Strand-resolved mutagenicity of DNA damage and repair.

DNA base damage is a major source of oncogenic mutations1. Such damage can produce strand-phased mutation patterns and multiallelic variation through the process of lesion segregation2. Here we exploited these properties to reveal how strand-asymmetric processes, such as replication and transcription, shape DNA damage and repair. Despite distinct mechanisms of leading and lagging strand replication3,4, we observe identical fidelity and damage tolerance for both strands. For small alkylation adducts of DNA, our results support a model in which the same translesion polymerase is recruited on-the-fly to both replication strands, starkly contrasting the strand asymmetric tolerance of bulky UV-induced adducts5. The accumulation of multiple distinct mutations at the site of persistent lesions provides the means to quantify the relative efficiency of repair processes genome wide and at single-base resolution. At multiple scales, we show DNA damage-induced mutations are largely shaped by the influence of DNA accessibility on repair efficiency, rather than gradients of DNA damage. Finally, we reveal specific genomic conditions that can actively drive oncogenic mutagenesis by corrupting the fidelity of nucleotide excision repair. These results provide insight into how strand-asymmetric mechanisms underlie the formation, tolerance and repair of DNA damage, thereby shaping cancer genome evolution.

Cows' Milk Allergy-Associated Constipation: When to Look for It? A Narrative Review.

Constipation is a very common disorder, mostly functional in nature, that may persist for years in up to 35-52% of children. Food allergy prevalence, severity and persistence are increasing over time, and cows' milk protein is the commonest food allergen recognised to affect gastrointestinal motility in children. There is mounting evidence of the role of cows' milk (CM) allergy (CMA) in children with constipation. With this narrative review, we aim to provide clinicians with an updated and critical overview of food allergy-associated constipation. We searched Embase, Medline and the Cochrane Library, using keywords related to the topic. Only reviews and studies including children aged 0-17 years that were published in English were considered. Constipation has been reported in 4.6% of infants with CMA; the prevalence of food allergy underlying chronic constipation in children resistant to conventional treatment and presenting to tertiary clinics ranges between 28% and 78%. The identification of predisposing risk factors and of a specific phenotype of food allergy-induced constipation remains elusive. No allergic tests, radiological or motility investigations achieve sufficient sensitivity and specificity to screen children for CMA-related constipation. A 4-week cows' milk protein (CMP) elimination diet may be considered for children with chronic constipation resistant to conventional treatment and who lack alarm sign/symptoms of organic diseases. In subjects with ameliorated symptoms on CMP elimination, the diagnosis of CMA should be confirmed by a food challenge to avoid an unnecessary protracted diet.

Pervasive lesion segregation shapes cancer genome evolution.

Cancers arise through the acquisition of oncogenic mutations and grow by clonal expansion1,2. Here we reveal that most mutagenic DNA lesions are not resolved into a mutated DNA base pair within a single cell cycle. Instead, DNA lesions segregate, unrepaired, into daughter cells for multiple cell generations, resulting in the chromosome-scale phasing of subsequent mutations. We characterize this process in mutagen-induced mouse liver tumours and show that DNA replication across persisting lesions can produce multiple alternative alleles in successive cell divisions, thereby generating both multiallelic and combinatorial genetic diversity. The phasing of lesions enables accurate measurement of strand-biased repair processes, quantification of oncogenic selection and fine mapping of sister-chromatid-exchange events. Finally, we demonstrate that lesion segregation is a unifying property of exogenous mutagens, including UV light and chemotherapy agents in human cells and tumours, which has profound implications for the evolution and adaptation of cancer genomes.

Mutational landscape of a chemically-induced mouse model of liver cancer.

BACKGROUND & AIMS: Carcinogen-induced mouse models of liver cancer are used extensively to study the pathogenesis of the disease and are critical for validating candidate therapeutics. These models can recapitulate molecular and histological features of human disease. However, it is not known if the genomic alterations driving these mouse tumour genomes are comparable to those found in human tumours. Herein, we provide a detailed genomic characterisation of tumours from a commonly used mouse model of hepatocellular carcinoma (HCC). METHODS: We analysed whole exome sequences of liver tumours arising in mice exposed to diethylnitrosamine (DEN). Mutational signatures were compared between liver tumours from DEN-treated and untreated mice, and human HCCs. RESULTS: DEN-initiated tumours had a high, uniform number of somatic single nucleotide variants (SNVs), with few insertions, deletions or copy number alterations, consistent with the known genotoxic action of DEN. Exposure of hepatocytes to DEN left a reproducible mutational imprint in resulting tumour exomes which we could computationally reconstruct using six known COSMIC mutational signatures. The tumours carried a high diversity of low-incidence, non-synonymous point mutations in many oncogenes and tumour suppressors, reflecting the stochastic introduction of SNVs into the hepatocyte genome by the carcinogen. We identified four recurrently mutated genes that were putative oncogenic drivers of HCC in this model. Every neoplasm carried activating hotspot mutations either in codon 61 of Hras, in codon 584 of Braf or in codon 254 of Egfr. Truncating mutations of Apc occurred in 21% of neoplasms, which were exclusively carcinomas supporting a role for deregulation of Wnt/ß-catenin signalling in cancer progression. CONCLUSIONS: Our study provides detailed insight into the mutational landscape of tumours arising in a commonly used carcinogen model of HCC, facilitating the future use of this model to better understand the human disease. LAY SUMMARY: Mouse models are widely used to study the biology of cancer and to test potential therapies. Herein, we have described the mutational landscape of tumours arising in a carcinogen-induced mouse model of liver cancer. Since cancer is a disease caused by genomic alterations, information about the patterns and types of mutations in the tumours in this mouse model should facilitate its use to study human liver cancer.

Paediatric constipation: An approach and evidence-based treatment regimen

BACKGROUND: Constipation affects 5-30% of children and is responsible for 3% of primary care visits. General practitioners (GPs) are frequently the first medical encounter for concerned parents regarding their child's bowel habit. OBJECTIVE: The aim of this article is to review the assessment and management of children with constipation to empower GPs to initiate treatment and know when to refer to a paediatrician. DISCUSSION: In the absence of organic aetiology, childhood constipation is almost always functional and often due to painful bowel movements that prompt the child to withhold stool. It is important to initiate a clear management plan for the family, as what is an easily treatable condition can escalate into a vicious cycle of pain if not addressed early. The medical approach should consider organic disease, the use of appropriate toileting habits, and dietary modifications. Laxatives are often required to re-establish regular, painless defaecation.

Interplay of cis and trans mechanisms driving transcription factor binding and gene expression evolution.

Noncoding regulatory variants play a central role in the genetics of human diseases and in evolution. Here we measure allele-specific transcription factor binding occupancy of three liver-specific transcription factors between crosses of two inbred mouse strains to elucidate the regulatory mechanisms underlying transcription factor binding variations in mammals. Our results highlight the pre-eminence of cis-acting variants on transcription factor occupancy divergence. Transcription factor binding differences linked to cis-acting variants generally exhibit additive inheritance, while those linked to trans-acting variants are most often dominantly inherited. Cis-acting variants lead to local coordination of transcription factor occupancies that decay with distance; distal coordination is also observed and may be modulated by long-range chromatin contacts. Our results reveal the regulatory mechanisms that interplay to drive transcription factor occupancy, chromatin state, and gene expression in complex mammalian cell states.

Aging increases cell-to-cell transcriptional variability upon immune stimulation.

Aging is characterized by progressive loss of physiological and cellular functions, but the molecular basis of this decline remains unclear. We explored how aging affects transcriptional dynamics using single-cell RNA sequencing of unstimulated and stimulated naïve and effector memory CD4+ T cells from young and old mice from two divergent species. In young animals, immunological activation drives a conserved transcriptomic switch, resulting in tightly controlled gene expression characterized by a strong up-regulation of a core activation program, coupled with a decrease in cell-to-cell variability. Aging perturbed the activation of this core program and increased expression heterogeneity across populations of cells in both species. These discoveries suggest that increased cell-to-cell transcriptional variability will be a hallmark feature of aging across most, if not all, mammalian tissues.

Successful transmission and transcriptional deployment of a human chromosome via mouse male meiosis.

Most human aneuploidies originate maternally, due in part to the presence of highly stringent checkpoints during male meiosis. Indeed, male sterility is common among aneuploid mice used to study chromosomal abnormalities, and male germline transmission of exogenous DNA has been rarely reported. Here we show that, despite aberrant testis architecture, males of the aneuploid Tc1 mouse strain produce viable sperm and transmit human chromosome 21 to create aneuploid offspring. In these offspring, we mapped transcription, transcriptional initiation, enhancer activity, non-methylated DNA, and transcription factor binding in adult tissues. Remarkably, when compared with mice derived from female passage of human chromosome 21, the chromatin condensation during spermatogenesis and the extensive epigenetic reprogramming specific to male germline transmission resulted in almost indistinguishable patterns of transcriptional deployment. Our results reveal an unexpected tolerance of aneuploidy during mammalian spermatogenesis, and the surprisingly robust ability of mouse developmental machinery to accurately deploy an exogenous chromosome, regardless of germline transmission.

Vitamin D receptor-mediated stromal reprogramming suppresses pancreatitis and enhances pancreatic cancer therapy.

The poor clinical outcome in pancreatic ductal adenocarcinoma (PDA) is attributed to intrinsic chemoresistance and a growth-permissive tumor microenvironment. Conversion of quiescent to activated pancreatic stellate cells (PSCs) drives the severe stromal reaction that characterizes PDA. Here, we reveal that the vitamin D receptor (VDR) is expressed in stroma from human pancreatic tumors and that treatment with the VDR ligand calcipotriol markedly reduced markers of inflammation and fibrosis in pancreatitis and human tumor stroma. We show that VDR acts as a master transcriptional regulator of PSCs to reprise the quiescent state, resulting in induced stromal remodeling, increased intratumoral gemcitabine, reduced tumor volume, and a 57% increase in survival compared to chemotherapy alone. This work describes a molecular strategy through which transcriptional reprogramming of tumor stroma enables chemotherapeutic response and suggests vitamin D priming as an adjunct in PDA therapy. PAPERFLICK:

Impaired JNK signaling cooperates with KrasG12D expression to accelerate pancreatic ductal adenocarcinoma.

The c-Jun N-terminal protein kinase (JNK) and its two direct activators, namely the mitogen-activated protein kinase (MAPK) kinase 4 (MKK4) and MKK7, constitute a signaling node frequently mutated in human pancreatic ductal adenocarcinoma (PDAC). Here we demonstrate the cooperative interaction of endogenous expression of Kras(G12D) with loss-of-function mutations in mkk4 or both, mkk4 and mkk7 genes in the pancreas. More specifically, impaired JNK signaling in a subpopulation of Pdx1-expressing cells dramatically accelerated the appearance of Kras(G12D)-induced acinar-to-ductal metaplasia and pancreatic intraepithelial neoplasias, which rapidly progressed to invasive PDAC within 10 weeks of age. Furthermore, inactivation of mkk4/mkk7 compromised acinar regeneration following acute inflammatory stress by locking damaged exocrine cells in a permanently de-differentiated state. Therefore, we propose that JNK signaling exerts its tumor suppressive function in the pancreas by antagonizing the metaplastic conversion of acinar cells toward a ductal fate capable of responding to oncogenic stimulation.

Ability of commonly used prediction equations to predict resting energy expenditure in children with inflammatory bowel disease.

BACKGROUND: Paediatric onset inflammatory bowel disease (IBD) may cause alterations in energy requirements and invalidate the use of standard prediction equations. Our aim was to evaluate four commonly used prediction equations for resting energy expenditure (REE) in children with IBD. METHODS: Sixty-three children had repeated measurements of REE as part of a longitudinal research study yielding a total of 243 measurements. These were compared with predicted REE from Schofield, Oxford, FAO/WHO/UNU, and Harris-Benedict equations using the Bland-Altman method. RESULTS: Mean (±SD) age of the patients was 14.2 (2.4) years. Mean measured REE was 1566 (336) kcal per day compared with 1491 (236), 1441 (255), 1481 (232), and 1435 (212) kcal per day calculated from Schofield, Oxford, FAO/WHO/UNU, and Harris-Benedict, respectively. While the Schofield equation demonstrated the least difference between measured and predicted REE, it, along with the other equations tested, did not perform uniformly across all subjects, indicating greater errors at either end of the spectrum of energy expenditure. Smaller differences were found for all prediction equations for Crohn's disease compared with ulcerative colitis. CONCLUSIONS: Of the commonly used equations, the equation of Schofield should be used in pediatric patients with IBD when measured values are not able to be obtained.

Gastro-oesophageal reflux treatment for prolonged non-specific cough in children and adults.

BACKGROUND: Gastroesophageal reflux disease (GORD) is said to be the causative factor in up to 41% of adults with chronic cough. Treatment for GORD includes conservative measures (diet manipulation), pharmaceutical therapy (motility or prokinetic agents, H(2)-antagonist and proton pump inhibitors (PPI)) and fundoplication. OBJECTIVES: To evaluate the efficacy of GORD treatment on chronic cough in children and adults with GORD and prolonged cough that is not related to an underlying respiratory disease, i.e. non-specific chronic cough. SEARCH STRATEGY: We searched the Cochrane Airways Group Specialised Register, the Cochrane Register of Controlled Trials (CENTRAL), MEDLINE, EMBASE, review articles and reference lists of relevant articles. The date of last search was 8 April 2010. SELECTION CRITERIA: All randomised controlled trials (RCTs) on GORD treatment for cough in children and adults without primary lung disease. DATA COLLECTION AND ANALYSIS: Two review authors independently assessed trial quality and extracted data. We contacted study authors for further information. MAIN RESULTS: We included 19 studies (six paediatric, 13 adults). None of the paediatric studies could be combined for meta-analysis. A single RCT in infants found that PPI (compared to placebo) was not efficacious for cough outcomes (favouring placebo OR 1.61; 95% CI 0.57 to 4.55) but those on PPI had significantly increased adverse events (OR 5.56; 95% CI 1.18 to 26.25) (number needed to treat for harm in four weeks was 11 (95% CI 3 to 232)). In adults, analysis of H(2) antagonist, motility agents and conservative treatment for GORD was not possible (lack of data) and there were no controlled studies of fundoplication. We analysed nine adult studies comparing PPI (two to three months) to placebo for various outcomes in the meta-analysis. Using intention-to-treat, pooled data from studies resulted in no significant difference between treatment and placebo in total resolution of cough (OR 0.46; 95% CI 0.19 to 1.15). Pooled data revealed no overall significant improvement in cough outcomes (end of trial or change in cough scores). We only found significant differences in sensitivity analyses. We found a significant improvement in change of cough scores at end of intervention (two to three months) in those receiving PPI (standardised mean difference -0.41; 95% CI -0.75 to -0.07) using generic inverse variance analysis on cross-over trials. Two studies reported improvement in cough after five days to two weeks of treatment. AUTHORS' CONCLUSIONS: PPI is not efficacious for cough associated with GORD symptoms in very young children (including infants) and should not be used for cough outcomes. There is insufficient data in older children to draw any valid conclusions. In adults, there is insufficient evidence to conclude definitely that GORD treatment with PPI is universally beneficial for cough associated with GORD. Clinicians should be cognisant of the period (natural resolution with time) and placebo effect in studies that utilise cough as an outcome measure. Future paediatric and adult studies should be double-blind, randomised controlled and parallel-design, using treatments for at least two months, with validated subjective and objective cough outcomes and include ascertainment of time to respond as well as assessment of acid and/or non-acid reflux.

Colonic hyperactivity results in frequent fecal soiling in a subset of children after surgery for Hirschsprung disease.

BACKGROUND AND AIM: Fecal soiling is a challenging problem in some children after pull-through surgery for Hirschsprung disease (HSCR). The prevailing perception is that soiling results from overflow incontinence; however, its treatment with laxatives yields mixed results. Colonic manometry studies are reported to be normal in most patients in this population. The interpretation of these findings does not support the physiology of fecal overflow incontinence in these children. The aim of the present study was to define the physiology underlying daily, frequent fecal soiling in children after surgery for HSCR using manometric techniques. PATIENTS AND METHODS: Four pediatric motility centers in the United States participated in the study; medical records and manometric tracings (anorectal and colonic) of children (n = 59; 6.5 years; 48 boys) who had pull-through surgery for HSCR and presented with daily, frequent fecal soiling were examined. Children referred for evaluation of constipation who had normal colonic manometry served as controls (n = 25; 6.7 years; 12 boys). The patients with HSCR were divided into 2 groups (Hirschsprung disease groups 1 and 2 [HD1, HD2]) based on the absence or presence of high-amplitude propagated contractions (HAPCs). A control group that included children with chronic constipation was also studied. We compared the mean HAPC frequency between the HD2 and control groups. RESULTS: HD1 included 21 patients who had no HAPCs in fasting or postprandial periods. HD2 included 38 patients who had an average of 0.07 HPACs/min while fasting and 0.13/min in the postprandial state. In this subset the number of HAPCs in the fasting state (P = 0.04) and the postprandial state (P < 0.001) was greater when compared with controls. Additionally, there was a significant increase in HAPCs/min from the fasting to the postprandial state (P = 0.01). In the HD2 group 40% had colonic hyperactivity. CONCLUSIONS: Daily, frequent fecal soiling after pull-through surgery for HSCR may be due to colonic hyperactivity in some children. It is imperative that this unique subset be identified because the management strategy would include avoidance of laxatives, contrary to standard current practice.

Bone health in children with inflammatory bowel disease: adjusting for bone age.

OBJECTIVES: Clinical results of bone mineral density for children with inflammatory bowel disease are commonly reported using reference data for chronological age. It is known that these children, particularly those with Crohn disease, experience delayed growth and maturation. Therefore, it is more appropriate to compare clinical results with bone age rather than chronological age. MATERIALS AND METHODS: Areal bone mineral density (aBMD) was measured using dual energy x-ray absorptiometry, and bone age was assessed using the Tanner-Whitehouse 3 method from a standard hand/wrist radiograph. Results were available for 44 children ages 7.99 to 16.89 years. Areal bone mineral density measurements were converted to z scores using both chronological and bone ages for each subject. RESULTS: Areal bone mineral density z scores calculated using bone age, as opposed to chronological age, were significantly improved for both the total body and lumbar spine regions of interest. When subjects were grouped according to diagnosis, bone age generated z scores remained significantly improved for those with Crohn disease but not for those diagnosed with ulcerative colitis. Grouping of children with Crohn disease into younger and older ages produced significantly higher z scores using bone age compared with chronological for the older age group, but not the younger age group. CONCLUSIONS: Our findings, in accordance with those presented in the literature, suggest that aBMD results in children with Crohn disease should include the consideration of bone age, rather than merely chronological age. Bone size, although not as easily available, would also be an important consideration for interpreting results in paediatric populations.

Gastrointestinal complications of fundoplication.

In children with medically refractory gastroesophageal reflux disease (GERD), fundoplication is effective and safe. However, in a subset of patients, gastrointestinal dysfunction occurs postoperatively. Symptoms include chest pain, persistent dysphagia in 5%, gas bloat in 2% to 4%, diarrhea in up to 20%, and dumping syndrome in up to 30%. Symptoms are often nonspecific, arising from recurrent or persistent GERD, anatomic complications such as disrupted or herniated wrap, functional disturbances such as rapid gastric emptying or altered gastric accommodation, or alternative diagnoses such as cyclic vomiting syndrome or food allergy. Detailed investigation, including various combinations of pHmetry, videofluoroscopy, endoscopy, motility studies, and dumping provocation testing, may be required to clarify pathophysiology and guide management.

Age and gender affect ventricular-vascular coupling during aerobic exercise.

OBJECTIVES: The goal of this study was to examine the age-associated differences in ventricular-vascular coupling, defined by the ratio of arterial elastance (EaI) to left ventricular systolic elastance (E(LV)I), and its components, at rest and during exercise. BACKGROUND: Ejection fraction (EF) increases during exercise, but the EF reserve decreases with aging. Ejection fraction is inversely related to EaI/E(LV)I, an index of the interaction between arterial and ventricular properties, which is an important determinant of cardiac performance. Thus, age differences in EaI/E(LV)I during exercise, due to age differences in EaI, E(LV)I, or both, may help to explain the age deficit in EF reserve. METHODS: We noninvasively characterized EaI/E(LV)I = end-systolic volume index (ESVI)/stroke volume index (SVI) and its two determinants EaI = end-systolic pressure/SVI, and E(LV)I = end-systolic pressure/ESVI, at rest and during exercise in 239 healthy men and women (age range, 21 to 87 years). Blood pressures were assessed with cuff sphygomanometry, and cardiac volumes with gated blood pool scintingraphy. RESULTS: Resting EaI/E(LV)I was not age related in men or women. In both sexes, EaI/E(LV)I decreased during exercise and declined to a lesser extent in older subjects. There were gender differences in the components of EaI/E(LV)I during exercise: EaI was greater in older versus young women (p = 0.01) but was unaffected by age in men. Left ventricular systolic elastance increased to a greater extent in young versus older subjects (p = 0.0001 for men, p = 0.07 for women). CONCLUSIONS: Age-associated differences in EaI/E(LV)I occur in both genders during exercise. Sub-optimal ventricular-vascular coupling helps to explain the age-associated blunting of maximal exercise EF, and its underlying mechanisms appear to differ between men and women.

Successful resection of localized intestinal lymphangiectasia post-Fontan: role of (99m)technetium-dextran scintigraphy.

Intestinal lymphangiectasia is a well-recognized complication of the Fontan procedure, occurring in up to 24% of patients. Because of the loss of chylous fluid into the gut lumen, protein-losing enteropathy results as well as lymphopenia and hypogammaglobulinaemia. In some cases, dilated lymphatics in the intestinal serosa or mesentery also rupture, causing chylous ascites. Standard medical and cardiac surgical interventions are generally ineffective and the condition is frequently lethal. We report a case of intractable and life-threatening chylous ascites and chylothorax in a 14-year-old girl, associated with intestinal lymphangiectasia and protein-losing enteropathy after a Fontan procedure for tricuspid atresia. The condition was refractory to all standard medical therapies, including dietary modifications, diuretics, corticosteroid therapy, albumin infusions, octreotide, heparin, bowel rest, and parenteral nutrition. Cardiac surgery to optimize her hemodynamic status was also ineffective and large volume pleural and ascitic fluid losses continued. Having exhausted all other therapeutic modalities, (99m)technetium-dextran scintigraphy was performed to assess the extent of intestinal protein loss and the potential for surgical intervention. Scintigraphy suggested localized protein loss from the proximal jejunum and subsequent segmental resection was effective. Postoperatively, ascites and pleural effusions resolved, and there was no evidence of short bowel syndrome. Growth has accelerated and the patient has entered puberty. There is mild persistent intestinal protein loss requiring diuretic therapy. Ascites or pleural effusions are absent, and the patient remains well >2 years after surgery. Intestinal lymphangiectasia post-Fontan procedures has traditionally been ascribed to hemodynamic factors such as raised systemic venous pressure, which would predispose to a generalized intestinal lesion. However, in this case, scintigraphy demonstrated a localized, surgically correctible lesion. To our knowledge, this is the first reported case of the use of (99m)technetium-dextran scintigraphy for this indication and of successful partial small bowel resection in such a case.

Cell cycle and genetic background dependence of the effect of loss of BRCA2 on ionizing radiation sensitivity.

Carriers of mutations in the BRCA2 gene are at a highly elevated risk of breast and other cancers. The BRCA2 gene encodes a very large protein thought to play a role in DNA repair. To examine the effect of mutation of BRCA2 on sensitivity to ionizing radiation, we used a previously described mouse model system (Brca2(Tr)) in which the Brca2 open reading frame is truncated. Mouse embryo fibroblasts carrying this mutation have a proliferative defect, which we show here can be substantially rescued by genetic ablation of p53. Proliferating Brca2(Tr/Tr)/p53(-/-) cells, like Brca2(Tr/Tr) cells, show genomic instability. We used the clonogenic survival assay, which depends on the ability of cells to proliferate, to examine the cell cycle dependence of radiation sensitivity of Brca2(Tr/Tr)/p53(-/-) compared to p53(-/-) and wild-type cells. This showed that the Brca2 mutation had little effect on cells irradiated in quiescence but sensitized proliferating cells to ionizing radiation on a p53(-/-) background. These results suggest that the major role of Brca2 in mediating cell survival after irradiation is in the S and G(2) phases of the cell cycle.

Oxidative stress and hemorheological changes induced by acute treadmill exercise.

The present investigation was designed to evaluate the acute effect of aerobic exercise on oxidative stress and the flow properties of the blood. Fourteen clinically healthy subjects (7 men and 7 women aged 56+/-19 yr) underwent maximal treadmill exercise with blood samples drawn prior to and immediately after exercise. Post-exercise significant increases were observed in plasma lipid hydroperoxides from 6.5+/-2.0 microM to 7.9+/-1.9 microM (p<0.0001) and the relative concentration of plasma fluorescent products associated with red cell peroxidation from 138+/-28 RF to 220+/-92 RF (p<0.005). After exercise there was a rise in the hematocrit from 41.4+/-3.7% to 44.4+/-4.1% (p<0.0001), increases in whole blood viscosity at shear rates of 22.5/sec to 450/sec (p<0.0005), an increase in plasma viscosity from 1.27+/-0.12 cP to 1.36+/-0.11 cP (p<0.01), an increase in red cell rigidity from 2.44+/-0.48 cP to 2.62+/-0.42 cP (p<0.001) and a decrease in erythrocyte sedimentation rate from 26.9+/-18.6 mm/h to 22.5+/-15.9 mm/h (p<0.01). The findings suggest that acute aerobic exercise induces oxidative damage to red blood cells and adversely affects rheological properties of the peripheral blood.