Denis C. Lehotay

Doxorubicin-induced acute changes in cytotoxic aldehydes, antioxidant status and cardiac function in the rat

Doxorubicin (DOX)-induced cardiotoxicity is thought to be caused by free radical-mediated mechanisms. An in vivo rat model was developed to investigate the DOX-induced cascade of early biochemical changes focusing on the central role of the aldehydic lipid peroxidation products. Antioxidant status was evaluated by glutathione measurements. Creatine Kinase (CK) activity was measured as an index of cardiac injury. Development of functional abnormalities were documented by echocardiography. The results showed that aldehydes in rat plasma and heart tissues increased significantly following DOX treatment. The changes occurred early, peaked around 2 h after DOX administration, and the levels declined or returned to baseline value within 8-24 h. Toxic aldehyde levels including malondialdehyde, hexanal and 4-hydroxy-non-2-enal also increased. Acyloin levels, metabolic products of aldehydes, increased early and then decreased in plasma, and there was a significant decrease in heart tissues after DOX treatment. GSH levels decreased early, then increased by 24 h, while GSSG levels decreased initially, then increased after DOX treatment, suggesting early depletion of GSH and a later rebound phenomenon. CK levels were elevated after treatment. The functional abnormalities were documented by stress echocardiography in some rats although the changes were not consistent at such an early stage following treatment. Our data confirmed the involvement of free radicals, and suggested that the cytotoxic aldehydes play a central role in initiating the steps that lead to functional impairment of the myocardium following DOX administration. Scavengers and the metabolic removal of some of the aldehydes also play a role in protecting the myocardium against injury.

L-carnitine attenuates doxorubicin-induced lipid peroxidation in rats

Doxorubicin (DOX) was administered intraperitoneally to rats in six equal, 2.5 mg/kg doses over a 2-week period with or without L-carnitine. Injury was monitored by echocardiography, release of myosin light chain-1 (MLC-1), and by measurement of aldehydic lipid peroxidation products. General observation revealed that DOX alone caused more ascites than DOX plus L-carnitine. Animals sacrificed 2 h after the sixth dose had significantly higher aldehyde concentrations than 2 h after a single dose of DOX. Aldehydes in plasma and heart remained elevated for 3 weeks after the final dose of DOX, whereas L-carnitine prevented or attenuated the DOX-induced increases in lipid peroxidation. The increase in MLC-1 2 h after the sixth dose of DOX was greater than after a single dose, suggesting cumulative damage. Echocardiography did not detect either early injury or the protective effects of L-carnitine. These data indicate that lipid peroxidation following DOX occurs early, and parallels the cumulative characteristics of DOX-induced cardiotoxicity. The protective effects of L-carnitine may be due to improved cardiac energy metabolism and reduced lipid peroxidation.

Activation of guanylate cyclase by α-toxins from krait and cobra venom

Abstract The effects of purified neurotoxins from krait and cobra venom were tested on guanylate cyclase activity in rat tissues. Both α-bungarotoxin and α-cobrotoxin stimulated the activity of the soluble form of this enzyme in lung, spleen and kidney, but were without effect in liver, muscle and brain. Half maximal stimulation of guanylate cyclase occurred at about 1 μM with α-bungarotoxin and at about 0·25 μM with α-cobrotoxin. Reduction and alkylation, or oxidative detoxification of the toxins abolished their ability to stimulate the guanylate cyclase enzyme. Treatment with dithiothreitol also greatly reduced the effect of the toxins. These data suggest that the toxins may act in vitro by altering the redox state of guanylate cyclase. Neither curare nor atropine blocked the stimulatory effect of these toxins on the enzyme.

Adenylate Cyclase: General Properties and Role of Phospholipids in Hormone Activation

In 1957–1958 Rall and Sutherland (1958; Rall et al., 1957) described a smallmolecular-weight, heat-stable factor, chemically characterized as adenosine 3′,5′-monophosphate (cyclic AMP), which appeared to mediate the effects of epinephrine and glucagon on glycogenolysis. Production of the nucleotide is catalyzed by the enzyme adenylate cyclase (EC 4.6.1.1.).

Modulation of Rat Guanylate Cyclase Activity in vitro by Chemical Carcinogens

The nucleotide cyclic GMP has been reported to be involved in cell proliferation and malignant transformation. Nitroso chemical carcinogens activate the enzyme guanylate cyclase (EC 4.6.1.2) which catalyzes the production of cyclic GMP. The present investigation demonstrates that compounds from other major classes of carcinogens including (1) alpha-halo ethers (chloromethyl methyl ether); (2) aromatic amines (benzidine and B-naphthylamine); (3) polycyclic hydrocarbons (1,2-benzanthracene and acridine); (4) azo dyes (p-dimethylaminoazobenzene), and (5) aflatoxins (B1, B2, G1, G2) produced a striking and significant inhibition of guanylate cyclase over a general concentration range of 0.5-13 mmol/1 in a variety of tissues. Some of the nitrosamides which increase guanylate cyclase activity, increase DNA synthesis whereas carcinogens which decrease guanylate cyclase activity inhibit DNA or RNA synthesis suggesting a relationship between cyclic GMP, DNA synthesis, and chemical carcinogenesis.

A Peptide Inhibitor of Glucagon-Responsive Adenylate Cyclase in Liver

The effects of a peptide inhibitor of adenylate cyclase produced by the isolated, perfused rat liver under hypocalcemic conditions were studied. This inhibitory peptide non-competitively abolished the activation of adenylate cyclase in particulate preparations of rat liver by glucagon, epinephrine, and parathyroid hormone, as well as cyclic AMP production in glucagon-stimulated rat liver slices. Higher concentrations of inhibitor also decreased basal adenylate cyclase activity and its fluoride-responsiveness. The data suggest that this substance is normally present in liver, but is released only under hypocalcemic conditions. The peptide does not crossreact in the radioimmunoassay of glucagon, insulin, or parathyroid hormone. Its inhibitory effects are not duplicated by somatostatin, angiotensin I, renin substrate, or the desoctadecapeptide of insulin.