Healthy Human Adults Research Articles

Dietary protein and bone health: a systematic review and meta-analysis

BackgroundThere has been a resurgence of interest in the controversial relation between dietary protein and bone health. ObjectiveThis article reports on the first systematic review and meta-analysis of the relation between protein and bone health in healthy human adults. DesignThe MEDLINE (January 1966 to September 2007) and EMBASE (1974 to July 2008) databases were electronically searched for all relevant studies of healthy adults; studies of calcium excretion or calcium balance were excluded. ResultsIn cross-sectional surveys, all pooled r values for the relation between protein intake and bone mineral density (BMD) or bone mineral content at the main clinically relevant sites were significant and positive; protein intake explained 1–2% of BMD. A meta-analysis of randomized placebo-controlled trials indicated a significant positive influence of all protein supplementation on lumbar spine BMD but showed no association with relative risk of hip fractures. No significant effects were identified for soy protein or milk basic protein on lumbar spine BMD. ConclusionsA small positive effect of protein supplementation on lumbar spine BMD in randomized placebo-controlled trials supports the positive association between protein intake and bone health found in cross-sectional surveys. However, these results were not supported by cohort study findings for hip fracture risk. Any effects found were small and had 95% CIs that were close to zero. Therefore, there is a small benefit of protein on bone health, but the benefit may not necessarily translate into reduced fracture risk in the long term.

Effects of Lorazepam and Citalopram on Human Defensive Reactions: Ethopharmacological Differentiation of Fear and Anxiety

Drugs that are clinically effective against generalized anxiety disorder preferentially alter rodent risk assessment behavior, whereas drugs that are clinically effective against panic disorder preferentially alter rodent flight behavior. The theoretical principle of "defensive direction" explains the pattern of associations between emotion and defensive behavior in terms of the differing functional demands arising from cautious approach to threat (anxiety) versus departure from threat (fear), offering the prospect that clinically important emotions may be explained using a single rubric of defense. We used a within-subjects, placebo-controlled, design to test this theory, measuring the effects of citalopram and lorazepam on the defensive behavior of 30 healthy adult male humans. We indexed human defensive behavior with a translation of an active avoidance task used to measure rodent defense and found that lorazepam significantly reduced the intensity of defensive behavior during approach to threat (hypothetically anxiety-related) but not departure from threat (hypothetically fear-related). Contrary to prediction, citalopram did not affect either form of defensive reaction. Since lorazepam is a drug with well established anxiety reducing properties, these data support the hypothesis that anxiety is an emotion elicited by threat stimuli that require approach. These data also contribute to the validation of a novel human analog of an established experimental model of rodent fear and anxiety.

Biomarkers of human gastrointestinal tract regions

Dysregulation of intestinal epithelial cell performance is associated with an array of pathologies whose onset mechanisms are incompletely understood. While whole-genomics approaches have been valuable for studying the molecular basis of several intestinal diseases, a thorough analysis of gene expression along the healthy gastrointestinal tract is still lacking. The aim of this study was to map gene expression in gastrointestinal regions of healthy human adults and to implement a procedure for microarray data analysis that would allow its use as a reference when screening for pathological deviations. We analyzed the gene expression signature of antrum, duodenum, jejunum, ileum, and transverse colon biopsies using a biostatistical method based on a multivariate and univariate approach to identify region-selective genes. One hundred sixty-six genes were found responsible for distinguishing the five regions considered. Nineteen had never been described in the GI tract, including a semaphorin probably implicated in pathogen invasion and six novel genes. Moreover, by crossing these genes with those retrieved from an existing data set of gene expression in the intestine of ulcerative colitis and Crohn's disease patients, we identified genes that might be biomarkers of Crohn's and/or ulcerative colitis in ileum and/or colon. These include CLCA4 and SLC26A2, both implicated in ion transport. This study furnishes the first map of gene expression along the healthy human gastrointestinal tract. Furthermore, the approach implemented here, and validated by retrieving known gene profiles, allowed the identification of promising new leads in both healthy and disease states.

Establishment of Reference Values of CD4 and CD8 Lymphocyte Subsets in Healthy Nigerian Adults

A total of 2,570 apparently healthy human immunodeficiency virus-negative adults from the six geopolitical zones in the country were enrolled in our study in 2006. The samples were assayed using the Cyflow technique. Data were analyzed using the Statistical Package for Social Scientists (SPSS). The majority (64%) of the participants had CD4 counts within the range of 501 to 1,000 cells/microl. The reference range for CD4 was 365 to 1,571 cells/microl, while the reference range for CD8 was 145 to 884 cells/microl.

Imaging incorporation of circulating docosahexaenoic acid into the human brain using positron emission tomography

Docosahexaenoic acid (DHA; 22:6n-3) is a critical constituent of the brain, but its metabolism has not been measured in the human brain in vivo. In monkeys, using positron emission tomography (PET), we first showed that intravenously injected [1-(11)C]DHA mostly entered nonbrain organs, with approximately 0.5% entering the brain. Then, using PET and intravenous [1-(11)C]DHA in 14 healthy adult humans, we quantitatively imaged regional rates of incorporation (K*) of DHA. We also imaged regional cerebral blood flow (rCBF) using PET and intravenous [(15)O]water. Values of K* for DHA were higher in gray than white matter regions and correlated significantly with values of rCBF in 12 of 14 subjects despite evidence that rCBF does not directly influence K*. For the entire human brain, the net DHA incorporation rate J(in), the product of K*, and the unesterified plasma DHA concentration equaled 3.8 +/- 1.7 mg/day. This net rate is equivalent to the net rate of DHA consumption by brain and, considering the reported amount of DHA in brain, indicates that the half-life of DHA in the human brain approximates 2.5 years. Thus, PET with [1-(11)C]DHA can be used to quantify regional and global human brain DHA metabolism in relation to health and disease.

High Incidence of Metabolically Active Brown Adipose Tissue in Healthy Adult Humans

OBJECTIVEThe significant roles of brown adipose tissue (BAT) in the regulation of energy expenditure and adiposity are established in small rodents but have been controversial in humans. The objective is to examine the prevalence of metabolically active BAT in healthy adult humans and to clarify the effects of cold exposure and adiposity.RESEARCH DESIGN AND METHODSIn vivo 2-[18F]fluoro-2-deoxyglucose (FDG) uptake into adipose tissue was measured in 56 healthy volunteers (31 male and 25 female subjects) aged 23–65 years by positron emission tomography (PET) combined with X-ray computed tomography (CT).RESULTSWhen exposed to cold (19°C) for 2 h, 17 of 32 younger subjects (aged 23–35 years) and 2 of 24 elderly subjects (aged 38–65 years) showed a substantial FDG uptake into adipose tissue of the supraclavicular and paraspinal regions, whereas they showed no detectable uptake when kept warm (27°C). Histological examinations confirmed the presence of brown adipocytes in these regions. The cold-activated FDG uptake was increased in winter compared with summer (P < 0.001) and was inversely related to BMI (P < 0.001) and total (P < 0.01) and visceral (P < 0.001) fat areas estimated from CT image at the umbilical level.CONCLUSIONSOur findings, being against the conventional view, indicate the high incidence of metabolically active BAT in adult humans and suggest a role in the control of body temperature and adiposity.

Functional Brown Adipose Tissue in Healthy Adults

Using positron-emission tomography (PET), we found that cold-induced glucose uptake was increased by a factor of 15 in paracervical and supraclavicular adipose tissue in five healthy subjects. We obtained biopsy specimens of this tissue from the first three consecutive subjects and documented messenger RNA (mRNA) and protein levels of the brown-adipocyte marker, uncoupling protein 1 (UCP1). Together with morphologic assessment, which showed numerous multilocular, intracellular lipid droplets, and with the results of biochemical analysis, these findings document the presence of substantial amounts of metabolically active brown adipose tissue in healthy adult humans.

Effect of Standardized Lycium barbarum (Goji) Juice, GoChi® Intake on Resting Metabolic Rate and Waist Circumference: Randomized, Placebo‐controlled, Double‐blind Clinical Studies

We examined the effects of consuming Lycium barbarum fruit juice (GoChi®, 120 ml/day) on morphometric parameters and resting metabolic rate (RMR) in healthy human adults in 2 separate randomized, double‐blind, placebo‐controlled clinical studies. GoChi juice is standardized for its main active constituents, Lycium barbarum polysaccharides, based on the amount of fresh berries traditionally used.Study‐1Under free‐living conditions, subjects (average age=33.6, body mass index (BMI) =29.3kg/m2) took either GoChi or placebo samples in a 30‐day intervention trial. Waist circumference in the placebo group (N=19) increased significantly by 2.2 cm on Day 30 at post‐intervention compared to pre‐intervention. GoChi group (N=20) maintained pre‐intervention measurements. Changes in waist circumference per caloric intake in GoChi group tended to be lower than placebo group. Body weight and other parameters were not significantly different between groups or pre‐ and post‐intervention.Study‐2The effect of a single bout of consuming either GoChi or placebo control samples on RMR was investigated by hand‐held indirect calorimeter (average age=34.5, BMI=28.2 kg/m2). GoChi intake (120 ml) (n=6) significantly increased RMR 53% more than placebo (n=10) at 2 hours after consumption.These results suggest that GoChi may have metabolic effects which are reflected in waist circumference.

The role of innate immunity in atherogenesis

Lipid peroxidation is a common event in health and is greatly accelerated in pro-inflammatory settings such as hypercholesterolemia. Consequently, oxidation-specific epitopes are generated, which are pro-inflammatory and immunogenic, leading to both adaptive and innate responses. Because innate immune mechanisms use conserved germline pattern recognition receptors (PRRs) that are preformed and present at birth, it is not obvious why they should bind to such epitopes. In this review, we put forward the hypothesis that because oxidation-specific epitopes are ubiquitous in both health and disease, and because they in essence represent "danger signals," they constitute a class of pathogen-associated molecular patterns leading to the natural selection of multiple innate PRRs that target such epitopes. We suggest that apoptotic cells, and the blebs and microparticles released from such cells, which are rich in oxidation-specific epitopes and thus pro-inflammatory, constitute an endogenous set of selecting antigens. In turn, natural antibodies, scavenger receptors, and soluble innate proteins, such as pentraxins, all represent PRRs that target such epitopes. We discuss the evidence for this hypothesis and the consequences of such responses in health and disease, such as atherosclerosis.

Effects of endothelin‐1 on endothelial progenitor cell function

Circulating endothelial progenitor cells (EPCs) play an important role in maintaining and repairing the vascular endothelium and restoring functional activity. Endothelin (ET)‐1, a potent vasoconstrictor peptide, is released by the endothelium and contributes to endothelial damage and atherogenesis. The effects of ET‐1 on EPC function are unknown. We tested the hypothesis that ET‐1 impairs EPC function. Peripheral blood samples were collected from 10 healthy adult humans. Cells with phenotypic EPC characteristics were isolated and EPC clonogenic (colony forming unit assay) and migratory (Boyden chamber) capacity as well as apoptotic susceptibility (TUNEL assay) were determined in the absence and presence and ET‐1 (100 pM). The number of EPC colony‐forming units (42±12 vs. 39±11) and migratory capacity (910±146 vs. 936±148) was not significantly different between the ET‐1 treated and untreated cells. In response to staurosporine (1 mM), EPCs treated with ET‐1 demonstrated a 20% increase (P&lt;0.05) in cellular apoptosis. The proapoptotic effect of ET‐1 was abolished with ET receptor blockade as well as with apocynin, an NADPH inhibitor. These results indicate that ET‐1 does not affect EPC colony formation or migratory capacity but does increase EPC susceptibility to apoptosis through a NADPH‐dependent mechanism. Increased EPC apoptosis may contribute to the proatherogenic effects of ET‐1.

A pilot study of sleep, cognition, and respiration under 4 weeks of intermittent nocturnal hypoxia in adult humans

Study objectives A pilot study to examine the effects of intermittent nocturnal hypoxia on sleep, respiration and cognition in healthy adult humans. Methods Participants were eight healthy, non-smoking subjects (four male, four female), mean age of 26.4 ± 5.2 years, and BMI 22.3 ± 2.6 kg/m 2, exposed to 9 h of intermittent hypoxia between the hours of 10 P.M. and 7 A.M. for 28 consecutive nights. At a simulated altitude of 13,000 feet (FIO 2 0.13), intermittent hypoxia was achieved by administering nasal nitrogen, alternating with brief (approximately 5 s) boluses of nasal oxygen. Pre- and post-exposure assessments included polysomnography, attention (20-min Psychomotor Vigilance Test), working memory (10-min verbal 2 and 3-back), Multiple Sleep Latency Test, and the Rey Auditory Verbal Learning Test. Obstructive and non-obstructive respiratory events were scored. Results Overall sleep quality showed worsening trends but no statistically significant change following exposure. There was no difference after hypoxia in sleepiness, encoding, attention or working memory. Hyperoxic central apneas and post-hyperoxic respiratory instability were noted as special features of disturbed respiratory control induced by intermittent nocturnal hypoxia. Conclusions In this model, exposure to nocturnal intermittent hypoxia for 4 weeks caused no significant deficits in subjective or objective alertness, vigilance, or working memory.

Co‐ordination of spontaneous swallowing with respiratory airflow and diaphragmatic and abdominal muscle activity in healthy adult humans

Co-ordination of breathing and swallowing is essential for normal pharyngeal function and to protect the airway. To allow for safe passage of a bolus through the pharynx, respiration is interrupted (swallowing apnoea); however, the control of airflow and diaphragmatic activity during swallowing and swallowing apnoea are not fully understood. Here, we validated a new airflow discriminator for detection of respiratory airflow and used it together with diaphragmatic and abdominal electromyography (EMG), spirometry and pharyngeal and oesophageal manometry. Co-ordination of breathing and spontaneous swallowing was examined in six healthy volunteers at rest, during hypercapnia and when breathing at 30 breaths min(-1). The airflow discriminator proved highly reliable and enabled us to determine timing of respiratory airflow unambiguously in relation to pharyngeal and diaphragmatic activity. During swallowing apnoea, the passive expiration of the diaphragm was interrupted by static activity, i.e. an 'active breath holding', which preserved respiratory volume for expiration after swallowing. Abdominal EMG increased throughout pre- and post-swallowing expiration, more so during hyper- than normocapnia, possibly to assist expiratory airflow. In these six volunteers, swallowing was always preceded by expiration, and 93 and 85% of swallows were also followed by expiration in normo- and hypercapnia, respectively, indicating that, in man, swallowing during the expiratory phase of breathing may be even more predominant than previously believed. This co-ordinated pattern of breathing and swallowing potentially reduces the risk for aspiration. Insights from these measurements in healthy volunteers and the airflow discriminator will be used for future studies on airway protection and effects of disease, drugs and ageing.

Heart rate variability, overnight urinary norepinephrine and C‐reactive protein: evidence for the cholinergic anti‐inflammatory pathway in healthy human adults

C-reactive protein (CRP) has been identified as an independent predictor of cardiovascular mortality and morbidity in population-based studies. Recent advances have suggested a prominent role for the autonomic nervous system (ANS) in the regulation of inflammation. However, no in vivo human studies have examined indices of sympathetic and parasympathetic nervous system activity simultaneously in relationship to inflammatory markers in apparently healthy adults. Therefore, the objective of this study was to assess the immunomodulatory effects of the ANS. The study population comprised 611 apparently healthy employees of an airplane manufacturing plant in southern Germany. Urinary NE was positively associated with white blood cell count (WBC) in the total sample. We found an inverse association between indices of vagally mediated heart rate variability and plasma levels of (CRP), which was significantly larger in females than in males after controlling for relevant covariates including NE. Similar results were found using the percentage of interbeat interval differences >50 ms and WBC. We report here for the first time, in a large sample of healthy human adults, evidence supporting the hypothesis of a clinically relevant cholinergic anti-inflammatory pathway after controlling for sympathetic nervous system activity. This suggests an important role for the vagal control of systemic inflammatory activity in cardiovascular disease.

Relationship between the plasticity of a set to an emotional facial expression and the load on working memory

The effects of increasing the loading on working memory (by introduction of an additional cognitive task into the experimental context) on the recognition of an emotional facial expression using a visual set model were studied in healthy adult humans. A relationship was found between the plasticity of the cognitive set to an emotional facial expression and working memory: increases in the load on memory slowed set substitution when the situation changed. The set became more rigid, as indicated by an increase in the number of trials showing erroneous assessments of facial expressions, i.e., contrast and assimilative illusions, at the test stage of the experiment. The role of internal states in the increase in the number of erroneous assessments of emotional facial expressions when working memory was loaded is discussed.

Magnetic field correlation as a measure of iron‐generated magnetic field inhomogeneities in the brain

The magnetic field correlation (MFC) at an applied field level of 3 Tesla was estimated by means of MRI in several brain regions for 21 healthy human adults and 1 subject with aceruloplasminemia. For healthy subjects, highly elevated MFC values compared with surrounding tissues were found within the basal ganglia. These are argued as being primarily the result of microscopic magnetic field inhomogeneities generated by nonheme brain iron. The MFC in the aceruloplasminemia subject was significantly higher than for healthy adults in the globus pallidus, thalamus and frontal white matter, consistent with the known increased brain iron concentration associated with this disease.

Aging and endothelial progenitor cell telomere length in healthy men

Telomere length declines with age in mature endothelial cells and is thought to contribute to endothelial dysfunction and atherogenesis. Bone marrow-derived circulating endothelial progenitor cells (EPCs) are critical to vascular health as they contribute to both reendothelialization and neovascularization. We tested the hypothesis that EPC telomere length decreases with age in healthy adult humans. Peripheral blood samples were collected from 40 healthy, non-obese, sedentary men: 12 young (age 21-34 years), 12 middle-aged (43-55 years) and 16 older (57-68 years). Putative EPCs were isolated from peripheral blood mononuclear cells and telomere length was determined using genomic DNA preparation and Southern hybridization techniques. EPC telomere length (base pairs) was approximately 20% (p=0.01) lower in the older (8492+523 bp) compared to the middle-aged (10,565+572 bp) and young (10,205+501 bp) men. Of note, there was no difference in EPC telomere length between the middle-aged and young men. These results demonstrate that EPC telomere length declines with age in healthy, sedentary men. Interestingly, telomere length was well preserved in the middle-aged compared to young men, suggesting that EPC telomere shortening occurs after the age of 55 years.

Tangerine tomatoes increase total and tetra-cis-lycopene isomer concentrations more than red tomatoes in healthy adult humans

Lycopene, or the foods that contain it, may prevent prostate cancer. Studies suggest that some cis-lycopene isomers are more bioavailable than the trans-lycopene isomer. We hypothesized that tangerine tomatoes, which predominantly contain the tetra-cis isomer, should be a good source of bioavailable lycopene. We fed lunches containing 300 g tangerine or red tomato sauce per day to 21 healthy adults in a double-blind crossover design. We collected blood at baseline and after each treatment and washout period. We measured tetra-cis, other cis, and trans lycopene, as well as other carotenoids, by reversed-phase high-performance liquid chromatography. Both tomato sauces increased lycopene concentrations in blood, but the tangerine tomato sauce caused a greater increase of total and tetra-cis-lycopene. The cis isomer(s) may also have facilitated absorption of the trans-lycopene isomer. Indices of oxidative damage decreased as serum lycopene concentrations increased. Our results suggest that total lycopene concentrations can be increased by substituting tetra-cis-lycopene-rich tangerine tomatoes for common red tomatoes in the diet.

The influence of whey protein and glycomacropeptide on satiety in adult humans

Protein is often considered the most satiating macronutrient. The objective was to determine the short-term effect of mixtures of whey protein and glycomacropeptide (GMP) versus a carbohydrate control on satiety in healthy adult humans. The study was a randomised crossover Latin Square design. On 4 separate days, fifty healthy subjects (19 males and 31 females) received a subject-specific breakfast (08:00 h), a preload drink (12:00 h) and lunch (12:30 h). The preload drink was presented as a milkshake with either maltodextrin carbohydrate (control), whey protein isolate (WPI) with no GMP, WPI with naturally present 21% GMP or WPI with naturally present 21% GMP plus added GMP. Satiety was assessed using visual analogue scales (VAS) and by determining ad libitum food intake during a cafeteria style meal offered 30 min after the preload. The VAS indicated that the lower GMP treatment induced a greater feeling of fullness immediately after consumption of the preload compared with the other treatments. Energy and macronutrient intake at lunch did not differ significantly ( p > 0.05) between treatments although subjects chose to eat foods higher in carbohydrate and lower in protein after the protein preloads. Women consumed the least amount of protein after the protein preloads whereas no difference was found in men. There was some evidence that whey proteins and their components enhance satiety over a short-term period compared to carbohydrate but there was no consistent effect of either whey protein alone or glycomacropeptide.

Dosing and Efficacy of Glutamine Supplementation in Human Exercise and Sport Training

Some athletes can have high intakes of L-glutamine because of their high energy and protein intakes and also because they consume protein supplements, protein hydrolysates, and free amino acids. Prolonged exercise and periods of heavy training are associated with a decrease in the plasma glutamine concentration and this has been suggested to be a potential cause of the exercise-induced immune impairment and increased susceptibility to infection in athletes. However, several recent glutamine feeding intervention studies indicate that although the plasma glutamine concentration can be kept constant during and after prolonged strenuous exercise, the glutamine supplementation does not prevent the postexercise changes in several aspects of immune function. Although glutamine is essential for lymphocyte proliferation, the plasma glutamine concentration does not fall sufficiently low after exercise to compromise the rate of proliferation. Acute intakes of glutamine of ∼20–30 g seem to be without ill effect in healthy adult humans and no harm was reported in 1 study in which athletes consumed 28 g glutamine every day for 14 d. Doses of up to 0.65 g/kg body mass of glutamine (in solution or as a suspension) have been reported to be tolerated by patients and did not result in abnormal plasma ammonia levels. However, the suggested reasons for taking glutamine supplements (support for immune system, increased glycogen synthesis, anticatabolic effect) have received little support from well-controlled scientific studies in healthy, well-nourished humans.

Cyclical and Dose-Dependent Responses of Adult Human Mature Oligodendrocytes to Fingolimod

Fingolimod is a sphingosine-1-phosphate (S1P) analogue that has been used in clinical trials as a systemic immunomodulatory therapy for multiple sclerosis. Fingolimod readily accesses the central nervous system, raising the issue of its direct effects on neural cells. We assessed the effects of active fingolimod on dissociated cultures of mature, myelin-producing oligodendrocytes (OLGs) derived from adult human brain. Human OLGs express S1P receptor transcripts in relative abundance of S1P5>S1P3>S1P1, with undetectable levels of S1P4. Low doses of fingolimod (100 pmol/L to 1 nmol/L) induced initial membrane elaboration (2 days), subsequent retraction (4 days), and recurrence of extension with prolonged treatment (8 days). Higher doses (10 nmol/L to 1 mumol/L) caused the opposite modulation of membrane dynamics. Retraction was rescued by co-treatment with the S1P3/S1P5 pathway antagonist, suramin, and was associated with RhoA-mediated cytoskeletal signaling. Membrane elaboration was mimicked using the S1P1 agonist SEW2871. Fingolimod rescued human OLGs from serum and glucose deprivation-induced apoptosis, which was reversed with suramin co-treatment and mimicked using an S1P5 agonist. High doses of fingolimod induced an initial down-regulation of S1P5 mRNA levels relative to control (4 hours), subsequent up-regulation (2 days), and recurrent down-regulation (8 days). S1P1 mRNA levels were inversely regulated compared with S1P5. These results indicate that fingolimod modulates maturity- and species-specific OLG membrane dynamics and survival responses that are directly relevant for myelin integrity.