Effects of acute ethanol on ventricular myofibrillary protein synthesis in vivo in normotensive and hypertensive rats

Acute doxorubicin (adriamycin) dosage does not reduce cardiac protein synthesis in vivo, but decreases diaminopeptidase I and proline endopeptidase activities

Anthracycline antibiotics are effective anticancer agents but their use is limited due to unwanted adverse side effects. The toxic effects of doxorubicin (adriamycin) include the development of defined cardiac lesions leading to cardiomyopathy in some patients. This has been reported to be due to reductions in cardiac protein synthesis. However, virtually all of these previous studies have failed to consider the specific radioactivity of the precursor pool in their measurements or have carried out their studies in vitro. To further resolve the above we measured fractional rates of cardiac protein synthesis using the "flooding dose" method in rats treated with adriamycin (5 mg/kg body wt). Controls were identically treated and injected with saline. At 2.5 or 24 h after adriamycin injection, rates of protein synthesis were measured with a flooding dose of l-[4-(3)H]phenylalanine. Measurements included free (S(i)) and protein-bound (S(b)) phenylalanine-specific radioactivities, the protein synthetic capacity (RNA/protein ratio; C(s)), the fractional rates of protein synthesis calculated from the ratio S(b)/S(i), and the protein synthetic efficiency calculated from the ratio k(s)/C(s). Complementary analyses included assays of lysosomal (cathepsins B, D, H, and L and diaminopeptidases I and II) and cytoplasmic proteases (alanyl aminopeptidase, arginyl aminopeptidase, leucyl aminopeptidase, diaminopeptidase IV, tripeptidyl aminopeptidase, and proline endopeptidase). These enzymes constitute the most active proteases in this tissue and represent an index of protein degradation capacity in cardiac muscle. The results showed that in 2.5-h dosed rats, adriamycin had no effect on S(i), S(b), C(s), k(s), or k(RNA) (P > 0.05, not significant (NS) in all instances). In 2.5-h dosed rats, levels of diaminopeptidase I activity were reduced (P < 0.05), whereas the activities of other proteases were not significantly altered (NS in all instances). In 24-h dosed rats, adriamycin reduced cardiac S(b) (P < 0.001), which would normally be interpreted as a reduction in protein synthesis. However, S(i) was also decreased in 24-h adriamycin-injected rats (P < 0.025%). C(s) was not changed (NS). Consequently, the calculated k(s) and k(RNA) values were not significantly affected in 24-h adriamycin-dosed rats (NS). There were also significant reductions in proline endopeptidase activities in rats exposed for 24 h to adriamycin. The activities of other proteases were not significantly affected at this time point (NS in all instances). In conclusion, adriamycin reduces amino acid labeling of cardiac proteins, an effect that is a consequence of altered free phenylalanine-specific radioactivities. There was some evidence of limited altered intracellular proteolysis.

In vivo rates of skeletal muscle protein synthesis in rats are decreased by acute ethanol treatment but are not ameliorated by supplemental alpha-tocopherol

Some studies have shown that reductions in tissue protein synthesis, under a variety of cytotoxic conditions, are ameliorated by alpha-tocopherol (ATC) supplementation. We have also shown evidence of increased oxidative stress and reduced protein synthesis rates in alcohol-exposed muscle. Serum levels of ATC fall and rates of muscle protein synthesis are reduced in patients with alcoholic myopathy. We therefore tested the hypothesis that treatment with ATC could ameliorate the ethanol-induced changes in muscle protein synthesis, a contributory event in the pathogenesis of alcoholic muscle disease. Studies were carried out on gastrocnemius (Type II fiber-predominant and usually considered representative of the musculature as a whole), soleus (Type I fiber-predominant) and plantaris (Type II fiber-predominant) muscles. For comparative purposes, we also investigated the liver. Young male Wistar rats (90 g body weight) were injected intraperitoneally (i.p.) daily with ATC (30 mg/kg body weight) in Intralipid fat emulsion (0.1 mL/100 g body, i.p.) for 5 d. Controls were similarly injected with the Intralipid vehicle alone. After ATC supplementation, rats were given ethanol (75 mmol/kg body weight, i.p., 2.5 h) or saline (0.15 mol/L NaCl, i. p.). Fractional rates of tissue protein synthesis (i.e., the percentage of the tissue protein pool renewed each day, k(s), %/d) and RNA activities [i.e., the amount of protein synthesis each day per unit RNA, k(RNA), mg protein/d/mg RNA)] were then measured. Supplementation increased ATC concentrations in plasma, gastrocnemius and liver. There was no effect of ATC supplementation alone on k(s) in any of the tissues. ATC supplementation in the absence of alcohol increased k(RNA) in the plantaris muscle. In nonsupplemented groups, acute ethanol treatment reduced skeletal muscle (soleus, plantaris and gastrocnemius) k(s). Hepatic k(s) was not altered by ethanol, although ATC concentrations in this tissue increased due to ethanol. However, none of the changes in muscle k(s) or k(RNA) due to ethanol were significantly affected by ATC supplementation. In conclusion, ATC supplementation does not appear beneficial in ameliorating acute alcohol toxicity in skeletal muscle as defined by reductions in protein synthesis.

Inability of propranolol to prevent alcohol-induced reductions in cardiac protein synthesis in vivo

Rats were acutely injected with alcohol (75 mmol/kg body weight) and at the end of 2.5 h changes in cardiac synthesis rates were assessed with a 'flooding dose' of L-[4-(3)H]phenylalanine. The results showed that acute alcohol dosage reduced the fractional rates of cardiac protein synthesis (k(S), %/day). This effect was also seen when data were expressed relative to either RNA (i.e. k(RNA), mg protein/day/mg RNA) or DNA (i.e. k(DNA), mg protein/day/mg DNA). Both left and right ventricles responded similarly to ethanol. However, propranolol pre-treatment (at doses of 17 and 170 micromol/kg body weight; i.p.) did not prevent these effect of ethanol in either the left or right ventricle. Indeed, there was evidence that propranolol per se perturbed cardiac protein synthesis in vivo in control (i.e. without ethanol) rats particularly in the right ventricle. In conclusion, the results suggest that alcohol is cardiotoxic to the myocardium, which may cause its effects on protein synthesis independently of beta-receptors and/or xanthine oxidase inhibition.

A comparative investigation into the effect of chronic alcohol feeding on the myocardium of normotensive and hypertensive rats: an electrophoretic and biochemical study

We investigated whether the imposition of chronic alcohol in hypertension leads to greater biochemical and cellular abnormalities of the myocardium than those arising in normotension. Fifteen-week-old spontaneously hypertensive rats (SHR) and Wistar Kyoto (WKY) rats were fed ethanol-containing diets for six weeks. Particular attention was focused on the composition of contractile proteins identified by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), fractional rate of protein synthesis, and synthesis rates relative to RNA (RNA activity) or DNA (cellular efficiency). In addition, myocardial enzymes and adenine nucleotides were measured. In both SHR and WKY rats chronic ethanol caused a general decrease in the contents of all nine contractile proteins with myosin heavy chain predominantly affected. Fractional rates of mixed (i.e., total) and myofibrillary proteins remained unaltered in both WKY rats and SHR, as were cellular efficiencies. The RNA activity was significantly reduced in ethanol-treated SHR but not in WKY rats. In ethanol-treated SHR, cardiac creatine kinase (CK) and malate dehydrogenase (MDH) activities were increased, AMP levels were elevated, whilst ATP levels and the energy charge were reduced. In WKY rats, the only significant change related to increased aspartate aminotransferase activities in response to alcohol feeding. Although there were only subtle differences between the response of the normotensive and hypertensive rats due to ethanol dosage, the reduced ATP levels and increased CK and MDH activities in SHR may reflect a greater susceptibility to ischaemic damage. Reduced contractile protein content, particularly myosin heavy chain, may contribute to contractile defects, a common feature of subclinical and clinical alcoholic cardiomyopathy.

Alcohol-induced reductions in cardiac protein synthesis in vivo are not ameliorated by treatment with the dihydropyridine calcium channel blocker amlodipine

BACKGROUND

Various studies have indicated that acute ethanol dosage perturbs cardiac function and/or structure with concomitant reductions in protein synthesis. Cellular calcium homeostasis is also perturbed, which may contribute to altered protein synthesis. This is supported by the observation that calcium channel blockers can prevent numerous features of alcohol-induced pathology. However, many of these studies have been carried out in vitro, employing supraphysiological levels of alcohol, or have failed to address whether their results obtained in isolated systems have direct relevance in vivo. The aim of the present investigation was to examine the response of cardiac protein synthesis in vivo due to a physiologically relevant dose of ethanol and determine whether a calcium channel antagonist could prevent these effects.

METHODS

Changes in cardiac protein synthesis rates in vivo were assessed by measuring the fractional rates of protein synthesis (i.e., ks) using a "flooding dose" of [3H]phenylalanine. Rats were treated either acutely (10 mg/kg body weight, 3 hr) or chronically (10 mg/kg body weight/day, 30 days) with amlodipine, a dihydropyridine-type calcium channel blocker, before dosing with ethanol (75 mmol/kg body weight, 2.5 hr).

RESULTS

Ethanol (75 mmol/kg body weight) inhibited cardiac protein synthesis after 1 hr. Similar responses were recorded at 2.5 and 6 hr after ethanol dosage. At 24 hr, ethanol decreased food intakes. However, a direct comparison between pair-fed controls and alcohol-dosed rats also showed a decrease in cardiac protein synthesis after 24 hr. Acute alcohol dosage reduced cardiac protein synthesis in mixed, myofibrillary, and sarcoplasmic protein fractions. Similar results were obtained when data were expressed relative to ribonucleic acid (i.e., kRNA). Neither acute nor chronic treatments with the calcium antagonist amlodipine ameliorated the deleterious actions of ethanol on protein synthesis.

CONCLUSIONS

Ethanol may affect cardiac protein synthesis independently of altered calcium entry.

Non-cardiac nucleic acid composition and protein synthesis rates in hypertension: studies on the spontaneously hypertensive rat (SHR) model

Various studies have shown the involvement of extracardiac tissues in hypertension, including the hepato-intestinal tract, musculo-skeletal system, skin, and the kidney. It was our hypothesis that these perturbations in non-cardiac tissues would also include alterations in protein metabolism. Thus, the reported differences in soleus contractile protein composition may be related to changes in muscle protein synthesis or reduced protein synthetic efficiencies. The aim of the present study was to characterise tissue composition of nucleic acids and rates of protein synthesis in non-cardiac tissues, such as liver, skeletal muscle (i.e., the Type I fibre-predominant soleus and Type II fibre-predominant plantaris), kidney, bone (tibia), skin and the gastrointestinal tract in a genetic model of hypertension (i.e., spontaneously hypertensive rats (SHRs), 15 weeks old) compared to their genetic aged-matched counterparts, i.e., normotensive Wistar-Kyoto (WKY) controls. Rates of protein synthesis were measured in vivo after injection with a flooding dose of L-[4-(3)H]phenylalanine. The results showed changed tissue wet weights (g per organ) for plantaris (+10%, P<0.05), liver (+25%, P<0.01), brain (-9%, P<0.01), jejunum (+39%, P<0.001) and tibia (+17%, P<0.001) in SHRs compared to WKY controls. Protein content (g or mg per organ) was increased in the liver (+32%, P<0. 01) and tibia (+37%, P<0.05). RNA contents (mg per organ) were increased in plantaris (+17%, P<0.01), liver (+22%, P<0.01) and jejunum (+11%, P<0.05). DNA (mg per organ) was increased in plantaris (+16%, P<0.025) and jejunum (+12%, P<0.025). The protein synthetic capacities (i.e., C(s), mg RNA/g protein) were higher in soleus (+41%, P<0.01) and plantaris (+6%, P<0.05) muscles of SHRs compared to WKYs, whereas values were lower in liver (-11%, P<0.01) and kidney (-6%, P<0.01) of SHRs compared to WKYs. The fractional rate of protein synthesis (i.e., k(s), the percentage of the protein pool renewed each day) was not significantly different for any of the tissues, though the rate of protein synthesis per unit RNA (i.e., k(RNA), mg protein/day per mg RNA) was reduced in the soleus (-24%, P<0.05) and the synthesis rate per unit DNA, i.e., k(DNA) (mg protein/day per mg DNA) was increased in the tibia (+31%, P<0.025). This is the first report of significant differences between indices of protein metabolism in extracardiac tissues in hypertension, which may reflect endocrine factors and/or the systemic influence of hypertension per se.

Alcohol and the myocardium

Structural and functional abnormalities are prominent in alcoholic cardiomyopathy (ACM). Histological features in affected subjects are almost identical to the characteristics of dilated cardiomyopathy. Quantitative morphometry, however, can distinguish between ACM and dilated cardiomyopathy. Biopsies from patients with ACM show increases in the activities of some myocardial enzymes (alpha-hydroxybutyric dehydrogenase, creatine kinase, lactate dehydrogenase, malic dehydrogenase) which are correlated with the bimodal distribution of alcohol intake and may represent an adaptive response. One-third of patients with ACM have serum antibodies against cardiac acetaldehyde-protein adducts. Animal models of ethanol toxicity have shown that acutely, alcohol and acetaldehyde reduce the synthesis of cardiac contractile proteins in vivo. Two-dimensional SDS-PAGE has also shown that in rats chronically fed alcohol, the relative amounts of over 10% of heart muscle proteins are altered. The heat shock proteins (HSP) Hsp60 and Hsp70 are decreased in alcohol-fed rats, as is desmin. Reduction in HSPs may indicate reduced myocardial protection whilst a fall in desmin may indicate structural defects. In conclusion, ACM is a complex process that is due to altered protein synthesis, the formation of acetaldehyde adducts and a reduction of cardiac HSPs and desmin. Both acetaldehyde and alcohol are myocardial perturbants.