R B Melchert

University of Oklahoma Health Sciences Center, Oklahoma City, OK, United States

Are you R B Melchert?

Claim your profile

Publications (14)57.86 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: In clinical reports during the last decade, acute myocardial infarction has been reported in young, otherwise healthy, persons after cocaine use. These clinical reports suggest that recreational use of cocaine has adverse effects on the vasculature of the heart. The purpose of this investigation was to evaluate cocaine-induced injury to heart-derived endothelial cells (ECs) obtained from adult male Sprague-Dawley rats. Alterations in lactate dehydrogenase release (LDH), lyso-somal neutral red retention (NR), and cell proliferation were evaluated after treatment of the ECs with cocaine doses ranging from 1 X 10-7 to 1 X 10-3 M at 1,4, and 24 h. Intracellular calcium levels were determined immediately after exposure to 1 X 10-3 and 1 X 10-2 M cocaine. LDH release, an index of cytoplasmic membrane injury, was significantly elevated after 24 h only with those ECs exposed to the highest dose of cocaine, 1 X 10-3 M. In using NR as a score for lysosomal integrity and cell viability, no significant differences were observed for all treatment groups. However, all doses of cocaine suppressed EC proliferation by 10 days. Intracellular calcium levels were elevated on acute exposure to high concentrations of cocaine. These data suggest that both low and high doses of cocaine are injurious to ECs maintained in culture. Although the EC cultures remained viable, the integrity of cytoplasmic membrane was compromised with high doses of cocaine as demonstrated by LDH release and elevated intracellular calcium levels, whereas all doses inhibited EC growth and proliferation.
    09/2008; 3(2):109-118.
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: The application of in vitro model systems to evaluate the toxicity of xenobiotics has significantly enhanced our understanding of drug- and chemical-induced target toxicity. From a scientific perspective, there are several reasons for the popularity of in vitro model systems. From the public perspective, in vitro model systems enjoy increasing popularity because their application may allow a reduction in the number of live animals employed in toxicity testing. In this review, we present an overview of the use of in vitro model systems to investigate target organ toxicity of drugs and chemicals, and provide selective examples of these model systems to better understand cutaneous and ocular toxicity and the role of drug metabolism in the hepatotoxicity of selected agents. We conclude by examining the value and use of in vitro model systems in industrial development of new pharmaceutical agents.
    Annual Review of Pharmacology 02/1998; 38:63-96. · 21.54 Impact Factor
  • R B Melchert, A A Welder
    [Show abstract] [Hide abstract]
    ABSTRACT: Evidence has accumulated over the pst several years which associates androgenic-anabolic steroid (AAS) use with sudden cardiac death, myocardial infarction, altered serum lipoproteins, and cardiac hypertrophy in humans who habitually use these drugs. Even though some experimental data obtained from animals correlate well with the human findings, the adverse cardiovascular effects of AAS use are poorly understood. The evidence presented in this review suggests that there are at least four hypothetical models of AAS-induced adverse cardiovascular effects: 1) an atherogenic model involving the effects of AAS on lipoprotein concentrations; 2) a thrombosis model involving the effects of AAS on clotting factors and platelets; 3) a vasospasm model involving the effects of AAS on the vascular nitric oxide system; and 4) a direct myocardial injury model involving the effects of AAS on individual myocardial cells. Future studies should be directed at determining the exact mechanisms responsible for AAS-induced adverse cardiovascular effects, at determining the relative contribution of each of these models, and at identifying other possible contributing factors such as metabolism of these steroids and the effects of potential metabolites on various target organs.
    Medicine &amp Science in Sports &amp Exercise 10/1995; 27(9):1252-62. · 4.48 Impact Factor
  • A A Welder, J W Robertson, R B Melchert
    [Show abstract] [Hide abstract]
    ABSTRACT: Hepatic complications in athletes and bodybuilders after abusing anabolic-androgenic steroids (AAS) have been reported. Hepatic injury, including cholestasis, peliosis hepatis, hyperplasia, and tumors, have been attributed to abuse of the 17 alpha-alkylated AAS. Some of these pathological conditions have been reversed when individuals were converted to nonalkylated AAS regimens. The purpose of this study was to determine and compare the direct toxic effects of commonly abused AAS (both 17 alpha-alkylated and nonalkylated) in primary hepatic cell cultures. Primary cultures, established from 60-day-old Sprague-Dawley rats, were exposed to doses of 1 x 10(-8), 1 x 10(-6), and 1 x 10(-4)M 19-nortestosterone, fluoxymesterone, testosterone cypionate, stanozolol, danazol, oxymetholone, testosterone, estradiol, and methyltestosterone for 1, 4, and 24 hr. Lactate dehydrogenase (LDH) release, neutral red (NR) retention, and glutathione (GSH) depletion were evaluated to determine plasma membrane damage, cell viability, and possible oxidative injury, respectively. Those cultures exposed to the 17 alpha-alkylated AAS, methyltestosterone and stanozolol, at doses of 1 x 10(-4) M for 24 hr and the 17 alpha-alkylated AAS, oxymetholone, at 1 x 10(-4) M for 4 and 24 hr showed significant increased in LDH release and decreases in NR retention while there were no significant differences with the nonalkylated steroids (testosterone cypionate, 19-nortestosterone, testosterone, and estradiol). GSH depletion was evaluated in cultures treated with 1 x 10(-8), 1 x 10(-6), and 1 x 10(-4) M concentrations of methyltestosterone, stanozolol, and oxymetholone for 1, 2, 4, and 6 hr. Cultures exposed to 1 x 10(-4) M oxymetholone were significantly depleted of GSH at 2, 4, and 6 hr; cultures exposed to 1 x 10(-4) M methyltestosterone were significantly depleted of GSH at 4 and 6 hr; and cultures exposed to stanozolol were not significantly depleted of GSH at any of the time periods tested. These data indicate that the 17 alpha-alkylated steroids (methyltestosterone, oxymetholone, and stanozolol) are directly toxic to hepatocytes, whereas the nonalkylated steroids (testosterone cypionate, 19-nortestosterone, testosterone, and estradiol) show no effects at similar doses. These data demonstrate a trend toward a structural-activity relationship to AAS-induced toxicity in primary cultures of rat hepatocytes.
    Journal of Pharmacological and Toxicological Methods 09/1995; 33(4):187-95. · 2.15 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Recent literature reports of myocardial infarction in athletes who self-administer anabolic-androgenic steroid (AAS) and previous animal studies of the effects of AASs on the heart suggest that these drugs may be directly injurious to the myocardium. We have previously demonstrated that 100 microM testosterone cypionate (TC) inhibits all beating activity of primary neonatal rat myocardial cell cultures within 1 hr of exposure and causes significant LDH release by 4 hr of exposure, indicating a direct toxic effect of TC. The purpose of this investigation was to evaluate the effects of commonly abused AASs on primary neonatal rat myocardial cell cultures and to provide insight into early cellular changes that may lead to TC-induced toxicity. Significant LDH release was observed in 5-day-old primary myocardial cell cultures (obtained from 3-to-5-day-old Sprague-Dawley rats) exposed to 100 microM testosterone enanthate (TE), testosterone propionate (TP), and oxymetholone (O) for 4 and 24 hr and in cultures exposed to 100 microM testosterone (T) for 24 hr. Neutral red retention and MTT formazan production were significantly decreased in cell cultures exposed to 100 microM TE, TP, and O after only 4 hr of exposure, indicating a loss of viability and mitochondrial activity. However, there was no effect on viability of cell cultures exposed for 24 hr to 100 microM of a variety of other commonly abused AASs. Phase-contrast microscopy revealed complete disruption of the monolayer in cell cultures treated with 100 microM TE, TP, and O for 4 hr. Treatment of fura-2-loaded myocardial cell cultures with 100 microM TC produced no significant changes in calcium transients or baseline calcium levels for up to 13 min of exposure. These results indicate that O, T, TC, TE, and TP produce a direct toxic effect in heart cell cultures and that early (< 13 min) changes in calcium homeostasis are unlikely to participate in the mechanism of toxicity.
    Toxicology and Applied Pharmacology 08/1995; 133(2):328-42. · 3.98 Impact Factor
  • Allison A. Welder, Paula Grammas, Russell B. Melchert
    [Show abstract] [Hide abstract]
    ABSTRACT: Although cocaine abuse has been a major drug problem in the United States for over 100 years, it has only been in the last decade that the adverse effects of cocaine on the cardiovascular system have become a serious health issue. The cardiotoxic effects of cocaine are multifactorial and remain a puzzle for investigators to solve. Evidence suggests that cocaine-induced toxic effects on the cardiac and vascular cells include both direct as well as indirect components. In addition, other chemical, physiologic, and environmental factors may further complicate and alter mechanisms and endpoints of cocaine-induced cellular toxicity. In order to fully understand the overall cardiotoxic response to cocaine, the cellular mechanisms and endpoints of toxicity of each of these potentially injurious factors must be identified.
    Toxicology Letters 10/1993; · 3.15 Impact Factor
  • A A Welder, R B Melchert
    [Show abstract] [Hide abstract]
    ABSTRACT: Cocaine and anabolic-androgenic steroid abuse have become major drug problems in the United States. Cocaine has been designated as "the drug of greatest national health concern" while as many as 1 million Americans have used or are currently using anabolic-androgenic steroids to promote athletic performance and/or improve physical appearance. Unfavorable cardiovascular events have been linked to both cocaine and anabolic-androgenic steroid abuse in healthy, physically active individuals. Deaths of several United States athletes in 1986 focused attention on the life-threatening cardiovascular consequences of cocaine abuse. Reports of myocardial injury with anabolic-androgenic steroid abuse are anecdotal. Nevertheless, case reports have illustrated the alarming cardiotoxic potential of these steroids in athletes. Anabolic-androgenic steroids were correlated to myocardial infarction in weight lifters and cardiomyopathy in a former professional football player. From the total emergency room episodes where cocaine was mentioned in 1990, approximately 66% of these episodes occurred in young individuals 18-29 years of age. Over 500,000 of the individuals currently taking anabolic-androgenic steroids for nonmedical purposes are high-school children. Because cocaine and anabolic-androgenic steroids are used improperly, more focus needs to be paid to the toxic mechanisms of their adverse effects. Therefore, the purpose of this review is to discuss mechanisms whereby exercise and/or exercise training may alter the cardiovascular responses to these drugs. Furthermore, we would like to illustrate that contrary to the popular belief, acute and chronic abuse of cocaine and anabolic-androgenic steroids have a negative impact on exercise performance.
    Journal of Pharmacological and Toxicological Methods 05/1993; 29(2):61-8. · 2.15 Impact Factor
  • A A Welder, L J Dickson, R B Melchert
    [Show abstract] [Hide abstract]
    ABSTRACT: Cocaethylene is a unique cocaine metabolite formed in the presence of ethanol by the liver. Neither acute nor chronic cardiotoxic effects of this metabolite have been investigated. The purpose of this study was to establish a time- and dose-dependent toxicity profile for cocaethylene in primary myocardial cell cultures established from 3-5-day-old Sprague-Dawley rats. Alterations in lactate dehydrogenase (LDH) release, lysosomal neutral red (NR) retention, thiobarbituric acid-reactive substances (TBARS), morphology, and beating activity were evaluated after treatment of cultures with cocaethylene doses ranging from 1.0 x 10(-3) to 1.0 x 10(-9) M from 1 to 24 h. LDH release was significantly elevated after 24 h only with those cultures exposed to the highest dose of cocaethylene (1.0 x 10(-3) M). The highest dose of cocaethylene also significantly depressed NR retention. While all doses of cocaethylene depressed contractile activity and altered cellular morphology by 24 h, there were no TBARS formed up to 15 h. Thus, both low and high doses of cocaethylene are injurious to the cellular integrity and contractility of myocardial cell cultures. Future studies are warranted to determine mechanisms of cocaethylene toxicity in this in vitro model of spontaneously contracting myocardial cells.
    Alcohol 01/1993; 10(4):285-90. · 2.26 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Cocaine induces acute lethal cell injury in rat hepatocytes following N-oxidative metabolic activation by cytochrome P450-dependent and flavin-dependent monooxygenases. Beside this oxidative bioactivation pathway, hepatic carboxylesterases may cleave the carboxymethylester or the benzoylester linkage which leads to molecules found to be non-toxic in vivo. To elucidate the structural requirements of the cocaine molecule for its bioactivation and inactivation, the cytotoxic potential of the natural (-)-cocaine relative to two isomeric forms, (+)-cocaine* (the unnatural enantiomer) and (-)-psi-cocaine (the C2 epimer of the unnatural cocaine) were investigated. Primary short-term cultures of rat hepatocytes obtained from phenobarbital (PB)-pretreated rats were exposed to the drugs for up to 24 h. (-)-Cocaine produced marked time- and concentration-dependent release of lactate dehydrogenase (LDH) into the extracellular medium, whereas the other forms were not cytotoxic (0-1 mM). Furthermore, depletion of cellular glutathione (GSH) with diethylmaleate enhanced LDH release in (-)-cocaine-treated cells and caused marginal cytotoxicity in hepatocytes exposed to the other isomers. To investigate the mechanisms that could be responsible for these isomer-specific effects, the time-dependent metabolic degradation was determined both in cultured hepatocytes and in hepatic microsomes in the presence or absence of the serine carboxylesterase inhibitors, phenylmethylsulfonylfluoride (PMSF) or NaF. All three cocaine analogs were enzymatically degraded, but the rates of ester cleavage greatly varied among the stereoisomers. (-)-Cocaine was primarily N-oxidized via SKF-525A-sensitive pathways, whereas (+)-cocaine was predominantly hydrolyzed by PMSF-sensitive carboxylesterases. In contrast, (-)-psi-cocaine, which is very stable in the absence of cells at 37 degrees C and pH 7.4, was subject to extremely fast enzymatic ester cleavage. In conclusion, these results indicate that the isomer-specific differential cytotoxicity of (-)-cocaine, (+)-cocaine and (-)-psi-cocaine in hepatocytes may be related to stereoselective differences in the rates of hydrolytic inactivation by hepatic carboxylesterases and that the N-oxidative pathway, resulting in hepatocyte injury, may thus be relevant only for (-)-cocaine.
    Chemico-Biological Interactions 12/1992; 84(3):243-58. · 2.97 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Sudden cardiac death associated with cocaine (Coc) abuse in healthy, physically active individuals became a grave concern in the late 1980s. It is well documented that physical activity increases circulating plasma catecholamine levels. Catecholamines as well as Coc are independently capable of inducing toxic cardiac effects. The purpose of this investigation was to evaluate the synergistic or additive toxic effects of norepinephrine (NE) and Coc in primary myocardial cell cultures obtained from 3- to 5-d-old Sprague-Dawley rats. Alterations in lactate dehydrogenase release (LDH), lysosomal neutral red retention (NR), beating activity, and morphology were evaluated after treatment of the cells for 1-24 h with 1 x 10(-3) M Coc alone, 1 x 10(-5) M Coc alone, 1 x 10(-5) M NE alone, 1 x 10(-3) M Coc with 1 x 10(-5) M NE, or 1 x 10(-5) M Coc with 1 x 10(-5) M NE. LDH release was elevated significantly after 24 h only with those cells exposed to 1 x 10(-3) M Coc alone and 1 x 10(-3) M Coc + 1 x 10(-5) M NE. Using NR retention as a score for lysosomal treatment of the cells with 1 x 10(-5) M Coc and 1 x 10(-3) M Coc alone did not decrease dye retention significantly. However, 1 x 10(-5) M NE combined with 1 x 10(-3) M Coc significantly reduced lysosomal dye retention as early as 1 h after treatment. After 24 h, 1 x 10(-5) M NE alone and 1 x 10(-5) M NE combined with 1 x 10(-5) M Coc significantly increased lysosomal fragility. Beating activity was altered in all treatment groups. Contractile activity was slow and irregular or completely absent with 1 x 10(-5) and 1 x 10(-3) M Coc, respectively. When NE (1 x 10(-5) M) was combined with both concentrations of Coc, there was distinct focalization of sharp, rapid contractions within the cells, which were asynchronous and/or arrhythmic in nature. Those cells exposed to 1 x 10(-5) M NE with 1 x 10(-5) M Coc for 24 h appeared hypercontracted with marked pseudopodia and cytoplasmic granule formation distinctly different from that exhibited by the cells exposed to 1 x 10(-5) M Coc alone. These data demonstrate that NE potentiates the adverse effects of Coc on contractile activity and morphology of spontaneously contracting neonatal myocardial cells maintained in culture.
    Journal of Toxicology and Environmental Health 07/1992; 36(2):75-90. · 1.81 Impact Factor
  • R B Melchert, T J Herron, A A Welder
    [Show abstract] [Hide abstract]
    ABSTRACT: Although recent case reports suggest that anabolic-androgenic steroids may be directly injurious to the cardiovascular system, the direct myocardial cellular consequences of abuse of these drugs are not known. Therefore, the purpose of this study was to describe the concentration- and time-dependent effects of testosterone cypionate (TC), stanozolol (S), and fluoxymesterone (F) on primary myocardial cell cultures. Evaluation of drug effects were made in 4-d-old primary myocardial cell cultures obtained from 3- to 5-d-old Sprague-Dawley rats. The cultures were exposed to 1 x 10(-4) M, 1 x 10(-6) M, and 1 x 10(-8) M concentrations of TC, S, and F each for 1, 4, and 24 h. Cellular injury was evaluated by alterations in beating activity, induction of morphological alterations, lactate dehydrogenase (LDH) release, neutral red retention, and tetrazolium (MTT) formazan production. Significant alterations in beating activity were observed in the 1 x 10(-4) M TC group in which no beating activity was seen at 1, 4, and 24 h. Morphological integrity was disrupted for the 1 x 10(-4) M TC group at 24 h where destruction of the monolayer was observed. Unlike the cultures treated with the three concentrations of both S and F, significant LDH release was seen at 4 and 24 h with those cultures exposed to 1 x 10(-4) M TC. In the evaluation of neutral red retention, 1 x 10(-4) M TC at 24 h showed a significant decrease in ability to retain the dye.(ABSTRACT TRUNCATED AT 250 WORDS)
    Medicine &amp Science in Sports &amp Exercise 03/1992; 24(2):206-12. · 4.48 Impact Factor
  • R B Melchert, A A Welder
    [Show abstract] [Hide abstract]
    ABSTRACT: Recent reports demonstrated that perinatal exposure to cocaine (Coc) and amphetamines (Amph) predisposed the infant to adverse cardiovascular consequences. Dose- and time-dependent effects of Coc and Amph on postnatal rat myocardial cell cultures are described. Contractile activity, morphology, lactate dehydrogenase (LDH) release, MTT formazan production, and neutral red (NR) retention were determined. No contractile activity was observed in cultures treated with the highest drug doses. After 24 h, the percentage of areas exhibiting contractile activity was decreased in cultures exposed to the lowest doses of both drugs. When Coc and Amph were combined, beating rates were significantly altered. Morphologic alterations were observed in all treatment groups. LDH release occurred in cultures exposed to the highest doses of both drugs. No significant differences were observed for MTT or NR. These data demonstrate that Coc and Amph doses > or = 1 x 10(-5) M induce adverse effects on morphology and contractile activity of postnatal myocardial cell cultures.
    Reproductive Toxicology 01/1992; 6(6):467-73. · 3.14 Impact Factor
  • R B Melchert, J A Eselin, J F O'Dell, A A Welder
    [Show abstract] [Hide abstract]
    ABSTRACT: Currently, there is no uniform treatment for abnormal cardiac events precipitated by cocaine use. However, clinical strategies include use of calcium channel antagonists for cardiovascular emergencies. In experimental situations using rats, simultaneous administration of nitrendipine (NIT) with cocaine to the whole animal (1.46 x 10(-3) mg/kg/min of NIT; 2 mg/kg/min of cocaine) and isolated retrograde perfused hearts (Langendorff; 1 x 10(-7) M NIT; 1 x 10(-7) to 1 x 10(-4) M cocaine) normalized cocaine-induced abnormalities in heart rhythm and provided protection from acute cocaine-induced morphological lesions. Using similar concentrations of NIT and cocaine, the purpose of this study was to evaluate the direct cardiac cellular effects of NIT on cocaine-induced alterations in beating activity, morphology, and lactate dehydrogenase (LDH) release in a controlled in vitro system of primary myocardial cell cultures. Cultures were established from hearts of 3-5-day-old Sprague-Dawley rats. After the cells had been maintained in culture for 4 days, evaluation of drug effects were made with exposure to 1 x 10(-3) and 1 x 10(-5) M cocaine alone and combinations of these two concentrations of cocaine with simultaneous exposure to 1 x 10(-7) M NIT for 1 to 24 h. Those cells exposed to 1 x 10(-5) M cocaine alone maintained some beating activity after 1, 4, and 24 h. Beating activity was significantly depressed after treatment with 1 x 10(-3) M cocaine alone and with both combinations of cocaine and NIT. Morphological integrity was maintained in all treatment groups for 1 h.(ABSTRACT TRUNCATED AT 250 WORDS)
    Journal of Pharmaceutical Sciences 08/1991; 80(7):700-4. · 3.13 Impact Factor
  • A A Welder, J F O'Dell, R B Melchert, J A Eselin
    [Show abstract] [Hide abstract]
    ABSTRACT: Since 1978, the most prevalent drug used in conjunction with cocaine in cocaine-associated myocardial deaths is ethanol. Primary myocardial cell cultures were used to evaluate the acute additive cardiotoxic effects of cocaine and ethanol. The cultures were exposed to 1 x 10(-3)m or 1 x 10(-5)m-cocaine or combinations of both concentrations of cocaine with 600 mg ethanol/100 ml. Alterations in beating activity, morphology, and lactate dehydrogenase (LDH) release were evaluated after 1, 4 and 24 hr of treatment. Although cells exposed to 1 x 10(-5)m-cocaine or to 1 x 10(-5)m-cocaine and ethanol were able to retain some beating activity, no beating activity occurred in cells exposed to 1 x 10(-3)m-cocaine with or without ethanol. Morphologically, pseudopodia and disruption of the monolayer were more extensive in cells treated for 4 or 24 hr with the combinations of cocaine and ethanol in comparison with those treated with cocaine alone. After 24 hr, LDH release in cells exposed to 1 x 10(-3)m-cocaine or 1 x 10(-3)m-cocaine with ethanol was elevated over the level in untreated controls. These data suggest that ethanol enhances cocaine-induced beating abnormalities and morphological alterations in primary myocardial cell cultures.
    Toxicology in Vitro 01/1991; 5(3):247-55. · 2.65 Impact Factor

Publication Stats

260 Citations
57.86 Total Impact Points

Institutions

  • 1991–2008
    • University of Oklahoma Health Sciences Center
      • College of Pharmacy
      Oklahoma City, OK, United States
  • 1998
    • University of Arkansas at Little Rock
      Little Rock, Arkansas, United States
  • 1995
    • Oklahoma City University
      Oklahoma City, Oklahoma, United States
  • 1992
    • ETH Zurich
      Zürich, Zurich, Switzerland