Health risks from PAHs and potentially toxic elements in street dust of a coal mining area in India.

Polycyclic aromatic hydrocarbons (PAHs) and potentially toxic elements (PTEs) (Ba, Zn, Pb, Cu, Cr, Ni, As, Co) were determined in the road dusts of a coal mining area (Dhanbad, India) to assess their content and potential human health risks. Dust samples were collected from sign boards of the heavy traffic road connecting Dhanbad and Sindri. The total PAHs (∑PAHs, all values in mg/kg) content in the road dust samples varied from 3.98 to 13.1, with carcinogenic PAHs content of 14.8-34.4% of the ∑PAHs. Phenanthrene (2.72), fluorene (0.715) and pyrene (0.575) are the major PAHs. Principal component analysis revealed that these PAHs are probably originated from pyrogenic (coal combustion and traffic emission) and petrogenic (coal dust, tyre and road particles) sources. Among the PTEs, the mean content was higher for Ba (293 mg/kg) followed by Zn (224), Pb (128), Cu (52.6), Cr (45.2), Ni (22.0), As (17.5) and Co (8.11). The overall pollution load index varied from 0.43 to 1.0. Source analysis showed that PTEs in the road dust of the study site were derived from traffic emission (Zn, Fe, Mn, Co and Pb), coal dust (Cr, As and Ni) and soil (K, Mg, Ba, Sr and Ca). In general, the PTEs are lower, but the PAHs contents were elevated in the road dust samples. Although the exposure risks from PTEs are low, the risk to children (expressed as hazardous quotient) for As and Pb is near to the permissible limit of 1.0. Cancer risk from PAHs for adult (4.8 × 10-6) and child (5.3 × 10-6) has exceeded the acceptable limit of 10-6.

Clinical evaluation of immediate implants using different types of bone augmentation materials.

BACKGROUND: The immediate placement of implants into fresh extraction socket has proven to be a safe and predictable procedure. However, there is lack of scientific evidence regarding the healing pattern and osseointegration associated with immediate implants especially with different grafting materials. METHODS: A total of 30 patients male or female, with a mean age of 23.1 years ± 6.0 in the age group of 18-38 years, each having at least one tooth indicated for extraction (either maxillary or mandibular anterior teeth) were selected and randomly divided in to two groups. 30 Implants (Xive(®) friadent, Germany) were placed into fresh extraction sockets during this study. Two types of graft materials namely Dembone(®) (freeze-dried bone allograft) for group A and G-Bone(®) (modified hydroxyapatite) for group B were used. After implant placement all implants were evaluated clinically and radiographically at baseline, 3 months, 6 months, 9 months and 12 months. All clinical and radiographic parameters were subjected to statistical analysis. Intragroup comparisons were made with paired 't' test and intergroup comparisons with unpaired 't' test (P > 0.05 NS, ≤0.05 S, ≤0.01 HS). RESULT: During the 1-year interval, no implant was lost and the mean bone level at the implants was maintained or even improved. CONCLUSION: Immediate restoration of single tooth implants placed in fresh extraction sockets could be considered a valuable option to replace a missing tooth. The graft materials used in both groups have been found to be equally effective.

Fate of radionuclides present in Indian fly ashes on its application as soil ameliorant.

Natural radioactivity depends primarily on the geological and geographical conditions, and appears at different levels in the soils. Coal contains various organic and inorganic substances including trace quantities of the naturally occurring radionuclides, which are of human health concern. The combustion of coals releases natural radioactive elements in the form of their oxides to the environment. In view of the current researches on fly ash (FA) applications as soil ameliorants, the present study deals with the presence of the natural radionuclides ((226)Ra, (232)Th and (40)K) in the coal ash and their mobilisation through the amendment of coal ash to the soil and crop produce. The study shows the variation in the content of radionuclides in soil, FA and crop produce depending on types of soil and FA, mobilisation of the radionuclides from soil/FA to the plant and interactions between radionuclides and soil, etc. The content of the radionuclides in the soil, FA and crop produce is within the permissible limits.

Management of mine spoil for crop productivity with lignite fly ash and biological amendments.

Long-term field trials using lignite fly ash (LFA) were carried out in rice crops during the period 1996-2000 at Mine I, Neyveli Lignite Corporation, Tamil Nadu. LFA, being alkaline and endowed with an excellent pozzolanic nature, silt loam texture, and plant nutrients, has the potential to improve the texture, fertility, and crop productivity of mine spoil. The rice crops were the first, third, fifth, and sixth crops in rotation. The other crops, such as green gram (second) and sun hemp (fourth), were grown as green manure. For experimental trials, LFA was applied at various dosages (0, 5, 10, 20, 50, 100, and 200 t/ha), with and without press mud (10 t/ha), before cultivation of the first crop. Repeat applications of LFA were made at the same dosages in treatments of up to 50 t/ha (with and without press mud) before cultivation of the third and fifth crops. Press mud, a lightweight organic waste product from the sugar industry, was used as an organic amendment and source of plant nutrients. Also, a recommended dosage of chemical fertilizer, along with gypsum, humic acid, and biofertilizer as supplementing agents, was applied in all the treatments, including control. With one-time and repeat applications of LFA, from 5 to 20 t/ha (with and without press mud), the crop yield (grain and straw) increased significantly (p < 0.05), in the range from 3.0 to 42.0% over the corresponding control. The maximum yield was obtained with repeat applications of 20 t/ha of LFA with press mud in the third crop. The press mud enhanced the yield in the range of 1.5-10.2% with various dosages of LFA. The optimum dosage of LFA was 20 t/ha for both one-time and repeat applications. Repeat applications of LFA at lower dosages of up to 20 t/ha were more effective in increasing the yield than the corresponding one-time applications of up to 20 t/ha and repeat applications at 50 t/ha. One-time and repeat applications of LFA of up to 20 t/ha (with and without press mud), apart from increasing the yield, evinced improvement in the texture and fertility of mine spoil and the nutrient content of crop produce. Furthermore, some increase in the content of trace and heavy metals and the level of gamma-emitters in the mine spoil and crop produce was observed, but well within the permissible limits. The residual effect of LFA on succeeding crops was also encouraging in terms of eco-friendliness. Beyond 20 t/ha of LFA, the crop yield decreased significantly (p < 0.05), as a result of the formation of hardpan in the mine spoil and possibly the higher concentration of soluble salts in the LFA. However, the adverse effects of soluble salts were annulled progressively during the cultivation of succeeding crops. A plausible mechanism for the improved fertility of mine spoil and the carryover or uptake of toxic trace and heavy metals and gamma-emitters in mine spoil and crop produce is also discussed.

Changes in HNK-1 epitope and collagen type IX in the aqueous humour of patients with pseudoexfoliation syndrome.

PURPOSE: To investigate alterations in the proteoglycan (PG) and glycosaminoglycan (GAG) content of the aqueous humour in patients with pseudoexfoliation syndrome (PEX). MATERIALS AND METHODS: Aqueous humor samples were obtained during cataract surgery from nineteen patients bearing PEX features and twenty-three age-matched normal controls. Protein and IgG were quantified densitometrically after their electrophoretic separation. Collagen type IX, 3-sulphoglucuronic acid (HNK-1 epitope), biglycan and heparan sulphate proteoglycans were detected in Western and dot blots by using specific monoclonal antibodies (MAbs). The immunochemical analysis was performed in native aqueous humour or after degradation of the glycosaminoglycans with chondroitinases. RESULTS: Degradation of the samples with chondroitinases ABC, AC and B revealed that, in the aqueous humour from PEX eyes, collagen type IX and biglycan had a more dermatan sulphate than did normal eyes. In addition, more HNK-1 epitope was observed in PEX eyes, which after similar enzymatic treatment was found to be located mainly in dermatan sulphate sequences. 3-sulphoglucuronic acid was a constituent of the GAG chains of the collagen type IX. We found that the electrophoretic mobility of the bands of collagen type IX and HNK-1 epitope was exactly the same in the aqueous humour of normal and PEX samples; both migrated as four bands at 120, 113, 92.6 and 56 kDa. The PGs bearing heparan sulphate were found only in normal samples. Other PGs were not detected. CONCLUSIONS: Because no significant difference was observed in the concentration of albumin and IgG in PEX and normal samples, the blood-aqueous barrier was probably not significantly compromised in PEX patients with cataract but without open-angle glaucoma. The results support the hypothesis that the pathogenesis of PEX can be linked to disturbed metabolism of GAGs and PGs.

Alterations in conjunctival cytology and tear film dysfunction in patients with beta-thalassemia.

PURPOSE: Patients with beta-thalassemia (beta-tha) represent a group with lifelong transfusion-dependent anemias. This study aimed to describe the conjunctival changes and tear film parameters in these patients. METHODS: A total of 52 patients (104 eyes) with beta-tha major and 22 normal control subjects (44 eyes) were studied during 1999 through 2000. Tear film break-up time (BUT), Schirmer test, rose Bengal staining, and cytologic evaluation of the conjunctival epithelium were performed in all subjects. The Papanicolaou and May-Grümwald-Giemsa staining procedures were performed on all smears. Patients and control subjects were compared for tear function parameters and conjunctival changes. RESULTS: The BUT, Schirmer test, and rose Bengal staining values were significantly lower (P < 0.001) in beta-tha patients than in control subjects. Keratinized cells were observed in conjunctival samples in 41% of patients, with a decrease in the number of goblet cells per slide in 64% of patients. In 9% of beta-tha patients, there were a slightly greater number of inflammatory cells than in control eyes. CONCLUSION: Ocular surface disorder of these patients was characterized by goblet cell loss and conjunctival squamous metaplasia. Our findings were correlated positively with the variable age. Epithelial damage by toxic reaction and disorder of tear quality and quantity are implicated as important factors in the pathogenesis of the ocular surface disease in beta-tha patients.

An extensive system of extravascular smooth muscle cells exists in the choroid of the rabbit eye.

We investigated the structural organization of the choroid especially with regard to the presence of extravascular smooth muscle (EVSM) cells in albino rabbits. The eyes were fixed by intracardiac perfusion and processed for light, confocal, and electron microscopy. An unlabeled monoclonal antibody against alpha-actin of smooth muscle and a horseradish-peroxidase-conjugated secondary antibody were used for immunodetection of smooth muscle actin by light microscopy. For confocal microscopy, whole mount choroids were immunostained with a fluorescein isothiocyanate-conjugated (FITC) antibody. Our investigations revealed that the choroidal vessels are enveloped by bundles of EVSM. In contrast to the circular orientation of the smooth muscle cells of the tunica media of the choroidal vessels, the cells of the EVSM system were oriented longitudinally along the external surface of the vessel wall. The EVSM cells were strongly immunopositive for smooth muscle alpha-actin and exhibited a green fluorescence of the FITC-labeled anti-alpha-actin antibody. Individual cells were elongated and spindle-shaped, had the usual ultrastructural features of smooth muscle cells and, in places, were organized as 20 layers. EVSM cells were present throughout the thickness of the choroid, but not between the fenestrated endothelial lining of the choriocapillaris and Bruch's membrane, and extended from the optic nerve to the ciliary body where they merged with the ciliary muscles. Based on the three dimensional organization, immunoreactivity, and cellular and subcellular features of the EVSM system as well as information in the literature, we hypothesize that, functionally, this system, in conjunction with the choroidal vasculature, contributes to the myogenic control of choroidal blood flow and tissue volume, and also affects the intraocular pressure as well as the refractive and accommodative state of the eye.

Synthesis, molecular modeling and QSAR studies in chiral 2,3-disubstituted-1,2,3,4-tetrahydro-9H-pyrido(3,4-b)indoles as potential modulators of opioid antinociception.

In view of coexistence of opioid and cholecystokinin (CCK) in the brain areas concerned with pain processing, some semirigid racemic and chiral analogues of a potent CCK receptor antagonist (benzotript) have been synthesized and tested for their modulatory role on opioid antinociception, which may be mediated by CCK-B receptor. Some of these compounds, 3e, 3g, 3h, 4a, 4b and 4h, exhibited antinociceptive potentiation comparable to benzotript and proglumide. In order to identify the essential chemical structural features important for this potentiation, molecular modeling and quantitative structure activity relationship (QSAR) studies have been carried out in the S and R enantiomers of some of these semi-rigid compounds. The 3D-biophore models, common to all molecules of the training set have been derived. These models with superimposition (match value >0.25) depicted three biophoric sites one each for, pi/hydrophobic interactions, hydrogen bonding and ionic interactions among the phenyl/pyrrole ring, indole nitrogen, amidic oxygen, pyridyl nitrogen and lone pair of amidic oxygen. The total hydrophobicity and S absolute stereochemistry are found to positively contribute to potentiation of antinociception induced by morphine and the resulting quantitative pharmacophoric model with good correlation is found to well describe the observed activity.

Maximum likelihood estimation for longitudinal data with truncated observations.

We obtain maximum likelihood estimates of the parameters when the observations on the response variable in a repeated measures design are truncated above a cutpoint. The maximum likelihood equations are solved iteratively using an EM-like procedure. It is observed that these estimates have smaller mean squared error than recently proposed iterative weighted least-squares estimates. The results are applied to data arising from a study of dioxin elimination in Air Force veterans. Published in 2000 by John Wiley & Sons, Ltd.

Modulation of pre-mRNA splicing and protein production of fibronectin by TGF-beta2 in porcine trabecular cells.

PURPOSE: To determine the effect of transforming growth factor (TGF)-beta2 on the pre-mRNA splicing pattern of fibronectin, as well as on the synthesis and secretion of this glycoprotein by porcine trabecular cells. METHODS: First-passage porcine trabecular cells were rendered quiescent and incubated in culture medium containing 15% newborn calf serum, in serum-free culture medium containing either activated TGF-beta2 (concentration range: 0.2-2.7 ng/ml) or activated TGF-beta1 (1 ng/ml), or in serum-free medium alone (untreated control samples). For investigation of alternative splicing, total RNA was extracted, and reverse transcription-polymerase chain reaction (RT-PCR) was performed with primer pairs located in exons flanking the exon (extra domain [ED]A, or EDB) that undergoes alternative splicing. The polymerase chain reaction (PCR) products were verified by Southern hybridization and quantified by using laser densitometry. The percentage of EDA-positive (+) isoforms was compared with that of the EDB+ isoforms among the groups. To study the effect of TGF-beta2 on the synthesis and secretion of fibronectin, total protein was extracted from both cultured cells and conditioned medium, Western blot analysis was performed using an anti-fibronectin antibody, and the products were quantified by laser densitometry. Immunocytochemical analysis was also performed on cultured trabecular cells to detect fibronectin. RESULTS: Fibronectin mRNA that was detected in untreated serum-starved control cells was EDA and EDB negative. Incubation of trabecular cells in medium containing 1 ng/ml TGF-beta2, 1 ng/ml TGF-beta1, or 15% newborn calf serum induced the expression of EDA+ and EDB+ mRNA to varying degrees. At concentrations of 0.2, 0.5, 1.5, and 2.7 ng/ml, TGF-beta2 increased the concentration of fibronectin by 2-, 3-, 3.8-, and 5-fold in the conditioned medium, and by 3-, 3.7-, 4-, and 4.3-fold in the cell extracts, respectively. The trabecular cells treated with TGF-beta2 exhibited strong immunoreaction for fibronectin, whereas the cells incubated in serum-free medium showed only minimal immunoreactivity. CONCLUSIONS: Our results demonstrate that TGF-beta2 and TGF-beta1 modified the alternative splicing pattern of fibronectin pre-mRNA and enhanced the synthesis and secretion of this extracellular matrix molecule by trabecular cells in a dose-dependent fashion. These findings indicate a mechanism whereby TGF-beta2, the concentration of which is elevated in aqueous humor of patients with primary open-angle glaucoma, contributes to the increased deposition of extracellular matrix molecules in the outflow pathway.

Synthesis and SAR studies of 1-substituted-n-(4-alkoxycarbonylpiperidin-1-yl)alkanes as potent antiarrhythmic agents.

Synthesis and SAR studies of the title compounds have resulted in the identification of structural and physicochemical parameter (Vw) contributing for antiarrhythmic activity. Among the two most promising compounds 3a & 3b, the 3a has shown antiarrhythmic activity comparable to quinidine.

Pharmacokinetics of TCDD in veterans of Operation Ranch Hand: 15-year follow-up.

Using multiple measurements from serum collected over 15 yr (in 1982, 1987, 1992, and 1997), the half-life of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) in 97 veterans of Operation Ranch Hand, the Air Force unit responsible for the aerial spraying of Agent Orange in Vietnam, was estimated. The potential influences of age, percent body fat, and changes in percent body fat on the half-life estimate were also examined. The elimination rate of TCDD for these veterans was 0.0915 per year with 95% confidence interval 0.0844 to 0.0986 per year; the corresponding half-life estimate was 7.6 yr with 95% confidence interval 7.0 to 8.2 yr. The elimination rate decreased significantly with increasing body fat, but not with age or relative changes in percent body fat.

Corticosteroids and glaucoma risk.

Corticosteroids (glucocorticoids), used frequently as potent anti-inflammatory agents, increase the risk of glaucoma by raising the intraocular pressure (IOP) when administered exogenously (topically, periocularly or systemically) and in certain conditions of increased endogenous production (e.g. Cushing's syndrome). Approximately 18 to 36% of the general population are corticosteroid responders. This response is increased to 46 to 92% in patients with primary open-angle glaucoma (POAG). Patients over 40 years of age and with certain systemic diseases (e.g. diabetes mellitus, high myopia) as well as relatives of patients with POAG are more vulnerable to corticosteroid-induced glaucoma. The association of corticosteroid-induced ocular hypertension in other conditions which are considered as risk factors for glaucoma (racial origins, hypertension, migraine, vasospasm) is likely but not fully established. The proposed mechanism of corticosteroid-induced glaucoma includes morphological and functional changes in the trabecular meshwork system and is similar to the pathogenesis of POAG. Trabecular cells exposed to corticosteroids in vitro show endoreplication of nuclei, an increase in cell size and excessive production of an approximately 56kD glycoprotein, identified as myocilin and transcribed by the GLC1A gene. Induction of ocular hypertension after corticosteroid administration depends on the specific drug, the dose, the frequency of administration and the corticosteroid responsiveness of the patient. The risk of corticosteroid-induced glaucoma can be minimised with judicious use of corticosteroids, as well as education of patients and medical practitioners. New treatment modalities include modified steroids and nonsteroidal anti-inflammatory agents that will have less effect on the elevation of IOP.

Levels of 2,3,7,8-tetrachlorodibenzo-p-dioxin in 1,302 unexposed Air Force Vietnam-era veterans.

We summarize the distribution of 2,3,7,8-tetrachlorodibenzo-p-dioxin (dioxin) in 1,302 Air Force veterans who serve as controls in a 20-year prospective epidemiologic study of health and exposure to herbicides and their dioxin contaminant in Air Force veterans of Operation Ranch Hand, the unit responsible for aerial spraying of Agent Orange and other herbicides in Vietnam. We present statistics summarizing the dioxin distribution overall and by stratum of age and body mass index of these veterans. The average dioxin measurement was 4.23 and the standard deviation was 2.53 parts per trillion. With 95% confidence, 99% of the distribution is less than or equal to 10.4 parts per trillion.

Increased level of vascular endothelial growth factor in aqueous humor of patients with neovascular glaucoma.

PURPOSE: This study aimed to quantitate and compare the concentration of vascular endothelial growth factor (VEGF) in aqueous humor samples from patients with neovascular glaucoma (NVG), primary open-angle glaucoma (POAG), and cataract, as well as in serum samples of healthy human subjects. METHODS: The authors collected aqueous humor samples by using their previously published technique of limbal paracentesis. The authors determined the concentration of VEGF by using a competitive enzyme immunoassay system and four-parameter logistic curve fitting and performed statistical analysis by using the Mann-Whitney-Wilcoxon test. RESULTS: The authors detected VEGF in 12 of 12 samples from patients with NVG (mean +/- standard error of the mean, 29.267 +/- 7.350 ng/ml), 15 of 28 samples from patients with POAG (0.726 +/- 0.204 ng/ml), 4 of 20 aqueous humor samples from patients with cataract (0.257 +/- 0.043 ng/ml), and 16 of 16 human serum samples (20.246 +/- 1.568 ng/ml). The mean concentration of VEGF in aqueous humor of patients with NVG was 40- and 113-fold higher than that in patients with POAG and cataract, respectively, and the difference was statistically significant (P < 0.01). The VEGF level in patients with POAG was elevated compared with that in patients with cataract (P < 0.05). Although the mean concentration of VEGF in aqueous humor of patients with NVG was approximately 1.45-fold higher than that in serum, the difference was not significant (P > 0.05). CONCLUSION: The authors' findings show that patients with NVG had a significantly increased level of VEGF in the aqueous humor and implicate VEGF as an important factor in the pathogenesis of intraocular neovascularization in these patients. The authors discuss the possible role of the ciliary epithelium, in addition to retina, in the production of VEGF and the complementary function of basic fibroblast growth factor and other growth factors.

Maximum (Max) and Mid-P confidence intervals and p values for the standardized mortality and incidence ratios.

The authors present algorithms to compute the confidence interval for a Poisson parameter (lambda) and the p value for testing the hypothesis that lambda is equal to a constant, which can be used to make inferences about the standardized mortality ratio and the standardized incidence ratio. The p value and confidence interval always agree, despite the discrete nature of the Poisson distribution. The authors also give simple equations to compute numeric approximations of the confidence limits that do not require the use of any probability distributions. An example based on data arising from a study of cancer incidence is given.

Quantitative characterization of high- and low-affinity binding sites for basic fibroblast growth factor on trabecular cells of the eye.

By radioligand binding followed by Scatchard analysis, we characterized and quantitated the specific binding sites for bFGF on cultured trabecular meshwork cells obtained from freshly enucleated porcine eyes. We detected two binding sites: 1.67 x 10(4) +/- 5.75 x 10(2) high-affinity receptors per cell with a Kd of 33.4 +/- 7.90 pM, and 1.70 x 10(4) +/- 7.57 x 10(5) low-affinity binding sites per cell with a Kd of 3.84 +/- 1.41 nM. At low concentrations of 125I-bFGF (< 1.50 ng ml-1), binding was primarily determined by the high-affinity receptors and, at high concentrations (> 2.50 ng ml-1), binding was dependent on the low-affinity binding sites. By phase-contrast time-lapse video micrography and sequential photomicrography, we demonstrated that at a concentration of 1 ng ml-1, bFGF significantly stimulated the rate of mitosis of the trabecular meshwork cells in G0-phase compared with control cultures maintained in serum-free medium alone. Treatment with higher concentrations of bFGF did not reveal more potent effects on these cells. Our findings demonstrate that trabecular meshwork cells do possess low- and high-affinity receptors for bFGF and that bFGF induces these cells in vitro to re-enter the cell cycle. Because the low-affinity interactions of 125I-bFGF were reduced by 75% following pretreatment of the trabecular meshwork cells with heparinase, these sites represent cell-associated heparin-like molecules and heparan sulfate proteoglycans, and may control the bioavailability of bFGF to ocular tissues. Heparinase treatment also resulted in a 30% reduction in high-affinity binding, which may be secondary to the decreased low-affinity binding. This finding agrees with the well-established scheme for bFGF-receptor interaction. We conclude that bFGF at the concentration present in aqueous humor is capable of stimulating the mitotic activity of trabecular meshwork cells in vitro, suggesting a possible paracrine role of aqueous humour bFGF in vivo. The results obtained in this study, together with our previous findings on bFGF mRNA expression by trabecular meshwork cells and protein deposition in this tissue, also indicates that trabecular cells of the eye may utilize bFGF by an autocrine mechanism.

Age-related changes in trabecular cells in vitro.

The changes in the morphology and the amounts of selected extracellular matrix proteins in serially passaged porcine trabecular cells cultured from young animals (age range, 4-6 months) were investigated. After 4 weeks incubation, trabecular cells in primary confluent cultures had a flattened elongated profile, whereas the cells in secondary or tertiary cultures, after an additional 4 to 8 weeks incubation, respectively, were epithelioid in shape. Time-lapse micrography of the passaged cells revealed membrane ruffling at the cell periphery, but sparse cell movement. No mitotic events took place in either the secondary or tertiary cultures for 24 hr prior to harvesting the cells. No remarkable differences were observed in the total polypeptide profile of primary, secondary or tertiary cells analysed by SDS gel electrophoresis and silver staining. However, laser densitometry of immunoblots treated with antibodies against type VI collagen, thrombospondin, fibronectin, and laminin demonstrated that, compared to primary cultures of trabecular cells, the amount of type VI collagen was elevated 20.5-fold in tertiary cultures, thrombospondin 6-fold, and fibronectin 5-fold, but laminin was not detectable. Because aging trabecular cells in vitro exhibit specific biochemical characteristics that are comparable to those known to occur in the human trabecular meshwork in vivo, the present method provides a model for the investigation of age-related changes in this tissue at the cellular level under defined and controlled conditions.