Differential effects of cyclosporine and tacrolimus on mycophenolate pharmacokinetics in patients with impaired kidney function.

In a single-center prospective randomized controlled study, the impact of calcineurin inhibitor (CNI) reduction or withdrawal on the pharmacokinetics of mycophenolic acid (MPA) was studied in a group of renal transplant recipients with impaired renal function. Mycophenolate mofetil (MMF) was added to a baseline regimen of prednisolone and CNI. Afterwards the patients were randomized into "CNI withdrawal" and "CNI continuation" groups. The dosage of CNIs, cyclosporine or tacrolimus, was gradually reduced and withdrawn within 6 weeks from patients in the withdrawal group. The continuation group was maintained on therapy with CNI, MMF, and steroids. These regimens were maintained until the ninth month. In contrast to the withdrawal of tacrolimus, which has no significant effect on MPA pharmacokinetics, cyclosporine withdrawal was associated with a significant increase in the trough levels and areas under the curve of MPA. Serum creatinine and urine albumine levels stabilized on average after CNI withdrawal in this population. The results are consistent with the hypothesis that cyclosporine attenuates the enterohepatic recirculation of MPA. The withdrawal of CNI has a positive effect on renal function in chronic allograft dysfunction.

Switching immunosuppression from cyclosporine to tacrolimus improves long-term kidney function: a 6-year study.

To improve long-term kidney graft function, acute graft rejection, hyperlipidemia, hypertension, and toxic influences must be avoided because they may contribute to chronic allograft nephropathy. Many studies have demonstrated greater efficacy and tolerability of tacrolimus compared with cyclosporine with regard to these conditions. Our study investigated whether 30 patients with deteriorating renal function benefitted from conversion to tacrolimus based upon a retrospective analysis using data recorded from 3 years before to 3 years after conversion. Renal function (GFR) deteriorated progressively under cyclosporine (creatinine: baseline 1.5 mg/dL; delta(Cyc) = +1.4 mg/dL within 3 years; GFR: delta(Cyc) = -35 mL/min within 3 years). After switching to tacrolimus, kidney function stabilized and even improved (creatinine: baseline after switching 2.9 mg/dL; delta(Tac) = -0.7 mg/dL; GFR: delta(Tac) = 14 mL/min). Conversion from cyclosporine to tacrolimus is recommended for patients with a kidney transplant in which there has been a progressive decrease in renal function. It may lead to stabilization of or even improvement in transplant function.

Cyclosporine and tacrolimus: influence on cardiovascular risk factors.

After allogenic transplantations, a dramatic increase in the development of arteriosclerotic plaques can be observed, which might be due to metabolic alterations, changes in the transplant organ, or the immunosuppression regimen. Many studies have demonstrated beneficial effects of tacrolimus compared with cyclosporine with regard to these conditions. These results have suggested that conversion to tacrolimus from cyclosporine is advantageous. Our study investigated whether patients with deteriorating renal function profit from this conversion. Thirty renal transplant patients were studied retrospectively, using data recorded from 3 years before to 3 years after conversion from cyclosporine to tacrolimus. While renal function (GFR) deteriorated progressively under cyclosporine, it stabilized and even improved under tacrolimus (creatinine: DeltaCyc = +1.4 mg/d; DeltaTac = -0.7 mg/dL; GFR: DeltaCyc = -35 mL/min; DeltaTac = 14 mL/min). In addition, uric acid levels (7.0 mg/dL vs 6.4 mg/dL, P < .05) and cholesterol levels (258 mg/dL vs 225 mg/dL, P < .05) were both significantly lower under tacrolimus. Conversion from cyclosporine to tacrolimus is recommended for kidney transplant patients in whom there has been a progressive fall in renal function. It leads to stabilization or even improvement of transplant function and a reduction in cardiovascular risk factors.

Conversion from cyclosporine to tacrolimus after renal transplantation improves cardiovascular risk factors.

BACKGROUND: It is vital that after, renal transplantation, immunosuppression is efficacious and causes few complications. It is especially important that hyperlipidaemia, hypertension and toxic influences should be avoided because these conditions can reduce patient and transplant survival. Many studies have demonstrated beneficial effects of tacrolimus in comparison with cyclosporine with regard to these conditions. These results have suggested that a conversion to tacrolimus from cyclosporine is advantageous. Our study investigated whether patients with deteriorating renal functions can profit from this conversion. METHODS: Thirty patients with a renal transplant were studied retrospectively, using data recorded from 3 years before to 3 years after conversion from cyclosporine to tacrolimus. RESULTS: While renal function (glomerular filtration rate [GFR]) deteriorated progressively under cyclosporine, it stabilised and even improved under tacrolimus (creatinine: Delta(Cyc)=+1.4 mg/d; Delta(Tac=)-0.7 mg/dl; GFR: Delta(Cyc)=-35 ml/min; Delta(Tac)=14 ml/min). In addition, uric acid level (7.0 vs. 6.4 mg/dl, p<0.05) and cholesterol level (258 vs. 225 mg/dl, p<0.05) were both significantly lower under tacrolimus. CONCLUSION: Conversion from cyclosporine to tacrolimus is recommended for patients with a kidney transplant, in which there has been a progressive fall in renal function. It leads to stabilisation or even improvement of transplant function and a reduction in cardiovascular risk factors.

Engineering of cysteine and methionine biosynthesis in potato.

Methionine and cysteine, two amino acids containing reduced sulfur, are not only an important substrate of protein biosynthesis but are also precursors of various other metabolites such as glutathione, phytochelatines, S-adenosylmethionine, ethylene, polyamines, biotin, and are involved as methyl group donor in numerous cellular processes. While methionine is an essential amino acid due to an inability of monogastric animals and human beings to synthesise this metabolite, animals are still able to convert methionine consumed with their diet into cysteine. Thus, a balanced diet containing both amino acids is necessary to provide a nutritionally favourable food or feed source. Because the concentrations of methionine and cysteine are often low in edible plant sources, e.g. potato, considerable efforts in plant breeding and research have been and are still performed to understand the physiological, biochemical, and molecular mechanisms that contribute to their synthesis, transport, and accumulation in plants. During the last decade molecular tools have enabled the isolation of most of the genes involved in cysteine and methionine biosynthesis, and the efficient plant transformation technology has allowed the creation of transgenic plants that are altered in the activity of individual genes. The physiological analysis of these transgenic plants has contributed considerably to our current understanding of how amino acids are synthesised. We focused our analysis on potato (Solanum tuberosum cv. Désirée) as this plant provides a clear separation of source and sink tissues and, for applied purposes, already constitutes a crop plant. From the data presented here and in previous work we conclude that threonine synthase and not cystathionine gamma-synthase as expected from studies of Arabidopsis constitutes the main regulatory control point of methionine synthesis in potato. This article aims to cover the current knowledge in the area of molecular genetics of sulfur-containing amino acid biosynthesis and will provide new data for methionine biosynthesis in solanaceous plants such as potato.

Antisense inhibition of threonine synthase leads to high methionine content in transgenic potato plants.

Methionine (Met) and threonine (Thr) are members of the aspartate family of amino acids. In plants, their biosynthetic pathways diverge at the level of O-phosphohomo-serine (Ser). The enzymes cystathionine gamma-synthase and Thr synthase (TS) compete for the common substrate O-phosphohomo-Ser with the notable feature that plant TS is activated through S-adenosyl-Met, a metabolite derived from Met. To investigate the regulation of this branch point, we engineered TS antisense potato (Solanum tuberosum cv Désirée) plants using the constitutive cauliflower mosaic virus 35S promoter. In leaf tissues, these transgenics exhibit a reduction of TS activity down to 6% of wild-type levels. Thr levels are reduced to 45% wild-type controls, whereas Met levels increase up to 239-fold depending on the transgenic line and environmental conditions. Increased levels of homo-Ser and homo-cysteine indicate increased carbon allocation into the aspartate pathway. In contrast to findings in Arabidopsis, increased Met content has no detectable effect on mRNA or protein levels or on the enzymatic activity of cystathionine gamma-synthase in potato. Tubers of TS antisense potato plants contain a Met level increased by a factor of 30 and no reduction in Thr. These plants offer a major biotechnological advance toward the development of crop plants with improved nutritional quality.

Approaches towards understanding methionine biosynthesis in higher plants.

Plants are able to synthesise all amino acids essential for human and animal nutrition. Because the concentrations of some of these dietary constituents, especially methionine, lysine, and threonine, are often low in edible plant sources, research is being performed to understand the physiological, biochemical, and molecular mechanisms that contribute to their transport, synthesis and accumulation in plants. This knowledge can be used to develop strategies allowing a manipulation of crop plants, eventually improving their nutritional quality. This article is intended to serve two purposes. The first is to provide a brief review on the physiology of methionine synthesis in higher plants. The second is to highlight some recent findings linked to the metabolism of methionine in plants due to its regulatory influence on the aspartate pathway and its implication in plant growth. This information can be used to develop strategies to improve methionine content of plants and to provide crops with a higher nutritional value.

Transgenic potato plants reveal the indispensable role of cystathionine beta-lyase in plant growth and development.

Methionine (Met) is an essential amino acid that is often unavailable at sufficient dietary levels. In order to better understand Met pathway regulation, a cDNA encoding cystathionine beta-lyase (CbL; EC 4.4.1.8) has been cloned from Solanum tuberosum. An antisense construct of this gene was used to generate transgenic potato plants with reduced CbL levels. Transgenic plants exhibiting leaf CbL activity levels of up to 50% below wild-type levels were obtained. Metabolite analysis revealed a reduction in Met levels in these CbL antisense plants, as well as remarkable increases in the pathway intermediates cystathionine, homoserine and cysteine. Unexpectedly, an increase in homocysteine was also observed. Levels of aspartate amino acid pathway intermediates (including aspartate, lysine and threonine) remained essentially unaffected. Neither transcript levels nor protein products of other pathway-relevant genes were altered significantly in these plants. CbL antisense plants exhibited an altered phenotype characterized by a bushy growth habit, small light-green leaves and small tubers. This phenotype could be alleviated upon Met supplementation, suggesting that low Met levels, rather than pathway intermediate accumulation, is responsible for the phenotypic effects of CbL transgene expression. These data unequivocally demonstrate the central role of CbL in Met biosynthesis, and, subsequently, in plant growth and development.

Role of albumin and glomerular capillary wall charge distribution on glomerular permselectivity: studies on the perfused-fixed rat kidney model.

The charge-related determinants of albumin permeability are the subject of controversial discussion. To study this question we have developed an isolated perfused rat kidney model in which metabolic processes are eliminated by perfusion fixation with glutaraldehyde. The fixed kidneys were perfused with albumin solutions using the following approaches: 1. Modification of the charge of both the glomerular capillary wall (GCW) and albumin using different buffer systems in a pH range spanning the isoelectric points of albumin and the glomerular basement membrane (GBM), the extracellular matrix of the GCW. 2. Modification of the charge of the GCW by perfusing the isolated kidney with cations either before or after fixation. 3. Modification of the charge of albumin by cationization. In the model, the inulin "urine" to perfusate ratio was one. This shows that the tubules have no metabolic activity, that the glomerular filtration rate (GFR) is equal to "urine" flow rate and that the "urine" collected is identical to the ultrafiltrate. Therefore, sieving coefficients in this model can simply be calculated as the ratio between "urine" and perfusate protein concentrations. We could show that: 1. pH has a significant effect on the albumin sieving coefficient: it was maximally increased at pH 4.0 [(70.3 +/- 15.9) x 10(-3), n = 10 versus (8.7 +/- 3.7) x 10(-3), n = 11, at pH 7.4]. Only a pH as low as 4.0 should lead to a pronounced neutralization of the anionic charges of albumin and the GBM; the charge density of the GCW calculated with these data is 43 mEq/l at pH 7.4. 2. Modifying the ionic composition of the GCW with protamine before fixation with glutaraldehyde causes a bigger increase in the glomerular permeability for albumin [(51.2 +/- 22.5) x 10(-3), n = 10, glomerular charge density 21 mEq/l] than modifying the albumin charge by cationization. 3. Modifying the albumin charge by cationization increases the glomerular permeability for albumin [(20.0 +/- 6.7) x 10(-3), n = 8]. These findings support the hypothesis that at the onset of proteinuria changes in the charge and configuration of the GCW could be more important pathogenetic factors than changes in the charge of serum-derived proteins.

Relative income expectations, expected malpractice premium costs, and other determinants of physician specialty choice.

We analyze the effects of relative income expectations, expected malpractice premium cost, and other economic and noneconomic factors on physician specialty choice. The data for this paper are taken from responses of medical students who completed the Association of American Medical Colleges' Medical School Questionnaire and graduated from medical school in 1995. A random utility model is used to guide our thinking; the econometric technique is multinomial logit regression. Selection of a surgical or support specialty is found to be positively income motivated, while the influence of expected relative income is negatively related to the choice of primary-care and medical practices. Concern over malpractice premium cost is negatively related to surgical and positively related to primary-care selection. Other important determinants of choice are planned location of practice, length of residency, type of medical school attended, score on the science problems section of the Medical College Admission Test, predictable working hours and perceived prestige of the specialty. Policies that alter expected relative income, length of residency, desired location of practice, medical school attended, predictable working hours, and prestige of practice, rather than financial aid, may be appropriate for correcting a perceived maldistribution of physicians among specialties.

Effect of debt on U.S. medical school graduates' preferences for family medicine, general internal medicine, and general pediatrics.

The authors assess the importance of educational debt in graduates' primary care specialty choices, and the variety of mechanisms through which debt may influence career decisions. Logistic regression models were used to identify significant predictors of the primary care specialty choices made by the 1991 and 1992 graduates of U.S. medical schools. These predictors were debt itself; other financial indicators; certain medical school characteristics; certain practice location plans; certain demographic factors; aspects of academic performance; and students' predisposition to a primary care specialty. Data for this study were gathered from a variety of sources at the Association of American Medical Colleges and from the Health Education Assistance Loans program. Both direct and indirect effects of debt were identified under specific conditions. The study revealed complex relationships between debt and the other predictors identified. For example, debt operated in relation to the levels of the graduates' expected incomes; debt from subsidized loan sources was significant for women who chose general internal medicine; debt was important in choices of family practice; and debt by itself was significant for those planning to practice in the West and who chose general internal medicine. Also, seemingly opposing effects of debt occurred. For example, in the family practice model used in this study, the threshold effect of debt was positive, while the linear effect of debt above the threshold was negative. Such vriations help explain the conflicting findings of some past research. These and other findings prompt the authors to state that when investigating the effects of debt, it is not fruitful to ask what the effect of the debt is on all three primary care fields as a group. It is more appropriate to ask several questions, such as: under what conditions does debt influence specialty plans? Among which groups of students does debt have an impact on specialty plans? Are all of the primary care specialties similarly affected by the issues surrounding debt? Does the effect of debt change over time? The authors conclude by indicating possible policy implications of their findings.

The physiological and pathophysiological basis of glomerular permeability for plasma proteins and erythrocytes.

The barrier function of glomerular capillaries in vivo, which prevents the leakage of plasma proteins and cellular elements, depends on the basic morphological and electro-chemical fine structure of the glomerular capillary wall, and on a functional barrier maintained by components obtained from blood, which effect the definitive barrier against the leakage of plasma proteins and cellular elements. The functional component of the barrier may explain the variability and some of the phenomena known as functional proteinuria. A certain size and number of morphological "defects" are thought to represent the normal condition, but under pathological conditions they may increase in size and number, resulting in a shift to an increasing permeability for higher molecular mass proteins; also an increase of the size and number of larger defects may enable more red cells to pass the barrier compared with the normal condition. These defects are different from the minimal glomerular lesions which are due to charge defects in the glomerular capillary membrane, primarily the lamina rara interna and the lamina rara externa of the basement membrane.