Inhaled human insulin treatment in patients with type 2 diabetes mellitus

BACKGROUND

Despite demonstrated benefits, intensive insulin therapy has not gained widespread clinical acceptance for several reasons: Multiple daily injections are inconvenient, adherence is a concern, and the time-activity profile may not mimic normal insulin secretion. As such, alternate means of administering insulin are being evaluated.

OBJECTIVE

To assess the efficacy and safety of pulmonary delivery of insulin in type 2 diabetic patients who require insulin.

DESIGN

Randomized, open-label, 3-month study consisting of a screening visit, a 4-week baseline lead-in phase, and a 12-week treatment phase.

SETTING

General clinical research center and outpatient research clinics.

PATIENTS

26 patients (16 men, 10 women) with type 2 diabetes (average age, 51.1 years; average duration of diabetes, 11.2 years).

INTERVENTION

Patients received inhaled insulin before each meal plus a bedtime injection of ultralente insulin, performed home glucose monitoring, and had weekly adjustment of insulin dose; target level for preprandial plasma glucose was 5.55 to 8.88 mmol/L (100 to 160 mg/dL).

MEASUREMENTS

Glycemic control (hemoglobin A(1c) level) obtained at baseline and monthly for 3 months. Pulmonary function tests were done at baseline and at the end of the study.

RESULTS

Inhaled insulin treatment for 3 months significantly improved glycemic control compared with baseline: Mean hemoglobin A(1c) levels decreased by 0.0071 +/- 0.0072 (0.71% +/- 0.72%). Patients experienced an average of 0.83 mild to moderate hypoglycemic event per month; no severe events were recorded. Patients showed no significant weight gain or change in pulmonary function compared with baseline.

CONCLUSIONS

Pulmonary delivery of insulin in type 2 diabetic patients who require insulin improved glycemic control, was well tolerated, and demonstrated no adverse pulmonary effects. Larger-scale studies are ongoing to provide long-term efficacy and safety data.

Efficacy of inhaled human insulin in type 1 diabetes mellitus: a randomised proof-of-concept study

BACKGROUND

Effective glycaemic control in type 1 diabetes mellitus usually requires two or more insulin injections daily. Inhaled intrapulmonary delivery of insulin offers a potential new way to deliver meal-related insulin, eliminating the need for preprandial injections.

METHODS

73 patients with type 1 diabetes mellitus were studied in an open-label, proof-of-concept, parallel-group randomised trial. Patients in the experimental group received preprandial inhaled insulin plus a bedtime subcutaneous ultralente insulin injection. Patients in the control group received their usual insulin regimen of two to three injections per day. Participants monitored their blood glucose four times daily, and adjusted insulin doses weekly to achieve preprandial glucose targets of 5.6-8.9 mmol/L. The primary outcome measure was change in glycosylated haemoglobin (HbA1c) after 12 weeks. Secondary outcomes were fasting and postprandial glucose response to a mixed meal; hypoglycaemia frequency and severity; pulmonary function; and patients' satisfaction.

FINDINGS

Changes in HbA1c were indistinguishable between groups (difference 0.2% [95% CI -0.2 to 0.5]). Changes in fasting and postprandial glucose concentrations, and occurrence and severity of hypoglycaemia were also similar between groups. Inhaled insulin was well tolerated and had no effect on pulmonary function (ie, spirometry, lung volumes, diffusion capacity, and oxygen saturation).

INTERPRETATION

This proof-of-concept study shows that preprandial insulin can be given by inhalation in individuals with insulin-deficient type 1 diabetes as a less invasive alternative to conventional preprandial insulin injections.

Monocarboxylate transporter expression in mouse brain

Although glucose is the major metabolic fuel needed for normal brain function, monocarboxylic acids, i.e., lactate, pyruvate, and ketone bodies, can also be utilized by the brain as alternative energy substrates. In most mammalian cells, these substrates are transported either into or out of the cell by a family of monocarboxylate transporters (MCTs), first cloned and sequenced in the hamster. We have recently cloned two MCT isoforms (MCT1 and MCT2) from a mouse kidney cDNA library. Northern blot analysis revealed that MCT1 mRNA is ubiquitous and can be detected in most tissues at a relatively constant level. MCT2 expression is more limited, with high levels of expression confined to testes, kidney, stomach, and liver and lower levels in lung, brain, and epididymal fat. Both MCT1 mRNA and MCT2 mRNA are detected in mouse brain using antisense riboprobes and in situ hybridization. MCT1 mRNA is found throughout the cortex, with higher levels of hybridization in hippocampus and cerebellum. MCT2 mRNA was detected in the same areas, but the pattern of expression was more specific. In addition, MCT1 mRNA, but not MCT2, is localized to the choroid plexus, ependyma, microvessels, and white matter structures such as the corpus callosum. These results suggest a differential expression of the two MCTs at the cellular level.

Differentiation-induced gene expression in 3T3-L1 preadipocytes: CCAAT/enhancer binding protein interacts with and activates the promoters of two adipocyte-specific genes

Previous studies have shown that differentiation of 3T3-L1 preadipocytes leads to the transcriptional activation of a group of adipose-specific genes. As an approach to defining the mechanism responsible for activating the expression of these genes, we investigated the binding of nuclear factors to the promoters of two differentiation-induced genes, the 422(aP2) and stearoyl-CoA desaturase 1 (SCD1) genes. DNase I footprinting and gel retardation analysis identified two binding regions within the promoters of each gene that interact with nuclear factors present in differentiated 3T3-L1 adipocytes. One differentiation-induced nuclear factor interacts specifically with a single binding site in the promoter of each gene. Competition experiments showed that the interaction of this nuclear factor with the SCD1 promoter was prevented specifically by a synthetic oligonucleotide corresponding to the site footprinted in the 422(aP2) promoter. Several lines of evidence indicate that the differentiation-induced nuclear factor is CCAAT/enhancer binding protein (C/EBP), a DNA-binding protein first isolated from rat liver. Bacterially expressed recombinant C/EBP binds to the same site at which the differentiation-specific nuclear factor interacts within the promoter of each gene. Northern analysis with RNA from 3T3-L1 cells shows that C/EBP mRNA abundance increases markedly during differentiation. Transient cotransfection studies using a C/EBP expression vector demonstrate that C/EBP can function as a trans-activator of both the 422(aP2) and SCD1 gene promoters.

CCAAT/enhancer binding protein activates the promoter of the serum albumin gene in cultured hepatoma cells

An expression vector capable of encoding full-length CCAAT/enhancer-binding protein (C/EBP) has been constructed and tested in transient transfection assays for its capacity to activate transcription from the promoter of the serum albumin gene. When tested in cultured hepatoma cells, the C/EBP expression vector achieved potent trans-activation of the albumin promoter. Less substantial activation was observed when the same experiment was conducted using cultured mouse fibroblasts. Expression vectors that encoded defective forms of C/EBP failed to activate the albumin promoter. Moreover, mutated variants of the albumin promoter that lack the C/EBP-binding site failed to be trans-activated. The data are consistent with the interpretation that C/EBP is a bona fide transcription factor. During the course of these experiments it was noted also that C/EBP is more than an order of magnitude less concentrated in cultured hepatoma cells than it is in adult liver cells. Given these findings, we speculate that C/EBP may play a general role in establishing and maintaining the differentiated, nonproliferative state.

Tissue-specific expression, developmental regulation, and genetic mapping of the gene encoding CCAAT/enhancer binding protein

This paper presents the results of experiments that determine the chromosomal location of the mouse gene encoding CCAAT/enhancer binding protein (C/EBP) and measure its expression as a function of tissue type and temporal period of development in mice and rats. Three alleles of the C/EBP gene were identified according to restriction fragment length polymorphisms. The strain distribution pattern of the three alleles was determined in recombinant inbred mouse strains and compared to that of other mouse genes. These results mapped the gene to a position within 2.5 centimorgans (cM) of the structural gene encoding glucose phosphate isomerase on chromosome 7 of the mouse. The expression pattern of the C/EBP gene was studied by a combination of nucleic acid hybridization and antibody staining assays. High levels of C/EBP mRNA were observed in tissues known to metabolize lipid and cholesterol-related compounds at uncommonly high rates. These included liver, fat, intestine, lung, adrenal gland, and placenta. More detailed analysis of two of these tissues, liver and fat, showed that C/EBP expression was limited to fully differentiated cells. Moreover, analysis of the temporal pattern of expression of C/EBP mRNA in two tissues, liver and intestine, revealed a coordinated induction just prior to birth. These observations raise the possibility that the synthesis of C/EBP may be responsive to humoral factors and that modulation in C/EBP expression might mediate coordinated changes in gene expression that facilitate adaptive challenges met during development or during the fluctuating physiological states of adult life.

The DNA binding domain of the rat liver nuclear protein C/EBP is bipartite

C/EBP is a rat liver nuclear protein capable of sequence-specific interaction with DNA. The DNA sequences to which C/EBP binds in vitro have been implicated in the control of messenger RNA synthesis. It has therefore been predicted that C/EBP will play a role in regulating gene expression in mammalian cells. The region of the C/EBP polypeptide required for direct interaction with DNA has been identified and shown to bear amino acid sequence relatedness with the product of the myc, fos, and jun proto-oncogenes. The arrangement of these related amino acid sequences led to the prediction of a new structural motif, termed the "leucine zipper," that plays a role in facilitating sequence-specific interaction between protein and DNA. Experimental tests now provide support for the leucine zipper hypothesis.

In situ detection of sequence-specific DNA binding activity specified by a recombinant bacteriophage

We have used a recombinant bacteriophage that expresses the DNA-binding domain of C/EBP to optimize conditions for a screening technique that may facilitate the cloning of genes that encode sequence-specific DNA-binding proteins. The method relies on the expression of cDNA inserts in bacteriophage lambda gt11. Fusion protein adsorbed onto nitrocellulose filters is probed with radioactive, double-stranded DNA as a ligand. Two procedures greatly increase the level of binding between ligand and recombinant fusion protein. First, nitrocellulose filters are processed through a denaturation/renaturation regimen using 6 M guanidine hydrochloride. Second, synthetic DNA corresponding to the specific binding site is catenated extensively using DNA ligase. The combination of these procedures leads to remarkably strong detection signals. Specific DNA-binding signals can be detected on duplicate filters, and filters can be washed and reused by repeating the cycle of denaturation/renaturation.

Isolation of a recombinant copy of the gene encoding C/EBP

In two previous studies we described the properties of a heat-stable DNA-binding protein present in rat liver nuclei. This protein, hereafter termed C/EBP, is capable of selective binding to the CCAAT homology of several viral promoters (Graves et al. 1986), as well as the core homology common to many viral enhancers (Johnson et al. 1987). We now report the isolation of a recombinant clone of the gene that encodes C/EBP. Expression of the clone in bacterial cells yields a protein that binds in vitro to both the CCAAT homology and the enhancer core homology, providing conclusive evidence that a single gene product accounts for both binding activities. By examining the properties of protease-derived fragments of C/EBP, we have localized its DNA-binding domain to a 14-kD fragment. A 60-amino-acid segment located within the DNA-binding domain of C/EBP bears sequence similarity to the products of the myc and fos oncogenes.

The leucine zipper: a hypothetical structure common to a new class of DNA binding proteins

A 30-amino-acid segment of C/EBP, a newly discovered enhancer binding protein, shares notable sequence similarity with a segment of the cellular Myc transforming protein. Display of these respective amino acid sequences on an idealized alpha helix revealed a periodic repetition of leucine residues at every seventh position over a distance covering eight helical turns. The periodic array of at least four leucines was also noted in the sequences of the Fos and Jun transforming proteins, as well as that of the yeast gene regulatory protein, GCN4. The polypeptide segments containing these periodic arrays of leucine residues are proposed to exist in an alpha-helical conformation, and the leucine side chains extending from one alpha helix interdigitate with those displayed from a similar alpha helix of a second polypeptide, facilitating dimerization. This hypothetical structure is referred to as the "leucine zipper," and it may represent a characteristic property of a new category of DNA binding proteins.

Identification of a rat liver nuclear protein that binds to the enhancer core element of three animal viruses

This report describes the identification and purification of a nuclear protein from rat liver that binds selectively to DNA sequences associated with several animal virus enhancers. The binding activity was tracked by direct DNase I footprinting through four steps of biochemical fractionation. These procedures led to the identification of a polypeptide species exhibiting an apparent molecular weight of 20 kD that accounts for enhancer binding activity. DNase I and dimethyl sulfate footprinting assays were used to examine the manner in which the purified protein binds to enhancer elements associated with SV40, murine sarcoma virus, and polyoma virus. The results of these assays indicate that the initial interaction established between the 20-kD protein and each viral enhancer occurs via a common DNA sequence known as the enhancer core homology.