Determination of proteins at nanogram levels by a resonance light-scattering technique with tetra-substituted sulphonated aluminum phthalocyanine

This is the first report on the determination of proteins with tetra-substituted sulphonated aluminum phthalocyanine (AlS(4)Pc) by resonance light-scattering (RLS). At pH 3.0, the weak RLS of AlS(4)Pc can be enhanced by the addition of proteins. Based on this, a novel quantitative method has been developed for the determination of proteins in aqueous solutions. Under optimal conditions, the linear ranges of the calibration curves were 0.050-2.0 mug ml(-1) for both human serum albumin (HSA) and human r-IgG. The detection limits were 12.7 ng ml(-1) for HSA and 16.1 ng ml(-1) for human r-IgG. The method has been applied to the analysis of total protein in human serum samples collected from the hospital and the results were in good agreement with those reported by the hospital, which indicates that the method presented here is not only sensitive, simple, but also reliable and suitable for practical applications.

[Determination of heavy metal by AAS in railway rock-cut slope soil]

Heavy metal contents in railway rock-cut slope soil have directly influenced ecosystem on rock-cut slope and eco-envi- ronment safety of farmland nearby. In the study heavy metal Pb, Cd, Zn, Cu and Mn was determined by AAS in railway rock-cut slope and control soil samples on Cheng-Da Railway crossing purple soil in Sichuan province. The results showed that Pb and Mn were significantly higher in rock-cut soil than in control soil, that is 29.7%-35.4%, while Cd, Zn and Cu were similar in both soils.

In vitro culture and characterization of alveolar bone osteoblasts isolated from type 2 diabetics

In order to understand the mechanisms of poor osseointegration following dental implants in type 2 diabetics, it is important to study the biological properties of alveolar bone osteoblasts isolated from these patients. We collected alveolar bone chips under aseptic conditions and cultured them in vitro using the tissue explants adherent method. The biological properties of these cells were characterized using the following methods: alkaline phosphatase (ALP) chemical staining for cell viability, Alizarin red staining for osteogenic characteristics, MTT test for cell proliferation, enzyme dynamics for ALP contents, radio-immunoassay for bone gla protein (BGP) concentration, and ELISA for the concentration of type I collagen (COL-I) in the supernatant. Furthermore, we detected the adhesion ability of two types of cells from titanium slices using non-specific immunofluorescence staining and cell count. The two cell forms showed no significant difference in morphology under the same culture conditions. However, the alveolar bone osteoblasts received from type 2 diabetic patients had slower growth, lower cell activity and calcium nodule formation than the normal ones. The concentration of ALP, BGP and COL-I was lower in the supernatant of alveolar bone osteoblasts received from type 2 diabetic patients than in that received from normal subjects (P < 0.05). The alveolar bone osteoblasts obtained from type 2 diabetic patients can be successfully cultured in vitro with the same morphology and biological characteristics as those from normal patients, but with slower growth and lower concentration of specific secretion and lower combining ability with titanium than normal ones.

Effects of local delivery of bFGF from PLGA microspheres on osseointegration around implants in diabetic rats

OBJECTIVE

Diabetes mellitus may impair bone healing after dental implant placement. The objective of this study was to evaluate the effects of the local delivery of basic fibroblast growth factor (bFGF) from poly(lactide-co-glycolide) (PLGA) microspheres on osseointegration around titanium implants in diabetic rats.

STUDY DESIGN

The bFGF-PLGA microspheres were prepared by the W/O/W double-emulsion solvent evaporation method. A total of 20 rats were used to create diabetic animal models by giving them a high-fat and high-sugar diet and a low-dose streptozotocin intraperitoneal injection. Titanium implants were planted into the tibias of the diabetic rats and into 10 normal rats. Microspheres were loaded on the surfaces of the implants in the bFGF intervention group before they were placed into the rats. After 4 or 8 weeks, the tibias containing the implants were removed and embedded with resin. Uncalcified tissue slices were prepared to compare osseointegration.

RESULTS

At 4 weeks, the bone-implant contact rate in the diabetic control group was less than that in the control group and the bFGF intervention group (P < .05). At 8 weeks, the results among the 3 groups were similar to those at 4 weeks.

CONCLUSIONS

The local delivery of bFGF from PLGA microspheres into areas around titanium implants may improve osseointegration in diabetic rats.

Abstract 2330: Citicoline Is A Strong Pro-angiogenic Molecule And Protects Brain Endothelial Cells From Apoptosis After Stroke

Background and purposes - Citicoline is neuroprotective agent used in stroke patients. Citicoline induces angiogenesis i n vitro ; however, the molecular mechanisms induced by citicoline have not been fully investigated. The present study was designed to investigate the key signalling mechanisms through which citicoline modulates angiogenesis-associated with stroke recovery.

Methods - In vitro angiogenesis assays: migration (Bodyen chamber, a chemotaxis assay and wound recovery), proliferation and differentiation into tube-like structures in Matrigel TM as well as spheroid development assays were carried out using human brain microvessel endothelial cells (HBMECs). Western blotting was performed on the protein extraction from HBMEC stimulated with citicoline. Citicoline signalling pathway was studied using a phospho-protein screening array performed by Kinexus. A Staurosporin/calcium ionophore-induced apoptosis assay was performed by seeding HBMEC on the glass coverslips. Cells were pre-incubated with citicoline and the apoptosis was induced by addition of the ionophore or staurosporin. Cells were examined by microscoy and/or stained using propidium iodide and Hoechst stain solution and then counted under fluorescence microscope. Transient MCAO was carried out on Sprague Dawley rats (n=4 per group) with and without citicoline treatment (1000mg/Kg) applied at the time of occlusion and subsequently every 3 days until euthanasia (21 days). Vascularity of the stroke-affected regions was examined with antibodies recognising the microvessels (CD34) and active cells (CD105).

Results - Citicoline presented no mitogenic and chemotactic effects on HBMEC; however, it significantly increased wound recovery, the formation of tube-like structures in Matrigel TM -with a stronger effect than FGF-2, and enhanced spheroid development and sprouting. Citicoline induced the expression of ERK-1/2, known to be involved in last step of signalling pathways of angiogenesis. Kinexus results showed an over-expression of ASK-1, HER2, IRS-1 and Jun and inhibition of Hsp27, Integrin alpha4, MEK1 (MAP2K1) and Histone H2B proteins. Knock-down of IRS-1 with targeted siRNA inhibited the pro-angiogenic effects (sprouting and tube-formation) of citicoline in HBMECs. The percentage of surviving cells was higher in the presence of citicoline after inducing apoptosis. Histology of infarcted regions showed that citicoline significantly increased the numbers of new active (CD105-positive) microvessels.

Conclusion - The findings demonstrate both a pro-angiogenic and protective effect of citicoline on HBMECs in vitro and following MCAO in vitro. Additionally, this molecule may play a key role in the modulation of angiogenesis thereby and ultimately, improving tissue function, revascularisation and neuronal survival after ischaemic stroke.

UV light emitting transparent conducting tin-doped indium oxide (ITO) nanowires

Multifunctional single crystalline tin-doped indium oxide (ITO) nanowires with tuned Sn doping levels are synthesized via a vapor transport method. The Sn concentration in the nanowires can reach 6.4 at.% at a synthesis temperature of 840 °C, significantly exceeding the Sn solubility in ITO bulks grown at comparable temperatures, which we attribute to the unique feature of the vapor-liquid-solid growth. As a promising transparent conducting oxide nanomaterial, layers of these ITO nanowires exhibit a sheet resistance as low as 6.4 Ω/[Symbol: see text] and measurements on individual nanowires give a resistivity of 2.4 × 10(-4) Ω cm with an electron density up to 2.6 × 10(20) cm(-3), while the optical transmittance in the visible regime can reach ∼ 80%. Under the ultraviolet excitation the ITO nanowire samples emit blue light, which can be ascribed to transitions related to defect levels. Furthermore, a room temperature ultraviolet light emission is observed in these ITO nanowires for the first time, and the exciton-related radiative process is identified by using temperature-dependent photoluminescence measurements.

[Construction and expression of recombinant human serum albumin-EPO fusion protein]

OBJECTIVE To construct the recombinant plasmid pCI-HLE encoding human serum album-EPO (HSA-EPO) fusion protein and to express it in CHO cell.

METHODS

The cDNA encoding human serum album and EPO were amplified by PCR, and then spliced with the synsitic DNA fragment encoding GS (GGGGS), by overlap PCR extension to form LEPO. After BamH I digestion, the HSA and LEPO was ligated to generate the fusion HSA-EPO gene and was then cloned into the expression vector pCI-neo to generate the recombinant plasmid pCI-HLE. The plasmid pCI-HLE was transfected into CHO cell by liposome protocol. Then, the recombinant cells were screened by G418 and identified by PCR and Western blot. Expression of fusion protein was evaluated by Enzyme Linked Immunosorbent Assay (ELISA).

RESULTS

Restrictive enzymes digestion and DNA sequencing revealed that HSA-EPO fusion gene was cloned into expression vector pCI-neo successfully. PCR and Western blot analysis confirmed that the fusion gene was integrated in the genome of CHO cells and expressed successfully. The HSA-EPO production varied from 86 Iu/(mL x 10(6) x 72 h) to 637 IU/(mLx 10(6) x 72 h).

CONCLUSION

The results confirmed that HSA-EPO fusion gene can be expressed in the CHO cells, with EPO immunogenicity, which could serve as foundation for the development of long-lasting recombinant HSA-EPO protein.

Growth and antioxidant system of Escherichia coli in response to microcystin-RR

Microcystins are a kind of cyclic hepatoxins produced by many species of cyanobacteria. The toxic effects of microcystins on animals and plants have been well studied. However, the reports about the effects of microcystins on microbial cells are very limited. In present paper, Escherichia coli was undertaken to determine the effect of microcystin-RR. These results suggested that microcystin-RR could prolong the growth of E. coli when exposed to high concentrations of microcystin-RR and cause the accumulation of ROS and induce the oxidant stress for a short time. The antioxidant system protects E. coli from oxidative damage.

Zinc finger protein A20 promotes regeneration of small-for-size liver allograft and suppresses rejection and results in a longer survival in recipient rats

BACKGROUND

Small-for-size liver allografts without immunosuppression have decreased survival compared with full-for-size grafts for the concomitant regeneration-induced accelerated rejection. This study was designed to examine the effect of zinc finger protein A20 on liver allograft regeneration and acute rejection using a high responder rat model (DA-->Lewis) of 30% partial liver transplantation.

MATERIALS AND METHODS

Adenovirus carrying the full length of A20 was introduced into liver grafts by ex vivo perfusion via the portal vein during preservation, physiological saline (PS), and empty Ad vector rAdEasy served as controls; then small-sized liver transplants were performed. Liver graft regeneration was assessed, as well as graft rejection, hepatocyte apoptosis, nuclear factor kappa B activation, and intercellular adhesion molecule-1 mRNA expression in liver graft sinusoidal endothelial cells (LSECs), infiltration of liver graft infiltrating mononuclear cells (LIMCs), and the subproportion of NK and NKT cells, activity of liver graft NK-like cells, interferon gamma (IFN-gamma) production, and animal survival.

RESULTS

Ex vivo transfer of the A20 gene resulted in overexpression of A20 protein in LSECs and hepatocytes 24 h after partial liver transplantation. Regeneration of the small-sized liver allograft was augmented by A20 overexpression, the DNA synthesis of hepatocytes on d 4 post-transplant was increased in A20 group compared with PS and rAdEasy groups (P < 0.01). Hepatocyte apoptosis was inhibited by A20 (P < 0.001). On d 4 after transplantation, histological examination revealed a more exiguous cellular infiltration and mild rejection in A20 group but a more vigorous cellular infiltration in the sinusoidal area and more severe rejection in PS and rAdEasy group. Nuclear factor kappa B activation and intercellular adhesion molecule-1 mRNA expression in LSECs were suppressed by A20 overexpression. Flow cytometry analysis showed a marked down-regulation of LIMCs number by A20, including more prominent decrease in the subproportion of NK and NKT cells. Activity of liver graft NK-like cells, IFN-gamma mRNA expression in LIMCs, and serum IFN-gamma protein level were also suppressed by A20 overexpression (P < 0.05), respectively. Survival days of A20 rats were longer than those of PS rats and rAdEasy rats (P < 0.01), whereas survival days of rAdEasy rats were shorter than those of PS rats (P < 0.01).

CONCLUSIONS

These data suggest that A20 overexpression could effectively promote small-sized liver allograft regeneration, suppress rejection, and prolong survival of recipient rat. These effects of A20 could be related to an inhibition of LSECs activation, suppression of infiltration of LIMCs, and the subpopulations such as NK and NKT cells into liver graft, and inhibition of hepatocyte apoptosis.

[Line intensities of upsilon2 perpendicular band and the change of intensities with temperature for H12C14N]

The total internal partition sums (TIPS) were calculated for H12C14N with the product approximation. For rotational partition sums Q(rot), the centrifugal distortion corrections were taken into account. The calculation method for the vibrational partition sums Q(vib) is the harmonic oscillator approximation. The line intensities of upsilon2 perpendicular band (0110-0000 transition) of H12C14N were calculated at normal temperatures and several high temperatures by using the calculated partition functions and experimental transition moment squared and Herman-Waills factor coefficients. Results showed that our line intensities data at 296 and 3 000 K are in excellent agreement with the data in HITRAN, which provide a strong support for the calculations of partition function and line intensity at high temperature. Thereby, the line intensities and spectral simulations of upsilon2 perpendicular band at the higher temperatures 4 000 and 5 000 K were presented and the chang in line intensities with the temperature was discussed. For those transitions corresponding to rotational quantum number J > or = 32 (including P, Q and R branch), the line intensities increase when temperature gradually increase from 296 K. The line intensities are up to the largest at around 1000 K and then weaken rapidly. For J < 32 (also including P, Q and R branch), the line intensities are the largest at 296 K and then weaken rapidly as temperature gradually increase.

[Optimized thread pitch design and stress analysis of the cylinder screwed dental implant]

OBJECTIVE

To determine the optimal thread pitch for an experimental cylinder implant in Ansys Work-bench Design Xplorer environment.

METHODS

Finite element models of segment jaw bone with a V-shaped thread implant were created. The thread pitch (P) was set from 0.5 mm to 1.6 mm. The maximum Equivalent stresses (EQV stresses) in jaw bone and in implant were evaluated.

RESULTS

Under axial load, the amplification of maximum EQV stresses in cortical bone, cancellous bone and implant were 7.1%, 123.4% and 28.7% respectively. Under bucco-lingual load, the amplification of maximum EQV stresses in cortical bone, cancellous bone and implant were 2.8%, 28.8% and 14.9% respectively. When P exceeded 0.8 mm, the response curve curvature of maximum EQV stresses in jaw bone and in implant to P was ranged from -1 to 1.

CONCLUSION

Stresses in cancellous bone are more sensitive to thread pitch than in cortical bone. Stresses in jaw bone under axial load are easier affected by thread pitch than under bucco-lingual load. Thread pitch plays a greater role in protecting dental implant under axial load than under bucco-lingual load. Thread pitch exceed 0.8 mm should be the optimal design in a cylinder implant, but oversized pitch should be avoided too.

Effects of multidrug resistance, antisense RNA on the chemosensitivity of hepatocellular carcinoma cells

BACKGROUND

Multidrug resistance is a major obstacle in cancer chemotherapy. We examined whether the antisense RNA of multidrug resistance gene 1 (mdr1) could reverse multidrug resistance in the human hepatocellular carcinoma (HCC) cell line SMMC7721/ADM.

METHODS

The recombinant adenoviruses pAdEasy-GFP-ASmdr1 product was produced by the adenoviral vector AdEasy system, which can express antisense RNA against the mdr1 gene. Following that, the recombinant adenovirus was transfected into the P-glycoprotein-producing multidrug resistance cell line, SMMC7721/ADM human HCC cells resistant to adriamycin (ADM) and daunorubicin (DNR). In order to investigate the reversal of multidrug resistance phenotype, we measured the expression of mdr1 mRNA by RT-PCR and the production of P-glycoprotein by flow cytometry. The sensitivities for ADM and DNR SMMC7721/ADM cells were examined by [3-(4, 5-dimethylthi-azol-2-yl)-2,5 diphenyl-terazolium bromide] (MTT) analysis.

RESULTS

The low-level expression of mdr1 mRNA and P-glycoprotein production were observed in parental sensitive cells SMMC/7721 in addition to the overexpression of mdr1 mRNA and P-glycoprotein in SMMC7721/ADM cells. The transfection of antisense-RNA into SMMC7721/ADM cells resulted in decreases of mdr1 mRNA and P-glycoprotein, but increase of drug sensitivities. The sensitivities of transfected SMMC7721/ADM cells to ADM and DNR in IC50 reduced by 31.25% and 62.96% respectively.

CONCLUSIONS

Mdr1 antisense RNA can increase the sensitivities of SMMC7721/ADM cells to anticancer drug by decreasing the expression of the mdr1 gene and inhibiting P-glycoprotein expression. This strategy may be applicable to cancer patients with P-glycoprotein mediated multidrug resistance.

Nationwide monitoring of polychlorinated biphenyls and organochlorine pesticides in sediments from coastal environment of Korea

To assess the organochlorine contamination in the Korean marine environment, a nationwide monitoring study was conducted. A total of 138 surface sediments, covering the whole Korean coast, were collected and analyzed. Organochlorine compounds (OCs) were widely distributed in the Korean coastal environment, with PCB and DDT contamination being particularly prevalent. The overall concentrations of PCBs, DDTs, HCHs, CHLs, and HCB in surface sediments were in the range of 0.088-199ngg(-1) (median value: 1.56ngg(-1)), 0.006-135ngg(-1) (0.68ngg(-1)), not detected (ND)-5.46ngg(-1) (0.32ngg(-1)), ND-3.26ngg(-1) (0.14ngg(-1)), and ND-2.59ngg(-1) (0.05ngg(-1)), respectively. The southeastern coast was found to be highly contaminated. Overall contamination status of Korean coastal sediments with regard to OCs is lower than that of USA. With the exception of highly industrialized sites, Korean coastal areas in general showed similar OC concentrations to those of other Asian countries. There was a significant correlation between distributions of most organochlorine contaminants with each other. OC contamination is closely related to shipping and industrial activities. Of the 7 sites categorized as highly polluted, 4 are in a harbor zone. Adverse effects to benthic communities are expected at the levels of OC contamination observed from harbor and industrial areas.

[Influence of bicortical anchorage on the natural frequencies of dental implant]

OBJECTIVE

To investigate the influences of bicortical anchorage on values of natural frequencies of dental implants utilizing the 3-dimensional finite element analysis.

METHODS

Using the commercial code of Solidworks, 3-D models of a screw-shaped dental implant and a mandibular bone segment were generated. After the 3-D implant-bone complex was meshed by ABAQUS software, effects of bicortical anchorage on the buccolingual and axial first-order natural frequencies of the implant were computed.

RESULTS

Bicortical anchorage increased both the buccolingual and axial natural frequencies remarkably. As the bicortical anchorage got deeper, the frequencies correspondingly got higher.

CONCLUSION

Bicortical anchorage can increase the buccolingual and axial primary stability of dental implants.

Construction of the recombinant adenovirus vector carrying antisense multidrug resistance gene

BACKGROUND

Multidrug resistance proteins serve as transporters for chemical drugs in human malignancies. The objective of this study was to construct a homologous recombinant adenovirus carrying a reversal fragment of multidrug resistance gene 1 (mdr1) gene cDNA sequence.

METHODS

The fragment of the mdr1 gene from the plasmid pHaMDR1-1 carrying the whole human mdr1 cDNA sequence was inserted reversely into the shuttle plasmid pAdTrack-CMV of adenoviral vector system AdEasy. The homologous recombination process was taken place in E. coli BJ5183 with the backbone plasmid pAdEasy-1. After packaging in 293 cells, recombinant adenoviral plasmid was generated. The recombinant adenoviral plasmid was identified by polymerase chain reaction (PCR), restriction endonucleases digest, DNA sequence analysis and fluorescence microscopic photograph, respectively.

RESULTS

The recombinant adenovirus pAdEasy-GFP-ASmdr1 was successfully constructed and identified by PCR, restriction digest, and sequencing with strong green fluorescence expression in fluorescence microscopic photograph.

CONCLUSIONS

The recombinant adenoviral mdr1 vector would introduce the antisense mdr1 gene into the human multidrug resistance hepatocellular cell line effectively, which would provide an experimental basis to study the multidrug resistance in human hepatocellular carcinoma.

[Construction of recombinant adeno-associated virus vectors carrying double gene of antisense multidrug resistance-associated protein and antisense multidrug resistance]

OBJECTIVE

To construct a recombinant adeno-associated virus vectors carrying double gene of antisense multidrug resistance-associated protein (MRP) and antisense multidrug resistance (MDR1) for use in studying the gene therapy to reverse the multidrug resistance (MDR) in hepatocellular carcinoma (HCC).

METHODS

The 500 bp fragment (mrp) of MRP cDNA 5' region and the 600 bp fragment (mdr1) of MDR1 cDNA 5' region were amplified through polymerase chain reaction (PCR), and then they were linked to a combined gene fragment (mrp+mdrl) by overlapping technique. The combined gene fragment(mrp+mdrl) was cloned reversely into the multiple cloning site (MCS) of the expression plasmid pAAV-IRES-hrGFP in AAV Helper-Free System to construct the recombinant expression plasmid pAAV-IRES-hrGFP-(mrp + mdr1)AS. The packaging cell line (HEK 293 cell) was co-transfected with the pAAV-IRES-hrGFP-(mrp+mdr1)AS together with the control plasmid pAAV-RC and pHelper in AAV Helper-Free System by means of lipofectamine. The recombinant adeno-associated virus vector : rAAV2-(mrp+mdr1)AS carrying the double gene of antisense multidrug resistance-associated protein (MRP)and antisense multidrug resistance (MDR1) was packaged. Then the viral titer was checked by GFP.

RESULTS

The recombinant adeno-associated virus vector : rAAV2-(mrp + mdr1)AS carrying antisense MRP and antisense MDR1 was constructed successfully, the strong green fluorescence was observed in HEK 293 cells under a fluorescence microscope. The viral titer was 2.5 X 10(6) efu/ml.

CONCLUSION

The rAAV2-(mrp+mdr1)AS thus constructed could introduce the antisense MRP and antisense MDR1 into the human drug-resistant hepatocellular cell line effectively, which might provide a sound basis for the mechanisms and reversal methods of the multidrug resistance in HCC.

[Recombinant adenovirus vectors carrying antisense MMP2 inhibit invasion of HCC cells in vitro]

OBJECTIVES

To construct a recombinant adenoviral vector carrying antisense matrix metalloproteinase-2 (MMP2) and to study its inhibitory effects on the invasiveness and migratory capacity of hepatocellular carcinoma (HCC) cell line HepG2 in vitro.

METHODS

Total RNA was extracted from HCC. Then a 500 bp fragment at the 5' end of the human MMP2 cDNA sequence was synthesized by polymerase chain reaction (PCR) and was reversely inserted into the multiclone site (MCS) of the shuttle plasmid pAdTrack-CMV. With the resultant plasmid and the backbone plasmid pAdEasy-1, the homologous recombination took place in the E.coli BJ5183 and the recombinant adenoviral plasmid carrying the antisense MMP2 gene was constructed. The adenovirus (Ad-MMP2AS) was packaged and amplified in the HEK 293 cells and the viral titer was checked by GFP. Using the Boyden chamber model, the influence of Ad-MMP2AS on the invasion ability of HepG2 cells was determined in vitro.

RESULTS

The recombinant adenovirus vector carrying antisense MMP2 was constructed successfully and a strong green fluorescence was observed in HepG2 cells under a fluorescence microscope. The viral titer was 1 x 10(8); Ad-MMP2AS can effectively inhibit the penetrating capacity of HepG2 cells through Matrigel in vitro.

CONCLUSION

The recombinant adenovirus with antisense MMP2 can effectively inhibit the invasiveness and migratory capacity of HepG2 in vitro and may have potential in treating HCC.

Real-time studies on microalgae under microgravity

Using remote sensing technique, we investigated real-time Nostoc sphaeroides Kütz (Cyanobacterium) in Closed System under microgravity by SHENZHOU-2 spacecraft in January 2001. The experiments had 1 g centrifuges in space for control and ground control group experiments were also carried out in the same equipments and under the same controlled condition. The data about the population growth of Nostoc sp. of experiments and temperature changes of system were got from spacecraft every minute. From the data, we can find that population growth of Nostoc sp. in microgravity group was higher than that of other groups in space or on ground, even though both the control 1 g group in space and 1 g group on ground indicated same increasing characteristics in experiments. The growth rate of 1.4 g group (centrifuged group on ground) was also promoted during experiment. The temperature changes of systems are also affected by gravity and light. Some aspects about those differences were discussed. From the discussion of these results during experiment, it can be found that gravity is the major factor to lead to these changes.