Differential growth of sensory neurons in vitro in presence of dermis and epidermis. A quantitative time-lapse analysis

The influence of dermal and epidermal cells on the growth of nerve fibres from chick embryo sensory neurons was investigated in vitro. A previous quantitative analysis showed that the growth of nerve fibres is profoundly modified in the close vicinity of epidermis. This change is mainly characterized by erratic trajectories of nerve fibres resulting from numerous lateral displacements of the growth cones. In contrast, no such behaviour is observed far away from the epidermis or in the presence of dermis. In this latter case, neurites exhibit a straighter direction of extension. These observations suggest that the epidermis exerts some kind of control on the establishment of nerve fibre pattern in the dermis.     

The effect of age on the recognition thresholds of three sweeteners: sucrose,saccharin and aspartame

It iS believed that people's sensitivity to taste declines with age but the evidence is inconclusive. This study was designed to test the hypothesis that taste recognition thresholds (TRTs) for sweetness are higher in older than in younger individuals, using groups of 16 younger subjects (18–30) and 16 older subjects (60–85). Three test substances were used: sucrose, aspartame and saccharin. A questionnaire recorded variables which might have affected TRTs, but data failed to show any trend that might have biased the principle variate-age. There was a significant alteration with age of recognition thresholds, at least for sucrose and saccharin. The differences between the groups for the three sweeteners were due to the fact that all the very sensitive subjects were young. None of the older subjects had particularly poor discrimination: all but one had TRTs within the range of younger subjects. Although there are age-related taste changes, they are much less dramatic than commonly occurs with other senses, such as sight and hearing. The findings of this study have implications for institutional catering and the dietary management of older people using non-sugar sweeteners.     

UVA-induced oxidative damage in retinal pigment epithelial cells after H2O2 or sparfloxacin exposure

Retinal impairment is one of the leading causes of visual loss in an aging human population. To explore a possible cause for retinal damage in the human population, we have monitored DNA oxidation in human retinal pigment epithelial (RPE) cells after exposure to hydrogen peroxide (H₂O₂) or the quinolone antibacterial sparfloxacin. When H₂O₂- or sparfloxacin-exposed cells were further exposed to ultraviolet A (UVA) irradiation, oxidative damage to the DNA of these cells was greatly increased over baseline values. This RPE+pharmaceutical-UVA cell system was developed to mimic in vivo retinal degeneration, seen in mouse studies using quinolone and UVA exposure. DNA damage produced by sparfloxacin and UVA in RPE cells could be remedied by the use of antioxidants, indicating a possible in vivo method for prevention or minimization of retinal damage in humans This revised version was published online in July 2006 with corrections to the Cover Date.     

Pleural malignant mesothelioma, genetic susceptibility and asbestos exposure

Pleural malignant mesothelioma (MM) is a rare but extremely aggressive cancer. The limited impact of standard therapeutic treatments on survival rates makes the identification of factors that increase the individual risk a leading priority. The high proportion of cases explained by exposure to asbestos has guided intervention policies to an effective ban of this compound from our environment. However, MM cannot be solely attributed to this agent, and the role of predisposing factors and their interaction with asbestos exposure is increasingly studied. The role of mEH, GSTM1, GSTT1, NAT2, and CYP1A1 genotypes in modulating susceptibility to MM was examined in a case-control study of 80 subjects with a confirmed diagnosis of MM and 255 controls. Subjects with low mEH activity showed a significantly increased risk of MM (OR, 2.51; 95% CI, 1.11-5.68). The association was stronger in the group with low asbestos exposure (OR, 7.83; 95% CI, 0.98-62.60). A significant increased risk of MM was also found in NAT2 fast acetylators (OR, 1.74; 95% CI, 1.02-2.96). The presence of synergisms between genotypes, i.e., mEH and NAT2 (LRT for heterogeneity p<0.023), mEH and GSTM1 (LRT p<0.061), and NAT2 and GSTM1 (LRT p<0.049), combined with the interaction observed with exposure to asbestos, suggests the presence of gene-environment and gene-gene interactions in the development of MM, although the size of the study group does not allow to draw clearcut conclusions. Since genetic polymorphisms can also modify the extent of genetic damage occurring in subjects exposed to carcinogens, we measured the frequency of micronuclei in peripheral blood lymphocytes of a subgroup of MM cases. The limited number of cases (28) did not allow to observe significant effects. In conclusion, these results strengthen the hypothesis that individual susceptibility to MM can be modulated by the interaction between polymorphic genes involved in the metabolism and the intensity of asbestos exposure.     

Adaptor protein ARH is recruited to the plasma membrane by low density lipoprotein (LDL) binding and modulates endocytosis of the LDL/LDL receptor complex in hepatocytes

ARH is a newly discovered adaptor protein required for the efficient activity of low density lipoprotein receptor (LDLR) in selected tissues. Individuals lacking ARH have severe hypercholesterolemia due to an impaired hepatic clearance of LDL. It has been demonstrated that ARH is required for the efficient internalization of the LDL-LDLR complex and to stabilize the association of the receptor with LDL in Epstein-Barr virus-immortalized B lymphocytes. However, little information is available on the role of ARH in liver cells. Here we provide evidence that ARH is codistributed with LDLR on the basolateral area in confluent HepG2-polarized cells. This distribution is not modified by the overexpression of LDLR. Conversely, the activation of the LDLR-mediated endocytosis, but not the binding of LDL to LDLR, promotes a significant colocalization of ARH with LDL-LDLR complex that peaked at 2 min at 37 degrees C. To further assess the role of ARH in LDL-LDLR complex internalization, we depleted ARH protein using the RNA interference technique. Twenty-four hours after transfection with ARH-specific RNA interference, ARH protein was depleted in HepG2 cells by more than 70%. Quantitative immunofluorescence analysis revealed that the depletion of ARH caused about 80% reduction in LDL internalization. Moreover, our findings indicate that ARH is associated with other proteins of the endocytic machinery. We suggest that ARH is an endocytic sorting adaptor that actively participates in the internalization of the LDL-LDLR complex, possibly enhancing the efficiency of its packaging into the endocytic vesicles.     

The Sodium Bicarbonate Cotransporter (NBCe1) Is Essential for Normal Development of Mouse Dentition

Proximal renal tubular acidosis (pRTA) is a syndrome caused by abnormal proximal tubule reabsorption of bicarbonate resulting in metabolic acidosis. Patients with mutations to the SLC4A4 gene (coding for the sodium bicarbonate cotransporter NBCe1), have pRTA, growth delay, ocular defects, and enamel abnormalities. In an earlier report, we provided the first evidence that enamel cells, the ameloblasts, express NBCe1 in a polarized fashion, thereby contributing to trans-cellular bicarbonate transport. To determine whether NBCe1 plays a critical role in enamel development, we studied the expression of NBCe1 at various stages of enamel formation in wild-type mice and characterized the biophysical properties of enamel in NBCe1^−/− animals. The enamel of NBCe1^−/− animals was extremely hypomineralized and weak with an abnormal prismatic architecture. The expression profile of amelogenin, a known enamel-specific gene, was not altered in NBCe1^−/− animals. Our results show for the first time that NBCe1 expression is required for the development of normal enamel. This study provides a mechanistic model to account for enamel abnormalities in certain patients with pRTA.     

Bronchial malondialdehyde DNA adducts, tobacco smoking, and lung cancer

Tobacco smoking is a major risk factor for lung cancer causing, among other effects, oxidative stress and lipid peroxidation. Malondialdehyde (MDA)-DNA adducts can be induced by direct DNA oxidation and by lipid peroxidation. We measured the relationship between bronchial MDA-DNA adducts and tobacco smoking, cancer status, and selected polymorphisms in 43 subjects undergoing a bronchoscopic examination for diagnostic purposes. MDA-DNA adducts were higher in current smokers than in never smokers (frequency ratio (FR) = 1.51, 95% confidence interval (CI) 1.01-2.26). MDA-DNA adducts were also increased in lung cancer cases with respect to controls, but only in smokers (FR = 1.70, 95% CI 1.16-2.51). Subjects with GA and AA cyclin D1 (CCND1) genotypes showed higher levels of MDA-DNA adducts than those with the wild-type genotype (FR = 1.51 (1.04-2.20) and 1.45 (1.02-2.07)). Lung cancer cases with levels of MDA-DNA adducts over the median showed a worse, but not statistically significant, survival, after adjusting for age, gender, and packyears (hazard ratio = 2.48, 95% CI 0.65-9.44). Our findings reinforce the role of smoking in lung carcinogenesis through oxidative stress. Subjects who carry at least one variant allele of the CCND1 gene could accumulate DNA damage for altered cell-cycle control and reduced DNA repair proficiency.     

Differentiation of pure chick embryo epidermis grown in primary serum-free culture

The differentiation of precocious embryonic epidermis in serum-free primary culture was analyzed by light and electron microscopic methods. Explants of 7-day chick embryo epidermis were grown on collagen or poly-L-lysine substrates in the absence of dermal mesenchyme. The serum substitute consisted of a mixture of insulin, transferrin, putrescine and seleneous acid together with (or without) Nerve Growth Factor. These culture conditions were shown to support proliferation, growth and development (evaluated using morphological criteria) of the epidermal explants up to 4-5 days; during this period, the epidermis underwent stratification; well-developed desmosomes as well as tonofilaments were formed and the epidermis achieved a morphology close to that of 10-11 day epidermis in ovo. However long-term survival of the explants was not obtained as cellular death, starting on day 5, progressively led to the necrosis of most parts of the explant. This morphological study demonstrates that the early phases of epidermal growth and maturation can occur to some extent in the virtual absence of dermal elements and serum factors. Chick embryo epidermal cells may thus possess the intrinsic ability to go through, at least for short periods in vitro, their differentiation programme. Then, at the onset of epidermal keratinization (12 days in ovo), they require specific exogenous factors to fully differentiate in vitro.     

A novel double nucleotide substitution in the HMG box of the SRY gene associated with Swyer syndrome

We describe a novel double nucleotide substitution in the SRY gene of a 46,XY female with gonadal dysgenesis or Swyer syndrome. The SRY sequence was analysed by both the single-strand conformational polymorphism assay and direct DNA sequencing of products from the polymerase chain reaction. A double nucleotide substitution was identified at codon 18 of the conserved HMG box motif, causing an arginine to asparagine amino-acid substitution. The altered residue is situated in the high mobility group (HMG)-related box of the SRY protein, a potential DNA-binding domain. Since the mutation abolishes one HhaI recognition site, the results were confirmed by HhaI restriction mapping. No other mutations were found in the remaining regions of the gene. The corresponding DNA region from the patient’s brother was analysed and found to be normal. We conclude that the SRY mutation in the reported XY female occurred de novo and is associated with sex reversal. Received: 16 December 1996 / Accepted: 5 May 1997