MELAS: Phenotype Classification into Classic-versus-Atypical Presentations.

BACKGROUND AND PURPOSE: An increased number of pathogenic variants have been described in mitochondrial encephalomyopathy lactic acidosis and strokelike episodes (MELAS). Different imaging presentations have emerged in parallel with a growing recognition of clinical and outcome variability, which pose a diagnostic challenge to neurologists and radiologists and may impact an individual patient's response to therapeutic interventions. By evaluating clinical, neuroimaging, laboratory, and genetic findings, we sought to improve our understanding of the sources of potential phenotype variability in patients with MELAS. MATERIALS AND METHODS: This retrospective single-center study included individuals who had confirmed mitochondrial DNA pathogenic variants and a diagnosis of MELAS and whose data were reviewed from January 2000 through November 2021. The approach included a review of clinical, neuroimaging, laboratory, and genetic data, followed by an unsupervised hierarchical cluster analysis looking for sources of phenotype variability in MELAS. Subsequently, experts identified "victory-variables" that best differentiated MELAS cohort clusters. RESULTS: Thirty-five patients with a diagnosis of mitochondrial DNA-based MELAS (median age, 12 years; interquartile range, 7-24 years; 24 female) were eligible for this study. Fifty-three discrete variables were evaluated by an unsupervised cluster analysis, which revealed that two distinct phenotypes exist among patients with MELAS. After experts reviewed the variables, they selected 8 victory-variables with the greatest impact in determining the MELAS subgroups: developmental delay, sensorineural hearing loss, vision loss in the first strokelike episode, Leigh syndrome overlap, age at the first strokelike episode, cortical lesion size, regional brain distribution of lesions, and genetic groups. Ultimately, 2-step differentiating criteria were defined to classify atypical MELAS. CONCLUSIONS: We identified 2 distinct patterns of MELAS: classic MELAS and atypical MELAS. Recognizing different patterns in MELAS presentations will enable clinical and research care teams to better understand the natural history and prognosis of MELAS and identify the best candidates for specific therapeutic interventions.

Atmospheric aerosols: increased concentrations during the last decade.

Atmospheric turbidity values calculated each month from solar radiation observations at MaunaLoa Observatory, Hawaii, show an increase of aerosols from 1958 through the present. These data indicate that either the effects of the Mount Agung eruption are still being observed or a longer-term trend of increasing turbidity is in evidence.

Matrix metalloproteinase inhibition attenuates left ventricular remodeling and dysfunction in a rat model of progressive heart failure.

BACKGROUND: Matrix metalloproteinase (MMP) activation contributes to tissue remodeling in several disease states, and increased MMP activity has been observed in left ventricular (LV) failure. The present study tested the hypothesis that MMP inhibition would influence LV remodeling and function in developing LV failure. METHODS AND RESULTS: LV size and function were measured in 5 groups of rats: (1) obese male spontaneously hypertensive heart failure rats (SHHF) at 9 months (n=10), (2) SHHF at 13 months (n=12), (3) SHHF rats treated with an MMP inhibitor during months 9 to 13 (PD166793 5 mg. kg(-1). d(-1) PO; n=14), (4) normotensive Wistar-Furth rats (WF) at 9 months (n=12), and (5) WF at 13 months (n=12). Plasma concentrations of the MMP inhibitor (116+/-11 micromol/L) reduced in vitro LV myocardial MMP-2 activity by approximately 100%. LV function and geometry were similar in WF rats at 9 and 13 months. LV peak +dP/dt was unchanged at 9 months in SHHF but by 13 months was reduced in the SHHF group compared with WF (3578+/-477 versus 5983+/-109 mm Hg/s, P

Gas6 receptors Axl, Sky and Mer enhance platelet activation and regulate thrombotic responses.

Gas6 (encoded by growth arrest-specific gene 6) is a vitamin-K dependent protein highly homologous to coagulation protein S that is secreted from platelet alpha-granules and has recently been demonstrated to participate in platelet thrombus formation. The current study evaluated the contribution of each of the three known Gas6 receptors (Axl, Sky and Mer) in human and mouse platelet function. Flow cytometry analyses confirmed that all three receptors are present on both human and mouse platelets. Pre-incubation of human platelets with either an anti-Gas6 antibody or blocking antibodies to Sky or Mer inhibited platelet aggregation and degranulation responses to both ADP and the PAR-1 activating peptide, SFLLRN, by more than 80%. In contrast, a stimulatory anti-Axl antibody increased activation responses to these agonists, suggesting a potentiating role for Gas6 in platelet activation. Moreover, in a mouse model of thrombosis, administration of Gas6 or Sky blocking antibodies resulted in a decrease in thrombus weight similar to clopidogrel but, unlike clopidogrel, produced no increase in template bleeding. Thus, Gas6 enhances platelet degranulation and aggregation responses through its known receptors, promoting platelet activation and mediating thrombus formation such that its inhibition prevents thrombosis without increasing bleeding.

MMP/TIMP expression in spontaneously hypertensive heart failure rats: the effect of ACE- and MMP-inhibition.

OBJECTIVE: Determine the effect of a matrix metalloproteinase inhibitor (MMPi) and angiotensin converting enzyme inhibitor (ACEi) on collagen, MMP, tissue inhibitors of MMPs (TIMPs) expression in the spontaneously hypertensive heart failure (SHHF) rat. METHODS: Six groups were tested: normotensive 9- and 13-month-old Wistar-Furth (WF) rats, 9-month-old SHHFs (compensatory hypertrophy), 13-month-old SHHFs with HF, and 13-month-old SHHFs orally administered with either an MMPi (PD166793, 5 mgkg(-1)day(-1)) or ACEi (quinapril, 10 mgkg(-1)day(-1)) for 4 months. Collagen volume fraction was assessed histomorphometrically. Left ventricular (LV) mRNA [MMP-1,-2,-3,-7,-9,-11,-13,-14; TIMP-1,-2,-3,-4; and collagen alpha1(I) and alpha1(III)] and protein (MMP-2 and MMP-9 zymographic activity; Western blot analysis of MMP-13, and TIMP-1,-2,-4) levels could be quantified. RESULTS: Collagen mRNA levels were elevated in SHHFs compared to age-matched controls, but collagen volume fraction was elevated only in 13-month-old SHHFs (approximately 2x). Only MMP-2 mRNA levels increased significantly with HF. However, MMP-2 and MMP-9 zymographic activity, and MMP-13 protein levels increased. TIMP-1 and TIMP-2 mRNA and protein levels increased, and TIMP-4 protein levels decreased in SHHFs vs. controls. Both drug treatments reduced LV dilation; preserved systolic function; and normalized MMP/TIMP expression. Both drug treatments also reduced collagen volume fraction, but only quinapril reduced collagen mRNA levels and LV hypertrophy. CONCLUSIONS: The divergent effect of MMPi and ACEi on collagen mRNA levels and hypertrophy indicate that drug efficacy is mediated by different pathways in the SHHF rat.

Evolution of matrix metalloprotease and tissue inhibitor expression during heart failure progression in the infarcted rat.

OBJECTIVE: Characterize the timecourse of matrix metalloproteinase (MMP-1, -2, -3, -7, -9, -11, -12, -13, and -14) and endogenous tissue inhibitors of MMPs (TIMP-1, -2, -3, and -4) upregulation during left ventricular (LV) remodeling following myocardial infarction (MI) in rats. METHODS: The descending left coronary artery of male rats (Rattus norvegicus) was ligated to produce a MI. LV function and dilation were assessed from 1 day to 16 weeks post-MI. Protein and mRNA extraction was done on LV samples containing scar and myocardium together. Gelatinase activity was measured by zymography. Westerns were run on the MMPs known to cleave fibrillar collagen in the rat (MMP-8, -13, and -14) as well as TIMP-1, -2, and -4. RESULTS: Average infarct size was 38.6+/-1.1%, and produced LV dysfunction and progressive LV dilation. Thoracic ascites, a marker of congestive heart failure (HF), was not present until 12 weeks post-MI. Upregulation of MMP-2, -8, -9, -13, and -14 and TIMP-1 and TIMP-2 was detected at different timepoints during HF progression. Increased MMP protein levels occurred sometimes without a corresponding elevation in mRNA levels, and increased TIMP mRNA levels without increased protein levels. MMP-13 active form was elevated during the first 2 weeks post-MI while TIMP-1 and TIMP-2 protein levels were not significantly elevated until 2 weeks post-MI. MMP-8 and MMP-14 protein levels increased later during heart failure progression. CONCLUSION: MMP/TIMP upregulation evolves over time following infarction in the rat LV. Some MMPs were significantly elevated during the first week post-MI (MMP-13, -2, and -9) and another was not until 16 weeks post-MI (MMP-14). The dissociation between LV MMP/TIMP mRNA and protein levels shows that post-translation processing occurs in the rat heart.

Variable non-linearity in end systolic pressure-volume relationships results from interaction between end diastolic and developed pressure-volume relations.

OBJECTIVE: The aim was to determine the contributions of diastolic pressure to the shape of the relationship of total systolic left ventricular pressure with volume (pressure-volume relationship). STUDY DESIGN: The pressure-volume relationship was approximated (by least squares fit) to a parabola P = aV2 + bV + C. Non-linearity was indicated by values "a" significantly different from zero. Negative values indicated concavity to the volume axis, positive values convexity to the volume axis. MATERIALS: Langendorff perfused rabbit hearts (n = 8) with intraventricular balloon were used. Balloon pressure was measured for varying balloon volumes. RESULTS: The total systolic pressure-volume relationship was concave towards the volume axis at 2.4 mM extracellular calcium ions concentrations ([Cae++]) a = -47.2 (SD 5.4), p less than 0.05. It was nearly linear at [Cae++] = 0.6 mM; a = -0.8(5.8), p greater than 0.05. It was convex at [Cae++] = 0.3 mM; a = 25.3(4.0), p less than 0.01. The diastolic pressure-volume relationship was always convex: a = 30.1(6.7), 33.5(7.6), 42.2(6.6) for [Cae++] = 2.4, 0.6, and 0.3 mM respectively. When these diastolic values were subtracted from the total pressures, pressure-volume curves for developed pressure were obtained which were always concave: a = -76.9(10.2), -33.5(3.7), -16.3(2.9) for [Cae++] = 2.4, 0.6, and 0.3 mM. CONCLUSIONS: The true systolic pressure-volume relationship of the left ventricle is not linear but concave to the volume axis. The slope is therefore variable and not an index of contractility. Apparently linearity or convexity is due to inappropriate addition of the diastolic pressure-volume properties.

Myocardial infarct size is smaller in dogs with pacing-induced heart failure.

OBJECTIVE: Determine if ischemic tolerance is reduced in the setting of experimental heart failure (HF). METHODS: Dogs were paced for 3 weeks at 240 BPM to induce heart failure which was confirmed with hemodynamic and echocardiographic measurements. The pacemaker was turned off 30 min prior to the ischemia study. Normal (n = 9) and HF dogs (n = 12) were anesthetized with sodium pentobarbital, instrumented for cardiovascular assessment through a left lateral thoracotomy, and myocardial blood flow was measured with radioactive microspheres. The left circumflex (LCX) artery was occluded for 90 min followed by 3 h of reperfusion. Infarct size was determined with triphenyl tetrazolium chloride staining. RESULTS: Two-dimensional echocardiograms were obtained before and after 3 weeks of pacing in the HF group. Ejection fraction was reduced from 67 +/- 1 to 32 +/- 2% (P < 0.001) and left ventricular end-diastolic volume (LVEDV) increased from 29 +/- 4 ml before pacing to 47 +/- 5 ml (P < 0.001). HF dogs were characterized by a smaller peak positive dP/dt (1110 +/- 72 vs. 2546 +/- 41 mmHg/s, P < 0.01), a greater LV end-diastolic pressure (34 +/- 3 vs. 9 +/- 2 mmHg, P < 0.01), and lower LV end-systolic pressure (99 +/- 5 vs. 130 +/- 5 mmHg, P < 0.05) compared to control dogs. Heart rate was not significantly different between the two groups throughout the experiment. More HF dogs died from ventricular fibrillation (4/12) than control dogs (1/9), but this difference was not statistically significant (P > 0.2). The LCX occlusion produced a comparable decrease in blood flow in HF and normal dogs (0.08 +/- 0.01 vs. 0.09 +/- 0.01 ml/min/g), but infarct size as a percentage of the region at risk was smaller in HF dogs compared to normal dogs (21 +/- 4 vs. 45 +/- 4%, P < 0.01). Region at risk size was also smaller in HF versus normal dogs (29 +/- 3 vs. 40 +/- 2%, P < 0.05). Accordingly, a subgroup analysis of 6 HF and 5 control dogs with similar RAR sizes (35 +/- 2% vs. 37 +/- 2%) was performed and it also demonstrated that infarct size in HF dogs was smaller than in control dogs (19 +/- 5 vs. 40 +/- 4%, P < 0.01), suggesting that disparities in risk region size did not explain the differences in infarct size. CONCLUSION: Infarct size produced by a standardized ischemia-reperfusion protocol was smaller in dogs with pacing-induced HF. The reduced extent of infarction could not be attributed to differences in collateral blood flow or the size of the region at risk. Although the hearts in HF dogs were dilated, LV systolic blood pressure and the strength of contraction were lower than controls potentially reducing myocardial oxygen demand and explaining the smaller infarct size in HF dogs. Other mechanisms, however, cannot be discounted. Thus, ischemic tolerance is not reduced and may be augmented in dogs with pacing-induced heart failure.

Subclasses of cyclic GMP-specific phosphodiesterase and their role in regulating the effects of atrial natriuretic factor.

Two subclasses of cyclic guanosine monophosphate (GMP)-specific phosphodiesterases were identified in vascular tissue from several beds. The activity of one subclass (phosphodiesterase IB) was stimulated severalfold by calmodulin and selectively inhibited by the phosphodiesterase inhibitor TCV-3B. The activity of the other subclass (phosphodiesterase IC) was not stimulated by calmodulin and was selectively inhibited by the phosphodiesterase inhibitor M&B 22,948. To assess the involvement of both subclasses in regulating cyclic GMP-dependent responses, the ability of TCV-3B and M&B 22,948 to potentiate the in vitro and in vivo responses to the endogenous guanylate cyclase stimulator atrial natriuretic factor (ANF) was evaluated. Both TCV-3B and M&B 22,948 relaxed isolated rabbit aortic and pulmonary artery rings and also potentiated the relaxant effect of ANF. In addition, both inhibitors produced small increases in urine flow and sodium excretion in anesthetized rats and potentiated the diuretic and natriuretic responses to exogenous ANF. M&B 22,948 (30 micrograms/kg/min) produced a threefold increase in the natriuretic response to simultaneously administered ANF, and TCV-3B (10 micrograms/kg/min) produced a twofold increase in the response to ANF. The results of the present experiments suggest that both the calmodulin-sensitive and calmodulin-insensitive subclasses of cyclic GMP-specific phosphodiesterase play a role in regulating the in vitro and in vivo response to ANF.

Molecular sieving and mass spectroscopy reveal enhanced collagen degradation in rabbit atheroma.

BACKGROUND: Collagen degradation is the major mechanism of atherosclerotic plaque destabilization. It is unknown whether collagen breakdown is involved into formation of early atherosclerotic lesions. METHODS: Current paper describes a novel collagen degradation assay based on a combination of molecular sieving and mass spectroscopy. The first step of the assay consists of the extraction of total collagen from tissue. This extract includes both intact collagen and its breakdown products. Molecular sieving is used to isolate low molecular weight collagen fragments. Since the low molecular weight fraction of the extract may contain some non-collagenous molecular species, the collagen-specific amino acid hydroxyproline is quantified using mass spectroscopy. RESULTS: This assay was validated in various experimental systems with known/predictable level of collagen breakdown in vitro, ex vivo and in vivo. When applied to cholesterol-fed rabbit aorta, it revealed enhanced collagen degradation in rabbit atheromas compared to unaffected aortic regions. CONCLUSION: A novel assay has been developed to demonstrate enhanced collagen degradation in rabbit atherosclerotic plaques. Accurate quantification of collagen breakdown products should provide a new relevant end point in the analysis of plaque development and stability.

Neuroendocrine and beta-adrenoceptor response to chronic ethanol and aggression in rats.

Male rats were administered either ethanol (6-8 g/kg/day) or dextrin-maltose, an isocaloric equivalent, for two weeks prior to a 24-hour resident-intruder test. After the first 20 minutes of the aggression test residents showed a greater increase in norepinephrine than intruders (216% vs. 97%), while intruders showed a greater increase in epinephrine (394% vs. 51%) and corticosterone (338% vs. 129%) than residents. Ethanol administration increased the initial epinephrine response of intruders almost two-fold compared to dextrin-maltose intruders. After 24 hours of aggression testing plasma norepinephrine was still elevated in residents (92%) and intruders (71%), however, only intruders continued to show an elevation in plasma corticosterone (98%) and epinephrine (107%). Using a cumulative dose-response technique, the dose of isoproterenol required to produce 50% of the maximal heart rate response (ED50) increased in intruders by 108% following aggression testing with ethanol intruders showing significantly smaller mean change. The increase in ED50 was related to drug type, behavior, and plasma corticosterone and epinephrine levels. Rats treated with ethanol had a greater beta-adrenoceptor density than control rats. However, no relationship was found between receptor density and the other measures in this study.

The development of a microprocessor system for simultaneously monitoring heart rate from multiple subjects.

Two computer systems developed in our laboratory to monitor the heart rate of freely moving rats are described below. The first system uses the Commodore CBM microcomputer and monitors a single rat. The second system uses the IBM CS9000, monitors up to four rats simultaneously, and provides real-time graphics. Both systems rely on a Schmitt-trigger circuit which digitizes the electrical signal generation by the heart during every cardiac cycle. Both systems also employ the same algorithm to handle the appreciable levels of noise generated by subject movement. The algorithm developed for filtering this noise and its effectiveness are presented. This paper illustrates a software-intensive approach to handling signal timing, and the advantages provided by 16/32-bit versus an 8-bit microcomputer.

An adult case of acute biphenotypic leukemia with characteristic mixed morphology.

A case of acute biphenotypic leukemia with mixed blast morphology and combined myeloid and T-lymphoid features is reported. The leukemic cells consisted of small lymphoid hand-mirror blasts and large blasts with cytoplasmic granules and rare Auer rods. The cells expressed myeloid and immature T-lymphoid features by cytochemistry and immunophenotyping, however T cell receptor genes were in germline configuration. Cases of biphenotypic leukemia with similar morphological and immunophenotypic findings have been described previously in children. This case represents a morphologically and phenotypically distinct subtype of acute biphenotypic leukemia.

An in vivo cumulative dose-response assay of the myocardial beta-adrenoceptor system.

This paper describes an in vivo computer-based cumulative dose-response assay of the myocardial beta-adrenoceptor system. The technique involves measuring the ability of isoproterenol, a beta-adrenergic agonist, administered through a jugular catheter to increase heart rate in rats. The computer system monitors heart rate, provides real-time graphics of incoming data and a detailed graphic review of responses following testing, coordinates drug injections by the experimenter, performs a nonlinear line analysis to determine the dose required to produce 50% maximal responding (ED50) following the data review, and generates a diskette and printer report at the completion of testing. Data are presented and discussed on how well this system meets the assumptions underlying the cumulative dose-response methodology. The results of a study on the effect of acute footshock on the myocardial beta-adrenoceptor system as measured by this technique is also presented and discussed. This technique permits chronic studies of an important myocardial receptor system and allows receptor changes to be tracked within individual subjects.

Development of tolerance to ethanol-induced tachycardia in rats.

Development of tolerance to ethanol was examined using heart rate as a measure. Ethanol-treated rats were infused IG with 8-11 g/kg/day (in 3 divided doses), control rats received similar infusions of either equicaloric dextrin-maltose or water (equivolumetric) for a period of 17 days. On days 1, 5, 9, 13 and 17 of treatment heart rate was recorded before and at 10, 20 and 30 minutes after injection of a challenge dose of 2 g/kg ethanol, dextrin-maltose or water. The tachycardia produced by ethanol increased with days of chronic treatment to a maximum on the 9th day of treatment. Significant tolerance to the tachycardia was evident only on the 17th day of treatment. Neither control showed significant changes in heart rate.

Non-asbestos-related malignant mesothelioma. A review.

Malignant mesothelioma is an uncommon, but increasingly important, neoplasm. The existing English-language medical literature concerning non-asbestos-related malignant mesotheliomas was reviewed for evidence of other agents associated with the induction of malignant mesothelioma. Both animal and human data were reviewed. In most reviews of malignant mesothelioma, there are a significant proportion of cases without documented asbestos exposure (range, 0% to 87%). Furthermore, there are several fairly well-documented agents other than asbestos that induce malignant mesothelioma in animals, and strong evidence exists that such is the case in man. In reviews of malignant mesothelioma, the percentage of cases with asbestos exposure varies, but a significant number are apparently not asbestos related. It is believed that sufficient evidence exists to suggest that non-asbestos agents can induce malignant mesotheliomas in man, and additional epidemiologic studies in this area are needed.

Characteristics of single isovolumic left-ventricular pressure waves of dog hearts in situ.

By fitting isovolumic phases of an ejecting beat with a model-wave function, one can predict source pressure of the ejecting beat (Sunagawa et al. Trans Biomed Eng 1980; 27:299-305), this being a major determinant of systolic performance. Prior applications of this principle have involved two assumptions: (1) that the isovolumic pressure wave is shaped like an inverted cosine wave, and (2) that duration of an isovolumic beat is the same as that of an ejecting beat. The first assumption might cause overestimation of source pressure, since an isovolumic pressure wave begins declining before the midpoint of the wave. The second assumption might cause underestimation of source pressure, since an ejecting beat is always shorter than an adjacent isovolumic beat at the ejecting beat's end-diastolic volume. Although the two errors tend to cancel, it would be more rational and accurate to use a realistic model wave shape and a realistic isovolumic beat duration. To acquire the information necessary for this, pressure and volume time courses were measured during ejecting beats and adjacent isovolumic beats in dogs under the following steady-state conditions: basal, atrial pacing at various rates, infusion of dobutamine, infusion of verapamil, coronary ligation(s), and ventricular pacing at various sites. These conditions affected the amplitude and duration of isovolumic pressure waves substantially but did not affect the shape of the waves significantly. The duration of each isovolumic beat exceeded that of the previous ejecting beat to a degree which corresponded approximately to the ejecting beat's normalized pressure reserve (source pressure minus peak ejection pressure)/(source pressure). A more accurate source-pressure prediction should be possible by use of a realistic isovolumic pressure-wave shape and by taking account of the effect of pressure reserve on contraction duration.

Matrix metalloproteinase inhibition during the development of congestive heart failure : effects on left ventricular dimensions and function.

The development of congestive heart failure (CHF) is associated with left ventricle (LV) dilation and myocardial remodeling. The matrix metalloproteinases (MMPs) play a significant role in extracellular remodeling, and recent studies have demonstrated increased MMP expression and activity with CHF. Whether increased MMP activity directly contributes to the LV remodeling with CHF remains unknown. Accordingly, this study examined the effects of chronic MMP inhibition (MMPi) on LV size and function during the progression of CHF. Pigs were assigned to the following groups: (1) CHF, rapid pacing for 3 weeks at 240 bpm (n=12); (2) CHF/MMPi, rapid pacing and concomitant MMPi (PD166793, 20 mg/kg per day [n=10]), and (3) control (n=11). With pacing CHF, LV fractional shortening was reduced (19+/-1 versus 45+/-1%), and end-diastolic dimension increased (5.67+/-0.11 versus 3.55+/-0.05 cm), compared with baseline values (P<0.05). In the CHF/MMPi group, LV endocardial shortening increased (25+/-2%) and the end-diastolic dimension was reduced (4.92+/-0.17 cm) compared with CHF-only values (P<0.05). LV midwall shortening was reduced to a comparable degree in the CHF-only and CHF/MMPi groups. LV peak wall stress increased 3-fold with pacing CHF compared with controls and was significantly reduced in the CHF/MMPi group. LV myocardial stiffness was unchanged with CHF but was increased in the CHF/MMPi group. LV myocyte length was increased with pacing CHF compared with controls (180+/-3 versus 125+/-4 microm, P<0.05) and was reduced in the CHF/MMPi group (169+/-4 microm, P<0.05). Basal-state myocyte shortening velocity was reduced with pacing CHF compared with controls (33+/-2 versus 66+/-1 microm/s, P<0.05) and was unchanged in the CHF/MMPi group (31+/-2 microm/s). Using an ex vivo assay system, myocardial MMP activity was increased with pacing CHF and was reduced with chronic MMPi. In summary, concomitant MMPi with developing CHF limited LV dilation and reduced wall stress. These results suggest that increased myocardial MMP activity contributes to LV myocardial remodeling in developing CHF.