Mucopolysaccharidosis and lipidosis in rats treated with tilorone analogues

Differences in MPS I and MPS II Disease Manifestations

Mucopolysaccharidosis (MPS) type I and II are two closely related lysosomal storage diseases associated with disrupted glycosaminoglycan catabolism. In MPS II, the first step of degradation of heparan sulfate (HS) and dermatan sulfate (DS) is blocked by a deficiency in the lysosomal enzyme iduronate 2-sulfatase (IDS), while, in MPS I, blockage of the second step is caused by a deficiency in iduronidase (IDUA). The subsequent accumulation of HS and DS causes lysosomal hypertrophy and an increase in the number of lysosomes in cells, and impacts cellular functions, like cell adhesion, endocytosis, intracellular trafficking of different molecules, intracellular ionic balance, and inflammation. Characteristic phenotypical manifestations of both MPS I and II include skeletal disease, reflected in short stature, inguinal and umbilical hernias, hydrocephalus, hearing loss, coarse facial features, protruded abdomen with hepatosplenomegaly, and neurological involvement with varying functional concerns. However, a few manifestations are disease-specific, including corneal clouding in MPS I, epidermal manifestations in MPS II, and differences in the severity and nature of behavioral concerns. These phenotypic differences appear to be related to different ratios between DS and HS, and their sulfation levels. MPS I is characterized by higher DS/HS levels and lower sulfation levels, while HS levels dominate over DS levels in MPS II and sulfation levels are higher. The high presence of DS in the cornea and its involvement in the arrangement of collagen fibrils potentially causes corneal clouding to be prevalent in MPS I, but not in MPS II. The differences in neurological involvement may be due to the increased HS levels in MPS II, because of the involvement of HS in neuronal development. Current treatment options for patients with MPS II are often restricted to enzyme replacement therapy (ERT). While ERT has beneficial effects on respiratory and cardiopulmonary function and extends the lifespan of the patients, it does not significantly affect CNS manifestations, probably because the enzyme cannot pass the blood-brain barrier at sufficient levels. Many experimental therapies, therefore, aim at delivery of IDS to the CNS in an attempt to prevent neurocognitive decline in the patients.

Modeling diseases in multiple mouse strains for precision medicine studies

The genetic basis of the phenotypic variability observed in patients can be studied in mice by generating disease models through genetic or chemical interventions in many genetic backgrounds where the clinical phenotypes can be assessed and used for genome-wide association studies (GWAS). This is particularly relevant for rare disorders, where patients sharing identical mutations can present with a wide variety of symptoms, but there are not enough number of patients to ensure statistical power of GWAS. Inbred strains are homozygous for each loci, and their single nucleotide polymorphisms catalogs are known and freely available, facilitating the bioinformatics and reducing the costs of the study, since it is not required to genotype every mouse. This kind of approach can be applied to pharmacogenomics studies as well.

Drugs affecting glycosaminoglycan metabolism

Glycosaminoglycans (GAGs) are charged polysaccharides ubiquitously present at the cell surface and in the extracellular matrix. GAGs are crucial for cellular homeostasis, and their metabolism is altered during pathological processes. However, little consideration has been given to the regulation of the GAG milieu through pharmacological interventions. In this review, we provide a classification of small molecules affecting GAG metabolism based on their mechanism of action. Furthermore, we present evidence to show that clinically approved drugs affect GAG metabolism and that this could contribute to their therapeutic benefit.

SAR of α7 nicotinic receptor agonists derived from tilorone: exploration of a novel nicotinic pharmacophore

The well-known interferon-inducer tilorone was found to possess potent affinity for the agonist site of the α7 neuronal nicotinic receptor (K(i)=56 nM). SAR investigations determined that both basic sidechains are essential for potent activity, however active monosubstituted derivatives can also be prepared if the flexible sidechains are replaced with conformationally rigidified cyclic amines. Analogs in which the fluorenone core is replaced with either dibenzothiophene-5,5-dioxide or xanthenone also retain potent activity.

A clinical flow cytometric biomarker strategy: validation of peripheral leukocyte phospholipidosis using Nile red

Phospholipidosis, or intracellular accumulation of phospholipids, is caused by specific classes of xenobiotics. This phenomenon represents a challenge for risk assessment that could benefit from the use of biomarkers in the clinical development of new drug candidates. Flow cytometry, coupled with the lipophilic fluoroprobe Nile red, was correlated to histopathology, electron microscopy and inorganic phosphorus detection to validate the utility of this method for monitoring phospholipidosis in peripheral blood leukocytes. Replicate studies with model test compounds were conducted in which F344 rats were given 4 or 7 doses of either maprotiline hydrochloride, imipramine hydrochloride, tilorone dihydrochloride, amikacin hydrate or vehicle control. Transmission electron and light microscopy were used to examine peripheral blood smears and tissue samples for the presence of cytoplasmic vacuoles. Unstained and Nile red stained lysed peripheral blood samples were acquired for analysis using a FACScan flow cytometer. Inorganic phosphorus concentration in the liver was determined from extracted phospholipids and compared with flow cytometry and histological data. It was demonstrated that flow cytometric analysis of Nile red stained lysed whole blood can be used to detect drug-induced phospholipid accumulation in circulating peripheral leukocytes. Furthermore, clinically detectable leukocyte phospholipidosis may be a useful surrogate for coincident or premonitory detection of target organ phospholipidosis.

Inhaled cationic amphiphilic drug-induced pulmonary phospholipidosis in rats and dogs: time-course and dose–response of biomarkers of exposure and effect

This study compares the pulmonary response to an inhaled highly soluble hydrochloride (CAD-HCl) with a low soluble sulphate salt (CAD-SO4) of a dicationic amphiphilic drug (CAD). These salts are known to accumulate in the lung. The bioavailability through gastrointestinal uptake is poor. Wistar rats and beagle dogs received repeated 1 h/day inhalation exposures over 1-4 weeks. The focus of this analysis is to appraise the correlation of markers of effects related to pulmonary phospholipidosis and cytotoxicity relative to the concentration of CAD in the lung tissue, alveolar macrophages and serum. Rats and dogs are known to experience remarkable differences in their respiratory minute volumes and respiratory patterns. In order to facilitate dosimetric comparisons, identical exposure paradigms and methodological procedures were selected. Over a wide range of cumulative dosages, the CADs bound to lung tissue and cells in bronchoalveolar lavage (BAL) paralleled, whilst no clear association existed in terms of plasma concentrations. This suggests that analysis of the fractional loading of BAL-cells (mainly alveolar macrophages) with CAD or CAD-surfactant complexes is amenable to monitor the accumulation of CADs in the lung. In terms of the comparative phospholipidosis-inducing potency, the CAD-HCl was more potent as compared to CAD-SO4. Following dosimetric adjustments, rats and dogs appeared to be equally susceptible to phospholipidosis. In summary, when exposed to equivalent concentrations of CADs, dogs did not demonstrate a markedly different susceptibility than rats. With regard to the relative intensity of changes, the increase of phospholipids in BAL-fluid and especially BAL-cells correlated with the cumulative exposure dose. Thus, with regard to probing the extent of CAD-induced 'overloading' of alveolar macrophages pharmacokinetic determinations in BAL-cells are considered superior to determinations in plasma. Additional advantages of using the alveolar macrophage as denominator to normalize pulmonary drug concentrations include comparisons across species, and exposure regimens are feasible based on almost readily available endpoints in both pre-clinical and selected clinical studies.

Use of physicochemical calculation of pKa and CLogP to predict phospholipidosis-inducing potential: a case study with structurally related piperazines

Several cationic amphiphilic compounds are known to induce phospholipidosis, a condition primarily characterized by excessive accumulation of phospholipids in different cell types, giving the affected cells a finely foamy appearance. Excessive storage of lamellar membranous intralysosomal inclusion bodies is the hallmark for phospholipidosis on the electron microscopic level. In case of alveolar phospholipidosis, foamy macrophages accumulate within the alveolar spaces of the lung. Based on such findings in a one-year toxicity study with gepirone in rats, we studied the molecular properties of this compound and compounds suspected of being phospholipidosis inducers by means of physicochemical calculations. Physicochemical molecular calculations of molecular weight, ClogP (partition coefficient octanol/water), logD at pH 7.4, and pKa were performed, for the cationic amphiphilic compounds chlorpromazine, amiodarone, imipramine, propranolol and fluoxetine, and for the structurally related compounds 1-phenylpiperazine (1-PHP), gepirone (and its major metabolites, 3-OH-gepirone and 1-pyrimidinylpiperazine [1-PP]), and buspirone. ClogP and calculated pKa cluster differently for the amphiphilic drugs compared to the chemical series of piperazines. In line with this analysis, lamellar inclusion bodies were found in an in vitro validation experiment in the human monoblastoid cell line U-937, incubated for 96 h at 10 microg/mL with cationic amphiphilic drugs (amiodarone, imipramine, or propranolol). No such lamellar inclusion bodies were seen for any of the compounds from the chemical series of piperazines including gepirone and its metabolites. The data presented support the use of simple physicochemical calculations of ClogP and pKa to discriminate rapidly between compounds suspected of being phospholipidosis inducers. Finally, the discriminative power of these physicochemical ClogP and pKa calculations to predict phospholipidosis-inducing potential was further validated by extension of the set of compounds.

Lysosomotropic agents and cysteine protease inhibitors inhibit scrapie-associated prion protein accumulation

We report that lysosomotropic agents and cysteine protease inhibitors inhibited protease-resistant prion protein accumulation in scrapie-infected neuroblastoma cells. The inhibition occurred without either apparent effects on normal prion protein biosynthesis or turnover or direct interactions with prion protein molecules. The findings introduce two new classes of inhibitors of the formation of protease-resistant prion protein.

Lysosomal glycosaminoglycan storage as induced by dicationic amphiphilic drugs: investigation into the mechanisms underlying the slow reversibility

Several dicationic amphiphilic compounds, such as the immunomodulator tilorone and analogues, impair the lysosomal catabolism of sulphated glycosaminoglycans (GAGs). Thereby they cause lysosomal GAG storage in rats and in cultured fibroblasts of several species including man. The GAG storage is rather slowly reversible in vivo; it persists for months after discontinuance of drug treatment. In the present study, we investigated the mechanisms underlying the slow reversibility. Cultured bovine corneal fibroblasts were pretreated for 4 days with tilorone (5 and 20 microM) or with compound CL-90.100 (3 and 10 microM) and further cultured in drug-free medium for periods up to 11 days. The intracellular GAG storage was analysed biochemically and demonstrated histochemically. The subcellular drug distribution (CL-90.100) was demonstrated by fluorescence microscopy. Dermatan sulphate (DS) provided the predominant contribution towards the GAG storage. After pretreatments with the low, as well as the high concentrations of either drug, the storage of DS was irreversible during the period of observation, whereas the minor storage of heparan sulphate was resolved. The enhanced secretion of the lysosomal enzyme beta-hexosaminidase (E.C. 3.2.1.52) caused by pretreatment with the high concentration of tilorone was also readily reversible. Thus, enzyme deprivation could not be the explanation for the sustained DS storage. The localization of the drug-related fluorescence within perinuclear cell organelles, presumably lysosomes, resembled that of the stored GAGs as visualized by histochemical staining. Both, the fluorescence and the positive GAG staining persisted with unchanged intracellular distribution throughout the recovery period. The present results suggest that the persistence of the DS storage is due to the formation of long-lived, non-degradable DS-drug complexes within the lysosomes.

Drug-induced lysosomal storage of sulphated glycosaminoglycans

1. Certain compounds (e.g., the immunomodulator tilorone and congeners) are able to induce lysosomal storage of sulphated glycosaminoglycans (GAG), thus, producing cytological and biochemical alterations reminiscent of the inherited mucopolysaccharidoses. The drug-induced GAG storage has been studied in cultured fibroblasts of several species and in rats, and it is likely to occur also in humans. 2. The cytological hallmarks of GAG storage are enlarged lysosomes congested with material that is intensely stained by cationic dyes. With respect to fixation techniques, one has to keep in mind that the GAGs are highly water-soluble and are leached during conventional fixation and tissue processing. Biochemically, the elevation of GAG contents in tissues and cultured fibroblasts is due to storage of dermatan sulphate, predominantly. 3. The molecular structure of the potent inducers of GAG storage is characterized by a planar tricyclic aromatic ring system that is symmetrically substituted with two side chains of 4-5 sigma bond length, each carrying a protonizable nitrogen atom. The lysosomal storage of GAG is accompanied by lysosomal accumulation of the inducing drug, with the molar ratio of drug to GAG-disaccharide unit amounting to > 1:1. The reversibility of GAG storage is rather slow. 4. The pathogenic mechanisms underlying the drug side effects are discussed and the following hypothesis is put forward: The compounds in question are lysosomotropic weak bases. They get trapped in the acidic lysosomes and accumulate highly there. Physicochemical data suggest that the drugs form complexes with the sulphated GAGs, particularly with dermatan sulphate: The positively charged nitrogen atoms of the drug side chains interact with the negative charges of sulphate and carboxy groups of the GAGs, thereby crosslinking at least two GAG helices. Moreover, the interlinking drug molecules form parallel stacks resulting from interaction of the aromatic pi-electrons of the planar ring systems. This further stabilizes the complexes. The GAGs within the complexes are thought to be resistant to the degrading lysosomal enzymes. 5. Drug-induced GAG storage has not been directly demonstrated in man. Yet, clinical reports on keratopathy and basophilic cytoplasmic inclusions in blood lymphocytes of tilorone-treated patients suggest that this drug side effect may also occur in man.

Drug-induced glycosaminoglycan storage: dose-dependent changes in the pattern of accumulated glycosaminoglycans in cultured bovine and human fibroblasts

The present study determines the amounts and patterns of glycosaminoglycans stored in cultured corneal fibroblasts after treatment with tilorone and three related compounds. The compounds have immunomodulatory properties and have been shown to impair the lysosomal degradation of glycosaminoglycans as a side effect. This side effect has been described as drug-induced mucopolysaccharidosis because the induced lysosomal storage of glycosaminoglycans leads to cellular lesions resembling those in patients with inherited mucopolysaccharidosis. In the present study, the dose-dependency of glycosaminoglycan storage was analyzed after treatment (96 hr) of bovine corneal fibroblasts. The investigated drug concentrations ranged from low concentrations inducing cytological lesions typical of drug-induced mucopolysaccharidosis to high concentrations at the borderline of cytotoxicity. The intracellular amounts of dermatan sulfate, heparan suflate, and chondroitin sulfate were quantified by densitometric scanning of Alcian Blue-stained bands after electrophoresis. All investigated compounds induced a predominant dermatan sulfate storage (3-4-fold accumulation) at low drug concentrations. With rising drug concentrations, a shift of the pattern of stored glycosaminoglycans was observed, characterized by the additional accumulation of heparan sulfate (up to 5-fold of control levels). In cultured human fibroblasts, tilorone also caused a marked dermatan sulfate storage, reaching maximum values at 5 microM and marked heparan sulfate storage at 20 microM. The present data provide evidence: (a) that selective dermatan sulfate accumulation is a characteristic feature of drug-induced glycosaminoglycan storage in cultured bovine and human fibroblasts, if these cells are treated with low concentrations (< or = 5 microM), that are likely to reflect the situation in vivo; and (b) that additional heparan sulfate storage is induced in vitro only by treatment with high concentrations that induce nonspecific cellular lesions.

The antimalarials quinacrine and chloroquine induce weak lysosomal storage of sulphated glycosaminoglycans in cell culture and in vivo

The antimalarial agents quinacrine and chloroquine are well known as potent inducers of lysosomal storage of polar lipids (lipidosis) in cell culture and in vivo. In previous experiments on cultured fibroblasts, chloroquine was shown to additionally cause weak lysosomal storage of sulphated glycosaminoglycans (GAGs) thus inducing mucopolysaccharidosis (MPS). In the present study, quinacrine was investigated for this ability, because we wished to know whether or not the acridine ring system in quinacrine would enhance the MPS-inducing potency as compared to chloroquine carrying an isoquinoline ring system. Tilorone (2,7-bis[2-(diethylamino)ethoxy]fluoren-9-one) known as a potent inducer of MPS served as reference compound. The compounds were compared at a concentration (3 microM) which did not enhance the secretion of the lysosomal enzyme beta-hexosaminidase (E.C. 3.2.1.52), since this would be an indication of unspecific drug effects upon the endosomal/lysosomal compartments of the cell. Additionally the liver of quinacrine- and chloroquine-treated rats was examined with the question whether the lysosomal GAG storage induced by either drug in cell culture had an equivalent in intact organisms. Both, in cell culture and in vivo, quinacrine was found to be a more potent inducer of lysosomal GAG storage than was chloroquine. The results suggest that the acridine ring system favours this drug side effect as compared with the bicyclic isoquinoline ring system. On the other hand, quinacrine was significantly less potent than tilorone and the Symmetrically substituted acridine derivative 3,6-bis[2-(diethylamino)ethoxy]acridine investigated previously. This suggests that the asymmetric structure of the quinacrine molecule reduces the potency as compared to the symmetrically substituted bisbasic compounds with planary tricyclic ring systems such as tilorone and congeners.

Tilorone-induced lysosomal lesions: the bisbasic character of the drug is essential for its high potency to cause storage of sulphated glycosaminoglycans

The immunomodulatory agent tilorone -2,7-bis-[2-(diethyl-amino)ethoxy]fluoren-9-one- and congeners are potent inducers of lysosomal storage of sulphated glycosaminoglycans (GAGs) in animals and cultured fibroblasts of animals and man. All potent inducers of GAG storage hitherto described are bisbasic polycyclic aromatic compounds. They are accumulated in lysosomes and disturb the degradation of GAGs, mainly dermatan sulphate. It has been proposed that the drugs cross-link the polyanionic GAG chains giving rise to undergradable drug-GAG complexes. This hypothesis implies that the bisbasic character of the drug molecules is essential for the side effect in question. In the present study, this was tested by comparing tilorone and its monobasic derivative (MT) with respect to (i) induction of GAG storage in cultured bovine corneal fibroblasts and (ii) physicochemical interactions with GAGs in vitro. The intralysosomal concentration of MT achieved after 1-3 days was of the same order of magnitude as previously shown for tilorone. Nevertheless, under conditions that did not enhance the secretion of a lysosomal enzyme (beta-hexosaminidase, EC 3.2.1.52), the ability of MT to cause storage of [35S]GAGs was significantly lower than that of tilorone. Morphological observations showed that MT was much more potent in causing lysosomal storage of polar lipids than of GAGs. CD spectroscopy with tilorone revealed that the presence of GAGs caused the primarily achiral drug molecules to display CD. This suggested a helical orientation of the tilorone molecules within GAG-drug complexes, and short intermolecular distances which allowed electronic coupling of the aromatic ring systems of adjacent drug molecules. In contrast, MT failed to display any induced optical activity, indicating the absence of highly ordered GAG-drug complexes. In conclusion, the present results show that the substitution of the planar aromatic ring system with two basic side chains is essential for the high potency of tilorone in inducing lysosomal GAG storage. This is paralleled by, and presumably causally related to, strong physicochemical interactions with GAGs.

Tilorone-induced lysosomal storage of glycosaminoglycans in cultured corneal fibroblasts: biochemical and physicochemical investigations

Tilorone (2,7-bis[2-(diethylamino)ethoxy]-fluoren-9-one) and several other bis-basic compounds are known to induce lysosomal glycosaminoglycan (GAG) storage. The responsible pathomechanism has not been elucidated yet. The assumption of an unspecific disturbance of lysosomal proenzyme targeting due to elevation of endosomal pH is opposed by the hypothesis of formation of a complex between tilorone and GAGs within the lysosomes, which renders GAGs indigestible to glycosidases. In cultures of bovine corneal fibroblasts the amounts of intracellular GAGs [dermatan sulphate (DS), heparan sulphate (HS) and chondroitin sulphate (CS)] were quantified. The fibroblasts were exposed to tilorone (5 microM), which was found to be readily taken up by the cells and to be accumulated within acidic compartments to finally achieve millimolar concentrations. Under these conditions the GAG storage is predominantly due to the accumulation of DS; however, the DS secretion into the culture medium was not affected. The HS accumulation was much less pronounced, accounting only for 3% of total GAG storage. Ammonium chloride (10 mM), which is known to diminish lysosomal enzyme activity by interfering with the mannose 6-phosphate receptor-mediated transport, prevents both HS and DS breakdown. By means of NMR spectroscopy it was shown that tilorone itself tends to display a concentration-dependent aggregation which was enhanced in the presence of GAGs. The diethylamino groups of tilorone interact physicochemically with DS, and to a smaller extent with HS, but not with chondroitin 4-sulphate. Thus, the strength of the interaction between tilorone and the different GAGs in vitro correlates with the potency of tilorone to inhibit the breakdown of the individual GAGs in cultured bovine fibroblasts. The results support the hypothesis of a specific interaction between tilorone and particular GAGs, rendering these resistant to enzymic degradation.

Abnormal dendritic maturation of neurons under the influence of a Tilorone analogue (R 10.874)

Tilorone analogue (R 10.874) has a close affinity to the lysosomal compartment of cells and forms a non degradable carbohydrate-lipid-drug complex accumulated within digesting organelles. Resembling biochemical and structural changes are seen in hereditary mucopolysaccharidoses accompanied with abnormal dendritogenesis. On the other hand, developmental toxicity (TERRY et al. 1992), antiproliferative effects (ALGARRA et al. 1993) and interactions with DNA (GELLER et al. 1985) are generated by tilorone. Therefore it should be interesting to know whether the amphiphilic cationic compound is able to produce an abnormal dendritogenesis as in storage diseases or an impaired arborisation of dendrites and what could be the reason for the misdevelopment. We demonstrate that there was a fetal retardation in the development of dendritic network, even under influence of low dosis of the analogue R 10.874. The dendritic dismaturation was concomitant with an increased amount of fatty acids and a slightly disarranged metabolic pathway of gangliosides. The dendritic arborisation closed the gap of retarded development between intrauterine treated and untreated rats after 7 days of postnatal drug elimination. We suppose that a fetotoxic effect and not the lysosomopathy is responsible for the reduced dendritic network.

Tilorone-induced lysosomal storage of sulphated glycosaminoglycans can be separated from tilorone-induced enhancement of lysosomal enzyme secretion

This investigation deals with a drug side-effect. The immunomodulatory drug tilorone (2,7-bis[2-(diethylamino)ethoxy]fluoren-9-one) and congeners induce lysosomal storage of sulphated glycosaminoglycans (GAGs) in animals and in cultured cells. At high tilorone concentrations, GAG storage in cultured fibroblasts was previously reported to be accompanied, and presumably caused by, disturbance of intracellular targeting of lysosomal enzyme precursors, which leads to enhanced secretion and thus loss of lysosomal enzymes. The purpose of the present study was to examine whether the GAG storage induced in cultured bovine fibroblasts by low tilorone concentrations is also accompanied by enhanced lysosomal enzyme release. Enhanced secretion of beta-hexosaminidase (EC 3.2.1.52) was taken as indicating the intracellular mistargeting of lysosomal enzyme precursors. Dose-response curves were established for (a) the intracellular accumulation of 35S-GAGs and (b) the release of beta-hexosaminidase after exposure (72 hr) to tilorone (1-35 microM). For positive controls, the classical lysosomotropic agents NH4Cl (1-30 mM) and chloroquine (1-60 microM) were used. With NH4Cl, 35S-GAG storage was accompanied by enhanced enzyme release throughout the concentration range (EC50 at 3.3 mM for either effect). With chloroquine, low concentrations (< or = 5 microM) caused a small increase in 35S-GAG accumulation without abnormal enzyme secretion; at higher concentrations both drug effects were produced (EC50 around 15 microM for either effect). With tilorone, low concentrations (< or = 5 microM) caused marked 35S-GAG accumulation without enhancement of enzyme release. The EC50 for tilorone-induced 35S-GAG storage was 3 microM, as opposed to 15 microM for enzyme release. The results indicate that GAG storage induced by low concentrations of tilorone is due to mechanisms other than mistargeting and loss of lysosomal enzymes. On the basis of previous results it may be hypothesized that tilorone and other symmetrically substituted dicationic compounds form complexes with the polyanionic GAG chains and thereby impair their enzymic degradation.

Drug-induced intralysosomal storage of sulfated glycosaminoglycans (GAGs): a methodical pitfall occurring with acridine derivatives

The present communication deals with an adverse drug action which is exerted by a series of dicationic amphiphilic compounds such as the immunomodulatory drug tilorone and congeners. The drugs induce lysosomal storage of sulfated glycosaminoglycans (GAGs) in intact organisms and in cultured cells by impairing the lysosomal GAG degradation. This impairment was proposed to be due to the formation of non-degradable GAG-drug complexes. GAGs are highly water-soluble and not preservable by aldehyde fixatives. Therefore, usually the lysosomes appear optically empty in histological preparations, unless the fixative is supplemented with a GAG-precipitating agent. When acridine derivatives were used for the induction of GAG-storage, the lysosomal storage material displayed unexpected and unsystematic variability with regard to its preservability and ultrastructure. In the present study, evidence is presented that the acridine derivatives (a) remain bound to the stored GAGs for some time after glutaraldehyde fixation; and (b) they precipitate GAGs in vitro. Thus, apart from their unwanted action in the living cell, i.e., disturbing lysosomal GAG-degradation, the drugs function as precipitants and "fixatives" for the intralysosomal GAGs. The uncontrolled persistence of the drugs after tissue fixation leads to variable degree of GAG-preservation and thus to unpredictable variability of the ultrastructure of the storage lysosomes. If this pitfall is not realized, the resulting inconsistencies may rise confusion among toxicologic pathologists who deal with drug-induced lysosomal storage disorders.

Drug-induced lysosomal storage of sulfated glycosaminoglycans. Studies on the underlying structure-activity relationships

Some immunomodulatory drugs have previously been shown to induce lysosomal storage of sulfated glycosaminoglycans (sGAG) in intact organisms and cultured cells. These compounds consist of a planary aromatic ring system and two symmetric side chains each carrying a protonizable nitrogen. The purpose of this study was to test a larger collection of such compounds for their potencies to induce lysosomal storage of sGAG in cultured fibroblasts of rat cornea. The cells were exposed (72 h) to various compounds differing with respect to the aromatic ring system or the side chains. Lysosomal sGAG-storage was demonstrated by selective cytochemical staining with cuprolinic blue. The threshold concentration, i.e., the concentration necessary to induce cuprolinic blue-positive cytoplasmic inclusions in at least 1% of the cells, was determined for each compound. The threshold concentrations were distributed over a range of 0.3-30 microM. It should be emphasized that the threshold concentration of a given compound is not a constant, but depends on the volume of cell culture medium per surface area of cell monolayer, since the lysosomal accumulation lowers the initial drug concentration in the medium. If the ratio of medium volume:cell monolayer surface is increased as compared with standard cell culture conditions, the threshold concentration will be lowered. The compounds were ranked according to their threshold concentrations as determined under standard conditions. The following conclusions can be drawn from the ranking: the type of the central aromatic ring system and the distance between the ring system and the protonizable nitrogen atoms of the side chains influence the potency to induce lysosomal sGAG-storage. Regarding the ring system, the potency decreases as follows: acridine approximately anthrachinone > fenfluorenone approximately fenfluorene > xanthenone; xanthene > dibenzofuran approximately dibenzothiophene. In intact organisms, these structure-activity relationships may be superimposed by drug metabolism and pharmacokinetic factors.

Induction of mucopolysaccharidosis in rats by treatment with immunostimulatory acridine derivatives

In the accompanying paper, four dibasic acridine derivatives were reported to induce lysosomal storage of sulfated glycosaminoglycans (sGAG), i.e., mucopolysaccharidosis, in cultured fibroblast (Handrock et al. Toxicol. Appl. Pharmacol. 114, 1992). The purpose of the present morphological and biochemical investigation was to examine whether two representatives of the acridine derivatives, namely 3,6-bis[2-(diethylamino)ethoxy]-acridine and the piperidino analogue, induce mucopolysaccharidosis in intact organisms. Rats were orally treated with 60-80 mg/kg up to 22 weeks. Morphological examination of liver, spleen, and blood lymphocytes yielded cytochemical evidence of mucopolysaccharidosis. Biochemically, up to a 48-fold increase of the urinary excretion of sGAG was found. In the liver and spleen of chronically treated rats, the sGAG contents were elevated by factors up to 56 and 23, respectively. Heparan sulfate and dermatan sulfate contributed most to the total increase of sGAG; chondroitin sulfate was stored to a minor degree. For one compound, the tissue concentrations were determined. It was found that the drug was accumulated in the tissues. Due to their fluorescent properties, the drugs could be detected by fluorescence microscopy to be present in high concentrations within the sGAG-storing lysosomes. On the basis of these observations and of the biochemical data it appears justified to assume a ratio of at least one drug molecule per disaccharide unit of the sGAG to be present in the lysosomes. It is proposed that this leads to the formation of sGAG-drug complexes in the lysosomes. Such complexes may be indigestible substrates for the lysosomal enzymes, thus leading to mucopolysaccharidosis. For toxicologic practice, the cytochemical examination of lymphocytes is recommended as a simple measure for early detection and monitoring of this adverse drug effect.

Lysosomal storage of sulfated glycosaminoglycans in cultured fibroblasts exposed to immunostimulatory acridine derivatives

The purpose of the present cytological and radiochemical study was to investigate whether the immunomodulatory agent 3,6-bis[2-(diethylamino)ethoxy]acridine (CL-90.100) and three congeners induce lysosomal storage of sulfated glycosaminoglycans (sGAG) in cultured rat corneal fibroblasts. The reason for asking this question was as follows: The four acridine derivatives have molecular similarities with the dicationic amphiphilic compound tilorone, which has previously been shown to cause sGAG storage in cultured cells and in intact rats. The cells were exposed to the drugs for 72 hr. Tilorone served as reference. All acridine derivatives caused cytological alterations which, on the basis of the cytochemical results, were indicative of lysosomal sGAG storage. The threshold concentrations ranged from 0.3 to 0.7 microM. Radiochemical experiments showed that CL-90.100 up to 10 microM induced [35S]GAG storage in a dose-dependent manner, with an EC50 of 2 microM. Concentrations above 10 microM were cytotoxic. Experiments with equimolar concentrations (3 microM) demonstrated that three of the acridine derivatives were more potent and one was less potent than tilorone. Additionally, CL-90.100 was tested on bovine corneal fibroblasts, with cytochemical and radiochemical results similar to those in rat cells. The present findings show that (a) the four acridine derivatives induce lysosomal sGAG storage; (b) the acridine ring, compared with the fenfluorenone ring (tilorone), enhances this potency; and (c) the substituents at the nitrogens can have some influence on the potency to induce sGAG storage.

Drug-induced lysosomal storage of sulfated glycosaminoglycans in cultured bovine and human fibroblasts

Several di-cationic amphiphilic compounds are known to cause lysosomal accumulation of sulfated glycosaminoglycans (sGAG) in intact rats and in cultured rat fibroblasts. The purpose of the present investigation was to examine whether this drug side effect also occurs in bovine and human cells. Cultured fibroblasts from both species were exposed to tilorone (3 microM and 5 microM) for 72 h; lysosomal sGAG-storage was demonstrated by cytochemical staining with cuprolinic blue and by measuring the intracellular accumulation of [35S]-GAG. The cytological alterations as well as the radiochemical results in both species were in good agreement with previous data from rat fibroblasts. The present findings indicate that the drug-induced lysosomal storage of sGAG is a species-independent phenomenon. Thus, cultured bovine and human fibroblasts are a suitable model for further studies concerning the as yet unknown molecular mechanisms underlying this adverse drug action.

Acridine Orange, a precipitant for sulfated glycosaminoglycans, causes mucopolysaccharidosis in cultured fibroblasts

The purpose of the present investigation was to examine whether or not a di-cationic amphiphilic compound that is known (1) to be accumulated in lysosomes and (2) to form insoluble complexes with sulfated glycosaminoglycans (sGAG) in vitro, is able to interfere with the lysosomal degradation of sGAG, thus causing mucopolysaccharidosis (MPS) in cultured cells. Acridine Orange (AO) was chosen for this study since it is known to meet the above requirements. Cultured fibroblasts from rat cornea were exposed to AO (0.7 microM to 30 microM) for 72 h; tilorone served as reference compound. AO (1.75 microM to 10 microM) caused MPS in a concentration-dependent manner, higher concentrations were cytotoxic. MPS was demonstrated by cytochemical staining with cuprolinic blue and by measuring the intracellular accumulation of [35S]-GAG. The sGAG-complexing properties of AO were demonstrated by using it as a fixative for the intralysosomal sGAG accumulated in tilorone-treated cells. The present findings give support to the working hypothesis that the MPS induced by di-cationic amphiphilic drugs is due to the formation of insoluble sGAG-drug complexes, with the result that the sGAG become resistant to lysosomal degradation.

Human accumulation potential of xenobiotics: potential of catamphiphilic drugs to promote their accumulation via inducing lipidosis or mucopolysaccharidosis

1. Drug accumulation without a concomitant elevation of blood level may occur if the capacity of the tissue to bind drug increases during chronic treatment. 2. This special type of accumulation is found with cationic-amphiphilic drugs, which induce the formation of lysosomal inclusion bodies containing undergraded lipids or mucopolysaccharides (drug-induced lipidosis or mucopolysaccharidosis, respectively); the stored material provides the additional binding sites for the drug. 3. Factors determining the potential for inducing lipidosis or mucopolysaccharidosis are: (a) affinity of the drugs to phospholipid layers (governed by hydrophobicity) or mucopolysaccharides (drug-induced lipidosis or mucopolysaccharidosis, respectively); the free intra-lysosomal concentration, which is elevated compared with the blood level due to lysosomal trapping (especially with dicationic drugs); (c) the therapeutically required drug concentration in the blood: the therapeutic concentrations are high with drugs that do not act via binding to specific high-affinity receptors.

Cultured corneal fibroblasts as a model system for the demonstration of drug-induced mucopolysaccharidosis

The purpose of the present investigation was to establish a cell culture system suitable for demonstrating the drug-induced lysosomal storage of sulfated glycosaminoglycans (GAGs). This is a drug side-effect which was previously studied in animals treated with the di-cationic amphiphilic compound tilorone and congeners, and which is likely to occur in humans, too. Cultured corneal fibroblasts of rats were exposed to tilorone for 72 h. They developed histochemical and cytochemical alterations indicative of mucopolysaccharidosis and resembling those occurring in vivo. The threshold drug concentration was found to be below 0.7 microM. The reversibility of the lysosomal GAG storage was low. An increase in the drug concentration to 10 microM produced additional unspecific lysosomal alterations, while the mucopolysaccharidosis-like lesions became less prominent. Concentrations of 40 microM and 80 microM caused unspecific cytoplasmic vacuolation and cell death, respectively. The present model system appears suitable for screening investigations of newly developed drugs with respect to their mucopolysaccharidosis-inducing potential and for investigating the structure-activity relationships underlying this adverse drug effect. Care should be taken not to use too high drug concentrations which cause unspecific lysosomal lesions.

Experimental mucopolysaccharidosis: preservation and ultrastructural visualization of intralysosomal glycosaminoglycans by use of the cationic dyes cuprolinic blue and toluidine blue

The cationic dyes Cuprolinic Blue (CB) and Toluidine Blue (TB) were used to preserve the intralysosomal storage material accumulating in tilorone-induced mucopolysaccharidosis. As shown in previous studies, the stored glycosaminoglycans (GAGs) are leached during the conventional fixation procedure, with the result that the lysosomes appear empty. In the present study, the liver, spleen, and cornea-conjunctiva of tilorone-treated rats were examined. The application of CB in the presence of 0.1 M or 0.3 M MgCl2 simultaneously with, or subsequently to the primary fixative yielded electron-dense precipitates within the storage lysosomes. When TB (0.1%) was added to the primary fixative, the storage lysosomes contained filamentous structures arranged in reticular patterns. With increasing TB concentrations (up to 1%) the lysosomes increasingly often showed apparently amorphous storage material which was continuous with the reticular filamentous structures. Similar ultrastructural patterns were obtained with GAG-TB complexes prepared in vitro. The intralysosomal storage material preserved by TB is interpreted as GAG-TB precipitates. In conclusion, the use of CB provides a method which allows direct cytochemical demonstration of the subcellular sites of GAG-storage. The use of TB represents an easy method to obtain electron micrographs pathognomonic of the mucopolysaccharidosis induced by tilorone and congeners. Either method may be helpful to detect this adverse drug effect at the subcellular level.