Calcium Oxalate Monohydrate Precipitation at Membrane Lipid Rafts

Endothelium corneum gigeriae galli extract inhibits calcium oxalate formation and exerts anti-urolithic effects

ETHNOPHARMACOLOGICAL RELEVANCE

Traditional Chinese Medicine is preferred because of its safety and minimal/reduced side effects. Endothelium Corneum Gigeriae Galli (ECGG) extract, a traditional Chinese drug consisting of the dried gizzard membrane of Gallus gallus domesticus Brisson, was assessed for its effects and mechanism on urolithiasis.

AIMS OF STUDY

To evaluate the effects of ECGG extract on calcium oxalate (CaOx) crystal formation in vitro, and assess the anti-urolithic effects of ECGG extract in vivo and explore the underlying mechanism.

MATERIALS AND METHODS

In vitro, CaOx crystals were treated with ECGG extract (0.05, 0.2, and 0.8 g/mL), and assessed by scanning electron microscopy, Fourier-transform infrared spectroscopy, X-ray powder diffraction and electrical conductivity. Then, a rat model of renal calculi was established by ethylene glycol and ammonium chloride treatment, and ECGG extract (5.0, 10.0 and 20.0 g/kg) was administered orally. After treatment, urine, serum and kidney bioindicators were analyzed, as well as kidney's pathological features.

RESULTS

In the presence of ECGG extract, calcium oxalate dihydrate (COD) crystals with typical tetragonal bipyramidal morphology were obtained; meanwhile, the formation of calcium oxalate monohydrate (COM), a major urinary stone component, was inhibited; in addition, the equilibration time of the chemical reaction of Ca²⁺ and C₂O₄^2- ions was delayed in a concentration dependent manner. ECGG extract actually showed anti-urolithic effects; the incidence rates of crystal formation in the kidney in the model, low, middle and high dose groups were 100%, 90%, 70% and 60%, respectively, with a dose-dependent alleviation of kidney stone amounts and kidney damage. Treatment with middle and high ECGG extract doses significantly decreased urine uric acid and oxalic acid amounts, serum creatinine, urea nitrogen and uric acid contents, and kidney tissue oxalic acid and calcium levels, while increasing kidney and urinary magnesium and superoxide dismutase levels (P < 0.05).

CONCLUSION

ECGG extract has outstanding anti-urolithic effects, potentially with included bioorganic molecules inducing COD crystal nucleation and growth. Therefore, ECGG extract is a promising drug for preventing and treating urolithiasis.

Effect of Ca2+ to Sphingomyelin Investigated by Sum Frequency Generation Vibrational Spectroscopy

The interactions between Ca²⁺ ions and sphingomyelin play crucial roles in a wide range of cellular activities. However, little is known about the molecular details of the interactions at interfaces. In this work, we investigated the interactions between Ca²⁺ ions and egg sphingomyelin (ESM) Langmuir monolayers at the air/water interface by subwavenumber high-resolution broadband sum frequency generation vibrational spectroscopy (HR-BB-SFG-VS). We show that Ca²⁺ ions can induce ordering of the acyl chains in the ESM monolayer. An analysis of the one alkyl-chain-deuterated ESM revealed that the Ca²⁺ ions do not affect the N-linked saturated fatty acid chain, although they make the sphingosine backbone become ordered. Further analysis of the SFG-VS spectra shows that the interactions between ESM and Ca²⁺ ions make the orientation of the methyl group at the end of sphingosine backbone change from pointing downward to pointing upward. Moreover, a large blue shift of the phosphate group at the CaCl₂ solution interface indicates, to our knowledge, new cation binding modes. Such binding causes the phosphate moiety to dehydrate, resulting in the conformation change of the phosphate moiety. Based on these results, we propose the molecular mechanism that Ca²⁺ ions can bind to the phosphate group and subsequently destroy the intramolecular hydrogen bond between the 3-hydroxyl group and the phosphate oxygen, which results in an ordering change of the sphingosine backbone. These findings illustrate the potential application of HR-BB-SFG-VS to investigate lipid-cation interactions and the calcium channel modulated by lipid domain formation through slight structural changes in the membrane lipid. It will also shed light on the interactions of complex molecules at surfaces and interfaces.

Effect of phospholipase A2 hydrolysis products on calcium oxalate precipitation at lipid interfaces

Urinary stones are commonly composed of an inorganic component, calcium oxalate, or calcium phosphate and an organic matrix of lipids, carbohydrates, and proteinaceous matter. Of interest is the role that the organic matrix elements may play as catalysts for the heterogeneous nucleation of the calcium salts, and a number of studies have examined the role of lipids in calcium oxalate monohydrate (COM) formation. In this study, products of lipid hydrolysis from phospholipase A(2) (PLA(2)) are examined for their effect on COM formation using Langmuir monolayers as model lipid membrane assemblies. The enzyme PLA(2) hydrolyzes DPPC monolayers in the presence of a supersaturated calcium oxalate subphase, inducing the rapid and plentiful nucleation of calcium oxalate at the lipid interface. To investigate the cause of increased crystal formation in the presence of the enzyme, Langmuir monolayers modeling the hydrolysis products were investigated. Calcium oxalate crystal growth at a ternary monolayer of dipalmitoylphosphatidylcholine (DPPC), palmitic acid (PA), and a 22-carbon chain lysophospholipid (22:0 Lyso PC) dramatically increases relative to monolayers of just DPPC. Binary monolayers of DPPC with either PA or the 22:0 Lyso PC and single-component monolayers of PA were also studied. It is demonstrated that the fatty acid generated during lipid hydrolysis causes a significant increase in the extent of heterogeneous nucleation of calcium oxalate from supersaturated solutions. The results imply a possible link between increased phospholipase activity, which is associated with hyperoxaluria, and calcium oxalate precipitation.

Role of lipids in urinary stones: studies of calcium oxalate precipitation at phospholipid langmuir monolayers

This article reviews the authors' experiments on calcium oxalate growth at lipid monolayers. Calcium oxalate is the principal mineral component of most urinary stones. Membrane constituents associate either actively or passively with calcific minerals during stone formation, and it has been proposed that lipid assemblies play a significant role, possibly providing sites for the initial nucleation event. Langmuir monolayers allow systematic studies of the heterogeneous precipitation of calcium oxalate at lipid assemblies. The influences of the chemical identity of the lipid headgroup, the organization of the monolayer, and the presence of heterogeneities and phase boundaries within the monolayer have been explored.