Phosphatidylinositol-4-phosphate-5-kinase alpha deficiency alters dynamics of glucose-stimulated insulin release to improve glucohomeostasis and decrease obesity in mice

OBJECTIVE

Phosphatidylinositol-4-phosphate-5-kinase (PI4P5K) has been proposed to facilitate regulated exocytosis and specifically insulin secretion by generating phosphatidylinositol-4,5-bisphosphate (PIP₂). We sought to examine the role of the α isoform of PI4P5K in glucohomeostasis and insulin secretion.

RESEARCH DESIGN AND METHODS

The response of PI4P5Kα^−/− mice to glucose challenge and a type 2-like diabetes-inducing high-fat diet was examined in vivo. Glucose-stimulated responses and PI4P5Kα^−/− pancreatic islets and β-cells were characterized in culture.

RESULTS

We show that PI4P5Kα^−/− mice exhibit increased first-phase insulin release and improved glucose clearance, and resist high-fat diet-induced development of type 2-like diabetes and obesity. PI4P5Kα^−/− pancreatic islets cultured in vitro exhibited decreased numbers of insulin granules docked at the plasma membrane and released less insulin under quiescent conditions, but then secreted similar amounts of insulin on glucose stimulation. Stimulation-dependent PIP₂ depletion occurred on the plasma membrane of the PI4P5Kα^−/− pancreatic β-cells, accompanied by a near-total loss of cortical F-actin, which was already decreased in the PI4P5Kα^−/− β-cells under resting conditions.

CONCLUSIONS

Our findings suggest that PI4P5Kα plays a complex role in restricting insulin release from pancreatic β-cells through helping to maintain plasma membrane PIP₂ levels and integrity of the actin cytoskeleton under both basal and stimulatory conditions. The increased first-phase glucose-stimulated release of insulin observed on the normal diet may underlie the partial protection against the elevated serum glucose and obesity seen in type 2 diabetes-like model systems.Failure of pancreatic β-cells to release adequate amounts of insulin contributes to the onset of type 2 diabetes and obesity (1). Elevated serum glucose transported into pancreatic β-cells is metabolized to increase cytosolic ATP levels, which then promote closure of ATP-sensitive K⁺ (KATP) channels, causing membrane depolarization. Membrane depolarization triggers opening of L-type Ca²⁺ channels, influx of Ca²⁺, and exocytosis. The first phase of exocytosis entails fusion of primed insulin granules predocked at the plasma membrane (2). A second phase involving mobilization of distal insulin vesicles occurs after approximately 10 min (3), preceded by actin cytoskeletal reorganization (4–6) and generation of lipid second messengers (7,8). The majority of type 2 diabetes is only weakly associated with specific genetic defects and is characterized by inadequate release of insulin, in addition to insulin resistance exhibited by fat and muscle target cells. Prolonged stimulation of β-cells by elevated levels of glucose, such as is encountered in the typical western-style high-fat diet, eventually suffices to trigger changes in insulin secretion in many individuals with otherwise seemingly normal physiology and genetics.Lipid kinases and their phosphoinositide products play important roles in secretory vesicle trafficking (9). Type I phosphatidylinositol-4-phosphate-5-kinases (PI4P5Ks) α, β, and γ generate the signaling lipid phosphatidylinositol-4,5-bisphosphate (PIP₂). Elegant studies in neurons and neuroendocrine cells on the role of PI4P5Kγ (10,11) and PIP₂ (12–14) have revealed that PIP₂ generation at the plasma membrane is critical during regulated exocytosis. PIP₂ directly facilitates some types of Ca⁺⁺ signaling (15,16), recruits proteins that facilitate the fusion process (13,14), and is required for docked secretory vesicles to undergo priming to become part of the ready-releasable pool and then fuse into the plasma membrane (10,11). Although less well understood mechanistically, decreased levels of PIP₂ have also been shown to inhibit insulin secretion in pancreatic β-cell model systems (7,17–19).However, PIP₂ also carries out functions that potentially oppose regulated exocytosis (20). First, PIP₂ supports the open state of the KATP channel (21,22); thus, because it is ATP-driven closure of the KATP channel that triggers secretion, PIP₂ deficiency might be anticipated to decrease K⁺ efflux, triggering membrane depolarization and thus increasing Ca⁺⁺ currents, resulting in increased secretion (23–25). In support of this model, expression of a dominant-negative isoform of PI4P5K to lower levels of PIP₂ changes the responsiveness of mutant KATP channels with decreased ATP sensitivity. However, expression of the dominant-negative PI4P5K does not alter function of wild-type (WT) KATP channels, suggesting that under normal physiologic conditions, the level of PIP₂ on the plasma membrane is not high enough to strongly affect KATP channel activity (26). PIP₂ has also been suggested to restrain fusion of docked vesicles by inhibiting SNARE complex function (14,27), with the restraint being alleviated through sequestration of the PIP₂ by Syntaxin-1 (14) or Ca²⁺-triggered PIP₂ destruction (28).Taken together, the action of PIP₂ is complex, and both its synthesis and its turnover are required at different steps in the fusion process.Another function undertaken by PIP₂ is to promote assembly of actin filaments (F-actin) (29,30). F-actin at the periphery of the cell (cortical F-actin) has also been proposed to have both positive and negative regulatory functions in exocytosis. Cortical F-actin has been proposed to act as a barrier to block access of undocked secretory vesicles to the plasma membrane; consistent with this model, cortical F-actin is disassembled during regulatory exocytosis events (31), and pharmacologic agents that disassemble F-actin enhance movement of insulin granules to the plasma membrane and insulin release, whereas agents that stabilize the actin cytoskeleton decrease insulin release (4,18,32–34). F-actin may also affect SNARE complex function by binding to and inhibiting Syntaxin-4 function in a glucose stimulation-relieved manner (32,33). To further complicate matters, F-actin can also undertake a positive role in regulated exocytosis by mediating translocation of more internal secretory vesicles to the periphery, particularly in poorly granulated or recently degranulated cells (4,35). Thus, dynamic regulation of the actin cytoskeleton is also important in the progression of regulated exocytosis and can play positive or negative roles depending on the setting.Changes in PIP₂ and cortical F-actin can have positive and negative effects on the secretory process, making it difficult a priori to predict the outcomes of their physiologic and experimental manipulation. Critically, individual PI4P5K isoforms may generate subpools of PIP₂ that regulate distinct components of the fusion process. Deletion of PI4P5Kγ markedly decreases levels of PIP₂ at the plasma membrane in resting neurons and neuroendocrine cells, and inhibits secretion at the stage of vesicle priming and fusion without notable effect on the actin cytoskeleton (10,11). In contrast, deletion of PI4P5Kα increases mast cell degranulation triggered by cross-linking of the IgE receptor, accompanied by minor decreases in cellular PIP₂, but significantly increased levels of Ca²⁺ signaling and decreased levels of total F-actin (36). PI4P5Kα knockdown using RNAi has also been reported to alter Ca²⁺ signaling, disrupt F-actin, and affect insulin release in a pancreatic β-cell line (37).This report examines insulin secretion in PI4P5Kα^−/− mice and finds that first-phase insulin release is augmented, and on a high-fat diet, fasting and stimulated serum insulin levels are even more elevated, conferring faster glucose clearance and resistance to the development of obesity. In this setting, K⁺ and Ca⁺⁺ signaling is seemingly normal; in contrast, the determinative factor seems to be a dramatic stimulation-dependent loss of PIP₂ at the plasma membrane that leads to reorganization of the actin cytoskeleton resulting in a near-total loss of cortical F-actin and decreased numbers of insulin granules docked at the plasma membrane.     

Association between electrocardiographic left ventricular hypertrophy with strain pattern and left ventricular structure and function

BACKGROUND AND PURPOSE: Electrocardiographic left ventricular hypertrophy (LVH) with strain pattern has been documented as a marker for LVH. Its presence on the ECG of hypertensive patients is associated with poor prognosis. The study was carried out to assess the association of the electrocardiographic strain with left ventricular mass (LVM) and function in hypertensive Nigerians. MATERIAL AND METHODS: ECG as well as echocardiograms were performed in 64 hypertensive patients with ECG-LVH and strain pattern, 65 patients with ECG-LVH by Sokolow-Lyon (SL) voltage criteria and 62 normal controls. RESULTS: The study showed that electrocardiographic left ventricular (LV) strain pattern is associated with dilated left atrium, larger LV internal dimensions and greater absolute and indexed LVM in hypertensive Nigerians compared with ECG-LVH by SL voltage criteria alone or normal controls. CONCLUSION: The findings of this study support the fact that the ECG strain pattern is associated with increased LVM and an increased risk of developing abnormal LV geometry.     

Asymptomatic Urinary Tract Infection among Pregnant Women Receiving Ante-Natal Care in a Traditional Birth Home in Benin City,Nigeria

Background

A good proportion of pregnant women patronize traditional birth homes in Nigeria for ante-natal care. This study aimed at determining the prevalence, risk factors, and susceptibility profile of etiologic agents of urinary tract infection among ante-natal attendees in a traditional birth home in Benin City, Nigeria.

Methods

Clean-catch urine was collected from 220 pregnant women attending a traditional birth home in Benin City, Nigeria. Urine samples were processed, and microbial isolates identified using standard bacteriological procedures. A cross-sectional study design was used.

Results

The prevalence of urinary tract infection among pregnant women was 55.0%, significantly affected by parity and gestational age (P<0.05). Mixed infection was recorded among 13(10.7%) pregnant women, and was unaffected by maternal age, parity, gravidity, gestational age, and educational status. Irrespective of trimester Escherichia coli was the most prevalent etiologic agent of urinary tract infection, followed by Staphylococcus aureus. The flouroquinolones were the most effective antibacterial agents, while Sulphamethoxazole-trimetoprim, Amoxicillin, Nalidixic acid, and Nitrofurantoin had poor activity against uropathogens isolated.

Conclusions

The prevalence of urinary tract infection among pregnant women was 55.0% and significantly affected by gestational age and parity. The most prevalent etiologic agent observed was Escherichia coli. With the exception of the flouroquinolones, aminoglycoside, and Amoxicillin-cluvanate, the activity of other antibiotics used on uropathogens were poor. Health education of the traditional birth attendant and her clients by relevant intervention agencies is strongly advocated.     

Target-organ damage and cardiovascular complications in hypertensive Nigerian Yoruba adults: a cross-sectional study

Background

Hypertension is a major challenge to public health as it is frequently associated with sudden death due to the silent nature of the condition. By the time of diagnosis, some patients would have developed target-organ damage (TOD) and associated clinical conditions (ACC) due to low levels of detection, treatment and control. TOD and ACC are easy to evaluate in a primary healthcare (PHC) setting and offer valuable information for stratifying cardiovascular risks in the patient. The aim of this study was to evaluate the prevalence and correlates of TOD and established cardiovascular disease (CVD) in hypertensive Nigerian adults.

Methods

A cross-sectional study was conducted on 2 000 healthy Yoruba adults between 18 and 64 years who lived in a rural community in south-western Nigeria. Participants diagnosed to have hypertension were examined for TOD and ACC by the presence of electrocardiographically determined left ventricular hypertrophy (LVH), microalbuminuria or proteinuria, retinopathy, or history of myocardial infarction and stroke.

Results

A total of 415 hypertensive participants were examined and of these, 179 (43.1%) had evidence of TOD and 45 (10.8%) had established CVD. TOD was associated with significantly higher systolic (SBP) and diastolic blood pressure (DBP). The prevalence of LVH was 27.9%, atrial fibrillation 16.4%, microalbuminuria 12.3%, proteinuria 15.2%, hypertensive retinopathy 2.2%, stroke 6.3%, congestive heart failure (CHF) 4.6%, ischaemic heart disease 1.7%, and peripheral vascular disease 3.6%. Compared with those with normal blood pressure (BP), the multivariate adjusted odds ratios (95% confidence interval) of developing TOD was 3.61 (0.59–8.73) for those with newly diagnosed hypertension; 4.76 (1.30–13.06) for those with BP ≥ 180/110 mmHg; and 1.85 (0.74–8.59) for those with diabetes mellitus.

Conclusions

This study provides new data on TOD and its correlates in a nationally representative sample of hypertensive adults in Nigeria. In this low-resource setting, attempts should be made to detect hypertensive patients early within the community and manage them appropriately before irreversible organ damage and complications set in. The methods used in this study are simple and adaptable at the primary healthcare level for planning prevention and intervention programmes.     

Early diastolic functional abnormalities in normotensive offspring of Nigerian hypertensives

Background

Some studies have suggested that diastolic dysfunction precedes the clinical manifestation of hypertension. Whether changes in cardiac structure and function predate the clinical manifestation of hypertension later in life is now being investigated. The aim of this study was to assess the differences in cardiac structure and function between the offspring of hypertensive and normotensive parents.

Methods

Eighty normotensive offspring of hypertensive parents (OHyp) (41 females and 39 males) and 62 normotensive offspring of normotensive parents (ONorm) (31 males and 31 females) were recruited for echocardiography.

Results

The mean age was 25.0 (5.31) and 24.3 (3.60) years in the OHyp and ONorm participants, respectively (p = 0.369). Other baseline parameters were comparable between the two groups. Septal wall thickness in systole was higher in the OHyp than the ONorm subjects [1.3 (0.35) vs 1.1 (0.25), p = 0.0173]. Indexed left ventricular mass [28.1 (7.33) vs 27.5 (7.23), p = 0.631] and relative wall thickness [(0.3 (0.10) vs 0.3 (0.90), p = 0.280] were similar in the two groups. The offspring of hypertensives had lower deceleration time [149.9 (38.89) vs 169.0 (50.08) ms, p = 0.012], prolonged duration of pulmonary A reverse flow [113.5 (70.69) vs 81.7 (38.31) ms, p = 0.024], increased myocardial isovolumic relaxation time [173.4 (47.98) vs 156.1 (46.74) ms, p = 0.033] and a lower myocardial Em [0.2 (0.05) vs 0.3 (1.38), p = 0.037] and myocardial Em/Am ratio [1.6 (0.01) vs 2.1 (0.01), p = 0.019] than the offspring of normotensives.

Conclusion

This study showed that offspring of OHyp subjects had early diastolic functional abnormalities when compared with offspring of ONorm participants. Longitudinal studies are needed to determine the implications of this finding in this African population.     

Effects of Aqueous Extracts of Petals of Red and Green Hibiscus sabdariffa. on Plasma Lipid and Hematological Variables in Rats

Abstract

The effects of administrating aqueous extracts of the petals of red and green Hibiscus sabdariffa. (1.0 and 1.5 mg/kg body weight) on hematological and plasma lipid variables were examined in rats. Animals were randomly divided into group A (control), groups B and C (treated with 1.0 and 1.5 mg/kg body weight, respectively, of the extract of petals of red Hibiscus sabdariffa.), and groups D and E (treated with 1.0 and 1.5 mg/kg body weight, respectively, of the extract of petals of green Hibiscus sabdariffa.). The chronic administration of both extracts for 28 days resulted in significant decreases in the plasma total cholesterol levels at 1.5 mg/kg body weight (p < 0.05) while the extracts led to significant decreases in LDL-cholesterol levels at both 1.0 and 1.5 mg/kg body weight only (p < 0.05). In contrast, the administration of the extracts did not have any significant effect on HDL-cholesterol, triglycerides, hematocrit, hemoglobin, red blood cell count, white blood cell count, and platelet count values when compared with the controls (p > 0.05). These results indicate that the lowered plasma total cholesterol concentrations induced by aqueous extracts of either red or green Hibiscus sabdariffa. petals is strongly associated with decreased LDL-cholesterol concentrations. Thus, both extracts could exert similar cardiovascular protective effects.     

Acceptability and feasibility of medical abortion with mifepristone and misoprostol in Nigeria

Objective

To examine the acceptability and feasibility of medical abortion in Nigeria.

Methods

In total, 250 women who were eligible for legal pregnancy termination with a gestational age of up to 63 days since last menstrual period were enrolled in Benin City and Zaria between May 2005 and October 2006. Participants received 200 mg of oral mifepristone in the clinic and then took 400 μg of oral misoprostol 2 days later—choosing to either return to the clinic or take it at home. Women returned 2 weeks later for an assessment of abortion status.

Results

The vast majority (96.3%) of women had successful complete abortions. Ultrasound was used to determine outcome in less than one-third (28.9%) of participants. Most women (83.2%) took the misoprostol at home. Almost all (96.2%) participants were satisfied or very satisfied with the abortion method.

Conclusion

The introduction of medical abortion with mifepristone and misoprostol could greatly expand current method options and improve the quality of reproductive health care in Nigeria and other settings in which access to legal abortion services is limited.     

Cabenuva®: Differentiated service delivery and the community Pharmacists’ roles in achieving UNAIDS 2030 target in Nigeria

The approval of the novel long-acting HIV injection; Cabenuva®- Cabotegravir and Rilpivirine injectable formulation) and the recent call by the World Health Organization for promoting community-based ART management, underscore the remarkable progress towards meeting the Joint United Nations Programme on HIV/AIDS (UNAIDS) 95–95–95 targets by 2030.As the availability of antiretroviral therapy (ART) for the treatment of HIV/AIDS has increased in resource-limited settings, there has been a move to develop and implement alternative treatment delivery models such as Differentiated Service Delivery (DSD) in high prevalence countries to meet the global targets for HIV treatment while maintaining the quality of care. However, there is limited data on the involvement of community pharmacies in the delivery of ART within the community. Although, in western countries, several studies have documented the different roles community pharmacists can play in the management of HIV/AIDS. Community pharmacists are the most accessible and first points of health care for most clients. They are trusted, highly trained health care professionals. They should be incorporated and allowed to administer the Cabenuva® injection if the battle against the HIV pandemic is to be totally won. In this paper, we, therefore, aim to explore how the community pharmacist can be positioned in HIV service delivery regarding the administration of the Novel long-acting Cabenuva® injection formulation. It is therefore recommended that the Nigerian government embrace community pharmacy-led drug administration initiatives and embark on accredited training programmes for the profession in line with drug administration services. The government should also put in place necessary funding mechanisms for community pharmacists for the extra workload placed on them in administering injection drug formulation in their respective pharmacies.