[Anatomo-clinical and epidemiologic study of Chagas disease]

Chagas' disease is a chronic form caused by a parasite, the Trypanosoma Cruzi, endemic of Latin America. The Trypanosoma Cruzi is transmitted by hematophageous bugs, particularly in dilapidated rural areas. Three phases of the disease can be distinguished: 1) acute phase, with high tissue and blood parasitic involvement; 2) undetermined phase, in which the diagnosis requires sophisticated clinical investigations; 3) chronic phase (10-30 years following the infection), characterized particularly by cardiac disease manifestations. The present 120 patients were subdivided into four groups: 1) 43 asymptomatic serum-positive subjects; 2) 25 serum-positive patients with electrocardiographic abnormalities; 3) 14 serum-positive patients with cardiomegaly; 4) 38 with classic chagasic cardiopathy. Comparative studies among these four groups were carried out employing Holter monitoring (24h), ergometric and phonomechanographic tests, M-mode and bidimensional echography and radionuclide ventriculography. A significant difference between the first 3 groups and, respectively, the fourth group (p < 0.001) was found. Deadly-risk (p < 0.001) manifestation were pointed out, such as a third tone, right bundle branch block with left anterior hemiblock and left ventricle's dilation. Autoptic controls were performed and in 4 patients the myocardial biopsy showed C3 and IgG deposition in capillaries and myocardial fibers, at electron microscopic examination, some thickening of capillary and myocytic basal membrane, interstitial collagen proliferation, besides non-specific myocellular abnormalities were detected.

Azidothymidine homodinucleotide-loaded erythrocytes and bioreactors for slow delivery of the antiretroviral drug azidothymidine

A new Azidothymidine derivative, di-(thymidine-3'- azido-2',3'-dideoxy-D-riboside)-5'-5'-p1-p2-pyrophosphate (AZTp2AZT), was encapsulated in human erythrocytes according to a conservative procedure of hypotonic shock-isotonic resealing and reannealing. Like in erythrocyte lysates supplemented with 1 mM ATP, intact red cells too were found to convert AZTp2AZT to 3'-Azido-3'-deoxythymidine which was then released linearly in plasma. The major metabolic pathway involved in this conversion was the symmetrical hydrolysis of AZTp2AZT to yield two 3'-Azido-3'- deoxythymidine-5'-phosphate molecules which were then dephosphorylated to 3'-Azido-3'-deoxythymidine. At late times of incubation, also a limited asymmetrical hydrolysis of AZTp2AZT became apparent in the intact erythrocytes, yielding 3'-Azido-3'-deoxythymidine-5'-diphosphate that was then converted to the triphosphorylated derivative. Therefore, erythrocytes loaded with AZTp2AZT act "in vitro" as bioreactors ensuring sustained and potentially useful release of 3'-Azido-3'-deoxythymidine.

N-[5-nitro-2-furfurylidene]-3-amino-2-oxazolidinone activation by the human intestinal cell line Caco-2 monitored through noninvasive electron spin resonance spectroscopy

The pathways participating in the metabolism of the nitrofuran antimicrobial drug N-[5-nitro-2-furfurylidene]-3-amino-2-oxazolidinone (furazolidone) in intact cells were investigated in the human intestinal cell line Caco-2. One-electron reduction of furazolidone led to the formation of a free radical intermediate that could be monitored in dense cell suspensions by noninvasive electron spin resonance spectroscopy. The effects of enzyme inhibitors on the kinetics of radical production and decay were used to estimate the relative contribution of different enzymes to the reductive activation of the drug. Although many enzymes are known to reduce nitrofurans in vitro (e.g., xanthine oxidase, aldehyde oxidase, DT-diaphorase, mitochondrial redox chain components), their contributions were insignificant in living Caco-2 cells. The first reducing equivalent required for the formation of the nitroanion derivative of furazolidone appeared to be provided essentially by the microsomal cytochrome P450 reductase. This was confirmed through studies of the NADPH-dependent radical formation by microsomes. Differentiated Caco-2 cells, an established enterocyte model, showed only modestly increased radical formation and the same enzyme-specificity pattern as undifferentiated cells. Consistently, only a small increase in P450 reductase activity was found in differentiated cells, in contrast to the 10-fold increase seen in typical differentiation marker enzymes. With the electron spin resonance method that we describe, it is possible to distinguish between sites of bioactivation of redox active drugs in intact cells.

[Youthful sudden cardiac death and the Kawasaki syndrome. An anatomopathological case report]

In 1967 Kawasaki studied 50 cases with the same features as mucocutaneous lymph node syndrome, further reported throughout Japan with the eponym of Kawasaki's disease. It is frequent in Japan and in USA, whereas in Europe it is sporadic and often misinterpreted. It presents as an acute fever, attended by irritation of the skin and oral mucosa, with swelling of cervical lymph nodes, easily misdiagnosed as scarlet fever, Stevens Johnson syndrome, or infantile exanthema or allergy. After the acute phase, Kawasaki's disease becomes chronic and sudden death is possible even if many years have elapsed. In the chronic phase, coronaritis, coronary aneurysms, marked stenosis and/or occlusive thrombosis are often present. Cardiac Lesions were classified from stage I to IV according to the duration of illness at death. The present work deals with the case of a 17 year old man, dying from undiagnosed coronary artery chronic Kawasaki disease. The patient had been hospitalized for Wolff-Parkinson-white syndrome; ten months after discharge he died suddenly, while performing gymnastics at school. Occluding thrombosis of cylindrical aneurysm of both coronary arteries, from undiagnosed Kawasaki arteritis, was found and the young boy succumbed to hyperacute infarction. The heart was fixed in buffered formalin 10% and embedded in paraffin. Histological examination of the cardiac conduction system has been carried out on serial sections, with the technique usually adopted by one of the present authors (L. Rossi). Hema-toxylin-eosin (H-E) and trichromic (Hei-denhein-azan) stainings have routinely employed.

In vivo uptake of Cu, Zn superoxide dismutase. Morphological evidence for preferential endocytosis and accumulation by sinusoidal liver cells

Bovine Cu, Zn superoxide dismutase (SOD), conjugated to colloidal gold, was intravenously administered to rats and its distribution studied by electron microscopy. Liver was the preferential site of accumulation of gold-labelled SOD. Among liver cells types, Kupffer and endothelial cells showed the presence of the protein earlier than hepatocytes. Uptake by kidney showed slower kinetics than liver. No uptake by heart could be detected. The gold-labelled SOD was localized inside coated pits, coated vesicles and other non-coated endocytic compartments. Absence of binding by BSA-gold complexes and competition between free SOD and the gold-labelled one demonstrated the specificity of the uptake process. Our morphological evidences suggest that in vivo internalization of SOD occurs most likely through receptor-mediated endocytosis.

Anatomic thoracoscopic lobectomy (ATL) without minithoracotomy: preliminary experience

The purpose of this review is to outline our experience with a completely thoracoscopic approach to major pulmonary resection (lobectomy). There were 23 patients in this study selected by the usual criteria of resectability. The preoperative workup included chest x-ray, pulmonary function studies, computed tomography (CT) of the chest and abdomen, bronchoscopy, mediastinoscopy, and brain and bone scans in the majority of patients. ATL was attempted in 23 patients. In four patients the procedure was converted to the "open" approach for the following reasons: inability to identify the location of the primary lesion (two patients), obscurative bleeding (one patient), and inability to diagnose the pathology (one patient). The underlying pathology of the ATL group was as follows: bronchiolitis obliterans-organizing pneumonia = 1, granuloma = 2, non-small cell lung cancer = 14, solitary colonic metastases = 2. The breakdown by site of the 19 ATL resections is as follows: right upper lobe = 5, right middle lobe = 1, right lower lobe = 1, right upper and right middle lobes = 1, left upper lobe = 6, left lower lobe = 5. Group A patients (n = 11) were those who had no postoperative complications. Length of stay was short, ranging from 4 to 8 days, median 5 days. Group B patients (n = 8) had complications (prolonged air leak = 4, supplemental postoperative oxygen requirement = 3, pain control = 1) and stayed longer (range 10-21 days, median 13). There were no deaths, no blood transfusions, no chest tube reinsertions and no reoperations. The most significant complication in the ATL group was prolonged air leak in one patient (21 days).

CONCLUSIONS

(a) ATL without minithoracotomy is feasible; (b) ATL has potential benefits in terms of reduction of pain and hospital stay; (c) ATL had better cosmetic and functional results.

Tetrasomy 8 and t(1;11)(p32;q24) in acute myelo-monocytic leukemia with extensive leukemic cutaneous involvement

We report a case of tetrasomy 8 in a patient suffering from acute myelomonocytic leukemia with extensive leukemic cutaneous infiltration. In all metaphases analyzed t( I;11)(p32;q24) was concomitantly observed. Similarly to other cases with tetrasomy 8, the patient showed monocytic involvement and poor response to chemotherapy. We conclude that this kind of cytogenetic aberration is associated with distinct morphologic and clinical features.

Integration of complete transferred DNA units is dependent on the activity of virulence E2 protein of Agrobacterium tumefaciens

Agrobacterium tumefaciens transfers transferred DNA (T-DNA), a single-stranded segment of its tumor-inducing (Ti) plasmid, to the plant cell nucleus. The Ti-plasmid-encoded virulence E2 (VirE2) protein expressed in the bacterium has single-stranded DNA (ssDNA)-binding properties and has been reported to act in the plant cell. This protein is thought to exert its influence on transfer efficiency by coating and accompanying the single-stranded T-DNA (ss-T-DNA) to the plant cell genome. Here, we analyze different putative roles of the VirE2 protein in the plant cell. In the absence of VirE2 protein, mainly truncated versions of the T-DNA are integrated. We infer that VirE2 protects the ss-T-DNA against nucleolytic attack during the transfer process and that it is interacting with the ss-T-DNA on its way to the plant cell nucleus. Furthermore, the VirE2 protein was found not to be involved in directing the ss-T-DNA to the plant cell nucleus in a manner dependent on a nuclear localization signal, a function which is carried by the NLS of VirD2. In addition, the efficiency of T-DNA integration into the plant genome was found to be VirE2 independent. We conclude that the VirE2 protein of A. tumefaciens is required to preserve the integrity of the T-DNA but does not contribute to the efficiency of the integration step per se.

[Protective efficacy of 3 anesthetic methods with reference to surgical stress in children]

Hormonal-metabolic stress responses have beyond doubt an effect on morbidity/mortality related to surgery. The present study med to determine which anaesthetic technique could afford the best protection in children, through analysis of the perioperative cortisol, prolactin and beta-endorphin plasma levels. Thirty-six young patients 3-10 years old, ASA I-II, scheduled for hypospadias or vesicoureteral reflux surgery of a duration > 60 min, were randomized into three groups (n = 12). Children of group I were given initially propofol and fentanyl then isoflurane 1%; group 2 received TIVA with propofol and fentanyl, group 3 received initially propofol then an epidural lumbar block with bupivacaine 0.25% (single shot) and continuous propofol i.v. infusion. Cortisol, prolactin and beta-endorphin levels increased significantly in group 1 only. No significant differences were observed between group 2 and 3. Early postoperative analgesia was better in group 3. These data suggest that TIVA and particularly epidural block could afford a better protection against the surgical stress in children submitted to subumbilical operations.

Selenium, zinc, and thyroid hormones in healthy subjects: low T3/T4 ratio in the elderly is related to impaired selenium status

Iodothyronine 5' deiodinase, which is mainly responsible for peripheral T3 production, has recently been demonstrated to be a selenium (Se)-containing enzyme. The structure of nuclear thyroid hormone receptors contains Zinc (Zn) ions, crucial for the functional properties of the protein. In the elderly, reduced peripheral conversion of T4 to T3 with a lower T3/T4 ratio and overt hypothyroidism are frequently observed. We measured serum Se and RBC GSH-Px (as indices of Se status), circulating and RBC Zinc (as indices of Zn status), thyroid hormones and TSH in 109 healthy euthyroid subjects (52 women, 57 men), carefully selected to avoid abnormally low thyroid hormone levels induced by acute or chronic diseases or calorie restriction. The subjects were subdivided into three age groups. To avoid under- or malnutrition conditions, dietary records were obtained for a sample of 24 subjects, randomly selected and representative of the whole population for age and sex. Low T3/T4 ratios and reduced Se and RBC GSH-Px activity were observed only in the older group. A highly significant linear correlation between the T3/T4 ratio and indices of Se status was observed in the older group of subjects (r = 0.54; p < 0.002, for Se; r = 0.50; p < 0.002, for RBC GSH-Px). Indices of Zn status did not correlate with thyroid hormones, but RBC Zn was decreased in older as compared with younger subjects. We concluded that reduced peripheral T4 conversion is related to impaired Se status in the elderly.

An epidemiological study of canine filarioses in north-west Italy: what has changed in 25 years?

A field survey aimed at updating knowledge of the distribution and prevalence of filarial infections in the Piedmont region was undertaken. Blood samples were collected from 2628 dogs (10-15 dogs/100 km2) which had remained in the local area, were kept in the open overnight, were more than 2 years old and had not previously been treated with microfilaricidal drugs. Infection was diagnosed by a modified Knott test. Comparison of the results with those from a similar survey carried out 25 years ago showed a 3-fold increase in the size of the endemic area, with the colonization of new habitats, and a 4-fold increase in the prevalence of Dirofilaria immitis infection.

Sudden cardiac death in the indeterminate phase of Chagas' disease associated with acute infarction of the right carotid body

We recently came across a case of a patient in the indeterminate phase of Chagas' disease who died suddenly with cardiac arrhythmia associated with acute infarction of the right carotid body due to occlusive thrombosis in the glomic artery. Although the available data in this case do not offer definite evidence to support a cause-and-effect relationship between carotid body infarction and patient's sudden cardiac arrest, it is very likely that the acute infarction of the carotid body could be the distinct morphological counterpart of the functional disturbance. The infarction would affect the vagal-sympathetic interactions augmenting sympathetic action.

Immunocytochemical study of binding and internalization of carrier-free Cu, Zn Superoxide dismutase by cultured rat hepatocytes

Internalization of superoxide dismutase-gold complex by isolated liver cells has been shown to occur via receptor-mediated endocytosis. As colloidal gold may act as a carrier in this process, carrier-free human Cu, Zn superoxide dismutase was incubated with cultured rat hepatocytes. Light and electron microscopy immunocytochemistry revealed the binding and internalization of free native human Cu, Zn superoxide dismutase (hSOD) by cultured rat hepatocytes. Immunocytochemical demonstration of binding to the cell surface (hepatocytes were incubated with hSOD for 15 min. at 4 degrees C) and internalization (hepatocytes were incubated with hSOD for 15, 30 and 60 min. at 37 degrees C) of the carrier-free superoxide dismutase was achieved by using a monoclonal antibody selectively reacting with the human protein. The results obtained indicate that carrier-free superoxide dismutase is bound and internalized by rat hepatocytes in primary cultures and that the enzyme can enter the cells via a receptor-mediated endocytosis pathway. We followed the binding and the internalization process of hSOD thus validating the use of the native enzyme in the therapy of free radical-related diseases.

Lactate catabolism by enzyme-loaded red blood cells

Two different enzymes that metabolize lactate in the presence of oxygen, either to acetate plus CO2 (lactate 2-mono-oxygenase; Lmox) or to pyruvate plus H2O2 (lactate oxidase; Lox) were encapsulated in human and murine red blood cells (RBCs). Lmox shows a low affinity for lactate (Km 22 mM) and thus works at a low rate at the lactate concentrations found in hyperlactataemia (5-20 mM). Encapsulation of Lox provides a constant catabolic rate under the same range of blood lactate concentrations, but generates H2O2, which is toxic to the enzyme-loaded RBCs. Co-encapsulation of both enzymes at a ratio of 20 units of Lmox/unit of Lox results in significant rates of lactate metabolism over a wide range (1-30 mM) of lactate concentrations with modest methaemoglobin formation (5-8.5%) and normal cellular ATP concentrations (1.1-1.23 mM). In vitro experiments with [1-14C]glucose and [U-14C]glucose have shown that Lmox/Lox-loaded RBCs counteract the production of H2O2 by increasing the amount of glucose metabolized in the pentose phosphate pathway. In vivo attempts to prove the efficacy of these engineered RBCs in removal of blood lactate in mice have failed because of the high aerobic capacity and high lactate metabolism of these animals. However, the results obtained in vitro suggest that the encapsulation of lactate-catabolizing enzymes may be useful in the treatment of hyperlactataemia.

The epizootiology of sarcoptic mange in chamois, Rupicapra rupicapra, from the Italian eastern Alps

Sarcoptic mange is the most severe infection in chamois in the Eastern Alps. This study analyses and discusses data from two mange foci in the Foresta Demaniale di Tarvisio (NE Italy). The first impact of mange on naive host populations was dramatic, with mortality rates of over 80%. The chamois herds were decimated, but they recovered quite fast and two later epizootics were observed to have a far less severe impact on the chamois population. Intervals between successive waves lasted 10 to 15 years. No sign of low reproductive performance nor evidence of a poor physical condition of the animals was observed in the years preceding the new epizootic waves. Mortality rates were only slightly influenced by the density of the host population. In a long lasting focus of disease, adult males appeared more vulnerable to mange than other sex and age classes. Cases of mange were also more frequent in winter and spring. This seasonal trend may be explained by the interaction between the dynamics of mites, ethological patterns-rut activity-and the poorer physical condition of the host during this period.

2',3'-Dideoxycytidine metabolism in a new drug-resistant cell line

2',3'-Dideoxycytidine (ddC) is a nucleoside analogue that inhibits human immunodeficiency virus type 1 (HIV-1) replication in vitro and is currently used in the therapy of acquired immune deficiency syndrome (AIDS). This compound exerts a delayed cytotoxicity due to inhibition of mitochondrial DNA (mDNA) synthesis. Long-term exposure of U937 human monoblastoid cells to ddC resulted in a time- and concentration-dependent decrease in mDNA content and Rhodamine 123 fluorescence. However, after 2 months on 0.1 microM ddC, a drug-resistant cell line (U937-R) with 66% of the normal amount of mDNA was isolated. ddC transport in U937 and U937-R cell lines was similar. In contrast, U937-R accumulated ddC phosphorylated derivatives at a much lower rate and to a reduced concentration into acid-soluble material. The rate of 2',3'-dideoxycytidine 5'-triphosphate (ddCTP) formation in U937-R cells was almost one-third of that measured in normal cells, although the rate of ddCTP catabolism was similar in both cell lines. Dideoxyliponucleotide (ddCDP-choline and ddCDP-ethanolamine) formation was also much slower (between one-half and one-third as fast) in U937-R than in control cells, although catabolism occurred at similar rates. ddC was phosphorylated by a cytoplasmic deoxycytidine kinase in both cell lines. This enzyme showed Km values for ddC of 80 +/- 7 and 140 +/- 9 microM in U937 and U937-R cells respectively. Furthermore, Vmax was 12 +/- 1.1 and 7.8 +/- 0.5 pmol/min per mg of protein in U937 and U937-R. Thus resistance to ddC toxicity may be due to cells' decreased ability to accumulate intracellular ddC anabolites, which may depend on cytoplasmic deoxycytidine kinase.

Reduced serum levels of immunoreactive erythropoietin in patients with cirrhosis and chronic anemia

Chronic anemia is frequently observed in patients affected by cirrhosis. To investigate the possible role of erythropoietin (Epo) in the pathogenesis of anemia in cirrhosis, we measured the immunoreactive Epo levels and the respective hemoglobin (Hb) concentrations in 48 anemic and nonanemic cirrhotic patients and in a control group of healthy subjects and patients with iron-deficiency anemia. Epo concentrations were determined in serum using a sensitive enzyme immunoassay. The regression curve between Epo values and Hb concentrations showed a significant inverse exponential trend both in cirrhotic patients (r = -.55; P < .0001) and controls (r = -.92; P < .0001). In a semilogarithmic plot, the line slope obtained in cirrhotic patients was significantly lower (P < .005) than that of controls, suggesting a blunt Epo response to anemia in cirrhosis. Moreover, covariance analysis showed that the Epo levels for a given degree of anemia were further reduced in the patients with a more severe disease, suggesting a close relation between cirrhosis and the mechanisms involved in the derangement of the Epo feedback system. Finally, the Epo concentrations measured in the cirrhotic patients without anemia did not significantly differ from Epo values obtained in healthy subjects. An impaired Epo response may play a role in maintaining low Hb concentrations in cirrhotic patients with anemia. However, the evidence of a residual Epo response to anemia in cirrhosis and the presence of normal basal Epo levels in nonanemic cirrhotic patients do not support an inadequate Epo secretion as one of the primary causes of anemia in cirrhosis.

Reduced serum levels of immunoreactive erythropoietin in patients with cirrhosis and chronic anemia

Chronic anemia is frequently observed in patients affected by cirrhosis. To investigate the possible role of erythropoietin (Epo) in the pathogenesis of anemia in cirrhosis, we measured the immunoreactive Epo levels and the respective hemoglobin (Hb) concentrations in 48 anemic and nonanemic cirrhotic patients and in a control group of healthy subjects and patients with iron-deficiency anemia. Epo concentrations were determined in serum using a sensitive enzyme immunoassay. The regression curve between Epo values and Hb concentrations showed a significant inverse exponential trend both in cirrhotic patients (r = -.55; P < .0001) and controls (r = -.92; P < .0001). In a semilogarithmic plot, the line slope obtained in cirrhotic patients was significantly lower (P < .005) than that of controls, suggesting a blunt Epo response to anemia in cirrhosis. Moreover, covariance analysis showed that the Epo levels for a given degree of anemia were further reduced in the patients with a more severe disease, suggesting a close relation between cirrhosis and the mechanisms involved in the derangement of the Epo feedback system. Finally, the Epo concentrations measured in the cirrhotic patients without anemia did not significantly differ from Epo values obtained in healthy subjects. An impaired Epo response may play a role in maintaining low Hb concentrations in cirrhotic patients with anemia. However, the evidence of a residual Epo response to anemia in cirrhosis and the presence of normal basal Epo levels in nonanemic cirrhotic patients do not support an inadequate Epo secretion as one of the primary causes of anemia in cirrhosis.

[Intramuscular injections--an outdated form of administration? 6 cases of Staphylococcus aureus sepsis following intramuscular injections]

Intramuscular injections can lead to local and systemic complications, such as abscess and sepsis. These are often caused by Staphylococcus aureus, occur in immunocompromised as well as in immunocompetent persons, and often need extensive medical and surgical treatment. We describe 6 cases with sepsis and multiple abscesses caused by Staphylococcus aureus after intramuscular injections. In view of possible serious complications, the indication for intramuscular injection as a method of drug administration is critically analyzed.

Effect of antiviral treatments on the bone marrow in murine aids

Blood cytopenia is a common feature in HIV infection, occurring in up to 70% of patients with AIDS. Since at present it is not clear to what extent this is intrinsic to HIV infection or due to opportunistic infections and antiretroviral agents we have investigated the long-term effects of conventional and new antiviral drugs on the bone marrow of normal and immunodeficient mice. The results show that azidothymidine (AZT), dideoxycytidine (DDC) and dideoxycytidine 5'-triphosphate (DDCTP) alone or in combination are all effective in inhibiting the expression of the retroviral protein Pr60gag in bone marrow cells. However, DDCTP was the most effective in preventing bone marrow cytopenia. Combined treatments of AZT plus DDCTP result in a reduction in erythroid precursors compared to that resulting from DDCTP administration, while DDC plus DDCTP results in a differential cell count similar to that found in uninfected mice. Thus, the bone marrow in murine AIDS may prove useful as a model for therapy of retroviral infections and for treating blood cytopenias.

Ascites free-water dynamics in decompensated cirrhosis: effects of acute and chronic frusemide treatment

OBJECTIVE

To evaluate the effects of acute (60 mg intravenous bolus) and protracted (75 mg per day orally for 1 week) frusemide administration on ascites volume, free-water peritoneal clearance (FWPC), intra-abdominal pressure (IAP) and body weight in 30 decompensated cirrhotic patients.

METHODS

Individual ascites volume and FWPC were estimated by means of a previously validated methylene-blue dilution test.

RESULTS

All the investigated parameters showed a significant reduction after the protracted diuretic treatment (ascites volume 9.0 +/- 1.0 to 4.9 +/- 0.61, P < 0.001; FWPC 99.8 +/- 6.7 to 76.2 +/- 6.6 ml/min, P < 0.001; IAP 17.0 +/- 1.5 to 11.3 +/- 0.8 cmH2O, P < 0.001; body weight 75.2 +/- 1.9 to 66.3 +/- 1.8 kg, P < 0.001). A significant FWPC reduction (89.5 +/- 14.6 to 68.8 +/- 12.1 ml/min, P < 0.02) was also observed after the acute frusemide administration in the absence of any appreciable modifications to ascites volumes and IAP.

CONCLUSION

Frusemide treatment appears to be able to exert a direct significant effect on FWPC, which does not appear to be mediated by ascites volume or IAP modifications.

2',3'-Dideoxycytidine induced drug resistance in human cells

2',3'-Dideoxycytidine (ddC) is a nucleoside analogue that inhibits HIV-1 replication in vitro and is currently used in AIDS therapy. This compound exerts a delayed cytotoxicity due to inhibition of mitochondrial DNA (mDNA) synthesis. We have found that long term exposure of U937 human monoblastoid cells to ddC allowed the selection of a drug-resistant cell line (U937-R) with 66% mDNA, normal ddC transport and altered deoxycytidine kinase kinetic properties. In this paper we show that U937-R cells contain an increased number of mitochondria per cell and a reduced copy number of mDNA/mitochondria. Furthermore, the intracellular concentrations of deoxycytidine 5'-triphosphate (dCTP) and 2',3'-dideoxycytidine 5'-triphosphate (ddCTP) are also reduced although with a higher dCTP/ddCTP ratio in U937-R compared to the parental cells. This mechanism of drug resistance, with drug-resistance based on viral mutations, can provide an explanation for drug failure in antiviral therapy.