Linezolid-induced inhibition of mitochondrial protein synthesis.

BACKGROUND: Linezolid is an oxazolidinone antibiotic that is increasingly used to treat drug-resistant, gram-positive pathogens. The mechanism of action is inhibition of bacterial protein synthesis. Optic and/or peripheral neuropathy and lactic acidosis are reported side effects, but the underlying pathophysiological mechanism has not been unravelled. METHODS: We studied mitochondrial ultrastructure, mitochondrial respiratory chain enzyme activity, and mitochondrial DNA (mtDNA) in muscle, liver, and kidney samples obtained from a patient who developed optic neuropathy, encephalopathy, skeletal myopathy, lactic acidosis, and renal failure after prolonged use of linezolid. In addition, we evaluated mtDNA, respiratory chain enzyme activity, and protein amount in muscle and liver samples obtained from experimental animals that received linezolid or placebo. RESULTS: In the patient, mitochondrial respiratory chain enzyme activity was decreased in affected tissues, without ultrastructural mitochondrial abnormalities and without mutations or depletion of mtDNA. In the experimental animals, linezolid induced a dose- and time-dependent decrease of the activity of respiratory chain complexes containing mtDNA-encoded subunits and a decreased amount of protein of these complexes, whereas the amount of mtDNA was normal. CONCLUSION: These results provide direct evidence that linezolid inhibits mitochondrial protein synthesis with potentially severe clinical consequences. Prolonged courses of linezolid should be avoided if alternative treatment options are available.

Effect of transferrin polymorphism on the metabolism of vitamin C in Zimbabwean adults.

BACKGROUND: Transferrin is the major iron binding protein in human plasma. In black persons, the transferrin CD phenotype has been associated with alterations in certain markers of iron status. OBJECTIVE: We studied vitamin C status in a Zimbabwean population according to transferrin phenotype because vitamin C metabolism is influenced by iron-driven oxidative stress. DESIGN: The study population consisted of 150 black African adults, 90 of whom were at risk of iron overload on the basis of high dietary iron content in the form of traditional beer. Transferrin phenotypes, indirect measures of iron status, and leukocyte ascorbic acid concentrations were determined. The in vitro rate of L-ascorbic acid depletion in sera from different transferrin phenotypes was investigated. RESULTS: The transferrin phenotype frequencies of transferrin CC and CD were 0.893 and 0.107, respectively. The iron status of transferrin CC and CD subjects was similar. After adjustment for traditional beer consumption, baseline leukocyte vitamin C concentrations were significantly higher in 16 transferrin CD subjects ( +/- SE: 2.10 +/- 0.34 and 2.61 +/- 0.28 fmol/leukocyte in men and women, respectively) than in 134 transferrin CC subjects ( +/- SE: 1.65 +/- 0.11 and 1.99 +/- 0.11 fmol/leukocyte in men and women, respectively; P = 0.024). Oral administration of ascorbic acid (2.0 g every 24 h for 48 h) led to slower rises in leukocyte vitamin C concentrations in subjects with the transferrin CD phenotype than in subjects with the transferrin CC phenotype (P = 0.028). After in vitro supplementation of serum with 570 micromol vitamin C/L, the rate of L-ascorbic acid depletion was significantly lower in subjects of a transferrin CD phenotype than in subjects with the transferrin CC phenotype. CONCLUSION: Transferrin polymorphism may affect vitamin C status in blacks.

Effects of chloroquine on viral infections: an old drug against today's diseases?

Chloroquine is a 9-aminoquinoline known since 1934. Apart from its well-known antimalarial effects, the drug has interesting biochemical properties that might be applied against some viral infections. Chloroquine exerts direct antiviral effects, inhibiting pH-dependent steps of the replication of several viruses including members of the flaviviruses, retroviruses, and coronaviruses. Its best-studied effects are those against HIV replication, which are being tested in clinical trials. Moreover, chloroquine has immunomodulatory effects, suppressing the production/release of tumour necrosis factor alpha and interleukin 6, which mediate the inflammatory complications of several viral diseases. We review the available information on the effects of chloroquine on viral infections, raising the question of whether this old drug may experience a revival in the clinical management of viral diseases such as AIDS and severe acute respiratory syndrome, which afflict mankind in the era of globalisation.

Iron overload exacerbates experimental meningoencephalitis by Cryptococcus neoformans.

This study was aimed at investigating the effects of iron overload on the onset and outcome of cerebral cryptococcosis. To this purpose, iron dextran-administered mice were intracerebrally challenged with virulent melanogenic and avirulent non-melanogenic strains of Cryptococcus neoformans. The results shown here provide the first evidence that iron overload exacerbates the outcome of cryptococcal meningoencephalitis, irrespective of the fungal strain employed; pathogen colonization of the brain is facilitated, local cytokine response is delayed and/or prevented.

Renal angiomyolipoma in association with pulmonary lymphangioleiomyomatosis.

The authors report on a premenopausal female hemodialysis patient with relapsing pneumothorax, in whom the diagnosis of pulmonary lymphangioleiomyomatosis (LAM) was made. Ten years earlier, she had retroperitoneal bleeding from a kidney tumor corresponding to an angiomyolipoma (AML). The association between renal AML and pulmonary LAM is reviewed. Renal AML represents the most frequent extrapulmonary manifestation of pulmonary LAM. It is found in 32% to 60 % of cases in which a systematic search with abdominal computed tomography (CT) scan is done. The latter approach is advised to help avoid complications caused by renal AML. Therapeutic recommendations for renal AML are based on tumor size or presence of symptoms. Conversely, premenopausal women presenting with AML should be investigated for associated pulmonary LAM with high-resolution CT scan. Because LAM is very likely estrogen dependent, one of the several proposed antiestrogen therapies should be considered. Finally, there is significant overlap between renal AML, pulmonary LAM, and tuberous sclerosis. The latter should therefore be actively searched for in case of either AML or LAM.

Association of haptoglobin phenotypes with the development of Kaposi's sarcoma in HIV patients.

Kaposi's sarcoma (KS) is a rare cutaneous tumor caused by human herpes virus-8 (HHV-8) infection that preferentially develops in case of severe immunosuppression, such as in HIV/AIDS disease. Haptoglobin (Hp), a polymorphic multifunctional plasma protein, exerts several immunomodulatory effects and is characterized by a genetic polymorphism leading to three major phenotypes (Hp 1-1, Hp 2-1 and Hp 2-2). This study investigated the influence of Hp genetic polymorphism on the development of KS in HIV-positive patients. 661 HIV patients were enrolled in the study with a median age of 35 years and a median follow-up time of 57 months. Hp phenotyping was performed using hemoglobin-supplemented starch gel electrophoresis. In case of low Hp concentration high pressure gel permeation chromatography (HPGPC) was used. The Hp 1-1 phenotype was associated with a significant higher risk of KS compared to the combined group of Hp 2-1 and Hp 2-2 patients (p < 0.0005) which remained significant after adjustment for possible confounding variables (age, gender and AIDS status) (p < 0.001). In contrast, the Hp 2-1 phenotype carried the lowest risk. These findings point to the involvement of Hp phenotypes in the pathogenesis of KS, which may be due to a difference in skin immunosurveillance between the Hp phenotypes.

Staphylococcus aureus infections in hemodialysis: what a nephrologist should know.

Staphylococcus aureus is a formidable pathogen that has the ability to colonize approximately half the dialysis population without any sign of disease but is also capable of causing wound and tissue infections; fulminant septicemia; and chronic, difficult-to-eradicate and often foreign body-related infections. S. aureus is the main cause of infectious morbidity and mortality in hemodialysis patients. This review highlights the importance of S. aureus infections in daily hemodialysis practice from a clinical viewpoint, starting from some key issues in the pathogenesis of staphylococcal infections.

The effect of the host's iron status on tuberculosis.

Several lines of evidence have suggested that iron is critical for Mycobacterium tuberculosis growth in macrophages. Macrophage iron loading in patients with African iron overload increases the risk of tuberculosis (TB) and may worsen TB outcome. Likewise, macrophage iron loading may contribute to an increased predisposition toward TB in HIV infection. Human genetic disorders or variations may increase the risk of TB or worsen its outcome through macrophage iron loading, including the haptoglobin 2-2 phenotype, NRAMP1 polymorphisms (at least in Africans and Asians), and possibly ferroportin 1 mutations, but not HFE hemochromatosis. Thus, the host's iron status may be an important yet underevaluated factor in TB prevention and therapy and in TB vaccine design.

Prevention of Staphylococcus aureus biofilm on dialysis catheters and adherence to human cells.

BACKGROUND: Dialysis patients, often carriers of Staphylococcus aureus in their nares, are at high risk of S. aureus infections. METHODS: We examined whether RNAIII inhibiting peptide (RIP), which interferes with quorum sensing mechanisms, reduces adherence of S. aureus to host cells and to dialysis catheter polymers in vitro. Adherence was tested by spectroscopy using safranin staining, by confocal scanning laser microscopy and by atomic force microscopy. RESULTS: RIP inhibited bacterial adherence to HaCat and HEp-2 cells and reduced adherence and biofilm formation not only on polystyrene, but also on both polyurethane- and silicone-made dialysis catheters, with a preponderant effect on silicone, to which bacteria were more adherent. CONCLUSION: RIP opens a new perspective in anti-S. aureus prophylaxis, particularly in dialysis patients.

Differential cytokine pattern in the spleens and livers of BALB/c mice infected with Penicillium marneffei: protective role of gamma interferon.

Penicillium marneffei is an intracellular opportunistic fungus causing invasive mycosis in AIDS patients. T cells and macrophages are important for protection in vivo. However, the role of T-cell cytokines in the immune response against P. marneffei is still unknown. We studied by semiquantitative reverse transcription-PCR and biological assays the patterns of expression of Th1 and Th2 cytokines in the organs of wild-type (wt) and gamma interferon (IFN-gamma) knockout (GKO) mice infected intravenously with P. marneffei conidia. At 3 x 10(5) conidia/mouse, a self-limiting infection developed in wt BALB/c mice, whereas all GKO mice died at day 18 postinoculation. Splenic and hepatic granulomas were present in wt mice, whereas disorganized masses of macrophages and yeast cells were detected in GKO mice. The infection resolved faster in the spleens than in the livers of wt mice and was associated with the local expression of type 1 cytokines (high levels of interleukin-12 [IL-12] and IFN-gamma) but not type 2 cytokines (low levels of IL-4 and IL-10). Conversely, both type 1 and type 2 cytokines were detected in the livers of wt animals. Disregulation of the cytokine profile was seen in the spleens but not in the livers of GKO mice. The inducible nitric oxide synthase mRNA level was low and the TNF-alpha level was high in both spleens and livers of GKO mice compared to wt mice. These data suggest that the polarization of a protective type 1 immune response against P. marneffei is regulated at the level of individual organs and that the absence of IFN-gamma is crucial for the activation of fungicidal macrophages and the development of granulomas.

Iron withdrawal strategies fail to prevent the growth of SiHa-induced tumors in mice.

OBJECTIVE: Cervical carcinoma is a human papillomavirus (HPV)-associated cancer for which treatment options still mainly rely on surgical procedures, with or without adjuvant radiotherapy and chemotherapy. We have previously shown that the chemically unrelated iron chelators desferrioxamine and deferiprone inhibit the growth and induce the apoptosis of HPV-positive cervical carcinoma cell lines, suggesting that iron chelators may represent a potential therapeutic approach for the treatment of cervical carcinoma. The present study was designed to investigate the effect of iron deprivation on the growth of human cervical carcinoma xenografts in athymic nude mice. METHODS: Nude mice (nu/nu) of BALB/c background were treated with iron chelators [desferrioxamine (DFO), deferiprone (L1), or starch-DFO conjugate] or were fed with an iron-poor diet 6 weeks prior to subcutaneous injection of Si-Ha cells. These treatments were continued for 5 weeks after injection of the tumor cells. Treatment with the maximum tolerated doses of DFO, L1, or starch-DFO conjugate induced no significant iron deprivation in non-iron-overloaded mice, while an iron-poor diet led to a dramatic decrease in serum iron, transferrin iron saturation, and ferritin levels. However, neither iron chelators nor an iron-poor diet could significantly inhibit tumor growth. CONCLUSION: Despite a potent antitumor effect in vitro, iron chelators fail to prevent the growth of cervical carcinoma xenografts in mice. On the basis of these results, clinical trials with iron chelators in patients with cervical carcinoma appear inappropriate.

Prohepcidin accumulates in renal insufficiency.

BACKGROUND: The understanding of iron metabolism has increased substantially during the last decade. Several new transporters and iron regulating molecules have been described. Hepcidin, a small hepatic peptide has recently been proposed as a central mediator of dietary iron absorption. We have investigated the relationship between prohepcidin, the prohormone of hepcidin, and renal function and iron status. METHODS: Forty six patients, referred for 51Cr-EDTA clearance were included in this study. Renal function was assessed by determination of serum creatinine, creatinine clearance, serum cystatin C and serum beta-trace protein. Iron status was evaluated by determination of serum iron, transferrin, transferrin saturation and serum ferritin. All determinations were performed using commercial reagents (Roche Diagnostics, Dade Behring). Serum prohepcidin was determined using an ELISA kit. RESULTS: Serum prohepcidin was found to correlate with 51Cr-EDTA clearance (r = -0.44; p = 0.005), creatinine clearance, serum creatinine, beta-trace protein and cystatin C. No significant relationship was observed between serum prohepcidin concentrations and red cell count, hemoglobin concentration or hematocrit. No significant correlation was found in this population between prohepcidin concentrations and iron status. CONCLUSION: Increased serum prohepcidin concentrations were observed with declining kidney function. We observed no relationship between red cell indices or iron status and serum prohepcidin concentrations.

Antiproliferative and apoptotic effects of iron chelators on human cervical carcinoma cells.

OBJECTIVE: Cervical carcinoma is a human papillomavirus (HPV)-associated cancer for which treatment options still mainly rely on surgical procedures, with or without adjuvant radiotherapy and chemotherapy. As iron may participate in the pathogenesis of viral infections and cancer in several ways, the present study was designed to investigate the effect of iron chelation on HPV-16- and HPV-18-positive cervical carcinoma cell lines. METHODS: Desferrioxamine and deferiprone, two chemically unrelated iron chelators, were used to investigate the effect of iron chelation on SiHa and HeLa cells. Proliferation was investigated by cells counts, by [(3)H]thymidine uptake assay, and by immunostaining with Ki-67 and proliferating cell nuclear antigen (PCNA). Apoptosis was determined by morphological analysis, by a TUNEL assay, and by flow cytometry detecting FITC-conjugated annexin-V. RESULTS: Desferrioxamine and deferiprone induced a time- and dose-dependent inhibition of SiHa and HeLa cell growth. The inhibition of cell growth was associated with a decrease in the expression of both stable and total PCNA and Ki-67, a proliferation marker whose expression may predict survival in uterine cervical carcinoma. TUNEL assay, flow cytometry with annexin-V-fluorescein, and morphological analysis indicated that iron chelation also induced a time- and dose-dependent apoptosis of both cell lines. This apoptotic effect was prevented by the addition of exogenous iron. CONCLUSION: These results show that iron chelation inhibits the growth and induces the apoptosis of HPV-positive carcinoma cells. This suggests that iron chelators may represent a potential therapeutic approach for the management of cervical carcinoma.

Effect of dialyser membrane pore size on plasma homocysteine levels in haemodialysis patients.

BACKGROUND: Hyperhomocysteinaemia is a putative risk factor for atherothrombotic cardiovascular disease in the haemodialysis population. High-dose vitamin B therapy does not entirely normalize elevated plasma total homocysteine (tHcy) levels in haemodialysis patients. Alternative therapies to reduce tHcy further are therefore required. Modifications of the dialysis regimen may result in a better removal of Hcy. We examined the effect of dialyser membrane pore size on tHcy levels in vitamin-replete chronic haemodialysis patients. METHODS: Forty-five haemodialysis patients were dialysed during 4 weeks with a low-flux, a high-flux and a super-flux membrane, in random order. Pre-dialysis tHcy was determined at baseline and every 4 weeks. In 18 patients, plasma tHcy before and after dialysis and dialysate tHcy concentrations were measured. RESULTS: Pre-dialysis tHcy decreased significantly during 4 weeks super-flux dialysis (-14.6 +/- 2.8%), whereas it remained stable during high-flux (+0.5 +/- 2.4%) and low-flux dialysis (+1.7 +/- 3.2%). The homocysteine reduction ratio was not different for the three membranes: 0.39 +/- 0.03 for the super-flux, 0.47 +/- 0.02 for the high-flux and 0.39 +/- 0.02 for the low-flux dialyser. The amount of Hcy recovered in the dialysate during a single dialysis session was also similar: 117.5 +/- 3.6 micro mol during super-flux, 95.3 +/- 11.5 micro mol during high-flux and 116.5 +/- 11.6 micro mol during low-flux dialysis. CONCLUSION: Super-flux dialysis significantly lowers tHcy in chronic haemodialysis patients. Improved removal of middle-molecule uraemic toxins with inhibitory effects on Hcy-metabolizing enzymes, rather than better dialytic clearance of Hcy itself, may explain the beneficial effect of the super-flux membrane.

Anti-HIV effects of chloroquine: inhibition of viral particle glycosylation and synergism with protease inhibitors.

OBJECTIVE: We tested the effects of chloroquine (CQ) on glycosylation of HIV particles and in combination with protease inhibitors (PIs) on HIV replication and on P-glycoprotein (P-gp)/multidrug resistance protein-1 (MRP1). DESIGN: CD4 cell lines were infected with laboratory strains and peripheral blood mononuclear cells were infected with primary isolates for evaluation of the anti-HIV effects. Peripheral blood lymphocytes were evaluated for of P-gp and MRP1 functions. METHODS: HIV replication was assessed by enzyme-linked immunosorbent assay. HIV glycosylation was measured by metabolic labeling of viral particles with [H] glucosamine. Synergism was tested using isobolograms. P-gp and MRP1 functions were assayed using rhodamine 123 (Rh123) and carboxyfluorescein (CF) efflux assays, respectively. RESULTS: CQ alone inhibited HIV replication and glycosylation in a dose-dependent manner. In combination with indinavir (IDV), ritonavir, or saquinavir (SQV), CQ had a synergistic effect at concentrations found in plasma of subjects receiving malaria prophylaxis. CQ decreased the 50% effective concentration of IDV in primary isolates from Africa and restored the response to IDV or SQV in 3 PI-resistant isolates. CQ increased the block of Rh123 and CF efflux activity exerted by PIs. CONCLUSION: The inhibitory effects of CQ on HIV glycosylation are associated with synergistic effects in combination with PIs. The CQ/PI combination exerts combined inhibitory effects on P-gp and MRP1 function.

Iron status in black persons is not influenced by haptoglobin polymorphism.

Iron status in man is influenced by environmental and genetic factors. The molecular variation of haptoglobin is one of the genetic factors influencing iron status in Caucasians. Differences in iron metabolism between blacks and whites have been reported. We wanted to investigate the effect of haptoglobin polymorphism on iron status in blacks. We studied 300 African subjects who were apparently healthy with normal erythrocyte sedimentation rate and with no increase in dietary iron because of traditional beer consumption. We determined haptoglobin (Hp) phenotypes using starch gel electrophoresis and measured indirect iron status indices using standard methods. We compared iron status indices according to haptoglobin type. Ninety two individuals (31%) had Hp 1-1, 114 persons (38%) had Hp 2-1, 20 subjects (7%) had Hp 2-1(Modified) and 54 individuals (18%) had Hp 2-2 type. Haptoglobin was not detectable in 19 subjects and Hp 2-1(Johnson) was found in one subject. In both males and females, serum iron concentration, total iron binding capacity, transferrin saturation and ferritin concentration were not different with regard to Hp phenotype. These results suggest that haptoglobin phenotypic variation may not be a factor which influences iron status in black persons.

Desferrioxamine enhances AIDS-associated Kaposi's sarcoma tumor development in a xenograft model.

Iron is suspected to be involved in the induction and/or progression of various human tumors. More particularly, we have previously shown that iron may be involved in the pathogenesis of Kaposi's sarcoma (KS). We have also shown that the iron chelator desferrioxamine (DFO) has a potent anti-KS activity in vitro, suggesting that it may represent a potential therapeutic approach for the treatment of KS. The present study was designed to investigate the effect of DFO on the growth of human KS xenografts in immunodeficient mice. Unexpectedly, we found that mice treated with DFO (400 mg/kg, 3 times weekly) (n = 30) exhibited a marked enhancement of tumor growth compared with control mice (n = 33) (230 +/- 134 mm(2) versus 143 +/- 70 mm p < 0.01). No enhancement of tumor growth was seen in mice treated with iron-saturated DFO. At least 2 findings suggest that this paradoxic pro-KS activity occurred independently of mice iron stores. First, treatment with DFO had only a marginal effect on ferritin and hematocrit levels. Second, induction of effective iron depletion by an iron-poor diet (6.7 mg iron/kg diet) (n = 23) did not have a deleterious effect on the growth of the KS xenografts. The lesions obtained from the DFO-treated animals exhibited a significantly decreased apoptotic index (p < 0.05), indicating that some antiapoptotic mechanism induced by DFO may be operating in vivo to favour tumor growth. In conclusion, our data show that DFO has a stimulatory effect on KS growth in immunodeficient mice, suggesting that this drug is not indicated in patients with KS.