Association of Cardiometabolic Index and Insulin Resistance with Serum Levels of Peroxisome Proliferator-activated Receptor-γ in Polycystic Ovary Syndrome

INTRODUCTION

Polycystic ovary syndrome (PCOS) was first described by “Stein and Leventhal” in 1935.^1,2 It is called a “Syndrome” since PCOS encompasses many signs and symptoms clubbed together in a single entity. Although the most accepted documented prevalence of PCOS is found to be about 5–10% in women of childbearing age group, a common consensus in this regard is still lacking.³ This could be possibly because of the considerable heterogeneity in the presentation of its signs and symptoms, lack of agreement over the diagnostic criteria used to define this condition, and last but not the least due to logistic difficulties in diagnosing PCOS.⁴

PCOS is regarded as a multifaceted disorder. No single diagnostic criterion is enough for clinical diagnosis of PCOS. Thus, different criteria have been proposed for PCOS diagnosis, namely, Modified Rotterdam’s criteria (most widely accepted), NIH Criteria, AES Criteria, and so on. Out of the various clinical features of PCOS, most seen include hyperandrogenism, hyperinsulinemia, insulin resistance, menstrual irregularities, and radiologically visible features such as polycystic ovaries (≥12 follicles measuring 2–9 mm in diameter).^5–8

The interrelationship among the various risk factors and clinical features of PCOS can be briefly described through the following flowchart (Flowchart 1)

Peroxisome proliferator activated receptors (PPARs) are a group of nuclear receptor proteins, which act as transcription factors regulating gene expression.⁹ These are so called because these were first identified in studies examining cholesterol-lowering effects of fibrates in peroxisomes.¹⁰

A typical PPAR consists of two main components i.e. DNA binding domain and ligand binding domain. DNA binding domain has two zinc finger motifs which bind to hormone response element (HRE). Ligand binding domain has alpha helices and beta pleated sheets. It activates or represses the receptor by binding with certain ligands.¹¹ Ligand binding domain mutation of PPAR-γ is supposed to be involved in causing PCOS.¹²

Among the various subtypes of PPARs (PPAR-α, PPAR-β/δ, and PPAR-γ), the most widely studied in relation to PCOS is PPAR-γ. PPAR-γ is further subdivided into PPAR-γ₁, PPAR-γ₂, and PPAR-γ₃.¹³ The present study mainly concentrates around PPAR-γ₂ subtype, which is the main subtype of PPAR-γ present in adipose tissues.¹⁴ In the present study, serum levels of PPAR-γ were estimated and further correlated with insulin resistance and a relatively new parameter cardiometabolic index (CMI).

PPAR-γ, also known by the name of “Glitazone or Thiazolidinedione Receptors,” is involved in the treatment of type 2 diabetes mellitus by their insulin-sensitizing effects.^15,16 Moreover, their role in PCOS management is also related to their insulin-reducing effects in such subjects. In the present study, the insulin resistance was measured through HOMA-IR.

The CMI is a relatively newer parameter that encompasses the deranged lipid profile TG and HDL with anthropometric parameters of height and weight.¹⁷ It reflects the biochemical derangements associated with PCOS much more efficiently than these parameters show individually.

MATERIALS AND METHODS

A hospital-based observational case–control study was conducted in the Department of Biochemistry in collaboration with the Department of Obstetrics and Gynaecology, Lady Hardinge Medical College and associated Smt. Sucheta Kriplani Hospital, New Delhi. The study subjects included 50 diagnosed cases of PCOS meeting the inclusion criteria and 50 apparently healthy women volunteers as controls in the age-group of 15–45 years after taking bilingual written informed consent and approval from institutional ethical committee.

RESULTS AND OBSERVATIONS

The present study was conducted taking a total of 100 subjects, 50 PCOS cases and 50 controls in the age group of 15–45 years. In order to carry out the study, anthropometric parameters along with several biochemical tests were performed with their correlations. There was statistically significant difference observed between cases and controls with respect to weight, BMI, WC, and WHR (Table 1). Among the biochemical tests, serum TG and PPAR-γ levels were found to be significantly different between cases and controls (Table 2). Also, it was seen that serum PPAR-γ was positively and significantly correlated with serum TG levels. (Table 3). Since insulin resistance (IR) forms a very important component of PCOS, HOMA-IR was also calculated, and it was found to be positively correlated with serum TG levels (Table 4). In the present study, a relatively newer parameter, that is CMI, was also deduced from the various test parameters in order to find out a relationship (if any) with CMI sand PCOS in view of its associated cardiovascular diseases’ risk. Interestingly, it was seen that serum TG, HOMA-IR, and PPAR-γ were showing highly significant and positive correlation with CMI (Table 5).

DISCUSSION

The present study was conducted in Department of Biochemistry in collaboration with the Department of Obstetrics and Gynaecology, Lady Hardinge Medical College and associated Smt. Sucheta Kriplani Hospital, New Delhi, after obtaining institutional ethical clearance and bilingual informed and written consent from 50 diagnosed patients with PCOS according to Rotterdam’s Criteria as cases along with 50 apparently healthy women volunteers as controls.

PCOS or “Stein-Leventhal Syndrome” is associated with multifactorial risk factors. Although PCOS has got quite variable presentation among different populations, some of its clinical features are common and overlap even in different ethnic subgroups. Based on these, PCOS is classified according to many criteria. The most used of these is modified Rotterdam’s criteria concentrating around two out of the three of oligomenorrhea; hyperandrogenic features like hirsutism, alopecia, etc.; and polycystic ovaries.⁷

Out of the various orally effective management modalities of PCOS, Thiazolidinedione group of drugs or “Glitazones” constitute one of the treatment options. These drugs act through PPAR-γ or Glitazone receptors and are distributed all around the body tissues. The present study mainly focused on PPAR-γ₂ subtype of these nuclear transcriptional receptors and their role in the etiopathogenesis of PCOS. Their main mechanism of action is via reducing insulin resistance in PCOS cases.^18–21

In the present study, all the subjects were age matched. The difference between weight, BMI, waist circumference, and waist-to-hip ratio among the cases and controls were found to be statistically significant with their p values <0.05 (Table 1). This finding is supported with results from several studies such as Papalou et al.²² who reported significantly higher BMI (27.89 ± 7.73 kg/m²) in cases compared to controls (22.34 ± 2.34 kg/m²). A study by Bahcecı et al.²³ in Turkey reported that patients with PCOS have significantly higher waist circumference compared to their healthy counterparts. Legro et al.²⁴ also found waist to hip ratio significantly higher in PCOS women, with a mean value of (0.84 ± 0.08) in cases and (0.78 ± 0.05) in controls.

Further, serum triglyceride levels were found to be significantly higher in cases (121.08 ± 57.6 mg/dL) than controls (97.6 ± 44.2 mg/dL) (Table 2). These findings are in concordance with the study done on Korean women with PCOS which suggested TG to be a useful marker of insulin resistance.²⁵ Similarly, Tai et al.²⁶ showed a significant difference in triglyceride levels in Asian subjects with a mean difference of (1.3 ± 0.70 mmol/L). These findings suggest that dyslipidemia is associated with PCOS, with hypertriglyceridemia being an important component of it.

Among the glycemic parameters, none was found to have statistically significant difference between cases and controls (Table 2).

This study also reported significantly lower levels of PPAR-γ in the cases when compared to controls (p value < 0.05) (Table 2). PCOS is known to be associated with insulin resistance. The lower levels of PPAR-γ in cases are supportive of the fact that insulin sensitivity is related to more PPAR-γ expression.²⁷ A significant positive correlation was found between the serum levels of PPAR-γ and triglycerides in PCOS cases (p value < 0.05) (r = 0.295) (Table 3). Similar correlation was also reported by Semple et al.²⁸ who proposed that PPAR-γ modifies triglyceride synthesis by FFA esterification via acyl CoA synthase. It was also observed in the present study that HOMA-IR was significantly and positively correlated with the TG (Table 4).

The present study also included CMI as a relatively newer biochemical parameter of cardiovascular and metabolic diseases that may be associated with PCOS. CMI is an index related to adiposity and hence associated with the risk of diabetes. As with diabetes, derangement in lipid profile is seen in many cases of PCOS as well.²⁹ Moreover, according to some studies, hyperandrogenism associated with PCOS is a risk factor for cardiovascular diseases, hypertriglyceridemia, and insulin resistance.^30–34 CMI can be of great help in evaluating such a condition. Hence, relationship of PCOS and CMI can be studied further. It was interesting to observe that CMI showed highly significant and positive correlation with TG, HOMA-IR, and PPAR-γ serum levels in women with PCOS (Table 5). As there are very few studies on serum levels of PPAR-γ in PCOS women, this study adds to the evidence regarding the association between PCOS and PPAR-γ levels.

CONCLUSION

The present study showed many significant differences with respect to anthropometric and biochemical parameters in PCOS cases when compared to their respective age-matched healthy Controls. Statistically significant difference was seen in weight, BMI, waist circumference, waist-to-hip ratio, TG, and PPAR-γ between cases and controls. It was also observed that there was significant and positive correlation in PCOS cases with respect to HOMA-IR and TG. When talking about CMI, it was observed that CMI had significant and positive correlation with TG, HOMA-IR, and PPAR-γ serum levels.

REFERENCES

1. Stein IF. Amenorrhoea associated with bilateral polycystic ovaries. Am J Obstet Gynaecol 1935;29(2):181. DOI: 10.1016/S0002-9378(15)30642-6.

2. Hayek SE, Bitar L, Hamdar LH, et al. Polycystic ovarian syndrome: an updated overview. Front Physiol 2016;7:1–15. DOI: 10.3389/fphys.2016.00124.

3. Ramanand SJ, Ghongane BB, Ramanand JB, et al. Clinical characteristics of polycystic ovary syndrome in Indian women. Indian J Endocrinol Metab 2013;17(1):138–145. DOI: 10.4103/2230-8210.107858.

4. Mohammad MB, Seghinsara AM. Polycystic ovary syndrome (PCOS), diagnostic criteria, and AMH. Asian Pac J Cancer Prev 2017;18(1):17–21.

5. Shaikh N, Mukherjee A, Shah N, et al. Peroxisome proliferator activated receptor gamma gene variants influence susceptibility and insulin related traits in Indian women with polycystic ovary syndrome. J Assist Reprod Genet 2013;30(7):913–921. DOI: 10.1007/s10815-013-0025-y.

6. Geller DH, Pacaud D, Gordon CM, et al. State of the art review: Emerging therapies: The use of insulin sensitizers in the treatment of adolescents with PCOS. Int J Pediatr Endocrinol 2011;2011(1):9. DOI: 10.1186/1687-9856-2011-9.

7. Wehr E, Trummer O, Giuliani A, et al. Vitamin D-associated polymorphisms are related to insulin resistance and vitamin D deficiency in polycystic ovary syndrome. Eur J Endocrinol 2011;164(5):741–749. DOI: 10.1530/EJE-11-0134.

8. Mukherjee S, Maitra A. Molecular and genetic factors contributing insulin resistance in polycystic ovary syndrome. Indian J Med Res 2010;131:743–776.

9. Gorniak BG. Peroxisome proliferator-activated receptors and their ligands: Nutritional and clinical implications–a review. Nutr J 2014;13(1):17. DOI: 10.1186/1475-2891-13-17.

10. Lalloyer F, Staels B. Fibrates, glitazones, and peroxisome proliferator-activated receptors. Arterioscler Thromb Vasc Biol 2010;30(5):894–899. DOI: 10.1161/ATVBAHA.108.179689.

11. Xu HE, Lambert MH, Montana VG, et al. Structural determinants of ligand binding selectivity between the peroxisome proliferator-activated receptors. Proc Natl Acad Sci U S A 2001;98(24):13919–13924. DOI: 10.1073/pnas.241410198.

12. Minge CE, Robker RL, Norman RJ. PPAR Gamma: Coordinating metabolic and immune contributions to female fertility. PPAR Res 2008;2008:243791. DOI: 10.1155/2008/243791.

13. Tenenbaum A, Fisman EZ, Motro M. Metabolic syndrome and type 2 diabetes mellitus: focus on peroxisome proliferator activated receptors (PPAR). Cardiovasc Diabetol 2003;2(1):4. DOI: 10.1186/1475-2840-2-4.

14. Abbott BD, Wood CR, Watkins AM, et al. Peroxisome proliferator-activated receptors alpha, beta, and gamma mRNA and protein expression in human fetal tissues. PPAR Res 2010. 2010. DOI: 10.1155/2010/690907.

15. Molavi B, Rassouli N, Bagwe S, et al. A review of thiazolidinediones and metformin in the treatment of type 2 diabetes with focus on cardiovascular complications. Vasc Health Risk Manag 2007;3(6):967–973.

16. Kintscher U, Law RE. PPARγ-mediated insulin sensitization: the importance of fat versus muscle. Am J Physiol Endocrinol Metab 2005;288(2):E287–E291. DOI: 10.1152/ajpendo.00440.2004.

17. Shi WR, Wang HY, Chen S, et al. Estimate of prevalent diabetes from cardiometabolic index in general Chinese population: a community-based study. Lipids Health Dis 2018;17(236):1–9. DOI: 10.1186/s12944-018-0886-2.

18. Day C. Thiazolidinediones: a new class of antidiabetic drugs. Diabet Med 1999;16(3):179–192. DOI: 10.1046/j.1464-5491.1999.00023.x.

19. Ravikumar B, Gerrard J, Dalla Man C, et al. Pioglitazone decreases fasting and postprandial endogenous glucose production in proportion to decrease in hepatic triglyceride content. Diabetes 2008;57(9):2288–2295. DOI: 10.2337/db07-1828.

20. Staels B, Dallongeville J, Auwerx J, et al. Mechanism of action of fibrates on lipid and lipoprotein metabolism. Circulation 1998;98(19):2088–2093. DOI: 10.1161/01.CIR.98.19.2088.

21. Quinn CE, Hamilton PK, Lockhart CJ, et al. Thiazolidinediones: Effects on insulin resistance and the cardiovascular system. Br J Pharmacol 2008;153(4):636–645. DOI: 10.1038/sj.bjp.0707452.

22. Papalou O, Livadas S, Karachalios A, et al. White blood cells levels and PCOS: direct and indirect relationship with obesity and insulin resistance, but not with hyperandogenemia. Hormones 2015;14(1):91–100.

23. Bahcecı M, Aydemır M, Tuzcu A. Effects of oral fat and glucose tolerance test on serum lipid profile, apolipoprotein, and CRP concentration, and insulin resistance in patients with polycystic ovary syndrome. Fertil Steril 2007;87(6):1363–1368. DOI: 10.1016/j.fertnstert.2006.11.031.

24. Legro RS, Finegood D, Dunaif A. A fasting glucose to insulin ratio is a useful measure of insulin sensitivity in women with polycystic ovary syndrome. J Clin Endocrinol Metab 1998;83(8):2694–2698. DOI: 10.1210/jc.83.8.2694.

25. Park SY, Cho YJ, Lee SR, et al. Triglyceride is a useful surrogate marker for insulin resistance in korean women with polycystic ovary syndrome. Yonsei Med J 2015;56(3):785–792. DOI: 10.3349/ymj.2015.56.3.785.

26. Tai ES, Corella D, Deurenberg-Yap M, et al. Differential effects of the C1431T and Pro12Ala PPARgamma gene variants on plasma lipids and diabetes risk in an asian population. J Lipid Res 2004;45(4):674–685. DOI: 10.1194/jlr.M300363-JLR200.

27. Jiang X, Ye X, Guo W, et al. Inhibition of HDAC3 promotes ligandindependent PPARγ activation by protein acetylation. J Mol Endocrinol 2014;53(2):191–200. DOI: 10.1530/JME-14-0066.

28. Semple RK, Chatterjee VK, O’Rahilly S. PPAR gamma and human metabolic disease. J Clin Invest 2006;116(3):581–589. DOI: 10.1172/JCI28003.

29. Wakabayashi I. A U-shaped relationship between alcohol consumption and cardiometabolic index in middle-aged men. Lipids Health Dis 2016;15(1):50. DOI: 10.1186/s12944-016-0217-4.

30. Studen KB, Pfeifer M. Cardiometabolic risk in polycystic ovary syndrome. Endocr Connect 2018;7(7):R238–R251. DOI: 10.1530/EC-18-0129.

31. Barber TM, Vojtechova P, Franks S. The impact of hyperandrogenism in female obesity and cardiometabolic diseases associated with polycystic ovary syndrome. Horm Mol Biol Clin Investig 2013;15(3):91–103. DOI: 10.1515/hmbci-2013-0014.

32. Ehrmann DA, Liljenquist DR, Kasza K, et al. PCOS/troglitazone study group. Prevalence and predictors of the metabolic syndrome in women with polycystic ovary syndrome. J Clin Endocrinol Metabol 2006;91(1):48–53. DOI: 10.1210/jc.2005-1329.

33. Abbott DH, Dumesic DA, Franks S. Developmental origin of polycystic ovary syndrome – a hypothesis. J Endocrinol 2002;174(1):1–5. DOI: 10.1677/joe.0.1740001.

34. Elbers JMH, Asscheman H, Seidell JC, et al. Long-term testosterone administration increases visceral fat in female to male transsexuals. J Clin Endocrinol Metabol 1997;82(7):2044–2047. DOI: 10.1210/jc.82.7.2044.