Biological rhythms and medications: a source of variability often neglected in pharmacology

Several factors are known to induce changes in pharmacological response to drugs. The existence of biological rhythms is often neglected when assessing drug effects. Nevertheless, the best knowledge of biological rhythms have lead to medical applications, particularly chronopharmacology. Drug tolerance as well as drug effects are changing according to the hour of administration. These chronopharmacological phenomena may be explained by temporal changes in receptors drug binding or transductional effects, as well as pharmacokinetic variations in absorption, distribution, metabolism and elimination according to the moment of administration. Medical applications of such findings lead to choose the best moment of administration of the drug in order to improve the benefit/risk ratio.     

Chemistry and pharmacology of neglected helminthic diseases

Neglected helminthic diseases cause many social, economic and health care challenges in developing countries. The high number of patients suffering from these parasitic infections and the lack of sufficient treatment options represent severe problems. Research on new drugs and therapies to meet this urgent requirement has to be intensified. This review focuses on infections caused by four helminthic parasites, which have been declared as neglected diseases by the World Health Organization: namely drancunculiasis, lymphatic filariasis, onchoceriasis, and schistosomiasis. They show a considerable overlap in their world-wide prevalence and treatment strategies. Nevertheless, treatment is not without complications. The most efficient lymphatic filariasis drug, diethylcarbamazine, causes severe adverse effects in onchocerciasis patients and completely fails in the treatment of drancunculiasis. In this review, we discuss these incongruities at the molecular and cellular level. Furthermore, established or investigational drug combination regimens are highlighted. In the past years, progress has been made in the area of schistosomiasis and onchocerciasis. The molecular biology of underlying mechanisms, signalling pathways and related targets affected by drug therapy are discussed in detail. Finally, successful treatment strategies and remaining future challenges are summarized.     

Guanidino-containing drugs in cancer chemotherapy: biochemical and clinical pharmacology

The pharmacology and clinical application of three guanidino-containing compounds are reviewed in this commentary with special focus on a new member of this group of drugs, CHS 828 [N-(6-(4-chlorophenoxy)hexyl)-N'-cyano-N"-4-pyridylguanidine]. m-Iodobenzylguanidine (MIBG) and methylglyoxal bis(guanylhydrazone) (MGBG) have been extensively studied, preclinically as well as clinically, and have established use as anticancer agents. MIBG has structural similarities to the neurotransmitter, norepinephrine, and MGBG is a structural analog of the natural polyamine spermidine. CHS 828 is a pyridyl cyanoguanidine newly recognized as having cytotoxic effects when screening antihypertensive compounds. Apart from having the guanidino groups in common, there are many differences between these drugs in both structure and their mechanisms of action. However, they all inhibit mitochondrial function, a seemingly unique feature among chemotherapeutic drugs. In vitro in various cell lines and primary cultures of patient tumor cells and in vivo in various tumor models, CHS 828 has cytotoxic properties unlike any of the standard cytotoxic drugs with which it has been compared. Among these are non-cross-resistance to standard drugs and pronounced activity in tumor models acknowledged to be highly drug-resistant. Similar to MIBG, CHS 828 induces an early increase in extracellular acidification, due to stimulation of the glycolytic flux. Furthermore, ATP levels decrease, and the syntheses of DNA and protein are shut off after approximately 30 hr of exposure, indicating active cell death. CHS 828 is now in early clinical trials, the results of which are eagerly awaited.     

Disposition in rats and dogs of ciglitazone, a new antidiabetic agent

Oral 14C-ciglitazone was well absorbed by rats to give a maximum plasma level at two hours and an apparent half-life of 4.9 h. In dogs, the plasma level of the compound, after oral administration, reached a plateau at one hour, persisted till ten hours and then declined with a half-life of 23.5 h. In rats, plasma levels of metabolites were higher than those of unchanged ciglitazone, whereas the reverse was noted in dogs. Plasma metabolites were the monohydroxycyclohexyl derivatives (mono-ol) and monoketocyclohexyl derivatives (mono-oxo), together with other components consisting largely of dihydroxycyclohexyl derivatives (di-ol) and unknown polar metabolites. Metabolites found in rats were pharmacologically active trans-4'-ol, 3'-ol, 4'-oxo, cis-4'-ol, 3'-oxo and 2'-ol in the decreasing order listed, and those in dogs were 3'- and/or 4'-ols. Ciglitazone was highly bound to plasma protein of both animals. After oral administration of 14C-ciglitazone to rats, 14C was widely distributed in tissues, with the highest concn. in the gastrointestinal tract, followed by liver, adipose, plasma, adrenal gland, kidney, pancreas, spinal cord, heart and lung, and the lowest in the brain. The concn. of 14C in erythrocytes of rats and dogs was very low, as was the level of 14C in rat fetuses. Elimination of 14C-ciglitazone was complete within 96 h in rats and 144 h in dogs. In both animals, the dosed 14C was excreted largely in faeces as metabolites, with the remainder appearing in urine. Biliary excretion and reabsorption of 14C were obvious in rats. In both rats and dogs, the major metabolites found in faeces were 3'- and/or 4'-ols and other components derived from bile, and those in urine were other components. On repeated oral administration of 14C-ciglitazone to rats for seven days, no accumulation of 14C occurred in plasma and tissues, and 97.5% of the dose was eliminated from the body within 96 h after the last administration.     

Mitochondria in chronic liver disease

Mitochondria are the main energy source in hepatocytes and play a major role in extensive oxidative metabolism and normal function of the liver. This key role also assigns mitochondria a gateway function in the center of signaling pathways that mediate hepatocyte injury, because impaired mitochondrial functions affect cell survival and contribute to the onset and perpetuation of liver diseases. Altered mitochondrial functions have indeed been documented in a variety of chronic liver diseases including alcohol-induced liver disease, nonalcoholic fatty liver disease, viral hepatitis, primary and secondary cholestasis, hemochromatosis, and Wilson's disease. Major changes include impairment of the electron transport chain and/or oxidative phosphorylation leading to decreased oxidative metabolism of various substrates, decreased ATP synthesis, and reduced hepatocyte tolerance towards stressing insults. Functional impairment of mitochondria is often accompanied by structural changes, resulting in organelle swelling and formation of inclusion in the mitochondrial matrix. Adequate mitochondrial functions in hepatocytes are maintained by mitochondrial proliferation and/or increased activity of critical enzymes. The assessment of mitochondrial functions in vivo can be a useful tool in liver diseases for diagnostic and prognostic purposes, and also for the evaluation of (novel) therapeutic interventions.     

Rat-plasma metabolites of ciglitazone, a new antidiabetic agent

The rat-plasma metabolites of ciglitazone, a new antidiabetic agent, were characterized by g.l.c.-mass spectrometry as follows: the 2'-, cis-3'-, trans-3'-, cis-4'- and trans-4'-hydroxycyclohexyl derivatives, and 3'- and 4'-oxocyclohexyl derivatives. The 2'-hydroxycyclohexyl derivative contains cis- and/or trans-isomers (unresolved). Three other metabolites, which were postulated to be dihydroxy derivatives of ciglitazone, were also detected in the plasma. All monohydroxy and monoketo metabolites showed hypoglycaemic and hypotriglyceridemic activities in genetically obese-diabetic mice. These results suggest that the pharmacological activities of ciglitazone are due, at least partly, to the metabolites.     

VPAC receptors: structure, molecular pharmacology and interaction with accessory proteins

The vasoactive intestinal peptide (VIP) is a neuropeptide with wide distribution in both central and peripheral nervous systems, where it plays important regulatory role in many physiological processes. VIP displays a large biological functions including regulation of exocrine secretions, hormone release, fetal development, immune responses, etc. VIP appears to exert beneficial effect in neuro-degenerative and inflammatory diseases. The mechanism of action of VIP implicates two subtypes of receptors (VPAC1 and VPAC2), which are members of class B receptors belonging to the super-family of GPCR. This article reviews the current knowledge regarding the structure and molecular pharmacology of VPAC receptors. The structure-function relationship of VPAC1 receptor has been extensively studied, allowing to understand the molecular basis for receptor affinity, specificity, desensitization and coupling to adenylyl cyclase. Those studies have clearly demonstrated the crucial role of the N-terminal ectodomain (N-ted) of VPAC1 receptor in VIP recognition. By using different approaches including directed mutagenesis, photoaffinity labelling, NMR, molecular modelling and molecular dynamic simulation, it has been shown that the VIP molecule interacts with the N-ted of VPAC1 receptor, which is itself structured as a 'Sushi' domain. VPAC1 receptor also interacts with a few accessory proteins that play a role in cell signalling of receptors. Recent advances in the structural characterization of VPAC receptor and more generally of class B GPCRs will lead to the design of new molecules, which could have considerable interest for the treatment of inflammatory and neuro-degenerative diseases.     

Design, biochemical pharmacology, electrochemistry and tumour biology of anti-tumour anthrapyrazoles

Chromophore modification of the anthracenediones related to mitoxantrone in an attempt to provide agents with diminished or no cardiotoxicity has resulted in a novel class of DNA binders, the anthrapyrazoles. Selected biochemistry, electrochemistry and tumour biology were carried out for a series of compounds possessing the same upper and lower side chains but with varying A-ring hydroxylation patterns. The anthrapyrazoles bind strongly to DNA, are selective and potent inhibitors of DNA synthesis and cause the formation of single-strand breaks in DNA. They also induced far less (20-200-fold) superoxide dismutase-sensitive oxygen consumption than doxorubicin in the rat liver microsomal system, a property that may be indicative of reduced cardiotoxicity. This result is in accord with their polarographic properties in which the anthrapyrazoles show a much greater resistance to reduction (E'1/2 = -0.983- -1.085 V) relative to daunorubicin (E'1/2 = -0.625 V) and mitoxantrone (E'1/2 = -0.775 V). The anthrapyrazoles demonstrate high levels of activity against a broad range of murine tumours in vivo including the P388 leukaemia and mammary adenocarcinoma 16c lines detailed in this study.     

L-Dopa and imipramine: biochemical and behavioral interaction

The effects of L-dopa and its interaction with imipramine and chlorimipramine on rat behavior and brain amine levels were studied.     

Rabies, a neglected threat

Rabies is a viral infection causing about 55,000 deaths worldwide every year. However, the occurrence of rabies virus is neglected not only among people living in endemic areas, but especially among travellers. Furthermore, many persons are not aware of the fact that rabies is almost always lethal. Some of the indications for a prophylactic vaccination are travelling to rabies-endemic areas, contact with possibly contaminated tissues as well as working as a veterinarian. Besides prophylactic vaccination it is possible to have post-exposure treatment after a contact with animals or tissue suspect of being infected with rabies. It is important to only use new vaccines where the virus has been cultivated on cell culture because vaccines of earlier generations bear immense risks for health. Adequate information on danger of rabies infection should be given to travellers and persons potentially at risk.     

Primary monolayer culture of liver parenchymal cells and kidney cortical tubules as a useful new model for biochemical pharmacology and experimental toxicology

Freshly isolated liver parenchymal cells were maintained in either shortterm monolayer, suspension or long-term monolayer culture. Rapidly occurring processes through hepatocellular membrane, e.g., the enhanced amino acid transport and the concomitantly increased potassium influx following progressive starvation, were kinetically evaluated best in short-term monolayer culture. The inducibility of tyrosine aminotransferase by glucagon, dexamethasone, and a combination of both was compared in suspension and in monolayer culture. The induction of slowly inducible foreign compound-metabolizing enzymes, (e.g., ethoxycoumarin-O-dealkylase, p-nitroanisole-O-demethylase, and UDP-glucuronyltransferase) by phenobarbital, 3-methylcholanthrene, and dexamethasone were studied in long-term monolayer culture. The latter system was also used to maintain isolated kidney cortical tubules for the investigation of renal enzyme adaptation during progressive time in culture.Abbreviations Used AIB -aminoisobutyric acid - TAT tyrosine aminotransferase - EOD ethoxycoumarin-O-dealkylase - pNA-OD p-nitroanisole-O-demethylase - UDP-GT uridine diphosphate glucuronyltransferase - PDG phosphate-dependent glutaminase - LDH lactate dehydrogenase - GLDH glutamate dehydrogenase - Cyt. Ox cytochrome oxidase - Al. Phos alkaline phosphatase - -GT -glutamyltranspeptidase - DEX dexamethasone - GLN glucagon - PB phenobarbital - 3-MC 3-methylcholanthrene - FBS fetal bovine serum - TPB tryptose phosphate broth - SEM scanning electron micrograph - TEM transmission electron micrograph     

Bioavailability studies with ciglitazone in beagles. I. Effect of a meal on the bioavailability of three ciglitazone dosage forms

Three separate Latin square crossover studies were conducted in beagles to examine the effect of a meal on the bioavailability of a ciglitazone tablet, suspension, and solution. In these studies, drug was administered to fasted animals with either 50 ml water or with 180 g Purina Dog Chow and 20 g butter. The data indicated that the meal significantly increased the AUC by about 40 per cent for both the tablet and the suspension but had no significant effect on the solution treatment. Comparisons across studies indicated low bioavailability in fasted animals from either the tablet or suspension relative to the solution. When drug was co-administered with a meal, however, bioavailability appeared to be independent of dosage form.     

Phase 2 ventricular arrhythmias in acute myocardial infarction: a neglected target for therapeutic antiarrhythmic drug development and for safety pharmacology evaluation

Ventricular fibrillation (VF), a cause of sudden cardiac death (SCD) in the setting of acute myocardial infarction (MI), remains a major therapeutic challenge. In humans, VF may occur within minutes or hours after the onset of chest pain, so its precise timing in relation to the onset of ischaemia is variable. Moreover, because VF usually occurs unobserved, out of hospital, and is usually lethal in the absence of intervention, its precise timing of onset is actually unknown in most patients. In animal models, the timing of susceptibility to VF is much better characterised. It occurs in two distinct phases. Early VF (defined as phase 1 VF, with possible subphases 1a and 1b in some animal species) occurs during the first 30 min of ischaemia when most myocardial injury is still reversible. Late VF, defined as phase 2 VF, occurs when myocardial necrosis is becoming established (after more than 90 min of ischaemia). Although much is known about the mechanisms and pharmacology of phase 1 VF, little is known about phase 2 VF. By reviewing a range of different types of data we have outlined the likely mechanisms and clinical relevance of phase 2 VF, and have evaluated possible future directions to help evolve a strategy for its suppression by drugs. The possibility that a proarrhythmic effect on phase 2 VF contributes to the adverse cardiac effects of certain cardiac and noncardiac drugs is also discussed in relation to the emerging field of safety pharmacology. It is concluded that suppression of phase 2 as well as phase 1 VF will almost certainly be necessary if drugs of the future are to achieve what drugs of the past and present have failed to achieve: full protection against SCD. Likewise, safety will require avoidance of exacerbation of phase 2 as well as phase 1 VF.     

Toxocariasis: a neglected entity

Toxocara canis infects many dogs yet has been seldom implicated as a cause of human disease in New Zealand. Nine patients with diagnostic titres for Toxocara canis who were seen in Christchurch Hospital over a five-year period are described. Ophthalmoscopic signs of toxocaral infection were visible at the optic disc or posterior pole of all ten affected eyes. A localised disciform detachment of the macula or a focal granuloma on the disc or retina were the commonest lesions. Vision was reduced to 6/60 or less in five affected eyes while the remaining five eyes lost 2-4 lines of vision on the test chart.