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Biomedical subjects

G Hoppe

Publications and source records attributed to G Hoppe.

At least 19 recordsLinked to original sources
PubMed2004

Accumulation of oxidized lipid-protein complexes alters phagosome maturation in retinal pigment epithelium.

Lipid peroxidation has been implicated in many age-associated disorders including macular degeneration of the retina. We sought to elucidate the mechanism by which accumulation of oxidized LDL (oxLDL) reduces the ability of retinal pigment epithelium (RPE) to process photoreceptor outer segments (OS) as a model of peroxidation-induced disruption of phagocytosis. OxLDL did not reduce the lysosomal hydrolytic capacity of the RPE, but efficiently inhibited processing of various internalized proteins. OxLDL caused a delay in the acquisition of late lysosomal markers by newly formed phagosomes. At the same time, an excessive accumulation of markers of early phagosomal compartments was also observed. The activity of phosphatidylinositol 3-kinase (PI3K) was reduced in phagosomes of the RPE treated with oxLDL. These results suggest that accumulation of oxidized lipid-protein complexes in the RPE impedes phagosome maturation by blocking PI3K recruitment to the phagosomal membrane, leading to delayed processing of internalized OS.

Cells, Cultured↗
PubMed2001

Oxidized low density lipoprotein-induced inhibition of processing of photoreceptor outer segments by RPE.

PURPOSE: To examine the effects of oxidized low-density lipoproteins (oxLDL) on phagocytosis and processing of photoreceptor outer segments (OS) by retinal pigment epithelial (RPE) cells. METHODS: Confluent cultures of RPE-J cells were pretreated with oxLDL or LDL, and the effects of such treatment on the processing of added OS was determined. Processing was determined either by the degradation of 125I-labeled OS to trichloroacetic acid-soluble label or by the cleavage of rhodopsin observed on Western blot analysis of cell lysates separated by sucrose density gradient fractionation. Binding to and uptake of OS by RPE-J cells was assessed by determining the fluorescence of FITC-labeled OS before and after quenching with trypan blue. RESULTS: OxLDL induced a significant decrease in the degradation of 125I-OS in RPE-J cells but no reductions in either binding or uptake, when a 24-hour recovery period was inserted between treatment with oxLDL and challenge with OS. Rhodopsin cleavage increased in a time-dependent manner after phagocytosis of OS by RPE-J cells. The small guanosine triphosphatase (GTPase), Rab5, was first found in phagosome fractions containing rhodopsin and its cleavage products, and at later times of challenge, in more dense fractions representing phagolysosomes. These were assessed by the colocalization of rhodopsin cleavage products in density fractions with cathepsin D, a marker of lysosomes. OxLDL induced a reduction in rhodopsin cleavage product formation and in phagosome-lysosome fusion (maturation). It also reduced the time-dependent shift of rhodopsin to higher density fractions containing more cathepsin D without any detectable reduction in the expression of cathepsin D or in acid protease activity. CONCLUSIONS: OxLDL induces a reduction in the processing of OS by RPE by perturbing the fusion of lysosomes with phagosomes.

Animals↗
PubMed2000

Macrophage receptors responsible for distinct recognition of low density lipoprotein containing pyrrole or pyridinium adducts: models of oxidized low density lipoprotein.

Oxidation of low density lipoproteins (LDL) induced by incubation with Cu(2+) ions results in the formation of a heterogeneous group of aldehydic adducts on lysyl residues (Lys) of apolipoprotein B (apoB) that are thought to be responsible for the uptake of oxidized LDL (oxLDL) by macrophages. To define the structural and chemical criteria governing such cell recognition, we induced two modifications of lysines in LDL that mimic prototypic adducts present in oxLDL; namely, epsilon-amino charge-neutralizing pyrrolation by treatment with 2,5-hexanedione (hdLDL), and epsilon-amino charge-retaining pyridinium formation via treatment with 2,4,6-trimethylpyrylium (tmpLDL). Both modifications led to recognition by receptors on mouse peritoneal macrophages (MPM). To assess whether the murine scavenger receptor class A-I (mSR-A) was responsible for recognition of hdLDL or tmpLDL in MPM, we measured binding at 4 degrees C and degradation at 37 degrees C of these modified forms of (125)I-labeled LDL by mSR-A-transfected CHO cells. Although uptake and degradation of hdLDL by mSR-A-transfected CHO cells was quantitatively similar to that of the positive control, acLDL, tmpLDL was not recognized by these cells. However, both tmpLDL and hdLDL were recognized by 293 cells that had been transfected with CD36. In the human monocytic cell line THP-1 that had been activated with PMA, uptake of tmpLDL was significantly inhibited by blocking monoclonal antibodies to CD36, further suggesting recognition of tmpLDL by this receptor. Macrophage uptake and degradation of LDL oxidized by brief exposure to Cu(2+) was inhibited more effectively by excess tmpLDL and hdLDL than was more extensively oxidized LDL, consistent with the recognition of the former by CD36 and the latter primarily by SR-A.Collectively, these studies suggest that formation of specific pyrrole adducts on LDL leads to recognition by both the mSR-A and mouse homolog of CD36 expressed on MPM, while formation of specific pyridinium adducts on LDL leads to recognition by the mouse homolog of CD 36 but not by mSR-A. As such, these two modifications of LDL may represent useful models for dissecting the relative contributions of specific modifications on LDL produced during oxidation, to the cellular uptake of this heterogeneous ligand.

Animals↗
PubMed1997

Non-conventional modification of low density lipoproteins: chemical models for macrophage recognition of oxidized LDL.

To define the structural and chemical criteria governing recognition of oxidized LDL (oxLDL) by mouse peritoneal macrophages (MPM), we exposed LDL to novel chemical modification agents that induce defined neutralizing and non-neutralizing alterations of lysine as models for distinct apoB adducts present in oxLDL. We found some exceptions to the usual notion that neutralization of lysine positive charges is the principal determinant governing MPM recognition. In addition, competitive binding experiments using chemically modified 125I-LDL preparations revealed that, whereas some modifications engendered recognition principally by the classical scavenger receptor class A (SRA), as seen for acetylated LDL (acLDL), chemical models of advanced aldehydic modifications of LDL led instead to MPM uptake mainly by oxLDL receptors distinct from SRA.

Animals↗
PubMed1997

Macrophage recognition of LDL modified by levuglandin E2, an oxidation product of arachidonic acid.

Levuglandin (LG) E2, a secoprostanoic acid levulinaldehyde derivative, is a product of free radical oxidation that forms covalent adducts with lysyl residues on proteins. Treatment of LDL with LGE2 leads to uptake and degradation by mouse peritoneal macrophages. Oxidized LDL, but not acetyl LDL efficiently competed for binding and uptake of LGE2-modified 125I-LDL. This result suggests that LGE2-modified LDL was recognized by a class of scavenger receptor that demonstrated ligand specificity for oxidized LDL but not for acetyl LDL.

Acetylation↗
PubMed1997

Inactivation of cathepsin B by oxidized LDL involves complex formation induced by binding of putative reactive sites exposed at low pH to thiols on the enzyme.

We recently showed that the poor degradation of apo B in oxidized (ox-) LDL by mouse peritoneal macrophages could be attributed to the inactivation of cathepsin B by ox-LDL. In this current study, we show that enzyme inactivation involves complex formation of ox-LDL with cathepsin B rather than the diffusion of reactive components from ox-LDL to the enzyme. Complex formation between ox-LDL and cathepsin B was far greater at pH 4.5 than at pH 7.4 and far greater with ox-LDL than with LDL. Even though complexes were also formed between ox-LDL and other proteins such as BSA, insulin, and LDL, ox-LDL bound up to 30 times more cathepsin B than BSA, when compared on a molar level and under the same conditions. Unlike ox-LDL alone, complexes of ox-LDL and BSA were unable to inactive cathepsin B, suggesting that BSA was sequestering reactive sites on ox-LDL. The interaction of ox-LDL with proteins such as cathepsin B appears to represent aldehydic modifications of apo B, since treatment of ox-LDL with the reductant NaBH4, which stabilizes such adducts, greatly decreased the binding of ox-LDL to BSA and prevented ox-LDL from inactivating cathepsin B. It is likely that thiols on cathepsin B or other proteins interact with reactive groups on ox-LDL, since BSA in which thiols were blocked with N-ethylmaleimide (NEM), failed to bind to ox-LDL. Moreover, NEM-treated BSA had no effect on the ability of ox-LDL to inactivate cathepsin B. Similar results were obtained with LDL modified with 4-hydroxynonenal (HNE). These data suggest that aldehydic adducts on ox-LDL that are unreactive at neutral pH, possibly HNE bound to apo B, become exposed at acidic pH and then covalently bind thiols on neighboring proteins such as cathepsin B in lysosomes, inducing crosslinking of proteins and enzyme inactivation.

Aldehydes↗
PubMed1997

Oxidation products of cholesteryl linoleate are resistant to hydrolysis in macrophages, form complexes with proteins, and are present in human atherosclerotic lesions.

Accumulation of the insoluble lipid-protein complex, ceroid, is a characteristic of atherosclerotic plaques. To determine whether deficient processing of cholesteryl esters in oxidized (ox) low density lipoprotein (LDL) contributes to ceroid formation, we studied the hydrolysis of internalized [3H] cholesteryl linoleate (CL) in oxLDL by mouse peritoneal macrophages (MPM). The hydrolysis by MPM of [3H]CL incorporated into oxLDL or LDL did not differ, suggesting that products of lipid and/or apoB oxidation had no impact on the lysosomal hydrolysis of [3H]CL. To evaluate the hydrolysis of oxCL by MPM, we subjected extensively ox[3H]CL to fractionation by TLC. The predominant fraction (D) consisted of sterols and oxysterols esterified to scission products of oxidized fatty acids containing terminal carbonyl groups, i.e., lipid core aldehydes. The extent of hydrolysis of [3H]-fraction D by MPM cultures, as well as by MPM extracts at pH 4.0, was significantly reduced when compared to the hydrolysis of intact [3H]CL. Fraction D also formed complexes with serum proteins, and the purified core aldehyde, cholesteryl 9-oxononanoate reacted with epsilon-amino group of lysines. Finally, several cholesteryl ester aldehydes were detected in lipid extracts of human atheroma. These results suggest that decomposition products of extensively oxidized cholesteryl linoleate that are also present in atherosclerotic lesions, are not adequately degraded by mouse peritoneal macrophage lysosomes and could interact with proteins to form ceroid.

Aldehydes↗
PubMed1995

Structure of cholesterol-containing particles accumulating in atherosclerotic lesions and the mechanisms of their derivation.

Structural and chemical modifications of plasma lipoproteins retained in atherosclerotic lesions, especially LDL, are a characteristic of atherogenesis. The major cholesterol-containing structures believed to be derived primarily from LDL are monomeric or aggregated native or modified LDL particles, cholesteryl ester droplets, liposomes rich in unesterified cholesterol, and ceroid-lipofuscin. They are suggested to be formed primarily from LDL by combinations of oxidation, hydrolysis by proteases and esterases, fusion of neutral lipid components, and covalent interactions between lipid and protein components of oxidized LDL in lysosomes. Although many of these structures appear to be refractory to removal by reverse cholesterol transport mechanisms, they may possess functional properties that still need to be elucidated.

Arteries↗
PubMed1994

Inactivation of lysosomal proteases by oxidized low density lipoprotein is partially responsible for its poor degradation by mouse peritoneal macrophages.

Deficient processing of apo B in oxidized LDL (ox-LDL) by macrophage lysosomal proteases has been documented and attributed to modifications in apo B. We have investigated whether direct inactivation of lysosomal proteases by ox-LDL could also be responsible for this deficient degradation. When mouse peritoneal macrophages (MPM) were preincubated for 21 h at 37 degrees C with ox-LDL, LDL, or vortex-aggregated LDL, only ox-LDL inhibited the subsequent degradation of 125I-labeled forms of the above lipoproteins. Uptake of labeled lipoproteins was not appreciably affected by preincubation with ox-LDL, suggesting that the inhibition was at the level of lysosomal degradation. Thiol protease activity of cell extracts at pH 4.0, was reduced in MPM preincubated with ox-LDL relative to cells preincubated with LDL or medium alone. Extracts from untreated MPM, or mixtures of cathepsin B and D, showed a reduced ability to degrade 125I-LDL at pH 4.5 and reduced cathepsin B activity, after incubation with ox-LDL relative to incubation with LDL. Thus, the reduced degradation of lipoproteins in MPM pretreated with ox-LDL could be due to direct inactivation of the lysosomal protease, cathepsin B.

Animals↗
PubMed1990

The clinical relevance of oral contraceptive pill-induced plasma lipid changes: facts and fiction.

The changes in plasma lipids induced by the use of oral contraceptive pills have been shown in several studies to remain within normal physiologic limits. These changes are then probably without any clinical relevance because there is no evidence in the huge volume of oral contraceptive and cardiovascular literature that the use of oral contraceptives promotes or retards the development of atherosclerotic disease. What may appear to be favorable changes in the lipid profile attributed to oral contraceptive use may actually be associated with unfavorable changes in other parameters, such as the balance of clotting and fibrinolytic factors. A well-balanced, low-dose oral contraceptive formulation should alter any of the cardiovascular risk indicators as little as possible in either a supposedly positive or negative direction.

Animals↗
PubMed1989

A study comparing a gestoden triphasic formulation with a fixed combination OC.

Metabolic parameters were studied in 30 patients over 12 treatment cycles in a double-blind randomized comparative trial of the new progestogen gestoden in a triphasic formulation against a fixed dose combination pill containing desogrestrel, in Bandung, Indonesia. The results of this laboratory experience affirm findings in similar previous metabolic studies that: (1) the changes induced by modern low-dose pills are clinically and statistically insignificant; (2) throughout the treatment cycles, the values of the various laboratory tests remain well within the normal range; and (3) the favorable balance between coagulation and fibrinolysis is maintained. Results of lipoprotein, coagulation, fibrinolytic and liver function tests in 27 patients are presented. Gestoden's pharmacologic profile and the worldwide clinical experience with the triphasic gestoden formulation in 4285 women are discussed.

Blood Coagulation↗
PubMed1988

Gestoden, an innovative progestogen.

The most widely used estrogen component in oral contraceptive (OC) pills today is ethinylestradiol (EE), synthesized in the laboratories of Schering A.G. since the year 1938. Compared to natural estrogens, it has a much stronger effect on liver metabolism, thereby inducing greater metabolic and hemostatic changes. Some, but not all, epidemiological studies associated rare cardiovascular events to the use of the OC pills, although statistical and diagnostic deficiencies inherent in such studies may have created wrong associations. These events were either of thromboembolic or hypertensive but not of arteriosclerotic origin. If these associations were true, therefore EE-induced adverse changes on the blood coagulation and fibrinolytic systems and its stimulation of the renin-angiotensin-aldosterone mechanism would probably be more important than any changes on the lipid and lipoprotein pattern (e.g., HDL-cholesterol). To counteract adverse EE-induced changes, therefore, synthetic progestogens used in OC pills should have a pronounced anti-estrogenic effect, stronger than natural progesterone, like levenorgestrel, and if possible, an aldosterone-antagonistic effect, resembling natural progesterone. Gestoden is a new synthetic progestogen with a pronounced anti-estrogenic effect and a unique aldosterone-antagonistic effect, unlike other synthetic progestogens available. The high biological progestogenic activity allows very low hormonal content in the pill formulation. Multicentric clinical trials with a combination of only 75 mcg gestoden combined with 30 mcg EE confirm a reliable contraceptive efficacy combined with excellent cycle control and tolerance in 1,095 women over 14,281 treatment cycles. In about 60% of women with elevated blood pressure before treatment, the blood pressure normalized during treatment.(ABSTRACT TRUNCATED AT 250 WORDS)

Contraceptives, Oral↗
PubMed1988

Diflucortolone valerate. Asian experience.

More than 10 years ago, diflucortolone valerate (Nerisone, Nerisona) was introduced in Germany and soon after in Asian countries in a concentration of 0.1% in cream, ointment and fatty ointment bases. 897 patients were included in the first Southeast Asian multicentre trial with these 3 formulations, and good efficacy and tolerability combined with a rapid onset of effect were shown. These results were confirmed later in Indonesia in an extended follow-up trial which included 1295 patients. A combination of 0.1% diflucortolone valerate with 1.0% chlorquinaldol was introduced after a multicentre Southeast Asian trial involving 8668 patients with inflammatory or allergic skin conditions for which a supplementary anti-infective treatment, for prophylaxis or therapy, was considered to be indicated. Excellent results were obtained in terms of efficacy, tolerability and cosmetic properties. A randomised double-blind trial comparing this preparation with a so-called 'shotgun' combination containing 0.05% betamethasone 17-valerate, 0.1% gentamicin, 1.0% tolnaftate and 1.0% clioquinol in 288 patients in the Philippines resulted in a better efficacy for the diflucortolone preparation in the 80 patients with bacterially or mycotically infected skin diseases. A 0.3% concentration of diflucortolone valerate was developed and introduced as a high potency topical corticosteroid. A trial in the Philippines which involved 143 patients with mostly severe chronic recurrent and resistant corticosteroid-responsive skin disease confirmed a pronounced clinical efficacy with a low incidence of side effects. For the treatment of inflammatory or eczematised dermatomycosis. 0.1% diflucortolone was combined with 1.0% isoconazole nitrate (Travocort). In a randomised double-blind study of 294 patients in Thailand, this preparation was compared with a plain 1.0% clotrimazole formulation. The results were significantly better for the diflucortolone plus isoconazole nitrate combination in terms of remission of symptoms, and after 1 week the mycological cure rates were also better, as shown in potassium hydroxide and culture investigations. It is concluded, therefore, that diflucortolone valerate in the available galenic bases and in effective combinations with other agents has been proven in extensive clinical trials to be a valuable therapeutic tool in dermatological practice.

Asia↗
PubMed1987

Gestoden, an innovative progestogen.

The estrogen component used in virtually all oral contraceptive pills today was synthesized in the laboratories of Schering AG in 1938. The progestogen component varies, but levonorgestrel has become the standard among the lowest-dose pills available. Various attempts to modify the levonorgestrel molecule have resulted in new progestogens like norgestimate and desogestrel without much greater biological activity; therefore, further reduction in dose is unlikely. Gestoden, the newest progestogen from the levonorgestrel class, synthesized in Schering AG's laboratories, is different. Its enhanced biological activity allows for a progestogen content in a fixed combination pill half that in other low-dose pills available today. Furthermore, it has an improved pharmacologic profile with favorable dissociation of the androgenic and progestogenic activities. A unique anti-mineralocorticoid action is seen resembling natural progesterone, a property not presently shared with other synthetic progestogens. Results will be presented from clinical trials with a new monophasic gestoden preparation.

Blood Pressure↗