Postoperative Management of Osteochondral Lesions of the Ankle: A Survey Among German-Speaking Foot and Ankle Surgeons

OBJECTIVE

To assess the current treatment of osteochondral lesions of the ankle (OCLA) by German-speaking foot and ankle surgeons, focusing on the management of postoperative care and rehabilitation.

DESIGN

A questionnaire was created by a panel of 4 experienced foot and ankle surgeons on behalf of the "Clinical Tissue Regeneration" (CTR) working group of the German Society of Orthopaedics and Trauma Surgery (DGOU), and distributed electronically to members of the CTR, participants of the German Cartilage Registry (Knorpelregister DGOU©), and members of 6 German-speaking orthopedics or sports medicine societies. Results were classified depending on the consensus within the answers (agreement ≥75% "strong tendency," 50%-74% "tendency," 25%-49% "weak tendency," <25% "no tendency").

RESULTS

A total of 60 participants returned the questionnaire. The main results are as follows: regarding the frequency of surgical procedures for OCLA, refixation of the fragment, retrograde drilling, and bone marrow stimulation with or without using a matrix were performed by at least 75% of the surgeons and was considered a strong tendency. There was a strong tendency to stabilize the ankle (76.7%) and perform corrective osteotomies (51.7%). In total, 75.5% and 75% of the surgeons performed bone marrow stimulation with and without using a matrix, respectively. Corrective osteotomy and ankle stabilization were performed in 64.5% and 65.2% cases, respectively. Most participants included published recommendations on postoperative rehabilitation and the return to sports activities in their postoperative management. The main surgical procedures were considered the most critical factor in influencing the postoperative management by 81% of the participants (strong tendency). Adjunct surgical procedures such as corrective osteotomy and stabilization of the ankle were considered important by 67.8% of the respondents (tendency).

CONCLUSIONS

The management of OCLA varies among German-speaking foot and ankle surgeons. Therefore, guidelines remain essential to standardize the management of OCLA, to achieve improved and stable results. This survey will assist clinicians and patients with rehabilitation to return to sports after treating the ankle's cartilage injury.

Descriptive epidemiology of coronavirus disease 2019 in Nigeria, 27 February-6 June 2020

The objective of this study was to describe the epidemiology of COVID-19 in Nigeria with a view of generating evidence to enhance planning and response strategies. A national surveillance dataset between 27 February and 6 June 2020 was retrospectively analysed, with confirmatory testing for COVID-19 done by real-time polymerase chain reaction (RT-PCR). The primary outcomes were cumulative incidence (CI) and case fatality (CF). A total of 40 926 persons (67% of total 60 839) had complete records of RT-PCR test across 35 states and the Federal Capital Territory, 12 289 (30.0%) of whom were confirmed COVID-19 cases. Of those confirmed cases, 3467 (28.2%) had complete records of clinical outcome (alive or dead), 342 (9.9%) of which died. The overall CI and CF were 5.6 per 100 000 population and 2.8%, respectively. The highest proportion of COVID-19 cases and deaths were recorded in persons aged 31-40 years (25.5%) and 61-70 years (26.6%), respectively; and males accounted for a higher proportion of confirmed cases (65.8%) and deaths (79.0%). Sixty-six per cent of confirmed COVID-19 cases were asymptomatic at diagnosis. In conclusion, this paper has provided an insight into the early epidemiology of COVID-19 in Nigeria, which could be useful for contextualising public health planning.

Investigations into the antibacterial activities of phytotherapeutics against Helicobacter pylori and Campylobacter jejuni

The prevalence of gastric diseases is increasing with H. pylori, the causative agent of acute and chronic gastritis, being a major predisposing factor for peptic ulcer disease and gastric carcinoma. C. jejuni is the most common cause of enteric infections, particularly among children, resulting in severe diarrhoea. Increasing drug resistance of these bacteria against standard antibiotics, and the more widespread use of herbal medicines, favours investigations into additional anti-Helicobacter and anti-Campylobacter effects of phytotherapeutics that are already used for their beneficial effects on bowel and digestive functions. Twenty-one hydroethanol herbal extracts and four essential oils were screened for antibacterial activity using a modification of a previously described micro-dilution assay and compared with the inhibitory effects of antibiotics. The herbal extracts showing the highest growth inhibition of C. jejuni were Calendula officinalis, Matricaria recutita, Zingiber officinale, Salvia officinalis, Foeniculum vulgare and Silybum marianum. Agrimonia eupatoria, Hydrastis canadensis, Filipendula ulmaria and Salvia officinalis were the most active herbal extracts in inhibiting the growth of H. pylori. This study provides evidence for additional beneficial effects of phytotherapeutics marketed for their gastrointestinal effects and identifies new beneficial antibacterial effects for some herbal medicines not currently recommended for gastrointestinal problems.

Alkylamides from Echinacea Modulate Induced Immune Responses in Macrophages

The ability of Echinacea and its components to alter the immune response was examined in vitro in a macrophage cell line under either basal or immunostimulated conditions. Potential immunostimulatory and inflammatory activity was determined using a nuclear transcription factor (NFkappaB) expression, tumour necrosis factor alpha (TNFalpha) and nitric oxide (NO) production as biomarkers. In the absence of alternate stimulation, the only significant effects seen were a decrease in NFkappaB expression by a 2-ene alkylamide ((2E)-N-isobutylundeca-2-ene-8,10-diynamide (1)) and a decrease in TNFalpha levels by cichoric acid and an Echinacea alkylamide fraction (EPL AA). When the cells were stimulated by lipopolysaccharide (LPS), inhibition of the increased NFkappaB expression levels was caused by cichoric acid, an Echinacea preparation (EPL), EPL AA and a 2,4-diene ((2E,4E,8Z,10Z)-N-isobutyldodeca-2,4,8,10-tetraenamide (2)). Increases in TNFalpha levels were inhibited by cichoric acid, EPL and EPL AA but enhanced by 1 in the presence of LPS, while only EPL AA was able to inhibit the stimulated increases in NO. When using phorbol myristate acetate to stimulate the cells, NFkappaB and NO levels were unaffected by Echinacea or its components while only cichoric acid and 2 inhibited TNFalpha levels. Although cichoric acid was found to have an effect, it is probably not an important contributor to the Echinacea modulation of the immune response in vivo, as it is not bioavailable. Echinacea appears to attenuate the response of macrophages to an immune stimulus and its combination of phytochemicals exhibits different pharmacological properties to one or more of the isolated major individual components.

Cytotoxic activity of polyacetylenes and polyenes isolated from roots of Echinacea pallida

BACKGROUND AND PURPOSE

The n-hexane extracts of the roots of three medicinally used Echinacea species exhibited cytotoxic activity on human cancer cell lines, with Echinacea pallida found to be the most cytotoxic. Acetylenes are present in E. pallida lipophilic extracts but essentially absent in extracts from the other two species. In the present study, the cytotoxic effects of five compounds, two polyacetylenes (namely, 8-hydroxy-pentadeca-(9E)-ene-11,13-diyn-2-one (1) and pentadeca-(9E)-ene-11,13-diyne-2,8-dione (3)) and three polyenes (namely, 8-hydroxy-pentadeca-(9E,13Z)-dien-11-yn-2-one (2), pentadeca-(9E,13Z)-dien-11-yne-2,8-dione (4) and pentadeca-(8Z,13Z)-dien-11-yn-2-one (5)), isolated from the n-hexane extract of E. pallida roots by bioassay-guided fractionation, were investigated and the potential bioavailability of these compounds in the extract was studied.

EXPERIMENTAL APPROACH

Cytotoxic effects were assessed on human pancreatic MIA PaCa-2 and colonic COLO320 cancer cell lines. Cell viability was evaluated by the WST-1 assay and apoptotic cell death by the cytosolic internucleosomal DNA enrichment and the caspase 3/7 activity tests. Caco-2 cell monolayers were used to assess the potential bioavailability of the acetylenes.

KEY RESULTS

The five compounds exhibited concentration-dependent cytotoxicity in both cell types, with a greater potency in the colonic cancer cells. Apoptotic cell death was found to be involved in the cytotoxic effect of the most active, compound 5. Compounds 2 and 5 were found to cross the Caco-2 monolayer with apparent permeabilities above 10 x 10(-6) cm s(-1).

CONCLUSIONS AND IMPLICATIONS

Compounds isolated from n-hexane extracts of E. pallida roots have a direct cytotoxicity on cancer cells and good potential for absorption in humans when taken orally.

Permeability studies of Kavalactones using a Caco-2 cell monolayer model

OBJECTIVE

To examine the bioavailability of kavalactones in vitro and the possible differences in their bioavailability because of variations in either chemical structure or the method of extraction used.

RESEARCH DESIGN AND METHODS

Caco-2 cell monolayers were used to determine the potential bioavailability of kavalactones. Kavalactones were added to the apical layer and basolateral samples were taken over 150 min to examine the concentration diffusing across the cell monolayer. Kavalactone concentrations in these samples were determined by high pressure liquid chromatography.

RESULTS

Kavalactones were found to be potentially bioavailable as they all readily crossed the Caco-2 monolayers with apparent permeabilities (P(app)) increasing from 42 x 10(-6) cm/s and most exhibiting more than 70% crossing within 90 min. Not all differences in their bioavailability can be related to kavalactone structural differences as it appears that bioavailability may also be affected by co-extracted compounds. For example, the P(app) for kawain from ethanol extracts was higher than the values obtained for the same compound from water extracts or for the kavalactone alone.

CONCLUSIONS

While the extraction method used (ethanol or water) influences the total (but not the relative) concentrations of kavalactones, it does not markedly affect their bioavailability. Hence, any differences between an ethanolic or an aqueous extract in terms of the propensity of kava to cause liver damage is not because of differing kavalactone bioavailabilities.

Comparison of Echinacea alkylamide pharmacokinetics between liquid and tablet preparations

The relative oral bioavailability of alkylamides from two different Echinacea dosage forms (liquid and tablet) were compared in a small two-way crossover study in humans (n=3). The liquid preparation investigated contained a mixture of Echinacea purpurea root (300 mg/ml) and Echinacea angustifolia root (200 mg/ml) extracted in 60% ethanol. The tablet preparation investigated was also a mixture of E. purpurea root (675 mg/tablet) and E. angustifolia root (600 mg/tablet), but was prepared from the dried 60% ethanolic extracts of these two Echinacea species. Alkylamides were found to be rapidly absorbed and measurable in plasma from both preparations. No significant differences in the tetraene alkylamide pharmacokinetic parameters for T(1/2), AUC(t-lin) and C(max) in the two different preparations were found. T(max) increased from 20 min for the liquid to 30 min for the tablet, which is not unexpected as the tablet required time for disintegration before absorption could occur. These results suggested that there was no significant difference in the bioavailability of alkylamides from the liquid and tablet Echinacea formulations. Furthermore, the results also indicated that the absorption site and any alkylamide loss due to digestive processes were similar in both preparations.

Stereoselective synthesis, natural occurrence and CB(2) receptor binding affinities of alkylamides from herbal medicines such as Echinacea sp

A divergent synthesis of (2E,4E,8E,10E)- and (2E,4E,8E,10Z)-N-isobutyldodeca-2,4,8,10-tetraenamides from pent-4-yn-1-ol allowed identification of the (2E,4E,8E,10Z)-isomer for the first time in Echinacea species. A short, stereoselective synthesis of the (2E,4E,8E,10Z)-isomer is also described which allowed further biological evaluation of this material, and the demonstration that this isomer does not occur in Spilanthes mauritiana as previously reported.

Echinacea alkamide disposition and pharmacokinetics in humans after tablet ingestion

Echinacea is a widely used herbal remedy for the treatment of colds and other infections. However, almost nothing is known about the disposition and pharmacokinetics of any of its components, particularly the alkamides and caffeic acid conjugates which are thought to be the active phytochemicals. In this investigation, we have examined serial plasma samples from 9 healthy volunteers who ingested echinacea tablets manufactured from ethanolic liquid extracts of Echinacea angustifolia and Echinacea purpurea immediately after a standard high fat breakfast. Caffeic acid conjugates could not be identified in any plasma sample at any time after tablet ingestion. Alkamides were rapidly absorbed and were measurable in plasma 20 min after tablet ingestion and remained detectable for up to 12 h. Concentration-time curves for 2,4-diene and 2-ene alkamides were determined. The maximal concentrations for the sum of alkamides in human plasma were reached within 2.3 h post ingestion and averaged 336+/-131 ng eq/mL plasma. No obvious differences were observed in the pharmacokinetics of individual or total alkamides in 2 additional fasted subjects who took the same dose of the echinacea preparation. This single dose study provides evidence that alkamides are orally available and that their pharmacokinetics are in agreement with the one dose three times daily regimen already recommended for echinacea.

Echinacea intake induces an immune response through altered expression of leucocyte hsp70, increased white cell counts and improved erythrocyte antioxidant defences

OBJECTIVE

To study the effect of Echinacea tablets on the expression of leucocyte heat shock protein 70 (hsp70), erythrocyte haemolysis, plasma antioxidant status, serum chemistry, haematological values and plasma alkylamide concentrations.

METHOD

Eleven healthy individuals (26-61 years of age) were evaluated at baseline (day 1) and on day 15 after consuming two commercially blended Echinacea tablets daily for 14 days.

RESULTS

Echinacea supplementation enhanced the fold increase in leucocyte hsp70 expression after a mild heat shock (P=0.029). White cell counts (WCC) were also increased (P=0.043). We also observed a preventative effect against free radical induced erythrocyte haemolysis (P=0.006) indicative of an antioxidant effect.

CONCLUSION

The pilot study suggests that Echinacea may invoke an immune response through altered expression of hsp70 and increased WCC.

Cytochrome P450 enzyme-mediated degradation of Echinacea alkylamides in human liver microsomes

Echinacea preparations are widely used herbal remedies for the prevention and treatment of colds. In this study we have investigated the metabolism by human liver microsomes of the alkylamide components from an Echinacea preparation as well as that of pure synthetic alkylamides. No significant degradation of alkylamides was evident in cytosolic fractions. Time- and NADPH-dependent degradation of alkylamides was observed in microsomal fractions suggesting they are metabolised by cytochrome P450 (P450) enzymes in human liver. There was a difference in the susceptibility of 2-ene and 2,4-diene pure synthetic alkylamides to microsomal degradation with (2E)-N-isobutylundeca-2-ene-8,10-diynamide (1) metabolised to only a tenth the extent of (2E,4E,8Z,10Z)-N-isobutyldodeca-2,4,8,10-tetraenamide (3) under identical incubation conditions. Markedly less degradation of 3 was evident in the mixture of alkylamides present in an ethanolic Echinacea extract, suggesting that metabolism by liver P450s was dependent both on their chemistry and the combination present in the incubation. Co-incubation of 1 with 3 at equimolar concentrations resulted in a significant decrease in the metabolism of 3 by liver microsomes. This inhibition by 1, which has a terminal alkyne moiety, was found to be time- and concentration-dependent, and due to a mechanism-based inactivation of the P450s. Alkylamide metabolites were detected and found to be the predicted epoxidation, hydroxylation and dealkylation products. These findings suggest that Echinacea may effect the P450-mediated metabolism of other concurrently ingested pharmaceuticals.

Permeability studies of alkylamides and caffeic acid conjugates from echinacea using a Caco-2 cell monolayer model

BACKGROUND

Echinacea is composed of three major groups of compounds that are thought to be responsible for stimulation of the immune system--the caffeic acid conjugates, alkylamides and polysaccharides. This study has focussed on the former two classes, as these are the constituents found in ethanolic liquid extracts.

OBJECTIVE

To investigate the absorption of these two groups of compounds using Caco-2 monolayers, which are a model of the intestinal epithelial barrier.

RESULTS

The caffeic acid conjugates (caftaric acid, echinacoside and cichoric acid) permeated poorly through the Caco-2 monolayers although one potential metabolite, cinnamic acid, diffused readily with an apparent permeability (Papp) of 1 x 10(-4) cm/s. Alkylamides were found to diffuse through Caco-2 monolayers with Papp ranging from 3 x 10(-6) to 3 x 10(-4) cm/s. This diversity in Papp for the different alkylamides correlates to structural variations, with saturation and N-terminal methylation contributing to decreases in Papp. The transport of the alkylamides is not affected by the presence of other constituents and the results for synthetic alkylamides were in line with those for the alkylamides in the echinacea preparation.

CONCLUSION

Alkylamides but not caffeic acid conjugates are likely to cross the intestinal barrier.

Facilitation of renal autoregulation by angiotensin II is mediated through modulation of nitric oxide

AIMS

This study was designed to investigate the influence of angiotensin II (Ang II) and nitric oxide (NO) on autoregulation of renal perfusion.

METHODS

Autoregulation was investigated in isolated perfused kidneys (IPRK) from Sprague-Dawley rats during stepped increases in perfusion pressure.

RESULTS

Ang II (75-200 pM) produced dose-dependent enhancement of autoregulation whereas phenylephrine produced no enhancement and impaired autoregulation of GFR. Enhancement by Ang II was inhibited by the AT1 antagonist, Losartan, and the superoxide scavenger, Tempol. Under control conditions nitric oxide synthase (NOS) inhibition by 10 microm N-omega-nitro-L-arginine methyl ester (L-NAME) facilitated autoregulation in the presence of non-specific cyclooxygenase (COX) inhibition by 10 microm indomethacin. Both COX and combined NOS/COX inhibition reduced the autoregulatory threshold concentration of Ang II. Facilitation by 100 pm Ang II was inhibited by 100 microm frusemide. Methacholine (50 nm) antagonised Ang II-facilitated autoregulation in the presence and absence of NOS/COX inhibition. Infusion of the NO donor, 1 microm sodium nitroprusside, inhibited L-NAME enhancement of autoregulation under control conditions and during Ang II infusion.

CONCLUSIONS

The results suggest than an excess of NO impairs autoregulation under control conditions in the IPRK and that endogenous and exogenous NO, vasodilatory prostaglandins and endothelium-derived hyperpolarizing factor (EDHF) activity antagonise Ang II-facilitated autoregulation. Ang II also produced a counterregulatory vasodilatory response that included prostaglandin and NO release. We suggest that Ang II facilitates autoregulation by a tubuloglomerular feedback-dependent mechanism through AT1 receptor-mediated depletion of nitric oxide, probably by stimulating generation of superoxide.

Reversible inhibition of cellular respiration by nitric oxide in vascular inflammation

Incubation of rat aortas with endotoxin and interferon-gamma for 24 h resulted in an aortic oxygen consumption that was substantially inhibited and strongly oxygen dependent (37% inhibition at 160 microM O(2) and 62% inhibition at 80 microM O(2) relative to untreated aortas). This respiratory inhibition was reversed by a nitric oxide (NO) scavenger (oxyhemoglobin) or by an inhibitor of inducible NO synthase [N-(3-(aminomethyl)benzyl)acetamide x 2HCl, 1400W], but not by an inhibitor of soluble guanylate cyclase (1H-[1,2,4]oxadiazolo[4,3-a]-quinoxalin-1-one). Addition of 1 microM NO to untreated aortas caused rapid and reversible inhibition of oxygen consumption that was greater at lower oxygen concentrations. Incubation of endothelial cells isolated from rat aortas with endotoxin and interferon-gamma for 24 h resulted in a steady-state NO concentration of approximately 0.5 microM and 90% inhibition of cellular oxygen consumption that was immediately reversed by an NO scavenger (oxyhemoglobin). These results suggest that during inflammation and sepsis, tissue respiration may be substantially reduced due to inhibition by NO of cytochrome oxidase.

Life without UCP1: mitochondrial, cellular and organismal characteristics of the UCP1-ablated mice

Mice devoid of the original uncoupling protein UCP1 have provided opportunities to delineate UCP1 function in a series of biochemical and physiological contexts. The isolated brown-fat mitochondria from such mice are fully coupled (without the addition of GDP), but still exhibit a depressed capacity for ATP synthesis. However, they only show a 2-fold decrease in sensitivity to the de-energizing effect of free fatty acids, compared with UCP1-containing mitochondria, whereas they possess a (UCP1-independent) 50-fold higher sensitivity than liver mitochondria; the fatty acid sensitivities in wild-type and UCP1-deficient mitochondria may, however, be of different natures. Despite the fact that brown-fat cells from UCP1-ablated mice cannot produce heat when stimulated by noradrenaline ('norepinephrine') or fatty acids, UCP1-ablated mice can be induced to tolerate extended cold exposure, but the heat then fully results from shivering thermogenesis. Recruitable or adaptive (by cold acclimation or adaptation to a cafeteria diet) adrenergically-stimulated thermogenesis does not exist in the UCP1-ablated animals, demonstrating the unique ability of UCP1 to mediate recruitable non-shivering thermogenesis. In addition to information on the function of UCP1, the UCP1-ablated mice can be used to gain information concerning the function of the UCP1 homologues. Thus whereas an uncoupling function of the UCP1 homologues cannot be excluded, UCP1-ablated animals clearly lack any ability to recruit any UCP1 homologue to functionally replace the loss of thermogenesis resulting from UCP1. UCP1 (thermogenin) thus remains the only protein the activity of which can be recruited for the purpose of facultative thermogenesis.

Only UCP1 can mediate adaptive nonshivering thermogenesis in the cold

Adaptive nonshivering thermogenesis may have profound effects on energy balance and is therefore therefore is a potential mechanism for counteracting the development of obesity. The molecular basis for adaptive nonshivering thermogenesis has remained a challenge that sparked acute interest with the identification of proteins (UCP2, UCP3, etc.) with high-sequence similarity to the original uncoupling protein-1 (UCP1), which is localized only in brown adipose tissue. Using UCP1-ablated mice, we examined whether any adaptive nonshivering thermogenesis could be recruited by acclimation to cold. Remarkably, by successive acclimation, the UCP1-ablated mice could be made to subsist for several weeks at 4C during which they had to constantly produce heat at four times their resting levels. Despite these extreme requirements for adaptive nonshivering thermogenesis, however, no substitution of shivering by any adaptive nonshivering thermogenic process occurred. Thus, although the existence of, for example, muscular mechanisms for adaptive nonshivering thermogenesis has recurrently been implied, we did not find any indication of such thermogenesis. Not even during prolonged and enhanced demand for extra heat production was any endogenous hormone or neurotransmitter able to recruit any UCP1-independent adaptive nonshivering thermogenic process in muscle or in any other organ, and no proteins other than UCP1-not even UCP2 or UCP3-therefore have the ability to mediate adaptive nonshivering thermogenesis in the cold.

UCP1: the only protein able to mediate adaptive non-shivering thermogenesis and metabolic inefficiency

The uniqueness of UCP1 (as compared to UCP2/UCP3) is evident from expression analysis and ablation studies. UCP1 expression is positively correlated with metabolic inefficiency, being increased by cold acclimation (in adults or perinatally) and overfeeding, and reduced in fasting and genetic obesity. Such a simple relationship is not observable for UCP2/UCP3. Studies with UCP1-ablated animals substantiate the unique role of UCP1: the phenomenon of adaptive adrenergic non-shivering thermogenesis in the intact animal is fully dependent on the presence of UCP1, and so is any kind of cold acclimation-recruited non-shivering thermogenesis; thus UCP2/UCP3 (or any other proteins or metabolic processes) cannot substitute for UCP1 physiologically, irrespective of their demonstrated ability to show uncoupling in reconstituted systems or when ectopically expressed. Norepinephrine-induced thermogenesis in brown-fat cells is absolutely dependent on UCP1, as is the uncoupled state and the recoupling by purine nucleotides in isolated brown-fat mitochondria. Although very high UCP2/UCP3 mRNA levels are observed in brown adipose tissue of UCP1-ablated mice, there is no indication that the isolated brown-fat mitochondria are uncoupled; thus, high expression of UCP2/UCP3 does not necessarily confer to the mitochondria of a tissue a propensity for being innately uncoupled. Whereas the thermogenic effect of fatty acids in brown-fat cells is fully UCP1-dependent, this is not the case in brown-fat mitochondria; this adds complexity to the issues concerning the mechanisms of UCP1 function and the pathway from beta(3)-adrenoceptor stimulation to UCP1 activation and thermogenesis. In addition to amino acid sequences conserved in all UCPs as part of the tripartite structure, all UCPs contain certain residues associated with nucleotide binding. However, conserved amongst all UCP1s so far sequenced, and without parallel in all UCP2/UCP3, are two sequences: 144SHLHGIKP and the C-terminal sequence RQTVDC(A/T)T; these sequences may therefore be essential for the unique thermogenic function of UCP1. The level of UCP1 in the organism is basically regulated at the transcriptional level (physiologically probably mainly through the beta(3)-adrenoceptor/CREB pathway), with influences from UCP1 mRNA stability and from the delay caused by translation. It is concluded that UCP1 is unique amongst the uncoupling proteins and is the only protein able to mediate adaptive non-shivering thermogenesis and the ensuing metabolic inefficiency.

Thermogenic responses in brown fat cells are fully UCP1-dependent. UCP2 or UCP3 do not substitute for UCP1 in adrenergically or fatty scid-induced thermogenesis

To examine the thermogenic significance of the classical uncoupling protein-1 (UCP1), the thermogenic potential of brown adipocytes isolated from UCP1-ablated mice was investigated. Ucp1(-/-) cells had a basal metabolic rate identical to wild-type; the mitochondria within them were coupled to the same degree. The response to norepinephrine in wild-type cells was robust ( approximately 10-fold increase in thermogenesis); Ucp1(-/-) cells only responded approximately 3% of this. Ucp1(-/-) cells were as potent as wild-type in norepinephrine-induced cAMP accumulation and lipolysis and had a similar mitochondrial respiratory complement. In wild-type cells, fatty acids induced a thermogenic response similar to norepinephrine, but fatty acids (and retinoate) were practically without effect in Ucp1(-/-) cells. It is concluded that no other adrenergically induced thermogenic mechanism exists in brown adipocytes except that mediated by UCP1 and that entopic expression of UCP1 does not lead to overt innate uncoupling, and it is suggested that fatty acids are transformed to an intracellular physiological activator of UCP1. High expression of UCP2 and UCP3 in the tissue was not associated with an overt innate highly uncoupled state of mitochondria within the cells, nor with an ability of norepinephrine or endo- or exogenous fatty acids to induce uncoupled respiration in the cells. Thus, UCP1 remains the only physiologically potent thermogenic uncoupling protein in these cells.

The bioenergetics of brown fat mitochondria from UCP1-ablated mice. Ucp1 is not involved in fatty acid-induced de-energization ("uncoupling")

The bioenergetics of brown fat mitochondria isolated from UCP1-ablated mice were investigated. The mitochondria had lost the high GDP-binding capacity normally found in brown fat mitochondria, and they were innately in an energized state, in contrast to wild-type mitochondria. GDP, which led to energization of wild-type mitochondria, was without effect on the brown fat mitochondria from UCP1-ablated mice. The absence of thermogenic function did not result in reintroduction of high ATP synthase activity. Remarkably and unexpectedly, the mitochondria from UCP1-ablated mice were as sensitive to the de-energizing ("uncoupling") effect of free fatty acids as were UCP1-containing mitochondria. Therefore, the de-energizing effect of free fatty acids does not appear to be mediated via UCP1, and free fatty acids would not seem to be the intracellular physiological activator involved in mediation of the thermogenic signal from the adrenergic receptor to UCP1. In the UCP1-ablated mice, Ucp2 mRNA levels in brown adipose tissue were 14-fold higher and Ucp3 mRNA levels were marginally lower than in wild-type. The Ucp2 and Ucp3 mRNA levels were therefore among the highest found in any tissue. These high mRNA levels did not confer on the isolated mitochondria any properties associated with de-energization. Thus, the mere observation of a high level of Ucp2 or Ucp3 mRNA in a tissue cannot be taken as an indication that mitochondria isolated from that tissue will display innate de-energization or thermogenesis.

UCP1: the original uncoupling protein--and perhaps the only one? New perspectives on UCP1, UCP2, and UCP3 in the light of the bioenergetics of the UCP1-ablated mice

The availability of a UCP1-ablated mouse has enabled critical studies of the function of UCP1, UCP2, and UCP3. Concerning UCP1, its presence in brown-fat mitochondria is associated with innate uncoupling, high GDP-binding capacity, and GDP-inhibitable Cl- permeability and uncoupling--but the high fatty acid sensitivity found in these mitochondria is observed even in the absence of UCP1. The absence of UCP1 leads to low cold tolerance but not to obesity. UCP1 ablation also leads to an augmented expression of UCP2 and UCP3 in brown adipose tissue, making this tissue probably the one that boasts the highest expression of these UCPs. However, these very high expression levels are not associated with any inherent uncoupling, or with a specific GDP-binding capacity, or with a GDP-sensitive Cl- permeability, or with any effect of GDP on mitochondrial membrane potential, or with an increased basal metabolism of cells, or with the presence of norepinephrine- or fatty acid-induced thermogenesis in cells, and not with a cold-acclimation recruited, norepinephrine-induced thermogenic response in the intact animal. Therefore, it can be discussed whether any uncoupling effect is associated with UCP2 or UCP3 when they are endogenously expressed and, consequently, whether (loss of) uncoupling (thermogenic) effects of UCP2 or UCP3 can be invoked to explain metabolic phenomena, such as obesity.

Effects of noradrenaline and flow on lactate uptake in the perfused rat hindlimb

Skeletal muscle can release or take up lactate depending on the lactate concentration gradient across the cell membrane. In the perfused rat hindlimb without arterial lactate, both noradrenaline (NA) infusion and increased flow promote lactate release and oxygen consumption (VO2). However, it is unclear whether NA or increased flow rate have similar effects on lactate uptake. The present study compares these effects in the rat hindlimb perfused at a basal flow rate of 0.33 mL min-1 g-1 and 25 degrees C in the presence of added arterial lactate. When 10 mmol L-1 L-(+)-lactate was added to the arterial perfusate, lactate was taken up (16 +/- 1.0 mumol g-1 h-1, n = 13) by the hindlimb with a 35% higher VO2 than that without added lactate. Doubling perfusion flow rate enhanced lactate uptake and VO2 by 120% and 40%, respectively. Glucose uptake was also increased (by 253%) with increased flow. Infusion of NA increased perfusion pressure, VO2 and glucose uptake similarly to those induced by increased flow rate. However, lactate uptake was inhibited by NA. This inhibition was not altered by the beta-adrenergic antagonist propranolol. Vasopressin also showed similar effects to NA to decrease lactate uptake associated with increased VO2 and vasoconstriction. These data indicate that in the presence of a high arterial lactate concentration, NA has opposite effects from increased flow rate on skeletal muscle lactate uptake although both have similar effects on lactate release in the absence of arterial lactate. Inhibition of lactate uptake may relate to the vasoconstrictive action of NA.

Kinetics of the inhibition of mitochondrial respiration by NO

The kinetics of the inhibition of mitochondrial respiration by NO was examined in isolated mitochondria (here obtained from rat brown adipose tissue). The Ki of NO for the inhibition was approximately 27 nM; the IC50 of NO increased in proportion to the square of an increase in O2 tension. The Km of O2 for respiration was approximately 16 microM; in the presence of NO, the dependence of respiration on O2 tension had a Hill coefficient of approximately 2. The unusual kinetics is probably related to the ability of cytochrome c oxidase to use 2 NO or 1 O2 as electron acceptor. The interaction between NO and O2 in the control of respiration could be described by the formula VO2(O2, NO) = VO2max x ([O2]2/((16 microM x (1 + [NO]/27 nM))2 + [O2]2)). Thus, the kinetics is such that respiration in the presence of physiological levels of NO is very sensitive to decreasing O2 tension.

Characterization of perfused periaortic brown adipose tissue from the rat

A technique was developed for the perfusion of periaortic brown adipose tissue (BAT) with a view to assessing vascular system involvement in BAT thermogenesis. The procedure involved cannulation of the thoracic aorta and ligation of the intercostal branches and the distal thoracic aorta. Perfusion was conducted in a buffer-filled chamber using constant flow at 37 degrees C. Lactate dehydrogenase leakage was less than 2%/h, and after 30 min of perfusion the energy charge was 0.72 +/- 0.05 (n = 4) and differed little from freshly sampled interscapular BAT (0.71 +/- 0.03 (n = 7)). Periaortic BAT was indistinguishable from interscapular BAT in enzyme content, mitochondrial size, mitochondrial cristae, lipid content, and cell size. Basal oxygen consumption (VO2) was 64.3 +/- 7.4 mumol.h-1.g-1 wet weight, and basal perfusion pressure was 65 +/- 3 mmHg (1 mmHg = 133.3 Pa). Norepinephrine and isoproterenol each increased VO2 of perfused periaortic BAT in a time-dependent and reversible manner. Half-maximal stimulation of VO2 occurred at 12 nM norepinephrine and 8 nM isoproterenol; maximally stimulated tissue had a VO2 of approximately 150 mumol.h-1.g-1 wet weight. Norepinephrine (50 nM) had no consistent effect on perfusion pressure, but the increase in VO2 by this agonist was completely blocked by 10 microM DL-propranolol and unaffected by phentolamine (1-20 microM) or nitroprusside (0.01-1 mM). Increasing the perfusion flow rate increased pressure and had no effect on basal VO2 but increased the VO2 response due to norepinephrine.(ABSTRACT TRUNCATED AT 250 WORDS)