Pentamidine accumulates in rat liver lysosomes and inhibits phospholipid degradation

Glycosaminoglycans are potential pharmacological targets for classic DNA minor groove binder drugs berenil and pentamidine

It is shown that the antiprotozoal drugs berenil and pentamidine, conventional minor groove binders of DNA, form non-covalent complexes with polyanionic glycosaminoglycans.

Drug-drug interactions involving lysosomes: mechanisms and potential clinical implications

INTRODUCTION

Many commercially available, weakly basic drugs have been shown to be lysosomotropic, meaning they are subject to extensive sequestration in lysosomes through an ion trapping-type mechanism. The extent of lysosomal trapping of a drug is an important therapeutic consideration because it can influence both activity and pharmacokinetic disposition. The administration of certain drugs can alter lysosomes such that their accumulation capacity for co-administered and/or secondarily administered drugs is altered.

AREAS COVERED

In this review the authors explore what is known regarding the mechanistic basis for drug-drug interactions involving lysosomes. Specifically, the authors address the influence of drugs on lysosomal pH, volume and lipid processing.

EXPERT OPINION

Many drugs are known to extensively accumulate in lysosomes and significantly alter their structure and function; however, the therapeutic and toxicological implications of this remain controversial. The authors propose that drug-drug interactions involving lysosomes represent an important potential source of variability in drug activity and pharmacokinetics. Most evaluations of drug-drug interactions involving lysosomes have been performed in cultured cells and isolated tissues. More comprehensive in vivo evaluations are needed to fully explore the impact of this drug-drug interaction pathway on therapeutic outcomes.

Sirolimus-induced pneumonitis complicated by pentamidine-induced phospholipidosis in a renal transplant recipient: a case report

The proliferation signal inhibitors (PSIs)-sirolimus, everolimus, and temsirolimus-have been associated with a noninfectious pneumonitis characterized by lymphocytic alveolitis and bronciolitis obliterans with organizing pneumonia (BOOP). This condition usually occurs within the first year. Herein we presented a case of a deceased donor renal transplant with interstitial pneumonitis developing 6 years after a switch from tacrolimus to sirolimus due to chronic graft dysfunction. After the addition of intravenous pentamidine due to the suspicion of Pneumocystis pneumonia, there was marked clinical deterioration requiring intubation. Open lung biopsy revealed sirolimus-induced pulmonary toxicity (BOOP) with the additional finding of a drug-induced phospholipidosis (DIPL) that we ascribe to pentamidine treatment. After cessation of both drugs and application of corticosteroid therapy, there was only partial improvement. Eight months later the residual interstitial fibrosis demands supplemental home oxygen. We review the literature on PSI-induced pneumonitis and discuss the pathophysiology of a potential interaction with pentamidine. We caution against its use in the setting of PSI-induced pneumonitis. It is currently unknown whether these concerns also apply to prescription of other more commonly used medications associated with DIPL, eg, amiodarone and aminoglycosides.

In vitro activity of pentamidine against Tropheryma whipplei

Pentamidine is a group I intron splice inhibitor used as a chemotherapeutic agent to treat parasitic infections. It was recently found to be efficient intracellularly against Coxiella burnetii, the bacterial agent of Q fever. This in vitro activity was linked to the presence of self-splicing group I introns that disrupt the 23S rRNA of C. burnetii. However, there are several indications that pentamidine may have a wider range of antibacterial activity. The aim of this study was to determine the in vitro activity of pentamidine against Tropheryma whipplei, the agent of Whipple's disease, a chronic disease for which antibiotic treatment remains challenging. In vitro susceptibility testing of pentamidine and doxycycline was assessed both in axenic medium and in cell culture against three clinical isolates of T. whipplei using a quantitative real-time polymerase chain reaction (PCR) assay as previously described. Both doxycycline and pentamidine were found to be active against T. whipplei strains both in axenic medium and in cell culture, with minimum inhibitory concentration ranges of 0.5-1mg/L and 0.125-0.25mg/L for doxycycline and pentamidine, respectively. Pentamidine was effective in vitro against T. whipplei both intracellularly and in axenic medium. This is the first evidence of the direct efficacy of pentamidine against T. whipplei grown in axenic medium and in cells. Since pentamidine has been widely used in humans, we believe that it could be an alternative drug for the treatment of this chronic disease that should be further studied in clinical trials.

Pentamidine inhibits Coxiella burnetii growth and 23S rRNA intron splicing in vitro

Coxiella burnetii is the bacterial agent of Q fever in humans. Acute Q fever generally manifests as a flu-like illness and is typically self-resolving. In contrast, chronic Q fever usually presents with endocarditis and is often life-threatening without appropriate antimicrobial therapy. Unfortunately, available options for the successful treatment of chronic Q fever are both limited and protracted (>18 months). Pentamidine, an RNA splice inhibitor used to treat fungal and protozoal infections, was shown to reduce intracellular growth of Coxiella by ca. 73% at a concentration of 1 microM (ca. 0.6 microg/mL) compared with untreated controls, with no detectable toxic effects on host cells. Bacterial targets of pentamidine include Cbu.L1917 and Cbu.L1951, two group I introns that disrupt the 23S rRNA gene of Coxiella, as demonstrated by the drug's ability to inhibit intron RNA splicing in vitro. Since both introns are highly conserved amongst all eight genotypes of the pathogen, pentamidine is predicted to be efficacious against numerous strains of C. burnetii. To our knowledge, this is the first report describing antibacterial activity for this antifungal/antiprotozoal agent.

Ultrastructure of testicular macrophages in aging mice

Testicular macrophages of aging mice were studied by TEM. Testicular macrophages retained with Leydig cells the close morphological relationships observed in the adult young animals, but digitations were not found. Lipofuscin granules like those of the Leydig cells from aging mice were observed in the cytoplasm. These organelles were generally absent in the testicular macrophages of young adult mice. Testicular macrophages did not display phagocytosis of the lipofuscin granules. In addition, the latter were not found in the intercellular spaces. These observations indicated that lipofuscin granules were formed, at least in a great part, within testicular macrophages as a consequence of metabolic changes occurring with age. Fine lamellar organization was seen in the lipofuscin granules of both Leydig cells and testicular macrophages. Frequently, lipofuscin granules originated from secondary lysosomes containing lipidic vacuoles only. Together with accumulation of the lipofuscin granules, changes of testicular macrophage fine morphology were observed. Endoplasmic reticulum and Golgi apparatus became poorly developed, and coated vesicles were rarely found. Fewer mitochondria were encountered, but their ultrastructure was not altered. These results suggest that in testicular macrophages lipofuscin accumulation is associated with a functional involution.

Lipofuscin: mechanisms of formation and increase with age

Lipofuscin (age pigment) is a brown-yellow, electron-dense, autofluorescent material that accumulates progressively over time in lysosomes of postmitotic cells, such as neurons and cardiac myocytes. The exact mechanisms behind this accumulation are still unclear. This review outlines the present knowledge of age pigment formation, and considers possible mechanisms responsible for the increase of lipofuscin with age. Numerous studies indicate that the formation of lipofuscin is due to the oxidative alteration of macromolecules by oxygen-derived free radicals generated in reactions catalyzed by redox-active iron of low molecular weight. Two principal explanations for the increase of lipofuscin with age have been suggested. The first one is based on the notion that lipofuscin is not totally eliminated (either by degradation or exocytosis) even at young age, and, thus, accumulates in postmitotic cells as a function of time. Since oxidative reactions are obligatory for life, they would act as age-independent enhancers of lipofuscin accumulation, as well as of many other manifestations of senescence. The second explanation is that the increase of lipofuscin is an effect of aging, caused by an age-related enhancement of autophagocytosis, a decline in intralysosomal degradation, and/or a decrease in exocytosis.

Metabolism is an important route of pentamidine elimination in the rat: disposition of 14C-pentamidine and identification of metabolites in urine using liquid chromatography-tandem mass spectrometry

This study assesses the contribution of metabolism for the disposition of pentamidine in the rat. With the use of 14C-labelled compound, the excretion of radioactivity in urine and faeces has been studied in four rats during 44 days after a single intravenous injection of the drug. The urinary and faecal excretion of the radioactivity were of equal importance; 22 +/- 2% (mean +/- S.D.) and 25 +/- 4% being detected in urine and faeces, respectively. The activity in organs and tissues at 44 days after drug administration was also measured and amounted to 21 +/- 5% of the administered dose. Using HPLC the proportion of metabolites in urine in relation to unchanged pentamidine increased with time after dose, being 76 +/- 15% (mean +/- S.D.) of the total excreted radioactivity on day 1 and 97 +/- 1% on day 6. HPLC--tandem mass spectometry was used for identification of metabolites in urine obtained from four rats given unlabelled pentamidine. Using synthetic reference compounds and the selective MS/MS mode four oxidized metabolites of pentamidine were identified either by direct injection into the system or by analyses of extracted urine. Thus, a substantial part of pentamidine is excreted as metabolites in urine.