Downregulation of skeletal muscle UCP-3 gene expression during refeeding is prevented by cold exposure

We wished to gain insights into the role of skeletal muscle uncoupling protein-3 (UCP-3) in the elevated efficiency of fat recovery during refeeding after starvation. Previous observations have revealed that muscle UCP-3 expression is downregulated in rats during refeeding at 22 degrees C. Therefore, we investigated whether this also occurs during refeeding at thermoneutrality (29 C) or in the cold (6 C), since at these environmental temperatures the refed animals also show diminished thermogenesis and a higher rate of fat deposition than controls. The UCP-3 mRNA level in the skeletal muscles studied (soleus, gastrocnemius and tibialis anterior) was significantly lower in the refed group than in controls at thermoneutrality, but there were no such differences between these two groups in the cold. This effect of cold, namely abolishing refeeding-induced downregulation of skeletal muscle UCP, is specific to UCP-3 since the gene expression of skeletal muscle UCP-2 remained significantly lower in the refed than in the controls both at thermoneutrality and in the cold. These findings during refeeding in the cold therefore dissociate UCP-3 gene regulation from the adaptive reduction in thermogenesis that accelerates fat deposition during weight recovery. They also reveal differential responses of UCP-3 and UCP-2, whose significance is discussed in the light of our previously proposed hypothesis, which centers upon a role for these UCP homologues in the regulation of lipids as a fuel substrate.

Green tea and thermogenesis: interactions between catechin-polyphenols, caffeine and sympathetic activity

The thermogenic effect of tea is generally attributed to its caffeine content. We report here that a green tea extract stimulates brown adipose tissue thermogenesis to an extent which is much greater than can be attributed to its caffeine content per se, and that its thermogenic properties could reside primarily in an interaction between its high content in catechin-polyphenols and caffeine with sympathetically released noradrenaline (NA). Since catechin-polyphenols are known to be capable of inhibiting catechol-O-methyl-transferase (the enzyme that degrades NA), and caffeine to inhibit trancellular phosphodiesterases (enzymes that break down NA-induced cAMP), it is proposed that the green tea extract, via its catechin-polyphenols and caffeine, is effective in stimulating thermogenesis by relieving inhibition at different control points along the NA-cAMP axis. Such a synergistic interaction between catechin-polyphenols and caffeine to augment and prolong sympathetic stimulation of thermogenesis could be of value in assisting the management of obesity. International Journal of Obesity (2000) 24, 252-258

UCP2 and UCP3 rise in starved rat skeletal muscle but mitochondrial proton conductance is unchanged

The relationship between UCP2 and UCP3 expression and mitochondrial proton conductance of rat skeletal muscle was examined. Rats were starved for 24 h and the levels of UCP2 and UCP3 mRNA and UCP3 protein were determined by Northern and Western blots. Proton conductance was measured by titrating mitochondrial respiration rate and membrane potential with malonate. Starvation increased UCP2 and UCP3 mRNA levels more than 5-fold and 4-fold, respectively, and UCP3 protein levels by 2-fold. However, proton conductance remained unchanged. These results suggest either that Northern and Western blots do not reflect the levels of active protein or that these UCPs do not catalyse the basal proton conductance in skeletal muscle mitochondria.

Efficacy of a green tea extract rich in catechin polyphenols and caffeine in increasing 24-h energy expenditure and fat oxidation in humans

BACKGROUND

Current interest in the role of functional foods in weight control has focused on plant ingredients capable of interfering with the sympathoadrenal system.

OBJECTIVE

We investigated whether a green tea extract, by virtue of its high content of caffeine and catechin polyphenols, could increase 24-h energy expenditure (EE) and fat oxidation in humans.

DESIGN

Twenty-four-hour EE, the respiratory quotient (RQ), and the urinary excretion of nitrogen and catecholamines were measured in a respiratory chamber in 10 healthy men. On 3 separate occasions, subjects were randomly assigned among 3 treatments: green tea extract (50 mg caffeine and 90 mg epigallocatechin gallate), caffeine (50 mg), and placebo, which they ingested at breakfast, lunch, and dinner.

RESULTS

Relative to placebo, treatment with the green tea extract resulted in a significant increase in 24-h EE (4%; P < 0.01) and a significant decrease in 24-h RQ (from 0.88 to 0.85; P < 0.001) without any change in urinary nitrogen. Twenty-four-hour urinary norepinephrine excretion was higher during treatment with the green tea extract than with the placebo (40%, P < 0.05). Treatment with caffeine in amounts equivalent to those found in the green tea extract had no effect on EE and RQ nor on urinary nitrogen or catecholamines.

CONCLUSIONS

Green tea has thermogenic properties and promotes fat oxidation beyond that explained by its caffeine content per se. The green tea extract may play a role in the control of body composition via sympathetic activation of thermogenesis, fat oxidation, or both.

Low-protein overfeeding: a tool to unmask susceptibility to obesity in humans

In search for an approach to identify physiological targets for therapeutic intervention in obesity management, we have revisited the classic human overfeeding studies of the 1960s, with new emphasis on a 'subgroup' of volunteers who were shifted between overfeeding on a typical affluent (normal-protein) diet and overfeeding on a low-protein diet. Following a re-analysis of these data, the arguments are put forward that since low-protein overfeeding is not only a potent stimulus of thermogenesis, but also an amplifier (or magnifier) of the small inter-individual variations in thermogenesis on the affluent (normal-protein) diet, it can be used as a tool to unmask some of the genetic and metabolic basis underlying human susceptibility to leanness and fatness.

The control of partitioning between protein and fat during human starvation: its internal determinants and biological significance

Human subjects vary in the extent to which their body's protein and fat compartments are mobilized for fuel during starvation. Although an inverse association between the initial adiposity and the contribution of protein as fuel during starvation has been known for nearly a century, interest in the quantitative importance and functional significance of the initial percentage fat as a determinant of biological variation in energy-partitioning between protein and fat (and hence in determining the partitioning characteristic of the individual) is relatively recent. The present paper addresses these issues by revisiting the classic Minnesota experiment of semi-starvation and refeeding from a standpoint of system physiology. In a quantitative analysis of the relationship between the initial body composition (ration FAT0: fat-free mass (FFM)0) and the composition of weight loss (ratio delta FAT: delta FFM) in the thirty-two men in the Minnesota study, the arguments are put forward that the fraction of FFM lost when the fat stores reach total depletion is independent of the initial percentage fat, and that this fraction represents the 'dispensable' component of the protein compartment that is compatible with life (i.e. the protein energy-reserve, rp). The concepts are developed that (1) the initial percentage body fat (which reflects the initial ratio FAT0:FFM0) provides a 'memory of partitioning' which dictates the control of partitioning between protein and fat in such a way that both the protein energy-reserve (rp) and the fat energy-reserve (rf) each complete depletion simultaneously, a strategy that would ensure maximum length of survival during long-term food scarcity, and that (2) variability in the relative sizes of these two energy reserves (i.e. in rf:rp) could, in addition to the initial percentage fat, also contribute to human variability in energy-partitioning. The basic assumptions underlying this re-analysis of the Minnesota data, and the concepts that are derived from it, have been integrated in the simple mathematical model for predicting the partitioning characteristic of the individual. This model is used to explain how variability in the fraction of the protein compartment that could function as an energy reserve (rp) can be as important as the initial percentage fat in determining inter-individual variability in protein-sparing during the early phase of starvation, in fuel partitioning during prolonged starvation, or in the maximum percentage weight loss during starvation. The elucidation of factors underlying variability in the size of the protein energy-reserve may have important implications for our understanding of the pathophysiology of starvation and age-associated susceptibility to muscle wasting, and in the clinical management of cachexia and obesity.

Skeletal muscle UCP3 and UCP2 gene expression in response to inhibition of free fatty acid flux through mitochondrial beta-oxidation

Studies of starvation and refeeding have implicated the genes coding for uncoupling protein-3 and -2 (UCP3, UCP2) as candidate genes in the regulation of lipids as metabolic fuels in skeletal muscle. To gain insight into the role of free fatty acid (FFA) flux in regulating the expression of these muscle UCP homologues, we recently reported that, in response to the anti-lipolytic agent nicotinic acid, utilized to reduce FFA flux at the input supply (i.e. circulating) level in fed and fasted rats, expression of the UCP3 and UCP2 genes was reduced in the soleus (predominantly slow-oxidative fibres), but not in the gastrocnemius (predominantly fast-glycolytic fibres) or tibials anterior (predominantly fast-oxidative-glycolytic fibres) muscles. In the present study, we examined UCP2 and UCP3 gene expression in these muscles from fed or fasted rats treated with etomoxir, an inhibitor of FFA flux at the output (i.e. mitochondrial oxidation) level. Fasting per se resulted in a threefold increase in serum FFA (P < 0.001) and in marked increases in the messenger ribonucleic acid (mRNA) expression of both UCP2 and UCP3 in all three muscles (P < 0.001). Treatment with etomoxir had no significant effect on serum FFA in the fed rats, but further elevated serum FFA in the fasted rats (P < 0.001). The mRNA levels of both UCP3 and UCP2 in response to etomoxir were significantly reduced in the tibialis anterior muscle in both fed and fasted states (P < 0.01), unaltered in the gastrocnemius muscle in both fed and fasted states and unaltered in the soleus muscle in the fed state, but increased in the fasted state, in parallel with the etomoxir-induced changes in serum FFA levels. Taken together, these results suggest the existence of positive feedback loops between FFA flux and muscle UCPs only in oxidative muscles--with that loop operating at the input FFA supply level for muscles with predominantly slow-oxidative fibres, and at the output FFA oxidation level for muscles with predominantly fast-oxidative-glycolytic fibres.

Post-starvation gene expression of skeletal muscle uncoupling protein 2 and uncoupling protein 3 in response to dietary fat levels and fatty acid composition: a link with insulin resistance

UCP2 and UCP3 are two recently cloned genes with high sequence homology to the gene for uncoupling protein (UCP)-1, which regulates thermogenesis in brown adipose tissue. In the context of the current debate about whether UCP2 and UCP3 in the skeletal muscle may also function as mediators of thermogenesis or as regulators of lipids as fuel substrate, we have examined their mRNA expressions in rat gastrocnemius muscle in response to dietary manipulations known to differentially affect thermogenesis during the phase of weight recovery after starvation. Compared with ad libitum-fed control rats, the refeeding of isocaloric amounts of a low-fat (high-carbohydrate) diet resulted in lower energy expenditure and lower mRNA levels of muscle UCP2 and UCP3. This downregulation of UCP homologs was abolished by the refeeding of a high-fat diet, even though energy expenditure was significantly lower during refeeding on the high-fat than on the low-fat diet. Furthermore, major alterations in the fatty acid composition of the refeeding diet in favor of n-6 polyunsaturated or medium-chain fatty acids resulted in significant increases in energy expenditure, but with no significant changes in the expression of skeletal muscle UCP homologs. Regression analysis of gastrocnemius UCP mRNA levels against parameters that included body composition, energy expenditure, and plasma levels of free fatty acids (FFAs), insulin, and glucose as well as the increase in plasma glucose after a glucose load, revealed that only the latter (an index of insulin resistance) could explain the variability in muscle UCP2 and UCP3 mRNA expressions (r = 0.41, P < 0.02; r = 0.45, P < 0.01, respectively). Taken together, these data are at variance with a role for skeletal muscle UCP2 and UCP3 in dietary regulation (or modulation) of thermogenesis. However, they are consistent with the notion that these UCP homologs may function as regulators of lipids as fuel substrate and raise the possibility that high-fat induced upregulation of muscle UCP2 and UCP3 may be more closely linked to insulin resistance than to changes in circulating FFAs.

Interorgan signaling between adipose tissue metabolism and skeletal muscle uncoupling protein homologs: is there a role for circulating free fatty acids?

Uncoupling proteins 3 and 2 (UCP3 and UCP2) are two newly cloned genes that have been implicated in the regulation of lipids as fuel substrate in skeletal muscle on the basis that their mRNA expressions are upregulated during starvation (when fat stores are being rapidly mobilized) and downregulated during the early phase of refeeding (when fat stores are being rapidly replenished). To test the hypothesis that circulating free fatty acids (FFAs) may have a physiological role as an interorgan signal linking these dynamic changes in the fat stores to skeletal muscle expression of UCP3 and UCP2, the mRNA levels of these UCP homologs were examined in fed and fasted rats treated with the antilipolytic agent nicotinic acid. In 46-h fasted rats, we observed a threefold increase in serum FFA levels and increases in UCP3 and UCP2 mRNA levels that were more marked in the gastrocnemius and tibialis anterior muscles (predominantly fast-twitch fibers) than in the soleus muscle (predominantly slow-twitch fibers). Treatment with nicotinic acid blunted the fasting-induced increase in serum FFA levels and prevented the increase in mRNA levels of UCP3 and UCP2 in the soleus muscle, but had little or no effect on the elevated mRNA levels of these UCP homologs in the gastrocnemius and tibialis anterior muscles. Furthermore, treatment of ad libitum-fed animals with nicotinic acid resulted in a twofold reduction in serum FFA levels (i.e., by a magnitude similar to that observed during early refeeding) and significant reductions in UCP3 and UCP2 mRNA levels in the soleus muscle, but not in the gastrocnemius or tibialis anterior muscles. These results revealed a muscle-type dependency in the way UCP2 and UCP3 gene expression in skeletal muscle is regulated, and suggest that the hypothesis that circulating FFAs function as an interorgan signal between fat stores and skeletal muscle UCP3 and UCP2 gene expression is adequate only for slow-twitch (oxidative) muscles. Consequently, a signal(s) other than circulating FFAs must be implicated in the link between dynamic changes in body fat stores and UCP expression in predominantly fast-twitch (glycolytic/oxidative-glycolytic) muscles, which constitute the major fiber type of the total skeletal muscle mass and which have high susceptibility to developing insulin resistance and impairment in substrate utilization in metabolic diseases.

Role of cytokines in AIDS wasting

There is now a large literature implicating cytokines in the development of wasting and cachexia commonly observed in a variety of pathophysiologic conditions. In the acquired immunodeficiency syndrome (AIDS), cytokines elicited by primary and secondary infections seem to exert subtle and sustained effects on behavioral, hormonal, and metabolic axes, and their combined effects on appetite and metabolism have been postulated to drive wasting. However, correlations of increased blood levels of a particular cytokine with wasting in AIDS have not been consistent observations, perhaps because cytokines act principally as paracrine and autocrine hormones, as well as indirectly by activating other systems. A better understanding of the mechanisms underlying the catabolic effects of cytokines in clearly needed if more efficacious strategies are to be developed for the prevention and treatment of wasting in AIDS. In this review we first examine the interacting factors contributing to the AIDS wasting syndrome. We then analyze the complex and overlapping role of cytokines in the pathophysiology of this condition, and put forward a number of hypotheses to explain some of the most important features of this syndrome.

Adaptive reduction in basal metabolic rate in response to food deprivation in humans: a role for feedback signals from fat stores

We assessed the importance of lean and fat tissue depletion as determinants of the adaptive reduction in basal metabolic rate (BMR) in response to food deprivation by reanalyzing the data on BMR and body composition for the 32 men participating in the classic Minnesota experiment of semi-starvation and refeeding. We used individual data on BMR, body fat, and fat-free mass (FFM) assessed during the control (prestarvation) period, at weeks 12 and 24 of semistarvation (S12 and S24), and week 12 of restricted refeeding (R 12) to calculate an index of the reduction in thermogenesis at S12, S24, and R12, defined as the change in BMR adjusted for changes in FFM and fat mass, and an index of the state of depletion of the fat mass and FFM compartments at these times, defined as the deviation in fat mass or FFM relative to control values. The results indicated a positive relation between the reduction in thermogenesis and the degree of fat mass depletion (but not FFM depletion) during weight loss as well as during weight recovery (r = 0.5, P < 0.01). Furthermore, the residual variance was predicted by the initial (prestarvation) percentage fat and the cormic index (sitting height/height). Taken together, these results in normal-weight men responding to severe food deprivation reveal anthropometric predictors for human interindividual variability in the capacity for energy conservation and suggest that the adaptive reduction in BMR is partly determined by an autoregulatory feedback control system linking the state of depletion of fat stores to compensatory mechanisms that suppress thermogenesis.

Role of UCP homologues in skeletal muscles and brown adipose tissue: mediators of thermogenesis or regulators of lipids as fuel substrate?

The mRNA expressions of UCP2 and UCP3, two newly described genes with high sequence homology to the uncoupling protein UCP1 in brown adipose tissue (BAT), were examined in two skeletal muscles (gastrocnemius and soleus) as well as in interscapular BAT (IBAT) of the rat in response to food deprivation and controlled refeeding. In IBAT (a tissue highly dependent on lipids for thermogenesis), the pattern of mRNA expression of UCP2 and UCP3 closely follows that of UCP1: it was markedly down-regulated during food deprivation (when this tissue's thermogenesis and lipid fuel requirements are decreased) and restored to control levels by day 5 of refeeding. By contrast, in the gastrocnemius muscle (a mixed fiber type muscle with a high capacity to shift between glucose and lipids as fuel substrate), mRNA expression of both UCP2 and UCP3 mRNA was found to be markedly up-regulated during food deprivation (when this tissue's thermogenesis is also decreased but its lipid fuel utilization is increased). The expressions were subsequently found to be markedly down-regulated upon transition to refeeding, with mRNA levels remaining below control levels on days 3, 5, and 10 of refeeding (period of enhanced efficiency of body fat deposition). In the soleus muscle (an oxidative type muscle with higher dependency on lipids than the gastrocnemius, and hence with a lower capacity to shift between lipids and glucose as fuel substrate), UCP homologues were also found to be up-regulated during food deprivation, but changes in their mRNA expression contrast with those in the gastrocnemius muscle both in their much lower magnitude of response to food deprivation and in their more rapid restoration to control levels during refeeding. Up-regulation of UCP2 and UCP3 gene expressions in skeletal muscle during food deprivation was found to persist at thermoneutrality (i.e., under conditions of reduced thermoregulatory thermogenesis). Together, these tissue-dependent differential mRNA expressions of the UCP homologues in IBAT, gastrocnemius, and soleus muscles during food deprivation and refeeding are much more consistent with a role for UCP2 and UCP3 in the regulation of lipids as fuel substrate rather than as mediators of regulatory thermogenesis.

Metabolic-cytokine responses to a second immunological challenge with LPS in mice with T. gondii infection

Injection of 10 cysts of Toxoplasma gondii (Me49 strain) into Swiss Webster mice results in 1) an acute phase of infection lasting for 2-3 wk, characterized by weight loss, and 2) a chronic phase in which surviving mice show either partial weight recovery (Gainers) or persistent, although stable, cachexia (Nongainers). In response to a second immunological stimulation with lipopolysaccharide (LPS) in the chronic phase of the infection, it is shown that 1) the increase in energy expenditure was more prolonged in both groups of infected mice than in controls, 2) the intensity and duration of hypophagia were also differently affected with Nongainers > Gainers > controls, and 3) the infected mice had higher serum levels of tumor necrosis factor-alpha (TNF-alpha) and interleukin (IL)-10 and a lower ratio of IL-10 to TNF-alpha than controls. In contrast, serum IL-4 increased to the same level in all three groups. Evaluation of the permeability of the blood-brain barrier by intravenous injection of Evans blue revealed a marked staining in the brain of only the infected Nongainers. Taken together, these results indicate that, in mice with chronic toxoplasmosis, a second nonspecific challenge (with LPS) exacerbates the hypophagic and hypermetabolic states, the latter being associated with hyperresponsiveness in TNF-alpha and IL-10 production. Furthermore, the greater exacerbation of the hypophagic state in mice showing persistent cachexia may be due to a preexisting higher permeability of the blood-brain barrier, which would allow a greater access of plasma-borne cytokines and/or other neuroimmunologically active substances to the central nervous system.

Altered energy balance and cytokine gene expression in a murine model of chronic infection with Toxoplasma gondii

The temporal pattern of changes in energy balance and cytokine mRNA expression in spleen and brain were examined in a mouse model of infection with Toxoplasma gondii. During days 1-7 postinfection, food intake was unaltered, but energy expenditure was significantly increased, and this was associated with elevated tumor necrosis factor-alpha (TNF-alpha), interleukin (IL)-1, IL-5, and interferon (IFN)-gamma. The hypermetabolic state persisted during subsequent anorexia, whose onset coincided with elevated IL-2, and at the end of the acute phase of cachexia, the dual anorexic and hypermetabolic states were associated with the cytokines examined: TNF-alpha, IL-1 beta, IL-2, IL-4, IL-5, IL-6, IL-10, and IFN-gamma. In the chronic phase of the infection, the mice showed either partial weight recovery (gainers) or no weight regain (nongainers). The infected gainers, though still hypophagic, were no longer hypermetabolic, and their cytokine mRNA was no longer elevated, except for TNF-alpha and IL-10. In contrast, the infected nongainers continued to show both anoroxia and hypermetabolism, which were associated with elevations in all cytokines examined and particularly those of the TH2 profile (IL-4 and IL-5) and IL-6. Taken together, these studies reveal a distinct pattern of cytokine mRNA expression underlying 1) hypermetabolism vs. anorexia, 2) acute vs. chronic cachexia, and 3) stable weight loss vs. partial weight recovery.

Regulation of body composition during weight recovery: integrating the control of energy partitioning and thermogenesis

Studies of experimental starvation that were carried out in healthy volunteers during the first half of this century often provide an invaluable source of 'untapped' data. The motivation and desire to gain a better insight into the regulation of body composition by re-analysing these data in the light of more 'modern' concepts of energy partitioning and thermogenesis become irresistible when similar studies can no longer be performed in humans, if only for ethical reasons. This paper brings together new findings, largely centered upon recent re-analysis of data from the classical studies of experimental starvation, semi-starvation and refeeding, and proposes a theory of regulation of body composition during weight recovery in which the cardinal features rest upon three auto-regulatory control systems. These control systems--operating via energy partitioning and two distinct forms of adaptive thermogenesis--have been integrated into a compartmental model for the autoregulation of body composition during cycles of underfeeding/refeeding. This model can be used to explain the individual pattern of lean and fat tissue deposition during weight recovery in situations ranging from rehabilitation after malnutrition/cachexia to the relapse of obesity. It also provides a framework of 'system physiology' for integrating the advances in molecular biology into this area of nutritional energetics.

Poststarvation hyperphagia and body fat overshooting in humans: a role for feedback signals from lean and fat tissues

An increase in the sensation of hunger and overeating after a period of chronic energy deprivation can be part of an autoregulatory phenomenon attempting to restore body weight. To gain insights into the role of fat and lean tissue depletion as determinants of such a hyperphagic response in humans, we reanalyzed the individual data on food intake and body composition available for the 12 starved and refed men in the classical Minnesota Experiment after a shift from a 12-wk period of restricted refeeding to an ad libitum refeeding period of 8 wk. For each individual, the following were determined: 1) the total hyperphagic response during the ad libitum refeeding period, calculated as the energy intake in excess of that during the prestarvation (control) period; 2) the degree of fat recovery and that of fat-free-mass (FFM) recovery before ad libitum refeeding, calculated as the deviation in fat and FFM from their respective prestarvation values (ie, the amount of fat or FFM before ad libitum refeeding as a percentage of fat or FFM during the control period); and 3) the deficit in energy intake before ad libitum refeeding, calculated as the difference between the energy intake during the period of restricted refeeding and that during the control period. The results indicate that 1) the total hyperphagic response is inversely correlated with the degree of fat recovery (r = -0.6) as well as with that of FFM recovery (r = -0.5), 2) the correlation between hyperphagia and FFM recovery persists after adjustment for fat recovery, and 3) the correlations between hyperphagia and fat recovery or FFM recovery persist after adjustment for the variance in the energy deficit during the preceding period of restricted refeeding. Taken together, these results in humans suggest that poststarvation hyperphagia is determined to a large extent by autoregulatory feedback mechanisms from both fat and lean tissues. These findings, which have implications for both the treatment of obesity and for nutritional rehabilitation after malnutrition and cachexia, have been integrated into a compartmental model of autoregulation of body composition, and can be used to explain the phenomenon of poststarvation overshoot in body fat.

Dissociation of systemic GH-IGF-I axis from a genetic basis for short stature in African Pygmies

OBJECTIVES

To test the hypothesis that the primary cause of short stature in African Pygmies resides in low levels of insulin-like growth factor I (IGF-I), and to evaluate whether any observed alterations in their systemic IGF-I status can be dissociated from the effects of malnutrition and/or altered immune status.

SETTING

Expedition to camps of partially sedentarized African Pygmies and neighbouring Bantu farmers living in the equatorial rain forest of Eastern Cameroon.

DESIGN

Serum assays for hormonal and immune status were conducted for individuals (children, adolescents, young and old adults) showing no overt clinical nor biochemical signs of malnutrition, as judged from anthropometry, clinical examinations and serum assays of albumin, pre-albumin, retinol-binding protein, transferrin, iron, zinc, magnesium and calcium.

RESULTS

African Pygmies did not differ from Europeans or Bantus in mean serum IGF-I concentrations, nor in the relationship between serum IGF-I and its major binding protein (IGFBP-3). However, although in both African groups the immunoglobulins IgG, IgM and IgE as well as the C-reactive protein and ceruloplasmin were above the normal range of European references, the Pygmies differed from their Bantu neighbours in their much higher IgG and IgM serum levels. A plot of serum IGF-I against these immunoglobulins in Pygmies revealed a reverse sigmoidal relationship, with the low IGF-I values associated with serum levels of IgG and IgM which clearly exceeded those found in the Bantus.

CONCLUSIONS

This study indicates that in growing and adult African Pygmies showing no clinical nor biochemical signs of nutritional deficiency, serum IGF-I and IGFBP-3 (hence IGF-I bioavailability to its receptors) are essentially normal, and that low circulating levels of IGF-I in Pygmies reside in differential exposure and/or responsiveness to environmental challenge (e.g. infections) rather than in an inherited defect in the systemic growth-hormone (GH)-IGF-I axis.

Autoregulation of body composition during weight recovery in human: the Minnesota Experiment revisited

OBJECTIVES

To gain insights into the control systems underlying human variability in the regulation of body composition during weight recovery, as well as the disproportionate recovery of fat relative to lean tissue, the classical Minnesota Experiment conducted on 32 men subjected to long-term semi-starvation and refeeding was revisited with the following objectives: (1) to determine whether the control of energy-partitioning between lean and fat tissues during weight loss and weight recovery is an individual characteristic, and if a predictor can be statistically identified, (2) to determine whether the reduction in thermogenesis during weight loss persists during weight recovery, and underlies the disproportionate recovery of fat tissue and (3) to integrate the control of energy-partitioning and that of thermogenesis in order to explain the pattern of lean and fat tissue mobilisation and deposition during weight loss and weight recovery.

METHODS

Individual data on body weight, body fat, fat-free-mass (FFM), and basal metabolic rate (BMR), assessed during the control baseline period (i.e. prior to weight loss), at the end of 24 weeks of semi-starvation, and at the end of a 12 week period of restricted refeeding, were used to calculate the following parameters: (i) a quantitative index of energy-partitioning, the P-ratio, defined as the proportion of body energy mobilised as protein during weight loss, or as the proportion of body energy deposited as protein during weight recovery, (ii) a quantitative index of changes in thermogenesis, defined as the change in BMR adjusted for FFM (or for both FFM and fat mass) and (iii) the degree of replenishment of fat and FFM compartments, defined as the recovery of body fat and FFM (during refeeding) as a percentage of that lost during semi-starvation.

RESULTS

This re-analysis indicates the following: (i) a large inter-individual variability in P-ratio during both weight loss and weight recovery, but for a given individual, the P-ratio during refeeding is strongly correlated with the P-ratio during semi-starvation, (ii) body composition during the control period is the most important predictor of variability in P-ratio, such that the higher the initial % body fat, the lower the proportion of energy mobilised as protein, and hence the greater the propensity to mobilise fat during semi-starvation and to subsequently deposit fat during refeeding and (iii) at week 12 of refeeding, the change in adjusted BMR is found to be reduced by a magnitude which is inversely proportional to the degree of fat recovery, but is unrelated to the degree of FFM recovery. A quantitative relationship is derived between the P-ratio during refeeding, the % fat recovery, and the P-ratio during semi-starvation.

CONCLUSIONS

Evidence is presented here suggesting that (i) human variability in the pattern of lean and fat tissue deposition during weight recovery is to a large extent determined by individual variations in the control of energy-partitioning, for which the initial % body fat is the most important predictor and (ii) the disproportionate gain in fat relative to lean tissue during weight recovery is contributed by a reduction in thermogenesis (i.e. increased efficiency of food utilization) for accelerating specifically the replenishment of the fat stores. These control systems, operating via energy-partitioning and thermogenesis, have been integrated into a compartmental model for the regulation of body composition during underfeeding/refeeding, and can be used to explain the individual pattern of lean and fat tissue deposition during weight recovery in situations ranging from the rehabilitation after malnutrition to the relapse of obesity.

Twenty-four-hour energy expenditure and urinary catecholamines of humans consuming low-to-moderate amounts of medium-chain triglycerides: a dose-response study in a human respiratory chamber

OBJECTIVE

To determine whether medium-chain triglycerides, in low-to-moderate amounts consumed with meals (at breakfast, lunch and dinner), can increase daily energy expenditure (EE) and 24-h urinary excretion of catecholamines in humans.

DESIGN

Dose-response study conducted under double-blind randomised design.

SETTING

Respiratory chamber at the Faculty of Medicine, University of Geneva.

SUBJECTS

Eight healthy young men were recruited from the student population by advertisement in our Faculty.

METHODS

24-h EE and urinary catecholamines were measured in each subject during stay in a respiratory chamber on four separate occasions. These were randomised between four different combinations of medium-chain triglycerides (MCT) and long-chain triglycerides (LCT), a total 30g/day, which was consumed with their habitual diet in three equal parts (10g each) at breakfast, lunch, and dinner in the following ratio of MCT: LCT (g/g) 0:30, 5:25, 15:15 and 30:0.

RESULTS

24-h EE increased significantly with increasing MCT:LCT ratio (ANOVA, P < 0.001), with the diet providing a total of 15-30 g MCT per day stimulating 24-h EE by 5%: this corresponds to a mean absolute increase in daily EE of approximately 500kJ, with individual values varying between 268 kJ and 756 kJ. No significant differences were observed in respiratory quotient nor in urinary nitrogen losses across diets, but 24-h urinary noradrenaline was significantly increased (ANOVA, P < 0.025), whereas adrenaline and dopamine were unaltered.

CONCLUSIONS

This study suggests that relatively low-to-moderate intake of MCT (15-30 g per day) as part of habitual diet may play a role in the control of human body composition by enhancing daily EE, and that this effect is mediated at least in part through activation of the sympathetic nervous system.

Modulation of obese gene expression in rat brown and white adipose tissues

The ob gene mRNA expression in rat brown adipose tissue (BAT) and epididymal white adipose tissue (WAT) was measured on Northern blots hybridized with a rat ob gene probe. The level of ob gene mRNA in BAT was about 40% of that in WAT. Fasting (36 h) or semi-starvation (10 days) decreased the ob gene mRNA level in both tissues by 62-68%, and cold exposure at 6 degrees C (24 h) decreased it in BAT (-84%) but not in WAT. Acute administration of the beta 3-adrenergic agonist Ro 16-8714 decreased the ob gene mRNA level in BAT (-51%) and WAT (-28%) of lean Zucker rats and only in BAT (-74%) of obese falfa rats. This study demonstrates that, in the rat, the ob gene is not only expressed in WAT but also in BAT, and suggests that in these two tissues, the modulation of the ob gene expression might be more closely associated with known alterations in cell lipid content than with changes in sympathetic activity.

Dissociation of enhanced efficiency of fat deposition during weight recovery from sympathetic control of thermogenesis

Studies reported here examined the extent to which conditions known to suppress or markedly increase the sympathetic control of thermogenesis influence enhanced efficiency of fat deposition during weight recovery after caloric restriction. To this end, measurements of energy balance and changes in body energy compartments during refeeding of rats pair fed with weight-matched controls were conducted over a 2-wk period at 22 degrees C, at thermoneutrality (29 degrees C), or in the cold (6 degrees C). The results indicate that, despite identical (or slightly lower) energy intake relative to the respective controls, the refed animals showed greater gain in body fat (by 2- to 2.5-fold), 10-12% lower energy expenditure, and higher energetic efficiency (60-80%) than the controls at all three environmental temperatures. In contrast, protein gain was not different between the refed and control groups. Thus the energy-conserving mechanism specific to acceleration of fat deposition during weight recovery persists when sympathetically driven thermogenesis is shifted from very low to very high intensity. These findings raise the possibility that this energy-conserving mechanism during refeeding may be distinct from sympathetic-dependent mechanisms underlying adaptive reduction in thermogenesis during severe energy deficit and weight loss.

Fish oil enhances macrophage tumor necrosis factor-alpha mRNA expression at the transcriptional level

Dietary supplementation with fish oil has previously been shown to enhance in vivo and in vitro (macrophage) synthesis of tumor necrosis factor-alpha (TNF-alpha) in response to bacterial lipopolysaccharide (LPS) stimulation. The studies reported here were conducted to gain insight into the molecular mechanisms of this nutrient-immune interaction by comparing the concentration, rate of synthesis, and rate of decay of TNF-alpha mRNA upon LPS stimulation of macrophages obtained from mice fed high-fat diets, rich in either fish oil, corn oil, or coconut oil, or a low-fat diet for a period of 4 weeks. The results indicate that compared with the other diet groups, LPS stimulation of macrophages from mice fed fish oil resulted in (1) enhanced levels of mRNA and protein for TNF-alpha, and (2) increased transcription of TNF-alpha mRNA as assessed by nuclear run-on assays. Posttranscriptional studies showed that the rate of decay of TNF-alpha mRNA did not vary significantly for macrophages from mice fed with fish oil as compared with corn oil. Further studies using actinomycin D and cycloheximide suggested that RNA synthesis, but not protein synthesis, was necessary for TNF-alpha mRNA accumulation. Taken together, the present studies suggest that fish oil enhances macrophage TNF-alpha mRNA expression at the transcriptional level. Although such TNF-alpha upregulation may provide a mechanism for the beneficial effects of fish oil in certain inflammatory and immune disorders, it can also underlie its potential deleterious effects if the degree of upregulation leads to exaggerated TNF-alpha production that exceeds the limits of benefit to reach toxic levels.