S. aureus and IgE-mediated diseases: pilot or copilot? A narrative review

INTRODUCTION

S. aureus is a major opportunistic pathogen that has been implicated in the pathogenesis of several chronic inflammatory diseases including bronchial asthma, chronic rhinosinusitis with nasal polyps (CRSwNP), chronic spontaneous urticaria (CSU), and atopic dermatitis. S. aureus can induce the production of both polyclonal and specific IgE that can elicit an inflammatory cascade.

AREAS COVERED

The link between the sensitization to S. aureus enterotoxins and the severity of several chronic inflammatory diseases is reviewed in detail, as well as its therapeutic implications.

EXPERT OPINION

An anti-IgE strategy to inhibit S. aureus enterotoxins would be a valid approach to treat several endotypes of severe asthma, CRSwNP and CSU in which IgE against S. aureus enterotoxins should represent, not only a marker of severity of the diseases but also a target of a treatment.

Indacaterol/glycopyrronium/mometasone fixed dose combination for uncontrolled asthma

INTRODUCTION

Asthma symptoms can be relieved through a maintenance treatment combining long-acting β₂-agonist and inhaled corticosteroids (LABA/ICS). However, for patients with inadequately controlled asthma, the LABA/ICS combination might not be sufficient, and clinical guidelines recommend the administration of inhaled long-acting muscarinic antagonists (LAMA) as an add-on therapy to better control asthma and improve lung function. For nearly two decades, the only LAMA to be approved on the market has been tiotropium.

AREAS COVERED

We reviewed recent clinical studies evaluating the safety and efficacy of LABA/LAMA/ICS fixed dose combinations by searching the PubMed database. Molecular mechanisms and clinical data support the use of a once-daily, single-inhaler fixed dose combination of the LABA/LAMA/ICS indacaterol/glycopyrronium/mometasone (IND/GLY/MF), the first therapy combining three agents in a fixed dose approved in Europe for the treatment of uncontrolled asthma.

EXPERT OPINION

IND/GLY/MF was superior to both IND/MF and salmeterol/fluticasone, a well-established LABA/ICS combination improving the lung function in uncontrolled asthma. Moreover, IND/GLY/MF, delivered through the Breezhaler inhaler in a single inhalation, is the first inhaled therapy prescribed alongside a digital companion, a sensor and the Propeller app, allowing for improved treatment adherence, reduced rescue inhaler usage and hospitalizations, increased patient satisfaction and asthma control.

Self-administration of omalizumab: why not? A literature review and expert opinion

Introduction: Omalizumab is used to treat severe uncontrolled allergic asthma and chronic spontaneous urticaria (CSU), and is approved for self-administration in prefilled syringes. It is thus important to understand the advantages, critical issues, and indications for home administration.Areas covered: The present review summarizes the available evidence on home administration of omalizumab in asthma and CSU to illustrate the advantages derived from self-administration of patients in this setting.Expert opinion: The available data suggest that patients can safely administer biologics at home with suitable training, and that home administration is time saving and cost-effective. The majority of patients with severe asthma or CSU treated with omalizumab are likely to be suitable candidates for self-administration, which can be proposed to anyone that the clinician deems suitable. In addition to clinicians, pharmacists can also play a key role in managing patients who are prescribed home administration. A practical flow chart is proposed on selection of patients and their management during home administration. Self-administration of biologics can be considered as a valid alternative to traditional injections in a clinical setting, and the evidence has shown that no major issues need to be overcome in terms of safety or efficacy.

Not one, but many "publics": public engagement with global development in France, Germany, Great Britain, and the United States

Using new panel data from the Aid Attitudes Tracker (2013-18), this article draws on a set of 18 actions to map public engagement with global poverty in France, Germany, Great Britain and the United States. It introduces a new engagement segmentation comprised of five distinct groups - the totally disengaged, marginally engaged, informationally engaged, behaviourally engaged, and fully engaged. The data provide evidence of both aggregate and individual-level change in engagement over time but with an important distinction: respondents in less engaged groups are less likely to move out of these groups and tend to stay unengaged. Respondents in more engaged groups are more likely to move in and out of engagement.

Pharmacological approach and adherence to treatment recommendations in frequently and non-frequently exacerbating COPD patients from Italy: MISTRAL - The prospective cohort, observational study

BACKGROUND

Several documents and guidelines provide recommendations for effective management of COPD patients. However, there is often a significant imbalance between recommended treatment of COPD patients and the actual care provided both in primary care and specialty setting. This imbalance could result in a significant negative impact on patients' health status and quality of life, leading to increased hospitalisations and health resource utilisation in COPD patients METHODS: MISTRAL was an observational, longitudinal, prospective cohort study, designed to assess the overall pharmacological approach of COPD in routine clinical practice in Italy. Eligible patients were divided into two cohorts based on their exacerbation history in the year prior to the enrolment, frequent exacerbators (FEs; ≥2 exacerbations), and non-frequent exacerbators (NFEs; ≤1 exacerbation). The primary objective was to assess adherence to Global Initiative for Chronic Obstructive Lung Disease (GOLD) 2011 treatment recommendations in FEs and NFEs at baseline and follow-up visits RESULTS: Of the 1489 enrolled patients, 1468 (98.6%; FEs, 526; NFEs, 942) were considered evaluable for analyses. At baseline, 57.8% of patients were treated according to GOLD 2011 recommendations; a greater proportion of FEs were treated according to GOLD recommendations, compared with NFEs patients at baseline (77.1% versus 46.7%; P < 0.0001), and all study visits. At baseline, GOLD group D patients were the most adherent (81.2%) to treatment recommendations, while group A patients were the least adherent (30.3%) at baseline, attributed mainly to overuse of inhaled corticosteroids in less severe GOLD groups. Triple therapy with long-acting muscarinic antagonist (LAMA) + long-acting β₂-agonist/inhaled corticosteroid (LABA/ICS) was the most frequent prescribed treatment at all study visits, irrespective of patient's exacerbation history. Changes in treatment were more frequent in FEs versus NFEs CONCLUSIONS: The Mistral study reports a scarce adherence to the GOLD 2011 treatment recommendations in routine clinical practice in Italy. The adherence was particularly low in less severe, non-frequent exacerbating patients mostly for ICS overuse, and was higher in high-risk, frequent exacerbating COPD patients.

Feasibility of air plethysmography (BOD POD) in morbid obesity: a pilot study

The assessment of body composition (BC) in morbidly obese patients is a difficult procedure. Air-displacement plethysmography (ADP), which measures body density, is a very promising technique for BC assessment in health and disease. However, there are very few data about the feasibility of applying ADP on morbidly obese patients, which theoretically could be affected by large body size and difficulty in lung volume measurements. The main aim of this pilot study was to evaluate the feasibility of using ADP for BC assessment in morbidly obese patients. We studied nine subjects (6 males and 3 females) who had a mean age (+/-SD) of 47.0+/-13.5 years and body mass index (BMI) of 46.6+/-7.7 kg/m(2) (range 36.4-58.8). All patients could fit into the instrument chamber and perform the manoeuvre for pulmonary plethysmography. Mean lung volume was 3.9+/-1.2 l and mean percent body fat was 53.1+/-6.6 (range 46.0-67.5). These results indicate that ADP appears to be suitable for patients with BMI over 40 kg/m(2) and produces realistic BC data.

Assessment by bioimpedance of forearm cell mass: a new approach to calibration

OBJECTIVE

Changes in skeletal muscle mass are involved in several important clinical disorders including sarcopenia and obesity. Unlike body fat, skeletal muscle is difficult to quantify in vivo, particularly without highly specialized equipment. The present study had a two-fold aim: to develop a regional (40)K counter for non-invasively estimating cell mass in the arm, mainly skeletal muscle cell mass, without radiation exposure; and to test the hypothesis that cell mass in the arm is highly correlated with electrical impedance after adjusting for the arm's length.

METHODS

Forearm cell mass was estimated using a rectangular lead-shielded (40)K counter with 4-NaI crystals; impedance of the arm was measured at multiple frequencies using a segmental bioimpedance analysis (BIA) system. The system's within- and between-day coefficient of variation (CV) for (40)K-derived elemental potassium averaged 1.8+/-1.3 and 5.8+/-1.2%, respectively. The corresponding BIA system's CVs were 1.0+/-0.4 and 2.1+/-1.0%, respectively.

SUBJECTS AND RESULTS

Participants in the study were 15 healthy adults (eight females, seven males; age 39+/-2.8 y, BMI 22.9+/-4.5 kg/m(2)). The right arm's K (5.2+/-1.7 g) was highly correlated with length-adjusted impedance (r(2)=0.81, 0.82, and 0.83 for 5, 50 and 300 kHz, respectively; all P<0.001); multiple regression analysis showed no additional improvement by adding age or sex to the prediction models.

CONCLUSION

These results demonstrate the feasibility of calibrating BIA-measured electrical properties of the arm against estimates of arm cell mass, mainly of skeletal muscle, obtained by regional (40)K counting. This simple and practical approach should facilitate the development of BIA-based regional cell mass prediction formulas

Use of quality control indices in moderately hypocaloric Mediterranean diet for treatment of obesity

A large number of studies have been published on very-low calorie diets and markedly hypocaloric dietary regimens for treatment of obesity. However, scanty data are available on moderately hypocaloric diets based on the Mediterranean diet model. We evaluated the efficacy and safety of a moderately hypocaloric Mediterranean diet (MHMD) by assessing changes in body composition and in metabolic profile in 19 obese women, aged 32+/-4 years, body weight 84.7+/-9.6 kg, body mass index (BMI) 33.67+/-2.61 kg/m2. The energy content of the diet (mean 6.5 MJ/day) matched the resting metabolic rate and its content in macronutrients (55% carbohydrate, 25% fat, 20% protein, 30 g fibre) was based on the Italian Recommended Dietary Allowances (LARN). Based on the Mediterranean diet model, available nutritional indices like the animal/vegetable protein ratio, the Cholesterol/Saturated Fat Index, the Glycaemic Index, the Atherogenic Index, the Thrombogenic Index and the Mediterranean Adequacy Index were taken into account in elaborating diets. At baseline and after 2 months, body composition by dual energy X-ray absorptiometry, metabolic profile, uric acid, fibrinogen and oral glucose tolerance test (OGTT) were assessed. Following MHMD, body weight decreased to 78.1+/-10.5 kg and BMI to 31.18+/-2.74 kg/m2. Total (-4.9+/-0.9 kg) and segmental fat mass decreased, no significant loss of total and segmental lean body mass was observed. No decrease of fasting blood glucose (5.05+/-0.45 vs 4.98+/-0.43 mmol/l, NS), of the area under the curve (AUC) for glucose (29.50+/-6.24 vs 28.07+/-5.29, NS) as well as of HDL-cholesterol (1.30+/-0.30 vs 1.33+/-0.33 mmol/l, NS) and of triglycerides (1.70+/-1.00 vs 1.46+/-0.66 mmol/l, NS) was observed. However, a significant decrease of basal insulin (11.48+/-6.77 vs 8.07+/-4.17 mU/ml, p<0.01) as well as of the AUC for insulin (263+/-118 vs 208+/-82,p<0.005), of total (5.40+/-1.04 vs 4.97+/-0.92 mmol/l,p<0.05) and LDL-cholesterol (3.36+/-1.07 vs 2.90+/-0.74 mmol/l,p<0.005), of uric acid (0.30+/-0.06 vs 0.28+/-0.05 mmol/l,p<0.01) and fibrinogen (359+/-78 vs 324+/-87 mg/100 ml, p<0.0001) was observed. In conclusion, MHMD prevents loss of fat-free mass and improves metabolic parameters in obese people. We advocate a wider use of nutritional indices and body composition assessment as tools for quality control of hypocaloric diets.

Is body mass index a measure of adiposity in elderly women?

OBJECTIVE

To evaluate the accuracy of body mass index (BMI) as a predictor of body fat in elderly women.

RESEARCH METHODS AND PROCEDURES

A total of 1423 women aged 67 +/- 5 (mean +/- SD, range: 60 to 88) years were consecutively enrolled into the study. Fat mass (FM) was measured using DXA.

RESULTS

BMI explained 72.9% of FM variance (p < 0.0001), with a root mean square error of estimate (RMSE) of 3.5 kg. After standardization of RMSE on the dependent variable as RMSE%, the prediction error equaled 15%. BMI explained 54.8% of FM% variance (p < 0.0001), with an RMSE of 4.1%, corresponding to an RMSE% of 11%.

DISCUSSION

The relatively high RMSE% of the FM and FM%-BMI associations caution against the use of BMI as an adiposity index in individual elderly women. However, an error corresponding to 11% of FM% may be accepted for population studies of body fat in elderly women.

Cleaning Validation of a Multipurpose Plant for Active Pharmaceutical Ingredient Bulk Production

One of the key issues in the manufacture of active pharmaceuticals ingredients in multipurpose non-dedicated equipment is to adequately address the potential for cross-contamination. It is therefore important for a production manager to have a scientifically based and organisationally robust cleaning validation concept and program, where resources are neither over- or under-committed. In this paper technical tools, such as implementation of disassembling and cleaning SOPs, the implementation of cleaning and control levels, the definition of acceptance criteria, the execution of swab and rinse sampling methods, the development and validation of analytical methods, the use of worse-case tests, the definition of equipment-train and the preparation of validation protocols will be discussed. A cleaning validation program generates a huge amount of data. At Helsinn this data is processed, analysed and evaluated by means of tri-dimensional matrices. Cleaning validation programs have brought significant technical results that have led to production performance increases. Among them: The adopted model has permitted validation of the cleaning system in an overall manner for the entire production unit and for all products in question. It permits constant monitoring of the system and rapid theoretical verification of the impact of introducing new process/production runs. Allows earlier identification of critical cases where intervention with preventative solutions to avoid cross-contamination by use of more sophisticated cleaning/sampling/analysis methods can be implemented. The standardisation of methods for cleaning and analysis, and the introduction of the concept of cleaning levels, leading to faster product changeovers. The management has further criteria for the evaluation of new processes prior to introduction into the plant.

Changes of bioelectrical impedance after a body weight reduction program in highly obese subjects

We used bioelectrical impedance analysis (BIA) as an exploratory tool to monitor the changes in body composition induced by a short-term (3-wk) weight reduction (energy-restricted diet, moderate aerobic exercise conditioning and psychological counselling) in 175 highly obese subjects (body mass index, BMI=41.7+/-5.8 kg/m2). The decrease in weight and BMI after the weight reduction program was 3.4% (geometric mean, p<0.0001) and 3.7+/-1.3 kg/m2 (mean+/-SD, p<0.0001), respectively. Bioelectrical impedance (Z) increased of about the same value at each of the measured frequencies (from 6+/-10% at 5 kHz to 5+/-9% at 100 kHz, mean+/-SD, p<0.0001). A statistically significant increase in Z5:Z100 was also seen (p<0.0001), but its clinical significance is questionable owing to its low absolute value (<1%). Taken together, these data suggest that no clinically relevant change in body water distribution occurred in our subjects as a result of the weight reduction program. However, the changes in Z did not satisfactorily predict the changes in anthropometric dimensions despite the evidence of a substantial association between Z and anthropometry both before and after the weight reduction program. Thus, accurate predictions of body composition changes in obese subjects may require more than two BIA measurements so as to have a better description of the weight-losing process.

[Craniosynostosis: is prenatal diagnosis possible?]

The authors report a case which demonstrates how an interdisciplinary collaboration between the obstetrician and pediatrician may be activated in the event of a suspected fetal malformation, in this case craniosynostosis, although it is important to recognise the diagnostic limitations of ultrasonography regarding this type of pathology.

Appendicular skeletal muscle mass: prediction from multiple frequency segmental bioimpedance analysis

OBJECTIVES

Bioimpedance analysis (BIA) methods have potential to predict appendicular skeletal muscle mass (SM), although available 50 kHz prediction models include, in addition to impedance (Z), an independent age term. An age term in models is undesirable as it reflects incomplete understanding of underlying conduction physiology. This study tested the hypothesis, based on fluid distribution models related to aging, that appendicular SM bioimpedance analysis (BIA) prediction models would no longer include an independent age term, after first controlling for stature-adjusted appendicular impedance (height2/Z), at injected frequencies greater than 50 kHz.

DESIGN

Cross-sectional evaluation of adults who had segmental Z and phase angle (phi) measured with multiple frequency BIA, and arm and leg SM with dual-energy X-ray absorptiometry (DXA). Skeletal muscle prediction models were developed with appendicular SM as dependent variable and height2/Z, gender, age and phi as potential independent variables.

RESULTS

Examination of hypothesis in 49 subjects indicated: both arm and leg SM were highly correlated with height2/segmental Z at frequencies ranging from 1-300 kHz; gender was significant covariate in prediction models only at 1 kHz; age remained a significant covariate after controlling for height2/segmental Z at all frequencies; phi did not add significantly to models; and SM prediction models gave maximum R2 at 50 kHz for arm but R2 continued to rise up to 300 kHz for leg.

CONCLUSION

Although multifrequency BIA did not eliminate SM prediction model age term, our findings suggest injected frequencies up to 300 kHz may have advantages for evaluating leg SM over conventional 50 kHz method.

Anthropometric characteristics of healthy Italian nonagenarians and centenarians

Available anthropometric reference values for elderly people do not include specific norms for over-90-year-old subjects despite their increasing number. In the present study, weight, height and a number of anthropometric variables related to body muscle and fat mass were collected from fifty-seven nonagenarian and forty-one centenarian healthy, non-institutionalized subjects living in an Italian area. Recumbent anthropometry was used to avoid errors associated with impaired mobility. Nonagenarians and centenarian men were taller and heavier than women of corresponding age and had a greater amount of muscle and trunk fat, whereas women showed a marked peripheral adipose distribution. Anthropometric values of both age-groups were generally lower than published norms for 70-89-year-old American and European elderly people. However, differences were less marked when comparing Italian nonagenarians and centenarians with French and British people aged 85 years and over than when comparing Italian subjects with American octogenarians and younger European elderly people. Taken together these findings suggest a dramatic loss of muscle and fat mass in over-90-year-old subjects with respect to younger elderly people. However, changes between successive generations and geographical influences cannot be excluded. The need for local and age-specific norms in nutritional assessment of over-90-year-old people is emphasized. It is also suggested that current anthropometric indices may not be reliable when evaluating the oldest elderly subjects.

Microvascular capillaroscopic abnormalities in rheumatoid arthritis patients

Microvascular circulation was investigated by nailfold capillaroscopy in 32 patients affected by rheumatoid arthritis (RA). In all the patients elongated and tiny capillaries as well as tortuousity were the main shape abnormalities of the capillary loops. Higher subpapilar venous plexus (SPVP) visibility was evidentiated in patients presenting antinuclear and anti-RANA antibodies. No differences in the capillaroscopic pattern were found between rheumatoid factor positive and rheumatoid factor negative patients. In conclusion, elongated and tortuous capillaries seem to be the main alterations in RA, although they are not specific to the disease and are not correlated with the presence of rheumatoid factor. Higher SPVP visibility may be an expression of the endothelial damage induced by antinuclear antibodies in vessel walls.

The prediction of total body water from body impedance in young obese subjects

Almost all formulae for the prediction of total body water (TBW) from body impedance are based on the assumption of a constant conductor configuration--i.e. a constant subject section. In this paper we report on data obtained for a group of 19 young obese subjects (relative weight greater than 120%) and 10 young normal subjects (relative weight 80-110%). In obese subjects, the application of two different formulae generated from normal children gave biased results and led to an underestimation of TBW with respect to the reference value obtained by deuterium oxide dilution. Body mass index accounted for more than 40% of the inter-individual variability, suggesting that body size was not taken sufficiently into consideration by the predictive formulae used. We have used the body surface area as the anthropometrical parameter for the prediction of TBW from body impedance. The regression formula that we propose (TBW = 1.156 x (surface area/body impedance) - 2.356; R = 0.96), although requiring further validation on external populations, seems to provide a more realistic assessment of TBW in young obese subjects. We therefore suggest that the assessment of TBW in young obese subjects requires specifically designed prediction formulae.

Differential action of thyroid hormones on the activity of certain enzymes in rat kidney and brain

In rat kidney several mitochondrial and soluble enzyme activities are stimulated by thyroid hormones and the mitochondrial membrane fluidity is also increased. However, the ketone metabolism enzyme activities of D-3-hydroxybutyrate dehydrogenase and of 3-oxoacid CoA-transferase are not significantly affected by the hyperthyroid state and the ketone body concentration is not greatly changed. Therefore, in hyperthyroid rats the response of the kidney, as far as the ketone bodies and their metabolizing enzymes are concerned, is at variance with that of the liver and the heart. In the brain of young rats, age 8-9 weeks, the activities of the enzymes of ketone body metabolism and those responsible for other metabolic pathways are not influenced by the hyperthyroid state. In these animals, however, the activities of two enzymes, NAD-isocitrate dehydrogenase and pyruvate kinase, are still stimulated by 28 and 41%, respectively. This can be probably related to the higher energy requirement for definitive brain maturation in young hyperthyroid rats.

The response of rat liver lipid peroxidation, antioxidant enzyme activities and glutathione concentration to the thyroid hormone

1. In liver microsomes from hyperthyroid rats NADPH-dependent lipid peroxidation induces a hydroperoxide formation 56% higher than that in euthyroid ones. 2. The addition of 5 microM Fe2+ (or Fe3+) strongly decreases the hydroperoxide level in favour of that of TBA-reactive substances. Higher iron concentrations (30 microM) have no significant effect. 3. In hepatocytes from hyperthyroid rats CCl4-induced lipid peroxidation produces an amount of TBA-reactive substances four times higher than that in those from euthyroid rats. 4. In the liver of hyperthyroid rats a GSH concentration decrease (by about 35%) is found while the opposite occurs in the blood of the same animals where GSH increases 2.5 times. 5. It is shown that in the liver of hyperthyroid rats, besides higher lipid peroxidation, a more active defense mechanism is operating since both glutathione peroxidase and glutathione reductase specific activities are higher than in euthyroid rats.

Lipid peroxidation in rat liver microsomes. II. Response of hydroperoxide formation to iron concentration

When rat liver microsomes were incubated with NADPH, the major products were hydroperoxides which increased with time indicating that endogenous iron content is able to promote lipid peroxidation. The addition of either 5 microM Fe2+ or Fe3+ ions strongly enhanced the hydroperoxide formation rate. However, due to the hydroperoxide breakdown, hydroperoxide concentration decreased with time in this case. Higher ferrous or ferric iron concentration did not change the situation much, in that both hydroperoxide breakdown and formation were similar to those when NADPH only was present in the incubation medium. After lipid peroxidation, analysis of fatty acids indicated that the highest amount of peroxidized PUFA occurred in the presence of 5 microM of either Fe2+ or Fe3+. This analysis also showed that after 8 min incubation with low iron concentration, PUFA depletion was about 77% of that observed after 20 min, whereas without any iron addition or in the presence of 30 microM of either Fe3+, PUFA decrease was only about 37% of that observed after 20 min. As far as the optimum Fe2+/Fe3+ ratio required to promote the initiation of microsomal lipid peroxidation in rat liver is concerned, the highest hydroperoxide formation was observed with a ratio ranging from 0.5 to 2. These results indicate that microsomal lipid peroxidation induced by endogenous iron is speeded up by the addition of low concentrations of either Fe2+ or Fe3+ ions, probably because free radicals generated by hydroperoxide breakdown catalyze the propagation process. In experimental conditions unfavourable to hydroperoxide breakdown the principal process is that of the initiation of lipid peroxidation.

Concerning the decreased D-3-hydroxybutyrate dehydrogenase activity in the liver and heart of hyperthyroid rats

Whereas in rat liver mitochondria the hyperthyroid state causes an increase both in fatty acid unsaturation and in the Ea of D-3-hydroxybutyrate dehydrogenase and a decrease in phase transition temperature, in hyperthyroid rat heart mitochondria these changes are negligible. D-3-hydroxybutyrate dehydrogenase in both the liver and the heart mitochondria of hyperthyroid rats is reduced by about 35% [12] but this reduction is not due to changes in membrane fluidity in either tissue. Hypothyroidism, on the other hand, affects BDH activity in neither heart nor liver.

Lipid peroxidation in rat liver microsomes. I. Stimulation of the NADPH-cytochrome P-450 reductase-dependent process in hyperthyroid state

The effect of hyper- and hypothyroidism on lipid peroxidation has been studied in rat liver microsomes under three different experimental conditions. Under none of these conditions was the formation of TBA-reactive substances affected by either of these two pathological states. On the contrary, with NADPH as the only peroxidation inducer, hydroperoxide concentration increased some three fold in microsomes from hyperthyroid rats, while a small decrease was measured in those from hypothyroid animals. Similarly, the activity of NADPH-cytochrome P-450 reductase was found to be 45.1% higher in hyperthyroid and 40.3% lower in hypothyroid microsomes. The possibility discussed here is that two distinct peroxidative mechanisms (of which one, NADPH-cytochrome P-450 reductase-dependent, is influenced by the thyroid hormone) can compete with each other for the substrate polyunsaturated fatty acids.