Urinary citrate excretion in patients with renal stone: roles of leucocyte ATP citrate lyase activity and potassium salts therapy

Increasing Dietary Potassium Chloride Promotes Urine Dilution and Decreases Calcium Oxalate Relative Supersaturation in Healthy Dogs and Cats

Urine dilution is a strategy used to decrease the risk of crystallization in cats and dogs at risk of urolithiasis. Sodium chloride has been used in prescription diets to effectively promote urine dilution, but the effect of the salt-substitute potassium chloride (KCl) on urine parameters has not been extensively investigated. Two diets differing only in KCl (Diet A; K 0.44 g/MJ, Diet B; K 1.03 g/MJ) were fed to 17 cats and 22 dogs for seven days, followed by three days of urine collection. Urinary ion concentrations were determined by ionic chromatography, and SUPERSAT software was used to calculate the relative supersaturation (RSS) value for struvite and calcium oxalate. Water intake and urine volume increased, and USG decreased on diet B (p < 0.001). Urine concentration of potassium increased on diet B, but concentrations of all other ions did not change or decrease in line with urine dilution. Calcium oxalate RSS decreased on diet B (p < 0.05). This short-term study showed that increased dietary KCl in a dry extruded diet effectively dilutes the urine of cats and dogs and therefore offers a novel nutritional strategy for the prevention of urolithiasis. This finding is of interest for patients that would benefit from dietary sodium restriction.

The vital role of ATP citrate lyase in chronic diseases

Chronic or non-communicable diseases are the leading cause of death worldwide; they usually result in long-term illnesses and demand long-term care. Despite advances in molecular therapeutics, specific biomarkers and targets for the treatment of these diseases are required. The dysregulation of de novo lipogenesis has been found to play an essential role in cell metabolism and is associated with the development and progression of many chronic diseases; this confirms the link between obesity and various chronic diseases. The main enzyme in this pathway-ATP-citrate lyase (ACLY), a lipogenic enzyme-catalyzes the critical reaction linking cellular glucose catabolism and lipogenesis. Increasing lines of evidence suggest that the modulation of ACLY expression correlates with the development and progressions of various chronic diseases such as neurodegenerative diseases, cardiovascular diseases, diabetes, obesity, inflammation, and cancer. Recent studies suggest that the inhibition of ACLY activity modulates the glycolysis and lipogenesis processes and stimulates normal physiological functions. This comprehensive review aimed to critically evaluate the role of ACLY in the development and progression of different diseases and the effects of its downregulation in the prevention and treatment of these diseases.

Lime powder regimen supplement alleviates urinary metabolic abnormalities in urolithiasis patients

BACKGROUND

Urolithiasis has high recurrent rate after surgical removal within 3 years. Potassium citrate compound is used to prevent stone recurrence but it has intolerable gastrointestinal adverse effects. We conducted a phase 2 clinical study of lime power regimen (LPR), a limeade-based supplement containing potassium and citrate for 6 months period of treatment, to evaluate its effects on biochemical and clinical aspects of recurrent urolithiasis.

METHODS

Seventy-four urolithiasis patients were randomly allocated to receive either LPR or placebo for 6 months in a double-blinded manner. Plasma and 24 h urine samples were collected to measure urinary pH, mineral excretion and urinary total antioxidant status , plasma for creatinine and plasma protein carbonyl, and stone for elemental analysis at the initiation and end-of-treatment (6 month). Adverse effects were recorded.

RESULTS

Administration of LPR significantly increased urinary pH, citrate and potassium excretion. Urinary levels of calcium and oxalate, and plasma protein carbonyl content were reduced, while urinary total antioxidant status was elevated by LPR treatment. Urinary supersaturation was decreased and urinary protein excretion was ameliorated in LPR-treated patients. Gastrointestinal adverse effects were rarely observed. None of the participants developed stone recurrence for the duration of the trial.

CONCLUSION

Lime power regimen is a potential drug to correct urinary metabolic disorders associated with urolithiasis in high risk stone recurrent patients. A phase 3 clinical trial is underway to validate anti-stone recurrence property of LPR in long-term treatment.

Urinary stone risk factors in the descendants of patients with kidney stone disease

BACKGROUND

Evidence has indicated that immediate family members of nephrolithiasis patients had high opportunity to develop stones. However, they are usually not regarded to be at risk, since it is unclear if there are any lithogenic abnormalities found in non-stone-forming nephrolithiasis relatives. Our aim was to investigate urinary metabolic abnormalities in the children of nephrolithiasis patients, compared with the general population.

METHODS

The 24-h urinary metabolic profile was studied for 28 calcium oxalate nephrolithiasis patients (NL) and 46 of their descendants (ND), as well as 40 non-stone-forming volunteers (V) and 34 of their descendants (VD).

RESULTS

There was no difference between age, gender, and serum creatinine between NL vs. V (parental groups) and ND vs. VD (descendant groups). High urinary oxalate in nephrolithiasis and urinary calcium in their descendants was detected. In addition, an elevated urinary excretion rate of calcium, phosphate, protein, and albumin, along with low citrate excretion and high urinary supersaturation was observed in both the nephrolithiasis patients and their descendants. Approximate 17.8-24.4% of the nephrolithiasis descendants had a urinary supersaturation higher than the nephrolithiasis level, but none was found in VD group. The level of urinary supersaturation index was correlated with urinary protein and albumin excretion in nephrolithiasis family.

CONCLUSION

It was demonstrated that nephrolithiasis offspring carried several urinary metabolic risks predisposing to stone formation which are similar to their parents, and about one in every five nephrolithiasis children had nephrolithiasis level urinary supersaturation.

Generation of circularly permuted fluorescent-protein-based indicators for in vitro and in vivo detection of citrate

Indicators for citrate, particularly those applicable to its in vivo detection and quantitation, have attracted much interest in both biochemical studies and industrial applications since citrate is a key metabolic intermediate playing important roles in living cells. We generated novel fluorescence indicators for citrate by fusing the circularly permuted fluorescent protein (cpFP) and the periplasmic domain of the bacterial histidine kinase CitA, which can bind to citrate with high specificity. The ratiometric fluorescent signal change was observed with one of these cpFP-based indicators, named CF98: upon addition of citrate, the excitation peak at 504 nm increased proportionally to the decrease in the peak at 413 nm, suitable for build-in quantitative estimation of the binding compound. We confirmed that CF98 can be used for detecting citrate in vitro at millimolar levels in the range of 0.1 to 50 mM with high selectivity; even in the presence of other organic acids such as isocitrate and malate, the fluorescence intensity of CF98 remains unaffected. We finally demonstrated the in vivo applicability of CF98 to estimation of the intracellular citrate concentration in Escherichia coli co-expressing the genes encoding CF98 and the citrate carrier CitT. The novel indicator CF98 can be a specific and simple detection tool for citrate in vitro and a non-invasive tool for real-time estimation of intracellular concentrations of the compound in vivo.

Citraturic, alkalinizing and antioxidative effects of limeade-based regimen in nephrolithiasis patients

Potassium citrate has long been used as a prophylactic remedy for nephrolithiasis recurrence. Lemonade consumption is also suggested as an option. We compared the efficacy of consumption of solution containing manufactured lime powder with that of potassium citrate, on the improvement of metabolic risk factors, oxidative stress and renal tubular damage in nephrolithiasis patients. Patients with kidney stone were enrolled and randomly assigned to three treatment programs for 3 month period consisting of consumption of solution containing lime powder (Group 1, n=13), potassium citrate (Group 2, n=11) and lactose as placebo regimen (Group 3, n=7). Lime powder and potassium citrate contained equal amounts of potassium (21 mEq) and citrate (63 mEq). After treatment, there was an increase in urinary pH, potassium and citrate in Group 1 and 2. Increased plasma potassium and red blood cell glutathione (R-GSH) and decreased urinary malondialdehyde were found in Group 1, but not observed in Group 2. R-GSH was decreased in Group 2. Urinary N-acetyl-beta-glucosaminidase activity and fractional excretion of magnesium, as renal tubular damage indicators, were decreased only in Group 1. In Group 3, all measured parameters were unaltered except for an increased urinary chloride. In conclusion, consumption of our in-house lime powder exerted citraturic and alkalinizing actions as efficient as consumption of potassium citrate. In addition, it provided an antioxidative effect and was able to attenuate renal tubular damage. These pharmacological properties may be clinically useful to diminish the stone-forming potential in kidney stone patients and hence for preventing recurrent calculi.

Vitamin B6 deficiency augments endogenous oxalogenesis after intravenous l-hydroxyproline loading in rats

The effects of an intravenous hydroxyproline load on endogenous oxalogenesis were compared in rats fed a standard diet or a vitamin B6-deficient diet. Twelve male Wistar rats were randomized to two groups and were fed either a standard diet (control group) or a vitamin B6-deficient diet for 3 weeks. Then the animals were intravenously administered 100 mg (762.6 micromol)/ml hydroxyproline. In the control group, infusion of hydroxyproline increased the 5-h urinary oxalate and glycolate excretion above baseline to 0.27% (2.02 +/- 1.11 micromol) and 0.32% (2.43 +/- 1.60 micromol) of the administered dose (mol/mol), while it was respectively 2.01% (15.24 +/- 2.13 micromol) and 0.00% (-0.02 +/- 0.19 micromol) of the dose in the vitamin B6-deficient group. Therefore, vitamin B6 deficiency augmented endogenous synthesis of oxalate from hydroxyproline by 7.56-fold (15.24/2.02) compared with that in the control group. Urinary citrate excretion was significantly lower at baseline and all other times in the vitamin B6-deficient group compared with the control group. In conclusions, L-hydroxyproline loading augmented endogenous oxalogenesis in the vitamin B6-deficient group without causing hyperglycolic aciduria, and also led to significant hypocitraturia. These findings suggest that hydroxyproline is not metabolized to oxalate via glycolate, but rather via the 4-hydroxyglutamate to glyoxylate pathway (usually requiring vitamin B6-dependent enzymes) even in the presence of vitamin B6 deficiency.

A turn-on fluorescent indicator for citrate with micromolar sensitivity

A turn-on fluorescent indicator for citric acid (citrate) has been developed, displaying high emission enhancement (+1500%) and low interference by other carboxylates. The sensor is based on the non-emissive copper(II) complex of a fluorescent amino amide, which, upon addition of citrate decomplexates to yield the emissive ligand. The detection limit estimated for this new chemosensing system is about 0.5 microM. This novel approach to the analysis of citrate constitutes an alternative ca. 10(2)-10(3) times more sensitive than the standard method based on the enzyme citrate lyase.

Organic potassium salts or fibers effects on mineral balance and digestive fermentations in rats adapted to an acidogenic diet

BACKGROUND

Fibers and potassium (K) organic salts in plant foods are liable to affect Ca and Mg balance at digestive and renal levels, respectively. K organic salts could counteract the acidifying effects of western diets and consequences of excess NaCl.

AIM OF THE STUDY

To study this question, male rats were adapted to a basal acidifying low-K (LK) diet, or to diets supplemented with a fiber mix (LK/F), or K citrate (HK) or both (HK/F).

RESULTS

HK and HK/F diets displayed a marked alkalinizing effect in urine and promoted citraturia, but this effect was not modulated by fibers. The effect of fibers on Ca digestive absorption was more potent than K citrate effect on Ca renal excretion. In contrast, K citrate effect on kidney Mg excretion was more effective than that of fibers on Mg digestive absorption, a maximal effect on Mg balance was observed in rats fed the HK/F diet. Digestive fermentations in rats fed the LK/F diet were characterized by high-propionic acid fermentations and succinate accumulation. In rats adapted to the HK/F diet, K citrate supplementation depressed succinate and increased butyrate concentrations.

CONCLUSION

Organic anions arising from digestive fermentations seem to be not directly involved in the alkalinizing effects of plant foods. Fibers and organic K salts exert distinct effects on Ca and Mg metabolism, but with interesting interactions as to Mg balance, digestive fermentations and urine pH.

Effects of potassium-magnesium citrate supplementation on cytosolic ATP citrate lyase and mitochondrial aconitase activity in leukocytes: A window on renal citrate metabolism

BACKGROUND

An increase in urinary citrate excretion is associated with a decrease in activity of renal cortical cytosolic ATP citrate lyase (ACL) and mitochondrial aconitase (m-aconitase). Because potassium-magnesium citrate causes an increase in urinary citrate excretion, we decided to assess its effects on ACL and m-aconitase in the leukocytes of renal stone patients.

METHODS

Twenty male renal stone patients were supplemented with potassium-magnesium citrate twice daily (i.e. 42 mEq potassium, 21 mEq magnesium, and 63 mEq citrate per day) for a period of 1 month. Two 24-h urine and one 15-mL heparinized blood samples were collected from each patient before and after supplementation. Urine samples were analyzed for relevant biochemical compositions. Leukocytes were separated from blood samples by centrifugation and assayed for ACL and m-aconitase activity.

RESULTS

Supplementation with potassium-magnesium citrate significantly increased urinary pH (P < 0.005) and excretions of potassium (P < 0.001), magnesium (P < 0.001) and citrate (P < 0.0001). The activity of both ACL and m-aconitase were significantly decreased (P < 0.004 and P < 0.02 respectively). The decrease in ACL activity was inversely correlated with an increase in urinary excretion of both potassium (r = -0.620, P < 0.0001) and citrate (r = -0.451, P < 0.004). A similar inverse correlation was observed between m-aconitase activity and urinary excretion of citrate (r = -0.322, P < 0.043).

CONCLUSION

Changes in enzyme activity, related to citrate metabolism in leukocytes, might reflect the status of renal tubular cells.

Renal tubular cell damage and oxidative stress in renal stone patients and the effect of potassium citrate treatment

Our objective was to evaluate the oxidative stress and renal tubular cell damage in patients who have renal stones compared to normal subjects. The patients were re-evaluated after 1-months supplementation with potassium citrate. We recruited 30 patients (11 males and 19 females) diagnosed with kidney stones and scheduled for surgical stone removal the following month, and 30 healthy non-stone formers (14 males and 16 females). Two 24-h urine samples and one heparinized blood sample were collected from each subject. Plasma was separated from the erythrocytes and assayed for creatinine, potassium, sodium, calcium, magnesium, phosphate, malondialdehyde (MDA, a lipid peroxidation product) (P-MDA), protein thiol as an indicator of protein oxidation, and vitamin E. Erythrocytes were analysed for MDA (E-MDA), reduced glutathione (GSH) and cellular glutathione peroxidase (cGPx) activity. The urine was analyzed for pH, creatinine, potassium, sodium, calcium, magnesium, phosphate, oxalate, citrate, MDA (U-MDA), total protein (U-protein) and N-acetyl-beta-glucosaminidase (NAG) activity. For the stone patients, urine and blood samples were re-evaluated after supplementation with potassium citrate (60 mEq/day) for 1 month. Renal stone patients had higher plasma creatinine and lower plasma potassium, urinary pH, potassium, magnesium, phosphate and citrate than the controls. The patients had higher P-MDA, E-MDA, U-MDA, U-protein and NAG activity, but lower GSH, cGPx activity, protein thiol and vitamin E, when compared with controls. After potassium citrate supplementation, P-MDA and E-MDA decreased while plasma vitamin E, urinary NAG activity and citrate increased. Renal stone disease is associated with high oxidative stress and damage to renal tubular cells. These abnormalities are coincident with an increase in blood lipid peroxidation products and a decrease in antioxidant status. Although supplementation with potassium citrate improved urinary citrate levels and oxidative stress, it neither reduced urinary lipid peroxidation products nor remedied the damage to renal tubular cells, probably due to the existence of kidney stones.

In vivo 31P-MRS assessment of muscle-pH, cytolsolic-[Mg2+] and phosphorylation potential after supplementing hypokaliuric renal stone patients with potassium and magnesium salts

Renal stone patients in rural northeast Thailand have a low potassium and magnesium status and low urinary excretion of citrate. We measured the changes of urinary citrate excretion and assessed in vivo skeletal muscle metabolism for intracellular-pH, cytosolic-[Mg(2+)] and phosphorylation potential (using the phosphorus magnetic resonance spectroscopy (31)P-MRS) after oral supplementation to hypokaliuric renal stone patients with oral potassium and magnesium salts. The patients comprised four groups: Group 1 (n = 10) control, Group 2 (n = 3), Group 3 (n = 5) and Group 4 (n = 6) supplemented for a month with potassium citrate, potassium citrate plus amino acid chelated magnesium, and potassium-magnesium citrate, respectively. Though urinary citrate excretion was increased in all three supplemented groups, the increases in intracellular-pH, cytosolic-[Mg(2+)] and phosphocreatine (PCr)/beta-ATP were prominent only in Group 3. The increase in PCr/beta-ATP was also observed in Group 4.

Urinary lithogenic and inhibitory factors in preterm neonates receiving either total parenteral nutrition or milk formula

The aim of this study was to evaluate prospectively the influence of nutrition on certain factors which may inhibit or promote nephrocalcinosis in two groups of preterm infants, receiving total parenteral nutrition (TPN) and special preterm milk formula respectively, but not furosemide. A total of 37 preterm infants, 15 on TPN and 22 fed a special preterm formula were studied at the end of the 1st, 2nd and 3rd weeks of life, at which time serum and 8 h urine specimens were collected. High ratios of urinary calcium to urinary creatinine (UCa/cr), urinary oxalate to urinary creatinine (Uox/cr) and urinary calcium to urinary citrate (UCa/cit) indicates an increased risk for nephrocalcinosis while high urinary citrate to urinary creatinine (Ucit/cr) ratio indicates protection. Uox/cr increased significantly (P<0.05) in those infants fed preterm formula, from the end of 2nd week of life and was two-fold higher than in the TPN group of preterm infants (P<0.01). Ucit/cr was higher throughout the study period in the formula fed than in the TPN preterm infants. UCa/cit was five-fold higher (P<0.01) in the TPN group, by the end of the 3rd week. Urinary calcium and magnesium was similar in both groups during the study period. Two of the infants studied (5.4%), one from each group, developed nephrocalcinosis.

CONCLUSION

In preterm neonates on total parenteral nutrition, urinary oxalate -to-creatinine ratio (a potent lithogenic factor) was lower and urinary citrate -to-creatinine ratio (a lithoprotective factor) also lower than in formula fed neonates. The type of feeding (total parenteral nutrition or special preterm milk formula) seems to affect urinary oxalate and citrate but not calcium and magnesium in non-furosemide treated preterm infants during the first 3 weeks of life.