Enzymic Degradation of Hydroxyethyl Starch. Part I. Influence of the Distribution of Hydroxyethyl Groups on the Enzymic Degradation of Hydroxyethyl Starch

Ca2+-Responsive Glyco-insulin

Chemical modification of peptides and proteins, such as PEGylation and lipidation, creates conjugates with new properties. However, they are typically not dynamic or stimuli-responsive. Self-assembly controlled by a stimulus will allow adjusting properties directly. Here, we report that conjugates of oligogalacturonic acids (OGAs), isolated from plant-derived pectin, are Ca²⁺-responsive. We report the conjugation of OGA to human insulin (HI) to create new glyco-insulins. In addition, we coupled OGA to model peptides. We studied their self-assembly by dynamic light scattering, small-angle X-ray scattering, and circular dichroism, which showed that the self-assembly to form nanostructures depended on the length of the OGA sequence and Zn²⁺ and Ca²⁺ concentrations. Subcutaneous administration of OGA12-HI with Zn²⁺ showed a stable decrease in blood glucose over a longer period of time compared to HI, despite the lower receptor binding affinity.

Suppressing unspecific cell uptake for targeted delivery using hydroxyethyl starch nanocapsules

Synthesizing nanocarriers with stealth properties and delivering a "payload" to the particular organ remains a big challenge but is the prime prerequisite for any in vivo application. As a nontoxic alternative to the modification by poly(ethylene glycol) PEG, we describe the synthesis of cross-linked hydroxyethyl starch (HES, M(w) 200,000 g/mol) nanocapsules with a size range of 170-300 nm, which do not show nonspecific uptake into cells. The specific uptake was shown by coupling a folic acid conjugate as a model targeting agent onto the surface of the nanocapsules, because folic acid has a high affinity to a variety of human carcinoma cell lines which overexpress the folate receptor on the cell surface. The covalent binding of the folic acid conjugate onto HES capsules was confirmed by FTIR and NMR spectroscopy. The coupling efficiency was determined using fluorescence spectroscopy. The specific cellular uptake of the HES nanocapsules after folic acid coupling into the folate-receptor presenting cells was studied by confocal laser scanning microscopy (CLSM) and flow cytometry.

Bioequivalence Comparison between Hydroxyethyl??Starch??130/0.42/6???:???1 and??Hydroxyethyl Starch??130/0.4/9???:???1

OBJECTIVE

The aim of this study was to investigate whether a recently developed low molecular, low substituted hydroxyethyl starch (HES 130/0.42/6 : 1), altered in molar substitution and C2/C6 ratio, is bioequivalent to the former standard HES preparation (130/0.4/9 : 1).

METHODS

The two HES solutions were infused (60g as a single dose within 30 minutes) in healthy volunteers using a randomised, crossover design. HES serum concentrations were used for computation of pharmacokinetic parameters; area under the concentration-time curve from infusion start until 24 hours thereafter (AUC(24)) and maximum serum concentration (C(max)) were the primary criteria. Haemodilution, colloid osmotic pressure and plasma viscosity were measured as secondary criteria. Pentastarch (HES 200/0.5/5:1) was investigated in the same volunteers and manner during a subsequent period.

RESULTS

Using non-compartmental analysis, significant differences were found for AUC(24) (45.97 +/- 8.97 mg . h/mL vs 58.32 +/- 9.23 mg . h/mL; HES 130/0.42/6 : 1 vs HES 130/0.4/9 : 1) and total apparent clearance (CL; 1.14 +/- 0.4 L/h vs 0.81 +/- 0.34 L/h). C(max) and elimination half-life (t(1/2)) were similar, while the AUC(24), t(1/2) and CL of pentastarch were significantly different from those of low substituted HES solutions.

CONCLUSION

Being equivalent with pentastarch and HES 130/0.4/9 : 1 in terms of colloid osmotic and haemodilution effect, HES 130/0.42/6 : 1 shows the fastest clearance from the circulation.

[Hydroxethyl starch: effects on hemostasis]

HES are high-polymeric glucose compounds obtained via hydrolysis and subsequent hydroxyethylation from the highly-branched amylopectin contained in maize. Initially, the HES were only characterized by their in vitro molecular weight (Mw), without consideration of the in vivo hydrolysis by alpha-amylase. The degree of substitution and the molar substitution ratio quantify the hydroxyethylation. The glucose units can be substituted at carbon 2, 3 and 6 leading to various substitution patterns. This pattern is described with the C2/C6 hydroxyethylation ratio. The higher the degree of substitution and the C2/C6 ratio, the less the starch is metabolized. The in vitro Mw, the degree of substitution and the C2/C6 ratio are the main determinants of the in vivo Mw which is clinically relevant. Haemorrhagic complications that occur after infusing larger volumes of HES can be avoided with a starch of low in vivo Mw. This is not only due to a lesser effect on the coagulation system which prevents an acquired type I von Willebrand syndrome, but also to a smaller decrease in platelet volume, since platelet volume and platelet function are positively correlated. In addition, HES with low in vivo Mw has significantly better rheological effects than HES with a high in vivo Mw, as high Mw macromolecules affect plasma viscosity negatively. Furthermore high Mw HES macromolecules lead to a distinctive decrease in fibronectin concentration that reflects saturation of the reticuloendothelial system. Another advantage of low in vivo Mw HES is its rather short half-life. Patients with an increased bleeding risk, microcirculatory disturbance or affected RES should receive HES with low in vivo Mw. In the future, HES should be mainly characterized by the in vivo and not the in vitro Mw.

Enzymic analysis of the structure of oxidized potato starches

The possibility to use enzymic methods for the analysis of the positions of carboxyl and carbonyl groups in sodium hypochlorite oxidized (HO) and hydrogen peroxide oxidized (PO) potato starches was investigated. The HO-starch, that contained more modified glucosyl residues, possessed a lower beta-amylolysis limit and all of the polymer components were resistant to complete hydrolysis as judged from gel-permeation chromatograms. In contrast, the PO-starch contained 24% of apparently unmodified, linear chains that were hydrolysed by beta-amylase. After debranching, approximately 30% of the chains in the HO-sample and approximately 20% in the PO-sample remained partly resistant to successive beta-amylolysis.

Chemical characterization of the persistent fraction of hydroxyethyl starch in rat serum and spleen

Hydroxyethyl starch (HES) found in rat serum and spleen after single and daily administrations of 0.9 g/kg for 1 week was characterized by gas-liquid chromatography. There was very little difference in the degree of substitution (D.S.) and molar substitution (M.S.) of HES in serum samples obtained at 1 hour and 57 days after multiple doses and of HES in spleen samples obtained at 1 hour and 168 days after a single dose of HES. The small increase in D.S. and M.S. was due to a decrease in the glucose content and not due to a change in the ratio of mono- to poly-substituted glucoses.

Hetastarch: an overview of the colloid and its metabolism

Hetastarch, ethoxylated amylopectin, has found clinical utility as a plasma volume expansion agent, a sedimenting agent during pheresis, and a pump priming fluid. Hetastarch is a complex mixture of derivatized amylopectin molecules of various molecular sizes. The derivatization causes resistance to enzymatic hydrolysis, therefore, allowing hetastarch sufficient vascular residence time to be an effective vascular osmotic agent. This has led to its use as a volume expander and to its consequent use as a pump priming fluid. The metabolism of hetastarch proceeds through alpha-amylase hydrolysis of glycosidic bonds, yielding molecules small enough for renal clearance, but does not result in complete hydrolysis. Hence, glucose is not a significant product of hetastarch metabolism. Metabolism proceeds at such a rate that volume expansion is seen for 24-36 hours with a maximum effect (100-172 percent of the infused volume) occurring shortly after infusion. Ninety percent of the dose is eliminated with a half-life of about 17 days.

[The elimination of hydroxyethyl starch 200/0.5, dextran 40 and oxypolygelatine (author's transl)]

After withdrawal of 400 ml whole blood and subsequent infusion of 500 ml of a colloidal plasma substituent, the intravascular and renal colloid elimination was investigated in 40 test subjects. The individual colloidal solutions could no longer be demonstrated in the intravascular space after the following times: 10% hydroxyethyl starch 200/0.5 (anthrone method) after six weeks, 10% dextran 40 (anthrone method) after two weeks, 6% hydroxyethyl starch 200/0.5 (anthrone method) after four weeks and 5.5% oxypolygelatine (hydroxyproline method) after two days. Colloidal plasma substitutes are polydisperse solutions with various molecular weights and degree of hydroxyethylation and therefore, also have a large number of different elimination constants. With repeated application, the intravascular colloid concentration shifts in favour of the molecules with a longer half life which are difficult to eliminate. The elimination of the clinically employed dextran 40 and oxypolygelatine solution could be best described with an open two-compartment model. As a result of its greater heterogeneity, the elimination of the moderately high molecular weight hydroxyethyl starch 200/0.5 could only be characterized approximately even assuming three elimination constants. In the first four days, the hydroxyethyl starch 200/0.5 was more rapidly eliminated compared to dextran 40. However, subsequently a very much lower elimination from the intravascular space was found for about 3% of the administered hydroxyethyl starch 200/0.5. Oxypolygelatine was eliminated especially rapidly. Accordingly, the greatest renal clearance was found for oxypolygelatine, which showed a close relation to the molecular weight. On the other hand, a rapid elimination simultaneously is followed by a correspondingly lower volume effect.

Changes in the molecular composition of circulating hydroxyethyl starch following consecutive daily infusions in man

1 Changes in the circulating molecular composition of hydroxyethyl starch (HES) were determined in four normal men following three consecutive daily 500 ml infusions (total 1,500 ml), by passage of trichloroacetic acid filtrates of plasma through a Sepharose CL4B gel filtration column. 2 The HES recovered from the intravascular space 10 min following the injection on Days 1, 2 and 3, was of a narrower molecular size distribution than the injected material, with a noticeable shift to molecules of a low molecular weight (LMW) size. 3 The HES in the sampled plasma 24 h post-injection on Days 1, 2 and 3 consisted of molecules possessing a LMW distribution, concomitantly with a slight shift to molecules of a larger molecule size. 4 The HES recovered from the bloodstream 480 h after the third and final injection consisted of molecules possessing an intermediate size distribution, between LMW and high molecular weight (HMW) size material. 5 The results indicate that large HES molecules contained in the injected material are eliminated from the bloodstream; the HMW fraction at least partially by a alpha-amylase mediated catabolism, and the resulting LMW fraction by excretion.