On the relation between citrate and calcium in normal and stone-former subjects

Model-Based Assessment of Plasma Citrate Flux Into the Liver: Implications for NaCT as a Therapeutic Target

Cytoplasmic citrate serves as an important regulator of gluconeogenesis and carbon source for de novo lipogenesis in the liver. For this reason, the sodium-coupled citrate transporter (NaCT), a plasma membrane transporter that governs hepatic influx of plasma citrate in human, is being explored as a potential therapeutic target for metabolic disorders. As cytoplasmic citrate also originates from intracellular mitochondria, the relative contribution of these two pathways represents critical information necessary to underwrite confidence in this target. In this work, hepatic influx of plasma citrate was quantified via pharmacokinetic modeling of published clinical data. The influx was then compared to independent literature estimates of intracellular citrate flux in human liver. The results indicate that, under normal conditions, <10% of hepatic citrate originates from plasma. Similar estimates were determined experimentally in mice and rats. This suggests that NaCT inhibition will have a limited impact on hepatic citrate concentrations across species.

Sensing of mammalian IL-17A regulates fungal adaptation and virulence

Infections by opportunistic fungi have traditionally been viewed as the gross result of a pathogenic automatism, which makes a weakened host more vulnerable to microbial insults. However, fungal sensing of a host's immune environment might render this process more elaborate than previously appreciated. Here we show that interleukin (IL)-17A binds fungal cells, thus tackling both sides of the host-pathogen interaction in experimental settings of host colonization and/or chronic infection. Global transcriptional profiling reveals that IL-17A induces artificial nutrient starvation conditions in Candida albicans, resulting in a downregulation of the target of rapamycin signalling pathway and in an increase in autophagic responses and intracellular cAMP. The augmented adhesion and filamentous growth, also observed with Aspergillus fumigatus, eventually translates into enhanced biofilm formation and resistance to local antifungal defenses. This might exemplify a mechanism whereby fungi have evolved a means of sensing host immunity to ensure their own persistence in an immunologically dynamic environment.

Hypocitraturia: a risk factor for reduced bone mineral density in idiopathic hypercalciuria?

The association between idiopathic hypercalciuria (IH) and reduced bone mineral density (BMD) has been described in adults and children. Frequently, hypocitraturia (HC) is an associated condition. To determine the effect that HC may have on bone metabolism of these patients, we studied 88 children with IH at diagnosis, divided into the following groups: group 1-44 (50%) patients with associated HC; group 2-44 (50%) patients without HC; group 3 (29 subjects), a healthy control group. Urinary and blood electrolytes, as long as urinary N-telopeptide, were measured. Lumbar spine (L2-L4) and femoral neck bone mineral density (BMD) and bone mineral content (BMC) were measured by dual energy X-ray absorptiometry. There was no difference in age between the three groups (P=0.80), but weight, height, body mass index, and bone age were lower (P<0.01) and serum intact parathyroid hormone (iPTH) was higher (P<0.05) in group 1 than in groups 2 and 3. N-telopeptide, measured in urine, did not differ between groups. The following bone densitometry parameters: lumbar spine BMC, BMC adjusted for height (BMCh), BMC adjusted for width of vertebrae (BMCw) and BMD, as well as femoral neck BMD, were significantly lower in group 1 than in groups 2 and 3 (P<0.01). When we corrected densitometry parameters for height, BMC was lower in group 1 and not in group 2 when compared with controls.

CONCLUSIONS

Children with IH and associated HC may have a higher risk of bone mass loss and consequent osteopenia. Further studies are needed to assess the role that hypocitraturia may have in this form of bone disease.

Idiopathic calcium oxalate urolithiasis: risk factors and conservative treatment

Idiopathic calcium oxalate urolithiasis is a frequent and recurrent multifactorial disease. This review focuses on urinary and dietary risk factors for this disease and conservative strategies for rectifying them. Dietary oxalate and calcium and their respective urinary excretions have been extensively investigated during the last 10 years. Urinary oxalate has emerged as the most important determinant of calcium oxalate crystallization while the role of urinary calcium has shifted to bone balance and osteoporosis. Dietary calcium restriction increases urinary oxalate and contributes to a negative bone balance. It has therefore been abandoned as a means to reduce the risk of calcium oxalate kidney stone formation. Calcium oxalate kidney stone patients are advised to increase their fluid intake to achieve a urine volume of 2 l or more; the recommended calcium intake is 800-1200 mg/day; high oxalate foods should be restricted; daily protein intake should be between 0.8 and 1 g/kg body weight/day; essential fats should be included; vegetable and fruit (except oxalate-rich vegetables) intake should be increased. The use of calcium supplements has potential benefits but needs to be examined further.

Randomized double-blind study of potassium citrate in idiopathic hypocitraturic calcium nephrolithiasis

In an attempt to document the efficacy of potassium citrate in stone formation, 57 patients with active lithiasis (2 or more stones during the preceding 2 years) and hypocitraturia were randomly allocated into 2 groups, with 1 group taking 30 to 60 mEq. potassium citrate daily in wax matrix tablet formation and the other group receiving placebo. In 18 patients receiving potassium citrate for 3 years stone formation significantly declined after treatment from 1.2 +/- 0.6 to 0.1 +/- 0.2 per patient year (p < 0.0001), in 13 patients (72%) the disease was in remission and all patients showed a reduced stone formation rate individually. In contrast, 20 patients taking placebo medication for 3 years showed no significant change in stone formation rate (1.1 +/- 0.4 to 1.1 +/- 0.3 per patient year) and in only 4 patients (20%) was the disease in remission. The stone formation rate during potassium citrate treatment was significantly lower than during the placebo treatment (0.1 +/- 0.2 versus 1.1 +/- 0.3 per patient year, p < 0.001). Potassium citrate therapy caused a significant increase in urinary citrate, pH and potassium, whereas placebo did not. Adverse reactions to potassium citrate were mild causing only 2 patients in the potassium citrate group and 1 in the placebo group to withdraw from the study. In summary, our randomized trial showed the efficacy of potassium citrate in preventing new stone formation in idiopathic hypocitraturic calcium nephrolithiasis.

The origin and causes of struvite stones

The aim of this paper is to evaluate the possible causes of the origin of "infection stones". The main differences between the ordinary biochemical parameters of a group of patients with this type of stones was analyzed and compared with a group of oxalocalcic stone-formers and with a group of healthy subjects. The importance of persistent basic urinary pH values is pointed out as possible origin of "infection stones" in some instances. The main urinary citrate concentration in patients with "infection stones" was significantly lower than in healthy subjects, this being an important factor that favours this kind of stone formation.

Determination of citric acid based on inhibition of the crystal growth of calcium fluoride

Inhibition of the growth of calcium fluoride crystals in the presence of citrate was followed using a kinetic-potentiometric technique and a calcium ion-selective electrode, and as a consequence, a method for the determination of citrate in the range 0.5-2.4 micrograms ml-1 has been developed. The method was successfully applied to the determination of citrate contained in pharmaceutical products and urine. Urine analysis requires prior separation of phosphate, sulphate and magnesium(II). Elimination of these interferences was studied and accomplished using precipitation processes. Magnesium and phosphate were jointly eliminated in basic media by the addition of ammonium ions. Phosphate and sulphate were eliminated with barium(II). Phosphate was also eliminated as a lithium salt.