An HPLC/RIA method for dynorphin A1-13 and its main metabolites in human blood

Dynorphins in Development and Disease: Implications for Cardiovascular Disease

It is well-established that cardiovascular disease continues to represent a growing health problem and significant effort has been made to elucidate the underlying mechanisms. In this review, we report on past and recent high impact publications in the field of intracrine network signaling, focusing specifically on opioids and their interrelation with key modulators of the cardiovascular system and the onset of related disease. We present an overview of studies outlining the scope of cardiovascular and cerebrovascular processes that are affected by opioids, including heart function, ischemia, reperfusion, and blood flow. Specific emphasis is placed on the importance of dynorphin molecules in cerebrovascular and cardiovascular regulation. Evidence suggests that excessive or insufficient dynorphin could make an important contribution to cardiovascular physiology, yet numerous paradoxical observations frequently impede a clear understanding of the role of dynorphin. Thus, we argue that dynorphin-mediated signaling events for which an immediate regulatory effect is disputed should not be dismissed as unimportant, as they may play a role in cross-talk with other signaling networks. Finally, we consider the most recent evidence on the role of dynorphin during cardiovascular-related inflammation and on the potential value of endogenous and exogenous inhibitors of kappa-opioid receptor, a major dynorphin A receptor, to limit or prevent cardiovascular disease and its related sequelae.

Induced dysregulation of ACE2 by SARS-CoV-2 plays a key role in COVID-19 severity

Severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2), the cause of COVID-19, is reported to increase the rate of mortality worldwide. COVID-19 is associated with acute respiratory symptoms as well as blood coagulation in the vessels (thrombosis), heart attack and stroke. Given the requirement of angiotensin converting enzyme 2 (ACE2) receptor for SARS-CoV-2 entry into host cells, here we discuss how the downregulation of ACE2 in the COVID-19 patients and virus-induced shift in ACE2 catalytic equilibrium, change the concentrations of substrates such as angiotensin II, apelin-13, dynorphin-13, and products such as angiotensin (1–7), angiotensin (1–9), apelin-12, dynorphin-12 in the human body. Substrates accumulation ultimately induces inflammation, angiogenesis, thrombosis, neuronal and tissue damage while diminished products lead to the loss of the anti-inflammatory, anti-thrombotic and anti-angiogenic responses. In this review, we focus on the viral-induced imbalance between ACE2 substrates and products which exacerbates the severity of COVID-19. Considering the roadmap, we propose multiple therapeutic strategies aiming to rebalance the products of ACE2 and to ameliorate the symptoms of the disease.

Electroosmotic sampling. Application to determination of ectopeptidase activity in organotypic hippocampal slice cultures

We hypothesize that peptide-containing solutions pulled through tissue should reveal the presence and activity of peptidases in the tissue. Using the natural zeta-potential in the organotypic hippocampal slice culture (OHSC), physiological fluids can be pulled through the tissue with an electric field. The hydrolysis of the peptides present in the fluid drawn through the tissue can be determined using capillary HPLC with electrochemical detection of the biuret complexes of the peptides following a postcolumn reaction. We have characterized this new sampling method by measuring the flow rate, examining the use of internal standards, and examining cell death caused by sampling. The sampling flow rate ranges from 60 to 150 nL/min with a 150 microm (ID) sampling capillary with an electric field (at the tip of the capillary) from 30 to 60 V/cm. Cell death can be negligible with controlled sampling conditions. Using this sampling approach, we have electroosmotically pulled Leu-enkephalin through OHSCs to identify ectopeptidase activity in the CA3 region. These studies show that a bestatin-sensitive aminopeptidase may be critical for the hydrolysis of exogenous Leu-enkephalin, a neuropeptide present in the CA3 region of OHSCs.

Site specific 1:1 opioid:albumin conjugate with in vitro activity and long in vivo duration

A site-specific 1:1 dynorphin A-(1-13)-NH(2) derivative conjugated specifically to Cys 34 on human serum albumin (CCI-1035) was shown to be an opioid receptor agonist in vitro and to be a long lasting antinociceptive agent when administered intravenously to mice as assessed by an acetic acid writhing assay. When 10 micromol/kg of CCI-1035 was administered to mice, rapid antinociception was observed within 5 min following intravenous bolus injection and was sustained beyond 8 h. Antinociceptive activity was absent in a heat induced pain model using a mouse tail-flick assay. This finding represents the first report of a 1:1 albumin opioid conjugate retaining potent in vivo activity equal to or greater than dynorphin A, accompanied by a dramatic extension in duration of action. This novel site-specific bioconjugation technology produces an agent that may be useful for peripheral pain therapy.

Analysis of leucine enkephalin by high-performance liquid chromatography using enzymatic derivatization by tyrosinase and electrochemical or fluorescence detection

Two tyrosine specific, HPLC methods with either electrochemical (HPLC-ED) or fluorescence (HPLC-FL) detection are described for leucine-enkephalin (LE) in cerebrospinal fluid (CSF). Both approaches involve the hydroxylation of the Tyr1-moiety of LE by mushroom tyrosinase. Production of a catechol permitted the selective clean-up of the analyte using boronate gels and produced species which were more readily oxidizable than the LE. The controlled oxidation of the catechol to corresponding chinones enabled the reaction with 1,2-diamino-1,2-diphenylethane (DPE) and subsequent quantification by HPLC-FL. The HPLC-ED and HPLC-FL yielded limits of detection for LE in CSF of 360 and 500 fmol per injection, respectively. Inter-day variability of calibration curve samples was lower than 20% for the HPLC-ED with slightly higher variability for the HPLC-FL assay.

Pharmacokinetics of intravenous dynorphin A(1-13) in opioid-naive and opioid-treated human volunteers

BACKGROUND

Dynorphin A(1-13) is a fragment of the endogenous opioid neuropeptide dynorphin A. Previous research suggested that intravenously administered dynorphin A(1-13) has the ability to modulate morphine-induced analgesia. We designed this study to characterize the disposition of intravenous dynorphin immunoreactivity in humans and to determine whether concomitant long-term opioid therapy influenced the pharmacokinetics or side-effects profile of dynorphin A(1-13).

METHODS

The study subjects comprised 20 volunteers divided into two groups of 10 each, stratified by dose (low dose, 250 micrograms/kg; high dose, 1000 micrograms/kg). There were four volunteers receiving long-term opioid therapy and six opioid-naive volunteers (nonopioid group) within each dosing group. Dynorphin A(1-13) was infused over 10 minutes, and arterial blood samples were drawn and assayed for dynorphin immunoreactivity. A population modeling approach was used to characterize the pharmacokinetics. Dynorphin effects on heart rate and arterial blood pressure were also studied.

RESULTS

The pharmacokinetics of dynorphin immunoreactivity were linear over the dose range studied and were best described by a three-compartment mammillary model whose parameters were volume 1, 5.0 L; volume 2, 0.80 L; volume 3, 12 L; clearance 1, 6.0 L/min; clearance 2, 0.054 L/min; and clearance 3, 0.044 L/min. Concomitant opioid medication did not affect the disposition of dynorphin immunoreactivity. Tachycardia and flushing were commonly observed side effects. The incidence of side effects was dose dependent and was not influenced by long-term opioid use.

CONCLUSIONS

Intravenously administered dynorphin A(1-13) is very rapidly metabolized, on the basis of the time course of immunoreactivity in the blood. Long-term opioid therapy did not influence either the pharmacokinetics or incidence of side effects.