Effects of cholic acid and other enhancers on the bioavailability of insulin from a subcutaneous site

New polyfluorothiopropanoyloxy derivatives of 5β-cholan-24-oic acid designed as drug absorption modifiers

A series of final six propanoyloxy derivatives of 5β-cholan-24-oic acid (tridecafluoroctylsulfanyl- and tridecafluoroctylsulfinylethoxycarbonylpropanoyloxy derivatives) as potential drug absorption promoters (skin penetration enhancers, intestinal absorption promoters) was generated by multistep synthesis. Structure confirmation of all generated compounds was accomplished by (1)H NMR, (13)C NMR, IR and MS spectroscopy methods. All the prepared compounds were analyzed using RP-TLC, and their lipophilicity (RM) was determined. The hydrophobicity (log P), solubility (logS), polar surface area (PSA) and molar volume (MV) of the studied compounds were also calculated. All the target compounds were tested for their in vitro transdermal penetration effect and as potential intestinal absorption enhancers. The cytotoxicity of all the evaluated compounds was evaluated against normal human skin fibroblast cells. Their anti-proliferative activity was also assessed against human cancer cell lines: T-lymphoblastic leukaemia cell line and breast adenocarcinoma cell line. One compound showed high selective cytotoxicity against human skin fibroblast cells and another compound possessed high cytotoxicity against breast adenocarcinoma cell line and skin fibroblast cells. Only one compound expressed anti-proliferative effect on leukaemia and breast adenocarcinoma cells without affecting the growth of normal cells, which should be promising in potential development of new drugs. Most of the target compounds showed minimal anti-proliferative activity (IC50>37μM), indicating they would have moderate cytotoxicity when administered as chemical absorption modifiers. The relationships between the lipophilicity/polarity and the chemical structure of the studied compounds as well as the relationships between their chemical structure and penetration enhancement effect are discussed in this article.

New propanoyloxy derivatives of 5β-cholan-24-oic acid as drug absorption modifiers

A series of final twelve propanoyloxy derivatives of 5β-cholan-24-oic acid (O-propanoyl derivatives of cholic acid) as potential drug absorption modifiers (skin penetration enhancers, intestinal absorption promoters) was generated by multistep synthesis. Structure confirmation of all generated compounds was accomplished by 1H NMR, 13C NMR, IR and MS spectroscopy methods. All the prepared compounds were analyzed using RP-TLC, and their lipophilicity (RM) was determined. The hydrophobicity (log P), solubility (log S), polar surface area (PSA) and molar volume (MV) of the studied compounds were also calculated. All the target compounds were tested for their in vitro transdermal penetration effect and as potential intestinal absorption enhancers. The cytotoxicity of all the evaluated compounds was evaluated against normal human skin fibroblast cells. Their anti-proliferative activity was also assessed against human cancer cell lines: T-lymphoblastic leukemia cell line and breast adenocarcinoma cell line. One compound showed selective cytotoxicity against human skin fibroblast cells and another compound possessed the highest cytotoxicity against all the tested cell lines. Only one compound expressed anti-proliferative effect on leukemia cancer cells without affecting the growth of normal cells, which should be promising in potential development of new drugs. Most of the target compounds showed minimal anti-proliferative activity (IC50>37 μM), indicating they would have moderate cytotoxicity when administered as chemical absorption modifiers. The relationships between the lipophilicity/polarity and the chemical structure of the studied compounds as well as the relationships between their chemical structure and enhancement effect are discussed in this article.

Investigation of new acyloxy derivatives of cholic acid and their esters as drug absorption modifiers

Skin penetration enhancers are used in the formulation of transdermal delivery systems for drugs that are otherwise not sufficiently skin-permeable. Intestinal absorption promoters/enhancers are used as excipients in oral formulations of poorly oral-bioavailable drugs. Series of fourteen acyloxy derivatives of 5β-cholic acid as potential drug absorption modifiers was generated by multistep synthesis. The synthesis of all newly prepared compounds is presented here. Structure confirmation of all generated compounds was accomplished by (1)H NMR, (13)C NMR, IR and MS spectroscopy methods. All the prepared compounds were analyzed using RP-TLC, and their lipophilicity (R(M)) was determined. The hydrophobicity (logP) and solubility (logS) of the studied compounds were also calculated using two commercially available programs. All the target compounds were tested for their in vitro transdermal penetration activity and as potential intestinal absorption enhancers. The anti-proliferative activity of all the final compounds was also assessed against the human cancer cell lines: T-lymphoblastic leukemia cell line and the breast adenocarcinoma cell line. Their cytotoxicity was also evaluated against the normal human skin fibroblast cells. Two compounds showed anti-proliferative effect on cancer cells without affecting the growth of normal cells, which should be promising in potential development of new drugs. Most of the target compounds showed minimal anti-proliferative activity (IC(50)>37 μM), indicating they would have low cytotoxicity when administered as chemical absorption modifiers. The relationships between the lipophilicity and the chemical structure of the studied compounds as well as the relationships between their chemical structure and enhancement effects are discussed in this article.

Bioavailability and variability of biphasic insulin mixtures

Absorption of subcutaneously administered insulin is associated with considerable variability. Some of this variability was quantitatively explained for both soluble insulin and insulin suspensions in a recent contribution to this journal (Søeborg et al., 2009). In the present article, the absorption kinetics for mixtures of insulins is described. This requires that the bioavailability of the different insulins is considered. A short review of insulin bioavailability and a description of the subcutaneous depot thus precede the presentation of possible mechanisms associated with subcutaneous insulin degradation. Soluble insulins are assumed to be degraded enzymatically in the subcutaneous tissue. Suspended insulin crystals form condensed heaps that are assumed to be degraded from their surface by invading macrophages. It is demonstrated how the shape of the heaps affects the absorption kinetics. Variations in heap formation thus explain some of the additional variability associated with suspended insulins (e.g. NPH insulins) compared to soluble insulins. The heap model also describes how increasing concentrations of suspended insulins lead to decreasing bioavailability and lower values of Cmax. Together, the findings constitute a comprehensive, quantitative description of insulin absorption after subcutaneous administration. The model considers different concentrations and doses of soluble insulin, including rapid acting insulin analogues, insulin suspensions and biphasic insulin mixtures. The results can be used in both the development of novel insulin products and in the planning of the treatment of insulin dependent diabetic patients.

Effect of different bile salts on the relative hypoglycemia of witepsol W35 suppositories containing insulin in diabetic Beagle dogs

Insulin suppositories were formulated using Witepsol W35 as a base to investigate the effect of various bile salts/acids on the plasma glucose concentration of diabetic beagle dogs. Comparison of the effect of these formulations was made with that produced by insulin subcutaneous injections. Of the bile salts/acids studied, incorporation of 100 mg of deoxycholic acid (DCA), sodium cholate (NaC), or sodium deoxycholate (NaDC) with insulin (10 U/Kg) showed that suppositories containing NaDC produced the highest area under the curve (AUC) and relative hypoglycemia (RH) of 290 +/- 83 mg%h and 28% +/- 8.1%, respectively. To study the optimum amount of NaDC in insulin suppositories to produce the highest RH, 50-200 mg/suppository were used, and we found that 150 mg NaDC produced 35% +/- 13% RH. We also studied the influence of different doses of insulin (5-20 U/kg) in the presence of NaDC (100 mg). It was found that increase of the insulin dose was accompanied by an increase in AUC and maximum reduction in plasma glucose level Cmax. A combination of NaDC (100 mg) and NaC (50 mg) produced an AUC of 252 +/- 13mg%h and an RH of 49% +/- 2.6%, which were higher than produced by either of its individual components (NaC 50 mg or NaDC 100 mg) when used alone or when compared with an equivalent amount of NaDC (150 mg). When the effect of sodium taurocholate (NaTC) and sodium taurodeoxycholate (NaTDC) was studied, it was found that an insulin suppository containing 100 mg of either NaTC or NaTDC produced an RH equivalent to that produced previouslY with a mixture of NaDC (100 mg) and NaC (50 mg). On the other hand, NaC (50 mg) did not improve the hypoglycemic effect of NaTC any further. In conclusion, a relative hYpoglycemia of about 50% can be reached using insulin suppositories containing Witepsol W35 as a base and NaDC plus NaC (100 mg plus 50 mg, respectively), NaTDC (100mg), or NaTC (100 mg) as rectal absorption enhancers of insulin. A desirable hypoglycemia, expressed as Cmax, and/or AUC can be reached by adjusting the insulin dose in the formulation according to the degree of hyperglycemia.

Relative hypoglycemia of rectal insulin suppositories containing deoxycholic acid, sodium taurocholate, polycarbophil, and their combinations in diabetic rabbits

In this study, insulin suppositories containing 50 U insulin incorporated with 50 mg of deoxycholic acid, sodium taurocholate, or both were placed in the rectum of alloxan-induced hyperglycemic rabbits. A large decrease in plasma glucose concentrations was observed, and the relative hypoglycemias were calculated to be 38.0%, 34.9%, and 44.4%, respectively, compared with insulin subcutaneous (s.c.) injection (40 U). Insulin suppositories containing 50 mg polycarbophil alone or mixed with 50 mg deoxycholic acid produced relative hypoglycemia of 43.1% and 42.2%, respectively. The most pronounced effect was observed with the addition of polycarbophil to the suppository formulation containing a combination of deoxycholic acid and sodium taurocholate, which produced a 56% relative hypoglycemia compared with subcutaneous injection. These suppository formulations could be very promising alternatives to the current insulin injections, being roughly half as efficacious as subcutaneous injection.