Symposium review: Amino acid uptake by the mammary glands: Where does the control lie?

Milk protein yield responses to changes in the profile of essential amino acids absorbed by the gastrointestinal tract or circulating in blood plasma do not follow the classic limiting amino acid response, in part because of an ability of the mammary glands to modify their blood flow rate and net clearance of amino acids out of plasma. The hypothesis that mammary blood flow is locally regulated to maintain ATP balance accounts for observed changes in flow due to postruminal glucose, insulin, and essential amino acid (EAA) infusions. An additional hypothesis that net mammary uptakes of metabolites from blood are affected by perturbations in their respective arterial concentrations and the rate of mammary blood flow also appears to hold for the energy metabolites glucose, acetate, ß-hydroxybutyrate, and fatty acids. However, net EAA uptakes by the mammary glands are poorly predicted by models considering arterial concentrations and blood flow rates only. Evidence points to intramammary protein synthesis and secretion as the determinant of net EAA uptake. The intracellular signaling network anchored by the mechanistic target of rapamycin complex 1 stands as an excellent candidate to explain nutritional effects on milk protein synthesis because it integrates information on physiological and nutritional state to affect protein synthesis and cell metabolism, growth, proliferation, and differentiation in many cell types. In mammary cells in vitro and in vivo, the mechanistic target of rapamycin complex 1, integrated stress response, and glycogen synthase kinase-3 networks that contribute to regulation of initiation of mRNA translation are responsive to acute changes in nutrient supply and EAA profile. However, after several days of postruminal infusion of balanced and imbalanced EAA profiles, these signaling networks do not appear to continue to account for changes in milk protein yields. Gene expression evidence suggests that regulation of components of the unfolded protein response that control biogenesis of the endoplasmic reticulum and differentiation of a secretory phenotype may contribute to effects of nutrition on milk protein yield. Connections between early signaling events and their long-term consequences should be sought.

Supranutritional selenium intake from enriched milk casein impairs hepatic insulin sensitivity via attenuated IRS/PI3K/AKT signaling and decreased PGC-1α expression in male Sprague-Dawley rats.

Selenium (Se)-enriched milk provides antioxidant benefits and has therapeutic potential against cancer. However, both antidiabetic and prodiabetic effects have been attributed to Se. Our objective was to evaluate the effect of Se-enriched milk casein on insulin sensitivity in rats when given at the requirement of 0.25 ppm Se and supranutritionally on both low- and high-fat diets. Two hundred sixteen male Sprague-Dawley rats were fed low- or high-fat diets containing one, two or eight times the Se requirement in a randomized block design. After 7 weeks, 72 rats were subjected to the hyperinsulinemic-euglycemic clamp with [3-3H]glucose infusion to estimate glucose fluxes. Tissues were collected from the remaining 144 rats 8 min after ip saline or insulin injection. During hyperinsulinemic-euglycemic clamps, glucose infusion rate was 22% lower (P=.058), and endogenous glucose production was 76% higher (P=.054) when Se content increased from one to eight times the requirement on low-fat diets, indicating impaired hepatic insulin sensitivity. Se also decreased the ability for insulin to stimulate Akt phosphorylation at Thr308. Hepatic oxidation state and expression of selenoprotein P and glutathione peroxidase-1 were unaffected while expression of insulin receptor substrate (IRS)-1 and-2 and PPARγ coactivator-1α (PGC-1α) decreased with supranutritional Se and high-fat intake. In addition, hepatic expression of regulatory and catalytic subunits of phosphatidylinositol 3-kinase (PI3K) decreased with supranutritional intake of Se. Se intake from enriched casein up to eight times the requirement impairs hepatic insulin sensitivity in a mechanism similar to fat feeding, via attenuated IRS/PI3K/Akt signaling and decreased PGC-1α expression.

Selenized milk casein in the diet of BALB/c nude mice reduces growth of intramammary MCF-7 tumors.

BACKGROUND: Dietary selenium has the potential to reduce growth of mammary tumors. Increasing the Se content of cows' milk proteins is a potentially effective means to increase Se intake in humans. We investigate the effects of selenized milk protein on human mammary tumor progression in immunodeficient BALB/c nude mice. METHODS: Four isonitrogenous diets with selenium levels of 0.16, 0.51, 0.85 and 1.15 ppm were formulated by mixing low- and high-selenium milk casein isolates with a rodent premix. MCF-7 cells were inoculated into the mammary fat pad of female BALB/c nude mice implanted with slow-release 17 ß-estradiol pellets. Mice with palpable tumors were randomly assigned to one of the four diets for 10 weeks, during which time weekly tumor caliper measurements were conducted. Individual growth curves were fit with the Gompertz equation. Apoptotic cells and Bcl-2, Bax, and Cyclin D1 protein levels in tumors were determined. RESULTS: There was a linear decrease in mean tumor volume at 70 days with increasing Se intake (P < 0.05), where final tumor volume decreased 35% between 0.16 and 1.15 ppm Se. There was a linear decrease in mean predicted tumor volume at 56, 63 and 70 days, and the number of tumors with a final volume above 500 mm3, with increasing Se intake (P < 0.05). This tumor volume effect was associated with a decrease in the proportion of tumors with a maximum growth rate above 0.03 day-1. The predicted maximum volume of tumors (Vmax) and the number of tumors with a large Vmax, were not affected by Se-casein. Final tumor mass, Bcl-2, Bax, and Cyclin D1 protein levels in tumors were not significantly affected by Se-casein. There was a significantly higher number of apoptotic cells in high-Se tumors as compared to low-Se tumors. CONCLUSIONS: Taken together, these results suggest that turnover of cells in the tumor, but not its nutrient supply, were affected by dairy Se. We have shown that 1.1 ppm dietary Se from selenized casein can effectively reduce tumor progression in an MCF-7 xenograft breast cancer model. These results show promise for selenized milk protein as an effective supplement during chemotherapy.

Concurrent pulmonary Aspergillus fumigatus and mucor infection in a cardiac transplant recipient: a case report.

Invasive fungal infections are a significant complication of solid organ transplantation. Here we report the first case of concurrent invasive pulmonary fungal infection caused by Aspergillus fumigatus and Mucor species in a heart transplant recipient. Polymicrobial mold infection is rare but should be considered in solid organ transplant recipients who fail to respond to initial antifungal therapy targeting a single organism. It is also of interest that in addition to potent immunosuppression and prolonged voriconazole therapy, possible airway fungal colonization following hurricane Katrina cleaning efforts might have contributed to this dual invasive mold infection.

The effect of short-term hyperammonaemia on milk synthesis in dairy cows.

To test the hypothesis that ammonia detoxification in ruminants consumes amino acids to the detriment of milk protein production, we infused four lactating dairy cows with ammonium acetate or sodium acetate in switchback experiments. Plasma ammonia concentrations increased to 411 microm within 1 h of the start of infusion of ammonium acetate at 567 mmol/h. The rate constant for ammonia clearance from plasma was 0 x 054/min and the half-life was 12 x 9 min. Infusion at 567 mmol/h for 1 h followed by 1 h without infusion, repeated four times between am- and pm-milking, caused a decrease in feed intake. Compared with sodium acetate, continuous infusion of ammonium acetate at 360 mmol/h throughout an entire 10-h milking interval increased plasma ammonia concentrations to 193 microm and caused a 20% decrease in milk, protein and lactose production with no effect on percentage composition of milk or the yield of milk fat. Arterial concentrations of glucose and non-esterified fatty acids tended to increase; there was no effect on arterial acetate, beta-hydroxybutyrate or triacylglcerol, and branched-chain amino acids, Lys and Thr decreased. Mammary plasma flow, estimated by assuming 100% uptake/output of Phe+Tyr, was significantly correlated with milk yield. Mammary uptakes of acetate tended to be reduced by hyperammonaemia, but uptakes of other energy metabolites and amino acids were not affected. Thus, while an increase in amino acid consumption during hyperammonaemia was apparent from the drop in circulating concentrations of Leu, Ile, Val, Lys and Thr, there was no evidence to support the hypothesis that milk yield is affected by the lower concentrations. An ammonia-induced depression in feed intake may have caused the decrease in milk synthesis.

The sensitivity of ecosystem carbon exchange to seasonal precipitation and woody plant encroachment.

Ongoing, widespread increases in woody plant abundance in historical grasslands and savannas (woody encroachment) likely will interact with future precipitation variability to influence seasonal patterns of carbon cycling in water-limited regions. To characterize the effects of woody encroachment on the sensitivity of ecosystem carbon exchange to seasonal rainfall in a semi-arid riparian setting we used flux-duration analysis to compare 2003-growing season NEE data from a riparian grassland and shrubland. Though less seasonally variable than the grassland, shrubland NEE was more responsive to monsoon rains than anticipated. During the 2004-growing season we measured leaf gas exchange and collected leaf tissue for delta(13)C and nitrogen content analysis periodically among three size classes of the dominant woody-plant, Prosopis velutina and the dominant understory species, Sporobolus wrightii, a C(4) bunchgrass, present at the shrubland. We observed size-class and plant functional type independent patterns of seasonal plant performance consistent with greater-than-anticipated sensitivity of NEE in the shrubland. This research highlights the complex interaction between growing-season precipitation, plant-available alluvial groundwater and woody plant abundance governing ecosystem carbon balance in this semi-arid watershed.

Ventricular-vascular uncoupling increases expression of B-type natriuretic peptide in heart transplantation.

BACKGROUND: Allograft adaptation to a foreign circulation is imperfect as noted from persistent limitations to stress. Effective arterial elastance (Ea), a measure of afterload, provides an estimate of aortic impedance. End systolic elastance (Ees) is a load-independent measure of ventricular performance as well as its interaction in the periphery. The ratio (Ea to Ees) characterizes ventricular-vascular coupling; a value close to unity signifies poor mechanical efficiency. The purpose of this investigation was to correlate mechanical efficiency of work with expression of B-type natriuretic peptide BNP, a specific marker of ventricular stress and strain. METHODS: We measured BNP levels in 40 consecutive stable heart transplant recipients free from rejection. In addition, echocardiography was performed to obtain Ea, Ees, and their ratio (Ea to Ees) by the single-beat method. We examined correlates of BNP expression by assessing Ea to Ees, while correcting for mean arterial pressure, body mass index, left ventricular mass index, ejection fraction, and serum creatinine. RESULTS: BNP levels were significantly and positively correlated (r=0.38, P=.05) with an increased Ea to Ees ratio. By multivariable analysis, this relationship persisted independently (t=2.1, P=.04), while the five other measures were insignificant predictors. CONCLUSION: This investigation indicated that the transplanted heart demonstrates poor contractile efficiency and operates at maximal left ventricular work. This is paralleled by a tandem increase in BNP, suggesting that elevation in this stress peptide is at least partly explained by ventriculo-vascular uncoupling in heart transplantation, independent of alterations in blood pressure.

Corticosteroid weaning in the tacrolimus and mycophenolate era in heart transplantation: clinical and neurohormonal benefits.

BACKGROUND: Compared with cyclosporine, tacrolimus-based immunosuppression yields improved metabolic outcomes in heart transplantation. Whether corticosteroid freedom provides incremental metabolic benefits in tacrolimus and mycophenolate mofetil immunoprophylaxis remains uncertain. METHODS: In a prospective trial, 41 heart transplant patients treated with tacrolimus and mycophenolate mofetil underwent steroid weaning immediately after transplantation until weaning was complete. Weaning was interrupted only for treated rejection with or without hemodynamic compromise. Benefits of steroid weaning assessed following the first year included B-type natriuretic peptide (BNP), late infections, lipids, blood pressure, hyperglycemia, and body mass index (BMI). RESULTS: Of this 41 patient cohort (age 53 +/- 9 years, 50% black American, 35% women) followed for a total of 47 +/- 5 months, 25 had corticosteroids discontinued (62%) by an average of 20 +/- 11 months. No differences between the two groups were noted in baseline characteristics. Significant predictors of failure to wean steroids included higher rejection, BNP, and lower dose of mycophenolate mofetil. No significant benefits of steroid weaning were noted on lipids, blood pressure, hyperglycemia, and BMI. However, late infections (after 1 year) requiring hospitalizations were more frequent in the failure to wean group (0.60.4 vs 0 infections/patient/y, P <.001). INFERENCES: Unlike known metabolic benefits of steroid withdrawal with cyclosporine, heart transplant recipients treated with tacrolimus and mycophenolate mofetil demonstrate no incremental metabolic benefits, but instead experience benefits of decreased serious late infections. Furthermore, failure to discontinue corticosteroids in this series is predicted by early allograft rejection, use of lower doses of mycophenolate mofetil, and higher BNP levels suggesting poor cardiac adaptation.

Recurrence of giant cell myocarditis in cardiac allograft.

BACKGROUND: Giant cell myocarditis causes essentially irreversible fulminant left ventricular dysfunction with associated conduction abnormalities and congestive failure. Response to immunosuppressive therapy is poor and cardiac transplantation is the only viable treatment option. The histologic hallmarks of giant cell myocarditis include a polymorphous inflammatory response with numerous multinucleated giant cells and extensive myocyte necrosis in a geographic pattern. There were 38 patients who received a cardiac transplant for giant cell myocarditis in the Giant Cell Myocarditis Registry. Among these patients, there were 9 recurrences of disease in the allograft. Concern has been expressed that recurrence of giant cell myocarditis in the allograft might be a contraindication for cardiac transplantation in the future. METHODS: In our single-center analysis we describe the clinical and histologic findings of 5 patients transplanted for giant cell myocarditis at the Cleveland Clinic. RESULTS: All but 1 of the patients were New York Heart Association (NYHA) class 4 with an average cardiac index (CI) of 1.52 liters/min x m(2). Of the 5 patients transplanted, 1 developed recurrent giant cell myocarditis. Routine right ventricular endomyocardial biopsy at 1 week exhibited severe multifocal myocardial fibrosis in addition to mild acute vascular rejection and mild grade 1A cellular rejection. Follow-up biopsy in this patient indicated grade IIIA moderate acute rejection in addition to multinucleated giant cells. Two distinct inflammatory processes were noted consisting of foci of T-cell inflammation identified by immunohistochemistry to be consistent with rejection, and a second inflammatory process with few mononuclear cells staining for macrophage or T-cell markers with eosinophils and myocyte necrosis consistent with giant cell myocarditis. Follow-up right ventricular endomyocardial biopsies (RVBXs) in this patient have subsequently demonstrated improvement in the degree of inflammatory infiltrate without vascular or significant cellular rejection. Vascular rejection was noted in 1 of the remaining 4 patients and was treated successfully with muramab-CD3 and plasmapheresis. CONCLUSIONS: Giant cell myocarditis should be expected to recur in the allograft and often does so concurrently with rejection. However, the disease in the allograft responds to therapy in a favorable manner, which differs dramatically from that in the native heart. This might be the result of detection of the disease at an earlier stage than in the native heart, or the immunosuppression milieu in the allograft. The favorable response to therapy suggests that the likelihood of recurrence of giant cell myocarditis should not be considered a barrier to transplantation.