What is the impact of type 2 diabetes mellitus on CYP450 metabolic activities?

KEYWORDS:

• cytochrome P450 (CYP)
• CYP2C19
• nonalcoholic fatty liver disease
• nonalcoholic steatohepatitis
• obesity
• type 2 diabetes

1. Introduction

Type 2 diabetes mellitus (T2DM) is a common condition currently affecting over 10.5% of the world’s adult population, and the prevalence is forecast to increase, particularly in middle-income countries [1]. Patients with T2DM are usually taking multiple drug therapies to control their blood glucose level and the associated conditions of dyslipidemia and hypertension along with various other comorbidities including cardiovascular and renal disease. It is, therefore, pertinent to consider whether T2DM affects the activity of drug metabolizing enzymes. The cytochrome P450 (CYP) enzymes are the most important enzymes catalyzing the phase 1 metabolism of drugs and other xenobiotics, usually converting them to less active metabolites, although occasionally certain prodrugs may be activated by the CYP450 enzymes [2].

T2DM can impact on CYP450 metabolic activities in several ways in addition to the effects of hyperglycemia, high insulin levels, insulin resistance, and impaired β-cell function. T2DM is typically associated with obesity, especially central or visceral obesity, and obesity and diabetes are commonly associated with nonalcoholic fatty liver disease (NAFLD) which is said to affect 25% of the world’s population [3,4]. NAFLD can progress to nonalcoholic steatohepatitis (NASH), liver fibrosis, and eventually cirrhosis with increasing effects on liver function including CYP450 activity. All of these factors may influence CYP450 activity in various ways, and it is important to consider the combination of factors in individual patients. A common mechanism may be the low-grade inflammation associated with obesity and T2DM which is mediated by an increase in cytokines including interleukins (ILs), such as IL-6, tumor necrosis factor alpha (TNF-α) and interferon gamma (IFN-γ) and which is associated with increased C-reactive protein (CRP) levels. A similar inflammatory response effect is seen with viral infections, such as COVID-19 infection, which can result in reduced CYP3A4-mediated drug metabolism, as recently reviewed [5].

We reviewed the recent literature on the effects of T2DM and its associated conditions on CYP450 metabolic activities to prepare this editorial. Several studies have addressed these issues, but not always comprehensively as details of obesity and NASH were not always provided. The studies reviewed are summarized in Table 1. Some of the findings may be relevant to certain drug treatments, and the need for additional research is discussed.

Table 1. Summary of the main findings from the articles reviewed in this Editorial.

Authors/year	Study design and main findings	Ref
Gravel et al., 2019	38 T2DM and 35 non-T2DM subjects with probe drug cocktail assessment of 7 CYP450 activities. T2DM patients were older with more males (79% vs 43%) and had higher BMI and had mean HbA1c 7.1%. CYP2C19, CYP2B6, and CYP3A4/5 metabolic activity was significantly decreased in T2DM subjects by about 46%, 45%, and 38%, respectively. CYP1A2 and CYP2C9 activities showed a borderline increase in T2DM and there was no difference for CYP2D6 or CYP2E1 activities. Inflammatory markers, genotypes, diabetes and demographic-related factors influenced CYP450 activity,	[6]
Neyshaburinezhad et al., 2023	40 T2DM patients and 21 healthy controls using a cocktail of probe drugs. T2DM patients were older with fewer males (40% vs 67%) and higher BMI and had mean HbA1c 8.5%. Metabolic activities for CYP2B6 and CYP3A4/5 were significantly decreased in patients compared to controls, CYP2C19 was not significantly decreased after adjustments, CYP2C9 activity was slightly increased and CYP1A2 and CYP2D6 activities were similar in the 2 groups. CYP2B6 and CYP3A4/5 increased and CYP2C9 activity decreased after improved glycemic control.	[7]
Kvitne et al., 2022	29 with T2DM and obesity, 53 with obesity without T2DM and 17 controls without T2DM and obesity using a cocktail of probe drugs and jejunal and liver biopsies. Jejunal but not liver CYP2C19 concentrations were lower in T2DM with obesity compared to obesity alone and CYP2C19 activity was associated with both T2DM and NAFLD. T2DM was not associated with variability in CYP3A, CYP1A2, and CYP2C9 activities but CYP3A variability was associated with BMI.	[8]
Powell et al., 2023	93 liver biopsies with histologically staged NAFLD Activity Score. CYP2C19 showed the greatest degree of downregulation and CYP3A4, CYP1A2, and CYP2C8 were not significantly downregulated. A meta-analysis including 16 additional independent studies showed CYP2C19 is significantly downregulated to 46% in NASH.	[3]
Jamwal et al., 2018	24 normal, 26 NAFLD and 24 NASH human liver tissue samples showed lower CYP3A4 activity and protein expression in NAFLD and NASH compared to normal. About half the subjects in each group had diabetes and this was also associated with decreased CYP3A4 activity and protein expression.	[9]
Krogstad et al., 2021	Liver biopsies from 36 individuals with a range of BMI correlated body weight and composition with ex vivo activities of CYP3A, CYP2B6, CYP2C8, CYP2D6, CYP2C9, CYP2C19 and CYP1A2 in hepatic microsomes. Only CYP3A activity showed a significant negative correlation with all the measures of obesity.	[10]
Zarezadeh et al., 2021	Systematic review of 39 studies related to the effect of obesity and body weight on CYP450 activity. Obesity might decrease the activity of CYP3A4/5, CYP1A2 and CYP2C9 and increase the activity of CYP2E1.	[11]

Abbreviations: NAFLD, nonalcoholic fatty liver disease; NASH, nonalcoholic steatohepatitis.

2. Effects of glycemic control on CYP450 activity in T2DM

In a study comparing 38 T2DM patients with 35 non-T2DM controls using a cocktail of probe drugs to assess the activity of seven CYP enzymes, it was found that the mean metabolic activity for CYP2C19, CYP2B6, and CYP3A was significantly decreased in subjects with T2DM by about 46%, 45%, and 38%, respectively [6]. The activities of CYP1A2 and CYP2C9 seemed slightly increased in the T2DM patients, and there was no difference between patients and controls for CYP2D6 or CYP2E1 activities. Compared to the control subjects, the patients with T2DM were older with a greater proportion of males and had greater body weight and body mass index (BMI), lower creatinine clearance and higher values for indices of diabetes. NAFLD was not assessed. The diabetic control was relatively good with a mean glycosylated hemoglobin (HbA1c) value of 7.1%. Drug interactions were avoided between the patients’ medications and the probe drugs, but the T2DM patients were on various long-term treatments that might influence CYP450 activity.

An analysis of several covariables, such as inflammatory markers IL-1β, IL-6, IFN-γ, and TNF-α, genotypes, diabetes-related and demographic-related factors was performed to determine factors that influenced CYP450 activity, and the low chronic inflammatory status associated with T2DM appeared to modulate CYP450 activities in an isoform-specific manner.

Another recent study using the Geneva cocktail to assess CYP activity, given with fexofenadine to assess P-glycoprotein (P-gp) activity, in 40 T2DM patients and 21 healthy controls found the metabolic activity for CYP2B6 and CYP3A4/5 were significantly decreased in patients compared to controls, CYP2C19 activity was not significantly reduced after adjusting for age and gender, whereas CYP2C9 activity was slightly increased and there was no difference regarding CYP1A2 and CYP2D6 [7]. When the T2DM treatment regimen was intensified with various treatments for 3 months and HbA1c was reduced from 8.5% to 7.6%, the activities of CYP2B6 and CYP3A4/5 increased and CYP2C9 decreased and were not statistically different compared to the control group after adjustments. Again, the patients with T2DM were older and had greater body weight and BMI and lower creatinine clearance. IL-1β and IL-6 values were much higher in the T2DM patients than in controls, and these were reduced to a small but significant extent with improved glycemic control and body weight was slightly reduced. NAFLD was not assessed.

The effect of T2DM on the in vivo activities and protein expressions of CYP2C19, CYP3A, CYP1A2, and CYP2C9 was investigated in patients with obesity comparing 29 with T2DM and obesity, 53 with obesity without T2DM, and 17 controls without T2DM and obesity [8]. CYP2C19 activity and jejunal CYP2C19 concentrations were 63% and 40% lower in those with T2DM and obesity compared with the obesity without T2DM group, respectively, but there were no differences in the in vivo activities of CYP3A, CYP1A2, and CYP2C9 and protein concentrations of CYP3A4, CYP1A2, and CYP2C9. Multivariable regression analyses also indicated that T2DM was associated with interindividual variability in CYP2C19 activity but not CYP3A, CYP1A2, and CYP2C9 activities. The obesity alone group had higher body weight, BMI and hs-CRP levels than those with T2DM and obesity. The T2DM patients had mean HbA1c levels of 50 mmol/mol (6.7%), so were well controlled, and they had higher glucose, insulin, and Homeostatic Model Assessment of Insulin Resistance (HOMA-IR) and they all had NAFLD compared to 62% with NAFLD in the obesity without T2DM group.

3. Effects of NAFLD and obesity on CYP450 activity in T2DM

The worldwide increase in the prevalence of obesity and T2DM is most likely behind the increase in people with NAFLD [4]. Among patients with T2DM, the global prevalence of NAFLD was 55.5% and of NASH was 37.3% [12]. In patients with NAFLD and T2DM the estimated prevalence of advanced fibrosis was 17.0%. Therefore, it is important to consider the effects of underlying liver disease on CYP450 activity in T2DM.

In a study of 93 liver biopsies with histologically staged NAFLD Activity Score (NAS), fibrosis stage, and steatohepatitis (NASH), analyses to identify associations between liver expression of 255 pharmacogenes and NAS, fibrosis stage, and presence of steatohepatitis found there were 37 significant pharmacogene-NAFLD severity associations including downregulation of CYP2C19 [3]. CYP2C19 showed the greatest degree of downregulation out of 17 pharmacogenes commonly changed in all three liver disease subgroups, whereas aldehyde dehydrogenase 3A1 (ALDH3A1) was most upregulated. CYP3A4, CYP1A2, and CYP2C8 trended to be downregulated although not statistically significant and other major CYP enzymes did not appear to be consistently affected by NAFLD severity.

The authors of that study performed a meta-analysis including 16 additional independent studies, which demonstrated that CYP2C19 is significantly downregulated to 46% in NASH, to 58% in high NAS, and to 43% in severe fibrosis. In the liver biopsy samples, 69 came from patients with obesity and 36 from patients with diabetes. In an analysis to determine whether associated conditions influence the downregulation of CYP2C19 it was concluded that metabolic comorbidities like obesity and diabetes were not the primary drivers of the observed CYP2C19 downregulation [3].

Another study of 74 samples of human liver tissue from brain dead donors grouped into 24 normal, 26 NAFLD, and 24 NASH categories examined CYP3A4 protein expression and activity [9]. CYP3A4 activity in NAFLD and NASH was 1.9- and 3.1-fold lower than normal livers, respectively, and CYP3A4 protein expression was significantly lower in NAFLD and NASH. Diabetes was present in about half of the subjects in each of the three groups, and diabetes was also associated with decreased CYP3A4 activity and protein expression.

A study which correlated body weight and composition with hepatic CYP450 activity examined the ex vivo activities of CYP3A, CYP2B6, CYP2C8, CYP2D6, CYP2C9, CYP2C19 and CYP1A2 in hepatic microsomes from liver biopsies from 36 individuals with a BMI ranging from 18 to 63 kg/m² [10]. Only three of the subjects had T2DM. CYP3A activity showed a significant negative correlation with all the measures of obesity including body weight, waist circumference, hip circumference, fat percent, fat mass, and BMI. There were no correlations between body weight measures and activities for the other CYP enzymes investigated.

A systematic review identified 39 studies related to the effect of obesity and body weight on CYP450 activity and found that obesity might decrease the activity of CYP3A4/5, CYP1A2, and CYP2C9 and increase the activity of CYP2E1, whereas the effect of obesity on CYP2D6 was controversial and CYP2C19 activity was less susceptible to alterations compared to other CYPs [11].

4. Expert opinion

The few recent studies reviewed here show somewhat diverse findings which probably reflect the many factors involved that influence CYP450 activity in T2DM and the different methodologies used in the studies. It appears that T2DM is associated with altered activity of some CYP450 isoenzymes, most consistently with reduced expression and activity of CYP2C19, and sometimes also CYP3A. However, the mechanisms involved in this are not entirely clear as many of the studies have not considered all the possible contributing factors such as NAFLD.

Reduced activity of CYP2C19 may be related to poor glycemic control and accumulation of fat in the liver with NAFLD and NASH, whereas reduction of CYP3A activity may be more related to obesity and increased liver fat. Proinflammatory cytokines may be a mediating factor in some cases as these have been shown to be involved in downregulation of many drug metabolizing enzymes which may be at least in part due to transcriptional suppression [13].

A somewhat similar pattern of CYP450 activity modification was reported from a study of patients with COVID-19 infection using the Geneva cocktail where the activity of CYP2C19 was the most reduced by 74.7%, followed by CYP1A2 by 52.6%, and CYP3A by 22.8% [14]. CYP2B6 and CYP2C9 activity increased by 101.1% and 55.8%, respectively, in that study. The change in CYP2C19 activity did not correlate with any of the inflammatory markers measured but the reduction was greater with increasing age and CYP2C19 activity was higher in women than in men.

Reduced activity of CYP2C19 may affect the response to various drugs, the most obvious one being clopidogrel for which CYP2C19 is the key enzyme involved in the bioactivation of inactive clopidogrel to its active metabolite. Clopidogrel has been reported to be less effective in patients with T2DM [15]. Pharmacodynamic factors may also be involved as patients with T2DM often have increased platelet turnover and drug interactions, for instance with the proton pump inhibitors, may further complicate the issue. Therefore, it may be desirable to check the platelet aggregation response when using clopidogrel in patients with T2DM.

Many of the sulfonylureas are metabolized by CYP2C9 but gliclazide is also a substrate for CYP2C19 [16]. Patients with T2DM and poor glycemic control might conceivably have a greater response to gliclazide if CYP2C19 is downregulated and the response may become less as glycemic control improves and CYP2C19 activity increases. In fact, the percentage reduction in HbA1c is greater with higher baseline levels of HbA1c with most glucose lowering drugs [17], but this is unlikely to involve CYP2C19 activity as most of the glucose lowering drugs are not substrates for CYP2C19.

The reduction of CYP3A-mediated drug metabolism in poorly controlled T2DM and its associated conditions may be important for many drugs with a narrow therapeutic index. T2DM may be a risk factor for severe myopathy and rhabdomyolysis with statins [18]. Reduced activity of CYP3A may be a mechanism for this, especially with simvastatin. Reduction in renal function may also contribute, and this is another feature commonly associated with T2DM.

In conclusion, T2DM is commonly associated with altered activity of some of the CYP450 enzymes. This may be related to the level of glycemic control and the associated features of obesity, lipid accumulation in the liver and impaired renal function. These have not all been quantified in many of the studies examining the effects of T2DM on CYP450 activity. It is therefore difficult to predict the CYP450 activity in individual patients with T2DM and this is further complicated by the potential effects of other drugs on CYP450 activity as these patients are often taking multiple drug therapies for comorbid conditions. It might be predicted that the activity of CYP2C19 and CYP3A would be reduced in patients with poorly controlled T2DM, especially those with NAFLD or NASH, and this is likely to be relevant to the response to drugs like clopidogrel and other drugs with a narrow therapeutic index which are metabolized by CYP3A. Further large-scale studies addressing all the relevant variables are needed to clarify this situation.

Declaration of interests

The authors have no relevant affiliations or financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or materials discussed in the manuscript. This includes employment, consultancies, honoraria, stock ownership or options, expert testimony, grants or patents received or pending, or royalties.

Reviewer disclosures

Peer reviewers on this manuscript have no relevant financial or other relationships to disclose.

Additional information

Funding

This manuscript was funded by a grant for the “Overseas Famous Teachers” Project of Guangdong Provincial Department of Science and Technology and Research Funding from the Faculty of Medicine, Macau University of Science and Technology.