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Biomedical subjects

P T Cheng

Publications and source records attributed to P T Cheng.

At least 55 records · Page 3Linked to original sources
PubMed1985

Inhibition of hydroxyapatite formation in collagen gels by chondroitin sulphate.

Crystal growth in native collagen gels has been used to determine the role of extracellular matrix macromolecules in biological calcification phenomena. In this system, type I collagen gels containing sodium phosphate and buffered at pH 7.4 are overlayed with a solution containing CaCl2. Crystals form in the collagen gel adjacent to the gel-solution interface. Conditions were determined which permit the growth of crystals of hydroxyapatite [Ca10(PO4)6(OH)2]. At a Ca/P molar ratio of 2:1, the minimum concentrations of calcium and phosphate necessary for precipitation of hydroxyapatite are 10 mM and 5 mM, respectively. Under these conditions, precipitation is initiated at 18-24h, and is maximal between 24h and 6 days. Addition of high concentrations of chondroitin 4-sulphate inhibits the formation of hydroxyapatite in collagen gels; initiation of precipitation is delayed, and the final (equilibrium) amount of precipitation is decreased. Inhibition of hydroxyapatite formation requires concentrations of chondroitin sulphate higher than those required to inhibit calcium pyrophosphate crystal formation.

Calcium↗
PubMed1985

Octacalcium phosphate formation in vitro: implications for bone formation.

Octacalcium phosphate (OCP, Ca8H2(PO4)6 . 5H2O) has been found in kidney stones and dental calculi and proposed by Brown et al. [1] to be a precursor of hydroxyapatite in bone and teeth formation. As saliva and urine often have acidic pH which favors OCP formation, the question remains then whether OCP can form in the more basic extracellular fluid in the bone milieu. This paper shows that calcium phosphate crystal phases obtained from neutral and pH 7.4 solution mixtures containing [CaCl2] = 0.1-10.0 mM and [Na2HPO4] = 0.1-90.0 mM with 100-300 mosM at 37 degrees C include brushite (CaHPO4 . 2H2O), OCP, and hydroxyapatite (Ca5(OH)(PO4)3). In some solutions OCP transforms into hydroxyapatite after 1 or more days, but brushite has not been observed to transform into OCP. Assuming the extracellular bone fluid has [Ca2+] = 1.0 mM, 300 mosM, and pH 7.4, this work suggests that hydroxyapatite crystals would only form when the ambient [Pi] greater than 5 mM, and that octacalcium phosphate may be a precursor.

Bone and Bones↗
PubMed1985

Ultrastructural studies of crystal-organic matrix relations in renal stones.

Biochemically the organic matrix of kidney stones contains mucoproteins, mucopolysaccharides, inorganic material and bound water. Morphologically, the organic matrix exists as either amorphous or fibrous forms. We have attempted to critically evaluate results from analytical and morphological studies on stone matrices using light microscopy, histochemistry, x-ray diffraction, scanning electron microscopy, x-ray energy dispersive spectrometry, transmission electron microscopy and selected area electron diffraction. On the surface of calcium oxalate stones, there are usually large masses of randomly deposited calcium oxalate crystals each coated with organic matrix. Transmission electron microscopy shows these large surface crystals are composed of rows of smaller crystallites interleaved by organic matrix in a fairly orderly manner suggesting the crystallites are held together by organic matrix. In the core of a calcium containing stone, the organic matrix frequently exists as concentric laminations alternating as calcium apatite covered fibrous matrix layers and amorphous matrix layers. Transmission electron microscopy suggests that the fibrous area is probably just an area heavily populated by calcium apatite crystallites which give the fibrous appearance while the amorphous area is sparsely populated. Organic matrix richness in stones can be associated with infection and calcium apatite crystal deposition is favored in infection stones.

Apatites↗
PubMed1985

Low voltage scanning electron microscopy of uncoated kidney stones.

Some organic kidney stone components are easily damaged by a 10-30 kV electron beam used in conventional scanning electron microscopy. To avoid beam damage and reduce charging, it is desirable to study kidney stones by low voltage (1-5 kV) scanning electron microscopy (LVSEM) even though image resolution will suffer and X-ray microanalysis will not be available. If one is proficient in crystal morphology one can analyze gold-coated kidney stones by LVSEM without much difficulty. Stone components examined include calcium oxalate monohydrate, calcium oxalate dihydrate, struvite, calcium apatite, brushite, whitlockite, cystine, uric acid, uric acid dihydrate and ammonium acid urate. For all these components with the exception of the very small whitlockite and ammonium acid urate crystals, uncoated kidney stones can be examined with a 1 kV electron beam.

Calcium Oxalate↗
PubMed1984

Calcium oxalate kidney stones in patients on continuous ambulatory peritoneal dialysis.

Kidney stones were passed by ten out of 186 patients with endstage renal disease who were treated with continuous ambulatory peritoneal dialysis (CAPD). Stones from seven patients were examined by x-ray diffraction. In five of them the stones were composed of calcium oxalate monohydrate. The urine calcium oxalate activity product was determined in 44 CAPD patients, eight of whom were stone formers, and compared to that of 120 normal volunteers. In CAPD patients, mean urine ionic-calcium concentration was lower than in normal subjects whereas mean urine ionic-oxalate concentration was significantly higher than in normal subjects. In normal urine samples, the calcium oxalate activity product showed a significant correlation with both the urine ionic-calcium and the ionic-oxalate concentrations. In contrast, in CAPD patients the calcium oxalate activity product correlated with the ionic-calcium concentration but not with ionic-oxalate. Although the urine ionic-calcium concentration is lower in CAPD patients than in normal subjects, it is the relative increase in its concentration which appears to be associated with the increased risk of kidney stone formation in these patients. This relative hypercalciuria seems to follow 1,25(OH)2 vitamin D3 administration.

Calcitriol↗
PubMed1983

Multiple-crystal acute polyarthritis.

A patient with acute polyarthritis due to crystal-positive simultaneous gout and pseudogout affecting different joints is described. The case emphasises the importance of aspirating more than one involved joint and carefully searching for crystals in patients with acute arthritis involving 2 or more joints, particular those in whom the diagnosis of multiple crystalline joint disease is considered.

Acute Disease↗
PubMed1983

Analytical scanning and transmission electron microscopy and x-ray microdiffractometry of calcium pyrophosphate dihydrate crystal deposits in tissues.

This paper reviews current methods and applications for the detection and identification of calcium pyrophosphate dihydrate (CPPD) crystals. Methods reviewed include compensated polarized light microscopy, scanning electron microscopy, transmission electron microscopy, x-ray energy-dispersive elemental analysis, x-ray powder microdiffractometry, and selected area electron diffractometry. Although compensated polarized light microscopy is the best technique for crystal detection in pathologic fluids and tissues, because of crystal size this technique cannot discriminate easily between CPPD(M) and CPPD(T) polymorphs. To determine the presence and relative concentration of CPPD(M) and CPPD(T), x-ray or electron microdiffractometry is required. Analytical scanning and transmission electron microscopy are needed to localize crystals ultrastructurally and to determine the relationship of the crystal deposits to tissue components. The correlative application of multiple techniques on the same sample or adjacent samples provides more precise localization and identification than any single technique.

Calcium Pyrophosphate↗
PubMed1983

Pyrophosphate, phosphate ion interaction: effects on calcium pyrophosphate and calcium hydroxyapatite crystal formation in aqueous solutions.

The relationship between ambient ionic conditions that favor pyrophosphate (PPi) versus phosphate (Pi) biomineralization is important to understanding the pathogenesis of chondrocalcinosis. We studied aqueous solutions at pH 7.4, 37 degrees C, [Na+] = 140 mM, [Mg+ +] = 0.5 mM, [Ca+ +] = 1.0 or 1.5 mM over a range of pyrophosphate and phosphate concentrations to determine the effect of different ambient concentrations and ratios of Pi/PPi on calcium pyrophosphate dihydrate (CPPD) and calcium hydroxyapatite (HA) crystal formation. We found that the Pi/PPi ratio is an extremely important determinant of the crystal product formed. At low [Pi], CPPD crystal formation is partially inhibited by Pi; at higher [Pi], calcium pyrophosphate, calcium phosphate and calcium pyrophosphate-phosphate complexes amorphous to x-ray diffraction are formed; whereas at still higher [Pi], HA crystal formation partially inhibited by PPi. We conclude that CPPD forms when the ratio [Pi]/[PPi] less than 3 and HA forms when [Pi]/[PPi] greater than 100.

Calcium Pyrophosphate↗
PubMed1983

Ultrastructural studies of renal stones from patients on continuous ambulatory peritoneal dialysis.

Patients on haemodialysis or peritoneal dialysis due to renal failure have an unusually high incidence of kidney stones (from 5 to 51% depending on methodology). However, there is a controversy on the composition of these stones - whether they are calcium oxalate stones or matrix stones. This paper presents ultrastructural evidence that these stones are in fact heterogeneous, ranging from calcium oxalate stones with little organic matrix component, through calcium oxalate and calcium apatite stones with substantial organic matrix component, to matrix stones with little inorganic material component. The correlative analytical methodology developed in this laboratory employing analytical scanning and transmission electron microscopy, electron and x-ray diffraction, as well as biochemistry, was reported previously. For the calcium oxalate stones, scanning electron microscopy showed that numerous small crystals of 1-3 micron in size were exposed to stone surfaces, apparently in an unorganized manner. However, transmission electron microscopy sections showed orderly stacking of crystals held together by organic matrix, just like bricks held together by mortar. For the matrix stones, scanning electron microscopy showed smooth stone surfaces while transmission electron microscopy sections showed focal areas of calcium oxalate or apatite deposits as identified by selected area electron diffraction.

Apatites↗
PubMed1983

Ultrafiltrable calcium and magnesium in ultrafiltrates of serum prepared with the Amicon MPS-1 system.

We evaluated the Amicon micropartition system (MPS-1) for preparing ultrafiltrates of serum for use in evaluating ultrafiltrable Ca and Mg. We found no adsorption of either to the filter and 99.6% retention of serum proteins on the membrane. Ultrafiltrate volumes recovered (100-450 microL) varied with centrifugation time (10-30 min) and temperature. Centrifugation time did not affect the measured concentration of ultrafiltrable calcium and magnesium, and pH change in the 1-mL serum specimen during a 30-min centrifugation at room temperature was negligible. There was an inverse relationship between temperature and ultrafiltrable Ca and Mg concentrations. The precision (CV) between filters ranged from 1.2 to 5.1% for ultrafiltrable Ca and 1.5 to 2.7% for ultrafiltrable Mg. The correlation between ultrafiltrable Ca (y) and ionized Ca (x) in samples from 115 patients with calcium-related metabolic disorders was good (y = 1.04x + 0.18; r = 0.9128). We find the MPS-1 to be a simple and convenient tool for the rapid production of serum ultrafiltrates.

Adult↗
PubMed1982

Adrenal and hepatic calcium stearate crystal deposits in dogs fed a thiamine-deficient diet.

The nature and histologic environment of birefringent crystals found incidentally at necropsy in the liver and adrenal glands of dogs fed a thiamine-deficient diet were studied. The crystals were identified as calcium stearate by ultrastructural and x-ray microdiffraction techniques. Crystals were observed intracellularly within cytoplasmic vacuoles and extracellularly within sinusoids. Generally, crystals were also observed in pair-fed controls that were given a purified diet (equal in weight to that consumed by the thiamine-deficient animals) plus supplemental thiamine. Crystal deposits were found in trace amounts in a few of the ad libitum-fed controls. Although thiamine deficiency may be involved in promoting crystal deposition in the adrenal cortex, calcium stearate crystal formation within the adrenal glands and the liver appears unrelated to dietary thiamine deficiency per se, but is probably related to deficiency of an unidentified nutrient in the purified thiamine-deficient diet.

Adrenal Glands↗
PubMed1981

Calcite sputum lith. Characterization by analytic scanning electron microscopy and X-ray diffraction.

The chemical identification by x-ray diffraction and analytic scanning electron microscopy of a sputum lith weighing 1 mg is described. These technics demonstrated that the lith was composed of rhombohedral calcium carbonate (calcite). Since different crystal species form under different chemical conditions, these precise, nondestructive analytic technics should have wide application in the investigation not only of a bronchial liths but also of other microcrystalline tissue deposits.

Adult↗
PubMed1981

Analytical scanning electron microscopy and x-ray microdiffractometry of renal calculi using etched plastic sections.

We describe the technique and illustrate results of renal calculi analyses utilizing correlative analytical scanning electron microscopy and x-ray microdiffractometry on the same 100 micrometer Spurr embedded sections. Essential to the technique is the employment of an extremely sensitive x-ray microdiffractometer, and for morphological analysis, pretreatment of the sections with a sodium ethoxide etching solution. This technique facilitates more precise identification of crystalline constituents especially calcium apatite and magnesium ammonium phosphate hexahydrate (struvite). Further, the technique permits detection and mapping of both crystalline and amorphous constituents within calculi.

Calcium Oxalate↗