Diabetes Overview - Signaling Pathway. Diagnostics Marker. Targeted Therapy and Clinical Trials

1 Main Signaling Pathways in Diabetes Treatment

A mounting body of research has confirmed the association between the pathogenesis of diabetes and multiple signaling pathways, including the insulin signaling pathway and the AMPK pathway. Therefore, these signaling pathways have emerged as significant potential targets for novel drug treatments aimed at addressing metabolic diseases and diabetes mellitus.

1.1 AMPK signaling cascade

The AMPK signaling pathway plays a key role in maintaining energy metabolic homeostasis. It begins with the activation of AMP kinase (AMPK) through phosphorylation. Once activated, AMP kinase (AMPK) inactivates two enzymes involved in glucose metabolism, phosphoenolpyruvate carboxykinase (PEPCK), and glucose-6-phosphatase (G6P). As a result, hepatic glucose production is reduced. Additionally, AMPK induces the expression of the glucose transporter protein (GLUT), which leads to increased glucose uptake. AMPK also promotes lipid metabolism by decreasing the levels of malonyl coenzyme A. This is achieved by inhibiting acetyl coenzyme A carboxylase (ACC) and activating malonyl coenzyme A decarboxylase (MCD). Consequently, the main targets downstream of AMPK are glucose transporter 4 (GLUT4), acetyl-CoA carboxylase (ACC), and liver glycogen synthase (glucose-6-phosphatase, G6P). Furthermore, the AMPK signaling pathway interacts with other important metabolic pathways, such as apoptosis, mitochondrial function, autophagy, and inflammation. These interactions are closely linked to the development and progression of diabetes. Moreover, AMPK enhances tissue sensitivity to insulin and improves insulin effectiveness, resulting in lower blood glucose levels. By inhibiting glycogenolysis and fatty acid synthesis, AMPK activation also contributes to alleviating symptoms associated with diabetes, such as insulin resistance and hyperglycemia.

1.2 PI3K/Akt/mTOR signaling cascade

The PI3K/AKT signaling pathway plays a crucial role in the development and progression of diabetes. AKT is responsible for regulating glucose and lipid metabolism. When certain growth factors or insulin are active, they activate the PI3K enzyme and cause its phosphorylation on the membrane. PI3K responds to signaling from receptor tyrosine kinases, resulting in the formation of PIP3 (phosphatidylinositol triphosphate), a molecule that attracts AKT and other signaling molecules. PIP3 attracts AKT and localizes it to the cell membrane, where it becomes activated through the phosphorylation of other kinases. Once activated AKTs (such as AKT2) can enter the cell interior and influence various downstream targets. Activated AKT2 promotes the translation of glucose transporter 4 (GLUT4). Within the intracellular compartment, AKT stimulates hexokinase, converting glucose into glucose 6-phosphate. AKT primarily targets FoxO proteins, especially FoxO1, which impact energy homeostasis in the body. FoxO1, along with peroxisome proliferator-activated receptor coactivator 1α (PGC1α), coordinate gene expression regulation to increase gluconeogenesis and fatty acid oxidation. On the other hand, FoxO1 induces the expression of PEPCK and the glucose 6 phosphatase gene (G6PC), leading to increased gluconeogenesis. AKT directly inhibits FoxO1, reducing glucose levels, while FoxO1 simultaneously activates AKT to enhance energy production and inhibit mTOR complex 1 (mTORC1), reducing lipid and protein production. Finally, GSK3 inhibits glycogen synthase (GS), hindering glycogen synthesis. AKT counteracts GSK3 by phosphorylating it, thus exerting an inhibitory effect. AKT also regulates lipid metabolism through sterol regulatory element binding proteins (SREBPs), which promote the accumulation of cholesterol and fatty acids, including SREBP-1c, SREBP-1a, and SREBP-2. Therefore, the PI3K/AKT pathway regulates glucose metabolism through FoxO1 and GSK-3, and lipid metabolism through mTORC1 and SREBP. Several drugs targeting the PI3K/AKT/mTOR pathway are available for diabetes treatment, such as Metformin, Insulin, Rapamycin, and Pioglitazone. These drugs improve glycemic control, reduce the risk of diabetes-related complications, and increase insulin sensitivity in patients with diabetes.

1.3 Wnt signaling cascade

The central mediator of the Wnt signaling pathway is the dichotomous transcription factor β-cat/TCF. Wnt proteins work together with Frizzled receptors and LRP5/6. When Wnt binds to its receptor, it hampers the activity of GSK3β and other protein complexes, enabling β-catenin to evade phosphorylation and degradation and enter the nucleus. Once in the nucleus, β-catenin forms complexes with TCF/LEF transcription factors, which stimulates the transcription of various genes, including cyclin D1, c-myc, and MMP-7. Studies have shown that the Wnt signaling pathway can also impact insulin sensitivity by inhibiting the composition and nuclear translocation of the FoxO1 protein. Inhibiting of the Wnt signaling pathway using drugs or other methods can reduce damage to islet cells and insulin resistance, ultimately regulating blood glucose levels. For example, some current diabetes medications like pioglitazone and sitagliptin can inhibit the Wnt signaling pathway, leading to improved insulin sensitivity and metabolic function.

1.4 JAK-STAT signaling cascade

The JAK-STAT signaling pathway provides a means for cells to secrete ligands (e.g., insulin-like growth factor) that can bind to receptors during conditions like inflammation. Upon receptor binding, JAK proteins are activated and in turn phosphorylate the receptor, recruiting STAT proteins. Once STAT is phosphorylated, it can self-aggregate and dissociate from the receptor, allowing it to transfer to the nucleus and activate the expression of specific genes. Within the nucleus, STAT can bind to the promoter region of target genes, promoting their expression and influencing physiological processes such as cell growth, differentiation, and immune response. By inhibiting the JAK-STAT signaling pathway using biological and/or chemical compounds, it is possible to reduce the inflammatory response, improve insulin sensitivity and metabolic function, and thus control blood glucose levels.

1.5 ROS-ERK-NF-κB signaling cascade

The ROS-ERK-NF-κB signaling pathway plays a role in various physiological processes, such as inflammation and oxidative stress. In diabetes, cells produce excessive amounts of reactive oxygen species (ROS) in conditions such as hyperglycemia and hyperlipidemia. ROS activates peripheral neuronal regulatory protein kinase (ERK), which undergoes phosphorylation and enters the nucleus. Inside the nucleus, ERK promotes the activation of nuclear factor-κB (NF-κB), which then moves into the cytoplasm. NF-κB triggers the production of inflammatory mediators, such as IL-6 and TNF-α, initiating the inflammatory response. Some current diabetes treatments, like metformin and thiazolidinediones, can inhibit the ROS-ERK-NF-κB signaling pathway, thereby improving insulin sensitivity and metabolic function.

1.6 IGF-1 signaling cascade

The IGF-1 signaling pathway is involved in a range of physiological processes including insulin resistance, insulin secretion, and cell growth. Insulin-like growth factor 1 (IGF-1) binds to the IGF-1 receptor on the cell membrane, activating it. The activated IGF-1 receptor then undergoes autophosphorylation and recruits insulin receptor substrate (IRS) proteins. IRS proteins, in turn, activate phosphatidylinositol 3-kinase (PI3K), and PIP3 activates protein kinase B (AKT), which translocates into the cytoplasm. Once in the cytoplasm, AKT initiates various downstream effects, such as the expression of GLUT4 transporters and the synthesis of nitric oxide (NO). Activation of this pathway promotes insulin sensitivity and cell growth, thereby counteracting the progression of diabetes. Molecules that modulate this pathway, such as IGF-1 receptor antagonists, PI3K inhibitors, and AKT inhibitors, can be potential targets for diabetes treatment.

2 Diagnosis of Diabetes Mellitus

The diagnosis of diabetes is based on measuring indicators such as blood glucose levels and glycated hemoglobin. Diagnostic criteria for diabetes have been published by the World Health Organization (WHO), the American Diabetes Association (ADA), and other organizations. Molecular markers and protein markers are important indicators for studying the pathogenesis and early diagnosis of diabetes. In recent years, several studies have identified various molecular markers and protein markers associated with diabetes, including:

• Blood glucose: Glucose levels in the blood are a key indicator for diagnosing diabetes.
• Glycosylated hemoglobin (HbA1c): HbA1c is a derivative of hemoglobin that reflects the average blood glucose level over the past 2-3 months.
• Insulin and C-peptide: Insulin is a hormone secreted by pancreatic islet cells that lowers blood glucose levels, while C-peptide is a byproduct secreted by insulin-secreting cells and is proportional to insulin levels. In diabetic patients, insulin levels are low while C-peptide levels are elevated.
• Urinary ketone bodies: Ketone bodies found in urine are metabolic byproducts that can indicate a lack of insulin secretion or the inability of cells to utilize glucose in diabetic patients.
• Glucose transporter 2 (GLUT2): It is a key molecule in the process of insulin release, and its abnormal expression may lead to insulin resistance and abnormal glucose metabolism.
• Insulin-like growth factor (IGF): It is an important molecule involved in the insulin signaling pathway, and its abnormal expression may affect insulin sensitivity and metabolic function.
• Leptin and adiponectin: These are hormones secreted by adipose tissue, and their abnormal expression may contribute to problems such as insulin resistance and metabolic abnormalities.
• Glycosylation end products (AGEs): AGEs are compounds produced by the reaction of glucose and proteins. Their levels are high in diabetic patients and can affect processes such as insulin sensitivity, inflammatory response, and oxidative stress. Additionally, dietary glutaminyl transferase (GGT) has been suggested as an early diagnostic marker for diabetes.

In clinical practice, there is a trend towards using combinations of multiple markers and building models or algorithms to determine the risk, diagnosis, and classification of diabetes. For example, one study utilized multiple protein markers in serum to create a model combining serum markers that can effectively differentiate and diagnose diabetes from non-diabetes.

3 Targeted Therapy for Diabetes Mellitus

Targeted therapy for diabetes is an approach that intervenes and modulates the pathogenesis of diabetes by acting on specific molecular targets to achieve therapeutic effects. It should be noted that targeted therapy for diabetes is still undergoing continuous exploration and improvement. In this summary, we present potential targets and new drugs that have been developed and used in recent, ongoing, and future clinical trials with the aim of improving the clinical outcomes for this disease (see Table 1-8).

3.1 Diabetes therapy targeting the AMPK signaling pathway

Drugs targeting the AMPK signaling pathway in diabetes can potentially achieve therapeutic effects by activating the pathway. Various therapies affect the AMPK signaling pathway through different mechanisms, but they all share the common goal of promoting AMPK activation to improve metabolic status.

Current drugs targeting the AMPK signaling pathway in diabetes include Metformin, Sitagliptin, Roglitazone, etc. Metformin is currently one of the preferred drugs for treating type 2 diabetes. It works by increasing AMPK activation through the inhibition of mitochondrial complex I and ATP synthesis. This reduces hepatic gluconeogenesis and promotes glucose uptake and utilization. Metformin may also improve metabolic status through other mechanisms such as enhancing insulin sensitivity. Sitagliptin is an orally administered drug that increases the activity of GLP-1 and GIP hormones by inhibiting the DPP-4 enzyme. This promotes insulin secretion and inhibits glucagon secretion. Sitagliptin may also stimulate AMPK activation by inhibiting mitochondrial complex I, thereby reducing hepatic gluconeogenesis and promoting glucose uptake and utilization. Troglitazone, a GLP-1 receptor agonist, improves glucose metabolism and insulin sensitivity through AMPK activation of. In conclusion, these drugs that target the AMPK signaling pathway in diabetes have the potential to regulate intracellular energy metabolism and growth homeostasis, thereby improving the symptoms associated with type 2 diabetes, obesity, and other metabolic diseases. Ongoing clinical trials are underway to determine the efficacy and safety of these drugs to further advancing their potential clinical applications.

Table 1 Clinical trial of Metformin, an activator of AMPK

According to statistics, there are currently 186 Metformin projects targeting diabetes in the clinical stage. Out of these, 117 projects are recruiting participants, while 69 projects are not recruiting.

3.2 Diabetes therapy targeting the PI3K/Akt/mTOR signaling pathway

The drugs targeting the PI3K/AKT/mTOR signaling pathway in diabetes include Ragaglitazar, Everolimus, Sunitinib, and Apalutamide. Ragaglitazar acts as a PPARα and PPARγ agonist, exerting therapeutic effects by inhibiting the PI3K/AKT/mTOR pathway. Lapatinib, a dual HER2 and EGFR inhibitor, also inhibits the PI3K/AKT/mTOR pathway and shows antitumor effects. Currently, clinical trials are underway to evaluate the efficacy and safety of Lapatinib in patients with type 2 diabetes and non-alcoholic fatty liver disease. Sunitinib is a multi-targeted tyrosine kinase inhibitor that affects glucose metabolism by inhibiting the PI3K/AKT/mTOR pathway. Clinical trials are also in progress to assess its effectiveness and safety in treating type 2 diabetes. Everolimus, an mTOR inhibitor, has the potential to treat diabetes and obesity by inhibiting the PI3K/AKT/mTOR pathway. Another drug, Apalutamides, acts as an androgen receptor antagonist and inhibits the same pathway. Phase II clinical trials are currently underway to evaluate its efficacy and safety in type 2 diabetes. There are also other inhibitors of the PI3K/AKT/mTOR pathway, such as Metformin and Insulin. These drugs activate the AMPK pathway or mimick the effects of natural insulin to inhibit the PI3K/AKT/mTOR pathway. Additionally, drugs like Rapamycin and Everolimus target key molecules downstream of this pathway. They are mTOR inhibitors that interfere with the activity of molecules downstream, leading to reduced insulin resistance and improved insulin sensitivity. Furthermore, novel PI3K inhibitors such as Buparlisib and Copanlisib are currently undergoing clinical trials to assess their effectiveness in treating diabetes.

Table 2 Clinical trial of Everolimus, an mTOR inhibitor

Table 3 Clinical trial of Insulin, a PI3K/AKT/mTOR pathway inhibitors

According to statistics, there are currently 1273 insulin projects in the clinical stage. Out of these, 843 are recruiting participants, while430 are not recruiting.

3.3 Diabetes therapy targeting the Wnt signaling pathway

Although there are only a few drugs that target the diabetic Wnt signaling pathway,several drugs are being studied or have been applied in clinical trials. These include Carlsatib, ICG-001, LGK-974, ONO-7569, and PRI-724. Carlsatib is a Wnt inhibitor that acts on Porcupine, a protein in the Wnt signaling pathway, to inhibit its function and reduce Wnt signaling. ICG-001 is a CBP/β-catenin inhibitor that regulates the Wnt signaling pathway by inhibiting the formation of the CBP/β-catenin complex. LGK-974 is also a Wnt signaling pathway inhibitor that acts on Porcupine, a protein in the Wnt signaling pathway, to inhibit its function and thereby reduce Wnt signaling. ONO-7569 is a GSK-3β inhibitor that plays a negative regulatory role in the Wnt signaling pathway. PRI-724, another CBP/β-catenin inhibitor, regulates the Wnt signaling pathway by inhibiting the formation of the CBP/β-catenin complex. Clinical trials are currently underway to evaluate the effectiveness of these drugs in the treatment of diabetes and liver fibrosis.

3.4 Diabetes therapy targeting the JAK-STAT signaling pathway

Regarding the drugs targeting the JAK-STAT signaling pathway in diabetes, some examples are Apabetalone, Englitazone, Abacavir, etc. Apabetalone is a BET protein antagonist that acts in the nucleus of the BET family of proteins, promoting the transcription of cellular DNA and inflammatory responses. Englitazones are PPARγ agonists that enhance cellular metabolism and reduce the inflammatory response associated with diabetes. Abacavir is a nucleoside reverse transcriptase inhibitor (NRTI) that inhibits HIV replication and reduces the inflammatory response. Clinical trials are currently underway to evaluate the effectiveness of these drugs in treating HIV-related diabetes and cardiovascular disease.

Table 4 Clinical trial of Abacavirs, a nucleoside reverse transcriptase inhibitor

3.5 Diabetes therapy targeting the ROS-ERK-NF-κB signaling pathway

Targeted drugs for the ROS-ERK-NF-κB signaling pathway in diabetes include NAC, Metformin, Alogliptin, Nitroglycerin, and RAS blockers (ACEI and ARB). NAC (N-acetylcysteine) is an antioxidant that inhibits the ROS-ERK pathway by reducing intracellular levels of the ROS-NF-κB signaling pathway. Clinical trials are currently underway to assess its effectiveness in treating complications such as diabetic nephropathy. Alogliptin begins to the class of DPP-4 inhibitors that promote insulin secretion, inhibit glucagon secretion, and can also reduce insulin resistance and inflammatory response by inhibiting the NF-κB signaling pathway. Nitroglycerin can inhibit the ROS-ERK-NF-κB signaling pathway and attenuate diabetes-related inflammation and oxidative stress. Clinical trials are currently underway to evaluate its effectiveness in treating diabetes and its complications. RAS blockers, including ACEI and ARB, can reduce ROS production and inhibit NF-κB signaling pathway activation by inhibiting the RAS system. This, in turn, improves complications such as insulin resistance, inflammatory response, and kidney damage in diabetic patients. The aforementioned two drugs have been widely used in the treatment of diabetes and have shown good efficacy.

Table 5 Clinical trial of Alogliptin, a DPP-4 inhibitors

According to statistics, there are currently 6 Alogliptin projects in the clinical stage, with 4 actively recruiting and 2 not recruiting.

Table 6 Clinical trial of Nitroglycerin, an inhibitor for ROS-ERK-NF-κB signaling pathway

Table 7 Clinical trial of ACEI, a RAS blocker

According to statistics, there are currently 26 ACEI projects in the clinical stage, with 21 actively recruiting and 6 not recruiting.

Table 8 Clinical trial of ARB, a RAS blocker

According to statistics, there are currently 41 ARB projects in the clinical stage, with 31 recruiting and 10 not recruiting.

3.6 Diabetes therapy targeting the IGF-1 signaling pathway

Targeted drugs for the IGF-1 signaling pathway in diabetes mainly consist of IGF-1R inhibitors, such as Figitumumab, Cixutumumab, Ganitumab, Dalotuzumab, etc. These drugs, classified are monoclonal antibodies, reduce the progression of the diabetic process by targeting the IGF-1R receptor. IGF-1R inhibitors can inhibit the IGF-1R signaling pathway, thereby reducing insulin resistance and promoting insulin sensitivity. Several IGF-1R inhibitors are currently undergoing clinical trials to evaluate their effectiveness in the treatment of diabetes.