Insulin Complex for Oral Delivery

Diabetic patients have to administer insulin regularly. Injecting it into the dorsal subcutaneous tissues is very painful for children, pregnant women, elderly and arthritis patients. It can also cause cardiovascular complications resulting in weight gain. Insulin has poor bioavailability and it diffuses very slowly through the mucus layer.

To beat the challenge of bioavailability of Insulin, scientists at CSIR-National Chemical Laboratory (CSIR-NCL), Pune, have come up with a better option.

Insulin is a 51 amino acid peptide that cannot be taken orally because it gets degraded by the Gastro-Intestinal Tract (GIT) proteolytic enzymes. A study was conducted on diabetic patients at a Pune-based diabetes hospital. Blood samples from pre-diabetic and non-diabetic patients were collected for different diagnostic tests such as Glycated haemoglobin, fasting blood sugar and lipid profile. Samples were obtained based on the test results and divided into pre-diabetic and normal condition.

The protein samples were separated and analysed to find out the uniqueness. It was found that glucose can bind to serum albumin protein from the blood. In pre-diabetic condition, glucose was found to bind with three special peptides in large amounts. This parameter was used to assess the pre-diabetic condition. The strategy to protect insulin from proteolytic enzyme and pH shift of stomach and intestine was adapted to design a new peptide. A peptide having 16-20 L-amino acid was designed and prepared to carry out in-vitro testing.

A non-covalent insulin–peptide complex was prepared from the L-amino acids at CSIR-NCL. The complex was prepared by mixing insulin and peptide and allowed to form a complex using non-covalent interactions between the molecules of insulin and peptide without any form of artificial chemical modification. The use of L-amino acids minimised the carrier toxicity problem. The use of non-covalent interactions to prepare insulin–peptide complex helped in retaining insulin bioavailability.

The non-covalent insulin-peptide complex was subjected to hydrolysis by different proteolytic enzymes. The insulin-peptide complex was treated at 37oC for one hour with pepsin at pH 2 and with trypsin and chymotrypsin at pH 7.4. The peptides showing higher protection against one or more proteolytic enzymes were selected to carry out in-vivo testing. The in-vivo testing was carried out at the National Laboratory Animal Centre, CSIR-CDRI, Lucknow, to verify the presence of bioactive insulin in blood plasma after feeding the insulin-peptide complex through GIT.

In comparison with control, 30.61% ± 0.48% and 41.22% ± 21.41% oral insulin bioavailability was obtained after 60 min and 30 min respectively GIT feeding of insulin–peptide complex. It appears to be a significant improvement in oral insulin bioavailability as 5-20% is reported so far. Earlier, scientists have reported 50% bioavailability when insulin solutions were injected into the dorsal subcutaneous tissues of rat. It strongly suggests that the strategy used in the present study has a high potential for achieving better oral insulin bioavailability comparable with subcutaneous injection.

The work features the peptide in the formation of an insulin-peptide complex that gets partially hydrolysed in the stomach by pepsin and completely hydrolyses in the intestine by trypsin and chymotrypsin. This means that peptide enters into the blood in the form of L-amino acids and not in the peptide form. It has eliminated the chances of the toxicity that may be involved with intact peptide. The insulin bioavailability was tested using the entire gastrointestinal tract including oesophagus, stomach and intestine, proving it promising.

This work has been done by Dr H.V. Adikane, a former scientist of CSIR-NCL and is protected by filing of an Indian Patent.

Contributed by Ganesh Mane and Prabhakar Ingle (, Publication and Science Communication Unit, CSIR–National Chemical Laboratory, Pune.

Artwork by Manisha Tayade