Francis I. Achike

Nitric oxide, human diseases and the herbal products that affect the nitric oxide signalling pathway

1. Nitric oxide (NO) is formed enzymatically from l‐arginine in the presence of nitric oxide synthase (NOS). Nitric oxide is generated constitutively in endothelial cells via sheer stress and blood‐borne substances. Nitric oxide is also generated constitutively in neuronal cells and serves as a neurotransmitter and neuromodulator in non‐adrenergic, non‐cholinergic nerve endings. Furthermore, NO can also be formed via enzyme induction in many tissues in the presence of cytokines.

Obesity, metabolic syndrome, adipocytes and vascular function: A holistic viewpoint.

1. Obesity is a metabolic disease of pandemic proportions largely arising from positive energy balance, a consequence of sedentary lifestyle, conditioned by environmental and genetic factors. Several central and peripheral neurohumoral factors (the major ones being the anorectic adipokines leptin and adiponecin and the orexigenic gut hormone ghrelin) acting on the anorectic (pro‐opiomelanocortin and cocaine‐ and amphetamine‐regulated transcript) and orexigenic (neuropeptide Y and agouti gene‐related protein) neurons regulate energy balance. These neurons, mainly in the arcuate nucleus of the hypothalamus, project to parts of the brain modulating functions such as wakefulness, autonomic function and learning. A tilt in the anorectic–orexigenic balance, perhaps determined genetically, leads to obesity.

DIRECT EFFECTS OF QUERCETIN ON IMPAIRED REACTIVITY OF SPONTANEOUSLY HYPERTENSIVE RAT AORTAE: COMPARATIVE STUDY WITH ASCORBIC ACID

1 There is a growing interest in the anti‐oxidant characteristics and use of flavonoids in the management of cardiovascular diseases. The cardiovascular mechanism of action of these plant derivatives remains controversial. This study compared the effects of the flavonoid quercetin with those of the anti‐oxidant vitamin ascorbic acid (vitamin C) on the reactivity of aortic rings from spontaneously hypertensive rats (SHR). 2 The phenylephrine (PE)‐induced contractile and the endothelium‐dependent and independent relaxant responses of aortic rings from 21 to 22 week old SHR and age‐matched normotensive Wistar (WKY) rats were observed in the presence of quercetin or ascorbic acid. All the experiments were performed in the presence of the cyclooxygenase inhibitor, indomethacin (10 mmol/L). 3 The endothelium‐dependent and independent relaxations to acetylcholine (ACh) and sodium nitroprusside (SNP), respectively, were significantly lesser in the SHR compared to the WKY tissues whereas the contractile responses to PE were similar in both tissues. Pretreatment of WKY rings with quercetin or ascorbic acid had no effect on the responses to ACh or PE. In the SHR tissues, however, quercetin or ascorbic acid significantly improved the relaxation responses to ACh and reduced the contractions to PE with greater potency for quercetin. Both compounds lacked any effects on the responses to SNP in either aortic ring types. Nw‐nitro‐L‐arginine methyl ester (l‐NAME, 10 mmol/L) significantly attenuated the vasodepressor effects of quercetin and ascorbic acid, raising the responses to PE to a level similar to that observed in the control SHR tissues. In l‐NAME pretreated aortic rings, quercetin and ascorbic acid inhibited the contractile responses to PE with the same magnitude in WKY and SHR tissues. 4 The present results suggest that acute exposure to quercetin improves endothelium‐dependent relaxation and reduces the contractile responses of hypertensive aortae with a greater potency than ascorbic acid. This suggests a better vascular protection with this flavonoid than ascorbic acid in the SHR model of hypertension and possibly in human cardiovascular diseases.

Boldine protects endothelial function in hyperglycemia-induced oxidative stress through an antioxidant mechanism

Increased oxidative stress is involved in the pathogenesis and progression of diabetes. Antioxidants are therapeutically beneficial for oxidative stress-associated diseases. Boldine ([s]-2,9-dihydroxy-1,10-dimethoxyaporphine) is a major alkaloid present in the leaves and bark of the boldo tree (Peumus boldus Molina), with known an antioxidant activity. This study examined the protective effects of boldine against high glucose-induced oxidative stress in rat aortic endothelial cells (RAEC) and its mechanisms of vasoprotection related to diabetic endothelial dysfunction. In RAEC exposed to high glucose (30 mM) for 48 h, pre-treatment with boldine reduced the elevated ROS and nitrotyrosine formation, and preserved nitric oxide (NO) production. Pre-incubation with β-NAPDH reduced the acetylcholine-induced endothelium-dependent relaxation; this attenuation was reversed by boldine. Compared with control, endothelium-dependent relaxation in the aortas of streptozotocin (STZ)-treated diabetic rats was significantly improved by both acute (1 μM, 30 min) and chronic (20mg/kg/daily, i.p., 7 days) treatment with boldine. Intracellular superoxide and peroxynitrite formation measured by DHE fluorescence or chemiluminescence assay were higher in sections of aortic rings from diabetic rats compared with control. Chronic boldine treatment normalized ROS over-production in the diabetic group and this correlated with reduction of NAD(P)H oxidase subunits, NOX2 and p47(phox). The present study shows that boldine reversed the increased ROS formation in high glucose-treated endothelial cells and restored endothelial function in STZ-induced diabetes by inhibiting oxidative stress and thus increasing NO bioavailability.

Promoting problem-based learning (PBL) in nursing education: A Malaysian experience

Since the introduction of problem-based learning (PBL) into medical education in the late 1960s, several new and old medical schools have adopted this approach the main attraction of which includes the promotion of student-centered and life-long learning, team spirit, communication skills and enquiry. With an ever-increasing information base and changing attitudes in the health sciences, these are highly desirable characteristics of the health worker of the future, who will be required to grapple with these phenomenal changes. From medical education, the PBL approach has inevitably spread to other disciplines, especially the health-related disciplines. In the Asia-pacific region (Malaysia in particular), PBL was introduced into medical education in the early 1970s, but the growth has been slow; the reasons are discussed. Only recently (in the 1990s) have more medical and non-medical schools started to adopt PBL. The management of the Pantai Institute of Health Science and Nursing decided to adopt PBL for the Nursing curriculum. A one-day introductory workshop was, therefore, organized to expedite the process. Post-workshop feedback obtained through a five-point Likert scale questionnaire indicated a successful outcome. The workshop process is, therefore, documented as reference especially for Nursing colleges in places where PBL expertise is in short supply.

Effect of des-aspartate-angiotensin I on the actions of angiotensin II in the isolated renal and mesenteric vasculature of hypertensive and STZ-induced diabetic rats.

The present study investigated the action of des-aspartate-angiotensin I (DAA-I) on the pressor action of angiotensin II in the renal and mesenteric vasculature of WKY, SHR and streptozotocin (STZ)-induced diabetic rats. Angiotensin II-induced a dose-dependent pressor response in the renal vasculature. Compared to the WKY, the pressor response was enhanced in the SHR and reduced in the STZ-induced diabetic rat. DAA-I attenuated the angiotensin II pressor action in renal vasculature of WKY and SHR. The attenuation was observed for DAA-I concentration as low as 10(-18) M and was more prominent in SHR. However, the ability of DAA-I to reduce angiotensin II response was lost in the STZ-induced diabetic kidney. Instead, enhancement of angiotensin II pressor response was seen at the lower doses of the octapeptide. The effect of DAA-I was not inhibited by PD123319, an AT2 receptor antagonist, and indomethacin, a cyclo-oxygenase inhibitor in both WKY and SHR, indicating that its action was not mediated by angiotensin AT2 receptor and prostaglandins. The pressor responses to angiotensin II in mesenteric vascular bed were also dose-dependent but smaller in magnitude compared to the renal vasculature. The responses were significantly smaller in SHR but no significant difference was observed between STZ-induced diabetic and WKY rat. Similarly, PD123319 and indomethacin had no effect on the action of DAA-I. The findings reiterate a regulatory role for DAA-I in vascular bed of the kidney and mesentery. By being active at circulating level, DAA-I subserves a physiological role. This function appears to be present in animals with diseased state of hypertension and diabetes. It is likely that DAA-I functions are modified to accommodate the ongoing vascular remodeling.

The aporphine alkaloid boldine improves endothelial function in spontaneously hypertensive rats

Boldine, a major aporphine alkaloid found in Chilean boldo tree, is a potent antioxidant. Oxidative stress plays a detrimental role in the pathogenesis of endothelial dysfunction in hypertension. In the present study, we investigated the effects of boldine on endothelial dysfunction in hypertension using spontaneously hypertensive rats (SHR), the most studied animal model of hypertension. SHR and their age-matched normotensive Wistar-Kyoto (WKY) rats were treated with boldine (20 mg/kg per day) or its vehicle, which served as control, for seven days. Control SHR displayed higher systolic blood pressure (SBP), reduced endothelium-dependent aortic relaxation to acetylcholine (ACh), marginally attenuated endothelium-independent aortic relaxation to sodium nitroprusside (SNP), increased aortic superoxide and peroxynitrite production, and enhanced p47phox protein expression as compared with control WKY rats. Boldine treatment significantly lowered SBP in SHR but not in WKY. Boldine treatment enhanced the maximal relaxation to ACh in SHR, but had no effect in WKY, whereas the sensitivity to ACh was increased in both SHR and WKY aortas. Boldine treatment enhanced sensitivity, but was without effect on maximal aortic relaxation responses, to SNP in both WKY and SHR aortas. In addition, boldine treatment lowered aortic superoxide and peroxynitrite production and downregulated p47phox protein expression in SHR aortas, but had no effect in the WKY control. These results show that boldine treatment exerts endothelial protective effects in hypertension, achieved, at least in part, through the inhibition of NADPH-mediated superoxide production.

Effect of acidosis on the mechanism(s) of insulin-induced vasorelaxation in normal Wistar-Kyoto (WKY) rat aorta

The effect of acidosis on insulin-induced relaxation was studied in thoracic aortic rings (from Wistar-Kyoto (WKY) rats) with (+ED) or without (-ED) endothelium. The rings were mounted in normal (pH 7.4) or acidotic (pH 7.2) Krebs solution for isometric tension recording. Phenylephrine (PE, 3.0 microM)-contracted tissues were exposed to insulin in the presence or absence of various inhibitors. Insulin exerted similar concentration-dependent relaxation of +ED tissues in normal and acidotic pH. Endothelium denudation, significantly (p<0.05) reduced insulin effect in normal, but not acidotic pH. Under normal pH, treatment with L-NAME or methylene blue significantly (p<0.05) reduced insulin responses in the +ED (but not the -ED) tissues. The insulin effect was also significantly (p<0.05) inhibited by tetraethylammonium (TEA; BK(Ca) blocker), 4-Aminopyridine (4-AP; K(V) channel blocker), combined treatments (L-NAME+4-AP+TEA, in +ED tissues) or (4-AP+TEA, in -ED tissues). In either +ED or -ED tissues, indomethacin (cyclo-oxygenase inhibitor), glibenclamide (K(ATP) channel blocker), barium chloride (K(ir) channel blocker) or Ouabain (a Na(+)/K(+)-ATPase inhibitor) had no effect. Except for methylene blue (effect on +ED tissues), none of the drug treatments inhibited insulin vasodilator effect in acidosis (+ED or -ED tissues). These data indicate that insulin exerts an endothelium-dependent and -independent vasodilatation in rat aorta which in normal pH is mediated via BK(Ca) and K(v) channels, including the EDNO-cGMP cascade. Acidosis abolishes the endothelium-dependent relaxation mechanism unraveling a novel mechanism that is as efficacious and is cGMP-, but not EDNO-, BK(Ca)- or K(v)-mediated.

Teaching Pharmacology in an Innovative Medical Curriculum: Challenges of Integration, Technology, and Future Training

The Flexner report of 1910 set the stage for significant improvements in the growth and development of the individual subject disciplines that made up medicine. Aided by the chip technology in the latter half of the century, research grew without bounds and with it the individual disciplines and the body of knowledge required from each to produce the composite, fit-to-practice medical doctor. This posed serious challenges with regards to accommodating the ever-increasing knowledge base within the fixed timeframe for training the medical doctor. This scenario has been described by many medical educationalists in very impressionable terms. Guilbert describes “curriculopathy” as a syndrome that arises from the failure of the curriculum to catch up with factors that influence training, such as the increasing body of knowledge, lack of relevance, predominance of basic and biological sciences, faculty attitude to teaching, cost, and the organization of the delivery of medical education. These challenges largely constitute the forces that gave birth to innovative medical curricula, classical among which is the problem-based learning (PBL) paradigm that was developed in McMaster, Canada, in the mid-1960s. With increasing awareness in medical education, other curricular notions have since emerged, including the hybrid PBL curriculum, outcome-based curriculum, concept-based learning, case-based learning, and task-based learning. A critical analysis of these educational philosophies reveals a significant overlap of concepts with most (if not all) deriving largely from or are basically variants of the PBL philosophy, or what we choose to describe as the “metoo curriculum.” The undisputable common goal of innovative curricula is the training of a tomorrow’s doctor who enters medical practice with a holistic mind-set achieved through a curriculum regimen that emphasizes the horizontal and vertical integration of the basic and clinical sciences, respectively, while promoting lifelong learning skills through self-directed learning. Innovative curricula also emphasize the application of information and communication technology (ICT) in the teaching-learning process, with ICT being, perhaps, the main engine that drives information growth and access. It is our experience, however, that the implementation of these essential elements (integration and use of ICT) of innovation paradoxically portends challenges to the teaching/learning of pharmacology and its growth/ development. These are challenges that all teachers of pharmacology and curriculum managers should be aware of. In this editorial exploring these challenges in the innovative (PBL) curriculum, we focus on the challenges of integration in the teaching of pharmacology, the challenges of ICT in the teaching of pharmacology, and the challenges of training tomorrow’s pharmacologist.

Exploring the mechanism of endothelial involvement in acidosis-induced vasodilatation of aortic tissues from normal and diabetic rats.

Acidosis modulates physiologic and pathophysiologic processes but the mechanism of acidotic vasodilatation remains unclear. We therefore explored this in aortic rings from normal and streptozotocin-induced diabetic Sprague-Dawley rats. Phenylephrine (PE)-induced contraction in endothelium-intact and -denuded rings were recorded under normal and acidotic pH with or without drug probes. Acidosis exerted a relaxant effect in endothelium-intact and -denuded euglycaemic and diabetic tissues. l-NAME or methylene blue partially inhibited acidotic relaxation in these endothelium-intact but not the -denuded tissues, with greater inhibition in the diabetic tissues, indicating that acidosis induces relaxation by endothelium-dependent and -independent mechanisms, the former being EDNO-cGMP mediated. Indomethacin had no effect on the tissues, indicating that cyclooxygenase products are neither involved in acidosis-induced vasodilatation nor in the modulation of phenylephrine-contraction. In euglycaemic tissues under normal pH, no K(+) channel blocker altered phenylephrine-contraction, but all (except glibenclamide) enhanced diabetic tissue contraction, indicating that normally, these channels (K(ir), K(V), BK(Ca), K(ATP)) do not modulate phenylephrine-contraction, but they (except K(ATP)) are expressed in diabetes where they attenuate phenylephine-induced contraction and modulate acidosis. Only the K(ir) channel modulates acidotic relaxation in euglycaemic tissues. Only tetraethylammonium and iberiotoxin enhanced phenylephrine-induced contraction in endothelium-denuded diabetic tissues indicating that BK(Ca) attenuates phenylephrine-contraction and that acidotic relaxation in this condition is modulated by a tetraethylammonium-sensitive mechanism. In conclusion, acidosis causes vasodilatation in normal and diabetic tissues via endothelium-dependent and -independent mechanisms differentially modulated by a combination of a NO-cGMP process and K(+) channels, some of which are dormant in the normal state but activated in diabetes mellitus.