James M. Ritter

Impaired endothelium-dependent vasodilation of forearm resistance vessels in hypercholesterolaemia

Endothelium-dependent vasodilation in response to acetylcholine is impaired in the coronary microvasculature of hypercholesterolaemic subjects. Outside the coronary circulation, however, it has been suggested that hypercholesterolaemia results in a functional abnormality of vascular smooth muscle rather than in endothelial dysfunction. We examined vasodilator responses to acetylcholine, methacholine, and the endothelium-independent vasodilator sodium nitroprusside in the forearm resistance vessels of 12 men with primary hypercholesterolaemia and 12 normocholesterolaemic male controls. Endothelium-dependent vasodilation in response to acetylcholine was impaired in hypercholesterolaemic patients compared with controls: at the highest dose of drug (15 micrograms per min) mean blood flow in the forearms of the hypercholesterolaemic group was only 52% (95% Cl 31-88%) of that in the control group. Responses to sodium nitroprusside and to methacholine in the two study groups were not significantly different. These results indicate that endothelial dysfunction in hypercholesterolaemic subjects is generalised and extends to vascular beds outside the coronary circulation. Selective impairment to acetylcholine suggests that, at a molecular level, the defect is limited to a specific pathway.

Effect of an RNA interference drug on the synthesis of proprotein convertase subtilisin/kexin type 9 (PCSK9) and the concentration of serum LDL cholesterol in healthy volunteers: a randomised, single-blind, placebo-controlled, phase 1 trial

BACKGROUND Proprotein convertase subtilisin/kexin type 9 (PCSK9) binds to LDL receptors, leading to their degradation. Genetics studies have shown that loss-of-function mutations in PCSK9 result in reduced plasma LDL cholesterol and decreased risk of coronary heart disease. We aimed to investigate the safety and efficacy of ALN-PCS, a small interfering RNA that inhibits PCSK9 synthesis, in healthy volunteers with raised cholesterol who were not on lipid-lowering treatment. METHODS We did a randomised, single-blind, placebo-controlled, phase 1 dose-escalation study in healthy adult volunteers with serum LDL cholesterol of 3·00 mmol/L or higher. Participants were randomly assigned in a 3:1 ratio by computer algorithm to receive one dose of intravenous ALN-PCS (with doses ranging from 0·015 to 0·400 mg/kg) or placebo. The primary endpoint was safety and tolerability of ALN-PCS. Secondary endpoints were the pharmacokinetic characteristics of ALN-PCS and its pharmacodynamic effects on PCSK9 and LDL cholesterol. Study participants were masked to treatment assignment. Analysis was per protocol and we used ANCOVA to analyse pharmacodynamic endpoint data. This trial is registered with ClinicalTrials.gov, number NCT01437059. FINDINGS Of 32 participants, 24 were randomly allocated to receive a single dose of ALN-PCS (0·015 mg/kg [n=3], 0·045 mg/kg [n=3], 0·090 mg/kg [n=3], 0·150 mg/kg [n=3], 0·250 mg/kg [n=6], or 0·400 mg/kg [n=6]) and eight to placebo. The proportions of patients affected by treatment-emergent adverse events were similar in the ALN-PCS and placebo groups (19 [79%] vs seven [88%]). ALN-PCS was rapidly distributed, with peak concentration and area under the curve (0 to last measurement) increasing in a roughly dose-proportional way across the dose range tested. In the group given 0·400 mg/kg of ALN-PCS, treatment resulted in a mean 70% reduction in circulating PCSK9 plasma protein (p<0·0001) and a mean 40% reduction in LDL cholesterol from baseline relative to placebo (p<0·0001). INTERPRETATION Our results suggest that inhibition of PCSK9 synthesis by RNA interference (RNAi) provides a potentially safe mechanism to reduce LDL cholesterol concentration in healthy individuals with raised cholesterol. These results support the further assessment of ALN-PCS in patients with hypercholesterolaemia, including those being treated with statins. This study is the first to show an RNAi drug being used to affect a clinically validated endpoint (ie, LDL cholesterol) in human beings. FUNDING Alnylam Pharmaceuticals.

Therapeutic Clearance of Amyloid by Antibodies to Serum Amyloid P Component

BACKGROUND The amyloid fibril deposits that cause systemic amyloidosis always contain the nonfibrillar normal plasma protein, serum amyloid P component (SAP). The drug (R)-1-[6-[(R)-2-carboxy-pyrrolidin-1-yl]-6-oxo-hexanoyl]pyrrolidine-2-carboxylic acid (CPHPC) efficiently depletes SAP from the plasma but leaves some SAP in amyloid deposits that can be specifically targeted by therapeutic IgG anti-SAP antibodies. In murine amyloid A type amyloidosis, the binding of these antibodies to the residual SAP in amyloid deposits activates complement and triggers the rapid clearance of amyloid by macrophage-derived multinucleated giant cells. METHODS We conducted an open-label, single-dose-escalation, phase 1 trial involving 15 patients with systemic amyloidosis. After first using CPHPC to deplete circulating SAP, we infused a fully humanized monoclonal IgG1 anti-SAP antibody. Patients with clinical evidence of cardiac involvement were not included for safety reasons. Organ function, inflammatory markers, and amyloid load were monitored. RESULTS There were no serious adverse events. Infusion reactions occurred in some of the initial recipients of larger doses of antibody; reactions were reduced by slowing the infusion rate for later patients. At 6 weeks, patients who had received a sufficient dose of antibody in relation to their amyloid load had decreased liver stiffness, as measured with the use of transient elastography. These patients also had improvements in liver function in association with a substantial reduction in hepatic amyloid load, as shown by means of SAP scintigraphy and measurement of extracellular volume by magnetic resonance imaging. A reduction in kidney amyloid load and shrinkage of an amyloid-laden lymph node were also observed. CONCLUSIONS Treatment with CPHPC followed by an anti-SAP antibody safely triggered clearance of amyloid deposits from the liver and some other tissues. (Funded by GlaxoSmithKline; ClinicalTrials.gov number, NCT01777243.).

Paradoxical effect of bicarbonate on cytoplasmic pH

The effect of an abrupt rise in bicarbonate concentration on cytoplasmic pH was studied in human platelets suspended in a Tyrodes buffer. Addition of bicarbonate raised extracellular pH but simultaneously caused pronounced cytoplasmic acidification. This effect may be due to combination of bicarbonate with hydrogen ions in extracellular fluid to form carbonic acid, which is converted by carbonic anhydrase to water and carbon dioxide. Bicarbonate ions do not diffuse rapidly across cell membranes, whereas carbon dioxide is highly diffusible and can combine with water in the cytoplasm, forming carbonic acid and reducing the intracellular pH. In accord with this explanation cytoplasmic acidification by bicarbonate was antagonised by acetazolamide (an inhibitor of carbonic anhydrase). Cytoplasmic acidification could contribute to adverse effects of intravenous sodium bicarbonate in patients with severe acidaemia. These findings add weight to the body of opinion that such treatment is both illogical and dangerous.

Thromboxane A2 receptor antagonism and synthase inhibition in essential hypertension.

Short-term effects of ridogrel, a combined thromboxane synthase inhibitor and receptor antagonist, were investigated in 16 patients with uncomplicated essential hypertension. After a 2-week placebo period without antihypertensive medication, patients were admitted to the hospital overnight on two occasions 3 weeks apart. On each occasion, they received two doses of either placebo or ridogrel (300 mg) 12 hours apart according to a double-blind crossover protocol. Renal and systemic thromboxane A2 and prostacyclin biosynthesis were investigated by measuring urinary excretion of thromboxane B2, 6-oxo-prostaglandin F1 alpha, and their respective 2,3-dinor metabolites using gas chromatography/mass spectrometry. Responses of platelets to a thromboxane A2 mimetic and to adenosine diphosphate were studied turbidometrically. Blood pressure was measured automatically at 20-minute intervals. Ridogrel reduced excretion of 2,3-dinor-thromboxane B2 and thromboxane B2 compared with placebo (21 +/- 6 versus 279 +/- 28 and 14 +/- 4 versus 39 +/- 9 ng/g creatinine, respectively; P < .0001 and P < .05). Excretion of 2,3-dinor-6-oxoprostaglandin F1 alpha and 6-oxoprostaglandin F1 alpha was increased by ridogrel compared with placebo (184 +/- 20 versus 146 +/- 11 and 86 +/- 9 versus 58 +/- 6 ng/g creatinine, respectively; P < .05). Ridogrel selectively antagonized platelet aggregation to the thromboxane mimetic (P < .0001). Blood pressure did not differ significantly between ridogrel and placebo treatment periods. Thus, in patients with essential hypertension, acute administration of ridogrel reduces renal and extrarenal thromboxane A2 biosynthesis, increases renal and extrarenal prostacyclin biosynthesis, inhibits thromboxane receptor-activated platelet aggregation, but has no effect on systemic arterial pressure.

Repeat doses of antibody to serum amyloid P component clear amyloid deposits in patients with systemic amyloidosis

Repeat cycles of miridesap, to deplete circulating serum amyloid P component (SAP), followed by the anti-SAP antibody, dezamizumab, cleared visceral amyloid deposits in patients with systemic amyloidosis. Making amyloid vanish Fatal systemic amyloidosis is caused by extracellular amyloid deposition that disrupts tissue structure and function. The normal plasma protein, serum amyloid P component (SAP), is always present within amyloid deposits. Richards et al. now show that previous depletion of circulating SAP by the drug, miridesap, uniquely enables subsequent administration of the humanized anti-SAP antibody, dezamizumab, to patients with systemic amyloidosis. Dezamizumab bound to residual SAP in the amyloid deposits and triggered their removal. Repeat cycles of miridesap followed by dezamizumab progressively removed amyloid from the liver, spleen, and kidneys of the patients. Evidence of clinical benefit suggests that this new approach has potential to improve management and outcome for patients with systemic amyloidosis. Systemic amyloidosis is a fatal disorder caused by pathological extracellular deposits of amyloid fibrils that are always coated with the normal plasma protein, serum amyloid P component (SAP). The small-molecule drug, miridesap, [(R)-1-[6-[(R)-2-carboxy-pyrrolidin-1-yl]-6-oxo-hexanoyl]pyrrolidine-2-carboxylic acid (CPHPC)] depletes circulating SAP but leaves some SAP in amyloid deposits. This residual SAP is a specific target for dezamizumab, a fully humanized monoclonal IgG1 anti-SAP antibody that triggers immunotherapeutic clearance of amyloid. We report the safety, pharmacokinetics, and dose-response effects of up to three cycles of miridesap followed by dezamizumab in 23 adult subjects with systemic amyloidosis (ClinicalTrials.gov identifier: NCT01777243). Amyloid load was measured scintigraphically by amyloid-specific radioligand binding of 123I-labeled SAP or of 99mTc-3,3-diphosphono-1,2-propanodicarboxylic acid. Organ extracellular volume was measured by equilibrium magnetic resonance imaging and liver stiffness by transient elastography. The treatment was well tolerated with the main adverse event being self-limiting early onset rashes after higher antibody doses related to whole body amyloid load. Progressive dose-related clearance of hepatic amyloid was associated with improved liver function tests. 123I-SAP scintigraphy confirmed amyloid removal from the spleen and kidneys. No adverse cardiac events attributable to the intervention occurred in the six subjects with cardiac amyloidosis. Amyloid load reduction by miridesap treatment followed by dezamizumab has the potential to improve management and outcome in systemic amyloidosis.

Responses to angiotensin with and without angiotensin-converting enzyme inhibition in the canine left anterior descending coronary artery

Abstract Angiotensin-converting enzyme (ACE) cleaves angiotensin I to generate the active vasoconstrictor angiotensin II. The pulmonary vascular bed is rich in ACE activity 1 and it was believed that the lung is the exclusive site of generation of angiotensin II. However, potent ACE activity has subsequently been demonstrated in other vascular beds. 2 Indeed, the fractional conversion of angiotensin I to angiotensin n across the human forearm (approximately 40%) 3 is similar to that across the lung. ACE is present on endothelial cells and may regulate local vascular responses to angiotensin I. Locally generated angiotensin II could function as a paracrine rather than an endocrine mechanism. This is a flexible and potentially important means of regulating regional blood flow since local generation could vary in different vascular beds, whereas systemic tissues are all exposed to the same circulating concentration of angiotensin II. Messenger ribonucleic acid for renin is present in the heart, 4 and local generation of angiotensin n in the coronary circulation could be of considerable functional importance. This study investigates effects of locally infused angiotensin I and II, with and without an ACE inhibitor, on canine coronary blood flow in vivo.

1974–2014: Reflections on the evolution of clinical pharmacology in the past 40 years and a message to our readers

In youth, each birthday is eagerly anticipated. By 30 some of the enthusiasm at another milestone may have worn a bit thin – though the British Journal of Clinical Pharmacology (BJCP) was in buoyant spirits [1]. Staid 40-year-olds are still less likely to be dropping not-so-subtle hints to their loved ones of the impending anniversary. However, BJCP eschews all such modesty and takes this opportunity to reflect briefly on our subject while glancing into the mirror. The first number of the Journal back in 1974 contained (among others) research articles on pharmacodynamics (PD), pharmacokinetics (PK), drug metabolism, therapeutics and analytical methodology. Now, as then, we consider papers on all aspects of drug action in man. How has this approach stood up to the challenges posed by the profound changes in biomedicine that have ensued over the intervening 40 years? These changes include revolutions in intellectual approach and theory as much as dizzying practical advances that have occurred in some areas of therapeutics.