Presence Of Calcium Phosphate Research Articles

Fragments of luxury: Opaque glass from the Palace of Mystras, Greece

The present study focuses on the analysis of nine opaque or translucent glass samples of white, grey/blue and red colour, recovered from the Palace Complex of Mystras in southern Peloponnese, Greece. Their date cannot be determined with specificity but has to span between the mid-13th and mid-19th c. AD, the period since the construction of the site and throughout its continuous use as the administrative centre of the Despotate of Mystras. The extremely rare occurrence of opaque glass vessels of this period in Greece, as well as the recovery of most samples within Building E of the Complex, suggest that the samples were precious objects, possibly owned by high ranking members of the Palace. A multi-technique approach, including Optical microscopy, SEM/EDS, Raman spectroscopy and TEM analysis, was implemented in order to determine the microstructure and raw materials of the samples.Despite the small number of samples, a remarkable variability was revealed in terms of the raw materials and manufacturing processes employed. Overall, three different opacification techniques were documented among the white and grey/blue samples: The Na-rich glasses were opacified using either cassiterite, a typical opacifier for the period, or calcium antimonate, a less common opacifier in the post-Medieval glassmaking. The K-rich white glasses were opacified with the addition of the ashes of animal bones, as suggested by the presence of calcium phosphates, a Byzantine tradition that was possibly also used by Bohemian glassmakers.Finally, the red glasses present certain atypical traits in their microstructure and chemical composition. The samples contain multiple calcite, tin oxide and lead oxide particles. The colour is due to copper, which could only be identified with the application of TEM analysis, in the form of copper oxide nanoparticles.The present study highlights the complicated traditions employed for the production of opaque glass in the post-Medieval European workshops and it underscores the need for a more thorough study of related material.

Characterization of Novel Cement-Based Carboxymethyl Chitosan/Amorphous Calcium Phosphate.

This study aimed to analyze, evaluate, and characterize novel cement-based carboxymethyl chitosan/amorphous calcium phosphate (CMC/ACP). The three cement groups studied were gypsum (Gyp), and CMC/ACP-gypsum cement-based 5% (5% CAG) and 10% (10% CAG). The groups were characterized using Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), setting time, and scanning electron microscopy (SEM) data. The characterization results were analyzed qualitatively, but the data for setting time were analyzed using SPSS (p < 0.05). Data were statistically analyzed. One-way analysis of variance was used to compare numerical (parametric) data between more than two separate groups followed by post hoc Tukey. FTIR showed phosphate groups indicate the presence of calcium phosphate in the form of amorphous (ACP) in the CMC/ACP, CMC/ACP post-milled powder, and CMC/ACP cement-based (5% CAG and 10% CAG). XRD showed no difference in the diffraction spectra among the Gyp, 5% CAG, and 10% CAG groups. SEM images revealed that the CMC/ACP cement-based groups (5% CAG and 10% CAG) showed CMC/ACP cluster filled with hollow spaces between the gypsum crystals and aggregations surrounding the gypsum crystals. The CMC/ACP showed envelopes and attached to the crystalline structures of the gypsum. Setting times of 5% CAG and 10% CAG showed significant differences compared with Gyp (p < 0.05). The result of our study showed that CMC/ACP cement-based (5% CAG and 10% CAG) demonstrated amorphous characteristic, which can stabilize calcium ions and phosphate group (ACP). In addition, the modification of gypsum using CMC/ACP as cement-based extended the time of setting.

Mineralization of Phosphorylated Fish Skin Collagen/Mangosteen Scaffolds as Potential Materials for Bone Tissue Regeneration.

In this study, a potential hard tissue substitute was mimicked using collagen/mangosteen porous scaffolds. Collagen was extracted from Tilapia fish skin and mangosteen from the waste peel of the respective fruit. Sodium trimetaphosphate was used for the phosphorylation of these scaffolds to improve the nucleation sites for the mineralization process. Phosphate groups were incorporated in the collagen structure as confirmed by their attenuated total reflection Fourier transform infrared (ATR-FTIR) bands. The phosphorylation and mangosteen addition increased the thermal stability of the collagen triple helix structure, as demonstrated by differential scanning calorimetry (DSC) and thermogravimetry (TGA) characterizations. Mineralization was successfully achieved, and the presence of calcium phosphate was visualized by scanning electron microscopy (SEM). Nevertheless, the porous structure was maintained, which is an essential characteristic for the desired application. The deposited mineral was amorphous calcium phosphate, as confirmed by energy dispersive X-ray spectroscopy (EDX) results.

A Mineral By-Product from Gasification of Poultry Feathers for Removing Cd from Highly Contaminated Synthetic Wastewater

Ash from poultry feather gasification was investigated as an adsorbent for Cd removal from synthetic wastewater under a range of operational conditions: initial pH (2–8) and salinity (8–38 mS/cm) of wastewater, ash dosage (2.5–50 g/L), Cd concentration (25–800 mg/L) and contact time (5–720 min). The ash was highly alkaline and had low surface area and micropores averaging 1.12 nm in diameter. Chemical/mineralogical analysis revealed a high content of P2O5 (39.9 wt %) and CaO (35.5 wt %), and the presence of calcium phosphate, hydroxyapatite and calcium. It contained only trace amounts of heavy metals, BTEX, PAHs and PCBs, making it a safe mineral by-product. Cd adsorption was described best with Langmuir and pseudo-second order models. At pH 5, an ash dosage of 5 g/L, 40 min contact time and 100 mg Cd/L, 99% of Cd was removed from wastewater. The salinity did not affect Cd sorption. The maximum adsorption capacity of Cd was very high (126.6 mg/g). Surface precipitation was the main mechanism of Cd removal, possibly accompanied by ion exchange between Cd and Ca, coprecipitation of Cd with Ca-mineral components and Cd complexation with phosphate surface sites. Poultry ash effectively removes high concentrations of toxic Cd from wastewater.

Transforming salty whey into cleaning chemicals using electrodialysis with bipolar membranes

Large quantities of salty whey are produced during cheese manufacturing, posing an environmental problem. Here the feasibility of electrodialysis with bipolar membranes (EDBM) is evaluated for the first time as a mechanism to transform this saline effluent into sodium hydroxide and hydrochloric acid for reuse within the factory. This work also seeks to find the maximum acid and base concentration that can be achieved. For a pure sodium chloride solution, maximum acid/base concentrations of 3.6 ± 0.2 mol/L and 3.0 ± 0.3 mol/L are achieved using a stack of ten membranes including four bipolar membranes. The effects of proton leakage and water migration limit the generation of higher concentrations. The presence of calcium phosphate also has a negative effect on the EDBM performance, suggesting that pretreatment to remove this impurity is needed. In industrial practice, this pretreatment could be achieved by recycling around 9% of the base produced to precipitate these salts. The use of a partially cyclic operation allows 99% demineralization of pretreated salty whey, with high purity acid/base solutions of concentration near 3.5 mol/L. This work demonstrates EDBM as an effective process for transforming salty whey into chemicals for clean in place and ion exchange resin regeneration.

Soy protein hydrolysate grafted cellulose nanofibrils with bioactive signals for bone repair and regeneration.

TEMPO oxidized cellulose nanofibers (T-CNF) were prepared from cellulose pulp which is extracted from bagasse. Soy protein hydrolysate (SPH) was grafted on T-CNF via amidation of carboxylic groups. Biomineralization was, then, assessed via calcium phosphates (CaP) precipitation in twice-simulated body fluid until formation of a new bioactive material. Protein was efficiently grafted without alteration of morphology and nanofibrils packing as reported by Fourier Transform infrared analysis /X Ray Diffraction /Scanning and Transmission Electron Microscopy / Atomic Force Microscopy. Highly crystalline calcium phosphate deposits - ca. 22.1% - were detected, with a Ca/P ratio equal to 1.63, in agreement with native bone apatite composition. In vitro response of human Mesenchymal Stem Cells confirmed the biocompatibility. No significant differences in terms of cell adhesion were recognized while a significant increase in cell proliferation was detected until 7 days. The presence of calcium phosphates tends to cover the nanofibrillar pattern, inducing the inhibition of cell proliferation and promoting the ex-novo precipitation of mineral phases. All the results suggest a promising use of these biomaterials in the repair and/or the regeneration of hard tissues such as bone.

Supersaturation of calcium citrate as a mechanism behind enhanced availability of calcium phosphates by presence of citrate

Dissolution of amorphous calcium phosphate (ACP) in aqueous citrate at varying pH has been studied with perspective of increasing availability of calcium from sidestreams of whey protein, lactose and/or cheese production or on development of new functional foods. ACP formed as an initial precipitate in 0.10 mol L−1 equimolar aqueous calcium chloride, sodium citrate, and sodium hydrogenphosphate was used as model for mineral residues formed during milk processing. Upon acidification of the ACP suspension by hydrochloric acid decreasing pH from 6.5 to 4.5, the transformations of ACP occurred through an 8 h period of supersaturation prior to a slow precipitation of calcium citrate tetrahydrate. This robust supersaturation, which may explain increased availability of calcium phosphates in presence of citrate, presented a degree of supersaturation of 7.1 and was characterized by precipitation rates for 0.10 mol L−1 equimolar aqueous calcium chloride, sodium hydrogencitrate, and sodium hydrogenphosphate with pH 5.5, and for 0.10 mol L−1 equimolar aqueous calcium chloride, sodium hydrogencitrate, and sodium dihydrogenphosphate with pH 4.1, with a degree of supersaturation of 2.7. The crystallization processes were similar according to Avrami's model with a half-life for precipitation of approximately 5 h independent of the degree of supersaturation. Ion speciation based on measurement of pH, and total concentrations of calcium, phosphate and citrate, and of conductivity and calcium ion activity during precipitation indicates a low driving force for precipitation with calcium citrate complex dominating at pH 5.5 and calcium hydrogencitrate complex dominating at pH 4.1. Calcium hydrogencitrate is suggested to be the species involved in the crystal growth followed by solid state transformation to calcium citrate tetrahydrate.

Novel multifunctional of magnesium ions (Mg++) incorporated calcium phosphate nanostructures

Magnesium ions incorporated calcium phosphate was synthesized by wet chemical route and followed by microwave assisted method. XRD analysis was confirmed that the presence of calcium phosphate (hydroxyapatite). TEM analysis was exhibited rod-like morphology. XRF results were showed the percentage of calcium, phosphate, magnesium and oxygen. There was a slight blue shift observed in magnesium ions based samples. Higher magnesium (0.1 Mg-HAp) was revealed the greater discharging time with capacitance voltage (0.55 V). Magnesium based calcium phosphate was showed prolonged rate of drug release. At higher frequency, the Nyquist plot was showed the electrochemical behavior, however at lower frequency, revealed mass transfer process. Magnesium ions tailor the specific capacitance of calcium phosphate. Therefore, magnesium ions based phosphate samples could be an outstanding multifunctional candidate for drug release and supercapacitor applications.

In vivo study of osteogenerating properties of calcium-phosphate coating on titanium alloy Ti-6Al-4V.

The method of formation of bioactive calcium-phosphate coating on medical titanium alloy Ti-6Al-4V (3.5-5.3% V; 5.3-6.8% Al; balance -Ti) by plasma electrolytic oxidation (PEO) has been developed. Evaluation of osteogenerating properties of the coating at fractures of the shaft of the femur on Wistar line laboratory rats has been performed. It has been established that the calcium-phosphate PEO coating accelerates osteogenesis and promotes the formation of a pronounced periosteal callus in the fracture area. The presence of calcium phosphates in the PEO coating surface layer significantly accelerates the growth of bone tissue on the titanium surface.

On oral calcifications: sialoliths, dental calculi and tonsilloliths

The oral cavity is susceptible to several calcifications such as salivary calculi (sialoliths), dental calculus (tartar) and tonsillar concretions (tonsilloliths). Although several individual studies had been already carried out, a comprehensive morphological and elemental comparison between them is still missing.Sialoliths are most commonly found in the submandibular glands and are composed of regions rich in Ca and P minerals, namely hydroxyapatite, whitlockite and brushite, and regions consisting of organic matter with high-sulphur content. These regions are organized in alternating concentric layers. Several bacterial species have also been identified in sialoliths microstructure showing that infection occurs recurrently throughout the stone formation.Generally, tartar presents an inorganic structure rich in Ca and P minerals, such as brushite, octacalcium phosphate, hydroxyapatite and whitlockite, and an organic matrix, mainly constituted by aerobic bacteria and yeast or just anaerobic bacteria.Tonsilloliths occur most commonly on the crypts of the palatal tonsils and are composed of a mixture of organic matter, namely bacterial cells and epithelial debris, as well as inorganic material rich in Ca and P minerals such as hydroxyapatite. Volatile sulphur compounds produced by anaerobic bacteria are usually associated to these, in general, innocuous structures.The current study involved the ultrastructure and chemical characterization of the calcified structures by scanning electron microscopy (SEM) combined with energy dispersive spectroscopy carried out with a JEOL JSM 7001F instrument with an INCA pentaFetx3 Oxford spectrometer operated at 15 kV. Higher resolution characterization has been performed by transmission electron microscopy (TEM) using a H8100 Hitachi instrument operated at 200 kV. SEM samples were prepared following metallographic procedures, whereas TEM samples were obtained following standard biological sample preparation procedures.The results show that sialoliths present the most complex structure, with a central core surrounded by concentric layers, while tartar and tonsilloliths do not have a distinctive architecture (Figures 1 (a), 2 (a) and 3 (a). At higher magnifications, layered structures, as well as crystals could be found in sialoliths and tartar (Figures 1 (b) and 2 (b). Bacteria were common in all the calcified structures, although in tonsilloliths their abundance is higher (Figure 3 (b)). All calcifications have similar elemental constitution, with Ca and P, indicating the presence of calcium phosphates (Figures 1 (c), 2 (c) and 3 (c). Sulphur was also found associated with the organic matter in sialoliths and tonsilloliths, though the amounts found in the latter were much smaller than initially expected.Based on the similarities found, new correlations between these calcification will be available. For instance, the mineralization process described in tartar can help understand the similar processes occurring in sialoliths and tonsilloliths, while the association between bacteria and sulphur in tonsilloliths can be a clue for their presence in sialoliths.The work was carried out with financial support of the Portuguese Foundation for Science and Technology through PTDC/SAU-ENB/111941/2009 and PEst-OE/CTM-UI0084/2011 grants.

Two step synthesis of CaP/TiO2 nanorod composite coatings with improved protein adsorption

Titanium dioxide (TiO2) nanorods and calcium phosphate (CaP) composite coatings were prepared and characterized. TiO2 nanorod films were grown on titanium substrates via a hydrothermal method. Then, calcium phosphate was deposited into TiO2 nanorod films electrochemically in an aqueous electrolyte containing calcium and phosphorus species. As a result, CaP/TiO2 nanorod coatings were obtained. The amount of calcium phosphate deposited could be controlled through varying temperature, voltage and duration. It was found that both the presence of calcium phosphate and UV treatment could affect the surface wettability of the composite coatings. A bovine serum albumin adsorption test showed that the protein adsorption ability of the composite coatings was also improved with the presence of calcium phosphate and UV treatment. Moreover, the presence of calcium phosphate could promote the deposition of bone-like minerals. It is suggested that such coatings may exhibit promising initial cellular responses and thus be a good alternate for bioactive coatings.

Detection of calcium phosphates in calcium oxalate patinas

Calcium oxalate patinas have been studied on historical monuments for years. In some cases they are associated with calcium phosphate, the presence of which has received contrasted attention and may have been overlooked with the characterisation techniques used. This study addresses the state of the art, the most suitable characterisation techniques for identifying calcium phosphate – the most effective and reliable being SEM-EDS of thin sections – and the shortcomings of other methods such as XRD, FT-IR or optical microscopy. It also describes examples of the presence of calcium phosphate analysed in patinas on Spanish monuments. Calcium phosphates were found to appear in these patinas in different ways and shapes: in small aggregates, in a layer mixed with other patina components, as a uniform layer, or constituting a layer with filaments, or forming a porous layer with a sponge-like texture. These findings add new data for the debate about the origin of calcium oxalate patina. Moreover, a comparison of these with other findings is the basis for a proposal of a new denomination for such patinas.

Study of the biocidal properties of R2O–RO–TiO2–P2O5–R2O3–SiO2 glass ceramic coatings

It is found that the most informative and universal method of determining the biocidal properties of glass coatings is a quantitative method that takes account of the level of growth of biotest microorganisms seeded in liquid nutrients. It is shown that biocidality with respect to the bacteria Escherichia coli and the fungi Candida albicans of glass ceramic and composite glass coatings based on Na2O–CaO–ZnO–TiO2–Al2O3–P2O5–B2O3–SiO2 glass is determined by the presence of calcium phosphates, zinc titanates, the bactericidal filler zinc phosphate in their structure. Depending on their inhibiting action biocidal glass ceramic and composite glass coatings can be used to protect different kinds of steel enamelware.

Abstract 1871: Role of CYP1B1 gene polymorphisms in anticancer drug cytotoxicity as studied on isogenic cell lines

Abstract Cytochrome P450 1B1 (CYP1B1) is found in tumour tissue and is suspected to play a role in oncogenesis and drug resistance. CYP1B1 gene polymorphisms have been associated with the risk of developing lung and other cancers. We have recently shown that one of them (rs1056836, 1697C&amp;gt;G, L432V) was significantly associated with the cytotoxicity of DNA-damaging anticancer drugs in two independent panels of tumour cell lines, the NCI-60 panel and the JFCR-45 panel (Mol Cancer Ther 2010; 9: 3315-21). The present study was aimed at identifying the molecular mechanisms involved in anticancer drug resistance associated with this polymorphic variation. We have cloned the wild-type human CYP1B1 cDNA (1697C) in a lentiviral vector pDesti-pGK and obtained the variant cDNA (1697G) by directed mutagenesis. The two polymorphic variants were then used for the generation of viruses and the infection of cell lines. The CYP1B1 viruses were produced by cotransfection of 293T cells with viral plasmid DNA and either pER51CYP1B1WT-pGK or pER51CYP1B1VAR-pGK plasmid DNA in the presence of calcium phosphate. Cell supernatants containing the virus were harvested 24 h after transfection, filtered through a 0.45 μm membrane and stored at −80°C. Five different cell lines devoid of CYP1B1 expression were infected (COS-1 [Fibroblastic cell line], SW620 [colorectal cancer cell line], CAL27, CAL33 and SQ20B [HNSCC cell lines]). We thus generated five pairs of isogenic cell lines differing only by the polymorphic status of one nucleotide in the CYP1B1 gene. mRNA and protein expression were evaluated by qRT-PCR and western blotting, respectively. The cytotoxicity of a panel of anticancer drugs was evaluated on these cell lines (cisplatin, oxaliplatin, gemcitabine, doxorubicin, etoposide, camptothecin, irinotecan and its active metabolite [SN38]). A systematically higher IC50 was noticed for the cell lines harbouring the variant cDNA as compared to those harbouring the wild-type cDNA, the variant cell lines being 2-3-fold resistant to all agents. These results obtained on isogenic cell lines were in perfect agreement with what could be expected from the study of the cell line panels. The catalytic activity of the two CYP1B1 variants is being studied using ethoxyresorufine O-deethylation. A population of 125 head-and-neck cancer patients treated by chemotherapy in the palliative setting has been prospectively constituted and will be used for the clinical validation of the interest of CYP1B1 genotyping for predicting anticancer drug activity. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 1871. doi:1538-7445.AM2012-1871

Antibacterial glass-composite coatings for protection of special purpose steel panels

It has been established that the most informative and universal method for determination of biocide properties of vitreous coatings is qualitative method that takes into account the growth level of biotest microorganisms inoculated into liquid nutrient media. It is shown, that biocidity of glass-composite coatings on the basis of glasses of Na2O – K2O – CaO – ZrO2 – TiO2 – Al2O3 – P2O5 – B2O3 – SiO2 system is determined by the presence of calcium phosphates in them and depends on the type of bactericide filler. The most effective ones by the action on Pseudomonas aeruginosa bacterium and Aspergillus niger and Candida albicans fungi are zinc titanate and Ag+, to Escherichia coli– only zinc phosphate.

In Vitro studies of bioactive glass/polyhydroxybutyrate composites

Bioactive materials can help bone reparation and regeneration by offering support to bone growth. In vitro studies of bioactive glass/polyhydroxybutyrate composites were carried out to evaluate the influence of the composition on the bioactivity through the presence of calcium phosphate (Ca-P) on the layer formed when the substrates were immerse in simulated body fluid (SBF). The in vitro tests were carried out by soaking the composites bioactive glass/polyhydroxybutyrate 30/70 and 40/60 in SBF. The surface of the composites was analyzed by Scanning Electron Microscopy (SEM) with Energy Dispersive Spectroscopy (EDS) and also via x ray Diffraction (XRD). The solutions were analyzed by Inductively Couple Plasma (ICP). SEM images show a formation of a Ca-P rich layer on surface of composites. XRD results characterized the layer as calcium hydrogen phosphate. Ca/P ratios found via EDS results show a value close to 1.67. According to ICP results, the Ca e P ions are from SBF.

In Vitro Mineralization and Cell Adhesion on Surface Modified Poly (2 - hydroxy ethyl methacrylate-co-methyl methacrylate

Poly(2-hydroxyethyl methacrylate-co- methyl methacrylate) HM, was synthesized by free radical copolymerization, cross-linked with ethylene glycol dimethacrylate and phosphorylated. The phosphate coupling was ensured by ATR spectroscopy. The in vitro mineralization ability of the phosphorylated HM (designated as PHM) was investigated by studying the nucleation and growth of calcium phosphate on its surface by immersing in simulated body fluid (SBF) solution. The coating morphology was studied by SEM and the Ca/P ratio of the coating by EDX analysis. The cell adhesion behaviour of PHM was studied by seeding Human osteosarcoma (HOS) cells for one week followed by SEM analysis along with HM as control. It was observed that HOS cells exhibited biomineralization of calcium phosphate on the surface of HM as well as on PHM with a significantly higher amount on the surface of PHM as observed by von kossa staining method. The results show that PHM is capable of in vitro mineralization under simulated physiological condition, promotes cell adhesion by providing an excellent cell friendly surface and it exhibits biomineralization of calcium phosphate in presence of HOS cells.

Calcium Phosphates and Human Beings

This article describes the general importance of calcium phosphates for human beings. The basic information on the structure and chemical properties of the biologically relevant calcium phosphates is summarized. Basic facts on the natural occurrence and the industrial use of natural calcium phosphates are discussed. Fundamental details on the presence of calcium phosphates in major calcified tissues (bones and teeth) of humans and mammals, as well as on biomaterials made of calcium phosphates are discussed. The article will be of value for chemistry teachers for expansion of their general background and point the students' attention to the rapidly growing topic of bone-substituting biomaterials.

Corrosion behavior of titanium in the presence of calcium phosphate and serum proteins

The effect of calcium phosphate surface deposit and the surface adsorption of the serum proteins, bovine serum albumin (BSA) and fibrinogen, on the corrosion resistance and electrochemical behavior of (cp)titanium in phosphate buffer saline solution (pH 7.4) was investigated at physiological temperature, 37 °C, using electrochemical impedance spectroscopy and dc electrochemical polarization techniques. The formation of calcium phosphate deposit on the Ti surface decreased both the corrosion rate at the open circuit potential (OCP) and the anodic reaction current in the high anodic potential range (>2.6 V). Addition of BSA significantly moved the OCP towards a more negative (cathodic) potential and inhibited the cathodic corrosion reaction, but did not significantly change the corrosion resistance at the OCP. Addition of fibrinogen showed a similar, but less pronounced effect than BSA. The possible mechanisms leading to these observed effects are discussed.

Calcium enhances the transfection potency of stabilized plasmid–lipid particles

Previous work from this laboratory has shown that plasmid DNA can be encapsulated in small (70-nm-diameter) stabilized plasmid–lipid particles (SPLP) that consist of a single plasmid encapsulated within a bilayer lipid vesicle. SPLP preferentially transfect tumor tissue following intravenous administration. Although the levels of transgene expression in vivo are greater for SPLP than can be achieved with naked DNA or complexes, they are lower than may be required for therapeutic benefit. In the present work we examine whether Ca 2+ can enhance the transfection potency of SPLP. It is shown that Ca 2+ can enhance SPLP transfection potency in bovine hamster kidney cells by 60- to 100-fold when treated in serum containing medium and an additional 60-fold when serum is absent for the initial 10 min of the transfection period. When cells are treated with SPLP in the presence of Ca 2+, there is a fivefold increase in intact plasmid in the cell. It is also shown that this Ca 2+ effect involves the formation of calcium phosphate precipitates; however, these precipitates are not directly associated with the SPLP plasmid DNA. The ability of calcium phosphate to facilitate delivery of other macromolecules without direct association is also demonstrated by the release of large-molecular-weight dextrans from endosomal/lysosomal compartments in the presence of calcium phosphate. Finally, it is shown that, unlike naked DNA, SPLP transfection potency in the presence of calcium phosphate is not affected by nuclease activity.