J. R. Snyman

Genetic polymorphism of CYP2D6 and CYP2C19 in East- and Southern African populations including psychiatric patients

Abstract. Objectives: The study was carried out to investigate the distribution of cytochrome P450 2D6 (CYP2D6) and CYP2C19 genotype frequencies in three African populations and to compare these frequencies between healthy individuals and psychiatric patients. Methods: Three hundred and eighty-four subjects from South Africa (Venda), Tanzania, and Zimbabwe who consented to the study were genotyped for CYP2D6 (CYP2D6*1, *2, *3, *4, *5, and *17) and CYP2C19 (CYP2C19*1, *2, and *3) by PCR-RFLP (polymerase chain reaction restriction fragment length polymorphism) techniques. Results: The genotypes for CYP2D6 predicted a poor metaboliser frequency of 2.3% (2/88) in Tanzanian psychiatric patients, 1.9% (2/106) in Tanzanian healthy controls and 2.6% (2/76) in the South African Venda. The low-activity CYP2D6*17 allele frequency was higher in psychiatric patients (30%, 53/176) than in healthy individuals (20%, 43/212) in Tanzanians. The frequencies for CYP2C19*2 genotypes were predictive of a low prevalence of poor metabolisers (PMs). The CYP2C19*3 allele was absent in the three populations studied. There was no difference in CYP2D6 or CYP2C19 PM genotype frequencies between psychiatric patients and healthy subjects. Conclusion: The genotype results predict a low prevalence of people with deficient CYP2D6 and CYP2C19 activity among linguistically (Bantu) related populations of East and Southern Africa. The high frequency of the low-activity CYP2D6*17 allele predicts that the Bantu people have a reduced capacity to metabolise drugs that are CYP2D6 substrates.

Genetic polymorphism of cytochrome P450 1A1 (Cyp1A1) and glutathione transferases (M1, T1 and P1) among Africans.

Abstract The co-ordinate expression and regulation of the drug metabolising enzymes, cytochrome P4501A1 (CYP1A1) and glutathione transferases (GSTM1, GSTT1 and GSTP1), and their metabolic balance in the cells of target organs may determine whether exposure to carcinogens results in cancer. Besides showing variability in activity due to induction and inhibition, these enzymes also exhibit genetic polymorphism that alter enzyme levels and activity. We determined frequencies of common allelic variants of CYP1A1 and glutathione (M1, T1 and P1) among Tanzanians, South African Venda and Zimbabweans using PCR/restriction fragment length polymorphism techniques. The CYP1A1 Val462 mutant variant was found at a frequency of 1.3% among 114 subjects. The GSTM1*0 genotype was found at a frequency of 29% and 33% among Tanzanian psychiatric patients and healthy volunteers, respectively. Similarly, the GSTT1*0 polymorphism was present with a frequency of 25% in both the psychiatric patients and healthy controls. The frequency of GSTP1 Val105 variant was 16%, 12% and 21% among Tanzanians, South African Venda and Zimbabweans, respectively. We conclude here that CYP1A1 Val462 polymorphism is very rare among Africans. This is the first report of the GSTP1 Val105 variant frequency in African populations. We show here that there are no differences in frequencies of the variant alleles for CYP1A1, GSTM1, GSTT1 and GSTP1 in the three African populations.

Arylamine N-acetyltransferase (NAT2) genotypes in Africans: the identification of a new allele with nucleotide changes 481C>T and 590G>A

This study was carried out to characterize the distribution of NAT2 allelic variants among a sample of three African populations. We determined the frequencies of major NAT2 allele clusters (NAT2*4, *6, *7 and *14) using PCR/restriction fragment length polymorphism and sequencing techniques. The genotypes predict slow acetylator phenotypes of 49, 38 and 52% among Tanzanians, Venda and Zimbabweans, respectively. The most common genotype was NAT2*4/*5. NAT2* 5 was the most common allele while NAT2* 7 was the least common. A new allele with two base changes occurring together, 481C>T and 590G>A, is reported. The frequency of the occurrence of the combination 481C>T and 590G>A, was found to be 9% (30/326), 7% (14/192) and 8% (18/234) among Zimbabweans, Venda and Tanzanians, respectively. The allele has been named NAT2*6E. Among Africans, the change 481C>T is not only associated with 341C>T (i.e. the NAT2* 5 allele cluster) as in other populations, but also with 590G>A on the same allele.

Effects of calcitriol on eosinophil activity and antibody responses in patients with schistosomiasis

AbstractObjective: Parasitic infestations are known to elicit T-helper lymphocyte type 2 (Th-2) reactions, characterized by a pronounced eosinophila and high IgE levels. In humans both elevated specific IgE levels and eosinophil counts are associated with resistance to reinfection with schistosomiasis. This study aimed to establish whether the Th-2 reaction could be enhanced with calcitriol (vitamin D3). Calcitriol has been shown to cause a shift from Th-1 to Th-2 type reactions when applied locally to the skin. Methods: Fifty-nine patients with Schistostomahaematobium infection were randomized to one of four treatment modalities, i.e. (a) praziquantel (PZQ) 60 mg · kg−1orally on day 1, (b) PZQ 60 mg · kg−1 on day 1 plus calcitriol 1 μg per day orally for 5 consecutive days, (c) calcitriol 1 μg per day for 5 consecutive days or (d) placebo. Blood for differential counts, eosinophil cationic protein (ECP), specific IgE and IgG to whole-worm antigen, as well as urine samples for egg counts, were collected on days 0 and 21. Results: Baseline values did not differ significantly between the groups. Calcitriol alone resulted in significant increases in circulating lymphocytes (median increase of 5.5%) and the percentage of eosinophil vacuolization (mean increase 28%). It, however, significantly decreased ECP levels (mean decrease 46%). PZQ in combination with calcitriol significantly enhanced production of specific IgE (mean increase 213%) and IgG (mean increase of 170%) and tended to increase eosinophil vacuolization (mean increase 22%). All these changes also differed significantly from those in the placebo group. The specific IgE and IgG levels were also significantly higher than the already increased levels seen with PZQ treatment only. ECP levels were, however, not significantly affected by combination therapy, whereas PZQ alone significantly enhanced ECP production (mean increase 93%). Conclusions: The increases in specific IgE responses and percentage of eosinophil vacuolization favour a Th-2 type of reaction. The ECP values viewed in isolation may, paradoxically, indicate a Th-1 response; this could, however, have been an artefact due to the method of ECP detection ex vivo. Finally, it would seem that calcitriol does cause some immune augmentation when combined with PZQ therapy in patients with schistosomiasis. However, long-term follow-up is needed to prove that these findings would translate into resistance against reinfection.

Effect of cetirizine, ketotifen and chlorpheniramine on the dynamics of the cutaneous hypersensitivity reaction: a comparative study.

SummaryAllergic cutaneous challenge causes mast cell and basophil mediator release which recruit inflammatory cells to the site of antigen administration. This secondary cell infiltration and mediator release is responsible for the changes seen during the late phase of allergic diseases.In this randomised, double-blind, cross-over, placebo controlled study, it was demonstrated that, at steady-state drug concentrations, chlorpheniramine reduced the wheal-and-flare reaction by about 50% compared to the 75% reduction, on average, by cetirizine and ketotifen. Cetirizine significantly reduced eosinophil vacuolisation at all observation periods, i. e. 2, 6, 10 and 24 h, and also inhibited basophil accumulation significantly at 10 h (75% reduction), while chlorpheniramine had a negligable effect on these variables.These changes would indicate that the late phase reaction was modified, especially as eosinophil vacuolisation is known to correlate with late phase intensity, T-lymphocyte infiltration and subsequent tissue damage. It further supports previous speculation that cetirizine inhibit late histamine release by acting on basophils. The extent of induration in the late phase reaction did not differ significantly among the three treatments.Cetirizine and ketotifen, noticeably although not significantly, reduced eosinophil and lymphocyte recruitment. As these two antihistamines differ structurally and in regard to receptor specificity, it is possible that they exert their actions on other, unspecified, receptors.

Evaluation of cisplatin and a novel platinum polymer conjugate for drug toxicity and drug distribution in mice

The toxicity and distribution of cisplatin and two novel platinum (Pt) polymer conjugates (Pt-6 and Pt-7) were determined in serum and tissue of BALB/c mice at specific time points after i.p. administration of a drug bolus containing identical Pt concentrations. Pt concentrations were determined in serum, liver and kidney at 5 and 15 min, respectively, after drug administration by inductively coupled plasma mass spectrometry. It was found that the Pt polymer Pt-7 gave rise to a considerably lower Pt concentration in serum and considerably higher concentration in liver and kidney than cisplatin. LD25 measurements indicated that the Pt-7 polymer is considerably less toxic than cisplatin. In vitro experiments and determination of IC50 values in a variety of human tumor cell lines, normal lymphocytes and fibroblasts confirmed that Pt-6 and Pt-7 polymers are 40–500 times more toxic for tumor cells than for normal cells, perhaps reflecting preferential uptake. The toxicity of cisplatin was found to be only 1.6–40 times more effective in tumor cells. These inter-relationships are supported by the observation that the tumor enrichment factor (TEF) for cisplatin is only in the region of 6, and much lower than for Pt-6 and Pt-7, where TEFs are in the region of 40 and 150, respectively. These results demonstrate that the Pt polymer conjugates exhibit greater tumor specificity than cisplatin, killing tumor cells more effectively while being considerably less toxic for normal cells. It is concluded that the Pt polymer conjugates may be superior for cancer therapy and warrant further testing to assess their full clinical potential.

Dexfenfluramine-induced prolactin release as an index of central synaptosomal 5-hydroxytryptamine during treatment with fluoxetine

Serotonin (5-HT) stimulates prolactin release. In the present study the ability of dexfenfluramine to increase serum prolactin was used as an index of central 5-HT function after acute and chronic pretreatment of volunteers with fluoxetine.Following a single-blind, random design, on each experimental day each volunteer received 60 mg dexfenfluramine taken with 250 ml water at zero time and no other treatment, or pretreatment with 40 mg fluoxetine at -8 h, or pretreatment with 20 mg fluoxetine daily for 14 days, or the dexfenfluramine alone 14 days after cessation of 14 days of fluoxetine treatment.There were no significant differences between the prolactin levels found after dexfenfluramine only, dexfenfluramine after a single dose of fluoxetine, and dexfenfluramine 14 days after cessation of fluoxetine treatment. However, baseline levels and those 3 and 4 h after dexfenfluramine administration were significantly lower after pretreatment for 14 days with fluoxetine compared to the other three regimens. At 5 h the levels were still lower, but not significantly so, as the prolactin level rose approximately 110% compared to the baseline and 4 h values.The reduction in the median basal serum prolactin level by almost two-thirds after 14 days of fluoxetine treatment suggests a decrease in 5-HT turnover. Furthermore, the delayed surge in prolactin release produced by dexfenfluramine with this regimen suggests 5-HT release from a less accessible pool or accumulation of fluoxetine in the neuronal cytosol and consequent competitive inhibition of 5-HT transport out of the nerve terminal.5-HT turnover is reduced in depression. The present results suggest similar impairment of central 5-HT function in normal volunteers treated with fluoxetine. Thus, rather than cause an increase in 5-HT turnover, anti-depressants may correct defects in the 5-HT system. We speculate that anti-depressant treatment which decrease 5-HT turnover may lead to disturbed aggression regulation and violent self-destructive impulses.

Hemoglobin glutamer‐250 (bovine) in South Africa: consensus usage guidelines from clinician experts who have treated patients

Hemopure (hemoglobin glutamer‐250 [bovine]; HBOC‐201) is a hemoglobin (Hb)‐based oxygen carrier registered with the Medicines Control Council of South Africa. It is indicated for the treatment of adult patients who are acutely anemic, for the purpose of maintaining tissue oxygen delivery thus eliminating, delaying, or reducing the need for allogeneic red blood cells (RBCs). Hemopure is a volume expander, and circulatory volume must be carefully monitored for signs of fluid overload. Hemopure is not as effective as RBCs for restoring Hb content and concentration, but in cases of severe anemia where allogeneic blood is not an option or is unavailable, it may offer an immediate alternative for improving oxygen transport. This document provides clinical recommendations on the safe and effective use of Hemopure based on the postmarketing experience in South Africa as well as a better understanding of Hemopure properties reflected in recent publications.

Generic versus non-generic formulation of extended-release clarithromycin in patients with community-acquired respiratory tract infections: a prospective, randomized, comparative, investigator-blind, multicentre study.

AbstractBackground and objective: There is a general concern about the use of multi-source (generic) antibacterials in the clinical setting with registration based solely on bioequivalence data. In order to address this concern, two modified-release formulations of clarithromycin (i.e. the originator Klacid XL® and the generic Klarithran MR®) were compared in patients with acute community-acquired respiratory tract infections. Methods: Patients presenting with tonsillopharyngitis, sinusitis or pneumonia were randomized to receive either of the test drugs provided they clinically qualified for empirical clarithromycin treatment. The study endpoints were clinical and bacteriological cure rates, tolerability and safety. The study was designed to test for non-inferiority with regard to cure rates. Results: The main outcome of this study was that both agents had similar clinical (non-inferior) and bacteriological cure rates and demonstrated no difference in tolerability in patients. The study also demonstrated the clinical efficacy of clarithromycin when used as empirical treatment in patients with respiratory tract infections in community practice (i.e. 95% clinical cure rate). Conclusion: The clarithromycin extended-release multisource product (Klarithran MR®) does not differ significantly from the originator (Klacid XL®) and the clinical cure rate of the generic formulation is non-inferior to that of the originator. The two formulations are tolerated similarly.

Effects of glycopyrrolate on capsaicin-induced cough in normal volunteers treated with captopril

The effects of inhibition of angiotensin converting enzyme (ACE) and glycopyrrolate on cough caused by inhaled capsaicin were investigated in a double-blind, randomised cross-over study in twelve normal volunteers. The capsaicin challenge was performed before and 2 h after dosing with 75 mg captopril or matched placebo given orally, and 20, 40 and 60 min after giving 1 mg glycopyrrolate IV to each subject.Captopril and placebo did not alter the cough response when compared to baseline. Glycopyrrolate, however, caused a significant increase in the threshold sensitivity (D2) from baseline, and a significant decrease in the total cough response at 40 and 60 min both after captopril and placebo. The D2-baseline and D2-40 min after glycopyrrolate (mean (SD), respectively, were 3.2 (1.0); 17.9 (4.2) after placebo and 2.5 (8.5); 23.6 (6.9) after captopril.Elimination of vagal influences implies attenuation of the effects of tachykinins but not those prostaglandins. We postulate that tachykinins, such as substance P, play a more important role than prostaglandins in capsaicin-induced cough.We conclude that the vagus is important in the capsaicin-induced cough reflex, but, as suppression of this reflex by glycopyrrolate was delayed, the relevant receptors are either poorly accessible peripheral receptors or they are located in the central nervous system.