Calorie restriction and resveratrol supplementation prevent age-related DNA and RNA oxidative damage in a non-human primate

Oxidative stress is a key factor in the aging process and in the development of age-related diseases. Because nutritional interventions such as caloric restriction (CR) delay the onset of age-related diseases and increase the lifespan of many species, the impact of a moderate CR was tested on male grey mouse lemur (Microcebus murinus), which have a median survival time of 5.7 years in captivity. The effects of CR on these lemurs were compared with a potential mimetic, resveratrol (RSV), a polyphenol naturally found in grapes. We hypothesized that both CR and RSV impact oxidative DNA and RNA damage compared to standard-fed control (CTL) animals. Adult (3-4 years old) male mouse lemurs were assigned to three dietary groups: a CTL group, a CR group receiving 30% fewer calories than the CTL and a RSV group receiving the CTL diet supplemented with RSV (200 mg·day(-1)·kg(-1)). Oxidative stress was estimated after 3, 9, 15 and 21 months of treatment using the measurement of oxidized nucleosides in urine samples by mass spectrometry. The resting metabolic rate, adjusted for changes in body composition, was also measured to assess the potential relationship between oxygen consumption and oxidative damage markers. This study provides evidence for oxidative stress accumulation with age in grey mouse lemur. Dietary interventions resulted in a short-term increase in oxidative stress levels followed by reduced levels with increasing age. Moreover, in this photoperiod-dependent heterotherm primate, seasonal variations in oxidative stress were observed, which was likely due to a season-dependent, cost-benefit trade-off between torpor use and oxidative stress.

The grey mouse lemur: a non-human primate model for ageing studies

The use of non-human primate models is required to understand the ageing process and evaluate new therapies against age-associated pathologies. The present article summarizes all the contributions of the grey mouse lemur Microcebus murinus, a small nocturnal prosimian primate, to the understanding of the mechanisms of ageing. Results from studies of both healthy and pathological ageing research on the grey mouse lemur demonstrated that this animal is a unique model to study age-dependent changes in endocrine systems, biological rhythms, thermoregulation, sensorial, cerebral and cognitive functions.

Food poisoning outbreaks linked to mussels contaminated with okadaic acid and ester dinophysistoxin-3 in France, June 2009

In June 2009, 11 outbreaks of food poisoning occurred in France, involving 45 individuals who had consumed mussels harvested in Vilaine Bay (Northwestern France). Because the toxic dinoflagellate Dinophysis spp. had been detected in the area from mid-May, okadaic acid (OA) and dinophysistoxins were suspected to be the cause of these outbreaks, although the weekly monitoring tests by mouse bioassay had been negative. With the help of the French reporting system for food-borne disease outbreaks, the detailed data on epidemiology, mussel consumption and complete product traceback, were collected for 11 individuals involved in three reported outbreaks. The batch of mussels identified as the source of these three outbreaks contained concentrations of toxins of the okadaic acid group that were approximately eight times higher than the European regulatory limit. Moreover, based on the consumption data available for the 11 cases, a lowest observable adverse effects level (LOAEL) was deduced. The LOAEL calculated from this study, although based on a very limited number of individuals, was in the same range, i.e. approximately 50 μg OA equivalents per person, as the LOAEL established by the European Food Safety Authority in 2006.

Mechanical, tribological, and biocompatibility properties of ZrN-Ag nanocomposite films

Nanocomposite films of ZrN-Ag were produced by reactive unbalanced magnetron sputtering, and their structural, chemical, mechanical, tribological, haemocompatibility, and antibacterial properties were studied as a function of film composition. The films formed a dense and homogeneous microstructure whereby nanocrystals of Ag are distributed evenly throughout the ZrN matrix. For small additions of silver, the hardness was found to increase, whereas the elastic modulus was found to decrease drastically. In the process of optimizing the deposition conditions, three kinds of coatings were prepared on 316 L surgical steel and tested by accelerated electrochemical polarization tests in order to detect the influence of Ag and the value of the bias potential on the corrosion performance of the system. Films produced under the optimum deposition conditions were, subsequently, deposited on medical grade Ti-Al-V and worn against ball-bearing steel using a ball-on-disk tribotester in bovine serum and were found to have superior tribological properties compared with single-phase ZrN coatings. The haemocompatibility of the films was assessed by investigating the adsorption of human serum albumin and fibrinogen on samples with different phase compositions. Quantification of the protein adsorption was carried out using spectroscopic ellipsometry, which confirmed the haemocompatibility of the films. Antibiotic activity of the films was quantified by incubating the films in bacterial cultures, namely, Staphylococcus epidermis, Staphylococcus aureus, and Escherichia coli. Films with a silver content > 10% exhibited superior antibacterial activity compared with the uncoated samples.

Chain orientation in natural rubber, Part II: 2H-NMR study

Stress-induced crystallisation (SIC) and stress-induced melting (SIM) in natural rubbers (NR), unfilled and filled with carbon black (CB) have been studied by (2)H-NMR measurements. Various materials have been swollen with small amount (< 2%) of deuterated alkane chains. The orientation of the amorphous chains, then the local deformation of the amorphous chains during deformation cycles and during stress relaxation, permits to clarify the SIC and SIM processes during hardening and recovery. By mechanical, WAXS and NMR measurements one determines the same critical draw ratio for appearance lambda(A) and disappearance lambda(E) of the crystallites. It is demonstrated that the hysteresis observed by the different techniques (stress sigma, crystallinity chi, NMR splitting Deltanu) are due to the supercooling effect ( lambda(A) > lambda(E), at constant temperature). During hardening at constant strain rate it is found that the local draw ratio remains constant and equal to lambda(A), whereas the crystallinity increases linearly with the macroscopic draw ratio lambda. The hardening sigma approximately (lambda - lambda(A))(2) is then interpreted as a reinforcement effect due to the crystallites, which act as new crosslinks. This confirms the prediction of Flory. In filled rubber the same effects are observed, and the stress amplification factor is determined as a function of the CB content. It is found that the fillers act as nucleation centres for the NR crystallites. The reinforcement of such materials is due principally to this nucleation effect and to the presence of a super network formed by both the NR crystallites and the CB fillers.

Chain orientation in natural rubber, Part I: the inverse yielding effect

Inhomogeneous deformations are observed in stretched natural rubber of different crosslink density; the conditions of observation, nucleation and propagation are given in the first part of the paper. In samples of low crosslink density these inhomogeneities recall necking observed in others materials and in glassy polymers when the materials are drawn above a critical draw ratio. The difference is that in natural rubbers, NR, they nucleate and propagate at constant stress during unloading. This phenomenon, called inverse yielding appears during recovery only if the samples have been drawn previously in the hardening domain. During necking propagation the stress is constant. The mechanical and crystallinity properties of samples with and without inverse yielding are studied as a function of draw ratio, crosslink density and temperature. In the second part of the paper this transition zone (neck) of thickness 2 mm is studied by WAXS at the synchrotron source. From the orientation of NR crystallites and from the orientation of the stearic acid (2%, present in this type of rubber) we conclude that the deformation in the neck follows the flow lines. From the local crystallinity of the NR crystallites one deduces the local draw ratio across this transition zone. We suggest that in all these rubbers, which present a plateau of the recovery stress strain curve, micronecking exists. This effect is discussed in the framework of the Flory theory.

Expression of apoptosis-regulatory proteins in lesions of pulmonary Langerhans cell histiocytosis

AIMS

Pulmonary Langerhans cell histiocytosis (PLCH) is characterized by the presence of lesions containing numerous activated Langerhans cells (LCs). An uncontrolled immune response sustained by activated LCs seems to be involved in the pathogenesis of the disease. The aim of this study was to establish whether disruption of LC apoptosis related to the expression of the Bcl-2 family proteins is implicated in the maintenance of PLCH lesions.

METHODS

Six patients with PLCH were evaluated by morphological and immunohistochemical techniques to explore the incidence of apoptosis in pathological LCs and to characterize the expression of Bcl-2-related proteins by these cells.

RESULTS

Very few LCs present in PLCH lesions exhibited nuclear apoptotic changes or expressed cleaved caspase-3, whereas they all strongly expressed the anti-apoptotic molecule Bcl-x(L). Interestingly, pulmonary LCs present in intervening lung tissue not involved by the pathological process and known to be immature dendritic cells did not express Bcl-2 family proteins.

CONCLUSIONS

These findings suggest that activated LCs present within PLCH lesions are poorly susceptible to apoptosis and, thus, are able to sustain the pathological process by causing continuous local stimulation of T cells. Functional studies are needed, however, to demonstrate that they are actually resistant to programmed cell death.

Consequences of transvaginal follicular puncture on well-being in cows

The purpose of this study was to evaluate the impact of repeated follicular puncture used in the ovum pick-up technique on the welfare of cows. The evaluation relies on the physiological measurement of stress, milk production criteria, immune status, and the histological examination of ovaries. Two groups of five Holstein cows were submitted to epidural anaesthesia and genital palpation with insertion of an intravaginal ultrasound probe for transvaginal puncture (the puncture was not performed in the control group). Animals were manipulated twice a week for 8 weeks (16 manipulation sessions). The blood cortisol concentrations increased after each session; however, the concentrations were the same in both the control and the punctured groups. Two adrenocorticotrophic hormone challenge tests, performed before the first session and after the last session, showed an unchanged adrenal sensitivity through repeated puncture sessions. The transvaginal puncture did not affect milk production, or blood and milk somatic cell counts. Ovariectomies were performed on another group of four Holstein cows at various intervals (0 to 30 days) after five similar puncture sessions. Histological examination of the ovaries 4 days after puncture revealed blood-filled follicles and haemorrhagic foci in ovarian stroma, but the examination 30 days after the last puncture session demonstrated very limited, if any, fibrosis. On the basis of the criteria chosen for this study, repeated transvaginal follicular puncture on its own does not impact adversely on the welfare of cows.

Corticospinal pathway and exercise hyperpnea: lessons from a patient with Arnold Chiari malformation

The study of a patient with an Arnold Chiari malformation gave us the opportunity to test the hypothesis that the motor cortex contributes significantly to respiratory control during muscular exercise through the corticospinal pathway. The patient was a 25 years old woman who exhibited a severe impairment of the 'automatic' ventilatory control due to a type I Arnold Chiari malformation. Since she never complained of being breathlessness even on exertion, the breath-by-breath ventilatory (VE) and pulmonary gas exchange responses to a three minute bout of constant work rate exercise at 60 W, 90 W and 120 W were studied before then 16 and 23 months after posterior fossa decompression. The VE response to the three different levels of exercise was dramatically blunted so that the expected vertical relationship between PET(CO(2)) and VE during moderate exercise was replaced by an almost horizontal relationship with a slope ranging from 0.15 to 0.17 l/min/Torr. The reduced VE response was associated with a total lack of respiratory sensation during and following the exercise bouts. This abnormal ventilatory response to exercise persisted despite posterior fossa decompression. There was however no evidence of an alteration of the corticospinal pathway. Indeed, not only was there no sign of motor deficit but the patient was able both to mobilize 96% of her expected vital capacity and to voluntarily increase her ventilation to the level expected in a normal subject during exercise. This observation suggests that during exercise, motor control of respiratory muscles via a direct corticospinal pathway does not play a major role in adjusting phrenic motoneuron activity to the magnitude of the motor inputs to the exercising skeletal muscles.

Lymphoid hypoplasia and somatic cloning

BACKGROUND

Adult somatic cloning by nuclear transfer is associated with high rate of perinatal mortality but there is still no evidence that nuclear transfer itself is responsible for these failures. We report on a longlasting defect linked to somatic cloning.

METHODS

Skin cells grown from an ear biopsy specimen from a 15-day-old calf were used as a source of nuclei. The donor animal was a clone of three females obtained from embryonic cells. Clinical examination, haematological, and biochemical profiles, and echocardiography of the somatic clone were done from birth to death.

FINDINGS

After 6 weeks of normal development, the somatic cloned calf had a sudden and rapid fall in lymphocyte count and a decrease in haemoglobin. The calf died on day 51 from severe anaemia. Necropsy revealed no abnormality except thymic atrophy and lymphoid hypoplasia.

INTERPRETATION

Somatic cloning may be the cause of long-lasting deleterious effects. Our observation should be taken into account in debates on reproductive cloning in human beings.

Cloning in cattle: from embryo splitting to somatic nuclear transfer

The ability to obtain genetically identical offspring in cattle (clones) is useful for research and for potential applications to breeding schemes. Experimental possibilities for generating such animals have evolved considerably in the last two decades. Embryo splitting has become a relatively simple technique but is limited to twinning. Embryonic nuclear transfer has improved and is associated with sexing to generate sets of clones despite a great variability of results between parent embryos. The factors of progress are reviewed here. Recently, somatic cells used as a source of nuclei in bovine nuclear transfer has been demonstrated. Here we present the results of the developmental potential of nuclei from skin and muscle cells.

Assessment of apoptosis occurring in spleen cells from nitrogen mustard-treated or gamma-irradiated mice

The short-term consequences on spleen cells of the intraperitoneal administration of nitrogen mustard (HN-2) to mice or of a whole-body gamma irradiation have been evaluated. Experiments were designed to assess the induction of apoptosis in spleen cells following exposure to these agents. The occurrence of this type of cell death was analysed by several methods, in particular the quantification in the blood of phosphotidylserine-bearing microparticles shed by apoptotic cells. In response to HN-2 or radiations, spleens undergo a rapid involution of their weight and cellularity. Ex vivo apoptosis occurs within 24 hours in cultured lymphocytes in a dose-dependent manner after both treatments. As compared with untreated controls, circulating microparticles increased 3-fold after the injection of 5 mg/kg of HN-2.

Nuclear transfer from sexed parent embryos in cattle: efficiency and birth of offspring

The objectives of this study were to evaluate the efficiency and reliability of embryo sexing from isolated single blastomeres, and after nuclear transfer to examine the influence of the sex of donor embryos on development in vitro and in vivo up to calving. The sex of the donor embryo was determined by revealing a specific Y DNA sequence by PCR and electrophoresis after isolation of one, two, three, or more than five cells. The efficiency of sex determination was over 90% and reliability was 100% independent of the number of blastomeres used. In a second experiment, sex was determined from a single cell and the other cells were used for nuclear transfer. The effect of sex on in vitro development was studied in 386 male and 314 female reconstructed embryos derived from 19 male and 14 female parent embryos, respectively. Developmental competence in vitro of male and female constructs over 7 days was not statistically different (25.2 and 23.1% blastocysts on day 7, respectively; P > 0.05). After the transfer of predetermined male (n = 30) and female (n = 27) cloned embryos into recipient heifers, no effect of sex was observed on pregnancy rates at day 21, 35 and 90, or on calving rates (P > 0.05). These rates did not differ between single and twin transfer (P > 0.05). The sex of the calves born always corresponded to that determined from a single blastomere. These results show that sex can be determined accurately when using a single blastomere before nuclear transfer and that the sex of the parent embryo does not affect in vitro development or in vivo survival rates of cloned embryos.

Effect of 6(5H)-phenanthridinone, a poly (ADP-ribose)polymerase inhibitor, and ionizing radiation on the growth of cultured lymphoma cells

The ability of 6(5H)-phenanthridinone (Phen), a new potent poly(ADP-ribose)polymerase (PARP) inhibitor, to potentiate the effect of ionizing radiation on tumour cells was evaluated. RDM4 murine lymphoma cells were irradiated using a 60Co panoramic source and then examined for their growth, cell cycle distribution and apoptosis. Phen (100 microM) was found to inhibit more than 90% of the PARP activity in control and irradiated cells. Cell proliferation was assessed using Alamar Blue, a new fluorometric assay. Phen was found to sharply increase the radiation-induced inhibition of cell proliferation. Indeed, at 2.5 Gy the relative cell number of Phen-treated cells was 60% below control levels. At the same radiation dose, the G2M arrest was also significantly reinforced by the addition of Phen. Furthermore, this PARP inhibitor was shown to significantly increase the amount of DNA fragmentation as revealed by the DNA migration pattern in agarose gel electrophoresis. Comparable results were obtained with 3-aminobenzamide, another PARP inhibitor, but at concentrations 200-fold higher. Taken together, these results indicate the potential interest of Phen as a valuable pharmacological probe for investigating the role of PARP in cellular responses to radiation. They also suggest a possible use of Phen as an adjuvant in radiotherapy.

Cytotoxic properties of a phosphoglycoconjugated derivative of 7 beta-hydroxycholesterol upon normal and tumor cells in culture

The cytotoxic activity of a new hydrosoluble axysterol derivative, a phosphoric acid diester of 7 beta-hydroxycholesterol (7 beta-OHC, one of the most toxic oxysterol) and of galactose has been evaluated using cultured tumor cells of various origins, and compared with 7 beta-OHC. As its parent compound, XG-142 exhibits a significant cytotoxic activity against all the cell lines tested, but the IC50's were higher than those obtained with 7 beta-OHC. Moreover, the cytotoxicity was slower to appear than after a 7 beta-OHC treatment. Cell phase distribution was analysed, and revealed some differences between the two compounds. Both oxysterols induced apoptosis at micromolar concentrations, as evidenced by several methods including agarose gel electrophoresis of fragmented DNA and flow cytometry of propidium iodide labeled cells. Apoptosis was also obtained when 7 beta-OHC and XG-142 were combined at concentrations unable to induce this type of cell death when used separately. Upon normal murine spleen cells, XG-142 was found to be less toxic than 7 beta-OHC, and the capacity to respond to Con A stimulation was preserved. Therefore, XG-142 can be considered as a promising soluble analogue of 7 beta-OHC, and its application as anticancer agent should be considered.

N-acetylcysteine protects lymphocytes from nitrogen mustard-induced apoptosis

The ability of the antioxidant N-acetylcysteine to prevent apoptosis induced in lymphocytes by nitrogen mustard (HN2) was investigated. HN2 caused a concentration-dependent induction of apoptosis on C3H murine spleen cells, as identified by two criteria: morphological features revealed by microscopical observations and DNA fragmentation visualized by the characteristic "ladder" pattern observed upon agarose gel electrophoresis, as well as by hypodiploid DNA-containing cells revealed by the flow cytometric analysis of propidium iodide labelled cells. The antioxidant N-acetylcysteine (NAC) was found to markedly reduce the occurrence of HN2-induced apoptosis in these cells. This protective effect will still obtained when NAC was added 30 min after HN2. In contrast, the pretreatment of spleen cells with this antioxidant did not provide any significant protection. We also showed that lymphocytes protected by NAC are still able to respond to a mitogenic stimulation. To gain some insight into the mechanisms underlying the cytoprotective action of NAC against HN2, we tested whether or not poly(ADP-ribose) polymerase (PARP, EC 2.4.2.30), a nuclear enzyme that participates in the triggering of apoptosis induced by alkylating agents, is involved. We report that 6(5H)-phenanthridinone, a potent PARP inhibitor, did not affect the ability of NAC to prevent HN2-induced apoptosis under our experimental conditions. Thus, the exact mechanism by which NAC protects lymphocytes from HN2 cytotoxicity has yet to be determined.

Oxysterol-induced apoptosis in human monocytic cell lines

Oxysterols constitute a large family of natural compounds, endowed with various biological activities including cholesterol regulation, immunosuppression and antitumoral potency. In the present study, we examine and compare the cytotoxic effects of two representative members of this family: 7 beta-hydroxycholesterol (7 beta-OH) and 25-hydroxycholesterol (25-OH), in two human monocytic cell lines, U-937 and HL-60. In both cell lines 7 beta-OH at 30 mu M induces cell death by apoptosis within the first hours of treatment. Under the same conditions and in contrast with results previously obtained with lymphoma cells, 25-OH is cytostatic only. It is interesting to note that the simultaneous treatment of U-937 cells by equimolar concentrations of 7 beta-OH and 25-OH leads to a considerably decreased induction of apoptosis. Such an effect is not observed with HL-60 cells. Taken together, these results indicate for the first time that: 1) oxysterols hydroxylated on the sterol nucleus are also able to induce apoptosis, 2) apoptosis can be induced by these substances in cells belonging to the myeloid lineage and 3) as far as apoptosis is concerned, a combined treatment with 7 beta-OH and 25-OH can lead to opposite effects depending on the cell type.

Psychoeducational multiple family groups: four-year relapse outcome in schizophrenia

Earlier studies of family psychoeducation and clinical reports on multiple family groups (MFGs) have reported substantial reductions in relapse rates for patients with schizophrenia. These groups offer an expanded social network and thereby may confer a margin of protection against relapse. However, to date, there has not been an empirical trial of this modality. The advent of family psychoeducational and behavioral management strategies provided the basis for an experimental, three-way comparison of psychoeducational MFGs to psychoeducation in a single-family format and to MFGs without psychoeducation, using symptomatic relapse as the outcome criterion. After 4 years, the psychoeducational MFGs were significantly more effective in extending remission than the single-family format, while the MFGs without psychoeducation approximated outcome in the psychoeducational MFGs. The respective relapse rates at 4 years were 50%, 78%, and 57%; MFGs averaged 12.5% and 14% per year. These results point toward an enhanced and independent, long-term therapeutic effect for multiple family groups, when combined with antipsychotic medication and psychoeducation, with especially promising cost-effectiveness.

Immunosuppressive activities of 6(5H)-phenanthridinone, a new poly(ADP-ribose)polymerase inhibitor

6(5H)-phenanthridinone, a recently identified poly(ADP-ribose)polymerase (PARP) inhibitor, is able, at micromolar concentrations, to inhibit concanavalin A-induced lymphocyte proliferation and to potentiate the effect of gamma radiation upon murine spleen cells. When added at the onset of a mixed lymphocyte culture, this compound strongly depresses the induction of primary allogeneic (anti-H2k) cytotoxic T-lymphocytes (CTLs). Lymphokine-activated killer (LAK) induction was also found to be impaired by the PARP inhibitor. Taken together, these results clearly indicate that PARP plays a key-role in immune reactions involving cytotoxicity and that 6(5H)-phenanthridinone could be considered as a potent immunomodulator.

Functional aspects of bacterial polysomes during limited protein synthesis

The effects of amino acid starvation on the metabolic behavior of polysomes and the size distribution of proteins have been studied in an otherwise isogenic pair of stringent (relA+) and relaxed (relA) strains of Escherichia coli. The stability of polysomes has been analyzed by using two different approaches. First, the process of their degradation has been followed after treating the cells with rifampicin, an inhibitor of the synthesis of all classes of RNA including messenger RNA. Secondly, the process of their assembly has been studied after their previous conversion to monosomes, as induced by glucose deprivation of cells. It is shown that, in either type of bacterial strain, polysomes are continually broken down and re-synthesized during amino acid starvation. However, such polysome turnover is then less rapid than in normally growing bacteria and, moreover, it seems amino acid specific since it occurs at a lower rate during arginine starvation than during histidine starvation, namely, in the relaxed strain. The molecular weight distribution of proteins has been determined after labeling of cells with radioactive methionine and separation of polypeptides by one-dimensional polyacrylamide gel electrophoresis. The average size of polypeptides synthesized in the stringent strain during starvation is quite similar to that measured during normal growth. By contrast, a significant shift towards smaller molecules is observed in the relaxed strain deprived of an essential amino acid. Here again, this reduction of the size of polypeptides seems amino acid specific since it is especially marked during arginine starvation. These results are discussed in terms of ribosomes translocation and premature peptide chain termination in connection with the accuracy of the translational process.

[Curable asystole in an adult caused by a diffuse and complete arteriovenous aneurysm of the liver. Cure by ligation of the hepatic artery]

A case of cardiac failure in a 54 year old man with a diffuse total arteriovenous aneurysm of the liver is reported. The aneurysm was arteriolarvenous, without a wide bore localised fistula. It occupied the whole hepatic mass, including the territories of the right subphrenic and anterior collateral of the gastroduodenal artery. The cause of cardiac failure was the elevated cardiac output, 15 1/min, which fell to 6 1/min at each peroperative occlusion of the hepatic artery. After ligature of this vessel, the cardiac output stabilised at 9 1/min and remained at this value 4 months after surgical cure. This case is comparable to the neonatal cardiac failure due to multinodular hepatic angioma with respect to the clinical, angiographic and CAT scan characteristics, and the surgical cure of the high cardiac output syndrome. Some of the histological features were suggestive, in places, of the structure of hepatic cavernoma, which makes the exact pathological classification of this diffuse aneurysm difficult; the closest possibility being an involuted from of diffuse capillary hemangioma of childhood allowing such long survival and, occasionally taking on the appearances of a cavernoma. Permanent surgical cure by ligature of the hepatic artery was an additional rare feature of this case.

[Level of polysomes in cells of Escherichia coli treated with sublethal doses of aminoglycosides]

Polysome level was measured in Escherichia coli cells grown in the presence of sublethal doses of four different aminoglycosides which all induce mistranslation: streptomycin, neomycin, kanamycin and gentamycin. No significant variation was noticed as referred to the level of polysomes in normally growing cells. This observation indicates that the erroneous incorporation of amino acids into polypeptide chains does not necessarily result in the release of ribosomes from messenger RNA molecules.