Methionyl-lysyl-bradykinin, a new kinin from ox blood

Metabolically stable bradykinin B2 receptor agonists enhance transvascular drug delivery into malignant brain tumors by increasing drug half-life

BACKGROUND

The intravenous co-infusion of labradimil, a metabolically stable bradykinin B2 receptor agonist, has been shown to temporarily enhance the transvascular delivery of small chemotherapy drugs, such as carboplatin, across the blood-brain tumor barrier. It has been thought that the primary mechanism by which labradimil does so is by acting selectively on tumor microvasculature to increase the local transvascular flow rate across the blood-brain tumor barrier. This mechanism of action does not explain why, in the clinical setting, carboplatin dosing based on patient renal function over-estimates the carboplatin dose required for target carboplatin exposure. In this study we investigated the systemic actions of labradimil, as well as other bradykinin B2 receptor agonists with a range of metabolic stabilities, in context of the local actions of the respective B2 receptor agonists on the blood-brain tumor barrier of rodent malignant gliomas.

METHODS

Using dynamic contrast-enhanced MRI, the pharmacokinetics of gadolinium-diethyltriaminepentaacetic acid (Gd-DTPA), a small MRI contrast agent, were imaged in rodents bearing orthotopic RG-2 malignant gliomas. Baseline blood and brain tumor tissue pharmacokinetics were imaged with the 1st bolus of Gd-DTPA over the first hour, and then re-imaged with a 2nd bolus of Gd-DTPA over the second hour, during which normal saline or a bradykinin B2 receptor agonist was infused intravenously for 15 minutes. Changes in mean arterial blood pressure were recorded. Imaging data was analyzed using both qualitative and quantitative methods.

RESULTS

The decrease in systemic blood pressure correlated with the known metabolic stability of the bradykinin B2 receptor agonist infused. Metabolically stable bradykinin B2 agonists, methionine-lysine-bradykinin and labradimil, had differential effects on the transvascular flow rate of Gd-DTPA across the blood-brain tumor barrier. Both methionine-lysine-bradykinin and labradimil increased the blood half-life of Gd-DTPA sufficiently enough to increase significantly the tumor tissue Gd-DTPA area under the time-concentration curve.

CONCLUSION

Metabolically stable bradykinin B2 receptor agonists, methionine-lysine-bradykinin and labradimil, enhance the transvascular delivery of small chemotherapy drugs across the BBTB of malignant gliomas by increasing the blood half-life of the co-infused drug. The selectivity of the increase in drug delivery into the malignant glioma tissue, but not into normal brain tissue or skeletal muscle tissue, is due to the inherent porous nature of the BBTB of malignant glioma microvasculature.

Met-Lys-bradykinin-Ser, the kinin released from human kininogen by human pepsin

This study was carried out to show the site in kininogen, using synthetic substrates, that is cleaved by a purified human pepsin component with a molecular weight of 35,000 daltons. The study used 4 (four) intramolecularly quenched fluorogenic substrates containing N- and C-terminal sequences around the methionyl-lysyl-bradykinin (MLBK) region of kininogen: Abz-LMKRP-Eddnp, Abz-MISLMKRP-Eddnp, Abz-FRSSR-Eddnp and Abz-RPPGFSPFRSSRQ-Eddnp. The hydrolysis on N-terminal sequences Abz-LMKRP-Eddnp and Abz-MISLMKRP-EDDnp occurred at L-M linkage and on C-terminal sequences Abz-FRSSR-Eddnp, and Abz-RPPGFSPFRSSRQ-Eddnp occurred at S-S linkage. The released peptide Abz-RPPGFSPFRS was able to contract rat uterus muscle. The results suggest that Met-Lys-Bradykinin-Ser, should be the peptide released from human kininogen by a purified human pepsin component.

Kinins are generated in vivo following nasal airway challenge of allergic individuals with allergen

Using a recently developed model of nasal challenge, we have obtained data that clearly demonstrate, for the first time, kinin generation during a local allergic reaction in vivo. Allergic individuals (n = 8) and matched nonallergic controls (n = 8) were challenged intranasally with the appropriate antigen and nasal washes were taken before and after challenge. Washes were assayed for kinin, histamine, and [3H]-N-alpha-tosyl-L-arginine methyl ester (TAME)-esterase activity. Increased kinin generation was found by radioimmunoassay (RIA) in the nasal washes of all the allergics (5,560 +/- 1,670 pg/ml) but in none of the controls (38 +/- 16 pg/ml). The presence of kinin was highly correlated with that of histamine and TAME-esterase activity and with the onset of clinical symptoms (P less than 0.001). Serial dilutions of nasal washes produced RIA displacement curves that paralleled the standard curve, and recovery of standard kinins that were added to nasal washes was 100 +/- 4% (n = 14). Kinin recovery was identical in both allergics and controls and did not vary significantly with antigen challenge. The immunoreactive kinin in nasal washes was stable to boiling and not precipitated by ethanol, but completely destroyed by carboxypeptidase B. It was evenly distributed between the sol and gel phases of nasal washes. High performance liquid chromatography analysis of the immunoreactive kinin in nasal washes showed it to be a mixture of lysylbradykinin and bradykinin. We conclude that kinins are produced during local allergic reactions in the nose and may contribute to the symptomatology of the allergic response.

Isotachophoretic analysis of peptides

Operating conditions for the qualitative and quantitative determination of plasma kinins, human angiotensin, reduced and oxidized glutathiones and oligopeptides with the same amino acid residues by capillary-tube isotachophoresis using a potential gradient detector have been established. The potential unit (PU) value is proposed as a qualitative index for capillary-tube isotachophoresis with a potential gradient detector. As it is unaffected by changes in the operating conditions, the PU value permits inter-laboratory comparison of data. The coefficient of variation of this index under the various operating conditions used was less than 1.69%.

Intracellular enzymes and kinin enzymes in synovial fluid in joint diseases. Origin and relation to disease category

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