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Recent investigations indicate that Burkitt's lymphoma consists of several subtypes, defined by their clinical and molecular features. Each geographical region so far studied appears to consist of a different mixture of subtypes. Interestingly, there appear to be geographic 'gradients' with respect to the fraction of tumors associated with EBV and the type of 8;14 chromosomal translocation. The rate of EBV association is highest in Equatorial Africa, lowest in North America and intermediate in South America. The fraction of tumors with breakpoints far upstream of the c-myc gene follows a similar pattern. These findings strongly suggest that the subtypes of Burkitt's lymphoma are environmentally determined, and we propose that the pattern of infection (e.g. malaria) to which the young child is exposed influences the tumor subtype distribution by altering the relative and absolute numbers of various B cell precursors at sites of B cell ontogeny (the bone marrow, and possibly mesentery). These B cell precursors are the cells which are susceptible to the specific chromosomal translocations associated with Burkitt's lymphoma. We further propose that immunoglobulin enhancers (recognized and unrecognized) both influence the likelihood of the translocation occurring, and in at least a fraction of cases, contribute to the deregulation of a c-myc. EBV, via EBNA-1, the only invariably expressed latent-gene in Burkitt's lymphoma, probably influences c-myc expression in Burkitt's lymphoma by increasing immunoglobulin enhancer function. Thus, in effect, EBV collaborates with the translocations associated with Burkitt's lymphoma in causing c-myc deregulation. This collaboration is independent of the breakpoint location. While other molecular abnormalities must be able to contribute to myc deregulation in the same way, EBV association in Burkitt's lymphoma is probably determined by the age at which EBV infection occurs (being more likely when infection occurs in very young children) and perhaps also by other infectious diseases that numerically influence the fraction, and predominant stage of differentiation (and hence translocation breakpoint sites) of immature B cells infected by EBV. The presence of EBV in many such cells greatly increases the incidence rate of Burkitt's lymphoma, since one of the genetic lesions needed to deregulate c-myc is already present.
Semin Cancer Biol 1992 Oct
PMID:Epstein-Barr virus and Burkitt's lymphoma. 133 92

Tumor necrosis factor is a cytokine that participates in the mediation of numerous diseases associated with inflammation, cachexia, shock, and tissue injury. Early studies of the biology of TNF delineated its hormonal actions as well as its systemic toxicity. More recent investigations have drawn attention to its paracrine actions that predominate when it is produced locally in the brain or vital organs. For instance, when compartmentalized production of TNF occurs in the central nervous system it directly mediates fever, anorexia, and altered whole-body metabolism. Since these changes are mediated within the neural network they occur independently of simultaneously sampled serum TNF levels. These paracrine actions of TNF have implications for diseases associated with production of TNF in tissues (e.g. HIV cerebritis, multiple sclerosis, cerebral malaria and cancer), because they may differ markedly from the hormone like-actions associated with systemic release. Since TNF may be beneficial in some diseases yet injurious in others, both the hormonal and paracrine actions must be precisely defined in order to formulate novel treatment strategies based on either enhancing its useful effects, or suppressing toxicity.
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PMID:Tumor necrosis factor in metabolism of disease: hormonal actions versus local tissue effects. 134 May 27

The Industrial Revolution ushered in a rapid transition from agriculture to industrialization. Some biological effects of this transition included increasing life expectancy, reduced infant mortality, and some decline in fertility. Reduced infant mortality first brought about an increase in life expectancy, but as humans were able to control infectious diseases, child and adult mortality also decreased. Now, accidents and chronic diseases are responsible for most mortality in many age groups. This shift from infectious diseases to accidents and chronic diseases is called the health transition. Japan and US are Pacific Basin countries which have relatively high life expectancy and low infant mortality (1988, 75.54 years vs. 71.38 years, and 4.4 vs. 9.9, respectively). These figures suggest that these countries rather advanced in the health transition. Japan may have better life expectancy than the US because of the effect of environmental factors, ethnic diversity, and health care differentials by social class on cardiovascular disease and cancer mortality. China and Thailand hold intermediate positions (67.98 years (1985-1990) vs. 63.82 years (1985-1986), and 32.4 vs. 39, respectively). Some research indicates that urban conditions and factory work increase the cardiovascular disease risk among the Chinese. Recent research suggests that access to immunization and modern medical care for acute disease are the only critical variables of the health transition rather than other variables. Papua New Guinea is not progressing very well (53.18 years and 58). Papua New Guinea has not yet been able to control infectious diseases, especially malaria. This comparison illustrates that populations progress through the health transition at different rates.
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PMID:Health transition: examples from the western Pacific. 142 38

This article reports survey results to Ghanaian nursing students' perceptions of public health issues. Their views were ascertained through a questionnaire designed to capture ratings of educational curriculum concerns and perceptions of the importance of public health factors. Both frequency data and chi-square analysis were used to assess the ordinal position of health factors and gender differences, respectively. Chi-square analysis was also done to assess differences by age. Differences between men and women respondents existed on six of 15 health factors (p less than .05) including malaria, heart disease, measles, cancer, malnutrition and car accidents, while differences between age groups were found on two of the 15 factors (violence and cancer). Based on the ascertained student perceptions, current efforts in Ghana suggest that preventive health is an emerging concern to public health officials. As such, Ghanaian nursing students hold perceptions not dissimilar to those of U.S. health professions students.
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PMID:Nursing student perceptions of public health issues in Ghana. 155 72

Mortality trends of missionary staff serving in sub-Saharan Africa were tracked for the period 1945-1985. For 1945-1970, when more complete incidence data were available, the missionary death rate was approximately 40% lower, after adjustment, than would be expected in a comparable US population. This trend persisted through 1985. Between 1945 and 1970, the largest number of fatalities was attributable to malignancy, atherosclerosis, accidents, and infectious disease, and the greatest mortality risks, compared with the US experience, were from homicides, the complications of pregnancy, and infections, notably malaria, hepatitis, and polio. Beginning in the late 1950s, motor vehicle accidents became the leading cause of death. Since the 1960s, accidental causes of death have been approximately 50% higher than in the US, and homicides have been four times higher. During this same period, the infectious disease death rate decreased to approximately that within the US. Currently, the leading causes of mortality are motor vehicle accidents, malignancy, and atherosclerosis, followed by other accidental causes, notably aircraft mishaps and drownings. Viral hepatitis is presently the leading infectious disease cause of death. Other contemporary lethal infections include malaria, rabies, typhoid, Lassa fever, and retroviral infection. It was concluded that missionaries in sub-Saharan Africa had a death rate approximately half that expected in a comparable domestic control population. Preventive strategies, particularly relative to accident and infectious disease prevention, could effectively reduce mortality risk further.
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PMID:Mortality trends of American missionaries in Africa, 1945-1985. 162 93

Burkitt's lymphoma (BL) is a highly malignant B cell tumor characterized by three types of chromosomal translocation which constitutively activate the c-myc oncogene by juxtaposing it to Ig coding sequences. Epstein-Barr virus (EBV) infection, hyperendemic malaria and HIV-caused immunosuppression are thought to contribute to the pathogenesis of the tumor. Cell lines derived from EBV carrying and EBV negative BLs often show altered MHC class I antigen expression. The defects include a lower expression of all HLA class I antigens compared to EBV transformed normal B-blasts, and selective down-regulation of certain HLA-A and HLA-C alleles. As a consequence BL cells are often resistant to cytotoxic T lymphocyte (CTL) mediated destruction. Alleles selective down-regulations are found only in cell lines that maintain the tumor cell phenotype while shift towards a more activated 'B-blast like' phenotype is accompanied by HLA class I up-regulation. A similar pattern of HLA class I expression can be found in a subpopulation of germinal center B cells which express a 'BL like' phenotype. Our findings suggest that the HLA class I expression of BL cells reflects the characteristics of the normal B cell precursor and is probably not the result of immune selection.
Semin Cancer Biol 1991 Feb
PMID:Cell phenotype dependent expression of MHC class I antigens in Burkitt's lymphoma cell lines. 165 15

Following previous studies of verapamil reversal of multidrug resistance in cancer cells and chloroquine resistance in malaria, the effect of the calcium channel blocker verapamil was investigated on multidrug-resistant and susceptible Trypanosoma brucei brucei. Resistance of cloned parasites to diminazene aceturate (Berenil) and isometamidium chloride (Samorin) was expressed in a cell-free in vitro culture system. Verapamil showed antitrypanosomal activity against both, multidrug-resistant and susceptible trypanosomes at concentrations above 1 micrograms/ml. Verapamil did not reverse multidrug resistance when used at concentrations of 0.1 or 1.0 micrograms/ml in combination with diminazene aceturate or isometamidium chloride. Results obtained in vitro correlate with observations in mice. It is suggested that multidrug resistance in African trypanosomes is due to mechanisms other than those occurring in cancer cells, malaria or South-American trypanosomiasis.
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PMID:The effect of verapamil alone and in combination with trypanocides on multidrug-resistant Trypanosoma brucei brucei. 168 2

Malaria constitutes one of the major health threats in the tropical and sub-tropical areas of the world. Yet, few advances were made in recent years in revealing the mode of action of the common and most economically affordable antimalarial drugs, the schizontocidal 4-aminoquinolines. Data presented indubitably repudiate the previous notions that these drugs act by either halting the feeding of the parasite on its host erythrocyte cytosol or repressing nucleic acid synthesis due to intercalation into the parasite's DNA. A novel target for drugs is outlined, i.e. they are shown to inhibit in vitro the release of iron from acidified host cell cytosol, consisting mostly of hemoglobin, a process that could provide this trace element to the parasite. Resistance to quinoline-containing drugs is the principal reason for the present resurgence of malaria. Drug-resistant parasites accumulate less of these weak base-like drugs in the acidic digestive vacuoles. A kinetic model is presented, indicating that diminishing drug accumulation is due to decreased vacuolar proton pump activity and is not a result of a putative multidrug resistance (MDR) efflux pump. Findings to date on the molecular biology of parasite mdr genes are reviewed. These indicate no correlation between gene expression or mutations and phenotypic drug resistance. Reversal of parasite drug resistance by relevant compounds in MDR cancer cells seems to involve mechanism(s) different from the inhibition of the MDR pump in cancer cells.
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PMID:Quinoline-containing antimalarials--mode of action, drug resistance and its reversal. An update with unresolved puzzles. 173 99

Free radicals, intermediates in the tissue damage caused by radiation, are formed, inter alia, in interactions catalyzed by iron, which synergizes with radiation and some cytostatics (anthracyclins) in causing cell damage. Conversely, iron chelators can counteract cell damage. Similarly, antioxidants can slow atherogenesis, caused in part by oxidative stress and free radicals. Cell damage is also prevented by physiological defense systems like superoxide dismutase, against endogenous free radicals formed by granulocytes, monocytes, etc. Iron can thus induce free radicals which cause DNA double strand breaks and oncogene activation. This is suggested by four epidemiological studies suggesting a higher cancer risk in patients with larger iron stores than in those with small iron stores. In addition to its effect on carcinogenesis, iron can also maintain the growth of malignant cells as well as growth of pathogens. Breast cancer cells, for instance, display 5-15 times more transferrin receptors than normal breast tissue. Iron-carrying transferrin is in fact a growth factor. Hyposideremia in patients with cancer or infection is not a paraphenomenon but a functioning defense mechanism ('nutritional immunity'). If this immunity is broken by iron administration, relapses of diseases like tuberculosis, brucellosis, and malaria have been described. While iron-deficiency anemia should of course be diagnosed, treated and if possible prevented, there are good reasons to avoid over-utilization of medicamental iron.
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PMID:Iron, free radicals and cancer. 182 Apr 88

Reversal of multidrug resistance (MDR) has been obtained in vitro by a variety of agents but clinical use of these resistance modifiers is hampered by their own toxicity. Quinine, the natural isomer of quinidine, is demonstrated to circumvent doxorubicin (DXR) resistance of an MDR human leukemic cell-line, K562/DXR. In culture medium, quinine (5 mu/ml or more) significantly increases cytotoxicity and accumulation of DXR in the resistant cells but not in the parental sensitive cells. When quinine is administered by continuous intravenous infusion in the doses conventionally used in chloroquino-resistant malaria (30 mg/kg/d), serum levels reach 8-11 micrograms/ml without prohibitive toxicity. Sera from quinine-treated patients enhance DXR uptake in K562/DXR cells in dose-dependent fashion. The conditions for the safe use of quinine as an MDR modifier in the treatment of refractory human hemopoietic malignancies are defined.
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PMID:Quinine circumvents the doxorubicin resistance of a multidrug resistant human leukemic cell-line, K562/DXR. 209 12


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