Insulin Aspart Precursor

Endpoint summary

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

basic toxicokinetics, other

Type of information:

read-across from supporting substance (structural analogue or surrogate)

Adequacy of study:

weight of evidence

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

data from handbook or collection of data

Details on absorption:

Oral absorption:
In the gastrointestinal tract proteins and polypeptides are broken down into a mixture of subunits that are sufficiently small for absorption (i.e. amino acids , di-and tripeptides). Degradation of peptides within the lumen of the gastrointestinal tract may be due to instability in an acidic environment, metabolism by digestive enzymes or luminal microorganisms. Proteolysis starts in the stomach in the presence of pepsin and continues throughout the intestine. Lumenal degradation of peptides is due to exposure to enzymes released from the the pancreas into the intestine (Hamman et al. 2005). Insulin has been shown to be completely inactivated within 3 minutes in gastric fluids from pigs, and in rats less than 1% of insulin was found to be absorbed after oral administration (Smart et al. 2014). The major problem for therapeutic oral insulin administration, besides proteolysis in the stomach and the small intestine, is that there are no selective insulin transport mechanisms across the gut wall and the epithelial cells of the intestinal tract normally do not transport macromolecules. Therefore, even if insulin is applied directly to the gut, extremely high doses are required to achieve at least some measurable insulin absorption (Heinemann et al 2001).
Thus, due to the structural similarities, the absorption of insulin aspart precursor and the read-across source substances from oral exposure may be considered to be minute, which is expected very much to reduce any toxic potential from oral exposure.

Dermal absorption:
Insulin aspart precusor and the read-across source substances are large proteinaceous molecule and absorption through the skin is expected to be low. Skin is generally considered as a very effective barrier for larger molecules such as polypeptides and proteins. For smaller molecules it has been shown that dermal penetration and absorption has a steep decline when the molecular size of a chemical exceeds 500 Dalton (Bos et al., 2000; Heinemann et al., 2001). An absorption at a very low percentage of insulin has been observed in hairless mice when applying an electrcial potential across the skin (iontophoresis) with the aim of promoting the skin penetration (Heinemann et al. 2001). However, under normal conditions, systemic uptake from dermal exposure to insulin and similar proteins at a molecular size of about 6000 Dalton is considered to be very low / insignificant.

Inhalational absorption:
Heinemann et al. (2001) reviewed human data on the relative biopotency of insulin from inhalational exposure compared to subcutaneous exposure. Overall it was concluded that when using optimal conditions for pulmonary uptake a relative potency of about 10% could achieved from inhalational exposure. Thus, such an overall absorption rate may be considered as a valid assumption for both insulin aspart precursor and the read-across source substances.

Details on excretion:

T1/2 in plasma of insulin aspart of 22 minutes and 76 minutes have been measured in rats and humans, respectively (Novo Nordisk 1998)

Details on metabolites:

No studies regarding identification of metabolites of inuslin aspart have been conducted. As for human insulin a fast degradation of insulin aspart into inactive fragments is expected. The amino acids from the substance is expected to take part in the general metabolic pool of the body (Novo Nordisk 1998).

Conclusions:

For human insulin and insulin aspart the oral and demal absorption is considered negligible, because of degradation of the protein in the gastrointestinal tract and due to lack of dermal penetration and absorption of the large, proteinaceous molecule.
From human experiments for the development of inhalation therapy with insulin a relative absorption compared to s.c. injection of 10% has been found.

T1/2 in plasma of insulin aspart of 22 minutes and 76 minutes have been measured in rats and humans, respectively.

No studies regarding identification of metabolites of inuslin aspart have been conducted. As for human insulin, insulin aspart is expected to undergo fast degradation into inactive fragments. The amino acids from the substance is expected to take part in the general metabolic pool of the body.

Executive summary:

For human insulin and insulin aspart the oral and demal absorption is considered negligible, because of degradation of the protein in the gastrointestinal tract and due to lack of dermal penetration and absorption of  the large,  proteinaceous molecule.

From human experiments for the development of  inhalation therapy with insulin a relative absorption compared to s.c. injection of 10% has been found.

T1/2 in plasma of insulin aspart of 22 minutes and 76 minutes have been measured in rats and humans, respectively.

No studies regarding identification of metabolites of inuslin aspart have been conducted. As for human insulin, insulin aspart is expected to undergo fast degradation into inactive fragments. The amino acids from the substance is expected to take part in the general metabolic pool of the body.

Reference 2

Endpoint:

basic toxicokinetics, other

Type of information:

experimental study

Adequacy of study:

key study

Study period:

2015

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

test procedure in accordance with national standard methods

Objective of study:

other: receptor binding

GLP compliance:

no

Preliminary studies:

From insulin receptor binding assays (Novo Nordisk 2015) the following relative binding was observed for insulin APIs and the various insulin intermediates:                        
Human insulin (API, two chains):               100 %                                                                                                                                                                                             
Human insulin methyl ester (two chains):    108 %                                                                                                                                                                                                
DesB 30 human insulin (two chains) :   133 %                                                                                                                                                                  
X14DesB30 (S3, two chains):  not examined                                                                                                                                                                            Insulin aspart (API, S1, two chains):     100% %                                                                                                                                                                                                                  
Insulin aspart ethyl ester (two chains):     103%                                                                                                                                                                                                                                                                                                                                                    
Insulin aspart precursor (T, one chain) :   0.03 %                                                                                                                                                                                               
MI3 (S2, one chain):   0.22%                                                                                                                                                                                                                                                                                                                                                                                                                                                 
These data indicate that receptor binding affinity is lost when the two amino acids chains are linked together in one chain,
most probably due to a great change in the steric form of the molecule.

From insulin receptor binding assays (Novo Nordisk 2015) the following relative binding was observed for insulin APIs and the various insulin intermediates:                        

Human insulin (API, two chains):               100 %                                                                                                                                                                                             

Human insulin methyl ester (two chains):    108 %                                                                                                                                                                                                

DesB 30 human insulin (two chains) :        133 %                                                                                                                                                                  

X14DesB30 (S3, two chains):                   not examined                                                                                                                                                                           

Insulin aspart (API, S1, two chains):          100 %                                                                                                                                                                                                                  

Insulin aspart ethyl ester (two chains):      103%                                                                                                                                                                                                                                                                                                                                                    

Insulin aspart precursor (T, one chain) :   0.03 %                                                                                                                                                                                               

MI3 (S2, one chain):   0.22%                                                                                                                                                                                                                                                                                                                                                                                                                                                 

These data indicate that receptor binding affinity is lost when the two amino acids chains are linked together in one chain,

most probably due to a great change in the steric form of the molecule.

Conclusions:

Human insulin receptor affinity of insulin aspart precurser relative to the API, insulin aspart, was found to be 0.03% [0.02 to 0.06]. Results are given as weighted means of three independent experiments with the corresponding 95% confidence intervals

Executive summary:

Human insulin receptor affinity of insulin aspart precurser relative to the API, insulin aspart, was found to be 0.03% [0.02 to 0.06]. Results are given as weighted means of three independent experiments with the corresponding 95% confidence intervals.

Description of key information

Absorption

Oral absorption: In the gastrointestinal tract proteins and polypeptides are broken down into a mixture of subunits that are sufficiently small for absorption (i.e. amino acids, di-and tripeptides). Degradation of peptides within the lumen of the gastrointestinal tract may be due to instability in an acidic environment, metabolism by digestive enzymes or luminal microorganisms. Proteolysis starts in the stomach in the presence of pepsin and continues throughout the intestine. Lumenal degradation of peptides is due to exposure to enzymes released from the the pancreas into the intestine (Hamman et al. 2005). Insulin is completely inactivated within 3 minutes in gastric fluids from pigs, and in rats less than 1% of insulin was found to be absorbed after oral administration (Smart et al. 2014). The major problem for therapeutic oral insulin administration, besides proteolysis in the stomach and the small intestine, is that there are no selective insulin transport mechanisms across the gut wall and the epithelial cells of the intestinal tract normally do not transport macromolecules. Therefore, even if insulin is dosed directly into the gut, extremely high doses are required to achieve at least some measurable insulin absorption (Heinemann et al 2001).

Thus, due to the structural similarities, the oral absorption of insulin aspart precursor and the read-across source substances may be considered to be minute, which is expected very much to reduce any toxic potential from oral exposure. 

 

Dermal absorption: Insulin aspart precusor and the read-across source substances are large proteinaceous molecule and absorption through the skin is expected to be low. Skin is generally considered as a very effective barrier for larger molecules such as polypeptides and proteins. For smaller molecules it has been shown that dermal penetration and absorption has a steep decline when the molecular size of a chemical exceeds 500 Dalton (Bos et al., 2000; Heinemann et al., 2001). An absorption at a very low percentage of insulin has been observed in hairless mice when applying an electrical potential across the skin (iontophoresis) with the aim of promoting the skin penetration (Heinemann et al. 2001). However, under normal conditions, systemic uptake from dermal exposure to insulin and similar proteins at a molecular size of about 6000 Dalton is considered to be very low / insignificant.

Inhalational absorption: Heinemann et al.(2005) reviewed data on the relative biopotency of insulin from inhalational exposure compared to subcutaneous exposure. Overall, it was concluded that when using optimal conditions for pulmonary uptake a relative potency of about 10% could achieved from inhalational exposure. Thus, such an overall absorption rate may be considered as a valid assumption for both insulin aspart precursor and the read-across source substances.

Insulin Receptor binding

Human insulin receptor affinity of insulin aspart precurser relative to the API, insulin aspart, was found to be 0.03% [0.02 to 0.06]. Results are given as weighted means of three independent experiments with the corresponding 95% confidence intervals.

Key value for chemical safety assessment

Absorption rate - oral (%):

0

Absorption rate - dermal (%):

0

Absorption rate - inhalation (%):

10