Modulation of gut microbiota: The effects of a fruits and vegetables supplement

The consumption of an optimal amount of fruits and vegetables is known to improve physical fitness and physiological body functions. Healthy eating habits, including intake of fruits and vegetables, can modify gut microbiota. This study aimed to demonstrate the effectiveness of a formulated fruit and vegetable supplement (FVS) in modulating the antioxidant capacity and the gut microbiota composition. We enrolled 30 healthy volunteer subjects, matched for age, gender, BMI, and smoking habits, and randomized them into the FVS and the placebo (PLA) groups. Among the serum vitamins, the folic acid level was significantly higher (p = 0.001) in the FVS group than in the PLA group, whereas the vitamin B2 level was significantly higher in the PLA group than in the FVS group (p = 0.028). The antioxidant capacity, measured by using the oxygen radical absorbance capacity (ORAC) method, was also slightly higher in the FVS group than in the PLA group but did not reach statistical significance. The dietary intake, assessed by 24-h recalls, did not show any significant changes after the supplementation in both the groups. The gut microbiome composition, measured by 16S rDNA sequencing, showed no difference in both alpha and beta diversities, whereas the LEfse analysis revealed a microbial shift after the treatment, with a decreased abundance of the genus Ruminococcus from the Lachnospiraceae family (p = 0.009), and the unclassified genus from the family Erysipelotrichaceae (UC36, p = 0.003) in the FVS group compared with the PLA group (confirmed by SIAMCAT analysis, AUC = 74.1%). With a minor effect, the genus Faecalibacterium and unclassified genus and family from the order Lactobacillales (UC31) were also increased in the FVS group compared with the PLA group (p = 0.0474, p = 0.0352, respectively). SCFA measurement by gas chromatography–mass spectrometry showed an increased level of 2-methylbutyrate in the FVS group compared with the PLA group (p = 0.0385). Finally, the Spearman correlation analysis showed that in the FVS group, the genus Faecalibacterium positively correlated with 2-methyl butyrate (p = 0.040). In the PLA group, none of the significant bacteria correlated with either SCFA or serum biomarkers. The network analysis confirmed the positive correlation between genus Faecalibacterium and 2-methyl butyrate. We can conclude that the FVS in healthy individuals modified the gut microbiota composition and metabolites, and it can potentially contribute to reduce the pro-inflammatory response along with the antioxidant capacity.

Impact of the environment on the health: From theory to practice

The Erice 56 Charter titled "Impact of the environment on the health: from theory to practice" was unanimously approved at the end of the 56th course of the "International School of Epidemiology and Preventive Medicine G. D'Alessandro" held from 3rd to November 7, 2019 in Erice - Sicily (Italy) and promoted by the Study Group of "Environment and Health" of the Italian Society of Hygiene, Preventive Medicine and Public Health. The course, that included lectures, open discussions and guided working groups, was aimed to provide a general training on epidemiological and toxicological aspects of the environmental health impact, to be used by public health professionals for risk assessment, without forgetting the risk communications. At the end of the course 12 key points were agreed among teachers and students: they underlined the need of specific training and research, in the perspective of "One Health" and "Global Health", also facing emerging scientific and methodological issues and focusing on communication towards stakeholders. This Discussion highlight the need to improve knowledge of Health and Environment topic in all sectors of health and environmental prevention and management.

Nutritional management of lactose intolerance: the importance of diet and food labelling

Worldwide, 70% of the adult population has limited expression of lactase enzyme with a wide variation among different regions and countries. Lactase deficiency may lead to lactose intolerance (LI). Depending both on the amount of lactose ingested and on the lactase activity, people who suffer from lactose malabsorption might experience numerous gastrointestinal and extra-intestinal symptoms and manifestations. Treatment of LI mainly consists of reducing or eliminating lactose from the diet until the symptoms disappear as well as supplementing lactase, and inducing colon microbiome adaptation by probiotics. Cow’s milk is one of the major source of calcium and several other vitamins and minerals. Thus, a complete exclusion of dairy products may favor the development of bone diseases such as osteopenia and osteoporosis. Therefore, the dietetic approach has a crucial role in the management of LI patients. Additionally, the use of lactose and milk-derived products in non-dairy products (e.g., baked goods, breakfast cereals, drinks, and processed meat) has become widespread in the modern industry (the so-called “hidden lactose”). In this regard, a strict adherence to the lactose-free diet becomes challenging for LI patients, forced to continuous check of all products and food labels. In fact, lactose-free product labeling is still controversial. Considering that nowadays a specific cut-off value establishing “lactose-free” labeling policy is lacking and that there is no universal law regulating the production and commercialization of “delactosed” products, identification of specific safe and suitable products with a well-recognized lactose-free logo might help consumers. This narrative review aims to identify the dietary management for lactose intolerant people, avoiding symptoms and nutrients deficiencies, helped by the use of specific labelling to guide them to choose the safer product on the market.

The benefits of nutritional counselling for improving sport performance

BACKGROUND

It is well known that the synergy between physical activity and healthy eating habits is an important combination for the achievement of different objectives. However, recent studies in the literature focused mainly on the effect of this synergy on weight loss or different non communicable diseases. In this study, we aimed to investigate the effect of healthy eating, based on the Mediterranean diet, on physical performance of kickboxers and runners.

METHODS

Forty athletes were recruited from the University Sports Center of Bergamo. Twenty participants practiced kickboxing, an High Energy Expenditure Rate sport, whereas twenty subjects practiced half marathon, a typical High Energy Expenditure Volume sport. Kickboxers and runners were randomly divided into two sub-groups of ten subjects each: one was the control group (CG) and one the nutritional counselling group (NCG), in which subjects were instructed to follow a nutritional counselling.

RESULTS

At the baseline, runners started with greater VO2max and lower resting metabolic rate compared to kickboxers. After three months of controlled diet and training, kickboxers in NCG improved their results in Counter Movement Jump (CMJ) Test (P=0.015) and squat (P=0.012). Moreover, athletes had a decrease in body fat percentage (P=0.008). Runners in NCG, had a significant VO2max (P=0.007) increase and a reduction in body fat percentage (P=0.002). They also showed an increase of squat (P=0.012) and CMJ test (P=0.024).

CONCLUSIONS

Significant benefits were achieved in all groups of athletes, but results were maximized by training plus nutritional counselling.

Interaction between polyphenols intake and PON1 gene variants on markers of cardiovascular disease: a nutrigenetic observational study

Background

Paraoxonase 1 (PON1) gene polymorphisms and polyphenols intake have been reported independently associated to lipid profile and susceptibility to atherosclerosis and cardiovascular disease. However, the interaction between these factors remains to be investigated. We performed an observational nutrigenetic study to examine whether the interaction between polyphenols and anthocyanins intake and PON1 genetic variants can modulate biomarkers of cardiovascular health in an Italian healthy population.

Methods

We recruited 443 healthy volunteers who participated in the EC funded ATHENA project (AnThocyanin and polyphenols bioactive for Health Enhancement through Nutritional Advancement). Data collection included detailed demographic, clinical, dietary, lifestyle, biochemical and genetic data. Polyphenols and anthocyanins intake was measured by 24 h dietary recall repeated three times a year in order to get seasonal variations. We tested the interaction between 18 independent tagging SNPs in PON1 gene and polyphenols intake on HDL, LDL, cholesterol, triglycerides and atherogenic index of plasma.

Results

Without considering the genetic background, we could not observe significant differences in the lipid profile between high and low polyphenols and anthocyanins intake. Using a nutrigenetic approach, we identified protective genotypes in four independent polymorphisms that, at Bonferroni level (p ≤ 0.0028), present a significant association with increased HDL level under high polyphenols and anthocyanins intake, compared to risk genotypes (rs854549, Beta = 4.7 per C allele; rs854552, Beta = 5.6 per C allele; rs854571, Beta = 3.92 per T allele; rs854572, Beta = 3.94 per C allele).

Conclusions

We highlight the protective role of genetic variants in PON1 towards cardiovascular risk under high polyphenols and anthocyanins consumption. PON1 variants could represent novel biomarkers to stratify individuals who might benefit from targeted dietary recommendation for health promotion and strategies of preventive medicine.

Electronic supplementary material

The online version of this article (doi:10.1186/s12967-016-0941-6) contains supplementary material, which is available to authorized users.

Dietary style and acid load in an Italian population of calcium kidney stone formers

BACKGROUND AND AIMS

Animal protein intake may cause an acid load that predisposes individuals to stones by influencing calcium and citrate excretion. These associations were not confirmed in recent studies. Therefore the present study was aimed to compare acid load of diet in stone formers and controls.

METHODS AND RESULTS

Participants to the study were 157 consecutive calcium stone formers and 144 controls. Diet was analyzed in these subjects using a software that evaluated nutrient intake from a three-day food intake diary. This software also estimated the potential renal acid load (PRAL, mEq/day). Twenty-four-hour urine excretion of ions and citrate was measured in stone formers. Stone former diet had lower intake of glucose, fructose, potassium and fiber and higher PRAL in comparison with controls. The multinomial logistic regression analysis showed that stone risk decreased in association with the middle and the highest tertiles of fiber intake and increased in association with the highest tertile of PRAL. The linear multiple regression analysis showed that calcium excretion was associated with the sodium excretion and that citrate excretion was associated with the PRAL and animal protein intake in stone formers.

CONCLUSION

Our findings suggest that stone formers may undergo a greater dietary acid load sustained by a low vegetable intake and base provision. Dietary acid load does not appear as the main determinant of calcium excretion, but may promote stone risk by decreasing citrate excretion. Sodium intake may predispose to stones by stimulating calcium excretion.

Functional and molecular defects of hiPSC-derived neurons from patients with ATM deficiency

Loss of ataxia telangiectasia mutated (ATM) kinase, a key factor of the DNA damage response (DDR) pathway, causes the cancer predisposing and neurodegenerative syndrome ataxia-telangiectasia (A-T). To investigate the mechanisms of neurodegeneration, we have reprogrammed fibroblasts from ATM-null A-T patients and normal controls to pluripotency (human-induced pluripotent stem cells), and derived from these neural precursor cells able to terminally differentiate into post-mitotic neurons positive to >90% for β-tubulin III+/microtubule-associated protein 2+. We show that A-T neurons display similar voltage-gated potassium and sodium currents and discharges of action potentials as control neurons, but defective expression of the maturation and synaptic markers SCG10, SYP and PSD95 (postsynaptic density protein 95). A-T neurons exhibited defective repair of DNA double-strand breaks (DSBs) and repressed phosphorylation of ATM substrates (e.g., γH2AX, Smc1-S966, Kap1-S824, Chk2-T68, p53-S15), but normal repair of single-strand breaks, and normal short- and long-patch base excision repair activities. Moreover, A-T neurons were resistant to apoptosis induced by the genotoxic agents camptothecin and trabectedin, but as sensitive as controls to the oxidative agents. Most notably, A-T neurons exhibited abnormal accumulation of topoisomerase 1-DNA covalent complexes (Top1-ccs). These findings reveal that ATM deficiency impairs neuronal maturation, suppresses the response and repair of DNA DSBs, and enhances Top1-cc accumulation. Top1-cc could be a risk factor for neurodegeneration as they may interfere with transcription elongation and promote transcriptional decline.

Relevance of Mediterranean diet and glucose metabolism for nephrolithiasis in obese subjects

BACKGROUND

Nephrolithiasis is more frequent and severe in obese patients from different western nations. This may be supported by higher calcium, urate, oxalate excretion in obese stone formers. Except these parameters, clinical characteristics of obese stone formers were not extensively explored.

AIMS

In the present paper we studied the relationship between obesity and its metabolic correlates and nephrolithiasis.

MATERIALS AND METHODS

We studied 478 Caucasian subjects having BMI ≥ 25 kg/m². The presence of nephrolithiasis, hypertension, diabetes mellitus and metabolic syndrome were noted. They underwent measurements of anthropometry (BMI and waist circumference, body composition), serum variables (fasting glucose, serum lipids and serum enzymes) and Mediterranean diet (MedDiet) nutritional questionnaire.

RESULTS

45 (9.4%) participants were stone formers. Subjects with high serum concentrations of triglycerides (≥ 150 mg/dl), fasting glucose (> 100 mg/dl) and AST (>30 U/I in F or >40 U/I in M) were more frequent among stone formers than non-stone formers.Multinomial logistic regression confirmed that kidney stone production was associated with high fasting glucose (OR = 2.6, 95% CI 1.2-5.2, P = 0.011), AST (OR = 4.3, 95% CI 1.1-16.7, P = 0.033) and triglycerides (OR = 2.7, 95% CI 1.3-5.7, P = 0.01). MedDiet score was not different in stone formers and non-stone formers. However, stone formers had a lower consumption frequency of olive oil and nuts, and higher consumption frequency of wine compared with non-stone formers.

CONCLUSIONS

Overweight and obese stone formers may have a defect in glucose metabolism and a potential liver damage. Some foods typical of Mediterranean diet may protect against nephrolithiasis.

Influence of lean and fat mass on bone mineral density and on urinary stone risk factors in healthy women

Background

The role of body composition (lean mass and fat mass) on urine chemistries and bone quality is still debated. Our aim was therefore to determine the effect of lean mass and fat mass on urine composition and bone mineral density (BMD) in a cohort of healthy females.

Materials and methods

78 female volunteers (mean age 46 ± 6 years) were enrolled at the Stone Clinic of Parma University Hospital and subdued to 24-hour urine collection for lithogenic risk profile, DEXA, and 3-day dietary diary. We defined two mathematical indexes derived from body composition measurement (index of lean mass-ILM, and index of fat mass-IFM) and the cohort was split using the median value of each index, obtaining groups differing only for lean or fat mass. We then analyzed differences in urine composition, dietary intakes and BMD.

Results

The women with high values of ILM had significantly higher excretion of creatinine (991 ± 194 vs 1138 ± 191 mg/day, p = 0.001), potassium (47 ± 13 vs 60 ± 18 mEq/day, p < 0.001), phosphorus (520 ± 174 vs 665 ± 186 mg/day, p < 0.001), magnesium (66 ± 20 vs 85 ± 26 mg/day, p < 0.001), citrate (620 ± 178 vs 807 ± 323 mg/day, p = 0.002) and oxalate (21 ± 7 vs 27 ± 11 mg/day, p = 0.015) and a significantly better BMD values in limbs than other women with low values of ILM. The women with high values of IFM had similar urine composition to other women with low values of IFM, but significantly better BMD in axial sites. No differences in dietary habits were found in both analyses.

Conclusions

Lean mass seems to significantly influence urine composition both in terms of lithogenesis promoters and inhibitors, while fat mass does not. Lean mass influences bone quality only in limb skeleton, while fat mass influences bone quality only in axial sites.

Decreased transcriptional activity of calcium-sensing receptor gene promoter 1 is associated with calcium nephrolithiasis

BACKGROUND

CaSR gene is a candidate for calcium nephrolithiasis. Single-nucleotide polymorphisms (SNPs) encompassing its regulatory region were associated with calcium nephrolithiasis.

AIMS

We tested SNPs in the CaSR gene regulatory region associated with calcium nephrolithiasis and their effects in kidney.

SUBJECTS AND METHODS

One hundred sixty-seven idiopathic calcium stone formers and 214 healthy controls were genotyped for four CaSR gene SNPs identified by bioinformatics analysis as modifying transcription factor binding sites. Strontium excretion after an oral load was tested in 55 stone formers. Transcriptional activity induced by variant alleles at CaSR gene promoters was compared by luciferase reporter gene assay in HEK-293 and HKC-8 cells. CaSR and claudin-14 mRNA levels were measured by real-time PCR in 107 normal kidney medulla samples and compared in patients with different CaSR genotype.

RESULTS

Only rs6776158 (A>G), located in the promoter 1, was associated with nephrolithiasis. Its minor G allele was more frequent in stone formers than controls (37.8% vs 26.4%, P = .001). A reduced strontium excretion was observed in GG homozygous stone formers. Luciferase fluorescent activity was lower in cells transfected with the promoter 1 including G allele at rs6776158 than cells transfected with the A allele. CaSR mRNA levels were lower in kidney medulla samples from homozygous carriers for the G allele at rs6776158 than carriers for the A allele. Claudin-14 mRNA levels were also lower in GG homozygous subjects.

CONCLUSIONS

Minor allele at rs6776158 may predispose to calcium stones by decreasing transcriptional activity of the CaSR gene promoter 1 and CaSR expression in kidney tubules.

Nephrolithiasis: nutrition as cause or therapeutic tool

Nephrolithiasis is a very common disease with an increasing prevalence among industrialized populations. Kidney stone formation is a complex phenomenon, involving genetic and metabolic patterns, and nutrition can play an important role in this match both as a promoter or as a protective factor. To promote a deeper knowledge of such a challenging disease, clinicians and researchers have met in Rome, Italy, last March 2013, at the International Congress “Nephrolithiasis: a systemic disorder” to discuss patho-physiology and possible treatment of kidney stones. During the meeting, a whole session was dedicated to nutrition, seen both as a cause or a therapeutic tool for nephrolithiasis. Due to its etiopathogenesis, nephrolithiasis is also an ideal model for a nutrigenetics and nutrigenomics approach. Nutrigenomics and nutrigenetic respectively study the effects of a dietary treatment on gene expression and, on the other hand, the impact of an inherited trait on the response to a specific dietary treatment.

Nutrition in calcium nephrolithiasis

Idiopathic calcium nephrolithiasis is a multifactorial disease with a complex pathogenesis due to genetic and environmental factors. The importance of social and health effects of nephrolithiasis is further highlighted by the strong tendency to relapse of the disease. Long-term prospective studies show a peak of disease recurrence within 2–3 years since onset, 40-50% of patients have a recurrence after 5 years and more than 50-60% after 10 years. International nutritional studies demonstrated that nutritional habits are relevant in therapy and prevention approaches of nephrolithiasis. Water, right intake of calcium, low intake of sodium, high levels of urinary citrate are certainly important for the primary and secondary prevention of nephrolithiasis.

In this review is discussed how the correction of nutritional mistakes can reduce the incidence of recurrent nephrolithiasis.

DNA damage response by single-strand breaks in terminally differentiated muscle cells and the control of muscle integrity

DNA single-strand breaks (SSB) formation coordinates the myogenic program, and defects in SSB repair in post-mitotic cells have been associated with human diseases. However, the DNA damage response by SSB in terminally differentiated cells has not been explored yet. Here we show that mouse post-mitotic muscle cells accumulate SSB after alkylation damage, but they are extraordinarily resistant to the killing effects of a variety of SSB-inducers. We demonstrate that, upon SSB induction, phosphorylation of H2AX occurs in myotubes and is largely ataxia telangiectasia mutated (ATM)-dependent. However, the DNA damage signaling cascade downstream of ATM is defective as shown by lack of p53 increase and phosphorylation at serine 18 (human serine 15). The stabilization of p53 by nutlin-3 was ineffective in activating the cell death pathway, indicating that the resistance to SSB inducers is due to defective p53 downstream signaling. The induction of specific types of damage is required to activate the cell death program in myotubes. Besides the topoisomerase inhibitor doxorubicin known for its cardiotoxicity, we show that the mitochondria-specific inhibitor menadione is able to activate p53 and to kill effectively myotubes. Cell killing is p53-dependent as demonstrated by full protection of myotubes lacking p53, but there is a restriction of p53-activated genes. This new information may have important therapeutic implications in the prevention of muscle cell toxicity.

Calcium-sensing receptor and calcium kidney stones

Calcium nephrolithiasis may be considered as a complex disease having multiple pathogenetic mechanisms and characterized by various clinical manifestations. Both genetic and environmental factors may increase susceptibility to calcium stones; therefore, it is crucial to characterize the patient phenotype to distinguish homogeneous groups of stone formers. Family and twin studies have shown that the stone transmission pattern is not mendelian, but complex and polygenic. In these studies, heritability of calcium stones was calculated around 50%

Calcium-sensing receptor (CaSR) is mostly expressed in the parathyroid glands and in renal tubules. It regulates the PTH secretion according to the serum calcium concentration. In the kidney, it modulates electrolyte and water excretion regulating the function of different tubular segments. In particular, CaSR reduces passive and active calcium reabsorption in distal tubules, increases phosphate reabsorption in proximal tubules and stimulates proton and water excretion in collecting ducts. Therefore, it is a candidate gene for calcium nephrolithiasis.

In a case-control study we found an association between the normocitraturic stone formers and two SNPs of CaSR, located near the promoters region (rs7652589 and rs1501899). This result was replicated in patients with primary hyperparathyroidism, comparing patients with or without kidney stones. Bioinformatic analysis suggested that the minor alleles at these polymorphisms were able to modify the binding sites of specific transcription factors and, consequently, CaSR expression.

Our studies suggest that CaSR is one of the candidate genes explaining individual predisposition to calcium nephrolithiasis. Stone formation may be favored by an altered CaSR expression in kidney medulla involving the normal balance among calcium, phosphate, protons and water excretion.

Role of nucleotide excision repair proteins in oxidative DNA damage repair: an updating

DNA repair is a crucial factor in maintaining a low steady-state level of oxidative DNA damage. Base excision repair (BER) has an important role in preventing the deleterious effects of oxidative DNA damage, but recent evidence points to the involvement of several repair pathways in this process. Oxidative damage may arise from endogenous and exogenous sources and may target nuclear and mitochondrial DNA as well as RNA and proteins. The importance of preventing mutations associated with oxidative damage is shown by a direct association between defects in BER (i.e. MYH DNA glycosylase) and colorectal cancer, but it is becoming increasingly evident that damage by highly reactive oxygen species plays also central roles in aging and neurodegeneration. Mutations in genes of the nucleotide excision repair (NER) pathway are associated with diseases, such as xeroderma pigmentosum and Cockayne syndrome, that involve increased skin cancer and/or developmental and neurological symptoms. In this review we will provide an updating of the current evidence on the involvement of NER factors in the control of oxidative DNA damage and will attempt to address the issue of whether this unexpected role may unlock the difficult puzzle of the pathogenesis of these syndromes.

[Hyperparathyroidism as a cardiovascular risk factor in chronic kidney disease: an update from a biological-cellular perspective]

Cardiovascular complications are the main cause of death in patients with chronic kidney disease (CKD). Among these complications, calcific arteriosclerosis and myocardial hypertrophy are the main predictors of cardiovascular morbidity and mortality. Epidemiological studies have shown their association with hyperparathyroidism, which has therefore been included among the non-traditional cardiovascular risk factors. Studies in laboratory animals have shown that PTH administration may induce calcific arteriosclerosis and myocardial hypertrophy. The former develops independently of hyperphosphatemia, but its mechanisms remain unknown. The latter is characterized by increased thickness of the myocardial fibers and especially the fibrous interstitium; its development is influenced by protein kinase C activation and the subsequent increase in cytosolic calcium as well as activation of intracellular signaling pathways inducing protein synthesis and proliferation. Different from these findings, in other studies PTH infusion was able to produce vasodilatation and to favor myocardial cell contraction and regeneration. These effects depend on protein kinase A activation. PTH may produce different and sometimes contradictory functional effects in the arteries and myocardium that are probably related to different experimental or clinical conditions. In patients with CKD and hyperparathyroidism, PTH may be considered a uremic toxin exerting its effects mainly by increasing cellular calcium. Thus, hyperparathyroidism is confirmed to be a target for the conservative therapy of CKD.

Calcium sensing receptor and renal mineral ion transport

Calcium sensing receptor (CaSR) is a component of the C family of the G protein-coupled receptors. It is ubiquitously expressed in human and mammal cells but is more expressed in parathyroid glands and kidney cells. It is located on the cell plasma membrane and senses the changes of extracellular calcium concentrations. Thus, it may modify cell functions according to serum calcium levels. CaSR has a key role in calcium homeostasis because it allows parathyroid glands and kidney to regulate PTH secretion and calcium reabsorption in order to keep serum calcium concentration within the normal range. CaSR appears as an important player in the regulation of renal calcium handling and body calcium metabolism. Thus, CaSR may protect human tissues against calcium excess. In kidneys, its protective effect includes the stimulation of diuresis and phosphate retention, along with the potential prevention of calcium precipitation and deposition in kidney tubules and interstitium.

Polymorphisms at the regulatory regions of the CASR gene influence stone risk in primary hyperparathyroidism

BACKGROUND AND OBJECTIVE

Single nucleotide polymorphisms (SNPs) of the calcium-sensing receptor (CASR) gene at the regulatory region were associated with idiopathic calcium nephrolithiasis. To confirm their association with nephrolithiasis, we tested patients with primary hyperparathyroidism (PHPT).

DESIGN

A genotype-phenotype association study.

METHODS

In all, 332 PHPT patients and 453 healthy controls were genotyped for the rs7652589 (G>A) and rs1501899 (G>A) SNPs sited in the noncoding regulatory region of the CASR gene. Allele, haplotype, and diplotype distribution were compared between PHPT patients and controls, and in stone forming and stone-free PHPT patients.

RESULTS

The allele frequency at rs7652589 and rs1501899 SNPs was similar in PHPT patients and controls. The A minor alleles at these two SNPs were more frequent in stone forming (n=157) than in stone-free (n=175) PHPT patients (rs7652589: 36.9 vs 27.1%, P=0.007; rs1501899: 37.1 vs 26.4%, P=0.003). Accordingly, homozygous or heterozygous PHPT patients for the AA haplotype (n=174, AA/AA or AA/GG diplotype) had an increased stone risk (odds ratio 1.83, 95% confidence interval 1.2-2.9, P=0.008). Furthermore, these PHPT patients had higher serum concentrations of ionized calcium and parathyroid hormone (1.50 ± 0.015 mmol/l and 183 ± 12.2 pg/ml) than patients with the GG/GG diplotype (n=145, 1.47 ± 0.011 mmol/l (P=0.04) and 150 ± 11.4 pg/ml (P=0.049)). Using a logistic regression model, the increase in stone risk in PHPT patients was predicted by AA/AA or AA/GG diplotype, the highest tertile of serum ionized calcium values and the lowest tertile of age.

CONCLUSIONS

Polymorphisms located in the regulatory region of the CASR gene may increase susceptibility of the PHPT patients to kidney stone production.

Calcimimetic R-568 effects on activity of R990G polymorphism of calcium-sensing receptor

Previous studies have demonstrated a gain-of-function of the calcium-sensing receptor (CASR) gene R990G polymorphism. In this study, activation of the R990G CASR stably transfected in HEK-293 (HEK-990G) cells compared with that of the common variant (HEK-wild-type (WT)) by increasing concentrations of CaCl(2) or calcimimetic R-568 caused significantly higher intracellular free calcium concentration ([Ca(2+)](i)) and lower Ca-EC(50). Moreover, the [Ca(2+)](i) oscillation percentage was higher with a larger sinusoidal pattern in HEK-990G. R-568 induced a shift of the oscillatory events from 4 to 2  mmol/l extracellular calcium concentration in HEK-990G cells and increased the sinusoidal oscillation percentage in comparison with HEK-WT. Preincubation with thapsigargin or phospholipase C inhibitors completely prevented oscillations in both cell lines, consistent with the involvement of the inositol trisphosphate pathway, while protein kinase C inhibitor prevented oscillations in HEK-WT cells only. Finally, CaCl(2) and R-568 caused a significant increase in p44/42 extracellular signaling-regulated kinase phosphorylation, with the mean Ca-EC(50) values being significantly lower in HEK-990G. Our findings demonstrated that the 990G allele is associated with high sensitivity to R-568, which provided new evidence for differences in CASR signaling.

Mechanisms of dealing with DNA damage in terminally differentiated cells

To protect genomic integrity living cells that are continuously exposed to DNA-damaging insults are equipped with an efficient defence mechanism termed the DNA damage response. Its function is to eliminate DNA damage through DNA repair and to remove damaged cells by apoptosis. The DNA damage response has been investigated mainly in proliferating cells, in which the cell cycle machinery is integrated with the DNA damage signalling. The current knowledge of the mechanisms of DNA repair, DNA damage signalling and cell death of post-mitotic cells that have undergone irreversible cell cycle withdrawal will be reviewed. Evidence will be provided that the protection of the genome integrity in terminally differentiated cells is achieved by different strategies than in proliferating cells.

[What do we know after ten years of genetic research into calcium kidney stones?]

Genetic studies of calcium kidney stones have so far assessed single candidate genes by testing linkage disequilibrium or association between a locus and stone disease. They showed the possible involvement of the calciumsensing receptor gene, vitamin D receptor gene, and bicarbonate-sensitive adenylate cyclase gene. In addition to research in humans, the study of different strains of knock-out mice let us include the gene of phosphate reabsorption carrier NPT2, caveolin-1, protein NHERF-1 modulating calcium and urate reabsorption, osteopontin and Tamm-Horsfall protein among the possible determinants. However, the interactions between genes and also between environmental factors and genes are generally considered fundamental in calcium stone formation. Thus, the genetic studies carried out to date have not led to a significant growth of the knowledge about the causes of calcium kidney stones, even though they have allowed us to assess the size of the problem and define criteria to address it. Further knowledge of the causes of calcium stones may be obtained using the instruments that modern biotechnology and bioinformatics have made available to researchers.

Renal osteodystrophy and vascular calcification

Chronic kidney disease (CKD) is characterized by phosphate retention and reduced synthesis of 1.25(OH)2-vitamin D stimulating parathyroid hyperplasia. These changes cause a complex osteopathy, defined as renal osteodystrophy, and vascular calcification. Renal osteodystrophy increases the risk of fracture and causes deformities and disability. Vascular calcification occurs in a large proportion of hemodialysis patients and is a marker of arteriopathy. Calcifying arteriopathy induces arterial stiffness and contributes to the high cardiovascular mortality and morbidity among CKD patients. Vascular calcification results from a process of local bone formation induced by osteoblast-like cells developing in the vascular wall from resident cells. Osteoblast differentiation of resident vascular cells may be mediated by metabolic factors and may be induced by high concentrations of phosphate. Therefore, phosphate retention appears as the most detrimental factor affecting arteries in CKD patients. There is no specific therapy to revert soft tissue calcification, but calcification must be prevented in the early stages of CKD.

Resveratrol inhibits cell growth in a human cholangiocarcinoma cell line

BACKGROUND/AIMS

Cholangiocarcinoma is a devastating tumour with a poor prognosis. An efficient therapy is unavailable in unoperable patients and new drugs are widely sought for and required. Resveratrol (RES) is a natural molecule with a reported anticancer effect, evaluated on different tumour cell lines. We tested the efficacy of RES on a cholangiocarcinoma cell line for the first time.

METHODS

We used the human SK-ChA-1 cell line, cultured in the classical two-dimensional model and in the three-dimensional spheroids. After RES exposure morphology, cell viability (colony-forming assay), lactate dehydrogenase (LDH), alkaline phosphatase (ALP) and cancer antigen (CA) 19-9 medium releases, cellular transglutaminase activity, karyotype and cell cycle were evaluated.

RESULTS

Resveratrol inhibited cell growth in both the cell culture systems used (from -15 to -80% vs untreated controls) and induced a 40-fold increase of LDH and ALP activities in the culture medium. Also, transglutaminase (TG) activity increased in the cell lysates, together with a cell cycle perturbation characterised by an accumulation in the G(1)/S phase. Karyotype and CA 19-9 expression were not influenced by the treatment.

CONCLUSIONS

The observed cytotoxic effect of RES on the human cholangiocarcinoma SK-ChA-1 cell line cultured two- and three-dimensionally suggests to further analyse its chemotherapic/chemopreventive possibilities for this kind of cancer.

Resveratrol impairs the formation of MDA-MB-231 multicellular tumor spheroids concomitant with ceramide accumulation

Resveratrol exerts a drastic growth inhibitory effect on human breast cancer MDA-MB-231 cells grown both in vitro and in vivo. Here we show that resveratrol affects the aggregation properties of MDA-MB-231 cells into multicellular tumor spheroids (MCTSs), in association with induction of de novo synthesis of ceramide. After 9 days of 3D growth in the presence of resveratrol (64 microM), MDA-MB-231 cells formed significantly smaller MCTSs. Further, cells from these aggregates failed to form colonies. Addition of resveratrol (64 microM) to preformed MDA-MB-231 MCTSs caused no significant size change, consistent with lack of ceramide induction. Only some apoptotic blebs were found on the MCTSs surface. Altogether these findings indicate that resveratrol might be effective for prevention of breast cancer cell growth.

The role of CSA in the response to oxidative DNA damage in human cells

Cockayne syndrome (CS) is a rare genetic disease characterized by severe growth, mental retardation and pronounced cachexia. CS is most frequently due to mutations in either of two genes, CSB and CSA. Evidence for a role of CSB protein in the repair of oxidative DNA damage has been provided recently. Here, we show that CSA is also involved in the response to oxidative stress. CS-A human primary fibroblasts and keratinocytes showed hypersensitivity to potassium bromate, a specific inducer of oxidative damage. This was associated with inefficient repair of oxidatively induced DNA lesions, namely 8-hydroxyguanine (8-OH-Gua) and (5'S)-8,5'-cyclo 2'-deoxyadenosine. Expression of the wild-type CSA in the CS-A cell line CS3BE significantly decreased the steady-state level of 8-OH-Gua and increased its repair rate following oxidant treatment. CS-A cell extracts showed normal 8-OH-Gua cleavage activity in an in vitro assay, whereas CS-B cell extracts were confirmed to be defective. Our data provide the first in vivo evidence that CSA protein contributes to prevent accumulation of various oxidized DNA bases and underline specific functions of CSB not shared with CSA. These findings support the hypothesis that defective repair of oxidative DNA damage is involved in the clinical features of CS patients.

Interleukin-1 gene polymorphisms and gastric cancer risk in a high-risk Italian population

OBJECTIVES

Host genetic factors, including the IL1 gene cluster, play a key role in determining the long-term outcome of Helicobacter pylori infection. The aim of the study was to investigate the relationship between selected IL1 loci polymorphisms and gastric cancer risk in an Italian population.

METHODS

In a case-control study we compared the IL1B-31 and IL1B+3954 biallelic and IL1RN pentaallelic variable number of tandem repeats (VNTR) polymorphisms in 185 gastric cancer patients and 546 controls randomly sampled from the general population of an area at high gastric cancer risk (Tuscany, Central Italy).

RESULTS

Genotype frequencies of the IL1B-31 T/C, IL1B+3954 C/T, and IL1RN polymorphisms among our population controls were in Hardy-Weinberg equilibrium. In multivariate analyses, no increase in gastric cancer risk was observed for the IL1B-31*C- and IL1B+3954*T- carriers; a significant 50% increase emerged for IL1RN*2 allele carriers (OR = 1.49; 95% CI: 1.01-2.21). Analyses based on combined genotypes showed also that the association with IL1RN*2 allele was limited to two-variant allele carriers who were also homozygous for the IL1B-31*T allele (OR = 2.23; 95% CI: 1.18-4.23) with a statistically significant interaction between these two genotypes (p= 0.043). Haplotype analysis showed an increased risk for the haplotype IL1RN*2/IL1B-31*T.

CONCLUSIONS

Our results suggest that host genetic factors (such as the IL1RN and the IL1B-31 polymorphisms) interact in the complex process of gastric carcinogenesis in this high-risk Italian population. Overall, this effect appears more modest than previously reported in other populations, supporting the hypothesis that other still-to-be-defined factors are important in gastric carcinogenesis. These findings might be due to a haplotype effect.

The base excision repair: mechanisms and its relevance for cancer susceptibility

Base damage or loss occurs at high frequency in the cells (almost 10(4) bases are damaged and hydrolysed per cell per day). DNA repair is fundamental to maintain genomic integrity. Base excision repair (BER) is the main mechanism by which cells correct various types of damaged DNA bases generated either by endogenous or exogenous factors. The widely accepted model for BER mechanism involves five sequential reactions: (i) base removal; (ii) incision of the resulting abasic site; (iii) processing of the generated termini at the strand break; (iv) DNA synthesis, and (v) ligation. In this review, we will briefly summarise the biochemistry of each BER step and will concentrate on the biological relevance of BER as inferred from in vitro and in vivo studies. This information will be the basis for speculation on the potential role of malfunction of BER in human pathology.

8-Oxoguanine DNA damage: at the crossroad of alternative repair pathways

Radical oxygen species (ROS) generate various modified DNA bases. Among them 8-oxo-7,8-dihydroguanine (8oxoG) is the most abundant and seems to play a major role in mutagenesis and in carcinogenesis. 8oxoG is removed from DNA by the specific glycosylase OGG1. An additional post-replication repair is needed to correct the 8oxoG/A mismatches that are produced by persistent 8oxoG residues. This review is focused on the mechanisms of base excision repair (BER) of this oxidized base. It is shown that, in vitro, efficient and complete repair of 8oxoG/C pairs requires a core of four proteins, namely OGG1, APE1, DNA polymerase (Pol) beta, and DNA ligase I. Repair occurs predominantly by one nucleotide replacement reactions (short-patch BER) and Pol beta is the polymerase of election for the resynthesis step. However, alternative mechanisms can act on 8oxoG residues since Pol beta-null cells are able to repair these lesions. 8oxoG/A mismatches are repaired by human cell extracts via two BER events which occur sequentially on the two strands. The removal of the mismatched adenine is followed by preferential insertion of a cytosine leading to the formation of 8oxoG/C pairs which are then corrected by OGG1-mediated BER. Both repair events are inhibited by aphidicolin, suggesting that a replicative DNA polymerase is involved in the repair synthesis step. We propose that Pol delta/epsilon-mediated BER (long-patch BER) is the mode of repair when lesions persist or are formed at replication. Finally, we address the issues of the relative contribution of the two BER pathways to oxidative damage repair in vivo and the possible role of BER gene variants as cancer susceptibility genes.

Characterization of the ultraviolet B and X-ray response of primary cultured epidermal cells from patients with disseminated superficial actinic porokeratosis

BACKGROUND

Disseminated superficial actinic porokeratosis (DSAP) is the most common porokeratosis and is characterized by multiple keratotic lesions which tend to occur at sun-exposed sites. A mild hypersensitivity to X-rays has been reported for DSAP-derived fibroblasts and frequent over-expression of p53 has been found in lesional epidermis.

OBJECTIVES

In order to clarify whether genome maintenance mechanisms might be compromised in this disease the following approaches were undertaken: (i) primary cultured keratinocytes and fibroblasts from DSAP patients were characterized for ultraviolet (UV) B and X-ray response; (ii) 15 lesions were studied for p53 mutations, and (iii) the differentiation status of DSAP-derived keratinocytes was evaluated.

METHODS

Primary cultures of keratinocytes and fibroblasts were established from lesional and nonlesional skin biopsies of two subjects with DSAP. p53 mutations were analysed by DNA sequencing of the conserved region of the TP53 gene. Differentiation was evaluated both in stratified epithelial sheets from confluent keratinocyte cultures and in organotypic skin cultures.

RESULTS

The cytotoxic and apoptotic response to UVB or X-irradiation was similar in DSAP-derived keratinocytes and fibroblasts when compared with normal cells. Two of 15 lesions examined presented p53 mutations located at nondipyrimidine sites. A strikingly decreased expression of filaggrin was observed both in reconstructed epidermis and in reconstructed skin.

CONCLUSIONS

The UVB and X-ray response of DSAP-derived keratinocytes and fibroblasts indicates that the actinic character of this skin pathology is not due to radiation hypersensitivity. In agreement with this finding, mutations in the p53 gene, which are often associated with UV-related skin carcinogenesis, were rarely detected in DSAP lesions and were not UV-specific. Reconstructed epidermis and reconstructed skin models successfully reproduced the main features of this genodermatosis, showing that DSAP-derived keratinocytes bear an inherent defect in the terminal differentiation programme.

Influence of DNA torsional rigidity on excision of 7,8-dihydro-8-oxo-2'-deoxyguanosine in the presence of opposing abasic sites by human OGG1 protein

The human protein OGG1 (hOGG1) targets the highly mutagenic base 7,8-dihydro-8-oxo-2'-deoxyguanosine (8-oxodG) and shows a high specificity for the opposite DNA base. Abasic sites can arise in DNA in close opposition to 8-oxodG either during repair of mismatched bases (i.e. 8-oxodG/A mismatches) or, more frequently, as a consequence of ionizing radiation exposure. Bistranded DNA lesions may remain unrepaired and lead to cell death via double-strand break formation. In order to explore the role of damaged-DNA dynamics in recognition/excision by the hOGG1 repair protein, specific oligonucleotides containing an 8-oxodG opposite an abasic site, at different relative distances on the complementary strand, were synthesized. Rotational dynamics were studied by means of fluorescence polarization anisotropy decay experiments and the torsional elastic constant as well as the hydrodynamic radius of the DNA fragments were evaluated. Efficiency of excision of 8-oxodG was tested using purified human glycosylase. A close relation between the twisting flexibility of the DNA fragment and the excision efficiency of the oxidative damage by hOGG1 protein within a cluster was found.

Reconstitution of the base excision repair pathway for 7,8-dihydro-8-oxoguanine with purified human proteins

In mammalian cells, repair of the most abundant endogenous premutagenic lesion in DNA, 7,8-dihydro-8-oxoguanine (8-oxoG), is initiated by the bifunctional DNA glycosylase OGG1. By using purified human proteins, we have reconstituted repair of 8-oxoG lesions in DNA in vitro on a plasmid DNA substrate containing a single 8-oxoG residue. It is shown that efficient and complete repair requires only hOGG1, the AP endonuclease HAP1, DNA polymerase (Pol) beta and DNA ligase I. After glycosylase base removal, repair occurred through the AP lyase step of hOGG1 followed by removal of the 3'-terminal sugar phosphate by the 3'-diesterase activity of HAP1. Addition of PCNA had a slight stimulatory effect on repair. Fen1 or high concentrations of Pol beta were required to induce strand displacement DNA synthesis at incised 8-oxoG in the absence of DNA ligase. Fen1 induced Pol beta strand displacement DNA synthesis at HAP1-cleaved AP sites differently from that at gaps introduced by hOGG1/HAP1 at 8-oxoG sites. In the presence of DNA ligase I, the repair reaction at 8-oxoG was confined to 1 nt replacement, even in the presence of high levels of Pol beta and Fen1. Thus, the assembly of all the core proteins for 8-oxoG repair catalyses one major pathway that involves single nucleotide repair patches.

The mechanism of switching among multiple BER pathways

To preserve genomic beta DNA from common endogenous and exogenous base and sugar damage, cells are provided with multiple base excision repair (BER) pathways: the DNA polymerase (Pol) beta-dependent single nucleotide BER and the long-patch (2-10 nt) BER that requires PCNA. It is a challenge to identify the factors that govern the mechanism of switching among these pathways. One of these factors is the type of DNA damage induced in DNA. By using different model lesions we have shown that base damages (like hypoxanthine and 1, N6-ethenoadenine) excised by monofunctional DNA glycosylases are repaired via both single-nucleotide and long-patch BER, while lesions repaired by a bifunctional DNA glycosylase (like 7,8-dihydro-8-oxoguanine) are repaired mainly by single-nucleotide BER. The presence of a genuine 5' nucleotide, as in the case of cleavage by a bifunctional DNA glycosylase-beta lyase, would then minimize the strand displacement events. Another key factor in the selection of the BER branch is the relative level of cellular polymerases. While wild-type embryonic mouse fibroblast cell lines repair abasic sites predominantly via single-nucleotide replacement reactions (80% of the repair events), cells homozygous for a deletion in the Pol beta gene repair these lesions exclusively via long-patch BER. Following treatment with methylmethane sulfonate, these mutant cells accumulate DNA single-strand breaks in their genome in keeping with the fact that repair induced by monofunctional alkylating agents goes predominantly via single-nucleotide BER. Since the long-patch BER is strongly stimulated by PCNA, the cellular content of this cell-cycle regulated factor is also extremely effective in driving the repair reaction to either BER branch. These findings raise the interesting possibility that different BER pathways might be acting as a function of the cell cycle stage.

Risk factors for basal cell carcinoma in a Mediterranean population: role of recreational sun exposure early in life

OBJECTIVE

To investigate the role of pigmentary traits, different patterns of sun exposure, artificial sources of UV radiation, and lifestyle-related factors on the risk of basal cell carcinoma (BCC) in a Mediterranean population from central-southern Italy.

DESIGN

Hospital-based case-control study.

SETTING

A referral dermatological hospital in Rome, Italy.

PATIENTS

A convenience sample of 166 case patients with histologically confirmed BCC and 158 cancer-free control subjects with minor dermatological conditions observed between March 1995 and June 1997.

RESULTS

In the multivariate analysis, the mean number of weeks per year spent at the beach before the age of 20 years was significantly associated with BCC. A dose-response trend was found for subjects who had spent 3 to 4 (odds ratio, 1.8; 95% confidence interval, 0.8-4.4), 5 to 8 (odds ratio, 3.7; 95% confidence interval, 1.5-9.0), or more than 8 (odds ratio, 4.5; 95% confidence interval, 1.9-10.5) weeks per year at the beach (P =.01 for trend). There was a significant association with the presence of actinic keratoses or solar lentigines, whereas no effect was found for skin type, history of sunburns, exposure to nonsolar UV radiation, and lifestyle-related habits such as cigarette smoking, alcohol consumption, and coffee drinking. Subjects reporting a family history of skin cancer had an extremely increased risk of BCC.

CONCLUSION

The definite association with recreational sun exposure during childhood and adolescence and the strong relation with family history of skin cancer suggest that genetic predisposition and peculiar exposure patterns to UV radiation are key independent risk factors for the development of BCC in a southern European population.

DNA polymerase beta is required for efficient DNA strand break repair induced by methyl methanesulfonate but not by hydrogen peroxide

The most frequent DNA lesions in mammalian genomes are removed by the base excision repair (BER) via multiple pathways that involve the replacement of one or more nucleotides at the lesion site. The biological consequences of a BER defect are at present largely unknown. We report here that mouse cells defective in the main BER DNA polymerase beta (Pol beta) display a decreased rate of DNA single-strand breaks (ssb) rejoining after methyl methanesulfonate damage when compared with wild-type cells. In contrast, Pol beta seems to be dispensable for hydrogen peroxide-induced DNA ssb repair, which is equally efficient in normal and defective cells. By using an in vitro repair assay on single abasic site-containing circular duplex molecules, we show that the long-patch BER is the predominant repair route in Pol beta-null cell extract. Our results strongly suggest that the Pol beta-mediated single nucleotide BER is the favorite pathway for repair of N-methylpurines while oxidation-induced ssb, likely arising from oxidized abasic sites, are the substrate for long-patch BER.

Multiple mutations and frameshifts are the hallmark of defective hPMS2 in pZ189-transfected human tumor cells

Two HeLa variants defective in the mismatch repair protein hPMS2 were isolated by selection for methylation tolerance. Neither variant expressed detectable hPMS2 protein as determined by western blotting. Cell extracts were defective in correcting a single base mispair and were unable to perform mismatch repair-dependent processing of a methylated DNA substrate. Correction of the repair defect and restoration of sensitivity to a methylating agent was achieved by introducing a wild-type copy of chromosome 7 on which the hPMS2 gene is located. Loss of hPMS2 function in the HeLa variants was associated with a 5-fold increase in mutation frequency in the supF gene of the pZ189 shuttle vector. Wild-type levels of mutagenesis were restored by the transferred chromosome 7. Comparisons of mutational spectra identified multiple base substitutions, frameshifts and, to a lesser extent, single base pair changes as the types of mutation which are selectively increased in a hPMS2-defective background. The location of multiple mutations and frameshifts indicates that misalignment-mediated mutagenesis could underlie most of these events. Thus the mutator phenotype associated with loss of hPMS2 most likely arises because of the failure to correct replication slippage errors. Our data also suggest that a considerable fraction of mutagenic intermediates are recognized by the hMutSbeta complex and processed via the hMLH1/hPMS2 heterodimer.

UV mutation signature in tumor suppressor genes involved in skin carcinogenesis in xeroderma pigmentosum patients

Molecular analysis of p53 and patched (PTCH), two candidate tumor suppressor genes for non-melanocytic skin cancer, was performed in skin tumors from six patients affected by the cancer-prone disease xeroderma pigmentosum (XP). UV-specific p53 mutations were detected at a frequency of 38-50% in all the tumor types analysed, including melanomas. Additional analysis of PTCH mutations in the subset of eight basal call carcinomas (BCC) revealed a very high mutation frequency of this gene (90%) which exceeded that detected in the p53 gene in the same tumors (38%). PTCH mutations were predominantly UV-specific C>T transitions. This mutation pattern is different from that reported in BCC from normal donors where PTCH mutation frequency is 27% and mutations are frequently deletions and insertions. These findings suggest that PTCH mutations represent an earlier event in BCC development than p53 alterations and that the inability of XP patients to repair UV-induced PTCH mutations might significantly contribute to the early and frequent appearance of BCC observed in these patients.

Long patch base excision repair with purified human proteins. DNA ligase I as patch size mediator for DNA polymerases delta and epsilon

Among the different base excision repair pathways known, the long patch base excision repair of apurinic/apyrimidinic sites is an important mechanism that requires proliferating cell nuclear antigen. We have reconstituted this pathway using purified human proteins. Our data indicated that efficient repair is dependent on six components including AP endonuclease, replication factor C, proliferating cell nuclear antigen, DNA polymerases delta or epsilon, flap endonuclease 1, and DNA ligase I. Fine mapping of the nucleotide replacement events showed that repair patches extended up to a maximum of 10 nucleotides 3' to the lesion. However, almost 70% of the repair synthesis was confined to 2-4-nucleotide patches and DNA ligase I appeared to be responsible for limiting the repair patch length. Moreover, both proliferating cell nuclear antigen and flap endonuclease 1 are required for the production and ligation of long patch repair intermediates suggesting an important role of this complex in both excision and resynthesis steps.

Factors that influence the DNA repair capacity of normal and skin cancer-affected individuals

DNA repair capacity (DRC) was studied in 49 patients affected by basal cell carcinoma (BCC) and 68 cancer-free controls belonging to a larger case-control population enrolled for studying BCC risk factors. DRC was measured in the subjects' peripheral blood lymphocytes by using a host-cell reactivation assay that measures cellular activation of a reporter gene irradiated with UV light. A statistically significant age-related decline in DRC was observed in the controls from 20 to 70 years of age but not in the BCC cases. When the DRC values of the BCC patients and controls were compared by age, young BCC cases (age, < or =40 year) repaired less than the controls, although the difference was not statistically significant. Conversely, older BCC patients (age, >40 years) presented an enhanced repair capacity (P < 0.001) as compared with their controls. The search for possible factors associated with the high repair rate of elderly BCC cases revealed that both target cell physiology and life-style habits may affect host DNA repair. Smoking was the variable that explained most of the increase in DRC among older patients. The understanding of how these factors affect host DRC will be relevant for a correct use of this biomarker.

The type of DNA glycosylase determines the base excision repair pathway in mammalian cells

The base excision repair (BER) of modified nucleotides is initiated by damage-specific DNA glycosylases. The repair of the resulting apurinic/apyrimidinic site involves the replacement of either a single nucleotide (short patch BER) or of several nucleotides (long patch BER). The mechanism that controls the selection of either BER pathway is unknown. We tested the hypothesis that the type of base damage present on DNA, by determining the specific DNA glycosylase in charge of its excision, drives the repair of the resulting abasic site intermediate to either BER branch. In mammalian cells hypoxanthine (HX) and 1,N6-ethenoadenine (epsilonA) are both substrates for the monofunctional 3-methyladenine DNA glycosylase, the ANPG protein, whereas 7,8-dihydro-8-oxoguanine (8-oxoG) is removed by the bifunctional DNA glycosylase/beta-lyase 8-oxoG-DNA gly- cosylase (OGG1). Circular plasmid molecules containing a single HX, epsilonA, or 8-oxoG were constructed. In vitro repair assays with HeLa cell extracts revealed that HX and epsilonA are repaired via both short and long patch BER, whereas 8-oxoG is repaired mainly via the short patch pathway. The preferential repair of 8-oxoG by short patch BER was confirmed by the low efficiency of repair of this lesion by DNA polymerase beta-deficient mouse cells as compared with their wild-type counterpart. These data fit into a model where the intrinsic properties of the DNA glycosylase that recognizes the lesion selects the branch of BER that will restore the intact DNA template.

Mammalian base excision repair by DNA polymerases delta and epsilon

Two distinct pathways for completion of base excision repair (BER) have been discovered in eukaryotes: the DNA polymerase beta (Pol beta)-dependent short-patch pathway that involves the replacement of a single nucleotide and the long-patch pathway that entails the resynthesis of 2-6 nucleotides and requires PCNA. We have used cell extracts from Pol beta-deleted mouse fibroblasts to separate subfractions containing either Pol delta or Pol epsilon. These fractions were then tested for their ability to perform both short- and long-patch BER in an in vitro repair assay, using a circular DNA template, containing a single abasic site at a defined position. Remarkably, both Pol delta and Pol epsilon were able to replace a single nucleotide at the lesion site, but the repair reaction is delayed compared to single nucleotide replacement by Pol beta. Furthermore, our observations indicated, that either Pol delta and/or Pol epsilon participate in the long-patch BER. PCNA and RF-C, but not RP-A are required for this process. Our data show for the first time that Pol delta and/or Pol epsilon are directly involved in the long-patch BER of abasic sites and might function as back-up system for Pol beta in one-gap filling reactions.

Different DNA polymerases are involved in the short- and long-patch base excision repair in mammalian cells

Mammalian cells possess two distinct pathways for completion of base excision repair (BER): the DNA polymerase beta (Pol beta)-dependent short-patch pathway (replacement of one nucleotide), which is the main route, and the long-patch pathway (resynthesis of 2-6 nucleotides), which is PCNA-dependent. To address the issue of how these two pathways share their role in BER the ability of Pol beta-defective mammalian cell extracts to repair a single abasic site constructed in a circular duplex plasmid molecule was tested in a standard in vitro repair reaction. Pol beta-deficient extracts were able to perform both BER pathways. However, in the case of the short-patch BER, the repair kinetics was significantly slower than with Pol beta-proficient extracts, while the efficiency of the long-patch synthesis was unaffected by the loss of Pol beta. The repair synthesis was fully dependent on PCNA for the replacement of long patches. These data give the first evidence that in cell extracts DNA polymerases other than Pol beta are specifically involved in the long-patch BER. These DNA polymerases are also able to perform short-patch BER in the absence of PCNA, although less efficiently than Pol beta. These findings lead to a novel model whereby the two BER pathways are characterized by different protein requirements, and a functional redundancy at the level of DNA polymerases provides cells with backup systems.

Mutation spectra resulting from carcinogenic exposure: from model systems to cancer-related genes

The events leading to cancer are complex and interactive. Alteration of cancer genes, such as the tumor suppressor gene p53, plays a central role in this process. Analysis of the frequency, type and site of mutations in important cancer-related genes may provide clues to the identification of etiological factors and sources of exposure. In this chapter we have selected a few examples of environmental human carcinogens and have attempted to use the knowledge of their mechanisms of mutagenesis, as derived from in vitro cell systems, as a key to understanding the complexity of p53 mutation spectra in tumors arising at the putative target organ. The analysis will focus on environmental exposure to UV radiation. The examples of tobacco smoke, dietary aflatoxin and vinyl chloride will be also briefly discussed.