Evaluation of USP apparatus 3 for dissolution testing of immediate-release products.
(49/527)
We sought to evaluate whether U.S. Pharmacopeia (USP) apparatus 3 can be used as an alternative to USP apparatus 2 for dissolution testing of immediate-release (IR) dosage forms. Highly soluble drugs, metoprolol and ranitidine, and poorly soluble drugs, acyclovir and furosemide, were chosen as model drugs. The dissolution profiles of both innovator and generic IR products were determined using USP apparatus 2 at 50 rpm and apparatus 3 at 5, 15, and 25 dips per minute (dpm). The dissolution profiles from USP apparatus 3 were compared to those from USP apparatus 2 using the f(2) similarity test. The dissolution profile from USP apparatus 3 generally depends on the agitation rate, with a faster agitation rate producing a faster dissolution rate. It was found that USP apparatus 3 at the extreme low end of the possible agitation range, such as 5 dpm, gave hydrodynamic conditions equivalent to USP apparatus 2 at 50 rpm. With appropriate agitation rate, USP apparatus 3 can produce similar dissolution profiles to USP apparatus 2 or distinguish dissolution characteristics for the IR products of metoprolol, ranitidine, and acyclovir. Incomplete dissolution was observed for the furosemide tablets using USP apparatus 3. Although it is primarily designed for the release testing of extended-release products, USP apparatus 3 may be used for the dissolution testing of IR products of highly soluble drugs, such as metoprolol and ranitidine, and some IR products of poorly soluble drugs, such as acyclovir. USP apparatus 3 offers the advantages of avoiding cone formation and mimicking the changes in physiochemical conditions and mechanical forces experienced by products in the gastrointestinal tract. (+info)
Losartan reduces central and peripheral sympathetic nerve activity in a rat model of neurogenic hypertension.
(50/527)
We have developed a new model of neurogenic hypertension in the rat, in which hypertension is caused by injecting 50 microL of 10% phenol in the lower pole of one kidney. Administration of phenol in the kidney causes an immediate and persistent rise in blood pressure (BP), norepinephrine (NE) secretion from the posterior hypothalamic nuclei (PH), and renal sympathetic nerve activity (RSNA). Because angiotensin II (Ang II) is known to stimulate central and peripheral sympathetic nervous system (SNS) activity, we have tested the hypothesis that losartan, a specific Ang II AT1 receptor antagonist, may lower BP, at least in part, by SNS inhibition. To this end, we studied the effects of losartan on BP and SNS activity following intrarenal phenol injection. Central SNS activity was measured by NE secretion from the PH using a microdialysis technique, and peripheral SNS activity was measured by direct recording of renal nerve activity. At the end of the experiments, brains were isolated and interleukin (IL)-1beta and nitric oxide synthase (NOS) mRNA gene expression was measured by RT-PCR in the PH, paraventricular nuclei (PVN), and locus ceruleus (LC). The intrarenal injection of phenol raised BP, as well as central and renal SNS activity, but reduced the abundance of IL-1beta and neuronal NOS (nNOS) mRNA in the PH, PVN, and LC. Whether injected intravenously or in the lateral ventricle, losartan caused a significant (P<0.01) and dose-dependent inhibition of the effects of phenol on BP, NE secretion from the PH, and RSNA. Losartan also caused a significant (P<0.01) and dose-dependent rise in IL-1beta and nNOS-mRNA gene expression in the PH, PVN, and LC of phenol-injected rats. In conclusion, these studies have shown that the intrarenal injection of phenol causes a rise in central and renal SNS activity and a decrease in IL-1beta and nNOS-mRNA in the PH, PVN, and LC. Losartan prevented the rise in BP and SNS activity, as well as the decrease in IL-1beta and nNOS mRNA abundance caused by phenol. These studies have demonstrated that the antihypertensive action of losartan in the phenol renal injury model is largely mediated by inhibition of central and peripheral SNS activity and suggest that activation of IL-1beta and nNOS, 2 important modulators of central SNS activity, mediates the inhibitory action of losartan on SNS activity. (+info)
Increased dopamine receptor signaling and dopamine receptor-G protein coupling in denervated striatum.
(51/527)
Chronic interruption of the nigrostriatal dopaminergic pathway leads to sensitized dopaminergic responses in striatum. We attempted to explore the mechanism(s) underlying this dopaminergic supersensitivity by assessing dopamine receptor signaling and receptor-G protein coupling in unilateral 6-hydroxydopamine-lesioned rats. Dopamine-stimulated adenylyl cyclase activity as well as dopamine-activated guanosine 5'-O-(3-[(35)S]thiotriphosphate) ([(35)S]GTPgammaS) binding and [(3)H]palmitate incorporation by Galpha proteins were enhanced in tissues obtained from denervated striata without apparent changes in Galpha protein levels. Moreover, high-affinity binding sites of the D(1) dopamine receptor increased in lesioned compared with control striata without altering the expression level of the receptor. These denervation-mediated changes appear to correlate with the increase in D(1) dopamine receptor binding sites that co-immunoprecipitated with Galphas(olf)/q(11) proteins. In contrast, the total number of D(2) receptor binding sites was increased, yielding an increase in absolute number of high-affinity sites without significant changes in the proportion of high-affinity sites. Stimulation of the D(2) dopamine receptor enhanced coupling to Galphai protein; this was increased in the striata lesioned. The results provide an important molecular mechanism by which dopamine receptor-regulated signaling is enhanced following denervation of dopaminergic input to striatum. Although D(1) dopamine receptor supersensitivity appears to be mediated by enhanced coupling of the receptor to its G proteins, sensitization in the D(2) dopamine receptor system is mediated by increased D(2) receptor density and enhanced D(2) receptor-Gi protein coupling. (+info)
Early, selective, and marked loss of sympathetic nerves from the islets of BioBreeder diabetic rats.
(52/527)
To discover whether islet sympathetic nerves are damaged during the autoimmune destruction of islet B-cells, we immunostained sections of pancreas from BioBreeder (BB) diabetic rats, using antibodies against vesicular monoamine transporter 2 (VMAT2), a marker of sympathetic nerve terminals. We found a marked decrease in the VMAT2-positive fiber area in the islets of BB rats that had been diabetic for only 1-2 weeks compared with their nondiabetic controls. In contrast, there was no significant decrease in the VMAT2-positive fiber area in the exocrine pancreas in these early diabetic BB rats. Furthermore, streptozotocin-diabetic rats showed no decrease in VMAT2-positive fiber area in their islets compared with controls. The classical diabetic autonomic neuropathy (DAN) that eventually occurs in the heart was not present in BB diabetic rats at this early stage as evidenced by normal cardiac VMAT2 immunostaining and normal cardiac norepinephrine content. Also, in contrast to DAN, this islet neuropathy did not worsen with duration of diabetes. These data provide evidence of a heretofore unrecognized early sympathetic islet neuropathy (eSIN). Because eSIN occurs selectively in the islet, is rapid in onset, and is associated with autoimmune but not chemically induced diabetes, it is distinct from DAN in location, time course, and mechanism. (+info)
Managing nicotine addiction.
(53/527)
Nicotine addiction has been identified as the primary contributor to continued widespread tobacco use worldwide. Although the health benefits of smoking cessation are well publicized, few smokers successfully quit on a long-term basis. A number of pharmacological agents have been shown to approximately double long-term smoking cessation rates and have, therefore, been recommended as first-line therapy for the treatment of nicotine dependence in the clinical practice guidelines recently released by the Agency for Healthcare Research and Quality (AHRQ). These include the currently available dosage forms of nicotine replacement therapy (gum, patch, nasal spray, and inhaler) and bupropion. Other agents that have exhibited some efficacy in increasing smoking cessation rates are nortriptyline and clonidine. All pharmacological treatments are most effective in conjunction with behavioral therapy. Other approaches to treating tobacco use disorder now being investigated include additional ways to administer nicotine, a vaccine to prevent nicotine from crossing the blood-brain barrier, and agents that alter the metabolism of nicotine. This review summarizes the characteristics of nicotine addiction, reviews the pharmacological agents currently used to treat tobacco use disorder, and describes possible approaches to treat nicotine dependence in the future. (+info)
Inhibition of protein tyrosine/mitogen-activated protein kinase phosphatase activity is associated with D2 dopamine receptor supersensitivity in a rat model of Parkinson's disease.
(54/527)
Previous work demonstrated that stimulation of D(2) dopamine receptors (D(2)DRs) in the unilaterally 6-hydroxydopamine (6-OHDA)-lesioned rat enhanced striatal extracellular signal-regulated kinase (ERK) activity ipsilateral to the lesion. The present work was designed to explore the mechanism underlying the activation of ERK in the denervated striatum. Stimulation of D(2)DR induced a 60% inhibition in protein tyrosine phosphatase (PTP) activity but not in PSP activity in lesioned striata. The D(2)DR antagonist spiperone blocked quinpirole-elicited PTP inhibition, and the D(1) receptor agonist 2,3,4,5-tetrahydro-7,8-dihydroxy-1-phenyl-1H-3-benzazepine (SKF38393) did not inhibit PTP activity, indicating that PTP inhibition is a specific effect mediated by stimulation of D(2)DR. We further discovered that striatal mitogen-activated protein kinase phosphatase (MKP), a protein phosphatase that is responsible for ERK dephosphorylation, is inhibited in response to D(2)DR stimulation in 6-OHDA-lesioned rats. More specifically, MKP1 was identified to be the isozyme affected by D(2)DR stimulation. In PC12 cells that express D(2)DR, quinpirole elicited no change in PTP or MKP activity, whereas ERK was activated by D(2) dopamine receptor stimulation. The results indicate that 6-OHDA-induced striatal denervation leads to abnormal coupling between D(2)DR and PTP/MKP pathway. Moreover, unilateral inhibition of striatal PTP by an intrastriatal injection of vanadate induced contralateral rotation in control rats in response to D(2)DR stimulation, thus mimicking the response observed in the unilateral 6-OHDA-lesioned rat. The results indicate that attenuation of the PTP/MKP pathway may be responsible for the development of D(2)DR supersensitivity. (+info)
Cytoplasmic aggregates of phosphorylated extracellular signal-regulated protein kinases in Lewy body diseases.
(55/527)
A better understanding of cellular mechanisms that occur in Parkinson's disease and related Lewy body diseases is essential for development of new therapies. We previously found that 6-hydroxydopamine (6-OHDA) elicits sustained extracellular signal-regulated kinase (ERK) activation that contributes to neuronal cell death in vitro. As subcellular localization of activated kinases affect accessibility to downstream targets, we examined spatial patterns of ERK phosphorylation in 6-OHDA-treated cells and in human postmortem tissues representing the full spectrum of Lewy body diseases. All diseased human cases exhibited striking granular cytoplasmic aggregates of phospho-ERK (P-ERK) in the substantia nigra (involving 28 +/- 2% of neurons), which were largely absent in control cases (0.3 +/- 0.3%). Double-labeling studies and examination of preclinical cases suggested that these P-ERK alterations could occur relatively early in the disease process. Development of granular cytoplasmic P-ERK staining in 6-OHDA-treated cells was blocked by neuroprotective doses of catalase, supporting a role for oxidants in eliciting neurotoxic patterns of ERK activation. Evidence of nuclear translocation was not observed in degenerating neurons. Moreover, granular cytoplasmic P-ERK was associated with alterations in the distribution of downstream targets such as P-RSK1, but not of P-Elk-1, suggesting functional diversion of ERK-signaling pathways in Lewy body diseases. (+info)
Endoplasmic reticulum stress and the unfolded protein response in cellular models of Parkinson's disease.
(56/527)
6-hydroxydopamine, 1-methyl-4-phenyl-pyridinium (MPP+), and rotenone cause the death of dopaminergic neurons in vitro and in vivo and are widely used to model Parkinson's disease. To identify regulated genes in such models, we performed serial analysis of gene expression on neuronal PC12 cells exposed to 6-hydroxydopamine. This revealed a striking increase in transcripts associated with the unfolded protein response. Immunoblotting confirmed phosphorylation of the key endoplasmic reticulum stress kinases IRE1alpha and PERK (PKR-like ER kinase) and induction of their downstream targets. There was a similar response to MPP+ and rotenone, but not to other apoptotic initiators. As evidence that endoplasmic reticulum stress contributes to neuronal death, sympathetic neurons from PERK null mice in which the capacity to respond to endoplasmic reticulum stress is compromised were more sensitive to 6-hydroxydopamine. Our findings, coupled with evidence from familial forms of Parkinson's disease, raise the possibility of widespread involvement of endoplasmic reticulum stress and the unfolded protein response in the pathophysiology of this disease. (+info)