Effect of smoking cessation on mitochondrial respiratory chain function

A modelling approach to disentangle the factors limiting muscle oxygenation in smokers

Cigarette smoking is associated with a lower exercise capacity and lower muscle fatigue resistance. This is at least partly attributable to carboxyhaemoglobin (HbCO) in the blood that via reduction in the oxygen-carrying capacity, and the left-shift of the Hb-dissociation curve would reduce tissue oxygenation. On the other hand, a reduced oxygen uptake due to mitochondrial dysfunction would result in improved oxygenation. We used previously collected capillarisation, myoglobin and estimated cellular maximal muscle oxygen consumption data derived from succinate dehydrogenase-stained sections from the vastus lateralis muscle from six smokers and five non-smokers. These data were fed into an expanded Krogh tissue oxygenation model to assess whether an impaired muscle fatigue resistance in smokers is primarily due to HbCO or impaired mitochondrial respiration. The model showed that in smokers with 6% and 20% HbCO (causing a left-shift of the Hb-dissociation curve) average muscle oxygenation was reduced by 1.9% and 7.2%, respectively. Muscle oxygenation was increased by 13.3% when maximal mitochondrial respiration was reduced by 29%. A combination of a 29% reduction in maximal mitochondrial respiration and 20% HbCO led to no significant difference in muscle oxygenation from that in non-smokers. This indicates that while HbCO may explain the reduced exercise capacity after just one smoking session, in chronic smokers impaired mitochondrial respiration appears more important in reducing oxygen extraction and exercise capacity with only a small contribution of the left-shift of the Hb-dissociation curve.

The role of lifestyle in the association between frailty and all-cause mortality amongst older adults: a mediation analysis in the UK Biobank

OBJECTIVE

frailty is a syndrome characterised by increased vulnerability to stressors, which manifests as higher death risk. Whilst guidelines for frailty management usually entails lifestyle modifications (e.g. physical exercise, diet), the mediating role of lifestyle on the excess mortality associated with frailty is unclear. This study estimates the death risk due to frailty that could be avoided with a healthy lifestyle in older adults.

SUBJECTS AND METHODS

we analysed data from 91,906 British individuals aged ≥60 years recruited between 2006 and 2010. At baseline, frailty was identified according to Fried's phenotype, and a four-item Healthy Lifestyle Index (HLS) was calculated based on physical activity, diet, smoking and alcohol consumption. Mortality was ascertained from baseline through 2021. A mediation analysis under the counterfactual framework was performed adjusting for the main confounders.

RESULTS

during a median follow-up of 12.5 years, 9,383 deaths occurred. Frailty was directly associated with all-cause mortality (hazard ratio: 2.30 [95% confidence interval {CI} 2.07, 2.54]), and inversely associated with the HLS (ß: -0.45 points [-0.49, -0.40]). The hazard ratio [95%CI] for the direct effect of frailty on mortality was 2.12 [1.91, 2.34], whilst for the indirect effect (mediated by HLS) was 1.08 [1.07, 1.10]. The mediated proportion of HLS on mortality was 13.55% [11.26, 16.20], with physical activity having the highest proportion amongst the four HLS items (7.69% [5.00, 10.40]).

CONCLUSIONS

a healthy lifestyle partly mediates the association between frailty and mortality in British older adults. Since this was an exploratory mediation analysis, these results should be specifically tested in future research.

Plasma GDF-15 concentration is not elevated in open-angle glaucoma

Aim

Recently, the level of growth differentiation factor 15 (GDF-15) in blood, was proposed as biomarker to detect mitochondrial dysfunction. In the current study, we evaluate this biomarker in open-angle glaucoma (OAG), as there is increasing evidence that mitochondrial dysfunction plays a role in the pathophysiology of this disease.

Methods

Plasma GDF-15 concentrations were measured with ELISA in 200 OAG patients and 61 age-matched controls (cataract without glaucoma). The OAG patient group consisted of high tension glaucoma (HTG; n = 162) and normal tension glaucoma (NTG; n = 38). Groups were compared using the Kruskal-Wallis nonparametric test with Dunn’s multiple comparison post-hoc correction. GDF-15 concentration was corrected for confounders identified with forward linear regression models.

Results

Before correcting for confounders, median plasma GDF-15 levels was significantly lower in the combined OAG group (p = 0.04), but not when analysing HTG and NTG patients separately. Forward linear regression analysis showed that age, gender, smoking and systemic hypertension were significant confounders affecting GDF-15 levels. After correction for these confounders, GDF-15 levels in OAG patients were no longer significantly different from controls. Subgroup analysis of the glaucoma patients did not show a correlation between disease severity and plasma GDF-15, but did reveal that for NTG patients, intake of dietary supplements, which potentially improve mitochondrial function, correlated with lower plasma GDF-15.

Conclusion

The present study suggests that plasma GDF-15 is not suited as biomarker of mitochondrial dysfunction in OAG patients.

Two Weeks of Smoking Cessation Reverse Cigarette Smoke-Induced Skeletal Muscle Atrophy and Mitochondrial Dysfunction in Mice

INTRODUCTION

Apart from its adverse effects on the respiratory system, cigarette smoking also induces skeletal muscle atrophy and dysfunction. Whether short-term smoking cessation can restore muscle mass and function is unknown. We, therefore, studied the impact of 1- and 2-week smoking cessation on skeletal muscles in a mouse model.

METHODS

Male mice were divided into four groups: Air-exposed (14 weeks); cigarette smoke (CS)-exposed (14 weeks); CS-exposed (13 weeks) followed by 1-week cessation; CS-exposed (12 weeks) followed by 2 weeks cessation to examine exercise capacity, physical activity levels, body composition, muscle function, capillarization, mitochondrial function and protein expression in the soleus, plantaris, and diaphragm muscles.

RESULTS

CS-induced loss of body and muscle mass was significantly improved within 1 week of cessation due to increased lean and fat mass. Mitochondrial respiration and protein levels of the respiratory complexes in the soleus were lower in CS-exposed mice, but similar to control values after 2 weeks of cessation. Exposing isolated soleus muscles to CS extracts reduced mitochondrial respiration that was reversed after removing the extract. While physical activity was reduced in all groups, exercise capacity, limb muscle force, fatigue resistance, fiber size and capillarization, and diaphragm cytoplasmic HIF-1α were unaltered by CS-exposure. However, CS-induced diaphragm atrophy and increased capillary density were not seen after 2 weeks of smoking cessation.

CONCLUSION

In male mice, 2 weeks of smoking cessation reversed smoking-induced mitochondrial dysfunction, limb muscle mass loss, and diaphragm muscle atrophy, highlighting immediate benefits of cessation on skeletal muscles.

IMPLICATIONS

Our study demonstrates that CS-induced skeletal muscle mitochondrial dysfunction and atrophy are significantly improved by 2 weeks of cessation in male mice. We show for the first time that smoking cessation as short as 1 to 2 weeks is associated with immediate beneficial effects on skeletal muscle structure and function with the diaphragm being particularly sensitive to CS-exposure and cessation. This could help motivate smokers to quit smoking as early as possible. The knowledge that smoking cessation has potential positive extrapulmonary effects is particularly relevant for patients referred to rehabilitation programs and those admitted to hospitals suffering from acute or chronic muscle deterioration yet struggling with smoking cessation.

Deciphering the genetic and epidemiological landscape of mitochondrial DNA abundance

Mitochondrial (MT) dysfunction is a hallmark of aging and has been associated with most aging-related diseases as well as immunological processes. However, little is known about aging, lifestyle and genetic factors influencing mitochondrial DNA (mtDNA) abundance. In this study, mtDNA abundance was estimated from the weighted intensities of probes mapping to the MT genome in 295,150 participants from the UK Biobank. We found that the abundance of mtDNA was significantly elevated in women compared to men, was negatively correlated with advanced age, higher smoking exposure, greater body-mass index, higher frailty index as well as elevated red and white blood cell count and lower mortality. In addition, several biochemistry markers in blood-related to cholesterol metabolism, ion homeostasis and kidney function were found to be significantly associated with mtDNA abundance. By performing a genome-wide association study, we identified 50 independent regions genome-wide significantly associated with mtDNA abundance which harbour multiple genes involved in the immune system, cancer as well as mitochondrial function. Using mixed effects models, we estimated the SNP-heritability of mtDNA abundance to be around 8%. To investigate the consequence of altered mtDNA abundance, we performed a phenome-wide association study and found that mtDNA abundance is involved in risk for leukaemia, hematologic diseases as well as hypertension. Thus, estimating mtDNA abundance from genotyping arrays has the potential to provide novel insights into age- and disease-relevant processes, particularly those related to immunity and established mitochondrial functions.

Cigarette Smoking Is Associated With Lower Quadriceps Cross-sectional Area and Attenuation in Older Adults

INTRODUCTION

In addition to well-established links with cardiovascular and respiratory diseases, cigarette smoking may affect skeletal muscle; however, associations with quadriceps atrophy, density, and function are unknown. This study explored the associations of current and former smoking with quadriceps muscle area and attenuation as well as muscle force (assessed as knee extension peak torque) and rate of torque development-a measure of muscle power in older adults.

METHODS

Data from 4469 older adults, aged 66-95 years at baseline in the Age, Gene/Environment Susceptibility-Reykjavik Study with measurements of thigh computed tomography, isometric knee extension testing, self-reported smoking history, and potential covariates were analyzed.

RESULTS

Sex differences were observed in these data; therefore, our final analyses are stratified by sex. In men, both former smokers and current smokers had lower muscle area (with β= -0.10, 95% confidence interval [CI] = -0.17 to -0.03 and β = -0.19, 95% CI = -0.33 to -0.05, respectively) and lower muscle attenuation (ie, higher fat infiltration, β = -0.08, 95% CI = -0.16 to -0.01 and β = -0.17, 95% CI = -0.34 to -0.01, respectively) when compared with never smokers. Smoking status was not associated with male peak torque or rate of torque development. In women, current smoking was associated with lower muscle attenuation (β = -0.24, 95% CI = -0.34 to -0.13) compared to never smoking. Among female smokers (current and former), muscle attenuation and peak torque were lower with increasing pack-years.

CONCLUSIONS

Results suggest that cigarette smoking is related to multiple muscle properties at older age and that these relationships may be different among men and women.

IMPLICATIONS

This article presents novel data, as it examined for the first time the relationship between smoking and computed tomography-derived quadriceps muscle size (cross-sectional area) and attenuation. This study suggests that current cigarette smoking is related to higher muscle fat infiltration, which may have significant health implications for the older population, because of its known association with poor physical function, falls, and hip fractures.

Assessment of mitochondrial function following short- and long-term exposure of human bronchial epithelial cells to total particulate matter from a candidate modified-risk tobacco product and reference cigarettes

Mitochondrial dysfunction caused by cigarette smoke is involved in the oxidative stress-induced pathology of airway diseases. Reducing the levels of harmful and potentially harmful constituents by heating rather than combusting tobacco may reduce mitochondrial changes that contribute to oxidative stress and cell damage. We evaluated mitochondrial function and oxidative stress in human bronchial epithelial cells (BEAS 2B) following 1- and 12-week exposures to total particulate matter (TPM) from the aerosol of a candidate modified-risk tobacco product, the Tobacco Heating System 2.2 (THS2.2), in comparison with TPM from the 3R4F reference cigarette. After 1-week exposure, 3R4F TPM had a strong inhibitory effect on mitochondrial basal and maximal oxygen consumption rates compared to TPM from THS2.2. Alterations in oxidative phosphorylation were accompanied by increased mitochondrial superoxide levels and increased levels of oxidatively damaged proteins in cells exposed to 7.5 μg/mL of 3R4F TPM or 150 μg/mL of THS2.2 TPM, while cytosolic levels of reactive oxygen species were not affected. In contrast, the 12-week exposure indicated adaptation of BEAS-2B cells to long-term stress. Together, the findings indicate that 3R4F TPM had a stronger effect on oxidative phosphorylation, gene expression and proteins involved in oxidative stress than TPM from the candidate modified-risk tobacco product THS2.2.

Minimising failure in critical lower limb ischaemia intervention: Adjuvant capillary bed recruitment is the missed opportunity

Critical limb ischaemia is the end stage of peripheral arterial disease before limb loss. Contemporary interventions to restore blood flow have high morbidity and mortality and fail to provide sustained restoration of peripheral circulation. Cell-based therapies designed to promote neovascularisation or angiogenesis have been shown in trials to be safe but clinically ineffective. Notwithstanding endless research in the area, no headway has been made in identifying a successful therapy designed specifically to target muscle disease in critical lower limb ischaemia. Thus, the quest to find an effective, lasting solution for critical lower limb ischaemia continues and requires more innovative therapeutic tactics. Our aim is to highlight the crucially interlinked role of the capillary bed, skeletal muscle mass and mitochondria in critical lower limb ischaemia patients and to identify novel therapeutic mechanisms that the vascular interventionalist can add to their armamentarium.

Mitochondrial toxicity in human pregnancy: an update on clinical and experimental approaches in the last 10 years

Mitochondrial toxicity can be one of the most dreadful consequences of exposure to a wide range of external agents including pathogens, therapeutic agents, abuse drugs, toxic gases and other harmful chemical substances. However, little is known about the effects of mitochondrial toxicity on pregnant women exposed to these agents that may exert transplacental activity and condition fetal remodeling. It has been hypothesized that mitochondrial toxicity may be involved in some adverse obstetric outcomes. In the present study, we investigated the association between exposure to mitochondrial toxic agents and pathologic conditions ranging from fertility defects, detrimental fetal development and impaired newborn health due to intra-uterine exposure. We have reviewed data from studies in human subjects to propose mechanisms of mitochondrial toxicity that could be associated with the symptoms present in both exposed pregnant and fetal patients. Since some therapeutic interventions or accidental exposure cannot be avoided, further research is needed to gain insight into the molecular pathways leading to mitochondrial toxicity during pregnancy. The ultimate objective of these studies should be to reduce the mitochondrial toxicity of these agents and establish biomarkers for gestational monitoring of harmful effects.

Metabolic profiling detects early effects of environmental and lifestyle exposure to cadmium in a human population

BACKGROUND

The 'exposome' represents the accumulation of all environmental exposures across a lifetime. Top-down strategies are required to assess something this comprehensive, and could transform our understanding of how environmental factors affect human health. Metabolic profiling (metabonomics/metabolomics) defines an individual's metabolic phenotype, which is influenced by genotype, diet, lifestyle, health and xenobiotic exposure, and could also reveal intermediate biomarkers for disease risk that reflect adaptive response to exposure. We investigated changes in metabolism in volunteers living near a point source of environmental pollution: a closed zinc smelter with associated elevated levels of environmental cadmium.

METHODS

High-resolution ¹H NMR spectroscopy (metabonomics) was used to acquire urinary metabolic profiles from 178 human volunteers. The spectral data were subjected to multivariate and univariate analysis to identify metabolites that were correlated with lifestyle or biological factors. Urinary levels of 8-oxo-deoxyguanosine were also measured, using mass spectrometry, as a marker of systemic oxidative stress.

RESULTS

Six urinary metabolites, either associated with mitochondrial metabolism (citrate, 3-hydroxyisovalerate, 4-deoxy-erythronic acid) or one-carbon metabolism (dimethylglycine, creatinine, creatine), were associated with cadmium exposure. In particular, citrate levels retained a significant correlation to urinary cadmium and smoking status after controlling for age and sex. Oxidative stress (as determined by urinary 8-oxo-deoxyguanosine levels) was elevated in individuals with high cadmium exposure, supporting the hypothesis that heavy metal accumulation was causing mitochondrial dysfunction.

CONCLUSIONS

This study shows evidence that an NMR-based metabolic profiling study in an uncontrolled human population is capable of identifying intermediate biomarkers of response to toxicants at true environmental concentrations, paving the way for exposome research.

Association Between Glycosylated Hemoglobin and Intentional Weight Loss in Overweight and Obese Patients With Type 2 Diabetes Mellitus

Purpose

The purpose of this study is to assess the relationship between magnitude of weight loss and improvement in percentage A1C (A1C%) among overweight and obese patients with type 2 diabetes mellitus (DM) undergoing weight reduction.

Methods

Case records of patients enrolled in 2 university-based weight management programs were reviewed. Patients were sampled if they had a diagnosis of DM and had at least 1 documented A1C% reduction from their baseline value. Weight loss treatment was individualized and consisted of a calorie-restricted diet, a behavior modification plan, and a plan for increasing physical activity. Patient weights were measured at bimonthly visits. A1C% was measured every 3 months.

Results

Seventy-two patients formed the study cohort. Mean baseline body mass index was 35.1 kg/m2, mean age was 52.6 years, and 59% were males. Mean starting A1C% was 8.6. Patients achieved significant mean weight loss (10.7 kg) at study exit. Weight loss of 6.5 kg (4.5% of baseline body weight), 12.2 kg (8.7%), and 15.9 kg (10.3%) was required to reduce A1C% by 0.5, 1, and 1.5, respectively, and it took a mean of 5.6, 8.7, and 10.1 months, respectively, to achieve this. After adjustment for antidiabetic medication intake, for every 10% weight loss, the predicted reduction in A1C% was 0.81.

Conclusions

Intentional weight loss of 10% can potentially decrease A1C% by 0.81 among patients with type 2 DM. This finding may be clinically useful in encouraging and counseling a patient attempting weight loss.

Lung glutathione adaptive responses to cigarette smoke exposure

Background

Smoking tobacco is a leading cause of chronic obstructive pulmonary disease (COPD), but although the majority of COPD cases can be directly related to smoking, only a quarter of smokers actually develop the disease. A potential reason for the disparity between smoking and COPD may involve an individual's ability to mount a protective adaptive response to cigarette smoke (CS). Glutathione (GSH) is highly concentrated in the lung epithelial lining fluid (ELF) and protects against many inhaled oxidants. The changes in GSH that occur with CS are not well investigated; therefore the GSH adaptive response that occurs with a commonly utilized CS exposure was examined in mice.

Methods

Mice were exposed to CS for 5 h after which they were rested in filtered air for up to 16 h. GSH levels were measured in the ELF, bronchoalveolar lavage cells, plasma, and tissues. GSH synthesis was assessed by measuring γ-glutamylcysteine ligase (GCL) activity in lung and liver tissue.

Results

GSH levels in the ELF, plasma, and liver were decreased by as much as 50% during the 5 h CS exposure period whereas the lung GSH levels were unchanged. Next, the time course of rebound in GSH levels after the CS exposure was examined. CS exposure initially decreased ELF GSH levels by 50% but within 2 h GSH levels rebound to about 3 times basal levels and peaked at 16 h with a 6-fold increase and over repeat exposures were maintained at a 3-fold elevation for up to 2 months. Similar changes were observed in tissue GCL activity which is the rate limiting step in GSH synthesis. Furthermore, elevation in ELF GSH levels was not arbitrary since the CS induced GSH adaptive response after a 3d exposure period prevented GSH levels from dropping below basal levels.

Conclusions

CS exposures evoke a powerful GSH adaptive response in the lung and systemically. These data suggests there may be a sensor that sets the ELF GSH adaptive response to prevent GSH levels from dipping below basal levels. Factors that disrupt GSH adaptive responses may contribute to the pathophysiology of COPD.

Crohn's disease: evidence for involvement of unregulated transcytosis in disease etio-pathogenesis

Crohn's disease (CD) is a chronic inflammatory bowel disease. Research has identified genetic predisposition and environmental factors as key elements in the development of the disease. However, the precise mechanism that initiates immune activation remains undefined. One pathway for luminal antigenic molecules to enter the sterile lamina propria and activate an immune response is via transcytosis. Transcytosis, although tightly regulated by the cell, has the potential for transepithelial transport of bacteria and highly antigenic luminal molecules whose uncontrolled translocation into the lamina propria can be the source of immune activation. Viewed as a whole, the evidence suggests that unregulated intestinal epithelial transcytosis is involved in the inappropriate presentation of immunogenic luminal macromolecules to the intestinal lamina propria. Thus fulfilling the role of an early pre-morbid mechanism that can result in antigenic overload of the lamina propria and initiate an immune response culminating in chronic inflammation characteristic of this disease. It is the aim of this paper to present evidence implicating enterocyte transcytosis in the early etio-pathogenesis of CD.

Mitochondrial injury in human acute carbon monoxide poisoning: the effect of oxygen treatment

The best oxygen therapy for acute carbon monoxide poisoning (ACOP) remains unestablished. Reported mitochondrial complex IV (mtCIV) inhibition, together with carboxyhaemoglobin (COHb)-induced hypoxia, may influence acute clinical symptoms and outcome. To "mitochondrially" evaluate treatment efficacy, we correlated intoxication severity and symptoms with mitochondrial function (mtCIV activity) and oxidative stress (lipid peroxidation) in 60 poisoned patients and determined ACOP recovery depending on either normobaric or hyperbaric oxygen therapy along a 3-month follow-up. In the present article we positively evaluate mtCIV as a good marker of ACOP recovery, treatment effectiveness, and late neurological syndrome development, which advocates for hyperbaric oxygen therapy as the treatment of choice. However, we discourage its usefulness as a severity marker because of its excessive sensitivity. We additionally evaluate oxidative stress role and prognostic factors for neurological sequelae development.

Skeletal muscle properties and fatigue resistance in relation to smoking history

Although smoking-related diseases, such as chronic obstructive pulmonary disease (COPD), are often accompanied by increased peripheral muscle fatigability, the extent to which this is a feature of the disease or a direct effect of smoking per se is not known. Skeletal muscle function was investigated in terms of maximal voluntary isometric torque, activation, contractile properties and fatigability, using electrically evoked contractions of the quadriceps muscle of 40 smokers [19 men and 21 women; mean (SD) cigarette pack years: 9.9 (10.7)] and age- and physical activity level matched non-smokers (22 men and 23 women). Maximal strength and isometric contractile speed did not differ significantly between smokers and non-smokers. Muscle fatigue (measured as torque decline during a series of repetitive contractions) was greater in smokers (P = 0.014), but did not correlate with cigarette pack years (r = 0.094, P = 0.615), cigarettes smoked per day (r = 10.092, P = 0.628), respiratory function (%FEV_1pred) (r = −0.187, P = 0.416), or physical activity level (r = −0.029, P = 0.877). While muscle mass and contractile properties are similar in smokers and non-smokers, smokers do suffer from greater peripheral muscle fatigue. The observation that the cigarette smoking history did not correlate with fatigability suggests that the effect is either acute and/or reaches a ceiling, rather than being cumulative. An acute and reversible effect of smoking could be caused by carbon monoxide and/or other substances in smoke hampering oxygen delivery and mitochondrial function.

Severe acute poisoning due to a glufosinate containing preparation without mitochondrial involvement

Glufosinate is a non-selective herbicide widely used in domestic gardens and agriculture. Few cases of glufosinate poisoning have been reported although there has been an increase in recent years, particularly in Japan. Glufosinate toxicity is related to its capacity to inhibit glutamine synthetase and glutamate decarboxylase, which may lead to a potentially fatal multiorgan failure. We report the case of a 41-year-old woman who ingested between 30 and 50 mL of a herbicide (Finale®) containing glufosinate (14%) in a suicide attempt. One hour after ingestion, the patient attended the Emergency Department of her own volition. Her overall status was good, and the physical examination was unremarkable. Gastric lavage was carried out, 25 g of activated charcoal was administered, and the patient was admitted for observation. Seventeen hours later, the patient presented drowsiness and a sinus bradycardia of 40 bpm. Thirty-two hours after ingestion, the Glasgow Coma Score was 8, and orotracheal intubation and mechanical ventilation were begun. At 3 days, the patient presented a self-limiting episode of ventricular tachycardia. She recovered consciousness progressively and was extubated without complications. The evolution was favorable, but the sinus bradycardia persisted up to 8 days after the ingestion. A study of lymphocyte mitochondrial function showed no alteration in mitochondrial oxidative capacity or the enzymatic activity of the complexes of the electron transport chain. A small ingestion of glufosinate can cause severe poisoning, whose manifestations predominantly involve the central nervous system and heart rhythm. Signs and symptoms may not appear for several hours and may persist for several days. In spite of these multi-organ manifestations, no alteration in lymphocyte mitochondrial function has been reported.

Muscle fatigue resistance during stimulated contractions is reduced in young male smokers

AIM

To determine whether muscle function is compromised in healthy smokers in comparison with activity-matched non-smokers.

METHODS

Nine male smokers (aged 22.2 +/- 2.5 years: mean +/- SD) with a smoking history of 2.5 +/- 3.1 pack years, and ten male control participants (25.4 +/- 2.9 years) matched for physical activity level participated in this study. Knee extensor strength was measured using isometric maximal voluntary contractions. Voluntary activation of the quadriceps and co-activation of the biceps femoris were determined using interpolated twitches and surface electromyography respectively. The frequency-torque relationship and fatigue resistance were assessed with electrically evoked contractions. A fatigue index was determined as the ratio of final torque to initial torque during a series of isometric contractions (2 min; 30 Hz; 1 s contraction/1 s rest). Quadriceps anatomical cross sectional area was measured with MRI at 50% of femur length.

RESULTS

Maximal voluntary contraction torque, quadriceps anatomical cross sectional area, knee extensor torque/quadriceps cross sectional area, activation, co-activation and force-frequency relationship were similar, whereas the fatigue index was 17% lower in smokers than non-smokers.

CONCLUSION

In young men smoking does not significantly affect quadriceps muscle mass and contractile properties, but does reduce fatigue resistance of the quadriceps muscle, which was not attributable to differences in physical activity.

Acute Effects of Smoking on Skeletal Muscle Microcirculation Monitored by Near-Infrared Spectroscopy

BACKGROUND

Cigarette smoking predisposes to vascular disease. Our study aimed to assess the acute effects of cigarette smoking on peripheral microcirculation using near-infrared spectroscopy (NIRS) and to compare microcirculatory function of smokers with that of nonsmokers.

METHODS

We examined 65 healthy volunteers: 25 smokers (14 men and 11 women; age range, 20 to 27 years) and 40 nonsmokers (31 men and 9 women; age range, 19 to 38 years). Smokers had refrained from smoking for 2 h prior to the examination. Tissue O(2) saturation (Sto(2)), defined as the percentage of hemoglobin saturation in the microvasculature compartments, was measured with a probe placed on the thenar muscle. Sto(2) baseline values were recorded for 5 min. Subsequently, the brachial artery occlusion technique was applied to evaluate microcirculatory function before, during, and after smoking one cigarette.

RESULTS

Sto(2) before smoking was 85 +/- 6% (mean +/- SD), not differing significantly between men and women (84.4 +/- 6.6% vs 85.6 +/- 5.8%, respectively; p = 0.721). Sto(2) did not change significantly during smoking. O(2) consumption rate was significantly greater in women (33.4 +/- 6.7 Sto(2) U/min vs 25.7 +/- 7.1 Sto(2) U/min, p = 0.032) at baseline and throughout the smoking session. O(2) consumption rate was reduced during smoking (p < 0.001) and at 5 min after the smoking session. Smoking had a significant effect on vascular reactivity (p = 0.015), with no significant differences between genders. Five minutes after smoking, vascular reactivity had returned to approximately normal levels.

CONCLUSION

Smoking acutely affects microcirculatory function. NIRS is a noninvasive, operator-independent technique that can document these effects. It seems promising for the prospective evaluation of the effects of long-term exposure to cigarette smoke.

Aerobic capacity, oxidant stress, and chronic obstructive pulmonary disease--a new take on an old hypothesis

Chronic obstructive pulmonary disease (COPD) is a smoking-related disorder that is a leading cause of death worldwide. It is associated with an accelerated rate of age-related decline in lung function due to the occurrence of destructive pathological changes such as emphysema, small airway remodeling, and mucus hypersecretion. Smokers are exposed to trillions of radicals and thousands of reactive chemicals and particles with every cigarette, thus oxidant stress is believed to be a central factor in the pathogenesis of COPD. The molecular activities of radicals, reactive oxygen, and nitrogen species can, over time, lead to a number of the detrimental changes in the lung. For instance, smoke can directly damage the mitochondrion, an organelle that has long been linked to age-related diseases associated with oxidant stress. Mitochondria are involved in a number of important cellular processes and are the largest source of endogenous reactive oxygen species (ROS) in the cell; therefore, any impairment of mitochondrial function can lead to greater oxidant damage, cellular dysfunction, and eventually to disease. Only a subset of smokers (15-50%) develops COPD, suggesting that there are polygenetic and/or environmental susceptibility factors involved in this complex disease. Here, we propose that the aerobic capacity for an individual may determine whether one is susceptible to developing COPD. Aerobic capacity is a polygenetic trait closely associated with mitochondrial function, and we suggest antioxidant defenses. Thus, those smokers who have the greatest aerobic capacity will be most resistant to the effects of chronic cigarette smoke exposure and be less likely to develop COPD.