

Development and expression of amyloid-β peptide 42 in retinal ganglion cells in rats

The previous studies have shown that amyloid-β peptide (Aβ) was mainly found in neurons of neurodegenerative diseases, such as Alzheimer's disease (AD) and glaucoma and little is known about its expression in normal nerve cells. The aim of the present study was to investigate the expression of amyloid-β peptide 42 (Aβ-42) in retinal ganglion cells of the postnatal rats. Rats were divided into seven experimental groups: 3, 6, 13, 15, 25, 60, and 90 days postnatal groups. Rats from 15 and 25 days postnatal groups were further divided into light-exposure and non light-exposure group. Cryosections or flat-mounted retinas of rat eyes were used for testing Aβ-42 by immunocytochemistry staining. Aβ-42 expression was not observed in rats within 13 days after birth, but was easily detectable in all groups of rats over 15 days after birth. In addition, the expression of Aβ-42 in retina was increasing as the rats got older, reached to highest level in 60 days after birth. Furthermore, the expression of Aβ-42 was not detected in rats kept under dark indicating that light is required for the expression of Aβ-42 in retina. This is the first report showing that normal retinal ganglion cells express Aβ-42, and that the expression of Aβ-42 in retinal ganglion cells requires the exposure to light. These data suggest that Aβ-42 may play a important role in vision development.

Retinal nerve fibre layer thickness measurements in patients using chloroquine

PURPOSE

Previous investigations have suggested that initial retinal damage from chloroquine toxicity occurs in ganglion cells, and other ocular tissues are affected only later on. The aim of this study was to evaluate retinal nerve fibre layer (RNFL) thickness measurements, as assessed by scanning laser polarimetry, in a group of patients under long-term treatment with chloroquine.

METHODS

This case-control study included 34 patients using chloroquine diphosphate and 34 age-matched healthy subjects with no previous history of chloroquine intake. All subjects underwent RNFL assessment using the GDx -- Nerve Fibre Analyser (software v.2.0.01). One eye of each patient was randomly selected for statistical analysis. Peripapillary RNFL measurements were compared between the two groups. For patients using chloroquine, the correlation between RNFL measurements and chloroquine dosage was assessed.

RESULTS

Mean +/- SD RNFL thickness for patients using chloroquine was 60.6 +/- 11.2 microm, 65.6 +/- 13.2 microm, 74.8 +/- 14.8 microm, 36.2 +/- 9.6 microm and 43.8 +/- 7.9 microm for global, superior, inferior, temporal and nasal regions, respectively. In the control group, the corresponding values were 72.1 +/- 12.7 microm, 79.9 +/- 14.8 microm, 88.3 +/- 14.0 microm, 44.2 +/- 12.8 microm and 49.7 +/- 11.9 microm. Mean RNFL thickness measurements from patients using chloroquine were significantly different from those in the control group in all regions (P < 0.05). Thinner RNFL thickness measurements were associated with higher daily dosages of chloroquine.

CONCLUSION

Patients under long-term chloroquine treatment had significantly lower RNFL thickness measurements than healthy subjects, and the RNFL loss was correlated to chloroquine daily dosage.

Amyloid fibril formation by macrophage migration inhibitory factor

We demonstrate herein that human macrophage migration inhibitory factor (MIF), a pro-inflammatory cytokine expressed in the brain and not previously considered to be amyloidogenic, forms amyloid fibrils similar to those derived from the disease associated amyloidogenic proteins beta-amyloid and alpha-synuclein. Acid denaturing conditions were found to readily induce MIF to undergo amyloid fibril formation. MIF aggregates to form amyloid-like structures with a morphology that is highly dependent on pH. The mechanism of MIF amyloid formation was probed by electron microscopy, turbidity, Thioflavin T binding, circular dichroism spectroscopy, and analytical ultracentrifugation. The fibrillar structures formed by MIF bind Congo red and exhibit the characteristic green birefringence under polarized light. These results are consistent with the notion that amyloid fibril formation is not an exclusive property of a select group of amyloidogenic proteins, and contribute to a better understanding of the factors which govern protein conformational changes and amyloid fibril formation in vivo.

Function of the ubiquitin proteolytic pathway in the eye

The ubiquitin pathway (UP) is involved in regulation of many essential cellular processes usually by the degradation of regulators of these processes. For example the UP is involved in regulation of cell cycle, proliferation, differentiation, organogenesis, development, and signal transduction in the lens and retina. A functional UP has also been documented in the cornea. Upon aging or exposure to stress there is an accumulation of damaged proteins, including ubiquitinated proteins, in the lens and retina. Some of these proteins may be cytotoxic. Thus, an active UP may be required to avoid such age and disease-related accumulation of damaged proteins. In this review we will explain the biochemistry of the UP and we will document the most important studies regarding UP function in the lens, retina and cornea.

Efficient gene delivery to vascular smooth muscle cells using a nontoxic, synthetic peptide vector system targeted to membrane integrins: a first step toward the gene therapy of chronic rejection

BACKGROUND

Chronic rejection is now the major cause of allograft failure. A prominent characteristic of the histopathology is extensive intimal proliferation of vascular smooth muscle cells. Targeting vascular smooth muscle cells by gene therapy techniques offers a possible avenue for arresting or reversing chronic rejection. Defining suitable non-viral DNA vectors for this application is the objective of this study.

METHODS

A 31 amino acid synthetic peptide has been evaluated as a DNA vector for primary cultures of vascular smooth muscle cells of man, rabbit, and rat. The vector comprises a 15 amino acid integrin-binding domain and a chain of 16 lysines for electrostatic binding of DNA. Three agents known to promote exit of vector/DNA complexes from endocytic vesicles were studied systematically to define optimal, non-toxic conditions for gene delivery.

RESULTS

Initial binding studies on frozen sections showed that the integrin-binding domain binds strongly to vascular smooth muscle cells in all three species, thereby establishing vascular smooth muscle cells as a potential target for this receptor-targeted DNA vector system. Primary cultures of vascular smooth muscle were therefore studied. The use of chloroquine to assist endocytic exit, which works well on immortalized cell lines, was of little value because of toxicity to the primary vascular smooth muscle cells. The addition of cationic lipids to polylysine-molossin/DNA conjugates gave excellent reporter gene expression, but required mildly toxic doses of cationic lipid, and resulted in some loss of integrin specificity of the vector system. The optimal system involved the use of the amino terminal 20 amino acids of the hemagglutinin of the influenza virus. This peptide, when added to polylysine-molossin/DNA complexes at an optimal w/w ratio of 5:1:2 (polylysine-molossin/DNA/fusogenic peptide) resulted in 25-30% transfection of vascular smooth muscle cells with good levels of gene expression and no toxicity.

CONCLUSION

This represents an effective and safe DNA vector, comprised entirely of small synthetic peptides, and therefore readily standardized for clinical and experimental application.

Expression of beta-amyloid precursor and Bcl-2 proto-oncogene proteins in rat retinas after intravitreal injection of aminoadipic acid

In order to investigate the role of glia in relation to factors that affect the expression of beta-amyloid precursor protein (betaAPP) and B cell lymphoma oncogene protein (Bcl-2) in the central nervous tissue, the patterns of expression of betaAPP and Bcl-2 in developing and mature rat retinas were studied immunocytochemically after intravitreal injection of alpha-aminoadipic acid (alpha-AAA), a glutamate analogue and gliotoxin that is known to cause injury of retinal Müller glial cells. In normal developing retinas, betaAPP and Bcl-2 were expressed primarily but transiently in a small number of neurons in the ganglion cell layer during the first postnatal week. Immunoreactivity of betaAPP and Bcl-2 appeared in the endfeet and proximal part of the radial processes of Müller glial cells from the second postnatal week onwards. In rats that received intravitreal injection of alpha-AAA at birth, there was a loss of immunoreactivity to vimentin, and a delayed expressed on betaAPP or Bcl-2 in Muller glial cells until 3-5 weeks post-injection. Immunoreactive neurons were also observed in the inner retina especially in the ganglion cell layer from 5 to 35 days after injection. A significant reduction in numerical density of cells with large somata in the ganglion cell layer was observed in the neonatally injected retinas at P56, which was accompanied by an increased immunostaining in radial processes of Müller glial cells. In contrast, no detectable changes in the expression of betaAPP and Bcl-2 were observed in retina that received alpha-AAA as adults. These results indicate that the gliotoxin alpha-AAA has long lasting effects on the expression of betaAPP and Bcl-2 in Müller glial cells as well as neurons in the developing but not mature retinas. The loss of vimentin and delayed expression of betaAPP and Bcl-2 in developing Müller glial cells suggests that the metabolic integrity of Müller cells was temporarily compromised, which may have adverse effects on developing neurons that are vulnerable or dependent on trophic support from the Müller glial cells.