EFFECT OF METFORMIN ON PRO-INFLAMMATORY MEDIATORS IN URINE AND BLOOD IN TYPE 2 DIABETIC PATIENTS – A SYSTEMATIC REVIEW STUDY

Introduction:

Diabetes mellitus is a metabolic disorder characterized by elevated blood glucose levels, which arise from either insufficient insulin production or the body's resistance to insulin. In over 90% of type 2 diabetes cases, there is a diminished response of body cells to insulin, known as insulin resistance. This condition ranks as the seventh leading cause of death in the United States and is associated with various health complications, including cardiovascular disease, vision impairment, renal failure, and amputations of the lower limbs. The onset of diabetes involves multiple pathogenic mechanisms, primarily resulting from the destruction of β-cells in the pancreas, leading to a deficiency of insulin, or from dysfunctions that induce insulin resistance in target tissues. It has been established that abnormal inflammatory responses play a crucial role in the onset and progression of type 2 diabetes. Specifically, pro-inflammatory cytokines like interleukin (IL)-6 and tumor necrosis factor (TNF)-α contribute to increased insulin resistance and are correlated with a greater likelihood of developing type 2 diabetes. In contrast, the anti-inflammatory cytokine IL-10 is found to be lower in patients suffering from type 2 diabetes. Thus, treatments that exhibit anti-inflammatory effects could be beneficial for managing this condition [1].

Metformin is recognized as the primary treatment for type 2 diabetes, primarily functioning by inhibiting hepatic gluconeogenesis. The drug's molecular action is linked to the activation of AMP-activated protein kinase (AMPK) and protein kinase A (PKA), alongside the suppression of the mitochondrial respiratory chain (specifically complex I) and glycerophosphate dehydrogenase [2]. Research indicates that metformin may enhance various metabolic parameters, including hyperglycemia, insulin resistance, and atherogenic dyslipidemia, which in turn may mitigate chronic inflammatory responses. Nonetheless, the impact of metformin on inflammatory responses within the systemic circulation and urine of type 2 diabetes patients remains uncertain. It is commonly acknowledged that the use of metformin in diabetic individuals with chronic kidney disease necessitates careful consideration, as it may lead to lactic acidosis in the context of renal dysfunction. This study aimed to evaluate the effects of metformin at varying doses and durations on the levels of pro-inflammatory cytokines (such as IL-6, TNF-α, and MCP-1) and the anti-inflammatory mediator IL-10 in the blood and urine of individuals with type 2 diabetes [2].

A research study carried out between January 2015 and December 2015 at Anhui Provincial Hospital involved 210 patients diagnosed with type 2 diabetes. These patients were randomly assigned to two groups: one receiving metformin (n = 112) and the other receiving non-metformin treatments, which included gliclazide, acarbose, and repaglinide (n = 98). The levels of cytokines were assessed using the ELISA method. The results indicated that metformin significantly lowered serum levels of IL-6 and TNF-α when compared to acarbose and repaglinide, while serum IL-10 levels remained unchanged across the treatments. Additionally, metformin treatment led to a significant reduction in urinary MCP-1 levels compared to gliclazide and repaglinide. Overall, metformin was found to be more effective in reducing inflammatory cytokine levels than the individual treatments of gliclazide, acarbose, and repaglinide [1].

 

The Role of Inflammatory Chemicals

Many years ago, scientists observed that individuals with type 2 diabetes exhibited increased levels of inflammation within their bodies. Specifically, the concentrations of certain inflammatory substances known as cytokines tend to be elevated in those with type 2 diabetes when compared to individuals without the condition. It has long been established that obesity and physical inactivity are significant risk factors that contribute to the onset of type 2 diabetes. Researchers found that in individuals suffering from type 2 diabetes, cytokine levels are heightened within adipose tissue. Their findings suggest that excess body fat, particularly in the abdominal region, leads to persistent (chronic) low-grade inflammation, which disrupts insulin function and plays a role in the progression of the disease.

 The link between hyperglycemia and systemic inflammation.

Significant clinical studies, like the United Kingdom Prospective Diabetes Study (UKPDS) and the Diabetes Control and Problems Trial (DCCT), have demonstrated a correlation between the severity of microvascular problems and the duration and extent of hyperglycemia. Both direct and indirect processes, such as the activation of detrimental inflammatory pathways in endothelial cells and the involvement of immune cells, especially those with myeloid ancestry, can cause vascular problems due to hyperglycemia. Subclinical chronic systemic inflammation has been proposed as the cause of diseases that result in vascular damage. A modest increase in inflammatory cytokines, such as TNFα, IL-1β, and IL-6, which can be brought on by a variety of internal or external triggers, is usually indicative of chronic inflammation. In chronic inflammation, macrophages are the main source of these inflammatory cytokines.

Hyperglycemia can trigger an epigenetic inflammatory response in innate immune cells, as seen by the increased activating histone marks on the promoters of the S100A9 and S100A12 genes, which are implicated in vascular inflammation in diabetes. However, in addition to releasing  pro-inflammatory molecules, macrophages also control inflammation through their diverse scavenging activities, which can either trigger further inflammatory processes or be non-inflammatory and tolerogenic. It is still unknown how hyperglycemia affects these essential functions of macrophages and monocytes.

Persistent low-grade inflammation is a hallmark of diabetes mellitus (DM), and it plays a key role in the development of long-term complications by causing insulin resistance and high blood glucose levels. When DM patients get COVID-19, this chronic inflammatory disease is thought to amplify their immunological and inflammatory responses compared to those who do not, which results in elevated cytokine production and hyperglycemia spikes. A harmful loop is created when hyperglycemia exacerbates oxidative damage and inflammatory markers. In patients hospitalized with COVID-19, the interplay between inflammatory cytokines and hyperglycemia may have a substantial impact on the incidence of multi-organ damage and elevated mortality rates.

Introduction to metformin as a cornerstone therapy for type 2 diabetes.

Many treatments are available to reduce blood sugar levels, such as oral hypoglycemic drugs or injectable insulin. The American Diabetes Association care guidelines consider, Metformin is the primary therapy for people with type 2 diabetes who wish to reduce their blood sugar levels.  Metformin has been on the market for more than 50 years, Because of its efficacy, stability, and benefits for the heart and metabolism. Metformin is now the medication of choice for treating type 2 diabetes because [3]. Metformin doesn't cause many adverse effects however it can cause lactic acidosis, which is a serious illness having symptoms such as; muscle ache, extreme drowsiness, shivering, fever, breathlessness, abnormal heartbeat, fatigue, vomiting and diarrhea. However, metformin is not advised for usage in CKD patients, because of the potential risk of lactic acidosis [2].

 Metformin's anti-inflammatory properties beyond glycemic control.

Various mechanisms are implicated in the impaired insulin secretion and response observed in type 2 diabetes, including glucotoxicity, lipotoxicity, oxidative stress, and the accumulation of amyloid deposits within the islets. Notably, all these mechanisms are linked to inflammatory responses. This connection is supported by evidence indicating that chronic inflammation significantly contributes to the pathogenesis of type 2 diabetes, leading to islet dysfunction and insulin resistance through both inflammasome-dependent and -independent pathways [1]. Consequently, the most effective anti-diabetic medications would ideally possess anti-inflammatory properties alongside their ability to lower blood glucose levels. In a comparative analysis, metformin was found to decrease serum levels of IL-6, TNF-α and urinary MCP-1 more effectively than gliclazide, acarbose, and repaglinide in patients with type 2 diabetes. Furthermore, metformin demonstrates a targeted impact on inflammatory responses, which varies with dosage and duration of treatment. Collectively, these observations indicate that metformin's anti-diabetic effects stem from its capacity to lower both glucose levels and inflammatory responses [2].

Metformin and kidney disease

Chronic kidney disease (CKD) is often associated with a significant presence of persistent systemic inflammation. This inflammatory response, whether acute or chronic, commonly occurs alongside the deterioration of renal function. The pre-clinical investigations have yielded strong evidence indicating that metformin offers protection against renal injuries by mitigating inflammation caused by various stimuli  [4]. An in vitro study reveals that hyperglycemia negatively affects the expression of glucagon-like peptide-1 receptor (GLP-1R) in the HBZY-1 rat mesangial cell line, which is associated with the activation of NF-κB and elevated levels of MCP-1 protein. Metformin has the capability to restore GLP-1R mRNA expression and reduce inflammation triggered by high glucose levels in HBZY-1 cells.

Metformin demonstrates positive effects on renal damage caused by obesity in young C57BL/6 mice subjected to a high-fat diet. The administration of Metformin restores renal Mitogen-activated protein kinase (AMPK) activity and enhances fatty acid oxidation. Furthermore, it significantly reduces the expansion of the glomerular mesangial matrix and the infiltration of macrophages within the kidney tissues of the mice. Metformin preconditioning prevents renal tubular epithelial cell apoptosis and inflammation in kidneys of Sprague-Dawley (SD) rats challenged with ischemia and renal arteriovenous perfusion. Histologically, there are fewer renal tubular necrotizing changes in the metformin group than that in the ischemia group. The phosphorylation of AMPK is enhanced, but caspase 3 and COX-2 levels are decreased by metformin treatment.

Notably, another investigation indicates that in AMPK β1 deficient mice subjected to unilateral ureteral obstruction (UUO), metformin continues to provide histological and functional protection against renal injury. This finding implies that the protective effects of metformin are not solely reliant on the activation of AMPK within mouse kidney tissue. The application of cyclosporine A (CsA) as an immunosuppressive drug is frequently constrained due to its nephrotoxic effects. However, the combination of metformin and silymarin has been shown to mitigate the functional damage to the kidneys in Wistar albino rats induced by CsA. Marked protection against oxidative stress, evidenced by increased superoxide dismutase (SOD) activity and glutathione (GSH) levels, as well as reduced inflammation indicated by decreased myeloperoxidase (MPO) and tumor necrosis factor-alpha (TNF-α), is observed in the kidney tissues of rats treated with metformin. Additionally, the normalization of histological alterations and the immunoreactivity scores for COX-2 and inducible nitric oxide synthase (iNOS) further corroborate these results.

Although metformin has shown renal protective effects in both cellular and animal models, there is significant caution regarding its clinical application in patients with kidney diseases due to the associated risk of lactic acidosis. The complex interactions between metformin, kidney injury, and lactic acidosis have been extensively reviewed. Conversely, several recent studies indicate that metformin treatment may still be pharmacologically effective and safe for patients with renal impairment. It is crucial, however, to adjust the dosage based on the patient's renal function. The recommended daily dosages are 1,500 mg for those with severe chronic kidney disease (CKD) stage 3A, 1,000 mg for CKD stage 3B, and 500 mg for CKD stage 4. Importantly, hyperlactatemia has not been detected among the various CKD stage groups.

Metformin and Neurodegenerative Diseases

Recent studies have also highlighted the genetic factors associated with microglial activity, indicating a possible link to the pathophysiology of Alzheimer disease (AD). Nevertheless, the primary risk factors for the onset of Alzheimer's disease include advanced age, genetic predispositions such as the presence of the APOE-ε4 allele, specific variants in the TREM2 gene, and multiple loci identified through genome-wide association studies (GWAS). Additionally, factors such as traumatic brain injuries, cardiovascular health issues, and various environmental influences have been recognized as significant contributors to the risk of developing this debilitating condition [5].

A high-fat diet has been shown to induce insulin resistance, which in turn exacerbates amyloidosis and cognitive decline in both the Tg2576 mouse model of AD and other APP transgenic mice. Furthermore, the impact of high-fat diets or obesity may extend to memory impairments in even wild-type animals. Despite these findings, some studies, as reviewed by Agusti and colleagues, reported no significant effects on cognitive function, indicating that the relationship between diet, metabolism, and cognition remains a contentious issue due to the presence of conflicting evidence [6].

The effect of metformin on cognitive decline has only been examined in a small number of animal trials, and the results have been mixed. The variations in the findings about metformin's effects in this area may be due to the different ways that researchers have manipulated mice' energy metabolism to cause cognitive deficits [5]. While some rodents, like the (db/db) mice, have a spontaneous mutation that causes insulin resistance and obesity, other rodents are fed a diet heavy in fat. Metformin treatment was linked to a decrease in cognitive impairments in three studies including high-fat diets, although one research found no change. One study showed that metformin improved memory in (db/db) mice, but another found no discernible impact. It is worth noting that a study that looked at normal aging in wild-type mice found that metformin had a detrimental effect on memory impairment. The effectiveness of the metformin regimen in these animals is unknown because the phosphorylation-induced activation of AMPK was not measured in this investigation. It is obvious that more research with suitable controls is necessary to clarify how metformin affects natural aging [6].

Pancreatic cancer and diabetes

The occurrence of pancreatic cancer is observed to be 2 to 3 times greater in individuals with diabetes. This relationship between hyperglycemia and pancreatic cancer is further substantiated by the finding that approximately 80% of patients diagnosed with pancreatic cancer exhibit glucose intolerance or overt diabetes. Numerous studies have indicated that diabetes in patients with pancreatic cancer is associated with peripheral insulin resistance [7].

The occurrence of diabetes mellitus (DM) or glucose intolerance is found in up to 75% of patients with pancreatic cancer, a statistic that is considerably higher than the prevalence seen in other types of cancer, which is generally below 30%. The connection between DM and pancreatic cancer is twofold; research has shown that individuals with chronic diabetes are at a heightened risk for pancreatic cancer, while the emergence of pancreatic cancer is frequently associated with an increase in diabetes cases. Many investigations into DM as a risk factor have targeted patients who were diagnosed with diabetes several years prior to their pancreatic cancer diagnosis, in order to rule out cases where diabetes may have developed as a result of the cancer. This methodology is predicated on the understanding that pancreatic cancer is often rapidly fatal, thus making it unlikely for diabetes diagnosed years earlier to be attributed to the cancer. Additionally, various studies have indicated that DM may not merely be a risk factor but could also be a consequence of pancreatic cancer. One study explored the timing of DM in relation to pancreatic cancer and found a significant rise in DM cases starting 36 months before the cancer diagnosis, with numbers continuing to grow until the diagnosis, suggesting that the cancer itself may be the causative agent [8].

 

 

References

1.            Chen, W., X. Liu, and S. Ye, Effects of metformin on blood and urine pro-inflammatory mediators in patients with type 2 diabetes. Journal of Inflammation, 2016. 13(1): p. 34.

2.            Hotamisligil, G.S. and E. Erbay, Nutrient sensing and inflammation in metabolic diseases. Nature Reviews Immunology, 2008. 8(12): p. 923-934.

3.            Blitzer, A.L., S.A. Ham, K.A. Colby, and D. Skondra, Association of metformin use with age-related macular degeneration: a case-control study. JAMA ophthalmology, 2021. 139(3): p. 302-309.

4.            Lamanna, C., M. Monami, N. Marchionni, and E. Mannucci, Effect of metformin on cardiovascular events and mortality: a meta‐analysis of randomized clinical trials. Diabetes, Obesity and Metabolism, 2011. 13(3): p. 221-228.

5.            Lennox, R., D.W. Porter, P.R. Flatt, C. Holscher, N. Irwin, and V.A. Gault, Comparison of the independent and combined effects of sub-chronic therapy with metformin and a stable GLP-1 receptor agonist on cognitive function, hippocampal synaptic plasticity and metabolic control in high-fat fed mice. Neuropharmacology, 2014. 86: p. 22-30.

6.            Li, Z.-g., W. Zhang, and A.A. Sima, Alzheimer-like changes in rat models of spontaneous diabetes. Diabetes, 2007. 56(7): p. 1817-1824.

7.            Chari, S.T., C.L. Leibson, K.G. Rabe, L.J. Timmons, J. Ransom, M. De Andrade, and G.M. Petersen, Pancreatic cancer–associated diabetes mellitus: prevalence and temporal association with diagnosis of cancer. Gastroenterology, 2008. 134(1): p. 95-101.

8.            Sahra, I.B., K. Laurent, A. Loubat, S. Giorgetti-Peraldi, P. Colosetti, P. Auberger, J.-F. Tanti, L. Marchand-Brustel, and F. Bost, The antidiabetic drug metformin exerts an antitumoral effect in vitro and in vivo through a decrease of cyclin D1 level. Oncogene, 2008. 27(25): p. 3576-3586.