P-FLUX: A phosphorus budget dataset spanning diverse agricultural production systems in the United States and Canada

Quantifying spatial and temporal fluxes of phosphorus (P) within and among agricultural production systems is critical for sustaining agricultural production while minimizing environmental impacts. To better understand P fluxes in agricultural landscapes, P-FLUX, a detailed and harmonized dataset of P inputs, outputs, and budgets, as well as estimated uncertainties for each P flux and budget, was developed. Data were collected from 24 research sites and 61 production systems through the Long-term Agroecosystem Research (LTAR) network and partner organizations spanning 22 U.S. states and 2 Canadian provinces. The objectives of this paper are to (a) present and provide a description of the P-FLUX dataset, (b) provide summary analyses of the agricultural production systems included in the dataset and the variability in P inputs and outputs across systems, and (c) provide details for accessing the dataset, dataset limitations, and an example of future use. P-FLUX includes information on select site characteristics (area, soil series), crop rotation, P inputs (P application rate, source, timing, placement, P in irrigation water, atmospheric deposition), P outputs (crop removal, hydrologic losses), P budgets (agronomic budget, overall budget), uncertainties associated with each flux and budget, and data sources. Phosphorus fluxes and budgets vary across agricultural production systems and are useful resources to improve P use efficiency and develop management strategies to mitigate environmental impacts of agricultural systems. P-FLUX is available for download through the USDA Ag Data Commons (https://doi.org/10.15482/USDA.ADC/1523365).

Acute responses of hepatic fat content to consuming fat, glucose and fructose alone and in combination in non-obese non-diabetic individuals with non-alcoholic fatty liver disease

We have recently demonstrated that a high-fat load can induce immediate increase in hepatic fat content (HFC) and that such an effect can be modified differently by co-administration of fructose or glucose in healthy subjects. Therefore, we addressed the question how consumption of these nutrients affects changes in HFC in subjects with non-alcoholic fatty liver disease (NAFLD). Eight male non-obese non-diabetic patients with NAFLD underwent 6 experiments each lasting 8 hours: 1. fasting, 2. high-fat load (150 g of fat (dairy cream) at time 0), 3. glucose (three doses of 50 g at 0, 2, and 4 hours), 4. high-fat load with three doses of 50 g of glucose, 5. fructose (three doses of 50 g at 0, 2, and 4 hours), 6. high-fat load with three doses of 50 g of fructose. HFC was measured using magnetic resonance spectroscopy prior to meal administration and 3 and 6 hours later. Plasma triglycerides, non-esterified fatty acids, glucose and insulin were monitored throughout each experiment. HFC increased by 10.4 ± 6.9% six hours after a high-fat load and by 15.2 ± 12.5% after high-fat load with fructose. When co-administering glucose with fat, HFC rose only transiently to return to baseline at 6 hours. Importantly, NAFLD subjects accumulated almost five times more fat in their livers than healthy subjects with normal HFC. Consumption of a high-fat load results in fat accumulation in the liver of NAFLD patients. Fat accumulation after a fat load is diminished by glucose but not fructose co-administration.

Calcium and magnesium infusions for prevention of oxaliplatin-induced peripheral neuropathy

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Background: Oxaliplatin plays an important role in chemotherapy regimens for colorectal and other GI malignancies. Debilitating peripheral neuropathy (PN) often develops with use of this drug. One study (Grothey A et al, ASCO 2009, abst #4025) has shown that pre- and post-oxaliplatin infusions with calcium (Ca) and magnesium (Mg) may reduce this toxicity. To confirm this in an unselected indigent minority population, a retrospective review was performed comparing development of PN in oxaliplatin exposed patients treated with or without Ca/Mg.

Methods: Records of patients who received oxaliplatin from 1/2008 to 12/2009 at MetroHealth Medical Center, a large safety net hospital in Cleveland, OH, were reviewed. 47 patients received Ca/Mg + oxaliplatin and 46 oxaliplatin alone. Data collected included age, race, gender, insurance status, performance status, tumor type, stage, concomitant diseases (DM and EtOH), number of cycles and cumulative dose of oxaliplatin. PN was determined using the Common Terminology Criteria of Adverse Events (CTCAE) version 3.0. Patients were followed 6 months after completion of oxaliplatin.

Results: Demographic data was similar between the two groups. Colorectal cancer compromised 77% of the treatment group and 85% of control group. Patients who received Ca/Mg had significantly less PN in all three grades (1-3) compared with the control group (grade 1 89.4% vs. 71.7%, grade II 10.6% vs. 19.6%, grade 3 0% vs. 8.7%, respectively). The cumulative dose of oxaliplatin did not differ between the two groups (Ca/Mg median 1,143 range 260-2,169; control median 1,425 range 137-2,635). The combined total grades 2 and 3 in both the treatment and control (10.6% vs. 28.3%, p = 0.038) favored use of Ca/Mg.

Conclusions: This small, retrospective study confirms that Ca/Mg infusions reduce the incidence of clinically significant (grade 2/3) PN in pts receiving oxaliplatin.

No significant financial relationships to disclose.

Modified method for isolation of langerhans islets from mice

Successful isolation of Langerhans islets is a crucial prerequisite for their experimental or possible clinical use such as transplantation. Centrifugation in a Ficoll gradient is a common step used for separation of Langerhans islets from exocrine tissue. However, islets have been reported to be negatively affected by employing Ficoll gradients. Therefore, the aim of this study was to modify the isolation procedure by excluding Ficoll gradient centrifugation to obtain a similar or better yield of viable, functional islets. In our modification of the isolation procedure, the separation of islets from exocrine tissue was based on their sedimentation rate combined with their differential ability to attach to the surface of culture dishes for suspension cells. The resulting purity of islets facilitated their handpicking from the suspension. The mean yield was 900 viable, insulin-producing islets per mouse, which was comparable to or even higher than the yield in commonly used protocols. Our modification of the isolation method may be useful when centrifugation in Ficoll gradient is undesirable due to potential toxicity.

Replacement of dietary saturated FAs by PUFAs in diet and reverse cholesterol transport

Dietary intervention is the first and usually successful approach in the treatment of high LDL cholesterol (LDL-C) concentration, but it is frequently accompanied by a decrease in HDL concentration. We studied 14 male volunteers on two different diets, high saturated fatty acid (SFA) and high PUFA, in a crossover design to test whether a decrease in HDL can affect reverse cholesterol transport from relabeled macrophages. A significant decrease of LDL-C (in mmol/l) after a PUFA diet compared with an SFA diet from 3.15 +/- 0.65 to 2.80 +/- 0.56 (P < 0.01) was accompanied by a significant decrease of HDL cholesterol (HDL-C) (in mmol/l) from 1.21 +/- 0.30 to 1.10 +/- 0.32 (P < 0.05). These changes did not affect cholesterol efflux (CHE) from macrophages (9.74 +/- 1.46% vs. 9.53 +/- 1.41%). There was no correlation between individual changes of HDL-C and changes of CHE. It is concluded that the decrease of HDL-C after successful dietary intervention of LDL-C is not accompanied by a decrease of CHE.

Association of MHC class I chain related gene-A microsatellite polymorphism with the susceptibility to T1DM and LADA in Czech adult patients

The results in this study suggest that microsatellite polymorphism within the transmembrane region of MIC-A gene is associated with genetic susceptibility to adult-onset of type 1 diabetes mellitus (T1DM), MIC-A5.1 allele, corrected P = 0.001, whereas it is not associated with latent autoimmune diabetes in adults (LADA) in Czech population. According to our findings, we can hypothesize that adult-onset T1DM and LADA may have partly different immunogenetic aetiopathogenesis.

[Typology of age structures in the Czech Republic]

The authors evaluate the age structure of the Czech Republic. "The basis of the evaluation rests in numbers of population of productive age while the participation of the pre- and post-productive population has been expressed in relation to it.... This approach has been applied [to] the preliminary results of the 1991 population census for the Czech Republic, its regions, districts, hinterland centres of district and local importance as well as for the communities." (SUMMARY IN ENG AND RUS)

Sources and properties of triglyceride-rich lipoproteins containing apoB-48 and apoB-100 in postprandial blood plasma of patients with primary combined hyperlipidemia

Although editing of apolipoprotein (apo)B in the small intestine, yielding apoB-48, is thought to be nearly complete in adult humans, small amounts of intestinal apoB-100 may also be produced. We have evaluated the fraction of unedited apoB secreted from the intestine postprandially in subjects with primary combined hyperlipidemia, a disorder in which secretion of apoB-100 into the blood is increased. Three hours after these subjects and healthy controls were fed a fat-rich meal containing retinol, the distribution of retinyl esters (RE) between plasma triglyceride-rich lipoprotein (TRL) fractions containing apoB-100 and apoB-48 was measured under conditions minimizing transfer of RE between lipoprotein particles. The estimated maximal percentage of unedited intestinal apoB-100 (approximately 3%) was not increased in subjects with primary combined hyperlipidemia, suggesting that reduced editing of intestinal mRNA does not contribute to the pathogenesis of this disorder. Postprandially, the triglyceride content of TRL containing apoB-48 more than doubled, leading to a 20% increase in mean diameter, yet the surface concentration of phospholipids and soluble apolipoproteins (apoE and total apoC) was unchanged. Furthermore, the surface concentrations of these components did not differ among TRL containing apoB-48 and two smaller fractions of apoB-100 TRL with distinct immunoreactivities. These findings suggest that available surface area is a major determinant of the particle content of each of these surface components of TRL species of differing size and origin.

Sex differences in response to steroids in preterm sheep lungs are not explained by glucocorticoid receptor number or binding affinity

We recently reported that prenatal glucocorticoid therapy is less effective at promoting an improvement in lung function in male than in female sheep. This observation, and the higher incidence of respiratory distress syndrome in human males, suggests that the male fetal lung may be less responsive to glucocorticoids than is the female fetal lung. Since glucocorticoids are known to exert their effects via specific cytoplasmic glucocorticoid receptors (GR), we hypothesized that there may be sexual dimorphism in either the number or binding affinity of lung GR. To test the hypothesis, binding of dexamethasone (a synthetic glucocorticoid, 0.5-40 nM) by cytosolic fractions of male (n = 16) and female (n = 16) fetal sheep lung was measured at 125 days gestation (term = 148 days). Scatchard analysis of dexamethasone binding showed that the total number of GR (Bmax) did not significantly differ between male (346 +/- 42 fmol/mg protein) and female (277 +/- 23 fmol/mg protein) fetuses. The measured binding affinity (Kd) in male fetal lungs (6.85 +/- 0.43 nM) was not significantly different from that in females (8.46 +/- 1.02 nM). In conclusion, this study suggests that sex differences in fetal sheep lung responses to glucocorticoid therapy are not due to differences in the number or binding affinity of lung GR.

Lung Morphometry after Repetitive Antenatal Glucocorticoid Treatment in Preterm Sheep

Antenatal glucocorticoids are thought to be less effective when delivery occurs more than 7 d after initiation of treatment; therefore, repeat courses are often administered. We examined lung structure after single or repetitive antenatal glucocorticoid injections in fetal sheep. Pregnant ewes received single or repetitive doses of 0.5 mg/kg betamethasone at 7-d intervals by maternal or fetal injection, beginning at D104 or D114 with delivery at D125, D135, or D146 gestation (term = 150 d). Changes in lung structure were more pronounced after repetitive versus single injections. Repetitive fetal or maternal injections beginning at D104 (delivery at D125) resulted in comparable structural changes: alveolar volume increased by 50 to 80%, alveolar numerical density decreased by 30 to 40%, and pleural and interlobular septal volumes decreased by as much as 70%. Similar changes were seen in animals delivered at D135 after repetitive maternal injections beginning at D114. There were no structural differences between control and repetitive betamethasone animals when delivery was delayed until D146, indicating that betamethasone induced structural changes were reversible.

Plasma levels of remnant particles are determined in part by variation in the APOC3 gene insulin response element and the APOCI-APOE cluster

Remnant particles of triglyceride-rich lipoproteins (RLP) are known to be a strong predictor of atherogenicity. The serum concentrations of remnant-like particle triglyceride (RLPTG) and remnant-like particle cholesterol (RLPC) have been determined in a representative sample of the Czech MONICA study (n = 285). The relationship was investigated between remnant particle triglyceride/cholesterol concentrations and polymorphisms in the genes APOC3 (-482C-->T/3238C-->G), APOE (epsilon2/epsilon3/epsilon4), APOCI (-317-321ins), APOB (signal peptide), hepatic lipase (LIPE, -480C-->T), and lipoprotein lipase (LPL, S447X). Univariate analysis showed significant effects on RLPTG associated only with the APOE genotype (P = 0.009), the APOC3 -482C-->T genotype (P = 0.018), and the APOCI -317-321ins (P = 0.014) genotype and significant effects on RLPC with APOE (P = 0.01) and APOCI -317-321ins (P = 0.021). The raising effect of the APOE genotype for both remnant cholesterol and triglyceride was confined to the epsilon2/4 (n = 6) and varepsilon4/4 (n = 3) groups, and thus when the epsilon2/4 group was omitted in order to analyze by allele (epsilon2+/epsilon3+/epsilon4+), significance was lost (P = 0.6). There was strong linkage disequilibrium between the APOE and APOCI alleles (chi(2), P < 0.001) and a multivariate ANOVA of RLPTG with all three significantly associated variants as factors demonstrated that while the APOC3 -482C-->T effect was independent of the others (P = 0.003), the APOCI -317-321ins and APOE effects were not. This was also true for the APOCI -317-321ins and APOE effects on RLPC. To assess whether APOE-CI effects on RLPC were independent of their effects on total cholesterol and triglyceride levels, multiple linear regression was used. Using multiple linear regression, it appeared that the APOE-CI effects on RLPC were independent of their effects on plasma cholesterol, but the effects of APOC3 and APOE-CI on RLPTG could not be separated from their effects on plasma Tg levels. Further characterization of this remnant particle phenotype and its genetic determinants may lead to a better understanding of its metabolism and contribution to atherosclerosis.

Direct evidence that iron deprivation induces apoptosis in murine lymphoma 38C13

We found that the mouse B cell lymphoma 38C13 underwent apoptosis in vitro when deprived of iron by three independent methods: (1) exposure to a synergistic pair of rat IgG monoclonal antibodies against the mouse transferrin receptor; (2) exposure to the iron chelator deferoxamine (DFO), and (3) exposure to a defined culture medium without any added iron (iron-poor medium). When each antibody was present at a concentration of 5 micrograms/ml, the number of living cells declined to approximately 25% after a 24-hour incubation. After 48 h, there were no surviving cells. When DFO was present at a concentration of 10 microM, the effects were similar, but delayed by 24 h. when iron-poor medium was used, the effects and kinetics were similar to those seen with antibody treatment. For each method of iron deprivation, the reduction in cell viability correlated with the development of apoptosis, as assessed by DNA fragmentation analysis and propidium iodide staining. Electron microscopy studies provided additional confirmation of apoptotic cell death. The addition of 500 microM ferric citrate completely prevented apoptosis for each of the three methods of iron deprivation. These studies provide new and compelling evidence to support the view that iron deprivation can specifically induce apoptosis and serve to strengthen the rationale for further studies of iron deprivation as a form of cancer treatment.

Growth of human tumor cell lines in transferrin-free, low-iron medium

Iron is essential for tumor cell growth. Previous studies have demonstrated that apart from transferrin-bound iron uptake, mammalian cells also possess a transport system capable of efficiently obtaining iron from small molecular weight iron chelates (Sturrock et al., 1990). In the present study, we have examined the ability of tumor cells to grow in the presence of low molecular weight iron chelates of citrate. In chemically defined serum-free medium, most human tumor cell lines required either transferrin (5 micrograms/ml) or a higher concentration of ferric citrate (500 microM) as an iron source. However, we have also found that from 13 human cell lines tested, 4 were capable of long-term growth in transferrin-free medium with a substantially lower concentration of ferric citrate (5 microM). When grown in medium containing transferrin, both regular and low-iron dependent cell lines use transferrin-bound iron. Growth of both cell types in transferrin medium was inhibited to a certain degree by monoclonal antibody 42/6, which specifically blocks the binding of transferrin to the transferrin receptor. On the contrary, growth of low-iron dependent cell lines in transferrin-free, low-iron medium (5 microM ferric citrate) could not be inhibited by monoclonal antibody 42/6. Furthermore, no autocrine production of transferrin was observed. Low-iron dependent cell lines still remain sensitive to iron depletion as the iron(III) chelator, desferrioxamine, inhibited their growth. We conclude that low-iron dependent tumor cells in transferrin-free, low-iron medium may employ a previously unknown mechanism for uptake of non-transferrin-bound iron that allows them to efficiently use low concentrations of ferric citrate as an iron source. The results are discussed in the context of alternative iron uptake mechanisms to the well-characterized receptor-mediated endocytosis process.

Differing sensitivity of non-hematopoietic human tumors to synergistic anti-transferrin receptor monoclonal antibodies and deferoxamine in vitro

We tested non-hematopoietic human tumors for in vitro sensitivity to either a pair of synergistic IgG antitransferrin (Tf) receptor monoclonal antibodies (MAbs), deferoxamine (DFO) or the combination thereof. With an equimolar mixture of the two MAbs (A27.15, E2.3), two prostate tumors showed similar degrees of maximal growth inhibition (PC-3: 35%, DU 145: 38%), two breast tumors showed more variability (MDA-MB-231: 26%, SK-BR-3: 52%) and two neuroblastomas showed the most variability (SK-N-SH: 4%, SK-N-MC: 76%). When the MAbs were applied together with DFO, the D50 for DFO was reduced for all tumors (PC-3: 2.5x, DU 145: 3.7x; MDA-MB-231: 2.9x, SK-BR-3: 1.9x, and SK-N-SH: 2.6x, SK-N-MC: 7.0x). Sensitivity to MAbs was more closely correlated with the relative decrease in Tf receptor density resulting from antibody exposure than with initial receptor density. The degree of reduction of D50 for DFO resulting from the joint application with the MAbs was, however, most closely related to the growth rate of the tumors. Since some non-hematopoietic tumors exhibit sensitivity to the effects of a synergistic pair of IgG anti-Tf receptor MAbs and DFO, it appears that further preclinical studies with such tumors, especially those with higher Tf densities, would be of interest.

Essential fatty acids and iron are involved at distinct stages of the proliferative cycle but not in the activation of human T cells

In the absence of serum, optimal lymphocyte proliferation is obtained when cultures are supplemented with transferrin and an essential fatty acid (EFA). In order to study the effects of iron in conjunction with EFA on T-cell proliferation, we have utilized a chemically defined serum-free culture system to achieve better control of the variables involved. This system includes three different serum-free media (SFM) that differ in total iron content and source of iron: (i) transferrin-free medium containing a high concentration (500 microns) of a soluble iron salt in the form of ferric citrate (Fe-SFM); (ii) iron-saturated human transferrin (5 micrograms/ml) (T-SFM); and (iii) iron-free medium (SFM(-Fe)) without any apparent source of iron. None of these SFM supported proliferation of T cells stimulated by the combination of phorbol 12,13-dibutyrate/ionomycin or phytohemagglutinin. Restoration of the proliferative response was only observed following supplementation of the iron-containing media with linoleic acid (complexed to bovine serum albumin (LA/BSA)). In cultures containing LA/BSA, the addition of iron alone in the absence of transferrin (Fe-SFM) resulted in similar responses to the transferrin-containing medium (T-SFM). Low levels of RNA synthesis in mitogen-stimulated T cells could be demonstrated in the presence or absence of iron and the addition of LA/BSA resulted in marked enhancement of RNA synthesis, regardless of the availability of iron. Cell cycle analysis showed that 91-94% of the cells cultured in SFM were arrested in G0/G1. These cells could progress through the cell cycle following the addition of LA/BSA, but only in the iron-containing media. Unlike DNA or RNA synthesis, activation of T cells could be demonstrated in SFM with or without iron as shown by the normal induction of c-fos and early growth response gene mRNA, normal expression of IL2 and transferrin receptors, and normal IL2 production, despite the arrest of cells in G0/G1. These results suggest that although human T-cell growth is iron and EFA dependent, the early events of T-cell activation are both iron and EFA independent.

Lymphocyte proliferation is controlled by both iron availability and regulation of iron uptake pathways

Cell culture data have demonstrated that transferrin, the major iron (Fe) transport protein, is a necessary requirement for cellular proliferation. Evidence suggests that transferrin supports proliferation by providing Fe for critical cellular processes including DNA synthesis. Lymphocytes, similar to other cell types, respond to an increased Fe requirement during proliferation by increased synthesis and expression of surface transferrin receptors. Moreover, under transferrin-Fe-deplete conditions, certain lymphocyte lines exhibit other specialized adaptations that allow for sufficient Fe uptake to support cellular proliferation. These other adaptations include specialized transferrin synthesis and utilization of a transferrin-independent Fe uptake pathway. Lymphocyte proliferation is inhibited by agents that interfere with cellular Fe metabolism; these agents include Fe chelators, class 3a metals that bind to transferrin, and antibodies directed against the transferrin receptor. The data presented in this paper, demonstrate that differences in sensitivity to the effects of these agents are influenced by the amount of available transferrin-Fe and differences in the mechanisms that individual lymphocyte cell lines utilize to ensure adequate Fe uptake to support proliferation. These data support the hypothesis that these agents, if used appropriately, will be useful in the treatment of different lymphoproliferative disorders.

Intraglomerular proteinase activity in adriamycin-induced nephropathy

Adriamycin (ADR)-induced nephropathy is characterized by focal and segmental glomerulosclerosis and is supposed to be an ideal model of chronic progressive renal disease. The aim of our study was to investigate whether there might be an altered activity of glomerular proteinases in ADR nephropathy, thereby aggravating glomerular protein accumulation as an important initiating hallmark of glomerulosclerosis. In fact, we could demonstrate significantly enhanced levels of intraglomerular protein and DNA content in the experimental animals at week 7, 12 and 22 after administration of ADR. When relating intraglomerular proteinase activity, which was measured in ultrasonically destroyed isolated glomeruli, obtained by differential sieving techniques, to the intraglomerular protein and DNA content, this enzyme activity was significantly reduced throughout the observation period. Based on these data, we suggest that this relatively decreased proteinase activity in glomeruli exposed to ADR might play a pathogenetic role in the development of glomerular hypertrophy, an important harbinger of glomerulosclerosis.

Transferrin-independent iron uptake supports B lymphocyte growth

Raji, a malignant B-lymphocyte cell line containing Epstein-Barr virus genomic elements, has been conditioned to proliferate optimally in transferrin (Tf)-free medium containing a very low concentration of an iron salt. We provide evidence that an Tf-independent iron uptake system is physiologically important for maintaining the growth of these cells. The data show that Raji cells take up iron from iron salts using a relatively high-capacity, low-affinity, temperature- and calcium-dependent uptake system. The apparent capacity of this system increases when: (1) cells are cultured in Tf-free medium containing high concentrations of iron salt as opposed to medium containing Tf; and (2) when the iron salt concentration of Tf-free medium is lowered to about 1.6 mumol/L. Cellular iron uptake also increases when a maximum number of cells are in S and G2 and M cell phases of the cell cycle. The cells are sensitive to growth inhibition by the addition of deferoxamine. This evidence supports the hypothesis that certain malignant lymphocytes, under iron deplete conditions, fulfill an iron requirement for proliferation by an adaptation such as Tf-independent iron uptake.

Proteinase activity in isolated glomeruli of Goldblatt hypertensive rats

In Goldblatt rats, the kidney exposed to high blood pressure reveals glomerulosclerosis. Moreover, in preexisting parenchymal renal disease, the development of glomerulosclerosis is accelerated in the unclipped kidney. Up to now, the pathogenetic mechanism underlying the development of glomerulosclerosis due to systemic hypertension has not completely been resolved. Traditionally, hemodynamic mechanisms have been discussed. This study was performed to investigate whether there might be a decreased activity of glomerular proteinases in the unclipped kidney of Goldblatt rats as a potential pathogenetic factor for glomerulosclerosis. 20 weeks after the surgical intervention, we found a reduced proteinase activity in ultrasonically destroyed isolated glomeruli obtained by differential sieving technique in comparison with the contralateral clipped kidney and the kidneys of sham-operated normotensive controls. This could be confirmed, when proteinase activity was related to DNA instead of protein. When investigating glomerular cathepsin B-content, a lysosomal enzyme, which is able to degrade glomerular structural as well as non-structural proteins, we found a decreased level in the kidney of Goldblatt rats exposed to systemic hypertension in comparison with normotensive control animals. Basing on these results we presume that glomerular protein accumulation and concomitant glomerulosclerosis due to systemic hypertension might be a result of a synergistical interaction between hemodynamic factors and biochemical ones; we suggest one of the latter to be a decreased glomerular proteinase activity.

Differential growth-inhibitory effects of gallium on B-lymphocyte lines in high versus low iron concentrations

The growth inhibitory effects of gallium on a murine and human B-cell line were studied using two different serum-free culture systems: (a) ferric citrate medium containing 500 microM iron and (b) transferrin medium containing 5 micrograms/ml of iron-saturated transferrin (0.125 microM iron). For the human cell line in ferric citrate medium, 50% growth inhibition achieved in the presence of transferrin-gallium represented a gallium concentration 80-fold lower than the concentration required when gallium nitrate was added. In the transferrin system, significantly higher transferrin-gallium concentrations were required to achieve the same inhibitory effects. Monoclonal antibody to the transferrin receptor significantly decreased the growth inhibiting effect of transferrin-gallium in the mouse ferric citrate system. Thus, under very different culture conditions, gallium and iron appear to compete via the transferrin-transferrin receptor pathway for cellular uptake. The growth inhibitory effects of gallium are markedly potentiated when the metal is taken up by functional transferrin receptors even in cells continuously cultured in transferrin-free medium.